GB2104664A - Apparatus for indicating injection timing and fuel per stroke in an internal combustion engine - Google Patents

Abstract

Apparatus for indicating timing and fuel/stroke in a pulse fuel injection system for an internal combustion engine, especially a diesel engine, includes a magnetic piston 40 axially movable in a cylindrical bore 37 in a fuel line to and from a stopped position blocking an inlet 38. The piston 40 is included in a magnetic circuit including an actual coil 46 having an inductance varying with piston position. Circuitry provides a DC current pulse to the coil 46 prior to injection to move the piston 40 to its stopped position and then provides an AC current to the coil and monitors the voltage and rate of change of voltage thereacross. Change of voltage past a first reference is sensed to generate an injection timing signal; and decrease of rate of change of voltage past a second reference with voltage past the first reference triggers sensing of the voltage as a signal indicating fuel quantity per injection stroke. <IMAGE>

Description

SPECIFICATION Apparatus for indicating injection timing and fuel per stroke in an internal combustion engine This invention relates to the delivery of injected fuel pulses to an internal combustion engine and particularly to the sensing and indication of the timing and fuel quantity of injected fuel pulses during engine operation. This information is useful either for engine calibration or as a source of feedback control parameters in certain engine fuel injection systems, especially for diesel engines.

The prior art shows numerous systems and devices for signalling the timing of fuel injection pulses during engine operation, these devices being generally based on the detection of a pressure or shock pulse in the fuel injection line or the detection of a noise or vibration having a certain signature in the injector or some other component of the fuel injection system. Many of these devices undoubtedly operate adequately in a diesel engine. In addition, a number of fuel injection quantity indicating devices and systems are shown in the prior art; but these devices are generally too complex, cumbersome or slow to operate in actual engine operation and are generally used for calibration for testing purposes only.

It is an object of this invention to provide apparatus which signals both the timing and quantity of fuel per stroke in an internal combustion engine fuel injection system.

It is a further object of this invention to provide such an apparatus suitable for use with a vehicle mounted diesel engine in normal engine operation.

These objects are obtained with a body inserted in the fuel line and having a cylindrical bore with an inlet and outlet at opposite axial ends, a magnetic piston axially movable in the bore to and from a stopped position blocking the inlet and sized so as to allow restricted fuel flow thereby, a magnetic circuit including the piston and an actuating coil, means effective to apply a direct electrical current to the coil to move the piston to its stop position before each injection event, means effective to apply an alternating electrical current to the coil so that the voltage thereacross varies with the piston position, means effective to sense the voltage thereacross and generate a start of injection signal when the voltage exceeds a first predetermined reference and means effective to indicate the sensed voltage at the moment when the time rate of voltage change decreases below a second predetermined reference while the sensed voltage is greater than the first predetermined reference, which voltage indicates the fuel quantity injected. Further details and advantages of this invention will be apparent from the accompanying drawings and foilowing description of a preferred embodiment, in which: Figure 1 is a schematic drawing of a fuel injection system for a diesel engine.

Figure 2 is an axial cutaway view of a preferred embodiment of a portion of this invention adapted for insertion in one of the fuel injection lines of Figure 1.

Figure 3 is a diagram of an electrical control which comprises another portion of this invention and is adapted for use with the portion of Figure 2.

Figure 4 is a diagram of a reference signal generator for use in the apparatus of Figure 3.

Referring to Figure 1, a diesel engine 10 is provided with a fuel injection system comprising a plurality of fuel injectors 11, one for each cylinder of engine 10, supplied by high pressure fuel lines 12 from an injection pump 14. Injection pump 14 receives fuel from a fuel tank 1 5 by way of a low pressure fuel line 1 6 and a low pressure pump 18 and returns fuel to tank 1 5 by a bypass return line 19. A fuel filter 20 is included in low pressure line 1 6. The system shown in Figure 1 is, as described above, standard and well known in the art. It is used with diesel engines made by the Oldsmobile Division of the assignee of this invention and is described in repair manuals and other publications.The injection pump 14 may be one manufactured by the Stanadyne Corporation and described in their publications.

Figure 2 shown one of the fuel injectors 11 of Figure 1 combined with a sensing unit 30. Injector 11 includes a housing 22 and a spring loaded, pressure actuated poppet valve 24 which is ordinarily closed but which is opened by the high pressure pulse of fuel from injector pump 14 through high pressure line 12 to allow a portion of this fuel to enter the cylinder of engine 10 for combustion. The injector 11 is shown in Figure 2 in a somewhat idealized or functional manner for explanatory purposes only; and the structure as shown is not to be taken as any preferred structure, since this portion of the Figure is concerned with a device already known in the prior art. Any suitable pressure actuated injector valve unit can be used in this invention as long as its upstream end 26 is adaptable to receive a sensing unit such as that shown at 30.

Sensing unit 30 has a housing 31 having an inlet end 32 defining an inlet opening 33 and adapted for connection with one of the high pressure lines 12. Housing 31 further has an outlet end 35 defining an outlet opening 36 and adapted for connection with inlet end 26 of the injector 11. Inlet opening 33 and outlet opening 36 communicate with opposite axial ends of a cylindrical bore member 37, the connection with inlet opening 33 being through a smaller diameter passage 38. A generally cylindrical piston 40 is axially movable within bore member 37 and is provided with an outer diameter slightly smaller than the inner diameter of bore member 37 but greater than the inner diameter of passage 38.

Thus, when the piston 40 is moved to its leftmost limit in Figure 2, it abuts and blocks the passage 38, so that a sudden pulse of incoming high pressure fuel will start it moving to the right. The relationship between the outer diameter of piston 40 and the inner diameter of bore member 37 is such that the fuel may flow around and pass piston 40 on its way to injector 11 but is somewhat restricted so that it tends to pull piston 40 along in the same direction. A stop 42 is provided at the outlet end of bore member 37; but the apparatus is designed such that the piston 40 is not expected to reach the stop 42 in normal injection operation.

First and second magnetic polepieces 43 and 44 are contained within the housing 31. A portion 45 of magnetic polepiece 43 and bore member 37 define a spool upon which a coil 46 is wound.

Piston 40 is made of a magnetic material so that it completes a magnetic circuit with cup-shaped magnetic polepiece 43 and disk-shaped magnetic polepiece 44 with a reluctance that varies with the axial position of piston 40. Since this reluctance helps determine the inductance of coil 46, that inductance also varies with axial position of piston 40. Terminals 47 and 48 provide a connection for the ends of coil 46.

In a brief description of the operation of the apparatus of Figure 2 during an injection pulse of the system of Figure 1 , the apparatus is initally set with piston 40 blocking inlet passage 38 and a suitable alternating current supplied to coil 46.

When the injector pump 14 injects a high pressure pulse of fuel into the high pressure line supplying injector 11 of Figure 2, the pulse reaches piston 40, pushes it away from the inlet passage 38 and flows through bore member 37, dragging piston 40 with it and increasing the pressure in injector 11 so as to open the valve 24 and allow injection of fuel into the cylinder of engine 10. The initial movement of piston 40 creates a change in the inductance of coil 46, which in turn, creates a change in the voltage across terminals 47 and 48 which can be detected by appropriate apparatus as the voltage passes a first reference to signal the start of injection at the injector itself.

At the end of the high pressure pulse, when the pressure begins to drop and the injector valve 24 begins to close, the rate of change of piston displacement, and therefore of voltage across terminals 47 and 48, will fall below a second reference. The actual displacement of piston 40 and therefore the voltage across terminals 47 and 48 at this instant is an indication of the actual quantity of fuel that has moved through cylindrical bore member 37 and therefore through injector valve 24 into the cylinder. The movement of the piston will accurately indicate the quarrtity of fuel which moves by it and thus the quantity which is injected because, it is believed, there will be an overshoot by the piston as the fluid flow begins to flow which makes up for the initial lag of the piston at the beginning of fluid flow.Thus, by setting the apparatus of Figure 2 with the application of a direct current across terminals 47 and 48 before each injection event and then, while supplying an alternating current across terminals 47 and 48, monitoring the voltage and rate of change of voltage across those terminals, one can determine the actual start of the injection pulse and the quantity of fuel delivered during the injection pulse.

Figure 3 shows electrical apparatus adapted for use with the apparatus of Figure 2 in the above described manner. The apparatus of Figure 3 includes a source of direct current 50, which may be the vehicle battery, and a source of alternating current 51 which is, in this embodiment, a 100 kilohertz oscillator. Oscillator 51, of course, ultimately derives its power from battery 50. Coil 46, which symbolizes the inductance of the same numbered coil in Figure 2, is shown connected in series with a resistor 52 across oscillator 51. A diode 53 is connected across coil 46; and the junction 54 of the anode of diode 53, coil 46 and the oscillator 51 is grounded. A PNP transistor 55 has its collector connected to the junction 56 of the cathode of diode 53, coil 46 and resistor 52; and its emitter is connected to the ungrounded side of battery 50.The output of oscillator 51 is provided directly to a synchronizing input 58a of a synchronous detector 58; while junction 56 is connected through a capacitor 59 to a detecting input 58b of synchronous detector 58. The output of oscillator 51 is further provided to a reference generating circuit 60, which generates, in a manner to be described at a later point, a first reference voltage A applied to a comparator 61 and a second reference voltage B applied to a comparator 62. The output of synchronous detector 58 is provided to the other input of comparator 61, and through a differentiator 63, to the other input of comparator 62. The outputs of comparators 61 and 62 are combined in an AND gate 64, the output of which is provided to the set input of a sample gate 65 and to the trigger input of a sample timer 66.The output of synchronous detector 58 is further provided to the sampling input of sample gate 65; and the output of sample timer 66 is provided to the reset input of sample gate 65 and to the trigger input of a reset timer 67, the output of which is provided to the base of the transistor 55. The output of sample gate 65 is connected to a hold amplifier 68, which holds the fuel per stroke signal voltage. The start of injection pulse is an edge signal obtained from the output of comparator 61.

Before describing the operation of the system of Figure 3, some of the elements of that system will first be described in more particular detail.

Oscillator 51 can be any appropriate oscillator adapted for use with a DC source such as battery 50. Because of its presence, of course, suitable shielding should be provided for the circuit to prevent electromagnetic interference of the 100 kilohertz signal with the vehicle radio or other electronic controls on the vehicle. Synchronous detector 58 can be any suitable synchronous detector or detector circuit capable of providing a direct current analog of the AC voltage across coil 46. Sample timer 66 and reset timer 67 can be any suitable one shot circuits which, when triggered, generate an output signal a predetermined time after the trigger. Sample gate 65 is a simple gating circuit which passes the signal on its sampling input when it receives a set input and stops passing that signal when it receives a reset input.Hold amplifier 68 is a device which maintains the signal supplied on its input after that signal ceases until another signal is supplied. Reference signalgenerator 60 is described more thoroughly in Figure 4, in which it is shown to comprise a detector 70, which may be synchronous, with a filter 71 on its output and a pair of voltage divider potentiometers 72 and 73 on the output of the filter providing output voltages A and B respectively. Detector 70 and filter 71 provide a DC analog of the voltage across oscillator 51; and potentiometer 72 and 73 provide fixed ratios of that voltage as references A and B to comparators 61 and 16, respectively.

Now the operation of the system of Figure 3 will be described. Prior to the commencement of an injection event, reset timer 67 turns on transistor 55 to supply a direct current therethrough to coil 46 which generates a magnetic force that draws piston 40 into abutment with the magnetic polepiece 43 at the end of inlet passage 38. The current through transistor 55 is sufficient to overcome the 100 kilohertz signal from oscillator 51, which appears only as a ripple thereon. This ripple is of no consequence to the resetting of piston 40; but the oscillator could obviously be turned off during the DC pulse if desired.

With the end of the period of reset timer 67, transistor 55 turns off and the 100 kilohertz alternating current signal from oscillator 51 is supplied by itself across the series combination of resistor 52 in coil 46, as well as to synchronous detector 58 and reference signal generator 60. The voltage across coil 46 is applied through capacitor 59, which is included for DC isolation, to synchronous detector 58 which generates in its output a DC representation thereof for comparison with reference A in comparator 61. Reference A is adjusted by potentiometer 72 so that it is just greater than the output of synchronous detector 58 with the piston in this initial position. The output of differentiator 63 at this time, of course, zero, which is below the reference B supplied from potentiometer 73.The outputs of comparators 61 and 62 to AND gate 64 at this time are a low or O output from comparator 61 .and a high or 1 output from comparator 62.

With the commencement of injection and the initial movement of piston 40 to the right in Figure 2, the output of differentiator 63 immediately increases past the level of reference B to generate a low or 0 output from comparator 62 to AND gate 64. As the output of synchronous detector 58 rises, it next passes reference level A so that comparator 61 provides a high or 1 input to AND gate 64 as well as a start of injection pulse signal, which is a pulse edge signal that can be used in other apparatus for a variety of purposes. In all the preceding actions, there has not yet been a combination of two high or 1 inputs to AND gate 64. However, when the injection pulse ends, the increase in voltage output of synchronous detector 58 begins to slow and the output of differentiator 63 rapidly falls below reference level B. At this point the output of comparator 62 switches high so that AND gate 64 is enabled to set sample gate 65 and trigger the sample timer 66. The output of synchronous detector 58 is thus passed by sample gate 65 to hold amplifier 68 where it is held as a quantitative fuel per stroke signal. Almost immediately, sample timer 66 causes a reset of sample gate 65 and triggers reset timer 67 to reset the apparatus of Figure 2 as previously described.

Claims (5)

1. Sensing apparatus for sensing quantity of fuel per pulse in a fuel line with a fuel injector in an internal combustion engine pulse fuel injection system comprising: a body inserted in the fuel line, the body defining a cylindrical bore with an inlet and outlet at opposite axial ends thereof; a magnetic piston axially movable in the bore to and from a stopped position, the piston having an outer diameter of such a size in relation to the inner diameter of the cylindrical bore that fluid flow past the piston exerts an axial force thereon; means comprising, with the piston, a magnetic circuit including an actuating coil having an inductance varying with axial piston position over the range of piston movement resulting from a fuel injection pulse;; reset means effective, before each injection event, to apply an electrical current to the coil so as to move the piston to its stopped position; and means effective, at least when the piston is within said range of piston movement, to measure a parameter varying with the inductance of the coil and to determine therefrom substantially how far the piston moves axially in response to a fuel injection pulse, which axial movement is a measure of the injected fuel quantity.

2. A sensing apparatus according to claim 1, in which the means effective, at least when the piston is within said range of piston movement, to measure a parameter varying with the inductance of the coil and to determine therefrom substantially how far the piston moves axially in response to a fuel injection pulse, also determine the time of initial piston axial movement so as to provide a measure of the time of injection.

3. A sensing apparatus according to claim 1 or 2, in which the reset means, before each injection event, apply a strong electrical current to the coil so as to move the piston to its stopped position; and the parameter-measuring means apply an alternating current weaker than the strong current to the actuating coil, measure the voltage across said coil, and determine from said voltage and the time rate of change thereof substantially how far the piston moves axially in response to a fuel injection pulse.

4. A sensing apparatus according to any one of the preceding claims, in which the magnetic piston, in the stopped position, blocks the inlet of the cylindrical bore.

5. A sensing apparatus according to any one of the preceding claims, in which the parameter measuring means generate a start of injection signal when the voltage sensed across the coil exceeds a first predetermined reference; and then indicate the sensed voltage at the moment when the time rate of voltage change decreases below a second predetermined reference.