GB2165003A

GB2165003A - Shock-absorbing device for cushioning pressure variations in fuel pipes

Info

Publication number: GB2165003A
Application number: GB8520950A
Authority: GB
Inventors: Gunter Kromer
Original assignee: Audi AG
Current assignee: Audi AG
Priority date: 1984-09-26
Filing date: 1985-08-21
Publication date: 1986-04-03
Also published as: GB8520950D0; JPS6179093A; DE3435248C2; DE3435248A1

Abstract

A shock-absorbing device designed to be positioned in a fuel tank for cushioning pressure vibrations in a fuel pipe leading to a fuel injection system of a vehicle engine, has a shock- absorber housing (1, 2) divided by a diaphragm (4) into a first chamber (5) communicating with the fuel pipe (8), and a second chamber (6) which contains a spring (11) acting between the diaphragm (4) and the remote end wall (13) of the second chamber 6 and pressing the diaphragm (4) against a stop 10. The spring bias can be adjusted by shifting one support point of the spring, and to avoid an increased pressure developing in the chamber (6) when the spring bias is adjusted, an orifice (14) is provided in the wall of the chamber (6). The orifice may be closed by a plug after the spring bias is adjusted, or a ventilation tube may be connected thereto, the tube opening into the atmosphere outside the fuel tank. <IMAGE>

Description

SPECIFICATION Shock-absorbing Device for Cushioning Pressure Variations in Fuel Pipes This invention relates to a shock-absorbing device for cushioning pressure variations in a fuel pipe leading to a fuel injection system of a vehicle engine. The invention is concerned in particular with such a device which comprises a housing divided by a diaphragm into a first chamber which communicates with the fuel pipe, and a second chamber containing a spring which presses the diaphragm against a stop.

In shock-absorbing devices of this type, a problem may arise when the engine is switched off. The fuel pump is of course switched off simultaneously, but the spring of the shock-absorbing element may cause the fuel pressure to be maintained which may lead to injection of fuel into the combustion chambers and hence to the engine continuing to run, if the lift of the diaphragm in the shockabsorbing element exceeds a certain value. For this reason in prior devices of this type the spring bias is so adjusted during assembly of the shock-absorbing element, that at a certain fuel pressure the displacement of the diaphragm does not exceed a selected value.

It has been found that in spite of accurate adjustment of the spring bias during assembly, considerable variations in the displacement of the diaphragm can occur during running and as a result, after the fuel pump has been switched off, there may still be sufficient fuel under pressure for the engine to run on.

Adjustment of the spring bias is normally achieved by introducing a fluid into the first chamber with the fuel pipe connection, and then varying the spring bias by compressing the part of the housing which forms the second chamber and in which the spring is located: the diaphragm may be pressed inwards by, for example, 0.2 mm against the spring bias at the given pressure. Since the shock-absorbing device is positioned inside the fuel tank together with the fuel pump, the second chamber must be hermetically sealed, otherwise if there should be fuel present in the second chamber, uncontrolled cushioning would occur and undesirable noise would follow from transmission of the vibrations of the diaphragm through the fuel.

It will be understood that as a result of the aforementioned compression of that part of the housing which contains the spring, the air pressure in the second chamber will be increased, so that the total force acting on that side of the diaphragm is the sum of the spring force, and the force exerted by air pressure. It has now been found that the beading which runs around the edge of the diaphragm between the two parts of the housing is in fact impervious to fluid, but not absolutely impervious to gas, so that in course of time, air can escape from the second chamber, leading to a lowering of the air pressure prevailing therein and therefore to a reduction of the counterforce acting on the diaphragm.

The result of this is that the displacement of the diaphragm under fuel pressure is increased, so that after switching-off the engine and the fuel pump, a quantity of fuel exceeding the permitted amount continues to be delivered under pressure, which leads to the engine continuing to run.

An object of the present invention is to provide a shock-absorbing device of the type referred to, in which the counter-force acting on the diaphragm may be more nearly constant over a long period of time.

This problem is solved according to one proposal of the invention by providing in the wall of the second chamber an orifice which is closed after the spring bias has been adjusted. The result of this is that when one support point of the spring is shifted in order to adjust the spring bias, the air pressure in the second chamber is not raised above the atmospheric pressure, and therefore can also not decrease later, so that the counter-force acting on the diaphragm is determined only by the spring resistance, if the influence of temperature on the volume of air enclosed in the second chamber is disregarded. Even this influence can be precluded if the aforementioned orifice is not sealed, but a ventilation pipe is connected to the latter which opens to the atmosphere outside the fuel tank.

The invention may be performed in various different ways and two embodiments will now be described by way of example with reference to the accompanying drawings, in which:~ Figure 1 is a section through the first embodiment, and Figure 2 is a section through the second embodiment.

Referring firstly to Figure 1, the shock-absorbing device illustrated includes a housing which is composed of two rotationally symmetrical housing members 1 and 2, connected together by a circumferential beading 3. Between the two parts 1 and 2 of the housing is located a diaphragm 4 which is connected firmly and in a fluid-tight manner to the housing members 1 and 2 by the beading 3. The diaphragm 4 divides the housing into a first chamber 5, which is essentially defined by the diaphragm 4 and the housing member 1, and a second chamber 6, defined by the diaphragm 4 and the housing member 2. The housing member 1 has a fluid connection 7, communicating with a diagrammatically indicated fuel pipe 8, through which fuel is conveyed to a fuel injection system of a vehicle engine by an intermittently acting fuel pump 9.

The pressure in the fuel pipe 8 is thus admitted to the chamber 5 and actuates the diaphragm 4. The top end 10 of the connection 7 forms a stop for the diaphragm 4. The other side of the diaphragm 4 is engaged by a helical compression spring 11, which is located in the second chamber 6 and abuts at one end against the diaphragm 4 through a spring plate 12, and at the other end against the end wall 13 of the housing member 2.

The object of the shock absorbing device as illustrated is to cushion the pressure vibrations in the fuel pipe 8 which are induced by the intermittent pumping action of the fuel pump 9 and can cause considerable noise. When the engine and the fuel pump 9 are switched off, there occasionally arises a situation in which fuel is forced by the shockabsorbing element through the fuel pipe connection 8 into the injection system, which may lead to the engine running on if the quantity of fuel continuing to be under pressure exceeds a certain amount.

Normally an attempt is therefore made to keep the lift of the diaphragm so small that adequate cushioning of the pressure vibrations occurs, but on the other hand the quantity of fuel continuing to be supplied under pressure remains below a critical value. In normal practice, this is achieved while the shock-absorbing device is being assembled, the diaphragm 4 being subjected to a pressure at a predetermined value of, for example, 6 bars, and the spring bias of the spring 11 is then so adjusted that the diaphragm shifts through a maximum travel of, say, 0.4 mm, at this pressure.Adjustment of the spring bias is achieved by shifting one or other of the support points of the spring 11, either by deforming the wall 13 of the housing member 2 downwards, or by pressing inwards the connection 7, whose end 10 via the diaphragm forms the second limiting abutment for the spring 11.

In prior shock-absorbing devices of this type, the chamber 6 is hermetically sealed, since the device is intended to be positioned inside the fuel tank, and fuel penetrating into the chamber 6 can influence the cushioning action to an uncontrolled degree and may also cause corrosion. Adjustment of the spring bias in the manner described above therefore causes the volume of the chamber 6 to be reduced, and hence the air pressure is increased. The force available to limit the lift of the diaphragm 4 is consequently composed of the force of the spring 11 combined with the force exerted by air compressed in the chamber 6.

It has now been found that the clamping of the diaphragm 4, because of the beading 3, is usually in fact fluid-tight, but not absolutely air-tight in every case, with the result that the overpressu re in the chamber 6 is gradually lost, the result being that the counter-force loading the diaphragm 4 is reduced and the lift of the diaphragm at a given fuel pressure is increased, so that the quantity of fuel continuing to be supplied under pressure after the engine and the fuel pump have been switched off reaches an unacceptably high value which leads to the engine continuing to run on.

To solve this problem, there is provided in the first embodiment of Figure 1 an orifice 14 in the housing member 2 to ensure that no rise in pressure in the chamber 6 occurs during the adjustment of the spring bias which has already been described. The counter-force acting on the diaphragm 4 is therefore created solely by the bias of the spring 11. After adjustment of the spring bias, the orifice 14 may be sealed in an air-tight manner by a plug 15, which is soldered in, for example. Since no overpressure occurs in the chamber 6, no loss of pressure can occur, so that no alteration of the counter-force loading of the diaphragm 4 and hence no variation in the degree of lift of the diaphragm 4 can occur.

In orderto produce conditions which are as near as possible the same in all shock-absorbers of a series, the influence of variations in atmospheric pressure should be precluded at the manufacturing location, which can be achieved by the pressure in the chamber 6 being brought to a predetermined value before the orifice 14 is closed.

The embodiment of Figure 2 basically differs from that of Figure 1 only by the fact that the orifice 14 is not sealed after the adjustment of the spring bias, but a ventilation pipe 16 is connected to this orifice, opening to the atmosphere outside the fuel tank.

This construction is slightly more costly than that of Figure 1, but it has the added advantage that variations in temperature do not affect the pressure of the air in the chamber 6.

Claims

1. A shock-absorbing device designed to be positioned in a fuel tank to cushion pressure vibrations in a fuel pipe leading to a fuel injection system of a vehicle engine, the device comprising a shock-absorber housing divided by a diaphragm into a first chamber communicating with the fuel pipe, and a second chamber containing a spring which acts between the diaphragm and the remote end wall of the second chamber, and presses the diaphragm against a stop, and including means for adjusting the bias of the spring by moving one of the spring abutments, the end wall of the second chamber having an orifice which is closed, or is connected to a pipe which opens to atmosphere outside the fuel tank.

2. A shock absorbing device for a fuel line substantially as described with reference to Figure 1 or Figure 2 of the accompanying drawings.