Method for limiting a negative target acceleration

Abstract

The invention relates to a method for limiting a negative target acceleration during an automated braking process of a motor vehicle, wherein the limitation is carried out according to a limiting characteristic curve (31, 32) in which a maximum negative target acceleration (a max ) depending on the speed (v) of the motor vehicle. A selection of the limiting characteristic curve (31, 32) from several predefined limiting characteristic curves (31, 32) is made if a test shows that the braking process occurs due to the motor vehicle approaching a stationary object.

Description

[0001] The present invention relates to a method for limiting a negative target acceleration during an automated braking process of a motor vehicle. Furthermore, the present invention relates to a computer program configured to perform each step of the method, as well as to a machine-readable storage medium on which the computer program is stored. Finally, the invention relates to an electronic control unit configured to perform the method. State of the art

[0002] Modern motor vehicles feature assistance functions that, based on environmental sensors such as radar or cameras, control vehicle speed, including maintaining a safe distance from vehicles ahead. Automated braking is limited to a speed-dependent maximum negative target acceleration in accordance with the ISO 15622 standard.

[0003] DE 102 31 584 A1 describes a method for automatically triggering a vehicle's deceleration to prevent a collision or to mitigate the consequences of an impending collision. One or more variables representing a risk of collision with another object must be within a predeterminable trigger range, which can be changed depending on the driver's reaction. Disclosure of the invention

[0004] The method provides for limiting a negative target acceleration during an automated braking maneuver of a motor vehicle. The limitation is implemented according to a limiting characteristic curve in which a maximum negative target acceleration occurs as a function of the speed of the motor vehicle. For the approach of the motor vehicle to a moving object, such a limiting characteristic curve is specified in the ISO 15622 standard. However, if a test reveals that the braking maneuver is due to the approach of the motor vehicle to a stationary object, the method provides for the selection of the limiting characteristic curve from several predefined limiting characteristics.If the approach to a stationary object is detected by means of an environmental sensor system, in particular a radar sensor system or a camera sensor system, the method can in particular allow a greater maximum negative target acceleration than would be permissible when approaching a moving object.

[0005] This addresses the problem that the limited range of the environmental sensors makes it difficult to detect a stationary object as such quickly and early enough. The method therefore enables more effective collision avoidance when approaching stationary objects than methods that use a limiting characteristic according to the ISO 15622 standard, regardless of the state of movement of an object in the path of travel. In particular, successful collision avoidance can thus be achieved with a high probability through automatic braking at a vehicle speed of up to 130 km / h, even when the vehicle is approaching a stationary object. When using a limiting characteristic according to the ISO 15622 standard, collision avoidance through automatic braking is usually no longer possible in this situation at a vehicle speed of more than 80 km / h.

[0006] By not only switching to a different limiting characteristic curve when the motor vehicle approaches a stationary object, but by offering several limiting characteristics to choose from, it is possible, on the one hand, to allow a high maximum negative target acceleration and, on the other hand, to continue to guarantee the requirements for functional safety.

[0007] For this purpose, it is preferred that a first predetermined limiting characteristic curve corresponds to a limiting characteristic curve used during the automated braking process to limit the negative target acceleration of the motor vehicle when the braking process occurs due to the motor vehicle approaching a moving object. This is, in particular, a limiting characteristic curve according to the ISO 15622 standard. A second limiting characteristic curve has a lower limit for the negative target acceleration than the first limiting characteristic curve. This means that, at least for some speeds, the absolute value of the maximum negative target acceleration of the second limiting characteristic curve is higher than the absolute value of the maximum negative target acceleration of the first limiting characteristic curve.Furthermore, it is preferred that different maximum negative target accelerations are provided for different speeds in the first limiting characteristic curve, and the same maximum negative target acceleration is provided for different speeds in the second limiting characteristic curve. The method thus makes it possible, on the one hand, to use the second limiting characteristic curve for strong automated braking when approaching a stationary object and, on the other hand, in situations where this is not appropriate, to use the first limiting characteristic curve, which the motor vehicle also uses for automated braking operations that do not occur due to the motor vehicle approaching a stationary object.

[0008] In principle, more than two limiting characteristics can be specified, from which a selection can be made depending on the situation. However, a particularly easy-to-implement embodiment of the method provides for exactly two limiting characteristics, in particular the first limiting characteristic and the second limiting characteristic.

[0009] Preferably, the selection between the characteristic curves is made depending on whether a driver assistance system of the motor vehicle is active that is included in a predefined group of driver assistance systems. Particularly preferably, this group contains at least one of the driver assistance systems selected from ABS (Anti-Lock Braking System), VDC (Vehicle Dynamics Controller), or TCS (Traction Control System). The activity of one of these driver assistance systems indicates an unstable driving situation. In such an unstable driving situation, high tolerances occur in the measured negative actual acceleration, so that an increased maximum negative target acceleration could lead to an increased risk for the driver. Therefore, when one of these driver assistance systems is active, it is particularly preferred that the first predefined limiting characteristic curve is selected.

[0010] Furthermore, it is preferred that the selection be made depending on whether the magnitude of the negative actual acceleration of the motor vehicle exceeds a threshold value and how long this exceedance lasts. In particular, if the threshold value is exceeded for too long, it is preferable to select the first predefined limiting characteristic curve to ensure driver safety.

[0011] Particularly preferred is the threshold value selected based on an ASIL risk level. ASIL (Automotive Safety Integrity Level) risk levels are standardized in ISO 26262. Particularly preferred is the threshold value selected so that the automated braking process complies with the ASIL-QM or ASIL-A risk level.

[0012] Furthermore, it is preferred that the use of at least one of the limiting characteristics be limited to a maximum number of applications within a predefined time interval or within a predefined distance interval. This serves to deactivate the use of a limiting characteristic if it is selected unexpectedly often, indicating a system error. In particular, the use of the second limiting characteristic is limited in this way, since only a rare approach to a stationary object is to be expected.

[0013] The computer program is configured to perform each step of the method when running on a computer or electronic control unit. It enables the method to be implemented on a conventional electronic control unit without requiring any structural modifications. For this purpose, it is stored on the machine-readable storage medium.

[0014] By loading the computer program onto a conventional electronic control unit, the electronic control unit is obtained which is configured to limit a negative target acceleration during an automated braking process of a motor vehicle by means of the method. Short description of the drawings

[0015] Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Fig. 1 schematically shows a motor vehicle whose negative target acceleration can be limited during an automated braking process by means of embodiments of the method according to the invention. Fig. 2 shows a limiting characteristic curve for limiting a negative target acceleration when approaching a moving object in an embodiment of the invention. Fig. 3 shows two limiting characteristics for limiting a negative target acceleration when approaching a stationary object in an embodiment of the method according to the invention. Fig. 4 shows a flowchart of an embodiment of the method according to the invention. Fig. 5 shows a diagram in which several temporal courses of a negative actual acceleration in embodiments of the method according to the invention are compared with ASIL risk levels. Embodiments of the invention

[0016] Fig. 1 shows a motor vehicle 10 that can be operated using a method according to an exemplary embodiment of the invention. It has an electronic control unit 11 in which the method is implemented as a computer program. The electronic control unit 11 is connected to a sensor 12 arranged at the front of the motor vehicle 10. This sensor is, for example, a radar sensor with which a moving or stationary object 20 in front of the motor vehicle 10 can be detected. An acceleration sensor 13, which is also connected to the electronic control unit 11, is arranged on a wheel of the motor vehicle 10 and configured to measure an actual acceleration of the motor vehicle 10.

[0017] The computer program is configured to automatically brake the motor vehicle 10 when the sensor 12 detects that the vehicle is approaching an object 20 in front of it. If this object 20 is moving, for example, a motor vehicle traveling ahead, the automated braking occurs with a negative target acceleration a max , which is limited to a value dependent on the speed v of the motor vehicle 10. This value results from a limitation characteristic curve, which is Fig. 2 is shown.

[0018] In the event that the object 20 is stationary, for example a stationary motor vehicle, one embodiment of the method according to the invention provides that, depending on the situation, a selection is made between two different limiting characteristics 31, 32 for the automated braking process. These are shown in Fig. 3. The first limiting characteristic 31 corresponds to the limiting characteristic from Fig. 2. The second limiting characteristic 32 provides for a limitation of the target acceleration a max to a value that is the same for all speeds v of the motor vehicle 10.

[0019] The sequence of this embodiment of the method is shown in Fig. 4. The method is started 40 when the automatic braking process is triggered. Several tests are then performed. A first test 41 checks whether the object 20 is stationary. Only if this condition is met is a second test 42 checked to determine whether, for example, in the distance interval of the last 1,000 km of travel of the motor vehicle 10, a number of automated braking processes of the motor vehicle 10 has occurred according to the second limiting characteristic curve 32 that exceeds a maximum number of applications. Only if this maximum number of applications stored in the electronic control unit 11 has not been exceeded is a third test 43 performed. This checks whether one of the driver assistance systems ABS, VDC, or TCS of the motor vehicle 10 is active.If this is not the case, a fourth test 44 checks whether the current amount of negative actual acceleration of motor vehicle 10, measured by acceleration sensor 13, has not yet exceeded a predefined threshold value for a maximum tolerable predefined period of time. If the conditions of all four tests 41 to 44 are met, the second limiting characteristic curve 32 is selected 45 to limit the negative target acceleration of motor vehicle 10. If a further test 46 shows that motor vehicle 10 has come to a standstill, the process is terminated 47. Otherwise, the third test 43 and the fourth test 44 are continuously repeated, and the automated braking process is only carried out according to the second limiting characteristic curve 32 as long as the conditions are met.

[0020] If one of the conditions of the four tests 41 to 44 is not met immediately after the start 40 of the procedure, the negative target acceleration of the motor vehicle 10 is subsequently limited according to the first limitation characteristic curve 31. This continues until a further test 49 shows that the motor vehicle 10 has come to a standstill and the procedure can be terminated 47. If, during the course of the automated braking process, which is initially limited by means of the second limitation characteristic curve 32, the ABS, VDC or TCS is activated and thus the condition of the third test 43 is no longer met, or if the condition of the fourth test 44 is no longer met due to the negative actual acceleration exceeding a threshold value, a switchover to the first limitation characteristic curve 31 takes place, which is then used for the further braking process until the motor vehicle 10 comes to a standstill.

[0021] In Fig.5 shows the sequence of the fourth test 44 in detail. In the electronic control unit 11, a curve of the negative actual acceleration a ist with time t, assigned to the risk levels ASIL-QM 51, ASIL-A 52, ASIL-B 53 and ASIL-C 54. A first curve 61 shows a temporal progression of the negative actual acceleration a ist in an ideal case in which this is linear up to the maximum negative target acceleration a specified by the second limiting characteristic 32 max of 5.0 m / s 2 and then maintains this value. If it is specified that the risk level ASIL-A is to be tolerated, the conditions of the fourth test 44 are consistently met in this case. In a second curve 62, the negative actual acceleration a follows. istinitially the same linear progression as in the first curve 61. After 1.0 seconds, a measurement error occurs in the acceleration sensor 13, due to which the measured negative actual acceleration a ist suddenly to 7.0 m / s 2 increases. It decreases only slowly from this value. It initially remains in the ASIL-A range 52, but leaves this after 5.0 seconds towards the ASIL-B range 53. After remaining in this range for 0.5 seconds, the fourth test 44 detects that the specified threshold value of the negative actual acceleration a ist was violated and this violation has occurred for such a long period of time that a switch to the first limiting characteristic curve 31 must occur. A third curve 63 shows a realistic course of the negative actual acceleration a ist. Initially, the braking is less severe than in the ideal case of the first curve 61. After 2.5 seconds, the negative actual acceleration a ist However, the maximum negative target acceleration a specified by the second limiting characteristic 32 max of 5 m / s 2 However, since it remains within the ASIL-A range 52 over the entire period shown, this exceedance is tolerated and the fourth test 44 permits continued braking according to the second limiting characteristic 32 for the entire automated braking process. The risk of injury to the driver of the motor vehicle 10 and other road users remains acceptable according to the ASIL-A risk level. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 102 31 584 A1

[0003]

Claims

[1] Method for limiting a negative target acceleration during an automated braking process of a motor vehicle (10), wherein the limitation is carried out according to a limitation characteristic curve (31, 32) in which a maximum negative target acceleration (a max ) as a function of a speed (v) of the motor vehicle (10), characterized by that a selection (45, 48) of the limiting characteristic curve (31, 32) from a plurality of predetermined limiting characteristic curves (31, 32) is made if a test (41) shows that the braking process occurs due to the motor vehicle (10) approaching a stationary object (20). [2] Method according to claim 1, characterized byin that a first predetermined limiting characteristic curve (31) corresponds to a limiting characteristic curve which is used during the automated braking process to limit the negative target acceleration of the motor vehicle (10) when the braking process occurs due to the motor vehicle (10) approaching a moving object (20) and a second limiting characteristic curve (32) has a lower limit of the negative target acceleration than the first limiting characteristic curve (31). [3] Method according to claim 1 or 2, characterized by that the selection (45, 48) is made depending on whether a driver assistance system of the motor vehicle (10) is active that is included in a predetermined group of driver assistance systems (43). [4] Method according to claim 3, characterized by that the group includes at least one of the driver assistance systems selected from ABS or VDC or TCS. [5] Method according to one of claims 1 to 4, characterized by that the selection (45, 48) is made depending on whether an amount of a negative actual acceleration (a ist ) of the motor vehicle (10) exceeds a threshold value and how long this excess lasts (44) [6] Method according to claim 5, characterized by that the threshold is chosen depending on an ASIL risk level. [7] Method according to one of claims 1 to 6, characterized by that the selection (45, 48) of at least one of the limiting characteristics (31, 32) is limited to a maximum number of applications within a predetermined time interval or distance interval. [8] A computer program arranged to carry out each step of a method according to any one of claims 1 to 7. [9] A machine-readable storage medium on which a computer program according to claim 8 is stored. [10] Electronic control unit (11) which is configured to limit a negative target acceleration during an automated braking operation of a motor vehicle (10) by means of a method according to one of claims 1 to 7.

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