Ignition Timing Control
Field of the Invention:
This invention relates to ignition timing control and more particularly for 4 stroke engine
Background of the Invention:

Generally in a 4-stroke IC engine, ignition timing is specified based on the engine speed & throttle position. Based on these two input parameters, ignition timing is derived from a 2D timing map and the same is used in the engine for its operating speed range. In such configurations it is seen that due to variation in the engine speed specifically at lower engine speed, engine crankshaft can rotate in the opposite direction causing the engine kick-back. This condition needs to be detected so as not to cause damage to engine and other parts like one-way clutch, starter motor, etc.

Therefore, it is the object of the present invention to provide ignition timing control which prevents the engine crankshaft to rotate in opposite direction.

Summary of the Invention:
The present invention provides ignition timing control for 4 stroke engine which prevents the condition when the engine crankshaft rotates in opposite direction. An object of the present invention is to supress the ignition spark soon after the detection of the above said condition.

Another object of the present invention is to delay the ignition spark soon after the detection of the above said condition.

Further object of the present invention is to eliminate the amplification of engine kick back force. Yet further object of the present invention is to eliminate the warranty of one-way clutch, starter motor due to engine kick-back force 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 Drawing:

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 conventional motorcycle.
Figure. 2 shows block diagram according to the present invention.
Figure. 3 shows the flow chart for kickback detection and spark suppression according to the present invention.

Detail Description of the Drawings:

The present invention now will be described more fully hereinafter with different embodiments. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather those embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the invention to those skilled in the art.

The present invention is illustrated 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 (201) of the vehicle frame, a front wheel (103) attached to these front forks (102), a handle bar (104) connected to the front forks (102), a fuel tank (105) attached so as to straddle an upper part of the vehicle frame, a seat (106) attached to the upper rear portion of the vehicle frame, an engine unit (107) attached to the lower front section of the vehicle frame, a swing arm (108) attached to a lower rear section of the vehicle frame, suspended by a rear shock absorber (not shown) from the vehicle frame and a rear wheel attached to a rear end of swing arm (108). The intake system of the engine comprises of a fuel air metering device such as a carburettor (109), 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 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 (110) for covering an upper part of the front wheel (103), and a rear fender (111) for covering an upper part of the rear wheel (112). The drive from the engine (107) is transmitted from the engine to the driven wheel sprocket mounted on the rear wheel hub mounted on the rear wheel assembly.

According to the present invention and referring to Figure 2 and Figure 3, the engine speed is continuously calculated and monitored with the help of crank sensor (preferably a variable reluctance sensor). During, reversal of engine crankshaft (kick¬back condition), the same is sensed by monitoring the crank angle sensor signal. Depending upon the time delay between the leading & the trailing edge of the crank sensor signal and the calculations in the previous engine speed cycle, kick back condition is established and the subsequent spark is either suppressed or delayed by a time duration more than 10 times or more than the time of the current crank shaft rotation.

The engine speed is monitored with the help of crank sensor signal which is further fed to engine speed detection circuit block. The input from engine speed detection circuit goes to ignition timing determination circuit block. The said ignition timing determination circuit determines the ignition timing and accordingly feeds it to the ignition coil. The said ignition timing determination block also receives inputs from throttle position calculation block for determining the ignition timing in conjunction with the inputs from engine speed detection block.

The time delay between a leading and a trailing edge of crank signal is monitored and if the time delay is greater than a predetermined time t1, the system supresses the occurrence of next spark for a predetermined time t2. If the time delay is less than the predetermined time t1, it follows the loop of monitoring the time delay between the leading and trailing edge of crank signal till the delay is found greater than the predetermined time t1.

Kickback condition is determined when the delay between the leading and trailing edge is greater than equal to 20ms (which is the predetermined time t1). The supress of the occurrence of next spark is done for a time which is greater than equal to 250ms, this is what is referred above as a predetermined time t2.

Position of the crankshaft is calculated using a tooth in the magneto rotor & crank sensor on every raising & trailing edge of the pulse. During engine kick-back there will be a delay in the time duration between raising and trailing edge of the crank sensor pulse. By monitoring the delay, the information is received for the kick-back of the engine and the system described above is further used to delay the subsequent spark in the system.

When a condition for kickback is satisfied the occurrence of the next spark may be supressed or delayed and further the time for delay or supress is preferably for time duration more than 10 times the current crank shaft rotation.

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. An ignition timing control for 4 stroke engine comprising the method of: calculating the engine speed continuously; monitoring crank sensor signal for reversal of engine crankshaft; establishing kick back condition by judging the time delay between leading and trailing edge of the crank signal; and delaying the spark after the establishment of kick back condition.

2. An ignition timing control for 4 stroke engine comprising the method of: calculating the engine speed continuously; monitoring crank sensor signal for reversal of engine crankshaft; establishing kick back condition by judging the time delay between leading and trailing edge of the crank signal; and supressing the spark after the establishment of kick back condition.

3. The ignition timing control as claimed in claimed in claim 1 and claim 2, wherein the delay and supress of the spark is for time duration more than 10 times the current crank shaft rotation.

4. The ignition timing control as claimed in claimed in claim 1 and claim 2, wherein the delay and supress of the spark is for time duration more than the time of the current crank shaft rotation.

5. An ignition timing control for 4 stroke engine substantially as herein described and shown in the specification.