WO2017032917A1

WO2017032917A1 - Safety valve arrangement

Info

Publication number: WO2017032917A1
Application number: PCT/FI2015/050550
Authority: WO
Inventors: Janne ENLUND; Ossi LAAKSO
Original assignee: Wärtsilä Finland Oy
Priority date: 2015-08-26
Filing date: 2015-08-26
Publication date: 2017-03-02

Abstract

The safety valve arrangement (8) for a fuel injection system of a piston engine (1) comprises a valve body (30) having a fuel inlet (13) that is connectable to the high-pressure side of the fuel injection system and a fuel outlet (15) that is connectable to a pressure release duct (9), a valve member (12) that is movable between a closed position preventing fuel flow between the fuel inlet (13) and the fuel outlet (15), and an open position allowing fuel flow between the fuel inlet (13) and the fuel outlet (15), and means (17) for biasing the valve member (12) towards the closed position. The biasing means comprise an air spring portion (17) that is provided with a fluid chamber (28) and with a first piston (18) arranged in the fluid chamber (28), wherein the air spring portion (17) is configured to direct a force at the valve member (12) for biasing the valve member (12) towards the closed position when pressure is applied on the first piston (18).

Description

Safety valve arrangement Technical field of the invention

The present invention relates to a safety valve arrangement for a fuel injection system of a piston engine in accordance with the preamble of claim 1 .

Background of the invention

In piston engines, where fuel is injected directly into the cylinders, the pressure in the fuel injection system can be very high. For example in a common rail fuel injection system the pressure can be up to 3000 bar. To prevent overpressure in the fuel injection system, it is important that the high-pressure side of the fuel injection system is provided with a reliable safety valve (pressure relief valve). A conventional safety valve comprises a mechanical spring, usually a helical spring made of steel, which is used for biasing a valve member towards a closed position. When the hydraulic force created by the pressure in the fuel injection system exceeds the pretensioning force of the spring, the safety valve opens and releases pressure from the fuel injection system. Safety valves with mechanical springs are widely available for different pressure ranges and they are also inexpensive. However, the lifetime of the mechanical springs is limited and the properties of the mechanical safety valves are not optimal for the use in fuel injection systems.

Summary of the invention

An object of the present invention is to provide an improved safety valve arrangement for a high pressure side of a fuel injection system of a piston en- gine. The safety valve arrangement comprises a valve body having a fuel inlet that is connectable to the high-pressure side of the fuel injection system and a fuel outlet that is connectable to a pressure release duct, a valve member that is movable between a closed position, in which position the valve member prevents fuel flow between the fuel inlet and the fuel outlet, and an open position, in which position the valve member allows fuel flow between the fuel inlet and the fuel outlet, the safety valve arrangement further comprising means for bias- ing the valve member towards the closed position. The characterizing features of the arrangement according to the invention are given in the characterizing part of claim 1 .

According to the invention, the means for biasing the valve member towards the closed position comprise an air spring portion that is provided with a fluid chamber and with a first piston arranged in the fluid chamber, wherein the air spring portion is configured to direct a force at the valve member for biasing the valve member towards the closed position when pressure is applied on the first piston in the fluid chamber. The safety valve which is biased by an air spring has good stability and damping properties. The air spring is also durable and inexpensive to manufacture.

According to an embodiment of the invention, the safety valve arrangement comprises a mechanical spring, which is configured to function as an additional means for biasing the valve member towards the closed position. The mechan- ical spring can be arranged in the fluid chamber. The mechanical spring keeps the safety valve closed even when the fluid chamber is pressureless, provided that the fuel pressure is sufficiently small.

According to an embodiment of the invention, the fluid chamber is provided with a second piston, which is configured to eliminate the biasing force of the mechanical spring when a predetermined pressure is applied on the second piston. In normal operation, the safety valve is thus kept closed solely by the air spring.

According to an embodiment of the invention, the pressure in the fluid chamber is adjustable.

Brief description of the drawings

Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which

Fig. 1 shows schematically a common rail fuel injection system of a piston en- gine, Fig. 2 shows a safety valve arrangement according to an embodiment of the invention in a pressureless state,

Fig. 3 shows the arrangement of figure 2 when the fluid chamber is pressurized, and Fig. 4 shows the arrangement of figures 2 and 3 when the safety valve is open.

Description of embodiments of the invention

In figure 1 is shown schematically a fuel injection system of a piston engine 1 . The engine 1 is a large internal combustion engine, such as a main or an auxil- iary engine of a ship or an engine that is used at a power plant for producing electricity. In figure 1 is shown an engine 1 with four cylinders 2, but the engine

1 can comprise any reasonable number of cylinders 2, which can be arranged, for instance, in line or in a V-configuration. The fuel injection system of figure 1 is a common rail fuel injection system. The fuel injection system of figure 1 comprises a low-pressure pump 5 and a high-pressure pump 6. The low- pressure pump 5 supplies fuel to the high-pressure pump 6 from a fuel tank 7. A fuel feed duct 1 1 connects the high-pressure pump 6 to the low-pressure pump 5. The fuel is liquid fuel, such as light fuel oil or marine diesel oil. The high-pressure pump 5 supplies fuel to a fuel rail 4, where the fuel is stored at a high pressure before fuel injection. A high-pressure duct 10 connects the high- pressure pump 6 to the fuel rail 4. Each cylinder 2 of the engine 1 is provided with a fuel injector 3, which is arranged to inject the fuel directly into the cylinder 2. Each fuel injector 3 can be individually controlled, for instance electrically, for adjusting the fuel injection timing and the fuel injection amount in each cylinder 2 of the engine 1 .

The low-pressure pump 5 raises the pressure of the fuel to a first pressure level, which is suitable for feeding the high-pressure pump 6. The pressure after the low-pressure pump 5 can be in the range of 5 to 15 bar. The high-pressure pump 6 raises the pressure of the fuel from the first pressure level to a second pressure level, which is suitable for injecting the fuel directly into the cylinders

2 of the engine 1 . The second pressure level is higher than the first pressure level. The second pressure level can be for instance in the range of 800 to 3000 bar. The part of the fuel injection system that is downstream from the high-pressure pump 6 forms a high-pressure side of the fuel injection system. Although figure 1 shows only one low-pressure pump 5, high-pressure pump 6 and fuel rail 4, the fuel injection system could comprise several low-pressure pumps 5, high-pressure pumps 6 and/or fuel rails 4 or other fuel accumulators. For instance, each cylinder 2 of the engine 1 could be provided with an own fuel accumulator.

To regulate the pressure on the high-pressure side of the fuel injection system and to prevent excessive pressures, the fuel injection system is provided with a safety valve arrangement 8, which is connected to the high-pressure side of the fuel injection system. Via the safety valve arrangement 8, fuel can be released from the high-pressure side of the fuel injection system into a pressure release duct 9. Via the pressure release duct 9, the fuel can be supplied back to the tank 7. The safety valve arrangement 8 is configured to open fluid communication between the high-pressure side of the fuel injection system and the pressure release duct 9 when the pressure on the high-pressure side exceeds a predetermined limit value.

Figures 2 to 4 show a simplified cross-sectional view of a safety valve arrangement 8 according to an embodiment of the invention. The safety valve arrangement 8 comprises a valve portion 16 and an air spring portion 17. The valve portion 16 and the air spring portion 17 can be either separate units or they can form a single module. The valve portion 16 comprises a valve body 30, which is provided with a fuel inlet 13 and a fuel outlet 15. A valve member 12 is arranged inside the valve body 30 for opening and closing fluid communication between the fuel inlet 13 and the fuel outlet 15. The valve member 12 has a closed position, in which fuel flow from the fuel inlet 13 to the fuel outlet 15 is prevented, and an open position, in which fuel flow from the fuel inlet 13 to the fuel outlet 15 is allowed. In figures 2 and 3 the valve member 12 is in the closed position and in figure 4 the valve member 12 is in the open position. The valve body 30 is provided with a valve seat 14, against which the valve member 12 rests in the closed position. In the embodiment of the figures, the fuel inlet 13 is arranged at a first end of the valve body 30. The fuel outlet 15 is arranged in a cylindrical side wall of the valve body 30. The fuel inlet 13 and the fuel outlet 15 could also be arranged in many different ways. The valve portion 16 is configured so that the pressure in the fuel inlet 13 pushes the valve member 12 towards the open position. The valve member 12 is biased towards the closed position by the air spring portion 17. The valve member 12 moves towards the open position when the force created by the pressure on the high-pressure side of the fuel injection system exceeds the force created by the air spring portion 17.

The air spring portion 17 comprises a fluid chamber 28. The fluid chamber 28 has a first end 28a and a second end 28b. A first piston 18 is arranged inside the fluid chamber 28. The first piston 18 is movable in the longitudinal direction of the fluid chamber 28, i.e. in the direction from the first end 28a towards the second end 28b. A closed space 31 is formed between the second end 28b of the fluid chamber 28 and the first piston 18. The volume of the closed space 31 thus depends on the position of the first piston 18. In the embodiment of the figures, the fluid chamber 28 is open at the first end 28a. The first piston 18 thus forms a movable end wall of the fluid chamber 28. The fluid chamber 28 is provided with a fluid inlet 22, through which pressurized air can be introduced into the fluid chamber 28 between the first piston 18 and the second end 28b of the fluid chamber 28. In the embodiment of the figures, the fluid inlet 22 is arranged in the cylindrical side wall of the fluid chamber 28, but the fluid inlet could also be in the first piston 18 or in the end wall at the second end 28b of the fluid chamber 28. A pressure medium duct 24 connects the fluid inlet 22 to a pressure medium source 26. The pressure medium source can be a com- pressor or an air tank. The pressure medium duct 24 is provided with a check valve 23, which allows air flow towards the fluid chamber 28, but prevents flow in the opposite direction. A pressure adjusting device 25 is connected to the pressure medium duct 24 for regulating the pressure in the pressure medium duct 24.

The first piston 18 is in force transmission connection with the valve member 12 of the safety valve arrangement. The first piston 18 can thus exert a force on the valve member 12 for biasing it towards the closed position. In the embodiment of the figures, the safety valve arrangement is provided with a push rod 29 that is arranged between the first piston 18 and the valve member 12. There is thus a mechanical force transmission connection between the first piston 18 and the valve member 12. However, the first piston 18 and the valve member 12 could also be in hydraulic force transmission connection with each other. The valve member 12 could also be integral with the first piston 18. The diameter of the first piston 18 is significantly larger than the diameter of the valve member 12. A relatively small pressure in the fluid chamber 18 can thus create a force that exceeds the force created by the hydraulic pressure that affects the valve member 12.

The air spring portion 17 of the safety valve arrangement 8 comprises a second piston 20, which is arranged in the fluid chamber 28. Also the second pis- ton 20 is movable in the longitudinal direction of the fluid chamber 28, i.e. co- axially with the first piston 18. The second end 28b of the fluid chamber 28 is provided with an opening 21 , which is closed by the second piston 20. A pressure applied on the second piston 20 creates a force that is directed away from the first piston 18, i.e. towards the second end 28b of the fluid chamber 28. The second end 28b of the fluid chamber 28 is provided with a section with a reduced diameter, and the second piston 20 is arranged to be movable in the area of the reduced diameter. The diameter of the second piston 20 is thus smaller than the diameter of the first piston 18.

The air spring portion 17 is provided with a mechanical spring 19, which is con- figured to bias the second piston 20 towards the first end 28a of the fluid chamber 28. In the embodiment of the figures, the mechanical spring 19 is a helical spring, which is arranged inside the fluid chamber 28. The piston 20 is provided with a flange 27, which supports one end of the spring 19. One end of the spring 19 is supported against the second end 28b of the fluid chamber 28. When the pressure in the fluid chamber 28 equals the atmospheric pressure, the spring 19 urges the flange 27 against the first piston 18, as shown in figure 2. The spring 19 thus creates a biasing force that pushes the valve member 12 of the valve portion 16 towards the closed position. The spring 19 works as an additional biasing means, which keeps the valve member 12 in the closed po- sition even when the fluid chamber 28 is pressureless, provided that the pressure on the high-pressure side of the fuel injection system is sufficiently small.

In figure 3 is shown a situation, where the pressure in the fluid chamber 28 is raised. The pressure inside the fluid chamber 28 creates a force, which pushes the second piston 20 towards the second end 28b of the fluid chamber 28. In the situation of figure 3 the force created by the pressure exceeds the preten- sioning force of the spring 19 and the second piston 20 has moved to a position, where the pneumatic force and the spring force are balanced. The pressure applied on the first piston 18 affects in the opposite direction. The first piston 18 thus maintains the position shown in figure 2 and remains in mechanical contact with the valve member 12. A gap 32 is formed between the first piston 18 and the second piston 20. Now the mechanical spring 19 does not affect the biasing force directed at the valve member 12, but the biasing force is created solely by the pressure in the fluid chamber 28. During normal operation of the safety valve arrangement 8, the mechanical spring 19 does thus not expe- rience dynamic forces, which extends the lifetime of the safety valve arrangement 8. Also the stability of the safety valve arrangement 8 is better that in mechanical safety valves.

In figure 4 is shown a situation, where the force created by the hydraulic pressure in the fuel injection system has exceeded the pressure created by the pressure in the fluid chamber 28. The pressure of the fuel has pushed the valve member 12 to the open position. Since the valve member 12 is in force transmission connection with the first piston 18, the first piston 18 has moved towards the second end 28b of the fluid chamber 28.

It will be appreciated by a person skilled in the art that the invention is not lim- ited to the embodiments described above, but may vary within the scope of the appended claims.

Claims

1 . A safety valve arrangement (8) for a fuel injection system of a piston engine (1 ), the fuel injection system comprising at least one fuel injector (3) and at least one high-pressure pump (6) for pressurizing the fuel to be injected through the fuel injector (3), the downstream side of the high-pressure pump (6) forming a high-pressure side of the fuel injection system, the safety valve arrangement (8) comprising a valve body (30) having a fuel inlet (13) that is connectable to the high-pressure side of the fuel injection system and a fuel outlet (15) that is connectable to a pressure release duct (9), a valve member (12) that is movable between a closed position, in which position the valve member (12) prevents fuel flow between the fuel inlet (13) and the fuel outlet (15), and an open position, in which position the valve member (12) allows fuel flow between the fuel inlet (13) and the fuel outlet (15), the safety valve arrangement further comprising means (17) for biasing the valve member (12) towards the closed position, characterized in that the means for biasing the valve member (12) towards the closed position comprise an air spring portion

(17) that is provided with a fluid chamber (28) and with a first piston (18) arranged in the fluid chamber (28), wherein the air spring portion (17) is configured to direct a force at the valve member (12) for biasing the valve member (12) towards the closed position when pressure is applied on the first piston

(18) in the fluid chamber (28).

2. A safety valve arrangement according to claim 1 , wherein the safety valve arrangement comprises a mechanical spring (19), which is configured to function as an additional means for biasing the valve member (12) towards the closed position.

3. A safety valve arrangement according to claim 2, wherein the mechanical spring (19) is arranged in the fluid chamber (28).

4. A safety valve arrangement according to claim 2 or 3, wherein the fluid chamber (28) is provided with a second piston (20), which is configured to eliminate the biasing force of the mechanical spring (19) when a predetermined pressure is applied on the second piston (20).

5. A safety valve arrangement according to any of the preceding claims, wherein the pressure in the fluid chamber (28) is adjustable.

6. A fuel injection system for a piston engine (1 ), the fuel injection system comprising at least one fuel injector (3) and at least one high-pressure pump (6) for pressurizing the fuel to be injected through the fuel injector (3), the downstream side of the high-pressure pump (6) forming a high-pressure side of the fuel injection system, characterized in that a safety valve arrangement (8) according to any of the preceding claims is connected to the high-pressure side of the fuel injection system.