Speed sensor fault detection system and method

Claim 3

The control method of claim 1 wherein said absolute value of the rate of change in S is determined by a comparison of the current calculated value for S and the last calculated value for S.

Claim 4

The control method of claim 1 wherein the calculated value for the rate of change in S is the first derivative of the value of S with respect to time.

Claim 5

The control method of claims 1, 2 or 3 wherein said function is defined by the relationship S is a function of (N-1)K/(C N -C 0 ) where S=rotational speed of the monitored object; N=number of pulse counts per fixed time duration cycle loop; K=a constant; C N =time of last N count; and C 0 =time of first N count.

Claim 6

A control system for detecting and responding to "dropped tooth type" faults in the output signals from tooth rotor type speed sensor assemblies, said control system including a control unit (ECU) for processing input signals according to either a non-fault sensed set of predetermined logic rules and a separate fault sensed (fail safe, fail soft) set of predetermined logic rules and a speed sensor assembly (10) of the type comprising a tooth rotor (12) rotatably associated with the monitored rotatable member (14) and a relatively fixed sensor member (16), said sensor assembly providing an output signal (20, 22, 24, 26) comprising a plurality of pulses having a frequency indicative of the rotational speed of said rotor, the rotational speed determined as a function of the number (N) of said tooth pulses sensed in a time period, said system characterized by: means for setting the time period such that if the actual value of (N-1) is sensed as equaling (N-2) or less, then a determined absolute value of the rate of change in S will be greater than a reference value equal to at least a largest expected deceleration rate of the monitored object; means for determining a value indicative of the rate of change with respect to time in S; means for comparing the absolute value of said value indicative of the rate of change in S to said reference value (REF) and if the absolute value of the value indicative of the rate of change of S is greater than said reference value, causing said control unit to process said input signals according to said fault sensed set of predetermined logic rules.

Claim 7

A control system for detecting and responding to "dropped tooth type" faults in the output signals from tooth rotor type speed sensor assemblies, said control system including a control unit (ECU) for processing input signals according to either a non-fault sensed set of predetermined logic rules and a separate fault sensed (fail safe, fail soft) set of predetermined logic rules and a speed sensor assembly (10) of the type comprising a tooth rotor (12) rotatably associated with the monitored rotatable member (14) and a relatively fixed sensor member (16), said sensor assembly providing an output signal (20, 22, 24, 26) comprising a plurality of pulses having a frequency indicative of the rotational speed of said rotor, the rotational speed determined as a function of the number (N) of said tooth pulses sensed in a time period, said system characterized by: means for setting the time period such that if the actual value of (N-1) is sensed as equaling (N-2) or less, then a determined absolute value of the rate of change in S will be greater than a reference value equal to at least a largest expected deceleration rate of the monitored object; means for determining a value indicative of the rate of change with respect to time in S; means for comparing the absolute value of said value indicative of the rate of change in S to said reference value (REF) and if the absolute value of the value indicative of the rate of change of S is greater than said reference value, causing said control unit to process said input signals according to said fault sensed set of predetermined logic rules.

Claim 8

The control system of claim 5 wherein the calculated value for the rate of change in S is the first derivative of the value of S with respect to time.

Claim 9

The control system of claims 5, or 6 wherein said function is defined by the relationship S is a function of (N-1)K/(C N -C 0 ) where S=rotational speed of the monitored object; N=number of tooth pulse counts per fixed time duration cycle loop; K=a constant; C N =time of last N count; and C 0 =time of first N count.