JP3884842B2 - Vehicle steering system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle steering device, and more particularly to a steering device configured to be able to generate an appropriate steering reaction torque and a steering torque that suppresses vehicle behavior when a disturbance is generated by an electric motor.
[0002]
[Prior art]
As a so-called power steering device for reducing the driver's steering force, for example, a device of the type described in Japanese Patent Publication No. 50-33584 is known. This is designed to assist the steering force of the steering wheel with the output torque of the electric motor, and detect the amplification of the detection signal of the steering torque applied by the driver to the steering wheel, such as the vehicle speed and road conditions. By changing in accordance with the signal, the output torque of the auxiliary motor is increased or decreased so that the optimum steering torque is always obtained.
[0003]
By the way, if the vehicle receives a strong crosswind or travels along a narrow road while traveling, the vehicle may be deflected in a direction away from the target travel line. Further, the road surface reaction force decreases when traveling on a road surface with 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 a low speed.
[0004]
In the case of the above-described conventional power steering device, since the electric motor generates auxiliary steering torque only after the driver steers, even if the vehicle is deflected by receiving a crosswind during driving, the electric motor does not generate auxiliary steering torque. Does not occur. Therefore, in order to suppress the deflection of the vehicle, the driver himself has to operate the steering wheel. On the other hand, the power steering device generally requires a larger steering force as the lateral acceleration and yaw rate of the vehicle increase. Therefore, in the case of the deflection of the vehicle due to disturbance, there is a disadvantage that the larger the value is, the larger the steering torque required for correction becomes.
[0005]
Therefore, for example, in Japanese Patent Laid-Open No. 5-105100, vehicle behavior such as yaw rate and lateral acceleration is detected, an auxiliary reaction force torque value is determined based on the detected value, and the auxiliary reaction force torque value and steering torque are determined. There has been proposed one that controls the driving torque of the electric motor based on the auxiliary steering torque value determined based on the detected value.
[0006]
According to this structure, it is possible to improve the deflection suppression performance when disturbances such as crosswinds and rutted roads are applied to the vehicle, and improve the running stability of the vehicle. Even the steering operation load is reduced.
[0007]
[Problems to be solved by the invention]
Incidentally, the auxiliary steering reaction torque described above includes a damping torque whose parameter is the steering angular velocity and a yaw rate torque whose parameter is the yaw rate. As shown in FIG. 12, for example, the yaw rate is about 60 km / h, for example. The frequency response characteristics differ between the low-speed traveling and the high-speed traveling 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 traveling. 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 in the vicinity of the peak. Therefore, it is conceivable that the steering input in the frequency range is affected, and that the vehicle feels unnatural, such as an unnaturally heavy steering wheel.
[0008]
In particular, in order to increase the vehicle behavior suppression effect during disturbances, the ratio α of the reaction force component determined based on the yaw rate and the steering angular velocity corresponding to the steering angle with respect to the total steering torque (= auxiliary steering reaction torque / (auxiliary The above problem becomes significant when (steering reaction torque + self-aligning torque) = (auxiliary steering reaction torque / total steering torque)) is increased.
[0009]
The present invention has been devised in order to improve such disadvantages of the prior art, and its main purpose is to improve the deflection suppression performance at the time of disturbance action and to appropriately set the steering force at the time of normal turning. Another object of the present invention is to provide a vehicle steering apparatus that does not cause a sense of discomfort during normal driving, particularly during high-speed driving.
[0010]
[Means for Solving the Problems]
According to the present invention, such an object is to provide a manual steering means for manually steering a steering wheel of a vehicle, a steering torque detecting means for detecting a steering torque applied to the manual steering means, An auxiliary steering torque determining unit that determines an auxiliary steering torque based on a detection value of the steering torque detecting unit, a vehicle behavior detecting unit that detects the behavior of the vehicle, and a detection value detected by the vehicle behavior detecting unit Auxiliary reaction force torque determining means for determining auxiliary reaction force torque, an electric motor for applying auxiliary torque to the steering wheel, and the auxiliary reaction force torque determination to the auxiliary steering torque value determined by the auxiliary steering torque determining means In the vehicle steering apparatus, the vehicle behavior detection has a control means for controlling the electric motor with an auxiliary torque value obtained by adding an auxiliary reaction force torque value determined by the means In order to correct the detection value, such as a detected yaw rate by the step has a characteristic compensator frequency response characteristic is changed in accordance with the vehicle speed, the auxiliary reaction force torque determining means is characteristic compensation by the characteristic compensator This is achieved by providing a vehicle steering system characterized in that the auxiliary reaction force torque is determined based on the correction value.
[0011]
In this way, the yaw rate detection value is compensated for by a characteristic compensator such as a filter, and, for example, by reducing or eliminating the peak due to yaw resonance of the yaw rate frequency response characteristic, a flat frequency over the entire steering frequency. It becomes a response characteristic, and the uncomfortable feeling of steering caused by the change in the auxiliary steering reaction torque near the resonance point can be reduced or completely eliminated.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0013]
FIG. 1 shows a schematic configuration of a vehicle steering apparatus to which the present invention is applied. This device includes a pinion 4 connected to a steering shaft 2 integrally connected to a steering wheel 1 via a connecting shaft 3 having a universal joint, and can reciprocate in the vehicle width direction while meshing with the pinion 4 and a tie rod 5. Manual steering force generating means comprising a rack and pinion mechanism having rack shafts 8 connected at both ends to knuckle arms of left and right front wheels 6 as steering wheels. In addition, an electric motor 9 constituting an electric power steering device is coaxially disposed at an intermediate portion of the rack shaft 8 so as to generate an auxiliary steering force for reducing a manual steering force via the rack and pinion mechanism. Has been.
[0014]
Near the pinion 4 of the rack and pinion mechanism, there are a steering angular velocity sensor 11 for detecting the steering angular velocity from the rotation angle of the steering wheel 1, and a torque sensor 12 for detecting the manual steering torque acting on the pinion 4. Is provided. Further, a yaw rate sensor 15 for outputting a signal corresponding to the yaw rate (yaw angular velocity) of the vehicle and a vehicle speed sensor 16 for outputting a signal corresponding to the traveling speed of the vehicle are provided. It is connected to a steering control unit 17 for controlling the output of the electric motor 9 based on the detected value.
[0015]
As shown in FIG. 2, in the steering control unit 17 described above, auxiliary steering torque determining means 17a for calculating auxiliary steering torque as an electric power steering device and auxiliary for calculating auxiliary reaction force torque are provided. Reaction force torque determining means 17b is provided. The detection signals of the steering angular velocity sensor 11, the torque sensor 12, and the vehicle speed sensor 16 are input to the auxiliary steering torque determining means 17a, and the auxiliary steering torque for performing normal assist control is determined according to these detection signals. Is done.
[0016]
The auxiliary reaction force torque determining means 17b receives detection signals from the steering angular velocity sensor 11, the yaw rate sensor 15, and the vehicle speed sensor 16 constituting the vehicle behavior detecting means, and these signals are described later. The target auxiliary reaction torque is obtained by an algorithm.
[0017]
Further, in the steering control unit 17, target current determining means 17c for setting a target current for the electric motor 9 according to each torque value output from the auxiliary steering torque determining means 17a and the auxiliary reaction force determining means 17b, and its Output current control means 17d for controlling the current flowing through the electric motor 9 according to the target current is provided. 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 electric motor 9, and the drive circuit 19 drives the electric motor 9 by, for example, PWM control. In addition, feedback control of output current is performed between the drive circuit 19 and the output current control means 17d.
[0018]
In the auxiliary reaction force torque determining means 17b in the steering control unit 17, the process 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 target steering reaction torque value TA is limited in step 3. In step 4, this control signal is added to the output signal from the auxiliary steering torque determining means 17a.
[0019]
This process will be described in more detail with reference to FIGS. First, in step 1, as shown in the flowchart of FIG. 4, processing for reading vehicle speed V (step 11), steering wheel angular velocity ω (step 12), and yaw rate γ (step 13) is performed.
[0020]
Next, in step 2, as shown in the flowchart of FIG. 5, first, a data table in which the steering angular velocity ω as shown in FIG. From this, the auxiliary reaction force torque T1 (damping torque component) is obtained (step 21). Next, the detected yaw rate γ is subjected to a low-pass filter F as a characteristic compensator set to a different characteristic for each vehicle speed V as shown in FIG. 7B to obtain a corrected yaw rate γf. (Step 22).
[0021]
Next, at step 23, the auxiliary reaction force torque T2 (yaw rate torque component) is obtained from the data table set with different characteristics for each vehicle speed V using the corrected yaw rate γf as shown in FIG. Ask. Then, the auxiliary reaction force torque value TA is obtained by adding the components T1 and T2 of the steering reaction force torque (step 24).
[0022]
Next, it is determined whether or not the target steering reaction force value TA exceeds the maximum value (Tmax) in order to eliminate the auxiliary reaction force torque more than necessary, and the target steering reaction force value TA exceeds the maximum value. In this case, the target steering reaction force value TA is set to the above Tmax. If the target steering reaction force value TA does not exceed the maximum value (Tmax), the target steering reaction force value TA is similarly set to the negative maximum value (− Tmax) is exceeded. If the target steering reaction force value TA exceeds the negative maximum value, a limiter process (step 25) is performed to set the target steering reaction force value TA to the -Tmax value. Then, the target auxiliary reaction force torque determination value TA is determined.
[0023]
The control block diagram of the above step 2 is as shown in FIG. 6, and steps 21 to 25 correspond to the respective blocks in FIG.
[0024]
The target auxiliary reaction torque determination value TA determined in this way is added to the target auxiliary steering torque determination value obtained separately, converted into a target current value by the target current determination means 17c, and output.
[0025]
By performing the above processing, as shown in FIG. 8, when the vehicle 20 is separated from the travel line 21 due to the crosswind when traveling forward, the yaw rate γ of the vehicle 20 at this time is detected, and these The electric motor 9 is driven in a direction to cancel the yaw rate γ, that is, in a direction to return the deflection of the vehicle 20 at that time to the travel line 21, and the front wheels 6 are automatically steered so that the vehicle 20 always travels straight ahead against disturbance. In addition, it is possible to stabilize the irregular behavior, and even when traveling on a road surface with a trap or a puddle, an effect such as automatically correcting the trajectory so that the vehicle 20 moves straight is obtained. .
[0026]
Here, FIGS. 9 to 11 show frequency response characteristics of the auxiliary steering reaction force torque in a certain vehicle when the filter F is a first-order lag low-pass filter with a cutoff frequency of 0.9 Hz, for example. 9A shows the relationship between the frequency and gain of the filter F, and FIG. 9B shows the relationship between the frequency and 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 and gain of the auxiliary steering reaction torque with respect to the steering angle, and FIG. 11B shows the relationship between the frequency and phase. The solid line is the characteristic at high speed (180 km / h) when the filter F is used, the wavy line is the characteristic at high speed (180 km / h) when the filter F is not used, and the imaginary line is when the filter F is not used. The characteristics at low speed (60 km / h) are shown.
[0027]
As shown in FIGS. 10 and 11, in the high speed region, when the filter F is not used, the yaw resonance peak appears and a desirable characteristic is not obtained, and the steering feels strange, but by using the filter F, This peak is almost eliminated, and a frequency response characteristic substantially matching the desired characteristic can be obtained, and the steering feeling is improved. By making the cut-off frequency of the filter F variable according to the vehicle speed V as shown in FIG. 7B, a frequency response characteristic that always matches a desired characteristic can be obtained at all vehicle speeds.
[0028]
In the low speed region (for example, a vehicle speed of 60 km / h), yaw resonance hardly occurs even if the filter F is not used, and a generally desirable frequency response characteristic is exhibited even if the filter F is not used. However, in practice, it is possible to finely set the steering force by applying an appropriate filter even in the low speed region, and it is possible to obtain a frequency response characteristic that matches a more desirable characteristic.
[0029]
Further, in the above configuration, the yaw rate sensor is used as the vehicle behavior detecting means, but the same operation and effect can be obtained by using a lateral acceleration sensor instead of or in addition to this. In the above embodiment, the first-order lag low-pass filter is used as the characteristic compensator for the input value of the yaw rate γ. However, a more advanced filter, amplifier, or the like may be used in practice.
【The invention's effect】
Thus, according to the vehicle steering apparatus of the present invention, in the vehicle steering apparatus that controls the drive torque of the auxiliary steering force torque and the auxiliary steering reaction torque generating motor based on the detected value of the vehicle behavior detecting means. By compensating the vehicle behavior detection value according to the vehicle speed, for example, the peak due to yaw resonance in the frequency response characteristic of the yaw rate can be reduced or eliminated, and the change in the auxiliary steering reaction force torque near the resonance point Steering discomfort can be reduced or completely eliminated, and appropriate steering force and vehicle behavior suppression force during disturbance can be achieved at a high level over the entire speed range without sacrificing steering feeling during normal driving. .
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram schematically showing a vehicle steering apparatus 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 a control process of the steering device.
FIG. 5 is a flowchart showing a control process of the steering device.
FIG. 6 is a circuit block diagram of a control system of the steering apparatus 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 movement of a vehicle when a crosswind is received during straight traveling.
9A is a graph showing the relationship between the steering frequency and the gain of the yaw rate filter F of the steering apparatus, and FIG. 9B is a graph showing the relationship between the steering frequency and the phase.
10A is a graph showing a relationship between a steering frequency and a yaw rate gain according to a difference in vehicle speed of the steering apparatus, and FIG. 10B is a graph showing a relationship between a steering frequency and a phase of the yaw rate.
11A is a relationship between a steering frequency and a gain of an auxiliary steering reaction torque according to a difference in vehicle speed of the steering device, and FIG. 11B is a phase difference between a steering frequency and a phase of the auxiliary steering reaction torque. A graph showing the relationship.
12A is a relationship between a steering frequency and a yaw rate gain according to a difference in vehicle speed of a steering device having a conventional electric auxiliary steering force generator, and FIG. 12B is a relationship between a steering frequency and a phase of the yaw rate. Graph showing.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 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 traveling line

Claims (2)

A manual steering means for manually steering the steered wheels of the vehicle, a steering torque detecting means for detecting a steering torque applied to the manual steering means, and an auxiliary steering based on a detected value of the steering torque detecting means Auxiliary steering torque determination means for determining torque, vehicle behavior detection means for detecting the behavior of the vehicle, and auxiliary reaction force torque determination for determining auxiliary reaction force torque based on a detection value detected by the vehicle behavior detection means Means, an electric motor for applying auxiliary torque to the steering wheel, and an auxiliary reaction torque value determined by the auxiliary reaction force torque determining means added to the auxiliary steering torque value determined by the auxiliary steering torque determining means A vehicle steering apparatus having a control means for controlling the electric motor with an auxiliary torque value.
A characteristic compensator in which a frequency response characteristic is changed according to a vehicle speed in order to correct a detection value detected by the vehicle behavior detection unit;
The vehicle steering apparatus according to claim 1, wherein the auxiliary reaction force torque determining means determines the auxiliary reaction force torque based on a correction value whose characteristic is compensated by the characteristic compensator.     The vehicle steering apparatus according to claim 1, wherein the vehicle behavior detected by the vehicle behavior detection means includes a yaw rate.

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