【正文】 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 top ten achievements (Section ), designers must grapple with peting constraints and specifications. Third Concept: SectorShaped Gear 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 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 engaging or disengaging the two band brakes, the two clutches, or the reverse lock. The entire transmission prises a fluid coupling, three plaary geartrains, two clutches, two band brakes, a reverse lock, and a hydraulic control system. Those ponents operate as follows. Fluid Coupling This ponent transfers power from the engine to the transmission without a rigid mechanical connection, a feature that is advantageous for two reasons. First, when the brakes are applied and the transmission is placed in gear, the engine can continue to .operate at its idle speed even though the wheels do not rotate. Second, when there is a sudden speed change, the fluid coupling acts as a buffer to isolate other ponents in the drivetrain from shock. You can view the fluid coupling as being analogous to two household fans that face one another. Imagine that one fan (which we call the pump) is powered up to speed and blows air directly at the (otherwise unpowered) second fan (which we call the turbine). In the ideal situation, the second fan would spin up to the same speed as the first fan and be powered entirely by the air blown on it. In a similar manner, the pump and turbine blades in the fluid coupling of the transmission smoothly transfer power from the engine to the plaary geartrains. The pump and turbine in Figure (a) are made up of multiple blades, and they are connected to separate shafts placed along the centerline of the transmission. The main shaft is connected to the turbine, and it rotates within the hollow intermediate shaft, which in turn is connected to the pump. The housing in which the pump and turbine rotate is filled with a light oil called transmission fluid. As the pump rotates, its blades force oil against the blades on the turbine, causing it to rotate. When the automobile is traveling at a steady speed, the rotation of the turbine on the main shaft follows the rotation of the pump on the hollow intermediate shaft, and they rotate in the same direction and with the same angular velocity. Plaary Geartrains The front, rear, and reverse plaary geartrain stages each include a sun gear, pla gears, a ring gear, and a carrier. The tooth numbers for each gear are listed in Figure (b). The front and rear geartrains set the velocity ratios of the transmission in the first through fourth speed settings, and the reverse stage is used only for the reverse setting. A noteworthy aspect of the transmission is the manner in which the cascade of three plaary geartrains is interconnecte