Abstract An electric power steering system is disclosed which includes an electric motor adapted to supply steering assist directly to the steering system to thereby reduce the steering torque to be exerted to the system by a driver. The steering system includes a phase compensative device which is formed of a phase delay circuit, or the phase delay circuit and a low-pass filter connected in series thereto, and is positioned in a loop connecting a motor current detector in the steering system and a drive controller in a control block, so that high-frequency components may be removed from motor current signals in the feedback loop. As a result, it is possible to suppress lag of the phases of the signals and hence to prevent parasitic oscillations, leading to the steering system being capable of providing steering assist most suited to particular steering operations and comfortable steering feel to a driver.
An electric power steering system for use in an automotive vehicle, comprising: steering torque sensor means for sensing a steering torque in the steering system, an electric motor for supplying steering assist to the steering system, motor current detector means for detecting current through the electric motor, target current generator means for determining a target current for said electric motor based on a steering torque signal from said steering torque sensor, control means including a drive controller for controlling operations of said electric motor based on the deviation between said target current and said motor current, said drive controller having at least a proportional element and an integral element, and phase compensating means disposed in a path connecting said motor current detector means and said drive controller for reducing undesirable noises and preventing parasitic oscillations.
Claim 2
Dependent Claim
135 words
An electric power steering system for use in an automotive vehicle, comprising: steering torque sensor means for sensing a steering torque in the steering system, an electric motor for supplying steering assist to the steering system, motor current detector means for detecting current through the electric motor, target current generator means for determining a target current for said electric motor based on a steering torque signal from said steering torque sensor, control means including a drive controller for controlling operations of said electric motor based on the deviation between said target current and said motor current, said drive controller having at least a proportional element and an integral element, and phase compensating means disposed in a path connecting said motor current detector means and said drive controller for reducing undesirable noises and preventing parasitic oscillations.
Claim 3
Dependent Claim
19 words
An electric power steering system according to claim 1, wherein said phase compensating means comprises a phase delay means.
Claim 4
Dependent Claim
31 words
An electric power steering system according to claim 1, wherein said phase compensating means comprises a phase delay means and a low-pass filter connected in series to said phase delay means.