Патент USA US2110754код для вставки
MarärS, 1938. c. H. T. ALs'roN 2,110,754 COMBUSTION ENGINE Filed Nov. l25. 1936 5 Sheets-Sheet vl Marchß, 1938. ' c, H, T_ ALSTON 2,110,754 C-OMBUSTION ENGINE Filed Nov. 25, 195e E _ @1% CW 5 sheets-shea 2 March 85,1938. 2,110,754 c. H. T. ALsToN COMBUSTION ENGINE ‘ Filed NOV. 25. 1936 5 Sheets-Sheet 3, f J.du, ,g _T77 ven-far, . my MarchS, 1938. ' ¢_ H, T_ ALSTQN ’ y' ‘ 2,110,754 coMBUsTloN ENGINE v Filed Nov. 25. 195e s sheets-sheet 4 Patented Mar. 8, 1938 ~2,110,754 " UNITED »STATI-:s Pn'rlëzlsrry OFFICE ~ coMnUs'rroN ENGINE l Charles Henry Thomas Alston, Sidmouth, Devon, _ England - f l Application November 2.5, 1936, Serial No. 112,804. v t. In Great Britain November 30, 1935 12 claims. (ci. 12s-'16)` This invention is for improvements in? four str'oke cycle internal-combustion engines of the kind in which one- or more inlet and-exhaust ports in the cylinder wall communicate lwith a rotary 5 ‘ distributing valve by which the inlet and exhaust gases are controlled. inder displacing the exhaust gases therein out at the main ports. ` A The piston rises displacing the exhaust gas remaining immediately above it through the main ports until it covers the latter. Thereafter, until the top of the upstroke, the piston compresses the 'I'he invention is principally intended >for appli-f v air, or air and exhaust products, above it- into cation to lcompression-ignition engines but may ' the-combustion chamber absorbing the inertia of also be applied to engines having spark-ignition. the piston line and cushioning theparts. The principal objects of this invention are >to On the succeedingv downstroke this air reex provide a four-stroke -cycle engine capable of. high pands restoringmost or all of the work done in -10 speciñc output .(with a clean- exhaust) having a compressing it until the mainA ports in the wall' combustion chamber lfree from valves and also are again uncovered. to dispense with reciprocating valve gear and to ‘y By this time the rotary valve has turned clos- ' 15 cushion the inertia of ¿the parts on the exhaust ing the opening to the exhaust pipe and opening , stroke. " ` that to the air inlet. ‘ The engine belongs to that type in which a portI or ports are placed in the wall of the working cylinder so arranged as to 'be covered by thev pis ton lwhen at the top of its stroke which ports communicate with a rotary distributing valve for inlet and exhaust, the intention `being to protect the valve from the highest temperature and pres sure. - ' M ~ In such' engines as hitherto constructedit has ' Thereafter the piston drawsin air through the ‘ main ports until near the end of its >’downstroke when the air inlet port shuts _and the auxiliary ports through which lthe scavenging air was ad-r mitted again open and air under pressure once more enters the cylinder and. since there is now no outlet, supercharges the contents of the cylin der to a pressure above atmospheric. >Specific embodiments of the present invention been found that these ports cannot be placed ’will now be described by way of example with suiliciently >far down the 'piston stroke for the reference to the Vaccompanying diagrammatic adequate` shielding of the rotary valve from ex cessive temperature and-pressure without the per formance of the engine suii’ering on account of the very imperfect expulsion of the exhaust -gases and restriction of_the'volume .off the new charge In the drawings, Figure 1 shows one form of the invention in y _ - f- ' . In carrying this invention into eiîect the ports Ã leading to the‘rotary valve (hereinafter termed the “main ports”) are placed well down the stroke, say'about' the middle of the stroke, so as to be uncovered by the top ofthe piston when it has performed about 40% or 50% of its down 40 drawings of a four-stroke cycle compression-ig nition engine. although in certain cases the in vention ma also be applied to engines having 30 spark-ignit on'. , p from this cause. 25 I » which the piston of the engine also constitutes a supercharging and scavenging pump, _ ' VFigure 2 is a sectional plan on the line 2-2 of Figure 1, ‘ - ` t: eil V Figure 3 is a valve-diagram of the engine of Figures 1 and 2; n , „ ' Figure 4 illustrates an alternative form of» Fig ¿By that time the temperature and pressure of n ure 1, _Figure 5 being a sectional plan on the line 40 the expanding gases are much reduced and, 5_5 of Figure 4, „ . ' . ’ therefore, the leakage past the valve is less as ` Figure 6 illustrates anarrangement in -which are also Vthe ill eiîects of such leakage, and-the an external supercharger is used, Figure rI'being ,- conditions _under which the. valve operates are an alternative to Figure 6, much improved.Í ~ . Figure 8 illustrates anl alternative'formof Figs 'I As the piston approachesv the end of its power ures y6 and 7, in which compressed air is admitted _stroke the rotary valve` in turning opens the main to the cylinder through a doublefvalve, ports in the cylinder wall to the exhaust pipe . Figure 9 'is a plan showing» one' arrangement and the expanded gases discharge themselves to of supercharger’for-the engine of Figure 4 or the latmosphere. Shortly afterwards scavenging Figure 8, Whilst Figures 10- and 1l show alterna ~air is admitted through` another port' or ports tives to Figure 9, n . » stroke. from a source under pressure. - ` , This air is' directed upwards towards the com? 55 bustion chamber and the upper part of the cyl ' Figure l2 illustrates a modification inwhich the twol valves are arranged at the- same level,1~ and on opposite sides oi’ the cylinder Wall,` 2 ' . 2,110,754 -the port 20 so that the 'piston sucks air from the atmosphere into the chamber I9. The port 22 Figure 131s- a valve diagram of the engine ' shown in Figure 12.k being closed by the valve 23, upward movement Figure 14 is an alternative Aformo! the engine A of the piston compresses the charge of air in~ shown in Figure 12, l the cylinder, which compression continues until ' »Figure 15 illustrates a modiilcation in which the supercharging -air is supplied through the the top dead-centre (E, Figure 3) has been reached. At or near the top of the stroke o! the piston, fuel is injected through the nozzle I2 and inlet valve, - Figure 16 isa valve diagram‘of the engine of combustion ensues. Figure 15, '10 ' ‘ tion of Figure 15, whilst other charge of air in the chamber I9, the port ' Like parts are denoted by the same reference numerals throughout the several ilgures of the drawings. Y ' ' power stroke and as it does so it compresses an l Figure- 18 shows how the valves and blowers of AFigure-17 Imay be driven from the crankshaft. V15 ' The piston no'w begins to move down on its 10». ‘ Figure 17 is an alternative _form'of the inven-f> 2li again being closed by the valve 2|. . During the power stroke the rotary valve 23 is protected from the intense pressure and heat' in the combustion chamber until the crown of - ‘ As' shown’ilrst in Figures l and 2, the cylinder I0 is formed with an injection chamber II at the top, with which chamber an injection nozzle vI2 the piston uncovers the port 22-and by this time the heat and pressure will have considerably di mini’shed owing to the expansion >oi! the charge. At a point (F, Figure 3) between the uncovering 20 2.0 communicates, being supplied with liquid fuel « of the port 22 and the end of the stroke, the _ through a conduit I3. ' The piston I4 is formed with a portion I5 of reduced diameter which is guided in a crosshead guide I3 and which is connected by a gudgeon 25 pin'I1 and connecting rod Il to the crank pin in theS usual way. Surrounding the lower end of the cylinder I3 is a chamber I! having a port 20 communicating with 'a rotary valve 2l., port 25_in the rotary valve 23 moves into regis ter with the port 22 whereby the products of com bustion are discharged through an exhaust pas sage. Finally, as the piston nears the position 25 shownv in.Figure l, the ports 21 again open (G, ‘ Figure 3) and compressed air from the chamber I9 enters the cylinder and is -directed upwardly in a central column as shown by the arrows in About half-way up the cylinder wall is a port Figure 1 so as to displace the exhaust gases. By' 22 communicatingwith a rotary valve 23 which e 30 this arrangement the exhaust gases at the top of is formed with two ports _24 and 25 whose i’unc the cylinder are driven out by the scavenging air tion is to admit a charge of air to the cylinder and the remainder of the exhaust is expelled by . and to open the cylinder to exhaust, respectively. the rising piston. ' As shown also in Figure 2, the rotary valve 2| Early in the succeeding up-stroke of the piston- 35 is‘rormed with two ports 2s through which ahv v I4, the ports 21 are closed, this point being 35 is admitted to the chamber >I9 for a Purpose de shown by H in Figure 3. Expulsion of the ex scribed below. However the invention is not lim# haust gases continues, however, until the crown ited to the use_of rotary valves for the control of of the piston passes the port 22and`soon after the scavenging or supercharging air. ' The cycle performed by the engine of Figures wards, at the point J, Figure 3, the valve 23 closes 40 the port 22. The top of the cylinder nowV con 1 and 2. will now be described with reference tains clean air with a small proportion of prod also to Figure 3 which is the ~usual valve diagram, - the charging revolution being shown on the-lei'tl ucts of combustion mixedwith it, and this mix and the power revolution on the right. l The piston will be considered as starting from the beginning of the charging stroke so that it is ,at the top of the cylinder. This positionA is shown by A in Figure 3. .The -chamber II, for ture is compressed during the remaining part of the up-stroke of the piston, thereby absorbing the inertia of the piston and other moving parts. The'point -A is now reached again and the cycle has been completed. l ~ 'I'he valves 2i and 23 may be driven by a reasons explained below, already containscom- , vsprocket 12 on the crankshaft', which engages a 50 pressed air land as the piston moves down, this air expands so that substantially the whole of the energy which was used in compressing it is regained. When the crown vof the piston i 4 reaches the port 22, the valve 23 will have rotated into a position in which the port 24 registers with llili theport 22 so that air is now free to enter the cylinder. 'I'his position is shown as B. in Figure 3. Suction of-the charge into the cylinder con tinues until nearly the end of the stroke, when the valve `23 closes the port 22. ~ - During the downward movement oi' the piston the annular overhanging portion represented by the difference in diameter between thev parts I4 and I5 ofthe piston compresses the air in the 65 chamber I9, the port 2l remaining-closed by` the rotary valve 2i, so that when the piston reaches ~ a point near the bottom of its stroke as shown by C in Figure 3, the compressed airfrom the cham ber I9 enters` the cylinder through 21 70 formed at the bottom of the cylinder wall. The cylinderl is thus supercharged and the ports 21 chain 14 driving a sprocket 13 carried by the valve 23. The valve 23 also carries a gear 10 which meshes with a gear 1I carried by the valve 2|. The sprocket 13 is twice the diameter of the sprocket 12 and the gears 1U' and 1I are of equal diameter so that the valves 2 I~ and 23 are driven - in the directions of the arrows"'-at one-half of the crankshaft speed. Similar drivingarrange ments may be employed for the valves of the ' forms of the invention illustrated in the other 60 ilgures of the drawings. , f In the arrangement described with reference to Figures 1 and 2, the differential piston I4, I5 'providesvthe compression both i'or scavenging and for supercharging, but in the modiiled ar 65 rangement of Figures 4 and 45, the valve 2l is replaced by a composite valve 28 having two chambers; an inner chamber 2l which commu nicates with the .port 2l through a port 3l and an outer chamber 3i which communicates with the port 20 through a port 32. As shown in _Fig-, ure 5,~ the chamber 2l is connected by a suitable y remain open until a point early inn the succeed- _ rotating joint to the discharge pipe 33 oi' a ro ing up-stroke of the piston denoted by D in Fis tary pump 34 on the intake side of whichis a . ure 3. Early in the up-stroke of the piston, one of . 75 theports 28intherotaryvalve 2I rw’th controlling or reducing valve 3i. The 2,110,754 \ 3| on the other hand,_ is permanentlxgopen to the atmosphere. ' ß - . - 3 . into the chamber 23 which, as has already been explained, supplies the supercharging air to the 'I'he cycle of the engine shown in Figures 4 and Acylinder. The controlling valvew35 is arranged in the communicating conduit 44'so that the de 5 'reference to/ Figures 1, 2,l and 3 but itlhas the `gree of supercharge may be regulated thereby. 5 ì 5 is identical with that already described with ~advantage/that the degree of supercharge can . The .pressure of the scavenging air, however, is be augmented and regulated by the controlling produped by the blower 4i and remains constant. -valve-3 , the pressure necessary for scaveng- ^ A modified form of the invention is shown in l ing being constant _and obtained by- the differ vthe diagram of Figure 12in which 'the rotary valve l0 _ential/piston as before. - ' 23 is similar to that already described with ref They form ofthe invention shown in Figures 1 erence to Figure 1, but the ports 21 for the inlet ‘ and 4' may employ, in combination.' a'rotary of scavenging and supercharging «air are arranged pump or blower to increase thel supercharging not at the bottom of the cylinder but at a point pressure‘produced by the pumping »chamber be on a level with. the port 22. 'I'he ports 21 are15 low the piston. The blower- could be »connected controlled'by a rotary valve 2l having ports 45 to the pumping- chamber through a distributing and 46. 'I'he cycle of- the engine shown in Figure ' valve in such manner that the scavengingair -12 will now be described with reference .to the , pressure is unaugmented and only the super charging air has its pressure increased. ‘ 20 » In some cases, instead of constructing the pis-` valve diagram of Figure 13,` like letters being used for points in the cycle corresponding to those » shown in Figure 3. . ' ton with a reduced portion i5 working in a cross head as shown in Figuresl and 4, the arrange At the top dead-centre A the chamber Il con tains compressed air as in the «case of Figure jl ment shown in Figure 6A may be used with ad and as the piston moves down on the charging vantage. Here the port or ports 21 are supplied stroke, this air expands and the energyfwhich A25 with air- under, pressure throughv a conduit 36 was expended on 'compressing it is substantially from the discharge side' of a' rotary pump134 regained. When the piston .i4 uncovers the portl which thus serves- for supplying both the scaveng- - 22 the valve 23 has moved into a. position in which ing' air and the supercharging air. ' 'I‘he scaveng the inlet port 24 registers with the port 22 so' ing air rises to the top of the cylinder as shown that air for combustion can be sucked into thei 30 by the arrows. In the arrangement of Figure 6, ~»cylinder by the> remaining part of the down-‘30 the ports 21 are opened and closed-solely by the stroke of the piston. Suction` takes place from f movement of the piston I4, butin the alternative B to K. When the piston .is nearly at the bottom arrangement shown in Figure'l, the ports 21Y of its lstroke the valve 2| brings the port 45 into ‘may be controlled by a rotary valve 2| similar register-~ with the port` or ports 21,. whereby air 35 to that shown in Figure 1. 'I'he interior of the under pressure is admitted to the cylinder and 85 valve. is, in this case, supplied with air under continues to be admitted over a period CD, D o_c pressure >by arotary pump similar to the pump curring during the early part of the succeeding 34 of Figures 5 `and 6. Y l upward4 travel of the piston. ' A `further alternative possibility is shown in Figures 8 and 9. In this form of 1the invention the ports 21 are controlled by a rotary valve 28 -similar to that shown in Figure 4, but whereas the chamber 3| in Figure 4 is directly open to the _ atmosphere, in Figure 9 this chamber is supplied 7,' with air under pressure vthrough aseparate con-duit 31 4from therotary pump 34, The conduit 33, -in this case, through which the supercharg All the ports are now closed and the charge of air is compressed until >the piston again reaches the top dead-centre at VE. Fuel injection and combustion ensue and the piston moves4 down >on its power stroke. About half-way down its stroke it uncovers the ports 22 and 21 so that'the valves 2i and 23 are exposed'A to the heat and pressure of the burn- ing charge in the cylinder, but' by the time this point is reached the heat and pressure have con ing air is supplied to the central chamber 29 of _ siderably diminished so that the valves are not the valve‘is fitted with the regulating valve 35 damaged. -At a point F near theend of the so that the scavenging air and the supercharg- , down-stroke, the valve 23 brings the port 25 into ' ing air are both supplied-‘by the rotary pump 34, register ‘with the port 22 so that exhaust takes but whereas the pressure of the scavenging air place and continues well into the succeeding up- remains constant; the pressure ’ of the super ginning of suchv up-stroke (G, Figure 13), the valve 35. „ valve 2ll brings the port 46 into register with the o ports 21, whereby air under pressure is blown into the cylinder and the exhaust gases are swept out through theport 22 and are largely replaced by clean air. This scavenging action continues » . f f _ Instead of using a single pump 34 for suñply-. ing both scavenging air and supercharging air, V60 „ stroke of the piston. However, soon after the be charging air may be controlled by vmeans Iof the separate pumps 39. 40 respectively, may be used as shown in Figure 10 which is an alternative to that shown in Figure 9. Here the twoconduits until the crown 4of the piston covers the ports 22 33 and 31 are'entirely separate and the control ‘ and 21, this point being shown by the point HJ ling valve 35 may be arranged on the intake side s in Figure 13. The remaining part of the up~ of the pump 33 which is- an advantageous ar# ,stroke of` the piston is occupied by compressing the substantially clean air remaining in the cyl AYet another possibility ’is illustrated in Fig inder until the point A is again reached and the ure liin which the rrotary pumps are replaced cycle has been completed. ' _ ‘ _ - 'f l by a two-stage centrifugal blower 4I, 42 the ro- ' ’I'he arrangements shown in Figures 12, 14, and rangement. . , ' ' ` , - torsof'which are carried on a common shaft 43 which maybe driven by any suitable means 7o such as an exhaust-driven turbine. The iirst stage 4I discharges through‘a conduit 31 into the chamber~3i ofthe rotary ,valve 28- and.l part of the compressed air ‘passes b'y way of a conduitl s 4'4 into the intake ofthe second-stage blower 42. 75 The blower 42 discharges through a 'conduit133 15 may be used in combination with a pumping chamber of the kind Adescribed with reference to Figure l for supplyingthe compressed air. That is to say, the piston `would compress the air but the valve 2i similar to that shown in Figure 12 would supply a port abou alf-'way up the wall of the cylinder. Such an arra gement has the ad vantage that it obviates the diii’iculties caused by ’ 2,110,754. 4 leakagev past the piston near the end of the down-stroke. In a further _modification of this form of the invention, the clearance volume be low the piston may be replaced by a separate re ceiver in which the air is compressed prior to its admission to the cylinder. Such an arrange ment has the advantage that it provides morev scope for' timing the entry of thev scavenging air. In the alternative arrangement shown in Fig ure 14, the valve for controlling the ports 2'| is modified to correspond to the‘valve 23 of Figure 4 `in which there >are separate compartments for jsupercharging and scavenging air. These sep _ _ ating cycle the contents of the cylinder may bev discharged through-thev port and during another period of the operating cycle air may be _admitted to the cylinder through the port. ' - 2. In an internal combustion engine of the -four-cycle type, a- cylinder, a piston in the cyl inder, a port in the cylinder wall so located that it is uncovered by the piston only after a portion, of its stroke has been completed, a rotary dis tributing valve' connected to said port and of, 10 such, a character that at one period of the oper ating cycle the contents of the. cylinder may be _ -discharged through the port and duringy another period of the operating cycle air may be admitted tively with sources of air at different pressure. to the cylinder through .the port, and means for Otherwise the arrangement is identical with that admitting scavenging air to the, cylinder during part of the exhaust period. described with reference to Figures 12 and 13. 3. In an internal combustion engine ofthe In the modiñed arrangement of Figure 15 the four-cycle type,.a cylinder, aA piston in the cyl valve 2| is used solely for supplying .the scaveng inder, a port in the cylinder wall so located that 20 20 ing air to the cylinder and~ supercharging is ef fected by supplying air under pressure to the port it is uncovered by the piston only after a portion 2l in the valve 23. A rotary pump 34 discharges of its stroke has been completed, a rotary dis through a conduit 49 to the chamber ‘50 in the ltributing valve connected to -said port and of valve 23 with\ which the port 24 communicates. such a character that at one period of the oper The conduit 9 -contains a controlling >valve 34 ating cycle the contents of the cylinder may be discharged through the port and during -another whereby the ydegree of supercharge may be reg ulated. A branch pipe 5| delivers compressed _period of the operating cycle air may be'admitted .\ ' arate compartmentsmay communicate respec- ` . air from the pump to the interior of the valve 2| from which it passes through the ports 45 and 21 into the cylinder. ` The cycle obtained with the engine .of Figure 15 is shown in the valve diagram of Figure 16. 'I‘he arrangement of Figure 15 may be modiiied as shown in Figure 17 by the employment of sep arate pumps 39 and 40 ‘for the supercharging and scavenging air respectively. In this arrangement the controlling valve 35 may be advantageously disposed on the intake‘side of the pump 39. y The various rotating accessories of Figure 17 40 may be driven by the crankshaft as shown in Figure 18. The crankshaft 53`carries a pinion 54 which drives a gear 55 on a lay-shaft 56. The lay-shaft also carries a chain-sprocket 51 and similar sprockets 59 and 59 are carried respec tively by the valves 2| and 23. A single chain 60 passes around all three sprockets. The gear y to the cylinder through the port, means for `ad mitting scavenging air to the cylinder during part-> of the exhaust`period, and means for supercharg ing the cylinder. ’ 4. A four-stroke cycle internal combustion en gine comprising a piston, a cylinder having _a wall, an inlet and exhaust port soplaced in said. `wall as_to be covered by the piston when at the top of its stroke, a rotary distributing valve com municating with said rt, and means for admit ting scavenging air to the cylinder during partof the exhaust period to prevent the trapping of exhaust gas in the cylinder. - 5. `A four-stroke cycle internal combustion en gine comprising a piston, a cylinder- having a wall. an inlet and exhaust port so, placed in said wall as to be covered by the piston when at the top of its stroke, a rotary distributing valve com 45 municating with said port, means for admitting 'scavengingair to the cylinder during pai-tof the `_exhaust period to prevent the trapping of exhaust crankshaft speed which is the requirement for gas in thecylinder, and means for supercharging 55 has twice as many teeth as the pinion 5l so that the valves 2| and 23 are driven at one-half the cycle above described. the cylinder. j The crankshaft also carries a sprocket 6| ,and the vblowers _39 and 40 carry similar sprockets Bland 63. A chain 64 engages‘all three sprockets whereby the blowers 39 and 40 are driven at ' " v 50 n 6. A four-stroke cycle internal combustion en gine ‘comprising a piston, a cylinder wall, an inlet and exhaust port so placed in said wall as to be covered by the piston when at the top of its stroke,_ a rotary distributing _valve com- , _ municating with said port, and scavenge ports It will beunderstood that the accompanying arranged near the -bottom of the swept space oi ' crankshaft speed; although any suitable gear ratio may be employed. ' - drawings are`"merely diagrammatic and that the external and general arrangement of an engine according tothe invention may be of conven tional form. Any number of cylinders may be employedrand the blowers illustrated may supply all the cylinders. Where the cylinders are ar ranged inline, each of the valves shown may the cylinder. ,_ y 7. A four-stroke cycle internal combustion en gine Acomprising a piston, a cylinder wall, an inlet and exhaust port so placed in said wall as to be covered by the piston when at the top'of its stroke, a rotary -distributing valve communi c'ating with saidÍ port, and scavenge ports ar ranged at a point about half way down the extend continuously- along 'the line, of cylinders swept space of the cylinder. ' _ having ports»suitably_v arranged according to the , 8. A lfour-stroke cycle internal combustion en gine comprising a piston, a cylinder wall, an inlet and exhaust port so placed in said wall as l. In an internal _combustion engine of the , to be covered by the pistbn when at the top oi' 70 four-cycle type,»a cylinder, a piston in the cyl its stroke, a rotary distributing valve communi inlder, a port inthe cylinder wall so located that _ cating withsaid-port, scaveng'e ports arranged _ itgis uncovered bythe piston only after a portion _ at or near the bottom of the swept‘space of the wof its strokehas been completed, and a rotary cylinder, and means forsupercharging the cyl _distributing valve connected vto said port and of inder through said inlet and exhaust port. 75 ` 75 such a character that at one- period of the oper 5 2,1 10,754 9. A four-stroke cycle internal combustion en tures claimed in claim 5, means for supplying - gine comprising a piston, 'a cylinder wall, anA the scavenging air and the supercharging air at inlet and exhaust port so placed in said wall as different pressures. to be covered by the piston when at the top of its stroke, a rotary distributing valve communi eating with said port, ports disposed near the bottom of the swept space of the cylinder for the admission of super-charging and scavenging 11. A four-stroke cycle internal combustion engine comprising, in combination with the fea tures claimed in claim 6, means for .supplying the scavenging air and the supercharging air at diife?ent pressures. air, a valve-controlled conduit leading to the said,I 12. A four-stroke-cycle internal-combustion, 10 ports, and means for compressing by the piston - engine comprising, in combination with the fea 10 the scavenging air and the air for supercharging tures- claimed in claim 7, means for supplying prior to their admission to the cylinder. scavenging air and supercharging air to the said 10. A four-stroke cycle internal combustion` scavenge. ports at'diiiîerent pressures. engine comprising, in combination with the fea CHARLES HENRY THOMAS ALSTON. .