ICAR AICE-JRF/SRF Tractor Systems & Controls: practice questions

1 · Clutch: single and dual plate · hard

A tractor engine develops a maximum torque of 250 N·m. The single-plate dry clutch must carry 1.4 times this torque. Linings: outer radius 140 mm, inner radius 90 mm, μ = 0.35. Using the uniform-wear assumption, the total spring force needed is closest to

1. 4,348 N
2. 8,696 N
3. 3,106 N
4. 3,571 N

2 · Brakes · medium

An oil-immersed disc brake has 8 friction faces, clamping force 8,000 N, μ = 0.12 and mean radius 90 mm. Its braking torque is

1. 173 N·m
2. 1,382 N·m
3. 5,760 N·m
4. 691 N·m

3 · Tyres and ballasting · hard

A 2WD tractor must develop a net pull of 18 kN on a soil where the usable net traction ratio at acceptable slip is 0.45. The dynamic load on the rear wheels is at present 32 kN. The ballast to add over the rear wheels is about

1. 4,077 kg
2. 1,835 kg
3. 8,000 kg
4. 815 kg

4 · Tractor types and selection · medium

The main advantage of a track-type tractor over a wheeled tractor of similar mass on soft soil is

1. higher road speed, since the track links act like a continuous set of gears
2. lower ground pressure and higher tractive efficiency from a long contact patch
3. lower purchase price
4. tighter turning without skidding, because the tracks pivot on a central kingpin

5 · Brakes · hard

A tractor pulls to the right under road braking with the pedals latched. The most probable cause is

1. too much toe-in on the front wheels pulling the tractor to the right
2. low PTO speed
3. unequal brake adjustment or oil-contaminated linings on the left
4. an engaged differential lock that drags the right-hand wheel

6 · Steering geometry (Ackermann) and power steering · medium

In a hydrostatic power steering system, if the engine stops while moving

1. steering usually locks solid
2. steering becomes lighter
3. it can still be steered, with more effort, because the metering unit acts as a hand pump
4. the wheels return to the straight-ahead position automatically under the caster action of the kingpins

7 · Hydraulic system: open and closed centre · hard

Compared with an open-centre system, the main disadvantages of a closed-centre load-sensing system are

1. higher cost and greater sensitivity to oil contamination
2. higher standby energy loss
3. inability to run two functions together
4. lower maximum pressure

8 · Tyres and ballasting · medium

Rear drive tyres with chevron lugs should be mounted so that

1. the open end of the chevron contacts the ground first, so mud is squeezed out
2. the point of the chevron contacts the ground first as the wheel rolls forward
3. direction does not matter
4. the lugs point towards the tractor centre

9 · Tyres and ballasting · hard

If an MFWD tractor is fitted with front tyres of a smaller rolling circumference than specified, the likely result is

1. better traction with no drawback, as smaller front tyres dig in harder under the drive torque
2. higher road speed
3. the front wheels lag the rear, causing tyre scrub, power circulation and drive-train wear
4. lighter steering

10 · Operator controls and ROPS · medium

The international standard that sets the location, direction of movement and actuating forces of tractor operator controls is

1. ISO 500
2. ISO 15077
3. ISO 730
4. ISO 5353