WO2013160536A1

WO2013160536A1 - Fuel injector

Info

Publication number: WO2013160536A1
Application number: PCT/FI2013/050416
Authority: WO
Inventors: Vesa Voutilainen
Original assignee: Wärtsilä Finland Oy
Priority date: 2012-04-24
Filing date: 2013-04-16
Publication date: 2013-10-31
Also published as: EP2852752A1; EP2852752B1; CN104302905B; KR102012162B1; KR20150003816A; FI20125450A; CN104302905A; FI123570B

Abstract

A fuel injector (1) comprising a movable control piston (10), a fuel space (15) delimited by the control piston (10) and the injector needle (8), whereby fuel pressure in the fuel space (15) is arranged to press the injector needle (8) toward a closed position. The fuel injector further comprises a first outlet flow path (14, 21, 19) for connecting the fuel space (15) to the fuel outlet (18) and a second outlet flow path (26, 22, 19) for connecting the fuel space (15) to the fuel outlet (18) and a piezoelectric actuator (17, 20) for opening and closing the flow communication through the first outlet flow path (14, 21, 19). The control piston (10) has a first position, where the fuel space (15) is in flow communication with the fuel inlet (5) and the flow communication between the fuel space (15) and the fuel outlet (18) is closed, and a second position, where the fuel space (15) is in flow communication with the fuel outlet (18) through first outlet flow path (14, 21, 19) and the second outlet flow path (26, 22, 19).

Description

Fuel injector

The invention relates to a fuel injector for a reciprocating engine. In diesel engines, the fuel is injected as a fine mist from the fuel injector into the combustion space of the cylinder such that with eddies of air is achieved a good mixture of fuel and combustion air and combustion that is as perfect as possible. Fuel injected by the fuel injector as tiny droplets vaporizes quickly as combustion begins after a short ignition delay. A spring-loaded injector needle is typically used as a shut-off element in the fuel injector. The injector needle is generally guided hydraulically by the pressure of the fuel or other hydraulic fluid.

Due to ever more stringent emissions regulations, the emissions created by diesel engines must be decreased. It is, however, at the same time desired that the per- formance of the engine be kept at the same level or even improved. One means of achieving these goals is to adjust with greater accuracy the amount of fuel injection and the timing and duration of injection during the injection event. The accuracy of adjustment of fuel injection can be improved by guiding the injector needle of the fuel injector by a piezoelectric actuator.

An object of the present invention is to provide an improved fuel injector for a reciprocating engine.

According to the invention, this object can be achieved by a fuel injector according to claim 1. The fuel injector according to the invention comprises an injector body having a fuel chamber for storing fuel before injection, a nozzle opening through which fuel is injected into a cylinder of the engine, an injector needle for opening and closing flow communication between the fuel chamber and the nozzle opening, a fuel inlet for feeding pressurized fuel into the fuel chamber, a fuel outlet for dis- charging fuel from the fuel injector and a movable control piston, a fuel space de- limited by the control piston and the injector needle, wherein fuel pressure in the fuel space is arranged to press the injector needle toward a closed position. The fuel injector according to the invention further comprises a first outlet flow path for connecting the fuel space to the fuel outlet, a second outlet flow path for connect- ing the fuel space to the fuel outlet and a piezoelectric actuator for opening and closing the flow communication through the first outlet flow path. The control piston has a first position, where the fuel space is in flow communication with the fuel inlet and the flow communication between the fuel space and the fuel outlet is closed, and a second position, where the fuel space is in flow communication with the fuel outlet 18 through first outlet flow path and the second outlet flow path.

Considerable advantages can be achieved by means of the present invention. The fuel injector according to the invention comprises two passages through which pressure prevailing in the fuel space is released when the piezoelectric actuator opens the flow communication through the other passage. In this way the movement of the piezoelectric actuator can be quickly forwarded to the injector needle. This enables fast and accurate injection control. The stroke of the piezoelectric actuator is typically quite limited. In the fuel injector according to the invention the travelling length of the piezoelectric actuator can be multiplied by a suitable dimen- sioning of the fuel space. Thus, the travelling length of the injector needle is multiple compared to that of the piezoelectric actuator.

According to an embodiment of the invention the control piston surface that delimits the fuel space comprises a projection, inside which the fuel space is arranged. The second flow path comprises a collector space that surrounds the projection. When the control piston is in its first position, the projection is against the injector body and thus closes the flow communication between the fuel space and the collector space. When the control piston moves toward the second position, the flow communication is opened between the fuel space and the collector space through a gap between the projection and the injector body. As the gap between the projec- tion and the injector body has a relatively large cross-sectional flow area, fuel pressure prevailing in the fuel space can be quickly released. This increases the opening speed of the injector needle. In the following the invention will be described by way of an example with reference to the accompanying drawings, in which

Figure 1 shows a fuel injector according to an embodiment of the present invention in its closed position,

Figure 2 is a partial enlargement of the portion A shown in fig. 1.

Figure 3 shows the fuel injector of fig. 1 in its open position. Figure 4 is a partial enlargement of the portion B shown in fig. 3.

Figure 5 shows a fuel injector according to another embodiment of the present invention. The drawings disclose a fuel injector 1 for a diesel engine. The engine can be a large diesel engine, which refers here to such engines that can be used for instance as main and auxiliary engines in ships or in power plants for production of heat and/or electricity. The engine is provided with a common rail fuel injection system, in which fuel is fed by means of a high pressure pump into a pressure accu- mulator, from which it is led into the fuel injector 1. From the fuel injector 1 fuel is injected into a cylinder 4 of the engine.

The fuel injector 1 comprises an injector body 2, which has a fuel chamber 3 for storing fuel before injection into the cylinder 4. The fuel chamber 3 is arranged to receive pressurized fuel from the pressure accumulator. The fuel injector 1 com- prises a fuel inlet 5 for feeding pressurized fuel into the fuel chamber 3. The fuel inlet 5 is in flow communication with the pressure accumulator. The fuel inlet 5 is in continuous flow communication with the fuel chamber 3 through an inlet duct 6. The fuel injector 1 further comprises a fuel outlet 18 for discharging fuel from the injector 1. Fuel pressure at the fuel outlet 18 is lower than fuel pressure at the fuel inlet 5.

The fuel injector 1 comprises at least one nozzle opening 7, through which fuel is injected from the fuel chamber 3 into the cylinder 4. The fuel injector 1 further comprises an injector needle 8 for opening and closing the flow communication between the fuel chamber 3 and the nozzle opening(s) 7. The first end of the injector needle 8 extends into the fuel chamber 3. The fuel injector 1 comprises a spring 9, which is arranged to press the injector needle 8 toward its closed position, in which flow communication is closed between the fuel chamber 3 and the nozzle opening^) 7. The spring 9 is placed in a spring chamber 25, which is in flow communication with the fuel outlet 18. The spring chamber 25 collects fuel that leaks from the fuel chamber 3 through a clearance between the injector needle stem and the injector body 2. The force caused by the fuel pressure in the fuel chamber 3 presses the injector needle 8 towards its open position, in which flow communication is open between the fuel chamber 3 and the nozzle opening(s) 7. The injector needle 8 is provided with a collar 24, on which the fuel pressure in the fuel chamber 3 acts to move the injector needle 8.

The fuel injector 1 comprises a movable control piston 10. The control piston 10 is movable in the direction of the longitudinal axis of the injector needle 8. The control piston 10 faces the injector needle 8. The control piston 10 has a first surface 12 that faces the injector needle 8. Further, the control piston 10 has a second surface 13 that faces the injector body 2. The first surface 12 and the second surface 13 are on the opposite sides of the control piston 10. The control piston 10 comprises a connecting duct 14, which forms flow communication between the first surface 12 and the second surface 13. The control piston 10 can be a cylindrical part, the ends of which form the first surface 12 and the second surface 13.

The fuel injector 1 further comprises a fuel space 15, which is delimited by the con- trol piston 10 and the injector needle 8. The fuel space 15 is delimited by the first surface 12 of the control piston 10 and the second end of the injector needle 8. Force caused by the fuel pressure in the fuel space 15 is arranged to press the injector needle 8 toward its closed position. The connecting duct 14 forms flow communication between the fuel space 15 and the second surface 13.

The first surface 12 of the control piston 10 is provided with a projection 27, inside which the fuel space 15 is located. The projection 27 can be annular. A collector space 26 is arranged between the control piston 10 and the injector body 2. The collector space 26 surrounds partially or entirely the projection 27. The collector space 26 is in flow communication with the fuel outlet 18.

The fuel injector 1 is provided with a first outlet duct 21 , which is in flow communication with the fuel outlet 18. The fuel injector 1 is also provided with a second outlet duct 22 which is in flow communication with the fuel outlet 18. The collector space 26 is in flow communication with the second outlet duct 22. A discharge duct 19 connects the first outlet duct 21 and the second outlet duct 22 to the fuel outlet 18. The connecting duct 14, the first outlet duct 21 and the discharge duct 19 form a first outlet flow path that connects the fuel space 15 to the fuel outlet 18. The collector space 26, the second outlet duct 22 and the discharge duct form a second outlet flow path that connects the fuel space 15 to the fuel outlet 18.

The fuel injector 1 further comprises a piezoelectric actuator 17 for guiding the injector needle 8 i.e. for moving it between the open and closed positions. The piezoelectric actuator 17 is arranged to open and close flow communication through the first outlet flow path i.e. through the first outlet duct 21. The function of the pie- zoelectric actuator 17 is based on the piezoelectric phenomenon. The actuator 17 comprises piezo elements 29 made of a piezoelectric material. The length of piezo elements 29 changes in response to an electrical field. The piezo elements 29 comprise piezo crystals, which are ordinarily made from PZT ceramics, which comprise lead, zirconium and titanium. The piezo elements 29 are arranged one above the other to form a piezo stack. The actuator 17 comprises a control needle 20 that is attached to the piezo element 29 of the piezo stack. Depending on the position of the piezoelectric actuator 17, the control needle 20 either opens or closes the flow communication through the first outlet duct 21.

The control piston 10 has a first position, where the fuel space 15 is in flow communication with the fuel inlet 5 (fig. 1 ). The fuel space 15 is in flow communication with the fuel inlet 5 through the connecting duct 14 and a gap 16, which is between the second surface 13 of the control piston and the injector body 2. A feed duct 23 is arranged between the inlet duct 6 and the gap 16. In the first position of the control piston 10, the flow communication between the fuel space 15 and the fuel outlet 18 is closed. The control needle 20 closes the flow communication through the first outlet flow path. Further, the flow communication from the fuel space 15 to the fuel outlet 18 through the second outlet flow path is closed by the projection 27, which is against the injector body 2 and thus closes the flow communication from the fuel space 15 to the collector space 26.

The control piston 10 has a second position, where the fuel space 15 is in flow communication with the fuel outlet 18 through the first outlet flow path and the se- cond outlet flow path (fig. 3). The fuel space 15 is in flow communication with the collector space 26 through a gap 1 1 between the projection 27 and the injector body 2. The flow communication between the fuel space 15 and the fuel inlet 5 is closed. The second surface 13 of the control piston 10 is against the injector body 2. Due to high fuel pressure, some fuel flows from the feed duct 23 to the first out- let duct 21 along the gap 16 between the second surface 13 and the injector body 2. The second end of the injector needle 8 is against the first surface 12 of the control piston. Further, in the second position of the control piston 10, the connecting duct 14 is in flow communication with the fuel 18 outlet via the first outlet duct 21. When the control piston 10 is in the second position, the effective cross-sectional flow area of the feed duct 23 is smaller than that of the first outlet duct 21.

To initiate the fuel injection, the piezoelectric actuator 17 is energized. The piezoelectric actuator 17 opens the flow communication from the fuel space 15 to the fuel outlet 18. This is achieved by the control needle 20, which opens the flow commu- nication through the first outlet duct 21. Consequently, fuel pressure in the fuel space 15 is released through the connecting duct 14 and the first outlet duct 21. The control piston 10 moves from its first position toward the second position. Simultaneously the flow communication is opened from the fuel space 15 to the collector space 26 through the gap 1 1 between the injector body 2 and the projection 27. This further releases the fuel pressure in the fuel space 15. Force caused by the fuel pressure in the fuel chamber 3 moves the injector needle 8 to its open position and the fuel injection through the nozzle openings 7 into the cylinder 4 starts.

To terminate the fuel injection, the piezoelectric actuator 17 is de-energized. The piezoelectric actuator 17 closes the flow communication between the fuel space 15 and the fuel outlet 18. This achieved by the control needle 20, which closes the flow communication through the first outlet duct 21. Fuel pressure in the fuel inlet 5 acts on the second surface 13 of the control piston and presses the control piston 10 toward its first position. Simultaneously flow communication is opened between the fuel inlet 5 and the fuel space 15. The control piston 10 closes the flow communication from the fuel space 15 to the collector space 26. The fuel pressure acting on the second end of the injector needle 8 presses the injector needle 8 to its closed position and the fuel injection through the nozzle openings 7 into the cylinder 4 stops. Figure 5 shows an embodiment where the spring chamber 25 is in flow communication with the fuel chamber 3 vial a clearance 28 between the injector needle 8 and the injector body 2. The spring chamber 25 is not in flow communication with the fuel outlet 18. In this embodiment the amount of fuel leaking from the injector 1 can be reduced. In other respects the embodiment of fig. 5 is similar to the embodiment of figs. 1 -4.

Claims

Claims:

1. A fuel injector (1 ) for a reciprocating engine, the fuel injector (1 ) comprising

- an injector body (2) having a fuel chamber (3) for storing fuel before injection, - a nozzle opening (7) through which fuel is injected into a cylinder (4) of the engine,

- an injector needle (8) for opening and closing flow communication between the fuel chamber (3) and the nozzle opening (7),

- a fuel inlet (5) for feeding pressurized fuel into the fuel chamber (3), and

- a fuel outlet (18) for discharging fuel from the fuel injector (1 ),

characterized in that the fuel injector (1 ) further comprises:

- a movable control piston (10),

- a fuel space (15) delimited by the control piston (10) and the injector needle (8), whereby fuel pressure in the fuel space (15) is arranged to press the injector nee- die (8) toward a closed position,

- a first outlet flow path (14, 21 , 19) for connecting the fuel space (15) to the fuel outlet (18),

- a second outlet flow path (26, 22, 19) for connecting the fuel space (15) to the fuel outlet (18),

- a piezoelectric actuator (17, 20) for opening and closing the flow communication through the first outlet flow path (14, 21 , 19), and

which control piston (10) has a first position, where the fuel space (15) is in flow communication with the fuel inlet (5) and the flow communication between the fuel space (15) and the fuel outlet (18) is closed, and a second position, where the fuel space (15) is in flow communication with the fuel outlet (18) through first outlet flow path (14, 21 , 19) and the second outlet flow path (26, 22, 19).

2. The fuel injector according to claim 1 , characterized in that the control piston (10) is arranged to move from the second position to the first position when the flow communication is closed through the first outlet flow path (14, 21 , 19).

3. The fuel injector according to claim 1 or 2, characterized in that the control piston (10) is arranged to move from the first position to the second position when the flow communication is opened through the first outlet flow path (14, 21 , 19).

4. The fuel injector according to claim 1 , characterized in that the control piston (10) has a first surface (12) that delimits the fuel space (15), a second surface (13), and that the first flow path comprises a connecting duct (14) for forming flow communication between the first surface (12) and the second surface (13).

5. The fuel injector according to claim 4, characterized in that when the control piston (10) is in its first position, the fuel space (15) is in flow communication with the fuel inlet (5) through the connecting duct (14) and a gap (16) between the second surface (13) and the injector body (2).

6. The fuel injector according to claim 5, characterized in that the first outlet flow path comprises a first outlet duct (21 ), which is in flow communication with the connecting duct (14) when the control piston (10) is in its second position, and that the piezoelectric actuator is arranged to open and close the flow communication through the first outlet duct (21 ).

7. The fuel injector according to claim 4, characterized in that the first surface (12) of the control piston is provided with a projection (27), inside which the fuel space (15) is located.

8. The fuel injector according to claim 7, characterized in that the second flow path comprises a collector space (26) surrounding the projection (27).

9. The fuel injector according to claim 8, characterized in that when the control piston (10) is in the second position the fuel space (15) is in flow communication with the collector space (26) through a gap (1 1 ) between the projection (27) and the injector body (2).

10. The fuel injector according to claim 8 or 9, characterized in that when the control piston (10) is in the first position, the projection (27) is against the injector body (2) and thus closes the flow communication between the fuel space (15) and the collector space (26).

1 1. The fuel injector according to claim 5, characterized in that the injector com- prises a feed duct (23) for feeding fuel to the gap (16) between the second surface

(13) of the control piston and the injector body (2), and that an effective cross- sectional flow area of the feed duct (23) is smaller than the effective cross- sectional flow area of the first outlet duct (21 ).