OBSERVATION OF COMBUSTION IN A SPARK IGNITION INTERNAL COMBUSTION ENGINE

Abstract: Spark discharge voltage follows a falling flank (11) for at least a predetermined period (B) of at least 0.1 ms during normal combustion of the fuel/air mixture in the combustion chamber of an internal combustion engine. Should combustion not take place, the voltage on the ignition coil falls to zero along a flank (12) from a point (A') and the absence of any subsequent discharge voltage at the end of the predetermined period (B) can be monitored to indicate that unburnt fuel will find its way to the exhaust system where it may burn and cause the exhaust system to overheat. Such exhaust system may contain a catalyser which could be destroyed by such overheating. This is prevented by using the result of monitoring the discharge voltage to interrupt the fuel supply to the engine, at least up to the following ignition operation.

Description: DESCRIPTION OBSERVATION OF COMBUSTION IN A SPARK IGNITION INTERNAL COMBUSTION ENGINE. Prior art The invention relates to a method of and device for observing combustion in an internal combustion engine operable with spark ignition in accordance with the pre-characterizing clauses of claims 1 and 4. If, in an internal combustion engine operable with separate ignition, the inducted fuel is not burnt in the engine combustion chambers, such unburnt fuel becomes purged into the exhaust system. The high temperature prevailing in the exhaust system can cause such fuel to be ignited there, and in particular in an exhaust gas catalyser, which can lead to destruction of the exhaust system. An object of the invention is to observe whether correct combustion of the inducted fuel/air mixture is taking place. It has been proposed to monitor the combustion of the fuel/air mixture by measuring the combustion pressure in an engine cylinder. This is not very practical except for research purposes. It has also been proposed to measure ionisation current at the spark plugs. This needs sophisticated equipment. Advantages of the invention. The above object is met by a method having the characterizing feature of claim 1 and a device having the characterizing feature of claim 4. The invention is thus based on the evaluation of electrical signals which can be measured at the ignition coil or at the final stage of an ignition control system. The invention employs the phenomenon that the saprk discharge voltage characteristic differs according as to whether combustion of the fuel/air mixture inducted into and compressed in the combustion chamber does or does not take place. By adopting the features of claims 2 and 5, use can be made of the fact that the duration of the discharge voltage is longer when combustion takes place than when it does not. It is a relatively simple matter to monitor the voltage on the primary winding of the ignition coil in accordance with claims 3, 6, 7 and 8. The invention is useful in that it enables the fuel supply to the engine to be temporarily interrupted by adopting the feature of claim 9. The accumulation of ambient fuel in the exhaust system, and in particular in an exhaust catalyzer can be avoided, thereby reducing the risk of the catalyzer being destroyed or damaged. Drawings The invention is further described, by way of example, with reference to the accompanying drawings, in which:- Fig.l is a graph of the voltage at the primary side of an ignition coil, measured with respect to time, and Fig.2 is a block circuit diagram of a device in accordance with the invention for monitoring the discharge voltage in order to observe the combustion in a spark-ignited internal combustion engine. Description of the preferred embodiment Fig.l shows a typical curve 10 for the voltage as measured across the primary winding of the ignition coil of a spark-ignited internal combustion engine when the inducted fuel/air mixture is ignited and burns properly. It can be seen that the core voltage U c follows the falling flank 11 from the peak voltage A for a period of 0.4 to 2.5 ms. Should combustion not take place, the voltage U across the primary winding of the ignition coil falls at the flank -3- 12 to zero from a peak voltage A* • During proper combustion, the discharge voltage U c and thus the coil voltage lasts for a period significantly longer than a predetermined period B. Thus, the absence of any discharge voltage at the end of the period B following the falling flank indicates that the fuel in the combustion chamber has not burnt. In Fig.2, a microprocessor 13 controls a fuel injection system and a fuel ignition system of an 0 internal combustion engine (not shown) . The output of the final stage 14 of the ignition control system (contained mostly within the microprocessor 13) is connected to the primary winding of the ignition coil 15 whose secondary winding is connected to an ignition 5 cable 16 leading to the various spark plugs via an ignition distributor. The device according to the invention includes a low-pass filter 17 which connects the output of the ignition end stage 14, that is to say, the primary 0 winding of the ignition coil 15, to an analog-to- digital converter which is connected to other parts of the device within the microprocessor 13. The microprocessor detects the falling flank 11 or 12 and checks whether the discharge voltage U c is still 25 present at the end of the predetermined period B of for example 0.1 ms after the detected flank. Should no such discharge voltage be detected, the microprocessor 13 ensures that no more fuel is injected prior to the next ignition operation in the --- respective engine cylinder. Since the duration of combustion varies in accordance with operating parameters, such as battery voltage, engine speed, load and temperature, it is advantageous to take account of such parameters in the ,_ evaluation of the discharge voltage, particularly for cold starting and using the engine as a retarder. Such operating parameters are in any event supplied to the microprocessor 13 for the control of the fuel injection and fuel ignition systems. One advantage of the above evaluation of the ignition voltage is its immediate availability. Another advantage is the evaluation of a signal that originates from the combustion chamber. Also, absence of the discharge voltage outside the combustion chamber can also be detected. Such absence may be due to a disconnected or severed ignition cable or wrongly connected plug leads or due to a faulty distributor. The immediate response after each ignition operation enables appropriate measures to be taken, e.g. switching off a cylinder. An effective means of protecting the catalyser is thereby possible.

Claims: CLAIMS 1. Method of observing combustion in an internal combustion engine operable with spark ignition, which method uses the engine discharge system, characterized in that the ignition voltage is monitored to determine whether combustion in the engine combustion chamber has taken place. 2. Method according to claim 1, characterized in that the duration of the discharge voltage is monitored. 3. Method according to claim 1 or 2, characterized in that the voltage at the primary side of the ignition coil is monitored. 4. Device for observing combustion in an internal combustion engine operable with spark ignition, in which the device is connected to the ignition system, characaterized in that the discharge voltage is monitored. 5. Device according to claim 4, characterized in that a computer (13) monitors the duration of the discharge voltage, and in particular checks the duration of the discharge voltage following a falling flank (11 or 12) . 6. Device according to claim 4 or 5, characterized in that the computer (13) is connected to the primary side of the ignition coil (15) of the ignition system. 7. Device according to claim 6, characterized in that a low-pass filter (17) is connected to the primary winding of the ignition coil (15). 8. Device according to claim 7, characterized in that the low-pass filter (17) is connected via an analog-to-digital converter (18) to the computer (13) . 9. Device according to any of claims 4 to 8, characterized in that the evaluation of the discharge voltage takes into account operating parameters of the internal combustion engine. 10. Device according to any of claims 4 to 9, characterized in that the computer (13) produces a signal in the event of the duration of the discharge voltage being less than a predetermined value and delivers the signal to a fuel injection system of the internal combustion engine to inhibit injection of fuel for at least one working stroke immediately subsequent to the working stoke for which such signal was produced.

Inventors: ENTENMANN ROBERT, KUGLER KARL-HEINZ, PHILIPP MATHIAS, ROHDE SIEGFRIED, ROTHAAR ULRICH, STENGEL BERNHARD, TORNO OSKAR, UNLAND STEFAN, ENTENMANN, ROBERT, KUGLER, KARL-HEINZ, PHILIPP, MATHIAS, ROHDE, SIEGFRIED, ROTHAAR, ULRICH, STENGEL, BERNHARD, TORNO, OSKAR, UNLAND, STEFAN
Applicants: BOSCH GMBH ROBERT, ROBERT BOSCH GMBH
Application year: 1988
Main classification: F02D41
IPC codes: F02D35, F02D41, F02D45, F02P17, G01M15