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Self-contained electric vehicle and transmission

Short answer

A self-contained electric vehicle carries its own energy source on board. Transmission systems include DC–DC (diesel engine–DC generator–DC motors), AC–DC (alternator–rectifier–DC motors), AC–AC (alternator–rectifier–inverter–three-phase induction motor), and battery-electric with chopper or inverter driving the motor.

What is self-contained electric vehicle? What are transmission system employed in these types of electric vehicle? Explain.

A self-contained electric vehicle (self-contained locomotive) carries its own source of electrical energy on board, so it needs no overhead wire or third rail. The energy is produced or stored on the vehicle and supplied to electric traction motors that drive the wheels.

Types

  • Diesel-electric locomotive: diesel engine drives a generator/alternator; output feeds traction motors.
  • Battery electric vehicle: lead-acid or lithium-ion batteries feed dc motors (shunting locos, mine locos, e-cars, e-rickshaws).
  • Petrol-electric / hybrid vehicles: engine plus generator and battery.
  • Steam/gas-turbine electric locomotives (rare).

Transmission systems

The transmission connects the prime mover to the driving axles. In electric vehicles it is mainly electrical, followed by a gear drive.

1. DC–DC transmission (diesel-electric)

 Diesel -> DC generator -> DC series motors -> gear -> axle
 engine    (sep. excited)   (axle hung)
  • Generator voltage varied by its field; engine runs at its best speed.
  • Simple and robust, but generator commutator limits power.

2. AC–DC transmission

 Diesel -> 3-ph alternator -> rectifier -> DC series motors
  • Alternator is lighter and cheaper, no commutator on the generator; widely used.

3. AC–DC–AC (AC–AC) transmission

 Diesel -> alternator -> rectifier -> inverter (VVVF) -> 3-ph IM
  • Uses rugged cage induction motors, high adhesion, regenerative/rheostatic braking; modern locomotives.

4. Battery vehicles: battery → chopper (dc motor) or inverter (ac motor) → motor → reduction gear/differential.

Mechanical part: a single-reduction spur gear (gear ratio about 3–5) between motor pinion and axle, with axle-hung nose-suspended or frame-mounted motors.

Advantages

  • Independent of track electrification; can run on any route; low initial cost of line.
  • Electric transmission gives smooth control and high starting torque.

Disadvantages

  • Heavy and costly per kW; low overall efficiency (diesel 25–30 %).
  • Limited overload capacity; maintenance of engine; fuel cost and pollution; battery vehicles have limited range.

✓ Answer checked by Claude Opus 5.5 (high effort)

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