GB2267581A - System for driving a setting element in a vehicle - Google Patents

Abstract

A system for driving a setting element (114, 116, 118) in a motor vehicle by a pulse-width-modulated signal (uPWM) comprises a switch (124) to change the frequency of the signal between at least two frequencies (f1 and f2), which cause oscillations of different amplitude of the setting element, according to a selectable time sequence. The time sequence and the frequencies themselves can be selected freely or can be dependent on the engine operational state. Measures can also be present to avoid a disturbing influence on sensor signals by the oscillating setting element. <IMAGE>

Description

2267581 - 1 - SYSTEM FOR DRIVING A SETTING ELEMENT IN A VEHICLE The

invention relates to a system for driving a setting element in a vehicle, especially a motor vehicle.

A system for selective driving of a setting element in a motor vehicle is described in DE-37 43 309 Al, in particular a method and a device for the recognition and freeing of jammed setting elements.

When jamming of a setting element is recognised, the setting element is caused to execute a periodic shaking movement in order to overcome the mechanical resistance. For this purpose, the control signal for the element is increased or reduced in a certain time raster or the frequency of the signal is reduced until it is disposed in the proximity of the resonant frequency of the setting element. The jamming of the element is recognised from, for example, a deviation between a target value and an actual value.

A time control device for a fuel injection pump is disclosed in is DE-33 25 651 C2, in which the injection lead is set according to the keying ratio of a pulse-shaped control signal. The frequency of the signal in that case is selected so that resonance phenomena do not arise. For this purpose, a frequency/rotational speed diagram is set up, with entry of the ranges in which resonance occurs.

Frequency/rotational speed characteristics are established in the resonance-free ranges therebetween. The frequency of the control signal is then read out from these characteristics during operation.

Alternatively, the frequency can be ascertained by computation during operation.

2 It is thus desirable, in the case of a system for driving a setting element, to prevent jamming of the element so as to ensure reliable functioning of the element over the greatest possible time. For preference this should be achieved with the use of a conventional setting element without the need for contructional modifications, and preferably also the measures taken for achieving this purpose should not lead to falsification of sensor signals.

According to the present invention there is provided a system for driving a setting elemen in a vehicle, comprising means for providing a pulsed drive signal modulated in pulse width to cause oscillation of the setting element in such a manner that the mean position thereof is determined by the signal keying ratio and means for changing the signal in dependence on time between at least two frequencies causing respectively different amplitudes of oscillation of the element.

is A system embodying the invention may have the advantage that it does not react just when jamming of the setting element occurs, but instead takes measures which should prevent jamming or at least postpone it to a substantial degree. As a result, trouble-free operation of the setting element may be possible over a longer period of time. Moreover, the danger does not exist that jamming of the setting element is not recognised and consequently not eliminated. A further advantage consists in that a possible influencing of sensor signals by the setting element may be redisposed in time predominantly into operating ranges in which it does not have a disturbing effect.

Thus, a greater degree of freedom may exist in the combination of sensors and the setting element.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a basic circuit diagram showing a system embodying the invention in conjunction with bypass idling regulation in an internal combustion engine; Figs. 2a and 2b are diagrams plotting the temporal course of driving signals for a setting element in a system embodying the invention; Fig. 3 is a flow chart illustrating signal frequency changeover in the system; and Fig. 4 is a diagram showing the relationship between the temporal course of engine speed and the is frequency of a drive signal for the setting element.

Referring now to the drawings there is shown in Fig. 1 a circuit diagram illustrating use of a system embodying the invention in conjunction with bypass idling regulation in an internal combustion W engine 100 of a motor vehicle. Disposed in sequence, as seen in the direction of flow of air inducted by the engine, in the induction duct 102 of the engine 100 are an air mass or flow rate meter 104, a sensor 106 for detection of the temperature of the inducted air and a throttle flap 108 with a sensor 109 for the detection of the flap angle and an idling switch 110. A bypass duct 112 leads around the throttle flap 108. A flap 114, which can be moved by an electrical drive 118 by way of a linkage 116, is mounted in the bypass duct 112.

The flap 114, the linkage 116 and the drive 118 together form a setting element.

The drive 118 is selectively driven by a signal uPWM from a control device 120. The device 120 receives as input signals a signal c for the throttle flap angle, which is provided by the sensor 109, a signal rh for the air mass flow, which is provided by the air mass meter 104, a signal n for the rotational speed of the engine 100, which is provided by a"rotational speed sensor 122 mounted at the engine 100, and,depending on the setting of a switch 124, either the output signal fl of a first oscillator 126 (switch setting S1) or the output signal f2 of a second oscillator 128 (switch setting S2).

The switch 124 is controlled by way of a control line 130 from a time control 132. The time control 132 receives a signal LL, which is indicative of the idling state and provided by the idling switch 110, as an input signal and optionally also, as indicated by the dashed arrows, further input signals. Such further signals can be, for example, the air mass flow ifi, the throttle flap angle <, the temperature TA of the inducted air detected by the sensor 106, the engine speed n and the temperature TO of the engine coolant, as detected by a sensor 134 at the engine. The signals here enumerated and, in a given case, further signals can be present individually or in combinations at the time control inputs. The signal LL can be replaced by the output signal of a device 138 for recognition of the idling state from the throttle flap angle This alternative is shown in dashed lines.

In a variant of the circuit illustrated in Fig. 1, control lines and 142 from the time control 132 to the oscillators 126 and 128 are provided to enable setting of the frequencies fl and f2 of the oscillators.

In a further variant. a block 144 for influencing of sensor signals is present, the block being controlled by signals supplied on a control line 146 from the time control 132.

The alternatives or variants can be present individually or in different combinations.

The functioning of the system illustrated in Fig. 1 is as follows:

The control device 120 controls the drive 118 by way of the pulse width-modulated signal uPWM, the keying ratio of which determines the setting of the flap 114 and thus the air flow through the bypass duct 112. However, the flap 114 assumes the thus determined setting only on average over time, since the signal uPWM generally causes an oscillating movement of the flap. The amplitude of the oscillating movement depends on the amplitude and the frequency of the signal uPWM and the resonant frequency of the setting element 114, 116, 188. In the embodiment of Fig. 1, the amplitude of the oscillating movement of the flap 114 is fixed by way of the frequency of the signal uPWM. As a rule, a frequency above the resonant frequency of the setting element is selected for the signal uPWM. The closer the frequency of the signal uPWM to the resonant frequency, the greater the amplitude of oscillation of the flap. This effect arises on the one hand due to the increasing self -reinforcement of the oscillation in the proximity of the resonant frequency and on the other hand due to the setting element being increasingly better able to follow the signal uPWM with reducing frequency. A similar behaviour is to be observed in the case of frequencies of the signal uPWM below the resonant frequency, then, however, the afore-mentioned causes counteract each other. The following boundary conditions are to be observed for the selection of an optimum frequency for the signal uPWM:

If the flap 114 oscillates at a small amplitude or not at all, then wedging or jamming of the -flap can occur and thus lead to an impairment of function. The jamming is due to, for example, deposits or other contaminations. On the other hand, large oscillation amplitudes of the flap 114 cause a strong modulation of the air flow through the bypass duct 112, which can have a disturbing influence on sensor signals, for example on the meter 104, and reduce idling smoothness.

This conflict of interests is resolved in that the drive 118 is not driven at a fixed frequency, but..switched over between the two different frequencies fl and f2. The first frequency fl is selected so that a disturbing influencing on sensor signals does not occur and jamming of the flap 114 does not arise in normal operation. For the selection of the second frequency f2, the influence on sensor signals has only a subordinate role. The frequency f2 is selected so that, in the case of operation of the drive 118 by a pulse-width-modulated signal uPWM with the frequency f2, jamming of the flap is improbable even after a longer period of operation or any such jamming that has occurred is released with a high degree of probability.

The pulse-width-modulated signal uPWM is, as already explained, produced by the control device 120. The device 120 ascertains the keying ratio of the pulse-width-modulated signal uPWM from the input signals <, rfi and n and a target value nO, which is filed in, for example, a characteristic values field, for the idling speed. The frequency of the signal uPWM depends on the frequency at which the control device 120 is acted on by way of the switch 124. When the switch 124 is in the setting sl, the device 120 is acted on by the frequency fl produced by'the oscillator 126. In the setting s2 of the switch 124, the device 120 is acted on by the frequency f2 from the oscillator 128. The switch 124 is in turn controlled by way of a control line 130 from the time control 132. In the previously mentioned vairant, the time control 132 sets the frequencies fl and/or f2 of the oscillators 126 and 128 by way of control lines 140 and 142.

In this variant, the frequencies fl and/or f2 are determined in dependence on at least one operational magnitude of the engine 100, for example engine load, in particular idling, partial load, full load and overrun operation, inducted air temperature, coolant temperature, engine temperature, engine speed, and functional state of the setting element.

In one embodiment, the time control 132 operates according to a fixedly preset time sequence. In that case, it causes the switch 124 to switch over from the setting S1 into the setting S2 after elapsing of a time interval tl. When a time interval t2 has elapsed after the switching-over, switching back into the setting S1 is caused. This operation is repeated continuously so that the control device 120 is acted on in alternation by the frequency fl for the time interval tl and by the frequency f2 for the time interval t2 and correspondingly delivers a signal uPWM of either the frequency fl or the frequency f2.

Figs. 2a and 2b show the course of the signal uPWM, plotted against time, for two different embodiments. For the time interval tl, the signal uPWM has the frequency fl, which is, for example, 200 hertz. Thereafter, the signal uPWM has the frequency f2, which is, for example, 100 hertz, for the time interval t2. A time interval tl with the frequency fl 'again follows, and so forth. If the setting element is operated above its resonant frequency, the flap 114 executes oscillations of greater amplitude in the time interval t2 than in the time interval tl.

Immediately after a switching over between the frequencies fl and f2, a correction of the signal uPWM is performed. In a first embodiment, in which there is a signal uPWM according to Fig. 2a, the first current flow gap after the switching from the frequency fl to the frequency f2 is shortened by a time dt12. Without this shortening, the first pulse of the s.ignal uPWM will have the course, illustrated in dashed lines, after the switching over of the frequency. After the switching from the frequency f2 to the frequency fl, the first current flow gap is prolonged by a time dt21. 'Again, the course of the signal uPWM, which would result without this measure, is illustrated in dashed lines.

9 In a second embodiment, in which there is a signal uPWM according to Fig. 2b, the current flow duration in the first period after the switching from the frequency fl to the frequency f2 is shortened by a time dt12. Without this shortening, the signal uPWM would have the course illustrated in dashed lines. After the switching from the frequency f2 to the frequency fl, the current flow duration in the first period is prolonged by a time dt21. Here, too, the course of the signal uPWM, which would result without this measure, is illustrated in dashed lines. The times dt12 and dt21 can both be, for example, 0.75 milliseconds.

The reason for the shortening and prolongation of the current flow duration or current flow gap consists in that the mean value over time of the current flow through the drive 118 would, without this, measure, change after each switching from fl to f2 or from f2 to fl.

The mid-position of the flap would also change correspondingly and in that case influence the air flow through the bypass duct. The times dt12 and dt21 are so selected that the mid-position of the flap remains approximately the same during the switching over between the frequencies fl and f2.

Fig. 3 is a flow chart illustrating the manner of function of the time control 132. The start 300 is followed by a step 302, in which the switch 124 is brought into the setting S1. During the following step 304, elapsing of the time interval tl is waited for. In the following step 306, a switching-over of the switch 124 into the setting s2 is caused. Finally, a last step 308 follows, in which the elapsing of the time interval t2 is waited for. The step 302 follows the step 308.

In one embodiment, the fixed time sequence, which is illustrated in the Figs. 2a, 2b and 3 according to which switching-over is effected between the frequencies fl and f2 of the signal uPWM, can be interrupted in dependence on the temporal course of the engine speed n or on other operational parameters. When the speed n is outside a range nLL (Fig. 4) around the target value nO of the idling speed, then f2 is selected as frequency for the signal uPWM. The fixed time sequence described above runs within the rotational speed range nLL, wherein the frequency f2"is maintained for the time t2 after the entry into the speed range nLL.

An example for the temporal course of the engine rotational speed and the respectively resulting frequency of the signal uPWM is illustrated in Fig. 4. The speed course is drawn either as single or as double line according to whether the frequency of the signal uPWM is equal to the frequency fl or f2. The rotational speed range nLL around the target value nO of the idling speed is bounded by two horizontal dashed lines. Vertical dashed lines distinguish different time ranges, which are denoted by roman numerals, from each other.

In the time range I, the actual value of the engine speed is outside the speed range nLL and the signal uPWM in the time range 1 consequently has the frequency f2 (double line).

At the beginning of the time range II, the engine speed assumes a value within the speed range nLL. The frequency of the signal remains unchanged as f2 (double line) until the time t2 since the entry into the speed range nLL has elapsed.

This is the case at the beginning of the time range III. Consequently, the frequency fl is then switched over to (single line). The frequency fl is maintained for the time interval tl.

Thereafter, the frequency f2 is maintained for the time interval t2 in the time range IV (double line) and the frequency fl is again switched over to at the beginning of the time range V (single line).

During the time range V, the engine speed n leaves the speed range nLL. Consequently, the frequency f2 is switched over to immediately on leaving the speed range nLL (double line), although the time interval t2 has elapsed only at the end of the time region V.

Instead of monitoring whether the engine speed n lies within the rotational speed range nLL, the signal LL of the idling switch 110 or another idling signal can also be utilised.

In an advantageous embodiment, at least one of the magnitudes tl, t2, fl and f2 is influenced by the time control 132 in dependence on its input signals. Input magnitudes of that kind are, for example, the engine load (idling, partial load, full load, overrun operation), the inducted air temperature, the coolant temperature, engine speed and the functional state of the setting element. It is thus possible to achieve optimum adaptation to the operational state of the engine 100.

In a further embodiment, instead of or in addition to the time sequence for the switching-over between the frequencies fl and f2, conditions forbidding, permitting or forcing a switching-over between the frequencies are checked for by the time control 132. For example, it can be checked whether the operational state of idling is present.

The idling state can be recognised from the signal LL of the idling switch 110, which is present as input signal at the time control 132. If no idling switch is present, a corresponding signal can be obtained from the device 138 for recognition of the idling state from the throttle flap angle Since susceptibility to faults is particularly high in the idling state, a switch-over to the frequency fl is forced in this embodiment when the idling state has been recognised. Outside the idling state, a switching-over to the frequency f2 is forced or switching between the frequencies fl and f2 is carried out according to the time sequence of tl and t2. This embodiment could also be structured similarly to the embodiment described by reference to Fig. 4 if the susceptibility to faults is not unduly high in the idling state. In this case, there would be switching over between fl and f2 according to the sequence, but f2 would be used continuously.

A significant advantage is provided by an embodiment which includes the block 144 for the influencing of sensor signals which are disturbed directly or indirectly by the oscillations of the flap 114, for example load signals, especially the signals of the air mass meter 104. In this embodiment, the drive 118 is selectively driven by the frequencies fl and f2 in alternation. The sensor signals are always influenced when the drive 118 is selectively driven by signals of the frequency f2, since the disturbances arise or are particularly strong in that case. Different possibilities exist for the influencing of the sensor signal. One possibility consists in interrupting the feed lines (signal lines or supply voltage lines) to the sensors concerned, so that either no disturbed sensor signals are produced at all or the disturbed sensor signals are not entered into the computer of a control device. A further possibility consists in entering the sensor signals, but not processing them further. Moreover, it is possible to modify the evaluation of the sensor signals or to provide the sensor signals with a correction.

In a further embodiment, a logical switching system is present, which recognises whether an impermissibly high static friction occurs at the setting element. This is so, for example, when a large deviation between target value and actual value of the mid-position of the flap 114 is present continuously or when the flap 114 does not react in orderly manner to the drive signal uPWM. The latter circumstance can be ascertained by, for example, a plausibility test of the signals uPWM and rh, or uPWM and n, or uPWM, rfi and n. The higher the static friction, the greater the risk that the setting element jams. For that reason, it is distinguished in this embodiment between operation with low static friction and operation with high static friction. In the case of low static friction, the oscillation of the setting element caused by the frequency fl is sufficient to prevent or eliminate jamming. For that reason, a switching-over to the frequency f2 is dispensed with in the case of low static friction. If, however, a high static friction is present, jamming of the setting element can be prevented with great probability only if the frequency f2 is switched over to at least for a time. Accordingly, a switching- over to the frequency f2 is permitted or even forced in the case of high static friction.

The system can also be used in connection with an idling control without a bypass duct. In that case, the throttle flap 108 is driven instead of the flap 114 in the bypass duct.

In addition, use is also possible with outer electromagnetically driven setters in a vehicle, which are suitable for driving by pulsewidth-modulated signals and in which jamming can be prevented or overcome by a shaking movement.

Claims (27)

1 A system for driving a setting element in a vehicle, comprising means for providing a pulsed drive signal modulated in pulse width to cause oscillation of the setting element in such a manner that the mean position thereof is determined by the signal keying ratio and means for changing the signal in dependence on time between at least two frequencies causing respectively different amplitudes of oscillation of the element.

2. A system as claimed in claim 1, the means for changing the drive signal frequency being arranged to so change the frequency according to a time sequence comprising at least two time intervals that the signal has a first frequency during one of the intervals and a second frequency during the other interval.

3. A system as claimed in claim 2, wherein the intervals follow one another in alternation.

4. A system as claimed in claim 2 or claim 3, comprising means to predetermine at least one of the intervals.

5. A system as claimed in any one of claims 2 to 4, wherein at least one of the intervals is dependent on at least one of vehicle engine load, induction air temperature, coolant temperature, engine speed and functional state of the setting element.

6. A system as claimed in claim 5, wherein the engine load is represented by at least one of the states of idling, part load, full load and overrun.

7. A system as claimed in any one of the preceding claims, comprising means to predetermine at least one of the frequencies.

8. A system as claimed in any one of the preceding claims, wherein one of said at least two frequencies is substantially 100 hertz and the other is substantially 200 hertz.

9. A system as claimed in any one of the preceding claims wherein at least one of the frequencies is dependent on at least one of vehicle engine load, induction air temperature, coolant temperature, engine speed and functional state of the setting element.

10. A system as claimed in claim 9, wherein the engine load is represented by at least one of the states of idling, part load, full load and overrun.

11. A system as claimed in any one of the preceding claims, comprising means to determine a parameter of the drive signal in dependence on sensor signals issued during driving of the element, but excluding, or only after correction of, sensor signals influenced by the oscillation of the element and issued during oscillation at the greater one of the amplitudes caused by said at least two drive signal frequencies.

12. A system as claimed in claim 11, wherein said sensor signals are indicative of engine load.

13. A system as claimed in claim 12, wherein the load-indicative signals represent air induction rate.

14. A system as claimed in any one of the preceding claims, the means for changing the drive signal frequency being arranged to effect the change only after recognition of a level of static friction at the element in excess of a predetermined permissible level.

15. A system as claimed in any one of the preceding claims, the means for changing the drive signal frequency being arranged to effect the change only in operational states in which the element oscillation at the greater one of the amplitudes caused by said at least two drive signal frequencies has substantial influence on a sensor signal and in which the element is otherwise continuously driven to oscillate at that amplitude. -

16. A system as claimed in any one of claims 1 to 14, the means for changing the drive signal frequency being arranged to effect the change only in operational states in which the element oscillation at the greater one of the amplitudes caused by said at least two drive signal frequencies has an insubstantial influence on a sensor signal and in which the element is otherwise continuously driven to oscillate at the smaller one of the amplitudes.

17. A sensor as claimed in any one of the preceding claims, wherein the setting element is an idling regulation element of the vehicle engine.

18. A system as claimed in any one of the preceding claims, the means for changing the drive signal frequency being arranged to effect the change only when the vehicle engine speed is disposed within a predeterminable range or when an idling switch of the engine is closed, the element otherwise being -continuously driven to oscillate at the greater one of the amplitudes caused by said at least two drive signal frequencies.

19. A system as claimed in claim 18 when appended to claim 2, the means for changing the drive signal frequency being arranged to maintain the frequency causing the greater amplitude of oscillation for the duration of the respective time interval after entry of the engine speed into said range or after closing of said switch and thereafter to effect change between the frequencies according to the time sequence.

20. A system as claimed in claim 18, the means for changing the drive signal frequency being arranged to change from the frequency causing the lesseramplitude to the frequency causing the greater amplitude immediately following departure of the engine speed from said range or opening of said switch.

21. A system as claimed in any one of the preceding claims, comprising means for causing a first current flow gap after change from a lower to a higher one of said at least two frequencies to be prolonged by a selectable period of time and a first current flow gap after change from said higher to said lower frequency to be shortened by a selectable period of time.

22. A system as claimed in claim 21, wherein said time periods are so selected that the mean Value of the current for driving the element remains substantially constant during the frequency changes.

23. A system as claimed in any one of the claims 1 to 20, comprising means for causing current flow duration in a first period after change from a lower to a higher one of said at least two frequencies to be prolonged by a selectable time and current flow duration in a first period after change from said higher to said lower frequency to be 15 shortened by a selectable period of time.

24. A system as claimed in claim 23, wherein said time periods are so selected that the man value of the current for driving the element remains substantially. constant during the frequency changes.

25. A system substantially as hereinbefore described with reference 20 to the accompanying drawings.

26. A motor vehicle provided with a setting element and with a system as claimed in any one of the preceding claims for driving the element.

27. A vehicle as claimed in claim 26, wherein the setting element is an idling regulation element in the vehicle engine.