TECHNICAL FIELD

[0001] The present subject matter relates generally to an internal combustion engine, and more particularly, to an ignition system for a single cylinder internal combustion engine.

BACKGROUND

[0002] Generally, in vehicles having an internal combustion (IC) engine, an ' ignition system plays a vital role. Combustion of air-fuel mixture in the IC engine, especially in IC engines using petrol/gasoline as fuel, is performed by the ignition system. The ignition system comprises of a spark plug for generation of spark. Generally, a four-stroke IC engine comprises of an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. During the compression stroke, "the "air-fuel "mixture is compressed in a combustion chamber/cylinder. A spark is generated by the ignition system, for combustion of the compressed air-fuel mixture. The combustion of air-fuel mixture results in a power , stroke. The power stroke generates power and torque. Effective functioning of the ignition system is essential for generation of power and torque.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The detailed description of an ignition system of the present subject matter is described with reference to the accompanying figures. Same numbers are used throughout the drawings to reference like features and components.

[0004] Fig. 1 illustrates a side view of an exemplary engine, in accordance with an embodiment of the present subject matter.

[0005] Fig. 2 illustrates a schematic diagram of an ignition system, in accordance with an embodiment of the present subject matter.

[00.06] Fig. 3 illustrates a flow chart depicting the method of functioning of the ignition system, in accordance with an embodiment of the- present subject matter.

[0007] Fig. 4 (a) illustrates a graph depicting a variation of rate of change of rotations per minute (RPM) with angle theta against time, in accordance with an embodiment of the present subject matter.

[0008] Fig. 4 (b) illustrates the graph depicted in Fig. 4 (a) on an enlarged scale.

[0009] Fig. 5 illustrates a graph depicting the charging and discharging status of an ignition coil against time, in accordance with an embodiment of the present subject matter.

DETAILED DESCRIPTION

[00010] Typically, in an internal combustion (IC) engine, air fuel mixture is combusted in a combustion chamber/cylinder of the IC engine. An ignition system of the engine generates a spark, enabling the combustion of the air-fuel mixture. The ignition system comprises of a power source such as a battery or an alternator, an ignition coil and a spark plug. The spark is triggered depending on the output of the cam position sensor. Generally, in vehicles without a cam position sensor, a crankshaft position sensor is used. In an IC engine with four strokes, a spark should be triggered during the compression stroke when a piston travels to a top dead centre (TDC) of the cylinder. The combustion of the air-fuel mixture results in power stroke thereby pushing a piston downwards resulting in linear motion of the piston. Generally, a flywheel is connected to the crankshaft for providing the necessary momentum for driving the piston upwards, during the compression stroke. The crankshaft position sensor helps in triggering the spark when the flywheel rotates to a particular angle. The crankshaft is connected to the piston through a connecting rod. During the four strokes, the piston reaches the TDC twice, once during the compression stroke and once during an exhaust stroke. The flywheel connected to the crankshaft completes two complete rotations during the four strokes. Using a crankshaft position sensor will result in triggering of spark once every rotation. Thus for a four stroke IC engine, the spark is triggered twice during the four stroke cycle. However, the spark triggered during the exhaust stroke is a redundant spark. Therefore, lack of spark triggering mechanism to identify the four-stroke cycle results in -triggering the spark twice during the four strokes.

[00011] Further, the output voltage from the power source is stepped-up for generation of spark at a gap provided between two or more ground electrodes of the spark plug. Moreover, as the number of operating cycle increases, the spark plug will wear out faster. Also, due to the triggering of the spark twice during the four-stroke cycle, the lifetime of the spark plug is reduced by 50 percent. Furthermore, the coil used, requires high speed charging coils due to need for triggering in every rotation. A weak spark will lead to improper combustion of the air-fuel mixture thereby carbon deposition occurs on the spark plug. Improper combustion of air-fuel mixture also leads to damage of ceramic insulation on the spark plug. Any damage to the spark plug effects the functioning of the ignition system. Further, failure of the ignition system results in poor engine starting and damages of the engine. Further, the fuel efficiency of the vehicle is reduced due to improper combustion.

[00012] Hence, an objective of the present subject matter is to provide an ignition system and a method thereof, for a single cylinder four-stroke IC engine. Further, The ignition method identifies the four-stroke cycle when the engine is cranked, thereby enables triggering of the spark in a required stroke of the engine. The ignition system of the present subject matter eliminates the redundant spark thereby improving the lifetime of the spark plug.

[00013] In an embodiment, the proposed method comprises the step of identifying IC engine dynamic parameters, including rotations per minute (RPM) of the crankshaft, angular position of the crankshaft, rate of change of RPM and rate of change of RPM with respect to angle theta is calculated. The ignition system identifies the rate of change of RPM with respect to angle theta of the crankshaft, thereby identifying the power stroke. The identified power stroke enables identification of the four-stroke cycle. The spark is triggered accordingly during the compression stroke.

[00014] In an embodiment, the proposed ignition method comprises the steps of determining a four-stroke cycle thereby enabling the triggering of the spark during the compression stroke, which is performed only during one rotation out of two rotations of the rotor to complete said four-stroke cycle. Firstly, a first rate of change of RPM with respect to angle theta is calculated in a first rotation of the rotor. Further, a second rate of change of RPM with respect to angle theta is calculated during a second rotation of the rotor. Further, when the second rate of change of RPM with respect to angle theta is identified to be greater than the first rate of change of RPM with respect to angle theta, then the second stroke is identified as power stroke or otherwise.

[00015] In the engine, the reciprocating motion of a piston puts a crankshaft coupled to the piston in rotational motion. One or more profile ignition pick-ups (PIPs) are included on a rotor, for example a magneto or a flywheel, which is connected to the crankshaft. When the IC engine is cranked, the rate of change of RPM with respect to angle theta during every rotation is calculated by an engine control unit. The rotation in which the value is observed to be substantially higher than that a previous rotation, the later stroke is identified as rotation including the power stroke. The power stroke identification enables the identification of the four-stroke cycle. The engine control unit triggers the spark plug for generation of spark in the compression stroke through the identified rotation. [00016] The ignition system of the present subject matter, in accordance with an embodiment, enables use of coils with low charging time, which reduces cost of the coil. Improved time of charging the coil enables better spark generation. Further, the space near the cylinder head is compact, where a camshaft is located. The proposed ignition system eliminates installation of a cam sensor. The ignition system is reliable as the life of spark plug is improved. Better spark generation improves the combustion of air-fuel mixture. The better combustion of air-fuel mixture further improves the fuel efficiency of the system. A flywheel or a rotor installed on the engine itself is used for identifying the crankshaft position. [00017] In a preferred embodiment, the engine control unit initially enables triggering of said spark plug for every rotation of the rotor. Typically, the rotor completes two rotations during the four-stroke cycle that includes a first stroke and a second stroke. Further, the engine control unit calculates a first rate of change of rotations per minute of said rotor during the first rotation thereof, and a second rate of change of rotations per minute during the second rotation. The power stroke may be present in either the first rotation or the second rotation. Comparing said first rate of change of rotations per minute with said second rate of change of rotations per minute for selecting a rotation having a higher rate of change of rotations per minute. The engine control unit subsequently triggers said spark plug only during the rotation other than the selected rotation. The engine control unit henceforth triggers said spark plug only during the rotation(s) other than the selected rotation. The engine control unit; identifies a power stroke of said four-stroke cycle to be in' said selected rotation, said selected rotation includes an exhaust stroke.

[00018] The aforesaid and other advantages of the present subject matter would be described in greater detail in conjunction with the figures in the following description.

[00019] Fig. 1 illustrates a side view of a single cylinder four-stroke internal combustion engine 100 as an example, in accordance with aiuembodiment of .the present subject matter. The engine 100 comprises of a cylinder body 110. A cylinder head 120 is mounted on the cylinder body 110. The cylinder head 120 and cylinder body 110 form a cylindrical combustion chamber, internally. A cylinder head cover 130 is mounted on the cylinder head. 120. An intake port 140 and an exhaust port 150 are positioned on the opposite sides of the cylinder head 120. A spark plug 160 is mounted to the cylinder head 120. A rotor 170 is connected to a crankshaft 180. The crankshaft 180. is connected to one end of a connecting rod (not shown) and other end of the connecting rod is connected to a piston (not shown). Air-fuel mixture is directed into the combustion chamber through the inlet port 140. The air-fuel mixture is compressed in the combustion chamber and a spark is generated by the spark plug 160 enabling combustion of the compressed air-fuel mixture. The combustion of air-fuel mixture results in reciprocating motion of the piston thereby creating a rotational motion of the crankshaft 180.
[00020] Fig. 2 illustrates a schematic view of an ignition system 200, in accordance with an embodiment of the present subject matter. The ignition system 200 comprises of an engine control unit 210, which receives a pulse data from a crankshaft position sensor 220. The pulse data may be a pulse count that is generated by the crankshaft position sensor 220. A magnetic field/variable reluctance sensor or a hall effect sensor is example of the crankshaft position sensor 220. A high-tension (HT) coil 240 is used to step-up voltage generated by a driving element 260. The driving element 260 drives the HT coil 240. A rotor 170. comprises of plurality of PEPs 230A, which are angularly disposed from each other, on a circular circumferential surface of the rotor 170. In the current embodiment 23 PIPs 230A and an empty PIP location, which is a reference point 230B is provided in total 24 PIP locations are provided. Each PIP 230A is separated by 15° angle. The PIPs 230A on either sides of*the empty PIP location 230B are separated by 30°. The reference point 230B acts as a reference point for the engine control unit 210 to identify the position of the piston. The plurality of PEPs 230A and the at least one reference point 230B together act as position detection elements 230A, 230B. Time taken by the rotor 170 to complete 15° of rotation is t$, where the angle 0 is 15°. The engine control unit 210 detects the reference point 230B when the time to detect two adjacent PIPs 230A is almost double the time taken to detect two previous adjacent PIPs 230A. For the piston to reach TDC, the rotor 170 should rotate a pre-defined angle from a reference point. For example, with respect to the crankshaft position sensor 220, the angle of rotation of rotor 170 required from the reference point 230B for the piston to reach TDC, is pre-defined.

[00021] Initially, when the engine 100 is cranked, the engine control unit 210 triggers the spark for every rotation of the rotor 170, which is during the compression stroke and the exhaust stroke. The pulse count is generated by the . crankshaft position sensor 220. Plurality of PIPs 230A, which are positioned on the rotor 170, are detected by the crankshaft position sensor 220. The crankshaft position sensor 220 is positioned in close proximity to the rotor 170. Every PIP 230A detected by the crankshaft position sensor 220, during the rotation of the rotor 170, will result in the generation of pulse. A raising edge of the pulse indicates PIP 230A detection. The plurality of PIPs 230A are positioned such that each PIP 230A is equidistant from the adjacent PIP 230A by an angle theta. The reference point 230B acts as a reference point on the rotor 170. The angle of rotation required by the rotor 170 for a piston to reach the TDC is pre-defined. Upon detecting the reference point/empty PEP location 230B, the engine control unit 210 calculates the time after which the spark plug 160 should be triggered.

[00022] The engine control unit 210 measures the RPM, and rate of change of RPM dRPM/d9 values for every rotation of the rotor 170. A first rate of change of RPM dRPMl/d9 value during a first rotation is calculated from during a point when the piston is at TDC and till an angle of rotation of alpha a of the rotor 170. In a successive rotation, a second rate of change of RPM dRPM2/d9 is calculated from a point when the piston is at TDC and till an angle of rotation of alpha a of the rotor 170. The engine control unit 210 initially enables triggering of the spark for every rotation till .the.four-stroke .cycle is identified. The engine control unit 210 selects a rotation by the identified higher rate of change of RPM between said first rate of change of RPM dRPMl/dO compared with the second rate of change of RPM dRPM2/d9 value, then the selected rotation includes is identified to included the power stroke. The engine control unit 210 synchronizes the triggering of the spark according to the identified four-stroke cycle and triggers the spark plug 120 at specific angle of rotor 170, only during the rotation other then the selected rotation, with reference to the reference pulse position 230B.

[00023] In another embodiment, the rate of change of RPM dRPM/d9 value is calculated by first measuring a rate of change of time di^/dQ taken for the rotor 170 to rotate an angle theta 9. As the PIPs 230A are separated by 15°, the time taken for the crankshaft position sensor 220 to sense two successive PIPs 230A is considered. The measured rate of change of time dte/d9 value is inversely proportional to rate of change of RPM dRPM/d9 value. When the time taken to detect two adjacent PIPs 230A decreases, it signifies an increase in the RPM value. In the preferred embodiment, the detected four-stroke cycle is preferably confirmed during.next two rotations of the rotor 170.

[00024] jn yet another embodiment, difference between the first rate of change of RPM dRPMl/d9 value and a second rate of change of RPM dRPM2/d9 value is calculated. If calculated difference is substantially high then the rotation with the higher rate of change of RPM dRPM/d9 value is high is identified to include the power stroke. Once the power stroke is identified by the engine control unit 210, the four-stroke cycle is also identified.

[00025] Fig. 3 illustrates a flow chart 300 depicting the steps of the proposed method of functioning of ignition system, in accordance with an embodiment. At step 305, a user tries to crank an engine 100. At step 310, the engine control unit 210 checks status of an ignition switch, if the ignition is ON, then the engine control unit 210 checks the crank status. The user can crank the vehicle using a kick-start mechanism or-eiectric start mechanism. At step 310, if the ignition is in OFF state then the engine control unit 210 waits for an ignition ON. When user tries to crank the engine, at step 315, the engine control unit 210 calculates the engine 100 RPM and the pulse count. At step 320, the engine control unit 2i0 checks for pulse synchronization. In the pulse synchronization step, the engine control unit 210 identifies the position of the empty PIP location 230B.At step 325, the engine control unit 210 calculates rate of change of RPMs dRPM/d0 for every rotation of the rotor 170. At step 330, the engine control unit 210 calculates a first rate of change of dRPMl/d8 value of the rotor 170 from the pulse data received from the crankshaft position sensor 220. The rotation of the rotor 170 from a reference point, when the piston is at TDC position, till an angle alpha a of rotation of the rotor 170 is considered. The angle alpha a can be in the range of 30°-60°as the effect of ignition is reflected within this range. The angle alpha a is selected such that the increase in rate of change of RPM dRPM/d9 resulting in power stroke is reflected. At step 335, in the successive rotation, a second rate of change of RPM dRPM2/d0 value is calculated during the alpha a angle of rotation of the rotor 170.The difference between the calculated first rate of change of RPM dRPMl/d0 and the calculated second rate of change of RPM dRPM2/d9 is observed, and if there is substantial difference then the stroke with .

higher rate of change of RPM dRPM/d0 is identified as rotation involving the power stroke. In this particular embodiment, at step 340, if there is a substantial increase in the calculated second rate of change of dRPM2/d0 value, then the respective rotation involves is identified to have the power stroke at step 345A, 345B. Further, the four-stroke cycle is identified at step 350. In an embodiment, a reference value may be provided in the engine control unit for comparing the difference between the first rate of change of RPM and second rate of change of RPM. Therefore, the engine control unit compares with the reference value and identifies the stroke, when the rate of change is higher than the reference value provided.

[00026] Fig. 4 (a) illustrates a graph depicting a variation of rate of change of .change of REM ...with respect ,ta.angle theta against time, in accordance with an embodiment of the present subject matter. Fig. 4 (b) illustrates the graph depicted in Fig. 4 (a) on an enlarged scale. In the graph 400A, the variation of rate of the change of RPM dRPM/d9 value from a point 410, when engine 100 is cranked, to another point 440, when the engine reaches idling state, is depicted. During the cranking of the engine 100, the engine control unit 210 enables triggering of spark for every rotation of the crankshaft or the rotor 170. In the rotation involving power stroke, triggering of the spark will result in combustion of air-fuel mixture. Positive spikes 420A, 420B, 420C indicate an increase in rate of change of RPM dRPM/dG value as calculated by the engine control unit 210. The spikes 420A, 420B, 420C indicate that the corresponding stroke is power stroke. At points 430A, 430B, 430C, there is no significant change in rate of change of RPM dRPM/d0 value for the corresponding stroke during the rotation. The engine control unit 210 compares rate of change of RPM dRPM/d8 for every successive rotation and identifies a rotation involving the power stroke, where there is a positive spike. Identification of power stroke enables identification of four-stroke cycle 470, which is also referred to as Otto cycle, and the spark is triggering after a pre-defined time or a pre-determined angle from the reference point 230B of the rotor 170. In the graph 400B, the four-stroke cycle 470 is depicted. The four-stroke cycle 470 forms between three consecutive points A, B, C, where between the first point A, and second point B the compression stroke and power stroke occur and between second point B, and third point C the exhaust stroke and suction stroke occur.

[00027]. The engine control unit 210 synchronizes the spark triggering with the identified four-stroke cycle 470. Once the engine 100 starts and reaches an idle state, the positive spike is not visible, after the point 440, because of the ■momentum obtained in the idle state. During the cranking state 450, the engine control unit 210, receives data from the crankshaft positional sensor 220 and calculates rate of change of RPM dRPM/d9 value corresponding to a rotation. During the idling state 460, the positive spike is absent. However, the engine control unit 210 enables triggering of spark during the identified rotation involving power stroke.

[00028] Fig. 5 illustrates a graph 500 depicting the charging and discharging of coil with time, in accordance with an embodiment of the present subject matter. The graph 500 depicts the triggering of spark plug during four-stroke cycle. Pulses 510A, 510B, which are triggered during an exhaust stroke, which are necessary sparks. Pulses 520A, 520B are waste sparks, which are triggered during the exhaust stroke. The ignition system 200, identifies the four-stroke cycle and enables triggering of the spark in synchronization with the identified four-stroke cycle, thereby eliminating waste spark triggering as depicted in successive modified pulse cycles 530. Further, waste spark triggering is eliminated thereby improving the.ignition system and thereby improving the lifetime of spark plug.

[00029] Many modifications and variations of the present subject matter are possible in the light of above disclosure. Therefore, within the scope of claims of the present subject matter, the present disclosure may be practiced other than as specifically described.

I/We claim:

1. An ignition system (200) for an internal combustion engine (100) having a four-stroke cycle, said ignition system (200) comprising: a rotor (170) comprising one or more position detection element(s) (230A, 230B) is mounted to a crankshaft (180) of said internal combustion engine (100) and performs .two rotations including a first rotation and a second rotation to complete said four-stroke cycle;

an engine control unit (210) functionally coupled to a position sensor (220), said position sensor (220) adapted to function with said position detection element(s) (230A, 230B) to enable detection of angle (0) of rotation of said rotor (170); and a spark plug (160) capable of providing a spark upon triggering by said engine control unit (210),wherein said engine control unit (210) initially enables triggering of said spark plug (160) for every rotation of said two rotations of said rotor (170), and calculates a first rate of change of rotations per minute (dRPMl/d8) of said rotor (170) during the first rotation thereof, and a second rate of change of rotations per minute (dRPM2/d0) during the second rotation, and compares said first rate of change of rotations per minute (dRPMl/dO) with said second rate of change of rotations per minute (dRPM2/d9) for selecting a rotation having a higher rate of change of rotations per minute between said first rate of change of rotations per minute (dRPMl/d9) and said second rate of change of rotations per minute (dRPM2/d9), and wherein said engine control unit (210) subsequently triggers said spark plug (160) only during the rotation other than the selected rotation.

2. The system (200) of claim 1, wherein the engine control unit (210) henceforth triggers said spark plug (160) during the rotation other than the selected rotation.

3. The system (200) of claim 1, wherein the engine control unit (210) identifies a power stroke of said four-stroke cycle to be in said selected rotation, said selected rotation includes an exhaust stroke.

4. The system (200) of claim 1, wherein said position detection element(s) , (230A, 230B) includes plurality of PIPs (230A) and at least one reference point(s) (230B) includes at least one empty PIP (230A).

5. The system of claim 1 or 4, wherein said position detection element(s) (230A, 230B) are angularly disposed about the rotor with an angular distance of said angle (9).

6. The system (200) of claim 1 or 4, wherein said engine control unit (210) detects angular rotation of said rotor (170) through said position sensor (220) by identifying said position detection elements (230A, 230B) that enable identification of position that is functionally coupled to said rotor (170), whereby the spark plug (160) can be triggered with reference to angular position of said rotor (170).

7. The system (200) of claim 1 or 5, wherein the engine control unit (210) triggers the spark plug (160) after a pre-determined angle of rotation of rotation of said rotor (170) from said at least one reference point(s) (230B).

8. A method for triggering a spark plug (160) of an ignition system (200) for an internal combustion engine (100) having a four stroke cycle, said engine (100) provided with a rotor* (170X'comprisih*g a'plurality of position detection elements (230A, 230B) coupled to a crankshaft (180) of said engine (100), said rotor (170) performs two rotations including a first rotation and a second rotation to complete said four stroke cycle, said method comprising the steps of:

triggering of said spark plug (160) for every rotation of said two rotations of said rotor (170) by an engine control unit (210), calculating a first rate of change of rotations per minute (dRPMl/d0) of said rotor (170) during the first rotation thereof, and a second rate of change of rotations per minute (dRPM2/d0) during the second rotation, and comparing said first rate of change of rotations per minute (dRPMl/d9) with said second rate of change of rotations per minute (dRPM2/dG) for selecting a rotation having a higher rate of change of rotations per minute between said first rate of change of rotations per minute (dRPMl/d0) and said second rate of change, of rotations per minute (dRPM2/d9), and wherein subsequently triggering said spark plug (160) only during the rotation other than the selected rotation by said engine control unit (210).

9. The method of claim 8 further comprises triggering said spark plug (160) after pre-determined angle of rotation said rotor (170).

10. The method of claim 8 or 9, wherein calculating said rate of change of rotations per minute (dRPM/d9) is measured during a pre-set angle (a) of rotation of said rotor (170) from "a point when the piston reaches a top dead centre, said pre-set angle (a) is in range of 30-60 degrees.