JPH08133049A - Braking force controller - Google Patents

Abstract

PURPOSE: To provide a braking force controller in which braking force according to the deflection condition of each tire at the time of braking can be distributed to each wheel. CONSTITUTION: When a brake switch 67 is turned on, acceleration detected by an acceleration sensor 62, a rotational speed of each wheel detected by a wheel rotation sensors 63 to 66 and a vehicle body speed detected by a speed sensor 61 are read in an anti-lock braking force controller 60. When the slip ratio of a rear wheel is smaller than the threshold value of an anti-lock braking force control region, the correction value of the actual outer diameter of a tire with the movement of a load is computed. After that, the target wheel speed of a rear wheel on the basis of the actual outer diameter of a tire with the deflection condition of the tire with the movement of a load being taken into consideration is computed, and pressure-increase hydraulic switching valves 13, 14 or pressure-reduction hydraulic switching valves 17, 18 on the rear wheel side are opened and closed by comparing the target wheel speed of the rear wheel with the wheel speed of the rear wheel which is detected by the wheel rotational speed sensors 64, 65.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking force control device,
In particular, the present invention relates to a braking force control device configured to distribute a braking force to each wheel according to the degree of bending of each tire during braking.

[0002]

2. Description of the Related Art In a braking force control device for braking each wheel of an automobile, the braking force during braking is controlled depending on the road surface condition (for example, a dry road surface, a wet road surface, a frozen road surface, etc.). In order to prevent the wheels from locking due to sudden braking on the easy road surface and making the vehicle difficult to control,
An anti-lock braking force control system is adopted. In this anti-lock braking force control system, when the driver brakes and brake pressure is supplied to each wheel, if each wheel is rotating, the pressure increasing mode or the holding mode is set to increase the braking force of the wheel. Immediately before the wheels are locked, the pressure reducing mode is set to prevent the wheels from locking.

Further, the anti-lock braking force control system switches the brake pressure between pressure increase, pressure retention and pressure decrease according to each wheel speed, and the brake pressure (control) between the front wheels and the rear wheels due to load movement during braking. Control systems that automatically set the distribution of power are also being developed. An example of a braking force control device that controls the distribution of the braking pressure (braking force) between the front wheels and the rear wheels is disclosed in Japanese Patent Laid-Open No. 5-116.
There is a device as seen in Japanese Patent No. 608.

In the device of this publication, the braking force is distributed so that the rear wheel having the slowest wheel speed travels a predetermined value slower than the front wheel having the fastest wheel speed when the traveling vehicle is braked. ing.

[0005]

However, in the device disclosed in the above publication, the rotation speed of each wheel is detected by the wheel rotation sensor, and the diameter of the wheel (the outer diameter of the tire when no load is applied) is used as the rotation speed. The rotation speed of each wheel is calculated by multiplying. However, since the actual wheel supports the weight of the vehicle, the ground contact portion of the tire bends flat in accordance with the weight of the wheel.

Therefore, in the structure in which the brake pressure of the rear wheels is controlled so that the rear wheel speed becomes a target value calculated based on the front wheel speed as in the above publication, the amount of bending of the tire causes
When the difference between the actual wheel speed and the theoretical wheel speed becomes large, the rear wheel braking force is controlled to be small. In addition, when the vehicle is braked in a straight ahead state, load movement occurs due to the generation of acceleration in the front-rear direction, which reduces the outer diameter of the tire. The front wheel speed is detected faster than it actually is, and the outer diameter of the tire increases. The rear wheel speed will be detected slower than it really is.

Therefore, in the conventional braking force control device, since the rear wheel speed is detected slow for the above reason, the brake pressure to the rear wheels is set low, the rear wheel braking force becomes small, and the braking force on the rear wheel side is reduced. The performance could not be fully exerted.
Therefore, in view of the above problems, it is an object of the present invention to adjust the brake pressure to each wheel based on the actual outer diameter of the tire due to the movement of the load during braking so that an optimum braking force can be obtained at each wheel.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a wheel speed detecting means for detecting the speed of each wheel of a vehicle, and a target rear wheel wheel speed based on the wheel speed of a front wheel detected by the wheel speed detecting means. A braking force control device comprising: a calculating means for calculating; and a control means for controlling the braking force of the rear wheels so that the rear wheel speed during braking becomes the target rear wheel speed calculated by the calculating means. A tire flexure amount estimating means for estimating a flexure amount of a tire due to a load movement during braking, and a braking force change for changing a braking force to a rear wheel based on the flexure amount of the tire estimated by the tire flexure amount estimating means Means and
It is characterized by comprising.

[0009]

According to the present invention, the tire flexure amount estimating means estimates the flexure amount of a tire due to load movement during braking, and the braking force applied to each wheel is changed based on the estimated flexure amount of the tire. As a result, a braking force according to the actual wheel speed is applied to each wheel, and even if the tire bends due to load movement during braking and the outer diameter changes, an optimum braking force is obtained at each wheel.

[0010]

1 shows an antilock braking force control system to which an embodiment of a braking force control device according to the present invention is applied. In the figure, 1 is a brake pedal, 2 is a vacuum booster, 3 is a master cylinder (actuator) that generates a brake fluid pressure according to the depression force of the brake pedal 1 and the boosting action of the vacuum booster 2, and 4 and 5 are brakes. Reservoir 6 for replenishing liquid (hydraulic oil) to a reflux system passage described later, 6
Reference numerals 9 to 9 are wheel cylinders of a brake mechanism that receives brake fluid pressure from the master cylinder 3 to brake each wheel.

The brake fluid pressure generated from the master cylinder 3 when the brake pedal 1 is depressed is applied to the wheel cylinders 6 to 9 via the first and second brake pipe lines 10 and 11.
It is connected to the. Reference numerals 12 to 15 are hydraulic pressure switching valves for increasing pressure, which are normally-open solenoid valves. Normally, the valve bodies 12a to 15a are urged to open positions, and the brake hydraulic pressure from the master cylinder 3 is applied to each wheel cylinder 6 to. 9 is being supplied. However, the hydraulic pressure switching valves 12-15 for increasing pressure have the solenoids 12b-15b excited immediately before the wheels are locked, so that the valve bodies 12a-
15a switches to the valve closing position and operates to stop the supply of brake fluid pressure from the master cylinder 3.

Depressurizing hydraulic pressure switching valves 16 to 19 are normally closed solenoid valves. Normally, the valve bodies 16a to 19a are urged to the closed positions, and the brake hydraulic pressure to the wheel cylinders 6 to 9 is increased. Holding However, the pressure reducing fluid pressure switching valve 16 to
19 is a solenoid 16b to 19b immediately before the wheels are locked.
Is excited to switch the valve elements 16a to 19a to the valve opening positions, and the brake fluid pressures to the wheel cylinders 6 to 9 are released to the reservoirs 4 and 5 to reduce the brake fluid pressures.

Supply pipelines 20 to 23, which are communicated with the first and second brake pipelines 10 and 11, and one end thereof are communicated with the pressure increasing hydraulic pressure switching valves 12 to 15 and the pressure reducing hydraulic pressure switching valves 16 to 19. The supply pipe passages 24 to 27 having the other ends communicated with the wheel cylinders 6 to 9 form supply system passages 28a to 28d for the wheel cylinders 6 to 9, respectively. Further, one end communicates with the pressure-reducing hydraulic pressure switching valves 16 to 19 and the other end communicates with the reservoirs 4, 5
Reflux lines 29 to 32, which are communicated with the
The return conduits 33 and 34 extending from 5 so as to be connected to the first and second brake conduits 20 and 21 are the return system passage 35.
a and 35b are formed.

The pressure-increasing hydraulic pressure switching valves 12 to 15 are provided with a throttle 3 provided in a flow path communicating with the supply-side pipelines 20 to 23.
6 to 39, the bypass flow passages 40 to 43 bypassing the throttles 36 to 39, and the brake fluid on each wheel cylinder 6 to 9 side is allowed to return to the master cylinder 3 side via the bypass flow passages 40 to 43. And check valves 44 to 47 for preventing the brake fluid from flowing from the master cylinder 3 side to the wheel cylinders 6 to 9 side.

Further, the depressurizing hydraulic pressure switching valves 26 to 29 are throttles for restricting the amount of brake fluid recirculated from each wheel cylinder 6 to 9 to a predetermined amount in the flow path communicating with the downstream recirculation pipes 29 to 32. 50-53. Suction pumps 54 and 55 for sucking the brake fluid of the reservoirs 4 and 5 to circulate the fluid to the master cylinder 3 side, and reverse pumps arranged upstream of the suction pumps 54 and 55 are provided in the respective circulation pipe lines 33 and 34. Stop valve 56, 57
And check valves 58 and 59 arranged downstream of the suction pumps 54 and 55.

The suction pumps 54 and 55 are constantly driven by a pump motor (not shown) while the antilock braking force control is being executed. Then, the suction pump 54,
55 is a suction process when a pump plunger (not shown) moves down, and a discharge process when a pump plunger (not shown) moves up. Then, in the suction process, the check valves 56 and 57 arranged upstream of the suction pumps 54 and 55 are opened, and the check valves 58 and 59 arranged downstream of the suction pumps 54 and 55 are closed. To do. Then, in the discharge step, the check valves 56, 57 arranged upstream of the suction pumps 54, 55 are closed and the suction pumps 54, 55 are
The check valves 58 and 59 arranged downstream of the check valve are opened.

As described above, the suction pumps 54, 55 are selected depending on the operating direction of the pump plungers of the suction pumps 54, 55.
The brake fluid is recirculated to the master cylinder 3 by opening and closing the check valves 56, 57 and the check valves 58, 59 disposed upstream and downstream of the above. In the brake device having the antilock braking force control system configured as described above, when the brake pedal 1 is depressed, the master cylinder 3 increases the brake fluid pressure to enter the pressure increasing mode. In this pressure increasing mode, the pressure increasing hydraulic pressure switching valves 12 to 15 are held in the open state, and the pressure reducing hydraulic pressure switching valves 16 to 19 are held in the closed state. Therefore, the increased brake fluid pressure is supplied to the wheel cylinders 6 to 9 via the first and second brake conduits 10 and 11, the supply conduits 20 to 23, and the supply conduits 24 to 27. , Each wheel is braked.

Then, for example, when the vehicle is traveling on a low μ road and the wheels are braked just before the wheels are locked, the antilock braking force control system is switched to the pressure reducing mode or the holding mode. In this pressure reducing mode, the solenoid 12b of the pressure increasing hydraulic pressure switching valves 12 to 15 corresponding to the wheel immediately before being locked.
~ 15b is excited and switched to the closed state,
Solenoids 16b to 19 of the pressure reducing fluid pressure switching valves 16 to 19
b is switched to the valve open state. As a result, the brake fluid pressure in the wheel cylinders 6 to 9 escapes to the reservoirs 4 and 5 via the recirculation pipes 29 to 32, so that the braking force on the wheels is released and the wheels are prevented from locking.

In the holding mode, the pressure increasing hydraulic pressure switching valve 1
2 to 15 and the pressure-reducing hydraulic pressure switching valves 16 to 19 are kept closed, and the brake hydraulic pressures of the wheel cylinders 6 to 9 are retained. During such anti-lock braking operation, the suction pumps 54 and 55 are always activated in order to prevent the master cylinder 3 from running out of brake fluid. Therefore, when the pressure reducing mode is set during the anti-lock braking operation and the pressure reducing hydraulic pressure switching valves 16 to 19 are opened, the brake fluid from the wheel cylinders 6 to 9 side flows out to the return pipe lines 29 to 32. Then, the brake fluid in the return conduits 29 to 32 is sucked into the return conduits 33 and 34 by the suction operation of the suction pumps 54 and 55.

After that, the brake fluid sucked by the suction pumps 54, 55 passes through the check valves 58, 59 and is returned to the first and second brake pipelines 10, 11. However, during the anti-lock braking operation, for example, when the rotation speed of each wheel becomes high, the pressure reducing mode is switched to the pressure increasing mode or the holding mode, and the pressure reducing hydraulic pressure switching valves 16 to 19 are closed and the pressure increasing hydraulic pressure is increased. The switching valves 12 to 15 open.

When the pressure reducing mode is switched to the pressure increasing mode or the holding mode in this way, the brake fluid continues to be circulated to the master cylinder 3 side by the suction operation of the suction pumps 54 and 55, so that the reservoirs 4 and 5 are filled. The brake fluid is sucked into the return conduits 33 and 34. The pressure increasing hydraulic pressure switching valves 12 to 15, the pressure reducing hydraulic pressure switching valves 16 to 19 and the suction pumps 54 and 55 are operated by a command from the antilock braking force control circuit 60. Further, the antilock braking force control circuit 60 includes a vehicle speed sensor 61 for detecting the traveling speed of the vehicle, an acceleration sensor 62 for detecting the acceleration of the vehicle, and a wheel rotation sensor 6 for detecting the rotational speed of each wheel.
3 to 66 and a brake switch 67 that switches from off to on when the brake pedal 1 is depressed are connected.

Therefore, the anti-lock braking force control circuit 60
When the brake switch 67 is turned on, the pressure increasing hydraulic pressure switching valve 1 is generated based on the signals output from the vehicle speed sensor 61, the acceleration sensor 62, and the wheel rotation sensors 63 to 66.
2 to 15 and the pressure reducing hydraulic pressure switching valves 16 to 19 are controlled to adjust the brake hydraulic pressure to each wheel so that each wheel does not lock while the vehicle is traveling.

Here, the traveling state such as cornering, ascending / descending or accelerating / decelerating changes in a complicated manner during traveling. As the running state of the vehicle changes, the load acting on each wheel also changes. The tire of each wheel is held at a predetermined outer diameter by air pressure, but the outer diameter of each wheel fluctuates when the load moves. For example, during acceleration, the load of the vehicle moves to the rear wheel side, so that the load on the wheel on the rear wheel side increases and the ground contact portion of the tire on the rear wheel side bends flat. As a result, the tire diameter of the front wheels increases, while the tire diameter of the rear wheels decreases.

On the other hand, at the time of deceleration (braking), the load of the vehicle moves to the front wheels, so that the load on the wheels on the front wheels increases and the ground contact portion of the tires on the front wheels bends flat. As a result, the tire diameter of the front wheels becomes smaller, while the tire diameter of the rear wheels becomes larger. The relationship between such a load and the amount of bending of the tire is in a proportional relationship as shown in FIG. Therefore, if the magnitude and direction of the acceleration of the vehicle are known, the load movement with respect to each wheel can be obtained, and the amount of bending of each tire can be calculated from the magnitude of the load acting on each wheel.

ROM of antilock braking force control circuit 60
In (not shown), a map having data of changes in the amount of flexure of the tire with respect to changes in load as shown in FIG. 2 is stored. Also, R of the antilock braking force control circuit 60
The OM (not shown) includes a tire flexure amount estimation control program for estimating a flexure amount of a tire due to load movement during braking, which will be described later, and a braking force applied to a rear wheel based on the estimated flexure amount of the tire. And a braking force change control program for changing.

According to the present invention, the pressure increasing hydraulic pressure switching valves 12 to 15 and the pressure reducing hydraulic pressure switching valve 16 described above are corrected by correcting the fluctuation of the wheel rotation speed due to the change of the bending amount of each tire due to the load movement.
By performing the switching control of ~ 19, the braking force distribution to each wheel is set as a target distribution, and the braking performance of each wheel is enhanced.
Here, the rear wheel target wheel speed is VWR *, the actual front and rear wheel wheel speeds VWF∧, VWR∧, the wheel speed sensor value VWF,
Let VWR be the target wheel speed coefficient of the rear wheels, K be the ratio of the relationship between the load and the deflection of the tire, the rear wheel values be kf, kr, and the tire static load radius be R, and the rear wheel target wheel speed (VWR *) Can be expressed as

VWR * = VWR∧ = K × VWF∧ (1) When this (1) is corrected based on the relationship between the load and the amount of tire deflection in FIG. 2, VWF∧; VWF = (R-kf × GX ); R ... (2) VWR∧; VWR = (R + kr × GX); R ... (3) When the above equations (2) and (3) are substituted into equation (1), VWR * = K × (1- kf / R × GX) / (1 + kr / R × GX) × VWF (4) As described above, when the coefficient of the rear wheel target wheel speed (VWR *) is corrected by the acceleration in the front-rear direction, the reduction amount of the rear wheel brake hydraulic pressure is reduced, and the braking force control close to the target braking force distribution can be performed.

Further, a control method based on the calculation by the above equation (4) will be described. A case where the braking operation is performed while the vehicle is traveling straight will be described. In order to effectively use the braking force of the rear wheels, a control method when the braking force distribution of the front and rear wheels is 1: 1 will be described. If the target wheel speed coefficient K of the rear wheels is K = 0.96 in the above equation (4),
The rear wheel target wheel speed (VWR *) can be expressed by the following equation.

VWR * = 0.96 × (1-kf / R × GX) / (1 + kr / R × GX) × VWF (4) Here, when the friction coefficient μ of the road surface is 1.0, the front wheels The distribution of the braking force and the rear wheel braking force is the braking force distribution as shown by the center line I in FIG. Further, when the friction coefficient μ of the road surface is 0.5, the distribution of the front wheel braking force and the rear wheel braking force becomes the distribution of braking force as shown by the middle line II in FIG. This diagram II is
It is a graph when the rear wheel target wheel speed coefficient K = 0.96 (corresponding to straight braking).

In FIG. 3, the broken line substantially parallel to the horizontal axis is the rear wheel lock limit value according to the magnitude of the friction coefficient μ of each road surface, and the broken line substantially parallel to the vertical axis is each road surface. It is a front wheel lock limit value according to the magnitude of the friction coefficient μ. Further, the middle line diagram III in FIG. 3 is a graph in the case where the rear wheel target wheel speed coefficient K = 1 (corresponding to straight-ahead braking).
The braking force distribution of the front and rear wheels was adjusted to be lower than I, and the braking force was distributed so that the braking force to the front wheels was greater than the braking force to the rear wheels. In that case, the braking force of the rear wheels is kept small in order to ensure stability during braking. Moreover, in the conventional case, since the rear wheels are provided with a large margin so as not to be locked, the braking performance on the rear wheels side cannot be sufficiently exhibited.

A midline diagram IV in FIG. 3 is a graph of a basic distribution line showing a boundary value at which the pressure increasing mode is switched to the pressure reducing mode. And in the case of the line I and the line diagram II, they can be classified into three patterns of the pressure increasing mode (-), the pressure reducing mode (-), and the antilock braking force control mode (-) in FIG.

From the above equation (4), in the pressure increasing mode (-), VWR> VWR * = 0.96 * (1-kf / R * GX) / (1 + kr / R * GX) * VWF ... (5) That is, the rear wheel target wheel speed (VWR *) becomes smaller than the front wheel speed, and the rear wheel rotates faster than the front wheel. Therefore, the pressure increasing hydraulic pressure switching valves 12 to 15 and the pressure reducing hydraulic pressure switching valve are used. 16 to 19 are not controlled, and the brake fluid pressure from the master cylinder 3 is in the open state.
It is directly supplied to the wheel cylinders 7 and 8 for the rear wheels via 5. In the case of the pressure reduction mode (-), VWR <VWR * = 0.96 * (1-kf / R * GX) / (1 + kr / R * GX) * VWF (6). Therefore, the rear wheel target wheel speed (VWR *) is higher than the front wheel wheel speed, and the rear wheel is rotating slower than the front wheel. 12 to 15 and depressurizing hydraulic pressure switching valves 16 to 19
To reduce the braking force on the rear wheels. That is, in the depressurizing hydraulic pressure switching valves 17 and 18 for the rear wheels, the solenoids 17b and 18b are excited immediately before the rear wheels are locked, and the valve bodies 17a and 18a are switched to the open valve positions, so that the wheel cylinders 7 and 8 are closed. The brake fluid pressure is released to the reservoirs 4 and 5 to reduce the brake fluid pressure. Anti-lock braking force control mode (~)
In the case of, the rear wheel is in the antilock braking force control region immediately before being locked, and the pressure increasing hydraulic pressure switching valves 12 to 15 and the pressure reducing hydraulic pressure switching valve 1 are set so that the above expression (4) is satisfied.
The braking force is weakened by controlling 6 to 19 so that the rear wheels are not locked.

A case where the vehicle is braked in a turning state such as during cornering will be described. The target wheel speed coefficient K of the rear wheels is corrected by the wheel speed and the lateral acceleration of the turning braking. As shown in FIG. 4, the values of the target wheel speed coefficient K of the rear wheels are set to K1 to K4 (K1 <K2) according to the relationship between the vehicle speed (V: estimated vehicle body speed) and the lateral acceleration (GY).
By correcting to any value of <K3 <K4), the braking efficiency at the time of straight braking and at the time of cornering braking can be improved, and the vehicle stability at the time of turning braking can be enhanced.

Next, the braking force control process executed by the antilock braking force control circuit 60 will be described with reference to FIG. In FIG. 5, when the driver depresses the brake pedal 1 to perform a braking operation, the brake switch 67 is turned on. Therefore, when the brake switch 67 is turned on in step S1 (hereinafter “step” is omitted), S
2, the longitudinal acceleration GX and the lateral acceleration GY detected by the acceleration sensor 62, and the rotation speed VWi of each wheel detected by the wheel rotation sensors 63 to 66.
Read (i = FL, FR, RL, RR).

At the next step S3, the vehicle speed VB detected by the vehicle speed sensor 61 is read. Then, in S4, the slip ratio S (= (VB-VRi) / VB) of the left and right rear wheels is calculated from the rear wheel rotation speed VRi and the vehicle body speed VB. The vehicle body speed VB is not detected by the vehicle speed sensor 61, and the vehicle body speed VB may be an estimated vehicle body speed used in antilock control as is well known.

At next S5, it is checked whether the slip ratio S calculated at S4 is a value larger than the threshold value α of the antilock braking force control region. In this S5, S> α
If so, the routine proceeds to S6, where normal antilock braking force control is executed. That is, in S6, the pressure increasing hydraulic pressure switching valve 1
The braking force is adjusted so that each wheel is not locked during traveling by controlling the opening and closing of the hydraulic pressure switching valves 2 to 15 and the hydraulic pressure switching valves 16 to 19 for pressure reduction. Since the detailed control of the anti-lock braking force control is well known, its explanation is omitted here.

However, if S <α in S5, the process proceeds to S7, in which the target wheel speed coefficient K is determined from the relationship between the lateral acceleration GY and the vehicle speed VB shown in FIG. In the next S8, a correction value for the tire outer diameter is calculated based on the longitudinal acceleration GX. That is, the radius to the ground contact portion of each wheel is calculated by the load movement due to the acceleration GX in the front-rear direction, and the amount of bending of the tire due to the load movement during braking is estimated.

After that, the program proceeds to S9, and the rear wheel target wheel speed (VWR *) is calculated by the calculation of the equation (4). As described above, since the actual wheels support the weight of the vehicle, the ground contact portion of the tire is bent in a flat shape according to the amount of weight acting on each wheel. Therefore, in S9, the rear wheel target wheel speed (VWR *) is calculated based on the actual tire outer diameter in consideration of the degree of bending of the tire due to the load movement.

In the next S10, the rear wheel target wheel speed (VWR *) calculated in S9 is the wheel rotation sensors 64,6.
It is checked whether it is smaller than the wheel speed (VWR) of the rear wheels detected by 5. In this S10, VW
When R * <VWR, the wheel speed of the rear wheels (VWR)
Is greater than the rear wheel target wheel speed (VWR *), S
Proceeding to 11, the brake fluid pressure from the master cylinder 3 is supplied to the wheel cylinders 7 and 8 for the rear wheels while keeping the pressure increasing fluid pressure switching valves 13 and 14 on the rear wheel side open.

As a result, the brake fluid pressure to the wheel cylinders 7 and 8 for the rear wheels is increased, and the braking force of the rear wheels is increased. As a result, the braking force distribution becomes larger for the rear wheels than for the front wheels, and braking is performed so that the wheel speed (VWR) of the rear wheels approaches the rear wheel target wheel speed (VWR *). However, in S10, if VWR *> VWR, then S
In step 12, it is checked whether the rear wheel target wheel speed (VWR *) calculated in S9 is larger than the rear wheel speed (VWR) detected by the wheel rotation sensors 64 and 65. In this S12, when VWR * <VWR, the wheel speed (VWR) of the rear wheels is equal to the rear wheel target wheel speed (VWR *), so the routine proceeds to S13, where the pressure increasing hydraulic pressure switching valve 13 for the rear wheels is used. , 14 are closed and the brake fluid pressure from the master cylinder 3 is maintained at the current pressure.

As a result, the brake fluid pressure to the wheel cylinders 7 and 8 for the rear wheels is kept constant. as a result,
The wheel speed (VWR) of the rear wheels is equal to the target wheel speed of the rear wheels (VWR).
*) The vehicle is braked to approach. Also, in S12,
When VWR *> VWR, the rear wheel speed (VW
R) is smaller than the rear wheel target wheel speed (VWR *),
Proceeding to S14, the brake fluid pressures of the rear wheel wheel cylinders 7, 8 are released to the reservoirs 4, 5 by keeping the rear wheel pressure reducing fluid pressure changeover valves 17, 18 in the open state to reduce the brake fluid pressures. .

As a result, the brake fluid pressure in the wheel cylinders 7, 8 for the rear wheels is reduced, and the braking force for the rear wheels is reduced. As a result, the rear wheel speed (VWR) is braked so as to approach the rear wheel target wheel speed (VWR *). In this way, the wheel speeds (VWR) of the rear wheels are supplied to the wheel cylinders 7 and 8 for the rear wheels in accordance with the actual tire outer diameter accompanying the load movement so that the rear wheel target wheel speed (VWR *) matches. Since the brake fluid pressure to be controlled is controlled, during braking, the braking force distribution on the rear wheel side is made larger than that on the front wheel side to effectively use the braking performance on the rear wheel side as shown in FIG. You can

In the above embodiment, the braking force of the left and right rear wheels is controlled individually. However, the present invention is not limited to this. For example, the braking force of the left and right rear wheels is the same as the braking speed of the front wheels. The braking force may be controlled so that the hydraulic pressure is obtained.

[0044]

As described above, according to the present invention, the tire flexure amount estimating means estimates the flexure amount of the tire due to the movement of the load during braking, and the tire flexure amount is estimated based on the estimated flexure amount of the tire. Since the braking force is changed, the braking force according to the actual wheel speed is applied to each wheel, and even if the outer diameter changes due to the tire bending due to the load movement during braking, the optimum braking force can be obtained for each wheel. The braking distance can be shortened. Therefore, for example, it is possible to prevent the rear wheel braking force from being controlled to be small by increasing the difference from the actual wheel speed due to the bending of the tire.
The brake pressure can be set according to the amount of bending of the tire due to the movement of the load, and the rear wheel braking force can be increased to sufficiently exert the braking performance on the rear wheel side.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a braking force control device according to the present invention.

FIG. 2 is a graph showing a relationship between a load and a bending amount of a tire.

FIG. 3 is a graph showing distribution of front wheel braking force and rear wheel braking force.

FIG. 4 is a graph showing a region of a target wheel speed coefficient K.

FIG. 5 is a flowchart of a braking force control process executed by an antilock braking force control circuit.

[Explanation of symbols]

 1 Brake Pedal 3 Master Cylinder 4, 5 Reservoir 6-9 Wheel Cylinder 10 1st Brake Pipeline 11 2nd Brake Pipeline 12-15 Pressure Increase Hydraulic Pressure Switching Valve 16-19 Pressure Reduction Hydraulic Pressure Changeover Valve 20-27 For Supply Pipe lines 28a to 28d Supply system line 29 to 34 Reflux line pipes 54, 55 Suction pump 60 Antilock braking force control circuit 61 Vehicle speed sensor 62 Acceleration sensor 63 to 66 Wheel rotation sensor 67 Brake switch

Claims (1)

[Claims] 1. A wheel speed detecting means for detecting a speed of each wheel of a vehicle, a calculating means for calculating a target rear wheel speed based on a wheel speed of a front wheel detected by the wheel speed detecting means, and a braking time. A braking force control device comprising: a control unit that controls the braking force of the rear wheels so that the rear wheel speed becomes the target rear wheel velocity calculated by the calculation unit. A tire flexure amount estimating means for estimating the flexure amount of the tire, and a braking force changing means for changing the braking force to the rear wheels based on the tire flexure amount estimated by the tire flexure amount estimating means. A braking force control device.