Flexible drive shaft and drive shaft and rotor assembly

Abstract: A flexible drive shaft for connection to the rotor of a progressive cavity pump or motor, in which the drive shaft 7, provided with a coating 26, is formed of titanium or similar metal. A relatively inexpensive metal flanged head portion is fastened, e.g. by adhesive, to an end portion 12, of the drive shaft, and is bolted to the rotor 10. The structure enables a relatively shorter drive shaft to be used which is capable of transmitting heavy torque.

Description: The present invention relates to a rotor and flexible drive shaft assembly for a progressive cavity pump or motor, and to a flexible drive shaft used in such an assembly. The invention is particularly concerned with a progressive cavity pump or motor having an outer member, usually a stator, which has a female helical gear formulation thereon having N starts and a rotor, rotatable within said stator, and having a male helical gear formation of a same pitch, but with N ± 1 starts. In former years, the rotor was driven by means of a drive shaft having a universal joint or pinned joint at each end. More recently, however, the rotor has been driven by a flexible drive shaft as taught, for example, in GB-A-1220848; GB-A-1285377; GB-A-1562277; GB-A-2244517; EP-A-399696 and EP-A-657649. EP-A-0155755 discloses a pump with a flexible drive shaft connected to the rotor via a separate, flanged head portion substantially in accordance with the preamble of claim 1. Such a drive arrangement has been very satisfactory. The various patents listed above indicate a number of different ways of connecting the flexible drive shaft to the rotor. Traditionally the drive shaft is formed of a steel, in particular a stainless steel, and is coated with a non-permeable and non-porous layer such as a plastics material thereby to prevent corrosion fatigue and thus greatly enhance the working life of the flexible drive shaft. Now one disadvantage of the use of a flexible drive shaft is that the length of the whole pump or motor is increased somewhat as compared with that using the conventional universal joint or pin connection. According to the present invention, there is provided a flexible drive shaft for connection to the rotor of a progressive cavity pump or motor, said drive shaft having an elongate body, an end portion of said body, at each end of the drive shaft, and a flanged head portion on one or each of said end portions, said head portion(s) being provided with means for securing the head portion to a progressive cavity pump or motor rotor and/or to the drive or driven member connected to the other end of the drive shaft; wherein the flanged head portions are formed as separate element(s) from the elongate body; characterised in that the elongate body is formed of titanium. Because the titanium metal is used, the length of the shaft can be significantly shortened. However, titanium, in particular, is very expensive and if the pump is relatively heavy duty, the torque required to turn the rotor is large. For this reason a flange on the end of the drive shaft is necessary to transmit the torque. However, if the drive shaft were made wholly of titanium and machined out of solid titanium stock, it would be prohibitively expensive to machine. According to the present invention, the flanged head portion is fastened to an end of portion of the drive shaft, this flanged head portion being made of separate elements, thereby reducing the amount of machining necessary. Preferably it is formed of a relatively inexpensive metal such as stainless steel. The fastening of the flanged head portion to the drive shaft can be effected in a number of different ways. In one preferred construction the fastening is achieved by use of an adhesive, such as that sold under the trade mark LOCTITE. Additionally or alternatively, a cross-pin may be provided to fasten the flanged head portion to the end portion of the drive shaft. Both of the end portions are of a larger diameter than the elongate body, thereby to provide a better fastening connection. Advantageously the or each flanged head portion is provided with a plurality of holes for the passage of securing bolts. According to another aspect of the present invention, there is provided a rotor and flexible drive shaft assembly for a progressive cavity pump or motor, comprising a rotor, a flexible drive shaft according to the invention, and a bolt passing through each of the holes and threadedly engaged in a bore in the rotor. Preferably a protective sleeve is provided to overlie the bolts thereby to prevent corrosion of these bolts. Advantageously, a radially inwardly extending flange is formed on the inner surface of said sleeve, said annular flange being provided with apertures for the passage of said bolts, and an annular cover is fitted over the drive shaft and engages and is retained against the sleeve, seals being provided between the sleeve and the rotor, between the sleeve and the cover and between the cover and the drive shaft. In order that the present 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:- Figure 1 is a schematic cross-section through a progressive cavity pump of the general type to which the present invention relates; Figure 2 is an enlarged cross-section showing the connection between the rotor and the flexible drive shaft; and Figure 3 is a view similar to Figure 2 of a modified embodiment. Referring first to Figure 1, a stator 1 is provided with a female helical gear formation 2, and is mounted in a barrel 3, connected to a pump housing 4, having an inlet 5. At the left hand of the stator is shown the pump outlet 6. A drive shaft is indicated by the general reference numeral 7, and is driven by an electric motor 8, the outward shaft of which passes through a seal assembly 9. The drive assembly 7, is connected to a rotor 10, having a male helical gear formation. The female helical gear formation has N starts, usually 2 starts, and the male helical gear formation has N ± 1 starts, usually 1 start. When driven by the motor 8, via the flexible drive shaft assembly 7, the rotor is caused to rotate and to orbit. This is a standard helical gear pump also known as a progressive cavity pump. If reference is now made to Figure 2, the helical drive shaft 7 is made of titanium and has a slightly enlarged end portion 12. Surrounding this end portion 12, is a head portion 13, having a radially outwardly extending flange 14, provided with a plurality of circumferentially spaced holes 15. Surrounding the head portion 13 is an annular cover 16, provided with an annular inwardly extending flange 17, which in turn is provided with an equal number of circumferentially spaced apertures 18. Bolts 19 are passed through the apertures 18, and holes 15, and are screwed into threaded bores 19A, in the rotor. An annular cover 20 is fitted over the end portion 12, of the drive shaft 7, and is retained in place by a circlip 21. Seals 22,23,24 are provided between the sleeve 16, and the rotor 10, between the sleeve 16, and the cover 20, and between the cover 20, and the end portion 12, of the drive shaft 7, respectively. In order to fasten the flanged head portion 13, to the enlarged end portion 12, adhesive, such as that sold under the trade mark LOCTITE, is shown at the location 25. It has been found that this adhesive is adequate to fasten the flanged head portion to the drive shaft and to enable it to withstand the necessary rotational forces in use. The drive shaft 7 is shown as being provided with a plastics material coating 26 which extends just into the enlarged end portion 12, and is engaged by the seal 24. Figure 3 illustrates a very similar construction and like parts have been indicated by like reference numerals. In the construction, however, a cross-pin 30 is provided to fasten the enlarged portion 12, to the flanged head portion 13. This pin may be provided alternatively, or additionally, to the adhesive. Either of the two structures of Figures 2 and 3 are robust and are capable of transmitting adequate torque to the rotor. Because titanium is used, the length of the flexible drive shaft is significantly reduced as compared with that of a conventional stainless steel drive shaft.

Claims: A flexible drive shaft (7) for connection to the rotor (10) of a progressive cavity pump or motor, said drive shaft having an elongate body (26), an end portion (12) of said body, at each end of the drive shaft, and a flanged head portion (13) on one or each of said end portions, said head portion(s) (13) being provided with means (15, 19) for securing the head portion to a progressive cavity pump or motor rotor and/or to the drive or driven member connected to the other end of the drive shaft; wherein the flanged head portions (12) are formed as separate element(s) from the elongate body; characterised in that the elongate body (26) is formed of titanium. A flexible drive shaft according to claim 1, wherein the flanged head portions (13) are formed of a different metal from the elongate body, such as stainless steel. A flexible drive shaft according to claim 1 or 2, wherein the or each flanged head portion (13) is fastened to the end portion (12) by adhesive (25). A flexible drive shaft according to claim 1, 2 or 3, wherein the or each flanged head portion (13) is fastened to the end portion (12) by means of a cross-pin (30). A flexible drive shaft according to any preceding claim, wherein the end portions (12) are of larger diameter than the elongate body (26). A flexible drive shaft according to any preceding claim, wherein the or each flanged head portion (13) is provided with a plurality of holes (15) for the passage of securing bolts (19). A flexible drive shaft according to any preceding claim, wherein the body (26) of the shaft is coated in a non-permeable, non-porous coating (26) and in that the end portions (12) of the body extend beyond the coating. A rotor and flexible drive shaft assembly for a progressive cavity pump or motor, comprising a rotor (10), a flexible drive shaft (7) according to claim 5, a bolt (19) passed through each of said holes (15) and threadedly engaged in a bore (19A) in said rotor. An assembly according to claim 8, further comprising a protection sleeve (16) overlying said bolts. An assembly according to claim 9, further comprising a radially inwardly extending annular flange (17) formed on the inner surface of said sleeve (16), said annular flange being provided with apertures (18) for the passage of said bolts (19); an annular cover (20) fitted over said drive shaft (7) and engaging and retained against said sleeve (17); and seals (22, 23, 24) provided between the sleeve and rotor, between the sleeve and cover, and between the cover and drive shaft.

Inventors: SILVER MICHAEL, SILVER, MICHAEL
Applicants: MONO PUMPS LTD, MONO PUMPS LIMITED
Application year: 1997
Main classification: F04C15
IPC codes: F16D1, H02K7, F04C2, F01C1, F04C15, F16C1