Maximum life spiral bevel reduction design

Optimization is applied to the design of a spiral bevel gear reduction for maximum life at a given size. A modified feasible directions search algorithm permits a wide variety of inequality constraints and exact design requirements to be met with low sensitivity to initial values. Gear tooth bending strength and minimum contact ratio under load are included in the active constraints. The optimal design of the spiral bevel gear reduction includes the selection of bearing and shaft proportions in addition to gear mesh parameters. System life is maximized subject to a fixed back-cone distance of the spiral bevel gear set for a specified speed ratio, shaft angle, input torque, and power. Significant parameters in the design are: the spiral angle, the pressure angle, the numbers of teeth on the pinion and gear, and the location and size of the four support bearings. Interpolated polynomials expand the discrete bearing properties and proportions into continuous variables for gradient optimization. After finding the continuous optimum, a designer can analyze near optimal designs for comparison and selection. Design examples show the influence of the bearing lives on the gear parameters in the optimal configurations. For a fixed back-cone distance, optimal designs with larger shaft angles have larger service lives

Results of NASA/Army transmission research

Since 1970 the NASA Lewis Research Center and the U.S. Army Aviation Systems Command have shared an interest in advancing the technology for helicopter propulsion systems. In particular, that portion of the program that applies to the drive train and its various mechanical components are outlined. The major goals of the program were (and continue to be) to increase the life, reliability, and maintainability, reduce the weight, noise, and vibration, and maintain the relatively high mechanical efficiency of the gear train. Major historical milestones are reviewed, significant advances in technology for bearings, gears, and transmissions are discussed, and the outlook for the future is presented. The reference list is comprehensive

Bearing optimization for SSME HPOTP application

The space shuttle main engine (SSME) high-pressure oxygen turbopumps (HPOTP) have not experienced the service life required of them. To improve the life of the existing turbopump bearings, modifications to the bearings that could be retrofitted into the present bearing cavity are being investigated. Several bearing parameters were optimized using the computer program SHABERTH, which performs a thermomechanical simulation of a load support system. The computer analysis showed that improved bearing performance is feasible if low friction coefficients can be attained. Bearing geometries were optimized considering heat generation, equilibrium temperatures, and relative life. Two sets of curvatures were selected from the optimization: an inner-raceway curvature of 0.54, an outer-raceway curvature of 0.52, and an inner-raceway curvature of 0.55, an outer-raceway curvature of 0.53. A contact angle of 16 deg was also selected. Thermal gradients through the bearings were found to be lower with liquid lubrication than with solid film lubrication. As the coolant flowrate through the bearing increased, the ball temperature decreased but at a continuously decreasing rate. The optimum flowrate was approximately 4 kg/s. The analytical modeling used to determine these feasible modifications to improve bearing performance is described

Optimal design of tapered roller bearings for maximum rating life under combined loads

Using the relationships of the ISO 281 standard, this paper optimizes the internal dimensions of tapered roller bearings for maximum rating life. The bearing system addressed contains two identical bearings subjected to an arbitrary combination of centred radial and axial forces. It is shown that the basic rating life increases more than quadratically with the roller infill and the aspect ratio of the rollers, increases with the sixth power of the pitch diameter of the roller set and decreases with the third power of the applied radial force. Further, for any given ratio of axial to radial force, an optimal contact angle exists which maximizes the rating life of the bearing pair, irrespective of the actual bearing size and ratio of roller diameter to pitch diameter. The optimization procedure can either be used to design custom-made bearings or to select from manufacturers\u2019 catalogues the bearing with the best contact angle for any assigned loading condition

Identification and proposed control of helicopter transmission noise at the source

Helicopter cabin interiors require noise treatment which is expensive and adds weight. The gears inside the main power transmission are major sources of cabin noise. Work conducted by the NASA Lewis Research Center in measuring cabin interior noise and in relating the noise spectrum to the gear vibration of the Army OH-58 helicopter is described. Flight test data indicate that the planetary gear train is a major source of cabin noise and that other low frequency sources are present that could dominate the cabin noise. Companion vibration measurements were made in a transmission test stand, revealing that the single largest contributor to the transmission vibration was the spiral bevel gear mesh. The current understanding of the nature and causes of gear and transmission noise is discussed. It is believed that the kinematical errors of the gear mesh have a strong influence on that noise. The completed NASA/Army sponsored research that applies to transmission noise reduction is summarized. The continuing research program is also reviewed

Design and Manufacturing of a Mecanum Wheel for the Magnetic Climbing Robot

An AndyMark Mecanum Wheel has been re-designed for better performance and utilization by Helical Robotics. Mecanum Wheel is a complex Omni-Directional wheel that currently contains several drawbacks. The drawbacks include design, usage of hobby grade material, bumps in rollers, etc. A comprehensive design of the Mecanum wheel is being presented using Computer Aid Software, CAD and analysis tools, such as Finite Element Analysis, FEA. The different concepts were hand sketched using various parameters and then implemented in a CAD software-- CATIA. The Mecanum Wheel\u27s feasibility was thoroughly studied through ANSYS software. Load analysis was performed using various materials and several manufacturing processes carefully, to check the achievability of the wheel. In conclusion, the Mecanum wheel was successfully re-designed and manufactured to meet the requirements and specifications of Helical Robotics

Small Engine Component Technology (SECT) studies

A study was conducted to identify component technology requirements for small, expendable gas turbine engines that would result in substantial improvements in performance and cost by the year 2000. A subsonic, 2600 nautical mile (4815 km) strategic cruise missile mission was selected for study. A baseline (state-of-the-art) engine and missile configuration were defined to evaluate the advanced technology engines. Two advanced technology engines were configured and evaluated using advanced component efficiencies and ceramic composite materials; a 22:1 overall pressure ratio, 3.85 bypass ratio twin-spool turbofan; and an 8:1 overall pressure, 3.66 bypass ratio, single-spool recuperated turbofan with 0.85 recuperator effectiveness. Results of mission analysis indicated a reduction in fuel burn of 38 and 47 percent compared to the baseline engine when using the advanced turbofan and recuperated turbofan, respectively. While use of either advanced engine resulted in approximately a 25 percent reduction in missile size, the unit life cycle (LCC) cost reduction of 56 percent for the advanced turbofan relative to the baseline engine gave it a decisive advantage over the recuperated turbofan with 47 percent LCC reduction. An additional range improvement of 10 percent results when using a 56 percent loaded carbon slurry fuel with either engine. These results can be realized only if significant progress is attained in the fields of solid lubricated bearings, small aerodynamic component performance, composite ceramic materials and integration of slurry fuels. A technology plan outlining prospective programs in these fields is presented

Preliminary power train design for a state-of-the-art electric vehicle

Power train designs which can be implemented within the current state-of-the-art were identified by means of a review of existing electric vehicles and suitable off-the-shelf components. The affect of various motor/transmission combinations on vehicle range over the SAE J227a schedule D cycle was evaluated. The selected, state-of-the-art power train employs a dc series wound motor, SCR controller, variable speed transmission, regenerative braking, drum brakes and radial ply tires. Vehicle range over the SAE cycle can be extended by approximately 20% by the further development of separately excited, shunt wound DC motors and electrical controllers. Approaches which could improve overall power train efficiency, such as AC motor systems, are identified. However, future emphasis should remain on batteries, tires and lightweight structures if substantial range improvements are to be achieved

Mechanical Systems Technology Branch research summary, 1985 - 1992

A collection of significant accomplishments from the research of the Mechanical Systems Technology Branch at the NASA Lewis Research Center completed during the years 1985-1992 is included. The publication highlights and accomplishments made in bearing and gearing technology through in-house research, university grants, and industry contracted projects. The publication also includes a complete listing of branch publications for these years

Lightweight, affordable, low power solar groundwater piston pump for rural remote regions.

Solar photovoltaic powered groundwater pumping systems (SPWPS) are popular way of fetching water from boreholes in semi-arid areas in rural remote regions of most developing countries, where commercial water and electricity supply is out of reach. As the climate changes and the water table drops in such marginal regions, borehole depth is ever increasing into hundreds of metres below the ground surface. In a SPWPS, the required energy to fulfil water demand at a certain head is termed as the required hydraulic energy which is maintained by the pump unit of SPWPS. However, this acts ultimately as a load on the PV generator. The pump unit typically requires more power in order to maintain this hydraulic energy. For high head systems, groundwater piston pumps perform better than centrifugal pumps. A detailed literature review established that the current piston pumps have design limitations that act as load on the pump driver, which uses extra external and internal mechanical components. These include long piston drive rods, connecting rod, meshing gears, crossheads and crossways. This study put forth a new concept design of a groundwater piston pump optimised for power consumption using a scotch-yoke mechanism that excludes unnecessary components in the pump in order to conserve power usage. A mathematical model was built to support the claim of low power consumption by the new pump design. The widely-used computer aided design and finite element analysis (CAD/FEA) technique was used to ensure the structural viability of the concept design for high head application, which is based on material selection process. The study also compares the concept pump power consumption among existing photovoltaic (PV) operated pumps including piston rod and non-piston rod pumps. The developed mathematical model for power consumption finds significant power savings when compared with benchmarked low-power long-piston rod pumps. For example, with a 200 m head and 10.2 lpm flow demand, the proposed pump uses up to 22.4% and 7% less power than a pump that uses either a steel or glass fibre reinforced composite (GFRC - e.g. polyester) rod, respectively. Hydraulic efficiency calculations show an increase of up to 76.7% compared to 59.5% and 71.4% using steel and GFRC piston rods, respectively. Additionally, significant energy savings of 1505.7 Wh/day and 383.7 Wh/day are also found for daily pump operation compared to commercial steel and GFRC piston rods pumps, which consequently reduces the associated costs of PV panels. Design safety factors of the conceived pump for high head loads such as 200 m are evaluated using structural FEA. Material selection process based on performance indices is also carried out using the Cambridge Engineering Selector (CES Selector) program. The design of the proposed pump components was also optimised for mass, based on the fatigue life constraint of selected materials using a FE parametric approach coupled with material variation. The optimisation model developed in this study reduces the mass with optimum fatigue safety factors contrary to yield strength criteria, incorporating performance factors such as material cost and energy consumption. Stainless steel 'BioDur 108' was found overall to be the best contender, with optimised dimensions saving up to 29.39% of mass and material cost, along with 29.25% reduction in power consumption. In conclusion, the developed design for a groundwater piston pump in this study is optimised for low power consumption, along with structural suitability for SPWPS with high head requirements in rural remote areas. The pump design's structural adequacy is checked by FEA, material selection and design optimisation. The pump is also suitable for other locations depending on its structural ability to withstand loads with suitable materials