HYBRID BASICS

To ensure that a hybrid lives up to its owners' expectations, it is important for an owner to understand a hybrid's features and to choose the vehicle that best meets their needs.  This section introduces the key features of a hybrid and explains their impact on performance. 

For more technical information please see:
Government of Manitoba, Climate Change Branch
How Stuff Works: Introduction to Hybrid Cars
US Department of Energy

Series vs. Parallel Drive Train Systems
Most hybrids use a combination of mechanical and electrical power to move a vehicle. These two systems work together to deliver energy to the wheels. Manufacturers are using two different design approaches, either a Parallel and Series system. 

Parallel Hybrid: In a parallel system the battery and engine are both connected to the transmission. As a result either the battery via the electric motor, or the engine directly to the transmission, or a combination of both, can provide propulsion power.

Source:Toyota

Series Hybrid: In the series type of hybrid the engine turns a generator and the generator can either charge the batteries or power an electric motor that drives the transmission. The engine never powers the vehicle directly.

Source:Toyota

          

Series/Parallel Hybrid: The Series/Parallel system combines both the Series and Parallel systems. The system has a power diverter which can direct the energy from the engine to the wheels or to the generator.  This means that depending on the situation the engine can provide propulsion to the wheels or energy to the battery. 

Source: Toyota

Note: Manufacturers have chosen a particular hybrid architecture because they believe that it will deliver superior performance, reliability, and operational compatibility when compared to the other. In terms of performance, all systems systems have shown that they have the potential to dramatically reduce fuel consumption and emissions.

     

The following are the most common features of hybrids:

• Idle Stop
• Regenerative Braking
• Motor Assist
• Engine-Off Drive - EV Mode
  

  Idle Stop: Turns off the engine when the vehicle is stopped. Once the accelerator is pressed the engine immediately turns back on. This ensures that the vehicle is not using fuel when the engine is not required to propel the vehicle.

  Regenerative Braking: When decelerating the brakes capture the energy and store it in the battery for later use. Regenerative braking helps keep the battery packs charged without having to plug in the vehicle. Read a technical explanation of regenerative braking. 

  Motor Assist: The electric motor will provide extra power drawn from the battery when the internal combustion engine is performing a more energy intensive activity (e.g. accelerating). The motor assist enables the vehicle to use a smaller more fuel-efficient engine without giving up vehicle performance.

  Engine-Off Drive- EV Mode: The electric motor propels the vehicle at lower speeds. Since the engine is not being used during acceleration no fuel is being used and no emissions are being released.  When the hybrid is in this mode, it is essentially an electric vehicle.

“Mild” vs. “Strong” Hybrids
While the term hybrid refers to a type of vehicle there are different levels of “hybridization” among hybrids on the market. Different manufacturers have implemented their respective hybrid technology package in different ways.

Two broad terms (and variation of these terms) have evolved to differentiate hybrids based on the features used in a vehicle - Mild and Strong. Generally, a mild hybrid will incorporate Idle Stop and Regenerative Braking while a strong hybrid offers Idle Stop, Regenerative Braking, Motor Assist, and Engine-Off Drive-EV Mode.  A mild hybrid system has an advantage of costing less but saves less fuel compared to a strong hybrid.

Each vehicle manufacturer has made its decision on which hybrid type to implement based on its assessment of the market niche for a particular model. Examples of two very different hybrids serving different markets are GM’s Silverado light truck (a mild hybrid in which the hybrid system is not used for motive power) and Ford’s Escape SUV (a strong hybrid).

Visit the Benefits of Hybrids to see how impact the different features have on fuel performance.