GB2051230A - Ignition System for an Internal Combustion Engine Employing Fuel Injection - Google Patents

Abstract

Each fuel injection valve has an electrically conductive needle 222 biassed into contact with a conductive valve seat 251 by a metal spring 220 otherwise insulated from the valve body. The needle lifts from the seat by fuel pressure and a thin film of fuel forms between the needle and the valve body to create a high resistance path therebetween. An electrical signal is developed by a comparator circuit and used to initiate an electric spark for the injected fuel. <IMAGE>

Description

SPECIFICATION Ignition System for an Internal Combustion Engine Employing Fuel Injection The invention relates to ignition systems for internal combustion engines employing fuel injection and an electric spark to ignite a combustible mixture of such injected fuel. A system according to the invention is particularly applicable to a diesel type engine that employs spark assist. The designation diesel type engine is intended to include a fuel injection system where the fuel pressure acts to lift the fuel injection valves.

U.S. Patent No 4,066,059 discloses an ignition system which makes use of direct amplification of an injection valve initiated signal in order to control the generation of a high voltage spark signal. The injection valve described in that patent requires special electrical insulating material elements to isolate the valve needle, or plunger from the body of the valve except where it touches the valve seat when closed.

U.S. Patent No. 3,942,366 discloses the use of a fuel injection needle valve to act as a switch for operating test equipment in order to monitor a fuel injection nozzle. The electrical switch structure therein is separate from the valve plunger and seat, so that special valve and switch structures are involved which add cost to the ordinary valve construction.

An object of this invention is to provide a system for generating a signal to control a spark voltage for an internal combustion engine which signal originates at the injector valve.

According to the present invention there is provided an ignition system for an internal combustion engine employing fuel injection and a high tension electric spark to ignite a combustible mixture of said injected fuel, said system including a fuel injection valve having an electrically conductive material plunger in seating contact with an electrically conductive material body of said valve when the valve is closed, characterised in that said plunger (222, 272) is arranged to be actuated by fuel pressure to open the valve (11,78-81,251,276), and by first electrical circuit means for connecting a resister (15, 91--94) in series with said plunger, a comparator (21, 104) having two inputs and an output, second circuit means (24, 1 06) for connecting a predetermined EMF to one of said comparator inputs, and third circuit means (20, 11 3) for connecting the other of said comparator inputs to said plunger, said comparator output (132) providing a signal to initiate said electric spark when said plunger is actuated by the fuel pressure.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram illustrating a basic arrangement of a fuel injector valve and a comparator; Figure 2 is another schematic circuit diagram illustrating an arrangement including a plurality of fuel injector valves connected to comparators for providing an ignition control signal to a spark generator or the like; Figure 3 is a schematic circuit diagram illustrating a complete system according to the invention for applying ignition spark signals to an internal combustion engine; Figure 4 is a schematic illustration showing an injection nozzle with an electrical circuit connection for making test signal indications;; Figure 5 is an enlarged longitudinal crosssectional view illustrating the internal elements of an injection nozzle valve like that shown in Figure 4; and Figure 6 is an enlarged cross-sectional view showing another type of injection nozzle valve, with elements according to this invention included therein.

It has been discovered that while the aforementioned Patent No. 4,066,059 provided insulation at various points along the length of the valve plunger, such additional insulation is unnecessary. Thus, the fuel under pressure which lifts the valve plunger, forms a thin film of fuel between the valve plunger and the valve body.

This creates a high resistance path electrically, and consequently it is the basis for creating a control signal to be used with the ignition system.

In accordance with the foregoing basic discovery, an electrical system may be employed according to the Figure 1 circuit. Such system includes a fuel injector 11 that is schematically indicated with the caption applied thereto. The injector 11 is connected into a circuit with a battery 12 and a resistor 1 5 in series with it. It will be understood that the body of the fuel injector valve (not shown) is grounded. This is indicated by a ground circuit 16, and the series circuit is completed through the ground connection of the battery 12.

It may be pointed out that when the fuel injector 11 has no fuel pressure applied thereto, the valve therein will be closed and consequently its plunger (not shown) will be in contact with the body (not shown) of the injector valve within the injector 11. In this state, the electrical potential at a point 1 9 on the circuit mentioned above will be substantially zero, or ground potential, so long as the plunger maintains contact with the body of the valve in the fuel injector 11.

The circuit point 12 is connected via circuit connection 20 to a comparator 21. The circuit connection 20 forms one input to the comparator 21 while there is another input circuit connection 24 that forms the other input connection. The input circuit 24 applies a predetermined potential, or EMF to the comparator by reason of a potentiometer connection across the battery 12.

The potentiometer is formed by a resistor 25 and another resistor 26. These are in series with one another and with the battery 12 via a grounded circuit connnection 29.

It is important to note that the fuel injector 11 may be any of various standard type injectors so long as it has an electrically conductive material plunger which is in seating contact with an electrically conductive material body of the valve, when the valve is closed. And, of course, with the valve plunger structure such that an ungrounded electrical circuit may be electrically connected to it. Examples of such standard injector valves which are commercially available, include those manufactured by Stanadyne of Hartford, Connecticut and designated Roosa Master Pencil Nozzles. Another commercially available type is that manufactured by Robert Bosch, GMBH of Stuttgart, West Germany which has nozzle bodies designated KDALZ which take DLUZ nozzle tips, and bodies KDAL with tips DLLA.

It will be appreciated by anyone skilled in the art that the comparator 21 is a well known electronic circuit element which acts to create an output signal that goes from a high voltage (so long as the input on one of its two inputs is less than the predetermined voltage on the other input) to a low voltage when the input on that one of the inputs exceeds the predetermined voltage.

In other words, whenever the input on the first indicated input exceeds the predetermined input on the other of the two comparator inputs, the comparator will switch to a low output, and it is this change that creates an output signal for use in an ignition system.

Figure 2 illustrates an application of the basic principles indicated above in connection with Figure 1. This application is to a multi-cylinder engine (not shown) which includes a plurality of fuel injector valves 33 through 36 inclusive. Each of these fuel injector valves 33, 34, 35 and 36 is connected to one input of a corresponding plurality of comparators 39-42. It will be observed that in this case there is a potentiometer connected across a battery 45 which has one terminal grounded. The other terminal of battery 45 is connected via a circuit connection 46 to a pair of resistors 49 and 50 which are connected in series with one of the resistor 50 connected to ground, as illustrated.This provides a predetermined EMF, or potential on a circuit connection 51 that is connected, in turn, to each of the comparators 39, 40, 41 and 42 in parallel.

These parallel connections go to one of the inputs of each of the comparators 39-42. The other input of each comparator has one of the fuel injector valves 33-36, respectively, connected thereto.

It will be noted that the outputs of all of the comparators 39--42 42 are connected together to a single output circuit connection 53. This goes to a spark generator, as indicated by the caption. The signal on this output circuit 53 goes from a high voltage to a low (substantially ground) voltage whenever one of the comparators 39--42 switches state. Such change of output signal, i.e. voltage, is caused by the change from no current flow, to current flow through a resistor 54. It will be appreciated that the output signal on circuit connection 53 will not go directly to a distributor, .but rather will act as a control signal for an ignition signal voltage which may be distributed.

Figure 3 illustrates a practical ignition system circuit diagram which incorporates the basic invention and includes a time delay lockout circuit arrangement. The latter is for holding the injector valve-initiated signal long enough to overcome the uneven nature of the signal developed when a valve plunger is lifted off its seat as the fuel pressure acts upon it.

The high tension electric spark generating portion of the ignition system illustrated is like that shown and described in connection with a co-pending patent application Serial No. 885,844 filed March 13th, 1978, and assigned to the same assignee as this application. However, it will be appreciated that the ignition system for generating spark signals may also be like various other systems such as that shown and described in connection with Patent No. 4,022,177 issued May 1 0th, 1 977 and earlier patents mentioned therein. All of the foregoing ignition systems employ a high-frequency square-wave spark signal that has a controlled duration during each sparking interval.

The aforementioned portion of the system is illustrated in the upper right-hand part of Figure 3.

While the details of such a spark signal generating system are dscribed in more detail in the various patents and the application mentioned above, it is explained briefly here. Thus, in Figure 3 there is shown an output transformer 57 that supplies high voltage high-frequency spark signals from a pair-of secondary, or output high-voltage windings 58 and 59 to a plurality of spark plugs 60 as indicated. The transformer 57 includes a center tapped primary winding 63, along with a feedback winding 64 which together are employed in an oscillator circuit such as is clearly explained in the above-mentioned patents. In addition, there is a control winding 65 which controls the time duration of a continuous AC type spark as determined by the beginning and ending of periods of oscillation of the oscillator.

Such oscillation control of stopping and starting is determined by an electronic switch, i.e. transistor 68. This transistor (spark control switch) is in series with a source of DC current supply which is a battery 69. The control circuit goes to the upper end (as viewed in Fig. 3) of the control winding 65 via a diode 70 and a resistor 71. The lower end of the control winding 65 goes to the transistor switch 68 via another diode 74.

There is a relay 75 shown that has circuit connections to the control winding 65. However, the details need not be described here as they are not relevant to this invention. The purpose is to ensure shut down of the oscillator whenever the ignition system is turned off.

The basic principles of this invention are described above in connection with the Figures 1 and 2 illustrations. In Figure 3, a practical ignition system circuit for a four cylinder engine is shown.

The system includes the invention as applied thereto. It shows a plurality of fuel injector valves 78, 79, 80 and 81 which are connected in parallel to the battery 69 via the illustrated circuit connections. Such circuit connections include a connection 84 from the positive terminal of the battery 69 to another circuit connection 85 which leads to a circuit connection 86 and connections 87 and 88 that connect to common circuit connector 89 for all of the injector valves 78 81, plus breaker points to be described below.

These circuit connections go via individual resistors to be described, to the conductive material plunger (not shown) in each of the four fuel injector valves 78-81. However, there is a separate resistor 91, 92, 93 and 94 between the circuit connections 88 and 89 and each of the plungers of the valves 78-1. Similarly, the circuit connections 88 and 89 also lead to one end of another resistor 97 that has the other end thereof connected via the contacts of a relay controlled switch 98 to breaker points 101 that act as an auxiliary to the fuel injector valves 79 81, as will be described in more detail hereafter.

It should be noted that there are two comparators 104 and 105. As explained above, a comparator is a well known electronic circuit element. These comparators have a predetermined EMF connected in parallel to one input of each. The circuit for thus connecting an EMF of predetermined amplitude, includes a circuit connection 106 for the comparator 104 and a connection 107 for comparator 105, respectively. These connections 106 and 107 both go to one end of a resistor 109, the other end of which is connected to a potentiometer output connection that is between two resistors 110 and 111. The lower end (as viewed in Figure 3) of resistor 111 is connected to ground, as indicated, while the upper end of resistor 110 is connected via a circuit connection 114 to the circuit connection 87 described above.

Connection 87 leads back via circuit connections 86, 85 and 84 to the positive terminal of the battery 69.

The other input of comparator 104 is connected via a circuit connection 113 to a common circuit that leads from the cathodes of a pluralityofdiodes 115,116,117,118 and 119.

The other electrodes of these diodes are each connected via capacitors 121, 122, 123 124 and 125 respectively to each of the plungers of the fuel injector valves 78-81, plus the breaker points 101.

It may be observed that the circuits for each of the fuel injector valves are substantially similar.

The action involves the change of electrical conductivity when the conductive material plunger (not shown) for each of the valves is lifted by fuel injection pressure. Such action may be described in connection with the fuel injector valve 78. When the injection pressure raises the plunger, this breaks the ground connection that was made via the valve seat and the body of the valve. Then, the electrical potential at a circuit point 128 will go from ground potential up to a high potential, as produced by the positive electrode of the battery 69. That change is reflected through the capacitor 121 to the ungrounded side of a resistor 129, and via the diode 11 5 to the circuit connection 113 that goes to one of the inputs of the comparator 104.It may be noted that each of the circuits for the other injector valves 79,80,81 and the breaker points 101 is similar to the foregoing and that separation between these circuits is maintained by the diodes 115-119.

The output of the comparator 104 goes to the base electrode of a transistor 132 which transmits a signal to initiate the electric spark signals that are created by the oscillator described above. The oscillator, of course, has outputs via the transformer 57 to the spark plugs 60.

A important aspect of the invention includes the function of the second comparator 105 and related circuits. Comparator 105 is connected to have its other (from that of circuit connection 107) input connection lead from the output of the comparator 104 via the transistor 132 and a time delay circuit. The arrangement acts as a time delay means to hold the output signal from comparator 104 for a predetermined length of time. Such length to time is determined by an RC circuit which includes a capacitor 135 and a resistor 136. These RC circuit elements are both in a circuit that goes through a resistor 139 to the other input of the comparator 105. The output of comparator 105 goes via circuit connections 141 and an resistor 1 42 to that other input connection 11 3 of the first comparator 104.

As indicated, this arrangement acts to hold the comparator 104 in its shifted state so long as the comparator 105 remains shifted, which latter time duration is determined by the RC circuit (capacitor 135 and resistor 136).

The output of transistor 132 goes via a capacitor 145 to an inverse (with repetition rate) pulse-width circuit 146. Pulse-width circuit 146 has its output connected via a circuit connection 149 to the base electrode of the electronic-switch transistor 68 (described above). This inverse pulse-width circuit 146 per se is not relevant to this invention. It merely acts to vary the pulse width of the output signals from the valve injectors, so as to create an inverse relationship relative to the speed (pulse repetition rate) of the internal combustion engine. Such an inverse pulse width circuit is known per se consequently the details of its operation need not be described here.

It may be noted that the breaker points 101 and the related circuits, are so employed as to be particularly useful in connection with cold starting of the engine when the fuel injection pressure may not build sufficiently to actuate the fuel injection valves 78-81. Thus, the breaker points 101 are keyed to the engine operation so that they open approximately ten to fifteen degrees before top dead centre, or in any event so that the points will open somewhat before the fuel injection which would have taken place under normal operation. In this manner, a spark signal will be obtained which is effective during engine cranking whether or not fuel injection takes place, and also when the cylinders are primed for cold starting. It will be noted that the switch 98 is controlled by a coil 1 52 of the switch relay.This relay may be actuated by a special cold start switch (not shown) in order to control energization of the coil 1 52 which actuates the switch 98. There is a second pole 1 51 of the switch 98 which controls the introduction of a resistor 1 54 in the pulse-width circuit 146, under cold start. conditions.

Operation Normal operation of the ignition may be reviewed in connection with one of the fuel injector valve circuits. Thus, considering conditions when the injector valves ar not actuated because no fuel pressure has been applied to the plungers thereof, they make a direct connection to ground so that the voltage at the circuit point 128 is substantially zero. Then when the plunger of valve 78 is lifted, the voltage at point 128 will rise to the battery voltage of battery 69. This voltage increase will be transmitted through the capacitor 121 and the diode 11 5 to the input circuit connection 113 of the comparator 104.When this input voltage rise exceeds the predetermined voltage on circuit connection 106, the comparator will switch and an output signal will be applied via a circuit connection 1 55 and a resistor 1 56 to the base of the transistor 132. That causes the transistor 132 to conduct and thus pass a signal on via the capacitor 1 35 and over a circuit connection 1 59 to one end of the grounded resistor 136 as well as through the other resistor 1 39 to the other input of the comparator 105. That signal causes comparator 105 to switch immediately after comparator 104.

Now when comparator 105 switches, the output thereof goes over the circuit connections 141 and via the resistor 142 to the input connection 113 of the comparator 104. This holds comparator 104 in its switched position until the time delay period as determined by the RC circuit of the capacitor 135 and resistor 136, is completed. It will be understood that the holding action will eliminate the difficulty which would otherwise exist due to the uneven nature of the signal developed when the valve plunger is lifted by the fuel pressure. Also, during cold starting, if a valve plunger is lifted it will generate the signal that will actuate the comparator 104 and the breaker point signal will come during the time delay period so that it will be eliminated along with any unwanted signals.

Referring now to Figure 4, there is shown a commercial type of injection nozzle 211. It has connected thereto an electrical circuit for connecting a test instrument, e.g. a cathode ray oscilloscope 212 for displaying a dynamic test signal under operating conditions. It will be understood by anyone skilled in the art that a signal thus developed may also be employed in an ignition spark signal system, if desired, such as that described in relation to Figs. 1 to 3.

The type of fuel injection nozzle 211 that is illustrated in Figures 4 and 5 is basically a commercial nozzle like that manufactured by Stanadyne, In., Windsor, Connecticut. It is designated as their Roosa Master pencil-type nozzle. This nozzle 211 has a leak-off boot 21 5 at the top. In Figure 4 it is shown above the main body of the valve 211 in an exploded view. It will be understood that when the whole nozzle 211 is assembled, the parts will be as illustrated in Figure 5. Thus, the boot 21 5 fits over an adjustable valve-lift stop-screw 216.

The lift stop 21 6 is threadably received inside a metallic sleeve 21 7 that at the internal (of nozzle 211) end thereof a pressure adjusting spring 220 (Figure 5). Spring 220 is in contact with a spring seat 221 which is located at the upper end (as viewed in Figure 5) of a valve needle 222. Needle 222 is axially movable against the pressure of the spring 220 by the hydraulic force of fuel pressure which is applied via a conduit 223 from a fuel pump (not shown) actuated by the engine (not shown).

There is a lift adjusting lock nut 225 that threads onto the stop screw 216 and there is an upper spring 226 that is located inside the boot 215 when the whole nozzle is assembled. This spring 226 makes good electrical contact against the lock nut 225 at the lower end (as viewed in Figure 5) of the spring while at the other end it contacts the head of a screw 227 for making an electrical circuit (including the spring 226) that goes out the top of the boot 215 via a pair of nuts 230 that secure an electrical connector 231 therebetween.

Additional elements of the nozzle valve will be described in greater detail hereafter, particularly in connection with Figure 5. However, an electrical circuit for developing a test signal is indicated in Figure 4. Thus, there is a circuit connection 232 that goes to one end of a resistor 233 which has the other end thereof connected via circuit connection 236 to one terminal of a battery 237. The other terminal of battery 237 is grounded as indicated by a ground connection 238. This circuit continues via a grounded circuit connection 241 that goes to the conduit 223 and a fuel inlet connector 242 that is firmly secured onto a metallic body 243 of the injector nozzle valve structure 211. The circuit then continues via the needle 222 (Figure 5) when it is in contact with its valve seat at the tip of the nozzle. Then the circuit goes via the needle 222 and the spring seat 221 to the pressure adjusting spring 220.

The top of the spring 220 contacts the metallic sleeve 2-17 and so the electrical circuit continues up to and through the spring 226, the upper end of which makes contact with the head of screw 227 where the electrical connector 231 is fastened by the pair of nuts 230.

It will be understood that when the above electrical circuit is closed because the nozzle needle is in contact with the valve seat therefor, there is current flow from the battery through the circuit described above which includes the resistor 233. But, the voltage at a point 246 will be at ground potential or zero. Then, when the fuel pressure lifts the needle 222 from its seat, there is an accompanying electrically insulating film (not shown) that is formed around the needle including the tip where the fuel is being injected.

Consequently, the aforementioned electrical circuit which carries current through the resistor 233, is broken. This causes a sharp rise in potential at the circuit point 246, and such change is transmitted to the oscilloscope 212 via a circuit connection 247. It will also be understood that the oscilloscope 21 2 has an input pair of connectors 248. These are for introducing a trigger signal to the oscilloscope.

Such trigger signal (not shown) may be developed by a magnetic pickup (not shown) on the engine crankshaft (not shown), or similarly with some other connection to the engine so that a trigger signal is developed at a desired point in the operation of the internal combustion engine, for example as shown in Figure 3.

Referring to Figure 5, it may be noted that the elements of the fuel injection nozzle 211 include, as the standard parts according to the commercial unit, a metallic spring 220 which acts on the axially movable needle 222. Needle 222 is part of the nozzle Z11, and it cooperates with a valve seat 251 that is on the inside of a metallic tip 252. It will be noted that the spring 220 acts on the opposite end of the needle 222 from the valve seat 251.

It will be observed that there is no electrical insulation at the lower portion, or in fact the whole length of the needle 22, with respect to the body 243 of the nozzle 211. However, at the upper end (as viewed in Figure 5) of the spring 220, there is an electrically insulating material sleeve 255 that is located between the metallic sleeve 21 7 (described above) and an outer threaded sleeve 257. This threaded sleeve 257 screws into the upper end (as viewed in Figure 5) of the body 243. The lock nut 225 screws onto the stop screw 216, and it bears against the upper end of the sleeve 21 7 which consequently locks the internal threads of sleeve 21 7 with the external threads of the lift-stop-screw 216.

There may be a guide washer (not shown) between the lock nut 225, and the top of the sleeve 21 7 for guiding and centralizing the leak off boot 215 onto the top of the nozzle 211.

It will be observed that there is an electrically insulated conductive path from the upper end (as viewed in Figure 5) (i.e. of the spring 220 where it bears against the inner sleeve 217) to the lock nut 225 via the sleeve 217 and lift-stop screw 216.

This path continues to the lower end of the spring 226 which has the upper end thereof in contact with the electric contact screw 227. From there the path continues via the connector 231 that is clamped between the pair of nuts 230.

It may be noted that there is an insulating material bushing 261 that surrounds the screw 227 where it passes through the leak-off boot 21 5. Also, there is a rubber o-ring 262 which is a standard part of the nozzle 211. Of course, if the fuel return lines (not shown) which attach to male connectors 265 and 266, are made of electrically insulating material, then the bushing 261 could be omitted.

Figure 6 illustrates another type of commercial injection nozzle which is substantially the type manufactured by the German company Robert Bosch, GmbH, of Stuttgart, West Germany. This type of injection nozzle has a metallic body 271 that carries a metallic needle 272 therein. Needle 272 has a metallic spring 273 in contact with a spring seat 274. The spring 273 biases the needle 272 into closed position against a valve seat 276 which is located at the tip of the body 271 of the Bosch type nozzle. There is a cavity 277 just above (as viewed in Figure 6) the seat 276. This cavity 377 receives the fuel under pressure that is to be injected. Such fuel for injection is supplied through a conduit or fuel passage 278 which is located within the body 271 of the valve.

The upper end (as viewed in Figure 6) of the spring 273 bears against a metallic washer 282, the thickness of which acts as an adjustment for the tension on the spring 273. An electrically insulating material washer 283 separates the washer 282 from a metallic washer 275 and so electrically isolates the top end of the spring 273 and the washer 275 from the metallic elements.

Also, there is an electrically insulating material sleeve 284 that surrounds the spring 273 and the washer 275, in order to ensure electrical isolation from the body 271 of the Bosch type nozzle. It may be noted that the sleeve 284 is preferably constructed of the well known Teflon shrink tubing.

In this type nozzle valve, the fuel leak-off takes place from a central open space 286 through a central passage 287 and out through the interior open portion of a fuel leak-off connector 288.

However, there is an insulated electrical conductor 292 that goes in through the interior of the connector 288 and a connecting passage 289 to the central passage 287. The conductor 292 is soldered, to otherwise electrically connected firmly to the washer 275.

In this type of nozzle, it may be noted that substantially the only modification to a standard Bosch type nozzle that is required to provide for this invention, is the addition of the insulating washer 283 and sleeve 284. This insulates the upper end of the spring 273 electrically from the body 271 and the other electrically conductive elements. Of course, the electrical circuit connection must be carried out from the conducting material washer 275 which is done via the insulated electrical wire 292.

It may be observed that it is the discovery according to this invention which permits the minimal change and/or additional structure that is required in order to create the desired electrical circuit. Such circuit is one that is broken when the needle 272 breaks contact with its seat 276 at the tip of the valve. It is the fuel flowing under pressure which provides a film of fuel surrounding the needle 272 that creates the necessary insulation to thus provide for the desired electrical signal. This nozzle valve as described thus makes feasible the development of an electrical signal when the needle breaks contact with the valve seat, with minimal modification of a commercial injection nozzle.

Claims (11)

Claims

1. An ignition system for an internal combustion engine employing fuel injection and a high tension electric spark to ignite a combustible mixture of said injected fuel, said system including a fuel injection valve having an electricalily conductive material plunger in seating contact with an electrically conductive material body of said valve when the valve is closed, said plunger being arranged to be actuated by fuel pressure to open the valve, first electrical circuit means for connecting a resistor in series with said plunger, a comparator having two inputs and an output, second circuit means for connecting a predetermined EMF to one of said comparator inputs, and third circuit means for connecting the other of said comparator inputs to said plunger, said comparator output providing a signal to initiate said electric spark when said plunger is actuated by the fuel pressure.

2. A system according to claim 1 including time delay means connected to said comparator output for maintaining said signal long enough to substantially eliminate dynamic changes in the electrical resistance between said valve plunger and said valve body after the initial opening by fuel pressure.

3. A system according to claim 2 wherein said time delay means comprises a second comparator having two inputs and an output, one of said second comparator inputs being connected in parallel with said one first comparator input to said predetermined EMF, the other of said second comparator inputs being connected to said spark initiating signal with an RC circuit to determine said time delay, and the output of said second comparator being connected to said other first comparator input to hold said spark initiating signal long enough to substantially eliminate said dynamic changes.

4. A system according to any one of claims 1 to 3 including a plurality of said injection valves, and wherein said third circuit means comprises a diode in series with each of said plungers for maintaining electrical separation.

5. A system according to claim 4 including auxiliary engine-actuated spark timing signal generating means, and wherein said third circuit means also comprises a diode in series with said auxiliary means for maintaining its electrical separation.

6. A system according to claim 5 wherein said auxiliary engine-actuated spark timing signal generator means comprises breaker points.

7. An ignition system according to any one of claims 1 to 6 wherein said valve comprises a metallic needle operating in a metallic said body incorporating a valve seat and a metallic bias spring acting at the opposite end of said needle from said valve seat to normally close said valve, means for electrically insulating said spring from said metallic body, and an electrical connector connected to said metallic spring at the other end thereof from said needle.

8. An ignition system according to any one of claims 1 to 6 wherein said valve comprises a metallic needle operating in a metallic said body incorporating a valve seat, and mechanical bias means acting at the opposite end of said needle from said valve seat to normally close said valve, means for electrically insulating said mechanical bias means from said metallic body, and circuit means for electrically connecting a test instrument to said needle in order to create a test signal when said needle breaks contact with said valve seat, said needle becoming insulated from said metallic body upon said fuel injection.

9. A system according to claim 8 wherein said mechanical bias means is a metallic spring.

10. A system according to claim 8 or claim 9 wherein said circuit means comprises an electrical connector connected to said metallic spring at the other end thereof from said needle.

11. An ignition system substantially as described herein with reference to the accompanying drawings.