CLIAMS:I Claim:
1. A device to detect speed and position of an internal combustion engine, comprising:
a piston 100;
a crank shaft 102; and
a transmission mechanism 104 connects said crank shaft 102 and a cam shaft 106, characterized in that
a tone wheel 108 mounted on said cam shaft 106; and
a measuring element 110;
said tone wheel 108 having at least missing tooth, said missing tooth defines at least one position of said internal combustion engine.
2. The device of claim 1, wherein said measuring element 110 is a speed sensor.
3. The device of claim 1, wherein said measuring element 110 is mounted in proximity of said tone wheel 108.
4. The device of claim 1, wherein speed of said tone wheel indicates speed of said cam shaft 106.
5. An electronic control unit, comprising;
a receiving means to receive information on frequency of rotation of a

tone wheel 108 so as to determine speed of a cam shaft 106; and

a computing means to determine speed of an engine based on the drive
ratio of a transmission means connecting a crank shaft 102 and said cam shaft 106, said crank shaft 102 in mechanical connection with a piston 100 of said engine.
6. A method for detecting speed and position of an internal combustion engine, said method comprising:
Determining the frequency of rotation of tone wheel 108 as a function of rate of change of magnetic flux with respect to the missing tooth of said tone wheel 108;

Calculating speed of said cam shaft 106 based on said determined frequency; and

Calculating the speed of crank shaft 102 based on the drive ratio of a transmission means connecting a crank shaft 102 and said cam shaft 106. ,TagSPECI:FIELD OF THE INVENTION
[001] This invention relates to field of determining engine speed and position of piston position in an internal combustion engine.

BACKGROUND OF THE INVENTION
[002] Engine condition determination and sensing is of utmost importance for optimizing engine performance. In fuel injection engine systems, it is also important to know the position of each cylinder in order to properly time fuel injection. In conventional systems, the cam wheel and the crank wheel are provided with sensors to determine different aspects of engine condition like engine speed, engine position and direction. The use of different sensors that is one each in cam wheel and crank wheel leads to complexity as we need to get the data from two different sources separately.

[003] Hence there is a need to simplify the above mentioned process of determination of engine condition.

[004] Patent number US 5165271 discloses a single sensor apparatus and method for determining engine position and engine speed is disclosed. The apparatus includes a gear rotating in synchronism with the camshaft of an internal combustion engine. The gear includes a number of equiangular spaced teeth, and an additional tooth mechanically synchronized with top dead center position of a particular cylinder of the engine. An algorithm is disclosed for detecting the added tooth with a high reliability and accuracy. In addition, engine speed is determined by measuring the time interval required for a predetermined quantity of gear teeth to pass the sensor by detecting the pulses corresponding to the gear teeth. The resulting time interval is converted into engine speed through a known relationship between the number of teeth on the gear and their angular spacing.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
[005] The invention is disclosed in detail in the description and illustrated in the accompanying drawing:

[006] FIG. 1 illustrates a device to detect speed and position of an internal combustion engine; and

[007] FIG. 2 illustrates a method for detecting speed and position of an internal combustion engine.

DETAILED DESCRIPTION OF THE EMBODIMENTS
[008] FIG. 1 illustrates a device to detect speed and position of an internal combustion engine.The device comprises a piston 100 and a crank shaft 102. A transmission mechanism 104 connects the crank shaft 102 and a cam shaft 106. The device is characterized in having a tone wheel 108 that is mounted on the cam shaft 106 and a measuring element 110. In an embodiment the measuring element 110 is a speed sensor. The measuring element 110 is mounted in proximity to the tone wheel 108. The tone wheel 108 has at least one missing tooth. The missing tooth defines at least one position of the internal combustion engine.

[009] The relation between the missing tooth of the tone wheel 108 and top dead centre (TDC) of at least one piston of the engine will be fixed during mounting of the tone wheel 108 on cam shaft 106. During operation, when the missing tooth approaches the sensor, based on the frequency of the signals or rate of change of magnetic flux shaft speed will be calculated. Since drive ratio of the cam shaft 106 and crankshaft is already defined, the electronic control unit (ECU) software can calculate the speed of crank shaft 102 and hence the speed of the engine. The drive ration of the cam shaft 106 is 0.5 with respect to the crank shaft 102. That is for a single for a single rotation of crank shaft 102 the cam shaft 106 would have rotated by half the amount. That is speed of the crank shaft 102 is twice the speed of the cam shaft 106. Also, since the missing tooth of the tone wheel 108 and the position of the TDC are known during the mounting arrangement, the ECU can also determine the position of the piston 100 during a given stroke. The ECU comprises a receiving means to receive information on frequency of rotation of a tone wheel 108 so as to determine speed of a cam shaft 106, and a computing means to determine the speed of an engine based on the drive ratio of a transmission means connecting the crank shaft 102 and the cam shaft 106, where the crank shaft 102 is in mechanical connection with the piston 100 of the engine.

[0010] FIG. 2 illustrates a method for detecting speed and position of an internal combustion engine. The frequency of rotation of tone wheel 108 is determined 201 as a function of the rate of change of magnetic flux with respect to the missing tooth of the tone wheel 108. The speed of the cam shaft 106 is calculated 202 based on the determined frequency. The speed of the crank shaft 102 is calculated 203 based on the drive ratio of a transmission means connecting a crank shaft 102 and the cam shaft 106.

[0011] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.