Why and how to joyfully move our butts around town, without mucking the place up.

Fuel efficiency & hybrid drive train technologies in cars and trucks

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Parallel hybrid

In a parallel hybrid the single electric motor and the internal combustion engine are installed so that they can both individually or together power the vehicle. That is, the petrol and electric halves operate in parallel.

Mild parallel hybrid

These types use a generally compact electric motor (usually <20 kW) to provide auto-stop/start features and to provide extra power assist during the acceleration, and to generate on the deceleration phase (aka regenerative braking).

Power-split or series-parallel hybrid

The power-split hybrid electric drive train has two motors: an electric motor and an internal combustion engine. The two motors are connected to a shared transmission, generally a simple planetary gear set, enabling sharing of power to drive the wheels. The power sharing ratio can be from 0-100% for the petrol engine, or 0-100% for the electric motor, or an anything in between. Additionally the electric motor can be used as a generator to recharge the battery pack.

Series hybrid

Series-hybrid vehicles are driven by the electric motor, and there is no mechanical connection between the petrol engine and the wheels. Instead the petrol engine is used solely as a generator, and is operated at the ideal RPM for maximum fuel efficiency.

The arrangement is common in diesel-electric locomotives and ships. Ferdinand Porsche (the founder of the Porsche brand) originally developed this arrangement for race cars in the early 20th century. Porsche named the arrangement "System Mixt". His system used multiple hub motors, and a gasoline generator to charge the on-board battery pack.

With the Chevy Volt, GM invented the term "Extended Range Electric Vehicle or Range-Extended Electric Vehicle (EREV/REEV)". However the Volt is not a true Series Hybrid because the petrol engine and electric motor share mechanical connection to the wheels via a planetary gear transmission.

Plug-in hybrid electric vehicle (PHEV)

This is a hybrid vehicle with a larger battery pack and arrangements allowing the battery pack to be charged by plugging into the electric grid. The drive train can be built in any of the above configurations. What's important for the PHEV is that one can plug in, charge the battery pack, and drive a significant distance on electricity.

Some use terms like PHEV10, PHEV20, PHEV40, etc to indicate the approximate range of a given PHEV. For example the Prius Plug-in with its 15 mile electric range would be considered a PHEV15.

Auto Start-Stop

A start-stop system or stop-start system automatically shuts down and restarts the internal combustion engine to reduce the amount of time the engine spends idling, thereby reducing fuel consumption and emissions. This is an innate feature of hybrid vehicles, and is starting to appear in non-hybrid vehicles.

In describing the 2013 Fusion with Auto Start-Stop, Ford said:

Auto Start-Stop saves fuel use when the car is standing and running at idle. Savings vary depending on driving patterns, but owners who spend most time in heavy urban areas and city traffic will benefit the most � up to 10 percent. On average, Auto Start-Stop improves fuel efficiency by about 3.5 percent.

Ford is making Auto Start-Stop � one of the most popular features of hybrid vehicles � available with the new 1.6-liter EcoBoost-powered Fusion. When the Fusion comes to a stop, the engine can automatically switch off, consuming no gasoline and emitting no exhaust gases. As soon as the driver releases brake pedal, the engine seamlessly re-starts itself and is ready to go by the time the driver presses the accelerator pedal.

Mild hybrids

These are are essentially conventional fossil-fuel vehicles equipped with an electric motor/generator allowing the engine to be turned off whenever the car is coasting, braking, or stopped, yet restart quickly. A mild hybrid may use regenerative braking to recharge a small battery pack. Mild hybrids have a low power electric motor that's essentially unable to move the car on its own, meaning the mild hybrid doesn't need the larger battery pack.

Mild hybrids may provide some of the benefits of the application of hybrid technologies, with less of the cost�weight penalty.

It may be that the Auto Start Stop and Mild Hybrid vehicles are the same ..

Idle reduction

This primarily refers to big trucks and the practice of truck drivers to leave the truck idling to, for example, run air conditioning equipment in the sleeper, or to keep the freezer unit running in the back of the truck. A vehicle with idle reduction technology will shut off the engine entirely, saving on fuel and reducing pollution, while other functions like accessories and lighting are powered by an electrical source other than the alternator.

In one version of this, truck stops have services such as AireDock, IdleAire and Shorepower, providing a power outlet for trucks to plug in and run the accessory systems without keeping the engine idling.

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