Vehicle brake hydraulic pressure control apparatus and road surface friction coefficient estimating device

• US 9,550,480 B2
• Filed: 10/17/2012
• Issued: 01/24/2017
• Est. Priority Date: 10/21/2011
• Status: Active Grant

• Current Assignee: Autoliv Nissin Brake Systems Japan Co., Ltd.
• Original Assignee: Autoliv Nissin Brake Systems Japan Co., Ltd.
• Inventors: Asano, Kiyonori
• Primary Examiner(s): Olszewski, John R
• Assistant Examiner(s): Wiltey, Nicholas K
• Application Number:
  US13/653,876
• Publication Number:
  US 20130103279A1
• Time in Patent Office: 1,560 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: B60T 2201/16 Curve braking control, e.g. turn control within ABS control algorithm
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 2270/313 with less than three sensors (yaw rate, steering angle, lateral acceleration)
• CPC Class Codes: B60T 8/1755 Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve road vehicle drive control systems for control of driving stability otherwise than by controlling a particular sub-unit B60W30/02
• CPC Class Codes: B60T 8/17551 determining control parameters related to vehicle stability used in the regulation, e.g. by calculations involving measured or detected parameters
• CPC Class Codes: B60T 8/17616 Microprocessor-based systems
• CPC Class Codes: B60T 8/17636 Microprocessor-based systems

Abstract

One embodiment provides a vehicle brake hydraulic controller including: an antilock braking controlling module configured to perform an antilock braking control in which a brake hydraulic pressure applied to wheel brakes is reduced under the condition that a slip-related amount has reached a pressure reduction threshold value; and a turning judging module configured to judge whether a vehicle is turning based on a steering angle, wherein, when the antilock braking control is performed and in the case that the turning judging module judges that the vehicle is turning, the antilock braking controlling module performs a turning pressure reduction control so as to: change the pressure reduction threshold values to be more easily reached by the slip-related amount than at the time of straight running; and change the pressure reduction amounts to be larger than that at the time of straight running.

Claims

1. A vehicle brake hydraulic controller including:

an antilock braking controlling module configured to perform an antilock braking control in which a brake hydraulic pressure applied to wheel brakes is reduced under the condition that a slip-related amount has reached a pressure reduction threshold value, the slip-related amount being calculated using a vehicle speed and a wheel speed; and

a turning judging module configured to judge whether a vehicle is turning based on a steering angle,

wherein, when the antilock braking control is performed and in the case that the turning judging module judges that the vehicle is turning, the antilock braking controlling module performs a turning pressure reduction control so as to;

change the pressure reduction threshold values at the time of turning smaller than the pressure reduction threshold values at the time of straight running,

wherein the pressure reduction threshold value at the time of straight running is a first threshold value, the pressure reduction threshold value at the time of turning is a second threshold value, and the first threshold value is larger than the second threshold value, and further comprising;

a road surface friction coefficient judging module configured to judge whether a road surface on which the vehicle is running is at least a low friction coefficient road surface, and

wherein the antilock braking controlling module performs the turning pressure reduction control only in the case that the road surface is judged to be the low friction coefficient road surface, and

wherein the road surface friction coefficient judging module includes;

a first estimating module configured to estimate a first road surface friction coefficient based on a lateral acceleration;

a second estimating module configured to estimate a second road surface friction coefficient based on a longitudinal acceleration; and

a selecting module configured to select either the first road surface friction coefficient or the second road surface friction coefficient as a road surface friction coefficient of the road surface,

wherein the selecting module has a limit steering judgment section configured to judge whether steering exceeding the limit of road surface conditions is performed based on at least the steering angle and the vehicle speed, and

wherein the selecting module selects;

the first road surface friction coefficient or the second road surface friction coefficient, whichever smaller, as the road surface friction coefficient when limit steering judgment section judges that steering exceeding the limit of road surface conditions is performed; and

the second road surface friction coefficient as the road surface friction coefficient when limit steering judgment section judges that steering exceeding the limit of road surface conditions is not performed.

2. The controller of claim 1, further including:

a turning state judging module configured to judge whether the vehicle is in an under- steering state, a neutral-steering state or an over-steering state,

wherein the antilock braking controlling module performs;

the turning pressure reduction control only for the front wheels in the case that the turning state judging module judges that the vehicle is in the under-steering state;

the turning pressure reduction control for the front wheels and the rear wheels in the case that the turning state judging module judges that the vehicle is in the neutral-steering state; and

the turning pressure reduction control only for the rear wheels in the case that the turning state judging module judges that the vehicle is in the over-steering state.

3. The controller of claim 2,

wherein, in the turning pressure reduction control that is performed only for the front wheels in the under-steering state, and the pressure reduction amount is adjusted to be larger more than at the neutral-steering state.

4. The controller of claim 2,

wherein, in the turning pressure reduction control that is performed only for the front wheels in the under-steering state.

5. The controller of claim 2,

wherein, in the turning pressure reduction control that is performed only for the rear wheels in the over-steering state, and the pressure reduction amount is adjusted to be larger than at the neutral-steering state.

6. The controller of claim 2,

wherein the turning state judging module includes:

a normative yaw rate calculation section configured to calculate a normative yaw rate using the steering angle and the vehicle speed;

a road surface limit yaw rate calculation section configured to calculate a road surface limit yaw rate using a lateral acceleration and the vehicle speed; and

a target yaw rate calculation section configured to calculate a target yaw rate from the normative yaw rate and the road surface limit yaw rate,

wherein the turning state judging module compares the target yaw rate with an actual yaw rate actually applied to the vehicle to thereby judge;

that the vehicle is in the under-steering state in the case that the actual yaw rate is smaller than a value obtained by subtracting a first given value from the target yaw rate;

that the vehicle is in the over-steering state in the case that the actual yaw rate is larger than a value obtained by adding a second given value to the target yaw rate; and

that the vehicle is in the neutral-steering state in the case that the vehicle is not judged to be in the under-steering state or the over-steering state.

7. The controller of claim 1,

wherein the slip-related amount is a slip amount obtained by subtracting the wheel speed from the vehicle speed, and

wherein, when the slip amount becomes larger than the pressure reduction threshold value, the antilock braking controlling module reduces the brake hydraulic pressure applied to the wheel brakes.

8. The controller of claim 1,

wherein the road surface friction coefficient judging module further includes:

a low friction coefficient (μ

) road judging module configured to judge that the road surface is the low friction coefficient road surface when the road surface friction coefficient selected by the selecting module is smaller than a fourth given value.

9. The controller of claim 1,

wherein the limit steering judgment section includes:

a normative yaw rate calculation section configured to calculate a normative yaw rate from the steering angle and the vehicle speed;

a road surface limit yaw rate calculation section configured to calculate a road surface limit yaw rate from a lateral acceleration and the vehicle speed; and

a yaw rate judgment section configured to judge whether the deviation obtained by subtracting the road surface limit yaw rate from the normative yaw rate is larger than a third given value, and

wherein the limit steering judgment section judges;

that steering exceeding the limit of road surface conditions is performed in the case that the deviation is larger than the third given value; and

that steering exceeding the limit of road surface conditions is not performed in the case that the deviation is not larger than the third given value.

10. The controller of claim 1,

wherein the first estimating module calculates the first road surface friction coefficient from a lateral acceleration filter value obtained by performing a filtering process.

11. The controller of claim 1,

wherein the road surface friction coefficient judging module further includes:

a low friction coefficient (μ

) road judging module configured to judge whether the road surface is the low friction coefficient road surface,

wherein the low μ

road judging module includes;

a first judgment section configured to judge whether a first condition that the road surface friction coefficient is smaller than a fourth given value is satisfied; and

at least one of a second judgment section configured to judge whether a second condition that an estimated lateral acceleration calculated based on an actual yaw rate actually applied to the vehicle is smaller than a fifth given value is satisfied, and a third judgment section configured to judge whether a third condition that a locking hydraulic pressure in the antilock braking control is smaller than a sixth given value is satisfied, and

wherein the low μ

road judging module judges that the road surface is the low friction coefficient road surface when the first condition and at least one of the second and third conditions are satisfied.

12. The controller of claim 11,

wherein the road surface friction coefficient judging module estimates the road surface friction coefficient using an actual lateral acceleration obtained by a lateral acceleration sensor.

13. The controller of claim 11,

wherein the second judgment section calculates:

a tentatively estimated lateral acceleration obtained from the absolute value of the actual yaw rate and the vehicle speed; and

the estimated lateral acceleration obtained by subjecting the tentatively estimated lateral acceleration to a filtering process.

14. The controller of claim 11,

wherein the third judgment section judges that the third condition is satisfied when the locking hydraulic pressures of the right front wheel and the left front wheel are respectively smaller than the sixth given value that is the same for all the wheels or different for the respective wheels.

15. The controller of claim 1, wherein the antilock braking controlling module sets an opening time of an outlet valve at the time of turning longer than an opening time at the time of straight running, whereby as a result, a pressure reduction timing at the time of turning is advanced from a pressure reduction timing at the time of straight running by making the pressure reduction threshold values smaller than those at the time of straight running, and the wheel speed made close to the vehicle speed by making the pressure reduction amounts larger than those at the time of straight running.

16. The controller of claim 15, wherein the antilock braking controlling module is configured to perform the turning pressure reduction control only when receiving a low friction coefficient signal from a road surface friction coefficient judging module.

19. The controller of claim 1, wherein the selecting module selects the first road surface friction coefficient or the second road surface friction coefficient as the road surface friction coefficient depending on a judgment of a steering limit.

24. The controller of claim 1, wherein the antilock braking controlling module is configured to perform the antilock braking control in which a brake hydraulic pressure applied to four wheel brakes.

17. A vehicle brake hydraulic controller including:

an antilock braking controlling module configured to perform an antilock braking control in which a brake hydraulic pressure applied to wheel brakes is reduced under the condition that a slip-related amount has reached a pressure reduction threshold value, the slip-related amount being calculated using a vehicle speed and a wheel speed; and

a turning judging module configured to judge whether a vehicle is turning based on a steering angle,

wherein, when the antilock braking control is performed and in the case that the turning judging module judges that the vehicle is turning, the antilock braking controlling module performs a turning pressure reduction control so as to;

change the pressure reduction threshold values at the time of turning smaller than the pressure reduction threshold values at the time of straight running,

wherein the pressure reduction threshold value at the time of straight running is a first threshold value, the pressure reduction threshold value at the time of turning is a second threshold value, and the first threshold value is larger than the second threshold value,

wherein the antilock braking controlling module sets an opening time of an outlet valve at the time of turning longer than an opening time at the time of straight running, whereby as a result, a pressure reduction timing at the time of turning is advanced from a pressure reduction timing at the time of straight running by making the pressure reduction threshold values smaller than those at the time of straight running, and the wheel speed made close to the vehicle speed by making the pressure reduction amounts larger than those at the time of straight running,

wherein the antilock braking controlling module is configured to perform the turning pressure reduction control only when receiving a low friction coefficient signal from a road surface friction coefficient judging module, and

wherein

in an under-steering state, the pressure reduction threshold value of front wheels is set to a value (Sf3) smaller than a value (Sf1) at the time of straight running, and the pressure reduction amount of the front wheels is set to a value (Pf3) larger than a value (Pf1) at the time of straight running;

both the pressure reduction threshold value and the pressure reduction amount of rear wheels are set to be equal to values (Sr1) and (Pr1) at the time of straight running, respectively;

in a neutral-steering state, the pressure reduction threshold values of the front and rear wheels are set to values (Sf2) and (Sr2) smaller than the values (Sf1) and (Sr1) at the time of straight running, and the pressure reduction amounts of the front and rear wheels are set to values (Pf2) and (Pr2) larger than the values (Pf1) and (Pr1) at the time of straight running;

in an over-steering state, the pressure reduction threshold value of the rear wheels is set to a value (Sr3) smaller than the value (Sr1) at the time of straight running, and the pressure reduction amount of the rear wheels is set to a value (Pr3) larger than the value (Pr1) at the time of straight running; and

both the pressure reduction threshold value and the pressure reduction amount of the front wheels are set to be equal to the values (Sf1) and (Pf1) at the time of straight running.

18. The controller of claim 17, wherein:

the turning pressure reduction control is performed only for the front wheels in the under-steering state, wherein the pressure reduction threshold value is set to the value (Sf3) smaller than the pressure reduction threshold value (Sf2) of the front wheels in the neutral state, and the pressure reduction amount is set to the value (Pf3) larger than the pressure reduction amount (Pf2) of the front wheels in the neutral state;

the turning pressure reduction control is performed only for the rear wheels in the over-steering state, wherein the pressure reduction threshold value is set to the value (Sr3) smaller than the pressure reduction threshold value (Sr2) of the rear wheels in the neutral state, and the pressure reduction amount is set to the value (Pr3) larger than the pressure reduction amount (Pr2) of the rear wheels in the in the neutral state;

a difference between the pressure reduction threshold value in the neutral state and the pressure reduction threshold value at the time of straight running for the front wheels is nearly equal to a difference therebetween for the rear wheels; and

a difference between the pressure reduction amount in the neutral state and the pressure reduction amount at the time of straight running for the front wheels is nearly equal to a difference therebetween for the rear wheels.

20. A vehicle brake hydraulic controller including:

an antilock braking controlling module configured to perform an antilock braking control in which a brake hydraulic pressure applied to wheel brakes is reduced under the condition that a slip-related amount has reached a pressure reduction threshold value, the slip-related amount being calculated using a vehicle speed and a wheel speed; and

a turning judging module configured to judge whether a vehicle is turning based on a steering angle,

wherein, when the antilock braking control is performed and in the case that the turning judging module judges that the vehicle is turning, the antilock braking controlling module performs a turning pressure reduction control so as to;

change the pressure reduction threshold value to thereby advance a start timing of the turning pressure reduction control compared to at the time of straight running; and

change the pressure reduction amounts to be larger than that at the time of straight running,

wherein the antilock braking controlling module performs the turning pressure reduction control only in the case that a road surface is judged to be a low friction coefficient road surface, and further comprising;

a selecting module configured to select either a first road surface friction coefficient or a second road surface friction coefficient as a road surface friction coefficient of the road surface, wherein;

the selecting module has a limit steering judgment section configured to judge whether steering exceeding the limit of road surface conditions is performed based on at least the steering angle and the vehicle speed, and

the selecting module selects;

the first road surface friction coefficient or the second road surface friction coefficient, whichever smaller, as the road surface friction coefficient when the limit steering judgment section judges that steering exceeds the limit of road surface conditions is performed; and

the second road surface friction coefficient as the road surface friction coefficient when the limit steering judgment section judges that steering exceeds the limit of road surface conditions is not performed.

21. The controller of claim 20, wherein a pressure reduction timing at the time of turning is advanced from a pressure reduction timing at the time of straight running by making the pressure reduction threshold values smaller than those at the time of straight running, and the wheel speed made close to the vehicle speed by making the pressure reduction amounts larger than those at the time of straight running.

23. The controller of claim 21, wherein the antilock braking controlling module is configured to perform the antilock braking control in which a brake hydraulic pressure applied to four wheel brakes.

22. A vehicle brake hydraulic controller including:

an antilock braking controlling module configured to perform an antilock braking control in which a brake hydraulic pressure applied to wheel brakes is reduced under the condition that a slip-related amount has reached a pressure reduction threshold value, the slip-related amount being calculated using a vehicle speed and a wheel speed; and

a turning judging module configured to judge whether a vehicle is turning based on a steering angle,

wherein, when the antilock braking control is performed and in the case that the turning judging module judges that the vehicle is turning, the antilock braking controlling module performs a turning pressure reduction control so as to;

change the pressure reduction threshold value to thereby advance a start timing of the turning pressure reduction control compared to at the time of straight running; and

change the pressure reduction amounts to be larger than that at the time of straight running,

wherein a pressure reduction timing at the time of turning is advanced from a pressure reduction timing at the time of straight running by making the pressure reduction threshold values smaller than those at the time of straight running, and the wheel speed made close to the vehicle speed by making the pressure reduction amounts larger than those at the time of straight running, and

wherein;

in an under-steering state, the pressure reduction threshold value of front wheels is set to a value (Sf3) smaller than a value (Sf1) at the time of straight running, and the pressure reduction amount of the front wheels is set to a value (Pf3) larger than a value (Pf1) at the time of straight running;

both the pressure reduction threshold value and the pressure reduction amount of rear wheels are set to be equal to values (Sr1) and (Pr1) at the time of straight running, respectively;

in a neutral-steering state, the pressure reduction threshold values of the front and rear wheels are set to values (Sf2) and (Sr2) smaller than the values (Sf1) and (Sr1) at the time of straight running, and the pressure reduction amounts of the front and rear wheels are set to values (Pf2) and (Pr2) larger than the values (Pf1) and (Pr1) at the time of straight running;

in an over-steering state, the pressure reduction threshold value of the rear wheels is set to a value (Sr3) smaller than the value (Sr1) at the time of straight running, and the pressure reduction amount of the rear wheels is set to a value (Pr3) larger than the value (Pr1) at the time of straight running; and

both the pressure reduction threshold value and the pressure reduction amount of the front wheels are set to be equal to the values (Sf1) and (Pf1) at the time of straight running.