Subtopic: Power transmission systems – gear trains, differential, final drives and power take-off
Question Statement:
When a tractor operates in wet puddled rice fields and one rear drive wheel enters a muddy hollow with near-zero traction while the other wheel is on firm ground, what occurs if the differential lock is NOT engaged?
Options:
(A) Both wheels continue rotating at equal speeds with high tractive output
(B) The wheel in the mud spins at twice the crown wheel speed while the wheel on firm ground stops, resulting in zero net tractor forward motion
(C) The differential crown wheel stalls and kills the engine
(D) Torque is automatically transferred entirely to the wheel on firm ground
Answer Key:
B
Step-by-Step Solution & Explanation
- **Standard Open Differential Characteristic:**
- An open differential always equalizes torque to both axle half-shafts ($T_L = T_R$).
- If one wheel loses traction, the torque delivered to that wheel drops to near zero.
- Consequently, the torque delivered to the high-traction wheel also drops to near zero.
- The slipping wheel spins at $2 N_{\text{cage}}$ while the firm wheel remains stationary, causing the tractor to become completely bogged down unless the differential lock is engaged.