JP2005081986A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of improving a steering feeling by determining accurately whether operation is in a steering wheel turning condition. <P>SOLUTION: The electric power steering device has an assist characteristic memory 22 in which a fundamental assist characteristic is stored and a shift amount computation part 24 which varies and sets a shift amount when the fundamental assist characteristic is shifted for acquiring a virtual corrective assist characteristic on the basis of a steering angular velocity, a vehicle speed, and steering torque and its differential value. An assist torque target value setting part 21 sets a target value for assist torque complying with a corrective assist characteristic by searching it in the assist characteristic memory 22 on the basis of the steering torque and the shift amount. An electric motor M is put under drive control in conformity to an assist torque target value. The shift amount is made zero at the time of cut-in steering and decided so that a greater steering assist force than in the case of the fundamental assist characteristic is obtained at the time of keeping steering and returning it. Whether the operation is in the cut-in steering condition or not is determined on the basis of the steering torque T and steering torque differential value T'. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus configured to transmit a driving force generated by an electric motor as a steering assist force to a steering mechanism.

2. Description of the Related Art Conventionally, an electric power steering apparatus configured to assist steering by mechanically transmitting a driving force generated by an electric motor to a steering mechanism by a gear mechanism (deceleration mechanism) or a direct drive system has been used.
In such an electric power steering apparatus, an assist characteristic that defines a relationship between a steering torque applied to the steering wheel and a target assist torque value applied from the electric motor to the steering mechanism is determined in advance, and stored as an assist map in a memory. Has been. Then, an assist torque target value corresponding to the steering torque is read from the assist map, and the electric motor is driven and controlled based on the read assist torque target value.

  As shown in FIG. 9, the assist characteristic is determined so that the assist torque target value increases as the steering torque increases. As the steering torque, for example, a positive value is assigned to the right steering direction, and a negative value is assigned to the left steering direction. The assist characteristic is determined so that a positive assist torque target value corresponds to a positive steering torque value and a negative assist torque target value corresponds to a negative steering torque value. Yes.

When the assist torque target value is a positive value, a steering assist force that tries to steer the steering wheel to the right acts on the steering mechanism. On the other hand, when the assist torque target value is a negative value, a steering assist force that tries to steer the steering wheel to the left acts on the steering mechanism. When the steering torque takes a value in the dead zone in the vicinity of zero, the assist torque target value is set to zero.
Japanese Patent Laid-Open No. 9-58501

  In the electric power steering apparatus to which such assist characteristics are applied, when the return steering is performed by rotating the steering wheel toward the steering angle midpoint, the steering power is returned to the steering angle midpoint more strongly than the driver intends. There is a problem that a steering feeling (so-called spring feeling) occurs. That is, when the return steering is performed, the steering torque is reduced, so that the assist force is reduced accordingly, and the steering wheel is strongly returned to the steering angle midpoint by the reverse input from the wheel.

In addition, there is a problem in that a steering burden is large at the time of a steering holding operation in which the steering wheel is held at a constant steering angle.
These problems can be solved by increasing the slope of the assist characteristic curve so that a larger assist torque target value is set for the steering torque. However, in this case, there is a problem that the feeling of response at the time of turning steering is impaired.

  This problem can be solved by the configuration proposed in Japanese Patent Application No. 2003-51539 previously filed by Koyo Seiko Co., Ltd., one of the present applicants. In the configuration according to this proposal, it is determined whether the steering is turning or returning based on the steering angular velocity, and the assist torque target value is determined based on the basic assist characteristic at the time of turning steering, and the basic assist is used at the time of holding and returning steering. The assist torque target value is determined based on the modified assist characteristic obtained by shifting the characteristic by a certain shift amount in the direction in which the assist torque increases.

As a result, it is possible to obtain a sufficiently responsive feeling during the turning steering, and during the return steering, a sufficient steering assist force is transmitted to the steering mechanism, so that the driver is more neutral than intended by the driver. Thus, an undesired steering feeling (spring feeling) that is strongly returned can be eliminated, and the steering burden during steering can be reduced.
However, this configuration is based on the assumption that the determination of the infeed steering / return steering based on the steering angular velocity is performed accurately, and without using the steering angle sensor, the electric Based on the output of the motor current detection circuit that calculates the motor current of the motor and the output of the voltage detection circuit between terminals that detects the voltage across the terminals of the electric motor, the counter electromotive force generated between the terminals of the electric motor is determined. When adopting a configuration for estimating the corresponding steering angular velocity, it cannot be said that the estimation accuracy of the steering angular velocity is very good, and thus the desired effect may not necessarily be achieved.

  For example, in an electric power steering apparatus using a motor with a brush, a steering angle sensor is usually not provided, and the steering angular velocity has to depend on the above estimation calculation. In such a case, in particular, even in the steered state, the steering angular velocity obtained by the estimation calculation may not be “0”, but may retain a value of a certain size. There is a risk of erroneous determination of whether or not. As a result, an uncomfortable feeling of steering occurs, and a good steering feeling may be hindered.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device that can improve steering feeling by accurately determining whether or not the vehicle is in a turning steering state.

  In order to achieve the above object, an invention according to claim 1 is an electric power steering device for assisting steering by transmitting a driving force of an electric motor (M) to a steering mechanism (3), and for steering the vehicle. A torque sensor (5) for detecting a steering torque applied to the operation member (1) for the operation, and a basic assist characteristic for setting a basic assist characteristic that is a basic characteristic of a motor drive target value with respect to the steering torque detected by the torque sensor The motor corresponding to the steering torque detected by the torque sensor according to the setting means (22) and the corrected assist characteristic obtained by shifting the basic assist characteristic set by the basic assist characteristic setting means in the coordinate axis direction of the steering torque. The motor drive target value setting means (21, S12) for setting the drive target value and the torque sensor Torque differentiation means (25) for differentiating the detected steering torque to obtain a steering torque differential value, and the operation based on the steering torque detected by the torque sensor and the steering torque differential value obtained by the torque differentiation means When it is determined by the incision steering determination means (24, S7) whether or not the incision steering for operating the member in the direction away from the rudder angle midpoint is being performed, The shift amount of the correction assist characteristic with respect to the basic assist characteristic is set to zero, and when it is determined that the inversion steering is not being performed by the incision steering determining means, the shift amount of the correction assist characteristic with respect to the basic assist characteristic is Motor drive eye for steering torque detected by torque sensor Based on the motor drive target value set by the shift amount setting means (24, S8, S11) and the motor drive target value setting means for setting the correction assist characteristic with the absolute value of the increased value to be obtained. An electric power steering apparatus including motor drive means (28, 29, 30) for driving a motor. The alphanumeric characters in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.

According to the present invention, the corrected assist characteristic obtained by correcting the basic assist characteristic set by the basic assist characteristic setting means is applied to the steering torque detected by the torque sensor. That is, the motor drive target value is set according to the correction assist characteristic.
The basic assist characteristic is corrected by shifting the basic assist characteristic in the direction of the coordinate axis of the steering torque. However, the shift amount is zero at the time of turning steering (steering away from the steering angle midpoint). The absolute value of the motor drive target value is larger than that of the basic assist characteristic at the time other than the turning steering (at the time of return steering (steering in the direction toward the steering angle midpoint) or at the time of steering). The shift amount is determined so that the correction assist characteristic can be obtained.

The cutting steering determination means determines whether or not the cutting steering state is in effect based on the steering torque actually detected by the torque sensor and the steering torque differential value obtained based on the detected steering torque. Is possible.
More specifically, for example, the steering torque detected by the torque sensor takes a positive value with respect to the right steering direction and takes a negative value with respect to the left steering direction. It is assumed that a positive value of the motor drive target value is assigned to a positive value, and a negative value of the motor drive target value is set for a negative steering torque.

  In this case, for example, when the steering torque is a positive value, it is determined that the infeed steering is being performed in response to the steering torque differential value exceeding the positive first threshold value (γ1). Thereafter, in response to the steering torque differential value falling below the negative second threshold value (−γ2), it is determined that the turning steering is no longer being performed (returning steering or holding state has been established). Can do.

Further, when the steering torque is a negative value, it is determined that the turning steering is being performed in response to the steering torque differential value falling below the negative third threshold (−γ1), and then the steering is performed. In response to the torque differential value exceeding the positive fourth threshold value (γ2), it can be determined that the turning steering is not being performed.
Since the shift amount setting means sets the shift amount to zero during the turning steering, the motor drive target value is determined according to the basic assist characteristics during the turning steering.

On the other hand, the shift amount is determined so as to obtain a correction assist characteristic that increases the absolute value of the motor drive target value at times other than the turning steering (at the time of turning back steering or holding).
That is, when the steering torque takes a positive value, a shift amount that shifts the basic assist characteristic in the negative direction of the steering torque coordinate axis is determined. That is, the shift amount in this case takes a negative value. As a result, the portion of the positive steering torque range in the basic assist characteristic is shifted toward the origin, so that the steering assist force increases, the spring feeling during return steering can be improved, and the steering burden during steering is reduced. Can be reduced.

  Further, when the steering torque is a negative value, a shift amount that shifts the basic assist characteristic in the positive direction of the steering torque coordinate axis is determined. That is, the shift amount in this case takes a positive value. As a result, the portion of the negative steering torque range in the basic assist characteristic is shifted toward the origin, so that the steering assist force increases, the spring feeling during return steering can be improved, and the steering burden during steering is reduced. it can.

  By setting the motor drive target value according to the corrected assist characteristic thus obtained, different assist characteristics can be set at the time of turning steering and return steering. As a result, it is possible to obtain a sufficiently responsive feeling during the turning steering, and during the return steering, a sufficient steering assist force is transmitted to the steering mechanism, so that the driver is more neutral than intended by the driver. Undesirable steering feeling (spring feeling) that is strongly returned can be eliminated, and the steering burden during steering can be reduced.

In addition, since it is possible to accurately determine whether or not the turning steering is being performed, the assist characteristics are appropriately corrected, and there is no sense of incongruity in steering, so that a good steering feeling can be realized.
The electric power steering device includes a vehicle speed detecting means (6) for detecting a traveling speed of a vehicle on which the electric power steering device is mounted, and the basic assist characteristic according to the vehicle speed detected by the vehicle speed detecting means. Vehicle speed adaptive shift amount setting means (24, S9, S11) for variably setting the shift amount of the correction assist characteristic may be further included.

According to this configuration, since the shift amount of the basic assist characteristic can be variably set according to the vehicle speed, for example, even when the assist characteristic is not required to be modified so much as in the case of a steering operation when the vehicle is stopped or traveling at a low speed. Yes.
Further, the electric power steering apparatus includes a steering torque adaptive shift amount setting means (24, S10, S11) that variably sets a shift amount of the correction assist characteristic with respect to the basic assist characteristic in accordance with a steering torque detected by a torque sensor. ) May be further included.

  With this configuration, for example, when the steering torque takes a small value in the vicinity of zero, the shift amount can be suppressed or reduced to zero, thereby restricting the steering assistance in a minute steering torque range where steering assistance is unnecessary. it can.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention. The steering torque applied to the steering wheel 1 as the operation member is mechanically transmitted to the steering mechanism 3 including the rack shaft via the steering shaft 2. A steering assist force is mechanically transmitted from the electric motor M to the steering mechanism 3 via a driving force transmission mechanism such as a gear mechanism (deceleration mechanism) or by a direct drive system.

  The steering shaft 2 is divided into an input shaft 2A coupled to the steering wheel 1 side and an output shaft 2B coupled to the steering mechanism 3 side. The input shaft 2A and the output shaft 2B are connected to the torsion bar 4. Are connected to each other. The torsion bar 4 is twisted according to the steering torque, and the direction and amount of the twist are detected by the torque sensor 5.

For example, the torque sensor 5 is configured by a magnetic sensor that detects a magnetic resistance that changes in accordance with a change in the positional relationship between the input shaft 2A and the output shaft 2B in the rotational direction. The output signal of the torque sensor 5 is input to the controller 10 (ECU: electronic control unit).
The controller 10 further receives an output signal of a vehicle speed sensor 6 that detects a traveling speed of a vehicle on which the electric power steering device is mounted.

  The controller 10 includes a microcomputer 20 and a motor driver 30 that drives the electric motor M based on a control signal from the microcomputer 20. The controller 10 further includes a motor terminal voltage detection unit 11 that detects a voltage between terminals of the electric motor M, and a motor current detection unit 12 that detects a current (motor current) flowing through the electric motor M. The output signals of the motor terminal voltage detector 11 and the motor current detector 12 are input to the microcomputer 20 together with the output signals of the torque sensor 5 and the vehicle speed sensor 6.

  The microcomputer 20 operates the electric motor according to the steering torque T detected by the torque sensor 5, the vehicle speed V detected by the vehicle speed sensor 6, and the steering angular velocity ω estimated by calculation based on the voltage between the motor terminals and the motor current. An assist torque target value to be applied from M to the steering mechanism 3 is determined, and the electric motor M is driven and controlled so that a steering assist force corresponding to the steering torque or the like is applied to the steering mechanism 3.

  The microcomputer 20 includes an assist torque target value setting unit 21 which is a function processing unit realized by executing program processing, and an assist characteristic storage unit 22 configured by a storage area of a memory in the microcomputer 20. ing. The assist characteristic storage unit 22 stores a plurality of basic assist maps respectively corresponding to a plurality of basic assist characteristics predetermined for each of a plurality of vehicle speed ranges. The basic assist characteristic defines the basic characteristic of the assist torque target value with respect to the steering torque. The basic value of the assist torque target value is assisted in the form of an assist map (table) in association with a plurality of steering torque values. It is stored in the characteristic storage unit 22.

  The microcomputer 20 further functions as a function processing unit, a torque differential value calculation unit 25 that calculates a steering torque differential value T ′ that is a time differential value of the steering torque T detected by the torque sensor 5, and a steering angular velocity calculation unit 23. And. The steering angular velocity calculator 23 is based on the following equation based on the motor terminal voltage Vm detected by the motor terminal voltage detector 11 and the motor current Im detected by the motor current detector 12 according to the following equation. ) Is estimated.

The microcomputer 20 also includes a shift amount calculation unit 24 that calculates a shift amount when the virtual assist assist characteristic is obtained by shifting the basic assist characteristic in the steering torque coordinate axis direction as a function processing unit.
The shift amount calculation unit 24 includes a steering angular velocity ω calculated by the steering angular velocity calculation unit 23, a vehicle speed V detected by the vehicle speed sensor 6, a steering torque T detected by the torque sensor 5, and a torque differential value calculation unit 25. Based on the steering torque differential value T ′ calculated by the shift amount ΔT for obtaining a virtual correction assist characteristic obtained by shifting the basic assist characteristic in the direction of the steering torque coordinate axis (the shift direction is indicated by its sign, and its absolute The amount representing the shift length by the value) is calculated.

Based on the steering torque T detected by the torque sensor 5, the vehicle speed V detected by the vehicle speed sensor 6, and the shift amount ΔT calculated by the shift amount calculation unit 24, the assist torque target value setting unit 21 reads from the assist characteristic storage unit 22. Then, the assist torque target value Ta corresponding to the correction assist characteristic is read out.
A deviation between the read assist torque target value Ta and the assist torque corresponding to the motor current Im detected by the motor current detection unit 12 is obtained by the deviation calculation unit 28, and is obtained by the deviation calculation unit 28. Based on the deviation, a control signal (for example, a PWM (Pulse Width Modulation) control signal) to be given to the motor driver 30 is generated by the control signal generator 29.

FIG. 2 is a diagram for explaining basic assist characteristics corresponding to the basic assist map stored in the assist characteristic storage unit 22 and modified assist characteristics obtained by shifting the basic assist characteristics in the steering torque coordinate axis direction.
The steering torque T detected by the torque sensor 5 takes a positive value when torque for steering in the right direction is applied to the steering wheel 1, and torque for steering in the left direction is applied to the steering wheel 1. Takes a negative value when The basic assist characteristic is indicated by a curve L0 in FIG. In this basic assist characteristic, a positive value of the assist torque target value Ta is associated with a positive value of the steering torque T, and a negative value of the assist torque target value Ta is associated with a negative value of the steering torque T. It is prescribed as follows. As described above, the assist characteristic storage unit 22 stores a plurality of basic assist maps corresponding to a plurality of vehicle speed ranges. However, in order to simplify the explanation, FIG. One basic assist characteristic is shown.

In the basic assist characteristic indicated by the curve L0, in the vicinity of the steering torque T = 0, the assist torque target value Ta = 0 is set regardless of the value of the steering torque T. Such a steering torque range is the dead zone NS.
In this embodiment, the basic assist characteristic is set in the direction of the coordinate axis of the steering torque T by the shift amount ΔT calculated by the shift amount calculation unit 24 based on the steering angular velocity ω, the vehicle speed V, the steering torque T, and the steering torque differential value T ′. The assist torque target value Ta is set based on virtual correction assist characteristics (for example, characteristics indicated by the curves L11 and L12) shifted in the positive direction or the negative direction.

However, as will be described below, in a situation where the steering torque T is zero or more, the basic assist characteristic is shifted only in the negative direction of the coordinate axis of the steering torque T (see the curve L11), and the steering torque T takes a negative value. In the situation, the basic assist characteristic is shifted only in the positive direction of the coordinate axis of the steering torque T (see curve L12).
If the basic assist characteristic is expressed as Ta = f (T) using the function f, a value obtained by subtracting the shift amount ΔT from the steering torque T detected by the torque sensor 5 is used as the steering torque value T ^* for searching the assist map. What is necessary is just to search the basic assist map memorize | stored in the assist characteristic memory | storage part 22 using this search steering torque value T ^* (namely, T ^* = T- (DELTA) T). Thus, the assist torque target value Ta (= f (T ^* )) can be determined according to the virtual correction assist characteristic.

  At the time of return steering or steering while steering the steering wheel 1 toward the steering angle midpoint, the virtual correction assist characteristic shifts the basic assist characteristic toward the origin along the steering torque coordinate axis direction. The shift amount ΔT is determined so as to obtain the desired characteristics. As a result, when the steering torque T is the same, the absolute value of the assist torque target value Ta takes a larger value than in the case of the basic assist characteristics, so that there is no shortage of steering assistance at the time of return steering or holding. . As a result, the feeling (spring feeling) that the steering wheel is returned stronger than intended by the driver can be eliminated, and the steering burden at the time of steering can be reduced.

  On the other hand, at the time of infeed steering in which the steering wheel 1 is turned away from the neutral position, the shift amount ΔT is set to zero so that the virtual correction assist characteristic matches the basic assist characteristic. Thus, the steering assist force applied from the electric motor M to the steering mechanism 3 becomes a value according to the basic assist characteristics. As a result, when the steering wheel 1 is cut, a good feeling of response can be given to the driver.

FIG. 3 is a flowchart for explaining the operation of the microcomputer 20. The microcomputer 20 repeatedly executes the process of FIG. 3 every control cycle (for example, 0.1 second).
The vehicle speed V detected by the vehicle speed sensor 6 and the steering torque T detected by the torque sensor 5 are read (steps S1, S2). The steering torque differential value T ′ is obtained by time-differentiating the read steering torque T by the torque differential value calculation unit 25 (step S3). Further, the output signals of the motor terminal voltage detector 11 and the motor current detector 12 are read (steps S4 and S5), and the steering angular velocity calculator 23 obtains the steering angular velocity ω (step S6).

The shift amount calculation unit 24 determines whether or not incision steering, which is steering in a direction away from the steering angle midpoint, is performed based on the steering torque T, the steering torque differential value T ′, and the steering angular velocity ω. The incision steering determination process is executed (step S7). The shift amount calculation unit 24 further executes a basic shift amount calculation process for obtaining a basic shift amount ΔT _B that is a basic value of the shift amount ΔT based on the result of the turning steering determination process and the steering torque T. (Step S8).

Further, the shift amount calculation unit 24 obtains a vehicle speed gain G _V based on the vehicle speed V detected by the vehicle speed sensor 6 (step S9). The shift amount computing section 24 finds the torque gain G _T on the basis of the steering torque T detected by the torque sensor 5 (Step S10). Then, by multiplying the thus determined vehicle speed gain G _V and the torque gain G _T to the basic shift amount [Delta] T _B, the shift amount _{ΔT (= G V × G T} × ΔT B) is calculated (step S11).

The obtained shift amount ΔT is given to the assist torque target value setting unit 21. The assist torque target value setting unit 21 calculates a search steering torque value T ^* = T−ΔT as T ^* ← T−ΔT, and stores it in the assist characteristic storage unit 22 based on the search steering torque value T ^*. The searched basic assist map is searched (step S12).
Thus, the assist torque target value Ta according to the virtual correction assist characteristic obtained by shifting the basic assist characteristic along the steering torque coordinate axis direction by the shift amount ΔT is read from the assist characteristic storage unit 22. . Based on the read assist torque target value Ta, the motor driver 30 is controlled, and a driving force corresponding to the motor driver 30 is applied from the electric motor M to the steering mechanism 3.

  FIG. 4 is a flowchart for explaining the cutting steering determination processing (step S7 in FIG. 3). First, in order to determine whether or not the steering wheel 1 is in the neutral position, the absolute value of the steering torque T is less than a predetermined value α (for example, 0.5 Nm), and the absolute value of the steering angular velocity ω is a predetermined value β. It is determined whether it is less than (eg, 10 deg / sec) (step S21). If this determination is affirmative and it is determined that the steering wheel 1 is in the neutral position, the cut flag is set to “1” (step S22). The turning flag indicates that the turning steering is being performed when “1”, and that the turning steering is not being performed (ie, that the turning back steering or the steering is being held) when “0”.

When the steering wheel 1 is in the neutral position, the shift amount ΔT is set to zero by setting the notch flag to “1”. Therefore, the basic assist characteristics can be applied as they are to assist the steering.
On the other hand, if it is determined that the steering wheel 1 is not in the neutral position (NO in step S21), it is further determined whether or not the steering torque T is a positive value (step S23).

  When the steering torque T is a positive value, it is further determined whether the steering torque differential value T ′ exceeds a predetermined first threshold value γ1 (where γ1> 0, for example, γ1 = 1.0 Nm / sec). Judgment is made (step S24). If the steering torque differential value T ′ is large enough to exceed the first threshold value γ1, it can be determined that the cutting steering has started, so the cutting flag is set to “1” (step S25).

On the other hand, the steering torque T is a positive value (YES in step S23), and the steering torque differential value T ′ is a predetermined second threshold value −γ2 (where γ2> 0. For example, γ2 = 1.0 Nm / sec) (YES in step S26), it can be determined that it is the timing from the turning steering toward the turning-back steering through the steering holding state, so that the turning flag is reset to “0” and the turning steering is performed. The release of the state is indicated (step S27).
When the steering torque T is a positive value (rightward steering) (YES in step S23) and the steering torque differential value T ′ is a value between the first and second threshold values γ1, −γ2 ( NO in step S26), the process returns without changing the cut flag.

  When the steering torque T is a negative value (leftward steering), it is determined whether or not the steering torque differential value T ′ is below a predetermined third threshold value −γ1 through steps S23 to S28. (Step S29). If the steering torque differential value T ′ is so small that the absolute value is smaller than the third threshold value −γ1, it can be determined that the cutting steering has started, and therefore the cutting flag is set to “1”. (Step S30).

On the other hand, when the steering torque T is a negative value (YES in step S28) and the steering torque differential value T 'exceeds a predetermined fourth threshold value γ2 (YES in step S31), the steering is turned. Therefore, the cutting flag is reset to “0”, indicating that the cutting steering state is released (step S32).
When the steering torque T is a negative value (YES in step S28) and the steering torque differential value T 'is a value between the third and fourth threshold values -γ1, γ2 (NO in step S31). Return without changing the cut flag.

FIG. 5 is a diagram for explaining the principle of the cutting steering determination process shown in FIG. FIG. 5 (a) shows the time change of the steering angle during steering in the right direction, FIG. 5 (b) shows the time change of the steering torque T at that time, and FIG. 5 (c) shows the steering at that time. The time change of the torque differential value T ′ is shown, and FIG. 5D shows the change of the value of the cut flag at that time.
The steering angle and the steering torque T rise during the period D1 in which the steering wheel 1 is turned to the right from the steering angle midpoint, and they are held at a substantially constant value during the steering state D2. During the switchback steering period D3, both of them decrease to zero.

The steering torque time differential value T ′ rises greatly and exceeds the first threshold value γ1 in the initial stage of the cutting steering period D1, thereby setting the cutting flag to “1”. However, in this embodiment, since the cutting flag is set to “1” even when the steering wheel 1 is in the neutral position, the cutting flag is held at “1” from the previous period.
The steering torque differential value T ′ falls below the second threshold value −γ2 before and after the time t1 when the infeed steering period D1 shifts to the steering holding period D2. As a result, the cut flag is reset to “0”. Thereafter, during the steering holding period D2, the steering torque differential value T ′ takes a value between the first and second threshold values γ1, −γ2, and therefore the cut flag is held at “0”.

  In the switchback period D3, the steering torque differential value T ′ takes a negative value having a large absolute value. However, since the condition of step S26 in FIG. 4 is satisfied, the cut flag is held at “0”. At the time t2 when the neutral state is reached after the switchback period D3 (step S21 in FIG. 4), it is set to “1”. During the switch-back period D3, the steering torque T always takes a positive value from start to finish, so that the processing after step S28 in FIG. 4 (processing corresponding to leftward steering) is not performed.

FIG. 6 is a flowchart for explaining the basic shift amount calculation processing in step S8 of FIG. When the cut flag is set to “1” (YES in step S41), the basic shift amount ΔT _B is set to “0” (step S42). Therefore, the assist torque target value is obtained according to the basic assist characteristics.
When the cut flag is “0” (NO in step S41), if the steering torque T is zero or a positive value (YES in step S43), the basic shift amount ΔT _B has a negative value −A (however, A is a positive constant) (step S44), and if the steering torque T is a negative value (NO in step S43), a positive value A is set for the basic shift amount ΔT _B (step S45). . Therefore, the basic shift amount ΔT _B is determined so as to obtain a corrected assist characteristic obtained by shifting the basic assist characteristic toward the origin along the coordinate axis of the steering torque T.

Therefore, the basic shift amount ΔT _B is zero at the time of turning steering (when steering away from the steering angle midpoint), and at the time of return steering (when steering toward the steering angle midpoint) and at the time of steering The basic shift amount ΔT _B is set to a value that shifts the basic assist characteristic along the steering torque coordinate axis toward the origin.
In this way, while ensuring sufficient responsiveness at the time of turning steering, it is possible to eliminate the feeling of spring at the time of return steering and to reduce the steering burden at the time of steering. Moreover, since the steering steering determination process based on the steering torque T that is actually detected and the steering torque differential value T ′ that is the time differential value thereof can be accurately performed, there is no steering discomfort due to an error in the steering steering determination. Good steering feeling can be realized.

FIG. 7 is a diagram for explaining variable setting of the shift amount ΔT corresponding to the vehicle speed V, and FIG. 8 is a diagram for explaining variable setting of the shift amount ΔT corresponding to the steering torque T. Shift amount calculation unit 24, by multiplying the vehicle speed gain G _V defined according to the characteristics shown in FIG. 7, a torque gain G _T to be determined in accordance the characteristic shown in FIG. 8 to the basic shift amount [Delta] T _B, the shift The quantity ΔT (= ΔT _B × G _V × G _T ) is determined. By using this shift amount ΔT, the assist torque target value setting unit 21 searches the basic assist map stored in the assist characteristic storage unit 22, thereby correcting assist that is virtually determined according to the vehicle speed V and the steering torque T. The assist torque target value Ta according to the characteristic is read out.

The vehicle speed gain G _V is monotonously (linear in this example) with a predetermined upper limit (“1” in the example of FIG. 7) as the upper limit as the vehicle speed V increases within the range from zero to a predetermined speed. To) increase.
Thus, it is possible to cope with a case where the assist characteristic is not so much corrected, such as a steering operation when the vehicle is stopped or when traveling at a low speed.

On the other hand, the torque gain G _T, and dead band region in the vicinity of the steering torque T = 0, in this dead zone outside with the increase of the absolute value of the steering torque T, the predetermined upper limit value (in this example "1") Is set to increase monotonously (linearly in this example). Thereby, the steering assistance in the range where the steering assistance in the vicinity of the steering torque T = 0 is unnecessary is limited.
As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, the vehicle speed V and the steering torque T are added to the shift amount ΔT of the assist characteristic. However, the variable setting of the shift amount depending on the vehicle speed V and the steering torque T is not necessarily required. That is, it may be used directly as the shift amount [Delta] T the basic shift amount [Delta] T _B in the above embodiment, the shift amount [Delta] T by multiplying only the vehicle speed gain G _V without the torque gain G _T to the basic shift amount [Delta] T _B determined or may be asking for the shift amount [Delta] T only torque gain G _T without using the vehicle speed gain G _V by multiplying the basic shift amount [Delta] T _B.

In the above embodiment, the assist characteristic storage unit 22 stores an assist map corresponding to the basic assist characteristic, and the assist torque target value Ta is read from the assist map. Thus, the assist torque target value Ta corresponding to the search steering torque value T ^* may be determined.
The same is true for operations of the torque gain G _T with respect to the vehicle speed gain G _V and the steering torque T with respect to the vehicle speed V.

In the above embodiment, the assist torque target value is set as the motor drive target value, and the assist torque target value characteristic with respect to the steering torque is described as the assist characteristic. However, the present invention is not limited to this, and the motor current target value or the motor The voltage target value may be a motor drive target value, and the steering torque and the relationship between them may be assist characteristics.
In addition, various design changes can be made within the scope of matters described in the claims.

1 is a block diagram showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention. It is a figure for demonstrating the basic assist characteristic and the correction assist characteristic obtained by shifting this to a steering torque coordinate-axis direction. It is a flowchart for demonstrating the process relevant to the drive control of the electric motor by a microcomputer. It is a flowchart for demonstrating a cutting steering determination process (step S7 of FIG. 3). It is a figure for demonstrating the principle of a cutting steering determination process, (a) shows the time change of the steering angle at the time of steering to the right direction, (b) shows the time change of the steering torque at that time, (c) shows the time change of the steering torque differential value at that time, and (d) shows the time change of the value of the cut flag at that time. It is a flowchart for demonstrating basic shift amount calculation processing (step S8 of FIG. 3). It is a figure for demonstrating the variable setting of the shift amount with respect to a vehicle speed. It is a figure for demonstrating the variable setting of the shift amount with respect to a steering torque. It is a figure which shows an example of an assist characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 3 Steering mechanism 5 Torque sensor 6 Vehicle speed sensor 7 Steering angle sensor 10 Controller 20 Microcomputer 21 Assist torque target value setting part 22 Assist characteristic memory | storage part 23 Steering angular velocity calculating part 24 Shift amount calculating part 25 Torque differential value calculating part 30 Motor driver M Electric motor

Claims (1)

An electric power steering device for assisting steering by transmitting a driving force of an electric motor to a steering mechanism,
A torque sensor for detecting a steering torque applied to an operation member for steering the vehicle;
Basic assist characteristic setting means for setting a basic assist characteristic that is a basic characteristic of the motor drive target value with respect to the steering torque detected by the torque sensor;
A motor for setting a motor drive target value corresponding to the steering torque detected by the torque sensor according to a corrected assist characteristic obtained by shifting the basic assist characteristic set by the basic assist characteristic setting means in the coordinate axis direction of the steering torque. Drive target value setting means;
Torque differentiating means for differentiating the steering torque detected by the torque sensor to obtain a steering torque differential value;
Based on the steering torque detected by the torque sensor and the steering torque differential value obtained by the torque differentiating means, it is determined whether or not the cutting steering for operating the operation member in the direction away from the steering angle midpoint is performed. Cutting steering determination means;
When it is determined by the incision steering determining means that the inversion steering is being performed, the shift amount of the modified assist characteristic with respect to the basic assist characteristics is set to zero, and when the incision steering determining means determines that the incision steering is not in progress A shift amount setting means for setting a shift amount of the correction assist characteristic with respect to the basic assist characteristic to a value at which a correction assist characteristic with an increased absolute value of a motor drive target value with respect to the steering torque detected by the torque sensor is obtained; ,
An electric power steering apparatus comprising: motor drive means for driving the electric motor based on the motor drive target value set by the motor drive target value setting means.

Images