JPH04252738A - Control unit for four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To intend prompt and reliable return from a spinning condition in front wheel drive operation in conjunction with the activation of a parking brake to a normal running condition with the parking brake reset. CONSTITUTION:Even if a parking brake is reset in a spinning condition, front wheel drive operation is kept until a yaw rate is smaller than a preset value and two-wheel drive operation is made after the yaw rate is smaller than the preset value.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for a four-wheel drive vehicle.

0002

2. Description of the Related Art A conventional control device for a four-wheel drive vehicle is disclosed in Japanese Patent Application Laid-open No. 166727/1983. The four-wheel drive vehicle control device shown in this figure is a control device for four-wheel drive vehicles that controls so-called spin turns (changing the direction of the vehicle by reducing the cornering force of the rear wheels and creating an extreme oversteer condition). In order to do this, when the parking brake acting on the rear wheels is operated, the four-wheel drive state is switched to the rear-wheel drive state. That is, when the parking brake is applied while the vehicle is turning in a four-wheel drive state, the vehicle is simultaneously switched to a rear-wheel drive state. As a result, the driving force is no longer applied to the front wheels, so the cornering force on the front wheels increases, making the vehicle more likely to spin. As soon as the parking brake is released, the vehicle returns to four-wheel drive.

0003

[Problem to be solved by the invention] The above-mentioned conventional 4
The control device for wheel drive vehicles does not specify the conditions for returning from 2-wheel drive to 4-wheel drive when the parking brake is activated, and the system returns to 4-wheel drive at the same time as the parking brake is released. It is thought that he will return. However, if the driving force is transmitted to the rear wheels at the same time as the parking brake is released, the yaw rate will increase, the vehicle will continue to spin, and there will be a time delay when returning the vehicle to normal driving conditions. There is. The present invention aims to solve these problems.

0004

[Means for Solving the Problems] The present invention solves the above problems by transmitting driving force to the rear wheels when the yaw rate becomes smaller than a predetermined value. That is, the control device for a four-wheel drive vehicle according to the present invention includes a drive state switching device (16) that can switch between a state in which the driving force of the engine is transmitted only to the front wheels and a state in which it is transmitted to the front wheels and the rear wheels;
A parking brake operation detection device (24) that detects the operation of the parking brake that brakes the rear wheels, and a switching command to change the drive state switching device to the front wheel drive side when the parking brake operation detection device detects the parking brake operation state. means (steps 106, 108, 110, 11
2) A yaw rate detection device (22) for detecting a yaw rate of the vehicle in a control device for a four-wheel drive vehicle,
Front wheel drive holding command means for maintaining the front wheel drive state even if the parking brake is released until the yaw rate detected by the yaw rate detection device becomes equal to or less than a predetermined value (steps 114, 116, 118, 120)
It has The yaw rate detection device can be configured with a lateral acceleration sensor that detects lateral acceleration of the vehicle.

[0005] From a spin state in which the parking brake is applied and the front wheels are driven, even if the parking brake is released, if the yaw rate is greater than a predetermined value, the front wheel drive state is maintained. Therefore, the yaw rate does not increase rapidly. When the yaw rate becomes smaller than a predetermined value in this state, the vehicle enters a four-wheel drive state and the driving force is transmitted to the rear wheels. Even if the driving force is transmitted to the rear wheels, the yaw rate is already smaller than the predetermined value and the spin state has been released, so no more spin will occur.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 2, the driving force of an engine 10 is transmitted to front wheels 14 via a transmission 12 and to rear wheels 18 via a clutch 16. That is, when the clutch 16 is released, the vehicle becomes a front-wheel drive state, and when the clutch 16 is engaged, the vehicle becomes a four-wheel drive state. The engagement and disengagement of the clutch 16 is controlled by signals from a control unit 20 constituted by a microcomputer. The control unit 20 includes a lateral acceleration sensor 22,
Signals from a parking brake activation detection switch 24 and a vehicle speed sensor 26 are input.

In the control unit 20, the operation of the clutch 16 is controlled according to the control flow shown in FIG. First, the signals from the lateral acceleration sensor 22, the parking brake activation detection switch 24, and the vehicle speed sensor 26 are read (step 102), and then it is determined whether a flag is set (step 104), and if the flag is not set. If the vehicle speed is greater than a predetermined value (106), if the vehicle speed is greater than a predetermined value, it is determined whether the parking brake is operating (108), and the parking brake is activated. If so, a flag is set (110), and then a signal to release the clutch 16 is output (112). If the vehicle speed is smaller than the predetermined value in step 106 and if the parking brake is not activated in step 108, the process returns directly.

If the flag is set in step 104, it is determined whether the parking brake is operating (step 114), and if it is operating, the process returns directly. When the parking brake is released, it is determined whether the lateral acceleration is smaller than a predetermined value (
116), if the lateral acceleration is larger than a predetermined value, it returns as is, but if the lateral acceleration becomes smaller than the predetermined value, the flag is cleared (11
8), and then outputs a signal to engage the clutch 16 (120). In the end, if the parking brake is activated when the vehicle speed exceeds a predetermined value by the above control, the front wheels are driven (steps 106, 108, 110, 112).
). By doing so, it is possible to easily spin and turn the vehicle. The front wheel drive state achieved in this way is released when the parking brake is released and the lateral acceleration becomes smaller than a predetermined value.
Return to wheel drive (steps 114, 116, 118,
120). Therefore, after the lateral acceleration becomes small and the spin state ends, the four-wheel drive state is restored. When the vehicle returns to four-wheel drive, the driving force is transmitted to the rear wheels.
An attempt is made to increase the yaw rate, but since the vehicle has already finished spinning, spin does not occur as a result of the transmission of driving force to the rear wheels, and the vehicle returns to its normal driving state. Return.

[0009]

[Effects of the Invention] As explained above, according to the present invention, when the parking brake is applied and the front wheels are spun in the front wheel drive state, and then the parking brake is released, the yaw rate becomes smaller than a predetermined value. 4
Since the vehicle is returned to the wheel drive state, it is possible to quickly and reliably return from the spin-turn state to the normal running state.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between components of the present invention.

FIG. 2 is a diagram showing, as a skeleton diagram, a vehicle to which the present invention is applied.

FIG. 3 is a diagram showing a control flow.

[Explanation of symbols]

16 Clutch (drive state switching device) 20 Control unit 22 Lateral acceleration sensor (yaw rate detection device) 2
4 Parking brake operation detection switch (parking brake operation detection device) 26 Vehicle speed sensor

Claims (2)

[Claims] 1. A drive state switching device capable of switching between a state in which engine driving force is transmitted only to the front wheels and a state in which it is transmitted to the front wheels and rear wheels, and a parking system that detects the operation of a parking brake that brakes the rear wheels. A control device for a four-wheel drive vehicle comprising a brake operation detection device and a switching command means for switching a drive state switching device to a front wheel drive side when the parking brake operation detection device detects a parking brake operation state. and a front wheel drive hold command means for maintaining the front wheel drive state even if the parking brake is released until the yaw rate detected by the yaw rate detection device becomes equal to or less than a predetermined value. Features: Control device for four-wheel drive vehicles. 2. The control device for a four-wheel drive vehicle according to claim 1, wherein the yaw rate detection device is a lateral acceleration sensor that detects lateral acceleration of the vehicle.