Patent Number: 
Section: abstract

An operating device pressure Po into a regulator valve and a degree of opening X from the regulator valve are sampled. A speed of change vPo (k) of the Po (k) is calculated from the current Po (k) and the previous Po (k −1). A speed of change vX (k) of the X (k) is calculated from the current X (k) and the previous X (k −1). If both vPo (k) and vX (k) are small, then a weighting value w1 (k) is set to 1 (and set to 0 otherwise), where a fault check indicator Fq (i) for each degree-of-opening category i during a fault check evaluation time interval is calculated from the vPo (k) and vX (k) when w1 (k) is 1 and from a linear approximation formula F1 that indicates the steady-state input/output relationships in the regulator valve when operating properly.