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1、关 联 题 （173题）Passage 1Valve drive mechanismThe valve drive mechanism commands the inlet and exhaust valves at the required timing.The valve drive mechanism consists of an inlet and exhaust cam follower (8) each suspended in a plunger of the tappet assembly (7), two tubular push rods (4) with ball joi
2、nts, two nodular cast iron rocker arms (2) suspended in a rocker arm bearing bracket, two yokes (5) and a yoke guide pins. See Fig. 4-1.The tappet rollers follow the cam profiles and transfer the movements through push rods to the rocker arms. The rocker arms operate the inlet and exhaust valves thr
3、ough yokes (5).Lubrication for the rocker arms comes from the engines secondary oil supply manifold through drillings in the cylinder head and rocker arm bracket.The tappet assembly receives lubricating oil via channels in the engine block from the main supply manifold. For the roller and shaft, the
4、 oil is supplied through the guiding plunger. To compensate for heat expansion a clearance must exist between the rocker arm and yoke. All adjustments have to be done on a cold engine only.Fig-4-1 Valve drive mechanism1. According to the passage, the best time to adjust the valve clearance is _.A. b
5、efore the engine is started B. when the engine is runningC. after the engine has just been stopped D. when something has gone wrong with the engine2. The roller and the tappet assembly are lubricated by means of _. A. the main lube system B. the secondary oil system C. the special pumping system D.
6、the turbine oil system3. According to the passage, the valve drive mechanism does not include _. A. tappet rollers B. push rods C. nodular cast iron D. yokes and guide pins4. To close valves tightly, which clearance should be inspected according to the maintenance schedule? A. The one between the ca
7、m and the tappet roller. B. The one between the push rods and the ball joints. C. The one between the rocker aims and the yoke D. The one between two tubular push rods.AACCPassage 2Compressor cleaning during engine operation The compressor may be cleaned by water injection during the engine operatio
8、n. The cleaning process will have good results as long as the deposit formation has not gone too far. In ease a very thick hardened crest of dirt the compressor has to be dismantled for cleaning. In this method of cleaning the water is not acting as a solvent but instead removes the deposits mechani
9、cally by the impact of the water droplets. It is therefore recommended to use clean water without additives. The water should not contain any additives which might remain on the compressor blades. Periodically cleaning of the compressor (Fig. 4-2) prevents or delays excessive build-up of dirt but in
10、 no way replaces the usual overhauls where the turbocharger is completely dismantled. The turbocharger is provided with a water container (1). During the cleaning procedure the container is pressurized with the charge air (2) and from where the water is forced to the compressor inlet (3).1. Which of
11、 the following statements can be used to clean the compressor with the engine running? A. Water droplets Water with additives C. Charge air D. Hard crust2. What principal is used in this method of cleaning? A. The cleanser solves the deposits. B. The cleanser melts the deposits. C. The cleanser beat
12、s the deposits mechanically. D. The high pressure of the cleanser removes the deposits.3. Which of the following statements is not correct? A. The compressor needs regular cleaning. B. Periodical cleaning of the compressor contributes to reducing build-up of dirt. C. Its not necessary to dismantle t
13、he turbocharger if periodical cleaning of the compressor is performed. D. Additives should better be avoided during the cleaning process.4. The cleaning water should not contain any additives, because_. A. they may delay build-up of dirt B. they might remain on the blades of the compressor C. they m
14、ay be forced to the compressor inlet D. they are not good solventsACCBPassage 3Charge air cooler The engine is equipped with a charge air cooler. The insert type charge air cooler is mounted in a welded casing (air trunk) . The trunk is bolted to the engine block. Standard is a two-stage cooler moun
15、ted. The first stage, through which the charge air flows, is cooled with water from the HT cooling system and cools the charge air till approx. 90 -100. The second stage is supplied with water coming from the LT water system and cools the charge air further till the required temperature of approx. 50. By controlling the water flow through the LT cooler the charge air temperature can be kept constant at the required temperature. The circulating coolant water should always be under positive pressure and should be as clean as possible. The oper
