Method for adjusting the slip rate of a wheel, controller for a vehicle, and vehicle

Abstract

The invention relates to a method for adjusting the slip rate of wheels of a vehicle, in which a controller is used which outputs a manipulated variable on the basis of a determined adjustment deviation, the adjustment deviation comprising a slip-based component in which a target slip is calculated from an actual slip, and a rotational speed-based component in which the target slip is calculated from the actual slip. And calculating the slip-based component with a normalized quantity dependent on the vehicle speed in the rotational speed-based component, and weighting the slip-based component and the rotational speed-based component in relation to the slip in order to determine a manipulated variable.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for adjusting the slip ratio of a vehicle wheel, a controller for a vehicle and a vehicle, in particular a motor vehicle. BACKGROUND

[0002] Slip regulators are generally used in the traction control of vehicles. In this regard, DE 195 42 294 B4 discloses, for example, a system for adjusting the drive slip in a motor vehicle, wherein at least one adjustment variable related to the wheel rotational speed and at least one target value are input to the regulator. It is often difficult to ensure that such a regulator reliably works over a wide operating range. The properties of the tires, therefore, change quite significantly at higher slip ratios. At a slip of more than 30%, the tire longitudinal force remains essentially constant and independent of the slip. This leads to the fact that a regulator that reliably works at low slip ratios can reach its limits at higher slip ratios, or vice versa. SUMMARY

[0003] It is therefore the task of the present application to specify a method for adjusting the slip ratio of a vehicle wheel, a controller for a vehicle and a vehicle, in which, in particular, a method is to be provided that enables reliable adjustment not only at low slip ratios, but also at high slip ratios.

[0004] This task is achieved by the method according to claim 1, the controller according to claim 8 and the vehicle according to claim 9. Further advantages and features result from the dependent claims, the description and the figures.

[0005] The present application relates to a method for adjusting the slip ratio of a vehicle wheel, wherein a regulator is used, which outputs a control variable on the basis of a determined adjustment deviation, which comprises a slip-based component and a rotational speed-based component, in which the target slip is operated on the actual slip in the slip-based component and a normalization quantity depending on the vehicle speed is operated on the slip-based component in the rotational speed-based component, and the slip-based component and the rotational speed-based component are weighted in relation to the slip in order to determine the control variable. In other words, "slip" always refers to the (tire longitudinal) slip at the moment.

[0006] In order to implement traction control in the adjustment technology, slip regulators, such as PID slip regulators, are often used. Such a slip regulator first calculates the actual slip k Rad of the wheel to be regulated from the circumferential speed v FZG of the wheel to be regulated and the vehicle speed v ist :

[0007] .

[0008] Furthermore, the target longitudinal slip k soll is calculated in consideration of the vehicle state and other parameters ist The difference between the actual slip k soll and the target slip k k is the regulation deviation e

[0009] .

[0010] This regulation deviation serves as an input quantity for a slip regulator, which thereby calculates a drive torque or brake torque that is required for adjusting to the target slip k soll on the wheel to be regulated, in consideration of other parameters and measured variables.

[0011] The longitudinal force F x,Rad that a vehicle or motorcycle tire can transmit (in addition to the wheel load F z,Rad and the friction coefficient μ between tire and road surface) is determined by the longitudinal slip k ist . What is problematic here (for the coordination of traction control or regulators) is that tire behavior changes strongly at higher slip rates, for example at slip rates k > 30%. From this slip rate, the tire longitudinal force remains essentially constant and independent of the slip. At this time, the regulation path (Regelstrecke) is approximately equivalent to a rotating mass body with a constant torque offset.

[0012] If a conventional slip regulator is adjusted to a high target slip greater than 30%, the torque intervention of the regulator is too aggressive (regulator oscillation) at low vehicle speeds and too slow (regulator only slowly tracks the target slip) at high vehicle speeds, because the same wheel rotational speed deviation corresponds to a higher slip deviation and thus to a stronger regulator intervention at low speeds than at high speeds.

[0013] The method according to the invention advantageously provides a "hybrid" regulator that is able to switch its operating mode between a pure slip regulator and a pure rotational speed regulator depending on the current tire longitudinal slip rate k ist . It thus advantageously provides a method or a regulator that is able to reliably work over a very wide operating range. To this end, the method works with a slip-based component and a rotational speed-based component, wherein the two components are respectively weighted depending on the current slip. This means that the slip-based component dominates at low slip rates, while the rotational speed-based component dominates at high slip rates.

[0014] Appropriately, the higher the actual slip, the greater the weight of the speed-based component. Therefore, the following consideration is taken into account: that is, when the slip ratio is high, adjust as much as possible according to the speed, and when the slip ratio is low, adjust as much as possible according to the slip. For weighting, a weighting coefficient is appropriately used.

[0015] It has proven advantageous that the weight of the speed-based component increases linearly with slip, while the weight of the slip-based component decreases linearly with slip. Here, slip specifically refers to the value of the target slip or actual slip. According to a preferred embodiment, the speed-based component is weighted, for example, with 0 until a slip rate of 10% to 20%, particularly, for example, 15%, so that the speed-based component is then weighted with 0.9, preferably linearly, until a slip rate of about 30% to 40%, particularly, for example, 35%. For this purpose, a corresponding characteristic curve is preferably stored, which provides corresponding weighting coefficients based on the value of the actual slip or target slip. The weight of the slip-based component changes inversely accordingly. For the (mixed) adjustment deviation e hybr In other words, this means the following formula:

[0016] ,

[0017] Among them, e k For (traditional) slip adjustment deviation, e k,norm For speed adjustment deviation, and f hybr These are weighting coefficients. Slip adjustment deviation constitutes a slip-based component, and speed adjustment deviation constitutes a speed-based component.

[0018] As already mentioned, the slip ratio adjustment deviation e is calculated as follows. k :

[0019] .

[0020] The calculation of the normalized value, which depends on vehicle speed, is preferably achieved by multiplying the normalized value by the slip-based component. The speed regulation deviation e is then calculated. k,norm (This is also known as the normalized adjustment bias), which is calculated as follows:

[0021] ,

[0022] Among them, f k,norm This is a normalized value that depends on the vehicle speed.

[0023] Appropriately, the normalized quantity includes vehicle speed v. FZG and constant v norm Preferably, the constant is the denominator, and the vehicle speed is the numerator:

[0024] .

[0025] In particular, the normalized quantity is designed in such a way that the function of the method is currently achieved:

[0026]

[0027]

[0028] with the rolling radius r Rad and the actual wheel angular velocity w ist and the target wheel angular velocity w soll the rotational speed regulation deviation or "normalized regulation deviation" e k,norm Thus, the characteristic of the rotational speed regulation is precisely reflected.

[0029] It has proven to be advantageous for the constant, for example, to lie in the range of two digits. The constant v norm for example, lies in the range of 40 to 50, but can also be smaller or larger depending on the vehicle.

[0030] The application also relates to a control unit for a vehicle, in particular a motor vehicle, comprising a computing unit which is parameterized and / or designed to carry out the method according to any one of the preceding claims.

[0031] The method is preferably implemented in the form of a regulator, preferably a PID regulator (PID, proportional-integral-derivative regulator). This function advantageously enables easy implementation in existing traction controls, so that only the calculation of the regulation deviation needs to be expanded. For the regulator, accordingly, only the application of the constant v norm and the weight f hybr is required.

[0032] The application also relates to a vehicle, in particular a motor vehicle, comprising a control unit according to the application. Motor vehicles in the sense of the present application are in particular land vehicles, for example passenger cars or in particular motorized bicycles, for example mopeds or motorcycles, which are electrically operated or operated with an internal combustion engine.

[0033] This method or a regulator designed in this way enables optimal regulation of the slip over the entire slip range. In particular, it is thus possible to regulate to a (very high) target slip. Thus, an extended customer function can be advantageously implemented, in which a high braking slip or a high driving slip is desired.

[0034] Further advantages and features result from the following description of the method with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0035] In which:

[0036] Figure 1 Tire longitudinal force is shown in relation to tire longitudinal slip;

[0037] Figure 2 The weighting factor is shown in relation to the slip. DETAILED DESCRIPTION

[0038] Figure 1 The tire longitudinal force F is shown in the graph in relation to the tire longitudinal slip ratio k x,Rad It is clear from the graph that the behavior of the tire changes strongly at higher slip ratios from approximately k > 30%. The tire longitudinal force is then essentially constant and independent of the slip. Within the range B1, a slip regulator which calculates the adjustment deviation from the difference between the actual slip and the target slip is advantageous, while within the operating range B2 a rotational speed regulator which calculates the adjustment deviation from the difference between the actual rotational speed and the target rotational speed is desirable. The method according to the application advantageously enables an adjustment which can be switched steplessly between the operating mode of a pure slip regulator and the operating mode of a pure rotational speed regulator depending on the current tire longitudinal slip. In particular, the adjustment deviation, which is the input quantity for the regulator, is calculated in such a way that the same regulator works optimally not only in the low-slip range but also in the high-slip range, or that the method works optimally not only in the low-slip range but also in the high-slip range.

[0039] Figure 2 The weighting factor f is shown in relation to the tire longitudinal slip ratio k hybr The weighting factor f hybr may be calculated, for example, from the value of the actual slip or the target slip with the aid of a characteristic curve as shown in Figure 2 Thus, a method for adjusting the slip ratio of a vehicle wheel can be provided which functions optimally over the entire slip range.

[0040] LIST OF REFERENCE SIGNS

[0041] B1 operating range of the slip regulator

[0042] B2 operating range of the rotational speed regulator

[0043] F x,Rad longitudinal force

[0044] k slip

[0045] f hybr weighting factor

Claims

1. Method for regulating the slip ratio of a vehicle wheel, wherein a regulator is used, which outputs a steering quantity on the basis of a determined regulation deviation; the regulation deviation comprises a slip-based component and a rotational speed-based component, in the slip-based component, a target slip is operated on an actual slip, and in the rotational speed-based component, the slip-based component is operated on a normalization quantity which depends on the vehicle speed, and the slip-based component and the rotational speed-based component are weighted in relation to the slip in order to determine the steering quantity.

2. The method of claim 1, wherein, The greater the actual slip or the target slip, the higher the weight of the rotational speed-based component.

3. The method of claim 1 or 2, wherein, The weight of the rotational speed-based component rises linearly with the slip (k) and the weight of the slip-based component falls linearly with the slip (k).

4. The method according to any one of the preceding claims, wherein, In order to determine the rotational speed-based component, the slip-based component is multiplied by the normalization quantity.

5. The method according to any one of the preceding claims, wherein, The normalization quantity comprises a vehicle speed and a constant.

6. The method of claim 5, wherein, The constant is the denominator and the vehicle speed is the numerator.

7. The method of any one of claims 5-6, wherein, The constant lies in the range of two middle digits.

8. Controller for a vehicle, comprising a computing unit, which is parameterized and / or designed to carry out the method according to any one of the preceding claims.

9. Vehicle, in particular motor vehicle, comprising a controller according to claim 8.

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