Method and device for controlling a vehicle during µ-split braking

Abstract

The invention provides a method (100) for controlling a vehicle during µ-split braking, wherein the vehicle is equipped with a braking system having a brake pressure regulation or brake pressure control function for exerting a wheel-specific brake pressure on at least two wheel brakes of two vehicle wheels of the vehicle, and with an automated driving system having an autonomous steering system for at least partially autonomously maneuvering the vehicle, wherein a communication connection exists between the braking system and the automated driving system, and wherein the method comprises the following steps: - Detection of a µ-split braking by the braking system (101), - specifying a steering angle request by the braking system to the automated driving system (102), and - Setting a brake pressure by the brake system depending on the specified steering angle requirement (104). The invention further provides a device designed to carry out such a method (100).

Description

[0001] The invention relates to a method for controlling a vehicle during μ-split braking. The invention further relates to a device designed to carry out such a method.

[0002] In order to prevent the vehicle wheels from locking when the wheel brakes are applied, for example as a result of excessive brake pressure being applied, and the vehicle therefore losing its stability or ability to steer, a vehicle usually has a braking system with a brake pressure regulating or brake pressure control function, in particular with an anti-lock control function, for exerting wheel-individual brake pressure on the wheel brakes of vehicle wheels, wherein the brake pressure of each vehicle wheel can be controlled or regulated independently of the rotational behavior of the other vehicle wheels. If locking or a risk of locking of one or more vehicle wheels is detected, the brake pressure is automatically modulated, i.e. reduced, held constant and / or increased again, for at least some of the wheel brakes until locking or anti-lock braking is no longer detected.there is no longer any risk of locking, thus enabling a certain degree of directional stability and steering ability of the vehicle.

[0003] When a vehicle brakes on inhomogeneous road surfaces, i.e., roads with significantly different friction coefficients (µ) on the left and right sides of the road or vehicle, asymmetric braking forces typically occur on the right and left sides of the vehicle due to the different friction coefficients. These asymmetric braking forces result in a yaw moment around the vehicle's vertical axis, which can cause the vehicle to yaw toward the side of the road with the higher friction coefficient, the so-called high-friction side.

[0004] In today's vehicles, it is therefore common practice to regulate the brake pressure of at least the two rear wheels of a vehicle depending on the wheel currently operating with the lowest friction coefficient. This means that in the operating situation described above, the wheel brake of the rear wheel rotating with the higher friction coefficient, the so-called high-friction rear wheel, is only subjected to the same comparatively low brake pressure as the wheel brake of the other rear wheel rotating with the lower friction coefficient, the so-called low-friction rear wheel, even though it could be braked more strongly without locking due to its higher friction coefficient. In this case, the braking forces applied to both rear wheels are equal or equal to the same level, meaning that they do not contribute to generating a yaw moment.Since the high-friction rear wheel is braked less than possible, it has a correspondingly high potential for dissipating lateral forces, which benefits the vehicle's directional and driving stability. However, this good directional and driving stability comes at the cost of a longer braking distance, since the vehicle wheels, which rotate at higher friction values, are braked less than the existing traction would normally allow.

[0005] In vehicles with a braking system, particularly an anti-lock braking system, with a brake pressure regulation or brake pressure control function for exerting individual brake pressure on both wheel brakes of the vehicle's front wheels, it is common practice to mitigate the effect of a yaw moment that builds up as a result of different braking forces on the right and left front wheels by means of a so-called yaw moment limiter. The yaw moment limiter ensures that the brake pressure on the front wheel rotating with the higher coefficient of friction, the so-called high-friction front wheel, is built up more slowly than is otherwise possible or is even reduced. The resulting delayed buildup of the yaw moment provides additional time for reaction, i.e., in particular, for countersteering. The yaw moment limiter naturally also contributes to a deterioration in the achievable braking or stopping distance.

[0006] In a braking system, particularly an anti-lock braking system with a wheel-specific brake pressure regulation or control function, there is generally a conflict of objectives when braking on a road surface with different friction coefficients on each side, i.e., in a so-called µ-split braking situation. On the one hand, the aim is to achieve the shortest possible braking or stopping distances when braking, but on the other hand, it is also important to at least achieve a reduction in the yaw moment when braking and thus maintain the directional or driving stability as well as the steerability of the vehicle. Furthermore, the known methods for controlling a vehicle during µ-split braking are generally designed for vehicles in which a driver (manually) controls the steering of the vehicle and thus also any compensatory steering when a corresponding yaw moment occurs.

[0007] Today, however, vehicles with automated driving systems are already known, which partially or completely assume control or guidance of the vehicle as part of semi-autonomous or autonomous operation or driving. Such an automated driving system typically features an autonomous steering system that autonomously controls the vehicle's (wheel) steering angle.

[0008] Against this background, it is now the object of the invention to provide a method for controlling the vehicle during µ-split braking and a corresponding device for a vehicle that is equipped with a braking system with a brake pressure regulation or brake pressure control function for exerting a wheel-individual brake pressure on at least two wheel brakes of two vehicle wheels of the vehicle and with an automated driving system with an autonomous steering system for at least partially autonomous maneuvering of the vehicle, which enables high vehicle stability with the shortest possible stopping or braking distance.

[0009] The above object is achieved by the entire teaching of claim 1 and claim 12. Expedient embodiments and further developments of the invention are set out in the subclaims and the following description.

[0010] In the method according to the invention for controlling a vehicle during a μ-split braking, wherein the vehicle is equipped with a braking system having a brake pressure control or brake pressure regulation function, in particular with an anti-lock regulation function, for exerting a wheel-individual brake pressure on at least two wheel brakes of two vehicle wheels of the vehicle, and with an automated driving system having an autonomous steering system for at least partially autonomous maneuvering of the vehicle, there is a communication connection between the braking system and the automated driving system and the method comprises the following steps: - Detecting a μ-split braking by the braking system, - Specifying a steering angle requirement by the braking system to the automated driving system, and - Adjusting a brake pressure by the braking system as a function of the specified steering angle requirement.

[0011] The embodiment according to the invention has the advantage of providing a method by means of which high vehicle stability with the shortest possible stopping or braking distance is enabled during µ-split braking. Through communication between the braking system and the automated driving system and the resulting exchange of information between the two systems, a braking pressure and a steering angle can be optimally adjusted in combination or jointly and in a coordinated manner. In particular, a braking pressure can be adjusted directly based on the predetermined steering angle request communicated by the braking system to the automated driving system, without the braking system having to wait, for example, for the corresponding steering angle to be adjusted in accordance with the steering angle request.

[0012] In this case, one wheel brake is assigned to each vehicle wheel of the vehicle. Advantageously, one of the at least two vehicle wheels is arranged on a first, in particular a left, side of the vehicle, and the other vehicle wheel is arranged on a second, in particular a right, side of the vehicle opposite the first side of the vehicle. The two vehicle wheels are preferably arranged on a common vehicle axle, in particular on a front axle of the vehicle.

[0013] The automated driving system is advantageously designed for semi-autonomous or autonomous lateral and longitudinal guidance of the vehicle, wherein during at least semi-autonomous maneuvering an autonomous steering function is active, by means of which a wheel steering angle of the steering system of the vehicle can be (autonomously) controlled.

[0014] The automated driving system and the braking system can each have their own electronic control unit, with the communication connection between the two systems or control units advantageously being implemented via a bus system, in particular a CAN bus. Alternatively, the automated driving system and the braking system can have a common electronic control unit, with the communication connection between the two systems being implemented via one or more signal lines internal to the control unit.

[0015] In the context of this invention, µ-split braking is understood to mean a situation in which the vehicle is moving on a roadway with different friction values ​​on each side, i.e. different friction values ​​are present on the left and right side of the roadway or vehicle, whereby as a result of the different friction values, asymmetrical braking forces occur on the right and left side of the vehicle and this results in a yaw moment and / or a yaw rate about a vehicle vertical axis, or whereby as a result of a braking command on the wheel brakes of the vehicle, different brake pressures are set on each side and due to a brake pressure difference formed thereby between the brake pressures on the wheel brakes of a (common) vehicle axle, in particular a front axle of the vehicle, a yaw moment and / or a yaw rate about a vehicle vertical axis arises.

[0016] In addition, a high-friction wheel is understood to be a vehicle wheel on the side of the road or of the vehicle with the higher of the two friction values, and a low-friction wheel is understood to be a vehicle wheel on the side of the road or of the vehicle with the lower of the two friction values.

[0017] In an advantageous embodiment, μ-split braking is detected based on the detection of a, particularly impending, slippage or a, particularly impending, locking of a vehicle wheel. Preferably, μ-split braking is detected when the braking system detects that one vehicle wheel locks earlier than another vehicle wheel by a predetermined period of time. In this way, μ-split braking can be detected particularly early and reliably.

[0018] In a further advantageous embodiment, the steering angle is adjusted by the automated driving system according to the specified steering angle requirement at least partially simultaneously with the step of adjusting the brake pressure. This allows a stopping or braking distance to be further shortened while improving vehicle stability.

[0019] In a further advantageous embodiment, the brake pressure is adjusted as a function of the time required by the automated driving system to adjust the specified steering angle requirement. In other words, the brake pressure is adjusted as a function of the time required for the automated driving system to adjust the steering angle according to the specified steering angle requirement, i.e., as a function of how quickly the automated driving system can adjust the steering angle. This required time is preferably dependent on a mechanical and / or electrical design of a steering actuator of the steering system.

[0020] In a further advantageous embodiment, the automated driving system informs the braking system of the required time as soon as the automated driving system receives the steering angle request. Immediately thereafter, and depending on this, the braking system can then adjust the appropriate braking pressure.

[0021] Alternatively, in a further advantageous embodiment, the automated driving system compares the required time period with a predetermined time period limit value as soon as the automated driving system has received the steering angle request, the result of the comparison being transmitted to the braking system, and the braking pressure being adjusted as a function of the result of the comparison.

[0022] In a further advantageous embodiment, if the required time is less than or equal to the predetermined time limit, the increase in the current brake pressure at a high-friction wheel of the vehicle is not terminated. In particular, in this case, the current brake pressure at the high-friction wheel can be (further) increased.

[0023] In a further advantageous embodiment, if the required time is greater than the predetermined time limit, the current brake pressure at a high-friction wheel of the vehicle is maintained or reduced. Alternatively, the current brake pressure increase can be slowed down, i.e., the current brake pressure increase can occur at a slower rate than a previous brake pressure increase.

[0024] In a further advantageous embodiment, the steering angle request is determined and specified as a function of a yaw moment determined by the braking system and / or a yaw rate determined by the braking system about a vehicle's vertical axis in such a way that the yaw moment and / or the yaw rate is at least partially compensated after the steering angle request has been set on a steerable vehicle axle. The steering angle request or the ultimately resulting (set) steering angle therefore counteracts the yaw moment and / or the yaw rate. In particular, the steering angle request is determined and specified in such a way that the yaw moment and / or the yaw rate is fully compensated after the steering angle request has been set on a steerable vehicle axle. Preferably, the degree of the steering angle request is greater the greater the determined yaw moment and / or the determined yaw rate, and vice versa.

[0025] In a further advantageous embodiment, the yaw moment and / or the yaw rate are determined based on a brake pressure difference between the brake pressures at the wheel brakes of a vehicle axle, in particular a front axle of the vehicle. Preferably, the greater the brake pressure difference, the greater the steering angle requirement, and vice versa.

[0026] In a further advantageous embodiment, the vehicle has an environmental sensor system, wherein the automated driving system determines a road course ahead and / or a course of a planned trajectory of the vehicle on the basis of the data from the environmental sensor system, and wherein the brake pressure is also adjusted as a function of the determined road course and / or the determined course of the planned trajectory of the vehicle.Preferably, based on the determined road course and / or the determined course of the planned trajectory of the vehicle, the automated driving system determines a brake pressure request to enable driving through the determined road course and / or the determined course of the trajectory and the determined brake pressure request is transmitted from the automated driving system to the brake system, wherein the brake system then also sets the corresponding brake pressure depending on the communicated brake pressure request.Alternatively, information regarding the determined road course and / or the determined course of the planned trajectory of the vehicle is transmitted from the automated driving system to the braking system, wherein the braking system determines a brake pressure requirement based on the transmitted information to enable driving along the determined road course and / or the determined course of the trajectory and then adjusts the corresponding brake pressure also depending on the determined brake pressure requirement. In this way, a driving scenario can be taken into account in particular in which a certain yaw rate of the vehicle is even desired or necessary in order to follow the determined road course and / or the determined course of the planned trajectory. Example scenarios for this include a potential collision object having to be avoided during µ-split braking or the vehicle being in a curve.Preferably, the environmental sensor system of the vehicle comprises a camera and / or a radar sensor and / or a lidar sensor and / or an ultrasonic sensor and / or a communication interface for wirelessly receiving data, in particular current environmental data. In particular, the environmental sensor system can also comprise a plurality of sensors of a specified sensor type, for example a plurality of cameras and / or a plurality of ultrasonic sensors.

[0027] Furthermore, the present invention comprises a device for controlling a vehicle during µ-split braking, comprising a braking system with a brake pressure regulation or brake pressure control function, in particular with an anti-lock control function, for exerting a wheel-individual brake pressure on at least two wheel brakes of two vehicle wheels of the vehicle, as well as an automated driving system with an autonomous steering system for at least partially autonomously maneuvering the vehicle, wherein a communication connection exists between the braking system and the automated driving system, and wherein the device is configured to carry out the method according to the invention.

[0028] The advantages and preferred embodiments described for the method according to the invention also apply accordingly to the device according to the invention.

[0029] An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. The single figure shows a flowchart of a method for controlling a vehicle during µ-split braking.

[0030] The single figure shows a flowchart of a method 100 for controlling a vehicle during µ-split braking. The vehicle has a braking system with a brake pressure control function, for example with an anti-lock control function, for exerting a wheel-specific brake pressure on the wheel brakes of the vehicle's wheels. Furthermore, the vehicle has an automated driving system with an autonomous steering system for at least partially autonomous maneuvering of the vehicle. The automated driving system is designed, for example, at least for partially autonomous lateral and longitudinal guidance of the vehicle, wherein an autonomous steering function is active during at least partially autonomous maneuvering, by means of which a wheel steering angle of the vehicle's steering system can be (autonomously) controlled.For example, the automated driving system and the braking system each have their own electronic control unit, with a communication connection between the two systems or control units being implemented via a CAN bus.

[0031] In a step 101, the braking system first detects a µ-split braking based on the detection of a slip of a vehicle wheel, wherein, for example, it is detected that a vehicle wheel locks earlier than another vehicle wheel of the vehicle by a predetermined period of time.

[0032] In a next step 102, the braking system determines a steering angle request based on a yaw moment about a vehicle's vertical axis determined by the braking system such that the yaw moment is at least partially compensated for on a steerable vehicle axle after the steering angle request has been adjusted. The determined steering angle request is transmitted from the braking system to the automated driving system via the communication connection.

[0033] In a step 103, the automated driving system then compares the time required by the automated driving system to adjust a steering angle according to the specified steering angle request with a predetermined time limit. The comparison reveals, for example, that the required time is less than the predetermined time limit, meaning that the automated driving system can adjust the requested steering angle sufficiently quickly. This information is communicated to the braking system by the automated driving system.

[0034] In a step 104, the braking system further increases the current brake pressure on a high-friction wheel of the vehicle based on the communicated information. At least partially simultaneously, the automated driving system also adjusts the steering angle according to the steering angle request.

[0035] Through communication between the braking system and the automated driving system and the resulting exchange of information between the two systems, a braking pressure and a steering angle can be optimally adjusted in combination or jointly and in a coordinated manner. In particular, a braking pressure can be adjusted immediately based on the specified steering angle request communicated by the braking system to the automated driving system, without the braking system having to wait for the corresponding steering angle to be adjusted in accordance with the steering angle request. This enables a high level of overall vehicle stability and, at the same time, the shortest possible stopping or braking distance for the vehicle during µ-split braking of a suitably equipped vehicle.

Claims

[1] Method (100) for controlling a vehicle during µ-split braking, wherein the vehicle is equipped with a braking system with a brake pressure regulation or brake pressure control function, in particular with an anti-lock control function, for exerting a wheel-individual brake pressure on at least two wheel brakes of two vehicle wheels of the vehicle, and with an automated driving system with an autonomous steering system for at least partially autonomously maneuvering the vehicle, wherein a communication connection exists between the braking system and the automated driving system, and wherein the method comprises the following steps: - Detection of a µ-split braking by the braking system (101), - specifying a steering angle request by the braking system to the automated driving system (102), and - Setting a brake pressure by the brake system depending on the specified steering angle requirement (104). [2] Method (100) according to claim 1, wherein a µ-split braking is detected based on the detection of a, in particular impending, slip or a, in particular impending, locking of a vehicle wheel, wherein preferably the µ-split braking is detected when it is detected by the braking system that one vehicle wheel locks earlier than another vehicle wheel by a predetermined period of time. [3] Method (100) according to claim 1 or 2, wherein at least partially simultaneously with the step of adjusting the brake pressure, the steering angle is adjusted by the automated driving system in accordance with the predetermined steering angle request. [4] Method (100) according to one of the preceding claims, wherein the adjustment of the brake pressure takes place as a function of a time period required by the automated driving system to adjust the predetermined steering angle requirement. [5] The method (100) of claim 4, wherein the automated driving system informs the braking system of the required time period as soon as the automated driving system has received the steering angle request. [6] Method (100) according to claim 4, wherein the automated driving system compares the required time duration with a predetermined time duration limit value as soon as the automated driving system has received the steering angle request, wherein the result of the comparison is transmitted to the braking system, and wherein the adjustment of the braking pressure takes place as a function of the result of the comparison. [7] Method (100) according to claim 6, wherein, in the event that the required time period is less than or equal to the predetermined time period limit value, no termination of an increase in a current brake pressure occurs at a high-friction wheel of the vehicle. [8] Method (100) according to claim 6 or 7, wherein, in the event that the required time period is greater than the predetermined time period limit, a current brake pressure is maintained or reduced at a high-friction wheel of the vehicle. [9] Method (100) according to one of the preceding claims, wherein the steering angle request is determined and specified as a function of a yaw moment determined by the braking system and / or a yaw rate about a vehicle vertical axis determined by the braking system in such a way that the yaw moment and / or the yaw rate is at least partially compensated after setting the steering angle request on a steerable vehicle axle. [10] Method (100) according to claim 9, wherein the yaw moment and / or the yaw rate is determined based on a brake pressure difference between the brake pressures at the wheel brakes of a vehicle axle, in particular a front axle of the vehicle. [11] Method (100) according to one of the preceding claims, wherein the vehicle has an environmental sensor system, wherein the automated driving system determines a road course ahead and / or a course of a planned trajectory of the vehicle on the basis of the data from the environmental sensor system, and wherein the brake pressure is also adjusted as a function of the determined road course and / or the determined course of the planned trajectory of the vehicle. [12] Device for controlling a vehicle during µ-split braking, comprising a braking system with a brake pressure control function, in particular with an anti-lock control function, for exerting a wheel-individual brake pressure on at least two wheel brakes of two vehicle wheels of the vehicle, and an automated driving system with an autonomous steering system for at least partially autonomously maneuvering the vehicle, wherein a communication connection exists between the braking system and the automated driving system, and wherein the device is designed to carry out a method (100) according to one of the preceding claims.

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