GB2055961A

GB2055961A - Control System for an Internal Combustion Engine

Info

Publication number: GB2055961A
Application number: GB8024188A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-07-24
Filing date: 1980-07-24
Publication date: 1981-03-11
Also published as: DE2929907A1; GB2055961B; DE2929907C2; JPS5620733A

Abstract

A control system for an internal combustion engine comprises a valve 22 for controlling E.G.R. in dependence on the intake air flow rate, a fuel metering device 11 for controlling the fuel supply to the combustion chambers in dependence on the oxygen content of the exhaust gas, and a control 19, 20 for adjusting the ignition timing in dependence on the detection of knocking by sensors 21. The device 11 is responsive to signals from an air flow meter 12, an oxygen probe 15 and an engine speed sensor 35 to control the fuel supply to injectors 10. The knock sensor 21 control the timing of the sparking of plugs 17 via a distributor 18 and an advance-retard mechanism 19. An after burner 9 reduces NOx, HC and CO in the exhaust gas and a swirl generator (not shown) is provided in the intake manifold to maintain a constant swirl independently of comburant flow rate and engine speed. <IMAGE>

Description

SPECIFICATION Control System for Influencing Combustion in an Internal Combustion Engine The present invention relates to internal combustion engines.

It is known to reduce the tendency of combustion mixture to detonate or knock in the combustion chambers of internal combustion engines by means of strong turbulence and measures for reducing the combustion temperature, so that the engine can have a high compression ratio. It is known that by such means compression ratios of 11:1 can be reached (MTZ 1979, page 166). A reduction in the knocking tendency can also be achieved by recirculating high proportions of exhaust gas, the adoption of exhaust gas recirculation also leading to lowering of the peak combustion chamber temperatures.

Since the ignitability of fuel/air mixtures becomes less as the proportion of recycled exhaust gas increases, in a method for improving flammability disclosed in German (Federal Republic) patent specification No. 26 13 586 a plurality of sparking plugs is provided in the combustion chamber. Instead of a multi-plug ignition, equally good flammability properties can be obtained by a so-called flare ignition. Control of the proportion of recirculated exhaust gas is effected, in a known control device, approximately proportionally to the sucked-in airflow, in that the pressure in the venturi of the mixture generator is used for controlling a pneumatically actuated exhaust gas recycling valve.Furthermore, in this known device for ensuring a specific gas composition, regulation of the fuel/air ratio of the operating mixture is provided by using an oxygen measuring probe subjected to the exhaust gas.

Another known device, disclosed in German (Federal Republic) patent specification No.

27 10 761 possesses, for the purpose of increasing combustion speed so that the supply of high exhaust gas recycled proportions is possible without reaching the operating limit of the engine, swirl-forming means in the region of the inlet of the fresh charge into the combustion chamber. In this way, by generating turbulence, the preparation of the fuel arriving in the combustion chamber of the engine is improved, which is a precondition for a good flammability and a high rate of combustion. Furthermore, in this known device, the flammability of the operating mixture is increased by multi-plug ignition. Considered overall, very high recirculated exhaust gas proportions can be realised in this manner.

It is also known to recognise combustion detonation with the assistance of an appropriate sensor and to so influence parameters, such as the ignition point, as a function of the output signal of the sensor with the assistance of a control circuit, that detonation or knocking is avoided.

The aforementioned known devices have as their objective keeping of the NOX proportion in the resultant exhaust gas as low as possible. With the described measures, exhaust gas recirculation proportions of up to 50% are possible without exceeding the operating limit of the engine. On the other hand, however, the increase in the recirculated exhaust gas proportion has the disadvantage that the fuel consumption rises as a consequence of the inert gas flow acting as ballast. Therefore the emitted proportion of NOx is indeed reduced, but the fuel utilisation decreases.

According to the present invention there is provided an internal combustion engine comprising at least one cylinder having a combustion chamber providing a compression ratio of up to substantially 1 1 :1, and a control system for influencing combustion in the chamber, the control system comprising control means for controlling a return feed of exhaust gas to the cylinder in dependence on the rate of induction into the cylinder of a combustible charge, mixture regulating means for regulating the composition of fuel/air mixture for the cylinder in dependence on the oxygen content of the exhaust gas, and ignition control means for controlling the timing of ignition of mixture in the chamber, the ignition control means being controllable by signals from sensing means sensing the onset of knocking in the combustion phase.

Such an engine has the advantage that a considerable reduction in fuel consumption may be able to be achieved. The major part of this is a consequence of the increase in compression ratio made possible. By this increase, the specific performance is substantially improved and correspondingly the specific fuel consumption is reduced. Through the control of the combustion mixture composition, it is possible to maintain an air co-efficient A at which an optimally low consumption is achieved, which is also reduced by an optimum exhaust gas recycled proportion.

By the exhaust gas recyciing, a higher volumetric efficiency is achieved by the reduction cf the throttling losses in the induction region. By the control of the ignition point as a function of the output signal from a knock sensor, it is ensured that the knock limit or margin of safety from detonation is not exceeded. In this way an upper limit to the achievable compression ratio can be utilized to the full without the engine being subject to risk of destruction if manufacturing and adjustment inaccuracies are present.

It is specially advantageous to include in the engine a swirl-generating means, at which a constant pressure drop can be maintained, so that at virtually any engine speed a constant quentity of energy is converted into a swirl. Thus the degree of turbulence is no longer speeddependent, so that the extreme limits of knockfree combustion can be maintained over the entire operating range of the engine.

It is also advantageous to provide, for determining the oxygen content of the exhaust gas, an oxygen measuring probe, the operating temperature of which can be maintained in all operating conditions with the assistance of temperature-regulated heating. In this manner it is ensured that even during warming-up and at reduced exhaust gas temperatures, the probe is fully effective and transmits accurate control valves.

An embodiment 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 diagrammatic representation of an internal combustion engine with a control system, according to the said embodiment, and Figure 2 is a schematic elevation of means for generating a constant pressure drop in an induction duct of the engine of Figure 1.

Referring now to the drawings, there is shown a mixture-compressing, applied ignition internal combustion engine 1 with an induction system 2 and exhaust gas collecting system 3. From an exhaust gas collector pipe 4, an exhaust gas.

recirculation line 5 leads back to an induction duct 6 leading to the induction system 2. The entry of the exhaust gas recirculation line is situated downstream of a throttle valve 8 disposed in the induction duct 6 and serving in the usual manner for the load control. The pipe 4 leads into an afterburning device 9 of known design, by which NOx can be reduced and unburnt contituents such as HC and CO oxidized.

The supply to the engine of operating mixture consisting of fuel and air is provided, in the illustrated example, by a regulated induction duct injection by fuel injection valves 10, which are disposed immediately upstream of the engine inlet valves. Fuel metering is carried out by a metering device 11, which receives a control signal from an air flow meter 12 disposed in the induction duct upstream of throttle valve 8 and from a A control device 14, which processes the signal from an oxygen measuring probe 1 5 disposed in the exhaust pipe 4. Such devices are generally known and are not explained in more detail.

Fuel is metered by the metering device according to the sucked-in air flow rate, which in turn is varied by the actuation of the throttle valve according to the desired load. The fuel/air ratio regulated by the metering device 11 can be additionally so varied by the A control device that a desired A value, situated around A=1, is measurable at the measuring zone of the oxygen measuring probe 1 5. The metering device may meter the fuel either mechanically or by electrical means. Similarly, the air flow rate measuring signal may be transmitted as a mechanical variable or as an electrical variable to the metering device 11. Instead of injection into the induction duct, it is equally possible to use a conventional carburettor in which the pressure in the venturi serves as the air flow variable.

The illustrated engine also comprises an ignition system consisting of sparking plugs 1 7 and an ignition voltage distributor 1 8. The distributor is so constructed that the ignition point can be adjusted earlier or later via a device 1 9 for changing the ignition angle. The device 1 9 for adjusting the ignition point is controlled by a control device 20, which receives signals from knock sensors 21 associated with, for example, each cylinder. Knock sensors as such are known with various principles of action. In addition it is known, for example from German (Federal Republic) patent specification No. 25 46 705 and United States patent specification No. 4 111 035, to use signals from sensors with the assistance of an appropriately constructed control device for adjusting the ignition point.These known devices therefore do not need to be described in more detail.

The illustrated control systems also comprises in the exhaust gas recirculation line 5, a flow control valve 22, which in the present case has a pneumatic actuating drive 23. Adjustment is carried out as a function of the rate of flow of sucked-in air or mixture, so that a percentual proportion of the recirculated exhaust gas flow in the operating mixture supplied to the engine can be maintained. By appropriate, generally known measures, the desired values of the exhaust gas recirculation proportion can be set. The control of the actuating variable, in the example here an actuating pressure, is carried out with the assistance of a control device 24 as a function of the signal from an air flow meter or of the vacuum downstream of the throttle valve 5.The air flow meter can, in known manner, emit either an electrical signal or a mechanical control variable, which after possible amplification is converted in the control device 24 to the actuating variable and is supplied to the actuating drive 23. Pressure sensing by means of a pressure sensor 25 at the induction duct can also serve for generating a mechanical variable or an electrical variable which is then supplied to the control device 24.

For the control of the flow control valve for the recirculated exhaust gas, various known possibilities are available without it being necessary here to specify a particular construction in the example described.

Furthermore, in an alternative embodiment,sthe oxygen measuring probe 1 5 may with advantage comprise a heating device, by which the probe temperature can be maintained at its optimum operating temperature. Such temperature control devices are likewise known and do not need to be described in more detail.

With the particular combustion chamber form (not illustrated) of the engine, in spite of high compression, detonation is avoided. The measures achieving this include generation in the combustion chamber of a high movement of air so that after the ignition of the fuel/air mixture by the spark of the ignition device an overall more rapid and uniform course of combustion can take place. For generating high air movement in the combustion chamber, squish surfaces or slits and swirl generators are provided, disposed in the induction duct. Swirl generators for this purpose are available in numerous forms, for example as described in German (Federal Republic) patent specification No. 27 38 843. As mentioned therein, swirlgenerators may be of various constructions and controlled according to operating parameters.

In the embodiment according to Fig. 2, there is shown a swirl generator comprising a slide valve 27 projecting into the duct of the induction system 2.

The slide valve 27 is connected to an actuating diaphragm 28, which separates two pressure chambers of an actuating means. On one side, the actuating diaphragm is loaded by a compression spring 29, disposed in a first pressure chamber 30, in such a manner that the slide valve 27 moves under the force of spring 29 in a direction which reduces the free cross-section of the duct of the induction system. The first pressure chamber 30 is connected via a line 31 with the exhaust system 2 downstream of the slide valve 27. A second pressure chamber 32 on the opposite side of the diaphragm 28 is connected via a line 33 with the induction system stream of slide valve 27.

With this device it is possible to set a constant pressure drop at the slide valve 27 or correspondingly formed swirl generator. The known swirl generators have the disadvantage that the generated swirl is highly dependent upon load and speed. Usually, therefore, the swirl generation is so designed that at maximum flow rate there are no unduly excessive adverse effects on performance. This means, however, that at low engine speeds only a slight swirl is generated. If, however, the swirl is coresponsible for the freedom from knock of the combustion, then in this case at low engine speeds the admissible compression must be reduced, otherwise detonation on acceleration will occur. With the design according to Fig. 2 it is now possible to keep the swirl constant, independently of flow rate and engine speed.Such an element as shown in fig. 2 can be associated with each individual inlet of the engine or, instead, a single actuating element for all the swirl generators can be provided. By the described devices, it is possible to operate a mixture-sucking, applied ignition internal combustion engine with a compression ratio of approximately 11:1 or higher, which has a substantial effect in improving consumption. In order to utilize to the full the upper limit of compression made possible by the form of the combustion chamber and swirl generation and also by exhaust gas recirculation, a knock recognition system is provided, by means of which the ignition point can be so regulated that detonation is avoided. In this way, the risk is eliminated of the knock limit being exceeded as a result of manufacturing tolerances in the engine and the engine being thereby destroyed.The flow rate of recirculated exhaust gas is so designed that operation is within the achievable fuel consumption optimum.

More recent results have shown that in individual cases, even with exhaust gas recirculation rates of approximately 5%, an improvement in fuel consumption of 3 to 5% can be achieved. By controlling the exhaust gas recirculation proportion as a function of the uneven running of the engine using a known smooth-running detection device 34, the exhaust gas recirculation proportion can be optimized in an advantageous manner. The leaner running limit, i.e. a mixture composition for which an unacceptably high unevenness of running of the engine occurs, is thereby shifted with the help of the high compression into the range of air coefficient A=1 of the operating mixture used. In Fig. 1, the control device 34 is connected to an emitter 35, which detects the engine speed at its crankshaft 36. The exhaust gas recirculation also favours the initial adjustment of the desired A values with the help of the A control. Additionally, by the heating of the oxygen measuring probe 1 5, the possibility is provided of using the A control virtually over the entire operating range of the engine, so that as a whole an optimum exhaust gas composition can be achieved.

Claims

1. An internal combustion engine comprising at least one cylinder having a combustion chamber providing a compression ratio of up to substantially 11:1, and a control system for influencing combustion in the chamber, the control system comprising control means for controlling a return feed of exhaust gas to the cylinder in dependence on the rate of induction into the cylinder of a combustible charge, mixture regulating means for regulating the composition of fuel/air mixture for the cylinder in dependence on the oxygen content of the exhaust gas, and ignition control means for controlling the timing of ignition of mixture in the chamber, the ignition control means being controllable by signals from sensing means sensing the onset of knocking in the combustion phase.

2. An engine as claimed in claim 1, comprising swirl-generating means arranged in induction ducting of the engine to generate a swirl in inducted combustion mixture.

3. An engine as claimed in claim 2, the swirlgenerating means being adapted to provide a variable resistance to mixture flow and being operatively connected to means for maintaining said resistance to be constant.

4. An engine as claimed in any one of the preceding claims, the mixture regulating means comprising a probe for measuring the oxygen content of the exhaust gas and temperatureregulated heating means for maintaining the probe at a constant temperature.

5. An engine as claimed in any one of the preceding claims, further comprising means responsive to the running evenness of the engine to additionally regulate the exhaust gas return feed.

6. An internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.