The present invention relates to an injection and ignition arrangement in fuel injected spark igni¬ tion engines.

A problem in the design of such engines is always to accommodate the necessary components in the minimum of space to ensure that the engine is not too bulky. Therefore designers are continually looking at ways to reduce the number of necessary components. A particular area of interest is the ignition equipment and the fuel injector valves. In known engine designs the ignition coils, the spark plugs and the fuel injec¬ tor valves are all separate components. The general problem with which the present invention is concerned is to accommodate these components in as little space as possible.

One solution to this problem has been put forward for a system having static ignition with one coil per cylinder. It has been proposed to combine an ignition coil and a spark plug in a single unit. Thus, one such unit would be provided for each cylinder of the engine. Although this arrangement does save space to some extent it has not proved particularly practical because spark plugs have to be changed comparatively frequently and to do so is more complicated and more expensive if each spark plug forms part of a unit with an ignition coil.

The present invention has resulted from the realisation that ignition timing signals may also be used to control the opening and closing of the fuel injection valves.

According to the present invention, there is provided a valve assembly for use in an internal com¬ bustion engine comprising a valve for injecting fuel into a cylinder or intake manifold of the engine having an electromechanical actuator including a coil for effecting its opening and closing, characterised in that the coil also acts as part of the engine ignition system in use.

The invention enables the number of compo¬ nents of the engine ignition system to be reduced. In the preferred embodiment of the invention the injection valve actuator and an ignition coil of the engine ignition system have a common primary winding and/or core. Thus, an injection valve and an ignition coil for an internal combustion engine may be manufactured as a single unit, namely a valve assembly according to the invention.

As well as reducing the number of coils necessary for injection and ignition, less wiring is required using the invention because there are less separate components to be connected. The result is an overall reduction in the weight of the engine.

The valve assembly of the invention is par¬ ticularly applicable to an internal combustion engine having one coil per cylinder, i.e. static distribution, and a separate injection valve for each cylinder. The number of output stages is halved as compared to the conventional arrangement with separate coils for the valves themselves. With each injection valve being formed as a unit with an ignition coil, an output stage for the coil/valve assembly may be integrated into the assembly itself, further saving on space and number of components.

here the ignition and/or injection are fully electronically controlled a control processing unit for controlling the operation of the fuel injection system and/or ignition system may be integrated into the valve assembly of the invention. This is particularly pref¬ erable in an arrangement having central injection in which one fuel injector is provided for injecting fuel into the inlet manifold of the engine.

The invention is applicable to an internal combustion engine having group injection and distribu¬ tion over one or more distributors, e.g. a cylinder engine having two groups of four injection valves and two distributors each providing high voltage pulses for ignition to four cylinders. A high voltage secondary winding may be wound around the coils of the injection valves in the or each group for supplying a respective distributor with high voltage. Thus, a separate ignition coil for the or each distributor does not have to be provided.

The invention is also applicable to an inter¬ nal combustion engine having central injection and an ignition system having a distributor. A high voltage secondary winding may be wound around the coil of the injector for supplying high voltage to the distributor. Again a separate ignition coil does not have to be provided for the distributor.

According to a second aspect of the inven¬ tion, there is provided a method of controlling the ignition and fuel injection systems of an internal combustion engine in which the or each fuel injection valve of the injection system has an electromechanical actuator including a coil for effecting its opening and closing, characterised in that the coil is used in the ignition system.

In an arrangement having one fuel injection valve per cylinder and one coil per cylinder, the coil

of an injection valve of one cylinder may be connected ignition-wise to another cylinder. In other words, the coil of an injection valve of one cylinder may be used as part of the ignition circuit of a different cylin¬ der. As will be explained in more detail below, such an arrangement may be necessary if ignition is required to take place in each particular cylinder when both inlet and exhaust valves are both shut. If it is not required for injection to take place when the inlet and exhaust valves are both shut, for reasons which will be described below, the coil of the injection valve of each cylinder may be used to form part of the ignition of the same cylinder.

According to the method of the invention the coil of the or each valve is preferably supplied with electrical pulses which switch between at least one "ON" state and an "OFF" state, the lengths of time for which the pulses are "ON" determining the fuel injection periods of the valve and the points at which the pulses switch to the "OFF" state determining ignition timing for one of the engine cylinders.

The coil current required for opening the injection valve is usually less than that required to ensure ignition. Thus, the pulses may be arranged to vary the current supplied to the or each coil during each fuel injection period longer than a predetermined length of time so as to minimise power dissipation in the coil(s) whilst still ensuring satisfactory opera¬ tion.

The current applied to the coils until a predetermined length of time before ignition is re¬ quested may be less than the current applied during the predetermined length of time. The lower coil current may be selected so as to be just sufficient to ensure opening of the injection valve. The higher coil cur¬ rent and the predetermined length of time may be chosen

so as to be just sufficient to ensure ignition. An embodiment of the invention will now be described by way of example only and with reference to the accompa¬ nying drawings in which:

Figure 1 is a schematic diagram of an elec¬ trical circuit for controlling injection and ignition of a four cylinder internal combustion engine according to the method of the invention;

Figure 2 is a graph showing the variation with time of the coil current of each valve shown in Figure 1 ;

Figure 3 is a graph showing the variation with time of the coil current of each valve shown in Figure 1 when current limiting is applied;

Figure 4 shows the relationships between the inlet and exhaust valve positions, the ignition timing and the injection timing for the arrangement shown in Figure 1.

Referring firstly to Figure 1 , four valve assemblies according to the invention are shown sche¬ matically, indicated by reference numerals 10. Each valve assembly is associated with a respective cylinder of the engine. The cylinders are indicated by Roman Numerals I, II, III, IV. Each valve assembly comprises an injection valve having an actuator including a coil and a closing element. In Figure 1 only the closing elements and the coils are illustrated, the closing element being indicated by reference numerals 11 and the coils being indicated by reference numerals 12.

According to the invention each coil of a valve assembly forms part of the ignition system of the engine in use. According to this embodiment, each coil 12 includes a primary and a secondary winding and acts as the ignition coil for a respective cylinder. Thus, a separate coil is provided for each cylinder of the engine so that the engine has so-called "static distri-

bution". A separate ignition circuit is provided for each cylinder and each coil forms part of one of the ignition circuits. In this embodiment each coil of a valve assembly is connected in the ignition circuit of a different cylinder from that with which the valve is associated.

Only part of each ignition circuit is shown in Figure 1 , the spark plugs being indicated by refer¬ ence numerals 15. The dotted lines separate components associated with different cylinders. Thus it is clear that in the arrangement of Figure 1 , the coil of the valve assembly of cylinder I is connected in the igni¬ tion circuit of cylinder III, the coil of the valve assembly of cylinder II is connected in the ignition circuit of cylinder I, the coil of the valve assembly of cylinder III is connected in the ignition circuit of cylinder IV and the coil of the valve assembly of cylinder IV is connected in the ignition circuit of cylinder II.

In each ignition circuit the battery voltage is applied to the primary winding of the coil 12 via a switching circuit A. Current is conducted from the primary winding to earth via a transistor T1 , biassed by resistors R1 and R2. While current is flowing through the primary winding a magnetic field is gener¬ ated which causes the closing element 11 to move so as to open the fuel injection valve so that fuel is in¬ jected into the cylinder. As is well known in the art, ignition is brought about by interrupting the current to the primary winding so that the field in the primary winding suddenly decreases. When this occurs the rapidly changing magnetic field in the primary winding causes a high voltage to be induced in the secondary winding, causing a spark across the electrodes of a spark plug. Thus, in the arrangement described herein when the current in the primary coil of cylinder I is

interrupted a spark is produced across the electrodes of the spark plug of cylinder III.

The switching circuit A is provided to regu¬ late the current in the primary winding and thereby protect the transistor T1. Each switching circuit includes the same components but only one is shown in detail. Each includes a comparator K1 , a diode D1 , a second transistor T2 and resistors R3 and R4. Resistor R3 is connected between a positive voltage supply and the inverting input of the comparator K1 to provide a positive voltage at that input. Resistor R4 connects the junction of K1 and R3 to ground. The output of the comparator is connected to the base of transistor T2 so that when the output of K1 is low i.e. at a level representing logic "0" a base current is supplied to T2 and T2 conducts current from the battery to the coil 12. The emitter of T1 is connected to the non- inverting input of the comparator. Thus, when a current is flowing through the primary coil and transistor T1 a voltage is applied to the non-inverting input of K1. Normally this voltage is smaller than the voltage at the inverting input of K1 and therefore the output of K1 remains in the logic "0" state. However, if the current in the primary coil exceeds a certain value the voltage at the inverting input of K1 will become greater than the voltage at the non-inverting input thereby switching the output of K1 to the logic "1" state and terminating the base current to T2. T2 is then switched off and stops conducting current to the primary winding. The current in transistor T1 will immediately fall so that the output of comparator K1 returns to logic state "1 " after some time and the supply of current to the primary coil is resumed. The time depends on the hysteresis of the comparator K1 and the losses in the circuit including the coil 12, diode D1 transistor T1 and Resistor R1. This momentary switching off of transistor T2 protects transistor T1 from high power dissipations since it acts as a switch with low collector voltage.

Since the maximum voltage change of the priority of the coil when the supply of current is momentarily stopped is no more than the applied voltage +V, the corresponding secondary voltage stays below the crcing over voltage and no spark is produced.

Other details of the ignition circuit for each coil and spark plug such as the interrupter itself and the connections to the battery are conventional and will not be described further herein.

Figure 2 shows the variation of coil current with time for each of the four coils shown in Figure 1. The length of time for which current flows through the coils depends on the required fuel injection times which will in turn depend on various running conditions of the engine. For the arrangement shown in Figure 1 the injection time must include sufficient time for charging the coil. The solid lines shown the minimum lengths of time for which current must flow in the primary windings in order to ensure that a sufficient voltage is induced in the secondary windings , on inter¬ ruption, for spark production. The minimum length of time is generally about 3ms. The dotted lines show the extent of variations in injection times. The injection times may vary between the maximum values shown by the dotted lines and the minimum values shown by the solid lines. The arrow marked X in Figure 2 indicates 720° rotation, i.e. a full four-stroke cycle. The circuitry for controlling the lengths of the injection times is conventional and will not be described further herein. In practice a fuel injection time of less than 3ms is not usually required, and thus there are no difficul¬ ties in using the coil of valve assembly as an ignition coil in terms of timing. Generally, in the arrangement described herein, injection times varying from about 3ms at idling to about 15ms at full throttle. The coil currents may be varied during each injection time in order to reduce power dissipation in the coils. This possibility results from the fact that the current required in order to ensure operation of the valve closing members 11 through energisation of

the coil is less than the current required to produce a spark. Therefore when the injection times are greater than the minimum time required to ensure spark produc¬ tion, as described above, the current applied of the beginning of each fuel injection time may be limited. The variation of coil current with time according to this modification of the invention is shown in Figure 3. Again, the solid lines show the minimum lengths of time for which current must flow through the coil in order to ensure spark production. During these times the coil currents must also exceed a predetermined value in order to ensure that sparks are produced. The dotted lines again show the extent of variation of injection times. The current applied to the coils up to a predetermined time before ignition is required, about 3ms in this example, is smaller than the current applied during that predetermined time but sufficient to ensure the opening of the injection valve. The current limiting may be controlled through the voltage applied at pins XY shown in Fig. 1.

Figure 4 shows the relationships between the positions of the inlet and exhaust valves and the ignition and fuel injection times in this embodiment of the invention. The vertical axes indicate valve posi¬ tion measured relative to the closed position. The solid lines represent the positions of the exhaust valves and the dotted lines represent the positions of the inlet valves. This relationship of valve positions is characteristic of the four-stroke process. The horizontal axes on the graphs represent time. The maxima on the graphs represent the fully open positions of the valves.

The zigzag arrows on the graphs represent ignition points and the horizontal arrows indicate the ends of the fuel injection times. As mentioned above the lengths of the fuel injection times and hence the

points at which they begin are variable. The arrangement shown is chosen to inject fuel when both values are closed. This is the presently preferred arrangement. According to this embodiment of the invention in which each valve assembly coil is linked ignition-wise to a different cylinder, it is possible to ensure that ignition takes place when both valves are fully closed with injection taking place just before the exhaust valve opens. This is clear from Figure 3 in which it can be seen, for example, that ignition takes place in cylinder I at the same time as fuel injection ceases in cylinder II. Ignition in cylinder I takes place when both its inlet and exhaust valves are closed. Corresponding fuel injection takes place in cylinder II and ceases just before the exhaust valve opens, while the inlet valve is still closed.

The arrangement described above is thus suitable for a system in which ignition and injection are separately occurring events for each cylinder. Nevertheless, the invention is also applicable to the so called "direct injection" systems which are now being developed in which the end of the injection period is simultaneous with ignition for a particular cylinder. The direct injection system has certain advantages. For example cylinder control can take place, i.e. one cylinder can be switched off at a time. This might be desirable if there is a fault in that cylinder. The engine will then run only on the remaining cylinders. With the arrangement described above the same sort of cylinder control is not possible because two cylinders would be switched off at the same

time - switching off injection for one cylinder would switch off ignition for another. The invention is in fact advantageous in a direct injection system since switching off one cylinder ignition-wise automatically switches it off injection-wise.

It will be noted that if the fuel is cut off from the engine at any time e.g. idling at full speed, the ignition will also be switched off in the arrange¬ ment described above. Once fuel has been cut off ignition is not required and therefore this simulta¬ neous switching off reduces power consumption.