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Патент USA US3095233

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June 25, 1963
O.KAUP
-
3,095,221
PISTON CONSTRUCTION
Filed Oct. 25, 1961
2 Sheets-Sheet 1 -
m venz‘or
OTMAR KA UP
19% gm
June 25, 1963
o. KAUP
,
Filed Oct. 25, 1961
PISTON
CONSTRUCTION
‘
3,095,221
'
,
2 Sheets-Sheet 2
INVENTOR
07'MAR KAUP
BYWMM/W
ATTORNEY5
United States Patent 0 "ice
1
3,995,221
Patented June 25,‘ 1963
2
will be positioned at the intersection of the projected
ellipse with the minor axis of this ellipse. In this posi
3,095,221
PISTON CGN§TRUCTIGN
tion the connecting rod is inclined with respect to the
Gtmar Kaup, Aschaifenburg, Germany, ‘assignor to Ge
major axis of the ellipse. The major axis of the ellipse
sellschaft fur Linde’s Eismasc‘ninen Aktiengesellschaft,
also represents the intersection of a plane which is
Wiesbaden, Germany
perpendicular to the longitudinal axis of the cylinder
Filed Oct. 25, 1961, Ser. No. 147,604
drum with the inclined plane of the socket ring.
Claims priority, application Germany Nov. 2, 1966
In order to limit the inclination of the connecting rod
6 Claims. (Cl. 287-21)
when its piston is in the dead center position, the dis
The present invention relates to a piston which is 10 tance between the socket ring end of the connecting rod
and the rotational axis of the socket ring must be greater
particularly adapted for a swash-plate axial piston unit
such as a pump, more particularly, to the provision of
a resilient member in said piston to equalize the lateral
than the radius of the above-mentioned cylindrical sur
face. As a result, the circle through which the socket
ring ends of the connecting rods move has a greater
forces exerted by the connecting rods against the pistons
15 diameter than the circle through which the piston ends
and accordingly against the cylinder walls.
The conventional axial-piston unit as involved in this
invention comprises a swash-plate axial-piston pump or
a wobble~plate engine. The present invention can best
be understood when described in connection with the
of the connecting rods are guided. The di?erence be
tween the diameters of these two circles is so chosen,
that the inclination of a connecting rod with respect to
within the cylinders are connected by ball—headed con
necting rods to a socket ring. The socket ring is ro
In general, this ‘angle of inclination is from 1 to 2°.
The connecting rod will have its greatest inclination
or slope with respect to the longitudinal axis of the
cylinder barrel when its socket ring end will have moved
from the dead center position by an angle of 45“. In
the central longitudinal axis of the ellipse, when its
20 corresponding piston is in a dead center position, is at
so-called swash-plate or wobble-plate engine.
least approximately equal to the inclination of this con
This type of engine essentially comprises a cylinder
necting rod in the opposite direction when the socket
barrel having an odd number of cylinders which are ar
ring end of the connecting rod is positioned at the in
ranged in the cylinder barrel in the form of a circle with
.tersection of the ellipse with the major axis thereof.
the axes of the cylinders being parallel. The pistons
tatably mounted about its central axis. The socket ring
may be tilted to an angle with respect to the central
axis of the cylinder barrel. Thus, the axis of the socket
ring will form an acute angle with the axis of the cylinder 30 this position the connecting rod in previously known axial
piston units will engage the inner surface of the piston
barrel when the socket ring is in its operating position.
skirt. Thereby a force is transmitted from the con
One end of each connecting rod is fastened by a ball
necting rod to the piston and from the piston to the
and socket connection to the piston and the other end
cylinder barrel. This force effects the rotation of the
by a ball and socket connection to the socket ring.
The plane in which the ring socket ends of the connecting 35 cylinder barrel about its longitudinal axis.
Because of the inclination of the connecting rod irre
rods are guided is inclined with respect to the longi
spective of its contact with the interior surface of the
tudinal axis of the cylinder barrel.
piston skirt, a lateral force is produced which is at right
When such an engine is being operated, the explosions
angles to the axis of the cylinder barrel. This lateral
in each cylinder force the respective pistons from out of
the cylinder. Since the end of the connecting rod is 40 force is a component of the force created by the pressure
exerted by the expanding gases in the cylinder on the pis
supported on an inclined plane, as provided by the socket
ring, the ring end of the connecting rod will move along
ton. This component force PS can be represented by the
following relationship:
this inclined plane until the piston has been displaced its
maximum distance within the cylinder and the connect
PS=P- sin ,8
ing rod socket end is at its maximum distance from the 45
cylinder head. The cylinder barrel rotates to follow this
wherein P is the force acting on the piston and exerted
movement of the connecting rod. Accordingly, in the
along the connecting rod and [3 is the angle between the
operation of such an engine, when the socket ring end
longitudinal axis of the connecting rod and the axis of
of the connecting rod ?rst begins to move along the in
the cylinder. Therefore, in order to rotate the cylinder
clined socket ring plane, the connecting rod will first
barrel, not only must the friction between the cylinder
be tilted as far as possible and then the cylinder barrel
barrel and its mounting thereof be overcome, but also
will be rotated about its longitudinal axis to permit
the sum of the above-mentioned component forces which
the socket end of the connecting rod to travel to its
are opposite to the direction of rotation of the cylinder
maximum position on the inclined plane.
barrel.
The piston ends of the connecting rods will always 55
In the conventional axial piston unit the force neces
move on a cylindrical surface whose longitudinal axis
sary for rotating the cylinder barrel is obtained by one
is identical with that of the cylinder barrel. The di
connecting rod contacting the inner surface of its respec
ameter of this cylindrical surface is determined by the
tive piston skirt. In an axial piston unit having an odd
arrangement of the cylinders in the cylinder barrel.
number of cylinders the connecting rod which transmits
The path of movement of the socket ring ends of the 60 the peripheral force to rotate the cylinder barrel alter
connecting rods de?nes a circle but one whose rotational
nates between that connecting rod which is just being
axis is inclined with respect to the axis of the cylinder
positioned on the pressure side and that connecting rod
barrel. The projection of the circle onto a plane which
which is just being positioned on the low-pressure or suc
is perpendicular to the longitudinal axis of the cylinder 65 tion portion of the cycle for the piston. Because of the
barrel would produce an ellipse. As previously pointed
out, the projection of the paths of the piston ends of
relatively high speed at which the cylinder barrel rotates,
the rapid sequence of sounds formed by the contact of the
the connecting rods onto the plane which is perpen
connecting rods With the piston skirts produces a very
dicular to the longitudinal axis of the cylinder barrel
loud and disturbing noise. The acoustic frequency of
would produce a circle.
70 this sound is equal to rthe product of the revolutions of
When a piston is positioned in one of its dead center
the cylinder barrel and twice the number of connecting
positions, the socket ring end of its connecting rod
rods since at each rotation of the cylinder barrel each
3,095,221
3
4
connecting rod will successively twice engage its respec
tive piston skirt. In view of the odd number of cylin
ders and therefore the connecting rods, it is apparent that
and the piston skirt, not only will compression forces
be transmitted to the piston where the connecting rod
approaches the inner surface of the piston skirt, but also
the connecting rods do not simultaneously contact the
respective piston skirts at each of the four points of in
tersection of the ellipse with its major and minor axes.
It is therefore the principal object of the present inven
tension forces where the connecting rod moves away from
the piston skirt portion 9.
There are several other structures by which the resilient
material may be mounted within the piston skirt. The
rubber sleeve 10 may be introduced into the piston skirt
tion to provide a piston for an axial piston unit which
and then secured in place by means of a ?ange or collar
eliminates the objectionable noises caused by the engage
ment of the connecting rods with the piston skirts.
10 mounted on the lower end of the inner surface of the
It is a further object of this invention to provide a pis
skirt. In addition, an annular groove could be cut in
ton for an axial piston unit wherein, instead of only one
connecting rod applying the force to rotate the cylinder
barrel, all of the connecting rods contribute in varying
the lower end of the skirt and a split retainer ‘ring in
serted therein to hold the resilient material in position.
The rubber sleeve or resilient material can be secured
degrees dependent upon theirposilrion to the total force 15 within the piston skirt so as to'tightly retain the piston
ball end 3 of the connecting rod in locking engagement
for rotating the cylinder barrel.
with the piston. As a result, locking rings and grooves
The objects of the present invention are attained by
for securing the ball end 3 in the piston may be eliminated.
coating at least that portion of the connecting rod which
is positioned within the piston skirt and/or the interior
As seen in FIGURE 1, the resilient material virtually
surface of the piston skirt with an elastic resilient ma 20 ?lls the space in the skirt portion between the connecting
terial. Since the connecting rods have relatively short
horizontal movements with respect to the axis of the cylin
der barrel, the several connecting rods will transmit a
peripheral force to the cylinder drum wherein the force
transmitted by each individual connecting rod depends 25
rod and the inner surface of the skirt. However, the
results of this invention can also be obtained by merely
applying a layer of the resilient material tothe inner
surface of the skirt portion and to the shank of the con
necting rod enclosed within the skirt portion.
on the extent to which the resilient material of that con
As can be seen in FIGURE ‘Lthe longitudinal axis of
necting rod is deformed by the inclination of the con
necting rod. Since a plurality of peripheral forces are
the piston is indicated at 11 and the longitudinal axis of‘
the connecting rod is indicated at 12. The connecting
applied, the shock-like impacts of single connecting rods
rod is illustrated in an inclined position so that an angle
against the piston skirts are eliminated and the metallic 30 is formed between the two axes 11 and 12. As a result,
sounds are prevented.
the elastic material is compressed on the left-hand side of
the connecting rod and is placed in tension on the right
As a modi?cation of this invention the entire space
within the skirt of a piston between the connecting rod
hand side of the connecting rod. These tension and com
and the inner surface of the piston skirt can be filled with
pression forces contribute to the-peripheral force neces
a resilient material. Accordingly, those connecting rods 35 sary for rotating the cylinder barrel.
which at any one time are inclined a relatively small
Proceeding next to FIGURE 2, the piston 1 is shown
angle from the axis of the cylinder, will transmit some
having a connecting rod 2 the ‘ball end 13 of which is
peripheral force onto the piston. This arrangement simul
secured in the piston 1. An annular groove 14 is pro
taneously reduces the component forces which are trans
vided in the upper end of the skirt portion 9 and a lock
mitted from a wall of the piston to the cylinder wall and 40 ing ring 15 is positioned in the groove to lock the ball
accordingly skin friction in the cylinder is reduced.
end 13 in position and thereby prevent the withdrawal
A further modi?cation of this invention comprises se
of the connecting rod 22 from the piston ‘1.
curing the elastic or resilient material to the inner surface
The shank of the connecting rod 22 is provided with
of the piston skirt and the connecting rod.
a reduced diameter portion 16 with the elastic material
Other objects and advantages of this invention will be 45 19 being positioned between the shank portion 16 and
apparent upon reference to the accompanying description
the skirt 9. The lower end of the shank of the connect
when taken in conjunction with the following drawings,
ing rod is provided with an increased diameter portion '
wherein:
FIGURE 1 is a longitudinal sectional view of a piston
17 at that area of the shank where the connecting rod
engages the skirt 9. The lower end of the inner surface
and connecting rod embodying the present invention; and 50 of the skirt 9 is bevelled so as to have a conical surface
FIGURE 2 is a view similar to that of FIGURE 1
but showing a modi?cation of the invention.
FIGURE 3 is a view similar to that of FIGURE 2,
but showing a still further modi?cation of the invention.
Returning now to the drawings, wherein like reference
symbols indicate the same parts throughout the various
views, with particular reference to FIGURE 1 there is
shown a piston *1. The piston 1 is connected to its re
spective connecting rod 2 by a ball end 3. There is an
axial passage 4' in the end of the piston which provides 00
a source of lubrication for theball end 3.
The other end of the connecting rod comprises the
socket end which has also a ball 5 which is connected
as indicated at 18. The angle of this conical surface is‘
so chosen that when the shank portion 17' engages the
conical surface, a linear contact will occur between the
conical surface 18 and the shank portion 17. The engage
ment of the enlarged diameter portion 17 of the con
necting rod with the conical surface 18 on the piston
skirt limits the compression of the elastic material 10
to an unreasonably high degree.
Since the connecting rod portion '17 is not covered with
elastic material, a metal-to-metal contact between the
connecting rod portion 17 and the skirt 9 will occur.
Therefore, this modi?cation as illustrated in FIGURE 2
is desirable when the force to be transmitted between the
to a socket ring 6 by means of a fastening ring 7, which
connecting rod and the piston is of such a high value,
is retained in place by a retaining ring 8.
65 that the elastic material may be compressed or distorted
Depending from the lower end of the piston 1 and
beyond its limits and therefore damaged.
'
integral therewith is a piston skirt portion 9. Rubber
FIGURE 3 di?ers from FIGURE 2 by the provision
or some other suitable resilient and elastic material is
of an inner ?ange 23 on the lower end of the inner
positioned between the skirt 9 of the piston and the con
surface of the skirt portion.
necting rod 2, as shown at 10.
Thus it can be seen that the present invention provides
70
The rubber 10 is vulcanized to both the inner surface
an improved piston which is particularly adapted for axial
of the skirt 9 and the outer surface of the connecting rod
piston units such as swash-plate pumps or wobble-plate
shank which, as can be seen in FIGURE 1, has its major
portion enclosed within the skirt 9. Because of this
engines.
It will be understood that this invention is susceptible
tight connection between the rubber, the connecting rod 75 to modi?cation in order to adapt it to different usages
3,095,221
and conditions and, accordingly, it is desired to compre~
inner surface ‘of said skirt portion and said connecting
hend such modi?cations within this invention as may fall
rod, said resilient material being fastened to one of said
connecting rod and the inner surface of said skirt por
Within the scope of the appended claims.
What is claimed as this invention is:
tion.
,
,
1. A piston particularly adapted for a swash-plate
axial-piston unit, and comprising a piston body having a
5. A piston particularly adapted for a swash‘plate
axial-piston unit, and comprising a piston body having
depending skirt portion on one end thereof, a connecting
rod pivotally connected to said one end of said piston
a depending skirt portion on one end thereof, a connect
ing rod pivotally connected to said one end of said piston
body with a major portion of said rod extending within
body with a major portion of said rod extending Within
said skirt portion, and a layer of resilient material on the 10 said skirt portion, and a resilient material member sub
stantially occupying the space in said piston between the
portion of the connecting rod Within said skirt portion
inner surface of said skirt portion and said connecting
and the inner surface of said skirt portion.
rod, said resilient material being fastened to both said
2. A piston particularly adapted for a swash-plate axial
connecting rod and the inner surface of said skirt portion.
piston unit, and comprising a piston body having a de
6. A piston particularly adapted for ‘a swash~plate
pending skirt portion on one end thereof, a connecting rod 15
axial-piston unit, and comprising a piston body having
pivotally connected to said one end of said piston body
a depending skirt portion on one end thereof, a connect
with a major portion of said rod extending within said
ing rod pivotally connected to said one end of said piston
‘skirt portion, and a resilient material member substantial
body with a major portion of said rod extending within
ly occupying the space in said piston between the inner
said skirt portion, said connecting rod having an en
surface of said skirt portion and said connecting rod.
larged portion on the shank thereof and engageabie with
3. A piston particularly adapted for a swash-plate
said skirt portion, and a resilient material member sub
axial-piston unit, and comprising a piston body having a
stantially occupying the space in said piston between the
skirt portion depending from one end thereof, arr inner
inner surface of said skirt portion and said connecting
?ange on the ‘lower end of the inner surface of said
skirt portion, a connecting rod pivotally connected to 25 rod above said enlarged portion whereby said enlarged
portion is not covered by said ‘resilient material.
one end of said skirt body with a major portion of said
rod extending within said skirt portion, and a resilient
References Cited in the ?le of this patent
material member substantially occupying the space in said
UNITED STATES PATENTS
piston between the inner surface of said skirt portion and
said connecting rod and secured in position by said ?ange
891,993
Hess ________________ __ June 30, 1908
4. A piston particularly adapted for a swash~plate
1,996,826
()hmart ______________ __ Apr. 9, 1935
axial-piston unit, and comprising a piston body having a
2,436,908
‘Weenen et al. ________ __ Mar. 2, 1948
depending skirt portion on one end thereof, a connecting
2,569,669
Doeg ________________ __ Mar. 14, 1950
rod pivotally connected to said one end of said piston
2,847,261
Cornelius ____________ __ Aug. 12, 1958
body with a major portion of said rod extending within 35 2,856,250
Thoma ______________ __ Oct. 14, 1958
said skirt portion, and a resilient material member sub
2,889,042
Budzich ____________ __ Mar. 31, 1959
stantially occupying the space in said piston between the
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