DE102012103181B4 - Method for impact detection on the basis of a pressure signal from a pressure sensor - Google Patents

Abstract

A method for impact detection on the basis of the signal of at least one pressure sensor which detects the pressure in a deformable cavity in the exterior of a vehicle and evaluates a pressure change normalized to the ambient air pressure as a pressure signal, and from this the type or a parameter of the impact is derived, characterized in that the change this pressure signal is detected, a maximum value (Max) of this change in this pressure signal is determined and this maximum value is taken into account in the derivation, and that in deriving the maximum value (Max) based on a previously determined vehicle speed or a relative speed between vehicle and vehicle determined by means of an environment detection sensor Impact object is assessed.

Description

The invention relates to a method for impact detection using a pressure signal from a pressure sensor according to the preamble of claim 1.

From the EP 0 937 612 A2 For example, various configurations of impact detection devices for vehicles can be found in which, among other things, a pressure sensor is proposed which detects the pressure in a deformable cavity in the outer area of a vehicle.

All pressure sensors are permanently exposed to the ambient pressure and, therefore, in the event of an impact due to a change in volume in the cavity, the sensors always record the relative pressure increase compared to a reference pressure, preferably the ambient air pressure. However, since the ambient air pressure is not constant but changes in particular due to the weather conditions and the height of the vehicle above sea level, on the other hand, the pressure change in an impact is not constant due to the different density of the air, it is useful to adjust the pressure change accordingly to normalize to the ambient air pressure. The formation of a difference between the current pressure and ambient pressure, a quotient formation or a combination of both can be used for normalization. For example, from the DE 196 19 468 C1 a corresponding method for triggering a restraint means of side impact protection in a vehicle can be found in which a pressure change normalized to the ambient air pressure is used as the pressure signal. The generation of this normalized pressure signal, or more precisely the pressure change signal, can take place directly in the pressure sensors located in the vehicle outer zone, but alternatively also only in a central control unit as part of the signal processing there.

For the triggering of protective devices for occupants or pedestrians, it is crucial that, in addition to the strength of the impact, the type of impact is correctly identified as early as possible in order to only trigger the appropriate protective devices and to trigger all protective devices that are not required for this impact to let.

From the DE 101 14 465 A1 For example, a contact sensor can be found for this purpose, in which, for example, conclusions can be drawn about the type of impact from the amplitude of the signal from the pressure sensor and the rate of increase. Also from the DE 10 2004 012 550 A1 For a pedestrian protection system, information about the impact is derived from the change in the collision area over time.

The object of the present invention is therefore to further develop the method for impact detection in such a way that even more precise conclusions about the type of impact as well as suitable parameters for triggering protective devices and a corresponding protective system are available.

This object is achieved by the features of the independent claims. Advantageous developments of the invention emerge from the subclaims, combinations and developments of individual features with one another also being conceivable.

An essential idea of the invention is that the change in this pressure signal is detected, the maximum value of this change in this pressure signal is determined and the type or a parameter of the impact is derived therefrom. It should be pointed out that the pressure signal itself already represents a pressure change related to the ambient air pressure, i.e. the maximum change in the pressure change is sought.

A time window within which the maximum value is expected and the determination of the maximum value is aborted and the current value is used as the maximum value is preferably specified from the point at which the pressure signal exceeds a minimum threshold if the maximum value exceeds a specified value. This is because only a limited time window is available for triggering protective devices and, on the other hand, by parameterizing the triggering thresholds, it can be ensured that the maximum values reached within the time window can be evaluated accordingly.

If the change in the pressure signal decreases within the time window, the previous value is used as the maximum value. If the pressure signal later rises again above a maximum value higher than the previous value within the time window, then of course the highest maximum value is preferably used.

If the change in the pressure signal continues to increase within the time window, the current value at the end of the time window is used as the maximum value.

The maximum value of the change in the pressure signal determined in this way can be used as a good approximation to infer the width of the impact area or impact object, in particular if one considers the relative speed between the Can approach the impact object and the vehicle from the vehicle's own speed.

Alternatively, the relative speed between the vehicle and the impact object or the severity of the impact can be deduced from the maximum value of the change in the pressure signal determined in this way, in particular if the impact width is estimated. According to the invention, during the derivation, the maximum value is evaluated on the basis of a previously determined vehicle speed or a relative speed between the vehicle and the impact object determined by means of an environment detection sensor.

This method is suitable both for a pedestrian protection system with at least one pedestrian protection device and an occupant protection system with at least one occupant protection device and a combined protection system for occupants and pedestrians, whereby the comparison values and threshold values for the maximum value or parameters derived therefrom can of course be different.

• Die 1 skizziert einen typischen Verlauf des Drucksignals, wobei nochmals darauf hingewiesen sei, dass es sich bei diesem Drucksignal um eine auf den Umgebungsluftdruck normierte Druckänderung aufgrund des Aufpralls des Kollisionsobjekts auf den Hohlraum im Außenbereich des Fahrzeugs handelt.

The invention will now be explained in more detail below on the basis of exemplary embodiments with the aid of the figures. In the following, the same reference numbers may be used for functionally identical and / or identical elements. Show it

• The 1 outlines a typical course of the pressure signal, whereby it should be pointed out again that this pressure signal is a pressure change normalized to the ambient air pressure due to the impact of the collision object on the cavity in the outer area of the vehicle.

With the penetration of the collision object, the pressure in the cavity rises suddenly, with the change in this pressure (change) signal usually reaching the maximum value (Max) of this change in this pressure signal at an early stage, which in this example is at time t1 and thus occurs well before the absolute maximum value Δp _max is reached.

The maximum value (Max) of the change in this pressure signal is therefore a value that is available very early in order to derive the type or a parameter of the impact from it. In the simplest case, this maximum value itself is used as a parameter or converted into such a parameter by numerical conversion or characteristic curves.

m

Massen-Dichte bzgl der Breite des Impaktors $\left[\frac{kg}{m}\right]$

M

Masse des Impaktors [kg]

B

Breite des Impaktors [m]

k

Federsteifigkeits-Breiten-Dichte $\left[\frac{N}{m^2}\right]$

K

Feder-Steifigkeit des gesamten getroffenen Bereichs $\left[\frac{N}{m}\right]$

τ

Oszillationsdauer eines Feder-Massen-System Segments [s]

T

Oszillationsdauer des Feder-Massen-Systems des gesamten getroffenen Bereichs [s]

xmax

maximale Intrusion eines Feder-Massen-System Segments [m]

Xmax

maximale Intrusion des Feder-Massen-Systems des gesamten getroffenen Bereichs [m]

V0

Relativgeschwindigkeit zwischen Impaktor und Frontend zum Zeitpunkt des ersten Kontakts $\left[\frac{m}{s}\right]$

U

Proportionalitätsfaktor $\left[\frac{bar}{m^2}\right]$

Pmax

Maximaler Gesamt(über)druck im PPS-System [bar]

und folgende an sich aus der Physik bekannte Zusammenhänge:

• 1) $x_{\text{max}}=v_0*\sqrt{\frac{m}{k}}$
  
  maximale Auslenkung eines Feder-Masse-Systems
• 2) $\tau =2\pi *\sqrt{\frac{m}{k}}$
  
  Schwingungsdauer eines Feder-Masse-Systems
• 3) $M=m*B$
  
  Gesamtmasse des Impaktors
• 4) $K=k*B$
  
  Steifigkeit der Feder bezogen auf die ganze Impaktorbreite
• 5) $P_{\text{max}}=U*B*X_{\text{max}}$
  
  so erhält man bei Division von 1) durch 2): $\frac{X_{\text{max}}}{T}=\frac{V_0}{2\pi }.$
  
  Ersetzt man Xmax unter Verwendung von 5): $\frac{P_{\text{max}}}{U*B*T}=\frac{V_0}{2\pi }$
  
  stellt man dies nun nach der Breite B um, ergibt sich: $B=\frac{2\pi }{U}*\frac{1}{V_0}*\frac{P_{\text{max}}}{T}$
  
• 6) $B=\frac{2\pi }{U}*\frac{1}{V_0}*\frac{P_{\text{max}}}{T}B=\frac{2\pi }{\underset{\text{konstant}}{\underbrace{U}}}*\frac{1}{\underset{\text{CAN}}{\underbrace{V_0}}}*\frac{P_{\text{max}}}{\underset{\underset{\propto \text{Max}\left(\frac{P\left(t\right)}{CD\left(t\right)}\right)}{\underset{\text{oder}}{\propto \text{Max}\left(\dot{P}\left(t\right)\right)}}}{\underbrace{T}}}$
  

Es lässt sich also auch modellseitlich die besondere Relevanz der Größe des Maximalwerts der Änderung des Drucksignals für die Abschätzung der Breite des Kollisionsobjekts darstellen und so beispielsweise ein Aufprall eines Fußgängers mit einer üblicherweise kleinen Breite B gegenüber der Breite der Fahrzeugfront von einer Kollision mit einem anderen Fahrzeug unterscheiden, wobei die Näherung der Relativgeschwindigkeit durch die Eigengeschwindigkeit deshalb für diese Betrachtung unerheblich ist, weil bei einer hohen Geschwindigkeit des Kollisionsobjekts sich aus dem Maximalwert dann in der Regel eine Breite B größer als die Fahrzeugfront ergibt.From the maximum value of the change in the pressure signal determined in this way, the width of the impact area or impact object can be inferred to a good approximation, especially if the relative speed between the impact object and the vehicle can be approximated from the vehicle's own speed. If one assumes a pedestrian impact, the pedestrian's own speed is relatively low compared to the own speed of the vehicle and thus the relative speed between the collision objects can be adequately approximated by the information available via the CAN on the vehicle's own speed. This can also be derived from a physical model of a spring-mass system. If one considers the following sizes:

m

Mass density with respect to the width of the impactor $\left[\frac{kG}{m}\right]$

M.

Mass of the impactor [kg]

B.

Width of impactor [m]

k

Spring stiffness width density $\left[\frac{N}{m^2}\right]$

K

Spring stiffness of the entire hit area $\left[\frac{N}{m}\right]$

τ

Oscillation duration of a spring-mass system segment [s]

T

Oscillation duration of the spring-mass system of the entire affected area [s]

xmax

maximum intrusion of a spring-mass system segment [m]

Xmax

maximum intrusion of the spring-mass system of the entire affected area [m]

V0

Relative speed between the impactor and the front end at the time of the first contact $\left[\frac{m}{s}\right]$

U

Proportionality factor $\left[\frac{bar}{m^2}\right]$

Pmax

Maximum total (over) pressure in the PPS system [bar]

and the following relationships known from physics:

• 1) $x_{\text{Max}}=v_0*\sqrt{\frac{m}{k}}$
  
  maximum deflection of a spring-mass system
• 2) $\tau =2\pi *\sqrt{\frac{m}{k}}$
  
  Period of oscillation of a spring-mass system
• 3) $\mathrm{M.}=m*\mathrm{B.}$
  
  Total mass of the impactor
• 4) $K=k*\mathrm{B.}$
  
  Stiffness of the spring related to the entire impactor width
• 5) ${\mathrm{P.}}_{\text{Max}}=U*\mathrm{B.}*X_{\text{Max}}$
  
  dividing 1) by 2) gives: $\frac{X_{\text{Max}}}{T}=\frac{V_0}{2\pi }.$
  
  Replacing Xmax using 5): $\frac{{\mathrm{P.}}_{\text{Max}}}{U*\mathrm{B.}*T}=\frac{V_0}{2\pi }$
  
  if you convert this to the width B, the result is: $\mathrm{B.}=\frac{2\pi }{U}*\frac{1}{V_0}*\frac{{\mathrm{P.}}_{\text{Max}}}{T}$
  
• 6) $\mathrm{B.}=\frac{2\pi }{U}*\frac{1}{V_0}*\frac{{\mathrm{P.}}_{\text{Max}}}{T}\mathrm{B.}=\frac{2\pi }{\underset{\text{constant}}{\underbrace{U}}}*\frac{1}{\underset{\text{CAN}}{\underbrace{V_0}}}*\frac{{\mathrm{P.}}_{\text{Max}}}{\underset{\underset{\propto \text{Max}\left(\frac{\mathrm{P.}\left(t\right)}{\mathrm{C.}\mathrm{D.}\left(t\right)}\right)}{\underset{\text{or}}{\propto \text{Max}\left(\dot{\mathrm{P.}}\left(t\right)\right)}}}{\underbrace{T}}}$
  

The particular relevance of the size of the maximum value of the change in the pressure signal for the estimation of the width of the collision object can also be represented on the model side and thus, for example, an impact of a pedestrian with a usually small width B compared to the width of the front of the vehicle from a collision with another vehicle differ, the approximation of the relative speed by the vehicle's own speed is therefore irrelevant for this consideration, because at a high speed of the collision object, the maximum value then usually results in a width B greater than the front of the vehicle.

A pedestrian protection device can thus be triggered in a pedestrian protection system when the evaluation unit determines a maximum value of the change in the pressure signal and compares it with at least one default value for pedestrian protection. For example, for the maximum value of the change in the pressure signal or the width B derived therefrom, in addition to a lower limit for the detection of a relevant impact, an upper limit is also provided for the assignment of an impact that is too strong for a pedestrian impact and the pedestrian protection device is only triggered in the area in between.

During the derivation, the maximum value is therefore evaluated on the basis of the vehicle's own speed determined beforehand or a relative speed between the vehicle and the impact object determined by means of an environment detection sensor.

Alternatively, the maximum value of the change in the pressure signal determined in this way can be used to infer the relative speed between the vehicle and the impact object or the severity of the impact, in particular if the impact width is estimated.

Assuming that the impact width B can correspond at most to the width of the front of the vehicle and assumes a width of, for example, 50% of the front of the vehicle for the assessment of a frontal impact, then equation 6 can of course also be converted to v ₀ and from the maximum value of Change in the pressure signal, this relative speed can be determined. Because of this relationship, the maximum value of the change in this pressure signal is also suitable for comparing the occupant protection using an evaluation unit and corresponding default values and triggering the occupant protection device as a function thereof.

Claims (9)

A method for impact detection on the basis of the signal of at least one pressure sensor which detects the pressure in a deformable cavity in the exterior of a vehicle and evaluates a pressure change normalized to the ambient air pressure as a pressure signal, and from this the type or a parameter of the impact is derived, characterized in that the change this pressure signal is detected, a maximum value (Max) of this change in this pressure signal is determined and this maximum value is taken into account in the derivation, and that in deriving the maximum value (Max) based on a previously determined vehicle speed or a relative speed between vehicle and vehicle determined by means of an environment detection sensor Impact object is assessed. Procedure according to Claim 1 , characterized in that after a minimum threshold (Δp0) of the pressure signal is exceeded, a time window is specified within which the maximum value (Max) is expected and the determination of the maximum value (Max) is aborted and the current value is used as the maximum value (Max), if the maximum value exceeds a specified value. Method according to one of the preceding claims, characterized in that if the change in the pressure signal decreases within the time window, the highest value achieved so far is used as the maximum value. Method according to one of the preceding claims, characterized in that if the change in the pressure signal continues to increase within the time window, the current value at the end of the time window is used as the maximum value. Method according to one of the preceding claims, characterized in that the width of the impact area or impact object is deduced from the maximum value of the change in the pressure signal. Method according to one of the preceding claims, characterized in that the relative speed between the vehicle and the impact object or the impact severity is deduced from the maximum value (Max) of the change in the pressure signal. Pedestrian protection system with at least one pedestrian protection device and a pressure sensor, a pressure change standardized to the ambient air pressure being generated in a deformable cavity in the exterior of a vehicle as the pressure signal, characterized in that an evaluation unit is provided to determine the maximum value of the change in the pressure signal and based on a previously determined own speed of the vehicle or a relative speed determined by means of an environment detection sensor between vehicle and impact object to evaluate and to compare with at least one default value for pedestrian protection and depending on this, the pedestrian protection device can be triggered. Occupant protection system with at least one occupant protection device and a pressure sensor, a pressure change standardized to the ambient air pressure being generated in a deformable cavity in the exterior of a vehicle as the pressure signal, characterized in that an evaluation unit is provided to determine the maximum value of the change in this pressure signal and based on a previously determined speed of the vehicle or a relative speed between the vehicle and the impact object determined by means of an environment detection sensor and compared with at least one default value for occupant protection and depending on this, the occupant protection device can be triggered. Protection system for occupants and pedestrians with at least one occupant protection device and at least one pedestrian protection device as well as a pressure sensor, a pressure change normalized to the ambient air pressure being generated in a deformable cavity in the outer area of a vehicle as a pressure signal, characterized in that an evaluation unit is provided to measure the maximum value of the To determine the change in this pressure signal and to evaluate it on the basis of a previously determined speed of the vehicle or a relative speed between the vehicle and the impact object determined by means of an environment detection sensor and to compare it with at least one default value for pedestrian protection and at least one default value for occupant protection deviating therefrom, and depending on this the protective devices can be triggered.

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