JP2005199835A - Steering wheel drive device, and four-wheel drive vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve rotation reaction of a steering wheel, and improve maintenance performance. <P>SOLUTION: This steering wheel drive device 13 or 15 comprises a housing 27 including a hydraulic motor 10 or 80 for driving an axle fixed to a vehicle frame 2, a steering case 28 to support a single axle 35, and front wheels 36 and 36 or rear wheels 79 and 79 fixed to the end parts of the single axle 35. The steering case 28 is composed in such a way that it is rotatable to the vehicle frame 2 through a king pin part 27a extended downward of the housing 27. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a steering wheel driving device and a technology of a work vehicle using the steering wheel driving device, and more specifically, a steering wheel driving device in which a variable displacement hydraulic motor is built in and integrated with a housing to which a steering case is connected. And a technique for improving the running performance and turning performance of the work vehicle.

  Work vehicles are required to be improved in running performance and turning performance because they are repeatedly run and turned even in a narrow road and soft ground. Therefore, in order to improve the traction performance while facilitating the turning in the left-right direction, there are some known ones in which each of the steered wheels and the non-steered wheels turning left and right are driven by a fixed displacement hydraulic motor. It has become.

  For example, in Patent Documents 1 and 2, fixed displacement type hydraulic motors are respectively installed above the front, rear, left and right ends of the vehicle frame, and housings for storing reduction gear trains are stacked to each of the left and right front wheels and rear wheels. Linked together. A hydraulic four-wheel drive vehicle is configured by fluidly connecting the front and rear pair of the left hydraulic motor to the left variable displacement hydraulic pump and fluidly connecting the front and rear pair of the right hydraulic motor to the right variable displacement hydraulic pump. To do. By switching the volume of these hydraulic pumps synchronously by operating levers, the forward / reverse switching and the traveling speed are changed. In this embodiment, the front wheels are steerable wheels that can be steered by a round handle.

Shokai 58-58932 Shoko Sho 62-37775

  However, in Patent Documents 1 and 2, since the fixed displacement type hydraulic motor and the housing for housing the reduction gear train are vertically stacked and installed on the vehicle frame, the entire apparatus is large. And restricting the layout of the vehicle.

  In addition, when turning, the rotational speed of the steered wheels cannot be controlled, which may result in lack of running stability or rough ground (aggression on the ground). Further, since the travel speed range is determined by the volume of the variable displacement hydraulic pump, it is narrow and unusable. Moreover, since two variable displacement hydraulic pumps are used, the cost is high.

  Therefore, in the present invention, it relates to a steering wheel drive device and a four-wheel drive vehicle equipped with the same, and solves the above-mentioned conventional problems, improving the running performance and turning performance of the steering wheel, and at low cost and compact. Furthermore, it aims at proposing the steering wheel drive device and four-wheel drive vehicle with a wide adaptation range with respect to a vehicle form.

  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 of the present invention, a housing incorporating a hydraulic motor for driving an axle fixed to a vehicle frame, a steering case for supporting a single axle, and a steering wheel fixed to an end of the single axle. The steering case is disposed so as to be rotatable with respect to the vehicle frame via a king pin portion extending downward from the housing.

  According to a second aspect of the present invention, in the first aspect, the output shaft of the hydraulic motor as a shaft center of the kingpin portion is rotated from the upper side to the single axle that is supported substantially horizontally outward. The output shaft is movably inserted, and the output shaft is linked to the axle by a reduction gear train disposed in the steering case.

  According to a third aspect of the present invention, in the first or second aspect, the hydraulic motor is a variable displacement type, and the volume of the hydraulic motor is changed by a relative displacement between the housing and the steering case. .

  According to a fourth aspect of the present invention, there is provided a work vehicle in which at least one of the front and rear drive wheels is configured to be steerable, and includes a first hydraulic motor and a second hydraulic motor that drive each of the front and rear drive wheels. There is a common hydraulic pump that supplies oil to the first and second hydraulic motors, and both the hydraulic pumps are connected to the hydraulic pumps in a hydraulic circuit that fluidly connects the first and second hydraulic motors to the hydraulic pumps. A shift switching valve is provided that enables switching between a state in which the hydraulic motors are connected in series and a state in which the hydraulic motors are connected in parallel.

  According to a fifth aspect of the present invention, in the fourth aspect, the first hydraulic motor coupled to the steerable drive wheel is a variable displacement type, and the volume controller of the hydraulic motor is configured to perform a steering operation of the steerable drive wheel. It is linked to the steering mechanism of the steerable drive wheel so as to change the volume of the hydraulic motor in linkage.

  A sixth aspect of the present invention provides the shift switching valve according to the fourth or fifth aspect, wherein, in addition to the parallel connection state and the serial connection state, the oil from the hydraulic pump is allowed to flow only to one of the two hydraulic motors. It is possible to switch to a state.

  According to a seventh aspect of the present invention, in the sixth aspect, the vehicle is configured to connect the first hydraulic motor to a steerable drive wheel and connect the second hydraulic motor to a non-steerable drive wheel. At the same time, the second hydraulic motor is of a variable displacement type, and the volume regulator of the hydraulic motor is configured such that the shift switching valve is switched so that oil from the hydraulic pump flows only to the second hydraulic motor. The hydraulic motor is linked to the shift switching valve so as to be operated in a direction to reduce the volume of the hydraulic motor.

  According to an eighth aspect of the present invention, in the fourth aspect, at least one of the first and second hydraulic motors is connected to each of the left and right drive wheels, and a pair of the first and second hydraulic motors are provided. A first circuit configuration in which two hydraulic motors are fluidly connected in parallel to the hydraulic pump, and oil is divided into both hydraulic motors with their flow rates adjusted while fluidly connected in parallel to the hydraulic pump. And a hydraulic circuit configured to be settable in either of the first and second circuit configurations.

  According to a ninth aspect of the present invention, in the fourth aspect, at least one of the first and second hydraulic motors is connected to each of the left and right drive wheels, and a pair of the first and second hydraulic motors are provided. A first circuit configuration in which two hydraulic motors are fluidly connected in parallel to the hydraulic pump; and a second circuit that restricts a flow rate supplied to one hydraulic motor while fluidly connecting in parallel to the hydraulic pump. A circuit configuration and a third circuit configuration that restricts the flow rate of oil supplied to the other hydraulic motor while fluidly connected in parallel to the hydraulic pump, and the difference in the amount of oil discharged from each hydraulic motor. Basically, when the amount of oil discharged from the other hydraulic motor is smaller than the amount of oil discharged from one hydraulic motor, the first circuit configuration is changed to the second circuit configuration, and the amount of oil discharged from one hydraulic motor is changed. Compared with the other hydraulic When the discharge amount of oil over data increases in which are provided a hydraulic circuit configured to the third circuit configuration from the first circuit configuration, the switchable automatically.

  As effects of the present invention, the following effects can be obtained.

  That is, since the structure shown in claim 1 is adopted, the steered wheels in the steered wheel drive device can be driven separately, the left and right turning performance of the four-wheel drive vehicle is improved, and smooth acceleration / deceleration by the hydraulic motor is achieved. This makes it possible to improve the steerability of the four-wheel drive vehicle. In addition, a case dedicated to the hydraulic motor is not required and can be manufactured at low cost, and the entire drive device can be configured compactly.

  Since the structure shown in claim 2 is adopted, a compact high-speed rotation / low-torque type hydraulic motor can be adopted, and the steering case can be made smaller and more compact.

  When the steering case is steered to the left and right from the rectilinear position, the relative displacement of the housing with reference to the rectilinear position of the steering case is used and the housing is based on the amount of displacement. The volume of the internal hydraulic motor can be automatically converted, so that the running stability can be improved and the aggression against the ground can be reduced.

  With the configuration shown in claim 4, since the operation of the discharge amount and the discharge direction of the hydraulic pump can be performed continuously, it is used as a main transmission that can be operated during traveling, and the first hydraulic motor and the speed change valve are used. By changing the oil flow rate to the second hydraulic motor stepwise and selecting the speed range according to the running situation, the driving speed of the left and right front and rear wheels can be changed over a wide range. In addition, each hydraulic motor can be connected to a hydraulic pump to easily drive the front and rear drive wheels to four-wheel drive, and the power transmission is not via a rotating shaft but via an oil conduit. Since this is done, it is possible to easily secure a space for disposing a mower or the like between the front and rear drive wheels. Furthermore, since only one hydraulic pump is used for the four hydraulic motors, the cost is reduced.

  With the configuration shown in claim 5, the effect of the invention of claim 4 can be obtained by changing the driving speed of the left and right driving wheels in conjunction with the steering angle of the driving wheels.

  With the configuration shown in claim 6, each steered wheel and traveling drive wheel can be easily switched from four-wheel drive to two-wheel drive, and the maneuverability of the four-wheel drive vehicle vehicle is improved.

  Since it is set as the structure shown in Claim 7, economical high-speed driving | running | working by two-wheel drive is attained. Such switching can be performed instantaneously when traveling on a flat ground, and the traveling time can be shortened, resulting in high work efficiency.

  Since the configuration shown in claim 8 is used, when one wheel is stuck in the mud or the like, the second circuit configuration is used so that the oil is supplied with the flow rate adjusted to the left and right hydraulic motors. The driving force can be transmitted to one of the wheels. In particular, when the flow rates to both the hydraulic motors are made substantially equal, the same action as the differential lock is exhibited, and the four-wheel drive vehicle can escape from the mud.

  Since the configuration shown in claim 9 is adopted, the circuit configuration is switched by simply detecting the degree of load applied to each of the left and right hydraulic motors based on the unbalance of the amount of oil flowing through each of the left and right hydraulic motors instead of electronic control. Can do.

Next, embodiments of the invention will be described.
1 is a plan view showing the overall configuration of a work vehicle according to a first embodiment of the present invention, FIG. 2 is a schematic plan view of a steering mechanism used in the first embodiment, and FIG. 3 is a steering wheel applied to a left front wheel. It is rear surface sectional drawing of a drive device. FIG. 4 is an explanatory schematic view of the steering mechanism showing the turning state of the work vehicle, and FIG. 5 is a plan view showing the turning state of the work vehicle. 6 is an enlarged rear sectional view of the upper part of the steering wheel driving device in FIG. 3, FIG. 7 is an enlarged rear sectional view of the lower part of the steering wheel driving device, FIG. 8 is an upper plan view of the housing with the center section removed, and FIG. FIG. 10 is an explanatory view showing the operating state of the motor volume control mechanism, (a) is when traveling straight, (b) is when turning, and FIG. 11 is the first embodiment. It is a hydraulic circuit diagram concerning an example. FIG. 12 is a hydraulic circuit diagram obtained by changing a part of the hydraulic circuit diagram of FIG. 13 is a rear cross-sectional view of the steering wheel drive device in FIG. 3 changed to a high clearance specification, FIG. 14 is a lower enlarged rear cross-sectional view of the steering wheel drive device in FIG. 13, and FIG. 15 is an application of the steering wheel drive device in FIG. It is a top view which shows the whole structure of the constructed working vehicle. FIG. 16 is a plan view showing the overall configuration of the work vehicle according to the second embodiment of the present invention, FIG. 17 is a front sectional view of a non-steered wheel drive device applied to the left rear wheel, and FIG. FIG. 19 is an explanatory view showing the operating state of the motor volume control mechanism, in which (a) shows a straight traveling state, (b) shows a turning state, and FIG. 20 shows a second embodiment. It is a hydraulic circuit diagram. FIG. 21 is a hydraulic circuit diagram obtained by changing a part of the hydraulic circuit diagram of FIG.

(First Example)
First, the overall configuration of the work vehicle 1 according to the present embodiment will be described below.
As shown in FIG. 1, the working vehicle 1 according to the present embodiment is a four-wheel steering / four-wheel drive type in which the steering wheel device according to the present invention is applied to both the front wheels 36 and the rear wheels 79. The left and right vehicle frames 2 along the direction have an engine 3, a mower 4, a hydraulic pump 5, a front wheel 36 that can be steered and driven, a rear wheel 79 that can be steered and driven, a handle 16, and a duct 74 for rear discharge. Etc. are arranged respectively.

  The engine 3 is supported by a vibration isolating member at the rear end of the vehicle frame 2 (not shown), and a device group such as a radiator, a battery, an air cleaner, and a muffler is disposed around the engine 3 (not shown). ). A mower 4 having three cutting blades 4a, 4a, 4a is supported on the abdomen of the work vehicle 1 (mid-mount mower), and the mower 4 has an engine 3 and an input shaft (not shown) above it. It is connected through. A rear discharge duct 74 extending rearward between the rear wheels 79 of the work vehicle 1 is provided. The duct 74 is connected to the mower 4 so that turf grass cut by the mower 4 is sent to a grass collecting container (not shown) installed behind the work vehicle 1 via the duct 74. .

  A variable displacement hydraulic pump 5 is disposed in the vicinity of the engine 3 mounted at an appropriate location on the vehicle frame 2. The hydraulic pump 5 is driven by power from the engine 3 via pulleys disposed on the engine 3 and respective input shafts and output shafts (not shown). The hydraulic pump 5 is fluidly connected to first and second hydraulic motors 10 and 80, which will be described later, via oil passages (first circuit 89, second circuit 90, etc.) provided in the work vehicle 1. This is a common hydraulic pressure source (see FIG. 11). In addition, the arrangement positions of the engine 3 and the hydraulic pump 5 in the work vehicle 1 are not limited to this, and the hydraulic pump 5 is laid out at an appropriate position in the engine 3 according to the direction of the crankshaft.

  The oil discharge amount and the discharge direction from the hydraulic pump 5 are changed by operation of a volume adjuster such as a movable swash plate, and the volume adjuster is connected to the driver's seat of the work vehicle 1 via connecting means such as an arm or a link. It is connected to a main speed adjustment operation tool 106 provided in the vicinity. In this embodiment, a main speed change pedal is used for the speed adjustment operation tool 106. If the stepping direction of the main speed change pedal is changed, the oil discharge direction is changed and the forward / backward movement of the work vehicle 1 is switched. Further, if the stepping amount is changed, the oil discharge amount is changed, and an output rotation that is continuously variable from the steering wheel driving devices 15L and 15R and the steering wheel driving devices 13L and 13R can be obtained.

  A pair of left and right steered wheel drive devices 15L and 15R each having a front wheel 36 at the left and right ends of the cross member 14 are provided on the front of the vehicle frame 2 in the horizontal direction. A center pin CP provided at the center in the width direction of the frame 2 is arranged so as to be rotatable left and right. Similarly, a cross member 78 is horizontally provided in the left and right direction at the rear portion of the vehicle frame 2, and a pair of left and right steering wheel drive devices 13 </ b> L and 13 </ b> R each having a rear wheel 79 at both left and right ends of the cross member 78 are provided. It is arranged. The steering wheel drive devices 15L and 15R are each provided with a variable displacement first hydraulic motor 10, and the steering wheel drive devices 13L and 13R are each provided with a variable displacement second hydraulic motor 80. The left and right first hydraulic motors 10 and the second hydraulic motor are fluidly connected to the hydraulic pump 5 in parallel in a closed circuit through a pipe (not shown), whereby loads acting on the left and right first hydraulic motors 10 respectively. In response to this, a hydraulic differential effect is produced. The same applies to the left and right second hydraulic motors 80.

Next, a steering mechanism for the front wheels 36 and the rear wheels 79 as steering wheels will be described.
In the present embodiment, the steering wheel drive device 15L will be described below unless otherwise specified. That is, in this embodiment, the left and right steering wheel drive devices 15L and 15R (or the steering wheel drive devices 13L and 13R) are not different from each other, and are substantially the same and arranged symmetrically. The configurations of the steering wheel driving device 15 and the steering wheel driving device 13 are not different from each other, and are substantially the same and arranged vertically symmetrically.

  As shown in FIGS. 2 and 3, the work vehicle 1 is formed with a steering link mechanism 18 by left and right steering gear mechanisms 17, 17 linking the front wheels 36, 36 to the handle 16. The handle 16 is connected to an output shaft 21 at a substantially central portion of the steering link 20 via a steering gear box 19. By turning the handle 16, the turning of the steering link 20 is transmitted to the steering link mechanism 18, and the left and right steering wheel drive devices 15L and 15R are turned left and right via the left and right steering gear mechanisms 17 and 17, respectively. It is. Note that a hydraulic power steering may be interposed between the handle 16 and the output shaft 21 in order to convert the turning force of the handle 16 into hydraulic pressure. In such a case, instead of the gear box 19, a hydraulic control device such as a power steering cylinder is provided.

  The steering link mechanism 18 has a fan-shaped gear 22 as a drive gear 22 at a position opposite to the left and right above the cross member 14 with a substantially vertical fulcrum pin 23 in a state in which the tooth circumference is directed left and right. Each is pivotally supported. One end of a rod 25 is attached to each inner end of the drive gear 22 (from each fulcrum pin 23 from the left and right center of the work vehicle 1) via a pivot joint 24. On the other hand, the other end of the rod 25 is attached to both ends of the steering link 20 attached to the output shaft 21 of the steering gear box. Thus, when the handle 16 is turned to the left and right, the drive gears 22 are rotated in opposite directions.

  At the left and right end portions of the cross member 14, mounting stays 26 having a fixing surface at the front and rear and having a substantially U-shape in plan view project, and the front and rear wall surfaces of the housing 27 are formed on the front and rear fixing surfaces of the mounting stay 26. Screwed and fixed with bolts so that it cannot rotate left and right. The housing 27 is formed in a substantially cylindrical shape that opens in the vertical direction, and the first hydraulic motor 10 is built in the upper large diameter portion so that the motor shaft 56 extends in the vertical direction. A center section 41 of the hydraulic motor 10 is fixed so as to cover the opening with the lower plane in contact with the opening end of the large-diameter portion at the top of the housing 27. A small-diameter portion at the bottom of the housing 27 is formed in a long and downward shape to form a kingpin portion 27a. A motor shaft 56 is disposed at the center of the kingpin portion 27a and is rotatably supported via two upper and lower bearings 33 and 33. The tip of the motor shaft 56 protrudes downward from the kingpin portion 27a.

  Further, a long plate-like fixing plate 29 protrudes outward from the vehicle frame 2 at the left and right ends of the cross member 14 and above the mounting stay 26, and is formed on the lower plane of the fixing plate 29. The upper plane of the center section 41 is attached. A pivot pin 31 is provided on the upper plane of the fixed plate 29 so as to project on the same axis as the king pin portion 27a, and a receiving hole 32a for the pivot pin 31 formed in the upper end portion of the knuckle arm 32 is formed in the pivot pin 31. It is fitted so as to be relatively rotatable from above. Further, on the upper surface of the upper end portion of the knuckle arm 32, a fan-shaped gear as the driven gear 30 is screwed and fixed by a bolt so as not to rotate relative to the knuckle arm 32, and the teeth inside the driven gear 30 are driven. The teeth are meshed with the outer teeth of the gear 22. Therefore, when the driven gear 30 is rotated by the drive gear 22, the knuckle arm 32 is rotated to the left and right substantially integrally with the driven gear 30 with the pivot pin 31 serving as the pivot center of the driven gear 30.

  The king pin portion 27a of the housing 27 is inserted into a receiving tube portion 28c formed at the upper end portion of a steering case 28 having a single axle 35, so that the housing 27 and the steering case 28 can be rotated relative to each other (left and right). As shown, the upper and lower bearings 57 and 57 are supported. The upper end portion of the receiving tube portion 28c of the steering case 28 is connected to the lower end portion of the knuckle arm 32 to constitute the steering wheel drive device 15. The steering case 28 is attached to the housing 27 through the knuckle arm 32 so as to be rotatable relative to the housing 27 around the kingpin portion 27a and the pivot pin 31.

  As shown in FIGS. 4 and 5, when the handle 16 is rotated to the left or right, one steering gear mechanism 17 is rotated so that the drive gear 22 moves forward in the periodontal region, The driven gear 30 meshed with the drive gear 22 is rotated so that the periodontal portion is moved forward. The other steering gear mechanism 17 is rotated such that the driven gear 30 moves rearward along the periodontium together with the drive gear 22. Then, in conjunction with the rotation of the driven gear 30, one of the front wheels 36 is rotated left and right so that the front end faces outward and the other turns the front end inward. The driving gear 22 and the driven gear 30 have the front end of the front wheel 36 facing inward and leftward as the front end of the driving gear 22 approaches the front end of the driven gear 30 (in other words, the rear ends move away from each other). On the contrary, the front end of the front wheel 36 is configured to face the left and right outer side as the front end of the drive gear 22 and the front end of the driven gear 30 move away (in other words, the rear ends approach each other).

  In particular, in this embodiment, the Ackerman-Jantt mechanism is provided in which the inner and outer wheels are provided with a left and right turning angle so that the left and right turning angles of the inner wheel are larger than those of the outer wheel. I try to increase it. Specifically, the left and right turning angle difference is realized by making the shapes of the drive gear 22 and the driven gear 30 non-circular. That is, the radius R1 of the drive gear 22 is longer than the radius R2 of the driven gear 30 regardless of the rotation direction and angle thereof, thereby amplifying the left-right rotation allowable angle of the front wheel 36. Further, the drive gear 22 is formed such that the radius R1 changes with rotation, and the driven gear 30 is also shaped so that the radius R2 compensates for this.

  When the steering gear mechanism 17 is interlocked with the inner ring, the radius R1 increases as the rear ends of the drive gear 22 and the driven gear 30 approach each other, and the radius R2 decreases as the radius R1 increases. To do. On the other hand, when the steering gear mechanism 17 is interlocked with the outer wheel, the radius R1 decreases as the front ends of the drive gear 22 and the driven gear 30 approach each other, and the radius R2 is reduced by the amount of the decrease of the radius R1. Increase. Therefore, as the turning angle of the handle 16 is increased, the gear diameter ratio R2 / R1 of the steering gear mechanism 17 interlocked with the outer wheel is increased, and the increasing rate of the left and right rotation angle of the outer wheel is decreased. At the same time, the gear diameter ratio R2 / R1 of the steering gear mechanism 17 linked to the inner wheel decreases by the increase of that of the steering gear mechanism 17 linked to the outer wheel, and the rate of increase of the left and right rotation angle of the inner ring is large. Become.

  On the other hand, as shown in FIG. 1, a cross member 78 extending in the left-right direction is laterally provided at the rear portion of the vehicle frame 2 symmetrically with the steering wheel drive devices 15L and 15R. Steering wheel drive devices 13L and 13R for rear wheels 79 and 79 serving as steering wheels are suspended so as to be steerable. As shown in FIG. 2, left and right steering gear mechanisms 37, 37 that interlockly connect the rear wheels 79, 79 to the handle 16 are formed. The steering gear mechanism 37 is configured such that a fan-shaped gear as a drive gear 42 is pivoted above the cross member 78 so as to be substantially horizontally rotatable by a fulcrum pin 23 in a substantially vertical direction with a tooth circumference facing left and right. It is supported. A pivot joint 44 is attached to each inner end of the drive gear 42. Of the left and right rods 45, one end of which is pivotally connected to the steering link 20, the rod 45L is connected to the right drive gear 42R. The rod 45R is pivotally connected to the left drive gear 42L via a pivot joint 44 in a cross shape.

  Similar to the steering wheel drive devices 15L and 15R described in detail with reference to FIG. 3, a housing 27 is fixed to the left and right ends of the cross member 78 so as not to rotate relative to each other. A steering case 28 is pivotally supported so as to be relatively rotatable.

  The configuration of the steering wheel drive devices 13L and 13R is the same as that of the steering wheel drive devices 15L and 15R described in detail with reference to FIG. 3, and therefore detailed description thereof is omitted. In other words, the steering wheel drive devices 13L and 13R are such that the steering case 28 and the knuckle arm 32 are attached to the housing 27 in which the second hydraulic motor 80 for driving the rear wheel 79 is incorporated so as to be relatively rotatable. It is. Therefore, the steering wheel drive devices 13L and 13R are substantially the same as the front wheel steering wheel drive devices 15L and 15R.

  When the handle 16 is turned to the left, the steering link 20 is tilted in the same direction, the rod 25L is pulled backward, the rod 25R is pushed forward, and the front wheel 36 is turned to the left. At the same time, the rod 45R is pushed forward, the rod 45L is pulled backward, and the rear wheel 79 is turned to the right. That is, when the handle 16 is rotated to the left or right from the neutral position (the straight traveling position of the work vehicle 1), the front wheel 36 is turned left and right on the same left and right sides corresponding to the rotation direction of the handle 16, and the rear The wheel 79 is turned left and right in the direction opposite to the direction in which the handle 16 rotates.

  As with the steering gear mechanism 17, the steering gear mechanism 37 is configured such that the shape of the drive gear 42 and the driven gear 50 is a non-circular gear, thereby providing left and right turning angles on the inner and outer wheels, and among the rear wheels 79, A so-called Ackermann-Jantt mechanism in which the left and right rotation angles of the inner ring are larger than those of the outer ring is adopted to improve the steering ability of the left and right turning. That is, the radius R1 of the drive gear 42 is longer than the radius R2 of the driven gear 50 regardless of the rotation direction and angle thereof, and the drive gear 42 is formed such that the radius R1 changes with rotation. The driven gear 50 is also shaped such that the radius R2 compensates for this.

  As the turning angle of the handle 16 is increased, the gear diameter ratio R2 / R1 of the steering gear mechanism 37 interlocked with the outer wheel is increased, and the rate of increase of the left and right rotation angle of the outer wheel is decreased. At the same time, the gear diameter ratio R2 / R1 of the steering gear mechanism 37 linked to the inner wheel decreases by the increase of that of the steering gear mechanism 37 linked to the outer wheel, and the rate of increase of the left and right rotation angle of the inner wheel is large. Become. As described above, the steering gear mechanism 37 is also configured such that the difference between the left and right rotation angles of the inner and outer wheels increases as the rotation angle of the handle 16 increases.

  With the configuration as described above, the difference between the left and right rotation angles of the inner wheel and the outer wheel of the front wheel 36 and the rear wheel 79 can be increased as the rotation angle of the handle 16 increases. In addition, the steering wheel drive devices 15L and 15R and the steering wheel drive devices 13L and 13R can be greatly rotated by providing a difference in the left and right rotation angles of the inner and outer wheels with a small operation amount of the handle 16. As described above, the work vehicle 1 is configured to be a four-wheel drive / four-wheel steering type, has high traction performance, and can turn with a small turning radius while maintaining a very good balance.

  Here, as shown in FIG. 5, in the plan view, the left-right center line in the front-rear direction of the work vehicle 1 (vehicle frame 2) is the line A1, the left-right rotation centers of the left and right front wheels 36, 36, The straight line in the left-right direction connecting the shaft centers of the king pin portions 27a of the steering drive wheel devices 15L and 15R is a line A2, and the shaft centers of the left and right rear wheels 79 and 79, that is, the king pin portions of the left and right steering wheel drive devices 13L and 13R. If the straight line in the left-right direction connecting the axis centers of 27a is a line A3, the intersection point of the line A1 and the line A2 is a point 111, and the intersection point of the line A1 and the line A3 is a point 112, the turning center point 110 Is the turning radius of the vehicle center between the left and right front wheels 36 and 36 (hereinafter simply referred to as “turning radius 111a of the front wheel 36”), and the distance from the turning center point 110 to the point 112 is the rear left and right. Between wheel 79 and 79 Both the center of the turning radius (hereinafter, simply referred to as "turning radius 112a of the rear wheel 79") it becomes.

  In the present embodiment, the front wheel 36 and the rear wheel 79 are rotated by the same angle, although they are opposite in the left and right directions with respect to the rotation direction of the handle 16 by the rotation operation of the handle 16. The turning center point 110 appears at a position substantially half the distance from the wheel 79, and the turning radius 111a of the front wheel 36 and the turning radius 112a of the rear wheel 167 are turned to be equal. Specifically, as shown in FIG. 5, when the handle 16 is fully turned to the left, the turning radius 111a of the front wheel 36 and the turning radius 112a of the rear wheel 167 are substantially equal. Compared to the case where only the front wheel 36 is a steered wheel (see FIG. 18), when the steering angle of the handle 16 is approximately the same, both the turning radius 111a of the front wheel 36 and the turning radius 112a of the rear wheel 167 are small, The turnability of the work vehicle 1 is further improved. In addition, in this case, since the turning center point 110 appears just to the side of the mower 4, it can be turned 180 ° while mowing the grass growing around the tree. Thus, since the front wheels 36 and the rear wheels 79 as the steering wheels are provided, the work vehicle 1 is excellent in turning performance, and can be applied to a vehicle that requires a small turn, a sudden turn, or an in-situ turn (zero turn) described later. (See FIG. 15).

  Note that the front wheel 36 and the rear wheel 79 in the present embodiment are rotated in directions opposite to the rotation direction of the handle 16, respectively, but the turning radius 111a of the front wheel 36 and the turning radius 112a of the rear wheel 167 are substantially equal. When turning, the front wheel 36 and the rear wheel 79 do not slip even if the front wheel 36 and the rear wheel 79 rotate at the same speed on the turning locus, and there is no fear of damaging the ground or tires. Therefore, the first and second hydraulic motors 10 and 80 may be fixed displacement types. On the other hand, if the hydraulic pump 5 is in a high discharge amount state when making a sudden turn or a zero turn, which will be described later, the front wheels 36 and the rear wheels 79 enter a turning posture in a high speed state, and the driver receives a centrifugal force and shakes. Unable to make a stable turn such as turning on. In order to cope with such a case, the first and second hydraulic motors 10 and 80 are of a variable displacement type, and as will be described later, the left and right first hydraulic motors 10 and second hydraulic motors 165 are automatically turned when turning. By increasing the respective volumes at the same rate and reducing the rotational speed of the front wheels 36 and the rear wheels 79 in accordance with the turning radius of the vehicle, the turning performance of the work vehicle 1 is enhanced.

  In this embodiment, when the volumes of the first hydraulic motor 10 and the second hydraulic motor 80 are increased, the volumes of the first and second hydraulic motors 10 and 80 are set to the same ratio (X) on the left and right as will be described later. On the other hand, the left and right wheel rotation difference between the inside and outside of the turn is absorbed by the hydraulic differential effect of each of the left and right first and second hydraulic motors 10 and 80. The volume increase rate is changed independently on the left and right sides of the first and second hydraulic motors 10 and 80, that is, the volume change amount (Y) corresponding to the left and right wheel rotation difference between the inside and outside of the turn is the ratio (X). On the other hand, the first and second hydraulic motors 10 and 80 inside the turning are subtracted and the first and second hydraulic motors 10 and 80 outside the turning are added to positively rotate the difference. May be generated.

Next, the left side device 15L of the steering wheel drive device 15 for the pair of front wheels 36 will be described in detail below. The right side device of the steering wheel drive device 15 has the same structure symmetrically. The structure of the left and right side devices in the steering wheel drive device 13 for the pair of rear wheels 79 is also the same.
As shown in FIGS. 3, 6, and 7, in the steering wheel driving device 15 </ b> L, a steering case 28 is integrated with a housing 27 fixed to the mounting stay 26 of the cross member 14 via a knuckle arm 32. And is pivotally supported. The housing 27 of the steering wheel drive device 15L houses a motor volume control mechanism 43 that is linked to the first hydraulic motor 10 and the movable swash plate (volume adjuster) 53, and the steering case 28 has a single unit. A reduction gear train including a planetary gear type reduction mechanism 38 and an axle clutch 61 for drivingly connecting the axle 35 and the axle 35 to the hydraulic motor 10, a brake mechanism 39 for braking the axle 35, and the like. It is stored.

  As described above, the housing 27 is integrated with the axial piston type first hydraulic motor 10. That is, the center section 41 of the first hydraulic motor 10 is fixed so as to cover the upper opening end of the housing 27. Further, a pedestal 55 is attached to a bottom wall portion corresponding to the base of the kingpin portion 27a in the housing 27, and a cradle type movable swash plate 53 is slidably guided and supported thereon, and the motor shaft 56 is movable. It penetrates downward from the swash plate 53 and the pedestal 55 and extends into the kingpin portion 27a.

  The center section 41 is formed in a plate shape, and has a pair of oil supply / discharge ports 41 b and 41 b that communicate with the kidney ports 41 a and 41 a and a drain port that communicates with the oil reservoir of the housing 27 (see FIG. (Not shown) are arranged and opened along the plate surface direction, and pipe joints 46a, 47a, and 48a are screwed, and three oil pipes 46, 47, and 48 respectively connected to the cross member 14 Along the facility. Oil pipes 47 and 48 communicating with the kidney ports 41 a and 41 a are fluidly connected to the hydraulic pump 5. The oil pipe 46 is connected to a reserve tank (not shown) mounted at an appropriate place in the vehicle. The kidney ports 41a and 41a are opened in a motor mounting surface on which a cylinder block 51 constituting the first hydraulic motor 10 is rotatably installed, and suction / discharge oil from the cylinder block 51 is supplied to the kidney port 41a. -It is introduced into 41a. Further, one end of a motor shaft 56 that is locked onto the rotational axis of the cylinder block 51 is pivotally supported at a substantially central position of the motor mounting surface.

  Pistons 52, 52... Are reciprocally fitted in a plurality of cylinder holes drilled in the cylinder block 51 via biasing springs, and the heads of the pistons 52, 52. A thrust bearing 54 of a movable swash plate 53 as a volume adjuster is in contact. Thus, the axial piston type first hydraulic motor 10 is formed. An opening is formed at the center of the movable swash plate 53, and a motor shaft 56 is passed through the opening. A convex arc surface is formed on the lower surface of the movable swash plate 53 and is in sliding contact with a pedestal 55 having a concave arc surface installed in the housing 27. By adopting such a shape, the movable swash plate 53 can be tilted along the pedestal 55. The movable swash plate 53 may be a trunnion type that is supported on the housing 27 by a pair of shaft portions without requiring the pedestal 55 as described above. In the present invention, the first hydraulic motor 10 is not limited to the axial piston type, but may be a radial piston type. In this case, the volume adjuster is a cam ring.

  The oil pumped from the hydraulic pump 5 to the pipe joint 47a (48a) via the oil pipe 47 (48) is sent to the cylinder block 51 from a kidney port 41a introduced into the center section 41. . In this way, the first hydraulic motor 10 and the hydraulic pump 5 are fluidly connected to each other. The initial position (straight vehicle position) is set so that the movable swash plate 53 tilts the contact surface portion of the piston 52 by a predetermined angle from a surface (horizontal plane) perpendicular to the rotational axis of the cylinder block 51. To do. When the contact surface portion is operated away from the vertical direction from this position, the volume of the first hydraulic motor 10 is changed to increase, and the rotational speed of the front wheel 36 is decelerated compared to the initial position. Details of the motor volume control mechanism 43 will be described later.

  As described above, each steering wheel drive device 15 is provided with the first hydraulic motor 10 for driving the front wheels 36, and can be driven individually for each front wheel 36. Further, since the hydraulic pump 5 and the first hydraulic motor 10 mounted at appropriate positions of the vehicle are connected via an oil passage that can be laid out in an arbitrary shape, the engine 3 to the left and right steering wheel drive devices 15L and 15R. It is not necessary to separately provide a drive shaft or a mechanical transmission mechanism in the space in the vehicle frame 2 when transmitting the power of the vehicle, and the lower space of the vehicle frame 2 is equipped with vehicle equipment such as a mower 4 and a rear discharge duct 74. It is possible to secure a wide space for placing products.

  As shown in FIGS. 3 and 7, the steering case 28 is formed in a substantially L shape in front view by forming a receiving tube portion 28c at the upper portion thereof, and the housing 27 is placed in the upper opening of the receiving tube portion 28c. The king pin portion 27a is inserted and pivotally supported by the bearings 57 and 57 so as to be relatively rotatable, and an oil seal 57a disposed at the base of the king pin portion 27a of the housing 27 is interposed so that the steering case 28 is provided. The housing 27 is supported so as to be stably rotatable. The steering wheel drive device 15 can easily remove the steering case 28 from the housing 27 by removing the steering case 28 from the knuckle arm 32. Therefore, maintenance, replacement, and the like of the housing 27, the steering case 28, and the first hydraulic motor 10 disposed in these can be easily performed.

  The steering case 28 includes two halved steering cases 28a and 28b that can be separated and joined in the left-right direction through a joint surface perpendicular to the axis of the axle 35. In this way, by configuring the left and right halves, it is easy to replace and maintain each mechanism such as the speed reduction mechanism 38 disposed in the steering case 28, and each member constituting them. The steering case 28 may be constituted by two halved steering cases that can be separated and joined in the vertical direction through a joint surface parallel to the axis of the axle 35.

Next, a reduction gear train for drivingly connecting the motor shaft 56 to the axle 35 will be described.
The motor shaft 56 protrudes into the steering case 28 from the lower opening end of the king pin portion 27a of the housing 27, and a small bevel gear 58 is fixed to the protruding portion. Further, the steering case 28 is laterally arranged so that the transmission shaft 59 and the axle 35 are located on the same axis, and the inner end of the transmission shaft 59 is cantilevered on the inner side wall of the inner steering case 28a. Axis. A large bevel gear 60 is loosely fitted on the inner side (right side in FIG. 7) of the transmission shaft 59 so as to be relatively rotatable. The large bevel gear 60 is meshed with the small bevel gear 58 to constitute a first-stage bevel gear type reduction mechanism.

  An axle clutch 61 that engages and disengages the large bevel gear 60 with respect to the transmission shaft 59 is configured as follows. That is, the spline hub 62a is fixed on the transmission shaft 59 on the outer side of the large bevel gear 60, and the clutch climber 62b is fitted to the spline hub 62a so as to be slidable in the axial direction. In this state, the clutch climber 62b can be engaged with the clutch teeth 60a of the large bevel gear 60. The clutch slider 62b is connected and interlocked with an operation lever (not shown), and is slid in the axial direction by operating the operation lever, or alternatively meshed only with the spline hub 62a, or , Meshed with both the spline hub 62a and the clutch teeth 60a.

Here, the planetary gear type reduction mechanism 38 provided in the reduction gear train will be described in detail below.
As shown in FIGS. 3 and 7, the work vehicle 1 according to the present embodiment has a planetary gear mechanism between the inner steering case 28 a and the outer steering case 28 b as the second stage reduction mechanism 38. ing. A sun gear 63 is fixed to a free end portion of the transmission shaft 59 that is not supported, and is meshed with a plurality of planetary gears 64, 64,. The The planetary gears 64, 64... Mesh with the internal gear 66 at the same time. The internal gear 66 is interposed between the inner steering case 28a and the outer steering case 28b so as not to rotate. The carrier 65 is spline-fitted with the inner end portion of the axle 35 so as not to rotate relative to it, and is supported by a bearing on the outer steering case 28b. An outer end portion of the axle 35 protrudes from the outside of the steering case 28, and a front wheel 36 is fixed to a hub 35a formed at the protruding end.

  The rotation of the cylinder block 51 of the first hydraulic motor 10 is as follows: motor shaft 56 → small bevel gear 58 → large bevel gear 60 → axle clutch 61 → transmission shaft 59 → sun gear 63 → planetary gears 64, 64. The work vehicle 1 can travel by being transmitted from the axle 35 to the front wheel 36.

  If it is necessary to pull the work vehicle 1 due to an engine failure or the like, the first hydraulic motor 10 of the steering wheel drive device 15 can be idled to reduce the hydraulic resistance. That is, when the vehicle is towed, the axle 35 is reversely driven from the front wheel 36, but the clutch slider 62b is slid in order to cut the power drive from the motor shaft 56 of the first hydraulic motor 10 to the axle 35. The connection between the large bevel gear 60 and the axle 35 can be disconnected. As a result, the hydraulic motor 10 does not perform the pumping action, and the front wheels 36 and 36 can be idled with a light force, so that the traction can be performed easily.

  In addition, as a reduction gear train from the hydraulic motor 10 of the steering wheel drive device 15 to the axle 35, a two-stage reduction mechanism in which the above-described bevel gear type reduction mechanism and planetary gear type reduction mechanism are combined is shown. For example, depending on the specification of the vehicle, only a one-stage bevel gear type reduction mechanism, a two-stage reduction type planetary gear mechanism, a two-stage reduction type parallel gear mechanism, or the like may be used.

Next, the brake mechanism 39 will be described in detail below.
As shown in FIGS. 3 and 7, a wet disk-type brake mechanism 39 is provided on a transmission shaft 59 extending to the outside of the inner steering case 28a. A friction plate 68 is fitted to a protruding portion outside the steering case 28a of the transmission shaft 59 so as not to be relatively rotatable. The brake mechanism 39 is connected to a brake operation tool (not shown). When the brake operation tool is operated, the cam 81 is rotated through a brake wire, a brake arm, and the like that are linked and linked to the brake operation tool, and the pressure member 67 is slid in the axial direction. The pressure member 67 presses the friction plate 68 toward the inner steering case 28a to give a rotational resistance to the transmission shaft 59 and to generate a braking action on the axle 35.

  The brake mechanism 39 in this embodiment is disposed on the side of the outer wall of the inner steering case 28a. However, the position of the brake mechanism 39 is not limited to this, and the brake mechanism 39 is disposed in the steering case 28. It may be arranged.

Next, the motor volume control mechanism 43 will be described in detail below.
As shown in FIGS. 3, 6 to 10, the steering wheel drive device 15 has the tilt angle of the movable swash plate 53, which is a capacity adjuster of the first hydraulic motor 10, from the initial position to a predetermined volume increase position. A motor volume control mechanism 43 to be changed is configured. As described above, the work vehicle 1 according to the present embodiment is set so that the turning radius 111a of the front wheel 36 and the turning radius 112a of the rear wheel 79 are equal to each other, and can freely turn from a slow turn to a sudden turn. it can. Therefore, in each of the front wheel 36 and the rear wheel 79, if the traveling speeds of the work vehicle 1 traveling straight and turning are the same, the stability during turning is impaired. Therefore, the motor volume control mechanism 43 provided in each of the left and right steering wheel drive devices 15 increases the respective volumes of the first hydraulic motor 10 and the second hydraulic motor 80 in accordance with the turning degree of the work vehicle 1. Thus, the rotational speeds of all the left and right front wheels 36 and rear wheels 79 are decelerated compared to when traveling straight.

  As shown in FIGS. 6 and 8 to 10, the control shaft 69 is rotatably supported on the side wall surface of the housing 27 in which the first hydraulic motor 10 is disposed so as to face the left and right directions of the machine body. 27, a swing arm 70 is fitted to one end of the control shaft 69 located inside the control shaft 69 so as not to rotate relative to the control shaft 69, and the free end of the swing arm 70 has a locking pin. It is engaged with a groove formed on the side surface of the movable swash plate 53. A base portion of the control arm 71 having a first arm portion 71a and a second arm portion 71b and having a substantially V shape in front view is fitted to the other end of the control shaft 69 so as not to be relatively rotatable. In this fitted state, as shown in FIG. 9, the entire control arm 71 is curved so that the free end side of the first arm portion 71a is positioned on the outer peripheral edge of the upper surface of the steering case 28.

  On the free end side of the second arm portion 71 b of the control arm 71, an engagement pin 72 for positioning the movable swash plate 53 at the initial tilt position via the swing arm 70 protrudes. A return spring 73 that is a torsion coil spring is fitted on the control shaft 69. Both ends of the return spring 73 extend in parallel toward the tip of the second arm portion 71b, intersect in the middle, and are eccentric pins 77 attached to the outer wall of the housing 27 at the end of the extended portion. And the engaging pin 72 is inserted | pinched. The eccentric pin 77 can be arbitrarily rotated and fixed, and is set so that the initial capacity of the first hydraulic motor 10 during straight travel can be adjusted.

  As shown in FIG. 10, an engagement pin 75 is pivotally supported at the free end of the first arm portion 71a. On the upper surface of the steering case 28 below the control shaft 69, an arc-shaped volume control plate 76 along the shape of the outer peripheral edge thereof is fixedly installed. The volume control plate 76 has a guide groove 76a into which the engagement pin 75 is inserted. When the steering case 28 is rotated in the left-right direction with the king pin portion 27a of the housing 27 as a rotation center, the volume control plate 76 has a volume. The control plate 76 is relatively displaced with respect to the engagement pin 75 in the circumferential (left and right) direction. In particular, in this embodiment, when the steering case 28 is rotated left and right, the guide groove 76a of the volume control plate 76 is so tilted that the movable swash plate 53 is tilted in the direction of increasing the volume of the hydraulic motor 10. Inclined in an inverted V shape so as to protrude upward from both ends in the circumferential direction to substantially the center of the left and right.

  As shown in FIG. 10, the guide groove 76a of the volume control plate 76 is formed so as to be inclined from the position P1 that is the top toward both ends in the circumferential direction, and such end positions are the position P2 and the position P3, respectively. Deviations, which are the height differences from position P1 to position P2 and position P3, are all formed to be ΔL, and the inner cutting angle of the wheel is larger than the outer cutting angle, so that the position P1 is changed to the position P2. The distance to reach is longer than the distance from position P1 to position P3. In the volume control plate 76 formed in this way, the state in which the engagement pin 75 is at the position P1 indicates that the left front wheel 36 is in the rectilinear position and the movable swash plate 53 is in the initial inclined position (first hydraulic pressure during rectilinear travel The initial capacity of the motor 10). The state in which the left front wheel 36 is turned to the left and the engaging pin 75 of the control arm 71 reaches the position P2 of the guide groove 76a is the maximum inner cutting position of the left front wheel 36. Similarly, at the position P3, the guide groove The state in contact with 76a is the maximum outer cutting position of the front wheel 36.

  Specifically, as shown in FIG. 10A, when the engagement pin 75 is at the position P1 in the guide groove 76a, the control arm 71 is determined by the eccentric pin 77 via the return spring 73. Further, the volume of the first hydraulic motor 10 is set to be linearly moved while being elastically held at the initial position. 10B, when the handle 16 is rotated to the left, the steering case 28 is rotated, and the guide groove 76a of the volume control plate 76 is interlocked with the control arm 71. It is displaced relative to the engagement pin 75, and moves in the guide groove 76a so that the engagement pin 75 changes from the position P1 to the position P2. In such a case, the control arm 71 is rotated by a deviation ΔL in the X direction around the control shaft 69, and the swing arm 70 is rotated in conjunction with the control shaft 69 to move the movable swash plate 53. However, the swing arm 70 is tilted so that the swash plate angle becomes larger than the initial position.

  Although illustration is omitted, when the handle 16 is rotated to the right, the guide groove 76 a of the volume control plate 76 is displaced relative to the engagement pin 75 of the control arm 71 in conjunction with the movement of the steering case 28. Then, the engaging pin 75 is moved from the position P1 to the position P3. In such a case, the control arm 71 is rotated by a deviation ΔL in the X direction around the control shaft 69, and the swing arm 70 is rotated in conjunction with the control shaft 69 to move the movable swash plate 53. However, the swing arm 70 is tilted so that the swash plate angle becomes larger than the initial position.

  In the present embodiment, the shape of the guide groove 76a of the volume control plate 76 is such that the same deviation ΔL appears at the time of the inner cut and the outer cut, so that the steering wheel turns left and right by the deviation ΔL. In some cases, the volume of the left and right first hydraulic motors 10 is reduced at the same rate as compared to when traveling straight, and the difference in wheel rotation between the inside and outside of the turn is absorbed by the hydraulic differential effect of the left and right first hydraulic motors 10. Is a thing

  Thus, when the steering case 28 is steered to the left and right from the straight traveling position, the relative displacement amount with respect to the housing 27 is automatically determined based on the straight traveling position of the steering case 28. Since the amount of operation of the swash plate 53 in the direction of increasing the swash plate angle is converted, the steered wheels of the work vehicle 1 can be adapted to the ideal turning speed when turning. In other words, by rotating the handle 16, the rotational speed of both the front wheel 36 and the rear wheel 79 is automatically decelerated without the troublesome operation of reducing the discharge amount of the hydraulic pump 5. Further, the front wheel 36 and the rear wheel 79 simply return to the rotational speed defined by the common hydraulic pump 5 simply by returning the handle 16 to the original straight position. Therefore, a sudden turn of the work vehicle 1 and a zero turn described later can be stably performed, and the turnability of the work vehicle 1 can be further improved.

  The shape of the guide groove 76a of the volume control plate 76 is not limited to this. The left and right shapes of the guide groove 76a may be changed to independently change the tilting amount of the movable swash plate 53 and the oil flow rate to the first hydraulic motor 10 and the second hydraulic motor 80. Further, in order to drive the rear wheel 79, in addition to the steering wheel driving device 13 provided with the left and right second hydraulic motors 80, for example, a single hydraulic motor 80 and left and right rear wheels 79. A structure may be combined with a mechanical differential mechanism that differentially connects 79. The rear wheel 79 may be a non-steered wheel. That is, the steered wheel drive device according to the present invention is applied only to the front wheels.

Next, the hydraulic circuit of the work vehicle 1 will be described below.
In the hydraulic circuit shown in FIG. 11, a first circuit 89 for connecting the first hydraulic motors 10 and 10 to the hydraulic pump 5 is formed in the steering wheel drive devices 15L and 15R for the front wheels 36, and the rear wheels 79 are formed. In the steering wheel driving devices 13L and 13R, a second circuit 90 for connecting the second hydraulic motors 80 and 80 to the hydraulic pump 5 is formed. A charge pump 94 for supplying hydraulic oil and a relief valve 95 are connected to a pair of oil supply / discharge circuits 91 in which the hydraulic pump 5 is disposed via a pair of check valves 96. The oil supply / discharge circuit 91 is connected to the first circuit 89 and the second circuit 90 via a shift switching valve 92. The first circuit 89 has a pair of main oil passages 89a and 89b that connect the first hydraulic motors 10 and 10 in parallel to each other, and the second circuit 90 connects the second hydraulic motors 80 and 80 in parallel to each other. A pair of main oil passages 90a and 90b is provided.

  Both of the main oil passages 89a and 89b of the first circuit 89 are connected to the shift switching valve 92. One of the main oil passages 90 b of the second circuit 90 is connected to the shift switching valve 92, and the other main oil passage 90 a of the second circuit 90 is connected to one side of the oil supply / discharge circuit 91 via the oil passage 100. Connected with. Electromagnetic switching valves 98 and 99 for differential lock are provided on the suction side and suction side of the first hydraulic motor 10 and the second hydraulic motor 80, respectively, and are electrically switched by a current on / off operation to the solenoids 98a and 99a. The first and second hydraulic motors 10 and 10 and the second hydraulic motor 80 are routed to the first hydraulic motor 10 and the second hydraulic motor 80 under the flow rate adjustment through the constant capacity diversion valve 108 and the check valve. A circuit configuration (diff lock position) in which the two hydraulic motors 80 and 80 are connected in parallel, and the first hydraulic motors 10 and 10 and the second hydraulic motors 80 and 80 are connected in parallel without adjusting the flow rate, respectively. It is configured to be switched to a circuit form (unlock position). Through the constant-capacity diversion valve 108, the flow rate of oil flowing from the hydraulic pump 5 to the left and right first hydraulic motors 10 and 10 is forcibly equalized, and the left and right front wheels 36 and 36 and the rear wheel 79 are forced to equalize. -It is controlled so that the rotational speed of 79 becomes equal. Details will be described later.

  The shift switching valve 92 is a manual valve that is mechanically linked and interlocked with a switching operation means 93 such as a lever. In this embodiment, the shift switching valve 92 can be switched to three positions L, M, and H. The switching operation means 93 may be switched by a hydraulic actuator or the like for ease of operation and control. When the shift switching valve 92 is operated to the position L by the switching operation means 93, the first circuit 89 and the second circuit 90 are connected in parallel. That is, the hydraulic pump 5 is set so as to be discharged from the port on the left side of the drawing when the vehicle moves forward, and the pressure oil discharged from the hydraulic pump 5 passes through the shift switching valve 92 and the oil path 100 to the first circuit 89. The main oil passage 89a and the main oil passage 90a of the second circuit 90 are sent to the main oil passage 89a so as to be distributed. The return oil after driving the first and second hydraulic motors 10 and 80 is collected in the shift switching valve 92 from the main oil passages 89b and 90b and sucked into the hydraulic pump 5. In such a case, the left and right front wheels 36 and 36 and the rear wheels 79 and 79 are driven, and the work vehicle 1 is optimal for heavy traction work and can be driven at a low speed with four-wheel drive excellent in climbing performance.

  When the shift switching valve 92 is operated to the position M, the first circuit 89 and the second circuit 90 are connected in series. That is, the pressure oil from the hydraulic pump 5 is discharged from the port on the left side of the page when the vehicle moves forward, but is first sent from the oil supply / discharge circuit 91 to the main oil path 90a of the second circuit 90 via the oil path 100. After the second hydraulic motor 80 is driven, it is sent to the main oil passage 89a of the first circuit 89 via the gear change valve 92, and after the first hydraulic motor 10 is driven, the gear change is switched from the main oil passage 89b. It is sucked into the hydraulic pump 5 through the valve 92. In such a case, the left and right front wheels 36 and 36 and the rear wheels 79 and 79 are driven, but the work vehicle 1 is faster and more efficient in operation than the case where the above-described shift switching valve 92 is operated to the position L. Medium speed running with four-wheel drive is possible. When the first circuit 89 and the second circuit 90 are connected in series rather than being connected in parallel, the total amount of oil discharged from the hydraulic pump 5 is sent to the second hydraulic motor 80, This is because it can then be fed into the first hydraulic motor 10.

  When the shift switching valve 92 is operated from the position L or the position M to the position H, the oil supply to the first circuit 89 is stopped, and the oil supply / discharge circuit 91 and the second circuit 90 Are connected via a shift switching valve 92. That is, the pressure oil from the hydraulic pump 5 is sent to the shift switching valve 92 via the second circuit 90, and the two-wheel drive is performed by driving only the rear wheels 79 and 79. Oil circulation when the first hydraulic motor 10 that is not sent to the first circuit 89 and stops driving is pumped during travel is permitted via the shift switching valve 92. 89c is an oil replenishment check valve for preventing negative pressure in the circuit due to oil leakage at various points when oil circulates in the first circuit 89.

  In this way, a hydraulic circuit capable of supplying oil individually from the hydraulic pump 5 to the first hydraulic motor 10 and the second hydraulic motor 80 disposed in each of the steering wheel drive devices 13 and 15 is formed. . Therefore, by controlling the flow direction of the pressure oil sent to the first hydraulic motor 10 and the second hydraulic motor 80, the drive speeds of the left and right front wheels 36 and 36 and the rear wheels 79 and 79 can be easily synchronized. It can be increased or decreased. Further, it can be easily switched to four-wheel drive or two-wheel drive.

  Further, since the operation of the discharge amount and the discharge direction of the hydraulic pump 5 can be performed continuously, it is used as a main transmission that can be operated during traveling, and the first hydraulic motor 10 and the second hydraulic motor 80 are operated by the shift switching valve 92. By switching the oil flow rate in stages and selecting the speed range according to the driving situation, the rotational speeds of the left and right front wheels 36 and 36 and the rear wheels 79 and 79 are comprehensively determined. The speed can be changed over a wide range. In this embodiment, when the hydraulic pump 5, the first hydraulic motor 10, and the second hydraulic motor 80 are connected in series, the oil discharged from the hydraulic pump 5 when the vehicle moves forward is driven first by the rear wheels. However, due to the characteristics of the vehicle, the rear wheel is firmly grounded to the road surface even when the front wheel is lifted due to the center of gravity moving backward when suddenly starting. This is because driving torque is reliably transmitted to the ground to improve running stability.

  The first and second hydraulic motors 10 and 80 may be fixed displacement type as long as it is not necessary to change the speed in conjunction with the steering angle of the front and rear wheels as described above. If a variable displacement type interlocking with the shift switching valve 92 is employed on the second hydraulic motor 80 side, the vehicle speed is further increased when the two-wheel drive state is set at the position H of the shift switching valve 92 as shown in FIG. You can plan up.

Here, the electromagnetic switching valves 98 and 99 will be described in detail below.
In this embodiment, the amount of inflow into the left and right of the first hydraulic motors 10 and 10 and the right and left of the second hydraulic motors 80 and 80 is limited, and the number of rotations thereof can be controlled. By providing the switching valves 98 and 99 in the first and second circuits 89 and 90, the rotational speeds of the left and right sides of the first hydraulic motors 10 and 10 and the left and right sides of the second hydraulic motors 80 and 80, respectively, It can be controlled according to various conditions of the vehicle.

  As such a control function, specifically, there is a differential lock function for controlling the left and right front wheels 36 and 36 and the rear wheels 79 and 79 so that the rotational speeds are forcibly equal. The electromagnetic switching valves 98 and 99 have two positions, that is, an unlock position shown in the drawing and a differential lock position on the right side of the drawing. Of the solenoids 99a and 99b provided in each valve, the solenoid 99a is a differential lock-unlock when the vehicle is moving forward. The lock is switched, and the solenoid 99b switches between diff lock and unlock when the vehicle is moving backward. That is, when the vehicle is moving forward, both the solenoids 98a and 99a are de-energized and the electromagnetic switching valves 98 and 99 are in the unlocked position, and the loads acting on the left and right front wheels 36 and 36 and the rear wheels 79 and 79, respectively. Accordingly, hydraulic differential functions appear on the left and right sides of the first hydraulic motors 10 and 10 and on the left and right sides of the second hydraulic motors 80 and 80, respectively.

  Here, when it is detected by a sensor or the like that the driver has stepped on the differential lock pedal (not shown) due to one wheel being removed, the controller (not shown) excites the solenoid 99a and the electromagnetic switching valve 9 In FIG. 5, the hydraulic oil is switched from the unlock position shown to the adjacent differential lock position, and the pressure oil fed to the left and right sides of the first hydraulic motors 10 and 10 and the left and right sides of the second hydraulic motors 80 and 80 is Therefore, the left and right front wheels 36 and 36 and the rear wheels 79 and 79 are differentially locked.

  In this embodiment, each of the left and right front wheels 36 and 36 and the rear wheels 79 and 79 is configured to have a differential lock function. However, only the left and right front wheels 36 and 36 or the rear wheels 79 and 79 have a differential lock function. A function may be obtained. In that case, in the first circuit 89 or the second circuit 90, the electromagnetic switching valves 98 and 99, the constant flow diversion valve 108 and the check valve are removed, and the first hydraulic motors 10 and 10 or the second hydraulic motors 80 and 80 are removed. May be connected in parallel to the pair of main oil passages 89a and 89b or 90a and 90b.

  Further, a so-called limited slip differential (LSD) function for temporarily limiting the hydraulic differential function in accordance with the rotation state of the rear wheels 79 and 79 without requiring a driver's differential lock operation is used. -It is possible to prepare for 13R. In other words, the second hydraulic motor 80 includes three circuit configurations (first, second, and third circuit configurations) connected in parallel. According to the hydraulic circuit in the present embodiment, the circuit configuration can be changed purely hydraulically / mechanically without electronic control. Hereinafter, the second circuit 90 will be described, but the same applies to the first circuit 89, and furthermore, it may be applied to only one of the circuits.

  As shown in FIG. 12, the second circuit 90 in this embodiment includes a first circuit configuration in which the second hydraulic motors 80 and 80 are fluidly connected in parallel to the hydraulic pump 5, and a second hydraulic motor 80. A second circuit configuration for limiting the amount of oil fed to one of the second hydraulic motors 80 and 80 while fluidly connecting 80 to the hydraulic pump 5 in parallel, and the second hydraulic motors 80 and 80 Can be switched to a third circuit configuration that restricts the amount of oil fed to the other of the second hydraulic motors 80 and 80 while fluidly connecting to the hydraulic pump 5 in parallel. That is, in the first circuit 89, an LSD valve 109 for switching from the first circuit configuration to the second or third circuit configuration is arranged on the upstream side of the second hydraulic motors 80 and 80 at the time of forward movement. Has been. A pressure receiving chamber having a neutral return spring is formed at both ends of the LSD valve 109 to constitute a reciprocating switching type hydraulic pilot valve.

  On the downstream side of each of the second hydraulic motors 80 and 80, switching valves 110L and 110R that operate in an integrated manner are disposed via a connecting portion 110a. At the time of forward movement, the switching valves 110L and 110R are at the illustrated positions by the pilot pressure based on the hydraulic pressure flowing through the main oil passage 90a on the upstream side of the second hydraulic motors 80 and 80 (and the LSD valve 109). The return oil after driving the hydraulic motors 80 and 80 is sent to the main oil passage 90b via the check valve, and at the same time, pilot pressure is sent to each pressure receiving chamber of the LSD valve 109, and it is switched during reverse travel. The valves 110L and 110R are switched from the illustrated position to the left adjacent position by the pilot pressure based on the hydraulic pressure of the main oil passage 90b on the upstream side of the pump, and the hydraulic pressure of the main oil passage 90b is sent without sending the pilot pressure to the LSD valve 109. It is comprised so that it may send in into the 2nd hydraulic motor 80 * 80.

  The LSD valve 109 has left and right second hydraulic motors 80 and 80 connected in parallel at the center position N, and the left and right second hydraulic motors 80 and 80 are connected at flow rate adjustment positions A and B on both sides of the center position N. The flow rate to one of the hydraulic motors is reduced while being connected in parallel. In a state where the amount of oil flowing into each of the pressure receiving chambers is substantially equal, the LSD valve 109 is biased to the central position N by the opposing spring forces in both directions. Then, the discharge oil amount (return oil amount to the hydraulic pump 5 after passing through the second hydraulic motors 80, 80) of either one of the second hydraulic motors 80, 80 is greater than a certain amount. At the time, the flow is automatically switched to one of the flow rate adjustment positions A and B against the spring biasing force.

  When the vehicle is traveling straight forward, the load applied to the left and right rear wheels 79L and 79R is substantially equal, and the amount of return oil discharged from each of the left and right second hydraulic motors 80 and 80 is substantially equal. In this state, for example, when the rear wheel 79L is removed or slips, the load applied to the right second hydraulic motor 80 for driving the rear wheel 79R increases, and the return oil sent from the right second hydraulic motor 80 is small. Become. Conversely, since the load applied to the left second hydraulic motor 80 becomes extremely small, the oil easily flows into the left second hydraulic motor 80, and the return oil discharged therefrom increases. Therefore, when the LSD function is not provided, oil does not flow into the right second hydraulic motor 80 and the drive is stopped. In the present invention, such a situation is avoided, and in such a case, the pilot pressure oil sent from the switching valve 110L is relatively larger than the pilot pressure oil sent from the switching valve 110R. As a result, the LSD valve 109 is switched to the flow rate adjustment position B, and the flow of oil to the left second hydraulic motor 80 with a small load is reduced. Then, the oil flow into the right second hydraulic motor 80 is inevitably performed, and the driving force of the right second hydraulic motor 80 is not interrupted. Therefore, the rear wheel 79R keeps pulling the vehicle forward, so that the vehicle is removed from the wheel or slips. You can escape from.

  On the other hand, if the rear wheel 79R slips, the pilot pressure from the switching valve 110R to the LSD valve 109 becomes relatively higher than the pilot pressure from the switching valve 110L. Therefore, the LSD valve 109 is switched to the flow rate adjustment position A, and the flow of oil to the right second hydraulic motor 80 with a small load is reduced. The driving force of the second hydraulic motor 80 is not interrupted.

  By adopting the above-described configuration, the difference in the amount of return oil from each of the second hydraulic motors 80 and 80 is sensed and the LSD function is exhibited. It should be noted that the spring biasing force of the LSD valve 109 (force held at the center position N) is set so as to exceed the differential pressure of the return oil of the second hydraulic motors 80 and 80 generated at the time of turning. Sometimes the LSD valve 109 is not switched to the flow adjustment positions A and B, and the LSD function for the rear wheels 79L and 79R unless an abnormal situation (extreme load fluctuation) occurs such as when one wheel is removed or slips. Will not appear.

  A steering wheel drive device 15 shown in FIG. 13 is a front wheel supported by a steering case 128 in a four-wheel steering / four-wheel drive work vehicle 1 in which the steering wheel drive device according to the present invention is applied to both front and rear wheels. The high clearance structure in which the housing 127 and the steering case 128 and the like are formed longer in the vertical length than the housing 27 and the steering case 28 and the like shown in FIG. It is. By adopting such a structure, the work vehicle 1 can be turned with a small turning radius, and can be turned by turning the handle (not shown) to the maximum. Hereinafter, the steering wheel drive device 15 applied to the front wheel 36 will be described, but the same applies to the steering wheel drive device 13 applied to the rear wheel 79.

  The steering wheel drive device 15 is pivotally supported so that the knuckle arm 32 and the steering case 128 can rotate together as a unit via a housing 127 fixed to a mounting stay 26 protruding from the cross member 14. ing. In the housing 127, the first hydraulic motor 10, the motor volume control mechanism 43, and the like are disposed. The steering case 128 is provided with an axle 131, a speed reduction mechanism 129, a brake mechanism 39, and the like. A front wheel 36 as a steering wheel is fixed to the outer end of the axle 35 so as to be driven. The lower opening portion of the housing 127 is inserted into the upper end portion of the steering case 128 so that the king pin portion 127a of the housing 127 can rotate relative (left and right).

  The vertical length L1 of the king pin portion 127a of the housing 127 and the receiving tube portion 128c of the steering case 128 is formed to be longer, and the axis line of the axle 131 is set to be vertically higher than the axis line of the transmission shaft 130 of the steering case 128b. The shaft arrangement is such that the length L2 is offset downward. In this embodiment, an internal gear type single reduction gear mechanism is configured as the reduction mechanism 129 disposed in the steering case 128.

  As shown in FIG. 14, the motor shaft 56 of the first hydraulic motor 10 protrudes into the steering case 128 from the lower opening end of the kingpin portion 127a of the housing 127, and a small bevel gear 58 is fixed to the protruding portion. Further, the steering case 128 is horizontally provided so that the transmission shaft 130 and the axle 131 are substantially parallel to each other, and the axle 131 is positioned below the transmission shaft 130 in the vertical direction. One end of the transmission shaft 130 is supported by the inner steering case 128 b and the other end is supported by the bearing plate 132. A large bevel gear 60 is loosely fitted on the inner side (right side in FIG. 14) of the transmission shaft 130 so as to be rotatable relative to the transmission shaft 130.

  The large bevel gear 60 is meshed with the small bevel gear 58. A spline hub 62 a is fixed on the transmission shaft 130 on the outer side of the large bevel gear 60. A clutch cliner 62b is fitted to the spline hub 62a so as to be axially slidable and relatively non-rotatable, and the spline hub 62a can be connected to the clutch teeth 60a of the large bevel gear 60 to constitute an axle clutch 61. ing. Further, an internal gear 133 is fitted to the inner end portion of the axle 131 so as not to be relatively rotatable, and the inner teeth 133a of the internal gear 133 are connected to the outer teeth 130b engraved on the outer end portion of the transmission shaft 130. Meshed.

  Then, the rotation of the cylinder block 51 of the first hydraulic motor 10 is transmitted to the motor shaft 56 → the small bevel gear 58 → the large bevel gear 60 → the axle clutch 61 → the transmission shaft 130 → the internal gear 133 → the axle 131 → the front wheel 36, The work vehicle 1 is allowed to travel.

  By adopting the high clearance configuration as described above, a space can be secured below the vehicle frame 2 so that the front wheel 36 and the rear wheel 79 can turn around without interference when the front wheel 36 and the rear wheel 79 are steered. The maximum inner cutting angle can be increased, and the turning performance of the work vehicle 1 can be further improved. In particular, the front wheel 36 and the rear wheel 79 are rotated by the same angle although they are opposite to the rotation direction of the handle 16 by the rotation operation of the handle 16, and the work vehicle 1 is turned to the left or right. In this case, the turning radius of the front wheel 36 and the turning radius of the rear wheel 167 can be made equal, and the work vehicle 1 can be turned in the interlining. Therefore, the steerability is improved and the work efficiency is further improved.

  Specifically, as shown in FIG. 15, when the handle 16 is turned to the left and FIG. 15 is turned to the left through the state of FIG. 5, the handle 16 is turned to the left ( When the maximum break occurs, the turning center point 110 moves to the vehicle frame 2 side while the turning radius 111a of the front wheel 36 and the turning radius 112a of the rear wheel 79 remain substantially equal. Thus, it substantially overlaps the center between the front and rear wheels of the work vehicle 1 and between the left and right wheels. In such a case, the work vehicle 1 is zero-turned around the turning center point 110 without traveling in any direction.

(Second embodiment)
The work vehicle 1 according to this embodiment shown in FIG. 16 is a two-wheel steering / four-wheel drive type, and the steering wheel driving devices 15L and 15R that support the front wheels 36 so as to be steerable and drivable are provided on the vehicle frame 2. Non-steered wheel drive devices 141L and 141R that are mounted at the front and support the rear wheels 140 so that they cannot be steered and can be driven are mounted at the rear of the vehicle frame 2.

  As shown in FIG. 16, at the front part of the vehicle frame 2, a pair of left and right steering wheel drive devices 15L and 15R each having a front wheel 36 as a steering wheel are provided at the center pin in the width direction center of the vehicle frame. A pair of left and right non-steering wheel drive devices 141L and 141R, which are arranged so as to be rotatable left and right around the CP, and each have rear wheels 140 which are non-steering wheels, are provided at the rear of the vehicle frame 2. It is arranged so that position change (left-right rotation) is impossible. The steering wheel drive devices 15L and 15R are provided with variable displacement type first hydraulic motors 10 and 10, respectively, and the non-steering wheel drive devices 141L and 141R are provided with variable displacement type second hydraulic motors 138 and 138, respectively. Yes.

Here, the non-steered wheel drive devices 141L and 141R applied to the rear wheels 140 and 140 will be described in detail below.
As shown in FIG. 17, the non-steered wheel drive device 141L is provided with a second hydraulic motor 138 fluidly connected to the hydraulic pump 5, a speed reduction mechanism 38, a brake mechanism 39, and the like. About the structure of the deceleration mechanism 38, the brake mechanism 39, etc., it is the same as that of the structure in the above-mentioned steering wheel drive device 15, The description about the same code | symbol is abbreviate | omitted. The second hydraulic motor 138 may be a fixed displacement type, but in this embodiment, a variable displacement type is used for the reason described later, and the volume is changed by the external actuator 101 connected to the movable swash plate 139. The

  A substantially L-shaped bracket 142 in front view is fixed to the rear outer surface of the vehicle frame 2, and the upper plane of the center section 41 of the second hydraulic motor 138 is attached to the lower plane of the bracket 142. A second hydraulic motor 138 connected to the center section 41 is disposed in the drive case 144. The drive case 144 is fixed to the vehicle frame 2 so as not to be steered, and is arranged in the rear discharge duct 74. Located on the side.

  The drive case 144 includes an inner drive case 144a and an outer drive case 144b that are divided into left and right halves, and the inner drive case 144a is partitioned into an upper housing portion 144c and a lower housing portion 144d. The second hydraulic motor 138 is disposed along the substantially vertical direction in the upper housing portion 144c, the motor shaft 146 of the second hydraulic motor 138 protrudes into the lower housing portion 144d, and the small bevel gear 58 is formed in the protruding portion. Is fixed. A transmission shaft 59 is provided laterally on the lower housing portion 144d, and an inner end portion of the transmission shaft 59 is cantilevered by the inner drive case 144a. The transmission shaft 59 is provided with a large bevel gear 60, an axle clutch 61, and the like that mesh with the small bevel gear 58 to form a bevel gear type reduction mechanism. The outer drive case 144b is provided with an axle 145 on the same axis as the transmission shaft 59, and the axle 145 and the transmission shaft 59 are connected to each other via a planetary gear type reduction mechanism 38. One end of the axle 145 protrudes from the outer surface of the outer drive case 144b toward the outside of the work vehicle 1, and a rear wheel (not shown) is fixed to a hub 145a formed at the protruding end. Although the description is omitted, the non-steered wheel drive device 141R has a similar configuration arranged symmetrically.

  In the configuration as described above, as shown in FIG. 18, when the work vehicle 1 is turned, when the sizes of the turning radii 111a and 112a of the front wheels 36 and the rear wheels 140 are compared, the turning radius 111a of the front wheels 36 is Is bigger. This is because the turning center point 110 does not appear between the front wheel 36 and the rear wheel 140 when the front wheel 36 is steered by the handle 16 while the rear wheel 140 is not steered left and right. This is because it appears on the rotational axis of the rear wheel 140. Therefore, in order to obtain a smooth turn in the four-wheel drive state, it is necessary to increase the rotational speed of the front wheel 36 relative to the rear wheel 140 at a rate commensurate with this turning radius difference. In the present invention, as described later, Although the first hydraulic motor 10 and the second hydraulic motor 138 rotate synchronously when traveling straight, the volume of the first hydraulic motor 10 is automatically reduced when the handle 16 is turned. By increasing the speed of the front wheel 36, the turning performance of the work vehicle 1 is enhanced.

Therefore, the motor volume control mechanism 43 of the steering wheel drive device 15 as the front wheel 36 will be described in detail below.
As described above, in the present embodiment, the turning radius 111a of the front wheel 36 is larger than the turning radius 112a of the rear wheel 140, and therefore the tilt angle of the movable swash plate 53 of the first hydraulic motor 10 is set to a straight angle. A motor volume control mechanism 43 that automatically changes from the initial position to a predetermined volume reduction position according to the turning state is configured. Hereinafter, the configuration of the steered wheel drive device 15 is substantially the same as that of the first embodiment, the description of the same reference numerals is omitted, and the motor volume mainly constituted by the combination of the control arm 71 and the volume control plate 176. The action of tilting the movable swash plate 53 in the control mechanism 43 will be described in detail.

  As shown in FIG. 19, in the present embodiment, the piston contact surface of the movable swash plate 53 is tilted in the direction perpendicular to the motor shaft as the steering case 28 rotates left and right from the straight position. It is comprised as follows. Specifically, the guide groove 176a of the volume control plate 76 fixed to the upper surface of the steering case 28 is V-shaped so as to be recessed downward from the left and right ends to substantially the center. The guide groove 176a is inclined from the bottom position P1 to the left and right along the shape of the guide groove 176a, and the end positions of the inclined surfaces are formed to be the position P2 and the position P3, respectively. Further, since the deviation, which is the height difference from P1 to position P2 and position P3, is ΔL, the inner cutting angle of the wheel is larger than the outer cutting angle, so that the position until reaching position P2 from position P1. Is longer than the distance from the position P1 to the position P3.

  In the volume control plate 176 formed in this way, the state in which the engagement pin 75 disposed at the tip of the control arm 71 is placed at the position P1 defines the initial capacity of the first hydraulic motor 10 when traveling straight. ing. When the left front wheel 36 is turned to the left, the state where the engagement pin 75 of the control arm 71 reaches the terminal position P2 of the guide groove 76a is the maximum inner cutting position of the front wheel 36, and the guide groove 176a The state of reaching the end position P3 is the maximum outer cutting position of the front wheel 36.

  As shown in FIG. 19A, in conjunction with the steering operation of the steering case 28, the guide groove 176a of the volume control plate 176 is rotated relative to the engagement pin 75 of the control arm 71, and the engagement pin 75 Is slidably contacted on the guide groove 176a of the volume control plate 176 so as to be from the position P1 to the position P2 or from the position P1 to the position P3. Due to the V-shaped guide groove 176a, the control arm 71 is always rotated in a certain direction regardless of the direction in which the handle 16 is cut about the control shaft 69 (hereinafter, this direction is referred to as the Y direction). Is rotated by a deviation ΔL via the engagement pin 75. When the control arm 71 is rotated in the Y direction, the swing arm 70 is rotated in conjunction with the control shaft 69, and the movable swash plate 53 is moved by the swing arm 70 as in the first embodiment. On the other hand, the piston abutment surface is tilted so as to approach a direction perpendicular to the motor shaft.

  On the other hand, as shown in FIG. 19B, when the control arm 71 is rotated in the Y direction, one end side of the return spring 73 is stopped by the eccentric pin 77 and the other end side is engaged with the control arm 71. The pin 72 is expanded. Therefore, the return spring 73 gives the control arm 71 a biasing force to the initial volume position of the motor defined by the eccentric pin 77. Therefore, when the handle 16 is returned to the straight-ahead position and the steering case 28 is rotated to the original state again, the control arm 71 holds the initial volume position of the motor by the biasing force of the return spring 73. is there.

  As described above, when the steering case 28 is steered to the left and right from the straight traveling position, the relative displacement amount with respect to the housing 27 with respect to the straight traveling position of the steering case 28 is automatically determined as the movable swash plate of the first hydraulic motor 10. 53, the steering wheel of the work vehicle 1 is rotated so as to match the ideal turning speed when turning, and the steering performance described above is further improved. Enhanced.

Next, the hydraulic circuit of the work vehicle 1 will be described below.
In the present embodiment, the steering wheel drive devices 15L and 15R each including the first hydraulic motors 10 and 10 according to the present invention are arranged on one side of the work vehicle, and the second hydraulic motor 138. Non-steered wheel drive devices 141L and 141R having 138 are arranged symmetrically in the longitudinal direction, and main oil passages 89a and 89b of the first hydraulic motors 10 and 10 and main oil of the second hydraulic motors 138 and 138 are arranged. The hydraulic circuit that fluidly connects the passages 150a and 150b to the common hydraulic pump 5 is substantially the same as FIG. 11 described in detail, as shown in FIG. The description thereof is omitted.

  That is, if the shift switching valve 92 is at the position L shown in the figure, the low-speed four-wheel drive state in which the first hydraulic motor 10 and the second hydraulic motor 138 are connected in parallel to the hydraulic pump 5, or the position M If there is, the first hydraulic motor 10 and the second hydraulic motor 138 can be switched to the hydraulic pump 5 so as to be in a high-speed four-wheel drive state. When the shift switching valve 92 is operated from the position L or the position M to the position H, the oil supply to the first circuit 89 is stopped, and the oil supply / discharge circuit 91 and the second circuit 90 are stopped. Are connected via a shift switching valve 92. That is, the pressure oil from the hydraulic pump 5 is sent to the second circuit 150 via the shift switching valve 92, and the two-wheel drive is performed by driving only the rear wheels 140 and 140. At this time, the hydraulic pressure generated by the pump action of the first hydraulic motor 10 due to the rotation of the front wheel 36 is circulated in the first circuit 89 via the shift switching valve 92. 89c is an oil replenishment check valve for preventing negative pressure in the circuit due to oil leakage at various points when oil circulates in the first circuit 89. As long as it is sufficient to provide the four-wheel drive / two-wheel drive switching function at the position H of the shift switching valve 92, it is not necessary to use a variable displacement type as the hydraulic motor 80, as will be described later.

  In the present embodiment, the following configuration is employed in order to obtain another shift step number at this position H. That is, the sensor 103 disposed in the vicinity of the switching operation means 93 detects that the shift switching valve 92 has been operated to the position H, and is connected to the movable swash plates 139 and 139 of the second hydraulic motors 138 and 138. By the external actuator 101, the swash plate angles of the movable swash plates 139 and 139 are tilted at the same rate in the direction of reducing the volumes of both motors. As a result, the rotational speed of the second hydraulic motors 138 and 138 becomes faster than when the shift switching valve 92 is operated to the position L and position M, and economical high-speed traveling by two-wheel drive is possible. Instead of using the external actuator 101, the switching operation means 93 and the movable swash plates 139 and 139 may be mechanically linked with each other using a rod or a wire.

  By adopting such a configuration, the work vehicle 1 can be easily switched from four-wheel drive to two-wheel (rear wheel) drive, particularly by switching so that oil is fed only into the second circuit 150. . In this embodiment, the oil in the hydraulic circuit is sent only to the second hydraulic motor 138 and tilted so that the swash plate angle of the movable swash plate 139 of the second hydraulic motor 138 is smaller than that in the case of four-wheel drive. Thus, the driving speed of the rear wheels 140 and 140 is increased. For this reason, the traveling performance of the work vehicle 1 is enhanced by high-speed traveling by two-wheel drive. For example, when such switching is instantaneously performed when traveling on a flat ground, the traveling time is shortened and the working efficiency is good.

  In the present embodiment, each of the rear wheels 140 and 140 is driven by the second hydraulic motor 138, but the present invention is not limited to this. That is, the non-driving wheel drive device 141 is not necessarily configured by the pair of left and right second hydraulic motors 138. For example, the single second hydraulic motor 138 and the rear wheels 140 and 140 are mechanically different from each other. It is good also as a structure which combined with the differential mechanism to connect dynamically. If the various gears and the like constituting the reduction gear train of the non-steering wheel drive device 141 are shared with those of the steering wheel driving device 15, the production cost can be further reduced by sharing the parts.

  Further, as shown in FIG. 21, in the hydraulic circuit, a part of the hydraulic circuit shown in FIG. 20 is changed so that the second hydraulic motors 138 and 138 that drive the left and right rear wheels 140 are connected to the hydraulic pump 5. When connecting in parallel, the circuit configuration that does not restrict the oil feed to both motors and the two circuit configurations that restrict the oil feed to either the left or right motor (first, second, second) Three circuit forms). In such a case, the rear wheel 140 is changed according to the difference in the amount of return oil from each of the second hydraulic motors 138 and 138 without changing electronically, as in FIG. On the other hand, a hydraulic limited slip differential function appears. The same circuit configuration can be adopted not only for the rear wheels 140 and 140 but also for the first hydraulic motors 10 and 10 that drive the left and right front wheels 36 and 36.

  In addition, although the mid-mount mower type riding lawn mower was cited as an embodiment of the working vehicle, the present invention is not limited thereto, and the riding lawn mower may be a front-mount mower type. Utility tractors and construction machines may be used.

1 is a plan view showing an overall configuration of a work vehicle according to a first embodiment of the present invention. 1 is a schematic plan view of a steering mechanism used in the first embodiment. The rear surface sectional view of the steering wheel drive device applied to the left front wheel. Brief description of the steering mechanism showing the turning state of the work vehicle. The top view showing the turning state of a work vehicle. FIG. 4 is a rear enlarged cross-sectional view of the upper part of the steering wheel drive device in FIG. 3. The lower part expanded rear sectional view of a steering wheel drive device similarly. The upper top view of the housing which removed the center section. AA arrow sectional drawing in FIG. Explanatory drawing which shows the operating state of the motor volume control mechanism at the time of straight advance and turning. 1 is a hydraulic circuit diagram according to a first embodiment. The hydraulic circuit diagram which changed a part of hydraulic circuit diagram of FIG. The rear surface sectional view which changed the steering wheel drive device in FIG. 3 into the high clearance specification. FIG. 14 is a rear enlarged rear cross-sectional view of the steering wheel drive device in FIG. 13. The top view which shows the whole structure of the work vehicle to which the steering wheel drive device of FIG. 13 is applied. The top view which shows the whole structure of the working vehicle which concerns on the 2nd Example of this invention. Front sectional drawing of the non-steering wheel drive device applied to the left rear wheel. The top view showing the turning state of a work vehicle. Explanatory drawing which shows the operating state of the motor volume control mechanism at the time of straight advance and turning. The hydraulic circuit figure concerning a 2nd example. The hydraulic circuit diagram which changed a part of hydraulic circuit diagram of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Work vehicle 2 Vehicle frame 3 Engine 4 Mower 5 Hydraulic pump 10 1st hydraulic motor 13, 15 Steering wheel drive device 14, 78 Cross member 27, 127 Housing 27a, 127a Kingpin part 28, 128 Steering case 36 Front wheel 38, 129 Deceleration Mechanism 39 Brake mechanism 43 Motor volume control mechanism 53, 139 Movable swash plate (volume controller)
74 Duct 79, 140 Rear wheel 80, 138 Second hydraulic motor 141 Non-steered wheel drive device

Claims (9)

  Steering wheel drive device having a housing with a built-in hydraulic motor for driving an axle fixed to a vehicle frame, a steering case for supporting a single axle, and a steering wheel fixed to an end of the single axle The steering wheel drive device is characterized in that the steering case is disposed so as to be rotatable with respect to the vehicle frame via a kingpin portion extending downward from the housing.   In the steering case, the output shaft of the hydraulic motor as the axis of the kingpin portion is rotatably inserted from the upper side with respect to the single axle supported substantially horizontally on the outer side, and the output shaft is connected to the steering case. 2. The steered wheel drive device according to claim 1, wherein the steered wheel drive device is linked to the axle by a reduction gear train disposed in the steering case.   3. The steered wheel drive device according to claim 1, wherein the hydraulic motor is a variable displacement type, and the volume of the hydraulic motor is changed by a relative displacement between the housing and the steering case. .   At least one of the front and rear drive wheels is configured to be steerable, and is a work vehicle including a first hydraulic motor and a second hydraulic motor that drive each of the front and rear drive wheels, the first and second hydraulic motors A common hydraulic pump that supplies oil to the hydraulic pump is provided, and both hydraulic motors are connected in series to the hydraulic pump in a hydraulic circuit that fluidly connects the first and second hydraulic motors to the hydraulic pump. A four-wheel drive vehicle comprising a shift valve that can be switched between a connected state and a state connected in parallel.   The first hydraulic motor connected to the steerable drive wheel is a variable displacement type, and the volume controller of the hydraulic motor changes the volume of the hydraulic motor in conjunction with the steering operation of the steerable drive wheel. The four-wheel drive vehicle according to claim 4, wherein the four-wheel drive vehicle is linked to the steering mechanism of the steerable drive wheel.   5. The shift switching valve can be switched to a state in which oil from the hydraulic pump is allowed to flow only to one of the two hydraulic motors in addition to the parallel connection state and the serial connection state. Or the four-wheel drive vehicle of 5.   The vehicle is configured to connect the first hydraulic motor to a steerable drive wheel, and to connect the second hydraulic motor to a non-steerable drive wheel, and the second hydraulic motor is a variable displacement type. And the volume controller of the hydraulic motor is operated in a direction to reduce the volume of the hydraulic motor when the shift switching valve is switched to flow the oil from the hydraulic pump only to the second hydraulic motor. The four-wheel drive vehicle according to claim 6, wherein the four-wheel drive vehicle is linked to the shift switching valve.   A pair of at least one of the first and second hydraulic motors is connected to each of the left and right drive wheels, and the pair of first or second hydraulic motors are parallel to the hydraulic pump. A first circuit configuration that fluidly connects to the hydraulic pump and a second circuit configuration that splits and supplies oil to both hydraulic motors while adjusting the flow rate while fluidly connecting in parallel to the hydraulic pump. 5. The four-wheel drive vehicle according to claim 4, further comprising a hydraulic circuit configured to be settable in any of the first and second circuit configurations.   A pair of at least one of the first and second hydraulic motors is connected to each of the left and right drive wheels, and the pair of first or second hydraulic motors are parallel to the hydraulic pump. A first circuit form that is fluidly connected, a second circuit form that restricts the flow rate of oil supplied to one hydraulic motor while being fluidly connected in parallel to the hydraulic pump, and a parallel form to the hydraulic pump A third circuit configuration that restricts the flow rate of oil supplied to the other hydraulic motor while fluidly connected to the hydraulic motor, and the amount of oil discharged from one hydraulic motor based on the difference in the amount of oil discharged from each hydraulic motor When the amount of oil discharged from the other hydraulic motor is smaller than that of the first hydraulic circuit, the amount of oil discharged from the other hydraulic motor is compared to the amount of oil discharged from the first hydraulic motor. The first time to increase Four-wheel drive vehicle according to claim 4, wherein the the circuit form a third circuit embodiment is provided with a hydraulic circuit that is configured to be switched automatically.