Acceleration sensor for vehicles.

p0001The invention relates to a sensor according to the preamble of claim 1.

p0002Such a sensor is known from DE-OS 36 09 841 and GB-A 2022822nd Within a pyramidal or conical as housing is a gas disposed as a display medium, which sits at rest above the liquid. Accelerations are determined by means of a transceiver path that leads above the liquid level and is located in the station at the geodetically highest point of the housing. Recipients sit side of the housing and receiving the light reflected at the surface of the liquid or by these refracted radiation.

p0003Such a sensor is problematic in several respects. Due to the relatively large mass of the moving fluid and the manifold interactions between it and the housing of the mirror is subject to constant, totally inconsistent and unpredictable movements generally. The consequence of this is that the receiver will often already briefly irradiated with transmission power by the overlapping of the manifold, generally relatively undamped movements, although the acceleration is to be detected far below a critical limit value. Thus, such a sensor is likely to be only limited operational. This applies for example for triggering occupant protection devices such as airbags or rollover bar, which may be triggered irreversible only when there actually was such a critical acceleration value.

p0004The known sensor requires a sufficiently effective additional electronic equipment that eliminates the mentioned interference. This is usually only by means of filters and integration elements possible. Both require a certain time commitment with the result that such a sensor is not critical in terms of its temporal responsiveness.

p0005The invention has for its object to provide a sensor of the aforementioned type which is of simple construction and allows reliable and rapid detection of an acceleration to be detected value.

p0006The invention achieves this object by the characterizing features of claim 1.

p0007Essential to the present invention is that the display medium within the liquid moves in dependence on acceleration. Vibrations, if they can ever occur in the liquid have no effect on the movement and position of the display medium, because the liquid compensates for these vibrations in himself. The position of the display medium thus provides an accurate indication of the acceleration to be detected. This is particularly true when the difference in density between the liquid display medium and is sufficiently large. The setting of the display medium is determined by the resultant acceleration of the liquid. This acceleration is made up of the gravity and the optionally present dynamic acceleration component of the liquid in the manner specified by the orientation of the spirit level direction and provides the impetus for the display medium.

p0008The formation of the sensor is possible in various ways. So it can be a conductivity sensor is immersed in an electrically conductive liquid. The display medium is different in its conductivity of the fluid and, for example, has no conductivity. The sensor is then arranged so that the display medium is located at the acceleration to be detected value at the sensor location. Thus, the value of the acceleration detected by the conductivity jump in this case.

p0009A structurally particularly advantageous embodiment of the sensor consists of a transmitter / receiver path for electromagnetic or acoustic waves, which is oriented so that the display medium is the acceleration to be detected value therein. So that there is in this case a change in the attenuation of the transmitter / receiver circuit. Usually then increases the damping. This is due to the two-time passage of the radiation through the boundary layer between the liquid and a display medium.

p0010Due to the simple design structure, it is also possible to determine a plurality of differently directed acceleration components by means corresponding to a plurality of such sensors. In this case, each of the sensors is used to determine the relevant acceleration in the corresponding direction. With appropriate orientation it is also possible to choose the number of sensors less than the number of the components to be determined acceleration.

p0011A structural configuration of the invention is possible by forming the housing for the sensor as a straight tube vial, which is inclined to the acceleration to be determined. Is it, for example, a matter of determining a longitudinal acceleration of the vehicle, so the tube is inclined to the longitudinal direction. The display medium is located in the rest position or during acceleration of free movement of the vehicle at the geodetically highest point of the tube and is with the additional acceleration, determined from the vectorial addition of gravity, and dynamic acceleration of the liquid that provides the buoyancy for the display medium.

p0012Using a thus constructed sensor, it is also possible to determine a plurality of mutually perpendicular acceleration components. For this purpose, the tubes are aligned with a common vertex towards. The transmitter / receiver paths of the individual sensors extend toward a common end point, which is with respect to the individual tubes and the projection point of the apex of the plane in which lie the acceleration components.

p0013Other means to improve the function of the acceleration sensor, the subject of the claims 7 to 11 are an advantageous design configuration can be found in claim 12, serve the means to do so, and then trigger an occupant protection device, when the vehicle is in a zero gravity at least close coming and therefore particularly critical state.

p0014In microgravity, the acceleration values ​​in the motor vehicle are relatively low. Nevertheless, it is already as during freefall needed to trigger the occupant protection device, since at the completion of the weightless condition often extremely high acceleration values ​​occur (collision). By development of the invention is achieved that during the weightless condition already the occupant protection device comes into action, so as to provide adequate protection of the vehicle occupant at the end of weightlessness.

p0015Because sometimes a gravity close coming condition of the vehicle is achieved during normal driving conditions, the described in claim 8 of the invention is used to distinguish between such situations "normal" and "critical". To avoid an unnecessary triggering of the occupant protection device in such situations that occur, for example when driving over a crest, the duration of the critical state is determined by means of a timer. If the duration is small, that is only a very short in terms of time-critical state, so should not be triggered, the occupant protection device.

p0016The various preferred ways to substantiate the moving status sensor, are indicated in the claims 9 to 11 in detail.

p0017A distance meter provides the state of weightlessness set a distance from a surface, which is well above the normal value. The sensor for the vertical acceleration gives a value close to zero when weightless state. Finally, the rebound of one or more of the vehicle wheels, if it is equal to the maximum possible value, a good indication of the condition of weightlessness.

p0018Although is known from DE-PS 35 45 874 a safety device for a roll bar of a motor vehicle which is controlled by a wheel suspension sensor. It is not considered contrary to the invention, the state of free fall, as the signal of the wheel suspension sensor only becomes effective if the same appeal to a actuated when a certain inclination exceeded tilt switch. A functional relationship with the inclination of the motor vehicle, however, is often not given the weightless state.

p0019In the drawing, embodiments of the invention are shown.

p0020It shows<ul><li>Fig.1 A first embodiment of an inventive sensor for more acceleration,</li><li>2 shows an alternative to the sensor of Fig. 1 for two equal and opposite acceleration values,</li><li>Figure 3 is a further sensor device schematically for determining a rollover and an extreme acceleration in the longitudinal direction of the vehicle and</li><li>4 shows a further embodiment in which also the also the condition of weightlessness is considered.</li></ul>

p0021In the embodiment of Fig. 1 is a circular tube bubble 1 is used as the acceleration sensor of a vehicle. The use of the sensor for example is possible in conjunction with a device for body roll or level stabilization for detecting the longitudinal or transverse force or in conjunction with a safety device such as airbag or roll bar to detect a critical acceleration value.

p0022The dragonfly 1 essentially comprises a housing 2 with disposed therein liquid 3. This is, for example, water or alcohol, which, if necessary, prepared in accordance with the common conditions of use of the motor vehicle, remain liquid. In the liquid 3 there is a display medium which is opposite to the liquid 3 has a lower specific gravity and a significantly smaller volume and does not react with these chemically or physically.

p0023The display medium, which is commonly is the so-called. Bubble 4 in dependence on acceleration takes a the highest point. Without dynamic accelerations, this is the geodetically highest point. This is shown in parts a) and c) for a flat or inclined position of the sensor.

p0024If a dynamic transverse acceleration component in the direction of the dragonfly 1 added, the result is the setting of the bubble 4 from the vectorial addition of gravitation and this acceleration component of the liquid 3. This is in parts b) and d) for a Transversalbeschleunigungskomponente towards a arrow a shown.

p0025The position of the air bubble 4 is detected by means of a transmitter / receiver path 5 and 6, respectively, each with a transmitter 5 'or 6' and a receiver 5˝ and 6˝. The location of the lines 5 and 6 is so chosen that the air bubble 4 passes just in this route in which to be detected value of the acceleration, thereby changing the attenuation of the radiation received significant.

p0026If it is necessary to identify several rectified transversal acceleration component, so this can be arranged at the Dragonfly 1 with corresponding location several transmitter / receiver distances corresponding to the distances 5 and 6 respectively.

p0027. In the embodiment of Figure 2, instead of the circular vial 2 two straight tubes Dragonfly 1 'at an angle (here: 66 °) set, tipping the motor vehicle in the static case in which. Within the dragonflies 1 'respectively bubbles 7 and 8 are provided to the liquid 9 and 10 within the vial 1' experienced a boost.

p0028The vials 1 'are located in a housing 11 in which further comprises two light emitting diodes 12 and 13 are arranged as a transmitter to a common receiver fourteenth In one resulting from a dynamic and / or static acceleration acceleration of dragonflies 1 ', which reaches a critical value, there is an interruption between the transmitters 12 and 13 and the receivers 14 existing transmitter / receiver distances. This gives the receiver 14 a correspondingly altered in the intensity signal. This can be used as a triggering signal for a safety device, such as an extendable rollover bars. By nested clocking the channels 12 and 13, the page can also be detected by the imminent overturning or rollover of the vehicle.

p0029Through a relative to the longitudinal direction of the vehicle to a 90 ° rotation Replacing the dragonflies 1 ', the sensor device shown in FIG. 2 are also used to detect accelerations in the longitudinal direction of the vehicle and, for example, trigger airbags.

p0030In the embodiment of FIG. 3 three dragonflies (not shown) in accordance with the dragonflies 1 'of Fig. 2 inclined towards each other and provided with common apex S toward the drawn straight lines 14, 15 and 16. The inclination of the three dragonflies is such that the projected angle of inclination of dragonflies on the main planes, which are perpendicular to the longitudinal and transverse axis, are equal to the critical angles for a rollover in longitudinal and transverse directions. This makes it possible to manage instead of initially deemed necessary four dragonflies with only three dragonflies. In addition, when using a synchronized transmission mode corresponding transmitter, which may be arranged as shown in Fig. 2 the side of the vial and a common, at the foot of the solder arranged from the vertex S on the base plane receivers work, the direction can be detected in the overturning occurs. Accordingly, a suitable safety device, as described, placed in position or to effect.

p0031Fig. 4 shows a control apparatus for the occupant protection device which can be triggered by the sensor 1 and, independently thereof from a moving status sensor 22. This is symbolized by an OR-functional member.

p0032The motion state sensor 22 may, for example, responsive to the vertical acceleration of the vehicle and be formed together with the sensor device 1 as a compact unit 23rd In the simplest case, to the sensor 22 to a scale 24, with the weight of a mass body 25 is determined.

p0033Under normal driving conditions, the balance displays 24 at a value which fluctuates around the value of the actual weight. The fluctuations are caused by transient relative small vertical accelerations experienced by the motor vehicle during driving operation.

p0034Loses the vehicle contact with the ground, so there is set a state of motion, which is at least similar to the weightlessness. The balance 24 now provides a value in the "ideal case", ie the uninterrupted free fall, is equal to zero or lies within a small range around this value.

p0035The controller recognizes the state of weightlessness. Keeps this a certain time, for example, 100 msec. , so triggered by the control apparatus of the airbag or of the roll bar and is brought into function. The specified time period is determined with the aid of a timer 26 via which the output signal of the scale 24 is guided.

p0036The triggering of the occupant protection device by the motion state sensor 22 is independent of the possible initiation by the acceleration sensor 1, and thus, when it has established no critical value of the measured acceleration. This ensures that under all possible states of motion of the motor vehicle safety device is triggered in time and performed their function safely.

p0037Instead of the illustrated horizontal similar driving condition sensor 22 may also be by means of a distance meter, not shown, which determines the distance of the vehicle from the road surface and a wheel suspension sensor, which responds when maximum rebounded vehicle, be appreciated that the motor vehicle contact with the road lost or only has a very low and the state of free fall comes close contact with the road.