Patent ID: 7158866

Claim:
A method of calculating a physical parameter value (X) of a wheeled vehicle indirectly using at least two directly measurable input signals, comprising the steps of: (a) receiving a first input sensor signal (y 1 (t)) that is dependent on a first physical input parameter affecting a condition of the wheeled vehicle; (b) receiving a second input sensor signal (y 2 (t)) that is dependent on a second physical input parameter affecting a condition of the wheeled vehicle, wherein the second physical input parameter can be any one of the same as physical parameter value (X), the same as the first physical input parameter, and different from the first physical input parameter; (c) recursively filtering the first and second physical input parameters by means of an adaptive filter based on a predetermined model of the condition of the wheeled vehicle, wherein the input signals to said model include the first physical input parameter (y 1 (t)), the second physical input parameter (y 2 (t)), a first offset scaling factor (c 1 (t)) for the first sensor signal, and a second offset scaling factor (c 2 (t)) for the second sensor signal, and wherein the model output signals include a first offset error signal (b 1 (t)) and a second offset error signal (b 2 (t)), and the physical parameter value (X); (d) estimating the values of said first offset error (b 1 (t)) and the second offset error (b 2 (t)) by means of said adaptive filter, wherein at least one offset error relates to the wheel radius; and (e) calculating the physical parameter value (X) using the adaptive filter from the input sensor signals y 1 (t) and y 2 (t) such that offset errors in the calculation are compensated for by means of the first and second offset error parameters (b 1 (t)) and (b 2 (t)) and the offset scaling factors c 1 (t) and c 2 (t).