JP3103050B2 - 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 the signal, so that an optimum steering torque can always be 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 effect of suppressing the vehicle behavior at the time of occurrence of a disturbance by the above-described structure is the ratio of the auxiliary steering reaction torque to the total steering torque α (= auxiliary steering reaction torque / (auxiliary steering reaction torque). + Self-aligning torque)), but if this α is increased, it becomes difficult for the driver to recognize the actual road surface condition (road information), and the yaw rate used for setting the auxiliary steering torque is a yaw resonance. Therefore, when α is increased, there is a problem that the influence of the yaw resonance increases and it becomes difficult for the driver to set a favorable steering torque.

[0008] The present invention has been devised to improve such disadvantages of the prior art, and its main objects are as follows.
An improved vehicle steering system that improves the deflection suppression performance when a disturbance such as a cross wind acts on the vehicle, does not impair road information, and allows the steering force during normal turning to be set appropriately. To provide.

[0009]

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 behavior of the vehicle including yaw rate, and the vehicle Auxiliary reaction torque determining means for determining an auxiliary reaction torque based on a detection value detected by the behavior detecting means, an electric motor for applying an auxiliary torque to the steered wheels, and an auxiliary steering torque determining means. Control means for controlling the electric motor with an auxiliary torque value obtained by adding the auxiliary reaction torque value determined by the auxiliary reaction torque determination means to the auxiliary steering torque value. In the vehicle steering system, the control means determines an upper limit and a lower limit of a ratio α of the auxiliary reaction torque to the total steering torque, and controls the electric motor within the range. This is achieved by providing a vehicle steering system. In particular, the upper limit αmax and / or the lower limit αmin may be determined according to the vehicle speed.

In this manner, the upper limit αmax and the lower limit αmin of the ratio α of the auxiliary reaction torque to the total steering torque are determined, that is, the lower limit αmin for securing a certain steering torque.
And sensitively detect road information,
In addition, by setting the upper limit αmax at which the setting of the steering torque is easy, it is possible to achieve both a proper steering force and a vehicle behavior suppression force at the time of disturbance at a high level over the entire speed range during traveling.

[0011]

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, an auxiliary steering torque determining means 17a for calculating an auxiliary steering torque as an electric power steering apparatus and an auxiliary reaction torque are calculated in the steering control unit 17 described above. 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, 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, as shown in the flowchart of FIG. 5, the steering angular velocity ω as shown in FIG. Using the yaw rate γ as an address as shown in FIG. 8B and the table shown in FIG. 8B, the auxiliary reaction torque T1 (damping torque component)
T2 (Yaw rate torque component) is obtained (step 21,
22) Then, the auxiliary reaction force torque components TA and T2 are added to obtain an auxiliary reaction force torque value TA (step 23).

[0020] Here, the proportion of auxiliary reaction force torque value TA for Zenmisao steering torque T plus the auxiliary reaction force torque value TA and the self-aligning torque Tsat and alpha, alpha is the vehicle speed V
It is set to the data table of the yaw rate torque component T2 side to fall between the maximum value (.alpha.max) and minimum value (.alpha.min) corresponding to.

[0021]

Α = TA / (TA + Tsat) αmax> α> αmin

Actually, when the vehicle speed V is lower than the predetermined vehicle speed V1, the maximum value of α is inversely proportional to the vehicle speed when the vehicle speed V is lower than the predetermined vehicle speed V1. The value (αmax) may be changed so that αmax = 100% when stopped (FIG. 6). This means that it is necessary to make it possible to appropriately set the steering force at the time of normal turning without losing the road information at a predetermined vehicle speed V1 or higher, and to secure a certain degree of deflection suppression performance when a disturbance acts on the vehicle. However, in a relatively low vehicle speed range less than the predetermined vehicle speed V1, especially on a dry road, a driver with a lighter steering wheel is preferred by a driver, and road information does not cause much problem, and at an intersection where the vehicle runs at a low speed. The reason is that it is necessary to improve the deflection suppression performance when a disturbance acts on the vehicle because there are many deep ruts that can be taken by the steering wheel.

Further, it is determined whether or not the target steering reaction force value TA exceeds a maximum value (Tmax) in order to eliminate unnecessary auxiliary reaction force torque, and the target steering reaction force value TA exceeds the maximum value. If the target steering reaction force value TA is equal 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 24) 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. 7 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 determination value TA determined in this way is added to the separately determined target auxiliary steering torque determination value, converted into a target current value by the target current determination means 17c, and output. .

By performing the above processing, as shown in FIG. 9, 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.

In the above structure, 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.

[0028]

As described above, according to the vehicle steering system of the present invention, the upper limit αmax and the lower limit αmin of the ratio α of the auxiliary reaction torque to the total steering torque are determined, that is, a certain level of the holding force. By setting a relatively low upper limit αmax that makes it possible to detect the lower limit αmin and road information sensitively and to easily set the steering force, it is possible to set the appropriate steering force over the entire speed range during driving and the vehicle during disturbance. The behavior suppressing force can be compatible at a high level. Further, by setting the upper limit αmax and / or the lower limit αmin in accordance with the vehicle speed, for example, during high-speed traveling, the lower limit αmin and road information that secure a certain level of steering-holding force can be sensitively sensed. Set a relatively low upper limit αmax, which is easy to set, and since road information is not so important at low speeds, steering on a dry road where steering force that can deal with ruts, etc., and especially light steering is preferable. Lower limit αmin to secure force and relatively higher upper limit αmax
By setting, the appropriate steering force and the vehicle behavior suppression force at the time of disturbance can be achieved at a higher level over the entire speed range during traveling.

[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 graph showing a relationship between a range of a ratio α of an auxiliary reaction torque TA to a total steering torque T and a vehicle speed V;

FIG. 7 is a circuit block diagram of a control system of the steering device and a data table used for the control processing.

FIGS. 8A and 8B are enlarged views of a data table used for the control processing.

FIG. 9 is a schematic diagram showing the movement of the vehicle when a crosswind is received during straight running.

[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-5-105100 (JP, A) JP-A-8-104249 (JP, A) JP-A-8-40293 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00 B62D 5/04

Claims (2)

(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. Control means for controlling the electric motor with an auxiliary torque value obtained by adding a force torque value, the control means comprising: Define the upper and lower limits of the ratio α with respect to the steering torque, vehicle steering system, characterized by being adapted to control the electric motor within the range. 2. The control system according to claim 1, wherein the control means determines an upper limit and / or a lower limit of a ratio α of the auxiliary reaction torque to the total steering torque according to a vehicle speed. Vehicle steering system.