JPH05338521A - Rear wheel braking force control device for vehicle - Google Patents

Abstract

PURPOSE:To provide a rear wheel braking force control device for vehicle of which the reliability on operation is increased. CONSTITUTION:A rear wheel braking force control device is provided with proportioning valves (PCV) 12R and 12L interposed in rear wheel brake lines 7 and 10, respectively, bypass lines 13 connected to the rear wheel brake lines 7 and 10, respectively, by bypassing the PCV 12, bypass valves 14L and 14R comprising a normally closed solenoid valve provided in these bypass lines 13, respectively, and a BV controller 16 to control the opening and closing of these bypass valves 14 according to the on-off operation of a brake switch 18 and a master cylinder pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel braking force control device for a vehicle which controls distribution of front wheel braking force and rear wheel braking force during braking.

[0002]

2. Description of the Related Art When a brake pedal is depressed, a brake pressure, that is, a master cylinder pressure is generated in a master cylinder, and this master cylinder pressure is transmitted to a wheel cylinder of each wheel through a brake pipe, so that Braking force is generated on each wheel. At the time of braking, the load on the rear wheel is reduced due to the movement of the load on the vehicle. Therefore, if the master cylinder pressure is transmitted to the front wheel and the rear wheel with the same distribution, the rear wheel will be compared to the front wheel. The vehicle will be locked first and the braking stability of the vehicle will be impaired.

Therefore, a control valve called a proportioning valve (PCV) is conventionally inserted in the rear wheel brake line connecting the master cylinder and the rear wheel wheel brake. When the master cylinder pressure reaches or exceeds the set pressure, the rate of increase of the rear wheel brake pressure transmitted from the master cylinder to the wheel cylinders of the rear wheels is reduced.
This prevents early locking of the rear wheels.

By the way, since the above-mentioned set pressure of the PCV is a constant value, the distribution of the braking force to the rear wheels is also uniquely determined, and therefore the rear wheel brake pressure can still be sufficiently increased. Even in a braking situation, the rear wheel brake pressure is kept low by the action of PCV. For this reason, the inventor of the present invention has studied a rear wheel braking force control device in which a bypass pipe for bypassing PCV is provided in the rear wheel brake pipe and a bypass valve made of a solenoid valve is inserted in the bypass pipe. This rear wheel braking force control device normally opens the bypass valve to invalidate the function of the PCV, and then closes the bypass valve to operate the PCV according to the braking situation. Therefore, if such a bypass valve is provided, the set pressure of the PCV can be substantially changed, and the braking force distribution to the rear wheels can be controlled appropriately according to the braking situation.

[0005]

By the way, since the bypass valve is normally opened as described above, a normally open solenoid valve is used for this bypass valve. However, in the case of a normally open solenoid valve, if a trouble occurs in the electrical system, such as disconnection of the energization path to the solenoid or failure of the controller that controls the opening and closing of the bypass valve, the bypass valve remains open. Then, it becomes impossible to operate PCV.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to ensure that the PCV can be operated reliably even if a trouble occurs in the electric system or the like, and fail-safe is ensured. Another object of the present invention is to provide a rear wheel braking force control device for a vehicle.

[0007]

A rear wheel braking force control device of the present invention is inserted in a rear wheel brake pipe line connecting a master cylinder and a rear wheel wheel brake, and the master cylinder pressure is equal to or higher than a set pressure. Control valve for reducing the brake pressure of the rear wheels with respect to the brake pressure of the front wheels at a constant ratio when reaching, a bypass pipe line provided by bypassing the control valve in the rear wheel brake pipe line, A normally closed electromagnetic valve inserted in the bypass pipe line and a control means for controlling the opening / closing of the electromagnetic valve according to the braking state of the vehicle are provided.

[0008]

According to the above-described rear wheel braking force control device, when the normally closed solenoid valve is opened, the master cylinder pressure generated in the master cylinder is transmitted to the rear wheel wheel brake by bypassing the control valve. Therefore, in this case, the function of the control valve is invalidated, and the braking force of the rear wheels is increased at the same rate as that of the front wheels. On the other hand, when the solenoid valve is closed, the brake pressure of the master cylinder is transmitted to the wheel cylinders of the rear wheels through the control valve, so that the brake pressure of the rear wheels is controlled by the control valve.

Even if a failure occurs in the electric system or the like and the solenoid valve cannot be opened, this solenoid valve is held in the closed position. Therefore, the rear wheel wheel cylinder is controlled by the control valve. The applied brake pressure is transmitted.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a vehicle braking system is schematically shown, which comprises a tandem master cylinder 1. The master cylinder 1 is operated by a brake pedal 2 via a vacuum type brake booster 3.

A pair of main brake conduits 4 and 5 extend from each pressure chamber of the master cylinder 1, and one main brake conduit 4 includes front and rear wheel brake conduits 6 and 7.
The front wheel brake line 6 is connected to the wheel cylinder 8FL for the left front wheel, and the rear wheel brake line 7 is connected to the wheel cylinder 8RR for the right rear wheel. The other main brake pipe line 5 is also branched into front and rear wheel brake pipe lines 9 and 10, and the front wheel brake pipe line 9 is connected to the wheel cylinder 8FR of the right front wheel.
Further, the rear wheel brake conduit 10 is connected to the wheel cylinder 8RL for the left rear wheel.

Anti-skid valves 11 are inserted in the brake lines of each wheel, and these anti-skid valves 11 control the brake pressure of the corresponding wheel cylinders 8. It should be noted that FIG. 1 does not show a pump system for supplying a pressure liquid to the wheel cylinder 8 through the antiskid valve 11 or a return route of the pressure liquid from the antiskid valve 11.

Proportioning valves (PCV) 12L, 1 serving as control valves are also located downstream of the anti-skid valves 11 in the rear wheel brake pipes 7, 10 and serve as control valves.
2R are respectively inserted, and these PCVs 12 increase the pressure transmitted to the wheel cylinder 8R of the rear wheel, that is, the rear wheel brake pressure when the master cylinder pressure supplied from the master cylinder 1 reaches or exceeds the set pressure. It has the function of lowering the rate. That is, as is clear from the characteristic indicated by the solid line C in FIG. 2, when the master cylinder pressure is smaller than the set pressure P0, the rear wheel brake pressure, that is, the rear wheel braking force, is the same as the master cylinder pressure increase rate. However, when the master cylinder pressure reaches the set pressure P0 or higher, P increases.
The CV 12 reduces its rising rate and transmits it to the wheel cylinder 8R. The set pressure P0 of the PCV 12 is uniquely determined by the set load of the valve spring.

Further, the rear wheel brake pipelines 7 and 10 are provided with bypass pipelines 13 that bypass the PCV 12, and bypass valves 14L and 14R are inserted in these bypass pipelines 13. Bypass valve 14
Is composed of a normally closed electromagnetic on-off valve, as is apparent from FIG. Each of the above-described anti-skid valves 11 is electrically connected to the controller (ABS controller) 15 of the anti-skid brake system, receives an ABS signal from the ABS controller 15, and is switched to operate.
The CVs 12L and 12R are opened by receiving a valve opening signal from the controller (BV controller) 16 of the bypass valves 14L and 14R. The ABS controller 15 and the BV controller 16 are each composed of a microcomputer and its peripheral circuits.

The ABS controller 15 includes wheel speed sensors 17, 18, 19, 20 for each wheel and a vehicle speed sensor 21.
Are electrically connected, and the sensor signals detected by these sensors are supplied to the ABS controller 15. A
The BS controller 15 calculates the slip ratio for each wheel based on the sensor signals VFL, VFR, VRL, VRR, V from the wheel speed sensor and the vehicle speed sensor, and then the corresponding anti-skid valve according to the calculated slip ratio. A towards 11
It outputs BS signals a1, a2, a3, a4. Where ABS
The signal is a pressure increasing signal for injecting brake fluid into the wheel cylinder 8 depending on the signal level.
A holding signal for holding the brake fluid therein and a decompression signal for draining the brake fluid from the wheel cylinder 8 are generated, and the anti-skid valve 11 is operated according to these signals. In addition,
When the slip ratio of a wheel exceeds a predetermined value, the ABS controller 15 of this embodiment first outputs a holding signal to the anti-skid valve 11 corresponding to the wheel, and then outputs a pressure reducing signal. There is.

The ABS controller 15 also outputs the ABS signal of each wheel to the BV controller 16, and the BV controller 16 receives the depression of the pressure sensor 17 for detecting the master cylinder pressure of the master cylinder 1 or the brake pedal 2. The brake switch 18 for detection is also electrically connected, and the sensor signals PM and SW from these are input.

The BV controller 16 has memories m1 and m.
2, m3 are provided, and the memory m1 stores the master cylinder pressure that determines the closing time of the bypass valve 14L for the left rear wheel, that is, the target switching pressure PL of the bypass valve 14L, while the memory m2 stores the right rear Wheel bypass valve 14R
The target switching pressure PR is stored. Further, the memory m3 stores the switching pressure P1 of the bypass valve 14 which is suitable when the vehicle brakes about 0.6 G on a high μ road.

The BV controller 16 receives the input AB
A control program for setting the target switching pressures PL and PR in the memories m1 and m2 based on the S signals a1 to a4 is stored, and as will be described later, the BV controller 16 sets the master cylinder pressure PM at a predetermined sampling time. Memory m1,
By comparing the target switching pressures PL and PR set to m2, when PM ≧ PL, the bypass valve 14L is closed from the open position, and similarly when PM ≧ PR, the bypass valve 14R is opened from the open position. Close it.

Here, as shown in FIG. 2, when the target switching pressure PL (PR) is set to a pressure P1 higher than the set pressure P0, the bypass valve 14L sets the master cylinder pressure PM to P1. It is operated to open until it reaches, which causes the rear wheel braking force to increase as indicated by the solid line A. Here, even if the master cylinder pressure PM rises above the switching pressure P1, the rear wheel braking force is maintained constant until the master cylinder pressure PM reaches PX. That is, the master cylinder pressure PM rises above P1 and the bypass valve 1
When 4 is closed, the rear wheel braking force, that is, the brake pressure of the rear wheels is controlled by the PCV 12, and at this time, as is clear from the solid line C, the master cylinder pressure PM does not reach PX. That is because the valve is not opened.

Further, in FIG. 2, the solid line B shows the ideal braking force distribution of the front and rear wheels, which is assumed to cause the four wheels of the vehicle to lock simultaneously during braking.
Is determined based on the road surface μ and the deceleration of the vehicle. Therefore, even when the rear wheel braking force defined by the switching pressure P1 is in the area on the ideal braking force distribution line B, Depending on the road surface μ, the rear wheels are not locked, and in this case, it is possible to apply a larger braking force to the rear wheels. That is, the rear wheel braking force PCV1
If controlled only by 2, the rear wheel braking force is suppressed to a low level by the action of the PCV 12, as shown by the broken line area in FIG. 2, even if there is still a margin to increase the rear wheel braking force depending on the road surface condition. As a result, the ratio of the front wheel braking force to the total braking force becomes large, but if the rear wheel braking force is effectively increased, the burden of the front wheel braking force can be reduced.

The flowcharts of FIGS. 3 and 4 show the contents of a control program for setting the target switching pressure PL of the bypass valve 14L for one rear wheel, for example, the left rear wheel, that is, the target switching pressure setting routine. Since the target switching pressure setting routine for the bypass valve 14R has the same contents, its description is omitted. Target Switching Pressure Setting Routine First, the BV controller 16 stores the switching pressure P1 in the memory m1 and sets this switching pressure P1 as the target switching pressure PL (step S1). The switching pressure P1 is the value stored in the memory m3 as described above.

Then, the BV controller 16 determines whether or not the ABS signal a3 supplied to the antiskid valve 11 for the left rear wheel is a holding signal (step S2). If the determination result here is positive, whether or not the ABS signal a1 supplied to the anti-skid valve 11 for the left front wheel is a holding signal or a pressure reducing signal, that is, the anti-skid brake control (ABS) for the front wheel is It is determined whether or not it is in operation (step S3). If the determination result here is negative, the master cylinder pressure PM is read into the memory m1 in step S4, and when it is determined in step S4 'that the master cylinder pressure PM is less than or equal to the target switching pressure PL, the step is performed. S
At 5, the target switching pressure PL is updated to the master cylinder pressure PM. That is, if the determination result of step S3 is negative even though the determination result of step S2 is positive, the left rear wheel tends to lock more than the left front wheel, and the rear wheel braking force is too high. In this case, the target switching pressure PL is corrected by substituting the master cylinder pressure PM at that time into the target switching pressure PL. If the determination result in step S4 ′ is negative, it can be determined that a braking operation much stronger than the road surface friction force is performed, and therefore the target switching pressure is not updated.

In step S2, the ABS signal a3
Instead of this, it may be determined whether or not the slip ratio of the left rear wheel exceeds a predetermined threshold value. On the other hand, if the result of the determination in step S2 is positive, it means that the left rear wheel does not tend to lock, and step S2
From step S3 to step S3, in a situation where the determination result of this step is positive, it is shown that the left front wheel is more likely to lock than the left rear wheel. When it is determined that the switching pressure PL is properly set, the process returns to step S1.

When the target switching pressure PL is updated, the timer T1 starts counting time (step S6), and it is determined whether or not the value of the timer T1 has reached the predetermined time t1. (Step S7). If the determination result here is NO, it is determined whether or not the ABS signal a3 of the anti-skid valve 11 for the left rear wheel is a pressure reduction signal (step S8), and the determination result here is also NO. The determination in step S7 is repeated. Here, the determination result of step S8 is
Since the counting by the timer T1 is simply continued while it is maintained at NO, the target switching pressure PL is set to the step S
It is held at the value updated in 5. Note that step S8
Regarding this, similarly to the case of step S4, the determination may be performed based on the slip ratio of the left rear wheel instead of the ABS signal a3.

If the lock tendency of the left rear wheel is progressing, A
The BS signal a3 switches from the hold signal to the pressure reduction signal. However, even if the hold signal is output, if the pressure reduction signal does not occur within the predetermined time t1, it can be determined that the locking tendency of the left rear wheel has not progressed. .. Therefore, in this case, it is considered that the braking force distribution of the rear wheels is appropriate without updating the target switching pressure PL in step S5.
Returning to step S1, the target switching pressure PL is set to P1 again.

However, in a situation where the determination result of step S8 becomes positive before the determination result of step S7 becomes positive, the process proceeds to step S9 of FIG. 4, and in this step, for example, from a map not shown, Based on the master cylinder pressure PM at that time, the target switching pressure PL is updated in the decreasing direction. Here, instead of using the map, a calculated value (for example, simply PM / 2) based on the master cylinder pressure PM at that time may be set as the target switching pressure PL.

After the target switching pressure PL is further updated in the decreasing direction, the timer T2 starts counting time (step S10), and it is judged whether or not the value of the timer T2 has reached the predetermined time t2. (Step S11). Then, after this, whether or not the ABS of the left front wheel anti-skid valve 11 is operating (step S12), and next, whether or not the ABS of the left rear wheel anti-skid valve 11 is operating. The determination of (step S13) is performed.

Here, before the value of the timer T2 reaches the predetermined time t2, the left rear wheel tends to lock before the left front wheel, and the ABS operates on the rear wheel side, the target is switched in step S14. The pressure PL is set to zero. That is, in such a situation, even if the target switching pressure PL is updated in the decreasing direction again in step S9, it means that the braking force of the left rear wheel is too high. Therefore, the braking force of the rear wheel is further increased. In order to lower it, the target switching pressure PL is set to 0.

While the counting operation is continued by the timer T2,
In the situation where the ABS is operating on the front wheel side or the ABS is not operating on both the front wheel side and the rear wheel side,
The target switching pressure PL is held at the value updated in step S9 until the determination result in step S11 becomes positive.
That is, when the ABS operates on the left front wheel before the value of the timer T2 reaches t2, the ABS controller 15 controls the lock of the left front wheel while maintaining the target switching pressure PL.

As described above, when the target switching pressure PL is set to 0 in step S14, the time counting operation of the timer T3 is started (step S15), and then the value of the timer T3 reaches the predetermined time t3. It is determined whether or not (step S
16). Therefore, in this case, the situation where the target switching pressure PL is 0 is continued for t3 hours. When the result of the determination in step S16 is positive, the process returns to step S1 and the target switching pressure PL is set to P1.

The target switching pressure PL set or updated in the above-described setting routine is used as a criterion for closing the bypass valve 14L, and the opening / closing routine of the bypass valve shown in FIG. 5 will be described below. To do. The opening / closing routine of the bypass valve 14R is also the same as the opening / closing routine of FIG. 5, and therefore its description is omitted. Bypass Valve Open / Close Routine First, in step S20, it is determined whether or not the master cylinder pressure PM has reached the target switching pressure PL or higher. If the determination result is positive, it is determined whether or not the brake switch 18 has been turned on. It is determined (step S21) whether or not the braking is started, and the bypass valve 14L is immediately opened (step S22).

Although it is possible to determine the start of braking from the rise of the master cylinder pressure PM in step S21, it is faster to determine the start of braking based on the operation of turning on the brake switch 18. Can be done. On the other hand, if the determination result in step S20 is negative, the process proceeds to step S23, and by executing this step, the bypass valve 14L is immediately closed.

If the result of the determination in step S21 is negative, it is determined whether or not the brake switch 18 is in the state where the brake switch 18 has been operated to be turned off. If the result of the determination here is positive, After elapse of the predetermined time Δt (step S2
5) In step S23, the bypass valve 14L is closed. That is, when the bypass valve 14L is opened by the ON operation of the brake switch 18, the bypass valve 14L is closed when the master cylinder pressure PM reaches the target switching pressure PL, as shown in FIG. Alternatively, the brake switch 18 is closed after a lapse of a predetermined time Δt after the brake switch 18 is switched from ON to OFF. Even if the brake switch 18 is switched from on to off in this way, the bypass valve 14L is not immediately closed, so that hunting does not occur in opening and closing the bypass valve 14L.

In the situation where the determination results in steps S21 and S24 are both negative, the brake pedal 2 is not depressed, so in this case step S23 is executed to maintain the bypass valve 14L in the closed position. To do.
Here, as to the target switching pressure PL used for the determination in step S20, as described in the target switching pressure setting routine, after the constant pressure P1 is given at the start of braking, the ABS of the rear wheel is changed. According to the control, the value is updated in the direction of gradually decreasing, so that the rear wheel braking force can be increased within a range in which the rear wheel is not locked.

Further, when the target switching pressure PL is set to 0 in step S14 of the target switching pressure setting routine, in such a situation, step S in the opening / closing routine is executed.
The determination result of 20 is always positive, and the bypass valve 14L
Is maintained in the closed position. Therefore, in this case,
The PCV 12L on the left rear wheel always works, and the braking force distribution indicated by the solid line C in FIG. 2 is obtained.

In the embodiment described above, the bypass valve 14
Since normally closed solenoid valves are used for L and 14R, disconnection occurs in the electric system between these bypass valve 14 and BV controller 16, or BV controller 1
Even if failure occurs in 6 itself, bypass valves 14L, 1
The 4R is kept closed to allow its PCV 12 to work, and the rear wheel braking force does not increase beyond the permissible range and cause the lock.

Since the PCVs 12L and 12R are combined with the bypass valves 14L and 14R, respectively, even when the friction coefficient of the road surface is different between the left and right rear wheels, or when the vehicle is being braked by turning, the bypass valves 14L and 14R are combined. The target switching pressure that determines the closing operation timing of 14L and 14R can be optimally set. The present invention is not limited to the above-described embodiment, and for example, the ABS controller and the BV controller may be configured by one controller, and instead of the anti-skid valve 11, the hydraulic pump may be used. Using the ABS hydro unit that does not use
Various modifications are possible, such as BS control may be performed.

[0038]

As described above, according to the rear wheel braking force control device of the present invention, in addition to the control valve for reducing the rear wheel braking force at a constant ratio with respect to the front wheel braking force during braking, Since the solenoid valve is provided so as to bypass the control valve, by appropriately controlling the opening / closing of this solenoid valve in accordance with the braking state, the rear wheel braking force can be sufficiently secured without the rear wheel being locked. Of course, even in the present invention, since the solenoid valve is a normally closed type valve, a disconnection of the electric system or a failure of the control means may occur. Also, the solenoid valve can be maintained in the normally closed state to operate the control valve, and the reliability of the device is greatly improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a rear wheel braking force control device according to an embodiment.

FIG. 2 is a graph showing the input / output characteristics of PCV.

FIG. 3 is a flowchart showing a part of a target switching pressure setting routine for a bypass valve.

FIG. 4 is a flowchart showing the remaining part of the setting routine.

FIG. 5 is a flowchart showing an opening / closing routine of a bypass valve.

FIG. 6 is a time chart showing opening and closing times of a bypass valve.

[Explanation of symbols]

 1 Master Cylinder 7, 10 Rear Wheel Brake Pipe 8 Wheel Cylinder 11 Anti-Skid Valve 12 PCV 13 Bypass Pipe 14 Bypass Valve 15 ABS Controller 16 BV Controller 17 Pressure Sensor 18 Brake Switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadao Tanaka 5-3-8, Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation

Claims (1)

[Claims] 1. When the master cylinder pressure reaches a set pressure or higher, the rear wheel is inserted into a rear wheel brake line connecting the master cylinder and the rear wheel wheel brake, and when the master cylinder pressure reaches or exceeds a set pressure, the rear wheel brake pressure is increased. A control valve for reducing the brake pressure at a constant ratio, a bypass pipeline provided by bypassing the control valve in the rear wheel brake pipeline, and a normally closed solenoid valve inserted in this bypass pipeline. A rear wheel braking force control device for a vehicle, comprising: a control unit that controls opening / closing of the electromagnetic valve according to a braking state of the vehicle.