JP6682943B2 - Fuel flow restriction valve for large internal combustion engines - Google Patents

Description

  The present invention relates to fuel flow restriction valves for multiple large internal combustion engines.

  The valve according to the invention is particularly intended for use in large marine engines having multiple common rail fuel injection systems.

  Multiple common rail fuel injection systems allow for pressure selection and injection timing selection, as well as injection flow modulation with multiple injections, regardless of engine speed and multiple fuel cam designs. It has provided greater flexibility in controlling multiple internal combustion engines.

  All of these are by assigning the pressure generator and multiple injection control functions that were previously delegated to the fuel injection pump to the various components (high pressure pump and electrically controlled injector, respectively). Has been realized.

  In this type of injection system, a plurality of injectors are continuously coupled to the high pressure fuel accumulator so that injection can be performed when requested by the injection control unit. From this it follows that if the injector remains locked in the open position due to a malfunction, all the fuel present in the high pressure accumulator is discharged into the cylinder, with multiple catastrophic consequences for the engine. .

  Therefore, from the early stages of the development of multiple common rail injection systems, there has been a need for an apparatus that limits the amount of fuel injected per cycle for each injector.

  A first example of a fuel flow limiting valve for multiple common rail injection systems is described in US Pat. No. 3,780,716. This document describes a fuel flow restriction valve having an inlet connected to a fuel accumulator and an outlet connected to an injector. The restriction valve comprises a piston movable in a linear direction within the housing and the valve chamber. The compression coil spring pushes the piston toward the intake channel of fuel flow. When the injector opens, the valve outlet pressure drops and the piston begins to move towards the outlet channel. The pressure drop between the upstream chamber and the downstream chamber of the piston is such that at each position and moment the spring force and the inertial force of the piston itself are balanced. In normal operating conditions, injection is stopped before the piston reaches the exhaust valve seat. Therefore, the pressure levels upstream and downstream of the piston in the chambers reach values that allow the spring to push the piston back into its original position. Conversely, if the injection is too long, the piston will reach the exhaust valve seat and close the connection to the injector, thus ending the injection and avoiding further depressurization of the high pressure accumulator.

  In large internal combustion engines, especially diesel engines that process heavy oil fuels, it is essential to heat the fuel from 120 to 160 ° C. to reduce the viscosity of the fuel and enable optimal pumping and atomization. Become. In order to be able to start the engine with this fuel, all components of the injection system must be kept warm in order to ensure that the viscosity does not rise to values that hinder the injection of fuel.

  This is done by continuously circulating hot fuel at low pressure from the accumulators to the injectors in the injection system. The injectors are provided with a circulation valve that opens a flow path to the fuel tank when the fuel is maintained at low pressure and closes the flow path when the pressure increases. In this way, both circulation at low pressure and normal operation at high pressure are possible. If the injector valve seat is not in perfect condition due to component wear, fuel can flow out through the injector seat and into the cylinder during low pressure circulation. Since multiple large marine engines can remain in circulation mode for several days, this loss due to severe damage that can occur when restarting an engine with a cylinder filled with fuel can result in multiple serious losses. Can cause problems.

  For this reason, designed to hermetically close the pressure of the fuel typical of circulation modes, above these pressure levels to allow normal operation, suitable for opening the fuel flow path. By arranging the valve upstream of this region, it is necessary to prevent fuel circulation in the region of the needle seat. In other words, a pre-installed check valve is required.

  This feature can be integrated into the flow restriction valve by adding a second valve seat to the fluid intake channel. This second valve seat cooperates with a corresponding sealing element formed on the piston of the flow limiting valve. In this way, important safety features are added without the need for additional components.

  A particular embodiment of this idea is described in EP 2423498. This document describes a pressure limiting valve comprising a valve housing, a suction channel with a suction valve seat, and a valve housing having a cylindrical surface surrounding a discharge channel with a discharge valve seat. A valve piston with a cylindrical wall is housed in the valve chamber, which is guided longitudinally by the inner cylindrical surface of the valve housing. The valve piston is longitudinally elongated and carries pin-shaped sealing elements with sealing surfaces at opposite ends, which cooperate with the intake valve seat and the exhaust valve seat, respectively.

  Due to the deep groove that must be provided in the piston to accommodate the spring, this configuration makes it convenient and convenient to machine the piston and the pin-shaped sealing element as one piece. is not. This has led to the need to manufacture the piston and pin-shaped sealing elements as two separate parts that are fixed together and to carry out subsequent machining to ensure the coaxiality of the seat and guide surfaces. Connect Without these machining processes, sealing of the valve seat would be compromised.

  The present invention has the objective of providing a fuel flow restriction valve that overcomes the limitations of the prior art. In particular, the present invention reduces manufacturing costs, increases operational reliability, and reduces the pressure drop required to accelerate the piston, thereby improving the dynamic behavior of the fuel flow limiting valve. Is intended.

  According to the invention, these objects are achieved by a fuel flow limiting valve having the features forming the subject of claim 1.

  The claims form an integral part of the disclosure provided herein regarding the invention.

The invention will now be described in detail with reference to the accompanying drawings, given purely by way of non-limiting example.
FIG. 3 is an axial cross-sectional view of the fuel flow restriction valve according to the present invention in a first operating position. FIG. 6 is an axial cross-sectional view of the fuel flow restriction valve according to the present invention in a second operating position.

  Referring to the drawings, 10 shows a fuel flow limiting valve intended for use in common rail injection systems of large internal combustion engines. The fuel flow restriction valve 10 includes a valve housing 12 having a valve chamber 14 defined therein. The valve housing 12 is formed by a first housing housing 16 and a second housing housing 18 fixed to each other.

  The first housing housing 16 comprises a bottom wall 20 and a sidewall 22 extending from the bottom wall 20 and having an inner cylindrical surface 24 surrounding the valve chamber 14. The side wall 22 of the first housing housing 16 has an open end 26 into which the second housing housing 18 is inserted and fixed. An intake channel 28 is formed in the bottom wall 20 of the first housing housing 16 in communication with the valve chamber 14. The inner end of the intake channel 28 has an intake valve seat 30. In the example shown, the intake valve seat is formed by a concave conical surface.

  The second housing housing 18 comprises a pin-shaped portion 34 extending along the major axis A in the base 32 and the valve chamber 14 in a single housing. The base 32 of the second housing housing 18 is sealed and fixed to the open end portion 26 of the first housing housing 16. The pin-shaped portion 34 projects from the inner surface 36 of the base 32. The exhaust channel 38 is formed in the pin-shaped portion 34, which communicates with the valve chamber 14. The discharge valve seat 40 is formed at the inner end of the pin-shaped portion 34. In the example shown, the exhaust valve seat 40 is a spherical convex surface.

  The valve 10 has a valve piston 42 housed in the valve chamber 14 and movable in the longitudinal direction A. The valve piston 42 is formed by a single housing having a base wall 44 and a cylindrical wall 46. The cylindrical wall 46 has an outer cylindrical surface 48, which is in inductive contact with the inner cylindrical surface 24 of the first housing housing 16.

  The base wall 44 of the valve piston 42 has an integral projection 50 arranged on the side of the first housing housing 16 facing the bottom wall 20. The integral protrusion 50 has a first sealing surface 52 formed by a convex surface designed to seal the intake valve seat 30. The base wall 44 has a second sealing surface 54 located on the side of the second housing housing 18 facing the base 32. The second sealing surface 54 is formed by a concave conical surface recessed into the base wall 20 and is intended to seal the exhaust valve seat 40. The first sealing surface 52 and the second sealing surface 54 are machined directly on the base wall 44 of the valve piston 42. Machining of the sealing surfaces 52, 54 is accomplished by machining the sealing surfaces 52, 54 to ensure the coaxiality of the sealing surfaces 52, 54 with respect to the outer cylindrical surface 48 required to seal the respective valve seat 30, 40. It may be performed on the same machine that performs the 48 machining operations.

  The valve piston 42 has a calibrated fluid flow path that connects together two portions of the valve chamber 14 that are located on opposite sides of the valve piston 42. In the example shown, the calibrated flow path is formed by a calibrated hole 56 formed in the base wall 44 of the valve piston 42.

  A compression coil spring 58 is arranged coaxially outside the pin-shaped portion 34. The first end of the spring 58 bears against the inner surface 36 of the second housing housing 18, and the second second end of the spring 58 bears against the base wall 44 of the valve piston 42. The coil spring 58 is arranged inside the cylindrical wall 46 of the valve piston 42. The coil spring 58 tends to push the valve piston 42 against the bottom wall 20 of the first housing housing 16.

  In operation, the intake channel 28 is connected to the accumulator of the common rail injection system and the exhaust channel 38 is connected to an electrically controlled injector. When the injector is closed, the valve piston 42 is in the position shown in FIG. In this position, the first sealing surface 52 seals and closes the intake valve seat 30 and prevents fluid from entering the valve chamber 14. When the injector opens, the pressure in the valve chamber 14 drops and the valve piston 42 begins to move towards the exhaust valve seat 40. In normal operating conditions, injection is blocked before the valve piston 42 reaches the exhaust 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 intake valve seat 30. The valve piston 42 must be returned to the closed position of the intake valve seat 30 before performing the subsequent injection. The closing speed is determined by the designer through proper selection of spring force and size of the calibration hole 56.

  If the duration of the injection becomes too long, the valve piston 42 will reach the position illustrated in FIG. In this position, the second sealing surface 54 of the valve piston 42 seals and closes the exhaust valve seat 40. In this way, the injection is impeded, preventing further discharge of fuel from the high pressure accumulator. Each cylinder of the engine remains deactivated, but overfueling and shutting down of the engine's fuel due to insufficient injection pressure is prevented.

  The maximum volume of fuel injection is determined by the volume of the valve chamber 14 downstream of the valve piston 42 and the flow through the plurality of calibration holes 56 during movement of the valve piston 42 toward the exhaust valve seat 40. Depends on.

  The valve design according to the present invention reduces the number of components and precision machining processes required to assemble the valve. Specifically, each of the three major components of the valve (the first housing housing 16, the second housing housing 18, and the valve piston 42) is made of a single metal part. The machining of the sealing surface and the guide surface can be carried out in a simple and quick way, since the shape of the components does not envisage areas that are located in positions that are difficult to reach by machining with tools. The total mass of the moving parts (or rather only the valve piston 42) is reduced by 20% compared to that performed by EP 2423498. Therefore, the inertial force in the acceleration phase and the reduction of the pressure loss between the upstream chamber and the downstream chamber of the piston 42 are considerable. This allows multiple injections of higher pressure during the open phase of the injector.

  Of course, without detracting from the principles of the invention, structural details and embodiments may vary widely from those described and shown, thereby departing from the scope of the invention as defined by the following claims. It does not deviate.

Claims (4)

A fuel flow limiting valve for a plurality of large internal combustion engines, comprising:
A valve housing having an inner cylindrical surface surrounding the valve chamber, an inlet channel with an inlet valve seat and an outlet channel with an outlet valve seat;
A valve piston housed within the valve chamber, the valve piston having a base wall and a cylindrical wall longitudinally guided to the inner cylindrical surface of the valve housing, the valve piston cooperating with the intake valve seat. A sealing surface and a second sealing surface associated with the discharge valve seat, wherein the valve piston has a first position in which the first sealing surface closes the intake valve seat and the second sealing surface. A valve piston movable in a longitudinal direction between a surface and a second position closing the discharge valve seat;
An elastic element disposed between the housing and the valve piston, the elastic element tending to push the valve piston towards the first position;
The first sealing surface and the second sealing surface are machined directly on the base wall of the valve piston, the valve housing having a longitudinally extending pin shaped portion within the valve chamber. The exhaust channel extends through the pin-shaped portion, the discharge valve seat is formed at an inner end of the pin-shaped portion ,
The valve housing has a first housing housing including a bottom wall and a sidewall extending from the bottom wall and including an open end, the pin-shaped portion of the first housing housing. A flow rate limiting valve that is integrally formed with a second housing casing that is sealed and fixed to the open end . A flow restrictor valve according to claim 1 , wherein the elastic element is a compression coil spring disposed outside the pin-shaped portion and within the cylindrical wall of the valve piston. 3. The flow restrictor valve of claim 1 or 2 , wherein the first sealing surface is a convex surface formed on an integral protrusion of the base wall of the valve piston. 4. The flow restriction valve according to any one of claims 1 to 3 , wherein the second sealing surface is a recessed concave surface in the base wall of the valve piston.

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