Title:
IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINE
United States Patent 3791364
Abstract:
The disclosed ingition system includes a monostable multivibrator passing into its semistable state each time the associated engine is to be ignited to put a normally conducting switching transistor in its nonconducting state. This causes the interruption of a current flowing through an ignition coil to generate an ignition voltage across it. In the monostable multivibrator a capacitor is serially connected to a resistor high in magnitude of resistance to increase a time constant for charging and a semiconductor diode is connected across the resistor to decrease a time constant for discharging.


Inventors:
SALTA T
Application Number:
05/146934
Publication Date:
02/12/1974
Filing Date:
05/26/1971
Assignee:
Mitsubishi Denki Kabushiki Kaisha (Tokyo, JA)
Primary Class:
International Classes:
F02P3/045; F02P3/00; F02P5/155; (IPC1-7): F02P3/02
Field of Search:
123/148E
View Patent Images:
US Patent References:
3605713N/A1971-09-20Le Masters
3554169FUEL INJECTION ARRANGEMENT FOR INTERNAL COMBUSTION ENGINES1971-01-12Wahl
3473061IGNITION ARRANGEMENTS FOR INTERNAL COMBUSTION ENGINES1969-10-14Soehner
3357416Transistorized ignition system having an integrating circuit1967-12-12Huntzinger
3322107Ignition system1967-05-30Mieras
Primary Examiner:
Goodridge, Laurence M.
Assistant Examiner:
Flint, Cort
Attorney, Agent or Firm:
Burns, Robert Lobato Emmanuel E. J.
Claims:
What is claimed is

1. An ignition system for use with an internal combustion engine comprising: ignition time-detection means for developing in use ignition signals corresponding to the ignition timing of an internal combustion engine varying in time in dependence upon the speed of rotation of said engine; a switching circuit receptive of said ignition signals and having two states and comprising means responsive to said ignition signals for switching into one state for a predetermined time for each ignition signal inversely proportional to the frequency of said ignition signals and means for developing switching signals corresponding in frequency and duration to said one state; and an ignition circuit receptive of said switching signals for developing spark signals for developing ignition sparks said spark signals corresponding in frequency and duration to said switching signals; wherein said switching circuit comprises a monostable multivibrator including a pair of first and second semiconductor elements, each having an operating state, a chargeable and dischargeable capacitor being dischargeable when said second semiconductor element is in said operating state, means defining a capacitor charging circuit connected to said capacitor including a resistor, and means defining a capacitor discharging circuit connected to said capacitor including a semiconductor rectifier element connected across said resistor, said rectifier element being so poled as to be conductive with respect to a flow of discharging current from said capacitor and when conductive, shortcircuiting said resistor.

2. An ignition system for use with an internal combustion engine comprising; ignition time-detection means for developing in use ignition signals corresponding to the ignition timing of an internal combustion engine varying in time in dependence upon the speed of rotation of said engine; a switching circuit receptive of said ignition signals and having two states and comprising means responsive to said ignition signals for switching into one state for a predetermined time for each ignition signal inversely proportional to the frequency of said ignition signals and means for developing switching signals corresponding in frequency and duration to said one state; and an ignition circuit receptive of said switching signals for developing spark signals for developing ignition sparks, said spark signals corresponding in frequency and duration to said switching signals; wherein said switching circuit comprises a monostable multivibrator including a pair of first and second semiconductor elements, each having an operating state, a triggering circuit for triggering said first semiconductor element, a chargeable and dischargeable capacitor being dischargeable when said second semiconductor element is in said operating state, means defining a charging circuit connected to said capacitor including a resistor, and means defining a discharging circuit connected to said capacitor including a semiconductor rectifier element connected across said resistor, said rectifier element being so poled as to be conductive with respect to a flow of discharging current from said capacitor and when conductive, shortcircuiting said resistor, and wherein said ignition time-detection means includes a signal generator responsive to the rotational movement of the engine for generating said ignition signal, a third semiconductor element having an inoperative state and an operating state responsive to said ignition signal from said signal generator, another chargeable and dischargeable capacitor charged when said third semiconductor element is in said inoperative state and discharged through said semiconductor element when it is in said operating state, a first semiconductor rectifier element poled forwardly with respect to the polarity with which said another capacitor is charged, and a second semiconductor rectifier element poled reversely with respect to said polarity of said another capacitor and connected to said triggering circuit for said first semiconductor element included in said monostable multivibrator.

3. An ignition system for use with an internal combustion engine comprising: means for developing in use first signals corresponding to the ignition timing of an internal combustion engine varying in frequency in dependence upon the speed of rotation of said engine; a switching circuit receptive of said first signals and having two states and comprising means responsive to said first signals for switching into one state for each first signal for a variable duration of time determinable by the frequency of said first signals, and means for developing second signals corresponding in frequency and duration to said one state thereby having a frequency corresponding to the frequency of said first signals; an ignition circuit receptive of said second signals for developing engine ignition signals corresponding in frequency and duration to said second signals;

4. An ignition system according to claim 3, wherein said rectifier element comprises a semiconductor diode.

Description:
BACKGROUND OF THE INVENTION

This invention relates to an ignition system for use with an internal combustion engine including a semiconductor switch adapted to be put in its nonconducting state to interrupt a current flowing through an ignition coil involved thereby to induce an ignition voltage across the secondary of the coil each time the engine is to be ignited. More particularly it concerns improvements in such an ignition system further including a monostable multivibrator for shaping a waveform of an ignition signal for controlling the semiconductor switch.

In the conventional type of ignition systems for internal combustion engines, a time interval for which a current flowing through the ignition coil is interrupted has remains unchanged independently of a variation in speed of rotation of the engine. This is because the interrupting time interval for the ignition coil has been determined by the operating time of the monostable multivibrator for which it is put in its semistable state. On the other hand, the ignition coil has been designed to have flowing therethrough a current for a time interval long enough to permit ignition voltage or sparks produced thereby to be sufficiently high or strong even in the case the engine increases in speed of rotation to proportionally decrease a time interval between the successive ignition sparks or an interspark time. Therefore the ignition coil has been energized through a supply circuit having a time constant in the low speed mode of operation equal to that in the high speed mode of operation of the engine. Accordingly, in the low speed mode of operation the current continues to flow through the ignition coil after a sufficiently high quantity of electromagnetic energy has been accumulated by the ignition coil. This has resulted in the generation of heat on the ignition coil due to its electric resistance and therefore in an increase in temperature of the coil. Thus the ignition coil might decrease in useful life causing a decrease in reliability of the associated ignition circuit.

SUMMARY OF THE INVENTION

Accordingly it is an object of the invention to eliminate the abovementioned disadvantages of the conventional ignition systems for internal combustion engines.

The invention accomplishes this object by the provision of an ignition system for use with an internal combustion engine comprising means including an ignition time-detection circuit responsive to the rotational movement of the engine to generate one first signal or ignition signal each time the engine is to be ignited, a switching circuit triggered into one state or its operating state with the ignition signal, the switching circuit including means for determining the operating time thereof including a capacitor, and an ignition circuit responsive to the triggering of the switching circuit into its operating state to interrupt a current flowing therethrough to produce an ignition spark, characterized in that means is provided for changing an electric charge on the capacitor in accordance with the speed of rotation of the engine.

The switching circuit may be formed preferably of a monostable multibivrator including a pair of first and second semiconductor elements, the capacitor capable of charging when the first semiconductor element is in its operating state, and a resistor high in magnitude of resistance and connected in a charging circuit for the capacitor.

In order to discharge the capacitor of a minimum time constant when the second semiconductor element is in its operating state, a rectifier element may be connected in a discharging circuit for the capacitor and across the resistor connected in the charging circuit for the capacitor, the rectifier element being so poled as to be forward with respect to a flow of discharging current from the capacitor and when conducted, short-circuiting the resistor.

BRIEF DESCRIPTION OF THE DRAWING

The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a graph useful in explaining the principles of the invention; and

FIG. 2 is a schematic circuit diagram of an ignition system constructed in accordance with the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 of the drawing, there is illustrated a graph useful in explaining the principles of the invention. In FIG. 1, wherein the axis of ordinates represents time in an arbitrary unit and the axis of abscissas represents a speed of rotation of an internal combustion engine in an arbitrary unit, a straight line A depicts the ignition characteristic of the conventional type of engines that a time interval between successive ignition sparks or an interspark time interval gradually decreases with an increase in speed of rotation of the engine. Another straight line C shows an operating time of a monostable multivibrator used in a conventional ignition system such as above outlined. That is the operating time of the monostable multivibrator for which it is in its semistable state remains substantially unchanged in spite of an increase in speed of rotation of the engine. Since the monostable multivibrator is put in its operating state to open the associated semiconductor switch as above described, a current flowing through the ignition coil is kept interrupted for the operating time of the monostable multivibrator. In other words, the ignition coil has a current interrupting time equal to the operating time of the monostable multivibrator and remaining substantially unchanged regardless of a change in speed of rotation of the engine.

Therefore, for the particular speed of rotation of the engine, a time interval for which a current is flowing through the ignition coil or the conduction time thereof is equal to a difference in ordinate between the respective points on the lines A and C corresponding to that speed of rotation of the engine. It has been commonly practiced to render this conduction time long enough to permit sufficiently strong ignition spark to be produced even at the high speed mode of operation of the engine. Therefore the ignition coil has been energized through a supply circuit having a time constant remaining unchanged between the high and low speed modes of operation of the engine with the result that in the low speed mode of operation the current continues to flow through the ignition coil even after a sufficiently high quantity of electromagnetic energy has accumulated by the coil. This has led to the generation of heat on the ignition coil due to its electric resistance and therefore to an increase in temperature of the coil. Therefore the ignition coil might decrease in useful life while the associated ignition system might have a less reliability.

The invention contemplates to eliminate the disadvantages of the prior art type ignition systems as above described by the provision of improved means for rendering a time interval for which the current flowing through the ignition coil is interrupted, longer in the low speed mode of operation of the associated internal combustion engine and rendering it shorter as the speed of rotation of the engine becomes higher. Namely, as shown at straight line B in FIG. 1, the interrupting time for the ignition coil is caused to change in proportion to a variation in interspark time relative to a change in speed of rotation of the engine as shown at line A in the same Figure. Thus, in the high and low speed modes of operation of the engine the ignition coil is given a sufficiently high quantity of electromagnetic energy while eliminating a thermal loss of the ignition coil.

Referring now to FIG. 2, there is illustrated an ignition system for an internal combustion engine constructed in accordance with the principles of the invention. The arrangement illustrated means comprising an ignition time-detection circuit ID for detecting time points at which the associated internal combustion engine (not shown) is to be ignited, a transistor switching circuit MM and an ignition circuit IC. The ignition detection circuit ID includes a signal generator 10 of the conventional construction responsive to the rotational movement of the engine to produce one ignition signal at each ignition time-point a semiconductor diode 12 and an NPN type transistor 14 disposed in series circuit relationship in the named order. The transistor 14 has a base electrode connected to the cathode electrode of the diode 12, an emitter electrode connected to ground and a collector electrode connected through a collector resistor 16 to a positive terminal of a source of direct current B with the generator also connected to ground. The collector electrode of the transistor 14 is connected to a capacitor 18 which is, in turn, connected to both an anode electrode of a semiconductor diode 20 and a cathode electrode of another semiconductor diode 22. The diode 20 is connected at the cathode electrode to ground and the diode 22 is connected at the anode electrode to the transistor switching circuit MM.

The transistor switching circuit MM is formed of a monostable multivibrator including an NPN type transistor 24 of common emitter configuration having a collector electrode connected to the positive terminal of the source B through a collector resistor 26 and a base electrode connected to the anode electrode of the diode 22 and also to ground through a resistor 28. The collector electrode of the transistor 24 is further connected through a resistor 30 to a base electrode of another NPN type transistor 32 of common emitter configuration. The transistor 32 has a collector electrode connected to the base electrode of the transistor 24 through a series combination of a capacitor 34 and a resistor 36 and also to the positive terminal of the source B through a collector resistor 38. The junction of the capacitor 34 and the base electrode of the transistor 24 is connected to the positive terminal of the source B through a resistor 40 and the resistor 36 is connected across a rectifier a semiconductor diode 42 so poled as to be permit a discharging current from the capacitor 34 to flow therethrough.

The ignition circuit IC includes an NPN type transistor 44 of common emitter configuration having a base electrode connected to the collector electrode of the transistor 32 and a collector electrode connected to ground through a constant voltage diode 46 such as a Zener diode and also to the positive terminal of the source B through a primary winding of an ignition coil 48 having a secondary winding operatively coupled to the associated engine (not shown) in the well known manner.

It is assumed that, the switching circuit or the monostable multivibrator circuit MM is in its stable state in which the transistor 24 is conducting while the transistor 32 is not conducting and that a base current is applied to the switching transistor 44 from the source B through the resistor 38 to put it in the conducting state thereby to permit a current to flow through the primary winding of the coil 48 from the source B. Under the assumed condition, the capacitor 18 of the ignition detection circuit ID has been charged from the source B through the resistor 16 and the diode 20 with the polarity illustrated in FIG. 2.

If a time point where the engine (not shown) is to be ignited is reached the signal generator 10 produces a voltage indicative of an ignition signal. This voltage is then applied through the diode 12 to the transistor 14 to put it in its conducting state. Therefore the capacitor 18 charged with the illustrated polarity discharges through a circuit traced from the capacitor 18 through the nonconducting transistor 14, ground, the resistor 28 and the diode 22. This discharge of the capacitor 18 causes the monostable multivibrator circuit MM to pass into its semistable state or its operating state where it remains for a given time interval before returning back to its original stable state. In the semistable state of the monostable multivibrator circuit MM the transistor 24 becomes nonconducting through the interruption of its base current while the transistor 32 is put in its conducting state.

The conduction of the transistor 32 develops a second signal or switching signal that causes the base current to the switching transistor 44 to be interrupted thereby to put the transistor 44 in its nonconducting state. Thus the primary current flowing through the ignition coil 48 is interrupted resulting in the generation of a high voltage on the secondary of the coil 48 sufficient to apply an ignition spark to the engine.

As well known, the monostable multivibrator circuit MM remains in its semistable or operating state until the capacitor 34 has been completely discharged. Therefore as long as the monostable multivibrator circuit MM is maintained in its operating state the transistor 44 is in its nonconducting state in which the current is prevented from flowing through the ignition coil.

The invention includes means for controlling the discharging time of the capacitor 34 in accordance with the speed of rotation of the associated engine, the discharging time determining the operating time of the monostable multivibrator MM for which it remains in its semistable state. More specifically, the resistor 36 is preselected to be high in magnitude of resistance and serially connected, in addition to the collector resistor 38 for the transistor 32, to the capacitor 34 to impart a large time constant to a circuit for charging the capacitor 34 and also connected across the diode 42 poled to so as to permit discharging current from the capacitor 34 to flow therethrough. This measure is effective for decreasing an electric charge on the capacitor 34 in the high speed mode of operation of the engine where the inter-spark time is short and also for decreasing the discharging time of the capacitor 34 by means of the diode 42 conducting to shortcircuit the resistor 36.

It is therefore appreciated that in the low speed mode of operation the electric charge on the capacitor increases to lengthen the operating time of the monostable multivibrator for which it remains in its semistable state whereas an increase in speed of rotation of the engine is accompanied by a gradually decrease in interspark time and therefore a decrease in electric charge on the capacitor resulting in a gradual decrease in discharging time thereof.

In this way, the ignition system for internal combustion engines has been provided having the desired characteristics that a current flowing through the ignition coil has its interrupting time longer by the low speed mode of operation of the engine and shorter with an increase in speed of rotation of the engine as determined by the operating time of the associated monostable multivibrator. In other words, the current flowing through the ignition coil is interrupted for a time interval shorter in proportion to an increase in speed of rotation of the engine as shown at line B in FIG. 1.

The invention has several advantages. For example, even with the current conducting time of the ignition coil determined so as to produce sufficiently strong ignition sparks in the high speed mode of operation of the engine, the current conducting time thereof in the low speed mode of operation can be fixed to a minimum possible limit. Also the current is permitted to flow through the ignition coil only for a predetermined fixed time interval regardless of the speed of rotation of the associated engine. Therefore the thermal loss due to the ignition coil can reduce to a minimum necessary magnitude.

While the invention has been illustrated and described in conjunction with a single preferred embodiment thereof, it is to be understood that various changes and modifications may be resorted to without departing from the spirit and scope of the invention. For example, the NPN type transistor illustrated may be replaced by a PNP type transistor.