JPS61135866A - Four-wheel steering device - Google Patents

Abstract

PURPOSE:To prevent a vehicle from touching obstructions when there are obstructions at the sides of the vehicle, by devising that when there are no obstructions at the sides of the vehicle, the rear wheel steering angle is determined to be in a normal running mode, and when there are obstructions it is determined to be in a obstruction detecting mode, and also by returning the rear wheel steering angle to the same phase or zero as the front wheel steering angle. CONSTITUTION:When a supersonic sensor 41 does not detect obstructions at the sides of a vehicle, a control means 11 determines a rear wheel steering angle and direction according to the normal running mode steering ratio of No.1 data select means 38. Then, the control means 11 drives and controls a rear wheel steering mechanism 10 so as to become these determined steering angle and direction. Also, when the control means 11 detects obstructions at the sides of the vehicle, it determines a rear wheel steering angle and direction according to the obstruction detecting mode steering ratio of No.2 data select means 39. At this time, the rear wheel steering angle is determined to be the same phase as the front wheel or to be returned to zero.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a four-wheel steering device that is configured to be able to steer not only the front wheels but also the rear wheels by steering operation, and in particular, when an obstacle is present on the side of the vehicle body.
The present invention relates to a device configured to control the steering angle of the rear wheels to be 0 or to be in the same phase as the front wheels.

[Conventional technology]

The idea of steering not only the front wheels but also the rear wheels in a predetermined direction according to a steering operation is already known, mainly for the purpose of improving steering stability. For example, in the system disclosed in Japanese Patent Application Laid-Open No. 58-20563, a pinion at the front end of a shaft for transmitting operating force extending to the rear of the vehicle body is engaged with a rack rod in a steering gear box for the front wheels, and this operating force is transmitted. The four-wheel steering system disclosed in this publication inputs the rotation of the rear wheel steering shaft into the rear wheel steering mechanism and steers the support shaft in a predetermined direction. The steering mechanism is configured to mechanically transmit a part of the freezing steering force to the rear wheel steering mechanism, and the rear wheel steering angle is determined only by the front wheel steering angle. The device disclosed in Japanese Patent Publication No. 59-20563 is basically configured so that the steering angle of the rear wheels is controlled by an electric control device, and the steering angle of the rear wheels is controlled by the steering angle of the front wheels. The steering angle is controlled by the magnitude of the steering angle of the front wheels and the vehicle speed. Incidentally, in order to optimize drivability at any vehicle speed, there is almost no need to consider the influence of centrifugal force. The steering ratio, which is the ratio of the rear wheel steering angle to the front wheel steering angle, changes as shown in Figure 4 at low speeds and at high speeds where the influence of centrifugal force must be taken into account. Here, a region where the steering ratio k is positive indicates that the rear wheels are steered in the opposite direction to the front wheels, which is a so-called reverse phase. This region indicates that the rear wheels are steered in the same direction as the front wheels, that is, they are in the same phase.As is clear from the graph in Figure 4,
At low speeds, the rear wheels are steered in the opposite direction to the front wheels, resulting in an extremely small turning radius of the vehicle body; conversely, at high speeds, the rear wheels are steered in the same direction as the front wheels, resulting in a very small turning radius of the vehicle body. is greater than the steering feel. Such changes in the steering ratio according to vehicle speed range from low speeds, where centrifugal force has little effect, to high speeds, where centrifugal force has a large effect.
This is determined so that the slip angle of the vehicle body does not occur, but in this case, the following problems may occur. In other words, as shown in Fig. 7, for example, when attempting to start by making a large turn toward the center of the road from a state where there is an obstacle on the side, such as in a parallel parking state, the rear wheels are on the side of the obstacle. As a result, the rear of the vehicle may move toward the shoulder of the road, potentially causing the rear of the vehicle to come into contact with an obstacle. As a conventional example of providing a four-wheel steering device that solves such problems, for example, Japanese Patent Laid-Open No. 56-163969 discloses that when the front wheel steering angle is very large, the rear wheel steering angle is set to 0.
In this example, the vehicle body is prevented from coming into contact with an obstacle due to the rear wheels being steered in the opposite direction.

[Problems to be Solved by the Invention] However, in the device disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 56-163969, the turning angle of the rear wheels returns to 0 whenever the turning angle of the front wheels is large. Another problem is that you cannot take advantage of the four-wheel steering even if you want to. Furthermore, when the steering angle of the front wheels exceeds a certain amount, the steering angle of the rear wheels suddenly returns from the opposite phase to O, which causes the problem that the steering stability at low speeds deteriorates. The present invention was devised under the above circumstances, and the problems to be solved are basically to be able to exhibit optimal steering stability over the entire vehicle speed range, and to To provide a four-wheel steering device which can prevent a vehicle body from contacting an obstacle when turning at low speed and in a short turn by returning the rear wheel steering angle from an opposite phase to the same phase or 0 when an obstacle exists on the side of the vehicle body. That's true. [Hands for Solving the Problems v11] The four-wheel steering system of the present invention solves the above problems by having the following configuration. 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 the steering shaft; a rear wheel steering mechanism that is controlled by a control device and is capable of steering the rear wheels; A front wheel steering angle sensor, a rear wheel steering angle sensor,
A vehicle speed sensor, an ultrasonic sensor that detects the presence of obstacles on the sides of the vehicle, and a sensor that is selected during normal driving and sends steering ratio data to the control means, which determines the steering ratio of the rear wheels relative to the front wheels according to the vehicle speed. The first data sending means is set to be optimal and is selected when the ultrasonic sensor detects an obstacle.
a second data sending means for sending to the control means 0 data of a rear wheel steering angle or steering ratio data in which the steering direction of the rear wheels is set to be in the same phase as the steering direction of the front wheels; and the steering of the front wheels. determining a steering angle of the rear wheels according to the angle, vehicle speed, and data from the first data sending means or the second data sending means;
and control means for II-controlling the rear wheel steering mechanism so that the steering angle is achieved. [Operation] The first data sending means stores data indicating the relationship between the speed and the corresponding optimum steering ratio, as shown in FIG. The means stores, for example, data in which the steering ratio k is fixed at -1 regardless of the speed, or data in which the steering angle of the rear wheels should be O, as shown in No. 5M. During normal driving, that is, when the ultrasonic sensor does not detect an obstacle on the side of the vehicle body, the control means selects the first data sending means as one of the elements that should control the rear wheel steering mechanism (normal driving mode), specifically, the control means receives from the first data transmission means a steering ratio according to the current vehicle speed input from the vehicle speed sensor, and receives the steering ratio of the front wheels input from the front wheel steering angle sensor. The steering angle of the rear wheels is calculated from the steering ratio received from the first data sending means, and the rear wheel steering mechanism is controlled in accordance with the steering angle thus determined. On the other hand, if the ultrasonic sensor detects an obstacle on the side of the vehicle body, the control means selects the second data sending means as one of the elements to which the rear wheel steering mechanism should be turned.
II book detection mode). Thereby, the control means determines the steering angle of the rear wheels based on the steering angle of the front wheels and the steering ratio = -1. In this case, the steering angle of the rear wheels is the opposite phase and the same angle as the steering angle of the front wheels. ), the rear wheel steering mechanism is controlled accordingly, or the rear wheel steering mechanism is controlled to return the rear wheel steering angle to zero. In addition, in order to prevent the ultrasonic sensor from detecting another vehicle running beside the vehicle while traveling at a speed above a certain level, the control of the control means will not be shifted from the normal traveling mode to the obstacle detection mode. As a condition for switching to the obstacle detection mode for selecting the second data sending means, it is preferable to add that the speed of the tree chain is below a certain certain speed, for example, below 10 km/h.

【effect】

As described above, in the four-wheel steering system of the present invention, during normal driving, the rear wheels are steered optimally according to the vehicle speed and the steering angle of the front wheels, thereby providing the optimal steering feeling at all vehicle speeds. can be obtained. In addition, even if you start by steering away from an obstacle from the side of the obstacle, the steering angle of the rear wheels will automatically return to 0,
Or, since it is in the same phase as the front wheels, the rear wheels will not be steered toward the obstacle and the rear of the vehicle will not come into contact with the obstacle. In this case, the vehicle can be steered with the feeling of two-wheel steering using the front wheels, and safety is improved when a four-wheel steering device is provided.

[Explanation of Examples]

Embodiments of the four-wheel steering system of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic diagram of the overall configuration of an example of a four-wheel steering system according to the present invention. Here, a conventionally known front wheel steering mechanism 1 is used. That is, in the case of a rack and pinion type steering mechanism, the rotation of the steering shaft 3 that rotates along with the steering wheel 2 is converted by the gear box 4 into reciprocating motion of the lever 5 in the vehicle width direction, and further this The reciprocating motion of the rack rod 5 is converted into a rotation of the knuckle arm 7.7 about the axes 8, 8 via the tie rods 6.6 at both ends, and this rotation of the knuckle arm 7.7 causes
The front wheels 9.9 are steered about the axis 8.8. On the other hand, in the rear wheel steering mechanism 10 in this example, the control hand VIt
It is composed of a stepping motor 12 controlled by a micro combinator 11' forming part 11, and a known power steering device 13 to which the rotation of the stepping motor 12 is input. Further, signals from the front wheel steering angle sensor 14, the rear wheel steering angle sensor 15, the vehicle speed sensor 16, and the ultrasonic sensor 41 are input to the microcomputer 11', and the stepping motor 12
A control line extends to. The front wheel steering angle sensor 14 is constructed, for example, by attaching a circular plate with a large number of small holes circumferentially to the steering shaft 3, and attaching a light emitting element and a light receiving element to sandwich this disk. For example, the number of times the light from the light emitting element is blocked is counted by the number of stitches, and the displacement of mechanical parts such as the rack rod 5 and the knuckle arm 7.7 from the reference position is detected by a potentiometer. realizable. Further, the rear wheel steering angle sensor 5 can also be realized in the same manner as the front wheel steering angle sensor 14 described above. Further, the ultrasonic sensor 41 includes a sound wave generator and a sound wave receiver installed on the side of the vehicle body, and the time from when the sound wave is generated from the sound wave generator until the sound wave receiver receives the sound wave reflected by hitting an obstacle. Accordingly, a known method for measuring the distance from the vehicle body to the obstacle can be adopted. Reference numeral 17 designates an input section of a power steering device 13, for example, a rack-binion type, which is normally used for front wheel steering, and in this example, this input section 17 is connected to the stepping motor 12. There is. That is, the power cylinder 18 (FIG. 2) is driven in accordance with the rotational direction of the output shaft of the stepping motor 12, and reciprocates the rack rod 19 extending in the vehicle width direction. The movement of the rack rod 19 is transmitted to the knuckle arm 21.21 by tie rods 20.20 connected to both ends thereof, causing this knuckle arm 21.21 to rotate about an axis 22.22, thus causing this knuckle arm 21 to rotate.
．． The rear wheel 23.23 attached to the shaft 22.21 is attached to the shaft 22.21.
It is steered around 22. The above stepping motor 12 and power steering device! The details of the connection structure with 3 are shown in Fig. 2. In this example, the rotation of the output shaft 24 of the stepping motor 12 is decelerated and inputted to the input section 17 of the power steering system f113. That is, a small gear 26 attached to the output shaft 24 and a large gear 28 attached to the transmission shaft 27 and meshing with the small gear 26 are incorporated into the gear housing 25 attached to the stepping motor 12, and the transmission shaft 27 and It is connected to the input shaft 29 of the power steering device 13 by a shaft 30 whose both ends are connected by a universal shaft. The input shaft 29 of the power steering device 13 passes through a control valve section 31 and has a pinion 32 formed at its tip, which meshes with a rack rod 19 that can slide left and right inside a gear box 33. The part indicated by reference numeral 34 on the left side of the gear box 33 is a power cylinder part, and a cylinder space is formed so as to sandwich the piston 35, and a pair of hydraulic cylinders connected to the control pulp are used to drive the piston 35 in both directions. Boats 36.37 are provided. This rack/binion type power steering system Wi1
3, the rack rod 19 is moved in a direction that follows the rotational direction of the stepping motor 12, and the rear wheel 23 is steered in a predetermined direction by a predetermined angle. As shown in FIG. 3, the microcomputer 11' constituting the control means 11 stores the vehicle speed V during normal driving,
A first data sending means 38 that stores the relationship between the steering ratio of the rear wheels 23 and the front wheels 9, and a steering ratio k that stores the relationship between the rear wheels 23 and the front wheels 9;
A second data sending means 39 is formed in which is fixed to -1. The first data sending means 3B is configured such that during normal driving, that is, when the ultrasonic sensor 41 does not detect a harmful object,
Together with the data from the vehicle speed sensor 16 and the data from the front wheel steering angle sensor 14, it is selected as an element to determine and control the steering angle of the rear wheels. On the other hand, the second data transmitter WIt
39 is selected as an element that should determine the steering angle of the rear wheels 23 when the ultrasonic sensor 41 detects an obstacle on the side of the vehicle body. As shown in FIG. 5, the data to be stored in the second data sending means includes, in addition to the steering ratio fixed at -1, data for setting the steering angle of the rear wheels 23 to 0; That is, a steering ratio fixed to 0 may be stored. Here, the relationship between the vehicle speed (d) and the steering ratio during normal running shown in FIG. 4 will be explained as follows. At low speeds, the rear wheels 23 are steered in opposite phase to the front wheels. In two-wheel steering, when the front wheels are steered, the center of rotation of the vehicle body is located behind the center of the vehicle body. Therefore, the direction in which the center of the vehicle body attempts to move is displaced diagonally from the longitudinal direction of the vehicle body, resulting in a so-called slip angle. However, when the rear wheels are steered in the opposite phase, the turning center of the vehicle body will be located on a line in the vehicle width direction that passes through the center of the vehicle body, and as a result, the direction in which the center of the vehicle body is moving will match the longitudinal direction of the vehicle body. , the so-called slip angle becomes 0. On the other hand, as the vehicle speed increases, the influence of centrifugal force increases. This centrifugal force generates a cornering force between the front and rear wheels and the road surface, creating a slip angle in the front and rear wheels, which tends to shift the turning center forward. By steering the wheels in the same phase direction as the front wheels, the actual turning center can be located on the vehicle width direction line passing through the center of the vehicle body. This eliminates the slip angle of the car body and therefore
By steering the rear wheels 23 according to the steering ratio shown in FIG. 4, it is possible to obtain the best drivability with no slip angle of the vehicle body at both low and high speeds. Next, control by the controller fall will be explained with reference to the flowchart shown in FIG. During normal driving, that is, when no obstacles are detected on the side of the vehicle body (step 102), the control means 11 collects vehicle speed data from the vehicle speed sensor 16 (step 103), data from the front wheel steering angle sensor 14 (step 104). ) and the steering ratio k from the first data sending means 38 (step 105
), the steering angle and direction of the rear wheels 23 are determined (step 107), and the rear wheel steering mechanism 10 is controlled (step 108). The rear wheel steering mechanism 10 is driven until the data fed back from the rear wheel steering angle sensor 15 to the controller vjt11 becomes the determined steering angle. In this manner, when there is no obstacle, the control in the normal driving mode described above is repeatedly performed, and the rear wheels 23 are optimally steered according to the steering angle of the front wheels 9 and the vehicle speed. In this embodiment, the rear wheels 23 are moved in the same direction as the front wheels 9 even at low speeds so that the vehicle body can be actively moved diagonally in parallel at low speeds, for example, when parallel parking. In-phase switch 42 so that steering can be performed in phase.
(see FIGS. 1 and 3) In this example, when this in-phase switch 42 is turned on (step 109), the controller 1! &11 is the set vehicle speed (
In this case, the steering ratio k is set to -1 on the condition that the vehicle speed is quite slow, i.e., below the region where the rear wheels are in opposite phase to the front wheels in the graph of FIG. 4 (step 106).
The process is performed by fixing it to . On the other hand, when the ultrasonic sensor 41 detects an obstacle (step 102), the steering ratio k is set to -l, for example, based on the data from the second data sending means 39 (step 111). Then, it is determined whether the data from the vehicle speed sensor 16 (step 112) exceeds the set vehicle speed (step 113). If the vehicle speed is higher than the set vehicle speed, the program jumps to the normal driving mode loop, and if the vehicle speed is lower than the set vehicle speed, the following steps are performed. Obstacle detection mode processing continues. In the above step 113, it is determined whether the 1I4i harmful object detected by the ultrasonic sensor 41 is another vehicle running on the side or a fixed obstacle, and it is determined whether the 1I4i harmful object is detected by the ultrasonic sensor 41 or is a fixed obstacle. This prevents the vehicle from entering obstacle detection mode. Next, data from the front wheel steering angle sensor 14 (step 114
) and the steering ratio set above = 71, the steering angle of the rear wheels is determined (step 115), and the rear wheel steering mechanism 10 is controlled based on it (step 116), which is fixed to the side of the vehicle body. As long as there is an obstacle like this, the loop of the obstacle detection mode as described above is repeated, and the rear wheels 23 are steered to the same phase as the front wheels, or are returned to the steered angle of 0. As explained above, the four-wheel steering system of the present invention not only achieves optimal steering performance that does not cause a slip angle on the vehicle body, but also achieves optimal steering performance in accordance with the steering angle of the front wheels and the vehicle speed during normal driving. When there is an obstacle on the side, the steering angle of the rear wheels is automatically steered to the same phase as the front wheels, or the steering angle is controlled to return to O. If you try to start moving away from an obstacle, the problem of the rear part of the main body coming into contact with the obstacle cannot occur. This further increases the safety of the four-wheel steering system.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an example of a four-wheel steering device of the present invention, Fig. 2 is a detailed sectional view of a connecting part between a stepping motor and a power steering device, and Fig. 3 is a control device and its components. 4 is a graph showing an example of a data table to be sent out from the first data sending means, @5 is a graph showing an example of data to be sent out from the second data sending means, FIG. 6 is a flowchart showing an example of the flow of control by the control means, and FIG. 7 is a diagram for explaining problems in the conventional example. DESCRIPTION OF SYMBOLS 1... Front wheel steering mechanism, 3... Steering shaft, 9... Front wheel, 10... Rear wheel steering mechanism, 11...
Control means, 14... Front wheel steering angle sensor, 15... Rear wheel steering angle sensor, 16... Vehicle speed sensor, 23... Rear wheel,
38... First data sending means, 39... Second data sending means, 41... Ultrasonic sensor

Claims (1)

[Claims] (1) A front wheel steering mechanism that steers the front wheels according to the rotation of the steering shaft, and a control device that controls the
and a rear wheel steering mechanism that can steer the rear wheels, a front wheel steering angle sensor, a rear wheel steering angle sensor, a vehicle speed sensor, an ultrasonic sensor that detects the presence of obstacles on the side of the vehicle, and a A first data sending means is selected and sends steering ratio data to the control means, and the steering ratio of the rear wheels to the front wheels is set to be optimal according to the vehicle speed, and an ultrasonic sensor detects an obstacle. a second data sending means for sending to the control means 0 data of the rear wheel steering angle or steering ratio data in which the steering direction of the rear wheels is set to be in the same phase as the steering direction of the front wheels; and a rear wheel steering mechanism that determines the steering angle of the rear wheels according to the steering angle of the front wheels, the vehicle speed, and the data from the first data sending means or the second data sending means, and adjusts the steering angle to the steering angle. A four-wheel steering device comprising: a control means for controlling a four-wheel steering device;