Method and device for controlling fuel injection at start-up of an internal combustion engine

Abstract

To solve a problem that, when injection is performed by diving it into a plurality of times at starting of an internal combustion engine, a fuel pressure in a common rail is decreased by preceding injection, and atomization at succeeding injection is deteriorated.SOLUTION: A high pressure fuel pump constituted by a plunger pump is driven by a cam crest provided on a valve camshaft, and an intake stroke and a compression / discharge stroke alternately occur in synchronous with a crank angle. At starting, the injection is divided into three, and a second fuel injection timing INJ2 and a third fuel injection timing INJ3 are set in the compression / discharge stroke timing of the plunger pump. In the compression / discharge stroke of the plunger pump, a fuel pressure in a common rail tends to increase, and therefore, the fuel pressure decreasing in accordance with the first injection is immediately recovered, and deterioration of atomization can be avoided.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to fuel injection control at the time of starting in a direct-injection spark-ignition internal combustion engine equipped with a high-pressure fuel pump consisting of a plunger pump that is mechanically driven in synchronization with the rotation of the crankshaft. [Background technology]

[0002] In a direct-injection spark-ignition internal combustion engine, in which fuel is injected into a cylinder and the resulting air-fuel mixture is ignited, if the entire amount of fuel required is injected in one go, for example during the intake stroke, when the engine is cold, a large amount of soot and smoke is generated. For this reason, it is known that fuel is injected in multiple divided injections when the engine is cold.

[0003] Furthermore, since a relatively high fuel pressure is required to inject fuel directly into the cylinders, many common rail fuel injection systems are used, in which fuel is pressurized by a high-pressure fuel pump consisting of a plunger pump that is mechanically driven in synchronization with the rotation of the crankshaft and supplied to a high-pressure fuel pipe, known as a common rail, to which the fuel injection valves of each cylinder are connected, and the high-pressure fuel in this common rail is injected into the cylinders as the fuel injection valves of each cylinder open. As disclosed in Patent Document 1, the high-pressure fuel pump consisting of a plunger pump is driven, for example, by a cam lobe for the plunger pump provided at the end of the camshaft of the intake valve or exhaust valve.

[0004] Patent Document 2 discloses that in a port-injection spark-ignition internal combustion engine in which a fuel injection valve is provided toward an intake port rather than a direct-injection type, the fuel pressure supplied to the fuel injection valve is increased and split injection is performed when the internal combustion engine is started. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-042748 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-336509 Summary of the Invention [Problem to be solved by the invention]

[0006] In a direct-injection spark-ignition internal combustion engine using a high-pressure fuel pump consisting of a plunger pump mechanically driven in synchronization with the rotation of the crankshaft, fuel pressure in the common rail is not necessarily sufficiently stored during startup (for example, within several to several tens of cycles from the first combustion cycle), and a transient drop in fuel pressure is likely to occur with fuel injection.As a result, for example, in the case of three divided injections, even if a predetermined fuel pressure is achieved during the first fuel injection, the fuel pressure will be lower during the subsequent second and third fuel injections, resulting in a deterioration in the quality of the fuel spray.

[0007] In other words, after a certain amount of time has passed since starting, the fuel pressure in the common rail is maintained at the target fuel pressure and a sufficient amount of high-pressure fuel is supplied to the common rail by the high-pressure fuel pump, so even if multiple split injections are performed, each fuel injection can be performed under the target fuel pressure.In contrast, during starting, it can be difficult to maintain the fuel pressure for the second, third, etc. fuel injections.

[0008] It should be noted that Patent Document 2 is a port injection type with a relatively low fuel pressure, and the fuel pressure can be variably controlled by an electric fuel pump. Patent Document 2 does not solve the problem of split injection at the start of a direct-injection spark-ignition internal combustion engine that uses a high-pressure fuel pump consisting of a plunger pump as described above. [Means for solving the problem]

[0009] The method for controlling fuel injection at the start of an internal combustion engine according to the present invention is directed to a direct injection spark ignition internal combustion engine in which fuel pressurized by a high-pressure fuel pump consisting of a plunger pump mechanically driven in synchronization with the rotation of the crankshaft is supplied to a common rail and injected into each cylinder as the fuel injection valve of each cylinder opens. Method for controlling fuel injection at start-up of an internal combustion engineIn the above When starting an internal combustion engine, the number of fuel injections per cycle is set to multiple times, The timing of the first fuel injection is set within the intake stroke of the plunger pump. At least the final fuel injection timing Set within the compression and discharge stroke periods of the plunger pump.

[0010] A plunger pump repeatedly draws in and compresses and discharges fuel through the reciprocating motion of the plunger. During the compression and discharge strokes, pressurized fuel is sent into the common rail. Therefore, if the injection timing is set within the compression and discharge strokes, for example, a drop in fuel pressure caused by the previous fuel injection is more easily recovered, resulting in a relatively high fuel pressure at the time of injection. [Effects of the Invention]

[0011] According to this invention, when split injection is performed at start-up, high fuel pressure can be obtained during multiple injections (e.g., average fuel pressure of multiple injections), and deterioration of fuel spray properties due to a drop in fuel pressure can be suppressed. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram illustrating the configuration of an internal combustion engine according to an embodiment of the present invention; [Figure 2] 4 is a timing chart showing the relationship between the stroke of a plunger pump and the fuel injection timing in one embodiment. [Figure 3] FIG. 4 is an explanatory diagram schematically showing a change in fuel pressure immediately before the fuel injection valve. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described in detail below with reference to the drawings. Fig. 1 is an explanatory diagram showing a schematic configuration of an internal combustion engine 1 of one embodiment to which the present invention is applied. The internal combustion engine 1 of the one embodiment is an in-line three-cylinder, four-stroke, spark-ignition internal combustion engine (a so-called gasoline engine), in which a pair of intake valves 2 and a pair of exhaust valves 3 are provided in a combustion chamber 5 of each cylinder, and an ignition plug 4 is disposed in the center of the combustion chamber 5. As a direct-injection engine, a fuel injection valve 6 that injects fuel into the cylinder is disposed, for example, on the side of the intake valve 2.

[0014] An electronically controlled throttle valve 10, the opening of which is controlled by a control signal from an engine controller 9, is installed upstream of a collector section 8a of an intake passage 8 connected to an intake port 7 of each cylinder. An exhaust port 12 of each cylinder is connected to an exhaust manifold 13.

[0015] The fuel injection valves 6 for each cylinder are connected to a common rail 14. Fuel pressurized by a high-pressure fuel pump 15 is supplied to the common rail 14. Fuel is introduced from a fuel tank (not shown) to the high-pressure fuel pump 15 via a feed pump 16, which is, for example, an electric pump. The fuel pressure in the common rail 14 is maintained at a target fuel pressure via a pressure regulator (not shown). The fuel injection valves 6 inject fuel by opening and closing a valve element via a solenoid, a piezoelectric element, or the like, and the amount of fuel injected is basically proportional to the fuel injection time.

[0016] The high-pressure fuel pump 15 is a plunger pump that is mechanically driven in synchronization with the rotation of the crankshaft. In one embodiment, the plunger pump, i.e., the high-pressure fuel pump 15, is driven by a plunger pump cam lobe provided at the end of a camshaft (not shown) for the intake valve 2 or the exhaust valve 3. More specifically, the camshaft has three cam lobes spaced equally apart at 120° intervals. The cam lobes press the plunger, thereby achieving the pumping action of the plunger pump. That is, the plunger reciprocates as the cam lobes rotate, alternately performing an intake stroke in which low-pressure fuel is drawn into the cylinders of the high-pressure fuel pump 15 and a compression / discharge stroke in which high-pressure fuel is discharged from the cylinders of the high-pressure fuel pump 15 to the common rail 14. Because the rotational speed of the valve camshaft is half that of the crankshaft, the compression / discharge stroke of the plunger pump that constitutes the high-pressure fuel pump 15 occurs every 240° CA. The plunger pump may be of a type having a plurality of plungers, and in this case too, the pump is configured so that the compression and discharge strokes occur every 240° CA.

[0017] The engine controller 9 receives detection signals from a number of sensors, such as an air flow meter 20 that detects the amount of intake air upstream of the throttle valve 10, a crank angle sensor 21 that detects the engine speed and crank angle position, a water temperature sensor 22 that detects the coolant temperature, an accelerator opening sensor 23 that detects the amount of depression of the accelerator pedal operated by the driver, an air-fuel ratio sensor 24 that detects the exhaust air-fuel ratio in the exhaust passage downstream of the exhaust manifold 13, and a fuel pressure sensor 25 that detects the fuel pressure in the common rail 14. Based on these input signals, the engine controller 9 optimally controls the amount and timing of fuel injection by the fuel injection valve 6, the ignition timing by the spark plug 4, the opening of the throttle valve 10, etc.

[0018] Next, fuel injection control at startup, which is a key aspect of this invention, will be described with reference to Figures 2 and 3. Figure 2 is a timing chart showing the relationship between (a) the plunger pump stroke and (b) the fuel injection timing, with the horizontal axis representing the crank angle. In the figure, "#1 TDC," "#2 TDC," and "#3 TDC" represent the compression top dead center of cylinder #1, cylinder #2, and cylinder #3, respectively. These three compression top dead centers are spaced 240° CA apart. "#1 exhaust TDC" is the exhaust top dead center of cylinder #1, which is 360° CA behind "#1 TDC," i.e., midway between "#2 TDC" and "#3 TDC."

[0019] The three isosceles triangles shown in column (a) are schematic representations of the strokes (plunger positions) of the plunger pump that constitutes the high-pressure fuel pump 15. The first half of the triangle up to the peak is the compression / discharge stroke, and the second half after the peak is the intake stroke. As mentioned above, the compression / discharge stroke and intake stroke occur every 240° CA. Microscopically, the fuel pressure in the common rail 14 tends to rise during the compression / discharge stroke, but does not rise during the intake stroke.

[0020] In the illustrated example, the start of the compression / discharge stroke is slightly delayed from the compression top dead center of each cylinder; in one example, it is delayed by 24° CA from the compression top dead center. For example, for cylinder #1, the intake stroke of cylinder #1 is between "#1 exhaust TDC" and 180° CA, so a portion of the compression / discharge stroke of the plunger pump overlaps with the intake stroke of cylinder #1. This relationship is similar for cylinders #2 and #3.

[0021] Column (b) shows the fuel injection timing, particularly the fuel injection timing for cylinder #1 during startup of the internal combustion engine 1. Injecting the entire required amount of fuel in one injection during startup, especially when the engine is cold, can result in the generation of a large amount of soot and smoke. Therefore, in this embodiment, the number of fuel injections per cycle is set to multiple injections during startup. Specifically, fuel is injected in three separate injections. "INJ1," "INJ2," and "INJ3" in the figure indicate the timings of the first, second, and third fuel injections, respectively. The first fuel injection, INJ1, is performed midway through the intake stroke of cylinder #1, e.g., 100° CA after exhaust top dead center. The second fuel injection, INJ2, is performed late in the intake stroke of cylinder #1, e.g., 150° CA after exhaust top dead center. The third fuel injection, INJ3, is performed early in the compression stroke, e.g., 200° CA after exhaust top dead center. Comparing these injection timings with the plunger pump strokes in column (a), the first fuel injection timing INJ1 is within the suction stroke of the plunger pump, but the second fuel injection timing INJ2 and the third fuel injection timing INJ3 are both within the compression and discharge strokes of the plunger pump. Note that the second fuel injection timing INJ2 is within the compression and discharge strokes of the plunger pump and within the intake stroke of the cylinder in question.

[0022] In this way, by setting the second fuel injection timing INJ2 and the third fuel injection timing INJ3 within the compression and discharge stroke periods of the plunger pump, it is possible to avoid a drop in the actual fuel pressure at each injection timing, and to obtain the desired fuel spray characteristics (e.g., atomization).

[0023] That is, during startup (for example, within several to several tens of cycles from the first combustion cycle), high-pressure fuel pump 15 is driven in conjunction with the rotation of the crankshaft, so fuel pressure is not necessarily sufficiently stored in common rail 14, and there is a delay in replenishing the injected amount of fuel, which makes it easy for a drop in fuel pressure to occur with fuel injection (more specifically, a drop in fuel pressure immediately before fuel injection valve 6). Therefore, when three divided injections are performed, even if there is a sufficiently high fuel pressure at the first fuel injection timing INJ1, the fuel pressure at the subsequent second fuel injection timing INJ2 and third fuel injection timing INJ3 is likely to be low.

[0024] In the above embodiment, the second fuel injection timing INJ2 and the third fuel injection timing INJ3 are set within the compression and discharge strokes of the plunger pump, so that the fuel pressure drop that occurs with each fuel injection is quickly recovered, and deterioration of the spray quality due to the fuel pressure drop is avoided. In other words, a high average fuel pressure is obtained during the three fuel injections.

[0025] FIG. 3 is an explanatory diagram that shows a schematic diagram of the change in fuel pressure immediately before the fuel injection valve 6 due to three fuel injections during startup. Because fuel injection begins after the fuel pressure reaches a predetermined level, the fuel pressure is maintained at a relatively high level (PO) before fuel injection. However, the fuel pressure drops to P1 with the first fuel injection (INJ1). If the second fuel injection (INJ2) and the third fuel injection (INJ3) are timed so as not to coincide with the compression and discharge strokes of the plunger pump, the fuel pressure drops to P2 with the second fuel injection (INJ2) and further drops to P3 with the third fuel injection (INJ3), as shown by the dashed line. In the comparative example shown by the dashed line, the plunger pump begins its compression and discharge stroke immediately after the third fuel injection (INJ3), allowing the fuel pressure to recover after all injections are completed.

[0026] In contrast, the characteristic shown by the solid line shows an example in which the plunger pump enters the compression / discharge stroke after the second fuel injection timing INJ2, and the fuel pressure rises from the level of fuel pressure P2, with the third fuel injection INJ3 being performed midway through the rising process. Therefore, the third fuel injection INJ3 is performed under sufficiently high fuel pressure.

[0027] In the explanatory diagram of FIG. 3, only the third fuel injection timing INJ3 occurs within the compression / discharge stroke period of the plunger pump, but in the setting of the embodiment shown in FIG. 2, both the second fuel injection INJ2 and the third fuel injection INJ3 are performed in the middle of the fuel pressure increase process.

[0028] As described above, according to the above embodiment, when split injection is performed during engine startup, high fuel pressure (e.g., the average fuel pressure of the multiple injections) can be achieved during multiple injections, thereby preventing deterioration of fuel spray quality due to a drop in fuel pressure. In particular, in the above embodiment, the first fuel injection (INJ1) maintains relatively high fuel pressure even during the plunger pump's intake stroke, ensuring sufficient atomization. Furthermore, the long time until ignition ensures sufficient mixing. On the other hand, the second fuel injection (INJ2) and the third fuel injection (INJ3) have relatively short times until ignition, making them more susceptible to a drop in fuel pressure due to the preceding injections. However, by setting the injection timings (INJ2 and INJ3) during the fuel pressure rise phase, as in the above embodiment, these effects can be offset. In other words, it is advantageous to prioritize the later injection timings among the multiple injections and set them during the plunger pump's compression and discharge strokes.

[0029] After starting, the control mode may be one in which the entire amount of fuel required is injected in one go, or an appropriate number of divided injections may be performed. After some time has passed after starting, the fuel pressure that had dropped due to the fuel injections will immediately recover, so the problem of fuel pressure drop will not occur even if multiple divided injections are performed at any timing.

[0030] The crank angle positions of the compression and discharge strokes of the plunger pump (in other words, the positions where the cam lobes are formed on the camshaft) are not limited to the positions shown in Figure 2. Therefore, for example, it is also possible to first determine the fuel injection timing based on other conditions and requirements, and then appropriately set the compression and discharge strokes of the plunger pump for this injection timing.

[0031] Although one embodiment of the present invention has been described above in detail, the present invention is not limited to the above embodiment and various modifications are possible. For example, the present invention can naturally be applied to multi-cylinder engines other than in-line three-cylinder engines, and can also be applied to split injections at a number of times other than three. Furthermore, the specific numerical examples of crank angles described above are merely examples. [Explanation of symbols]

[0032] 1...Internal combustion engine 6...Fuel injection valve 9...Engine controller 14...Common rail 15...High-pressure fuel pump 16...Feed pump

Claims

1. A method for controlling fuel injection at the start of an internal combustion engine that is a direct injection spark ignition internal combustion engine in which fuel pressurized by a high-pressure fuel pump consisting of a plunger pump mechanically driven in synchronization with rotation of a crankshaft is supplied to a common rail and injected into each cylinder as a fuel injection valve of each cylinder opens, comprising: When starting the internal combustion engine, the number of fuel injections per cycle is set to a plurality of times, The first fuel injection timing is set within the intake stroke period of the plunger pump. At least the final fuel injection timing is set within the compression and discharge stroke period of the plunger pump. A method for controlling fuel injection at the start of an internal combustion engine.

2. The internal combustion engine is a three-cylinder internal combustion engine, The compression and discharge strokes of the plunger pump are every 240°CA.

2. The method for controlling fuel injection at the start of an internal combustion engine according to claim 1.

3. When starting the internal combustion engine, the number of fuel injections per cycle is three, The first fuel injection timing is set within the intake stroke period of the plunger pump. The timing of the second and third fuel injections is set within the compression and discharge stroke periods of the plunger pump.

2. The method for controlling fuel injection at the start of an internal combustion engine according to claim 1.

4. A method for controlling fuel injection at the start of an internal combustion engine that is a direct injection spark ignition internal combustion engine in which fuel pressurized by a high-pressure fuel pump consisting of a plunger pump mechanically driven in synchronization with the rotation of the crankshaft is supplied to a common rail and injected into the cylinders as the fuel injection valves of each cylinder open, comprising: When starting the internal combustion engine, the number of fuel injections per cycle is set to a plurality of times, At least a part of the latter injection timings among the plurality of injection timings is set within the compression / discharge stroke period of the plunger pump, At least a part of the compression and discharge strokes of the plunger pump is set to overlap with the intake stroke of each cylinder, At least one of the multiple injection timings is set within the intake stroke of the cylinder and within the compression / discharge stroke of the plunger pump. A method for controlling fuel injection at the start of an internal combustion engine.

5. A start-up fuel injection control device for an internal combustion engine that is a direct-injection spark-ignition internal combustion engine in which fuel pressurized by a high-pressure fuel pump consisting of a plunger pump mechanically driven in synchronization with the rotation of a crankshaft is supplied to a common rail and injected into each cylinder as the fuel injection valve of each cylinder opens, When starting the internal combustion engine, the number of fuel injections per cycle is set to a plurality of times, The first fuel injection timing is set within the intake stroke period of the plunger pump. At least the final fuel injection timing is set within the compression and discharge stroke period of the plunger pump. A fuel injection control device for an internal combustion engine at start-up.

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