JPS6280174A - Four wheel steering device - Google Patents

Abstract

PURPOSE:To attain a mode change with no unsatisfactory feeling, by providing such an arrangement that when the speed of a vehicle exceeds a predetermined value in such a condition that front wheels are steered in the same phase mode, rear wheels alone are smoothly returned into their neutral positions, and the vehicle may be returned into an AUTO mode only after the vehicle running straightforward. CONSTITUTION:A four wheel drive steering device is set in an AUTO mode unless a same phase switch 17 is turned on, and therefore, rear wheels 27 are set under control to a steering angle delivered from an AUTO mode steering ratio data delivering means 28 in accordance with a steering angle of front wheels and a vehicle speed transmitted from sensors 15, 16. When the vehicle speed is below a predetermined value and therefore, the same phase switch 17 is turned on, a means 29 delivers data of the same phase steering ratio so that the rear wheels 27 are steered by a predetermined amount in the same direction as the steering direction of front wheels. Further, when the speed of the vehicle exceeds a predetermined vehicle speed in such a condition that the same phase mode is selected, a means 30 delivers data of a transitional steering ratio according which the rear wheels 27 is smoothly moved until their steering ratio comes to be zero, that is, the wheels are steered to be set to the neutral position.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a four-wheel steering device configured to steer not only the front wheels but also the rear wheels in a predetermined direction by steering operation. The wheels are steered by the steering ratio ^ [In vehicles with ITO mode and in-phase mode in which the rear wheels are steered in the same direction as the front wheels provided the vehicle speed is below a certain level, in-phase mode is This invention relates to an improved system that prevents the direction of the rear wheels from changing suddenly when switching to AUTO mode after release, and achieves a mode change that does not give an unnatural feeling. [Conventional technology]

In order to achieve the best drivability in a car equipped with a four-wheel steering system, it is important to avoid vehicle slippage at both low speeds, where the influence of centrifugal force is small, and at high speeds, where centrifugal force must be taken into account. In order to bring the angle close to 0, it is necessary to change the steering ratio k, which represents the ratio of the rear wheel steering angle to the front wheel steering angle, according to the vehicle speed, and the relationship between the vehicle speed and the steering ratio is roughly as follows. It is known that the relationship shown in FIG. 2 is preferable. Here, the region where the steering ratio is positive indicates that the front wheel steering direction and the rear wheel steering direction are opposite to each other, so-called antiphase, and the region where the steering ratio is negative indicates that the front wheel steering direction and the rear wheel steering direction are opposite to each other. This indicates that the direction and the steering direction of the rear wheels are in the same phase with each other, so-called in-phase. At low speeds, the rear wheels are steered in the opposite phase, so the turning center of the vehicle approaches the line passing through the center of the vehicle, the slip angle of the vehicle approaches O, and the turning radius is such that only the front wheels are steered. becomes smaller compared to . On the other hand, at high speeds, a slip angle occurs between the front wheels and the road surface due to the influence of centrifugal force, which tends to shift the turning center forward, but this tendency can be avoided by steering the rear wheels in the same phase as the front wheels. By doing so, the turning center can be brought closer to the vehicle width direction line passing through the center of the vehicle body. Regardless of whether the vehicle is running at low or high speeds, the fact that the center of rotation of the vehicle is on the line passing through the center of the vehicle in the vehicle width direction means that there is no slip angle of the vehicle, which significantly improves drivability when turning. do. By the way, in a vehicle equipped with such a four-wheel steering system, there is an AUTO mode that automatically controls the rear wheels depending on the relationship between vehicle speed and steering ratio, as shown in Figure 2, and an AUTO mode that automatically controls the rear wheels at low speeds. The conditions are that the rear wheels are in the same phase and at the same angle as the front wheels (
In other words, the same phase mode for steering (steering ratio=-1) may be selected. This in-phase mode is a mode that should be selected especially when parallel parking with the vehicle body parallel to each other, provided that the vehicle speed is 5 km/h or less, so if the vehicle speed exceeds a predetermined value It is necessary to automatically return to AUTO mode.

[Problem to be solved by the invention]

By the way, simply returning the in-phase mode to the AUTO mode will result in the AU
The steering ratio k in the low speed region in TO mode is in opposite phase,
In other words, since the value is close to 1, when the vehicle speed exceeds a predetermined speed, the rear wheels are suddenly steered from left to right or from right to left, regardless of the driver's steering sense, and the direction of travel of the vehicle is changed. Changing situations may emerge and are dangerous. An object of the present invention is to solve the above-mentioned problem when the in-phase mode is automatically switched to the AUTO mode.

[Means to solve the problem]

In order to solve the above problem, the four-wheel steering system of the present invention is configured as follows. That is, the four-wheel steering device of the present invention includes a front wheel steering mechanism that steers the front wheels according to the rotation of a steering shaft, and a front wheel steering mechanism that is controlled by a control means and that steers the rear wheels according to each steering ratio data. The rear wheel steering mechanism is equipped with an in-phase switch that switches from AUTO mode to in-phase mode, and when in AUTO mode, the steering ratio of the rear wheels to the front wheels is set to be optimal depending on the vehicle speed. A steering ratio data sending means for AUTO/mode that sends steering ratio data to a control means, and a steering ratio that is selected when the same phase switch is turned on and the vehicle speed is below a predetermined value and is set as the same phase. In-phase mode steering ratio data sending means that sends data to the control means; selected when the in-phase switch is turned on and the vehicle speed is above a predetermined value, and smoothly changes the steering ratio from the in-phase state; A means for transmitting steering ratio data for transition to make the transition to O, and selecting an AUTO mode when the front wheel steering angle returns to O after the rear wheel steering angle returns to the neutral position according to the above steering ratio data for transition. AUTO/mode return means is provided.

[Effect]

Unless the in-phase switch is turned on, the four-wheel steering system will
The vehicle is in the UTO mode, and the rear wheels are automatically controlled to the optimum steering angle calculated from the AUTO mode steering ratio data according to the front wheel steering angle and vehicle speed. When the same-phase switch is turned on when the vehicle speed is below a predetermined value, the same-phase mode steering ratio data sending means sends the same-phase mode steering ratio data to the control means, and the rear wheels accordingly The vehicle is steered by a predetermined amount in the same direction as the front wheels. When the vehicle exceeds a predetermined vehicle speed with the same phase mode selected, the transition steering ratio data transmission means sends data to the control means, and according to this, the rear wheels smoothly move to adjust the steering ratio. 0, that is, the steering angle is turned to the neutral position. Next, when the front wheels return to the neutral position, the four-wheel steering system returns to AUTO mode, and from then on, the rear wheels adjust the vehicle speed and front wheel steering according to the steering ratio data for AUTO mode. The steering angle is automatically controlled to be optimal depending on the angle.

【effect】

As a result of the above, in the four-wheel steering system of the present invention, when the vehicle speed exceeds a predetermined vehicle speed with the front wheels being steered in the same phase mode, only the rear wheels are returned to the neutral position with smooth movement,
The vehicle returns to AUTO mode only when the vehicle is in a straight-ahead state. Therefore, the rear wheels will not suddenly change direction from the same phase state to the opposite phase state relative to the front wheels, such as when suddenly returning to AUTO mode when the vehicle speed exceeds a predetermined speed while in the same phase state. At least by the time the front wheels return to the straight-ahead state, the driver no longer feels the discomfort of the vehicle body turning in the opposite direction to the direction intended by the driver.

[Explanation of Examples]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is an overall configuration diagram of an example of a four-wheel steering system of the present invention. Here, a conventionally known front wheel steering mechanism 1 is used. That is, in the case of a rank-binion type steering mechanism, the rotation of the steering shaft 3 that rotates together with the steering wheel 2 is converted by the gear box 4 into reciprocating motion of a rack rod 5 in the vehicle width direction, and further The reciprocating motion of the knuckle arm 7.5 is converted into a rotation about the axis 8.8 of the knuckle arm 7.7 via the tie rods 6.6 at both ends, and this rotation of the knuckle arm 7.7 causes the front wheel 9.9 to rotate. is adapted to be steered about the axis 8.8. On the other hand, the rear wheel steering mechanism 10 in this example includes a stepping motor 12 controlled by a control means 11 constituted by a microcomputer;
The power steering device 14 is configured by a known power steering device 14 into which the rotational output of 2 is inputted via a reduction gear device 13. The microcomputer 11 receives signals from a front wheel steering angle sensor 15, a vehicle speed sensor 16, and a same-phase switch 17, and has a control line extending to the stepping motor. As the power steering device 14, a known rack-and-binion type power steering device can be used. That is, the control valve section 19 attached to the input section of the gear box 18 directs the pressure oil from the pump 20 to the gear box 18 according to the rotational direction of the input shaft 21.
Pressure oil is sent to a double-acting power cylinder section 22 formed inside, and this power cylinder section 22 supports the movement of the rack rod 23. The movement of the rack rod 23 is controlled by the knuckle arms 25, 2 by tie rods 24, 24 connected to both ends of the rack rod 23.
5 to rotate this knuckle arm 25.25 to shaft 26.
．． 26, thereby rear wheel 27.2
7 is steered in a predetermined direction about the axis 26.26. In the microcomputer, an AUTO mode steering ratio data sending means 28 is formed which is selected in the AUTO mode and sends out optimum steering ratio information according to the vehicle speed. This steering ratio data for AUTO/mode is as follows:
For example, the relationship between the vehicle speed (2) and the steering ratio as shown in FIG. 2 is selected, and this is stored as a data table in the ROM or non-volatile RAM. The microcomputer also contains steering ratio data for in-phase mode, which is selected when the in-phase switch 17 is turned on and the vehicle speed is below a predetermined value, and sends out steering ratio data as in-phase. Delivery means 29 are formed. As for the same phase mode steering ratio data, the normal steering ratio =
-1 is selected. Furthermore, in the microcomputer, there is a steering wheel for transition, which is selected when the in-phase switch 17 is turned on and the vehicle speed is above a predetermined value to smoothly transition the steering ratio from the in-phase state to O. A ratio data sending means 30 is formed. As the steering ratio data for this transition, the relationship between the steering ratio and the vehicle speed ■ is shown, for example, as shown in FIG. Alternatively, as shown in FIG. 4, the steering ratio k may be gradually changed from -1 to 0 as time T elapses from the time when the vehicle speed exceeds a predetermined vehicle speed. It may also be possible to shift to . Furthermore, in the microcomputer, there is an AU that detects that the front wheels have been returned to the neutral state by steering operation in the above situation and selects the AUTO mode.
TO/mode return means 31 is formed. The operation of the four-wheel steering system having the above configuration will be explained according to the control flowchart shown in FIG. The vehicle speed signal from the vehicle speed sensor 16 is the set vehicle speed, for example 5.
km/h or less (YES in S 101) and the in-phase switch 17 is not turned on (No in S I O6), and if the vehicle speed is above the set vehicle speed (NO in S 101), the in-phase switch 17 is turned on. is not turned on (
S102: No), the four-wheel steering system is a normal AUT.
The vehicle is in the O mode (S105), and the rear wheels 27 are controlled by the control means 11 according to the At1TO mode steering ratio data shown in FIG. Specifically, the steering ratio k corresponding to the vehicle speed information (■) from the vehicle speed sensor 16 is read out, and based on this steering ratio and the front wheel steering angle information G from the front wheel steering angle sensor 15, the target of the rear wheels 27 is determined. The steering angle is calculated, the direction and number of pulses in which the stepping motor 12 should be rotated is determined, and this control information is sent to the stepping motor 12. This routine is repeated. The meaning of the A[ITO/mode steering ratio data shown on the side of Figure 2] is as explained above, and the relationship between the vehicle speed V and the steering ratio is controlled as shown in this data. This allows the vehicle to turn in an optimal state with no slip angle at both high and low speeds. If the vehicle speed is below the set vehicle speed and the in-phase switch 17 is turned on (YES in S106), the AUTO mode is canceled and the steering ratio k becomes -1, and the rear wheels 27 are rotated according to this steering ratio. controlled. Specifically, the target steering angle of the rear wheels 27 is calculated to be the same direction and angle as the steering angle of the front wheels, and the stepping motor 12 is rotationally controlled in the same manner as described above. In this same phase mode, for example, by steering the front wheel 9, turn it to the right! When the vehicle is steered twice, the rear wheels 27 are also steered all the way to the right. This allows the vehicle to move in parallel diagonally forward to the right. Furthermore, if the vehicle exceeds the set vehicle speed with the in-phase switch 17 turned on (NOl and
5102), the steering ratio data for transition shown in FIG. 3 or 4 is selected, and as the vehicle speed increases in the low speed region, the rear wheels 27 are smoothly returned to the steering ratio O1, that is, the neutral position. Alternatively, the rear wheels 27 are smoothly returned to the neutral position over a certain period of time. At this time,
For example, when the front wheels 9 and the rear wheels 27 are steered all the way to the right and the vehicle speed exceeds a predetermined value, only the rear wheels are smoothly returned to the neutral position as the vehicle speed increases. Assuming that the in-phase mode suddenly switches to the AUTO mode, the rear wheels will be abruptly steered from the in-phase state to the anti-phase state, and when the set vehicle speed is exceeded, the direction of travel of the vehicle will change to the driver's direction. Although it changes drastically regardless of the will,
According to the present invention, such a situation does not occur, and there is only a smooth transition to the front wheel steering state. Further, when the front wheels 9 are returned to neutral, that is, when the vehicle is traveling straight (YES in S104)
, returns to AUTO mode (S105). Thereafter, the steering direction of the rear wheels 27 is automatically controlled using a steering ratio that is optimally selected based on the relationship between the front wheel steering angle and the vehicle speed (2). As explained above, according to the present invention, after the same phase mode control, the same phase mode is automatically canceled as the vehicle speed increases, so the driver does not need to select the 80 To mode, and becomes very easy. Moreover,
The transition from same-phase mode to AUTO mode is performed by first returning only the rear wheels to neutral, and then at the point when the front wheels are returned to neutral by steering operation, so there is no discomfort for the driver and safety is maintained. Can be secured.

[Brief explanation of drawings]

Figure 1 is an overall configuration diagram of the four-wheel steering system of the present invention, Figure 2 is a graph showing an example of steering ratio data for AUTO/mode, and Figures 3 and 4 are steering ratio data for transition. FIG. 5 is a flowchart showing an example of the control flow of the four-wheel steering system of the present invention, and FIG. 6 is a graph for explaining problems in a four-wheel steering system other than the present invention. l... Front wheel steering mechanism, 3... Steering shaft, 10... Rear wheel steering mechanism, 11... Control means, 17
. . . same phase switch, 28 . . . steering ratio data transmission means for A11TO mode, 29 . . . steering ratio data transmission means for same phase mode, 30 . . . steering ratio data transmission means for transition. , 31...^UTO mode return means.

Claims (1)

[Claims] (1) A front wheel steering mechanism that steers the front wheels according to the rotation of the steering shaft; a rear wheel steering mechanism that is controlled by a control means and that can steer the rear wheels according to each steering ratio data; An in-phase switch that switches from mode to in-phase mode, and steering ratio data that is selected in AUTO mode and is set so that the steering ratio of the rear wheels to the front wheels is optimal according to the vehicle speed is sent to the control means. AUTO/mode steering ratio data sending means, which is selected when the same phase switch is turned on and the vehicle speed is below a predetermined value, and sends steering ratio data as the same phase to the control means. A phase mode steering ratio data sending means, and a transition time switch that is selected when the in-phase switch is turned on and the vehicle speed is above a predetermined value to smoothly transition the steering ratio from the in-phase state to 0. A steering ratio data sending means; and an AUTO/mode return means for selecting an AUTO mode when the front wheel steering angle returns to 0 after the rear wheel steering angle returns to the neutral position in accordance with the transition steering ratio data. A four-wheel steering device characterized by: