tailieunhanh - Mechanism Design - Enumeration of Kinematic Structures According to Function P8

Automotive Mechanisms In this chapter, we illustrate the usefulness of the systematic design methodology by enumerating a few automotive related mechanisms, including variable-stroke engine mechanisms, constant-velocity shaft couplings, and automatic transmission mechanisms. For each case, we first identify the functional requirements. Then, we translate some of the requirements into structural characteristics for the purpose of enumeration of the kinematic structures. Lastly, we apply the remaining functional requirements along with other requirements, if any, for qualitative evaluation of the kinematic structures. This results in a class of feasible mechanisms or design alternatives | Chapter 8 Automotive Mechanisms Introduction In this chapter we illustrate the usefulness of the systematic design methodology by enumerating a few automotive related mechanisms including variable-stroke engine mechanisms constant-velocity shaft couplings and automatic transmission mechanisms. For each case we first identify the functional requirements. Then we translate some of the requirements into structural characteristics for the purpose of enumeration of the kinematic structures. Lastly we apply the remaining functional requirements along with other requirements if any for qualitative evaluation of the kinematic structures. This results in a class of feasible mechanisms or design alternatives. Since we are primarily concerned with the enumeration and qualitative evaluation of various design alternatives other phases of design such as dimensional synthesis design optimization and design detailing will not be considered. Variable-Stroke Engine Mechanisms Most automobiles employ internal combustion engines as the source of power. Such a vehicle is typically equipped with an engine that is large enough to meet desired performance criteria such as maximum acceleration and hill climbing capability. On the other hand only a fraction of the engine power is needed for highway cruising. To meet various load requirements it is necessary to incorporate some kind of engine load control mechanism. Most internal combustion engines employ the crank-and-slider mechanism with a constant stroke length as the engine mechanism. Load control is achieved by throttling the inlet. Throttling however introduces pumping losses. It becomes clear that engine efficiency can be improved if the throttling can be eliminated or reduced. One approach is to employ a mechanism to vary the valve lift and the valve opening and closing points with respect to the engine top-dead-center as a function 2001 by CRC Press LLC of vehicle load requirements. Another approach is to vary the piston .