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July 16, 1946. w. H. @ILLE 2,403,917 CONTROL APPARATUS Filed April 20, 1942 5\ 54 BRWGE cmLm-r AMPLmáR ANI) Powaw. um-r 5 Sheets-Sheet 1 July 169 1946. w. H. GILLE 2,403,917 CONTROL APPARATUS Filed April zo, 1942 ANO POWER UN\T s sheets-sheet 2 mmm’ July 16, 194:6o w. H. GILLE 2,403,917 CONTROL APPARATUS Filed April 2o„ 1942 s sheets-sheet a §15. ê Patented July 16, 1946 2,403,917 _UNITED STATES PATENT OFFICE 2,403,917 ' n CONTROL APPARATUS Willis H. Gille, St. Paul, Minn., assignor to Min neapolis-Honeywell Regulator Company, Min neapolis, Minn., a corporation of Delaware Application _April 20, 1942, Serial No. 439,673 19 Claims. (Cl. 23.6-1) 2 The present invention relates to temperature control systems, and more particularly to tem Another object of the present invention is to provide a system for controlling the temperature perature control systems for use on aircraft. The construction of a satifactory temperature control system for use on aircraft presents many its walls are quite thin, and it is subjected to rapid variations in outside temperature. If an even temperature is to be maintained within the of an aircraft cabin. A further object is to pro vide, in such a control system, means for regulat ing the fuel supply to a heater. Another object of the present invention is to -provide an improved system for regulating the temperature of an aircraft engine. Other objects and advantages of the present invention will become apparent from a considera aircraft, it is therefore necessary that a tempera ture responsive element be employed which re tion of the appended specification, claims, and drawings, in which sponds- rapidly to changes in temperature. Figure 1 represents a, plan view of a section of an aircraft, showing the installation of a cabin unusual problems. For example, the space whose temperature is to be controlled is relatively small, Furthermore, it is necessary that the system con trolled by the temperature responsive element 15 temperature control system embodying my inven also be capable of quick response. The required tion in a somewhat diagrammatic manner, rapidity of response must be much greater than Figure 2 is a 'circuit diagram showing in greater that required in buildings and vehicles operated detail the connections of the bridge, ampliñer, on the ground, because the temperature changes motor and power supply units used in the system encountered are much more rapid. 20 disclosed in Figure 1, In addition to the requirement of high sensi Figure 3 shows, somewhat diagrammatically, tivity, a practical temperature control system for the application of vmy invention to a different type of aircraft cabin temperature control sys use on aircraft must be insensitive to the changes in barometric pressure which occur with changes tem. in altitude. It must also be insensitive to vibra 25 Figure 4 illustrates somewhat diagrammatlcally tion, both of the high frequency type sometimes the application of my invention to an aircraft resulting from the operation 0f the aircraft engine temperature control system employing a engine, and the rough irregular bouncing en hydraulic servo-motor. countered in rough air conditions. An aircraft Figure 5 shows a modified form of- hydraulic temperature control system must also be light in 30 motor which may be utilized in the system shown Weight and must produce no objectionable radio in Figure 4,and interference. Figure 6 shows a diiïerent embodiment of my It is therefore an object of the present inven invention as applied to an aircraft engine tem tion to -provide an improved temperature control perature control system. system for use on aircraft. A further object of Referring to Figure 1, there is shown a plan the present invention is to provide a tempera View of a portion of an airplane. The view is ture control system which shall be very sensitive taken looking downward at the floor of a com to temperature changes, While remaining insensi tive to atmospheric pressure changes and to vibration. ` Another object of the present invention is to provide an aircraft temperature control system which is light in weight and which does not pro~ duce objectionable radio interference. Another object is to construct an automatic temperature control system which may be readily installed on existing aircraft to operate existing temperature changes devices of various types which are at present usually controlled manually. A further object of the present invention is to provide an improved electrical control system for a hydraulic servo-motor. A still further ob ject is to provide an improved control system for a rotary electrical motor adapted to operate valves controlling a hydraulic motor. panionway I0 between a passenger cabin II and . a. Vpilot’s compartment (not shown). A wall I2, 40 provided with a suitable door I3, separates the companionway from the passenger cabin. Walls I4 and I5 at the sides of the companionway I0 separate the latter from spaces IB and Il, which may, for example, be used for cargo or baggage. Portions of the floor are shown in the drawings as broken away in order to better illustrate the tem perature control systems, of which the chief parts are mounted under the floor. An air intake duct 20, which may be connected with a suitable air intake (not shown) near the front of the plane, is divided by a wall 2 I, into a pair of parallel ducts 22 and 23. Air flowing through the duct 23 passes over a radiator 24,` which may be supplied with a. suitable heating 56 fluid, for example steam, through supply and re 3 2,403,917 turn pipes 25 and 2l. The duct 22 is provided to by-pass fresh air around the heater 24. The parallel ducts 22 and 2l rejoin each other at 21 and are connected to a suitable distributing duct 2l in the cabin Il. , 'I'he relative amounts of air passing through the ducts 22 and 2l are controlled by a set of mixing dampers 30, suitably attached to an op 4 . The ratio of the controlling effects ci' theseîre sistances on the unbalance of the bridge was therefore about twenty to one. -This ratio may vary considerably in particular installations, and the ratio between the resistance of the cabin tem perature responsive element and that of the dis charge temperature responsive element may be different than the ratio between the resistance erating bar 3|. The bar 3| is attached to a crank of the cabin temperature responsive element and , arm 32 driven by a motor mechanism 33. The 10 that of the outside temperature compensating motor mechanism 33 includes a split-phase motor element. It has been found, however, that the I4, and a gear train (not shown). ratio should be at least ten to one in any case, The split-phase motor 34 includes a pair of and may be as high as fifty to one. windings 35 and 35, which are spaced 90 electrical 'I'he bridge circuit 54 is provided with output degrees apart. in accordance with the conven 15 terminals B5 and 61 connected to the input ter tional construction of such motors. A condenser minals 42 and 43 of the amplifier and power unit 31 is connected in parallel with winding 36. The 4|, respectively. _ common terminal oi' windings 35 and 38 is The bridge circuit 54 also includes a rebalanc grounded as at 4I. ` lng potentiometer generally indicated at 10, hav The capacitance of condenser 31 and the in 20 ing a slide wire resistance 1| and a slider 12 co ductance of winding 3l are so proportioned that operating therewith. Slider 12 is connected to the two form a series resonant loop circuit. This the bridge circuit through a conductor 13, while loop circuit is supplied with energy by trans the end terminals of slide wire 1| are connected former action from winding 35, but the current to the bridge circuit 54 through conductors 14 flow in winding 36 caused by this transformer 25 and 15. action- is not sumcient, or of the proper phase Referring now to Figure 2, it will be seen that relationship, to cause rotation of motor 34. When the upper left arm of bridge circuit 54 connects a slight additional amount of energy is supplied input terminal 52 with output terminal 4G and to winding J8, however, it is energized sufficiently includes a manually adjustable resistance 80, con» to start rotation of motor I4 in a direction de 30 ductor 51, temperature responsive resistance elc termined by the phase of the energy supplied by ment 55, and conductor 5B. The upper right arm the amplifier. ' of bridge circuit 54 -connects output terminal $0 Motor 34 is supplied with electrical energy from with input terminal 53 and includes a conductor an amplifier and power unit generally indicated 5|, a ñxed resistance 82, and a conductor 83. at 4|. This unit has input terminals 42 and 43 35 The lower left arm of bridge circuit 54 connects and output terminals 44 and 45. Power is sup input terminal 52 and the slider 12, and includes plied to the amplifier and power unit 4| from a battery 46 through power supply terminals 41 a conductor B4, a fixed resistance 85. conductor 14, and that part of slide wire 1| between its and 48. The amplifier and power unit 4| also left hand terminal and the slider 12. The lower has terminals 50 and 5| through which electrical 40 right hand arm of bridge circuit 54 connects energy is conducted to input terminals 52 and 53 slider 12 and input terminal 53, and includes of a bridge circuit generally _ndicated at 54. that portion of slide wire 1| between slider 12 The bridge circuit 54 includes a first tempera and its right hand terminal,l conductor 15, a fixed ture responsive element 55. which may be an resistance 86, and temperature responsive re electrical resistance element having an appre 45 sistance elements 60 and 63. ciable temperature coefncient of resistance. The A variable resistance 81 is connected in parallel resistance element 55 is shown diagrammatically with slide wire 1|. The function of resistance in Figure l, and may be mounted on the wall I2. 81 is to determine the amount of movement of 'I'he particular form oi' the temperature respon slider 12 required to correct a given unbalance sive resistance element and the means for mount of the bridge circuit 54. ing it on the wall |2 may preferably be as de The function of adjustable resistance 80 is to scribed in the copending application of Russell determine the value of temperature adjacent the H. Whempner, Serial No. 439,679, dated April resistance 55 at which the bridge 54 will be bal 20, 1942. The resistance element 55 is connected to bridge circuit 54 by a'Dair of conductors 55 55 anced. In other words, it operates to set the control point of the system. and 51. ' The amplifier and power unit 4| includes an A second temperature responsive resistance ele amplifier generally indicated at 90, which may be ment 00 is mounted in the discharge duct 28 and of any type well known in the art in which the is connected to the bridge circuit 54 by means of conductors 6I and 52. A third temperature 60 phase of the output voltage is reversible with a reversal of the phase of the input voltage. A typi responsive resistance element 63 is mounted in cal amplifier of this type is shown in the Beers the intake duct 20 and is connected to bridge circuit 54 by means of conductors 54 and 55. Patent 2,020,275. Another desirable type of am It has been found desirable that the tempera plifler for this purpose is one of the type disclosed ture responsive element 55 should have the larg 65 in Figure 1 of the copending application of Al est eifect on the system, while the elements 50 bert P. Upton, Serial No. 437,561, dated April 3, and 53 should have smaller effects. The ratio 1942. Amplifier 90 has input terminals 42 and between the effects of these ele’nents on the sys 43 and output terminals 9| and 92. Bridge out tem may be controlled by properly designing their relative resistances. For example, in one system built in accordance with the present invention, the cabin temperature responsive element had a resistance of 500 ohms at 70° F., while the compensating resistance elements had a resist ance of about 25 ohms at the same temperature. 75 put terminal 6B is connected to amplifier input terminal 42 by a conductor B8. Bridge output terminal 61 is connected lto amplifier input termi nal 42 by a conductor 69. Input terminal 43 is grounded at 93, and also serves as an output ter minal of the amplifier 90. It will be readily un derstood that the conductor 69 may be omitted, „ 2,403,911 " ì 5 6 \ and bridge output terminal 61 connected to open, and the slider 12 is at'the mid-point of slide ground instead. wire 1|. Let it be assumed that the bridge 54 is While the amplifier referred to in the above balanced, and that the adjustable resistance 80 mentioned Upton application is one which has has been set so that the bridge remains balanced been found to be particularly desirable for use when the temperature in the cabin || is 70°. in the present apparatus, it is possible to employ When the bridge circuit 54 is balanced, the any amplifier capable of supplying at the output output terminals 66 and 61 are at the same po terminals a voltage which reverses in phase with tential, so that no signal is applied to the input reversal of the phase of the out-put voltage of terminals of amplifier 90. Under these condi the bridge. Such amplifiers are well known in 10 tions, no alternating current flows through wind the prior art. It is accordingly not considered ing 36 of motor 34. Although winding 35 of necessary to completely illustrate the details motor 34 is continuously energized by its connec thereof. However in order to facilitate an under tions to transformer secondary |02, both wind standing of the general operation of the ampli ings 35 and 36 must be energized with currents fier, the final amplifier stage is indicated in the 15 of the proper phase relationship in order to cause drawing. This stage is provided by a double tri rotation of motor 34, in accordance with the well ode tube 90a having two anodes 90b and 90e. A known characteristics of split phase motors. double cathode 9 la is associated with «both anodes Condenser ||5 is connected in series with motor 90b and 90C. Associated with anode 90b is a winding 35 in order to shift the phase of the cur grid 92h and with anode 90e is a grid 92e. 'I'he 20 rent supplied to that winding approximately 90 cathode Sla is connected by a lead 91 to the in electrical degrees with respect to the potential put terminal 43 which in turn is connected to and the terminals of transformer secondary ground 93 as previously noted. 'I'he two grids winding |02. ` 92h and 92e are connected together. The junc When the bridge circuit 54 is balanced, the tion of the connection to these two grids is indi 25 output terminals 66 and 61 are at the same cated by the reference numeral 94a. This junc potential, which is _at some value intermediate tion is shown as being connected by a dotted line the potentials of input terminals 52 and 53. If, connection 95a to the input terminal 42. This after the bridge is balanced, the resistance of connection is shown in dotted lines because in element 55 ldecreases, the potential of output actual practice two or more stages of amplifica 30 terminal 66 assumes a new value closer to that tion would be provided between the input termi of input terminal 52. Since the output terminal nals 42 and 43 and the grids 92h and 92o. As far 61 retains its original potential value, it will be as the essential operation of the amplifier is con seen that there is a potential difference between cerned, however, it may be considered as though output terminals 66 and 61. As between the two grids 92h and 92e are directly connected to the output terminals, the potential of output ter input terminal 42 and that the cathode 96 is minal 66 is closer to that of input terminal 52, directly connected by conductor 91 to terminal while the potential of output terminal 61 is 43 and hence to ground. closer to that of input terminal 53. Therefore, Power is supplied to amplifier '90, bridge circuit the unbalance potential appearing between out 54, and motor 36 from battery 46 through an 40 put terminals 66 and 61 is in phase with the inverter 94 which may be of the well known vi potential supplied to input terminals 52 and 53. brator type. Inverter 94 is connected to a pri 0n the other hand, if the resistance of element mary winding 95 of a transformer 96 having sec ondary windings |00, |01, |02 and |03. Secondary winding |00 supplies power to ampli fier 90 through conductors |01 and |08. Secondary winding |0| supplies power to am pliñer 90 and to winding 36 of motor 34. A con 55 increases after the bridge is balanced, the potential of output terminal 66 assumes a value closer to that of input terminal 53. The output terminal 61 retains its original potential value, and therefore a potential difference appears be tween output terminals 66 and 61. In this case, nection may be traced from the upper terminal however, as between the two output terminals, of transformer winding |0| through a conductor 50 the potential of terminal 66 is closer to that of ||0 to amplifier output terminal 9|. Another input terminal 53, While the potential of terminal connection may be traced from the lower termi 61 is closer to that of input terminal 52. There nal of secondary winding |0| through a conduc fore, it may be seen that the unbalance poten tor || | to amplifier output terminal 92. A third tial appearing between output terminals 66 and connection may be traced from the midpoint of 55 61 is opposite in phase to that supplied to input _ secondary winding |0| through a conductor ||2, terminals 52 and 53. terminal 45, a conductor | I3, winding 36 and con Consider now the effects upon the balance of denser 31 in parallel, ground connection 40, and the bridge circuit of changes in the resistance ground connection 93 to amplifier terminal 43. of elements 60 and 63. If, after the bridge is Transformer secondary winding |02 supplies balanced, the resistance of either element 60 ci power t0 winding 35 of motor 34 through a cir 63 decreases, the output terminal 61 thereby cuit which may be traced from the lower termi assumes a potential closer to that of input ter nal of winding |02 through a conductor ||4, a minal 53. The potential of output terminal 66 condenser H5, a conductor ||6, terminal 44, a retains its original value, so that, as between the conductor | I1, winding 35, ground connection two output terminals, the potential of terminal 40, a ground connection |20, and a conductor |2| 66 is closer to that of input terminal 52, while to the upper terminal of secondary winding |02. the potential of terminal 61 is closer to that of Secondary winding |03 is connected to termi output terminal 53. Therefore, the unbalance potential appearing between output terminals 66 nals 50 and 5I, which are connected to input and 61 is in phase with the potential supplied terminals 52 and 53 of bridge 54 through con to input terminals 52 and 53. ' ductors |05 and |06 respectively. On the other hand. if the resistance of either Operation of Figures 1 and 2 -element 60 or 63 increases after the bridge is When the parts are in the positions shown in balanced. the output terminal 61 thereby assumes the drawings, both sets of dampers 30 are half a potential closer to that oi' input terminal 52. 2,408,917 7 The potential o! output terminal 8B retains its that the voltages applied to these two grids are identical and hence .in phase with each other. The voltages applied to the two anodes llb and original value, so that, as between the` two cut put terminals, the potential of terminal EI is closer to that of input terminals 53, while that of terminal I1 is closer to that of input terminal l2. Therefore, the imbalance potential appear in! between output terminals .I and B1 is op "c are out of phase with each other. As a re sult, the amplifier signal voltage applied to the grids B2b and 82e will be in phase with the> anode voltage applied to either one or the other oi' the posite in phase to that supplied to input ter two anodes so that current will ilow through one minals I2 and B3. or the other of the two paths traced. The phase Recapitulating, it will lbe seen that a decrease of the signal volta-ge is dependent upon the phase in the resistance oi' any of the elements il, SII of the output voltage oi' the bridge which, as or ß cause an alternating potential to previously explained, is dependent upon the di appear at output terminals “and l1, which is rection in which the bridge is unbalanced. Thus, in 'phase with the potential supplied to input one or the >other o_i' the two circuits traced is terminals l2 and BI. 0n the other hand, an 15 rendered effective depending upon the unbalance increase in resistance oi' any of the elements oi the bridge. Since the voltages applied to these Il, Il or Il will cause an alternating potential " two circuits are 180° displaced in phase with to appear at output terminals It and 61 which respect to each other, it will be obvious that the is opposite in phase to that of the potential current ilowing through winding Il when the supplied to input terminals l! and B3. ' 20 bridge is unbalanced in one direction will be 180° A rise in temperature either in the intake d-uct displaced with respect to that ilowing through the 2l adjacent resistance element C3,l in the dis same winding when the bridge is unbalanced in charge duct 28 adjacent the resistance element the opposite direction. Since the output voltage Il, or in the cabin II itself adjacent resistance of secondary III is in phase with the output voit element I! indicates that less heat is necessary 25 age oi.' secondary IBI which supplies the input to maintainthe cabin II at the desiredtemper ature. voltage to the bridge, it will be readily apparent that the current ñowing in winding il will be oi When such a rise in one of the three temperatures referred to occurs, the resistance of the corresponding one of the temperature re sponsive elements t5, 6I and I3 increases, there the same or opposite phase as the terminal volt 30 by unbalancing the bridge circuit 5l in such a direction that an alternating potential appears. at output terminals 88 and 61 having a phase' opposite to that of the potential supplied to terminals 52 and 53. On the other hand, when a decrease in any of these temperatures occurs, a need for the supply oi' additional heat to the cabin II is indicated, and the bridge is uxr balanced -in such a direction that a potential appears between terminals 6B and 61 having the 40 same phase as the power supplied to input ter minals I2 and B3. Two possible circuits may be traced through the motor neld winding 3i. One of these cir cuits extends from the upper terminal of sec 45 ondary III through conductor III, terminal DI, anode IIb. cathode sla, conductor 91, ground connections 93 and l0, neld winding 3B, conductor Ill, terminal l5 and conductor H2 to the center tap o! secondary IIII. The other circuit extends from the lower terminal of secondary Ill through conductor III, terminal 92. anode 80c, cathode lla, conductor l1, ground connections 93 and ll, ileld winding Il, conductor III, terminal ll, and conductor Il! to the center tap of secondary IIII. Current will ilow through the iirst traced circuit only during the half cycle in which the anode IIb is positive with respect to the cathode. This will occur only during the half cycle when the upper end of the secondary IOI is positive with respect to the lower. Current will i‘iow through the last mentioned circuit, on` the other hand, only when anode lic is positive with respect to the cathode and hence the lower end of second ary III is positive with respect to the upper end. 50 age of the secondary winding |02. Since the current ilowing in winding Il is of the same or opposite phase as the terminal volt age of the transformer secondary winding, while the current flowing in winding 35 is shifted 90 degrees in phase in respect to the terminal voltage of the transformer secondary winding, motor Il will be driven in one direction or the other de pending upon whether the current in winding ll is of the same or the opposite phase asthat of the secondary terminal voltage. The connections between the bridge circuit 5l and the amplifier 90, and between amplifier 8l and motor Il, are such that when the bridge is unbalanced in a direction indicating the need for less heat in the cabin II, motor 36 is driven in a direction to close the dampers in the heater duct 2l and open the dempers in the by-pass duct 22, thereby supplying less heat to the cabin II. This operation of motor Il also drives slider 'l2 to the right along slide wire 'II, thereby rebalanc ing the bridge circuit Il. When the temperature adjacent either of the three temperature controlling resistance elements Il, Il and 83 decreases. the bridge is unbalanced in such a direction that amplifier l0 responds to drive motor I4 so as to close the dampers in by pass duct 22 and open the dampers4 in heater duct 2l, thereby supplying more heat to the cabin II. This is done by driving lever arm 3| and slider 'l2 to the left. Motion oi’ slider 'I2 to the leit rebalances the bridge circuit so as to stop the motor Il. It should be noted that in the amplifier and power unit 4I, the only wound coils or electro magnetic devices using iron cores are those asso It is furthermore possible for ciated with inverter 94, transformer 98, and mo tor Il. The weight oi the amplifier and power unit has thereby been maintained at a minimum. current to ilow through either one of these cur rent paths only when the eilect oi the amplifier signal potential as applied to the grid is to tend verter Il, which may be readily shielded so as Thus It is possible only during alternating hall' cycles for current to ilow through the respective 4 circuits traced. to raise the potential of the grid during the halt cycle in which the anode is positive. Since, as was previously noted, the grids' B2b and 92e are connected together. it will be readily apparent Furthermore, there are no switch contacts in the entire system, except those associated with in to produce no radio interference. , Figure 3 In Figure 3 is disclosed an aircraft cabin tem perature control system in which the control is 42,403,917 9 accomplished by modulating the fuel supply to a 10 , . As in Figure 1 the motor mechanism 33 modu lated the position of the damper 30 in response to temperature changes, so in Figure 3 the motor mechanism 33 modulates the position of the valve |22. It is believed that this operation of valve |22 by motor mechanism 33 will be readily un derstood from what has gone before, and need not be further described. ñuid fuel burning heater arrangement. In this ligure, all parts of the system which correspond exactly to similar parts in Figure 1 have been given the identical reference numerals. It will be noted that the bridge circuit 54, the ampliñer and power unit 4|, the motor mechanism 33, are the same asin Figure 1. Furthermore, the loca tion of the temperature responsive resistance 63 As the valve |22 moves towards its closed 'posi- _ in the intake duct 20, the location of temperature 10 tion from the position shown, the cam |33 is ro.. responsive resistance 60 in the discharge duct 28, tated in a counter-clockwise direction. The con and the location of temperature responsive re struction is such that when the valve |22 reaches sistance 55 in the cabin I I are the same as the its minimum position, the follower |32 of switch location of the corresponding elements in Fig arm |3| has nearly reached the end of the high ure 1. 15 dwell portion of cam |33. Ii' the bridge circuit In Figure 3, the air supplied to the cabin || 54 then becomes unbalanced so as to indicate passes through the intake duct 20, over a plu a need for further reduction in the supply of fuel rality of fluid fuel burning »heaters |20, and to the heaters |20, cam |33 rotates a slight addi through the discharge duct 28 to the cabin ||. tional amount in a counter-clockwise direction. Fuel is supplied to the heaters |20 through a fuel 20 This moves the high dwell portion out from under supply pipe |2|. The supply of fuel to the heaters follower |32, allowing it to drop to the low dwell |20 is controlled by a modulating valve |22, and portion, thereby opening switch |21. Opening by a shut-off valve |23.' Any suitable source of of switch |21 shuts out the supply of electrical iluid fuel may be used. For example, in certain energy to the operator |25 and to the» igniters installations, the fuel has been a combustible ‘_ |26. Deenergization of operator |25 causes shut oil' valve |23 to close. It should therefore be apparent that the supply The modulating valve |22 is operated by the of fuel to the heaters |20 is modulated from a motor mechanism 33. The valve |22 has an maximum to a> minimum value and that if a fur opening |24 in the center thereof to insure that 30 ther reduction in the supply of fuel is necessary, it never fully closes, but always permits a mini the supply is cut off completely and the igniters mum flow of fuel therethrough. are deenergized. In heaters using highly com The shut olf valve» |23 is provided with an elec bustible fuels of the type described, it is neces tricai operator |25, which may be a solenoid or sary that a minimum supply of fuel be maintained a rotatory motor, for example. Each of the heat in order to prevent a flash back, a phenomenon ers |20 is provided with a suitable ignition mech in which the flame moves back along the fuel 'anism such as the hot wire igniter shown some supply pipe to the source of fuel. This minimum what diagrammatically at |26. Energization of supply is maintained by the system shown, until the system is completely shut down. valve operator |25 and the igniters |26 is con trolled by a switch | 21 comprising a stationary 40 Figure 4 contact |30 and a movable switch arm |3|. The mixture of gasoline and air drawn from the in take manifold of one of the aircraft engines. switch arm |3| carries a follower |32 of insulat ing material, cooperating with a cam |33 driven In Figure 4 is shown an engine temperature control system embodying my invention. An air by the motor mechanism 33. craft engine |50, of the air cooled type. is pro vided for driving a propeller |5|. The engine Operation of Figure 3 |50 has a. cowl |52, of conventional form. Air For purposes of clarity, the modulating valve for cooling the engine |50 flows through an open |22 has been shown in Figure 3 in its fully open ing at the front of the engine, which is not shown position. The slider 12 of rebalancing poten in detail in the drawings, but Whose general tiometer 10 is shown at its corresponding posi 50 location is shown at |53. After passing over the tion at the upper extremity of slide wire 1|. engine, the heated air passes out through nap |54 in the cowl |52. Likewise, the cam |33 is shown in a position wherein it has closed switch |21, thereby com A temperature responsive device |55 is mounted pleting energizing circuits for shut-off valve op on the engine |50. It may, for example, be con erator |25 and igniters |26. 55 veniently attached to a spark plug |59. Resist ance element |55 is connected in a. bridge circuit The energizing circuit for operator |25 may be generally indicated at |56, having input terminals traced from the upper terminal of battery 46 |51 and |58, and output terminals |60 and |6|. through a conductor |34, switch |21, a conductor |35, a conductor |36, operator |25, and ground Input terminals |51 and |58 are connected connections |31 and |38 to the lower terminal 60 through conductors |62 and |63 into terminals 50 of battery 46. The energizing circuit for igniters ' |46 may be traced from the upper terminal of battery46 through conductor |34, switch |21, and 5| respectively of an amplifier and power unit 4|, similar to the corresponding amplifier and power unit shown in Figures l. 2, 3. Output terminal |60 of bridge |56 is connected through conductors I 35 and |40, and a plurality of parallel conductors |4| to the respective igniters |26, 65 a conductor |64 to input terminal 42 of amplifier only one of which is shown, the frame of burners , and power unit 4|. Output terminal |6| of bridge |20, supply pipe |2|, and ground connections |42 |56 is grounded at |65, and is therefore connected and |38 to the lower or grounded terminal of through ground connections |65 and 03 to input battery 46. terminal 43 of amplifier and power unit 4|. The construction of operator |25 is such that 70 The upper left hand arm of bridge circuit |56 when energized it maintains valve |23 in open connects input terminal |51 with output terminal position. Therefore, when the parts are in the |60, and includes a conductor |66, resistance ele position shown in the drawings, a maximum sup ment |55, conductors |61 and |66, and' that por ‘ ply of fuel to the burners |20 is maintained, and tion of a slide wire resistance |10, between its the fuel is ignited by the igniters |26. 75 left hand terminal and its cooperating slider |1|, 2,403,917 ’ ll which is electrically connected to output terminal |00. Slide wire |10 and slider |1| constitute-a rebalancing potentiometer |12, hereinafter re ferred to as the ultimate rebalancing poten tiometer. attached to the piston rod 2|8, as at 220, are a pair of links 22|, whose opposite ends are pivot ally attached to the cowl ñaps |54. Another link The upper right arm of bridge circuit |58 con 223 is attached at one endv to an intermediate point on link 22| and at its opposite end to the slider |1|. Either some portion of link 222 or a nects output terminal |80 and input terminal |58, and includes that portion of slide wire |10 be tween slider |1| and its right hand terminal, a suitable part of its pivotal connection with slider |1| may .be made of insulating material in order to prevent grounding oi! the slider |1|. conductor |18, and a fixed resistance |14. An 10 Operation of Figure 4 adjustable resistance |15 is connected in parallel with slide wire |10 in order to determine the amount oi movement oi' slider |1| necessary to correct a given imbalance oi the bridge circuit When the parts are in the position shown in the drawing, the ilaps |54 are half-way open, and the piston 2 I3 is in a central position in the cylin I 58. _ 15 der 2| 2. The bridge circuit |58 is balanced, the The lower left arm of bridge circuit |58 con sliders |1| and |8| are in their center positions, nects input terminal | 51 with output terminal I 8 I , and all the valves |9|, |92, |93 and |84 are closed. and includes a conductor |18, a iixed resistance Under these conditions, let is be assumed that the |11, and that part of a slide wire resistance |80 ytemperature of the engine |50 increases, thereby between its left hand terminal and its cooperat 20 increasing the resistance of sensitive element |55, 1118 slider |8|. Slide wire |80 and slider |8| i’orm thus increasing the resistance between input ter a rebalancing potentiometer hereinafter referred minal |51 and output terminal |1| of bridge |58. to as the proximate rebalancing potentiometer. This unbalance of bridge circuit |56 causes a sig The lower right arm of bridge circuit |58 con nal to be impressed on the amplifier and power nects output terminal |8| with input terminal 25 unit 4|, which in turn transmits a control im |58 and includes that portion of slide wire |80 pulse to the motor mechanism 33. The connec ybetween slider |8| and its right hand terminal, tions are so arranged that the control impulse a conductm' |88, a i'ixed resistance |84, and a transmitted to motor 33 is in the proper direction variable resistance |85. ’I‘he variable resistance to cause it to rotate shaft |90 in a clockwise direc |85 is provided in order to adjust the temperature tion, and also to rotate shaft |88 in a clockwise at which the control system maintains the engine direction. Rotation oi shaft |88 clockwise causes |50. A variable resistance |88 is connected in movement of slider |8| to the right along slide parallel with slide wire |80 in order to determine wire |80, thereby producing an increase in the the amount of movement oi' slider |8| necessary resistance between input terminal |51 and output to correct a given unbalance of bridge |58. 35 terminal |8| to balance the increase between in~ Motor mechanism 88. which is controlled in put terminal |51 and output terminal |80 caused response to the unbalance potential of bridge |58 by the increase in engine temperature. This re acting through amplifier and power unit 4|, balancing of the bridge circuit |58 causes motor drives, through a gear mechanism schematically indicated at |81, a shaft |88 connected to slider (0 |8|, and a shaft |90 which carries a series of cams |8|, |82, |98 and |84. The cams |8|, |82, |88 and |84 operate a series 33 to stop substantially as soon as the valves are opened. - / Rotation of shaft |90 in a clockwise direction causes opening of valves |95 and |91 under the influence of cams ‘| 8| and |93. Valves |98 and of four poppet valves |85, |88, |91 and |98, respec tively. These poppet valves control the ilow of 45 |98 remain closed. High pressure ñuid is then admitted to the right hand end of cylinder 2|2 high pressure iluid to a hydraulic servo motor from inlet chamber 203 through valve |91, valve 280, of conventional design. chamber 208, and conduit 2 |4. At the same time, A suitable source o! high pressure iluid is pro the pressure on the iluid in the left hand end of vided for operating servo motor 200. this source being shown in the drawing as a pump and high 50 cylinder 2| 2 is released through conduit 2 | 5, valve chamber 205, valve |85. and outlet chamber 201. pressure chamber associated therewith and num 'Therefore a pressure differential is established bered 20|. High pressure fluid may rlow from between the opposite faces of piston 2|8, there the high pressure chamber 28| through a suitable by forcing it to the left from the position shown conduit 282 to an inlet chamber 202 in a valve casing 204, which contains the poppet valves |95, 55 in the drawings. Movement of piston 2|3 and its associated piston rod 2|8 to the left causes |88, |81 and |88. Valves | 88 and |81 control the the links 22| and 222 to push the cowl ñaps |54 i'low of high pressure fluid from inlet chamber further open, thereby causing an increased flow 288 to valve chambers 288 and 208, respectively. of air over engine |50 to provide additional cool Valves |85 and |88 control the iiow of iiuid from ing thereof, so as to tend to restore its temper valve chambers 205 and 208 to outlet chambers ature to the value previously determined by the 201 and 208, respectively. Outlet chambers 201 setting of resistance |85. and 208 are connected by conduits 209 and 2|0 Movement of piston rod 2|6 to the lei't is also respectively, to a sump or receiver of low pressure transmitted through links 22| and 223 to the iiuid 2| |. slider |1|. Movement of slider |1| to the left The servo motor 208 comprises a cylinder 2|2 causes a decrease in the resistance between input having a piston 2|8 reciprocatable therein. One terminal |51 and output terminal |80. This end of the cylinder 2|2 is connected through a causes an unbalance of bridge circuit |58 in the conduit 2|4 to the valve chamber 208, and the other end oi' the cylinder 2 I2 is connected through opposite direction from that caused by the pre a conduit 2|5 to the valve chamber 205. 70 vious unbalance, so that a control impulse is A piston rod 2|8 is attached tc the piston 2|8 transmitted to motor mechanism 33 causing it to and passes through a suitable gland, not shown, rotate shafts |88 and |90 in a counter-clockwise in the end of cylinder 2|2, and through a bearing direction. Rotation of `shaft |88 counter-clock 2|1, of any suitable construction, which may be wise causes slider | 8| to be driven to the left attached to a iixed part of the aircraft. Pivotally 75 across slide wire |80, thereby rebalancing the 2,403,917 13 bridge circuit, while rotation of shaft |90 in a counter-clockwise direction causes closure of valves I9| and |93, thereby stopping operation of servo motor 200. 14 tion to a certain te to‘h t" extent without causing the sys m ‘m1, . I Figure 5 ' There is shown in Figure 5` a modified form of 'I‘he _resistance of slide wire |80 is made much hydraulic servo motor which may be used in the smaller than/the resistance of slide wire |10. Be cause oi' this, the effect of potentiometer |12 on system disclosed in Figure 4, and when used the balance of the bridge circuit |50 is greater therein results in a substantially different mode than the effect of potentiometer |82. In other of operation of the system. The servo motor 225 words, if the slider I1| moves through a given 10 of Fig. 5 comprises a. cylinder 226 and a loosely ñtting piston 221 reciprocable therein. The other portion of its range of travel, the slider |8| must move through a greater portion of its range in order to rebalance the bridge-circuit |55. There fore, a small movement of slider |1| in response to opening of the valves |9| and |93, for example, 15. by their reference characters. It will be under stood that a tightly iltting piston with a, leak port or any similar' arrangement might be used. is sufllcient to cause movement of slider |8| cor so long as there is a small leak between the ends parts are the same as in Figure 4, as indicated \of the cylinder. The size of the leak as it ap responding to the full closing movement of the pears in Figure 5 has been exaggerated for the valves. sake of clarity. In practice, a very small orifice Therelative effects of sliders |1| and |8| on the balance of the bridge, and hence the amount 20 between the ends of the cylinder would be sum cient. of movement of slider |1| required to cause clo When servo motor 225 is used in the system sure of the valves, may be regulated by adjusting the variable resistances |15 and |88. ‘ of Figure 4, the system is completely stable only when the piston 221 is at a position determined tentiometers |12 and |82 in the manner >de- 25 by the bias of the load on it. In the present case, the ñaps |54, due to the balance between the out scribed, fullopening and closure of the valves side and inside air pressures acting on them, may be controlled by very small unbalancing ef always tend to return to a central position, which fects in the bridge circuit. Full power is there is approximately the position shown in the draw by made available for control purposes even ings. The load on the servo motor may therefore through the correction required is small. be said to bias it for movement to its center posi It should be apparent that the rebalancing ac By proportioning the relative effects of po tion of the proximate rebalancing potentiometer „ |82 is only temporary, and that the slider |8| al- ways ñnally comes to rest at or near its center tion. When the servo motor 225 is used in the system of Figure 4, and the bridge is balanced, the piston 221 therefore moves slowly toward its position. The ultimate rebalancing of the bridge 35 center position, the movement being controlled by the flow of ñuid through the leak or orifice be tween the ends of the cylinder 225. Therefore plished by the slider |1| in accordance with the the slider | 1| also moves slowly to its center new position of cowl ilaps |54. When the bridge position. During this movement the bridge cir |58 is ultimately balanced the slider |8| is always in or near its center position and all the valves> 40 cuit is maintained in balance by the rebalancing action of slider | 8|, driven by motor 33. |9|, |92, |93, and |94 are closed. ' When the rebalancing action required of slider When the temperature of the sensitive resist |8| carries it to a, point where one pair of valves ance element |55 drops below the value which begins to open, the servo motor piston -221 is maintains the bridge circuit |55 balanced, a sig 45 given an impulse in the opposite direction away nal of the opposite phase is applied to the ampli from its center position. This of course causes iler and power unit 4|, thereby causing rotation slider |1| also to move away from its center posi oi' motor mechanism 33 in the opposite direction tion and unbalances the bridge in the opposite di so as to rotate shafts |88 and |90 in a counter rection so that motor mechanism 33 again closes clockwise direction, thereby moving slider |8| to 50 the valves which were opened. 'I'he net result is the left and opening valves |92 and |94. It will that the position of piston 221 tends to slowly be readily understood that this causes movement oscillate about a point such that the balance of of piston 2|3 to the right, thereby movingvslider the bridge is maintained with the slider |8| at |1| to theright and causing slider .|8| to be re one end or the other of its “dead spot.” The pis turned to its center position as the valves |92 55 ton 2|3 moves toward its center position just far and |94 are closed by rotation of motor 33. enough to unbalance the bridge so as to cause one It should be apparent from the shape of cams set of poppet valves to open slightly, whereupon |9|, |92, |93 and |94 that this system has a con the piston is given an impulse in the opposite siderable “dead spot.” In other words, there is direction by the high pressureiluid, thereby un a considerable angle through which the shaft |90 60 balancing the bridge in the opposite direction and may rotate without actuating any of the valves causing >closure of the poppet valves. This ac |95, |98, |91 and |98. There is of course a cor tion is cyclically repeated. responding range of movement of slider |8| on When the system is operating under these con either side of its center position in which the ditions, a slow variation in the temperature of bridge circuit may be balanced by the movements 65 the engine |50 will cause a change in the median oi' this slider without causing movements of the position about which the piston 221 oscillates. slider Ill. Since- it is permissible to allow the The slider |8| will continue to oscillate about the engine temperature to vary about the desired ' same end of its dead spot, thereby causing oper value by a considerable range, for example 10 ation of the same setv of valves as long as the or 15°, this construction of the cam permits the 70 rate of change of resistance |55 is lower than the slider |8| to take care of minor variations in rate of change of resistance |12 to the movement temperature without causing unnecessary control of slider |1|. When the temperature of engine operations of the servo motor 200. The rela |50 chan-ges rapidly however, resistance |55 also tively wide "dead spot” also permits either slider changes rapidly, causing a greater movement of |1| or |8| to overrun its exact rebalancing posi 75 slider |8| to open the valves fully. Ii the change circuit following an unbalance thereof is accom 15 2,403,917 is in the opposite direction, the slider will be Output terminal 215 is- connected through a conductor .215, winding 218 of relay 211, a con moved clearacross its dead spot and will open the opposite set of valves to produce the required con trol eiïect on the cowl flaps |54. ductor 215, transformer secondary winding 255, ' and a conductor 25| to ground at 252. It should be understood that this type of con Output terminal 214 is connected through a trol is not limited to the system described herein, but may be applied to other control systems. In a system where a rapid response is not required under certain conditions, one set of poppet valves could be dispensed with, and the system allowed conductor 255, coil 254 of a relay 255, a conductor 255, the lower half of transformer secondary winding 255, and conductor 25| to ground at 252. Secondary winding 255 forms a part of a trans form'er 251 having a primary winding 255 and additional- secondary windings 259 and 255. to oscillate under the control of a single set of poppet valves. ’ Secondary winding 255 is connected through con Figure 6 cooled engine |55 by modulating the position of ductors 255 and 25|, respectively to input ter minals 25| and 252 of bridge circuit 255. The secondary winding 255 is connected through con ductors 255 and 254 to power supply terminals 21| and 212 of amplier 255. Primary winding 255 is supplied with alternat the cowl naps |54 in a manner generally similar ing current by means of an inverter 255 of any to that disclosed in Figure 4. The system shown well known type, which is in turn supplied with In Figure 6 is shown an aircraft engine tem perature control system utilizing a modiiied em bodiment of my invention. Figure 6 shows a sys tem for controlling the temperature of an air direct current from a battery 255 through con ductor 251 and 255. Relay 211 includes a switch arm 555 movable that used in Fig. 4. A different type of bridge cir into engagement with a stationary contact 55| cuit is used however, and a somewhat different amplifier and motor control system is also used, 25 upon energization of coil 215. Relay 255 includes in Figure 6 utilizes a temperature responsive re sistance element |55 which may be the same as the system being completely electrical, rather a switch arm 552 movable into engagement with than partly electrical and partly hydraulic as in Fig. 4. a stationary contact 555 upon energization of coil 254. Temperature responsive resistance element |55 is connected in a bridge circuit 255 having input terminals 25| and 252 and output terminals 255 and 254. The upper left arm of bridge circuit 255 connects input terminals 25| with output ter minal 255 and includes temperature responsive resistance element |55. The upper right arm of bridge circuit 255 connects output terminal 255 and input terminal 252, and includes a fixed re sistance 255. The lower left arm of bridge cir cuit 255 connects input terminal 25| and output terminal 254, and includes a ñxed resistance 255, a conductor 251, and that part of a slide wire resistance 255 between its left hand terminal and its cooperating slider 255. Slide wire 255 and slider 255 constitute a rebalancing potentiometer for the bridge circuit 255. The lower right arm of bridge circuit 255 con nects output terminal 254 with input terminal 252 and includes that part of slide wire 255 between the slider 255 and its right hand terminal, the conductor 25|, and an adjustable resistance 252. The function of resistance 252 is to determine the control point of the system, in order words, it determines that temperature adjacent to resist ance |55 which causes the bridge to be balanced - The switches 555 and 552 control the energiza 30 tion of a reversible direct current motor generally indicated at 554, comprising an armature 555 and a. pair of field windings 555 and 551. The field windings 555 and 551 are so connected with re spect to the armature 555 that their selective 35 energization causes rotation of the motor in op posite directions. - Motor 554 drives, through a gear train schemat ically indicated at 5|5, a pinion III, which co operates with a rack 5|2 on a thrust rod 5|5. 40 The thrust rod 5|5 is slideable through a bear ing 5|4 of any suitable construction, which may be attached to a fixed part of the air craft. Pivotally attached to the thrust rod 5|! are a pair of links 5|5 and 5|5, pivotally connected at their opposite ends to cowl flaps |54. A motion reversing link 5 |1 is mounted on a fixed pivot, as at 5|5, and has one end attached by a suitable connection such as a pin and slot arrangement, to the thrust rod 5|5. The other end of link 5|1 50 is pivotally attached to a link 5|5, whose opposite end is attached to slider 255. Operation of Figure 6 ' The ampliiier 255 is so constructed that when when the rebalancing potentiometer 255 is in a i an alternating signal of a predetermined phase is given position. A variable resistance 255 is con nected in parallel with the slide wire 255. The function of resistance 255 is to determine the amount of movement of slider 255 necessary to connect a given unbalance of the bridge 255. Output terminal 255 is connected to an input terminal 255 or an electronic amplifier 255. applied to the input terminals 255 and 215, that branch of the output circuit extending through output terminal 215 and relay 211 is energized. When an alternating current signal of the op posite phase is applied to input terminals 255 and 215, the other branch of the output circuit including terminal 214 and relay 255 is energized. It will therefore be apparent that the relays 211 and 255 are selectively energized in accordance with the direction of unbalance of bridge cir \ Amplifier 255 may be of any desired type, but I `prefer to use one of the type disclosed in Figure 2 of the copending application of Albert P. Upton, Serial No. 437,561, dated April 3, 1942. Output terminal 254 of bridge'circuit 255 is connected to ground at 251. and through ground connec tions 255 to input terminal 215 of amplifier 255. Amplifier 255 has a pair of power supply ter mlnals 21| and 212, and a pair of selectively energizable output terminals 215 and 214. Input terminal 215. serves. through ground connection 255 as a common return terminal for the output terminals 215 and 214. cuit 255. With the parts in the positions shown in the drawings, let it Vbe assumed that the temperature adjacent the temperature responsive element |55 increases above the value which it is desired to maintain. This increases the resistance between input terminal 25| and output terminal 255 of 1 bridge circuit 255. This unbalances the bridge 255 in such a direction that an alternating poten 75 tial is applied to ampliiler 255 with the proper 9,403,917 Y n 18 . phase relationship to cause energization ofthe relay winding 215. 'Energization of relay winding 213 causes switch arm 300 to move into engage ment with contact 30|, thereby completing an- - . a space within said aircraft, duct means for sup plying air to said space, means i'or utilizing the motion of the aircraft to induce a iiow oi air through said duct means, a heater mounted in said duct means including a iluid fuel burner, valve means for modulatingly controlling the energizing circuit for field winding 301 and armature 355 of motor 304. This energizing cir cuit may be traced from the lower terminal oi' supply of fuel to said burner, an element having battery 2g! through a conductor 320, switch arm an appreciable temperature coeiiicient -oi' re 300, contact 30|, a conductor 32|, field winding sistance, means for mounting said element in a 301, brush 322, armature 305, brush 323, and a 10 position exposed to the temperature of the air conductor 324 to the upper terminal of bat in said space, a normally substantially balanced tery 235. ` electrical network including said element, an Energization of winding 301 and armature 305 electronic ampliner having an input circuit and causes'rotation or motor 304 in such a direction an output circuit, means for rebalancing said net as to rotate pinion 3| I counter-clockwise, thereby work, electrical motor means for operating said driving thrust rod 3|3 to the left. and opening - cowl flaps |54. Movement of thrust rod 3l! to the left also acts through links 3|1 and 3|3 to move slider 253 to the right, thereby increasing the ressitance between bridge input terminal 25| 20 and output terminal 254, and balancing the in creased resistance between input terminal 25| and output terminal 253 due to the increase in engine temperature. When the bridge is again balanced, the relay 211 is deenergized and motion ol.' the cowl ilap |54 and the slider 259 ceases. If the engine temperature decreases below the value it is desired to maintain, the bridge 250 is unbalanced in the opposite direction, thereby causing energizati'on of winding 284 of relay 285. Energization of relay winding 284 causes switch arm 302 to be closed against stationary contact 303, thereby completing an energizing circuit for winding 306 and armature 305 of motor 304. This circuit may be traced from the lower terminal of battery 295 through conductor 320, switch arm 302, contact 303, a conductor 325, iield winding 306, brush 322, armature 305, brush-323, and conductor 324 to the upper terminal of battery 296. Completion of this circuit causes rotation of motor 304 in such a direction as to rotate pinion 3|| clockwise thereby driving thrust rod 3I3 to the right and moving the cowl flaps |54 toward closed position. This movement of thrust rod 3|3 to the right also drives slider 259 to the left, thereby rebalancing the bridge circuit 250. I v valve means and said rebalancing' means simul taneously, a, continuously conductive electrical connection between said network and said input circuit, and another continuously conductive elec trical connection between said output circuit and said motor means. i 3. A system for controlling the temperature of ' an aircraft engine, comprising in combination, means for cooling said engine, an element having 25 an appreciable temperature coeñicient of resist ance, means for mounting said element in prox imity to a part oi said engine, an electronic amplifier having an input circuit and an output cir cuit, electrical motor means for controlling said 30 cooling means, a connection between said ele ment and said input circuit, and a connection between said output circuit and said motor means. 4. A system for controlling the temperature of an aircraft engine, comprising in combination, 35 means for cooling said engine, hydraulic means for operating said cooling means, an element hav ing an appreciable temperature coemcient of re sistance, means for mounting said element in proximity to a part of said engine, an electronic 40 ampliñer having an input circuit and an output circuit, electrical motor means for` controlling said hydraulic means, a connection between said element and said input circuit, and a connection between said output circuit and said motor means. ' 5. uA system for controlling a iluid operated servo-motor, comprising in combination, means While I have shown and described certain for supplying iluid under pressure, valve means specific embodiments of my invention, other mod controlling the flow of iluid from said supply iiications thereof will readily occur to those skilled means to said servo-motor, a device having an in the art, and I therefore wish to be limited 50 electrical characteristic variable in accordance only by the scope of the appended claims. with a condition indicative of the need for opera.' I claim as my invention: tion of said servo-motor, a normally balanced l. In combination, an aircraft, means deiining electrical network including said device, said de a space within said aircraft, duct means iorsup vice being operative upon a change in said con plying air to said space, means for utilizing the 55 dition to unbalance said network, means operated motion oi’ said aircraft to induce a ilow of air by said servo-motor for rebalancing said network, through said duct means, heater means in said an electronic amplifier having an input circuit duct means, means for controlling the amountv and an output circuit, means connecting said of heat transferred by said heater to the air iiow device and said input circuit, electric motor ing through said duct means, a temperature re means for operating said valve means. and means sponsive resistance element, means for mounting connecting said electric motor means and said said element in a position exposed to'the tem output circuit. perature of the air in said space, a second tem 6. A system for controlling a fluid operated perature responsive resistance element, means servo-motor, comprising in combination, means for mounting said second element in said duct 65 for supplying iiuid under pressure, valve means means on the ‘up-stream side of said heater means, » controlling the flow of iluid from said supply a normally substantially balanced electrical cir» vmeans to said servo-motor, a device having an cuit including both said elements, electronic am electrical characteristic variable in accordance plifier means having an input circuit and an ' with a condition indicative oi the need for opera output circuit, electrical motor means for operat 70 tion of said servo-motor, a normally balanced ing said control means, an electrical connection electrical network including said device, said de between said balanced circuit and said input cir vice being operative upon a change in said con cuit, and another electrical connection between dition to unbalance said network, an electronic ysaid output circuit and said motor means. ampliñer having an input circuit and an output 2. :in4 combination, an aircraft, means deñning 15 circuit, means connecting said device and said 2,403,917 . ' 19 . input circuit, electric motor means for operating controlling the flow of iluid from said supply` said valve means, means connecting said electric means to said fluid motor, leak means in said motor for permitting slow operation ot said motor ~ motor means'and said output circuit, means op erated by said electrical motor means for chang ing the balance condition of said network, and additional means' operated by said- servo-'motor for changing‘the balance condition oi said net,- under the influence of said biased load device whenl said valve means is closed, a device having an electrical characteristic variable in accordance with a condition indicative of the need i’or oper ation of said load device, a normally balanced work. ’1. A control system, comprising in t'z'oxnbiniei-` electrical network including said device, said de-> tion. a pressure operated reversible fluid motor. means for supplying fluid under pressure, at least two selectively operable valve means for oo_n trolling the flow of fluid from said supply means vice being operative upon a change in said condi.. tion to unbalance said network, means driven by said nuid motor for changing the balance to said fluid motor so as to cause operation there of selectively in either direction, reversible elec trical motor means .for operating said valve means, said electrical motor means having\-a normal position wherein all of said valve means are closed. and `being operable in opposite direc tions from said position to selectively open said valve means, a device having an electrical char acteristic variable in accordance with a condi tion indicative of the need for operation o! said fluid motor, a normally -balanced electrical net work including said device, said device being operative upon a change in said condition to unbalance said network, means responsive to un balance of said network to energize said electrical , condition 4of said network, and means responsive to the balance or unbalance of said network for operatingsaid valve means. 10. A control lsystem, comprising in combina tion, a load device biased to a predetermined position, a pressure operated fluid motor for ~driving said load against its bias, means for 20' supplying fluid under pressure, valve means i'or controlling the flow of fluid from said supply means to said fluid motor, leak means in said motor for permitting slow operation of said motor under the influence of said biased load device 25 when said valve means is closed, a device having an electrical characteristic variable in accord ance with a condition indicative of the need for operation of said load device. a normally balanced electrical network including said de motor means for operation in a direction corfresponding to the direction of said unbalance. 30 vice, said device being operative upon a change in said condition to unbalance said network, thereby opening one of said valve means. means means driven by said fluid motor for changing driven by said electrical motor means to re the balance 'condition of said network, second `balance said network. and means driven by said valve means for controlling the flow of fluid to fluid motor to unbalance said network in the opposite sense, thereby energizing said motor i'or` 35 said motor, said second valve means when open, permitting the ilow of iluid to said motor so operation in a direction to close said one valve as to drive said load -rapidly in the direction of means and again rebalance said network. its bias, and means responsive to the balance 8. A control system, comprising in combina condition of said network for operating said valve tion, a load device biased to a predetermined position, a pressure operated fluid motor for 40 means, said balance responsive means opening said first valve means upon an unbalance of said driving said load device in opposite directions,' network in a direction indicative of a need for means for supplying fluid under pressure, a pair movement of said load against its bias, and open ot valve means for controlling the flow of fluid ing said second valve means only upon a rel from said supply means to said fluid motor so atively large unbalance of said network in a as to cause operation thereof selectively in either direction indicative o! a need for movement oi direction, leak means in said motor for permit said load in the direction of its bias. ting slow operation of said motor under the ln 11. In combination, an aircraft, means defining iluence of said biased load device when both said valve means are closed. reversible electrical motor means for operating said valve means, said elec- f trical motor means having a normal position wherein both oi said valve means are closed, and being operable in opposite directions from said position to selectively open said valve means, a device having an electrical characteristic vari able in accordance with a condition indicative of the need for operation of said fluid motor, a normally balanced electrical network including said device, said device being operative upon a change in said condition to unbalance said net work, means responsive to unbalance of said net work to energize said electrical motor means for operation in a direction corresponding to the direction of said unbalance, thereby opening one of said valve means. means driven by said elec trical motormeans to rebalance said network, and means driven by said iluid motor to change the balance condition oi' said network in the same a space within said aircraft, duct means for sup plying air to said space, means for utilizing the motion of said aircraft to induce a flow oi‘air through said duct means, heater means,in said duct means, means for controlling the amount of heat transferred by said heater to the air flow ing through said duct means, a first temperature responsive resistance element, means for mount» ing said element in a position exposed to the tem perature of the air in said space, a second tem perature responsive resistance element, means for mounting said second element in said duct means on the up-stream side of said heater means, a third temperature responsive resistance element. means for mounting said third element in said duct means in the path oi air discharged from said heater means, said first element having a resistance at least ten times that of each of said second and third elements, a bridge circuit in cluding all said elements in such a manner that sense as said rebalancing means, so as to cause a change in any oi the elements in a certain sense reversal of said electrical motor. 9. A control system, comprising in combina unbalances the bridge circuit in the same sense, and means responsive to unbalance of said bridge tion, a load device biased to a predetermined position, a pressure operated fluid motor for means.` circuit tooperate said heat transfer controlling 12. In combination, an aircraft, means defining driving said load against its bias, means for supplying fluid under pressure, valve means ior 75 a, space within said aircraft, duct means for sup «- amaai? ' plying air to said space, means for utilizing the motion of said aircraft to induce a flow of air through said duct means, heater means in said duct means, means for controlling the amount of heat transferred by said heater to the air iiow ing through said duct means, a first temperature responsive resistance element, means for mount ing said element in a position exposed to the tem peî‘ature of the air in said space, a second tem 22 cient of resistance and exposed to the tempera ture of the air warmed by said heater, means including said element for producing an alter hating electrical signal of a phase dependent upon the direction in which said heat transfer control means needs to be operated, amplifier means for controlling the direction of operation of said mo tor means in accordance with the phase of said signal, said amplifier means having an input cir perature responsive resistance element, means for 10 cuit and an output circuit, means coupling said signal producing means and said input circuit, mounting said second element in said duct means means coupling said output circuit and said mo on the up-stream side of said heater means, a tor means, and means for supplying said signal third temperature responsive resistance element, producing means, said amplifier means, and said means for mounting said third element in said duct means in the path of air discharged from 15 motor means with alternating electrical energy of fixed frequency and predetermined phase rela said heater means, said first element having a tionships, said energy supplying means compris resistance at least ten times and not more than ing a transformer having a primary winding and fifty times that of each of said second and third at least three secondary windings, means con elements, a bridge circuit including all said ele ments in such a manner that a change in any of 20 necting one of said secondary windings to said signal producing means, means connecting a sec the elements in a certain sense unbalances the ond of said secondary windings to said amplifier means, means connecting a third of said sec sponsive to unbalance of said bridge circuit to ondary windings and said motor means, and operate said heater controlling means. 13. Electrical temperature control apparatus 25 means including a battery and an inverter for supplying said primary Winding with alternating for an aircraft, comprising in combination, heat bridge circuit in the same sense, and means re producing means on said aircraft, means for uti lizing the fiow‘of air caused by the motion of said aircraft to conduct air into heat exchange electrical energy. ` 15. Electrical temperature control apparatus for an aircraft, comprising in combination, an relation with said heat producing means, means 30 ï engine on said aircraft, means for utilizing the flow of air caused by the motion of said aircraft for controlling the amount of heat transferred to conduct air into heat exchange relation with from said heat producing means to said air, re said engine to cool said engine, damper means versible electrical motor means for operating said for controlling the iiow of air into heat ex heat transfer control means, an electrical re change relation with said engine, reversible elec 35 sistance element having an appreciable tempera trical motor means for operating said damper ture coefficient of resistance and exposed to a means, an electrical resistance element having temperature indicative of the need for operation an appreciable temperature coefficient of resist ance and exposed to the temperature of said cluding said element for producing an alternating engine, means including said element for produc electrical signal of a phase dependent upon the 40 `ing an alternating electrical signal of a phase direction in which said heat transfer control dependent upon the direction in which said of said heat transfer control means, means in means needs to be operated, amplifier means for controlling the direction of operation of said mo tor means in accordance with the phase of said signal, said amplifier means having an input cir cuit and an output circuit, means coupling said damper means needs to be operated to maintain the temperature of. said engine within a predeter mined range, ampliñer means for controlling the direction of operation of said motor means in accordance with the phase of said signal, said signal producing means and said input circuit, amplifier means having an input circuit and an means coupling said output circuit and said mo output circuit, means coupling said signal‘pro tor means, and means for supplying said signal 50 ducing means and said input circuit, means cou producing means, said amplifier means and said pling said output circuit and said motor means, motor means with alternating electrical energy and means fOr Supplying said signal producing of fixed frequency and predetermined phase re means, said amplifier means and said motor lationships, said energy supplying means com- ^ means with alternating electrical energy of nxed prising a transformer having a primary winding 55 frequency and predetermined phase relationships, said energy supplying means comprising a trans and at least three secondary windings, means connecting one of said secondary windings to said former having a primary winding and at least signal producing means, means connecting a sec three secondary windings, means connecting one of said secondary windings to said signal produc ond of said secondary windings to said amplifier means, means connecting a third of said second ary windings and said motor means, and means including a battery and an inverter for supplying said primary winding with alternating electrical energy. 14. Electrical temperature control apparatus for an aircraft, comprising in combination, a heater on said aircraft,_means for utilizing the flow of air caused by the motion of said aircraft to conduct air into heat exchange relation with said heater to warm said air, means for control ling the amount of heat transferred from said heat producing means to said air, reversible elec trical motor means for operating said heat trans fer control means, an electrical resistance elc _ ment having an appreciable temperature coem ing means, means connecting a second of said secondary windings to said amplifier means, means connecting a third of said secondary wind ings and said motor means, and means including a battery and an inverter for supplying said pri mary winding with alternating electrical energy. 16. Electrical control apparatus, comprising in combination, a load device to be controlled, re versible electrical motor means for controlling said load device, means including a device responsive to a condition indicative of the need for operation of said load device for producing an alternating electrical signal of a phase de pendent upon the direction in which said load device needs to be operated, ampliñer means for controlling the direction of operation of said Y 2,403,917 24 motor means in accordance with the phase of said signal, said amplißer means having an input cir cuit and an output circuit, means coupling said signal producing means and said input circuit, means coupling said output circuit and said 18. In electrical temperature control apparatus for an aircraft having heat producing means and means for utilizing the flow of air caused by motion oi said aircraft to conduct air into heat exchange relation with said heat producing means, means for modulatingly controlling the motor means, and means .for supplying said ' signal producing means, said amplifier means and amount of heat transferred from said heat pro ducing means to said air, an element having an said motor means with alternating electrical energy of ilxed frequency and predetermined phase relationships, saidenergy supplying means appreciable temperature coefficient of resistance and exposed to a temperature within said air comprising a transformer having a primary wind craft indicative of the need for operation of said heat transfer control means, a normally substan-~ ing and a plurality of secondary windings, means connecting one `oi’ said secondary windings to said signal producing means, means connecting a second of said secondary windings to said am pliiler means, means connecting a third of said secondary windings and said motor means, and means including a battery and an inverter for supplying said primary winding with alternating tially balanced electrical network including said 15 element, an electronic amplifier having an input circuit and an output circuit, means for rebalanc-. ing said network, electrical motor means ‘for operating said heat transfer control means and said rebalancing means simultaneously, a ccn~ tinuously conductive electrical connection be»1 electrical energy. 20 tween said network and said input circuit, and i7. In combination. an aircraft, means defining another continuously conductive electrical con-~ a space within said aircraft, duct means for sup nection between said output circuit and said mo DLViIiS air to said space, means for utilizing the tor means. motion of said aircraft to induce a flow of air 19. In electrical temperature control apparatus through said duct means, heater means in said 25 for an aircraft having an engine and means for duct means, 'means for controlling the amount of utilizing the ilow of air caused by motion of said aircraft to conduct air into heat exchange rela tion with said engine to cool the same, means for modulatingly controlling the flow of air into heat ing said element in a position exposed to the temperature of the air in said space, a second 30 exchange relation with said engine, an element having an appreciable temperature coefficient oi" temperature responsive resistance element, means Y resistance and exposed to the temperature of said for mounting said second element in said duct heat transferred by said heater to the air flowing through said duct means, a iirst temperature responsive resistance element, means for mount means on the up-stream side of said heater engine, a normally substantially balanced elec means, a third temperature responsive resistance 85 trical network including said element, an elec~ tronic amplifier having an input circuit and an element, means for mounting said third element output circuit, means for rebalancing said net in said duct means in the path of air discharged work, eiectrical motor means for operating said from said heater means, one of said elements air flow controlling means and said rebalancing having a resistance at least ten times that of each oi' the other two elements, a bridge circuit 40 means simultaneously, a continuously conductive electrical connection between said network and including all said elements in such a manner that said input circuit, and another continuously con a change in any of said elements in a certain ductive electrical connection between said output sense unbalances the bridge circuit in the same circuit and said motor means. sense, and means responsive to unbalance of said bridge circuit to operate said heat transfer con trolling means. WILLIS H. GELE.