Brake fluid pressure control device for vehicles with bar handle
A brake fluid pressure control device for vehicles with bar handle, includes: an acceleration acquiring unit which is configured to acquire acceleration that occurs in the vehicle; and a control unit which is configured to judge a probability of occurrence of a rear-wheel lift based on the acceleration acquired by the acceleration acquiring unit, and which is configured to perform a pressure reduction control on a front wheel brake when judging that the occurrence of the rear-wheel lift is probable, the control unit which is configured to adjust a degree of pressure reduction of the pressure reduction control based on a differentiation value of the acceleration acquired by the acceleration acquiring unit.
1. A brake fluid pressure control device for vehicles with bar handle, the brake fluid pressure control device comprising:
an acceleration acquiring sensor which is configured to acquire acceleration that occurs in a vehicle; and
a controller which is configured to judge a probability of occurrence of a rear-wheel lift based on the acceleration acquired by the acceleration acquiring sensor, and which is configured to perform a pressure reduction control on a front wheel brake when judging that the occurrence of the rear-wheel lift is probable,
the controller which is configured to set a pressure reduction pulse, wherein a pulse width of the pressure reduction pulse when a differentiation value of the acceleration acquired by the acceleration acquiring sensor is smaller than or equal to a threshold value is wider than a pulse width of the pressure reduction pulse when the differentiation value of the acceleration is larger than the threshold value,
the controller which is configured to adjust a degree of pressure reduction of the pressure reduction control based on the pressure reduction pulse.
2. The brake fluid pressure control device according to claim 1 , wherein
the acceleration acquiring sensor is configured to acquire acceleration in a vertical direction of the vehicle and acceleration in a front-rear direction of the vehicle, the acceleration in the front-rear direction being defined so as to be positive in a rearward direction in which the acceleration in the front-rear direction occurs when the vehicle is decelerating, and the acceleration in the vertical direction being defined so as to be positive in a downward direction that is a direction of acceleration of gravity, and
the controller is configured to calculate acceleration in a rear-wheel lift direction that is perpendicular to, at a center of gravity of the vehicle, a straight line connecting the center of gravity of the vehicle and a contact point of a front wheel and a ground at a time of the occurrence of the rear-wheel lift in a vertical plane including the straight line, based on the acquired acceleration in the vertical direction and the acquired acceleration in the front-rear direction, and is configured to adjust the degree of pressure reduction of the pressure reduction control based on a differentiation value of the acceleration in the rear-wheel lift direction.
3. The brake fluid pressure control device according to claim 2 , wherein
the controller is configured to calculate the differentiation value of the acceleration in the rear-wheel lift direction by calculating the acceleration in the rear-wheel lift direction every first prescribed time and dividing a difference between current acceleration in the rear-wheel lift direction and acceleration in the rear-wheel lift direction of a second prescribed time ago that is longer than the first prescribed time by the second prescribed time.
4. The brake fluid pressure control device according to claim 3 , wherein
the controller is configured to set the degree of pressure reduction higher as the differentiation value of the acceleration in the rear-wheel lift direction becomes smaller.
5. The brake fluid pressure control device according to claim 2 , wherein
the controller is configured to set the degree of pressure reduction higher as the differentiation value of the acceleration in the rear-wheel lift direction becomes smaller.
6. The brake fluid pressure control device according to claim 1 , wherein
the acceleration acquiring sensor is an acceleration sensor mounted to the vehicle at its center-of-gravity position and which detects acceleration in a X-axis direction defined as a front-rear direction, acceleration in a Y-axis direction defined as a left-right direction, and acceleration in a Z-axis direction defined as a vertical direction of the vehicle,
the acceleration in the X-axis direction directed rearward relative to the vehicle is positive and the acceleration in the X-axis direction directed forward relative to the vehicle is negative,
the acceleration in the Y-axis direction directed leftward relative to the vehicle in a front view is positive and the acceleration in the Y-axis direction directed rightward relative to the vehicle in the front view is negative, and
the acceleration in the Z-axis direction directed downward relative to the vehicle is positive and the acceleration in the Z-axis direction directed upward relative to the vehicle is negative.
7. The brake fluid pressure control device according to claim 6 , wherein
the controller includes a pressure reduction pulse setting unit, a speed/deceleration calculation unit and a GX axis/GZ axis acceleration calculation unit, which are connected to the pressure reduction pulse setting unit,
a GZ axis is an axis in a rear-wheel lift direction,
a GX axis is an axis that is perpendicular to the GZ axis in a vertical plane that is a center plane of a vehicle body,
the GZ axis is an axis that is perpendicular to the GX axis in a XZ plane, and
the GZ axis, directions extending obliquely downward and upward from a center of gravity Cg are defined as a positive direction and a negative direction, respectively.
8. The brake fluid pressure control device according to claim 7 , wherein
the speed/deceleration calculation unit calculates a vehicle body speed (Vv), front wheel deceleration (Df), and rear wheel deceleration (Dr) on a basis of a front wheel speed (Vf) that is output from a front wheel speed sensor and a rear wheel speed (Vr) that is output from a rear wheel speed sensor, and
the GX axis/GZ axis acceleration calculation unit calculates GX-axis acceleration (Agx) and GZ-axis acceleration (Agz) on a basis of the acceleration in the X-axis direction and the acceleration in the Z-axis direction.
9. The brake fluid pressure control device according to claim 8 , wherein the calculation by the speed/deceleration calculation unit is based according to equations (1) to (3), respectively:
Vv =( Vf+Vr )/2 (1)
Df={Vf (current front wheel speed)− Vf (front wheel speed of a very short time Δ t ago)}/Δ t (2)
Dr={Vr (current rear wheel speed)− Vr (rear wheel speed of the very short time Δ t ago)}/Δ t. (3).
10. The brake fluid pressure control device according to claim 8 , wherein the GX-axis acceleration (Agx) and the GZ-axis acceleration (Agz) are calculated according to equations (4) and (5), respectively:
Agx=Ax ( GX )+ Az ( GX )= Ax cos θ+ Az ( GX )= Ax cos θ+ Az sin θ (4)
Agz=Az ( GZ )+ Ax ( GZ )=− Az cos θ+ Ax sin θ (5),
Ax(GX) is the GX-axis component of the acceleration in the X-axis direction,
Az(GX) is the GX-axis component of the acceleration in the Z-axis direction,
Az(GZ) is the GZ-axis component of the acceleration in the Z-axis direction, and
Ax(GZ) is the GZ-axis component of the acceleration in the X-axis direction.
11. The brake fluid pressure control device according to claim 8 , wherein
the pressure reduction pulse setting unit is equipped with a differentiation unit that sets a predetermined parameter of pressure reduction pulses on a basis of the vehicle body speed (Vv), the front wheel deceleration (Df), and the rear wheel deceleration (Dr), the GX-axis acceleration (Agx) and the GZ-axis acceleration (Agz), and the differentiation value is defined by Dgz and is a differentiation value of the GZ-axis acceleration (Agz), and
the differentiation unit calculates the differentiation value (Dgz) of the GZ-axis acceleration (Agz).
12. The brake fluid pressure control device according to claim 11 , wherein
the differentiation value of the GZ-axis acceleration (Agz) at a present time n is a quotient obtained by dividing a difference between an acceleration value (Agz(n)) at the present time n and an acceleration value (Agz(n−x)) at a time point (n−x) that is x times a prescribed time ago according to:
Dgz ( n )={ Agz ( n )− Agz ( n−x )}/(Δ t×x ) (6).
13. The brake fluid pressure control device according to claim 11 , wherein
the controller judges whether the vehicle is running or stopped.
14. The brake fluid pressure control device according to claim 13 , wherein
if the vehicle is running, the controller judges whether the vehicle is decelerating by judging whether estimated vehicle body deceleration (Db) calculated according to equation (7) is negative (Db<0),
Db={Vv (current vehicle body speed)− Vv (vehicle body speed of a very short time Δ t ago)}/Δ t (7).
15. The brake fluid pressure control device according to claim 13 , wherein
if the differentiation value (Dgz) of the GZ-axis acceleration (Agz) is smaller than or equal to the threshold value, a pulse width of the pressure reduction pulses is set high, and
if the differentiation value (Dgz) of the GZ-axis acceleration (Agz) is larger than the threshold value, the pulse width of the pressure reduction pulses is set low.
16. The brake fluid pressure control device according to claim 1 , wherein
the acceleration acquiring sensor is a 3-axis acceleration sensor configured to acquire acceleration corresponding to GX-axis acceleration (Agx) and GZ-axis acceleration (Agz) occurring in the vehicle,
the controller is configured to judge the probability of occurrence of the rear-wheel lift on the basis of the GX-axis acceleration (Agx) and the GZ-axis acceleration (Agz), and perform flail the pressure reduction control on at least flail the front wheel brake if the rear-wheel lift is probable, and
the controller adjusts flail the degree of pressure reduction to a value corresponding to the differentiation value as defined as a differentiation value of the GZ-axis acceleration (Agz) of the acceleration acquired.
17. The brake fluid pressure control device according to claim 16 , wherein
the controller calculates the GZ-axis acceleration (Agz) in a rear-wheel lift direction that is perpendicular to, at a center of gravity Cg of the vehicle, a straight line connecting the center of gravity Cg of the vehicle and a contact point of a front wheel and a ground at the occurrence of the rear-wheel lift in a vertical plane including the straight line, based on an acquired Z-axis acceleration in a Z-axis direction and an acquired X-axis acceleration in a X-axis direction,
the controller adjusts the degree of pressure reduction according to the differentiation value of the GZ-axis acceleration (Agz) in the rear-wheel lift direction, and
the controller calculates the differentiation value of the GZ-axis acceleration (Agz) in the rear-wheel lift direction by calculating the GZ-axis acceleration (Agz) in the rear-wheel lift direction at a first prescribed time and dividing a difference between a GZ-axis acceleration value (Agz(n)) at a present time n and a past GZ-axis acceleration (Agz) times a second prescribed time ago by a number times the second prescribed time ago.
18. The brake fluid pressure control device according to claim 17 , wherein
the controller increases the degree of pressure reduction proportionally as the differentiation value of the GZ-axis acceleration (Agz) in the rear-wheel lift direction becomes smaller, and
a behavior of the vehicle in the rear-wheel lift direction becomes faster as an absolute value of the differentiation value of the GZ-axis acceleration (Agz) in the rear-wheel lift direction increases.