Fuel system shut-off valve

A fuel system shut-off valve includes a valve body bounding a fuel space, the valve body having an inlet opening and an outlet opening communicating with the fuel space. A piston assembly in the fuel space includes a main piston member that is movable relative to the valve body and an auxiliary piston member that is movable relative to the main piston member. The piston assembly either allows or prevents fuel flow through the valve from the inlet opening towards the outlet opening depending on the position of the auxiliary piston member. A force member urges the piston assembly towards the inlet opening.

BACKGROUND OF THE INVENTION

This invention relates to a fuel system shut-off valve.

It is conventional to use a so-called common rail storage injection system in connection with an internal combustion engine. In such a system, fuel under injection pressure is injected into a combustion chamber of the engine by controlling an injection valve. If the injection valve is defective, this enables the situation in which fuel may leak in uncontrolled fashion into the combustion chamber. To prevent this, the publications U.S. Pat. No. 3,780,716 and WO 95/17594 propose a shut-off valve for limiting the fuel flow volume. The shut-off valve has a cylinder space which contains a piston provided with a spring load acting against the fuel flow direction in an injection situation. In normal operation the fuel amount needed for each injection corresponds to the volume displaced by the piston movement. If for some reason the shut-off valve continues to leak, the piston moves to an extreme position in which it shuts the flow off.

In publication GB 2317922 there has been disclosed another shut-off valve for limiting the flow volume. In the initial situation, the pressure acts upon a smaller surface area on the fuel admission side in which case, at a given pressure, the force is naturally smaller being in proportion to the surface area acted upon. However, a disadvantage of this solution is the absolute tightness requirement and consequently it is very sensitive in regard to the fuel quality. If the sealing surface of this smaller surface area leaks, the solution does not work and the pressure is applied to the entire surface area and the piston may move to an extreme position in which it closes the flow. Especially in a large power plant or marine engine the fuel can be such that the solution does not function reliably enough.

Also, the prior art flow shut-off valves have generally problems related to situations in which the fuel viscosity is high, for example when heavy fuel oil is used and/or when the fuel temperature before starting the engine is lower than the normal operating temperature. Consequently, the equalization of the fuel pressure over the piston does not occur rapidly enough and the piston may move to an extreme position and close the injection connection.

An object of the present invention is therefore to provide a fuel system shut-off valve by which the prior art disadvantages are avoided. An objective of the present invention is especially to provide a shut-off valve by which the unintentional closure on starting phase can be avoided.

SUMMARY OF THE INVENTION

According to the present invention there is provided a fuel system shut-off valve comprising a valve body bounding a fuel space, the valve body having an inlet opening and an outlet opening communicating with the fuel space, a piston assembly in the fuel space and including a main piston member that is movable relative to the valve body and an auxiliary piston member that is movable relative to the main piston member, the piston assembly either allowing or preventing fuel flow through the valve from the inlet opening towards the outlet opening depending on position of the auxiliary piston member, and a force member urging the piston assembly towards the inlet opening.

In the preferred embodiment of the invention, the main piston member and the auxiliary piston member have, on the inlet opening side, a first surface area and a second surface area, respectively, bordering the fuel space and the second surface area, formed by the auxiliary piston member, is smaller than the first surface area, formed by the main piston member. The auxiliary piston member is arranged to be movable for providing the closing and opening of the flow connection between the inlet and outlet openings. For this purpose the auxiliary piston member is provided with a sealing surface.

In the preferred embodiment of the invention, the force member applies force to the auxiliary piston member and this influences the relative positions of the main piston member and the auxiliary piston member. Accordingly, the two piston members are advantageously influenced by a common force member.

The fuel space of the shut-off valve is preferably cylindrical and the diameter of the main piston member corresponds substantially to the fuel space diameter. The main piston member has a bore in the direction of its longitudinal axis, and the auxiliary piston member is movably arranged in the bore of the main piston member.

The counter surface of the auxiliary piston member sealing surface may be arranged in connection with the outlet opening or in connection with the main piston member, depending on the way the shut-off valve is implemented.

Several advantages are realized using the preferred embodiment of the invention. Firstly, the operation is reliable on starting of the engine. The operation pressure of the shut-off valve auxiliary piston member can easily be dimensioned as desired and, mainly, the operation of the shut-off valve depends only on the pressure. Further, the fuel qualities have only a slight effect on the operation and the presence of possible dirt particles in the fuel does not affect the starting operation.

DETAILED DESCRIPTION

As shown very schematically inFIG. 1, the shut-off valve4can be adapted to a common rail fuel storage injection system. The common rail storage injection system is conventional and is not described here in detail. The common rail storage injection system includes as its principal components a common rail storage1, in which there is fuel under high pressure to be injected into the engine and with which the injection valves2(only one of which is shown inFIG. 1) are in fluid flow connection for dosing fuel to the cylinders (not shown). From the common rail storage1there is arranged a fuel channel ductwork3,3′ for the injection valve2. A sufficient pressure is maintained in the common rail storage during the operation to provide an adequate injection pressure to the injection valves2. Each injection valve2comprises control means (not shown) for controlling the injection independently. In the fuel channel ductwork3,3′ there is arranged a shut-off valve4, the operation of which is explained in the following by referring toFIGS. 2-5.

The shut-off valve is shown in its initial state in FIG.2. The shut-off valve includes a body part5defining a cylindrical fuel space6. The fuel space has an inlet opening7and an outlet opening8for the fuel. In the fuel space6of the body part5there is fitted a piston assembly9comprising an outer or main piston and an inner auxiliary piston12. A narrow passage or throttle11passes through the outer piston and connects the regions of the fuel space6on different sides of the piston assembly9with each other. Depending on the position of the piston assembly9, fuel may either flow through the shut-off valve from the inlet opening to the outlet opening or the fuel flow may be prevented. The shut-off valve4further comprises a spring10, which urges the piston assembly9against a shoulder5′ of the body part5as shown in FIG.1. In normal running conditions between injections, the shut-off valve4is in the position of FIG.2.

When the injection valve2starts the injection during the normal operation, a pressure difference develops over the shut-off valve3, in other words between the inlet opening7and the outlet opening8, in which case the piston assembly9moves upwards until the injection stops and the pressure difference equalizes. This situation is shown in FIG.3. In this situation the amount of the fuel to be injected is equivalent to the volume displaced by the movement of the piston assembly9in the fuel space6.

The auxiliary piston12is movably arranged in connection with the main piston. The main piston has an area9′ limiting the fuel space6on the inlet opening7side of the fuel space6, whereupon the fuel space pressure acts and in normal operation the auxiliary piston12moves with the main piston without relative movement of these two members.

In the event that the injection valve2leaks or does not close up for some reason after the injection, the common rail storage pressure pushes the piston assembly9to the extreme position shown in FIG.4. In this position of the piston assembly9the flow into the injection valve2is strongly restricted, because the entire flow goes via the throttle11. The pressure difference across the piston assembly9increases and when it reaches a specific limit, the auxiliary piston12moves relative to the main piston and the sealing surfaces13,13′ close up and shut the flow off, which situation is shown in FIG.5. Here the counter surface13′ of the auxiliary piston12sealing surface13is arranged in connection with the outlet opening8. This mode of operation occurs because the auxiliary piston12has an area12′ bordering a space in the section on the fuel space6inlet connection7side and this area12′ is smaller than the corresponding area9′ of the main piston, in which case primarily a common movement of the main piston and the auxiliary piston12takes place and only when the pressure difference has exceeded a certain limit, such that the piston assembly9reaches the position shown inFIG. 4, does the auxiliary piston12move relative to the main piston. Consequently, the pressure moving the auxiliary piston12is directed only at the area determined by its diameter and the movement requires a greater pressure than the pressure enabling the movement of the whole piston assembly9.

The shut-off valve4operates on starting of the engine, for example in a heavy fuel application, as follows. When the fuel circulation is launched before the engine is started up, the pressure of the fuel system effects the inlet opening7. In this initial situation the outlet opening8side can be almost free of pressure or even full of air. In the next phase the piston assembly9moves to the position illustrated inFIG. 4, in other words to its second extreme position. It may be presumed, for example, that the pressure of the fuel system is around 7 bar. The shut-off valve4can be dimensioned for example so that the pressure difference needed for moving the auxiliary piston12to the position shown inFIG. 5is 25 bar. This means, in practice, that the shut-off valve4stays open and the region of the fuel space6on the outlet opening8side and the ducting3′ downstream of the shut-off valve are filled from the common rail storage injection system. The pressure at the outlet opening8increases. When the pressures at the inlet opening7and the outlet opening8are sufficiently equalized, the piston assembly9of the shut-off valve moves to the position illustrated in FIG.2and the engine can be started without problems. This way the throttle11can be dimensioned only according to the desired return speed of the piston assembly9(in the normal situation when the engine is running). If there is for example a pipe breakage on the outlet opening8side of the shut-off valve when the engine is operating, the shut-off valve closes up immediately.

Another shut-off valve embodiment is shown in FIG.6. This embodiment corresponds otherwise to the one represented inFIGS. 2-5, but the auxiliary piston12has been arranged differently to function with the main piston itself as flow closing means. In this embodiment the auxiliary piston12fitted in the bore of the main piston includes a threaded portion that is in threaded engagement with a spring retainer and a lock nut, whereby the auxiliary piston is fixed relative to the spring retainer. The auxiliary piston12also has an enlarged head12′. The channel11passes through the auxiliary piston11and opens at one end into the region of the fuel space6on the outlet side of the main piston, and at the other end into the region of the fuel space6on the inlet side of the main piston. Now, if the pressure difference across the piston assembly9exceeds a specific limit, the auxiliary piston12moves towards the outlet connection, in which case the sealing surfaces13,13′ end up against each other. Here the movement in question is just about to take place. In the embodiment shown inFIG. 6, the counter surface13′ of the auxiliary piston sealing surface13is arranged in connection with the piston assembly9.

The invention is not limited to the embodiments shown, but several modifications of the invention are reasonable within the scope of the attached claims.