JPH07304345A - Four-wheel drive - Google Patents

Abstract

PURPOSE:To provide a four-wheel drive which can suppress the deterioration of the fuel consumption in the high speed traveling without generating the physically discomfortable feeling on a driver, by gently reducing the max. transmission torque. CONSTITUTION:The driving force of an engine 1 is transmitted to front wheels 5 and the revolution shaft 6a of a piston pump 6 through a transmission 2 and a differential gear device 3. The discharge port 6c and the suction port 6b of the pump 6 are connected with the port of a selector valve 9 for the selection between advance and retreat which is built in the motor 10 of a swash plate type variable capacity pump through a high pressure pipe 8H and a low pressure pipe 8L, and a hydraulic transmission device is constituted. The flow rate characteristic of the pump motor 10 is set so that the rate of increase for the increase of the number of revolution reduces at the number of revolution where the max. transmission torque starts reduction, and the max. value is generated at the number of revolution which does not require the transmission torque of the pump 6.

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 a rotational driving force of a main engine is transmitted to front wheels and rear wheels, and particularly, the driving force is transmitted by a fluid pressure transmission mechanism. It relates to four-wheel drive vehicles.

[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 like a part-time system, the switching operation is Besides being troublesome, it is not suitable for passenger cars due to problems such as tight corner braking. On the other hand, a full-time four-wheel drive vehicle can eliminate the tight corner braking phenomenon, but it requires a differential limiting device for the center differential, which complicates the device. Further, regardless of the part-time type and the full-time type, since the drive system used in the current passenger cars has a propeller shaft, this increases the weight of the front-wheel drive vehicle, adversely affects the vehicle interior space, and deteriorates fuel efficiency. Noise and vibration are worsened, and even in the case of a rear-wheel drive vehicle, there is an unavoidable increase in weight and fuel consumption.

[0003] Therefore, conventionally, for the purpose of reducing the weight of the constituent members, for example, JP-A-3-224830 (hereinafter, referred to as
Power transmission of a four-wheel drive vehicle having front wheels that are directly driven by a prime mover and rear wheels that are driven via a clutch operated by fluid pressure, as described in the first conventional example). A device, which is driven in association with the front wheels
A fluid pressure pump, a second fluid pressure pump that is driven in conjunction with the rear wheel, and a connecting oil passage that connects the discharge port of the first fluid pressure pump and the suction port of the second fluid pressure pump. A first fluid pressure pump and a first fluid pressure pump due to a difference in rotation speed between the front wheel side and the rear wheel side, and a hydraulic pressure supply oil passage that connects and connects the connecting oil passage and the working hydraulic chamber of the fluid pressure clutch. A four-wheel drive vehicle has been proposed in which the transmission of driving force is controlled by controlling a clutch according to the flow rate difference between two fluid pressure pumps.

Further, for the purpose of transmitting a driving force by using a hydraulic power transmission device 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 (1), the first hydraulic pump configured by, for example, a vane pump that rotates in conjunction with the front wheels and generates oil pressure according to the rotation speed, and the rotation in conjunction with the rear wheels generate oil pressure according to the rotation speed. A configuration having a second hydraulic pump that is similarly formed of a vane pump and an oil passage that connects one of the discharge ports of the first and second hydraulic pumps and the other suction port, respectively. Is proposed.

[0005]

However, in the four-wheel drive vehicle of the first conventional example, 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 the weight reduction has a certain limit, and the adverse effect on the vehicle interior space cannot be improved at all.

In addition, in the four-wheel drive vehicle of the second conventional example, since the hydraulic transmission is used, the propeller shaft is omitted and the weight is reduced, the vehicle interior space is secured, the fuel consumption is improved, and noise and noise are reduced. Although vibration can be reduced, the front and rear wheels both rotate at high speed during high-speed travel, which increases the discharge flow rate of the hydraulic pump, which increases pipe resistance, which increases drag resistance of the system. The increase in pressure loss causes deterioration of fuel consumption, and also causes bubbles due to an increase in oil temperature in the system and an abnormal decrease in pressure because the suction of hydraulic oil cannot catch up at the suction port of the second hydraulic pump. There is an unsolved problem that cavitation is likely to occur. Here, in order to reduce the piping resistance when the flow rate increases, the diameter of the piping should be increased,
Considering space and cost, there is a certain limit.

In order to suppress such deterioration of fuel consumption during high-speed traveling, as shown in FIG. 12, the first hydraulic pump on the drive side has a variable capacity, and its flow rate characteristic is represented by a characteristic curve L _11. Maximum flow rate Q _1MAX with flow rate peaked at a rotation speed N _F2 equivalent to high-speed running that does not require four-wheel drive
It is conceivable to limit the flow rate characteristic to a maximum flow rate Q _2MAX higher than the maximum flow rate Q _1MAX as shown by a characteristic curve L ₁₂ by limiting the flow rate characteristic to the second hydraulic pump on the driven side and changing the second hydraulic pump to a variable capacity. In order to transmit the torque when such a flow rate characteristic is provided, the first hydraulic pump flow rate needs to exceed the second hydraulic pump flow rate, but the second hydraulic pump flow rate on the driven side becomes the drive side. The maximum transmission torque at the rotational speed N _R1 when the maximum flow rate Q _2MAX of the first hydraulic pump is reached is shown in FIG.
Then, as indicated by the characteristic curve L ₁₃ , there is a new problem that the driver may feel uncomfortable due to the rapid decrease.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and the maximum transmission torque is gently reduced to reduce the fuel consumption at high speed without causing the driver to feel uncomfortable. It is an object of the present invention to provide a four-wheel drive vehicle that can suppress deterioration.

[0009]

In order to achieve the above-mentioned object, a four-wheel drive vehicle according to a first aspect of the present invention comprises a drive axle driven by a main motor and a drive side driven in conjunction with the drive axle. A fluid pressure drive means and a driven side fluid pressure drive means that is driven in conjunction with a driven axle, wherein the drive side fluid pressure drive means and the driven side fluid pressure drive means are provided with a discharge port and a suction port of each other. In a four-wheel drive vehicle in which a fluid pressure transmission mechanism is configured by providing a flow path communicating with each other, and the flow rate of the drive side fluid pressure drive means is set to be equal to or less than the flow rate of the driven side fluid pressure drive means, the driven side fluid pressure drive The capacity of the means reduces the capacity from the first rotational speed at which the maximum transmission torque starts to decrease, and the flow rate of the drive side fluid pressure drive means becomes the maximum value at the second rotational speed at which transmission torque is not required. Is set to

According to another aspect of the present invention, there is provided a four-wheel drive vehicle having a drive axle driven by a main motor, a drive side fluid pressure drive means driven in conjunction with the drive axle, and a driven axle. A driven-side fluid pressure driving means to be driven, and a fluid-pressure transmission mechanism is provided by providing a flow path that connects the driving-side fluid pressure driving means and the driven-side fluid pressure driving means to each other's discharge port and suction port. In a four-wheel drive vehicle configured such that the flow rate of the drive side fluid pressure drive means is set to be equal to or less than the flow rate of the driven side fluid pressure drive means, the capacity of the driven side fluid pressure drive means starts decreasing the maximum transmission torque. The capacity is reduced from the number of revolutions of 1, and the capacity is reduced from the number of revolutions higher than the first number of revolutions in accordance with the flow rate of the drive side fluid pressure drive means in accordance with the capacity characteristic of the driven side fluid pressure drive means. The second, which eliminates the need for transmission torque It is characterized in that it is set to be the maximum value in a converter number.

Further, in the four-wheel drive vehicle according to a third aspect of the present invention, the drive axle driven by the main prime mover, the drive side fluid pressure drive means driven in conjunction with the drive axle, and the driven axle are interlocked. Driven side fluid pressure driving means, and the driving side fluid pressure driving means and the driven side fluid pressure driving means communicate with each other's discharge port and suction port through a high pressure side passage and a low pressure side passage. In a four-wheel drive vehicle in which the flow rate of the drive side fluid pressure drive means is set to be equal to or less than the flow rate of the driven side fluid pressure drive means, the capacity of the driven side fluid pressure drive means is maximum transmitted. The capacity is reduced from the first rotational speed at which the torque starts to be reduced, and the flow rate of the drive-side fluid pressure drive means is set to a maximum value at the second rotational speed at which transmission torque is no longer required. Before opening the valve between the high pressure passage and the low pressure passage It is characterized in that interposed a relief valve to reduce with increasing rotational speed between the first speed and the second speed.

Furthermore, a four-wheel drive vehicle according to a fourth aspect of the present invention includes a drive axle driven by a main prime mover, drive side fluid pressure drive means driven in conjunction with the drive axle, and interlocked with a driven axle. Driven side fluid pressure driving means, and the driving side fluid pressure driving means and the driven side fluid pressure driving means communicate with each other's discharge port and suction port through a high pressure side passage and a low pressure side passage. In the four-wheel drive vehicle in which the fluid pressure transmission mechanism is configured to set the flow rate of the drive side fluid pressure drive means to be equal to or less than the flow rate of the driven side fluid pressure drive means, the capacity of the driven side fluid pressure drive means is maximum. The capacity is reduced from the first rotation speed at which the transmission torque starts to be reduced, and the flow rate of the drive side fluid pressure drive means is set to the maximum value at the second rotation speed at which the transmission torque is no longer required, and Before opening the valve opening pressure between the high pressure passage and the low pressure passage A relief valve that reduces the rotation speed between the first rotation speed and the second rotation speed is inserted, and the discharge pressure of the drive-side fluid pressure drive means is greater than the maximum valve opening pressure of the relief valve. It is characterized in that suction amount limiting means for reducing the suction amount of the drive side fluid pressure driving means is provided when the set pressure exceeds a low level.

Furthermore, a four-wheel drive vehicle according to a fifth aspect is the four-wheel drive vehicle according to the third or fourth aspect, wherein the valve opening pressure of the relief valve is substantially zero at the second rotational speed. The feature is that it is set. A four-wheel drive vehicle according to a sixth aspect is the four-wheel drive vehicle according to any one of the third to fifth aspects, wherein the relief valve has a valve opening pressure of a driven fluid pressure drive means and a low pressure side flow passage. It is characterized in that the valve opening pressure is controlled by the pressure on the driven side fluid pressure driving means side of the throttle inserted between and.

Further, a four-wheel drive vehicle according to a seventh aspect is the 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 of the present invention, the rotation of the drive axle driven by the main prime mover causes the drive-side fluid pressure drive means to discharge a working fluid at a flow rate corresponding to the rotational speed, and the one-way communication is established. 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 passage, and discharged from this driven fluid pressure driving means, drives the fluid pressure driving means through the other communication passage. 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. However, as the rotational speed difference increases, the transmission torque increases and shifts to the four-wheel drive state. . At this time,
The capacity of the driven-side fluid pressure driving means is reduced from a first rotational speed at which the maximum transmission torque is started to decrease, and the flow rate of the driving-side fluid pressure driving means is maximized at a second rotational speed at which transmission torque is not required. Since the value is set to be a value, even when the driven-side fluid pressure drive means exceeds the first rotation speed,
The maximum transmission torque is gradually reduced until the flow rate of the driven fluid pressure drive means reaches the maximum flow rate of the drive fluid pressure drive means.

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 to the first rotation in accordance with the flow rate characteristic of the driven side fluid pressure drive means. Since the capacity is reduced when the rotational speed is higher than the number, the flow rate difference between the drive side fluid pressure drive means and the driven side drive means is reduced to facilitate the generation of the transmission torque, and the maximum reduction of the transmission torque is suppressed.

In the four-wheel drive vehicle according to the third aspect, in addition to the action of the first aspect, the opening pressure of the relief valve inserted between the high pressure side flow passage and the low pressure side flow passage has the first rotation speed. The predetermined set pressure is maintained until the temperature reaches the first rotation speed, but the pressure decreases as the rotation speed increases between the first rotation speed and the second rotation speed. The pressure in the high-pressure side passage between the pressure driving means is reduced, and the transmission torque is reduced more smoothly toward the second rotation speed.

In the four-wheel drive vehicle according to the fourth aspect, in addition to the action of the third aspect, before the relief valve is opened, the working fluid intake amount of the drive side fluid pressure drive means is the intake amount limit. Means that the discharge flow rate of the drive side fluid pressure drive means is reduced, and the relief valve opens to release the hydraulic oil from the high pressure side passage to the low pressure side passage. Controls 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 drive side fluid pressure drive means and the driven side fluid pressure drive means are connected. The pressure in the high-pressure side flow path communicating with each other becomes a gauge pressure, and the transmission torque can be smoothly zeroed without causing a step. In the four-wheel drive vehicle according to claim 6, the valve opening pressure of the relief valve is controlled based on the driven-side fluid pressure driving means side pressure of the throttle provided between the driven-side fluid pressure driving means and the low-pressure side passage. Therefore, the valve opening pressure can be controlled without separately providing another sensor or the like.

In the four-wheel drive vehicle according to the seventh aspect, 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, so that it is difficult to control the flow rate in multiple stages alone. Even with a pump, the flow rate 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 configuration diagram showing a first embodiment when the present invention is applied to a four-wheel drive vehicle based on a front-wheel drive vehicle, in which 1 is an engine as a main engine,
The rotational driving force of the engine 1 is input to the front wheel side differential device 3 via the transmission 2, and the front wheels 5 are connected to the output side of the differential device 3 via a front axle 4 as a drive axle. .

The front wheel side differential device 3 is rotationally driven by a ring gear 3b formed in a differential gear case 3a meshing 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 these pinion 3d, and a front axle 4 is connected to these side gears 3e.

Further, the 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 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, which is a strainer 7a having a reservoir tank 7 disposed therein.
Is connected to the low pressure pipe 8 as a low pressure flow path.
It is connected to the tank port T of the two-position four-port electromagnetic directional control valve 9 through L, and the discharge port 6c is connected to the pump port P of the electromagnetic directional control valve 9 for forward / backward switching through the high pressure pipe 8H as a high pressure passage. ing.

Here, the suction throttle type piston pump 6 is
The suction port and the discharge port do not interchange depending on the rotation direction of the rotating shaft 6a, and the discharge flow rate is shown by the characteristic curve L in FIG.
_As indicated by ₁ , the number of revolutions N of the rear axle 18 at which the maximum transmission torque described below starts to decrease from the number of revolutions of the front axle 4 being "0".
Until reaching a predetermined value N _F1 higher than _R1, it increases at a relatively large rate of increase in proportion to the increase of the rotation speed, and reaches a predetermined value N _F1.
The above _F1 increases at a relatively small rate of increase in proportion to the increase of the rotational speed, saturated at the maximum discharge flow rate Q _1MAX at a rotational speed N _F2 axle 4 before that it does not require a four-wheel drive state becomes faster running state Is set to.

In the electromagnetic directional control valve 9 for switching between forward and reverse, the pump port P communicates with the output port A and the tank port T communicates with the output port B at the normal position where the solenoid 9a is in the non-energized state, and the solenoid 9a is connected. 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 suction the swash plate type variable displacement pump motor 10 as a fluid pressure pump motor. Connected to the discharge ports 10a and 10b, the high-pressure oil of the high-pressure pipe 8H is connected to the suction / discharge port 10a of the variable displacement pump motor 10 and the low-pressure pipe 8L is connected to the suction / discharge port 10b in the normal position to rotate the rotary shaft. 10c
Is rotationally driven in a forward rotation direction, for example, clockwise as viewed from the left side surface, and conversely, the high pressure oil in the high pressure pipe 8H is sucked and discharged from the variable displacement pump motor 10b at the offset position.
Further, the low-pressure pipe 8L is connected to the suction / discharge port 10a, and the rotary shaft 10c is rotationally driven in the rotation direction during forward traveling, for example, counterclockwise when viewed from the left side surface.

The electromagnetic 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 a pipe. There is. Further, the solenoid 9a of the electromagnetic directional control valve 9 is energized, and the solenoid 9a is connected to the DC power source 9c via the shift position detection switch 9b which is turned on when the reverse lever is selected by the shift lever (not shown). Thus, the vehicle is controlled to be in a non-energized state during forward traveling and to be energized during backward traveling.

The flow rate of the variable displacement pump motor 10 is
Low pressure pipe 8L 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 configured to include the hydraulic cylinders 12a by the differential pressure generated at both ends of the differential pressure detecting orifice 11 inserted in the characteristic curve L in FIG. _As shown by ₂ , until the rear axle rotation speed reaches the first rotation speed N _R1 at which the maximum transmission torque begins to decrease, it is higher than the increase rate of the drive side piston pump 6 in proportion to the increase in the rotation speed. Rotation speed N increases at an increasing rate
Maximum flow rate Q of piston pump 6 when _R1 is reached
_The discharge flow rate Q ₂₁ becomes lower than _1MAX , and as the number of revolutions increases thereafter, the number of revolutions N _{F1 to} N _{F2 of} the piston pump 6 described above increases.
It is set to increase at a relatively low rate of increase, which is approximately equal to the rate of increase between.

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 unique discharge flow rate and the gear ratio of the gear connected to the rotary shaft are set so that the discharge flow rate of 0 is higher than the discharge flow rate of the piston pump 6, and the rotation speed is variable from "0" to a predetermined value N _F2. Capacity pump motor 10 and piston pump 6
It is preferable to set the discharge flow rate difference to about several percent in order to satisfactorily generate the transmission torque, and if the flow rate difference between the two is too large, the transmission torque is less likely to be generated.

Further, a relief valve 13 for defining the upper limit of 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 the hydraulic pump 6 is also provided. And the high-pressure pipe 8H from the low-pressure pipe 8L side to the communication pipe 14A that communicates between the high-pressure pipe 8H and the low-pressure pipe 8L between the electromagnetic direction switching valves 9.
A communication pipe 1 in which a check valve 15 that allows a fluid flow to the side is inserted and is arranged in parallel with the communication pipe 14A.
A fixed orifice 16 is connected to 4B in parallel relationship with the check valve 15.

On the other hand, a gear 10d is attached to the rotary shaft 10c of the swash plate type variable displacement pump motor 10.
A ring gear 17b formed in a differential gear case 17a of the rear wheel side differential device 17 is meshed with d. The rear wheel side differential device 17 has a configuration similar to that of the front wheel side differential device 3 described above, and a pair of pinion shafts 17 formed in the differential gear case 17a.
pinion 17d is attached to c, and these pinion 17
A pair of side gears 17e meshes with d, a rear axle 18 is connected to these side gears 17e, and a rear wheel 19 is connected to this rear axle 18.

Next, the operation of the above embodiment will be described. now,
When the vehicle stops on a high friction coefficient road such as a dry road surface and starts forward traveling in a braking state in which the engine 1 is in an idling state, by switching the shift lever to the forward traveling side, the vehicle can be started. However, at this time, the shift position detection switch 9b on the reverse traveling side is maintained in the OFF state, so that the solenoid 9a of the forward / reverse switching electromagnetic directional control valve 9 is maintained in the non-energized state, and the switching position is changed. 1
Continue the normal position shown in. In this state, release the brake pedal and step on the accelerator pedal,
The rotational force of the engine 1 is transmitted to the front wheel side differential device 3 via the transmission 2, and the front wheel side actuating device 3 rotationally drives the front wheels 5 in the forward direction to start the forward movement.

At this time, the rotary shaft 6a of the suction throttle type piston pump 6 is rotationally driven in the clockwise direction as viewed from the left side surface, so that the piston pump 6 discharges hydraulic oil at a discharge flow rate according to the rotational speed. 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 / reverse switching electromagnetic directional switching valve 9, but the rear wheel 19 and the front wheel 5 are connected to each other when the vehicle starts. Since it is driven to rotate in the same direction at the same rotation speed, the rear wheel side differential device 1
Rotating shaft 1 of swash plate type variable displacement pump motor 10
0c rotates clockwise as viewed from the left side surface, whereby the working oil is sucked from the suction / discharge port 10a and the working oil is discharged from the suction / discharge port 10b.

Here, the discharge flow rates of the suction throttle type piston pump 6 and the swash plate type variable displacement pump motor 10 are, as shown in FIG.
Since the discharge flow rate of the high pressure hydraulic fluid 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 is reduced. Does not go up. That is, the variable displacement pump motor 10 does not act as a hydraulic motor and the driving force is not transmitted to the rear wheel 19,
It travels forward in the same manner as 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 in the discharge flow rate between the piston pump 6 and the variable displacement pump motor 10 also allows a difference in the number of rotations of the front and rear axles 4 and 18 caused by a diameter change due to wear of the tire, and occurs in a tire having a different diameter. The driving force is not transmitted when the rotational speed difference is about the same, the front-wheel drive vehicle state is maintained, and it is possible to suppress deterioration of fuel consumption. Next, when the vehicle starts on a low friction coefficient road such as an icy road or a snowfall road, the front wheels 5 are first driven to rotate as described above, but since the road is a low friction coefficient road, the front wheels 5 slip. , The front wheel 5 and the rear wheel 19 have a high rotational speed difference between the front wheel 5 and the rear wheel 19, 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, the resistance of the variable displacement pump motor 10 becomes a load, and the operating oil pressure of the high-pressure pipe 8H rises. Therefore, the variable displacement pump motor 10 operates as a hydraulic motor, and the pressure of the high-pressure pipe 8H is adjusted accordingly. The driving force is transmitted to the rear wheel 19 via the rear wheel side differential device 17.

That is, as shown in FIG. 3, the torque transmitted to the rear wheel 19 side is generated only when there is a difference in the number of rotations between the front and rear wheels, and rapidly increases with an increase in the difference in the number of rotations. The pressure limit limits the maximum torque T _MAX . Due to this torque limiting action, it becomes possible to reduce the strength of the components such as the rear wheel differential device 17 and the drive shaft, as compared with the conventional four-wheel drive vehicle.
Weight, fuel consumption, and cost can be reduced.

The torque transmitted to the rear wheel 19 side is
As shown in FIG. 3, it has a characteristic that a driving force is easily generated with a smaller rotational speed difference at lower speeds. As shown in FIG. 2, this is due to the suction throttle piston pump 6 and the swash plate type variable displacement pump motor 10. This is because the flow rate in the proper range of the discharge flow rate characteristic is that the flow rate difference increases as the wheel speed increases until the wheel speed reaches V _R1 .

On the other hand, as shown in FIG. 2, the swash plate type variable displacement pump motor 10 has a displacement after the rear wheel speed V _R reaches V _{R1, that} is, the rear wheel rotational speed reaches the first rotational speed N _R1. decreases gradually, Therefore, the characteristic curve L ₃ maximum torque transfer in FIG. 2
As shown by, the wheel speed decreases as the wheel speed increases, and when the rear wheel speed V _R reaches a predetermined value V _{R2, that} is, the rear wheel axle rotation speed N _R reaches the second rotation speed N _R2, it changes. Since the discharge flow rate of the displacement pump motor 10 exceeds the maximum flow rate Q _1MAX of the piston pump 6, transmission torque cannot be generated and the maximum transmission torque becomes zero.

As described above, by setting the flow rate characteristics of the piston pump 6 and the variable displacement pump motor 10 as shown by the characteristic curves L ₁ and L ₂ in FIG. 2, the maximum transmission torque is the wheel speed V _R1 or the first. It gradually decreases when the number of revolutions N _R1 is exceeded, and it is possible to reliably prevent the maximum transmission torque from sharply decreasing as in the conventional example. It is possible to reliably prevent the driver from feeling uncomfortable by suppressing the change to.

Further, in the rise of torque in FIG. 3, the amount of leakage from the high pressure pipe 8H to the low pressure pipe 8L is controlled by the fixed orifice 16 inserted in the communication pipe 14B which connects the high pressure pipe 8H and the low pressure pipe 8L. The characteristics can be set arbitrarily by changing the rise of pressure. Due to the temperature characteristics associated with the viscosity change of the hydraulic oil possessed by the orifice, the amount of leakage decreases and the driving force is more likely to be generated at low temperatures than at high temperatures. There is an advantage that it becomes easy to use four-wheel drive in winter.

Next, when the vehicle is moved backward, the shift position detection 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 control valve 9 is energized. As shown in FIG. 4, the switching position is switched from the normal position to the offset position, whereby the working oil in the high-pressure pipe 8H is transferred to the suction / discharge port 1 of the swash plate type variable displacement pump motor 10.
0b, and the working oil discharged from the suction / discharge port 10a is returned to the low-pressure pipe 8L side, whereby the rotary shaft 10c of the variable displacement pump motor 10 is reversed from that during forward traveling, and the rear wheel 19 is reversed. Rotate. Therefore, when the vehicle is moving backward, the transmission of the driving force is exactly the same as when moving forward, and pressure is generated in the high-pressure pipe 8H only when the front wheel 5 slips and the rotational speed difference between the front and rear axles 4 and 18 occurs. However, when the driving force is transmitted to the rear wheel 19 and the difference in the rotational speeds of the front and rear axles 4 and 18 is small, the insufficient intake amount of the swash plate type variable displacement pump motor 10 is the low pressure pipe 8L and the communication pipe 14.
It is replenished via A and the check valve 15.

At this time, as described above, in the suction throttle type piston pump 6 on the front wheel side, the suction port and the discharge port of the pump are not interchanged even if the rotation direction is reversed, and
Since the forward / backward switching electromagnetic directional switching valve 9 is built in the variable displacement pump motor 10, expensive high pressure piping can be used only for the high pressure piping 8H, and the relief valve 13,
Since the check valve 15, the orifice 16 and the like may be provided so as to handle only one direction of flow, the oil passage structure can be extremely simplified as compared with the case of using a pump of another system.

In a vehicle equipped with an anti-skid control device based on a front-wheel drive vehicle, the rotational speed of the front wheels becomes smaller than the rotational speed of the rear wheels during braking, so that no driving force is generated by the hydraulic transmission mechanism and the anti-skid control is 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 drive side fluid pressure driving means is shown by the characteristic curve L _{1 in} FIG.
As described above, the case where the two-stage polygonal line is set has been described, but the present invention is not limited to this, and as shown by the characteristic line L ₂₁ shown by the alternate long and short dash line in FIG. It is also possible to use a characteristic that increases in accordance with an increase in the number of revolutions up to a predetermined value N _F2 . In short, it is possible to set an arbitrary flow rate characteristic within the shaded area in FIG. in this case,
If the difference between the discharge flow rates of the piston pump 6 and the variable displacement pump motor 10 is too large, it will be difficult to generate the transmission torque. Therefore, in reality, it can be set within the range on the characteristic curve L ₂ side of the characteristic line L _21. preferable.

In the first embodiment, the case where the suction throttle type piston pump 6 is applied as the drive side fluid pressure drive means has been described, but the present invention is not limited to this and a variable capacity of another type. It is also possible to apply a pump, and furthermore, for a single pump, the characteristic curve L ₁ of FIG.
When it is not possible to obtain the flow rate characteristic of, for example, as shown in FIG. 4, a radial piston pump that saturates at a rotation speed N _F1 as shown by a characteristic curve L ₁₃ and a rotation speed as shown by a characteristic curve L ₁₄ are shown. The characteristic of the characteristic curve L ₁ may be realized by connecting a radial piston pump saturated with N _F2 in parallel to the front axle 4 and adding the discharge flow rates of both.

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, but the invention is not limited to this, and the low pressure pipe 8L side. Differential pressure detection orifice 11
, The pressure on the outlet side of the differential pressure detection orifice 11 becomes the atmospheric pressure, which 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 working orifice 11, that is, the pressure on the tank port T side of the electromagnetic directional control valve 9 may be introduced into the head cover side hydraulic chamber 12b of the hydraulic cylinder 12a of the swash plate variable mechanism 12.

Further, in the first embodiment, the case where the relief valve 13 is applied as the transmission torque limiting means has been described, but the present invention is not limited to this, and as shown in FIG. 6, the discharge pressure of the piston pump 6 is volume-controlled. A suction throttle valve 21 may be provided, which receives the pressure as a pressure and controls the opening of the suction passage on the suction port 6b side of the piston pump 6 to be small when the discharge pressure exceeds a predetermined pressure. In this case, when the pump discharge flow rate exceeds the specified pressure, the pump suction amount decreases, so the pump discharge pressure decreases and it is possible to limit the torque. At the same time, when the relief valve is used, continuous operation is possible. Although the oil temperature rises at the time of high load use, when the intake throttle valve 21 is provided, the discharge flow rate decreases, so that heat generation can be suppressed.

Further, although the case where the rear wheel side differential device 17 is provided has been described in the first embodiment, the present invention is not limited to this, and as shown in FIG. 7, the rear wheel differential device is provided. 17 is omitted, and instead of this, the left and right rear wheels 19L, 1
The 9R left and right axles 18L, 18R may be individually provided with the swash plate type variable displacement pump motors 10L, 10R. In this case, when different loads are applied to the left and right wheels during turning, for example, Variable displacement pump motor 10L, 10
Since the discharge flow rate difference corresponding to the difference naturally occurs in R, the differential function equivalent to that of the differential device can be exerted. In this case also, the relief valve 13 shown in the figure serves as the torque limiting means.
However, any of the suction throttle valves 21 shown in FIG. 6 may be used.

Furthermore, the rotary shaft 6 is used as a fluid pressure pump.
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 is applied has been described, but the present invention is not limited to this.
As shown in FIG. 8, the pump port P and the tank port T are connected to the suction port 30b and the discharge port 30c of the hydraulic pump 30 whose rotary shaft 30a is connected to the gear 3g, and the output ports A and B are connected to the high pressure pipe 8H. And an electromagnetic directional control valve 31 for forward / reverse switching similar to the electromagnetic directional control valve 9 for forward / reverse switching connected to 8L and 8L, another hydraulic pump such as a gear pump or a vane pump whose discharge direction is switched by forward / backward movement. In this case, the hydraulic pump in this case is input with the fixed displacement type shown in FIG. 1 or the differential pressure across the differential pressure generating orifice 32 inserted in the low pressure pipe 8L as shown in FIG. Variable mechanism 33 including hydraulic cylinder 33a
It may be any of the variable capacitance type equipped with.

In the first embodiment, the drive side fluid pressure drive means and the driven side fluid pressure drive means are connected to the high pressure passage 8.
Although the case where the H and the low pressure passages 8L communicate with each other has been described, the present invention is not limited to this, and the forward / reverse switching electromagnetic directional control valves 9 and 31 are omitted and the high pressure passage and the low pressure passage are separated. The present invention can be applied even when there is no such a case. next,
A second embodiment of the present invention will be described with reference to FIGS.

In the second embodiment, the transmission torque can be smoothly reduced when the second rotation speed N _R2 or more is reached. That is, in the second embodiment, as shown in FIG. 9, the relief valve 13 is composed of a pilot operated relief valve 13P, and the relief valve 13P connects the high pressure pipe 8H and the low pressure pipe 8L to the communication pipes 14A and 1L.
4B, which is inserted in the middle of a communication pipe 14C connected in parallel with the vent port of the relief valve 13P and is formed by the pressure on the high pressure side of the differential pressure detecting orifice 11, that is, on the tank port T side of the electromagnetic directional control valve 9. Plate type variable displacement pump motor 1
Except that a discharge pressure of 0 is input as the pilot pressure, it has the same configuration as the above-described embodiment of FIG.
The parts corresponding to those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

Here, the pilot operated relief valve 13
As shown in FIG. 10, the valve opening pressure of P is a characteristic curve until the discharge flow rate Q ₂ of the swash plate type variable displacement pump motor 10 reaches the first rotational speed N _R1 at which the discharge flow rate Q ₂₁ is reached. As shown by L ₂₄ , the maximum discharge pressure of the piston pump 6 that is set in advance is maintained at the maximum set pressure P _RMAX that regulates the maximum discharge pressure. However, when the rear wheel axle rotation speed N _R increases from this state, the slope is correspondingly increased. When the discharge flow rate Q _{2 of the} plate type variable displacement pump motor 10 gradually rises as shown by the characteristic curve L ₂ , the pressure on the high pressure side of the differential pressure detecting orifice 11 rises accordingly, and this is vented as pilot pressure. in order to be supplied to the port, and decreases in inverse proportion to the increase of the rear wheel axle rotation speed N _R, reaches the second rotational speed N _R2 reaches the minimum relief pressure P _RMIN, second rotational speed N _R2 or Maintain the minimum relief pressure P _RMIN .

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

However, when the rear wheel axle rotational speed N _R exceeds the first rotational 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 is opened. As the pressure on the high pressure side rises, the valve opening pressure of the pilot operated relief valve 13P decreases in inverse proportion to the increase of the rear wheel axle speed N _R as shown by the characteristic curve L ₂₄ of FIG. . Therefore, 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
Forward / reverse switching electromagnetic directional control valve 9 connected to the suction side of 0
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 As compared with the characteristic curve L ₃ of FIG. 2 in the first embodiment, the decrease rate of the transmission torque T becomes large, and the discharge flow rate Q ₂ of the variable displacement pump motor 10 reaches the maximum discharge flow rate Q _1MAX of the piston pump 6 and is transmitted. Immediately before reaching the second rotational speed N _{R2 at} which the torque T cannot be generated, the value becomes approximately zero, and the transmission torque T is smoothly reduced during this time, and when the second rotational speed N _R2 is reached. The transmission torque T suddenly becomes zero, but the amount of reduction of the transmission torque T at this time is extremely small, so it is possible to reliably prevent the driver from feeling uncomfortable.

Moreover, the valve opening pressure of the pilot operated relief valve 13P changes from the first rotational speed N _R1 to the rear wheel axle rotational speed N _R.
By decreasing in inverse proportion to the increase of the maximum pressure, the maximum pressure use range of the high-pressure pipe 8H that connects the discharge side of the piston pump 6 and the suction side of the variable displacement pump motor 10 via the electromagnetic directional control valve 9 for switching the front-rear direction is reduced. Up to the first rotational speed N _R1, the valve opening pressure of the relief valve 13 is constant as in the first embodiment described above, and the maximum pressure use range is the second rotational speed N _R2.
It is possible to reduce the frequency of action of maximum pressure and the high-pressure operating area compared to the case of up to, and the cost due to the use of high-pressure resistant materials and surface treatment required to secure the durability of the high-pressure pipe 8H. The cost can be reduced without increasing the cost.

Further, since the pressure on the upstream side 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. Since it is not necessary to provide a pressure sensor or the like, the structure can be simplified by this amount. Further, the valve opening pressure of the pilot operated relief valve 13P is set to the second
When the rotational speed N _R2 is reached to zero, that is, the gauge pressure is set, the transmission torque T does not have a step when the second rotational speed N _{R2 is} exceeded.
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. The third embodiment is different from the second embodiment described above when the relief valve 13P is opened.
The temperature rise of the working oil discharged from the high pressure side to the low pressure side through the relief valve 13P is prevented.
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 discharged accordingly. A piston pump is provided with a suction throttle valve 40 as suction amount limiting means for controlling the pressure to be small when the pressure exceeds a preset set pressure lower than the maximum opening pressure of the pilot operated relief valve 13P in the second embodiment. 6 has the same configuration as that of the second embodiment described above except that it is inserted on the suction port 6b side of FIG. 6, and the parts corresponding to those of FIG. This is omitted.

According to the third embodiment, when the vehicle starts to travel forward or backward, the low friction coefficient road is set until the rear wheel axle speed N _R reaches the first speed N _R1. When a rotational speed difference is generated between the front and rear wheels to increase the transmission torque T to the rear wheels, as in the case of traveling in the vehicle
When the pressure rises and reaches the pressure just before reaching the maximum opening pressure P _RMAX of the pilot operated relief valve 13P, the valve opening degree of the suction throttle valve 40 is decreased and the discharge of the piston pump 6 is reduced. Since the increase in the internal pressure of the high pressure pipe 8H is suppressed by the decrease in the flow rate, and the flow rate discharged to the low pressure pipe 8L side through the pilot operated relief valve 13P can be suppressed, the relief valve 1
It is possible to reliably prevent the temperature rise of the hydraulic oil due to passing through 3P.

In the second and third embodiments, the case where the valve opening pressure of the pilot operated relief valve 13P is controlled on the basis of the pressure on the upstream side of the differential pressure detecting orifice 11 has been described. It is not limited, but since the axle speed and the vehicle speed are in a proportional relationship, the governor pressure of the automatic transmission is controlled by the pilot operated relief valve 13
Even if the valve opening pressure is controlled by supplying it to the vent port of the above, the same operation as above can be obtained. Further, a proportional electromagnetic relief valve is applied as the relief valve, and the vehicle speed is detected based on the rotational speed of the output shaft of the transmission 2, for example, and the valve opening pressure of the proportional electromagnetic relief valve is detected based on the detected vehicle speed. By forming an exciting current for controlling, the valve 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 detected wheel speed value.

Further, also in the second and third embodiments, the rear wheel side actuating device 17 is used as in the first embodiment described above.
Omitted, the left and right axles 18 of the left and right rear wheels 19L and 19R
Swash plate type variable displacement pump motor 10L separately for L and 18R
And 10R may be provided, and another hydraulic pump such as a gear pump or a vane pump, in which a forward / reverse switching electromagnetic directional control valve is provided on the front wheel side pump side and the discharge direction is switched in forward / backward, is applied. Get out.

Furthermore, in the above-described first to third embodiments, the electromagnetic motor directional control valve 9 for switching between forward and reverse is used as the pump motor 1.
Although the case where the pump motor 10 is built in is described above, the present invention is not limited to this, and may be separately provided outside the pump motor 10. Furthermore, in the above-mentioned first to third embodiments, the embodiments based on the front-wheel drive vehicle have been described, but the present invention is not limited to this, and when the rear-wheel drive vehicle is also the base, the pump 6 is mounted on the rear wheel side. In addition, by arranging the pump motor 10 on the front wheel side, it is possible to obtain the same operational effect as that of 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 side fluid pressure drive means driven in conjunction with the drive axle. And a driven-side fluid pressure driving means that is driven in conjunction with the driven axle, and a flow path that connects the driving-side fluid pressure driving means and the driven-side fluid pressure driving means to each other's discharge port and suction port. In a four-wheel drive vehicle in which a fluid pressure transmission mechanism is provided and the flow rate of the drive side fluid pressure drive means is set to be equal to or less than the flow rate of the driven side fluid pressure drive means, the capacity of the driven side fluid pressure drive means is A configuration in which the capacity is reduced from the first rotational speed at which the maximum transmission torque starts to be reduced, and the flow rate of the drive-side fluid pressure drive means is set to a maximum value at a second rotational speed at which transmission torque is no longer required. Therefore, the maximum of the drive side fluid pressure drive means Can be the difference between the flow rates and the driven-side fluid pressure driving means to be gradually reduced, thereby, when the rotation speed than the first rotational speed is increased,
The maximum transmission torque can be gradually reduced to prevent the maximum transmission torque from abruptly decreasing, and the driver feels uncomfortable by gently changing from the four-wheel drive state to the two-wheel drive state. This has the effect of reliably preventing this.

According to the four-wheel drive vehicle of the second aspect, the drive axle driven by the main prime mover, the drive side fluid pressure drive means driven in conjunction with the drive axle, and the driven axle are interlocked. And a driven-side fluid pressure driving means that is driven by the above-mentioned method, wherein the driving-side fluid pressure driving means and the driven-side fluid pressure driving means are provided with a flow path that connects the discharge port and the suction port to each other. In a four-wheel drive vehicle that configures a mechanism and sets the flow rate of the drive side fluid pressure drive means to be equal to or less than the flow rate of the driven side fluid pressure drive means, reduces the capacity of the driven side fluid pressure drive means and reduces the maximum transmission torque. The capacity is reduced from the first rotational speed at which the first side is started, and the flow rate of the drive side fluid pressure drive means is adjusted to the first flow rate according to the capacity characteristic of the driven side fluid pressure drive means.
Since the capacity is reduced from the number of revolutions higher than the number of revolutions and the maximum value is set at the second number of revolutions when the transmission torque is not required, the drive side fluid pressure drive means and the driven side fluid pressure are set. The effect that the increase in the flow rate difference of the drive means can be suppressed and the maximum transmission torque can be gradually decreased is obtained.

Further, according to the four-wheel drive vehicle of the third aspect, the drive axle driven by the main prime mover, the drive side fluid pressure drive means driven in conjunction with the drive axle, and the driven axle are interlocked. Driven side fluid pressure driving means, and the driving side fluid pressure driving means and the driven side fluid pressure driving means are provided with a high pressure side flow path and a low pressure side flow path with respect to each other's discharge port and suction port. In a four-wheel drive vehicle in which a fluid pressure transmission mechanism is configured to communicate with each other and the flow rate of the drive side fluid pressure drive means is set to be equal to or less than the flow rate of the driven side fluid pressure drive means, the capacity of the driven side fluid pressure drive means is The capacity is reduced from the first rotational speed at which the maximum transmission torque starts to be reduced, and the flow rate of the drive-side fluid pressure drive means is set to the maximum value at the second rotational speed at which transmission torque is no longer required. , Open the valve between the high pressure passage and the low pressure passage Since a relief valve that reduces the increase in the rotation speed between the first rotation speed and the second rotation speed is interposed, the first rotation speed and the second rotation speed are reduced. Increase the reduction rate of the transmission torque,
It is possible to suppress a sharp decrease in the transmission torque at the second rotation speed and to more smoothly perform a decrease change in the transmission torque, and further, to reduce the frequency of operation of the maximum pressure in the high-pressure passage and to increase the high-pressure operation region. It is possible to reduce the cost, and it is possible to reduce the cost by suppressing an increase in cost due to the use of a high breakdown voltage material required for ensuring durability and surface treatment.

Further, according to the four-wheel drive vehicle of the fourth aspect, the drive axle driven by the main prime mover, the drive side fluid pressure drive means driven in conjunction with the drive axle, and the driven axle are provided. Driven-side fluid pressure driving means that are driven in conjunction with each other, and the driving-side fluid pressure driving means and the driven-side fluid pressure driving means have a high-pressure side flow path and a low-pressure side flow path with their mutual discharge ports and suction ports. In a four-wheel drive vehicle in which the flow rate of the drive side fluid pressure drive means is set to be equal to or less than the flow rate of the driven side fluid pressure drive means, the capacity of the driven side fluid pressure drive means First starts to reduce the maximum transmission torque
The capacity is reduced from the number of rotations, and the flow rate of the drive side fluid pressure drive means is set to a maximum value at the second number of rotations at which transmission torque is no longer required, and the high pressure passage and the low pressure passage are provided. A relief valve that reduces 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, and the discharge pressure of the drive-side fluid pressure drive means is the relief pressure. Since the suction amount limiting means for reducing the suction amount of the drive side fluid pressure driving means is provided when the set pressure lower than the maximum valve opening pressure of the valve is exceeded, in addition to the effect according to claim 3, The effect that the amount of working fluid discharged from the side flow passage to the low pressure side passage through the relief valve can be suppressed and the temperature rise of the working fluid can be suppressed can be obtained.

According to the four-wheel drive vehicle of the fifth aspect, in the inventions of the third and fourth aspects, the valve opening pressure of the relief valve is set to be substantially zero at the second rotational speed. At the second rotation speed, the pressure in the high-pressure side flow path that communicates between the driving-side fluid pressure driving means and the driven-side fluid pressure driving means becomes a gauge pressure, and the transmission torque can be smoothly zeroed without causing a step. Therefore, it is possible to obtain the effect that the four-wheel drive state can be shifted to the two-wheel drive state without giving the driver any discomfort.

Further, according to the four-wheel drive vehicle of the sixth aspect, in the inventions of the third to fifth aspects, the relief valve is
Since the valve opening pressure is configured to control the valve opening pressure by the driven side fluid pressure driving means side pressure of the differential pressure detection orifice inserted between the driven side fluid pressure driving means and the low pressure side passage,
The effect that the valve opening pressure of the relief valve can be easily controlled by forming the pilot flow passage in the fluid pressure circuit without separately providing another sensor such as a vehicle speed sensor.

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 is a combination of a plurality of pumps having different flow rate characteristics with respect to the rotation speed. Since it is configured, the desired flow rate characteristic can be reliably obtained even when using a pump that cannot change the flow rate characteristic independently in multiple stages.

[Brief description of 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 rotation speed difference and a transmission torque in the first embodiment.

FIG. 4 is a characteristic diagram showing flow rate characteristics when a plurality of pumps whose flow rate 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 a 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 is 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,
It is a characteristic diagram which shows the maximum transmission torque characteristic and 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 rate characteristics of a conventional drive-side hydraulic pump and a driven-side hydraulic pump.

[Explanation of symbols]

 1 Engine 2 Transmission 3 Front Wheel Differential 4 Front Wheel 5 Front Wheel 6 Suction Throttling Piston Pump 7 Reservoir Tank 8H High Pressure Piping 8L Low Pressure Piping 9 Electromagnetic Directional Change Valve 10 Swash Plate Type Variable Capacity 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 device 18 Rear wheel axle 19 Rear wheel 21 Intake throttle valve 10L, 10R Swash plate type variable displacement pump motor 31 Forward / reverse switching Solenoid directional control valve 13P Pilot operated relief valve 40 Suction throttle valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Kamegaya 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd.

Claims (7)

[Claims] 1. A drive axle driven by a prime mover,
A drive-side fluid pressure drive means that is driven in conjunction with the drive axle, and a driven-side fluid pressure drive means that is driven in conjunction with the driven axle; and the drive-side fluid pressure drive means and the driven-side fluid pressure. A fluid pressure transmission mechanism is configured by providing the drive means with a flow path that connects the discharge port and the suction port to each other, and the flow rate of the drive side fluid pressure drive means is set to be equal to or less than the flow rate of the driven side fluid pressure drive means. In a four-wheel drive vehicle, the capacity of the driven-side fluid pressure drive means reduces the capacity from the first rotational speed at which the maximum transmission torque starts to decrease, and the flow rate of the drive-side fluid pressure drive means requires the transfer torque. A four-wheel drive vehicle, wherein the four-wheel drive vehicle is set to have a maximum value at a second rotation speed that disappears. 2. A drive axle driven by a prime mover,
A drive-side fluid pressure drive means that is driven in conjunction with the drive axle, and a driven-side fluid pressure drive means that is driven in conjunction with the driven axle; and the drive-side fluid pressure drive means and the driven-side fluid pressure. A fluid pressure transmission mechanism is configured by providing the drive means with a flow path that connects the discharge port and the suction port to each other, and the flow rate of the drive side fluid pressure drive means is set to be equal to or less than the flow rate of the driven side fluid pressure drive means. In a four-wheel drive vehicle, the capacity of the driven-side fluid pressure driving means is smaller than the first rotational speed at which the maximum transmission torque starts to decrease, and the flow rate of the driving-side fluid pressure driving means is set to the driven-side fluid pressure driving means. According to the capacity characteristic of the driving means, the capacity is reduced from a rotational speed higher than the first rotational speed, and further, it is set so as to reach the maximum value at the second rotational speed at which transmission torque is not required. A four-wheel drive vehicle. 3. A drive axle driven by a prime mover,
A drive-side fluid pressure drive means that is driven in conjunction with the drive axle, and a driven-side fluid pressure drive means that is driven in conjunction with the driven axle; and the drive-side fluid pressure drive means and the driven-side fluid pressure. A fluid pressure transmission mechanism is configured by connecting the driving means to the discharge port and the suction port of each other through the high pressure side flow passage and the low pressure side flow passage, and the flow rate of the drive side fluid pressure drive means is set to the driven side fluid pressure drive means. In the four-wheel drive vehicle set to be equal to or less than the flow rate of the driven-side fluid pressure driving means, the capacity of the driven-side fluid pressure driving means reduces the capacity from the first rotational speed at which the maximum transmission torque starts to decrease, and the flow rate of the driving-side fluid pressure driving means. The need for transmission torque is eliminated second
Is set to a maximum value at the number of rotations of the valve, and the valve opening pressure between the high-pressure passage and the low-pressure passage is reduced between the first rotation speed and the second rotation speed with respect to the increase of the rotation speed. A four-wheel drive vehicle having a relief valve inserted therein. 4. A drive axle driven by a prime mover,
A drive side fluid pressure drive means driven in conjunction with the drive axle and a driven side fluid pressure drive means driven in conjunction with the driven axle, wherein the drive side fluid pressure drive means and the driven side fluid pressure are provided. A fluid pressure transmission mechanism is configured by connecting the discharge means and the suction opening of the drive means to each other through the high pressure side flow path and the low pressure side flow path, and the flow rate of the drive side fluid pressure drive means is set to the driven side fluid pressure drive means. In the four-wheel drive vehicle set to be equal to or less than the flow rate of the driven-side fluid pressure drive means, the driven-side fluid pressure drive means has a capacity reduced from the first rotation speed at which the maximum transmission torque starts to decrease, and the flow rate of the drive-side fluid pressure drive means. The need for transmission torque is eliminated second
Is set to the maximum value at the number of revolutions of the valve, and the valve opening pressure is set between the high pressure passage and the low pressure passage at the first revolution speed and the second revolution speed.
When the discharge pressure of the drive-side fluid pressure drive means exceeds a set pressure lower than the maximum valve opening pressure of the relief valve, a relief valve that reduces the increase in the rotation speed between the A four-wheel drive vehicle comprising suction amount limiting means for reducing the suction amount of the drive side fluid pressure driving means. 5. The four-wheel drive vehicle according to claim 3, wherein the 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 on the driven fluid pressure drive means side of the differential pressure detection orifice, the valve opening pressure of which is interposed between the driven fluid pressure drive means and the low pressure side flow passage. The four-wheel drive vehicle according to claim 3, wherein the four-wheel drive vehicle is configured to control 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 rotation speed. car.