JP2005082119A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of fully alleviating a shock at the time of end abutting while a good steering feeling is secured even when a steering wheel is turned back at a point near the maximum steering angle. <P>SOLUTION: A target current setting part to set a target value of a current fed to a motor decides fundamental assist amperage Ia for obtaining a proper steering assist force on the basis of a steering torque sensing value and a vehicle speed sensing value and calculates a current target value It by multiplying the fundamental assist amperage Ia by an assist gain Ga. The assist gain GA is set so as to decrease as approaching the maximum steering angle if the steering angle sensing value exceeds a reduction starting angle set near the maximum steering angle and arranged so that the difference between the maximum steering angle and the reduction starting angle becomes large as a steering speed increases in case the steering wheel is turned toward the maximum steering angle, and in the case turned toward the neutral position, the difference becomes small steering speed increase. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus that applies a steering assist force to a steering mechanism of a vehicle by an electric motor, and more specifically, an impact that occurs when a steering angle reaches a maximum steering angle, that is, an impact at the time of end-fitting in a steering operation. Related to mitigation techniques.

  2. Description of the Related Art Conventionally, an electric power steering apparatus that applies a steering assist force to a steering mechanism by driving an electric motor in accordance with a steering torque applied to a steering wheel (steering wheel) by a driver has been used.

  In general, in a steering device, if the steering wheel is operated in either the left or right steering direction from the neutral position, the amount of steering wheel operation reaches the maximum steering angle corresponding to the maximum value, and the mechanism exceeds the maximum steering angle. The handle cannot be operated (hereinafter, the operation of the handle until the maximum steering angle is reached and the operation is forcibly stopped is referred to as “end contact”). When the steering wheel is operated quickly, that is, when the steering speed is high, the impact generated at the time of this end contact becomes large. As a result, the durability of the steering mechanism is reduced, or the driver does not perform the steering operation. You may feel uncomfortable.

  On the other hand, an electric power steering apparatus configured so as to alleviate such an impact at the time of end contact has been conventionally proposed. For example, Japanese Patent Laid-Open No. 2001-253356 (Patent Document 3) has an unloader correction unit that reduces and corrects the auxiliary steering torque of the electric motor when the steering angle exceeds a predetermined steering angle near the maximum steering angle. Discloses an electric power steering apparatus that increases and corrects the reduction correction amount of the auxiliary steering torque as the steering speed increases. However, even if the auxiliary steering torque reduction correction amount is increased and corrected according to the steering speed in the vicinity of the maximum steering angle by such a configuration, if the steering speed is fast, the impact at the time of end application is not necessarily due to the inertia of the motor. Cannot be relaxed sufficiently.

Japanese Patent Laid-Open No. 2001-30933 (Patent Document 2) discloses a driving force of an electric motor when it is detected that a steered wheel has approached a predetermined maximum steering angle and has exceeded a damping start steering angle. There is disclosed an electric power steering apparatus including attenuation means for attenuation, and attenuation start steering angle setting means for setting the attenuation start steering angle in accordance with the load on the steering wheel and the steering speed of the steering wheel. According to such a configuration, when the steering speed is high, the motor inertia is increased by increasing the difference between the maximum steering angle and the attenuation start steering angle (accelerating the time when the driving force of the electric motor is attenuated). Thus, it is possible to prevent a large impact from being generated at the time of end contact. However, when the steering wheel is turned back from the vicinity of the maximum steering angle toward the neutral position, there is a problem that the steering assist force becomes insufficient due to the attenuation of the driving force of the electric motor, and the steering feeling is deteriorated.
Japanese Patent Publication No. 6-4417 JP 2001-30933 A JP 2001-253356 A

  Therefore, the present invention provides an electric power steering device capable of sufficiently mitigating impact at the time of end contact while ensuring a good steering feeling even when the steering wheel is turned back in the vicinity of the maximum steering angle. Objective.

A first invention is an electric power steering device that applies a steering assist force to a steering mechanism of a vehicle by driving an electric motor in accordance with an operation by an operation means for steering the vehicle,
Steering angle detection means for detecting a steering angle indicating the amount of operation by the operation means;
Steering speed detecting means for detecting a steering speed indicating the speed of operation by the operating means;
Steering assist force reducing means for reducing the steering assist force when the steering angle exceeds a reduction start steering angle set in the vicinity of a maximum steering angle that is the maximum amount of operation by the operating means;
When the operation means is operated in a direction from a neutral position toward the position of the maximum steering angle, the difference between the maximum steering angle and the reduction start steering angle increases as the steering speed increases, When the operating means is operated in the direction from the position of the maximum steering angle toward the neutral position, the difference between the maximum steering angle and the reduction start steering angle is reduced as the steering speed increases. And a reduction start steering angle adjusting means for adjusting the reduction start steering angle in accordance with the steering speed.

According to a second invention, in the first invention,
A target current setting means for setting a target value of a current to be passed through the electric motor according to an operation by the operation means;
The steering assist force reducing means reduces the steering assist force by reducing the target value according to the steering angle when the steering angle exceeds the reduction start steering angle. .

According to a third invention, in the second invention,
Vehicle speed detecting means for detecting a vehicle speed indicating the traveling speed of the vehicle,
The steering assist force reducing means reduces the steering assist force by reducing the target value according to the vehicle speed when the steering angle exceeds the reduction start steering angle.

  According to the first aspect, when the operating means is operated in the direction from the neutral position toward the maximum steering angle, the difference between the maximum steering angle and the reduction start steering angle increases as the steering speed increases. Therefore, even when the steering speed is high, it is possible to avoid a large impact due to the inertia of the electric motor (the rotor) at the time of end contact. In addition, when the operating means is operated in the direction from the position of the maximum rudder angle to the neutral position, the difference between the maximum rudder angle and the reduction start rudder angle becomes smaller as the steering speed increases. When it is desired to quickly operate the operating means from the position of the maximum steering angle toward the neutral position (when it is desired to quickly switch back), the steering assist force is returned to a state where the steering assist force is not reduced in a short time. Therefore, it is possible to sufficiently reduce the impact at the time of end contact while ensuring a good steering feeling even when the operating means is switched back in the vicinity of the maximum steering angle.

  According to the second aspect, when the steering angle exceeds the reduction start steering angle, the steering assist force is reduced by reducing the target value of the motor current according to the steering angle, and the reduction start steering The angle is adjusted in the same manner as in the first invention according to the steering speed. As a result, it is possible to sufficiently reduce the impact at the time of the end contact while ensuring a good steering feeling even when the operating means is switched back in the vicinity of the maximum steering angle.

  According to the third aspect of the invention, when the steering angle exceeds the reduction start steering angle, the target value of the motor current is reduced according to the vehicle speed. Therefore, in the vehicle speed range where the steering force required for vehicle steering is small. By increasing the reduction amount of the target current value when the reduction start steering angle is exceeded, it is possible to sufficiently reduce the impact at the time of end-fitting even during traveling. Also, in medium and high speed vehicle speed ranges where the steering force required for vehicle steering is relatively large, operating means can be used to avoid danger, etc. by reducing the reduction amount of the current target value when the reduction start steering angle is exceeded. It becomes possible to operate quickly to the maximum steering angle position.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
<1. Overall configuration>
FIG. 1 is a schematic diagram showing a configuration of an electric power steering apparatus according to an embodiment of the present invention, together with a vehicle configuration related thereto. This electric power steering apparatus includes a steering shaft 102 having one end fixed to a handle (steering wheel) 100 as an operation means for steering, a rack and pinion mechanism 104 connected to the other end of the steering shaft 102, a handle A steering angle sensor 2 for detecting a steering angle of 100, a torque sensor 3 for detecting a steering torque applied to the steering shaft 102 by an operation of the steering wheel 100, and a driver's load in a steering operation (steering operation). The electric motor 6 that generates the steering assist force, the reduction gear 7 that transmits the steering assist force to the steering shaft 102, and the power supplied from the in-vehicle battery 8 via the ignition switch 9, the steering angle sensor 2 and the torque Sensor signals from sensor 3 and vehicle speed sensor 4 Based and an electronic control unit (ECU) 5 for controlling the driving of the motor 6.

  When the driver operates the steering wheel 100 in a vehicle equipped with such an electric power steering device, the steering torque by the operation is detected by the torque sensor 3, and the detected steering torque and the vehicle speed detected by the vehicle speed sensor 4 are detected. Based on this, the motor 6 is driven by the ECU 5. As a result, the motor 6 generates a steering assist force, and this steering assist force is applied to the steering shaft 102 via the reduction gear 7, thereby reducing the driver's load in the steering operation. That is, the sum of the steering torque applied by the steering operation and the torque due to the steering assist force generated by the motor 6 is given to the rack and pinion mechanism 104 via the steering shaft 102 as the output torque. Thus, when the pinion shaft rotates, the rotation is converted into a reciprocating motion of the rack shaft by the rack and pinion mechanism 104. Both ends of the rack shaft are connected to a wheel 108 via a connecting member 106 composed of a tie rod and a knuckle arm, and the direction of the wheel 108 changes according to the reciprocating motion of the rack shaft.

<2. Configuration of control device>
FIG. 2 is a block diagram showing a functional configuration of the ECU 5, which is a control device in the electric power steering apparatus. The ECU 5 generates a microcomputer (hereinafter abbreviated as “microcomputer”) 10 functioning as a motor control unit, and a pulse width modulation signal (PWM signal) having a duty ratio corresponding to a command value D output from the microcomputer 10. The PWM signal generation circuit 18 that performs this operation, the motor drive circuit 20 that applies a voltage corresponding to the duty ratio of the PWM signal to the motor 6, and the current detector 19 that detects the current flowing through the motor 6.

  The microcomputer 10 executes a predetermined program stored in its internal memory, so that the target current setting unit 12, the subtracter 14, and a feedback control calculation unit (hereinafter abbreviated as “FB control calculation unit”) 16 are used. Functions as a motor control unit. In this motor control unit, the target current setting unit 12 includes a steering torque detection value (hereinafter referred to as “steering torque detection value”) T output from the torque sensor 3, and a steering angle detection value output from the steering angle sensor 2. Based on θ (hereinafter referred to as “steering angle detection value”) and a vehicle speed detection value V (hereinafter referred to as “vehicle speed detection value”) V output from the vehicle speed sensor 4, a target value It of current to be supplied to the motor 6 is determined. . The subtractor 14 calculates a deviation It−Is between the current target value It and the detected value Is of the motor current output from the current detector 19. The FB control calculation unit 16 generates the command value D for feedback control to be given to the PWM signal generation circuit 18 by proportional-integral control calculation based on the deviation It-Is.

  The PWM signal generation circuit 18 generates a pulse signal having a duty ratio corresponding to the command value D, that is, a PWM signal whose pulse width changes according to the command value D. The motor drive circuit 20 applies a voltage corresponding to the pulse width (duty ratio) of the PWM signal to the motor 6. The motor 6 generates a torque having a magnitude and direction corresponding to the current that flows when the voltage is applied.

<3. Detailed Configuration and Operation of Target Current Setting Unit>
FIG. 3 is a block diagram showing a configuration of the target current setting unit 12 in the present embodiment. The target current setting unit 12 is realized by software by the microcomputer 10 executing the predetermined program, and includes a basic assist current calculation unit 121, a vehicle speed gain calculation unit 123, a differentiator 124, and a steering angle correction amount. A calculation unit 125, a current reduction gain calculation unit 127, multipliers 122 and 128, an adder 126, and a subtractor 129 are provided. A steering torque detection value T and a vehicle speed detection value V are input to the basic assist current calculation unit 121, a vehicle speed detection value V is input to the vehicle speed gain calculation unit 123, and a steering angle is input to the differentiator 124 and the adder 126. Is detected.

  In such a target current setting unit 12, the basic assist current calculation unit 12 is based on the steering torque detection value T and the vehicle speed detection value V, and serves as a basis for determining the current target value It. Ia is generated. Specifically, a map (referred to as an “assist map”) showing the relationship between the value of the assist current to be supplied to the motor 6 and the value of the steering torque in order to generate an appropriate steering assist force according to the vehicle speed. The assist current calculation unit 121 holds in advance, and by referring to the assist map, the assist current value corresponding to the steering torque detection value T and the vehicle speed detection value V is obtained, and this is calculated as the basic assist current value Ia. Output as. The assist map is set so that the basic assist current value Ia increases as the vehicle speed decreases and the steering torque increases. As a result, the heavier the steering wheel 100, the larger the steering assist force becomes, and the steering operation becomes easier.

  The differentiator 124 calculates a steering angular velocity ω that indicates the steering speed by differentiating the sensor signal indicating the steering angle detection value θ with respect to time, and the steering angle correction amount calculation unit 125 uses a current described later based on the steering angular velocity ω. A steering angle correction amount Δθ for obtaining a map reference steering angle θr, which is a steering angle for referring to the reduction gain map, is calculated. The adder 126 adds the steering angle correction amount Δθ to the steering angle detection value θ, and outputs θ + Δθ, which is the addition result, as the map reference steering angle θr. The current reduction gain calculator 127 reduces the current target value It in the vicinity of the maximum steering angle so as to reduce the impact at the time of end-to-end operation in the steering wheel operation, and a current reduction gain map, which will be described later, based on the map reference steering angle θr. The current reduction gain GRi is obtained by referring to (0 ≦ GRi ≦ 1).

  On the other hand, the vehicle speed gain calculation unit 123 obtains the vehicle speed gain GRv as a coefficient for correcting the current reduction gain GRi according to the vehicle speed by referring to a vehicle speed gain map described later based on the vehicle speed detection value V (0). ≦ GRv ≦ 1). The multiplier 128 multiplies the vehicle speed gain GRv by the current reduction gain GRi, and outputs the multiplication result GRi × GRv as a corrected current reduction gain. The subtractor 129 subtracts the corrected current reduction gain GRi × GRv from “1”, and outputs 1−GRi × GRv, which is the subtraction result, as the assist gain Ga.

  The assist gain Ga thus obtained is input to the multiplier 122, which multiplies the basic assist current value Ia by the assist gain Ga. The multiplication result Ga × Ia is output from the target current setting unit 12 as the current target value It, and feedback control is performed so that the current of the current target value It flows to the motor 6 as described above. Is called.

  In the target current setting unit 12 configured as described above, the current reduction gain calculation unit 127, together with the vehicle speed gain calculation unit 123, the multiplier 128, and the subtractor 129, reduces the impact when the handle 100 is applied to the end. The steering assist force reduction means is configured, and the steering angle correction amount calculation unit 125, together with the adder 126, configures a reduction start steering angle adjustment means that adjusts the steering angle at which the reduction of the steering assist force is started in the vicinity of the maximum steering angle. To do. The differentiator 124 constitutes a steering speed detecting means together with the rudder angle sensor 2. Hereinafter, operations of the steering assist force reducing means and the reduction start steering angle adjusting means having the above-described configuration will be described.

  The current reduction gain calculation unit 127 holds a current reduction gain map as shown in FIG. 4 as a map showing the relationship between the absolute value | θr | of the steering angle for map reference and the current reduction gain GRi. By referring to the gain map, the current reduction gain GRi corresponding to the map reference steering angle θr = θ + Δθ obtained from the steering angle detection value θ is calculated. According to this current reduction gain map, the steering wheel 100 is operated in the direction from the neutral position (the position where the steering angle is “0”) to the maximum steering angle (here, 630 degrees), and the map reference steering angle θr is 580 degrees. Exceeds the value, the current reduction gain GRi increases from “0” and becomes “1” when the map reference steering angle θr reaches the maximum steering angle of 630 degrees. That is, in this current reduction gain map, when the handle 100 is operated from the neutral position toward the maximum steering angle position in order to alleviate the impact at the time of end contact, the current target value It (and thus the steering assist generated by the motor 6). The steering angle for map reference for starting the reduction of force) is set to 580 degrees. The map reference rudder angle at which the steering assist force starts to be reduced is not limited to 580 degrees, and is appropriately determined based on experiments or the like according to the individual electric power steering apparatus.

  The vehicle speed gain calculation unit 123 holds a vehicle speed gain map as shown in FIG. 5 as a map showing the relationship between the vehicle speed and the vehicle speed gain GRv, and corresponds to the vehicle speed detection value V by referring to this vehicle speed gain map. The vehicle speed gain GRv to be calculated is calculated. This vehicle speed gain map is set corresponding to the relationship between the steering force required for vehicle steering and the vehicle speed, and is a vehicle speed range (10-20 [km / h] where the required steering force is reduced. ], The vehicle speed gain GRv is increased, and the vehicle speed gain GRv is set to be small so that the reduction of the steering assist force is suppressed in the medium to high speed range.

  The steering angle correction amount calculation unit 125 holds a steering angle correction amount map as shown in FIG. 6 as a map indicating the relationship between the steering angular velocity ω and the steering angle correction amount Δθ. Refer to this steering angle correction amount map. Thus, the steering angle correction amount Δθ corresponding to the steering angular velocity ω output from the differentiator 124 is calculated. In this steering angle correction amount map, when the steering speed (the absolute value of steering angular speed | ω |) is smaller than the predetermined value ω0, the steering angle correction amount Δθ is “0” and the steering speed (| ω |) Is equal to or greater than the predetermined value ω0, the steering angle correction amount Δθ is set to have the same sign as the steering angular velocity ω and its absolute value | Δθ | increases as the steering speed increases. The predetermined value ω0 is appropriately determined based on experiments and the like.

As described above, the map reference steering angle θr used for obtaining the current reduction gain GRi in the current reduction gain calculation unit 127 is an addition value θ + Δθ of the steering angle correction amount Δθ and the steering angle detection value θ. is there. Therefore, if the steering speed (| ω |) is equal to or greater than the predetermined value ω0, the map reference steering angle θr (= θ + Δθ) changes according to the steering speed, and the absolute value of the map reference steering angle increases as the steering speed increases. The value | θr | increases. By the way, as shown in FIG. 3, the assist gain Ga is
Ga = 1−GRv × GRi
The current reduction gain GRi is determined according to the map reference steering angle θr based on the map shown in FIG. Therefore, the assist gain map showing the relationship between the assist gain Ga and the detected steering angle value θ (actual steering angle) is a map as shown in FIG. However, the vehicle speed detection value V is in the range of 10 to 20 [km / h], and the vehicle speed gain GRv is “1”. FIG. 7 shows the relationship between the assist gain Ga and the detected steering angle value θ in the case of rightward steering, but the same is true in the case of leftward steering except for the positive / negative difference of θ. Since there is, explanation is omitted.

  According to the assist gain map shown in FIG. 7, when the steering speed is low (when | ω | <ω0), the assist gain Ga changes according to the detected steering angle θ as shown by the solid line in FIG. When the steering wheel 100 is operated from the neutral position (the position where the steering angle is “0”) toward the maximum steering angle (630 degrees) and the steering angle detection value θ exceeds 580 degrees, the steering angle detection value θ As the gain increases, the assist gain Ga decreases and becomes “0” at the maximum steering angle. Therefore, when the steering wheel 100 is operated from the neutral position toward the maximum rudder angle, when the rudder angle detection value θ exceeds 580 degrees, the reduction of the steering assist force is started in order to mitigate the impact at the time of end contact. That is, in this case, the steering angle at which the reduction of the steering assist force is started (hereinafter referred to as “reduction start steering angle”) is 580 [degrees]. On the other hand, for example, when the steering wheel 100 is operated from the neutral position toward the maximum steering angle at a steering angular velocity ω1 greater than the predetermined value ω0, the map reference steering angle θr is θ + Δθ1 (see FIG. 6). ) When the detected steering angle value θ exceeds 580−Δθ1 [degrees], the assist gain Ga starts to decrease. That is, in this case, the reduction start steering angle is θ1 = 580−Δθ1 [degrees]. However, Δθ1 is a steering angle correction amount Δθ (positive value) when the steering angular velocity ω is ω1. For example, when the steering wheel 100 is operated from the maximum steering angle position toward the neutral position at the steering angular velocity ω2 having an absolute value larger than the predetermined value ω0 (ω2 <−ω0), the map reference steering angle θr is Since θ + Δθ2 (FIG. 6), the assist gain Ga increases so as to be “1” when the steering angle detection value θ is 580−Δθ2 [degrees]. That is, in this case, the reduction start steering angle is θ2 = 580−Δθ2 [degrees]. However, Δθ2 is a steering angle correction amount Δθ (negative value) when the steering angular velocity ω is ω2.

<4. Effect>
According to the above embodiment, when the steering wheel 100 is operated at a certain steering speed (| ω |> ω0) from the neutral position toward the maximum steering angle position, as shown in FIG. The steering angle at which the reduction starts (reduction starting steering angle) shifts toward the neutral position, and the difference between the maximum steering angle and the reduction starting steering angle increases as the steering speed increases. Therefore, even when the steering speed is high, it is possible to avoid the occurrence of a large impact due to the inertia of the motor 6 (the rotor) at the time of end contact.

  Further, according to the above embodiment, when the handle 100 is operated at a steering speed (| ω |> ω0) of a certain level or more from the maximum steering angle position toward the neutral position, as shown in FIG. The difference between the maximum steering angle and the reduction start steering angle decreases as the starting steering angle shifts in the direction of the maximum steering angle and the steering speed increases. For this reason, when the driver wants to quickly operate the steering wheel 100 from the maximum rudder angle position toward the neutral position (when switching back quickly), the steering assist force is not reduced, that is, the motor 6 has a normal steering assist force ( It returns to the state which generate | occur | produces the steering assist force according to the basic assist electric current value Ia in a short time. Therefore, even when the steering wheel 100 is turned back in the vicinity of the maximum rudder angle, it is possible to sufficiently reduce the impact at the time of the end contact while ensuring a good steering feeling.

  Furthermore, according to the present embodiment, the current reduction gain GRi is corrected by multiplying it by the vehicle speed gain GRv shown in FIG. 5, and the assist gain Ga is calculated by Ga = 1−GRv × GRi. As a result, in a vehicle speed range (10 to 20 km / h) where the steering force required for vehicle steering is small, the assist gain Ga (steering assist force) is sufficiently small when the reduction start steering angle is exceeded. Also, the impact at the end can be sufficiently mitigated. On the other hand, in medium- and high-speed vehicle speed ranges where the steering force required for vehicle steering is relatively large, the degree of reduction of assist gain Ga (reduction of steering assist force) when the reduction start steering angle is exceeded is small, so avoiding danger For example, the handle 100 can be quickly operated to the maximum steering angle.

<5. Modification>
In the above embodiment, the steering angle (steering angle detection value θ) and the steering speed (steering angular speed ω) necessary for determining the current reduction gain GRi are obtained based on the sensor signal from the steering angle sensor 2. The steering angle and / or the steering speed may be obtained by other methods. For example, when a brushless motor is used as the drive source, the steering angle, the steering speed, and the like may be obtained based on a sensor signal from a position sensor such as a resolver that detects the rotational position of the motor.

  In the above embodiment, the assist gain Ga is reduced when the steering angle detection value θ is in the vicinity of the maximum steering angle in order to reduce the steering assist force so as to reduce the impact at the time of the end contact ( Instead of the method of reducing the assist gain Ga or in addition to this method, the steering assist force may be reduced by another method. For example, a means for setting an upper limit value of the assist current (current target value It) is provided, and the steering assist force is reduced by lowering the upper limit value when the steering angle detection value θ is near the maximum steering angle. May be.

It is the schematic which shows the structure of the electric power steering apparatus which concerns on one Embodiment of this invention with the vehicle structure relevant to it. It is a block diagram which shows the functional structure of ECU which is a control apparatus in the electric power steering apparatus which concerns on the said embodiment. It is a block diagram which shows the structure of the target electric current setting part in the said embodiment. It is a characteristic view showing a current reduction gain map (relationship between current reduction gain and map reference steering angle) in the embodiment. It is a characteristic view showing a vehicle speed gain map (relationship between vehicle speed gain and vehicle speed) in the embodiment. It is a characteristic view showing a steering angle correction amount map (relationship between the steering angle correction amount and the steering angular velocity) in the embodiment. It is a characteristic view which shows the assist gain map (relationship between an assist gain and a steering angle) in the said embodiment.

Explanation of symbols

2 ... Rudder angle sensor (steering angle detection means)
3 ... Torque sensor 4 ... Vehicle speed sensor (vehicle speed detection means)
5 ... Electronic control unit (ECU)
6 ... Motor 10 ... Microcomputer (motor controller)
12 ... Target current setting unit 14 ... Subtractor 16 ... Feedback control calculation unit (FB control calculation unit)
DESCRIPTION OF SYMBOLS 18 ... PWM signal generation circuit 19 ... Current detector 20 ... Motor drive circuit 121 ... Basic assist current calculation part 122,128 ... Multiplier 123 ... Vehicle speed gain calculation part 124 ... Differentiator 125 ... Steering angle correction amount calculation part 126 ... Addition 127: Current reduction gain calculator 129 ... Subtractor It ... Current target value Is ... Current detection value Ia ... Basic assist current value GRi ... Current reduction gain GRv ... Vehicle speed gain Ga ... Assist gain T ... Steering torque detection value V ... Vehicle speed Detection value θ ... Steering angle detection value (steering angle)
ω ... Steering angular velocity (steering speed)
Δθ ... Steering angle correction amount θr ... Map reference steering angle θ1, θ2 ... Reduction start steering angle

Claims (3)

An electric power steering device that applies a steering assist force to a steering mechanism of the vehicle by driving an electric motor in accordance with an operation by an operation means for steering the vehicle,
Steering angle detection means for detecting a steering angle indicating the amount of operation by the operation means;
Steering speed detecting means for detecting a steering speed indicating the speed of operation by the operating means;
Steering assist force reducing means for reducing the steering assist force when the steering angle exceeds a reduction start steering angle set in the vicinity of a maximum steering angle that is the maximum amount of operation by the operating means;
When the operation means is operated in a direction from a neutral position toward the position of the maximum steering angle, the difference between the maximum steering angle and the reduction start steering angle increases as the steering speed increases, When the operating means is operated in the direction from the position of the maximum steering angle toward the neutral position, the difference between the maximum steering angle and the reduction start steering angle is reduced as the steering speed increases. An electric power steering apparatus comprising: a reduction start steering angle adjustment unit that adjusts the reduction start steering angle according to the steering speed. A target current setting means for setting a target value of a current to be passed through the electric motor according to an operation by the operation means;
The steering assist force reducing means reduces the steering assist force by reducing the target value according to the steering angle when the steering angle exceeds the reduction start steering angle. The electric power steering apparatus according to claim 1. Vehicle speed detecting means for detecting a vehicle speed indicating the traveling speed of the vehicle,
The steering assist force reducing means reduces the steering assist force by reducing the target value according to the vehicle speed when the steering angle exceeds the reduction start steering angle. The electric power steering apparatus according to claim 2.

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