METHOD FOR DETERMINING THE DUTY FACTOR OF A PULSE-WIDTH-MODULATED SIGNAL AND VEHICLE CONTROL UNIT

Abstract

The present invention provides a method for the redundant measurement of the duty factor of pulse-with-modulated signals 12 via a vehicle control unit. According to the method, a direct determination of the duty factor of the signal 12 is performed by way of periodic sampling.

Claims

1. A method for the redundant determination of the duty factor of a pulse-width modulated signal via a vehicle control unit, wherein the signal is generated and/or provided by at least one sensor, said method comprising: measuring time durations of a state of the signal via a capture/compare unit (CCU), and periodically sampling the signal by the vehicle control unit in order to determine the duty factor.

2. The method as claimed in claim 1, wherein the signal comprises multiple possible states.

3. The method as claimed in claim 2, wherein a ratio of the time duration of the states represents the duty factor of the signal.

4. The method as claimed in claim 1, wherein a length of one or each state of the signal is determined by counting clock pulses of a clock signal, during which the signal is in a particular state.

5. The method as claimed in claim 1, wherein the duty factor of the signal is determined and/or calculated from a ratio of the duration of multiple states of the signal.

6. The method as claimed in claim 1, further comprising measuring at least one complete cycle of the signal.

7. The method as claimed in claim 1, further comprising regularly sampling the signal in fixed intervals or at a constant frequency.

8. The method as claimed in claim 1, further comprising generating and/or utilizing a periodic clock signal to periodically scan the signal.

9. The method as claimed in claim 8, wherein the signal is sampled during each clock event and/or every time after an established number of clock events.

10. The method as claimed in claim 1, wherein a clock signal has a constant clock rate.

11. The method as claimed in claim 10, wherein the clock intervals are constant or are equally long.

12. The method as claimed in claim 1, wherein a clock signal has a higher clock rate or modulation frequency than the signal.

13. The method as claimed in claim 12, wherein the clock signal has a clock rate or modulation frequency which is higher than the signal by at least approximately one order of magnitude.

14. The method as claimed in claim 1, wherein the duty factor of the states depends on an actuation of the sensor.

15. The method as claimed in claim 1, wherein the duty factor of the states depends on an extent and/or a speed of an actuation of the sensor.

16. The method as claimed in claim 1, wherein the steps for determining the duty factor are carried out independent of each other and/or are based on different principles.

17. The method as claimed in claim 1, further comprising determining a modulation frequency of the signal from the duty factor of the signal.

18. A vehicle control unit for carrying out the method of claim 1, said vehicle control unit comprising at least one recording device for recording at least one pulse-width-modulated signal, which is provided and/or generated by at least one sensor, wherein the recording device determines the duty factor of the signal, wherein the recording device is designed for periodically scanning a state of the signal in order to determine the duty factor of the signal.

19. The vehicle control unit as claimed in claim 18, further comprising a device for generating and/or evaluating a periodic clock signal to trigger the periodic scan of the signal.

20. The vehicle control unit as claimed in claim 18, wherein an interrupt request or an interrupt of the vehicle control unit is provided as a clock signal for triggering the periodic scan of the signal.

21. The vehicle control unit as claimed in claim 18, wherein the signal has multiple states, wherein a ratio of a duration of the states is used as a basis for calculating an actuation of the at least one sensor.

22. The vehicle control unit as claimed in claim 21, wherein the ratio of the duration of the states is used as a basis for calculating an extent and/or speed and/or acceleration of an actuation of the at least one sensor.

23. The vehicle control unit as claimed in claim 18, wherein at least one counter is provided for a particular number of clock pulses of a state of the signal.

24. The vehicle control unit as claimed in claim 18, wherein a redundant scan and/or determination of the duty factor of the signal is provided.

25. The vehicle control unit as claimed in claim 18, wherein multiple independent and/or differently functioning devices or methods for determining the duty factor of the signal are provided.

26. The vehicle control unit as claimed in claim 18, wherein a determination of a modulation frequency of the signal on the basis of the duty cycle thereof is provided.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The invention is described in greater detail below with reference to the accompanying figure, in which:

[0035] FIG. 1 shows a vehicle control unit for the redundant determination of the duty factor of a pulse-width-modulated signal according to the prior art;

[0036] FIG. 2 shows a vehicle control unit according to the invention for the redundant determination of the duty factor, and

[0037] FIG. 3 shows one representation of a pulse-width-modulated signal having an associated clock signal.

DETAILED DESCRIPTION

[0038] The vehicle control unit of the exemplary embodiment described herein is a brake control unit 10. The brake control unit 10 is used for initiating and controlling braking operations in a vehicle which is not shown here, for example, a truck or a bus. Inter alia, the brake control unit 10 contains a microcontroller, which is not represented here. The microcontroller performs the actual measuring, control, and monitoring tasks.

[0039] In the prior art, the vehicle comprises at least one source of a signal 12, i.e., a so-called signal emitter or a signal transmitter. Two such signal transmitters are each designed as a brake signal transmitter 14 in this case. The actuation of a corresponding device, such as a brake pedal 16 in this case, yields information regarding a braking demand of a driver of the vehicle, which is not shown here and in which the brake control unit 10 operates. The brake control unit 10 comprises an input for the processing of the signal 12. As soon as a braking demand is detected, a braking operation must be initiated immediately.

[0040] Initially, for that purpose, the information regarding the actuation of the brake pedal 16 is converted via the brake signal transmitter 14 into a pulse-width-modulated signal 12. Depending on how strong the braking effect is intended to be, the driver usually varies the extent or the travel of the actuation of the brake pedal 16. This means that, when the brake pedal 16 is slightly deflected, the intention is to achieve merely a low braking effect, while a greater deflection of the brake pedal 16 indicates the intention to achieve a great braking effect. The resultant signal 12 therefore represents a value which is proportional to the actuation of the brake pedal 16.

[0041] This is achieved via a pulse-width modulation of the signal 12. In this case, two different states 18 and 20 are usually provided. The states 18 and 20 are generally two different voltage levels. The duration of the two states 18 and 20 can be varied, wherein the total duration of the two states 18 and 20, taken together, is generally constant. The ratio of the duration of the first state 18 to the duration of the second state 20 therefore yields the so-called duty factor of the signal 12.

[0042] This ratio of the two states 18 and 20 then yields, overall, a value which is proportional to the pedal actuation. Actually, for this purpose, the lengths or time durations of the two states 18 and 20 with respect to one another are expressed as a ratio. The longer the signal 12 in the state 18 is, the shorter the signal 12 in the state 20 is, since the total length or the total duration of one cycle of the pulse-width modulation is typically constant. The durations of the two states 18 and 20, which have been expressed as a ratio, therefore yield a ratio which has a value between zero and infinity, wherein usually a maximum value is set.

[0043] The signal 12 is usually transmitted via electrical and/or lines from the brake pedal 16 to the brake control unit 10. Usually, the duty factor of the signal 12 is determined there by means of a so-called capture/compare unit (CCU). Although such a CCU is not represented here, it is supplied with the signal 12 via a line 22. In this capture/compare unit, the length or duration of each of the two states 18 and 20 of the signal 12 is detected and each is stored as a count value. By comparing multiple stored values, additional information regarding the speed of the actuation of the brake signal transmitter 14 or other information regarding the dynamics of the process can be determined.

[0044] The generation of the measured values by the brake signal transmitter 14, including the actual generation of the pulse-width-modulated signal 12 by the microcontroller 38, generally takes place outside of the brake control unit 10, namely in the region of the brake pedal 16. The signal 12 is then processed in the input stage 24 of the brake control unit 10.

[0045] A redundant recording of measured values usually takes place in order to increase the reliability of the data capture in the determination of the duty factor of the pulse-width-modulated signal 12. Typically, a separate unit 26 is provided for this purpose. In the prior art, such a unit comprises a low-pass filter 28 and an analog-digital converter 30. Through the low-pass filtering and the analog-digital conversion, a value is generated, which represents the duty factor of the pulse-width-modulated signal 12. The current measured value of the capture/compare unit, which is likewise supplied with the signal 12 via the line 22, can be compared with this value at any time.

[0046] The signal 12, with its two states 18 and 20, is processed within the brake control unit 10 at any time. Therefore, it is readily possible to detect both the presence of the state 18 and the state 20. In this case, a complete cycle of the signal 12 from the combination of a state 18 and a state 20 takes place before a switch back to the state 18 takes place.

[0047] According to the invention, however, the additional components of the unit 26 are no longer required, and so the low-pass filter 28 and the analog/digital converter 30 can be dispensed with. Instead of a filtering and a recording of measured values via analog-digital converters 30, the alternative measuring or determination method according to the invention is used here. In this case, a clock signal 32 is used, as is represented in FIG. 3, by way of example. The clock signal 32 comprises a plurality of clock events 34. These occur sequentially in fixed time intervals, and are therefore (strictly) periodic.

[0048] The core of the new method for determining the duty factor is that of scanning the current state of the signal 12 in a regular way, i.e., periodically. The clock signal 32 forms the basis therefor, in order to scan the current state of the signal 12 for each clock event 34. This is likewise depicted in FIG. 3. The number of clock events 34 for each state 18 or 20 are counted for this purpose. If the signal 12 is initially in the state 18, a first counter is incremented. This is repeated for every further clock event in the state 18. As soon as the state 20 is determined for a clock event 34, a second counter is incremented. This is repeated for all further clock events 34 until, in turn, a switch into the state 18 takes place.

[0049] In the exemplary embodiment of FIG. 3 shown, seven clock events in the state 18 are counted, while only three clock events in the state 20 are determined. The imprecision of the determination is in the range of the spacing between two clock events 34, i.e., within the modulation frequency of the clock signal 32. The duty factor Tv is calculated as follows

Tv=t(state 18)/(t(state 18)+t(state 20)).

[0050] In this case, the computation is therefore Tv=7/(7+3)=0.7. A linear relationship between the pedal travel and the measured value therefore results. Due to the spacings—which are of the same length—between the clock events 34, the counted events for the states 18 and 20 therefore yield the duty factor of the signal 12. After completion of such a test cycle, the two counters are therefore rested before the next measurement cycle begins.

[0051] The determined value of the duty factor Tv can then be compared directly with the values determined by the memory and comparison unit.

[0052] A separately generated signal as well as a signal which is already present within the brake control unit 10 or another microcontroller can be used as the clock signal 32. An interrupt request or an interrupt is suitable, in particular, for this purpose. This is utilized by the microcontroller in the brake control unit 10 for query purposes or for interrupting on-going processes, for example, in order to handle parallel tasks. Such clock-pulse generators, in particular interrupts, are present in practically every microcontroller. In addition, a unit for detecting the two states 18 and 20 is already present in the control unit 16. Therefore, a method for determining the duty factor Tv of the signal 12 can be implemented via two counters and a central processing unit. By increasing the sampling frequency, i.e., by means of a higher-frequency clock signal, the accuracy of the determination of the duty factor can be increased even further, if necessary.

[0053] Finally, in this method, the additional components 26, namely the low-pass filter 28 and the analog-digital converter 30, are no longer required. The signal 12 is therefore fed directly to the capture/compare unit via the line 22, as shown in FIG. 2.

[0054] If necessary, a Schmitt trigger 36 or a similar component can also be provided, in order to pull both states 18 and 20 of the signal 12 to a defined voltage level or to adjust the impedance, in particular by way of providing a driver having low impedance.

[0055] In addition, the modulation frequency of the signal 12 or the frequency of the pulse-width modulation can be determined directly from the signal 12. The frequency of the pulse-width modulation is the repetition rate of the cycles of the signal 12, wherein one cycle of the signal 13 consists of exactly two associated states 18 and 20.

[0056] In order to determine the frequency of the pulse-width modulation, the number of clock events 34, which result in one complete cycle of the signal 12 comprising the two states 18 and 20, is counted. When the frequency of the clock signal 32 is known, the duration of one clock event 34 is also known. Therefore, the number of counted clock events 34 of one cycle of the signal 12 is multiplied by the duration of one clock event 34. This results in the period of one cycle of the signal 12. The reciprocal of this period, i.e., a division of 1 by the period, then results in the frequency of the pulse-width modulation of the signal 12. The calculation can therefore be carried out as follows:

[00001]$\begin{array}{c}\mathrm{Frequency}=.Math.1/\mathrm{cycle}.Math..Math.\mathrm{time}\\ =.Math.1/\left(\mathrm{number\_clock}.Math..Math.\mathrm{events}\star \mathrm{duration\_clock}.Math..Math.\mathrm{event}\right)\end{array}$

[0057] The determination of the frequency of the pulse-width modulation therefore takes place independently of further external components. In this way, for example, a failure of one of the brake signal transmitters 14 or of the entire brake pedal 16 can be easily determined.