Quick Facts About Mild Hybrid Vehicles
- A mild hybrid vehicle drives on gas with a small electric battery feeding a low-output, 48-volt electric motor.
- The fuel savings from a mild hybrid system are modest.
- A mild hybrid system usually improves acceleration from a standstill.
Honda beat rivals to the punch in marketing the first mainstream mild hybrid electric vehicle (MHEV) in the United States: the 2000 Honda Insight. A quarter century later, there are now dozens of mild hybrid vehicles available in the U.S. market.
As carmakers broaden their offerings of electrified models, MHEV technology has provided a comparatively inexpensive solution for those shopping for vehicles. Consequently, such unlikely vehicles as the 2008 Chevrolet Silverado and 2008 GMC Sierra pickups boasted early MHEV systems. This begs the question: What constitutes a mild hybrid vehicle? We will answer that question, as well as present a short MHEV history and a list of some current MHEV models as you read on. Use the links below to skip forward in the article.
- What Is a Mild Hybrid?
- How Does a Mild Hybrid Work?
- Early History of Mild Hybrids
- Mild Hybrid Tech in More Cars
- Types of Hybrids
What Is a Mild Hybrid?
A mild hybrid system shoulders some of the electric load of the gasoline-fueled internal combustion engine (ICE) using a small electric battery feeding a low-output electric motor. These are most commonly referred to as 48-volt systems. Although it can’t power the car on its own, the 48-volt MHEV system usually starts the car and also brakes or slows it. During the braking process, the MHEV recovers the kinetic energy created as the vehicle slows.
This is called regenerative braking. That energy is transformed into electricity and stored in the MHEV’s battery. The MHEV system then draws on that stored energy to help the gas engine accelerate the car from a standstill. Therefore, the vehicle uses less fuel when accelerating from a stop, resulting in a modest gain in fuel economy.
Essentially, an MHEV system employs some or all of the following components to reduce the load on the ICE, lowing fuel consumption:
- Modest electric motor
- Small battery pack
- Regenerative braking system
- More powerful electrical system
Mild Hybrid vs. Traditional Hybrid
A traditional hybrid (or HEV) works in tandem with the ICE and can even power the vehicle for short distances at lower speeds on its own. This is because of its larger battery array and bigger motor. An MHEV, however, can’t power a vehicle on its own due to its aforementioned smaller battery and motor. In other words, the MHEV system’s role is much less substantial than that of an HEV. This is reflected in the modest boost an MHEV system provides on overall fuel economy versus the significant increase delivered by an HEV system. However, incorporating an MHEV system into a vehicle costs less than an HEV system.
Mild Hybrid Benefits
If you want to dip your toe into the sea of electrified vehicles, an MHEV is a sensible place to begin. Here are the benefits you can expect with an MHEV:
- Modest increase in fuel economy
- Slight decrease in tailpipe emissions
- Small increase in acceleration from a stop
- More affordable than hybrids or electric cars
- No need for charging the battery
Is a Mild Hybrid Worth It?
Mild hybrid systems are gaining in popularity, especially among European brands. However, more often than not, the primary MHEV benefit is keeping systems like the climate control functioning when the engine automatically shuts down at a red light. That, and providing a little extra boost during acceleration from a standstill. MHEV fuel savings are more of an added value to the other advantages. On the other hand, a mild hybrid system only modestly adds to a vehicle’s purchase price. We suspect that many drivers of such vehicles don’t even realize there is an MHEV assuming some of the engine’s workload. We wouldn’t include a mild hybrid system on our must-have list when car shopping; however, neither would we be disappointed to learn the car of our dreams has one.
How Much Does a Mild Hybrid Improve Gas Mileage?
In a controlled study of the effect of a mild hybrid system on fuel economy published in December 2021 in Case Studies in Thermal Engineering, the results showed an mpg improvement of about 8%. Some carmakers claim a savings of up to 20%. Odds are, it’s somewhere in between.
How Does a Mild Hybrid Work?
Unlike an HEV, which can travel short distances at low speeds solely on electricity, a mild hybrid never operates as an electric vehicle (EV). Instead, it allows the ICE to shut off when coasting or braking, eliminates the belt drives that an ICE requires to run certain components, and powers the more robust electrical architectures that modern vehicle technologies require.
As a result, a mild hybrid can be up to the aforementioned 20% more fuel-efficient than the same vehicle without this type of powertrain.
What Happens When a Mild Hybrid Battery Runs Out of Charge?
An MHEV battery depleting its entire charge is highly unlikely because it is constantly being charged by the combustion engine and regenerative braking system. However, if, for some reason, the battery runs out of juice or fails, the combustion engine simply picks up the slack.
Early History of Mild Hybrids
Honda beat General Motors to MHEV technology by adopting it for its groundbreaking 2-seat hybrid, the Insight. Honda’s Integrated Motor Assist (IMA) system used an electric motor placed between the engine and transmission. It started the car’s ICE, assisted with acceleration from a stop, and shut off the ICE when the Insight was stopped in traffic or at an intersection.
Honda improved its IMA technology with the debut of the 2006 Civic Hybrid, which could coast without the ICE turned on. However, because the system still couldn’t power the car solely on electricity like the Toyota’s Hybrid Synergy Drive in the Prius could, the Civic Hybrid remained a mild hybrid.
At about the same time the Civic Hybrid hit the market, General Motors rolled out the Saturn Vue Green Line. It was a plastic-clad compact crossover SUV equipped with a belt alternator starter (BAS) system assisting a 2.4-liter 4-cylinder engine. An electric motor, a 36-volt nickel-metal hydride battery, and a regenerative braking system improved fuel economy by turning the engine off when the SUV was stopped, while assisting with acceleration from a stop.
Ultimately, the Vue Green Line’s powertrain technology gave rise to eAssist, which became standard in the 2012 Buick LaCrosse and, in 2013, the Buick Regal. Making a mild hybrid powertrain standard in a car was an odd move, and GM was ahead of the curve.
More than 10 years later, many car companies started adopting standard mild hybrid solutions to improve fuel economy. Also, technology has evolved from the integration of 48-volt battery systems to improvements in regenerative braking. Additionally, mild hybrids these days support advanced driver technology, leading to improved performance and safety while driving.
Mild Hybrid Tech in More Cars
General Motors is out of the hybrid business, having phased out its mild hybrid eAssist system with the 2013 Chevy Malibu. However, other carmakers have picked up MHEV technology along the way. And some, like BMW, Volvo, and Audi employ it across the majority of their models.
BMW
BMW has aggressively pushed the MHEV envelope, using the technology in more than 50 models spread across its entire model landscape.
Land Rover
Land Rover powers its entire model lineup using engines with an MHEV system. If the MHEV assistance isn’t enough, Land Rover offers some models as fully electric (EV) or plug-in hybrid (PHEV). For example, the Range Rover has both.
Mercedes-Benz
Another carmaker offering an MHEV system across a wide swath of its model lineup, Mercedes-Benz offers SUVs, sedans, and coupes with some electric boost.
Jaguar
The Jaguar F-Pace compact SUV utilizes an MHEV system.
Ford
Pick the Ford Escape Hybrid to get an MHEV in addition to the conventional hybrid (HEV) or plug-in hybrid (PHEV) setup.
Volvo
You can check out MHEVs among Volvo models like the XC60 and XC40 SUVs, as well as the S90 sedan.
Ram
Ordering your Ram 1500 with the V6 gives you an MHEV system.
Audi
Most Audi models offer an MHEV system, beginning with the A3 and running up through the A8.
Types of Hybrids
There are three basic types of hybrid systems. We’ve touched on two of them already; however, for clarity, we briefly describe each below. We’ve also added a fourth hybrid type that’s rarely talked about because it isn’t currently available on production models.
Hybrid (HEV)
A full hybrid system combines an ICE with a battery and electric motor to share the duties of propelling a vehicle. Technically, this is called a parallel hybrid because the ICE and HEV components operate alongside one another. It’s possible for most such HEV systems to propel the vehicle for short distances at low speeds on its own. However, the vehicle’s drive wheels usually receive power from the ICE, or the ICE and HEV system combined. The HEV system is self-contained, feeding the battery with electric output from the ICE’s generator, as well as through the regenerative braking system.
Mild Hybrid (MHEV)
An MHEV is a less grand and more affordable ICE-and-hybrid setup producing less dramatic fuel savings. It’s still a combination of the ICE, a battery, and an electric motor, but the battery and motor are much smaller. Where a full HEV can send power directly to the wheels, an MHEV instead provides a boost of energy to the engine when accelerating from a standstill. It can also manage some of the load from power-hungry systems like air conditioning. As with an HEV system, an MHEV system’s battery is charged through the ICE and regenerative braking.
Plug-in Hybrid (PHEV)
A PHEV can usually propel a vehicle on electric power alone for roughly 25-50 miles. When the battery depletes, the ICE kicks in to power the wheels. Although a PHEV battery can draw a charge from the ICE and regenerative braking system, it needs to be recharged by plugging into an outside source. This plug-in capability, as well as a larger battery array than an HEV, is what allows a PHEV to travel on electric-only power.
Range Extender Hybrids
Think of range extender hybrids as full EVs in which the vehicle relies solely on battery power to spin the wheels but provides a small ICE to recharge the battery when it runs out of juice. That is, the ICE acts like a generator to create the electric current needed to keep the motor running and recharge the battery. The Chevy Volt was a range extender hybrid.
Editor’s Note: This article has been updated for accuracy since it was originally published. Christian Wardlaw contributed to this report.
