JPH05213222A - Handle restoration control device for electric power steering device - Google Patents

Abstract

PURPOSE:To perform return operation of a handle at a constant feeling by a driver regardless of the magnitude of a road surface friction factor. CONSTITUTION:A torque sensor 31 detects torque exerted on a steering shaft 12 and an steering angle sensor 32 detects the steering angle of a handle 11. A microcomputer 33 decides reference self-aligning torque based on a detected steering angle. By comparing the reference self-aligning torque with detected torque (representing actual self-aligning torque from a road surface), the magnitude of a road surface friction factor is decide. When the road surface friction factor is low, output torque of an electric motor is widely controlled based on a decided result, and when the factor is high, the output torque is controlled in a narrow range. When the road surface friction factor is low and self-aligning torque exerted on a steering shaft is small, an assist force of an electric motor 22 to perform return operation of a handle is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device for transmitting the rotation of an electric motor to a steering mechanism via a transmission mechanism to assist the turning operation of a steering wheel.
In particular, the present invention relates to a steering wheel restoration control device for an electric power steering device that rotates an electric motor in a direction in which the steering wheel is returned to the neutral position when the steering wheel is returned to the neutral position.

[0002]

2. Description of the Related Art Conventionally, an apparatus of this type is disclosed in, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent Laid-Open No. 175569, a friction coefficient between a traveling road surface and a tire (hereinafter, simply referred to as road surface friction coefficient) is detected by utilizing a rotational speed difference between a driving wheel and a driven wheel, and If the detected road surface friction coefficient is large, when returning the steering wheel to the neutral position, a control signal for generating a large output torque in the direction of returning the steering wheel to the neutral position is output to the motor. I have to. If the detected road surface friction coefficient is small,
A control signal for causing the electric motor to generate a small output torque is output to the motor. With this, if the road surface friction coefficient is large, the steering wheel is returned to the neutral position with a large assist force, and if the road surface friction coefficient is small, the steering wheel is returned to the neutral position with a small assist force. We are taking measures to prevent the return speed of the steering wheel in the vehicle from becoming too high.

[0003]

Generally, when the road surface friction coefficient is small, the self-aligning torque received by the tire of the steered steering wheel from the road surface is larger than that when the road surface friction coefficient is large. It is small, and the restoring force that the steering wheel receives from the road surface is small. However, in the above-described conventional device, when the road surface friction coefficient is small, the assisting force by the electric motor is made small. Therefore, when the road surface friction coefficient is large, the handle returning operation is felt lightly. When the coefficient of friction is small, the steering wheel returning operation is felt to be heavy, and the steering feeling in both cases is different. Therefore, the driver feels uncomfortable in the steering wheel returning operation. The present invention has been made to address the above problems, and an object of the present invention is to provide an electric power steering device that enables a driver to return a steering wheel with an equivalent steering feeling regardless of whether the road surface friction coefficient is large or small. To provide a handle restoration control device.

[0004]

In order to achieve the above object, a structural feature of the present invention is that an electric motor whose output torque is controlled by an input control signal is provided, and a steering shaft is used for turning a steering wheel. It is applied to an electric power steering device that applies the rotational driving force of an electric motor to assist the turning operation of the steering wheel, and transmits it to the steering wheel by steering to the steering wheel. In the steering wheel restoration control device that outputs a control signal to the electric motor to return the steering wheel to the neutral position when the steering wheel is returned, the torque sensor that detects the torque acting on the steering shaft and the steering angle of the steering wheel. And a reference self that determines a reference self-aligning torque that has a predetermined relationship with the steering angle based on the detected steering angle. Output torque of the electric motor when the detected torque is smaller than that when the detected torque is small by judging the magnitude of the detected torque based on the determined reference self-aligning torque. And a control signal output means for outputting a control signal for largely controlling the electric motor to the electric motor.

[0005]

In the present invention constructed as described above, the torque sensor detects the torque acting on the steering shaft. In this case, if the steering wheel is returned to the neutral position, the self-aligning torque that the tire of the steered wheel receives from the road surface acts on the steering shaft, and the detected torque represents the actual self-aligning torque. Become. On the other hand, if the road surface friction coefficient is set to a predetermined value (for example, the road surface friction coefficient value corresponding to a dry road), there is a predetermined relationship between the self-aligning torque and the steering angle of the steered wheels, The reference self-aligning torque determination means estimates the reference self-aligning torque based on the steering angle of the steering wheel detected by the steering angle sensor using the above relationship. Then, the control signal output means determines the magnitude of the detected torque on the basis of the determined reference self-aligning torque, and controls the magnitude of the output torque of the electric motor based on the determination result.

In this case, if the road surface friction coefficient is large, the actual self-aligning torque that the steered wheels receive from the road surface is large, and it is determined that the detected torque based on the reference self-aligning torque is large. The signal output means controls the output torque of the electric motor to be small.
If the road surface friction coefficient is small, the actual self-aligning torque that the steered wheels receive from the road surface is small, and it is determined that the detected torque based on the reference self-aligning torque is small. Greatly controls the output torque of the electric motor. Therefore, even if the road surface friction coefficient is small and the self-aligning torque that the steered wheel receives from the road surface is small, the same restoring force as when the road surface friction coefficient is large acts on the steering wheel, and the road surface friction coefficient is small. Even if it is large, the steering wheel return operation will be assisted so that the force is equivalent.

As a result, according to the present invention, the driver can always return the steering wheel with the same steering feeling regardless of the road friction coefficient of the traveling road surface.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows an electric power steering apparatus for a vehicle according to the present invention.

In this power steering system,
The steering wheel 11 is connected to front wheels 17a and 17b as steering wheels via a steering mechanism including a steering shaft 12, a pinion 13, a rack bar 14, tie rods 15a and 15b, and knuckle arms 16a and 16b. Steering shaft 12
A large gear 21 is fixed to an intermediate portion of the gear 2
A small gear 23 fixed to a rotating shaft 22 a of an electric motor 22 is meshed with the gear 1. The large gear 21 and the small gear 23 form a transmission mechanism that decelerates and transmits the rotation of the electric motor 22 to the steering shaft 12. The electric motor 22 is composed of a brushless motor or the like whose rotation direction and output torque are controlled by an input control signal.

A torque sensor 31 is provided at an intermediate portion of the steering shaft 12.
Is attached to the electric motor 22, and the steering angle sensor 32 is attached to the electric motor 22.
Is assembled. The torque sensor 31 is composed of a strain gauge, detects the steering torque Ts acting on the steering shaft 12, and outputs a detection signal representing the torque Ts. The steering angle sensor 32 is composed of a rotation angle sensor, and detects the steering angle θs of the steering wheel 11 (and the steering angles of the front wheels 17a and 17b) by measuring the rotation angle of the rotating shaft of the electric motor 22 to detect the steering angle. The detection signal that expresses θs is output. The steering torque Ts and the steering angle θs represent positive rotation of the steering wheel 11 in the right direction and negative rotation of the steering wheel 11 in the left direction.

The torque sensor 31 and the steering angle sensor 32 are connected to a microcomputer 33, and a vehicle speed sensor 34 is also connected to the computer 33. The microcomputer 33 is a CPU, RO
It is composed of M, RAM, I / O, etc., and controls the rotation of the electric motor 22 by executing a program corresponding to the flowchart shown in FIG. Further, in the ROM of the microcomputer 33, the assist torque Ta, the first vehicle speed coefficient Kv1, the return torque Tr, the second vehicle speed coefficient Kv2, and the reference self-aligning torque Tsa which change with the characteristics shown in FIGS. It is stored in the form of a map. The vehicle speed sensor 34 detects the vehicle speed V and outputs a detection signal indicating the vehicle speed V.

Next, the operation of the embodiment configured as described above will be described. When the ignition switch (not shown) is turned on, the microcomputer 33 starts executing the program in step 40 of FIG.
The circulation processing consisting of 48 to 51 to 57 is repeatedly executed. In this circulation processing, in step 41, the steering torque Ts, the steering angle θs, and the vehicle speed V are read from the torque sensor 31, the steering angle sensor 32, and the vehicle speed sensor 34, and in step 42, the steering angle θs is differentiated (dθs / d
The steering angular velocity θm is calculated by performing t), and it is determined in steps 43 and 44 whether the steering wheel 11 is in the returning state.

In this case, the fact that the handle 11 is returned to the neutral position is determined by the following conditions corresponding to the respective processes of steps 43 and 44. The steering angle θs indicates that the steering wheel 11 is in the right rotation position with respect to the neutral position (θs> 0), and the steering wheel 11 is
The steering speed .theta.m represents that the vehicle has not moved to the right (.theta.m.ltoreq.0). The steering angle θs indicates that the steering wheel 11 is in the left rotation position with respect to the neutral position (θs <0), and the steering wheel 11 is
Is not moving to the left as indicated by the steering speed θm (θm ≧ 0).

If the steering wheel 11 is not in the return state, that is, if the front wheels 17a and 17b are being steered to the left and right, it is determined to be "NO" in both steps 43 and 44, and in step 45, A map of the assist torque Ta (see FIG. 3) is referred to on the basis of the detected steering torque Ts to determine the assist torque Ta corresponding to the steering torque Ts, and at step 46, the first vehicle speed coefficient is determined based on the vehicle speed V. The first vehicle speed coefficient Kv1 corresponding to the vehicle speed V is determined by referring to the map of Kv1 (see FIG. 4).
Next, in step 47, the assist torque T determined above is determined.
The output torque value T0 (= Kv1 · Ta) is calculated by multiplying a by the determined first vehicle speed coefficient Kv1. Then, in step 48, the calculated output torque value T0 is obtained.
Is output to the electric motor 22. The electric motor 22 rotates under the control of the control signal, the rotation direction thereof corresponds to the positive or negative of the output torque value T0, and the magnitude of the output torque is the output torque value T0.
Corresponding to the absolute value | T0 |

In this case, as is apparent from FIG. 3, the steering wheel 11 is rotated rightward (or leftward) so that the steering torque Ts in the rightward rotation direction (or leftward rotation direction) acts on the steering shaft 12. For example, the assist torque Ta becomes positive (or negative), and the absolute value | Ta | of the torque Ta increases as the absolute value | Ts | of the steering torque Ts increases. On the other hand, at this time, the first vehicle speed coefficient Kv1 becomes smaller as the vehicle speed V increases. Therefore, these values T
The electric motor 22 controlled by the control signal corresponding to the output torque value T0 multiplied by a, Kv1 moves the steering shaft 21 in the turning direction of the steering wheel 11 and the absolute value | Ts of the steering torque Ts.
The larger the |, the larger the rotation speed V, and the larger the vehicle speed V, the smaller the drive torque. As a result, the turning operation of the steering wheel 11 is always appropriately assisted according to the operating force, the turning operation becomes light when the vehicle runs at low speed, and the turning operation becomes moderately heavy when the vehicle runs at high speed. As a result, the straightness of the front wheels 17a, 17b is increased, and the running stability of the vehicle is improved.

On the other hand, if the handle 11 is in the returned state,
It is determined to be “YES” in either step 43 or 44, and the map of the return torque Tr (see FIG. 5) is referred to based on the detected steering angle θs in step 51 to correspond to the same steering angle θs. The returned torque Tr is determined, and in step 52, the map of the second vehicle speed coefficient Kv2 (see FIG. 6) is referred to based on the vehicle speed V and the second vehicle speed V corresponding to the second vehicle speed V
The vehicle speed coefficient Kv2 is determined.

Next, at step 53, a map of the reference self-aligning torque Tsa based on the steering angle θs (FIG. 7).
The reference self-aligning torque Tsa corresponding to the steering angle .theta.s is determined by referring to the reference. This map is
On the condition that the front wheels 17a, 17b are on a dry road having a large road surface friction coefficient, the self-aligning torque given to the tires of the front wheels 17a, 17b from the road is applied to the steering shaft 12 while changing the steering angle θs. The reference self-aligning torque Tsa is set to a value slightly smaller than the measurement result. After the determination of the reference self-aligning torque Tsa, the absolute value | Tsa | of the reference self-aligning torque Tsa determined in step 54 and the absolute value of the detected torque Ts input from the torque sensor 31 by the processing of step 41 described above. Ts | is compared.

In this case, the detected torque Ts is equal to the front wheel 1
Since the tires 7a and 17b represent the actual self-aligning torque acting on the steering shaft by being received from the road surface, if the road surface friction coefficient is large, the absolute value | Ts | of the detected torque Ts is The absolute value of the determination criterion self-aligning torque Tsa is | Tsa |
At step 55, the torque coefficient Kt is set to "1.0". If the road surface friction coefficient is small, the absolute value of the detected torque Ts | Ts
| Is less than the absolute value | Tsa | of the determination reference self-aligning torque Tsa, and “YES” is determined in step 54.
It is determined that the torque coefficient Kt is "1.
It is set to "5".

After these steps 55 and 56, the output torque value T0 (= -Kt.multidot. = (-Kt.multidot.t) is multiplied by the return torque Tr determined in step 57 and the determined second vehicle speed coefficient Kv2 and torque coefficient Kt. Kv2 · Tr) is calculated. In the calculation of the output torque value T0, the negative sign (-) is added in order to apply the rotational torque in the opposite direction to the rotational position of the steering wheel 11 to the steering shaft 12. Then, in step 48, similarly to the above case, the control signal representing the calculated output torque value T0 is output to the electric motor 22. The electric motor 22 is also rotationally driven as in the above case. As a result, a driving force corresponding to the output torque value T0 from the electric motor 22 is applied to the steering wheel 11, so that the steering wheel 11 outputs the same output torque value T0.
The force corresponding to the absolute value | T0 | of 0 is urged to the neutral position.

In this case, as shown in FIG. 5, the steering angle θs
Return torque Tr in the range of 20 to 100 degrees
Has a large value, a large driving force is applied to the electric motor 22.
To the handle 11. This is because in this region, the steering reaction force applied to the front wheels 17a, 17b from the road surface is usually small, and the steering shaft 12 goes backward via the knuckle arms 16a, 16b, the tie rods 15a, 15b, the rack bar 14 and the pinion 13. This is because the reaction force is small and the force that the handle 11 naturally restores by the mechanical connection is small. In addition, FIG.
As shown in, the second vehicle speed coefficient Kv1 decreases as the vehicle speed V increases. This is because if the steering wheel 11 is returned to the neutral position by a large driving force of the electric motor 22 while the vehicle is traveling at high speed, the rotation of the steering wheel 11 becomes an overshoot when the steering wheel 11 is returned to the neutral position and the traveling of the vehicle becomes unstable. This is because there is a risk that

Further, as described above, the torque coefficient Kt is set to "1.0" when the road surface friction coefficient is large, and the torque coefficient Kt is "1.
Since it is set to "5", when the road surface friction coefficient is small, the electric motor 22 produces a larger output torque than when the coefficient is large. As a result, since the road surface friction coefficient is small, the self-aligning torque applied from the road surface to the front wheels 17a, 17b is small and the steering shaft 12
Even if the self-aligning torque that acts on the steering shaft 12 is small, the combined drive torque applied to the steering shaft 12 from the road surface and the electric motor 22 is the same as when the road surface friction coefficient is large, and the road surface friction coefficient is large or small. , Handle 1
The return operation of 1 is assisted so as to have the same force.

As a result, according to the above embodiment, the driver can return the steering wheel 11 to the neutral position with an appropriate force according to the steering state of the front wheels 17a and 17b and the traveling state of the vehicle, and the traveling road surface The steering wheel 11 can be returned and operated with an equivalent steering feeling regardless of whether the friction coefficient is large or small.

In the above embodiment, the road surface friction coefficient is discriminated into two types, large and small, and the magnitude of the output torque of the electric motor 22 is controlled into the large and small types according to the discrimination result. The output torque may be controlled so as to gradually change as the coefficient decreases.
In this case, a map of the reference self-aligning torque Tsa (see FIG. 7) is created based on the measurement result in the state where the road surface friction coefficient is maximum, and instead of the processing of steps 54 to 56, the determination reference self If the absolute value | Ts | of the detected torque Ts is subtracted from the absolute value | Tsa | of the aligning torque Tsa, and the torque coefficient Kt that increases in proportion to the subtraction result | Tsa |-| Ts | is determined. Good.

[Brief description of drawings]

FIG. 1 is an overall schematic view of an electric power steering device showing an embodiment of the present invention.

2 is a flowchart of a program executed by the microcomputer of FIG.

[FIG. 3] Assist torque Ta with respect to steering torque Ts
3 is a change characteristic graph of FIG.

FIG. 4 is a change characteristic graph of a first vehicle speed coefficient Kv1 with respect to a vehicle speed V.

FIG. 5 is a change characteristic graph of the return torque Tr with respect to the steering angle θs.

FIG. 6 is a change characteristic graph of a second vehicle speed coefficient Kv2 with respect to a vehicle speed V.

FIG. 7 is a change characteristic graph of the reference self-aligning torque Tsa with respect to the steering angle θs.

[Explanation of symbols]

11 ... Steering wheel, 12 ... Steering shaft, 14 ... Rack bar, 1
7a, 17b ... Front wheel, 21 ... Large gear, 22 ... Electric motor, 23 ... Small gear, 31 ... Torque sensor, 32 ... Steering angle sensor, 33 ... Microcomputer, 34 ... Vehicle speed sensor.

Claims (1)

[Claims] 1. A steering mechanism, comprising: an electric motor whose output torque is controlled by an input control signal, wherein a steering operation for transmitting a turning operation of a steering wheel to a steered wheel through a steering shaft to steer the wheel is performed by the electric motor. It is applied to an electric power steering device that applies a rotational driving force to assist the turning operation of the steering wheel, and outputs a control signal to the electric motor when returning the steering wheel to the neutral position to return the steering wheel to the neutral position. In a steering wheel restoration control device for rotating the electric motor in a direction, a torque sensor for detecting a torque acting on a steering shaft, a steering angle sensor for detecting a steering angle of a steering wheel, and a steering wheel for steering the steering wheel based on the detected steering angle. Reference self-aligning torque determining means for determining a reference self-aligning torque having a predetermined relationship with the angle, and the magnitude of the detected torque Is determined based on the determined reference self-aligning torque, and when the detected torque is small, a control signal for controlling the output torque of the electric motor to be larger than when the detected torque is large is output to the electric motor. A steering wheel restoration control device for an electric power steering device, comprising: a control signal output means.