JP2001163073A - Steering drive unit for running vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve progressiveness of a steering drive unit for running vehicle having two HST's for running and steering arranged to be capable of driving and steering left and right axles. SOLUTION: This steering drive unit comprises the running drive HST and the steering drive HST formed by communicating a hydraulic pump with a hydraulic motor, a differential gear connected with motor shafts of the hydraulic motor of the HST's and a drive train interlockingly connecting the differential gear with the HST's arranged inside a housing. In the steering drive unit for running vehicle to steer and drive the left, and right axles interlockingly connected with the differential gear, a circuit 500 that, is opened when the hydraulic pump of the steering HST is positioned in a set, range near a neutral position is mounted between a pair of conduits 75X, 75X hydraulically communicating the hydraulic pump of the steering HST with the hydraulic motor. The circuit 500 to be opened is formed with one spool 502 and connected with a drain circuit 514.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises two hydrostatic transmissions (hereinafter "HST"), one for driving and the other for steering (steering). The present invention relates to a steering drive device for a traveling vehicle configured to be steerable. More specifically, the present invention relates to a technique for improving steering responsiveness of a device while maintaining good straightness of a vehicle.

[0002]

2. Description of the Related Art Conventionally, two HSTs are arranged on the left and right sides, an axle is protruded to both sides from each HST type transmission, and wheels are fixed to ends of both axles. 2. Description of the Related Art A technique is known in which the angle of a swash plate is changed to drive left and right wheels. For example, the technology of US Pat. No. 4,782,650. In this technique, when traveling straight ahead, the traveling speeds of the left and right HSTs are the same,
When turning, the running speeds of the left and right wheels are different.

[0003]

However, the traveling vehicle equipped with the conventional steering driving device as described above has a problem that the left and right HS drives are not provided.
Unless the output rotations of the T-type transmission are completely matched, it is not possible to travel straight ahead accurately, and therefore adjustments at the time of shipment have been troublesome. In addition, if there is a deviation in the volumetric efficiency of the hydraulic pump or the hydraulic motor, the turning feeling differs depending on whether the vehicle turns left or right, which makes the steering very difficult. In addition, when working while turning, the conventional traveling vehicle as described above has a large turning radius.For example, when this technique is applied to a mower tractor, when mowing around a grove or the like, the same applies. It was necessary to travel around the position many times and work was inefficient.

In addition, when the steering operation tool is set to the neutral position, the vehicle is straightly moved accurately as described above, and at the time of the steering operation, a smooth and light operation feeling is provided so that the vehicle can turn quickly following the operation. There was also a need for steering drive technology that could be provided.

[0005]

The problems to be solved by the present invention are as described above. Next, means for solving the problems will be described.

That is, according to the first aspect, the traveling drive H is configured by fluid communication between the hydraulic pump and the hydraulic motor.
An ST and a steering HST, a differential device connected to the motor shafts of the two HST hydraulic motors, and a drive train for interlockingly connecting the differential device and the two HSTs are arranged in a housing. A steering driving device for a traveling vehicle that steers and drives a pair of left and right axles interlocked with the differential device.
A hydraulic pump is provided between a pair of paths that fluidly communicate the hydraulic pump and the hydraulic motor of the steering HST, and a circuit that is opened when the hydraulic pump is in a set range near the neutral position is provided. Constructed by spool,
A drain circuit for draining hydraulic oil of the circuit to be opened is provided in connection with the circuit.

According to a second aspect of the present invention, a traveling drive HST and a steering HST, which are formed by fluid communication between a hydraulic pump and a hydraulic motor, are connected to a motor shaft of the two HST hydraulic motors. A drive train for interlocking the differential and the two HSTs in a housing, wherein the drive train is adapted to steer and drive a pair of left and right axles interlocked to the differential; In the steering drive, a circuit that is opened when the hydraulic pump of the traveling drive HST is in a set range near the neutral position is provided between a pair of paths that fluidly communicate the hydraulic pump of the steering HST and the hydraulic motor. Provided, the circuit to be opened is constituted by one spool, and further, a drain circuit for draining hydraulic oil of the circuit to be opened,
It is provided connected to the circuit.

According to a third aspect of the present invention, a traveling drive HST and a steering HST, which are formed by fluid communication between a hydraulic pump and a hydraulic motor, and a differential device connected to the motor shafts of the two HST hydraulic motors, A drive train for interlocking the differential and the two HSTs in a housing, wherein the drive train is adapted to steer and drive a pair of left and right axles interlocked to the differential; In the steering drive device, a circuit that is opened when a pressure difference between the pair of paths is smaller than a set value is provided between a pair of paths that fluidly communicate the hydraulic pump of the steering HST and the hydraulic motor, The circuit to be opened is constituted by a single spool, and a drain circuit for draining hydraulic oil of the circuit to be opened is provided in connection with the circuit. .

[0009]

Next, embodiments of the present invention will be described. FIG. 1 is a side view showing an overall configuration of a mower tractor having the steering drive device of the present invention, FIG. 2 is a side view showing a first modification of the mower tractor, and FIG. It is a side view which showed the modification.

First, an overall configuration of an embodiment in which the present invention is applied to a mower tractor will be described. In the mower tractor 1 shown in FIG. 1, a front column 13 is provided upright on a front portion of a vehicle chassis 12, and a steering handle 14 serving as a steering operation means is provided on the front column 13.
Is protruded. On the side of the front column 13, a shift pedal 15 as a shift operation means and a brake pedal (not shown) are arranged.

The speed change pedal 15 is of a seesaw type having an intermediate portion pivotally supported and has two front and rear tread portions. The speed can be increased according to the amount. The pedal 15 is set to neutral (stop).
An unillustrated return spring for biasing the position is interposed.

On the left and right sides of the front lower part of the chassis 12,
Caster wheels 16 are arranged one by one as driven front wheels. In this embodiment, the caster wheels 16 are arranged one by one on the left and right. However, only one caster wheel 16 may be arranged at the center of the front part, or three or more casters may be arranged.

An engine 11 is disposed on a front portion of the chassis 12, and the engine 11 is covered with a hood.
A seat 17 is arranged above the rear part of the chassis 12, and a mower 9 is arranged below a middle part of the chassis 12. The mower 9 is a so-called mid-mount type, which is located substantially at the center of the body 1 in the front-rear direction. The mower 9 includes a case 19 having at least one rotary blade built therein. It is driven by the power of the engine 11. The mower 9 can be moved up and down via a link mechanism.

The engine 11 is of a vertical type in which an output shaft 11a projects vertically downward, and transmits power to a steering drive device 2 disposed at the rear of the chassis via a pulley, belt or the like (not shown). The steering driving device 2 includes an airframe 1
The driving drive wheels 43 arranged on the left and right are driven via a pair of left and right axles 40. Traveling drive wheels 43
Is a so-called rear drive system as a structure supported at the rear of the chassis.

However, the configuration of the traveling vehicle described above is an example, and the present invention is not limited to this. For example, it can be configured as a mower tractor of the first modification shown in FIG. The mower tractor 1a according to the first modification will be described. That is, the mower tractor 1a is provided with a step 12s protruding forward on a front portion of a vehicle chassis 12 ', and a front column 13 is provided upright on the front portion of the step 12s. , A steering handle 14 is protruded. The front column 13
The transmission pedal 15 and the brake pedal are arranged on the sides of the. The configurations of the steering handle 14 and the speed change pedal 15 are the same as those of the mower tractor 1 shown in FIG. In the rear lower part of the chassis 12 ', caster wheels 16 are disposed one by one on the left and right as driven rear wheels.

The engine 11 is mounted on the rear of the chassis 12 '.
Is disposed, and the engine 11 is covered with a bonnet. A mower 9 is disposed below the middle part of the chassis 12 ', and the mower 9 is located at a substantially central portion in the front and rear of the chassis 12' (behind the driving wheels 43, 43) to form a so-called mid-mount type. The configuration of the mower 9 is the same as that of the mower tractor 1 shown in FIG. The engine 11 is of a vertical type in which an output shaft 11a protrudes vertically downward.
2 'The motive power is transmitted to the steering drive device 2 disposed at the front. The steering driving device 2 drives traveling driving wheels 43 arranged on the left and right sides of the body 1a via axles 40,40. The running drive wheels 43 are of a so-called front drive type, which is supported at the front of the chassis.

Further, a mower tractor according to a second modified example described below can be used. That is, the mower tractor 1b shown in FIG. 3 is different from the mower tractor 1a according to the first modification only in the arrangement of the mower 9, and the mower 9 is provided in front of the chassis 12 '(the driving wheels 43 43), which is a so-called front mount method.

Next, the steering driving device 2 provided in the above mower tractor will be described in detail. 4 is a plan sectional view showing the inside of the housing of the steering drive device, FIG. 5 is a perspective view of the steering drive device viewed from the top, FIG. 6 is a perspective view of the steering drive device viewed from the bottom, and FIG. It is -A sectional drawing. FIG.
FIG. 9 is a cross-sectional view taken along the line BB in FIG. 4, FIG. 9 is a schematic view showing a state where the outputs of the two HSTs are input to the axle via the drive train and the differential, and FIG. 10 is an exploded perspective view of the differential. FIG. 11 is a side view of the steering drive, and FIG. 12 is a skeleton diagram of the steering drive.

That is, as shown in FIG. 4, the steering driving device 2 includes a traveling drive HST 21 for moving the body forward and backward.
And steering HST22 for turning the aircraft
A pair of left and right axles 40L and 40R;
The differential device 5, which is a planetary gear device that differentially couples the 40Rs, and the drive train that interconnects them are arranged in one housing 23. As shown in FIGS. 7, 8, and 11, the housing 23 is formed by joining upper and lower halves 23t and 23b to each other on a horizontal and flat peripheral joint surface. The bearings of the motor shafts (54, 77) of the hydraulic motors to be described later which constitute the two HSTs 21 and 22 are provided. Further, an inner wall 23i is formed integrally with the housing 23, and the inner wall 23i defines a space inside the housing 23 as a section R for accommodating the two HSTs 21 and 22.
1 and a section R2 that accommodates the axles 40L and 40R, the differential device 5, and the drive train. The inner wall 23i of the housing also functions as a support wall for supporting a shaft constituting the drive train (that is, a shaft 105 described later and a motor shaft (54, 77) of a hydraulic motor described later). I have. Axle 40L / 40R
As shown in FIG. 11 and the like, the bearing portion rotatably supports
It is provided at a position deviated above the joint surface of the housing 23.

A fixed amount of oil is filled in the housing 23, and a joint 100 projects from a side wall of the upper half portion 23t, and an external reservoir tank is connected to the joint 100 via a tube (not shown). Make sure you can connect. Also,
At an appropriate position on the inner wall 23i of the housing, a filter FF for filtering oil is arranged, and the oil in the two sections R1 and R2 can be circulated through the filter FF.

Then, as shown in FIGS. 4 to 6,
In the section R1 of the housing 23, one center section 51 is provided on the left side in a plan view inside the housing 23 (FIG. 4).
, And another center section 75 is disposed on the front side of the section R1. The hydraulic pump 52 and the hydraulic motor 53 of the traveling drive HST 21 are arranged on the center section 51, and the hydraulic pump 71 and the hydraulic motor 72 of the steering HST 22 are arranged on the center section 75. Each of the axles 40L and 40R is differentially coupled by a differential device 5 using a planetary gear, and both ends protrude to the left and right sides of the housing 23.

The center section 51 described later will be described later.
With the configuration of 75, the hydraulic pump 52 and the hydraulic motor 53 of the traveling drive HST 21 are attached to one axle (the left axle 40L in this embodiment) when viewed from the front (the direction indicated by the arrow V in FIGS. 4 and 5). It is located at the overlapping position and the steering H
In ST22, the hydraulic pump 71 and the hydraulic motor 72 in ST22 are arranged at positions overlapping the differential device 5, one axle (the right axle 40R in the present embodiment), and the drive train. Thereby, the left-right width and the up-down width of the steering drive device 2 can be reduced, and a compact steering drive device can be provided.

The two sections R1 and R2 described above, the two HSTs 21 and 22, the center section 51
The arrangement of the differential 75 and the differential device 5 is merely an example.

As shown in FIG. 6, a strainer 306 is attached to the lower surface of each of the two center sections 51 and 75. Hydraulic oil in the housing 23, which also serves as an oil reservoir, is sucked through the strainer 306. The oil is guided to the hydraulic oil circulation oil passages (51x, 75x) in the center sections 51, 75 through the check valves (291, 292) shown in FIG. It is configured to compensate.

The upper and lower halves 23t of the housing 23
Axle 40L at a position deviated above the joint surface of 23b
40R is supported, and the inner ends of the axles 40L and 40R are differentially coupled by the differential device 5, while
The outer end protrudes left and right outward of the housing 23 (FIGS. 4 to 6). The differential device 5, the steering HST7
5 and a drive train described later are arranged in a line in a direction perpendicular to the axles 40L and 40R in a plan view (FIG. 4), and the differential device 5 and the steering HST7 are arranged.
5 is located between the drive train. The above-mentioned traveling drive HST21 is arranged on the side of the drive train.

Next, a specific configuration of the two HSTs will be described.

First, the traveling drive HST 21 for driving the body forward and backward will be described in detail. This traveling drive HST
4 has a pair of hydraulic pumps 52 and a hydraulic motor 53, as shown in FIG. 7 and 1
2).

The center section 51 will be described. That is, the center section includes a pump mounting surface 51a and a motor mounting surface 51b that are perpendicular to each other,
In addition, the pump mounting surface 51a is offset from the motor mounting surface 51b and has a substantially "d" shape in plan view. More specifically, the pump mounting surface 51a is disposed horizontally, the motor mounting surface 51b is disposed vertically, and is disposed at a position offset from the pump mounting surface 51a. With the configuration of the center section 51, the pump attachment surface 51a and the motor attachment surface 51b are arranged so as to have a so-called "twist" positional relationship. Further, a rotation axis of a pump shaft 25 described later and a rotation axis of the motor shaft 54 are arranged at right angles.

The hydraulic pump 52 will be described. That is, in the hydraulic pump 52, the pump shaft 25 is vertically supported at the center of the pump attachment surface 51a of the center section 51, and the cylinder block 44 is fitted to the pump shaft 25 as shown in FIG. And, it is arranged so as to be rotatable and slidable on the pump attachment surface 51a. The cylinder block 44
The inside of a plurality of pistons 45.4 through an unillustrated urging spring
5 are reciprocally fitted, and the pistons 45
The movable swash plate 57 is in contact with the head of. By tilting the movable swash plate 57, the amount and direction of oil discharge from the hydraulic pump 52 can be changed. A mechanism for tilting the movable swash plate 57 will be described later. The pump shaft 25 protrudes above the housing 23 (FIG. 5), and an input pulley 27 is disposed on a protruding portion of the pump shaft 25. A belt is wound around the input pulley 27 to output the engine 11 output. As shown in FIG. 12, the output pulley fixed to the shaft 11a is operatively connected. That is, the projecting portion of the pump shaft 25, the input pulley 27
The above-mentioned belt constitutes an input means of the traveling drive HST21. A fan 42 for cooling may be provided at a portion of the pump shaft 25 protruding above the housing 23, as schematically indicated by a chain line in FIG.

The hydraulic motor 53 will be described. That is, in the hydraulic motor 53, the cylinder block 63 is horizontally supported on the motor attachment surface 51b of the center section 51 in a direction in which the rotation axis is parallel to the axles 40L and 40R.
It is rotatable (FIGS. 4 and 7). A plurality of pistons 64 are reciprocally fitted into the plurality of cylinder holes of the cylinder block 63 via a biasing spring (not shown), and the head of the piston 64 contacts the fixed swash plate 65. (FIG. 7). A motor shaft 54 is integrally arranged on the rotation axis of the cylinder block 63 and locked so as not to rotate relatively, thereby forming a fixed swash plate type (constant displacement type) hydraulic motor 53. The motor shaft 54 is directed toward a drive train described later while
The drive gear 69 extends through i to the section R2, and a drive gear 69 is formed at an intermediate portion thereof. The extended portion of the motor shaft 54 and the drive gear 69 constitute output means of the traveling drive HST 21. As a result, the drive gear 69 drives the later-described center gear 94, and the differential gear 5 described later. Of the sun gear 95 is driven.

As for the mechanism for tilting the movable swash plate 57 of the hydraulic pump 52, a control shaft 59 is supported on the side wall of the housing 23 in parallel with the axles 40L and 40R. An arm 192 is implanted at the end, and the movable swash plate 57 is connected to the tip of the arm 192 (FIG. 5) to form a so-called cradle type movable swash plate. Incidentally, a so-called trunnion type movable swash plate as shown in FIG. 13 may be used. On the other hand, as shown in FIGS. 4, 5, and 11, a control arm 60 is fixed on a control shaft 59 outside the housing 23. The control arm 6
Numeral 0 is linked to a shift operation means such as a lever or a pedal via a link mechanism or the like, in this embodiment, to the shift pedal 15.

With the above construction, the control arm 6 is rotated by rotating the speed change pedal 15.
0 is rotated, the movable swash plate 57 is tilted via the arm 192 by the rotation of the control shaft 59, and the discharge direction and discharge amount of the hydraulic oil from the hydraulic pump 52 can be changed. The hydraulic oil from the hydraulic pump 52 is supplied to a hydraulic motor 53 via hydraulic oil circulation oil passages 51x, 51x described below in the center section 51 to drive the hydraulic motor 53, and the motor shaft 54 To rotate. By this series of actions, the motor shaft 54 is driven in a direction corresponding to the rotation direction of the speed change pedal 15 and in a speed corresponding to the amount of depression.

The structure of the oil passage formed in the center section 51 will be described. That is, this circuit includes a pair of hydraulic oil circulation oil passages 51x formed inside the center section 51.
51x, and the hydraulic pump 52 and the hydraulic motor 53 are hydraulically connected by the hydraulic oil circulation oil passages 75x and 75x. A portion where an oil passage (reference numeral 295 in FIG. 12) for sucking hydraulic oil through the strainer 306 on the lower surface is connected to the hydraulic oil circulation oil passages 51x and 51x,
The above-described check valves 291 and 291 are provided to prevent a decrease in oil pressure in the hydraulic oil circulation oil passage 51x. A throttle 299 is provided in an oil passage of the two hydraulic oil circulation oil passages 51x and 51x that has a high pressure in reverse.
Therefore, even when the hydraulic pump 52 discharges the pressure oil even though the shift pedal 15 is not depressed because the neutral position of the movable swash plate 57 does not accurately come out and is slightly shifted to the reverse side, Since the hydraulic oil is drained from the throttle 299, the vehicle is prevented from being driven at a very low speed. Also,
Since the neutral range is expanded in this way, adjustment at the time of shipment, etc., can be easily performed. Also, as shown in FIG.
A bypass control shaft 391 is supported vertically so as to be rotatable in parallel with the motor mounting surface 51b of the center section 51. The bypass control shaft 391 protrudes above the housing 23 and has a bypass control arm The base end of 390 is fixed.
On the other hand, a push pin 392 is supported at a position near the motor shaft 54 on the motor attachment surface 51b and is slidable in a direction parallel to the motor shaft 54. One end of the push pin 392 is The other end side is close to the cam formed at the lower end of the bypass control shaft 391 while being close to the cylinder block 63. With this configuration, in the case where the mower tractor is connected to the rear end of the vehicle and towed, etc., by rotating the bypass control arm 390, the bypass control shaft 391 is rotated, and the pushing pin 392 is rotated via the cam. Is pushed, so that the tip protrudes from the motor-attached surface 51b. As a result, the cylinder block 63 is separated from the motor attachment surface 51b and the pressure oil in the hydraulic oil circulation oil passages 51x and 51x is drained, so that the hydraulic motor 53 can idle and reduce the resistance at the time of towing. be able to.

The motor shaft 54 is provided with a brake device 110 for performing braking. That is, as shown in FIGS. 4 and 7, the brake device 110 includes a brake disk 195 provided at one end of the motor shaft 54 so as not to rotate relatively, and a brake pad 196 disposed close to the brake disk 195. Receiving brake pad 1
99 and the brake pad 196
The brake control shaft 197 is provided with a cam 197a for pressing and contacting the side of the brake control shaft 5 and is vertically supported. A base end of a brake control lever 198 is fixedly mounted on the brake pedal (FIG. 7). The brake control lever 198 is connected to the above-mentioned brake pedal via a link or the like. 19
When the brake disk 6 contacts the brake disk 195 and presses the brake disk 195 against the receiving brake pad 199, a frictional resistance is generated to apply a braking action to the motor shaft 54.

Next, the steering HST 22 for turning the body will be described. This steering HS
T22 is a pair of hydraulic pumps 7 as shown in FIGS.
1 and a hydraulic motor 72, and hydraulic oil circulation oil passages 75x and 75x that fluidly communicate the two 71 and 72 are formed inside the other center section 75 (FIG. 1).
2).

The center section 75 will be described. That is, the center section 75 has a pump mounting surface 75a and a motor mounting surface 75b that are substantially perpendicular to each other, and is a center section 7 that is substantially “L” shaped in a side view.
5 (FIG. 8). Specifically, the pump mounting surface 5
1a is arranged horizontally, and the motor-attached surface 51b is arranged vertically. Thus, the rotation axis of the pump shaft 26 and the rotation axis of the motor shaft 77 described later are arranged to be orthogonal to each other.

The hydraulic pump 71 will be described. That is, in the hydraulic pump 71, the pump shaft 26 is vertically rotatably supported at the center of the pump mounting surface 71a of the center section 75, and the cylinder block 46 is fitted to the pump shaft 26 so that the pump mounting surface 71a Are rotatably slidable on the upper side (FIG. 8), and a plurality of pistons 47, 47... A movable swash plate 76 is in contact with the head of. By tilting the movable swash plate 76, the discharge amount and discharge direction of the oil from the hydraulic pump 71 can be changed. This movable swash plate 76
The mechanism for tilting is described later. Pump shaft 2
The second input pulley 28 is fixed to the protruding portion, and a belt (not shown) is wound around the second input pulley 28. The output shaft 11a is connected to the output shaft 11a.
That is, the steering H
It constitutes the input means of ST21.

The hydraulic motor 72 will be described. That is,
As shown in FIG. 8, a cylinder block 80 is horizontally supported on the motor-attached surface 71b of the center section 75 so that its axis is perpendicular to the axles 40L and 40R so as to be freely slidable. A plurality of pistons 82 are fitted in the plurality of cylinder holes of the cylinder block 80 via biasing springs in a reciprocating manner, and the heads of the pistons 82 It is in contact with the plate 85. Then, the motor shaft 77 is integrally arranged on the rotation axis of the cylinder block 80 and locked so as not to rotate relatively.
A fixed swash plate type (constant volume type) hydraulic motor 72 is configured. The motor shaft 77 penetrates through the inner wall 23i while facing the drive train to be described later, and
2 (FIGS. 4 and 8), and a bevel gear 104 is formed at its end. The steering HST is provided with the extended portion of the motor shaft 77 and the bevel gear 104.
22 as a result, the ring gears 99 of the differential device 5 are driven by the bevel gear 104 via a drive train described later.

Regarding a mechanism for tilting the movable swash plate 57 of the hydraulic pump 52, a control shaft 73 is horizontally supported on the ceiling surface of the housing 23 in parallel with the axles 40L and 40R (FIGS. 4 and 5). An arm 191 is fixed to a portion of the shaft 73 inside the housing 23, and a tip of the arm 191 is locked to the movable swash plate 76 to form a so-called cradle type movable swash plate 76 (FIG. 5). However, a trunnion-type movable swash plate may be used.
A base end of a control lever 193 is fixed to a portion where the control shaft 73 protrudes from the side of the housing 23 (FIGS. 4 and 5), and the control lever 193 is operated by a steering mechanism via a link mechanism (not shown). Means (the steering handle 14 in this embodiment). A neutral return spring (not shown) is externally fitted to a portion of the control shaft 73 inside the housing 23, and a movable swash plate 76 is provided.
Is biased to a neutral position so that the neutral position can be adjusted.

With the above construction, the control lever 193 is rotated by rotating the steering handle 14, and the movable swash plate 76 is tilted via the arm 191 by the rotation of the control shaft 73. Thus, the discharge direction and discharge amount of the hydraulic oil from the hydraulic pump 71 can be changed. As a result, the pressure oil from the hydraulic pump is sent to the hydraulic motor 72 via the hydraulic oil circulation oil passages 75x and 75x in the center section 75 to drive the hydraulic motor 72, and the motor shaft 77 is driven. You. By this series of actions, the motor shaft 77 moves in a direction corresponding to the turning direction of the steering handle 14, and
It is rotated at a speed corresponding to the rotation angle.

The structure of the hydraulic oil circulation oil passages 75x and 75x formed in the center section 75 will be described. That is, the hydraulic oil circulation oil passages 75x and 75x are a pair of oil passages drilled inside the center section 51, and connect the hydraulic pump 52 and the hydraulic motor 53 to the hydraulic oil circulation oil passage 75x.
It is configured to be hydraulically connected at x · 75x. The above-described check is provided at a portion where an oil passage (reference numeral 289 in FIG. 12) for sucking hydraulic oil through the strainer 306 on the lower surface of the center section 75 and the hydraulic oil circulation oil passages 75x in the center section 75 are connected. Valve 292 ・ 292
Is provided to prevent a decrease in hydraulic pressure in the hydraulic oil circulation oil passage 75x. Further, a return member 389 for short-circuiting the check valves 292 and 292 to drain the oil in the hydraulic oil circulation oil passage 75x is slidably provided. With this configuration, in a case where the mower tractor is connected to the rear end of the vehicle and the vehicle is towed, if the return member 389 is pushed (along with the rotation of the bypass control arm 390), the check valve 292 is short-circuited. As a result, the hydraulic oil in the hydraulic oil circulation oil passages 75x and 75x is drained, so that the hydraulic motor 72 can idle and reduce the resistance during towing. Further, the hydraulic oil circulation oil passage 75x
A circuit 500 that opens and closes by detecting a pressure difference between the oil passages 75x and 75x is provided between the oil passages 75x (see FIG. 4).
(FIG. 8). The specific configuration of this circuit will be described later. The circuit 500 is connected to a drain oil passage 514 having a drill hole formed in the center section 75 (FIG. 8).

Next, the configuration of a drive train connecting the above-described two HSTs 21 and 22 and the differential device 5 will be described.

First, a configuration for connecting the traveling drive HST 21 and the differential device 5 will be described. That is, the above-described drive gear 69 formed on the motor shaft 77 of the traveling drive HST 21 is meshed with a center gear 94 of the differential 5 described later, and drives the sun gear 95 of the differential 5.

Next, a configuration for connecting the steering HST 22 and the differential device 5 will be described. That is, at a position behind the above-described bevel gear 104 formed on the motor shaft 77 of the steering HST 22, the shaft 105 is disposed so as to be parallel to the axles 40L and 40R (perpendicular to the motor shaft 77). Both ends are fixed to the housing as shown in FIG. 4, and pipe-shaped idle members 111 are loosely fitted on the shaft 105, and the idle members 111
The bevel gears 106 are fixed on the upper surface 1. The two bevel gears 106 are arranged symmetrically with respect to the motor shaft 77, and both mesh with the bevel gear 104 on the motor shaft 77. Transmission gears 107 are mounted on the two idler members 111 so that they cannot rotate relative to each other (FIG. 4), and the transmission gears 107 are engaged with reduction gears 108 described later. The pair of reduction gears 108 are symmetrically disposed at a portion of the motor shaft 54 that sandwiches the drive gear 69, and each of them can idle. This reduction gear 10
Reference numerals 8 and 108 denote large-diameter and small-diameter double gears. The large-diameter gear meshes with the transmission gears 107 and the small-diameter gear is engraved on the outer peripheral surfaces of the internal gears 98 and 98 of the differential device 5. It is meshed with the gear 99.

Next, the configuration of the differential device 5 for differentially coupling the left and right axles 40L and 40R will be described mainly with reference to FIGS.
FIG.

That is, as shown in FIG.
A center gear 94 that is relatively rotatably disposed on the same axis as the axles 40L and 40R is meshed with the drive gear 69 that transmits the power by reducing the output rotation of the hydraulic motor 53 in ST21. The center gear 94 is provided with a central hole having a shape matching the tooth profile of the sun gear 95 of the differential gear 5, and the sun gear 95 is fitted into the central hole as shown in FIG. Is locked. And Figure 9
As shown in FIG. 10, a plurality of planetary gears 96 are arranged on the left and right sides of the sun gear 95 with the center gear 94 interposed therebetween. (FIG. 9), and the carriers 97, 97 are spline-fitted to the left and right axles 40L, 40R, respectively, so that they cannot rotate relative to each other. Then, ring-shaped internal gears 98 are externally fitted to and supported by the carriers 97 so as to be relatively rotatable (FIGS. 9 and 10). Thus, the internal gears 98, 98 are connected to the axles 40L, 40R.
Instead, the width of the differential device 5 in the axle 40L / 40R direction can be reduced by being supported by the carriers 97, 97, so that the steering drive device can be made compact. The above planetary gear 96.9
6 are the internal gears 98 on the outer side.
98 and the internal gear 98.9
Gears 99, 99 are engraved on the outer peripheral surface of the gear 8, respectively, and mesh with the small-diameter gears of the reduction gears 108, 108, respectively.

Next, how power is transmitted to the axles 40L and 40R via the drive train and the differential device 5 described above and the axles 40L and 40R are steered will be described.

That is, the hydraulic motor 5 of the traveling drive HST 21
The driving force from No. 3 is transmitted to the motor shaft 54 → the driving gear 69 → the center gear 94 as shown by the black arrow in FIG. On the other hand, steering HS
The driving force from the hydraulic motor 72 at T22 is branched from the bevel gear 104 to the two bevel gears 106, as shown by a white arrow in FIG. Gear 108
, The left and right internal gears 98 are driven in opposite directions to each other. Accordingly, the rotation of the sun gear 95 and the rotation of the internal gear 98 on the same side as the planetary gears 96 are transmitted to one of the left and right planetary gears 96. The rotation of the sun gear 95 is reduced by the rotation of the internal gear 98 on the same side as the planetary gears 96. As a result, there is a difference in the rotational speed between the left and right carriers 97, 97 that support the left and right planetary gears 96, respectively.
The configuration is such that the airframe turns with the difference in the number of rotations of R.

Next, a mechanism for expanding the neutral range of the steering, which is a main part of the present invention, will be described. FIG. 13 is a sectional development view showing a circuit provided in the center section of the steering HST, and FIG. 14 is a perspective view partially showing a configuration of a spool which opens and closes the circuit. FIG.
FIG. 16 is a sectional development view showing the force applied to the valve when the pressures of the pair of hydraulic oil circulation oil passages are equal to each other. FIG. 16 shows the force applied to the valve when the pressure of the pair of hydraulic oil circulation oil passages is different FIG. 17 is a sectional development view showing a state where the spool is slid from the state of FIG. 16 to a new equilibrium state and the orifice oil passage is closed.

That is, in the present invention, the steering HS
The neutral range of the steering handle 14 is expanded by providing a circuit 500 having a specific valve mechanism between a pair of hydraulic oil circulating oil passages 75x and 75x communicating the hydraulic pump 71 and the hydraulic motor 72 constituting the T22. It is doing. A specific configuration of the circuit 500 will be described. That is, as shown in FIG.
Reference numeral 1 is provided so as to straddle the two hydraulic oil circulation oil passages 75x and 75x, and a spool 502 is fitted inside the sleeve 501 so as to be slidable. Sleeve 501
Are closed by lids 503, 503, and both lids 50
A return spring 504 is provided between the spool 503 and the spool 503.
504 is arranged.

The spool 502 will be described. As shown in FIGS. 13 and 14, the spool 502 has a small-diameter portion 502a formed by cutting off a central portion of a cylindrical valve member having a diameter equal to the inner diameter of the sleeve 501. An end portion (that is, both end portions of the member; hereinafter, referred to as a "large diameter portion") 502b
A symmetrical shape in which the annular grooves 502c and 502c are respectively omitted from the 502b. A drill hole 502d is formed in the member in the axial direction, and an open end of the drill hole 502d is closed by a plug 502e. Further, a radial communication hole 502f is opened in the two annular grooves 502c in the valve member. Also,
The communication hole 502g is also provided in the small diameter portion 502a of the valve member.
Is provided. The communication holes 502f and 502g and the through hole 502d form two annular grooves 502c and 502c.
The small-diameter portion 502a and the small-diameter portion 502a communicate with each other. Thus, the two hydraulic oil circulation oil passages 75
By configuring the circuit for short-circuiting x × 75x with one spool 502, the mechanism for expanding the neutral range can be made compact, and the cost can be reduced.

The lids 503 and the return spring 50
The 4.504 will be described with reference to FIG. Each of the lids 503 has a threaded portion 503a for attaching to both ends of the sleeve 501 and an internal projection 503b for regulating a sliding range of the spool 502. Also, the return spring 504 is externally fitted and disposed on the internal projection 503b. As a result, the lid 5
When the return springs 03 and 503 are attached to the sleeve 501, the resilient forces (forces Fs and Fs shown in FIG. 15) of the two return springs 504 and 504 are applied to both ends of the spool 502. The spool 502 is stopped at the position where Fs · Fs is balanced. When no force other than the resilient force Fs / Fs is applied to the spool 502, the spool 502
The urging force and the like of the return springs 504 and 504 are adjusted so as to be stopped at the center position (the position shown in FIG. 13; hereinafter, referred to as a “neutral position”).
On both sides of the spool 502, two lids 503
A space is formed between each of the holes 503 and 503 so that oil can be introduced into the space as described later. Further, the spool 5 is moved a certain distance from the neutral position.
02 slides, one end of the spool 502 comes into contact with the internal projections 503b of the lids 503 on one side, so that the sliding range of the spool 502 is regulated. .

The sleeve 501 will be described with reference to FIG. The sleeve 501 is a cylindrical member, and pilot holes 511.5 are provided at both ends of the member.
11 are provided in the radial direction, respectively, and a pair of orifice holes 512, 512 is provided in a portion facing the hydraulic oil circulation oil passages 75x, 75x in the radial direction. In the pilot holes 511, 511, the two hydraulic oil circulation oil passages 75x
Pilot oil passages 510, 510 branched from and formed at 75x, respectively, are communicated. On the other hand, the orifice hole 512
• 512 is the ring groove 5 when the spool 502 in the sleeve 501 is in the neutral position.
A small diameter hole is formed by a method such as laser processing in accordance with the positions of 02c and 502c to communicate with the pair of hydraulic oil circulation oil passages 75x and 75x, respectively. A drain hole 513 is formed in the center of the sleeve 501 in the radial direction, and the drain hole 513 is formed in the center section 7.
5 is connected to a drain oil passage 514.

Next, a description will be given of the operation of the above construction in which the spool 502 slides according to the pressure difference generated between the pair of hydraulic oil circulation oil passages 75x and 75x to open and close the circuit.

That is, as described above, the hydraulic oil circulation oil passage 7
5x and 75x are pilot oil passages 510 and 51, respectively.
0 to the sleeve 5 through the pilot holes 511
01 communicates with the above space. Accordingly, the hydraulic oil in one hydraulic oil circulation oil passage 75x is guided into the sleeve 501, and applies a force proportional to the pressure to one end of the spool 502. Further, the hydraulic oil in the other hydraulic oil circulation oil passage 75x is guided into the sleeve, and acts on the other end of the spool 502 with a force proportional to the pressure (F shown in FIG. 15).
o ・ Fo).

Therefore, both hydraulic oil circulation oil passages 75x and 75x
Are equal to each other, equal forces act on both ends of the spool 502 in opposite directions, so that a balanced state of the forces as shown in FIG. 15 is maintained, and the spool 502 is slid from the neutral position. There is no. On the other hand, when there is a difference between the pressures of the two hydraulic oil circulation oil passages 75x and 75x, the force Fo applied to one end of the spool 502 exceeds the force Fo applied to the other end as shown in FIG. Torn, spool 502 slides. Here, the sliding of the spool 502 causes the return spring 5 on the sliding direction side to move.
Since 04 shrinks, its resilience Fs is increased, and the return spring 504 on the other side is expanded, so that its resilience Fs is reduced.
Accordingly, the spool 502 enters a new equilibrium state and stops at a position where the spool 502 slides by a distance corresponding to the pressure difference as shown in FIG.

Therefore, both hydraulic oil circulation oil passages 75x and 75x
If the pressure difference between the spools 502 is small and the sliding distance of the spool 502 from the neutral position is less than a certain value, the orifice holes 512
Since the communication state between the first and second ports c and 502c is maintained, the hydraulic oil is supplied to the orifice hole 51 as shown by a series of arrows in FIG.
2 and 512 through the annular grooves 502c and 502c to the drill holes 502d inside the spool 502,
02d through a central communication hole 502f and a drain hole 513 of the sleeve 501, and finally a drain oil passage 514.
(Or a part thereof flows into the low-pressure side working oil circulation oil passage 75x side). On the other hand, when the pressure difference between the two hydraulic oil circulation oil passages 75x and 75x is large and the sliding distance of the spool 502 from the neutral position is equal to or more than a certain value, the orifice holes 512 Since it is closed at the large diameter portion 502 (FIG. 17), the orifice hole 512.
512 is not in communication with the annular grooves 502c of the spool 502. Therefore, in this case, the hydraulic oil in the hydraulic oil circulation oil passages 75x and 75x is not drained,
All oil is sent to the hydraulic motor 72 of the steering HST22.

Next, how the circuit having the above configuration specifically expands the neutral range of the steering HST in the present embodiment will be described with reference to different cases.

That is, FIG. 15 shows a state in which the operator sets the steering handle 14 to the neutral position. In this case, the movable swash plate 76 of the hydraulic pump 71 of the steering HST 22 is also set to the neutral position. When the plate 76 is slightly tilted from the neutral position, the hydraulic pump 71 discharges a small amount of pressure oil, and both hydraulic oil circulation oil passages 75x
-Create a pressure difference between 75x. However, since the pressure difference in this case is small and the sliding of the spool 502 is slight, the orifice holes 512
The state where the path from to the drain oil path 514 is open is maintained. Therefore, as shown in a series of arrows in FIG. 15, the hydraulic oil in the hydraulic oil circulation oil passage 75x on the high pressure side orifice hole 512 → annular groove 502c → communication hole 502f → cut hole 502d → communication hole 502f → drain hole. 513 → the drain oil passage 514, and is finally drained to the oil reservoir in the housing 23. Therefore, the steering H
The hydraulic motor 72 in ST22 is not driven slightly. As a result, straightness when the steering handle 14 is set to the neutral position is favorably maintained.

On the other hand, FIG. 17 shows a case where the operator turns the steering handle 14, and in this case, the movable swash plate 76 of the hydraulic pump 71 of the steering HST 22 is also tilted greatly, so that the hydraulic oil is discharged from the hydraulic pump 71. By the action, the pressure difference between the two working oil circulation oil passages 75x and 75x increases. Therefore, the spool 502 is largely slid from the neutral position to one side, and the two orifice holes 512 formed in the sleeve 501 are connected to the spool 50.
When the position does not coincide with the position of the second annular groove 502c, both are closed, and the path from the orifice hole 512 to the drain oil passage 514 is closed (FIG. 17). As described above, when the steering handle 14 is turned, the orifice hole 512 is closed, and the hydraulic oil is not drained. As a result, a reduction in the volumetric efficiency of the steering HST 22 is prevented, and the response followability to the turning operation can be maintained satisfactorily.

Next, a modification of the above embodiment will be described. FIG. 18 is a sectional development view showing a modification of a circuit provided in the center section of the steering HST, and a state where a pair of hydraulic oil circulation oil passages are short-circuited via an oil passage in a spool. FIG. 19 is a modification. FIG. 20 is a partial cross-sectional view showing a configuration of a spool that opens and closes a circuit in FIG. 20. FIG. 20 is a cross-sectional view showing a state in which the spool is slid from the state of FIG. It is a development view.

That is, in this modified example, a circuit 600 described below is provided in a pair of hydraulic oil circulating oil passages 75x, 75x for connecting the hydraulic pump 71 and the hydraulic motor 72 of the steering HST 22 to the steering. The neutral range of the handle 14 is enlarged.

The circuit 600 will be described. That is, as shown in FIG. 18, the pair of hydraulic oil circulation oil passages 75x
A drill hole is formed in the center section 75 so as to straddle the valve housing chamber 610.
A spool 602 is reciprocally mounted on the reference numeral 10 via an urging spring 604, and a solenoid 601 is provided so that the spool 602 can be pushed.

A specific configuration of the spool 602 will be described.
This will be described with reference to FIGS. This spool 60
Reference numeral 2 denotes a columnar member having a diameter that matches the inner diameter of the valve storage chamber 610.
The part facing 5x / 75x is cut off and the small-diameter part 602a
602a (FIG. 19), and portions other than the small-diameter portion (hereinafter, "large-diameter portions") 602b and 602b have annular grooves 602c.
602c are respectively formed. A drill hole 602d is formed in the member in the axial direction, and an open end of the drill hole 602d is closed by screwing a plug 602e. And
The annular grooves 602c and 602c have communication holes 60 respectively.
2f and 602f are provided by drilling in the radial direction.
02d communicates with the annular grooves 602c. At one end of the spool 602, a disc-shaped spring receiving portion 602h is formed.

Hereinafter, the solenoid 601 and a controller (not shown) for controlling the solenoid 601 will be described. Solenoid 60
Numeral 1 is attached to the opening end side of the center section 75 of the valve chamber 610, and is electrically connected to a controller for controlling the operation thereof. The controller is configured to receive a signal from a detection means (for example, a potentiometer) (not shown) for detecting the angle of the movable swash plate 76 of the hydraulic pump 71 of the steering HST 22. The controller pushes the spool 602 against the urging spring 604 as indicated by a black arrow in FIG. 19 only when the tilt angle of the movable swash plate 76 is smaller than a set value based on the signal of the detection means. The solenoid 601 is controlled to move.

This detecting means is not limited to the structure directly attached to the movable swash plate 76 of the hydraulic pump 71 of the steering HST 22. For example, the control arm 193 for tilting the movable swash plate 76, the steering handle 14, the steering The handle 14 and the control arm 193 may be provided at an appropriate position of a link mechanism that links the control arm 193 and the like.

Next, how the circuit having the above configuration specifically expands the neutral range of the steering handle 14 in the present embodiment will be described with reference to different cases.

FIG. 18 shows a state in which the operator operates the steering handle 14 to the neutral position. In this case, the hydraulic pump 7 of the steering HST 22 is used.
The movable swash plate 76 is also set to the neutral position.
When the hydraulic pump 6 is slightly tilted from the neutral position, the hydraulic pump 71 discharges a small amount of pressure oil to
A pressure difference occurs between 5x and 75x. However, since the amount of tilt of the movable swash plate 76 is very small, the controller determines that the hydraulic pump is near the neutral position and
02 to push the solenoid valve 02 against the biasing spring 604.
01 is operated. Therefore, as shown in FIG.
2 is communicated with a pair of hydraulic oil circulation oil passages 75x and 75x, and a high pressure side oil passage 75x (FIG. 1).
FIG. 8 illustrates a case where the left oil passage has a high pressure. The hydraulic oil in parentheses flows from the annular groove 602c to the communication hole 602f → the drill hole 602d → the communication hole 602f as shown by a series of arrows in the figure, and flows into the low-pressure side oil passage 75x.
That is, when the amount of tilt of the movable swash plate 76 is very small, the controller pushes the spool 602, and the communication holes 602f and 602f and the through holes 60 formed inside the spool 602 are formed.
Since the two working oil circulation oil passages 75x and 75x are short-circuited via 2d, the hydraulic motor 72 of the steering HST 22 is not slightly driven. As a result, the straightness when the steering handle 14 is set to the neutral position is favorably maintained.

On the other hand, FIG. 20 shows a case where the operator turns the steering handle 14, and in this case, the movable swash plate 76 of the hydraulic pump 71 of the steering HST 22 is also tilted greatly. Therefore, the controller, which has detected that the hydraulic pump 71 has deviated from the vicinity of the neutral position by the detecting means, controls the solenoid 601 to release the pushing of the spool 602, so that the spool 602 is actuated by the action of the urging spring 604. It is slid as shown at 20. As a result, communication between the annular grooves 602c and 602c of the spool and the hydraulic oil circulation oil passages 75x and 75x is stopped, and the short-circuit state of both the hydraulic oil circulation oil passages 75x and 75x is released. In this way, when the steering handle 14 is rotated, the hydraulic oil circulation oil passages 75x and 75x are not short-circuited, so that all the hydraulic oil discharged by the hydraulic pump 71 is sent to the hydraulic motor 72. As a result, the volumetric efficiency of the steering HST 22 is favorably maintained, and the response followability to the turning operation of the steering handle 14 can be improved.

Note that the above-mentioned detecting means is provided by the traveling drive HST2.
It is also possible to detect the tilt angle of the movable swash plate 57 of the first hydraulic pump 52. That is, the traveling drive HST2
The movable swash plate 57 of the hydraulic pump 52 and the movable swash plate 57
Arm 60 for tilting the gear, the speed change pedal 15, and the speed change pedal 15 and the control arm 6
The detection means is provided at an appropriate position of the link mechanism that links the zeros. In this configuration, when the shift pedal 15 is neutral, the hydraulic oil circulation oil passages 75x and 75x are short-circuited. Therefore, even when the vehicle is stopped, the movable swash plate 7 of the hydraulic pump 71 of the steering HST 22 is stopped.
Since the vehicle 6 is slightly tilted, it is possible to prevent a situation in which the vehicle turns slightly on the spot. Further, even when the operator stops the vehicle and touches the steering wheel 14 when the operator moves up and down from the vehicle, the situation in which the vehicle turns on the spot is prevented.

Alternatively, a detecting means for detecting the movable swash plate 57 of the hydraulic pump 52 of the traveling drive HST 21 and a detecting means for detecting the movable swash plate 76 of the hydraulic pump 71 of the steering HST 22 are provided. 5
It is also possible to adopt a configuration in which the information of the tilt angle of 7.76 is input to the controller for control, and in this case, finer control is possible.

Although the embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the above-described embodiments, and the present invention can be clearly understood from the matters described in the present specification and the drawings. It covers a whole range of technical ideas that are truly intended.

[0073]

The present invention is configured as described above.
The following effects are obtained.

That is, as described in claim 1, the traveling drive H is constituted by fluid communication between a hydraulic pump and a hydraulic motor.
An ST and a steering HST, a differential device connected to the motor shafts of the two HST hydraulic motors, and a drive train for interlockingly connecting the differential device and the two HSTs are arranged in a housing. A steering driving device for a traveling vehicle that steers and drives a pair of left and right axles interlocked with the differential device.
A hydraulic pump is provided between a pair of paths that fluidly communicate the hydraulic pump and the hydraulic motor of the steering HST, and a circuit that is opened when the hydraulic pump is in a set range near the neutral position is provided. Constructed by spool,
A drain circuit for draining the hydraulic oil of the opened circuit is connected to the circuit, so that when the steering operation tool is operated to the neutral position, the steering H
Even if the neutral position of the hydraulic pump in ST is slightly shifted, the pair of paths is short-circuited, so that a situation in which the hydraulic motor is slightly driven and the vehicle cannot travel straight ahead is prevented. Therefore, the straightness of the vehicle can be maintained satisfactorily. On the other hand, when the steering operation tool is operated to turn the vehicle, the short-circuit state of the pair of paths is released, so that all the hydraulic oil discharged by the hydraulic pump is supplied to the hydraulic motor, and the steering HST Good volumetric efficiency can be maintained. Therefore, it can respond quickly to the operation of the steering operation tool,
A smooth and light operation feeling can be provided to the operator. Further, by configuring the opened circuit with a single spool, the mechanism for expanding the neutral range can be made compact, and the cost can be reduced.

A traveling drive HST, a steering HST, and a differential device connected to the motor shafts of the hydraulic motors of the two HSTs, wherein the hydraulic pump and the hydraulic motor are in fluid communication with each other. And a drive train for operatively connecting the differential and the two HSTs in a housing, wherein the driving vehicle steers and drives a pair of left and right axles operatively connected to the differential. In the steering drive device, a circuit opened when the hydraulic pump of the traveling drive HST is in a set range near the neutral position is provided between a pair of paths that fluidly communicate the hydraulic pump of the steering HST and the hydraulic motor. And the open circuit is constituted by one spool, and further, a drain circuit for draining hydraulic oil of the open circuit,
When the shift operation tool is operated to the neutral position, the pair of paths is short-circuited because the shift operation tool is operated in the neutral position. Even when the vehicle touches the vehicle, a situation in which the vehicle starts turning on the spot is prevented. On the other hand, when the shift operation tool is operated to drive the vehicle, the short-circuit state of the pair of paths is released,
The vehicle can be turned by a normal steering operation. Further, by configuring the opened circuit with a single spool, the mechanism for expanding the neutral range can be made compact, and the cost can be reduced.

According to a third aspect of the present invention, a traveling drive HST, a steering HST, and a differential device coupled to the motor shafts of the two HST hydraulic motors, the hydraulic drive and the hydraulic motors being fluidly connected to each other. And a drive train for operatively connecting the differential and the two HSTs in a housing, wherein the driving vehicle steers and drives a pair of left and right axles operatively connected to the differential. In the steering drive device, a circuit that is opened when a pressure difference between the pair of paths is smaller than a set value is provided between a pair of paths that fluidly communicate the hydraulic pump of the steering HST and the hydraulic motor, The circuit to be opened is constituted by a single spool, and a drain circuit for draining the hydraulic oil of the circuit to be opened is connected to the circuit. Since the neutral position of the hydraulic pump of the Alling HST is not accurately projected, even if the pump is slightly driven even when the steering operation tool is set to the neutral position and a slight pressure difference occurs between the pair of paths, in this case, Since the pair of paths is short-circuited, it is possible to prevent a situation in which the hydraulic motor is slightly driven to prevent the vehicle from traveling straight. Therefore, the straightness of the vehicle can be maintained satisfactorily. On the other hand, when the steering operation tool is operated to turn the vehicle, the pressure difference between the pair of paths increases due to the discharge of the hydraulic oil from the hydraulic pump, and the short-circuit state between the paths is released. All of the discharged hydraulic oil is sent to the hydraulic motor, so that the volumetric efficiency of the steering HST can be favorably maintained. Therefore, it is possible to promptly respond to the operation of the steering operation tool, and to provide the operator with a smooth and light operation feeling. Further, by configuring the opened circuit with a single spool, the mechanism for expanding the neutral range can be made compact, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a side view showing an overall configuration of a mower tractor including a steering drive device of the present invention.

FIG. 2 is a side view showing a first modification of the mower tractor.

FIG. 3 is a side view showing a second modification of the mower tractor.

FIG. 4 is a plan sectional view showing a state inside a housing of the steering drive device.

FIG. 5 is a perspective view of the same seen from the plane side.

FIG. 6 is a perspective view similarly viewed from the bottom side.

FIG. 7 is a sectional view taken along the line AA in FIG. 4;

FIG. 8 is a sectional view taken along line BB in FIG. 4;

FIG. 9 is a schematic diagram showing a state where outputs of two HSTs are input to an axle via a drive train and a differential device.

FIG. 10 is an exploded perspective view of the differential device.

FIG. 11 is a side view of the steering drive device.

FIG. 12 is a skeleton diagram of a steering drive device.

FIG. 13 is a sectional development view showing a circuit provided in a center section of the steering HST.

FIG. 14 is a perspective view, partly in section, showing the configuration of a spool that opens and closes a circuit.

FIG. 15 is a sectional development view showing a force applied to the valve when the pressures of a pair of hydraulic oil circulation oil passages are equal to each other.

FIG. 16 is a sectional development view showing a force applied to the valve when a difference occurs in the pressures of the pair of hydraulic oil circulation oil passages.

17 is a sectional development view showing a state in which the spool is slid from the state of FIG. 16 to a new equilibrium state, and the orifice oil passage is closed.

FIG. 18 is a sectional development view showing a modified example of a circuit provided in the center section of the steering HST and a state in which a pair of hydraulic oil circulation oil passages is short-circuited via an oil passage in a spool.

FIG. 19 is a perspective view, partly in section, showing the configuration of a spool that opens and closes a circuit in a modified example.

20 is a sectional development view showing a state in which the spool is slid from the state of FIG. 18 and the pair of hydraulic oil circulation oil passages is no longer short-circuited.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 traveling vehicle (more tractor) 2 steering drive device 5 differential device 21 traveling drive HST 22 steering HST 23 housing 40L / 40R axle 52 traveling drive HST hydraulic pump 53 traveling drive HST hydraulic motor 71 steering HST hydraulic pump 72 Hydraulic motor for steering HST 75x, 75x Hydraulic oil circulation line 500 circuit 502 spool 514 Drain oil line (drain circuit), which is a path that fluidly connects the hydraulic pump and the hydraulic motor for steering HST.

 ──────────────────────────────────────────────────続 き Continuing on the front page F-term (reference) JJ37

Claims (3)

[Claims] 1. A traveling drive system HST and a steering system HS configured to fluidly communicate a hydraulic pump and a hydraulic motor.
T, a differential coupled to the motor shafts of the two HST hydraulic motors, and the differential and the two HSTs
A drive train for operatively connecting a pair of left and right axles operatively connected to the differential device, wherein a hydraulic pump for steering HST is provided. Circuit is opened when the steering wheel is in the set range near the neutral position.
A hydraulic circuit provided between a pair of paths that fluidly communicate the hydraulic pump and the hydraulic motor, the open circuit is constituted by a single spool, and a drain circuit for draining hydraulic oil of the open circuit. Is connected to the circuit and provided. 2. A traveling drive system HST and a steering system HS configured to fluidly communicate a hydraulic pump and a hydraulic motor.
T, a differential coupled to the motor shafts of the two HST hydraulic motors, and the differential and the two HSTs
And a drive train for driving and driving a pair of left and right axles that are operatively connected to the differential device. The circuit that opens when the pump is in the set range near the neutral position
ST is provided between a pair of paths that fluidly communicate the hydraulic pump and the hydraulic motor in ST, the open circuit is constituted by a single spool, and a hydraulic fluid of the open circuit is drained. A steering drive device for a traveling vehicle, wherein a drain circuit is provided connected to the circuit. 3. A traveling drive system HST and a steering system HS configured to fluidly communicate a hydraulic pump and a hydraulic motor.
T, a differential coupled to the motor shafts of the two HST hydraulic motors, and the differential and the two HSTs
And a drive train for operatively connecting a pair of left and right axles to be operatively connected to the differential device. A circuit that is opened when a pressure difference between the pair of paths is smaller than a set value is provided between a pair of paths that fluidly communicate the pump and the hydraulic motor, and the opened circuit is configured by one spool. A steering drive device for a traveling vehicle, further comprising a drain circuit for draining hydraulic oil of the open circuit connected to the circuit.