Articulated universal joint with backlash reduction

A universal joint includes a joint housing and a joint shaft. The joint housing includes a socket having one or more recesses. The joint shaft includes a head positioned in the socket of the joint housing. The head includes one or more lobes corresponding with the recesses of the socket. The universal joint includes a drive key positioned between each lobe drive face and each recess drive face and an anti-backlash key positioned between each lobe back face and each recess back face.

TECHNICAL FIELD/FIELD OF THE DISCLOSURE

The present disclosure relates generally to power transmission mechanisms, and specifically to universal joints.

BACKGROUND OF THE DISCLOSURE

During a drilling operation, a drill bit may be rotated by rotation of the entire drilling string or by the use of a downhole motor. Typical downhole motors are positive displacement motors that include progressive cavity or Moineau pumps. Progressive cavity pumps traditionally include a stator and a multi-lobed eccentrically rotating rotor. Fluid flow through the stator causes eccentric rotation of the rotor. The eccentric rotation is typically transferred to a concentrically rotating drive shaft by a transmission assembly. In some instances, the transmission includes a transmission shaft coupled to the drive shaft and rotor by universal joints. Because downhole motors are used to rotate the drill bit in a single direction, the universal joints are typically designed to transfer rotational forces in one direction. However, during certain operations or operating conditions, the rotation of the drill bit and drive shaft may suddenly increase in speed relative to the transmission shaft, causing sudden rotational loading on the universal joint in the opposite direction. This change in speed may be caused, for example and without limitation, when the downhole motor is stopped and started, due to frictional effects such as stick-slip of the drill bit wherein the drill bit is periodically stopped due to frictional effects between the drill bit and the formation, or during other operations of the downhole motor. Backlash, defined as the looseness or play between adjacent moveable parts, within the universal joints may cause damage to the components of the universal joints as the components of the universal joints are loaded in the opposite direction to usual. In some cases, the backlash may allow components of the universal joints to suddenly contact each other, causing shock loading to the components.

SUMMARY

The present disclosure provides for a universal joint. The universal joint may include a joint housing. The joint housing may include a socket including a recess. The recess may include a recess drive face and a recess back face. The universal joint may include a joint shaft including a head. The head may be positioned in the socket. The head may include a lobe corresponding with the recess of the socket. The lobe may include a lobe drive face corresponding with the recess drive face and a lobe back face corresponding with the recess back face. The universal joint may include a drive key positioned between the lobe drive face and the recess drive face. The universal joint may include an anti-backlash key positioned between the lobe back face and the recess back face.

The present disclosure also provides for a downhole tool. The downhole tool may include a mud motor including a stator and a rotor. The downhole tool may include a drive shaft. The downhole tool may include a transmission shaft coupled to at least one of the rotor and the drive shaft by a universal joint. The universal joint may include a joint housing. The joint housing may include a socket including a recess. The recess may include a recess drive face and a recess back face. The joint housing may be mechanically coupled to the rotor or the drive shaft. The universal joint may include a joint shaft including a head. The head may be positioned in the socket. The head may include a lobe corresponding with the recess of the socket. The lobe may include a lobe drive face corresponding with the recess drive face and a lobe back face corresponding with the recess back face. The joint shaft may be mechanically coupled to the transmission shaft. The universal joint may include a drive key positioned between the lobe drive face and the recess drive face. The universal joint may include an anti-backlash key positioned between the lobe back face and the recess back face.

DETAILED DESCRIPTION

FIG. 1depicts a schematic cross section view of downhole tool15. In some embodiments, downhole tool15may be a bottomhole assembly (BHA) of a drill string. In some embodiments, downhole tool15may include bearing assembly20. Bearing assembly20may include one or more bearings22to couple bearing housing24to drive shaft25. Drive shaft25may be mechanically coupled to drill bit30. In some embodiments, drive shaft25and drill bit30may rotate relative to bearing housing24. In some embodiments, downhole tool15may include mud motor35. Mud motor35may be a positive displacement progressive cavity pump and may include stator40and rotor45. Rotor45may eccentrically rotate within stator40as drilling fluid is pumped through mud motor35. In some embodiments, rotor45may be mechanically coupled to drive shaft25by transmission shaft50. Transmission shaft50may transfer rotation from eccentrically rotating rotor45to concentrically rotating drive shaft25. In some embodiments, transmission shaft50may mechanically couple to rotor45, drive shaft25, or both by universal joint100. As used herein, a “universal joint” is a device that connects rigid members whose axes may be inclined to each other and for transferring rotary motion between the two rigid members. For the purposes of this disclosure, the term “universal joint” includes constant velocity joints. In some embodiments, as depicted inFIG. 2A, each end of transmission shaft50may be mechanically coupled to a respective universal joint100. In some embodiments, as depicted inFIG. 2B, transmission shaft50may be mechanically coupled to universal joint100at a first end and may include shaft coupler107at the other end. Shaft coupler107may allow transmission shaft50to directly couple to a shaft having a corresponding coupler such as rotor45or drive shaft25. In some embodiments, shaft coupler107may be, for example and without limitation, a male or female threaded coupler for coupling to rotor45or drive shaft25, splined coupling, welded connection, or any other suitable coupler.

In some embodiments, as depicted inFIGS. 2A-7, universal joint100may include joint housing101. Joint housing101may be generally cylindrical. Joint housing101may include coupler103formed at a first end of joint housing101and socket111formed at a second end of joint housing101. Joint housing101may include coupler103positioned to couple to an input or output shaft such as, for example and without limitation, drive shaft25or rotor45as shown inFIG. 1. In some embodiments, coupler103may be, for example and without limitation, a male or female threaded coupler allowing a shaft having a corresponding coupler such as drive shaft25or rotor45splined coupling, welded connection, or any other suitable coupler. Universal joint100may include joint shaft105.

In some embodiments, universal joint100may include joint shaft105. Joint shaft105may include head109positioned within socket111of joint housing101to mechanically couple joint shaft105to joint housing101. As further discussed below, head109may be positioned within one or more corresponding structures of socket111such that rotary motion is transferred between joint shaft105and joint housing101despite any angular misalignment between the axes of rotation of joint shaft105and joint housing101. In some embodiments, joint shaft105may be mechanically coupled to or formed as part of transmission shaft50as shown inFIG. 1. In an embodiment in which two universal joints100are used such as depicted inFIG. 2A, joint shaft105may include two heads109positioned within the socket111of the respective joint housings101.

In some embodiments, head109of joint shaft105may include one or more lobes113that extend radially outward from joint shaft105to engage one or more corresponding recesses115formed in socket111of joint housing101. Lobes113may, in some embodiments, act to transfer rotational force between joint shaft105and joint housing101. Each lobe113may include lobe drive face113athat engages with a recess drive face115aof each corresponding recess115of socket111when universal joint100is used to transfer rotational forces in the drive direction, denoted D inFIG. 4. In some embodiments, each lobe113may include lobe back face113band each recess115may include recess back face115b. Because universal joint100is used to rotate drill bit30in a single direction D, back faces113band115bare not used to transfer rotational forces during normal operation. However, during certain operations or operating conditions, rotation of drill bit30may change or suddenly increase in speed, causing back faces113band115bto be rotationally loaded, referred to herein as reverse loading of universal joint100. For example and without limitation, reverse loading between back faces113band115bmay occur when mud motor35is stopped and started, due to frictional effects such as stick-slip of drill bit30wherein drill bit30periodically stops due to frictional effects between drill bit30and the formation, or during other operation of downhole tool15.

In some embodiments, universal joint100may include one or more drive keys117and anti-backlash keys119. Drive keys117and anti-backlash keys119may be inserts positioned between each lobe113and each corresponding recess115and may, for example and without limitation, separate and provide bearing surfaces between lobes113and recesses115. In some embodiments, drive keys117may be positioned between lobe drive face113aof each lobe113and recess drive face115aof each corresponding recess115of socket111as depicted inFIGS. 4-6. In some embodiments, as depicted inFIG. 5, recess drive face115amay be shaped to receive drive key117. In some embodiments, for example and without limitation, drive key117may include curved portion117aadapted to fit into a corresponding surface of recess drive face115a. In some embodiments, curved portion117amay be substantially semicircular in cross section, allowing, for example and without limitation, drive key117to act as a Woodruff key. Such a drive key117may, for example and without limitation, self-align to engage with lobe drive face113aand recess drive face115a, and may therefore increase the surface area across which torque is transferred through universal joint100.

In some embodiments, one or more anti-backlash keys119may be positioned between lobe back face113bof each lobe113and recess back face115bof each corresponding recess115. Anti-backlash keys119may, for example and without limitation, take up otherwise open space between lobes113and recesses115and may therefore reduce or eliminate backlash. In such an embodiment, each lobe113is engaged to a corresponding recess115at both lobe drive face113aand lobe back face113bthrough drive keys117and anti-backlash keys119, respectively, regardless of the direction of loading of universal joint100. In some embodiments, anti-backlash keys119may impart a pre-loading force between lobe drive face113aof each lobe and recess drive face115aof each corresponding recess115of socket111. In some embodiments, as depicted inFIG. 6, recess back face115bmay be shaped to receive anti-backlash key119. In some embodiments, for example and without limitation, anti-backlash key119may include curved portion119aadapted to fit into a corresponding surface of recess back face115b. In some embodiments, curved portion119amay be substantially semicircular in cross section, allowing, for example and without limitation, anti-backlash key119to act as a Woodruff key. Such an anti-backlash key119may, for example and without limitation, self-align to engage with lobe back face113band recess back face115b, and may therefore increase the surface area across which torque is transferred through universal joint100in the case of reverse loading of universal joint100.

In some embodiments, drive keys117and anti-backlash keys119may be formed from a material that is less wear-resistant or more susceptible to damage than the material of joint housing101and joint shaft105. Wear caused by operation of universal joint100may thereby be more likely to occur to drive keys117and anti-backlash keys119than to lobes113and socket111, therefore reducing wear to lobes113and socket111. For example and without limitation, in some embodiments, drive keys117and anti-backlash keys119may be formed from a material that may have less material strength or less resilience; may have a lower yield strength, lower ultimate strength, or lower Young's modulus; or may be more ductile or malleable than lobes113and recess115, or a combination thereof. Because anti-backlash keys119take up the space between lobes113and recesses115, damage to universal joint100caused by reverse loading may be reduced due to the reduced backlash within universal joint100.

By reducing backlash, anti-backlash keys119may, for example and without limitation, reduce shock loading on joint housing101and joint shaft105caused by sudden reverse loading on universal joint100; may reduce wear to drive faces113a,115aby reducing radial movement between joint housing101and joint shaft105by maintaining more consistent alignment therebetween; may reduce operating temperature by reducing heat caused by repeated striking forces between drive faces113a,115aallowed by backlash; and may allow for smoother articulation of universal joint100due to more constant loading on drive faces113a,115a.