Hybrid powertrains are designed to make the most of every unit of energy. By combining an internal combustion engine with an electric motor, battery, and sophisticated control systems, they can switch between different sources of power depending on driving conditions.
But how do you know whether a hybrid powertrain is delivering the efficiency, performance and emissions benefits it promises? It all comes down to testing.
Testing every part of the powertrain
Testing begins long before a hybrid vehicle reaches the road. During powertrain development, engineers need to understand how the individual components perform, as well as how they work together as a complete system.
Engine dynamometers can measure the performance of the internal combustion engine, while dedicated equipment can test electric motors, inverters, transmissions, and other components.
Unlike conventional internal combustion powertrains, hybrid systems also need to be tested across both mechanical and electrical operating modes. This means measuring parameters such as speed, torque, electrical power, and energy consumption with a high degree of accuracy.
The aim of testing not just to confirm whether each component works. It is to understand how efficiently the complete powertrain converts energy into motion.
Read more about what makes up a hybrid powertrain?
Measuring power in both directions
One of the defining characteristics of a hybrid powertrain is its ability to repurpose energy that would be wasted in a traditional combustion vehicle.
During acceleration, a hybrid’s electric motors energy stored in the battery to assist the engine. To provide the charge for the battery, a hybrid powertrains motors reverse operations to act as electric generators: the starter-generator mounted to a crankshaft can tap into some of the engine’s rotational energy directly, and the traction motor can be used to rapidly convert a vehicle’s kinetic energy into electrical energy through regenerative braking.
This means a hybrid powertrain cannot be fully tested using equipment designed only to measure an engine producing power. Engineers need “four-quadrant” dynamometers capable of both applying a load and driving the powertrain, allowing them to recreate acceleration, deceleration, and regenerative braking.
Testing these different operating modes helps engineers understand how well the system captures and reuses energy, ultimately contributing to improved fuel efficiency.
After laboratory testing is complete, powertrains must also be evaluated on roads and test tracks
Read more with our guide to hybrid powertrain layouts.
Creating controlled conditions
For test results to be useful, they need to be repeatable. Laboratory testing allows engineers to control factors such as temperature, altitude, speed, and load, creating consistent conditions so that changes to the powertrain can be measured accurately.
Specialist facilities can even simulate different altitudes and environmental conditions, allowing engineers to understand how a powertrain behaves beyond the conditions of the test facility.
Battery testing is equally important. Because battery performance can vary depending on its state of charge, temperature, and age, controlled battery simulation can provide a consistent source of electrical power during development. This allows engineers to compare results from one test to another without changes in the battery influencing the outcome.
Read more about how hybrid transmissions work.
From laboratory testing to the real world
Laboratory testing provides precision, but a vehicle will not spend its life on a test bench.
Powertrains must also be evaluated on roads and test tracks, where changing traffic, gradients, temperatures, and driving styles create conditions that are tricky to replicate completely in a laboratory.
Engineers can use Portable Emissions Measurement Systems (PEMS) to measure emissions during real-world driving, complementing controlled laboratory testing and helping manufacturers assess performance against Real Driving Emissions (RDE) requirements.
Ultimately, testing a hybrid powertrain is about more than measuring horsepower or fuel consumption. It is about understanding how the engine, electric motor, battery, inverter, and control systems interact across a variety of different operating conditions.
As hybrid powertrains continue to evolve, increasingly sophisticated testing will be essential to ensure that every component works together efficiently, reliably, and as planned.
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