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Hybrid car
2017 Mattia Piron. All rights reserved.

  1. Introduction
  2. IMA (Integrated Motor Assist), Honda
  3. Hybrid Synergy Drive (Toyota)
  4. Diesel-electric hybrid

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DECEMBER 29th, 2018


Introduction       top

Hybrid cars are vehicles equipped with both an internal combustion engine and one (or more) electric motor, with the aim of reducing the inefficiencies of "classic" vehicles. A normal internal combustion engine has an efficiency that can reach 20-25%, but only under certain conditions of load and rotation speed. Outside these conditions, the efficiency drops dramatically. Coupling an electric motor to a heat engine helps it in all those situations where it would have very low efficiency. In addition, an electric motor can also act as a generator, to recover energy during braking, energy that would otherwise be lost in heat. Let's take a look at the main technologies:


IMA (Integrated Motor Assist), Honda       top

First introduced with the Honda Insight in 1999, the electric motor is mounted between the internal combustion engine and the transmission, and serves to reduce the load on the internal combustion engine. Starting in 2006, with the Civic Hybrid, the car can travel short distances with only the electric motor, keeping the heat engine in neutral. During braking, the electric motor acts as a generator and recovers energy.


Hybrid Synergy Drive (Toyota)       top

The Toyota system is composed of 2 electric motors, one of which is directly connected to the heat engine (In a manner quite similar to the Honda system, we will call it motor 1), while the other (motor 2) is mounted in parallel. These two powertrains are mounted at two degrees of freedom of a epicycle gear, while the third degree of freedom is connected to the wheels. An electronic management system locks the planetary gear in different configurations, thus allowing the vehicle to move forward either with the heat engine + electric motor, or with only the electric motor, keeping the heat engine switched off. In addition, the planetary gearing keeps the heat engine at an ideal speed for driving, similar to a CVT gearbox. This system can work in several ways:

  • Recharging batteries when the car is stationary;
  • starter motor, using motor 1;
  • reverse simply by applying a negative voltage to motor 2;
  • at low speeds and moderate torques, only engine 2 is used while the heat engine remains off;
  • In the low speed run, the heat engine rotates at a higher speed than necessary, the extra speed is used to generate power through engine 1, providing power to engine 2;
  • When driving at high speed, the heat engine rotates at a lower speed than necessary, engine 2 acts as a generator supplying power to engine 1 to help the heat engine rotate. When torque changes, the battery pack provides the necessary power;
  • regenerative brake;

    Diesel-electric hybrid       top

    In 2011, Volvo launched the first diesel-electric car. The diesel engine acts as a generator, which powers the electric motors located directly on the wheels. The advantage of this system is the elimination of the transmission, so the Diesel engine can run at optimal rpm.


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