EP1116879A2

EP1116879A2 - Spring seat

Info

Publication number: EP1116879A2
Application number: EP00311690A
Authority: EP
Inventors: Alan Conway Green; John William Stevens
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2000-01-14
Filing date: 2000-12-27
Publication date: 2001-07-18
Also published as: EP1116879A3; GB0000909D0

Abstract

The present invention provides a workpiece (10) having a blind bore (12) of stepped form defining a chamber (16a, 16b) within which a seating member (14) is arranged. A region of the seating member (14) is shaped to form an interference fit within a first part (12a) of the bore (12), the shaped region of the seating member (14) being provided with one or more relieved sections (18) to ease insertion of the seating member (14) into the bore (12) during assembly of the workpiece (10). Cooperation between the seating member (14) and the first part (12a) of the bore (12) serves to retain the seating member (14) in position within the bore (12).

The invention is particularly suited to being a nozzle holder body for a nozzle body of a fuel injector.

Description

The invention relates to a workpiece provided with a seating member. In particular, but not exclusively, the invention relates to a part of a fuel injector, such as a nozzle body holder, provided with a seating member. The invention also relates to a method of forming the workpiece.
Known fuel injectors of the two-stage lift type typically comprise a valve needle which is slidable within a bore provided in a nozzle body secured to a nozzle body holder. The nozzle body holder is provided with a blind bore which defines a chamber, a pair of springs being housed in axial relationship within the chamber and being operable to provide a two-stage biasing force on the valve needle. One of the springs remote from the valve needle engages a reaction surface disposed at the end of the chamber remote from the valve needle. The other of the springs engages a reaction element located part way along the length of the chamber. When in use, movement of the valve needle away from the seating against the spring force permits fuel delivery through one or more outlet openings of the injector, depending on the extent of movement of the valve needle within the bore.
European Patent Application No. 0653561 describes one such arrangement in which the reaction element comprises an annular component from which extends a plurality of axially extending and angularly spaced legs. During assembly of the reaction element within the chamber, the legs are urged outwardly into firm engagement with the wall of the chamber so as to maintain the reaction element in position within the chamber, the reaction element thereby providing an adequate bearing load for the spring.
A problem with known arrangements of this type is that, in order to ensure the reaction element provides an adequate reaction force for the compression spring, accurate machining of the surfaces of the reaction element is required. This can require an undesirable number of processing steps.
In an alternative known arrangement, the reaction element may take the form of a seating member having a surface of stepped form which is inserted into the bore of the nozzle holder body, the bore being provided with a further step with which the step in the surface of the seating member is engageable. Upon assembly of the injector, a first one of the springs is inserted into the blind end of the bore. The seating member is then inserted into the bore such that the step in the surface of the seating member abuts the further step in the bore. The second compression spring is then inserted into the chamber such that one end thereof abuts the seating member, abutment between the step in the surface of the seating member and the step in the bore serving to retain the seating member in position within the spring chamber so as to provide an adequate bearing load for the second spring. Alternatively, if an adequate step in the bore cannot be conveniently provided, the seating member may be retained within the bore by means of friction or staking.
One problem with this type of arrangement is that, as a step of relatively large size is required to provide an adequate bearing load for the seating member, the difference in diameter between the regions of the bore on either side of the seating member must be relatively large. It is therefore necessary for the first and second compression springs to be of different size. However, to simplify manufacture and to ensure both springs are subjected to similar stress forces, it is advantageous if both springs are of substantially the same size.
It is an object of the present invention to provide a workpiece having a seating member which alleviates or overcomes one or more of the aforementioned problems.
According to a first aspect of the present invention, there is provided a workpiece having a blind bore of stepped form defining a chamber within which a seating member is arranged, a region of the seating member being shaped to form an interference fit with a part of the bore, the shaped region being provided with one or more relieved sections to ease insertion of the seating member into the bore during assembly of the workpiece, cooperation between the seating member and the bore serving to retain the seating member in position within the bore.
Conveniently, the workpiece may form part of a fuel injector. For example, the workpiece may be a nozzle holder body for a nozzle body of a fuel injector. In use, the chamber may house first and second compression springs in axial relationship within the chamber and operable to provide a two-stage biasing force on a valve needle of the injector, the seating member providing a seating for a first one of the compression springs.
During assembly of the injector, the initial insertion load required to insert the seating member into the bore is reduced such that insertion of the seating member into the bore is relatively easy. Additionally, cooperation between the seating member and the bore ensures the seating member provides an adequate reaction force or bearing load for the first spring to be seated against the seating member, in use. Manufacture of the workpiece is also simplified as the step provided in the bore of the workpiece need only be of relatively small dimensions whilst still providing an adequate bearing load for the first spring.
Conveniently, the relieved sections provided on the seating member may take the form of flats extending along a part of the length of the seating member.
Preferably, the seating member has a substantially uniform diameter along its length.
According to a second aspect of the present invention, there is provided a method of forming a workpiece comprising the steps of;
providing the workpiece with a blind bore for receiving a seating member, the bore being provided with a step;
inserting a seating member into the bore under an insertion load, the seating member having a region shaped to form an interference fit with a part of the bore, the shaped region being provided with one or more relieved sections, whereby cooperation between the seating member and the bore serves to retain the seating member in position within the bore.
Preferably, the method may include the further step of monitoring the insertion load applied to the seating member as the seating member is inserted into the bore.
For the purpose of the specification, the phrase "relieved section" shall be taken to mean any form of flat, groove, slot, or other indentation provided on a surface.
The invention will now be described, by way of example, only with reference to the accompanying drawings in which;
Figure 1 is a sectional side view of a part of a fuel injector in accordance with an embodiment of the present invention;
Figure 2 is a sectional side view of a part of the fuel injector in Figure 1;
Figure 3 is a side-view of a seating member forming part of the fuel injector in Figure 1;
Figure 4 is an end view of the seating member in Figure 3; and
Figure 5 is a graph to illustrate insertion load against position during insertion of a seating member in a bore of the fuel injector in Figure 1.
Referring to Figures 1 to 4, there is shown a part of a housing 10 forming part of a fuel injector of the two-stage lift type, the housing 10 being provided with a blind bore 12 (the blind end of which is not shown) within which a seating member 14 is arranged. The bore 12 includes a first region 12a of reduced diameter and a second region 12b of slightly enlarged diameter, the first and second regions 12a, 12b being axially aligned. The interconnection between the first region 12a of the bore and the second region 12b of the bore defines a step or shoulder 24 in the bore 12. Typically, the enlarged second region 12b of the bore has a diameter of between 0.03 and 0.3 mm greater than the diameter of the first region 12a of the bore 12 such that the step 24 in the bore 12 is of relatively small dimension. This enables the step 24 in the bore 12 to be formed relatively easily. Typically, the housing 10 may take the form of a nozzle body holder for a nozzle body of the injector.
The bore 12 defines first and second spring chambers 16a,16b for housing first and second compression springs respectively (not shown), the springs being operable to provide a two-stage biasing force on the valve needle (not shown) of the fuel injector. The first spring may act directly on the valve needle or may act on the valve needle through another component, such as a shim or other load transmitting member. The valve needle is engageable with a valve needle seating, movement of the valve needle away from the seating against the action of the springs permitting fuel to be injected through one or more injector outlet openings depending on the extent of movement of the valve needle away from the seating.
As indicated in Figure 3, the seating member 14 has a substantially uniform diameter, D, along its length, an end region of the seating member 14 being provided with relieved sections 18 which extend along a part of the length of the seating member 14. The diameter of the first region 12a of the bore and the diameter, D, of the seating member 14 are chosen such that the seating member 14 forms an interference fit with the first region 12a of the bore 12. The seating member 14 is also provided with an axially extending through bore 20 (Figure 3), the through bore 20 permitting fuel within the first spring chamber 16a to escape to the second spring chamber 16b, in use, and for receiving a push rod (not shown) which is engaged with a portion of the valve needle of the injector. It will be appreciated that the seating member 14 may be provided with any number of relieved sections 18 depending on the particular requirements of the fuel injector.
Upon initial insertion of the seating member 14 into the bore 12 (from the left hand side in the illustration shown in Figure 1), the seating member 14 can be inserted freely up until the point at which the right hand end face of the seating member 14 aligns with the step 24 in the bore 12. Referring to Figure 5, there is shown a graph to illustrate the insertion load applied to the seating member 14 during insertion of the seating member 14 as a function of the position of the seating member 14 along the axis of the bore 12. At point, X, the right hand end face of the seating member 14 is aligned with the step 24 in the bore 12. From this point to the point at which the seating member 14 adopts the position shown in Figure 1, in which the relieved sections 18 are fully inserted in the first region 12a of the bore 12, the load required to insert the seating member 14 into the bore 12 is relatively low due to the provision of the relieved sections 18. Thus, during this stage of assembly, it is relatively easy to insert the seating member 14 into the bore 12.
When the seating member 14 is inserted further into the bore 12, such that the region comprising the relieved sections 18 is fully inserted into the first bore region 12a, the insertion load increases sharply (position Y in Figure 5) for any further displacement of the seating member 14 along the axis of the bore 12. For further insertion of the seating member 14 beyond this point, the bearing load is sufficiently high to ensure that the seating member 14 remains in a substantially fixed position within the bore 12. Cooperation between the seating member 14 and the bore 12 therefore ensures that the seating member 14 provides an adequate reaction force for the spring. It will be appreciated that, the extent to which the seating member 14 is inserted into the bore beyond position Y will depend on the requirements of the particular injector.
It will be appreciated that one of the advantages of this arrangement is that the step 24 in the bore 12 need only be of relatively small dimensions, thereby simplifying manufacture whilst ensuring an adequate bearing load is provided for the spring. Additionally, as the step 24 in the bore 12 is only of relatively small size, the first and second regions 12a,12b of the bore 12 are of similar diameter. This permits first and second compression springs of substantially the same size to be housed within the spring chambers 16a,16b.
The location of the step 24 in the bore 12 and the length of the relieved sections 18 provided on the seating member 14 are chosen to ensure the seating member 14 adopts the required position within the bore 12 when the fuel injector has been assembled. Additionally, the relative diameters of the seating member 14 and the region 12a of the bore 12 may be varied to change the characteristics of the interference fit between the seating member 14 and the first region 12a of the bore 12. For applications in which the location of the seating member 14 within the bore 12 and the bearing load provided by the seating member 14 are particularly critical, the insertion load may be monitored whilst the seating member 14 is inserted into the bore 12. This enables the position of the seating member 14 and the bearing load to be achieved accurately.
It will be appreciated that the number of relieved sections 18 on the seating member 14 can be chosen to suit the particular application and bearing load required for a given injector and that the number of relieved sections 18 may be different from that shown in the accompanying drawings. It will further be appreciated that the chambers 16a,16b may house other components, in addition to the compression springs.
Although the workpiece described with reference to the accompany drawings takes the form of a nozzle body holder 10 of a fuel injector, it will be appreciated that the present invention is not limited to forming part of a fuel injector but may be used in a variety of applications.

Claims

A workpiece (10) having a blind bore (12) of stepped form defining a chamber (16a, 16b) within which a seating member (14) is arranged, a region of the seating member (14) being shaped to form an interference fit with a first part (12a) of the bore, the shaped region of the seating member (14) being provided with one or more relieved sections (18) to ease insertion of the seating member (14) into the bore (12) during assembly of the workpiece (10), cooperation between the seating member (14) and the first part (12a) of the bore (12) serving to retain the seating member (14) in position within the bore (12).
A workpiece as claimed in Claim 1 wherein the workpiece (10) forms part of a fuel injector.
A workpiece as claimed in Claim 2 wherein the workpiece (10) is a nozzle holder body for a nozzle body of a fuel injector.
A workpiece as claimed in Claim 2 or Claim 3 wherein the chamber (16a, 16b) houses first and second compression springs in axial relationship within the chamber, said springs being operable to provide a two-stage biasing force on a valve needle of the injector, the seating member (14) providing a seating for a first one of the compression springs.
A workpiece as claimed in any preceding claim, wherein the first part (12a) of the bore (12) is cylindrical.
A workpiece as claimed in Claim 5 wherein a second cylindrical part (12b) of the bore (12) is connected to the first part of the bore by a step (24), the diameter of the second cylindrical part (12b) of the bore (12) being greater than the diameter of the first part (12a).
A workpiece as claimed in Claim 6 wherein said first and second parts (12a, 12b) of the bore are axially aligned.
A workpiece as claimed in any preceding claim, wherein the relieved sections provided on the seating member (14) are in the form of flats (18) extending along a part of the length of the seating member.
A workpiece as claimed in any preceding claim, wherein the seating member (14) has a substantially uniform diameter along its length.
A method of forming a workpiece (10) comprising the steps of;

providing the workpiece (10) with a blind bore (12) for receiving a seating member (14), the bore (12) being provided with a step (24) between first and second parts (12a, 12b) of the bore (12); and

inserting a seating member (14) into the bore (12) through the second part (12b) of the bore (12) towards the first part (12a) of the bore (12) under an insertion load, the seating member (14) having a region shaped to form an interference fit with the first part (12a) of the bore (12), the shaped region being provided with one or more relieved sections (18), whereby cooperation between the seating member (14) and the first part (12a) of the bore (12) serves to retain the seating member (14) in position within the bore (12).
A method as claimed in Claim 10, wherein the insertion load applied to the seating member (14) as the seating member (14) is inserted into the bore is monitored.