BACKGROUND INFORMATION

Pressure tube sensors (PTSs) have been used for a number of years for detecting a pedestrian collision on a front side of a motor vehicle. The pressure tube is generally situated between a bumper crossbeam and absorption foam situated in front of same. The pressure tube is filled with air, and is closed off with a pressure sensor at each end. The deformation of the foam that occurs during a pedestrian collision thus results in compression of the tube, as the result of which a pressure signal is measured by the two pressure sensors. This pressure signal is read in by a control unit, generally the central airbag control unit, where it is processed in order to detect a pedestrian collision.

Vehicle accidents are conventionally recognized by an airbag control unit, mounted on the vehicle tunnel, by use of an acceleration sensor system, optionally supplemented by an external sensor system.

SUMMARY

A particularly advantageous example method for generating a trigger signal for triggering at least one safety function of a motor vehicle in accordance with the present invention is presented herein. Advantageous refinements of the example method in accordance with the present invention are described herein.

The example method is based in particular on the finding that a pressure tube may be used not only for pedestrian recognition, but also for improved recognition of vehicle accidents. This applies in particular to particular types of vehicle collisions such as a pole impact in the mid-region of the vehicle. Since no crash structures of the vehicle are affected in a pole impact, it may be detected only relatively late with a conventional collision sensor system, whereas it may be recognized very quickly by the pressure tube. In addition, by use of the described method the pedestrian protection recognition may be enhanced and made more robust.

At least two pressure tube sensors are provided for the described method. Based on these sensors, in particular important features of collisions, such as a collision speed (which may also be referred to as an intrusion speed) and/or a direction of the collision, may be identified and used for improved collision recognition and triggering of safety functions (such as restraint means).

Thus, by use of the described method it is possible in particular to control restraint means in a more precise and robust manner. This may take place in particular in that the parameters of collision speed and direction of impact, which are vitally important for the severity of the collision, may be explicitly determined. This is not possible with a conventional sensor system. Instead, present collision algorithms operate with implicit features that allow only indirect conclusions to be drawn concerning these key parameters. This results in relatively inaccurate recognition of the type and severity of the collision.

A system that includes two pressure tube sensors (thus, a 2-PTS system) is preferably used for the described method. The pressure tube sensors are preferably situated apart from one another. A system that includes two pressure tube sensors is in particular a system with two well-defined contact switches (the pressure tube sensors). The pressure tube sensors are preferably situated in a (in particular front) crumple zone of the motor vehicle. Key parameters for the severity of the collision, in particular the collision speed and/or the direction of impact, may thus be determined. Explicitly determining the collision speed and/or the direction of impact may allow significantly more precise and accurate collision recognition, and thus, control of the restraint means required for the ascertained severity of the collision.

The described method includes in particular method steps a) through c), which are preferably carried out in the stated order.

Signals are received from each of at least two pressure tube sensors in step a) of the described method.

The pressure tube sensors preferably each include an air-filled tube (preferably made of a material containing silicone) that is closed off with a pressure sensor at one end, preferably at both ends. In the following discussion, as an example it is assumed that two pressure sensors are provided for each pressure tube sensor. Data may be recorded with the pressure sensors, from which an impact on the tube may be deduced. Based on these data, in particular a signal of the pressure tube sensor may be generated via an appropriate electronics system. The signal may in particular indicate the fact that an impact has been detected with the pressure tube sensor. The point in time that the signal is output may indicate the point in time of the impact (possibly delayed by a processing time). Alternatively, the signal may also be continuously output and changed in a predefined manner when an impact is detected.

The signals of the at least two pressure tube sensors are preferably received by a control unit that is intended and configured for carrying out the described method.

At least one collision parameter is determined from signals received according to step a), in step b) of the described method.

Any variable that may characterize an accident of a motor vehicle is suitable as a collision parameter. The collision parameter is preferably defined in such a way that it allows a conclusion to be drawn concerning the type and/or severity of an accident. The collision parameter may in particular be determined in the control unit, using appropriate software.

A trigger signal for the at least one safety function is output in step c) of the described method as a function of the at least one collision parameter determined in step b).

The at least one safety function may be, for example, an airbag, a seat belt tensioner, or an intervention into the control system of the motor vehicle (for example, via automatic emergency braking and/or an automatically initiated evasive maneuver). The motor vehicle preferably includes a plurality of safety functions. The at least one safety function may be triggered in particular by a trigger signal that is preferably output in particular by the control unit. The type and/or severity of the accident that is recognizable from the collision parameter may be taken into account in step c) of the described method in the triggering of the at least one safety function. Thus, the point in time and/or the type of triggering of the at least one safety function may be determined as a function of the collision parameter. In addition, it may be determined whether the at least one safety function is to be triggered at all. In addition, for multiple safety functions a selection of safety functions to be triggered may be made, and/or a decision may be made regarding the particular order in which they are to be triggered.

In one preferred specific embodiment of the example method, respective signals are received in step a) from at least two pressure tube sensors that are spaced apart from one another at least in the travel direction of the motor vehicle.

In the present context, the travel direction is understood to mean the direction in which the motor vehicle is moving during typical forward travel. A frontal impact may be detected initially by the pressure tube sensor situated farther to the front in the travel direction, and only after a delay, also detected by the other pressure tube sensor. In particular a collision speed may be determined by the time difference with which the two pressure tube sensors detect the impact.

The pressure tube sensors may likewise be spaced apart from one another in a vertical direction, in particular transverse (or perpendicular) to the travel direction. However, it is also possible for the pressure tube sensors to be situated at the same height in the vertical direction.

In another preferred specific embodiment of the example method, the signals of the at least two pressure tube sensors received in step a) in each case represent at least one of the following parameters:an impact time t1, t2andan impact location s1, s2.

The statement that the received signals represent mentioned parameters of impact time (t1, t2) and impact location (s1, s2) means the information contained in the received signals, from which the mentioned parameters are ascertainable. Pressure patterns regarding the signals received from the pressure tube sensors are preferably received in step a). Based on these pressure patterns, it is then possible to compute an impact time (t1, t2) and an impact location (s1, s2) in a control unit (preferably the control unit in which the further method steps are also carried out).

In the event of an impact with an obstacle, initially the first pressure tube (at point in time t1), and subsequently the second pressure tube (at point in time t2), are deformed in succession. Both deformations result in an immediate pressure rise, and thus a pressure signal to the pressure sensors that close off the particular pressure tubes. The particular points in time t1and t2may be detected in the control unit, for example via threshold value exceedances of a first pressure sensor of the respective pressure tube sensor.

Impact time t1or t2is understood to mean the point in time at which an impact is detected with the first or second pressure tube sensor. Impact location s1or s2is the location at which the impact has been detected with the first or second pressure tube sensor. s1and s2are preferably defined along the respective pressure tube sensors. Thus, for example, s1and s2may indicate the distance between the location of the impact and a midpoint of the pressure tube.

In another preferred specific embodiment of the method, the at least one collision parameter determined in step b) is at least one of the following parameters:a magnitude of a collision speedvintr,a component of collision speed vintr,xalong the travel direction of the motor vehicle,a collision angle α.

Collision speed vintris a vectorial variable that includes at least one component along travel direction x of the motor vehicle, vintr,x, and a component perpendicular thereto, vintr,y.vintris the magnitude of vector vintr. Collision angle α is the angle at which a collision object strikes the motor vehicle, i.e., its front side.

Based on time difference Δt=t2−t1between points in time t2(pressure rise in the second pressure tube) and t1(pressure rise in the first pressure tube), and longitudinal distance d in the travel direction between the two pressure tube sensors, (averaged) collision speedvintr,xmay be directly ascertained from
vintr,x=d/Δt.(1)

For the case that both pressure tube sensors are mounted a large distance apart in the motor vehicle (in particular in front of fairly hard crash structures such as crash boxes), in a good approximation it may be assumed that in the early collision phase, in which the two pressure tube sensors are deformed, an appreciable decrease in speed has not yet taken place due to the collision. This applies even more, the higher the collision speed. This means that the two collision partners are still moving virtually at the initial speed. This means that the averaged collision speed ascertained according to equation (1) also corresponds to initial collision speed vintr,x(0):
vintr,x≈vintr,x(0).   (2)

For the case that the second pressure tube sensor is situated farther to the rear in the motor vehicle in the travel direction, and fairly hard crash structures such as crash boxes must be deformed prior to the deformation of the second pressure tube sensor, a decrease in the collision speed is already present at point in time t2. This applies in particular for slow collisions, in which the deformation of the crash structures results in a greater decrease in speed. In such a case, the measured average collision speed will be slightly lower than the initial collision speed:
vintr,x<vintr,x(0),   (3)
and in particular will be more apparent the slower the collision. Interestingly,vintr,xmeasured in this way is even better suited for discriminating between fast and slow collisions than is the initially “more correct” information vintr,x(0).

If initial vintr,x (0)is still to be ascertained in this case, the decrease in the collision speed may be estimated via decrease in speed dv(t) of the motor vehicle during the collision. For this purpose, in another preferred specific embodiment of the method, in particular at least one deceleration of the motor vehicle due to a collision is taken into account in step b) in determining a collision speed vintras the at least one collision parameter.

The decrease in speed of the motor vehicle is preferably ascertained in the control unit (which in particular may be the central airbag control unit) by integrating measured longitudinal acceleration signal a(t). It is pointed out here that the collision speed during the collision may be determined from the relative speed of the other parties in the accident and the rigidity ratios, whereas the decrease in speed is determined from the relative speed of the other parties in the accident and the mass ratios. However, since vehicle masses and rigidities show a certain correlation, it is a good approximation to set the decrease in the collision speed to a decrease in speed that is rescaled with a vehicle-specific factor f. Ideally, factor f also contains information concerning the mass and rigidity of the other party in the accident that is obtained via C2X communication.

In general, the following may be set:
vintr,x(t)=vintr,x(0)−f·dv(t).   (4)
vintr,x(t1)=vintr,x(0)−f·dv(t1)≈vintr,x(0).   (5)
vintr,x(t2)=vintr,x(0)−f·dv(t2).   (6)

The simplification in equation (5) reflects the fact that there is no measurable decrease in speed of the overall vehicle during deformation of the bumper foam. Therefore, in particular dv(t1) may then be disregarded.

Assuming a linear drop, for example the following applies:
vintr,x=(vintr,x(t1)+vintrx,x(t2)/2=vintr,x(0)−(dv(t1)+dv(t2)/2   (7)
and thus,
vintr,x(0)=d/Δt+(dv(t1)+dv(t2))/2≈d/Δt+dv(t2)/2.   (8)

Although the dv(t) curve may be precisely determined, the assumption of a linear decrease does not absolutely have to be made. In addition, an exact determination of vintr,x(0) is possible. Integration of vintr,x(t) between points in time t1and t2results in particular in distance d between the two pressure tube sensors:

d=∫t⁢1t⁢2⁢vintr,x⁡(t)⁢d⁢t=vintr.x⁡(0)·Δ⁢⁢t-∫t⁢1t⁢2⁢d⁢v⁡(t)⁢dtand⁢⁢thus,vintr,x⁡(0)=d+∫t⁢1f⁢2⁢dv⁡(t)⁢dtΔ⁢t(9)

Thus, a particularly general rule for ascertaining the initial collision speed is as follows: determining points in time t1and t2and forming difference Δt; integrating the decrease in speed between these two points in time, and computing according to equation (9).

However, in practice, equations (8) and also (1) allow sufficiently accurate determinations.

In another implementation of equation (1), it is also possible to not explicitly compute the collision speed at all, but instead to consider only time difference Δt, which is inversely proportional to the collision speed.

Impact position s1or s2may be ascertained based on propagation time difference ΔT=TL−TRbetween the pressure signals on the left and right sides of a pressure tube sensor. Since the different paths from impact point s (measured from the center axis, for example) to the two pressure sensors (between which the path difference is thus 2s) result in different signal propagation times, impact position s is given by time difference ΔT and speed of sound c:
s=cΔT/2.   (10)

When this method is used on both pressure tube sensors in the present sensor configuration, two impact locations s1and s2are obtained. The differences between two locations allow conclusions to be drawn concerning the direction of the collision. For example, collision angle α may be directly ascertained via
tan(α)=(s1−s2)/d .(11)

Here as well, it is possible to not explicitly compute the collision angle according to equation (11) at all, but instead to use the difference between impact locations s1-s2.

For collisions where α≠0, in fact a longer intrusion path is necessary in order to go from a deformation of the first pressure tube sensor to a deformation of the second pressure tube sensor. This intrusion path is
I=√{square root over (d2+(s1−s2)2)}.   (12)

Instead of longitudinal collision speedvintr,xfrom equation (1), the magnitude of average vectorial collision speedvintrresults in

v_intr,x=IΔ⁢t=d2+(s⁢1-s⁢2)2Δ⁢t.(13)

The direction is already specified by collision angle α determined above.

The ascertained features, in particular the ascertained collision speed and/or the ascertained collision angle, may be used for directly or indirectly controlling the at least one safety function (in particular restraint means). In particular the following two specific embodiments are preferred for this purpose.

In one preferred specific embodiment of the method, the trigger signal is output in step c) when a component vintr,xof the collision speed along the travel direction of the motor vehicle or a magnitudevintrof a collision speed exceeds a first predefined threshold.

The ascertained features of the collision speed and the collision direction represent the key parameters for the severity of an accident, and could therefore be directly used for controlling the at least one safety function. However, this requires a very robust integration of the pressure tubes into the motor vehicle, and full capability for diagnosing errors in the pressure tube system (in particular including ruptures in the pressure tube).

In this specific embodiment, for trigger thresholds of a front algorithm (such as the seat belt tensioner, first stage airbag, second stage airbag, etc.), a first threshold Thd may be set to one of the collision speeds.

The first threshold may in particular be predefined as a fixed value.

In another preferred specific embodiment of the method, the predefined first predefined threshold is predefined at least as a function of an impact location s1, s2of at least one of the pressure tube sensors and/or of a collision angle α.

The first predefined threshold may be varied in particular as a function of collision angle α. A triggering decision may be made, for example, via averaged longitudinal collision speedvintr,xaccording to equation (2) when
vintr,x>Thd(α).   (14)

For example, for α=0° a first threshold of 20 km/h, and for α=30° a first threshold of 26 km/h, preferably applies. In particular, a threshold value curve may be defined as a continuous function of collision angle α. Alternatively, the threshold values may be varied in stages over certain angular ranges.

In addition, the further parameters of the collision speed described above may be used for the threshold value comparison. If the magnitude of the vectorial collision speed is used for a threshold value query, analogously to equation (14), the variation as a function of collision angle α may be less, for example.

In another preferred specific embodiment of the method, the trigger signal is output in step c) when a difference Δt between impact times t1, t2of at least two of the pressure tube sensors falls below a second predefined threshold.

The second threshold may in particular be predefined as a fixed value.

In another preferred specific embodiment of the method, the second predefined threshold is predefined at least as a function of an impact location s1, s2of at least one of the pressure tube sensors and/or of a collision angle α.

In this specific embodiment, in addition to the collision direction, impact location s1on the first pressure tube is also used. Thus, in particular so-called offset collisions (in which s1is much different from zero, but a is close to zero) may be differentiated from collisions with full coverage (in which both s1and α are close to zero). Equation (14) is then generalized to
vintr,x>Thd(α, s1)   (15)
or further generalized to
vintr,x>Thd(s1, s2),   (16)
since according to equation (11), collision angle α itself is a function of s1and s2.

It is also possible to set the threshold value queries directly to measured time difference Δt. An equivalent criterion for equation (16) would then be, for example,
Δt<Thd′(s1, s2).   (17)

In another preferred specific embodiment of the method, the trigger signal is output in step c) also as a function of at least one parameter of an additional collision recognition system.

In this specific embodiment, the triggering of the at least one safety function does not take place solely via the pressure tube sensor system in the front area of the motor vehicle. In addition, for example a conventional acceleration sensor system may be incorporated as an additional collision recognition system. A preferred approach is for a sensitivity of a conventional acceleration-based algorithm to be influenced in step c). This influencing is preferably a function of the recognized collision speeds, time difference Δt between impact times t1and t2, collision angle α, and/or impact locations s1and s2. For example, sensitization may take place when conditions similar to equations (14) through (17) are satisfied. The sensitization itself may take place by lowering trigger thresholds in the existing trigger logic systems, or also by switching over to other, more sensitive trigger logic systems. This procedure may also be referred to as a “path concept.”

As a further aspect, a control unit for a motor vehicle is presented which is configured for carrying out the described method. The particular advantages and embodiment features described above for the method are applicable and transferable to the control unit.

Furthermore, a computer program is presented which is configured for carrying out all steps of the described method. In addition, a machine-readable memory medium is presented, on which the described computer program is stored. The particular advantages and embodiment features described above for the method and the control unit are applicable and transferable to the computer program and the machine-readable memory medium.

Further particulars of the present invention as well as one exemplary embodiment, to which the present invention is not, however, limited, are described in greater detail with reference to the figures.

