Abstract:
A rotary vane type actuator includes a vane assembly for converting pressure from a pressurized medium within the actuator into rotational movement. The vane assembly has a rotatable vane and a vane seal for preventing leakage of pressurized medium through or around the vane assembly. A side-plate is attached to the rotatable vane and the side-plate has a limiting protrusion that abuts the vane to maintain a gap between the vane and the side-plate so that the seal in the gap is not extruded from between the vane and side-plate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to rotary vane actuators and in particular, the vane assembly of fluid rotary vane actuators. 
     2. Summary of the Prior Art 
     A typical rotary vane type actuator has a casing to provide a fixed volume space. The fixed volume space is separated into a first and second chamber by a rigid paddle or vane assembly. A pressurised fluid is introduced through a port into the first chamber and pressure difference between the first and second chambers produces a torque on the vane resulting in rotational movement of the vane. As the vane rotates, the pressurised fluid continues to be introduced into the first chamber to maintain the pressure. 
     The lower pressure in the second chamber is allowed to escape to maintain a pressure difference across the vane. 
     Energy is fed into the actuator by the flow of pressurised fluid and converted into mechanical work in the form of rotation of the output shaft against the torque imposed by its load. 
     The construction of the vane assembly is important to the efficiency of the actuator. In particular, it is important that the vane assembly provides a seal between the first and second chambers so that the energy from the input flow of pressurised fluid is efficiently converted into rotational work, rather than being wasted by leaking between chambers. 
     To provide this seal, a typical vane assembly has a seal made of a flexible material, such as a rubber, attached to a rigid vane. The seal is attached to the vane by a side-plate and a retaining nut and bolt extending through the side-plate, seal and vane. The seal is thus sandwiched between side-plate and vane so that the side-plate clamps the seal in position. A seal expander, made from a springy material such as steel, can also be sandwiched between the seal and side-plate and is shaped to contact and apply force to the inner surface of the seal lip and keep the seal lip in contact with the inner surface of the chamber cavity. It overcomes the problem of creep under stress of the seal material. 
     SUMMARY OF THE INVENTION 
     It is difficult to maintain an appropriate force under the fixing screws. If the screw is not tightened enough, the seal will leak between at the seal/vane interface. If the screw is overtightened, the seal will become extruded between the side-plate and vane. This extrusion leads to deformation of the seal and therefore imperfect seal geometry that will increase leakage, cause premature wear and high friction. The problem is accentuated under high temperature operating conditions. 
     The present inventors have found a way to overcome this problem so that the seal may not be over-clamped and the seal is maintained. 
     At its most general, the present invention provides a vane assembly for a rotary vane actuator, the vane assembly having a seal positioned between a vane and a side-plate, wherein the vane assembly has a limiting portion to limit the movement of the side-plate towards the vane so that a gap for the seal is maintained between the side-plate and the vane. 
     Accordingly, in a first aspect of the invention the present invention may provide a rotary vane actuator having a housing assembly and a vane assembly, wherein
         the housing has a cavity for accommodating the vane assembly, the vane assembly dividing the cavity into a first chamber and a second chamber, and   the vane assembly has a rotatable vane, the rotatable vane having a first and a second side; a vane axle, the vane axle projecting from the housing and being connected to the rotatable vane to convert pressure exerted on the vane into rotational motion; a first side-plate on the first side of the rotatable vane; a retaining means for connecting the first side-plate to the rotatable vane; a first seal gap, the first seal gap being between the rotatable vane and the first side-plate; a first vane seal for sealing the vane, the first vane seal being in the first seal gap; and a first limiting protrusion, the first limiting protrusion being connected to the first side-plate for maintaining the first seal gap and the first limiting protrusion abutting the first side of the rotatable vane so as to limit compression of the first vane seal between the first side-plate and the rotatable vane.       

     According to the second aspect of the invention there may be provided a rotary vane actuator having a housing assembly and a vane assembly, wherein
         the housing has a cavity for accommodating the vane assembly, the cavity being divided by the vane assembly in a first chamber and a second chamber, and   the vane assembly has a rotatable vane, the rotatable vane having a first and a second side; a vane axle, the vane axle projecting from the housing and being connected to the rotatable vane to convert pressure exerted on the vane into rotational motion; a first side-plate on the first side of the rotatable vane; a retaining means for connecting the first side-plate to the rotatable vane; a first seal gap, the first seal gap being between the rotatable vane and the first side-plate; a first vane seal for sealing the vane, the first vane seal being in the first seal gap; and a first limiting protrusion, the first limiting protrusion being connected to the first side of the rotatable vane for maintaining the first seal gap and the first limiting protrusion abutting the first side-plate so as to limit compression of the first vane seal between the first side-plate and the rotatable vane.       

     According to a third aspect of the invention there may be provided a rotary vane actuator having a housing assembly and a vane assembly, wherein
         the housing has a cavity for accommodating the vane assembly, the cavity being divided by the vane assembly in a first chamber and a second chamber, and   the vane assembly has a rotatable vane, the rotatable vane having a first and a second side; a vane axle, the vane axle projecting from the housing and being connected to the rotatable vane to convert pressure exerted on the vane into rotational motion; a first side-plate on the first side of the rotatable vane; a retaining means for connecting the first side-plate to the rotatable vane; a first seal gap, the first seal gap being between the rotatable vane and the first side-plate; a first vane seal for sealing the vane, the first vane seal being in the first seal gap; and a first limiting spacer, the first limiting spacer being positioned between the first side of the rotatable vane and the first side-plate for maintaining the first seal gap so as to limit compression of the first vane seal between the first side-plate and the rotatable vane.       

     The present invention also provides a vane assembly as for use in a rotary vane actuator according to the first to third aspects. 
     Thus, according to a fourth aspect of the invention there may be provided a vane assembly for use in a rotary vane actuator, the vane assembly having a rotatable vane, the rotatable vane having a first and a second side; a vane axle, the vane axle projecting from the housing and being connected to the rotatable vane to convert pressure exerted on the vane into rotational motion; a first side-plate on the first side of the rotatable vane; a retaining means for connecting the first side-plate to the rotatable vane; a first seal gap, the first seal gap being between the rotatable vane and the first side-plate; a first vane seal for sealing the vane, the first vane seal being in the first seal gap; and a first limiting protrusion, the first limiting protrusion being connected to the first side-plate for maintaining the first seal gap and the first limiting protrusion abutting the first side of the rotatable vane so as to limit compression of the first vane seal between the first side-plate and the rotatable vane. 
     According to a fifth aspect of the invention there may be provided a vane assembly for use in a rotary vane actuator, the vane assembly having a rotatable vane, the rotatable vane having a first and a second side; a vane axle, the vane axle projecting from the housing and being connected to the rotatable vane to convert pressure exerted on the vane into rotational motion; a first side-plate on the first side of the rotatable vane; a retaining means for connecting the first side-plate to the rotatable vane; a first seal gap, the first seal gap being between the rotatable vane and the first side-plate; a first vane seal for sealing the vane, the first vane seal being in the first seal gap; and a first limiting protrusion, the first limiting protrusion being connected to the first side of the rotatable vane for maintaining the first seal gap and the first limiting protrusion abutting the first side-plate so as to limit compression of the first vane seal between the first side-plate and the rotatable vane. 
     According to a sixth aspect of the invention there may be provided a vane assembly for use in a rotary vane actuator, the vane assembly having a rotatable vane, the rotatable vane having a first and a second side; a vane axle, the vane axle projecting from the housing and being connected to the rotatable vane to convert pressure exerted on the vane into rotational motion; a first side-plate on the first side of the rotatable vane; a retaining means for connecting the first side-plate to the rotatable vane; a first seal gap, the first seal gap being between the rotatable vane and the first side-plate; a first vane seal for sealing the vane, the first vane seal being in the first seal gap; and a first limiting spacer, the first limiting spacer being positioned between the first side of the rotatable vane and the first side-plate for maintaining the first seal gap so as to limit compression of the first vane seal between the first side-plate and the rotatable vane. 
     Note that in all aspects of the invention discussed above it is preferable that the actuator is a pneumatic actuator and the fluid is a gas, e.g. air. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will be described in detail, by way of example, with reference to the following drawings, in which: 
         FIG. 1  shows an exploded perspective view of a standard rotary vane actuator; 
         FIG. 2  shows a simplified cross section of a standard rotary vane actuator; 
         FIG. 3  shows a cross-section of a rotary vane actuator of the present invention; 
         FIG. 4  shows a cross-section of another rotary vane actuator of the present invention; and 
         FIG. 5  shows a cross-section of a further rotary vane actuator of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , the standard rotary vane actuator  2  has a vane assembly  4  that is housed within a case assembly  6 . 
     The vane assembly  4  has a rigid metal standard vane  8  with an output drive  10  having a cylindrical part and square parts which connect to an indicator  12  and a coupling device  14 . Shaft seals  16  provide a seal around the cylindrical part of the output drive  10 . 
     On each side of the standard vane  8 , a vane seal  18 , expander  20 , and side-plate  22  are attached by vane fixings  24 . 
     The case assembly  6  has a shell  26  in two parts for ease of assembly and bushes  28  to surround the bearings of the standard vane  8 . 
     Referring to  FIG. 2 , the cross-section shows an assembled standard actuator  52  having a shell wall  54  defining a cavity  56 . The cavity  56  has a first chamber  58  and a second chamber  60  separated by the vane assembly  62 . 
     The vane assembly  62  is layered to have a side-plate  64 , seal expander, vane seal  66 , vane  68 , seal expander and side-plate  64  construction. Each seal expander is a thin layer of material positioned between the side-plate  64  and the vane seal  66 . 
     Each vane seal  66  has sealing portions  70  that extend from the vane assembly  62  to abut the shell wall  54  of a case assembly  72  in order to provide a seal between the first  58  and second  60  chambers of the actuator  52 . 
     Preferably each side-plate forms at least 25% by volume of the vane assembly and preferably the vane assembly occupies at least 20% by volume of the cavity of the actuator. 
     The layered vane assembly  62  is held together with retaining fixtures having a retaining bolt  74  and a retaining nut  76 . The retaining bolt  74  and nut  76  are tightened to clamp the side-plates  64  and vane seal  66  to the vane  68 . 
     Although not shown in this embodiment, the actuator may have a stop embedded in the shell wall  54  to prevent the vane assembly  62  (when in use) from hitting the shell wall  54 . 
     Referring to  FIG. 3 , a cross-section of an actuator  100  of the present invention is shown. The actuator  100  has a vane assembly  102  held within a case assembly  104 . 
     The case assembly  104  has a shell wall  106  defining a cavity  108 . The cavity  108  is divided into a first chamber  110  and a second chamber  112  and the first  110  and second  112  chambers are separated by the vane assembly  102 . 
     The vane assembly  102  has a rigid metal vane  114  in the centre of the assembly  102 , a seal  116  of a flexible material such as polyurethane on each side of the vane  114  and a side-plate  118  to hold each seal  116  adjacent to the vane  114 . A thin seal expander is positioned between each side-plate  118  and seal  116 . 
     The side-plates  118  hold the seals  116  in position by two or more retaining fixings  120 , which each have a retaining bolt  122  and a retaining nut  124  to adjust the tightening of the retaining fixings  120 . The retaining bolt  122  extends through the side-plates  118 , seals  116  and the vane  114 . 
     Each side-plate  118  has two or more protrusions  126  extending from a body  128  of the side-plate  118 . Each protrusion  126  abuts the vane  114  in order to limit the clamping of the side-plate  118  to the vane  114  by the retaining fixings  120 . 
     When the retaining fixings  120  are tightened, the side-plate  118  moves towards the vane  114  in order to clamp the seal  116  to the vane  114 . In due course, the protrusions  126  of the side-plate  118  hit the vane  114  and further tightening of the retaining fixings  120  is prevented. 
     The protrusions  126  thus provide a seal gap between the vane  114  and the side-plate body  128  for the seal  116  so that the seal  116  is suitably fixed in position next to the vane  114  but is not compressed so as to extrude the seal  116  from between the vane  114  and side-plate  118 . 
     The vane  114  has indentations  132  in a body of the vane  134  to accommodate the protrusions  126  of the side-plate  118 . The depth of the indentation  132  with respect to the vane body  134  is smaller than the height of the protrusion  126  from the side-plate body  128 . So, when the protrusion  126  abuts the vane  114  at the indentation  132 , the difference between the depth of the indentation  132  and the height of the protrusion  126  provides the seal gap between the vane body  134  and the side-plate body  128  to accommodate the seal  116 . 
     The distance between the vane body  134  and the side-plate body  128  when the protrusion  126  abuts the vane  114  within the indentation  132  provides the seal gap width  136 . 
     The seal gap width is roughly the thickness of the seal layer  116 . If the seal gap width is significantly larger than seal  116  thickness, the seal  116  will not be held in position satisfactorily. On the other hand, if the seal gap width is significantly smaller than the seal  116  thickness, the seal  116  may be extruded from between the vane  114  and the side-plate  118 . Some compression of the seal  116  by the side-plate  118  may be tolerated. 
     In this embodiment, the protrusions  126  abut directly with the indentations  132  of the vane  114 . The seal may have an interstitial layer positioned around the side-plate protrusions  126  and contacting the vane  114  to provide local sealing with the vane  114 . Such an interstitial layer is compressible. It is also possible to provide a rigid interstitial layer in the same location, but the interstitial layer is then part of the vane. 
     When an interstitial layer is present, the seal gap width  130  must be maintained when the retaining fixings  120  &amp;  124  are fully tightened. In other words, the interstitial layer may be compressible so long as the compression of the interstitial layer does not reduce the seal gap width to a distance where the seal  116  may be extruded from the vane assembly  102 . 
     When assembled into the vane assembly, each seal  116  has protruding portions  140  projecting from both ends of the vane assembly  102  so as to extend to the shell wall  106  of the case assembly  104 . The protruding portions  140  maintain a seal between the first  110  and second  112  chambers. 
     The side-plates  118  can have a well  144  to surround each end  148  of the retaining fixings  120 . The wells  144  allow at least part of the retaining fixings  120  and  124  to be sunken into the side-plate  118 . 
     The side-plates  118  may be made of moulded plastics material or other rigid material. The side-plates  118  may be used to provide the majority of the volume of the vane assembly  102 . In this way, the vane-assembly  102  occupies a significant volume of the cavity  108  of the case assembly  104 . By increasing the volume of the side-plates  118 , the volume of dead-space within the cavity  108  of the case assembly  104  is reduced and the actuator  100  functions more efficiently. 
     The use of moulded plastics material for side-plates  118  is a cost effective way to manufacture them. In addition, the side-plates  118  absorbs shock when the vane assembly  102  hits an actuator stop (not shown) embedded in the shell wall  106  of the case assembly  104 . As a result, the vane assembly  102  is less likely to sustain damage during operation. Of course, the skilled person would recognise that the side-plate may be made of any suitable material In particular, the side-plate may be made of metal. 
     Referring to  FIG. 4 , a cross-section of another actuator  200  of the present invention is shown. The actuator  200  has a vane assembly  202  held within a case assembly  204 . 
     The embodiment of the present invention shown in  FIG. 4  is substantially the same as the embodiment shown in  FIG. 3  with respect to the case assembly, shell wall, cavity, first and second chambers, seal, retaining fixings, retaining nut and bolt, seal gap, seal gap width, interstitial layer, seal protruding portions and wells in the side-plate. However, the vane assembly  202  of  FIG. 4  varies from the embodiment in  FIG. 3  and so is described in more detail herein. 
     The vane assembly  202  has a rigid metal vane  206  in the centre of the assembly  202 , a seal  208  of a flexible material such as polyurethane on each side of the vane  206  and a side-plate  210  to hold each rubber seal  208  adjacent to the vane  206 . 
     The vane  206  has two protrusions  212  extending from each side of a body  214  of the vane. Each protrusion  212  abuts the side-plate  210  in order to limit the clamping of the side-plate  210  to the vane  206  by the retaining fixings  216 . 
     When the retaining fixings  216  are tightened, the side-plate  210  moves towards the vane  206  in order to clamp the seal  208  to the vane  206 . In due course, the protrusions  212  of the vane  206  hit the side-plate  210  and further tightening of the retaining fixings  216  is prevented. 
     The protrusions  212  of the vane  206  thus provide a seal gap between the vane body  214  and the side-plate  210  for the seal  208  so that the seal  208  is suitably fixed in position next to the vane  206  but is not compressed so as to extrude the seal  208  from between the vane  206  and side-plate  210 . 
     The top of the side-plate  210  is curved  220  at one end to accommodate the upper protrusion  212  of the vane  206 . The depth of the curve  220  with respect to the side-plate body is smaller than the height of the protrusion  212  from the vane body  214 . So, when the protrusion  212  abuts the side-plate  210  at the curve  220 , the difference between the depth of the curve  220  and the height of the protrusion  212  provides the seal gap between the vane body  214  and the side-plate body  222  in order to accommodate the seal  208 . 
     The distance between the vane body  214  and the side-plate body  222  when the protrusion  212  abuts the side-plate  210  within the curve  220  thus provides the seal gap width. In this embodiment, all the protrusions  212  abut directly with the side-plate  210 . 
     Referring to  FIG. 5 , a cross-section of a further actuator  300  of the present invention is shown. The actuator  300  has a vane assembly  302  held within a case assembly  304 . 
     The embodiment of the present invention shown in  FIG. 5  is substantially the same as the embodiment shown in  FIG. 3  with respect to the case assembly, shell wall, cavity, first and second chambers, seal, retaining fixings, retaining nut and bolt, seal gap, seal gap width, interstitial layer, seal protruding portions and wells in the side-plate. However, the vane assembly  302  shown in  FIG. 5  varies from the embodiment in  FIG. 3  and so is described in more detail herein. 
     The vane assembly  302  has a rigid metal vane  306  in the centre of the assembly  302 , a rubber seal  308  on each side of the vane  306  and a side-plate  310  to hold each rubber seal  308  adjacent to the vane  306 . 
     The vane assembly  302  also has four limiting spacers  312 , two per fixing screw. Two limiting spacers  312  are positioned between the vane  306  and each side-plate  310  in order to limit the clamping of the side-plate  310  to the vane  306  by the retaining fixings  314 . The spacers  312  have an aperture  316  for accommodating the retaining bolt  318 . 
     When the retaining fixings  314  are tightened, the side-plate  310  moves towards the vane  306  in order to clamp the seal  308  to the vane  306 . In due course, the side-plate  310  abuts each spacer  312  and in turn each spacer  312  abuts the vane  306 . The spacers  312  are substantially incompressible and, as a result, further tightening of the retaining fixings  314  is prevented. 
     The spacers  312  of the vane assembly  302  thus provide a seal gap between the vane  306  and the side-plate  310  for the seal  308  so that the seal  308  is suitably fixed in position next to the vane  306  but is not compressed so as to extrude the seal  308  from between the vane  306  and side-plate  310 . 
     The distance between the vane  306  and the side-plate  310  when the spacers  312  abut the side-plate  310  and vane  306  provides the seal gap width. In this embodiment, the spacers  312  directly abut the vane  306  and the side-plate  310 . 
     The spacers  312  may be any shape or configuration so long as they maintain the seal gap width in order to avoid over-compression of the seal in the seal gap. In this embodiment, the lower spacers are essentially flat cylindrical washers. The upper spacers are curved washers and are curved to fit the contour of the vane  306  and the side-plate  310 . 
     In all the embodiments described above, the seal assemblies are held onto the vane by nuts and bolts. It is also possible to provide threaded studs adhered to and extending from the vane which pass through the seals and side-plates and which receive nuts which, when tightened on the studs, hold the side-plates and seals to the vane in the same way as the bolts and nuts described in the embodiments.