JP2001151133A - Vehicular steering device with variable steering ratio - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vehicular steering device with a variable steering ratio capable of setting a steering gear ratio providing good handleability of a steering wheel such that the driver will not feel disagreeable at low speeds as well as at medium to high speeds. SOLUTION: The vehicular steering device with the variable steering ratio, for varying the steering gear ratio R according to vehicle speed V, varies the steering gear ratio R (as shown by the true line along the two-dot chain line), so that the ratio of the deflection angle α of the driver's visual line to the steering angle θ is held constant (α/θ = constant), at least at low speeds not higher than a predetermined vehicle speed V1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable steering angle ratio steering apparatus for a vehicle, and more particularly to a method of setting a steering gear ratio according to a vehicle speed.

[0002]

2. Related Background Art In recent years, a ratio between a steering angle (steering angle) of a steering wheel and a turning angle of a steered wheel, that is, a steering gear ratio (steering angle ratio) is changed according to the vehicle speed. A vehicle that can be variably controlled so as to be large has been put to practical use. Then, for example, Japanese Patent Application Laid-Open No. 9-58508
The publication discloses that the steering gear ratio is minimized in a low speed range, and a yaw rate gain (rotational angular speed gain) in a medium speed range.
A technique is disclosed in which the steering gear ratio is set so that the lateral G gain (lateral acceleration gain) is constant in a high-speed region so that the steering gear ratio is constant.

[0003] In addition, the Automotive Technology Association 9932827,
Based on the experimental data that "the driver is gazing at a point to be reached after about 1.2 seconds on the target route regardless of the vehicle speed when entering the corner", the current vehicle traveling direction and gazing point direction A technique is disclosed in which a steering gear ratio is set such that an angle formed by the steering gear ratio, that is, a target path angle is proportional to the steering angle.

[0004]

However, in the technique disclosed in Japanese Patent Application Laid-Open No. 9-58508, the steering gear ratio is minimized in a low speed range, but a specific minimum value and a method of setting the minimum value are disclosed. If the steering gear ratio is too small, the steering angle of the steered wheels is large relative to the steering angle of the steering wheel, and the steering becomes too quick, and the steering is difficult to handle and the driver feels discomfort. There is.

The technique disclosed in the Japanese Society of Automotive Engineers 9932827 means that the steering gear ratio is set so that the ratio between the steering angle and the target path angle after about 1.2 seconds is constant. This means that the steering gear ratio is set so that the yaw rate gain is constant. In such a setting, the steering gear ratio becomes extremely small in a low-speed range, and the steering angle is also changed with respect to the steering angle. There is a problem that the angle is large and the steering is too quick, and the driver feels uncomfortable as described above.

The present invention has been made to solve such a problem, and an object of the present invention is to handle the steering without causing the driver to feel uncomfortable not only in the middle and high speed ranges but also in the low speed range. It is an object of the present invention to provide a vehicular steering angle ratio variable steering device capable of setting a good steering gear ratio.

[0007]

In order to achieve the above-mentioned object, according to the first aspect of the present invention, there is provided a vehicle steering angle ratio variable steering device for changing a steering gear ratio according to a vehicle speed. In the region, the steering gear ratio is changed so that the ratio between the driver's line-of-sight deflection angle and the steering angle becomes constant.

That is, in a low-speed range below a predetermined vehicle speed, the ratio between the steering angle and the driver's line-of-sight swing angle, that is, the angle formed by the driver's line of sight (front-point direction) with respect to the forward direction of the vehicle is made constant. The steering gear ratio is set. As a result, when trying to make a large turn of the vehicle in a low speed range, the upper body of the driver is generally directed forward rather than in the traveling direction of the vehicle due to a problem in the vehicle structure. The driver must shift his / her gaze greatly from the direction to the point where the vehicle should reach, and at this time, the driver unknowingly, due to human habits, shifts the gaze with respect to the front direction of the vehicle, that is, corresponds to the gaze swing angle or There is a tendency to try to steer the steering in proportion to it, but the steering gear ratio is set appropriately so as to conform to such human habits, the steering gear ratio becomes too small and the steering gear It is possible to prevent the steering from becoming too quick with respect to the steering, and to prevent the driver from feeling uncomfortable, thereby improving the steering maneuverability in a low speed range.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Referring to FIG. 1, there is shown a schematic configuration diagram of a vehicular steering angle ratio variable steering device according to the present invention. Hereinafter, the configuration of the vehicular steering angle ratio variable steering device according to the present invention will be described with reference to FIG. I do.

As shown in FIG. 1, knuckle arms 2 and 3 are connected to wheel support members (not shown) for rotatably supporting a pair of front wheels (steering wheels) WFR and WFL of the vehicle. Arms 2 and 3 have tie rods 6
The steering gear box 4 is connected via a switch 7. Here, a rack and pinion type steering gear box 4 is employed as the steering gear box 4, and the rack and pinion type steering gear box 4 is used.
When the pinion rotates, the rack meshing with the pinion moves in the vehicle left-right direction accordingly.

More specifically, a steering wheel 12 is connected to the pinion via a steering shaft 10. When the steering wheel 12 is steered by a driver and the pinion rotates, the tie rods 6 and 7 together with the rack move in the lateral direction of the vehicle. Move, and this causes the front wheel WF
The R and WFL are steered in the same direction. As shown in the figure, a variable gear ratio mechanism 14 is interposed between the steering shaft 10 and the pinion of the steering gear box 4.

The variable gear ratio mechanism 14 is a mechanism that varies a steering gear ratio between the steering shaft 10 and the pinion, that is, a gear ratio (steering angle ratio) R. The rotation angle of the pinion with respect to the steering angle θ of the steering wheel 12 is changed. That is, the steering angles of the front wheels WFR and WFL can be changed. More specifically, the variable gear ratio mechanism 14 is configured by interposing a variable reduction mechanism between, for example, a planetary gear mechanism and a sector gear, and the steering speed of the steering wheel 12 is controlled at a constant gear ratio by the planetary gear mechanism. In addition to the speed reduction, the rotational speed of the sector gear is changed by the variable speed reduction mechanism, so that the gear ratio R between the steering shaft 10 and the pinion is made variable.

More specifically, the variable speed reduction mechanism is provided with an actuator for performing a shift operation, and the actuator includes an electronic control unit (ECU) 2.
Connected to 0. A wheel speed sensor 22 for detecting a wheel speed is provided near the front wheel WFL, and the wheel speed sensor 22 is connected to the ECU 20. That is,
When wheel speed information is detected by the wheel speed sensor 22, the wheel speed signal is supplied to the ECU 20 and is converted into vehicle speed information V by arithmetic processing.

When the vehicle speed V is obtained based on the information from the wheel speed sensor 22 in the vehicle steering angle ratio variable steering apparatus thus configured, the ECU 20 determines a predetermined command gear ratio signal based on the vehicle speed V. That is, the actuator operation signal is calculated, and the predetermined instruction gear ratio signal is supplied to the gear ratio variable mechanism 14. This allows
The variable speed reduction mechanism operates within the variable gear ratio mechanism 14, and the gear ratio between the steering shaft 10 and the pinion is variably controlled.

In practice, as shown in FIG. 2, the relationship between the vehicle speed V and the gear ratio R is set in advance as a map through experiments or the like, and the gear ratio R for determining the predetermined instruction gear ratio signal is: It is read from the gear ratio map according to the vehicle speed information V. According to the gear ratio map of FIG. 2, when the vehicle is in the middle to high speed range, Japanese Patent Application Laid-Open No. 9-585 shown as a conventional example is used.
The gear ratio R (solid line) is set in the same manner as in the technique described in Japanese Patent Application Publication No. 08-08,083. That is, when the vehicle is in the high speed range, the gear ratio R is set so that the lateral G gain is constant (for example, the lateral acceleration is 1 G when the steering angle θ is 90 deg) based on the lateral G gain constant characteristic (broken line). The gear ratio is set so that the yaw rate gain is constant (for example, when the steering angle θ is 4.4 deg, the yaw rate is 1 deg / sec) based on the constant yaw rate gain characteristic (dot-dash line) when in the middle speed range. R is set.

On the other hand, when the vehicle is in the low speed range, the gear ratio R (solid line) is set based on the constant line-of-sight swing angle characteristic (two-dot chain line). Hereinafter, a method of setting the gear ratio R based on the constant line-of-sight shake angle characteristic, that is, the operation of the vehicle steering angle ratio variable steering device according to the present invention will be described with reference to FIGS. .

In general, in a low speed range (for example, at a low speed such as 20 km / h or less), the vehicle is often driven to make a large turn at an intersection or the like. In such a case, due to the problem of the vehicle structure in which only the front wheels WFR and WFL are steered wheels,
Even if the driver starts steering the steering wheel 12,
As shown in FIG. 3, the upper body of the driver is not in the vehicle traveling direction but in the vehicle forward direction, that is, in the direction shifted by the center-of-gravity slip angle β with respect to the vehicle traveling direction. Therefore, in this case,
The driver enlarges his line of sight in order to see the point where the vehicle should reach, that is, the front gazing point P (eg, the value α).
1) will be shifted. The forward fixation point P is defined as a point at which the vehicle reaches after a predetermined time (about 1.2 seconds) irrespective of the vehicle speed V based on the above experimental data.

At this time, because of the vehicle response characteristics and the fact that the driving frequency is usually high in the middle speed range, the driver must:
There is a tendency that the steering wheel 12 is unconsciously steered while being aware of the gear ratio R in the middle speed range by an amount corresponding to or proportional to the gaze deflection angle α. Therefore, in the present invention, when the vehicle speed V is in a low speed range, the ratio between the line-of-sight deflection angle α (for example, the value α1) and the steering angle θ (for example, the value θ1) is constant in consideration of such human behavior. (Α /
The gear ratio R is set so that θ = α1 / θ1 = constant.

As a result, in the low speed range, the gear ratio R is set so as to conform to human habits. As shown in FIG. Is also set to a large value R0 (for example, value 5), the gear ratio R becomes too small, and the steering of the steering wheel 12 is turned too quickly to prevent the driver from feeling uncomfortable. Steering wheel 1
2, the maneuverability is improved, and the driving feeling is improved. Therefore, by combining the gear ratio characteristics in the low speed range and the gear ratio characteristics in the middle and high speed ranges described above, an optimum steering operation can be realized over the entire vehicle speed range from the low speed range to the high speed range. .

Further, as described above, the gear ratio R is set so that the yaw rate gain is constant in the medium speed range. However, the yaw rate is the rotational angular velocity around the center of gravity of the vehicle, and Based on an empirical rule that the viewpoint P is a point that the vehicle reaches after a predetermined time (about 1.2 seconds) regardless of the vehicle speed V, as shown in FIG. In a situation where the forward direction of the vehicle and the vehicle traveling direction are substantially the same (at a medium speed), the gaze deflection angle α is set to the predetermined time (approximately 1.2).
Second) means the yaw rate, the steering angle θ (for example, the value θ2) and the line-of-sight angle α
(For example, the value α2) is constant (α / θ = α2 / θ2 =
That is, it can be said that making the constant) means that the yaw rate gain is made constant.

Therefore, in this case, it can be considered that the vehicle speed V has increased from the low speed region as shown in FIG. 4 and has shifted to the medium speed region, and the predetermined vehicle speed V1 (for example, 50 km / h) is defined as the switching value between the low vehicle speed and the medium vehicle speed, and the gear ratio R is set so that the yaw rate gain is constant at the predetermined vehicle speed V1, that is, the value R1 (for example, the value 14). The ratio between the line-of-sight shake angle α and the steering angle θ is defined as the reference ratio K, and in the low-speed range, the ratio between the line-of-sight shake angle α and the steering angle θ is the reference ratio K (α / θ = α1 / θ1 = α2). / Θ2 = K). In addition, based on the above reason, this reference ratio K can be said to be a yaw rate gain in a middle speed range.

As a result, as shown by the solid line in FIG. 2, the gear ratio R can be continuously set between the low speed range and the middle speed range without any step, and the vehicle speed V is changed from the low speed range to the middle speed range or the middle speed range. When the vehicle shifts from the low speed range to the low speed range, the gear ratio R can be changed very smoothly. In addition to the effect of improving the maneuverability in the low speed range, the gear ratio R in the middle speed range where the driver frequently drives is increased. Even if the steering wheel 12 is steered while being conscious of the ratio R, it is possible to prevent the driver from feeling so strange.

In the above embodiment, the gear ratio R between the steering shaft 10 and the pinion is variably operated to mechanically control the front wheels WF with respect to the steering of the steering wheel 12.
Although the variable steering angle ratio steering device is configured to steer the R and WFL, the variable steering angle ratio steering device is a steer-by-wire system in which a pinion is rotated by a step motor based on an electric signal from the ECU. A configuration in which the rotation speed of the step motor is changed according to the vehicle speed V may be employed.

[0024]

As described above in detail, according to the variable steering angle ratio steering apparatus for a vehicle according to the first aspect of the present invention, the steering angle and the driver's line-of-sight swing angle in a low-speed range equal to or lower than a predetermined vehicle speed.
In other words, the steering gear ratio is set in accordance with human habits so that the ratio between the angle formed by the driver's line of sight (the direction of the gazing point) with respect to the forward direction of the vehicle is constant.
It is possible to preferably prevent the steering gear ratio from becoming too small and the steering from becoming too quick for the steering operation to cause the driver to feel uncomfortable, and to improve steering maneuverability in a low speed range.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a vehicle steering angle ratio variable steering device according to the present invention.

FIG. 2 is a map showing a relationship between a vehicle speed V and a gear ratio R.

FIG. 3 is a schematic diagram of the turning of the vehicle at a low speed, illustrating the operation of the present invention.

FIG. 4 is a schematic diagram of the turning of the vehicle at the time of middle speed, and is a diagram illustrating the operation of the present invention.

[Explanation of symbols]

 Reference Signs List 4 steering gear box 10 steering shaft 12 steering wheel 14 variable gear ratio mechanism 20 electronic control unit (ECU) 22 wheel speed sensor WFR, WFL front wheel (steering wheel)

Claims (1)

[Claims] 1. A vehicle steering angle ratio variable steering device that changes a steering gear ratio in accordance with a vehicle speed, wherein a ratio between a driver's line-of-sight swing angle and a steering angle is constant at least in a region equal to or lower than a predetermined vehicle speed. A variable steering angle ratio steering device for a vehicle, wherein a steering gear ratio is changed.