CN114735078A

CN114735078A - Steering control method

Info

Publication number: CN114735078A
Application number: CN202110018787.4A
Authority: CN
Inventors: 郭传真; 潘玉斌; 伍流; 廖巧丽
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2021-01-07
Filing date: 2021-01-07
Publication date: 2022-07-12

Abstract

The present invention relates to a steering control method. The steering control method is used for controlling a vehicle to perform pivot steering, and the vehicle comprises four wheels which can be driven and steered respectively and independently. The steering control method comprises the following steps: a part of the four wheels are selected as driving wheels to drive the vehicle to carry out pivot steering, so that at least one of the four wheels is used as a driven wheel to carry out passive rotation during the pivot steering. The steering control method can improve the pivot steering performance of the vehicle.

Description

Steering control method

Technical Field

The invention relates to the technical field of vehicles. In particular, the present invention relates to a steering control method for controlling pivot steering of a four-wheel independent drive and steering vehicle.

Background

With the development of technology, the control mode of modern motor vehicles is increasingly rich. Different control methods with pertinence are respectively formed for various vehicles. In particular, the maturity of electronic control technology provides more flexible possibilities for the control method of the vehicle. Four-wheel independent steering (4WIS) vehicles are one type of vehicle that has been developed under such circumstances. Such a vehicle can control the steering of the four wheels independently of each other so that all the wheels can move about a common center of steering when steering. Such vehicles are capable of performing a variety of modes of motion, including pivot steering. Meanwhile, four-wheel independent steering vehicles also generally adopt a four-wheel independent drive design, that is, each wheel is provided with a corresponding independent drive mechanism. Such a drive mechanism is typically a drive motor, which may be provided in the wheel hub (i.e. hub drive or in-wheel drive) or at the wheel side (i.e. wheel-side drive). Compared with the traditional front wheel or rear wheel drive vehicle, the maneuverability and the controllability of the vehicle with four wheels driven and steered independently are improved obviously, so that the vehicle is widely applied to the fields of scientific investigation, agriculture, logistics, intelligent transportation and the like.

As described in patent document CN 111497637 a, when the existing four-wheel independent drive and steer vehicle performs pivot steering, the steering center is generally set at the geometric center of the vehicle body, and the drive motors of the four wheels simultaneously drive the four wheels to rotate at the same rotation speed, thereby realizing the rotational movement of the vehicle around the geometric center thereof. However, in practical situations, since the actual centroid of the vehicle often cannot be completely coincident with the geometric center, and the condition of the road surface contacted by each wheel often is not completely consistent, the actual contact states of the four wheels with the road surface usually have certain differences. When four drive motors simultaneously input the same torque to the respective wheels, it tends to be difficult to completely synchronize the actual output torques of the four wheels. This makes the moving state of the vehicle as a whole unstable and easily causes tire wear. In addition, if the driving motor fails, simultaneous driving of the four wheels cannot be achieved.

Disclosure of Invention

Therefore, an object of the present invention is to provide a steering control method capable of improving the original steering performance of a vehicle.

The above technical problem is solved by a steering control method according to the present invention. The steering control method is used for controlling a vehicle to perform pivot steering, and the vehicle comprises four wheels which can be driven and steered respectively and independently. The steering control method comprises the following steps: a part of the four wheels are selected as driving wheels to drive the vehicle to carry out pivot steering, so that at least one of the four wheels is used as a driven wheel to carry out passive rotation during the pivot steering. That is, when the vehicle is performing pivot steering, all four wheels do not output driving torque at the same time, but only a part of the wheels output driving torque, and the other wheels follow the driving wheel to perform passive rotation only when the vehicle body rotates. Since the rotation of the driven wheel is performed only following the rotation of the driving wheel, the possibility of occurrence of a rotational incongruity between the driving wheel and the driven wheel is small, which can improve the motion stability of the vehicle as a whole and reduce the wear on the wheels, particularly on the driven wheel.

According to a preferred embodiment of the present invention, a single wheel or a pair of diagonally arranged wheels of four wheels may be selected as the driving wheel. The rotation incongruity of different wheels and the abrasion of the wheels can be reduced to a greater extent by only selecting a single wheel as the driving wheel. When it is desired to select two wheels as the driving wheels, for example, when the driving power of a single wheel is insufficient to drive the vehicle to rotate in place, it is preferable to select a pair of wheels arranged diagonally as the driving wheels, which makes the distribution of the driving force received by the vehicle more uniform, and thus the vehicle can rotate more stably.

According to another preferred embodiment of the present invention, the primary wheels may be selected according to the operating states of the four wheels. Preferably, the operating states of the four wheels may include at least one of: wear condition of each wheel and operating condition of the drive mechanism of each wheel. The main reference criterion for selecting the drive wheels here is to minimize wear on the wheels, in particular further wear on the wheels which have already been subjected to more severe wear, while ensuring that the selected drive wheels have sufficient capacity to drive the entire vehicle in a pivot motion.

According to another preferred embodiment of the present invention, when the power of the driving mechanism of at least one of the four wheels is sufficient to drive the vehicle alone for pivot steering, a single wheel may be selected from the at least one wheel as the driving wheel in order to rotate as many wheels as possible as the driven wheels to reduce wear. When the power of the driving mechanism of any one of the four wheels is not enough to drive the vehicle alone for pivot steering, a plurality of wheels can be selected as driving wheels so as to provide sufficient driving force for the vehicle. When a plurality of wheels are required to be selected as the driving wheels, two wheels can be selected, and three wheels can be selected.

According to another preferred embodiment of the present invention, when the power of the driving mechanism of any one of the four wheels is insufficient to drive the vehicle alone for pivot steering, it is preferable to select a pair of diagonally arranged wheels of the four wheels as the driving wheels so as to make the turning motion of the vehicle as a whole more stable. The precondition for making this choice is still that such a drive mechanism for a pair of wheels can provide sufficient drive power.

According to another preferred embodiment of the present invention, the wheel with the most severe wear of the four wheels may not be selected as the driving wheel, thereby avoiding further wear of the wheel.

According to another preferred embodiment of the invention, the driving wheels can be selected according to the environmental conditions to which the four wheels are subjected. Preferably, the environmental conditions to which the four wheels are subjected may include at least one of: the flatness of the area of the road surface contacted by each wheel and the adhesion between each wheel and the contacted area of the road surface. The main reference criterion for selecting the driving wheels here is to make the operating environment, in particular the road conditions, in which the driving wheels are located favorable for a stable rotation of the wheels.

According to another preferred embodiment of the present invention, it is preferable that the wheel having the worst flatness of the road surface area to be contacted is not selected as the driving wheel, thereby preventing the driving wheel from being bumpy. Similarly, the wheel with the smallest adhesion force with the contacted road surface area may not be selected as the driving wheel, for example, the wheel with wet and slippery road surface area is contacted, so as to ensure that the friction force between the driving wheel and the road surface can stably drive the vehicle to move.

Drawings

The invention is further described below with reference to the accompanying drawings. In the figures, elements having the same function are denoted by the same reference numerals. Wherein:

fig. 1 shows a plan view of a vehicle to which a steering control method according to an embodiment of the invention is applied; and

fig. 2 shows another plan view of a vehicle to which a steering control method according to an embodiment of the invention is applied.

Detailed Description

A specific embodiment of a steering control method according to the present invention will be described below with reference to the accompanying drawings. The following detailed description and drawings are illustrative of the principles of the invention, which is not to be limited to the preferred embodiments described, but is to be defined by the scope of the appended claims.

According to an embodiment of the present invention, there is provided a steering control method for controlling a four-wheel independent drive and steering vehicle to steer in place. The four-wheel independently driven and steered vehicle herein refers to a vehicle having four wheels that can be driven and steered independently, respectively. Fig. 1 and 2 each schematically show a top view of such a vehicle. The top views shown in fig. 1 and 2 are the case when viewed from the top of the vehicle in a direction perpendicular to the plane of movement of the vehicle. The upper side in the drawing corresponds to the front of the vehicle in the three-dimensional space, and the left side in the drawing corresponds to the left side of the vehicle in the three-dimensional space. As shown in fig. 1 and 2, four wheels of such a vehicle are arranged substantially symmetrically in the front-rear direction and in the left-right direction, respectively. The intersection of the symmetry axis x of the vehicle (in particular of the four wheels) in the front-rear direction and the symmetry axis z in the left-right direction is approximately the geometric centre O of the vehicle in the x-z plane (i.e. the plane parallel to the ground).

In the prior art, when the vehicle needs pivot steering, the vehicle usually rotates by taking the geometric center O of the vehicle as a steering center. At this time, the drivers of the four wheels of the vehicle simultaneously output torque so that the four wheels rotate at the same rotational speed. Theoretically, due to the symmetrical layout of the vehicle, if the pivot steering is performed around the geometric center O, the rotation speed and yaw angle of the four wheels should be the same. However, since the road surface tends to be uneven or the like under actual conditions, the actually required rotation speeds of the four wheels may be different. At this time, if the four wheels are all rotated as driving wheels at a prescribed rotation speed, some of the wheels will make sliding friction with the road surface. In other words, rotational non-coordination occurs between the four wheels. This will cause wear of the wheels.

For this reason, in the steering control method according to the embodiment of the present invention, torque is not output to all four wheels at the same time, but only some of the four wheels are selected as the driving wheels to drive the vehicle for pivot steering, and the remaining wheels are used as the driven wheels to follow the driving wheels for passive rotation. Three, two or one of the four wheels may be selected as the driving wheel. For example, in FIGS. 1 and 2, W is used₁And W₂Respectively representing a driving wheel and a driven wheel. In FIG. 1, two wheels, namely a left front wheel and a right rear wheel, are selected as driving wheels W₁And the left and right rear wheels serve as driven wheels W₂(ii) a In FIG. 2, only the left front wheel is selected as the driving wheel W₁And the left rear wheel, the right front wheel and the right rear wheel are all taken as driven wheels W₂. In this case, the driven wheel W₂Rotating only under the action of friction between the tyre and the road surface, and therefore at the driven wheel W₂Only rolling friction occurs with the road surface and no sliding friction occurs. In other words, due to the driven wheel W₂Follows the vehicle body only and thus is at the driven wheel W₂And a driving wheel W₁The phenomenon of rotation uncoordinated can not occur between the two. This can at least reduce wear on the driven wheel.

The method of selecting the drive wheel is described in detail below. The selection of the drive wheel should take into account a number of factors in combination. First, consideration needs to be given to how to better avoid wear on the wheels. Generally, the smaller the number of drive wheels, the lower the possibility of rotational mismatch between the drive wheels, and the less wear on the wheels, particularly the wheels that are driven wheels. Therefore, from the viewpoint of reducing wear, it is desirable to reduce the number of drive wheels as much as possible. Preferably, two or one of the four wheels may be selected as the driving wheel. Particularly when only one wheel is selected as the driving wheel (as shown in fig. 2), no rotational mismatch occurs between the different wheels, and thus wear can be minimized.

Second, the smoothness of the vehicle's steering needs to be considered. The distribution of the driving wheels can affect the steering stability of the vehicle. This is particularly evident when two wheels are selected as the driving wheels. If the two selected wheels are located on the same side of the vehicle body, for example, on the left side, the right side, the front side or the rear side, the vehicle may be unstable in movement, and the rotation mismatch between the two driving wheels may occur. In view of this, it is preferable to select a pair of wheels arranged diagonally as the driving wheels. For example, the left front wheel and the right rear wheel may be selected as the driving wheels as shown in fig. 1, or the right front wheel and the left rear wheel may be selected as the driving wheels instead. This makes the distribution of the driving force applied to the vehicle body by the two wheels more balanced, thereby helping to maintain the stability of the vehicle.

Third, the operating conditions of the four wheels need to be considered. The operating state of the wheels may include a wear condition of each wheel, an operating condition of a drive mechanism of each wheel, and the like. The wear conditions of each wheel are mainly considered in order to optimize the distribution of wear over the different wheels. Since the drive wheels are subjected to much higher levels of wear than the driven wheels, selecting a drive wheel also means selecting the primary recipient of wear. Therefore, the wheel with lower abrasion degree is selected as the driving wheel as far as possible, and the wheel with higher abrasion degree can be used as the driven wheel. In particular, it is preferable to avoid selecting the most worn wheel of the four wheels as the driving wheel.

The operational conditions of the drive mechanism of the wheels are taken into account in order to ensure that the selected drive wheels have a sufficient capacity to drive the entire vehicle body for steering. Since only a part of the four wheels is selected as the driving wheel, the steering power which can be provided by the driving wheel is necessarily smaller than that provided when the four wheels are driven together. While four-wheel independent drive and steering vehicles are often driven using electric motors that can provide drive power in relation to the amount of stored electricity, this results in possible differences in the maximum drive power that can be provided by the different wheels. For this purpose, the driving wheel can be selected in the following way, taking into account the first two items: firstly, judging whether wheels with enough power of a driving mechanism to drive the vehicle to carry out pivot steering exist or not, and if at least one wheel exists, selecting one wheel from the wheels as a driving wheel; if the power of the driving mechanism of any wheel is not enough to drive the vehicle to carry out pivot steering alone, a plurality of wheels are selected as driving wheels. When it is desired to select a plurality of wheels as the drive wheels, it is still preferable to select a pair of diagonally arranged wheels as the drive wheels.

Finally, the driving wheels are selected taking into account the environmental conditions to which the four wheels are subjected. The environmental conditions here refer primarily to external conditions that may have an influence on the operation of the wheels, in particular road conditions, such as the flatness of the road surface area contacted by each wheel and the adhesion between each wheel and the contacted road surface area. The road surface flatness condition affects the difficulty and stability of the rolling of the wheels, so that the selection of the wheels with poor flatness in the contacted road surface area as the driving wheels needs to be avoided. In particular, the wheel with the worst flatness of the road surface area contacted with the wheel can not be selected as the driving wheel. Similarly, the level of adhesion between the wheels and the road surface affects the overall driving force experienced by the vehicle body. The adhesion level is mainly influenced by the wetness of the road surface. For example, areas of the road surface where water is present can provide less traction and tend to cause wheel slip. Therefore, it is also necessary to avoid selecting wheels having low adhesion to the road surface as the driving wheels. In particular, it is not possible to select as the drive wheel the wheel with the least adhesion to the road surface area in contact with.

The various factors that need to be taken into account in selecting the capstan are provided exemplarily in the above embodiments. In practical situations, selecting the driver requires a combination of factors, which are not limited to the above. The operator needs to make the selection according to the actual situation and the specific needs and based on experience. Thus, such a method may be implemented manually. However, it is also possible to empirically quantify these factors and write them into a program automatically executed by the machine, and automatically detect various parameters required by sensors or the like, and finally automatically select an appropriate drive wheel by the controller of the vehicle.

Further, it should be noted that, although the steering center of the vehicle is predetermined as the geometric center of the vehicle in the above-described embodiment, the present invention is not limited thereto. The steering center of the vehicle may also be at other points on the vehicle. The steering center being on the vehicle means that the position of the steering center, when viewed in a plane parallel to the ground on which the vehicle is located, falls within the projected range of the vehicle body, and is not outside the vehicle body. The manner of steering around such a steering center, so-called pivot steering, may also be referred to as the rotation of the vehicle. When the vehicle is turned on the spot around different turning centers, the driving wheels can still be selected by the above-mentioned steering control method.

Although possible embodiments have been described by way of example in the above description, it should be understood that numerous embodiment variations still exist through all known and further combinations of technical features and embodiments that are easily imaginable to the skilled person. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. From the foregoing description, one of ordinary skill in the art will more particularly provide a technical guide to convert at least one exemplary embodiment, wherein various changes may be made, particularly in matters of function and structure of the components described, without departing from the scope of the following claims.

List of reference numerals

Geometric center of O

W₁Driving wheel

W₂Driven wheel

x axis of symmetry in the front-to-rear direction

z axis of symmetry in the left-right direction

Claims

1. A steering control method for controlling a vehicle to steer in place, the vehicle including four wheels that are capable of driving and steering independently from each other,

it is characterized in that the preparation method is characterized in that,

the steering control method includes:

selecting a portion of the four wheels as a driving wheel to drive the vehicle for pivot steering such that at least one of the four wheels is passively rotated as a driven wheel during pivot steering.

2. The steering control method according to claim 1, characterized in that a single wheel or a pair of diagonally arranged wheels of the four wheels is selected as a driving wheel.

3. The steering control method according to claim 1, wherein a drive wheel is selected in accordance with the operating states of the four wheels.

4. The steering control method according to claim 3, characterized in that the operating states of the four wheels include at least one of:

wear condition of each wheel; and

the operating condition of the drive mechanism of each wheel.

5. The steering control method according to claim 4, wherein when the power of the drive mechanism of at least one of the four wheels is sufficient to drive the vehicle alone for pivot steering, selecting a single wheel from the at least one wheel as a driving wheel; when the power of the driving mechanism of any one of the four wheels is not enough to drive the vehicle to perform pivot steering alone, a plurality of wheels are selected as driving wheels.

6. The steering control method according to claim 5, wherein when the power of the drive mechanism of any one of the four wheels is insufficient to drive the vehicle alone for pivot steering, a pair of diagonally disposed wheels of the four wheels is selected as a driving wheel.

7. The steering control method according to claim 4, wherein a wheel most worn out of the four wheels is not selected as a driving wheel.

8. The steering control method according to any one of claims 1 to 7, characterized in that a drive wheel is selected in accordance with an environmental condition in which the four wheels are located.

9. The steering control method according to claim 8, wherein the environmental conditions in which the four wheels are located include at least one of:

the flatness condition of the road surface area contacted by each wheel; and

the adhesion between each wheel and the area of the road surface contacted.

10. The steering control method according to claim 9,

wheels with the worst flatness of the contacted road surface area are not selected as driving wheels; and/or

The wheel with the least adhesion to the road surface area in contact with is not selected as the driving wheel.