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1、 第四章 关 联 题 79 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
2、joints, 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
3、through yokes (5).Lubrication for the rocker arms comes from the engine s 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,
4、 the 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
5、. before 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 systemC. the special pumping system D.
6、 the turbine oil system 3. 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 c
7、am and the tappet roller.B. The one between the push rods and the ball joints.C. The one between the rocker aims and the yokeD. The one between two tubular push rods.AACCPassage 2Charge air coolerThe engine is equipped with a charge air cooler. The insert type charge air cooler is mounted in a welde
8、d casing (air trunk) . The trunk is bolted to the engine block.Standard is a two-stage cooler mounted. 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 fro
9、m 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
10、and should be as clean as possible. The operating air temperature should be maintained by controlling the coolant inlet temperature.Whilst the engine is running the air and coolant temperatures and pressures at inlet and outlet should be checked and logged periodically. Variations from normal indica
11、te faults developing such as fouling of the film plates or obstruction of the water tubes.Check daily, during operation of the engine, the working of the telltale hole at the free end of the charge air receiver. The function of this hole is to inform the operator the presence of water in the charge
12、air receiver. Under normal condition only compressed air should escape from this hole.1. According to the passage, the expression HT probably means _.A. HIGH TANK B. HIGH TEMPERATUREC. HEAT TRANSMISSION D. HEAT TRANSFER2. In order to maintain the charge air temperature we should control _.A. the coo
13、lant inlet temperature coming from the first stage coolerB. the coolant flow coming from the second stage coolerC. the coolant outlet temperature coming from the second stage coolerD. the coolant flow coming from the first stage cooler3. The charge air temperature departing from normal may indicate
14、that _A. condensate can be formedB. only compressed air should escape from the telltaleC. the film plates are becoming dirty or the water tubes are blocked by scaleD. cooling water may have been carried into the cylinders 4. The function of the telltale hole is to _.A. detect whether compressed air
15、has escaped from the holeB. control the coolant inlet temperatureC. determine whether the coolant water is under positive pressureD. inform the operator the presence of water in the charge air receiverBBCDPassage 3Starting air systemThe engine is started with compressed air of max 30 bar. Minimum pr
16、essure required is 15 bar. A pressure transmitter PT301 mounted on the starting air line before the main starting valve has an indicator in the instrument panel. The supply line from the starting air bottles is provided with a non return valve and a drain valve.The solenoid valve is electrical (remote control) or manual ( on the engine) operated
