JPH11147476A - Steering unit for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steering unit for a vehicle to improve the deflection suppression performance under the effect of disturbances, enabling setting of the steering force in normal turn, without producing discomfort in normal running, high speed driving in particular. SOLUTION: In this steering unit for a vehicle, a driving torque for an electric motor to generate supplementary steering force is controlled based on the values detected by the vehicle behavior detection means. For example, the peak due to the yaw resonance of yaw rate frequency response characteristics is reduced or eliminated by compensating the characteristic of the detected values for vehicle behavior in accordance with the vehicle speed. Thus, discomfort in steering due to the change in reaction torque for active steering near the resonance point is reduced or completely eliminated. Therefore, correct steering force and vehicle behavior suppression force under the effect of disturbances are both made available throughout the entire running speed range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering apparatus for a vehicle, and more particularly to a steering apparatus configured to be able to generate an appropriate steering reaction torque and a steering torque for suppressing the behavior of the vehicle when a disturbance occurs by an electric motor. It is.

[0002]

2. Description of the Related Art As a so-called power steering device for reducing a driver's steering force, for example, Japanese Patent Publication No. 50-33
A type as described in Japanese Patent No. 584 is known. This is designed to assist the steering force of the steering wheel with the output torque of the electric motor. The amplification of the detection signal of the steering torque applied by the driver to the steering wheel is detected by detecting the vehicle speed and road conditions. The output torque of the auxiliary motor is increased or decreased by changing the output torque according to a signal, so that an optimum steering torque is always obtained.

[0003] By the way, if the vehicle receives a strong crosswind or travels on a rutted road while traveling, the vehicle may be deflected in a direction deviating from the target traveling line. In addition, the road surface reaction force decreases when traveling on a road surface having a low friction coefficient (μ) between the tire and the road surface such as a snowy road (hereinafter referred to as a low μ road) or when traveling at low speed.

In the case of the above-described conventional power steering device, the electric motor generates the auxiliary steering torque only after the driver turns the electric power steering device. No auxiliary steering torque is generated. Therefore, in order to suppress the deflection of the vehicle, the driver himself must operate the steering wheel. On the other hand, the power steering device generally requires a larger steering force as the lateral acceleration and the yaw rate of the vehicle increase. Therefore, in the case of the deflection of the vehicle due to the disturbance, there is a problem that the larger the deflection, the larger the steering torque required for the correction.

Therefore, for example, Japanese Patent Laid-Open No. 5-105100 discloses that a vehicle behavior such as a yaw rate and a lateral acceleration is detected, and an auxiliary reaction torque value is determined based on the detected value.
A motor that controls the drive torque of the electric motor based on the auxiliary reaction torque value and an auxiliary steering torque value determined based on a detection value such as a steering torque has been proposed.

According to this structure, the deflection suppressing performance when disturbance such as crosswind or running on a rutted road acts on the vehicle can be enhanced, and the running stability of the vehicle can be improved. The steering operation load is reduced even at low speeds.

[0007]

The auxiliary steering reaction torque described above includes a damping torque having a steering angular velocity as a parameter and a yaw rate torque having a yaw rate as a parameter, as shown in FIG. ,
For example, the frequency response characteristic of the yaw rate differs between when traveling at a low speed of, for example, about 60 km / h and when traveling at a high speed of up to 180 km / h. In particular, a peak due to yaw resonance appears in the gain in a relatively high frequency region during high-speed running. Then, in the conventional steering apparatus having the above-described structure, since the input yaw rate and the output yaw rate torque have a one-to-one correspondence, the yaw rate torque is large near the peak. It is conceivable that the steering input in the frequency domain is affected, and that the steering wheel becomes unnaturally uncomfortable.

In particular, in order to enhance the effect of suppressing the vehicle behavior during a disturbance, the ratio α of the reaction force component determined based on the yaw rate corresponding to the steering angle and the steering angular velocity with respect to the total steering torque (= the auxiliary steering reaction torque) When / (auxiliary steering reaction torque + self-aligning torque) = (auxiliary steering reaction torque / total steering torque)) is increased, the above problem becomes prominent.

The present invention has been made in order to improve such disadvantages of the prior art, and its main objects are as follows.
It can improve the deflection suppression performance at the time of disturbance action, and can appropriately set the steering force during normal turning.
In particular, it is an object of the present invention to provide a vehicle steering system that does not cause a feeling of steering discomfort during high-speed running.

[0010]

SUMMARY OF THE INVENTION According to the present invention, there is provided, in accordance with the present invention, a manual steering means for manually turning a steered wheel of a vehicle, and a steering torque applied to the manual steering means. Steering torque detecting means for detecting, auxiliary steering torque determining means for determining an auxiliary steering torque based on a detection value of the steering torque detecting means, vehicle behavior detecting means for detecting the behavior of the vehicle, and the vehicle behavior detecting means Reaction torque determining means for determining an auxiliary reaction torque based on the detection value detected by the motor, an electric motor for applying an auxiliary torque to the steered wheels, and an auxiliary steering determined by the auxiliary steering torque determining means. Control means for controlling the electric motor with an auxiliary torque value obtained by adding an auxiliary reaction force torque value determined by the auxiliary reaction force torque determination means to a torque value. A characteristic compensator for compensating a characteristic value according to a vehicle speed based on a detected value of a yaw rate or the like detected by the vehicle behavior detecting means, wherein the auxiliary reaction torque determining means is configured to perform characteristic compensation by the characteristic compensator. The present invention is achieved by providing a vehicle steering system characterized in that an auxiliary reaction torque is determined based on the detected value.

As described above, the detected value of the yaw rate is characteristic-compensated by the characteristic compensator such as a filter, and, for example, the peak of the frequency response characteristic of the yaw rate due to yaw resonance or the like is reduced or eliminated, so that the yaw rate can be controlled over the entire steering frequency. A flat frequency response characteristic is obtained, and the feeling of strange steering due to a change in the auxiliary steering reaction torque near the resonance point can be reduced or completely eliminated.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a schematic configuration of a vehicle steering system to which the present invention is applied. The apparatus comprises a pinion 4 connected to a steering shaft 2 integrally connected to a steering wheel 1 via a connection shaft 3 having a universal joint.
A rack-and-pinion having a rack shaft 8 having both ends connected to knuckle arms of left and right front wheels 6 as steerable wheels via tie rods 5 while being able to reciprocate in the vehicle width direction by meshing with the pinion 4 It has a manual steering force generating means composed of a mechanism. Further, an electric motor 9 constituting an electric power steering device is coaxially arranged at an intermediate portion of the rack shaft 8 so as to generate an auxiliary steering force for reducing a manual steering force via a rack and pinion mechanism. Have been.

In the vicinity of the pinion 4 of the rack and pinion mechanism, a steering angular velocity sensor 11 for detecting a steering angular velocity from the rotation angle of the steering wheel 1 and a torque for detecting a manual steering torque acting on the pinion 4 are provided. A sensor 12 is provided. Further, a yaw rate sensor 15 for outputting a signal corresponding to the yaw rate (yawing angular velocity) of the vehicle, and a vehicle speed sensor 16 for outputting a signal corresponding to the running speed of the vehicle are provided.
Each of these sensors is connected to a steering control unit 17 for controlling the output of the electric motor 9 based on the detected values.

As shown in FIG. 2, the steering control unit 17 includes an auxiliary steering torque determining means 17a for calculating an auxiliary steering torque as an electric power steering device, and an auxiliary reaction torque. And an auxiliary reaction torque determining means 17b. The auxiliary steering torque determining means 17a includes a steering angular velocity sensor 11
The detection signals of the torque sensor 12 and the vehicle speed sensor 16 are input, and the auxiliary steering torque for performing the normal assist control is determined according to the detection signals.

The auxiliary reaction torque determining means 17b includes:
Each detection signal of the steering angular velocity sensor 11, the yaw rate sensor 15, and the vehicle speed sensor 16 constituting the vehicle behavior detecting means is inputted, and the target auxiliary reaction torque is obtained from the respective signals by an algorithm described later. Has become.

Further, in the steering control unit 17, a target current determining means 17c for setting a target current for the electric motor 9 in accordance with each torque value output from the auxiliary steering torque determining means 17a and the auxiliary reaction force determining means 17b. And output current control means 17d for controlling a current flowing to the electric motor 9 in accordance with the target current. Then, a current control signal from the output current control means 17d is input to a drive circuit 19 provided between the steering control unit 17 and the motor 9, and the drive circuit 19 drives the motor 9 by, for example, PWM control. And the feedback control of the output current is performed between the drive circuit 19 and the output current control means 17d.

In the auxiliary reaction torque determining means 17b in the steering control unit 17, the processing shown in the flowchart of FIG. 3 is repeatedly executed at a predetermined cycle. First, the signal output of each sensor is read in step 1, the target steering reaction torque value TA is determined in step 2, and then the limit is applied to the target steering reaction torque value TA in step 3. In step 4, auxiliary steering torque determining means 1
This control signal is added to the output signal from 7a.

This processing will be described in more detail with reference to FIGS. First, in step 1 above,
As shown in the flowchart of FIG. 4, processing for reading the vehicle speed V (step 11), the steering wheel angular velocity ω (step 12), and the yaw rate γ (step 13) is performed.

Next, in step 2 described above, as shown in the flowchart of FIG. 5, first, the steering angular velocity ω as shown in FIG. 7A is used as an address, and different characteristics are set for each vehicle speed V. The auxiliary reaction torque T1 (damping torque component) from the stored data table (step 2).
1). Next, for the detected actual yaw rate γ,
A low-pass filter F is applied as a characteristic compensator having different characteristics for each vehicle speed V as shown in FIG. 7B to obtain a corrected yaw rate γf (step 22).

Next, at step 23, a data table set with different characteristics for each vehicle speed V using the corrected yaw rate γf as shown in FIG.
The auxiliary reaction torque T2 (yaw rate torque component) is obtained. Then, the auxiliary reaction torque value TA is obtained by adding the components T1 and T2 of the steering reaction torque (step 24).

Next, it is determined whether or not the target steering reaction force value TA exceeds a maximum value (Tmax) in order to eliminate an excessive auxiliary reaction force torque. If it exceeds, set the target steering reaction force value TA to the above Tmax.
And the target steering reaction force value TA is the maximum value (Tmax).
If the target steering reaction force value TA does not exceed the negative maximum value (-Tmax), it is determined in the same manner.
When the target steering reaction force value TA exceeds the negative maximum value, a limiter process (step 25) for setting the target steering reaction force value TA to the above-mentioned -Tmax value is performed, and the target auxiliary reaction force torque determination value TA is determined. I do.

FIG. 6 is a control block diagram of the above step 2, and steps 21 to 25 correspond to the respective blocks in FIG.

The target auxiliary reaction torque determining value TA determined in this way is added to the separately determined target auxiliary steering torque determining value, converted into a target current value by the target current determining means 17c, and output. .

By performing the above processing, as shown in FIG. 8, when the vehicle 20 comes off the traveling line 21 due to the crosswind during forward movement, the yaw rate γ of the vehicle 20 at this time is detected. In the direction to cancel the yaw rate γ, that is, the deflection of the vehicle 20 at that time is
Motor 9 is driven in the direction to return to
The front wheel 6 is automatically steered so that the vehicle 20 always travels straight, so that the irregular behavior can be stabilized, and the vehicle 20 travels straight even when traveling on a rutted road surface or a puddle road surface. In this way, the effect of automatically correcting the trajectory is obtained.

FIGS. 9 to 11 show the frequency response characteristics of the auxiliary steering reaction torque in a certain vehicle when the filter F is a first-order lag low-pass filter having a cut-off frequency of 0.9 Hz, for example. Show. FIG. 9A shows the relationship between the frequency and the gain of the filter F, and FIG. 9B shows the relationship between the frequency and the phase of the filter F. FIG.
10A shows the relationship between the yaw rate frequency and the gain with respect to the steering angle, and FIG. 10B shows the relationship between the frequency and the phase. FIG. 11A shows the relationship between the frequency of the auxiliary steering reaction torque against the steering angle and the gain.
(B) similarly shows the relationship between frequency and phase.
Note that the solid line represents the high speed (1
80 km / h), the dashed line indicates the characteristic at high speed (180 km / h) when the filter F is not used, and the imaginary line indicates the characteristic at low speed (60 km / h) when the filter F is not used. .

As shown in FIGS. 10 and 11, when the filter F is not used in the high-speed range, the yaw resonance peak appears and the desired characteristics cannot be obtained, and the steering feels uncomfortable. As a result, this peak is almost eliminated, and a frequency response characteristic substantially matching a desirable characteristic can be obtained, so that the steering feeling is improved. By setting the cutoff frequency of the filter F to be variable according to the vehicle speed V as shown in FIG. 7B, it is possible to obtain a frequency response characteristic consistent with a desirable characteristic at all vehicle speeds.

In a low-speed region (for example, a vehicle speed of 60 km / h)
In this case, the yaw resonance hardly occurs even if the filter F is not used, and a generally desirable frequency response characteristic is exhibited even without using the filter F. However, in practice, by applying an appropriate filter even in a low-speed region, fine setting of the steering force is possible, and it is also possible to obtain a frequency response characteristic more consistent with a more desirable characteristic.

In the above configuration, the yaw rate sensor is used as the vehicle behavior detecting means. However, a similar operation and effect can be obtained by using a lateral acceleration sensor instead or in addition to this. Further, in the above embodiment, a first-order lag low-pass filter is used as the characteristic compensator for the input value of the yaw rate γ, but a more sophisticated filter, amplifier, or the like may be used in practice.

As described above, according to the steering apparatus for a vehicle according to the present invention, the driving torque of the electric motor for generating the auxiliary steering force torque and the auxiliary steering reaction torque is controlled based on the value detected by the vehicle behavior detecting means. The characteristic of the vehicle behavior detection value in the steering device is compensated according to the vehicle speed, for example, the peak of the frequency response characteristic of the yaw rate due to the yaw resonance can be reduced or eliminated, and the auxiliary steering response near the resonance point can be reduced. Steering discomfort due to changes in force torque can be reduced or completely eliminated, and a high level of proper steering force and vehicle behavior suppression force during disturbances can be achieved over the entire speed range during driving without sacrificing steering feeling during normal driving. Can be compatible.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram schematically showing a vehicle steering system to which the present invention is applied.

FIG. 2 is a circuit block diagram of a control system of the steering device.

FIG. 3 is a flowchart showing a control process of the steering device.

FIG. 4 is a flowchart showing control processing of the steering device.

FIG. 5 is a flowchart showing control processing of the steering device.

FIG. 6 is a circuit block diagram of a control system of the steering device and a data table used for the control processing.

FIGS. 7A, 7B, and 7C are enlarged views of a data table used for the control processing; FIG.

FIG. 8 is a schematic diagram showing the movement of the vehicle when a crosswind is received during straight running.

9A is a graph showing a relationship between a steering frequency and a gain of a yaw rate filter F of the steering device, and FIG. 9B is a graph showing a relationship between a steering frequency and a phase.

10A is a graph showing a relationship between a steering frequency and a yaw rate gain depending on a difference in vehicle speed of the steering device, and FIG. 10B is a graph showing a relationship between the steering frequency and a yaw rate phase.

11A is a diagram showing a relationship between a steering frequency and a gain of an auxiliary steering reaction torque due to a difference in vehicle speed of the steering device, and FIG.
Is a graph showing the relationship between the steering frequency and the auxiliary steering reaction torque due to the difference in the phase vehicle speed.

FIG. 12 (a) shows a relationship between a steering frequency and a yaw rate gain due to a difference in vehicle speed of a conventional steering device having an electric assisted steering force generator, and FIG. 12 (b) shows a relationship between the steering frequency and a phase of a yaw rate. The graph shown.

[Explanation of symbols]

 Reference Signs List 1 steering wheel 2 steering shaft 3 connecting shaft 4 pinion 5 tie rod 6 front wheel 8 rack shaft 9 electric motor 11 steering angular velocity sensor 12 torque sensor 15 yaw rate sensor 16 vehicle speed sensor 17 steering control unit 17a auxiliary steering torque determining means 17b auxiliary reaction force determining means 17c Target current determination means 17d Output current control means 19 Drive circuit 20 Vehicle 21 Straight running line

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI B62D 137: 00 (72) Inventor Hiroyuki Kawagoe 1-4-1, Chuo, Wako-shi, Saitama Pref.

Claims (2)

[Claims] 1. A manual steering device for manually turning a steered wheel of a vehicle, a steering torque detecting device for detecting a steering torque applied to the manual steering device, and a detection value of the steering torque detecting device. Auxiliary steering torque determining means for determining an auxiliary steering torque based on a vehicle behavior detecting means for detecting a behavior of the vehicle, and determining an auxiliary reaction torque based on a detection value detected by the vehicle behavior detecting means. An auxiliary reaction torque determining means, an electric motor for applying an auxiliary torque to the steered wheels, and an auxiliary reaction torque determined by the auxiliary reaction torque determining means to an auxiliary steering torque value determined by the auxiliary steering torque determining means. And a control means for controlling the electric motor with an auxiliary torque value obtained by adding the force torque value. A characteristic compensator for performing characteristic compensation according to the detected value according to the vehicle speed, wherein the auxiliary reaction torque determining means determines the auxiliary reaction torque based on the detection value characteristic-compensated by the characteristic compensator. A steering device for a vehicle, comprising: 2. The vehicle steering system according to claim 1, wherein the vehicle behavior detected by the vehicle behavior detection means includes a yaw rate.