Method for estimating reference speed and acceleration for traction and anti-skid braking control
AssigneeHughes Aircraft Company
InventorJames McEnnan
Life of this patent
Estimating the term…
Abstract
A method for estimating vehicle reference speed and acceleration utilizing an adaptive filter for providing periodically updated reference values given by a currently extrapolated value plus a correction term which is a function of current wheel slip, wheel acceleration and wheel velocity. The method may be successfully employed over a wide range of road friction coefficients and may be used for traction control as well as anti-skid braking, since the approach does not assure a fixed limiting wheel acceleration. The method avoids the necessity of maintaining low slip values on preselected wheels in order to obtain suitable reference speed values.
Claims18
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.
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.sub.ref, and the updated reference acceleration, a.sub.ref, to zero;
- (b) waiting for a preselected updated time interval dt;
- (c) generating extrapolated values of reference speed, v'.sub.ref, and reference acceleration, a'.sub.ref, such that
- v'.sub.ref =v.sub.ref +(a.sub.ref)(dt)
- a'.sub.ref =a.sub.ref ;
- (d) calculating a difference, e.sub.i, between a current wheel speed, v.sub.i, and v'.sub.ref, or e.sub.i =v.sub.i -v'.sub.ref ;
- (e) determining a polarity function, SIGN, in accordance with the following
- SIGN=+1, if v'.sub.ref =0
- SIGN=polarity of a.sub.ref, if a'.sub.ref .noteq.0
- SIGN=-1, otherwise;
- (f) calculating a current value of wheel slip, s.sub.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.sub.i, by da.sub.i =a.sub.i -a'.sub.ref, where a.sub.i is current wheel acceleration;
- (h) selecting positive constant reference slip, s.sub.o, and positive constant reference acceleration, a.sub.o, values;
- (i) calculating two auxiliary functions f.sub.i and f.sub.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-.vertline.da.sub.i .vertline./a.sub.o if .vertline.da.sub.i .vertline.<a.sub.o
- f.sub.2 =0, otherwise;
- (j) calculating two adaptive filter gains, K.sub.v and K.sub.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.sup.o.sub.v, k.sup.1.sub.v, k.sup.o.sub.a and k.sup.1.sub.a are constants selected to obtain a desired filter performance;
- (k) calculating new updated values of reference speed, v.sub.ref, and reference acceleration, a.sub.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).
Dependencies are inferred from the claim text.