The main problem with the electric vehicle is the battery. They are heavy, expensive, and -- when depleted of their value and tossed aside -- quite toxic to the environment. Owners of electric-only vehicles, like those from Tesla
Electric hybrids are somewhat less noxious in that regard because of their smaller batteries, but -- as my father used to tell me when I tried to keep my peas and potatoes separate -- they'll still end up in the same place.
Hybrids are a good, if not perfect, way of increasing the mileage and decreasing the direct pollution from an internal-combustion engine, but we really need an alternative to the battery for storing energy: something cheaper, more efficient, and less poisonous to our surroundings.
Pump up the mileage
Well, there is, and it's called an accumulator. This is about as simple a piece of equipment as you can imagine; it's just a tank that can hold hydraulic fluid under high pressure. That's it. That's the new "battery."
The rest of the drivetrain works pretty much like a typical electric-hybrid drivetrain. A gas or diesel engine pumps hydraulic fluid into a high-pressure accumulator, instead of generating electricity that's stored in a battery. Then the pressurized fluid is forced into pump motors that drive the wheels.
For now, hydraulic hybrid systems are most suited for large vehicles that engage in constant stop-and-go driving: city buses, delivery vehicles, and garbage trucks, for example. In 2006, UPS
Hydraulics for everyone?
Chrysler has been working since the beginning of the year on squeezing the EPA's hydraulic hybrid drivetrain technology -- which it patented -- into a Chrysler Town & Country minivan. The EPA claims that 60% fuel efficiency gains in city driving are feasible, and 30% to 35% in overall driving. Ford
But realistically, taxicabs and so-called "black cars" -- New Yorker-ese for Lincoln Town Cars that limo services often use -- are the smaller vehicle types that would probably see the greatest benefit from hydraulic hybrid drivetrains.
For real savings ...
In 2009, Altair Product Design began working on a hydraulic hybrid version of a city bus for the Department of Energy. It discovered significant efficiencies for a fleet of such buses:
- At best, a diesel-electric hybrid bus can recover only 25% of the heat energy expended during braking. Altair's hydraulic hybrid bus design was able to recover 75% of that braking energy.
- The hydraulic hybrid was able to get 6.9 mpg, the diesel-electric got 5.3 mpg, and the non-hybrid got 3.3 mpg.
- A city bus that travels a typical 37,000 miles per year would save more than 5,800 gallons of diesel fuel over a conventional bus, and more than 1,600 gallons over a diesel-electric hybrid.
- Though a hydraulic hybrid would cost more than a conventional bus, it would cost $100,000 less than a diesel-electric hybrid.
In addition, according to Tim Smith of Altair Product Design, speaking to Wired magazine, hydraulic hybrids requires nothing out of the ordinary in terms of tools or training for fleet maintenance. "There's nothing unique about our driveline that requires unique infrastructure," he said.
Back to the future
Until flux capacitor technology arrives, we have to work with what we've got. Every transportation technology has its downsides, but hydraulic hybrid drivetrains -- used in a stop-and-go environment, where they would work best -- could at least answer part of this age-old question: What happens to the battery?
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