Apparatus and method for diagnosing a wheel speed input system in a vehicle motion control apparatus

A method for diagnosing a wheel speed input system in a vehicle motion control apparatus comprising, a first wheel speed sensor outputting a first analog signal corresponding to a wheel speed of a first wheel, a second wheel speed sensor outputting a second analog signal corresponding to a wheel speed of a second wheel, a first waveform converting means for converting the first analog signal into a first pulse signal, a second waveform converting means for converting the second analog signal into a second pulse signal, and an electronic control unit controlling an operation of an actuator which modifies a motion of a vehicle in response to said first and second pulse signals, said method comprising the steps of:

• receiving first and second analog values outputted from said first and second wheel speed sensors;
• judging whether or not each of said first and second waveform converting means outputs a third pulse signal which is in correspondence with a wheel speed equal to or less than a minimum wheel speed that can be detected with said first and second wheel speed sensors;
• converting said first analog values into a first digital value at a predetermined sampling cycle when said electronic control unit judges that said first waveform converting means outputs the third pulse signal;
• and
• judging a failure in at least either of an operation of said first waveform converting means itself and an operation between said first waveform converting means and said electronic control unit in accordance with a variation of adjacent digital values thus sampled at said predetermined sampling cycle.

A diagnostic device for a wheel speed input system for a vehicle motion control device comprising:

• wheel speed sensors (1A, 1B, 1C, 1D) corresponding individually to a plurality of wheels;
• a plurality of waveform converting means (2A, 2B, 2C, 2D) for waveform converting analog signals outputted individually from said respective wheel speed sensors (1A to 1D) into individual pulse signals corresponding to wheel speeds of said respective wheel speed sensors;
• and
• an electronic control unit (4) for controlling the operation of an actuator (5) that can modify the motion of a vehicle in response to wheel speeds obtained based on outputs from said respective waveform converting means (2A to 2D),
• wherein said electronic control unit (4) judges whether or not said waveform converting means (2A to 2D) output a pulse signal corresponding to a speed equal to or less than a minimum wheel speed that can be detected with said wheel speed sensors (1A to 1D) with respect to each of said waveform converting means (2A to 2D), and wherein when said electronic control unit judges that said waveform converting means (2A to 2D) output a pulse signal corresponding to said speed equal to or less than the minimum wheel speed, said electronic control unit judges that there exists a failure in at least either of said waveform converting means (2A to 2D) themselves which are outputting a pulse signal corresponding to said speed equal to or less than the minimum wheel speed and somewhere between said waveform converting means (2A to 2D) and said electronic control unit (4) based on a fact that a variation of digital values which are obtained by converting at a predetermined sampling cycle analog values outputted from said wheel speed sensors (1A to 1D) corresponding to said waveform converting means (2A to 2D) so judged exceeds a threshold value.