GB2245720A - Regulating means for a setting mechanism - Google Patents

Description

Regulating means for a setting mechanism affected by friction in a motor

vehicle The present invention relates io regulating means for a setting mechanism, affected by friction, in a motor vehicle.

A regulating system for such a mechanism is disclosed in DE-OS 32 07 863 (US-PS-4 499 412), wherein a two-position regulator is arranged downstream of a non-linear regulator. The two-position regulator switches only when the difference between a target value and an actual value of the regulating circuit changes. The non linear regulator has a steep characteristic at the equalising point and a flat characteristic elsewhere. Limiting equipment suppresses switching frequencies that are too high, so that excessively frequent switching to and fro of the two-position regulator is avoided. The entire system operates on an analog basis.

Equipment is described in DE-OS-32 33 290 (US-PS 4 594 993) for regulation of the exhaust gas return rate for a diesel internal combustion engine. A linear regulator supplies an input magnitude for a three-point regulator. In this equipment, too, the three position regulator switches only when the difference between a target value and an actual value of the regulating circuit changes. A continuous switching to and fro of the three-position regulator is avoided by a hysteresis.

It is known from DE-OS 27 26 987 to divide a regulating equipment into a digital part and an analog part. In that case, the digital part processes the data present in digital form and the analog part processes the data present in analog form.

is There remains a need to reduce the influence of friction in a regulating system so that the dynamic range of the system is improved.

According to the present invention there is provided regulating means for a setting mechanism, affected by friction, in a motor vehicle comprising a first regulator for comparing a value indicative of the actual position of the setting mechanism with a value indicative of a desired position of the setting mechanism and for determining an output value in dependence on the comparison result, and a second, two-position regulator for regulating the setting mechanism in dependence on the output value, the second regulator having a variable hysteresis width controllable in dependence on operating parameter values.

The properties of the regulating means may be substantially is enhanced by the presetting of the hysteresis width of the twoposition regulator in dependence on operating parameter values.

Different hysteresis widths may be able to be set in dependence on different operating conditions, such as rotational speed or setting mechanism position. Thus, the influences of friction can be compensated for without causing spurious movement of the setting mechanism.

An embodiment 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 diagram showing the relationship between setting mechanism position (U1) and current (I) flowing through the setting mechanism; Fig. 2 Fig. 3 Fig. 4 Fig. 5 is a block circuit diagram of regulating means, embodying the invention, for a setting mechanism; is a diagram showing current flow through the setting mechanism as a function of time; is a block circuit diagram of part of a first regulator in the regulating means; and is a block circuit diagram of another part of the first regulato Referring now to the drawings there is shown regulating means for a setting mechanism of a diesel fuel pump. The regulating means can, however, be used for other setting mechanisms affected by friction, in particular electromagnetic setting members. Thus, for example, it is also usable for a throttle flap setter.

In the case of setting mechanisms affected by friction, the position of the setting mechanism does not change for small changes in the setting signal. The relationship between the current I which flows through the setting mechanism and the setting UI which the setting mechanism assumes is shown in Fig. 1. When the setting mechanism is to assume the position X, different current values I1 or 12 are required for this purpose according to the previous history. If the setting mechanism is in the position X with a setting mechanism current I1 and it is required to change its direction of movement, the setting mechanism current must first be raised to the value 12. The position of the setting mechanism changes only when the current changes by a minimum amount H.

depends on different operating parameter values.

This minimum amount Such influences are, for example, the position of the setting 1 mechanism, temperature, rotational speed or production of tolerances. It is particularly advantageous when the hysteresis width E (see Fig. 3) is selected so that it corresponds to half the minimum amount H.

A schematic illustration of the regulating means is shown in Fig. 2. A regulator 10 receives a signal UI, which indicates the actual position of a regulating rod of the setting mechanism, by way of an analog-to-digital converter 70. The regulator 10 also receives a signal US, which indicates the desired position of the rod, by way of an analog-to-digital converter 20. The regulator 10 computes from these and further data a desired setting mechanism current value IS, which is fed by way of a digital -to-analog converter 30 and a junction 35 to a two-position regulator 40. In addition, the regulator 10 computes the hysteresis width E of the two-position regulator 40 starting out from different magnitudes, the desired and is fed the measured period duration T. The hysteresis width value 1.

by way of a digital -to-analog converter 80 to the two-position regu l ator 40. The regulator 40 drives the setting mechanism 50 correspondingly. The setting current value II measured at the setting mechanism is fed back to the junction 35. Moreover, a signal UI in respect of the actual position of the setting mechanism is fed by way of an analog differentiating member 60 to the junction 35 and by way of the analog-to-digital converter 70 to the regulator 10.

It is particularly advantageous if the regulator 10 is of digital form, as illustrated in Fig. 2, and the remaining components such as the twoposition regulator and differentiating member are realised in analog form. An efficient adaptation is possible by'the digital operation of the regulator 10.

To improve the stability of the regulating circuit, the actual position value UI of the regulating rod is fed back by way of the differentiating member 60 to the input of the two-position regulator. This differentiating member 60 is constructed in analog form. This offers substantial advantages over a digital differentiator integrated into the regulator 10. By reason of the scanning time and the finite resolution of usual anal og-to-digital converters, it is not possible to achieve the necessary approximation quality with a digital differentiating member.

The digital regulator 10 thus determines the target current value IS and the hysteresis width value E for the two-position regulator 40 in deperdence on the desired position US of the regulating rod, the aztual position of the regulating rod UI and further operating parameter magnitudes. The two-position regulator controls the setting mechanism in dependence on the comparison between desired and actual setting mechanism current as well as in dependence on the desired hysteresis width E. For this purpose, makes or interrupts the connection between setting mechanism and the battery voltage.

When the two-position regulator 40 recognises that the actual setting mechanism current II is greater, by the hysteresis width E, than the desired setting mechanism current IS, it interrupts the connection to the battery voltage. If the actual setting mechanism current II falls by the hysteresis width E below the desired setting mechanism current IS, it restores the connection of the setting mechanism with the battery voltage. The instantaneous searching state of the two- position requlator is fed to the reaulator 10 for the measurement of the period duration T (Fig. 3). The measurement of the period duration can be carried out in the regulator 10 or can take place in a separate measuring member 205.

The temporal course of the setting mechanism current is illustrated in Fig. 3, in which the setting mechanism current II is entered as a function of time t. At the instant T1, the setting mechanism current is smaller by the hysteresis width E than the desired setting mechanism current IS and the setting mechanism is connected with the battery voltage at this instant, whereupon the setting mechanism current arises. At the instant T2, the setting mechanism current is greater by the hysteresis width than the desired current IS and the connection between setting mechanism and battery voltage is interrupted at this instant. This has the consequence that the setting mechanism current II again falls until it is below 15, the desired value IS by the hysteresis width E.

The value of the setting mechanism current thus fluctuates constantly between a value which is above the desired setting mechanism current by the hysteresis width E and a value which is below the desired setting mechanism current by the hysteresis width E. Through an appropriate presetting of the hysteresis width E, a fluctuation of the setting mechanism current to and fro between two current values can be achieved. The two-position regulator thus switches constantly between its two states. The switching time can be influenced through presetting of the hysteresis width. The switching time is so set that a reaction of the setting mechanism takes place very rapidly on changes in the desired setting mechanism current IS. In that case, no spurious movements of the setting i 7 mechanism arise for constant desired setting mechanism current IS.

The part of the regulator 10 (position regulator) which computes the target value for the setting mechanism current IS is illustrated in Fig. 4. The desired regulating rod 'position US and the actual rod position UI are fed by way of the converters 70 and 20 to a comparison point 10. The difference between these two signals is applied to an integrator 120 and to a proportional member 130.

The points 2 and 3 indicate that the proportionality constants P and the integrator setting magnitude can be influenced. The output signals of the proportional member 130 and of the integrator 120 are fed by way of the addition point 135 to a limiter 140. The output signal of the limiter 140 represents the output signal of the regulator 10 and is conducted to the digital-to-analog converter 30.

The output signal of the limiter 140 and the output signal of 1 the differentiating stage 110 (regulating difference) form the input signal of a block 150, the output signal of which influences the integrator 120 as indicated by the point 3. Different operating -ed to a parameter values and the regulating difference are conduct block 160. This block 160 can influence the proportional member as indicated by the point 2.

In dependence on the difference between the desired position US and actual position UI of the regulating rod, the integratcr 120 and the proportional member 130 determine respective output signals which are added together at the addition point 135. The two blocks 120 and 2 130 operate as regulators with at least proportional-integra behaviour and the sum value of the output signals of these blocks i restricted to a maximum value in the limiter 140. The output signa of the limiter is converted in the digital -to-analog converter 30 into a signal which represents the desired setting mechanism current is.

A particular advantage is that the'output signal of the limiter 140 and the regulating difference are applied to the block 150. This block 150 contains an anti reset wind-up function. When the output signal of the regulator device 120,130 exceeds a limit, which means that the signal is restricted by the limiter 140, the value of the integrator is frozen.

This means that the value of the integrator 120 is stored and not increased until the regulator output signal again leaves the limit. If the value of the integrator is not frozen and a regulating difference is present over a longer interval of time, the value of the integrator in some circumstances assumes very high figures. If the sign of the regulating deviation then changes, the regulator needs a long time until the value of the integrator has again decayed. The block 150 improves the regulating quality of the regulator. If the regulating deviation is additionally available at the block 150, the integrator begins to operate again immediately after a change in the sign of the regulating difference.

The block 160 also represents a particularly advantageous refinement. In this element, the proportionality constant of the proportional part is filed in dependence on one or more of the magnitudes of regulating difference, battery voltage, rotational speed and fuel temperature. The proportionality constant of the proportional member 130 can be set in dependence on these magnitudes.

It has proved to be particularly favourable when the proportionality constant P is greater for small regulating deviations than for large regulating deviations. A large proportionality constant P is favourable for small battery voltages or at low temperatures. A small proportionality constant P, thereagainst, is of advantage at higher rotational speeds.

The part of the regulator 10 which computes the hysteresis width E of the two-position regulator (period duration regulator) is shown in detail in Fig. 5. In dependence on different operating parameter values, such as rotational speed n and the position UI or US of the regulating rod, a target value computer 200 presets a value TS for the period duration. This desired value TS for the period duration is compared with the actual value T of the period duration. The difference between these two signals (regulating difference of the period duration regulator) is fed to a period duration regulator 210.

The regulator 210 possesses at least integral behaviour. Its output signal is limited downwardly and upwardly by a limiter 220.

The output signal value of a preliminary control parameter field device 230 is added in an addition point 225 to the output signal value of the limiter 220. The sum of these two signal values is suitably limited in a second limiter 240. Its output signal represents the hysteresis width E, which is fed by way of the digital-to-analog converter 80 to the two-position regulator 40.

The regulator 210 computes the values for the hysteresis width E in dependence on the comparison between the desired period duration value TS and the actual period duration value T. Since this value shall be greater than a minimum value, but not exceed a maximum value, the limiter 220 restricts the output signal of the regulator 210 to a certain range of values.

The device 230 ensures that rapid changes of the regulating rod position can be reacted to at once. Values for the hysteresis width E are filed in the preliminary control parameter field device in dependence on operating parameter values. In the case of a high level of friction, a large hysteresis width E is necessary in order to overcome the frictional force. A large hysteresis width E requires a great period duration P. For lower levels of friction, only a small hysteresis width E is necessary in order to overcome the frictional f orce. If a large hysteresis width is used here, this leads to spurious movements of the setting mechanism. The friction depends on, amongs other things, the setting mechanism position, and the hysteresis width E is therefore filed in the parameter field at least in dependence on the setting mechanism position. The friction is usually high for larger setting mechanism positions. In this case, a large hysteresis width is necessary. For smaller regulating rod positions, thereagainst, only a small hysteresis width is necessary, since the friction is less. In the case of rapid changes in the setting mechanism position, the new value for the hysteresis width E is immediately available at the output of the second limiter 240.

In a simplified embodiment, the measurement of the period duration is dispensed with. In this case, the hysteresis width is read out of a parameter field as a function of different operating parameter values. Serving for this purpose is a modified preliminary control parameter field device 230, in which the hysteresis width is filed in dependence on the setting position mechanism, the rotational speed and further magnitudes. Such a system can be realised in is particularly simple manner.

The described period duration regulator is of advantage in setting mechanisms affected by friction, in particular when the friction possesses different values in different operating points and different operational states.

Claims (10)

1. Regulating means for a setting mechanism, affected by friction, in a motor vehicle, comprising a first regulator for comparing a value indicative of the actual position of the setting mechanism with a value indicative of a desired position of the setting mechanism and for determining an output value in dependence on the comparison result, and a second, two-position regulator for regulating the setting mechanism in dependence on the output value, the second regulator having a variable dependence on operating parameter values.

hysteresis width control 1 abl e in

2. Regulating means as claimed in claim 1, wherein the first regulator is digital and comprises at least one of a position regulating member and a period duration regulating member.

3. Regulating means as claimed in either claim 1 or claim 2, wherein said output value of the first regulator is a target current val ue.

4. Regulating means as claimed in any one of the preceding claims, wherein the operating parameter values are indicative of at least one of regulating deviation, vehicle battery voltage, rotational speed and fuel temperature.

5. Regulating means as claimed in any one of the preceding claims, wherein the first regulator comprises a period duration regulating member to determine a value indicative of hysteresis width.

6. Regulating means as claimed in claim 5, wherein the period duration regulating member is arranged to determine the hysteresis width value by an integrating process.

7. Regulating means as claimed in either claim 5 or claim 6, wherein the period duration regulating member is arranged to impose a limitation on the hysteresis width value.

8. Regulating means as claimed in any one of the claims 5 to 7, wherein the period duration regulating member comprises preliminary control means to influence the hysteresis width value in dependence on the setting mechanism position.

9. Regulating means as claimed in any one of the preceding claims, comprising analog differentiating means to carry out differentiation of a value indicative of the actual position of the setting means, the second regulator being arranged to regulate the setting mechanism additionally in dependence on the differentiated actual position value.

10. Regulating means substantially as hereinbefore described with reference to the accompanying drawings.

Published 1991 at The Patent Office. Concept House, Cardiff Road, NewporL. Gwent NP9 I RH. Further copies may be obtained from Sales Branch. Unit 6, Nine Mile Point, Cwmfelinfach, Cross Keys. Newport. NP1 7HZ. Printed by Multiplex techniques)td. St Mary Cray. Kent.