Introduction to the E-Powertrain and Its Components

The electric powertrain is the electric drive system that powers electric vehicles. It consists of several key components, such as the battery, the electric motor and the energy management system.

This article presents the main components of the powertrain and illustrates a general scheme of an electric powertrain.

A vehicle’s powertrain comprises the main components responsible for generating and transmitting power to propel the vehicle. It serves as the mechanical heart of the vehicle, converting energy into motion.

A conventional powertrain relies on internal combustion engines powered by gasoline or diesel. In contrast, an e-powertrain uses electric motors powered by rechargeable batteries, resulting in zero tailpipe emissions and quieter operation.

Below is an overview of the main components of zero-emission powertrains and how they power the vehicle. There are three main types of energy source used to power a car: Batteries, fuel cells (hydrogen), and internal combustion (diesel and petrol). It is evident that batteries are the only renewable source of electrical energy. On the other hand, for the two other sources, it is emphasized that there is a process to obtain the electrical or mechanical energy (electrolysis in the case of the hydrogen source and synthesis in case of the internal combustion source).

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Main components of powertrain types. PEM Motion (2022)

An e-powertrain has 60% fewer components compared to an ICE vehicle.

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Electric powertrain inside the car. EV Reporter (2019)

Below is a schematic diagram of an e-powertrain, with the components in their conventional positions in an electric car. Note that the charging port is located near the edge of the car, from where the high and low voltage batteries are charged. These batteries in turn power the electric motor (and of course other components in the car), and the torque generated by the motor is distributed to the car’s wheels via the differential.

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General scheme of an electric powertrain. PEM Motion (2022)

Next, the components of the electric powertrain are presented.

Battery Pack (High Voltage and Low Voltage):

Made up of a large number of lithium-ion cells, the battery pack stores the energy needed to power the vehicle and provides a ‘direct current’ (DC) output.

DC/AC converter:

The battery packs provide direct current (DC) power, which is then converted to alternating current (AC) power, which is then sent to the electric motor.

Electric motor:

The electric motor converts electrical energy into mechanical energy, which is then transferred to the wheels via the transmission.

Charger:

Converts the alternating current received via the charging port into direct current and controls the amount of current flowing into the battery packs.

Differential:

The differential is a transmission system that allows individual drive wheels (the wheels that receive power) on the same axle to rotate at different speeds, particularly during vehicle manoeuvres such as turning.

Efficiency:

The efficiency of zero-emission powertrains can be assessed using a method called ‘well-to-wheel’.

Well-to-wheel is a method of assessing the efficiency and emissions of an energy source by considering its entire life cycle. Well-to-wheel emissions assess the greenhouse gas emissions generated throughout the entire life cycle of a fuel. This method is the most complete and accurate way to measure energy consumption and greenhouse gas emissions.

Efficiency losses, which include both well-to-tank and tank-to-wheel efficiencies, may also occur. Below you will find a diagram illustrating the different stages of these processes, starting with fuel extraction. Depending on the primary energy source, be it oil or electricity, the fuel is transformed through each of these stages. The fuel is then filled into the tank of a vehicle with an internal combustion engine (ICE) and used to power the vehicle. In contrast, once electricity has been generated, the energy is used at a charging point to recharge the battery of an electric vehicle. It is then used to power the vehicle.

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Well-to-Tank and Tank-to-Wheel process. PEM Motion (2023)

The table below shows the efficiency of fuels in different vehicle types. Primarily, from their extraction to their use in the vehicle to power its movement. It should be noted that direct electrification has the highest efficiency percentage in its production and storage (94%, well-to-tank) and the highest efficiency percentage in its use in the vehicle (82%, tank-to-wheel), giving an approximate total percentage from extraction to use in the vehicle of 77% (well-to-wheel). This makes it the most efficient option compared to all other energy sources for powering a vehicle.

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Well-To-Wheel efficiency overview of respective powertrains. PEM Motion (2022)

Next, the key characteristics of each method are explained:

Well-to-tank efficiency

Well-to-tank efficiency considers the losses and energy conversions that occur throughout the supply chain, including extraction, refining, transportation, and distribution.

It provides an assessment of how effectively the primary energy source is converted into a usable form of energy specifically for transport purposes, which can help to evaluate the overall efficiency and environmental impact of different energy systems or fuels.

Losses:

• Direct distribution of electricity to charging stations.
  • When electricity is transmitted from power plants to electric vehicle charging stations, losses can occur due to resistance in transmission lines, transformers and other components. These losses reduce the amount of energy available to charge electric vehicles.
• Conversion of electricity to hydrogen and transport/storage to refuelling stations.
  • In cases where electricity is converted to hydrogen for use as a fuel in certain vehicles, there are losses associated with the electrolysis process used to produce hydrogen and the subsequent transport and storage of hydrogen. These losses can occur at any stage and affect the overall efficiency of the energy pathway.
• Synthesis of diesel/petrol using electricity, CO2 and the Fischer-Tropsch process.
  • The process of synthesizing liquid fuels such as diesel or petrol using electricity and CO2 involves several steps, each of which involves energy losses. In addition, the Fischer-Tropsch process, a method of producing liquid hydrocarbons from synthesis gas, has its own inherent inefficiencies.

Tank-to-Wheel Efficiency

Tank-to-wheel efficiency takes into account several factors that affect energy conversion within the vehicle, including the efficiency of the engine or motor, transmission systems, drivetrain and other components involved in converting fuel energy or stored energy into propulsion.

It represents the actual energy efficiency experienced by the vehicle during operation and is an important metric for assessing the overall performance and environmental impact of different vehicles or transport technologies.

Losses:

• Drawing power directly from the battery to the electric motor.
  • When electrical energy is taken from the vehicle’s battery and sent to the electric motor for propulsion, losses can occur due to factors such as resistance in the wiring, motor inefficiencies and heat generation. These losses reduce the amount of usable energy reaching the motor and contribute to a reduction in overall efficiency.
• Conversion of hydrogen to electricity to power the electric motor.
  • In scenarios where hydrogen is used as a fuel for an electric vehicle, there are losses associated with the conversion of hydrogen to electricity through fuel cells or other methods. This conversion process may involve losses in efficiency, heat generation and other factors that affect the overall energy conversion efficiency of the vehicle.
• The liquid fuel (diesel/petrol) is burned in an internal combustion engine.
  • When liquid fuels such as diesel or petrol are burned in an internal combustion engine (ICE), there are losses due to the combustion process itself, as well as inefficiencies in converting the energy from the combustion into mechanical work that propels the vehicle. These losses include heat losses, friction losses and other factors that reduce the efficiency of the engine.

In summary, well-to-tank efficiency encompasses the entire energy supply chain, while tank-to-wheel efficiency focuses solely on vehicle energy conversion and use. Both are important in assessing the overall efficiency and environmental impact of transport systems.

Conclusion:

The electric powertrain is fast becoming the preferred choice for vehicle propulsion due to its many benefits, including increased energy efficiency, reduced environmental impact and lower maintenance costs.

The integration of key components such as the battery, electric motor, inverter and energy management system is critical to achieving optimal performance and a satisfying driving experience.

The future of transport is focused on the electric powertrain and its continuous technological evolution.