Ignition System for an internal combustion engine

Field of the Invention:

This invention relates to "Ignition System for an internal combustion engine' and more particularly for a two wheeled vehicle fitted with a spark ignition IC engine.

Background of the Invention:

Generally spark ignition internal combustion engines comprise a spark plug which is mounted to the cylinder head of the engine for spark generation. The spark plug has two electrodes separated by an air gap, across which a high voltage (5-15 kV) when applied causes ionization of the air gap and thereby generates spark.

The ignition control unit comprising an electronic circuit receives inputs from crank angle sensor, throttle position sensor and engine temperature sensor to calculate the appropriate timing for spark generation in order to ensure optimum performance, high fuel efficiency and reduced emissions.

In most engines, a pulsar coil mounted on the crankcase separated by an air gap with respect to a reluctor or pip fitted to a flywheel magneto provides a signal indicative of the crank angle.
An ignition coil comprising mutually coupled inductors is used for converting the ignition control unit output signal into high voltage for spark generation.

Capacitive discharge ignition (CDI) and Inductive Discharge Ignition (IDI) are two methods used for generating high voltage across the spark plug. In CDI, a high voltage capacitor is charged to a medium voltage (-300V) higher than the electrical

system voltage (12V) and is discharged through a low resistance primary coil of the ignition coil. The sudden high current produced in the primary coil, by mutual induction, generates a very high voltage (~30kV) across the secondary coil which is in turn connected to the spark plug. The rate of rise of secondary voltage in CDI is very high (~3kV/u.s) as the energy stored in the capacitor is instantaneously dissipated through the primary coil.

In IDI System the primary coil of the ignition coil is charged for a sufficient duration called as the dwell time by the 12V Battery through an electronic switch controlled by the Ignition Control Unit. The electronic switch is closed by detecting the leading edge of a reluctor and at the ignition timing instant calculated by the Ignition Control Unit, the current in the primary coil is interrupted causing a sudden collapse of the magnetic field. A high back emf produced across the primary coil, by mutual induction, creates the high voltage across the secondary coil.
In IDI System, the energy stored in the inductor is not completely utilised in causing air gap ionisation. The fraction of the energy available after air gap ionisation is used to sustain the spark and hence the spark duration is more in the IDI system when compared to CDI system.
The spark energy is high at low engine speed in IDI system because of high dwell time and is preferable for burning lean air fuel mixtures. Low trigger start rpm (minimum speed for continuous spark generation) and better fuel efficiency can be achieved by IDI System.
During the starting of the internal combustion engine, at engine speed below 1500rpm (less than idling speed), there is a tendency for the flywheel magneto to rotate in the reverse direction because of incorrect ignition timing, which is in turn due to sudden deceleration of the flywheel magneto near the Top Dead Centre. The high reverse torque applied called 'kick back' can lead to severe damage of engine parts like 'One Way Clutch', connecting rod and camshaft. Such conditions are more prevalent while the throttle is opened at a high rate during starting of the engine.

Japanese Patent JP 6330839 discloses a flywheel assembly with two reluctors with different arc length separated by an air gap wherein ignition is prohibited for a CDI system during reverse rotation by detecting and comparing the time delay between the pulses and hence the damage to the engine parts is prevented. This increases the cost of the flywheel magneto and is not directly applicable to an IDI system. Ignition prohibition in IDI system requires that the primary coil to be maintained in a charged condition for a long time which in turn leads to overheating and failure of the ignition coil. This is because, the charging of the primary coil is initiated by sensing the leading edge of the reluctor and an interruption will lead to spark generation.

Another patent JP 60026174 discloses an ignition controller wherein the reverse rotation of the engine and resulting kick back is prevented by delaying the ignition time of the very slowly rotating engine to be after the top dead centre at the end of the compression stroke. In an IDI system, delaying the ignition time will again lead to prolonged charging of the primary coil thereby causing coil overheating.

JP2005307855 discloses an ignitor for preventing reverse rotation of engine with an IDI system wherein the ignition is suppressed in low rotation speed of the engine. The charging of the primary coil is allowed only after reaching a predetermined engine speed. But this can lead to poor starting ability of the engine and increased cranking speed requirement.

Therefore the present invention provides a kick back prevention means for an IDI system which overcomes the disadvantages of the prior art.

Summary of the Invention:

The present invention has been devised in view of the above problems and it is therefore an object of the present invention to provide kickback prevention means which will not cause over heating of the ignition coil.

Another object of the present invention is to provide kickback prevention means which will not lead to poor startability.

Yet another object of the present invention is to provide kickback prevention means with increased cranking speed requirement which will improve the reliability of the engine.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Brief Description of the Drawings:

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein

Figure 1 is a side view of a conventional two wheeler according to this invention.

Figure 2 is the circuit diagram according to one embodiment of the present invention.

Detailed Description of the Invention:

The present invention relates to ignition system for internal combustion engine.
For the purpose of illustration, it will be described with the help of a motorcycle. Referring to figure. 1, a motorcycle comprises of a frame (101), front fork (102) attached to a pivot tube (103) of the vehicle frame, a front wheel (104) attached to these front forks (102), a handle bar (105) connected to the front forks (102), a fuel tank (106) attached so as to straddle an upper part of the vehicle frame, a seat (107) attached to the upper rear portion of the vehicle frame, an engine unit (108) attached to the lower front section of the vehicle frame, a swing arm (109) attached to a lower rear section of the vehicle frame, suspended by a rear shock absorber (not shown in the drawing) from the vehicle frame and a rear wheel (110) attached to a rear end of swing arm (109). The intake system of the engine comprises of a carburettor, intake duct and an air cleaner. The exhaust system of the engine comprises of exhaust pipe and a muffler. The motorcycle is also provided with a side cover (111) for covering a side section of the vehicle frame, a seat cover for covering a rear section of the vehicle frame below the seat, a front fender (112) for covering an upper part of the front wheel (104), and a rear fender (113) for covering an upper part of the rear wheel (110). The drive from the engine (108) is transmitted from the engine to the driven wheel sprocket mounted on the rear wheel hub mounted on the rear wheel assembly.

Referring to figure 2, a kick back preventing means for a spark ignition internal combustion engine with Inductive Discharge- Ignition comprises an electronic circuit (201) receiving crank angle signal from pulsar coil (202) and controlling an electronic device (203) for gradually decaying the primary coil current in order to prohibit ignition on prediction of kick back condition.

A battery (207) is connected to a primary coil (204) of the ignition coil which is in turn connected through an electronic device (203) to the common ground potential. A spark plug (206) is connected to the secondary coil (205) and mounted on the engine cylinder for spark generation. The electronic circuit (201) receives input from the pulsar coil (202) and throttle position sensor (209) for calculating ignition timing. The said electronic circuit (201) and the electronic device (203) are assembled within an ignition control unit (290).

The kick back condition is predicted by monitoring the time delay between the leading edge signal and trailing edge signal of the said pulsar coil (202). Other crank angle sensors like cam shaft position sensor or hall effect sensor can also be used to provide signal indicative of piston position with respect to Top Dead Centre (TDC). When the reluctor in the flywheel magneto passes along the said pulsar coil (202), distinguishable signals indicative of the leading edge of reluctor and trailing edge of the reluctor are produced across the pulsar coil (202).
The trailing edge signal indicates a base angle before Top Dead Centre. At low speeds, the said electronic circuit (201) on detecting the leading edge signal, biases the said electronic device (203) in the saturation region and thereby charges the primary coil (204) till the detection of trailing edge signal. On detecting the trailing edge signal, the said electronic circuit (201) biases the electronic device (203) in the cut-off region interrupting the primary coil current. The sudden collapse of the magnetic field leads to spark generation.

At speed beyond a predetermined value, in order to vary the ignition timing, the said electronic circuit (201) interrupts the charging current in primary coil (204) before the detection of the trailing edge by a predetermined time interval.

Beyond a predetermined engine speed, after successful starting of the engine, when the electronic control unit (201) detects the deceleration of the flywheel magneto to a predetermined value, the electronic control unit (201) provides control signal to the electronic device (203) to shift the operating region gradually from the saturation region to the cut-off region through the active region. The primary coil (204) that is charged due to the detection of the leading edge signal will gradually discharge through the electronic device (203) at a predetermined rate decided by the electronic circuit (201).

The deceleration of the flywheel magneto is detected by monitoring the time delay between the leading edge and trailing edge signals from the pulsar coil (202). When the electronic circuit (201) detects that the trailing edge has not passed the pulsar coil (202) even after a predetermined time delay, a probable kick back condition is predicted and the electronic device (203) is controlled to gradually decay the primary coil current. Gradual decay of the primary coil current results in a low back emf across the primary coil (204) which in turn produces a low voltage across the secondary coil (205). The low voltage across the said secondary coil (205) is insufficient to generate spark across the spark plug (206) electrodes. Hence spark generation is prohibited on prediction of kick back condition.

In another embodiment the charging of the primary coil (204) is enabled after a time lag after the leading edge signal is detected, in order to limit the dwell time at low engine speeds and thereby preventing the ignition coil overheating. The conditions for kick back prediction remain unchanged. Delay in the trailing edge signal beyond a predetermined time interval after the leading edge signal for engine speeds greater than a predetermined value is predicted to be a kick back condition and the gradual decay of the primary coil current is initiated.

As the current in the primary coil (204) is gradually decayed, over heating of the ignition coil is avoided. Since ignition is prohibited, kick back is also prevented. Thus the benefits of the IDI system can be utilised without increasing flywheel magneto cost and without deteriorating the reliability of the system.

The predetermined engine speed beyond which the time delay between the pulsar coil (202) leading edge and trailing edge signals are monitored, the predetermined time delay beyond which a kick back condition prediction occurs and the predetermined rate at which the primary coil current decays is set based on the specific engine performance studied at different conditions with respect to air fuel mixture, temperature and pressure.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the claims.

We Claim:

1. A kickback preventing ignition system for a spark ignition internal combustion engine comprising of:

a ignition coil;

a battery connected to the primary coil of the said ignition coil, the secondary coil of which is connected to the spark plug;

an electronic circuit responsive to leading edge and trailing edge of the reluctor for causing said ignition coil primary current to be decayed gradually for prohibiting ignition during kick back condition; and

an electronic device means for suppressing ignition on receiving control signal from the said electronic circuit.

2. The kickback preventing ignition system as claimed in claim 1, wherein the said electronic circuit and the said electronic device are assembled within an ignition control unit.

3. The kickback preventing ignition system as claimed in claim 2, wherein the said ignition control unit varies the said electronic device operating region gradually from the saturation region to the cut off region at a predetermined rate to suppress ignition.

4. The kickback preventing ignition system as claimed in claim 1, wherein the said electronic circuit receives the crank angle signal from pulsar coil.

5. The kickback preventing ignition system as claimed in claim 1, wherein the said electronic circuit on detecting the leading edge signal biases the said electronic device in the saturation region thereby charges the primary coil.

6. The kickback preventing ignition system as claimed in claim 1, wherein the said electronic circuit charges the primary coil after a predetermined time lag after detecting the leading edge.

7. The kickback preventing ignition system as claimed in claim 1, wherein the said electronic circuit on detecting trailing edge signal biases the said electronic circuit in the cut off region interrupting the primary coil current.

8. The kickback preventing ignition system as claimed in claim 1, wherein the kickback condition is predicted by monitoring the predetermined time delay between leading edge signal and trailing edge signal of the pulsar coil.