JPH07257211A - Four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To provide a four-wheel drive vehicle which can simplify a capacity control mechanism while suppressing occurrence of cavitation. CONSTITUTION:Driving force of an engine 1 is transmitted to front wheels 5 and a rotary shaft 6a of a piston pump 6 via a transmission 2 and a differential gear 3. A discharge port 6c and a suction port 6b of the pump 6 are connected to ports P and T of a selector valve for changing over forward and backward advance 9 which is built in a swash plate type variable capacity pump motor 10 via a high pressure pipe 8H and a low pressure pipe 8L to constitute a hydraulic C transmission device. A rotary shaft 10c of the pump motor 10 is connected to rear wheels 19 via a differential gear 17. Differential pressure between front and rear parts of an orifice for detecting differential pressure 11 which is provided in the low pressure pipe 8L on the tank port T side of the selector valve 9 is supplied to a swash plate variable mechanism 12 of the pump motor 10 and is maintained at the maximum flow rate which is set in advance when discharge flow rate of the pump motor 10 exceeds a predetermined value.

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, it is conceivable that the second hydraulic pump is made to have a variable capacity so that the flow rate is leveled off at a certain vehicle speed or higher. Since the vane pump is used as the hydraulic pump, the suction port and the discharge port are reversed depending on the rotation direction of the rotating shaft, so that the pair of flow paths communicating between the first hydraulic pump and the second hydraulic pump are connected. For example, one side of the road becomes the high pressure side when moving forward, and the low pressure side when moving backward.
The other side becomes a low pressure side when moving forward and becomes a high pressure side when moving backward, which means that the low pressure side and the high pressure side are reversed depending on the traveling direction of the vehicle. It is necessary to provide the differential pressure detection means in both of the flow paths of the above, and to select them according to the traveling direction of the vehicle, which complicates the configuration and the rotation speeds of the front and rear wheels are substantially equal and the driving force is not transmitted. At the time of no-load operation, the differential pressure detecting means provided on the high pressure side becomes a resistance against the suction of the hydraulic pump, which causes a new problem that cavitation easily occurs.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and provides a four-wheel drive vehicle capable of simplifying the capacity control mechanism while suppressing the occurrence of cavitation. It is intended to be provided.

[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 the driven axle, and the drive side fluid pressure drive means and the driven side fluid pressure drive means are formed by a high pressure passage and a low pressure passage. In a four-wheel drive vehicle in which a fluid pressure transmission mechanism is configured to communicate with each other, a differential pressure detecting means is disposed in the low pressure passage, and the driven side fluid pressure driving means has a capacity of the differential pressure detecting means. It is characterized in that a variable control mechanism for performing variable control based on the detected value is provided.

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. Four wheels having driven fluid pressure driving means to be driven, wherein the driving fluid pressure driving means and the driven fluid pressure driving means are communicated with each other through a high pressure passage and a low pressure passage to form a fluid pressure transmission mechanism. In a drive vehicle, a forward / reverse switching switching valve is inserted in the high pressure passage and the low pressure passage on the driven fluid pressure driving means side, and the low pressure flow on the driving fluid pressure driving means side of the forward / reverse switching switching valve. The differential pressure detecting means is disposed in the path, and the driven-side fluid pressure driving means is provided with a variable control mechanism for variably controlling the capacity thereof based on the differential pressure detection value of the differential pressure detecting means. .

Further, in the four-wheel drive vehicle according to a third aspect of the present invention, the variable control mechanism sets the capacity of the driven side fluid pressure drive means to the wheel speed when the differential pressure detection value of the differential pressure detection means is less than a predetermined value. It is characterized in that it is configured to be increased in proportion to, and to be maintained at the maximum capacity when it exceeds a predetermined value. Furthermore, the four-wheel drive vehicle according to claim 4 is characterized in that the driven-side fluid pressure drive means is composed of a swash plate type variable displacement pump motor that rotates in conjunction with the driven axle.

A four-wheel drive vehicle according to a fifth aspect of the invention is characterized in that the drive-side fluid pressure drive means is composed of an intake throttle piston pump that rotates in conjunction with the drive axle.

[0013]

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

In the four-wheel drive vehicle according to the second aspect, the forward / reverse switching switching valve is inserted in the high pressure passage and the low pressure passage on the driven fluid pressure driving means side, whereby the driven fluid pressure driving means is inserted. Even if the suction port and the discharge port change due to the change in the rotation direction of the driven shaft, the high-pressure flow passage and the low-pressure flow passage can be cut. By providing the differential pressure detecting means in the differential pressure detecting means, the differential pressure according to the discharge flow rate of the driven fluid pressure driving means is always accurately detected regardless of the change in the rotation direction of the driven axle, and the variable control mechanism is accurately driven. .

In the four-wheel drive vehicle according to a third aspect of the present invention, the capacity of the driven fluid pressure drive means is proportional to the wheel speed in order for the differential pressure detection value of the differential pressure detection means to be less than the predetermined value in the variable control mechanism. When the flow rate is increased to a predetermined value or more and maintained at the maximum capacity, the discharge flow rate of the driven-side fluid pressure drive means is capped and the occurrence of cavitation is suppressed when the flow rate is high.

In the four-wheel drive vehicle according to the fourth aspect, since the driven-side fluid pressure drive means is composed of the swash plate type variable displacement pump motor, when the difference in the rotational speeds of the front and rear wheels is small, the fluid pressure pump is used. When it is in a two-wheel drive state in which driving force is not transmitted to the driven shaft, and there is a large difference in the rotational speed of the front and rear wheels, it operates as a fluid pressure motor to transmit driving force to the driven shaft and becomes a four-wheel drive state. To do.

In the four-wheel drive vehicle according to the fifth aspect, since the drive side fluid pressure drive means is composed of the suction throttle type piston pump which rotates in conjunction with the drive axle, the rotation direction of the drive axle changes. Also, it prevents the pressure of the working fluid flowing through the high-pressure passage and the low-pressure passage from being exchanged without changing the discharge port.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic 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. .

In the front wheel side differential device 3, a ring gear 3b formed in a differential gear case 3a is meshed with a gear 2a connected to an output side of the transmission 2, and is rotationally driven.
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 type piston pump 6 as a fluid pressure pump constituting a drive side fluid pressure driving means via a gear 3g meshing with the ring gear 3f. . The suction throttle piston pump 6 has a suction port 6b connected to a strainer 7a arranged in a reservoir tank 7 and a 2-position 4-port electromagnetic directional control valve through a low-pressure pipe 8L serving as a low-pressure passage. 9 is connected to the tank port T,
The discharge port 6c is connected to the pump port P of the electromagnetic directional control valve 9 for forward / backward switching through a high pressure pipe 8H as a high pressure flow path. 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 , in the period from when the rotation speed reaches “0” to the predetermined value V ₁ , the rotation speed increases in proportion to the increase of the rotation speed,
It is set to saturate at the maximum discharge flow rate Q _1MAX at a predetermined value V ₁ or more.

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. When the pump port P is in communication with the output port B and the tank port T is in communication with the output port A at the offset position which is in the energized state, the output ports A and B are oblique as a fluid pressure pump motor constituting driven side fluid pressure driving means. Intake of plate type variable displacement pump motor 10
Connected to the discharge ports 10a and 10b, the high-pressure oil in the high-pressure pipe 8H is supplied to the variable displacement pump motor 10 at the normal position.
The low-pressure pipe 8L is communicated with the suction / discharge port 10a, and the rotary shaft 10c is rotationally driven in the rotation direction during forward traveling, for example, clockwise when viewed from the left side surface, and conversely with the high-pressure pipe at the offset position. The high-pressure oil of 8H communicates with the suction / discharge port 10b of the variable displacement pump motor 10 and the low-pressure pipe 8L communicates with the suction / discharge port 10a to rotate the rotary shaft 10c in the forward rotation direction, for example, counterclockwise when viewed from the left side surface. Drive to rotate.

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 indicated by ₂ , the rotation speed is V ₁
Until reaching the rotational speed V ₁ in proportion to the increase in the rotational speed, the maximum discharge flow rate Q _2MAX , which is larger than the maximum discharge flow rate Q _1MAX of the piston pump 6, becomes
After that, regardless of the increase in rotation speed, the maximum discharge flow rate Q _2MAX
To maintain. Here, the discharge flow rate of the variable displacement pump motor 10 and the discharge flow rate of the piston pump 6 are, as shown in FIG.
The specific discharge flow rate and the gear ratio of the gear connected to the rotating shaft are set so that the discharge flow rate of the piston pump 6 is higher than the discharge flow rate of the piston pump 6.

Further, a relief valve 13 for limiting 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 a hydraulic fluid at a discharge flow rate according to the rotation speed, which is the high pressure pipe. It is supplied to the suction / discharge port 10a of the swash plate type variable displacement pump motor 10 via the forward / reverse switching electromagnetic directional control valve 9 via 8H, but the rear wheel 19 also moves in the same direction as the front wheel 5 when the vehicle starts. Since it is driven to rotate at the same rotation speed, the rotary shaft 10c of the swash plate type variable displacement pump motor 10 rotates clockwise through the rear wheel side differential device 17 when viewed from the left side surface, whereby the suction / discharge port 10a.
The hydraulic oil is sucked in from the suction / discharge port 10b. Here, as shown in FIG. 2, the discharge flow rate of the suction throttle type piston pump 6 and the swash plate type variable displacement pump motor 10 is the same as that of the piston pump 6 at the same rotation speed Vr. Since the high pressure hydraulic oil discharged from the piston pump 6 is sucked by the variable displacement pump motor 10, the pressure in the high pressure pipe 8H does not rise. That is, the variable displacement pump motor 10 does not act as a hydraulic motor, the driving force is not transmitted to the rear wheels 19, and the variable displacement pump motor 10 travels forward in a state similar to that of 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. The flow rate in the proper range of the discharge flow rate characteristic is caused by the fact that the flow rate difference increases as the wheel speed increases. By adopting the flow rate characteristic of FIG. 2, the flow rate difference becomes larger as the speed becomes higher, so that it becomes a characteristic that a four-wheel drive vehicle is less likely to become a four-wheel drive vehicle at the time of high-speed traveling in which it is not necessary
In FIG. 2, when the vehicle speed is between 0 and Vr, the higher the vehicle speed is, the larger the torque rising rotational speed difference becomes, but when the wheel speed is Vr or higher, no torque is generated.

Further, the tank port of the electromagnetic directional control valve 9
The differential pressure detection switch inserted in the low pressure pipe 8L connected to T
Introducing the differential pressure before and after the refill 11 into the swash plate variable mechanism 12
The discharge flow rate of the swash plate type variable displacement pump motor 10 increases.
If the differential pressure before and after the orifice 11 increases, the swash plate type
By changing the swash plate angle of the variable displacement pump motor 10,
As shown, the wheel speed V is faster than the predetermined wheel speed Vr.₁Yo
Slower predetermined wheel speed V ₂Less than depending on increasing wheel speed
Increase to a predetermined wheel speed V₂When it is above, the variable capacity pon
The specific discharge amount of the pump motor 10 is set to the maximum discharge flow rate Q._2MAXMaintained in
Therefore, the flow rate increases excessively when driving at high speed.
Control and increase the diameter of valves and pipes without increasing the diameter.
System pressure loss or drag due to increased tube resistance.
It is possible to reliably suppress the increase in resistance and prevent deterioration of fuel efficiency.
It is possible and on the suction side of the variable displacement pump motor 10,
The differential pressure detecting orifice 10 is not inserted.
At the suction side of the variable displacement pump motor 10
The suction of hydraulic oil cannot catch up and the pressure drops abnormally.
Causes air bubbles to cause cavitation
That can be reliably suppressed, and low pressure piping 8L
Since the differential pressure detection orifice 11 is inserted in the
An extremely large differential pressure is generated before and after the orifice 11 of
Both can be prevented.

Incidentally, as shown in FIG. 4, the high pressure pipe 8H
When the differential pressure detecting orifice 11 is inserted on the pump port P side of the electromagnetic directional control valve 9, the driving force from the piston pump 6 to the variable displacement pump motor 10 is reduced with a small difference in the rotational speeds of the front and rear wheels. In a no-load operation state where there is almost no transmission, the variable displacement pump motor 10 becomes a resistance against suction on the suction side, cavitation is likely to occur, and the initial purpose cannot be achieved.

Further, the rising of the torque in FIG. 3 manages 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 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.

Further, in a vehicle equipped with a front wheel drive vehicle-based anti-skid control device, the rotation speed of the front wheels becomes smaller than the rotation speed of the rear wheels during braking, so that the driving force by the hydraulic transmission mechanism is not generated and the anti-skid control is performed. There is an advantage that interference with the device can be reduced. In addition, in the said 1st Example, although the case where the differential pressure before and behind the orifice 11 for differential pressure detection was supplied to the swash plate variable mechanism 12 was demonstrated, it is not limited to this, and it connects to the low pressure piping 8L side. When the differential pressure detecting orifice 11 is inserted, the pressure on the outlet side of the differential pressure detecting orifice 11 becomes atmospheric pressure.
Since it is the same as the drain pressure in the variable displacement pump 10,
As shown in FIG. 5, only the pressure on the high pressure side of the differential pressure detection orifice 11, that is, the pressure on the tank port T side of the electromagnetic directional control valve 9 is introduced into the head cover side hydraulic chamber 12b of the hydraulic cylinder 12a of the swash plate variable mechanism 12. However, in this case, there is an advantage that the number of hydraulic pipes can be reduced.

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

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

Also in this second embodiment, the above-mentioned first
Since the pressure on the downstream side of the differential pressure detection orifice 11 is atmospheric pressure as in the embodiment, the upstream pressure between the differential pressure detection orifice 11 and the communication pipe 14B is the same as in the case of FIG. Alternatively, only the head cover side hydraulic chamber 12b of the hydraulic cylinder 12a that constitutes the swash plate variable mechanism 12 may be supplied. In this case, the hydraulic piping can be reduced.

In the first and second embodiments, the case where the relief valve 13 is applied as the transmission torque limiting means has been described, but the present invention is not limited to this, and as shown in FIG. The discharge pressure of the pump 6 is input as a displacement control pressure, and in response to this, a suction throttle valve 21 for controlling 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 exceeds a predetermined pressure. May be provided. In this case, when the pump discharge pressure becomes equal to or higher than the specified pressure, the pump suction amount decreases, so that the pump discharge pressure decreases and the torque can be limited. When the valve is used, the oil temperature rises during continuous high load use, but when the suction throttle valve 21 is provided, the discharge flow rate is reduced, so that heat generation can be suppressed.

In the first and second embodiments, the case where the rear wheel side differential device 17 is provided has been described, but the present invention is not limited to this, and as shown in FIG. The differential device 17 may be omitted, and instead, the left and right axles 18L and 18R of the left and right rear wheels 19L and 19R may be respectively provided with the swash plate type variable displacement pump motors 10L and 10R. In this case, When the left and right wheels have different loads during turning, etc., each of the variable displacement pump motors 10L and 10R naturally produces a discharge flow rate difference corresponding to the difference, so that a differential function equivalent to that of a differential device is provided. In this case as well, the torque limiting means may be either the relief valve 13 shown or the suction throttle valve 21 shown in FIG. 7.

Further, in the first and second embodiments, when the suction throttle type piston pump 6 in which the suction port 6b and the discharge port 6c do not change regardless of the rotation direction of the rotary shaft 6a is applied as the fluid pressure pump. I explained about
As shown in FIG. 9, 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 in which the rotary shaft 30a is connected to the gear 3g, respectively, as shown in FIG. If a forward / backward switching electromagnetic directional control valve 31 similar to the forward / backward switching electromagnetic directional control valve 9 in which the output ports A and B are connected to the high-pressure pipes 8H and 8L is provided, the discharge direction is switched forward / backward. Other hydraulic pumps such as gear pumps and vane pumps can be applied. In this case, the hydraulic pump can be a fixed displacement type, as shown in FIG.
The hydraulic cylinder 33a into which the differential pressure across the differential pressure generating orifice 32 inserted in the low pressure pipe 8L is input as shown in FIG.
It may be of any variable displacement type including a variable mechanism 33 including the above, and the differential mechanism 17 is omitted, and two sets of swash plate type variable displacement pump motors 10L and 10R are provided as shown in FIG.
May be applied.

Furthermore, in the above-mentioned first and second embodiments, the case where the forward / reverse switching electromagnetic directional control valve 9 is incorporated in the pump motor 10 has been described, but the present invention is not limited to this. It may be separately provided outside the motor 10. Further, in the above-mentioned first and second embodiments, the embodiment based on the front-wheel drive vehicle has 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 arranged on the rear wheel side. By arranging the pump motor 10 on the front wheel side, it is possible to obtain the same effects as those of the above embodiment.

[0043]

As described above, according to the four-wheel drive vehicle of the first aspect, the drive axle driven by the main motor and the drive 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 connects the driving-side fluid pressure driving means and the driven-side fluid pressure driving means with a high-pressure passage and a low-pressure passage. In a four-wheel drive vehicle having a pressure transmission mechanism, a differential pressure detecting means is provided in the low-pressure passage, and the driven-side fluid pressure driving means has a capacity based on a differential pressure detection value of the differential pressure detecting means. Since a variable control mechanism for variable control is provided, it is possible to suppress an excessive discharge flow rate by the driven-side fluid pressure drive means when traveling at high vehicle speed, suppress cavitation, and suppress high-pressure flow. Differential pressure test separated from the road Since the means is inserted in the low-pressure flow path, cavitation does not occur even in the no-load operation state in which the driving force is not transmitted between the driving-side fluid pressure driving means and the driven-side fluid pressure driving means. The effect that it can be suppressed is obtained.

According to another aspect of the four-wheel drive vehicle of the present invention, the drive axle driven by the main prime mover, and the drive side fluid pressure drive means having the fluid pressure pump rotating in conjunction with the drive axle, Driven-side fluid pressure driving means having a fluid-pressure pump motor that rotates in conjunction with the driven axle, and the driving-side fluid pressure driving means and the driven-side fluid pressure driving means communicate with each other through a high-pressure passage and a low-pressure passage. In a four-wheel drive vehicle configured with a fluid pressure transmission mechanism, a forward / reverse switching switching valve is inserted in the high pressure passage and the low pressure passage on the driven fluid pressure driving means side, and the forward / reverse switching switching valve is A differential pressure detecting means is provided in the low pressure flow path on the drive side fluid pressure driving means side, and the capacity of the driven side fluid pressure driving means is variably controlled based on the differential pressure detection value of the differential pressure detecting means. Variable control mechanism provided When there is a change in the discharge side due to the rotation direction of the driven side fluid pressure drive means in the forward / reverse switching switching valve, the high pressure passage and the low pressure passage are selected in accordance with the change, and Regardless of the condition, the high-pressure flow path and the low-pressure flow path can be reliably separated, and the differential pressure detection means is reliably prevented from becoming the suction side of the driven fluid pressure drive means, and the occurrence of cavitation is reliably prevented. The effect of being able to do is obtained.

Further, in the four-wheel drive vehicle according to the third aspect, the variable control mechanism adjusts the capacity of the driven side fluid pressure drive means to the wheel to keep the differential pressure detection value of the differential pressure detection means less than the predetermined value. Since it is configured to increase in proportion to the speed and to maintain the maximum capacity when it becomes a predetermined value or more, it is possible to reliably suppress the occurrence of cavitation by making the discharge flow rate of the driven-side fluid pressure drive means reach a peak at the time of high flow rate. The effect of being able to do is obtained.

Further, according to the four-wheel drive vehicle of the fourth aspect, since the driven fluid pressure drive means is composed of the swash plate type variable displacement pump motor, when the rotational speed difference between the front and rear wheels is small, It operates as a fluid pressure pump and does not transmit driving force to the driven shaft, and when there is a large difference in rotation speed between the front and rear wheels, it operates as a fluid pressure motor to transmit driving force to the driven shaft. The wheel drive state can be achieved, and the pump motor itself can be downsized.

Furthermore, according to the four-wheel drive vehicle of the third aspect, since the suction throttle type piston pump that rotates in conjunction with the drive axle is used, the discharge port is changed depending on the rotation direction of the drive axle. It is not necessary to provide a switching valve for switching between the high pressure passage and the low pressure passage by moving forward and backward between the piston pump and the high pressure passage and the low pressure passage, and the entire configuration can be simplified. The effect is obtained.

[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 discharge flow rate characteristics 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 schematic configuration diagram showing a comparative example with respect to the first embodiment.

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

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

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

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

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

Claims (5)

[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. In a four-wheel drive vehicle in which a fluid pressure transmission mechanism is constituted by communicating the driving means with a high pressure passage and a low pressure passage, a differential pressure detection means is provided in the low pressure passage, and the driven fluid pressure driving means is provided. A four-wheel drive vehicle having a variable control mechanism for variably controlling the capacity thereof based on the differential pressure detection value of the differential pressure detection means. 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. In a four-wheel drive vehicle in which a fluid pressure transmission mechanism is configured by communicating the driving means with a high pressure passage and a low pressure passage, switching between forward and backward switching is performed on the high pressure passage and the low pressure passage on the driven fluid pressure driving means side. A differential pressure detecting means is disposed in the low pressure passage on the drive side fluid pressure drive means side of the forward / reverse switching valve, and the driven side fluid pressure drive means is provided with the capacity thereof. A four-wheel drive vehicle having a variable control mechanism for performing variable control based on a differential pressure detection value of a detection means. 3. The variable control mechanism increases the capacity of the driven-side fluid pressure drive means in proportion to the wheel speed so that the differential pressure detection value of the differential pressure detection means is less than a predetermined value, and increases it to a predetermined value or more. When it is, it is comprised so that it may maintain to the maximum capacity.
Alternatively, the four-wheel drive vehicle according to item 2. 4. The four-wheel drive vehicle according to claim 1, wherein the driven-side fluid pressure drive means is a swash plate type variable displacement pump motor that rotates in conjunction with a driven axle. 5. The four-wheel drive vehicle according to any one of claims 1 to 4, wherein the drive-side fluid pressure drive means is composed of an intake throttle piston pump that rotates in conjunction with a drive axle.