Patent Application
20130068057
This invention generally relates to an idler gear assembly for a generator and, more particularly, to a two-piece idler gear assembly for handling the expected stresses within the gear train of a generator oil supply pump.
Systems that include electrical generators can include a hydraulic pump for cooling the generator or other components of the system. The pump can be driven by the rotor of the generator though a gear train. Misalignment of the gears within the gear train relative to the shaft, bearings, or other components, may increase wear on the gears and contribute to a reduction in gear durability. For instance, axial misalignment of the gears may cause uneven wear of the gear teeth and eventually necessitate replacement. Pressure pulsations from the pump may also contribute to premature wear of the gears. Often, it is a combination of both axial misalignment and pressure pulsation conditions that contribute to premature wear of the gears.
According to one aspect of the invention, an idler gear assembly for a generator includes a first gear and a second gear. The first gear includes a first shaft aligned along a first shaft axis from a first end to a diametrically opposed second end. The first shaft has a first shoulder with a first axial face and a second shoulder with a second axial face diametrically opposed from the first axial face, diametrically opposed first and second grooves about a circumference of the first shoulder and a first set of teeth circumferentially located about the first shaft axis. Also, the first shaft includes a first axial distance from the first axial face to the second axial face. The second gear includes a second shaft aligned along a second shaft axis, the second shaft having a diametrically opposed first and second tangs, and a second set of teeth circumferentially located about the second shaft axis. Also, the second shaft includes a second axial distance from a third end to a diametrically opposed fourth end. The first gear is configured for coupling to the second gear such that the first axial distance and the second axial distance cooperate to locate the first and second gears between diametrically opposed journal bearings, while each of the first shaft axis and the second shaft axis are configured for being aligned along the axis of rotation. Also, the first and second groves are configured for coupling to the first and second tangs.
According to another aspect of the invention, a shaft gear for a generator includes a shaft aligned along a shaft axis from a first end to a diametrically opposed second end, the shaft having a first shoulder with first axial face and a second shoulder with a second axial face diametrically opposed from the first axial face, diametrically opposed first and second grooves about a circumference of the first shoulder and a set of teeth circumferentially located about the shaft axis. The shaft includes an axial distance from the first axial face to the second axial face. The shaft has a first bearing surface defined by the first axial face and the first end of the shaft, with the shaft being configured for rotation about the shaft axis.
According to yet another aspect of the invention, a spur gear for a generator includes a shaft aligned along a shaft axis from a first end to a diametrically opposed second end, the shaft having diametrically opposed first and second tangs at the first end and an axial distance from the first end to the second end. The spur gear also includes a circular portion having opposed top and bottom surfaces, the circular portion being aligned along an axis that passes through a geometric center of the top and bottom surfaces, while the circular portion is coupled to the shaft at the geometric center. Also, the shaft is configured for rotation about the shaft axis, while the circular portion includes a set of teeth circumferentially located at a perimeter of the circular portion.
Other aspects, features, and techniques of the invention will become more apparent from the following description taken in conjunction with the drawings.
Referring now to the drawings wherein like elements are numbered alike in the FIGURES:
Embodiments of an idler gear assembly include a first gear coupled to a second gear in a gear train of a generator. The first gear includes a first shaft that includes a first dimension for being received within a complementary bore of the second gear. The complementary bore has a second dimension for causing an interference lock between the first gear and the second gear. Additionally, drive tangs on a second shaft of the second gear are configured to be received within complementary apertures or grooves on a shoulder of the first shaft for reinforcing the connection between the first gear and the second gear and preventing the first gear from slipping out of frictional contact with the second gear and preventing rotation of the second gear relative to the first gear.
Referring to the drawings,
In one embodiment, the gear assembly 105 is configured as a two-piece gear assembly including a first gear 175 (also referred to as a “shaft gear”) coupled to a second gear 180 (also referred to as a “spur gear”). The first gear 175 includes a first set of gear teeth 185 that intermesh with teeth of the pump gear 155 and the second gear 180 includes a second set of gear teeth 190 that intermesh with teeth of the rotor gear 150. The gear teeth 185 and 190 may be involute gear teeth in one embodiment. The first gear 175 and the second gear 180 are coupled together for rotation about a central axis 195. Also, the gear assembly 105 is part of the gear train 145 for driving the hydraulic pump 115 via the dynamoelectric portion 110. In one embodiment, the gear train 145 is a gear reduction train to drive the hydraulic pump 115 at a relatively slower speed than the dynamoelectric portion 110. However, the gear train 145 may be modified in other embodiments. In one embodiment, the gear train 145 includes the rotor gear 150 mounted on the rotor shaft 120, a pump gear 155 mounted on a pump shaft 160 of the hydraulic pump 115, and the idler gear assembly 105 mounted for rotation on journal bearings 165 and 170. In one embodiment, the journal bearings 165 and 170 are constructed from a carbon material impregnated with copper. In an example, the dimensions of the journal bearings 165 and 170 may vary from part to part through normal manufacturing processes, design tolerances, or both such that there is possible position variation of the gear assembly 105 riding in the journal bearings 165 and 170, depending on the particular dimensions of the journal bearings 165 and 170. However, as will be described below in
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Each involute surface 405 may terminate on a radially outer end at the tip 410 and at a radially inner end at a point 425 near the base 415. In one example, the point 430 may represent the point at which the involute surface 405 inflects to form a valley between adjacent teeth 400.
In the profile shown, the involute surface 405 includes at least reference points A-D thereon, with reference point A near the base 415, reference point D near the tip 410, reference point B between reference points A and D, and reference point C being between reference points B and D. In embodiments, reference point A may essentially be at the point 430 of the terminal end of the involute surface 405 and reference point D may essentially be at the radially outer terminal end of the involute surface 405. In some examples, the locations of reference points B and C may be a function of a distance between reference points A and D. In one example, reference point B is located 20% of the distance (from reference point A), and reference point C is located 80% of the distance (from reference point A).
Each of the reference points A-D includes an associated roll angle, εA-εD, between a corresponding first line 435A-D and a second line 440 that is tangent at the point 430 to a reference base circle 445 having a center origin at the center axis 425. In one example, the roll angles εA-εD are subtended by a portion of the surface 405. The locations of the reference points A-D and the magnitudes of the roll angles εA-εD may be determined using a known surface checking machine.
The following examples assume that reference point A is at the point 430 of the terminal end of the involute surface 405, reference point D is at the radially outer terminal end of the involute surface 405, reference point B is located 20% of the distance (from reference point A), and reference point C is located 80% of the distance (from reference point A). In one example, the roll angles εA-εD of the first gear 175 are different than the roll angles εA-D of the second gear 180. That is, the first gear 175 tooth profile is tailored to accommodate the specific loads expected on the first gear 175 and the second gear 180 tooth profile is tailored to accommodate the specific loads expected on the second gear 180, which may be different from the loads on the first gear 175.
In the illustrated example, the gear assembly 105 includes ratios of the roll angles εA-εD for the teeth 185 of the first gear 175 to the roll angles εA-εD of the teeth 190 of the second gear 180. In one example, a first ratio of the roll angle εA of the first set of gear teeth 185 to the roll angle εA of the second set of gear teeth 190 may be 0.08-0.24, a second ratio of the roll angle εB of the first set of gear teeth 185 to the roll angle εB of the second set of gear teeth 190 may be 0.4-0.58, a third ratio of the roll angle εC of the first set of gear teeth 185 to the roll angle εC of the second set of gear teeth 190 may be 1.09-1.29, and a fourth ratio of the roll angle εD of the first set of gear teeth 185 to the roll angle εD of the second set of gear teeth 185 may be 1.26-1.46. In a further example, the first ratio may be 0.12-0.2, the second ratio may be 0.44-0.54, the third ratio may be 1.14-1.24, and the fourth ratio may be 1.31-1.41. In a further example, the first ratio may be 0.16, the second ratio may be 0.49, the third ratio may be 1.19, and the fourth ratio may be 1.36.
The above ratios may be achieved using the following exemplary roll angles εA-εD. For example, the roll angle εA is 1.51 degrees-3.51 degrees, the roll angle εB is 7.64 degrees-9.64 degrees, the roll angle εC is 26.03 degrees-28.03 degrees, and the roll angle εD is 32.16 degrees-34.16 degrees For the first gear 175, which is diametrically smaller than the second gear 180. For the diametrically larger second gear 180, the roll angle εA is 15.02 degrees-17.02 degrees, the roll angle εB is 16.7 degrees-18.7 degrees, the roll angle εC is 21.73 degrees-23.73 degrees, and the roll angle εD is 23.41 degrees-25.41 degrees.
Utilizing roll angles εA-εD within the given ranges for the first gear 175 and the second gear 180 provides a profile of the involute surface 405 that accommodates the expected specific loads on the gear assembly 105 for the expected rotational speeds of the generator 100. Particularly, the radian measures of the given roll angles εA-εD are the tangents of the pressure angles at the points on the involute surface 405 and are designed through the given roll angles εA-εD to accommodate a particular stress state on the teeth 400.
In a further example, the roll angle εA is 2.01 degrees-3.01 degrees, the roll angle εB is 8.14 degrees-9.14 degrees, the roll angle εC is 26.53 degrees-27.53 degrees, and the roll angle εD is 32.66 degrees-33.66 degrees for the first gear 175. In a further example, the roll angle εA is 2.51 degrees, the roll angle εB is 8.64 degrees, the roll angle εC is 27.03 degrees, and the roll angle εD is 33.16 degrees for the first gear 175.
In a further example for the second gear 180, the roll angle εA is 15.52 degrees-16.52 degrees, the roll angle εB is 17.2 degrees-18.2 degrees, the roll angle εC is 22.23 degrees-23.23 degrees, and the roll angle εD is 23.91 degrees-24.91 degrees. In a further example, the roll angle εA is 16.02 degrees, the roll angle εB is 17.7 degrees, the roll angle εC is 22.73 degrees, and the roll angle εD is 24.41 degrees for the second gear 180. In some examples, the exemplary gear assembly 105 may be used in combination with the rotor gear disclosed in U.S. Patent Application Publication No. 2010/0283343 entitled ROTOR GEAR FOR GENERATOR and the pump gear disclosed in U.S. Patent Application Publication No. 2010/0284835 entitled PUMP GEAR AND PUMP ASSEMBLY FOR A GENERATOR, which are incorporated by reference in their entirety. The gear assembly 105 may also include features of the idler gear disclosed in U.S. Pat. No. 7,926,381 entitled IDLER GEAR AND JOURNAL BEARING ASSEMBLY FOR A GENERATOR, which are incorporated by reference in their entirety.
The gear assembly 105 may be formed with the desired roll angles in a known gear manufacturing process. For instance, the process may include casting, forging, powder metallurgy, and/or machining from a blank. Thus, the process for forming the gear assembly 105 is not limited to any particular type as long as the selected process is capable of establishing the roll angles to be within the given example ranges. The gear assembly 105 may be incorporated into the generator 100 as part of a method of installing the gear train 145. For example, the gear assembly 105 may be a replacement to a prior gear set in the generator 100 that is an original component or a worn component that is to be replaced. In this case, the generator 100 may be at least partially disassembled in a known manner, and the gear assembly 105 may then be inserted into the generator 100 in place of the prior gear assembly.
The technical effects and benefits of embodiments include an idler gear assembly that includes a first gear coupled to a second gear in a gear train of a generator. The first gear includes a first shaft that is provided to receive a complementary bore of the second gear and cause an interference lock between the first gear and the second gear.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations, alterations, substitutions, or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while various embodiment of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
