Control method for an internal combustion engine and internal combustion engine

Abstract

The method for controlling the operation of an internal combustion engine comprises at least two operating modes. In a first operating mode, the intake valve is closed at a first predetermined crank angle, in accordance with the Miller cycle, before the piston reaches bottom dead center during the intake stroke for reducing pressure in the cylinder, and fuel is injected using first fuel injection means optimized for large amounts of fuel. In a second operating mode the intake valve is closed at a second predetermined crank angle, in accordance with conventional intake valve closing timing, after or slightly before the piston has passed bottom dead center, and fuel is injected using second fuel injection means optimized for small amounts of fuel. The invention also concerns an internal combustion engine.

Claims

1. A method for controlling the operation of an internal combustion engine, the engine comprising: at least one cylinder; a reciprocating piston arranged inside the cylinder; at least one intake valve arranged in connection with the cylinder; first fuel injection means; second fuel injection means optimized for injecting smaller amounts of fuel than the first fuel injection means; and means for variable intake valve closing, the method comprising at least two operating modes, wherein at a load that is at least 85 percent of the maximum load of the engine, the engine is operated in a first operating mode and in said first operating mode the intake valve is closed at a first predetermined crank angle, in accordance with a Miller cycle 15-70 degrees before bottom dead center for reducing pressure in the cylinder, and fuel is injected using the first fuel injection means, and wherein at a load that is at most 15 percent of the maximum load of the engine, the engine is operated in a second operating mode and in said second operating mode the intake valve is closed at a second predetermined crank angle, in accordance with conventional intake valve closing timing between 5 degrees before bottom dead center and 20 degrees after bottom dead center, and fuel is injected using the second fuel injection means.

2. The method according to claim 1, wherein the method comprises a third operating mode, in said third mode conventional intake valve closing timing is used and fuel is injected between 5 degrees before bottom dead center and 20 degrees after bottom dead center using the first fuel injection means.

3. The method according to claim 2, wherein the method comprises a fourth operating mode, in said fourth mode the Miller cycle is used and fuel is injected 15-70 degrees before bottom dead center using the second fuel injection means.

4. The method according to claim 3, wherein in the fourth operating mode later intake valve closing timing is used than in the first operating mode.

5. The method according to claim 4, wherein the intake valve is closed 5-15 degrees of crank angle later in the fourth operating mode.

6. The method according to claim 3, wherein the method comprises a fifth operating mode, in which mode the Miller cycle is used and the intake valve is closed 15-70 degrees before bottom dead center but later than in the first operating mode and fuel is injected using the first fuel injection means.

7. The method according to claim 6, wherein the intake valve is closed 5-15 degrees of crank angle later in the fifth operating mode.

8. The method according to claim 1, wherein in the first operating mode earlier intake valve opening timing is used than in the other operating modes.

9. The method according to claim 8, wherein in the first operating mode the intake valve is opened 10-30 degrees earlier than in the other operating modes.

10. The method according to claim 1, wherein the intake valve is closed 20-40 degrees of crank angle before bottom dead center.

11. The method according to claim 1, wherein fuel is injected using an injector comprising two needles.

12. An internal combustion engine comprising: at least one cylinder; a reciprocating piston arranged inside the cylinder; at least one intake valve arranged in connection with the cylinder; means for variable intake valve closing; first fuel injection means; second fuel injection means optimized for injecting smaller amounts of fuel than the first fuel injection means; and control means for controlling the valve closing means and the fuel injection means, wherein the control means is arranged to execute the method according to claim 1.

13. The internal combustion engine according to claim 12, wherein the engine comprises means for variable inlet opening.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows schematically a cylinder of an internal combustion engine.

(2) FIG. 2 shows a fuel injector of an internal combustion engine.

DETAILED DESCRIPTION OF THE INVENTION

(3) The invention is now described in more detail with reference to the accompanying drawings and tables.

(4) In FIG. 1 is shown a cylinder 1 of an internal combustion engine. The engine can comprise any reasonable number of cylinders 1 arranged for instance in-line or in a V-configuration. A reciprocating piston 2 is arranged inside the cylinder 1. Intake air can be introduced into the cylinder 1 via an intake air channel 6. The connection between the cylinder 1 and the intake air channel 6 is closable by an intake valve 3. Means 4 for closing and opening the intake valve 3 are arranged in connection with the valve 6. The closing and opening means 4 can be for instance a hydraulic or electrical actuator, or a mechanical camshaft-guided device. The engine also comprises an exhaust channel 7 and an exhaust valve 5 for opening and closing the connection between the cylinder 1 and the exhaust channel 7. Means 8 for closing and opening the exhaust valve 5 are arranged in connection with the valve 5. The closing and opening means 8 can be a similar hydraulic or electrical actuator or a mechanical camshaft-guided device as the means 4 for closing and opening the intake valve 3. A fuel injector 9 is arranged in the cylinder head for injecting fuel into the cylinder 1. The valve opening and closing means 4, 8 and the fuel injector 9 are controlled by a control unit 11.

(5) In FIG. 2 is shown an example of a fuel injector 9. The fuel injector 9 comprises two nozzles 9a, 9b. The first nozzle 9a is suitable for injecting fuel amounts that are large in relation to the fuel amounts that are injected when the engine is operated at the maximum load. The first nozzle 9a can thus be used when the engine is operated at high or intermediate loads, for instance when the engine load is 35-100 percent of the maximum load. The second nozzle 9b is suitable for injecting fuel amounts that are small in relation to the fuel amounts that are injected when the engine is operated at the maximum load. The second nozzle 9b can thus be used when the engine is operated at low loads, for instance when the load is less than 35 percent of the maximum load.

(6) The fuel injector comprises a first spring loaded needle 10a and a second spring loaded needle 10b. The needles 10a, 10b can be moved hydraulically for letting the fuel flow to the nozzles 9a, 9b.

(7) The method according to the present invention comprises at least two operating modes, which are used at different engine loads. According to an embodiment of the invention, the method comprises two operating modes, as shown in table 1.

(8) TABLE-US-00001 TABLE 1 Control strategy according to an embodiment of the invention. Engine load 0-35% 35-100% 2. mode 1. mode Valve No Miller X timing Miller cycle X Injection Small needle X needle Large needle X

(9) The first operating mode is optimized for higher engine loads and the second operating mode for lower loads. In the embodiment of table 1, the first operating mode is used at loads that are 35-100% of the maximum load of the engine, i.e. from part loads to high loads. In the first operating mode, the Miller cycle with early intake valve closing is used. The intake valve 3 can be closed for instance 20-40 degrees of crank angle before bottom dead center. The closing crank angle refers to that angle at which the valve 3 is completely closed. With the use of the Miller cycle low SFOC and NOx emissions are achieved. When the engine is operated at a high load, a large injection area is needed for achieving sufficient fuel injection rate. Therefore, fuel is injected into the cylinders 1 of the engine through the first nozzle 9a by moving the first needle 10a of the fuel injector 9. In practice, small fuel flow is periodically allowed also through the second nozzle 9b. The same applies to the other operating modes. This flushing that is done according to scheduled time intervals prevents sticking of the second needle 10b.

(10) The second operating mode is optimized for low or very low loads, in the embodiment of table 1 for loads that are 0-35% of the maximum load. In the second operating mode, variable inlet closing (VIC) is utilized and conventional intake valve closing timing is used instead of the Miller cycle. The intake valve 3 is closed after the piston 2 has passed bottom dead center, for instance 0-20 degrees of crank angle after BDC, or slightly before BDC, for instance 0-5 degrees of crank angle before BDC. At low loads, lower smoke emissions can be achieved with conventional valve timing than with the Miller cycle. Also the SFOC can be minimized when conventional intake valve closing timing is used. Fuel is injected into the cylinders 1 of the engine by using the second nozzle 9b. In practice, small fuel flow is periodically allowed also through the first nozzle 9a for preventing sticking of the first needle 10a. The same applies to the other operating modes.

(11) According to a second embodiment of the invention, the method comprises a third operating mode that is used at part loads, as shown in table 2. In the embodiment of table 2, the third operating mode is used at loads that are 35-50% of the maximum load. Accordingly, the first operating mode is used at loads that are 50-100% of the maximum load, i.e. from intermediate to high loads.

(12) TABLE-US-00002 TABLE 2 Control strategy according to a second embodiment of the invention. Engine load 0-35% 35-50% 50-100% 2. mode 3. mode 1. mode Valve No Miller X X timing Miller cycle X Injection Small needle X needle Large needle X X

(13) In the third operating mode, the Miller cycle is not used. Instead, conventional intake valve closing timing is used for achieving low smoke emissions. Fuel is injected into the cylinders 1 of the engine by using the first nozzle 9a.

(14) According to a third embodiment of the invention, the method comprises a fourth operating mode that is used at low loads, as shown in table 3. In the embodiment of table 3, the fourth operating mode is used at loads that are 15-35% of the maximum load. Accordingly, the second operating mode is used at loads that are 0-15% of the maximum load, i.e. at very low loads.

(15) TABLE-US-00003 TABLE 3 Control strategy according to a third embodiment of the invention. Engine load 0-15% 15-35% 35-50% 50-100% 2. mode 4. mode 3. mode 1. mode Valve No Miller X X timing Miller cycle X X Injection Small needle X X needle Large needle X X

(16) In the fourth operating mode, fuel is injected into the cylinders 1 of the engine by using the second nozzle 9b for achieving low smoke emissions. The Miller cycle is used for achieving low NOx emissions.

(17) According to a fourth embodiment of the invention, the method comprises a fifth operating mode that is used at intermediate loads, as shown in table 4. In the embodiment of table 4, the fourth operating mode is used at loads that are 50-85% of the maximum load. Accordingly, the first operating mode is used at loads that are 85-100% of the maximum load, i.e. at high loads. The fifth operating mode gives low NOx emissions and SFOC at intermediate loads.

(18) TABLE-US-00004 TABLE 4 Control strategy according to a fourth embodiment of the invention. Engine load 0-15% 50-85% 85- (very 15-35% 35-50% (interme- 100% low) (low) (part) diate) (high) 2. mode 4. mode 3. mode 5. mode 1. mode VIC ON No Miller X X Inter. X X miller VIC OFF Full Miller X VIO ON Long X overlap Injection Small X X needle needle Large X X X needle

(19) Another difference between the embodiment of table 4 and the embodiments of tables 1-3 is that in the embodiment of table 4, the Miller cycle of the first operating mode is different from the Miller cycles of the other operating modes. In the fourth and fifth operating modes the intake valve 3 is closed later than in the first operating mode. When extreme Miller cycle is used for controlling the firing pressure instead of an exhaust waste gate at high loads, low SFOC and NOx emissions are achieved. In the first operating mode, the intake valve 3 can be closed for instance 20-40 degrees of crank angle before BDC, and in the fourth and fifth operating modes 5-15 degrees of crank angle later than in the first operating mode.

(20) Still another difference between the embodiment shown in table 4 and the other embodiments is that variable intake valve opening (VIO) is utilized in the first operating mode in the embodiment of table 4. The intake valve 3 is opened earlier than in the other operating modes for achieving long overlap with the exhaust valve 5. The intake valve 3 is opened for instance 10-30 degrees of crank angle earlier than in the other operating modes. With early intake valve opening, surging risk of the turbocharger can be lowered. Instead of VIO, variable exhaust valve closing (VEC) can be utilized for having variable scavenging period.

(21) It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims. For instance, the fuel injection means can comprise two injectors instead of one injector having two nozzles. It is also possible that both fuel injection means are used when the engine is operated at high load. Different Miller cycles or inlet valve opening timings can be used in different operating modes. Although the operating modes are referred to with serial numbers, it is obvious that different combinations of the operating modes are possible. For instance, the method can comprise the first, second and fourth operating modes.