GB2127181A

GB2127181A - Automatic control of air/fuel ratio in i.c. engines

Info

Publication number: GB2127181A
Application number: GB08312414A
Authority: GB
Inventors: Reinhard Latsch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1982-08-26
Filing date: 1983-05-06
Publication date: 1984-04-04
Also published as: GB8312414D0; AU1417983A; AU565112B2; DE3231766A1; GB2127181B; JPH07103054A; DE3231766C2; JPS59122758A; JPH0694825B2

Abstract

The idling speed of an internal combustion engine is regulated by changing the mixture or air through-flow in the engine induction duct in dependence on the smoothness of running (LU) of the engine. The ignition timing and the mixture composition also can be influenced, and the latter may be enriched during warm-up. Minimum and maximum idling speed values (nLmin and nLmax) are set to restrict the operating range of the idling speed regulation. The smoothness of running signal may be derived from known measuring means of engine speed or combustion chamber conditions. <IMAGE>

Description

SPECIFICATION Engine idling speed regulation means The present invention relates to idling speed regulation means for regulating the idling speed of an internal combustion engine.

In German (Federal Republic) published patent specification (Offenlegungsschrift) No. 30 39 435 there is disclosed idling speed regulation means which detects the rotational speed of an internal combustion engine and regulates it relative to a target value by means of a P-l-D regulator. For this purpose, the fuel/air mixture or the air throughflow in the engine induction duct is varied by adjusting the position of throttle flap valve in the induction duct or changing the air throughflow in a bypass duct bypassing the throttle flap valve.

Apart from regulation of this nature, it is known to regulate the smoothness of running of the engine. Smoothness of running in this case signifies the uniformity of the rotation of the engine crankshaft. Smoothness of running is reduced, or roughness of running increases, when, for example, the fuel/air mixture in an applied ignition internal combustion engine is excessively weak, so that the combustion processes are no longer consistent. As a consequence, changes in engine torque occur, which leads to roughness of running and even to engine shake. If the roughness of running is due to too weak a mixture, then it can be countered by means of mixture enrichment.

Accordingly, for reasons of fuel economy, known running smoothness regulating devices operate on the basis of regulating towards a weak running limit by influencing the composition of the mixture, i.e. rich or weak. German (Federal Republic) published patent specifications (Offenlegungsschrift) Nos. 24 34 742, 24 1 7 187, and 29 39 590 and United States patent specification No. 3 789 816, for example, relate to running smoothness regulation with influence of the air factor (lambda) value.

The known idling speed regulation devices, such as those mentioned above, merely process an engine speed signal and carry out a comparison of desired and actual speed values. In that case, the target speed value can depend on temperature, as the risk of stalling of the engine is more pronounced when the engine is cold.

It is therefore disadvantageous in the known idling rotational speed regulation devices that certain safety margins must be fixed, although these margins are not desirable from the viewpoint of achieving the lowest possible idling speed value and hence optimum fuel economy.

According to one aspect of the present invention there is provided idling speed regulation means for regulating the idling speed of an internal combustion engine, the regulation means comprising running smoothness determining means for determining instantaneous running smoothness of said engine in dependence on an operating parameter of the engine and control means operative to vary the effective values of control inputs to control equipment of the engine in dependence on the instantaneous engine running smoothness determined by the determining means.

According to another aspect of the present invention there is provided idling speed regulation means for regulating the idling speed of an internal combustion engine, the regulation means comprising running smoothness determining means for determining instantaneous running smoothness of said engine in dependence on an operating parameter of the engine and control means operative to cause the rate of air or air/fuel mixture throughflow in induction duct means of the engine to be varied in dependence on the instantaneous engine running smoothness determined by the determining means.

Idling speed regulation means embodying the present invention may have the advantage that the afore-mentioned safety margins, which amongst other things are dependent on temperature, can virtually be dispensed with, because the instantaneous operating state of the engine is utilised for regulation purposes.

Thus, a low idling speed is made possible, which is determined by the quality of the engine combustion and at the same time results in a low fuel consumption. This idling speed has a lower limit determined by inter alia the required gas intake.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an internal combustion engine together with associated control systems: Figures 2 and 3 are diagrams showing engine running roughness recorded at different temperatures as a function of engine speed, the illustrated curves showing idling speed regulation by regulation means embodying the invention; and Figure 4 is a block circuit diagram of idling speed regulation means embodying the invention.

Referring now to the drawings, the embodiment to be described concerns regulation means for idling speed regulation in an internal combustion engine, wherein the smoothness of engine running is utilised as a measurement magnitude. The regulation means enables the furthest possible reduction in idling speed, which is important from the viewpoint of reducing fuel consumption. In town traffic, for example, reduction of the idling speed by 100 revolutions per minute can save up to 2% of fuel. If the roughness of running exceeds a certain value, then the quantity or flow rate of air/fuel mixture fed to the engine can be increased.In a petrol engine, this can be conveniently achieved by increased opening of the throttle flap valve or increased opening of a bypass duct bypassing the flap valve, whilst for the Diesel engine the desired smoothness of running can be achieved through supply of an additional quantity of fuel.

In Fig. 1 there is shown an applied ignition internal combustion engine 10, including its essential components and control equipment.

The engine has an air induction duct 11 and an exhaust pipe 1 2. Arranged one after the other in the induction duct 11 are an air throughflow sensor 13, a throttle flap 1 4 and at least one fuel injection valve 1 5. The throttle flap is bypassed by a bypass duct 16, in which a throughflow setting device 1 7 is arranged. An electronic control device 20 receives signals from a temperature sensor 21, an engine speed sensor 22 and an air throughflow sensor 1 3. Two arrows indicate the possibility of application of further control magnitudes to the control device 20 to influence output signals thereof.The control device is connected at its output to the or each injection valve 1 5 and to the setting device 1 7. The throttle flap 1 4 is influenced directly by an accelerator pedal 24. If this influence is effected by way of electronic control,the setting device 1 7 may be redundant in certain cases, so that the control device 20 can influence the setting of the throttle flap directly, as indicated by the dashed line 25.

Finally, the ignition timing can be controlled by the control device 20, as indicated by the line 23.

The basic arrangement illustrated in Fig. 1 is, as such, state of the art. The control device 20 determines injection quantity signals for the injection valve 1 5 in dependence on load (Q) and engine speed (n) signal magnitudes and correcting magnitudes, for example the temperature (#) of the engine coolant and, amongst other things, drive signals for the setting device 1 7.

In the embodiment of the present invention, however, a value indicative of the smoothness or roughness of running of the engine is formed in the control device 20 and adjustment of the setting device 1 7 or of the throttle flap 14 takes place in dependence thereon. A higher air throughflow in the induction duct then results, which is detected by means of the air throughflow sensor 1 3 and an increased injected quantity is effected.

Accordingly, by contrast to known systems, in the case of excessively rough running, it is not a fuel quantity control signal directly, but an air flow control signal and thereby the mixture quantity that is varied.

The diagrams of Figs. 2 and 3 serve to explain the principle of idling speed regulation on this basis.

In the Otto cycle engine, unevenness or scattering in the energy translation while the engine is idling is strongly dependent on marginal conditions, such as engine temperature, air temperature, air throughflow and so forth. As engine speed reduces, this scatter value, i.e. the roughness of running of the engine, increases progressively. Fig. 2 by way of example shows the course of running roughness values (LU) at different engine coolant (water) temperatures (9), 2 and #3). The roughness of running increases with falling temperature, especially as a consequence of poorer mixture preparation and distribution and unfavourable ignition conditions.

Idling speed regulation with the device of Fig. 1 can take place on the basis of Fig. 2 in such a manner that an upper idling speed nLma, which according to experience always ensures adequate smoothness of running (point a), initially serves as a target value. Subsequently, the quantity of the air/fuel mixture is reduced to a target value of the running roughness LUso (point b) at which an idling speed nL1 obtains. With increasing temperature and with the same running roughness target value, the engine speed can be reduced further to a value nL2 (point c).If a "learning" regulating system is used in conjunction with the control device 20, then the idling regulation need not always start from the point a; instead, the engine speed value obtained in an idling state is stored and this value is used as an intial magnitude for the regulation in the next following idling state.

In certain circumstances, for example after extended engine operation at full load, the desired idling speed value may fall below a useful speed value, for example through the accuracy of the mixture quantity or for a usable gas intake (curve *3 in Fig. 2). This can be excluded through the introduction of a lower idling speed value nLmjn. This results in regulation of the idling speed in the range between the minimum and the maximum idling speed values, in which case the regulation is directed to a certain running roughness target value.

Fig. 3 shows a variation of the idling speed regulation illustrated in Fig. 2, namely a combination of regulation of mixture leanness and engine speed. This variant has particular significance with a view to low carbon monoxide emission in the warming-up phase of the engine. In this case, a comparatively rich idling mixture composition is initally set (a, b), for example 2% carbon monoxide, which is weakened in the following step (c, d), for example to 0.5% carbon monoxide. Subsequently, regulation is performed in the man ner explained in connection with Fig. 2.

Finally, the regulation of smoothness of running by way of mixture control can be combined with ignition timing control, so as to achieve oPtimum regulation with respect to all operating mangitudes.

In the case of an idling speed regulation of a Diesel engine, the regulation system controls a regulating circuit for the fuel quantitydetermining element. Since a Diesel engine is as a rule operated with an excess of air, the alteration of mixture quantity in the case of a petrol engine essentially corresponds to the altaration of the injected fuel quantity in the case of a Diesel engine.

The detection of roughness of running can be carried out in different ways, for example: a) crankshaft r.p.m., with determination of changes in the r.p.m. or the differential quotients.

b) ion current measurement in the combustion chamber.

c) pressure fluctuations in the combustion chamber.

d) light intensity fluctuations.

e) measurement of these and other parameters in the exhaust pipe.

In view of the now generally common computer controls provided in motor vehicles, idling speed regulation means embodying the invention may be achieved by corresponding programming of the computer. Thus, Fig. 4 shows an arrangement, in block schematic form, for the realisation of such a function.

A roughness running detection stage is designated by 30 and a signal transmitter for maximum and minimum idling speeds nLmax and nLmjn are designated by 31 and 32. A target value control stage influenceable by external magnitudes is referenced 33 and an air factor (lambda) target value stage is referenced 34. A target value and the actual value of the running roughness are compared by a comparator 36 and the result is logically interlinked with signals from the stages 31 and 32 in intermediate stages 38 and 39, which serve to delimit the regulating range. A maximum value selection stage, namely stage 38, ensures that the running roughness regulation is possible only above a minimum idling speed, and a succeeding minimum value selection stage, namely stage 39, provides an upper speed limitation. Finally, a furtner maximum value selection stage 40 makes possible different air factor controls, the output signal of the stage 40 being supplied to the setting device 17.

The minimum and maximum selection stages 38 to 40 can be individually bypassed by means of lines (shown dashed) and switches 41 to 43 arranged within these lines.

Thus, the individual limiting stages can be used selectably, according to need.

The realisation of specific circuitry corresponding to the individual blocks presents no problem to the expert in the field of switching the regulation, so that a more detailed description is not necessary.

Claims

1. Idling speed regulation means for regulating the idling speed of an internal combustion engine, the regulation means comprising running smoothness determining means for determining instantaneous running smoothness of said engine in dependence on an operating parameter of the engine and control means operative to vary the effective values of control inputs to control equipment of the engine in dependence on the instantaneous engine running smoothness determined by the determining means.

2. Idling speed regulation means for regulating the idling speed of an internal combustion engine, the regulation means comprising running smoothness determining means for determining instantaneous running smoothness of said engine in dependence on an operating parameter of the engine and control means operative to cause the rate of air or air/fuel mixture throughflow in induction duct means of the engine to be varied in dependence on the instantaneous engine running smoothness determined by the determining means.

3. Idling speed regulation means as claimed in claim 2, the control means comprising setting means settable to determine the flow rate in a bypass induction duct bypassing flow rate control means of a main induction duct of the induction means.

4. Idling speed regulation means as claimed in either claim 2 or claim 3, the control means comprising electronically controlled flow rate control means controlling the flow rate in a main induction duct of the induction means.

5. Idling speed regulation means as claimed in any one of the preceding claims, the control means being operative to cause the ignition timing of the engine to be varied in dependence on the instantaneous engine running smoothness determined by the determining means.

6. Idling speed regulation means as claimed in any one of the preceding claims, the control means being operative to cause both the rate of flow and the composition of air/fuel mixture inducted by the engine to be varied.

7. Idling speed regulation means as claimed in claim 6, the control means being operative to cause the mixture composition to be varied during warming-up phases of the engine.

8. Idling speed regulation means as claimed in any one of the preceding claims, the control means being operative to cause the engine idling speed to be set to a value within a range defined by a predetermined maximum idling speed value and a predeter mined minimum idling speed value.

9. Idling speed regulation means as claimed in claim 1, the control means being operative to cause the quantity of fuel injected by fuel injection means of the engine in an injection phase to be varied.

10. Idling speed regulation means as claimed in any one of the preceding claims, the determining means being adapted to determine instantaneous running smoothness of the engine in dependence on at least one engine operating parameter selected from the group consisting of engine speed, ion current occurring during mixture combustion, combustion chamber pressure fluctuation and combustion chamber light fluctuation.

11. Idling speed regulation means substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

1 2. Idling speed regulation means substantially as hereinbefore described with reference to Figs. 1 and 3 of the accompanying drawing.

1 3. Idling speed regulation means substantially as herinbefore described with refrence to Fig. 4 of the accompanying drawings.