AN ELECTRICALLY CONTROLLED INJECTOR FOR ALTERNATIVE FUELS

Abstract

 An injector for alternative fuels, comprising:
- a body (14) including an injection chamber (16) provided with a valve seat (20) and a needle guide surface (34),
- a fuel supply line (22) that supplies pressurized fuel to the injection chamber (16),
- an injection needle (30) having a sliding surface (58) that cooperates with the needle guide surface (34) to guide the movement of the injection needle (30) between a closed position and an open position and vice versa, wherein an annular gap (66) is formed between the sliding surface (58) of the injection needle (30) and the needle guide surface (34),
- a control piston (70) having a first end (72) facing a control chamber (18), wherein a lubrication line (76) places the annular gap (66) in fluid communication with the control chamber (18), so that during operation the annular gap (66) is filled with control fluid.

Description

Field of the invention

[0001] The present invention relates to an electrically controlled injector, particularly for common-rail diesel engines.

[0002] More specifically, the invention concerns an electrically controlled injector for alternative fuels, in which the opening and closing commands of the injector are controlled by a control fluid different from the injected fuel.

[0003] The invention has been developed particularly for large engines, used - for example - in marine engines or in power plants.

Prior art

[0004] A traditional common-rail injection system includes a pump that pressurizes the fuel in a high-pressure accumulator (common-rail) that supplies the injectors. The injectors are equipped with a valve seat and a needle that moves between a closed position and an open position.

[0005] The pressurized fluid is simultaneously supplied to an injection chamber and a control chamber. The fluid pressure in the injection chamber acts in the direction of opening the injection needle. The fluid pressure in the control chamber generates a hydraulic force that acts in the direction of closing the injection needle.

[0006] An electrically controlled control valve modulates the hydraulic pressure in the control chamber. Opening the control valve causes a pressure reduction in the control chamber to the point where the force acting to open the injection needle is greater than the force acting to close it. In this condition, the injection needle lifts from the valve seat, thus causing the injection of fuel. To end the injection, the electrical command to the control valve is deactivated, causing the valve to close and the pressure in the control chamber to rise until the force acting in the closing direction is greater than the force acting in the opening direction, resulting in the movement of the injection needle towards the closed position.

[0007] The fuels traditionally used for large internal combustion engines are fossil fuels derived from petroleum distillation, typically LFO (Light Fuel Oil) and MFO (Marine Fuel Oil).

[0008] Fossil fuels for marine engines cause levels of atmospheric pollution that are not compatible with the latest anti-pollution regulations.

[0009] For this reason, alternative fuels obtained from renewable sources are gaining increasing attention in the maritime sector, as the need to reduce greenhouse gas emissions and promote sustainability becomes more urgent.

[0010] The most commonly used alternative fuels in the maritime sector as substitutes for fossil fuels are typically methanol, ammonia, and hydrogen.

[0011] The adoption of alternative fuels for marine engines is an important step toward reducing carbon oxide emissions.

[0012] However, it is essential to consider the risks associated with these new fuels. Methanol is toxic if inhaled or absorbed through the skin, is highly volatile, and extremely flammable. Ammonia is highly toxic to humans. Exposure can cause irritation to the eyes, skin, and respiratory tract. At high concentrations, it can be lethal. Additionally, ammonia is flammable and can form an explosive mixture with air. Hydrogen is not toxic but can be dangerous in case of leaks as it is highly volatile and flammable, requiring special attention during handling and storage.

[0013] Therefore, it is crucial to adopt strict safety measures for the handling, storage, and use of these alternative fuels.

[0014] If the fuel is toxic or flammable, it is not advisable to use the same fuel as the control fluid to operate the opening and closing of the injector. In this case, a fluid different from the fuel is generally used as the control fluid.

[0015] When the fuel is gaseous or liquid with low viscosity, it is also necessary to keep the injector needle guide lubricated and to prevent fuel leakage through the guide.

[0016] In general, in this type of injector, to ensure that the injector needle guide is well lubricated, an intermediate groove of the injector needle guide is supplied with a viscous oil, which generally also acts as a sealing element against fuel leakage through the needle guide.

[0017] In known solutions, the intermediate groove of the injector needle guide is connected to a sealing oil line. In some cases, the intermediate groove of the injector needle guide is connected to the control oil supply line, but it must be ensured that the pressure in said groove always remains higher than the pressure in the injection chamber to avoid fuel leakage.

[0018] These known solutions result in increased size of the injector and considerable additional complexity to ensure the sealing of the additional line for sealing oil.

Object and summary of the invention

[0019] The object of the present invention is to provide an electrically controlled injector for alternative fuels that overcomes the problems of the prior art.

[0020] According to the present invention, this object is achieved by an injector having the features set forth in claim 1.

[0021] Preferred embodiments are the subject of the dependent claims.

Brief description of the drawings

[0022] The present invention will now be described in detail with reference to the accompanying drawings, provided purely by way of non-limiting example, in which:

• Figure 1 is a schematic longitudinal section of an injector according to the present invention,
• Figure 2 is a schematic longitudinal section of a second embodiment of an injector according to the present invention, and
• Figure 3 is a schematic enlarged detail of the part indicated by the arrow II in Figure 2.

Detailed description

[0023] With reference to Figures 1 and 2, 10 denotes an injection system for large combustion engines, such as marine engines or power plant engines.

[0024] The injection system 10 comprises an injector 12 having a body 14 in which an injection chamber 16 and a needle guide surface 34 are formed. The injection chamber 16 is provided with a valve seat 20 and injection holes 60.

[0025] The injector 12 comprises a fuel supply line 22 that supplies pressurized fuel to the injection chamber 16. The injector 12 is configured to inject an alternative fuel from renewable sources, which may be, for example, methanol, ammonia, or hydrogen. The fuel supply line 22 receives fuel from a fuel accumulator 40 that is pressurized to a pressure p_F by a fuel pump 62. A flow-limiting valve (not shown) may be arranged between the fuel accumulator 40 and the injection chamber 16.

[0026] The injector 12 comprises an injection needle 30 having a closing surface 32 that cooperates with the valve seat 20 and a sliding surface 58 that cooperates with the needle guide surface 34 to guide the movement of the injection needle 30 along a longitudinal axis X between a closed position and an open position and vice versa. An annular gap 66 is formed between the sliding surface 58 of the injection needle 30 and the needle guide surface 34, which can have a thickness between 1 and 50 µm.

[0027] The injector 12 comprises a control circuit 52 including: a control chamber 18, an inlet line 23 for supplying a control fluid to the control chamber 18, an exhaust line 28 for connecting the control chamber 18 to an exhaust volume 54, and an electrically controlled control valve 26 for selectively opening and closing a hydraulic communication between the control chamber 18 and the exhaust line 28. The inlet line 23 is provided with a calibrated inlet orifice 24.

[0028] The injector 12 is configured to operate with a control fluid different from the fuel and having a substantially higher viscosity than the viscosity of the fuel. The control fluid Cf may be an oil, for example, lubricating oil: SAE 40, SAE 30, or equivalent; fuel oil: LFO, MFO, or similar.

[0029] The inlet line 23 receives the control fluid from a control fluid accumulator 44 that is pressurized to a pressure p_CTRL by a control fluid pump 64. The control fluid pressure p_CTRL in the control fluid accumulator 44 is higher than the fuel pressure p_F in the fuel accumulator 40.

[0030] The injector 12 comprises a control piston 70 having a first end 72 facing the control chamber 18.

[0031] The control piston 70 may be formed as an integral extension of the injection needle 30, as shown in Figure 1, or it may be a separate component from the injection needle 30, coaxial to the injection needle 30 and movable along the longitudinal axis X, as shown in Figure 2.

[0032] If the control piston 70 is a separate component from the injection needle 30, the control piston 70 has a second end 74, opposite the first end 72, which is pressed against the head surface 56 of the injection needle 30.

[0033] The injector 12 comprises a lubrication line 76 extending through the control piston 70 and through the injection needle 30. The lubrication line 76 places the annular gap 66 in fluid communication with the control chamber 18 so that during operation the annular gap 66 is filled with control fluid.

[0034] The lubrication line 76 extends between the first end 72 of the control piston 70 and the sliding surface 58 of the injection needle 30.

[0035] The lubrication line 76 may include a control orifice 108 that regulates the pressure and flow rate of the control fluid directed toward the annular gap 66.

[0036] With reference to Figures 2 and 3, when the control piston 70 is formed as a separate component from the injection needle 30, the lubrication line 76 comprises a first channel 78 extending between the first end 72 and the second end 74 of the control piston 70, and a second channel 80 extending between the head surface 56 and the sliding surface 58 of the injection needle 30. The first channel 78 and the second channel 80 communicate with each other through respective holes 82, 84 open on mutually contacting surfaces 86, 88 of the second end 74 of the control piston 70 and the head surface 56 of the injection needle 30.

[0037] The mutually contacting surfaces 86, 88 may have spherical or toroidal concave and convex shapes.

[0038] With reference to Figures 1 and 2, the lubrication line 76 may have a longitudinal section 90 and a radial section 92 open on the sliding surface 58 of the injection needle 30.

[0039] The needle guide surface 34 may have an annular groove 94, and the radial section 92 of the lubrication line 76 may have at least one outlet hole 96 facing the annular groove 94.

[0040] In a possible embodiment, the annular groove 94 may be formed on the sliding surface 58 of the injection needle 30, and the outlet hole 96 of the lubrication line 76 may be open in the annular groove 94.

[0041] In possible embodiments, a first annular groove may be provided on the surface of the needle guide 34 and a second annular groove on the sliding surface 58 of the injection needle 30.

[0042] The body 14 may comprise a first body section 100 in which the control chamber 18 and a piston guide surface 104 to guide the control piston 70 are formed, and a second body section 102 in which the injection chamber 16 and the needle guide surface 34 are formed.

[0043] The first body section 100 may include an intermediate chamber 106 extending between the needle guide surface 34 and the piston guide surface 104. One or more compression springs 50 that press the control piston 70 against the head surface 56 of the injection needle 30 may be housed in the intermediate chamber 106.

[0044] Between the first and second body sections 100, 102, an interface section 110 is defined, which fluidly communicates with the annular gap 66 and is fluidly connected to an exhaust line 112.

[0045] The position of the injection needle 30 is determined by the balance between the forces of the springs 50 and the hydraulic forces generated by the action of the pressurized fuel and the control fluid on the respective influence surfaces.

[0046] The pressurized fuel contained in the injection chamber 16 upstream of the valve seat 20 acts in the direction of lifting the injection needle 30 from the valve seat 20.

[0047] The electrically actuated control valve 26 modulates the pressure of the control fluid in the control chamber 18, generating a force that acts on the control piston 70 in the direction of closing the injection needle 30.

[0048] The opening of the control valve 26 causes a reduction in the pressure in the control chamber 18 to the point where the force acting to lift the injection needle 30 prevails over the force acting to keep it closed, causing the injection needle 30 to rise from the valve seat 20, thus allowing the injection of fuel through the injection holes 60.

[0049] As long as the control valve 26 remains open, the control fluid contained in the control chamber 18 remains at an intermediate pressure between the pressure in the inlet line 23 and the pressure in the exhaust line 28.

[0050] The section of the calibrated inlet orifice 24 is designed to ensure that the pressure in the control chamber 18 is sufficiently low to keep the injection needle stationary in its maximum lift position.

[0051] When the control valve 26 closes, the control chamber 18 remains in communication only with the inlet line 23. The flow of control fluid that continues to enter through the calibrated inlet orifice 24 during this phase causes the injection needle 30 to move toward the closed position.

[0052] Since the control fluid in the inlet line 23 is at a pressure p_CTRL higher than the fuel pressure p_F, when the injection needle 30 is closed and at rest, between one injection and the next, there is a continuous leakage of control fluid from the control chamber 18 towards the injection chamber 16, ensuring that the annular gap 66 is completely filled with control fluid that lubricates the needle guide surface 34 and the sliding surface 58.

[0053] In the solution according to the present invention, the annular gap 66 is not supplied through channels formed in the body 14 but instead utilizes a spillover of the control fluid contained in the control chamber 18, which supplies the annular groove 94 through the lubrication line 76 extending inside the control piston and the injection needle 30.

[0054] This solution makes the injector 12 more compact and with a simpler structure to manufacture. Moreover, this solution reduces the forces required to ensure sealing at the separation planes of the different parts 100, 102 that make up the injector.

[0055] The present invention could be applied in all cases where it is necessary to inject a liquid or gaseous fuel with a viscosity much lower than the fluid (typically oil) used to control the opening and closing of the injector. The solution according to the present invention is particularly advantageous for common-rail injectors for four-stroke engines powered by methanol, ammonia, or gas.

[0056] Of course, while remaining within the principle of the invention, the construction details and embodiments may be widely varied from what has been described and illustrated without thereby departing from the scope of the invention as defined by the following claims.

Claims

1. An injector for internal combustion engines, comprising:

- a body (14) including an injection chamber (16) provided with a valve seat (20) and a needle guide surface (34),

- a fuel supply line (22) feeding pressurized fuel to said injection chamber (16),

- a control circuit (52) including: a control chamber (18), an inlet line (23) for supplying a control fluid to said control chamber (18), a exhaust line (28) for connecting the control chamber (18) to a discharge volume (54), and an electrically operated control valve (26) for selectively opening and closing a hydraulic communication between the control chamber (18) and the exhaust line (28),

- an injector needle (30) having a closing surface (32) which cooperates with said valve seat (20), and a sliding surface (58) which cooperates with said needle guide surface (34) to guide a movement of the needle injector (30) along a longitudinal axis (X) between a closed position and an open position and vice versa, wherein an annular gap (66) is formed between the sliding surface (58) of the injector needle (30) and the needle guide surface (34) in communication with the injection chamber (16), and

- a control piston (70) having a first end (72) facing into said control chamber (18), wherein a lubrication line (76) extends through the control piston (70) and places said annular gap (66) in fluid communication with the control chamber (18), so that in operation said annular gap (66) is filled with control fluid.

2. The injector of claim 1, wherein said control piston (70) is a separate component from the injector needle (30) and has a first end (72) facing into said control chamber (18) and a second end (74) pressed against a head surface (56) of the injector needle (30), wherein the lubrication line (76) extends through the control piston (70) and through the injector needle (30) and places said annular gap (66) in fluid communication with the control chamber (18).

3. The injector of claim 2, wherein said lubrication line (76) includes a first channel (78) extending between the first end (72) and the second end (74) of the control piston (70), and a second channel (80) which extends between the head surface (56) and the sliding surface (58) of the injector needle (30).

4. The injector of claim 3, wherein the first channel (78) and the second channel (80) communicate with each other through respective holes (82, 84) open on mutual contacting surfaces (86, 88) of the second end (74) of the control piston (70) and the head surface (56) of the injector needle (30).

5. The injector of claim 2 or claim 3, wherein said second channel (80) has a longitudinal section (90) open on said head surface (56) and a radial section (92) open on said sliding surface (58) of the injector needle (30).

6. The injector of any of the preceding claims, wherein said needle guide surface (34) has an annular groove (94) and wherein the radial section (92) of said second channel (80) has at least one outlet hole (96) facing said annular groove (94).

7. The injector of any of claims 1 to 5, wherein said sliding surface (58) of the injector needle (30) has an annular groove (94) and wherein the radial section (92) of said second channel (80) has at least one outlet hole (96) open in said annular groove (94).

8. The injector of any of the preceding claims, wherein the body (14) comprises a first body section (100) in which the control chamber (18) and a piston guide surface (104) in which said control piston (70) is guided are formed, and a second body section (102) in which the injection chamber (16) and the needle guide surface (34) are formed.

9. The injector of claim 8, wherein the first body section (100) includes an intermediate chamber (106) which extends between the needle guide surface (34) and the piston guide surface (104) and in which a compression spring (50) is housed which presses the injector needle (30) against said valve seat (20).

10. The injector of claim 8 or claim 9, wherein an interface section (110) between the first and second body sections (100, 102) fluidly communicates with said annular gap (66) and is fluidly connected to an exhaust line (112).

Drawing