JP3198794B2 - 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 deterioration of fuel consumption during such a high speed, as shown in FIG. 12, a first hydraulic pump driven side variable capacity, shows the flow characteristic at the characteristic curve L ₁₁ The maximum flow rate Q _1MAX is reached by flattening the flow rate at a rotation speed N _F2 corresponding to high-speed running that does not require a four-wheel drive state.
Or limited to, the second hydraulic pump driven by a variable capacity, it is conceivable to limit its maximum flow characteristics higher than the maximum flow rate Q _1MAX as indicated by the characteristic curve L ₁₂ flow Q _2MAX, In order to transmit torque when such flow characteristics are provided, the first hydraulic pump flow needs to exceed the second hydraulic pump flow, but the driven second hydraulic pump flow is the drive side. The maximum transmission torque at the rotation speed N _R1 that has reached the maximum flow rate Q _2MAX of the first hydraulic pump is as shown in FIG.
In as indicated by the characteristic curve L _13, results in a new problem that there is a possibility that a driver feels discomfort due to decrease rapidly.

Therefore, the present invention has been made in view of the above-mentioned unsolved problems of the prior art, and the fuel consumption during high-speed traveling without causing the driver to feel uncomfortable by gradually lowering the maximum transmission torque. An object is to provide a four-wheel drive vehicle that can suppress deterioration.

[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 each have a discharge port and a suction port. In a four-wheel drive vehicle in which a fluid passage is provided by providing a communicating flow path and a flow rate of the driving fluid pressure driving means is set to be less than a flow rate of the driven fluid pressure driving means, the driven fluid pressure driving means The capacity of the means decreases the capacity from the first rotation speed at which the maximum transmission torque starts to decrease, and the capacity of the drive-side fluid pressure driving means is higher than the first rotation speed. Set to the maximum value at the second rotation speed where It is characterized in that it is.

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 driven hydraulic pressure driving means having a driven hydraulic pressure driving means, wherein the driving fluid pressure driving means and the driven fluid pressure driving means are provided with a flow path communicating between the discharge port and the suction port, and a fluid pressure transmission mechanism is provided. In a four-wheel drive vehicle, wherein the flow rate of the drive-side fluid pressure driving means is set to be less than the flow rate of the driven-side fluid pressure drive means, the capacity of the driven-side fluid pressure drive means begins to decrease the maximum transmission torque. reducing the volume from 1 rpm, and the driving-side fluid pressure capacity of the first rotary rotation speed higher rather of the 2 <br/> than in accordance with the capacitance characteristic of the driven-side fluid pressure driving means of the driving means Reduce the capacity from lower than the number of revolutions ,
Further, it is characterized in that the maximum value is set at the second rotation speed at which the transmission torque is not required.

Further, the four-wheel drive vehicle according to claim 3 is a drive axle driven by a main motor, drive-side fluid pressure drive means driven in conjunction with the drive axle, and a drive axle in conjunction with a driven axle. The driven fluid pressure driving means and the driven fluid pressure driving means communicate with each other through a discharge port and a suction port through a high pressure side flow path and a low pressure side flow path. In a four-wheel drive vehicle in which the fluid pressure transmission mechanism is configured to set the flow rate of the driving fluid pressure driving means to be less than the flow rate of the driven fluid pressure driving means, the capacity of the driven fluid pressure driving The capacity is reduced from the first rotation speed at which the torque starts to decrease, and the capacity of the drive-side fluid pressure driving means is increased to a maximum value at the second rotation speed at which the transmission torque is no longer required higher than the first rotation speed. And the high-pressure flow path and It is characterized in that the valve opening pressure was interposed a relief valve to reduce with increasing rotational speed between the first speed and the second rotational speed between the low-pressure line.

Further, a four-wheel drive vehicle according to a fourth aspect is a drive axle driven by a main prime mover, drive-side fluid pressure drive means driven in conjunction with the drive axle, and a driven axle. And a driven fluid pressure driving means, which is driven by the hydraulic fluid, wherein the driving fluid pressure driving means and the driven fluid pressure driving means communicate their discharge ports and suction ports with each other through a high pressure side flow path and a low pressure side flow path. and by a fluid pressure transmission kinematic mechanism, the flow rate Not of the driven-side fluid pressure drive means the flow rate of the driving-side hydraulic drive means
In four-wheel drive vehicle which is set to full, the capacity of the driven side hydraulic drive means decreases the first capacitor from the rotational speed of the start to reduce the maximum transmission torque, and wherein the flow rate of the driving-side hydraulic drive means It is set to be a maximum value at a second rotation speed that is higher than the first rotation speed and does not require transmission torque, and further , the valve opening pressure is increased between the high-pressure flow path and the low-pressure flow path. A discharge valve of the driving fluid pressure driving means has exceeded a set pressure lower than a maximum valve opening pressure of the relief valve while a relief valve for decreasing the rotation speed is increased between the second rotation speeds. In some cases, suction amount limiting means for reducing the suction amount of the drive-side fluid pressure driving means is provided.

Still further, in the four-wheel drive vehicle according to the fifth aspect, in the four-wheel drive vehicle according to the third or fourth aspect, the valve opening pressure of the relief valve may be substantially zero at the second rotation speed. It is characterized by having been set. In the four-wheel drive vehicle according to claim 6, in the four-wheel drive vehicle according to any one of claims 3 to 5, the relief valve is configured such that the valve opening pressure is controlled by the driven-side fluid pressure driving means and the low-pressure side flow passage. The valve opening pressure is controlled by the pressure on the driven fluid pressure driving means side of the restrictor inserted between the throttle valve and the throttle valve.

According to a seventh aspect of the present invention, there is provided a four-wheel drive vehicle according to any one of the third to sixth aspects, wherein the drive-side fluid pressure drive means has a plurality of different flow rate characteristics with respect to rotation speed. It is characterized by being configured by combining pumps.

[0015]

In the four-wheel drive vehicle according to the first aspect, the rotation of the drive axle driven by the main prime mover discharges the working fluid of a flow rate corresponding to the rotation speed from the drive-side fluid pressure drive means, which is connected to one of the communicating means. The working fluid supplied to the suction side of the driven fluid pressure driving means driven by the rotation of the driven axle through the flow path, and the working fluid discharged from the driven fluid pressure driving means is supplied to the driving fluid pressure driving means through the other communication flow path. Is returned to. 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, but as the rotational speed difference increases, the transfer torque increases and the vehicle shifts to the four-wheel drive state. . At this time,
The capacity of the driven fluid pressure driving means is reduced below the first rotation speed at which the maximum transmission torque starts to decrease, and the capacity of the driving fluid pressure driving means is higher than the first rotation speed, so that transmission torque is not required. Since the setting is made to be the maximum value at the second rotation speed, even when the driven fluid pressure driving means exceeds the first rotation speed, the flow rate of the driven fluid pressure driving means is maintained at the driving fluid pressure driving means. until the maximum flow rate of the means reduces gradually the maximum transmission torque.

In the four-wheel drive vehicle according to the second aspect, in addition to the operation of the first aspect, the flow rate of the drive-side fluid pressure drive means is adjusted in accordance with the flow rate characteristic of the driven-side fluid pressure drive means. since the capacity of a high Ku lower rotational speed than the second rotational speed than the number decreases, and easily generate a transmission torque by reducing the flow rate difference between the drive-side hydraulic drive means and the driven side means, the maximum torque transfer Suppress sharp decline.

In the four-wheel drive vehicle according to the third aspect, in addition to the function of the first aspect, the valve opening pressure of the relief valve interposed between the high-pressure side flow path and the low-pressure side flow path is increased to the first rotation speed. Is maintained until reaching the first rotation speed, but between the first rotation speed and the second rotation speed, the pressure decreases as the rotation speed increases, whereby the driving fluid pressure driving means and the driven fluid The pressure in the high-pressure side passage between the pressure driving means decreases, and the transmission torque decreases more smoothly toward the second rotation speed.

In the four-wheel drive vehicle according to the fourth aspect, in addition to the effect of the third aspect, before the relief valve is opened, the working fluid suction amount of the drive-side fluid pressure drive means is limited to the suction amount. Means, the discharge flow rate of the drive side fluid pressure drive means will be reduced, and the relief valve will open to release the hydraulic oil from the high pressure side flow path to the low pressure side flow path. Suppress temperature rise.

In the four-wheel drive vehicle according to the fifth aspect, when the second rotational speed is reached, the valve opening pressure of the relief valve becomes substantially zero, and the pressure between the driving fluid pressure driving means and the driven fluid pressure driving means is reduced. The pressure in the high pressure side flow path communicating with the pressure becomes the gauge pressure, and the transmission torque can be smoothly reduced to zero without generating a step. In the four-wheel drive vehicle according to the sixth aspect, the opening pressure of the relief valve is controlled based on the pressure on the driven fluid pressure driving means side of the throttle provided between the driven fluid pressure driving means and the low pressure flow path. Therefore, the valve opening pressure can be controlled without providing another sensor or the like separately.

In the four-wheel drive vehicle according to the seventh aspect, since the drive-side fluid pressure drive means is configured by combining a plurality of pumps having different flow rate characteristics with respect to the number of revolutions, it is difficult to control the flow rate in multiple stages by itself. Even with a pump, the flow characteristics can be set in multiple stages.

[0021]

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 to a rotary shaft 6a of a suction throttle type piston pump 6 as a fluid pressure pump via a gear 3g meshing with the ring gear 3f. The suction throttle type piston pump 6 has a suction port 6b having a strainer 7a provided in a reservoir tank 7.
And a low-pressure pipe 8 as a low-pressure flow path
The discharge port 6c is connected to the pump port P of the electromagnetic directional control valve 9 for forward / reverse switching through a high-pressure pipe 8H as a high-pressure flow path through L. ing.

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 N of the rear axle 18 starts to decrease after the rotation speed of the front axle 4 is “0”.
Until the predetermined value N _F1 higher than _R1 is reached, the rotation speed increases at a relatively large increase rate in proportion to the increase of the rotation speed, and the predetermined value N
_{At F1} or higher, the rotation speed increases at a relatively small rate of increase in proportion to the rotation speed, and the rotation speed of the front axle 4 (second rotation speed) N _F2 which does not require the four-wheel drive state due to the high-speed running state It is set to be saturated at the maximum discharge flow rate Q _1MAX .

The electromagnetic directional control valve 9 for forward / reverse switching 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 not energized. 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 where the power is supplied, and the output ports A and B draw the swash plate type variable displacement pump motor 10 as a fluid pressure pump motor. The rotary shaft is connected to the discharge ports 10a and 10b, and connects the high pressure oil of the high pressure pipe 8H to the suction / discharge port 10a of the variable displacement pump motor 10 and the low pressure pipe 8L to the suction / discharge port 10b at the normal position. 10c
Is rotated clockwise when viewed from the left side, for example, when viewed from the left side. On the contrary, the high pressure oil of the high pressure pipe 8H is supplied to the suction / discharge port 10b of the variable displacement pump motor 10 at the offset position.
Then, the low-pressure pipe 8L is communicated with the suction / discharge port 10a, and the rotating shaft 10c is rotationally driven in the direction of rotation during forward running, for example, counterclockwise as viewed from the left side.

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 rear axle rotation speed is lower than the rotation speed N _{F1 of the} front axle 4 when the maximum transmission torque starts to decrease .
Until the first rotation speed N _R1 becomes lower, the rotation speed increases in proportion to the increase of the rotation speed at an increase rate higher than the increase rate of the piston pump 6 on the drive side, and reaches the first rotation speed N _R1 . At this time, the discharge flow rate Q ₂₁ becomes lower than the maximum discharge flow rate Q _1MAX of the piston pump 6, and thereafter, as the rotational speed increases, the increase rate between the rotational speeds N _{F1 and} N _{F2 of} the piston pump 6 is substantially equal to the above-described increase rate. It is set to increase at a low rate.

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.
0 Many made as specific discharge rate discharge flow rate from the discharge flow rate of the piston pump 6, is set a gear ratio of the gear connected to the rotary shaft, the variable from the rotational speed is "0" until a predetermined value N _F2 Displacement pump motor 10 and piston pump 6
It is preferable to set the discharge flow rate difference to about several percent in terms of favorably generating transmission torque. If the flow rate difference between the two is too large, it becomes difficult to generate the transmission torque.

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 this 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, the rotating shaft 6a of the suction throttle type piston pump 6 is driven to rotate clockwise as viewed from the left side, so that hydraulic oil having a discharge flow rate corresponding to the rotation speed is discharged from the piston pump 6. This is supplied to the suction / discharge port 10a of the swash plate type variable displacement pump motor 10 through the high-pressure pipe 8H and the forward / backward switching electromagnetic direction switching valve 9, and the rear wheel 19 is also connected to the front wheel 5 by the start of the vehicle. The rear differential 1 is driven in the same direction at the same rotational speed.
Rotating shaft 1 of swash plate type variable displacement pump motor 10 through 7
0c rotates clockwise as viewed from the left side, whereby hydraulic oil is sucked from the suction / discharge port 10a and hydraulic oil is discharged from the suction / discharge port 10b.

Here, as shown in FIG. 2, the discharge flow rates of the suction throttle type piston pump 6 and the swash plate type variable displacement pump motor 10 are varied at the same rotational speed as shown in FIG.
Is set to be always larger than that of the piston pump 6, the high-pressure hydraulic oil discharged from the piston pump 6 is sucked by the variable displacement pump motor 10, so that the pressure of the high-pressure pipe 8H Does not go up. 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.
The vehicle travels forward in the same state as the 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 different diameter tires. 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. When becomes, the resistance of the variable displacement pump motor 10 is that the hydraulic pressure of the high-pressure pipe 8H becomes load increases, the variable displacement pump motor 10 becomes <br/> and to operate as a hydraulic motor, the high-pressure pipe 8H Is transmitted to the rear wheels 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 is generated 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. The flow rate in the characteristic region of the discharge flow rate characteristic is caused by that the flow rate difference increases as the wheel speed increases until the wheel speed reaches _VR1 .

On the other hand, as shown in FIG. 2, the capacity of the swash plate type variable displacement pump motor 10, after the rear wheel speed V _R is V _R1 i.e. the rear wheel rotational speed has reached the first rotational speed N _R1 Gradually decreases, so that the maximum transmission torque is also reduced by the characteristic curve L _{3 in} FIG.
As shown in, will be reduced in accordance with the wheel speed is increased, the rear wheel speed V _R is the predetermined value V _R2 namely the rear axle rotational speed N _R reaches the rotational number N _R2, variable displacement pump The discharge flow rate of the motor 10 is the maximum flow rate Q of the piston pump 6.
_When it exceeds _1MAX , the transmission torque cannot be generated, and the maximum transmission torque becomes zero.

[0038] Thus, by setting the flow characteristics of the piston pump 6 and a variable displacement pump motor 10 as the characteristic curve L ₁ and L ₂ in FIG. 2, the maximum transmission torque wheel speed V _R1 or first When the rotational speed exceeds N _R1 , the torque gradually decreases, and it is possible to reliably prevent the maximum transmission torque from suddenly decreasing as in the conventional example. , The occurrence of discomfort to the driver can be reliably prevented.

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, 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, as described above.
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 rotation speed of the front wheels is smaller than the rotation 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 flow characteristic of the suction throttle type piston pump 6 as the driving fluid pressure driving means is represented by a characteristic curve L _{1 in} FIG.
As shown in, has been described as being set in two stages polygonal line, is not limited to this, as shown by the characteristic line L ₂₁ of the one-dot chain line shown in FIG. 2, the rotation speed is from "0" it is possible to increase characteristics in accordance with the increase in the rotational speed between the up to a predetermined value N _F2, short can set an arbitrary flow characteristics within the range shaded in FIG. in this case,
Since the discharge flow rate difference piston pump 6 and a variable displacement pump motor 10 will hardly occur and the transmission torque is too large, in practice be set in a range from the characteristic line L ₂₁ of the characteristic curve L ₂ side preferable.

Further, in the first embodiment, the case where the suction throttle type piston pump 6 is applied as the driving fluid pressure driving means has been described. However, the present invention is not limited to this. It is also possible to apply a pump, and in the case of a single pump, the characteristic curve L ₁ of FIG.
If the inability to obtain flow characteristics, as shown in FIG. 4, the rotational speed N _F1 saturated for example a radial piston pump as indicated by the characteristic curve L _13, rotational speed as indicated by a characteristic curve L ₁₄ a radial piston pump is saturated at N _F2 connected in parallel to the front axle 4, by adding the discharge flow rate of both may be realized the characteristics of the characteristic curve L _1.

Further, in the above 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. Orifice 11 for detecting differential pressure
Is inserted, the pressure at the outlet side of the differential pressure detecting orifice 11 becomes the atmospheric pressure, and is the same as the drain pressure in the variable displacement pump 10. Therefore, as shown in FIG. Only the pressure on the high pressure side of the orifice 11, that is, the pressure on the tank port T side of the electromagnetic directional switching valve 9 may be introduced into the head cover side hydraulic chamber 12 b of the hydraulic cylinder 12 a of the swash plate variable mechanism 12.

In the first embodiment, 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 the discharge pressure of the piston pump 6 is controlled by displacement as shown in FIG. A suction throttle valve 21 that inputs the pressure as a 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 flow rate exceeds the specified pressure, the pump suction amount decreases, so that the pump discharge pressure decreases and torque can be limited. Although the oil temperature increases when a high load is used, when the suction throttle valve 21 is provided, the discharge flow rate is reduced, so that heat generation can be suppressed.

Further, in the first embodiment, 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. 17 is omitted and the left and right rear wheels 19L, 1
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 9R. In this case, when different loads are applied to the left and right wheels during turning, etc. Variable displacement pump motor 10L, 10
R naturally produces a discharge flow rate difference corresponding to the difference, so that a differential function equivalent to that of a differential device can be exhibited. In this case, the relief valve 13 shown in FIG.
However, any of the intake throttle valves 21 shown in FIG. 6 may be used.

Further, the rotary shaft 6 is used as a fluid pressure pump.
Although the case where 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 a has been described, the present invention is not limited to this.
As shown in FIG. 8, a pump port P and a tank port T are respectively connected to a suction port 30b and a discharge port 30c of a hydraulic pump 30 in which a rotary shaft 30a is connected to a gear 3g, and output ports A and B are connected to a high pressure pipe 8H. And a hydraulic pump, such as a gear pump or a vane pump, in which the discharge direction is switched between forward and backward by providing a forward / backward switching electromagnetic directional switching valve 31 similar to the forward / backward switching electromagnetic directional switching valve 9 connected to 8L. In this case, the hydraulic pump receives the fixed displacement type shown in FIG. 1 and the differential pressure before and after the differential pressure generating orifice 32 inserted in the low pressure pipe 8L as shown in FIG. Mechanism 33 including hydraulic cylinder 33a
Any of the variable capacity types provided with

In the first embodiment, the driving fluid pressure driving means and the driven fluid pressure driving means are connected to the high pressure passage 8.
Although the case of communicating with the H and the low pressure passage 8L has been described, the present invention is not limited to this, and the high pressure passage and the low pressure passage are separated by omitting the forward / backward switching electromagnetic directional switching valves 9 and 31. The present invention can be applied even in the absence. next,
A second embodiment of the present invention will be described with reference to FIGS.

[0049] The second embodiment is obtained by the reduction of the transmission torque when a rotation number N _R2 above more smoothly performed so. That is, in the second embodiment, as shown in FIG. 9, the relief valve 13 is constituted by a pilot-operated relief valve 13P, and the relief valve 13P is connected in parallel with the communication pipes 14A and 14B between the high-pressure pipe 8H and the low-pressure pipe 8L. A swash plate type variable valve which is inserted in the middle of a communication pipe 14C connected to the pressure relief valve 13P and has a pressure on the high pressure side of the differential pressure detecting orifice 11, that is, on the tank port T side of the electromagnetic direction switching valve 9, Except that the discharge pressure of the displacement pump motor 10 is input as a pilot pressure, it has the same configuration as that of the embodiment of FIG. 5 described above, and the same reference numerals are given to portions corresponding to FIG. The detailed description is omitted.

Here, the pilot operated relief valve 13
Opening pressure of P, as shown in FIG. 10, the until discharge flow rate Q ₂ of the swash plate type variable displacement pump motor 10 reaches the first rotational speed N _R1 as a discharge flow rate Q _21, the characteristic curve While being maintained at the maximum setting pressure P _RMAX, the rear wheel axle rotation speed N _R is increased from this state, in response to this oblique regulating the maximum delivery pressure of the piston pump 6 which is set in advance as shown by L ₂₄ discharge flow rate Q ₂ is a characteristic curve L of the plate-type variable displacement pump motor 10
When gradually rises as shown in _2, the pressure of the high pressure side of the differential pressure detection orifice 11 increases in response to this, since it is supplied to the vent port as a pilot pressure, an increase of the rear wheel axle rotation speed N _R decreases in inverse proportion to, rotation number N
_R2 is reached when reaching the minimum relief pressure P _RMIN, rotational speed N _R2
Thus, the minimum relief pressure _PRMIN is maintained.

According to the second embodiment, the pilot-operated relief valve is used until the rear axle rotation speed N _R reaches the first rotation speed N _R1 after the vehicle starts running forward or backward. Since the valve opening pressure of 13P is set to the maximum relief pressure P _RMAX , the rotational speed difference between the front and rear wheels 5 and 19 when traveling on the road with a high friction coefficient as in the first embodiment described above. , The variable displacement pump 10 does not operate as a hydraulic motor, the driving force is not transmitted to the rear wheel 19, and the two-wheel drive state similar to that of the front wheel drive vehicle is maintained. Since a rotational speed difference is generated between the wheels 5 and 19, the variable displacement pump 10 operates as a hydraulic motor and shifts to a four-wheel drive state, at which time the maximum transmission torque T
_MAX is to be regulated at the maximum relief pressure P _RMAX as indicated by the characteristic curve L ₂₃ in FIG. 10.

However, when the rear wheel axle rotation speed N _R exceeds the first rotation speed N _R1 , the discharge flow rate of the variable displacement pump motor 10 exceeds the set value Q ₂₁ , and the differential pressure detecting orifice 11 by the pressure of the high pressure side is increased, it will be reduced in inverse proportion to the increase of the rear wheel axle rotation speed N _R opening pressure of the pilot actuated type relief valve 13P is as indicated by a characteristic curve L ₂₄ in FIG. 10 . For this reason, the discharge side of the piston pump 6 on the front wheel side and the variable displacement pump motor 1 on the rear wheel side
Electromagnetic switching valve 9 for forward / reverse switching connected to the suction side
By the pressure of the high-pressure pipe 8H communicating between the pump port P of is limited, the transmission torque T between the piston pump 6 and a variable displacement pump motor 10 is also described above as shown by the characteristic curve L ₂₃ in FIG. 10 compared to the reduction rate of the transmission torque T to the characteristic curve L ₃ of Figure 2 increases in the first embodiment, transfer discharge flow rate Q ₂ of the variable displacement pump motor 10 reaches the maximum discharge flow rate Q _1MAX piston pump 6 becomes a value substantially close to zero just before reaching that such can not generate torque T rotational speed N _R2, with decreasing during this time of the transmission torque T is smoothly performed, the transmitted torque when reaching the rotational speed N _R2 Although T suddenly becomes zero, the amount of decrease in the transmission torque T at this time is extremely small, so that it is possible to reliably prevent the driver from feeling uncomfortable.

Further, the valve opening pressure of the pilot-operated relief valve 13P is increased from the first rotational speed N _R1 to the rear wheel axle rotational speed N _R.
Decreases in inverse proportion to the increase of the pressure, the maximum pressure use range of the high-pressure pipe 8H that communicates the discharge side of the piston pump 6 and the suction side of the variable displacement pump motor 10 via the electromagnetic directional switching valve 9 for front-rear direction switching. be up to the first rotational speed N _R1, a valve opening pressure of the relief valve 13 as in the first embodiment described above is constant, as compared with the case where the maximum pressure range of use is up to rotational speed N _R2 The operation frequency of the maximum pressure and the high-pressure operation area can be reduced, and the cost can be reduced without using a high-pressure material required for securing the durability of the high-pressure pipe 8H or increasing the cost due to surface treatment. Can be achieved.

Further, since the upstream pressure of the differential pressure detecting orifice 11 for the swash plate variable mechanism 12 of the variable displacement pump 10 is utilized to control the valve opening pressure of the pilot operated relief valve 13P, it is separately provided. There is no need to provide a pressure sensor or the like, and the configuration can be simplified accordingly. Further, by setting such that zero i.e. gauge pressure upon reaching the opening pressure of the pilot actuated type relief valve 13P to rotation number N _R2, when a rotational speed N _R2 above, transmission torque There is no step at T, and the transition from the four-wheel drive state to the two-wheel drive state can be performed more smoothly.

Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, when the relief valve 13P is opened in the second embodiment described above,
This prevents the temperature of the hydraulic oil discharged from the high pressure side to the low pressure side through the relief valve 13P from rising.
That is, in the third embodiment, as shown in FIG. 11, the discharge pressure of the piston pump 6 is input as the displacement control pressure, and the opening degree of the suction passage on the suction port 6b side of the piston pump 6 is changed accordingly. When the pressure exceeds a preset pressure which is lower than the maximum valve opening pressure of the pilot-operated relief valve 13P in the second embodiment described above, a suction throttle valve 40 serving as a suction amount limiting means for controlling the pressure is reduced by a piston pump. 6, except that it is interposed on the suction port 6b side of FIG. 6, showing the same configuration as in FIG. 9 showing the above-described second embodiment, and the parts corresponding to FIG. This is omitted.

According to the third embodiment, when the vehicle starts traveling forward or backward, the low-friction coefficient road is maintained until the rear wheel axle rotation speed N _R reaches the first rotation speed N _R1. When the transmission torque T to the rear wheel side is increased by generating a rotational speed difference between the front and rear wheels as in the case of traveling
When the pressure reaches a pressure immediately before reaching the maximum valve opening pressure P _RMAX of the pilot-operated relief valve 13P, the valve opening of the suction throttle valve 40 is reduced, and the discharge of the piston pump 6 is reduced. By reducing the flow rate, an increase in the internal pressure of the high-pressure pipe 8H is suppressed, and the flow rate discharged to the low-pressure pipe 8L through the pilot-operated relief valve 13P can be suppressed.
It is possible to reliably prevent the temperature of the hydraulic oil from rising due to passing through 3P.

In the second and third embodiments, the case where the opening pressure of the pilot operated relief valve 13P is controlled based on the pressure on the upstream side of the differential pressure detecting orifice 11 has been described. The governor pressure of the automatic transmission is controlled by the pilot-operated relief valve 13 because the axle rotation speed and the vehicle speed are proportional to each other.
Even if the valve opening pressure is controlled by supplying to the vent port, the same operation as described above can be obtained. In addition, a proportional electromagnetic relief valve is applied as the relief valve, and the vehicle speed is detected based on, for example, the rotation speed of the output shaft of the transmission 2. Based on the detected vehicle speed, the valve opening pressure of the proportional electromagnetic relief valve is determined. By forming an exciting current to control the opening pressure of the relief valve may be electrically controlled, and instead of the vehicle speed detection value, the wheel speed of the rear wheel is detected by a wheel speed sensor,
An exciting current for controlling the valve opening pressure of the proportional electromagnetic relief valve may be formed based on the wheel speed detection value.

Further, in the above-described second and third embodiments, similarly to the above-described first embodiment, the rear wheel operating device 17 is provided.
Is omitted, the left and right axles 18 of the left and right rear wheels 19L, 19R are omitted.
Swash plate type variable displacement pump motor 10L for L and 18R individually
And 10R, and a hydraulic pump, such as a gear pump or a vane pump, in which a forward / reverse switching electromagnetic direction switching valve is provided on the front wheel side pump side and the discharge direction is switched between forward and backward. Get out.

Further, in the first to third embodiments, the forward / backward switching electromagnetic directional control valve 9 is connected to the pump motor 1.
Although the case where it is built in 0 has been described, the present invention is not limited to this, and it may be separately provided outside the pump motor 10. Furthermore, in the first to third 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, it is possible to obtain the same operation and effect as in the above embodiment.

[0060]

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, wherein the driving fluid pressure driving means and the driven fluid pressure driving means communicate with each other through a discharge port and a suction port. A four-wheel drive vehicle in which a fluid pressure transmission mechanism is provided and the flow rate of the driving fluid pressure driving means is set to be less than the flow rate of the driven fluid pressure driving means. A second rotation in which the capacity of the means is reduced from the first rotation speed at which the maximum transmission torque starts to decrease, and the capacity of the drive-side fluid pressure driving means is higher than the first rotation speed and no transmission torque is required. Because it was set to be the maximum value in number, The difference between the maximum flow rate of the driving-side fluid pressure driving means and the flow rate of the driven-side fluid pressure driving means can be gradually reduced, whereby when the rotation speed increases from the first rotation speed, By gradually lowering the maximum transmission torque, it is possible to reliably prevent the maximum transmission torque from suddenly lowering, and to give a sense of incongruity to the driver by gradually changing from the four-wheel drive state to the two-wheel drive state. That is, the effect of being able to surely prevent this is obtained.

According to the four-wheel drive vehicle of the present invention, the drive axle driven by the main motor, the drive fluid pressure drive means driven in conjunction with the drive axle, and the driven axle And a driven fluid pressure driving means that is driven in a hydraulically driven manner, wherein the driving fluid pressure driving means and the driven fluid pressure driving means are provided with a flow path for communicating the discharge port and the suction port with each other. In a four-wheel drive vehicle that constitutes a mechanism and sets the flow rate of the drive-side fluid pressure drive means to less than the flow rate of the driven-side fluid pressure drive means, the capacity of the drive-side fluid pressure drive means reduces the maximum transmission torque. reducing the first volume than the rotational speed of the start, and more EVEN second rotational speed than the first rotational speed in accordance with the capacitance characteristic of the driven-side fluid pressure drive means the capacity of the drive-side hydraulic drive means to reduce the volume lower rotational speed, further transmitted DOO In this configuration, the maximum value is set at the second rotation speed that eliminates the need for torque, so that the flow rate difference between the driving fluid pressure driving means and the driven fluid pressure driving means is prevented from increasing and the maximum transmission torque is reduced. The effect of being able to make the decrease change of gradually is obtained.

Further, according to the four-wheel drive vehicle according to the third aspect, the drive axle driven by the main prime mover, the drive fluid pressure drive means driven in conjunction with the drive axle, and the driven axle Driven-side fluid pressure driving means, which is driven in such a manner that the driving-side fluid pressure driving means and the driven-side fluid pressure driving means are connected to each other by a discharge port and a suction port in a high-pressure flow path and a low-pressure flow path. and a fluid pressure transmission kinematic mechanism communicating, the flow rate of the driving-side hydraulic drive means flow rate Not of the driven-side fluid pressure drive means
In four-wheel drive vehicle which is set to full, the capacity of the driven side hydraulic drive means decreases the first capacitor from the rotational speed of the start to reduce the maximum transmission torque, and wherein the capacitance of the drive-side hydraulic drive means The second rotation speed is higher than the first rotation speed and the transmission torque is not required. The second rotation speed is set to the maximum value, and the valve opening pressure between the high-pressure flow passage and the low-pressure flow passage is set to the first rotation speed and the second rotation speed. Since the relief valve that reduces the increase in the number of rotations between the second number of rotations is interposed, the reduction rate of the transmission torque between the first number of rotations and the second number of rotations is increased. As a result, it is possible to suppress a sudden decrease in the transmission torque at the second rotational speed, thereby making the transmission torque decrease change more smoothly, and to reduce the frequency of the maximum pressure in the high-pressure flow path, The area can be narrowed and durable Effect that it is possible to suppress the increase in cost due to use and surface treatment of the high withstand voltage materials required to ensure cost reduction.

Further, according to the four-wheel drive vehicle of the fourth aspect, the drive axle driven by the main motor, the drive fluid pressure drive means driven in conjunction with the drive axle, and the driven axle Driven fluid pressure driving means driven in conjunction with each other, wherein the driving fluid pressure driving means and the driven fluid pressure driving means are connected to each other by a discharge port and a suction port of a high pressure side flow path and a low pressure side flow path. And a fluid pressure transmission mechanism, and the flow rate of the drive-side fluid pressure drive means is controlled by the flow rate of the driven-side fluid pressure drive means.
In the four-wheel drive vehicle set to be less than the first , the capacity of the driven fluid pressure driving means starts to decrease the maximum transmission torque.
And the flow rate of the drive-side fluid pressure driving means is set to be a maximum value at a second rotational speed which is higher than the first rotational speed and does not require transmission torque, and A relief valve for reducing the valve opening pressure between the first rotation speed and the second rotation speed with respect to an increase in the rotation speed is interposed between the high-pressure flow passage and the low-pressure flow passage, and the drive-side fluid pressure When the discharge pressure of the drive means exceeds a set pressure lower than the maximum valve opening pressure of the relief valve, suction amount limiting means for reducing the suction amount of the drive side fluid pressure drive means is provided. In addition to the effect of 3, the effect of suppressing the amount of working fluid discharged from the high-pressure side flow passage to the low-pressure side flow passage through the relief valve and suppressing the temperature rise of the working fluid can be obtained.

According to the four-wheel drive vehicle of the fifth aspect, in the invention of the third and fourth aspects, the valve opening pressure of the relief valve is set to be substantially zero at the second rotation speed. At the second rotational speed, the pressure in the high-pressure side passage communicating between the driving fluid pressure driving means and the driven fluid pressure driving means becomes the gauge pressure, and the transmission torque can be smoothly reduced to zero without generating a step. It is possible to obtain an effect that it is possible to shift from the four-wheel drive state to the two-wheel drive state without giving the driver any uncomfortable feeling.

Further, according to the four-wheel drive vehicle according to claim 6, in the invention according to claims 3 to 5, the relief valve is
Since the valve opening pressure is configured to control the valve opening pressure by the driven fluid pressure driving means side pressure of the differential pressure detecting orifice inserted between the driven fluid pressure driving means and the low pressure side flow path,
The effect that the valve opening pressure of the relief valve can be easily controlled only by forming the pilot flow path in the fluid pressure circuit without providing another sensor such as a vehicle speed sensor separately is obtained.

Further, according to the four-wheel drive vehicle of the seventh aspect, in the invention of the first to sixth aspects, the drive-side fluid pressure drive means combines a plurality of pumps having different flow rate characteristics with respect to rotation speed. With this configuration, even when a pump whose flow characteristics cannot be changed in multiple stages by itself is used, an effect that a desired flow characteristics can be surely obtained can be 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 and a maximum transmission torque 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 characteristic diagram showing flow characteristics when a plurality of pumps whose flow characteristics cannot be changed in multiple stages are used as drive-side fluid pressure driving means.

FIG. 5 is a schematic configuration diagram showing another embodiment of the variable displacement pump motor.

FIG. 6 is a schematic configuration diagram showing another embodiment of the torque limiting means.

FIG. 7 is a schematic configuration diagram showing an embodiment in which a differential device is omitted.

FIG. 8 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.

FIG. 9 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 10 shows a discharge flow rate characteristic of a suction throttle type piston pump and a swash plate type variable displacement pump motor applied to the second embodiment;
FIG. 3 is a characteristic diagram showing a maximum transmission torque characteristic and a relief pressure characteristic.

FIG. 11 is a schematic configuration diagram showing a third embodiment of the present invention.

FIG. 12 is a characteristic diagram showing flow characteristics of a conventional drive side hydraulic pump and a driven side hydraulic pump.

[Explanation of symbols]

 REFERENCE SIGNS LIST 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 pipe 8L low pressure pipe 9 electromagnetic switching valve for forward / reverse switching 10 swash plate type variable displacement pump motor 11 difference Orifice for pressure generation 12 Variable swash plate mechanism 13 Relief valve 15 Check valve 16 Orifice 17 Rear wheel 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 Direction Control Valve 13P Pilot Operated Relief Valve 40 Suction Throttle Valve

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shigeru Kamagaya Nissan Motor Co., Ltd. 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture (56) References JP-A-5-169996 (JP, A) JP-A-63- 176734 (JP, A) JP-A-53-20231 (JP, A) JP-A-5-246259 (JP, A) JP-A-5-131859 (JP, A) JP-A-2-200350 (JP, A) JP-A-63-284037 (JP, A) JP-A-61-89059 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60K 17/34-17/356

Claims (7)

(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 The drive means is provided with a flow path communicating the discharge port and the suction port with each other to constitute a fluid pressure transmission mechanism, and the flow rate of the drive side fluid pressure drive means is set to be less than the flow rate of the driven side fluid pressure drive means. In a four-wheel drive vehicle, the capacity of the driven fluid pressure drive means is reduced from the first rotation speed at which the maximum transmission torque starts to decrease, and the capacity of the drive fluid pressure drive means is reduced to the first speed . A four-wheel drive vehicle characterized by being set to a maximum value at a second rotation speed that is higher than the rotation speed and does not require transmission torque. 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 The drive means is provided with a flow path communicating the discharge port and the suction port with each other to constitute a fluid pressure transmission mechanism, and the flow rate of the drive side fluid pressure drive means is set to be less than the flow rate of the driven side fluid pressure drive means. In a four-wheel drive vehicle, the capacity of the driven fluid pressure driving means is reduced from the first rotation speed at which the maximum transmission torque starts to decrease, and the capacity of the driven fluid pressure driving means is changed to the driven fluid pressure. in accordance with the capacitance characteristic of the drive means reducing the first high Ku than the revolving speed second capacitor lower rotational speed than the rotational speed of, so that the maximum value further by a second rotational speed which eliminates the need for transmission torque Four-wheel drive characterized by being set Car. 3. A drive axle driven by a prime mover,
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 The drive means communicates the discharge port and the suction port with each other through a high-pressure flow path and a low-pressure flow path to form a fluid pressure transmission mechanism, and the flow rate of the drive fluid pressure drive means is controlled by the driven fluid pressure drive means. In the four-wheel drive vehicle set to be less than the flow rate, the capacity of the driven fluid pressure driving means is reduced from the first rotation speed at which the maximum transmission torque starts to decrease, and the capacity of the driving fluid pressure driving means is reduced. Is set to a maximum value at a second rotation speed that is higher than the first rotation speed and no transmission torque is required, and the valve opening pressure between the high-pressure flow path and the low-pressure flow path is set to the first rotation speed. Between the number of revolutions and the second number of revolutions for an increase in the number of revolutions Four-wheel drive vehicle, wherein a relief valve is interposed that. 4. A drive axle driven by a prime mover,
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 The drive means communicates the discharge port and the suction port with each other through a high-pressure flow path and a low-pressure flow path to form a fluid pressure transmission mechanism, and the flow rate of the drive fluid pressure drive means is controlled by the driven fluid pressure drive means. In the four-wheel drive vehicle set to be less than the flow rate, the capacity of the driven fluid pressure driving means is reduced from the first rotational speed at which the maximum transmission torque starts to decrease, and the flow rate of the driving fluid pressure driving means is reduced. Is set to a maximum value at a second rotation speed that is higher than the first rotation speed and does not require transmission torque, and furthermore , the valve opening pressure is increased between the high pressure flow path and the low pressure flow path by the first rotation speed. Between the number of revolutions and the second number of revolutions, A suction valve that interposes a relief valve and reduces a suction amount of the driving-side fluid pressure driving unit when a discharge pressure of the driving-side fluid pressure driving unit exceeds a set pressure lower than a maximum valve opening pressure of the relief valve; A four-wheel drive vehicle characterized by having a quantity limiting means. 5. The four-wheel drive vehicle according to claim 3, wherein the valve opening pressure of the relief valve is set to be substantially zero at the second rotation speed. 6. The relief valve is opened by the pressure of the differential pressure detecting orifice, which is interposed between the driven fluid pressure driving means and the low pressure flow passage, on the driven fluid pressure driving means side. The four-wheel drive vehicle according to any one of claims 3 to 5, wherein the four-wheel drive vehicle is configured to control the pressure. 7. The four-wheel drive according to claim 1, wherein the drive-side fluid pressure drive means is configured by combining a plurality of pumps having different flow rate characteristics with respect to the number of rotations. car.