EP0247736A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Motor-driven power steering system for a vehicle
Assignee: Mitsubishi Electric Corp
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Filing: 1987-04-29
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Granted: —
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Expires: 2007-04-29
Abstract
Abstract ASotor-driven power steering system for a vehicle is disclosed which can be switched or transferred from power steering into manual steering or vice versa in an extremely smooth manner without causing any abrupt change in steering torque and hence unsure feelings on the part of the operator. The power steering system comprises: a torque sensor (3) for detecting steering force imparted to the steering wheel by an operator; a vehicle-speed sensor (10) for detecting the vehicle speed; a motor (13) adapted to be energized by a source of electric power (11) for power assisting the steering wheel (1); an electromagnetic switching clutch (16) adapted to be switched off for interrupting the transmission of the power-assisting force from the motor (13) toward the steerable road wheels when the vehicle speed increases above a prescribed level, and switched on for establishing the transmission of the powersteering force when the vehicle speed decreases below the prescribed level; and a control unit (9) adapted to receive output signals from the torque sensor (3) and the vehicle-speed sensor (10) for controlling the operations of the motor and the clutch in a manner such that the power assisting force transmitted from the motor to the steerable road wheels is controlled in accordance with the travelling speed of the vehicle and the steering torque imparted to the steering wheel (1) by the operator. The current supplied from the source of electric power (11) to the motor (13) is gradually decreased to reduce the power-assisting force transmitted from the motor to the steerable road wheels as the vehicle speed increases before the clutch is switched off, and gradually increased to increase the power-assisting force as the vehicle speed decreases after the clutch (16) is switched on. The current for the motor may be controlled in dependence upon coefficients which are stored in memories (109c and 109d).
Inventors
- 👤 Morishita C/O Himeji Seisakusho Mitsuharu
- 👤 Kohge C/O Himeji Seisakusho Shinichi
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 08:25
CPC Classifications
B; B62; B62D; B62D5/00; B62D5/06; B62D5/04; B62D5/0457; B62D5/046; B62D5/0463; B62D5/043; B62D5/0433
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
233 words
A motor-driven power steering system for a vehicle having a steering wheel operatively connected with steerable road wheels so that the steering wheel is turned by an operator to appropriately steer said 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 to generate an output signal representative of the detected steering force; a vehicle-speed sensor for detecting the vehicle speed to generate an output signal representative of the detected vehicle speed; a motor adapted to be energized by a source of electric power for power assisting the steering motion caused by the operator through said steering wheel; a clutch means adapted to be switched off for interrupting the transmission of the power-assisting force from said motor toward said steerable road wheels when the vehicle speed increases above a prescribed level, and switched on for establishing the transmission of the power-steering force when the vehicle speed decreases below the prescribed level; and a control unit adapted to receive output signals from said torque sensor and said vehicle-speed sensor for controlling the operations of said motor and said clutch means in a manner such that the power-assisting force transmitted from said motor to said steerable road wheels is controlled in accordance with the travelling speed of the vehicle and the steering torque imparted to the steering wheel by the operator.
Claim 2
Dependent Claim
233 words
A motor-driven power steering system for a vehicle having a steering wheel operatively connected with steerable road wheels so that the steering wheel is turned by an operator to appropriately steer said 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 to generate an output signal representative of the detected steering force; a vehicle-speed sensor for detecting the vehicle speed to generate an output signal representative of the detected vehicle speed; a motor adapted to be energized by a source of electric power for power assisting the steering motion caused by the operator through said steering wheel; a clutch means adapted to be switched off for interrupting the transmission of the power-assisting force from said motor toward said steerable road wheels when the vehicle speed increases above a prescribed level, and switched on for establishing the transmission of the power-steering force when the vehicle speed decreases below the prescribed level; and a control unit adapted to receive output signals from said torque sensor and said vehicle-speed sensor for controlling the operations of said motor and said clutch means in a manner such that the power-assisting force transmitted from said motor to said steerable road wheels is controlled in accordance with the travelling speed of the vehicle and the steering torque imparted to the steering wheel by the operator.
Claim 3
Dependent Claim
76 words
A motor-driven power steering system for a vehicle as set forth in claim 1, wherein the current supplied from said source of electric power to said motor is gradually decreased to reduce the power-assisting force transmitted from said motor to said steerable road wheels as the vehicle speed increases before said clutch means is switched off, and gradually increased to increase the power-assisting force as the vehicle speed decreases after said clutch means is switched on.
Claim 4
Dependent Claim
29 words
A motor-driven power steering system for a vehicle as set forth in claim 3, wherein the current supplied to said motor is increased or decreased in a stepwise fashion.
Claim 5
Dependent Claim
36 words
A motor-driven power steering system for a vehicle as set forth in claim 3, wherein the current supplied to said motor is increased as the steering torque imparted to said steering wheel by the operator increases.
Claim 6
Dependent Claim
31 words
A motor-driven power steering system for a vehicle as set forth in claim 4, wherein the current supplied to said motor is increased substantially in direct proportion to the steering torque.
Claim 7
Dependent Claim
234 words
A motor-driven power steering system for a vehicle as set forth in claim 1, wherein said control unit comprises: a steering-torque measuring means adapted to receive the output signal from said torque sensor for measuring the operator-induced steering torque; a vehicle-speed measuring means adapted to receive the output signal from said vehicle-speed sensor for measuring the vehicle speed; a first memory means for storing motor-current multipliers which correspond to varying vehicle speeds; a second memory means for storing motor-current values which correspond to varying steering torque values; a motor-current determining means adapted to receive the output signals from said steering-torque measuring means, said vehicle-speed measuring means, and said first and second memory means and read out from said first and second memory means an appropriate motor-current multiplier. corrresponding to the measured vehicle speed and an appropriate motor-current value corresponding to the measured steering torque to multiply the motor-current value by the motor-current multiplier so as to determine an appropriate motor-current value supplied to said motor; a motor-current controlling means for controlling the current supplied to said motor in accordance with the output from said motor-current determining means; and a clutch controlling means for controlling the operation of said clutch means in a manner such that said clutch means is switched off when the measured vehicle speed is above the prescribed level, and switched on when the measured vehicle speed is below the prescribed level.
Claim 8
Dependent Claim
117 words
A motor-driven power steering system for a vehicle as set forth in claim 6, wherein said motor-current determining means determines whether or not the measured vehicle speed is less than the prescribed speed level, and controls the operations of said motor and said clutch means in a manner such that the current, calculated by multiplying the read-out motor-current value by the read-out motor-current multiplier, is supplied to said motor and said clutch means is switched on, while on the other hand, if it is determined that the measured vehicle speed is equal to or greater than the prescribed level, the current supplied to said motor is made to be zero and said clutch means is switched off.
Claim 9
Dependent Claim
166 words
A motor-driven power steering system for a vehicle as set forth in claim 7, wherein said motor-current determining means further determines whether or not the current, calculated from the read-out motor current value and the read-out motor-current multiplier, is greater than a prescribed offset current level, and controls the operations of said motor and said clutch means in a manner such that if it is determined that the calculated motor current is greater than the prescribed offset current level and if the measured vehicle speed is less than the prescribed speed level, the calculated current is supplied to said motor and said clutch means is switched on, while on the other hand, if it is determined that the calculated motor current is equal to or less than the prescribed offset current level and if the measured vehicle speed is less than the prescribed speed level, the current supplied to said motor is made to be the offset current level and said clutch means is switched on.
Claim 10
Dependent Claim
54 words
A motor-driven power steering system for a vehicle as set forth in claim 7, wherein said control means further comprises a steering-interruption judging means adapted to determine whether or not steering operation is interrupted, and send out an output signal to said motor-current determining means when it is determined that steering operation is interrupted.
Claim 11
Dependent Claim
168 words
A motor-driven power steering system for a vehicle as set forth in claim 9, wherein said motor-current determining means further determines whether or not the absolute value of the measured steering torque is equal to or less than a prescribed reference value if it is determined that the measured vehicle speed is equal to or greater than the prescribed speed level, and controls the operations of said motor and said clutch means in a manner such that if it is determined that the absolute value of the measured steering torque is greater than the prescribed reference value, the current calculated from the read-out motor-current value and the read-out motor-current multiplier is supplied to said motor and said clutch means is switched on, while on the other hand, if it is determined that the absolute value of the measured steering torque is equal to or less than the prescribed reference value, the current supplied to said motor is made to be zero and said clutch means is switched off.
Claim 12
Dependent Claim
74 words
A motor-driven power steering system for a vehicle as set forth in claim 10, wherein said control unit further comprises a steering-torque change-rate calculating means adapted to calculate the rate of change per unit time of the steering torque on the basis of the presently measured steering torque value and the precedingly measured steering torque value, and sends out an output signal representative of the calculated steering-torque change rate to said motor-current determining means.
Claim 13
Dependent Claim
247 words
A motor-driven power steering system for a vehicle as set forth in claim 11, wherein said motor-current determining means further determines whether or not the calculated steering-torque change rate is equal to or less than a prescribed reference torque change rate if it is determined that the absolute value of the measured steering torque is equal to or less than the prescribed reference value, and controls the operations of said motor and said clutch means in a manner such that if it is determined that the calculated steering-torque change rate is greater than the prescribed reference torque change rate, it is then determined whether or not said clutch means is switched off and if it is so, the current supplied to said motor is made to be zero, but if not, the current calculated from the read-out motor-current value and the read-out motor-current multiplier is supplied to said motor, while on the other hand, if it is determined that the calculated steering-torque change rate is equal to or less than the prescribed reference torque change rate, said clutch means is switched off and the current supplied to said motor is made to be zero when the measured vehicle speed is equal to or greater than the prescribed speed level, but said clutch means is switched on and the current calculated from the read-out motor-current value and the read-out motor-current multiplier is supplied to said motor when the measured vehicle speed is less than the prescribed speed level.
Claim 14
Dependent Claim
135 words
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 torque signal and the speed of the vehicle, a motor (13) for power assisting the steering system, and clutch means (16) for interrupting transmission of power from the motor (13) to the steering system when the vehicle speed is above a predetermined level, characterised in that the motor (13) and the clutch means (16) are controlled in dependence upon the control signal such that the power-assisting force transmitted from the motor to the steering system is controlled in accordance with the vehicle speed and the torque applied to the steering system by the operator.
Claim 15
Dependent Claim
135 words
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 torque signal and the speed of the vehicle, a motor (13) for power assisting the steering system, and clutch means (16) for interrupting transmission of power from the motor (13) to the steering system when the vehicle speed is above a predetermined level, characterised in that the motor (13) and the clutch means (16) are controlled in dependence upon the control signal such that the power-assisting force transmitted from the motor to the steering system is controlled in accordance with the vehicle speed and the torque applied to the steering system by the operator.
Claim 16
Dependent Claim
35 words
A motor-driven power steering system for a vehicle according to claim 13, wherein the control signal is produced in dependence upon preset coefficients which correspond to changes in the vehicle speed and/or the steering torque.
Claim 17
Dependent Claim
23 words
A motor-driven power steering system for a vehicle according to claim 14, wherein memory means (109c,109d) is provided for storing the preset coefficients.
References Cited (Backward Citations)
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