Anti-lock braking system based on an estimated gradient of friction torque, method of determining a starting point for anti-lock brake control, and wheel-behavior-quantity servo control means equipped with limit determination means

An anti-lock brake controller comprising:

• wheel-deceleration sensing means for sensing a wheel deceleration;
• braking torque sensing means for sensing a braking torque;
• torque-gradient estimating means which estimates a gradient of friction torque with respect to a slip speed in accordance with time-series data concerning the wheel deceleration detected at given sampling intervals, and time-series data concerning the braking torque detected at given sampling intervals or a physical quantity related to the braking torque;
• and
• control means which controls braking forces acting on the wheels in such a way that the gradient of friction torque estimated by said torque-gradient estimating means falls within a predetermined range including a reference value,
• wherein said torque-gradient estimating means approximates a state of motion of the wheel obtained when the friction torque and the braking torque are exerted on the wheel, using a gradient model in which the friction torque changes linearly in accordance with the gradient of friction torque with respect to the slip speed,
• previously converts the thus-approximated state of motion into a relationship between the gradient of friction torque with respect to the slip speed, which is a parameter to be identified, a physical quantity which is related to a variation in the friction torque and a physical quantity which is related to a variation in the slip speed, which are both represented by the braking torque and the wheel deceleration;
• and
• estimates the gradient of friction torque with respect to the slip speed by applying an on-line system identification method to data obtained by sequentially applying to the relationship the time-series data concerning detected wheel deceleration and the time-series data concerning the braking torque or the physical quantity related to the braking torque.

A control start determination method comprising:

• a wheel speed sensing step for sensing the speed of a wheel at predetermined sampling intervals;
• a torque-gradient estimating step for estimating a friction torque gradient with respect to a slip speed based on time-series data regarding the wheel speed sensed in the wheel speed sensing step, the friction torque being received by a wheel from a road surface;
• and
• a determination step for determining a starting point for the control to bring the wheel into a predetermined state of motion in accordance with the friction torque gradient estimated in the torque-gradient estimating step.

A wheel-behavior-quantity servo controller comprising:

• wheel-behavior-quantity detecting means for detecting a quantity of behavior of a wheel which is a physical quantity associated with a motion of the wheel;
• limit determination means which calculates, as a quantity of limit determination, a friction torque gradient indicating a gradient of friction torque with respect to a slip speed or a physical quantity associated with the friction torque gradient via the wheel motion, and which determines the limit of the characteristics of the friction torque between the wheel and the road surface in accordance with the quantity of limit determination;
• target-behavior-quantity calculation means which calculates a target value of the quantity of wheel behavior used for controlling the quantity of limit determination to within the limit of friction torque characteristics in accordance with the result of limit determination of said limit determination means;
• and
• servo control means which controls the motion of the wheel so as to cause the quantity of wheel behavior detected by said wheel-behavior-quantity detecting means to follow the target value of the quantity of wheel behavior calculated by the target-behavior-quantity calculation means.

A torque gradient estimating apparatus compising:

• wheel-speed sensing means which senses a wheel speed at given sampling intervals;
• torque-gradient estimating means which estimates a gradient of friction torque or driving torque with respect to a slip speed in accordance with time-series data concerning the wheel speed detected by said wheel-speed sensing means, the friction torque being received by a wheel from a road surface;
• and
• output means which outputs the estimated gradient of friction torque or driving torque.