JP3196485B2 - Four-wheel drive vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive vehicle in which the rotational driving force of a main engine is transmitted to a front wheel and a rear wheel, and in particular, the driving force is transmitted by a hydraulic pressure transmission mechanism. It relates to a four-wheel drive vehicle.

[0002]

2. Description of the Related Art In a four-wheel drive vehicle of this type, in the case of a four-wheel drive vehicle in which the mechanical connection between two-wheel drive and four-wheel drive is manually switched as in a part-time system, the switching operation is performed. In addition to being troublesome, it has problems such as tight corner braking and is not suitable for passenger cars. On the other hand, a full-time four-wheel drive vehicle can eliminate the tight corner braking phenomenon, but requires a differential limiting device in the center differential, which complicates the device. In addition, regardless of the part-time type and full-time type, the current drive system used for passenger cars has a propeller shaft, which increases the weight of the front-wheel drive vehicle, adversely affects the cabin space, deteriorates fuel efficiency, Noise and vibration deteriorate, and even in the case of rear-wheel-drive vehicles, weight increase and fuel economy are inevitable.

Therefore, conventionally, for the purpose of reducing the weight of constituent members, for example, Japanese Patent Laid-Open Publication No.
Power transmission of a four-wheel drive vehicle having front wheels driven directly by a prime mover and rear wheels driven through a clutch operated by fluid pressure, as described in the first conventional example). A first device driven in conjunction with the front wheel
A fluid pressure pump, a second fluid pressure pump driven in conjunction with the rear wheel, and a connecting oil passage communicating and connecting a discharge port of the first fluid pressure pump and a suction port of the second fluid pressure pump. A hydraulic supply oil passage for connecting and connecting the connecting oil passage and an operating hydraulic chamber of the fluid pressure clutch, wherein the first hydraulic pump and the second hydraulic pump are driven by a rotational speed difference between a front wheel side and a rear wheel side. There has been proposed a four-wheel drive vehicle in which transmission of driving force is controlled by controlling a clutch in accordance with a flow difference between two fluid pressure pumps.

For the purpose of transmitting a driving force by using a hydraulic transmission instead of a propeller shaft, for example, Japanese Patent Laid-Open No. 1-223030 (hereinafter referred to as a second conventional example).
As described in, a first hydraulic pump that is configured to rotate in conjunction with the front wheels and generates a hydraulic pressure according to the rotation speed, for example, a vane pump, and that rotates in conjunction with the rear wheels to generate hydraulic pressure according to the rotation speed A second hydraulic pump which is also formed by a vane pump, and an oil passage which communicates one of the discharge ports and the other of the first and second hydraulic pumps with each other. Has been proposed.

[0005]

However, in the first prior art four-wheel drive vehicle, the propeller shaft can be reduced in weight by limiting the transmission torque, but the propeller shaft is omitted. Therefore, there is an unsolved problem that there is a certain limit to weight reduction and no improvement can be made against the adverse effect on the vehicle interior space.

In the second prior art four-wheel drive vehicle, since the hydraulic transmission is used, the propeller shaft is omitted to reduce the weight, secure the interior space of the vehicle, improve fuel efficiency, reduce noise and noise. Although vibration can be reduced, the front and rear wheels rotate at high speed during high-speed running, which increases the discharge flow rate of the hydraulic pump, thereby increasing piping resistance, and thus increasing drag resistance of the system. The increase in pressure loss causes deterioration of fuel efficiency, and also causes an increase in oil temperature in the system and an increase in oil pressure at the suction port of the second hydraulic pump, so that air bubbles are generated due to an abnormal decrease in pressure and pressure. There is an unsolved problem that cavitation is likely to occur. Here, in order to reduce the pipe resistance when the flow rate is increased, the diameter of the pipe may be increased,
Considering space, cost, etc., it also has certain limits.

In order to suppress such deterioration in fuel consumption during high-speed running, it is conceivable to make the second hydraulic pump variable in capacity so that the flow rate reaches a plateau at a certain vehicle speed or higher. Is a pair of flow paths communicating between the first hydraulic pump and the second hydraulic pump because the suction port and the discharge port are reversed depending on the rotation direction of the rotating shaft because a vane pump is employed as the hydraulic pump. One of the roads is, for example, high pressure side when moving forward, low pressure side when moving backward,
The other is a low-pressure side when moving forward, and a high-pressure side when reversing, so that the low-pressure side and the high-pressure side are reversed depending on the direction of travel of the vehicle. It is necessary to provide differential pressure detecting means in both of the flow paths, and to select these in accordance with the traveling direction of the vehicle, the configuration becomes complicated, and the rotational speeds of the front and rear wheels are substantially equal and the driving force is not transmitted At the time of the no-load operation, the differential pressure detecting means provided on the high pressure side becomes a resistance against the suction of the hydraulic pump, which causes a new problem that cavitation is easily caused.

Accordingly, the present invention has been made in view of the above-mentioned unsolved problems of the prior art, and provides a four-wheel drive vehicle capable of simplifying a capacity control mechanism while suppressing the occurrence of cavitation. It is intended to provide.

[0009]

According to a first aspect of the present invention, there is provided a four-wheel drive vehicle including: a drive axle driven by a main motor; and a drive side driven in conjunction with the drive axle. A fluid pressure driving means, and a driven fluid pressure driving means driven in conjunction with a driven axle, wherein the driving fluid pressure driving means and the driven fluid pressure driving means are connected by a high pressure flow path and a low pressure flow path. In a four-wheel drive vehicle having a fluid pressure transmission mechanism formed by communicating with each other, a differential pressure detecting means is provided in the low-pressure flow path, and the capacity of the driven fluid pressure driving means is changed by the differential pressure of the differential pressure detecting means. A variable control mechanism for performing variable control based on the detected value is provided.

According to a second aspect of the present invention, there is provided a four-wheel drive vehicle, wherein a drive axle driven by a main motor, drive-side fluid pressure drive means driven in conjunction with the drive axle, and a driven axle in association with the driven axle. A four-wheeled vehicle having a driven-side fluid pressure driving means to be driven, and having the driving-side fluid pressure driving means and the driven-side fluid pressure driving means communicating with each other through a high-pressure channel and a low-pressure channel. In the driving vehicle, a forward / backward switching valve is inserted in the high-pressure flow path and the low-pressure flow path on the driven fluid pressure driving means side, and the low-pressure flow on the driving fluid pressure driving means side of the forward / backward switching valve is provided. A differential pressure detecting means is provided on the road, and a variable control mechanism for variably controlling the capacity of the driven fluid pressure driving means based on a differential pressure detection value of the differential pressure detecting means is provided. .

Further, in the four-wheel drive vehicle according to claim 3, the variable control mechanism adjusts the capacity of the driven fluid pressure driving means to the wheel speed if the detected differential pressure value of the differential pressure detecting means is less than a predetermined value. , And is configured to maintain the maximum capacity when it exceeds a predetermined value. Furthermore, the four-wheel drive vehicle according to claim 4 is characterized in that the driven fluid pressure driving means is constituted by a swash plate type variable displacement pump motor which rotates in conjunction with a driven axle.

A four-wheel drive vehicle according to a fifth aspect is characterized in that the drive-side fluid pressure drive means is constituted by a suction throttle type piston pump which rotates in conjunction with a drive axle.

[0013]

In the four-wheel drive vehicle according to the first aspect of the present invention, the working fluid having a flow rate corresponding to the rotation speed is discharged from the drive-side fluid pressure drive means by the rotation of the drive axle driven by the main motor, and the high-pressure flow passage Is supplied to the suction side of the driven fluid pressure driving means driven by the rotation of the driven axle,
The working fluid discharged from the driven fluid pressure driving means is returned to the driving fluid pressure driving means through the low pressure passage. At this time, when the rotational speed difference between the drive axle and the driven axle is small, there is almost no transmission torque and the two-wheel drive state is maintained.
As the rotational speed difference increases, the transmission torque increases and the state shifts to the four-wheel drive state. At this time, a differential pressure detecting means is provided in the low pressure flow path, and the differential pressure detection value is supplied to a variable control mechanism of the driven fluid pressure driving means having a variable capacity, so that the driven fluid pressure at a high flow rate is controlled. The occurrence of cavitation is suppressed by limiting the discharge flow rate of the driving means.

[0014] In the four-wheel drive vehicle according to the second aspect, the forward-reverse switching valve is interposed in the high-pressure flow path and the low-pressure flow path on the driven-side fluid pressure driving means side, so that the driven-side fluid pressure driving means is provided. Even when the suction port and the discharge port change due to the change in the rotation direction of the driven shaft, the high-pressure flow path and the low-pressure flow path can be cut off. Provided with a differential pressure detecting means, the differential pressure corresponding to the discharge flow rate of the driven fluid pressure driving means is always accurately detected regardless of a change in the rotation direction of the driven axle, and the variable control mechanism is driven accurately. .

In the four-wheel drive vehicle according to the third aspect, the variable control mechanism makes the capacity of the driven fluid pressure driving means proportional to the wheel speed if the detected differential pressure value of the differential pressure detecting means is less than a predetermined value. By maintaining the maximum capacity when the flow rate becomes equal to or more than the predetermined value, the occurrence of cavitation is suppressed when the discharge flow rate of the driven fluid pressure drive unit reaches a maximum when the flow rate is high.

In the four-wheel drive vehicle according to the fourth aspect, since the driven fluid pressure driving means is constituted by a swash plate type variable displacement pump motor, when the rotational speed difference between the front and rear wheels is small, the fluid pressure pump is used. It operates as a two-wheel drive state in which no driving force is transmitted to the driven shaft, and when the rotational speed difference between the front and rear wheels is large, it operates as a fluid pressure motor to transmit the driving force to the driven shaft to change to a four-wheel drive state. I do.

In the four-wheel drive vehicle according to the fifth aspect, the drive-side fluid pressure drive means is constituted by a suction throttle type piston pump which rotates in conjunction with the drive axle, so that the rotation direction of the drive axle changes. This also prevents the pressure of the working fluid flowing through the high-pressure flow path and the low-pressure flow path from being changed without changing the discharge port.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a first embodiment in which the present invention is applied to a four-wheel drive vehicle based on a front-wheel drive vehicle. In the drawing, reference numeral 1 denotes an engine as a main engine,
The rotational driving force of the engine 1 is input to a front wheel differential 3 via a transmission 2, and a front wheel 5 is connected to an output side of the differential 3 via a front axle 4 as a drive axle. .

The front-wheel differential 3 is rotated by a ring gear 3b formed on a differential gear case 3a meshed with a gear 2a connected to the output side of the transmission 2.
A pinion 3d is attached to a pair of pinion shafts 3c formed in the differential gear case 3a. A pair of side gears 3e mesh with the pinion 3d, and the front axle 4 is connected to the side gears 3e.

Also, a differential gear case 3a
A ring gear 3f formed in parallel with the ring gear 3b is connected via a gear 3g meshing with the ring gear 3f to a rotary shaft 6a of a suction throttle type piston pump 6 as a fluid pressure pump constituting drive-side fluid pressure drive means. . The suction throttle type piston pump 6 has a suction port 6b connected to a strainer 7a disposed in the reservoir tank 7, and a 2-position 4-port electromagnetic directional control valve through a low-pressure pipe 8L as a low-pressure flow path. 9 connected to the tank port T,
The discharge port 6c is connected to a pump port P of an electromagnetic direction switching valve 9 for switching between forward and backward movement through a high-pressure pipe 8H as a high-pressure flow path. Here, the suction throttle type piston pump 6
The suction port and the discharge port are not interchanged depending on the rotation direction of the rotating shaft 6a, and the discharge flow rate is represented by the characteristic curve L in FIG.
_As shown by ₁ , the rotation speed increases in proportion to the increase in the rotation speed from “0” to the predetermined value V ₁ ,
In the predetermined value V ₁ above it is configured to saturate at the maximum discharge flow rate Q _1MAX.

The electromagnetic directional control valve 9 for switching between forward and backward connects the pump port P to the output port A and the tank port T to the output port B at the normal position where the solenoid 9a is in a non-energized state. The pump port P communicates with the output port B and the tank port T communicates with the output port A at the offset position in the energized state, and the output ports A and B are inclined as a fluid pressure pump motor constituting the driven fluid pressure driving means. Suction of plate-type variable displacement pump motor 10
The high-pressure oil in the high-pressure pipe 8H is connected to the discharge ports 10a and 10b at the normal position,
The low-pressure pipe 8L communicates with the suction / discharge port 10b to the suction / discharge port 10a, and the rotating shaft 10c is driven to rotate clockwise as viewed from the left side in the rotational direction during forward traveling, and conversely, the high pressure pipe is set at the offset position. The high-pressure oil of 8H is communicated with the suction / discharge port 10b of the variable displacement pump motor 10 and the low-pressure pipe 8L is communicated with the suction / discharge port 10a, and the rotating shaft 10c is rotated in the forward traveling direction, for example, counterclockwise as viewed from the left side. Drive rotationally.

The directional control valve 9 is built in the swash plate type variable displacement pump motor 10, and the output ports A and B are connected to the suction / discharge ports 10a and 10b of the pump motor 10 without passing through piping. I have. Also, the solenoid 9a of the electromagnetic direction switching valve 9 is energized, and is connected to the DC power supply 9c via the shift position detection switch 9b which is turned on when the reverse is selected by a shift lever (not shown). Accordingly, the vehicle is controlled to be in the non-energized state when traveling forward and to be in the energized state when traveling backward.

The flow rate of the variable displacement pump motor 10 is
8L low pressure pipe near the tank port T of the electromagnetic directional control valve 9
By controlling the swash plate variable mechanism 12 as a variable control mechanism including the hydraulic cylinder 12a by the differential pressure generated at both ends of the differential pressure detecting orifice 11 inserted in the _As shown by ₂ , the rotation speed is V ₁
Upon reaching the rotational speed V ₁ increases in proportion to the increase in the rotational speed between the up reached the maximum discharge flow rate Q _1MAX more maximum discharge flow rate Q _2MAX next piston pump 6,
Thereafter, regardless of the increase in rotation speed, the maximum discharge flow rate Q _2MAX
To maintain. Here, the discharge flow rate of the variable displacement pump motor 10 and the discharge flow rate of the piston pump 6 are, as shown in FIG.
The specific discharge flow rate and the gear ratio of the gears connected to the rotating shaft are set so that the discharge flow rate of the piston pump 6 becomes larger than the discharge flow rate of the piston pump 6.

A relief valve 13 for limiting the discharge pressure of the piston pump 6 as a torque limiting means is interposed between the suction port 6b and the discharge port 6c of the suction throttle type piston pump 6. And a high pressure pipe 8H from the low pressure pipe 8L side to a communication pipe 14A communicating between the high pressure pipe 8H and the low pressure pipe 8L between the electromagnetic directional switching valves 9.
A check valve 15 that allows fluid flow to the side is interposed, and a communication pipe 1 disposed in parallel with the communication pipe 14A.
A fixed orifice 16 is connected to 4B in parallel with the check valve 15.

On the other hand, a gear 10d is mounted on a rotating shaft 10c of the swash plate type variable displacement pump motor 10, and the gear 10d
A ring gear 17b formed on a differential gear case 17a of the rear wheel differential 17 is meshed with d. The rear wheel differential 17 has substantially the same configuration as the front differential 3 described above, and includes a pair of pinion shafts 17 formed in a differential gear case 17a.
The pinion 17d is attached to the pinion 17c.
A pair of side gears 17e mesh with d, a rear axle 18 is connected to the side gears 17e, and a rear wheel 19 is connected to the rear axle 18.

Next, the operation of the above embodiment will be described. now,
When the vehicle is stopped on a high friction coefficient road such as a dry road surface, and the engine 1 is in a braking state in an idling state, and the vehicle starts to travel forward, the shift lever is switched to the forward traveling side to change to a startable state. At this time, the shift position detection switch 9b on the reverse traveling side maintains the off state, so that the solenoid 9a of the forward / reverse switching electromagnetic directional switching valve 9 maintains the non-energized state, and the switching position is as shown in FIG. 1
The normal position shown in is continued. In this state, release the brake pedal and depress the accelerator pedal,
The rotational force of the engine 1 is transmitted to the front-wheel-side differential 3 via the transmission 2, and the front-wheel operating device 3 drives the front wheels 5 to rotate in the forward direction, thereby starting forward. At this time, when the rotating shaft 6a of the suction throttle type piston pump 6 is driven to rotate clockwise as viewed from the left side surface, the hydraulic oil having a discharge flow rate corresponding to the rotation speed is discharged from the piston pump 6, and this is supplied to the high pressure pipe. 8H, the air is supplied to the suction / discharge port 10a of the swash plate type variable displacement pump motor 10 via the forward / reverse switching electromagnetic direction switching valve 9, but the rear wheel 19 also moves in the same direction as the front wheel 5 due to the start of the vehicle. Since the rotary shaft 10c is driven to rotate at the same rotational speed, the rotating shaft 10c of the swash plate type variable displacement pump motor 10 rotates clockwise through the rear wheel differential 17 as viewed from the left side surface, whereby the suction / discharge port 10a
The hydraulic oil is sucked from and the hydraulic oil is discharged from the suction / discharge port 10b. Here, the discharge flow rate of the suction throttle type piston pump 6 and the discharge flow rate of the swash plate type variable displacement pump motor 10 are, as shown in FIG. Therefore, the high-pressure hydraulic oil discharged from the piston pump 6 is sucked by the variable displacement pump motor 10, so that the pressure in the high-pressure pipe 8H does not increase. That is, the variable displacement pump motor 10 does not act as a hydraulic motor and no driving force is transmitted to the rear wheels 19, and the vehicle travels forward in a state similar to a front wheel drive vehicle. At this time, since the suction flow rate of the variable displacement pump motor 10 exceeds the discharge flow rate of the piston pump 6, the shortage is replenished via the low pressure pipe 8L, the communication pipe 14A, and the check valve 15.

The difference between the discharge flow rates of the piston pump 6 and the variable displacement pump motor 10 allows a difference in the rotational speeds of the front and rear axles 4 and 18 caused by a change in diameter due to wear of the tires, and is caused by tires of different diameters. The driving force is not transmitted at about the rotational speed difference, the front wheel drive vehicle state is maintained, and deterioration of fuel efficiency can be suppressed. Next, when starting on a low friction coefficient road such as a frozen road or a snowfall road, the front wheel 5 is first driven to rotate as described above. However, since the road is a low friction coefficient road, the front wheel 5 slips. A difference in rotation speed between the front wheel 5 and the rear wheel 19 at which the front wheel 5 has a high rotation speed occurs, and the discharge flow rate of the suction throttle type piston pump 6 exceeds the discharge flow rate of the swash plate type variable displacement pump motor 10. Then, since the resistance of the variable displacement pump motor 10 becomes a load and the operating oil pressure of the high pressure pipe 8H rises, the variable displacement pump motor 10 operates as a hydraulic motor and responds to the pressure of the high pressure pipe 8H. The driving force is transmitted to the rear wheel 19 via the rear wheel differential 17.

That is, as shown in FIG. 3, the torque transmitted to the rear wheel 19 is generated only when a rotational speed difference occurs between the front and rear wheels, and increases rapidly with the increase in the rotational speed difference. The maximum torque _TMAX is regulated by the pressure limitation. This torque limiting action makes it possible to reduce the strength of components such as the rear wheel differential 17 and the drive shaft as compared to a conventional four-wheel drive vehicle.
Weight, fuel consumption, and cost can be reduced.

The torque transmitted to the rear wheel 19 is
As shown in FIG. 3, the lower the speed, the easier it is to generate a driving force with a smaller difference in the number of rotations. As shown in FIG. 2, the suction throttle type piston pump 6 and the swash plate type variable displacement pump motor 10 have a characteristic. This is because the flow rate in the characteristic region of the discharge flow rate characteristic increases as the wheel speed increases. By adopting the flow rate characteristic of FIG. 2, the flow rate difference becomes larger as the speed becomes higher, so that it becomes difficult to become a four-wheel drive vehicle at the time of high-speed running when it is not necessary to perform four-wheel drive,
In FIG. 2, while the wheel speed is between 0 and Vr, the difference in the number of rotations at which the torque rises increases as the vehicle speed increases, but no torque is generated when the wheel speed is equal to or higher than Vr.

Further, the tank port of the electromagnetic directional control valve 9
T for detecting differential pressure inserted in the low-pressure pipe 8L connected to the
The differential pressure across the orifice 11 is introduced into the swash plate variable mechanism 12
As a result, the discharge flow rate of the swash plate type variable displacement pump motor 10 increases.
When the differential pressure across the orifice 11 increases, the swash plate type
By changing the swash plate angle of the variable displacement pump motor 10,
As shown, the wheel speed V is higher than the predetermined wheel speed Vr.₁Yo
Predetermined wheel speed V _TwoLess than as the wheel speed increases
The wheel speed V_TwoAbove is a variable capacity pong
The specific discharge amount of the pump 10 to the maximum discharge flow rate Q_2MAXKeep in
To increase the flow rate excessively during high-speed driving.
Control without increasing the diameter of valves and piping.
System pressure loss or drag due to increased tube resistance
It is possible to reliably suppress the increase in drag and prevent deterioration of fuel efficiency.
On the suction side of the variable displacement pump motor 10
The orifice 10 for detecting differential pressure is not inserted
As the oil temperature rises or the suction side of the variable displacement pump motor 10
Hydraulic oil suction cannot keep up and pressure drops abnormally
Causes cavitation by generating bubbles
And low pressure piping 8L
The orifice 11 for detecting differential pressure is inserted in
Extremely high differential pressure is generated before and after the orifice 11
Can also be prevented.

By the way, as shown in FIG.
When the differential pressure detecting orifice 11 is inserted on the pump port P side of the electromagnetic directional control valve 9, the driving force of the piston pump 6 to the variable displacement pump motor 10 is reduced in a state where the rotational speed difference between the front and rear wheels is small. In the no-load operation state where there is almost no transmission, resistance is exerted on suction on the suction side of the variable displacement pump motor 10, cavitation is likely to occur, and the initial purpose cannot be achieved.

Further, the rise of the torque in FIG. 3 is controlled by controlling the amount of leakage from the high-pressure pipe 8H to the low-pressure pipe 8L by the fixed orifice 16 inserted in the communication pipe 14B communicating the high-pressure pipe 8H and the low-pressure pipe 8L. The characteristics can be arbitrarily set by changing the rise of the pressure. And, due to the temperature characteristic of the orifice due to the viscosity change of the hydraulic oil, the amount of leakage decreases at low temperatures compared to high temperatures and the driving force is easily generated, so that there is an opportunity to be required to function as a four-wheel drive vehicle. There is an advantage that four-wheel drive is likely to occur during winter months.

Next, when the vehicle is moved backward, the shift position switch 9b is turned on by switching the shift lever to the reverse position, so that the solenoid 9a of the forward / reverse switching electromagnetic directional switching valve 9 is energized. As shown in FIG. 4, the switching position is switched from the normal position to the offset position, whereby the hydraulic oil of the high pressure pipe 8H is supplied to the suction / discharge port 1 of the swash plate type variable displacement pump motor 10.
0b, and the hydraulic oil discharged from the suction / discharge port 10a is returned to the low-pressure pipe 8L side, so that the rotating shaft 10c of the variable displacement pump motor 10 is rotated in the reverse direction to that during forward running, and the rear wheel 19 is rotated in the reverse direction. Rotate. For this reason, even when the vehicle is moving backward, the transmission of the driving force is exactly the same as when the vehicle is moving forward, and pressure is generated in the high-pressure pipe 8H only when the front wheel 5 slips and a rotational speed difference occurs between the front and rear axles 4, 18. In addition, when the driving force is transmitted to the rear wheel 19 and the difference in rotation speed between the front and rear axles 4 and 18 is small, the shortage of the suction amount of the swash plate type variable displacement pump motor 10 is reduced by the low pressure pipe 8L and the communication pipe 14.
A and is supplied via the check valve 15.

At this time, as described above, the suction throttle type piston pump 6 on the front wheel side does not interchange the suction port and the discharge port of the pump even if the rotation direction is reversed.
Since the forward / reverse switching electromagnetic directional control valve 9 is built in the variable displacement pump motor 10, the expensive high pressure pipe can be used only for the high pressure pipe 8H.
Since the check valve 15, the orifice 16, and the like may be provided so as to be able to cope with only one-way flow, the configuration of the oil passage can be extremely simplified as compared with the case where another type of pump is used.

In a vehicle equipped with an anti-skid control device based on a front-wheel drive vehicle, the rotational speed of the front wheels is smaller than the rotational speed of the rear wheels during braking, so that no driving force is generated by the hydraulic transmission mechanism, and anti-skid control is not performed. There is an advantage that interference with the device can be reduced. In the first embodiment, the case where the differential pressure before and after the differential pressure detecting orifice 11 is supplied to the swash plate variable mechanism 12 has been described. However, the present invention is not limited to this. When the orifice 11 for detecting differential pressure is inserted, the pressure at the outlet of the orifice 11 for detecting differential pressure becomes atmospheric pressure.
Since it is the same as the drain pressure in the variable displacement pump 10,
As shown in FIG. 5, only the pressure on the high pressure side of the differential pressure detecting orifice 11, that is, the pressure on the tank port T side of the electromagnetic direction switching valve 9 is introduced into the head cover side hydraulic chamber 12 b of the hydraulic cylinder 12 a of the swash plate variable mechanism 12. In this case, there is an advantage that the number of hydraulic pipes can be reduced.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, when the difference in rotation speed between the front and rear wheels is small and the discharge flow rate of the variable displacement pump motor 10 is larger than the discharge flow rate of the piston pump 6, the variable displacement pump motor 1
The pressure drop on the side of the suction port 10a of 0 is suppressed. Therefore, in the second embodiment, as shown in FIG. 6, the differential pressure detecting orifice 11 is inserted downstream of the communication pipe 14A of the low-pressure pipe 8L, except that the orifice 11 is inserted. The same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

According to the second embodiment, when the front axle 4 and the rear axle 18 are rotating substantially equal, the variable displacement pump motor 1 is compared with the discharge flow rate of the piston pump 6.
Since the discharge flow rate of 0 is set to a large value, the suction flow rate of the variable displacement pump motor 10 becomes insufficient as described above, and the insufficient amount is supplied via the communication pipe 14A and the check valve 15. At this time, the communication pipe 14
A orifice 1 for detecting differential pressure is connected to low pressure pipe 8L of A
1, the pressure on the upstream side of the orifice 11 is higher than the drain pressure, so that the suction pressure of the forward suction port 10a or the reverse suction port 10b of the variable displacement pump motor 10 decreases. Can be reliably prevented, and the occurrence of cavitation can be suppressed more than in the first embodiment described above.

Also in the second embodiment, the first embodiment
Since the pressure on the downstream side of the differential pressure detecting orifice 11 is the atmospheric pressure as in the embodiment, the upstream pressure between the differential pressure detecting orifice 11 and the communication pipe 14B is the same as in the case of FIG. Only the swash plate variable mechanism 12 may be supplied to the head cover side hydraulic chamber 12b of the hydraulic cylinder 12a constituting the swash plate variable mechanism 12, and in this case, the number of hydraulic pipes can be reduced.

In the first and second embodiments, the case where the relief valve 13 is applied as the transmission torque limiting means has been described. However, the present invention is not limited to this, and as shown in FIG. A suction throttle valve 21 that inputs the discharge pressure of the pump 6 as a displacement control pressure and controls the opening degree of the suction passage on the suction port 6b side of the piston pump 6 to be small when the discharge pressure becomes equal to or higher than a predetermined pressure. In this case, when the pump discharge pressure becomes equal to or higher than a specified pressure, the pump suction pressure is reduced, so that the pump discharge pressure is reduced and the torque can be limited. When a valve is used, the oil temperature rises when the continuous high load is used, but when the suction throttle valve 21 is provided, the discharge flow rate is reduced, so that heat generation can be suppressed.

In the first and second embodiments, the case where the rear wheel differential 17 is provided has been described. However, the present invention is not limited to this, and as shown in FIG. The differential device 17 may be omitted, and instead, the swash plate type variable displacement pump motors 10L and 10R may be separately provided on the left and right axles 18L and 18R of the left and right rear wheels 19L and 19R. When a different load is applied to the left and right wheels at the time of turning or the like, each of the variable displacement pump motors 10L and 10R naturally generates a discharge flow rate corresponding to the difference. In this case as well, the torque limiting means may be either the illustrated relief valve 13 or the suction throttle valve 21 illustrated in FIG.

Further, in the first and second embodiments, the suction throttle type piston pump 6 in which the suction port 6b and the discharge port 6c do not change regardless of the rotation direction of the rotating shaft 6a is applied as the fluid pressure pump. Was explained,
The present invention is not limited to this. As shown in FIG. 9, the pump port P and the tank port T are respectively connected to the suction port 30b and the discharge port 30c of the hydraulic pump 30 in which the rotating shaft 30a is connected to the gear 3g. By providing a forward / backward switching electromagnetic directional switching valve 31 similar to the forward / backward switching electromagnetic directional switching valve 9 in which the output ports A and B are connected to the high pressure pipes 8H and 8L, the discharge direction is switched forward and backward. Other hydraulic pumps such as a gear pump and a vane pump can be applied.
The hydraulic cylinder 33a receives the differential pressure across the differential pressure generating orifice 32 inserted in the low pressure pipe 8L as shown in FIG.
Any one of a variable displacement type having a variable mechanism 33 including a differential mechanism 17 may be omitted, and two sets of swash plate type variable displacement pump motors 10L and 10R as shown in FIG.
May be applied.

Further, in the first and second embodiments, the case where the forward / backward switching electromagnetic directional control valve 9 is incorporated in the pump motor 10 has been described. However, the present invention is not limited to this. It may be provided separately outside the motor 10. Further, in the first and second embodiments, the embodiment based on the front wheel drive vehicle has been described. However, the present invention is not limited to this. By arranging the pump motor 10 on the front wheel side, the same operation and effect as in the above embodiment can be obtained.

[0043]

As described above, according to the four-wheel drive vehicle of the first aspect, the drive axle driven by the main motor and the drive fluid pressure drive means driven in conjunction with the drive axle are provided. And a driven fluid pressure driving means driven in conjunction with a driven axle, and the driving fluid pressure driving means and the driven fluid pressure driving means are communicated with each other through a high-pressure flow path and a low-pressure flow path. In a four-wheel drive vehicle having a pressure transmission mechanism, a differential pressure detecting means is provided in the low-pressure passage, and the capacity of the driven fluid pressure driving means is determined based on a differential pressure detection value of the differential pressure detecting means. And a variable control mechanism for variably controlling the hydraulic pressure, it is possible to suppress an excessive discharge flow rate by the driven-side hydraulic pressure drive means during high vehicle speed traveling, thereby suppressing the occurrence of cavitation and the high pressure flow. Differential pressure detection separated from the road Since the means is interposed in the low-pressure flow path, cavitation occurs even in a no-load operation state in which the driving force is not transmitted between the driving fluid pressure driving means and the driven fluid pressure driving means. The effect of being able to suppress is obtained.

Further, according to the four-wheel drive vehicle of the present invention, a drive axle driven by the main motor and a drive-side fluid pressure drive means having a fluid pressure pump rotating in conjunction with the drive axle, And a driven fluid pressure driving means having a fluid pump motor that rotates in conjunction with the driven axle. The driving fluid pressure driving means and the driven fluid pressure driving means are communicated with each other through a high pressure flow path and a low pressure flow path. In the four-wheel drive vehicle having a fluid pressure transmission mechanism, a forward / reverse switching valve is inserted into the high-pressure flow path and the low-pressure flow path on the driven fluid pressure driving means side, and the forward / reverse switching valve is A differential pressure detecting means is provided in the low pressure passage on the driving fluid pressure driving means side, and the capacity of the driven fluid pressure driving means is variably controlled based on the differential pressure detection value of the differential pressure detecting means. Variable control mechanism provided In the case where there is a change in the discharge side depending on the rotation direction of the driven fluid pressure driving means in the forward / backward switching valve, by selecting the high pressure flow path and the low pressure flow path in accordance with the change, the discharge side Regardless of the type, the high pressure flow path and the low pressure flow path can be reliably separated, and the differential pressure detection means is reliably prevented from being on the suction side of the driven fluid pressure drive means, and cavitation is reliably prevented. The effect is obtained.

Further, according to the four-wheel drive vehicle of the third aspect, the variable control mechanism adjusts the capacity of the driven fluid pressure driving means to the wheel when the differential pressure detection value of the differential pressure detecting means is less than a predetermined value. Since it is configured to increase in proportion to the speed and maintain the maximum capacity when it exceeds a predetermined value, it is possible to reliably suppress the occurrence of cavitation with the discharge flow rate of the driven fluid pressure driving means at the time of high flow rate peaking out Is obtained.

Further, according to the four-wheel drive vehicle according to the fourth aspect, since the driven-side fluid pressure driving means is constituted by a swash plate type variable displacement pump motor, when the rotational speed difference between the front and rear wheels is small, In a two-wheel drive state in which the driving force is not transmitted to the driven shaft by operating as a fluid pressure pump, and when the rotational speed difference between the front and rear wheels is large, the driving force is transmitted to the driven shaft by operating as a fluid pressure motor. The effect of being able to be in the wheel drive state and of being able to reduce the size of the pump motor itself is obtained.

Furthermore, according to the four-wheel drive vehicle of the third aspect, since the suction throttle type piston pump is configured to rotate in conjunction with the drive axle, the discharge port is changed depending on the rotation direction of the drive axle. Therefore, there is no need to provide a switching valve for switching between the high-pressure flow path and the low-pressure flow path by moving forward and backward between the piston pump and the high-pressure flow path and the low-pressure flow path, and the overall configuration can be simplified. The effect is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a discharge flow rate characteristic of a suction throttle type piston pump and a swash plate type variable displacement pump motor applied to the first embodiment.

FIG. 3 is a characteristic diagram showing a relationship between a front-rear axle rotational speed difference and a transmission torque according to the first embodiment.

FIG. 4 is a schematic configuration diagram showing a comparative example with respect to the first embodiment.

FIG. 5 is a schematic configuration diagram showing a modification of the first embodiment.

FIG. 6 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 7 is a schematic configuration diagram showing another embodiment of the torque limiting means.

FIG. 8 is a schematic configuration diagram showing an embodiment when a differential device is omitted.

FIG. 9 is a schematic configuration diagram showing an embodiment in which a fluid pressure pump whose discharge port is changed depending on the rotation direction is applied as the fluid pressure pump.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 2 Transmission 3 Front wheel differential 4 Front axle 5 Front wheel 6 Suction throttle type piston pump 7 Reservoir tank 8H High pressure piping 8L Low pressure piping 9 Electromagnetic direction switching valve for forward / reverse switching 10 Swash plate type variable displacement pump motor 11 Difference Pressure generating orifice 12 Swash plate variable mechanism 13 Relief valve 15 Check valve 16 Orifice 17 Rear wheel side differential 18 Rear wheel axle 19 Rear wheel 21 Suction throttle valve 10L, 10R Swash plate type variable displacement pump motor 31 Forward / reverse switching Solenoid directional control valve

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-169996 (JP, A) JP-A-2-200530 (JP, A) JP-A-6-11036 (JP, A) JP-A-5-16936 246259 (JP, A) JP-A-5-131859 (JP, A) JP-A-63-284037 (JP, A) JP-A-57-74224 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) B60K 17/10-17/356

Claims (5)

(57) [Claims] A drive axle driven by a main motor;
A drive-side fluid pressure drive unit driven in conjunction with the drive axle; and a driven-side fluid pressure drive unit driven in conjunction with a driven axle, wherein the drive-side fluid pressure drive unit and the driven-side fluid pressure In a four-wheel drive vehicle having a fluid pressure transmission mechanism constituted by communicating a drive means with a high pressure flow path and a low pressure flow path, a differential pressure detection means is provided in the low pressure flow path, and the driven fluid pressure drive means is provided. A four-wheel drive vehicle, further comprising a variable control mechanism for variably controlling the capacity based on the differential pressure detection value of the differential pressure detection means. 2. A drive axle driven by a main motor;
A drive-side fluid pressure drive unit driven in conjunction with the drive axle; and a driven-side fluid pressure drive unit driven in conjunction with a driven axle, wherein the drive-side fluid pressure drive unit and the driven-side fluid pressure In a four-wheel drive vehicle in which a driving means is communicated with a high-pressure flow path and a low-pressure flow path to constitute a fluid pressure transmission mechanism, switching between forward and backward switching to the high-pressure flow path and the low-pressure flow path on the driven fluid pressure driving means side is performed. A valve is interposed, a differential pressure detecting means is provided in the low-pressure flow path on the driving fluid pressure driving means side of the forward / reverse switching valve, and the capacity of the driven fluid pressure driving means is set to the differential pressure. A four-wheel drive vehicle comprising a variable control mechanism for performing variable control based on a differential pressure detection value of a detection means. 3. The variable control mechanism increases the capacity of the driven fluid pressure driving means in proportion to the wheel speed if the detected differential pressure value of the differential pressure detecting means is less than a predetermined value, 2. The system according to claim 1, wherein the maximum capacity is maintained.
Or the four-wheel drive vehicle according to 2. 4. The four-wheel drive vehicle according to claim 1, wherein said driven fluid pressure driving means is constituted by a swash plate type variable displacement pump motor which rotates in conjunction with a driven axle. 5. The four-wheel drive vehicle according to claim 1, wherein said drive-side fluid pressure drive means comprises a suction throttle type piston pump which rotates in conjunction with a drive axle.