ASRB NET Tractor Systems & Controls: practice questions

Question 1 · medium

A clutch lining has outer radius 160 mm and inner radius 100 mm. Under the uniform-pressure assumption its effective friction radius is

1. 130.0 mm
2. 160.0 mm
3. 198.5 mm
4. 132.3 mm

Question 2 · hard

In selecting a tractor for a farm, choosing a tractor that is much too powerful for the implements mainly causes

1. lower timeliness of operations, since larger tractors always work more slowly
2. overloading of the engine and transmission, because big engines run hot at part load
3. insufficient hydraulic lift capacity
4. higher ownership cost per hour of useful work and more soil compaction

Question 3 · hard

An independent PTO differs from a live PTO in that

1. it has its own clutch and control, separate from the travel clutch pedal
2. it stops whenever the clutch pedal is pressed, just like the gearbox drive
3. it always turns at ground speed
4. it uses the second stage of a dual clutch worked by the same pedal

Question 4 · hard

A transmission designer spaces field gears closely between about 4 and 12 km/h but leaves wider gaps above. The main reason is

1. draft work needs small steps to keep the engine near best load
2. road gears carry more torque and so need wider spacing between their gear ratios
3. wider gaps reduce the number of shafts needed in the field range
4. close spacing is required by the PTO standard for 540 and 1000 rev/min

Question 5 · medium

The main fuel-saving feature of a CVT tractor under light PTO or transport load is that

1. it disengages the PTO automatically whenever the load falls below a set level
2. engine speed can be lowered while ground speed is held, since ratio is stepless
3. it uses a larger engine
4. it keeps the engine at maximum speed so the governor can respond quickly to load

Question 6 · hard

Why is most of the overall reduction of a tractor drive train placed in the final drive rather than in the gearbox?

1. The final drive is cheaper to lubricate because it runs in the same oil as the brakes
2. The gearbox cannot carry any reduction, because its gears must run at engine speed
3. Torque rises as speed falls, so a late reduction keeps upstream parts lightly loaded
4. The PTO requires it

Question 7 · hard

Two Hooke's joints on a PTO drive shaft give constant output speed only if

1. the two joint angles are equal and the intermediate-shaft yokes lie in one plane
2. the shaft is fully extended so the telescoping sections cannot rotate out of phase
3. one joint is at zero angle
4. the implement uses a slip clutch to absorb the speed fluctuation

Question 8 · hard

A main traction benefit of draft control with a mounted plough, compared with a trailed plough of equal draft, is that

1. the hitch transfers part of the implement weight and soil reaction onto the rear wheels
2. the plough runs at a perfectly constant depth in all soils, which cuts wheel slip to zero
3. it reduces the draft force
4. it removes the need for ballast in every soil

Question 9 · hard

The difference between a free-link and a restrained-link mounted implement is that

1. the free-link implement has no top link and is carried entirely by the two lower links and their check chains
2. the restrained link applies only to trailed implements, while free-link covers all mounted ones regardless of how the hydraulic lift is set
3. free-link means the PTO is disengaged
4. in free-link the implement settles to its own equilibrium; in restrained-link the lift holds the links and carries part of its load

Question 10 · hard

A major ergonomic limitation of walking-type power tillers is

1. the high noise inside the cab
2. hand-arm vibration through the handles and the effort of walking behind the machine
3. excessive seat vibration
4. the complexity of hydrostatic steering, which needs trained operators to handle the pump