Scalable Software for Gearbox and Driveline Engineering

May 20, 2010
RomaxDesigner provides a suite of tools for mechanical analysis of rotating structural components such as gears, shafts, bearings, clutches and synchronizers, spline connections and housings

Jonathan Adler
Engineer – Specialist in product design and systems analysis
McLaren Performance Technologies Inc.
Livonia, Mich.

Edited by:
Leslie Gordon,
[email protected]

RomaxDesigner provides a suite of tools for mechanical analysis of rotating structural components such as gears, shafts, bearings, clutches and synchronizers, and spline connections and housings. Engineers designing gearboxes, transmissions, vehicle drivelines at a system level, as well as providers of components, will find value in the consolidated analysis approach this software provides. The unified approach is especially valuable when there are multiple nonlinear interactions contributing to load, component stress, and misalignment. When components are operating near to their limits, the increased accuracy provided by the detailed analysis modules lets users maintain adequate safety factors while avoiding defensive overdesigns.

RomaxDesigner is modular software, with a base package allowing system-level design and analysis, and with modules that allow the detailed analysis of individual components. The base software can analyze systems on parallel axes, with extensions available to analyze perpendicular shafts and planetary systems. Even in the base package, users can build and analyze complex systems, including nonlinear and 3D effects.

Users define each system component with a level of complexity appropriate to the needed analysis. Base modules let users define each component using an industry-standard closed-form equation. With more-advanced modules, individual components can be converted to models with finite-element attributes. For example, a housing can be defined according to its stiffness, (using a reduced-stiffness matrix from a finite-element model) or as a finite-element model solved in an advanced module. Users can define a bearing simply as a rotatable support with specified flexibility; a catalog-level design with ISO capacities and macrogeometry; or with full microgeometry, life adjustment factors, and high-speed inertial effects. As the model develops, users can add further detail to each component.

The software then simulates the effect of a duty cycle or series of loads on the entire system, with multiple conditions of speed, load, and temperature defined, allowing simultaneous cumulative damage analysis of all components. Users can define and apply multiple duty cycles, reflecting different applications.

RomaxDesigner models shafts for deflection and stress using closed-form equations for beam segments. Advanced modules provide the capability to use FE models for more-complex shaft geometry. Users can choose from predefined materials and stress concentration factors, or develop their own. The base package can model parallel and concentric shafts. Perpendicular shafts and moving axis (planetary) shafts are modeled with extended modules. An additional module analyzes shaft fatigue. The software can define and analyze shafts that are connected at non-90° angles, though the gear definitions for these systems are limited.

The base package provides standard bearing-life and load-capacity analysis using ISO 281:1990 or ISO 291:2007. The program also includes a modified rating with a closed-form calculation of effects of misalignment. A built-in database includes data from four bearing manufacturers’ catalogs. Users can define and save additional bearings. A bearing search tool allows quick access to all four catalogs and user-defined bearings.

Bearing models provide nonlinear stiffness interactions with adjacent components, which can be critical when calculating gear-support stiffness, gear-mesh misalignments and preload requirements. When calculating bearing life, the models include the effects of misalignments developed through the flexibility of any coupled components. A bearing preload tool automates studies of bearing life as a function of preload. RomaxDesigner does not currently include the effects of localized housing distortion on bearing roundness, nor a direct way to calculate the effects of thermal expansion on bearing fit and preload. These features have been proposed for a future release.

Advanced bearing-analysis modules provide detailed analyses (ISO 281 Supplement 4), including contact stress, fluid-film thickness, and stress-based life calculation. Advanced bearings can be defined with an assortment of predefined roller and raceway crowns, or with a measured crown.

RomaxDesigner models may include spur and helical gears, and with the perpendicular-axis module, bevel and hypoid gears. The base software models gears with enough detail to analyze their effects on the rest of the system. Additional modules allow design and rating to AGMA, DIN and ISO standards. For parallel-axis gears, additional modules permit macrogeometry definition and optimization for manufacturability as well as detailed analysis of microgeometry for contact stress and transmission error. RomaxDesigner graphics are suitable for a variety of reporting illustrations, such as system topology and component deflection.

For parallel and perpendicular-axis gears, modules provide interfaces to more detailed analysis software, such as Simpack, LDP, and AnSol. They act as a “front end” for even more-computationally intensive formulations of bending and contact stress. The combination of these software packages is particularly powerful, as it permits cumulative damage-life analysis including the nonlinear effects of gear-tooth deflection and bearing stiffness, acting on a fully developed tooth profile. Additional modules focus on NVH and dynamic characteristics, such as gear rattle and whine, system modal analysis, and clutch analysis. Modules are also available to automate optimization and for the sensitivity analysis of system and component designs.

The developer does not include self-directed tutorials with the software, but the company does provide user training directly. The trainers customize course content and duration to meet the needs of each organization. A one-week training session would be sufficient to cover the basic modules and a few advanced topics. Many highly specialized software packages require constant use to become and stay proficient. I find that RomaxDesigner does not require this level of attention. Engineers with other responsibilities will find this software functional even if not used on a regular basis.

The software comes from Romax Technology, based in Nottingham, U.K., with offices in Asia, Europe, and North America (

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