FIELD OF THE INVENTION

This invention relates to sliding ring seal assemblies. Such assemblies are used to allow relative movement between a seal carrying body and a chamber of cylinder while maintaining a pressure difference across the seal.

BACKGROUND TO THE INVENTION

Sliding seal assemblies for maintaining a pressure difference have been proposed previously. Piston rings in engines or pumps are an example of such seal assemblies.

One problem with known assemblies is that the pressure drop across the seal can affect the sealing force in the radial direction. If the pressure drop leads to a large radial force, this can lead to high friction and increased wear on the seal. This is turn can lead to the need to replace the seals more frequently, with associated loss of performance and reliability, and increased cost and downtime.

This invention aims to provide a seal assembly in which the effect of the pressure drop to produce a radial force on the sealing ring is reduced.

SUMMARY OF THE INVENTION

One aspect of the invention provides a sliding ring seal assembly, comprising: a sealing ring having an outer sliding seal surface, an inner face, and substantially parallel axial faces extending between the outer sliding seal surface and the inner face; and a wedge ring having a radial outer circumferential face, a radial inner face that is narrower in an axial direction than the radial outer circumferential face, an axial face extending between the radial outer circumferential face and the radial inner face for positioning adjacent to an axial face of the sealing ring, and an inclined face, angled with respect to the axial face and extending between the radial outer circumferential face and the radial inner face so that the wedge ring has a profile that tapers inwardly.

The assembly further comprises a cylindrical mounting body having a circumferential groove, wherein the circumferential groove as an axial face and an inclined face disposed at an angle to the axial face so that the circumferential groove tapers inwardly; wherein the sealing ring is located in the circumferential groove so that one axial face of the sealing ring is in contact with the axial face of the circumferential groove and the outer sliding seal surface of the sealing ring projects from the cylindrical mounting body; and wherein the wedge ring is located in the circumferential groove so that the axial face of the wedge ring is against the other axial face of the sealing ring and the inclined face of the wedge ring is in contact with the inclined face of the circumferential groove.

The wedge ring can be an inwardly sprung ring and the sealing ring can be an outwardly sprung ring.

The wedge ring can be used to force the sealing ring against a support surface and so improve sealing in the axial direction. The wedge ring can also act to insulate the sealing ring from a radial force arising from a pressure drop across the seal.

Each of the sealing ring and the wedge ring can be formed from a non- continuous ring member having overlapping ends. The overlapping ends of the wedge ring can have complementary step-shaped recesses in an axial direction. The overlapping ends of the sealing ring can have complementary step-shaped recesses at an angle to axial and radial directions. The use of an angled overlap can help in preventing leakage across the break in the sealing ring. The outer sliding seal surface of the sealing ring can project radially beyond the outer face of the wedge ring.

Where each of the sealing ring and the wedge ring is formed from a non- continuous ring member having overlapping ends, and the sealing ring and the wedge ring can be installed in the circumferential groove such that the overlapping ends of the sealing ring and wedge ring are at different azimuthal positions. This avoids potential leakage paths being aligned across the seal.

The inner faces of the sealing ring and the wedge ring can be spaced from the inward end of the circumferential groove.

The cylindrical mounting body can be located within a bore such that the outer sliding seal surface of the sealing ring is in sliding engagement with an inner surface of the bore so as to allow relative movement of the mounting body and the bore. The pressure in the bore can be higher on one side of the sealing ring than on the other. The higher pressure can be on the same side of the sealing ring as the wedge ring. In this way, the wedging effect of the wedge ring on the sealing ring can be increased. The inward end of the sealing ring can be vented to the bore on the lower pressure side of the sealing ring to further increase this effect.

Further aspects of the invention will be apparent from the description below.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a partial side view of a known sealing ring assembly.

Figure 2 shows a partial side view of a sealing ring assembly according to the invention.

Figure 3 shows a partial view of the sealing ring and wedge ring of Figure 2.

DETAILED DESCRIPTION Figure 1 shows a known sealing ring assembly. A typical example of this is a piston ring in a reciprocating cylinder engine or pump. A sealing ring 10 is located in a groove 12 in a cylindrical mounting body 14, such as a piston or shaft. The sealing ring is sprung outwardly so that it bears against the inner wall 16 of a bore 18, such as a cylinder. The contact between the sealing ring 10 and inner wall 16 provides a sliding seal surface allowing relating movement between the mounting body 14 and bore 18.

In use, there is a higher pressure HP on one side of the sealing ring 10 and a lower pressure LP on the other. The effect of this pressure difference is that the sealing ring 10 is forced against the axial face 20 of the groove 12. Also, the higher pressure HP acts on the inner face 22 of the sealing ring 10 forcing in outwards and increasing the contact pressure of the sealing face 24 on the inner wall 16.

While the net result of these forces is to provide a good sealing contact between the sealing ring 10 and the bore 16, the high frictional forces resulting from the pressure effects can lead to increased wear of the sealing ring 10 and ultimately reduction is sealing effectiveness.

Figure 2 shows a view corresponding to Figure 1 for an embodiment of the invention. An outwardly sprung sealing ring 30 is mounted in a circumferential groove 32 in a mounting body 34. The sealing ring has an outer sliding seal surface 44 that engages the inner surface 36 of a bore 38. The sides of the ring form axial faces 46, 48, i.e. they form faces transverse to the axial direction. The inner face 42 of the sealing ring 32 is generally parallel to the seal surface 44.

The circumferential groove 32 is tapered inwardly. One side of the groove 32 forms an axial face 40, i.e. a wall transverse to the axial direction. The other side of the groove 32 forms an inclined face 50 which is disposed at an angle to the axial face 40 so that the distance between them decreases in the inward direction. The sealing ring 30 is mounted in the circumferential groove so that the sealing ring axial face 46 is against the groove axial face 40.

An inwardly sprung wedge ring 52 is located in the circumferential groove 32 between the sealing ring 30 and the inclined face 50. The wedge ring 52 has an outer face 54 and an inner face 56 that is narrower in an axial direction than the outer face 54. The outer face 54 is set back from the sealing surface 44 of the sealing ring.

An axial face 58 extends between the outer face 54 and the inner face 56. The wedge ring axial face 58 is against the sealing ring axial face 48. The wedge ring 52 has an inclined face 60 which extends between the outer face 54 and the inner face 56 and is angled with respect to the wedge ring axial face 58 so that the wedge ring 52 has a profile that tapers inwardly. The wedge ring inclined face 60 is against the groove inclined face 50.

Both the sealing ring 30 and the wedge ring 52 are non-continuous. Figure 3 shows the non-continuous part of each ring 30, 52. The sealing ring 30 has overlapping ends 62, 64. The opposing faces of each end 62, 64 are formed with a recessed step 66, 68 at an angle to the seal surface 44 and axial faces 46, 48. The steps 66, 68 are asymmetric, with the step 66 being deeper than the step 68. This results in the contact between the steps 66, 68 being to one side of the centre line of the sealing ring 30. The steps 66, 68 are configured such that there is a gap 70, 72 at either end of the overlap. This allows the ring to expand and contract due to thermal effects in use without distorting and compromising the contact with the surface 36. The sealing ring 30 is installed in the groove 32 such that the deeper step 66 is on the higher pressure side. This means that the gap 70 provides a communication path between the bottom 74 of the groove 32 and the lower pressure side.

The wedge ring 52 has a different form for the overlapping ends 76, 78. In this case, the opposing faces are formed as recessed steps 80, 82 in the axial direction, i.e. one step 80 is over the other step 82 in the axial direction. Gaps 84, 86 are provided to allow for thermal expansion and contraction.

The sealing ring 30 and wedge ring 52 are installed in the groove such that the non-continuous parts are at different azimuthal positions. This avoids the gaps 70, 72, and 84, 86 becoming aligned and providing a communication path across the seal from the higher pressure side to the lower pressure side. When installed in the manner shown in Figure 2, the effect of the pressure drop across the seal means that pressure applied to the wedge ring 52 will force it into the groove 32 and the interaction of the inclined faces 50, 60 will force the wedge ring 52 axially against the sealing ring 30 to hold it securely against the axial face 40 of the groove 32. This also has the effect of sealing the bottom 74 of the groove 32 from the higher pressure side. As is noted above, the gap 70 means that the bottom of the groove 32 is vented to the lower pressure side which means that an outward force on the sealing ring 30 is avoided. The combination of these effects is that the outward force at the interface between the seal surface 44 and the inner surface 36 is established by the spring properties of the sealing ring 30 and is not increased by the pressure across the seal.

Various changes can be made within the scope of the invention.