EP0702750A1

EP0702750A1 - Multi-function feedback control system for internal combustion engines

Info

Publication number: EP0702750A1
Application number: EP94903988A
Authority: EP
Inventors: Giovanni Barbanti
Original assignee: Lotus Cars Ltd
Current assignee: Lotus Cars Ltd
Priority date: 1992-12-18
Filing date: 1993-12-14
Publication date: 1996-03-27
Also published as: CN1096564A; ITBO920446A1; WO1994015086A1; ITBO920446A0; AU5822794A; IT1260234B

Abstract

A multi-function feedback control system for internal combustion engines comprises: a feeding device (1) fitted with feeding elements (35) which control the flow of the fuel; an engine; a catalytic muffler (7); a central control unit (9) which elaborates electrical signals in accordance with parameters which act on the carburation to supply control signals which act continuously on devices delivering a controlled flow of fuel; at least one oxygen sensor (8) placed in the exhaust system of the engine and electrically connected to the unit (9), a flowmeter for measuring the air-flow amount, said flowmeter being placed in the feeding device (1), which sends to the unit (9) electrical signals in accordance with the measured air-flow amount; the unit (9) elaborating the signal coming from the sensor (8) so that a reciprocal correspondence between the values of the signal of the sensor (8) and the corresponding values of the air-fuel ratio of the mixture is established.

Description

Multi-function feedback control system for internal combustion engines.

The present ιn\ cntion relates to a feedback system which controls the mixture whic feeds an internal combustion engine, the system compπsing essentially feeding devices, a internal combustion engine, at least one oxygen sensor placed in the exhaust system of th engine, a catalytic muffler and a central control unit with electronic components which elabo rates the signals coming from the oxvgcn sensor to obtain control signals to control the air fuel ratio of the mixture continuously.

Control systems equipped with devices to control the air-fuel ratio in accordance wit the levels of the signal coming from an oxygen sensor are known. The traditional system arc used to optimise the quantιt> of pollutants which arc emitted from the engine exhaus manilold and which undergo a process oi oxidation reduction inside a catalytic ufller. Th known feeding systems for internal combustion engines are open loop systems, that is, the do not have regulating members or systems of regulating members, which act in response t the signal of an oxygen sensor to control the engine in every operating condition, or mor precisely, to regulate the air-fuel ratio according to the operating conditions. These know open loop systems operate on the basis of an operating diagram of the engine which is store in a recorder.

In order to obtain a similar diagram, the prototype of an engine is used which will b mounted on mass manufactured cars Al ter being placed on a test bench, every possible op crating condition is examined, and the amount of f uel is defined which is most suitable lo that condition, with regard to economic consumption, pollutant levels and performance i general. An operating diagram of the engine in n dimensions is obtained, in which the rela tion between operating condition and the quantity of fuel to be sent to the engine is estab lished in accordance w ith predetermined parameters (load, opening of the throttle, revolutio speed, environmental temperature, humidity, temperature of the engine, etc.).

A similar diagram can be memoπsed in electronic or mechanical recorders (three-di mensional cams, or similar).

EP - A - 0 046 305 refers to a system which controls an internal combustion engine consisting of de\ ices which work on the ilow ol the luel injected and on the spark advanc using the output signal of a computer which receives the signals from a pressure senso placed in the suction pipe and from a sensor of the angular speed of the engine. The comput er calculates the difference in the pressure ΔPm of the air in the suction pipe and the differ ence in the angular speed ΔN betw een two successive moments and establishes the corrcc tion values between values calculated for ΔPm and ΔN so as to change the control value fo the engine.

The main problems which remain unresolved by this system are the following

1. The correction values to change the control value of the engine are established on th basis of an operating diagram of the engine memorised in the computer;

2- The signal levels of the oxygen sensor placed in the engine's exhaust pipe, duly pro¬ cessed by the computer, have the function of changing the correction value between the val¬ ues calculated for ΔPm and ΔN; however, this modification does not actually control th process of carburation in all the working conditions of the engine, but obtains an air-fuel ra- tio which is sufficiently close to the stoichiomctπc value in urban working conditions, in or der to make the catalytic muffler work correctly.

In connection with point 1, we may add that the operating diagram of the engine has been calculated b\ measuring the performance of a new sample engine in numerous different load conditions on a test bench in a test laboratory and in pre-established environmental conditions. An engine which has tens of thousands of kilometres on the clock for all sorts o road surfaces and different environmental conditions will no longer react like a sample en¬ gine.

The present use of the diagram to control the air-fuel ratio is owing to the following rea¬ sons: there are still no systems for measuπng the air-flow amount sucked by the engine, the feeding elements capable of controlling the flow of the fuel present wide dimensional tol¬ erances and hence excessive errors of supply; the oxygen sensors are not used properly.

The known svstcms lor measuring the air-flow amount are very imprecise, presenting errors which are particular!) noticeable in estimated values of the weight of the air which passes through the intake manifold. This makes these systems fails to deliver mixture rates properly. In addition the flowmeters which are used most widely today have an adverse ef¬ fect on the engine because of the losses of load due to the same flowmeters

With regard to point 2, we may e that only two levels of the oxygen sensor sig¬ nal are taken into consideration for a correct functioning of the catalytic muffler, a first level indicating an air-fuel ratio leaner than the stoichiometπc value and the second level indicating an air-fuel ratio πcher than the stoichiometπc value, as if the curve representing the values in tension of the oxygen sensor had a slope in correspondence with the stoichiometπc value of the mixture.

A regulation based on a similar curve has an irregular development owing to the correct¬ ing effects of the computer on the feeding elements capable of controlling the flow of the fuel, these correcting effects ha\ ing the commutation Irequcncy ol the sensor signal from the first to second level, and vice-versa. In addition, the use of only two levels of the oxyge sensor signal limits the effective capacity of the sensor, which is capable of supplying mor useful information and to a greater extent. In fact, the sensor does not only indicate errors i the air-fuel ratio of the mixture supplied on the basis of the parameters of the operating dia gram of the engine, but can indicate that even if the quantity of fuel sent to the engine is cor rect, the fuel is not sufficiently vapoπsed, as a result of which the engine has not functione properly. Essentially, the oxygen sensor, showing the final results of carburation, indicate how combustion has taken place.

A single oxygen sensor placed in the engine's exhaust manifold measures the averag concentrations of oxygen in the exhaust gasses coming from all the combustion chambers.

This has certain disadvantages

The first disadvantage is ow ing to the fact that, even in the case of correct combustio ol the mixture, the measurement docs not demonstrate if there arc any deviations in the aver age values of the concentrations of oxygen in the exhaust gasses from the combustion cham bers, or what is the extent of the deviations

An even greater disadvantage occurs in the case of incomplete combustion of the mix ture in one or more combustion chambers, for example, because of a sparking plug not func tioning, or a timing valve which is not correctly timed. In these case, the concentration o oxygen in the exhaust gasses is extremely high, not because the mixture is particularly lean but because the oxygen is not chemically combined with the hydrocarbons. The value of th sensor signal, howe\ cr, indicates a lean mixture; and the computer to which the sensor i connected enables the feeding elements capable of controlling the flow of the fuel to make th mixture πcher. If the failure in ignition is due to a lean mixture, an enπchment of the mixtur can improve the combustion. Generally, however, an enπched mixture is damaging on tw counts: firstly, because it aggravates the problems of ignition with a flooded sparking plug and secondly, because the exhaust gasses contain concentrations of oxygen and hydrocar bons which increase at each operating cycle. The chemical reactions which take place in th catalytic muffler are changed by the high concentration of oxygen and hydrocarbons, and th result is this alteration accompanied by overheating, with the possible destruction of th muffler.

The purpose of this invention is to remedy these defects.

The invention, as claimed, solves the problem of creating a ulti -function feedbac control system for internal combustion engines, without using operating diagrams, an which is fitted w ith self regulating means to control every working state of the engine; in system according to the present invention the signals of the oxygen sensors are used to con trol the entire process of carburation in every operating condition of the engine.

The advantages offered by the present invention consist essentially of the fact that, i addition to providing a more accurate regulation than that obtained by the system descπbed in EP - A - 0 046 305, it docs not include the use of an operating diagram of the engine, it indi¬ cates to the driver any malfunctioning of the engine and the catalytic muffler, adapts the air- fuel ratio to suit different working states and prevents knocking.

Other advantages, features and aims of the invention, may be more readily understood by referring to the accompanying drawings, which concern preferred embodiments, in which:

Fig.1 shows the diagram of the values in tension of an oxygen sensor, that is generally used to control the exhaust gasses of an internal combustion engine;

Fιg.2 illustrates schematically a lateral view of a cylinder of an engine fitted with a con¬ trol system according to the present invention; Fιg.3 illustrates schematically a plan of an engine fitted with temperature and oxygen sensors placed m the exhaust system of the engine;

Fig. 4 represents schematically a first embodiment of a flowmeter for measuπng the air¬ flow amount in the system shown in Fιg.2;

Fιg.5 represents schematically a second embodiment of a flowmeter for measuπng the air-flow amount in the system shown in Fιg.2;

Fιg.6 represents schematically a fast idle device with a shutter in an intercepting posi¬ tion to intercept a by-pass canalisation,

Fig.7 represents the fast idle device with the shutter in the open position to open the by¬ pass canalisation; Fιg.8 represents schemaucally the part of the suction duct in which a socket for a senso is inserted which measures the vacuum after the throttle valve.

The cun c of Fig. 1 represents the \ alucs ol the oxygen sensor signal, said signal havin two levels L] and I_2, which indicate, respectively, a lean and a rich air-fuel ratio of the mix¬ ture. It should be noted that currently only the two tension levels, Lj and L2, are taken int consideration to correct the air-fuel ratio with the aim of approximating it to the value λ=l which represents the stoichiometπc value of the mixture. The value λ is defined as the "ai number" and represents the ratio between the mass of the air which is contained in the mix¬ ture supplied by the feeding devices and the mass of air which is required to obtain the stoi chiometπc value. Following a convention which has existed for about twenty years the axis of abscissas which represents the "air number" shows decreasing values of λ. In the know control systems the values of Li and L2, are comprised between 0,2 and 0,8 V., th commutation between levels L] and l_2 occurs in a fairly limited range of λ-=l.

Trials carried by the applicant demonstrated that an oxygen sensor gives valid indica tions for controlling the engine in the whole field of the curve of the values of the sensor sig nal. In order to obtain sufficiently reliable experiments the curve of the sensor signal was di vided into a certain number of parts. It was noted that it is also possible to maintain a correc combustion in transitory phases for values of λ which lie within predetermined fields Δλ of values, constituting groupings of the subdivision.

By using suitable methods for adjustment, it is possible to reduce the field to ensure very accurate control of combustion, even for values of λ which are relatively distant fro λ=l .

The control system illustrated in Figs. 2 and 3 comprises a feeding device 1 whic consists essentially of a flowmeter for measuring the amount of air which feeds the engin and one or more feeding elements 35 capable of controlling the flow of the fuel. The latte may be injectors or carburettors, and their quantity depends on the type of engine to be fed.

The feeding device 1 is connected to suction-valves 2 of combustion chambers 3 b means of suction pipes 4; each of the combustion chambers 3 is provided with an exhaust valve 5 which leads to an exhaust pipe 6 which opens up into an exhaust manifold fitted wit catalytic muffler 7 before which a main oxygen sensor 8 is inserted. In each of the exhaus pipes 6 there is a secondary oxygen sensor 8.

The sensors 8 are electrically connected to a central control unit 9 which receives othe electric signals from a large number of sensors (not illustrated). These sensors measure th angular speed R.P.M. and the temperature T of the engine, the temperature Ta, the humid ity U and the pressure Pa of the sucked air in the intake system and similar parameters whic have an effect on the running of the engine and process of carburation.

A first thermometer 10 is provided in each of the exhaust pipes 6 to measure the tem perature of the exhaust gasses which come from chambers 3 through the valves 5, and a sec ond thermometer 1 1 is placed after the catalysing mass 12 to measure the temperature of th gasses which co e from the muffler 7 after going through the process of oxidation rcduc tion.

Thermometers 10 and 11 are connected to inlets of unit 9 so as to send it the respectiv electric signals. Other sensors, which are situated in the feeding device 1 and in the part o the intake manifold which is after a throttle-valve 13, are connected to the unit 9, as will b explained below. In addition, there is a knock sensor 14 connected to another inlet of unit 9. For each combustion chamber 3 there are corresponding thermometers 10 and, if th engine has a feeding device for each combustion chamber 3, the sensors cooperating with th feeding ducts are equal the number of chambers 3

The flowmeter represented in Fig. 4 is an integral part of the feeding device 1. A Ven tun 15 has an entrance 16 connected to an air filter (not represented) and an outlet 17 whic is connected to the suction pipes 4.

A diaphragm 18 divides two chambers 19 and 20 which are closed inside a box 21, an connected to the throttling of the Vcntuπ 15 and to a side of the tube which is located befor said throttling, the connections being obtained by pipe-fittings 22 and 23. A spring 24 situat ed in the chamber 19 presses on the diaphragm 18 to restrict its movements owing to th vacuum Δp existing in the throttling of the Ventuπ. A sensor 25 of the position of the di aphragm 18, ol the t pc without contact (capacitivc sensor or similar sensor) measures th position of the diaphragm 18 and is connected to unit 9 so as to send to unit 9 an electrica signal, the value of w hich represents the position of the diaphragm 18. An adjusting elemen 26 is provided to adjust the load of the spπng 24, the thread of said element 26 bein screwed in the part of the box 21 delimited by the chamber 19.

Unit 9 is connected to one or more injectors 35 or other feeding elements capable o controlling the flow of the fuel to control the air-fuel ratio of the mixture that is delivered i accordance with the value of the signal of the sensor 25. Fig. 5 represents a second embodiment of a flowmeter for meteπng the flow amount o the air sucked by the motor; this flowmeter dif fers from that of Fig. 4 in one respect, that is leaf spring 27 presses on diaphragm 18, the load of the spring 27 being regulated by an ad justing screw 28.

Figs. 6 and 7 represent a fast idle device consisting of a shutter-valve 29 placed in first closed position and a second open position, respectively, of a by-pass canalisation 30 the by-pass canalisation 30 connecting a hole 31 before the throttle 13 with a hole 32 after th same throttle 13. The fast idle device is controlled by the central control unit 9 according t the value of the signal of the second thermometer 11, the fast idle device being capable o shortening the warming-up time of the catalysing mass 12 and of maintaining it in function The shutter \ al\ c 29 is clcctπcall connected to the unit 9 which is capable of movin said valve 29 Iron, f irst to second position or maintains it in a position between the first an the second position, which allows a preestablished low running speed when the temperatur measured by the second thermometer 1 1 shows that the catalysing mass 12 is working.

Fig 8 illustrates a dc\ ice to measure the vacuum in the intake manifold after the throttl 13. The device consists of a pressure sensor 33 connected by means of a tube 34 to a part the intake manifold placed alter the throttle 13; said pressure sensor 33 being connected to th unit 9 which, after elaborating of the signal of the pressure sensor 33 compares the values o the same signal which follow each other and calculates the gradients according to a timer (no shown) having a predetermined frequency. The central control unit 9 consists of electrical networks and of electronic component which control the feeding elements 35 by means of control signals. Customarily, these func tions are aimed at maintaining the air-fuel ratio of the mixture which feeds the chambers 3 at the best value in every working condition of the engine.

There are two reasons for the precise and continuous control of air-fuel ratio: the first i to allow the catalytic muffler 7, in which the reactions of oxidisation reduction take place t remove the pollutants, to function correctly; the second more important and innovative reason is the control of the process of carburation in each working condition of the engine.

Customarily, the unit 9 sends control signals to the feeding elements 35 in differen ways in accordance with the type ol^" same elements in order to define the air-fuel ratio; in an case the control signals of the unit 9 arc sent in accordance with the position of the diaphragm

18, and corrected according to the values of the signals from main and secondary oxyge sensors 8. In the case of injectors, the unit 9 sends said control signals to the injectors to es tablish the timing of their opening; in the case of carburettors, unit 9 is connected to an elec¬ tromagnetic actuator and sends said control signals to the latter to vary the passage section o the main jet, the jet of the air of emulsion or the other jets capable of defining the quantity o fuel and/or air of emulsion.

The phases which concern the operations of the engine are essentially the following:

1. idle phase;

2. slow running at low and medium load; 3 constant running at high speed and full load;

4 transitory phases of acceleration;

5 transitory phases of deceleration and of released gas pedal.

These phases may occur both in the period of warming up the engine and at the norma working temperature. The running phases are recognised by unit 9 in accordance with the temperature Tm, th angular speed R.P.M. of the engine, the flow amount indicated by the sensor 25 and th variation of the vacuum in intake manifold.

In conditions of "static" running, according to the load applied to the engine, the tem perature Tm, the flow amount of air and other parameters cited, the unit 9 sends control sig nals to the feeding elements 35 to define an air-fuel ratio which can be slightly richer o leaner in accordance with the running phase. After an interval τi of some milliseconds, which corresponds to the time taken by the mixture to enter the combustion chamber 3, to be transformed into the exhaust gasses and surround the sensors 8, plus the response time ol the sensors 8,. the value of the signal of the sensors 8 indicates to unit 9 if the result of the carburation is correct or not. In the first case the unit 9 sends control signals to the feeding elements 35 to confirm this action; in the second case the unit 9 sends control signals to the feeding elements 35 to modify this action in order to obtain the correct result.

The transitory phases of acceleration follow a sudden opening of the throttle 13. The first effect following this opening is the vaπation of the load applied to the engine, which may be sensed by reading the vaπation of the position of the throttle 13 with a calibrated po¬ tentiometer, or by reading the vaπation of vacuum in the intake manifold after the throttle 13

The start of a transitory phase may be recognised by means of the pressure sensor 33. The sudden opening of the throttle 13 is followed by an increase in pressure in the intake manifold. If the value of the increasing of pressure in a pre-established interval of time ex- ceeds a prescribed threshold, which is defined according to the type of engine's running, the unit 9 will temporarily increase the richness of the mixture for the phase of acceleration; thus, in an instant immediately following the opening of the throttle 13, said unit 9 sends control signals to the feeding elements 35 to immediately increase the richness of the mixture. After an interval of time T2_, which can be different from or the same as x\ the sensors 8 inform the unit 9 of the results of cnπchmcnt. If the result is correct, unit 9 sends control signals to the feeding elements 35 to confirm this action, or alternatively, sends control signals to the feeding elements 35 to modify this action in order to obtain the correct result.

Expenmental tπals earned out by the applicant have shown that an air-fuel ratio slightly richer than the stoichiomctπc ratio can be maintained by defining the carburation so that each sensor 8 will work in field Δλ. By this means, a mixture which is suitable for an acceleration may be guaranteed without having a negative effect on the emission by establishing the addi¬ tional quantity of fuel for the acceleration, and by means of the sensors 8, it may be veπfied at the end of peπod T2 if the additional quantity is insufficient, sufficient or excessive.

All this ma\ be obtained by sell regulating means. If unit 9 recognises that the addi- tional quantity established in a phase of acceleration is, for example, excessive, and reaches excessive quantities of pollutants, the next time the unit 9 recognises an analogous condition of acceleration, it sends a control signal to the feeding elements 35 so as to dimmish the ad¬ ditional quantity without waiting for the signals ol the sensors 8. This can be obtained with suitable networks, making the system capable of learning the best interventions for the run- ning of that particular engine. The self regulating means are capable of memoπsing the vaπa- tion of the flow ratio of fuel defined for each variation of load, each angular speed of the en¬ gine and each variable working condition of the engine, the parameters of the variation of load and the result of the combustion; for each variation of load at analogous angular speed and variable working condition, the unit 9 sends analogous control signals to the feeding el- ements 35 so as to define independently the variation of the fuel flow ratio in accordance with the previous analogous results.

During a transitory of deceleration by released gas pedal the unit 9 sends control signals to the feeding elements 35 to cut-off the fuel flow, except when beginning again to send control signals to rcfeed the engine near idle speed so as not to have an irregular carburation. The flowmeter for metering the amount of air-flow in Fig. 5 is particularly designed for this control system. The diaphragm 18 which is loaded by the very flexible leaf spring 27 is preferably of the type for gas meters, and constitutes a measuring system with very low iner¬ tia and hysteresis, which is in equilibrium between the pressures which act on the two sides of the diaphragm 18; therefore, for every value of the difference Δp between said pressures, there is a corresponding position of the diaphragm 18, which is measured by the sensor 25.

Since the displacement of the diaphragm 18 measured by the sensor 25 is a linear function of Δp, it is possible to ascertain the air-flow amount which passes through the Venturi 15; this amount being proportional to the square root of Δp. Once this device for metering the amount of air-flow has been adjusted, the value of the output signal of the sensor 25 indi- cates the amount of air- flow which passes through the Venturi 15.

A suitably differential pressure sensor may be used instead of the diaphragm 18 to mea¬ sure the field of the quantities from minimum to maximum, the ratio of which may exceed the value of one in forty.

The problem solved by a similar flowmeter lies in the fact that, if the ratio between the minimum and maximum amount of air-flow is one in thirty-five, the ratio between the maxi¬ mum and minimum difference in pressure Δp is about one in a thousand; therefore a ratio of one in a thousand must be read. We have a Δp ranging from a maximum of several meters to a minimum of a few millimetres of H2O. The flowmeter is designed to measure the dis¬ placement of the diaphragm 18 owing to the differences in pressure of a few millimetres and to withstand the differences in pressure of several meters of H2O.

The advantage of a flowmeter with a diaphragm is that if the latter is loaded by a suit¬ able spring, for example, a leaf spring 27, when the diaphragm 18 is in a first state of equi¬ librium, a difference in pressure Δp of one millimetre of H2O, for example, can move it by a millimetre, thus demonstrating that the flowmeter is extremely sensitive. When the di- aphragm 18 is in a second position of equilibrium, where the spring has a greater load, a dif- 1 0

ference in pressure of hundred millimetres of H2O, for example, is needed to move the di¬ aphragm by a millimetre. This measuring device increases its rigidity according to the in¬ crease of the air-flow amount.

The flowmeter with a Venturi measures the volume of the of air-flow amount. To obtain a measurement in weight it must be equipped with a thermometer and an air pressure sensor placed in the entrance 16 of the Venturi 15.

A measuring device for the amount of air has been realised which permits a sufficiently refined carburation. One value of the air-flow amount corresponds to each position of the di¬ aphragm 18, the position being recognised by the sensor 25 connected to the unit 9, which, in accordance with the position recognised, sends control signals to the feeding elements 35 so as to feed the engine with a fuel amount which is in proportion to the amount of air. At the end of intervals of time T] and T , in accordance with the value of the signals from the sen¬ sors 8, all corrections to maintain the correct mixture ratio arc carried out, if necessary.

The unit 9 is capable of ascertaining and correcting any errors of the flowmeter by com- paring the theoretic curve of the differences in pressure Δp expressed as a radical function with the actual curve of the flowmeter. The unit 9, after ascertaining one or more anomalies in the curve, is capable of correcting the curve. Thus, after the system has functioned several times, it eliminates the errors and corrects itself.

It is possible to realise an unit 9 which, in accordance with the of air-flow amount mea- sured by the flowmeter with Venturi establish the fuel flow amount to be fed. In theory, the Venturi device should function by a law of a radical type, but in view of the way the engine, the diaphragm 18 and the intake manifolds are made, the curve of the Venturi is not always regular, i.e. at certain points of the curve it is necessary to enrich the mixture and at certain points to make it leaner. The main and secondary sensors 8 recognise this behaviour of the curve. It is possible to develop an unit 9 which learns to recognise and correct the error of the

Venturi device by noting the behaviour of the sensors 8 which have measured values differ¬ ent from the predetermined air-fuel ratio in some points of the curve. The unit 9 can be able to reason in this way: if I have found a rich ratio when passing a certain number of times at a given point, and therefore it was necessary to thin it, when I pass that point again I will have to thin it without the sensor 8 telling me to. In other words, I will correct this curve and con¬ struct a curve which w ill be correct.

A Venturi device used as a flowmeter has a great advantage over flowmeters with sluice valves which penalise the engine on account of heavy load loss in the zone of the sluice valve. A properly shaped Venturi device causes much smaller load losses and increases the volumςtric efficiency of the engine. 1 1

To obtain the variation of the air-fuel ratio in every running condition of the engine (ac¬ celeration, warming up and so on), unit 9 sends control signals to the feeding elements 35 to enrich the mixture according to the information of the sensors 8 and of the flowmeter, elimi¬ nating the necessity for any operating diagram. Since the Venturi device measures the a mass air-flow amount, notes the amount and knows that the stoichiometric ratio of the mixture is 14.7, the mass of air is divided by 14.7 to ascertain the mass of fuel flow to feed the engine. When the characteristic of the injectors, which for each unit of time of opening supply a known quantity of fuel, is known, the time for the opening of the injectors may be established. Similarly the position of the actuator may be established in cases where carburettors are used.

In actual fact, no one cylinder functions like another, and with a single oxygen sensor the averages of the emissions from all the cylinders can be read.

If a secondary oxygen sensor 8 is placed in the exhaust pipe 6 of each combustion chamber 3, the sensor 8 is heated better, being surrounded by very hot gas, but above all, the proper control of the engine may be obtained. The chambers 3 fed by a rich and a lean mix¬ ture may be discerned, and the problem of the dimensional differences in size and fuel flow amount from the injectors may be solved, the injectors which deliver more and those that de¬ liver less both being discerned.

Basically, the control system according to the invention comprises: a feeding device 1 fitted with feeding elements capable of controlling the flow of the fuel (injectors, carburet¬ tors, etc.); an engine; a catalytic muffler 7 with a catalytic mass 12 to remove the pollutants coming from the engine; a central control unit 9 with electronic components which elaborates electrical signals in accordance with parameters which act on the carburation to supply con¬ trol signals which act continuously on said feeding elements 35; at least one oxygen sensor 8 placed in the exhaust system of the engine and electrically connected with the central control unit 9, said system also includes an air-flow amount measuring device for measuring the air¬ flow amount, said measuring device being placed in the feeding device 1, which sends to the central control unit 9 electrical signals in accordance with the measured air-flow amount; the central control unit 9 being capable of elaborating the signal coming from the oxygen sensor 8 so that a reciprocal correspondence between the values in tension of the signal of the oxy¬ gen sensor 8 and the corresponding values of the air-fuel ratio of the mixture is established; by means of said correspondence a corresponding value of the control signal is obtained, said value optimising the air-fuel ratio of the mixture in every operating condition of the en¬ gine. A feedback control system is thus obtained. All known systems for the control of vehicle engines make the oxygen sensor cut out and go out of control, for example, under full power. The system according to the present invention controls the engine by regulating itself in any running state of the engine.

The fact that there is a secondary oxygen sensor 8 for each exhaust pipe 6 of each com- bustion chamber 3 means that the process of carburation can be controlled cylinder by cylin¬ der.

Advantageously, the second thermometer 1 1 is placed after the catalysing mass 12 to obtain a measurement of the working of the muffler 7. If for every hundred ignitions in one of said combustion chambers 3 one is missing because the sparking plug is badly fitted or a valve is not timed correctly, the relevant secondary oxygen sensor 8 will read a lean mixture because a lot of oxygen is present in the exhaust gas with a large quantity of hydrocarbons. By using a single sensor 8 without said second thermometer 11, an abnormally rich mixture will obviously be obtained and the unburnt gasses reach the muffler 7 because a large amount of oxygen is recognised by main sensor 8. The phenomenon tends to increase rapidly and the efficient functioning of the catalytic muffler 7 is impaired.

With the second thermometer 1 1 (for example, a thermocouple) placed in the outlet of the catalysing mass 12, if one of the oxygen sensors 8 reads "lean" and the temperature is in¬ creasing, it means that there are missing ignitions. By means of the signals from the ther¬ mometer 11 and from the sensors 8, a diagnosis of the missing ignitions and of the malfunc- tioning of the timing valves may be obtained.

With an arrangement of this kind, if the temperature of the muffler 7 exceeds a deter¬ mined temperature threshold, for example 900 degrees, an acoustic or visual signaller (not represented) connected to unit 9 warns the driver of the dangerous thermic state of the muf¬ fler 7 and advises him to slow down so as not to damage the muffler 7 and the vehicle. Preferably, the acoustic or visual signaller sends a first danger warning at 850 degrees.

If the driver does not slow down and 900 degrees are reached, unit 9 sends control signals to the feeding elements 35 to diminish the power. In fact, the unit 9 is designed to act in such a way that if the signal of the thermometer 11 of the catalytic muffler 7 indicates that if the tem¬ perature rises above a determined threshold unit 9 will elaborate control signals which, sent to feeding device 1, enable it to lessen the power by degrees. At first it reduces the power by a certain percentage, but if the temperature continues to remain above the threshold, the re¬ duction of the power proceeds gradually until the temperature is below the danger level.

In order to reduce the power, a device may be used which chokes the amount of air¬ flow in the intake manifold, or the unit 9 may send control signals to feeding elements 35 to make the mixture lean until it reaches a ratio above, for example, 20 - 22 kilograms of air per kilogramme of fuel, which keeps the engine at an inefficient thermic state.

The fact that according to the present invention there is a signal of the sensor 8 in every running state of the engine permits it to be established if the increase in temperature in the catalytic muffler 7 is on account of its malfunctioning, its faulty ignition or a timing valve which has not been properly timed. If the signals of the oxygen sensors signal indicate that the mixture is lean and the thermometer signal 11 indicates an excessively high temperature, ignition does not occur properly or a valve is not timed properly.

This may also be obtained with the main sensor 8, provided the thermometer 1 1 has been placed after the catalysing mass 12.

The system diagnoses any breakdown: unit 9 memorises the data, making it possible for the driver to reach a mechanic, and informs him that there are problems in the ignition or valve timing.

The strategy that is adopted when unit 9 receives the above signals from the oxygen sensors 8 and the thermometer 11 is original: power is reduced in defined dangerous situa¬ tions and a diagnosis is made. Unit 9 shows what is the cause of the increase in temperature. One of the sensors 8 has read "lean" and the thermometer 11 indicates an increase in tempera¬ ture. It is not therefore necessary to enrich the mixture as requested by the sensor 8, but in¬ stead to maintain it at the value calculated by the flowmeter which, however, permits the en- gine to function reasonably well, even with regard to pollutants. Unit 9 shows that the mal¬ functioning is due to the fact that unburnt fuel is coming from at least one combustion cham¬ ber 3, with consequent lack of ignition, or that there is insufficient compression, informs the driver of the need for mechanical repair work and indicates the type of fault, as well as pre¬ venting damage to the engine and the muffler 7, and keeping the engine functioning so that the vehicle is not out of control, for example when overtaking.

It is not easy to carry out this strategy with the known systems using an operating dia¬ gram of the engine because the diagram is a rigid system. If the oxygen sensor signals a lean ratio and the thermometer 1 1 indicates an increase in temperature so that the system is in er¬ ror, it is not possible to drive the engine unless the sensor is completely inactivated. This would result in the inevitable increase in pollutants, even when the temperature descends to a level which is not dangerous.

In a system equipped with flowmeter, however, which permits a reasonably correct carburation, unit 9 can be made to complete the diagnosis of the fault and will provide a suf¬ ficiently correct process of carburation simply by means of the flowmeter so that the vehicle can conti nue .to ru n . A sensor 8 in the exhaust pipe 6 of every combustion chamber 3 is used for a more ac¬ curate control. This eliminates the feeding of a cylinder which is not igniting or a badly ad¬ justed valve. This prevents the catalysing mass catching fire or the flooding of the cylinder barrel. The engine functions with reduced power and the driver is able to get to a mechanic without the engine suffering any great damage.

By adopting the thermometer 1 1 and one oxygen sensor 8 in the exhaust manifold the advantages that have been outlined can be obtained, but with one sensor 8 in the exhaust pipe 6 of every combustion chamber 3, there are many more. A further advantage is provided by the thermometer 10 for the temperature of the gasses coming from each combustion chamber 3. By using this thermometer 10 together with the thermometer 11 for measuring the tem¬ perature of the catalytic muffler 7 indicated by the thermometer 11, the deterioration of the muffier 7 is impeded. By means of measuring the temperature of the gasses which come from each combustion chamber 3, what is happening in each combustion chamber may be immediately observed. If one of the combustion chambers 3 is not igniting or the valve is badly timed, the temperature of the gasses from this chamber 3 is lowered. By linking the thinness with the lowering of the temperature it is very easy to indicate which combustion chamber is defective. In this way a complete control involving each combustion chamber as well as other procedures may be carried out.

The system with one sensor 8 in the exhaust manifold and one thermometer 11 also permits it to be ascertained when the muffler 7 has reached the working temperature. One of the most serious disadvantages of vehicles with a catalytic muffier lies in the fact that given that the average journey in a town is not sufficiently long for the muffler to reach working temperatures, since the time to reach the temperature in which oxidisation reduction can begin is linked to the average journey time. The mufflers of vehicles used in journeys lasting for a few minutes do not reach the temperature for catalysis. It is therefore important that the muf¬ fler 7 should reach the working temperature as soon as possible.

Various strategies may be employed to obtain rapid efficiency of the muffler 7. One method consists of making the exhaust gasses sufficiently hot, which may be done by mak¬ ing the engine function with a lean mixture or by retarding the ignition. Another method consists of increasing the low running speed of the engine until the muffier 7 has reached its working temperature. This can be effected by using a fast idle de¬ vice, like that illustrated in Figs. 6 and 7.

Another way is to indicate to the driver that the catalysing mass is not working.

If the driver is aware of these indications, he can keep the motor at a high angular speed. At 3000 R.P.M. the catalysing mass will warm up quickly. An indicating light connected to unit 9 can show when the muffler 7 is starting to work, for example it can come on when the thermometer 11 measures a temperature which is lower than that at which the catalysing mass was working at the start.

This indicating light is also very uselul in analysing the efficiency of the catalysing mass. If the carburation is correct when the reaction begins, the CO and the HC are oxidised to the detπment of the residual oxygen. The NOx are reduced afterwards.

The indicating light showing the efficiency of the catalysing mass can also make a diag¬ nosis. If, for example, a year ago the muffler 7 started to work efficiently forty seconds after the engine has started, and now takes place a minute and a half after, this means that the muffler 7 is detenoratmg. If it never comes on it means that the muffler has completely dete- πorated. A timer connected to the unit 9 measures the time in which the muffler 7 has reached a predetermined temperature; if said temperature is not reached in a predetermined time, ac¬ cording to the load, angular speed and variable working condition, the unit 9 shows by means of a signaller the inefficiency of the catalysing muffier 7. In general, the temperatures measured by thermometers 10 and 11 together with the values of the signals from the oxygen sensors 8 indicate any malfunctioning of the engine If the temperature ol the burnt gasses and the catalysed gasses diminish and the values of the signals from one sensor 8 of a chamber 3 and of the mam oxygen indicate a lean mixture, this means that the combustion in that chamber 3 is not complete owing to a badly connected sparking plug, a timing valve which is not timed properly or likewise. The deficient chamber is indicated by one of the thermometers 10 which indicates a loweπng of the temperature. If the temperature measured by the thermometer 11 increases, the temperatures measured by the thermometer 10 do not change, and a sensor 8 indicates a πch mixture, this means that one of the feeding elements 35 has not functioned. The defect is indicated by that sensor 8 which shows an enπchment of the mixture. It is obvious that these indications may easily be sent to unit 9 to be signalled to the driver or to obtain the correct strategies for improvement. The part of the engine which is not functioning properly will be isolated, the part in question which will be indicated.

The central control unit of known control systems also have a diagram of the ignition time, and carries out a correction of ad . anced ignition according to the level the signal of main oxygen sensor.

The system according to the present invention uses a knock sensor 14 connected to unit 9 to prevent the engine knocking. If the knock sensor 14 is placed in the external wall of one combustion chamber 3, the maximum ignition ad\ anced can be maintained in every running condition without knocking, so as to improve the performance of the engine. An automatic spark ignition advance device is provided, which has the effect of increas¬ ing the advance of the ignition of the engine; the knock sensor 14 being connected to the unit 9 which, indicating a knocking, acts on the spark ignition device to reduce the advance of the ignition in order to prevent the knocking immediately; immediately after, the spark ignition device increases the advance of the ignition again.

This also allows the ignition of the engine to be integrated in unit 9 to eliminate the use of a diagram, establishes an arranged spark advance in the starting phase and closes the loop immediately after the engine starts. As the sensor 14 is able to recognise knocking immedi¬ ately after a few working cycles, ignition is advanced until knocking no longer takes place. When the sensor 14 indicates knocking, unit 9 retards ignition until knocking stops.

By affecting the ignition, the lambda factor of the engine may be changed. Advanced ignition may be effected in accordance with the signal from one or more sensors 8.

Claims

1. A multi-function feedback control system for internal combustion engines compπs- mg: a feeding device ( 1) fitted with feeding elements (35) capable of controlling the flow of the fuel (injectors, carburettors, etc.); an engine; a catalytic muffler (7) with a catalytic mass (12) to remove the pollutants coming from the engine; a central control unit (9) with electron¬ ic components which elaborates electrical signals in accordance with parameters which act on the carburation to supply control signals which act continuously on said feeding elements (35); at least one oxygen sensor (8) placed in the exhaust system of the engine and electncal- ly connected with the central control unit (9), characterised by the fact that said system also includes an air-flow amount measuring device for measuring the air-flow amount, said mea¬ suπng device being placed in the feeding device ( 1), which sends to the central control unit (9) electπcal signals in accordance with the measured air-flow amount; the central control unit (9) being capable of elaborating the signal coming from the oxygen sensor (8) so that a recip- rocal correspondence between the values in tension of the signal of the oxygen sensor (8) and the corresponding values of the air- fuel ratio of the mixture is established; by means of said correspondence a corresponding value of the control signal is obtained, said value op¬ timising the air-fuel ratio of the mixture in every operating condiuon of the engine.

2. A multi-function feedback control system as in claim 1, wherein an oxygen sensor (8) is placed in the exhaust pipe (6) of every combustion chamber (3) of the engine.

3. A multi-function feedback control system as in claim 1, wherein a primary ther¬ mometer (11) is provided at the outlet of the catalysing mass (12) of the muffler (7), the pri¬ mary thermometer ( 11 ) being connected to the central control unit (9) to send to the central control unit (9) an electπcal signal, the value of which represents the temperature of the gases coming from the catalysing mass ( 12).

4. A multi-function feedback control system as in claim 3, wherein a fast idle device is provided which is controlled by the central control unit (9) according to the value of the sig¬ nal of the pπmary thermometer ( 1 1), the fast idle device being capable of shortening the warming-up time of the cataKsing mass ( 12) and of maintaining it in function

5. A multi-function feedback control system as in claim 4, wherein the fast idle device compπses a movable element (29) placed in a by-pass canalisation (30) which moves from a first position to close the canalisation (30) to a second position to open the canalisation (30), the movable element (29) allowing an accelerated low running, which increases progressive¬ ly when the ablc element (29) mo\ es towards the second position; the movable element (29) being connected to the central control unit (9), which moves said movable element (29) from first to second position or maintains said movable element (29) in a position between the first and the second position, which allows a pre-established low running speed when the temperature measured by the primary thermometer ( 11 ) shows that the catalysing mass (12) is working.

6. A multi-function feedback control system as in claim 3, wherein a signaller is pro¬ vided, which is connected to the central control unit (9) controlled by the primary thermome¬ ter ( 1 1); the signaller showing the state at which the catalysing mass (12) is failing to work for a temperature value measured by the primary thermometer (11) is lower than the value at which the catalysing mass (12) begins to work.

7. A multi-function feedback control system as in claim 3, wherein an acoustic or visual signaller is provided, which is connected to the central control unit (9) to signal to the driver the dangerous thermic state of the muffier (7) when said primary thermometer (11) shows the temperature of the gases is higher than a predetermined value.

8. A multi-function feedback control system as in claim 7, wherein when the tempera- ture measured by the primary thermometer ( 1 1 ) is higher than a first temperature threshold, which is close to the temperature which is dangerous for the muffler (7), the acoustic or vi¬ sual signaller sends a first danger signal; when the driver does not reduce the required power and a second threshold of temperature dangerous for the muffler (7) is reached, the central control unit (9) acts on the feeding device (1) to decrease the power of the engine by stages; at first the central control unit (9) decreases the power by a first predetermined amount; if the temperature remains still higher than the second threshold, the central control unit (9) de¬ creases the power by stages again until the value of the temperature is lower than the danger¬ ous value.

9. A multi-function feedback control system as in claim 3, wherein when the central control unit (9) receives signals from the oxygen sensors (8), which show an excessive con¬ centration of oxygen in the exhaust gases and, at the same time, signals from the primary thermometer (11), which show an excessive temperature, said unit (9) defines the carbura¬ tion so as to prevent the engine and the muffler (7) from being damaged, in addition the unit (9) docs not stop the engine, but indicates by means of suitable signallers, to which it is con- nected, that the anomalous working of the engine is due to the fact that unburnt fuel is com¬ ing out from at least one of the combustion chambers (3)

10. A multi-function feedback control system as in claim 1, wherein a measuring device is provided to measure the variation in the pressure in the intake manifold after the throttle valve ( 13), the measuring device consisting of a pressure sensor (33) which measures the pressure value in the intake manifold and is connected by means a tube (34) to a part of said intake manifold after the throttle valve ( 13); said pressure sensor (33) being connected to the unit (9) which, after elaborating of the signal of the pressure sensor (33), compares the val¬ ues of the same signal which follow each other and calculates the gradients according to a timer having a predetermined frequency.

11. A multi-function feedback control system as in claim 10, wherein for a gradient higher than a predetermined threshold defined according to the working phase, the unit (9) sends control signals to the feeding elements (35) for a temporary variation of the air-fuel ra¬ tio during a transitory phase; after a time (T2), which corresponds to the time that the mixture takes to enter the combustion chamber (3) to be burned and to surround an oxygen sensor (8) in addition with the response time of the same oxygen sensor (8), the system starts its feed¬ back system working again; thus the unit (9) sends the control signals to the feeding elements (35) according to the signals coming from the air-flow amount measuring device and the oxygen sensors (8).

12. A multi-function feedback control system as in claim 1 , wherein a secondary ther- mometcr ( 10) is provided in the exhaust pipe (6) of each combustion chamber (3), said sec¬ ondary thermometer (10) cooperating with said primary thermometer (11) to prevent the muffler (7) or other devices of the engine (timing valves or the like) from being damaged.

13. A multi-function feedback control system as in claim 12, wherein each of the sec¬ ondary thermometers (10) cooperate with the oxygen sensor (8) of the relevant exhaust pipe (6) and with main oxygen sensor (8) placed before the muffler (7) to obtain diagnoses of the malfunctioning of parts of the engine; if the combustion in one of the chambers (3) is not completed, the temperature of the gases coming from the same chamber (3) has not a normal value; by reading the values of the signals of the oxygen sensors (8) and the value of the temperature measured by the secondary thermometer (10) relevant to one chamber (3), the unit (9) shows by means of a suitable device the state of any damage in one or more cylin¬ ders and controls all the cylinders.

14. A multi-function feedback control system as in claim 12, wherein the main oxygen sensor (8) and one of the secondary oxygen sensors (8) placed in the exhaust pipe (6) of one of the combustion chambers (3) cooperate with one of the secondary thermometers (10) of the gases coming out from that chamber (3) and with the primary thermometer ( 11) of the temperature of the muffler (7) to send signals to the unit (9), the values of which show mal¬ functioning of one or more devices of the engine; by elaborating said signals, the unit (9) acts on the feeding elements (35) to eliminate this malfunctioning and/or to minimise the danger¬ ous effects.

15. A multi-function feedback control system as in claim 12, wherein the main oxygen sensor (8) and one of the secondary oxygen sensors (8) cooperate with one of the secondary thermometers (10) of the gases coming out from one of the chambers (3) and with the prima¬ ry thermometer (11) to send signals to the unit (9), the values of which show changes in the functioning of one or more devices of the engine; by elaborating said signals, the unit (9) in¬ dicates the malfunctioning by activating signallers to which it is connected.

16. A multi-function feedback control system as in claim 1, wherein an automatic spark ignition advance device is provided, which has the effect of increasing the advance of the ignition of the engine; a knock sensor ( 14) being connected to the unit (9) which, indicating a knocking, acts on the spark ignition device to reduce the advance of the ignition in order to prevent the knocking immediately; immediately after, the spark ignition device increases the advance of the ignition again.

17. A multi-function feedback control system as in claim 1, wherein the unit (9) is pro¬ vided with self regulating means which memorise the variation of the flow amount of fuel defined for each variation of load, each angular speed of the engine and each variable work¬ ing condition of the engine, the parameters of the variation of load and the result of the com¬ bustion; for each variation of load at analogous angular speed and variable working condi¬ tion, the unit (9) acts on the feeding elements (35) by means of a direct command so as to define independently the variation of the fuel flow amount in accordance with the previous analogous results.

18. A multi-function feedback control system as in claim 1, wherein it further compris¬ es a timer connected to the unit (9) which measures the time in which the muffier (7) has reached a predetermined temperature; if said temperature is not reached in a predetermined time, according to the load, angular speed and variable working condition, the unit (9) shows by means of a signaller the inefficiency of the catalysing muffier (7).

19. A multi-function feedback control system as in claim 1, wherein the air-flow amount measuring device consists of a Venturi (15), a diaphragm (18) having a first side, on which the vacuum of the throttling of the Venturi (15) acts, and a second side, on which the pressure of the part of the Venturi ( 15) before said throttling acts, a spring (24,27) which acts on the diaphragm ( 18) to restrict the movements due to the difference (Δp) of the pres¬ sures which act on said first and second sides of the diaphragm (18), and a sensor (25) of the position of the diaphragm (18), the sensor (25) being connected to the unit (9) to sent to said unit (9) an electric signal, the level of which indicates the position of the diaphragm (18).

20. A multi-function feedback control system as in claim 19, wherein the diaphragm (18) is of the type for gas meters, and is a metering system with very low inertia and hys- teresis and is in equilibrium between the pressures which act on the two sides of the di¬ aphragm (18).

21. A multi-function feedback control system as in claim 19, wherein the spring (27) is a leaf spring the load of which increases with the displacement of the diaphragm (18) in the direction of the increasing air-flow amount to meter the displacements of the diaphragm (18) due to differences in pressure of few mm./ I-bO and to support differences in pressure of several m./ H2O.

22. A multi-function feedback control system as in claim 19, wherein the sensor (25) of the position of the diaphragm ( 18) is of the type without a contact, for example a capacitive sensor.

23. A multi-function feedback control system as in claim 1 , wherein the air-flow amount measuring device consists of a differential pressure sensor capable of metering the range of the air-fiow amounts from minimum to maximum.