Patent Application
20070004235
1. Field of the Invention
The present invention relates to methods and system of limiting arcing of rotating members.
2. Background Art
In engines and other devices having rotating elements, electrical potentials can develop between the rotating element and a bearing or other housing used to facilitate the rotation thereof. For example, a bearing is commonly used with an engine crankshaft to facilitate the rotation of the crankshaft. If a sufficient difference in electrical potential develops between the bearing and the crankshaft, current may arc across a gap between the two features, which may negatively influence the crankshaft and/or bearing.
One non-limiting aspect of the present invention relates to a system of regulating an electrical potential of an element rotating within a housing so as to limit arcing. The system may include an electrically conducting device in electrical communication with the element. The device may include a rotating portion coupled to the element and a non-rotating portion coupled to the rotating portion and in electrical communication with the housing. An electrical potential of the element may be coupled with the housing by way of a current path provided through the conducting device between the element and the housing. The current coupling may be used to limit differences in electrical potential between the element and housing and thereby arcing.
In accordance with one non-limiting aspect of the present invention, the non-rotating portion may include at least one electrically conducting brush for electrically communicating with the rotating portion. Optionally, the brush may be biased against the rotating portion.
In accordance with one non-limiting aspect of the present invention, the system may further include an electric machine connected to one end of the element whereby an electrical potential imparted to the element from the electrical machine is coupled to the housing by way of the device to limit arcing.
One non-limiting aspect of the present invention relates to an engine having an engine block, a crankshaft, and at least one oil-film bearing for facilitating rotation of the crankshaft within the engine block. The engine may include an electrical coupling device in electrical communication with the crankshaft and engine block. An electrical potential of the crankshaft may be coupled with the engine block by way of a current path provided through the coupling device between the element and the housing such that the current coupling limits differences in electrical potential between the crankshaft and engine block and thereby preventing arcing.
One non-limiting aspect of the present invention relates to an engine-generator system for use with heavy-haul trucks. The engine-generator system may include a engine having an crankshaft connected at one end thereof to a generator. The generator may be configured to provide electric energy for use in driving a heavy-haul truck as a function of cranking provided by the crankshaft. The system may further include a coupling device in communication with the crankshaft for limiting a difference in electrical potential between the crankshaft and bearings used to support the crankshaft within the engine. Optionally, at least a portion of the electrical potential difference between the crankshaft and bearing is due to energy imparted to the crankshaft by the generator.
One non-limiting aspect of the present invention relates to a method of limiting arcing of an element rotating within a housing. The method may include affixing an electrically conducting member to the rotating element; affixing an electrically conducting member to the housing; and electrically coupling the electrically conducting members together to provide a current path between the rotating member and the housing, the current path coupling the electrical potential of the housing with the electrical potential of the rotating member to limit arcing therebetween. Optionally, the method may further include configuring the electrically conducting members to maintain electrical connections during lateral motion of the rotating member.
The above features and advantages, along with other features and advantages of the present invention, are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings.
A pulley 32 and generator or other electric machine 34 may be connected to opposite ends of the crankshaft 16. The pulley 32 may be configured to drive a fan or other system features as a function of cranking provided by the crankshaft 16. The generator 34 may be configured to generate electrical power as a function of cranking provided by the crankshaft 16.
The bearings 20-26 may be roller bearings, oil film bearings, or other bearings suitable for facilitating rotation of the crankshaft 16 within the engine block 14. The bearings 20-26 may include a lubricant to facilitate rotation of the crankshaft 16, oil in the case of an oil film bearing or grease or other lubricant in the case of a roller bearing, as one having ordinary skill in the art will appreciate.
The system 10 shown in
Arcing, as one skilled in the art will appreciate, occurs when an electrical potential difference between two elements becomes such that electrons arc across a gap therebetween. With respect to metallic objects, such as the engine block 14 or bearings 20-26 and crankshaft 16, arcing may negatively influence the operation thereof. For example, arcing may cause pitting, electroplating like deposits, and other damage or wear on the features. This can negatively influence the operation and performance of the system.
The system 10 may include an electrically conducting unit 40 for electrically coupling the crankshaft 16 with the engine block 14. The coupling device 40 may comprise any suitable electrically conducting material. It may provide a current path or other electrical connection between the crankshaft 16 and the engine block 14, or other element other that the engine block 14 which is sufficient to ameliorate a difference in electrical potential between the crankshaft 16, bearings 20-26, and/or engine block 14. Ameliorating differences in electrical potential in this manner may be sufficient to minimize the likelihood of arcing, i.e., by limiting significant differences in electrical potential to levels below those associated with arcing.
The non-rotating portion 46 may include features for mounting to the engine block 14 and the rotating portion may include features for mounting to the crankshaft 16. The rotating and non-rotating portions may include an electrical connection therebetween to establish a current path between the engine block 14 and crankshaft 16. This connection may be used to couple or otherwise balance the electrical potential associated therewith.
The flange 50 may include features for mounting the rotating portion to one axial end of the crankshaft 16, preferably in a location that does obstruct other functions of the engine drive system, such as nested within the optional accessory drive pulley 32 used to drive a cooling fan. The bearing housing 52 may extend outwardly from the flange 50 to define an area for receiving the shaft 60. The dust shield 58 and retaining sleeve 70 may compress or otherwise secure to the flange 50 for retaining the shaft 60 within the bearing housing 52. The clip 58 may be configured to permit rotation of the shaft 60 within the roller bearing 56.
The brush 72 may be a carbon-graphite brush or other brush having characteristics suitable for conducting electricity. A spring or other biasing member 68 may be included within a cavity of the shaft 60 to bias the brush against the plate 54. When contacting the plate 54, a current path is provided by the brush 66 between the rotating and non-rotating portions 42-44.
As one skilled in the art will appreciate, the crankshaft 16 may move laterally within the engine block 14 causing a deflection of roller bearing 56. A gap may be included between the shaft 60 and plate 54 to permit such lateral movement. The brush 66, cavity, and spring 68 may be selected and dimensioned to correspond with expected lateral movement of the crankshaft 16 so that the brush 66 may remain in contact with the plate 54 during such lateral motion.
In addition to lateral motion of the crankshaft 16, radial “wobble” caused by deflections of the crankshaft 16, whether induced by the force of the piston connecting rods (not shown) or by tension forces from the fan drive belt, may be further compensated for with flexibility provided by the elongated portion 66 of the of the coupling device 40. Compensating for motion with the elongated portion 66 and limiting movement requirements of the brushes 66 may be more beneficial for maximizing longevity of the brushes 72.
One non-limiting aspect of the present invention, as generally described above, relates to limiting electrical potentials between the crankshaft 16 and engine block 14 and/or bearings 20-26, or other features within the system 10 that may lead to arcing and other problems stemming for significant differences in electrical potential. For example, electrical potentials of 0.6 volts may cause current to flow that results in surface damage to the crankshaft bearings 20-26 with thin oil film clearances between the crankshaft 16 and bearings 20-26. The coupling device 40 of the present invention may be used to limit such electrical potentials.
Induced axial, electrical bias potentials equal to or greater than 0.3 volts from tail shaft to engine flywheel connection end of generator shafts may occur as a result of imperfections in the magnetic induction components of generators. In electrical propulsion installations, such as in electric drive haul trucks, a generator tail shaft may be attached a hydraulic pump, which effectively grounds the tail shaft of the generator, completing the circuit, and thereby, endangering the crankshaft bearings. The coupling device 40 of the present invention may be used in such environments to protect from the possibility of such bearing damage in engine-to-generator connections, and thereby, eliminate the need to engineer a non-conductive engine-to-generator drive coupling system.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
