Motor-driven power steering system for a vehicle

Claim 2

A motor-driven power steering system for a vehicle, the system comprising sensor means (3) for providing a signal indicative of torque applied to the steering system by an operator, control means (9) for providing a control signal in dependence upon the signal and the speed of the vehicle, and a motor (13) for power assisting the steering system, characterised in that clutch means (14.17) is provided for enabling control of transmission of power from the motor (13) to the steering system, wherein the motor and the clutch means are controlled in dependence upon the control signal provided by the control means (9).

Claim 3

A motor-driven power steering system according to claim 1. wherein means (19; 19b,19c.19d; 109d; 209b.209c.209d) is provided for detecting an abrupt or sudden change in magnitude and/or direction of steering torque applied to the steering system, and for controlling operation of the clutch means (14,17) in dependence upon the abrupt or sudden change thereby to improve responsiveness of the motor-driven power steering system.

Claim 4

3 . 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 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 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 clutch interposed between said motor and said second pinion for selectively establishing or disconnecting the operative connection between said motor and said second pinion; and a control unit adapted to receive output signals from said speed sensor and said torque sensor for controlling the operations of said motor, said first clutch and said second clutch.

Claim 5

3 . 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 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 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 clutch interposed between said motor and said second pinion for selectively establishing or disconnecting the operative connection between said motor and said second pinion; and a control unit adapted to receive output signals from said speed sensor and said torque sensor for controlling the operations of said motor, said first clutch and said second clutch.

Claim 6

A motor-driven power steering system as set forth in claim 3 , wherein said first clutch is disposed between said motor and said speed-reduction clutch.

Claim 7

5 . A motor-driven power steering system as set forth in claim 3, wherein said first clutch comprises an electromagnetic sliding clutch.

Claim 8

6 . A motor-driven power steering system as set forth in claim 5 , wherein said electromagnetic sliding clutch comprises a powder clutch.

Claim 9

A motor-driven power steering system as set forth in claim 5 , wherein said electromagnetic sliding clutch comprises a hysteresis clutch.

Claim 10

A motor-driven power steering system as set forth in claim 4. wherein said second clutch is disposed between said speed-reduction gear and said second pinion.

Claim 11

9 . A motor-driven power steering system as set forth in claim 8 . wherein said second clutch comprises an electromagnetic switching clutch.

Claim 12

10 . A motor-driven power steering system as set forth in claim 3 , wherein said speed-reduction gear comprises a worm operatively connected through said first clutch with said motor and a worm wheel connected through said second clutch with said second pinion.

Claim 13

11 . A motor-driven power steering system as set forth in claim 3 , wherein said control unit comprises: a steering-torque measuring means adapted to receive an output signal from said torque sensor for measuring the operator-induced steering torque; a steering-torque abrupt-change judging means adapted to judge an abrupt change in steering torque from a fresh steering torque value freshly measured by said steering-torque measuring means and a preceding steering torque value precedingly measured by said steering-torque measuring means; a memory means for storing an arbitrary number of previously measured steering torque values periodically taken therein in case of normal changes in steering torque, but replacing the arbitrary number of said previously measured steering torque values with said precedingly measured steering torque value for storing in case of abrupt changes in steering torque as judged by said steering-torque abrupt-change judging means; a steering-torque averaging means for averaging the contents stored in said memory means; a motor-voltage determining means for determining an appropriate level of voltage to be imposed on said motor on the basis of the freshly measured steering torque value; a clutch-current determining means for determining an appropriate level of clutch current from an average steering torque value calculated by said steering-torque averaging means: a motor-voltage controlling means for controlling the voltage to be imposed on said motor on the basis of an output of said motor-voltage determining means; a clutch-current controlling means for controlling the current flowing through said first clutch on the basis of an output of said clutch-current determining means; and a clutch controlling means for switching said second clutch on or off in accordance with the travelling speed of the vehicle.

Claim 14

A motor-driven power steering system as set forth in claim 3. wherein said control unit comprises: a steering-torque measuring means for measuring the steering torque on the basis of an output signal of said torque sensor; a motor-voltage determining means for determining, from a steering torque value freshly measured by said steering torque measuring means, an appropriate level of voltage to be imposed on said motor; a motor-current measuring means for measuring the current supplied to said motor; a motor-current judging means for judging whether or not the motor current measured by said motor-current measuring means is equal to or less than a predetermined level; a clutch-current determining means for determining an appropriate level of current to be supplied to said first clutch in a manner such that the clutch current is decreased to zero if said motor-current judging means judges that the motor current measured is greater than the predetermined level, whereas the clutch current is determined by the measured steering torque value if it is judged that the motor current is equal to or less than the predetermined level; a motor-voltage controlling means for controlling the voltage to be imposed on said motor on the basis of an output from said motor-voltage determining means; a clutch-current controlling means for controlling the current flowing through said first clutch on the basis of an output of said clutch-current determining means; and a clutch controlling means for switching said second clutch on or off in accordance with the travelling speed of the vehicle.

Claim 15

A motor-driven power steering system as set forth in claim 3. wherein said control unit comprises: a steering-torque measuring means for measuring the steering torque on the basis of an output signal of said torque sensor; a memory means for storing an arbitrary number of previously measured steering torque values; a steering-torque averaging means for averaging the contents stored in said memory means; a steering-direction change judging means adapted to compare a freshly measured steering torque value and the precedingly measured steering torque value stored in said memory means for judging whether or not the steering direction has changed; a motor-voltage determining means for determining from the freshly measured steering torque value an appropriate level of voltage to be imposed on said motor; a clutch-current determining means for determining an appropriate level of current to be supplied to said first clutch in a manner such that the clutch current is decreased to zero in a predetermined period of time if said steering-direction change judging means judges that the steering direction has changed, whereas the clutch current is determined on the basis of an average steering torque value calculated by said steering-torque averaging means if it is judged that the steering direction remains unchanged; a motor-voltage controlling means for controlling the voltage to be imposed on said motor on the basis of an output from said motor-voltage determining means; a clutch-current controlling means for controlling the current flowing through said first clutch on the basis of an output of said clutch-current determining means; and a clutch controlling means for switching said second clutch on or off in accordance with the travelling speed of the vehicle.

Claim 16

1 4. 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 vehicle-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 steering-speed sensor for detecting the steering speed of said steering wheel and generating an output signal representative of the detected steering speed; 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 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 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 clutch interposed between said motor and said second pinion for selectively establishing or disconnecting the operative connection between said motor and said second pinion; and a control unit adapted to receive output signals from said vehicle-speed sensor, said torque sensor and said steering-speed sensor for controlling the operations of said motor, said first clutch and said second clutch.

Claim 17

1 4. 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 vehicle-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 steering-speed sensor for detecting the steering speed of said steering wheel and generating an output signal representative of the detected steering speed; 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 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 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 clutch interposed between said motor and said second pinion for selectively establishing or disconnecting the operative connection between said motor and said second pinion; and a control unit adapted to receive output signals from said vehicle-speed sensor, said torque sensor and said steering-speed sensor for controlling the operations of said motor, said first clutch and said second clutch.

Claim 18

A motor-driven power steering system as set forth in claim 14, wherein said first clutch is disposed between said motor and said speed-reduction clutch.

Claim 19

A motor-driven power steering system as set forth in claim 14, wherein said first clutch comprises an electromagnetic sliding clutch.

Claim 20

. A motor-driven power steering system as set forth in claim 16, wherein said electromagnetic sliding clutch comprises a powder clutch.

Claim 21

A motor-driven power steering system as set forth in claim 16, wherein said electromagnetic sliding clutch comprises a hysteresis clutch.

Claim 22

A motor-driven power steering system as set forth in claim 15, wherein said second clutch is disposed between said speed-reduction gear and said second pinion.

Claim 23

A motor-driven power steering system as set forth in claim 19, wherein said second clutch comprises an electromagnetic switching clutch.

Claim 24

21 .. A motor-driven power steering system as set forth in claim 14, wherein said speed-reduction gear comprises a worm operatively connected through said first clutch with-said motor and a worm wheel connected through said second clutch with said second pinion.

Claim 25

22 . A motor-driven power steering system as set forth in claim 1 4, wherein said control unit comprises: a steering-torque measuring means adapted to receive an output signal from said torque sensor for measuring the operator-induced steering torque; a motor-voltage determining means for determining an appropriate level of voltage to be imposed on said motor from a steering torque value measured by said steering-torque measuring means; a steering-speed measuring means for measuring the steering speed of said steering wheel on the basis of an output of said steering-speed sensor; a motor-field-current determining means for determining an appropriate level of field current of said motor from a steering speed measured by said steering-speed measuring means; a clutch-current determining means for determining an appropriate level of current to be supplied to said first clutch on the basis of the measured steering torque value; a motor-field-current controlling means for controlling the motor field current on the basis of an output of said motor-field-current determining means; a motor-voltage controlling means for controlling the voltage imposed on said motor on the basis of an output of said motor-voltage determining means; a clutch-current controlling means for controlling the current supplied to said first clutch on the basis of an output of the clutch-current determining means; and a clutch controlling means for switching said second clutch on or off in accordance with the travelling speed of the vehicle.

Claim 26

A motor-driven power steering system as set forth in claim 14, wherein said control unit comprises: a steering-torque measuring means adapted to receive an output signal from said torque sensor for measuring the operator-induced steering torque; a motor-voltage determining means for determining an appropriate level of voltage to be imposed on said motor from a steering torque value measured by said steering-torque measuring means; a steering-speed measuring means for measuring the steering speed of said steering wheel from an output of said steering-speed sensor; a clutch-current determining means for determining an appropriate level of current to be supplied to said first clutch on the basis of an output of said steering-speed measuring means in a manner such that the sliding clutch current is decreased if it is judged that the steering speed measured is greater than a predetermined level, whereas the sliding clutch current is determined by the measured steering torque if it is judged that the steering speed measured is equal to or less than the predetermined level; a motor-voltage controlling means for controlling the voltage to be imposed on said motor on the basis of an output of said motor-voltage determining means; a clutch-current controlling means for controlling the current supplied to said first clutch on the basis of an output of said clutch-current determining means; and a clutch controlling means for switching said first clutch on or off in accordance with the travelling speed of the vehicle.