【正文】 ze, and fuel economy needs. Occupancy per unit volume is high in automotive applications. The air conditioner (and auxiliary evaporators and systems) must be matched to the intended vehicle occupancy. Other Concerns Infiltration varies with relative windvehicle velocity. It also varies with assembly quality. Body sealing is part of airconditioning design for automobiles. Occasionally, sealing beyond that required for dust, noise, and draft control is required. Due to cost, insulation is seldom added to reduce thermal load. Insulation for sound control is generally considered adequate. Roof insulation is of questionable benefit, as it retards heat loss during the nonoperating, or soak, periods. Additional dashboard and floor insulation helps reduce cooling load. Typical maximum ambient temperatures are 90176。C for other floor areas, 63176。C for sides and top. The following three solar effects add to the cooling load: Vertical . Maximum intensity occurs at or near noon. Solar heat gain through all glass surface area normal to the incident light is a substantial fraction of the cooling load. Horizontal and Reflected Radiation. The intensity is significantly less, but the glass area is large enough to merit 山東建筑大學(xué)畢業(yè)設(shè)計(jì)外文文獻(xiàn)及譯文 5 consideration. Surface Heating. The temperature of the surface is a function of the solar energy absorbed, the interior and ambient temperatures, and the automobile’s velocity. The temperature control should not produce objectionable sounds. During maximum heating or cooling operation, a slightly higher noise level is acceptable. Thereafter, it should be possible to maintain fort at a lower blower speed with an acceptable noise level. Compressorinduced vibrations, gas pulsations, and noise Surface Transportation must be kept to a minimum. Suction and discharge mufflers are often used to reduce noise. Beltinduced noises, engine torsional vibration, and pressor mounting all require particular attention. COMPONENTS Compressors Scroll and piston pressors are used in mobile applications. They have the following characteristics: Displacement. Fixed displacement pressors have displacements of to L/rev. Variable displacement pressors have a minimum displacement of about L/rev, about 10% of their maximum displacement. A typical variable capacity scroll pressor has a maximum displacement of L/rev and a minimum displacement of just 3% of the maximum. Physical Size. Fuel economy, lower hood lines, and more engine accessories all decrease pressor installation space. These features, along with the fact that smaller engines have less accessory power available, promote the use of smaller pressors. Speed Range. Because pressors are belt driven directly from the engine, they must withstand speeds of over 100 rev/s and remain smooth and quiet down to rev/s. In the absence of a variable drive ratio, there are instances when the maximum pressor speed may need to be higher in order to achieve sufficient pumping capacity at idle. Torque Requirements. Because torque pulsations cause or aggravate vibration problems, it is best to minimize them. Minimizing peak torque benefits the pressor drive and mount systems. Multicylinder reciprocating and rotary pressors aid in reducing vibration. An economical singlecylinder pressor reduces cost。 production and service procedures must emphasize the need for system dehydration and limited exposure of the lubricants to atmospheric moisture. Older Vehicles. Vehicles originally equipped with R12 do not require retrofit to another refrigerant as long as an affordable supply of new or reclaimed R12 exists. When circumstances require it, most air conditioners can be modified to use R134a and POE. When PAG oil is used in a retrofit, the remaining mineral oil should be removed to levels established by the original equipment manufacturer to prevent residual chlorides from breaking down the PAG. R22 is not suitable for topping off or retrofit in R12 systems, as it will produce unacceptable discharge pressures (up to MPa at idle) and temperatures. R12 idle discharge pressures can reach