US3744377A

US3744377A - Hydraulic motor drive

Info

Publication number: US3744377A
Application number: US00133358A
Authority: US
Inventors: J Lauck
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-04-12
Filing date: 1971-04-12
Publication date: 1973-07-10
Anticipated expiration: 1990-07-10

Abstract

A hydraulic drive device having a hydraulic motor section fixedly connected to a gear reduction section. The hydraulic motor section includes movable pistons disposed within a rotatable cylinder barrel and maintained in engagement with an inclined swash or cam plate for causing rotation of the cylinder barrel. The cylinder barrel is rotatably connected to and drives a shaft, which shaft has a gear thereon disposed in meshing engagement with a further enlarged gear disposed within the gear reduction section. Suitable passages and grooves are provided in the cylinder barrel to permit leakage fluid within the pump section to be discharged into the reduction gear section. One-way check valve devices coact between the motor ports and the gear reduction section for enabling discharge of leakage fluid into the low pressure or discharge port.

Description

I Umted States Patent [191 [111 3,744,377 Lauck July 10, 1973 HYDRAULIC MOTOR DRIVE [57] ABSTRACT Inventor! J Lallck, Colfax Avenue, A hydraulic drive device having a hydraulic motor sec- Benton Harbor, Mlch- 49022 tion fixedly connected to a gear reduction section. The h draulic motor section includes movable istons dis- I 7 y P [22] Filed Apr 12 19 l posed within a rotatable cylinder barrel and maintained PP N01 ,358 in engagement with an inclined swash or cam plate for causin rotation of the cylinder barrel. The cylinder b l bl d d d h f 91 89 1 499, 92 86 we Y mes a S a g M i /F04b 4 which shaft has a gear thereon disposed in meshing en- [58] Field oisQQiEiQIIIIIIIIIIIIIIIIIIIBiM, 486, 489, gagemem with a further enlarged gear disPosed Within 91/506 92/86 865 the gear reduction section. Suitable passages and grooves are provided in the cylinder barrel to permit [56] References Cited leakagle fluiid within the pump secotion to be gisclhargled into t e re uction gear section. ne-way c ec va ve UNITED STATES PATENTS devices coact between the motor ports and the gear re- 3,006,284 10/1961 Pitt et al. 92/86 X duction section f enabling discharge f leakage fl id gglglgy Q into the low pressure or discharge port. 3:514:223 5/1970 Hare 91/499 12 C i 8 Drawing Figures 3,237,569 3/1966 Reaume 9l/499 Primary ExaminerManuel A. Antonakas Att0rneyW00dhams, Blanchard and Flynn l2 I7 28 2754- 29 47 I IN V EN TOR.

K/ w v m A 0 1 I AM HYDRAULIC MOTOR DRIVE FIELD OF THE INVENTION This invention relates to a hydraulic drive device which includes a hydraulic motor section and a gear reduction section and, in particular, to an improved hydraulic drive device having suitable pressure release means for preventing excessive pressure build-up within the device during operation or during rapid rotation reversals.

BACKGROUND OF THE INVENTION Piston-type hydraulic motors which utilize an inclined cam or swash plate are well known, and numerous modifications and variations of this type of hydraulic motor have been developed for different use situations. However, hydraulic motors of this type have long been plagued with the problem of fluid seepage or leakage into the housing chamber which surrounds the cylinder barrel. Such leakage fluid, if permitted to collect within the housing chamber, will result in a substantial pressure build-up and, since the pressurized leakage fluid is in contact with the pistons, it can exert an undesirable counteracting force on the pistons which tends to retard the pistons during their power stroke, thus disrupting the efficient operation of the fluid motor.

Hydraulic motors of the cam or swash plate type have also not performed successfully in use situations wherein the motor is subject to rapid rotation reversals, which rotation reversals result in at least a short duration pressure build-up in the fluid trapped within the motor housing. These pressure build-ups or pressure pulses can be extremely damaging to the motor seals and other related components.

Accordingly, it is an object of the present invention to provide an improved hydraulic drive device which includes a piston-type hydraulic motor connected to and in communication with a gear box, and wherein the hydraulic drive device includes suitable pressure release means for preventing the development of excessive fluid pressures within either the motor section or the gear box.

It is another object of the present invention to provide an improved hydraulic drive device, as aforesaid, which includes suitable one-way check valve systems coacting with the motor ports for enabling leakage fluid to be freely discharged to the low pressure or discharge motor port.

A further object of the invention is to provide an improved hydraulic drive device, as aforesaid, which will permit instant reversing of the hydraulic motor without causing excessive pressures to be developed in either the motor section or the gear box section.

It is still a further object of the present invention to provide an improved hydraulic drive device, as aforsaid, which includes a desirable vent passageway system within the motor section for preventing excessive quantities of leakage fluid from accummulating within the motor housing.

Still a further object of the present invention is to provide an improved hydraulic drive device, as aforesaid, which is particularly suitable for use in conveyors or driving vehicles, such as lift trucks and the like, for permitting instant reversing or hydraulic braking of the vehicle.

Other objects and purposes of the invention will be apparent to persons acquainted with devices of this type upon reading the following specification and inspecting the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an improved hydraulic drive device constructed according to the present invention.

FIG. 2 is a front view, as taken from the right side of FIG. 1, of the hydraulic drive device of the present invention.

FIG. 3 is a fragmentary sectional view taken substantially along the line III-III of FIG. 2.

FIG. 4 illustrates the rear wall of the port plate.

FIG. 5 is an enlarged, fragmentary sectional view taken substantially along the line VV of FIG. 4.

FIG. 6 illustrates the front wall of the cylinder barrel.

FIG. 7 is a fragmentary sectional view of the front end of the cylinder barrel as taken substantially along the line VII-VII of FIG. 6.

FIG. 8 is an enlarged, fragmentary sectional view of the pressure release means.

Certain terminology will be used in the following descriptions for convenience in reference only and will not be limiting. The words upwardly, downwardly, rightwardly and leftwardly will designate directions in the drawings to which reference is made. The words front and rear will refer to the right and left sides of the device, respectively, as illustrated in FIG. 1. The words inwardly and outwardly will refer to directions toward and away from, respectively, the geometric center of the device and designated parts thereof. Said terminology will include the words above specifically mentioned, derivatives thereof, and words of similar import.

SUMMARY OF THE INVENTION In general, the objects and purposes of the invention are met by providing a hydraulic drive device which includes a hydraulic motor section and a gear reduction section fixedly connected to the motor section. The motor section includes a cylinder barrel having a plurality of bores for slideably supporting reciprocating pistons, which pistons coact with an inclined cam or swash plate for causing rotation of the cylinder barrel. The cylinder barrel rotates a pump shaft which is drivingly connected to the gear reduction section. The motor section includes a pair of ports which permit fluid to be supplied to or discharged from the cylinder bores for causing actuation of the motor section. The motor section includes suitable passages which provide communication between the motor chamber and a chamber in the gear reduction section to permit the leakage fluid in the motor section to escape into the gear reduction chamber. Pressure release devices, particularly one-way check valves, coact between the ports of the motor section and the gear reduction chamber for enabling the leakage fluid to be discharged to the low pressure or discharge port of the motor section.

DETAILED DESCRIPTION FIG. 1 illustrates therein a hydraulic drive device 11 constructed according to the present invention. The

drive device 11 includes a hydraulic motor section 12 Considering first the hydraulic motor section 12, same includes a housing 16 defining a cylindrical chamber 17 therein. A swash plate cover 18 and a port plate 19 are fixedly connected to the housing 16 adjacent the opposite ends thereof. A rotatable pump shaft 21 is concentrically disposed within the chamber 17 and is rotatably supported adjacent the opposite ends thereof by

antifriction bearings

22 and 23. A bearing cover 24 is fixedly secured to the swash plate cover 18 for closing the one end of the housing.

The pump shaft 21 has a cylinder barrel 26 nonrotatably but axially slideably mounted thereon and interconnected by conventional means, such as a key (not shown). Cylinder barrel 26 has a plurality, such as five, of circumferentially spaced cylinders or bores 27 formed therein in a direction substantially parallel to the longitudinal axis of the pump shaft 21. A piston 28 is slideably disposed within each of the bores 27 and is resiliently urged outwardly of the bore by a compression spring 29 disposed between the piston and the bottom wall of the bore. The springs 29 resiliently urge the rounded nose or end portions of the pistons 28 into bearing engagement with a rotatable cam or swash plate 31. The swash plate 31 is rotatably supported on the inclined inner wall 32 of the swash plate cover 18 by a radial roller bearing 33 and a thrust roller bearing 34, the latter being disposed in rolling engagement with a hardened thrust washer 36.

The pump shaft 21 extends through the swash plate 31 and has a thrust washer 37 axially secured thereto, which thrust washer functions as a seat for one end of a compression spring 38. The other end of the spring 38 bears against the cylinder barrel 26 and, in conjunction with the piston springs 29, resiliently urges the cylinder barrel 26 axially relative to the pump shaft 21 so that the axial end wall 39 (FIG. 3) of the rotating cylinder barrel 26 is resiliently urged into rotatable sliding and sealing engagement with the inner wall 41 of the port plate 19.

The port plate 19 has a pair of radial port openings 42 and 43 (FIG. 4) formed therein, which openings respectively communicate at their inner ends with kidney-

shaped ports

44 and 46 formed in the inner wall 41. The

ports

44 and 46, which function as either fluid supply or discharge ports, are disposed for intermittent communication with further kidney-shaped ports 47 (FIG. 6) formed in the axial end wall 39 of the cylinder barrel 26, which ports 47 respectively communicate with the cylinder bores 27.

The cylinder barrel 26 has a small bleed passage 48 extending axially therethrough whereby the rearward end of passage 48 communicates with the motor chamber 17. The forward end of the bleed passage 48 communicates with an annular groove 49 (FIG. 7) formed in the axial end wall 39. Groove 49, through intermediate radial passages 51, communicates with art annular clearance space 52 (FIG. 1) provided between the pump shaft 21 and the port plate 19.

The cylinder barrel 26 has a further annular groove 53 (FIG. 7) formed on the axial end wall 39, which groove 53 is disposed radially outwardly of and encircles the kidney-

shaped ports

44, 46 and 47. The annular groove 53 communicates through intermediate radial passages 56 with an annular clearance space 54 (FIG. 1) provided between the housing 16 and the cylinder barrel 26. The bleed passage 48 and the

annular grooves

49 and 53 permit leakage fluid within the motor section 17 to be supplied to the annular clearance space 52, from which the leakage fluid flows through the antifriction bearing 22 into the gear box 13. The manner in which this flow occurs will be explained in greater detail hereinafter.

Considering now the gear box 13, same includes a housing 61 which defines a chamber 62 therein in communication with the annular clearance space 52. The housing 61 includes a front cover member 63 fixedly connected to an intermediate member 64, which in turn is fixedly connected to the front face of the port plate 19. The intermediate member 64 supports a radial roller bearing 66 which rotatably supports the inner end of the output shaft 14. The intermediate member 64 also cooperates with a suitable shoulder or abutment formed on the shaft 14 for confining a conventional thrust roller bearing 67 therebetween. The forward end of the output shaft 14 extends outwardly of the front cover 63 and is disposed in rotatable sealing engagement with a resilient elastomeric O-ring 68 mounted on the front cover 63.

A driven gear 71 is disposed within the gear box chamber 62 and is supported on and nonrotatably connected to the output shaft 14, as by the integral hub portion 72. A roller bearing 73 coacts between the hub portion 72 and the front cover 63 for rotatably supporting both the driven gear 71 and the output shaft 14.

The driven gear 71 has internal gear teeth 74 thereon disposed in meshing engagement with similar external gear teeth formed on a drive gear 76. The drive gear 76 is coaxial with and nonrotatably connected to the pump shaft 21 so as to be rotatably driven thereby. The drive gear 76 is, in the illustrated embodiment, formed integrally on the forward end of the pump shaft 21. The drive gear 76, as illustrated in FIG. 1, preferably has a diameter which is only a small fraction of the diameter of the internal driven gear 71 to provide a rather large gear ratio therebetween, whereby the rotational speed of the drive gear 76 is several times greater than the rotational speed of the output shaft 14. This arrangement of the

gears

76 and 71 results in the output shaft 14 being substantially parallel to but laterally offset from the pump shaft 21.

The gear box 13 also has associated therewith suitable pressure release means 81 for preventing excessive fluid pressure from developing within the gear box chamber 62. The pressure release means 81 specifically comprises a one-way check valve system (FIG. 8) which includes a check valve member 82 slideably disposed within a bore 83 formed in the front face of the port plate 19. The bore 83 communicates at its rearward end with the kidney-shaped port 46 and at its forward end with the gear box chamber 62 by means of an intermediate opening 84 formed in the intermediate member 64. An annular valve seat member 86 is disposed in the bore 83 adjacent the interface between the port plate 19 and the intermediate member 63 for creating a sealing relationship with the check valve member 82, thereby normally preventing flow of fluid through the bore 83.

The check valve member 82, as illustrated in FIG.8, has a cuplike configuration and includes a conical end wall 87 which is fixedly, here integrally, connected to an annular skirt or sidewall 88 which is slideably disposed within the bore 83. The check valve has a recess 89 in the interior thereof disposed for communication with the kidney-shaped port 46, and a plurality of ports or openings 91 extend through the conical end wall 87 for providing flow communication between the opposite sides of the check valve 82 when the check valve is moved (upwardly in H0. 8) out of seating engagement with the seat member 86.

A further pressure release means 92 (FIG. 3) provides communication between the gear box chamber 62 and the other kidney-shaped port 44. The pressure release means 92 is also a one-way check valve system and is identical to the pressure release means 81. Further description thereof is thus not believed necessary.

OPERATION The operation of the invention will be briefly described in detail hereinbelow for a better understanding thereof.

Assuming that a pressurized fluid is continuously supplied to one of the port openings, such as the port opening 42, then the fluid will flow into kidney-shaped port 44 and then through the further port 47 into the bores 27 formed in the cylinder barrel 26. The pressure fluid causes the pistons 28 to be urged axially. rearwardly (leftwardly) in FIG. 1) and, due to the coaction between the pistons 28 and the rotatable swash plate 31, causes the cylinder barrel 26 and the shaft 21 to be rotated. Due to the angular orientation of the swash plate 31, the pistons 28 are under pressure during approximately one-half a revolution, during which the pistons are axially extended outwardly from their respective bores. During the other half revolution, the swash plate 31 causes the pistons to be slideably moved back into their bores causing a discharge of the fluid from the bores 27 into the other kidney-shaped port 46 and thence out the other port opening 43. The kidneyshaped cylinder ports 47 are thus connected to the inlet pressure fluid during approximately 180 of rotation, and to the discharge or low pressure side of the system during approximately the remaining 180 of rotation. The rotation of the pump shaft 21 by the cylinder barrel 26 also causes a corresponding rotation of the drive gear 76, which in turn drives the driven gear 71 and the output shaft 14. The operation of the hydraulic motor section 12 is thus substantially conventional and further description thereof is not believed necessary. However, it should be noted that, in many use situations, the pressurized fluid is alternately supplied to the

port openings

42 and 43 to permit reverse rotation of the cylinder barrel, whereby the

port openings

42 and 43 thus also alternately act as discharge ports.

During operation of the hydraulic motor section 12, some fluid inherently leaks or seeps into the motor chamber 17. For example, some fluid leaks between the relatively sliding faces 39 and 41, which leakage fluid flows into the

collection grooves

49 or 53. The fluid in the collection groove 53 flows throughthe radial passages 56. and through the annular clearance space 54 into the motor chamber 17. Other fluid will also seep or leak between the pistons 28 and the surrounding walls of the bores 27 into the motor chamber 17. The leakage fluid within the motor chamber 17, if permitted to remain, would gradually collect and cause a substantially high pressure build-up to occur within the motor chamber 17, which pressure build-up would reduce or entirely disrupt the efficient operation of the motor section 12. To prevent any pressure build-up of the leakage fluid within the motor chamber 17, the present invention provides the bleed passage 48 which extends axially through the cylinder barrel 26, whereupon the leakage fluid within the motor chamber 17 passes through the bleed passage 48 into the annular collection groove 49. The leakage fluid then flows through the radial passages 51 into the annular clearance space 52, and thence through the roller bearing 22 into the gear box chamber 62. The leakage fluid within the chamber 62 thus effectively lubricates the gears 71- and 76.

When the pressure of the leakage fluid within the gear box chamber 62 increases to a predetermined level, then the fluid in chamber 62 will flow through whichever pressure release means 81 or 92 is associated with the low pressure or discharge port, thereby permitting the leakage fluid to be discharged to the low pressure side of the external fluid system. For example, when the port openings 43 and kidney-shaped port 46 constitutes the discharge port, then the fluid in gear box chamber 62 will cause the check valve 82 of the pressure release means 81 to be moved away from the seat 86, thereby enabling the leakage fluid to flow into the port 46 and thence out the opening 43. In situations where pressureized fluid is continuously supplied to the other port 44, then the other pressure release means 92 will be continuously maintained in the closed position and all pressure relief will occur through the pressure release means 81. However, when the supply pressure is alternated betweeen the

ports

44 and 46, then the leakage fluid within gear box chamber 62 will be alternately discharged through the pressure release means 81 or 92, depending upon which pressure release means is connected to the discharge or low pressure port.

The latter-mentioned mode of operation is essential in situations where the hydraulic device 11 is used for driving vehicles where instant reversing of the hydraulic motor is necessary. This instant reversing of the hydraulic motor is accomplished by reversing the supply of pressure fluid from one of the

openings

42 and 43 to the other of the

openings

42 and 43, which reversal causes the hydraulic cylinder barrel 26 and pump shaft 21 to be rotated in the opposite direction. This reversal also tends to cause excessive, short duration pressure build-ups to occur within the hydraulic motor. These short duration pressure build-ups or pressure pulses are instantaneously released, according to the present invention, due to the provision of the pressure release means 81 and 92, which pressure release means are connected to both of the

port openings

42 and 43 so that discharge to the low pressure port is possible at all times, even during such instantaneous reversals of rotatron.

However, in some use situations both

port openings

42 and 43 of the hydraulic motor are subjected to a relatively high pressure. This can occur when the high pressure supply fluid is supplied to one of the

openings

42 and 43, and the-

other opening

42 and 43 is restricted, as for braking the motor. In this situation, since the pressure within both of the

port openings

42 and 43 is relatively high, niether pressure release means 81 nor 92 can be opened to permit venting of the leakage fluid within the gear box chamber 62. Accordingly, to permit the hydraulic drive device 11 of the present invention to be utilized in this type of use situation, the front cover 63 of the gear box is provided with one or more discharge ports 93 formed therein, which discharge ports can be suitabley connected to the low pressure side of the fluid system, such as a fluid reservoir. However, in situations where hydraulic braking is not utilized, and where the pressure release means 81 and 92 are sufficient to relieve the pressure within the chamber 62 due to instant shifting of the supply pressure between the

openings

42 and 43, then the discharge ports 93 are closed, as by use of conventional threaded plugs 94. The auxiliary discharge ports 93 must be utilized only in use situations where high pressure may exist for any substantial period of time on both of the

port openings

42 and 43.

Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

I. A hydraulic drive device, comprising in combination:

housing means defining therein a motor chamber; shaft means disposed within said motor chamber and rotatably supported on said housing means;

hydraulic motor means disposed within said motor chamber and interconnected to said shaft means for rotating same, said motor means including relatively sliding seal means disposed between high and low pressure zones for substantially preventing pressure fluid from flowing into the low pressure zone;

first and second port means formed in said housing means for enabling pressure fluid to be supplied to or discharged from said motor means; passage means providing communication between said low pressure zone and the discharge one of said first and second port means for permitting flow therebetween of pressure fluid which leaks from said motor means, said passage means including first and second passageways communicating with said first and second port means, respectively; and

normally-closed pressure release means disposed with said passage means for preventing excessive pressure build-up of the leaded pressure fluid contained within said low pressure zone, said pressure release means including first and second check valves disposed within said first and second passageways, respectively, and oriented to be normally held closed by pressure in the port means.

2. In a hydraulic device having housing means defining a chamber therein, shaft means rotatably supported on said housing means and extending into said chamber, a cylinder block disposed within said chamber and provided with a plurality of cylinder bores formed axially therein, said cylinder block being nonrotatably connected to said shaft means and having a cylinder port for each cylinder bore opening through one axial end thereof, an inclined plate mounted on said housing means and disposed adjacent the other axial end of said cylinder block, a piston slideably disposed within each of said cylinder bores and positioned for engagement with said inclined plate, and said housing means includ ing a port plate disposed adjacent and in slideably engagement with said one end of said cylinder block, said port plate having two port openings formed therein and positioned to alternately communicate with the cylin' der ports upon rotation of the cylinder block,

the improvement comprising pressure release means disposed in communication with said chamber for enabling external discharge of the pressure fluid which leaks past said pistons or past said axial end of said cylinder barrel and collects within said chamber;

said pressure release means including passage means providing communication between said chamber and one of said port openigns, and one-waycheck valve means associated with said passage means for permitting flow therethrough only when the pressure in said chamber exceeds the pressure in said one port opening; and

said passage means including an elongated bleed passage formed in said cylinder block and extending between the opposite axial ends thereof.

3. A device according to claim 2 wherein said pressure release means includes further passage means providing communication between said chamber and said other port opening and further one-way check valve means associated with said further passage means for permitting flow therethrough only when the pressure in said chamber exceeds the pressure in said other port opening.

4. A hydraulic drive device, comprising in combination:

housing means defining therein a motor chamber and a gear box chamber;

a shaft disposed within said motor chamber and rotatably supported on said housing means, said shaft extending into said gear box chamber;

hydraulic motor means disposed within said motor chamber and interconnected to said shaft for rotating same, said motor means including a cylinder barrel nonrotatably connected to said shaft and having a plurality of cylinder bores formed therein and a piston slideably disposed within each of said bores, said cylinder barrel also having cylinder ports formed therein and communicating with each of said cylinder bores for enabling pressure fluid to be supplied to or discharged from said cylinder bores;

port meansformed in said housing means and communicating with said cylinder ports for enabling pressure fluid to be supplied to or discharged from said cylinder bores, said port means including two port openings formed in said housing means and positioned for communication with the cylinder ports formed in said cylinder barrel, said two port openings functioning as inlet and outlet ports for enabling pressure fluid to be supplied to and discharged from said cylinder bores;

output means rotatably supported on said housing means and extending into said gear box chamber;

reduction gear means disposed within said gear box chamber and drivingly interconnecting said shaft and said output means, said reduction gear means including a drive gear nonrotatably connected to said shaft and a driven gear nonrotatably connected to said output means;

passage means providing free communication between said motor chamber and said gear box chamher for permitting flow therebetween of pressure fluid which leaks from said motor means; and

pressure release means for preventing excessive pressure build-up of the leaked pressure fluid contained within said chambers, said pressure release means including a flow passage providing communication between said gear box chamber and one of said port openings, and a one-way check valve disposed within said flow passage for permitting flow of fluid therethrough whenever the pressure of the fluid within the gear box chamber exceeds the pressure of the fluid within said one port opening.

5. A device according to claim 4, wherein said pressure release means includes a further flow passage providing communication between said gear box chamber and the other port opening, and a further one-way check valve disposed in said further passage for permitting flow therethrough whenever the pressure of the fluid within the gear box chamber exceeds the pressure of the fluid in said other port opening.

6. A device according to claim 4, wherein said passage means includes a bleed passage formed in said cylinder barrel and extending substantially axially thereof, one end of said bleed passage communicating with said gear box chamber and the other end of said bleed passage communicating with said motor chamber for enabling leakage fluid within said motor chamber to freely flow into said gear box chamber.

7. A device according to claim 4, wherein said drive gear comprises an externally toothed gear member and said driven gear comprises an internally toothed gear member disposed in meshing engagement with said drive gear, said driven gear having a diameter substantially larger than the diameter of said drive gear, and said output means including an output shaft nonrotatably connected to said driven gear and disposed for rotation about an axis substantially parallel to but laterally spaced from the rotational axis of said shaft means.

8. A device according to claim 4, wherein said cylinder bores extend axially of said cylinder barrel in substantiqlly parallel relationship to said shaft means, said motor means including an inclined plate mounted on said housing means and axially spaced from one axial end of said cylinder barrel for engagement by said pistons, and said gear reduction means being disposed adjacent the other axial end of said cylinder barrel.

9. A device according to claim 8, wherein said housing means includes a fixed porting member having a surface thereon in sliding engagement with said other axial end of said cylinder barrel, said other axial end of said cylinder barrel having said cylinder ports formed therein, and said two port openings being formed in said porting member and communicating with said surface of said porting member whereby said port openings intermittently communicate with said cylinder ports.

10. A device according to claim 9, wherein said pressure release means includes a second one-way check valve means providing communication between said gear box chamber and the other said port opening, each said check valve means permitting free flow therethrough whenever the pressure in said gear box chamber is greater than the pressure in the respective port opening.

11. A device according to claim 10, wherein said cylinder barrel has a bleed passage extending axially between the opposite ends thereof with one end of said bleed passage terminating at said one axial end of said cylinder barrel and being in communication with said motor chamber, and the other axial end of said bleed passage terminating adjacent said other axial end of said cylinder barrel and being disposed in communication with said passage means.

12. A device according to claim 10, wherein said passage means for providing communication between said motor chamber and said gear box chamber includes an annular clearance passage disposed between said shaft means and said housing means, and antifriction bearing means disposed in said clearance space for rotatably supporting said shaft on said housing means, said bearing means having clearance spaces therein for enabling free flow of pressure fluid therethrough, and said cylinder barrel having a bleed passage extending substantially axially therethrough with opposite axial ends of said bleed passage communicating with said annular clearance space and said motor chamber.

Claims

1. A hydraulic drive device, comprising in combination: housing means defining therein a motor chamber; shaft means disposed within said motor chamber and rotatably supported on said housing means; hydraulic motor means disposed within said motor chamber and interconnected to said shaft means for rotating same, said motor means including relatively sliding seal means disposed between high and low pressure zones for substantially preventing pressure fluid from flowing into the low pressure zone; first and second port means formed in said housing means for enabling pressure fluid to be supplied to or discharged from said motor means; passage means providing communication between said low pressure zone and the discharge one of said first and second port means for permitting flow therebetween of pressure fluid which leaks from said motor means, said passage means including first and second passageways communicating with said first and second port means, respectively; and normally-closed pressure release means disposed with said passage means for preventing excessive pressure build-up of the leaded pressure fluid contained within said low pressure zone, said pressure release means including first and second check valves disposed within said first and second passageways, respectively, and oriented to be normallY held closed by pressure in the port means.

2. In a hydraulic device having housing means defining a chamber therein, shaft means rotatably supported on said housing means and extending into said chamber, a cylinder block disposed within said chamber and provided with a plurality of cylinder bores formed axially therein, said cylinder block being nonrotatably connected to said shaft means and having a cylinder port for each cylinder bore opening through one axial end thereof, an inclined plate mounted on said housing means and disposed adjacent the other axial end of said cylinder block, a piston slideably disposed within each of said cylinder bores and positioned for engagement with said inclined plate, and said housing means including a port plate disposed adjacent and in slideable engagement with said one end of said cylinder block, said port plate having two port openings formed therein and positioned to alternately communicate with the cylinder ports upon rotation of the cylinder block, the improvement comprising pressure release means disposed in communication with said chamber for enabling external discharge of the pressure fluid which leaks past said pistons or past said axial end of said cylinder barrel and collects within said chamber; said pressure release means including passage means providing communication between said chamber and one of said port openigns, and one-way check valve means associated with said passage means for permitting flow therethrough only when the pressure in said chamber exceeds the pressure in said one port opening; and said passage means including an elongated bleed passage formed in said cylinder block and extending between the opposite axial ends thereof.

4. A hydraulic drive device, comprising in combination: housing means defining therein a motor chamber and a gear box chamber; a shaft disposed within said motor chamber and rotatably supported on said housing means, said shaft extending into said gear box chamber; hydraulic motor means disposed within said motor chamber and interconnected to said shaft for rotating same, said motor means including a cylinder barrel nonrotatably connected to said shaft and having a plurality of cylinder bores formed therein and a piston slideably disposed within each of said bores, said cylinder barrel also having cylinder ports formed therein and communicating with each of said cylinder bores for enabling pressure fluid to be supplied to or discharged from said cylinder bores; port means formed in said housing means and communicating with said cylinder ports for enabling pressure fluid to be supplied to or discharged from said cylinder bores, said port means including two port openings formed in said housing means and positioned for communication with the cylinder ports formed in said cylinder barrel, said two port openings functioning as inlet and outlet ports for enabling pressure fluid to be supplied to and discharged from said cylinder bores; output means rotatably supported on said housing means and extending into said gear box chamber; reduction gear means disposed within said gear box chamber and drivingly interconnecting said shaft and said output means, said reduction gear means including a drive gear nonrotatably connected to said shaft and a driven gear nonrotatably connected to said output means; passage means providing free communication between said motor chamber and said gear box chamber for permitting flow therebetween of pressure fluid which leaks from said motor means; and pressure release means for preventing excessive pressure build-up of the leaked Pressure fluid contained within said chambers, said pressure release means including a flow passage providing communication between said gear box chamber and one of said port openings, and a one-way check valve disposed within said flow passage for permitting flow of fluid therethrough whenever the pressure of the fluid within the gear box chamber exceeds the pressure of the fluid within said one port opening.