GB2544974A

GB2544974A - An accumulator for use in a fuel line to attenuate pressure peaks

Info

Publication number: GB2544974A
Application number: GB1521126.1A
Authority: GB
Inventors: J Mccrindle Christopher; Buckley Paul
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2015-12-01
Filing date: 2015-12-01
Publication date: 2017-06-07
Anticipated expiration: 2035-12-01
Also published as: GB2544974B; GB201521126D0

Abstract

An accumulator 10 is described for use in a flow line 12, in particular in a fuel line, to attenuate pressure peaks in the flow line. The accumulator has a chamber 24, a piston 28 disposed for movement within the chamber 24, a first space 30 defined in the chamber in front of the piston and adapted to communicate with a fluid inside the flow line, and a second space 34 defined within the chamber behind the piston. A spring 36 is provided to urge the piston to reduce the volume of the first space 30 and increase the volume of the second space 34. A non-return valve 38 is provided which communicates with the second space 34 and is adapted to allow fluid leaking past the piston into the second space to be discharged when pressure in the fluid in the flow line displaces the piston against the action of the spring to increase the volume of the first space and decrease the volume of the second space.

Description

An accumulator for use in a fuel line to attenuate pressure peaks

The present invention relates to an accumulator for use in a flow line to attenuate pressure peaks in the flow line, the accumulator having a chamber, a piston disposed for movement within the chamber, there being a first space defined in the chamber in front of the piston and adapted to communicate with a fluid inside the flow line, and a second space defined within the chamber behind the piston. The accumulator is particularly intended for use in a fuel delivery system, but is not restricted to such systems and can have general use in hydraulic systems of diverse kinds.

Reciprocating pumps, particularly single plunger pumps, often have problems filling at higher speeds. This is partly caused by the stop start behavior of the fluid in the liquid supply line or inlet pipe as the inlet valve opens and closes during the pumping cycle. The inertia of the fluid resists the pumping action and gives rise to pressure waves along the liquid supply line. These waves are reflected at both ends and, as the engine speed and thus the pump speed varies, lead to significant variation in pressure at the inlet of the pump. It should be noted that this problem arises both with liquid supply lines which have an open end in the liquid storage tank, from which they draw liquid to supply to the pump, and to liquid supply lines which are fed with liquid by a primary pump. A primary pump of this kind feeds liquid to the liquid supply line and is, for example, located in or at the liquid storage tank. Low pressure during filling can lead to under filling and cavitation and can mean that the pump does not meet the delivery requirements. Cavitation is worse at higher temperatures due to the fact that vapor pressure increases with higher temperature. Furthermore, there is a problem at lower temperatures because the rubber pipes get stiffer so damping is also reduced at lower temperatures. Damping is in any case reduced as pipes become stiffer. Thus a stiffer pipe inherently has less damping capability.

In certain pump configurations this stop start nature of the liquid column can also lead to large pressure fluctuations which, in some cases, can lead to system component damage or life reduction.

Another cause of pressure fluctuations is the lower end of the pumping plunger moving in and out of the cambox during the cycle. This has the effect of continuously changing the cambox volume. On fuel lubricated pumps this volume is often connected to the inlet circuit so pressure fluctuations occur as the fuel moves in and out with the change in volume.

This proposal is particularly suited to reducing fluctuations caused in this way.

It is known to use accumulators/dampers having a liquid side and a gas side to reduce the magnitude of pressure fluctuations by storing liquid during peak pressures and returning it during the low pressure part of the cycle. The known accumulators and dampers are relatively bulky, which can be problematic in the limited space available in modern engine bays. Moreover, they add cost to the fuel delivery system. Other configurations use a flexible diaphragm plate to separate the fluid side from the gas side without leakage. It is clearly important to prevent leakage from an environmental viewpoint but it is also important for functionality. If fluid acts on both sides of the diaphragm pressures will build up on the outer side reducing the accumulator effect.

The principal object underlying the present invention is to provide a simple, compact, accumulator or liquid damping structure which overcomes the problems of pressure fluctuations in the liquid supply line due to operation of the pump and the inlet valve (or otherwise) and which can be manufactures at favorable cost.

In order to satisfy this object there is provided, an accumulator of the initially named kind which is characterized in that a spring is provided to urge the piston to reduce the volume of the first space and increase the volume of the second space and in that a non-return valve is provided which communicates with the second space and is adapted to allow fluid leaking past the piston into the second space to be discharged when pressure in the fluid in the flow line displaces the piston against the action of the spring to increase the volume of the first space and decrease the volume of the second space.

The present invention recognizes that the use of pistons and springs would be a convenient and robust method of providing an accumulator function but in practice fluid leakage between the piston and bore slowly fills the volume behind the piston. It is not possible to completely prevent this leakage as, to move freely, some level of clearance is required between the piston and the bore.

As the space behind the piston fills with liquid - such as fuel -, the gas provided there is replaced giving an increased level of stiffness until the accumulator function of the piston is adversely affected or removed completely. The present invention overcomes this disadvantage by recognizing that a non-return valve can be used to allow movement of the piston to discharge liquid from the second space as movement of the piston reduces the volume of that space.

This allows the chamber to operate in a partial vacuum. Volume change is compensated without having to displace full fluid volume.

The space required to accommodate the chamber containing the piston and spring as well as the associated non-return valve can be made very compact so that the accumulator can readily be accommodated in the space available. This is particularly true when the chamber is made generally cylindrical or tubular, particularly since the chamber can have the form of a relatively long chamber of narrow diameter.

The spring is preferably disposed in the second space and is realized as a compression coil spring. The coil spring can bear directly against the base of the cylinder. In such a design the coil spring can be made relatively narrow in diameter, while nevertheless being made sufficiently strong and no particular complications exist in attaching the spring to the piston (as would occur if the spring is realized as a tension spring), since the compression coil spring accommodated in the second space simply has to push against the rear of the piston and can be braced against the closed base or end wall of the cylinder.

It is however also possible to use a tension spring as the spring, in which case it is positioned in the first space and anchored at its two ends to the chamber and the piston.

In an arrangement using a compression coil spring in the second space to damp pressure fluctuations communicated from the liquid line to the first space, where they act on the piston, it can be expedient to provide a second spring at an opposite side of the piston from the first spring. Such an arrangement would also permit the attenuation of low pressure excursions in the liquid line, by ensuring that the piston is spaced from the end of the first space which communicates with the liquid supply line.

The non-return valve preferably communicates with a geometrically lower region of the chamber. This ensures that fuel rather than gas such as air is preferentially expelled through the non-return valve. Thus the proposed design adds a nonreturn valve of some description to allow the piston to push fluid out of the spring chamber as it moves back.

There is no need to replace air which may be lost from the second space because the second space can readily operate under a partial vacuum. From time to time the piston will move sufficiently to close the vacuum and expel the small quantity is fluid that has collected in the chamber. The accumulator function should not be affected by operating with a vacuum as the spring force and stiffness can be increased to compensate for the loss of gas pressure behind the piston.

If it is desired to allow air to reenter the second space then this can be done by providing a second non-return valve which is disposed, i.e. orientated, so as to admit air into the second space when the piston is urged by the spring to reduce the volume of the first space.

The first non-return valve for the expulsion of liquid from the second space preferably has an outlet connectable to or connected to a return line leading to a fluid storage tank. In this way fuel expelled from the second space is not lost and does not contaminate the engine bay or the environment.

In addition a spill port can be expediently provided in a wall of the chamber and can be uncovered by displacement of the piston during its movement to reduce the volume of the second space, whereby to realize a pressure limiting or pressure restricting action. In such an arrangement the spill port or orifice can conveniently communicates with a return line leading to a fluid storage tank.

The pressure restricting or limiting function can be obtained either by suitable dimensioning of the free flow area of the spill port, if necessary taking account of the restriction inherently present due to the piston clearance, or by providing a pressure restricting valve in the return line from the spill port to the fluid storage tank.

The present invention also relates to an improved non-return valve which is suited to use in the accumulator of the present invention but can also be used in other applications. The improved non-return valve is the subject of claims 12 to 15.

The accumulator in accordance with the invention is preferably used in a fuel system of a motor vehicle. The fuel system can comprise a fuel injection system and the accumulator is then conveniently positioned in a fuel line upstream of a fuel pump or in the pump, the flow line being connected to a fuel supply tank, to convey fuel from the fuel tank to the fuel pump.

The fuel system can be adapted for use with one of gasoline and diesel fuel, the fluid respectively being gasoline or diesel.

The fuel pump is a reciprocating piston fuel pump and the reciprocating piston furl pump is typically one of a single cylinder fuel pump, a twin cylinder fuel pump and a multi-cylinder fuel pump.

The invention will now be explained in more detail by way of example only and with reference to the accompanying drawings in which are shown:

Fig. 1 a schematic drawing of an accumulator incorporating a piston and a spring in the initial state when used in a fuel line,

Fig. 2 a schematic drawing similar to Fig. 1 but illustrating the problem of fuel leakage past the piston,

Fig. 3 a schematic drawing similar to Figs. 1 and 2 but showing the use, in accordance with the invention, of a non-return valve for fuel leaking past the piston,

Fig. 4 a schematic drawing similar to Fig. 3 but additionally showing a spill port,

Fig. 5 a further drawing similar to Fig. 4 but additionally showing a second spring,

Fig. 6 a highly schematic view of a preferred fuel system incorporating the accumulator of the invention,

Fig. 7 a side view of the body of the preferred design of the accumulator of the present invention as schematically shown in Fig. 6,

Fig.8 an axially sectioned view of the body of the accumulator of Fig. 7 showing further details,

Fig. 9 a cross section through the body of the accumulator as seen in the plane IX-IX of Fig. 8 to an enlarged scale and showing further details,

Fig. 10 a perspective view of a first embodiment of the valve member shown in Figs. 6 to 9,

Fig. 11 a perspective view of an alternative embodiment of a valve member suitable for use in the accumulator of Figs. 6 to 9,

Fig. 12 a view showing a more detailed view of the way the accumulator of Figs. 6 to 11 is incorporated into the cam box of the fuel system of Fig. 6,

Fig. 13 a drawing similar to Fig. 8 but showing an alternative embodiment and

Fig. 14 a diagram similar to Fig 12 but showing the embodiment of Fig. 13 incorporated into the cambox of the fuel system of Fig. 6.

Turning first to Fig. 1 there can be seen an accumulator 10 used in a liquid fuel flow line 12 extending from a fuel storage tank 14 to a fuel pump 16 used to supply fuel from the fuel storage tank 14 to an internal combustion engine schematically shown at 18. The accumulator 10 is also described as a regulator in this application. The engine 18 can be a diesel or gasoline engine or even an LPG engine and the fuel system can be any fuel injection system such as a common rail system or a direct fuel injection system. The pump 16 can be a pressure pump for gasoline or a high pressure pump for diesel and can be fed by a low pressure pump associated with the tank and schematically indicated at 20.

The fuel pump is typically a reciprocating piston fuel pump, since it is with such pumps that pressure fluctuations in the fuel line 12 are a problem. This is particularly the case with a single cylinder fuel pump, but can also be a problem with multiple piston pumps such as a twin cylinder fuel pump and a multi-cylinder fuel pump.

The fuel line 12 from the fuel storage tank 14 to the pump 16 can also include other non- illustrated items such as a shut off valve for crash protection purposes, to prevent loss of fuel in an accident, and a filter. A fuel return line 22 is typically provided to return excess fuel to the fuel storage tank 14. When the reciprocating pump 16 operates, the opening and closing of the inlet valve 23 of the pump repeatedly starts and stops the flow of fuel through the liquid supply line 12. The fuel in the liquid supply line 12 has inertia and the starting and stopping of the fuel flow causes pressure fluctuations.

The purpose of the accumulator 10 is to attenuate pressure peaks in the flow line thereby regulating the fuel pressure in the flow line. As shown in Fig. 1 the accumulator 10 has a chamber24 defined within a cylinder 26 and a piston 28 disposed for movement within the chamber 24 along the axis of the cylinder 26. A first space 30 is defined in the chamber 26 in front of the piston 28 and communicates via an inlet 32 with the fluid inside the flow line 12. A second space 34 is defined within the chamber 24 behind the piston 28:

The second space 34 would normally be at a partial vacuum as shown by the white space in Fig. 1. In the present case a spring 36 is disposed in the second space 34 and is a compression coil spring. The spring 36 thus urges the piston 28 to the left in an attempt to reduce the volume of the first space 30 and increase the volume of the second space 34. In an alternative (not shown) the spring could be a tension spring adapted to pull the piston 28 towards the left end of the cylinder 26.

The resilient increase in volume of the first space 30 due to movement of the piston 28 to the right reduces the peak amplitude of any pressure wave generated in the fuel line 12, i.e. attenuates it. As the pressure wave is effectively attenuated by the increase in volume of the first space 30 any pressure reductions at the inlet valve 23 that may result from pressure waves travelling down the liquid supply line 12 (in this case the fuel line) and being reflected at the open end of the liquid supply line, or at any other optional items built into the liquid supply line are minimized. If a primary pump 20 is provided it can also cause reflections of a pressure wave, such reflections can occur at open or closed ends of a fuel line or at components incorporated therein, there is simply a difference in phase of the reflected wave. The timing of the pressure waves varies with the speed of the pump16 which is normally linearly related to the engine speed. The precise timing of the pressure waves is generally unimportant because the accumulator 10 is able to dampen all such pressure waves regardless of the time at which they occur. The double arrow 35 indicates the variable direction flow associated with pressure flue-tuations in the fuel line 12 (arrowhead to the right shows the direction of flow for pressure peaks and the arrowhead to the left for the flow when under-pressure is present between pressure peaks). Both over-pressure and under-pressure are damped by the accumulator 10.

In all figures the same reference numerals are used for components having the same design or function and the description of such components will not be unnecessarily repeated. Thus the description given with respect to a particular component in any one figure will be understood to apply for the correspondingly numbered component in another figure unless something to the contrary is stated. In all figures spaced apart dots indicate the presence of liquid fuel. Although liquid fuel is present in the fuel line 12 it is not shown there by spaced apart dots, simply for the sake of simplicity of the drawings. In all figures the accumulator is shown in the preferred horizontal orientation.

Fig. 2 shows that the initial state of Fig. 1 does not endure for long because in practice fluid leakage 37 between the piston 28 and the bore24 slowly fills the volume of the second space 34 behind the piston. It is not possible to completely avoid this leakage as, to move freely, some level of clearance is required between the piston28 and the bore 24 of the cylinder 26. As the second space34 progressively fills with fuel, the gas is replaced giving an increased level of stiffness until the accumulator function of the piston is adversely affected or removed completely.

Fig. 3 shows that this problem is overcome in accordance with the invention by the provision of a non-return valve 38 which communicates with the second space 34 and is adapted to allow fluid leaking past the piston 28 into the second space 34 to be discharged in accordance with the arrow 39 when pressure in the fluid in the flow line 12 displaces the piston 28 against the action of the spring 36 to increase the volume of the first space 30 and decrease the volume of the second space 34.

The non-return valve 38 communicates with a geometrically lower region of the second space 34 where the fuel 37 tends to collect so that the fuel is preferentially expelled from the second space 34. The (first) non-return valve 38 preferably has its outlet connected via the line 41 to the return line 22 leading to the fluid storage tank 14.

It is not necessary to top up the fluid in the second space since the spring 36 can be made stronger to compensate for any loss of fluid. However, if desired - and as shown in Fig. 4 - a second non-return valve 40 can be provided. The second nonreturn valve 40 shown in Fig 4 is orientated the opposite way to the non-return valve 38 so that it admits fluid into the second space 34 when the piston 28 is moved by the spring to reduce the volume of the first space 30. The direction of the non-return valve 40 is such that fuel cannot be expelled via this valve 40. As shown in Fig. 4 a spill port 44 can be provided in a wall of the cylinder 26 and can be uncovered by displacement of the piston 28 in a direction to reduce the volume of the second space 34. This permits a pressure limiting or pressure restricting action to be realized, either by the size of the spill port or by a pressure limiting valve (not shown) provided in a return line 46 from the spill port 44 to the fuel storage tank 14.

Fig. 5 shows an alternative embodiment of the accumulator 10 on its own. This accumulator could be used in the embodiments of the previous figures. In Fig. 5 a second spring 48 is provided at an opposite side of the piston 28 from the first spring 36. The task of such a second spring 48, typically also a compression coil spring, is to allow the accumulator to better damp pressure drops which may also occur at the inlet 32, i.e. in the fuel line 12, by ensuring that the piston is not tight up against the left hand end of the cylinder in use and is thus able to move to the left to compensate for sudden pressure reductions. It may also be helpful in the reduction of noise which may be generated if the piston vibrates against its seat.

The general principle of the accumulator 10 of the present invention has been described above with reference to a schematically illustrated fuel system, which may, however, be regarded as a simple practical embodiment. However; the accumulator 10 is intended for use in a rather differently conceived fuel system which will now be outlined with reference to Fig. 6. In the embodiment of Fig. 6 a primary pump 20 in the fuel storage tank delivers diesel fuel at low pressure, typically at around 2 bar, via the fuel line 12 and an optional filter 49 to a cambox 50 of the engine. It will be noted that the cambox 50 actually comprises a hollow space 52 shown schematically within the outline 54 and an outer wall shown schematically by the outline 56. The region between the outline 56 and the outline 54 can be considered to be the metal wall of the cambox 50, it is only shown highly schematically in Fig. 6. The hollow space 52 of the cambox 50 within the outline 55 is thus pressurized by the fuel received via the fuel line 12. Fig. 6 also schematically shows the reciprocating piston fuel pump 16 with its inlet valve 20 and an outlet valve 58 which delivers fuel in the direction of the arrow 60 to the engine 18 (Fig. 1), for example to a common rail system of the engine (not shown). The high pressure fuel pump 16 is mounted externally of the cambox 50 but is driven by a plunger 62 operated by a camshaft (not shown) within the cambox. The camshaft is mounted in bearings 64, 66 provided in the cambox 50 and lubricated by the pressurized fuel within the cambox 50. The fuel leaving the bearings 64, 66 passes via the lines 68 and 70 to the fuel return line 22. As shown in Fig.6 a variable restrictor 72 is provided in the cambox 50 in a drilling 74 which communicates from the hollow space 52 via a further filter 76 in a line 12' leading to the inlet valve 20. The variable restrictor 72 enables the maximum flow to the high pressure pump 16 to be restricted. It is not an optional feature and could be omitted. The accumulator 10, which is shown in more detail in the following figures, is incorporated into a further drilling 78 communicating via the line section 80 with the drilling 74.

Fig. 6 also schematically illustrates lines 77 which pass fuel from the accumulator 10 to the line 70 and from there into the return line 22.

The preferred design of the accumulator 10 will now be described with reference to the further Figures 7 to 11.

Figs. 7 to 11 show that the accumulator or regulator 10 can be screwed as a unit into the drilling 78 of the cambox. For this the accumulator 10 has a hexagon 82 for rotating the unit and a threaded portion 84 at flange 88 which engages with a mating female thread in the drilling 78. A conical seat 86 to the left of the threaded portion 84 serves to secure the unit in the cambox and also acts as a seal between the accumulator 10 and the cambox 50. A further seal is also provided in the form of an O-ring (not shown) which sits in the ring groove 90 and seals against the wall of the drilling 78. Immediately to the left of the ring groove 90 is a conical face 92 and beyond this a spring member 94 which forms part of the nonreturn valve 38. Further to the left of the spring member 94 is a tubular region 96 of the accumulator 10 having an open end 98 which communicates via the line section 80 with the drilling 74. After the piston 28 has been moved to the right against the force of the spring36 in the event of pressure increases, cross drillings 100 in the tubular region 96 permit fuel entering the space 30 in front of the piston 28 to escape, into an annular space 102 (shown in Figs. 12 and 14) and from there via the line 70 into the return line 22.

The piston 28 shown in Figs. 8 and 12 to 14 is provided with a bore 104 which includes a restrictor 106 to damp the flow of fuel from the space 30 into the space 34 when pressure increases arise in the drillings 74 and 80. This bore 104 and the restrictor 106 are optional features since the leakage past the piston 28 also constitutes a restrictor.

The specific design of the non-return valve 38 in Figs 7 will now be described with further reference to Figs. 8 to 12 and with reference to a modification in Figs. 13 and 14.

As can be seen from Figs. 8 and 9 a port 108 such as a radial drilling is provided in the wall or body 110 of the accumulator 10 and the spring member 94 at least partially surrounds the wall 110. The spring member 94 has a first portion 112 at one end adapted to cover and close the port 108 due to the spring force of the spring member. If an increased pressure arises in the hollow space 34 behind the piston 28 it acts on the end portion 112 and dilates the spring member forcing the end portion 112 away from the port 108 thus freeing it in response to internal pressure in the second hollow space 34.

The wall 110 has a blind recess 114 at a circumferential position removed from the port 108 for locating a tail or tongue 116 provided at a second end of the spring member 94 remote from the first end portion 112. The blind recess 114 can, for example, be formed by a blind bore or a slot.

As can be seen from the drawings the spring member 94 is of part circular shape and extends over more than 180° of the circumference of the tubular wall 110, with the spring member having a curvature slightly smaller than that of the wall 110 at the position of the spring member 94. In this way the spring member 94 grips the accumulator 10, with the first end portion 112, which acts as the valve member, covering and thereby closing the port 108. The engagement of the tail 116 in the blind recess 114 facilitates the assembly of the spring to the housing and ensures that the first end portion 112 is aligned with the port 108. This could however be achieved differently, the first end portion 112 could, for example, be provided with a radially inwardly facing dimple which locates in the generally circular opening of the port 108.

The tail of the spring member 94 thus preferably comprises an end portion or tongue 116 turned inwardly to engage the blind recess 82 and locate the spring member 94 on the housing 110. However the tail end does not necessarily have to be an end portion of the spring member 94, it could, for example, be an inwardly bent portion of the spring intermediate of its two ends.

Turning now to Fig. 12 there can be seen a more detailed view of the attenuator 10 when inserted into the cambox 50. Only a portion of the cambox is shown. The piston 28 is shown immediately after it has started to move to the right against the pressure of the spring 36 in response to a pressure increase in the drilling 74 (here actually a curved passage cast into the cambox 50) which is communicated to the line section 80 and thus acts on the end of the piston 28. The movement of the piston 28 to the right damps the pressure increase, i.e. counteracts it. As soon as the cross drillings 100 start to be uncovered fuel passes into an annular groove surrounding the accumulator 10 (and identified by the reference numeral 102 in Fig. 14) and from there into the passage or line 70 which communicates with the fuel return line 22. It can be seen from Fig. 12 that the non-return valve 38 also opens into the annular groove (102 in Fig. 14) so that fuel accumulating in the second space 34 and ejected from there by movement of the piston spills through the second non-return valve 38 into the annular groove and also passes via the passage 70 into the return line 22.

It should be noted that Fig. 12 does not show the restrictor illustrated in Fig. 6. In Fig.6 there are shown two lines 77 communicating with the line 70 with one of these two lines including a schematically illustrated restrictor 79. In actual fact, as shown in Fig. 12, there is only one line 70 communicating with the annular space and the fuel return line 22) and the restrictor 79 in Fig. 6 simply illustrates the restriction caused by the non-return valve 38 opening into the annular groove. That is to say the lines 77 in Fig. 6 are shown simply for the sake of illustration and do not really exist as separate lines or passages.

Figs. 13 and 14 show an alternative embodiment very similar to Figs. 8 and 12 but in which a spherical ball cooperating with a conical seat and normally urged against the conical seat by the spring member 94 forms the non-return valve 38. If the pressure in the second space 34 rises due to movement of the piston 28 to the right then the ball is urged away from the seat dilating the spring member 94 and opening the non-return valve to allow fuel to spill into the annular groove 102.

This present invention can therefore be considered to combine two valves by using a circular leaf-spring 94 on the outside of the accumulator body.

Described in other words, the accumulator body 110 of the embodiments of Figs. 1 to 6 is modified to have a blind drilling 114 or slot opposite the drain orifice or port 108. Generally this will be 180° away from the drain orifice 108 to provide ease of assembly by virtue of symmetry. It is not, however essential to function.

Ideally (and assuming 180° between body features) the leaf spring 94 will cover between 180° and 270° of arc. One end 112 will be a regular curved profile to cover the drain orifice 108. The other end 116 will be turned inwards to engage the blind drilling 113 to ensure correct orientation and position of the functional end 112.

It would also be possible for the spring member 94 to extend over more than 360° of arc and it would then resemble a helical spring with a rectangular cross section.

The curvature of the unstressed spring 94 will be slightly smaller than the diameter of the body 110 to provide the desired preload. In use, pressure inside the device will act on an area of the inside surface of the spring corresponding to the diameter of the drain orifice 108. The force created by the pressure can overcome the preload to permit outwards flow. Inwards flow is prevented by the spring member 94 covering the drain orifice 108.

The drain orifice 108 may be stepped as shown in Figs. 8 and 9, in which case the larger counter-bore will determine the opening pressure relative to the preload.

The larger is the counter-bore, the lower is the opening pressure.

The section and width of the leaf spring 94 can be optimized to suit the opening characteristic desired. Thus Fig. 11 shows a spring member 94 with a reduced with away from the larger area portion 112 which covers the port 108, whereas the tail portion 116 is reduced in size relative to the larger width leaf spring in the embodiment of Fig. 10.

Finally, it should be noted that the non-return valve 38 of Figs. 6 to 14 can be used in a whole variety of applications, not just in an accumulator or regulator 10 as described herein.

Reference numeral list 10 accumulator 12 fuel line, liquid supply line 14 fuel storage tank, liquid storage tank 16 reciprocating piston pump 18 engine 20 primary pump 22 fuel return line 23 inlet valve of pump 16 24 chamber of accumulator 10 26 cylinder of accumulator 10 28 piston of accumulator 10 30 first space of accumulator 10 32 open inlet from fuel line 12 to accumulator 10 34 second space of accumulator 10 35 double arrow 36 first spring of accumulator 10 37 leakage fuel 38 first non-return valve 39 fuel leaving first non-return valve 40 second non-return valve 41 line connecting first non-return valve 38 to return line 22 44 spill port 46 line from spill port 44 to return line 22 48 second spring 49 filter 50 cambox 52 hollow space 54 outline of hollow space 52 56 outline of outer wall of the cambox 50 58 outlet valve of pump 16 60 arrow 62 plunger 64 camshaft bearing 66 camshaft bearing 68 return line 70 flow line 72 variable restriction 74 drilling 76 filter 77 lines or passages 78 drilling 79 restrictor80 line section 82 hexagon 84 threaded portion at flange 88 86 conical seat 88 flange 90 ring groove 92 conical face 94 spring member 96 tubular region 98 open end of tubular region 100 cross drillings 102 annular groove 104 bore 106 restrictor 108 port 110 wall (body of accumulator, housing of accumulator 112 end portion of spring member 94 114 blind recess 116 tail or tongue 118 spherical ball cooperating with port 108 120 conical seat for spherical ball

Claims

Patent Claims

1. An accumulator (10) for use in a flow line (12) to attenuate pressure peaks in the flow line, the accumulator (10) having a chamber (24), a piston (28) disposed for movement within the chamber (24), there being a first space (30) defined in the chamber (24) in front of the piston (28) and adapted to communicate with a fluid inside the flow line (12), and a second space (34) defined within the chamber (24) behind the piston (28), characterized in that a spring (36) is provided to urge the piston (28) to reduce the volume of the first space (30) and increase the volume of the second space (34) and in that a non-return valve(38) is provided which communicates with the second space (34) and is adapted to allow fluid leaking past the piston (28) into the second space (34) to be discharged when pressure in the fluid in the flow line (12) displaces the piston (28) against the action of the spring (36) to increase the volume of the first space (30) and decrease the volume of the second space (34).

2. An accumulator (10) in accordance with claim 1, wherein the spring (36) is disposed in the second space (34) and is a compression coil spring.

3. An accumulator (10) in accordance with claim 1 or claim 2, wherein a second spring (48) is provided at an opposite side of the piston (28) from the first spring (36).

4. An accumulator (10) in accordance with any one of the preceding claims, wherein the chamber (24) is generally cylindrical.

5. An accumulator (10) in accordance with any one of the preceding claims, wherein the first non-return valve (38) has an outlet connectable to or connected to a return line (39, 22) leading to a fluid storage tank (14).

6. An accumulator (10) in accordance with any one of the preceding claims, wherein a spill port (44) is provided in a wall of the chamber (24) and can be uncovered by displacement of the piston to reduce the volume of the second space (34), whereby to realize a pressure limiting or pressure restricting action the spill orifice (44) preferably communicating with a return line (46, 22) leading to a fluid storage tank (14).

7. An accumulator (10) in accordance with any one of the preceding claims when used in a fuel system of a motor vehicle.

8. An accumulator (10) in accordance with claim 7, wherein the fuel system comprises a fuel injection system and the accumulator (10) is positioned in a flow line (12) upstream of a fuel pump (16), the flow line (12) being connected to a fuel supply tank (14).

9. An accumulator (10) in accordance with claim 8, wherein the fuel system is adapted for use with one of gasoline and diesel fuel, the fluid respectively being gasoline or diesel..

10. An accumulator (10) in accordance with either one of claims 8 or 9, wherein the fuel pump is a reciprocating piston fuel pump (16).

11. An accumulator (10) in accordance with any one of the preceding claims when used in a fuel pressurized cam box (50).

12. A non-return valve (38), optionally for use in an accumulator (10) in accordance with any one of the preceding claims, the non-return valve (38) comprising a housing having a wall (110) defining a hollow space (34), a port (108) in the wall (110) and a spring member (94) at least partially surrounding the wall (110) of the housing and having a first portion (112) adapted to close the port (108) and free it in response to internal pressure in the hollow space (34).

13. A non-return valve (38) in accordance with claim 12, wherein the wall (110) of the housing has a blind recess (114) for locating a second portion (116) of the spring member (94) remote from the first portion (112).

14. A non-return valve (38) in accordance with claim 12 or claim 13, wherein the spring member (94) is of part circular shape and extends over more than 180° of the circumference of the housing, with the spring member (94) having a curvature smaller than that of the local wall (110) of the housing, whereby the spring member (94) grips the housing, with the first portion (112) covering and thereby closing the port (108).

15. A non-return valve (38) in accordance with claim 13 or 14, wherein the second portion (116) of the spring member comprises an end portion turned inwardly to engage the blind recess (114) and locate the spring member (94) on the housing.