Abstract:
A vane motor is modified to increase the sealing effectiveness of the gap made at the interface of the spindle and cylinder by undercutting the cylinder a predetermined amount and distance so as to increase the effectiveness of the spindle to cylinder gap and to decrease the requirements for lubrication of the vane motor.

Description:
This application claims the benefits under 35 U.S.C. § 119( e ) of the U.S. provisional patent application 60/567,188 and 60/567,189 filed on Apr. 30, 2004 

   RELATED APPLICATIONS 
   This invention relates to the pneumatic motor entitled SURGICAL PNEUMATIC MOTOR and was invented by myself and co-inventor Douglas Perry and identified as Ser. No. 11/082,124 and SURGICAL PNEUMATIC MOTOR FOR USE WITH MRI invented by myself and identified as Ser. No. 11/074,821 both of which were recently filed as non-provisional applications and are incorporated herein by reference and are commonly assigned with this application to The Anspach Effort, Inc. 
   FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable 
   TECHNICAL FIELD 
   This invention relates to pneumatic vane motors of the type that is utilized in surgical drills and more particularly to the interface between the bore surface of the cylinder and the outer surface of the spindle and its sealing characteristics. 
   BACKGROUND OF THE INVENTION 
   Rotary machines typically utilize vane motors that are pneumatically powered to cause rotation of the output shaft. As is well known these machines comprise a cylinder, sometimes referred to as a casing and an eccentrically mounted spindle in the cylinder, sometimes referred to as a rotor. The cylinder is stationary and through apertures in the cylinder lead pressurized air to impinge on the working face of the reciprocating vanes mounted in slots formed in the spindle to cause the spindle to rotate and then exhaust the spent air through additional holes formed in the cylinder. The outer edge of the vanes is in contact with the inner surface of the cylinder and the vanes extend in their respective slots during the power stroke of the vane motor and during the exhaust portion of the stroke the vanes retract back into their respective slots. Heretofore, the cylinder had apertures formed therein that were configured in the shape of slots. The pressurized air that is admitted to the spindle and impinges on the working face of the vanes to cause them to rotate the spindle. 
   This invention is directed toward the interface between the spindle and cylinder so as to enhance the sealing of the gap between the two components resulting in an improvement in the requirements to lubricate the vane motor and rotating machine. The terms “seal” and “sealing” in the context of this application does not refer to independent hardware that typically is inserted at strategic areas in the rotating machine to prevent or reduce leakage, but rather to the configuration of the complementary components that are contoured to reduce the gap between the interfacing parts and therefore eliminate or reduce leakage of fluid from upstream of the configuration to downstream thereof. When this inventive feature is employed in a cylinder at the interface of the cylinder and spindle of a vane motor so as to configure the surface of the inner diameter of the cylinder shape of this surface this change contours this surface from a circular shape to a crescent shape. Accordingly, for use in this description this portion of the interface os referenced as a crescent seal. 
   SUMMARY OF THE INVENTION 
   An object of this invention is to provide for a vane motor an improved cylinder/vane of a vane motor. 
   A feature of this invention is to provide for a rotary machine that includes a pneumatic vane motor an undercut of the cylinder so that the surface of the bore of the cylinder defines an elongated seal at the interface of the spindle surface. 
   Another feature of this invention is to provide a crescent seal at the interface of the cylinder and vane of a vane motor of a rotary machine that is characterized as enhancing the cylinder to spindle gap to decrease the lubrication requirements of the rotary machine. 
   The foregoing and other features of the present invention will become more apparent from the following description and accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view in perspective of the vane motor of this invention; 
       FIG. 2  is a view of a prior art configuration in schematic of the spindle and cylinder of a vane motor; and 
       FIG. 3  is a view of the configuration in schematic of the spindle and cylinder of a vane motor modified in accordance with this invention. 
   

   These figures merely serve to further clarify and illustrate the present invention and are not intended to limit the scope thereof. 
   DETAILED DESCRIPTION OF THE INVENTION 
   While this invention is being described in its preferred embodiment as a vane motor that is utilized in a surgical pneumatic drill, as will be understood by those skilled in this art, this invention can by utilized with any type of pneumatic vane motor which can be modified in accordance with this invention and while the dimensions may change such modification is within the scope of this invention. 
   The invention is best seen by referring to all the Figs. where  FIG. 1  shows the vane motor generally illustrated by reference numeral  10  as having a cylinder  14 , a spindle  16  rotary mounted in the cylinder and vanes  18  reciprocally mounted into axial slots formed in the spindle  16 . The spindle  16  may include the stub shafts  20  and  22  which are typically supported by bearings. This particular vane and cylinder is specifically detailed in the provisional patent applications, supra, and for details thereof reference should be made thereto which are incorporated herein by reference. Suffice it to say that air enters the cylinder  14  via inlet  50  and flows through the axial passage or through passageway  24  and the air is admitted into inlet holes  26  via the circumferential slots  28 . In some designs all the pressurized air is admitted via this axial through passageway or passage  24 . However in this embodiment the air is circulated around the bearing (not shown) for cooling purposes and re-admitted into the axial flow through passageway or slot  30  where the remaining pressurized air is admitted into the vane motor via the inlet holes  26 . Obviously, as is well known the pressurized air impinges on the vanes during the power stroke to rotate the spindle and produce power and the remaining portion is discharged through the discharge holes (not shown) during the exhaust stroke. 
   Reference is next made to  FIG. 2  which illustrates by the schematic the cylinder  14   a  and spindle  16   a  of the vane motor of the type that is depicted in  FIG. 1 . This is a representation of the prior art configuration where the spindle that is eccentrically mounted in the bore  32  of the cylinder  14   a  comes into contact at the tangent of the interface of these two components which is sometimes referred to as the pinch point and is being represented by reference letter A. As shown by the dimensions in  FIG. 2  the contact point is at five ten thousand of an inch (0.0005″) and the space adjacent the pinch point becomes progressively larger as say by 0.0027″ to 0.005″ at the edge  34  of the slot  36  and continues. 
   In accordance with this invention as best seen in  FIG. 3  the cylinder surface  40  in bore  32   b  is undercut at the interface of the cylinder  14  and spindle  16  just upstream of the power stroke as represented by the exaggerated dash lines  42 . For clarity a partial showing of the housing  12  is included to show the relationship of the spindle and cylinder and the vanes are eliminated from their respective slots. The undercut distorts the circular shape of the cylindrical surface  40  which allows the spindle to increase the area of contact so as to define the crescent seal indicated by reference numeral  44 . The crescent seal  44  by virtue of this invention spans the contact distance to a dimension that includes the arc that measures substantially 76 degrees and the arc is between adjacent vane slots  46  and  48 . Obviously, the dimension of the crescent seal would be predicated on the size of the vane motor and the dimension of the depth of the undercut. These factors will, of course, determine the length of the seal. It should be realized from the foregoing that the crescent seal extends from the exhaust stroke position where the interface of the spindle and cylinder are in close contact and the position of the vane (or slot) when it is at the beginning of the power stroke which is adjacent to inlet  26 . The consequence of length of the crescent seal and its attendant gap enhances the sealing ability of the spindle to cylinder gap. This increased effectiveness of the seal, in turn, is translated into the vane motor&#39;s ability to operate with significantly less lubrication without impairing the life of the rotary machine. 
   Although this invention has been shown and described with respect to detailed embodiments thereof, it will be appreciated and understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the disclosed invention.