SPECIFICATION

AREA OF INVENTION

The invention at hand is concerned to a method for checking a capacitor or a capacitive sensor of a steering system.

BACKGROUND OF THE INVENTION

As state of the art it is already well-known to use capacitors and capacitive sensors for steering systems.

SUMMARY OF THE INVENTION

A steering system comprises a huge amount of capacitors and capacitive sensors. Even the malfunction of one single capacitor can lead to failure of the whole system.

Therefore, a task is to prevent malfunction of a steering system because of the failure of a capacitor or a capacitive sensor.

As a first variant of the invention it is provided a method for checking a capacitor or a capacitive sensor of a steering system, comprising the steps: charging the capacitor or the capacitive sensor, Measuring the voltage line of charging and/or discharging and Evaluating the voltage line.

It is also possible to apply the method for the discharging process.

Exemplary applications will be described as follows: According to an exemplary variant of the invention it is provided a method, comprising the step: Evaluating the voltage line, wherein a low and a high threshold is applied. By using only two thresholds for the method, it is very easy to apply the method.

According to an exemplary variant of the invention it is further provided a method, comprising the additional step: if the voltage line is increasing during the charging period, then the capacitor or capacitive sensor is ready for operation.

It is also possible to use the discharging voltage line for applying the method.

According to an exemplary variant of the invention it is more further provided a method, comprising the additional step: If the voltage line is nearly equal to the low threshold, then the capacitor or the capacitive sensor is shorted and not ready for operation.

According to an exemplary variant of the invention it is provided a method, comprising the additional step: if the voltage line is nearly equal to the high threshold, then the capacitor or the capacitive sensor is opened and not ready for operation.

According to an exemplary variant of the invention it is further provided a method, wherein the low threshold is between 0 Volt to 2 Volt, especially 0 Volt to 1 Volt. The thresholds depend upon the tolerance of supply voltage and used resistors.

Therefore, these values are only typical examples, which can differ depending on the special electrical situation.

According to an exemplary variant of the invention it is more further provided a method, wherein the high threshold is between 3 Volt to 5 Volt, especially 4 Volt to 5 Volt or 10 Volt to 12 Volt, especially 11 Volt to 12 Volt or 2 Volt to 3 Volt, especially 2.5 Volt to 3 Volt. According to an exemplary variant of the invention it is provided a method, wherein there are 1, 2, 3, 4, 5, 6, 7 or more samples, comprising the step: If the majority of the samples determine the capacitor or capacitive sensor as open, it is assumed, that the capacitor or capacitive sensor is open and if the majority of the samples determine the capacitor or capacitive sensor as short, it is assumed, that the capacitor or capacitive sensor is short and if the majority of the samples determine the capacitor or capacitive sensor as ready for operation, it is assumed, that the capacitor or capacitive sensor is ready for operation. The samples can be read by an ADC (Analog Digital Converter). When the capacitor or capacitive sensor is charged for the time toN, ADC read the capacitor or capacitive sensor charging voltage in different time intervals, e.g. tl, t2, t3... (within toN time). ADC reads the capacitor or capacitive sensor charging voltage for those time intervals (samples) to determine the voltage line behavior like "short", "open" or "normal".

According to an exemplary variant of the invention it is further provided a method, wherein the number of samples is odd, especially 3, 5 or 7.

According to an exemplary variant of the invention it is more further provided a method, wherein a capacitive sensor is under check, wherein the sample is taken during a time period of not working and/or wherein the steps are executed before starting the steering system.

The term "not working" means especially that the system, to which the capacitive sensor belongs, is not in normal operation mode.

As an idea of the invention it can be regarded to provide a method for detecting the malfunction of a capacitor or a capacitive sensor of a steering system by charging and discharging the capacitor or capacitive sensor concerned. The load currents, which were charged and discharged will be evaluated. In case the load current, which was charged is small, there is an open circuit. In case the load current, which was charged is high and the load current, which was discharged is small, there is a short-circuit. Otherwise, the capacitor or capacitive sensor is ready to work. The invention can be summarized as a diagnostics of the charging/discharging performance of a capacitor or a capacitive sensor under control, wherein the charging/discharging voltage will be applied for a short time and the same charging/discharging voltage is read by an ADC (analog digital converter). The diagnostics is applied usually before the whole system starts to work in normal mode in order to avoid a failure mode of the steering system concerned. A failure mode of the device under control can be identified if a short circuit or an open circuit can be detected. A failure mode of the device can also be identified in normal operation for short time without disturbing system normal operation. SHORT SPECIFICATION OF THE DRAWINGS

Further details will be described with the help of the following figures, wherein the figures describe: Fig. 1 a capacitor diagnostics circuit diagram,

Fig. 2 a capacitor diagnostics timing sequence,

Fig. 3 a capacitance sensor diagnostics circuit diagram,

Fig. 4 a diagnostic timing sequence,

Fig. 5 a flow chart and Fig. 6 a further flow chart.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Fig. 1 depicts a transistor resistor topology #1 1 and a transistor resistor topology #2 2 with two transistors and one resistor and a mosfet #2 3, a microcontroller 4 and a mosfet #1 5. Fig. 1 shows a circuit, which applies a diagnostics strategy for a capacitor as follows: capacitor C 27 is used as a buffer capacitor, Mosfet #1 5 is in series, for example for reverse polarity protection, which is usually on switched. The capacitor C 27 is under observation. The resistor R is used to charge the capacitor C 27 for short time (ΪΟΝ) and microcontroller 4 is applied as control unit for the mosfet #1 5. The resistors 25 are used as resistor divider to transform the voltage of the load 26 into readable values for the ADC of the microcontroller 4. The circuit can be used to apply a diagnostics strategy for capacitors as follows, wherein it is preferred to apply the strategy before the system starts with normal operation mode. At first mosfet #1 5 is off- switched and mosfet #2 is on-switched to charge the capacitor C 27 for a time toN. Next, the load is switched off to avoid load inductance property in charging. Fig. 2 shows a voltage line 6, if the capacitor is opened, a voltage line 8, if the capacitor is normal and a voltage line 10, if the capacitor under surveillance is short. The lines 7 and 9 define thresholds. Therefore, the area A illustrates the region, which shows, that the capacitor or the capacitive sensor under observation is opened. The region C depicts the area, which stands for a shorted capacitor or shorted capacitive sensor. The area B reflects the region, where the voltage line for a normal capacitor or capacitive sensor should be.

Fig. 3 shows an Analog Digital Converter 11, a transistor topology 12, an analog switch #1 13, an amplifier 14, a filter 15 and an analog switch #2 16. The capacitive sensor 28 is under observation.

Fig. 4 shows a voltage line 17 if capacitance sensor is opened, a voltage line 19 if capacitance sensor is normal, a voltage line 21, if capacitance sensor is short and lines 18 and 20, which represent thresholds. Therefore, the area A illustrates the region, which shows, that the capacitor or the capacitive sensor under observation is opened. The region C depicts the area, which stands for a shorted capacitor or shorted capacitive sensor. The area B reflects the region, where the voltage line for a normal capacitor or capacitive sensor should be. Fig. 5 shows a flow chart of an inventive method, wherein at first a capacitor or a capacitive sensor is charged 22. If the resulting voltage line is a high threshold or higher 23 then the capacitor is not ready for operation 26. If the voltage line is a low threshold or underneath 24 then the capacitor is also not ready for operation 26.

Otherwise the capacitor or capacitive sensor is ready for operation 25. Fig. 6 shows a method, wherein there are 1, 2, 3, 4, 5, 6, 7 or more samples 29, comprising the step: if the majority of the samples determine the capacitor or capacitive sensor as open 32, it is assumed, that the capacitor or capacitive sensor is open 33 and If the majority of the samples determine the capacitor or capacitive sensor as short 30, it is assumed, that the capacitor or capacitive sensor is short 31 and If the majority of the samples determine the capacitor or capacitive sensor as ready for operation, it is assumed, that the capacitor or capacitive sensor is ready for operation. The number of samples can be odd, especially 3, 5 or 7. The samples can be taken during a time period of not working, especially a period of no normal operation mode, and/or wherein the steps are executed before starting the steering system.