FLOW RESTRICTION MEMBER

The present invention relates to a member which is insertable into a flow passage to restrict the flow of fluid through the passage. In particular, the present invention relates to a member which is insertable into an oil flow passage of an a vacuum pump to restrict the flow of oil therethrough.

An automotive vacuum pump is typically supplied with oil from the engine lubrication system. The oil is required to both lubricate movable components of the pump and to assist with sealing of pump components with respect to one another. There is often a requirement that the flow of oil to the pump be limited so as not to exceed a defined flow rate. Limiting of the flow ensures that sufficient oil is supplied to the pump without affecting the circulation of oil around the remainder of the engine lubrication system. The required limiting of the flow rate of oil to the pump may be achieved by providing a restriction in the oil supply line to the pump. The restriction may be provided by reducing the diameter of an oil conduit. A problem with this solution is that the bore may require to be narrowed to such an extent that, in certain circumstances, the flow of oil may be overly restricted and the pump starved of oil. Oil starvation may, for example, occur when the oil is cold and hence more viscous than when hot.

An alternative method for providing the restriction involves placing an obstruction in the oil conduit which partially occludes the conduit. Taking the example of a tubular conduit, the obstruction may comprise a cylindrical member having an outer diameter which is less than the conduit diameter. The cylindrical member is positioned within the conduit such that an annular flow path is defined in the conduit around the member. A problem with this solution is that the cross-sectional dimensions of the annular flow path may be so small as to be susceptible to blockage by particles in the oil.

According to a first embodiment of the present invention there is provided a flow restriction member which is insertable into a fluid conduit of a vacuum pump to restrict the

flow of fluid through the conduit, the member comprising a core having a cross sectional area which is less than that of the conduit and a rib extending around the core in a substantially helical manner, the height of the rib being such that, in use, the rib contacts the wall of the conduit and defines a substantially helical flow path between the core and the wall of the conduit.

The present invention thus provides a member which is insertable into a conduit to restrict the flow of fluid therethrough. For a conduit of a given cross-sectional dimensions the degree by which the fluid flow is restricted is determined by the cross-sectional dimensions and path length of the helical flow path. From a manufacturing perspective, the present invention permits the relatively straightforward provision of a flow restriction within the casing of a vacuum pump. An oversize oil conduit may be formed in the casing into which the member is inserted in order to define the appropriate restriction.

The core may be substantially cylindrical, with uniform cross-sectional dimensions along its length about a central, longitudinal axis.

In one embodiment the helical rib may extend around the body for more than 360°. For example, the may rib extend around the body for about 720°.

The rib may comprise opposed side walls, and a curved top wall, the top wall being concentric with respect to the longitudinal axis of the body.

The member may further comprise at least one end portion, the end portion including at least one longitudinal rib. The end portion may be provided with a plurality of ribs. In one embodiment the end portion may include at least three longitudinal ribs. Alternatively, the end portion may include four longitudinal ribs. The longitudinal ribs may be spaced equidistantly about the end portion.

The end portion is provided with an end face, and the or each longitudinal rib may taper in the direction of the end face. In such an embodiment the or each longitudinal rib may taper

for approximately one third of its overall length. The or each longitudinal rib may include opposed and substantially parallel side walls and an outwardly curved top wall, the curve of the top wall being concentric with respect the longitudinal axis of the body.

The flow restriction member may be made from plastics material.

According to a further embodiment of the present invention there is provided a flow restriction member which is insertable into a fluid conduit to restrict the flow of fluid through the conduit, the member comprising a core having a cross sectional area which is less than that of the conduit and a rib extending around the core in a substantially helical manner, the height of the rib being such that, in use, the rib contacts the wall of the conduit and defines a substantially helical flow path between the core and the wall of the conduit, wherein the member further comprises an end portion, the end portion including a longitudinal rib.

According to a further aspect of the present invention there is provided a method of providing a flow restriction in a fluid conduit of a vacuum pump, the method comprising the steps of: providing a fluid conduit; providing member comprising a core having a cross sectional area which is less than mat of the conduit, a rib extending around the core in a substantially helical manner and an end portion having a longitudinal rib; and inserting the member into the conduit such that said helical rib contacts a wall of the conduit to define a substantially helical flow path between the member and the wall of the conduit.

An embodiment of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 shows a side view of an insertable member according to the present invention;

Figure 2 shows a further side view of the insertable member of figure 1;

Figure 3 shows an end view of the insertable member; and Figure 4 shows the cross-sectional view indicated by arrows A-A in figure 2.

Referring to the figures there is shown an insertable flow restriction member generally designated 10. In use, the flow restriction member is insertable into a tubular liquid or fluid conduit in order to create a restriction to the flow of liquid or fluid through the conduit. The member 10 is of unitary construction and may be formed from a plastics material by an injection moulding process. The member 10 includes a substantially cylindrical core 12 of uniform cross-sectional dimensions along its length which is provided about a central, longitudinal axis 14. Extending from the core 12 are a plurality of projections, the function and configuration of which are described in greater detail below. The member 10 may be considered to comprise opposed end portions 16,18 separated by a mid portion 20.

Each end portion 16,18 includes a plurality of longitudinal ribs 22. In the embodiment shown, each end portion 16,18 is provided with four ribs 22. In alternative embodiments each end portion 16,18 may be provided with a greater or lesser number of ribs. The number of ribs 22 for a given member 10 will depend upon such factors as, for example, the viscosity of the liquid which is intended to flow around the member 10, and the diameter of the conduit into which the member 10 is to be inserted. Each end portion 16,18 may have the same number of ribs 22. Alternatively, each end portion 16,18 may have a different number of ribs 22. In the embodiment shown, each rib 22 extends outwardly from the core 12 in a direction substantially perpendicular to the longitudinal axis 14, and along the core 12 in a direction substantially parallel to the longitudinal axis 14. Each rib 22 includes opposed and substantially parallel side walls 24 which merge smoothly into the core 12, and an outwardly curved top wall 26. A portion 32 of the core 12 is exposed between adjacent ribs 22. The curve of the top wall 26 is concentric with respect the longitudinal axis 14 of the core 12. Each rib 22 further includes an end wall 27 which is proximal to the mid portion 10 of the member 10. The ribs 22 are spaced equidistantly about the core 12. The end 28 of each rib 22 which is distal to the mid portion 20 of the member 10 is tapered in the direction of the respective end of the member

10. In the embodiment shown, each rib 22 tapers into the core 12 a short distance before each end face 30 of the core 12. Each rib 22 is tapered for approximately one third of its overall length.

The mid portion 20 includes a rib 36 which extends around the core 12 in a substantially helical manner. The helical rib 36 comprises opposed side walls 38, end walls 40 and a top wall 42. The end and side walls 38,40 merge smoothly into the core 12. The top wall 42 is concentric with respect to the longitudinal axis 14 of the core 12. In the embodiment shown the helical rib 36 extends around the core 12 for two full revolutions or 720 degrees. The helical rib 36 and the exposed portion 44 of the core 12 define between them a substantially helical flow path 46. The helical rib 36 is positioned about the core 12 of the mid portion 20 such that it is spaced from the end walls 27 of the ribs 22. There is thus provided an exposed region 48 of the core 12 to either side of the helical rib 36. The helical rib 36 projects from the core 12 at a substantially constant height along its length around the core 12. The height of the helical rib 36 is substantially the same as that of the non-tapered portions of the longitudinal ribs 22.

In use, the member 10 is inserted into a tubular conduit 50 so as to create a flow restriction. The tapered ends 28 of the longitudinal ribs 22 assist with the location of the member 10 in the conduit 50 during the introduction of the member 10. The outer diameter of the member 10, as defined by the top walls 26, 42 of the longitudinal and helical ribs 22, 36 is slightly greater than the inside diameter of the conduit 50. As such, the member 10 is press fit to the conduit 50. Once inserted, the member 10 is retained in the conduit 50 by the frictional engagement of the rib top walls 26,42 with the conduit 50.

Once in the member 10 has been placed in the conduit 50, a number of liquid flow passages are defined between the member 10 and the conduit. Firstly, a substantially straight rib flow passage 52 is defined between the side walls 24 of adjacent ribs 22, the exposed core portion 32 and the conduit 50. In the embodiment shown, each end portion 16,18 of the member 10 is provided with four such rib flow passages 52. A helical rib flow passage is defined about the mid portion 20 of the member 10. The helical flow passage is

defined between side walls 38 of the helical rib 36, the exposed portion of core 12 around which the helical rib 36 winds, and the conduit 50. The straight rib flow passages 52 and the helical rib flow passage are separated from one another by a substantially annular chamber defined between the exposed region 48 of the core 12 between the rib end walls 27 and the helical rib 36, and the conduit 50.

Liquid, such as oil, encountering the member 10 within a conduit 50 is first split between the four rib flow passages 52. As the combined cross-sectional area of the four passages 52 is less than that of the cross-sectional area of the unobstructed conduit 50, then the flow of liquid is initially restricted by entry into the rib flow passages 52. Liquid entering the rib flow passages 52 subsequently enters the annular chamber situated between the rib end walls 27 and the helical rib 36. This liquid then enters the helical flow passage defined between the helical rib 36, core 12 and the conduit 50 and then travels in a helical path around the core 12 to the second annular chamber. The cross-sectional area of the helical flow passage is less than the combined cross-sectional area of the rib flow passages 52. The movement of the liquid around this helical path thus provides a further restriction to the flow of liquid through the conduit 50. Upon exiting the helical flow passage, the liquid passes into the second annular chamber before passing through the remaining four rib flow passages 52. It will be understood that the symmetrical nature of the member 10 ensures that the flow of liquid is restricted by the member 10 irrespective as to which direction flow encounters the member 10.

It will be appreciated that a member 10 according to the present invention can be constructed and configured so as to meet desired flow restriction requirements and performance. For example, the diameter of the core 12 may be varied, as may the number, spacing, thickness and length of the longitudinal ribs 22. Additionally, the dimensions of the helical rib 36, and hence the helical flow path may also be varied. Depending upon the required flow restriction properties, the helical rib 36 may wind around the core 12 for less than 720 degrees or more than 720 degrees.

In the embodiment shown the member 10 is double ended and as such may be inserted either way into the conduit. It will be appreciated that for alternative installations, the member 10 may be handed or otherwise configured so as to be insertable into the conduit in a single direction. In the embodiment shown, both of the end portions 16,18 are substantially equal in length and rib configuration. In an alternative embodiment, the •lengths and rib configurations of the end portions 16,18 may be different. In yet a further embodiment only one end portion of the member may be ribbed.