Method for controlling the slip value of a wheel, control unit for a vehicle, and vehicle

Abstract

The invention relates to a method for controlling the slip value of a wheel of a vehicle, wherein: a controller is used which outputs a manipulated variable on the basis of a determined control deviation; the control deviation comprises a slip-based component and a rotational-speed-based component; in the case of the slip-based component, the target slip is offset against the actual slip; in the case of the rotational-speed-based component, the slip-based component is offset against a normalization variable dependent on the vehicle speed; and the slip-based component and the rotational-speed-based component are weighted according to slip for the determination of the manipulated variable.

Description

[0001] Method for controlling the slip value of a wheel, control unit for a vehicle and vehicle

[0002] The present invention relates to a method for controlling the slip value of a wheel of a vehicle, a control device for a vehicle and a vehicle, in particular a motor vehicle.

[0003] Slip controllers are typically used in vehicle traction control systems. For example, DE 195 42 294 B4 discloses a system for controlling traction slip in a motor vehicle, in which a controller is supplied with at least one controlled variable dependent on the rotational speed of the wheels and at least one target value. It is often difficult to ensure that such controllers operate reliably over a wide operating range. For example, the tire's behavior changes quite significantly at higher slip values. At a slip of over 30%, the tire's longitudinal force remains largely constant and independent of the slip. This means that a controller that operates reliably at low slip values ​​may reach its limits at higher slip values, or vice versa.

[0004] It is therefore an object of the present invention to provide a method for controlling the slip value of a wheel of a vehicle, a control device for a vehicle and a vehicle, wherein in particular a method is to be provided which enables reliable control of both low and high slip values.

[0005] This object is achieved by a method according to claim 1, a control device according to claim 8 and a vehicle according to claim 9. Further advantages and features emerge from the subclaims as well as the description and the attached figures.

[0006] The invention relates to a method for controlling the slip value of a wheel of a vehicle, wherein a controller is used which outputs a manipulated variable based on a determined control deviation, wherein the control deviation, hereinafter also referred to as "hybrid control deviation", comprises a slip-based component and a speed-based component, wherein in the slip-based component the desired slip is offset against the actual slip, and wherein in the speed-based component the slip-based component is offset against a standardization variable dependent on the vehicle speed, and wherein the slip-based component and the speed-based component are weighted depending on the slip to determine the manipulated variable. The term "slip" in this context always refers to (longitudinal tire) slip.

[0007] Slip controllers, such as PID slip controllers, are often used to implement traction control. These first calculate the actual slip Kact of the wheel to be controlled from its circumferential speed v Ra c / and the vehicle speed VFZG.

[0008] > v bike~ v Vehicle is vVehicle

[0009] In addition, a target longitudinal slip Ksoii is calculated, taking into account the driving condition and other parameters. The difference between the actual slip Kact and the target slip Ksoii is the control deviation e K :

[0010] This serves as the input variable of the slip controller, which, taking other parameters and measured variables into account, calculates the drive or braking torque required to adjust the target slip Ksoii at the wheel to be controlled.

[0011] The longitudinal force F x,Wheel, which a car or motorcycle tire can transmit, is (besides wheel load F z The friction coefficient (wheel and tire-road friction coefficient) is largely determined by the longitudinal slip K. A problem (for tuning a traction control system or controller) is that the tire's behavior changes significantly at higher slip values, for example, at slip values ​​of K > 30%. Above these slip values, the tire's longitudinal force remains largely constant and independent of the slip. The controlled system then approximately corresponds to a rotating mass with a constant torque offset.

[0012] If a conventional slip controller is to regulate a high target slip of over 30%, the torque interventions of the controller are too aggressive at low vehicle speeds (controller builds up) and too sluggish at high vehicle speeds (controller can only slowly follow the target slip), since the same speed deviation of the wheel at low speeds corresponds to a higher slip deviation and thus a stronger controller intervention than at high speeds.

[0013] Advantageously, the method according to the invention provides a "hybrid" controller that can continuously adjust its operation between that of a pure slip controller and that of a pure speed controller depending on the current tire longitudinal slip Kactual. This advantageously provides a method or controller that can operate reliably over a very wide operating range. To this end, the method uses the slip-based component and the speed-based component, with the two components being weighted accordingly depending on the current slip. This means that the slip-based component takes precedence at low slip values ​​and the speed-based component at high slip values.

[0014] The weighting of the speed-based component is appropriately higher the higher the actual slip. This takes into account the fact that at higher slip values, control is based on the speed as much as possible, while at lower slip values, control is based on the slip as much as possible. A weighting factor is appropriately used for weighting.

[0015] It has proven advantageous for the weighting of the speed-based component to increase linearly with the slip, while the weighting of the slip-based component decreases linearly with the slip. Slip refers in particular to the amount of the target slip or the actual slip. According to a preferred embodiment, for example, the speed-based component is weighted with 0 up to slip values ​​of 10 to 20%, in particular 15%, for example, and then, preferably linearly, weighted with 0.9 up to a slip value of approximately 30 to 40%, in particular 35%, for example. For this purpose, a corresponding characteristic curve is preferably stored, which provides a corresponding weighting factor depending on the amount of the actual or target slip. The weighting of the slip-based component is accordingly in the opposite direction. For the (hybrid) control deviation ehybr, this means the following:

[0016] ^hybr fhybr * ^K,norm + (1 fhybr') * K' where e K the (classical) slip control deviation is, e K norm is the speed control deviation, and fhybr is the weighting factor. The slip control deviation represents the slip-based component, while the speed control deviation represents the speed-based component.

[0017] The slip control deviation e K is, as already mentioned, calculated as follows:

[0018] The calculation of the standardization variable dependent on the vehicle speed is preferably carried out by multiplying the standardization variable by the slip-based component. The speed control deviation e K ,norm, which is also called standardized control deviation, is calculated as follows: where f K , norm is the normalization value dependent on the vehicle speed.

[0019] The standardization quantity conveniently includes the vehicle speed vpzg and a constant v n orm- Preferably, the constant is in the denominator, the vehicle speed in the numerator: f _ v Vehicle

[0020] JK,norm "norm

[0021] In particular, the design of the standardization variable enables the functionality of the procedure:

[0022] Ksoll .norm fc,norm * K so u wheel r ad * ^ist

[0023] With the roll radius rp a d and the actual and desired wheel angular velocities w, s r and ujsou reflects the speed control deviation or “normalized control deviation” e K , nO rm thus exactly reflects the behavior of a speed control.

[0024] It has been found that the constant preferably lies in the double-digit range. The constant v norm, which conveniently has the unit [km / h], is for example in a range of 40 to 50, but depending on the vehicle it can also be lower or higher.

[0025] The invention also relates to a control device for a vehicle, in particular a motor vehicle, comprising a computing unit which is parameterized and / or designed to carry out a method according to one of the preceding claims.

[0026] The method is preferably implemented in the form of a controller, preferably a PID controller (Proportional-Integral-Derivative). Advantageously, the functionality can be easily implemented in existing traction control systems, since only the calculation of the control deviation needs to be expanded. Accordingly, only the constant v norm and apply the weighting fhybr.

[0027] The invention also relates to a vehicle, in particular a motor vehicle, comprising a control unit according to the invention. Motor vehicles of the type in question are, in particular, land vehicles, such as passenger cars or, in particular, motorcycles, such as scooters or motorbikes, whether powered by electricity or an internal combustion engine.

[0028] Such a method or a controller designed in this way is capable of optimally controlling the slip across the entire slip range. In particular, it can be used to control a (very high) target slip. This makes it useful for implementing extended customer functions where high braking or traction slip is desired.

[0029] Further advantages and features will become apparent from the following description of the method with reference to the attached figures.

[0030] They show:

[0031] Fig. 1 : the tire longitudinal force as a function of the tire longitudinal slip;

[0032] Fig. 2: the weighting factor depending on the slip.

[0033] Fig. 1 shows a diagram of the tire longitudinal force F x,wheel as a function of the longitudinal tire slip K. The diagram clearly shows that the behavior of the tire changes significantly at higher slip values ​​from approximately K > 30%. The longitudinal tire force is then largely constant and independent of the slip. While in range B1 a slip controller is advantageous, which calculates the control deviation from the difference between the actual and target slip, in operating ranges B2 a speed controller is desirable, which calculates the control deviation from the difference between the actual and target speed. Advantageously, the method according to the invention enables a control which, depending on the current longitudinal tire slip, can be continuously adjusted between the operation of a pure slip controller and that of a pure speed controller. Specifically, the control deviation, which is the input variable of the controller, is calculated in such a way that the same controller works optimally in both low and high slip ranges.the process works optimally in both low and high slip ranges.

[0034] Fig. 2 shows the weighting factor fhybr as a function of the tire's longitudinal slip K. The weighting factor fhybr can be calculated, for example, using a characteristic curve as shown in Fig. 2, as a function of the actual or desired slip. This provides a method for controlling the slip value of a vehicle wheel that functions optimally across the entire slip range.

[0035] B1 Working range slip controller

[0036] B2 Working range speed controller F x ,Wheel longitudinal force

[0037] K slip fhybr weighting factor

Claims

Claims 1. Method for controlling the slip value of a wheel of a vehicle, wherein a controller is used which outputs a manipulated variable on the basis of a determined control deviation, wherein the control deviation comprises a slip-based component and a speed-based component, wherein in the slip-based component the desired slip is offset against the actual slip, and wherein in the speed-based component the slip-based component is offset against a standardization variable which is dependent on the vehicle speed, and wherein the slip-based component and the speed-based component are weighted in accordance with slip to determine the manipulated variable.

2. The method according to claim 1, wherein the weighting of the speed-based component is higher the higher the actual slip or the target slip is.

3. Method according to claim 1 or 2, wherein the weighting of the speed-based component is linear with the slip (K) increases, and the weighting of the slippage-based portion decreases linearly with the slippage (K).

4. Method according to one of the preceding claims, wherein the slip-based component is multiplied by the normalization value to determine the speed-based component.

5. Method according to one of the preceding claims, wherein the normalization variable comprises the vehicle speed and a constant.

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

7. The method according to one of claims 5 to 6, wherein the constant is in the mid-double-digit range.

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

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

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