HEV, MHEV, FHEV, PHEV, BEV, Parallel, Series Hybrid, EFFV, EREV, REEV: Compare

HEV, MHEV, FHEV, PHEV, Parallel Hybrid, Series Hybrid, REEV, EREV, RexEV, BEV, EV – In depth analysis of Mild, Strong, Full Hybrid, Plugin Hybrid, Parallel Hybrid, Series Hybrid, Electrified Flexfuel hybrid, Battery Electric vehicle. Also commonly known as HEV, MHEV, FHEV, PHEV, BEV, EFFV, REEV, RexEV and EV.

The automotive landscape is undergoing a profound transformation, with hybrid and electric vehicles at the forefront of innovation. These technologies act as a transition between conventional Internal Combustion Engine (ICE) vehicles and fully electric vehicles (EVs) or battery electric vehicles (BEV) by combining different fuel sources or electric assistance to improve efficiency and reduce cost, emissions.

This article provides an in-depth, data-rich exploration of hybrid vehicle types (such as HEV, MHEV, FHEV, PHEV, BEV) categorized into ICE-Based and Electric Motor-Based systems.

Hybrid electric vehicles (HEV): HEV, MHEV, FHEV, PHEV, BEV, Parallel Hybrid, EFFV, EREV, RexEV

What are Hybrid vehicles?

Hybrid vehicles, by definition, combine two or more power sources (In this context it is fossil fuels, Bio Fuels, Syn fuels AND Electricity stored in batteries) .

Hence here we are discussing only on the category of Hybrid vehicles which combine fossil fuel or flex fuel or any other zero carbon fuel (like green hydrogen) based internal combustion engines (ICE) and electric motors for improved efficiency and reduced emissions. These are called as hybrid electric vehicles (HEV). They can be broadly classified into two categories:

• ICE-Dominant Hybrids – Primarily use an engine with electric assistance.
• Electric Motor-Dominant Hybrids – Primarily use electric motors with an ICE or fuel cell as a backup.

We here focus only on hybrid electric vehicles (HEV, MHEV, FHEV, PHEV, BEV)

Why do we need Hybrids? (vs. Immediate BEV Shift):

Why not simply transition to battery electric vehicles (BEV)? Hybrids persist because fully transitioning to low-cost, efficient, economical Battery Electric Vehicles (BEVs) faces current limitations:

• ICE based vehicles are low cost, economical, less maintenance cost, well matured technology, established fossil fuel supply chain infrastructure, known safety hazards
• Battery Cost: BEV batteries are still very expensive, just evolving, hindering low-cost BEVs.
• Range/Infrastructure: BEV range anxiety and charging infrastructure gaps remain concerns. Hybrids offer gasoline/fuel backup.
• Heavy duty, trucks, long range transportation is now only evolving on BEV, long path to go
• Charging Time: BEV charging takes longer than hybrid refueling.

What are other categories of hybrid vehicles?

Bi-fuel vehicles (Non-Electric Hybrids) do not use electric motors but run on two different fuel types, switching between them as needed. They have two separate fuel tanks and can operate independently on either fuel on the same engine. Examples are CNG-Petrol Bi-Fuel Vehicle and LPG-Petrol Bi-Fuel Vehicle. These vehicles are sometimes mistakenly called “hybrids,” but they technically fall under bi-fuel or dual-fuel vehicles rather than hybrid vehicles. However, they do offer efficiency and environmental benefits. We are not covering them here.

Hybrid Electric Vehicles (HEV): Combining ICE & Electric Motors

1️⃣ Micro Hybrid (Only Start-Stop System) – A conventional ICE Vehicle, typical, gasoline/petrol/diesel/flex fuel vehicle

🔹 ICE: ✅ Yes (Primary, 100% always runs)
🔹 Electric Motor: ❌ None (One Self start or Starter Motor)
🔹 Battery: ✅ Small (12V Lead Acid mostly, Only for basic vehicle functions)
🔹 Charging Method: Dynamo or Alternator coupled to the ICE or Regenerative braking
🔹 Can Drive Short Distances on Battery?: ❌ No Way

How It Works:

• Uses start-stop technology, turning the engine off when idle (e.g., at traffic signals) to reduce fuel consumption. No electric motor assists in propulsion.
• Level of hybridization is zero (in the scale of 1 to 5)

Examples: Most of the fossil fuel based ICE vehicles today on Road, across the Globe. Fuel Savings: No, high CO2 emission. Complexity: Low, Cost: Low, Maintenance cost: Low, Very matured technology.

2️⃣ Mild Hybrid Electric Vehicle (MHEV)

MHEV → Electric motor assists ICE but never drives wheels alone.

🔹 ICE: ✅ Yes (Primary, always runs)
🔹 Electric Motor: ✅ Small motor (only assists), low torque
🔹 Battery: ✅ 48V (mostly), Small (~0.4-1 kWh)
🔹 Charging Method: (Recuperation) Regenerative braking, No external charging
🔹 Can Drive Short Distances on Battery or Pure electric mode?: ❌ No

How It Works:

• The ICE is always running, but a small electric motor (up to 12 kw/16 hp) assists in acceleration.
• Regenerative braking stores energy in the battery, but the vehicle cannot drive on electricity or using the battery power alone.
• No external charging of the battery, only Fuel is required as source
• Level of hybridization is basic (1-2/5 in the scale of 1 to 5)

Examples: Maruti Suzuki Grand Vitara (Mild Hybrid), Audi A6 Mild Hybrid. Fuel Savings: 5-10%, Complexity: Low, Cost: Low, matured technology.

Semi-Hybrid remains ambiguous: Best to interpret as MHEV unless specific details indicate otherwise. Semi-Hybrid is not a formally defined term in the automotive industry. It’s often used for marketing over enhancements like adding more powerful motors for just moving the vehicle or larger batteries or electric system with high voltages.

Mild Hybrids are evolving: MHEVs are becoming more sophisticated with higher voltage systems and engine-off coasting, pushing the boundaries of “mild” hybridization.

Technically, Mild Hybrid is a subset of Parallel Hybrid architecture, representing a low level of electrification within that architectural framework.

3️⃣ Strong Hybrid (Full Hybrid) Electric Vehicle (FHEV)

HEV or FHEV- A broad category that includes both series and parallel hybrids, or a combination of both as Series-Parallel Hybrid offering varying degrees of electric assistance. Not a separate hybrid type but rather an umbrella term for hybrids that can operate in different modes. Can drive on electric power alone for short distances depending on its configuration (Series or Series-Parallel).

🔹 ICE: ✅ Yes (Primary, but electric motor can take over)
🔹 Electric Motor: ✅ One or more (supports independent driving)
🔹 Battery: ✅ Medium (~1-2 kWh)
🔹 Charging Method: On regenerative braking + Engine generator. External charging ❌
🔹 Can Drive Short Distances on Battery? or electric mode only? ✅ Yes (Limited, short range) depending upon the hybrid architecture

How It Works:

• Switches between ICE and electric motor automatically.
• At low speeds, the electric motor alone can drive the car.
• The ICE recharges the battery, eliminating the need for external charging
• Electric motor operates at much higher voltage and much bigger battery power (key difference with MHEV)
• Level of hybridization is medium, 3/5 (in the scale of 1 to 5)
• Examples: Toyota Prius, Honda City e:HEV

Fuel Savings: 20-40%, Complexity: Medium, Cost: Medium

Within Full Hybrids (HEVs), there are three key architecture configurations:

1️⃣ Series Hybrid (Electric-Driven with ICE as Generator)
2️⃣ Parallel Hybrid (ICE-Driven with Electric Assist)
3️⃣ Series-Parallel Hybrid (Combination of both modes for maximum efficiency)

Hybrid Architectures are Crucial: Understanding Parallel, Series, and Series-Parallel architectures is essential for a deeper understanding of hybrid technology and its capabilities.

Series Hybrid (Only Electric-Driven with ICE as Generator) Also known as EREV, REEV, RexEV

🔹 ICE: ✅ Yes (Acts as generator, does NOT drive wheels))
🔹 Electric Motor: ✅ Yes (Primary drives wheels)
🔹 Battery: ✅ Large
🔹 Charging Method: Regenerative braking, ICE generator, ❌ External Charging: No (Charges via ICE & regenerative braking)

How It Works:

• The ICE only generates electricity, while the electric motor drives the wheels.
• The ICE never directly powers the wheels, making this system similar to an electric vehicle with a backup generator
• ICE runs on any fossil fuel (gasoline/CNG) or Flex fuel
• High efficiency in stop-and-go traffic as ICE runs at optimal RPM for electricity generation.

Series hybrid is sometimes referred to as range-extended EV (REx EV), ensuring longer range without charging dependency. Other names for a series hybrid Extended-range electric vehicle (EREV), Range-extended electric vehicle (REEV), and Range-extended battery-electric vehicle (BEVx).

Examples: Nissan e-Power, BMW i3 REx. Fuel Savings: 40-60%, Complexity: Medium, Cost: High

Parallel Hybrid (ICE-Driven with Electric Assist)

✅ ICE: Yes (Primary, directly drives wheels)
✅ Electric Motor: Yes (Supports ICE, does not drive independently)
✅ Battery: Yes (Small to Medium)
❌ External Charging: No (Charges via regenerative braking & ICE)
❌ Can Drive Short Distances on Electric Power Alone: Mostly No (Electric motor only assists). Very limited electric drive alone in practical terms. (parking maneuvers, creeping forward at very low speeds, maybe inching in gridlock traffic).

🔹 How It Works:

• The ICE and electric motor work together to drive the wheels.
• The electric motor assists the engine but is not powerful enough to drive the car independently.
• Regenerative braking recharges the small battery.
• Simple, fuel-efficient, and cost-effective hybrid system
• Example: Toyota Camry Hybrid, Honda Accord Hybrid

Key Difference:

• Series Hybrid: The ICE never drives the wheels directly; the electric motor is primary. ✅
• Parallel Hybrid: The ICE is primary, and the electric motor only assists (no full-electric driving). ❌

Series-Parallel Hybrid (Combination of Both Modes for Maximum Efficiency)

Series-Parallel Hybrid is the most advanced and flexible form of HEV, as it combines both Series and Parallel modes for better efficiency.

✅ ICE: Yes (Can either generate electricity or drive wheels)
✅ Electric Motor: Yes (Can assist ICE or drive independently)
✅ Battery: Yes (Medium to Large)
❌ External Charging: No (Charges via ICE & regenerative braking)
✅ Can Drive Short Distances on Electric Power Alone: Yes (Electric motor can drive wheels directly)

🔹 How It Works:

• Combines the best of both Series and Parallel Hybrid systems.
• At low speeds, the car can drive on electric power alone (like a Series Hybrid).
• At higher speeds, the ICE can either directly power the wheels or generate electricity (like a Parallel Hybrid).
• A power-split device (eCVT or planetary gear) allows smooth switching between modes.

🔹 Examples: Toyota Prius, Hyundai Ioniq Hybrid, Ford Escape Hybrid

🔹 Most efficient hybrid system as it optimizes energy usage. Most complex and expensive due to advanced power-split transmission.

4️⃣ Plug-in Hybrid (PHEV): Designed for daily electric commutes (20-80+ miles)

🔹 ICE: ✅ Yes (Supports longer trips)
🔹 Electric Motor: ✅ One or more (stronger than HEV), pure electric mode driving
🔹 Battery: ✅ Large (~8-20 kWh)
🔹 Charging Method: Plug-in charging + Regenerative braking
🔹 Can Drive Short Distances on Battery, electric mode only?: ✅ Yes (< 100 km)

How It Works:

• A full hybrid, but with a much larger battery that allows for extended electric-only driving.
• A larger battery allows pure electric driving for < 80km or more depending upon the battery capacity (kwh), after which the ICE takes over.
• External charging is required, reducing fuel dependency.
• Level of hybridization is maximum (5/5 in the scale of 1 to 5)

Examples: BMW X5 xDrive45e, Toyota RAV4 Prime

Fuel Savings: 50-80%, Complexity: Very High, Cost: High, Maturity: Recent, evolving

5️⃣ Purely Electric Vehicles (EV) or Battery Electric Vehicles – BEV

Battery Electric Vehicles (BEVs) are not Hybrids

• Purely Electric – Not Hybrids: Battery Electric Vehicles (BEVs) are powered solely by electric motors and batteries 100%. They have no combustion engine at all.
• Not Part of Hybrid Categories: Therefore, BEVs do not fit into either the ICE-Based Hybrid or Electric Motor-Based Hybrid categories or any other hybrid categories. They are a distinct class of vehicle – purely electric vehicles. (EV)
• Important for Context: While not hybrids, BEVs are crucial in the broader discussion of vehicle electrification and are often compared to hybrid vehicles in terms of efficiency, emissions, and performance. They represent the ultimate of the “electric motor-based” propulsion spectrum, without any hybrid element.

6️⃣ Electrified Flex Fuel Vehicle (EFFV)

An Electrified Flex Fuel Vehicle (FFHV) is a hybrid electric vehicle (HEV) that combines two key technologies:

Flex Fuel Capability: the vehicle’s internal combustion engine (ICE) is designed to run on a blend of gasoline and ethanol, including gasoline, pure gasoline, and ethanol-rich blends like E85 (which can be up to 85% ethanol and 15% gasoline), or ethanol lean blends like E20, etc., Next it incorporates a hybrid electric powertrain system. “Electrified” in this context simply means it’s a hybrid electric vehicle (HEV). It’s not referring to some separate, additional form of electrification.

Degrees of Electrification in FFHVs: Just like regular hybrids, Electrified Flex Fuel Vehicles can come in different degrees of hybridization:

• Mild Hybrid Electrified Flex Fuel Vehicle (MHEV FFHV): This is a flex-fuel vehicle with a mild hybrid system. It will have enhanced start-stop, engine assist, and regenerative braking, but no electric-only driving capability.
• Full Hybrid Electrified Flex Fuel Vehicle (FHEV FFHV): This is a flex-fuel vehicle with a full hybrid system (strong hybrid). Yes, with electric-only driving capability for shorter range
• Plug-in Hybrid Electrified Flex Fuel Vehicle (PHEV FFHV): This is a flex-fuel vehicle with a plug-in hybrid system. Currently very rare, in the market than MHEV and FHEV FFHVs).

Conclusion: HEV, MHEV, FHEV, PHEV, BEV, Parallel Hybrid, EFFV, RexEV

The automotive landscape is complex and rapidly evolving. Understanding these distinctions – not just by degree of hybridization, but also by architectural approach and fuel source (including flex fuels) is essential for experts in fuels and automobiles to navigate the transition towards more sustainable and diverse transportation solutions.

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