Text by James M. Flammang
When hybrid cars first appeared on the automotive scene, early in the current century, their arrival wasn’t always greeted warmly. Environmentally-minded drivers praised their promise of greater fuel economy and reduced tailpipe emissions. Some critics considered the hybrid powertrain a gimmick rather than a true step forward, predicting that they wouldn’t last long. True believers in gasoline engines – especially those who favored muscular V8s – adopted attitudes ranging from skepticism to annoyance, if not anger.
What is a Hybrid?
Hybrid History
Considering that two powerhouse Japanese brands led the hybrid charge, though, most Americans had to wonder if there might be more to this new phenomenon than the critics insisted. All the more so when Ford entered the picture with a hybrid version of its Escape compact crossover, and other domestic brands gradually began to join the gasoline/electric parade.
Hybrids Today
Today, despite a few firm holdouts, most automakers offer a hybrid model of some sort. Electric vehicles (EVs) might have captured public attention lately, but hybrid electric vehicles (HEVs) have proven to be far more than a passing fad.
Hybrid Concept
The basic hybrid principle is quite simple. A hybrid promises greater fuel-efficiency and fewer emissions than a similar gasoline-engine model because it makes use of energy that would otherwise be wasted.
Hybrid System
Every hybrid vehicle on the market contains three elements:
- An internal-combustion engine (ICE) that runs on gasoline
- A large battery, known as the traction battery (separate from, and larger than, the low-voltage battery found in all vehicles)
- At least one electric motor. More sophisticated systems, aiming at improved performance, tend to incorporate an additional motor. Electric motors are compact, produce abundant torque output for energetic acceleration, and have only one moving part.
An electronic controller coordinates the potential outputs provided by each element of the hybrid system. Drivers never need to take any particular action related to the hybrid powertrain. It’s entirely automatic. A low-voltage auxiliary battery provides energy to start the vehicle and power accessories.
Hybrid Types
Electronic and constructional details vary among hybrid powertrains, but basic operation – and the driving experience – are similar. What varies between the two hybrid versions – Full and Mild – is the manner in which electric power works with the gasoline engine to get the most out of each element.
Full Hybrid (Strong Hybrid)
In a regular (full) hybrid, the electric motor alone can propel the car at lower speeds (typically, from a standstill up to 30 mph or so). At that point, the gasoline engine automatically “kicks in,” taking over at least part of the propulsion duties. It’s often called a “parallel” hybrid because the two energy-producing components can function at the same time. Parallel hybrid layouts connect the engine and electric motor to the car’s wheels via mechanical coupling, thus driving them directly.
Exactly when that gasoline/electric transition takes place depends upon the battery’s current charge level and the degree of power demanded by the driver. Push the accelerator pedal hard, and the gas engine starts soon after takeoff, to provide additional power for quicker acceleration or hill-climbing. Go easy on the pedal and the gasoline engine remains idle for a longer period, ensuring less fuel usage. The controller automatically determines whether gasoline or electric power (or both) will be most efficient for the immediate task requested by the driver.
As a rule, full hybrid vehicles can run steadily on electric power alone, for short distances. More often, the gas engine and the electric motor(s) operate together, jointly.
If you’re already moving forward but need a quick burst of power, such as merging onto an expressway, a parallel hybrid will almost certainly activate the gasoline engine. But when you’re stopped at a red light and it turns green, the control computer might first select the electric motor.
Mild Hybrid
A mild hybrid (MHEV) operates differently, led by the fact that it can never operate on electric power alone. Instead of moving out from a standstill under battery power, the mild-hybrid system starts the idle gasoline engine as soon as the driver releases the brake pedal and moves to the accelerator. Because it needs to produce less electricity, the MHEV battery can be smaller, working with a low-output 48-volt electric motor. Because its system is less complex, a mild hybrid tends to cost considerably less than an otherwise comparable full hybrid–but its fuel economy benefit also is lower.
Regenerative Braking
Both full and mild hybrids make use of regenerative braking. That system makes use of the car’s momentum, whenever it slows down or coasts, to produce energy that recharges the battery, instead of being wasted as heat. Essentially, it converts the mechanical (kinetic) energy of the moving vehicle into electrical energy that helps keep the battery sufficiently charged.
Neither type of hybrid has a provision for plugging into an electric outlet for charging. Traction batteries, usually lithium-ion, are stacked within a secure container near the rear axle, thus well-protected during a collision.
Series Hybrid
Several manufacturers have offered a full hybrid in series (not parallel) configuration. Often called a Range Extender system, it was used in the original Chevrolet Volt and was featured in a version version of BMW’s now discontinued i3. In a series hybrid, the electric motor handles most of the work of driving the wheels, using power from either the battery pack or a generator run by the gasoline engine. Transition between the two sources tends to be seamless, but they cannot operate together.
Continuously Variable Transmission
In any hybrid, the gasoline engine can be smaller than would be necessary in a comparable non-hybrid model. Yet, it can achieve an overall horsepower rating comparable to that of a gasoline-only car, further increasing overall efficiency. Instead of the familiar gear-type automatic transmission, hybrids often employ an electronic continuously variable transmission (eCVT).
City Driving
It’s important to note that, unlike gas-only vehicles, hybrid fuel economy is normally improved more in city driving than at higher speeds or on long highway trips. Why? Because the electric motor has a greater impact on efficiency at lower speeds.
Hybrid Cost
Although hybrids used to be more expensive than their gas-only counterparts, that’s not necessarily the case anymore. Even if the purchase price is higher, both manufacturers and advocates advise that any extra cost can be recouped over time, simply because the hybrid consumes less fuel. Replacement hybrid batteries are definitely expensive, but have generally proven to be reliable for long periods.
First Hybrids
Back at the inception of hybrids in the U.S., Honda took the lead with its 2000 Insight two-seater: a mild hybrid with an Integrated Motor Assist (IMA) system. Like subsequent mild hybrids, at standstill a customary electric motor started the gas engine, boosted acceleration, then shut off the gas engine when the car stopped again.
Toyota Prius
Because the first Insight seated only two, it wasn’t a candidate for the family market. That role was undertaken soon after the Insight’s debut by the Toyota Prius sedan, which had been sold in Japan since 1997. Ford took the concept a bit further by offering its 2005 Escape compact crossover in both regular and hybrid form.
Honda Hybrids
Honda improved its IMA for the 2006 Civic Hybrid sedan. Unlike the previous two-seater, it could coast without aid from the gas engine, but still couldn’t run solely on electricity. Before long, the word “hybrid” came to mean any small, fuel-efficient hybrid-powertrain sedan. One by one, most other automakers turned to hybrids over the next decade or so.
Hybrid Models
After launching a hybrid version of its compact Saturn Vue in 2007, General Motors largely backed away from hybrids–until, surprisingly, the recent arrival of the Chevrolet Corvette E-Ray. Stellantis (formerly Chrysler) also has offered only a handful of gasoline/electric models, notably the Pacifica minivan. Today, a number of luxury brands are producing hybrid models. Nearly all Toyota models can have a hybrid powertrain, either standard or optional. Toyota reports that in 2024, 43 percent of U.S. sales were “hybridized” models.
Hybrid Issues
Hybrids do have (or used to have) a few demerits. Drivers of earlier mild hybrids typically felt a slight shudder (sometimes not so slight) as the gasoline engine kicked in at a stoplight. Modern models aren’t as likely to annoy. Regenerative braking can feel a bit odd if you’re not accustomed to it – but again, less so today. Like other vehicles with continuously variable transmissions, the hybrid’s eCVT tends to transmit a droning sound from the gas engine. Under certain conditions, that gas engine may sound like it’s revving loudly, in an unrestrained manner.
In everyday operation, all full hybrids aren’t quite equal. Neither are all mild hybrids. How the transition between electrical and mechanical power sources takes place varies a bit between manufacturers.
Plug-in Hybrids
In recent years, Plug-in Hybrids (PHEV) have caught the attention of shoppers. As the name suggests, they can be plugged into an electrical outlet either at home or at a charging station, like an EV, to charge the battery. That ability increases their level of efficiency, boosting fuel economy even higher.
Hybrid Availability
According to the Department of Energy, in 2025 about 140 hybrid vehicle models are available in the U.S. Comparisons are difficult, though, because each manufacturer appears to identify and count its hybrids differently. Audi, for instance, is listed with 15 models, BMW 26, Land Rover and Toyota each 11, and Mercedes-Benz a whopping 36.
An additional 26 models are plug-in hybrids, while dealers offer a total of 118 distinct EV models.
Shoppers can compare costs between HEV and non-hybrid models using the “Can a Hybrid Save Me Money?” tool at FuelEconomy.gov.
Listen to the Car Stuff Podcast
Hybrid Pictures
Click below for enlarged images