JP3110891B2 - 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 system for a vehicle, and more particularly to a steering system capable of generating a steering torque in a direction for suppressing a vehicle behavior generated when a disturbance such as a cross wind is applied. It concerns the device.

[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] If the vehicle receives a strong crosswind while traveling straight, the vehicle may be deflected in a direction deviating from the target straight traveling line. In such a case, in order to keep the vehicle running straight, a reaction force opposing the disturbance must be applied to the steered wheels.

[0004]

However, in the case of the conventional power steering apparatus described above, the auxiliary motor generates the steering torque only after the driver turns the steering wheel.
Even if the vehicle deflects due to a crosswind while traveling straight, the electric motor does not generate any auxiliary torque.

Therefore, in order to suppress the deflection of the vehicle, the driver himself must operate the steering wheel. However, in the case of the conventional power steering device, generally, as the lateral acceleration and the yaw rate of the vehicle increase, the steering is performed. In the case of vehicle deflection due to disturbances, the larger the force, the greater the steering force required for correction, which is disadvantageous.

[0006] In addition to this, a general power steering device requires a small steering force of the driver, but it is difficult to transmit information on the vehicle behavior from the steering wheel, so that the vehicle behavior may suddenly change. In such a case, the information was obtained only from the driver's sight and experience. For this reason, the correction operation is delayed, and the operation amount tends to increase.

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 an improved vehicle steering system capable of improving deflection suppression performance when a disturbance such as a cross wind acts on a vehicle, and improving straight running stability.

[0008]

SUMMARY OF THE INVENTION According to the present invention, there is provided, in accordance with the present invention, a manual steering means for manually steering a steered wheel of a vehicle, and a means for applying an auxiliary steering torque to the steered wheel. In a vehicle steering apparatus having an electric motor and control means for controlling a driving torque of the electric motor based on a detection value of the vehicle behavior detection means, a steering torque command value given to the electric motor is a detection value of the vehicle behavior detection means. This is attained by providing a vehicle steering system characterized by including a component for canceling a rate of change per unit time.

[0009]

In this manner, the irregular behavior of the vehicle caused by the disturbance is detected from the yaw rate or the lateral acceleration of the vehicle, and a force opposing this is generated by the electric motor for generating the auxiliary steering torque. As a result, vehicle behavior due to disturbance can be suppressed. In addition, by adding a torque command based on a differential value of the detection value of the vehicle behavior detecting means, it acts particularly on a transient component of the vehicle behavior, so that the responsiveness to the suppression of the vehicle behavior change is enhanced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to specific embodiments shown in the accompanying drawings.

FIG. 1 shows the configuration of a vehicle steering system to which the present invention is applied. This device comprises a manual steering force generator 1 and an electric auxiliary steering force generator 2, and is connected to a steering shaft 4 integrally connected to a steering wheel 3 via a connecting shaft 5 having a universal joint. The pinion 6 of the pinion mechanism is connected, and the knuckle arms of the left and right front wheels 9 are connected via tie rods 8 to both ends of a rack 7 which can mesh with the pinion 6 and reciprocate in the vehicle width direction. As a result, a normal rack-and-pinion steering operation can be performed.

An electric motor 10 is provided coaxially with the rack 7 so as to penetrate the rack 7 in the axial direction.
In the electric motor 10, a rack 7 is inserted into a hollow rotor, and a driving helical gear 11 is attached to the rotor.
Helical gear 1 attached to the axial end of a screw shaft 12 of a ball screw mechanism extending in parallel with
3 are engaged. The nut 14 of the ball screw mechanism is fixed to the rack 7.

The steering shaft 4 has a steering angle sensor 15 for outputting a signal corresponding to the rotation angle of the steering wheel 3 and a torque sensor 16 for outputting a signal corresponding to the steering torque of the steering shaft 4.
And are attached.

A lateral acceleration sensor 17 for outputting a signal corresponding to the lateral acceleration of the vehicle is provided at an appropriate position on the vehicle body.
A yaw rate sensor 18 for outputting a signal corresponding to the yaw rate (yawing angular velocity) of the vehicle and a vehicle speed sensor 19 for outputting a signal corresponding to the running speed of the vehicle are mounted.

In this embodiment, the steering wheel 3 and the front wheel 9 which is the steered wheel are mechanically connected, and the output of each of the sensors 15 to 19 is controlled by the control unit 20.
The output torque of the electric motor 10 is controlled by giving the control signal obtained by the processing described above to the electric motor 10 via the drive circuit 21.

FIG. 2 is a schematic block diagram showing a control system to which the present invention is applied. Each signal output of the steering angle sensor 15, the torque sensor 16, the lateral acceleration sensor 17, the yaw rate sensor 18, and the vehicle speed sensor 19 is input to the control unit 20. These signal inputs are input to the electric power steering control means 22 and the active steering reaction force calculating means 23, respectively, and are processed. The output current determining means 24 determines the target current value to be given to the electric motor 10.

In the electric power steering control means 22, control relating to normal steering force assist is performed.
For this control means, for example, a known electric power steering control for obtaining a desired target steering torque value according to the lateral acceleration and the yaw rate can be applied, and therefore a detailed description thereof is omitted here.

In the active steering reaction force calculating means 23, a target steering torque value is obtained by an algorithm described later based on each signal output from each of the sensors 15 to 19 inputted.

In the output current determining means 24, a target drive current signal which corresponds to the deviation between the target steering torque value and the actual steering torque value from the torque sensor 16 and which is increased or decreased by reversing the sign is obtained. I have.

The target drive current value obtained in this way is input to the drive circuit 21. This drive circuit 21
For example, the drive of the electric motor 10 is controlled by PWM control, and an actual current detection value by a current detection sensor is fed back to a target drive current value which is an input signal of the drive circuit 21.

In the active steering reaction force calculating means 23 in the control unit 20, the processing shown in the flowchart of FIG. 3 is repeatedly executed at a predetermined cycle. First, in step 1, the signal output of each sensor is read, and the steering angular velocity and yaw angular acceleration are calculated. In step 2, the steering reaction force TA is determined. Then, in step 3, the target steering reaction force is determined. The control signal is added to the electric power steering control means 22 in step 4.

This processing will be described in more detail with reference to FIGS. In the above step 1, first, the steering angle θ is read (step 21), and the steering angle θ is differentiated to calculate the steering angular velocity dθ / dt (step 22). Then, the vehicle speed V, the lateral acceleration G, and the yaw rate γ are read together (steps 23 to 25). Further, the yaw rate γ is differentiated and the yaw rate change rate per unit time (yaw angular acceleration) dγ
/ Dt is obtained (step 26).

Next, in step 2, the steering angular velocity dθ / dt, the lateral acceleration G, the yaw rate γ, and the yaw angular acceleration dγ / dt are respectively obtained from a data table having the vehicle speed V as an address as shown in FIG. Corresponding coefficients f1 and f2
F3 and f4 are obtained (step 31), and the steering reaction forces T1, T2, T3 and T4 for each component are calculated from these (step 32), and the components T1 and T2 of these steering reaction forces are calculated.
The target steering reaction force TA is determined by adding T3 and T4 (step 33).

Here, the yaw rate γ and the yaw angular acceleration d
The coefficients f3 and f4 for γ / dt employ a linear function that increases in accordance with the vehicle speed V. Since the influence of disturbance increases as the vehicle speed V increases, the weight is increased in an area where the vehicle speed V is high. This is to increase the effect.

Next, in step 3, it is determined whether or not the target steering reaction force TA exceeds a predetermined value (Tmax) (step 41), and the target steering reaction force TA exceeds the predetermined value. In this case, the Tmax value is defined as the target steering reaction force TA (step 42). If the target steering reaction force TA does not exceed the predetermined value (Tmax), it is similarly determined whether the target steering reaction force TA is smaller than the predetermined value (-Tmax) (step 43). If the reaction force TA is smaller than the predetermined value, the target steering reaction force TA is set to the above-mentioned -Tm.
An ax value is defined (step 44). These steps 4
The processing from 1 to step 44 corresponds to the limiter L in FIG.

The target steering reaction force T thus determined
A is added to the separately obtained target auxiliary steering torque, converted into a target current value by the output current determining means 24, and output to the drive circuit 21.

In this way, as shown in FIG. 9, when the vehicle 25 comes off the straight traveling line 26 due to the crosswind, the yaw rate γ and the lateral acceleration G of the vehicle 25 at this time are detected. Regardless of whether the steering wheel 3 is steered or not, the electric motor 10 is driven in a direction to cancel the yaw rate γ and the lateral acceleration G, that is, in a direction to return the deflection of the vehicle 25 to the straight traveling line 26 at that time.

For this reason, when the yaw rate γ and the lateral acceleration G occur in the vehicle 25 due to a disturbance such as a cross wind, the front wheels are so arranged that the vehicle 25 always runs straight against the disturbance even if the driver is in a released state. 9 is automatically steered, and irregular behavior can be stabilized. Also, when the driver holds the steering wheel 3, the same effect can be obtained if the driver leaves the movement of the steering wheel 3 by the steering reaction torque. Further, even in the steering in general traveling, the driver can experience the behavior of the vehicle body with the steering torque acting on the steering wheel 3 from the steering reaction force generated by the electric motor 10, so that a better steering feeling can be obtained.
In addition, if the driver steers or maintains the steering torque against this steering torque, the vehicle can be freely turned by the driver.

FIG. 10 shows characteristics in comparison with the conventional one. When a disturbance such as a cross wind is received, it can be seen that the steering is turned in the opposite direction to the behavior of the vehicle in which the control of the present invention indicated by the dotted line is not performed, and both the yaw rate and the lateral shift amount are suppressed.

When the vehicle is traveling on a rutted road surface or a puddle road surface, the steering wheel 3 is easily taken off. In such a case, however, the yaw rate γ and the lateral acceleration become the same as in the case of crosswind traveling. G is the vehicle 25
Therefore, by executing the above control, the trajectory is automatically corrected so that the vehicle 25 goes straight.

In addition to this, even when the yaw rate γ and the lateral acceleration G occur during a normal turning operation, etc.,
The electric motor 10 generates the steering torque in a direction to suppress these, that is, in a direction to return the vehicle to the straight traveling state, and this becomes the self-aligning torque, and the steering when returning to the straight traveling can be easily performed. Also, when the vehicle suddenly shows an oversteer tendency, a strong return force acts in accordance with the yaw rate γ at that time, so that countersteering becomes easy, and the return force is weak in a drift tendency where the yaw rate γ is low, It is easy to make more cuts.

In the above series of processing, the yaw rate value γ is differentiated, but the lateral acceleration value G
The same effect can be obtained by adding the same processing to the above.

[0033]

As described above, according to the present invention, the steering torque in the direction of suppressing the vehicle behavior acts on the steered wheels regardless of the presence or absence of the driver's steering. The irregular behavior of the vehicle due to the above is suppressed without requiring the driver to actively steer, and the running stability of the vehicle can be improved. In addition, the steering wheel can be held or steered at the driver's will with respect to the steering torque of the auxiliary motor acting on the steering wheel, so that the degree of freedom of driving does not decrease, and the steering reaction applied to the steering wheel is further reduced. The effect that the driver can sense the behavior of the vehicle with the force torque is also obtained.

[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 flowchart showing control processing of the steering device.

FIG. 7 is a circuit block diagram of a control system of the steering device.

FIG. 8 is 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.

FIG. 10 is a graph for explaining the operation of the present invention in comparison with a conventional configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Manual steering force generator 2 Electric auxiliary steering force generator 3 Steering wheel 4 Steering shaft 5 Connecting shaft 6 Pinion 7 Rack 8 Tie rod 9 Front wheel 10 Electric motor 11 Drive helical gear 12 Screw shaft 13 Driven helical gear 14 Nut 15 Steering angle sensor 16 Torque Sensor 17 Lateral acceleration sensor 18 Yaw rate sensor 19 Vehicle speed sensor 20 Control unit 21 Drive circuit 22 Electric power steering control means 23 Active steering reaction force calculating means 24 Output current determining means 25 Vehicle 26 Straight running line

────────────────────────────────────────────────── (5) Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI B62D 119: 00 137: 00 (56) References JP-A-62-155170 (JP, A) JP-A-4-138611 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B62D 6/00 B62D 5/04

Claims (2)

(57) [Claims] An electric motor for manually steering a steered wheel of a vehicle, an electric motor for applying an auxiliary steering torque to the steered wheel, and the electric motor based on a detection value of a vehicle behavior detecting means. Control means for controlling the driving torque of the vehicle, the steering torque command value given to the electric motor, the reaction force component to the rate of change per unit time of the detection value of the vehicle behavior detection means, A steering device for a vehicle, comprising: 2. The vehicle steering system according to claim 1, wherein a ratio of the reaction force component to the total control amount increases in proportion to a vehicle speed.