EV-09 — EV Transmission / Driveline

ASSUMPTION — This lesson covers the driveline at the system level. No model-specific gear-count claim is made.

1. Single-Speed Reduction

Because the electric machine delivers high torque from low speed, it can cover a wide speed range with a single gear ratio. Most BEVs therefore use a single-speed reduction.

FACT — The reduction gearbox steps the motor’s high speed down to low wheel speed, multiplying torque.

2. Multi-Speed EV Transmission

Some high-performance or heavy-duty applications may use multi-speed solutions for efficiency/torque optimization, but this adds complexity and mass.

3. Differential

It enables the speed difference between wheels (cornering). In single-motor layouts it is integrated into the reduction gearbox.

4. e-Axle and Integrated Drive Unit

• e-Axle — motor + inverter + reduction in one unit; packaging and assembly advantages.
• Integrated drive unit — a compact drive that also includes the differential.

5. Configurations

Configuration	Drive
Single front motor	FWD
Single rear motor	RWD
Dual motor	AWD (one machine per axle)
Triple/quad motor	AWD + torque vectoring

FACT — In a dual-motor AWD there is no mechanical shaft between axles; torque split is done in software (EV-24).

6. FAQ

Why do EVs use a single-speed reduction instead of a multi-speed gearbox?

FACT — The electric machine delivers high torque from low speed, so a single ratio covers a wide speed range; multi-speed adds complexity and mass.

What is the advantage of an e-axle?

FACT — Motor, inverter, and reduction combine into one unit, giving packaging, assembly, and mass advantages.

7. Summary

• A single-speed reduction is usually sufficient.
• The differential enables cornering speed difference.
• The e-axle integrates motor + inverter + reduction.
• FWD/RWD/AWD offer different drive/torque-distribution behaviors.

8. Sources and Verification Note

Concepts are established textbook-level knowledge; no model-specific claim.

• DOE AFDC, SAE J1715.

Next Lesson

• EV-10 — Battery: cell, module, pack, chemistries, and CTP/CTC.