Method for detecting wheel slip of a motor vehicle and corresponding motor vehicle

Abstract

Method for detecting slippage of wheels (16, 17) of a motor vehicle (10) having the following features: - based on the drive torque of the wheels (16, 17) and the driving resistance of the motor vehicle (10), a calculated acceleration of the motor vehicle (10) is determined on a model-based basis, and - the slip is derived from any deviation between the calculated and actual acceleration of the motor vehicle (10), characterized by the following feature: - during braking with unknown braking torque, the detection is deactivated, suspended or corrected based on the brake pressure.

Description

[0001] The present invention relates to a method for detecting wheel slippage in a motor vehicle. The present invention also relates to a corresponding motor vehicle, a corresponding computer program, and a corresponding storage medium. State of the art

[0002] In the automotive industry, it is common practice to equip vehicles with a so-called anti-judder function. This function is designed to prevent an undesirable phenomenon known as "judder," which occurs when the vehicle is operated under certain driving conditions. This typically occurs when the driver presses or releases the accelerator pedal too quickly, which can lead to an abrupt change in torque and thus an unpleasant driving experience. To counteract this phenomenon, on appropriately equipped vehicles, the anti-judder function intervenes when a vibration is detected—within specified limits—and applies an opposing torque to calm it down.

[0003] The current state of the art uses wheel speeds as a reference for the anti-judder function. To reduce external excitations, the averaged wheel speeds are filtered before being used to calculate the reference speed.

[0004] DE 10 2019 217 318 A1, US 2009 / 0 210 128 A1 and DE 10 2015 212 948 A1 each disclose the subject matter of the preamble of claim 1.

[0005] DE102019135087A1 discloses a method for slip control, in which a torque control is carried out via an electric drive acting on the respective vehicle wheel in a torque control step, and actual drive torques or forces are applied, which can have both an accelerating and a braking effect. In this process, wheel slip of the respective vehicle wheel is determined, and a check is carried out to determine whether instability is present. If instability of the vehicle wheel is detected, wheel slip is advantageously controlled to a target slip of the vehicle wheel, or the speed of the electric drive is controlled to this target slip, since such slip control or speed control enables, in particular, a high transmission of the longitudinal forces, in particular the longitudinal forces leading to braking, and furthermore ensures suitable lateral force transmission.The actual drive torque transmitted from the electric drive to the vehicle wheel, which can be accelerating or braking, is determined and evaluated using an end criterion. If the end criterion or termination criterion is met, the superimposed speed control or slip control of the electric drive is terminated.

[0006] DE102012216220A1 discloses a sensor system for a vehicle, comprising at least two wheel speed sensor elements, at least one steering angle sensor element and a signal processing device which is designed to at least partially jointly evaluate the sensor signals of the sensor elements, wherein the signal processing device comprises a vehicle model unit which is designed to calculate at least the speed along a first defined axis, the speed along a second defined axis and the rotation rate about a third defined axis from the sensor signals of the wheel speed sensor elements and the steering angle sensor element.

[0007] DE102011100814A1 relates to a traction control system for a vehicle with an electric vehicle drive, which comprises one or more electric drive motors, in which, in order to limit the traction slip, the speed of the drive wheels is controlled by controlling the speed of the rotating field generated in at least one electric drive motor, wherein each electric drive motor is fed by a controllable converter assigned to it and, for speed control, the ASR control unit constantly communicates to each converter the maximum permissible speed of the drive motor or drive wheel assigned to it.

[0008] A method for controlling a vehicle powertrain according to DE102011084220A1 includes using current conditions to estimate the wheel slip probability and the demand for vehicle dynamic handling assistance, resulting in two-wheel drive if said slip probability and the demand for handling assistance are low and no condition for forced powertrain connection exists. It results in four-wheel drive if said slip probability and / or the demand for handling assistance are high and no condition for forced powertrain disconnection exists.

[0009] DE10203422A1 relates to a method for controlling the traction of slipping wheels of at least one drive axle, which are driven via an open differential gear and can be clamped together by means of braking intervention to a certain, predeterminable degree to effect a differential lock function. It is proposed to detect the wheel slip of the wheels, compare the detected wheel slip profile with predefined wheel slip patterns to detect and observe a current driving condition, and, if the detected wheel slip profile matches at least one predefined wheel slip pattern, perform a braking intervention that effects the differential lock function.

[0010] EP3106360A1 discloses a method for estimating a friction coefficient between tires of a tire-mounted two-axle dual-track road vehicle and the ground, comprising the following steps: when the longitudinal speed of the vehicle is above a first threshold and the wheel angle and / or yaw rate is below a second threshold, applying a positive torque to both wheels on a first axle and an opposite, negative torque to both wheels on a second axle, following a driver-requested longitudinal acceleration of the vehicle; measuring wheel speeds; estimating tire forces; estimating the friction coefficient between the tires and the ground from the measured wheel speeds and the estimated tire forces; providing the estimated friction coefficient to other systems of the vehicle.

[0011] DE19549259A1 discloses a drive system with a traction control system, in which the (or an) electric machine is designed in such a way that it can be used to reduce the traction slip by reducing the drive torque (of the drive unit), in particular by braking and / or - in the case of an electric machine acting as a clutch - by clutch slip effect.

[0012] WO2017215751A1 discloses a decentralized wheel control device arranged in connection with a wheel of a vehicle, comprising: a wheel slip calculation module arranged to calculate a wheel longitudinal slip value for a wheel slip between a surface of the wheel and a road surface; a wheel force estimation module arranged to estimate a wheel longitudinal force value for a wheel force between the surface of the wheel and the road surface; a tire model generator arranged to receive wheel longitudinal slip values ​​from the wheel slip calculation module and wheel longitudinal force values ​​from the wheel force estimation module;wherein the tire model generator is configured to generate a model representing a relationship between the calculated longitudinal wheel slip and the estimated longitudinal wheel force by using at least three longitudinal wheel force values ​​and three corresponding longitudinal wheel slip values, the model representing the relationship between the calculated longitudinal wheel slip and the estimated longitudinal wheel force comprising a longitudinal wheel slip stiffness measured at zero slip between the wheel surface and the road surface, an absolute maximum wheel friction level, and a wheel friction level corresponding to a maximum wheel slip level;and a vehicle wheel performance module arranged in communication with the tire model generator, the vehicle wheel performance module configured to determine an absolute maximum wheel friction level between the surface of the wheel and the road surface thereof by acquiring a longitudinal wheel force value from the model of the tire model generator for a calculated wheel slip value;

[0013] WO2004067307A1 discloses a method for controlling the wheel slip of at least one wheel of a vehicle, comprising the following steps: detecting at least one dynamic state parameter of the vehicle, adaptively estimating parameters of a parametric slip-friction force model of the vehicle, determining a slip reference value indicating the wheel slip at a specific drive torque from a dynamic model of the relevant vehicle components comprising the adaptive parametric slip-friction force model, and controlling the drive torque of the vehicle by determining a torque manipulation signal based on the dynamic state parameters and the slip reference value. Disclosure of the invention

[0014] One problem is that known anti-judgment mechanisms in motor vehicles do not work optimally under certain conditions. This is particularly the case on surfaces with a low coefficient of friction, such as those found in wet or icy conditions. In these situations, unwanted wheel slip can occur, causing the vehicle to slide on the road surface.

[0015] In such cases, a conventional anti-judgment function tends to intervene strongly because it detects large differential speeds between the wheels. However, these strong interventions can significantly weaken the driver's input and make the vehicle's response difficult to understand. The result is suboptimal vehicle controllability, which impairs the driving experience and increases the risk of accidents.

[0016] This problem is exacerbated in vehicles with internal combustion engines, which implement the anti-judder function partially or entirely on the internal combustion engine by releasing its ignition angle during anti-judder intervention, because the strong negative interventions place greater strain on the catalytic converter and reduce efficiency.

[0017] The described problem is solved by a method for detecting wheel slippage of a motor vehicle, a corresponding motor vehicle, a corresponding computer program and a corresponding storage medium according to the independent claims.

[0018] This approach has the advantage of enabling fast and accurate wheel slip detection, applicable to a wide range of driving situations and conditions. It therefore offers greater flexibility and accuracy in detecting and responding to wheel slip to enhance the driving experience and optimize vehicle performance.

[0019] Furthermore, this method helps mitigate the problems associated with conventional anti-judder techniques by reducing the potential for disruptive and unwanted intervention of the anti-judder function under certain driving conditions, particularly wheel slip. This is achieved by deactivating the anti-judder function once a wheel slip condition is detected until the vehicle or the slip condition has stabilized.

[0020] Finally, the proposed approach offers another advantage for internal combustion engine vehicles. By reducing the likelihood of unnecessary catalytic converter stress, it contributes to improved performance and efficiency for this vehicle category.

[0021] Further advantageous embodiments of the invention are specified in the dependent patent claims. Short description of the drawing The single figure shows the typical application of a method according to the invention. Embodiments of the invention

[0022] An exemplary embodiment will now be explained with reference to the figure. It shows a vehicle (10) rolling or driving on a wet or icy surface (12) up an incline (13). The driver (14) abruptly depresses the accelerator pedal (15). As a result, the front wheels (16) and rear wheels (17) spin (technically known as "slip"), so that the anti-judgment function of the vehicle (10) threatens to release the ignition angle of its combustion engine (11).

[0023] According to the invention, this unstable driving condition is detected within a few seconds and continuously checked for plausibility. For this purpose, the expected acceleration of the vehicle (10) is calculated using a stored model based on the drive torques of the wheels (16, 17) and the driving resistance of the vehicle (10). These operating parameters enable a sufficiently accurate and robust estimation of the acceleration that the vehicle (10) should have under the current driving conditions with a circumferential slip of less than 20%.

[0024] The actual wheel acceleration is derived in parallel from the angular acceleration of the front wheels (16) and rear wheels (17). This information can be retrieved directly from the vehicle's wheel sensors (10). The actual acceleration thus determined is then compared with the calculated acceleration. Alternatively, the actual vehicle acceleration can be determined by an acceleration sensor and used. In this case, the sign of the deviation changes compared to the comparison with the wheel acceleration.

[0025] Any deviation between the calculated and actual acceleration is considered an indication of wheel slip. To avoid false alarms and increase system reliability, wheel slip detection is only triggered when the deviation exceeds a certain difference and reaches a certain hysteresis threshold.

[0026] The difference may depend on various parameters, including the measured speed of the wheels (16, 17), the brake pressure exerted on them, the gear position of the vehicle (10), or the activity of its electronic stability control (ESC). Furthermore, the gradient (13), the calculated acceleration, the sideslip angle, or—in the case of a switchable four-wheel drive—the (two- or four-wheel) drive type of the vehicle (10) may influence the difference relevant for detection.

[0027] The system is also designed to debounce detection based on the calculated acceleration to increase the robustness of the triggering. This means that short-term fluctuations in acceleration, which can be caused, for example, by uneven road surfaces, do not mislead the system and lead to false triggering.

[0028] During braking – for example, mechanical braking – with an unknown braking torque, the detection is deactivated, suspended or corrected based on the brake pressure.

[0029] As soon as wheel slip is detected, the vehicle's anti-judder function (10) is deactivated until the slip condition stabilizes. This improves vehicle response and prevents unwanted interventions by the anti-judder function, which could otherwise irritate the driver (14).

Claims

[1] Method for detecting wheel slippage (16, 17) of a motor vehicle (10) having the following features: - based on the drive torque of the wheels (16, 17) and the driving resistance of the motor vehicle (10), a model-based calculation determines the acceleration of the motor vehicle (10) and - the slip is derived from any deviation between the calculated and actual acceleration of the motor vehicle (10), characterized by the following characteristic: - During braking with an unknown braking torque, the detection is deactivated, suspended, or corrected based on the brake pressure. [2] Method according to claim 1, characterized by at least one of the following characteristics: - the actual acceleration is derived from the angular acceleration of the wheels (16, 17) or - the actual acceleration of the motor vehicle (10) is determined by an acceleration sensor. [3] Method according to claim 1 or 2, characterized by at least one of the following characteristics: - Detection requires that the deviation exceeds a certain difference amount and - Detection requires that the deviation reaches a certain hysteresis threshold. [4] Method according to claim 3, characterized by , that the difference depends on at least one of the following: - a measured rotational speed of the wheels (16, 17), - a braking pressure exerted on the wheels (16, 17), - a gear shift stage of the motor vehicle (10), - any vehicle dynamics control system (10), - a type of propulsion of the motor vehicle (10), - a skew angle of the motor vehicle (10), - a gradient (13) to be overcome by the motor vehicle (10) or - the calculated acceleration of the motor vehicle (10). [5] Method according to any one of claims 1 to 4, characterized by the following characteristic: - the detection is debounced depending on the computational acceleration. [6] Method according to any one of claims 1 to 5, characterized by the following characteristics: - unless the detection is deactivated or suspended, it takes place continuously and - as long as the detected slip exceeds a certain level, an anti-jerk function of the motor vehicle (10) is suspended. [7] Motor vehicle (10), characterized by the following characteristics: - the motor vehicle (10) has wheels (16, 17), - the motor vehicle (10) has an anti-jerk function and - the motor vehicle (10) is equipped to carry out a procedure according to claim 6. [8] Computer program which is configured to perform all steps of a method according to any one of claims 1 to 6. [9] Machine-readable storage medium with a computer program stored thereon according to claim 8.

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