Hybrid Car Cocktail Party Cheat Sheet

Defining Hybrids- Hybrid systems are typically described as micro, mild or strong depending on the amount of electrical power available to drive the vehicle. The most basic function of hybrid systems is automatic start-stop to shut the engine down when the car stops. Preventing idling in this way conserves fuel and lowers emissions. In Europe there are a number of these micro-hybrids that really aren't hybrids at all because they only provide the start-stop function but no electric drive or regenerative braking capability.

Mild and Strong Hybrids - The mild and strong hybrids add an electric boost or drive motor to the package. Since electric motors are generally able to produce electricity when they are driven mechanically, this also allows for regenerative braking. In these hybrids, lifting off the accelerator and coasting causes the wheels to turn the motor to produce electricity and recharge the battery. While this is happening it increases drag and the vehicle slows, just like it does under engine braking in a conventional vehicle. The battery powers the electric motor during acceleration or cruising. This cuts the workload on the gasoline engine and reduces its fuel consumption. In a mild hybrid, the motor typically has an output of 15 kilowatts or less, which is enough to provide boost and start-stop capability, but not enough to drive the vehicle on electricity alone. Strong hybrids typically have motor/generators with 30 kW or more, which allows them to be driven on electricity alone for short distances (1-2 miles) at speeds under 65 miles per hour.

Parallel Hybrids - All the hybrids on the market today are so-called "parallel" hybrids, so named because multiple propulsion sources can drive the wheels at the same time. These systems consist of a conventional internal combustion engine combined with one or more electric motor/generator(s) and a battery. Let's take a look at representatives of each hybrid camp, and see how they differ.

Power-Split Strong hybrid, continued - Besides being highly efficient, electric motors have another important functional advantage over internal combustion engines. Motors produce their maximum torque from idle and basically maintain that torque through most of their operating range. When incorporated into a hybrid powertrain, this allows the engine designers to modify the behavior of the internal combustion engine for improved efficiency. Gasoline engines in conventional vehicles run on what is known as the Otto four-stroke cycle, while hybrids use the Atkinson cycle. The main difference between the Otto and Atkinson is that the intake valves close later in the cycle to reduce pumping losses. This makes Atkinson more fuel-efficient but produce less torque. Normally drivers wouldn't like the way this feels but the electric motor fattens up the combined torque curve. Power-split hybrids have proven to be efficient but the transmission integrated with the motors is mechanically complex and expensive to build.