Technical field of the invention

The present invention relates to a fuel injection unit for an internal combustion engine according to the preamble of claim 1. The invention also concerns a fuel injection sys- tern in accordance with the preamble of the other independent claim.

Background of the invention

In large compression ignition internal combustion engines, such as those used in ships or at power plants, smoke formation at low loads is a common problem. The fuel injec- tors of the engines must be capable of delivering the fuel amount needed for the operation at maximum load. Since large internal combustion engines need to run reliably and efficiently at maximum or near maximum power, the injectors are usually optimized for high loads. This means that at low loads the injectors do not work optimally and smoke is formed. If the injector performance at low loads is improved, this usually leads to higher fuel consumption at high loads.

Summary of the invention

An object of the present invention is to provide an improved fuel injection unit for an internal combustion engine. The characterizing features of the fuel injection unit accord- ing to the present invention are given in the characterizing part of claim 1. Another object of the invention is to provide an improved fuel injection system for an internal combustion engine. The characterizing features of the fuel injection system according to the present invention are given in the characterizing part of the other independent claim. According to the present invention, the fuel injection unit comprises a body, a first fuel gallery and a second fuel gallery, a first fuel injection nozzle and a second fuel injection nozzle, a first injector needle for opening and closing flow communication between the first fuel gallery and the first fuel injection nozzle, and a second injector needle for opening and closing flow communication between the second fuel gallery and the se- cond fuel injection nozzle. The fuel injection system in accordance with the invention comprises a fuel injection pump and a fuel injection unit for each cylinder of the engine, means for connecting the fuel injection pump to the fuel injection unit, and a control valve for controlling the op- eration of the fuel injection unit. The fuel injection unit comprises a body, a first fuel gallery and a second fuel gallery, a first fuel injection nozzle and a second fuel injection nozzle, a first injector needle for opening and closing flow communication between the first fuel gallery and the first fuel injection nozzle, and a second injector needle for opening and closing flow communication between the second fuel gallery and the se- cond fuel inj ection nozzle .

With the fuel injection unit and system in accordance with the invention, a suitable fuel injection nozzle can be chosen for different operating conditions of the engine. As a result, the fuel consumption of the engine can be reduced and at the same time it is pos- sible to achieve lower NOx, CO and hydrocarbon emissions and lower smoke formation.

According to an embodiment of the invention, the flow area past the second injector needle is smaller than the flow area past the first injector needle. The first fuel injection nozzle can thus be used for injecting large amounts of fuel and the second fuel injection nozzle can be used for injecting smaller amounts of fuel. For instance, the first fuel injection nozzle can be used when the engine load is over 30 percent of the maximum load, and the second fuel injection nozzle can be used for lower engine loads. According to an embodiment of the invention, the control valve comprises a valve member having at least a first position where fuel flow from an inlet port of the control valve to the first fuel gallery is allowed and fuel flow from the inlet port to the second fuel gallery is prevented, and a second position where fuel flow from the inlet port to the second fuel gallery is allowed and fuel flow from the inlet port to the first fuel gal- lery is prevented. According to another embodiment of the invention, the valve member has a third position, where fuel flow from the inlet port to both the first and the second fuel gallery is allowed. The control valve can be integrated into the fuel injection unit or into the fuel injection pump. According to another embodiment of the invention, the system comprises means for pneumatically actuating the valve member.

Brief description of the drawings

Fig. 1 shows a cross-sectional view of a fuel injection unit according to an embodiment of the invention.

Fig. 2 shows a cross-sectional view of the fuel injection unit of Fig. 1 from another direction.

Fig. 3 shows the fuel injection unit of Fig. 1 in connection with a cylinder head.

Fig. 4 and Fig. 5 show a detailed cross-sectional view of a valve member that controls fuel injection.

Detailed description of the invention

Embodiments of the invention are now described in more detail with reference to the accompanying drawings.

Figures 1 and 2 show a fuel injection unit 1 for a large internal combustion engine, such as an engine that is used in a ship or at a power plant. In figure 3 is shown the same fuel injection unit 1 in connection with a cylinder head 21 of an internal combustion engine. The fuel injection unit 1 is arranged to receive pressurized fuel directly from a fuel injection pump 22. According to the embodiment shown in the figures, the fuel injection unit 1 comprises an injector part 20, a middle part 30, a control valve 9 and a pneumatic actuator 11. The fuel injection unit 1 is connected to the fuel injection pump 22 with a fuel delivery duct 23. Each cylinder 33 of the engine is provided with an own fuel injection pump 22. The fuel injection pump 22 is a high-pressure pump that comprises means for controlling injection timing and the amount of the injected fuel.

The fuel injection unit 1 comprises a body 29, which can consist of several parts. Two fuel injection nozzles 3, 4 are arranged in the injector part 20 of the fuel injection unit 1. The first fuel injection nozzle 3 is intended for injecting large amounts of fuel and the second fuel injection nozzle 4 is intended for injecting small amounts of fuel into a cyl- inder 33 of the engine. The same fuel is injected through both fuel injection nozzles 3, 4. The second fuel injection nozzle 4 can be used for instance when the engine load is 30 percent or less of the maximum load, and the first fuel injection nozzle 3 is used when the engine load is more than 30 percent of the maximum load. Conventionally, fuel injection nozzles have been optimized for the full load, which has led to higher fuel consumption and smoke formation at part load. Also NOx, CO and hydrocarbon emissions have been higher. With two different fuel injection nozzles 3, 4, each nozzle can be optimized for different engine load. It is also possible that the fuel injection nozzles 3, 4 are identical and only one of the nozzles 3, 4 is used at low engine loads and both nozzles 3, 4 are used at high engine loads.

A first fuel gallery 31 is arranged inside the body 29 of the fuel injection unit 1 upstream from the first fuel injection nozzle 3, and a second fuel gallery 32 is arranged upstream from the second fuel injection nozzle 4. The fuel galleries 31, 32 are used for storing the fuel before injection. The fuel injection unit 1 further comprises a first injector needle 7 and a second injector needle 8. The first injector needle 7 opens and closes flow communication between the first fuel gallery 31 and the first fuel injection nozzle 3. The second injector needle 8 opens and closes flow communication between the second fuel gallery 32 and the second fuel injection nozzle 4. The diameter of the second injector needle 8 is smaller than the diameter of the first injector needle 7. Therefore, also the flow area past the second injector needle 8 is smaller than the flow area past the first injector needle 7. The injector needles 7, 8 are pushed towards their closed positions by springs 27, 28. The injector needles 7, 8 are actuated by the pressure of the fuel that is supplied to the fuel injection unit 1 by the fuel injection pump 22. The injection unit 1 further comprises leakage bores 5 for draining leakages out of the injection unit 1.

For choosing through which of the fuel injection nozzles 3, 4 the fuel is injected into the cylinder 33, the fuel injection unit 1 is provided with a control valve 9. The control valve 9 comprises an inlet port 14 that is in flow communication with the fuel inlet 2 of the fuel injection unit 1. The fuel delivery duct 23 from the fuel injection pump 22 is connected to the fuel inlet 2 of the fuel injection unit 1. The control valve 9 further comprises two outlet ports 15, 16. The first outlet port 15 is connected to a first fuel duct 25 that connects the control valve 9 to the first fuel gallery 31 , and the second out- let port 16 is connected to a second fuel duct 26 that connects the control valve 9 to the second fuel gallery 32. The control valve 9 comprises a valve member 10 that has three different positions. In the first position of the valve member 10, fuel flow from the inlet port 14 through the first outlet port 15 to the first fuel duct 25 is allowed. Fuel flow from the inlet port 14 to the second outlet port 16 is prevented. In the second position of the valve member 10, fuel flow from the inlet port 14 through the second fuel port 16 to the second fuel duct 26 is allowed. Fuel flow from the inlet port 14 to the first outlet port 15 is prevented. In the third position of the valve member 10, the valve member 10 is in its middle position, where flow both to the first fuel duct 25 and the second fuel duct 26 is allowed. In the figures is shown a situation where the valve member 10 is in its first position. The second outlet port 16 is thus blocked and flow through the first outlet port 15 into the first fuel duct 25 is allowed. Through the first fuel duct 25, fuel can flow to the first fuel gallery 31. The control valve 9 comprises a spring 17 that pushes the valve member 10 towards the first position.

Instead of being integrated into the fuel injection unit 1, the control valve 9 can also be integrated into the fuel injection pump 22. In that case, separate fuel delivery ducts are needed for the first fuel injection nozzle 3 and the second fuel injection nozzle 4. A first fuel delivery duct from the first outlet port 15 of the control valve 9 would be connected to the first fuel duct 25 of the fuel injection unit 1 and a second fuel delivery duct from the second outlet port 16 would be connected to the second fuel duct 26.

For selecting the position of the control valve 9, the fuel injection unit 1 is provided with an actuator. In the embodiment of the figures, the actuator is a pneumatic actuator 11. However, also other types of actuators can be used, for instance mechanic, hydraulic or electric actuators. In the embodiment of the figures, the actuator 11 comprises a first piston 18 that is arranged in a cylindrical chamber 24. A second piston 12 is arranged inside the first piston 18. The second piston 12 is provided with a rod 19 that is contact with the valve member 10 of the control valve 9. When the pneumatic actuator 11 is not activated, the spring 17 of the control valve 9 pushes via the valve member 10 of the control valve 9 the rod 19 of the second piston 12 upwards. The second piston 12 pushes also the first piston 18 upwards. A spring 13 is arranged above the first piston 18 for pressing the first piston 18 downwards. The spring 13 keeps the first piston 18 in con- tact with the second piston 12 and the rod 19 of the second piston 12 in contact with the valve member 10 of the control valve 9 even when the pneumatic actuator 1 1 is not activated. When pressurized air is introduced between the first piston 18 and the second piston 12, the second piston 12 is pushed downwards, i.e. towards the control valve 9. The rod 19 of the second piston 12 pushes the valve member 10 of the control valve 9 to the second position. This position is used when the engine is operated at low load, for instance at load that is 30 percent or less of the maximum load.

When pressurized air is introduced into the chamber 24 above the first piston 18, the first piston 18 is pushed downwards, i.e. towards the control valve 9. The first piston 18 pushes also the second piston 12 downwards, and the rod 19 of the second piston 12 pushes the valve member 10 of the control valve 9 to the third position. The third position can be used occasionally to prevent sticking of the injector needles 7, 8. For instance, when the engine is operated for a long period of time at high load, the control valve 9 can be switched to the third position for a short period of time to allow fuel injection also through the second nozzle 4. This flushing can take place according to a predetermined schedule.

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.