JPH09309352A - Four-wheel drive vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accelerating performance and stability of a vehicle through the prevention of swerve by starting driving force control when the rotating speed difference between driving wheels and driven wheels becomes the specified start reference value or more, and setting the driving force control start reference value on the basis of body speed. SOLUTION: When a vehicle makes a sudden start on a low friction coefficient road so as to generate the slip of front wheels 1FL, 1FR (1F), rotating speed difference is generated between front and rear wheels. The resistance of a variable capacity motor becomes load so as to generate maximum driving torque, and this driving torque is transmitted to the rear wheels 1RL, 1RR to make the vehicle travel in a four-wheel drive state. When the front wheels 1F slip, front and rear wheel speed difference exceeds the control start set value so as to be shifted to driving force control processing, and slipping of the front wheels 1F is reduced by adjusting throttle opening in a controller 52. This control start set value is set to the second start reference value smaller than the first start reference value at the time of body speed being not less than low speed requiring two-wheel drive travel.

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 the rotational driving force of a main prime mover is transmitted from a drive wheel to a driven wheel through a fluid pressure transmission mechanism, and more particularly to a driving force of the drive wheel. The present invention relates to a four-wheel drive vehicle equipped with a traction control system for controlling a drive wheel to prevent a slip of a drive wheel.

[0002]

2. Description of the Related Art A four-wheel drive vehicle having improved running performance on rough roads, rough terrain, etc., is equipped with a propeller shaft and a differential device for distributing drive torque from a prime mover to a plurality of axles. Further, in recent four-wheel drive vehicles, in order to distribute the driving force according to changes in the road surface condition, a viscous coupling or clutch is used between the drive shafts to make the distribution ratio of the driving force variable. doing. However, a four-wheel drive vehicle that variably controls the driving force distribution by such a mechanical system is likely to have a complicated device structure, and a propeller shaft passing under the floor of the vehicle body and a differential limiting device between axles are required. Therefore, the weight increases, which may hinder the miniaturization and weight reduction of the vehicle body.

In order to solve such a problem, as described in Japanese Patent Application No. 6-262639 by the present applicant, the drive axle driven by the main prime mover and the drive axle are rotated in association with the drive axle. A first swash plate type variable displacement motor having a swash plate as a displacement changing means, a discharge port of the fluid pressure pump and a suction port of the variable displacement motor, which are in communication with each other. A flow path, a second flow path that connects the suction port of the fluid pressure pump and the discharge port of the variable displacement motor, and an urging means that drives the swash plate in a direction in which the displacement of the variable displacement motor decreases. There is a four-wheel drive vehicle equipped (hereinafter referred to as "prior art 1"). According to the related art 1, in a swash plate type variable displacement motor, a cylinder block is coaxially connected to a motor rotation shaft, and the cylinder block is parallel to the motor rotation shaft and along the rotation direction of the cylinder block. The bores are formed at equal intervals. A piston is arranged in each bore, and a swash plate is arranged at a position facing the tip of these pistons so as to swing to a predetermined tilt angle. The stroke of the piston pushed out from inside is restricted. Also,
Each of the bores in which the pistons are arranged can be alternately communicated with the working fluid intake port and the working fluid return port by the rotation of the cylinder block.

In the prior art 1 having the above structure, when the rotational speed of the drive shaft is higher than the rotational speed of the driven axle and four-wheel drive traveling is required, the discharge flow rate of the fluid pressure pump is a variable displacement motor. Since the high-pressure hydraulic oil is supplied from the hydraulic fluid intake port into the bore, the torque corresponding to the high-pressure hydraulic oil is generated on the motor rotating shaft, and the drive torque is distributed to the driven axle to distribute the four-wheel drive. The drive running state is set.

By the way, in the four-wheel drive vehicle of the above-mentioned prior art 1, the rotational speed of the drive shaft increases too much when the vehicle is in the four-wheel drive traveling state. In addition, when the drive torque distributed to the driven axle suddenly drops at the time of shifting from the four-wheel drive traveling state to the two-wheel drive traveling state due to the increase of the vehicle speed, the idling (slip) of the drive wheels increases and the driving vehicle May give a feeling of strangeness.

Therefore, a traction control system capable of improving the startability and acceleration of the vehicle and improving the vehicle stability by preventing the tail swing is mounted on the four-wheel drive vehicle of the prior art 1 to solve the above problems. It is possible to solve it.

As the traction control system, as described in, for example, Japanese Patent Application Laid-Open No. 4-66336 (hereinafter referred to as "prior art 2"), the wheel speeds of the drive wheels and the driven wheels are detected, and Calculates the slip value for throttle control and the slip value for brake control from the wheel speed, sets the target slip value for throttle control and the target slip value for brake control, and starts two controls with a small threshold value and a large threshold value. When a threshold value is set and the wheel speed of the drive wheels exceeds a small threshold value, the throttle control is performed so that the slip value for throttle control matches the target slip value for throttle control, and the throttle control for brake control is performed. Feedback control is performed so that the slip value matches the target slip value for brake control. System to perform the key control is known.

[0008]

However, when this traction control system is mounted on a four-wheel drive vehicle, there is a possibility that the functions of both of them cannot be fully exhibited.

That is, for example, it is possible to detect the rotational speed difference between the driving wheel and the driven wheel and start the control of the traction control system when the rotational speed difference becomes equal to or larger than the reference start value. However, if the reference start value is set to a small constant value, the number of rotations of the drive shaft decreases before the transmission torque is generated, which causes a problem that the four-wheel drive traveling state cannot be obtained. Conversely, if the reference start value is set to a large constant value,
When the vehicle travels in the two-wheel drive state, the traction control system may not operate, the drive wheels may idle, the acceleration may not be improved, and the tail swing may not be prevented.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and transmits the rotational driving force of the main prime mover from the drive wheel to the driven wheel through the fluid pressure transmission mechanism. It is an object of the present invention to provide a four-wheel drive vehicle capable of sufficiently exhibiting the performance of both a wheel drive state and a traction control system for improving vehicle stability.

[0011]

In order to achieve the above object, a four-wheel drive vehicle according to a first aspect of the present invention comprises a drive axle driven by a main motor and a fluid pressure pump that rotates in conjunction with the drive axle. A fluid pressure motor that rotates in conjunction with a driven axle; a first flow path that connects the discharge port of the fluid pressure pump and the suction port of the fluid pressure motor; the suction port of the fluid pressure pump; The second flow path communicating with the discharge port of the fluid pressure motor and the maximum discharge pressure of the working fluid flowing to the fluid pressure motor when the discharge amount of the fluid pressure pump exceeds the suction amount of the fluid pressure motor. In a four-wheel drive vehicle having a torque limiting means for restricting and setting a maximum value of a transmission torque to the driven axle side, a wheel speed of a drive wheel connected to the drive axle and a driven wheel connected to the driven axle. Wheel speed detection means for detecting A vehicle speed detecting means for detecting a speed, a rotational speed difference detecting means for detecting a rotational speed difference between the driving wheel and the driven wheel, a braking force for the driving wheel and a driving force output from the main drive source. Driving force control means for adjusting and controlling the driving force, and control for starting control of the driving force control means when the rotational speed difference detected by the rotational speed difference computing means becomes equal to or greater than a predetermined start reference value. Start setting means, the start reference value of the control start setting means, based on the vehicle speed detected by the vehicle speed detection means,
When the vehicle speed is a low speed that requires four-wheel drive, the first start reference value is set to a large value, and when the vehicle speed is at least the low speed that requires two-wheel drive, the first start is performed. It was set to a second starting reference value that was smaller than the reference value.

According to a second aspect of the present invention, in the four-wheel drive vehicle according to the first aspect, the first start reference value is the maximum value of the torque transmitted to the driven wheels by the operation of the torque limiting means. Was set to a value equal to or higher than a predetermined rotation speed difference.

According to a third aspect of the present invention, in the four-wheel drive vehicle according to the first or second aspect, the second start reference value is set to a rotational speed difference generated when the driving wheels spin during acceleration. Set to.

According to a fourth aspect of the present invention, in the four-wheel drive vehicle according to any one of the first to third aspects, the first start reference value is based on a vehicle speed detected by the vehicle speed detecting means. Then, the value is set to gradually increase as the vehicle speed increases.

On the other hand, a four-wheel drive vehicle according to a fifth aspect of the present invention includes a drive axle driven by a main motor, a fluid pressure pump rotating in conjunction with the drive axle, and a fluid pressure rotating in conjunction with the driven axle. A motor, a first flow path that connects the discharge port of the fluid pressure pump and the suction port of the fluid pressure motor, and a second flow path that connects the suction port of the fluid pressure pump and the discharge port of the fluid pressure motor. When the discharge amount of the fluid pressure pump exceeds the suction amount of the fluid pressure motor, the maximum discharge pressure of the working fluid flowing to the fluid pressure motor is regulated to reduce the transmission torque of the driven axle side. In a four-wheel drive vehicle having a torque limiting means for setting a maximum value, a wheel speed detecting means for detecting a wheel speed of a drive wheel connected to the drive axle and a driven wheel connected to the driven axle, and a vehicle speed Vehicle speed detecting means for detecting Rotational speed difference detecting means for detecting a rotational speed difference between the driven wheel and the driven wheel, and driving force control means for controlling the driving force by adjusting the braking force on the driving wheel and the driving force output from the main drive source. And a control start setting means for starting control of the driving force control means when the rotation speed difference detected by the rotation speed difference calculation means becomes equal to or greater than a predetermined start reference value, the control start setting means The starting reference value of is set to a rotational speed difference generated when the driving wheels spin during acceleration, and the starting reference value requires two-wheel drive traveling based on the vehicle speed detecting means. Only set when the vehicle speed is higher than the high speed.

[0016]

According to the invention of claim 1, the start reference value of the control start setting means for starting the control of the driving force control means is set to
When the vehicle is in the four-wheel drive traveling state, the first start reference value is set to a large value when the vehicle body speed is a low speed that requires four-wheel drive traveling based on the vehicle body speed detected by the vehicle body speed detecting means. When the rotational speed of the drive axle increases too much, the drive force control means operates to suppress unnecessary idling of the drive axle, which does not give the driver a feeling of strangeness. At the same time, since the start reference value is set to the second start reference value that is smaller than the first start reference value when the vehicle body speed is equal to or higher than the low speed that requires two-wheel drive traveling, the vehicle is in the two-wheel drive state. When the vehicle travels on the vehicle, the drive force control means can be actuated to quickly prevent the drive wheels from idling.

According to the second aspect of the invention, the effect of the first aspect can be obtained, and the first start reference value is set to the maximum value of the torque transmitted to the driven wheels by the operation of the torque limiting means. Since the value is set to be equal to or more than the predetermined rotational speed difference, the transmission torque can be reliably transmitted to the driven wheels, and the four-wheel drive control can be sufficiently exerted.

Further, according to the invention of claim 3, the effect of claim 1 or 2 can be obtained, and the second start reference value is set to the rotational speed generated when the drive wheels spin the wheel during acceleration. Since the difference is set, it is possible to prevent the drive wheels from idling, improve the acceleration performance, and prevent the vehicle from swinging back and forth.

According to the fourth aspect of the invention, the lower the vehicle speed is, the smaller the rotational speed difference is, so that the maximum transmission torque is easily generated, and the higher the vehicle speed is, the larger the rotational speed difference is not generated. Maximum transmission torque is hard to generate. Therefore, in the present invention, the first start reference value is set to gradually increase as the vehicle body speed increases based on the vehicle body speed detected by the vehicle body speed detecting means, so that it is transmitted to the driven wheels more reliably. It becomes possible to transmit torque,
The four-wheel drive state can be sufficiently exhibited.

Further, according to the invention of claim 5, the start reference value of the control start setting means for starting the control of the driving force control means is set to the rotational speed difference generated when the drive wheels spin the wheel during acceleration. Since this start reference value is set only when the vehicle speed is medium or high speed that requires two-wheel drive traveling based on the vehicle speed detection means,
It is possible to perform four-wheel drive control without performing complicated control, and control that prevents idling of the drive wheels to improve acceleration and prevent the vehicle from swaying.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram in the case of being applied to a four-wheel drive vehicle based on a front-wheel drive vehicle according to the present invention, in which 10 is an engine as a prime mover, and rotational drive of the engine 10 is performed. The force is input to the front wheel side differential device 13 via the transmission 12, and the differential device 1
The front wheels are connected to the output side of 3 via a front axle 14 as a drive axle (in FIG. 1, only the right front wheel 1FR is shown).

In the front wheel side differential device 13, the ring gear 13b formed in the differential gear case 13a meshes with the gear 12a connected to the output side of the transmission 12 to be rotationally driven to be formed in the differential gear case 13a. The pinion 13 on the pair of pinion shafts 13c
d is attached, a pair of side gears 13e mesh with these pinions 13d, and the front axle 14 is connected to these side gears 13e.

Further, the differential gear case 13
A ring gear 1 formed in a in parallel with the ring gear 13b
3f is connected to a rotary shaft 16a of a suction throttle piston pump (hereinafter abbreviated as piston pump) 16 as a fluid pressure pump via a gear 13g meshing with the gear 3g.

The piston pump 16 has a suction port 1
Strainer 1 having 6b disposed in the reservoir tank 17
The electromagnetic directional control valve 1 is a two-position, four-port solenoid valve connected to 7a and through the low-pressure pipe 18L serving as the second flow path.
9, the discharge port 16c is connected to the pump port P of the forward / backward switching electromagnetic directional control valve 19 through the high-pressure pipe 18H serving as the first flow path.

Further, the electromagnetic directional control valve 19 for switching between forward and backward movement.
At the normal position where the solenoid 19a is not energized, the pump port P is connected to the output port A, and the tank port T is connected to the output port B when the solenoid 19a is energized, and the pump port P is output port at the offset position where the solenoid 19a is energized. The tank port T is connected to the output port A, and the output ports A and B are connected to the inlet and outlet ports 20a of a swash plate type variable displacement motor (hereinafter referred to as variable displacement motor) 20 as a fluid pressure motor. 20b, the high-pressure oil of the high-pressure pipe 18H is connected to the inflow port 20a of the variable displacement motor 20 and the low-pressure pipe 18L is connected to the outflow port 20b of the high-pressure pipe 18H in the normal position so that the rotary shaft 20c rotates in the forward traveling direction, for example, the left side. It is driven to rotate clockwise as viewed from the surface, and conversely, the high-pressure oil in the high-pressure pipe 8H is moved to the outflow port of the variable displacement motor 20 at the offset position. 20b, the drive rotates the low-pressure pipe 18L rotating shaft 20c and communicated as viewed from the rotational direction, for example left side at the time of reverse running in the counterclockwise direction to the inflow port 20a.

The electromagnetic directional control valve 19 is built in the variable displacement motor 20 so that the output ports A and B do not have to be connected to the inflow / outflow port 20 of the variable displacement motor 20.
It is connected to a and 20b. In addition, the electromagnetic directional control valve 1
Although the solenoid 19a is energized, the solenoid 19a is connected to the DC power source 19c via the shift position detection switch 19b which is turned on when the solenoid 19a selects the backward movement by the shift lever (not shown), so that the vehicle is traveling forward. It is controlled to be in the non-energized state and to be in the energized state when traveling backward.

Further, the suction port 16b of the piston pump 16
Between the discharge port 16c and the discharge port 16c, a relief valve 21 serving as a torque limiting unit that determines the upper limit of the discharge pressure of the piston pump 16 is provided.
Is inserted. Further, the low-pressure pipe 18 is connected to the communication pipe 22A that communicates between the high-pressure pipe 18H and the low-pressure pipe 18L between the piston pump 16 and the electromagnetic directional control valve 19.
A check valve 23 that allows a fluid flow from the L side to the high pressure pipe 18H side is inserted, and a fixed orifice is provided in a parallel relationship with the check valve 23 in the communication pipe 22B arranged in parallel with the communication pipe 22A. 24 is connected.

On the other hand, the rotary shaft 20c of the variable displacement motor 20.
A gear 20d is attached to the gear 20d, and a ring gear 27b formed in a differential gear case 27a of the rear wheel side differential 27 is meshed with the gear 20d. The rear wheel side differential device 27 has substantially the same configuration as the front wheel side differential device 3 described above, and has a differential gear case 27a.
A pinion 27d is attached to a pair of pinion shafts 27c formed inside, a pair of side gears 27e mesh with these pinion 27d, a rear axle 28 is connected to these side gears 27e, and a rear wheel is connected to this rear axle 28. (In FIG. 1, only the right rear wheel 1RR is shown.).

2 and 3 show a specific structure of the variable displacement motor 20 described above.
In the variable displacement motor 20, a rotary shaft 20c supported by a bearing 101 is rotatably arranged in a pump housing 100, and a cylindrical cylinder block 102 is coaxially fixed to the outer periphery of the rotary shaft 20c. ing. Further, the cylinder block 102 is formed with a plurality of bores 103 parallel to the rotating shaft 20c at predetermined intervals in the circumferential direction, and a piston 104 is housed in each bore 103. The cylinder block 102 shown in FIG.
A swash plate 105 is swingably disposed at a position facing the right end surface of the.

The swash plate 105 has a cylindrical portion 105a and a protruding portion 105b protruding from the upper end of the cylindrical portion 105a in FIG.
And a shoe holder 107 that locks the shoe 106 engaged with the end of each piston 104 so as to be slidable in the circumferential direction. Then, the shoe holder 107 is attached to the swash plate 1 via the needle 109 by the pressing spring 108.
It is pressed to the 05 side. Further, the position indicated by the symbol P in FIG. 2 is the swing shaft of the swash plate 105, and the swing shaft P is provided at a position offset by a predetermined amount ε in the direction orthogonal to the axis of the rotary shaft 20c. The swash plate 105 swings about the swing axis P up to a predetermined tilt angle α. In addition, a stopper 110 is provided in the pump housing 100 at a position facing the swash plate 105.
When 5 comes into contact with this stopper 110, swing is restricted,
The maximum inclination angle α _max of the swash plate 105 is set.

The left end surface of the cylinder block 102 in FIG. 2 is in sliding contact with the valve plate 111 fixed to the pump housing 100. This valve plate 11
As shown in FIG. 3, an inflow port 20a (an outflow port when traveling in reverse) and an outflow port 20b (an inflow port when traveling in reverse) are formed in 1, and the inflow port 20a and the outflow port 20b accommodate the piston 104. Each of the bores 103 is in communication with each other via a communication hole 112.

When traveling forward, the inflow port 20
The hydraulic oil is supplied from the a into the bore 103 and the piston 10
4 is pushed out from the bore 103, an axial force proportional to the working hydraulic pressure is transmitted to the swash plate 105, and the cylinder block 102 is rotated by the reaction force to transmit the driving torque to the rotary shaft 20c. Also, when traveling backwards,
Hydraulic oil is supplied into the bore 103 from the outflow port 20b, the piston 104 is pushed out of the bore 103, an axial force proportional to the hydraulic pressure is transmitted to the swash plate 105, and the reaction force causes the cylinder block 102 to rotate in the reverse direction. Rotating shaft 20
The drive torque is transmitted to c.

The swash plate 105, which is swingably arranged in the hoop housing 100, is urged by the urging means 120 in the direction in which the inclination angle α becomes smaller. That is, the biasing means 120 has a structure in which the control piston 120b and the coil spring 120c are housed in the housing chamber 120a, and the control piston 120b presses the swash plate 105 by the biasing force applied by the coil spring 120c.

By the way, the aforementioned piston pump 16
Depending on the direction of rotation of the rotary shaft 16a
Is not changed, and the discharge flow rate is
Curve L ₁As shown by, the vehicle speed changes from "0" to a predetermined value Va.
In the meantime, it will increase in proportion to the increase in vehicle speed,
Maximum discharge flow rate Q above the constant value Va_maxTo saturate with
Is set.

The discharge flow rate of the variable displacement motor 20 is
The inclination angle α of the swash plate 105 increases as the inclination angle α increases, and the swash plate 105 abuts the stopper 110 so that the maximum inclination angle α
_The maximum discharge flow rate is reached at the time of _max , but the flow rate characteristic is that the vehicle speed is “0” as shown by the characteristic curve L ₂ in FIG.
From when it reaches a predetermined value V ₁ (V ₁ <Va),
The maximum discharge flow rate Q _max is maintained because the piston pump 16 saturates at the maximum discharge flow rate Q _max at a predetermined value V ₁ or higher as the vehicle speed increases.

Therefore, when the vehicle speed is V ₁ or higher, the pump discharge flow rate of the piston pump 16 is the swash plate type variable displacement motor 2
It will not be possible to transmit the drive torque to the rear wheels without exceeding the motor flow rate of zero. Where “0” to V ₁
The vehicle speed in the range is a low speed traveling area that requires four-wheel drive traveling, and the vehicle speed of V ₁ or higher is a high speed traveling area that requires two-wheel drive traveling.

Next, FIG. 5 is a schematic configuration diagram showing a traction control control device which is mounted on the four-wheel drive vehicle having the above-mentioned configuration and which performs a brake control process and a throttle control process in accordance with a slip state of a drive wheel (front wheel). Is. In the figure,
1FL and 1FR are left and right front wheels, 1RL and 1RR are left and right rear wheels, and the rotational driving force of the engine 10 is transmitted to the front wheels 1FL and 1FR via a transmission 12 and a front wheel side actuating device 13. Further, braking cylinders 40FL and 40FR are attached to the front wheels 1FL and 1FR, respectively.

Further, wheel speed sensors 42FL and 42FR for outputting a wheel speed signal composed of a sine wave having a frequency corresponding to the rotational speed of these wheels are attached to the front wheels 1FL and 1FR, respectively, and the rear wheels 1RL and 1RR. Also, wheel speed sensors 42RL, 42RR that output a wheel speed signal composed of a sine wave having a frequency corresponding to these rotation speeds are attached.

When the brake pedal 44 is stepped on, the stepping force is doubled by the hydraulic booster HB and transmitted to the master cylinder 46, and the master cylinder pressure generated in the master cylinder 46 is transferred to the actuator 4
8 for controlling each braking cylinder 40FL, 40F
It is supplied to R.

Further, the brake pedal 44 is provided with a stop lamp switch 44a which responds to the depression of the brake pedal 44. From this stop lamp switch 44a, when the brake pedal 44 is released, a low level switch signal, the brake pedal 44 A high level switch signal is output to the controller 52 when the user is stepping on the switch.

Further, a main throttle valve 10b, the opening of which is adjusted in accordance with the depression amount of the accelerator pedal 50, is controlled by the controller 52 in the intake pipe line (specifically, intake manifold) 10a of the engine 10. A sub-throttle valve 10d, which is connected to the step motor 10c and whose opening is adjusted by a rotation angle according to the number of steps, is provided. Here, the opening of the sub throttle valve 20d is set to the main throttle valve 2
By setting the opening to 0b or less, the engine output can be reduced.

Here, the actuator 48 is shown in FIG.
The configuration is as shown in FIG. That is, the first drive force control switching valve 53A is inserted in the hydraulic pipe 49a connected to the master cylinder 46, and the second drive force control switching is performed in the hydraulic pipe 49b connected to the hydraulic booster HB. Valve 5
3B is inserted, and the first and second drive force control switching valves 53A and 53B are connected in parallel to the hydraulic pipe 49c. The solenoids 54F are attached to the braking cylinders 40FL and 40FR described above.
The supply ports 54s of L and 54FR are connected, and the discharge ports 54r of these solenoid valves 54FL and 54FR are connected.
Is the hydraulic pipe 49d through the throttles 56FL and 56FR.
It is connected to the. The hydraulic pipe 49d is connected to the hydraulic pipe 49a connected to the master cylinder 46 described above. Then, the solenoid valves 54FL, 5
The 4FR input port 54i is connected to the hydraulic pipe 49c. An actuator pump 62 driven by an electric motor 60 controlled by the controller 52 is inserted in the hydraulic pipe 49c. further,
By-pass check valves 55FL and 55F, which allow passage of brake fluid from the supply port 54s to the input port 54i, are provided to the solenoid valves 54FL and 54FR.
R is connected. And the actuator pump 6
Hydraulic pipe 49c and hydraulic pipe 49 connected to the suction side of 2
A reservoir tank 64 is arranged at the connecting portion of d.
The reservoir tank 64 has a piston 64b biased by a coil spring 64a, and when the master cylinder pressure drops, the brake fluid remaining in the reservoir tank 64 is pushed out by the elasticity of the coil spring 64a, and when the brake is not applied. It is configured so that no brake fluid remains.

The first drive force control switching valve 53A described above is in the normal position for communicating the hydraulic pipe 49a when the solenoid is in the non-energized state, and the solenoid is energized, whereby the master cylinder 46 is turned on. It is switched to the offset position through which a check valve that blocks the inflow of hydraulic oil from the valve is inserted.

The second driving force control switching valve 53B is
Conversely, when the solenoid is in the non-energized state, the solenoid valve 54 is in the normal position where it blocks the inflow of hydraulic fluid from the hydraulic booster HB, and the solenoid is energized to release the hydraulic fluid from the hydraulic booster HB at a predetermined pressure.
It is switched to the offset position for supplying to FL and 54FR.

In addition, solenoid valves 54FL and 54FL
FR is at a pressure increasing position that shuts off the discharge port 54r when the exciting current to the solenoid SL is not energized, and when the exciting current to the solenoid SL has a medium current value,
Input port 54i, supply port 54s and discharge port 5
The holding position is such that all 4r is cut off, and when the exciting current supplied to the solenoid SL has a high current value, the input port 54i is cut off and the supply port 54s and the discharge port 54r are communicated with each other in a depressurized position.

The above-mentioned wheel speed sensor 42FL.about.
The detection signals of the 42RL and the stop lamp switch 44a are input to the controller 52. Controller 52
Is, as shown in FIG. 7, the wheel speed sensors 42FL to 42R.
A waveform shaping circuit 52a that amplifies the R AC voltage signal and shapes the waveform into a rectangular wave, a rectangular wave signal output from the waveform shaping circuit 52a, and a stop lamp switch 44.
Input interface circuit 5 for inputting the switch signal of a
2b ₁ , an arithmetic processing unit 52b ₂ that calculates the wheel speed / estimated vehicle speed, and executes a driving force control process according to the rotational speed difference between the front and rear wheels, and a storage unit 52b ₃ that stores the processing procedure, the calculation result, and the like. And a microcomputer 52b having an output interface circuit 52b ₄ for outputting a control signal according to the processing result.

Here, the storage device 52b ₃ stores in advance control data necessary for executing the arithmetic processing of the arithmetic processing device 52b ₂ . The characteristic diagram shown in FIG. 8 is stored as one of the control data. This characteristic diagram shows the rear wheel 1R
FIG. 3 shows the relationship between the driving torque T transmitted to the L and 1RR sides and the rotational speed difference (rotational speed difference) between the front and rear wheels. The maximum drive torque T _MAX is regulated by the pressure limit of the relief valve 21 that causes the above-mentioned increase in the rotational speed difference and sharply increases with an increase in the rotational speed difference. In the characteristic diagram of FIG. 8, the rotation speed difference for starting the driving force control process described later, that is, the control start set value, is stored when the rotation speed difference between the front and rear wheels reaches a predetermined value. That is, the symbol ΔN in FIG. 8 indicates the rear wheel 1R.
L, while indicating the reference rotational speed difference capable of transmitting the maximum driving torque T _{MA X} in 1RR, first control start setting value as a larger value than the rotational speed difference ΔN of the reference Δ
N _H (ΔN _H > ΔN) is stored, and the second control start set value ΔN _L (as the rotational speed difference between the front and rear wheels that is smaller than the reference rotational speed difference ΔN and generates almost no driving torque to the rear wheels). ΔN _L <ΔN) is stored. Further, as other control data, map data used for the brake pressure control shown in FIG. 9 is stored.

Returning to FIG. 7, the controller 52
Is the output interface circuit 52b_FourFrom motor drive signal
No. S_MIs input and the electric motor of the actuator pump 62 is
Motor drive circuit 52c for driving the motor 60₁And output
Interface circuit 52b_FourTo throttle opening control signal
θ is input, and according to this throttle opening control signal θ
Step motor 10c of sub-throttle valve 10d
Motor drive circuit 52c for driving_TwoAnd the output interface
Face circuit 52b_FourFrom decompression signal DS_FL, DS _FRas well as
Hold signal HS_FL, HS_FRIs input to the solenoid drive circuit
Road 52c_Three, 52c_FourAnd the output interface circuit 52
b_FourFrom the driving force control signal S_TSolenoid drive input
Drive circuit 52c_Five, 52c₆It has and.

Each of the solenoid driving circuits 52c ₃ and 52c ₄ has a pressure reducing signal DS _i and a holding signal HS _i (i = F).
(L, FR) are both at a low level, the solenoid valves 54FL, 54FR are de-energized, and when only the holding signal HS _i is at a high level, a medium current exciting current is energized to the solenoid SL of the solenoid valve 54i. However, when only the pressure reduction signal DS _i is at a high level, a high-current exciting current is supplied to the solenoid SL of the solenoid valve 54 i.

Solenoid drive circuits 52c ₅ and 52c
_6, the first and second driving force control switch valve 53A and 5 when the drive force control signal S _T that is input is high
The solenoid SL of 3B is energized to switch from the normal position to the offset position, and when the driving force control signal _ST is at a low level, the energization to the first and second driving force control switching valves 53A and 53B is cut off. Hold in normal position.

Next, the control processing executed by the arithmetic processing unit 52b ₂ of the microcomputer 52b will be described with reference to FIGS.
It will be described with reference to the flowchart of No. 1. The control process of FIG. 10 is executed as a timer interrupt process for each predetermined time (for example, 5 msec). First, in step S1, the wheel speed detection values V _{FL to} V _RR of the wheel speed sensors 42FL to 42RR are read and used. From the tire diameter, the wheel peripheral speed, that is, the wheel speed V
Calculate w _{FL to} Vw _RR .

Next, in step S2, the following equation (1) is calculated to calculate the front wheel average speed MV _WF, and then the process _proceeds to step S3. MV _WF = (Vw _FL + Vw _FR ) / 2 (1) In step S3, the following formula (2) is calculated to calculate the rear wheel average speed MV _WR, and then the process proceeds to step S4.

MV _WR = (Vw _RL + Vw _RR ) / 2 (2) In step S 4, the rear wheel average speed MV _WR calculated in step S 3 is set as the estimated vehicle speed V _C, and this estimated vehicle speed V
_C is updated and stored in the estimated vehicle body speed storage area of the storage device 52b _{3, and} the process proceeds to step S5.

In step S5, the following equation (3) is calculated to calculate the front / rear wheel speed difference ΔMV, and then step S6.
Move to ΔMV = MV _WF −MV _WR (3) In step S6, the estimated vehicle body speed V _C and the reference vehicle speed V ₁ (the four-wheel drive shown in FIG. 4) which is the preset maximum value in the low speed region of the vehicle. (Comparison with the speed at the boundary between running and two-wheel drive). When the estimated vehicle body speed Vc is lower than the reference vehicle speed V ₁ by this comparison determination (Vc <
V ₁ ), the process proceeds to step S7, while the estimated vehicle speed V
When c is equal to or higher than the reference vehicle speed V ₁ (Vc ≧ V ₁ ),
Move to step S8.

Then, in step S7, the front-rear wheel speed difference ΔMV is compared with the first control start set value ΔN _H, and the front-rear wheel speed difference ΔMV is determined to be the first control start set value ΔN _H.
When N _H or more (ΔMV ≧ ΔN _H ), the process proceeds to step S9, while when the front and rear wheel speed difference ΔMV is less than the first control start set value ΔN _H (ΔMV <Δ
N _H ), end the timer interrupt process, and return to the predetermined main program.

In step S8, the front and rear wheel speed difference Δ
MV and the second control start set value ΔN _L are compared and determined, and the front and rear wheel speed difference ΔMV is the second control start set value ΔN _L.
When it is above (ΔMV ≧ ΔN _L ), step S9
On the other hand, when the front-rear wheel speed difference ΔMV is less than the second control start set value ΔN _L (ΔMV <ΔN _L ), the timer interrupt process is ended and the process returns to the predetermined main program.

Then, in step S9, the drive wheels 1
After the driving force control process for performing the brake control process and the throttle control process is executed according to the slip state of RL, 1RR, the timer interrupt process is ended and the process returns to the predetermined main program.

As shown in FIG. 11, in the driving force control process of step S9 described above, first, in step S10, the following (4) and () are calculated based on the wheel speed Vw _i (i = FL, FR, RL, RR). 5) is calculated to obtain the brake control slip amount SB _FL of the front wheels 1FL and 1FR as the driving wheels,
Calculate SB _FR .

SB _FL = Vw _FL −MV _WR = Vw _FL − (Vw _RL + Vw _RR ) / 2 (4) SB _FR = Vw _FR −MV _WR = Vw _FR − (Vw _RL + Vw _RR ) / 2 (5) Next, the process proceeds to step S11, and the slip amount S
It is determined whether or not either B _FL or SB _FR is equal to or greater than the brake control start threshold value K _H , and when either of the slip amounts SB _FL and SB _{FR is} equal to or greater than the threshold value K _H , the process proceeds to step S12. , A high-level driving force control signal S _T is output to the solenoid drive circuits 52c ₅ and 52c ₆ , and then the process proceeds to step S13 to maintain the brake control.
_{After B} is cleared to "0", the process proceeds to step S14.

[0060] In the step S14, the wheel speed Vw _i on the basis of the following (6) and (7) the front wheel is a driving wheel by performing the calculation of the equation 1FL, current slip ratio S _L of 1FR (n),
S _R (n) is calculated, and the previous slip ratio S _L (n-1), stored in the current value storage area of the storage device 52b ₃ , is calculated.
S _R (n-1) is stored in the previous value storage area, and the calculated current values S _L (n) and S _R (n) are stored in the current value storage area.

S_L(n) = (Vw_FL-Vw_RL) / Vw_RL ………… (6) S_R(n) = (Vw_FR-Vw_RR) / Vw_RR (7) Then, the process proceeds to step S15, and the current value storage area and
And the current value of the slip ratio stored in the previous value storage area
S_L(n), S_R(n) and the previous value S_L(n-1), S_R(n-1) and also
And the slip ratio is calculated by calculating the following equations (8) and (9).
Change amount α_L, Α _RTo calculate.

Α _L = S _L (n) -S _L (n-1) (8) α _R = S _R (n) -S _R (n-1) (9) Then , And proceeds to step S16, referring to the brake pressure control map of FIG. 9 based on the current values S _L (n), S _R (n) of the slip ratio and the slip ratio change amounts α _L, α _R. The control mode for each solenoid valve 54FL, 54FR of the actuator 48 is set, and then the process proceeds to step S17, where the pressure reduction signal DS corresponding to the set control mode is set.
_After outputting _FL , DS _FR and holding signals HS _FL , HS _FR to the solenoid drive circuits 52c ₃ and 52c ₄ , step S1
Move to 8.

On the other hand, the judgment result of the step S11 is
When SB _j <K _H , the process proceeds to step S18, and it is determined whether or not the control variable N _B is equal to or greater than a preset set value N _BS, and when N _B <N _BS , the process proceeds to step S19. Then, after incrementing the variable N _B , the process proceeds to step S20 to set the gentle decompression mode and then proceeds to step S22. When N _B ≧ N _BS , the process proceeds to step S21 and the low level driving force is set. Control signal S _T
Is output to the solenoid drive circuits 52c ₅ and 52c ₆ , and then the process proceeds to step S22.

In step S22, each wheel speed Vw_FL~ V
w_RRThe following formula (10) is calculated based on
And a storage device 5 for calculating the slip ratio SS for control.
2b _ThreeThe current slip ratio for throttle control stored in
The previous value SS (n of the slip ratio stored in the value storage area
-1) is stored in the previous value storage area and the calculated current value S
Store S (n) in the current value storage area.

SS (n) = {(Vw _FL + Vw _FR ) / 2}-{(Vw _RL + Vw _RR ) / 2} (10) Then, the process proceeds to step S23, where the current value storage area and the previous value storage are stored. Based on the current value SS (n) and the previous value SS (n-1) of the throttle control slip ratio stored in the area, the calculation of the following equation (11) is performed to calculate the slip ratio change amount β.

Β = SS (n) -SS (n-1) (11) Next, the process proceeds to step S24, and the above-described brake control start in which the current value SS (n) of the slip ratio is preset. It is determined whether or not the throttle control start threshold value K _L is smaller than the threshold value K _H , and if SS (n) <K _L , the process proceeds to step S25 to increase the throttle opening θ stepwise. The variable N _S that represents the waiting time of "0"
If N _S = 0, the process proceeds to step S26, the variable N _S is incremented, and then the process proceeds to step S27.

In step S27, it is determined whether or not the throttle opening θ has reached a set value θ _MAX representing the fully open state. If θ <θ _MAX , the process proceeds to step S28 and the throttle opening θ is set. A value obtained by adding the predetermined value Δθ _U is set to a new throttle opening θ, and this is output to the motor drive circuit 52c ₂ and then the process ends. When θ = θ _MAX , the process proceeds to step S29. Set the control flag FS set to "1" at the start of throttle control to "0"
To the variable N and then to step S30.
_The processing is ended after _S is cleared to "0".

The determination result of step S25 is N ≠
When it is 0, the process proceeds to step S31 and the variable N
_S is incremented and then the process proceeds to step S32 to determine whether or not the variable N _S has reached a preset value N _SS corresponding to a preset waiting time, and when N _S = N _SS , the above step S30 When N _S <N _SS , the process ends.

On the other hand, the judgment result of the step S24 is
The lip ratio SS (n) is the threshold K_LIf it is above,
The control flag FS is set to "1" at step S33.
It is reset and this is reset to "0".
If it is, it is determined that the throttle control is starting.
Disconnect and proceed to step S34 to set the throttle opening θ
Set value θ close to fully closed_MINSet this to
Motor drive circuit 52c _TwoTo step S3
Go to 5 and set the control flag FS to "1".
Ends the process.

Further, the judgment result of the step S33 is
When the control flag FS is set to "1", it is determined that the process is the second or later process, the process proceeds to step S36, and it is determined whether the slip ratio change amount β is positive. This determination is to determine whether or not the slip ratio SS (n) has an increasing tendency. When β ≦ 0, it is determined that the slip ratio does not change or is decreasing, and the processing is ended as it is. By doing so, when the throttle opening θ is held at the previous value and β> 0, it is determined that the slip ratio is increasing, and step S3
7, the predetermined value Δθ from the current throttle opening θ
A value obtained by subtracting _D is set as a new throttle opening θ, which is output to the motor drive circuit 52c ₂ and then the processing ends.

Here, the wheel speed sensors 42FL, 42FL of FIG.
2, 42RL, 42RR and step S1 of FIG. 10 correspond to the wheel speed detecting means of the present invention, and step S4 of FIG.
Corresponds to the vehicle body speed detecting means of the present invention, steps S2, S3 and S5 of FIG. 10 correspond to the rotational speed difference detecting means of the present invention, and steps S9 and 11 of FIG. 10 drive the present invention. 10 corresponds to the force control means, and steps S6, S7 and S8 of FIG. 10 correspond to the control start setting means of the present invention, and the first control start set value ΔN _H shown in step S7 of FIG. 10 corresponds to the present invention. The second control start set value ΔN _L shown in step S8 of FIG. 10 corresponds to the first start reference value of the present invention.

Next, the operation of the driving force control process will be described with reference to the time chart of FIG. Wheel speed Vwj (j = FL, FR) of front wheels 1FL, FR which are driving wheels
12 becomes faster than the rear-wheel average wheel speed MV _WR to enter the slip state, and when the throttle control slip amount SS becomes equal to or larger than the throttle control start threshold K _L at time t ₁ in FIG. 12A, step S24 of the process in FIG. From step S35
And the minimum set value θ _MIN is set, and this is output to the motor drive circuit 52c ₂ . Therefore, the step motor 10 is rotationally driven, and the throttle opening θ of the sub-throttle valve 10d sharply decreases as shown in FIG. 12 (b), which reduces the engine output.

Thereafter, when the brake control slip amount SBj becomes equal to or greater than the threshold value K _H at the time point t ₂ in FIG. 12, the process proceeds from step S11 to step S12, and the high level driving force control signal S _T is sent to the solenoid drive circuit 52c. ₅ , 52c
₆ and outputs these solenoid drive circuits 52c ₅ , 52
Switching valve 53 for controlling the driving force of the actuator 48 from c ₆
By energizing the solenoids SL of A and 53B, these switching valves 53A and 53B are switched to the offset positions.

Therefore, the solenoid valve 54j of the actuator 48 is in communication with the hydraulic booster HB which is maintained at a predetermined pressure in place of the master cylinder 46. Then, the control variable N _B is cleared to “0” in step S13, the brake control slip amount S _j is calculated in step S14, and the step S1 is performed.
At 5, the slip amount change amount α _j is calculated.

Then, in step S16, the slip ratio S _j
By referring to the control map of FIG. 9 based on the slip rate change amount α _j and the slip ratio change amount α _j , the rapid pressure increase mode is set in step S17, and both the pressure reduction signal DS _j and the hold signal HS _j become the logical value “0”. Is set.

Therefore, the solenoid valve 54j is maintained at the pressure increasing position and the high brake hydraulic pressure of the hydraulic booster HB is supplied to the braking cylinder 40j, so that the wheel cylinder pressure rapidly increases and becomes the driving wheel. Front wheel 1FL,
A large braking force is applied to 1FR.

As described above, the engine output decreases and the braking force acts on the front wheels 1FL and 1FR, whereby the increasing tendency of the wheel speed Vw _j is suppressed, and the slip ratio change amount α _j at time t _3. Is changed from zero to negative, the holding mode is set, whereby the holding signal HS _j is inverted to the logical value "1", whereby the solenoid valve 54j is switched to the holding position and the braking cylinder 40j.
The brake fluid pressure is maintained as shown in FIG.

After that, at time t ₄ , when the brake control slip amount SB _j reaches the wheel speed Vw _j which is lower than the threshold value K _H , the process proceeds from step S11 to steps S18, S19 to step S20 in the process of FIG. , The gentle decompression mode is set, and the decompression signal DS _j and the hold signal H are set.
When S _j repeats the logical value “1” and the logical value “0” in an inverse relationship with each other at a predetermined duty ratio, the solenoid valve 54 j is switched between the pressure reducing position and the holding position at a predetermined interval, and the braking cylinder 40 j of the braking cylinder 40 j is switched. The brake fluid pressure decreases stepwise as shown in FIG.

Then, at time t_FiveFor throttle control pickpocket
The amount SS is the threshold K_LIf it becomes less than,
The step S24 to step S25,
Number N _SIs cleared to "0", step S2
Move to 6 and variable N_SIs incremented and throttled
The angle θ is the minimum value θ_MINTherefore, from step S27
Go to step S28 and set the current throttle angle θ
Value Δθ_UIs set as a new throttle angle θ.
The motor drive circuit 52c_TwoOutput to
As a result, the throttle angle θ is shown as a broken line in FIG.
It is increased stepwise like.

After that, the throttle control slip amount SS
Continues to be less than the threshold value K _L , and at this time, the variable N _S has a positive value other than “0”, the process proceeds from step S25 to step S31, and the variable N _S is sequentially incremented. The opening degree θ is not changed, and when this is repeated and the variable N _S reaches the predetermined number N _SS , step S
The process proceeds from step 32 to step S30 and the variable N _S is "0".
Is cleared.

[0081] Therefore, step S24 at time t ₆ after the variable N _S is reset to "0", S25, S26,
By shifting from S27 to S28, the throttle opening θ is increased stepwise by Δθ _U again,
The engine power is increased.

As described above, the throttle opening θ is increased stepwise while the slip amount SS for throttle control continues to be less than the threshold value K _L , and in the brake control, the gentle depressurization mode is continued during this period. are so, the brake fluid pressure of the brake cylinder 6j becomes zero at time t _7, the control variable N _B is the predetermined value N driving force control signal shifts to the low level to the step S22 when it reaches the _BS S _T Is output to the driving force control transistor 42,
Switching valve 53A, 53 for controlling the driving force of the actuator 48
B is switched to the normal position and solenoid valve 54
j is communicated with the master cylinder 46 instead of the hydraulic booster HB.

After that, when the throttle control slip amount SS becomes equal to or more than the threshold value K _L at the time point t ₈ , the process proceeds from step S24 to step S33, and the control flag FS is set to "1", so the process proceeds to step S36. However, since the slip amount change amount β is positive, the process proceeds to step S37, and a value obtained by subtracting the predetermined value Δθ _D from the current slot opening θ is set as the new slot opening θ and the slot opening is also performed. The degree θ is output to the motor drive circuit 52c ₂ , whereby the throttle opening θ is reduced as shown in FIG. 12 (b), and the engine output is reduced.

After that, when the slip amount change amount β changes to zero and changes to a decreasing tendency at time t ₉ , the processing is ended as it is from step S36, and the throttle opening θ
When the throttle control slip amount SS becomes less than the threshold value K _L at time t ₁₀ , the throttle opening θ is increased to the step state and the engine output is gradually increased.

After that, the throttle control slip amount SS
There continues the state of less than the threshold value K _L, the throttle opening theta reaches the maximum value theta _MAX, the process proceeds from step S27 to step S29, the control flag FS is reset to "0", then at step S30 The variable N is also cleared to “0”, and the driving force control ends.

Therefore, in the driving force control process, the idling of the front wheels 1FL and FR, which are the driving wheels, is reduced by controlling the throttle output θ to increase or decrease the engine output to increase or decrease the brake fluid pressure. Is possible.

Next, the overall operation of the four-wheel drive vehicle of this embodiment will be described with reference to the flowcharts of FIGS. 1 and 10 and FIG.
This will be described with reference to the changes in the vehicle speed and the rotational speed difference between the front and rear wheels shown in FIG.

Now, when the ignition switch is turned on while the vehicle is stopped with the ignition switch turned off and the brake pedal 44 is depressed, the microcomputer 52b is powered on by the ignition switch in the initial state. Various flags are reset to "0".

When the engine 10 starts to travel forward from the idling state of the braking state, step S
In FIG. 1, the wheel speed sensors 42FL and 42FR detect the wheel speeds Vw _FL and Vw _FR of the front wheels 1FL and 1FR that are the driving wheels, and the wheel speed sensors 42FL and 42FR detect the wheel speeds Vw _RL of the rear wheels 1RL and 1RR that are the driven wheels. , Vw _RR is detected.
Then, in steps S2 and S3, the front wheel average speed MV _WF and the rear wheel average speed MV _WR are calculated, and in step S4, the estimated vehicle body speed V is calculated from the rear wheel average speed MV _WR.
w _c is calculated, and in step S5 the front and rear wheel speed difference ΔM
Calculate V.

Then, in step S6, the vehicle is traveling at a speed that requires four-wheel drive traveling (is it traveling below the reference vehicle speed V ₁ ) or is it traveling at a sufficient speed in two-wheel drive traveling. Whether the vehicle is running (whether the vehicle is traveling at the reference vehicle speed V ₁ or higher), the estimated vehicle body speed Vw _H is compared with the reference vehicle speed V ₁ .

Now, assuming that the vehicle travels forward on a high friction coefficient road such as a dry road surface and no slip occurs on the front wheels 1FL and 1FR which are drive wheels, the shift lever is switched to the forward travel side. Since the shift position detection switch 19b on the reverse traveling side is maintained in the off state, the solenoid 19a of the forward / reverse switching electromagnetic directional control valve 19 is maintained in the non-energized state, and the switching position continues the normal position shown in FIG. . By depressing the accelerator pedal 50 in this state, the rotational force of the engine 10 is transmitted to the front wheel side differential device 13 via the transmission 12, and the front wheel side actuating device 13 rotates the front wheels 1FL, 1FR in the forward direction. Driving the vehicle starts forward traveling.

At this time, the rotary shaft 1 of the piston pump 16
By rotating 6a, the piston pump 1
From 6, the hydraulic fluid having a discharge flow rate according to the rotation speed is discharged. The discharged hydraulic oil is supplied to the variable displacement motor 20 via the high pressure pipe 18H and the forward / reverse switching electromagnetic direction switching valve 19.
Is sucked into the inflow port 20a and discharged from the outflow port 20b.

When the vehicle travels in the low speed region (vehicle speed lower than the reference speed V ₁ ), the piston pump 16
As shown in FIG. 4, the discharge flow rate of the variable displacement motor 20 is set so that the discharge flow rate of the variable displacement motor 20 at the maximum swash plate inclination angle is larger than that of the piston pump 16. In a state where the rear wheels 1RR, 1RL and the front wheels 1FR, 1FL are rotationally driven at the same rotational speed during normal traveling, almost no driving torque is transmitted to the rear wheels 1R.

At this time, in the control processing of FIG. 10, since the vehicle is traveling at a speed lower than the reference speed V ₁ , step S
From 6 to step S7, the front wheel 1F, which is the driving wheel
Since no slip has occurred in L and 1FR, step S
After execution 7 to step S8, the execution of the program is interrupted, and the drive force control processing of step S9 is not executed. When the vehicle travels on the high friction coefficient road at a speed equal to or higher than the reference vehicle speed V ₁ and the front wheels 1FL and 1FR do not slip, the program execution is interrupted after the process proceeds from step S6 to step S8. , And does not proceed to the driving force control process of step S9.

Next, assuming that the vehicle suddenly starts on a low friction coefficient road such as an icy road or a snowy road, and the front wheels 1FL and 1FR slip at that time, the front wheels 1FL and 1FR and the rear wheels 1RL and 1RR are assumed. And the front wheels 1FL and 1FR have high rotational speed differences. As a result, the discharge flow rate of the piston pump 16 exceeds the discharge flow rate of the variable displacement motor 20, so that the resistance of the variable displacement motor 20 acts as a load to generate the maximum drive torque T _MAX. Since the power is transmitted to the rear wheels 1RL and 1RR via the driving device 27, the vehicle travels in the four-wheel drive state.

At this time, in the control processing of FIG. 10, step S is performed immediately after the vehicle has started (the vehicle speed is equal to or lower than the reference speed V ₁ ).
The process moves from 6 to step S7. And the front wheel 1FL,
Since 1FR is in a slipping state due to high rotation,
As shown in the vicinity of the vehicle speed “0” in FIG. 13, the front and rear wheel speed difference ΔMV
Exceeds the first control start set value ΔN _H , the process proceeds from the step S7 to the driving force control process of step S9. Then, in the driving force control process, as described above, by controlling the throttle output θ to increase or decrease the engine output to increase or decrease the brake fluid pressure, the idling of the front wheels 1FL and FR, which are the driving wheels, is reduced. I will let you.

As a result, immediately after the vehicle starts moving, even if the front-rear wheel speed difference ΔMV becomes larger than the rotation speed difference (the rotation speed difference ΔN shown in FIG. 8) that produces the maximum drive torque T _MAX , the rear wheels 1RL, The drive torque to 1RR does not increase, and in the present embodiment, the idling of the front wheels 1FL and FR that is equal to or more than the rotation required to generate the maximum drive torque T _MAX is reduced by the drive force control process in step S9. , It is possible to shift to the four-wheel drive state without giving the driver a feeling of strangeness.

When the vehicle speed is increased by depressing the accelerator pedal 50, the slip state of the front wheels 1FL, 1FR decreases, and the front-rear wheel speed difference ΔMV decreases as shown in FIG. At that time, in the control process of FIG. 10, when the vehicle speed reaches the reference speed V ₁ , the process proceeds from step S6 to step S8. Then, in the vicinity of this vehicle speed, the front-rear wheel speed difference ΔMV exceeds the second control start set value ΔN _L , and therefore, the driving force control process of step S8 is shifted to step S9. Then, in the driving force control processing, the throttle opening θ
The control for increasing / decreasing the engine output to increase / decrease the brake fluid pressure is performed to reduce the idling of the front wheels 1FL, FR.

Here, when the vehicle speed exceeds the reference speed V ₁ ,
The discharge flow rate of the piston pump 16 does not exceed the motor capacity of the variable displacement pump 20, and the drive torque is not transmitted to the rear wheels 1RL, 1RR, so the vehicle shifts to the two-wheel drive state, but the vehicle speed is the reference speed. The driving force control process of step S9 is continuously executed until the four-wheel drive state when the vehicle speed is below V ₁ changes to the two-wheel drive state described above, and the drive torque to the rear wheels 1RL, 1RR rapidly increases. Since the front wheels 1FL, 1FR can be effectively prevented from idling in response to the decrease, the driver does not feel uncomfortable.

Further, when the vehicle is traveling at a vehicle speed V ₁ or higher, the front wheels 1F are
When L and 1FR are in the idling state, in the control process of FIG. 10, since the front-rear wheel speed difference ΔMV exceeds the second control start set value ΔN _L in step S8, step S8 is performed.
The process shifts from 8 to the driving force control process of step S9.

By this control of increasing / decreasing the engine output and increasing / decreasing the brake fluid pressure by adjusting the throttle opening θ by this driving force control processing, the idling of the front wheels 1FL and FR, which are the driving wheels, is decreased to reduce the wheel spin. As a result, traction control control can be performed that improves the starting performance and acceleration performance of the vehicle and improves the vehicle stability by preventing the tail swing.

Next, when the vehicle is moved backward, the shift lever is switched to the reverse position to turn on the shift position detection switch 19b, and the electromagnetic direction switching valve 19 is turned on.
The solenoid 19a is turned on and the switching position is switched from the normal position to the offset position. As a result, the hydraulic oil inside the high pressure pipe 18H is transferred to the variable displacement motor 20.
Of the hydraulic oil discharged from the inflow port 20a to the low pressure pipe 18L,
The rotary shaft 20c of the variable displacement motor 20 is rotated in the reverse direction to that during forward traveling, and the rear wheels 1RL, 1RR are rotated in reverse. Therefore, when the vehicle is moving backward, the same operation as when moving forward is performed.

Next, a second embodiment of the present invention will be described with reference to FIGS. 14 to 16. The same components as those in the first embodiment shown in FIGS. 1 to 13 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 14 shows the storage device 52b _{3 of} this embodiment.
Control data necessary for execution of the arithmetic processing of the arithmetic processing unit 52b ₂ stored in. This control data is for the rear wheel 1
It shows the relationship between the driving torque T transmitted to the RL and 1RR sides and the rotational speed difference (rotational speed difference) between the front and rear wheels.
Due to the fact that the higher the vehicle speed is, the larger the flow rate difference in the characteristic range of the discharge flow rate characteristics of the piston pump 16 and the variable displacement motor 20 becomes, the driving torque T becomes smaller as the vehicle speed becomes lower. The driving torque T is less likely to occur unless a large difference in rotational speed between the front and rear wheels occurs as the vehicle speed increases. The vehicle speed range is a speed equal to or lower than the reference vehicle speed V ₁ .

Therefore, in this embodiment, a plurality of drive torque diagrams are set according to changes in the vehicle speed, and a value larger than the rotational speed difference that produces the maximum drive torque T _MAX of each of the drive torque diagrams is set. A plurality of first control start set values ΔN
_H1 , ΔN _H2 , and ΔN _H3 are stored in correspondence with the vehicle speed.
That is, the low vehicle speed correspondingly stores a small first control start setting value .DELTA.N _H1, in response to the vehicle speed increases by a predetermined value, a large first control start setting value .DELTA.N _H2 than the value .DELTA.N _H1 described above, ΔN _H3 is stored in order.

FIG. 15 shows the microcomputer 5
The arithmetic processing unit 52b _{2 of} 2b shows the control processing executed by using the control data of FIG. In this control process, the same step numbers are given to the same parts as the step numbers shown in FIG. 10, and the description thereof will be omitted. Note that this control process also takes a predetermined time (for example, 5 ms).
It is executed as a timer interrupt process for each ec).

In the control process of FIG. 15, the estimated vehicle body speed Vc is determined as a result of the comparison judgment of the estimated vehicle body speed V _C and the preset reference vehicle speed V _{1 in} the low speed region of the vehicle in step S6. When it is below the reference vehicle speed V ₁ (Vc <V ₁ ), the routine proceeds to step S40, while when the estimated vehicle body speed Vc is equal to or higher than the reference vehicle speed V ₁ (Vc
≧ V ₁ ) and the process proceeds to step S8.

Then, in step S40, as shown in FIG.
The first control start set value ΔN _{H (n)} (n = 1, 2, 3) corresponding to the estimated vehicle body speed Vc is calculated with reference to the control data of No. 1, and the process proceeds to step S41.

In step S41, the front and rear wheel speed difference ΔMV
And the first control start set value ΔN _{H (n)} are compared and determined,
When the front-rear wheel speed difference ΔMV is equal to or larger than the first control start set value ΔN _{H (n)} (ΔMV ≧ ΔN _{H (n)} ), step S9
On the other hand, when the front-rear wheel speed difference ΔMV is below the first control start set value ΔN _{H (n)} (ΔMV <Δ
N _{H (n)} ), the timer interrupt process is terminated, and the process returns to the predetermined main program.

Then, in step S8, the front and rear wheel speed difference
ΔMV and the second control start set value ΔN _LPerforms comparison judgment with
And the front / rear wheel speed difference ΔMV is the second control start set value ΔN._L
When it is above (ΔMV ≧ ΔN_L), Step S9
On the other hand, the front and rear wheel speed difference ΔMV starts the second control.
Set value ΔN_LBelow (ΔMV <ΔN_L),
Ends the interrupt processing and returns to the specified main program
I do.

Then, in step S9, the control processing of FIG. 11 executes the driving force control processing for performing the brake control processing and the throttle control processing according to the slip state of the driving wheels 1RL, 1RR, and then the timer interrupt processing. Upon completion, the program returns to the predetermined main program.

Here, step S6, step S40, step S41 and step S8 of FIG. 15 correspond to the control start setting means of the present invention, and the first control start set value ΔN _{H (n} shown in step S41 of FIG. 15 is used. ₎ Corresponds to the first starting reference value of the present invention.

In the present embodiment, the vehicle suddenly starts on a low friction coefficient road such as an icy road or a snowy road, in which case the front wheels 1FL, 1FL,
When the FR slips, the discharge flow rate of the piston pump 16 exceeds the discharge flow rate of the variable displacement motor 20, and the resistance of the variable displacement motor 20 acts as a load, causing a maximum drive torque T.
_{Since MAX} is generated and this drive torque is transmitted to the rear wheels 1RL, 1RR via the rear wheel side differential device 27, the vehicle runs in the four-wheel drive state.

At this time, in the control process of FIG. 15, immediately after the vehicle starts moving (the vehicle speed is close to "0"), the process proceeds from step S6 to step S40. Then, with reference to the control data of FIG. 14, for example, the first control start set value ΔN _H1 corresponding to the vehicle speed close to “0” is calculated, and step S
At 41, a comparison determination is made between the front-rear wheel speed difference ΔMV and the first control start set value ΔN _H1 . Then, since the front-rear wheel speed difference ΔMV exceeds the first control start set value ΔN _H1 as in the vicinity of the vehicle speed “0” in FIG. 16, the process proceeds from the step S41 to the driving force control process of the step S9. Then, in the driving force control process, as described above, by controlling the throttle opening θ to increase / decrease the engine output to increase / decrease the brake fluid pressure, the front wheels 1F which are the driving wheels.
The idle rotation of L and FR is reduced.

Then, when the vehicle speed (reference vehicle speed V ₁ or less) increases by depressing the accelerator pedal 50, in step S40, for example, the first control start set value ΔN corresponding to the increased vehicle speed by referring to the control data of FIG.
_H2 is calculated, and the first control start set value ΔN _H2 is used as a comparison target, the process proceeds from step S41 to step S9, and the driving force control process is performed.

As described above, in this embodiment, the vehicle speed is increased.
According to the first control start set value ΔN _{H (n)}Also from a small value
Since it is controlled by changing it to a larger value,
Maximum drive torque T due to change_MAXFront and rear wheel times
Even if the speed difference changes, the maximum drive torque T_MAXGenerate
Only the front wheels 1FL and FR that have more rotation than necessary for idling
Can be reduced by the driving force control process. say
In other words, the maximum drive torque T for four-wheel drive_MAXBut
The problem that the driving force control process is executed before it occurs
It is possible to eliminate the convenience and improve the performance of the four-wheel drive vehicle.
Traction that enhances vehicle stability while fully exhibiting
Control can be reliably performed.

In this embodiment, as in the first embodiment, the driving force control is performed from the four-wheel drive state when the vehicle speed is below the reference speed V ₁ to the two-wheel drive state described above. Since the processing is continuously executed, it becomes possible to effectively prevent the front wheels 1FL, 1FR from idling in response to a sudden decrease in the driving torque applied to the rear wheels 1RL, 1RR, and the driver can be prevented. There is no feeling of strangeness.

When the vehicle is traveling at a vehicle speed V ₁ or higher, the front wheels 1F are passed by passing through a low friction coefficient road.
Even when L and 1FR are in the idling state, the driving force control process adjusts the throttle opening θ to increase or decrease the engine output to increase or decrease the brake fluid pressure, so that the front wheels 1FL and FR that are the driving wheels are controlled. Since the idling can be reduced and the wheel spin can be prevented, it is possible to perform the traction control control aiming at the improvement of the starting property and the acceleration property of the vehicle and the improvement of the vehicle stability by preventing the tail swing.

Next, a third embodiment of the present invention will be described with reference to FIGS. In this embodiment as well, the same components as those in the first embodiment shown in FIGS. 1 to 13 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 17 shows the microcomputer 52b.
Processor 52b_TwoIt shows the control process executed by
is there. The control process of FIG. 17 is performed in step S42.
Estimated vehicle speed V_CAnd the preset low speed range of the vehicle
Reference vehicle speed V that is a large value₁As a result of the comparison judgment with
The constant vehicle speed Vc is the reference vehicle speed V₁When it is above (V
c ≧ V₁), The process proceeds to step S43, while the estimated vehicle body
Speed Vc is reference vehicle speed V ₁Below (Vc <
V₁), End the timer interrupt process, and
Return to Ram.

Then, in step S43, the front and rear wheels are
Speed difference ΔMV and second control start set value ΔN_LComparison with
And the front and rear wheel speed difference ΔMV is the second control start set value.
ΔN _LWhen it is above (ΔMV ≧ ΔN_L), Step
On the other hand, the front and rear wheel speed difference ΔMV becomes the second control.
Start set value ΔN_LWhen less than (ΔMV <Δ
N _L), End the timer interrupt process, and
Return to Ram.

Then, in step S9, the driving force control process for executing the brake control process and the throttle control process according to the slip state of the drive wheels 1RL, 1RR is executed by the control process of FIG. 11 and then the timer interrupt process is executed. Upon completion, the program returns to the predetermined main program.

Here, steps S42 and S43 of FIG. 17 correspond to the control start setting means of the present invention, and FIG.
The second control start set value ΔN _L shown in step S43 of corresponds to the start reference value of the present invention.

In this embodiment, the vehicle has a reference vehicle speed V.
Front wheels 1FL when traveling below the _1, when slip occurs in 1FR, the discharge flow rate of the piston pump 16 exceeds the discharge flow rate of the variable displacement motor 20, the variable displacement motor 2
Since the resistance of 0 acts as a load to generate the maximum drive torque T _MAX , the vehicle travels in the four-wheel drive state. Further, unlike the first and second embodiments described above, the present embodiment does not execute the driving force control process at a vehicle speed lower than the reference vehicle speed V ₁ .

On the other hand, when the vehicle travels in the two-wheel drive state where the reference vehicle speed is V ₁ or more, steps S42 to S43 are executed.
Then, the front-rear wheel speed difference ΔMV is compared with the second control start set value ΔN _L. Then, as shown in FIG. 18, when the vehicle passes through the low friction coefficient road and the front wheels 1FL, 1FR become idling at the time of acceleration to the vehicle speed V ₂ (V ₂ > V ₁ ), in the control processing of FIG. , Step S43
The front and rear wheel speed difference ΔMV is the second control start set value Δ
Since it exceeds N _L , the process proceeds from step S43 to the driving force control process of step S9.

By performing the control for increasing / decreasing the engine output and increasing / decreasing the brake fluid pressure by adjusting the throttle opening θ by this driving force control process, the idling of the front wheels 1FL, FR, which are the driving wheels, is decreased to reduce the wheel spin. As a result, traction control control can be performed that improves the starting performance and acceleration performance of the vehicle and improves the vehicle stability by preventing the tail swing.

Thus, in this embodiment, the reference vehicle speed V
_{Since the} driving force control process is executed only at a vehicle speed of ₁ or more, it is possible to achieve both four-wheel drive control and traction control control without performing complicated control.

In addition, in the actuator 48 shown in FIG. 6, the solenoid valve 54FL of 3 ports and 3 positions,
Although the case where the solenoid valve 54F is configured is described above, the invention is not limited thereto.
Each of L and 54FR may be replaced with two switching valves, an inflow-side electromagnetic switching valve and an outflow-side electromagnetic switching valve, which are located at two ports and two positions.

Further, in the above embodiment, the case where the hydraulic booster HB is applied and used as the hydraulic power source for controlling the driving force has been described, but the present invention is not limited to this, and it is driven by an electric motor separately. The fluid pressure pump described above may be applied and used as a hydraulic power source for controlling the driving force.

Further, in the above embodiment, the case where both the brake control and the throttle control are performed in the driving force control process has been described, but the present invention is not limited to this, and only the brake control or the throttle control may be performed. May be.

In the above embodiment, the case where the rear wheel braking cylinders 40FL and 40FR are individually controlled has been described, but they may be controlled by a common actuator.

In the four-wheel drive vehicle shown in FIG. 1, the case where the rear wheel side differential device 27 is provided has been described, but the present invention is not limited to this, and the rear wheel differential device 27 is not limited thereto.
Alternatively, instead of this, variable displacement motors may be individually provided on the left and right axles 28 of the left and right rear wheels 1RL, 1RR.

Furthermore, in the above-described first to third embodiments, the embodiment based on the front-wheel drive vehicle has been described, but the present invention is not limited to this, and the rear-wheel drive vehicle can also be used as the base. By providing each component with 1RL and 1RR as driving wheels, it is possible to obtain the same effects as the above-described embodiment.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a four-wheel drive vehicle according to the present invention.

FIG. 2 is a sectional view of a swash plate type axial piston motor as a fluid pressure motor according to the present invention.

FIG. 3 is a conceptual diagram showing a mechanism of a swash plate type axial piston motor.

FIG. 4 is a diagram showing characteristics of discharge flow rates of a fluid pressure pump and a fluid pressure motor according to the present invention.

FIG. 5 is a schematic configuration diagram showing a traction control control device according to the present invention.

6 is a configuration diagram showing a specific example of the actuator of FIG.

7 is a block diagram showing a specific example of the controller of FIG.

FIG. 8 is a diagram showing data of control start set values used in the first embodiment of the present invention.

FIG. 9 is a diagram showing a control map for brake control in driving force control.

FIG. 10 is a flowchart illustrating a procedure of control processing according to the first embodiment of this invention.

FIG. 11 is a flowchart showing a procedure of driving force control processing according to the present invention.

FIG. 12 is a time chart for explaining the operation of driving force control.

FIG. 13 is a diagram showing a relationship between a control start set value and a vehicle speed in the control processing of the first embodiment.

FIG. 14 is a diagram showing data of control start set values used in the second embodiment of the present invention.

FIG. 15 is a flowchart showing a procedure of control processing according to the second embodiment of the present invention.

FIG. 16 is a diagram showing a relationship between a control start set value and a vehicle speed in the control processing of the second embodiment.

FIG. 17 is a flowchart showing a procedure of control processing according to the third embodiment of the present invention.

FIG. 18 is a diagram showing a relationship between a control start set value and a vehicle speed in the control processing of the third embodiment.

[Explanation of symbols]

10 Engine (Main Motor) 14 Drive Axle 16 Piston Pump (Fluid Pressure Pump) 18H High Pressure Pipe (First Flow Path) 18L Low Pressure Pipe (Second Flow Path) 20 Variable Capacity Motor (Fluid Pressure Motor) 21 Relief Valve ( Torque limiting means) 42FL, 42FR, 42RL, 42RR Wheel speed sensor (wheel speed detecting means) 52 Controller ΔN _H , ΔN _{H (n)} First control start set value (first start reference value) ΔN _L Second control Start set value (second start reference value) ΔMV Front-rear wheel speed difference (rotational speed difference) Vc Estimated vehicle speed (vehicle speed)

Claims (5)

[Claims] 1. A drive axle driven by a prime mover,
A fluid pressure pump that rotates in conjunction with the drive axle, a fluid pressure motor that rotates in conjunction with a driven axle, and a first flow that connects the discharge port of the fluid pressure pump and the suction port of the fluid pressure motor. A passage, a second flow path communicating the suction port of the fluid pressure pump and the discharge port of the fluid pressure motor, and when the discharge amount of the fluid pressure pump exceeds the suction amount of the fluid pressure motor, A four-wheel drive vehicle including: a torque limiting unit that regulates a maximum discharge pressure of a working fluid flowing to a fluid pressure motor and sets a maximum value of a transmission torque to the driven axle side, the drive wheel being connected to the drive axle. And a wheel speed detecting means for detecting a wheel speed of a driven wheel connected to the driven axle, a vehicle speed detecting means for detecting a vehicle speed, and a rotational speed difference for detecting a rotational speed difference between the drive wheel and the driven wheel. For detecting means and the drive wheel The braking force and the driving force output from the main drive source to control the driving force, and the rotational speed difference detected by the rotational speed difference calculating means is equal to or greater than a predetermined start reference value. Control start setting means for starting control of the driving force control means when the four-wheel speed is reached based on the vehicle speed detected by the vehicle speed detecting means. The vehicle speed is set to a large first start reference value when the vehicle speed is a low speed that requires driving, and the first start reference value is set when the vehicle speed is a low speed or more that requires two-wheel driving. A four-wheel drive vehicle characterized by being set to a smaller second start reference value. 2. The first start reference value is set to a value equal to or larger than a predetermined rotational speed difference at which the torque transmitted to the driven wheels becomes maximum by the operation of the torque limiting means. The four-wheel drive vehicle described in 1. 3. The four-wheel drive vehicle according to claim 1, wherein the second start reference value is set to a rotational speed difference generated when the drive wheels spin the wheels during acceleration. 4. The first start reference value is set to gradually increase as the vehicle speed increases, based on the vehicle speed detected by the vehicle speed detecting means. The four-wheel drive vehicle according to any one of Items 1 to 3. 5. A drive axle driven by a prime mover,
A fluid pressure pump that rotates in conjunction with the drive axle, a fluid pressure motor that rotates in conjunction with a driven axle, and a first flow that connects the discharge port of the fluid pressure pump and the suction port of the fluid pressure motor. A passage, a second flow path communicating the suction port of the fluid pressure pump and the discharge port of the fluid pressure motor, and when the discharge amount of the fluid pressure pump exceeds the suction amount of the fluid pressure motor, A four-wheel drive vehicle including: a torque limiting unit that regulates a maximum discharge pressure of a working fluid flowing to a fluid pressure motor and sets a maximum value of a transmission torque to the driven axle side, the drive wheel being connected to the drive axle. And a wheel speed detecting means for detecting a wheel speed of a driven wheel connected to the driven axle, a vehicle speed detecting means for detecting a vehicle speed, and a rotational speed difference for detecting a rotational speed difference between the drive wheel and the driven wheel. For detecting means and the drive wheel The braking force and the driving force output from the main drive source to control the driving force, and the rotational speed difference detected by the rotational speed difference calculating means is equal to or greater than a predetermined start reference value. And a control start setting means for starting control of the driving force control means when
The start reference value of the control start setting means is set to a rotational speed difference generated when the drive wheels spin the wheels during acceleration, and the start reference value is set to two-wheel drive traveling based on the vehicle speed detecting means. A four-wheel drive vehicle characterized in that it is set only when the vehicle body speed is higher than medium speed, which requires