An Electric Power Assisted Steering System

Patent metadata

Field	Value
Publication number	US-2018208239-A1
Application number	US-201515320377-A
Country	US
Kind code	A1
Filing date	Jun 23, 2015
Priority date	Jun 25, 2014
Publication date	Jul 26, 2018
Grant date	—

Abstract

An electric power assisted steering system comprising a torque sensor assembly comprising an input shaft, an output shaft, a torsion bar that interconnects the input shaft and the output shaft, and a processing means which produces a torque signal indicative of the torque carried by the torsion bar, an electric motor that is connected to the output shaft, and a motor position sensor that provides a motor position signal dependent on the angular position of the motor rotor that repeats each time the motor has rotated through a known angular range. The apparatus further including processing means that generates an absolute output shaft position signal from the motor position signal by adding to the output of the motor position sensor a first term indicative of the fixed offset between the motor position sensor zero position and the zero position of the input shaft and a second term indicative of the number of turns of the motor rotor away from the zero position of the input shaft. The processing means determines the base motor position value at start up of the system by comparing the motor position signal from the position sensor with the signal from the sensor associated with the sensing means of the upper shaft to determine three candidates and during subsequent unpowered motion of the steering system rules out candidates until only one remains plausible candidate.

First claim

1 . An electric power assisted steering system comprising:
a torque sensor assembly comprising an upper shaft that in use is operatively connected to a steering wheel of a vehicle, a lower shaft that in use is operatively connected to road wheels of the vehicle, a torsion bar that interconnects the upper shaft and the lower shaft, and a processing means which produces a torque signal indicative of the torque carried by the torsion bar, an electric motor that is connected to the lower shaft so that a change in an angular position of the motor produces a corresponding change in an angular position of the lower shaft, and a motor position sensor that provides a motor position signal dependent on an angular position of a motor rotor that repeats each time the motor has rotated through a known angular range, the system further including processing means that generates an absolute lower shaft position signal from the motor position signal by adding to an output of the motor position sensor a first term indicative of a fixed offset between the motor position sensor zero position and a zero position of the upper shaft and a second term indicative of a number of turns of the motor rotor away from the zero position of the upper shaft, and in which the processing means is adapted to determine a base motor position value at start up of the system by comparing the motor position signal from the motor position sensor with the signal from the sensor associated with the sensing means of the upper shaft to determine a central candidate, choosing a higher candidate that is one repeat of the motor sensor signal above this and a lower candidate that is one motor position value below this, and during subsequent unpowered motion of the steering system producing a torsion bar deflection value from each candidate by comparing a signal indicative of the absolute angular position of the lower shaft signal with the signal from the upper shaft sensor and ruling out the candidates that give implausible torsion bar deflection values over time as the steering system moves until only one plausible candidate remains.

2 . The system according to claim 1 in which the upper shaft sensing means comprises a position sensor or sensors that provide a signal indicative of an absolute angular position of the upper shaft.

3 . The system according to claim 1 in which the torsion bar is restrained so that it cannot twist beyond a defined angle, and a candidate may be ruled out when the torsion bar twist estimated from the candidate exceeds that defined angle.

4 . The system according to claim 1 in which the processing means is arranged to continue to monitor until a time in which only one candidate remains and only after this time start providing an assistance torque from the motor, assistance being prevented or restricted prior to that time.

5 . The system according to claim 1 in which the processing means that generates the torque signal comprises:
a first torque signal generating means that generates a first torque signal based on angular deflection of the torsion bar,
a second torque signal generating means that generates a second torque signal based on angular deflection of the torsion bar.

6 . The system according to claim 1 which further comprises an absolute position signal generating means that in use produces an absolute upper column position signal indicative of the angular position of the upper column shaft that is used in generating the candidates.

7 . The system according to claim 1 which comprises include an upper column angular position sensing means that produces at least one output signal that is dependent on an angular position of the upper column shaft;
a lower column position sensing means that produces at least one output signal that is dependent on an angular position of the lower column shaft, and the processing means may be configured to produce a first torque signal from an output signal from the upper and lower column angular position sensing means, and produces a second, independent, torque signal from the output signals from the upper and lower column angular position sensing means.

8 . A method for use in controlling an electric power assisted steering system which includes a torque sensor assembly comprising an input shaft that in use is operatively connected to a steering wheel of a vehicle, an output shaft that in use is operatively connected to road wheels of the vehicle, a torsion bar that interconnects the upper shaft and the lower shaft, and a processing means which produces a torque signal by comparing the output signals from angular position sensing means fixed to the upper and lower shafts,
an electric motor that is connected to the output shaft so that a change in an angular position of the motor produces a corresponding change in an angular position of the lower shaft, and a motor position sensor that provides a motor position signal dependent on an angular position of a motor rotor that repeats each time the motor has rotated through a known angular range, the method comprising the steps of: generating an absolute lower shaft position signal from the motor position signal by adding to an output of the motor position sensor a first term indicative of a fixed offset between the motor position sensor zero position and a zero position of the upper shaft and a second term indicative of the number of turns of a motor rotor away from the zero position of the upper shaft, determining a base motor position value at start up of the system by comparing the motor position signal from the motor position sensor with the signal from the sensor associated with the sensing means of the input shaft to determine a central candidate, choosing a higher candidate that is one repeat of the motor sensor signal above this, choosing a lower candidate that is one motor position value below this, and during subsequent reduced authority motion of the steering system producing a torsion bar deflection value from each candidate by comparing a signal indicative of the absolute angular position of the lower shaft signal with the signal from the upper shaft sensing means and ruling out the candidates that give implausible torsion bar deflection values over time as the steering system moves until only one plausible candidate remains.

9 . The system according to claim 1 wherein the known angular range is once per motor rotor electrical rotation.

10 . The method according to claim 8 wherein the known angular range is once per motor rotor electrical rotation.

Assignees

• Trw Ltd

Inventors

• Farrelly James Owen Patrick

Classifications

• B62D15/0235

  by measuring or deriving directly at the electric power steering motor · CPC title

• B62D5/049

  detecting sensor failures · CPC title

• B62D5/0493

  detecting processor errors, e.g. plausibility of steering direction · CPC title

• B62D6/10 Primary

  characterised by means for sensing {or determining} torque · CPC title

• B62D15/0215

  by measuring on the steering column · CPC title