JPH057225B2 - - Google Patents

Description

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

The present invention relates to a four-wheel steering device configured to be able to steer not only the front wheels but also the rear wheels by steering operation, and in particular, the steering direction of the rear wheels changes from the same phase to the opposite phase during sudden deceleration. By doing so, it is possible to avoid the occurrence of a so-called notch in which the turning radius of the vehicle suddenly decreases regardless of the driver's intention.

[Conventional technology]

The idea of steering not only the front wheels but also the rear wheels in a predetermined direction in accordance with a steering operation is already known, mainly for the purpose of improving steering stability. For example, JP-A-58-
In the system disclosed in Publication No. 20563, a pinion at the front end of a shaft for transmitting operating force that extends to the rear of the vehicle body is engaged with a rack rod in a steering gear box for the front wheels, and the rotation of the shaft for transmitting operating force is transmitted to the rear wheels. The input signal is input to the steering mechanism for steering the rear wheels in a predetermined direction. In other words, the four-wheel steering device disclosed in this publication is configured to mechanically transmit a part of the steering force for steering the front wheels to the rear wheel steering mechanism. The steering angle is determined only by the steering angle of the front wheels. Furthermore, the device disclosed in Japanese Patent Application Laid-Open No. 59-77968 is basically configured so that the steering angle of the rear wheels is controlled by an electrical control device, and the steering angle of the front wheels is The steering angle of the rear wheels is controlled according to the magnitude of the steering angle of the front wheels and the vehicle speed.

[Problem to be solved by the invention]

The conventional example disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 58-20563 has the following problems. That is,
The steering angle of the rear wheels is determined only by the steering angle of the front wheels, so even if it is possible to maintain steering performance according to the steering angle, at low speeds where the influence of centrifugal force is small and at high speeds where centrifugal force is large. It is not possible to improve both steering performance. Furthermore, the method disclosed in Japanese Patent Application Laid-Open No. 59-77968 has the following problems. In other words, only the vehicle speed and front wheel steering angle are used as factors to determine the rear wheel steering angle, so if there is sudden deceleration during a turn, the rear wheel steering angle will change regardless of the driver's intention. However, there is a risk that the turning radius will suddenly become smaller, resulting in a so-called notch. By the way, in order to achieve the best drivability in a car equipped with a four-wheel steering system, it is necessary to achieve the best drivability at both low speeds, where the influence of centrifugal force is small, and at high speeds, where centrifugal force needs to be taken into consideration. In order to bring the slip angle of the vehicle closer 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, and the relationship between vehicle speed and steering ratio k is approximately It is known that the relationship shown in FIG. 4 is desirable. Here, a region where the steering ratio k is positive indicates that the steering direction of the front wheels and the steering direction of the rear wheels are opposite to each other, so-called antiphase, and the steering ratio k
A region where is negative indicates that the steering direction of the front wheels and the steering direction of the rear wheels are in the same direction, that is, in the same phase. Therefore, at low speeds, the rear wheels are preferably steered in phase opposite to the front wheels, and at high speeds, the rear wheels are preferably steered in the same phase as the front wheels. At low speeds, the rear wheels are steered in the opposite phase, so
The turning center of the vehicle body approaches a line in the vehicle width direction passing through the center of the vehicle body, so the slip angle of the vehicle body approaches 0, and the radius of rotation becomes smaller than when only the front wheels are steered. 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, it is possible to offset the rotational angle and bring the turning center closer to the vehicle width direction line passing through the center of the vehicle body. Whether at low speeds or high speeds, the center of rotation of the vehicle body must be on the line in the vehicle width direction that passes through the center of the vehicle body.
This means that the slip angle of the vehicle body is eliminated, which significantly improves drivability when turning. When controlling the direction and amount of steering of the rear wheels only according to the relationship between vehicle speed and steering ratio shown in the graph of Fig. 4 above, as explained earlier, when turning There is a problem in that when the vehicle suddenly decelerates, the rear wheels are steered from the same phase to the opposite phase regardless of the driver's intention, and the turning radius suddenly becomes smaller. This invention was devised under the above circumstances, and solves the problems of each of the conventional examples described above.The rear wheels are steered in the opposite phase to the front wheels at low speeds, and the rear wheels are steered at high speeds in an opposite phase to the front wheels. In a four-wheel steering system that steers the front wheels in the same phase, the rear wheels are steered from the same phase to the opposite phase when there is sudden and significant deceleration from the same phase area to the opposite phase area. The task is to avoid this.

[Means to solve the problem]

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 rotation of a steering shaft, and a rear wheel steering mechanism that is controlled by a control device and that can steer the rear wheels. , the front wheel steering angle sensor, the rear wheel steering angle sensor, the vehicle speed sensor, and the steering ratio of the rear wheels to the front wheels are set to be in the same phase when the vehicle speed is high and to be in opposite phase when the vehicle speed is low. a standard data table, a data table for sudden deceleration in which the steering ratio of the rear wheels and the front wheels are set to be in the same phase, a sudden deceleration detection means for detecting that the vehicle is in a sudden deceleration state, and the standard data table mentioned above. While determining the steering angle of the rear wheels according to the above standard data table, when the vehicle is traveling at a vehicle speed in the same phase range in the above standard data table, the sudden deceleration detection means indicates that the vehicle has entered a predetermined sudden deceleration state. When a signal indicating that The present invention is characterized by comprising a control means for performing feedback control on the rear wheel steering mechanism so as to control the steering angle.

[Effect]

For example, as shown in Figure 4, the standard data table includes the relationship between vehicle speed and the corresponding optimal steering ratio, i.e., the steering ratio is in opposite phase in the low speed range, and in the high speed range. Data representing the relationship between the vehicle speed and the steering ratio with the steering ratios in the same phase is stored, and the data table for sudden deceleration includes, for example, the speed data as shown in Figure 5 or Figure 6. and data representing the relationship between the steering ratio and the corresponding steering ratio are stored. As is clear from Figures 5 and 6, in the data table for sudden deceleration,
The steering ratio is in the same phase in all vehicle speed ranges. During normal driving, the control means controls the rear wheel steering mechanism according to the standard data table. Specifically, the control means reads the steering ratio according to the current vehicle speed input from the vehicle speed sensor from a standard data table, and reads the steering ratio of the front wheels input from the front wheel steering angle sensor from the standard data table. The steering angle of the rear wheels is calculated from the read steering ratio, and the rear wheel steering mechanism is feedback-controlled in accordance with the determined steering angle. On the other hand, when a signal indicating that the vehicle has entered a predetermined rapid deceleration state is input from the sudden deceleration detection means when the vehicle is traveling at a vehicle speed in the same phase range in the standard data table, the sudden deceleration occurs. While the state continues, the control means selects the data table for sudden deceleration as the data table for reading the steering ratio, determines the steering angle of the rear wheels in the same manner as above, and controls the rear wheel steering mechanism as feedback. Control.

【effect】

As described above, the four-wheel steering system of the present invention performs optimal rear wheel steering in accordance with the vehicle speed and front wheel steering angle in accordance with the standard data table in normal times. Optimal steering sensation can be obtained at any vehicle speed. Further, according to the four-wheel steering system of the present invention, when turning at a relatively high speed in which the rear wheels are steered in the same phase as the front wheels, according to the standard data table, the rear wheels shift from the same phase region to the opposite phase region. Even if a situation arises in which the driver is forced to significantly and rapidly decelerate, the rear wheels will shift to the opposite phase regardless of the driver's will, and the turning radius will suddenly become smaller, resulting in a so-called cut, which will continue to progress. This has the effect of preventing serious dangers such as those caused by the vehicle spinning out.

[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. In other words, easy
In the case of a pinion type steering mechanism, the steering shaft 3 rotates along with the steering wheel 2.
The rotation of the gear box 4 is, for example, the rotation of the rack rod 5.
This reciprocating motion of the rack lever 5 is further converted into a rotation of the knuckle arms 7, 7 about their axes 8, 8 via the tie rods 6, 6 at both ends. By rotating the knuckle arms 7, 7, the front wheels 9, 9 are steered about the axes 8, 8. On the other hand, the rear wheel steering mechanism 10 in this example is controlled by a microcomputer 11' that constitutes the control means 11.
a stepping motor 12 controlled by;
It is constituted by a known power steering device 13 to which the rotation of the stepping motor 12 is input. Further, signals from a front wheel steering angle sensor 14, a rear wheel steering angle sensor 15, and a vehicle speed sensor 16 are input to the microcomputer 11', and a control line to the stepping motor 12 is extended. As will be described later, the stepping motor 12 is connected to, for example, a rack-and-pinion power steering device 13, and a power cylinder 34 (a second (Fig.) is driven to reciprocate a rack lever 19 extending in the vehicle width direction. The movement of the rack rod 19 is transmitted to the knuckle arms 21, 21 by tie rods 20, 20 connected to both ends thereof, causing the knuckle arms 21, 21 to rotate about the shafts 22, 22. ,2
The rear wheels 23, 23 attached to the shaft 2
It is steered around 2 and 22. A connection structure between the stepping motor 12 and the power steering device 13 is shown in FIG. In this example, the rotation of the output shaft 24 of the stepping motor 12 is decelerated and the power steering device 1
The configuration is such that the data is input to the input section 17 of No. 3.
That is, in a gear housing 25 attached to the stepping motor 12, 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, and the transmission shaft 27 and the input shaft 2 of the power steering device 13
9 are connected by a shaft 30 whose both ends are connected by a universal joint. The input shaft 29 of the power steering device 13 is connected to the control valve section 3
1, a pinion 32 is formed at the tip,
This meshes with a rack rod 19 that can slide left and right inside the gearbox 33. The part indicated by the reference numeral 34 on the left side of the gearbox 33 is the power cylinder part, which has a cylinder space formed to sandwich the piston 35, and a pair of hydraulic cylinders connected to the control valve so that the piston 35 can be driven in both directions. Ports 36 and 37 are provided. The rack and pinion type power steering device 13 increases the power, and the rack lever 19 is rotated in the direction of rotation of the stepping motor 12.
is moved, and the rear wheels 23 are steered by a predetermined angle in a predetermined direction. In the microcomputer 11' constituting the control means 11, as shown in FIG. 38, a sudden deceleration data table 39 representing the relationship between the vehicle speed V during sudden deceleration and the steering ratio k of the rear wheels 23 with respect to the front wheels 9 is formed. These data tables 3
8, 39, for example, ROM or non-volatile
Stored in RAM. Standard data table 38
The steering ratio k expressed by is determined, for example, so that the slip angle of the vehicle body becomes 0 in accordance with the vehicle speed V, and is as shown in the graph shown in FIG. 4, for example. On the other hand, the steering ratio k shown in the sudden deceleration data table 39 is determined so that the sign of the steering ratio k does not reverse between high speed and low speed, and the steering ratio k in that case is different from the vehicle speed. The relationship is as shown in FIG. 5 or 6, for example. In the case of Figure 5,
As the vehicle speed decreases, the steering ratio decreases, but the phase does not reverse. Moreover, in the case of FIG. 6, the steering ratio is constant regardless of the vehicle speed. The control means 11 selectively reads data from the standard data table 38 and the sudden deceleration data table 39 depending on whether the vehicle speed is suddenly decelerating or not, and performs feedback control on the rear wheel steering mechanism 10 based on this data. However, such selection is made by determining whether the signal input from the sudden deceleration detection means 40 to the control means 11 exceeds a predetermined value. An acceleration sensor (not shown) may be used as the sudden deceleration detection means 40, but data from the vehicle speed sensor 16 may be differentiated with respect to time. The control by the control means 11 will be explained with reference to the flowchart shown in FIG. During normal driving, the vehicle speed signal from the vehicle speed sensor 16 (step 102) and the steering ratio corresponding to the vehicle speed are read from the standard data table 38 (step 104), and this steering ratio k and the steering ratio are sent from the steering angle sensor 14. The steering angle and direction of the rear wheels 23 are determined from the front wheel steering angle data (step 105) (step 107), and the rear wheel steering mechanism 10 is controlled to steer the rear wheels 23 in a predetermined direction (step 107). 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 control means 11 reaches the determined steering angle. Such control is repeated, and the rear wheels 23 are steered to an optimal state according to the steering angle of the front wheels 9 and the vehicle speed. In this embodiment, the rear wheels 23 are kept in the same phase as the front wheels 9 even at low speeds so that the vehicle body can be moved diagonally in parallel at low speeds, for example when parallel parking. An in-phase switch 41 is provided to enable steering (first
(see Figures and Figure 3). In this example, when the in-phase switch 41 is turned on (step 109), the control means 11 controls the vehicle speed at a certain set vehicle speed (in this case, the vehicle speed is quite low, that is, the rear wheels are opposite to the front wheels in the standard data table). (step 106), the steering ratio k
For example, the process is performed with the value fixed to -1 (step 110). On the other hand, if it is detected that the vehicle has entered a sudden deceleration state when the vehicle speed is in the same phase region in the standard data table by the signal from the sudden deceleration detection means 40 exceeding a predetermined value (step 103), the control The means 11 reads out the steering ratio corresponding to the vehicle speed from the sudden deceleration data table 39 (step 111), and combines this steering ratio k with the front wheel steering angle data sent from the front wheel steering angle sensor 14 (step 112). The steering angle and direction of the rear wheels 23 are determined from (step
113), and performs feedback control on the rear wheel steering mechanism 10 to steer the rear wheels 23 in a predetermined direction (step 114). The rear wheel steering mechanism 10 is driven until the data fed back from the rear wheel steering angle sensor 15 to the control means 11 reaches the determined steering angle. Such control is repeated, and therefore, while the rapid deceleration state continues, the rear wheels 23 are steered to an appropriate steering angle that is in the same phase as the front wheels, as before the deceleration. Furthermore, when a sudden deceleration state is detected at the vehicle speed in the same phase range in the standard data table shown in Fig. 4, the data table for feedback control of the rear wheels is the data table for sudden deceleration shown in Fig. 5 or 6. The steering ratios on the data table at the speed at the moment of this switching may be slightly different values even though they are in the same phase, but for the following reason, this is not so important. Not a problem. That is, when the vehicle speed is in the same phase region in the standard data table, the vehicle is traveling at a relatively high speed, and in this case, the steering angle of the front wheels is not so large in fact. Therefore, even if the steering ratio for control changes slightly due to switching of the data table to be based on in control, the change in the rear wheel steering angle due to this is minute. Furthermore, the control of the rear wheel steering mechanism in the present invention is basically feedback control based on a comparison between the target steering angle and the actual steering angle, and therefore, it is possible to The rear wheels are not steered instantly. There is a time lag due to feedback control, and due to the drive speed limit of the rear wheel steering mechanism, it is not possible to turn the rear wheels instantly, and in reality, the rear wheels do not turn smoothly as they approach the target steering angle. It will be steered. In this way, even if the target steering angle changes instantaneously based on a change in the data table, the actual movement of the rear wheels will change smoothly toward the target steering angle, and moreover, even when driving at high speed, Therefore, the amount is so small that it hardly becomes a problem. Further, after switching from the standard data table to the data table for rapid deceleration, when the sudden deceleration state is canceled, control based on the standard data table is performed again. Therefore, based on the data table for sudden deceleration, the data table may be switched to the standard data table when the rear wheels reach a low speed state while remaining in the same phase. In this case, the target rear wheel steering angle is instantaneously changed from the same phase to the opposite phase, but in this case as well, the rear wheels are not instantaneously turned from the same phase to the opposite phase, but are controlled by feedback control. This allows smooth steering based on the drive capacity limit of the rear wheel steering mechanism. Furthermore, since this situation occurs at low speeds, even if the vehicle feels a little strange while driving, it does not impede safety. As explained above, the four-wheel steering system of the present invention not only achieves optimal steering performance in which no slip angle occurs in 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 turning while steering the wheels in the same phase direction as the front wheels, even if a situation arises that requires a sudden deceleration from the same phase region to the opposite phase region according to the standard data table, the rear The wheels are suddenly steered from the same phase to the opposite phase, and the turning radius is rapidly reduced, making it possible to avoid the risk of the vehicle spinning out.

[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 various components. Figure 4 is a graph showing an example of a standard data table, Figures 5 and 6 are graphs each showing an example of a data table for sudden deceleration, and Figure 7 is a flow of control by the control means. This is a flowchart showing an example. 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...Standard data table, 39...
Data table for sudden deceleration, 40...Sudden deceleration detection means.

Claims (1)

[Scope of 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 device and is capable of steering the rear wheels; and a front wheel steering angle. Sensor, rear wheel steering angle sensor, vehicle speed sensor, and standard data table that sets the steering ratio of the rear wheels to the front wheels to be in the same phase when the vehicle speed is high and to be in opposite phase when the vehicle speed is low. , a data table for sudden deceleration in which the steering ratio of the rear wheels and the front wheels is set to be in the same phase, a sudden deceleration detection means for detecting that the vehicle is in a sudden deceleration state, and according to the above standard data table. While determining the turning angle of the rear wheels, when the vehicle is running at a vehicle speed in the same phase range in the standard data table, a signal indicating that the vehicle has entered a predetermined sudden deceleration state from the sudden deceleration detection means. is input, while this sudden deceleration state continues, the steering angle of the rear wheels is determined according to the data table for sudden deceleration, and the steering angles are respectively determined as above. A four-wheel steering device comprising: control means for feedback-controlling the rear wheel steering mechanism so as to perform feedback control on the rear wheel steering mechanism.