Method for limiting target deceleration

Abstract

The invention relates to a method for limiting a target deceleration during an automated braking process of a motor vehicle, the limiting being carried out according to a limiting characteristic curve (31, 32) in which a maximum target deceleration (amax) is achieved as a function of the speed (v) of the motor vehicle. The limiting characteristic curve (31, 32) is selected from a plurality of predetermined braking characteristic curves (31, 32) if it is checked that a braking process occurs as a result of the motor vehicle approaching a stationary object.

Description

Technical Field

[0001] The invention relates to a method for limiting a setpoint deceleration during an automated braking process of a motor vehicle. The invention also relates to a computer program product, which is designed to carry out each step of the method, and to a machine-readable storage medium, on which the computer program product is stored. Finally, the invention relates to an electronic control unit, which is designed to carry out the method. Background Art

[0002] Modern motor vehicles have assistance functions that, based on environmental sensors (e.g. radar or camera), take over the control of the vehicle speed, including compliance with the distance to the vehicle ahead. In this case, according to the ISO 15622 standard, the automated braking process is limited to a maximum rated deceleration that is speed-dependent.

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

[0004] In the method, provision is made for limiting a set deceleration / set negative acceleration (negative Soll-Beschleunigung) during an automated braking process of a motor vehicle, wherein the limitation is carried out according to a limiting characteristic curve in which a maximum set deceleration is achieved as a function of the speed of the motor vehicle. For situations where the motor vehicle approaches a moving object, such a limiting characteristic curve is predefined in the ISO 15622 standard. However, if a check shows that a braking process is carried out due to the motor vehicle approaching a stationary object, provision is made in the method for selecting a limiting characteristic curve from a plurality of predefined braking characteristic curves. If an approaching stationary object is detected by means of an environmental sensor system, in particular a radar sensor system or a camera sensor system, a maximum set deceleration which is greater than the maximum set deceleration permitted when approaching a moving object can be permitted by means of the method.

[0005] The following problem is encountered as a result: Due to the limited range of the surrounding sensor system, it is difficult to detect stationary objects themselves quickly and early enough. Therefore, when approaching non-moving objects, the method can achieve a more effective collision avoidance than the following method: the method uses the limiting characteristic curve according to the ISO 15622 standard independently of the movement state of the object located in the driving path. Therefore, in particular, when the motor vehicle approaches a stationary object, a successful collision avoidance can be achieved with a high probability by automatic braking even at a vehicle's own speed of up to 130 km / h. When using the limiting characteristic curve according to the ISO 15622 standard, in this situation, at a vehicle's own speed of more than 80 km / h, collision avoidance by automatic braking is generally no longer possible.

[0006] Since, when the motor vehicle approaches a stationary object, a switch is not made only to another limiting characteristic curve, but rather a plurality of limiting characteristic curves are provided for selection, a high maximum rated deceleration can be permitted on the one hand, while the requirements for functional safety are ensured on the other hand.

[0007] For this purpose, it is preferred that the first predetermined limiting characteristic curve corresponds to the following limiting characteristic curve: when the braking process is carried out due to the motor vehicle approaching a moving object, the limiting characteristic curve is used to limit the rated deceleration of the motor vehicle during the automated braking process. This is in particular a limiting characteristic curve according to the standard ISO 15622. Compared with the first limiting characteristic curve, the second limiting characteristic curve has less restriction on the rated deceleration. This is understood to mean that, at least for some speeds, the magnitude of the maximum rated deceleration of the second limiting characteristic curve is greater than the magnitude of the maximum rated deceleration of the first limiting characteristic curve. It is also preferred that in the first limiting characteristic curve, different maximum rated decelerations are set for different speeds, and in the second limiting characteristic curve, the same maximum rated deceleration is set for different speeds. That is, the method can achieve, on the one hand, using the second limiting characteristic curve for strong automated braking when approaching a stationary object, and on the other hand, using the first limiting characteristic curve in a situation where the strong automated braking is not suitable, and the motor vehicle also uses the first limiting characteristic curve for automated braking processes that are not carried out due to the motor vehicle approaching a stationary object.

[0008] In principle, more than two limiting characteristic curves can be predefined: the selection among these limiting characteristic curves can be made depending on the situation. However, a particularly easy to implement embodiment of the method provides exactly two limiting characteristic curves, in particular a first limiting characteristic curve and a second limiting characteristic curve.

[0009] Preferably, the selection between the characteristic curves is made as a function of whether a driver assistance system of the motor vehicle, which is included in a predefined group of driver assistance systems, is activated. Particularly preferably, the group includes at least one driver assistance system selected from the group consisting of ABS (Anti-Blockier System) or VDC (Vehicle Dynamics Controller) or TCS (Traction Control System). The activation of one of these driver assistance systems indicates an unstable driving situation. In such an unstable driving situation, a high tolerance occurs in the measured actual deceleration / actual negative acceleration (negative Ist-Beschleunigung), so that an increased maximum setpoint deceleration can lead to an increased risk for the driver. Therefore, in the case of an activation of one of these driver assistance systems, it is particularly preferred to select a predefined first limiting characteristic curve.

[0010] In addition, it is preferred that the selection is performed according to whether the magnitude of the actual deceleration of the motor vehicle exceeds a threshold value and how long the exceeding lasts. In particular, when the threshold value is exceeded for too long, it is preferred to select a predetermined first limiting characteristic curve to ensure the safety of the driver.

[0011] The threshold value is particularly preferably selected according to the ASIL risk level. The ASIL (Automotive Safety Integrity Level) risk levels are standardized in the standard ISO 26262. Very particularly preferably, the threshold value is selected such that during the automated braking process, the risk level ASIL-QM or ASIL-A is adhered to.

[0012] Furthermore, it is preferred that the selection of at least one of the limiting characteristic curves is limited to a maximum number of applications within a predetermined time interval or distance interval. This serves to deactivate the use of a limiting characteristic curve if the limiting characteristic curve is selected unexpectedly frequently, which indicates a system malfunction. In particular, the use of the second limiting characteristic curve is limited in this way, since only rare approaches to stationary objects can be expected.

[0013] The computer program product is configured to execute each step of the method when the computer program product is run on a computer or an electronic controller. The computer program product enables the method to be implemented on a conventional electronic controller without requiring structural changes on the electronic controller. For this purpose, the computer program product is stored on a machine-readable storage medium.

[0014] By uploading the computer program product to a conventional electronic control unit, an electronic control unit is obtained which is designed to limit the target deceleration during an automated braking process of the motor vehicle using the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

[0016] Figure 1 A motor vehicle is schematically shown, the target deceleration of which can be limited during an automated braking process by means of an exemplary embodiment of the method according to the invention.

[0017] Figure 2 In the exemplary embodiment of the present invention, a limiting characteristic curve for limiting the setpoint deceleration when approaching a moving object is shown.

[0018] Figure 3 In an exemplary embodiment of the method according to the invention, two limiting characteristics are shown for limiting the setpoint deceleration when approaching a stationary object.

[0019] Figure 4 A flow chart showing an embodiment of the method according to the invention is shown.

[0020] Figure 5 A diagram is shown in which a plurality of time profiles of the actual deceleration in an exemplary embodiment of the method according to the invention are compared with the ASIL risk level. DETAILED DESCRIPTION

[0021] Figure 1 A motor vehicle 10 is shown, which can be operated with the method according to an exemplary embodiment of the present invention. The motor vehicle has an electronic control unit 11, in which the method is implemented as a computer program product. The electronic control unit 11 is connected to a sensor 12 arranged at the front of the motor vehicle 10. The 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 is configured to measure the actual acceleration of the motor vehicle 10.

[0022] The computer program product is designed to automatically brake the motor vehicle 10 when the motor vehicle approaches an object 20 located in front of the motor vehicle by means of the sensor 12. If the object 20 is moving, for example a motor vehicle traveling ahead, the automated braking is performed with a set deceleration a max The set deceleration is limited to a value related to the speed v of the motor vehicle 10. Figure 2 The limiting characteristic curve shown in FIG.

[0023] If the object 20 is not moving, for example a stationary motor vehicle, then in the exemplary embodiment according to the invention it is provided that for the automated braking process a selection is made between two different limiting characteristic curves 31, 32 depending on the situation. These limiting characteristic curves are Figure 3 Here, the first limiting characteristic curve 31 corresponds to Figure 2 The second limiting characteristic curve 32 sets the rated deceleration a max The limit is a value that is the same for all speeds v of the motor vehicle.

[0024] exist Figure 4 The flow of this embodiment of the method is shown in FIG. When the automated braking process is triggered, the method starts 40. Then, a plurality of checks are performed. In the first check 41, it is checked whether the object 20 is not moving. Only when this condition is met, it is checked in the second check 42 whether, for example, the automated braking process of the motor vehicle 10 has been performed for a number of times exceeding the maximum number of applications in the distance interval of the last 1000 km of the driving route of the motor vehicle 10. Only when the maximum number of applications stored in the electronic controller 11 is not exceeded, the third inspection 43 is performed. It is checked whether one of the driver assistance systems of the motor vehicle 10, ABS, VDC or TCS, is activated. If not, it is checked in the fourth check 44 whether the current value of the actual deceleration of the motor vehicle 10, measured by means of the acceleration sensor 13, still does not exceed the predetermined threshold value within the maximum permissible predetermined time period. If the conditions of all four checks 41 to 44 are met, the second limiting characteristic curve 32 is selected 45 in order to limit the rated deceleration of the motor vehicle 10. If the other check 46 shows that the motor vehicle 10 is stationary, the method ends 47. Otherwise, the third check 43 and the fourth check 44 are repeated continuously and the automated braking process is only carried out according to the second limiting characteristic curve 32 as long as the conditions are met.

[0025] If one of the conditions of the four checks 41 to 44 is not already met immediately after the method is started 40, the setpoint deceleration of the motor vehicle 10 is then limited according to the first limiting characteristic curve 31. This continues until a further check 49 shows that the motor vehicle 10 has come to a standstill and the method can be terminated 47. If during the course of the automated braking process the automated braking process is initially limited by means of the second limiting characteristic curve 32, the ABS, VDC or TCS is activated and therefore the condition of the third check 43 is no longer met, or the condition of the fourth check 44 is no longer met because a threshold value for the actual deceleration is exceeded, a switch is made to the first limiting characteristic curve 31, which is used for further braking processes until the motor vehicle 10 comes to a standstill.

[0026] exist Figure 5 The process of the fourth check 44 is shown in detail in FIG. In the electronic controller 11, the actual deceleration a ist The curves over time t are assigned to the risk levels ASIL-QM51, ASIL-A52, ASIL-B53 and ASIL-C54. The first curve 61 shows the actual deceleration a under ideal conditions. ist In the ideal case, the actual deceleration increases linearly up to the maximum setpoint deceleration a predefined by the second limiting characteristic curve 32. max And then maintain this value, the pre-given maximum rated deceleration is 5.0m / s 2 If it is predefined that the risk level ASIL-A should be allowed, then in this case the condition of the fourth check 44 is always met. In the case of the second curve 62, the actual deceleration a ist First, the same linear progression as in the case of the first curve 61 follows. After 1.0 second, a measurement error of the acceleration sensor 13 occurs, due to which the measured actual deceleration suddenly increases to 7.0 m / s. 2 The actual deceleration only drops slowly from this value. Here, the actual deceleration initially remains in the ASIL-A range 52, but leaves the ASIL-A range in the direction of the ASIL-B range 53 after 5.0 seconds. After the actual deceleration remains in this range for 0.5 seconds, it is detected in the fourth check 44 that the actual deceleration a has been violated. ist The third curve 63 shows the actual deceleration a ist Here, a less intense braking occurs at first than in the ideal case of the first curve 61. However, after 2.5 seconds, the actual deceleration a istexceeds the maximum setpoint deceleration a predefined by the second limiting characteristic curve 32 max The maximum rated deceleration is 5m / s. 2 However, since the actual deceleration remains in the ASIL-A range 52 during the entire period shown, the exceeding is tolerated and the fourth check 44 allows for continued braking according to the second limiting characteristic curve 32 for the entire automated braking process. According to the risk level ASIL-A, the risk of harming the driver of the motor vehicle 10 and other road users remains acceptable.

Claims

1. A method for limiting a setpoint deceleration during an automated braking process of a motor vehicle (10), wherein: The limitation is carried out according to a limiting characteristic curve (31, 32), in which a maximum setpoint deceleration (a) is achieved as a function of the speed (v) of the motor vehicle (10). max ), characterized in that if a check (41) shows that a braking process is carried out due to the motor vehicle (10) approaching a stationary object (20), the limiting characteristic curve (31, 32) is selected (45, 48) from a plurality of predetermined braking characteristic curves (31, 32).

2. The method according to claim 1, characterized in that A predetermined first limiting characteristic curve (31) corresponds to the following limiting characteristic curve: when a braking process is carried out due to the motor vehicle (10) approaching a moving object (20), the limiting characteristic curve is used to limit a set deceleration of the motor vehicle (10) during the automated braking process, and a second limiting characteristic curve (32) has a smaller limitation on the set deceleration than the first limiting characteristic curve (31).

3. The method according to claim 1 or 2, characterized in that: The selection (45, 48) is performed as a function of whether a driver assistance system of the motor vehicle (10) which is contained in a predefined group of driver assistance systems is activated (43).

4. The method according to claim 3, characterized in that The group comprises at least one driver assistance system selected from ABS or VDC or TCS.

5. The method according to any one of claims 1 to 4, characterized in that The selection (45, 48) is performed according to the following conditions: the actual deceleration (a) of the motor vehicle (10) ist ) exceeds a threshold and how long the exceeding lasts (44).

6. The method according to claim 5, characterized in that The threshold is selected according to the ASIL risk level.

7. The method according to any one of claims 1 to 6, characterized in that The selection (45, 48) of at least one of the limiting characteristic curves (31, 32) is limited to a maximum number of applications within a predetermined time interval or distance interval. 8 . A computer program product, which is designed to carry out each step of the method according to claim 1 .

9. A machine-readable storage medium on which the computer program product according to claim 8 is stored.

10. An electronic control unit (11) which is designed to limit a target deceleration during an automatic braking process of a motor vehicle (10) by means of a method according to any one of claims 1 to 7.

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