JPH0899551A - Four-wheel drive vehicle - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a four-wheel drive vehicle that can improve the starting performance and the feeling of starting by increasing the transmission torque when the vehicle starts. [Structure] The driving force of an engine 1 is applied to a transmission 2 and a differential device 3.
It is transmitted to the front wheel 5 and the rotary shaft 6a of the piston pump 6 via. The discharge port 6c and the suction port 6b of the pump 6 are connected to the ports P and T of the forward / reverse switching switching valve 9 incorporated in the swash plate type variable displacement pump motor 10 via the high pressure pipe 8H and the low pressure pipe 8L. A transmission device is configured, and an intake throttle valve 13 is inserted on the intake side of the piston pump 6, and the discharge pressure of the piston pump 6 is used as a pilot pressure for controlling the opening area of the intake throttle valve 13. By supplying via a parallel circuit of the check valve 22 with a spring and the check valve 23 as the delay limit defining means, a transient maximum torque larger than the steady maximum torque is temporarily generated at the time of starting.

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 kind, 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 In addition to being troublesome, it is not suitable for passenger cars due to problems such as tight corner braking phenomenon. 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
(Referred to as "first conventional example"), through a first fluid pressure pump driven in conjunction with front wheels directly driven by a prime mover and a fluid pressure clutch operated by fluid pressure on the front wheels. A second fluid pressure pump that is driven in conjunction with the rear wheel that is driven by the first fluid pressure pump, a connection oil passage that connects and connects the discharge port of the first fluid pressure pump and the suction port of the second fluid pressure pump, and this connection oil. A hydraulic supply oil passage connecting the passage and the working hydraulic chamber of the fluid pressure clutch via a forward / reverse switching valve,
There has been proposed a four-wheel drive vehicle including a relief valve that relieves when a pressure acting on an operating hydraulic chamber of a fluid pressure clutch exceeds a predetermined value. In this conventional example, since there is a propeller shaft that connects the front and rear wheels via a fluid pressure clutch, there is no effect in increasing the vehicle interior space, but the upper limit value of the torque transmitted to the rear wheels causes the relief valve to open. By being regulated by the pressure, it becomes possible to lower the strength of the components such as the rear wheel side differential device 17 and the drive shaft as compared with a conventional four-wheel drive vehicle having a propeller shaft, which reduces weight, fuel consumption, and cost. It can be reduced.

Further, as described in JP-A-63-176734 (hereinafter referred to as the second conventional example),
A hydraulic pump that works with the drive wheels driven by the engine,
A hydraulic motor that works with a driven shaft that communicates with this hydraulic pump via a hydraulic line, and a relief that relieves the pressure oil in the hydraulic line to a low-pressure hydraulic source when the discharge pressure of the hydraulic pump exceeds a set pressure. A valve and a check valve that supplies pressure oil from a hydraulic source when the hydraulic line pressure inserted in parallel with the valve drops below a set pressure, thus omitting the propeller shaft and reducing the weight. A four-wheel drive vehicle has also been proposed in which both the vehicle interior space and the vehicle interior space are increased.

[0005]

However, in the four-wheel drive vehicles of the first conventional example and the second conventional example, when the discharge pressure of the hydraulic pump on the drive wheel side becomes equal to or higher than the set pressure. By opening the relief valve, the upper limit value of the discharge pressure of the hydraulic pump is regulated.However, since the opening pressure of this relief valve is set to a constant pressure, the strength of the components on the driven wheel side is reduced. In order to achieve this, it is preferable to keep the upper limit of the relief valve low to reduce the maximum value of the transmission torque to the driven wheel side.However, when high torque is required such as when starting, the relief valve It is preferable to increase the upper limit of the above, and since the contradictory requirements of both can not be satisfied at the same time, it is necessary to set the relief valve opening pressure at the middle point of both or to sacrifice either. There is a problem to be solved .

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and temporarily increases the maximum torque in a transient state such as at the time of starting to improve the starting performance and the feeling of starting. It is an object of the present invention to provide a four-wheel drive vehicle that is improved and at the same time regulates the transmission torque to reduce the weight and solves conflicting requirements at the same time.

[0007]

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 driving means, a driven fluid pressure driving means which is driven in conjunction with a driven axle, and a flow which connects the discharge port and the suction port of the driving fluid pressure driving means and the driven fluid pressure driving means. In a four-wheel drive vehicle including a road, the discharge pressure of the drive-side fluid pressure drive means is input, and the opening degree of the suction-side passage of the drive-side fluid pressure drive means is changed to the closing direction in accordance with the increase of the discharge pressure. It is characterized in that it is provided with a torque limiting valve means for controlling and an operation delaying means for delaying the operation of the torque limiting valve means in accordance with a change in discharge pressure.

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 four-wheel drive vehicle comprising: driven side fluid pressure driving means to be driven; and a flow path that connects the discharge port and the suction port of the driving side fluid pressure driving means and the driven side fluid pressure driving means. Torque limiting valve means for inputting the discharge pressure of the drive side fluid pressure drive means and controlling the opening degree of the suction side passage of the drive side fluid pressure drive means in the closing direction according to the increase of the discharge pressure, and the torque limit It is characterized in that it comprises an operation delay means for delaying the operation of the valve means in accordance with a change in discharge pressure, and a delay limit defining means for defining a delay limit of the operation delay means.

Further, a four-wheel drive vehicle according to a third aspect is the four-wheel drive vehicle according to the second aspect, wherein the delay limit defining means is provided with a check valve that opens when a predetermined set pressure is reached. It is characterized by that. Furthermore, the four-wheel drive vehicle according to claim 4 is the four-wheel drive vehicle according to any one of claims 1 to 3,
It is characterized in that the operation delay means is composed of an orifice.

Furthermore, a four-wheel drive vehicle according to a fifth aspect is the four-wheel drive vehicle according to any one of the first to fourth aspects, in which the torque limiting valve means is allowed to operate in the opening direction. The valve is provided in an oil passage separate from the operation delay means.

[0011]

According to the first aspect of the present invention, the working fluid is driven by the driving prime mover to discharge the working fluid at a flow rate corresponding to the rotation speed from the driving fluid pressure driving means, and the working fluid is driven through the one communicating passage. The working fluid supplied to the suction side of the driven fluid pressure driving means driven by the rotation of the axle and discharged from this driven fluid pressure driving means is returned to the driving fluid pressure driving means through the other communication flow path. At this time, when the rotational speed difference between the drive axle and the driven axle is small, the discharge pressure of the drive side fluid pressure drive means is small, and the torque limiting valve means provided on the suction side is in an open state, and Although there is almost no transmission torque, the two-wheel drive state is maintained, but as the rotational speed difference increases, the discharge pressure of the drive side fluid pressure drive means increases, and accordingly, the torque limiting valve means is controlled in the closing direction. The discharge pressure of the drive side fluid pressure drive means is suppressed. Since the operation of the torque limiting valve means is delayed by the operation delay means in accordance with the change in the discharge pressure, when the discharge pressure of the drive side fluid pressure drive means transiently increases at the time of starting the vehicle, the torque limiting valve means is used. The delay of the operation of the valve means temporarily relaxes the torque limit,
The discharge pressure of the drive-side fluid pressure drive means increases, and a large transmission torque can be generated.

In the invention of claim 2, the above-mentioned claim 1
In addition to the operation of the invention described above, since the delay limit of the operation delay means is defined by the delay limit defining means, the generation of excessive transmission torque is suppressed. According to the invention of claim 3, when the discharge pressure of the drive side fluid pressure drive means reaches a predetermined set pressure, the check valve constituting the delay limit defining means is opened,
The delay of the operation delay means is eliminated and the torque limiting valve means is operated according to the discharge pressure.

According to the fourth aspect of the present invention, the actuation delay means is constituted by a throttle, and when the discharge pressure of the drive side fluid pressure drive means suddenly increases, this delay amount is increased,
When the change in discharge pressure is small, the delay amount is small, and the delay amount can be adjusted without providing a complicated delay unit. In the invention of claim 5, the check valve for allowing the torque control valve means to operate in the opening direction is provided in the oil passage separate from the operation delay means. When the device is operated in the opening direction, the discharge pressure in the driving fluid pressure driving device is immediately allowed to increase without causing a delay.

[0014]

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 piston pump 6 as a fluid pressure pump via a gear 3g meshing with the ring gear 3f. The suction throttle type piston pump 6 has a suction port 6b, which is a strainer 7a having a reservoir tank 7 disposed therein.
Is connected to the low pressure pipe 8 as a low pressure flow path.
It is connected to the tank port T of the two-position four-port electromagnetic directional control valve 9 through L, and the discharge port 6c is connected to the pump port P of the electromagnetic directional control valve 9 for forward / backward switching through the high pressure pipe 8H as a high pressure passage. ing.

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

In the electromagnetic directional control valve 9 for switching between forward and reverse, the pump port P communicates with the output port A and the tank port T communicates with the output port B at the normal position where the solenoid 9a is not energized. The pump port P communicates with the output port B and the tank port T communicates with the output port A at the offset position 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 of the variable displacement pump motor 10 is
Low pressure pipe 8L near the tank port T of the electromagnetic directional control valve 9
By controlling the swash plate variable mechanism 12 as a variable control mechanism configured to include the hydraulic cylinders 12a by the differential pressure generated at both ends of the differential pressure detecting orifice 11 inserted in the characteristic curve L in FIG. _As shown by ₂ , until the rear axle rotation speed reaches the first rotation speed N _R1 at which the maximum transmission torque begins to decrease, it is higher than the increase rate of the drive side piston pump 6 in proportion to the increase in the rotation speed. Rotation speed N increases at an increasing rate
Maximum flow rate Q of piston pump 6 when _R1 is reached
_The discharge flow rate Q ₂₁ becomes lower than _1MAX , and as the number of revolutions increases thereafter, the number of revolutions N _{F1 to} N _{F2 of} the piston pump 6 described above increases.
It is set to increase at a relatively low rate of increase, which is approximately equal to the rate of increase between.

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

Further, a suction throttle valve 13 for restricting the upper limit value of the discharge pressure of the piston pump 6 as a torque limiting valve means is inserted in the suction port 6b of the suction throttle type piston pump 6. This suction throttle valve 13 is, as shown in FIG.
A spool valve type is constituted by a spool 13b slidably arranged in a cylindrical valve housing 13a.
In the valve housing 13a, a cylinder 7 is provided with a suction port 13c to which the tank 7 and the low-pressure side pipe 8L are connected, and a discharge port 13d connected to the suction port 6b of the suction throttle piston pump 6 at a predetermined interval. And a pilot port 13e is formed at the right end. Lands 13f and 13g facing the suction port 13c and the discharge port 13d are formed on the spool 13b, and the left end surface of the spool 13b and the valve housing 13a are formed.
The return spring 13h is interposed between the inner peripheral surface of the pilot port 13e and the right end surface of the spool 13b.
Control plunger 13i supplied with pilot pressure from
Are abutted. Reference numeral 13j is a through hole that penetrates between the left and right ends of the spool 13b to allow movement of the hydraulic oil between them and to move the spool 13b quickly.

When the pilot pressure supplied to the pilot port 13e is zero, the spool 13b
Is in the fully open position where it slides to the right by the return spring 13h and communicates the suction port 13c and the discharge port 13d with a large opening area.
From this state, the amount of hydraulic oil supplied to the suction port of the piston pump 6 becomes maximum, and as the pilot pressure increases from this state, the spool 13b moves left against the return spring 13h, so that the suction port 13c and the discharge port 13d. The opening area between and is gradually reduced, and the amount of hydraulic oil supplied from the discharge port 13d to the suction port 6b of the piston pump 6 is reduced.

Then, a throttle as an operation delay means is provided in the middle of the pipe 20 which connects the pilot port 13e of the suction throttle valve 13 and the high pressure side pipe 8H connected to the discharge port 6c of the suction throttle type piston pump 6. Orifice 21
Is inserted in parallel with the orifice 21, and when the discharge pressure of the piston pump 6 becomes equal to or higher than the set pressure P _TMAX set to a value higher than the steady-state maximum pressure P _MAX , the discharge pressure is opened to the pilot port 13e. The check valve 22 with spring as a delay limit regulating means for supplying the oil to the valve is connected to the check valve 23 which allows the hydraulic oil to flow out from the pilot port 13e to the high-pressure side pipe 8H and quickly moves the spool 13b to the right. Has been done.

Further, a check valve which allows a fluid flow from the low pressure pipe 8L side to the high pressure pipe 8H side in a communication pipe 14A which communicates between the high pressure pipe 8H and the low pressure pipe 8L between the hydraulic pump 6 and the electromagnetic directional control valve 9. 15 is inserted, and the communication pipe 14 arranged in parallel with the communication pipe 14A.
A fixed orifice 16 is connected to B in parallel 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,
It is assumed that the vehicle is stopped on a high friction coefficient road such as a dry road surface, the engine 1 is in the idling state, and the shift lever is in the neutral range, for example, in the braking state. In this state, the shift position detection switch 9b on the backward traveling side is provided.
Keeps the off state, the solenoid 9a of the forward / reverse switching electromagnetic directional switching valve 9 maintains the non-energized state, and its switching position continues to the normal position shown in FIG. On the other hand, in this state, since the output shaft of the transmission 2 is not rotating, the suction throttle type piston pump 6 is also in the rotation stopped state, and its discharge pressure P _H is zero, which is supplied as the pilot pressure. Since the pilot pressure of the intake throttle valve 13 is zero, the spool 13b has the return spring 13
has been moved to the fully open position by h, and the suction port 13
c and the discharge port 13d are in communication with each other with a large opening area.

When starting the forward running on the high friction coefficient road from this stopped state, it is possible to make the vehicle ready to start by switching the shift lever to the forward running side. Shift position detection switch 9b
Keeps the off state, the solenoid 9a of the forward / reverse switching electromagnetic directional control valve 9 maintains the non-energized state, and the switching position continues the normal position shown in FIG.

In this state, by releasing the brake pedal and depressing 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. By driving the front wheels 5 to rotate in the forward direction, the vehicle starts to move forward. At this time, when the accelerator pedal is stepped on to start the vehicle, the rotary shaft 6a of the suction throttle type piston pump 6 is driven to rotate clockwise as viewed from the left side surface, and the suction throttle valve 13 is fully opened. The piston pump 6 discharges the hydraulic oil at a discharge flow rate according to the rotation speed, whereby the high pressure pipe 8H
The pressure P _H of the swash plate type variable displacement pump motor 10 is supplied to the suction / discharge port 10a of the swash plate type variable displacement pump motor 10 through the high pressure pipe 8H and the forward / reverse switching electromagnetic directional control valve 9, but the vehicle starts. As a result, the rear wheels 19 are also driven to rotate in the same direction as the front wheels 5 at the same rotational speed, so that the rotary shaft 10c of the swash plate type variable displacement pump motor 10 is clockwise through the rear wheel side differential device 17 when viewed from the left side surface. The working oil is sucked from the suction / discharge port 10a, and the working oil is discharged from the suction / discharge port 10b.

The discharge flow rates of the suction throttle type piston pump 6 and the swash plate type variable displacement pump motor 10 are, as shown in FIG.
Since the discharge flow rate of the high pressure hydraulic fluid is set to be always larger than that of the piston pump 6, the high pressure hydraulic oil discharged from the piston pump 6 is sucked by the variable displacement pump motor 10, so that the pressure of the high pressure pipe 8H is reduced. Does not go up. That is, the variable displacement pump motor 10 does not act as a hydraulic motor and the driving force is not transmitted to the rear wheel 19,
It travels forward in the same manner as a front-wheel drive vehicle. At this time, since the suction flow rate of the variable displacement pump motor 10 exceeds the discharge flow rate of the piston pump 6, the shortage is replenished via the low pressure pipe 8L, the communication pipe 14A, and the check valve 15. On the other hand, the intake throttle valve 13 is maintained in a fully open state because the pilot pressure supplied to the pilot port 13e is maintained in a low state.

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 suddenly starts on a low friction coefficient road such as an icy road or a snowfall road, as described above, the front wheels 5 are first driven to rotate, but since the road is a low friction coefficient road, the front wheels 5 slip. As a result, there occurs a difference in rotation speed between the front wheels 5 and the rear wheels 19 so that the front wheels 5 have a high rotation speed, and the discharge flow rate of the suction throttle piston pump 6 exceeds the discharge flow rate of the swash plate type variable displacement pump motor 10. In that case, the resistance of the variable displacement pump motor 10 becomes a load, and the working oil pressure of the high-pressure pipe 8H, that is, the discharge pressure P of the piston pump 6
_{Since H} increases rapidly as shown in FIG. 4, the variable displacement pump motor 10 operates as a hydraulic motor, and the driving force corresponding to the pressure of the high pressure pipe 8H drives the rear wheel side differential device 17. It is transmitted to the rear wheel 19 via the.

That is, the discharge pressure P _{H of the} piston pump 6
Due to the rapid increase of the pilot port 1 of the intake throttle valve 13
The pilot pressure supplied to 3e also tries to increase sharply,
The pilot pressure from the high pressure side pipe 8H side is the orifice 21
Since it is supplied to the pilot port 13e via the orifice 21, the rapid increase in pilot pressure at the pilot port 13e is delayed by the orifice 21. Therefore, during this delay time, the suction throttle valve 13 is maintained in a substantially fully open state, the discharge pressure P _H of the piston pump 6 suddenly increases beyond the steady maximum pressure P _MAX as shown in FIG. By gradually increasing the pilot pressure supplied to the pilot port 13e of the intake throttle valve 13, the spool 13b gradually moves to the left against the return spring 13h, and accordingly, the intake flow rate of the piston pump 6 is increased. Is narrowed down.
Therefore, increase of the discharge pressure P _H of the piston pump 6 is suppressed by further pilot pressure rises, the spool 13b is moved to the left, by throttling the intake amount of the piston pump 6, its discharge pressure P _H Constant maximum pressure P _MAX
It is stepped down and stabilized.

Therefore, as shown in FIG. 5, the relationship between the discharge flow rate Q of the piston pump 6 and the discharge pressure P _H is that the discharge flow rate Q is a large discharge flow rate by maintaining the intake throttle valve 13 in a substantially fully opened state. Even if the flow rate reduction pressure value P _U due to the start of the suction throttle of the suction throttle valve 13 in the steady state is maintained, the decrease in the flow rate is suppressed as shown by the broken line in FIG. Maintained. After that, when the delay due to the orifice 21 elapses, the pilot pressure increases, and accordingly, the discharge flow rate of the suction throttle valve 13 decreases, so that the discharge flow rate Q of the piston pump 6 sharply decreases. Accordingly, the discharge pressure P _H is also the maximum pressure P in the steady state.
It will be reduced to _MAX .

In this way, the discharge pressure P of the piston pump 6 is
_As shown in FIG. 4, when _H exceeds the maximum pressure P _MAX in the steady state, the torque transmitted to the rear wheel 19 side also increases as in the characteristic curve of FIG. In a transient state such as a sudden start on a friction coefficient road, a maximum transient torque T _TMAX larger than that in a steady state can be generated, and the starting performance and the feeling of starting during a sudden acceleration can be improved.

The difference in the number of rotations of the front and rear wheels is reduced,
When the discharge pressure P _H of the piston pump 6 decreases below the steady-state maximum pressure P _MAX , the intake throttle valve pilot port 1
Discharge pressure P _H with respect to the pilot pressure being input to 3e
Therefore, the check valve 23 opens and the pilot pressure immediately decreases. In response to this, the thrust of the control plunger 13i decreases, so the spool 13b moves right by the return spring 13h, the opening area between the suction port 13c and the discharge port 13d of the suction throttle valve 13 increases, and the piston pump 6 Due to the increase in the suction amount in (1), the discharge amount Q increases without causing a delay time.

On the other hand, when the vehicle is slowly started on a low friction coefficient road, as described above, the front wheels 5 slip and there is a difference in rotational speed between the front wheels 5 and the rear wheels 19 at which the front wheels 5 have a high rotational speed. Although it occurs, this difference in rotational speed becomes smaller than that at the time of sudden start, and when 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, the variable displacement pump motor 10 Resistance acts as a load and the working oil pressure of the high-pressure pipe 8H, that is, the discharge pressure P of the piston pump 6.
_H gradually rises, whereby the variable displacement pump motor 10 operates as a hydraulic motor, and the driving force corresponding to the pressure of the high-pressure pipe 8H is applied to the rear wheel 19 via the rear wheel side differential device 17. Transmitted.

However, the discharge pressure P _{H of the} piston pump 6
Is gradually increased, the delay effect at the orifice 21 is hardly exerted, and the pilot pressure to the pilot port 13e of the suction throttle valve 13 is increased substantially in synchronization with the increase of the discharge pressure P _H. 13b moves to the left faster than in the sudden start state, and the suction amount of the piston pump 6 is throttled. Therefore, the transmission torque during slow start is restricted by the steady maximum torque T _UMAX .

As described above, according to the above embodiment, when a large rotational speed difference occurs between the front and rear wheels, such as when the vehicle is suddenly started on a low friction coefficient road, the transient maximum torque T _UMAX is transiently exceeded. The maximum dynamic torque T _TMAX can be obtained, the starting performance and the feeling of starting can be improved, and the steady maximum torque T _UMAX lower than the transient maximum torque T _TMAX is constantly regulated. Due to the restricting action, the strength of the rear wheel side differential device 17, the drive shaft, and the like can be reduced compared to the conventional four-wheel drive vehicle, and weight, fuel consumption, and cost can be reduced.

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

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

As described above, by setting the flow rate characteristics of the piston pump 6 and the variable displacement pump motor 10 as shown by the characteristic curves L ₁ and L ₂ in FIG. 2, the maximum transmission torque is the wheel speed V _R1 or the first. When the number of revolutions exceeds N _R1 , it gradually decreases, and it is possible to reliably prevent the maximum transmission torque from suddenly decreasing, and it is possible to suddenly change from the four-wheel drive state to the two-wheel drive state. It is possible to reliably prevent the driver from feeling uncomfortable by restraining.

Further, the rising of the torque in FIG. 6 controls 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. Then, the switching position is switched from the normal position to the offset position, thereby supplying the working oil of the high-pressure pipe 8H to the suction / discharge port 10b of the swash plate type variable displacement pump motor 10,
The hydraulic oil discharged from the suction / discharge port 10a is supplied to the low pressure pipe 8
By returning to the L side, the rotating 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, 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 check valve 15, the orifice 16 and the like can also be used in one direction. Therefore, the oil passage structure can be extremely simplified as compared with the case where a pump of another system is used.

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 drive 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. Next, a second embodiment of the present invention will be described with reference to FIG.

The second embodiment is different from the first embodiment in that the rise of pilot pressure is delayed by the orifice 21 and the movement of the spool 13b is delayed.
The movement of the spool 13i itself is delayed. That is, as shown in FIG. 7, the orifice 21, the check valve 22 with spring, and the check valve 23 in the first embodiment.
Instead, a through hole 13k is bored in the spool 13b in parallel with a through hole 13j penetrating in the left-right direction, and an orifice 31 as an operation delay means is inserted in the middle of one through hole 13j, and the other is inserted. A check valve 33 that allows the hydraulic oil to flow from the left side to the right side is inserted in the middle of the through hole 13k of the above, and a transient passage is formed in a flow path 34 that communicates between the pilot port 13e and the discharge port 13d. Maximum torque T
_It has the same configuration as that of FIG. 2 described above except that a check valve 32 with a spring configured by a check valve with a spring that regulates _TMAX is inserted. The same reference numerals are given and detailed description thereof is omitted.

According to the second embodiment, when the discharge pressure P _H of the piston pump 6 suddenly increases as in the case of a sudden start on a low friction coefficient road, the discharge pressure P _H is directly used as the pilot pressure in the suction throttle. Since it is supplied to the pilot port 13e of the valve 13, the control plunger 13i immediately generates a large thrust to move the spool 13b to the left, but in order to move the spool 13b to the left, the return spring 13h is housed. It is necessary to discharge the working oil in the oil chamber 13m to the oil chamber 13n side that houses the control plunger 13i, and this is performed through the through hole 13j in which the orifice 31 is inserted. The hydraulic fluid passing through the through hole 13j is suppressed by the flow path resistance of the orifice 31, so that the leftward movement of the spool 13b is delayed, and the suction port 13c and the discharge port are the same as in the first embodiment. The state where the opening area between 13d is large is maintained, and the discharge pressure P _H of the piston pump 6 is the steady maximum pressure P.
_{It is possible} to increase the transient maximum pressure P _TMAX higher than _MAX to make the transmission torque during sudden start larger than the steady state maximum torque T _UMAX, and to _improve the starting performance and start feeling during sudden start on a low friction coefficient road. Can be improved. Moreover,
In the second embodiment, the amount of hydraulic oil passing through the through hole 13j from the left oil chamber 13m to the right oil chamber 13n is larger than that in the first embodiment described above, so that the delay effect at the orifice 31 is further improved. The effect that it is easy to exhibit is also obtained.

When the discharge pressure P _H of the piston pump 6 reaches the set pressure P _S of the check valve 32 with spring, the check valve 32 with spring is opened, so that the discharge flow rate of the piston pump 6 with spring is increased. Bypassing to the suction port 6b side of the piston pump 6 via the check valve 32, the pilot pressure of the pilot port 13e of the suction throttle valve 13, that is, the pressure of the high pressure side pipe 8H is limited to the transient maximum pressure P _TMAX . When the operation delay of the spool 13b by the orifices 31 is eliminated, by the intake-air flow rate of the piston pump 6 is throttled spool 13b is moved to the left, the discharge pressure P _H is constant maximum pressure P _MAX of the piston pump 6 Regulated.

After that, when the difference in the number of rotations between the front and rear wheels becomes smaller, the discharge pressure P _H of the piston pump 6 becomes correspondingly smaller, and the pilot pressure supplied to the intake throttle valve 13 also becomes smaller, resulting in control. The thrust generated by the plunger 13h becomes small, and the return spring 13i moves the spool 13b to the right. When the spool 13b moves to the right, the hydraulic oil in the right oil chamber 13n passes through the through hole 13k and the check valve 33 and moves to the left oil chamber 13m, so that the fluid resistance is small and the spool 13b can be easily moved to the right. Can move.

In the second embodiment, the case where the through hole 13k and the check valve 33 are formed in the spool 13b has been described, but the present invention is not limited to this.
As shown in FIG. 8, the through hole 13k and the check valve 33 are omitted, and instead of these, the left oil chamber 13m and the suction port 13c are replaced.
And a check valve 33 that allows passage of hydraulic oil from the suction port 13c to the left oil chamber 13m is inserted in the flow path 13o, and the spool 13b is connected to the right oil chamber 13m. Through hole 13p communicating with the suction port 13c
The right oil chamber 13n and pilot port 1
Even if the check valve 32 with a spring is inserted in the flow path 13q formed between the check valve 3e and 3e, it is possible to obtain the same effect as the second embodiment.

Further, as shown in FIG. 9, the through hole 13j and the orifice 31 in FIG. 8 are omitted, and instead of these, the flow passage 13 is provided between the left oil chamber 13m and the suction port 13c.
Even if the flow path 13o is formed by inserting the orifice 31 into the flow path 13o, the left oil chamber 1 can be moved when the spool 13b moves to the left.
It is possible to delay the leftward movement of the spool 13b by giving flow resistance to the hydraulic oil discharged from 3 m, and it is possible to obtain the same effect as that of the second embodiment.

Further, in the above-mentioned first and second embodiments, the case where the orifices 21 and 31 are applied as the throttles has been described, but the present invention is not limited to this, and chokes are applied instead of the orifices. May be. Further, in the first and second embodiments, the flow rate characteristic of the suction throttle type piston pump 6 as the drive side fluid pressure driving means is set in a two-step broken line shape as shown by the characteristic curve L ₁ in FIG. Although the case has been described, the present invention is not limited to this, and the number of revolutions increases from “0” to a predetermined value N _F2 as indicated by a characteristic line L ₂₁ indicated by a chain line in FIG. It can also be a characteristic that increases according to
In short, any flow rate characteristic can be set within the shaded area in FIG. In this case, if the difference in the discharge flow rate between the piston pump 6 and the variable displacement pump motor 10 is too large, it will be difficult to generate the transmission torque, so in reality, it is set within the range on the characteristic curve L ₂ side from the characteristic line L _21. Preferably.

Further, in the first and second embodiments, 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. 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 the atmospheric pressure, and therefore is the same as the drain pressure in the variable displacement pump 10. Therefore, as shown in FIG. 10, 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 limited to the head cover side hydraulic chamber 1 of the hydraulic cylinder 12 a of the swash plate variable mechanism 12.
You may make it introduce | transduce into 2b.

Furthermore, in the first embodiment,
The case where the rear wheel side differential device 17 is provided has been described.
The present invention is not limited to this, and as shown in FIG.
The rear wheel differential device 17 is omitted, and instead of this, the left and right rear wheels 19
The left and right axles 18L and 18R of the L and 19R may be individually 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, such as when turning. , Each variable displacement pump motor 10
Since the discharge flow rate difference naturally occurs in L and 10R, the differential function equivalent to that of the differential device can be exhibited.

Furthermore, in the first and second embodiments, 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. Although the case has been described, the present invention is not limited to this, and as shown in FIG. 12, the hydraulic pump 4 in which the rotary shaft 40a is connected to the gear 3g.
A forward / backward movement similar to the forward / backward switching electromagnetic directional control valve 9 in which the pump port P and the tank port T are connected to the suction port 40b and the discharge port 40c of 0, respectively, and the output ports A and B are connected to the high-pressure pipes 8H and 8L. By providing the switching electromagnetic directional switching valve 41 and inserting the suction throttle valve 13 into the B port of the forward / backward switching electromagnetic directional switching valve 41, a gear pump, a vane pump or the like whose discharge direction is switched by forward / backward movement is provided. Other hydraulic pumps can be applied, and the hydraulic pump in this case is the fixed displacement type shown in FIG. 1 or the differential pressure generating orifice 42 inserted in the low pressure pipe 8L as shown in FIG.
Any of the variable displacement type may be used which is provided with the variable mechanism 43 including the hydraulic cylinder 43a to which the differential pressure between the front and rear is input.

In the first and second embodiments described above, the case where the drive side fluid pressure drive means and the driven side fluid pressure drive means are connected by the high pressure passage 8H and the low pressure passage 8L has been described. However, the present invention can be applied even when the electromagnetic direction switching valves 9 and 31 for forward / reverse switching are omitted and the high-pressure flow path and the low-pressure flow path are not separated from each other. Not only when the fluid pressure transmission mechanism is constituted by the driving means and the driven fluid pressure driving means, but as described in, for example, JP-A-3-224830, the driving fluid pressure driving means and the driven fluid pressure are disclosed. The present invention can also be applied to the case where the transmission torque is varied by actuating a fluid pressure clutch inserted in the drive shaft between the front and rear wheels by the pressure difference with the drive means.

[0057]

As described above, according to the four-wheel drive vehicle of the first aspect, the discharge pressure of the drive side fluid pressure drive means is input and the suction side passage of the drive side fluid pressure drive means is opened. Since the torque limiting valve means for controlling the closing direction in accordance with the increase of the discharge pressure and the operation delaying means for delaying the operation of the torque limiting valve means according to the change of the discharge pressure are provided, When a large torque is required, such as during a sudden start on a low friction coefficient road, a transient maximum torque that is larger than the steady maximum torque can be temporarily generated, and the starting performance and starting feeling can be improved. The effect is obtained.

In addition, according to the four-wheel drive vehicle of the second aspect, in addition to the above-mentioned structure, the delay limit defining means for defining the delay limit of the operation delay means is provided, so that the vehicle suddenly starts on a low friction coefficient road. At times, it is possible to reliably control the generation of excessive transmission torque. Further, claim 3
According to the four-wheel drive vehicle of the present invention, since the delay limit regulating means is composed of a check valve that opens when a predetermined set pressure is reached, the discharge pressure of the drive side fluid pressure drive means is set to the predetermined set pressure. When the check valve is opened, the check valve is opened, so that the delay operation of the operation delay means can be canceled and the torque limiting valve means can be operated according to the discharge pressure, and the delay limit defining means can be configured with a simple configuration. The effect of being able to do is obtained.

Furthermore, according to the four-wheel drive vehicle of the fourth aspect, since the operation delay means is constituted by the throttle, when the discharge pressure of the drive side fluid pressure drive means increases, the discharge pressure change. When the amount is large, the delay amount becomes large,
When the amount of change in discharge pressure is small, the amount of delay is small, so that the amount of delay can be adjusted without providing a complicated delay unit.

Still further, according to the four-wheel drive vehicle of the fifth aspect, the check valve for allowing the torque control valve means to operate in the opening direction is provided with an oil passage separate from the operation delay means. Therefore, when the torque control valve means operates in the opening direction, it is possible to immediately allow an increase in the discharge pressure in the drive side fluid pressure drive means without causing a delay and improve the responsiveness. The effect of being able to be obtained 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 a discharge flow rate characteristic and a maximum transmission torque characteristic of a suction throttle type piston pump and a swash plate type variable displacement pump motor applied to the first embodiment.

FIG. 3 is a sectional view showing an intake throttle valve applicable to the first embodiment.

FIG. 4 is a characteristic diagram showing changes in the discharge pressure P _H and the transmission torque T of the piston pump with respect to time during a sudden start on a low friction coefficient road.

FIG. 5 is a characteristic diagram showing a relationship between a discharge flow rate Q of a piston pump and a discharge pressure P _H.

FIG. 6 is a characteristic diagram showing a relationship between a front and rear axle rotation speed difference and a transmission torque according to the first embodiment.

FIG. 7 is a sectional view of an intake throttle valve showing a second embodiment of the present invention.

FIG. 8 is a sectional view showing a modification of the second embodiment.

FIG. 9 is a sectional view showing another modification of the second embodiment.

FIG. 10 is a schematic configuration diagram showing another embodiment of the variable displacement pump motor.

FIG. 11 is a schematic configuration diagram showing an embodiment in which a differential device is omitted.

FIG. 12 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 Orifice for pressure generation 12 Swash plate variable mechanism 13 Suction throttle valve 17 Rear wheel side differential 18 Rear wheel axle 19 Rear wheel 21,31 Orifice 22,32 Spring check valve 23,33 Check valve

Claims (5)

[Claims] 1. A drive axle driven by a prime mover,
In the drive side fluid pressure drive means driven in conjunction with the drive axle, the driven side fluid pressure drive means driven in conjunction with the driven axle, and the drive side fluid pressure drive means and the driven side fluid pressure drive means. In a four-wheel drive vehicle having a flow path that connects a discharge port and a suction port to each other, the discharge pressure of the drive-side fluid pressure drive means is input and the suction-side passage of the drive-side fluid pressure drive means is opened. Of the torque limiting valve means for controlling the degree of closing in accordance with the increase of the discharge pressure, and an operation delay means for delaying the operation of the torque limiting valve means according to the change of the discharge pressure. Four-wheel drive vehicle. 2. A drive axle driven by a prime mover,
In the drive side fluid pressure drive means driven in conjunction with the drive axle, the driven side fluid pressure drive means driven in conjunction with the driven axle, and the drive side fluid pressure drive means and the driven side fluid pressure drive means. In a four-wheel drive vehicle having a flow path that connects a discharge port and a suction port to each other, the discharge pressure of the drive-side fluid pressure drive means is input and the suction-side passage of the drive-side fluid pressure drive means is opened. Limiting valve means for controlling the valve closing direction in accordance with the increase of the discharge pressure, an operation delay means for delaying the operation of the torque limiting valve means according to the change of the discharge pressure, and a delay limit of the operation delay means. A four-wheel drive vehicle, comprising: a delay limit defining means for defining 3. The four-wheel drive vehicle according to claim 2, wherein the delay limit defining means includes a check valve that opens when a predetermined set pressure is reached. 4. The four-wheel drive vehicle according to any one of claims 1 to 3, wherein the operation delay means is composed of a diaphragm. 5. A check valve for allowing the torque control valve means to operate in the opening direction is provided in an oil passage separate from the operation delay means. The four-wheel drive vehicle according to any one of 1.