Axle driving apparatus

1. Field of the Invention

The present invention relates to an axle driving apparatus for driving a vehicle, and more particularly, the invention relates to a pair of displacement hydraulic systems where at least one of the systems is of a variable capacity type having a movable swash plate.

2. Description of Related Art

U.S. Pat. Nos. 4,914,907, 4,903,545, 5,156,576 and 5,201,692 disclose a type of axle driving apparatus, which houses in a common housing a hydrostatic transmission including a pair of displacement type hydraulic systems fluidly connected with each other and axles driven by the hydrostatic transmission. At least one of the displacement type hydraulic systems is of a variable displacement type having a movable swash plate in contact with heads of pistons fitted into a cylinder block. The pistons reciprocate and the movable swash plate slants with respect to the rotary axis of the cylinder block.

This type of movable swash plate is convex at a rear surface opposite to an abutting surface that abuts against the heads of the pistons. An inner surface of the housing facing the rear surface of the piston is made concave corresponding to the convex rear surface of the movable swash plate. A U-shaped thrust metal is positioned on the concave inner surface so that the rear surface of the swash plate is slantingly movable along a circular-arched guide surface of the thrust metal.

Since the movable swash plate is usually subjected to thrust from the piston, frictional resistance generated between the rear surface of the movable swash plate and the guide surface of thrust metal increases. Thus, the sliding resistance of the movable swash plate increases. Accordingly, a large force is necessary to operate the movable swash plate. Especially problematic is the case where the movable swash plate is spring biased to automatically return to a neutral position when an operation is stopped. In such case, when the sliding resistance is greater than the biasing force of the spring, the movable swash plate does not return to the neutral position. Further, the sliding resistance cannot be diminished merely by polishing the rear surface of movable swash plate, which contacts the thrust metal.

In accordance with the invention, an axle driving apparatus houses in a common housing a hydrostatic transmission and axles driven by the hydrostatic transmission. One of the pair of displacement type hydraulic systems comprising the hydrostatic transmission is of variable-capacitive type having a movable swash plate, which is operable, for example, manually operable to move the swash plate to slanted positions. A primary object of the invention is to provide legs for supporting the movable swash plate inside the housing, so that the movable swash plate is suspended in the housing. Thus, the sliding resistance is reduced when the movable swash plate is slantingly moved. Accordingly, the necessary operating force is reduced and the movable swash plate can easily return to the neutral position. Another object of the invention is to reduce processing costs and simplify construction of the movable swash plate in the housing.

Preferred embodiments of the invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements and wherein:

FIG. 1 is a side view of an axle driving apparatus;

FIG. 2 is an exploded plan view of an upper half of a housing of the axle driving apparatus provided with the variable displacement type hydraulic system of the invention, and a partial sectional view thereof;

FIG. 3 is a sectional view taken in the direction of the arrows 3 — 3 in FIG. 2;

FIG. 4 is a sectional view taken in the direction of the arrows 4 — 4 in FIG. 2;

FIG. 5 is a sectional view taken in the direction of the arrows 5 — 5 in FIG. 4;

FIG. 6 is a perspective exploded view of a movable swash plate and a swinging arm;

FIG. 7 is a sectional view of an embodiment of the invention, which supports a movable swash plate by a lid member;

FIG. 8 is a perspective exploded view of a support shown in FIG. 7;

FIG. 9 is a sectional view of an embodiment for supporting the movable swash plate at an upper half of the housing;

FIG. 10 is a perspective view of the support shown in FIG. 9;

FIG. 11 is a sectional side view of an embodiment of the invention, which supports the movable swash plate at the upper half of the housing;

FIG. 12 is a sectional side view of another embodiment of the invention, which supports the movable swash plate at the upper half of the housing;

FIG. 13 is a sectional side view of an embodiment of the invention, which supports the movable swash plate in a center section;

FIG. 14 is a perspective exploded view of a support in the embodiment shown in FIG. 13;

FIG. 15 is a sectional view of a modified embodiment, which supports the movable swash plate by a lid member;

FIG. 16 is a sectional view taken in the direction of the, arrows 6 — 6 in FIG. 15; and

FIG. 17 is a sectional view of another modified embodiment, which is provided outside the housing with a control shaft.

FIGS. 1, 2 , 3 , 4 and 5 illustrate an axle driving apparatus. A housing of the axle driving apparatus is constructed by joining first and second halves, for example, an upper half 1 of the housing and a lower half 2 of the housing at joining surfaces, for example, horizontal joining surfaces to form a joint, respectively. An oil sump is formed in the housing. Positioned in the joint of upper half 1 and lower half 2 are axles including an output shaft 4 and a counter shaft 26 , and bearings for receiving the output shaft 4 and the counter shaft 26 . A pair of axles 7 are rotatably supported inside upper half 1 of the housing and apart from, for example, above the joint of upper half 1 and lower half 2 of the housing. The pair of axles 7 are differently connected by a differential gear 23 in the housing and extend outwardly from the housing.

A projection, for example, an upward projection is formed at a portion of the upper half 1 of the housing in which differential gear 23 is disposed. This portion is used as an oil tank 1 a. An input shaft 3 projects from the upper half 1 of the housing to input power from an engine (not shown) for driving a hydraulic pump of the variable displacement hydraulic system vertically and outwardly.

In a portion of the upper half 1 of the housing is mounted a center section 5 having substantially an L-shaped sectional side view. Center section 5 is positioned such that a surface, for example, an upper horizontal surface, of the center section 5 is in substantially the same plane or is parallel to a plane defined by the joint. The upper horizontal surface forms a pump setting surface 100 , which is for rotatably and slidably mounting a cylinder block 16 of a hydraulic pump. In a plurality of cylindrical bores provided at cylinder block 16 are pistons 13 , which move in a reciprocating manner through the use of, for example, springs. A movable swash plate 8 , when viewed from one side, for example, a front side, is positioned in a substantially central position. Movable swash plate 8 has openings 8 b, for example, a longitudinal opening through which input shaft 3 penetrates. Thrust bearings 8 c are held at a surface, for example, a lower surface of the movable swash plate. Thrust bearings 8 c form abutting surfaces against which pistons 13 abut respectively. From side surfaces of movable swash plate 8 project shaft portions 8 a and 8 a′ along an axis of slanting movement of movable swash plate 8 . The shaft portions 8 a and 8 a′ are supported by supports in accordance with the present invention and are discussed in greater detail in the following discussion. The cylinder block 16 engages input shaft 3 . The variable displacement type hydraulic pump is discussed above. Cylinder block 16 is rotated by input shaft 3 , and movable swash plate 8 is moved to slant with respect to the rotary axis of cylinder block 16 . Thus, a discharge amount and a discharge direction of oil from the hydraulic pump is changed.

A side surface, for example, a vertical side surface perpendicular to the upper horizontal surface of center section 5 forms a motor setting surface 101 . A cylinder block 17 is rotatably, slidably mounted on the vertical side surface. Pistons 12 are fitted into a plurality of cylinder bores in cylinder block 17 for reciprocating movement respectively. A head of each piston 12 abuts against a contact surface (or a thrust bearing surface) of a fixed swash plate 37 . Fixed swash plate 37 is fixedly sandwiched substantially between upper half 1 and lower half 2 . Cylinder block 17 engages with an output shaft 4 to comprise a fixing displacement type hydraulic motor. Within center section 5 is a closed circuit for connecting suction ports and discharge ports of the hydraulic pump and hydraulic motor, respectively, to circulate pressurized oil. Cylinder block 17 of the hydraulic motor receives the pressurized oil discharged from the hydraulic pump. Thus, output shaft 4 is capable of obtaining stepless output rotation to form a hydrostatic transmission.

At a surface, for example, a lower, substantially horizontal surface, of center section 5 is attached a pump casing 10 , into which a trochoid charge pump 11 is disposed. Charge pump 11 is driven by an end, for example, a lower end of input shaft 3 projecting away from, for example, in a downward direction from the lower surface of center section 5 . As shown in FIG. 4, a suction oil passage at charge pump 11 is open into the oil sump through an oil filter 40 . At the closed circuit of center section 5 are disposed a pair of check valves (not shown), which provide for connection with an operating oil supply circuit. Accordingly, the pressurized oil discharged from a discharge oil passage 63 of charge pump 11 opens a check valve to guide the pressurized oil from the operating oil supply circuit into the closed circuit. The pressurized oil discharged from discharge oil passage 63 is channelled through an oil take-out pipe 64 and a piping joint 65 for driving a hydraulic actuator (not shown) outside the housing. Oil returning from the hydraulic actuator is returned into the housing through a piping joint (not shown) and an oil return pipe (not shown) for being guided into the operating oil supply circuit at the center section 5 . In addition, within pump casing 10 is a relief valve (not shown) for adjusting the discharge oil in charge pump 11 to a predetermined pressure. Oil filter 40 is a porous member of cylindrical shape and supported substantially, between the side wall of pump casing 10 and the inner wall of lower half 2 of the housing. When the oil filter 40 is checked, cleaned or replaced, a blind cover 76 is opened for extracting oil filter 40 from a fitting bore 2 b at lower half 2 of the housing. Also, a support base 2 a for supporting oil filter 40 projects from the inner bottom surface of the housing.

As shown in FIG. 3, an oiling pipe 45 is fitted onto the lower surface of center section 5 and projects at an end, for example, an extreme end outwardly from a surface, for example, a lower surface of lower half 2 of the housing and is closed. The oiling pipe 45 is for charging the operating oil into the closed circuit at center section 5 after building the hydraulic pump and hydraulic motor in the housing.

Within the center section 5 is a suction oil passage 66 for check valve 47 . Check valve 47 is open so that the oil taken into the housing through an oil filter 46 is taken in from an oil passage 67 in a direction toward a negative pressure side of the closed circuit in center section 5 .

As shown in FIGS. 1 and 2, opening push rods 51 and 52 enable the pair of check valves (not shown), as discussed above, to be opened from a position outside of the housing or apart from center section 5 . A C-shaped by-passing operating member 36 is disposed adjacent to the ends of opening push rods 51 and 52 for simultaneously pushing opening rods 51 and 52 to open both of the pair of check valves and open the closed circuit in the oil sump for freely rotating the hydraulic motor. A by-pass operating lever shaft 15 is rotated from the outside of the housing, so that a cam pin 77 fixed to lever shaft 15 pushes the rear of the by-pass operating member 36 . The extreme end of lever shaft 15 simultaneously presses opening push rods 51 and 52 to open the pair of check valves, thereby enabling the hydraulic motor to rotate freely.

An arm 98 is fixed to a portion, for example, a lower portion of by-passing operating lever shaft 15 . Arm 98 and an arm 48 at a side of a brake operating shaft 14 , discussed in greater detail in the following discussion, are connected with each other through a rod 49 . When the brake operating shaft 14 rotatably operates a brake actuator 20 to exert the braking action to output shaft 4 , then, only when by-pass operating member 36 is operated simultaneously to put the pair of the check valves in an open state, are the valves adapted to automatically close. An indented gear 25 is provided at output shaft 4 . Indented gear 25 engages with a larger diameter gear 24 on a counter shaft 26 . A smaller diameter gear 21 on counter shaft 26 engages with a ring gear 22 at differential gear 23 . Power generated from the hydraulic motor and input to ring gear 22 is transmitted to left and right axles 7 through differential gear 23 . In an embodiment as discussed above, one end of counter shaft 26 is journalled to a side wall of fixed swash plate 37 .

A braking device in accordance with an embodiment of the invention includes arm 48 fixed to brake operating shaft 14 . Arm 48 engages with a projection provided at annular brake actuator 20 . When brake actuator 20 is rotated around the axis of the output shaft 4 , a cam mechanism 19 positioned substantially between fixed swash plate 37 and brake actuator 20 moves brake actuator 20 forward toward a braking friction plate 18 fixed to the output shaft 4 . Braking friction plate 18 rotatable together with output shaft 4 is sandwiched substantial between brake actuator 20 and the housing, thereby exerting the braking action onto output shaft 4 .

The operating device for slantingly moving movable swash plate 8 will be discussed in the following. In particular, at a wall, for example, the upper wall of the upper half of the housing, a control shaft 35 is rotatably supported in a manner of extending parallel to the input shaft 3 for slantingly operating the movable swash plate 8 . A control arm 42 is fixed to one end of control shaft 35 positioned exteriorly of the housing. Control arm 42 is connected to a manually operating member, such as a pedal or a lever on a vehicle (not shown). At another end of control shaft 35 extending into the housing is fixed an L-shaped swinging arm 39 . At a portion of swinging arm 39 along control shaft 35 is fixed a ball 30 forming an engaging portion as shown in FIG. 6 . Ball 30 engages through a pair of joint blocks 78 a and 78 b with an engaging portion 29 a of an arm 29 fixed to the shaft portion 8 a of a movable swash plate 8 . Accordingly, when control shaft 35 pivots, for example, horizontally pivots ball 30 and joint blocks 78 a and 78 b, movable swash plate 8 pivots such that a surface, for example, an upper surface of movable swash plate 8 pivots between lateral and slanted orientations relative to a plane, for example, a horizontal plane and relative to the axis of rotation of cylinder block 16 . Arm 29 can be of any type of shape, design, or construction, however, it is preferably of a length sufficient to achieve a link ratio and slanting movement of movable swash plate 8 relative to the amount control shaft 35 pivots. For example, with the link ratio, if a long arm 29 is used, the movable smash plate 8 can be made to slant move with a smaller rotation of the control shaft 35 . Arm 29 and control shaft 35 are in connection with each other, although not necessarily directly, within the housing. Thus, they are not affected by extraneous matter such as dust or rust.

A coiled torsion spring 31 is fitted onto control shaft 35 to return movable swash plate 8 to the neutral position once control shaft 35 is stationary, for example, is no longer pivoted. Torsion spring 31 has one end of the coil that extends on one side of axles 7 , for example, on a side above axles 7 , and extends in one direction for a portion of its length. Torsion spring 31 has another end of the coil that extends on another side of axles 7 , for example, on a side below axles 7 , and extends in another direction for a portion of its length different from the direction of the one end of the coil such that a portion of the ends are in a crossed position. The free ends of the coil are positioned on the sides of a fixing pin 33 . Fixing pin 33 is fixed to the housing and is adjustable in a translational direction. A movable pin 32 is provided on swinging arm 39 . Torsion spring 31 also serves as a guide for assembling axles in the housing, in particular, simplifying assembly of axles 7 .

A neutral position adjusting screw 34 is for adjusting the neutral position of movable swash plate 8 outwardly. Adjusting screw 34 projects from upper half 1 of the housing. Fixing pin 33 is positioned eccentric to and at an end, for example, a lower end of neutral position adjusting screw 34 . Accordingly, neutral position adjusting screw 34 is rotated in an appropriate direction to shift fixing pin 33 around neutral position adjusting screw 34 to enable adjustment of the neutral position of swinging arm 39 . When swinging arm 39 pivots in one or another direction, one end of torsion spring 31 is expanded by way of movable pin 32 to apply to swinging arm 39 a return biasing force in the neutral direction. As a result, movable swash plate 8 is subject to a return force toward the neutral position of movable swash plate 8 . Also, at one end of swinging arm 39 are a pair of engaging projections 39 a and 39 b for restricting rotation. Accordingly, when one of projections 39 a and 39 b abuts against fixing pin 33 during rotation of swinging arm 39 , swinging arm 39 a is stopped.

Swinging arm 39 includes a cam bore 39 c for returning movable swash plate 8 to the neutral position when brake operating shaft 14 rotates to brake movement of output shaft 4 . A pin 81 is fitted in cam bore 39 c and fixed to an arm 80 rotatably around a relay shaft 83 . When output shaft 4 is braked, a rod 79 connected to brake operating shaft 14 rotates arm 80 around relay shaft 83 and pin 81 rotates along the cam bore 39 c. Accordingly, pin 81 forces movement of swinging arm 39 toward the neutral position by way of cam bore 39 c. In a non-braking state, pin 81 is in a wider portion of cam bore 39 c, thus swinging arm 39 can freely rotate therein. In addition, a magnet 41 attracts iron powder produced in the housing.

In an embodiment of the invention shown in FIGS. 7 and 8, movable swash plate 8 is supported by a lid 9 for closing an opening 1 b at upper half 1 of housing. A hydraulic pump shaft 3 is journalled to a central portion of lid 9 . A pair of legs 9 a and 9 b extend from lid 9 toward movable swash plate 8 along, for example, in parallel with a rotary axis of cylinder block 16 . Legs 9 a and 9 b are integral with lid 9 . Legs 9 a and 9 b have a portion coincident with shaft portions 8 a and 8 a′. A first support S 1 and a second support S 2 for rotatably supporting shaft portions 8 a and 8 a′ are provided at legs 9 a and 9 b respectively. First support S 1 includes a round bore 9 c for inserting shaft portion 8 a. Shaft portion 8 a is greater in axial length than the thickness of bore 9 c. An axial end of shaft portion 8 a is fixed to arm 29 . A substantially semicircular surface 9 d for supporting shaft portion 8 a′ is formed at the lower surface of leg 9 b. A holder 6 is detachably mounted onto the lower surface of leg 9 b by screw bolts 27 . Holder 6 has a receiving surface 6 a of a substantially semicircular shape for being positioned opposite to semicircular surface 9 d. Second support S 2 includes a combination of semicircular surface 9 d and holder 6 . In addition, the shape of receiving surface 6 a and surface 9 d are not limited to a semicircular arc, but may be any shape acceptable for cooperation with shaft portion 8 a.

Shaft portions 8 a and 8 a′ of movable swash plate 8 are supported by legs 9 a and 9 b. Accordingly, movable swash plate 8 is suspended in the housing for being slantingly moved by way of shaft portions 8 and 8 a′. Therefore, sliding resistance or friction created when movable swash plate 8 slantingly moves, is reduced, and the force necessary to move movable swash plate 8 is reduced. Due to the reduced sliding resistance, movable swash plate 8 easily returns to the neutral position. In an embodiment where legs 9 a and 9 b extend internally from lid 9 , legs 9 a and 9 b can be molded integrally with lid 9 . Accordingly, the manufacturing costs are lower. Since movable swash plate 8 is supported by lid 9 , this embodiment is particularly adaptable to various types of axle driving apparatuses. For example, movable swash plate 8 , in accordance with the invention, can be effectively assembled into a housing. In addition, the invention is adaptable for use in a housing having a joint with surfaces defining a plane perpendicular to a longitudinal direction of the axles as disclosed, for example, in U.S. Pat. No. 4,899,541, thus achieving efficient assembly.

When movable swash plate 8 is assembled with lid 9 , shaft portion 8 a may be inserted into bore 9 c and shaft portion 8 a′ is then disposed in semicircular surface 9 d for being held by holder 6 . In addition, it is within the scope of the invention to form first support S 1 to be the same as that of second support S 2 . In particular, at the lower surface of leg 9 a, a substantially semicircular surface is formed and a holder having a semicircular receiving surface is mounted opposite to the semicircular surface. Accordingly, the labor required for boring bore 9 c can be eliminated and lid 9 with legs 9 a and 9 b can be manufactured without mechanical processing.

Once movable swash plate 8 is supported by lid 9 , arm 29 is connected to shaft portion 8 a and fixed by a bolt 28 . Thus, assembly of movable swash plate 8 with lid 9 is facilitated.

A biasing spring housed in cylinder block 16 in combination with a hydraulic reaction creates thrust F, which is transferred from each piston 13 to movable swash plate 8 supported by legs 9 a and 9 b. Thrust F pushes, for example, upwardly pushes movable swash plate 8 . Thus, lid 9 bears the force of thrust F by way of shaft portions 8 a and 8 a′ and legs 9 a and 9 b. More particularly, the lid bears the force of thrust F by way of the upper surfaces of shaft portions 8 a and 8 a′ of movable swash plate 8 and shaft bore 9 c of legs 9 a and semicircular surface 9 d of leg 9 b. Hence, there is no need to increase the rigidity of first and second supports S 1 and S 2 to bear the thrust F because in accordance with the invention, the thrust F is diverted, for example, in one embodiment, to the lid 9 .

A modified embodiment of the invention where movable swash plate 8 is supported by legs 9 a and 9 b of lid 9 in shown in FIGS. 15 and 16. In this embodiment, control shaft 35 for rotatably operating movable swash plate 8 is disposed proximate to cylinder block 16 . In particular, an arm 8 e is provided at one lateral side of movable swash plate 8 in the vicinity of, for example, above shaft portion 8 a. Arm 8 e is positioned in opening 9 e provided in leg 9 a. Opening 9 e is of a width sufficient to allow for rotation of arm 8 e when movable swash plate 8 slantingly moves. Arm 8 e engages ball 30 by way of joint blocks 78 a and 78 b. Thus, swinging arm 39 is connected with movable swash plate 8 . Hence, shaft portion 8 a does not require extra length beyond the depth of legs 9 a and 9 b to enable mounting of arm 29 to shaft portion 8 a. Thus, control shaft 35 can be disposed proximate to cylinder block 16 .

In accordance with another embodiment of the invention, shown in FIGS. 9 and 10, a pair of legs 1 d and 1 e are integrally extended from inner surfaces of walls, for example, upper walls of the housing and on either side of a shaft bore 1 c and extend toward movable swash plate 8 along, for example, parallel to the rotary axis of cylinder block 18 . Shaft bore 1 c is for journalling input shaft 3 to upper half 1 of the housing. Legs 1 d and 1 e are formed such that extends, for example, lower ends of legs 1 d and 1 e are level with each other. Semicircular surfaces 1 f and 1 g are formed in a portion of the lower end surfaces of legs 1 d and 1 e respectively. Holders 6 are detachably mounted to the lower end surfaces of legs 1 d and 1 e by bolts 27 respectively. On a surface, for example, a upper surface of each holder 6 is a semicircular receiving surface 6 a for being positioned opposite to semicircular surface 1 f or 1 g. Accordingly, holder 6 and legs 1 d and 1 e, and more particularly, receiving surfaces 6 a and semicircular surfaces 1 f or 1 g are connected to form first and second supports S 1 and S 2 for rotatably supporting shaft portions 8 a and 8 a′.

In this embodiment, thrust F applied by piston 13 to shaft portions 8 a and 8 a′ on movable swash plate 8 bears on the entire upper half 1 of the housing, which is of high rigidity, by way of semicircular surfaces 1 f and 1 g of legs 1 d and 1 e. Hence, when thrust F is increased, it is unnecessary to increase the rigidity of first and second supports S 1 and S 2 because upper half 1 is capable of bearing thrust. During assembly, the upper half 1 of the housing is turned over and shaft portions 8 a and 8 a′ of movable swash plate 8 are disposed on semicircular surfaces 1 f and 1 g of legs 1 d and 1 e and holders 6 are mounted to legs 1 d and 1 e, thereby simplifying assembly. Also, when upper half 1 of the housing is molded, legs 1 d and 1 e can be simultaneously and integrally molded with upper half 1 , thereby reducing manufacturing costs.

FIG. 11 is an embodiment in accordance with the invention, in which movable swash plate 8 is supported by upper half 1 . First support S 1 for holding shaft portion 8 a includes a round bore 1 i in leg 1 d, which extends for example, downwardly extends from the inner surface of the upper wall of upper half 1 of the housing. An end of shaft portion 8 a extends beyond bore 1 i and is fixed to arm 29 . A second support S 2 is formed on lid 43 provided at an opening 1 j of a wall, for example, a side wall of upper half 1 of the housing. Opening 1 j provides access for a cutting tool to enter the housing and is capable of being closed by lid 43 . Lid 43 is fixed to the housing by a bolt 44 . A round recess 43 a concentric with bore 1 i, receives and rotatably supports shaft portion 8 a′. Thus, opening 1 j and lid 43 are provided to enable access to construct or repair first and second supports S 1 and S 2 .

In another embodiment, shown in FIG. 17, lid 43 is formed so that a control arm 42 can be positionally adjusted from the exterior, such as, on the upper surface and the side surface of upper half 1 of the housing. In particular, a round recess 43 b in lid 43 is a through bore. Another shaft portion 8 a″, which is an alternate embodiment of shaft portion 8 ′, for example, an extended version of 8 ′, of movable swash plate 8 is of a sufficient length for being supported in recess 43 b. An end of shaft portion 8 a″ projects beyond a periphery of the housing or lid 43 so that control arm 42 can be fixed shaft portion 8 a″. Accordingly, when control arm 42 in accordance with this embodiment is rotated for example, where the control arm 42 is on a lateral side of the housing then control arm 42 is longitudinally rotated, the movable swash plate 8 is directly slanted by the shaft portion 8 a″. Thus, shaft portion 8 a simultaneously rotates thereby rotating swinging arm 39 by way of arm 29 , ball 30 , and joint blocks 78 a and 78 b. Accordingly, torsion spring 31 exerts a return biasing force on movable swash plate 8 in a direction toward the neutral position. In accordance with an embodiment of the invention, further to shaft portions 8 a and 8 a′ or 8 a″ supporting movable swash plate 8 , shaft portions 8 a and 8 a′ or 8 a″ function also to transfer the biasing force biased toward the neutral position to movable swash plate 8 . Furthermore, shaft portion 8 a″ functions to slantingly move movable swash plate 8 , for example, by control arm 42 .

In another embodiment in accordance with the invention, as shown in FIG. 12, movable swash plate 8 is supported by upper half 1 . First support S 1 , as discussed above for FIG. 17, is formed so that leg 1 d extends from upper half 1 of the housing and a bore 1 i receives a shaft portion 8 a. Second support S 2 is formed by a cylindrical member 55 provided at a lid 56 for closing an opening 1 j at a wall, for example, a side wall of the housing. In addition, on a surface, for example, a side surface of cylindrical movable swash plate 8 opposite to shaft portion 8 a is a cylindrical recess 8 d coaxial with shaft portion 8 a. The extreme end of cylindrical member 55 is inserted into recess 8 d to support movable swash plate 8 . Therefore, single shaft portion 8 a and movable swash plate 8 is sufficient because opening 1 j and lid 56 are utilized to enable supports S 1 and S 2 to be simplified in construction.

In addition, in another embodiment in accordance with the invention, movable swash plate 8 can be supported by center section 5 fixed into the housing as shown in FIGS. 13 and 14. A pair of legs 5 a integrally extend from two sides of a pump setting surface 100 on center section 5 toward movable swash plate 8 along, for example, parallel with the rotary axis of cylinder block 16 . Semicircular receiving surfaces 5 b are formed on end surfaces, for example, upper end surfaces of legs 5 a respectively. Holders 6 are detachable mounted on the upper end surfaces of legs 5 a by bolts 27 . One surface, for example, a lower surface of holders 6 have a semicircular surface 6 a′for being positioned opposite to receiving surfaces 5 b respectively. Semicircular surfaces 6 a′ and receiving surfaces 5 b are combined with each other to form first and second supports S 1 and S 2 for holding shaft portions 8 a and 8 a′. Hence, when center section 5 is molded, it is possible to simultaneously and integrally mold legs 5 a. Thus, lower manufacturing costs are achieved. In addition, the entire variable displacement type hydraulic pump including movable swash plate 8 can be pre-assembled to center section 5 before being assembled in the housing.

In this embodiment, thrust F from pistons 13 is absorbed by center section 5 by way of holders 6 . In addition, when movable swash plate 8 is supported by center section 5 , first and second supports S 1 and S 2 on legs 5 a can be formed as shown in FIG. 8 . In particular, either one or both of holders 6 can be substituted with round bore 9 c being disposed in leg 5 a.

For slanting the movable swash plates, the above-mentioned various structures and combinations thereof may be applied.

Although the invention has been described with reference to several different embodiments, these embodiments are merely exemplary and not limiting of the invention which is defined by the appended claims.