by Jacques Gordon
The federal Energy Policy Act of 2005 provides tax credits to taxpayers who purchase specific “fuel efficient” vehicles. The list originally included hybrid vehicles, but tax credits for most hybrids ended in 2011. Why? Governments use tax incentives to promote specific activities, in this case, development of hybrid vehicles. Evidently the feds feel that goal has been reached, but the real effect of those tax credits goes beyond hybrid powertrains.
A hybrid powertrain utilizes two or more different energy sources to drive the vehicle. The success of today’s hybrid vehicles is not just that they utilize multiple types of energy, but that they recover energy that would otherwise be lost. Everything in the universe is either mass or energy, and we cannot create or destroy either one, we can only convert it to another form. When we press the accelerator pedal, we’re converting fuel or electrical energy into kinetic energy, which is the energy of a mass in motion. When the brakes are applied, we’re converting kinetic energy to heat and quite literally dumping it overboard into the air. The hybrid vehicles we have today capture that kinetic energy and store it for the next acceleration. This is called “regenerative braking,” and that’s the real breakthrough.
Before the Honda Insight was introduced in 1999, regenerative braking wasn’t used in any real-world application. Now it’s in every electric vehicle and gas-electric hybrid on the road, and a growing number of off-road applications too. Regenerative braking debuted in Formula 1 racing in 2009, using batteries and a motor/generator built into the transmission. Porsche has taken a similar approach with their all-wheel-drive GT3 R racecar, using two motor/generators to drive/brake just the front wheels. Pure electric vehicles like the Tesla also have regenerative braking, and it’s even used on golf carts.
Batteries are not the only place to store recovered energy. A kinetic energy recovery system (KERS) uses a flywheel that spins up to 80,000 rpm and returns that energy directly to the transmission. Originally designed for Formula 1 racing, Volvo is currently demonstrating a 60,000 rpm KERS for production cars that they say will boost fuel economy by 25 percent. Eaton Corporation has developed a hydraulic regenerative braking system. During braking, a pump is engaged that absorbs kinetic energy to pressurize a hydraulic accumulator. During acceleration, the pressure is released back to the hydraulic circuit and the pump becomes a hydraulic motor, returning energy to the drivetrain. Called “hydraulic launch assist” (HLA), it’s big and heavy and best suited for stop-and-go driving in heavy vehicles, like a trash truck, but Eaton says it recovers 70 percent of the braking energy.
Someday hybrid vehicles may become obsolete, but regenerative braking is here to stay, thanks to federal tax policy.
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