METHOD FOR IMPACT DETECTION AND ACTIVATION OF OCCUPANT PROTECTION DEVICES

Description

[0001] The invention relates to a method for impact detection and activation of occupant protection devices according to the preamble of claim 1. For example, DE 197 29 960 discloses a method for impact detection, particularly for motor vehicles, for activating occupant protection devices. In this method, an acceleration signal from an acceleration sensor is measured. The acceleration signal itself, or a signal derived therefrom, such as the integrated acceleration signal, is then compared with an adjustable trigger threshold. For this method, at least one so-called pre-crash sensor is provided, which registers the change in the relative speed and / or the relative distance of collision objects within a close range of the vehicle's surroundings.If the pre-crash sensor detects a safety-critical condition, such as an impending collision, the trigger threshold for activating occupant protection systems is lowered. So-called pre-crash sensors can include radar and camera sensors, as well as lidar or ultrasonic sensors, or a fusion of data from multiple such sensors.

[0002] EP 0728624 A2 also discloses a device for controlling occupant protection devices, in which, in addition to acceleration sensors for determining an impact value, environmental sensors are also present in order to adapt the triggering behavior depending on the environmental sensors.

[0003] Although the actual triggering still occurs depending on an impact value that is functionally related to the impact acceleration and which is compared with a triggering threshold, the triggering threshold is varied depending on information from the environment sensor, in particular the relative speed, angle of impact and time, particularly at high relative speeds, a severe impact is assumed and the triggering threshold is reduced in order to enable early triggering.

[0004] However, it has proven disadvantageous that lowering the trigger threshold for acceleration sensors in the event of an impending impact can lead to premature activation of the occupant restraint system if the reduced acceleration trigger threshold is already exceeded in the period before the impact. This can happen, for example, in the case of uneven ground or a curb crossing immediately before the actual obstacle detected by the proximity sensor, or in the case of corresponding malfunctions at the beginning of an accident, but especially in so-called non-triggering cases, i.e., crash events of lesser severity that do not actually require the activation of these restraint devices.Therefore, WO 2002 / 30716 A1 provides a method for activating occupant protection devices, in which an approach speed to a collision object is determined within a predetermined close range of the vehicle environment and, if the approach speed is above a predefined threshold value, an expected time of impact on the collision object and a time range starting from the expected time of impact are defined, in which the activation of the assigned occupant protection devices takes place after a plausibility check.

[0005] However, the determination of the time range of the plausibility check is adapted depending on the signal quality of at least one proximity sensor, the driving dynamics, and the geometry of the collision object. Furthermore, for the plausibility check, an acceleration signal or an equivalent signal is checked to determine whether it exceeds a predefined threshold and matches the sign of the impact direction determined by the at least one proximity sensor. While this approach takes the signal quality of the proximity sensor into account, the fixed plausibility check still poses the risk that even collisions at lower speeds, possibly in combination with other vibrations or disturbances, could trigger the occupant protection devices, thereby causing significant disturbance to the driver, even though the severity of the impact does not actually justify this.

[0006] The object of the present invention is to further increase road safety. This object is achieved by the features of the independent claims. Advantageous developments of the invention emerge from the subclaims, whereby combinations and developments of individual features are also conceivable.

[0007] An essential idea of ​​the invention is that an adaptation of the trigger threshold takes place in a procedure that is almost inverse to the previous reduction of the trigger threshold.

[0008] It is planned that a starting time for the algorithm and the threshold adjustment will be set to the expected impact time, provided at least one parameter of the environment sensor meets a specified condition. The environment sensor can and will therefore be able to derive this starting time from the known trajectory considerations even before it occurs, essentially waking up the algorithm.

[0009] From this starting point in time, the trigger threshold is increased even further, starting from a starting value, provided that the acceleration signal or the signal derived from it meets a minimum condition. If the acceleration signal or the signal derived from it rises above the minimum condition, the trigger threshold is also increased at the same time. However, if the acceleration signal or the signal derived from it is still below the minimum condition at the starting point in time, the trigger threshold initially remains at the starting value and only increases when the minimum condition is met, so that false triggering is still avoided if the trigger time is incorrectly determined. However, the minimum condition is significantly smaller than the starting value for the trigger threshold and therefore the acceleration signal or the signal derived from it is by no means sufficient to simultaneously exceed the starting value and the minimum condition.Rather, even in triggering cases, there is always a phase in which the trigger threshold is also increased. The early start time and the immediate adaptation of the trigger threshold upon fulfillment of the minimum condition increase the safety margin between typical non-triggering patterns and the trigger threshold, making the algorithm more robust against disturbances and false triggering. Actual triggering cases will nevertheless exceed the trigger threshold within the specified time, possibly even slightly earlier due to the start time set by the environmental sensor. However, the goal of the targeted increase is not to trigger earlier, but rather to more reliably distinguish between triggering and non-triggering cases.

[0010] Preferably, the minimum condition for increasing the trigger threshold is that the acceleration signal or the signal derived therefrom exceeds a minimum threshold.

[0011] Preferably, however, there is an upper limit for the trigger threshold. The trigger threshold is continuously increased from the starting value until a specified maximum trigger threshold value is reached. Furthermore, the acceleration signal or the signal derived from it must generally also meet the minimum condition.

[0012] In order to ensure safety in the overall concept even in the event of a failure of the environment sensor or insufficient signal quality or if the conditions for the parameters for setting the start time are not met, the time at which the acceleration signal or the signal derived from it exceeds a predetermined threshold is used as an alternative start time, provided that no start time has been set previously by the environment sensor.

[0013] In a further embodiment, described in more detail in the figures below, the increase in the gradient is also adapted again, namely, the trigger threshold is increased with a first gradient as long as the acceleration signal or the signal derived from it meets a minimum condition and is also subject to a second condition. Once the second condition is exceeded, the trigger threshold is increased with a second gradient that is higher than the first. This generally adapts the trigger threshold even better to the typical signal curves at the beginning of the various non-triggering cases.Through this adjustment, the safety margin achieved by the early start time and increasing the trigger threshold is also maintained in the particularly critical second time range, in which even non-triggering cases in the acceleration signal or the signal derived from it can assume considerable amplitudes, especially if additional disturbances on the road, e.g. curb impacts, etc., also influence and increase the signal.

[0014] The method is implemented in an algorithm of a control unit for impact detection and activation of occupant protection devices for a motor vehicle and is stored in its memory for this purpose.

[0015] The invention will be explained in more detail below using exemplary embodiments with reference to the figures. Figure 1 the functional sequence in the algorithm of the control unit using a flow chart, while Figure 2 tries to illustrate this using the signals.

[0016] Phase P1 outlines the process before the start of the actual triggering algorithm at the start time T0 and phase P2 outlines the process after the start time T0.

[0017] Function block 0 outlines the environment sensor and the evaluation of the signals from this environment sensor, in particular the derivation of an expected time of impact (TTC) and, if necessary, other predefined parameters, such as the assessment of the expected collision object in terms of its type, the severity of the expected impact, and the signal or decision quality, i.e., the probability of occurrence. Given the predefined conditions for the signals or parameters of the environment sensor, the start time (t0) is set to the expected time of impact (TTC).

[0018] In addition, the Figure 1in the function block marked with ">sth0?" also the preferably second, alternative path for activating the actual triggering algorithm, in which the acceleration signal (G) or the signal derived therefrom (f(G)) is compared with a predetermined start threshold (sth0) and if this is exceeded, the actual triggering algorithm is also activated.

[0019] The two alternatives—setting the start time using the environment sensor or the acceleration sensor—are functionally alternative, meaning they can be understood as a logical OR operation. If the two options mentioned are not met, the actual triggering algorithm is not activated (No). Accordingly, the microprocessor can still be operated in power-saving mode, leaving parts of the algorithm inactive.

[0020] From the start time t0, however, the actual triggering algorithm becomes active and the triggering threshold (dth1 or dth0) is now also increased starting from a start value (dth0) in function block 2, provided that it was also determined in function block 1 that the acceleration signal or the signal derived from it fulfills at least one minimum condition and the specified maximum value (dth3) of the triggering threshold has not yet been reached.

[0021] In function block 3, the actual triggering decision is finally made by comparing it with the adaptively matching triggering threshold and, if the triggering threshold is exceeded by the acceleration signal or the signal derived from it, the triggering of at least certain individual or all occupant protection devices, whereby the assignment of the occupant protection devices to be triggered and, of course, other parameters, such as the detected direction of the impact and the detected severity, can be further adapted.

[0022] The Figure 2 Now, purely as an example, the signal curve of a triggering case is sketched as function F1 (solid line shape) and the non-triggering cases, which are sometimes difficult to distinguish, especially at the beginning of the collision, are sketched as function F2 (line shape - ** -).

[0023] The dotted line dth0 shows the trigger threshold curve for the case in which the actual trigger algorithm is only activated based on the acceleration signal or the signal derived from it and the exceedance of the start threshold sth0. Therefore, this line only begins when this threshold sth0 is exceeded.

[0024] The curve of the trigger threshold is shown with dth1 and shown as a dashed line for the case in which the environment sensor has already set the start time T0 to the expected collision time and the actual triggering algorithm is already activated when this start time occurs.

[0025] If the acceleration signal has not yet reached the minimum condition for the increase at this start time, the trigger threshold dth1 also remains at the starting value dth0 for such a short period of time. However, since the minimum condition for the increase can be set relatively low, the increase dtha1 for dth1 begins earlier, and thus the trigger threshold dth1 in particular achieves a greater safety margin compared to the sketched dash-dot-dot-dash-(-**-) signal curve of the non-triggering case. It should be emphasized again that the slightly delayed trigger time (Fire) between the two characteristic curves dth0 and dth1 is less important than the greater safety margin to the non-triggering cases, which is achieved by the early algorithm start—essentially the parallel shift of the areas with the increases dtha1 and dtha2.

[0026] In order to be able to functionally set an even better distinction between triggering and non-triggering cases, an adjustment of the increase dtha1 to dtha2 of the triggering threshold value is also provided in this preferred embodiment.

[0027] As long as the acceleration signal or the signal derived from it meets a minimum condition and is also subject to a second condition, the trigger threshold is increased with a first increase, dtha1. If the second condition is exceeded, the trigger threshold is increased with a second increase, dtha2, which is higher than the first. This allows the trigger threshold to be adapted even more precisely between the defined cases, further increasing safety against false triggering.

[0028] It should be noted that the specific values ​​and curves of the characteristic curve are only to be understood as examples and can be adapted to the individual case of the respective vehicle, its crash behavior, but also to the manufacturer's specifications.

Claims

1. Method for detecting an impact and activating occupant protection devices, in which at least one acceleration signal of at least one acceleration sensor is measured directly or a signal derived therefrom is compared with a trigger threshold, wherein there is provision for at least one environment sensor for detecting an imminent impact and at least one parameter of this imminent impact, in particular an expected impact time and impact severity, and the trigger behaviour is adapted on the basis of the parameters of the environment sensor, characterized in that the trigger threshold (dth1=dth0+fth(G,t)) is increased fth(G,t) from a starting value (dth0) from a starting time (t0) if the acceleration signal or the signal derived therefrom satisfies a minimum condition, wherein the starting time (t0) is set to the expected impact time (TTC) if at least one parameter of the environment sensor satisfies a predefined condition.

2. Method according to Claim 1, characterized in that the trigger threshold (dth1) is increased continuously from the starting value while the acceleration signal or the signal derived therefrom satisfies a minimum condition or a predefined maximum value (dth3) of the trigger threshold has been reached.

3. Method according to either of the preceding claims, characterized in that the acceleration signal or the signal derived therefrom exceeds a minimum threshold as the minimum condition for increasing the trigger threshold.

4. Method according to one of the preceding claims, characterized in that, as an alternative, the time at which the acceleration signal or the signal derived therefrom exceeds a predefined threshold (sth0) is also used as the starting time if no starting time has been set by the environment sensor beforehand.

5. Method according to one of the preceding claims, characterized in that while the acceleration signal or the signal derived therefrom satisfies a minimum condition, and moreover under a second condition, the trigger threshold is increased with a first rise, whereas, when the second condition is exceeded, the trigger threshold is increased with a second rise, which is higher than the first.

6. Control unit for detecting an impact and activating occupant protection devices for a motor vehicle, having a memory containing an algorithm for carrying out the method according to one of the preceding claims.