Method for estimating reference speed and acceleration for traction and anti-skid braking control

Claim 1

A method for estimating a vehicle reference speed and reference acceleration suitable for determining relative wheel slip of an individual wheel of the vehicle, the method comprising: periodically determining extrapolated values of reference speed and reference acceleration from previously updated values thereof; estimating a current wheel slip of the individual wheel from the extrapolated value of the reference speed; computing first and second adaptive filter gains which are functions of a current estimate of slip and a current estimate of wheel acceleration, respectively; generating an error signal as a function of a difference between current wheel speed and the extrapolated value of the reference speed; and generating updated values of reference speed and reference acceleration by adding a product of the first gain and the error signal to the extrapolated value of reference speed and by adding a product of the second gain and the error signal to the extrapolated value of reference acceleration.

Claim 2

A method for estimating a vehicle reference speed and reference acceleration suitable for determining relative wheel slip of an individual wheel of the vehicle, the method comprising: periodically determining extrapolated values of reference speed and reference acceleration from previously updated values thereof; estimating a current wheel slip of the individual wheel from the extrapolated value of the reference speed; computing first and second adaptive filter gains which are functions of a current estimate of slip and a current estimate of wheel acceleration, respectively; generating an error signal as a function of a difference between current wheel speed and the extrapolated value of the reference speed; and generating updated values of reference speed and reference acceleration by adding a product of the first gain and the error signal to the extrapolated value of reference speed and by adding a product of the second gain and the error signal to the extrapolated value of reference acceleration.

Claim 12

A method for estimating a vehicle reference speed and reference acceleration suitable for determining wheel slip of an individual wheel of the vehicle, the method comprising: (a) initially setting the updated reference speed, v ref , and the updated reference acceleration, a ref , to zero; (b) waiting for a preselected updated time interval dt; (c) generating extrapolated values of reference speed, v' ref , and reference acceleration, a' ref , such that v'.sub.ref =v.sub.ref +(a.sub.ref)(dt) a'.sub.ref =a.sub.ref ; (d) calculating a difference, e i , between a current wheel speed, v i , and v' ref , or e i =v i -v' ref ; (e) determining a polarity function, SIGN, in accordance with the following SIGN=+1, if v' ref =0 SIGN=polarity of a ref , if a' ref ≠0 SIGN=-1, otherwise; (f) calculating a current value of wheel slip, s i , in accordance with the following s.sub.i =1-v.sub.i /v'.sub.ref, if v.sub.i <v'.sub.ref and SIGN<0, s.sub.i =1-v'.sub.ref /v.sub.i, if v.sub.i>v'.sub.ref and SIGN>0, s.sub.i =0, otherwise; (g) defining a relative wheel acceleration, da i , by da i =a i -a' ref , where a i is current wheel acceleration; (h) selecting positive constant reference slip, s o , and positive constant reference acceleration, a o , values; (i) calculating two auxiliary functions f i and f 2 in accordance with the following f.sub.i =1-s.sub.i /s.sub.o, if s.sub.i <s.sub.o, f.sub.i =0, otherwise, f.sub.2 =1-|da.sub.i |/a.sub.o if |da.sub.i |<a.sub.o f.sub.2 =0, otherwise; (j) calculating two adaptive filter gains, K v and K a , in accordance with the following K.sub.v =k.sup.o.sub.v +k.sup.1.sub.v (f.sub.1)(f.sub.2) K.sub.a =k.sup.o.sub.a +k.sup.1.sub.a (f.sub.1)(f.sub.2) where k o v , k 1 v , k o a and k 1 a are constants selected to obtain a desired filter performance; (k) calculating new updated values of reference speed, v ref , and reference acceleration, a ref , in accordance with the following v.sub.ref =v'.sub.ref +K.sub.v e.sub.i a.sub.ref =a'.sub.ref +K.sub.a e.sub.i ; and (1) returning to step (b).

Claim 13

A method for estimating a vehicle reference speed and reference acceleration suitable for determining wheel slip of an individual wheel of the vehicle, the method comprising: (a) initially setting the updated reference speed, v ref , and the updated reference acceleration, a ref , to zero; (b) waiting for a preselected updated time interval dt; (c) generating extrapolated values of reference speed, v' ref , and reference acceleration, a' ref , such that v'.sub.ref =v.sub.ref +(a.sub.ref)(dt) a'.sub.ref =a.sub.ref ; (d) calculating a difference, e i , between a current wheel speed, v i , and v' ref , or e i =v i -v' ref ; (e) determining a polarity function, SIGN, in accordance with the following SIGN=+1, if v' ref =0 SIGN=polarity of a ref , if a' ref ≠0 SIGN=-1, otherwise; (f) calculating a current value of wheel slip, s i , in accordance with the following s.sub.i =1-v.sub.i /v'.sub.ref, if v.sub.i <v'.sub.ref and SIGN<0, s.sub.i =1-v'.sub.ref /v.sub.i, if v.sub.i>v'.sub.ref and SIGN>0, s.sub.i =0, otherwise; (g) defining a relative wheel acceleration, da i , by da i =a i -a' ref , where a i is current wheel acceleration; (h) selecting positive constant reference slip, s o , and positive constant reference acceleration, a o , values; (i) calculating two auxiliary functions f i and f 2 in accordance with the following f.sub.i =1-s.sub.i /s.sub.o, if s.sub.i <s.sub.o, f.sub.i =0, otherwise, f.sub.2 =1-|da.sub.i |/a.sub.o if |da.sub.i |<a.sub.o f.sub.2 =0, otherwise; (j) calculating two adaptive filter gains, K v and K a , in accordance with the following K.sub.v =k.sup.o.sub.v +k.sup.1.sub.v (f.sub.1)(f.sub.2) K.sub.a =k.sup.o.sub.a +k.sup.1.sub.a (f.sub.1)(f.sub.2) where k o v , k 1 v , k o a and k 1 a are constants selected to obtain a desired filter performance; (k) calculating new updated values of reference speed, v ref , and reference acceleration, a ref , in accordance with the following v.sub.ref =v'.sub.ref +K.sub.v e.sub.i a.sub.ref =a'.sub.ref +K.sub.a e.sub.i ; and (1) returning to step (b).