WO2009093061A2

WO2009093061A2 - Downhole motor gearbox

Info

Publication number: WO2009093061A2
Application number: PCT/GB2009/050035
Authority: WO
Inventors: Philip Head
Original assignee: Artificial Lift Company Limited
Priority date: 2008-01-25
Filing date: 2009-01-19
Publication date: 2009-07-30
Also published as: WO2009093061A3; GB0801392D0

Abstract

A gearbox comprises an input shaft and an output shaft, the input shaft and the output shaft are linked by a plurality of gearing members. Each gearing member bears a male gear wheel having n outwardly projecting engaging means on the outer circumference and/or a female ring gear having n+1 or n+2 inwardly projecting engaging means on the inner circumference, and at least one gearing member bearing both a male gear wheel and a female ring gear on opposite sides. The gearing members are placed in series such that each male gear wheel engages with a female ring gear, at least one of the outwardly projecting engaging means of the male gear wheel interlocking with at least one of the inwardly projecting engaging means of the female ring gear. The gearing members are constrained in a housing such that a male gear wheel rotates about a first axis while the female ring gear that engages with the male gear wheel rotates about a second axis, the first and second axes being parallel but offset, and the first axis falling within the circumference of the female ring gear. The rotation of male gear wheel transferring motion to the female ring gear through the interlocking of the inwardly projecting engaging means of the male gear to the outwardly projecting engaging means of the female ring gear causes the female ring gear to rotate, (or vice versa). Each gearing member is constrained at its axis by a semilunar bearings placed between the gearing member and the inner surface of the housing. Ideally, n=2. The axes of rotation of each alternating gearbox elements alternates, and there are provided an odd number of gearing elements such that the axes or rotation of the input shaft and the output shaft are coincident.

Description

Downhole motor gearbox

This invention relates to gearboxes, that is, a device to change the speed and torque of a motor output especially but not exclusively in a downhole environment.

Many downhole applications that use a motor also require a gearbox to modify the speed or revolution and the torque of the motor's output, most usually to decrease the speed and increase the torque. This is often effected using an planetary gear system, as is well known in the art.

Planetary gear systems typically take up a relatively large diameter. Sometimes a well bore has a limited diameter, and it would be advantagous to provide a gearbox that change the power output of a motor which also has a relatively narrow diameter.

According to the present invention, there is provided a gearbox comprising an input shaft and an output shaft, the input shaft and the output shaft being linked by

a plurality of gearing members each bearing a male gear wheel having n outwardly projecting engaging means on the outer circumference and/or a female ring gear having n+1 or n+2 inwardly projecting engaging means on the inner circumference at least one gearing member bearing both a male gear wheel and a female ring gear

the gearing members being placing in series such that each male gear wheel engages with a female ring gear, at least one of the outwardly projecting engaging means of the male gear wheel interlocking with at least one of the inwardly projecting engaging means of the female ring gear

the gearing members being constrained in a housing such that a male gear wheel rotates about a first axis while the female ring gear that engages with the male gear wheel rotates about a second axis, the first and second axes being parallel but offset, and the first axis falling within the circumference of the female ring gear

the rotation of male gear wheel transferring motion to the female ring gear through the interlocking of the inwardly projecting engaging means of the male gear to the outwardly projecting engaging means of the female ring gear causing the female ring gear to rotate, or vice versa.

Figure 1 is a perspective view of the gearbox

Figure 2 is another perspective view of the gearbox

Figure 3 is another perspective view of the gearbox with the housing

Figures 4a to 4d are cross sectional views of the gearbox with the housing Referring to figure 1, a gearbox comprises seven gerotor elements 34, 35, 36,

37, 38, 39, 40 and seven eccentric bearing elements 24, 25, 26, 27, 28, 29, 30, and an end element 69.

The gerotor elements are arranged in series. Gerotor elements 35, 36, 37, 38, 39, 40 each feature an outer rotor shape 45, 46, 47, 48, 49, 50 on one face, best seen in figure 1. Gerotor elements 34, 35, 36, 37, 38, 39 each feature an inner rotor shape 55, 56, 57, 58, 59, 60 on one face, best seen in figure 2.

When assembled, each gerotor element 34, 35, 36, 37, 38, 39, 40 sits in a corresponding eccentric bearing elements 24, 25, 26, 27, 28, 29, 30, alternately arranged as shown. Referring to figure 3, the gerotor elements 34, 35, 36, 37,

38, 39, 40 and eccentric bearing elements 24, 25, 26, 27, 28, 29, 30 are arranged in a housing 10.

Each gerotor element engages with the neighbouring gerotor elements, so for example, the inner rotor surface 57 of gerotor element 37 engages with the outer rotor surface 48 of gerotor element 48, whilst the outer rotor surface 47 of gerotor element 37 engages with the inner rotor surface 56 of gerotor element 36. Of course the two end gerotor elements 34 and 40 only engage in this way with the gerotor elements 35 and 39 respectively. Gerotor 34 engages with an end element 68 having a bore 72, so that a power input shaft 69 extends through the bore 72 and is linked to the output of the motor. Similarly gerotor 40 has a power output shaft 71 that can be used to drive a downhole tool, such as a pump. Referring to Figures 4a to 4d, inner rotor shape 59 of gerotor element 39 (only the inner rotor shape here visible) engages with outer rotor shape 50 of gerotor element 40. The bore of the casing 10 is shaped to accept the gerotor elements and the eccentric elements. The inner surface of the casing 10 includes two axial grooves 91, 92 which accept lugs 84 to 90 included on the surface of each eccentric element 24 to 30 which constrains the eccentric elements.

The outer rotor element 50 comprises a three lobed shape recessed into the gerotor element 40, whilst the inner rotor element 59 comprises a two lobed shape raised from the gerotor element 39. Gerotor element 39 and its inner rotor element 59 are constrained to rotate about an axis xl, whilst gerotor element 40 and its outer rotor element 50 are constrained to rotate about an axis x2.

Referring to figure 4a, as gerotor element 39 is rotated, a lobe of inner rotor element 59 engages with a lobe of outer rotor element 50, causing gerotor element 40 also to rotate. Referring now to figure 4b, as gerotor element 39 continues to rotate, the other lobe of inner rotor element 59 engages with a second lobe of outer rotor element 50 causing gerotor element 40 to rotate further. Referring now to figure 4c, as gerotor element 39 continues to rotate, the lobe of inner rotor element 59 which had engaged with the outer rotor element 50 in figure 4a disengages, while the other lobe of inner rotor element 59 continues to engage with the outer rotor element 50 and continue the rotation of gerotor element 40. Figure 4d shows the lobe of inner rotor element 59 which had engaged with the outer rotor element 50 in figure 4a once again re-engage with the outer rotor element 50. The dots labelled a and b represent fixed points on the inner rotor element 59 which had engaged with the outer rotor element 50 respectively.

It will be seen that as each of the two lobes on the inner rotor element 59 sequentially engages with each of the three lobes of the outer rotor element 50 in turn, a complete revolution of gerotor element 39 causes two-thirds of a revolution of gerotor element 40. Each gerotor element in the assembly engages with its neighbouring gerotor elements in this way, gerotor elements 35, 37, 39 being aligned on and rotating about axis xl, while the alternate gerotor elements 34, 36, 38, 40 are aligned on and rotating about axis x2. Thus, for this embodiment having seven gerotor elements, the output of the gearbox will have a rotational speed (2/3 )⁶ or about 8.8% of the input speed, and the torque will correspondingly increase by a factor of (3/2 )⁶ or about 11.4.

It will be seen that both the number of gerotor elements, and the number of lobes on both the inner rotor elements and outer rotor element, may be varied to obtain different gearing factors, and that the gearbox may be set up in reverse to provide an increase in speed with a decrease in torque if desired. However, the use of an inner rotor element having two lobes and an outer rotor element having three lobes ensures that the two axes xl and x2 and kept fairly closely aligned, which in turn ensures that the diameter of the assembly can be kept relatively narrow. It will be seen that in the embodiment shown, with an odd number of gerotor elements, the axis of the input and output shafts are coincident, since the axes of rotation alternate with every gerotor element. Ideally then, the gearbox will also include an odd number of gerotor elements.

Claims

1. A gearbox comprising an input shaft and an output shaft, the input shaft and the output shaft being linked by

a plurality of gearing members each bearing a male gear wheel having n outwardly projecting engaging means on the outer circumference and/or a female ring gear having n+1 or n+2 inwardly projecting engaging means on the inner circumference at least one gearing member bearing both a male gear wheel and a female ring gear on opposite sides

2. A gearbox according to claim 1 wherein each gearing member is constrained at its axis by a semilunar bearings placed between the gearing member and the inner surface of the housing.

3. A gearbox according to either previous claim wherein n=2.

4. A gearbox according to any previous claim wherein the axes of rotation of each alternating gearbox elements alternates, and there are provided an odd number of gearing elements such that the axes or rotation of the input shaft and the output shaft are coincident.

5. A downhole motor assembly having a gearbox according to any previous claim.