GB2091823A - Gland - Google Patents

Abstract

A gland with a frontal-sliding seal of the kind in which the sealing pressure between a graphite ring (22) and a hub (14) of a pump rotor (12) is applied by an elastomeric cup spring (24) cooperating with a helical spring (34), the front face of the base (26) of the cup spring having a number of concentric annular crests (28A, 30A, 32A) in sealing contact with the graphite ring (22) has, to improve this sealing contact, a pressure distributing ring (36) incorporated in the base (26) of the cup spring, and a circumferential groove (38) provided in the outer circumference of the base. <IMAGE>

Description

SPECIFICATION Gland This invention relates to a gland with a frontal sliding seal, of the kind comprising a cylindrical sheet metal housing which is open at one end and has an annular bottom wall at its other end, a rigid frontallysliding sealing ring which is movable axially but not rotatably in the housing adjacent the open end, an elastomeric cup spring without undercuts which is compressed axially between the ring and the bottom wall of the housing the free edge of the cup spring being in sealing circumferential contact with the transition zone between the bottom and the side wall of the housing, and the side wall of the cup spring being convex towards the side wall of the housing so as to establish with this wall a sealing contact which increases as the spring is compressed, the cup spring further including at its smaller end an annular elastomeric base which is directed radially towards the axis of the spring, and is in sealed frontal contact with the rigid ring by a number of concentric circular crests formed on the front face of the base, and a helical compression spring which is placed in the cavity of the cup spring, coaxial with the latter, the helical spring being in axial pressing contact with the base of the cup spring at one end and with the bottom of the housing at its other end.

Glands of this kind form the subject of a prior Patent Application No. 68358-A/79 by the same Applicant, filed 26th June, 1979.

An object of the present invention is to improve the seal between the circular crests and the rigid sliding sealing ring.

According to the invention in its broadest aspect, a gland with a frontal seal of the kind referred to is characterised in that a rigid pressure distributing ring, which is flat in cross-section and circumferentially continuous, is provided in the annular part of the base of the cup spring subjected to pressure by the helical spring, and in that the outer circumferential surface of the base is formed with a circumferential radial re-entrant groove. The pressure distributing ring serves to distribute the pressure of the helical spring evenly over the whole circumference of all the circular crests surrounded by the outermost crest. At the same time, the sealing contact between this latter crest and the sliding sealing ring is improved by the hydraulic pressure acting within the groove.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is an axial sectional view of this embodiment of the invention, and Figure 2 is an enlarged view of part of Figure 1.

In accordance with the prior Patent Application referred to above, there is shown the axis X of a circulation pump comprising a casing 10, a rotor 12, a rotor hub 14, and a drive shaft 16 which passes through an opening 18 in the casing. The drive shaft 16 is supported radially and axially in the opening by bearings which are not illustrated. The rotor 12 is immersed in the engine cooling water, the maximum pressure P of which depends upon the calibration of the outlet plug to the cooling circuit.

Typically, this is in the region of 0.8 to 1 Kg/cm2.

In order to prevent the leakage of water along the shaft 16, the casing 10 is provided with a gland, generally indicated at G. This gland comprises a cylindrical sheet metal housing 20 which is sealed within the casing 10 and has an annular bottom wall 20A, arranged concentrically about the axis X. The housing 20 is open towards the rotor 12, and contains a flat graphite ring 22 which is slidable axially in the open end of the housing but is prevented from rotating by the engagement of radial projections 20B in the housng with corresponding indentations 22B in the ring 22. The opposite faces of the ring 22 are flat and smooth, and the outer face is in sealed frontal sliding contact with the corresponding flat, smooth face 14A of the rotor hub 14, which may be rotating or stationary.

The ring 22 is thrust axially into sealed frontal contact with the hub 14 by two resilient members.

The first resilient member comprises a cup spring 24 which is made from rubber or other elastomeric material. The cup spring 24 is outwardly convex, that is, open towards the bottom wall 20A of the housing 20, and its free end 24A engages the transition zone between the bottom 20A and side wall of the housing 20 to effect a continuous circumferential seal. In accordance with the prior Patent Application mentioned initially, this sealing engagement may also extend to the side wall of the housing, depending on the degree of axial compression of the cup spring. The latter further comprises an annular rubber base 26 which is formed integrally with the cup-shaped body of the spring at its smaller and and is directed radially towards the axis X.The outer frontal face of the base 26 has three circular ribs 28, 30, 32, which are concentric with the axis X and which, being triangular in cross-section with vertex angles of about 90 , form three continuous circular crests 28A, 30A, 32A lying in a common plane perpendicular to the axis X. When assembled, these corners are pressed by the body of the cup spring 24 into sealing contact with the flat smooth inner face of the graphite ring 22, so as to prevent the escape of water under pressure P along the path indicated by the arrows F in Figure 1.

The second resilient member which maintains the contact pressure between the graophite ring 22 and the face 14Aofthe hub 14comprisesa helical spring 34 which is placed in the cavity of the cup spring 24 coaxial with the latter. One last coil of the spring 34 is in axial pressing contact with the inner transverse face 26A of the base 26 of the cup spring, whilst the opposite last coil reacts against the bottom wall 20A of the housing 20 and is centred relative to the axis X by a swaged-over edge 20C of the bottom wall 20A.

In a normal gland for motor vehicles, the cup spring 24 applies to the graphite ring 22 an axial pressure of about 4 Kg, to which is added a force of some 5 to 6 Kg exerted by the helical spring 34.

The structure described so far corresponds essentially to that forming the subject of the prior Patent Application referred to above.

In practice, the pressure P tends to increase, due to faulty calibration of the breather pipe plug of the cooling circuit, or to a defect (for example, encrustations) developing in the plug during use of the vehicle, and in this event the water in the cooling circuit tends to leak out between the graphite ring 22 and the crests 28A, 30A, 32A along the path indicated by the arrows F in Figure 1. This leakage, even when limited, leads to erosion of the crusts and/or the graphite ring, so that the tightness of the seal is adversely affected. It has been found that, with reference to the circle described by the last coil 34A of the helical spring 34, the most noticeable erosion occurs in an area (of the ring 22 and/or of the crests 30A and 32A) which is aligned axially with a break in the circle, that is, with the end of the coil.

According to this embodiment of the present invention, a substantially rigid and unbroken flat ring 36 is incorporated in the annular area ofthe base 26 of the cup spring subjected to the pressure of the helical spring 34, to distribute the pressure of the spring uniformly over the whole circumference of the crests 30A, 32A situated in front of this ring 36. In practice, the ring 36 is cut from sheet steel of suitable thickness, and pressed into the base 26 adjacent to the face 26A. The median diameter of the ring 36 is substantially equal to the diameter D of the coil 34A, and its radial width L encompasses the two crests 30A, 32A. In the embodiment illustrated, the width L substantially overlaps the radial width of the two ribs 30, 32 which form the two aforesaid crests.

Regarding the outermost corner 28A, it can be seen in Figure 2 that an axial component P' of the hydraulic pressure P acts on the outer side 28B of the rib 28, tending to reduce the contact pressure between the crest 28A and the graphite ring 22 (Figure 1). This tendency becomes greater with a greater pressure P in the cooling circuit. According to this embodiment of the present invention, the outer cylindrical circumferential surface 26B of the base 26 is formed with a circumferential radial groove 38. Thus, the water at pressure acts upon one side 38A of the groove 38 to give rise to an axial component P" in opposition to P'. The greater the depth S' of the groove 38, measured from the surface 26B, the greater the component P" becomes.

Therefore, it is evident from Figure 2 that, when the depth S' is equal to the radial distance S between the crest 28A and the surface 26B, the components P' and P" are constantly balanced. This effect is independent of the cross-sectional shape and width of the groove. In order to eliminate the leaks referred to above in practice, it is sufficient for the value of S' to be at least 50% of S, whilst on the other hand it is preferable thatvalues of S' greaterthan S should be avoided since they make it more difficult to withdraw the cup spring from its production mould. For example, with a cup spring in which the diameter of the cylindrical surface 26B is 28 mm and S is 0.8 mm, the groove 38 can have a depth of about 0.6 to 0.7 mm and a width of the same value.

Claims (5)

1. A gland with a frontal sliding seal, of the kind comprising: a cylindrical sheet metal housing which is open at one end and has an annular bottom wall at its other end, a rigid frontally-sliding sealing ring which is movable axially but not rotatably in the housing adjacent the open end, and elastomeric cup spring without undercuts which is compressed axially between the ring and the bottom wall of the housing, the free edge of the cup spring being in sealing circumferential contact with the transition zone between the bottom and the side wall of the housing, and the side wall of the cup spring being convex towards the side wall of the housing so as to establish with this wall a sealing contact which increases as the spring is compressed, the cup spring further including at its smaller end an annular elastomeric base which is directed radially towards the axis of the spring and is in sealed frontal contact with the rigid ring by a number of concentric circular crests formed on the front face of the base, and a helical compression spring which is placed in the cavity of the cup spring, coaxial with the latter, the helical spring being in axial pressing contact with the base of the cup spring at one end and with the bottom of the housing at its other end, characterised in that a rigid pressure distributing ring, which is flat in cross-section and circumferentially continuous, is provided in the annular part of the base of the cup spring subjected to pressure by the helical spring, and in that the outer circumferential surface of the base is formed with a circumferential radial reentrant groove.

2. A gland according to claim 1, in which the width of the pressure distributing ring encompasses the radial width of all the crests surrounded by the outermost crest.

3. A gland according to claim 1 or 2, in which the radial depth of the groove, measured from the circumferential surface of the base of the cup spring, is at least 50% of the radial distance between the outermost crest and aid surface.

4. A gland according to claim 3, in which the depth does not exceed the radial distance.

5. A gland with a frontal sliding seal, substantially as described with reference to the accompanying drawings.