Diesel engine

Abstract

[Problem] To provide a diesel engine that can reduce noise during low idle operation. [Solution] This diesel engine comprises: a solenoid injector which is attached to a cylinder head, is exposed to an interior space of a sub-combustion chamber, and injects fuel into the interior space; and a control device that controls the injection timing of a main injection for injecting fuel from the solenoid injector and a pre-injection executed prior to the main injection. For the main injection, the control device carries out control using a first timing map indicating an injection timing as an advance angle, which is a crank angle before top dead center, with the injection amount of the fuel and the engine speed as parameters. The change in the advance angle for engine speeds between 800 rpm and 1600 rpm, inclusive, for a first injection amount on the first timing map has a portion that gradually decreases as the engine speed increases.

Description

diesel engine

[0001] This invention relates to a pre-chamber type diesel engine that injects fuel into a pre-combustion chamber.

[0002] For example, diesel engines equipped with a fuel accumulator, also known as a holder or rail, are known. The fuel accumulator stores fuel pumped from the fuel pump and supplies high-pressure fuel to the injector. The injector injects the high-pressure fuel supplied from the fuel accumulator into the combustion chamber (e.g., a sub-combustion chamber) at a predetermined timing.

[0003] When an injector injects high-pressure fuel into the combustion chamber, the atomization of the fuel spray injected from the injector progresses. As a result, the premixed fuel burns rapidly at the start of combustion, and the heat generation rate increases in a spike-like manner. It is known that this causes the rate of increase of the pressure inside the cylinder with respect to the crank angle (dP / dθ) to become excessively high, resulting in increased combustion noise. Thus, it is known that in diesel engines, increasing the pressure of the fuel injected from the injector tends to increase combustion noise.

[0004] In contrast, Patent Document 1 discloses a control device for a diesel engine that performs so-called pilot injection, which involves injecting a small amount of fuel prior to the main injection, in order to prevent combustion noise during transient operation. Because the fuel injected by pilot injection burns prior to the main injection, both the in-cylinder temperature and in-cylinder pressure rise during the main injection, improving the combustion state of the fuel injected by the main injection. Therefore, compared to the case where injection is not performed prior to the main injection, the ignition delay period of the fuel can be shortened, and the increase in combustion noise can be suppressed.

[0005] Here, for example, in diesel engines installed in industrial machinery such as construction machinery and agricultural machinery, there are idling operations such as high idle operation and low idle operation. High idle operation refers to idling where, for example, the diesel engine is running at high RPM, but the industrial machinery is not moving. Low idle operation refers to idling where, for example, the lever or dial that adjusts the rotational speed of the diesel engine is set to a low RPM, the diesel engine is running at a low RPM (for example, a speed that does not cause the engine to stall), and the industrial machinery is not performing any work.

[0006] According to the inventors' findings, even when pre-injection is performed prior to main injection, there is room for improvement regarding noise during low idle operation. Reducing noise during low idle operation is desired in diesel engines installed in industrial machinery.

[0007] Japanese Patent Publication No. 2002-276444

[0008] This invention has been made in view of the above circumstances, and aims to provide a diesel engine that can reduce noise during low idle operation.

[0009] One aspect of the present invention is a diesel engine having a main combustion chamber and a sub-combustion chamber connected to the main combustion chamber, comprising: a solenoid injector mounted on the cylinder head and exposed to the internal space of the sub-combustion chamber, which injects fuel into the internal space; and a control device that controls the injection timing of a main injection and a preceding injection performed before the main injection, wherein the control device controls the injection timing of the main injection using a first timing map that indicates the injection timing with the fuel injection amount and engine speed as parameters as an advance angle value which is the crank angle just before top dead center, and the change in the advance angle value in the first injection amount of the first timing map when the engine speed is 800 rpm or more and 1600 rpm or less has a portion that gradually decreases as the engine speed increases.

[0010] According to the present invention, it is possible to provide a diesel engine that can reduce noise during low-idle operation.

[0011] This is a conceptual diagram showing the main components of the diesel engine according to this embodiment. This is a cross-sectional view showing the vicinity of the main combustion chamber and sub-combustion chamber of the diesel engine according to this embodiment. This is a timing chart explaining the main injection and pre-injection performed by the control device of this embodiment. This is a first timing map showing the advance angle value for the main injection of this embodiment. This is a graph showing the relationship between engine speed and advance angle value during low idle operation of the diesel engine according to this embodiment. This is a graph showing the relationship between engine speed and advance angle value during operation of the diesel engine according to this embodiment. This is a graph showing the relationship between injection amount and advance angle value during low idle operation of the diesel engine according to this embodiment.

[0012] Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are preferred examples of the present invention and therefore have various technically preferred limitations. However, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description. Furthermore, in each drawing, similar components are denoted by the same reference numerals, and detailed descriptions are omitted as appropriate.

[0013] Figure 1 is a conceptual diagram showing the main components of the diesel engine according to this embodiment. Figure 2 is a cross-sectional view showing the vicinity of the main combustion chamber and the sub-combustion chamber of the diesel engine according to this embodiment.

[0014] The diesel engine 1 according to this embodiment is an internal combustion engine, for example, an industrial diesel engine. The diesel engine 1 is installed in industrial machinery such as construction machinery and agricultural machinery.

[0015] Diesel engine 1 is, for example, a turbocharged, supercharged three-cylinder engine, and is a vertical, in-line, multi-cylinder engine. However, the number of cylinders is not particularly limited and may be two or fewer, or four or more. The output of diesel engine 1 is less than approximately 19 kilowatts (kW). In other words, diesel engine 1 is a supercharged, small engine. However, the output of diesel engine 1 is not limited to less than 19 kW, and may be 19 kW or more.

[0016] As shown in Figure 1, the diesel engine 1 includes an injector 15 and a control device 4. Furthermore, the diesel engine 1 includes a fuel pressure accumulator pipe 23, a fuel pump 61, a cam 62, a rotation sensor 51, and a cam angle sensor 52.

[0017] As shown in Figure 2, the diesel engine 1 is a so-called pre-chamber type diesel engine, having a main combustion chamber 12 and a sub-combustion chamber 13. The diesel engine 1 includes a cylinder block 7. The cylinders 11 are located inside the cylinder block 7. The piston 71 is positioned inside the cylinder 11 and is reciprocally movable along the cylinder central axis P. The main combustion chamber 12 is formed at the top of the cylinder 11.

[0018] The cylinder head 2 is mounted on top of the cylinder block 7. The sub-combustion chamber 13 is formed inside the cylinder head 2. The sub-combustion chamber 13 is also called a sub-chamber, vortex chamber, or swirl chamber.

[0019] The main combustion chamber 12 is connected to the sub-combustion chamber 13 via a nozzle 50. The nozzle 50 has a nozzle 40 through which the combustion airflow G passes. The main combustion chamber 12 communicates with the sub-combustion chamber 13 through the nozzle 40 of the nozzle 50. The nozzle 40 is provided at an eccentric location relative to the main combustion chamber 12. For example, the nozzle 40 is formed in a diagonally downward direction along a nearly tangential direction to the inner circumferential surface of the sub-combustion chamber 13.

[0020] The injector 15 is a solenoid-type injector. As shown in Figures 1 and 2, the injector 15 is attached to the fuel pressure accumulator 23 and also to the cylinder head 2. The injection portion 151 of the injector 15 is positioned facing the inside of the sub-combustion chamber 13 and is exposed to the internal space of the sub-combustion chamber 13 from above, diagonally downward.

[0021] The injector 15 opens and closes a needle valve by a solenoid based on control signals regarding injection timing and injection amount transmitted from the control device 4, and injects fuel supplied from the fuel accumulator pipe 23 into the sub-combustion chamber 13 from the injection unit 151.

[0022] The fuel pump 61 pumps fuel to the fuel accumulator pipe 23 by the reciprocating movement of a plunger (not shown). The fuel pumped from the fuel pump 61 by the reciprocating movement of the plunger is sent to the fuel accumulator pipe 23 through the pressure supply pipe 612. The plunger is in contact with the cam 62 and reciprocates according to the shape of the cam lobe (i.e., the cam profile) as the cam 62 rotates.

[0023] The fuel accumulator pipe 23 is formed in a cylindrical shape and distributes the fuel pumped from the fuel pump 61 to multiple paths according to the number of cylinders in the diesel engine 1. In other words, the fuel accumulator pipe 23 is a holder or rail that stores the fuel pumped from the fuel pump 61 and supplies high-pressure fuel to the injector 15.

[0024] For example, the fuel pressure inside the fuel accumulator 23 is measured by a pressure sensor (not shown) attached to the fuel accumulator 23. The pressure sensor measures the fuel pressure inside the fuel accumulator 23 and outputs a signal related to the fuel pressure to the control device 4.

[0025] The fuel accumulator pipe 23 is equipped with a control valve (not shown) for adjusting the fuel pressure inside the pipe and an emergency valve (not shown) that opens when the fuel pressure rises above a certain level. Fuel released from the control valve and other components, as well as fuel that overflows from the fuel pump 61, are returned to the fuel tank (not shown) through the return pipe 613.

[0026] The rotation sensor 51, also known as a crank angle sensor, detects the reference position and rotation angle of the crankshaft of the diesel engine 1 based on the rotation of the first pulser 57, and also detects the rotational speed of the diesel engine 1. The rotation sensor 51 outputs detection signals related to the reference position and rotation angle of the crankshaft, as well as detection signals related to the rotational speed of the diesel engine 1, to the control device 4.

[0027] The camshaft angle sensor 52 detects the reference position and rotation angle of the camshaft of the diesel engine 1 based on the rotation of the second pulser 58, and outputs a detection signal regarding the reference position and rotation angle of the camshaft of the diesel engine 1 to the control device 4. The control device 4 receives the detection signal regarding the reference position and rotation angle of the camshaft of the diesel engine 1 output from the camshaft angle sensor 52 and performs cylinder discrimination.

[0028] The control device 4 is, for example, an electronic control unit (ECU), and controls the injection timing and amount of fuel injected from the injector 15. The control device 4 controls the injector 15 and performs multi-stage injection, which divides the fuel injection into multiple injections during one cycle. Specifically, the control device 4 performs a main injection and a pre-injection during one cycle. As a pre-injection, the control device 4 injects a smaller amount of fuel than the amount injected in the main injection, before the main injection.

[0029] In this specification, "pre-injection" includes at least one of pilot injection and pre-injection. That is, pre-injection may be pre-injection, pilot injection, or both pre-injection and pilot injection. The control performed by the control device 4 of this embodiment will be further described below with reference to the drawings.

[0030] Figure 3 is a timing chart illustrating the main injection and pre-injection performed by the control device of this embodiment. Figure 4 is a first timing map showing the advance angle value for the main injection of this embodiment. Figure 5 is a graph showing the relationship between engine speed and advance angle value during low idle operation of the diesel engine according to this embodiment. Figure 6 is a graph showing the relationship between engine speed and advance angle value during operation of the diesel engine according to this embodiment. Figure 7 is a graph showing the relationship between injection amount and advance angle value during low idle operation of the diesel engine according to this embodiment.

[0031] The control device 4 controls the fuel injection timing and injection amount using, for example, a governor map (not shown) stored in a memory unit, based on a detection signal related to the rotational speed of the diesel engine 1 output from the rotation sensor 51 (i.e., the "NE pulse" signal shown in Figure 3) and a detection signal related to the accelerator opening output from the accelerator opening sensor (not shown). Examples of the memory unit include ROM (Read Only Memory) and RAM (Random Access Memory).

[0032] The fuel injection timing is represented by the timing of the "injector drive pulse" shown in Figure 3. Specifically, at timing T1 shown in Figure 3, the control device 4 transmits a drive pulse signal for the pre-injection to the injector 15, and performs the pre-injection before the main injection. Also, at timing T2 shown in Figure 3, the control device 4 transmits a drive pulse signal for the main injection to the injector 15, and performs the main injection after the pre-injection.

[0033] The amount of fuel injected is represented by the width of the "injector drive pulse" shown in Figure 3, and is controlled by the energizing period of the injector 15. That is, as shown in Figure 3, the control device 4 controls the amount of fuel injected in the preliminary injection by setting the width W1 of the injector drive pulse related to the preliminary injection. The control device 4 also controls the amount of fuel injected in the main injection by setting the width W2 of the injector drive pulse related to the main injection.

[0034] As shown in Figure 3, the control device 4 controls the injection timing of the fuel injected from the injector 15. Specifically, the control device 4 sets the injection timing for the main injection to the timing when the crank angle is at a predetermined angle (i.e., advance angle value A1) just before top dead center in the compression stroke. In other words, the injection timing for the main injection is the timing when the crank angle is at an advance angle value A1 just before top dead center in the compression stroke.

[0035] The control device 4 performs control of the main injection using the first timing map shown in Figure 4. The first timing map shows the injection timing, with the fuel injection amount and the rotational speed of the diesel engine 1 as parameters, as an advance angle value A1, which is the crank angle just before top dead center. The first timing map is stored in the memory unit in advance, similar to the governor map mentioned above.

[0036] Furthermore, as shown in Figure 3, the control device 4 sets the timing at which the crank angle is at a predetermined angle (i.e., advance angle value A2) just before the injection timing of the main injection as the injection timing for the preceding injection. In other words, the injection timing for the preceding injection is the timing at which the crank angle is at an advance angle value A2 just before the injection timing of the main injection.

[0037] The control device 4 performs control of the pre-injection using a second timing map. Similar to the first timing map shown in Figure 4, the second timing map shows the injection timing, with the fuel injection amount and the rotational speed of the diesel engine 1 as parameters, as indicated by the advance angle value A2, which is the crank angle just before the injection timing of the main injection. The second timing map is stored in the memory unit in advance, similar to the governor map mentioned above.

[0038] Herein, according to the findings of the present inventors, it has been found that even when a control device controls the injector and performs multi-stage injection including pre-injection and main injection in one cycle, there is room for improvement regarding the noise level of the diesel engine during low idle operation.

[0039] In this specification, "low idle operation" means that, for example, a lever or dial for adjusting the rotational speed of a diesel engine is set to a low rotation speed, and the diesel engine is operating at a low rotation speed (for example, a rotation speed at which the engine does not stall), and the industrial machine is performing an idling operation without doing work. As shown in FIG. 4, the engine rotation speed during low idle operation is, for example, 800 rpm (revolutions per minute) or more and 1600 rpm or less.

[0040] In contrast, in the diesel engine 1 according to this embodiment, as shown by the arrow A11 in FIG. 4 and as shown in FIGS. 5 and 6, the change in the advance angle value A1 during low idle operation in the first injection amount of the first timing map has a portion that gradually decreases as the engine rotation speed increases. Specifically, the change in the advance angle value A1 at an engine rotation speed of 800 rpm or more and 1600 rpm or less in the first injection amount of the first timing map has a portion that gradually decreases as the engine rotation speed increases.

[0041] In the diesel engine according to the comparative example, the change in the advance angle value during low idle operation in the first injection amount of the first timing map gradually increases as the engine rotation speed increases.

[0042] As shown in FIG. 4, the first injection amount of the first timing map during low idle operation is 3 mm ３ / stroke (st) or more and 12 mm ３ / st or less. However, the first injection amount is not necessarily limited to 3 mm ３ / st or more and 12 mm ３ / st or less. For example, when the output of the diesel engine 1 is high (for example, when it is 19 kW or more), the range of the first injection amount is larger than the range of 3 mm ３ / st or more and 12 mm ３ / st or less.

[0043] In addition, in the diesel engine 1 according to the present embodiment, as shown by the arrow A12 in FIG. 4 and FIG. 7, the change in the advance angle value A1 during low idle operation gradually decreases in the direction in which the fuel injection amount increases. That is, the change in the advance angle value A1 when the engine speed of the first timing map is 800 rpm or more and 1600 rpm or less gradually decreases in the direction in which the first injection amount is 3 mm ３ / st or more and 12 mm ３ / st or less. On the other hand, when the first injection amount is 16 mm ３ / st or more, the change in the advance angle value A1 gradually increases in the direction in which the fuel injection amount increases.

[0044] Thus, the change in the advance angle value A1 at a predetermined engine speed of the first timing map gradually decreases and then turns to gradual increase in the direction in which the fuel injection amount increases. The predetermined engine speed is an example of the "first engine speed" of the present invention and is 800 rpm or more and 1600 rpm or less.

[0045] In the diesel engine according to the comparative example, the change in the advance angle value during low idle operation gradually increases as the fuel injection amount increases.

[0046] As described above, according to the diesel engine 1 according to the present embodiment, the change in the advance angle value A1 during low idle operation at the first injection amount of the first timing map has a portion that gradually decreases as the engine speed increases. Specifically, the change in the advance angle value A1 when the engine speed is 800 rpm or more and 1600 rpm or less at the first injection amount of the first timing map has a portion that gradually decreases as the engine speed increases. Thereby, the noise during low idle operation of the diesel engine 1 can be reduced.

[0047] Furthermore, during low idle operation, the change in the advance angle A1 gradually decreases in the direction of increasing the fuel injection amount before gradually increasing. Specifically, in the first timing map, when the engine speed is between 800 rpm and 1600 rpm, the change in the advance angle A1 gradually decreases in the direction of increasing the fuel injection amount before gradually increasing. This also helps to reduce the noise of the diesel engine 1 during low idle operation.

[0048] Furthermore, the control device 4 performs control of the pre-injection using a second timing map that shows the injection timing, with the fuel injection amount and the rotational speed of the diesel engine 1 as parameters, as an advance angle value A2, which is the crank angle just before the injection timing of the main injection. In other words, the control device 4 performs control of the pre-injection using a second timing map that shows the advance angle value A2 based on the main injection, rather than an advance angle value based on top dead center. As a result, the control device 4 can ensure a gap between the pre-injection and the main injection, suppress interference between the pre-injection and the main injection, and reduce noise during low idle operation of the diesel engine 1.

[0049] Embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims. The configurations of the above embodiments can be partially omitted or combined in any way different from those described above.

[0050] 1: Diesel engine, 2: Cylinder head, 4: Control unit, 7: Cylinder block, 11: Cylinder, 12: Main combustion chamber, 13: Sub-combustion chamber, 15: Injector, 23: Fuel accumulator, 40: Nozzle, 50: Nozzle fitting, 51: Rotation sensor, 52: Cam angle sensor, 57: First pulsar, 58: Second pulsar, 61: Fuel pump, 62: Cam, 71: Piston, 151: Injection unit, 612: Pressure piping, 613: Return piping

Claims

1. A diesel engine having a main combustion chamber and a sub-combustion chamber connected to the main combustion chamber, comprising: a solenoid injector mounted on the cylinder head and exposed to the internal space of the sub-combustion chamber, which injects fuel into the internal space; and a control device that controls the injection timing of a main injection and a preceding injection performed before the main injection, wherein the control device controls the injection timing of the main injection using a first timing map that indicates the injection timing with the fuel injection amount and engine speed as parameters as an advance angle value which is the crank angle just before top dead center, and the change in the advance angle value in the first injection amount of the first timing map when the engine speed is 800 rpm or more and 1600 rpm or less has a portion that gradually decreases as the engine speed increases.

2. The diesel engine according to claim 1, wherein the change in the advance angle value in the first injection amount of the first timing map when the engine speed exceeds 1600 rpm has a portion that gradually increases as the engine speed increases.

3. The first injection volume is 3 mm ３ / Stroke of 12mm or more ３ A diesel engine according to claim 1, wherein the stroke is less than or equal to / .

4. The diesel engine according to claim 1, wherein the change in the advance angle value at the first engine speed of the first timing map gradually decreases in the direction of increasing the injection amount.

5. The diesel engine according to claim 4, wherein the first engine speed is 800 rpm or more and 1600 rpm or less.

6. The diesel engine according to any one of claims 1 to 5, wherein the control device controls the preceding injection using a second timing map that indicates the injection timing, with injection amount and engine speed as parameters, as an advance angle value which is the crank angle before the injection timing of the main injection.

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