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DIAGNOSTIC METHOD AND APPARATUS FOR ELECTRIC POWER STEERING SYSTEM

  • US 20120035801A1
  • Filed: 08/03/2011
  • Published: 02/09/2012
  • Est. Priority Date: 08/04/2010
  • Status: Active Grant
First Claim
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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:

  • (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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