Measuring and testing – Speed – velocity – or acceleration
Reexamination Certificate
1999-09-30
2001-06-12
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
C701S070000, C303S121000
Reexamination Certificate
active
06244109
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device and a method for monitoring an acceleration sensor located in a vehicle.
BACKGROUND INFORMATION
A control device with an acceleration sensor and an error control unit for motor vehicles is described in German Patent No. 39 30 302. This control device includes a first acceleration sensor for detecting longitudinal accelerations and a second acceleration sensor, for example, for detecting transverse accelerations. The control device also includes a facility for recording the signals from the acceleration sensors and for deriving a data value on the basis of the two signals. The data value is compared to a preset comparison value in a further facility and an error in one of the sensor signals is detected. The data value is derived, for example, by adding up the acceleration signals or determined as the root of the sum of the squares of the acceleration signals.
With this monitoring method, the signals of both acceleration sensors are always used directly for sensor monitoring. This means, first of all, that an acceleration sensor cannot be monitored only on the basis of its own signal. In addition, there is no indication of how to prepare the acceleration quantity prior to monitoring so that it will be largely independent of driving maneuvers performed with the vehicle. In other words, it is not possible to monitor the sensor independently of vehicle movement.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a device and a method for monitoring an acceleration sensor located in a vehicle, with the device and method being used to monitor an acceleration sensor only on the basis of its own signal. Furthermore, it should be possible to monitor the acceleration sensor independently of driving maneuvers performed with the vehicle.
The device according to the present invention is used to monitor an acceleration sensor that is located in a vehicle and detects an acceleration quantity that describes an acceleration acting upon the vehicle. In particular, the acceleration sensor is a transverse acceleration sensor used to detect a transverse acceleration quantity that describes the transverse acceleration acting upon the vehicle.
To make acceleration sensor monitoring independent of driving maneuvers performed with the vehicle, and to make them largely independent of vehicle movement, the device advantageously includes averaging means used to generate a mean value of the acceleration quantity for a definable period of time. This mean value is largely independent of driving maneuvers performed with the vehicle. The averaging means are advantageously designed in the form of a low-pass filter. In particular, the low-pass filter has a high filter constant that is selected so that the mean value is largely independent of driving maneuvers performed with the vehicle. This makes it possible to monitor the acceleration sensor independently of vehicle movement, which means that the components of the acceleration quantity that are caused by vehicle movement or by vehicle maneuvers are filtered out by the averaging means. It is thus possible, for example, to determine whether the acceleration quantity, and therefore the acceleration sensor signal, has drifted out of its zero position, whether the acceleration sensor is properly seated in its mounting position, or whether the acceleration sensor is aging.
At this point what it means to monitor the acceleration sensor independently of driving maneuvers performed with the vehicle and make the mean value largely independent of driving maneuvers performed with the vehicle is examined. Each driving maneuver performed with the vehicle produces a change in the signal or acceleration quantity detected by the acceleration sensor. By generating a mean value of the acceleration quantity, the components of the acceleration quantity that are based on the driving maneuver are averaged. In other words, the mean value indicates the value of the acceleration quantity that would be obtained when driving the vehicle in a straight line. The value of the acceleration quantity when driving in a straight line is normally zero. If it is not zero, however, this means that a sensor malfunction has occurred (the sensor has aged or is not properly seated in its mounting position). During vehicle movement in any type of driving maneuver, the device according to the present invention can evaluate the mean value, thereby determining a malfunction in the acceleration sensor that would otherwise be detected only when driving in a straight line.
It is also advantageous to limit the increase in the acceleration quantity before the latter is supplied to the low-pass filter. One purpose of this is that it suppresses any jitter that may be present in the acceleration quantity. In addition, it also suppresses disturbances caused by a possible rocking contact. By limiting the increase, it is possible to determine that the acceleration quantity supplied to the averaging means, in this case the low-pass filter, was already filtered in advance.
The device contains monitoring means for monitoring the sensor. A comparison between the mean value of the acceleration quantity and a threshold value is carried out in these monitoring means. This comparison advantageously determines whether the amount of the mean value of the acceleration quantity is greater than the threshold value. A determination is made as to whether the acceleration sensor is defective based on this comparison. The acceleration sensor is defective if the amount of the mean value of the acceleration quantity is greater than the threshold value. The acceleration sensor is not defective if the amount of the mean value of the acceleration quantity is less than the threshold value.
A pointer quantity is advantageously used to indicate whether the acceleration sensor is defective. In the event that the acceleration sensor is defective, the pointer quantity is assigned a first value characterizing this fact. In the event that the acceleration sensor is not defective, the pointer quantity is assigned a second value characterizing this fact. On the basis of the monitoring means, this pointer quantity is used to notify, for example, a controller, that the acceleration sensor is defective.
Averaging makes it possible to filter out the components of the acceleration quantity caused by driving maneuvers from the acceleration quantity corresponding to the signal generated by the acceleration sensor. This means that the acceleration sensor can be monitored independently of vehicle movement. Variations in the acceleration quantity that are caused, for example, by turning the vehicle are therefore ignored when monitoring the acceleration sensor. This makes it possible, for example, to determine that the acceleration quantity has drifted from its zero position, the acceleration sensor is not properly seated in its mounting position, or the acceleration quantity has varied due to the acceleration sensor aging process.
Averaging makes it possible, for example, to eliminate changes in the acceleration quantity caused by steering movements. In other words, the effect of averaging is that the vehicle seems to be always driving in a straight line, at least based on the mean value, i.e., the filtered acceleration quantity. If the acceleration quantity, for example, drifts out if its zero position, the acceleration quantity continuously assumes a value other than zero, which is reflected by the mean value of the acceleration quantity. Consequently, a comparison between the mean value and a threshold value makes it possible to detect a malfunction in the acceleration sensor that was caused by drifting from the zero position or improper seating in the mounting position.
With the device according to the present invention, the error entry made in the pointer quantity can be advantageously reversed. This is accomplished by checking the condition of whether the amount of the mean value of the acceleration quantity has dropped back below the threshold value for a definab
Braun Guenter
Kohler Rolf
Kottmann Matthias
Schmitt Johannes
Zeobele Andreas
Kenyon & Kenyon
Moller Richard A.
Robert & Bosch GmbH
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