US 3810723 A
A device for pumping fluid or for converting the power in a flow of water into constant rotary motion. A Roots-type pump or motor utilizing two centrally-mounted oval rotors is coupled to a transmission designed to convert the non-constant speed characteristic of the Roots-type device into constant rotary motion. The rotors are synchronized through the transmission, thus eliminating the need for gear teeth on the rotors and allowing leakproof seals of a resilient material to be used to surface the rotors. Two embodiments of the transmission are disclosed, one involving angled Hooke joints and the other utilizing a gear train including focus-mounted elliptical gears.
Description (OCR text may contain errors)
United States Patent [1 1 Johnson [4 1 May 14,1974
FLUID PRESSURE DEVICE  Inventor: Robert Johnson, 215-A San Juan Rd., Watsonville, Calif. 95076  Filed: Sept. 21, 1972  Appl. No.: 291,131
 US. Cl. 418/205, 418/150  Int. Cl. F04b 17/10  Field of Search 418/205, 206, 150; 74/63, 74/393, 437
[5 6] References Cited UNITED STATES PATENTS 571,770 11/1896 Kurz 418/206 2,697,402 12/1954 Lindquist. 418/206 X 2,368,019 l/1945 Guibert.... 418/206 2,671,929 3/1954 Gayler .418/206 X 3,327,637 6/1967 Hotta 418/150 3,305,167 2/1967 Nagata 418/150 2,451,603 10/1948 Barker 418/206 X 3,274,894 9/1966 .lunger 418/206 2,897,765 8/1959 Kitano 418/206 FOREIGN PATENTS OR APPLICATIONS 612,867 5/1935 Germany 418/206 OTHER PUBLICATIONS Primary ExaminerC. J. Husar Assistant Examiner-Leonard Smith Attorney, Agent, or Firm-Townsend and Townsend  ABSTRACT A device for pumping fluid or for converting the power in a flow of water into constant rotary motion. A Roots-type pump or motor utilizing two centrallymounted oval rotors is coupled to a transmission designed to convert the non-constant speed characteristic of the Roots-type device into constant rotary motion. The rotors are synchronized through the transmission, thus eliminating the need for gear teeth on the rotors and allowing leakproof seals of a resilient material to be used to surface the rotors. Two embodiments of the transmission are disclosed, one involving angled Hooke joints and the other utilizing a gear train including focus-mounted elliptical gears.
1 Claim, 6 Drawing Figures FLUID PRESSURE DEVICE The present invention relates to a fluid pressure device based on the Roots-type pump or motor.
More specifically, it is directed to a Roots-type device of a particularly rugged design and capable of 5 pumping fluid at a uniform rate when driven by a constant speed source, or of producing a constant speed source of power, when fluid is forced through the device.
Roots-type motor refers generally to that class of machines that convert the power inherent in the flow of a fluid into rotary mechanical motion according to the following principle: The fluid is directed into a rigid housing through an inlet port. Mounted on two parallel shafts within the'housing are rotors, each having a noncircular cross-section (taken in a plane perpendicular to the shafts). The shafts are free to rotate in bearings mounted in the housing; at least one of the shafts penetrates the housing so as to provide a mechanical connection from outside the housing to the rotors within.
The cross-sectional configurations of the rotors, and of the housing (taken in the same plane) are designed so that several conditions are met. (a) The rotors rotate in constant contact with one another, synchronized so that their periods are the same. (b) At least one point on each rotor maintains constant sliding contact with the interior surface of the housing. (0) In a motor the pressure against the rotors of the fluid entering the housing at the inlet port causes the rotors to rotate in such a direction that the fluid is transferred to the outlet port, where it leaves the device. The mechanical seals at the above-referenced points of contact must be sufficient to prevent the fluid in'use from leaking past the points of contact. The rotary motion imparted to the rotors by the pressure of the fluid is available at the end of the shaft(s) that are exterior to the housing.
The basic principles of design of a Roots-type pump are identical to that of the motor. in operation, a source of rotary motion is coupled to one or both shaft-ends, thus causing the rotors to rotate. The motion of the rotors carries fluid from the inlet port to the outlet port, thereby functioning as a pump. Usually, in both Rootstype motors and pumps, the rotors have gear teeth on their peripheral surfaces, so as to synchronize the motion of the two rotors.
One problem inherent in the use of a Roots-type fluid pressure device is that of non-constant angular speed. Since the two rotors are non-circular, the distance between the axis of rotation of each rotor and the point of contact between the rotors varies with the position of the rotors in their cycle. Therefore, if the device is used as a motor, with fluid passing through the device at a uniform rate, each rotor will rotate at a cyclically varying rate of speed. A non-constant source of rotary motion is of limited utility. The Roots-type motor would be much more useful were it to be adapted to provide a constant speed output.
Similarly, when the Roots-type device is used as a pump, if one of the rotor shafts is driven by a constant speed source, the pumping speed will vary cyclically.
A second difficulty in the design and use of Rootstype devices is that of maintaining a leak-proof seal at the various points of Contact among the rotors and the housing. The problem is made doubly difficult by the use of gear teeth on the peripheral surfaces of the rotors, since the presence of teeth increases the complexity of the inter-relationship between the rotors.
Gear teeth are used on the rotors so as to synchronize their motions. Without them, or some other synchronizing method, the rotors would fall out of alignment, and the mechanism would jam. The use of gear teeth also introduces the problem of gear tooth strength.
The apparatus of the present invention answers the problem of non-constant speed by coupling one or both rotor shafts to a transmission, designed specifically to convert the varying speeds of a set of centrallymounted oval rotors into a constant speed motion. The transmission allows the Rootstype motor to be used even where a constant speed drive is needed. The Roots-type pump of the present invention when driven from a constant speed source, pumps fluid at a constant rate.
One embodiment of the present invention employs a Hooke or universal joint. The Hooke joint, when its drive and output shafts are forced to lie in two different planes, introduces a known distortion into the angular motions transmitted through it, the distortion depending on the angle between the two planes. The transmission means of this embodiment comprises an angled Hooke joint, the angle between the shafts planes being matched to the precise shape of the rotors, so that the distortion of the one exactly cancels that of the other. Hence, when the device is used as a motor, the Hooke joint converts the non-constant output of the Rootstype device into a constant speed source. in the pump configuration, the Hooke joint distorts the constant speed driving power into a non-constant motion, thereby causing the rotors to pump fluid at a constant rate.
' In an alternate embodiment the transmission means takes the form ofa gear train, including a set of gears to double the rotor shaft speed, then a set of focus mounted elliptical gears, the train being designed to perform the same distortion function as the Hooke joint.
in both of these two embodiments, each rotor shaft can be coupled to independent transmission means. At the constant speed end of the transmission means, the two independent transmissions can be. coupled by the use of identical spur gears or some other appropriate method. By thus coupling the two transmissions, the rotors themselves are coupled and synchronized. In this configuration gear teeth on the rotors are unnecessary for synchronization. The absence of gear teeth avoids the problems involving tooth strength and allows the rotors to be made of or clad in a resilient material. Utilizing this type of material provides two advantages. The rotors may be positioned relative to one another so that they press tightly against one another causing a compression of the resilient material of several thousandths of an inch. This would provide a positive and highly leak-proof seal. The use of a resilient material would also slow the wearing process of the rotors since there would be no metal-to-metal contact at the points between the rotors and the housing.
Thus, one advantage of the present invention is that it allows a-Roots-type fluid pressure device to be used with mechanisms that demand or deliver a constant rotary speed.
Another advantage of the present invention is that the use of transmission means on both rotor shafts allows both the elimination of gear teeth on the rotors and the use of a resilient material on the peripheral surface of the rotors for a leak-proof seal.
A feature of the present invention is the use of angled Hooke joints to provide angular speed distortion so as to compensate for the non-constant speed delivered or demanded by a Roots-type device.
A primary object of the present invention is to provide a Roots-type pump or motor of simple design and efficient operation that can be used in conjunction with constant speed devices.
Other objects, features and advantages will be more readily apparent after a reading of the following detailed description with references to the accompanying drawings, wherein:
FIG. la is a schematic cross-sectional view of the rotors and housing of the present invention;
FIG. lb is a schematic cross-sectional view of the rotors and housing wherein the rotors are 90 advanced from the position of FIG. la;
FIG. 2 is an elevational view of a single rotor a drawn upon a graph having Cartesian coordinates, x and y;
FIG. 3 is a schematic perspective drawing showing the rotors coupled to an angled Hooke joint transmission;
FIG. 4 is a schematic perspective view showing the rotors coupled to a transmission gear train including focus mounted elliptical gears; and
FIG. 5 is a cross-sectional view of two rotors having gear teeth on their peripheral surfaces.
Referring now to FIGS. la and 1b, operation of a Roots-type fluid pressure device is there shown generally. Fluid enters the device through inlet aperture 12 in housing 14 and leaves it through outlet aperture 16. During its passage through the device, the fluid interacts with rotors l8 and mounted at their centers on shafts 22 and 24, respectively. The peripheral surfaces of the rotors may be clad in a resilient material, so as to provide a leak-proof seal at the points of contact. The rotors l8 and 20 are oval in cross section; they are designed to maintain contact with one another through their full cycle. Referring now to the notation indicated in FIG. 2, one equation which describes the desired oval shape of the rotors is:
FIGS. la and lb show the rotors l8 and 20, at two different points in their cycle, separated in phase by 90. For clarity, assume the device is being used in a motor configuration. Fluid then enters under pressure through inlet aperture 12. In the position indicated in FIG. la, the pressure produces a torque on rotor 18 about its shaft 22 in the direction indicated by the arrow, while there will be no torque on rotor 20. Hence, rotor 18 will rotate in the direction shown. If the two rotors are coupled so that they rotate synchronously, then rotor 20 will also rotate in the direction shown by its arrow. After 90 of rotation the rotors will appear as shown in FIG. lb. Clearly, at this point in time, it is rotor 20 which will be driven by the fluid pressure. Though the driven rotor has changed, the directions of rotations have not. Rotation will continue; after 90 the rotors will again appear in the position of FIG. la. The shafts of either or both rotors may be used as a power source.
When the device is used in the pump configuration, rotors l8 and 20 are driven synchronously. In FIG. la, fluid is trapped in region 26 between rotor 18 and housing 14. As rotor 18 turns in the direction shown, that fluid is pushed toward outlet aperture 16. In FIG. lb, fluid is shown trapped in a similar region 28. This too will be delivered to the outlet aperture 16, as rotor 20 continues in its cycle. In this way fluid is pumped through the device.
The rotors and housing as described above, are common to all embodiments of the present invention.
Referring now to FIG. 3, the rotors l8 and 20 are shown coupled to the transmission. For clarity of the drawing the housing is not shown. Shafts 22 and 24 provide a mechanical connection between the rotors l8 and 20 and the Hooke joints 30 and 32. Note that bar 34 of Hooke joint 30 is parallel to the major axis of rotor 18 with a similar relationship for rotor 20. Shafts 36 and 38 couple the Hooke joints 30 and 32 to spur gears 40 and 42, which mesh with one another and thereby couple the two otherwise independent transmissions; in this way the motions of rotors l8 and 20 are synchronized.
Shafts 22 and 24 lie in a different plane than shafts 36 and 38; the angle between those planes determines the precise characteristics of the rotary motion distortion introduced by the Hooke joints. In practice the angle is set so as to compensate for the motions of the rotors used, so that the non-constant angular speeds of the rotors at the one end of the transmission correspond to constant rotary motion at the spur gears 40 and 42.
In an alternate embodiment of the present invention, the transmission takes the form of a gear train, as shown in FIG. 4. Rotors l8 and 20 are connected by shafts 22 and 24 to spur gears 44 and 46, which mesh with spur gears 48 and 50 mounted on shafts 52 and 54. This combination of gears is designed so that shafts 52 and 54 rotate twice as fast as shafts 22 and 24. Elliptical gears 56 and 58 are focus-mounted on shafts 52 and 54. Those gears mesh in constant contact with elliptical gears 60 and 62, focus mounted on shafts 64 and 66, onto which shafts are mounted spur gears 68 and 70. These spur gears 68 and 70 mesh with one another so as to couple the two gear trains, thus synchronizing the motions of rotors l8 and 20, just as in the previous transmission embodiment.
The set of elliptical gears 56, 58, 60 and 62 are designed to convert the non-constant angular rotation, characteristic of the rotors used, to a constant angular motion at the spur gears 68 and 70.
Optionally, the dual nature of the above transmission embodiments may be eliminated; one rotor shaft alone may be coupled to a single transmission train. Since the rotors then would not be coupled together through the flnal spur gears, an alternate method of rotor synchronization would have to be provided. One method is to form gear teeth 72 on the peripheral surfaces of the rotors, as shown in FIG. 5.
What is claimed is:
l. A Roots-type fluid pressure device comprising: a housing; two coplanar rotor shafts mounted for rotation in bearings in said housing; two identical rotors mounted at their centers upon said rotor shafts, said rotors having an oval cross section designed so that the rotors maintain constant contact with one another throughout their cycles and also maintain contact at speed shaft coupled to said Hooke joint at the other of said two points, said constant speed shaft being disposed so that it forms a fixed predetermined angle with the plane defined by said rotor shafts, said angle being chosen so that the non-constant angular rotation characteristic of said rotors corresponds to a constant speed rotation of the said constant speed shaft.