JP4470684B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device that applies a steering assist force to a steering mechanism of a vehicle by an electric motor. More specifically, the present invention relates to an impact that occurs when a steering angle reaches a maximum steering angle in a steering operation, that is, an impact at the time of end contact. 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 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 closer to a predetermined value than the maximum steering angle. A steering angle determining means for determining, and a correcting means for reducing the auxiliary torque by reducing the power supplied to the electric motor when the steering angle is a predetermined value before the maximum steering angle. An electric power steering apparatus is disclosed. In addition, it is configured to reduce the steering assist force (power assist in the turning direction) for mitigating impact at the time of end contact in consideration of the steering speed (for example, the steering speed when entering the large turning area). An electric power steering apparatus has also been proposed (for example, Patent Document 2).
Japanese Patent Publication No. 6-4417 Japanese Patent No. 2775267

  However, the degree of impact at the end of steering operation (steering operation) depends on the steering state at a position near the maximum steering angle, and it is not always possible to sufficiently mitigate the impact at the end by simply considering the steering speed. There is. For example, when the steering speed is high, the impact may not be sufficiently reduced depending on the inertia of the motor.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device capable of reliably and sufficiently mitigating impact at the time of end contact in a steering operation.

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;
A predetermined time so as to approach the maximum steering angle over time when the steering angle exceeds a predetermined steering angle set in the vicinity of the maximum steering angle that is the maximum amount of operation by the operating means. Steering assist force changing means for changing the steering assist force so that the steering angle follows a steering angle target value as a function of

According to a second invention, in the first invention,
The steering assist force changing means is
Reducing means for reducing the steering assist force so that the steering assist force decreases as the steering angle approaches the maximum steering angle when the steering angle exceeds the predetermined steering angle;
Increase / decrease means for increasing / decreasing a reduction amount of the steering assist force by the reduction means so that the steering angle follows the steering angle target value when the steering angle exceeds the predetermined steering angle. Features.

According to a third invention, in the first invention,
A steering speed detecting means for detecting a steering speed indicating a change speed of the operation amount by the operating means;
The steering assist force changing means is
Reducing means for reducing the steering assist force so that the steering assist force decreases as the steering angle approaches the maximum steering angle when the steering angle exceeds the predetermined steering angle;
When the steering angle exceeds the predetermined steering angle and the steering speed becomes equal to or higher than the predetermined value, the reduction amount of the steering assist force by the reduction means so that the steering angle follows the steering angle target value. And an increase / decrease means that does not increase / decrease the reduction amount of the steering assist force by the reduction means when the steering speed is less than a predetermined value and the steering angle is equal to or less than the steering angle target value. The electric power steering apparatus according to claim 1, characterized in that:

4th invention is 2nd or 3rd invention,
Vehicle speed detecting means for detecting a vehicle speed that is the traveling speed of the vehicle,
The steering assist force changing means further includes correction means for correcting a reduction amount of the steering assist force by the reduction means in accordance with the vehicle speed.

  According to the first aspect of the present invention, when the steering angle exceeds a predetermined steering angle in the vicinity of the maximum steering angle, the steering angle target value as a function of a predetermined time so as to approach the maximum steering angle as time elapses. The steering assist force is changed so that the steering angle follows. Therefore, by appropriately setting the rudder angle target value, the steering speed immediately before end contact (just before reaching the maximum rudder angle) is sufficiently reduced regardless of the steering state in the vicinity of the predetermined rudder angle. Can be relaxed reliably and sufficiently.

  According to the second aspect, when the steering angle exceeds a predetermined steering angle, the steering assist force decreases as the steering angle approaches the maximum steering angle, and the steering angle is a steering angle as a function of time. The amount of reduction in the steering assist force increases or decreases so as to follow the target value. Therefore, the amount of reduction in the steering assist force is increased or decreased according to the steering state by appropriately setting the steering angle target value, so that just before the end application (the maximum steering angle is reached) regardless of the steering state in the vicinity of the predetermined steering angle. The steering speed immediately before) can be sufficiently reduced, and the impact at the time of end contact can be surely and sufficiently mitigated.

  According to the third aspect of the invention, when the steering angle exceeds the predetermined steering angle, the steering assist force decreases as the steering angle approaches the maximum steering angle, the steering angle exceeds the predetermined steering angle, and When the steering speed is equal to or higher than a predetermined value, the amount of reduction in the steering assist force is increased or decreased so that the steering angle follows the steering angle target value as a function of time. Therefore, by appropriately setting the steering angle target value, the reduction amount of the steering assist force is increased or decreased according to the steering state, and when the steering speed is less than the predetermined value, the reduction amount of the steering assist force is not increased or decreased. The steering speed immediately before (just before reaching the maximum rudder angle) can be sufficiently reduced, and the impact at the time of end contact can be reliably and sufficiently mitigated.

  According to the fourth aspect of the present invention, when the steering angle exceeds the predetermined steering angle and the steering speed is equal to or higher than the predetermined value, the amount of reduction in the steering assist force for reducing the impact at the time of the end contact depends on the vehicle speed. In this way, the steering assist force is sufficiently reduced in the vehicle speed range where there is a high possibility of end contact, and the impact during end contact is surely mitigated. Unnecessary reduction of force can be suppressed and deterioration of steering feeling in the vicinity of the maximum steering angle can be avoided.

Hereinafter, first and second embodiments of the present invention will be described with reference to the accompanying drawings.
<1. First Embodiment>
<1.1 Overall configuration>
FIG. 1 is a schematic diagram showing the configuration of the electric power steering apparatus according to the first embodiment of the present invention, together with the 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 The steering angle sensor 2 for detecting the steering angle indicating the rotational position of 100, the torque sensor 3 for detecting the steering torque applied to the steering shaft 102 by the operation of the handle 100, and the driver's load in the steering operation (steering operation). An electric motor 6 that generates a steering assist force to reduce, a reduction gear 7 that transmits the steering assist force to the steering shaft 102, and a power supply from an in-vehicle battery 8 via an ignition switch 9, and a steering angle sensor 2, torque sensor 3 and vehicle speed sensor 4 And an electronic control unit (ECU) 5 for controlling the driving of the motor 6 based on sensor signals. In the following description, it is assumed that a motor with a brush is used as the motor 6 that is a drive source of the electric power steering apparatus.

  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.

<1.2 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 incorporates a timer as a time measuring means in addition to a program storage memory and a work memory.

  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 a proportional-integral control calculation based on this 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 is configured by using a plurality of power transistors as switching elements. By turning on / off these power transistors using a PWM signal, the motor drive circuit 20 corresponds to the pulse width (duty ratio) of the PWM signal. A voltage is applied 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.

<1.3 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 an assist current calculation unit 121, an angle gain target value calculation unit 123, an angle gain calculation unit 125, a position A control calculation unit 127, an adder 129, and a multiplier 130 are provided. The steering current detection value T and the vehicle speed detection value V are input to the assist current calculation unit 121, the vehicle speed detection value V is input to the angle gain target value calculation unit 123, and the angle gain calculation unit 125 and the position control calculation unit 127 are input. Is input with the detected steering angle value θ.

  In such a target current setting unit 12, the assist current calculation unit 121 is based on the steering torque detection value T and the vehicle speed detection value V, that is, the assist current value Ia that should be the basis for determining the current target value It, that is, In order to generate a steering assist force that facilitates steering operation, a value of a current to be supplied to the motor 6 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 (referred to as an “assist map”) is assisted. The assist current calculation unit 121 refers to the assist map to obtain the assist current value corresponding to the steering torque detection value T and the vehicle speed detection value V. Output as assist current value Ia. This assist map is set so that the assist current value Ia increases as the vehicle speed decreases and the steering torque increases. Thereby, the steering assist force becomes larger as the handle 100 is heavier, and the handle operation becomes easier.

  The multiplier 130 multiplies the assist current value Ia by an assist gain G, which will be described later, in order to reduce the steering assist force in the vicinity of the maximum steering angle so as to reduce the impact at the time of the end operation in the steering wheel operation. = G × Ia is calculated (where 0 <G ≦ 1). The assist gain G is calculated based on the angle gain G1 determined by the angle gain calculator 125 (where 0 <G1 ≦ 1).

  The angle gain calculation unit 125 holds an angle gain map as shown in FIG. 5 as a map indicating the relationship between the angle gain G1 and the detected steering angle value θ, and the steering angle sensor is referred to with reference to this angle gain map. The angle gain G1 corresponding to the steering angle detection value θ from 2 is determined and output. This angle gain map shows that the angle gain G1 is “1” when the steering wheel 100 is in a rotational position other than the vicinity of the maximum steering angle, but the steering wheel 100 has a maximum steering angle θmax (here) from the neutral position (position of θ = 0). 627 degrees), the angle gain G1 is changed from “1” to the steering angle detection value θ when a predetermined reduction start steering angle θ1 (here, 577 degrees) is exceeded in the vicinity of the maximum steering angle. It is set to decrease accordingly. The angle gain G1 when the steering wheel 100 is at the maximum steering angle θmax (hereinafter, the angle gain at this time is referred to as an “angle gain target value”, and indicated by the symbol “Gv”) is an angle gain. It is determined by the target value calculation unit 123. FIG. 5 shows the relationship between the angle gain G1 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. Therefore, the description thereof is omitted (this also applies to the drawings referred to below).

  The angle gain target value calculation unit 123 holds an angle gain target value map as shown in FIG. 6 as a map indicating the relationship between the angle gain target value Gv and the vehicle speed detection value V. This angle gain target value map The angle gain target value Gv corresponding to the vehicle speed detection value V from the vehicle speed sensor 4 is determined and output. In this angle gain target value map, the angle gain target value Gv becomes small in the vehicle speed range of 1 to 10 [km / h], which is required to mitigate the impact at the end of the steering operation, and the medium / high speed exceeding the vehicle speed range. In this range, the angle gain target value Gv is set to increase according to the vehicle speed.

  The position control calculation unit 127 holds a steering angle target value θt that is set in advance as a function of the elapsed time t from when the steering angle detection value θ exceeds the reduction start steering angle θ1 (this steering angle target value). When it is specified that the value θt is a function of time, it is referred to as a “steering angle target value function” and is represented by the symbol “θt (t)”), and the steering angle detection value θ is the reduction start steering angle. A position control gain G2 for correcting the assist gain G is determined and outputted so that the steering angle detection value θ follows the steering angle target value θt when it exceeds θ1. FIG. 7 shows an example of the steering angle target value function θt (t) as a function of the elapsed time t. In this example, the rudder angle target value function θt (t) is obtained when the rudder angle detection value θ exceeds the reduction start rudder angle θ1 = 577 degrees, as the time gradually approaches the maximum rudder angle θmax = 627 degrees as time t elapses. It is set as a function, and is set to reach the maximum steering angle θmax when 0.2 seconds elapses after the steering angle detection value θ exceeds the reduction start steering angle θ1. In the present specification, the “steering angle target value θt” also indicates the value (function value) of the steering angle target value function θt (t) at a predetermined time point.

  FIG. 4 is a flowchart showing a procedure of position control processing executed by the microcomputer 10 in order to realize the position control calculation unit 127 in software. When the ignition switch 9 is turned on, the microcomputer 10 operates as follows according to this procedure.

  First, the position control gain G2 is initialized to “0” (step S10), and the flag flg for measuring the elapsed time t from when the steering angle detection value θ exceeds the reduction start steering angle θ1 is set to “0”. Reset (step S11). Next, the steering angle detection value θ is acquired from the steering angle sensor 2 (step S12), and the steering operation amount, that is, the absolute value of the steering angle detection value | θ | (hereinafter, this absolute value | θ | ") Is larger than 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. As described above, in the present embodiment, the reduction start steering angle θ1 is set to 577 degrees (see FIGS. 5 and 7), but is not limited to this value, and when the maximum steering angle θmax is given. Then, the reduction start steering angle θ1 may be determined so that the impact at the time of the end contact can be sufficiently mitigated by reducing the steering assist force in the vicinity of the maximum steering angle θmax.

  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 (step S14: No), the process returns to step S10, and thereafter the steering angle | θ | is the reduction start steering angle θ1. Steps S10 to S14 are repeatedly executed until During this time, when the steering angle | θ | exceeds the reduction start steering angle θ1 (step S14: Yes), the process proceeds to step S16.

  In step S16, it is determined whether or not the flag flg is reset, that is, whether or not flg = 0. As a result, if the flag flg is reset (step S16: Yes), the timer built in the microcomputer 10 is started (step S18), the flag flg is set to “1” (step S20), and then Proceed to step S22. As a result, the elapsed time t from when the steering angle | θ | exceeds the reduction start steering angle θ1 can be acquired from the timer. On the other hand, if the result of determination in step S16 is that the flag flg has not been reset (step S16: No), the process proceeds directly to step S22 without operating the timer.

  In step S22, the elapsed time t is acquired from the timer, and the value of the steering angle target value function θt (t) at the elapsed time t is calculated as the steering angle target value θt. In the example shown in FIG. 7, when the elapsed time t acquired from the timer is tp, θp = θt (tp) is calculated as the steering angle target value θt.

Next, based on the steering angle target value θt thus obtained, the position control gain G2 is calculated by the following equation (step S24).
G2 = (θt− | θ |) × a (1)
Here, a is an experiment or simulation to appropriately set the relationship between the position control gain G2 and the steering angle target value function θt (t) so that the impact at the end of the steering wheel operation is sufficiently mitigated. It is a constant determined based on the above.

  When the position control gain G2 is calculated as described above, the process returns to step S12, and thereafter, while the steering angle | θ | exceeds the reduction start steering angle θ1, that is, the steering angle | θ | is θ1 <| While in the range of θ | ≦ θmax (hereinafter referred to as “maximum steering angle vicinity region”), steps S12 to S24 are repeatedly executed. During this time, since the flag flg is “1” and steps S18 and S20 are not executed, the steering angle target value θt corresponding to the elapsed time t from when the steering angle | θ | exceeds the reduction start steering angle θ1 is set. Based on the above equation (1), the position control gain G2 is sequentially calculated. Note that after the steering angle | θ | exceeds the reduction start steering angle θ1 and enters the region near the maximum steering angle, the steering wheel 100 is operated toward the neutral position and the steering angle | θ | departs from the region near the maximum steering angle. If the position control gain G2 is reset, the position control gain G2 is initialized to “0” and the flag flg is reset (steps S10 and S11). Therefore, after that, when the steering angle | θ | again enters the region near the maximum steering angle, steps S18 and S20 are executed, so that the steering angle | θ | exceeds the reduction start steering angle θ1 again. Is measured by a timer, and the position control gain G2 is calculated based on the steering angle target value θt corresponding to the elapsed time t.

  The position control gain G2 calculated in steps S10 and S24 in the position control process as described above is output from the position control calculation unit 127 and input to the adder 129, as shown in FIG. Further, the angle gain G 1 output from the angle gain calculation unit 125 is also input to the adder 129. The adder 129 adds the position control gain G2 to the angle gain G1, and outputs the addition result G1 + G2 as the assist gain G. As described above, the assist gain G is input to the multiplier 130. The multiplier 130 multiplies the assist gain G by the assist current value Ia, and outputs the multiplication result G × Ia as the current target value It.

  The current target value It obtained in this way is output from the target current setting unit 12, and as described above, feedback control is performed so that the current of the current target value It flows to the motor 6 (see FIG. 2). ).

<1.4 Operation for reducing steering assist force>
The assist current value Ia output from the assist current calculation unit 121 is a current value corresponding to the assist torque that should be generated by the motor 6 as a steering assist force for facilitating steering operation. The current target value It as a value is obtained by multiplying the assist current value Ia by the assist gain G as shown in FIG. When the steering angle | θ | is out of the maximum steering angle vicinity region (when | θ | ≦ θ1), the angle gain G1 is “1” as shown in FIG. Since the position control gain G2 is “0” from S14, the assist gain G = G1 + G2 is “1”, and the assist current value Ia corresponding to the steering assist force for facilitating steering operation is the current target value It. It becomes. In contrast, when the steering wheel 100 is operated in the direction toward the maximum steering angle position and the steering angle | θ | enters the region near the maximum steering angle (region of | θ |> θ1), the electric power steering according to the present embodiment. The apparatus starts an operation for reducing the steering assist force in order to reduce the impact at the time of end contact. The operation at this time will be described below.

  When the steering angle | θ | exceeds the reduction start steering angle θ1 and enters the region near the maximum steering angle, and the steering wheel 100 is further operated in the direction of the maximum steering angle position, as shown in FIG. When the steering angle | θ | reaches the maximum steering angle θmax, the angle gain target value Gv is reached. This angle gain target value Gv depends on the vehicle speed detection value V as shown in FIG. 6, and in the vehicle speed region (1 to 10 [km / h]) where there is a high possibility of end contact, the amount of reduction in the steering assist force In order to increase the angle gain target value Gv, the angle gain target value Gv becomes a small value. Value.

  Further, when the steering angle | θ | is in the vicinity of the maximum steering angle (when | θ |> θ1), the above formula (1), that is, G2 = (θt− ||) is based on the steering angle target value θt shown in FIG. The position control gain G2 is calculated from θ |) × a. The assist gain G to be multiplied by the assist current value Ia is calculated by adding the position control gain G2 to the angle gain G1 as shown in FIG. Accordingly, as can be seen from FIG. 7 and the above equation (1), when the steering angle | θ | is larger than the steering angle target value θt = θp at a certain time t = tp because the steering speed by the handle 100 is high. (Hereinafter, the steering angular velocity ω = dθ / dt at this time is assumed to be ωh), the position control gain G2 becomes a negative value, and the assist current value Ia is reduced by the assist gain G (a reduction amount of the steering assist force). Acts in the direction of increasing On the other hand, if the steering angle | θ | is smaller than the steering angle target value θt = θp at a certain time t = tp because the steering speed by the handle 100 is low (hereinafter, the steering angular velocity ω = dθ / dt at this time). ), The position control gain G2 becomes a positive value, and acts in the direction of decreasing the reduction amount of the assist current value Ia (the reduction amount of the steering assist force) by the assist gain G (see FIG. 7). In any case, the position control gain G2 is proportional to the difference θt− | θ | = Δθ1 or Δθ2 between the steering angle target value and the steering angle.

  In this way, the assist gain G is adjusted by the position control gain G2 so that the steering angle | θ | follows the steering angle target value θt. As a result, in the region near the maximum steering angle (region where θ1 <| θ | ≦ θmax), as shown in FIG. 8, the assist gain G has the steering angle | θ | approaches the maximum steering angle θmax = 627 [deg]. However, the manner of the reduction varies depending on the steering speed. That is, when the steering wheel 100 is quickly operated and the steering angular velocity ω = dθ / dt becomes ωh, the assist gain G decreases according to the downwardly convex curve Ch shown in FIG. 8, and the steering wheel 100 is operated slowly. When the steering angular velocity ω = dθ / dt is equal to ω1, the assist gain G decreases according to the upwardly convex curve Cl shown in FIG. 8, and the steering angle is set to the steering angle target value θt determined in advance as a function of time. When the handle 100 is operated so that the angles | θ | match, the assist gain G decreases according to the straight line Cm shown in FIG.

  As can be seen from the above description, in the present embodiment, the target current setting unit 12 shown in FIG. 3 multiplies the angle gain target value calculation unit 123, the angle gain calculation unit 125, the position control calculation unit 127, and the adder 129. A steering assist force changing means for changing the steering assist force in the vicinity of the maximum steering angle is realized by the device 130. Of the components of the steering assist force changing means, the angle gain target value calculation unit 123 and the angle gain calculation unit 125 realize a reduction unit that reduces the steering assist force in the region near the maximum steering angle, thereby enabling position control. The calculating unit 127 implements an increase / decrease unit that increases or decreases the reduction amount of the steering assist force by the reduction unit so that the steering angle | θ | follows the steering angle target value θt in the region near the maximum steering angle. Further, the angle gain target value calculation unit 123 realizes a correcting means for correcting the amount of reduction of the steering assist force by the reducing means according to the vehicle speed by changing the angle gain target value Gv according to the vehicle speed detection value V. Yes.

<1.5 Effect>
According to the above embodiment, when the handle 100 is operated from the neutral position toward the maximum steering angle position and enters the region near the maximum steering angle (region of | θ |> θ1), the angle depends on the steering angle | θ | As the gain G1 decreases as shown in FIG. 5, the steering assist force is reduced. Then, in this operation of reducing the steering assist force, as shown in FIG. 7, the calculation is performed in step S24 of FIG. 4 based on the steering angle target value θt whose value is determined according to the elapsed time from the time when it enters the region near the maximum steering angle. The position control gain G2 adjusts the assist gain G so that the steering angle | θ | follows the steering angle target value θt, and the amount of reduction in the steering assist force is increased or decreased accordingly (see FIG. 3). As a result, the steering speed immediately before the end contact can be reduced so that the impact at the end of the handle operation is sufficiently mitigated, and the steering angle target value θt as a function of time is appropriately set. The impact at the time of the end contact can be surely reduced regardless of the steering state in the vicinity of the reduction start steering angle θ1.

  For example, when the steering speed when the steering angle | θ | exceeds the reduction start steering angle θ1 is large and the steering wheel 100 is operated at a high steering speed for a while after that point (ω = ωh, | θ |> θt In the case), the position control gain G2 is reduced by decreasing the position control gain G2 according to the difference θt− | θ | between the steering angle target value and the steering angle (by increasing the absolute value as a negative value). The amount of reduction of the steering assist force based on the value increases with time (see FIG. 7). Accordingly, even in this case, the steering speed immediately before the end contact is sufficiently reduced, so that the impact at the end contact can be sufficiently mitigated. When the steering angle | θ | exceeds the reduction start steering angle θ1, the steering speed is small, and after that point, the steering wheel 100 is operated at a small steering speed for a while (ω = ωl and | θ | <θt In the case), the position control gain G2 increases according to the difference θt− | θ | between the steering angle target value and the steering angle, thereby suppressing the reduction of the steering assist force (see FIG. 7). As a result, even when end contact occurs, in the case of a steering state where the impact is sufficiently small, unnecessary reduction of the steering assist force can be suppressed.

  Further, according to the above embodiment, when the steering angle | θ | exceeds the reduction start steering angle θ1 and goes to the maximum steering angle θmax, the assist gain G moves toward the angle gain target value Gv as shown in FIG. However, the angle gain target value Gv depends on the vehicle speed detection value V as shown in FIG. 6, and the angle gain target value Gv becomes a small value in the vehicle speed region where the end contact is likely to occur. In the vehicle speed region where the possibility of hitting is low, the angle gain target value Gv is a large value. As a result, the steering assist force is sufficiently reduced in the vehicle speed range where there is a high possibility of end contact, and the impact during end contact is surely mitigated. Therefore, it is possible to avoid the deterioration of the steering feeling in the vicinity of the maximum steering angle by suppressing the reduction.

<1.6 Modification>
In the above embodiment, the steering assist force is reduced by reducing the angle gain G1 in the region near the maximum steering angle (region of | θ |> θ1) according to the steering angle | θ | (FIG. 5), and the steering angle | The position control gain G2 is calculated according to the difference between the steering angle target value θt and the steering angle | θ | so that θ | follows the steering angle target value θt (step S24 in FIG. 4, FIG. 7). A reduction amount of the steering assist force is adjusted. However, as long as the steering angle | θ | follows the steering angle target value θt in the region near the maximum steering angle, steering can be performed by appropriately setting the steering angle target value θt even in other configurations. By reducing the auxiliary force, it is possible to reliably and sufficiently reduce the impact at the time of end contact. The steering angle target value θt as a function of time, that is, the steering angle target value function θt (t) is not limited to the function shown in FIG. Any function that reduces the steering speed immediately before the hit may be used.

  Moreover, in the said embodiment, although the motor with a brush is used as the motor 6 which is a drive source of an electric power steering apparatus, it is not limited to this, When a brushless motor is used as a drive source The present invention can also be applied.

  In the above embodiment, as shown in FIG. 6, the angle gain target value Gv is changed according to the vehicle speed. However, even when the angle gain target value Gv is set to a constant value, the impact at the time of end contact is ensured and sufficient. In terms of relaxation, the same effect as in the above embodiment can be obtained.

<2. Second Embodiment>
<2.1 Overall configuration>
The overall configuration of the electric power steering apparatus according to the second embodiment of the present invention is substantially the same as that of the first embodiment shown in FIG. The difference is that an angular velocity sensor (not shown) is provided. This steering angular velocity sensor detects a steering angular velocity indicating the rotational angular velocity of the handle 100 by the driver. Instead of the steering angular velocity sensor, a differentiator for differentiating the steering angle detected by the steering angle sensor 2 with respect to time is provided, and the steering angular velocity obtained by differentiating the steering angle with time is used. Also good. Further, the configuration of the ECU 5 that is the control device shown in the second embodiment is the same as the configuration of the control device in the first embodiment shown in FIG. To do. Thus, the electric power steering apparatus according to the second embodiment differs from the first embodiment in the configuration of the target current setting unit. Hereinafter, the configuration and operation of the target current setting unit will be described in detail.

<2.2 Configuration of target current setting unit>
FIG. 9 is a block diagram illustrating a configuration of the target current setting unit 22 in the present embodiment. Similar to the target current setting unit 12 in the first embodiment, the target current setting unit 22 is realized by software by the microcomputer 10 executing the predetermined program, and the assist current calculation unit 121 and the angle gain A target value calculation unit 123, an angle gain calculation unit 125, an adder 129, and a multiplier 130 are provided. Since these components perform the same operation as the target current setting unit 12 in the first embodiment, the description thereof is omitted. Further, the target current setting unit 22 includes a position control calculation unit 227 that performs an operation different from the position control calculation unit 127 in the first embodiment, and further includes a vehicle speed gain calculation unit 228.

  The angle gain calculation unit 125 holds an angle gain map as shown in FIG. 5 as a map indicating the relationship between the angle gain G1 and the steering angle detection value θ. In the second embodiment, the first embodiment Numerical values different from the form are used, specifically, the maximum steering angle θmax is 630 degrees, and the reduction start steering angle θ1 is 580 degrees.

  The angle gain target value calculation unit 123 holds an angle gain target value map as shown in FIG. 6 as a map showing the relationship between the angle gain target value Gv and the vehicle speed detection value V. In the embodiment, a value different from that of the first embodiment is used. Specifically, the angle gain target value Gv decreases from 0.45 to 0.25 in a vehicle speed range of 0 to 1 [km / h], The angle gain target value Gv is 0.25 in the vehicle speed range of 1 to 20 [km / h], and the angle gain target value Gv is the vehicle speed in the vehicle speed range of 20 to 40 [km / h] exceeding the vehicle speed range. Accordingly, it is set to increase from 0.25 to 1.0.

  The vehicle speed gain calculation unit 228 holds a vehicle speed gain map as shown in FIG. 10 as a map indicating the relationship between the vehicle speed gain Gs and the vehicle speed detection value V, and the vehicle speed sensor 4 refers to the vehicle speed gain map. The vehicle speed gain Gs corresponding to the detected vehicle speed V is determined and output. In this vehicle speed gain map, the vehicle speed gain is 1.0 in the vehicle speed range of 0 to 20 [km / h], and the vehicle speed gain Gs is the vehicle speed in the vehicle speed range of 20 to 40 [km / h] that exceeds the vehicle speed range. Is set so as to decrease from 1.0 to 0 in accordance with. The vehicle speed gain calculation unit 228 may be similarly provided in the first embodiment.

  The position control calculation unit 227 determines that the steering angle detection value θ exceeds the reduction start steering angle θ1 and the detection value (hereinafter referred to as “steering angular velocity detection value”) ω output from the steering angular velocity sensor is a predetermined threshold value. Here, a predetermined steering angle target value θt is held as a function of the elapsed time t from the time when the steering angular velocity becomes 200 [deg / sec] or more, which is a steering angular velocity that can sufficiently mitigate the impact at the end. Here, this function is θt = 200t + α. This α is set every time when the elapsed time t becomes 0, that is, every time when the steering angle detection value θ exceeds the reduction start steering angle θ1 and the steering angular velocity detection value ω becomes 200 [deg / sec] or more. A value corresponding to the steering angle detection value θ at the time (t = 0) is set. When the steering angular velocity detection value ω is 200 [deg / sec] or more and the steering angle detection value θ exceeds the reduction start steering angle θ1, the position control calculation unit 227 sets the steering angle detection value θ to the steering angle target. The position control gain G2 for correcting the assist gain G so as to follow the value θt is determined and output. The position control gain G2 is multiplied by the vehicle speed gain Gs output from the vehicle speed gain calculation unit 228. Further, once the steering angle detection value θ exceeds the reduction start steering angle θ1 and the steering angular velocity detection value ω becomes 200 [deg / sec] or more, the steering angle detection value θ becomes the steering angle target value θt or less. In this case, or when the steering angle detection value θ is still less than or equal to the reduction start steering angle θ1, or the steering angular velocity detection value ω is less than 200 [deg / sec], the steering angle target value θt is set to the steering angle detection value θ. (Θt = θ) A position control gain G2 (= 0) that does not correct the assist gain G is output. The detailed processing contents will be described later.

  For example, with reference to FIG. 7, each numerical value in the figure is changed and the steering angle target value function θt (t) where θt = 200t + 580 is described. This steering angle target value function θt (t) is detected by the steering angle detection. When the value θ becomes the reduction start steering angle θ1 = 580 degrees or more, the steering angle detection value θ is set as a function of the time gradually approaching the maximum steering angle θmax = 630 degrees as the time t elapses. After 0.25 seconds have passed since the above, the maximum steering angle θmax is set.

  Here, for convenience of explanation, in the present embodiment, the detected steering angle value θ is a positive value, and the detected steering angle value θ approaches the maximum steering angle θmax when the detected steering angular velocity value ω is a positive value. Shall. When the steering angle detection value θ is a negative value and the steering angular velocity detection value ω is a negative value, the steering angle detection value θ approaches the maximum steering angle θmax (= −630). The function indicating the value θt is θt = −200t−α, and the position control calculation unit 227 indicates that the steering angular velocity detection value ω is −200 [deg / sec] or less and the steering angle detection value θ starts to be reduced. When the steering angle is less than the steering angle θ1 (= −580), the position control gain G2 for correcting the assist gain G is determined and output so that the steering angle detection value θ follows the steering angle target value θt.

  Next, a processing procedure of the position control calculation unit 227 in the present embodiment will be described. FIG. 11 is a flowchart showing a procedure of position control processing executed by the microcomputer 10 in order to implement the position control calculation unit 127 in software. When the ignition switch 9 is turned on, the microcomputer 10 operates as follows according to this procedure.

  First, the steering angle detection value θ is acquired from the steering angle sensor 2, and the steering angular velocity detection value ω is acquired from the steering angular velocity sensor (step S50). Next, the steering angle detection value θ acquired in step S50 is substituted into the steering angle target value θt (step S52).

  Subsequently, the condition that the steering angle θ (θ> 0 in the present embodiment as described above) is larger than the reduction start steering angle θ1 and the detected steering angular velocity value ω is 200 [deg / sec] or more is satisfied. It is determined whether or not. That is, here, it is determined whether or not two conditional expressions of θ> θ1 and ω ≧ 200 are simultaneously satisfied (step S54).

  As described above, in the present embodiment, the reduction start steering angle θ1 is set to 580 degrees. However, the present invention is not limited to this value, as in the description of the first embodiment. Further, the value compared with the steering angular velocity ω is 200 [deg / sec], but this value is also limited as long as it is a value corresponding to the steering angular velocity that can sufficiently reduce the impact at the time of end contact. is not.

  If the result of determination in step S54 is that the steering angle θ is less than or equal to the reduction start steering angle θ1, or the steering angular velocity ω is less than 200 [deg / sec] (step S54: No), steps S56 to S62 are performed. The process is skipped and the process proceeds to step S64. As a result of the determination, if the steering angle θ exceeds the reduction start steering angle θ1 and the steering angular velocity ω is 200 [deg / sec] or more (step S54: Yes), the process proceeds to the subsequent step S56.

  In step S56, a timer built in the microcomputer 10 is started. Next, the steering angle detection value θ is substituted for α (step S58), and the process proceeds to the subsequent step S60. As a result, the elapsed time t from when the steering angle θ exceeds the reduction start steering angle θ1 and the steering angular velocity ω becomes 200 [deg / sec] or more can be acquired from the timer.

  In step S60, the elapsed time t is acquired from the timer, and the value of the steering angle target value function θt (t) = 200t + α at the elapsed time t is calculated as the steering angle target value θt. Next, the latest steering angle detection value θ is acquired from the steering angle sensor 2 (step S62). Since the steering angular velocity ω is large (200 [deg / sec] or more), the latest steering angle detection value θ acquired in step S62 is actually the rudder just before acquired in step S50. The value is slightly larger than the detected angle value θ.

Subsequently, a position control gain G2 obtained by the following equation (2) is calculated based on the steering angle target value θt thus obtained (step S64).
G2 = (θt−θ) × a × Gs (2)

  Subsequently, it is determined whether or not the steering angle θ is larger than the steering angle target value θt (step S66). As a result of this determination, when the steering angle θ is larger than the steering angle target value θt (step S66: Yes), the process returns to step S60, and steps S60 to S66 are performed until the steering angle θ becomes equal to or less than the steering angle target value θt. The process is repeated (S66 → S60 → S62 → S64 → S66). If the result of determination is that the steering angle θ is equal to or smaller than the steering angle target value θt (step S66: No), the process returns to the first step S50 and the above processing is repeated (S66 → S50 → S52 →... → S64). → S66).

  As described above, while the steering angle θ is equal to or less than the reduction start steering angle θ1 or the steering angular velocity ω is less than 200 [deg / sec], 0 is substituted into the position control gain G2 in step S64 ( θt−θ = 0), when the steering angle θ exceeds the reduction start steering angle θ1 and the steering angular velocity ω becomes 200 [deg / sec] or more, steps S60 to S66 are repeatedly executed. During this time, based on the steering angle target value θt corresponding to the elapsed time t from when the steering angle θ exceeds the reduction start steering angle θ1 and the steering angular velocity ω becomes 200 [deg / sec] or more, the above formula (2 ), The position control gain G2 is sequentially calculated. Thereafter, when the steering angular velocity ω decreases from 200 [deg / sec] and the change amount of the steering angle θ becomes small, the steering angle θ becomes equal to or less than the steering angle target value θt at a certain time. In this case, since the current steering angle detection value θ is substituted for the steering angle target value θt (step S52), the position control gain G2 becomes 0 again in step S64.

  The position control gain G2 calculated in step S64 in the position control process as described above is output from the position control calculation unit 227 and input to the adder 129, as shown in FIG. Further, the angle gain G 1 output from the angle gain calculation unit 125 is also input to the adder 129. The adder 129 adds the position control gain G2 to the angle gain G1, and outputs the addition result G1 + G2 as the assist gain G. As described above, the assist gain G is input to the multiplier 130. The multiplier 130 multiplies the assist gain G by the assist current value Ia, and outputs the multiplication result G × Ia as the current target value It.

  The current target value It obtained in this way is output from the target current setting unit 22, and as described above, feedback control is performed so that the current of the current target value It flows to the motor 6 (see FIG. 2). ).

<2.3 Operation for reducing steering assist force>
The assist current value Ia output from the assist current calculation unit 121 is a current value corresponding to the assist torque, and the current target value It is obtained by multiplying the assist current value Ia by the assist gain G as shown in FIG. It is done. Here, as in the case of the first embodiment, when the steering angle θ deviates from the region near the maximum steering angle (when θ ≦ θ1), the angle gain G1 is “1” as shown in FIG. Since the position control gain G2 is “0” from steps S10 to S14 in FIG. 4, the assist gain G = G1 + G2 is “1”, and assist corresponding to the steering assist force for facilitating the steering operation. The current value Ia becomes the current target value It as it is.

  Further, in the present embodiment, unlike the case of the first embodiment, the steering angular velocity ω is less than 200 [deg / sec] even when the steering angle θ is in the maximum steering angle vicinity region (region of θ> θ1). In the meantime, the position control gain G2 is “0” from steps S50, S52, and S64. Therefore, in a state where the steering angle θ is in the region near the maximum steering angle, the driver stops the sudden operation in the direction toward the maximum steering angle position of the handle 100 or changes to a slow operation, or changes to the maximum steering. When an operation in the direction opposite to the direction toward the angular position is performed, that is, when the steering angular velocity ω is less than 200 [deg / sec], it is less necessary to mitigate the impact at the time of end contact. When the steering angle detection value θ is equal to or less than the steering angle target value θt, the steering assist force reduction operation by the position control process is stopped. The operations of the angle gain target value calculation unit 123 and the angle gain calculation unit 125 are the same as those in the first embodiment, and the steering assist force reduction operation based on the angle gain G1 is as described above.

  In contrast, when the steering angle θ is in the maximum steering angle vicinity region (region of θ> θ1) and the steering angular velocity ω is 200 [deg / sec] or more, the electric power steering device according to the present embodiment is Then, an operation for reducing the steering assist force based on the position control process is started in order to reduce the impact at the time of the end contact. Hereinafter, the start and stop of such an operation will be described with reference to FIG.

  FIG. 12 is a diagram illustrating a temporal change in the steering angle target value θt when the driver operates the steering wheel 100 in various ways. The elapsed time te in the figure indicates the elapsed time from when the steering angle detection value θ first exceeds the reduction start steering angle θ1 (= 580) (hereinafter referred to as “first time”). The elapsed time t shown in FIG.

  Until t1 (= 0.125) seconds have elapsed from the first time point shown in FIG. 12, the driver suddenly operates the steering wheel 100 at an angular velocity at which the detected steering angular velocity value ω is 200 [deg / sec] or more. Yes. During this period, the steering angle target value θt is set to be smaller than the steering angle θ at the same time, so that the steering assist force is reduced based on the position control process. Thereafter, from the time t1 to 0.25 seconds, the driver stops the operation of keeping the steering angle θ constant, that is, the steering operation of the steering wheel 100, but from the first time t2 (= 0.175) Since the steering angle θ coincides with the steering angle target value θt after 2 seconds, the position control gain G2 becomes “0” after this point, and the steering assist force is not reduced by the position control process. Thereafter, from the lapse time of 0.25 seconds to t3 (= 0.30) seconds, the driver again operates the steering wheel 100 rapidly at an angular velocity at which the detected steering angular velocity value ω is 200 [deg / sec] or more. Yes. In this period, the steering assist force is reduced based on the position control process as in the period from the first time point until t1 seconds elapse. In this way, when the driver suddenly operates the steering wheel 100 and then temporarily stops the operation and then further suddenly operates, according to the present embodiment, the steering angle θ is in the vicinity of the maximum steering angle (region where θ> θ1). A period during which the steering assist force is not reduced based on the position control process can be included as needed even during the entry, and the impact at the time of the end-contact can be surely mitigated.

  In addition, when t4 (= 0.375) seconds have elapsed from the first time, the driver starts operating the handle 100 in the direction opposite to the direction toward the maximum steering angle position, and the elapsed time t5 (= 0. 45) The steering operation of the steering wheel 100 is stopped during the period from the second to 0.50 second. Thereafter, during the period from 0.50 seconds to t6 (= 0.575) seconds, the driver suddenly operates the steering wheel 100 at an angular velocity at which the detected steering angular velocity value ω is 200 [deg / sec] or more. In this period, the steering assist force is reduced based on the position control process as described above. Thus, when the driver operates the handle 100 in the direction opposite to the direction toward the maximum steering angle position when the steering angle θ is in the maximum steering angle vicinity region (region of θ> θ1), the operation is once performed. In this case, according to the present embodiment, a period during which the steering assist force is not reduced by the position control process may be included as required even when the vehicle is stopped and further operated rapidly toward the maximum steering angle position. It is possible to reduce the impact at the time of end contact.

  In the period from 0.75 seconds to 1.00 seconds, the driver slowly operates the steering wheel 100 at an angular speed at which the detected steering angular speed value ω is less than 200 [deg / sec]. Then, the position control gain G2 is “0”, and the steering assist force is not reduced by the position control process. Thereafter, since the elapsed time is 1.00 seconds, the driver has suddenly operated the steering wheel 100 at an angular velocity at which the detected steering angular velocity value ω is 200 [deg / sec] or more. Further, the steering assist force is reduced based on the position control process. As described above, even when the driver slowly operates the steering wheel 100 after the steering angle θ is within the maximum steering angle vicinity region (region where θ> θ1), the present embodiment also applies. If necessary, it is possible to include a period in which the steering assist force is not reduced by the position control process, and it is possible to reliably reduce the impact at the time of end contact.

  In the present embodiment, similarly to the first embodiment, in the target current setting unit 22 shown in FIG. 9, the angle gain target value calculation unit 123, the angle gain calculation unit 125, the position control calculation unit 227, and the vehicle speed gain calculation unit 228. The adder 129 and the multiplier 130 realize steering assisting force changing means for changing the steering assisting force in the vicinity of the maximum steering angle. Of the components of the steering assist force changing means, the angle gain target value calculation unit 123 and the angle gain calculation unit 125 realize a reduction means for reducing the steering assist force in the vicinity of the maximum steering angle, thereby obtaining a vehicle speed gain. When the steering angular velocity ω is equal to or greater than 200 [deg / sec] in the vicinity of the maximum steering angle, the calculating unit 228 and the position control calculation unit 227 reduce the steering unit so that the steering angle θ follows the steering angle target value θt. Increase / decrease means for increasing / decreasing the amount of reduction of the steering assist force due to is realized. Further, the angle gain target value calculation unit 123 realizes a correcting means for correcting the amount of reduction of the steering assist force by the reducing means according to the vehicle speed by changing the angle gain target value Gv according to the vehicle speed detection value V. Yes.

<2.4 Effect>
According to the above embodiment, when the handle 100 is operated from the neutral position toward the maximum rudder angle position and enters the region near the maximum rudder angle (region of θ> θ1), the steering angle θ as in the first embodiment. Accordingly, the angle gain G1 decreases as shown in FIG. Then, it is calculated in step S64 of FIG. 11 based on the steering angle target value θt whose value is determined according to the elapsed time from the time when the steering angular velocity ω enters the region near the maximum steering angle and the steering angular velocity ω becomes 200 [deg / sec] or more. The position control gain G2 adjusts the assist gain G so that the steering angle θ follows the steering angle target value θt, and the amount of reduction of the steering assist force is increased or decreased accordingly (see FIG. 9). As a result, the steering speed immediately before the end contact can be reduced so that the impact at the end of the handle operation is sufficiently mitigated, and the steering angular speed ω is less than 200 [deg / sec] in the region near the maximum steering angle. When the steering angle θ is larger than the steering angle target value θt, the steering assist force is not reduced based on the position control process. Therefore, the steering assist force can be reduced by the position control process as necessary. While including a non-period, it is possible to reduce the impact at the time of contact.

  Further, according to the above-described embodiment, the angle gain target value Gv depends on the vehicle speed detection value V as shown in FIG. 6 as in the first embodiment. Sufficiently reduce the assist force to mitigate the impact at the time of end contact, and suppress the unnecessary reduction of the steering assist force in the vehicle speed region where the possibility of end contact is low, thereby reducing the steering fee in the region near the maximum steering angle. Degradation of the ring can be avoided.

<2.5 Modification>
In the above embodiment, as in the first embodiment, when the steering angular velocity ω is equal to or higher than the steering angular velocity (200 [deg / sec] in this case) that can sufficiently mitigate the impact at the time of end contact in the region near the maximum steering angle. As long as the steering angle θ follows the rudder angle target value θt, the impact at the time of end application can be reduced by reducing the steering assist force by appropriately setting the rudder angle target value θt even in other configurations. Can be relaxed reliably and sufficiently. Note that the steering angle target value θt as a function of time, that is, the steering angle target value function θt (t), is a function that reduces the steering speed immediately before the end contact so that the impact at the end contact can be surely and sufficiently mitigated. If it is.

  In the above embodiment, as in the first embodiment, the angle gain target value Gv is changed according to the vehicle speed, as shown in FIG. The same effect as the above-described embodiment can be obtained in terms of reliable and sufficient relaxation of the impact at the time.

It is the schematic which shows the structure of the electric power steering apparatus which concerns on the 1st 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 procedure of the process performed by the microcomputer in order to implement | achieve the position control calculating part in the said embodiment. It is a characteristic view which shows the angle gain map (relationship between an angle gain and a steering angle detection value) in the said embodiment. It is a characteristic view showing an angle gain target value map (relationship between an angle gain target value and a vehicle speed detection value) in the embodiment. It is a figure which shows the steering angle target value as a function of time when a steering angle exists in the maximum steering angle vicinity area | region in the said embodiment. It is a characteristic view which shows the relationship between the assist gain and steering angle detection value in the said embodiment. It is a block diagram which shows the structure of the target electric current setting part in the 2nd Embodiment of this invention. It is a characteristic view which shows the vehicle speed gain map (relationship between a vehicle speed gain and a vehicle speed detection value) in the said embodiment. It is a flowchart which shows the procedure of the process performed by the microcomputer in order to implement | achieve the position control calculating part in the said embodiment. It is a figure which illustrates the time change of the steering angle target value when a driver | operator variously operates a steering wheel 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 ... Assist current calculation part 123 ... Angle gain target value calculation part 125 ... Angle gain calculation part 127 ... Position control calculation part 129 ... Adder 130 ... Multiplier 227 ... Position control calculation unit 228 ... Vehicle speed gain calculation unit It ... Current target value Is ... Current detection value Ia ... Assist current value Gv ... Angular gain target value G1 ... Angular gain G2 ... Position control gain G ... Assist gain T ... Steering torque Detection value V: Vehicle speed detection value θ: Steering angle detection value θ1: Reduction start steering angle (predetermined steering angle)
θt ... Steering angle target 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 angle detection means for detecting a steering angle indicating the amount of operation by the operation means;
A predetermined time so as to approach the maximum steering angle over time when the steering angle exceeds a predetermined steering angle set in the vicinity of the maximum steering angle that is the maximum amount of operation by the operating means. An electric power steering apparatus comprising: steering assist force changing means for changing the steering assist force so that the steering angle follows a steering angle target value as a function of The steering assist force changing means is
Reducing means for reducing the steering assist force so that the steering assist force decreases as the steering angle approaches the maximum steering angle when the steering angle exceeds the predetermined steering angle;
Increase / decrease means for increasing / decreasing a reduction amount of the steering assist force by the reduction means so that the steering angle follows the steering angle target value when the steering angle exceeds the predetermined steering angle. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is characterized. A steering speed detecting means for detecting a steering speed indicating a change speed of the operation amount by the operating means;
The steering assist force changing means is
Reducing means for reducing the steering assist force so that the steering assist force decreases as the steering angle approaches the maximum steering angle when the steering angle exceeds the predetermined steering angle;
When the steering angle exceeds the predetermined steering angle and the steering speed becomes equal to or higher than the predetermined value, the reduction amount of the steering assist force by the reduction means so that the steering angle follows the steering angle target value. And an increase / decrease means that does not increase / decrease the reduction amount of the steering assist force by the reduction means when the steering speed is less than a predetermined value and the steering angle is equal to or less than the steering angle target value. The electric power steering apparatus according to claim 1, characterized in that: Vehicle speed detecting means for detecting a vehicle speed that is the traveling speed of the vehicle,
4. The electric power according to claim 2, wherein the steering assist force changing unit further includes a correction unit that corrects a reduction amount of the steering assist force by the reduction unit according to the vehicle speed. 5. Steering device.

Images