Fluid flow rotating machinery of lobe type

• US 4,145,168 A
• Filed: 11/12/1976
• Issued: 03/20/1979
• Est. Priority Date: 11/12/1976
• Status: Expired due to Term

• Current Assignee: Bobby J. Travis
• Original Assignee: Bobby J. Travis
• Inventors: Travis, Bobby J., Smith, Roy H. Jr.
• Primary Examiner(s): Vrablik, John J.
• Application Number:
  US05/741,505
• Time in Patent Office: 858 Days
• Field of Search: 418/150, 418/189-191, 418/196, 418/205, 418/206
• US Class Current: 418/150
• CPC Class Codes: F01C 1/20 with dissimilar tooth forms F01C1/16 takes precedence
• CPC Class Codes: F01C 1/36 having both the movements defined in sub-groups F01C1/22 and F01C1/24

Abstract

A positive displacement device utilizing at least two rotors which roll sealingly on one another at a common pitch surface speed. Outwardly extending lobes on one rotor sealing engage the cylindrical bore of the housing of the device, fluid traversing the device circumferentially in the annulus between such bore and the pitch surface of the rotor. Speed of rotation of the two rotors is controlled by a timing chain running between sprockets mounted on the rotor shafts.

When the lobe passes the line of sealing contact, a cavity is provided in the meshing rotor, and the lobe makes sealing contact with the wall of this cavity during at least that interval when there is no sealing contact between the pitch surfaces, i.e., the interval when the mouth of the cavity is passing through dead center. The inventor shows that the cavity is a modified path he calls the reentrant loop of an endoepicycloid, which is the path of the tip of a fixed radial extension of one circle as it rolls without slipping around the circumference of a second, fixed circle. From this he shows that, to accommodate a lobe having the general shape of an isoceles triangle truncated or blunted by a radial tip, the endoepicycloid should be split into two halves which are moved apart circumferentially the length of the arc of the lobe tip, and the inside ends of the halves joined by an arc centered on the center of the cavity rotor. Further modifications such as undercutting to avoid double sealing are also described.

Claims

1. A fluid flow rotating machine of the lobe type comprising first and second intermeshing rotors having pitch surfaces in sealing tangential contact, said rotors being disposed on parallel axes of rotation and rotating with a common pitch surface speed,

at least the first of said rotors having a generally chisel shaped lobe projecting radially outwardly from its pitch surface to terminate in a tip rounded with an arc centered on the center of said first rotor and with a radius equal to the sum of the radius of the pitch surface and the radial height of the lobe, said lobe tip having opposed leading and trailing corners, such lobe being symmetrical and having a cross-sectional base width greater than the width of said tip and not greater than approximately said height,

at least said second rotor having a lobe receiving peripheral sealing cavity extending inwardly from said pitch surface making sealing and moving contact with said lobe tip, said cavity having a cylindrical bottom surface coaxial with its pitch surface, a radius equal to the difference between the radius of said second rotor and the height of said lobe, and an arc length equal to that of said lobe tip, the ends of said bottom surface of the cavity being joined to leading and trailing surfaces extending outwardly to said pitch surface and having profiles defined by the leading and trailing corners of said lobe tip as the rotor with the lobe is rolled around the rotor with the cavity without slipping,

said lobe having a pair of opposed flanks extending between the leading and trailing corners of the tip and the pitch surface from which the lobe extends, said flanks being spaced from all surfaces of said cavity at all times, so that the only contacts between rotors when said pitch surfaces are not rolling over one another is between the tip of a lobe and the surfaces of the intermeshing cavity,

said pitch surface of each rotor having a net undisturbed circumference at least equal to the portion of its circumference interrupted by said lobes and cavities.

2. The rotor of claim 1 in which said rotor containing the sealing cavity is modified to avoid double sealing by undercutting a portion of at least one of said leading and trailing surfaces of the cavity, between the line of intersection between such surface and the pitch surface of the rotor and the sealing line between such surface and the corner of the lobe tip corresponding to the position of the lobe rotor and the cavity rotor when a line joining the centers of the two rotors passes through the intersection of the other cavity surface and the pitch surface of the cavity rotor.

3. The rotor of claim 1 in which said rotor is modified to prevent double sealing by undercutting a portion of the pitch surface on one or both sides of the mouth of the cavity, between one corner of the mouth and the sealing line between the pitch surfaces of the two rotors corresponding to the position of the lobe rotor when said lobe tip seals against the opposite corner of the cavity mouth.

4. A fluid flow rotating machine of the lobe type comprising:

first and second intermeshing rotors, the first rotor having a number of lobe-receiving peripheral cavities therein each adapted to make sliding and sealing contact with the tip of a lobe projecting radially from the circumference of the second rotor,

said rotors being mounted for rotation about parallel axes with their pitch surfaces in sealing contact and constrained to rotate with equal pitch surface velocities,

said lobe having a profile of generally chisel shape with its outer end or apex truncated by an arc centered on the center of the second rotor and intersecting the not necessarily flat flanks of the chisel in a leading corner and a trailing corner,

said cavity having a bottom surface, a leading surface extending from one end of the bottom surface to the pitch surface of its rotor and a trailing surface extending from the other end of the bottom surface to the pitch surface, said leading and trailing surfaces having profiles respectively determined by the leading and trailing half-loops of endoepicycloid formed by the traces of the leading and trailing corners of the lobe tip as the second rotor is rolled around the circumference of the first without slippage, and said bottom surface of the cavity having a circular arc profile centered on the center of the first rotor and a radius equal to the difference between the pitch surface radius of the first rotor and the radial height of said lobe,

said flanks of the lobe diverging from the leading and trailing corners of the apex and extending to and joining the pitch surface of the second rotor with a base width greater than the width of said apex,

said flanks being spaced from all surfaces of the first rotor at all times so that only said leading and trailing corners of the apex of the lobe contact said leading and trailing surfaces of the intermeshing cavity,

said pitch surface of each rotor having a net undisturbed circumferential portions after subtracting that portion of such surface which is interrupted by outwardly extending lobes and inwardly extending cavities,

said undisturbed portions of the pitch surfaces maintaining a rotor-to-rotor seal when the lobe apices are out of contact with said cavities.

5. The device of claim 4 in which said first and second rotors have unequal pitch diameters.

6. The device of claim 4 in which said first and second rotors have equal pitch diameters.

7. The device of claim 4 in which each of said first and second rotors has both lobes and lobe-receiving cavities, said lobes and cavities of the first rotor being circumferentially spaced from one another to make sealing contact with the cavities and lobes of the second rotor.

8. The device of claim 4 in which one of said rotors has only lobes and the other has only cavities.

9. The device of claim 4 which further includes a third rotor mounted for rotation about an axis parallel to the axes of said first and second rotor and making sealing peripheral contact with one of them, said third rotor having lobes and cavities disposed to make sealing engagement with the cavities and lobes of the rotor it engages.

10. A rotary fluid actuator comprising a pair of rotors disposed for rotation with equal pitch surface velocities about their individual axes and with said axes parallel, each said rotor having a cylindrical pitch surface making sealing contact with the cylindrical surface of the other, each said cylindrical pitch surface being interrupted by a plurality of engaging elements consisting of outwardly extending lobes and inwardly extending cavities, said engaging elements being circumferentially spaced so that during rotation each lobe of one rotor engages a cavity of the other and makes sealing contact with the wall of the cavity during at least that fraction of the engagement period when there is no sealing engagement between said cylindrical pitch surfaces, each said lobe having a cross-section having the general shape of an isosceles triangle with a slightly blunted tip, said tip having opposed leading and trailing corners, and each said cavity having a cross-section in the general form of an endoepicycloid having a maximum radial depth equal to the radial height of the engaging lobe, the halves of the endoepicycloid being separated from each other and joined by an arc having a radius equal to the difference between the radius of the circumferential surface of the rotor containing the cavity and the said maximum radial depth of the cavity, and a length equal to the width of the tip of the intermeshing lobe,

each said lobe having a pair of opposed flanks extending between the leading and trailing corners of the tip and the pitch surface from which the lobe extends, said flanks being spaced from all surfaces of said cavity at all times, so that the only contacts between rotors when said pitch surfaces are not rolling over one another is between the tip of a lobe and the surfaces of the intermeshing cavity,

said pitch surface of each rotor having a net undisturbed circumference at least equal to the portion of its circumference interrupted by said lobes and cavities.

11. The rotary fluid actuator of claim 10 in which the endoepicycloidal cavity is defined by the equations:

##EQU4## where a = the radius of a fixed circle having its center at the intersection of the x and y axes of a Cartesian coordinate scheme

b = the radius of a circle rolling around the circumference of the circle of radius "a", without slipping

θ

= the angle between the x-axis and a line joining the centers of the two circles

h = the radial distance between the circumference of the circle of radius "b" and a point rotating with such circle as though fixed thereto, and x and y are the coordinates of such moving point.