【正文】 d through the band brakes and clutches, which in turn are switched by hydraulic control to change speeds. The engine crankshaft supplies power to the transmission by rotating the housing of the fluid coupling. In Figure (a), the housing is connected to the ring gear of the first plaary geartrain. Therefore, at the input side of the transmission, the automobile engine directly drives the ring gear in the first plaary stage. On the other hand, at the output of the transmission, the driveshaft connects to the carriers on both the rear and reverse plaary stages. The main shaft rotates with the turbine in the fluid coupling, and at its other end, the shaft is connected to the sun gear in the rear plaary stage. Band Brakes and Reverse Lock Band brakes in the transmission wraparound drums in the front and rear plaary geartrains. Those brakes are applied or released by the two tensioners shown in Figure (a), which are activated by the hydraulic control system to effect a speed change. When either brake is applied, it locks the plaary geartrain ponent to which it is attached and prevents it from rotating. When the band brake in the front stage is applied, for instance, the sun gear is prevented from rotating. Similarly, when the second band brake is applied, the ring gear in the rear plaary stage, and the sun gear in the reverse stage, are both locked stationary. When the reverse lock is applied, the ring gear in the reverse plaary geartrain does not rotate． Clutches Like the band brakes and reverse lock, the two clutches in the HydraMatic transmission engage or disengage under hydraulic control to change speed settings. The clutches are interleaved disks and plates, and they are 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 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。 (2) the engine speed。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 v