JP2006182051A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of precisely judging hand-releasing of a steering wheel and improving convergence of the steering wheel. <P>SOLUTION: This electric power steering device furnished with a torque sensor 4 to detect steering torque applied on the steering wheel 1 and a motor 5 to add steering auxiliary force to a steering mechanism 2 and driving and controlling the motor 5 so as to generate the steering auxiliary force corresponding to the detected steering torque, is furnished with a motor rotating acceleration detection means (motor speed assuming part 13c and differentiator 13i) to detect rotating acceleration of the motor 5, a hand-releasing judging part 20 to judge a hand-releasing state in accordance with the detected steering torque and the motor rotating acceleration, a road surface input detection means to detect road surface input transmitted to a vehicle from a tire and a hand-releasing control part 21 to control and drive the motor in a direction to cancel the road surface input in accordance with the detected road surface input when it is judged as the hand-releasing state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the technical field of an electric power steering apparatus that reduces a driver's steering force by a motor output.

In a conventional electric power steering device, it is determined that the steering wheel is released from the steering torque, and a return current proportional to the steering wheel angle is given to the motor to promote convergence to the steering wheel position where the vehicle goes straight (for example, patent Reference 1).
JP 2002-166843 A

  Normally, the steering torque sensor has a predetermined spring rigidity and is disposed between a handle and a motor having a predetermined inertia, so that the steering detected even when the hand is released due to the vibration of the mass-spring system. Torque is not zero. Therefore, in the above-described conventional technology for determining the release from the steering torque, there is a problem that the release cannot be accurately determined and the convergence to the steering wheel position where the vehicle goes straight is poor.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide an electric power steering device that can accurately determine the release of the steering wheel and can converge the steering wheel to a steering wheel position where the vehicle goes straight. There is to do.

In order to achieve the above-mentioned object, in the electric power steering apparatus of the present invention,
Torque detecting means for detecting steering torque applied to the steering wheel;
A motor for applying steering assist force to the steering mechanism,
In the electric power steering that drives and controls the motor so as to generate a steering assist force according to the detected steering torque,
Motor rotational acceleration detecting means for detecting rotational acceleration of the motor;
Hand release determination means for determining a handle release state based on the detected steering torque and motor rotational acceleration;
Road surface input detection means for detecting road surface input transmitted from the tire to the vehicle;
A release control means for controlling and driving the motor in a direction to cancel the road surface input according to the detected road surface input when it is determined that the handle is released
It is characterized by providing.

  In the present invention, since the handle release state is determined based on the steering torque and the motor rotational acceleration, the handle release state can be accurately determined. In addition, when it is determined that the handle is released, the motor is controlled so that the road load (road surface input) becomes zero, so that the handle is converged to the handle position where the road load is zero, that is, the handle position where the vehicle goes straight. be able to.

  Below, the best form for implementing the power steering device of the present invention is explained based on Examples 1-5.

First, the configuration will be described.
FIG. 1 is a block diagram illustrating a vehicle steering system to which the electric power steering apparatus according to the first embodiment is applied.

  A torque sensor (torque detection means) 4 for detecting a steering torque applied to the handle 1 and a steering assisting motor 5 on a steering shaft 3 that couples a steering handle 1 for steering operation and a steering mechanism 2 for performing a steering operation. Is arranged. The handle 1 is fixed so as to be rotatable around an axis so as to face the driver in a vehicle interior (not shown). The steering mechanism 2 is constituted by a rack and pinion type steering device including a pinion 6 integrally formed at the lower end of the steering shaft 3 and a rack shaft 7 meshing with the pinion 6. The rack shaft 7 is fixed to the front portion of the vehicle (not shown) so as to be slidable in the left-right direction, and both ends of the rack shaft 7 are connected to the front wheels 10 for steering via the left and right tie rods 8 and 9. , 11. The motor 5 that assists steering is coupled to the steering shaft 3 via a speed reducer 12 that converts the generated torque into rotational torque of the steering shaft 3.

Subsequently, a control block diagram of the controller 13 of FIG. 2 will be added to describe the control system of the first embodiment.
When the steering wheel 1 is steered by the driver, the front wheels 10 and 11 mechanically connected to the steering wheel 1 are steered. At this time, the torsional load input to the torque sensor 4 is input to the controller 13 as a steering torque. Further, a signal from a vehicle speed sensor (vehicle speed detection means) 14 for detecting the traveling speed of the vehicle is given to the controller 13.

  The controller 13 includes a motor terminal voltage sensor 13a for detecting the motor voltage, a motor current sensor (motor current detecting means) 13b for detecting the motor current, and a motor speed estimation for estimating the rotation speed of the motor 5 from the motor voltage and the motor current. Part (motor rotation speed detection means) 13c is built-in.

  The output of the controller 13 is given to the motor 5 through the current control circuit 13d and the drive circuit 13e. The controller 13 calculates the drive current of the motor 5 using the steering torque, the rotation speed of the motor, the vehicle speed, etc., and controls and drives the motor 5 while referring to the motor current by the motor current sensor 13b. To do. Power supplied from the drive circuit 13e to the motor 5 is provided by the battery 15.

  The basic current command value calculation unit 13f of the controller 13 determines a basic current command value for obtaining an assist amount corresponding to the steering torque in order to reduce the operation load on the driver. In addition, the amount of assist is increased so that the steering wheel 1 is lightly turned off during stationary driving, and the amount of assist is reduced at high speed so that the steering torque becomes heavier as the speed increases and a solid steering characteristic is realized.

  Furthermore, an inertia compensation unit 13g and a viscosity compensation unit 13h are provided in the controller 13 in order to eliminate the uncomfortable feeling peculiar to electric power steering.

  The inertia compensation unit 13g compensates for the inertia of the steering system, particularly the motor. By differentiating the motor rotation speed estimated from the back electromotive force of the motor 5 by the differentiator 13i, the motor rotation acceleration is calculated, and the calculated motor rotation acceleration and the motor inertia measured in advance are integrated. An inertial force of the motor 5 is obtained, and an inertia compensation current that cancels the inertia is output.

  The viscosity compensation unit 13h performs viscosity compensation that makes the steering system appropriate. Electric power steering aims to reproduce characteristics equivalent to hydraulic power steering, and calculates a viscosity compensation current such that the viscosity of the steering system calculated from the vehicle speed and the motor rotation speed matches the viscosity equivalent to the hydraulic circuit.

  The inertia compensation and the viscosity compensation may be general, and the gain may be changed according to the vehicle speed, the steering speed, etc. as in the conventional example.

  The inertia compensation current value calculated by the inertia compensation unit 13g and the viscosity compensation current value calculated by the viscosity compensation unit 13h are added by the adder 13j, and then calculated by the basic current command value calculation unit 13f by the adder 13k. Is added to the basic current command value.

  The controller 13 includes a hand release determination unit (hand release determination unit) 20 and a hand release control unit (hand release control unit) 21. The hand release determination unit 20 differentiates the motor rotation speed calculated using the output from the torque sensor 4 and the back electromotive force of the motor 5 by the differentiator 13i, and the motor rotation acceleration compensated by the inertia compensation unit 13g. Is input, and the release torque is determined by processing the steering torque and the motor rotation acceleration, and the FLG signal indicating whether the release is in effect or not is output. The output FLG signal is input to the switch (SW) unit 13m. In the first embodiment, the motor speed estimation unit 13c and the differentiator 13i constitute a motor rotational acceleration detection unit.

  Based on the FLG signal, the SW unit 13m performs normal control using the output of the adder 13j as a current command value, or performs control during release using the output of the release control unit 21 described later as a current command value. Switch between.

  The hand release control unit 21 receives an output from the torque sensor 4, a motor rotation speed calculated using the back electromotive force of the motor 5, an output from the motor current sensor 13 b, and an output from the vehicle speed sensor 14. By processing the sensor signal, the current command value at the time of letting go is determined.

Next, the operation will be described.
[How to decide to let go]
As a model of the steering system, consider the steering wheel inertia Jh, the inertia Jm of the system closer to the road surface than the torque sensors such as the motor 5, the speed reducer 12, and the rack, and the rigidity ks of the torque sensor 4 that couples both.

Assuming that the steering torque Th and the steering wheel angle θh as the operation amount from the driver, the motor angle θm obtained by converting the rotation angle of the motor 5 into the steering axis, and the steering torque Ts detected by the torque sensor 4, the following equation (1) is established. At this time, it is determined that the hand is released.
α> Jh · (dot (dot (Ts)) / ks + ks · dot (dot (θm))) + Ts… (1)
Here, α is a predetermined value.

In the steering system model, the equation of motion around the steering wheel is expressed by the following equation (2).
Th = Jh · dot (dot (θh)) + ks · (θh − θm) (2)

In the equation (1), when letting go, Th becomes zero, so the equation of motion around the handle in the ideal state is the following equation (3).
0 = Jh · dot (dot (θh)) + ks · (θh − θm) (3)

In this equation (3), ks · (θh − θm) corresponds to the detected torque value Ts of the torque sensor 4. Therefore, in order to determine that it is let go in equation (3), calculate dot (dot (θh)) Just do it.
Ts = ks · (θh − θm) (4)

Therefore, the following equation (5) is obtained by differentiating both sides from the equation (4) of the detected torque value of the torque sensor 4.
dot (dot (Ts)) = ks ・ (dot (dot (θh)) − dot (dot (θm))) (5)

When transforming equation (5),
dot (dot (θh)) = dot (dot (Ts)) / ks + ks · dot (dot (θm))… (6)
Thus, when the equation (6) is substituted into the equation (3), the above equation (1) is obtained.

[Releasing action]
FIG. 3 is a block diagram illustrating the operation of the hand release determination unit 20 according to the first embodiment.
The torque sensor signal input to the release determination unit 20 is second-order differentiated by the two differentiation blocks 20a and 20b, and then the inverse 1 / ks of the torque sensor rigidity is accumulated by the gain block 20c having the gain 1 / ks. . The motor rotation speed is first-order differentiated by the differentiation block 20d, and then converted into a motor rotation acceleration to the steering shaft 3 by a gain block 20e having a gain 1 / N and a gain block 20f having a gain ks. The gear ratio is converted.

  The outputs of both gain blocks 20c and 20f are added by the addition block 20g, and then the handle inertia Jh is integrated by the gain block 20h having the gain Jh. The output of the gain block 20h is added to the torque sensor signal by the addition block 20i, and the right side of the above equation (1) is calculated. Subsequently, the absolute value is calculated by the absolute value calculation block 20j, and is compared with the predetermined value α by the comparison block 20k. When the absolute value is smaller than α, it is determined that the hand is in the released state, and the hand released FLG is output.

  Here, if the calculated value (the output of the addition block 20i) is zero, it is theoretically completely released, but for example, it is natural that the driver touches the handle 1 after inputting a predetermined handle angle. In the steering pattern in which the steering wheel 1 is returned to the steering wheel, the steering torque is slightly generated. Even in that case, in order to realize the stability improvement by this control, it is desirable that the judgment value which is the left side of the equation (1) is not zero but a predetermined α. In addition, it is possible to prevent malfunction due to noise included in various sensor signals.

[Road surface input estimation]
FIG. 4 is a block diagram of the hand release control unit 21 that determines the current command value when it is determined that the hand is released. In FIG. 4, the road surface input is estimated as follows.

Torque sensor 4 signals are steering torque Ts (known), road surface input torque Tsat (unknown disturbance), steering system inertia Jm (originally Jh + Jm, but Jh is very small compared to Jm and can be approximated), motor If the torque constant Kt of 5 (steering shaft conversion), motor generated torque Tm = Kt · im (steering shaft conversion), motor current im, and motor angular velocity ω, the equation of motion is the following equation (7).
Jm · dot (ω) = Ts + Tm + Tsat (7)

Here, in the state where Ts and Tsat equivalent to disturbance are not input to the plant,
Jm · dot (ω) = Tm = Kt · im… (8)
When this equation (8) is expressed by a transfer function, s is a Laplace operator,
ω / im = Kt / (Jm · s ² ) = P (s) (9)
In addition, the low-pass filter for disturbance removal, ωc is the cutoff frequency,
H (s) = ωc ² / (s + ωc ² )… (10)
And

  If a controller is configured around the plant as shown in FIG. 4 in this state, the estimated road surface input torque is calculated from (1) in FIG. 4 (corresponding to road surface input detection means). By supplying a motor current so as to cancel the road surface input with respect to the calculated road surface input torque, the stability at the time of releasing is ensured.

[Current command value characteristics when letting go]
As an example of the current command value when letting go, it is the simplest that the motor current flows in the direction to cancel the road surface input, and the amount is proportional to the road surface input. Therefore, when the road surface input is in the dead zone, the current command value to the motor 5 is set to zero.

  Further, in the first embodiment, when the detected road surface input exceeds a predetermined limit value, a limiter is provided for the current command value in order to prevent the release control current from flowing and the handle 1 from returning. Furthermore, the stability of letting go worse as the vehicle speed increases, so the handing-off control current is a function of the vehicle speed, and the current command value is increased as the vehicle speed increases.

[Prior art issues]
The electric power steering device takes a long time to release the hand and stabilizes the vehicle after inputting a predetermined handle angle during traveling due to the inertia of the motor and the friction of the motor and the speed reducer. Is repeated many times (the stability of letting go or the convergence is poor).

  In response to the above problem, in the technique described in Japanese Patent Laid-Open No. 8-332964, when the steering speed is high in the steering wheel returning process, it is determined that the hand is released, and damping is performed in proportion to the steering speed, thereby overshooting left and right. Suppressed. However, in this configuration, there is a problem that the steering torque becomes unnecessarily heavy because it is determined that the person has let go and the damping is added even when the person steers quickly.

  In the technique described in Japanese Patent Application Laid-Open No. 2002-166843, when the steering torque is small, it is determined that the steering torque is released, and a return current proportional to the steering wheel angle is supplied to promote convergence to neutrality. However, in this configuration, the steering torque sensor has a predetermined spring rigidity and is disposed between the handle and the motor having a predetermined inertia. Therefore, even when it is released, it is detected even when it is released due to the vibration of the mass-spring system. The torque that is generated is not zero, and it is impossible to accurately determine whether to let go. Furthermore, there is a problem in that the vehicle does not go straight when a shift between the neutral of the handle angle sensor and the straight steering wheel position of the vehicle occurs due to the difference between the left and right pneumatic pressures of the tires and the dispersion of the suspension.

[Road surface input estimation effect]
On the other hand, in the electric power steering apparatus of the first embodiment, the detected value of the torque sensor 4 and the rotational acceleration of the motor 5 are used. That is, the steering torque and the motor rotation speed are measured, and when the second-order differential between the two is smaller than the predetermined value α, it is determined that the release is allowed, so that accurate release determination can be made.

[Handle convergence improvement based on road surface input]
When the hand is released, the vibration force that vibrates the steering system is a road surface input, and the steering angle is delayed with respect to the vibration force due to the predetermined rigidity of the torque sensor 4 in the steering system. Therefore, when the release control current is determined so that the handle angle becomes zero as in the conventional example, there is an upper limit of the gain of the release current due to the delay, and as a result, the convergence time of the release tends to be long. become.

  FIG. 5 shows a time-series transition of the handle angle at the time of letting go of Example 1 and a time-series transition of the road surface input. In the first embodiment, the control input is determined so that the road surface input, which is the vibration generation force, becomes zero, and the control current is determined. Therefore, there is no delay, and the gain can be increased as compared with the conventional technique in which the steering wheel angle is zero. Yes, it is possible to shorten the time for convergence.

Next, the effect will be described.
In the electric power steering apparatus of the first embodiment, the effects listed below can be obtained.

  (1) A torque sensor 4 for detecting a steering torque applied to the steering wheel 1 and a motor 5 for applying a steering assisting force to the steering mechanism 2 are provided, and the motor generates a steering assisting force corresponding to the detected steering torque. In the electric power steering for driving and controlling the motor 5, the motor rotational acceleration detecting means (the motor speed estimating unit 13c and the differentiator 13i) for detecting the rotational acceleration of the motor 5 and releasing the handle based on the detected steering torque and the motor rotational acceleration. In the direction to cancel the road surface input according to the detected road surface input when it is determined that the hand release determining unit 20 for determining the state, the road surface input detecting means for detecting the road surface input transmitted from the tire to the vehicle, and the handle released state And a hand release control unit 21 for controlling and driving the motor 5, so that the state of the handle release can be accurately determined, and the vehicle The handle 1 can be converged to the position of the handle where the straight travels straight.

  (2) The hand release determining unit 20 is in the state of releasing the handle when the motor rotational acceleration dot (dot (θm))) obtained by converting the detected motor rotational acceleration into the steering axis and the steering torque Ts satisfy the expression (1). Since it is determined that there is a handle, it is possible to more accurately determine the handle release state.

  (3) A motor speed estimation unit 13c for detecting the rotation speed of the motor 5 and a motor current sensor 13b for detecting the current value of the motor 5 are provided, and the road surface input detection means includes the motor rotation speed, the steering torque, and the motor current. Therefore, the road surface input can be accurately estimated without providing a means for directly detecting the road surface input.

  (4) The vehicle speed sensor 12 that detects the vehicle speed is provided, and the hand release control unit 21 increases the current command value of the motor 5 as the vehicle speed increases. Therefore, the hand release stability can be improved regardless of the vehicle speed.

  (5) The release control unit 21 sets the range where the detected road surface input is equal to or less than a predetermined dead zone threshold value as the dead zone, and sets the current command value of the motor 5 to zero when the road surface input is in the dead zone area. It is possible to reduce malfunction of the motor 5 due to the influence of sensor noise or the like.

  (6) When the detected road surface input exceeds a predetermined limit value, the release control unit 21 keeps the current command value of the motor 5 constant, so that the current command value becomes excessive and the handle 1 is difficult to converge. Can be prevented.

First, the configuration will be described.
FIG. 6 is a block diagram illustrating a vehicle steering system to which the electric power steering apparatus according to the second embodiment is applied. In the second embodiment, an encoder 16 that measures the rotation angle of the motor is attached to the motor 5. Further, the second embodiment is different from the first embodiment in that a handle angle sensor 17 for measuring the rotation angle of the handle 1 is attached to the steering shaft 3.

  FIG. 7 shows a control block of the controller 19 of the second embodiment. The release control unit 22 includes an output from the torque sensor 4, a motor rotational acceleration obtained by second-order differentiation of the output of the encoder 16 using the two differentiators 13m and 13i, and the output of the handle angle sensor 17 as a differentiator 13n, A handle release determination is performed by processing the handle rotational acceleration obtained by second-order differentiation using 13p. In the second embodiment, the encoder 16 and the two differentiators 13m and 13i constitute a motor rotational acceleration detection means.

  The release control unit 23 receives the motor rotation acceleration obtained by second-order differentiation of the output from the torque sensor 4 and the output of the encoder 16, the output from the motor current sensor 13b, and the output from the vehicle speed sensor 12, and receives various sensor signals. Is processed to determine the current command value when the hand is released.

Next, the operation will be described.
[How to decide to let go]
FIG. 8 is a block diagram for explaining the operation of the hand release determination unit 22 according to the second embodiment, in which, instead of the motor rotation speed, the motor rotation angle detected by the encoder 16 is differentiated by the differentiation block 23a. Different from Example 1 shown in FIG.

[Road surface input estimation]
In the second embodiment, the road surface input is estimated as follows. The input from the road surface is Tsat determined by the tire angle, the vehicle behavior, the road surface μ, and the like. Further, let Tm be the torque that the motor 5 is taking out. Since the stiffness from the motor 5 to the tire is much higher than the stiffness of the torque sensor 4, the equation of motion around the tire is ignored and becomes the following equation (11).
Tsat = Jm · dot (dot (θm)) + Tm + Ts (11)

  Therefore, since the second-order differential value of the measured value of the motor rotation angle and the motor torque coincide with the product of the torque constant of the motor 5 and the motor current, the road surface input is estimated from the motor current value and the detected value of the torque sensor 4. It becomes possible. Alternatively, Tsat may be measured directly.

  Tsat is a value determined by the vehicle behavior and the tire angle, but it is always zero when the vehicle is traveling straight on the road surface. Therefore, by controlling and driving the motor 5 so that the detected or estimated road surface input becomes zero, it is possible to improve hand-off stability and to achieve straight traveling of the vehicle during convergence.

  Therefore, in the electric power steering apparatus of the second embodiment, the same effects as the effects (1) to (6) of the first embodiment can be obtained.

  FIG. 9 is a block diagram illustrating a vehicle steering system to which the electric power steering apparatus according to the third embodiment is applied. In the third embodiment, a rack axial force sensor 18 that measures rack axial force is steered as road surface input detection means. It differs from the first embodiment in that it is attached to the take-off mechanism 2.

FIG. 10 shows a control block of the controller 24 of the third embodiment.
A signal from the rack axial force sensor 19 is input to the hand release control unit 25. In the hand release assist control, the motor 5 is controlled and driven so that the rack axial force becomes zero. FIG. 11 shows a control rule when the hand is released in the third embodiment, and since the contents are the same as those in the first embodiment, the description thereof is omitted.

  Therefore, in the electric power steering apparatus of the third embodiment, the rack axial force sensor 18 for measuring the rack axial force is provided as the road surface input detecting means, and therefore the effects (1), (2), (4 In addition to (6) to (6), the road surface input can be obtained more accurately as compared with the first embodiment in which the road surface input is estimated from the motor rotation speed, the steering torque and the motor current.

  FIG. 12 is a diagram illustrating a control rule when the hand is released according to the fourth embodiment. In the fourth embodiment, the current command value of the motor 5 with respect to the road surface input when the hand is released depends on the motor rotation speed, that is, the rotation speed of the handle 1. It is an example to change. Other configurations are the same as those of the first embodiment.

  In the fourth embodiment, as shown in FIG. 12, by increasing the current command value as the motor speed increases, it is possible to effectively improve the release stability of the vehicle when the motor rotation is fast in the release state. .

Next, the effect will be described.
In the electric power steering apparatus of the fourth embodiment, the following effects can be obtained in addition to the effects (1) to (3), (5), and (6) of the first embodiment.

  (7) The motor speed estimation unit 13c for detecting the rotation speed of the motor 5 is provided, and the hand release control unit increases the current command value of the motor 5 as the motor rotation speed is higher, so that the rotation speed of the handle 1 is faster. In addition, it is possible to effectively improve the release stability of the vehicle.

First, the configuration will be described.
FIG. 13 is a control block diagram of the controller 28 according to the fifth embodiment.
The hand release determining unit 26 receives an output from the torque sensor 4 and a motor rotational acceleration calculated by using the back electromotive force of the motor 5, and performs a hand release determination by processing the steering torque and the motor rotational acceleration. The estimated driver torque is output.

  The hand release control unit 27 receives an output from the torque sensor 4, a motor rotation speed calculated using the back electromotive force of the motor 5, an output from the motor current sensor 13 b, and an output from the vehicle speed sensor 14. By processing the sensor signal, the basic current command value when released is determined.

  The estimated driver torque and the basic current command value are output to the correction unit 13q. The correction unit 13q determines the current command value when the hand is released by correcting the basic current command value using the estimated driver torque.

Next, the operation will be described.
[Releasing action]
FIG. 14 is a block diagram illustrating the operation of the hand release determination unit 26 according to the fifth embodiment, and the output of the addition block 20i is output as the estimated driver torque. Further, if the calculated estimated driver torque is equal to or less than the minimum torque value β that is generated when steering by the driver's will, it is determined that the hand 1 is lightly attached to the handle 1 only when it is completely released. Then, let go FLG is generated.

[Current command value reduction action according to estimated driver torque]
FIG. 15 is a diagram illustrating a method for calculating a current command value when the correction unit 13q is released.
The correction unit 13q corrects the basic current command value with respect to the estimated driver torque using a predetermined gain map 26a.

  The gain map 26a is a substantially constant value in a range where the estimated driver torque is smaller than a predetermined value γ determined by the estimation accuracy caused by a sensor error or the like. Thereby, in the case of complete release, that is, when the estimated driver torque is zero, it is possible to maximize the assist amount when releasing and improve the convergence of the vehicle and the steering wheel 1.

  Further, in the gain map 26a, as the estimated driver torque becomes larger than the predetermined γ, the gain decreases, and the gain becomes zero above the torque minimum value β generated when steering by the driver's intention.

  That is, as the estimated driver torque increases, the gain is reduced to reduce the amount of assist during hand release control, and the steering wheel return speed is almost the same when letting go and when lightly attached. It becomes possible. That is, regardless of whether or not the hand is attached to the steering wheel 1, the discomfort given to the driver can be suppressed by setting the steering wheel returning speed to be substantially constant.

  In addition, when the driver operates the steering wheel with intention (when the estimated driver torque exceeds β), it is possible to reliably return to the normal control, which affects the feeling during steering. There is no.

  Here, the value of β is determined by the characteristics of the vehicle and the steering system. Generally, the steering wheel 1 has friction caused by the steering system. In addition, in a steering system as an input device for controlling the vehicle, the vehicle moves simply in proportion to the steering amount in a range of minute operation amount so that the vehicle does not move in response to an unconscious human operation. It is said that it is better to set a dead zone so that there is no dead zone. Since the friction and dead zone correspond to seasoning of the vehicle, a target value is set for each vehicle and tuning is performed. Therefore, the torque β is determined in consideration of these points.

  As described above, in the fifth embodiment, by setting the assist amount for canceling the appropriate road surface input in the completely released state and in the state where the hand is lightly attached to the handle 1, Since it is not necessary to consider the steering feeling of the person, the amount of assist can be increased and the convergence time of the vehicle can be shortened. On the other hand, even when the hand is lightly attached, by making the convergence of the vehicle almost the same as in the completely released state, the uncomfortable feeling given to the driver can be suppressed.

Next, the effect will be described.
In the electric power steering apparatus according to the fifth embodiment, the following effects can be obtained in addition to the effects (1) to (6) of the first embodiment.

  (8) The release control unit 26 calculates the estimated driver torque based on the detected steering torque and motor rotation acceleration, and the release control unit 27 determines the current command value of the motor 5 as the estimated driver torque increases. In order to reduce the size, the return speed of the handle 1 can be made substantially constant regardless of whether the hand is completely released or the hand 1 is lightly attached to the handle 1, thereby preventing the driver from feeling uncomfortable.

  (9) The hand release control unit 27 sets the current command value of the motor 5 to zero when the estimated driver torque is equal to or greater than the estimated torque β generated when steering by the driver's will. When the vehicle is steered, the normal control can be surely restored, and the influence on the steering feeling can be suppressed.

(Other examples)
As mentioned above, although the best form which implements this invention was demonstrated based on Examples 1-5, the concrete structure of this invention is not limited to an Example, The range which does not deviate from the summary of invention. Any design change is included in the present invention.

  For example, in the first embodiment, the motor rotational speed estimated from the inter-terminal voltage of the motor 5 and the motor current is first-order differentiated to calculate the motor rotational acceleration, and in the second embodiment, the handle angle is second-order differentiated to obtain the motor. Although the rotational acceleration is calculated, the method for calculating the motor rotational acceleration is arbitrary. A tachometer for measuring the rotational speed of the motor may be provided, and the output thereof may be first-order differentiated.

It is a block diagram which shows the steering system of the vehicle to which the power steering apparatus of Example 1 is applied. FIG. 3 is a control block diagram of a controller 13 according to the first embodiment. It is a block diagram explaining the action | operation of the hand release judgment part 20 of Example 1. FIG. It is a block diagram explaining the action | operation of the hand release control part 21 of Example 1. FIG. It is a time series transition of the steering wheel angle at the time of letting go of Example 1, and a time series transition of road surface input. It is a block diagram which shows the steering system of the vehicle to which the electric power steering apparatus of Example 2 is applied. FIG. 6 is a control block diagram of a controller 19 according to a second embodiment. It is a block diagram explaining the action | operation of the hand release judgment part 22 of Example 2. FIG. FIG. 10 is a block diagram illustrating a vehicle steering system to which an electric power steering apparatus according to a third embodiment is applied. FIG. 10 is a control block diagram of a controller 24 according to a third embodiment. It is a figure which shows the hand release control law of Example 3. FIG. It is a figure which shows the control law at the time of hand release of Example 4. FIG. FIG. 10 is a control block diagram of a controller according to a fifth embodiment. It is a block diagram explaining the action | operation of the hand release judgment part 26 of Example 5. FIG. It is a figure which shows the electric current command value calculation method at the time of releasing in the correction | amendment part 13q.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Handle 2 Steering mechanism 3 Steering shaft 4 Torque sensor 5 Motor 6 Pinion 7 Rack 8, 9 Tie rod 10, 11 Front wheel 12 Reduction gear 13 Control unit 13a Voltage sensor 13b Current sensor 13c Motor speed estimation part 13d Current drive circuit 13e Drive circuit 13f Basic current command value calculation unit 13g Inertia compensation unit 13h Viscosity compensation unit 13i Differentiator 13j Adder 13k Adder 13m Switch unit 14 Vehicle speed sensor 15 Battery

Claims (9)

Torque detecting means for detecting steering torque applied to the steering wheel;
A motor for applying steering assist force to the steering mechanism,
In the electric power steering that drives and controls the motor so as to generate a steering assist force according to the detected steering torque,
Motor rotational acceleration detecting means for detecting rotational acceleration of the motor;
Hand release determination means for determining a handle release state based on the detected steering torque and motor rotational acceleration;
Road surface input detection means for detecting road surface input transmitted from the tire to the vehicle;
A release control means for controlling and driving the motor in a direction to cancel the road surface input according to the detected road surface input when it is determined that the handle is released
An electric power steering apparatus comprising: The electric power steering apparatus according to claim 1, wherein
The hand release determining means is configured such that a motor rotation acceleration dot (dot (θm)) obtained by converting the detected motor rotation acceleration into a steering axis and a steering torque Ts are expressed by the following formula: α> Jh · (dot (dot (Ts)) / ks + Ks · dot (dot (θm))) + Ts
(Where α is a predetermined value, Jh is the inertia of the handle, (dot (dot (Ts)) is the second-order differential value of Ts, and ks is the rigidity of the torque detection means.)
When the electric power steering apparatus is satisfied, the electric power steering apparatus is determined to be in a state in which the handle is released. In the electric power steering apparatus according to claim 1 or 2,
Motor rotation speed detection means for detecting the rotation speed of the motor;
Motor current detecting means for detecting a current value of the motor;
With
The electric power steering apparatus characterized in that the road surface input detecting means estimates a road surface input based on a motor rotation speed, a steering torque, and a motor current. In the electric power steering device according to any one of claims 1 to 3,
Vehicle speed detection means for detecting the vehicle speed,
The electric power steering apparatus characterized in that the hand release control means increases the current command value of the motor as the vehicle speed increases. The electric power steering apparatus according to any one of claims 1 to 4,
The release control means sets a range in which the detected road surface input is equal to or less than a predetermined dead zone threshold value as a dead zone, and sets the current command value of the motor to zero when the road surface input is in the dead zone area. Power steering device. The electric power steering apparatus according to any one of claims 1 to 5,
The electric power steering apparatus characterized in that the hand release control means makes the current command value of the motor constant when the detected road surface input exceeds a predetermined limit value. The electric power steering apparatus according to any one of claims 1 to 6,
A handle rotation speed detecting means for detecting the rotation speed of the handle;
The electric power steering apparatus characterized in that the hand release control means increases the current command value of the motor as the steering wheel rotational speed is higher. The electric power steering apparatus according to any one of claims 1 to 7,
The hand release determining means estimates the driver torque based on the detected steering torque and motor rotational acceleration,
The electric power steering apparatus according to claim 1, wherein the release control means decreases the current command value of the motor as the estimated driver torque increases. The electric power steering apparatus according to claim 8,
The electric power steering apparatus characterized in that the release control means sets the current command value of the motor to zero when the estimated driver torque is equal to or greater than a minimum torque value generated when steering is performed by the driver's will. .

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