Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2000-03-07
2003-07-01
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S104000, C700S117000, C703S001000, C706S919000
Reexamination Certificate
active
06587741
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to computer-based methods and systems for designing products, and more particularly to a computer-based method and system for designing a spline coupling.
BACKGROUND OF THE INVENTION
Splined couplings are most generally used in three types of applications: for coupling shafts when relatively heavy torque is to be transmitted without slippage, such between turbines and fans of gas turbine engines; for transmitting power to slidably-mounted or permanently-fixed gears, pulley and other rotating members, such from turbines to gas turbine engine fans; and for attaching parts that may require disassembly and removal. A spline is any of a series of projections on a shaft that fit into slots on a corresponding shaft, enabling both to rotate together. An external spline includes several projections formed on the shaft, and an internal spline includes the projections formed on the corresponding shaft or a mating bore. A spline coupling consists of mated splines which permit the transmission of rotation or translatory motion along the axis of the shaft, and which may also prevent the shaft and bore from slipping longitudinally, as well as axially.
The design of mated splines involves many factors and is difficult and time consuming. Many factors must be taken into account, including the shape of the spline teeth. For instance, while splines may have straight-sided teeth, splines with teeth having an involute shape have greater torque-transmitting capacity. Other common spline coupling design factors include the number of teeth in the spline, the closeness of fit of the splines, and pressure angles of the teeth. To make the design of splines easier, involute splines may be designed using ANSI (American National Standards Institute) tables and S.A.E. (Society of Automotive Engineers) tables which are calculated using the above spline coupling design specifications. However, the above tables do not contain specifications for the design of all couplings needed between a shaft and a bore. For example, if more teeth are required in the spline than are listed in a table, or a tooth pressure angle is employed which is not specified in a table, then spline equations must be used to generate the appropriate spline coupling design.
Other design factors for a spline coupling include weight, material characteristics, and performance requirements, such as torque transmission. In the aeronautics field, among others, weight is an extremely important design consideration. The ANSI and S.A.E. tables do not take into account the weight or durability of materials which form splines and spline couplings. In addition, the spline coupling may be required to fit within a limited space, such as between components of a gas turbine engine, or be subject to other configuration limitations. Spline coupling designs, especially in the aeronautics field, cannot be limited to particular predefined table selections, but must be optimized to meet predetermined performance and configuration requirements.
A method and system for designing a spline coupling is needed which is not limited to ANSI or S.A.E. tables, minimizes weight, includes material characteristics, and satisfies performance requirements. The spline coupling design method and system should be able to be used with other design applications, such as designing a low pressure turbine shaft for a gas turbine engine.
It is known to design various products using a computer-aided design (“CAD”) system, a computer-aided manufacturing (“CAM”) system, and/or a computer-aided engineering (“CAE”) system. For sake of convenience, each of these similar types of systems is referred to hereinafter as a CAD system. A CAD system is a computer-based product design system implemented in software executing on a workstation. A CAD system allows the user to develop a product design or definition through development of a corresponding product model. The model is then typically used throughout the product development and manufacturing process. An example is the popular Unigraphics system commercially available from Unigraphics Solutions, Inc. (hereinafter “Unigraphics”).
In addition to CAD systems, there is another type of computer-based product design system which is known as a “Knowledge-Based Engineering” (“KBE”) system. A KBE system is a software tool that enables an organization to develop product model software, typically object-oriented, that can automate engineering definitions of products. The KBE system product model requires a set of engineering rules related to design and manufacturing, a thorough description of all relevant possible product configurations, and a product definition consisting of geometric and non-geometric specifications which unambiguously define a product. An example is the popular ICAD system commercially available from Knowledge Technologies, Inc. KBE systems are a complement to, rather than a replacement for, CAD systems.
An ICAD-developed program is object-oriented in the sense that the overall product model is decomposed into its constituent components or features whose specifications are individually defined. The ICAD-developed programs harness the knowledge base of an organization's resident experts in the form of design and manufacturing rules and best practices relating to the product to be designed. An ICAD product model software program facilitates rapid automated engineering product design, thereby allowing high quality products to get to market quicker.
The ICAD system allows the software engineer to develop product model software programs that create parametric, three-dimensional, geometric models of products to be manufactured. The software engineer utilizes a proprietary ICAD object-oriented programming language, which is based on the industry standard LISP language, to develop a product model software program that designs and manipulates desired geometric features of the product model. The product model software program enables the capturing of the engineering expertise of each product development discipline throughout the entire product design process. Included are not only the product geometry but also the product non-geometry, which includes product configuration, development processes, standard engineering methods and manufacturing rules. The resulting model configuration and specification data, which typically satisfy the model design requirements, comprise the output of the product model software program. This output, from which the actual product may be manufactured, comprises files which may consist of data representing geometric features of the product model and/or listings of data (e.g., dimensions, material, and tolerances) defining the various specifications and configuration features associated with each component or element of the product.
Also, the product model software program performs a “what if” analysis on the model by allowing the user to change model configuration and/or physical specification values and then assess the resulting product design. Other analyses may be run to assess various model features with regard to such functional characteristics as performance, durability and manufacturability. The analytical results, e.g. temperature and stress, are functional specifications that are evaluated in terms of boundaries or limits. Limits on both physical and functional specifications have been developed over time based on knowledge accumulated through past design, manufacturing, performance, and durability experience. Essentially, these specification limits comprise rules against which the proposed product model design is measured. Use of these historically developed specifications, analyses, and design procedures in this way is typically referred to as product “rule-based design” or “knowledge-based design”. The rules determine whether the resulting product design will satisfy the component design requirements, such as weight, and whether the design is manufacturable, given various modern manufacturing processes. The rules for a particular product desig
Chetta Gregory E.
Dickerson Donna R.
Marra John J.
Garland Steven R.
Picard Leo
United Technologies Corporation
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