CLIAMS:I claim:
1. A method for synchronizing an internal combustion engine comprising two cylinders, said method comprising:
calculating an engine speed gradient before an occurrence of a top dead center (TDC) position for a first cylinder during a first rotation and a second cylinder during a second rotation of a crankshaft;
detecting a compression stroke during each rotation of the crankshaft based on said calculated engine speed gradient;
identifying a rail pressure peak during one of the first rotation or the second rotation of the crankshaft; and
distinguishing between the two cylinders based on the occurrence of the rail pressure peak and the detected compression stroke during each rotation of the crankshaft.
2. The method as claimed in claim 1, wherein the rail pressure peak is associated with one of the two cylinders.
3. The method as claimed in claim 1, wherein the first rotation and the second rotation of the crankshaft are consecutive rotations of the crankshaft.
4. The method as claimed in claim 1, wherein detecting the rail pressure peak using at least one rail pressure sensor.
5. 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.
6. 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.
7. 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.
8. 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 a first cylinder during a first rotation and a second cylinder during a second rotation of a crankshaft;
detect a compression stroke during each rotation of the crankshaft based on said calculated engine speed gradient;
identify a rail pressure peak during one of the first rotation or the second rotation of the crankshaft; and
distinguish between the two cylinders based on the occurrence of the rail pressure peak and the detected compression stroke during each rotation of the crankshaft. ,TagSPECI:Field of the invention
[0001] The invention relates to a method for synchronizing an 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 rotation for every two rotations 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. The piston reaches top dead center (TDC) twice in each engine cycle. In the four stroke engine, a 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. If engine has two cylinders, then both cylinders could be in different strokes. Hence, is not possible to detect the compression stroke corresponding to the cylinders. 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. Hence, a method with more flexibility to detect a compression stroke for a two cylinder engine followed by the synchronization and fuel injection during the detected compression stroke is required.
[0003] 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
[0004] An exemplifying embodiment of the invention is explained in principle below with reference to the drawing. The drawing is,
[0005] 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
[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. In step S1, the ECU calculates an engine speed gradient before an occurrence of a top dead center (TDC) position for a first cylinder during a first rotation and for a second cylinder during a second rotation of a crankshaft. In step S2, the ECU detects a compression stroke during each rotation of the crankshaft based on the calculated engine speed gradient. In step S3, the ECU identifies a rail pressure peak during one of the first rotation or the second rotation of the crankshaft. In step S4, the ECU distinguishes between the two cylinders based on the identified rail pressure peak and the detected compression stroke during each rotation of the crankshaft.
[0007] For an internal combustion engine comprising two cylinders, proper timing of fuel injection for the cylinder depends upon the crankshaft position of each of the two cylinders. The ECU receives the crankshaft position from a crankshaft position sensor. The ECU receives the position of the crankshaft for each of the two cylinders. The crankshaft position sensor also provides a plurality of pulses based on a crankshaft position. The TDC position for a piston of a cylinder is 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 when the piston of each of the two cylinders is at a TDC position. The ECU receives the TDC pulse from the crankshaft position sensor. The piston of the engine reaches TDC twice in each engine cycle. It is necessary to identify the cylinders and also 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.
[0008] For every rotation of the crankshaft, one TDC exists. 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 piston. 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 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. The ECU identifies the stroke as the compression stroke when the engine speed gradient is greater than unity.
[0009] The ECU detects the compression stroke for the first cylinder during a first rotation and for the second cylinder during a second rotation of a crankshaft. The ECU thus, detects two compressions strokes during the first rotation and the second rotation of the crankshaft respectively. The first rotation and the second rotation of the crankshaft are consecutive rotations of the crankshaft.
[00010] The fuel pump pressurizes the fuel and the fuel flows into the rail. The rail pressure is sensed by at least one rail pressure sensors. The ECU knows the cylinder which pumps the pressurized fuel into the rail. A rail pressure peak occurs when a cylinder pumps the pressurized fuel into the rail.
[00011] In a two cylinders engine with 1:2 drive ratio, the camshaft of the pump rotates at a speed which is half the speed of the crankshaft. The ratio of the camshaft speed to the crankshaft speed is known as the drive ratio. Since the camshaft rotates at half the speed of the crankshaft, a rail pressure peak occurs once in two crankshaft rotations. That is, one cylinder pumps the pressurized fuel into the rail once during two crankshaft rotations. The ECU identifies a rail pressure peak during one of the first rotation or the second rotation of the crankshaft. The ECU identifies the rail pressure peak using an input received from at least one rail pressure sensors. The cylinder associated with a pump stroke is pre calibrated and is stored in a database and the ECU recognizes the cylinder pumping the pressurized fuel into the rail based on the detected rail pressure peak associated with the pump stroke. Thus, the ECU relates the identified compression stroke with either the first cylinder or the second cylinder based on the detected rail pressure peak and distinguishes between the two cylinders.
[00012] By calculating the energizing time and releasing the fuel in the same compression stroke of the identified cylinder, the overall starting time of the internal combustion engine is considerably reduced since the time taken for two rotations 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 two cylinder internal combustion engine by calculating the energizing time and releasing fuel in the same 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.