【正文】 stic 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 drivetrain besides that shown in Figure , including frontwheeldrive, fourwheeldrive, and allwheeldrive systems. In some automobiles, the engine is mounted transversely or at the rear of the vehicle. Each configuration is well suited for a particular type of vehicle or niche in the consumer market (Figure ). Figure illustrates the layout of the engine, transmission, and driveshaft in a rearwheeldrive automobile. In the lowest transmission setting (which is called first gear), the engine crankshaft (the input to the transmission) rotates faster than the driveshaft (the transmission39。s output)． In fourth gear, the HydraMatic’s highest setting, the transmission has a velocity ratio of 1， and the engine and driveshaft rotate at the same speed. Together with those speed changes, automatic transmissions also modify the torque that is supplied by the engine to the driveshaft according to the ideal geartrain principle (VR) (TR)＝ 1， as discussed in Chapter 7. Of course, automobile transmissions also have a neutral setting, in which the engine is disconnected from the driveshaft, and a setting for reverse. Modern transmissions incorporate electronic and puter control， and although they are more sophisticated than the HydraMatic, they are similar in their basic operating principles． As depicted in Figure 8． 18， a fluid coupling serves as the clutch between the engine and the transmission. The HydraMatic transmission in Figure has four forward speeds, a neutral setting, and one reverse speed. The velocity ratio for each setting is determined by the operation of the three interconnected plaary geartrains, which are called the front, rear, and reverse stages． A hydraulic control unit, which is not shown in Figure 8． 18, performs the shifts between transmission settings. Each shift is acplished by engagi