【正文】 used either to connect two rotating ponents or to disconnect them from one another. When the plates and disks are pressed against one another by a hydraulic piston (not shown in Figure ), the two sides of the clutch rotate at the same speed. If that pressure is instead removed, then no friction or contact between the disks and plates occurs, and the two sides rotate independently. When the clutch in the front plaary geartrain is engaged, the carrier (which is also connected to the hollow intermediate shaft) rotates at the same speed as the sun gear. Likewise, when the clutch in the rear plaary geartrain engages, the hollow intermediate shaft rotates together with the ring gear in the rear stage, and the sun gear in the reverse stage. Hydraulic Control System Functioning as a mechanical puter, the hydraulic control system engages and disengages the clutches, band brakes, and reverse lock at the right instants and in the proper binations to produce smooth shifts in the speed setting. The inputs to the hydraulic control system are（ 1） the position of the driver39。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 on select models of the 1940 Oldsmobile line, and it added less than $60 to the purchase price. The HydraMatic was advertised as offering the glorious new sensation of driving w ithout the need to operate a clutch pedal. As automobiles were being more monplace and as speeds were increasing, the automatic transmission was further viewed as a safety feature to the extent that the driver did not need to remove a hand from the steering wheel to shift gears. The HydraMatic transmission was a mercial success, and within ten years, over 1 million cars with that transmission had been manufactured. Although the HydraMatic was originally intended for passenger automobiles, heavierduty models were adapted during World War II for military armored and amphibious vehicles (Figure ). Automobile engines operate most efficiently over a limited range of engine speed, neither too low nor too high. The transmission is the means by which vehicle speed can be varied while the engine continues to run within its peak performance range. In the rearwheeldrive vehicle of Figure , the transmission is located directly behind the engine. The ridge or bump in the floorboard along the vehicle centerline acmodates the transmission and driveshaft. There are other configurations for a vehicle39。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