JPH07257213A - Four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To provide a four-wheel drive vehicle which can securely prevent change-over of forward and backward advance due to abnormality of an electric system when the vehicle runs. 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 an electromagnetic direction 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 transmission device. A rotary shaft 10c of the pump motor 10 is connected to rear wheels 19 via a differential gear 17. The electromagnetic direction change-over valve 9 is at the change-over position for forward advance at the normal position where electricity is not conducted to an electromagnetic solenoid 9a and prevents securely the change- over to the change-over position for backward advance to ensure a fail-safe function even if an abnormality of an electric system occurs.

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 it is possible to reduce the vibration, it is possible to cope with the reversal of the flow direction of the hydraulic oil due to the different rotation directions of the axles during the forward movement and the reverse movement.
Both the pair of hydraulic pipes that communicate between the hydraulic pump and the second hydraulic pump have to be expensive high pressure pipes,
When a hydraulic element such as a valve is applied to a hydraulic transmission, it is necessary to handle both high and low pressures, and there is an unsolved problem that the entire configuration becomes complicated.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and communicates between the fluid pressure supply means and the fluid pressure drive means in order to reduce the piping cost. An object of the present invention is to provide a four-wheel drive vehicle in which a fail-safe measure for a forward / reverse switching switching valve, which is necessary when the hydraulic pipe is divided into a high pressure side and a low pressure side, is taken.

[0008]

In order to achieve the above 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 fluid pressure pump that rotates in conjunction with the drive axle. A fluid pressure supply means, a fluid pressure pump motor that rotates in conjunction with a driven axle and a forward / reverse switching means, a discharge port of the fluid pressure pump, and a suction side of the forward / reverse switching means. In a four-wheel drive vehicle having a high-pressure flow path communicating with each other, and a low-pressure flow path communicating with the discharge side of the forward-reverse switching means and the suction port of the fluid pressure pump,
The forward / reverse switching means is composed of an electromagnetic directional switching valve, and is characterized in that it is interlocked with the shift position to select the forward side when normally de-energized and the reverse side when energized.

A four-wheel drive vehicle according to a second aspect of the present invention includes a drive axle driven by a main prime mover, a fluid pressure supply means having a fluid pressure pump rotating in conjunction with the drive axle, and an idle axle. Fluid pressure pump motor that rotates in a rotating manner and fluid pressure drive means having a forward / reverse switching means, a high-pressure passage that connects the discharge port of the fluid pressure pump and the suction side of the forward / reverse switching means, and the forward / reverse switching. In a four-wheel drive vehicle provided with a low-pressure flow path that communicates the discharge side of the means with the suction port of the fluid pressure pump, the forward / reverse switching means is composed of a machine-operated directional switching valve, and is arranged in a shift position. It is characterized in that the forward drive side and the reverse drive side are switched and selected in conjunction with each other.

Further, the four-wheel drive vehicle according to claim 3 is characterized in that the fluid pressure pump is a suction throttle piston pump.

[0011]

In the four-wheel drive vehicle according to the first aspect, when the vehicle is traveling forward, the working fluid having a flow rate corresponding to the rotational speed is discharged from the fluid pressure supply means by the rotation of the drive axle driven by the main prime mover. The working fluid, which is supplied to the suction side of the fluid pressure driving means driven by the rotation of the driven axle through the normal position of the side flow passage and the electromagnetic directional control valve, and discharged from this fluid pressure driving means, flows through the low pressure side flow passage. Returned to the supply means. 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. . When an electric system abnormality such as a disconnection between the electromagnetic directional control valve and the control circuit for controlling the directional control valve or a disconnection of the power source occurs during forward traveling, the electromagnetic directional control valve is de-energized, but During traveling, the fluid pressure supply means and the fluid pressure drive means communicate with each other through the normal position of the electromagnetic directional control valve, so that the drive state can be maintained without being affected by the abnormality.

In the four-wheel drive vehicle according to the second aspect, similarly to the above, the two-wheel drive state and the four-wheel drive state are switched depending on the rotational speed difference between the drive axle and the driven axle, but they are machine-operated switching valves. The forward / reverse switching directional control valve is configured to mechanically interlock with the shift position to switch between the forward side and the reverse side, so that the forward / backward switching directional control valve will run even if an abnormality occurs in the electrical system. Be sure to prevent switching in.

In the four-wheel drive vehicle according to the third aspect, since the fluid pressure supply means is composed of a suction throttle type piston pump that rotates in conjunction with the drive axle, the fluid pressure is also discharged by a change in the rotational direction of the drive axle. It is possible to separate the high-pressure passage and the low-pressure passage without changing the outlet and providing the switching means.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment in which the present invention is applied to a four-wheel drive vehicle based on a front-wheel drive vehicle. In the figure, 1 is an engine as a main prime mover. The rotational driving force of No. 1 is input to the front wheel side differential device 3 via the transmission 2, and the front wheel 5 is connected to the output side of the differential device 3 via the 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 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 on the discharge side of the 2-position 4-port electromagnetic direction switching valve 9 as the forward / backward switching means through L, and the discharge port 6c is connected to the electromagnetic direction for forward / backward switching through the high pressure pipe 8H as the high pressure passage. It is connected to a pump port P on the suction side of the switching valve 9. Here, in the suction throttle type piston pump 6, the suction port and the discharge port do not interchange with each other depending on the rotation direction of the rotating shaft 6a, and the discharge flow rate is
As shown by the characteristic curve L ₁ in FIG. 2, the rotation speed N corresponds to the vehicle speed that does not require the four-wheel drive state from “0”.
Between to reach _1, increased in proportion to the increase of the rotational speed, it is configured to saturate at the maximum discharge flow rate Q _1MAX the rotational speed N ₁ or more.

In the electromagnetic directional control valve 9 for switching between forward and reverse, the pump port P on the suction side is the output port A and the tank port T on the discharge side is the output port B in the normal position where the solenoid 9a is in the non-energized state. To the pump port P at the offset position where the solenoid 9a is energized.
Is connected to the output port B and the tank port T is connected to the output port A, and the output ports A and B are connected to the suction / discharge ports 10a and 10b of the swash plate type variable displacement pump motor 10 as a fluid pressure pump motor. In the normal position, the high-pressure oil of the high-pressure pipe 8H is sucked and discharged into the suction / discharge port 10a of the variable displacement pump motor 10, and the low-pressure pipe 8L is sucked and discharged in the normal position.
To drive the rotary shaft 10c to rotate in the forward direction, for example, clockwise when viewed from the left side surface, and reversely drive the high pressure oil in the high pressure pipe 8H to the suction / discharge port 10b of the variable displacement pump motor 10 at the offset position. The low-pressure pipe 8L is connected to the suction / discharge port 10a to drive the rotary shaft 10c to rotate in the forward traveling direction, 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 , the rotational speed N is higher than the rate of increase of the piston pump 6 in proportion to the increase of the rotational speed until the rotational speed reaches the rotational speed N ₁ corresponding to the vehicle speed which does not require the four-wheel drive state. When the _engine speed increases at an increasing rate and reaches the rotation speed N ₁ , the maximum discharge flow rate Q _2MAX , which is larger than the maximum discharge flow rate Q _1MAX of the piston pump 6, is _maintained , and thereafter the maximum discharge flow rate Q _{2M AX} is maintained regardless of the increase in the rotation speed. To do. 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 rotary shaft are set so as to increase.

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, the discharge flow rates of the suction throttle type piston pump 6 and the swash plate type variable displacement pump motor 10 are shown in FIG.
As shown in (a), since the discharge flow rate of the variable displacement pump motor 10 is set to be higher than that of the piston pump 6 at the same rotation speed Vr, the high pressure hydraulic oil discharged from the piston pump 6 is set. Is sucked in by the variable displacement pump motor 10, so 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 from the reservoir tank 7 via the low pressure pipe 8L, the communication pipe 14A, and the check valve 15. It

The difference in the discharge flow rates of 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 thus 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 characteristic range of the discharge flow rate characteristic of the predetermined rotation speed N ₁ or less increases as the rotation speed, that is, the wheel speed increases. By adopting the flow rate characteristic of FIG. 2, the flow rate difference becomes larger as the flow rate becomes higher, so that the characteristic becomes less likely to be a four-wheel drive vehicle as it approaches a high-speed running state in which it is not necessary to be four-wheel drive. Between 0 and Vr, the torque rise rotation speed difference increases as the vehicle speed increases, but when the wheel speed is Vr or higher, the discharge flow rate of the variable displacement piston pump 10 becomes the maximum discharge flow rate Q _1MAX of the piston pump 6 or higher, and therefore the transmission is transmitted. The two-wheel drive state is continued without generating torque. At this time, since the discharge flow rate of the piston pump 6 is fixed to the maximum discharge flow rate Q _1MAX at a rotational speed N ₁ or higher that does not require the four-wheel drive state, an increase in pressure loss due to an unnecessary increase in flow rate is prevented, and as a result, fuel consumption is reduced. It is possible to suppress deterioration of oil temperature and increase of oil temperature. At the same time, it is possible to suppress the occurrence of cavitation caused by the suction of the variable displacement pump motor 10 not catching up due to the piping resistance.

Further, the differential pressure before and after the differential pressure detecting orifice 11 inserted in the low pressure pipe 8L connected to the tank port T of the electromagnetic directional control valve 9 is introduced into the swash plate variable mechanism 12 to make the swash plate. When the discharge flow rate of the swash plate type variable displacement pump motor 10 increases and the differential pressure before and after the orifice 11 increases, the swash plate angle of the swash plate type variable displacement pump motor 10 is changed to set a predetermined wheel speed as shown in FIG. When it becomes V ₁ or more, the inherent discharge amount of the variable displacement pump motor 10 is maintained at the maximum discharge flow rate Q _2MAX , so that an excessive increase in the flow rate during high-speed traveling is suppressed and the diameter of the valve or the pipe is increased. Without doing
It is possible to reliably suppress the pressure loss of the system, that is, the increase of drag resistance due to the increase of the pipe resistance, and prevent the deterioration of the fuel consumption. At the same time, the differential pressure detecting orifice 11 is inserted on the suction side of the variable displacement pump motor 10. Therefore, it is possible to reliably prevent the occurrence of cavitation due to the occurrence of bubbles due to the rise of the oil temperature and the suction of the variable displacement pump motor 10 cannot catch up with the working oil and the pressure is abnormally lowered. And low pressure piping 8L
Since the differential pressure detecting orifice 11 is inserted in the above, it is possible to prevent an extremely large differential pressure before and after the orifice 11.

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 in the reverse direction, the shift lever is switched to the reverse position to turn on the shift position detection switch 9b, so that the solenoid 9a of the forward / reverse switching electromagnetic directional control valve 9 is energized. Then, the switching position is switched from the normal position to the offset position, whereby the working oil in the high-pressure pipe 8H is supplied to the suction / discharge port 10b of the swash plate type variable displacement pump motor 10 and discharged from the suction / discharge port 10a. Low pressure piping 8L
By returning to the side, the rotary shaft 10c of the variable displacement pump motor 10 is reversed from that during forward traveling, and the rear wheel 19 is rotated in reverse. 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 wheels 19 and the intake amount shortage of the swash plate type variable displacement pump motor 10 when the rotational speed difference between the front and rear axles 4 and 18 is small, the low pressure pipe 8L, the communication pipe 14A, and the reverse pipe 14A. It is replenished via the stop valve 15.

At this time, in the suction throttle type piston pump 6 on the front wheel side, as described above, 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 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 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. As described above, according to the first embodiment, the forward / backward switching electromagnetic directional control valve 9 is maintained at the normal position where the electromagnetic solenoid 9a is in the non-energized state during forward traveling, and thus during forward traveling of the vehicle. Even when the supply of power to the electromagnetic solenoid 9a is cut off due to the disconnection of the power supply path to the electromagnetic solenoid 9a or the occurrence of power supply abnormality, the normal position in the non-energized state can be maintained, and the electromagnetic directional control valve 9 Since it can be reliably prevented from switching to the offset position, it is possible to exert a fail-safe function of maintaining the hydraulic transmission mechanism in a normal state.

When traveling in reverse, the electromagnetic directional control valve 9 for switching between forward and reverse is energized by the electromagnetic solenoid 9a to be switched to the offset position. In this state, when the power supply to the electromagnetic solenoid 9a is cut off, The electromagnetic directional control valve 9 can be switched to the normal position and cannot function as a hydraulic power transmission mechanism. However, since the vehicle speed is not so high during the reverse travel, even if the electromagnetic directional control valve 9 is switched. It does not significantly affect the reverse running.

In the first embodiment described above, 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 piping is not limited. Orifice 1 for differential pressure detection on 8L side
When 1 is inserted, the pressure on the outlet side of the differential pressure detection orifice 11 becomes atmospheric pressure, so the variable displacement pump motor 1
Since it is the same as the drain pressure in 0, as shown in FIG. 4, only 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 is changed.
Head cover side hydraulic chamber 12b of the second hydraulic cylinder 12a
It may be introduced into.

In the first embodiment described above, 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 FIG.
As shown in, the discharge pressure of the piston pump 6 is input as the displacement control pressure, and the opening of the suction passage on the suction port 6b side of the piston pump 6 is reduced accordingly when the discharge pressure becomes equal to or higher than a predetermined pressure. A suction throttle valve 21 to be controlled may be provided. In this case, when the pump discharge pressure becomes equal to or higher than a prescribed pressure, the pump suction amount is reduced, so that the pump discharge pressure is reduced and the torque is limited. At the same time, when the relief valve is used, the oil temperature rises during continuous high load use, but when the suction throttle valve 21 is provided,
Since the discharge flow rate decreases, 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. 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 the left and right wheels have different loads when turning, Each variable displacement pump motor 10L, 1
Since a discharge flow rate difference corresponding to the difference naturally occurs at 0R, it is possible to exhibit a differential function equivalent to that of a differential device. In this case also, the relief valve 1 shown in FIG.
3 or any of the suction throttle valves 21 shown in FIG.

Furthermore, in the first embodiment described above,
As the 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 the rotation shaft 6a is applied has been described, but the present invention is not limited to this and FIG. As shown in FIG. 5, 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, and the output ports A and B are connected to the high pressure pipe 8.
If a forward / reverse switching electromagnetic directional control valve 31 similar to the forward / backward switching electromagnetic directional control valve 9 connected to H and 8L is provided, other hydraulic pressures such as gear pumps and vane pumps whose discharge directions are switched by forward / backward traveling. Pump can be applied,
As the hydraulic pump in this case, a fixed capacity type is provided with a variable mechanism 33 including a 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. Any of the variable capacitance type may be used, and the differential mechanism 17 may be omitted, and as shown in FIG.
A pair of swash plate type variable displacement pump motors 10L and 10R may be applied.

In the first embodiment described above, the case where the forward / reverse switching electromagnetic directional control valve 9 is built in the pump motor 10 has been described, but the present invention is not limited to this, and the outside of the pump motor 10 is described. It may be installed separately. Next, a second embodiment of the present invention will be described with reference to FIG. In this second embodiment, as the forward / reverse switching means, a switching valve 40, which is mechanically interlocked with a shift operation for forward / reverse switching, is applied instead of the electromagnetic direction switching valve 9.

In the second embodiment, as shown in FIG.
A mechanical operation type switching valve 40 as a forward / backward switching unit is interposed between the high pressure pipe 8H and the low pressure pipe 8L and the swash plate type variable displacement pump motor 10. This machine operated switching valve 4
0 indicates that the operator 40a is mechanically connected to the forward / reverse switching shift mechanism of the manual transmission 2 via the link mechanism 41, and the forward side is selected by the transmission 2 so that the mechanical operation type switching valve 40 is operated. As shown in FIG. 8, a forward operation switching position is established in which the pump port P is connected to the output port A and the tank port T is connected to the output port B, and the reverse operation side is selected by the transmission 2 to change the machine operation type. The valve 40 connects the pump port P to the output port B and the tank port T to the output port A.
It has the same structure as that of the first embodiment except that it is configured to take the reverse switching positions which are connected to each of the parts. The description is omitted here.

According to the second embodiment, since the switching position of the switching valve 40 for switching between forward and reverse movements is mechanically interlocked with the forward or reverse movement shift position of the transmission 2, it is possible to switch the electric system such as power off. It is possible to exert a better fail-safe function without being affected by the abnormality at all and without the switching position being arbitrarily switched while the vehicle is traveling.

In the second embodiment as well, similar to the first embodiment described above, modified examples corresponding to FIGS. 4 to 7 are conceivable, and the connection between the transmission 2 and the switching valve 40 is also possible. The mechanism is not limited to the link, and other mechanical connecting means such as a wire can be applied. Further, as a mechanical input to the operator 40a of the mechanically operated switching valve 40, the manual transmission 2 is used.
When an automatic transmission is used instead of the forward / reverse switching shift mechanism, the operation amount of the shift lever may be transmitted to the operator 40a via a mechanical connecting mechanism such as a wire or a link. .

Further, in the above-mentioned first and second embodiments, the embodiment based on the front-wheel drive vehicle has been described. However, the present invention is not limited to this, and the pump 6 can also be applied to the case based on the rear-wheel drive vehicle. By arranging the pump motor 10 on the rear wheel side and the pump motor 10 on the front wheel side, it is possible to obtain the same effects as the above-described embodiment.

[0041]

As described above, according to the four-wheel drive vehicle of the first aspect, when the electromagnetic directional control valve is applied as the forward / reverse switching means, the normal non-energization is interlocked with the forward / reverse shift position. The forward side is selected when the vehicle is energized, and the reverse side is selected when the vehicle is energized.Therefore, even when an abnormality occurs in the electrical system when the vehicle is traveling forward and the electromagnetic direction switching valve is de-energized, the forward direction switching position of the electromagnetic direction switching valve Is not changed, and a good fail-safe function can be exerted.

According to the four-wheel drive vehicle of the second aspect, when the mechanical operation type switching valve is applied as the forward / reverse switching means, the forward and reverse sides are mechanically interlocked with the forward / reverse shift position. The forward / reverse side switching position is not changed unless the forward / reverse shift position is changed, and the forward / reverse side switching position is not changed unless the electric system malfunctions while the vehicle is traveling. It is possible to exert a better fail-safe function.

Further, according to the four-wheel drive vehicle of the third 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 discharge port is not changed by the rotation direction of the drive axle, and the high pressure passage and the low pressure passage are not provided between this piston pump and the high pressure passage and the low pressure passage without providing a switching valve for switching the passage by forward and backward movement. You can divide the flow path,
The overall structure can be simplified, and the cost can be reduced by using only the high-pressure flow path as an effective high-pressure piping.

[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 of FIG.

FIG. 3 is a characteristic diagram showing a relationship between a front-rear axle speed difference and a transmitted torque in the first embodiment of FIG.

FIG. 4 is a schematic configuration diagram showing a modified example of the first embodiment.

FIG. 5 is a schematic configuration diagram showing another embodiment of the torque limiting means.

FIG. 6 is a schematic configuration diagram showing an embodiment in which a differential device is omitted.

FIG. 7 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. 8 is a schematic configuration diagram showing a second embodiment of the present invention.

[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 Electromagnetic directional control valve 40 Machine operated directional control valve

Claims (3)

[Claims] 1. A drive axle driven by a prime mover,
A fluid pressure supply means having a fluid pressure pump rotating in conjunction with the drive axle, a fluid pressure driving means having a fluid pressure pump motor rotating in conjunction with the driven axle and a forward / reverse switching means, and the fluid pressure pump A four-wheel drive including a high-pressure flow passage that connects the discharge port and the suction side of the forward-reverse switching unit, and a low-pressure flow passage that connects the discharge side of the forward-reverse switching unit and the suction port of the fluid pressure pump. In the vehicle, the forward-reverse switching means is composed of an electromagnetic directional switching valve, and in association with the forward-reverse shift position, the forward drive side is selected when normally de-energized and the reverse drive side is selected when energized. Driving car. 2. A drive axle driven by a prime mover,
A fluid pressure supply means having a fluid pressure pump rotating in conjunction with the drive axle, a fluid pressure driving means having a fluid pressure pump motor rotating in conjunction with the driven axle and a forward / reverse switching means, and the fluid pressure pump A four-wheel drive including a high-pressure flow passage that connects the discharge port and the suction side of the forward-reverse switching unit, and a low-pressure flow passage that connects the discharge side of the forward-reverse switching unit and the suction port of the fluid pressure pump. In the vehicle, the forward-reverse switching means comprises a mechanically operated directional switching valve, and mechanically interlocks with a shift position to switch and select a forward drive side and a reverse drive side. 3. The four-wheel drive vehicle according to claim 1, wherein the fluid pressure pump is a suction throttle piston pump.