Method for determining the rear axle steering angle

Abstract

Rear axle steering angle δ RA,prop This relates to a method for determining (156). In this method, the rear axle steering angle δ RA,prop (156) The detected front axle steering angle δ FA (110) is determined by the rear axle steering angle δ RA,prop When determining (156), tire characteristics and the position of the vehicle's center of gravity are taken into consideration.

Description

Technical Field

[0001] The present invention relates to a method for determining the steering angle of a rear axle and an apparatus for implementing the method. The present invention further relates to a computer program and a machine-readable storage medium.

Background Art

[0002] Prior Art Rear axle steering makes it possible to rotate the wheels at the rear axle and thus directly influence the driving dynamics of the vehicle. For example, if the wheels of the rear axle are rotated in the opposite direction to the wheels of the front axle, the turning radius of the vehicle can be reduced. Therefore, modern driving dynamics control systems offer the possibility of influencing the steering angle of the rear axle using such rear axle steering.

[0003] Therefore, rear axle steering is used especially for forming the driving dynamics of the vehicle, especially the yaw gain. The yaw gain represents the static vehicle response to the steering input caused by the driver. Rear axle steering can increase or decrease the yaw gain of the vehicle.

[0004] It is known to use rear axle steering in the speed range up to about 80 km / h to increase the yaw gain of the vehicle. For this purpose, the rear axle is steered in the opposite direction to the front axle, thereby improving the agility of the vehicle. Compared to a vehicle without rear axle steering, the steering effort for the driver when passing through a curve is reduced.

[0005] It is also known to use rear axle steering in the speed range above about 80 km / h to reduce the yaw gain of the vehicle. For this purpose, the rear axle is rotated in the same direction as the front axle. This reduces the steering effort for the driver when passing through a curve and improves the stability of the vehicle.

[0006] In the known method, a proportional calculation of the rear axle steering angle, i.e., a proportional calculation of the rear axle steering angle proportional to the steering angle of the front axle, is known. In this case, the underlying proportionality coefficient i corr can be specified depending on the vehicle speed v x . The non-linear characteristic of the lateral force of the front axle is implicitly considered via an index Co Overpull indicating that the front axle steering is excessive. Depending on this index, the proportionality coefficient i corr can be attenuated: i corr = f(v x , Co Overpull ) (1) For the rear axle steering angle, δ RA = i corr ·δ FA (2) results.

Summary of the Invention

Means for Solving the Problems

[0007] Disclosure of the Invention Based on the above background, a method having the features of claim 1 and an apparatus according to claim 8 are presented. A computer program according to claim 9 and a machine-readable storage medium according to claim 10 are further presented. Embodiments will become apparent from the dependent claims and the specification.

[0008] The method of the present disclosure is used to determine the rear axle steering angle, which is determined depending on the detected front axle steering angle. Further, when determining the rear axle steering angle, tire characteristics and the position of the vehicle center of gravity are considered.

[0009] Thus, the method of the present disclosure is used to determine or calculate the value of the rear axle steering angle, and subsequently this value can be set via appropriate control for the rear axle.

[0010] The method of the present disclosure is based on the following recognition obtained from problems related to the prior art.

[0011] In known methods, the actual tire characteristics, particularly the nonlinear lateral force transitions of the front and rear axles, are ignored. See Figure 1 for details. Outside the linear lateral force region of the front axle, the lateral acceleration is typically about 4 m / s² on dry asphalt. 2 Beyond a certain point, the effect of proportional rear axle steering on the ratio of the lateral force of the front axle to the lateral force of the rear axle changes. In this case, this ratio shifts in the direction of the rear axle lateral force.

[0012] This effect occurs because the operating range for rear axle steering is significantly smaller than that for front axle steering, and in the linear region of lateral force transition, the rear axle operates for a significantly longer period. If front axle steering is excessive, the lateral force on the front axle may decrease, while the lateral force on the rear axle may increase simultaneously. This can result in an unpredictable and unnatural driving impression, especially in the boundary region of driving dynamics.

[0013] Therefore, it is assumed that by considering the static lateral force of the front axle, it becomes possible to generate a predictable and natural-feeling driving impression. This is particularly evident in the boundary region of driving dynamics. The ratio between the lateral force of the front axle and the lateral force of the rear axle remains constant throughout the entire lateral acceleration region.

[0014] Furthermore, the benchmark co Overpull The implicit effects are already explicitly implemented by considering tire characteristics. This reduces the effort required for application.

[0015] Furthermore, in known methods, vehicle characteristics such as mass and the position of the center of gravity are ignored in addition to tire characteristics. Therefore, the vehicle's center of gravity and the lateral force changes of the front and rear wheels do not affect the proportional rear axle steering angle. Thus, the proportionality constant i is used exclusively. corr We can derive only the qualitative effect that it has on the yoh gain. However, we cannot directly mention the quantitative effect.

[0016] According to the method presented here, quantitative inverse inference about the effect of yaw gain is also possible using the proportionality constant. This is possible because the proportionality constant is calculated at the level of yaw moment.

[0017] As already mentioned, the conventional method does not take into account any tire characteristics or vehicle characteristics. Therefore, it requires a relatively large amount of effort to determine the proportionality coefficient i corr It cannot be used for other different types, models, or vehicle types.

[0018] Therefore, the method presented here is intended to take into account the vehicle's tire characteristics and the position of the vehicle's center of gravity. This facilitates transitions between multiple different types, models, and vehicle types, and significantly reduces the effort required for application. In this case, it is assumed that the proportional rear axle steering angle is calculated by taking into account the tire characteristics and vehicle characteristics, depending on the static lateral force of the front axle.

[0019] The above-described device is configured to carry out the method presented herein and is implemented, for example, in hardware and / or software. The device may be incorporated into, for example, a vehicle control system, or may be configured as a vehicle control system. Therefore, the device may exist at least partially as a computer program, and the computer program itself may be stored in a machine-readable storage medium.

[0020] Further advantages and embodiments of the present invention will become apparent from the specification and the accompanying drawings.

[0021] It is obvious that the features described above and those to be further described below can be used not only in the combinations described but also in other combinations or individually, without departing from the scope of the present invention. [Brief explanation of the drawing]

[0022] [Figure 1]This graph shows the nonlinear lateral force transition over the slip angle. [Figure 2] This is a flowchart showing the calculation of the proportional rear axle steering angle. [Figure 3] This is a schematic diagram of a vehicle equipped with a device for carrying out the method presented here. [Modes for carrying out the invention]

[0023] Embodiments of the Invention The present invention is schematically shown in the drawings based on embodiments and will be described in detail below with reference to the drawings.

[0024] Figure 1 shows graph 10, in which the slip angle α [rad] is plotted on the horizontal axis 12 and the lateral force Fy [N] is plotted on the vertical axis 14. Curve 16 shows the change in lateral force over the slip angle.

[0025] In the present invention, in the embodiment, first, the steering angle δ of the front axle is FA And, static contact force Fz FA,stat Therefore, the tire characteristics of the front axle, that is, the maximum slip angle α max,FA Linear slip stiffness cy FA Taking into consideration the current coefficient of friction μ max,FA Taking this into consideration, the lateral force Fy of the front axle FA This is calculated. As shown in Figure 1, for this calculation, a tire model f maps the nonlinearity of the lateral force over the slip angle. Tyre This is used. Fy FA =f Tyre (Erotic manga) FA ,μ max,FA ,α max,FA ,cy FA Fz FA,stat ) (3)

[0026] This front axle lateral force Fy FA From the position of the vehicle's center of gravity l FA2COG Using the proportional yaw moment Mz prop This is calculated. Mz prop=Fy FA ·l FA2COG (4)

[0027] This yaw moment Mz prop The yaw gain coefficient i corr And the position of the vehicle's center of gravity l RA2COG Using this, the rear axle lateral force Fy RA It is converted to [amount]. Fy RA =( Mz prop ·i corr ) / l RA2COG (5)

[0028] After this, the axle lateral force Fy RA Therefore, the static contact force Fz of the rear axle RA,stat And the linear slip stiffness of the rear axle cy RA Using this, proportional rear axle steering angle δ RA,prop This is calculated. δ RA,prop =Fy RA / (Fz RA,stat ·C RA ) (6)

[0029] Linear slip stiffness cy RA Instead of linearly converting the rear axle lateral force to the rear axle steering angle via the method described above, it is also possible to use an inverse tire model for the conversion. In this case, the tire characteristics of the rear axle, i.e., the maximum slip angle α, can be used. max,RA Linear slip stiffness cy RA It depends on the current coefficient of friction μ max,RA Depending on the proportional rear axle steering angle δ RA,prop This is calculated. δ RA,prop =fTyre(Fy RA ,μ max,RA ,α max,RA ,cy RA ) / Fz RA,stat (7)

[0030] Figure 2 shows a block diagram of a possible sequence of methods for determining or calculating the proportional rear axle steering angle. In this context, "proportional" means that the rear axle steering angle is proportional to the front axle steering angle.

[0031] In the first block 100, the lateral force on the front axle is calculated. The input quantities are as follows: Steering angle δ of the front axle FA 110 Current coefficient of friction μ of the front axle max,FA 112 Maximum slip angle α of the front axle max,FA 114 Linear slip stiffness of the front axle cy FA 116 Static contact force Fz of the front axle FA,stat 118

[0032] The output is the lateral force Fy of the front axle. FA It is 120.

[0033] In block 130, conversion to yaw moment is performed. Front axle lateral force Fy FA 120 is another further input quantity, the position of the vehicle's center of gravity relative to the front axle l FA2COG It is 132. The output is the yaw moment Mz prop The answer is 134.

[0034] In block 140, the lateral force on the rear axle is calculated. Yaw moment Mz prop 134 Other input quantities are the yaw gain coefficient i corr 142 and the position of the vehicle's center of gravity relative to the rear axle l RA2COG The output is 144. The output is the rear axle lateral force Fy RA The number is 146.

[0035] In block 150, the rear axle steering angle is calculated. Rear axle lateral force Fy RA Other input quantities for 146 include the static contact force Fz of the rear axle. RA,stat 152 and the linear slip stiffness of the rear axle cy RA The value is 154. The output is proportional to the rear axle steering angle δ. RA,prop The number is 156.

[0036] Figure 3 shows a purely schematic and highly simplified diagram of a vehicle 200 equipped with a device 202 for carrying out the method presented herein. The vehicle 200 is provided with a front axle 210 and a rear axle 212. The device is used to determine the rear axle steering angle or a value for this rear axle steering angle. The rear axle 212 is then controlled via a control unit 220 so that it sets the rear axle 212 to this determined value.

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