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How does a hybrid car work?

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Quick answer

A hybrid car pairs a petrol engine with an electric motor and battery. A computer runs the car on electric power at low speeds, uses the engine for cruising, and combines both for strong acceleration. Braking turns the motor into a generator that recharges the battery, cutting fuel use, particularly in city traffic.

A hybrid car works by combining a petrol engine with one or more electric motors and a battery, switching between them or using both together. The battery is recharged by the engine and by regenerative braking, so the car burns less fuel, especially in stop-start city traffic.

Step by step

  1. Pulling away gently, the electric motor drives the wheels using stored battery energy while the engine stays off.
  2. As speed or power demand rises, the control computer starts the engine and blends its output with the motor's.
  3. While cruising, the engine runs near its efficient speed, and any surplus power can recharge the battery.
  4. When the driver brakes, the motor becomes a generator, slowing the wheels and sending electricity to the battery.
  5. At a standstill, the engine shuts down, and the battery powers lights, electronics and the next start.

Key things to understand

  1. A hybrid carries a combustion engine, an electric motor-generator and a high-voltage battery pack.
  2. At low speeds and gentle acceleration, the car can run on battery power alone with the engine switched off.
  3. Under hard acceleration the engine and motor work together, giving extra power without needing a larger engine.
  4. When braking or coasting, the motor acts as a generator and stores the car's kinetic energy in the battery.
  5. A control computer decides moment by moment which power source to use for the best efficiency.

Labelled diagram

  1. Petrol engine

    Provides power for cruising and hard acceleration, and can charge the battery.

  2. Electric motor

    Drives the wheels at low speed and acts as a generator when braking.

  3. Battery pack

    Stores electricity from regenerative braking and the engine for later use.

  4. Power electronics

    Converts battery DC into AC for the motor and back again when charging.

  5. Control computer

    Chooses engine, motor or both for each moment to minimise fuel use.

Main parts of a full hybrid car

Real-world examples

  • The Toyota Prius uses a planetary gearset to split power between its engine, generator and motor.
  • Strong-hybrid versions of the Maruti Suzuki Grand Vitara and Toyota Innova Hycross are sold in India.
  • Many city taxi fleets choose hybrids because stop-start traffic is where they save the most fuel.
  • Mild-hybrid systems in many family cars use a belt-driven starter-generator to restart the engine at traffic lights.

Common mistake

✗ Myth: A self-charging hybrid makes free electricity for itself.

✓ Fact: Its electricity comes from petrol burned in the engine or from braking energy that would otherwise be lost as heat. Recovering that braking energy and running the engine more efficiently is where the fuel savings come from.

People also ask

How does a hybrid car charge its battery?
A standard hybrid charges itself in two ways. When you brake or coast, the electric motor works as a generator, turning motion into electricity. The petrol engine can also drive the generator while cruising. A plug-in hybrid adds a charging socket so its larger battery can be filled from the mains.
What are the types of hybrid cars?
Mild hybrids use a small motor only to assist the engine. Full or strong hybrids can drive on electricity alone at low speeds. Plug-in hybrids add a bigger battery charged from a socket. Series hybrids use the engine purely as a generator, with only the electric motor turning the wheels.
Is a hybrid car better than an electric car?
It depends on how you drive and where. Hybrids need no charging infrastructure and refuel quickly, but still burn petrol. Battery electric cars produce no tailpipe emissions and cost less per kilometre to run, but need access to charging and usually cost more to buy.
Do you need to plug in a hybrid car?
Not a standard or self-charging hybrid. Its battery is charged only by the engine and regenerative braking. A plug-in hybrid has a larger battery that you charge from a socket, allowing longer distances on electricity alone.
What is the difference between a mild and a strong hybrid?
A mild hybrid has a small motor, often on a 48-volt system, that only assists the engine and restarts it smoothly. A strong or full hybrid has a bigger motor and battery that can drive the car on electricity alone at low speeds.
Why are hybrids more efficient in city traffic?
City driving involves frequent braking and idling, which wastes energy in a normal car. A hybrid recaptures braking energy, switches off its engine at stops, and uses the motor for low-speed creeping where engines are least efficient.
How long do hybrid batteries last?
Hybrid batteries are designed to last many years, and many outlast a typical period of ownership. The control system keeps them within a middle charge range, avoiding the full charges and deep discharges that wear cells fastest.

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