GB2238416A

GB2238416A - Circuit arrangement for detecting signal faults

Info

Publication number: GB2238416A
Application number: GB9023173A
Authority: GB
Inventors: Wilfried Burger; Werner Nitschke; Peter Taufer; Hugo Weller
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1989-11-23
Filing date: 1990-10-24
Publication date: 1991-05-29
Also published as: DE3938777A1; JPH03201752A; GB9023173D0

Abstract

For the purpose of detecting signal faults in a safety system of a motor vehicle, in particular in a restraint system, the analogue signals fed to an analogue-to-digital converter 1 are monitored to determine whether faults arise due to strong external electromagnetic fields. An identification which is stored in a memory 3 and assigned to reference values of the signals on the input side is used for error detection. <IMAGE>

Description

is Circuit arrangement for detectinq sicnal faults

Prior art

The invention relates to a circuit arrangement for detecting signal faults according to the generic type of the main claim.

In safety system of motor vehicles it is often of great importance to detect disturbing influences which are brought about by external electromagnetic fields. in order to avoid incorrect triggerings of safety systems. This is particularly important in restraint systems of a motor vehicle, in which the signals of an acceleration sensor are acquired via an analogue-to-digital converter and used to detect an accident for the purpose of activating a restraint system, in order to inflate, for example, an air bag in a fraction of a second.

To detect disturbing influences the signals emitted by sensors can be transmitted doubly via different signal lines and be tested for identity and thus for correctness by comparison with one another. However, such double signal transmission is very costly.

Adva,tages of the invention In the computer system of a motor vehicle there is always a memory which contains operation-specific data. Thus. only a very small expenditure in terms of memory is required to store the characteristic data of at least one of the analogue signals in the memory and to perform an error detection by means of this characteris tic data. In this process. the computer constantly compares the characteristic data with the associated digital signals received from the analogue-to-digital converter and can generate an error detection in the event of an inadmissible deviation. The error 1 is detection is used in the computer system to avoid an erroneous activation of the restraint system.

The characteristic data stored in the memory can be characteristic data of sensor signals or of a reference signal. If the characteristic data are assigned to a sensor signal, it is, however, necessary that, for example.. predetermined threshold values of the sensor signal are known. These threshold values can be stored as characteristic data in the memory, so that it is detected that a fault has occurred if the threshold values are exceeded. However, an additional analogue reference signal is preferably fed to an input of the analogue-todigital converter, the voltage value of which is stored in the memory as characteristic data item. If the analogue reference signal is degraded by a strong transmitter,, by lightning discharge or by other corresponding external influences, the computer detects this fault by comparison with the stored digitized voltage value. It is to be taken into account here that the signals fed to the analocjue-to-digital converter can mutually influence one another by crosstalk, that is to say that a disturbing influence occurring on one line can occur at least in a weakened form on the other input lines or inputs. It is therefore sufficient to monitor one of the inputs in respect of electromagnetic disturbing influences arising, in order to be able to draw conclusions for all the inputs in respect of faults arising. This is utilized in the circuit arrangement according to the invention in order to be able to detect such disturbing influences with a small degree of outlay in terms of circuitry.

Drawing The invention is explained below with reference to the drawing, in which:

Figure 1 shows a block circuit diagram of an exemplary embodiment with reference signal and Fig-ure 2 shows a sequence diagram for the test routine.

In Figure 1,, a motor vehicle safety system which 1 is has an analog-ue-to-digital converter 1, a computer 2 constructed as a microprocessor and a memory 3 is illustrated in the form of a block circuit diagram. Sensors S1, S2 are connected to the inputs of the analoguetodigital converter 1 via signalling lines 4, 5 and a reference voltage source RS is connected to said inputs via a signalling line 6. The refer ence voltage source delivers an analog-ue reference voltage UA to the analogue-to-digital converter 1, said reference voltage being fed as digital signal UD to the computer 2. The computer 2 is continuously connected to the memory 3, in which a digital identification KU is stored which identifies the voltage value of the reference voltage UA.

The signals of the sensors S1, S2 are transmitted in a corresponding manner to the computer 2 which controls the safety system in a manner known per se as a function of the sensor signals. The sensors S1, S2 can serve [lacuna) impact sensors, acceleration sensors for detecting an accident, so that the computer 2 can trigger a restraint system, for example an air bag, on the basis of corresponding sensor signals. In order to avoid incorrect triggerings of the restraint system. a routine for error detection is carried out by the computer 2.

Furthermore, further characteristic data KU1.

KU2, for example relating to sensor S1, which identify threshold values of the sensor signals of the sensor S1 can be stored in the memory 3. These characteristic data KU1,r KU2 can be evaluated additionally, or if appropriate also alone, in order to detect signal faults due to external electromagnetic influences. When the charac teristic data KU1, KU2 are exceeded, an 'error detec tion can also be triggered by the computer 2.

In Figure 2. this routine for detecting a disturbing influence due to external interference fields is explained with reference to a sequence diagram. When the vehicle is started, the continuously running routine for detection of a disturbing influence is also started. Firstly. the stored identification KU is compared with the digital signal value UD. By forming the difference Ku

4 - UD = X, with 'W' a value is obtained which is subsecjuently tested to determine whether this value is smaller or eclual to a maximum admissible difference XM. If the value X is still within the admissible threshold, no error detection is triggered. Only if the value X exceeds the value XM in value is an error detection FK generated in the computer 2. This error detection FK causes no activation of the safety system to occur as long as the error detection FK is present. The error detection FK is then not reset again at the RESET input until the magnitude of the value X lies again within admissible thresholds. The safety system can then be activated again.

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Claims

1 1. Circuit arrangement for detecting signal faults in a computer system with analogue-to-digital converter, in particular in a motor vehicle safety system, the analogue-to-digital converter having a plurality of analogue inputsi at which analogue signals are present, and feeding on the output side the digitized signals to a computer which has access to a memory,, characterized in that predetermined characteristic data (KU) of at least one of the analogue signals (UA) are stored in the memory (3) and in that the computer (2) continuously compares the characteristic data (KU) with the associated digital signal (UD) emitted by the analogue-to-digital converter (1) and triggers an " error detection (FK) in the case of inadmissible deviation (X) from the charac teristic data (KU).

2. Circuit arrangement according to Claim 1. characterized in that a reference voltage (UA) is present at an analogue input of the analogue-todigital converter (1), the digitized voltage value of said reference voltage being stored as characteristic data item (KU) in the memory (3).

13 Circuit arrangement according to Claim 1, characterized in that the threshold values of an analogue signal (S1), the voltage range of which is known., are stored in digital form as characteristic data (KU1. KU2) in the memory.

4. A circuit arrangement for detecting signal faults in a computer system substantially as herein described with reference to the accompanying drawing.

Published 1991 at The Patent Office. State House. 66/71 High Holborn. London WC I R4TP. Further copies may be obtained from Sales Branch. Unit 6, Nine Mile PoinL Cwmfelinfacb. Cross Keys, Newport, NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray, Kent.