CLIAMS:I claim:
1. A method of determining speed of an internal combustion engine, comprising:
receiving signals from a engine speed sensor assembly associated with a crank wheel of the internal combustion engine;
recording in an electronic control unit said received engine speed sensor information; and
determining average speed of the internal combustion engine based on the recorded samples of signals, said average speed is determined on completion of every 720 degrees of rotation of the crank wheel.

2. The method as claimed in claim 1, wherein said internal combustion engine is a two cylinder engine.

3. The method as claimed in claim 2, wherein said two cylinder engine is an unequal firing two cylinder engine.

4. The method as claimed in claim 1, wherein said determination of speed is average speed of said internal combustion engine.

5. The method as claimed in claim 4, wherein determination of average speed is done over one repetitive cycle of the operation of the internal combustion engine.

6. A device (20) to determine speed of an internal combustion engine, said device comprising:
- an engine speed sensor (22) located in proximity of a crank wheel (24);
- an electronic control unit (26) adapted to determine speed of said internal combustion engine on completion of every 720 degrees of rotation of said crank wheel (24).
,TagSPECI:FIELD OF THE INVENTION
[001] The present invention relates to the field of control of internal combustion engine. More specifically, the field of a method of determining speed of the internal combustion engine.

BACKGROUND OF THE INVENTION
[002] Determining speed of the internal combustion engine is of primary importance for it has direct impact on calculating different control parameters of the engine. For example, the determined speed is one of the factors taken into consideration while calculating fuel demand in the engine. Hence, inaccuracy in the speed may lead to in faulty fuel demand calculations and consequently, in fuel inefficiency.
[003] Further, conventional methods of determining speed of the internal combustion engine may not be applicable for all types of internal combustion engines. More particularly, the conventional methods may not be in adherence for use to ‘unequal distant firing’ type internal combustion engines where the firing sequence between successive engine cylinders is separated by time intervals that are not equal.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[004] Figure 1 illustrates a flow chart representing a method of determining speed of an internal combustion engine in accordance with an embodiment of the present invention; and
[005] Figure 2 illustrates a device to determine speed of an internal combustion engine in accordance with this disclosure.

DETAILED DESCRIPTION
[006] Figure 1 illustrates a flow chart representing a method of determining speed of an internal combustion engine 10 in accordance with an embodiment of the present invention. The method comprises the following steps: receiving signals from a engine speed sensor assembly associated with a crank wheel of the internal combustion engine represented as step 12 in the flow chart; recording in an electronic control unit said received engine speed sensor information represented as step 14 in the flow chart; and determining average speed of the internal combustion engine based on the recorded samples of signals represented as step 16 in the flow chart. The average speed is determined on completion of every 720 degrees of rotation of the crank wheel.
[007] In multi cylinder engine, average engine speed is calculated by averaging all instantaneous speed between two successive TDCs i.e. speed is average engine speed between 120ºCrank in 6 Cylinder, 180ºCrank in 4 Cylinder and 360ºCrank in 2 Cylinder Equal firing TDCs. In accordance with the method of this disclosure we will focus on two cylinder internal combustion engines. In particular the focus will be on two cylinder engines with un-equal firing TDC’s.
[008] In case of a two cylinder engine with un-equal firing the power generated in two successive TDC’s if different. The difference in power generated at the two TDC’s causes a continuously varying engine speed. This continuously varying engine speed leads to further difficulties in controlling engine parameters. Hence calculating average engine speed at two successive TDC’s will give engine speed variations. Thus in case of a two cylinder engine with un-equal firing the average engine speed is calculated over one repetitive cycle of the operation of the internal combustion engine. One repetitive cycle of the operation of the internal combustion engine is the 720 degrees rotation of the crank wheel mounted on the crank shaft.
[009] The determination of the speed of the internal combustion engine is done using a device 20 which is represented in figure 2. The device comprises: an engine speed sensor 22 located in proximity of a crank wheel 24. The device 20 also comprises an electronic control unit 26 adapted to determine speed of the internal combustion engine on completion of every 720 degrees of rotation of said crank wheel 24.
[0010] The working of the device 20 for determining the average speed of the internal combustion engine can be explained as follows. As mentioned earlier the determination of average speed is done for a two cylinder internal combustion engine with un-equal firing TDC’s. The engine speed sensor 22 which is located in proximity of the crank wheel 24 continuously generates an engine speed signal which is sent to the electronic control unit 26 of the device 20. The electronic control unit 26 records the continuously generated engine speed signal. The engine speed signal is a pulse train which is able to indicate each time the piston in the two cylinders reached TDC. The TDC is recognized using the missing tooth on the crank wheel 24. For calculation of the average engine speed of the two cylinder internal combustion engine, the electronic control unit 26 identifies 720 degrees rotation of the crank wheel 24 by identifying two successive missing tooth. When the two successive missing tooth signal are detected the electronic control unit calculates the average speed based on the engine speed signal received from the engine speed sensor.
[0011] It must be understood that description provided above is only illustrative and does not limit the scope of the invention in terms of the engine speed sensor being used or the components of the electronic control unit used to calculate the average speed of the internal combustion engine with un-equal firing TDC’s. Various embodiments of the engine speed sensor and the components used in the electronic control unit are envisaged and lie within the scope of this disclosure. The scope of this disclosure is only limited by the scope of the claims.