JPS63207761A - Power transmission method for part time type four-wheel-drive automobile provided with anti-skid device - Google Patents

Abstract

PURPOSE:To aim at enhancing both brake performance and anti-skid performance by variably controlling the coupling condition of a transfer clutch for changing over between the two wheel drive mode and the four wheel drive mode, in accordance with operation of an anti-skid device. CONSTITUTION:An anti-skid control unit 1 measures the friction coefficient of the surface of a road on the basis of a signal from a wheel speed sensor 3 during braking operation during which a brake switch 2 delivers a signal, and delivers a signal having the duty ratio which varies from 0 to infinite in accordance with increases in the coefficient, to a rectifier 9. Meanwhile a hydraulic transfer clutch 5 is fed with a source pressure Pa direct from a hydraulic pump 6. A transfer valve 7 for variably controlling the hydraulic passage from the hydraulic pump 6 to a drain in proportion to a voltage applied to a solenoid 7a is disposed downstream of the transfer clutch 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for controlling the power transmission of a part-time four-wheel drive vehicle with an anti-skid device.

In conventional hydraulic braking systems for automobiles, if the width of the vehicle suddenly locks and slips during sudden braking while the vehicle is running, the vehicle loses its ability to maintain direction, which is extremely dangerous.

Therefore, in order to prevent this kind of danger, during braking, when brake fluid pressure is supplied to the wheel cylinders by braking operation, the brake fluid pressure to the wheel cylinders is adjusted depending on the rate of decrease in wheel speed and the amount of decrease in wheel speed relative to the vehicle body speed. After the brake fluid pressure in the wheel cylinder is released, the wheel speed recovers due to road reaction force and approaches the vehicle speed, and then the brake is applied again in the wheel cylinder. Various brake hydraulic pressure control devices (i.e., anti-skid devices) have been developed in the past, which repeatedly repeat a control pattern of supplying (pressurizing) hydraulic pressure to perform effective braking. It is published in the official gazette.

Furthermore, a part-time four-wheel drive vehicle capable of switching between two-wheel drive and four-wheel drive has been developed in the past (see, for example, Japanese Utility Model Application Publication No. 55-54573) and is already in general use.

Part-time four-wheel drive vehicles such as those mentioned above are usually equipped with a transfer clutch in one of the two power transmission systems that transmit power from the output shaft of the power unit to the front wheels and the rear wheels, respectively. Operate the select lever or turn on the 4-wheel drive select switch.

Usually, switching between two-wheel drive and four-wheel drive is performed by controlling the transfer clutch by turning it off or the like.

Problems to be Solved by the Invention In a part-time four-wheel drive vehicle equipped with an anti-skid device as described above, when switching to the four-wheel drive side, the front and rear drive shafts are directly connected, so the sum of the rotation speeds of the left and right front wheels increases. and the sum of the rotational speeds of the left and right rear wheels must be satisfied. For example, if the friction coefficient of one wheel on the road surface is lower than that of other wheels, In this case, an internal circulating torque is generated which is influenced by the opposite wheel, and this internal circulating torque disturbs the timing of the anti-skid operation of each wheel.

Such a problem does not have much of an effect on a road surface with a high overall height, but on a road surface with a low height, the timing phase difference becomes large and the anti-skid function is significantly impaired.

The influence of internal circulation torque on anti-skid operation as described above can be eliminated by disengaging the transfer clutch during anti-skid operation, but under driving conditions where the influence of unidirectional partial circulation torque is relatively small, for example. Even when driving on a high road, the system switches to the two-wheel drive side when anti-skid is activated, and there is a problem in that the advantage of brake force distribution correction, which the four-wheel drive system has, cannot be fully utilized.

The present invention aims to address such problems.

Means for Solving the Problems The present invention releases the hydraulic pressure of the brake device when the wheel speed decreases due to an increase in brake hydraulic pressure caused by hydraulic pressure supply during braking operation, and prevents the wheel speed from recovering due to road reaction force. In a part-time 4-wheel drive vehicle equipped with an anti-skid control unit that employs a control method that repeats a brake fluid pressure control pattern in which the brake system is pressurized once again, 2-wheel drive and 4-wheel drive
A transfer clutch that switches wheel drive is configured to be able to maintain its engaged state in any state between disengaged and fully engaged, and the engaged state of the transfer clutch is changed from anti-skid to anti-skid when anti-skid operation is performed. This system is characterized by variable control according to information from the skid control unit.

Effect As described above, when driving on a low route that is susceptible to the influence of internal circulation torque when anti-skid is activated, the transfer clutch is in a state close to disengagement even if it is switched to the 4-wheel drive side, reducing the influence of internal circulation torque on anti-skid operation. When driving on rough roads, the transfer clutch is fully engaged or close to fully engaged, and braking force distribution correction is fully utilized to improve braking performance. control to,
As a result, anti-skid controllability can be improved by f.

Furthermore, the transfer clutch can be arbitrarily changed from a state close to fully engaged to a state close to disengaged, and this state change (or rate of change) can be changed suddenly or gradually depending on the situation, making it possible to It is also possible to flexibly respond to changes in vehicle running characteristics caused by a change from a state close to drive to a state close to two-wheel drive.

Example The present invention will be explained with reference to the accompanying drawings.

In FIG. 1, 1 is an anti-skid control unit; 2 is an anti-skid control unit;
is a brake switch that issues a braking signal when the brake pedal is depressed; 3 is a wheel speed sensor that detects the wheel speed and issues a wheel speed signal; 4 is an actuator that is installed in the brake fluid pressure piping system and controls the brake fluid pressure; In the anti-skid F control 2Js unit 1, when the brake pedal is depressed and the mask cylinder is activated, hydraulic pressure is supplied from the mask cylinder to the wheel cylinder of each wheel, and the wheel speed is reduced relative to the vehicle body speed. When the wheel speed decreases to a certain value (or when the rate of decrease in wheel speed reaches a certain value), actuator 4 installed in the brake hydraulic piping system is activated to issue a pressure reduction signal to reduce the pressure in the wheel cylinder and maintain the reduced pressure. When the wheel speed recovers due to the road reaction force, the actuator 4 is actuated to issue a pressurization signal to supply hydraulic pressure to the wheel cylinder and generate braking force again. It issues a brake fluid pressure control command to obtain accurate vehicle deceleration using a control pattern that repeats pressurization and depressurization, and the control mode of the anti-skid control unit described above is conventionally known as described above. It is.

In the known control mode of the anti-skid control unit as described above, when a braking torque is applied in a direction to stop the rotation of the wheel by supplying hydraulic pressure to the wheel cylinder, that is, pressurizing the wheel cylinder, the braking torque is applied to the wheel due to a road reaction force. A rotational torque in the opposite direction acts, and the anti-skid control unit controls the braking torque by emitting an increase/decrease pressure signal so that the wheels do not lock beyond the limit of the road reaction force (i.e., road friction force). This prevents the wheels from locking and ensures direction maintenance during braking.

However, on low road roads, the above road reaction force decreases, and when the brake pedal is depressed and hydraulic pressure is supplied from the mask cylinder to the wheel cylinder, the slight hydraulic pressure (braking force) causes the wheels to lock, causing anti-skid control. Even if the hydraulic pressure in the wheel cylinders is reduced by a command from the anti-skid control unit 1, the wheel speed does not recover easily, and the reduced pressure state continues for a long time. When pressure is applied, even if it is the minimum pressure, it will create a large braking force on the road surface, resulting in an excessive slip ratio and resulting in poor vehicle stability and an inability to steer. This has a particularly significant effect when internal circulation torque is likely to occur, such as when the vehicle is switched to four-wheel drive. In order to eliminate the influence of such internal circulation torque on the anti-skid operation, the transfer clutch may be disengaged at all times during the anti-skid operation and the switch can be made to the two-wheel drive side. This results in deterioration of wheel recovery performance and the loss of the advantage of braking force distribution correction for four-wheel drive on high-road roads.

Therefore, in the present invention, the transfer clutch that switches between two-wheel drive and four-wheel drive in a part-time four-wheel drive vehicle equipped with an anti-skid control unit is maintained in an arbitrary state between disengaged and fully engaged. and the engagement state of the transfer clutch is
The present invention is characterized in that when the anti-skid operation is performed, variable control is performed according to information from the anti-skid control unit.

That is, the hydraulic transfer clutch 5 is directly connected to the source line pressure Pa by the hydraulic pump 6 which is the source of the working hydraulic pressure.
is supplied to the downstream side of the hydraulic transfer clutch 5, and the hydraulic passage leading from the hydraulic pump 6 to the drain can be variably controlled from a fully closed state to a fully open state in proportion to the solenoid voltage applied to the solenoid 7a. A solenoid type transfer valve 7 is provided.

1 Valve body 7 of solenoid type transfer valve 7
b assumes the position shown in FIG. 1 when the solenoid 7a is energized, and the hydraulic passage is completely closed, so that the source line pressure Pa supplied from the hydraulic pump 6 remains unchanged and is applied to the hydraulic transfer clutch 5. The torque transmission capacity of the transfer clutch 5 is strengthened, and the drive is switched to the four-wheel drive side.

Further, as the duty ratio of the solenoid voltage applied to the solenoid 7a decreases, the electromagnetic force of the solenoid 7a gradually decreases, the pulp body 7b gradually moves to the right in FIG. 1, and the opening area of the hydraulic passage leading to the drain gradually increases. As the opening area of the hydraulic passage becomes larger, the transfer clutch line pressure Pt applied to the hydraulic transfer clutch 5 gradually decreases, and the coupling force between the front and rear axles is weakened, resulting in a state similar to two-wheel drive. Note that the amount of decrease in the transfer clutch line pressure Pt from the source line pressure Pa to the drain pressure Pd may be considered to be inversely proportional to the solenoid voltage applied to the solenoid.

Note that 8 is a relief valve that operates with a predetermined oil pressure.

The solenoid 7a is connected via a rectifier 9 to a duty ratio (
emit an output signal in which m=b/a) is (1), and emit an output signal having a duty ratio that increases in proportion to the coefficient of road friction when the anti-skid operation is performed during four-wheel drive. Anti-skid control unit 1 configured as follows
connected to. Reference numeral 11 denotes a drain that stores oil that serves as a power transmission element of the automatic hydraulic transmission.

That is, the anti-skid control unit 1 calculates, for example, the rate of decrease in wheel speed relative to the brake fluid pressure (or the wheel cylinder fluid The road surface lL (road surface friction coefficient) is measured based on the wheel speed recovery time when the pressure is reduced, and the duty ratio (m=b/a) is measured according to the increase in the road surface friction coefficient.
) changes in the range from O to (1) to the rectifier 9.
It is configured to supply

As shown in Figure 1, the duty ratio m is expressed as the ratio of the on time to the off time a of the output signal, where 0 means the voltage is zero and (1) means the voltage equal to the power supply voltage. It shows.

The solenoid voltage rectified by the rectifier 9 and supplied to the solenoid 7a has a duty ratio m as shown in FIG.
It can be seen that it is approximately proportional to , so on low-grade roads where the coefficient of road friction is low, the solenoid voltage is almost zero and the transfer clutch 5 is close to the disconnected state, so even in 4-wheel drive, the internal circulating torque does not affect the anti-skid operation. This can be improved to the extent that the recovery speed of the wheels, where the moment of inertia shared by the wheels is large, is not deteriorated while minimizing the impact.On high road roads where the negative influence of internal circulation torque is small, the solenoid voltage is almost equal to the power supply voltage, and the solenoid voltage is almost equal to the power supply voltage. The driving state can be maintained even when anti-skid is activated.
The advantages of wheel drive can be preserved.

In the above embodiment, the transfer valve 7 was arranged on the downstream side of the transfer clutch 5 to control the drain flow rate, but the transfer valve 7 was arranged on the L flow side of the transfer clutch 5 to control the supply flow rate of hydraulic oil. Of course, it's a good thing.

In the embodiment described above, the solenoid voltage was changed continuously according to the road surface friction coefficient, but it goes without saying that it may be changed stepwise.

Further, the rate of change of the duty ratio may be made to change suddenly in accordance with the motion characteristics of the vehicle, or may be made to change depending on the style.

Further, the transfer structure may be used in combination with a center differential and used as a feedback circuit for torque distribution of the center differential or as a locking mechanism for the center differential.

Effects of the Invention As described above, in the present invention, when the wheel speed decreases due to an increase in brake fluid pressure due to the hydraulic pressure supplied during a braking operation, the fluid pressure of the brake device is released to prevent the wheel speed from recovering due to road reaction force. A transfer clutch that switches between two-wheel drive and four-wheel drive in a part-time four-wheel drive vehicle equipped with an anti-skid control unit that uses a control method that repeats a brake fluid pressure control pattern in which the brake system is pressurized again. The transfer clutch is configured to be able to maintain its engaged state in any state between disengaged and fully engaged, and the engaged state of the transfer clutch is controlled according to information from the anti-skid control unit when anti-skid operation is performed. By adopting a variable control method, even if you are driving on a road with a low coefficient of friction and switching to 4-wheel drive, you can switch to a state almost like 2-wheel drive, and when braking, the internal circulation torque can be used to activate anti-skid. It is possible to perform stable anti-skid operation without affecting the recovery performance of the wheels, and when driving on a road surface where the internal circulation torque is higher than the coefficient of friction of the road surface, it is almost like 4-wheel drive. By maintaining this state, the braking force distribution correction of the four-wheel drive vehicle can be utilized upwardly to improve the braking performance, which can bring about a great practical effect.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing the relationship between duty ratio and solenoid voltage. l...Anti-skid control unit, 2...Brake switch, 3...Wheel speed sensor, 4...Actuator, 5...Transfer clutch, 6...Hydraulic pump, 7...Transfer pulp , 8... Relief valve, 9... Rectifier, lO... 4WD switch,
11...Drain. that's all

Claims (1)

[Claims] When the wheel speed decreases due to an increase in brake fluid pressure due to the hydraulic pressure supplied during braking operation, the hydraulic pressure of the brake system is released and the brake system is pressurized again after waiting for the wheel speed to recover due to road reaction force. In a part-time 4-wheel drive vehicle equipped with an anti-skid control unit that employs a control method that repeats a hydraulic control pattern, the transfer clutch that switches between 2-wheel drive and 4-wheel drive is switched between disengagement and full engagement. An anti-skid device configured to be able to hold the transfer clutch in any desired state, and variably control the engaged state of the transfer clutch in accordance with information from an anti-skid control unit when anti-skid operation is being performed. A power transmission control method for a part-time four-wheel drive vehicle.