DIAGNOSTIC METHOD AND APPARATUS FOR ELECTRIC POWER STEERING SYSTEM
First Claim
1. A method of diagnosing a correct operation of an isolation relay in an electric power steering system of the kind comprising a motor drive circuit and at least one phase isolation relay which connects a part of said motor drive circuit to a phase of said motor, said phase isolation relay being opened during shutdown to isolate said motor phase from said part of said drive circuit and being normally closed during operation of said motor to connect said phase to the part of said drive circuit, said method comprising:
- (a) closing said phase isolation relay;
(b) demanding a phase current having a predetermined value through the said motor phase associated with said phase isolation relay that is equal to a preset value;
(c) measuring at least one characteristic of said phase current in said motor phase after a predetermined period of time has elapsed, said elapsed time being less than a time needed for said phase current to reach said demanded predetermined current value;
(d) comparing said measured characteristic of said phase current with a reference characteristic of said phase current; and
(e) in the event that said measured characteristic of said phase current does not correspond with said reference characteristic of said phase current, opening said phase isolation relay and subsequently repeating steps (a) to (d).
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Accused Products
Abstract
A method and apparatus diagnoses a correct operation of a phase or star point isolation relay in an electric power steering system of the kind including a motor drive circuit and at least one phase isolation relay which connects a part of the drive circuit to a phase of the motor. The relay is opened during shutdown to isolate the motor phase from the part of the drive circuit and is normally closed during operation of the motor to connect the phase to the part of the drive circuit. The method includes the steps of: closing the relay; demanding a current through the motor phase associated with the relay that is equal to a preset value; measuring at least one characteristic of the phase current in that phase after a predetermined period of time has elapsed, the elapsed time being less than a time needed for the phase current to reach the demanded current value; comparing the measured characteristic of the phase current with a reference characteristic of the phase current; and, in the event that the measured characteristic does not correspond with the reference characteristic, opening the relay and subsequently repeating the steps.
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Citations
10 Claims
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1. A method of diagnosing a correct operation of an isolation relay in an electric power steering system of the kind comprising a motor drive circuit and at least one phase isolation relay which connects a part of said motor drive circuit to a phase of said motor, said phase isolation relay being opened during shutdown to isolate said motor phase from said part of said drive circuit and being normally closed during operation of said motor to connect said phase to the part of said drive circuit, said method comprising:
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(a) closing said phase isolation relay; (b) demanding a phase current having a predetermined value through the said motor phase associated with said phase isolation relay that is equal to a preset value; (c) measuring at least one characteristic of said phase current in said motor phase after a predetermined period of time has elapsed, said elapsed time being less than a time needed for said phase current to reach said demanded predetermined current value; (d) comparing said measured characteristic of said phase current with a reference characteristic of said phase current; and (e) in the event that said measured characteristic of said phase current does not correspond with said reference characteristic of said phase current, opening said phase isolation relay and subsequently repeating steps (a) to (d). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An electric power assisted steering system comprising:
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an electric motor, a motor drive circuit; at least one phase isolation relay which connects a part of said motor drive circuit to a phase of said motor, said phase isolation relay being opened during shutdown to isolate said motor phase from said part of said drive circuit and normally closed during operation of the motor to connect said phase from said part of the drive circuit; and a processor that is arranged to cause said system to perform a diagnostic sub-routine and is arranged to receive, during the sub-routine, a count signal which is indicative of an elapsed time following closing of said phase isolation relay and a value indicative of at least one characteristic of said phase current after said count signal indicates that a predetermined period of time has elapsed, and further in which said processor is arranged to compare said measured characteristic of said phase current with a reference characteristic of said phase current; and
in the event that said measured characteristic phase isolation does not correspond with said reference characteristic phase isolation to cause said relay to open and subsequently to repeat said diagnostic sub routine. - View Dependent Claims (10)
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Specification