Technology Articles
How Hybrids Work
ybrid vehicles for decades, thanks in large part to a pair of oil crises in the 1970s and 1980s that seemed to portend a need for more fuel-efficient vehicles in the years ahead. However, once gasoline shortages eased and long lines at the pump faded from memory, so did the desire for more fuel-efficient vehicles.
Toyota's hybrid electric powerplant, shown here in the 2006 Highlander Hybrid, combines parallel- and series-hybrid technology.
Even so, work on hybrids continued sporadically over the years, with interest in battery-electric and hybrid vehicles kicking into high gear with the advent of California's zero-emission vehicle mandate in the early 1990s. During this time, three distinct types of hybrid configurations were explored — the parallel hybrid, the series hybrid and a combination of both.
Honda's Integrated Motor Assist (IMA) system used in the Insight, Accord Hybrid and 2003-2005 Civic Hybrid typifies a parallel hybrid configuration, in which an internal combustion engine provides primary power with an electric motor supplying additional power during times of high demand. The electric motor never powers the car on its own.
A series hybrid uses an internal combustion engine solely to generate electricity for powering drive motors and not for vehicle propulsion. This configuration isn't used on its own in any production hybrid vehicle today.
Most hybrids — including those from Toyota and Ford — use a combination of parallel- and series-hybrid power so that they operate on internal combustion power most of the time, solely on electric power under certain conditions, and under both internal combustion and electric power in high-load conditions, such as intense acceleration or when climbing hills. Normally, non-hybrid vehicles are equipped with engines that offer much more power — and consequently consume much more fuel — than is needed most of the time in order to enable intense bursts of acceleration necessary for passing another vehicle on the highway or climbing a hill, for instance. Hybrids change this dynamic by using a small, fuel-efficient engine coupled with an electric motor to boost output when extra power is needed.
Unlike in older Honda Civic Hybrid models, which ran on both electric and gas power at all times, the 2006 model's IMA system runs on electric power alone at constant cruising speeds.
Unlike the IMA system in previous Honda Civic Hybrids, the fourth-generation system in the 2006 Civic Hybrid also operates on either internal combustion or electric power depending on driving circumstances. It does so differently than Toyota and Ford models by operating on electric power only under low-load conditions at cruising speed, rather than at low speeds.
Both hybrid configurations offer similar fuel economy and emissions advantages, with hybrids achieving either SULEV (Super Ultra Low Emission Vehicle) or AT-PZEV (Advanced Technology Partial Zero Emission Vehicle) emissions levels in California and certain Northeast states. These designations are specific to California and the Northeast states that have adopted its stringent emissions regulations. Federal designations do not use identifiers such as SULEV or PZEV, but rather classifications such as Tier 2/Bin 2, which is how a PZEV is identified on the federal level.
Lest you think these confusing acronyms are simply governmental bureaucracy, consider that a SULEV runs 90 percent cleaner than the average new vehicle today. Efficiency gets even better when adding zero evaporative emissions and a 150,000-mile emissions system warranty, the requisite upgrades to achieving AT-PZEV status.
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