INTERMITTENT FAILURE DIAGNOSTIC SYSTEM AND ELECTRIC POWER STEERING APPARATUS PROVIDED WITH THE SAME

• US 20160264173A1
• Filed: 11/13/2014
• Published: 09/15/2016
• Est. Priority Date: 11/22/2013
• Status: Active Grant

• Current Assignee: NSK Limited
• Original Assignee: NSK Limited
• Inventors: GOTO, Hiroki
• Granted Patent: US 9,783,228 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B62D 5/0481 monitoring the steering system, e.g. failures
• CPC Class Codes: G05B 23/0235 based on a comparison with predetermined threshold or range, e.g. "classical methods", carried out during normal operation; threshold adaptation or choice; when or how to compare with the threshold
• CPC Class Codes: G05B 23/0275 Fault isolation and identification, e.g. classify fault; estimate cause or root of failure

Abstract

An intermittent failure diagnostic system that, in addition to a failure detection of a conventional failure threshold, sets an intermittent diagnostic threshold inside of the failure threshold or sets the intermittent diagnostic threshold in an arbitrary scope with a detection resolving-power unit, securely detects the intermittent failure in a wide region by using a statistics way, suppresses an unprepared system down and improves the reliability and to an electric power steering apparatus provided with the same.

Claims

1-9. -9. (canceled)

10. An intermittent failure diagnostic system comprising a fail-counter to failure-settle 1 on an ordinary diagnosis by calculating a normal distribution based on a mean value and a standard deviation of measured values at a normal state of an electrical apparatus, by setting at least one failure threshold as a diagnostic threshold of said measured values, and by measuring a number or a time of said measured values exceeding said failure threshold:

wherein said intermittent failure diagnostic system sets an intermittent failure diagnostic threshold for an intermittent failure diagnosis between said mean value and said failure threshold, and said fail-counter measures a number or a time that said measured values exceed said intermittent failure diagnostic threshold; and

wherein said intermittent failure diagnostic system sets a counting value or a time to failure-settle 2 on said fail-counter so as to coincide a permissible value on a false-failure probability of said ordinary diagnosis with a permissible value on a false-failure probability of said intermittent failure diagnosis,

wherein assuming that a counting value of said fail-counter to failure-settle 1 on said ordinary diagnosis is n, a counting value of said fail-counter to failure-settle 2 is N, a permissible value on a false-failure probability of said ordinary diagnosis is P_Fⁿ and a permissible value on a false-failure probability of said intermittent failure diagnosis is P_T^N, a relation

N=(n*log P_F)/(log P_T)

is established.

11. The intermittent failure diagnostic system according to claim 10, wherein said failure threshold is set based on a physical requirement 1.

12. The intermittent failure diagnostic system according to claim 11, wherein said physical requirement 1 is a hard ware characteristic or a system usage condition.

13. The intermittent failure diagnostic system according to claim 10, wherein said counting value or said time to failure-settle 2 is set based on a physical requirement 2.

14. The intermittent failure diagnostic system according to claim 13, wherein said physical requirement 2 is at least one of a hard ware characteristic, a system usage condition, a supposing impulse-noise width and a continuous permissible time on a functional safety.

15. The intermittent failure diagnostic system according to claim 10, wherein said failure thresholds are set at an upper-limit side and a lower-limit side, and at least one of said intermittent failure diagnostic threshold is set between said failure thresholds and said mean-value.

16. The intermittent failure diagnostic system according to claim 10, wherein said failure counting is continuously or discontinuously performed.

17. The intermittent failure diagnostic system according to claim 10, wherein said intermittent failure diagnostic threshold is shifted to a whole region of diagnostic values by a detection resolving-power unit and is set.

18. An electric power steering apparatus is provided with the intermittent failure diagnostic system claimed in claim 10.