JP3103049B2 - Vehicle steering system - Google Patents

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.

The upper limit of the above-mentioned auxiliary steering reaction torque is set by a limiter in order to make the reaction torque within a desired range and to cope with a failure of each sensor. No torque is generated.

[0008]

However, the above-described auxiliary steering reaction torque includes a damping torque using the steering angular velocity as a parameter and a yaw rate torque using the yaw rate as a parameter. When it becomes large, even if the entire steering reaction torque is within the normal range, the viscous feeling due to the viscous feeling may lower the driver's degree of freedom of steering and give a sense of incongruity. Further, when the ratio of the yaw rate torque is increased based on an abnormal signal rarely generated from the yaw rate sensor, unexpected steering reaction torque is generated by the driver, and the driver may feel 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.

[0010] The present invention has been devised to remedy such disadvantages of the prior art, and its main objects are as follows.
It is an object of the present invention to provide a vehicle steering system capable of improving the deflection suppressing performance at the time of a disturbance action and appropriately setting a steering force at the time of normal turning, and not causing a feeling of steering discomfort during normal running.

[0011]

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. In the above, the auxiliary reaction torque determined by the auxiliary reaction torque determination means includes a reaction force component determined based on the yaw rate and a reaction force component determined based on the steering angular velocity, the control means, An upper limit is individually set for one or both of the reaction force component determined based on the yaw rate of the auxiliary reaction force torque and the reaction force component determined based on the steering angular velocity, and the motor is controlled within the range. This is achieved by providing a vehicle steering system characterized by being controlled.

As described above, the upper limit is individually set for the damping torque and / or the yaw rate torque constituting the auxiliary steering reaction force torque, so that the entire speed range during traveling without sacrificing the steering feeling during normal operation. , An appropriate steering force and a vehicle behavior suppressing force at the time of a disturbance can be achieved at the same time.

[0013]

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, in the steering control unit 17 described above, an auxiliary steering torque determining means 17a for calculating an auxiliary steering torque as an electric power steering device, and an auxiliary reaction force torque are calculated. 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 described above, as shown in the flowchart of FIG.
1), a process of reading the steering wheel angular velocity ω (step 12) and the yaw rate γ (step 13) are performed.

Next, in step 2 described above, as shown in the flowchart of FIG. 5, the steering angular velocity ω as shown in FIG. From the table and the data table in which the yaw rate γ as shown in FIG. 7B is set as an address and the characteristic is set differently for each vehicle speed V, the auxiliary reaction torque T1 (damping torque component)
Find T2 (Yaw rate torque component) (Step 2)
1, 22). Then, it is determined whether or not the absolute values of the components T1 and T2 of the auxiliary reaction torque exceed the upper limit values T1max and T2max, and either or both of the steering reaction forces T1 and T2 are set to the upper limit values (T1max and T2max). ), The upper limit (T1max, T2max) is input as the absolute value of the steering reaction force (T1 or T2) (steps 23 and 2).
4). Next, an auxiliary reaction torque value TA is obtained by adding the components T1 and T2 of the steering reaction torque (step 2).
5).

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.
If the target steering reaction force value TA exceeds the negative maximum value, a limiter process (step 26) 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 24 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.

Here, in order to obtain the above-mentioned auxiliary reaction force torque T1 (damping torque component), by setting an upper limit thereof, as shown by a solid line in FIG. In other words, the steering feeling and viscous feeling in the high frequency range are reduced, and a light steering feeling can be obtained. FIG. 9B shows the relationship between the steering frequency and the phase.

FIG. 10A, FIG. 10B, FIG.
As shown in FIG. 0 (c), in the case of an electric power steering device that does not generate an auxiliary steering reaction torque (imaginary line), when the steering wheel is turned, the return is too slow, and the driver must manually return the steering wheel. In the case of an electric power steering apparatus that generates an auxiliary steering reaction torque but does not set an upper limit of the yaw rate torque (T2), the return when the steering wheel is turned relatively large is too fast (broken line), but the yaw rate torque ( By setting the upper limit of T2), the return speed when the steering wheel is turned relatively large becomes an appropriate speed, and the steering feeling is improved (solid line).

Further, even if an excessive yaw rate torque (T2) is output due to, for example, a sensor abnormality or the like, a portion larger than T2max is cut, thereby preventing a sense of incongruity due to an unexpected steering reaction force in a normal steering region. be able to.

Although the yaw rate sensor is used as the vehicle behavior detecting means in the above configuration, a similar operation and effect can be obtained by using a lateral acceleration sensor instead or in addition to this.

As described above, according to the vehicle steering system of the present invention, the upper limit is individually set for the damping torque and / or the yaw rate torque constituting the auxiliary steering reaction torque, so that the ratio of the damping torque is reduced. It is possible to reduce or eliminate the harshness due to the viscous feeling generated when the steering wheel becomes large, and to reduce or eliminate the unexpected steering reaction torque of the driver based on the sudden return feeling of the steering wheel or the abnormal signal generated when the ratio of the yaw rate torque becomes large. Therefore, it is possible to achieve both a proper steering over the entire speed range during traveling and a suppression of the vehicle behavior at the time of disturbance at a high level without sacrificing the steering feeling during normal driving.

[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 and 7B are enlarged views of a data table used for the control processing.

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

FIG. 9A is a graph showing a relationship between a frequency of an auxiliary steering reaction torque and a gain with respect to a steering angle of the steering device;
(B) is a graph showing the relationship between frequency and phase.

10A is a graph showing a relationship between a steering wheel return operation time of the steering device and a steering angle, FIG. 10B is a graph showing a relationship between time and a yaw rate, and FIG. 4 is a graph showing a relationship between a force torque and a yaw rate torque.

[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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI B62D 137: 00 (72) Inventor Hiroyuki Kawagoe 1-4-1, Chuo, Wako-shi, Saitama Pref. Document JP-A 7-10023 (JP, A) JP-A 8-104249 (JP, A) JP-A 8-67267 (JP, A) JP-A 9-71253 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B62D 6/00 B62D 5/04

Claims (1)

(57) [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. A vehicle steering device having a control means for controlling the electric motor with an auxiliary torque value obtained by adding a force torque value, wherein the control means determines the auxiliary reaction torque determining means. The auxiliary reaction force torque includes a reaction force component determined based on a yaw rate and a reaction force component determined based on a steering angular velocity, and the control means is determined based on a yaw rate of the auxiliary reaction force torque. An upper limit is individually set for one or both of the reaction force component and the reaction force component determined based on the steering angular velocity, and the electric motor is controlled within the range. Steering gear.