JPH049708B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a steering device for an automobile that changes the transmission ratio of a steering wheel angle to wheels in accordance with vehicle speed.

(Prior Art) An automobile steering device converts the rotation of a steering wheel into a lateral displacement of a tie rod via a steering gear device such as a rack and pinion.
The direction of the left and right wheels connected to both ends of the tie rod is changed, but in this case, the amount of rotation of the steering wheel (handle steering angle) and the turning angle of the wheels (wheel steering angle) always have a constant correspondence. It is usually held in a relationship. However, for example, when driving at high speeds, it is desirable to increase the reduction ratio from the above-mentioned steering wheel steering angle to the wheel steering angle to reduce the wheel steering angle for a constant steering wheel steering angle in order to ensure driving stability, and when driving at low speeds, it is desirable to It is desirable to reduce the reduction ratio and increase the wheel steering angle with respect to a constant steering wheel steering angle in order to make the behavior of the automobile more agile and obtain a good driving feeling, and to make it easier to park the vehicle in a garage.

Therefore, as disclosed in, for example, Japanese Unexamined Patent Publication No. 58-224852, a speed-sensitive steering device has been proposed in which the ratio of the wheel steering angle to the steering wheel steering angle is changed depending on the vehicle speed. As shown in Fig. 5, a transmission mechanism F consisting of a pair of variable pitch pulleys C and D and a V-belt E wound between both pulleys is interposed between the handle A and the steering column B. In addition, the pitch diameter of the driven pulley D is controlled by the stepping motor G so that it becomes larger as the vehicle speed increases. According to this, handle A
The rotation transmission ratio (reduction ratio) from to steering column B increases at high speeds, and as a result, the wheel steering angle for a given steering wheel angle is small at high speeds and large at low speeds, resulting in good steering characteristics that correspond to the vehicle speed. will be obtained. However, when changing the transmission ratio according to the vehicle speed, simply changing the transmission ratio linearly (at a constant rate of change) with respect to the vehicle speed may cause the following problems, as shown in Figure 6. arise. In other words, if the ratio of the wheel steering angle to the steering wheel steering angle is changed according to the vehicle speed as described above, the wheel steering angle will change even if the steering wheel steering angle is constant due to changes in vehicle speed during a turn. Due to this change in vehicle speed and change in wheel steering angle, the vehicle body receives lateral acceleration and performs behaviors such as yawing and rolling, but this behavior becomes more pronounced at higher vehicle speeds, and this tendency increases as vehicle speed increases. increases exponentially. Therefore, as mentioned above, if the rate of change in the transmission ratio with respect to vehicle speed is constant, and therefore, at a constant steering wheel angle, the amount of change in wheel steering angle with respect to changes in vehicle speed is the same in the low vehicle speed range and the high vehicle speed range. In this range, the behavior of the vehicle body becomes more pronounced than in the low vehicle speed range. Therefore, the magnitude of vehicle body behavior such as yawing or rolling during a turn varies depending on the vehicle speed, making it impossible to maintain constant driving operability during a turn.

(Object of the Invention) The present invention addresses the above-mentioned problems regarding steering devices for automobiles.The present invention is intended to address the above-mentioned problems regarding steering devices for automobiles. In addition to obtaining good steering characteristics depending on the driving condition in both the high speed range and the high vehicle speed range,
By appropriately setting the rate of change of the reduction ratio with respect to the vehicle speed, the behavior of the vehicle body due to changes in vehicle speed when turning with a constant steering angle is always kept approximately constant regardless of the vehicle speed. The purpose of this is to improve the driving operability of the vehicle when turning.

(Structure of the Invention) That is, the steering device for an automobile according to the present invention includes a variable transmission ratio mechanism in the steering force transmission path between the steering wheel and the tie rod, a vehicle speed detection means for detecting vehicle speed, and a vehicle speed detection means for detecting the vehicle speed. The controller includes a controller that outputs a control signal in response to a signal from the controller, and an actuator that controls the transmission ratio variable mechanism in response to a control signal from the controller, and the controller is configured to adjust the wheel steering angle relative to the steering wheel steering angle. A control signal is output so that the reduction ratio increases as the vehicle speed increases, and the rate of change of the reduction ratio with respect to the vehicle speed in a low vehicle speed range is larger than the rate of change in a high vehicle speed range. Configure.

(Effects of the Invention) According to the steering device configured as described above, when driving at high speed, the reduction ratio of the wheel steering angle to the steering wheel steering angle becomes large, and the wheel steering angle to a constant steering wheel steering angle becomes small. Good driving stability is obtained, and when driving at low speeds,
As the reduction ratio becomes smaller and the wheel steering angle becomes larger with respect to a constant steering wheel steering angle, agility is obtained, and steering characteristics that correspond to the vehicle speed are obtained. In particular, the rate of change of the reduction ratio with respect to vehicle speed is large in the low vehicle speed range and small in the high vehicle speed range, so when the wheel steering angle changes due to a change in vehicle speed during a turn, the amount of change is large at low vehicle speeds and small at high vehicle speeds. As a result, when the amount of change in wheel steering angle due to a change in vehicle speed is constant, vehicle body behavior such as yawing and rolling, which increases at higher vehicle speeds, remains constant regardless of vehicle speed, and The steering amount of the steering wheel when attempting to perform a steady circular turn without changing the wheel steering angle due to the change in wheel steering angle becomes smaller at higher vehicle speeds, and driving operability is improved.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

1 to 3 show a transmission ratio variable mechanism that is installed in the steering force transmission path and changes the transmission ratio of the steering wheel angle to the wheels. a handle shaft 3 with one end fixed to the center of the handle shaft 3; an input shaft 6 disposed parallel to the handle shaft 3 and with a pair of input gears 4, 5 interposed between the shaft 3; 6, and a planetary gear type differential gear mechanism 8 provided between the input shaft 6 and the output shaft 7. The output shaft 7 is connected to a steering gear device (not shown), and further connected to left and right wheels via a link mechanism such as a tie rod.

The differential gear mechanism 8 includes a sun gear 9 fixed to the input shaft 6, a ring gear 10 fixed to the output shaft 7, and a plurality of gears arranged at equal angular intervals between the two gears 9 and 10 (in the illustrated example). 3) planetary pinions 11...11 are rotatably fitted onto the input shaft 6 to connect the pinions 11...11 to the pinion shaft 1, respectively.
2... Pinion carrier 13 supported via 12
It is made up of. A sector gear 14 is integrally provided on the carrier 13, and a pinion 16 fixed to the rotating shaft of a stepping motor 15 is meshed with the sector gear 14.

On the other hand, this steering device is equipped with a controller 17 that controls the rotation of the stepping motor 15. This controller 17
inputs the vehicle speed signal a from the vehicle speed sensor 18,
Based on the signal a, the stepping motor 15
The amount of rotation (including the direction of rotation) is set, and this is output to the stepping motor 15 as a control signal b.

According to the above configuration, when the steering wheel 2 is rotated while the automobile is running, the rotation is transmitted from the rotating steering wheel shaft 3 to the input shaft 6 via the pair of input gears 4 and 5, and the sun gear in the differential gear mechanism 8 is transmitted. Rotate 9. At this time, a control signal b is output to the stepping motor 15 from the controller 17 to which the signal a from the vehicle speed sensor 18 is input.
The motor 15 is rotated in accordance with the vehicle speed indicated by the signal a, and the pinion carrier 13 in the differential gear mechanism 8 is also rotated via the pinion 16 and sector gear 14. Therefore, in the differential gear mechanism 8, the sun gear 9 is rotated by an amount proportional to the amount of steering of the steering wheel 2, and at the same time, the pinion carrier 13 is rotated according to the amount of rotation of the stepping motor 15. Therefore, the ring gear 10 or the output shaft 7 in the differential gear mechanism 8 is rotated by an amount proportional to the amount of steering of the handle 2, which is increased or decreased according to the amount of rotation of the pinion carrier 13. . Then, depending on the amount of rotation of the output shaft 7, the wheels are steered via a steering gear device. In this case, since the amount of rotation of the stepping motor 15 or pinion carrier 13 is set according to the vehicle speed, the reduction ratio between the input shaft 6 and the output shaft 7, in other words, the wheel relative to the steering angle. The reduction ratio of the steering angle is changed according to the vehicle speed. As a result, if the reduction ratio is set to increase as the vehicle speed increases, and the wheel steering angle relative to a constant steering wheel steering angle is changed so that it becomes large in a low vehicle speed range and becomes small in a high vehicle speed range, This makes the vehicle more agile in the low speed range, and provides good driving stability in the high speed range.

However, as shown in FIG. 4, the reduction ratio does not simply change depending on the vehicle speed, but is set so that the rate of change is large in the low vehicle speed range and small in the high vehicle speed range. Therefore, when turning with a constant steering angle, the amount of change ΔR in the reduction ratio for a constant change in vehicle speed ΔV, in other words, the amount of wheel turning is greater at high speeds (ΔR ₂ ) than at low speeds (ΔR ₁ ). becomes smaller. In addition, in a high vehicle speed range equal to or higher than the set vehicle speed, the amount of change ΔR ₂ may be set to 0 as the case may be.

By the way, when a car turns, lateral acceleration acts on the car body depending on the amount of steering of the wheels, and this acceleration causes the car body to perform behaviors such as yawing and rolling. When the steering amount is the same, the larger the vehicle speed is, the larger the steering amount becomes.
However, as mentioned above, in the high vehicle speed range, the amount of wheel turning due to changes in vehicle speed is smaller than in the low vehicle speed range, so the behavior of the vehicle body is approximately constant regardless of the vehicle speed, and the wheel steering due to changes in vehicle speed is When trying to perform a steady circular turn without changing the angle, the amount of steering wheel steering by the driver becomes smaller at higher vehicle speeds. This improves the maneuverability when turning.

Incidentally, the characteristics of the transmission ratio with respect to the vehicle speed as shown in FIG. 4 can be obtained, for example, as follows.

In other words, steering wheel angle: θh, wheel steering angle: θw,
Reduction ratio: R = θh / θw, vehicle speed: V, wheelbase: l, stability factor: A, the lateral acceleration G during a steady circular turn is: G = V ² · θw / [l (1 + AV ² )] Therefore, the gain Ga (= ^G /θh) of the lateral acceleration G with respect to the ^steering wheel angle ^θh is given by ² )], and therefore, the reduction ratio R is expressed with respect to the gain Ga as R=V ² /[Ga·l(1+AV ² )]. Then, assuming that the gain Ga corresponding to the behavior of the vehicle body during turning is constant regardless of the vehicle speed, R=V ² /(α+βV ² ) () α=Ga・l (positive constant) β=Ga・It becomes l・A (positive constant).

Therefore, if this equation () is adopted as the equation showing the characteristics shown in FIG. 4, the behavior of the vehicle body when turning with a constant steering angle becomes approximately constant regardless of the vehicle speed.

Further, as an alternative to the above formula (), the following formula () that approximately represents the same characteristics can also be adopted. Here, α', β': positive constants, 0<n<
It is 1.

R=α′V ⁿ +β′ () Furthermore, the above equation () is the gain Ga of the lateral acceleration G.
However, instead of this, the gain of the yaw rate φ〓 with respect to the steering wheel angle θh
When Gb is kept constant, the reduction ratio R is as follows.

That is, the gain Gb (=φ〓/θh) of the yaw rate φ〓 with respect to the steering wheel angle θh is as follows: Gb=V・θw/[θh・l(1+AV ² )] =V/[R・l(1+AV ² )] Therefore, the reduction ratio R is as follows: R=V/[Gb·l(1+AV ² )]. Therefore, if the gain Gb of the yaw rate φ is constant regardless of the vehicle speed, R=V/(γ+δV ² ) () γ=Gb·l δ=Gb·l·A.

[Brief explanation of drawings]

1 to 4 show embodiments of the present invention. FIG. 1 is a cross-sectional plan view showing the configuration of the main parts of the steering device and the accompanying control circuit, and FIGS. 2 and 3 are respectively similar to FIG. 1. A cross-sectional view taken along the - line and the - line, and FIG. 4 is a control characteristic diagram. FIG. 5 is a schematic configuration diagram showing a conventional example, and FIG. 6 is a conventional control characteristic diagram. DESCRIPTION OF SYMBOLS 1... Transmission ratio variable mechanism, 2... Steering handle, 15... Actuator, 17... Controller, 18... Vehicle speed detection means (vehicle speed sensor).

Claims (1)

[Claims] 1. A variable transmission ratio mechanism that is provided in a steering force transmission path between the steering handle and the tie rod and changes the reduction ratio of the wheel steering angle to the steering wheel steering angle, a vehicle speed detecting means for detecting vehicle speed, and the vehicle speed detecting means a controller that inputs a signal from the controller and outputs a control signal, and an actuator that receives an output signal from the controller and operates the transmission ratio variable mechanism, and the controller adjusts the reduction ratio as the vehicle speed increases. 1. A steering device for an automobile, characterized in that the control signal is outputted so that the speed reduction ratio increases with respect to the vehicle speed in a low vehicle speed range, and so that the rate of change of the reduction ratio with respect to the vehicle speed in a low vehicle speed range is larger than the rate of change in a high vehicle speed range.