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第四章 关 联 题79题

Passage 1

Valve drive mechanism

The 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 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 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, 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 mechanism

1. According to the passage, the best time to adjust the valve clearance is_____. A. before the engine is started B. when the engine is running

C. after the engine has just been stopped D. when something has gone wrong with the engine 2. 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. 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 pins

4. To close valves tightly, which clearance should be inspected according to the maintenance schedule?

A. The one between the cam 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. AACC Passage 2

Charge 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 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 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 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 indicate 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 air receiver. Under normal condition only compressed air should escape from this hole. 1. According to the passage, the expression \probably means ________. A. HIGH TANK B. HIGH TEMPERATURE C. HEAT TRANSMISSION D. HEAT TRANSFER 2. In order to maintain the charge air temperature we should control ________. A. the coolant inlet temperature coming from the first stage cooler B. the coolant flow coming from the second stage cooler

C. the coolant outlet temperature coming from the second stage cooler D. the coolant flow coming from the first stage cooler

3. The charge air temperature departing from normal may indicate that _____ A. condensate can be formed

B. only compressed air should escape from the telltale

C. the film plates are becoming dirty or the water tubes are blocked by scale D. cooling water may have been carried into the cylinders

4. The function of the telltale hole is to ________.

A. detect whether compressed air has escaped from the hole B. control the coolant inlet temperature

C. determine whether the coolant water is under positive pressure D. inform the operator the presence of water in the charge air receiver BBCD

Passage 3

Starting air system

The engine is started with compressed air of max 30 bar. Minimum pressure 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 and send after activation a pilot air signal to the main starting air valve. Interruption of the control air doses the main starting air valve.

After the main starting air valve is activated the air flows through the flame arrestere to the starting air valves in the cylinder heads. Part of the air flows via the starting air distributor to each of the starting air valves in the cylinder heads. The starting air distributor controls the timing of opening and closing of the starting air valves. On the moment the main starting air valve is operated also the governor booster is energized. The main starting air line is provided of a safety valve. Interlock valve is a safety device to avoid an engine start with engaged turning gear.

1. As the engine is started with compressed air, the correct sequence of the following devices being activated is ________.

①solenoid valve; ② starting air valve; ③ starting air distributor; ④ main starting air valve ; ⑤governor booster. A. ①,⑤,④,②,③ B. ①,④,⑤,③,② C. ①,④,③,②,⑤ D. ④,③,①,②,⑤

2. The sentence \ A. the governor booster is supplied with electric power B. hydraulic oil is pumped into the governor booster C. the governor starts to work before starting the engine

D. the governor booster is supplied with pressurized air before starting the engine 3. Which of the following components are attached to the air bottles? A. a pressure transmitter FT 301

B. a non-return valve and a drain valve

C. a solenoid valve D. a starting air distributor

4. When the engine is engaged with turning gear,________ can keep the engine from starting A. the control air C. the main starting air valve BDBD Passage 4

B. the solenoid valve D. the interlock valve