MHEV vs PHEV – What’s the Difference?

MHEV and PHEV are both types of hybrid electric vehicles. The ‘P’ in PHEV stands for plugin. The ‘M’ in MHEV stands for mild. So essentially an MHEV is a mild hybrid and a PHEV is a plugin hybrid. To find out what is so mild about a mild hybrid, read on…

Comparison Table of Key Differences

Feature	MHEV	PHEV
Electric Only Drive Possible	NO	YES
Battery Voltage (typical)	48V	330V
Battery Capacity	0.5-1kWh	8-20kWh
Power (typical)	10-20kW	50-100kW
AC Outlet Charging	NO	YES

MHEVs (Mild Hybrid Electric Vehicles):

Mild Hybrid Electric Vehicles (MHEVs) are a type of hybrid vehicle that combines both an internal combustion engine (typically gasoline or diesel) and a small electric motor with a small battery pack. Unlike full hybrid or plug-in hybrid vehicles, MHEVs primarily rely on the internal combustion engine for propulsion, and the electric motor serves a supportive role to enhance efficiency and performance.

How MHEVs Work:

1. Start-Stop System: One of the key features of MHEVs is the start-stop system. When the vehicle comes to a stop, such as at a traffic light or in heavy traffic, the internal combustion engine shuts off automatically to save fuel and reduce emissions. The electric motor assists in restarting the engine quickly and smoothly when the driver releases the brake or accelerates.
2. Regenerative Braking: MHEVs use regenerative braking technology. When the driver applies the brakes or lifts off the accelerator, the electric motor acts as a generator, capturing some of the kinetic energy that would otherwise be lost as heat during braking. This energy is converted into electricity and stored in the small battery pack for later use. It is important to note that due to the small size of the battery, the amount of regenerative braking is severely limited (particularly compared to a PHEV)
3. Electric Assist: The electric motor in an MHEV can provide a mild electric boost to assist the internal combustion engine during acceleration or when climbing hills. This additional power reduces the strain on the engine, improving overall fuel efficiency and performance. This is particularly advantageous in stop start traffic. Where the motor assists to get the car moving and then regenerates back to a stop.
4. Battery (Energy Storage): MHEVs have a small battery pack, typically with a lower capacity compared to plug-in hybrids or electric vehicles. This battery stores the energy captured during regenerative braking. It is not typical for a mild hybrid to provide any electric only operation. The battery pack on mild hybrids is typically 48V, whereas a PHEV would be 300 volts.
5. Integrated Control System: The operation of MHEVs is managed by a sophisticated control system that seamlessly blends the internal combustion engine and the electric motor to optimize fuel efficiency and performance based on driving conditions.

PHEVs (Plug-in Hybrid Electric Vehicles):

PHEVs are a type of hybrid vehicle that combines an internal combustion engine (usually gasoline or diesel) with a larger battery pack and an electric motor. What sets PHEVs apart from MHEVs and traditional hybrids is their ability to be charged from an external power source, such as a standard electrical outlet or a dedicated charging station. Here are the key features and distinctions of PHEVs compared to MHEVs:

1. Electric-Only Mode:

• PHEVs can operate in electric-only mode for longer distances and at higher speeds compared to MHEVs.
• In electric-only mode, PHEVs produce zero tailpipe emissions, making them a cleaner option for short commutes and city driving.

2. Larger Battery Capacity:

• PHEVs have a larger battery pack compared to MHEVs, which allows them to store more electric energy for driving on electric power alone.
• This larger battery capacity enables PHEVs to provide a more substantial electric boost during acceleration and to rely on the electric motor for a more extended period.

3. External Charging:

• PHEVs can be charged from external power sources, either from a standard electrical outlet or a dedicated charging station. This allows drivers to replenish the battery’s charge without relying solely on the internal combustion engine or regenerative braking.
• Charging times vary depending on the charger type and the battery size but are generally much shorter than the time it takes to refuel a traditional vehicle.

4. Fuel Efficiency and Emissions:

• PHEVs typically offer higher fuel efficiency and lower emissions compared to MHEVs and traditional vehicles when driven in electric mode. This makes them an attractive option for environmentally conscious drivers.
• In hybrid mode (utilizing both the engine and electric motor), PHEVs still offer improved fuel efficiency compared to non-hybrid vehicles.

5. Extended Driving Range:

• PHEVs provide a greater overall driving range compared to purely electric vehicles (EVs) because they can rely on the internal combustion engine when the battery is depleted.
• This extended range eliminates concerns about “range anxiety,” making PHEVs a more versatile choice for long-distance travel.

6. Government Incentives:

• Many governments offer incentives and rebates to encourage the adoption of PHEVs, including tax credits, reduced registration fees, and access to carpool lanes. These government incentives have shifted more to full EVs (electric vehicles) more recently for 2024 .

Powertrains and Performance:

MHEVs (Mild Hybrid Electric Vehicles):

1. Engine Size:
   • MHEVs typically have a conventional internal combustion engine (ICE) with a size similar to that of traditional gasoline or diesel vehicles.
   • The engine in MHEVs is not downsized significantly, as its primary function is to provide propulsion and power the vehicle.
2. Electric Motor Capacity:
   • MHEVs have a relatively small electric motor, often referred to as a “mild” hybrid system.
   • The electric motor in MHEVs is designed primarily to assist the internal combustion engine during certain driving conditions, such as acceleration and deceleration.
   • The electric motor’s capacity in MHEVs is modest, usually providing only a limited amount of additional power to improve fuel efficiency and performance.
3. Acceleration:
   • MHEVs typically provide a mild improvement in acceleration compared to traditional gasoline or diesel vehicles.
   • The electric motor in MHEVs can provide a brief boost of additional power during acceleration, helping the vehicle achieve smoother and more efficient acceleration.
   • However, the acceleration boost in MHEVs is relatively modest, as the electric motor’s capacity is limited.
4. Top Speed:
   • MHEVs typically have a top speed similar to that of traditional gasoline or diesel vehicles.
   • The electric motor’s primary role in MHEVs is to assist with efficiency, start-stop functionality, and mild acceleration support, rather than achieving high top speeds.

PHEVs (Plug-in Hybrid Electric Vehicles):

1. Engine Size:
   • PHEVs also feature a conventional internal combustion engine (ICE) similar in size to that of MHEVs and traditional vehicles.
   • The ICE in PHEVs is used for primary propulsion and can operate independently or in conjunction with the electric motor.
2. Electric Motor Capacity:
   • PHEVs have a larger and more powerful electric motor compared to MHEVs.
   • The electric motor in PHEVs is capable of providing a substantial electric-only driving range and can assist the ICE during acceleration, enabling better performance.
   • PHEVs often have a greater electric motor capacity to support extended electric-only operation at higher speeds.
3. Acceleration:
   • PHEVs generally offer better acceleration performance than MHEVs due to their larger and more powerful electric motors.
   • The electric motor in PHEVs can provide a significant amount of instant torque, making PHEVs feel quite responsive and quick off the line.
   • When operating in electric-only mode, PHEVs can offer even more impressive acceleration since they rely entirely on electric propulsion
4. Top Speed:
   • Due to the heavy reliance on the electric motor element of the powertrain a PHEV vehicle may find it’s top speed limited by the maximum spinning RPM of the electric motor. This depends very much on the architecture, motor and final drive ratio.
   • Generally a PHEV powertrain is not any more capable at achieving a higher top speed than a more conventional, engine only equivalent

Fuel Efficiency and Emissions:

MHEVs (Mild Hybrid Electric Vehicles):

1. Fuel Efficiency Benefits:

• MHEVs are designed to improve fuel efficiency primarily in city and stop-and-go driving conditions, where internal combustion engines are less efficient.
• The key contributors to fuel efficiency in MHEVs are the start-stop system and regenerative braking:
  • Start-Stop System: MHEVs automatically turn off the internal combustion engine when the vehicle comes to a stop, such as at traffic lights. This eliminates idling, saving fuel.
  • Regenerative Braking: MHEVs capture and store some of the energy typically lost as heat during braking. This energy is converted into electricity and used to assist in propulsion, reducing the load on the engine and improving fuel economy.
• Overall, MHEVs offer modest fuel efficiency gains, typically in the range of 5-10% better fuel economy compared to their non-hybrid counterparts.

2. Emissions Benefits:
   • MHEVs help reduce emissions, particularly in urban areas where air quality is a concern.
   • The start-stop system in MHEVs reduces tailpipe emissions by preventing unnecessary idling.
   • Regenerative braking reduces the wear and tear on brake components and decreases the release of particulate matter and pollutants into the atmosphere.

A lot of people get confused between CO2 emissions (essentially fuel consumption) and clean air legislation (NOx – contributing to asthma and acid rain, Particulate Matter – soot!)

PHEVs (Plug-in Hybrid Electric Vehicles):

1. Fuel Efficiency Benefits:
   • PHEVs can provide significant fuel efficiency benefits, especially for those who have access to charging infrastructure and can drive shorter distances on electricity alone.
   • When operating in electric-only mode, PHEVs produce zero tailpipe emissions and consume no gasoline or diesel fuel, resulting in exceptionally high fuel efficiency (measured in miles per gallon of gasoline equivalent or MPGe).
   • PHEVs offer the potential for substantial fuel savings during daily commutes or short trips, as they can rely primarily on electricity for propulsion.
   • In hybrid mode (combining the internal combustion engine and electric motor), PHEVs still offer improved fuel efficiency compared to non-hybrid vehicles. The exact improvement depends on the driving conditions and the size of the battery.
2. Emissions Benefits:
   • PHEVs offer substantial emissions reductions, especially when operating in electric-only mode.
   • In electric mode, PHEVs produce no tailpipe emissions, contributing to improved air quality and lower greenhouse gas emissions.
   • The reduction in emissions is significant in areas with a high percentage of renewable energy sources powering the electric grid, as PHEVs indirectly benefit from cleaner electricity generation.
   • In hybrid mode, PHEVs still produce fewer emissions compared to traditional vehicles, thanks to the electric motor’s assistance and optimized engine operation.

Charging and Electric-Only Driving:

Charging Process for PHEVs:

The charging process for PHEVs involves replenishing the vehicle’s electric battery using an external power source. PHEVs are equipped with a charging port that allows them to connect to various charging devices, including:

1. Standard Electrical Outlets (Level 1 Charging): PHEVs can be charged using a standard household electrical outlet (120 volts) with the provided charging cable. This is the slowest charging option but is widely accessible.
2. Dedicated Charging Stations (Level 2 Charging): PHEVs can also be charged at dedicated charging stations using a Level 2 charger (typically 240 volts). Level 2 charging is significantly faster than Level 1 and is often found at public charging stations, workplaces, and in-home charging setups.
3. DC Fast Charging (Level 3 Charging): Some PHEV models support DC fast charging, which is the fastest charging option available. These stations are less common but can charge the PHEV’s battery to a significant level in a short amount of time.

The charging time for PHEVs depends on several factors, including the battery size, the charging power of the station, and the current battery state of charge. Level 1 charging is the slowest, taking several hours to fully charge the battery, while Level 2 and DC fast charging can significantly reduce charging times.

Impact on Daily Usage:

The charging process for PHEVs has several implications for daily usage:

1. Electric-Only Driving Range:
   • PHEVs offer an electric-only driving range, which is the distance the vehicle can travel solely on electricity before the internal combustion engine is engaged.
   • The electric-only range varies depending on the PHEV model but generally ranges from 20 to 50 miles (or more) on a single charge.
   • This range is sufficient for many daily commutes and short trips, allowing PHEV owners to use electricity for most of their driving needs.
2. Reduced Fuel Consumption:
   • When a PHEV is operated in electric-only mode, it consumes no gasoline or diesel fuel, resulting in zero tailpipe emissions and lower fuel costs.
   • PHEVs can achieve extremely high fuel efficiency (measured in miles per gallon of gasoline equivalent or MPGe) during electric-only operation, often surpassing the fuel efficiency of even the most efficient traditional hybrids.
3. Hybrid Mode for Longer Trips:
   • For longer trips or when the electric-only range is depleted, PHEVs can seamlessly transition to hybrid mode, utilizing both the internal combustion engine and the electric motor.
   • In hybrid mode, PHEVs still offer improved fuel efficiency compared to traditional vehicles, making them a versatile choice for various driving scenarios.
4. Charging Infrastructure:
   • The availability of charging infrastructure, both at home and in public places, can greatly affect the convenience of using a PHEV.
   • PHEV owners who can regularly charge their vehicles at home or at work have the advantage of maximizing electric-only driving and reducing reliance on the internal combustion engine.

Cost Considerations:

Initial Purchase Cost:

MHEVs (Mild Hybrid Electric Vehicles):

• MHEVs are generally more affordable than PHEVs due to their simpler hybrid systems and smaller batteries.
• The initial purchase price of an MHEV is often closer to that of a traditional gasoline or diesel vehicle, making them an attractive option for budget-conscious buyers.

PHEVs (Plug-in Hybrid Electric Vehicles):

• PHEVs typically have a higher initial purchase price compared to MHEVs and traditional vehicles.
• The larger battery, more advanced electric propulsion system, and additional features contribute to the higher cost.
• However, government incentives and rebates (discussed later) can help offset the higher upfront cost of PHEVs.

Maintenance:

MHEVs (Mild Hybrid Electric Vehicles):

• MHEVs generally have lower maintenance costs compared to traditional vehicles because of features like regenerative braking and the start-stop system:
  • Regenerative Braking: Reduces wear and tear on brake components, leading to longer brake pad and rotor life.
  • Start-Stop System: Reduces engine idling, extending the life of the engine and reducing oil consumption.

PHEVs (Plug-in Hybrid Electric Vehicles):

• PHEVs have similar maintenance advantages as MHEVs, thanks to their regenerative braking and start-stop systems.
• In addition, PHEVs may have slightly higher maintenance costs due to the complexity of their larger battery and electric motor systems.
• However, the potential for electric-only driving can reduce wear on the internal combustion engine, potentially extending its lifespan.

Potential Savings:

MHEVs (Mild Hybrid Electric Vehicles):

• MHEVs offer fuel savings compared to traditional vehicles, especially in urban and stop-and-go driving conditions.
• While the savings are significant over time, they may be less substantial compared to PHEVs due to the limited electric-only driving capability of MHEVs.

PHEVs (Plug-in Hybrid Electric Vehicles):

• PHEVs can provide substantial fuel savings, particularly for drivers who can regularly charge their vehicles and drive shorter distances on electricity alone.
• The electric-only driving range can result in significant reductions in fuel costs, making PHEVs an attractive choice for those with access to charging infrastructure.

Government Incentives or Rebates:

MHEVs (Mild Hybrid Electric Vehicles):

• Government incentives and rebates for MHEVs are less common than those for PHEVs and electric vehicles (EVs).
• Some regions may offer smaller incentives for MHEVs, such as tax credits or rebates, but they are generally not as generous as those for PHEVs and EVs.

PHEVs (Plug-in Hybrid Electric Vehicles):

• PHEV buyers often benefit from various government incentives and rebates designed to promote electrified vehicle adoption. These incentives can include:
  • Federal Tax Credits: In the United States, PHEV buyers can qualify for federal tax credits that can amount to several thousand dollars, depending on the vehicle’s battery capacity.
  • State and Local Incentives: Many states and local governments offer additional incentives, such as rebates, tax credits, reduced registration fees, or access to carpool lanes.
  • Utility Company Incentives: Some utility companies offer incentives to PHEV owners, including reduced electricity rates for charging during off-peak hours.
• These incentives can significantly reduce the initial purchase cost of a PHEV and accelerate the payback period through fuel savings.

Popular Models and Manufacturers:

MHEVs (Mild Hybrid Electric Vehicles):

As you may be aware I am a UK engineer and so this list is skewed to UK models. I recommend if you are interested in finding a mild hybrid search autotrader and set the fuel type to hybrid in the advanced search filter options. One key buying decision that may sway you to a mhev is they often have a manual transmission option, click here to find out more! Unfortunately with PHEV buyers are forced to drive automatic, due to the complexity of the PHEV powertrain rendering manual transmissions impossible.

Here is a quick list to whet your appetite, as you can see all manufacturers have jumped on the MHEV ‘bandwagon’!

• Audi A6 Mild Hybrid
• Audi Q8 Mild Hybrid
• Mercedes-Benz E-Class Mild Hybrid
• Mercedes-Benz GLE Mild Hybrid
• Land Rover Range Rover Evoque Mild Hybrid
• Land Rover Range Rover Sport Mild Hybrid
• Volvo XC60 Mild Hybrid
• Ford Kuga Hybrid
• Toyota C-HR Hybrid
• Toyota Corolla Hybrid
• Honda CR-V Hybrid
• Kia Niro Self-Charging Hybrid
• Hyundai Kona Hybrid
• Mazda6 Mild Hybrid
• Vauxhall Grandland X Hybrid

PHEVs (Plug-in Hybrid Electric Vehicles):

A similar list of PHEVs on offer:

• Mitsubishi Outlander PHEV: The Mitsubishi Outlander PHEV was one of the early pioneers in the PHEV segment in the UK, offering both electric and petrol power for flexibility. This is my car of choice and I enjoy the economy, size and tech that is on offer. Unfortunately Mitsubishi are no longer available in the UK.

• Volvo XC40 Recharge Plug-in Hybrid
• Volvo XC90 Recharge Plug-in Hybrid
• Vauxhall Grandland X Hybrid4
• Ford Kuga Plug-in Hybrid
• BMW 3 Series Plug-in Hybrid
• BMW 5 Series Plug-in Hybrid
• Mercedes-Benz A-Class Plug-in Hybrid
• Mercedes-Benz C-Class Plug-in Hybrid
• Audi Q5 TFSI e
• Porsche Cayenne E-Hybrid
• Peugeot 3008 Hybrid
• Peugeot 508 Hybrid
• Hyundai Ioniq Plug-in Hybrid

Future Trends and Developments:

The future of hybrid technology is expected to be dynamic and innovative, with several key trends and developments anticipated over the coming years:

1. Increased Electric-Only Range: Hybrid vehicles, particularly PHEVs, are likely to see improvements in their electric-only driving range. Advancements in battery technology will enable longer distances to be covered solely on electricity.
2. Higher Efficiency: Ongoing research and development efforts will focus on enhancing the overall efficiency of hybrid powertrains. This includes optimizing internal combustion engines, electric motors, and control systems to achieve greater fuel efficiency and reduced emissions.
3. Weight Reduction: Automakers will continue to explore lightweight materials and designs to reduce vehicle weight, improving overall efficiency and performance.
4. More Compact and Integrated Systems: Future hybrid systems may become more compact and seamlessly integrated into vehicle platforms, allowing for greater design flexibility and space savings.
5. Advanced Regenerative Braking: Regenerative braking systems will become even more efficient at recovering and storing kinetic energy, further improving fuel economy and reducing wear on braking components.
6. AI and Advanced Driver-Assistance Systems (ADAS): Integration of artificial intelligence and ADAS technologies will enable smart hybrid systems to adapt to driving conditions and driver behavior, optimizing power delivery for maximum efficiency.
7. Enhanced Charging Infrastructure: As hybrid and electric vehicles become more popular, the charging infrastructure will continue to expand, making it easier and more convenient for owners to charge their vehicles.
8. Reduced Cost: As production volumes increase and technology matures, the cost of hybrid vehicles and their components is expected to decrease, making them more accessible to a broader range of consumers.
9. Hybridization in Diverse Vehicle Segments: Hybrids will not be limited to specific vehicle types. We can expect to see hybrid technology applied to a wide range of vehicles, from sedans and SUVs to trucks and commercial vehicles.
10. Hydrogen Fuel Cell Hybrids: Hydrogen fuel cell hybrid vehicles, which combine fuel cells with electric propulsion, may gain more prominence as hydrogen infrastructure develops.
11. Sustainability and Emissions Standards: Increasingly stringent emissions regulations will continue to drive the development of hybrid technology, as automakers strive to meet environmental targets.

Before You Go…

Check out these other Carbant.com articles!

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