JPH032104B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an anti-skid control device for a four-wheel drive vehicle.

(Prior Art) There are two types of four-wheel drive vehicles: part-time four-wheel drive vehicles and full-time four-wheel drive vehicles. (For FR cars, the front wheels,
Engine power is also transmitted to the front wheels (for front-wheel drive vehicles), thereby enabling four-wheel drive, and the latter transfers engine power to the front wheels via a center differential gear (hereinafter referred to as center differential). This input is input to a differential gear for the rear wheels (hereinafter referred to as the front differential) and a differential gear for the rear wheels (hereinafter referred to as the rear differential), thereby enabling constant four-wheel drive. In addition, full-time 4
In the case of a wheel drive vehicle, in order to prevent the vehicle from being unable to drive due to slippage of only one of the front wheels or rear wheels, a differential lock mechanism is provided in the center differential, and when the differential lock mechanism is activated, the front differential and rear differential rotate at the same time. It is also configured so that it is input.

On the other hand, anti-skid devices individually control the front wheel brake hydraulic pressure and the rear wheel brake hydraulic pressure to prevent the wheels from locking. The front and rear wheel control hydraulic pressures are controlled to maintain the ideal slip ratio that maximizes the coefficient of road friction, so the braking hydraulic pressure, or braking torque, may differ between the front and rear wheels.
Four-wheel drive vehicles with anti-skid control devices have had the following problems.

(Problem to be Solved by the Invention) In other words, in a four-wheel drive vehicle, when the dog clutch or differential lock (hereinafter referred to as direct coupling means) is operated and the same rotation is input to the front differential and rear differential, the front and rear wheel drive systems are connected to each other via direct connection means. If the front and rear wheel control torques differ as described above in this state, torsional torque will be applied to the power transmission system between the front and rear wheels due to the difference, and if the difference in front and rear wheel braking torque is large, the component parts of the power transmission system will This will have a considerable negative impact on durability.

(Means for Solving the Problems) In view of the above-mentioned problems, the present invention prevents the front and rear wheel braking torque difference from exceeding a predetermined value while the direct means is in operation. As shown, the anti-skid device 2 prevents the wheels 1 from locking by individually controlling the front wheel brake fluid pressure P _F and the rear brake fluid pressure P _R , and the front wheel differential is controlled by the appropriate operation of the direct coupling means 3. A four-wheel drive vehicle 6 in which the same rotation is input to the gear 4 and the rear wheel differential gear 5 includes a direct coupling detection means 7 for detecting operation of the direct coupling means 3; and a direct coupling detection means 7 for detecting operation of the direct coupling means 3; , front and rear wheel brake fluid pressure P _F ,
It is characterized by a configuration in which a control signal changing means 8 is provided for changing one of the control signals S _F and S _R that respectively control PR with respect to the other so that the difference between the front _and rear wheel braking torques becomes equal to or less than a predetermined value.

(Function) When the direct coupling means 3 of the four-wheel drive vehicle 6 is activated and the power transmission systems between the differential gears 4 and 5 are interconnected, the means 8 receives the signal from the direct coupling detection means 7. In response, control signals S _{F ,} S _R in the anti-skid device 2 which control the front and rear wheel brake hydraulic pressures P _F , P _R
One of them is changed with respect to the other so that the difference between the front and rear wheel braking torques is equal to or less than a predetermined value.

Therefore, when the direct coupling means 3 is in operation, the difference in braking torque between the front and rear wheels is not the same as when the anti-skid device 2 is in operation, and the difference between the differential gears 4 and 5 connected by the direct coupling means 3 is not the same. It is possible to prevent large torsional torque from being applied to the power transmission system, and the durability of the components of the power transmission system is not impaired.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 2 shows an embodiment of the present invention, in which 10 indicates a left front wheel, 11 a right front wheel, 12 a left rear wheel, and 13 a right rear wheel. The left and right front wheels 10 and 11 are connected to a propeller shaft 15 via a front wheel differential gear (front differential) 14, and the left and right rear wheels 12,
13 is connected to a propeller shaft 17 via a rear wheel differential gear (rear differential) 16.

Both propeller shafts 15, 17 are connected to the engine via a transfer and a transmission in the case of a part-time four-wheel drive vehicle, and a center differential gear (center differential) and a transmission in the case of a full-time four-wheel drive vehicle. Connects to the engine via.
For part-time 4-wheel drive vehicles, transfer 2
In the wheel drive position, engine power is transmitted only to the front two wheels or the rear two wheels, and when the transfer shaft is placed in the four-wheel drive position and the internal dock clutch is actuated to directly connect the propeller shafts 15 and 17, the remaining two wheels are
Engine power is also transmitted to the wheels. In a full-time four-wheel drive vehicle, the vehicle is always in four-wheel drive mode, but the propeller shafts 15 and 17 can be directly connected as needed by operating the center differential differential lock.

The brake system of a four-wheel drive vehicle having the above drive system has the following configuration. That is, 18 is a brake pedal, 19 is a booster, 20 is a master cylinder, and master cylinder hydraulic pressure P _n from the master cylinder 20 according to the depression force of the brake pedal 18.
is supplied to an actuator 22 which together with a control unit 21 constitutes an anti-skid control device. The actuator 22 controls the master cylinder hydraulic pressure under the control of the control unit 21.
The pressure is regulated so that one of the rear wheels 12, 13 of P _n does not lock up, and the pressure is supplied to each Hall cylinder 23, 24 as a common rear wheel braking hydraulic pressure P _R , and the other of the master cylinder hydraulic pressure P _n is applied to the front wheels 10, 13. The front wheel brake fluid pressures P FL and P _FR are supplied to the respective wheel cylinders 25 and 26 while adjusting the pressure individually so that the front brake fluid pressures P _FL and P FR do not lock. Incidentally, a well-known proportioning valve (P valve) 27 is naturally inserted into the supply system for rear wheel braking hydraulic pressure P _R.

Actuator 22 is control unit 2
According to the brake hydraulic pressure control signal S from 1, that is, the rear wheel brake hydraulic pressure control signal S _R , the left front wheel brake hydraulic pressure control signal S _FL , the right front wheel brake hydraulic pressure control signal S _FR , the brake hydraulic pressure P _R ,
Control P _FL and P _FR individually, reduce the corresponding hydraulic pressure when each signal is -1, maintain the corresponding hydraulic pressure when each signal is 0, and change the corresponding hydraulic pressure to the original pressure when each signal is +1. Assume that the pressure is increased toward the master cylinder hydraulic pressure P _n .

For this reason, the control unit 21 has
A rear wheel rotation sensor 2 that detects the rotation speed of the propeller shaft 17, which is the average rotation speed of the two rear wheels 12 and 13.
RPM (pulse) signal R _R from 8, left front wheel 10
The rotation speed (pulse) signal R _FL from the left front wheel rotation sensor 29 that detects the rotation speed of the front right wheel 11 and the rotation speed (pulse) signal R _FR from the right front wheel rotation sensor 30 that detects the rotation speed of the right front wheel 11 are input. At the same time, a signal D from the direct coupling means operation detection switch 31 that detects the operation of the dog clutch or the differential lock (direct coupling means) described above, that is, the direct coupled four-wheel drive state in which the propeller shafts 15 and 17 are coupled (directly coupled four-wheel drive state).
Enter. The control unit 27 executes the control programs shown in FIGS. 3 and 4 based on this input information, determines the control signals S (S _R , S _FL , S _FR ), and outputs them to the actuator 22 . The present invention is a microcomputer that performs normal anti-skid control and the anti-skid control that is the object of the present invention.

FIG. 3 shows a control program for the front wheels (both the left and right front wheels are the same, so only the left front wheel control program will be explained here). First, in step 40, it is determined from signal D whether or not the direct 4WD state is in place, and if so. If not, normal control is performed by executing steps 41, 42, and 43. That is, the wheel speed, wheel acceleration, pseudo vehicle speed, and slip rate of the left front wheel 10 are calculated from the signal R _FL . In the next step 42, based on these calculation results, the left front wheel brake hydraulic pressure control signal is sent in accordance with the control pattern shown in FIG.
By determining S _FL and outputting this signal to the actuator 22 in step 43, the actuator 22 controls the braking fluid pressure to the left front wheel cylinder 25.
P _FL can be maintained at the highest possible value just before the left front wheel 10 locks up.

By the way, if it is determined in step 40 that the vehicle is in the direct 4WD state, after executing steps 44 and 45 similar to steps 41 and 42, the rear wheel braking hydraulic pressure control signal S _R is read in step 46, and the next step 47 is executed. So S _R
= -1, that is, _whether the rear wheel brake fluid pressure _P If the brake pressure is not changed and the pressure is being reduced, the left front wheel brake fluid pressure control signal is changed in step 49.
Set S _FL to -1, the same as the rear wheel brake fluid pressure control signal S _R.
The control signal S _FL determined in step 48 or 49 is supplied to the actuator 22 in the next step 43 to control the left front wheel hydraulic pressure P _FL , but when the control signal TS _FL determined in step 48 is used, this is supplied to the actuator 22 in step 43. By using the value determined in step 45, which is similar to the above, the brake fluid pressure P _FL can be made as high as possible just before the left front wheel 10 locks, and when using the control signal S _FL determined in step 49, , this is -1, so the brake fluid pressure P _FL
Even if the rear wheel braking fluid pressure P _R is reduced, the propeller shaft 1 in the directly connected state
It is possible to prevent twisting torque from being applied to 5 and 17 for the following reason.

That is, in the direct 4WD state, the propeller shaft 15,
The torsional torque T _S applied between 17 and 17 is expressed by the following equation when the clutch is released and no engine output is transmitted.

T _S = 1/2 (M _F・W _F −M _R・W _R ) R − (TQB _F −TQB _R ) where M _F : Road surface friction coefficient of front wheels M _R : Road surface friction coefficient of rear wheels W _F : Front Total supported load of two wheels W _R : Total supported load of two rear wheels R: Wheel rotation radius TQB _F : Total braking torque of two front wheels TQB _R : Total braking torque of two rear wheels While driving at a constant deceleration W _F・W _R is constant,
Therefore, from the above formula, the torsional torque T _S is the coefficient of road friction.
It changes depending on M _F , M _R and the front and rear braking torque difference TQB _F - TQB _R. By the way, during braking, W _F > F _R , but since the increase in rear wheel brake fluid pressure P _R is limited by the P valve 27, etc., TQB _F > TQB _R , and unless anti-skid control is performed, propeller shafts 15, 17 The torsional torque |T _S | applied between the two does not become large, and does not cause the problem that the present invention aims to solve.

However, during anti-skid control, if the road surface conditions are different between the front and rear wheels and the ideal slip ratio (slip ratio for each road surface condition where the road surface friction coefficient is maximum) is different, while the rear wheel control fluid pressure is being reduced ( S _R =-
During 1), increase the front wheel brake fluid pressure (S _FL = +
1 or S _FR = +1), or conversely, while reducing the front wheel brake fluid pressure (between S _FL = -1 or S _FR = -1), the rear wheel brake fluid pressure is Control is sometimes performed to increase the pressure (S _R = +1), and at this time, as is clear from the above equation, the torsional torque |T _S | increases, which reduces the durability of the propeller shafts 15, 17 and related parts. Greatly damaged. It can be seen that this problem can be solved by reducing the rear wheel brake hydraulic pressure while the front wheel brake hydraulic pressure is being reduced, and by also reducing the front wheel brake hydraulic pressure during the rear wheel brake hydraulic pressure.

Therefore, when it is determined in step 47 in FIG. 3 that S _R =-1, by setting S _FL to -1 in step 49, the torsional torque of the propeller shafts 15 and 17 can be reduced. Also, this S _FL =−
1 is a rear wheel locking system in which the front wheel brake hydraulic pressure is not forcibly braked through the propeller shafts 15 and 17, which are directly connected, and anti-skid control is performed so that the braking torque is reduced by S _R = -1. Prevention can be carried out reliably, and vehicle behavior can be prevented from becoming unstable.

Figure 4 shows the control program for the rear wheels.
50, if it is determined that it is not in a direct 4WD state,
In steps 51 to 53, steps 41 to 53 in FIG.
It performs normal anti-skid control for the rear two wheels, similar to the 43. If it is determined in step 50 that the vehicle is in a direct 4WD state, the same steps as steps 51 and 52 are performed.
Steps 54 and 55 are executed to determine the rear wheel brake hydraulic pressure control signal S _R , and then in step 56 the front wheel brake hydraulic pressure control signal is determined.
Read S _FL and S _FR . If it is determined in steps 57 and 58 that both S _FL and S _FR are not -1, in step 59 the control signal S _R is set to the value determined in step 55, and normal anti-skid control is continued. However, in step 57 S _FL = -1 or in step 58 S _FR = -1
In other words, the front wheel brake fluid pressure P _FL or P _FR
If the pressure is being reduced, the rear wheel brake hydraulic pressure control signal S _R is unconditionally set to -1 in step 60, and the rear wheel brake hydraulic pressure P _R is also reduced, thereby causing a large torsional torque to be applied to the propeller shafts 15 and 17. This prevents the vehicle from becoming unstable due to interference with anti-skid control of the front wheels.

(Effects of the Invention) Thus, as described above, the device of the present invention is configured to change one of the front and rear wheel braking hydraulic pressure control signals in a direct 4WD state so that the difference in front and rear wheel braking torque does not become large when compared with the other. , a power transmission system directly connected to each other between the front differential 14 and the rear differential 16 (system including propeller shafts 15 and 17)
It is possible to prevent a large torsional torque from being applied to the wheel, and to prevent the vehicle behavior from becoming unstable due to the anti-skid control of the wheel associated with the other control signal being obstructed by the wheel associated with the one control signal. .

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of the anti-skid control device of the present invention, Fig. 2 is a system diagram showing an embodiment of the invention, Figs. 3 and 4 are flowcharts showing the control program of the control unit in the same embodiment, FIG. 5 is a pattern diagram showing how the anti-skid device controls the brake fluid pressure and the brake fluid pressure control signal. 1...Wheel, 2...Anti-skid device, 3...
...Direct connection means, 4... Differential gear for front wheels, 5... Differential gear for rear wheels, 6...
...4-wheel drive vehicle, 7... Direct connection detection means, 8... Control signal changing means, 10, 11... Front wheels, 12, 13
...Rear wheel, 14... Front wheel differential gear, 15, 17... Propeller shaft, 16...
Rear wheel differential gear, 18...brake pedal, 19...boost device, 20...master cylinder, 21...control unit, 22
... Actuator, 23-26 ... Wheel cylinder, 27 ... Proportion valve, 28
... Rear wheel rotation sensor, 29, 30 ... Front wheel rotation sensor, 31 ... Direct connection means operation detection switch.

Claims (1)

[Scope of Claims] 1. An anti-skid device that prevents the wheels from locking by individually controlling the front wheel brake hydraulic pressure and the rear wheel brake hydraulic pressure; In a four-wheel drive vehicle in which the same rotation is input to differential gears for use in the vehicle, the direct coupling detection means detects the operation of the direct coupling means, and the front and rear wheel braking hydraulic pressures are respectively controlled during the operation of the direct coupling means. An anti-skid control device for a four-wheel drive vehicle, comprising control signal changing means for changing one control signal with respect to the other so that the difference between front and rear wheel braking torques is equal to or less than a predetermined value.