Hybrid Technology, Part One

By Romana Annette  12/11/2007

Overview:

Hybrid technology is about the creative fusion of different technologies to provide load-leveling or mechanical simplification.  In this case, it is the fusion of mechanical and electrical technologies.  This makes a lot of sense for modern vehicles, since the electrical load has become 10 to 20% of the total load.  Increasingly, batteries figure heavily into hybrid technology, so there is a push to develop ever higher-capacity batteries.

Other technologies, such as mechanical flywheels and chemical fuel cells, may become important in the future.  Still, these technologies would still interface using electricity.

History:

These ideas are not new.  The first fusion technologies were diesel-electric engines.  Gasoline and diesel engines are only efficient, in respect top power and torque, over a limited range of middle RPM’s.  Electric motors, on the other hand, have their highest torque at zero RPM.  Thus, a diesel generator that powers electric motors can make a lot of sense, especially if it can eliminate complex reduction gearing.

The first diesel-electric ship was launched in 1903, and the first diesel-electric locomotive became operational in 1920.  Historically, batteries have not figured much in diesel-electric technology, but that could change in the future.

Nuclear-powered ships carry the same ideas to higher levels of technology as nuclear-electric ships.

Automobiles have now become the leading edge of hybrid technology.  Unfortunately, in a market place driven by sports utility vehicles (SUV’s,) hybrid vehicles are rationed, as well as expensive.

With automobiles, hybrid technology is all about load-leveling: to reduce the amount of energy used under engine load, to reduce the total energy consumption, and to recapture energy that would otherwise be wasted.

Types of Hybrid Vehicles:

Unlike other essays of this type, I will describe hybrid technology in order of least complex to most complex.  Features found in one level, can always be part of the next, more complex levels.

Micro or Low Hybrids:

This type of hybrid has the cheapest (to implement) technology, but there are no vehicles currently sold that are specifically said to be low hybrids.  Low hybrid technology is as follows:

·      Multiple batteries: Multiple 12-volt batteries can be used to reduce power consumption by alternators under heavy vehicle load.

·      Electric Power Steering: Using electricity instead of engine power for power steering can reduce the load on an engine.  This feature has had mixed success.

·      Regenerative Braking: Using generators to recapture energy during braking can capture energy that would otherwise be lost to friction.  Also, this can save wear on brakes and greatly extend the time between brake jobs.

·      Engine Off: Automatically turning the engine off at stops can save fuel.  One catch is that heat and air conditioning might not be functional.

·      Continuously Variable Transmission: A CVT tries to set the best gearing for the current engine load and vehicle speed.  Usually, it only has the gear selections PRND, and no other user-input.

·      Special Braking: If a vehicle has regenerative braking, it can have a special switch to active downhill braking without pressing the brake pedal.  This has to be a manual operation, since a vehicle cannot know it is on a long downgrade.   A Prius has this as the B-gear option.

Mild Hybrids:

The first mild hybrid was the Honda Insight.  The new Saturn Vue Hybrid is also considered to be a mild hybrid.  Mild hybrid technology is as follows:

·      Electric Motor: A heavy-duty, high voltage electric motor assists the internal combustion engine.

·      High Voltage Batteries: Powerful high-voltage battery packs are used to power the electric assist motor.  These are currently NiMH batteries, but there is hope for lithium-ion batteries in the near future.  Currently, lithium-ion batteries have stability problems, while NiMH batteries lose energy too easily.

·      Electric A/C: Some vehicles have electric A/C, which can solve the A/C problem when the engine is shut off.  These A/C units require high voltage to operate.

·      Series Assist Mode Only: The electric motor is in series with the internal combustion engine; it can only assist; it cannot propel the vehicle on its own.

·      ULEV: The introduction of extreme low emission engines, such as those using the Atkinson cycle, can reduce polluting emissions way below those of the average internal combustion-powered vehicle.

Full Hybrids:

Full hybrids are the vehicles that all the fuss is about, since it is these vehicles that can promise much higher fuel mileage than vehicles powered by internal combustion engines alone.  Current models include the Toyota Prius, Camry, and Highlander, as well as the Ford Escape.  Full hybrid technology is as follows:

·      Electric Drive: A full hybrid can be driven on electric power alone.  This is especially helpful in stop and go traffic.

·      Parallel Operation:  There are several parallel operation options.  For a Prius, it means that the internal combustion engine and the electric motor are geared together in such a way that they can work separately or together.
Or, for large vehicle, it can mean that the internal combustion engines and the electric motors are totally separate; for instance, wheels could be direct electric drive.
Finally, reminiscent of diesel-electric vehicles, the internal combustion engine could be used for the generation of electricity only.  This offers weight-savings for large vehicles by eliminating bulky transmissions.

·      High/Low Hybrid: This is a complex system being implemented by General Motors, where much of the hybrid technology is combined with a standard transmission, in the form of added electric motors and CVT gearing.

·      Plug-in Options: The original hybrid concept was to eliminate having to plug-in, but it turns out that charging from a household circuit has great advantages.  This feature requires a manual switch, which would tell the hybrid vehicle to use only electric power for propulsion.  This would only be useful once one was close to home.  The advantage is that it is much cheaper to recharge batteries from a home circuit than from an automobile alternator.