Electric power steering device

Claim 2

A motor driven power steering system for a vehicle comprising: an electric motor; torque detecting means for detecting the steering torque applied to a steering shaft by a driver and producing a torque signal; electronic control means operatively connected to said motor and said torque detecting means for generating pulses for controlling said motor; wherein said electronic control means comprises: polarity detecting means for detecting the direction in which the steering torque is applied to said steering shaft and producing a direction signal; absolute value circuit means for detecting the magnitude of the steering torque and producing a magnitude signal; function generating means for de-energizing said motor when said magnitude signal is less than a predetermined level; pulse duration modulation means for controlling the energization of said motor by changing the pulse duration in response to said direction and magnitude signals; and closed loop control means for feeding a signal corresponding to the output of said motor back to the input side of said pulse duration modulation means.

Claim 3

A motor driven power steering system as set forth in claim 1 wherein said closed loop control system includes means for stopping the energization of said motor when said signal corresponding to the output of said motor exceeds a predetermined level signal.

Claim 4

A motor driven power steering system as set forth in claim 1 wherein said function generating means includes circuit means for delivering an output signal of constant amplitude when the magnitude of the steering torque is greater than a predetermined magnitude.

Claim 5

A motor driven power steering system as set forth in claim 1 wherein said control means includes means for detecting an abrupt change in the steering torque and means for shortcircuiting said motor when the abrupt change is detected.

Claim 6

A motor driven power steering system as set forth in claim 1 further comprising vehicle speed detecting means, setting means for setting a predetermined vehicle speed and control means for stopping the energization of said motor when the actual vehicle speed exceeds a predetermined speed.

Claim 7

A motor driven power steering system for a vehicle comprising: an electric motor; torque detecting means for detecting the steering torque applied to a steering shaft by a driver and producing a torque signal; electronic control means operatively connected to said motor and said torque detecting means for generating pulses for controlling said motor; wherein said electronic control means comprises: polarity detecting means for detecting the direction of torque detected by said torque detecting means and producing a polarity signal; absolute value circuit means for detecting the magnitude of torque detected by said torque detecting means and producing an absolute signal; torque signal processing means for producing a steering torque signal when said absolute signal exceeds a predetermined level; pulse duration modulation means producing a pulse duration signal in response to said steering torque signal; logic control circuit means for producing a plurality of predetermined output signals in response to said polarity signal and said pulse duration signal; and motor drive circuit means for supplying load current to said electric motor in response to said output signals of said logic control circuit means.

Claim 8

A motor driven power steering system for a vehicle comprising: an electric motor; torque detecting means for detecting the steering torque applied to a steering shaft by a driver and producing a torque signal; electronic control means operatively connected to said motor and said torque detecting means for generating pulses for controlling said motor; wherein said electronic control means comprises: polarity detecting means for detecting the direction of torque detected by said torque detecting means and producing a polarity signal; absolute value circuit means for detecting the magnitude of torque detected by said torque detecting means and producing an absolute signal; torque signal processing means for producing a steering torque signal when said absolute signal exceeds a predetermined level; pulse duration modulation means producing a pulse duration signal in response to said steering torque signal; logic control circuit means for producing a plurality of predetermined output signals in response to said polarity signal and said pulse duration signal; and motor drive circuit means for supplying load current to said electric motor in response to said output signals of said logic control circuit means.

Claim 9

A motor driven power steering system for a vehicle as set forth in claim 6 further including: current detecting means for detecting the level of current flow through said electric motor and producing a current signal; wherein said electronic control means includes: current signal processing means for producing an absolute value signal of current flow through said electric motor in response to said current signal of current detecting means; differential signal processing means for producing a differential output signal representing the difference between said steering torque signal and said absolute value signal of said current signal processing means; and said pulse duration modulation means producing a pulse signal in response to said differential output signal.

Claim 10

A motor driven power steering system for a vehicle as set forth in claim 7 wherein said current signal processing means produces an overcurrent signal when said current signal exceeds a predetermined level; and said logic control circuit means prevents the operation of said electric motor in response to said overcurrent signal.