JP2005088666A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of surely easing impact at end-abutting while restraining deterioration of steering feeling at a position near a maximum steering angle. <P>SOLUTION: A target electric current setting part 12 for setting a target value of the electric current to be supplied to a motor determines a basic assist electric current value Ia based on a steering torque detection value T and a vehicle speed detection value V, and multiplies the basic assist electric current value Ia by an assist gain Ga so as to calculate an electric current target value It. The assist grain Ga is calculated by Ga=1-GRv×GRi based on an electric current reduction gain GRi and a vehicle speed gain GRv, and the electric current reduction gain GRi is set as follows by an electric current reduction gain calculating part 127. That is, when a steering angle ¾θ¾ exceeds a reduction start steering angle set near the maximum steering angle, the steering torque detection value T to the direction approaching the maximum steering angle and a steering angle speed ω are multiplied, and the electric current reduction gain GRi is set to be larger as the multiplied value SUM gets larger. <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 the end contact becomes large, and as a result, the durability of the steering mechanism is lowered or a sound is generated at the end of contact. Or the driver may feel uncomfortable during the steering operation.

  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, in Japanese Patent Publication No. 6-4417 (Patent Document 1), in an electric power steering apparatus having an electric motor that generates an auxiliary torque corresponding to the steering torque of the steering system, the steering angle of the steering system is the maximum steering angle. Steering angle determination means for determining that the steering angle is closer to the predetermined value, and correction for reducing the auxiliary torque by reducing the power supplied to the motor when the steering angle is lower than the maximum steering angle by the predetermined value. There is disclosed an electric power steering device characterized by comprising: There has also been proposed an electric power steering device configured to reduce the steering assist force (attenuation of the driving force of the electric motor) for mitigating the impact at the time of end contact in consideration of the steering speed (for example, a patent) References 2 and 3).

However, the degree of impact at the time of end contact depends on the steering state in the vicinity of the maximum rudder angle, and it is not always possible to reliably mitigate the impact at end contact by simply considering the steering speed. The steering assist force may be reduced as necessary, and the steering feeling may deteriorate.
Japanese Patent Publication No. 6-4417 JP 2001-30933 A JP 2001-253356 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device capable of reliably mitigating impact at the time of end contact in a steering operation. Another object of the present invention is to provide an electric power steering device that suppresses deterioration of the steering feeling in the vicinity of the maximum steering angle while reliably mitigating the impact at the time of end contact.

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 torque detecting means for detecting steering torque applied to the steering mechanism by the operating means;
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 for reducing the steering assist force based on the steering torque and the steering speed when the steering angle exceeds a predetermined steering angle set in the vicinity of the maximum steering angle indicating the maximum amount of operation by the operation means. Auxiliary force reducing means is provided.

According to a second invention, in the first invention,
The steering assist force reducing means includes
An integrated value calculation means for integrating the product of the steering torque and the steering speed when the steering angle exceeds the predetermined steering angle, and outputting an integrated value of the product;
Current reducing means for reducing a current to be passed through the electric motor in accordance with the integrated value.

According to a third invention, in the second invention,
The integrated value calculation means stops the integration of the product when the steering speed is a predetermined value or less.

According to a fourth invention, in any one of the first to third inventions,
Vehicle speed detecting means for detecting a vehicle speed that is the traveling speed of the vehicle,
The steering assist force reducing means includes correction means for correcting a reduction amount of the steering assist force according to the vehicle speed.

  According to the first aspect, since the steering assist force is reduced based on the steering torque and the steering speed when the steering angle exceeds the predetermined steering angle set in the vicinity of the maximum steering angle, the vicinity of the maximum steering angle. In this position, the steering assist force can be greatly reduced as a stronger steering torque is applied in the direction toward the maximum rudder angle position and as the steering operation is performed at a higher steering speed in the direction toward the maximum rudder angle position. Thereby, the impact at the time of end contact in steering operation can be relieved reliably, and generation | occurrence | production of the sound by end contact can be suppressed.

  According to the second aspect of the invention, since the motor current is reduced according to the integrated value of the product of the steering torque and the steering speed when the steering angle exceeds the predetermined steering angle, the detection of the steering torque and the steering speed is performed. Even if the value includes variation or noise, the influence on the reduction amount of the motor current due to such variation or noise is suppressed. As a result, the operation of reducing the steering assist force for reducing the impact during the end contact is stabilized.

  According to the third aspect of the invention, when the steering speed is equal to or lower than the predetermined value, the integration of the product of the steering torque and the steering speed is stopped, so that the operation means goes beyond the predetermined steering angle position to the maximum steering angle position. Even in the state of being operated in the direction, if the steering speed is slow, the reduction amount of the motor current does not increase. Thereby, unnecessary reduction of the steering assist force can be avoided, and deterioration of the steering feeling in the vicinity of the maximum steering angle can be suppressed.

  According to the fourth aspect of the invention, since the amount of reduction in the steering assist force for reducing the impact at the time of the end contact is corrected according to the vehicle speed, in the vehicle speed range where the steering force required for vehicle steering is small, the steering assist force By increasing the reduction amount, it is possible to sufficiently reduce the impact at the time of end contact even during traveling. Also, in medium- and high-speed vehicle speed ranges where the steering force required for vehicle steering is relatively high, the operating means can be quickly operated to the maximum steering angle position to avoid danger by reducing the amount of reduction in steering assist force. Is possible.

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 steering angle is detected by the steering angle sensor 2, and the detected steering is detected. The motor 6 is driven by the ECU 5 based on the torque and the steering angle and the vehicle speed detected by the vehicle speed sensor 4. 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. Configuration 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 an integrated value calculation unit. 125, a current reduction gain calculation unit 127, multipliers 122 and 128, and a subtractor 129. 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 indicating a steering angle is input to the differentiator 124. The detected value θ is input, and the integrated value calculation unit 125 receives the steering torque detection value T and the steering angle detection value θ together with the steering angular velocity ω output from the differentiator 124.

  In such a target current setting unit 12, the basic assist current calculation unit 121 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. 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 basic assist current calculation unit 121 obtains the assist current value corresponding to the steering torque detection value T and the vehicle speed detection value V with reference to the assist map. This is output as the basic assist current value Ia. 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 the steering angular velocity ω indicating the steering speed by time-differentiating the sensor signal indicating the detected steering angle value θ. Then, the integrated value calculation unit 125 is based on the steering angular velocity ω, the steering torque detection value T, and the steering angle detection value θ as an index for reducing the steering assist force so as to reduce the impact at the time of the end operation in the steering wheel operation. A predetermined integrated value SUM is calculated. That is, the integrated value calculation unit 125 determines the steering angular velocity ω and the steering torque detection value T when the steering angle detection value θ exceeds the reduction start steering angle θ1, which is a predetermined steering angle value set near the maximum steering angle. Product T × ω is integrated, and an integrated value SUM of the product T × ω is output. FIG. 4 is a flowchart showing a procedure of integrated value calculation processing executed by the microcomputer 10 in order to implement the integrated value calculation unit 125 in software. The microcomputer 10 repeatedly executes the integrated value calculation processing routine at predetermined time intervals, whereby the integrated value SUM is calculated and updated sequentially, whereby the integrated value calculating unit 125 is realized. In this integrated value calculation process, the microcomputer 10 operates as follows.

  First, the steering angular velocity ω, the steering torque detection value T, and the steering angle detection value θ are acquired in order (steps S11 to S13), and then the absolute value | θ | of the steering angle detection value (hereinafter, this absolute value | θ | Is simply referred to as “steering angle”) is determined to be less than or equal to the reduction start steering angle θ1 (step S14). This reduction start steering angle θ1 is a positive steering angle value that is set in the vicinity of the maximum steering angle in order to mitigate the impact at the end of steering operation, and the handle 100 moves from the neutral position toward the maximum steering angle position. This is the steering angle at which the process for reducing the steering assist force is started when it is being operated. When the maximum steering angle is set to 630 degrees, the reduction start steering angle θ1 is set to, for example, 580 degrees.

  If the result of determination in step S14 is that the steering angle | θ | is less than or equal to the reduction start steering angle θ1, the integrated value SUM is initialized to “0”, and the integrated value calculation processing routine ends. On the other hand, if the result of determination in step S14 is that the steering angle | θ | exceeds the reduction start steering angle θ1, the steering angular velocity ω is greater than a predetermined positive value ω1 and the steering torque detection value T is “0”. It is determined whether or not the steering angular velocity ω is smaller than a predetermined negative value −ω1 and the steering torque detection value T is smaller than “0” (step S18). Here, the predetermined value ω1 (> 0) is a value set in consideration that it is not necessary to reduce the steering assist force when the steering wheel 100 is operated at a relatively slow speed. Set to [deg / sec].

  As a result of the determination in step S18, the steering angular velocity ω is larger than a predetermined positive value ω1 and the steering torque detection value T is “0” or more (non-negative value), or the steering angular velocity ω is a negative value having a predetermined value. If it is smaller than −ω1 and the detected steering torque value T is smaller than “0” (negative value) (determined as “Yes”), the product of the steering angular velocity ω and the detected steering torque value T is obtained. In order to integrate T × ω, the integrated value SUM is updated by setting a value obtained by adding the product T × ω to the current integrated value SUM as a new integrated value SUM (step S20). Therefore, in a state where the steering torque is applied in the direction toward the maximum steering angle position and the handle 100 rotates in the direction, the absolute value | ω | of the steering angular velocity (hereinafter, this absolute value is simply referred to as “steering speed”) is When the value is larger than the predetermined value ω1, the product T × ω is calculated and the integrated value SUM is updated (in this case, T × ω ≧ 0). After the integrated value SUM is updated in this way, the integrated value calculation process routine is terminated.

  On the other hand, if “No” is determined in step S18, the integrated value calculation process routine is terminated without updating the integrated value SUM. Therefore, when the steering speed | ω | is equal to or less than the predetermined value ω1, or when the steering torque is not applied in the direction toward the maximum steering angle position, the integration of the product T × ω is stopped.

  The integrated value calculation unit 125 outputs an integrated value SUM every time the integrated value calculation process as described above is executed, and this integrated value SUM is input to the current reduction gain calculation unit 127 as shown in FIG.

  The current reduction gain calculation unit 127 is a current reduction means for reducing the current target value It so as to alleviate the impact at the time of the end operation in the steering wheel operation, and refers to a later-described current reduction gain map based on the integrated value SUM. By doing so, the current reduction gain GRi is determined (0 ≦ GRi ≦ 1).

  On the other hand, the vehicle speed gain calculation unit 123 constitutes, together with the multiplier 128, correction means for correcting the reduction amount of the steering assist force according to the vehicle speed. That is, 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 a multiplier 122, which multiplies the assist gain Ga by the basic assist current value Ia. 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 integrated value calculation unit 125, the vehicle speed gain calculation unit 123, the multiplier 128, and the subtractor 129, is used when the handle 100 is applied. A steering assist force reducing means for reducing the impact is configured. The differentiator 124 constitutes a steering speed detecting means together with the rudder angle sensor 2. Hereinafter, the operation of the steering assist force reducing means will be described.

<4. Operation to reduce steering assist force>
As described above, the integrated value calculation unit 125 determines that the steering speed | ω | (the absolute value of the steering angular speed) is larger than the predetermined value ω1 in a state where the steering angle | θ | exceeds the reduction start steering angle θ1. Is multiplied by the product T × ω of the detected steering torque value T and the steering angular velocity ω (step S20 in FIG. 4), and the accumulated value SUM is output. However, when the steering torque is not applied in the direction toward the maximum steering angle position, the integration is not performed (No in step S18).

  The current reduction gain calculation unit 127 holds a current reduction gain map as shown in FIG. 5 as a map showing the relationship between the integrated value SUM and the current reduction gain GRi, and by referring to this current reduction gain map, A current reduction gain GRi corresponding to the integrated value SUM output from the integrated value calculation unit 125 is calculated. The current reduction gain map is not limited to that shown in FIG. 5, but is basically set so that the current reduction gain GRi increases to increase the reduction amount of the steering assist force as the integrated value SUM increases. ing.

  The vehicle speed gain calculation unit 123 holds a vehicle speed gain map as shown in FIG. 6 as a map indicating 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 set to be large so that the amount of reduction in the steering assist force is large, and in the medium and high speed ranges, the vehicle speed gain GRv is set to be small so that the reduction of the steering assist force is suppressed. ing.

As shown in FIG. 3, the assist gain Ga is based on the current reduction gain GRi and the vehicle speed gain GRv. Ga = 1−GRv × GRi
The target current value It is calculated by multiplying the basic assist current value Ia by this Ga. Therefore, when the steering angle | θ | exceeds the reduction start steering angle θ1 and the integrated value SUM of the product T × ω increases, the current reduction gain GRi increases accordingly, and the assist gain Ga decreases. It decreases and the steering assist force decreases accordingly. However, since the current reduction gain GRi is multiplied by the vehicle speed gain GRv as in the above equation, the reduction amount of the steering assist force increases when the vehicle speed is in the range of 10 to 20 [km / h], and in the middle to high speed range. Sometimes suppressed.

<5. Effect>
According to the above embodiment, when the steering wheel 100 is operated from the neutral position toward the maximum steering angle position and the steering angle | θ | exceeds the reduction start steering angle θ1, the steering torque is applied in the direction toward the maximum steering angle position. When the steering speed | ω | is larger than the predetermined value ω1, the product T × ω of the steering torque detection value T and the steering angular velocity ω is calculated, and the integrated value SUM is updated by the product T × ω ( (See steps S18 and S20 in FIG. 4). Then, the current reduction gain GRi is determined according to the integrated value SUM, and the current reduction gain GRi increases as the integrated value SUM increases (see FIG. 5). As shown in FIG. 3, the target value It of the current to be supplied to the motor 6 is a multiplication value Ga × Ia of the basic assist current value Ia and the assist gain Ga, and the assist gain Ga is 1−GRv × GRi. . Therefore, as the integrated value SUM of the product T × ω increases, the reduction amount of the current target value It with respect to the basic assist current value Ia increases. That is, the handle 100 is operated at a position near the maximum rudder angle (position where | θ |> θ1), and the stronger the steering torque is given toward the maximum rudder angle position, the more toward the maximum rudder angle position. As the operation is performed at a higher steering speed, the current target value It decreases more rapidly, and the steering assist force is greatly reduced. Thereby, the impact at the time of the end contact in the handle operation can be surely mitigated, and the generation of sound due to the end contact can be suppressed.

  On the other hand, even when the steering wheel 100 is operated in the direction of the maximum steering angle position, when the steering speed is low (when | ω | ≦ ω1), the product T × ω is not integrated. (See step S18 in FIG. 4), unnecessary reduction of the steering assist force is avoided. Therefore, even when the steering wheel 100 is operated in the vicinity of the maximum steering angle position, the reduction amount of the steering assist force does not increase when the steering speed is slow. Deterioration of the steering feeling can be suppressed while reducing the steering assist force.

  Further, since the current reduction gain GRi is determined in accordance with the integrated value SUM, the steering assist force is reduced due to variations in the steering torque detection value T and the steering angular velocity ω, and these values include some noise. Even if it is, the influence on the current reduction gain GRi due to such variation and noise is suppressed. Therefore, according to the above-described embodiment, the operation of reducing the steering assist force for reducing the impact during the end contact is stabilized.

  As described above, according to the above-described embodiment, it is possible to reliably reduce the impact at the time of end contact while suppressing deterioration of the steering feeling in the vicinity of the maximum rudder angle, and to reduce the steering assist force for that purpose. Stabilize.

  Furthermore, according to the above-described embodiment, the current reduction gain GRi is corrected by multiplication by the vehicle speed gain GRv shown in FIG. 6, and the assist gain Ga is calculated by Ga = 1−GRv × GRi. As a result, the assist gain Ga (steering assisting force) is sufficiently small in the vehicle speed range (10 to 20 km / h) where the steering force necessary for vehicle steering is small, so that the impact at the time of end contact is sufficient even during traveling. Can be relaxed. On the other hand, in the middle and high speed vehicle speed ranges where the steering force required for vehicle steering is relatively large, the degree of reduction of the assist gain Ga (the amount of reduction of the steering assist force) becomes small. It becomes possible to operate quickly to the rudder angle.

<6. Modification>
<6.1 First Modification>
In the above embodiment, the steering assist force (current target value It) is reduced by determining the current reduction gain GRi in accordance with the integrated value SUM in order to reduce the impact at the time of end-to-end operation in the steering wheel operation. Instead of this, the steering assist force may be reduced by reducing the upper limit value of the current flowing through the motor 6 (or the current to be passed) in accordance with the integrated value SUM. Hereinafter, such an electric power steering apparatus will be described as a first modification of the above embodiment. In the following description, portions similar to those in the above-described embodiment of the electric power steering apparatus according to the present modification are denoted by the same reference numerals, and detailed description thereof is omitted.

  The overall configuration of the electric power steering apparatus and the basic configuration of the control unit (ECU) 5 according to this modification are the same as those in the above embodiment, and are as shown in FIGS. The target current setting unit in the ECU 5 in this modified example is also realized by software by the microcomputer 10 executing a predetermined program. The configuration is the target current setting unit 12 in the above embodiment (see FIG. 3). Is different. That is, as shown in FIG. 7, the target current setting unit 13 in the present modification includes a basic assist current calculation unit 121, a vehicle speed correction amount calculation unit 133, a differentiator 124, an integrated value calculation unit 125, and a current upper limit value. A calculation unit 137, an upper limit correction unit 138, and a current limiter 139 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 correction amount calculation unit 133, and a rudder indicating a steering angle is input to the differentiator 124. The detected angle value θ is input, and the integrated value calculation unit 125 receives the detected steering torque value T and the detected steering angle value θ together with the steering angular velocity ω output from the differentiator 124. The steering angle detection value θ is also input to the upper limit correction unit 138.

  In such a target current setting unit 13, the basic assist current calculation unit 121 is the basis for determining the current target value It based on the steering torque detection value T and the vehicle speed detection value V, as in the above embodiment. A basic assist current value Ia is generated. The differentiator 124 also calculates the steering angular velocity ω indicating the steering speed by time-differentiating the sensor signal indicating the steering angle detection value θ, as in the above embodiment. Then, the integrated value calculation unit 125 is also based on the steering angular velocity ω, the steering torque detection value T, and the steering angle detection value θ as an index for reducing the steering assist force so as to reduce the impact at the end of the steering operation. A predetermined integrated value SUM is calculated. The calculation procedure of the integrated value SUM is the same as the calculation procedure in the above embodiment, and the integrated value calculator 125 outputs the integrated value SUM every time the integrated value calculation process shown in FIG. The integrated value SUM is input to the current upper limit value calculation unit 137.

  The current upper limit value calculation unit 137 is a current reduction means for reducing the current target value It so as to alleviate the impact at the end of the steering wheel operation, and based on the integrated value SUM, the current upper limit value map shown in FIG. To obtain the current upper limit value Imax1. In this current upper limit value map, Imax0 indicates the upper limit value of the motor current when the steering angle | θ | is smaller than the reduction start steering angle θ1 and the steering assist force is not reduced.

  On the other hand, the vehicle speed correction amount calculation unit 133 corrects the vehicle speed by referring to the vehicle speed correction amount map shown in FIG. 9 based on the vehicle speed detection value V as the current correction amount for correcting the current upper limit value Imax1 according to the vehicle speed. The quantity ΔIv is determined. The upper limit correction unit 138 determines the limiter current upper limit value Imax2 by correcting the current upper limit value Imax1 by the vehicle speed correction amount ΔIv in accordance with the steering angle detection value θ. That is, when the steering angle | θ | exceeds the reduction start steering angle θ1, the vehicle speed correction amount ΔIv is subtracted from the current upper limit value Imax1, and the subtraction result Imax1−ΔIv is used as the limiter current upper limit value Imax2. Output as. However, when the steering angle | θ | is equal to or smaller than the reduction start steering angle θ1, the current upper limit value Imax1 is output as it is as the limiter current upper limit value Imax2.

  The current limiter 139 outputs a current value obtained by limiting the basic assist current value Ia based on the limiter current upper limit value Imax2 as the current target value It. That is, when the basic assist current value Ia exceeds the limiter current upper limit value Imax2, the upper limit value Imax2 is output as the current target value It, and the basic assist current value Ia is less than or equal to the limiter current upper limit value Imax2. In this case, the basic assist current value Ia is output as the current target value It. This target current value It is output from the target current setting unit 13, and feedback control is performed so that the current of the target current value It flows to the motor 6 as described above.

  According to the present modification configured as described above, when the steering wheel 100 is operated from the neutral position toward the maximum steering angle position and the steering angle | θ | exceeds the reduction start steering angle θ1, the steering wheel 100 moves toward the maximum steering angle position. When the steering torque is applied in the direction and the steering speed | ω | is larger than the predetermined value ω1, the product T × ω of the steering torque detection value T and the steering angular velocity ω is calculated, and the integrated value SUM is updated. (See steps S18 and S20 in FIG. 4). The current upper limit value Imax1 is determined according to the integrated value SUM, and the current upper limit value Imax1 decreases as the integrated value SUM increases (see FIG. 8). As a result, as the integrated value SUM of the product T × ω increases, the reduction amount of the target current value It with respect to the basic assist current value Ia increases. Further, the current upper limit value Imax1 is corrected based on the vehicle speed correction amount map shown in FIG. Therefore, also in this modification, the same effect as the above embodiment can be obtained.

<6.2 Second Modification>
In the above embodiment, even if the steering angle | θ | exceeds the reduction start steering angle θ1, the integration of the product T × ω is performed when the steering torque is not applied in the direction toward the maximum steering angle position. However, instead of this, instead of this, the integrated value SUM may be initialized to “0” in such a case. Hereinafter, such an electric power steering apparatus will be described as a second modification of the embodiment. In the following description, portions similar to those in the above-described embodiment of the electric power steering apparatus according to the present modification are denoted by the same reference numerals, and detailed description thereof is omitted.

  The overall configuration of the electric power steering apparatus according to this modification, the configuration of the control unit (ECU) 5, and the configuration of the target current setting unit 12 are basically the same as those in the above-described embodiment, and are shown in FIGS. And as shown in FIG. The target current setting unit 12 in the ECU 5 in the present modification is also realized by software by the microcomputer 10 executing a predetermined program, but in order to realize the integrated value calculation unit 125 in the target current setting unit 12 The integrated value calculation process executed by the microcomputer 10 is different from the above embodiment. FIG. 10 is a flowchart showing an example of the procedure of the integrated value calculation process in the present modification. In this integrated value calculation process, the same step number or symbol (variable name) is assigned to the same part as the integrated value calculation process in the embodiment shown in FIG. As shown in FIG. 10, in the integrated value calculation process in this modification, the microcomputer 10 operates as follows.

  If the result of determination in step S14 is that the steering angle | θ | exceeds the reduction start steering angle θ1, whether or not the steering speed | ω | is greater than a predetermined value ω1 (for example, 50 [deg / sec]). Is determined (step S30). As a result, when the steering speed | ω | is larger than the predetermined value ω1, the product T × ω is added to the current integrated value SUM in order to integrate the product T × ω of the steering angular velocity ω and the steering torque detection value T. By making the added value a new integrated value SUM, the integrated value SUM is updated (step S32), and then the process proceeds to step S34. On the other hand, if the steering speed | ω | is equal to or less than the predetermined value ω1, the process proceeds to step S34 without updating the integrated value SUM. Thereafter, a condition determination based on the detected steering torque value T, the steering angular velocity ω, and a preset positive value ω2 is performed. As a result of the determination, if T> 0 and ω <−ω2 (“Yes” in step S34). ) And when T <0 and ω> ω2 (in the case of “Yes” in step S36), the integrated value SUM is initialized to “0”, and the integrated value calculation processing routine is executed. finish. Therefore, when the steering torque is not applied in the direction toward the maximum steering angle position (the handle 100 is about to be operated in the direction toward the neutral position), the integrated value SUM becomes “0” and the steering assist force Reduction is stopped. On the other hand, if T> 0 and ω <−ω2 are not satisfied and T <0 and ω> ω2 are not satisfied as a result of the above determination (when “No” is determined in both steps S34 and S36). Then, the integrated value calculation processing routine is terminated without initializing the integrated value SUM to “0”.

  Even in this modification in which the integrated value calculation unit 125 is realized by the integrated value calculation process as described above, the same effect as that of the above embodiment can be obtained by determining the current reduction gain GRi according to the integrated value SUM. . In addition to this, when the steering torque is applied in the direction from the position near the maximum steering angle to the neutral position in the state where the handle 100 is rotating in the direction toward the maximum steering angle position, Since the integrated value SUM is initialized to “0” and the reduction of the steering assist force is stopped (steps S34, S36, S16), the operability of steering at a position near the maximum steering angle is improved.

<6.3 Other Modifications>
In the embodiment and the modification described above, the product T × ω is integrated in order to suppress the influence of variations in the steering torque detection value T and the like and noise on the current reduction gain GRi, and the current reduction gain GRi according to the integration value SUM. Alternatively, the current upper limit value Imax1 is determined. However, when the influence of such variation and noise is small or acceptable, according to the product T × ω itself or according to other predetermined values based on the steering torque detection value T and the steering angular velocity, The current reduction gain GRi or the current upper limit value Imax1 may be determined.

  In the embodiment and the modification described above, the steering angle (steering angle detection value θ) and the steering speed (steering angular velocity ω) necessary for calculating the integrated value SUM are obtained based on the sensor signal from the steering angle sensor 2. However, the steering angle and / or the steering speed may be obtained by other methods. For example, when a brushless motor is used as a drive source, the steering speed or 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.

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 flowchart which shows the process sequence performed by the microcomputer in order to implement | achieve the integrated value calculating part in the said embodiment. It is a characteristic view showing a current reduction gain map (relationship between current reduction gain and integrated value) 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 block diagram which shows the structure of the target electric current setting part in the 1st modification of the said embodiment. It is a characteristic view which shows the electric current upper limit map (relationship between an electric current upper limit and an integrated value) in a 1st modification. FIG. 11 is a characteristic diagram showing a vehicle speed correction amount map (a relationship between a vehicle speed correction amount and a vehicle speed) in a first modification. It is a flowchart which shows the process sequence performed by the microcomputer in order to implement | achieve the integrated value calculating part in the 2nd modification of the said embodiment.

Explanation of symbols

2 ... Rudder angle sensor (steering angle detection means)
3 ... Torque sensor (steering torque detection means)
4 ... Vehicle speed sensor (vehicle speed detection means)
5 ... Electronic control unit (ECU)
6 ... Motor 10 ... Microcomputer (motor controller)
12, 13 ... 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 calculating part 122,128 ... Multiplier 123 ... Vehicle speed gain calculating part 124 ... Differentiator 125 ... Integrated value calculating part 127 ... Current reduction gain Calculation unit (current reduction means)
129 ... Subtractor 133 ... Vehicle speed correction amount calculation unit 137 ... Current upper limit value calculation unit (current reduction means)
138 ... Upper limit correction unit 139 ... Current limiter It ... Current target value Is ... Current detection value Ia ... Basic assist current value Imax1 ... Current upper limit value Imax2 ... Limiter current upper limit value ΔIv ... Vehicle speed correction amount 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 θ1 ... Reduction start steering angle ω ... Steering angular velocity SUM ... Integrated value

Claims (4)

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 torque detecting means for detecting steering torque applied to the steering mechanism by the operating means;
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 for reducing the steering assist force based on the steering torque and the steering speed when the steering angle exceeds a predetermined steering angle set in the vicinity of the maximum steering angle indicating the maximum amount of operation by the operation means. An electric power steering apparatus comprising: an auxiliary force reducing unit. The steering assist force reducing means includes
An integrated value calculation means for integrating the product of the steering torque and the steering speed when the steering angle exceeds the predetermined steering angle, and outputting an integrated value of the product;
The electric power steering apparatus according to claim 1, further comprising a current reduction unit that reduces a current to be passed through the electric motor in accordance with the integrated value.   The electric power steering apparatus according to claim 2, wherein the integrated value calculation means stops the integration of the product when the steering speed is equal to or less than a predetermined value. Vehicle speed detecting means for detecting a vehicle speed that is the traveling speed of the vehicle,
4. The electric power steering apparatus according to claim 1, wherein the steering assist force reducing unit includes a correction unit that corrects a reduction amount of the steering assist force according to the vehicle speed. 5. .

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