Brake fluid pressure control device for vehicles with bar handle
A brake fluid pressure control device for vehicles with bar handle which is configured to start a holding control of a fluid pressure of a wheel brake according to wheel deceleration calculated based on a wheel speed of the vehicle is provided. In the brake fluid pressure control device, the vehicle includes an acceleration sensor which is configured to detect acceleration in a front-rear direction of the vehicle, acceleration, detected by the acceleration sensor, which occurs in a rearward direction when the vehicle is decelerating is detected as a positive value, and the holding control is started when it is judged that the acceleration detected by the acceleration sensor is larger than or equal to a detection acceleration threshold value and the wheel deceleration is smaller than or equal to a wheel deceleration threshold value.
1. A brake fluid pressure control device for vehicles with bar handle which is configured to start a holding control of a fluid pressure of a wheel brake according to a wheel deceleration calculated based on a wheel speed of the vehicle, wherein
the vehicle includes an acceleration sensor which is configured to detect an acceleration in a front-rear direction of the vehicle,
the acceleration, detected by the acceleration sensor, which occurs in a rearward direction when the vehicle is decelerating is detected as a positive value, and
the holding control is started when it is judged that the acceleration detected by the acceleration sensor is larger than or equal to a detection acceleration threshold value and the wheel deceleration is smaller than or equal to a wheel deceleration threshold value.
2. The brake fluid pressure control device according to claim 1 , wherein
the detection acceleration threshold value is mapped so as to have a larger value as a vehicle body speed of the vehicle increases.
3. The brake fluid pressure control device according to claim 1 , wherein
the acceleration sensor is configured to detect an acceleration in a vertical direction of the vehicle, and the acceleration in the vertical direction, detected by the acceleration sensor, which occurs downward in the vertical direction is detected as a positive value, and
the detection acceleration threshold value is mapped using an acceleration in a straight direction connecting a center of gravity and a contact point of a front wheel and a ground at a time of occurrence of a rear-wheel lift and an acceleration in a rear-wheel lift direction perpendicular to the straight direction in a vertical plane, which are calculated based on the acceleration in the front-rear direction and the acceleration in the vertical direction.
4. The brake fluid pressure control device according to claim 3 , wherein
a plurality of maps each of which indicates the detection acceleration threshold value are provided according to a vehicle body speed of the vehicle, and set in such a manner that, as the vehicle body speed increases, the acceleration in the straight direction increases and the acceleration in the rear-wheel lift direction decreases.
5. The brake fluid pressure control device according to claim 1 , wherein
whether the vehicle is in a wheelie state is judged, and the holding control is started when it is judged that the vehicle is not in the wheelie state.
6. The brake fluid pressure control device according to claim 1 , further comprising a start timing control unit which judges whether to start the holding control on a basis of a vehicle body speed, a front wheel deceleration, and a rear wheel deceleration, a GX-axis acceleration and a GZ-axis acceleration.
7. The brake fluid pressure control device according to claim 1 , wherein the acceleration sensor detects Ax acceleration in a X-axis front-rear direction, Ay acceleration in a Y-axis direction, and Az acceleration in a Z-axis vertical direction of the vehicle.
8. The brake fluid pressure control device according to claim 7 , further comprising a fluid pressure control start timing control device composed of an electronic control unit (ECU), and a front wheel speed sensor, a rear wheel speed sensor, and the acceleration sensor which are connected to the ECU, wherein
the ECU is composed of a start timing control unit, and a speed/deceleration calculation unit and a GX axis/GZ axis acceleration calculation unit which are connected to the start timing control unit,
a GZ axis and a GX axis relate to a calculation performed by the GX axis/GZ axis acceleration calculation unit,
the GZ axis is an axis in a rear-wheel lift direction, and
the GX axis is an axis perpendicular to the GZ axis in a vertical plane that is a center plane of the vehicle.
9. The brake fluid pressure control device according to claim 8 , wherein
the speed/deceleration calculation unit calculates a vehicle body speed, front wheel deceleration, and rear wheel deceleration on a basis of a front wheel speed that is output from the front wheel speed sensor and a rear wheel speed that is output from the rear wheel speed sensor according to equations (1) to (3), respectively:
Vv =( Vf+Vr )/2 (1),
Df={Vf (current front wheel speed)− Vf (front wheel speed of a time Δ t ago)}/Δ t (2), and
Dr={Vr (current rear wheel speed)− Vr (rear wheel speed of the time Δ t ago)}/Δ t (3),
wherein:
Vv is the vehicle body speed,
Vf is the front wheel speed,
Vr is the rear wheel speed,
Df is the front wheel deceleration, and
Dr is the rear wheel deceleration.
10. The brake fluid pressure control device according to claim 9 , wherein
the GX axis/GZ axis acceleration calculation unit calculates GX-axis acceleration and GZ-axis acceleration on the basis of the Ax acceleration and the Az acceleration according to equations (4) and (5), respectively:
Agx=Ax ( GX )= Ax cos θ (4), and
Agz=Az ( GZ )− Ax ( GZ )= Az cos θ− Ax sin θ (5),
wherein:
Agx is the GX-axis acceleration,
Agz is the GZ-axis acceleration,
Ax(GX) is the GX-axis component of the Ax acceleration,
Az(GX) is the GX-axis component of the Az acceleration,
Az(GZ) is the GZ-axis component of the Az acceleration, and
Ax(GZ) is the GZ-axis component of the Ax acceleration.
11. The brake fluid pressure control device according to claim 10 , wherein
the start timing control unit judges whether to start the holding control on a basis of the vehicle body speed, the front wheel deceleration, and the rear wheel deceleration, the GX-axis acceleration and the GZ-axis acceleration.
12. The brake fluid pressure control device according to claim 11 , wherein
the ECU judges that the vehicle is running when the vehicle body speed is higher than or equal to a predetermined speed threshold value at which the vehicle is regarded as approximately stopped, and judges that the vehicle is not running when the calculated vehicle body speed is lower than the speed threshold value, and
when the vehicle is running, the ECU judges whether the vehicle is decelerating by judging whether an estimated vehicle body deceleration calculated according to Equation (6) is negative (Db<0),
Db=Vv (current vehicle body speed)− Vv (vehicle body speed of the time Δ t ago)/Δ t (6)
where Db is the estimated vehicle body deceleration.
13. The brake fluid pressure control device according to claim 12 , wherein
the ECU plots on a coordinate plane defined by the GX axis and the GZ axis, a combination of the GX-axis acceleration and the GZ-axis acceleration according to equations (4) and (5) on a basis of the Ax acceleration and the Az acceleration, and
the GZ-axis acceleration has a fixed value when the GX-axis acceleration varies from 0 G to a prescribed value and the GZ-axis acceleration increases in proportion to the GX-axis acceleration as the latter increases after passing the prescribed value so that a transition to a holding operation can be made with early timing.
14. The brake fluid pressure control device according to claim 13 , wherein
the ECU judges whether the vehicle is running in a wheelie state that may be caused by a temporal variation of deviation of differences between the front wheel speed and the rear wheel speed,
when the vehicle is not running in the wheelie state, the ECU judges whether the front wheel deceleration is smaller than or equal to a front wheel deceleration threshold value, and
the holding control is started at an instant when all of the following conditions are satisfied simultaneously: a coordinate point of the GX-axis acceleration and the GZ-axis acceleration is within a holding control start region, the vehicle is not in the wheelie state, and the front wheel deceleration≤the front wheel deceleration threshold value.
15. The brake fluid pressure control device according to claim 1 , wherein
the holding control is started at an instant when all of the following conditions are satisfied simultaneously: a coordinate point of a GX-axis acceleration and a GZ-axis acceleration is within a holding control start region of a predefined map, the vehicle is not in a wheelie state, and front wheel deceleration≤a front wheel deceleration threshold value.
16. The brake fluid pressure control device according to claim 15 , wherein
a GZ axis is an axis in a rear-wheel lift direction, and
a GX axis is an axis perpendicular to the GZ axis in a vertical plane that is a center plane of the vehicle.