US3858487A

US3858487A - Radial piston type hydraulic pump or motor

Info

Publication number: US3858487A
Application number: US257418A
Authority: US
Inventors: Katsuro Abe; Kozo Ono
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1968-02-05
Filing date: 1972-05-26
Publication date: 1975-01-07
Anticipated expiration: 1992-01-07
Also published as: NL6901744A; GB1249732A; NL144029B; FR2001321A1

Abstract

A radial piston type hydraulic pump or motor comprising one or a plurality of piston cylinder mechanisms arranged radially of a rotatable shaft thereof, and a casing surrounding said pistoncylinder mechanisms and having a waved inner cam surface for cooperation with the outer end of each piston, means being provided to direct a pressurized hydraulic oil between the cylinder wall and the piston at the portion where the piston and the cylinder wall is brought into contact due to the side thrust reaction force acting on the piston so as to counteract said reaction force.

Description

United States Patent 1 1 Abe et al.

1 1 Jan.7,1975

1 1 RADIAL PISTON TYPE HYDRAULIC PUMP OR MOTOR [75] Inventors: Katsuro Abe, Matsudo; Kozo Ono,

Tokyo, both of Japan [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: May 26, 1972 [21] Appl. No.: 257,418

Related U.S. Application Data [63] Continuation of Ser. No. 795,227, Jan. 30, 1969,

abandoned.

[30] Foreign Application Priority Data Feb. 5, 1968 Japan 43-7436 Feb. 21, 1968 Japan Feb. 21, 1968 Japan ..43-12236 [52] U.S. C1. 91/488, 91/489 [51] Int. Cl. F0lb 13/06 [58] Field of Search 91/491, 485, 488, 489

[56] References Cited UNITED STATES PATENTS 2,155,455 4/1939 Thoma 92/127 2,292,181 8/1942 Tucker... 91/489 2,528,739 11/1950 Carey i 92/127 2,815,718 12/1957 Avery 91/498 Douglas 92/127 3,046,950 7/1962 Smith 3,073,254 1/1963 Hoover 3,142,262 7/1964 Firth et a1.

3,153,987 10/1964 Thoma 3,228,346 1/1966 Johnson 3,255,706 6/1966 Eickmann 3,366,017 1/1968 Firth et a1.

3,554,095 1/1971 Bobst 91/489 Primary Examiner-William L. Freeh Attorney, Agent, or Firm-Craig & Antonelli [57] ABSTRACT A radial piston type hydraulic pump or motor comprising one or a plurality of piston cylinder mechanisms arranged radially of a rotatable shaft thereof, and acasing surrounding said piston-cylinder mechanisms and having a waved inner cam surface for cooperation with the outer end of each piston, means being provided to direct a pressurized hydraulic oil be tween the cylinder wall and the piston at the portion where the piston and the cylinder wall is brought into contact due to the side thrust reaction force acting on the piston so as to counteract said reaction force.

21 Claims, 9 Drawing Figures Patented Jan. 7, 1975 3,858,487

4 Shuts-Shut 3 RADIAL PISTON TYPE HYDRAULIC PUMP R oron This application is a continuation application of applicat'ion Ser. No. 795,227, filed Jan. 30, 1969, (now abandoned).

The present invention relates to a radial piston type hydraulic pump or motor. More particularly, the present invention relates to a radial piston type hydraulic pump or motor comprising one or a plurality of pistoncylinder mechanisms arranged radially of a rotatable shaft thereof, the piston of each of the piston-cylinder mechanisms having a rotatable ball or roller at its outer end, and a casing surrounding said piston-cylinder mechanisms and having a waved inner cam surface for co-operation with each of the balls or rollers.

In such a device, when a hydraulic oil pressure is applied on the inner ends of the pistons, the balls or rollers on the outer ends of the pistons are forced toward the waved inner peripheral surface of said casing whereby the piston-cylinder assembly is caused to rotate through the cam action of the waved surface. Thus, the device is operated as a motor. I

On the other hand, if an external power means such as an electric motor is employed to rotationably drive said rotatable shaft, the device operates as a hydraulic pump to discharge pressurized hydraulic oil.

Such a type of pump or motor is disadvantageous in that each of pistons is subjected to a side thrust and a substantial friction force is created between each piston and the corresponding cylinder wall. Therefore, an excessively large starting torque is required for starting the pump or motor. Further, seizing often occurs between the piston and the cylinder wall. Such a seizing will cause a damage on the cylinder wall and the damaged cylinder wall will further enhance the tendency of seizing. Thus, the pump or motor ultimeately becomes inoperative or the piston-cylinder mechanism is mechanically failed.

The present invention has an object to provide a radial piston type hydraulic pump or motor which is free from seizing between each piston and the corresponding cylinder wall.

The other object of the present invention is to supply a pressurized hydraulic oil between the piston and the cylinder wall only at the portion where seizing will possible occur.

A further object of the present invention is to substantially increase the effect of lubrication in a hydraulic pump or motor without decreasing the volumetric efficiency.

Another important feature of the present invention is to increase the torque efficiency of a hydraulic pump or motor.

These and further objects of the present invention will become apparent from the following descriptions taking reference to the accompanying drawings.

FIG. 1 is a partially cut-away side elevational view of a radial piston type pump or motor which is suitable to apply the present invention;

FIG. 2 is an enlarged fragmentary cross-sectional view taken substantially along the line II-II of FIG. 1 for illustrating the reaction force acting on a piston;

FIG. 3 is a cross-sectional view of one embodiment of the present invention, the section being taken substantially along the lines III-III of FIG. 1;

FIG. 4 is a fragmentary sectional view taken along the line lVlV of FIG. 3 and showing a valve mechanism;

FIG. 5 is a fragmentary crosssectional view corresponding to the section taken along the line IIII of FIG. 1 but showing another embodiment of the present invention;

FIG. 6 is a longitudinal section of a piston employed in the embodiment shown in FIG. 5;

FIG. 7 is a bottom plan view of the piston shown in FIG. 6;

FIG. 8 is a longitudinal section ofa piston to modified form which may be used in the embodiment of FIG. 5; and

FIG. 9 is a crosssectional view similar to FIG. 5 but showing a further embodiment of the present invention.

FIG. 1 is a side elevational view ofa radial piston type pump or motor which is operating as a motor, portions of the motor being shown in sections taken in a plane parallel to the plane of the drawing.

In FIG. 1, the numeral (1) shows a rotatable shaft, and (2) shows cylinders disposed radially on the shaft and secured thereto, each of the cylinders (2) having an internal bore comprising a small diameter portion (4) and a large diameter portion (5). The numeral (6) shows pistons, each of which includes a small diameter portion and a large diameter portion and disposed in one of said cylinders (2) for reciprocating movement. Each piston (6) has, at the end of the large diameter portion (8), a ball or roll (9) rotatably mounted thereon. In operation, the ball or roll (9) is maintained in engagement with a waved surface (11) provided in the inner peripheral surface of a casing (10) and is forced thereto by means of a hydraulic pressure, whereby the reciprocating motion of each piston (6) is controlled by the shape of said wave surface (11). The numeral (12) shows an annular valve member secured to the cylinder block and having oil supply passages (14) which can be put into communication with the oil chambers (13) provided at the radially inner end of the cylinder bores. The numeral (15) shows roller bearing assemblies constituted by rollers (16) and roller supports (17) provided at the opposite sides of cylinder block for rotatably supporting the shaft (1). Thus, the shaft (1) can rotate together with the cylinders (2) and the annular valve member (12). The numeral (18) shows securing bolts for securing the casing in assembled condition, and (19) shows a cylindrical valve body mounted within the casing (10). The ,valve body (19) has a valve surface (20) for sliding engagement with the annular valve member (12) which is rotating with the cylinders (2), whereby oil supply pasages (21) and oil exhaust passages (22) (only one of the passages (21) and (22) is shown in FIG. 1) are alternately put into communication with the oil passages (14) so as to introduce or exhaust the hydraulic pressure into or from the oil chambers (13) of the cylinders (2). The casing (10) is provided with an oil supply ports (23) and an oil exhaust port (24) which are respectively connected with the oil supply passages (25)(21) and the oil exhaust passages (26)(22). The numeral (27) shows a Cardins coupling for connecting the cylindrical valve body (19) with the casing (10), (28) shows a oil seal plate and (29) shows sealings. In the construction as shown in FIG. 1, when a pressurized hydraulic oil is supplied to the oil supply port (23), the hydraulic oil is introduced through. the passages (25), (21) and (14) into the oil chamber (13) and forces the'corresponding piston (6) outwardly. thus, the ball (9) of the piston (6) is urged onto the waved surface and rotates therealong, and the reaction force acting on the ball (9) causes the cylinder block and thus the rotatable shaft to rotate.

As the cylinder block rotates the ball (9) rides on a crest of'the waved surface so that the piston (6) is forced radially inwardly into the cylinder (2), the oil passage (14) is interrupted from the communication with the oil supply passage (21) in the valve body (19) and connected with the oil exhaust passage (22), whereby the oil in the oil chamber (13) is exhausted frornsaid chamber through the passages (14), (22) and (26) and the oil exhaust port (24). Thus, the oil is alter nately supplied into or exhaust from the oil chamber (13) so as to operate the piston-cylinder mechanism with the result that the rotatable shaft (1) is continuously rotated. Therefore, the device operates as a hydraulic motor. I

An important drawback in the construction shown in FIG. 1 is the problem of seizing between the piston and the cylinder wall. This problem will be explained with reference to FIG. 2.

FIG. 2 is a fragmentary sectional view in enlarged scale taken along the line II-II of FIG. 1, and the reference numerals identical to those in FIG. 1 show the same or corresponding parts. In FIG. 2, the ball (9) is shown as being pushed onto the waved surface (11) by means of 'a hydraulic pressure through the intervention ofthe piston (6). In this figure, the numeral (30) shows the longitudinal axis of the piston (6), (F) shows a reac' tion force acting on the ball (9) from the waved surface (11), (a) shows the angle between the direction of the reaction force (.F) and the axis (30), and (F shows the component of said reaction force (F) along the direction perpendicular to the axis (30), the component (F being equal to F sin a. I

In this condition, the piston (6') is strongly forced onto the right inner surface (5) of the cylinder (2) by the reaction force component (F causing to increase the frictional force therebetween, with the result that the torque efficiency is substantially decreased and that the motor is finally caused to stop. Further, there is a tendency of seizing between the piston (6) and the cylinder wall, which will cause the abrasion of the cylinder wall and prevent smooth operation of the piston. Thus, the motor performance is remarkably decreased.

According to one feature of the present invention, in order to eliminate the problem of seizing, either of the piston or the cylinder is provided with oil supply passages for supplying the pressurized hydraulic oil into the clearance between the piston and the cylinder wall, said passages being controlled to open or close in accordance with the positions of the piston. According to a further feature of the preent invention, there is provided an arrangement in which said oil supply passages are formed with flow restrictions for controlling the oil flow in accordance with the amount of said clearance, or said oil supply passages are provided with branch passages opening to the external surface of said ball for supplying the pressurized hydraulic oil thereto for lubrication purpose.

The structure of the present invention will now be described in detail.

FIG. 3 is a fragmentary cross-secti nal'vie w of the pump or motor embodying the principle of the present invention, the section being taken substantially along the line III-III of FIG. I. In FIG. 3, the parts corresponding to those in FIG. 1 are shown by the same reference numerals.

In FIG. 3, the cylindrical valve body secured within the casing (10) and identified by the reference numeral (19) has a plurality pairs of oil supply passages (21) and oil exhaust passages (22), the number of the pairs being equal to those of the wave of the waved surface (11) of said casing. The numeral (20) shows the valve surface which is adapted to engage with the annular valve member (12) which 'rotates with the cylinders (2). The valve surface (20) of said cylindrical valve body (19) is provided with oil passages'.(3l) and (32) respectively leading from oil supply and exhaust passages (21) and (22) and communicating with distrubution ditches (41) and (42). Each of the cylinders (2) is provided with an oil passage (33) and an oil passage (34) which are opened at one end so as to co-operate with the ditches (41) and (42) respectively. The other ends of the passages (33). and (34) are respectively opened to the diametrically opposite sides (35) and (36) of the cylinder (2).

The oil passage (31.) is located near side with respect to the oil passage (32). The relative position of the oil passages (31) and (32) are illustrated in FIG. 4 which is an enlarged sectional view taken along the line IV-IV of FIG. 3. In FIG. 3, it should be noted that the oil passages for alternatively connecting the oil supply passage (.14) and the oil supply and exhaust passages (21)and (22) are omitted in order to make the drawing clear. However, it will be easily understood that the oil supply passage (14) isarranged so as to communicate with the supply passage (21) while the ball (9) mounted on the piston is descended from the crest to the trough along the waved cam surface and with the oil exhaust passage (22) while the ball of the piston is ascending from the trough to the crest.

The piston of the piston-cylinder mechanism is, in the illustrated position, descending from the crest of the wave and the mechanism is being rotated in the counter-clockwise direction as shown by an arrow in FIG. 3. In this position, the pressurized hydraulic oil is introduced through the oil supply passage (14) into the oil chamber (13) whereby the piston (6) is subjected to a high oil pressure, so that a large reaction force (F acts onthe right hand portion of the cylinder inner wall. However, in this position, the pressurized'hydraulic oil in the oil supply passage can flow through the oil passage (31), the distribution ditch (41) and the oil passage (33) into the opening (35) so as to counteract to thereaction force. Thus, the seizing between the piston and cylinder wall can be completely prevented.

The pressurized hydraulic oil is supplied to the opening (35) as long as the oil passage (33) is in communication with the distribution ditch (41) during rotation of the piston-cylinder mechanism. The period during which the oil passage (33) is in communication with the ditch (41) corresponds to that during which the piston (6) descends along the wave of the surface (11) and the'reaction force is very high. Thus, in the period during which the piston (6) ascends along the waved surface (11), no hydraulic oil pressure is supplied to the cylinder side wall until the oil passage (33) is again put into communication with the next distribution ditch (41). Thus, the distance (b) between two adjacent distribution ditches (41) corresponds to the period in which the piston (6) ascends along the waved surface (11) including the period in which the piston (6) again starts to descend slightly and the reaction force is very small. In such a period, since no hydraulic pressure acts on the inner end of the piston (6), the reaction force acting at the left inner cylinder wall is very small, so that there is less tendency of seizing.

When the piston-cylinder mechanism is rotated counter-clockwise as referred to above, the line comprising the oil passage (32), the distribution ditch (42) and the oil passage (34) is connected with the oil exhaust passage (22) and takes no part in lubricating the cylinder. Said line comprising the oil pasage (32), the distribution ditch (42) and the oil passage (34) is provided for supplying the lubricating oil when the pistoncylinder mechanism is rotated in the clockwise direction. Namely, when the piston-cylinder mechanism is rotated clockwise by using the passage (22) as the oil supply passage and the passage (21) as the oil exhaust passage, the reaction force acts on the left hand portion of the cylinder wall. In this case, the pressurized oil is supplied to the portion (36) and the similar effect can be obtained.

The above descriptions with respect to the embodiment of the present invention were proceeded with the assumption that the structure is operated as a hydraulic motor, however, it is of course true that the structure can also advantageously be operated as a hydraulic pump for supplying pressurized hydraulic oil by simply driving the rotatable shaft by a suitable prime mover such as an electric motor or a gasoline engine. This is also true in the embodiments which will be described later.

FIG. 5 shows the second embodiment of the present invention in a sectional view corresponding to that taken along the line II-II of FIG. 1. In this figure, the parts corresponding to those shown in FIG. 1 are identified by the same reference numerals.

In FIG. 5, the piston cylinder mechanism is shown in a position in which the piston (6) is subjected to a by draulic pressure at its inner end and descending along the waved surface (11) whereby the mechanism is rotated in the counter-clockwise direction as shown by the arrow.

FIG. 6 is a longitudinal section of a piston used in the structure shown in FIG. 5, and FIG. 7 is a bottom plan view of the piston shown in FIG. 6.

The second embodiment of the present invention will now be described with reference to FIGS. 5 to 7. In the drawings, the numerals (51) to (54) show oil passages provided in the piston (6), one end of each passage being opened at (61) to (64) to the side surface of the piston at a position above an oil seal (55) on the piston. The other end of each of the oil passages (51) to (54) is opened at (71) to (74) to the side surface of the large diameter portion of the piston (6). The oil passages (51) to (54) are also connected with oil grooves (81) to (84) respectively formed on a concave surface (56) of the piston, the surface (56) being provided at the end of the piston (6) where the ball (9) is mounted. The numeral (57) shows partition grooves formed on the concave surface (56).

Considering now a position in which the piston (6) is subjected to a hydraulic pressure and descended along the waved surface (11) as shown in FIG. 5, the piston (6) is slightly inclined toward left (i.e., counterclockwise in FIG. 5) due to the reaction force (F), so that the piston and the cylinder wall are brought into mutual contact at the right side portion of the large diameter portion and the left side portion of the small diameter portion. Thus, a gap (58) is created between the piston (6) and the cylinder wall, whereby the pressurized hydraulic oil in the oil chamber (13) is introduced through the opening (62) and the passage (52) into the opening (72) and the oil groove (82) to provide lubrication between the piston (6) and the ball (9) and at the same time produce an oil film at the area around the opening (72), where the piston and the cylinder is otherwise brought into mutual contact, so as to counteract to the reaction force. The partition grooves (57) serves to divide the concave surface of the piston into four sections and to prevent the pressurized oil on one section from being introduced into others of the sections.

FIG. 8 shows in sectional view another form of the piston which can be used in the embodiment of the present invention. In the illustrated structure, each of the oil passages (51) and (52) is opened at the inner or top surface of the piston (6). The open ends of the passages (51) and (52) are provided with cylinders (65) and (66) respectively, in which piston valves (67) and (68) are respectively disposed. Thus, the pressurized hydraulic oil in the oil chamber (13) is passed through the piston valves (67) and (68) to the other open ends and (76) of said passages. The flow rate of the hydraulic oil through the passages (51) and (52) is determined by the gap between the piston and the cylinder wall at the exits. of the passages, so that the hydraulic pressure at the exits of the passages can be automamtically controlled in accordance with said gap between the piston and the cylinder wall. The reference numerals (77) and (78) show springs acting on the piston valves (67) and (68) respectively, and ().and (86) show caps for the cylinder portions (65) and (66). When there is a large gap (such as at the opening (75)) between the cylinder (2) and the piston (6), a large quantity of oil is initially allowed to pass through the oil passage (51), however, the oil flow is soon restricted by the piston valve (67) which is moved against the action of the spring (77) onto the valve seat (87) under the influence of pressure drop across the valve. Since there is a large gap between the piston (6) and the cylinder (2) at the opening (75), it is not necessary that the hydraulic oil is passed through the passage (51).

As at the opening (76), if the gap between the cylinder (2) and the piston (6) is as small as they almost contact with each other, the oil flow is restricted at the opening (76) so that the pressure drop across the piston valve (68) is reduced and thus the piston valve is maintained in an open position by the action of the spring (78). Thus the pressurized hydraulic oil is allowed to pass through the opening (76) to the gap between the cylinder (2) and the piston (6).

In this manner, the piston valve (68) is automatically operated in accordance with the gap between the cylinder (2) and the piston (6) to supply the hydraulic oil into said gap. This arrangement is advantageous in that the pressurized hydraulic oil is supplied to the gap between the cylinder (2) and the piston (6) only when necessary.

FIG. 9 shows in sectional view the third embodiment of the present invention, the section corresponding to that taken along the line 11-11 of FIG. 1. In FIG. 9, the parts corresponding to those in FIG. 1 are identified by the same reference numerals.

In FIG. 9, the piston-cylinder mechanism is shown in a position in which the piston (6) is subjected to a hydraulic oil pressure at its inner or top end and is moved to descend along the waved surface (11), and the mechanism is rotated in the counter-clockwise direction as shown by an arrow in the drawing.

In the structure shown in FIG. 9, the cylinder (2) is provided with oil passages (91) and (92) for connecting the oil chamber (13) of the cylinder with the large diameter portions thereof where seizing is apt to occur, each of the oil passages being provided with a restriction (95) or (96) near the opening (93) or (94) thereof.

Considering now to a position in which the piston is subjected to a hydraulic oil pressure and is moved to descend along the waved surface (11) as shsown in FIG. 9, the piston (6) is inclined toward left due to the reaction force (F) as in the case of FIG. 5. Therefore, the large diameter portion of the cylinder and the piston have a large gap at the area around the opening (93), while they are close with each other at the area around the opening (94). In this position, although the exit opening (93) of the restriction (95) is opened, the pressurized oil in the oil chamber (13) is restricted due to the existence of the flow restriction (95), and moreover, the oil pressure at the area adjacent to the opening (93) is not high.

On the other hand, since the exit opening 94) of the restriction (96) is closed, there is less pressure drop across the restriction (96) whereby high pressure is applied at the area around the opening (94). Thus,an oil film is formed around the opening (94) where seizing between the cylinder and the piston will possibly occur, and'the pressure difference at the openings (93) and (94) counteracts to the reaction force to restore the piston to the upright position, and to prevent seizing and substantially reduce the frictional force.

In FIG. 9, the oil passages (91) and (92) are in communication with the oil chamber (13) in the cylinder, however, the same effect can be achieved by connecting the passages (91) and (92) with the oil supply passage (14). It is only necessary to supply a pressurized hydraulic oil to such a part of the cylinder large diameter portion that has a tendency of seizing. This arrangement is advantageous in that, since said oil passages are provided in the cylinder but not in the piston, pressurized oil film can alwaysbe formed, irrespective of the position of the piston, on such aportion of the cylinder that is subjected to a high frictional force.

As described above, according to the present invention, the cylinder or the piston is provided with oil passages through which a pressurized hydraulic oil is sup- (which is defined as the ratio of the piston displacement to the total amount of the oil consumed in working) can be remarkably increased. Thus, the efficiency of the device can be increased. Further, as an additional advantage of the present invention, it should be pointed out that the wear of the cylinder and/or the piston can be reduced and the total life of the pump or motor can be substantially increased. It is important to note that the torque efficiency can be remarkably increased in response to the decrease of the frictional force. According to an experimental data, the torque efficiency can be increased by about 20 to 30 percent as compared with a conventional structure. For the same reason, the starting torque can also be reduced.

What we claim is:

l. A hydraulic machine operable as at least one of a pump and motor; said machine comprising a casing having 'a waved cam surface, a cylinder block mounted in the casing for relative movement with respect to said casing and having at least one cylinder, each of said cylinders having a piston arranged for reciprocating inward and outward movement therein, engagement plied to such a part of the cylinder large diameter porwhere said cylinder is subjected to a side thrust force from the piston during at least portions of the reciprocating movement of said piston,

wherein the inside dimensions of each cylinder are slightly greater than the corresponding outside dimensions of the associated piston along at least a portion of the length thereof such that a peripheral gap is formed between said cylinder and piston at each of respective opposite lateral sides of said piston when said piston is centrally positioned in and aligned with said cylinder, said piston and cylinder being configured suchthat relative lateral movementof said piston with respect to said cylinder resulting from said side thrust forces causes the width of the gap at one side of the piston to be reduced and the width of the gap at the other side of the piston to be enlarged,

and wherein said lubricant feed means includes at least one lubricant supply passage having an outlet end opening into one of said gaps and control means for controlling the supply of lubriccant to said outlet end, said control means being positioned upstream of said outlet end with respect to flow of lubricant through said supply passage and including means for varying said supply of lubricant to said outlet end as a direct function of the changes in lubricant back pressure in said passage resulting from changes in the width of said gap adjacent said outlet end.

2. A machine according to claim 1, wherein said cylinder block is rotatably mounted in said casing, wherein each of said respective cylinders and pistons extend and move radially with respect to the rotational axis of said cylinder block with the inner ends of the pistons being radially outwardly of the outer ends thereof with respect to said rotational axis, wherein said engagement means are rotatably mounted with respect to respective ones of said pistons, and wherein said waved cam surface is formed at the periphery of said casing for rolling engagement with the respective rotatably mounted engagement means.

3. A machine according to claim 1, wherein said control means includes flow restriction means in said lubricant passage at a position adjacent the outlet end openmg.

4. A machine according to claim 3, wherein said lubricant supply passages are arranged completely outside of the associated piston.

5. A machine according to claim 1, wherein a plurality of similar and separate lubricantpassages with similar control means are provided for each cylinder, and wherein the respective passage outlets of said lubricant passages are spaced from one another in a symmetrical manner with respectto a central axis extending in the direction of relative movement of a respective cylinder and piston.

6. A machine according to claim 5, wherein said by draulic fluid alsoserves as said lubricant with said pressurized lubricant source beingin respective ones of said cylinders, each of said lubricant passages including passage inlet openings into respective ones of said cylinders at a position directly communicated with the supply of said hydraulic fluid to said cylinder.

7. A machine according to claim 1, wherein said control means includes a valve disposed in a cavity formed in each of said lubricant passages, the opening of said valve being controlled by the back pressure build up in the lubricant disposed in said lubricant passage between said outlet end and said valve.

8. A machine according to claim 7, wherein each of said valves is a piston valve which includes resilient means disposed in said cavity for urging said piston to open said lubricant passage against the flow of lubricant.

9. A machine according to claim 7, wherein said cylinder block is rotatably mounted in said casing, wherein each of said respective'cylinders and pistons extend and move radially with respect to the rotational axis of said cylinder block with the inner ends of the pistons being radially outwardly of the outer ends thereof with respect to 'said rotational axis, wherein said engagement means are rotatably mounted with respect to respective ones of said pistons, and wherein said waved cam surface is formed at the periphery of said casing for rolling engagement with the respective rotatably mounted engagement means.

10. A machine according to claim 1, wherein each of said lubricant supply passages has a passage inlet end opening into said pressurized lubricant space adjacent the outer end of the piston.

11. A machine according to claim 10, further comprising seal means for sealing the space between the respective piston and cylinder adjacent the outer end of said piston, wherein said seal means is disposed intermediate the inlet and outlet end openings of said at least one lubricant passage such that supply of lubricant to the gaps adjacent the outlet end openings is only by way of said at least one lubricant passage.

12. A machine according to claim 11, wherein, for each cylinder, two separate and similar lubricant oil passages and associated control means are provided which open into the gaps at opposite sides of a respective piston which is movable within said cylinder.

13. A machine according to claim 12, wherein said control means includes a piston valve disposed in a cylindrical cavity formed in each of said lubricant passages adjacent the respective passage inlet end openings, the opening of said piston valve being controlled by the back pressure built up in the lubricant disposed in said lubricant passage between said passage outlet end and said piston valve.

14. A machine according to claim 13, wherein said cylinder block is rotatably mounted in said casing, wherein each of said respective cylinders and pistons extend and move radially with respect to the rotational axis of said cylinder block with the inner ends of the pistons being radially outwardly of the outer ends thereof with respect to said rotational axis, wherein said engagement means are rotatably mounted with respect to respective ones of said pistons, and wherein said waved cam surface is formed at the peripihery of said casing for rolling engagement with the respective rotatably mounted engagement means.

15. A machine according to claim 11, wherein said cylinder block is rotatably mounted in said casing, wherein each of said respective cylinders and pistons extend and move radially with respect to the rotational axis of said cylinder block with the inner ends of the pistons being radially outwardly of the outer ends thereof with respect to said rotational axis, wherein said engagement means are rotatably mounted with respect to respective ones of said pistons, and wherein said waved cam surface is formed at the periphery of said casing for rolling engagement with the respective rotatably mounted engagement means.

16. A machine according to claim 15, wherein said hydraulic fluid also serves as said lubricant with said pressurized lubricant source being in respective ones of said cylinders, each of said lubricant passages including passage inlet openings into respective ones of said cylinders at a position directly communicated with the supply of said hydraulic fluid to said cylinder.

17. A machine according to claim 1, wherein said hydraulic fluid also serves as said lubricant with said pressurized lubricant source being in respective ones of said cylinders, each of said lubricant passages including passage inlet openings into respective ones of said cylinders at a position directly communicated with the supply of said hydraulic fluid to said cylinder.

18. A machine according to claim 17, wherein said cylinder block is rotatably'mounted in said casing, wherein each of said respective cylinders and pistons extend and move radially with respect to the rotational axis of said cylinder block with the inner ends of the pistons being radially outwardly of the outer ends thereof with respect to said rotational axis, wherein said engagement means are rotatably mounted with respect to respective ones of said pistons, and wherein said waved cam surface is formed at the periphery of said casing for rolling engagement with the respective rotatably mounted engagement means.

. 19. A machine according to claim 17, wherein each of said lubricant supply passages is arranged completely within a respective one of said pistons.

20. A machine according to claim 17, wherein each of said lubricant supply passages are arranged completely outside of said pistons within housing means defining said cylinders.

21. A machine according to claim 17, wherein said engagement means are rotatably mounted on said piston, and wherein said lubricant passages also provide lubricant to the surface of said rotatably mounted means.

Claims

1. A hydraulic machine operable as at least one of a pump and motor; said machine comprising a casing having a waved cam surface, a cylinder block mounted in the casing for relative movement with respect to said casing and having at least one cylinder, each of said cylinders having a piston arranged for reciprocating inward and outward movement therein, engagement means mounted on the inner end of each piston for engagement on the waved cam surface, hydraulic supply means for supplying hydraulic fluid to the cylinder against the outer end of said piston during inward movement of the piston, hydraulic fluid exhaust means for exhausting hydraulic fluid from the cylinder during outward movement of the piston, and pressurized lubricant feed means for feeding pressurized lubricant from a pressurized lubricant source into a space between the cylinder and the piston in a region of the cylinder where said cylinder is subjected to a side thrust force from the piston during at least portions of the reciprocating movement of said piston, wherein the inside dimensions of each cylinder are slightly greater than the corresponding outside dimensions of the associated piston along at least a portion of the length thereof such that a peripheral gap is formed between said cylinder and piston at each of respective opposite lateral sides of said piston when said piston is centrally positioned in and aligned with said cylinder, said piston and cylinder being configured such that relative lateral movement of said piston with respect to said cylinder resulting from said side thrust forces causes the width of the gap at one side of the piston tO be reduced and the width of the gap at the other side of the piston to be enlarged, and wherein said lubricant feed means includes at least one lubricant supply passage having an outlet end opening into one of said gaps and control means for controlling the supply of lubriccant to said outlet end, said control means being positioned upstream of said outlet end with respect to flow of lubricant through said supply passage and including means for varying said supply of lubricant to said outlet end as a direct function of the changes in lubricant back pressure in said passage resulting from changes in the width of said gap adjacent said outlet end.

3. A machine according to claim 1, wherein said control means includes flow restriction means in said lubricant passage at a position adjacent the outlet end opening.

5. A machine according to claim 1, wherein a plurality of similar and separate lubricant passages with similar control means are provided for each cylinder, and wherein the respective passage outlets of said lubricant passages are spaced from one another in a symmetrical manner with respect to a central axis extending in the direction of relative movement of a respective cylinder and piston.

6. A machine according to claim 5, wherein said hydraulic fluid also serves as said lubricant with said pressurized lubricant source being in respective ones of said cylinders, each of said lubricant passages including passage inlet openings into respective ones of said cylinders at a position directly communicated with the supply of said hydraulic fluid to said cylinder.

9. A machine according to claim 7, wherein said cylinder block is rotatably mounted in said casing, wherein each of said respective cylinders and pistons extend and move radially with respect to the rotational axis of said cylinder block with the inner ends of the pistons being radially outwardly of the outer ends thereof with respect to said rotational axis, wherein said engagement means are rotatably mounted with respect to respective ones of said pistons, and wherein said waved cam surface is formed at the periphery of said casing for rolling engagement with the respective rotatably mounted engagement means.

18. A machine according to claim 17, wherein said cylinder block is rotatably mounted in said casing, wherein each of said respective cylinders and pistons extend and move radially with respect to the rotational axis of said cylinder block with the inner ends of the pistons being radially outwardly of the outer ends thereof with respect to said rotational axis, wherein said engagement means are rotatably mounted with respect to respective ones of said pistons, and wherein said waved cam surface is formed at the periphery of said casing for rolling engagement with the respective rotatably mounted engagement means.

19. A machine according to claim 17, wherein each of said lubricant supply passages is arranged completely within a respective one of said pistons.