yaw rate control activation

Abstract

The invention relates to a yaw angular velocity control method, wherein a yaw angular velocity control function (2) for stabilizing a vehicle performs wheel-specific brake interventions on the basis of a first reference yaw angular velocity. In order to ensure a higher safety, a deactivation function (3, 4) is provided and activates the yaw angular velocity control function (2) as soon as at least one activation prerequisite is fulfilled, wherein, as the activation prerequisite, at least the following is checked: - whether a longitudinal deceleration is greater than a longitudinal deceleration limit value, in particular, by a sensor tolerance, - whether a lateral acceleration is greater than a lateral acceleration limit value, in particular, by a sensor tolerance, and - whether a deviation between a second reference yaw angular velocity and a measured yaw angular velocity is greater than a yaw angular velocity deviation limit value, in particular, by a sensor tolerance.

Description

Technical Field

[0001] This invention relates to a yaw rate control method, wherein a yaw rate control function for stabilizing a vehicle performs wheel-specific braking intervention based on a first reference yaw rate. The yaw rate control function, or active yaw control (AYC), also known as ESC or electronic stability program, or as part of such a functional unit, performs wheel-specific braking intervention when there is a deviation between the yaw rate and the reference yaw rate. Background Technology

[0002] For systems that intervene in vehicle control (i.e., drive, steering, and / or braking) independently of the driver's request, ISO 26262 requires specific measures to limit risks with respect to functional safety, based on a risk assessment conducted during development. These risks are classified into QM category or ASIL A to ASIL D categories, depending on the estimated severity of the impact (Severity-S), the frequency of the driving situation (Exposure-E), and the driver's controllability over the failure (Controllability-C).

[0003] Due to the low probability of yaw rate control occurring in the use case, the system is rated ASIL B. On the other hand, the avoidance of instability caused by incorrect intervention in non-use cases is rated ASIL D. To avoid having to design the entire function according to ASIL D, an architecture was chosen in which a deactivated component (function disabled, FD) precedes the yaw rate control function, activating the actual function only in specific "use cases"; followed by a "safety barrier" that toggles or completely toggles the actuator-related requirements only when the deactivated component has activated the actual function in the use case. Otherwise, the requirement is restricted to no actuation at all.

[0004] Because overly stringent use case detection could lead to intervention occurring too late or being too weak, all situations except for stable straight-line driving without braking were defined as use cases for the previously implemented use case detection. This avoided an undesirable reduction in yaw rate control intervention. However, due to the very high activation frequency, the previous yaw rate control function still applies according to ASIL D requirements. Overall, the development work for ASIL D components is significantly more extensive than that for ASIL B components. One measure is that the function must operate in safety missions to ensure the required "interference-free" operation for ASIL D components for non-ASIL D components. Summary of the Invention

[0005] Therefore, the object of this invention is to describe a method that can be used to release yaw rate control function and meet the ASILB specification.

[0006] This objective is achieved by the yaw rate control method according to the invention, wherein the actual yaw rate control function for stabilizing the vehicle performs wheel-specific braking intervention based on a first reference yaw rate. This reference yaw rate is typically calculated based on the vehicle model and current driving parameters. The invention now provides a separate deactivation function such that the deactivation function activates the yaw rate control function once at least one activation prerequisite is met. The deactivation function can be separated from the yaw rate control function, for example, by switching between a safety task and a normal task with their own memory. This ensures that the memory contents of the safety task are not unintentionally altered by functions running in the normal task.

[0007] As a prerequisite for activation, at least the following must be checked:

[0008] - Is the longitudinal deceleration greater than the longitudinal deceleration limit, and in particular, is it larger than the sensor tolerance than the longitudinal deceleration limit?

[0009] - Whether the lateral acceleration exceeds the lateral acceleration limit, and specifically, whether it exceeds the sensor tolerance beyond that limit.

[0010] - Whether the deviation between the second reference yaw rate and the measured yaw rate is greater than the yaw rate deviation limit, and in particular, whether it is greater than the sensor tolerance. Specifically, a reference yaw rate different from the first reference yaw rate can be used as the second reference yaw rate. The second reference yaw rate can be calculated, for example, based on a vehicle model different from the first reference yaw rate. For example, a simple static Ackermann model can easily achieve ASIL D and therefore can be used for deactivation functions. More complex models, due to their complexity and additional input signals, can only achieve ASIL B and therefore can be used for yaw rate control functions.

[0011] In a preferred embodiment, a second reference yaw rate is calculated based on the vehicle's measured steering angle and / or measured lateral acceleration. A formula from a monorail model can be used to calculate the reference yaw rate based on the steering angle:

[0012]

[0013] in, Yaw rate, v: vehicle speed, δ: steering angle, l: track width, and EG: self-steering gradient. The self-steering gradient is derived from the different lateral stiffness of the front and rear axles, as well as the center of gravity position and vehicle mass. The self-steering gradient indicates the additional angle the steering wheel must turn to maintain the same turning radius and compensate for the different lateral slip angles of the front and rear axles as speed (and lateral acceleration) increases.

[0014] If the deviation between the actual yaw rate and the reference yaw rate calculated from the steering angle exceeds the allowable amount (i.e., the yaw rate deviation limit), it can be inferred that an unstable driving situation exists (synonymous with "use case"). Deactivating the function accordingly activates the yaw rate control function.

[0015] The following situation may occur: the driver uses the steering angle to specify a yaw rate that cannot be stably achieved under the existing road friction coefficient. In this case, although the actual yaw rate corresponds to the steering angle target specification, the vehicle will steer slowly and increase the sideslip angle. To identify this situation as a "use case," it is reasonable to use friction coefficient information to limit the reference yaw rate and / or calculate a second reference yaw rate based on the current lateral acceleration. Here, the deviation between the actual yaw rate and the reference yaw rate calculated from the lateral acceleration also leads to the conclusion that the driving situation is unstable. The relationship between yaw rate and lateral acceleration during steady-state circular motion is given by the following equation:

[0016]

[0017] Among them, a y : Lateral acceleration.

[0018] If at least one yaw rate comparison shows a significant deviation, it can be inferred that an unstable driving situation exists, and thus it can be inferred as a "use case".

[0019] Activating control intervention solely based on detected unstable driving conditions has drawbacks, namely, the existence of an actual yaw rate deviation is required before activating an intervention exceeding the yaw rate limit. The method according to the invention achieves early activation of the pilot control intervention, preventing instability from the outset. Evaluation of the frequency distribution of the driving characteristic curves indicates that specific situations, such as driving with very high lateral acceleration, strong braking, or large deceleration, occur very rarely. During risk assessment, such rare situations will be classified as E2 or E1 exposure rates based on frequency. Therefore, the actual yaw rate control function at a normal ASIL level B is sufficient, and additional reliable detection of unstable driving conditions is no longer required. Thus, reliable detection of such rare driving conditions is sufficient. Reliable detection is guaranteed if the sensor value minus the sensor tolerance exceeds the corresponding threshold.

[0020] Activating yaw rate control by detecting both instability and specific rare driving conditions means that activation occurs without delay in many use cases, especially under high friction coefficients: yaw rate control use cases typically only arise when the road's adhesion friction potential has been largely exhausted. At high friction coefficients, this use of adhesion friction is associated with high lateral acceleration and / or high vehicle deceleration, i.e., with conditions assessed as frequencies E2 or E1, and for these conditions, yaw rate control is typically activated via the aforementioned conditions. Because there is no need to wait for yaw rate deviation in these cases, yaw rate control intervention can be performed early and at full intensity.

[0021] At low friction coefficients, actual instability can be detected via yaw rate deviation, allowing for the differentiation between unstable driving at low friction coefficients and stable driving at high friction coefficients with comparable lateral acceleration levels. Utilizing this mechanism, the yaw rate control function is activated for less than 1% of normal driving at high friction coefficients, resulting in a frequency of only E2. Because situation detection is implemented entirely within ASIL D, it is not decomposed into B(D) use case detection and B(D) controller. The safety objective of avoiding vehicle instability caused by errors is defined by values ​​[S3; E4; C3] in severity, exposure, and controllability categories. Now, by restricting the activation of the yaw rate control function to driving situations with an occurrence probability of less than 1%, the exposure rate is reduced from E4 to E2. According to Table 4 of ISO 26262-3:201.8(E), the ASIL is thus reduced to B. This has several advantages: the controller does not necessarily need to operate during safety tasks, and for the controller portion, only the B metric needs to be met at the software level. Furthermore, because no independence is required, the deactivation function (function disabled) and the controller itself can be driven based on the same signal.

[0022] In a preferred embodiment, the limit values ​​of the activation prerequisites are selected such that they are satisfied in less than 1% of the operating time. Therefore, this is sufficient for the design according to ASIL B.

[0023] In a preferred embodiment, the deactivation function completely disables the yaw rate control function when the activation prerequisite is not met; that is, the yaw rate control function is not allowed to drive the actuators and therefore cannot interfere with the control of the motor vehicle. Alternatively, the deactivation function only partially disables the yaw rate control function. The control intervention of the yaw rate control function can then be sent to the corresponding actuators in a simplified form, such that only weak intervention occurs, which will not jeopardize vehicle safety if the intervention is incorrect. The deactivation can also be designed for different actuators in different ways. For example, if the activation prerequisite is not met, braking intervention can be reduced, and steering intervention can be completely disabled.

[0024] In a preferred embodiment, the deactivation function is upstream and / or downstream of the yaw rate control function. The upstream deactivation function sends a signal to the yaw rate control function, informing it whether it is activated or deactivated. The yaw rate control function can then perform intervention or not perform intervention accordingly. To maintain safety even in the event of an error in the yaw rate control function (performing incorrect intervention despite being actually deactivated), the deactivation function can also be downstream. This means that the yaw rate control function does not have a direct communication path to the actual actuator, but communicates with it via a safety barrier. When this safety barrier is activated, it can forward commands sent by the yaw rate control function to the actuator; when it is deactivated, it cannot forward the command or the command performs reduced intervention.

[0025] In a preferred embodiment, the longitudinal deceleration limit is greater than 2.5 m / s². 2 Preferably greater than 3m / s 2 Therefore, the possibility of needing yaw rate control is only assumed under conditions of greater deceleration. This effectively reduces the activation time.

[0026] In a preferred embodiment, the longitudinal deceleration limit is speed-dependent, and specifically decreases as vehicle speed increases. For example, below 100 km / h, 4 m / s² can be selected. 2 The longitudinal deceleration limit is set at 100 km / h, and for speeds above 100 km / h, 3 m / s² can be selected. 2 The longitudinal deceleration limit.

[0027] In a preferred embodiment, the longitudinal deceleration is determined by an acceleration sensor based on the derivative of the vehicle speed and / or based on data from the braking system. Longitudinal deceleration values ​​from multiple sources can be compared with longitudinal deceleration limits, and / or an average value can be generated and used for comparison.

[0028] In a preferred embodiment, the lateral acceleration limit is greater than 2.5 m / s². 2 For example, if the lateral acceleration limit is set to a 极限,E2 =3.5m / s 2 Furthermore, the sensor used has a tolerance of 2 m / s. 2 Therefore, the absolute value of the measured lateral acceleration must be at least 5.5 m / s². 2 Only then can the activation conditions be met. Including sensor tolerances can prevent excessive activation due to measurement errors.

[0029] In a preferred embodiment, the lateral acceleration is determined based on measurements from an acceleration sensor and / or a yaw rate sensor, along with the vehicle speed. Since different sensors have different tolerances, a yaw rate sensor can also be used instead of a lateral acceleration sensor to determine the lateral acceleration, thereby activating the yaw rate control function. For this purpose, the yaw rate and the relevant tolerances of the yaw rate sensor can be converted into lateral acceleration.

[0030] In a preferred embodiment, as an additional activation prerequisite, the presence of ABS intervention is checked. Once one of the above activation prerequisites is present or ABS intervention is present, the yaw rate control function is activated. Because ABS intervention is rated E2 due to its low probability of occurrence, normal yaw rate control function at ASIL B is sufficient during ABS intervention.

[0031] In a preferred embodiment, as an additional activation prerequisite, it is checked whether the absolute value of the sideslip angle signal is greater than the sideslip angle limit, specifically whether it is larger than the sensor tolerance. This is particularly useful in cases where a sideslip angle signal based on ASIL D exists. For example, the sideslip angle signal can be measured optically using an additional Correvit sensor. Alternatively, cameras already required for autonomous driving can be used to determine the sideslip angle, or the sideslip angle can be estimated using a model with normal ESP sensors. If the sideslip angle signal exceeds a specified threshold, it can be considered a "use case". Once one of the above activation prerequisites is met or a corresponding sideslip angle exists, the yaw rate control function is activated.

[0032] The threshold can be specified as a fixed value or calculated using a reference model, depending on the situation. In addition to the reference yaw rate, the well-known Ackermann monorail model also provides a reference sideslip angle that can be used for this purpose.

[0033] Alternatively, a specific rear axle slip angle can be defined as a standard, and this standard can be used to determine the threshold for the slip angle at the vehicle's center of gravity. The slip angle (β) at the center of gravity is compared to the rear axle slip angle (α). h There are purely geometric relationships between them:

[0034]

[0035] Here, δ h Refers to the steering angle set by any existing rear axle steering mechanism.

[0036] An additional benefit of activation via the sideslip angle signal is particularly evident in regions with low friction coefficients, where activation via a high lateral acceleration criterion is more difficult. At low friction coefficients, there exists a specific situation where the vehicle is slowly turning, where, as long as the driver does not reverse the steering, model-based detection using the deviation between the actual yaw rate and a reference yaw rate calculated based on the current steering angle or current lateral acceleration will either fail to respond or respond late due to the deviation being too small.

[0037] In a preferred embodiment, as an additional activation prerequisite, it is checked whether the longitudinal acceleration signal is greater than the longitudinal acceleration limit value, and in particular, whether it is larger than the sensor tolerance of the longitudinal acceleration limit value. Longitudinal acceleration should be understood here as a positive change in velocity. Similar to deceleration, there are specific acceleration states (e.g., >3 m / s²) that occur only very rarely and therefore allow the yaw rate control function to be activated. 2 Vehicle acceleration can be calculated using an acceleration sensor or by using the derivative of a speed signal determined from wheel speed, or estimated based on the effective driving torque. Once one of these activation conditions or the corresponding acceleration signal is present, the yaw rate control function is activated. In this way, instability, especially during startup, can also be detected in the early stages.

[0038] In a preferred embodiment, as an additional activation prerequisite, it is checked whether the vehicle speed exceeds the vehicle speed limit, specifically whether it exceeds the sensor tolerance. Since extremely high vehicle speeds are rare, vehicle speed can also be used directly as an alternative activation prerequisite. For example, activation can generally be performed at speeds above 160 km / h.

[0039] In a preferred embodiment, as an additional activation prerequisite, it is checked whether the absolute value of the steering angle is greater than, in particular, a speed-dependent steering angle limit, and especially, whether it is larger than the sensor tolerance. A reverse single-track model can be used to calculate the speed-dependent steering angle threshold. If this threshold is exceeded, it indicates that due to the current steering angle, there must be a driving situation with abnormally high lateral acceleration (which causes the yaw rate control function to be activated due to frequency distribution) or an unstable driving situation (by definition, this represents a use case). Once one of the above activation prerequisites or the corresponding steering angle exists, the yaw rate control function is activated.

[0040] In a preferred embodiment, the yaw rate control function is not executed during the safety task, while the deactivation function is executed during the safety task.

[0041] This objective is also achieved by a control unit for yaw rate control, which is configured to perform the above-described method.

[0042] Other features, advantages, and possible applications of the invention also arise from the following description of exemplary embodiments and the accompanying drawings. All features described and / or illustrated are individually and in any combination, and independently of their summary in the claims or their reverse reference, and are part of the subject matter of the invention. Attached Figure Description

[0043] Figure 1 The yaw rate control according to the present invention is illustrated schematically. Detailed Implementation

[0044] like Figure 1 As shown, yaw rate control 1 has actual yaw rate control function 2 as its central element, surrounded by deactivation functions 3 and 4. The upstream portion of deactivation functions 3 and 4 is called the function deactivator (function disabler) 3, and it checks the implemented activation prerequisites. These activation prerequisites are specifically the lateral acceleration, longitudinal deceleration, and yaw rate of the vehicle. Under normal circumstances, function deactivator 3 deactivates yaw rate control function 2 by sending a corresponding signal to yaw rate control function 2. Function deactivator 3 also sends a deactivation signal to downstream safety barrier 4. Safety barrier 4 connects yaw rate control function 2 and one or more corresponding actuators 5. Therefore, yaw rate control function 2 accesses actuators 5 via safety barrier 4; there is no direct communication path. Safety barrier 4 may forward commands to or not forward commands to actuators 5 based on signals from function deactivator 3.

[0045] This ensures that yaw rate control function 2 only intervenes in vehicle control in use cases.

Claims

1. A method for controlling yaw rate, wherein, The yaw rate control function (2) for stabilizing the vehicle performs wheel-specific braking intervention based on a first reference yaw rate, characterized in that the deactivation function (3, 4) activates the yaw rate control function (2) once at least one activation prerequisite is met, wherein, as the activation prerequisite, at least the following is checked: - Is the longitudinal deceleration greater than the longitudinal deceleration limit? - Whether the absolute value of the lateral acceleration is greater than the lateral acceleration limit, and -Whether the deviation between the second reference yaw rate and the measured yaw rate exceeds the yaw rate deviation limit. If the activation prerequisites are not met, the deactivation function (3, 4) completely or partially disables the yaw rate control function (2), and selects the limit values ​​of these activation prerequisites so that they are met in less than 1% of the operating time.

2. The method according to claim 1, characterized in that, The second reference yaw rate is calculated based on the vehicle's measured steering angle and / or measured lateral acceleration.

3. The method according to claim 1 or 2, characterized in that, The deactivation functions (3, 4) are upstream and / or downstream of the yaw rate control function (2).

4. The method according to claim 1 or 2, characterized in that, The longitudinal deceleration limit is greater than 2.5 m / s². 2 .

5. The method according to claim 1 or 2, characterized in that, The longitudinal deceleration limit depends on the speed, and the longitudinal deceleration limit decreases as the vehicle speed increases.

6. The method according to claim 1 or 2, characterized in that, The longitudinal deceleration is determined by an acceleration sensor based on the derivative of the vehicle speed and / or based on data from the braking system.

7. The method according to claim 1 or 2, characterized in that, The lateral acceleration limit is greater than 2.5 m / s². 2 .

8. The method according to claim 1 or 2, characterized in that, The lateral acceleration is determined based on measurements from an acceleration sensor and / or a yaw rate sensor, as well as the vehicle speed.

9. The method according to claim 1 or 2, characterized in that, As another alternative activation prerequisite, the presence of ABS intervention is examined.

10. The method according to claim 1 or 2, characterized in that, As another alternative activation prerequisite, check whether the absolute value of the sideslip angle signal is greater than the sensor tolerance than the sideslip angle limit value.

11. The method according to claim 1 or 2, characterized in that, As an alternative activation prerequisite, check whether the longitudinal acceleration signal is larger than the longitudinal acceleration limit value than the sensor tolerance.

12. The method according to claim 1 or 2, characterized in that, As an alternative activation prerequisite, check whether the vehicle speed exceeds the sensor tolerance beyond the vehicle speed limit.

13. The method according to claim 1 or 2, characterized in that, As an alternative activation prerequisite, check whether the absolute value of the steering angle is larger than the speed-dependent steering angle limit of the sensor tolerance.

14. The method according to claim 1 or 2, characterized in that, The yaw rate control function (2) is not executed during a safety mission, while the deactivation function (3, 4) is executed during a safety mission.

15. A control unit for yaw rate control, characterized in that, The control unit is configured to perform the method according to any one of claims 1 to 14.

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