GB2433495A

GB2433495A - Protective cap

Info

Publication number: GB2433495A
Application number: GB0520070A
Authority: GB
Inventors: Graham C Bushrod; Paul B Petley; Thomas F Jorgensen
Original assignee: DBI PLASTICS AS; Delphi Technologies Inc
Current assignee: DBI PLASTICS AS; Delphi Technologies Inc
Priority date: 2005-10-03
Filing date: 2005-10-03
Publication date: 2007-06-27
Also published as: GB0520070D0

Abstract

A protective cap for connection to an external screw thread (8) of a port (3) which defines an aperture (6) for a fuel volume (2), the protective cap comprising an inner sleeve (21) for receiving the port (3), the inner sleeve (21) including an outer surface (23) and an internal surface (24) having a portion of screw thread for co-operation with the external screw thread (8) of the port (3), and an outer cap (22) which cooperates with the inner sleeve (21) to seal an open end of the inner sleeve (21), and hence the aperture (6), when the port (3) is received within the sleeve (21). In this way the inner sleeve (21) serves to protect the external screw thread (8) of the port (3) while permitting access to the aperture (6).

Description

PROTECTIVE CAP

The present invention relates to a protective cap. In particular, but not exclusively, the present invention relates to a protective cap for a port of an accumulator fuel volume of the type used in common rail fuel injection systems.

Common rail fuel injection systems include an accumulator volume, or common rail, which is arranged to supply fuel at high pressure to a plurality of fuel injectors of the system. The common rail typically has a single inlet supply port for supplying fuel to the common rail fuel volume and several outlet supply ports, each of the outlet supply ports being connectable with a respective one of the injectors through a fuel pipe. The inlet and outlet supply ports are provided with an external screw thread, which mates with a corresponding internal screw thread formed in the pipe or in a pipe connector so that the pipes are connected to the common rail by means of screw thread connections.

During transportation of the common rail component and during any processing which the common rail may be subjected to prior to being fitted into an associated engine, it is desirable to keep the thread of the ports clean and to protect the thread from damage. It is also desirable to be able to seal the aperture of the port to prevent the ingress of dirt and debris into the fuel volume during transportation. Previously, this has been achieved through the use of a removable protective cap comprising a substantially hollow cylindrical body and a cap lid. The protective cap is fitted to each of the common rail ports by means of a screw thread so that the lid of the cap seals the port aperture. The known cap is screwed onto the thread of the port until the internal surface of the cap lid makes contact with the outermost end of the port.

A problem has been observed with protective caps of the aforementioned type in that over-tightening of the cap causes the outermost end of the port to exert pressure on the internal surface of the cap lid which can cause the cap to split, i.e. cause the cap lid to partially or wholly detach from the cap body (like punching the end of a top hat). This results in an ineffective seal at the port aperture.

I

Another problem arises if the internal thread of the known cap is damaged or altered so that it becomes ineffective at retaining the cap in position. One way in which the thread may be altered is again by over-tightening the cap. In the event of over-tightening, with the cap screwed onto the port such that the cap lid makes contact with the outermost end of the port, the start of the cap's internal thread, furthest from the cap lid, continues to travel around and down the thread of the port. However, the end of the cap's internal thread closest to the cap lid is prevented from travelling the same distance around and down the thread of the port because this end of the thread is rigidly connected to the cap lid. As a result, the internal cap thread begins to stretch and can reduce the engagement of the cap's thread with the port's thread to such an extent that the cap falls off. Therefore, the known cap does not protect the thread of the port effectively, nor does it provide an effective seal for the aperture.

Each of these disadvantages may result in premature replacement of the damaged common rail, which is costly, time consuming and inconvenient. However, in a worst-case scenario a reduced thread engagement between the port and its fuel pipe may result in the fuel pipe not being properly connected to the common rail and therefore fuel leakage occurs within the engine compartment.

The object of this invention is to provide an improved protective cap assembly which overcomes the problems with the aforementioned prior art and which can easily be fitted to and removed from the ports of a common rail accumulator volume.

According to a first aspect of the invention there is provided a protective cap for connection to an external screw thread of a port which defines an aperture for a fuel volume, the protective cap comprising: an inner sleeve for receiving the port, the inner sleeve including an outer surface and an internal surface having a portion of screw thread for co-operation with the external screw thread of the port, and an outer cap which cooperates with the inner sleeve to seal an open end of the inner sleeve, and hence the aperture, when the port is received within the sleeve, so that the inner sleeve serves to protect the external screw thread of the port while permitting access to the aperture.

In a preferred embodiment, the inner sleeve comprises a first engagement means for cooperation with a corresponding second engagement means of the outer cap so as to secure the sleeve and the outer cap together.

More preferably, the outer cap includes a tubular body for receiving the inner sleeve and an end piece for sealing open end of the inner sleeve, and wherein the second engagement means is provided on an internal surface of the tubular body for cooperation with the corresponding first engagement means of the inner sleeve.

Optionally, the first engagement means includes at least one formation projecting from the external surface of the inner sleeve.

In this embodiment, the second engagement means preferably includes at least one recess, which is cooperably shaped to receive the formation on the inner sleeve.

Alternatively, the second engagement means includes at least one formation projecting from the internal surface of the outer cap.

In this embodiment, the first engagement means preferably includes at least one recess, which is cooperably shaped to receive the formation on the internal surface of the outer cap.

Typically, the formation is a bead.

Preferably, the external surface of the outer cap includes a plurality of ribs angularly spaced around the circumference of the outer cap to aid removal of the assembled protective cap, such that the cap can be fitted and removed easily.

Typically, the protective cap is intended for connection to a port of a common rail.

According to another aspect of the invention, a common rail for a fuel injection system, the common rail including a plurality of ports defining apertures for the fuel volume, and wherein one or more of the ports is fitted with a protective cap is provided.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows four ports of a common rail (from left to right) fitted with a known protective cap, an inner sleeve part of a two-part protective cap of an embodiment of the invention, an assembled two-part protective cap of the invention and where one port is without a protective cap, Figure 2a (prior art) shows a common rail port of a known common rail, Figure 2b (prior art) shows a known protective cap attached to the port of Figure 2a, Figure 3a shows a perspective view of the inner sleeve part of a two-part protective cap as in Figure 1, Figure 3b shows a perspective view of an outer cap part of the two-part protective cap as in Figure 1, Figure 3c shows a cross-section of the assembled two-part protective cap attached to the port of Figure 2a, Figure 3d shows a perspective view of the assembled two-part protective cap attached to the port of Figure 2a, Figure 4 shows a flow chart of the typical method steps of use of a known protective cap, and Figure 5 shows a flow chart of the typical method steps of use of the two-part protective cap according to the present invention.

Figure 1 shows a conventional common rail 1 which is typically formed in one piece from forged steel and machined such that it has a hollow centre defining a fuel volume 2 (the common rail fuel volume) for storing high-pressure fuel. The fuel volume 2 communicates with a plurality of ports 3. Typically, there is one inlet and four outlet ports 3. The common rail 1 is further provided with securing lugs 4, which provide means for securing the common rail 1 to an appropriate location within the engine and a connection means for receiving a pressure sensor (not shown). It is to be appreciated that while Figure 1 shows a common rail 1 of spherical design this invention is also suitable for use with other designs, for example tubular common rails.

As shown in Figure 2a, each port 3 is a hollow cylindrical tube, which protrudes radially from the common rail 1. At either end of the cylindrical tube the port 3 defines first and second apertures 5, 6. The first aperture 5 opens into the fuel volume 2 and the second aperture 6, at the outermost end of the port 3, defines a port end face 7. In use, fuel flows into the fuel volume 2 via the inlet port 3 and then out of the fuel volume 2, in the direction indicated by the arrow A, through the first aperture 5 into an outlet port 3. Fuel flows out through the second aperture 6 through a fuel pipe towards a fuel injector.

Bach of the ports 3 include a threaded section 8a, provided with an external screw thread 8 which mates with the corresponding fuel pipe, and a base section 9 which mates with the fuel volume 2. The circumference of the base section 9 is greater than the circumference of the threaded section 8a such that at the junction where the base and threaded sections 9, 8a meet a shoulder 10, defining a flat surface, is formed. The flat surface extends from the outermost edge of the base section 9 to the start of the threaded section 8a at the radially innermost end of the port 3. The base section 9 has a curved outer surface, around the circumference of the port 3.

The internal surface 11 of the port 3 is substantially smooth (i.e. unthreaded) and defines a central flow path for fuel between the first and second apertures 5, 6. The central flow path includes a section of uniform diameter 12 and a conical section 13 towards its outer end which tapers out to the enlarged second aperture 6.

The rail 1 is provided with a protective cap 14 used for protecting the external thread 8 of the port 3 and preventing the ingress of dirt or debris into the fuel volume 2 during transportation. A known cap of this type is shown attached to a port 3 on the far left of Figure 1 and in Figure 2b.

The known cap 14 as shown in Figures 1 and 2b is moulded from plastic, for example high-density polyethylene. The cap 14 is a hollow cylindrical tube, which is open at one end and sealed at the other; the sealed end will be referred to as a cap lid 15. Part of the internal surface of the cylindrical tube section (cap body) 16 is threaded (not shown) such that the cap 14 may be screwed onto the port 3. When the cap 14 is screwed fully onto the port 3 the internal surface of the cap lid 15 makes contact with the port's end face 7.

The thread on the internal surface of the cap 14 is approximately one turn (i.e. 3600) and is situated relatively close to the internal surface of the cap lid 15. In other words, approximately one turn of the cap 14 is sufficient to screw the cap 14 onto the port's thread 8 until the end face 7 makes contact with the internal surface of the cap lid 15.

The external surface 17 of the cap 14 is substantially smooth and includes narrow ribs 18 that run the axial length of the cap 14 at regularly spaced intervals around the circumference. The overall diameter of the cap 14 is not much larger, relatively, than the diameter of the port 3. As such, caps of this type can be awkward to remove because there is not much surface area for a user to grip on to, when rotating the cap in order to remove it As described earlier, the problems associated with the known cap 14 are that it is easily damaged as a result of over-tightening the cap 14. The cap lid 15 may be wholly or partially detached from the cap body 16 such that the port's aperture 6 is not effectively sealed, permitting the ingress of dirt or debris into the fuel volume 2.

Furthermore, the thread on the internal surface of the cylindrical tube section 16 may be stretched to such an extent that the cap may fall off, meaning that the port 3 is not effectively sealed and that the external thread 8 of the port is not protected from damage during transportation of the common rail 1.

In addition, because the thread on the internal surface of the cylindrical tube section 16 is approximately only one-turn it does not offer much thread to retain the cap 14.

Therefore, if it is not fitted correctly the cap 14 may simply fall off.

The present invention relates to a protective cap 20 as shown in Figure 1 (on the second and third ports from the left) and Figure 3. The protective cap 20 of the invention will be referred to as a two-part cap to distinguish it from the known cap 14.

The two-part cap 20 consists of an inner sleeve 21 and an outer cap 22.

The inner sleeve 21 as shown in Figure 3a is manufactured from plastic, for example high-density polyethylene. As shown, the inner sleeve 21 is a hexagonal hollow tube defining six external sides 23 and has a substantially cylindrical internal surface 24.

The sleeve 21 has top and bottom annular end faces 25, 26, respectively, where the top is defined as being at the outermost end of the port 3 and the bottom is defined as being at the innermost end of the port when the inner sleeve 21 is fitted to the port 3.

Each of the external sides 23 of the inner sleeve 21 is predominately flat except for an engagement means 27, such as a protruding bead, for engaging with the outer cap 22 when fitted.

Part of the internal surface 24 of the inner sleeve 21 is threaded such that it may be screwed onto the thread 8 of the port 3. The thread 28 of the internal surface 24 takes the form of a protruding helical rib shaped to mate with the corresponding thread 8 of the port 3. The thread 28 is approximately one turn (i.e. 3600) and is situated relatively near the top of the inner sleeve 21. The height of the inner sleeve 21 is comparable, but shorter, than the height of the threaded section 8a of the port 3.

The outer cap 22, as shown in Figure 1 (on the third port from the left), and Figures 3b, 3c and 3d is a hollow cylindrical cap having a tubular body 36 that is open at one end and sealed at the other; the sealed end will be referred to as an outer cap lid 29.

The external surface 30 of the outer cap 22 is predominately cylindrical and has a number of ribs 31 that run the length of the outer cap 22 and are angularly spaced around the circumference of the outer cap 22. The overall diameter of the outer cap 22 is larger than the diameter of the inner sleeve 21, which in turn is larger than the diameter of the port 3. This offers the advantage that there is a larger circumference for a user to grip when removing the cap.

Unlike the known cap 14, the internal surface 32 of the outer cap 22 of the two-part cap is not threaded. Instead, the internal surface 32 is shaped to fit over and engage with the inner sleeve 21. As shown in Figure 3b, the internal surface 32 of the outer cap 22 comprises six waIls 33 forming a hexagonal cross-section, and a ceiling 34 defined by the internal surface of the cap lid 29. In addition, the cap 22 has a bottom end face 37, which is opposed and parallel to the cap ceiling 34. Each of the six walls 33 is provided with an engagement means including a recess 35, which is the same size and shape as the inverse of the protruding bead 27 on the inner sleeve 21.

Therefore, when fitted, each of the beads 27 of the inner sleeve 21 fits into and engages with a corresponding recess 35 in the internal surface 32 of the outer cap 22.

The beads 27 are smooth to allow the outer cap 22 to effectively snap-on' to the inner sleeve 21. The sides 33 of the outer cap 22 are relatively flexible, and give enough slack, to allow the outer cap 22 to fit onto the inner sleeve 21 as it is manoeuvred over the beads 27.

In a preferred embodiment of the present invention, the bottom end face 37 of the outer cap 22, when fitted to the inner sleeve 21, stops short of the shoulder 10 and the bottom end face 26 of the inner sleeve 21 such that a section of the inner sleeve 21 is visible when the outer cap 22 is fitted. This is advantageous as it provides a visible indicator that the outer cap 22 is fitted correctly because the section of inner sleeve 21, which is visible, should be of uniform height when the outer cap 22 is fitted correctly.

By way of comparison with the present invention, Figure 4 illustrates the typical method steps of use of a known protective cap 14 such as that shown in Figures 1 and 2b. In a first step 100, the common rail 1 is manufactured in a first location. During a second step 110 the common rail 1 is transported to a second location for further processing. Further processing occurs in a third step 120 and may involve unpacking, washing, assembling, testing and repacking the common rail 1. During this step, the port thread 8 is not protected and the port aperture 6 is not sealed. Therefore, the thread 8 may be damaged or become unclean during this stage and dirt or debris may end up inside the port.

Prior to transportation to a third location for fitting into an associated engine, the protective caps 14 are fitted to the ports 3 in a fourth step 130. In practice a cap 14 is fitted to each of the ports 3, although for simplicity Figure 4 shows the use of just one protective cap 14.

As the screw thread on the internal surface of the cap has approximately one turn, situated near the cap lid 15, approximately one clockwise turn of the cap is sufficient to screw the cap 14 onto the port 3 such that the thread of the cap engages with the thread 8 of the port 3. The cap 14 rotates easily and screws onto the port 3 until a point where the internal surface of the cap lid 15 bears against the port end face 7.

Continuing to turn the cap 14 clockwise is still possible but is more difficult because of friction generated between the internal surface of the cap lid 15 and the end face 7.

As mentioned earlier, over-tightening the cap 14 (i.e. continuing to rotate the cap) can cause the lid 15 to split away from the body 16 so that the aperture 6 is not sealed effectively. In addition, the thread on the internal surface of the cap may be stretched such that the engagement between the thread 8 of the port 3 and that of the cap 14 is reduced, which may in turn result in the cap 14 becoming detached from the port 3 and falling off.

In a fifth step 140 the common rail 1 is transported to the third location, where the protective cap, if still in place, is removed in a sixth step 150. The cap 14 is removed from the outlet port 3 by rotating the cap anti-clockwise for approximately one turn until the thread on the internal surface of the cap 14 disengages from the thread 8 of the port 3. Subsequently, in a seventh step 160, the common rail 1 is fitted into the engine.

As mentioned above, the protective cap 20 according to the present invention comprises two separate parts, the inner sleeve 21, which protects the thread 8 of the port 3 and the outer cap 22, which is effectively a snap on cap' that seals the aperture 6 of the port 3.

Figure 5 shows the typical method steps of use of both parts of the two-part cap 20 shown in Figures 1 and 3. The common rail 1 is manufactured in a first location during a first step 210. In a second step 220, and prior to being transported to a second location, inner sleeves 21 are fitted to each of the ports 3. In practice, a protective cap would be fitted to each outlet 3 but, for simplicity, Figure 5 relates only to the use of a single two-part cap 20.

The thread 28 on the internal surface 24 of the inner sleeve 21 has approximately one turn (i.e. 3600), situated relatively near the top end face. The inner sleeve 21 is screwed onto the port 3 by turning the sleeve 22 in a clockwise direction so that the thread 28 of the inner sleeve 21 engages with the thread 8 of the port 3. When fitted to the port 3 the inner sleeve 21 is rotated clockwise until the bottom end face 26 comes into contact with the flat surface of the shoulder 10 of the port 3. Continuing to rotate the inner sleeve 21 causes its bottom end face 26 to bear down onto the shoulder 10.

Cooperation between the thread 28 on the internal surface 24 engaging with the thread 8 of the port 3 ensures that the inner sleeve 21 does not freely rotate but instead tightens against the shoulder 10.

The number of rotations required until the point where the bottom end face 26 of the inner sleeve 21 bears against the shoulder 10 depends on the respective heights of the inner sleeve 21 and the threaded section 8a of the port 3. If the inner sleeve 21 is much shorter than the threaded section 8a of the port 3, the thread 28 will have to travel further down the port 3 until the bottom end 26 of the sleeve 21 meets the shoulder 10: the inner sleeve 21 will have to be rotated repeatedly in this example.

However, if the inner sleeve 21 is of a comparable shorter height than the threaded section 8a of the port 3, the inner sleeve 21 will have to be rotated fewer times until the bottom end face 26 of the sleeve 22 bears against the shoulder 10. A large number of turns is not desirable as this could lead to repetitive strain injury (RSI) of the user fitting or removing the cap 20.

When the bottom end face 26 of the inner sleeve 21 comes into contact with the shoulder 10, continuing to turn the sleeve 21 clockwise is still possible but is more difficult because of friction generated between the end face 26 and the shoulder 10.

During a third step 220 the common rail I is transported to the second location for further processing steps, and because the inner sleeve 21 is effectively retained in position the thread 8 of the port 3 is protected from damage and kept clean.

At the second location, the inner sleeve 21 is left in position fitted to the port 3 during any further processing steps of the common rail 1. This allows access to the aperture 6 of the port 3, while ensuring that the thread 8 of the port 3 is protected.

Prior to the common rail I being transported to a third location for fitting into the associated engine, the outer cap 22 is fitted to the inner sleeve 21 in a fifth step 240.

The outer cap 22 effectively snaps on' to the inner sleeve 21, with the beads 27 engaging with the recesses 35, in order to effectively seal the port aperture 6. This is the assembled configuration of the two-part cap 20.

During a sixth step 250, the common rail 1 is transported to the third location where the assembled cap 20, in a seventh step 260, is removed from the port 3 by rotating the cap 20 anti-clockwise until the thread of the inner sleeve 21, which is now engaged with the outer cap 22, disengages from the thread 8 of the port 3. Therefore, the inner sleeve 21 and the outer cap 22 are both removed together and the common rail 1 can be fitted into the engine in an eighth step 270.

While the outer cap 22, when fitted to the inner sleeve 21, is designed so that is does not simply fall off, the outer cap 22 can be detached from the inner sleeve 21, when fitted to the port 3, by applying a certain amount of torque to the outer cap 22. Being separable is not necessarily essential as caps for this purpose are generally intended for single use. However, in one embodiment the inner sleeve 21 and the outer cap 22 are designed so that the outer cap 22 can be removed, without causing damage to the parts.

The two-piece cap 20 according to the present invention has a number of advantages over the known cap 14. Firstly, the two-part cap 20 is not susceptible to damage in the same way as the known cap 14. The internal surface 34 of the outer cap lid 29 is never in contact with the end face 7 of the port 3 and cannot be caused to separate from the body of the cap if the inner sleeve 21 is over-tightened. Therefore, the seal of the port aperture 6 is guaranteed and ingress of dirt or debris into the fuel volume 2 is prevented when the outer cap 22 is correctly fitted.

Similarly, over-tightening the inner sleeve 21 does not cause the thread 28 on the internal surface 24 of the inner sleeve 21 to stretch, as can occur with the known cap 24. The thread 28 of the inner sleeve 21 is compressed if the inner sleeve 21 is over-tightened, ensuring effective retention of the inner sleeve 21. The tight fit of the outer cap 22 to the inner sleeve 21 ensures that the outer cap 22 cannot fall off. Therefore, the present invention provides a cap 20 that is effectively retained in position and which performs the necessary functions of protecting the thread 8 from damage and preventing the ingress of dirt/debris into the fuel volume 2.

A further advantage of the two-part cap is that the inner sleeve 21 can perform the thread protection function on its own while still permitting access to the port aperture 6 as required during any further processing steps that the common rail 1 is subjected to. This further ensures that the thread 8 is protected from damage and kept clean.

Furthermore, the ribs 31 present on the outer cap 22 help facilitate the rotation of the assembled cap 20 and also provide additional leverage when the outer cap 22 is being fitted to or removed from the inner sleeve 21. The overall diameter of the assembled cap 20 is larger than the known cap 14 and, because of this, the two-part cap 20 is easier to rotate making it easier to fit and remove.

It will be appreciated that other engaging means 27 may be used to engage the outer cap 22 with the inner sleeve 21. For example, the external surface of the inner sleeve 21 may comprise recesses, which are the inverse of engaging means protruding from the internal surface of the outer cap 22.

A person skilled in the art would comprehend that the protective cap detailed herein need not be limited to the specific illustrated embodiments, but only by the scope of the appended claims. For example, any threaded port such as those found in other rails and pumps.

A person skilled in the art would also comprehend that the term port used herein is intended to include an outlet, an aperture, an opening, or a flow path for example.

Claims

Claims 1. A protective cap for connection to an external screw thread

(8) of a port (3) which defines an aperture (6) for a fuel volume (2), the protective cap comprising: an inner sleeve (21) for receiving the port (3), the inner sleeve (21) including an outer surface (23) and an internal surface (24) having a portion of screw thread for co-operation with the external screw thread (8) of the port (3), and an outer cap (22) which cooperates with the inner sleeve (21) to seal an open end of the inner sleeve (21), and hence the aperture (6), when the port (3) is received within the sleeve (21), so that the inner sleeve (21) serves to protect the external screw thread (8) of the port (3) while permitting access to the aperture (6).

2. A protective cap (20), as claimed in Claim 1, wherein the inner sleeve (21) comprises a first engagement means (27) for cooperation with a corresponding second engagement means (35) of the outer cap (22) so as to secure the sleeve (21) and the outer cap (22) together.

3. A protective cap (20), as claimed in Claim 2, wherein the outer cap (22) includes a tubular body (36) for receiving the inner sleeve (21) and an end piece (29) for sealing the open end of the inner sleeve and wherein the second engagement means (35) is provided on an internal surface (32) of the tubular body (36) for cooperation with the corresponding first engagement means (27) of the inner sleeve (21).

4. A protective cap (20), as claimed in Claim 3, wherein the first engagement means (27) includes at least one formation projecting from the external surface of the inner sleeve (21).

5. A protective cap (20), as claimed in Claim 4, wherein the second engagement (35) means include at least one recess, which is cooperably shaped to receive the formation on the inner sleeve (21).

6. A protective cap (20), as claimed in Claim 3, wherein the second engagement means (27) includes at least one formation projecting from the internal surface of the outer cap (21).

7. A protective cap (20), as claimed in Claim 6, wherein the first engagement (21) means include at least one recess, which is cooperably shaped to receive the formation on the internal surface of the outer cap (21).

8. A protective cap (20), as claimed in any of Claims 4 to 7, wherein the formation is a bead (27).

9. A protective cap (20), as claimed in any preceding claim, wherein the external surface (30) of the outer cap (22) includes a plurality of ribs (31) angularly spaced around the circumference of the outer cap (22) to aid removal of the assembled protective cap (20).

10. A protective cap (20), as claimed in any preceding claim, for connection to an outlet port (3) of a common rail fuel volume (1).

11. A common rail (1) for a fuel injection system, the common rail including a plurality of ports defining apertures for the fuel volume, and wherein one or more of the ports is fitted with a protective cap (20) as claimed in any preceding claim.