JPH0899552A - Four wheel drive - Google Patents

Abstract

PURPOSE: To provide a four wheel drive vehicle that can obtain desirable initial bite sensation and torque controllability at the starting time of the vehicle. CONSTITUTION: The driving force of an engine 1 is transmitted to a front wheel 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 change-over valve 9, built in a cam plate type variable displacement pump motor 10, through a high pressure pipeline 8H and a low pressure pipeline 8L so as to form a hydraulic transmission gear. A differential pressure generating orifice OR and a relief valve 13A are interposingly inserted in series between the discharge side and suction side of the piston pump 6, and a relief valve 13B higher in cracking pressure than the relief valve 13A is interposingly inserted in parallel with the series circuit of the orifice OR and relief valve 13A so as to steeply increase transmission torque to the rear wheel side according to the increase when the front and rear wheel rotating speed difference is small and to slowly increase according to the increase when the rotating speed difference becomes large.

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, in order to reduce the weight of the constituent members, a hydraulic pump which is interlocked with driving wheels driven by an engine, and the hydraulic pressure of the hydraulic pump, are disclosed in Japanese Patent Laid-Open No. 176734/1988. A hydraulic motor that works with a driven shaft that communicates with the pump via a hydraulic line, and a relief valve that relieves the hydraulic oil in the hydraulic line to a low-pressure hydraulic source when the discharge pressure of the hydraulic pump exceeds a set pressure. By providing a check valve that supplies pressure oil from a hydraulic pressure source when the hydraulic line pressure inserted in parallel with this decreases below a set pressure,
A four-wheel drive vehicle has been proposed in which the propeller shaft is omitted and both weight reduction and increase in vehicle interior space are achieved.

[0004]

However, in the conventional four-wheel drive vehicle described above, by omitting the propeller shaft, it is possible to reduce both the weight and the space of the passenger compartment. In order to further reduce weight and improve fuel efficiency, it is necessary to limit the transmission torque transmitted from the drive shaft side to the driven shaft side to promote weight reduction on the driven side. May reduce the relief pressure of the relief valve. In this way, when the relief pressure of the relief valve is reduced, the torque transmitted to the driven wheels rises relatively steeply until the hydraulic line pressure reaches the relief pressure due to the difference in the rotational speeds of the front and rear wheels. After reaching, the transmission torque to the driven wheels does not increase even if a large difference in the number of rotations of the front and rear wheels occurs, and as shown in FIG. When trying to get an initial bite, the torque controllability of the driver deteriorates, and in order to eliminate this, increasing the leak flow rate in the system to moderate the rise curve of the transmission torque to the driven wheel side is the opposite. In addition, there is an unsolved problem that the initial bite feeling is insufficient and the driver feels uncomfortable and lacks controllability in any case.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example. Even after the predetermined pressure regulation value is reached, the pressure regulation value is adjusted according to the increase in the front-rear rotational speed difference. It is an object of the present invention to provide a four-wheel drive vehicle that is lifted to prevent the driver from feeling uncomfortable and lacking controllability.

[0006]

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. Fluid pressure driving means, driven side fluid pressure driving means driven in conjunction with the driven axle, and a pair for communicating the discharge port and the suction port of the driving side fluid pressure driving means and the driven side fluid pressure driving means. In a four-wheel drive vehicle, the first pressure regulating means interposed in the first bypass passage communicating with the pair of passages, and the first pressure regulating means in series with the first pressure regulating means. And a first pressure regulating member interposed in a second bypass flow passage arranged in parallel with the first bypass flow passage and a resistance member that generates a differential pressure according to the passing flow rate. Second pressure regulating means having a higher pressure regulation value than the means. It is.

A four-wheel drive vehicle according to a second aspect is characterized in that the resistance member according to the first aspect is composed of a line filter. Furthermore, a four-wheel drive vehicle according to a third aspect is characterized in that the first pressure regulating means and the second pressure regulating means according to the first aspect are constituted by a relief valve.

Furthermore, a four-wheel drive vehicle according to a fourth aspect of the present invention, as shown in the basic configuration diagram of FIG. 1, has a drive axle driven by a main motor and a drive side driven in conjunction with the drive axle. Fluid pressure driving means, driven side fluid pressure driving means driven in conjunction with the driven axle, and a pair for communicating the discharge port and the suction port of the driving side fluid pressure driving means and the driven side fluid pressure driving means. In a four-wheel drive vehicle including a flow path of the variable pressure control means inserted in a bypass flow path communicating between the pair of flow paths, and a pressure for detecting the upstream pressure of the variable pressure control means. A detection means, a rotation speed detection means for detecting the rotation speeds of the drive axle and the driven axle, and a rotation speed detection value of the rotation speed detection means when the pressure detection value of the pressure detection means exceeds a set value. Based on the pressure regulation of the variable pressure regulation means It is characterized in that a regulating value changing means for changing.

Still further, in a four-wheel drive vehicle according to a fifth aspect, the regulation value changing means in the fourth aspect is such that the pressure regulation value of the variable pressure regulation means is proportional to the increase in the rotational speed difference between the drive axle and the driven axle. It is characterized by changing so as to raise. Further, in the four-wheel drive vehicle according to a sixth aspect, the regulation value changing means according to the fourth aspect corresponds to the pressure regulation value of the variable pressure regulation means and the increase amount of the rotational speed difference between the drive axle and the driven axle. It is characterized in that the ratio with respect to the increase amount of the pressure regulation value is changed so as to gradually decrease as the increase amount of the rotational speed difference increases.

[0010]

In the four-wheel drive vehicle according to the first aspect of the present invention, the rotation of the drive axle driven by the main prime mover causes the drive side fluid pressure drive means to discharge a working fluid at a flow rate corresponding to the rotational speed, which is one flow. The working fluid supplied to the suction side of the driven side fluid pressure driving means driven by the rotation of the driven side axle through the passage and discharged from this driven side fluid pressure driving means is returned to the driving side fluid pressure driving means through the other passage. Be done. At this time, when the rotational speed difference between the drive axle and the driven axle is small, there is almost no transmission torque and the two-wheel drive state is maintained. However, as the rotational speed difference increases, the transmission torque increases and shifts to the four-wheel drive state. . At this time, when the pressure in the flow passage on the high pressure side reaches the pressure regulation value of the first pressure regulation means due to the increase in the rotational speed difference, the first pressure regulation means is opened, and the pressure is reduced. It is released to the low-pressure side flow path. In this state, a differential pressure is generated in the resistance member according to the flow rate, and the pressure in the high-pressure side flow path increases by this differential pressure, which increases the transmission torque to the driven shaft side. When the pressure in the high-pressure side communication passage reaches the pressure regulation value of the second pressure regulation means, the second pressure regulation means is opened and the pressure rise in the high-pressure side communication passage is stopped. , The increase of the transmission torque to the driven shaft side is stopped.

In the four-wheel drive vehicle according to the second aspect, in addition to the function of the first aspect, the resistance member is constituted by the line filter, so that it is not necessary to provide a filter in the system and a separate orifice is provided. The cost can be reduced as compared with the case of expanding. In the four-wheel drive vehicle according to the third aspect, in addition to the operation of the first aspect, the first and second pressure regulating means are configured by the relief valve, so that the set pressure is arbitrarily set. It is possible to easily adjust the occurrence of discomfort and lack of controllability.

In the four-wheel drive vehicle according to the fourth aspect, the variable pressure regulating means is interposed in the bypass flow passage that communicates between the pair of flow passages that communicate the drive side fluid pressure drive means and the driven side fluid pressure drive means. The pressure regulation value of the variable pressure regulation means is regulated by the regulation value changing means based on the rotation speed detection value of the rotation speed detection means when the upstream pressure becomes equal to or higher than the set pressure. The pressure regulation value of the means is changed to increase the transmission torque to the driven side.

In the four-wheel drive vehicle according to the fifth aspect, the regulation value changing means increases the pressure regulation value in proportion to the increase in the rotational speed difference between the drive shaft and the driven shaft, thereby transmitting torque to the driven side. To increase. In the four-wheel drive vehicle according to claim 6, the regulation value changing means sets the pressure regulation value of the variable pressure regulation means to the increase amount of the rotational speed difference between the drive axle and the driven axle and the corresponding increase amount of the pressure regulation value. The ratio is changed so as to gradually decrease as the amount of increase in the rotational speed difference increases, so that the transmission torque to the driven side changes smoothly.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 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 prime mover,
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 switch 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 of the high-pressure pipe 8H is connected to the suction / discharge port 10a of the variable displacement pump motor 10 and the low-pressure pipe 8L is connected to the suction / discharge port 10b in the normal position to rotate the rotary shaft. 10c
Is rotationally driven in a forward rotation direction, for example, clockwise as viewed from the left side surface, and conversely, the high pressure oil in the high pressure pipe 8H is sucked and discharged from the variable displacement pump motor 10b at the offset position.
Further, the low-pressure pipe 8L is connected to the suction / discharge port 10a, and the rotary shaft 10c is rotationally driven in the rotation direction during forward traveling, for example, counterclockwise when viewed from the left side surface.

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

The flow rate of the variable displacement pump motor 10 is
Low pressure pipe 8L near the tank port T of the electromagnetic directional control valve 9
By controlling the swash plate variable mechanism 12 as a variable control mechanism including the hydraulic cylinder 12a by the differential pressure generated at both ends of the differential pressure detection 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, between the suction port 6b and the discharge port 6c of the suction throttle type piston pump 6, a first cracking pressure is set which defines a first regulation value P _H1 of the discharge pressure of the piston pump 6 as a torque limiting means. A series circuit of a relief valve 13A as a pressure regulating means and a differential pressure generating orifice OR as a resistance member inserted upstream of the relief valve 13A, that is, on the side of the high pressure pipe 8H is inserted, and the series circuit is connected in parallel with the series circuit. A relief valve 13B as a second pressure regulating means set to a cracking pressure that defines a second regulation value P _H2 higher than the first regulation value P _H1 is connected, and the hydraulic pump 6 and the electromagnetic directional control valve 9 are connected. A check valve 15 that allows fluid flow from the low-pressure pipe 8L side to the high-pressure pipe 8H side is inserted in the communication pipe 14A that communicates between the high-pressure pipe 8H and the low-pressure pipe 8L. , Fixed orifice 16 in parallel relationship with the check valve 15 is connected to the communicating pipe 14B which is disposed in parallel with the communicating pipe 14A.

On the other hand, a gear 10d is attached to a 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. Two
Continue the normal position shown in. In this state, release the brake pedal and step on the accelerator pedal,
The rotational force of the engine 1 is transmitted to the front wheel side differential device 3 via the transmission 2, and the front wheel side actuating device 3 rotationally drives the front wheels 5 in the forward direction to start the forward movement.

At this time, the rotary shaft 6a of the suction throttle type piston pump 6 is rotationally driven in the clockwise direction as viewed from the left side surface, so that the piston pump 6 discharges hydraulic fluid at a discharge flow rate corresponding to the rotational speed. This is supplied to the suction / discharge port 10a of the swash plate type variable displacement pump motor 10 through the high-pressure pipe 8H and the forward / reverse switching electromagnetic directional switching valve 9, but the rear wheel 19 and the front wheel 5 are connected to each other when the vehicle starts. Since it is driven to rotate in the same direction at the same rotation speed, the rear wheel side differential device 1
Rotating shaft 1 of swash plate type variable displacement pump motor 10
0c rotates clockwise as viewed from the left side surface, whereby the working oil is sucked from the suction / discharge port 10a and the working oil is discharged from the suction / discharge port 10b.

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

The difference in the discharge flow rate between the piston pump 6 and the variable displacement pump motor 10 also allows a difference in the number of rotations of the front and rear axles 4 and 18 caused by a diameter change due to wear of the tire, and occurs in a tire having a different diameter. The driving force is not transmitted when the rotational speed difference is about the same, the front-wheel drive vehicle state is maintained, and it is possible to suppress deterioration of fuel consumption. Next, when the vehicle starts on a low friction coefficient road such as an icy road or a snowfall road, the front wheels 5 are first driven to rotate as described above, but since the road is a low friction coefficient road, the front wheels 5 slip. , A rotational speed difference N _D is generated between the front wheel 5 and the rear wheel 19 so that the front wheel 5 has a high rotational speed, and the discharge flow rate of the suction throttle type piston pump 6 exceeds the discharge flow rate of the swash plate type variable displacement pump motor 10. In that case, the resistance of the variable displacement pump motor 10 becomes a load, and the operating oil pressure of the high pressure pipe 8H rises. Therefore, the variable displacement pump motor 10 operates as a hydraulic motor, and the pressure of the high pressure pipe 8H varies. The driving force is transmitted to the rear wheels 19 via the rear wheel side differential device 17.

[0028] That is, the torque transmitted to the rear wheel 19 side, as shown in FIG. 4, the first time occurs caused the rotational speed difference N _D in the front and rear wheels, the high-pressure side pipe with increasing rotational speed difference N _D The pressure within 8H is the first regulation value P _H1 of the relief valve 13A.
Until it reaches the first specified torque T _MAX1 . When the specified torque T _MAX1 is reached, the high pressure side pipe 8
The pressure in H reaches the first regulation value P _H1 of the relief valve 13A, and the relief valve 13A opens, so that the hydraulic oil in the high-pressure side pipe 8H causes the differential pressure generation orifice O.
It escapes to the low pressure side pipe 8L through the R and the relief valve 13A. In this way, when the hydraulic oil in the high pressure side pipe 8H passes through the differential pressure generating orifice OR, a differential pressure is generated at this orifice OR, and the pressure in the high pressure side pipe 8H rises by this differential pressure. As a result, as shown in FIG. 4, the transmission torque gradually rises beyond the first regulation torque T _MAX1 , and the pressure in the high-pressure side pipe 8H becomes the second regulation value P of the relief valve 13B. _When the pressure reaches _H2 , the relief valve 13A opens and the high pressure side pipe 8H
Of would escape to the low pressure side pipe 8L through the hydraulic oil or the relief valve 13B, the torque transmitted to the rear wheel side is restricted by the first specified torque T is higher than _MAX1 second specified torque T _MAX2, hereafter rotational speed difference Regardless of the increase in N _D , it is regulated by the second specified torque T _MAX2 .

Due to this torque limiting action, the strength of the rear wheel side differential device 17, the drive shaft and other constituent members can be reduced as compared with the conventional four-wheel drive vehicle, and the weight,
The fuel consumption and cost can be reduced, and the increase rate of the transmission torque until reaching the regulation torque T _MAX1 when the relief valve 13A is opened is steep, so that the initial biting feeling at the time of starting the vehicle is good. Can be maintained at
Moreover, since the rate of increase of the transmission torque due to the subsequent increase in the rotational speed difference N _D becomes gentle, good torque controllability can be exhibited, and the driver does not feel uncomfortable or lack controllability. You can

The torque transmitted to the rear wheel 19 side is
As shown in FIG. 4, it has a characteristic that the driving force is more likely to be generated with a smaller rotational speed difference at lower speeds. As shown in FIG. 3, 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. 3, the displacement of the swash plate type variable displacement pump motor 10 is such that after the rear wheel speed V _R reaches V _{R1, that} is, the rear wheel rotational speed reaches the first rotational speed N _R1. It decreases gradually, Therefore, the characteristic curve L ₃ maximum torque transfer in Figure 3
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. 3, the maximum transmission torque is the wheel speed V _R1 or the first. It gradually decreases when the number of revolutions N _R1 is exceeded, and it is possible to reliably prevent the maximum transmission torque from sharply decreasing as in the conventional example. It is possible to reliably prevent the driver from feeling uncomfortable by suppressing the change to.

Further, in the rise of torque in FIG. 4, the amount of leakage from the high pressure pipe 8H to the low pressure pipe 8L is controlled by the fixed orifice 16 inserted in the communication pipe 14B which connects the high pressure pipe 8H and the low pressure pipe 8L. The characteristics can be set arbitrarily by changing the rise of pressure. Due to the temperature characteristics associated with the viscosity change of the hydraulic oil possessed by the orifice, the amount of leakage decreases and the driving force is more likely to be generated at low temperatures than at high temperatures. There is an advantage that it becomes easy to use four-wheel drive in winter.

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 moving forward, and pressure is generated in the high-pressure pipe 8H only when the front wheel 5 slips and the rotational speed difference between the front and rear axles 4 and 18 occurs. However, when the driving force is transmitted to the rear wheels 19 and the intake amount shortage of the swash plate type variable displacement pump motor 10 when the rotational speed difference between the front and rear axles 4 and 18 is small, the low pressure pipe 8L, the communication pipe 14A, and the reverse pipe 14A. It is replenished via the stop valve 15.

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

Further, in a vehicle equipped with a front-wheel drive vehicle-based anti-skid control device, 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 pressure transmission mechanism and the anti-skid control is performed. There is an advantage that interference with the device can be reduced. In addition, in the said 1st Example, although the case where the orifice OR was provided in the upstream of the relief valve 13A, ie, the high pressure side pipe 8H side, was demonstrated, it is not restricted to this, and the relief valve 1 is provided.
It is also possible to provide an orifice OR on the downstream side of 3A. In this case, since only the differential pressure generated by the orifice itself acts on the upstream side of the orifice OR, the pressure resistance strength of the orifice mounting portion can be significantly reduced. There is an advantage that becomes possible.

Further, in the first embodiment described above, the case where the orifice OR is applied as the resistance member has been described. However, as shown in FIG. 5, if the line filter LF is used as the resistance member, other elements are used. There is an advantage that it is not necessary to provide a line filter in the hydraulic circuit, and an increase in cost when adding a new orifice can be prevented.

Further, in the first embodiment, the suction throttle type piston pump 6 as the drive side fluid pressure drive means.
The case where the flow rate characteristic of _No. 2 is set in the shape of a two-step broken line as shown by the characteristic curve L ₁ in FIG. 3 has been described, but the present invention is not limited to this, and the characteristic line L ₂₁ shown by the one-dot chain line in FIG.
As shown in FIG. 3, the rotation speed may be increased from “0” to a predetermined value N _F2 in accordance with the increase in the rotation speed. Flow rate characteristics can be set. 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.

In the first embodiment described above, the case where the differential pressure before and after the differential pressure detecting orifice 11 is supplied to the swash plate variable mechanism 12 has been described, but the invention is not limited to this, and the low pressure pipe. Orifice 1 for differential pressure detection on 8L side
When 1 is inserted, the pressure on the outlet side of the differential pressure detection orifice 11 becomes the atmospheric pressure, and is the same as the drain pressure in the variable displacement pump 10. Therefore, as shown in FIG. Only the pressure on the high pressure side of the detection orifice 11, that is, the pressure on the tank port T side of the electromagnetic directional control valve 9 may be introduced into the head cover side hydraulic chamber 12b of the hydraulic cylinder 12a of the swash plate variable mechanism 12.

Further, the case where the rear wheel side differential device 17 is provided has been described, but the present invention is not limited to this.
As shown in FIG. 7, the rear wheel differential device 17 is omitted, and instead of this, the left and right axles 18L, 18 of the left and right rear wheels 19L, 19R are replaced.
Swash plate type variable displacement pump motors 10L and 10
R may be provided, and in this case, when different loads are applied to the left and right wheels during turning, the variable displacement pump motors 10L and 10R naturally adjust the discharge flow rate difference according to the difference. As a result, the differential function equivalent to that of the differential device can be exerted.

Furthermore, the rotary shaft 6 is used as a fluid pressure pump.
The case where the suction throttle type piston pump 6 in which the suction port 6b and the discharge port 6c do not change regardless of the rotation direction of a is applied has been described, but the present invention is not limited to this.
As shown in FIG. 8, the pump port P and the tank port T are connected to the suction port 30b and the discharge port 30c of the hydraulic pump 30 whose rotary shaft 30a is connected to the gear 3g, and the output ports A and B are connected to the high pressure pipe 8H. And an electromagnetic directional control valve 31 for forward / reverse switching similar to the electromagnetic directional control valve 9 for forward / reverse switching connected to 8L and 8L, another hydraulic pump such as a gear pump or a vane pump whose discharge direction is switched by forward / backward movement. In this case, the hydraulic pump in this case inputs the fixed capacity type shown in FIG. 2 or the differential pressure across the differential pressure generating orifice 32 inserted in the low pressure pipe 8L as shown in FIG. Variable mechanism 33 including hydraulic cylinder 33a
It may be any of the variable capacitance type equipped with.

Further, in the first embodiment, the drive side fluid pressure drive means and the driven side fluid pressure drive means are connected to the high pressure passage 8.
Although the case where the H and the low pressure flow paths 8L communicate with each other has been described, the present invention is not limited to this, and the two-way flow variable displacement pump 6 and the variable displacement pump motor 10 are applied, and the forward / backward switching electromagnetic direction switching is performed. The present invention can be applied even when the valves 9 and 31 are omitted and the high pressure passage and the low pressure passage are not separated. In this case, as shown in FIG. 9, the relief valve 13A and the differential pressure generating orifice are used. The input side of the parallel circuit of the OR series circuit and the relief valve 13B is connected to the high pressure side pipe 8H and the low pressure side pipe 8L via the check valves 21a and 21b, respectively, which allow the inflow of the high pressure hydraulic oil, and similarly. The high pressure side pipe 8H and the low pressure side pipe 8 are respectively provided via check valves 21c and 21d which permit the outflow of the high pressure hydraulic oil on the output side.
Connected to L, hydraulic oil is passed from the high pressure side to the low pressure side via the relief valves 13A and 13B, and switching operation is performed in forward and backward instead of the check valve 15 that compensates for the insufficient intake amount of the variable displacement pump motor 10. The electromagnetic switching valve 22 in which check valves having different directions are formed may be provided in the inside.

Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, as in the first embodiment, a proportional electromagnetic relief valve whose cracking pressure can be changed is applied instead of the case where the relief valves are provided in parallel, and the circuit configuration is simplified. . That is, in the second embodiment, as shown in FIG. 10, the relief valves 13A and 13B and the differential pressure generating orifice O in the first embodiment are provided.
R is omitted, and instead of these, the proportional electromagnetic relief valve 4 is provided between the discharge side and the suction side of the suction throttle piston pump 6.
1, a pressure sensor 42 is provided upstream of the proportional electromagnetic relief valve 41, and a rotation signal is output to the front wheel 5 and the rear wheel 19 to output pulse signals corresponding to their respective rotation speeds. The number sensors 43 and 44 are provided, and the detection values of the pressure sensor 42 and the rotation speed sensors 43 and 44 are input to the controller 45, and this controller 45 supplies the exciting current i _S to the solenoid 41a of the proportional electromagnetic relief valve 41. 2 has the same configuration as that of FIG. 2, except that the corresponding portions to those of FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

Here, the controller 45 includes, for example, a microcomputer and a solenoid drive circuit, and controls the cracking pressure of the proportional electromagnetic relief valve 41 by executing the control process shown in FIG. 11 by the microcomputer. Is configured. The control process of FIG. 11 is executed as a timer interrupt process every predetermined time (for example, 10 msec). First, the pressure detection value P _D of the pressure sensor 42 is read in step S1, and then the process proceeds to step S2 to detect the pressure. It is determined whether or not the value P _D is greater than or equal to the first regulation value P _{H1 described} above, and if P _D <P _H1 , the process proceeds to step S3 and the cracking pressure P _{C of the} proportional electromagnetic relief valve 41 is determined. _Is set to the first regulation value P _H1 , the cracking pressure P _C is updated and stored in a predetermined storage area, and then the process proceeds to step S4 where the pressure detection value P _D described later is the first regulation value P _H1. The control flag F indicating that the current has reached 0 is cleared to "0", and then the process proceeds to step S5 to solenoid-drive the command value for outputting the exciting current i _S corresponding to the cracking pressure P _C stored in the predetermined region. Output to the circuit To return from the output from the solenoid drive circuit exciting current i _S to the solenoid 41a of the proportional electromagnetic relief valve 41 to end the timer interrupt process to a predetermined main program.

On the other hand, the determination result of step S2 is P_D≧
P_H1If so, the process proceeds to step S6, and the rotation speed
Rotation speed detection value N of the sensors 43 and 44_FAnd N_RRead
Then, the process proceeds to step S7, where the difference in rotation speed between the front and rear wheels
N_D(= N_F-N_R) Is calculated, and then in step S8
Transition to pressure detection value P_DIs the first regulation value P_H1Reached
The control flag F indicating whether or not it is the time point is set to "1"
Control flag F is set to "1".
If it is turned on, the process directly moves to step S11.
However, when the control flag F is reset to “0”,
Is the pressure detection value P _DIs the first regulation value P_H1When it reaches
If there is, the process proceeds to step S9, and the rotation at that time
Number difference N_DInitial speed difference N_DSAs a predetermined storage area
The data is updated and stored, and then the process proceeds to step S10 and the control flag is set.
After setting F to "1", move to step S11.
It

In step S11, the current rotational speed difference N _D
The initial value N _DS of the rotational speed difference is subtracted from
_D is calculated, then the process proceeds to step S12, and the rotational speed difference increase amount Δ shown in FIG. 12 is calculated based on the rotational speed difference increase amount ΔN _D.
The cracking pressure increase amount ΔP _C is calculated by referring to the control map showing the relationship between N _D and the cracking pressure increase amount ΔP _C, and then the process proceeds to step S13 to move to the first regulation value P _H1.
The value obtained by adding the cracking pressure increase amount ΔP _C to the above is updated and stored in a predetermined storage area as the cracking pressure P _C , and then the process proceeds to step S5.

Here, the control map of FIG. 12 shows that when the rotational speed difference increase amount ΔN _D is zero, the cracking pressure increase amount ΔP.
_C also becomes zero, and the cracking pressure increase amount ΔN _D increases in proportion to the increase in the rotational speed difference increase amount ΔN _D , and the cracking pressure increase amount ΔP _C becomes the first regulation value P _H1 and the second regulation value P _{When the} maximum increase amount ΔP _MAX represented by the difference value of _H2 is reached, it is set to a constant value thereafter regardless of the increase in the rotational speed difference increase amount ΔN _D.

In the processing of FIG. 11, step S
The process of S2 to S13 corresponds to the regulation value changing means.
It According to the second embodiment, the proportional electromagnetic relief valve 4
1 upstream pressure detection value P _DIs the first regulation value P_H1Reach
Until the control process of FIG. 11 is executed,
Go to step S3 through steps S1 and S2
The cracking pressure P of the proportional electromagnetic relief valve 41
_CIs the first regulation value P_H1After being set to
As shown in Fig. 13, the torque transmitted to the wheel side is the number of front and rear rotations.
Difference N_DIt will rise sharply with the increase of
Pressure detection value P_DIs the first regulation value P_H1As described above, FIG.
When the control process of No. 1 is executed, the process starts from step S2.
Move to step S6 and rotate the front and rear axles in steps S6 and S7.
Turn difference N_DAnd the control flag F is reset to "0"
Therefore, the process proceeds to step S9 and the calculated number of times
Turn difference N_DInitial speed difference N_DSSet as, then
Step S11 after setting the control flag F to "1"
Move to. At this time, the rotation speed difference N_DAnd initial speed difference
N_DSAnd are equal, the rotational speed difference increase amount ΔN_DIs zero
In step S12, the cracking pressure increase amount ΔP is zero._C
Is calculated, the crack calculated in step S13 is calculated.
King pressure P_CIs the first regulation value P_H1Is equal to.

When the rotational speed difference N _D increases while the detected pressure value P _D remains above the first regulation value P _H1 , the rotational speed difference increase calculated in step S11 accordingly. The amount ΔN _D will increase, and in proportion to this,
Cracking pressure increase amount ΔP calculated in step S12
_{Since C} also increases, the cracking pressure P _C calculated in step S13 also increases, so that the torque transmitted to the rear wheels is represented by the characteristic curve L _T1 shown by the solid line in FIG. _It increases in proportion to the increase of _D , and when the maximum transmission torque T _MAX2 is reached, the cracking pressure P _C reaches the second regulation value P _H2 , so that even if the rotational speed difference N _D is further increased, The torque transmitted to the wheels is held at the maximum torque T _MAX2 , and the same effect as that of the first embodiment described above can be obtained.

In the second embodiment, the pressure detection
Outgoing price P_DIs the first regulation value P_H1Cracking after reaching
Pressure increase ΔP_CIs the rotation speed difference increase amount ΔN_DProportional to the increase of
However, it is not limited to this.
Control map, as shown in FIG.
Increase in rotation speed difference ΔN_DThe slope (ΔP _C
/ ΔN_D) Gradually decreases, a parabolic characteristic curve L_P
The transmission torque to the rear wheel side can be
A characteristic curve L indicated by a broken line 13_T2As shown in
N_DCan be changed smoothly as the
It's good to have good controllability without feeling uncomfortable to the driver.
There is an advantage that it can be changed favorably.

Further, the modified examples of FIGS. 7 to 9 can be applied to the second embodiment as in the first embodiment. Furthermore, in the first and second embodiments,
The case where the electromagnetic direction switching valve 9 for switching between forward and backward is incorporated in the pump motor 10 has been described, but the invention is not limited to this and may be separately provided outside the pump motor 10.

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

[0053]

As described above, according to the four-wheel drive vehicle of the first aspect, the drive axle driven by the main motor and the drive side fluid pressure drive means driven in conjunction with the drive axle. And a driven-side fluid pressure driving means that is driven in conjunction with the driven axle, and a pair of flow paths that connect the discharge port and the suction port of the driving-side fluid pressure driving means and the driven-side fluid pressure driving means to each other. In a four-wheel drive vehicle including: a first pressure regulating means interposed in a first bypass flow passage that communicates between the pair of flow passages, and the first pressure regulating means is arranged in series. A pressure higher than that of the resistance member for generating a differential pressure according to the passing flow rate and the first pressure regulating means interposed in the second bypass passage arranged in parallel with the first bypass passage. Since the second pressure regulating means having the regulation value is provided, the driven shaft side The transmission torque characteristic of is increased steeply with respect to the increase in the rotational speed difference between the driving axle and the driven axle until the first pressure regulation value is reached, and the initial biting feeling at the time of starting the vehicle is favorably maintained. The torque controllability can be improved by gradually increasing the rotational speed difference between the drive axle and the driven axle until the second pressure regulation value is exceeded after the pressure regulation value is exceeded. To be

According to the four-wheel drive vehicle of the second aspect, in the invention of the first aspect, since the resistance member is constituted by the line filter, it is not necessary to separately provide a line filter in the hydraulic circuit. The effect that the cost can be reduced by this amount without having to newly install an orifice is obtained. Further, according to the four-wheel drive vehicle of the third aspect, since the first pressure regulating means and the second pressure regulating means are relief valves, the first regulation value and the second regulation value. The value can be set arbitrarily,
The effect that the torque controllability can be easily adjusted is obtained.

Furthermore, according to the four-wheel drive vehicle of the fourth aspect, a variable passage inserted between a pair of flow passages connecting the drive side fluid pressure drive means and the driven side fluid pressure drive means. The pressure regulation means, the pressure detection means for detecting the pressure on the upstream side of the variable pressure regulation means, the rotation speed detection means for detecting the rotation speeds of the drive axle and the driven axle, and the pressure detection value of the pressure detection means are Since it is configured to include a regulation value changing means for changing the pressure regulation value of the variable pressure regulation means based on the rotation speed detection value of the rotation speed detection means when it becomes equal to or more than a set value, one variable pressure The effect of being able to change the characteristics of the torque transmitted to the driven shaft side in the same manner as in claim 1 and simplifying the circuit configuration can be obtained simply by providing the restricting means.

Furthermore, according to the four-wheel drive vehicle of the fifth aspect, in addition to the effect of the fourth aspect, the regulation value changing means includes:
Since the pressure regulation value of the variable pressure regulating means is changed so as to be increased in proportion to the increase in the rotation speed difference between the drive axle and the driven axle, the transmission torque to the rear wheel side can be changed. The effect that it can be gently changed according to the increase is obtained.

According to the four-wheel drive vehicle of the sixth aspect, in addition to the effect of the fourth aspect, the regulation value changing means sets the pressure regulation value of the variable pressure regulating means to the rotational speeds of the drive axle and the driven axle. Since the ratio of the increase amount of the difference and the corresponding increase amount of the pressure regulation value is changed so as to gradually decrease with the increase amount of the rotation speed difference, the first regulation value is set. The effect that the change of the transmission torque until reaching the second limit and the change of the transmission torque until reaching the second regulation value are smoothly continuous can exert the torque controllability well.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram showing a basic configuration of the present invention.

FIG. 2 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 3 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. 4 is a characteristic diagram showing a relationship between a front-rear axle rotation speed difference and a transmission torque according to the first embodiment.

FIG. 5 is a schematic configuration diagram showing an embodiment when a line filter is applied as a resistance member.

FIG. 6 is a schematic configuration diagram showing another embodiment of a variable displacement pump motor.

FIG. 7 is a schematic configuration diagram showing an embodiment in which a differential device is omitted.

FIG. 8 is a schematic configuration diagram showing an embodiment in which a fluid pressure pump whose discharge port is changed depending on a rotation direction is applied as the fluid pressure pump.

FIG. 9 is a schematic configuration diagram showing an embodiment in which the pipe is not divided into a high pressure side and a low pressure side.

FIG. 10 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 11 is a flowchart showing an example of a control processing procedure in the controller of the second embodiment.

FIG. 12 is a characteristic diagram showing an example of a control map.

FIG. 13 is a characteristic diagram showing the relationship between front and rear wheel rotation speed difference and transmission torque, which is used for explaining the operation of the second embodiment.

FIG. 14 is a characteristic diagram showing another example of the control map.

FIG. 15 is a characteristic diagram showing the relationship between front and rear wheel rotation speed difference and transmission torque, which is used for explaining the operation of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 engine 2 transmission 3 front wheel side differential 4 front axle 5 front wheel 6 suction throttle type piston pump 8H high pressure piping 8L low pressure piping 9 forward / reverse switching electromagnetic direction switching valve 10 swash plate type variable displacement pump motor 13A, 13B relief valve OR Differential pressure generating orifice (resistive member) LF line filter (resistive member) 17 Rear wheel side differential device 18 Rear wheel axle 19 Rear wheel 10L, 10R Swash plate type variable displacement pump motor 31 Forward / reverse switching electromagnetic direction switching valve 41 Proportional electromagnetic relief valve 42 Pressure sensor 43,44 Rotation speed sensor 45 Controller

Claims (6)

[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 including a pair of flow passages that communicate with each other's discharge port and suction port, a first pressure regulation inserted in a first bypass flow passage communicating with the pair of flow passages. Means, a resistance member arranged in series with the first pressure regulating means, for generating a differential pressure according to a flow rate, and the first pressure member.
And a second pressure regulating means having a higher pressure regulating value than the first pressure regulating means interposed in the second bypass channel arranged in parallel with the second bypass channel. A four-wheel drive vehicle. 2. The four-wheel drive vehicle according to claim 1, wherein the resistance member is a line filter. 3. The four-wheel drive vehicle according to claim 1, wherein the first pressure regulating means and the second pressure regulating means are relief valves. 4. 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 including a pair of flow passages that communicate with each other's discharge port and suction port, a variable pressure regulating means inserted into a bypass flow passage communicating between the pair of flow passages, and the variable pressure regulating means. When the pressure detection means for detecting the pressure on the upstream side of the pressure regulation means, the rotation speed detection means for detecting the rotation speeds of the drive axle and the driven axle, and the pressure detection value of the pressure detection means becomes equal to or more than a set value. A four-wheel drive vehicle, further comprising: a regulation value changing unit that changes the pressure regulation value of the variable pressure regulation unit based on the rotation number detection value of the rotation number detection unit. 5. The regulation value changing means changes the pressure regulation value of the variable pressure regulation means so as to increase the pressure regulation value in proportion to an increase in the rotational speed difference between the drive axle and the driven axle. The four-wheel drive vehicle described. 6. The regulation value changing means has a ratio of a pressure regulation value of the variable pressure regulation means to an increase amount of a rotational speed difference between the drive axle and the driven axle and a corresponding increase amount of the pressure regulation value in terms of a rotational speed. The four-wheel drive vehicle according to claim 2, wherein the four-wheel drive vehicle is changed so as to gradually decrease with an increase amount of the difference.