JP3268613B2 - Wheel brake pressure control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling a brake hydraulic pressure applied to a wheel brake, and more particularly, but not exclusively, to a wheel slip ratio or road surface friction during braking by a driver. By estimating the coefficient μ, the wheel brake pressure is reduced so as to avoid a complete stop of the wheel rotation (wheel lock) even though the vehicle body is moving, and then the braking distance is reduced as much as possible. Increase the pressure so that it becomes shorter,
In addition, anti-skid control that repeats pressure reduction and pressure increase as necessary.
Calculates the braking force distribution of front, rear, left and right wheel brakes to ensure running stability and steering performance when the vehicle changes or changes in acceleration or deceleration, road surface inclination, unevenness, etc. The present invention relates to a wheel brake pressure control device suitable for braking force distribution control for individually increasing and decreasing each wheel brake pressure according to the distribution.

[0002]

2. Description of the Related Art Normally, a brake pressure (first pressure) corresponding to a depression pressure of a brake pedal operated by a driver is applied to a wheel brake from a brake master cylinder. The vehicle speed (reference speed) is estimated and calculated from the rotation speeds of a plurality of wheels, and the wheel slip ratio or the road surface friction coefficient μ is calculated or estimated from the reference speed and the wheel rotation speed. The wheel brake pressure is reduced so as to avoid a complete stop of the wheel rotation (wheel lock) despite that the brake is stopped, and then the pressure is increased so that the braking distance becomes as short as possible. For anti-skid control in which pressure is repeatedly reduced and increased, a pressure (second pressure) higher than the first pressure is applied to the first pressure line to the pressure increasing and decreasing valve for decreasing and increasing the wheel brake pressure and the pressure increasing and decreasing valve. A pressure source comprising a fluid pump and an electric motor for driving the fluid pump. When an electronic control unit for executing anti-skid control determines that a change in wheel brake pressure (automatic intervention) is necessary, the pressure is increased. From the source Give 2 pressure to increase the pressure reducing valve and the wheel blur using increasing pressure reducing valve - key to a second pressure to a low pressure (drain pressure) selectively switches. The low pressure supply reduces the wheel brake pressure, and the second pressure supply increases the wheel brake pressure. One such type of anti-skid control is
It is presented in Japanese Patent Application Laid-Open No. 2-38175.

Recently, not only the wheel brake pressure has been controlled from the viewpoint of the wheel slip rate and the braking distance during the braking of the vehicle, but also according to the driving and running conditions of the vehicle and the load distribution on the vehicle. The electronic control unit calculates the braking force distribution of the front, rear, left and right wheel brakes for securing the directional stability of the vehicle during braking, and uses the pressure increasing / reducing valve to satisfy the distribution. Braking force distribution control for adjusting pressure has been proposed. The present inventors have disclosed in, for example,
85327, JP-A-5-85340 and JP-A-5-85336. Also,
In the above-described anti-skid control and braking force distribution control, a wheel brake pressure system in which the second pressure applied to the pressure increasing / decreasing valve is, for example, 20% higher than the first pressure by a hydro booster pressure is disclosed in Japanese Patent Application No. 4-330062. Presented.

In any of the above-mentioned conventional examples, the braking force distribution control as well as the anti-skid control requires the driver to depress the brake pedal. In the case of the anti-skid control, the wheel braking by depressing the brake pedal is so-called. When braking, the wheel brake is depressurized once, and then increased so that the desired wheel slip ratio and the braking distance are shortened as much as possible. Since the brake pressure is operated, it is reasonable to use the hydro booster pressure, which is a pressure corresponding to the depression and release of the brake pedal, for the pressure increase during the anti-skid control. However, in the case of the braking force distribution control, it is advantageous to secure the directional stability and the steering performance of the vehicle in accordance with changes in the driving state and running state of the vehicle, the load distribution on the vehicle body and the friction coefficient μ of the road surface. -The brake pressure of each wheel is adjusted to realize the brake pressure distribution (the allocation of the brake pressure to each of the front, rear, left and right wheel brakes), so that the required braking force distribution is realized with the hydro booster pressure. It may not be possible. For example, when the depression pressure of the brake pedal is low, the hydro booster pressure is low, but a higher brake pressure may be required for the distribution of braking force.

[0005] When the vehicle is suddenly started or turned without stepping on the brake pedal, the load distribution on the vehicle body and the friction coefficient μ of the road surface are temporarily changed, and the directional stability and steering performance of the vehicle may be deteriorated. In some cases, it is preferable to have a braking force distribution control. However, since the brake pedal is not depressed, the wheel brake pressure cannot be increased by the hydro booster pressure. Further, in the braking force distribution control, it is preferable that each of the brake pressures of the front, rear, left, and right wheels can be individually controlled. Depending on the vehicle type (engine position, driver's seat position, seat distribution, front wheel drive / rear wheel drive / all wheel drive, front wheel steering / rear wheel steering / front / rear wheel steering, presence / absence of a cargo bed), all the wheels may not be shaken. -Without having to control each of the pressures individually
In the braking force distribution control of the brake pressure of one or several specific wheels,
Directional stability and steering characteristics can be ensured.

[0006] The above problems and demands are such that when a braking force distribution is performed by providing an auxiliary pressure source for generating a substantially constant high pressure, the constant high pressure of the auxiliary pressure source is increased via a pressure increasing / reducing valve unit. It is improved by giving to the key.

[0007]

By the selective increase or hold of the front, rear, and left and right wheel brakes by the braking force distribution control, the wheel slip ratio increases, thereby increasing the anti-skid ratio. Skid control can be triggered. Alternatively, even if this is not the case, the braking force distribution control and the anti-skid control may be prioritized depending on the driving state or running state of the vehicle, but may be executed substantially concurrently. When the pressure adjustment (starting from the pressure reduction) by the anti-skid control is started while the wheel brake pressure adjustment by the braking force distribution control is being performed, the braking force distribution control has the first meaning in increasing the pressure. The anti-skid control is meaningful and the pressure reduction has the first meaning, so both controls collide.

It is a first object of the present invention to rationally harmonize anti-skid control and braking force distribution control,
In addition, a second object is to express each of the functions of the anti-skid control and the braking force distribution control as high as possible.

[0009]

According to a first embodiment of the present invention, an auxiliary pressure source (22) for generating a brake pressure irrespective of the operation of a brake pedal is provided. The braking force distribution control that supplies the brake pressure of the auxiliary pressure source to the brake of the wheel to be controlled and the wheel slip are compared with a predetermined control start wheel slip reference to determine whether anti-skid control is necessary. −
Control means for performing anti-skid control for increasing and decreasing pressure
In the wheel brake pressure control device provided with (10), the control means starts the control for the anti-skid control on the control target wheel at the time of executing the braking force distribution control as compared with the case where the braking force distribution control is not executed. The wheel slip standard is set higher.

In a second embodiment, an auxiliary pressure source (22) for generating a brake pressure independently of operation of a brake pedal is provided.
When it is determined that the braking force distribution control is necessary, the braking force distribution control that supplies the brake pressure of the auxiliary pressure source to the brake of the control target wheel and the anti-skid control by comparing the wheel slip with a predetermined wheel slip reference are performed. In the wheel brake pressure control device, which is provided with a control means (10) for performing anti-skid control for increasing and reducing the wheel brake pressure when it is determined that it is necessary, the control means controls the braking force distribution control. When the anti-skid control is induced for the wheel to be controlled by the execution, the braking force distribution control ends.
To determine Taka not, to abort the uninstall <br/> Chisukiddo control based on the determination result of the ends, characterized in that.

[0011] of the present invention, the preferred embodiment described below includes all of the first and second actual embodiments with features.

In the parentheses, for ease of understanding, symbols attached to the corresponding elements of the embodiment shown in the drawings are shown for reference.

[0013]

According to the first embodiment of the present invention, the control means (10)
However, when the braking force distribution control is executed, the control start wheel slip reference for the anti-skid control on the control target wheel is set higher than when the braking force distribution control is not executed.

Thus, when the control means (10) is executing the braking force distribution control on the wheel to be controlled, when the wheel slip is relatively high, the pressure adjustment (pressure reduction) of the wheel brake pressure by the anti-skid control is performed. ) Is started to reduce wheel slip, and at higher wheel slip pressure reduction is stopped and back to pressure buildup. That is, the start sensitivity of the anti-skid control is deepened, and accordingly, the probability of starting the anti-skid control during the braking force distribution control is reduced.

When the control means (10) does not substantially perform the braking force distribution control on the wheel to be controlled, the wheel brake pressure is adjusted by the anti-skid control (pressure reduction) when the wheel slip is relatively low. ) Is started to reduce wheel slip, and at relatively low wheel slip, depressurization is stopped and returns to pressure buildup. That is, the start sensitivity of the anti-skid control becomes shallower, and the braking force adjustment of the anti-skid control is more effectively exerted.

According to a second embodiment of the present invention, the control means
(10), in the case where for that controlled wheel anti-skid control has been induced by executing braking force distribution control, it is determined whether the braking force distribution control is finished, the final
The anti-skid control is stopped based on the determination result that the control has been completed. As a result, the wheel brake pressure becomes the output pressure of the brake master cylinder (2). When the control means (10) is executing the braking force distribution control, a high slip may occur due to the braking force distribution control pressure and the output pressure of the brake master cylinder (2). That is, the braking force distribution control pressure may induce pressure adjustment (start from pressure reduction) by anti-skid control. Such pressure regulation by anti-skid control becomes unnecessary and is stopped by stopping the braking force distribution control. If the pressure regulation by the anti-skid control is still required even after the braking force distribution control is completed, the anti-skid control restarts the pressure regulation. The restarted pressure adjustment is terminated when the pressure adjustment becomes unnecessary based on the pressure adjustment necessity determination of the anti-skid control because the braking force distribution control is not executed. Since the anti-skid control induced by the braking force distribution control is finished with the end of the braking force distribution control, the braking force distribution control is upon completion, Ru can be migrated to a normal running state.

[0017] The onset Ming Other objects and features will become apparent from the following description of embodiments with reference to the accompanying drawings.

[0018]

FIG. 1 shows a wheel brake pressure system according to an embodiment of the present invention. FIG. 2 shows a wheel brake 51 connected to various solenoid valves and sensors of the wheel brake pressure system. The outline of the electric system for controlling the pressure of each of Nos. To 54 will be described.

Referring first to FIG. 1, the brake pedal 3
When the driver (driver) steps on the front wheel brake fluid pressure (2
a) and the rear wheel brake fluid pressure (2b) is generated. In the state shown in FIG. 1, the front wheel brake fluid pressure (2a) is generated.
Are the wheel brakes 51 of the front right wheel FR and the wheel brakes 52 of the front left wheel FL through the electromagnetic switching valves 61 and 62.
Join. The rear wheel brake fluid pressure (2b) is regulated by the proportional control valve 6 and further passed through the electromagnetic switching valve 63 and the pressure increasing solenoid valve 35 of the pressure increasing / decreasing valve unit 356 to the rear right wheel RR.
And the wheel brake 54 of the rear left wheel RL via the pressure increasing solenoid valve 37 of the pressure increasing / reducing valve unit 378. These brake fluid pressures are hereinafter referred to as first pressures.

The pump 21 is driven by an electric motor 24 to suck the brake fluid in the reservoir 4 and to check the check valve 25.
To the accumulator 22. Accumule
The high pressure of the heater 22 is supplied to the hydro booster 5 and the electromagnetic switching valves 64 and 65. The pressure of the brake fluid in the accumulator 22 is detected by a pressure sensor 46. When the pressure of the accumulator 22 drops below the lower limit, the low pressure switch 47 is closed. Reservoir 4 and accumulator 22
A relief valve 23 is interposed therebetween, and when the pressure of the accumulator 22 reaches the upper limit value, the relief valve 23 releases the brake fluid of the accumulator 22 so that the pressure becomes lower than the upper limit value. Release to the reservoir 4 until it is.

The electronic control unit 1 shown in FIG.
0 indicates opening of the low pressure switch 47 (pressure has exceeded the lower limit)
/ Close (pressure is below the lower limit) and the pressure sensor 46
When the low pressure switch 47 is closed (the pressure is lower than the lower limit), the electric motor 24 is driven. When the detected pressure of the pressure sensor 46 reaches a set value lower than the upper limit, the electric motor is read. By stopping 24, the pressure of the accumulator 22 is maintained at a substantially constant pressure (range between the lower limit and the set value). This brake hydraulic pressure of the accumulator 22 is hereinafter referred to as a third pressure.

The pressure (third pressure) of the accumulator 22 is applied to the hydro booster 5, and
Regulates the pressure to a pressure proportional to the pushing force of the brake pedal 3 and supplies the pressure to the electromagnetic switching valves 64 and 65. This is the booster pressure, which is about 120% of the pressure output from the brake master cylinder 2. This booster pressure is hereinafter referred to as a second pressure.

The electromagnetic switching valves 64 and 65 are supplied with an accumulator pressure (third pressure) and a booster pressure (second pressure). When the electric coil is not energized, the electromagnetic switching valve 64, as shown in FIG. 1, increases the booster pressure (second pressure).
The pressure increasing solenoid valve 31 of the pressure increasing / decreasing valve unit 312 for regulating the pressure of the front right wheel brake 51 and the front left wheel brake 5
2. The pressure-increasing solenoid valve 3 of the pressure-increasing / decreasing valve unit 334
3, when the electric coil is energized, the accumulator pressure (third pressure) is input to the pressure increasing solenoid valves 31 and 33 instead of the booster pressure (second pressure). Po
Give to When the electric coil is not energized, the electromagnetic switching valve 65 supplies a booster pressure (second pressure) to the electromagnetic switching valve 63 as shown in FIG. An accumulator pressure (third pressure) is applied to the electromagnetic switching valve 63 instead of the star pressure (second pressure).

When the electric coils are not energized, the electromagnetic switching valves 61 and 62 change the output pressure (first pressure) of the brake master cylinder 2 to the front right wheel brake 51 and the front left as shown in FIG. When the electric coil is energized, the output port of the pressure increasing / decreasing valve unit 312 for regulating the pressure of the front right wheel brake 51 (the output port of the electromagnetic valve 31 for increasing pressure) and The front right wheel brake 51 and the front left wheel brake 52 are connected to the output port of the pressure increasing / reducing valve unit 334 for adjusting the pressure of the front left wheel brake 52 (the output port of the pressure increasing solenoid valve 33). Connecting.

When the electric coil is not energized, the solenoid-operated switching valve 63 increases the output pressure of the brake master cylinder 2 (first pressure) by the proportional control valve 6 as shown in FIG. The input port of the pressure increasing / decreasing valve unit 356 for adjusting the pressure of the right wheel brake 53 (the input port of the pressure increasing solenoid valve 35)
) And the input port of the pressure increasing / decreasing valve unit 378 (the input port of the pressure increasing solenoid valve 378) for adjusting the pressure of the rear left wheel brake 54. When the electric coil is energized, the unit 356 and The output pressure (second pressure or third pressure) of the electromagnetic switching valve 65 is applied to the input port 378.

The output port of the pressure increasing / decreasing valve unit 312 for adjusting the pressure of the front right wheel brake 51 (the output port of the pressure increasing solenoid valve 31) and the pressure increasing / decreasing valve unit for adjusting the pressure of the front left wheel brake 52. An electromagnetic on-off valve HSV is provided between the output port 334 (output port of the pressure increasing solenoid valve 33) and the front wheel first pressure line (output port of the master cylinder 2).
1 and HSV2 are inserted. Also, rear wheel system 1
Electromagnetic switching valves HSV3 and HSV4 are interposed between the pressure line (output port of the proportional control valve 6) and the rear right wheel brake 53 and the rear left wheel brake 54, respectively. These electromagnetic switching valves HSV1 to HSV4 are closed (cut off) as shown in FIG. 1 when the electric coil is not energized, and open (flow) when the electric coil is energized. When the valve is open, the check valve inside HSV1 to HSV4 applies the first pressure to the wheel brake when the first pressure is higher than the wheel brake pressure, but when the first pressure is lower than the wheel brake pressure, Wheel brake pressure is 1st
It does not change with pressure (the first pressure does not substantially add to the wheel brake).

In the brake pressure system shown in FIG. 1, a brake pressure transmission system for applying only the output pressure of the brake master cylinder 2 to the wheel brake, a brake pressure transmission system during anti-skid control, A brake pressure transmission system during power distribution control, and a brake pressure transmission system for adding to the wheel brake by adding the pressure by the braking force distribution control and the output pressure of the brake master cylinder 2 are configured. Elements to be applied to each wheel
Table 1 and Table 2 show the results by type. In these tables, the elements constituting each transmission system are extracted and displayed in the direction from the wheel brake toward the brake pressure source. In Tables 1 and 2, and in the drawings, “anti-skid control” is described as “ASB control”. "AS
"B" means "anti-skid" in this document.

[0028]

[Table 1]

[0029]

[Table 2]

In each of the columns of "anti-skid control pressure system", "braking force distribution control pressure system" and "foot brake pressure + braking force distribution control pressure system" in Tables 1 and 2, the pressure increasing / decreasing valve unit 312 is used. 334, 356 and 378 are controlled to increase and decrease in pressure by the electronic control unit 10 (FIG. 2). That is,
When pressure reduction is required, the pressure-increasing electromagnetic on-off valves 31, 33, 35, and 37 in these units are closed by energizing their electric coils, and the pressure-reducing electromagnetic on-off valves 32, 3
The valves 4, 36 and 38 are opened by energizing their electric coils.
1, 33, 35 and 37 are opened by de-energizing their electric coils, and the pressure reducing solenoid on-off valves 32, 34, 36 and 38 are closed by de-energizing their electric coils. When hold (maintaining the current pressure as it is) is required, the pressure-increasing electromagnetic on-off valves 31, 33, 35, and 37 are closed by energizing their electric coils, and the pressure-reducing electromagnetic on-off valves 32, 34 are provided. , 36 and 38 are closed by de-energizing their electric coils.

Referring to FIG. The main component of the electronic control unit 10 is a microcomputer 11, and the main components of the microcomputer 11 are a CPU 14, a ROM 15, and an RA.
M16 and timer 17. The electronic control unit 10 further includes a signal processing circuit 18a to 18m for energizing (energizing) the sensor to generate a detection signal, an electric circuit for supplying the detection signal to the microcomputer 11, that is, an input interface 12, There are a motor driver and a solenoid driver 19a to 19r, and an electric circuit for giving a control signal of the microcomputer 11 to the drivers 19a to 19r, that is, an output interface 13.

Front right, front left, rear right and rear left wheels 51-51
Each of the wheel speed sensors 41 to 44 detects the rotational speed of each of the wheels 54, and the signal processing circuits 18 a to 18 d generate electric signals (wheel speed signals) representing the respective wheel speeds and supply them to the input interface 12. Opening of the stop switch 45 which is closed while the brake pedal 3 is being depressed (pedal 3
Signal processing circuit 18e generates an electric signal indicating that the pedal is not depressed (OFF) / closed (the pedal 3 is depressed: ON) and supplies it to the input interface 12. The pressure sensor 46 detects the hydraulic pressure of the accumulator 22 and the signal processing circuit 18
f generates an electric signal (pressure signal) representing the detected pressure and supplies it to the input interface 12. Accumulator 2
The low pressure switch 47 which is closed when the hydraulic pressure of No. 2 is lower than the lower limit value
Open (pressure above the lower limit: off) / close (less than the lower limit:
The signal processing circuit 18g generates an electric signal indicating ON) and supplies the signal to the input interface 12. Output pressure of hydro booster 5 (1 of output pressure of brake master cylinder 2)
20%) is substantially closed when a predetermined value corresponding to a low pressure at which the wheel brake generates a braking force is opened (no wheel braking: off) / closed (with wheel braking: on).
Is generated by the signal processing circuit 18h and applied to the input interface 12.

The yaw rate of the vehicle body is determined by a yaw rate sensor YA.
Is detected, and the signal processing circuit 18i detects the yaw rate (actual yaw rate).
An electrical signal representing the rate is generated and applied to the input interface 12. The rotation angle of the steering wheel is detected by the front wheel steering angle sensor θF, and the signal processing circuit 18j generates an electric signal indicating the front wheel steering angle and supplies it to the input interface 12. The steering angle of the rear wheels is detected by a rear wheel steering angle sensor θR, and a signal processing circuit 18 k generates an electric signal indicating the rear wheel steering angle and supplies the electric signal to the input interface 12. An acceleration sensor (G sensor) detects the longitudinal acceleration of the vehicle body, and a signal processing circuit 181 generates an electric signal indicating the longitudinal acceleration and gives the signal to the input interface 12. The acceleration sensor (G sensor) detects the lateral acceleration of the vehicle body and a signal processing circuit 18
m generates and provides an electrical signal representing the lateral acceleration to the input interface 12.

FIG. 3 shows an outline of the processing functions of the microcomputer 11 shown in FIG. After the engine on the vehicle is started, the power of the electric system on the vehicle is turned on, and the voltage of the system is stabilized, the operating voltage is applied to the electronic control unit 10 (step 1 in FIG. 3; Words are omitted, and only the step No. numbers are described). When the operating voltage is applied, the microcomputer 11 sets the internal registers, the input / output ports and the internal timer to an initial state, and sets the input / output interfaces 12 and 13 to input / read connection and output signals during standby. Set to level (2). The electric motor 2 is supplied to the motor driver 19a.
4 (pump 21), and accumulator 2
In addition to the start of the hydraulic control of step 2, the processing from "operation board & sensor reading" (3) to "braking force distribution control 2" (8), that is, wheel brake The pressure control is executed repeatedly at a substantially predetermined cycle. In the hydraulic pressure control of the accumulator 22, when the pressure detected by the pressure sensor 46 reaches the upper limit, the electric motor 24 (the pump 2) is turned on.
1) is stopped, and the electric motor 24 (pump 21) is driven when the low pressure switch 47 is closed (the hydraulic pressure is lower than the lower limit).

The operation board & is substantially repeated at a predetermined cycle.
“Sensor reading” (3) to “braking force distribution control 2” (8)
In the "operation board & sensor reading" (3) in the process up to the wheel brake pressure control, first, all the input means (sensors, switches, etc.) connected to the input interface 12 are connected. The information is read, and it is determined whether the ASB control and the braking force distribution control need to be executed, whether the wheel brake pressure needs to be reduced, increased, and whether the hold should be performed, and the time for which these should be continued, and whether or not it needs to be terminated. Generate information to be referred to for the determination of. The main ones of the reference information in the present embodiment are as follows.

Information Information Source Actual yaw rate γ Detected value by yaw sensor YA Wheel speed VwFR Detected value by wheel speed sensor 41 Wheel speed VwFL Detected value by wheel speed sensor 42 Wheel speed VwRR By wheel speed sensor 43 Detected value Wheel speed VwRL Detected value by wheel speed sensor 44 Front / rear acceleration gx Detected value by front / rear acceleration sensor GX Lateral acceleration gy Detected value by lateral acceleration sensor GY Front wheel steering angle θf Detected value by steering angle sensor θF Rear wheel steering angle θr Steering angle Detected value by sensor θL Wheel braking ON / OFF Stop switch 45 ON / OFF Wheel acceleration dVwFR Calculated from past and present detected values by wheel speed sensor 41 Wheel acceleration dVwFL Calculated from past and present detected values by wheel speed sensor 42 Wheel Acceleration dVwRR Calculated from past and present detection values by wheel speed sensor 43 Wheel acceleration dVwRL Calculated from past and present detected values by wheel speed sensor 44 Calculated based on estimated vehicle speed Vso VwFR-VwRL and past estimated vehicle speed Vehicle acceleration dVs Calculated based on estimated vehicle speed Vso and past estimated vehicle speed Target yaw Calculated based on the rate γ * θf and Vso Calculated as: Yaw rate deviation Δγ = γ * −γ.

Judgment from turning direction DIR γ of vehicle Wheel slip ratio SwFR Calculated based on VwFR and Vso Wheel slip ratio SwFL Calculated based on VwFL and Vso Wheel slip ratio SwRR Calculated based on VwRR and Vso Wheel slip ratio SwRL VRL Calculated based on Vso.

When reading and calculating the information, the microcomputer 11 stops the stop switch 4.
5 is checked for opening / closing (4). I. Control when brake pedal 3 is not depressed: If stop switch 45 is open (no pedal 3 depressed), "ASB release" (5) is executed.

"ASB Release" (5): The contents of this processing are shown in FIG. Here, first, the contents of a register ASF for storing information as to whether or not pressure adjustment by ASB control has been started, and the contents of a register BDF to store information as to whether or not pressure adjustment by braking force distribution control have been started. Is checked (51, 52). And register A
If the content of SF is 0 (pressure regulation by ASB control is not started), the content of register ASF is updated to 0 (54), and the process of "ASB release" (5) ends (next The process proceeds to "braking force distribution control 1" (6)). Even if the content of the register ASF is 1 (pressure adjustment by ASB control is started), if the content of the register BDF is 1 (pressure adjustment by braking force distribution control is started), The content is updated to 0 (54), and the process of "ASB release" (5) ends. If the content of the register BDF is 0 (pressure adjustment by the braking force distribution control has not been started), the wheel brake pressure system (FIG. 1) is set to the "foot brake pressure system" shown in Tables 1 and 2. Connect to register A
The content of the SF is updated to 0 (54), and the process of "ASB release" (5) ends. That is, this "ASB
In the "release" (5), since there is no depression of the pedal 3 (the switch 45 is off), the ASB control is practically unnecessary and released, but when the pressure adjustment by the braking force distribution control is started (BDF = In (1), the connection of the wheel brake pressure system is not switched because the wheel brake pressure system cannot be returned to the "foot brake pressure system". next,
The microcomputer 11 performs the "braking force distribution control 1".
Proceed to (6).

"Brake force distribution control 1" (6): The contents of this processing are shown in FIG. Here, first, "braking force distribution calculation" (61) is executed. First of all,
Front and rear wheel steering angles θf, θr, reference speed and turning direction DI
Referring to R, the spin / drift amount of the vehicle is calculated, and it is determined from the spin / drift amount and the estimated vehicle speed Vso whether wheel brake pressure control for ensuring the directional stability and steering performance of the vehicle is necessary. However, when it is determined that it is necessary, the braking force is distributed from the steering angle θf and the spin / drift to secure the directional stability and the steering performance (assignment of pressure increase / reduction / hold of each of the wheel brakes 51 to 54). ) Is determined by a map search. Then, from the spin / drift amount and the estimated vehicle speed Vso,
Also, the pressure increase speed (pressure increase valves 31 and 3)
The energizing duty of the pressure reducing valves 3, 35, 37) and the pressure reducing speed (the energizing duty of the pressure reducing valves 32, 34, 36, 38) are determined.

Regarding any wheel brake, pressure increase,
When it is determined that neither the depressurization nor the hold is necessary, the acceleration slip ratio of each wheel (the wheel speed is higher than the vehicle speed when the pedal 3 is not depressed) is determined by referring to the slip ratio of each wheel. Rate), and when there is an acceleration slip of a predetermined level or more, the target slip rate and slip rate deviation (target slip rate−actual slip rate) of each wheel with reference to the slip rate and acceleration of each wheel and the estimated vehicle speed.
Is calculated, and the need for pressure increase, pressure reduction, or hold of each wheel brake is calculated, and if pressure increase or pressure reduction is required, the pressure increase / decrease speed (energization duty) is calculated (the above is 61 times). Content).

Then, the pressure of one of the wheel brakes is increased,
If it is determined that the pressure is to be reduced or held, a control signal for realizing the determined distribution of the braking force and the determined increase / decrease speed is output (63). Then, 1 indicating that the pressure is being adjusted by the braking force distribution control is written into the register BDF (64). The wheel brake pressure system is set to the connection of the "braking force distribution control pressure system" shown in Tables 1 and 2 only for the circuits related to the wheel brake determined to be increased, reduced or hold. Is connected to "foot brake pressure". Power is supplied to the pressure increasing valve or the pressure reducing valve of the pressure increasing / decreasing valve unit (312, 334, 356, 378) connected to the wheel brake determined as increasing, decreasing, or holding at the determined energizing duty. It is. In the case of the hold, the pressure increasing valve is continuously energized (energization duty 100%), and the pressure reducing valve is deenergized (electricity duty 0%).

Wheel brake pressure control for ensuring the directional stability and steering performance of the vehicle is unnecessary (for all wheels,
When it is determined that the increase, depressurization, or hold is not required), the wheel brake pressure system is changed from the connection of the "braking force distribution control pressure system" shown in Tables 1 and 2 to the "foot brake pressure system".
(65), and writes 0 (no pressure adjustment by braking force distribution control) to the register BDF (synonymous with register clear).

Referring again to FIG. 3, while the stop switch 45 is off, the microcomputer 11 reads "sensor reading"(3)-"stop switch 45 on?"
(4)-"ASB release"(5)-"braking force distribution control 1"
(6)-The loop of "sensor reading" (3) is followed. When the stop switch 45 is turned on, the microcomputer 11 proceeds to "ASB control" (7). II. Control when the brake pedal 3 is depressed: “ASB control” (7): FIGS. 6 and 7 show the contents. Here, first, the contents of the register BDF are checked (71), and the register BDF is checked.
Is 0 (no pressure adjustment by the braking force distribution control), the upper limit of the target range of the ratio of the wheel speed to the vehicle speed is set to 0.
9 (the deceleration slip rate of the wheel is 10%) and the lower limit is set to 0.
8 (the wheel deceleration slip rate is 20%) and the wheel speed upper limit V _SH corresponding to these upper and lower limits.
And the lower limit value _VSS is calculated, and the wheel acceleration reference value Gs for determining the necessity of pressure reduction is set to -3 (deceleration because it is a negative value) (72). However, when the content of the register BDF is 1 (the pressure is adjusted by the braking force distribution control), the upper limit of the target range of the ratio of the wheel speed to the vehicle speed is set to 0.8 (the wheel deceleration slip ratio is 20%). 0.7 (the wheel deceleration slip rate is 30%), and the wheel speed upper limit value V _SH and the lower limit value V corresponding to these upper limit value and lower limit value.
_SS is calculated, and a wheel acceleration reference value Gs for determining whether or not pressure reduction is necessary.
Is set to -4 (deceleration because it is a negative value) (73).

Next, the blur of the front right wheel FR - respect keys 51, on the speed VwFR of the wheel FR, as compared to the lower limit _{V SH} and _{V SS,} and the wheel acceleration (negative value deceleration) dV
By comparing wFR with the acceleration reference value Gs, the pressure is reduced as follows.
Pressure increasing or e - determining necessity of field (74FR); VwFR ≦ _{V SS} and when the dVwFR ≦ Gs reduced pressure (741,74
2,743), e when the VwFR ≦ _{V SS} and dVwFR> Gs - field (74
1,742,744), _{VwFR> V SS} and ASF = 1 (when already running pressure regulation of ASB control) pressure increase (741,745,746,747), and starts the pressure adjustment _{VwFR> V SS} and ASF = 0 (ASB control the pressure regulating when they do not) unnecessary, and, when the VwFR ≧ V _SH, release the pressure adjustment of the ASB control.

Next blur front left wheel FL - respect keys 52, on the speed VwFL of the wheel FL, compared with the lower limit value _{V SH} and _{V SS,} and the wheel acceleration (negative value deceleration) dV
The wFL is compared with the acceleration reference value Gs to reduce or increase the pressure or increase the pressure as in the case of the front right wheel brake 51 described above.
It is determined whether the field is necessary (74FL). Similarly, regarding the brake 53 of the rear right wheel RR, the speed VwRR of the wheel RR
Is compared with the upper and lower limit values V _SH and V _SS , and the wheel acceleration (negative value is deceleration) dVwRR is compared with the acceleration reference value Gs, as in the case of the front right wheel brake 51 described above. , Determine whether pressure reduction, pressure increase or hold is required (7.
4RR). Similarly, the shake of the rear left wheel RL - respect keys 54, on the speed VwRL of the wheel RL, compared to the lower limit _{V SH} and _{V SS,} and the wheel acceleration (negative value deceleration) dV
The wRL is compared with the acceleration reference value Gs to reduce or increase the pressure or increase the pressure as in the case of the front right wheel brake 51 described above.
Is determined (74RL).

Then, the above-mentioned steps 74FR, 74
If it is determined in any of the processing of FL, 74RR, and 74RL that pressure reduction, pressure increase or hold is required, a control signal for realizing the determined pressure regulation mode is output (76). Then, 1 indicating that the pressure is being adjusted by the ASB control is stored in the register AS.
Write to F (77). The wheel brake pressure system is set to the connection of the "ASB control pressure system" shown in Tables 1 and 2 only for the circuits related to the wheel brake determined to be increased, reduced, or hold, and the other wheels are set. The brake is connected to "foot brake pressure". Increase / decrease valve unit (312, 33) connected to a wheel brake determined to be increase, decrease, or hold
4, 356, 378) are energized at an energization duty corresponding to the determined pressure regulation mode. In the case of a hold, the pressure increasing valve is continuously energized (energization duty 100%), and the pressure reducing valve is deenergized (energization duty).
0%). Steps 74FR and 74F described above
If it is not determined that pressure reduction, pressure increase, or hold is required in any of the processing of L, 74RR, and 74RL, ASB control has been started so far (ASF
= 1), there is no need to do so, and the ASB control is terminated.
Is written to the register ASF (78D). Before that, it is checked whether the braking force distribution control is being performed (BDF = 1) (78B), and if the braking force distribution control is being performed, the pressure is adjusted by the ASB control. Since the wheel brake pressure may be lower than the master cylinder output pressure, "Hydraulic pressure compensation"
(78C), the pressure increase / decrease valve units 312, 334, 35
The pressure reducing valves 32, 34, 36 and 38 of Nos. 6 and 378 are closed, and the pressure increasing valves 31, 33, 35 and 37 are opened and a predetermined short time is awaited (78C). During this time, the wheel brake pressure rises through the pressure increasing valve. Then, when the predetermined short time has elapsed, 0 is written to the register ASF (78D). As a result, the ASB control is substantially completed, and thereafter the braking force distribution control is being performed (BDF = 1). Therefore, the wheel braking pressure is regulated by the braking force distribution control.

When the ASB control is terminated and the braking force distribution control is not being performed (BDF = 0), the "hydraulic pressure compensation"
(78C) does not execute, but sets the "foot brake pressure system" (78E) and writes 0 to the register ASF (7
8C). In this case, in the setting of the "foot brake pressure system" (78E), the wheel brake pressure system is switched to the connection of the "foot brake pressure system" shown in Tables 1 and 2, and the HSV is connected.
No. 1 to 4 are not energized. Next, the microcomputer 11
Executes "braking force distribution control 2" (8).

"Brake force distribution control 2" (8): The contents are shown in FIG. Here, first, "braking force distribution calculation" (81) is executed. "Brake force distribution calculation" (81)
Is the same as the above-described "braking force distribution calculation" (61), and a detailed description thereof will be omitted. If it is determined in the "braking force distribution calculation" (81) that any of the wheel brakes is to be pressurized, depressurized or held, the register A
Check the contents of SF (83) and find that it is 1 (ASB)
During the pressure adjustment by the control), the pressure adjustment mode determined in the "braking force distribution calculation" (81) is not output in order not to disturb the pressure adjustment by the ASB control. But register ASF
Is 0 (no pressure regulation by ASB control), the on / off valves HSV1 to HSV1 to 4 are first energized (thereby causing a brake).
(The output pressure of the master cylinder 2 also adds to the wheel brake.)
Then, a control output for realizing the pressure regulation mode determined in the "braking force distribution calculation" (81) is output (85). The content of the "output 2 of braking force distribution" (85) is similar to the "output 1 of braking force distribution" (63) described above, but the "decompression calculation" (81) determined in "braking force distribution calculation" (81). Is replaced by "hold". That is, if "pressure reduction" is executed, the pressure reducing valves (32, 34, 36, 38) are opened, and the output pressure of the master cylinder 2 is also reduced through the pressure reducing valve.
It escapes to BA4. This is contrary to the driver's will, so to prevent such wheel brake pressure from being released,
"Output 2 of braking force distribution" (85) replaces "decompression" instruction information with "hold" instruction information and does not execute "decompression". Accordingly, by executing the "braking force distribution calculation" (81) to the "braking force distribution output 2" (85), the wheel brake is supplied with the pressure increase determined by the "braking force distribution calculation" (81). The higher of the pressure and the output pressure of the master cylinder 2 is applied (see FIG. 9). When this output is made, 1 (with pressure adjustment by braking force distribution control) is written into the register BDF (86).

If it is determined in the "braking force distribution calculation" (81) that none of increase, decompression or hold is necessary, the contents of the registers BDF and ASF are checked (87, 87).
88). When the contents of the registers BDF and ASF are both 0 (no pressure adjustment by the braking force distribution control and no pressure adjustment by the ASB control), the wheel brake pressure system is set to the "foot brake pressure system" shown in Tables 1 and 2. And the HSV1-4 are de-energized (90) and the register AS
Write 0 to F and BDF.

If the content of the register BDF is 1, the pressure adjustment by the braking force distribution control that has already been executed is terminated at this stage. Here, the content of the register ASF is 1 (adjustment by the ASB control). Pressure), this ASB
There is a high probability that the pressure adjustment by the control is induced by the pressure adjustment by the braking force distribution control. Then, the pressure regulation by the ASB control is also terminated. That is, the wheel brake pressure system is shown in Table 1.
Then, the connection is switched to the "foot brake pressure system" connection shown in Table 2 and the HSV1 to 4 are de-energized (89), and 0 is written to the registers ASF and BDF (90, 91).

The microcomputer 1 described above
The wheel brake pressure is determined as follows by the first pressure control process. (1) Wheel brake pressure when there is no automatic intervention to wheel brake pressure by braking force distribution control (1, 2) or ASB control: The wheel brake pressure system is shown in Tables 1 and 2. When the “foot brake pressure system” is connected (all solenoid valves in FIG. 1 are not energized) and the driver does not depress the pedal 3,
Since the output pressure of the master cylinder 2 is substantially zero, the wheel brake pressure is also substantially zero. When the driver depresses the pedal 3, the output pressure of the master cylinder 2 becomes a pressure corresponding to the depressing pressure, and the wheel brake pressure becomes a value corresponding to the output pressure of the master cylinder 2. (2) Wheel brake pressure by ASB control: When there is automatic intervention in wheel brake pressure by ASB control, brake related to wheel brake with automatic intervention
The key pressure system is the “ASB control pressure system” shown in Tables 1 and 2.
, The pressure increasing / decreasing valve unit (312, 334, 3
56, 378), the wheel brake pressure is first reduced, and then reduced and increased in response to changes in wheel speed, and the wheel brake pressure fluctuates. (3) Wheel brake pressure by the braking force distribution control 1 when the pedal 3 is not depressed (stop switch 45 is ON): When the pedal 3 is not depressed, the pressure of each wheel brake is reduced by the braking force distribution control 1. , The pressure is increased, held or reduced, and the wheel brake pressure fluctuates in a time series according to the situation. Depressurization is meaningful for releasing the brake pressure once the pressure has been increased. (4) Wheel brake pressure by the braking force distribution control 2 while the pedal 3 is being depressed (stop switch 45 is on) (FIG. 9);
Hold or decompression is determined, but the decompression is replaced by hold so as not to perform the output operation for decompression.
Pressure increase or hold is performed, and pressure reduction is not performed. The output pressure of the master cylinder 2 is also applied to the wheel brake,
The wheel brake pressure is the higher of the pressure increase or hold pressure by the braking force distribution control 2 and the output pressure of the master cylinder 2.

When the ASB control is started during the braking force distribution control, when the ASB control is terminated during the braking force distribution control, the wheel is shaken once in order to smooth the effect of the pressure by the braking force distribution control. -The key pressure is increased, and the reduced pressure due to the ASB control is compensated. When terminating the braking force distribution control during the ASB control, the ASB control is also forcibly terminated. (5) Wheel brake pressure when the braking force distribution control 2 is executed due to depression of the pedal 3 during the execution of the braking force distribution control 1 (FIG. 9); When the control is switched to the braking force distribution control 2 due to the depression of the brake pedal, the wheel brake pressure changes as shown in FIG.

According to the embodiment of the present invention described above,
In the anti-skid control, it is determined whether each wheel brake needs to be increased or reduced in order to keep the wheel slip rate within a predetermined range, and when it is determined that it is necessary, the pressure increasing / decreasing valve units 312, 334, 35 are determined.
The wheel brake pressure is increased and reduced through 6,378, but within the predetermined range, the wheel brake pressure is increased by the braking force distribution control.
When the pressure is reduced, the wheel brake pressure is set to a high range, and when the pressure is not reduced, the wheel brake pressure is set to a low range (71 to 73 in FIG. 6). When the wheel brake pressure is high, the adjustment of the wheel brake pressure by the anti-skid control (pressure reduction) is started to reduce the wheel slip rate, and the pressure reduction is stopped at a relatively high wheel slip rate and the pressure is increased again. That is, the start sensitivity of the anti-skid control is deepened, and accordingly, the probability of starting the anti-skid control during the braking force distribution control is reduced.

In the braking force distribution control, when the wheel brake pressure is not increased or reduced, that is, when the braking force distribution control is not substantially performed, the wheel by the anti-skid control starts from a relatively low wheel slip ratio. Adjustment (decompression) of the brake pressure is started, and the wheel slip ratio decreases.
Then, the pressure reduction is stopped at a relatively low wheel slip ratio, and the pressure returns to the pressure increase. That is, the start sensitivity of the anti-skid control becomes shallower, and the braking force adjustment of the anti-skid control is more effectively exerted.

Further, the control of the wheel brake pressure by the anti-skid control is stopped in accordance with the end of the increase / decrease control of the wheel brake pressure for the distribution of the braking force. As a result, the wheel brake pressure becomes the output pressure of the brake master cylinder 2. When the pressure adjustment is being performed by the braking force distribution control, a high slip ratio may occur due to the pressure adjustment and the output pressure of the brake master cylinder 2. That is, the pressure adjustment by the braking force distribution control may induce the pressure adjustment (start from the pressure reduction) by the anti-skid control. Such pressure regulation by the anti-skid control becomes unnecessary when the pressure regulation is stopped by the braking force distribution control, that is, the braking force distribution is terminated, and is stopped. If the pressure adjustment by the anti-skid control is required even after the pressure adjustment by the braking force distribution control ends, the pressure adjustment by the anti-skid control is restarted. Since the restarted pressure adjustment is not performed by the braking force distribution control, the pressure adjustment is terminated when the pressure adjustment becomes unnecessary based on the pressure adjustment necessity determination in the anti-skid control. When the anti-skid control ends during the braking force distribution control, the "hydraulic pressure compensation"
At (78B), the wheel brake pressure is temporarily increased. As a result, when the anti-skid control is completed, the wheel brake pressure returns to a value close to the wheel brake pressure when the anti-skid control is started, that is, near the wheel brake pressure by the braking force distribution control, and the braking force distribution control is effectively performed. Works. That is, the wheel brake pressure quickly returns to the pressure by the braking force distribution control.

In the above-described embodiment, the brake pressure circuit shown in FIG. 1 is used. Therefore, in any of the anti-skid (ASB) control and the braking force distribution control, all of the front, rear, left, and right are controlled. The brake pressure of the wheel brakes can be individually adjusted. In particular, in the braking force distribution control, a substantially constant high pressure (third pressure) generated by the constant pressure sources (21, 22) is used instead of the booster pressure (second pressure) for each of the wheel brakes. The brake pressure for ensuring the directional stability and the steering performance can be adjusted to the front, rear and left and right even if the brake pressure by the driver's brake operation is low.
All wheel brakes can be supplied, resulting in higher directional stability and steerability. In addition, the high pressure generated by the constant pressure source (21, 22), which is different from the brake pressure by the driver's braking operation, is increased or decreased by the pressure increasing / decreasing means (312, 334, 35
6,378), so that even in the case of sudden starting or sudden turning without the driver's braking operation, the brake pressure of each of the front, rear, left and right wheels is individually controlled in order to maintain high directional stability and steering performance. Can.

[0058]

As described above, according to the present invention, when the braking force distribution control is being performed on the wheel to be controlled, the wheel brake pressure is adjusted by the anti-skid control when the wheel slip is relatively high. (Depressurization) is started to reduce wheel slip, and at relatively high wheel slip, depressurization is stopped and returns to pressure increase. That is, the start sensitivity of the anti-skid control is deepened, and the probability of starting the anti-skid control during the braking force distribution control is accordingly reduced. When the braking force distribution control is being executed, the braking force distribution control pressure and the brake force are reduced.
High slip may occur due to the output pressure of the master cylinder (2). That is, the braking force distribution control pressure may induce pressure adjustment by anti-skid control. Pressure regulation by such anti-skid control is based on braking force distribution control.
Please it is determined whether or not it is completed, the judgment result of the completed
Based is aborted.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of one embodiment of the present invention.

FIG. 2 is a block diagram showing an outline of a configuration of an electronic control device for controlling energization of a solenoid valve or the like of a wheel brake pressure system shown in FIG.

FIG. 3 is a flowchart showing an outline of a content of a wheel brake pressure control of a microcomputer 11 shown in FIG. 2;

FIG. 4 is a flowchart showing the contents of "ASB release" (5) shown in FIG.

FIG. 5 is a flowchart showing the contents of “braking force distribution control 1” (6) shown in FIG. 3;

FIG. 6 is a flowchart showing a part of the contents of “ASB control” (7) shown in FIG. 3;

FIG. 7 is a flowchart showing the rest of the contents of “ASB control” (7) shown in FIG. 3;

FIG. 8 is a flowchart showing the contents of "braking force distribution control" (8) shown in FIG.

FIG. 9 is a block diagram showing the brake force distribution control 1 and 2 when the brake pedal 3 shown in FIG. 1 is not depressed; the microcomputer 11 automatically intervenes in the wheel brake pressure; This is a time chart showing a change in wheel brake pressure when automatic intervention is continued.

[Explanation of symbols]

2: Brake master cylinder 3: Brake pedal 4: Brake fluid reservoir 5: Hydro booster 6: Proportional control valve 10: Electronic control unit 11: Microcomputer 12: Input interface 13: Output Interface 14: CPU 15: ROM 16: RAM 17: Timer 18a to 18m: Signal processing circuit 19a to 19r: Motor driver and solenoid driver 20: High pressure source 21: Pump 22: Accumulator 23: Relief valve 24: Electric motor 25: Check valve 31, 33, 35, 37: Pressure increasing solenoid valve 32, 34, 36, 38: Pressure reducing solenoid valve 312, 334, 356, 378: Pressure increasing / reducing valve unit 41 to 44: Wheel Speed sensor 45: Stop switch 46: Pressure sensor 47: Low pressure switch 48: Power pressure switch Switch YA: yaw rate sensor θF: front wheel steering angle sensor θR: rear wheel steering angle sensor GX: longitudinal acceleration sensor GY: lateral acceleration sensor 51-54: wheel brake 61-65: solenoid switching valve HSV1-4 : On-off valve

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takayuki Ito 2-1-1 Asahicho, Kariya-shi, Aichi Aisin Seiki Co., Ltd. (72) Shingo Sugiura 2-1-1 Asahicho, Kariya-shi, Aichi Address Aisin Seiki Co., Ltd. (72) Inventor Norio Yamazaki 2-1-1 Asahicho, Kariya City, Aichi Prefecture Aisin Seiki Co., Ltd. (72) Inventor Takumi Inagaki 1 Toyota Town, Toyota City, Aichi Prefecture Toyota (72) Inventor Makoto Yamamoto 1st Toyota Town, Toyota City, Aichi Prefecture Investigator, Toyota Motor Corporation Taketo Sato (56) References JP-A-5-24522 (JP, A) JP-A-4-243654 (JP, A) JP-A-4-243365 (JP, A) JP-A-4-131909 (JP, A) JP-A-60-107440 (JP, A) Int.Cl. ⁷ , DB name) B60T 8/58

Claims (2)

(57) [Claims] An auxiliary pressure source (22) for generating a brake pressure irrespective of brake pedal operation is provided, and when it is determined that braking force distribution control is necessary, the brake pressure of the auxiliary pressure source is applied to a brake of a wheel to be controlled. The braking force distribution control to be supplied and the anti-skid control for determining whether or not anti-skid control is necessary by comparing the wheel slip with a predetermined control start wheel slip reference, and increasing and reducing the wheel brake pressure when necessary are performed. In the wheel brake pressure control device provided with a control means (10), the control means performs an anti-skid control for the control target wheel at the time of executing the braking force distribution control as compared with a case where the braking force distribution control is not executed. A wheel brake pressure control device, wherein the control start wheel slip standard is increased. 2. An auxiliary pressure source (22) for generating a brake pressure irrespective of brake pedal operation, and when it is determined that a braking force distribution control is necessary, the brake pressure of the auxiliary pressure source is applied to a brake of a wheel to be controlled. The braking force distribution control to be supplied and the wheel slip are compared with a predetermined wheel slip reference to determine whether or not anti-skid control is necessary.
Control means for performing anti-skid control for increasing and decreasing pressure
In the wheel brake pressure control device provided with (10), the control means performs the braking force distribution control when the anti-skid control is induced for the controlled wheel by executing the braking force distribution control. To determine if
Constant, and to stop the anti-skid control based on the determination result of the finished wheel blur characterized in that - key pressure control device.