FUEL TIMING CONTROL

Abstract: The invention relates to a spark ignited engine in which charge stratification occurs within the combustion chamber and in which the burn quality of the charge is dependent upon the timing of the instant of introduction of the fuel into the charge. A sensor is provided to produce a signal representative of the burn quality and the fuelling timing is controlled in dependence upon the output signal of the sensor so as to optimise the charge stratification within the combustion chamber.

Description: FUEL TIMING CONTROL The present invention relates to the timing of the instant of introduction of fuel into the combustion chamber of a spark ignited internal combustion engine in which the charge is stratified. The concept of a stratified charge is known from many engine applications as will be described below. The basis of operation is that the overall mixture is too lean to burn correctly but by ensuring an uneven distribution of the fuel in the combustion chamber immediately before the spark, it is possible provide a richer mixture in the immediate vicinity of the spark plug electrodes to guarantee proper ignition, the powerful flame then being able to propagate and ignite the remaining charge which becomes progressively leaner. One application in which a stratified charge iε required is when the quantity of fuel is being used instead of the intake air volume to regulate the engine power output. Here, when operating under part load, there will be excess air and consequently it is essential in view of the overall weakness of the mixture to resort to a stratified charge if proper ignition is to be achieved. This is just one example of a lean burn and others will also come to mind. Charge stratification also occurs unintentionally when fuel is injected either directly into the cylinder or into the intake port while the inlet valve is open. The fuel injection creates a local concentration of the fuel in the combustion chamber and its timing has been found to be critical. Good performance is achieved if the rich mixture lies within the vicinity of the spark plug electrodes at ignition but not otherwise. Here the charge is meant to be homogeneous but the importance of the injection timing suggests otherwise. In the case of injection into the intake port, the best performance is produced if injection occurs in a narrow time window while the inlet valve is open but the timing is so critical and the performance is so degraded outside this window that it is generally preferred to time the injection to take place while the intake valve is closed. Here, the efficiency is not optimised but the injection timing is not critical. This ensures a homogeneous mixture but the efficiency is maximised if a weak mixture is burnt while the charge is correctly stratified. A still further application in which charge stratification is met is in the case of two-stroke engines. A two stroke engine running under part load conditions must resort to charge stratification because the mass of the trapped gas can only be controlled within narrow limits and the regulation of the power is carried out by limiting the fuel supply. It has been proposed in the case of a two stroke to provide in addition to the transfer passage and the exhaust port a valve controlled fuelling port in which fuel is accumulated during the engine cycle, the fuel being introduced into the combustion chamber at a time when it will not find its way to the exhaust port. As in the case of direct injection into the cylinder of a four stroke engine, the timing of such introduction of the fuel into the combustion chamber is important if advantage is to be taken of the charge stratification to maximise the engine efficiency. According to the present invention, there is provided a spark ignited internal combustion engine, in which charge stratification occurs within the combustion chamber and in which the burn quality of the charge is dependent upon the timing of the instant of introduction of the fuel into the charge, characterised in that a sensor is provided to produce a εignal representative of the burn quality and in that the fuel introduction timing is controlled in dependence upon the output signal of the sensor so as to optimise the charge stratification within the combustion chamber. It is known that spark timing and mixture strength also affect the burn quality of a charge and sensors are already known, such as ionisation sensors, pressure sensors and optical sensors, for feeding back a εignal to the ignition system or the fuelling system to maximise burning efficiency. Any such sensor may be used in the present invention for feedback control of the timing of the fuel introduction. The burn quality will be maximised at one value of fuel timing and to each side of this local peak, the burn quality will be degraded with changes in timing. The feedback signal must act in a direction to return the timing to its optimum but additional information iε required to determine the sense of the deviation from the optimum timing. To mitigate this problem, it is possible for two cylinders to be fuelled with a given phase difference between them. In this case the cylinders should at the optimum setting straddle the efficiency peak and the sense of any deviation can be determined by subtracting the signals of the two cylinder sensors from one another. Alternative approaches are possible for determining the sense of deviation for example long term trends of the corrections applied may be monitored to determine if the feedback control is aggravating an error instead of correcting it or the same cylinder may have its timing dithered between cycles to obtain analogouε data. Various fuelling and spark timing systemε have been proposed in the past which rely on a feedback signal from the combustion chamber. The present invention can utilise similar control systems to control the timing of the introduction of fuel into the combustion chamber and because of the analogy with the known systems, it is believed that the invention will be clear to the person skilled in art from the foregoing comments without the need for more detailed description.

Claims: CLAIMS 1. A spark ignited internal combustion engine, in which charge stratification occurs within the combustion chamber and in which the burn quality of the charge iε dependent upon the timing of the instant of introduction of the fuel into the charge, characterised in that a sensor is provided to produce a signal representative of the burn quality and in that the fuel introduction timing is controlled in dependence upon the output signal of the sensor so as to optimise the charge stratification within the combustion chamber. 2. An engine as claimed in claim 1, wherein the sensor for producing a signal indicative of burn quality is an ionisation sensor, a pressure sensor or an optical sensor disposed within the combustion chamber. 3. An engine as claimed in claim 1 or 2, further comprising means for indicating the sense of deviation of the fuelling timing from its optimum setting, to determine the sense in which the timing iε adjusted in dependence upon the feedback signal. 4. An engine as claimed in claim 3, wherein two cylinders of the engine are fuelled with a given phase difference between them and the signals from individual sensors associated with the cylinders are subtracted from one another to indicate the sense of deviation of the fuelling timing from its optimum setting.

Inventors: MA THOMAS TSOI-HEI, MA, THOMAS, TSOI-HEI
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, FORD FRANCE S.A., FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD WERKE A.G.
Application year: 1989
Main classification: F02D35
IPC codes: F02B75, F02D35, F02D41