Motor-driven power steering system for a vehicle

Claim 2

A motor-driven power steering system for a vehicle having a steering wheel operatively connected with steerable road wheels, said motor-driven power steering system comprising: a torque sensor for detecting steering force imparted to said steering wheel by an operator and generating a voltage representative of the detected steering force; a motor having a field coil and an armature both adapted to be energized by a battery and being operable to power assist the steering motion caused by the operator through said steering wheel; an electric switching means interposed between said battery and said field coil of said motor for controlling the supply of current to said field coil so as to change the rotational direction of said motor; and a control means adapted to receive an output signal of said torque sensor for controlling the operation of said electric switching means.

Claim 3

A motor-driven power steering system for a vehicle as set forth in claim 1, wherein said electric switching means comprises: a first electric switching element connected at its input side to a positive terminal of said battery and at its output side to one end of said field coil; a second electric switching element connected at its input side to the positive terminal of said battery and at its output side to the other end of said field coil; a third electric switching element connected at its input side to the other end of said field coil and at its output side to a negative terminal of said battery; and a fourth electric switching element connected at its input side to the one end of said field coil and at its output side to the negative terminal of said battery; whereby said first and third electric switching elements are simultaneously energized or deenergized by said control means, and said second and fourth electric switching elements are simultaneously energized or deenergized by said control means but alternatively with respect to said first and third electric switching elements.

Claim 4

A motor-driven power steering system for a vehicle as set forth in claim 2, wherein each of said first through fourth electric switching elements comprises a power transistor.

Claim 5

A motor-driven power steering system for a vehicle as set forth in claim 2, wherein each of said first through fourth electric switching elements comprises a power MOS FET.

Claim 6

A motor-driven power steering system for a vehicle as set forth in claim 2, wherein said control means is interposed between said first and second electric switching elements and the positive terminal of said battery.

Claim 7

A motor-driven power steering system for a vehicle as set forth in claim 1, further comprising another electric switching means interposed between the armature of said motor and said battery and adapted to be controlled by said control means for controlling the supply of current to said armature.

Claim 8

A motor-driven power steering system for a vehicle as set forth in claim 6, wherein said another electric switching means comprises a power transistor.

Claim 9

A motor-driven power steering system for a vehicle as set forth in claim 6, wherein said another electric switching means comprises a power MOS FET.

Claim 10

A motor-driven power steering system for a vehicle comprising: a steering wheel; a steering shaft fixedly connected with said steering wheel for integral rotation therewith; a speed sensor for detecting the travelling speed of a vehicle and generating an output signal representative of the detected vehicle speed; a torque sensor mounted on said steering shaft for detecting turning force imparted to said steering wheel by an operator and generating an output signal representative of the detected steering torque; a first pinion operatively connected with said steering shaft and adapted to be driven by said steering wheel through the intermediary of said steering shaft; a rack operatively connected through tie rods with a pair of steerable road wheels and having a first rack tooth portion and a second rack tooth portion formed thereon, said first rack tooth portion being in meshing engagement with said first pinion; a second pinion being in meshing engagement with said second rack tooth portion on said rack; a motor having a field coil and an armature adapted to be energized by a battery, said motor operatively connected through a speed-reduction gear with said second pinion for power assisting the steering motion of said rack induced by the operator through the intermediary of said steering wheel, said steering shaft, said first pinion and said first rack tooth portion; a first electromagnetic sliding clutch interposed between said motor and said second pinion for transmitting power therebetween substantially in proportion to the intensity of current supplied thereto; a second electromagnetic clutch interposed between said motor and said second pinion for selectively establishing or disconnecting the operative connection between said motor and said second pinion; an electric switching means interposed between said battery and said field coil of said motor for controlling the supply of current to said field coil so as to change the rotational direction of said motor; and a control means adapted to receive output signals from said speed sensor and said torque sensor for controlling the operations of said motor, said electric switching means, said first clutch and said second clutch.

Claim 11

A motor-driven power steering system for a vehicle comprising: a steering wheel; a steering shaft fixedly connected with said steering wheel for integral rotation therewith; a speed sensor for detecting the travelling speed of a vehicle and generating an output signal representative of the detected vehicle speed; a torque sensor mounted on said steering shaft for detecting turning force imparted to said steering wheel by an operator and generating an output signal representative of the detected steering torque; a first pinion operatively connected with said steering shaft and adapted to be driven by said steering wheel through the intermediary of said steering shaft; a rack operatively connected through tie rods with a pair of steerable road wheels and having a first rack tooth portion and a second rack tooth portion formed thereon, said first rack tooth portion being in meshing engagement with said first pinion; a second pinion being in meshing engagement with said second rack tooth portion on said rack; a motor having a field coil and an armature adapted to be energized by a battery, said motor operatively connected through a speed-reduction gear with said second pinion for power assisting the steering motion of said rack induced by the operator through the intermediary of said steering wheel, said steering shaft, said first pinion and said first rack tooth portion; a first electromagnetic sliding clutch interposed between said motor and said second pinion for transmitting power therebetween substantially in proportion to the intensity of current supplied thereto; a second electromagnetic clutch interposed between said motor and said second pinion for selectively establishing or disconnecting the operative connection between said motor and said second pinion; an electric switching means interposed between said battery and said field coil of said motor for controlling the supply of current to said field coil so as to change the rotational direction of said motor; and a control means adapted to receive output signals from said speed sensor and said torque sensor for controlling the operations of said motor, said electric switching means, said first clutch and said second clutch.

Claim 12

A motor-driven power steering system for a vehicle as set forth in claim 9, wherein said electric switching means comprises: a first electric switching element connected at its input side to a positive terminal of said battery and at its output side to one end of said field coil; a second electric switching element connected at its input side to the positive terminal of said battery and at its output side to the other end of said field coil; a third electric switching element connected at its input side to the other end of said field coil and at its output side to a negative terminal of said battery; and a fourth electric switching element connected at its input side to the one end of said field coil and at its output side to the negative terminal of said battery; whereby said first and third electric switching elements are simultaneously energized or deenergized by said control means, and said second and fourth electric switching elements are simultaneously energized or deenergized by said control means but alternatively with respect to said first and third electric switching elements.

Claim 13

A motor-driven power steering system for a vehicle as set forth in claim 10, wherein each of said first through fourth electric switching elements comprises a power transistor.

Claim 14

A motor-driven power steering system for a vehicle as set forth in claim 10, wherein each of said first through fourth electric swistching elements comprises a power MOS FET.

Claim 15

A motor-driven power steering system for a vehicle as set forth in claim 10, wherein said control means is interposed between said first and second electric switching elements and the positive terminal of said battery.

Claim 16

A motor-driven power steering system for a vehicle as set forth in claim 9, further comprising another electric switching means interposed between the armature of said motor and said battery and adapted to be controlled by said control means for controlling the supply of current to said armature.

Claim 17

A motor-driven power steering system for a vehicle as set forth in claim 14, wherein said another electric switching means comprises a power transistor.

Claim 18

A motor-driven power steering system for a vehicle as set forth in claim 14, wherein said another electric switching means comprises a power MOS FET.