JPH0820252A - Four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To maintain a four-wheel drive state at the starting time of a vehicle so as to suppress the unnecessary slip of driving wheels. CONSTITUTION:The driving force of an engine 1 is transmitted to front wheels 5 and the rotary shaft 6a of a piston pump 6 through a transmission 2 and a differential gear 3. The discharge port 6c and suction port 6b of the pump 6 are connected to the ports P, T of a forward/reverse switching valve 9 built in a cam plate type variable displacement pump motor 10 through high pressure piping 8H and low pressure piping 8L so as to form a hydraulic transmission gear. When the vehicle speed is less than the set speed, the discharge flow of the piston pump 6 is made larger than the discharge flow of the pump motor 10, and when the vehicle speed is the set speed or more, the discharge flow of the piston pump 6 is set to the discharge flow of the pump motor 10 or less. Until reaching the set speed from the start of a vehicle, transmission torque is constantly generated to the hydraulic transmission gear to maintain the four- wheel drive state. The unnecessary slip of driving wheels is thereby suppressed to make a smooth start.

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.

Therefore, conventionally, for the purpose of reducing the weight of the constituent members, as described in, for example, Japanese Patent Application Laid-Open No. 63-176734 (hereinafter referred to as the first conventional example), the drive wheels are driven by the output of the engine. The hydraulic pump is linked to any drive system from the output shaft of the engine to the drive wheels, and the hydraulic motor that drives the driven shaft is linked to this hydraulic pump via the hydraulic pipe to discharge the hydraulic pump. When the pressure oil discharge amount in the hydraulic motor is larger than the pressure oil discharge amount from the hydraulic pump between the pipeline side and the discharge pipeline side in the hydraulic motor, the discharge pipeline side in the hydraulic motor and the hydraulic pump Provided with a switching valve that communicates with the discharge pipe side and conversely shuts off the communication state when the amount of pressure oil discharged from the hydraulic pump is greater than the amount of pressure oil discharged from the hydraulic motor. Furthermore the relationship between the displacement volume of the volume and the hydraulic motor displacement of the hydraulic pump,
The discharge rate of the pressure oil discharged from the hydraulic pump is less than the discharge rate of the pressure oil discharged by the hydraulic motor, assuming that the vehicle is straight ahead and the drive wheels and wheels are not slipping on the road surface. A related four-wheel drive vehicle has been proposed.

Further, as described in JP-A-3-224831 (hereinafter referred to as a second conventional example), a first member that rotates in conjunction with the front wheels and a second member that rotates in conjunction with the rear wheels. , A power transmission of a four-wheel drive vehicle having a torque transmission device, which is interposed between the first member and the second member, and whose transmission torque changes according to a rotational speed difference between the front wheels and the rear wheels. In the device, the discharge flow rate of the first fluid pressure pump on the drive shaft side, which constitutes the torque transmission device, is reduced by the second fluid pressure on the driven shaft side so as to reduce the transmission torque of the torque transmission device in accordance with an increase in vehicle speed. A four-wheel drive vehicle has also been proposed in which the discharge flow rate of the pump is always set smaller than that of the pump, and the difference between the two is set to increase as the vehicle speed increases.

[0005]

However, in the four-wheel drive vehicles of the first conventional example and the second conventional example, the discharge flow rate of the hydraulic pump on the drive wheel side is the discharge rate of the hydraulic motor on the driven wheel side. Since it is always set to a value smaller than the flow rate,
When the vehicle starts, the drive wheels on the main engine side slip and the hydraulic pressure rises after exceeding the discharge amount of the other hydraulic pump, and the driven wheels are driven to the four-wheel drive state, so the four-wheel drive state is set. However, there is an unsolved problem in that the wheels on the drive wheel side feel more idle than necessary.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and immediately shifts to the four-wheel drive state at low speed running including starting, and the driving wheel side is not operated. It is an object of the present invention to provide a four-wheel drive vehicle capable of reliably preventing necessary idling.

[0007]

In order to achieve the above object, in a four-wheel drive vehicle according to a first aspect of the present invention, a drive force of a drive axle driven by a main prime mover is transmitted to a driven axle via a fluid pressure transmission mechanism. In the four-wheel drive vehicle configured to transmit, the fluid pressure transmission mechanism is configured to constantly generate a transmission torque at a speed lower than a set vehicle speed.

According to another aspect of the four-wheel drive vehicle of the present invention, the drive axle driven by the main motor, the drive side fluid pressure drive means driven in conjunction with the drive axle, and the driven axle are interlocked. A driven-side fluid pressure driving means to be driven, and a fluid-pressure transmission mechanism is provided by providing a flow path that connects the driving-side fluid pressure driving means and the driven-side fluid pressure driving means to each other's discharge port and suction port. In the configured four-wheel drive vehicle, when the discharge flow rate of the drive side fluid pressure drive means is less than the set vehicle speed in the initial state in which the rotational speed difference between the drive axle and the driven axle occurs, suction of the driven side fluid pressure drive means The flow rate is greater than the flow rate, and is set to be equal to or lower than the suction flow rate of the driven-side fluid pressure driving means at a set vehicle speed or higher.

Further, a four-wheel drive vehicle according to a third aspect is the four-wheel drive vehicle according to the second aspect, wherein the drive side fluid pressure drive means is composed of a variable displacement pump, and the flow rate characteristic of the variable displacement pump is It is characterized in that the flow rate at low speed rotation of the drive axle is set to be larger than that at high speed rotation.

[0010]

In the four-wheel drive vehicle according to the first aspect of the present invention, the fluid transmission mechanism that transmits the driving force of the drive axle driven by the main prime mover to the driven axle, and always produces the transmission torque when the vehicle speed is less than the set vehicle speed. As a result, when the drive axle starts to rotate when the vehicle starts moving, the transmission torque is immediately generated by the fluid transmission mechanism, thereby shifting to the four-wheel drive state and preventing unnecessary idling of the drive wheels.

Further, in the four-wheel drive vehicle according to the second aspect of the invention, the rotation of the drive axle driven by the main prime mover causes the drive side fluid pressure drive means to discharge a working fluid at a flow rate according to the rotational speed, which is Is supplied to the suction side of the driven side fluid pressure driving means driven by the rotation of the driven axle through the communication flow path of the driven side fluid, and the working fluid discharged from the driven side fluid pressure drive means is driven through the other communication path. It is returned to the driving means. At this time, when the vehicle speed is less than the set vehicle speed, the discharge flow rate of the drive-side fluid pressure drive means becomes larger than the suction flow rate of the driven-side fluid pressure drive means, so the transfer torque from the drive axle side to the driven axle side becomes large. It is possible to secure the four-wheel drive state by preventing the drive wheels from spinning unnecessarily when the vehicle starts, and at the set vehicle speed or higher, the discharge flow rate of the drive side fluid pressure drive means is the intake flow rate of the driven side fluid pressure drive means. As described above, when the rotational speed difference between the drive axle and the driven axle is small, the two-wheel drive state is maintained with almost no transmission torque, but as the rotational speed difference increases, the transmission torque increases and the four-wheel drive state is achieved. Transition.

Further, in the four-wheel drive vehicle according to the third aspect of the present invention, the drive side fluid pressure drive means is constituted by a variable displacement pump, so that the flow rate of the drive side fluid pressure drive means below the set vehicle speed and above the set vehicle speed. The setting can be done easily.

[0013]

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 of the two-position four-port electromagnetic directional control valve 9 through L, and the discharge port 6c is connected to the pump port P of the electromagnetic directional control valve 9 for forward / backward switching through the high pressure pipe 8H as a high pressure passage. ing. Here, 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 Q ₁ thereof is as shown by a characteristic curve L ₁ shown by a solid line in FIG. To
During the period from when the rotation speed of the front axle 4 reaches “0” to the set vehicle speed V ₁ which is lower than the set vehicle speed Vs described later, the rotation speed of the front axle 4 increases at a relatively large rate of increase in proportion to the increase of the rotation speed, and the set vehicle speed V increases.
Above ₁ it is set to increase at a relatively small rate of increase in proportion to the increase in the number of revolutions.

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

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

The flow rate Q ₂ of the variable displacement pump motor 10
Is a variable control mechanism including a hydraulic cylinder 12a with a differential pressure generated at both ends of a differential pressure detecting orifice 11 inserted in a low pressure pipe 8L near the tank port T of the electromagnetic directional control valve 9. By controlling the plate variable mechanism 12, as shown by a characteristic curve L ₂ shown by a broken line in FIG. 2, until the set vehicle speed V ₂ higher than the set vehicle speed Vs is reached, the drive side of the drive side is increased in proportion to the increase of the vehicle speed. When the vehicle speed increases at a rate lower than the rate of increase of the piston pump 6 and becomes equal to or higher than the vehicle speed V ₂ , the set vehicle speed V of the piston pump 6 is increased as the vehicle speed increases.
The discharge flow rate of the piston pump 6 becomes larger than the discharge flow rate of the variable displacement pump motor 10 below the preset vehicle speed Vs which is set so as to increase at a slightly higher increase rate than ₁ or more. In the above, on the contrary, the discharge flow rate of the piston pump 6 is set to be smaller than the discharge flow rate of the variable displacement pump motor 10. Here, the set vehicle speed Vs is, for example, 5 km / h or 1
It is set to an extremely low vehicle speed of about 0 km / h.

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, by releasing the brake pedal and stepping 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 operating device 3 operates. The forward movement is started by rotationally driving the front wheels 5 in the forward direction. 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, whereby the piston pump 6 discharges the 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 they are driven to rotate at the same rotational speed, the rotary shaft 10c of the swash plate type variable displacement pump motor 10 rotates clockwise as viewed from the left side surface through the rear wheel side differential device 17, and as a result, 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 rates of the suction throttle type piston pump 6 and the swash plate type variable displacement pump motor 10 of the piston pump 6 are from the stopped state until the set vehicle speed Vs is reached. Since the discharge flow rate is set to be higher than the discharge flow rate of the variable displacement pump motor 10, as shown in FIG. 3, even when the front wheel 5 starts to rotate, the rotational speed difference ΔN between the front and rear wheels is zero even when the difference is zero. A certain amount of transmission torque T ₁ can be generated, and the variable displacement pump motor 10 operates as a motor, so that the four-wheel drive state is set at the same time as starting.

After that, when the acceleration state is continued and the vehicle speed becomes equal to or higher than the set vehicle speed Vs, the discharge flow rate of the piston pump 6 becomes smaller than the discharge flow rate of the variable displacement pump motor 10, so that the high pressure operation discharged from the piston pump 6 is performed. Since the oil is sucked by the variable displacement pump motor 10, the pressure in the high pressure pipe 8H does not rise. In other words, 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 vehicle travels forward in a two-wheel drive 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 discharge flow rate difference between the piston pump 6 and the variable displacement pump motor 10 at the set vehicle speed Vs or higher is
The difference in the rotational speeds of the front and rear axles 4 and 18 caused by the diameter change due to the wear of the tires is also allowed, and the driving force is not transmitted at a difference in the rotational speeds of the tires having different diameters, and the front-wheel drive vehicle state is maintained. It is possible to suppress deterioration of fuel efficiency.

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. As a result of slippage, a rotation speed difference that causes the front wheels 5 to have a high rotation speed is generated between the front wheels 5 and the rear wheels 19, and the transmission torque T increases in accordance with the rotation speed difference ΔN. Therefore, when the vehicle starts on the low friction coefficient road, the transmission torque T becomes larger than when the vehicle starts on the high friction coefficient road, and the driving torque can be transmitted to the rear wheels 19 at the same time when the vehicle starts to move. The responsiveness is good, and the rear wheels 19 before the idling of the front wheels 5 increases.
Torque can be transmitted to a smooth start.

As shown in FIG. 3, the torque transmitted to the rear wheel 19 side can maintain a predetermined value T ₁ even when there is no rotation speed difference ΔN between the front and rear wheels. It increases as ΔN increases, and the relief valve 13
The maximum torque T _MAX is restricted by the pressure limitation due to. This torque limiting action makes it 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.
It is possible to reduce fuel consumption and cost.

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

As described above, by setting the flow rate characteristics of the piston pump 6 and the variable displacement pump motor 10 as shown by the characteristic curves L ₁ and L ₂ of FIG. 2, the discharge flow rate of the piston pump 6 is set below the set vehicle speed Vs. The discharge flow rate of the variable displacement pump motor 10 can be made larger to constantly generate the transmission torque to the rear wheels to maintain the four-wheel drive state.
As a result, idling of the drive wheels can be suppressed and a good start can be performed. At a set vehicle speed Vs or higher, on the contrary, the discharge flow rate of the piston pump 6 is set to be equal to or lower than the discharge flow rate of the variable displacement pump motor 10, and the difference between the front and rear wheel rotation speeds ΔN. It is possible to obtain an optimum four-wheel or two-wheel drive state according to As described above, by using the piston pump 6 driven by the drive shaft 4 corresponding to the vehicle speed and setting the displacement characteristics of the pump itself of the piston pump 6 and the variable displacement pump motor 10, the set vehicle speed Vs
Since it is possible to switch the front and rear capacitance characteristics, it is not necessary to separately provide a sensor or controller for this purpose, and the entire configuration can be simplified.

Incidentally, it is conceivable to use the longitudinal acceleration or the like as a parameter in addition to the vehicle speed, but in this case, a longitudinal acceleration sensor and a controller are required, which increases the manufacturing cost and simplifies the overall structure. In addition, when the fluid actuated clutch (viscus coupling) is applied as in the second conventional example described above, the vehicle speed sensitive type cannot be configured.

Further, in the rising of the transmission torque in FIG. 3, the amount of leakage from the high pressure pipe 8H to the low pressure pipe 8L is controlled by the fixed orifice 16 inserted in the communication pipe 14B connecting 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. 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 driving the vehicle forward, and the four-wheel drive state is maintained from the time when the vehicle starts to the set vehicle speed Vs, and the drive wheels, that is, the front wheels 5 run idle. The front wheel 5 slips at the set vehicle speed Vs or more and the front and rear axles 4,
The pressure is generated in the high-pressure pipe 8H only when there is a difference in the number of revolutions at 18, the driving force is transmitted to the rear wheel 19, and the swash plate type variable displacement in the case where the difference in the number of revolutions between the front and rear axles 4 and 18 is small. Insufficient intake amount of pump motor 10 is low pressure pipe 8
It is replenished through L, the communication pipe 14A 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 an anti-skid control device based on a front-wheel drive vehicle, the rotational speed of the front wheels becomes smaller than the rotational speed of the rear wheels during braking, so that no driving force is generated by the hydraulic transmission mechanism and the anti-skid control is performed. There is an advantage that interference with the device can be reduced. In the above embodiment, the case where the differential pressure before and after the differential pressure detecting orifice 11 is supplied to the swash plate variable mechanism 12 has been described.
The present invention is not limited to this, and when the differential pressure detecting orifice 11 is inserted on the low pressure pipe 8L side, the pressure on the outlet side of the differential pressure detecting orifice 11 becomes atmospheric pressure, so the variable displacement pump 10 Since it is the same as the drain pressure inside, 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 applied to the hydraulic cylinder of the swash plate variable mechanism 12. It may be introduced into the head cover side hydraulic chamber 12b of 12a.

In the above embodiment, the case where the relief valve 13 is applied as the transmission torque limiting means has been described, but the present invention is not limited to this, and as shown in FIG. 5, the discharge pressure of the piston pump 6 is reduced. Is input as the displacement control pressure, and the suction port 6b of the piston pump 6 is correspondingly input.
A suction throttle valve 21 may be provided to control the opening degree of the side suction passage to be small when the discharge pressure becomes equal to or higher than a predetermined pressure. In this case, when the pump discharge flow rate becomes equal to or higher than a prescribed pressure, the pump suction By reducing the amount, the pump discharge pressure is reduced and torque can be limited. At the same time, when the relief valve is used, the oil temperature rises during continuous high load use. When it is provided, heat generation can be suppressed because the discharge flow rate decreases.

Further, in the above embodiment, 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. Omitted, instead of this, the left and right rear wheels 19L, 19R
The left and right axles 18L and 18R may be individually provided with the swash plate type variable displacement pump motors 10L and 10R. In this case, when different loads are applied to the left and right wheels during turning, Variable displacement pump motor 10L, 10R
Since a discharge flow rate difference naturally occurs according to the difference, a differential function equivalent to that of a differential device can be exerted. In this case as well, the relief valve 13 shown in FIG. Any of the suction throttle valves 21 may be used.

Furthermore, the rotary shaft 6 is used as a fluid pressure pump.
The case where the suction throttle type piston pump 6 in which the suction port 6b and the discharge port 6c do not change regardless of the rotation direction of a is applied has been described, but the present invention is not limited to this.
As shown in FIG. 7, the pump port P and the tank port T are connected to the suction port 30b and the discharge port 30c of the hydraulic pump 30 whose rotary shaft 30a is connected to the gear 3g, and the output ports A and B are connected to the high pressure pipe 8H. And an electromagnetic directional control valve 31 for forward / reverse switching similar to the electromagnetic directional control valve 9 for forward / backward switching connected to 8L and 8L, another hydraulic pump such as a gear pump or a vane pump whose discharge direction is switched by forward / backward movement. Can be applied, as shown in FIG.
Any variable capacity type may be used, which includes a variable mechanism 33 including a hydraulic cylinder 33a to which the differential pressure across the differential pressure generating orifice 32 inserted in L is input, and the differential mechanism 17 may be omitted. As shown in FIG. 6, two sets of swash plate type variable displacement pump motors 10L and 10R may be applied.

Further, in the above embodiment, 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, and the electromagnetic motor can be provided outside the pump motor 10. It may be provided separately. Further, in the above-mentioned embodiment, the embodiment based on the front-wheel drive vehicle has been described. By arranging it on the front wheel side, it is possible to obtain the same effect as that of the above-described embodiment.

Further, in the above embodiment, the high pressure passage 8H is formed by connecting the driving side fluid pressure driving means and the driven side fluid pressure driving means.
And, the case where the low-pressure channel 8L communicates with each other has been described.
The present invention is not limited to this, and the present invention can be applied even in the case where the forward / reverse switching electromagnetic directional control valves 9 and 31 are omitted and the high pressure passage and the low pressure passage are not separated.

[0040]

As described above, according to the four-wheel drive vehicle of the first aspect, the driving force of the drive axle driven by the main prime mover is transmitted to the driven axle via the fluid pressure transmission mechanism. In the four-wheel drive vehicle, since the fluid pressure transmission mechanism is configured to constantly generate the transmission torque at a speed lower than the set vehicle speed, it is necessary to maintain the four-wheel drive state from the start of the vehicle until the set vehicle speed is reached. In addition to the above, it is possible to obtain an effect that unnecessary idling of the drive wheels can be suppressed and a smooth start can be performed.

According to the four-wheel drive vehicle of the second aspect, the drive axle driven by the main prime mover, the drive side fluid pressure drive means driven in conjunction with the drive axle, and the driven axle are interlocked. And a driven-side fluid pressure driving means that is driven by the above-mentioned method, wherein the driving-side fluid pressure driving means and the driven-side fluid pressure driving means are provided with a flow path that connects the discharge port and the suction port to each other. In a four-wheel drive vehicle having a mechanism, when the discharge flow rate of the drive-side fluid pressure drive means is less than a set vehicle speed in an initial state in which a rotational speed difference between the drive axle and the driven axle occurs, the driven-side fluid pressure drive means The intake flow rate of the driven side fluid pressure driving means is set to be equal to or less than the suction flow rate of the driven side fluid pressure driving means above the set vehicle speed. To operate as a motor It is possible to maintain the four-wheel drive state from the start of the vehicle, and to suppress unnecessary idling of the drive wheels to perform a smooth start. Even if a difference in the number of rotations of the wheels occurs, the effect of being able to maintain the two-wheel drive state and prevent deterioration of fuel consumption due to an increase in running resistance is obtained.

Further, according to the four-wheel drive vehicle of the third aspect, in the second aspect, the flow rate characteristics of the drive side fluid pressure drive means and the driven side fluid pressure drive means before and after the set vehicle speed are set to the flow rate characteristics of the variable displacement pump. Since the setting is made in step (1), the adjustment can be easily performed, and an accurate flow rate characteristic according to the vehicle speed can be obtained without separately providing a sensor or controller.

[Brief description of drawings]

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

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

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

FIG. 4 is a schematic configuration diagram showing another embodiment of a variable displacement pump motor.

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.

[Explanation of reference symbols] 1 engine 2 transmission 3 front wheel side differential device 4 front axle 5 front wheel 6 suction throttle type piston pump 7 reservoir tank 8H high pressure pipe 8L low pressure pipe 9 forward / reverse switching electromagnetic directional control valve 10 swash plate type variable Displacement pump motor 11 Orifice for generating differential pressure 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 Electromagnetic directional control valve for forward / reverse switching

Claims (3)

[Claims] 1. A four-wheel drive vehicle in which the drive force of a drive axle driven by a main prime mover is transmitted to a driven axle via a fluid pressure transmission mechanism, wherein the fluid pressure transmission mechanism is always less than a set vehicle speed. A four-wheel drive vehicle, which is configured to generate a transmission torque. 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 providing a flow path that connects the driving means with each other's discharge port and suction port,
If the discharge flow rate of the drive-side fluid pressure drive means is less than the set vehicle speed in the initial state where the rotational speed difference between the drive axle and the driven axle occurs, it is higher than the intake flow rate of the driven-side fluid pressure drive means, and is equal to or higher than the set vehicle speed. Then, the four-wheel drive vehicle is set such that the flow rate is not more than the suction flow rate of the driven-side fluid pressure drive means. 3. The drive-side fluid pressure drive means is composed of a variable displacement pump, and the flow rate characteristic of the variable displacement pump is such that the flow rate at low speed rotation of the drive axle is larger than the flow rate at high speed rotation. The four-wheel drive vehicle according to claim 2, wherein the four-wheel drive vehicle is set to.