【正文】 vehicle. The team noted on its sketch that puter pact discs could be used as the wheels, but the vehicle might post a better race time with differentdiameter wheels. The team records these questions and discussion topics in their notebook, but they leave them 杠桿臂 for future consideration. At this early point in the brainstorming process, no decisions will be made on dimensions or materials. However, if this concept eventually emerges as a promising candidate, the team will need to resolve these issues before a viable prototype could be constructed. Second Concept: Compound Geartrain As their discussions continue, the team next devises the option shown in Figure is which a pound geartrain transfers power from the mousetrap to the drive axle. This vehicle has only three wheels, and“ portion of the body has been removed to further reduce weight. The concept incorporates a twostage geartrain, and its velocity ratio is set by the numbers of teeth on the four gears shown in Figure (b). The team39。s design is the method by which the syringes are inserted, held in the automated injection system, and then removed. Our case study in puteraided engineering involves the connection or interface between the disposable syringe itself and the mechanism that automatically depresses the piston. Mechanical engineers design the connection between the syringe and the injection system so that a medical technician can quickly remove an empty syringe and install a fresh one. In addition, the connection must be strong enough to securely lock the syringe into place and to neither leak nor break when it is subjected to high pressure during the injection. Engineers designed the syringe and its connection to the injection system through a sequence of steps that draw extensively on puteraided design tools: 1. Concept. Engineers first created a puterbased drawing of each ponent in the injection system. The crosssectional view of Figure (a) illustrates how the syringe interface, cylinder, and piston connect to one another and to the body of the automated injection machine. At the design concept stage, engineers fixed their ideas with an approximate representation of the product。s accelerator pedal (or engine throttle). The control system in the HydraMatic transmission operated entirely by hydraulic pressure, and it contained a plex assemblage of valves, oil passageways, and pistons. The valves moved in response to the inputs of speed and throttle in order to cause the transmission to shift to a new speed setting at the appropriate time. The HydraMatic39。s final design. However, before the mold itself was machined, engineers first used puteraided engineering tools to analyze and refine it. As shown in Figure , the injection molding process was simulated as molten plastic flowed, into and filled the hollow portions of the mold. In virtual puter simulations, engineers were able to adjust the locations of the injection points, air bleed points, and seams in the mold until the results showed that air bubbles would not bee＿ trapped in the mold and that the plastic would not cool and solidify before the mold became pletely filled (Figure ). If a simulation revealed such problems, the engineers would iterate and change the design of the mold, or the temperature and pressure of the plastic when it is injected until the performance was judged to be satisfactory. Once the design was pleted, prototype pieces of the mold were produced for smallscale production. Figure depicts a virtual simulation of one mold ponent as it is machined on a putercontrolled mill. 5. Design implementation. Finally, the mechanical engineers prepared detailed technical drawings for the syringe interface and the mold that would be used for its largescale production (Finn 8:14). Technical reports test data and puter analyses were piled and archived electronically in, order to fully document and record the design. In the future, the syringe interface might be modified for use in a new product, and the engineers working, on that project would need to review the present design process before they build upon it and develop the nextgeneration product. A noteworthy aspect of puteraided, engineering technology is the manner in which each analysis tool can be integrated with the others. For instance, once the threedimensional solid model of the syringe interface was generated, it was directly imported by the other software tools. Such patibility greatly simplifies iteration between the design, analysis and manufacturing stages of product development. This case study highlights what has bee known as seamless or paperless puteraided engineering: A product can be designed, analyzed, prototyped, and manufactured by bining virtual simulation and puter analysis tools throughout the design cycle. CASE STUDY IN MACHINE DESIGN: THE HYDRAMATIC TRANSMISSION Automobile automatic transmissions are an intricate blend of mechanical, electronic, puter, and hydraulic ponents that operate in concert to produce smooth speed shifts. In this case study, we describe the design of an automatic transmission as an example of a plex machine that is clever, practical, and encountered every day. There are many vehiclespecific types of automatic transmissions, so by way of an introduction in this section, we will discuss the HydraMatic transmission, which was the first fully automatic system developed for the consumer market (Figure ). Quite aside from the technical aspects, this particular mechanical engineering technology made a remarkable business contribution to the automotive industry. The HydraMatic transmission was developed by the General Motors Corporation, and it represented a key milestone in the history of the automobile. The transmission was offered