In the known emergency call system described in the introduction, the emergency call is transmitted only if a sensor registers a collision.
解答例
For this purpose, the air bag signal is used, for example.
In contrast to this, the emergency call system according to the invention can be used to establish that the collision is no longer avoidable even before it occurs.
Consequently, the emergency call can therefore also be activated even before the collision occurs, that is to say at an instant when the emergency call system is still operable.
To this end, the relative speed of the motor vehicle in relation to another vehicle or an obstacle is determined in the same way as the distance of the motor vehicle from the other vehicle or obstacle.
If the relative speed exceeds a predetermined value for a given distance, it can be assumed that a collision is unavoidable.
Hence, for each distance between the motor vehicle and another vehicle or an obstacle, a maximum permissible limit value is defined for the relative speed.
This limit value can be determined in the arithmetic and logic unit using a defining equation for the respective distance.
However, it is also possible to store a plurality of value pairs, in each case for a distance and an associated maximum permissible relative speed, in a memory element, the memory element being connected to the arithmetic and logic unit.
The arithmetic and logic unit then retrieves the value pairs which are nearest to the current distance and uses them to determine the maximum permissible relative speed of the vehicle, for example by means of interpolation.
In addition, there may be a variety of such limit values for the maximum permissible relative speed.
By way of example, these can allow for the attributes of the road.
Thus, a higher limit value is permissible, for example, for a dry road than for a wet road or snow-covered road.
To determine the attributes of the road, the vehicle must be provided with appropriate sensors.
As an example, dry and wet roads can be distinguished optically using the portion of light reflected from the road.
Although, in principle, it is also possible to locate the motor vehicle transmitting an emergency call, the vehicle position is preferably transmitted to the receiving station together with the emergency call.
To this end, the vehicle is provided with, in particular, a navigation system which is known per se, in which case the position can be determined in a known manner using both satellite navigation (GPS navigation) and dead-reckoning navigation.
Amongst the various functions of a navigation system, only position determination is of importance to the emergency call system, and not route calculation.
Hence, it is also sufficient, for example, to use only a receiver with an evaluation unit for GPS navigation, rather than a full navigation system.
To prevent false alarms, in one particular embodiment, the arithmetic and logic unit in the emergency call system is connected to at least one sensor for detecting an accident.
The emergency call system also contains a timer which is connected to the arithmetic and logic unit and is started when the emergency call is activated.
If there is no signal signaling a collision from the sensor at the instant the timer runs out, the emergency call is automatically revoked.
If, for example, a driver still manages to steer clear of an obstacle and thus avoid a collision despite the relative speed being above the limit value, the revocation of the emergency call prevents auxiliary forces from being alerted.
The sensor for detecting an accident can, in particular, be an acceleration sensor or a temperature sensor.
Since acceleration sensors are already provided for releasing the air bag in motor vehicles, it is particularly advantageous if the emergency call system is connected to said acceleration sensors.
Thus, if the air bag is not released by the time the timer runs out, it is assumed that there has been no collision and the emergency call is revoked.
So that the revocation of the emergency call is not dependent on the signal from an individual sensor, a plurality of sensors can be provided.
If a temperature sensor is provided, a vehicle fire, in particular, can also be registered.
To activate a sufficient number of rescue forces, a further provision, in a preferred embodiment, is that the arithmetic and logic unit in the emergency call system is connected to seat-occupancy sensors, so that the number of occupied motor vehicle seats can be transmitted with the emergency call.
An important integral part of the emergency call system according to the invention are the measuring means for determining the relative speed and the distance of the motor vehicle in relation to another vehicle or an obstacle.
