US3612734A

US3612734A - Rotary pump or motor with an axially rotating rotor

Info

Publication number: US3612734A
Application number: US830733A
Authority: US
Inventors: Peter A Dawson; Hans G Pahl; Edward J Carpenter
Original assignee: Mono Pumps Ltd
Current assignee: NOV Process and Flow Technologies UK Ltd
Priority date: 1968-06-05
Filing date: 1969-06-05
Publication date: 1971-10-12
Anticipated expiration: 1988-10-12
Also published as: GB1220848A; DE1928318A1; DE1928318C3; DE1928318B2

Abstract

The specification discloses a rotary helical gear pump having a stator formed with at least one helical gear and a rotor mounted therein formed with at least one helical gear meshing therewith, the number of starts of the gear or gears and the stator differing by one from that of the rotor. A flexible drive shaft is secured to the rotor in one of a number of different ways, to drive the rotor, the drive shaft being coated with a nonpermeable and nonporous layer, which is effectively sealed to the rotor, to reduce the effects of corrosion fatigue.

Description

United States Patent ROTARY PUMP OR MOTOR WITH AN AXIALLY ROTATING ROTOR 5 Claims, 6 Drawing Figs.

US. Cl 418/48, 418/179 Int. Cl F01c U10, 7 F010 5/00, F046 1/06 Field of Search 103/117 M;

[56] References Cited UNITED STATES PATENTS 2,463,341 3/1949 Wade 418/48 2,502,512 4/1950 Demetriades 287/53 R 3,242,130 3/1966 Jackopin 106/14 3,479,960 11/1969 Cardoso 418/48 FOREIGN PATENTS 223,042 8/1962 Austria 418/48 Primary Examiner-Carlton R. Croyle Assistant Examiner.lohn J. Vrablik AttorneyCushman, Darby & Cushman ABSTRACT: The specification discloses a rotary helical gear pump having a stator formed with at least one helical gear and a rotor mounted therein formed with at least one helical gear meshing therewith, the number of starts of the gear or gears and the stator differing by one from that of the rotor. A flexible drive shaft is secured to the rotor in one of a number of different ways, to drive the rotor, the drive shaft being coated with a nonpermeabie and nonporous layer, which is effectively sealed to the rotor, to reduce the efiects of corrosion fatigue.

ROTARY PUMP OR MOTOR WITH AN AXIALLY ROTATING ROTOR The present invention relates to a rotary pump or motor with an eccenuically rotating rotor. One particular form of such pump is a helical gear pump which includes a stator provided with one or more internal helical gears or teeth, and a rotor provided with one or more external helical gears or teeth, meshing with those of the stator, the number of starts of the gear or gears of one member being one more than that of the other member. With such pumps, the rotor executes a rotary motion, and also orbits in either the same sense or the opposite sense as the rotary motion. Other forms of such pumps or motor are those of the Wankel type in which the rotor again executes a rotary action and an orbiting motion.

In the helical gear pump, the rotor is conventionally connected to a drive motor by an intermediate drive shaft, provided at each end with a universal joint, the universal joints accommodating both the rotary and the orbiting motion. Since these pumps are often used to pump corrosive liquids or powders, the universal joint, particularly at the rotor end of the drive-shaft, is subject to considerable wear and leaching of the joint lubricant.

According to the present invention there is provided a rotary pump or motor comprising a stator having a rotor eccentrically rotatable with respect thereto, a flexible drive shaft secured to the rotor to drive the rotor or receive drive therefrom, the flexible drive shaft being coated with a nonpermeable and nonporous layer. The invention also provides a rotary helical gear pump comprising a stator formed with at least one helical gear, a rotor formed with at least one helical gear meshing with the stator gear or gears, the number of starts of the gear or gears of the stator differing by one from the number of starts of the gear or gears of the rotor, and a flexible drive shaft secured to the rotor to drive the rotor, such shaft being coated with a nonpermeable and nonporous layer. Preferably, such a coating layer should be capable of flexing, and be sufficiently tough to permit handling and withstand abrasion.

It will be appreciated that the flexible shaft will be subject to a substantial cyclic stress variation. By providing the coating of nonpermeable and nonporous material, the effect of corrosion fatigue is eliminated, the shaft itself being only likely to fail under normal fatigue conditions.

While a few stainless steels have a high resistance to fatigue in the presence of corrosive'or reactive media such as atmospheric air containing moisture or water, these stainless materials are extremely costly and, in any event, are not entirely free from fatigue. By providing a coating of nonpermeable and nonporous material, it is possible to use a steel of moderate strength which is comparatively cheap and readily obtainable.

Suitable coating materials include a plastics material known under the trade name Penton, which is a chlorinated polyether, which is preferred, nitral rubber and certain epoxy resins.- A thin coating of gold also provides good results from a corrosion fatigue point of view, but its relative softness makes it liable to abrasion in certain uses of a pump. Penton" can be applied to the flexible shaft using a fluidized bed technique whilecertain epoxy resins have the advantage that they can simply be painted on. Generally, it is not possible to plate a coating onto the shaft, since such a process tends to induce certain tensile stresses in the shaft, which can affect the latters fatigue resistance.

In order that the invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a fragmentary scrap section, which is showing a helical gear pump rotor into which is fitted the end of a flexible shaft, according to the present invention;

FIG. 2 is a similar view showing a second method of fixing a coated flexible shaft to the rotor, the view being in half section;

FIGS. 3 and 4 are views similar to FIG. 2 of two further methods of fixing the flexible shaft to the rotor, and

FIGS. 5 and 6 show a cross section of the complete pumps of FIGS. 1 and 2 respectively to a smaller scale.

In the embodiment illustrated in FIGS. 1 and 5 a helical gear pump is shown as comprising a resilient stator 10 mounted in a housing 11 and having a helically threaded bore 12, the thread having one more or one less start than that of the helically threaded rotor 13. In order to drive the rotor 13 in its rotating and orbiting path, a drive shaft 14 is secured thereto. This drive shaft comprises an elongate steel member 15 provided at each end with an enlargement 16. The connection to the rotor is shown in greater detail in FIG. 1, and a similar connection is effected at the other end of the flexible drive shaft where it is connected to a key shaft (FIG. 5) which may be secured to the armature shaft of an electric motor (not shown).

To the left of the enlargement, as seen in FIG. 1, the shaft 14 is provided with an outwardly stepped portion 17, followed by a reduced-diameter portion 18 which is formed with a thread 19 which engages a corresponding thread formed in a bore 20 in the rotor 13.

Surrounding the shaft 15 is a coating 21 of a chlorinated polyether plastics material sold under the trade name Penton. This coating can be applied by the fluidized bed technique, and is applied on that portion of the shaft 15 between the step 17, and the corresponding step at the other end of the shaft. Before the shaft is threaded into the rotor, the coating 21 is of a thickness which is slightly greater than the depth of the step 17. Thus, when the shaft is threaded into the bore 20 of the rotor 13, the portion 22 adjacent the step is compressed against a countersunk portion or countersink 23 at the mouth of the bore 20.

The compression by the countersunk portion 23 of the coating 21 ensures the fluidtight seal between the rotor and the shaft, and prevents any liquid or other material being pumped from attacking the threaded portion of the shaft 15. In each of the four embodiments of pump described in the present specification, the shaft 15 is approximately 60 inches long and 0.75 inch in diameter over the majority of its length. For other sizes of pumps, the porportions of the shaft will be much the same while the actual dimensions may be larger or smaller. These proportions permit the shaft to flex sufficiently to allow for the eccentricity of the rotor. It will be apparent that considerable variations in stress will occur as the shaft rotates, but the coating or layer 21 serves to prevent corrosion fatigue causing failure of the shaft 15.

The method of securing the shaft 14 at the right-hand end, as indicated above, is similar. As can be seen in FIG. 5, a key shaft 100 is bolted to a hollow shaft 101 which is mounted for rotation in the housing 102 by means of

bearings

103 and 104, a seal between the shaft 101 and the housing 102 being effected by a suitable packing ring located between a gland 106 and a gland ring 107. In FIG. 5 the inlet to the pump is illustrated at 108 and the outlet at 109.

The embodiment of FIG. 1 has the advantage that it can be manufactured cheaply and readily, but it does also have the disadvantage that rotation may only be performed in one direction, since rotation in the opposite direction will tend to unscrew the thread 19 from the corresponding thread in the stator 13. In the other three embodiments this problem does not arise. In the construction of FIGS. 2 and 6, the pump includes a stator 24 and the rotor 25 as before, but in this embodiment the rotor is provided with an axial enlarged bore 26 which extends a substantial distance therethrough. At its lefthand end, as seen in FIG. 2, the bore 26 communicates with a tapered bore 27, the angle of which is such as to form a morse taper, to bores 26 and 27 extending through the complete length of the rotor. Engaged in this taper is the correspondingly tapered head 28 of a drive shaft 29 which is again provided with a coating 30 of plastics material. This coating 30 extends into an annular groove 31, in which is also seated an O-ring 32 which, together with the coating which engages in the taper 27 provides a seal between the shaft 29 and the rotor 25. In order to prevent the shaft 29 from disengaging from the taper 27 a locking bolt 33 engages in a threaded bore or recess 34 in the shaft 29, the head 35 of the bolt bearing against the end of the rotor. The complete pump is illustrated in FIG. 6, in which like parts have been given like reference numerals to those of FIG. 5, with the addition of the letter A.

The modified embodiment illustrated in FIG. 3 includes a resilient stator 36 and a rotor 37 formed with an axial bore 38 similar to the bore 26 of the FIG. 2 embodiment. A drive shaft 39 is of a generally similar shape to the drive shaft 14 of FIG. 1 and is provided with an enlargement 40 and a step 41, a plastics material coating 42 ending at the step 41. The shaft 39 is provided with a right-hand screw thread 43, which is screwed into a corresponding thread in a bore 44, and is also provided with an extension having a left-hand screw thread 45 which extends on a portion of the shaft beyond the end of the rotor 37. As in FIG. 1, the coating extends beyond the enlargement and engages against a countersink where the bore 44 meets the bore 38. Screwed onto the thread 45 is a cap locknut 46 having a groove 47, in the one end face which accommodates a sealing O-ring 48, which bears against the end face of the rotor 37, to seal the drive shaft from external material.

A generally similar arrangement is shown in FIG. 4, and like parts have been given like reference numerals, with the addition of the letter B. In this embodiment, instead of having a cap locknut 46, the drive shaft 398 is itself formed with a threaded bore or recess 50 having a left-hand thread 51 formed therein into which engages the thread of a lock bolt 52, the head of which bears against the end of the rotor 378.

We claim:

1. A rotary helical gear pump comprising, in combination:

i. a stator formed with at least one helical gear;

ii. a rotor formed with at least one helical gear meshing with said stator gear or gears, the number of starts to said gear or gears of said stator differing by one from the number of starts of said gear or gears of said rotor;

iii. an axial bore formed in said rotor and having a circumscribing wall therearound;

iv. a key shaft having an axial bore formed therein and a circumscribing wall therearound;

v. a solid flexible unitary drive shaft having a rotor-driving end engaged in said bore of said rotor and a driven end and a sealing portion axially inward of said driving end and said driven end;

vi. a first enlargement to said drive shaft axially inward of said rotor driving end and a second enlargement to said drive shaft axially inward of said driven end;

vii. a nonpermeable and nonporous corrosion-fatigue-resistant layer coating said drive shaft, portions of said layer overlying said first and second enlargements, said portions of said layer engaging between said drive shaft enlargementsand said rotor and said key shaft to seal said drive shaft against contact with fluid to the exterior of the drive shaft; and

viii. cooperating thread means on said rotor and said drive shaft and on said key shaft and said drive shaft effective to urge said portions of said coating into contact with said rotor and said key shaft respectively.

2. A pump as specified in claim 1, wherein said layer is formed of chlorinated polyether, nitral rubber or an epoxy resin.

3. A pump as specified in claim 1, wherein said axial bore is threaded, said pump further comprising a countersink to said threaded bore, a threaded end to said drive shaft engaged in said threaded bore, one of said portions of said layer engaging between said enlargement and said countersink to seal the said drive shaft.

4. A pump as specified in claim 1, wherein said axial bore is threaded with a thread of one hand, said pump further comprising an enlarged bore in said rotor communicating with said threaded bore, said enlarged bore and said threaded bore together extending through the full length of the rotor, a countersink to said threaded bore at the junction thereof with said enlarged bore, a threaded end to said flexible drive shaft, with a thread of said one hand, engaged in said threaded bore, said drive shaft extending through and beyond said enlarged bore, one of said portions of said layer engaging between said en largements and said countersink to seal the said drive shaft.

5. A pump as specified in claim 4, further comprising a threaded extension beyond said threaded end, having a thread of the opposite hand to said one hand, and a locknut, lockingly engaged on said threaded extension.

Claims

1. A rotary helical gear pump comprising, in combination: i. a stator formed with at least one helical gear; ii. a rotor formed with at least one helical gear meshing with said stator gear or gears, the number of starts to said gear or gears of said stator differing by one from the number of starts of said gear or gears of said rotor; iii. an axial bore formed in said rotor and having a circumScribing wall therearound; iv. a key shaft having an axial bore formed therein and a circumscribing wall therearound; v. a solid flexible unitary drive shaft having a rotor-driving end engaged in said bore of said rotor and a driven end and a sealing portion axially inward of said driving end and said driven end; vi. a first enlargement to said drive shaft axially inward of said rotor driving end and a second enlargement to said drive shaft axially inward of said driven end; vii. a nonpermeable and nonporous corrosion-fatigue-resistant layer coating said drive shaft, portions of said layer overlying said first and second enlargements, said portions of said layer engaging between said drive shaft enlargements and said rotor and said key shaft to seal said drive shaft against contact with fluid to the exterior of the drive shaft; and viii. cooperating thread means on said rotor and said drive shaft and on said key shaft and said drive shaft effective to urge said portions of said coating into contact with said rotor and said key shaft respectively.

4. A pump as specified in claim 1, wherein said axial bore is threaded with a thread of one hand, said pump further comprising an enlarged bore in said rotor communicating with said threaded bore, said enlarged bore and said threaded bore together extending through the full length of the rotor, a countersink to said threaded bore at the junction thereof with said enlarged bore, a threaded end to said flexible drive shaft, with a thread of said one hand, engaged in said threaded bore, said drive shaft extending through and beyond said enlarged bore, one of said portions of said layer engaging between said enlargements and said countersink to seal the said drive shaft.