JP2003094971A - Front-rear wheel driving force distribution control device for hydraulically driven vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a front-rear wheel driving force distribution control device for a hydraulically driven vehicle capable of automatically changing from 2WD to 4WD according to a traveling condition without needing a complicated sensor. SOLUTION: The rotation of a travel motor 7 is transmitted to a tire 11f through a transmission 8, a propeller shaft 9 and an axle 10f. An electromagnetic clutch 30 provided on the rear side fluctuates clutch transmission torque according to the inputted voltage to distribute driving force to front and rear wheels 11f, 11r. The inlet pressure Pin and outlet pressure Pout of the travel motor 7 are detected, and the differential pressure is made motor effective pressure Pm and used for estimating the driving torque of the travel motor 7. When the motor effective pressure Pm exceeds a threshold P1, clutch transmission torque is generated, and front-rear wheel driving force distribution is controlled to perform four-wheel drive travel in a condition with large driving torque.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front / rear wheel drive force distribution control device for a hydraulically driven vehicle, such as a wheel shovel, for controlling drive torque distribution of front / rear wheels.

[0002]

2. Description of the Related Art As a device for controlling drive torque distribution between front and rear wheels, there is, for example, one disclosed in Japanese Patent Laid-Open No. 2000-343974. This drive force distribution control device is a drive force distribution control device for a four-wheel drive vehicle that uses front and rear left and right wheel rotation sensors, an accelerator opening sensor, and an engine rotation sensor, and based on the detection values detected by these sensors. The target transmission torque is set. Further, whether or not the driving torque is low is estimated from the accelerator opening detected by the accelerator opening sensor, and when the driving torque is low, the tight corner braking phenomenon ( During turning, control is performed so that the torque distribution ratio on the two-wheel drive side is set in an extremely low vehicle speed region where braking torque is easily generated in the direct drive system due to the difference in average turning radius between the front and rear wheels.

[0003]

However, in the driving force distribution control device as described above, since the torque distribution ratio transmitted to the front wheels and the rear wheels is controlled based on the detected values from various sensors, a complicated control is required. There is a problem that a sensor is needed.

It is an object of the present invention to provide a front / rear wheel driving force distribution control device for a hydraulically driven vehicle which does not require a complicated sensor and can be automatically switched from 2WD to 4WD according to the traveling situation.

[0005]

The present invention will be described with reference to FIGS. 2 and 3 showing an embodiment. (1) In the invention described in claim 1, the hydraulic motor 7 for driving the hydraulically driven vehicle, the hydraulic pump 2 for driving the hydraulic motor 7, the pressure detector 32 for detecting the motor effective pressure of the hydraulic motor 7, 33, a power transmission device 30 that transmits the driving force generated by the hydraulic motor 7 to the front wheels 11f and the rear wheels 11r of the hydraulic drive vehicle, and the power transmission device 30 to the front wheels 11f and the rear wheels 11r of the hydraulic drive vehicle. The above object is achieved by including a control circuit 31 that controls the driving force according to the effective motor pressure detected by the pressure detectors 32 and 33. (2) The invention of claim 2 is the front-rear wheel driving force distribution control device for a hydraulically driven vehicle according to claim 1, comprising a control circuit 31.
Is characterized in that the power transmission device 30 is controlled so that the difference between the driving forces transmitted to the front wheels 11f and the rear wheels 11r becomes smaller as the motor effective pressure becomes higher. (3) The invention of claim 3 is the control circuit 31 for a front-rear wheel drive force distribution control device for a hydraulically driven vehicle according to claim 2.
When the motor effective pressure exceeds a threshold value, the power transmission device 30 reduces the difference in driving force transmitted to the front wheels 11f and the rear wheels 11r as the motor effective pressure increases.
It is characterized by controlling. (4) The invention according to claim 4 is the front-rear wheel drive force distribution control device for a hydraulically driven vehicle according to claim 1, further comprising a steering angle detector 35 for detecting a steering angle, and the control circuit 31A includes: The driving force transmitted to the front wheels 11f and the rear wheels 11r of the hydraulically driven vehicle by the power transmission device 30 is controlled based on the effective motor pressure and the steering angle detected by the steering angle detector 35. . (5) The invention according to claim 5 is the front-rear wheel drive force distribution control device for a hydraulically driven vehicle according to claim 4, comprising a control circuit 31.
A controls the power transmission device 30 such that the difference in driving force transmitted to the front wheels 11f and the rear wheels 11r becomes smaller as the motor effective pressure becomes higher, and the front steering wheel 11f and the rear wheels 11r become smaller as the steering angle becomes smaller. The power transmission device 30 is controlled so that the difference in driving force transmitted to the vehicle is reduced. (6) According to the invention of claim 6, in the front-rear wheel driving force distribution control device for a hydraulically driven vehicle according to claim 5, a control circuit 31 is provided.
When the motor effective pressure exceeds a threshold value, A controls the power transmission device 30 such that the difference in driving force transmitted to the front wheels 11f and the rear wheels 11r becomes smaller as the motor effective pressure becomes higher, and steering steering is performed. The power transmission device 30 is controlled so that the difference in driving force transmitted to the front wheels 11f and the rear wheels 11r becomes smaller as the steering angle becomes smaller from the maximum value to the threshold value. . (7) In the invention described in claim 7, the hydraulic motor 7 for driving the hydraulically driven vehicle, the hydraulic pump 2 for driving the hydraulic motor 7, the pressure detector 32 for detecting the effective motor pressure of the hydraulic motor 7, 33, a steering angle detector 35 that detects a steering angle, and a hydraulic motor 7 and a rear wheel 11r or a front wheel 11f provided between the hydraulic motor 7 and the hydraulic drive vehicle. Front wheel 11
f, the difference between the driving force transmitted to the front wheels 11f and the rear wheels 11r becomes smaller as the motor effective pressure detected by the power transmission device 30 transmitting to the rear wheels 11r and the pressure detectors 32 and 33 becomes higher. The power transmission device 30 is controlled, and the power transmission device 30 is controlled so that the smaller the steering angle detected by the steering angle detector 35, the smaller the difference between the driving forces transmitted to the front wheels 11f and the rear wheels 11r. By including the control circuit 31A, the above-described object is achieved. (8) The invention according to claim 8 is the front-rear wheel drive force distribution control device for a hydraulically driven vehicle according to claim 7, comprising: a control circuit 31;
When the motor effective pressure exceeds a threshold value, A controls the power transmission device 30 such that the difference in driving force transmitted to the front wheels 11f and the rear wheels 11r becomes smaller as the motor effective pressure becomes higher, and steering steering is performed. The power transmission device 30 is controlled so that the difference between the driving forces transmitted to the front wheels 11f and the rear wheels 11r becomes smaller as the steering angle becomes smaller from the maximum value to the threshold value. .

In the section of the means for solving the above-mentioned problems for explaining the structure of the present invention, the drawings of the embodiments of the invention are used for the sake of easy understanding of the present invention. It is not limited to this form.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment> An embodiment of a front / rear wheel driving force distribution control device for a hydraulically driven vehicle according to the present invention will be described with reference to the drawings. FIG. 1 is a side view (partially sectional view) of a wheel shovel equipped with a front and rear wheel drive force distribution control device according to the present invention.

As shown in FIG. 1, the wheel shovel is
The traveling body 101 and the traveling body 101 via the turning device 102
And a revolving structure 103 rotatably connected to the upper part of the. The revolving structure 103 includes a boom 104A and an arm 104.
B, a work front attachment 104 including a bucket 104C and a driver's cab 105 are provided. The traveling body 101 includes a chassis frame 107, a traveling hydraulic motor 7, a transmission 8, and a propeller shaft 9.
Also, tires 11f and 11r are provided, and the driving force from the propeller shaft 9 is transmitted to the tires 11f and 11r via the axles 10f and 10r.

FIG. 2 is a traveling hydraulic circuit diagram of a wheel hydraulic excavator to which the present invention is applied, and FIG. 3 is a schematic diagram of a drive system of a front and rear wheel drive force distribution control device for a hydraulically driven vehicle according to the present invention. Is. As shown in FIG. 2, the direction and flow rate of the discharge oil from the main pump 2 driven by the engine (motor) 1 are controlled by the control valve 3. The pressure oil whose direction and flow rate are controlled passes through the center joint 5 and is supplied to the traveling motor 7 through the counter balance valve 6. Traveling motor 7
Is rotated by the transmission 8 and transmitted to the tire 11f via the propeller shaft 9 and the front axle 10f. As a result, the front wheel drive type wheel hydraulic excavator runs. In the drive system for the wheel hydraulic excavator according to the embodiment of the present invention, an electromagnetic clutch is provided on the rear side to distribute the driving force to the rear wheels as well, which will be described later.

The transmission 8 is a well-known one having a planetary speed reduction mechanism composed of a sun gear, a planetary gear and a ring gear, and clutches CR1 and CR2 respectively provided on the sun gear side and the ring gear side thereof. The clutches CR1 and CR2 are brought into the engaged state by the biasing force of the springs, respectively, and are brought into the released state by the hydraulic pressure from the hydraulic pressure source 12 that acts against the spring force. Clutch CR1,
The hydraulic pressure acting on CR2 is controlled by driving the transmission control valve 30.

Transmission control valve 3
When a predetermined hydraulic pressure is applied to the clutch CR1 via the conduit 13 by driving 0, the clutch CR1 is released and the clutch CR2 is engaged. At this time, the predetermined gear ratio R
The value becomes 1, which enables low speed and high torque first speed running (Low range). Further, when a predetermined hydraulic pressure acts on the clutch CR2 via the pipe line 14, the clutch CR2 is disengaged, the clutch CR1 is engaged, and a predetermined gear ratio R2 (<
R1) and high speed and low torque 2nd speed running (Hi range)
Is possible. On the other hand, when hydraulic pressure does not act on either of the clutches CR1 and CR2, the clutches CR1 and C
Both R2 are brought into an engaged state by a spring force, the transmission 8 is locked, and the rotation of the propeller shaft 9 is blocked. The conduit 15 is a return conduit.

The traveling pilot circuit is the main pump 2
Similarly to the above, a pilot hydraulic power source 16 that is driven by the engine 1 to generate pressure oil, a traveling pilot valve 18 that generates a secondary pilot pressure in response to depression of an accelerator pedal 17, and a pilot valve that follows the pilot valve 18 It has a slow return valve 19 for delaying the return oil to 18, and a forward / reverse switching valve 20 connected to the slow return valve 19 for selecting forward, reverse or neutral of the vehicle. The forward / reverse switching valve 20 is the operation lever 2
It is switched by the operation of 1. Pilot hydraulic power source 1
The pilot pressure from 6 acts on the pilot port of the control valve 3 to drive the control valve 3. The valve stroke amount at this time is the accelerator pedal 1
The traveling speed of the vehicle can be adjusted by adjusting with 7.

FIG. 3 is a schematic diagram of a drive system according to an embodiment of the present invention. As shown in the schematic diagram of FIG. 3, the drive system according to the present embodiment is a front wheel drive (FWD) -based four-wheel drive (4
This is a so-called torque split type 4WD drive system that changes the torque distribution ratio to the front and rear wheels in the WD system.

Conventionally, in a hydraulically driven vehicle such as a wheel shovel, a drive system in which four wheels are always driven in a working mode and two wheels are always driven in a traveling mode, or two wheels driving and four wheels driving are manually operated while stopped. There is something to switch. However, if two-wheel drive is always used in the running mode, it is impossible to switch to four-wheel drive to prevent slippage on a low-friction road such as a snowy road. Further, two-wheel drive and four-wheel drive are manually switched. Since the objects are manually switched while the vehicle is stopped, there is a problem that the operation is troublesome. Therefore, in this embodiment, 2
A front-wheel drive-based four-wheel drive system is used to provide a front-rear-wheel drive force distribution control device for a hydraulically driven vehicle that can automatically switch from four-wheel drive to four-wheel drive.

The driving torque from the traveling motor is finally transmitted as a frictional force generated between the tire and the road surface.
The driving force per wheel transmitted from the traveling motor to each tire is about twice as large as that of the four-wheel drive in the two-wheel drive. This is because the driving force transmitted from the traveling motor to the tires is transmitted to the front wheels and the rear wheels in the case of four-wheel drive, but is transmitted only to the front wheels or the rear wheels in the case of two-wheel drive. The driving frictional force of the tire is represented by the product of the vertical load of the tire and the coefficient of sliding friction. Therefore, the driving frictional force of the tire becomes small on a snowy and snowy road having a small sliding friction coefficient or on a wet steel plate, and the driving force of the traveling motor exceeds the driving frictional force of the tire and the driving wheels slip. Therefore, in consideration of traveling on a low friction road, the vehicle is driven by four-wheel drive when the vehicle starts with a large driving torque.

Here, the tight corner braking phenomenon which is a problem of the four-wheel drive vehicle will be described. The tight corner braking phenomenon is a phenomenon in which it becomes difficult to run as if the brake was applied because the turning radii of the front wheels and the rear wheels are different when turning a small corner. Since the turning radius of the front wheels becomes larger than the turning radius of the rear wheels when turning at a low speed, the front wheels must rotate faster than the rear wheels to make a smooth turn. However, in the case of the direct connection 4WD, since the rotation difference between the front and rear wheels is always 0, the rotation of the front and rear wheels interferes with each other, and the brake is applied. The tight corner braking phenomenon becomes more prominent on a high friction road such as a dry asphalt road surface as the front wheel steering angle increases. Therefore, when turning left or right on a narrow alley with a high friction road, the driving force may stop due to insufficient driving force in the Hi range. On the other hand, during high-speed turning, the centrifugal force creates a slip angle between the direction of travel of the tire and the direction of speed at the tire contact surface, reducing the difference in the turning radii between the front and rear wheels. Get smaller.

Therefore, in the front and rear wheel drive force distribution control device according to the present invention, torque distribution to the front and rear wheels from two-wheel drive to direct-coupled four-wheel drive is controlled, and during steady running or when tight running without a large drive torque. During full steering where the corner braking phenomenon is likely to occur, front wheel drive (FWD) is used to prevent interference between the rotation of the front and rear wheels. Then, in order to obtain the driving frictional force only in a situation where a large driving torque is required, four-wheel drive (4WD) is adopted. In the case of direct connection 4WD, the drive torque is always distributed to the front and rear wheels, and the torque distribution ratio of the front and rear wheels at this time is substantially equal to the front and rear wheel load distribution ratio.

The motor driving force from the traveling motor 7 is directly transmitted to the front wheels 11f, and the electromagnetic clutch 3 is supplied to the rear wheels 11r.
The motor driving force is transmitted via 0. Therefore, the transmission torque of the clutch is changed by controlling the voltage supplied to the electromagnetic clutch 30, and the torque distribution between the front wheels 11f and the rear wheels 11r is controlled.

As described above, there are optimum drive systems depending on the traveling conditions. Below, the optimum drive system and clutch engagement state depending on the running situation are shown and used as a guide for drive torque distribution setting and clutch control. (1) Straight acceleration: (4WD) clutch directly connected (2) Turning acceleration: (4WD) clutch directly connected (3) Straight braking: (2WD) clutch released (4) Turning braking: (2WD) clutch released

Here, (1) When accelerating straight ahead, the clutch is directly connected to secure the driving frictional force of the tire, and the direct connection is 4WD.
And (2) At the time of turning acceleration, the clutch is directly connected so that the drive force is optimally distributed regardless of the slip friction coefficient of the road surface. When the driving force distribution for the front wheels is increased, the under-steering tends to increase as the speed increases, and when the driving force distribution for the rear wheels increases, the over-steering tends to decrease as the turning radius decreases. Even when the same driving force is distributed to the front and rear wheels, the load is applied to the rear of the normal during acceleration, so there is a tendency for understeer or oversteer depending on the coefficient of sliding friction on the road surface. In the direct connection 4WD, the driving force distribution changes depending on the load distribution on the front and rear wheels, so the driving force distribution to the rear wheels becomes large during acceleration when the load is applied to the rear of the vehicle, and it is optimal for the front and rear wheels regardless of the slip friction coefficient of the road It is possible to perform various driving force distributions.

(3) At the time of straight-ahead braking, the clutch is opened to prevent the front and rear wheels from being directly connected in order to prevent simultaneous locking of the four wheels.
(4) During turning braking, release the clutch to disconnect the front and rear wheels directly. In direct connection 4WD, the braking force distribution to the front and rear wheels is always equal to the dynamic load distribution, and during turning braking, the load tends to be applied earlier than usual and oversteering tends to occur. Remove.

As a traveling situation other than the above (1) to (4), in the case where the vehicle is traveling at a constant speed both during straight traveling and during turning and the driving force is small, in order to prevent a slight rotation interference between the front and rear wheels. Release the clutch. When the front wheel steering angle is increased to make a large turn, the clutch is opened to prevent the above-described tight corner braking phenomenon from occurring. Control during a large turn will be described in the second embodiment.

The transmission torque of the clutch is set on the basis of the optimum clutch engagement state according to the running condition described above. The greater the driving torque during acceleration or the like, the closer the torque is to the direct connection 4WD so that the driving frictional force of the tire is not exceeded and slippage occurs. Therefore, the transmission torque of the clutch is increased. Also, when the driving torque is small, such as when driving at a constant speed, the transmission torque of the clutch is reduced to approach 2WD in order to prevent interference of the rotation of the front and rear wheels, and when braking, all wheels are locked simultaneously when sudden braking is performed. Disengage the clutch to prevent

In the first embodiment, the drive torque distribution of the front and rear wheels is controlled by paying attention to the change in the drive torque of the traveling motor due to acceleration / deceleration or the like. Therefore, the transmission torque of the clutch is changed according to the drive torque of the traveling motor.
The drive motor drive torque estimation will be described below.

In order to estimate the drive torque of the traveling motor 7, the pressure of the traveling motor 7 is used in this embodiment. For the estimation of the driving torque of the wheel shovel, the pilot pressure by the traveling pedal 17 can be used. However, the operation of the travel pedal 17 is for controlling the flow rate to the travel motor 7. For example, even with a full pedal, the drive torque is not always high. It will be used for.

As shown in FIG. 2, the pressure sensor 3 is provided on the circuit.
2 and 33 are attached to detect the inlet pressure Pin and the outlet pressure Pout of the traveling motor 7. Inlet pressure Pin and outlet pressure P
The differential pressure of out is set as the motor effective pressure Pm. Here, when the outlet pressure Pout of the traveling motor 7 is higher than the inlet pressure Pin (Pout> Pin), the effective motor pressure Pm is regarded as 0 and the control is performed in order to open the clutch because braking is being performed. FIG. 4 shows the configuration of the clutch control system.

Signals from the pressure sensor 32 for detecting the inlet pressure Pin of the traveling motor 7 and the pressure sensor 33 for detecting the outlet pressure Pout of the traveling motor 7 are input to the control circuit 31. In the control circuit 31, the input motor inlet pressure P
The motor effective pressure Pm is calculated from in and the outlet pressure Pout, and the voltage supplied to the electromagnetic clutch 30 is calculated according to the motor effective pressure Pm. The electromagnetic clutch 30 is a clutch formed by magnetic coupling between conductors, and the dynamic friction torque transmitted by the friction surface of the clutch fluctuates according to the voltage supplied from the control circuit 31, so that the torque distribution ratio of the front and rear wheels is 100. %
It is possible to change from the FWD (front wheel drive) state to the direct connection 4WD. That is, when the voltage increases, the clutch transmission torque also increases to approach 4WD, while when the voltage decreases, the clutch transmission torque also decreases to approach 2WD, and the drive torque distribution control can be performed.

FIG. 5 shows the relationship between the motor effective pressure Pm and the clutch transmission torque Tm. The vertical axis of FIG. 5 indicates the clutch transmission torque Tm, and the clutch transmission torque Tm increases and approaches 4WD. The horizontal axis represents the motor effective pressure Pm, and the clutch transmission torque Tm is generated when the threshold value P1 is exceeded. It is possible to drive enough even with 2WD when the driving force is small,
Since 2WD is more effective for improving fuel economy, it is set to perform 2WD traveling when the motor effective pressure Pm is low.

The control circuit 31 calculates the voltage V supplied to the electromagnetic torque 30 so as to satisfy the relationship between the motor effective pressure Pm and the clutch transmission torque Tm shown in FIG. The electromagnetic torque 30 changes the dynamic friction torque according to the input voltage V, and thereby the front and rear wheel drive torque control is performed.

The above-mentioned threshold value P1 is set from the relationship between the pressure P of the pump 2 for driving the traveling motor 7 shown in FIG. 6 and the discharge flow rate Q. Here, the rotation speed of the pump 2 is constant. As can be seen from the PQ diagram of FIG. 6, when the pump pressure P further exceeds P1 and further rises, the pump flow rate Q, which was limited to a constant flow rate, gradually decreases (P × Q).
= Constant). Therefore, the pressure range higher than the pressure P1 is regarded as the high torque range of the traveling motor 7, and the pressure P1 is set as the threshold value of the motor effective pressure Pm shown in FIG. By generating the clutch transmission torque Tm after the effective motor pressure Pm exceeds the threshold value P1 in this way, 2WD traveling is performed as much as possible in a situation where the driving torque is not strong, and the effective motor pressure Pm rises to drive. It is only possible to run 4WD when the torque is high.

As described above, by setting the clutch transmission torque according to the effective motor pressure, it is possible to control so that 2WD traveling is performed when the driving torque is small and 4WD traveling when the driving torque is large. it can.
Further, since the effective pressure of the motor is calculated by detecting the inlet pressure and the outlet pressure of the traveling motor, a pressure sensor is sufficient for estimating the drive torque, and other complicated and expensive sensors are not necessary.

When the drive torque is estimated from the wheel rotation sensor or the accelerator opening sensor, the drive torque is estimated by detecting that the wheel actually slips. for that reason,
After the slip actually occurs, the transmission torque is changed to switch to 4WD. On the other hand, the front / rear wheel drive force distribution control device according to the present invention estimates the drive torque from the motor effective pressure, and therefore can switch to 4WD at an early point. For example, the wheels tend to slip when the vehicle starts on a low friction road, but the driving force that the drive device tries to output at the time of starting can be estimated by checking the motor effective pressure. Therefore, it is possible to obtain a drive torque sufficient for traveling by switching to 4WD before the wheels slip.

Further, since the switching from 2WD to 4WD is automatically performed according to the traveling condition, there is no need for the troublesome operation of manually switching while the vehicle is stopped.

<< Second Embodiment >> A front / rear wheel driving force distribution control device for a hydraulically driven vehicle according to a second embodiment focuses on steering, and at a large steering angle at which a tight corner braking phenomenon remarkably appears. The driving force distribution control is performed. The basic structure of the drive system is the first structure shown in FIG.
It is similar to that according to the embodiment. In the second embodiment of the front / rear wheel drive force distribution device for a hydraulically driven vehicle according to the present invention, the drive torque of the traveling motor is estimated from the motor effective pressure, and the steering angle is detected to determine the drive torque and the steering angle. The clutch transmission torque is calculated to control the front / rear wheel driving force distribution.

As described above, the tight corner braking phenomenon is caused by the difference in turning radius between the front wheels and the rear wheels.
The larger the steering angle, the larger the difference between the turning radii of the front and rear wheels. On the other hand, when the vehicle speed increases, a slip angle is generated in the speed direction on the tire contact surface, and the turning center changes, so that the difference in turning radius becomes small. In other words, the tight corner braking phenomenon has a great influence on the driving at a low speed and a large steering angle. In addition, giving a large steering angle during high-speed driving is an extremely rare case such as emergency avoidance, and it is determined that low-speed traveling is performed while turning at a large steering angle, and the traveling situation of high-speed full steering is excluded. Therefore, control is performed such that the clutch is released when the steering angle is large, regardless of the vehicle speed. As a result, the clutch control relating to the steering angle can be performed without attaching the vehicle speed sensor.

FIG. 7 shows the structure of the clutch control system according to the second embodiment. Not only the signals from the pressure sensors 32 and 33 but also the signal from the steering angle sensor 35 are input to the control circuit 31A. The control circuit 31A calculates the voltage supplied to the electromagnetic clutch 30 based on the signals input from the respective sensors. The method of calculating the voltage will be described later.

In the second embodiment, a direct displacement sensor that measures the stroke of a steering cylinder (not shown) that transmits steering steering to the front wheels is used as the steering angle sensor. The output voltage of this sensor increases as the steering angle increases, and the maximum voltage is output at full steering. The control circuit 31A directly calculates the steering angle θ from the output voltage of the displacement sensor. In addition,
A sensor that directly detects the steering rotation angle may be used to detect the steering angle θ.

FIG. 8 shows the relationship between the steering angle θ and the clutch transmission torque Ts. The vertical axis represents the clutch transmission torque Ts, and the horizontal axis represents the steering angle θ. The steering steering angle θ indicates a steering angle where the neutral position of the steering wheel is 0 regardless of the left steering or the right steering.

Here, the steering angle θm which is about half of the full steering θf is set as a threshold value, and the steering angle θm or more is set as the large steering angle region. From the neutral position 0 to the steering angle θm, it is determined that the steering angle is small and there is almost no influence of the tight corner braking phenomenon, and the direct transmission 4WD traveling is performed while the clutch transmission torque Ts remains at the maximum. When the vehicle enters the large steering angle region beyond the steering angle θm, the clutch transmission torque Ts is gradually reduced to approach 2WD traveling in order to prevent the tight corner braking phenomenon. As shown in FIG. 8, when the steering angle θ reaches the full-steer θf, the clutch transmission torque Ts becomes 0 and the vehicle travels in 2WD.

In the control circuit 31A, the relationship between the motor effective pressure Pm shown in FIG. 5 and the clutch transmission torque Tm used in the first embodiment, and the steering angle θ and the clutch transmission pressure Ts shown in FIG. From the relationship with electromagnetic torque 3
Calculate the voltage supplied to 0.

Regarding the motor effective pressure Pm, the pressure P1
After that, the clutch voltage Vm is increased according to the increase in pressure. Regarding the steering angle θ, the clutch voltage Vs is lowered in accordance with the increase of the steering angle after entering the large steering angle region of the steering angle θm or more. Figure 9 shows these relationships.
Shown in (a) and (b). The pressure P1 and the steering angle θm are the same values as the pressure P1 and the steering angle θm shown in FIGS. The voltage V finally supplied to the electromagnetic clutch 30 is

## EQU1 ## V = V1 × Vm × Vs (Equation 1) 0 <Vm <1 0 <Vs <1 where V1 is the direct connection with the maximum clutch transmission torque.
It is a voltage necessary for setting WD.

The voltage V calculated by (Equation 1) is supplied to the electromagnetic clutch 30, and the electromagnetic clutch 30 controls the torque distribution ratio between the front and rear wheels by changing the dynamic friction torque according to the input voltage V.

As described above, in the second embodiment, in order to control the clutch transmission torque, in addition to the running motor effective pressure, the steering steering angle is used as a parameter to automatically switch from 4WD to 2WD at a large steering angle. I did it. As a result, in addition to the effects described above, it is possible to reduce the influence of the tight corner braking phenomenon that the vehicle stops at the time of a large turn at a low speed. Also,
Since the clutch transmission torque is controlled based on the motor effective pressure, that is, the drive torque and the steering angle, the drive torque distribution can be controlled more finely according to the traveling condition of the vehicle.

In the embodiment of the present invention, the four-wheel drive system based on the front wheel drive is explained.
It may be a rear wheel drive base. In this case, the electromagnetic clutch is attached to the front side. However, it is preferable to use the front wheel drive base in consideration of the mounting position of the electromagnetic clutch and the running stability. Further, the clutch for transmitting the driving torque is 2WD and 4WD if the clutch transmitting torque is changed according to the effective motor pressure.
It is also possible to use an on / off clutch that switches the switches all at once. Also, a hydraulic clutch can be used.

In the above embodiment, the clutch transmission torque is changed after the motor effective pressure exceeds the threshold value. However, as shown by the broken line in FIG. 5, the motor effective pressure gradually increases. Alternatively, the clutch transmission torque may be increased. Similarly, as shown by the broken line in FIG. 8, the clutch transmission torque can be gradually increased as the steering angle becomes smaller.

[0046]

As described above, since the front and rear wheel drive force distribution control device for a hydraulically driven vehicle according to the present invention performs drive torque distribution control according to the drive torque of the traveling motor estimated by the motor effective pressure, it is complicated. It is possible to estimate the driving torque without using various sensors. Further, since the steering angle is detected and switched from 4WD to 2WD when the steering angle is large, the influence of the tight corner braking phenomenon can be reduced. Since the drive torque distribution of the front and rear wheels is controlled according to the motor effective pressure and the steering angle, it is possible to grasp the traveling situation in detail and perform the control according to it.

[Brief description of drawings]

FIG. 1 is a side view of a wheel shovel equipped with a front and rear wheel drive force distribution control device for a hydraulically driven vehicle according to an embodiment of the present invention.

FIG. 2 is a traveling hydraulic circuit diagram of the wheel hydraulic excavator of FIG.

FIG. 3 is a schematic diagram of a drive system of a front and rear wheel drive force distribution control device for a hydraulically driven vehicle according to an embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a clutch control system according to the first embodiment of the present invention.

FIG. 5: Effective motor pressure Pm and clutch transmission torque T
The figure which shows the relationship with m.

FIG. 6 is a diagram showing a relationship between a pump pressure P and a pump flow rate Q.

FIG. 7 is a diagram showing a configuration of a clutch control system according to a second embodiment of the present invention.

FIG. 8 is a diagram showing a relationship between a steering angle θ and a clutch transmission torque Ts.

9A and 9B are views showing clutch control for an effective motor pressure Pm and clutch control for a steering angle θ, respectively.

[Explanation of symbols]

1: Engine 2: Main pump 3: Control valve 7: Travel motor 8: Transmission 9: Propeller shaft 10f, 10r: Axle 11f, 11r: tires 30: Electromagnetic clutch 31, 31A: control circuit 32, 33: Pressure sensor 35: Steering angle sensor 101: running body 102: Revolving structure 104: Front attachment 105: Driver's cab

Claims (8)

[Claims] 1. A hydraulic motor that drives a hydraulically driven vehicle, a hydraulic pump that drives the hydraulic motor, a pressure detector that detects a motor effective pressure of the hydraulic motor, and a driving force generated by the hydraulic motor. A power transmission device for transmitting to front wheels and rear wheels of a hydraulically driven vehicle, and the driving force transmitted to the front wheels and rear wheels of the hydraulically driven vehicle by the power transmission device to a motor effective pressure detected by the pressure detector. A front and rear wheel drive force distribution control device for a hydraulically driven vehicle, comprising: 2. The front / rear wheel drive force distribution control device for a hydraulically driven vehicle according to claim 1, wherein the control circuit increases the motor effective pressure.
A front / rear wheel drive force distribution control device for a hydraulically driven vehicle, characterized in that the power transmission device is controlled so as to reduce the difference in drive force transmitted to the front wheels and the rear wheels. 3. The front-rear wheel drive force distribution control device for a hydraulically driven vehicle according to claim 2, wherein the control circuit increases the motor effective pressure when the motor effective pressure exceeds a threshold value. A front / rear wheel drive force distribution control device for a hydraulically driven vehicle, characterized in that the power transmission device is controlled so as to reduce the difference in drive force transmitted to the rear wheels. 4. The front / rear wheel drive force distribution control device for a hydraulically driven vehicle according to claim 1, further comprising a steering angle detector for detecting a steering angle, wherein the control circuit includes the motor effective pressure and the motor effective pressure. The front and rear of the hydraulically driven vehicle characterized in that the driving force transmitted to the front wheels and rear wheels of the hydraulically driven vehicle is controlled by the power transmission device based on the steering angle detected by the steering angle detector. Wheel drive force distribution control device. 5. The front / rear wheel drive force distribution control device for a hydraulically driven vehicle according to claim 4, wherein the control circuit increases the motor effective pressure.
The power transmission device is controlled so that the difference between the driving forces transmitted to the front wheels and the rear wheels is reduced, and the difference between the driving forces transmitted to the front wheels and the rear wheels is reduced as the steering angle is reduced. A front and rear wheel drive force distribution control device for a hydraulically driven vehicle, characterized in that the power transmission device is controlled. 6. The front / rear wheel drive force distribution control device for a hydraulically driven vehicle according to claim 5, wherein the control circuit increases the motor effective pressure when the motor effective pressure exceeds a threshold value. And the power transmission device is controlled so that the difference between the driving forces transmitted to the rear wheels becomes small, and until the steering steering angle reaches the threshold value from the maximum value, as the steering steering angle becomes smaller, the front wheels and the rear wheels become smaller. A front / rear wheel driving force distribution control device for a hydraulically driven vehicle, characterized in that the power transmission device is controlled so that a difference in driving force transmitted to the wheels becomes small. 7. A hydraulic motor for driving a hydraulically driven vehicle, a hydraulic pump for driving the hydraulic motor, a pressure detector for detecting a motor effective pressure of the hydraulic motor, and a steering angle detector for detecting a steering angle. A power transmission device that is provided between the hydraulic motor and a rear wheel or a front wheel of the hydraulic drive vehicle, and that transmits a driving force generated by the hydraulic motor to the front wheel and the rear wheel of the hydraulic drive vehicle; The steering system detects the steering angle by controlling the power transmission device such that the difference between the driving forces transmitted to the front wheels and the rear wheels decreases as the effective motor pressure detected by the detector increases. And a control circuit for controlling the power transmission device so that the difference between the driving forces transmitted to the front wheels and the rear wheels becomes smaller as the angle becomes smaller. Front-rear wheel driving force distribution control device for moving the vehicle. 8. The front / rear wheel drive force distribution control device for a hydraulically driven vehicle according to claim 7, wherein the control circuit increases the motor effective pressure when the motor effective pressure exceeds a threshold value. And the power transmission device is controlled so that the difference between the driving forces transmitted to the rear wheels becomes small, and until the steering steering angle reaches the threshold value from the maximum value, as the steering steering angle becomes smaller, the front wheels and the rear wheels become smaller. A front / rear wheel driving force distribution control device for a hydraulically driven vehicle, characterized in that the power transmission device is controlled so that a difference in driving force transmitted to the wheels becomes small.