Yaw rate control method and control unit for yaw rate control

Abstract

The present invention relates to a yaw rate control method in which a yaw rate control function (2) for stabilizing a vehicle performs wheel-specific braking intervention based on a first reference yaw rate. To ensure a higher level of safety, a deactivation function (3, 4) is provided, which activates the yaw rate control function (2) as soon as at least one activation precondition is satisfied, and as the activation precondition, at least - whether longitudinal deceleration is greater than a longitudinal deceleration limit value, particularly by a sensor tolerance, - whether lateral acceleration is greater than a lateral acceleration limit value, particularly by a sensor tolerance, and - whether the deviation between a second reference yaw rate and a measured yaw rate is greater than a yaw rate deviation limit value, particularly by a sensor tolerance.

Description

Technology Field

[0001] The present invention relates to a yaw rate control method in which 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), is also referred to as ESC or electronic stability program (ESP) or is part of such a functional unit and performs wheel-specific braking intervention when the yaw rate deviates from the reference yaw rate. Background Technology

[0002] For systems that intervene in the control of a vehicle—namely, driving, steering, and / or braking—regardless of the driver's request, ISO 26262 requires that specific measures be taken during development based on a risk assessment to limit risks related to functional safety. Depending on the potential risk, they are classified into QM or ASIL A to ASIL D grades, where the severity of the impact (Severity - S), the frequency of driving situations (Exposure - E), and the controllability of driver malfunction (Controllability - C) are evaluated.

[0003] Due to the low probability of occurrence, such systems are classified as ASIL B for yaw rate control in use cases. On the other hand, prevention of instability caused by inaccurate intervention in non-use cases is classified as ASIL D. To avoid having to design the entire function according to ASIL D, an architecture is selected in which a disabling component (FunctionDisabling (FD)) that enables the actual function only in specific "use cases" is placed prior to the yaw rate control function, followed by a "safety barrier" that switches only through requirements related to the actuator or switches completely when the disabling component enables the actuator in the use case. Otherwise, the requirements are limited to a point where it does not operate at all.

[0004] Since overly strict use case detection can result in interventions that are too late or 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 prevented the reduction of unwanted yaw rate control interventions. However, because the activation frequency is very high, the requirements under ASIL D continue to apply to the previous yaw rate control function. Overall, the development effort for ASIL D components is much greater than that for ASIL B components. One measure is that the function must be executed in a safe operation to ensure the "freedom from interference" required from non-ASIL D components to ASIL D components. The problem to be solved

[0005] Accordingly, the objective of the present invention is to specify a method that can be used to disable the yaw rate control function and satisfies the specifications for ASIL B. means of solving the problem

[0006] This objective is achieved by the yaw rate control method according to the present invention, wherein the actual yaw rate control function for stabilizing the vehicle executes wheel-specific braking intervention based on a first reference yaw rate. The reference yaw rate is generally calculated from the vehicle model and current driving parameters. The present invention now provides a separate deactivation function that activates the yaw rate control function as soon as at least one activation requirement is met. For example, the deactivation function can be separated from the yaw rate control function by switching between a safety operation and a normal operation that has its own memory. This ensures that the contents of the safety operation's memory cannot be unintentionally changed by the function running in the normal operation.

[0007] As an activation requirement, at least the following is verified:

[0008] - Whether the longitudinal deceleration is greater than the longitudinal deceleration limit value, particularly by the sensor tolerance,

[0009] - Whether lateral acceleration is greater than the lateral acceleration limit value, particularly by the sensor tolerance, and

[0010] - Whether the deviation between the second reference yaw rate and the measured yaw rate is greater than the yaw rate deviation limit value, particularly by the sensor tolerance. In particular, a reference yaw rate different from the first reference yaw rate may be used as the second reference yaw rate. The second reference yaw rate may be calculated, for example, from a vehicle model different from the first reference yaw rate. For example, a simple static Ackermann model in which ASIL D can be achieved with little effort may be used for the disable function. Subsequently, a more complex model in which only ASIL B can be achieved due to complexity and additional input signals may be used for the yaw rate control function.

[0011] In a preferred embodiment, the second reference yaw rate is calculated from the measured steering angle of the vehicle and / or the measured lateral acceleration. The reference yaw rate can be calculated from the steering angle using a formula from a single-track model, and:

[0012]

[0013] Here, ε is the yaw rate, v is the vehicle speed, δ is the steering angle, l is the wheelbase, and ε is the self-steering gradient. The self-steering gradient is caused by the different slip stiffness of the front and rear axles, as well as the center of gravity location and vehicle weight. This indicates how much more the steering wheel must be turned with increasing speed (and also lateral acceleration) to maintain the same curve radius and compensate for the different slip angles of the front and rear axles.

[0014] If the actual yaw rate deviates from the reference yaw rate calculated from the steering angle by more than the allowable amount, which is the yaw rate deviation limit value, an unstable driving situation synonymous with the "use case" can be estimated. The disable function enables the yaw rate control function accordingly.

[0015] There may be cases where the driver specifies a yaw rate using the steering angle that cannot be achieved in a stable manner from the existing road friction coefficient. In such cases, although the actual yaw rate corresponds to the steering angle target specifications, the vehicle rotates more slowly and forms a lateral slip angle. To recognize such cases as "use cases," it is reasonable to limit the reference yaw rate using friction coefficient information and / or calculate a second reference yaw rate based on the current lateral acceleration. Here, it can also be concluded that the driving situation is unstable due to the deviation between the actual yaw rate and the reference yaw rate calculated from the lateral acceleration. The relationship between the yaw rate and lateral acceleration during steady-state circular motion is given by the following:

[0016]

[0017] Here, a y is lateral acceleration.

[0018] As soon as at least one of the yaw rate comparisons shows a significant deviation, unstable driving conditions and, accordingly, "use cases" can be estimated.

[0019] Activation based solely on detected unstable driving conditions may have the disadvantage that an actual yaw rate deviation must exist before unrestricted yaw rate intervention is activated. The method according to the present invention enables early activation of pilot control intervention, which prevents instability at the start. An evaluation of the frequency distribution of the driving profile shows that specific situations, such as driving with very large lateral acceleration or sudden braking or deceleration, occur only extremely rarely. In such rare situations, classification to exposure E2 or E1 is executed during the risk assessment related to frequency. Therefore, a normal ASIL level B of the actual yaw rate control function is sufficient, and there is no longer any need to additionally reliably detect unstable driving conditions. Thus, it is sufficient to reliably detect these rare driving situations. Reliable detection is guaranteed when the sensor value minus the sensor tolerance exceeds the corresponding threshold value.

[0020] The activation of the yaw rate control function upon the detection of both instability and specific rare driving situations implies that, in most cases, activation in use cases occurs without any delay, especially at high friction coefficients: use cases for the yaw rate control function generally occur only when the road's traction potential has already been significantly lost. The use of such traction at high friction coefficients is associated with high lateral acceleration and / or vehicle deceleration, i.e., situations where the yaw rate control function is activated through conditions evaluated as frequency E2 or E1 and generally mentioned. In these situations, since there is no need to wait for a yaw rate deviation, yaw rate control intervention can occur early and at full force.

[0021] At low friction coefficients, actual instability can be detected through yaw rate deviations so that unstable driving at low friction coefficients can be distinguished from stable driving at high friction coefficients with a similar level of lateral acceleration. In the aforementioned mechanism, the yaw rate control function is activated for less than 1% of the time during normal driving at high friction coefficients and accordingly has a frequency of only E2. Since situation detection is fully implemented at ASIL D, it is not broken down into B(D) use case detection and B(D) controller. The safety objective to avoid instability caused by vehicle errors is defined by values ​​for severity classification, exposure classification, and controllability classification [S3;E4;C3]. Limiting the activation of the yaw rate control function to driving situations with a probability of occurrence of less than 1% now reduces the exposure from E4 to E2. According to Table 4 of ISO 26262-3:201.8(E), the ASIL is accordingly reduced to B. This has several advantages: the controller does not need to run during safety operations, and in the controller section, only the B metric needs to be satisfied at the software level. Additionally, since the FunctionDisable section and the controller itself do not require any independence, they can be controlled based on the same signal.

[0022] In a preferred embodiment, the limit value of the activation requirement is selected in such a way that it is satisfied for less than 1% of the operation time. Thus, a design according to ASIL B is sufficient.

[0023] In a preferred embodiment, the deactivation function completely blocks the yaw rate control function when the activation requirements are not met, that is, when the yaw rate control function should not control the actuator and consequently should not intervene in the control of the motor vehicle. Alternatively, the deactivation function partially deactivates the yaw rate control function. Subsequently, the control intervention of the yaw rate control function is transmitted to each actuator in a reduced form, and accordingly, only weak intervention occurs that does not endanger the safety of the vehicle in the event of incorrect intervention. It is also possible to design the blocking differently for other actuators. For example, when the activation requirements are not met, braking intervention may be reduced and steering intervention may be completely blocked.

[0024] In a preferred embodiment, the deactivation function is located upstream and / or downstream of the yaw rate control function. The upstream deactivation function transmits a signal to the yaw rate control function and informs the yaw rate control function whether such function is enabled or disabled. Subsequently, the yaw rate control function either executes or does not execute an intervention accordingly. To ensure safety in the event that an error occurs in the yaw rate control function, which executes an incorrect intervention despite actual deactivation, the deactivation function may also be located downstream. This means that the yaw rate control function does not have a direct communication path with the actual actuator but communicates through a safety barrier. When enabled, this safety barrier can transmit commands sent by the yaw rate control function to the actuator, and when not enabled, it cannot transmit commands or can command reduced intervention.

[0025] In a preferred embodiment, the longitudinal deceleration limit value is 2.5 m / s 2 Exceeding, preferably 3 m / s 2It is excessive. Therefore, the situation requiring yaw rate control is assumed only in cases of greater deceleration. This effectively reduces the activation time.

[0026] In a preferred embodiment, the longitudinal deceleration limit value varies with speed and, in particular, becomes smaller as the vehicle speed increases. For example, at less than 100 km / h, 4 m / s 2 A longitudinal deceleration limit value can be selected, and at speeds exceeding 100 km / h, 3 m / s 2 The longitudinal deceleration limit value can be selected.

[0027] In a preferred embodiment, longitudinal deceleration is determined by an acceleration sensor from the derivative of the vehicle speed and / or from data from a brake system. Longitudinal deceleration values ​​from a plurality of sources can be individually compared with longitudinal deceleration limit values ​​and / or form an average value and use it for comparison.

[0028] In a preferred embodiment, the lateral deceleration limit value is 2.5 m / s 2 It exceeds. For example, the lateral acceleration limit value is a limit,E2 = 3.5 m / s 2 It is set to and the sensor in use is 2 m / s 2 In the case of having a sensor tolerance, the absolute value of the measured lateral acceleration is at least 5.5 m / s² so that the activation condition is satisfied. 2 It must be so. Including sensor tolerances can prevent activation from occurring too frequently due to measurement errors.

[0029] In a preferred embodiment, lateral acceleration is determined from the measured values ​​from the acceleration sensor and / or yaw rate sensor and from the vehicle speed. Since the tolerances of each sensor are different, the lateral acceleration can also be determined using a yaw rate sensor instead of the lateral acceleration sensor, and the yaw rate control function can be activated accordingly. To this end, the yaw rate and the associated tolerance of the yaw rate sensor can be converted into lateral acceleration.

[0030] In a preferred embodiment, the presence of ABS intervention is confirmed as an additional activation requirement. As soon as one of the activation requirements or ABS intervention is confirmed, the yaw rate control function is activated. Since ABS intervention is graded as E2 due to its low probability of occurrence, ASIL B of the normal yaw rate control function is sufficient during ABS intervention.

[0031] In a preferred embodiment, as an additional activation requirement, it is determined whether the lateral slip angle signal is greater than the lateral slip angle limit value in absolute terms, particularly by the sensor tolerance. This can be utilized, particularly in the case where there is an ASIL D lateral slip angle signal. The lateral slip angle signal may be measured optically, for example, using an additional Correvit sensor. Alternatively, the lateral slip angle may be determined using a camera already required for autonomous driving, or estimated through a model using a general ESP sensor. If the lateral slip angle signal exceeds a specific threshold value, a "use case" may be estimated. As soon as one of the above activation requirements is satisfied or the corresponding lateral slip angle is determined, the yaw rate control function is activated.

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

[0033] Alternatively, a specific rear axle slip angle can be defined as a standard, and using this standard, a threshold value for the lateral slip angle at the vehicle's center of gravity can be determined. There is a purely geometric relationship between the slip angle at the center of gravity (β) and the rear axle slip angle (αH):

[0034]

[0035] δ H refers to the steering angle set by any existing rear axle steering here.

[0036] An additional advantage of activation via the lateral slip angle signal is particularly in the low friction coefficient region, as it is more difficult to activate via the high lateral acceleration reference in such cases. At low friction coefficients, there are specific situations where the vehicle turns slowly, and model-based detection using the deviation of the actual yaw rate from the reference yaw rate calculated from the current steering angle or current lateral acceleration does not respond or responds with delay because the deviation is too small unless the driver performs opposite steering.

[0037] In a preferred embodiment, as an additional activation requirement, it is verified whether the longitudinal acceleration signal is greater than the longitudinal acceleration limit value, particularly by the sensor tolerance. Longitudinal acceleration should be understood here as meaning a change in the amount of velocity. A specific acceleration state (e.g., 3 m / s²) that occurs very rarely, such as in deceleration, and thereby enables the yaw rate control function to be activated 2There is (excess). Vehicle acceleration can be calculated using an acceleration sensor or by using a derivation of a speed signal determined from wheel speed, or can be estimated from the effective driving torque. As soon as one of the above activation requirements or one of the corresponding acceleration signals is confirmed, the yaw rate control function is activated. In this way, instability, particularly at the start, can also be detected at an early stage.

[0038] In a preferred embodiment, as an additional activation requirement, it is verified whether the vehicle speed is greater than the vehicle speed limit value, particularly by the sensor tolerance. Since very high vehicle speeds also occur very rarely, the vehicle speed can also be directly used as an alternative activation requirement. For example, activation is basically possible even at speeds exceeding 160 km / h.

[0039] In a preferred embodiment, as an additional activation requirement, it is determined whether the steering angle is greater in absolute terms than a steering angle threshold value that varies with speed, particularly by a sensor tolerance. The steering angle threshold value that varies with speed can be calculated using an inverse single-track model. If this is exceeded, this indicates that there must be a driving situation with abnormally large lateral acceleration, or an unstable driving situation that represents a use case according to regulations, which allows the yaw rate control function to be activated by frequency distribution due to the current steering angle. As soon as one of the above activation requirements or one of the corresponding steering angles is confirmed, the yaw rate control function is activated.

[0040] In a preferred embodiment, the yaw rate control function is not performed during safety operation, and the deactivation function is performed during safety operation.

[0041] The objective is also achieved by a control unit for yaw rate control configured to execute the above method.

[0042] Further features, advantages, and possible applications of the present invention are also derived from the following description and drawings relating to exemplary embodiments. All features described and / or schematically illustrated also fall within the scope of the claims of the present invention, individually and in any combination, without regard to the summaries within the claims or any cross-references thereof. Brief explanation of the drawing

[0043] FIG. 1 schematically illustrates yaw rate control according to the present invention. Specific details for implementing the invention

[0044] As illustrated in FIG. 1, the yaw rate control (1) has a real yaw rate control function (2) surrounded by deactivation functions (3, 4) as a central element. An upstream portion of the deactivation functions (3, 4) is referred to as a FunctionDisable (3) and identifies the implemented activation requirements. These are, in particular, the lateral acceleration of the motor vehicle, the longitudinal deceleration of the motor vehicle, and the yaw rate of the motor vehicle. In general, the FunctionDisable (3) disables the yaw rate control function (2) by transmitting a corresponding signal to the yaw rate control function (2). The FunctionDisable (3) also transmits the deactivation signal to a downstream safety barrier (4). The safety barrier (4) is connected between the yaw rate control function (2) and the corresponding actuator or actuators (5). Accordingly, the yaw rate control function (2) accesses the actuator (5) through the safety barrier (4), and there is no direct communication path. The safety barrier (4) may or may not transmit a command to the actuator (5) based on a signal from the function deactivation unit (3).

[0045] This ensures that the yaw rate control function (2) intervenes in vehicle control only in the case of use.

Claims

Claim 1 A yaw rate control method in which a yaw rate control function (2) for stabilizing a vehicle performs wheel-specific braking intervention based on a first reference yaw rate, wherein, as soon as at least one activation requirement is satisfied, a deactivation function (3, 4) activates the yaw rate control function (2), wherein the activation requirement is, at least - whether longitudinal deceleration is greater than a longitudinal deceleration limit value, particularly by a sensor tolerance, - whether lateral acceleration is greater than a lateral acceleration limit value in absolute terms, particularly by a sensor tolerance, and - whether the deviation between a second reference yaw rate and a measured yaw rate is greater than a yaw rate deviation limit value, particularly by a sensor tolerance, and if the activation requirement is not satisfied, the deactivation function (3, 4) completely or partially blocks the yaw rate control function (2). Claim 2 A method according to claim 1, characterized in that the second reference yaw rate is calculated from the measured steering angle and / or measured lateral acceleration of the vehicle. Claim 3 A method according to claim 1, characterized in that the limit value of the activation requirement is selected in such a way that it is satisfied for less than 1% of the operation time. Claim 4 delete Claim 5 A method according to claim 1, wherein the deactivation function (3, 4) is located upstream and / or downstream of the yaw rate control function (2). Claim 6 In claim 1, the longitudinal deceleration limit value is 2.5 m / s 2 A method characterized by being in excess. Claim 7 A method according to claim 1, characterized in that the longitudinal deceleration limit value varies with speed and, in particular, becomes smaller as the vehicle speed increases. Claim 8 A method according to claim 1, wherein the longitudinal deceleration is determined by an acceleration sensor from the derivative of the vehicle speed and / or from data from a brake system. Claim 9 In claim 1, the lateral acceleration limit value is 2.5 m / s 2 A method characterized by being in excess. Claim 10 A method according to claim 1, characterized in that the lateral acceleration is determined from a measured value from an acceleration sensor and / or a yaw rate sensor and from the vehicle speed. Claim 11 A method according to claim 1, characterized in that the presence of ABS intervention is confirmed as an additional alternative activation requirement. Claim 12 A method according to claim 1, characterized in that, as an additional alternative activation requirement, it is confirmed whether the lateral slip angle signal is greater than the lateral slip angle limit value in absolute terms, particularly by the sensor tolerance. Claim 13 A method according to claim 1, characterized in that, as an additional alternative activation requirement, it is confirmed whether the longitudinal acceleration signal is greater than the longitudinal acceleration limit value, particularly by the sensor tolerance. Claim 14 A method according to claim 1, characterized in that, as an additional alternative activation requirement, it is confirmed whether the vehicle speed is greater than the vehicle speed limit value, particularly by the amount of sensor tolerance. Claim 15 A method according to claim 1, characterized in that, as an additional alternative activation requirement, it is confirmed whether the steering angle is greater in absolute terms than the steering angle limit value, particularly by the sensor tolerance, particularly depending on the speed. Claim 16 A method according to claim 1, characterized in that the yaw rate control function (2) is not performed during safety operation, and the deactivation function (3, 4) is performed during safety operation. Claim 17 A control unit for yaw rate control, characterized by being configured to execute a method as claimed in any one of claims 1 to 3 and claims 5 to 16.

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