GB2265423A - Delivery valves. - Google Patents

Description

-2265423 The invention relates to delivery valves.

A delivery valve, as described in German patent application P 41 268 792. is disposed in a delivery line between a pump working chamber and a fuelinjection point. A valve closure member is raised from its valve seat against the force of a spring by means of a highly pressurised medium. which is supplied to the delivery valve from the pump working chamber, and consequently the delivery valve is opened. The valve closure member returns to its seat at the end of the high-pressure delivery. Simultaneously, a fuel-injection valve closes at the fuel-injection point, causing pressure waves to flow to and fro in the enclosed volume between the delivery valve and the fuel-injection valve and these pressure waves are able to open the fuel-injection valve again. In order to avoid this, a return valve is disposed in the inside of the valve closure member and it is possible by way of the return valve for the pressure level in the delivery line to reduce even after the closure of the valve closure member to a static pressure, which is predetermined by pre-stressing the return spring of the return valve.

However. the fuel which subsequently overflows in 1 -2this case to the pump working chamber by way of the return valve causes problems relating to the durability of the return spring as a result of the cross-section through which the fuel can flow away. Owing to the relative large through-flow crosssection, a large mass flow of medium exerts a force during the course of the shut-off process against the return valve closure member, which is designed here as a sphere, and pushes it open rapidly and widely. This severe acceleration of the sphere causes a high mechanical load on the return spring and therefore reduces the durability thereof and consequently the serviceable life of the entire delivery valve.

In order to reduce this rapid, severe and wide opening process of the delivery valve. a throttle is connected in advance of the known return valve in the delivery valve formed as a pressure equalising valve. This throttle constricts the mass flow and reduces its flow rate in the larger through-flow cross-section connected to the throttle, as a result of which the opening movement of the return valve is retarded. This slower acceleration of the valve sphere causes on the other hand a reduction of the mechanical load on the return spring of the return valve. At the same time. the throttle is formed as a bore, having in each case a phase at the ends of the bore, so that a gradual transition to the contiguous chambers is 1 1 -3produced. In the case of this throttle bore, the fuel flow is severely contracted during the through-flow and this leads to a low pressure within the throttle, as a result of which vapour bubbles are formed at this point. On the one hand the vapour bubbles hinder the further through- flow, and on the other hand they cause cavitation damage within the delivery valve. In order to maintain the necessary through-flow cross- section during the contraction which occurs, it is necessary, in the known solution, to select a relatively large throttle bore diameter. which in the case of a flow which is not yet built up, on the other hand facilitates a large through-flow quantity, which opens the return valve in a manner which severely loads the spring.

As the pressure in the delivery line increases, so does the cavitation damage as described, so that the known delivery valves no longer satisfy the requirements for reliability and durability during high-fuelinjection pressures.

In accordance with the present invention there is provided a delivery valve for installation in a delivery line between a pump working chamber of a fuel-injection pump and a fuel-injection point in the internal combustion engine to be supplied by the delivery valve, the delivery valve having a valve body t having a valve seat and a through-flow channel, in which a delivery valve closure member is guided and disposed in the inside of the delivery valve closure member, a return valve which opens towards the pump working chamber and which comprises a valve closure member, disposed between a valve seat enveloping a through-flow bore in the delivery valve closure member and a compression spring fixedly supported at the delivery closure member and having a throttle which is disposed at the end of the through- flow bore remote from the pump working chamber, the throttle having a portion of reducing diameter of the through-flow cross-section which leads at its smallest crosssection to a portion of enlarging diameter which increases outwards from the smallest cross-section, wherein the smallest cross-section between the reducing diameter and the enlarging diameter is formed as an edge.

This has the advantage that, in spite of a high restricting effect of the throttle connected in advance of the return valve with its load-relieving effect for the return spring of the return valve, vapour bubbles are prevented from forming in the throttle. In so doing, the flow rate is severely reduced without producing at the same time a large pressure difference, which causes a low pressure, 1 -5between the chamber in advance of the throttle and the chamber following the throttle. This is achieved in an advantageous manner by arranging the narrowing and enlarging throttle parts immediately adjacent to each other and by means of their sharp-edged change in section, which prevents the flow from rapidly contracting within the throttle, as is the case in the known delivery valve, and the local pressure in the throttle drops below the vapour pressure, which represents the cause of the formation of vapour bubbles. In order to prevent a drop in local pressure, as a result of a higher flow rate than in the region of the channel in advance of the throttle, from also occurring in the continuation of the channel connected to the throttle. and to achieve a similar flow behaviour in both regions of the channel. the diameter of the channel in advance of the throttle should be substantially the same as the diameter of the channel following the throttle.

By way of example only, specific embodiments of the invention will now be described, with reference to the accompanying drawings, in which:- Fig.1 illustrates a longitudinal sectional view through a delivery valve formed as a pressure equalising valve, constructed in accordance with a first embodiment of the present invention; Fig.2 is an enlarged sectional view from Fig.1, representing the design of the throttle in a channel issuing towards the return valve, wherein the crosssection of the change in section of the throttle is conical in shape; and Fig.3 is analogous to the illustration of Fig.2 and illustrates a throttle having a rounded inlet funnel constructed in accordance with a second embodiment.

Fig.1 illustrates a longitudinal sectional view through a delivery valve 1, which is inserted in a housing (not illustrated) of a fuel-injection pump and sits in a delivery line 3 between a pump working chamber 5 (partially illustrated) of the fuelinjection pump and a fuel-injection point 7, in the form of a fuel-injection valve, of the internal combustion engine (likewise not illustrated) being supplied.

The delivery valve 1 comprises on the one side a tubular valve body 9, which comprises at its lower end at the pump side, a collar 11 at its external periphery and in its inside comprises a through-flow channel 13 in the form of an axial bore. At its upper end remote from the pump working chamber 5, the valve body 9 comprises a valve seat 15, against which a conical sealing surface 17 of a delivery valve closure j -7member 19 of the delivery valve 1 forming the other part of the delivery valve 1 comes to rest. The delivery valve closure member 19 comprises in a known manner below the sealing surface 17 wing-shaped guide surfaces 21, which are guided in the through-flow channel 13 of the valve body 9 and between which fuel can flow towards the valve seat 15.

The delivery valve closure member 19 comprises at its periphery a shoulder 23, against which a compression spring (not illustrated) engages and the compression spring is supported on the other side in a spring chamber (likewise not illustrated) which envelops the delivery valve closure member 19 and the delivery valve closure member 19 is therefore pressed with its sealing surface 17 against the valve seat 15. Moreover, the delivery valve closure member 19 comprises in its inside an axial longitudinal channel 25, which is formed as an axial stepped bore and one bore part of the axial longitudinal channel 25 forms, in the region of the guide surfaces 21, a step 27 to the other bore part. A stop bushing 29 comes to rest with its front face against the step 27 and the stop bushing 29 comprises in its inside a blind bore 33 which issues from the front face at the pump side and two radial bores 35 issue into the opposite end of the b lind bore 33, thus producing a connection between the -8longitudinal channel 25 of the delivery valve closure member 19 and the through-flow channel 13 of the valve body 9.

The stop bushing 29 is guided with its peripheral surface in the longitudinal channel 25 and forms a shoulder 31 by way of reducing the external diameter. A return spring which envelops the stop bushing 29 in the form of a compression spring 37 is supported on the shoulder 31, the compression spring 37 guides on the other side a spring plate 39 of a return valve 41, which acts upon the valve closure member 43 in the form of a sphere, wherein the upper front face of the stop bushing 29 remote from the pump working chamber 5 forms a travel-limiting stop 30 for the spring plate 39. The valve closure member 43 of the return valve 41 which opens towards the pump working chamber 5 is pressed by means of the compression spring 37 against a valve seat 45, which is formed by a sleeve 47 sealing the longitudinal channel 25 in the delivery valve closure member 19 at the side remote from the pump working chamber 5, the sleeve 47 comprises in its inside a through-bore 49, which enlarges conically towards the valve closure member 43 and forms therefor the valve seat 45. A throttle 51 is disposed in the upper region of the through-flow bore 49 remote from the pump working chamber 5.

An enlarged view of the structure in accordance with the invention of two embodiments of this throttle 51 in the through-flow bore 49 is illustrated in Figs. 2 and 3, wherein the description of these figures is limited to the structure of these throttles 51.

In the case of the throttle 51, illustrated in the enlarged view of Fig.2, at the end of the throughflow bore 49 which issues from the upper front face 53 of the sleeve 47 remote from the pump, there is a first funnelshaped inlet part of reducing diameter 60, which conically tapers to the smallest diameter and/or cross section d. The section of the bore 49 directly connected to the smallest diameter and/or cross section d once again enlarges conically to the diameter of the through-flow bore 49 and has an enlarging diameter 62. An edge 58 is formed between the reducing diameter 60 and the enlarging diameter 62. The enlarging diameter portion 62 forms a defuser which extends over a shorter axial progression than the reducing diameter portion 60 and the conical transitional surface of the enlarging diameter portion 62 also comprises therefor a steeper angle than that of the reducing diameter portion 60.

The second embodiment of the throttle 51 in accordance with the invention, as illustrated in F ig-3, differs from that illustrated in Fig.2, merely -lo- in the design of the reducing diameter 60, whose change in section reducing the cross-section, changes here on a decreasing scale towards the smallest crosssection of the throttle 51.

The progression of the wall surface of the throttle 51 is described in the axial sectional view through the throttle 51 by means of an arc of a circle or a curve similar to a circle.

The delivery valve 1 in accordance with the invention functions as follows:

If fuel is delivered to the fuel-injection point 7 of the internal combustion engine when a fuelinjection pump, in which the above described delivery valve 1 is installed, is in service, then the delivery valve closure member 19 is raised from the valve seat 15 of the valve body 9 under the pressure of the fuel flowing out of the pump working chamber 5 and the delivery valve 1 is opened. If the delivery pressure of the fuel drops at the end of the fuel delivery, the force of the fuel flow is no longer sufficient to hold the delivery valve closure member 19 open against the force of the compression spring 37, the delivery valve closure member 19 returns to its valve seat 15 and the delivery valve 1 closes. As a result of suddenly interrupting the delivery. pressure waves run to and fro in the enclosed volume between the delivery valve 1 -111 and the fuel-injection point 7. In order to avoid any further fuel being injected at the fuel-injection point. the pressure level of the pressure wave peak pressures in the delivery line 3 is now reduced_by way of the return valve 41 to a predetermined amount, in that the fuel raises the valve closure member 43 from its valve seat 45 against the force of the compression spring 37 and the fuel flows back by way of the radial bore 35 and the blind bore 33 into the pump working chamber 5, which is now relieved of pressure at the end of the high-pressure delivery phase.

In order to avoid the valve closure member 43 opening excessively and the associated excessive through-flow volume. the valve closure member 43 can only open as far as the stop 30 of the stop sleeve 29 at the front. Since the compression spring 37 of the return valve 41 is mechanically severely loaded during this rapid opening process, the throttle 51 is connected in the through-flow bore 49 of the sleeve 47 in advance of the return valve 41, this restricts a high mass fuel-flow and therefore also limits the acceleration of the opening process of the return valve 41. In order to avoid the low pressure in the through-flow bore 49, which is caused by the high flow rate in the narrow throttle 51 and which causes the formation of air bubbles leading to cavitation damage, 1 -12the throttle 51 is designed in such a way that the reducing diameter 60 changes in section in a sharpedged manner into the enlarging diameter 62, so that the effects of the wall do not produce any contractions in the spray and the throttle 51 maintains the identical effective through- flow crosssection during all operational points. In this way, it is possible for the throttle cross-section and the load of the return spring of the return valve 41 to correspond reliably with each other for all operational regions. In addition to this. a contracting. rapidly flowing fuel-flow is prevented from forming in the region of the reducing diameter, when the pressure would also drop below the vapour pressure.

1

Claims (7)

-13CLAIMS

1. A delivery valve for installation in a delivery line between a pump working chamber of a fuel-injection pump and a fuel-injection point in the internal combustion engine to be supplied by the delivery valve, the delivery valve having a valve body having a valve seat and a through-flow channel, in which a delivery valve closure member is guided and disposed in the inside of the delivery valve closure member, a return valve which opens towards the pump working chamber and which comprises a valve closure member, disposed between a valve seat enveloping a through-flow bore in the delivery valve closure member and a compression spring fixedly supported at the delivery closure member and having a throttle which is disposed at the end of the through-flow bore remote from the pump working chamber, the throttle having a portion of reducing diameter of the through-flow cross-section which leads at its smallest crosssection to a portion of enlarging diameter which increases outwards from the smallest cross-sectionj wherein the smallest cross-section between the reducing diameter and the enlarging diameter is formed as an edge.

2. A delivery valve according to claim 1, wherein the reducing diameter comprises a non-linear 1 -14change in cross-section which reduces in a decreasing scale towards the smallest cross section.

3. A delivery valve according to claim 1, wherein the reducing diameter is formed in a conical shape.

4. A delivery valve according to one of the aforementioned claims, wherein the enlarging diameter is formed in a conical shape.

5. A delivery valve according to one of the aforementioned claims, wherein the diameter of the flow-through bore immediately before the throttle is substantially the same as the diameter of the throughflow bore immediately after the throttle.

6. A delivery valve, as claimed in any preceding claim, wherein the enlarging diameter extends over a shorter axial progression than the reducing diameter.

7. A delivery valve constructed and adapted to operate substantially as hereinbefore described, with reference to, and as illustrated in the accompanying drawings.