JP2002316659A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict an unnatural steering feeling occurring at the time of turning and turning back affected by gaps in a transmission system from a motor for steering assist to a steering mechanism. SOLUTION: After a reference drive current I0 of the motor for steering assist is calculated on the basis of steering torque, a steering angle and speed, if turning or turning back is determined to be performed, until a steering angle difference Δαbetween an afterward steering angle α and a steering angle at the time of determination reaches a predetermined value α0 +α1 , a correction current I1 or Δ1 is added to the current I0 and a drive current I of the motor 4 is set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering assist system for driving a motor based on a result of detection of a steering torque applied to a steering wheel (steering wheel) for steering, and applying a rotational force of the motor to a steering mechanism. The present invention relates to an electric power steering device having such a configuration.

[0002]

2. Description of the Related Art In recent years, a steering assist motor is controlled based on a detection result of a steering torque applied to a steering wheel (steering wheel) for a steering operation, and the torque of the motor is transmitted to a steering mechanism to perform steering. An electric power steering device configured to assist the vehicle has been put to practical use.
Compared to a hydraulic power steering device that uses a hydraulic actuator as a source of steering assist force,
It has the advantage that it is easy to control the assisting force characteristics according to the running state such as the frequency of steering, and in recent years, its application range tends to be expanded.

[0003] On the other hand, the drawbacks of the electric power steering device are that it realizes both a size (small size) that can be arranged around the steering mechanism and the generation of a large enough assisting force (large output). It is difficult to obtain a steering assist motor that can be used, and conventionally, in order to solve this difficulty, at the output end of the motor, a reduction device such as a planetary gear reducer is provided, and the rotation of the motor is reduced by the reduction device. The vehicle is sufficiently decelerated (increased) and transmitted to the steering device.

The steering assist motor is controlled by current control for increasing or decreasing the drive current of the motor in accordance with the magnitude of the detection result of the steering torque. Correction according to the running state is performed to obtain an auxiliary force characteristic suitable for each case. Further, the control of the motor as described above is not performed while the detected value of the steering torque is within the predetermined dead zone.For example, the steering assist is performed in response to the "play" operation of the steering wheel during straight running at high speed. Therefore, the vehicle is prevented from wobbling.

[0005]

However, the rotation of the steering assist motor, which is current controlled as described above, is transmitted to the steering mechanism via the deceleration means. There is a backlash in the gears constituting the speed reducing means and a mechanical gap in each part of the steering mechanism. Therefore, in the initial stage of steering, such as when the steering operation (cutout) is performed in any direction from the straight traveling neutral state, or when the left and right reversing operation (turnback) is performed, the motor is operated in accordance with the operation of the steering wheel. Starts to rotate, and before the rotation is transmitted to the steering mechanism, extra movement for sequentially absorbing the backlash and the gap (hereinafter referred to as an initial gap) is required, and an appropriate time delay occurs.

FIG. 9 is an explanatory diagram of the above problem. FIG. 9A shows a transient change state of the steering torque with respect to the steering angle at the beginning of steering. As shown in FIG. 9, the steering torque is not changed until the steering angle reaches the steering angle α ₀ corresponding to the initial gap. Indicates a change mode in which the level is maintained at a low level, and after the initial gap is eliminated, abruptly increases by the action of resistance from the steering mechanism side.

FIG. 9 (b) shows how the drive current of the steering assist motor changes transiently at the beginning of steering. This drive current is calculated based on the steering torque applied to the steering wheel.However, until the steering angle α ₀ corresponding to the initial gap is reached, the steering torque during this period is small and exists in the dead zone. A change mode in which the steering angle is kept at zero level and rapidly increases after reaching the steering angle α ₀ is shown.

After the drive current of the steering assist motor has rapidly increased, the initial gap has been eliminated, and as a result of the motor applying a steering assist force to the steering mechanism, the steering applied to the steering wheel is increased. torque, as shown in FIG. 9 (a), started to decline after reaching an appropriate peak value, after a predetermined steering angle alpha ₁ after the steering angle alpha _0, in accordance with an increase in the steering angle It shifts to a steadily increasing mode of change. The drive current of the steering assist motor also changes following the change in steering torque as described above.

Therefore, in such a steering operation at the initial stage of steering, the driver, as a reaction force of the steering torque which changes as described above, receives the steering angle α ₀ corresponding to the initial gap and the steering angle α ₁ thereafter. First, the driver feels that the steering feels lighter first, then heavier and then lighter again, in other words, an unnatural steering feeling accompanied by "stuck" and "disengaged". There was a problem that can not be.

[0010] The present invention has been made in view of the above-described circumstances, and the "jagging" and "catching" generated at the time of cutting and turning back due to the influence of a gap existing in the transmission system from the steering assist motor to the steering mechanism. It is an object of the present invention to provide an electric power steering device capable of suppressing an unnatural steering feeling accompanied by "missing" and obtaining a good steering feeling.

[0011]

According to a first aspect of the present invention, there is provided an electric power steering apparatus comprising: a torque detecting means for detecting a steering torque applied to a steering wheel; a motor for applying a steering assist force to a steering mechanism; An electric power steering apparatus comprising: a control unit that controls a drive current of the motor based on a torque detected by a detection unit; a steering angle detection unit that detects a steering angle performed by an operation of the steering mechanism; A determination unit that determines the start of the steering from the steering or the change of the steering direction, and the control unit performs a period from the determination by the determination unit until the steering angle detected by the steering angle detection unit reaches a predetermined angle. In the transition period, the drive current is set by adding a transition period correction current to a reference current calculated based on the detected torque.

In the present invention, the start of the steering from the neutral state or the change of the steering direction, that is, the cutout or the return is determined, and when this determination is made, the drive current of the steering assist motor is absorbed by the initial gap. By adding a transient period correction current for driving the motor and driving the motor in advance, an unnatural steering feeling accompanied by catching and slipping is suppressed.

Further, in the electric power steering apparatus according to a second aspect of the present invention, the transient period correction current according to the first aspect is constant until the detected steering angle reaches a second angle smaller than the predetermined angle. The value is a decreasing value that decreases from the constant value to zero until the predetermined angle is reached from the second angle.

In the present invention, a transient period correction current that is constant until the steering angle corresponding to the initial gap is reached, and then decreases until the steering angle reaches the predetermined angle, is added to advance driving for absorbing the initial gap. From the normal drive to the normal drive.

In the electric power steering apparatus according to a third aspect of the present invention, the transient period correction current in the first aspect is constant until the detected steering angle reaches a second angle smaller than the predetermined angle. And a decrease value that decreases at a rate of change corresponding to a differential value of the detected torque from the second angle to the predetermined angle.

Further, in the electric power steering apparatus according to a fourth aspect of the present invention, the transient period correction current in the first aspect is constant until the detected steering angle reaches a second angle smaller than the predetermined angle. And a decreasing value that decreases at a rate of change corresponding to a differential value of the detected steering angle from the second angle to the predetermined angle.

In these inventions, the transient correction current after reaching the steering angle corresponding to the initial gap is calculated as the differential value of the detection result of the steering torque or the steering angle, that is, the change rate corresponding to each steering state. , The transition from the preceding drive to the normal drive for absorbing the initial gap is performed more smoothly, and a good steering feeling is realized.

The electric power steering apparatus according to a fifth aspect of the present invention is characterized in that the transient period correction current according to the first aspect is set according to a differential value of the detected torque.

In the present invention, the transient period correction current is set according to the differential value of the detected torque, and the steering assist motor is driven so as to respond steeply to the rise of the steering torque generated after the elimination of the initial gap. , Suppresses unnatural steering feeling.

Further, in the electric power steering apparatus according to a sixth aspect of the present invention, in the transition period after the determination by the determination means until the steering angle detected by the steering angle detection means reaches a predetermined angle, A low-pass filter acting on the output of the detecting means is provided.

In the present invention, the value detected by the torque detecting means is processed by a low-pass filter during a transition period from the occurrence of the cut-out or the return until a predetermined steering angle is reached,
The peak value of the steering torque generated after the elimination of the initial gap is erroneously recognized as lower than the actual value, and the drive current of the steering assist motor, which is set based on the detection result, is reduced to reduce the deterioration of the steering feeling. I do.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to the present invention. As shown in FIG. 1, a steering wheel (steering wheel) 1 for steering operation and a steering mechanism 2 for performing a steering operation are shown. A torque sensor 3 for detecting a steering torque applied to the steering wheel 1 and a motor 4 for assisting steering are arranged in the middle of the connected steering shaft 10 to constitute an electric power steering apparatus according to the present invention.

The steering wheel 1 is fitted and fixed to an upper end of the steering shaft 10 so as to face a driver seated inside a vehicle compartment (not shown). It is designed to rotate around the axis in response to the rotation operation of.

The steering mechanism 2 includes a pinion 20 integrally formed at a lower end of the steering shaft 10 and a rack shaft meshing with the pinion 20.
21 as a rack and pinion type steering mechanism. The rack shaft 21 is slidably extended in the left-right direction at a front portion of the vehicle (not shown). Both left and right ends of the rack shaft 21 are steered through separate tie rods 22, 22, respectively. Wheels (generally, front wheels) 23, 23 are connected. With this configuration, the steering mechanism 2 converts the rotation of the pinion 20 generated via the steering shaft 10 by the operation of the steering wheel 1 into the movement of the rack shaft 21 meshing with the pinion 20, and converts this movement to the tie rods 22 at both ends. , 22 to the steering wheels 23, 23,
A steering operation for changing the direction of the wheels 23, 23 to the operation direction of the steering wheel 1 is performed.

The steering assist motor 4 for assisting such a steering operation is provided at a middle portion of the steering shaft 10, and a worm 40 fixed to an output end of the motor 4 is provided at a middle portion of the steering shaft 10. It is engaged with the worm wheel 41 fitted and fixed. With this configuration, the rotation of the motor 4 is controlled by a worm
The rotation is transmitted to the steering shaft 10 via the worm wheel 40 and the worm wheel 41, and a rotational force is applied to the pinion 20 connected to the lower end of the steering shaft 10, and the steering performed as described above according to this rotation is performed. Assisted.

The steering assist motor 4 is disposed, for example, in the middle of the rack shaft 21 and its rotation is transmitted to the rack shaft 21 via a motion conversion mechanism such as a ball screw and a rack pinion. For example, a configuration in which a sliding force is applied to the motor 21 may be provided at an appropriate position around the steering mechanism 2 including the steering shaft 10 without being limited to the position shown in FIG.

During the steering operation as described above, the torque sensor 3 for detecting the steering torque applied to the steering wheel 1 moves the steering shaft 10 closer to the steering wheel 1 than the motor 4 is disposed.
The shaft is divided into an upper shaft and a lower shaft which are coaxially connected via a torsion bar, and a relative angular displacement is generated between the two shafts with the torsion of the torsion bar due to the action of the steering torque. It has a known configuration for detecting the steering torque through displacement.

The torque detected by the torque sensor 3 is provided to a drive control unit 5 that controls a motor 4 for assisting steering. The drive control unit 5 further includes a rotation sensor 50 for detecting a rotational position of the motor 4, a steering angle sensor 51 for detecting a steering angle realized by the above-described steering operation, and an electric power steering apparatus according to the present invention. Each detection signal is given from a vehicle speed sensor 52 that detects the traveling speed of a vehicle provided with.

The output of the drive control unit 5 is supplied to the steering assist motor 4 arranged in the middle of the steering shaft 10 as described above. The drive control unit 5 basically uses the steering torque detected by the torque sensor 3 and calculates the drive current of the motor 4 so as to generate a rotational force according to the magnitude of the detected torque. A current control operation for supplying the calculated drive current to the motor 4 with reference to the rotation position detected by the rotation sensor 50 is performed.

At this time, the steering angle detected by the steering angle sensor 51 and the vehicle speed detected by the vehicle speed sensor 52 are used for correcting the drive current of the motor 4 calculated as described above.
This correction reduces the drive current as the detected vehicle speed increases,
In addition, the drive current is increased with an increase in the detected steering angle, so that an assist force characteristic suitable for the traveling state, more specifically, an assist force characteristic corresponding to the magnitude of the road surface resistance that changes according to the traveling state is obtained. I am trying to be.

In the electric power steering apparatus according to the present invention, during the steering assist by the motor 4 driven by the above current control, the steering mechanism 2
Due to the action of the initial gap present in the transmission system to
The following control operation is performed to suppress an unnatural steering feeling accompanied by “stuck” and “disengagement” that occur as described above during a transition period during cutting or turning back, and to obtain a good steering feeling.

The initial gap is defined as a backlash at a meshing portion between the worm 40 and the wheel 41 which constitutes a speed reducing means between the steering assist motor 4 and the steering mechanism 2,
From the motor 4, such as a backlash at a meshing portion between the pinion 20 and the rack shaft 21 forming the steering mechanism 2, and a mechanical gap at a connecting portion between the rack shaft 20 and the tie rods 22 and 22 forming the steering mechanism 2, It is a combination of the backlash and the gap existing in each part of the transmission system to the steering mechanism 2, and the sum of the respective design values or the value obtained by converting the measured value in the operation test after assembly into a steering angle (hereinafter referred to as gap steering). The angle α ₀ is obtained in advance and stored in the drive control unit 5.

The term “cutout” refers to a state in which a steering operation has been performed in any direction from a neutral position in a straight traveling direction. In this case, the operation is performed, and in such a case, as described above, the gap steering angle absorbing operation is performed before the rotation of the steering assist motor is transmitted to the steering mechanism. A natural steering feeling is generated.

FIG. 2 is a flowchart showing an example of the operation of the drive control unit 5. The drive control unit 5 includes, for example,
The control operation is started in response to the ON operation of a key switch (not shown) for starting the engine. First, the detection values of the torque sensor 3, the steering angle sensor 51, and the vehicle speed sensor 52, that is, the steering torque, the steering angle, and the vehicle speed are determined. It takes in the detected value at a predetermined sampling period (step 1), by the above-described procedure using these to calculate the reference drive current I ₀ for the drive of the motor 4 (step 2).

Next, the drive control unit 5 determines whether or not the cutout or the cutback has been performed (step 3, step 3).
4) In cases other than these, the reference drive current I ₀ is set as the drive current I to drive and control the motor 4 (step 5). Note that the determination of the cutout or the return can be made based on the history of the steering angle detection value obtained by the steering angle sensor 51.

On the other hand, if it is determined in step 3 and step 4 that cutting or turning back has been performed, the drive control unit 5 takes in the detection value of the steering angle sensor 51 at a predetermined sampling cycle (step 6). ), The steering angle difference Δα between the detection value at each sampling time and the detection value at the first determination time, that is, the steering angle change amount from the cutout or return time is obtained (step 7).

Next, it is checked whether or not the obtained steering angle difference Δα is within the gap steering angle α ₀ (step 8). If it is determined that the steering angle difference Δα is within the gap steering angle α ₀ , the reference drive current by adding a predetermined correction current I ₁ to I ₀ by setting the drive current I drives and controls the motor 4 (step 9), the flow returns to the step 6.

The steering angle difference Δα is equal to the gap steering angle α _0.
If it is determined to be outside checks whether the gap steering angle alpha ₀ the predetermined steering angle alpha ₁ which is set beyond (step 10), steering angle difference Δα is, alpha ₀ + alpha ₁ When it is determined that the driving current I is equal to or less than the above, a driving current I is added to the reference driving current I ₀ by adding a correction current ΔI ₁ starting from the correction current I ₁ and decreasing proportionally with an increase in the steering angle difference Δα. After setting, the motor 4 is driven and controlled (step 11), and the process returns to step 6.

On the other hand, when it is determined that the steering angle difference Δα has exceeded α ₀ + α ₁ , the series of operations from step 6 to step 11 is completed, and the process returns to step 1 to determine whether to cut out or switch back again. Until the above, the normal control operation for driving the steering assist motor 4 based on the reference drive current I ₀ is performed.

FIG. 3 is an explanatory diagram of the contents of the operation when the cut-out or the cut-back is determined. FIG. 3 (a)
9 shows how the steering torque changes with respect to the steering angle after cutting or turning back. Steering torque as shown, until it reaches the gap steering angle alpha ₀ corresponding to the initial gap is kept at a low level, after reaching the gap steering angle alpha _0, increase the resistance from the steering mechanism 2 side FIG.

FIG. 3B shows how the drive current of the steering assist motor 4 changes. In the electric power steering apparatus according to the present invention, when cutout or turning back is performed, the operations of Steps 6 to 11 are performed according to the determination of Step 3 or Step 4, and after the cutout or turning back obtained as the steering angle difference Δα. Until the actual steering angle reaches the gap steering angle α ₀ , Step 9 is executed in accordance with the determination in Step 8, and the drive current I of the steering assist motor 4 is determined by the steering torque, the steering angle and the vehicle speed. It is set by adding a correction current I ₁ to the reference driving current I ₀ which is calculated on the basis of the detection value. During this time, since the steering torque applied to the steering wheel 1 is substantially zero as shown in FIG. 3A, the driving current I of the motor 4 is substantially constant (= I ₁ ) as shown in FIG. 3B. Becomes

[0042] That is, the motor 4 for steering assist, before reaching the gap steering angle alpha _0, becomes substantially be preceded driven by constant driving current I _1, the proper setting of the drive current I _1, the real When the steering angle reaches the gap steering angle α ₀ , the backlash and the gap existing in each part of the transmission system from the motor 4 to the steering mechanism 2 can be eliminated. Therefore, when the motor 4 is driven according to the steering torque generated after reaching the gap steering angle α ₀ , the rotational force of the motor 4 is promptly transmitted to the steering mechanism 2, and the steering torque Are offset by the rotational force of the motor 4 and, as shown in FIG. 3A, begin to decrease without reaching a large peak value.

Further, after the actual steering angle (= Δα) after the cut-out or the return has reached the gap steering angle α ₀ , α ₀ +
until reaching the alpha _1, by the operation of step 11 according to the determination in step 10, the driving current I of the motor 4 for steering assist
Is set by adding a correction current ΔI ₁ that decreases with an increase in the actual steering angle to the reference drive current I ₀ . During this time, the steering torque applied to the steering wheel 1 shows a change mode in which it decreases after a slight increase as shown in FIG. 3A, and the drive current I of the motor 4 becomes as shown in FIG. 3B. A change mode is shown in which the increase following the increase in the steering torque is followed by a gradual decrease due to the action of the correction current ΔI ₁ . FIG. 3 (c)
Shows a change mode of the correction current determined as described above.

That is, after reaching the gap steering angle α ₀ , the motor 4 is driven by a drive current I (= I ₀ + ΔI ₁ ) that gradually decreases continuously following the preceding drive before reaching the gap steering angle α ₀ . After reaching a steering angle (α ₀ + α ₁ ) that exceeds α ₀ by a predetermined angle, the motor is driven by the reference current I ₀ determined as described above. As a result, the transition from the preceding control immediately after the cutout or the switching back to the subsequent normal control is smoothly performed.

Therefore, the driver who operates the steering wheel 1 hardly feels "stuck" due to a sharp increase in the steering torque and "drop-out" due to a sudden decrease in the steering torque when cutting or turning back. It is possible to perform a steering operation under a good steering feeling.

FIG. 4 is a flowchart showing another example of the operation of the drive control unit 5. In the drive control unit 5 this embodiment, steering torque, steering angle and incorporation of the detection value of the vehicle speed (step 21), the calculation of the reference driving current I ₀ using these (step 22), and determination of the cut and crosscut performs (step 23, 24), as in the Figure 2, if the cut or crosscut is not performed, the motor 4 by setting the reference drive current I ₀ as the drive current I
Is driven (step 25).

If it is determined in steps 23 and 24 that cutting or turning back has been performed, the drive control unit 5 takes in the detected value of the steering angle sensor 51 (step 26), and calculates the steering angle difference Δα at each taking-in time. calculation of (step 27), and the calculated steering angle difference Δα is whether the gap steering angle α in ₀ determining (step 28) is performed in the same manner as in FIG. 2, the gap steering angle α within ₀ If it is determined that, by setting the driving current I by adding a constant correction current I ₂ to the reference driving current I ₀ drives and controls the motor 4 (step 29), step
Return to 26.

On the other hand, the steering angle difference Δα is the gap steering angle α ₀
If it is determined to be outside checks whether the gap steering angle alpha ₀ the predetermined steering angle alpha ₁ which is set beyond (step 30), is determined to be alpha ₀ + alpha ₁ and if obtains a differential value ΔT of the detected torque at current (step 31), the starting point of the correction current I _2, the differential value Δ
The correction current ΔI ₂ (= I
₂₋ G ₂ × ΔT) to set the drive current I to drive and control the motor 4 (step 32), and return to step 26.

Meanwhile, if the steering angle difference Δα is determined to be α ₀ + α ₁ out, the process returns to the step 21 after a series of operations of steps 26 to step 32, a determination is made again of the cut or crosscut Until the normal drive operation for driving the steering assist motor 4 is performed based on the reference drive current I ₀ .

FIG. 5 is an explanatory diagram of the contents of the operation in the case where the cutout or the return is determined in the flowchart shown in FIG. FIG. 5A shows a manner of change of the steering torque with respect to the steering angle after the cutout or the turning back. As in FIG.
The change level is maintained at a low level until the gap steering angle α ₀ corresponding to the initial gap is reached, and increases after reaching the gap steering angle α ₀ due to the resistance from the steering mechanism 2 side.

FIG. 5B shows how the drive current of the steering assist motor 4 changes. In the electric power steering apparatus according to the present invention, when cutout or turning back is performed, the operations of Steps 26 to 32 are performed according to the determination of Step 23 or Step 24, and after the cutting or turning back obtained as the steering angle difference Δα. Until the actual steering angle reaches the gap steering angle α ₀ , step 29 is executed in accordance with the determination in step 28, and the driving current I of the steering assist motor 4 is determined by the steering torque, the steering angle, and the vehicle speed. It is set by adding the correction current I ₂ to the reference driving current I ₀ which is calculated on the basis of the detection value. During this time, since the steering torque applied to the steering wheel 1 is substantially zero as shown in FIG. 5A, the drive current I of the motor 4 is substantially constant (= I ₂ ) as shown in FIG. Becomes

That is, the steering assist motor 4 is driven in advance by a substantially constant drive current I ₂ before reaching the gap steering angle α ₀ , and by setting this drive current I ₂ properly, When the steering angle reaches the gap steering angle α ₀ , the backlash and the gap existing in each part of the transmission system from the motor 4 to the steering mechanism 2 can be eliminated. Therefore, when the motor 4 is driven according to the steering torque generated after reaching the gap steering angle α ₀ , the rotational force of the motor 4 is promptly transmitted to the steering mechanism 2, and the steering torque Are offset by the rotational force of the motor 4 and, as shown in FIG. 5A, begin to decrease without reaching an excessive peak value.

After the actual steering angle (= Δα) after the cut-out or the return has reached the gap steering angle α ₀ , α ₀ +
Until α ₁ is reached, the drive current I of the steering assist motor 4 is differentiated from the reference drive current I ₀ by the operations of steps 31 and 32 according to the determination of step 30. It is set by adding a correction current ΔI ₂ that decreases in proportion to the value. As shown in FIG. 5A, the steering torque applied to the steering wheel 1 during this period shows a variation mode in which the steering torque decreases after a predetermined increase.
As shown in FIG. 5 (b), after the drive current I slightly increases following the increase in the steering torque, the correction current ΔI ₂
Shows a mode of change that gradually decreases due to the action of. FIG.
(C) shows a change mode of the correction current determined as described above.

That is, after reaching the gap steering angle α ₀ , the motor 4 is driven by the drive current I (= I ₀ + ΔI ₂ ) that gradually decreases continuously following the preceding driving before reaching the gap steering angle α ₀ . After reaching a steering angle (α ₀ + α ₁ ) that exceeds α ₀ by a predetermined angle, the motor is driven by the reference current I ₀ determined as described above. As a result, the transition from the preceding control immediately after the cutout or the switching back to the subsequent normal control is smoothly performed.

Therefore, the driver who operates the steering wheel 1 hardly feels "stuck" caused by a sharp increase in the steering torque and "slip" caused by a sudden decrease in the steering torque when cutting or turning back. It is possible to perform a steering operation under a good steering feeling.

Further, in this embodiment, the correction current ΔI ₂ after exceeding the gap steering angle α ₀ is set based on the differential value ΔT of the steering torque representing the steering state at that time, and FIG. As shown in FIG. 5C, a change mode in which the degree of initial decrease is large is shown. Therefore, as shown in FIG. 5A, the peak value of the steering torque can be further reduced, which contributes to the improvement of the steering feeling. it can.

As the state quantity representing the steering state, a differential value or a second-order differential value of the detected value of the steering angle, that is, the steering angular velocity or the steering angular acceleration is used instead of the steering torque, and the correction current is calculated based on these. May be set. Also in this case, similar to the case where the correction current based on the steering torque is applied, it is possible to realize a good steering feeling in which the bodily sensations of “stuck” and “disengaged” are reduced.

FIG. 6 is a flowchart showing another example of the operation of the drive control unit 5. In the drive control unit 5 this embodiment, steering torque, steering angle and incorporation of the detection value of the vehicle speed (step 41), the calculation of the reference driving current I ₀ using these (step 42), and determination of the cut and crosscut (steps 43 and 44) were performed in the same manner as in FIGS. 2 and 4, if the cut or crosscut is not performed, by setting the reference drive current I ₀ as the drive current I drive controlling the motor 4 (step 45).

If it is determined in steps 43 and 44 that cutting or turning back has been performed, the drive control unit 5 takes in the detection value α of the steering angle sensor 51 (step 46) and the steering angle at each time of taking in. Calculation of difference Δα (step 47)
Is performed in the same manner as in FIGS.

[0060] Then, the calculated steering angle difference Δα is checked whether it is within the angular range plus a predetermined steering angle alpha ₁ to the gap steering angle alpha ₀ (step 48), within this angular range Is determined, the differential value Δ of the current detected torque
T is obtained (step 49), and a correction current ΔI ₃ (= G ₃ × ΔT) obtained by multiplying the differential value ΔT by a predetermined gain is added to the reference driving current I ₀ to set a driving current I. The drive of the motor 4 is controlled (step 50). In this operation, the steering angle difference Δα is set to α ₀ +
repeated until it is determined that the alpha ₁ outside, if this determination is made, the process returns to step 41, until the next determination of the cut-out or crosscut is made, based on the reference drive current I ₀ of the steering assist motor 4 is performed.

FIG. 7 is an explanatory diagram of the contents of the operation when the cut-out or cut-back is determined in the flowchart shown in FIG. FIG. 7A shows a manner of change in the steering torque with respect to the steering angle after the cutting or the turning back. As shown in the drawing, the steering torque is not changed until the steering torque reaches the gap steering angle α ₀ corresponding to the initial gap. Maintained at a low level, after reaching the gap steering angle α ₀ , the steering mechanism 2
7 shows a variation that increases with resistance from the side.

FIG. 7B shows how the drive current of the steering assist motor 4 changes. In the electric power steering apparatus according to the present invention, when cutting or turning back is performed, the operations of steps 46 to 50 are performed according to the determination of step 43 or step 44, and the driving current I of the steering assist motor 4 is A correction current ΔI ₃ (= G ₃ × Δ) given as a differential term of the steering torque shown in FIG. 7A to the reference drive current I ₀ indicated by a broken line in FIG.
T) is added and set as shown by the solid line in FIG.

Therefore, the motor 4 has a gap steering angle α
_In this case, the drive current I is sharply increased in accordance with the rise of the steering torque generated at the time point when the drive current reaches _0, and the initial gap is quickly absorbed. As shown in FIG. 7 (a), as shown in FIG. 7 (a), it starts to decrease without reaching an excessive peak value, and promptly shifts to a steady change mode that gradually increases with an increase in the steering angle.

Therefore, the driver who operates the steering wheel 1 does not experience the feeling of "stuck" due to the sudden increase of the steering torque and the feeling of "disengagement" due to the rapid decrease of the steering torque when starting to cut or turn back. Thus, the steering operation can be performed under a good steering feeling.

In order to more remarkably improve the steering feeling by the addition of the correction current as described above, it is effective to filter the torque detected by the torque sensor 3 during the transition period after the above-described cutting or turning back. is there.

FIG. 8 is an explanatory diagram of the filtering process for the detected torque. FIG. 8 (a) shows how the actual detected torque changes during the transition period, and FIG. 8 (b) shows how the detected torque changes after the filtering process. As shown in FIG. 8B can be reduced as shown in FIG. 8B by a filtering process using a low-pass filter.

Accordingly, after such filter processing is determined to be cut out or turned back, the steering angle detection value becomes α ₀ + α _1.
The drive control unit 5 calculates the reference drive current I ₀ using a steering torque lower than the actual drive torque, and after reaching the gap steering angle α ₀ . The remaining peak of the drive current I of the motor 4 becomes smaller, and a better steering feeling can be obtained.

After the transition to the normal control, the filter processing is harmful because the actual steering torque is erroneously recognized, so that it is necessary to perform the filter processing only during the transition period. This is realized by adding a step for filtering before step 6 in FIG. 2, step 26 in FIG. 4, and step 46 in FIG.

[0069]

As described in detail above, in the electric power steering apparatus according to the first aspect of the present invention, the drive current of the steering assist motor is controlled after the cut-out or the return until the steering angle reaches a predetermined value. Since a transient period correction current is added to a reference current determined based on a detected value of the steering torque and set, a motor for steering assistance is absorbed so as to absorb an initial gap existing in a transmission system from the motor to the steering mechanism. Is driven in advance, and an unnatural steering feeling due to the influence of the initial gap is suppressed, and a good steering feeling can be obtained.

In the electric power steering apparatus according to the second aspect of the present invention, a transient period correction current which is constant until the angle corresponding to the initial gap is reached, and thereafter decreases at an appropriate rate is added. The transition from the preceding drive to the normal drive for absorbing the gap is smoothly performed, and a good steering feeling can be obtained.

In the electric power steering apparatus according to the third invention, the rate of change of the transition period correction current decreasing portion is set based on the differential value of the detection of the steering torque.
In the electric power steering apparatus according to the present invention, since the change rate is set based on the differential value of the detected steering angle, the transition from the preceding drive to the normal drive for absorbing the initial gap depends on the individual steering state. The steering operation is performed smoothly and a better steering feeling can be obtained.

Further, in the electric power steering apparatus according to the fifth aspect of the invention, since the transient period correction current is set according to the differential value of the detected torque, it is possible to respond steeply to the rise of the steering torque after absorbing the initial gap. Thus, an unnatural steering feeling due to the influence of the initial gap can be suppressed.

Further, in the electric power steering apparatus according to the sixth aspect of the present invention, the detected value of the steering torque obtained until the steering angle reaches the predetermined angle after the cut-out or the return is processed by the low-pass filter. The peak value of the steering torque generated after the absorption can be erroneously recognized as being lower than the actual value, and the drive current determined based on the detection result is suppressed to a lower value, thereby reducing the feeling of snagging experienced by the driver and reducing the steering The present invention has an excellent effect, for example, it is possible to alleviate the deterioration of the film.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating an example of an operation content of a drive control unit.

FIG. 3 is an explanatory diagram of an operation content when cutout or cutback is determined in the flowchart shown in FIG. 2;

FIG. 4 is a flowchart illustrating another example of the operation of the drive control unit.

FIG. 5 is an explanatory diagram of an operation content in a case where a cutout or a return is determined in the flowchart shown in FIG. 4;

FIG. 6 is a flowchart illustrating another example of the operation of the drive control unit.

FIG. 7 is an explanatory diagram of an operation content when cutout or cutback is determined in the flowchart shown in FIG. 6;

FIG. 8 is an explanatory diagram of a filtering process for a detected torque.

FIG. 9 is an explanatory diagram of a problem in a case where cutting or turning back is performed in a conventional electric power steering device.

[Explanation of symbols]

 Reference Signs List 1 steering wheel 2 steering mechanism 3 torque sensor 4 motor 5 drive control unit 6 vehicle speed sensor 20 pinion 21 rack shaft 50 rotation sensor 51 steering angle sensor 52 vehicle speed sensor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Motoo Nakai 3-5-8 Minamisenba, Chuo-ku, Osaka City, Osaka Prefecture Inside Koyo Seiko Co., Ltd. (72) Keisuke Izumaya 3-chome, Minamisenba, Chuo-ku, Osaka City, Osaka No. 8 F-term in Koyo Seiko Co., Ltd. (reference) 3D032 CC08 DA03 DA15 DA23 DA64 DC03 DC12 EB12 EC23 GG01 3D033 CA13 CA16 CA17 CA23

Claims (6)

[Claims] 1. A torque detecting means for detecting a steering torque applied to a steering wheel, a motor for applying a steering assist force to a steering mechanism, and a control unit for controlling a drive current of the motor based on the torque detected by the torque detecting means. An electric power steering apparatus comprising: a steering angle detection unit that detects an angle of steering performed by the operation of the steering mechanism; and a determination unit that determines whether to start steering from a neutral state or change a steering direction. The control unit, after the determination by the determination means, in a transition period until the steering angle detected by the steering angle detection means reaches a predetermined angle,
An electric power steering apparatus, wherein the drive current is set by adding a transient correction current to a reference current calculated based on the detected torque. 2. The transient period correction current has a constant value until the detected steering angle reaches a second angle smaller than the predetermined angle, and remains unchanged until the detected steering angle reaches the predetermined angle from the second angle. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus has a decreasing value that decreases from a constant value to zero. 3. The transient period correction current has a constant value until the detected steering angle reaches a second angle smaller than the predetermined angle, and remains unchanged until the detected steering angle reaches the predetermined angle from the second angle. 2. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus has a decreasing value that decreases at a change rate corresponding to a differential value of the detected torque. 4. The transient period correction current has a constant value until the detected steering angle reaches a second angle smaller than the predetermined angle, and the transient correction current remains constant until the detected steering angle reaches the predetermined angle from the second angle. 2. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus has a decreasing value that decreases at a change rate corresponding to a differential value of the detected steering angle. 5. The electric power steering apparatus according to claim 1, wherein the transient period correction current is set according to a differential value of the detected torque. 6. A low-pass filter that acts on the output of the torque detection means during a transition period after the determination by the determination means until the steering angle detected by the steering angle detection means reaches a predetermined angle. The electric power steering device according to any one of claims 1 to 5.