JP3328595B2 - Electric power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for reducing the steering force of a driver by applying a power generated by an electric motor to a steering system as a steering assist force. The present invention relates to an electric power steering apparatus that reduces or restricts a current flowing through an electric motor driving means in accordance with the detected voltage to prevent engine stall or the like.

[0002]

2. Description of the Related Art A conventional electric power steering apparatus is
As disclosed in Japanese Patent Application Laid-Open No. 62-181958, when the electric motor is stopped when the control device is stopped, the auxiliary steering force acting on the steering system disappears, and the manual steering force suddenly increases. Because steering feeling decreases,
When the control device is stopped, the driving stop of the electric motor is reduced for a predetermined time, and the auxiliary steering force acting on the steering system from the electric motor is gradually reduced to improve the steering feeling.

Further, as disclosed in Japanese Patent Application Laid-Open No. 8-127355, a conventional electric power steering apparatus boosts a vehicle-mounted power supply and applies it to a motor to reduce the size of the motor to a high voltage specification. The vehicle-mounted power supply is monitored during the steering assist control of the electric power steering device having a small boosted voltage variation with respect to the battery variation. When the voltage of the vehicle-mounted power supply falls below a first predetermined value, a rate of a voltage drop of the vehicle-mounted power supply. In accordance with, the boost voltage is gradually reduced at a predetermined slope, reducing the load and expecting the on-board power supply to recover.
When the voltage of the in-vehicle power supply becomes equal to or less than the second predetermined value, the boost voltage is gradually reduced at a predetermined slope, and the fail-safe is achieved while gradually reducing the assist force without discomfort. Are known.

[0004]

Problems to be Solved by the Invention
The electric power steering apparatus disclosed in Japanese Patent Application Publication No. 58-58 can gradually reduce the steering feeling because the auxiliary steering force is gradually reduced when the control is stopped. In the state where the voltage of the vehicle is rapidly decreasing, the current must be supplied from the vehicle-mounted power supply until the driving of the electric motor stops.If the voltage of the vehicle-mounted power supply is significantly reduced, the engine cannot be driven. Engine stall and the like.

A conventional electric power steering apparatus disclosed in Japanese Patent Application Laid-Open No. 8-127355 discloses a booster which is applied to an electric motor when the voltage of a vehicle-mounted power supply falls below a first predetermined value during steering assist control. The voltage is gradually reduced at a predetermined slope, and when the voltage becomes equal to or less than a second predetermined value, the boosted voltage is gradually reduced at a predetermined slope.
If the voltage of the vehicle-mounted power supply suddenly drops while the boost voltage is gradually reduced at a predetermined slope, not only the electric power steering device but also other systems such as electric components are stopped, and in the worst case, the engine There is a problem that it will be stopped.

The present invention has been made to solve such a problem, and an object of the present invention is to output a target current signal when the voltage of a vehicle-mounted power supply falls below a first reference value even during steering assist control. gradually reduced, further, it is to provide an electric power steering device in which the target current signal to stop controlling stop the steering assist force at the time of control stop in the 0 when equal to or less than the second reference value decreases.

[0007]

In order to solve the above-mentioned problems, an electric power steering apparatus according to the present invention comprises: an electric motor for applying an auxiliary steering force to a steering system; a steering torque sensor for detecting a steering torque of the steering system; A motor current detecting unit that detects a motor current flowing through the motor and outputs a motor current signal; a target current setting unit that sets a target current signal based on at least a steering torque signal from the steering torque sensor; and a target current signal. Deviation calculation means for calculating a deviation of a motor current signal, control means having a drive control means for outputting a motor control signal based on the deviation signal from the deviation calculation means, and motor drive means for driving the motor by the motor control signal And an electric power steering apparatus comprising: A power supply voltage detecting means for detecting the pressure signal, a power supply voltage signal is compared with a reference value, it is decreased with a target current signal time when the voltage value of the power supply voltage signal is less than the first reference value continuously a predetermined time, the electric motor The auxiliary steering force is gradually reduced by reducing the current of the motor with time, but when the current of the motor is gradually reduced when the current is smaller than the second reference value smaller than the first reference value, the target current signal is immediately set to 0. And fade-out control means for immediately setting the current of the motor to zero.

According to the electric power steering apparatus of the present invention, when the power supply voltage signal is equal to or less than the first reference value, the current of the motor based on the target current signal decreases with time .
Therefore , the steering assist force gradually decreases . When the current of the motor is equal to or smaller than the second reference value , the current of the motor immediately becomes zero by setting the target current signal to zero . others
Because, it is possible to prevent the voltage drop of the vehicle power supply.

The fade-out control means of the electric power steering apparatus according to the present invention reduces the target current signal with time when the power supply voltage signal is equal to or less than the first reference value, and reduces the target current signal when the power supply voltage signal is equal to or less than the second reference value. Coefficient generating means for generating a coefficient for limiting the coefficient to 0, switching means for switching between the target current signal and the target current signal reduced or limited by the coefficient from the coefficient generating means based on the comparison result between the power supply voltage signal and the reference value; It is characterized by having.

The fade-out control means of the electric power steering apparatus according to the present invention reduces the target current signal with time when the power supply voltage signal is equal to or less than the first reference value, and reduces the target current signal to 0 when the power supply voltage signal is equal to or less than the second reference value.
Coefficient generating means for generating a coefficient to be limited to the target current signal, and switching means for switching between the target current signal and the target current signal reduced or limited by the coefficient from the coefficient generating means based on a comparison result between the power supply voltage signal and the reference value. Therefore, by changing the coefficient, the target current signal can be reduced with time or limited to zero.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that, even when the steering assist is being controlled, when the voltage of the vehicle-mounted power supply decreases, the current flowing through the motor is gradually reduced for a certain period of time to stop the driving of the motor, thereby providing a steering feeling. The main function of the vehicle caused by the voltage drop, for example, engine stall, is prevented by reducing the current of the electric motor to 0 immediately even when the current of the electric motor is reduced, when the voltage of the vehicle-mounted power supply is lowered. is there.

FIG. 1 is an overall configuration diagram of an electric power steering apparatus according to the present invention. In FIG. 1, an electric power steering device 1 includes a steering wheel 17,
A rack & pinion mechanism 5 including a steering shaft 2, a hypoid gear 4, a pinion 5a, a rack shaft 5b, etc., a tie rod 8, a front wheel 9 as a steered wheel, and an electric motor 1 for applying an auxiliary torque (auxiliary steering force) to a steering system.
0, control means 15, motor driving means 16, and motor current detecting means 19.

Further, the electric power steering device 1 comprises:
A vehicle speed sensor 14 that detects a vehicle speed and outputs a vehicle speed signal Vs converted to an electric signal corresponding to the vehicle speed, detects a steering torque acting on the steering wheel 17, and converts the steering torque into an electric signal corresponding to the steering torque. A steering torque sensor 12 that outputs a signal Ts is provided.

The steering torque signal Ts has a magnitude and a direction and is supplied to the control means 15. The direction of the steering torque signal Ts is positive (plus) in the clockwise direction (right steering).
The counterclockwise direction (left steering) is assumed to be negative (minus).

When the steering wheel 17 is steered,
As for the manual steering torque applied to the steering shaft 2, the rotational force of the pinion 5 a is converted into the axial linear motion of the rack shaft 5 b via the rack & pinion mechanism 5, and the steering of the front wheel 9 is changed via the tie rod 8. Let it.

When the electric motor 10 is driven in response to the steering torque signal Ts to assist the manual steering torque, the electric motor torque is converted into an assist torque (assist torque) boosted via the hypoid gear 4. Acts on the steering shaft 2 to reduce the driver's steering force.

The vehicle speed sensor 14 detects an electric pulse signal having a frequency corresponding to the speed of the vehicle, and provides a control unit 15 with a vehicle speed signal Vs.

The control means 15 is composed of various arithmetic means, processing means, signal generation means, memory and the like based on a microprocessor. The motor control signal VO (for example, a motor control signal VO) corresponding to the steering torque signal Ts using the vehicle speed signal Vs as a parameter. It generates an ON signal, an OFF signal, and a mixed signal of a PWM signal) to drive and control the motor driving means 16.

The control means 15 includes a power supply voltage detection means and a fade-out control means, detects the power supply voltage of the vehicle-mounted power supply 11, and reduces or restricts the target current signal based on the detected power supply voltage signal to perform steering assist. If the power supply voltage drops even during the control, control to stop driving the electric motor 10 is performed.

The motor driving means 16 is constituted by a bridge circuit using four switching elements such as, for example, FETs (field effect transistors). The motor control means comprises a switch on / off signal and a PWM signal provided by the control means 15. In the signal VO, two pairs of Fs, each pair of two on the diagonal,
By driving and controlling each pair of ETs, the voltage value and the direction of the motor voltage VM to be supplied to the motor 10 are set. The direction of the motor voltage VM is determined according to the polarity of the motor control signal VO output from the control unit 15.

The motor current detecting means 19 differentially amplifies a voltage drop of the motor current IM flowing through a current detecting element (for example, a resistor) connected in series with the motor 10, and a motor current signal corresponding to the amplified output. The IMO is fed back (negative feedback) to the control means 15 to form a feedback path for a steering control system.

FIG. 2 is a block diagram of a main part of an embodiment of an electric power steering apparatus according to the present invention. FIG.
, The electric power steering device 1 includes a vehicle-mounted power supply 11, a steering torque sensor 12, a vehicle speed sensor 14, a control unit 15, a motor drive unit 16, and a motor current detection unit 1.
9, and the electric motor 10. The steering torque sensor 12, the vehicle speed sensor 14, the motor driving means 16, the motor current detecting means 19, and the motor 10 are the same as those in FIG.

The control means 15 includes a target current setting means 21,
A fade-out control unit 22, a deviation calculation unit 23, a drive control unit 24, and a power supply voltage detection unit 25 are provided.

The target current setting means 21 has a memory such as a ROM, and stores in advance data corresponding to the steering torque signal Ts using the vehicle speed signal Vs as a parameter and the target current signal IMS. The vehicle speed signal Vs and the steering torque signal Ts detected by the steering torque sensor 12
Is supplied, the corresponding target current signal IMS is read out and supplied to the fade-out control means 22.

The deviation calculating means 23 has a subtraction function, calculates a deviation between the calculated current signal IMH from the fade-out control means 22 and the motor current signal IMO from the motor current detecting means 19, and generates a deviation signal ΔI (= IMH- IMO) to the drive control means 24.

The drive control means 24 includes a PID (proportional / integral / differential) controller and a control signal generating means, and performs PID control on the deviation signal ΔI (= IMH−IMO),
An electric motor control signal VO comprising a composite signal of the PWM signal VPWM, the ON signal VON and the OFF signal VOF is supplied to the electric motor driving means 16 based on the controlled signal.

The fade-out control means 22 receives a power supply voltage signal Vd from the power supply voltage detection means 25 and compares it with a reference value, a comparison and selection means, a coefficient generation means for generating a reduction coefficient, and a multiplication means for calculating the generated coefficient. The target current signal IMS from the target current setting means 21 is multiplied by a reduction coefficient, and is supplied to the deviation calculating means 23 as the calculated current signal IMH via the switching means.

When the power supply voltage signal Vd from the power supply voltage detection means 25 exceeds the reference value, the fade-out control means 22 uses the target current signal IMS from the target current setting means 21 as a calculation current signal IMH as it is to calculate the deviation. Means 2
Output to 3.

The power supply voltage detecting means 25 comprises a voltage detecting circuit or the like, detects the power supply voltage Vc of the vehicle-mounted power supply 11, and supplies a corresponding power supply voltage signal Vd to the fade-out control means 22.

FIG. 3 is a block diagram of a main part of an embodiment of the fade-out control means according to the present invention. In FIG. 3, the fade-out control means 22 is
1, a coefficient generating means 32, a reference value storing means 33, a multiplying means 34, and a switching means 35.

The comparison / selection means 31 has two comparison functions and a logical operation function.
(The first reference value K1, the second reference value K2) and the power supply voltage signal Vd supplied from the power supply voltage detection means 25, and a correction signal Ve and a limit signal Vg are supplied to the coefficient generation means 32 based on the comparison result. At the same time, the switching signal Cd is supplied to the switching unit 35.

FIG. 4 is a block diagram of a main part of an embodiment of the comparison and selection means according to the present invention. In FIG. 4, the comparison and selection unit 31 includes a first comparison unit 41 and a second comparison unit 4.
2. It has a logical operation means 43. The first comparing means 41 includes:
A comparison function is provided. The power supply voltage signal Vd is compared with the first reference value K1. When the power supply voltage signal Vd exceeds the first reference value K1 (Vd> K1), for example, the H-level comparison signal V1 is logically operated. 43.

When the power supply voltage signal Vd is equal to or less than the first reference value K1 (Vd ≦ K1), the first comparison means 41 supplies the L-level comparison signal V1 to the logic operation means 43. When the power supply voltage signal Vd becomes lower than the first reference value K1, the first comparing means 41 does not cause erroneous detection due to noise or instantaneous voltage fluctuation but continuously drops for a certain time (for example, 100 ms). Is started and detected, and a comparison signal V1 is output based on the timer output and the output time of the comparator.

The second comparing means 42 has a comparing function and compares the power supply voltage signal Vd with the second reference value K2. When the power supply voltage signal Vd exceeds the second reference value K2 (Vd> K2), for example, The logical operation means 43 outputs the H level comparison signal V2.
To supply. Further, when the power supply voltage signal Vd is equal to or less than the second reference value K2 (Vd ≦ K2), the second comparison means 42 supplies the L-level comparison signal V2 to the logic operation means 43.

The logical operation means 43 has an AND function, an exclusive OR function, etc., and includes a NAND 43A, an exclusive OR 43B, inverters 43C, 43D and AND.
43E, and performs a logical operation based on the comparison signal V1 provided from the first comparison means 41 and the comparison signal V2 provided from the second comparison means 42, and supplies the switching signal Cd to the switching means 35. At the same time, the correction signal Ve and the limit signal Vg are supplied to the coefficient generator 32.

The NAND 43A outputs a comparison signal V of H level.
A logical AND operation of negation is performed based on 1 and the comparison signal V2 at the H level, and the switching signal Cd at the L level is supplied to the switching unit 35. The NAND 43A performs a logical operation based on the L-level comparison signal V1 and the H-level comparison signal V2, and supplies an H-level switching signal Cd to the switching unit 35. Further, the NAND 43A outputs the L-level comparison signal V
A logical operation is performed based on 1 and the L-level comparison signal V 2, and an H-level switching signal Cd is supplied to the switching unit 35.

The exclusive OR 43B performs an exclusive OR operation based on the H-level comparison signal V1 and the H-level comparison signal V2, and supplies an L-level correction signal Ve to the coefficient generator 32. In addition, exclusive OR
43B performs a logical operation based on the L-level comparison signal V1 and the H-level comparison signal V2, and supplies an H-level correction signal Ve to the coefficient generator 32. Further, the exclusive OR 43B outputs the L-level comparison signal V1 and the L-level comparison signal V1.
A logical operation is performed based on the level comparison signal V2 and L
The level correction signal Ve is supplied to the coefficient generator 32.

The two inverters 43C and 43D invert the H-level comparison signal V1 and the H-level comparison signal V2 to L level, respectively, and input them to the AND 43E.
43E performs a logical product operation based on the inverted input signal, and supplies an L level limit signal Vg to the coefficient generating means 32. The two inverters 43C and 43D invert the L-level comparison signal V1 and the H-level comparison signal V2 to H level and L level, respectively, and input them to the AND 43E. The AND 43E performs a logical operation based on the inverted input signal. An operation is performed, and the L-level limit signal Vg is output to the coefficient generation unit 32.
To supply. Furthermore, two inverters 43C and 43D
Are L-level comparison signal V1 and L-level comparison signal V2
Are inverted to the H level and input to the AND 43E, and the AND 43E performs a logical operation based on the inverted input signal, and outputs the H level limit signal Vg to the coefficient generating means 32.
To supply.

FIG. 5 shows a first reference value K1 and a second reference value K2.
FIG. This first reference value K1 is 12V
Of the in-vehicle power supply 11 is slightly lower than the normal value, for example, 1
At a value of 0 V, a power supply voltage value at which the assist current cannot be normally supplied to the electric motor, and the second reference value K2 is further reduced, for example, at a value of 8 V, the power supply voltage at which it is estimated that the electric component or the like cannot be started. Value.

FIG. 6 is a diagram showing input / output levels of the logical operation means according to the present invention. The output signal switching signal C depends on the state of the comparison signals V1 and V2 input to the logical operation means 43.
d, the correction signal Ve, and the limit signal Vg are logical outputs shown in FIG.

The input of the logical operation means 43 is compared with the case where the comparison signals V1 and V2 in the range shown in FIG. 5 are at the H level (Vd> K1, Vd> K2), respectively. When the signal V1 is at L level and V2 is at H level (Vd ≦ K
1, Vd> K2) and the comparison signal V in the range shown in FIG.
1 and V2 are each at L level (Vd ≦ K1, Vd ≦ K
2) There are three states.

The switching signal Cd at this time is output when the comparison signal V1 in the range shown in FIG. 5 is at L level and V2 is at H level, or when the comparison signals V1 and V2 in the range shown in FIG. It becomes H level. Therefore, when decreasing or limiting the target current signal IMS, the switching signal C
d becomes H level and switches the switching means 35.

The correction signal Ve is high when the comparison signal V1 in the range shown in FIG. 5 is at the L level and V2 is at the H level.
Become a level. Further, the limit signal Vg becomes H level when the comparison signals V1 and V2 in the range shown in FIG. 5 are each at L level.

Returning to FIG. 3, the coefficient generating means 32
And the like, and the correction signal Ve or the limit signal Vg
Is input at the H level, the coefficient is read from the memory and supplied to the multiplying means 34 as the reduction limiting coefficient KM (KM1, KM2). The coefficient generating means 32 outputs the correction signal V
When e is input at the H level, a reduction coefficient that reduces the ratio from 100 to 0 in a fixed time (for example, 2 seconds) is calculated in advance.
The data is sequentially read from the memory at regular time intervals (for example, 0.5 ms) and supplied to the multiplication means 34 as the reduction coefficient KM1. When the correction signal Ve is input at the L level, the readout from the memory is not performed, and the reduction coefficient KM1 is not supplied to the multiplication means 34.

Further, the coefficient generating means 32 outputs the limit signal V
When g is input at the H level, the numerical value of the coefficient 0 is read from the memory and supplied to the multiplying means 34 as the limiting coefficient KM2. When the limit signal Vg is input at the L level, the readout from the memory is not performed and the multiplication means 34 is not supplied with the reduction coefficient KM2.

As described above, the coefficient generating means 32 supplies the decreasing coefficient KM1 to the multiplying means 34 when the correction signal Ve is inputted at the H level, and supplies the multiplying means when the limiting signal Vg is inputted at the H level. 34, the limiting coefficient KM2 is supplied.

The multiplying means 34 has a multiplying function, and includes a reduction limiting coefficient KM (reducing coefficient KM 1 and limiting coefficient KM 2) supplied from the coefficient generating means 32 and a target current signal IMS supplied from the target current setting means 21. And the result of the multiplication is supplied to the switching means 35 as the target current decrease limit signal IM (the target current decrease signal IM1 and the target current limit signal IM2).

The target current decrease signal IM1 is output from the coefficient generation means 3
2 is a signal obtained by multiplying the reduction coefficient KM1 supplied from the target current setting means 21 by the target current signal IMS supplied from the target current setting means 21. The target current limit signal IM2 is obtained by multiplying the limit coefficient KM2 supplied from the coefficient generation means 32 by , Target current setting means 21
Is multiplied by a target current signal IMS supplied by

FIG. 7 is a characteristic diagram of the target current signal according to the present invention. FIG. 7A shows that the target current decrease signal IM1 is 10
FIG. 7B is a characteristic diagram in which the target current decrease signal IM1 is switched from 100 to 0 and switched to the target current limit signal IM2 at t2 seconds during the decrease from 100 to 0 in a period of t2 seconds. FIG. 7C is a characteristic diagram in which the target current limit signal IM2 is switched to the target current limit signal IM2 at t3 seconds immediately after the target current decrease signal IM1. When the in-vehicle power supply is abnormal, it changes as shown in the characteristic diagram of FIG. 7A, but in the in-vehicle power supply that has been used and deteriorated for a long time, FIG. 7B or FIG.
It changes as shown in the characteristic diagram of FIG.

The reference value storage means 33 is composed of a memory such as a ROM. The first reference value K1 and the second reference value K2 are stored in advance in the memory.
(First reference value K1, second reference value K2).

The switching means 35 has a switch function of software control, and switches the switches based on the L level and the H level of the switching signal Cd from the comparison and selection means 31. When the switching signal Cd is at L level, the switching unit 35
The target current signal IMS supplied from the target current setting means 21
Is supplied as it is to the deviation calculating means 23 as the calculated current signal IMH. Further, when the switching signal Cd is at the H level, the switching means 35 reduces the target current reduction limiting signal I which reduces or limits the target current signal IMS supplied from the multiplying means 34.
M (the target current decrease signal IM1 and the target current limit signal IM2) are switched so as to be output, and are supplied to the deviation calculating means 23 as the calculated current signal IMH.

When the power supply voltage signal Vd rises and is restored to K1 or more while the power supply voltage signal Vd of the vehicle-mounted power supply decreases and the target current signal IMS is corrected to decrease, a fade-in control (not shown) is performed. By means, the target current signal IMS is gently increased by an increase coefficient opposite to the decrease coefficient to prevent the steering feeling from deteriorating.

[0053]

As described in the foregoing, according to the electric power steering apparatus according to the present invention, electric power supply voltage signal
When the pressure value becomes equal to or less than the first reference value, the steering assist force is gradually reduced, so that it is possible to prevent a decrease in steering feeling.
In addition , when it becomes smaller than the smaller second reference value ,
Immediately reducing the current of the motor to 0 can prevent a voltage drop of the vehicle-mounted power supply, thereby preventing a system stop such as an engine stall.

Further, the fade-out control means of the electric power steering apparatus according to the present invention reduces the target current signal with time when the power supply voltage signal is less than the first reference value, and reduces the target current signal when the power supply voltage signal is less than the second reference value. Coefficient generating means for generating a coefficient for limiting the coefficient to 0, switching means for switching between the target current signal and the target current signal reduced or limited by the coefficient from the coefficient generating means based on the comparison result between the power supply voltage signal and the reference value; Since the target current signal can be reduced with time or limited to 0 by changing the coefficient, control of the motor drive by the target current signal can be easily performed, and stoppage of the system such as engine stall can be prevented. .

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an electric power steering device according to the present invention.

FIG. 2 is a block diagram of a main part of an electric power steering apparatus according to an embodiment of the present invention;

FIG. 3 is a block diagram showing a main part of an embodiment of a fade-out control means according to the present invention;

FIG. 4 is a block diagram of a main part of an embodiment of a comparison and selection means according to the present invention;

FIG. 5 is a characteristic diagram showing a first reference value K1 and a second reference value K2 according to the present invention.

FIG. 6 is a diagram showing input / output levels of a logical operation unit according to the present invention;

FIG. 7 is a characteristic diagram of a target current signal according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering axis, 4 ... Hypoid gear, 5 ... Rack & pinion mechanism,
5a: pinion, 5b: rack shaft, 8: tie rod, 9
... left and right front wheels, 10 ... electric motor, 11 ... in-vehicle power supply, 12 ...
Steering torque sensor, 14: vehicle speed sensor, 15: control means, 16: electric motor driving means, 17: steering wheel, 19: electric motor current detecting means, 21: target current setting means, 22: fade-out control means, 23: deviation calculating means .. 24 driving control means 25 power supply voltage detecting means 3
DESCRIPTION OF SYMBOLS 1 ... Comparison selection means, 32 ... Coefficient generation means, 33 ... Reference value storage means, 34 ... Multiplication means, 35 ... Switching means, 41, 4
2 first comparison means 43 logic operation means 43A NA
ND, 43B… Exclusive OR, 43C, 43D
... Inverter, 43E ... AND.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshinobu Muko 1-4-1, Chuo, Wako-shi, Saitama Prefecture Incorporated Honda R & D Co., Ltd. (72) Inventor Mitsunori Kawashima 1-4-1, Chuo, Wako-shi, Saitama Stock (56) References JP-A-8-127355 (JP, A) JP-A-2-30748 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6 / 00 B62D 5/04

Claims (2)

(57) [Claims] An electric motor for applying an auxiliary steering force to a steering system, a steering torque sensor for detecting a steering torque of the steering system, and a motor current detecting means for detecting a motor current flowing through the electric motor and outputting a motor current signal. When,
Target current setting means for setting a target current signal based on a steering torque signal from at least the steering torque sensor;
Driving means for calculating a deviation between the target current signal and the motor current signal, control means having a driving control means for outputting a motor control signal based on the deviation signal from the deviation calculating means, and driving the motor by the motor control signal An electric power steering device comprising: a power supply voltage detection unit configured to detect a power supply voltage signal of an in-vehicle power supply; comparing the power supply voltage signal with a reference value; When the value is continuously equal to or less than the first reference value for a certain period of time, the target current signal is decreased with time, and the auxiliary steering force is gradually decreased by decreasing the current of the motor with time. Electric when below two reference values
An electric power steering apparatus, comprising: a fade-out control unit that immediately sets the target current signal to 0 even when the current of the machine is gradually reduced, thereby immediately setting the current of the motor to 0. 2. The fade-out control means generates a coefficient for reducing the target current signal with time when the power supply voltage signal is equal to or less than a first reference value and for limiting the target current signal to 0 when the power supply voltage signal is equal to or less than a second reference value. And a switch for switching between a target current signal and a target current signal reduced or limited by a coefficient from the coefficient generator based on a comparison result between the power supply voltage signal and the reference value. The electric power steering apparatus according to claim 1, wherein