Method and apparatus for nullifying electrical offsets in a torsion sensor

• US 4,887,682 A
• Filed: 01/06/1988
• Issued: 12/19/1989
• Est. Priority Date: 01/06/1988
• Status: Expired due to Term

• Current Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Borza, John S., Drutchas, deceased, Gilbert H.
• Primary Examiner(s): HILL, MITCHELL
• Application Number:
  US07/142,837
• Time in Patent Office: 713 Days
• Field of Search: 180/79.1, 180/79, 364/424.01, 364/424.05
• US Class Current: 180/446
• CPC Class Codes: B62D 6/10 characterised by means for sensing or determining torque

Abstract

A method and apparatus is disclosed for nullifying electrical offsets present in an output signal from a torsion sensing device. The apparatus includes a detection circuit for outputting an electrical signal when a change between a no applied torque condition and an applied torque condition occurs in a member whose torsion is being monitored. A sample and hold circuit measures the output signal from the torsion sensing device, the sample and hold circuit being triggered in response to the detection circuit. A differencing circuit subtracts the output of the sample and hold circuit from a "zero torque" reference value and outputs an electrical signal having a value indicative of the difference therebetween. An offset compensating circuit is electrically connected to the output of the differencing circuit and to the torsion sensing device and outputs a modified torsion sensing signal having a value that varies as a function of the applied torque offset by the value of the output of the differencing circuit.

Claims

1. A power assist steering system having a vehicle steering wheel operatively connected to steerable wheels of the vehicle through a torsion bar, applied steering torque twisting the torsion bar, said power steering system including:

power assist means operatively connected to vehicle steering linkage for, when energized, providing power assist to an operator applied steering maneuver;

an electrical control signal having a value;

drive circuit means for energizing said power assist means in response to said value of said electrical control signal;

torsion sensing means for providing an electrical torsion signal having a value that varies as a function of applied steering torque;

means for detecting when no steering torque is applied and when steering torque is applied, said detecting means providing a first electrical signal when steering torque is applied and a second electrical signal when no steering torque is applied;

means responsive to said detecting means for measuring a value of said electrical torsion signal from said torsion sensor when the signal provided by said detecting means changes between said first electrical signal and said second electrical signal and for providing an output signal having a value indicative of the measured value of said electrical torsion signal;

means for providing a zero torque reference voltage having a predetermined value;

means for comparing said output signal from the measuring means against said value of said zero torque reference voltage and for providing an electrical output signal having a value equal to the difference therebetween;

compensating circuit means electrically connected to said torsion sensing means and said means for comparing, said compensating circuit means providing an electrical, compensated torsion signal having a value equal to the value of said electrical torsion sensing signal from said torsion sensing means offset by the value of the electrical output signal from said means for comparing; and

control circuit means electrically connected to said compensating circuit means and to said drive circuit means for providing said electrical control signal having a value responsive to the output signal of the compensating circuit means.

2. The power assist steering system of claim 1 wherein said power assist means is an electric motor.

3. The power assist steering system of claim 1 wherein said detecting means including a reversing switch connected to said drive circuit means and to said power assist means, means for closing a pair of switch contacts upon application of steering torque, means for monitoring switch closure and switch opening, and means for providing said first electrical signal when the switch contacts close and said second electrical signal when no switch contacts are closed.

4. The power assist steering system of claim 1 wherein said measuring means is a sample and hold circuit.