JPH06144270A - Steering system - Google Patents

Abstract

PURPOSE:To lighten the burden on a driver by determining a steering gear ratio in a high speed region on the basis of an upward convex yaw rate gain fixed curve, and determining a steering gear ratio in a low speed region on the basis of a downward convex lateral G gain fixed curve. CONSTITUTION:In a steering system, the operating angle signal of a steering shaft and the vehicle speed signal of a vehicle speed sensor are inputted into a control unit where a steering gear ratio Z is computed, and wheels are steered on the basis of a control command from the control unit. The control unit is provided with a central control unit. In the case of an X-axis being made the vehicle speed V and a Y-axis being made a steering ratio, the central control unit determines the steering gear ratio Z in a high speed region on the basis of an upward convex yaw rate gain fixed curve and determines the steering gear ratio Z in a low speed region on the basis of a downward convex lateral G gain fixed curve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system.

[0002]

2. Description of the Related Art Generally, in a four-wheeled vehicle, a rotary motion of a steering handle is converted into a linear motion by a rack and pinion, and a knuckle arm or the like is pushed to change the direction of a front wheel, thereby performing a so-called steering operation. There is also what is called power steering that facilitates the steering operation by using hydraulic or electric power. Further, a vehicle speed response type steering ratio varying device and a steering angle response type steering ratio varying device are known as means for achieving both handling and steering stability of the vehicle. The steering gear ratio (steering ratio) is (steering wheel angle ÷ actual steering angle)
And the steering gear ratio (turning ratio) is Z, the actual steering angle is calculated by (steering wheel angle / Z).

A vehicle speed response type steering ratio varying device has been proposed, for example, in Japanese Patent Laid-Open No. 224852/1983. According to the publication, this device measures the vehicle speed and the wheel steering angle (actual steering angle) is determined according to the vehicle speed. It is said that the steering ratio of the steering wheel angle with respect to (1) is variable, and the steering ratio can be increased at higher speeds to achieve both low-speed maneuvering and high-speed stability.

The steering angle response type steering ratio varying device changes the steering ratio according to the size of the steering wheel rotation angle. For example, the steering ratio becomes smaller as the steering wheel rotation angle becomes larger, so that the steering speed is changed at a low speed. It is said that it is possible to achieve both turning and stability at high speed.

[0005]

The movement that occurs when a vehicle turns is called yawing. The angular velocity around an axis perpendicular to the vehicle body (generally called the Z-axis) is called yaw rate. It has been found that the yaw rate against Yorate is different.

On the other hand, the vehicle speed response type steering ratio varying device cannot change the yaw rate of the vehicle because the steering ratio (steering gear ratio) change depends only on the vehicle speed. Therefore, in the vehicle speed response type steering ratio varying device, it is necessary for the driver to empirically predict the way the yaw rate is going to be steered, and the steering operation becomes complicated.

Further, the steering angle response type steering ratio varying device is good in high speed, but at other low speeds, the steering ratio becomes too large and a large steering wheel rotation is required, resulting in increased driver fatigue. Furthermore, since the change of the steering ratio (steering gear ratio) depends only on the steering angle, it cannot respond to the change of the yaw rate of the vehicle, and the driver needs to empirically predict the yaw rate and steer. Therefore, the steering operation becomes complicated. Then, the objective of this invention is providing the steering device which can reduce a driver | operator's burden.

[0008]

In order to achieve the above object, the present invention provides a control unit of a steering system for determining a steering gear ratio in a high speed region based on an upwardly convex yaw rate constant gain curve and projecting downwardly. A central control unit for determining the steering gear ratio in the low speed region based on the constant lateral G gain curve is provided.

Further, the central control unit sets the steering gear ratio in the extremely low speed region of the low speed region to a constant ratio at which the maximum actual steering angle reaches the maximum actual steering angle, and the steering gear ratios in other low speed regions are the lateral G It is even better if it is decided based on a constant gain curve.

[0010]

The control unit, which receives the operation angle signal of the steering rotation axis and the vehicle speed signal of the vehicle speed sensor, either of the yaw rate gain constant, the lateral G gain constant or the constant actual steering angle reaching the maximum actual steering angle according to the vehicle speed. The steering gear ratio is calculated on the basis of, and the wheels are steered based on a control command from the control unit.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings should be viewed in the direction of the reference numerals.
FIG. 1 is a side view of a grip type steering device of the present invention. The grip type steering device 1 includes a grip rod portion 3, a U ring 4, a pivot shaft 5, a grip absolute angle detection mechanism 6, and a torque on a steering rotation shaft 2. The sensor 7, the reaction force generation motor 8, and the grip rotation angle detection mechanism 9 are arranged in series.

More specifically, the first side of the torque sensor 7 is provided on one side.
The bracket 11 is attached with a plurality of hexagon socket head bolts 12, and the grip absolute angle detection mechanism 6 is attached to the first bracket 11 with a long and thin cross screw 13, and the first shaft 7a of the torque sensor 7 and the grip absolute angle detection. The pivot shaft 5 is inserted in common with the mechanism 6, the U ring 4 is attached to the other end of the pivot shaft 5, the flat washer 14 and the nut 15 are attached.
It is fixed at. The pivot shaft 5 and the U ring 4 are spline-coupled, and the relative mounting angle can be changed. The pivot shaft 5 is fastened to the first shaft 7a of the torque sensor 7 with a set screw 16 and a key 17. Set screw 16
Is screwed in with a driver or the like through a notch (not shown) opened in the first bracket 11.

Further, the sub-bracket 18 is attached to the reaction force generating motor 8 to which the grip rotation angle detecting mechanism 9 is attached in advance by a plurality of hexagon socket head cap screws 19, and the sub-bracket 18 and the second bracket 21 are different from each other. It is also fastened to the other side surface of the torque sensor 7 with the hexagon socket head cap screw 22. At this time, the motor shaft 8a is fitted to the second shaft 7b of the torque sensor 7.

FIG. 2 is a view taken in the direction of arrow 2 in FIG. 1. The mounting seat 23 formed on the first bracket 11 is joined and fixed to the inner surface of the front door 25, for example, with a bolt 24. The same applies to the second bracket 21.

In FIG. 1, the grip absolute angle detection mechanism 6 is, for example, a rotary variable resistor or potentiometer, and a brush rotating together with the pivot shaft 5 slides on a fixed resistance element to output voltage. Is an analog instrument for converting the absolute angle of the grip bar portion 3 into an electric signal.

The torque sensor 7 measures the relative torque difference between the pivot shaft 5 and the motor shaft 8a, has a piezoelectric element and a strain gauge inside, and converts the amount of strain into a current or a voltage.

The reaction force generation motor 8 applies a predetermined rotational reaction force, that is, a response force to the grip bar portion 3, and is appropriately decelerated by a built-in reduction gear. The grip rotation angle detection mechanism 9 is a rotary encoder, that is, a device that converts a rotation angle into an electric signal, and is, for example, a magnetic encoder,
It is a digital instrument that converts the rotation angle into the number of pulses.

FIG. 3 is a perspective view showing an example of use of the grip type steering device according to the present invention. The driver M holds the grip bar portion 3 of the grip type steering device 1 with his right hand and indicates as indicated by an arrow on the left or right. Rotate and steer. In the figure, 27 is a sheet, 28 is an instrument panel, and 29 is a rearview mirror.

FIG. 4 is a system diagram of the grip type steering device of the present invention. When the driver rotates the grip bar portion 3 to the left or right, the grip rotation angle detection mechanism 9 immediately outputs the rotation angle and the direction signal. Control unit 30 (hereinafter "ECU3
0 ”). The ECU 30 calculates the rotation reaction force in the calculation unit, and the motor 8 is transmitted via the motor drive unit 31.
Is started and a rotational reaction force is applied to the grip bar portion 3. The torque sensor 7 detects the difference between the torques acting on the first shaft and the second shaft (see FIG. 1), and sends this signal to the ECU 30 via the strain amplifier 32. The ECU 30 controls the motor 8 so that the torque difference has a predetermined value.

FIG. 5 is a flow chart showing the operation of the CPU (central control unit) shown in FIG. 4. In ST01 (step No. 1, hereinafter the same), the stick operation angle θ signal from the encoder and the vehicle speed V signal from the vehicle speed sensor are sent. Read. In this embodiment,
A determination step of ST02 and ST03 is provided to classify the vehicle speed V into high speed, low speed, and extremely low speed. If the vehicle speed V is at a low / high speed switching speed Vh or more, go to ST04, and if it is less than Vh, extremely low / low speed switching. If the speed is less than Vm, go to ST05,
If it is less than Vm, it selectively branches to ST06.

ST04 relates to a steering gear ratio function Zh called "a constant yaw rate gain line", and an arithmetic expression is given by "Equation 1". As a result, the yaw rate with respect to the operating angle does not differ depending on the vehicle speed, the driver does not need to perform the steering operation in anticipation, the stable drivability is secured, and the burden on the driver is reduced. .

[0022]

[Equation 1]

ST05 relates to the steering gear ratio function Zm called "horizontal G gain constant line", and the arithmetic expression is given by "Equation 2". As a result, agile maneuverability is ensured in the low-speed range where steering response of the vehicle is required, and the amount of operation by the driver is reduced.

[0024]

[Equation 2]

In ST06, the steering gear ratio is set to a steering gear ratio function Zl called "maximum actual steering angle achievement ratio". In this Zl, the stick angle at which the driver normally cuts smoothly is the normal operation angle. In this case, it is calculated by {maximum normal operation angle} ÷ {maximum actual front wheel steering angle}. As a result, it is possible to prevent the actual steering angle from becoming the maximum with a small operating angle, and the maximum actual steering angle can be realized with the maximum value of the operating angle, so that the maneuverability of the vehicle at extremely low speed can be secured.

FIG. 6 is a graph showing an example of the relationship between the vehicle speed and the steering gear ratio of the present invention. The x-axis is the vehicle speed and the y-axis is the steering gear ratio Z. That is, in the high speed region of Vh or higher, the steering gear ratio Z is determined by the "constant yaw rate gain line" which is an upwardly convex curve, and Vm-Vh
In the low speed region between the two, the steering gear ratio Z is determined by the "lateral G gain constant line" which is a downwardly convex curve, and 0-
In the extremely low speed range of Vm, the steering gear ratio Z becomes the "maximum actual steering angle achievement ratio". When the x coordinate is near Vm and Vh, adjacent curves are connected by a smooth line to prevent the value of the reading steering gear ratio Z from being significantly discontinuous.

After the above processing, the process returns to FIG. 5 and ST0
In step 8, the stick operation angle θ is divided by the steering gear ratio Z to obtain the front wheel actual steering angle command value αf1. Next, in ST09, vehicle response tuning filter processing is performed to determine the front wheel actual steering angle command value αf (ST10). As shown in FIG. 6, this may cause the vehicle to become responsive in an extremely low / low speed range. Therefore, a tuning filter is used to suppress the rise of the yaw rate so that the driver does not feel uncomfortable.

The control signal through the front wheel gear box control routine of ST11 is the PWM (pulse width
The modulation) generator 33 converts the pulse signal into a pulse signal, and the steering motor 37, the PWM interface unit 34 and the motor drive units 35, 36
38 is driven to steer wheels 39 and 40.

The grip absolute angle detection mechanism (potentiometer) 6 is a grip rotation angle detection mechanism (encoder).
As in the case of 9, the rotation angle from the neutral position of the grip bar portion 3 is monitored, and at the same time, the absolute angle of the grip is detected to determine the neutral position when the system is started up. In this embodiment, the grip rotation is performed. It is also provided as a backup of the angle detection mechanism 9. For example, the ECU 30 compares the digital signal of the grip rotation angle detection mechanism 9 with the analog signal of the potentiometer 6 and determines that the accuracy of each device is good if the difference between them is less than a certain value.

Next, the reason for selecting each curve in FIG. 6 will be described. Basically, by keeping the yaw rate gain constant, there is no difference in the way the yaw rate appears with respect to the operating angle depending on the speed of the vehicle, and the driver does not have to perform the steering operation in anticipation, ensuring stable drivability. As a result, the burden on the driver is reduced. However, in the low speed range, the lateral G gain is kept constant, and the rising of the vehicle, that is, the agility is emphasized. In the extremely low speed range such as garage parking with so-called stationary steering, it is necessary to reach the maximum actual steering angle at the maximum operating angle for normal use, so the maximum actual steering angle achievement ratio is selected, and a steering ratio lower than this is required. Not.

FIG. 7 is a diagram of another embodiment of FIG. 5, in which the calculation flow (ST02 to ST06) of FIG. 5 is replaced with a map ST02A. The map of ST02A is a chart or graph showing the relationship between the vehicle speed and the steering gear ratio, and the steering gear ratio is determined by giving the vehicle speed.

FIG. 8 is a graph showing the relationship between the vehicle speed and the steering gear ratio according to the present invention, and FIG. 6 shows an example of the relationship between the vehicle speed and the steering gear ratio according to the present invention. As shown in FIG. A vehicle speed-steering gear ratio relationship graph is selected according to the lateral G and the yaw rate.

Although the present invention has been described using the grip type steering device in the present embodiment, the present invention is not limited to this, and the present invention may be applied to a steering device using a normal steering wheel.

[0034]

As described above, according to the present invention, the yaw rate constant or the lateral G gain is constant according to the vehicle speed in the control unit to which the operation angle signal of the steering shaft and the vehicle speed signal such as the vehicle speed sensor are input. The steering gear ratio is calculated on the basis of the steering wheel, and the wheels are steered based on the control command from the control unit, so steering stability is ensured at high speeds, and the vehicle rises at low speeds, that is, The agility is improved, and the driver's burden can be reduced.

If the maximum actual steering angle is achieved at the maximum operating angle in normal operation in the extremely low and low range, so-called stationary steering becomes easy. As described above, according to the present invention, the driver can easily steer over all vehicle speeds without being aware of the motion of the vehicle.

[Brief description of drawings]

FIG. 1 is a side view of a grip type steering device of the present invention.

FIG. 2 is a view on arrow 2 of FIG.

FIG. 3 is a perspective view showing a usage example of the grip type steering device of the present invention.

FIG. 4 is a system diagram of a grip type steering device of the present invention.

FIG. 5 is a calculation flowchart of the CPU (central control unit) of FIG.

FIG. 6 is a graph showing an example of the relationship between vehicle speed and steering gear ratio of the present invention.

FIG. 7 is a diagram of another embodiment of FIG.

FIG. 8 is a graph showing the relationship between vehicle speed and steering gear ratio of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Steering device, 2 ... Steering rotating shaft, 3 ... Gripping rod part, 30 ... Control unit, Z ... Steering gear ratio, V
… Vehicle speed, θ… Stick operation angle.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B62D 137: 00

Claims (2)

[Claims] 1. An operation angle signal of a steering rotating shaft and a vehicle speed signal of a vehicle speed sensor are input to a control unit, a steering gear ratio is calculated by this control unit, and steering of a wheel is performed based on a control command from the control unit. In the steering apparatus, the control unit determines a steering gear ratio in a high speed region based on a yaw rate constant curve that is convex upward and a downward convex when the vehicle speed is on the x-axis and the steering gear ratio is on the y-axis. A steering system including a central control unit that determines a steering gear ratio in a low speed range based on a constant lateral G gain curve. 2. The central control unit sets a steering gear ratio in an extremely low speed region in a low speed region to a constant ratio that reaches a maximum actual steering angle at a maximum steering angle in normal use, and sets steering gear ratios in other low speed regions to the constant ratio. The steering apparatus according to claim 1, wherein the steering apparatus is determined based on a constant lateral G gain curve.