GB2229778A - Sealing arrangement and torsional actuator incorporating same - Google Patents

Abstract

A seal for facing surfaces (13, 41) of two relatively movable members comprises a sealing member (38) disposed in a groove in one member, having a sealing face (40) engaging the other member and an inclined wedge face (42) facing the base of the groove to be engaged by a complementary wedge face (43) of a thrust member (39). The fluid under pressure is supplied to the base of the groove to act on the thrust member so that the members (38, 39) fill the groove and the sealing member has its face (40) urged into engagement with the facing surface (41) of the member (16). The seal is advantageously applied to a fluid pressure operated torsional actuator, for sealing between end faces of the rotor and end parts of the actuator casing, annularly around the shaft on which the rotor is supported, and a shuttle valve arrangement supplies the seal with fluid from the actuator chamber containing fluid at the highest pressure.

Description

SEALING ARRANGEMENT AND TORSIONAL ACTUATOR INCORPORATING SAME This invention relates in the broadest aspect to a sealing arrangement, for sealing, against leakage at facing surfaces of two relatively movable members, of fluid under pressure confined by said members. The sealing arrangement is particularly applicable for use in a fluid pressure torsional actuator, wherein a particular sealing problem exists as will be described hereafter.

A fluid pressure torsional actuator of the type in relation to which the invention has been devised comprises a casing having spaced end walls and a peripheral wall defining an internal cavity, and a rotor disposed within the casing and movable angularly about an axis between the end walls thereof, the rotor having at least one vane formation cooperating with the peripheral and end walls of the casing to define at least two chambers whose volume is varied when the rotor undergoes its angular movement. Hence delivery of fluid under pressure to, and release thereof from, the variable volume chambers causes the rotor to move angularly. The fluid used is a liquid, typically a hydraulic oil.

Two sealing problems exist in respect of such a fluid pressure torsional actuator. The first is in respect of providing a fluid-tight seal between the or each vane formation of the rotor and the end walls and internal peripheral wall of the casing relative to which the vane formation moves, to prevent leakage of the fluid between the variable volume chambers. The second is in respect of providing a seal between the rotor and each end wall of the casing, to prevent leakage both between the variable volume chambers and also between such chambers and a shaft extending through the casing and upon which the rotor is supported for its angular movement.The latter seal requires an arrangement of annular configuration to prevent access of the fluid under pressure to the shaft, and must not provide, despite its annular form, a path for circumferential leakage of fluid between the variable volume chambers.

Because of the necessity of preventing such circumferential leakage, the type of seal which is suitable for sealing the vanes of the rotor, and which comprises a sealing member disposed in a groove in the rotor, the sealing member fitting in the groove with sufficient clearance to enable the fluid under pressure to enter the groove to cause the sealing member to be urged into engagement with the end wall of the casing, is not satisfactory. The necessary clearance of the sealing member in the groove to provide for entry of the fluidunder pressure necessarily would permit circumferential leakage of the fluid around the groove.

It is therefore an object of the present invention to provide a seal which is suitable for the abovedescribed use in a fluid pressure torsional actuator to overcome the problem of circumferential leakage of fluid.

However, it will be appreciated that the seal arrangement provided by the invention is applicable more widely where similar or analogous problems arise. It is a further object of the invention to provide an actuator including such a seal, and of advantageous design in other respects which will be pointed out hereafter.

According to the invention, we provide a sealing arrangement for sealing, against leakage at facing surfaces of two relatively movable members, of fluid under pressure confined by said members, comprising: a groove defined in one of said members, facing the surface of the other member; a sealing member disposed in the groove, having a sealing face engaging the surface of the other member and, viewed in a cross-section transverse to the groove, an inclined wedge face extending towards the base of the groove; a thrust member disposed in the groove between the sealing member and the base of the groove, the thrust member having an inclined wedge face, complementary to and engaging the wedge face of the sealing member, and a pressure face of substantially the same width as the groove and facing the base thereof;; and means for supplying the fluid under pressure to the groove to act on the pressure face of the thrust member.

In a seal arrangement according to the invention, the fluid under pressure exerts a force on the pressure face of the thrust member to urge it away from the base of the groove. In turn the thrust member exerts a force on the sealing member so that the sealing face thereof is urged into sealing engagement with the surface of the other of the relatively movable members. The complementary inclined wedge faces of the sealing member and thrust member have the result that together these two members completely occupy the groove in the direction of the width thereof and exert a pressure on the groove walls greater than the pressure of the fluid, so that there is no possibility of leakage of fluid in the direction along the groove.The sealing face of the sealing member engages the other relatively movable member to be effective against any leakage in the direction of the width of the groove.

Preferably there is provided spring means in the groove between the base thereof and the thrust member, to bias the thrust member away from the base of the groove into engagement with the sealing member even when no fluid pressure is applied thereto. Such a spring means may be, for example, an O-ring as described hereafter.

As it is applied to a torsional actuator in the embodiment described hereafter, the sealing arrangement is for sealing between generally radially extending faces of members movable angularly relative to one another about an axis, and the groove, sealing member and thrust member are all of annular configuration. Particularly, the sealing arrangement is for sealing between an end surface of the rotor of the actuator and a facing end wall surface of the casing thereof.

In application of a sealing arrangement according to the invention to a fluid pressure torsional actuator, the fluid under pressure must be supplied to the groove of the sealing arrangement from the variable volume chamber or chambers containing fluid at the highest pressure.

Therefore the invention provides that there is valve means operable automatically to afford communication between the chamber or chambers containing fluid at highest pressure and the groove of the sealing arrangement.

The invention will now be described by way of example with reference to the accompanying drawings, of which: Figure 1 is a transverse section through a fluid pressure torsional actuator provided with a sealing arrangement according to the invention, on the section line 1-1 of Figure 2; Figure 2 is a longitudinal section through part of the actuator, on the section line 2-2 of Figure 1; Figure 3 is an enlargement of part of Figure 2.

Figure 4 is a transverse section through a further embodiment of fluid pressure torsional actuator according to the invention, on the section line 4-4 of Figure 5; Figure 5 is a longitudinal section through the actuator, on the section line 5-5 of Figure 4;: Figure 6 is a further transverse section through the actuator, on the section line 6-6 of Figure 5.

Referring firstly to Figures 1 and 2 of the drawings, the torsional actuator there shown comprises a casing with a part 10 secured between two end plates 11.

The casing part 10 has an internal wall defining the periphery of a cavity, the wall having two opposed part-cylindrical portions 12. The end plates 11 afford planar end walls which face one another, parts of such walls being visible at 13 in Figures 2 and 3. The end plates 11 and casing part 10 are held together by a number of bolts extending through apertures 14 therein.

Within the cavity provided by the casing of the actuator there is disposed a rotor indicated generally at 15. The rotor 15 comprises a body portion 16 in the form of a hollow cylinder, with an internal bore 17 which has splined torque transmitting engagement with a shaft 18 extending through the actuator and supported by bearings 19, 20 in respective end plates 11, for rotation about an axis 21. The body part 16 of the rotor has part cylindrical oppositely facing external surfaces 22. The rotor further comprises vanes 23 extending radially outwardly from the body portion 16, diametrically opposite one another. Each vane 23 has at its tip a seal 24 engaging the respective part cylindrical peripheral wall portion 12 of the casing part 10. The vanes 23 further have side seals (not shown) which have sealing engagement with the end walls 13 facing one another on the end plates 11.Between the peripheral wall portions 12, the casing part 10 has inwardly extending abutments 25 provided with seals 26 which engage the cylindrical surface portions 22 of the rotor body 16. Thus there are defined between the casing and rotor a first pair of chambers 27 and a second pair of chambers 28 whose volume is variable when the rotor moves angularly within the casing about the axis 21. The seals 24, 26 are of conventional type.

It will be appreciated, therefore, that supply and release of fluid under pressure to and from the chambers 27, 28 causes angular movement of the rotor within the casing. Supply of fluid to the chambers 27 and release thereof from the chambers 28 will cause the rotor to move in a clockwise direction, with regard to Figure 1, whilst supply of fluid to the chambers 28 and release thereof from the chambers 27 will cause the rotor to move in the anti-clockwise direction. Shown in Figure 1 is a system comprising fittings 30, 31 and an external pipe 32 for supply and release of fluid to and from the chambers 27, communicating with such chambers by bores 33 in the casing part 10. Shown in outline are bores 34 for similar communication with the chambers 28 from another pipe, not illustrated, arranged generally as the pipe 32 and associated fittings.

For sealing between the ends of the body part 16 of the rotor 15 and the end plates 11, there are provided respective sealing arrangements which are visible in Figure 2 and one of which is shown enlarged in Figure 3.

The purpose of such sealing arrangements is to prevent fluid under pressure from the chambers 27, 28 from reaching the shaft 18 and its bearings, and also to prevent leakage of fluid between the chambers circumferentially between the ends of the rotor body part 16 and the surfaces 13 of the end plates 11. Each such sealing arrangement is of annular configuration, disposed as indicated in outline at 36 in Figure 1.

Referring now more particularly to Figure 3 of the drawings, each such seal arrangement comprises an annular groove generally of rectangular cross sectional shape, provided in the end plate 11 as indicated at 37. Within the groove 37 is disposed an annular sealing member 38 and an annular thrust member 39. The sealing member 38 has a sealing face 40 which engages the end surface 41 of the rotor body part, the width of the face 40 being somewhat less than the width of the groove 37. Towards the base of the groove the sealing member 38 has a face 42 which is frusto-conical, and as viewed in cross section is an inclined wedge face.The thrust member 39, disposed between the sealing member 38 on the base of the groove 37, has a complementary frusto-conical or inclined wedge face 43 engaging the face 42 of the sealing member, and a rear face 44 which faces the base of the groove 37 and is of substantially the same width as the groove.

The sealing member and thrust member may be of a material such as a suitable type of PTFE. Between the thrust member 39 and the base of the groove there is disposed an O-ring 45 of suitable elastomeric material, which biases the thrust member 39 and hence the sealing member 38 outwardly of the groove so that the sealing face 40 is brought into engagement with the face 41 of the rotor.

The sealing arrangement further comprises a passage 46 for delivering fluid under pressure to the groove 37 at the base thereof. Such fluid pressure, in addition to the force exerted by the O-ring 45, acts on the face 44 of the thrust member 39, to assist in urging the sealing member 38 and its face 40 into sealing engagement with the face 41 of the rotor. Because the sealing face 40 of the sealing member is of a width less than the width of the groove 37, whilst the fluid pressure is exerted on the face 44 of the thrust member of a width substantially the same as the width of the groove, it is ensured that the pressure with which the sealing face 40 engages the rotor is greater than the fluid pressure which the seal arrangement must resist, thereby giving enhanced sealing.

However, sealing would still be effective even if the sealing face 40 were of substantially the same width as the groove.

Further, the engaging wedge faces 42, 43 of the sealing member and thrust member, which may be at an angle as illustrated of about 40 , ensure that the sealing member engages the wall of the groove with a pressure greater than the pressure of the fluid it is sealing against, thereby ensuring that the sealing member remains firmly in contact with the wall of the groove and preventing any possibility of leakage around the groove itself circumferentially thereof.

If the pressure of fluid in the actuator causes distortion of the end plates 11 thereof, such that a larger gap appears between faces 13 and 41, the sealing member 38 will protrude farther from groove 37 and continue effectively to engage the face 41.

To ensure that the sealing arrangement is effective against leakage of fluid it is necessary to provide for delivery of the fluid under pressure to the passage 46 from whichever pair of chambers 27 or 28 it is contained in at the higher pressure. To achieve this, the passage 46 and the corresponding passage from the sealing arrangement at the other end of the rotor, which passages lead into bores 47 in the end plates 11, closed by plugs 48, communicate with a passage 49 extending through the casing part 10 parallel to the axis 21. This passage 49 intersects a further passage which extends perpendicularly thereto, having a first portion 50 leading into one of the chambers 28 and a second portion 51 which communicates with the fitting 30 and thus with the chambers 27. The passage portion 50 is provided, adjacent the intersection with the passage 49, with a seating 52, whilst the passage portion 51 contains an inserted sleeve 53 affording a seating 54 facing the seating 52. A ball 55 is held captive between the seatings 52, 54.

Thus if the chambers 27 contain fluid at greater pressure than the fluid in chambers 28, such fluid pressure will cause the ball 55 to seat on the seating 52, to block the passage part 50. Therefore the fluid at the pressure prevailing in chambers 27 is applied, via passages 49 and bores 47, to the sealing arrangements.

If, on the other hand, the fluid in chambers 28 should be at a greater pressure than that in chambers 27, the ball 55 is caused to engage the seating 54, so that the greater fluid pressure of chambers 28 is applied to the sealing arrangement whilst preventing any leakage from taking place between the chambers 27 and the chambers 28.

The ball 55 acts as a simple shuttle valve to ensure that the sealing arrangements are always supplied with fluid at the greatest pressure.

Referring now to Figures 4, 5 and 6 of the drawings, these show a further embodiment of torsional actuator according to the invention. This embodiment of actuator presents certain constructional advantages, which will be described hereafter, over the embodiment of Figures 1 to 3, but has the principal features of the sealing arrangement of the previous embodiment.

This further embodiment of actuator comprises a casing with a central part 110 secured between two end parts 108, 109. The casing defines an internal cavity in which is received a rotor: the cavity and rotor are of the same configuration as above described in relation to Figures 1 and 2 and therefore will not be described further in detail. Figure 4 shows in outline only the vanes 143 of the rotor and the part-cylindrical portions 112 of the internal peripheral wall of the casing part 110. Between the part-cylindrical wall portions 112, the casing part 110 has radially inwardly extending abutments, so that a first pair of variable volume chambers 127 and a second pair 128 of such chambers are provided.Figure 5 shows the body portion 116 of the rotor with its splined bore 117, but does not illustrate the shaft and bearings upon which the rotor is supported for angular movement about axis 121, such bearings and shaft being as shown in Figure 2.

The end parts 108, 109 of the casing are held together, with the part 110 clamped therebetween, by eight peripheral bolts of which four, 106, extend from the part 108 to the part 109, whilst the other four, 107, extend from the part 109 to the part 108.

The end parts 108, 109 of the casing are identical to one another in respect of the passages provided therein, as described hereafter. They differ from one another only in respect of the configuration and sizes of the recesses wherein the bearings are received for supporting the rotor shaft. The part 109 is, however, fitted to the part 110 in the inverted orientation, compared with the end part 108 as it is illustrated in Figure 4. The end parts have flat surfaces which abut the casing part 110 and which provide the end walls of the variable-volume chambers, and the ends of the body part 116 of the rotor are sealed to the end parts 108, 109 by annular sealing arrangements which are identical to those above described with reference to Figures 2 and 3 of the drawings. These seals, indicated at 103, will not therefore be described hereafter again in detail.

The end part 108 is provided in its upper part with a bore 120 which is screw-threaded for connection to an external pipe or flexible hose for supply and release of fluid under pressure. This bore leads into a chamber 121 from which a drilled passage 122 extends in a direction parallel to the axis 121 to communicate with one of the variable volume chambers 128 defined between the rotor and casing of the actuator. A drilling 123 intersects the chamber 121, and this drilling intersects a further drilling 124 extending parallel to the axis of bore 120 and chamber 121. The open ends of drillings 123, 124 are closed by screwed-in plugs 125, 126 respectively. The drilling 124 intersects yet a further drilling 130 which extends parallel to the drilling 122 to open into the other, opposite, chamber 128.

In line with the axis of the threaded bore 120 and chamber 121, there is a passage 131 of somewhat smaller diameter than the chamber 121. This passage leads into a further passage 132 of even smaller diameter, an annular seating 133 being defined between the passages 131, 132.

A hollow cylindrical plug 134 is inserted into the passage 131 from the chamber 121, and this plug affords a seating 135 facing the seating 133. A ball 136 is held captive between the seatings 133, 135 being free to move between the two.

From the passage 131 between the seatings 133, 135, a passage 137 extends in the direction parallel to the axis 121. This passage 137 intersects at right angles a drilled passage 138 which extends radially towards the axis 121 until it intersects the annular groove in the end part 108 wherein the sealing arrangement 103 is disposed. The open end of the drilled passage 138 is closed by a plug 139. The open end of the drilled passage 137 is closed by virtue of the fact that it faces the part of the casing part 110 which forms one of the abutments co-operating with the rotor body 116.

The end of passage 132 farthest from the chamber 121 opens into a passage 140 which extends parallel to the axis 121, to open into one of the chambers 127.

As above mentioned, the end part 109 has the same arrangement of intersecting drilled passages and associated parts as identified in Figure 4 by the reference numerals 120 to 126, and 130 to 139. As the end part 109 of the casing is fitted to the casing part 110 in inverted orientation compared with the part 108, however, the passages 122 and 130 of part 109 communicate with the variable volume chambers 127, whilst the passage 140 communicates with one of the variable volume chambers 128.

Thus, when fluid under pressure is delivered to the chamber 121 of the casing end part 108, it will enter the variable volume chambers 128 of the actuator. Assuming the fluid pressure in the chambers 127 is lower, having been released from the other casing end part 109 of the actuator by way of the passages therein communicating with the chambers 127, this will cause movement of the rotor of the actuator relative to the casing in the sense which causes the volumes of chambers 128 to increase relative to those of the chambers 127. Analogously fluid supplied under pressure to the casing end part 109 whilst fluid is released from the casing end part 108 will cause movement of the rotor of the actuator in the opposite sense.

The annular seal 103 provided in each of the casing end parts 108, 109 is supplied with fluid from whichever of the chambers 127, 128 of the actuator contains fluid at the highest pressure. Fluid reaches the seal by way of the passages 138, 137, 131, and either the passages 132 and 140 or the passage through the hollow cylindrical plug 134. Ball 136 acts as a simple shuttle valve to establish communication with whichever of the chambers 127, 128 is at highest pressure, and shut off communication with the other of such chambers.

As compared with the embodiment of Figures 1 and 2, it will be noted that the casing part 110 has no passages or apertures provided therein. All the passages required are provided in the casing end parts 108, 109 which, as above pointed out, differ only in minor respects from one another and may be manufactured by machining operations, of which the majority are common to both parts, from a single type of casting. The casing part 110 may conveniently be manufactured as a sintered component, requiring no subsequent machining since it has no internal passageways. All the passages in the casing end parts may conveniently be made by conventional drilling and counterboring techniques.

Otherwise the embodiment of Figures 4 to 6 presents the same advantages in respect of the operation of the seals 103 as does the above described advantages of the seal arrangement shown in detail in Figure 3.

Although the sealing arrangement according to the invention has been described in its application to sealing the rotor of a fluid pressure actuator, the sealing arrangement being of annular configuration, it will be appreciated that the invention is of more general usefulness. A sealing arrangement according to the invention could be made of linear configuration, for example as the seals provided at the tips and side of the vanes of the actuator rotor.

Claims (12)

1. A sealing arrangement for sealing, against leakage at facing surfaces of two relatively movable members, of fluid under pressure confined by said members, comprising: a groove defined in one of said members, facing the surface of the other member; a sealing member disposed in the groove, having a sealing face engaging the surface of the other member and, viewed in a cross-section transverse to the groove, an inclined wedge face extending towards the base of the groove; a thrust member disposed in the groove between the sealing member and the base of the groove, the thrust member having an inclined wedge face, complementary to and engaging the wedge face of the sealing member, and a pressure face of substantially the same width as the groove and facing the base thereof;; and means for supplying the fluid under pressure to the groove to act on the pressure face of the thrust member.

2. A sealing arrangement according to Claim 1 further comprising spring means in the groove between the base thereof and the thrust member, to urge the latter outwardly of the groove into engagement with the sealing member.

3. A sealing arrangement according to Claim 1 or Claim 2, for sealing between generally radially extending surfaces of members movable angularly relative to one another about an axis, said groove, sealing member, thrust member, and spring means when present, each being of annular configuration centred on said axis.

4. A fluid pressure torsional actuator comprising a casing having end walls and a peripheral wall defining an internal cavity, a rotor disposed within the casing and movable angularly about an axis between the end walls, the rotor having at least one more formation cooperating with the peripheral wall of the casing to define at least two chambers of volume variable by angular movement of the rotor, means for supplying fluid under pressure selectively to said chambers, and a sealing arrangement according to Claim 3 provided for sealing between an end surface of the rotor and a facing end wall surface of the casing.

5. An actuator according to Claim 4 wherein the groove is provided in the end wall of the casing.

6. An actuator according to Claim 4 or Claim 5 wherein the means for supplying the fluid under pressure to the groove comprises valve means operable automatically to afford communication between the groove and the chamber or chambers containing fluid at the highest pressure.

7. An actuator according to Claim 6 wherein said valve means comprises a valve element movable under a difference in fluid pressure to block a passage leading to the chamber or chambers containing fluid at lower pressure and to open a passage leading to the chamber or chambers containing fluid at the highest pressure.

8. An actuator according to Claim 5 and either Claim 6 or Claim 7, wherein said casing comprises respective end parts providing opposite end walls of said cavity and each having one of said sealing arrangements for sealing with the respective end surface of the rotor.

9. An actuator according to Claim 8 wherein each of said end parts has a respective valve means for supplying the fluid under pressure to its sealing arrangement.

10. An actuator according to Claim 9 wherein all said passages are provided entirely in said end parts.

11. A sealing arrangement substantially as hereinbefore described with reference to Figure 3 the accompanying drawings.

12. A fluid pressure torsional actuator substantially as hereinbefore described with reference to Figures 1 to 3 or Figures 4 to 6 of the accompanying drawings.