EP3023628A1

EP3023628A1 - A fuel flow limiting valve for large internal combustion engines

Info

Publication number: EP3023628A1
Application number: EP15192931.2A
Authority: EP
Inventors: Carlo Cocito
Original assignee: OMT Officine Meccaniche Torino SpA
Current assignee: O.M.T. OFFICINE MECCANICHE TORINO S.P.A.
Priority date: 2014-11-21
Filing date: 2015-11-04
Publication date: 2016-05-25
Anticipated expiration: 2035-11-04
Also published as: EP3023628B1; EP3023628B8; KR101800936B1; CN105626341B; CN105626341A; KR20160061252A; DK3023628T3

Abstract

A fuel flow limiting valve for large internal combustion engines, comprising:
- a valve housing (12) including an inner cylindrical surface (24) surrounding a valve chamber (14), an inlet channel (28) with an inlet valve seat (30), an outlet channel (38) with an outlet valve seat (40),
- a valve piston (42) housed in said valve chamber (14) and having a base wall (44) and a cylindrical wall (46), which is guided in a longitudinal direction (A) from said inner cylindrical surface (24) of the valve housing (12), the valve piston (42) having a first sealing surface (52) cooperating with the inlet valve seat (30) and a second sealing surface (54) cooperating with the outlet valve seat (40), the valve piston (42) being movable in said longitudinal direction (A) between a first position in which the first sealing surface (52) closes the inlet valve seat (30) and a second position in which the second sealing surface (54) closes the outlet valve seat (40), and
- an elastic element (58) arranged between the housing (12) and the valve piston (42) and tending to push the valve piston (42) towards said first position,
wherein the first and the second sealing surfaces (52, 54) are machined directly onto said base wall (44) of the valve piston (42) and wherein the valve housing (12) comprises a pin formation (34), which extends in the longitudinal direction within said valve chamber (14).

Description

TEXT OF THE DESCRIPTION

Field of the invention

The present invention relates to a fuel flow limiting valve for large internal combustion engines.
The valve according to the present invention is intended in particular to be used for large marine engines with common rail fuel injection systems.

Description of the prior art

Common rail fuel injection systems have resulted in greater flexibility in the control of internal combustion engines since they enable the selection of the pressure and of the timing of injection, irrespective of the engine speed and the design of the fuel cams, and the modulation of the injection flow by means of multiple injections.
All this has been achieved by assigning the pressure generator and injection control functions to various components (high-pressure pump and electronically-controlled injectors, respectively), which were previously delegated to the fuel injection pump.
In this type of injection system, the injectors are continuously connected to the high pressure fuel accumulator, so that the injection can be performed when requested by the injection control unit. It follows that if an injector were to remain locked in the open position due to a malfunction, all the fuel present in the high pressure accumulator would be discharged into the cylinder, with catastrophic consequences for the engine.
Therefore, from the early steps of development of common rail injection systems, there has been a need for a device which limits the amount of fuel injected per cycle from each injector.
A first example of a fuel flow limiting valve for common rail injection systems is described in US3780716 . This document describes a fuel flow limiting valve having an inlet connected to a fuel accumulator and an outlet connected to an injector. The limiting valve comprises a housing and a piston movable within a valve chamber in a rectilinear direction. A helical spring in compression pushes the piston towards the inlet channel of the fuel flow. When the injector opens, the pressure at the outlet of the valve decreases, and the piston starts to move towards the outlet channel. The pressure drop between the upstream and downstream chambers of the piston is such so that it balances, in each position and instant, the spring force and the inertia of the piston itself. In normal operating conditions, the injection is stopped before the piston reaches the outlet valve seat. Therefore, the pressure levels in the chambers upstream and downstream of the piston reach values that allow the spring to push the piston back to its original position. Conversely, in the case in which the injection becomes excessively long, the piston reaches the outlet valve seat and closes the connection to the injector, therefore ending the injection and avoiding further discharges of the high pressure accumulator.
In large internal combustion engines, especially diesel engines operating with heavy fuel oil, there is a requirement to heat the fuel up to 120-160°C to reduce its viscosity and to allow the optimal pumping and atomization. To allow the starting of an engine with this fuel, all the components of the injection system must be kept warm, to ensure that the viscosity does not increase to values that prevent fuel injection.
This is carried out by continuously circulating hot fuel at low pressure in the injection system from the accumulators to the injectors. The injectors are provided with a circulation valve which opens a passage towards the fuel tank when the fuel is maintained at a low pressure, and closes this passage when the pressure is increased. In this way, both the circulation at low pressure and the normal operation at high pressure are possible. If the valve seat of the injector is not in a perfect condition due to wear of the components, the fuel can flow out through the seat of the injector and reach the cylinder during circulation at low pressure. As large marine engines may remain in circulation mode for several days, this loss could cause serious problems because of serious damage which could occur when restarting the engine with a cylinder full of fuel.
For this reason, it is necessary to prevent the circulation of fuel in the area of the seat of the injection needle, by arranging a valve upstream of this area designed to hermetically close the fuel pressures typical of the circulation mode and suitable for opening the fuel passage above these pressure levels to allow normal operation. In other words, a preloaded non-return valve is required.
This function can be integrated into the flow limiting valve by adding a second valve seat to the inlet fluid channel and which cooperates with a corresponding sealing element formed on the piston of the flow limiting valve. In this way, an important safety function is added without requiring an additional component.
A particular embodiment of this concept is described in EP2423498 . This document describes a pressure limiting valve comprising a valve housing having a cylindrical surface which surrounds a valve chamber, an inlet channel with an inlet valve seat, and an outlet channel with an outlet valve seat. In the valve chamber, a valve piston having a cylindrical wall is housed, which is guided in a longitudinal direction by the inner cylindrical surface of the valve housing. The valve piston carries a closing element in pin-form, elongated in the longitudinal direction and having sealing surfaces at its opposite ends, which cooperate with the inlet valve seat and the outlet valve seat, respectively.
This arrangement is such that the machining of the piston and of the closing element in pin-form in one piece is not always feasible or convenient because of the deep recess which must be provided in the piston to accommodate the spring. This leads to the necessity of producing the piston and the closing element in pin-form in two separate parts which are fixed together, and to subsequently perform precision machining operations to ensure the coaxiality of the seats and the guide surface. In the absence of these machining operations, the sealing of the valve seats would be compromised.

Object and summary of the invention

The present invention has the object of providing a fuel flow limiting valve which overcomes the limits of the prior art. In particular, the present invention aims to reduce production costs, increase the reliability of operation and decrease the pressure drop required to accelerate the piston, thereby improving the dynamic behavior of the fuel flow limiting valve.
According to the present invention, these objects are achieved by a fuel flow limiting valve having the characteristics forming the subject of claim 1.
The claims form an integral part of the disclosure provided here in relation to the invention.

Brief description of the drawings

The present invention will now be described in detail, with reference to the attached drawings, given purely by way of non-limiting example, in which Figures 1 and 2 are axial cross-sections of a fuel flow limiting valve according to the present invention in a first and a second working position.

Detailed description

With reference to the drawings, 10 indicates a fuel flow limiting valve intended to be used in common rail injection systems for large internal combustion engines. The fuel flow limiting valve 10 comprises a valve housing 12 in which a valve chamber 14 is defined. The valve housing 12 is formed by a first housing body 16 and a second housing body 18 fixed to each other.
The first housing body 16 comprises a bottom wall 20 and a side wall 22 extending from said bottom wall 20 and having an inner cylindrical surface 24 surrounding a valve chamber 14. The side wall 22 of the first housing body 16 has an open end portion 26 in which the second housing body 18 is inserted and fixed. In the bottom wall 20 of the first housing body 16 an inlet channel 28 is formed, which communicates with the valve chamber 14. The inner end of the inlet channel 28 has an inlet valve seat 30. In the illustrated example, the inlet valve seat is formed by a concave conical surface.
The second housing body 18 comprises, in a unitary body, a base 32 and a pin formation 34, which extends within the valve chamber 14 along a longitudinal axis A. The base 32 of the second housing body 18 is sealingly fixed to the open end portion 26 of the first housing body 16. The pin formation 34 protrudes from an inner surface 36 of the base 32. An outlet channel 38 is formed within the pin formation 34, which communicates with the valve chamber 14. An outlet valve seat 40 is formed at the inner distal end of the pin formation 34. In the illustrated example, the outlet valve seat 40 is a convex surface with a spherical shape.
The valve 10 comprises a valve piston 42 housed within the valve chamber 14 and movable in the longitudinal direction A. The valve piston 42 is formed by a unitary body having a base wall 44 and a cylindrical wall 46. The cylindrical wall 46 has an outer cylindrical surface 48, which is in guiding contact with the inner cylindrical surface 24 of the first housing body 16.
The base wall 44 of the valve piston 42 has an integral protrusion 50 located on the side facing the bottom wall 20 of the first housing body 16. The integral protrusion 50 has a first sealing surface 52 formed by a convex surface which is designed to seal the inlet valve seat 30. The base wall 44 has a second sealing surface 54 located at the side facing the base 32 of the second housing body 18. The second sealing surface 54 is formed by a concave conical surface recessed in the base wall 20 and is intended to seal the outlet valve seat 40. The first sealing surface 52 and the second sealing surface 54 are machined directly onto the base wall 44 of the valve piston 42. The machining of the sealing surfaces 52, 54 can be carried out on the same machine that performs the machining of the outer cylindrical surface 48 of the valve piston 42 so as to ensure the concentricity of the sealing surfaces 52, 54 with respect to the outer cylindrical surface 48, necessary to seal the respective valve seats 30, 40.
The valve piston 42 comprises a calibrated fluid passage which connects together the two parts of the valve chamber 14 located on opposite sides of the valve piston 42. In the illustrated example, the calibrated passage is formed by calibrated holes 56 formed in the base wall 44 of the valve piston 42.
A helical spring in compression 58 is arranged coaxially outside of the pin formation 34. A first end of the spring 58 rests against the inner surface 36 of the second housing body 18 and a second end of the spring 58 rests against the base wall 44 of the valve piston 42. The helical spring 58 is located internally with respect to the cylindrical wall 46 of the valve piston 42. The helical spring 58 tends to push the valve piston 42 towards the bottom wall 20 of the first housing body 16.
During operation, the inlet channel 28 is connected to the accumulator of a common rail injection system and the outlet channel 38 is connected to an electronically-controlled injector. When the injector is closed, the valve piston 42 is located in the position illustrated in Figure 1. In this position, the first sealing surface 52 sealingly closes the inlet valve seat 30 and prevents the entry of fluid into the valve chamber 14. When the injector opens, the pressure in the valve chamber 14 decreases and the valve piston 42 starts to move towards the outlet valve seat 40. In normal operating conditions, the injection is interrupted before the valve piston 42 reaches the outlet valve seat 40. Therefore, the pressure levels in the valve chamber 14 upstream and downstream of the valve piston 42 reach values that allow the spring 58 to return the valve piston 42 to the closed position of the inlet valve seat 30. The valve piston 42 must return back to the closed position of the inlet valve seat 30 before performing the subsequent injection. The closing speed is determined by the designer with an appropriate choice of the spring force and the sizes of the calibrated holes 56.
When the injection duration becomes excessively long, the valve piston 42 reaches the position illustrated in Figure 2. In this position, the second sealing surface 54 of the valve piston 42 sealingly closes the outlet valve seat 40. In this way, the injection is interrupted and prevents further discharge of fuel from the high pressure accumulator. The respective cylinder of the engine remains deactivated, but over-fueling and stopping of the engine is prevented due to a lack of injection pressure.
The maximum volume of fuel injection depends on the volume of the valve chamber 14 downstream of the valve piston 42 and on the flow passing through the calibrated holes 56 during the movement of the valve piston 42 towards the outlet valve seat 40.
The design of the valve according to the present invention reduces the number of components and the number of precision machining operations required for constructing the valve. In particular, each of the three main components of the valve (the first housing body 16, the second housing body 18 and the valve piston 42) is constituted by a single metallic piece. The machining of the sealing surfaces and the guide surfaces can be carried out in a simple and rapid manner because the geometry of the components does not envisage areas located in difficult-to-reach positions to be machined with the tool. The total mass of the moving parts (or rather only the valve piston 42) is reduced by 20% compared to an execution according to EP2423498 . The reduction of the inertia force and the pressure drop between the upstream and downstream chambers of the piston 42 in the acceleration step is therefore considerable. This enables higher pressure injections during the opening step of the injector.
Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to those described and illustrated without thereby departing from the scope of the invention as defined by the following claims.

Claims

A fuel flow limiting valve for large internal combustion engines, comprising:
- a valve housing (12) including an inner cylindrical surface (24) surrounding a valve chamber (14), an inlet channel (28) with an inlet valve seat (30), an outlet channel (38) with an outlet valve seat (40),

- a valve piston (42) housed in said valve chamber (14) and having a base wall (44) and a cylindrical wall (46), which is guided in a longitudinal direction (A) from said inner cylindrical surface (24) of the valve housing (12), the valve piston (42) having a first sealing surface (52) cooperating with the inlet valve seat (30) and a second sealing surface (54) cooperating with the outlet valve seat (40), the valve piston (42) being movable in said longitudinal direction (A) between a first position in which the first sealing surface (52) closes the inlet valve seat (30) and a second position in which the second sealing surface (54) closes the outlet valve seat (40), and

- an elastic element (58) arranged between the housing (12) and the valve piston (42) and tending to push the valve piston (42) towards said first position, characterized in that the first and the second sealing surfaces (52, 54) are machined directly onto said base wall (44) of the valve piston (42) and in that the valve housing (12) comprises a pin formation (34), which extends in the longitudinal direction within said valve chamber (14), wherein said outlet channel (38) extends through said pin formation (34) and wherein said outlet valve seat (40) is formed at an inner distal end of said pin formation (34).
A flow limiting valve according to claim 1, characterized in that the valve housing (12) comprises a first housing body (16) including a bottom wall (20) and a side wall (22) extending from said bottom wall (20) and having an open end portion (26), and in that said pin formation (34) is integrally formed in a second housing body (18) sealingly fixed to said open end portion (26) of the first housing body (16).
A flow limiting valve according to claim 2, characterized in that said elastic element (58) is a helical compression spring arranged outside of said pin formation (34) and within said cylindrical wall (46) of the valve piston (42).
A flow limiting valve according to claim 1, characterized in that the first sealing surface (52) is a convex surface formed on an integral protrusion (50) of the base wall (44) of the valve piston (42).
A flow limiting valve according to claim 1, characterized in that the second sealing surface (54) is a concave surface recessed in the base wall (44) of the valve piston (42).