单选题Wear occurring at the tips of the reduction gear teeth is usually the result of （）.A surface fatigueB fretting corrosionC heavy overloadingD gear misalignment

When transmitted by a reduction gear, diesel engine speed is reduced and the torque available for work

A.remains the same

B.is reduced

C.is increased

D.is eliminated

Pitted reduction gear teeth having a deep blue color with evidence of overheating have been operated with _______.

A.excessive speed

B.improper warm-up

C.extreme misalignment

D.inadequate lubrication

Combustion knock occurring in a diesel engine can be caused by _____.

A.low coolant temperature

B.insufficient fuel

C.high ambient temperature

D.carbon buildup on the injector tips

Chafing gear ______.

A.reduces and prevents corrosion of standing rigging

B.prevents corrosion of running rigging

C.reduces and prevents wear caused by the rubbing of one object against another

D.protects the body against extreme cold

Which of the following is the guarantee of a better future for US economy?

［A］Motor vehicles.

［B］Housing market.

［C］Business equipment.

［D］Computer gear.

One of the most common causes of reduction gear failure is gear wear caused by scoring as a result of

A.surface fatigue of the gears

B.an inadequate lube oil film

C.plastic flow of the gears

D.fretting corrosion from water

第二组：Magnetic pickup (MPU) sensors are devices which can be used in conjunction with electronic control modules for monitoring of parameters such as speed, direction of rotation and a variety of alarm conditions. MPU sensors are available in various sizes and types. Following are some guidelines for their selection on industrial engines. MPUs are located near a flywheel, camshaft or other type of gear with rotation relative to engine speed. The passing of the gear teeth through the MPU tip (pole) generates a voltage and frequency. This frequency is converted to a speed reference by a control module. It should be noted here that most MPUs will develop similar signals. However, the magnitude and strength of the signal is dependent on the size of the sensor in relation to the gear teeth, the clearance between the pole piece and the gear teeth, and various other factors. As a general rule of thumb, the following standards should be met:

①Dimension of tooth top surface should be equal to or more than the pole piece diameter.

②Tooth height should be equal to, or more than the space between teeth.

③The space between teeth should be approximately three times the pole piece diameter.

④Air gap (clearance) between tooth and pole piece should be between 0.015" to 0.030". MPUs

normally have 3/8", 5/8" threads and 2", 3" and 4" lengths. Determining which size is appropriate

depends on the space available for installation, the availability of pre-drilled holes and consideration to

those rules mentioned above. In most cases, these will be the only factors affecting the selcetion of a

MPU.

MPUs can be used to ____.①sense speed ②supply alarm ③sense direction of rotation.

A.①②

B.②③

C.①③

D.①②③

A.benefits

B.affects

C.affects

D.effects

Wear occurring at the tips of the reduction gear teeth is usually the result of ______.

A.surface fatigue

B.fretting corrosion

C.heavy overloading

D.gear misalignment