GB2050512A - Rotary Fluid-pressure Actuators - Google Patents

Abstract

In an actuator having a shaft 14 extending from a rotor end-surface 30, a seal assembly 10 comprises an annular seal member 49 made of e.g. PTFE, and engaging with both the said surface and a cylindrical stator-surface 45. The seal member is biased towards the surfaces 30, 45 by fluid pressure transmitted from the working chamber e.g. owing to leakage of working fluid past the seal member. A resilient member 58 on a retainer 59 may be lodged behind the seal member. Another annular seal member 80 and a "washer" 75 biased by an O-ring 79 may be comprised in the assembly. Sealing assemblies for rotor and stator vanes are also described. <IMAGE>

Description

SPECIFICATION Seal Assemblies for Rotary Actuators The present invention relates to seal assemblies, and more particularly to an improved seal assembly for sealingly separating a "high pressure" chamber from a "low pressure" chamber in a rotary actuator.

Many types of rotary actuators have been developed. Among these it the limiteddisplacement rotary actuator, which typically has a rotor, from which one or more radial vanes extend, journalled in a stator. The vanes normally separate two chambers, and a pressure differential may be applied there-between to cause selective rotary movement of the rotor relative to the stator. These limited-displacement rotary actuators are of general utility, and have found application in controlling airplane and missile aerodynamic flight control surfaces, and in moving radar antennas, laser pointing surfaces, and the like.

The development and use of these rotary actuators has been impeded by the problem of sealingly separating the two chambers under a variety of load conditions.

According to a first aspect of the invention, there is provided apparatus having a rotor journalled in a stator, said rotor having a surface, said stator having a surface arranged proximate said rotor surface, and said rotor and stator defining a first chamber therebetween, said first chamber containing fluid at a first pressure, the apparatus further comprising a seal assembly for providing a seal zone between said rotor and stator in the vicinity of said first chamber, said seal assembly including a seal member provided with a first surface engaging said rotor surface, a second surface engaging said stator surface, a source of fluid pressure, the pressure of said source being greater than the pressure in said first chamber, a conduit operatively arranged to apply pressure from said source to said seal member, whereby the differential pressure between said source and first chamber urges said seal member surfaces into sealing engagement with said rotor and stator surfaces in the vicinity of said first chamber.

According to a second aspect of the invention there is provided apparatus having a rotor journalled in a stator, one of said rotor and stator having a vane extending toward the other of said rotor and stator, said vane having opposite first and second end surfaces separated by an intermediate third surface, said vane first, second and third surfaces being arranged to face corresponding first, second and third surfaces of the other of said rotor and stator, and having a seal assembly mounted on said vane for providing seal zones between said facing vane and rotor or stator surfaces, said seal assembly including a continuous length recess extending into said vane from said first, second and third surfaces thereof, said recess extending more deeply into said first and third vane surfaces proximate its distal ends, said recess having spaced side walls separated by an intermediate bottom, and a co-operativelyconfigurated resilient member arranged in said recess along its entire length and compressively engaged by said side walls, whereby, such compressuve engagement of said resilient member by said side wall causes said resilient member to bulge inwardly of said recess into sealed engagement with said bottom and to bulge outwardly of said recess into sealed engagement with the facing surfaces of the other of said rotor and stator.

The following is a more detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawings, in which: Fig. 1 is a fragmentary longitudinal vertical section view of a limited-displacement rotary actuator incorporating both improved seal assemblies, Fig. 2 is a fragmentary transverse vertical sectional view thereof, taken generally on line 22 of Fig. 1,and Fig. 3 is an enlarged fragmentary longitudinal vertical sectional view of the first improved seal assembly, this view being an enlargement of the structure within the indicated area of Fig. 1.

At the outset, it should be clearly understood that like reference numerals are intended to identify the same elements and/or structure consistently throughout the several drawing figures, as such elements and/or structure may be further described or explained by the entire written specification, of which this detailed description is an integral part.

Referring to the several drawing figures, and more particularly to Fig. 1 thereof, there is shown two improved seal assemblies, of which the presently preferred embodiments are generally indicated at 10 and 82, for use in suitable apparatus 11.

Referring now to Figs. 1 and 2, the illustrated specie of such apparatus 11 is shown as being a form of limited-displacement rotary actuator. This actuator 11 broadly includes a multiple-part body or stator 12 provided with a horizontallyelongated passageway, and a rotor 13 operatively arranged in this stator passageway and having a shaft 14 journalled on the stator by suitable bearings (not shown).

As best shown in Fig. 2, the stator includes three stationary vanes, severally indicated at 15, circumferentially spaced from one another at 120 degree centerline intervals and severally extending radially into the stator passageway. The stator passageway is provided with a cylindrically-segmented surface, severally indicated at 16, between each pair of adjacent stator vanes 1 5, 1 5.

In Fig. 1, the stator 12 is shown as including an open-ended intermediate tubular member 1 8 in which the passageway is provided, a left end cap 1 9 suitable secured to the left marginal end portion of stator member 18, and a right end cap 20 suitable secured to the right marginal end portion of stator member 18. The left end cap 19 is shown, in pertinent part, as having a rightwardly-facing annular vertical surface 21 arranged to close the left end of the stator passageway, and as having an axial bore 22 to accommodate the left margin of rotor shaft 14.

Conversely, the right end cap 20 has a leftwardlyfacing annular vertical surface 23 arranged to close the right end of the stator passageway, and has an axial bore 24 to accommodate the right margin of rotor shaft 14.

The rotor 13 is shown as having a cylindrical hub 25 operatively arranged in the stator passageway within the distal ends of the three stator vanes. Three circumferentiallyspaced rotor vanes, severally indicated at 26, extend radially outwardly from the rotor hub at nominal 120 degree centerline intervals so that their outer margins are arranged proximate the stator passageway surfaces 1 6. The rotor hub is provided with a cylindrically-segmented surface, severally indicated at 28, between each pair of adjacent rotor vanes 26, 26. In Fig. 1, the rotor hub is shown as having an annular vertical left end face 29 arranged to proximately face left end cap surface 21, and an opposite annular vertical right end face 30 arranged to proximately face right end cap surface 23.

Each of the rotor and stator vanes is provided with a partial perimetrical recess 31, which appears to be rectangular when viewed in transverse cross-section (Fig. 2), and which appears to be somewhat U-shaped when viewed in longitudinal section (Fig. 1). A cooperativelyconfigured seal, including a resilient member 32 compressively sandwiched between and extending radially outwardly beyond two washerlike members 33, 33, is arranged in each vane recess to provide a sealed wiping engagement with the proximate cylindrical surface, 1 6 or 28.

Hence, for the stator vanes, each seal longitudinal portion 34 is arranged to wipingly engage hub cylindrical surface 28, each left radial portion 35 is arranged to sealingly engage left end cap surface 21, and each right radial portion 36 is arranged to sealingly engage right end cap surface 23. Conversely, for the rotor vanes, each seal longitudinal portion 38 is arranged to wipingly engage stator cylindrical surface 1 6, each left radial portion 39 is arranged to wipingly engage left end cap surface 21, and each right radial portion 40 is arranged to wipingly engage right end cap surface 23.As best shown in Fig. 1, the distal end portions of these rotor and stator seals are inturned at 41, and received in suitable deepened recesses, severally indicated at 42, provided in the rotor and stator, respectively, to provide a mechanical connection between such seals and the associated vane. The resilient member 32 is compressively sandwiched between washer-like members 33, 33 along the entire of the seal. This has the effect of causing the resilient member to bulge both radially inwardly into sealed-engagement with recess 31, and radially outwardly into sealed engagement with the proximate structure. In addition to providing a mechanical connection, the inturned end portions cause the intermediate resilient member to bulge outwardly in the vicinity of the radial inner end of the seal.

Thus, each rotor vane 26 separates a first chamber 43 on one side thereof, from a second chamber 44 on the other side thereof. It is common for such an actuator to further include a fluid control means (not shown) for regulating the flow of fluid with respect to chambers 43, 44.

Hence, suitable valving and conduits (not shown) may be provided so that hydraulic fluid may be selectively supplied to each of chambers 43, 43, 43, and simultaneously withdrawn from each of chambers 44, 44, 44, or vice versa, so that a pressure differential between chambers 43, 44 may cause desired rotational movement of the rotor relative to the stator. When such a pressure differential exists between chambers 43, 44, the more highly pressurized chamber will expand in volume as the rotor moves, at the expense of its cooperative mate. Hence, when suitable pressurized, one of chambers 43, 44 may be regarded as being a "high pressure" chamber, and the other as being a "low pressure" chamber.Of course, the polarity of the pressure differential between chambers 43, 44 may be selectively reversed to cause reverse movement of the rotor.

If the pressures in chambers 43,44 are equal, the rotor will not move, presuming the absence of an external torque applied to rotor shaft 14. This condition may also obtain if the pressure differential is relatively small owing to frictional force between the rotor and stator.

It should be noted that the perimetrical seals provided on the rotor and stator are effective to partially seal the chambers, except circumferentially proximate the junction of rotor hub end surfaces 29, 30 with end cap surfaces 21,23, respectively. Persons skilled in this art will appreciate that the length of this unsealed region will vary for each of the chambers, depending on the position of the rotor relative to the stator at any point in time.

Referring now to Figs. 1 and 3, the first improved seal assembly 10 provides an arcuate seal zone between the rotor and stator in the vicinity of each "low pressure" chamber. As best shown in Fig. 1, one such seal assembly 10 is provided to act between the stator left end cap and the rotor left end face, and another is provided to act between the stator right end cap and the rotor right end face. The ensuing description will focus on the right seal assembly, it being understood that the left seal assembly is similarly configured.

As best shown in Fig. 3, an annular recess is provided in the right end cap to accommodate and house the right seal assembly 10. This recess is bounded by a cylindrical surface 45 extending axially into right end cap 20 from its annular vertical surface 23, a leftwardly-facing annular vertical shoulder surface 46, a cylindrical surface 47 continuing rightwardly and axially therefrom, and a leftwardly-facing annular vertical surface 48 joining right end cap bore 24.

The preferred embodiment of seal assembly 10 broadly includes a seal member 49, a holding member 50, a source of fluid pressure, and a conduit operatively arranged to apply pressure from such source to the seal member.

The seal member 49 is shown as being an annular ring-like member surrounding rotor shaft 14, and having a substantially Lshaped transverse cross-section (Fig. 3). Specifically, this seal member 49 has an annular vertical first surface 51 engaging proximate rotor surface 30, a cylindrical second surface 52 engaging proximate stator surface 45, an annular vertical end face 53, and a cylindrical end face 54. The seal member is also shown as having a rightwardly-facing annular vertical surface 55, and a cylindrical surface 56.

The seal member first face includes end face 53 and surface 55, and the seal member second face includes end face 54 and surface 56. The seal member 49 may be formed of a low-friction material, such as polytetrafluoroethylene or the like.

The holding member 50 is of two-piece construction and includes a resilierit member 58 and a retainer 59. The resilient member 58 is annular, and has a substantially rectangular transverse cross-section. Specifically, this resilient member has an annular vertical left face 60 arranged to engage seal member surface 55, an annular vertical right face 61, an inner cylindrical surface 62, and an outer cylindrical surface 63 arranged to engage seal member surface 56. The resilient member is preferably formed of a suitable elastomeric material, such as rubber or the like. The retainer 59 is shown as having an annular vertical left face 64, an annular vertical right face 65, a cylindrical inner surface 66 surrounding but spaced from shaft 14, a cylindrical outer surface 68, and a stepped portion between its outer surface and left face.

Specifically, this stepped portion includes a cylindrical surface 69 extending rightwardly from left face 64, an annular vertical surface 70 continuing outwardly therefrom, a cylindrical surface 71 continuing rightwardlytherefrom, and an annular vertical surface 72 continuing outwardly to join outer surface 68. An annular recess 73, having a substantially U-shaped crosssection, extends rightwardly into the retainer from surface 70. Moreover, the retainer 50 is shown as being provided with a passageway 74 communicating its inner and outer surfaces so that the pressures applied to the seal member first and second faces will be equal. The retainer is formed of a suitable metal, although other materials may be readily substituted therefor.

In the illustrated embodiment, a washer 75 is operatively arranged such that its annular vertical right face 76 will abut stator surface 46, and its annular vertical left face 78 will engage retainer right face 65. The function of this washer is merely to act as a spacer to compress the resilient member to the extent desired. Hence, washers of different thicknesses may be substituted to accommodate varying dimensions caused by manufacturing tolerances. If the end cap recess is accurately machine, washer 75 may be eliminated, in which case the retainer right face 65 may directly engage the stator surface 46. The function of the holding member is to urge the seal member first and second surfaces into engagement with the adjacent rotor and stator surfaces, and to insure that the seal member faces will be exposed to the same fluid pressure.

An O-Ring 79 is compressed between the washer right face 76 and stator recess surfaces 47, 48 to urge an annular seal 80 radially inwardly into compressive engagement with shaft 14. Hence, the function of this is to provide a fluid-tight seal between the stator and the shaft.

As previously noted, when the apparatus is operated, one of the chambers 43, 44 will be positively pressurized relative to the other. Such high pressure" chamber constitutes a source of fluid pressure. The chamber 81 in which the seal assembly is contained, is normally filled with hydraulic fluid. When a pressure differential exists between chambers 43, 44, pressure from the "high pressure" chamber may leak or bleed past the seal member 49 to charge the fluid in the seal assembly chamber 81 to substantially the same pressure as in the "high pressure" chamber. The reason for this is that pressurs in the vicinity of the "high pressure" chamber may displace the seal member 49 away from its engagement with the rotor or stator, or both, against the opposite bias exerted by the holding member.Such dispiacement of the seal member is effective to form, if even momentarily, a conduit communicating the "high pressure" chamber with the seal assembly chamber. Such pressurized fluid in the seal assembly chamber 81 will be applied to the seal member first and second faces to urge the seal member first and second surfaces into sealing engagement with the proximate rotor and stator surfaces in the vicinity of the "low pressure" chamber, where a pressure differential exist. Of course, the seal member may flex of deform to provide such a conduit communicating the "high pressure" chamber with the seal assembly chamber whenever a pressure differential exists therebetween sufficient to overcome the bias of the holding member.Since the pressure differential between chambers 43, 44 may vary in polarity and magnitude, such leakage or bleeding of pressure from the high pressure chamber into the seal assembly chamber may vary in position and duration. Hence the seal member will be pressure-loaded into tight sealing engagement with the rotor and stator in the vicinity of each "low pressure" chamber, regardless of the position of the rotor relative to the stator, while only the bias exerted by the holding member will impede leakage of pressure from the "high pressure" chamber into the seal assembly chamber. In other words, the force with which a particular arcuate segment of the seal member is pressed into engagement with the rotor and stator, will depend upon such segment's proximity to the "low pressure" chamber.After the pressures in the seal assembly and "high pressure" chambers have substantially equalized, the seal member will be urged into engagement with the rotor and stator in the vicinity of the "high pressure" chamber only by the constant normal bias exerted by the holding member.

However in the vicinity of the "low pressure" chamber, such holding member bias will be supplemented by the differential pressure between the seal assembly and "low pressure" chambers, acting on the area of the seal member first and second faces. In effect, the magnitude of the distributed load urging the seal member against the rotor and stator surfaces will be greater in the vicinity of the "low pressure" chamber, where the holding means bias is supplemented by differential fluid pressure, than in the vicinity of the "high pressure" chamber where such holding means bias is not so supplemented.

Referring now to Figs. 1 and 2, there is also provided a second improved seal assembly, generally indicated at 82, mounted on a vane 1 5 for providing seal zones between facing vane and rotor or stator surfaces. Each rotor vane 1 5 is shown as including a left vertical first surface 29 arranged to face stator first surface 21, an opposite right vertical second surface 30 arranged to face stator second surface 23, and an intermediate longitudinal third surface 83 arranged to face stator third surface 1 6.

Conversely, each stator vane 1 5 includes a left vertical first surface 84 arranged to face stator first surface 21, an opposite right vertical surface 85 arranged to face stator second surface 23, and an intermediate longitudinal third surface 86 arranged to face rotor third surface 28.

The improved seal assembly 82 broadly includes a continuous length recess 31 extending into the vane from its first, second and third surfaces. Proximate its distal ends, the recess extends more deeply, and preferably rectangularly, into the vane from its first and second surfaces, as indicated at 42. As best shown in Fig. 2, the recess is rectangular, having opposite side walls 88, 88 separated by an intermediate bottom 89. The resilient member 38 is cooperatively configured to the perimetrical shape of recess 32, and is compressively received in recess 32 through a pair of washer-like members 33, 33.

The compressive engagement of the resilient member 38 by recess walls 88, 88 causes the resilient member to bulge radially inwardly into sealed engagement with the recess bottom 89, and also causes the resilient member to bulge radially outwardly into sealed engagement with the proximate facing surface of the rotor or stator, as appropriate. The reception of resilient member inturned end portions 41 in recess distal end deepened recess 42, serves to provide a mechanical connection and to insure the sealing integrity of the resilient member with the facing first and second surface of the other of the rotor and stator, as appropriate.

While it is preferred to form the seal member 49 of polytetrafluoroethylene because of its low friction characteristics, other materials may be readily substituted therefor. If desired, the seal member may be formed of a suitable metal, such as bronze or the like. Similarly, the configuration of the seal member may be readily varied. If desired, the cross-sectional shape of the seal member may be square, rectangular, triangular, or some other shape. If the cross-sectional shape is triangular, the various included angles can be varied to modify the force components urging the seal member into engagement with the rotor and stator. However, the first and second surfaces of the seal member should each have a portion in substantial sealing contact with the adjacent surfaces of the rotor and stator, respectively.

Conceivably, the retainer 59 might be entirely omitted in favor of an enlarged resilient member engaging a stator shoulder surface, although care should be taken to ensure that sufficient fluid pressure will be applied to the seal member first and second faces. It might also be possible to eliminate the holding member altogether. For example, the seal member could be suitable configured to directly engage an appropriate stator surface. The seal member first and second surfaces need not necessarily be cylindrical or planar, as shown. If desired, such surfaces may be ribbed or be provided with some other means by which the applied load may be concentrated.

Such ribbed construction would also decrease the area of frictional contact between the seal member and the rotor and stator.

Of course, the improved seal assembly is not limited to use in a limited-displacement rotary actuator, but possesses a greater utility in providing a seal zone between suitable apparatus having a rotor and a stator. Hence, the terms "apparatus", "rotor", and "stator" should be broadly interpreted. Likewise, the term "chamber" is not intended to mean only a sealed chamber, but may include all types of chambers, or passageways communicating therewith, regardless of whether such chambers are sealed or communicate with atmosphere, and regardless of the exact pressure therein. Of course, the "fluid" may be either liquid or gaseous.

As an alternative to the "bleeding" selfpressurization of the seal assembly chamber, such chamber could be pressurized from another source, if desired. For example, a suitable conduit could be arranged to deliver supply pressure directly to the seal assembly chamber. Moreover, the pressure in the seal assembly chamber may, if desired, be greater than the pressure in the "high pressure" chamber, although this will increase the frictional forces between the seal member and the rotor in the vicinity of each "high pressure chamber.

The foregoing discussion is intended to demonstrate some of the many modifications which are contemplated. However, such list is not intended to be exhaustive.

Therefore, while the presently preferred embodiment of the improved seal assembly has been shown and described, and several modifications thereof discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the scope of the invention, as defined by the following claims.

Claims (17)

Claims

1. Apparatus having a rotor journalled in a stator, said rotor having a surface, said stator having a surface arranged proximate said rotor surface, and said rotor and stator defining a first chamber therebetween, said first chamber containing fluid at a first pressure, the apparatus further comprising a seal assembly for providing a seal zone between said rotor and stator in the vicinity of said first chamber, said seal assembly including a seal member provided with a first surface engaging said rotor surface, a second surface engaging said stator surface, a source of fluid pressure, the pressure of said source being greater than the pressure in said first chamber, a conduit operatively arranged to apply pressure from said source to said seal member, whereby the differential pressure between said source and first chamber urges said seal member surfaces into sealing engagement with said rotor and stator surfaces in the vicinity of said first chamber.

2. Apparatus according to claim 1 wherein a line in said seal member first surface is substantially parallel to a line in said rotor surface.

3. Apparatus according to claim 1 wherein a line in said seal member second surface is substantially parallel to a line in said stator surface.

4. Apparatus according to any one of claims 1 to 3 wherein said seal member is formed of polytetrafluoroethylene.

5. Apparatus according to any one of claims 1 to 4 wherein said seal member has a substantially L-shaped transverse cross-section.

6. Apparatus according to any one of claims 1 to 5 wherein said seal member is annular.

7. Apparatus according to claim 6 wherein said rotor and stator define a second chamber therebetween, said second chamber containing fluid at a pressure greater than the pressure in said first chamber, and wherein said pressurized second chamber functions as said source.

8. Apparatus according to claim 7 wherein a portion of said conduit is provided by compliant flexure of said seal member in the vicinity of said second chamber, such that the pressure of fluid leaking from said second chamber past said seal member is applied to said seal member.

9. Apparatus according to any one of claims 1 to 8 and further comprising a holding member acting between said seal member and stator for urging said seal member first and second surfaces into engagement with said rotor and stator surfaces.

10. Apparatus according to claim 9 wherein said holding member includes a resilient member engaging said stator and said seal member.

11. Apparatus according to claim 10 wherein said holding member includes a retainer operatively arranged between said resilient memberand said stator, and wherein said retainer has a passageway therethrough so that the pressure may be applied distributively to said seal member.

12. Apparatus having a rotor journalled in a stator, one of said rotor and stator having a vane extending toward the other of said rotor and stator, said vane having opposite first and second end surfaces separated by an intermediate third surface, said vane first, second and third surfaces being arranged to face corresponding first, second and third surfaces of the other of said rotor and stator, and having a seal assembly mounted on said vane for providing seal zones between said facing vane and rotor or stator surfaces, said seal assembly including a continuous length recess extending into said vane from said first, second and third surfaces thereof, said recess extending more deeply into said first and third vane surfaces proximate its distal ends, said recess having spaced side walls separated by an intermediate bottom, and a co-operatively-configured resilient member arranged in said recess along its entire length and compressively engaged by said side walls, whereby, such compressive engagement of said resilient member by said side walls causes said resilient member to bulge inwardly of said recess into sealed engagement with said bottom and to bulge outwardly of said recess into sealed engagement with the facing surfaces of the other of said rotor and stator.

13. Apparatus according to claim 1 2 wherein said recess is substantially U-shaped.

14. Apparatus according to claim 11 or claim 12 and further comprising a washer-like member configured to the shape of said recess and operatively positioned between said resilient member and one of said recess walls.

15. Apparatus according to any one of claims 1 2 to 14 wherein said recess walls are substantially parallel to one another.

1 6. Apparatus according to claim 1 5 wherein said bottom is substantially perpendicular to said recess walls.

17. Apparatus having a rotor journalled in a stator and substantially as hereinbefore described with reference to the accompanying drawings.