CLIAMS:We claim,

1. A method for synchronizing an internal combustion engine, comprising a cylinder, said method comprising:

calculating an engine speed gradient before an occurrence of a top dead center (TDC) position for the cylinder;

identifying a compression stroke based on the calculated engine speed gradient; and

calculating an energizing time and injecting fuel into the four stroke engine before an occurrence of the TDC position following the identified compression stroke.

2. The method as claimed in claim 1, wherein calculating the engine speed gradient based on an engine speed from a first crankshaft position to a second crankshaft position before the occurrence of the TDC position in the compression stroke.

3. The method as claimed in claim 1, wherein calculating the engine speed gradient between a bottom dead center (BDC) position and the occurrence of a next TDC position in the compression stroke.

4. The method as claimed in claim 1, wherein identifying the occurrence of the compression stroke when the calculated engine speed gradient is greater than a threshold.

5. An electronic control unit (ECU) for synchronizing an internal combustion engine, said ECU adapted to

calculate an engine speed gradient before an occurrence of a top dead center (TDC) position for the cylinder;

identify a compression stroke based on the calculated engine speed gradient; and

calculate an energizing time and injecting fuel into the four stroke engine before an occurrence of the TDC position of the identified compression stroke.
,TagSPECI:Field of the invention

[0001] The invention relates to a method for synchronizing a four stroke internal combustion engine.

Background of the invention

[0002] In an internal combustion engine, various techniques are used for sensing position of crankshaft which is required for proper timing of fuel injection into the engine. In a four stroke engine, the piston completes four separate strokes to constitute a single engine cycle. A camshaft performs one revolution for every two revolutions of the crankshaft. The state or the stroke of the engine cycle is determined, for example, by detecting a rotational position of the camshaft. The state of the engine cycle is determined by using a camshaft sensor and a crankshaft sensor. The crankshaft sensor provides an angular position of the crankshaft. Since the engine turns two revolutions, the engine reaches top dead center (TDC) twice in each engine cycle. In the four stroke engine, a crank signal from the crankshaft sensor cannot differentiate between the intake stroke and the power stroke. Similarly the crankshaft sensor cannot differentiate between the compression stroke and the exhaust stroke. The result obtained by the crankshaft sensor regarding the stoke of the engine cycle is thus ambiguous. A camshaft sensor is relatively expensive and also has to be timed in to provide accurate results. Using two sensors, that is, a camshaft sensor and a crankshaft sensor increases the cost and also consumes more space reducing system consistence.

[0003] Using a virtual cam sensor, the compression stroke is identified at the TDC following the compression stroke. That is, the compression stroke is identified at the end of the compression stroke as the engine speed gradient used to identify the compression stroke is calculated at the TDC following the compression stroke. Hence, synchronization of the internal combustion engine is established at the TDC following the compression stroke and the fuel can be released into the engine only during the next compression stroke. Hence, a method with more flexibility to detect a compression stroke followed by the synchronization and fuel injection during the detected compression stroke is required.

[0004] The patent US 5562082, discloses an internal combustion engine having a crankshaft sensor with an uneven tooth spacing to identify an index tooth corresponding in position to top dead center (TDC) of a cylinder. A microprocessor based engine controller determines each TDC event from the sensor pulses. During cranking, the cylinder’s compression stroke is detected from engine speed variations by measuring time periods over sample ranges before and after TDC. When a compression stroke occurs just before TDC, the period before TDC is greater than the period after TDC, whereas other TDC events are evidenced by the period before TDC being smaller than or equal to the period after TDC.

Short description of the drawing

[0005] An exemplifying embodiment of the invention is explained in principle below with reference to the drawing. The drawing is,

[0006] Figure 1 illustrates the method of using an electronic control unit (ECU) for synchronizing a four stroke internal combustion engine in accordance with this invention.

Description of the invention

[0007] Figure 1 illustrates the method of using an electronic control unit (ECU) for synchronizing a four stroke internal combustion engine in accordance with this invention. In step S1, the ECU is adapted to calculate an engine speed gradient before an occurrence of a top dead center (TDC) position for the cylinder. In step S2, the ECU identifies a compression stroke based on the calculated engine speed gradient. In step S3, the ECU calculates an energizing time and injects fuel into the four stroke engine before an occurrence of the TDC position of the identified compression stroke.

[0008] For an internal combustion engine comprising a cylinder, proper timing of fuel injection for the cylinder depends upon the crankshaft position. The ECU receives the crankshaft position from a crankshaft position sensor. The ECU receives the location of the crankshaft in a 360° revolution. The crankshaft position sensor also provides a plurality of pulses based on a crankshaft position for the cylinder. The TDC position for the cylinder occurs at the transition of the compression stroke to the power stroke and of the exhaust stroke to the intake stroke. The crankshaft position sensor provides a TDC pulse for each occurrence of a TDC position for the cylinder. The ECU receives the TDC pulse from the crankshaft position sensor. Since the engine turns two revolutions, the engine reaches TDC twice in each engine cycle. Thus, it is necessary to distinguish which occurrence of TDC follows the compression stroke and which occurrence follows the exhaust stroke. But the TDC pulse does not distinguish between the TDC following the compression stroke from that following the exhaust stroke.

[0009] To identify the TDC following the compression stroke from that following the exhaust stroke, the ECU calculates an engine speed gradient before an occurrence of the TDC position for the cylinder. The ECU calculates the engine speed gradient based on an engine speed from a first crankshaft position to a second crankshaft position before the occurrence of the TDC position. The ECU calculates the engine speed gradient between a bottom dead center (BDC) position and the occurrence of a next TDC position. The ECU records the engine speed at the first crankshaft position. The ECU calculates the engine speed gradient which is the change in the engine speed from the first crankshaft position to the second crankshaft position. The ratio of the engine speed at the first crankshaft position to the value of the engine speed at the second crankshaft position gives the engine speed gradient. The ECU identifies the stroke as the compression stroke when the engine speed gradient crosses a threshold. The value of the threshold is pre-calibrated to distinguish between the compression stroke and the exhaust stroke. In an embodiment, the ECU identifies the stroke as the compression stroke when the engine speed gradient is greater than unity.

[00010] For example, the ECU identifies the compression stroke 30° before the TDC. The ECU calculates the energizing time in the same compression stroke and releases the fuel in the same compression stroke. The fuel is injected in the identified compression stroke before the occurrence of the TDC

[00011] By calculating the energizing time and releasing the fuel in the same compression stroke, the overall starting time of the internal combustion engine is considerably reduced since the time taken for two revolutions of the crankshaft is eliminated. The synchronization of the internal combustion engine is realized without cam sensor. This results in achieving a low cost effective method of synchronization of the internal combustion engine by calculating the energizing time and releasing fuel in the same compression stroke.

[00012] When the ECU detects that the value of the engine speed gradient is lesser than the threshold, the ECU identifies that the stoke is an exhaust stroke. The ECU calculates the energizing time and fuel is injected in the subsequent compression stroke.

[00013] It must be understood that the embodiments explained in the above detailed description is only illustrative and does not limit the scope of this invention. The scope of this invention is limited only by the scope of the claims. Many modification and changes in the embodiments aforementioned are envisaged and are within the scope of this invention.