Hybrid electric vehicles (HEVs) are a crucial technology in transport’s road to net zero. They significantly improve a vehicle parc’s efficiency, reduce its emissions, and deliver a seamless driving experience for many consumers – all without demanding a significant change in driving patterns.
To fully understand what a HEV is and what it does, however, we need to look at how their powertrains work in detail.
Hybrid powertrains at a glance
A hybrid powertrain combines an internal combustion engine (ICE) with an electric motor and a high-voltage battery to drive the wheels. By switching between power sources, the system optimizes efficiency and performance.
Energy is continuously managed and redistributed - through regenerative braking, battery storage, or direct engine power - creating a tightly integrated system designed for efficiency.
Hybrids can achieve optimal efficiency in all driving conditions
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Internal combustion engine (ICE)
At the heart of many hybrid systems is a downsized, highly efficient combustion engine, often operating using designs that trade out power for fuel economy – such as an Atkinson cycle engine. It provides power at higher speeds and can also support battery recharging when needed, maintaining range and flexibility.
Read more about how hybrids can speed up decarbonization.
Electric motor and generator
The ICE is supported by an electric motor that delivers instant torque for smooth acceleration and efficient low-speed driving. In many systems, the motor is directly mounted onto the engine’s crankshaft and so can double as a generator for the vehicle’s battery. This dual functionality improves powertrain efficiency without increasing energy demand.
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Power split device / transmission
Hybrid vehicles use specialized transmissions or power split devices, often based on planetary gear sets, to determine how power is delivered to the wheels. They also need to often engage in complex real-time calculations to determine the moment-to-moment power split between the electric motor and the engine, which is mediated by the transmission system.
As a result, a hybrid transmission plays a key role in deciding whether the vehicle runs on the engine, the electric motor, or both - ensuring optimal efficiency in all driving conditions. Often, a HEV’s electric motors are directly built into hybrid transmissions, reducing space and further boosting efficiency.
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Traction battery
Alongside the traditional car battery, which powers systems like vehicle lights and air conditioning, a hybrid features a high-voltage battery designed to store the electrical energy used to power the motor. In modern days, these batteries often use materials like lithium-ion that are used in battery electric vehicle (BEV) batteries, which are designed for frequent charge and discharge cycles, supporting both electric driving and energy recovery.
Read more about vehicle types with what is a PHEV?
Power electronics and inverter
The power control unit acts as the “brain” of the hybrid system, managing energy flow between the engine, motor, and battery. At its core sits the inverter - a series of high-speed switches working in harmony to regulate the flow of power between the generator and electric motor.
Operating similarly to a computer processor, the inverter precisely regulates power conversion and delivery and converts direct current (DC) from the battery to alternating current (AC) for the wider vehicle. The inverter also enables communication between the vehicle and the battery, ensuring the system operates efficiently and in sync.
Today, many other power-related systems are bundled next to the inverter in all-in-one power electronics modules. These include fast-charging systems, cooling and thermal management units, DC/DC power converters, and power distribution systems.
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Regenerative braking system
Rather than wasting brake energy as heat, hybrid systems recover kinetic energy during braking and convert it into electricity. By turning the braking system into a generator, braking energy can be stored in the battery for later use, improving vehicle efficiency and reducing fuel consumption.
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A fully integrated system
A hybrid powertrain is more than the sum of its parts - it is a carefully orchestrated system where mechanical engineering meets advanced electronics and intelligent control.
From the combustion engine to the inverter and integrated power electronic module, each component works in harmony to deliver performance, efficiency, and practicality. As hybrid technology evolves, greater integration and smarter energy management will continue to support lower-emission mobility at scale. Take a look at Horse Powertrain’s portfolio of integrated systems to see how we are supporting the industry in meeting this challenge.
