US 8,798,844 B2Granted

Diagnostic method and apparatus for electric power steering system

AssigneeTRW Inc.

InventorsPhilip Owen Browne, Adrian Szabo

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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 predetermined 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.

Claims10

Dependent claims

A method of diagnosing a correct operation of an isolation relay in an electric power steering system including 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 the steps of:

(a) closing said phase isolation relay;
(b) demanding a phase current having a predetermined value through the motor phase associated with said phase isolation relay;
(c) measuring at least one characteristic of an actual said phase current in said motor phase after a predetermined period of time has elapsed, said predetermined period of time being that is less than an amount of time needed for said measured characteristic of said actual phase current to reach said demanded predetermined current value of said demanded phase current;
(d) comparing, using a processor, said measured characteristic of said actual phase current with a reference characteristic of said demanded phase current that is less than said predetermined value of said demanded phase current;
and
(e) in the event that said measured characteristic of said actual phase current does not correspond with said reference characteristic of said demanded phase current, opening said phase isolation relay and subsequently repeating steps (a) to (d).

3 more elements

An electric power assisted steering system comprising:

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 by:
(1) receiving 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 measured characteristic of an actual said phase current after said count signal indicates that a predetermined period of time has elapsed, wherein said predetermined period of time is less than an amount of time needed for said measured characteristic of said actual phase current to reach a predetermined value of a demanded phase current;
(2) comparing further in which said processor is arranged to compare said measured characteristic of said actual phase current with a reference characteristic of said demanded phase current that is less than said predetermined value of said demanded phase current;
and
(3) in the event that said measured characteristic of said actual phase current isolation does not correspond with said reference characteristic of said demanded phase isolation current, causing to cause said relay to open and subsequently repeating to repeat said diagnostic sub routine.

6 more elements

Dependencies are inferred from the claim text.