Hardware-in-the-loop simulation simplifies hybrid vehicle testing

December 15, 2014 // By Graham Prophet
National Instruments hardware and software have been employed by Subaru for advance hybrid vehicle testing. In a hybrid vehicle, the motor ECU plays an even more complicated role as it manages the interaction between the conventional engine and the electric motor, along with its power systems.

The Subaru XV Crosstrek Hybrid was a preliminary attempt to deliver a production model hybrid vehicle targeting both domestic Japanese and North American markets. Engineers had developed a motor ECU for an earlier hybrid prototype, but the component did not meet the rigorous requirements to take a vehicle to market. For the production model vehicle, the ECU needed various control functionalities to prevent damage to the vehicle body and to ensure driver and passenger safety under various operating conditions, even in scenarios that would be impossible or impractical to test on physical hardware.

For example, under icy driving conditions, a wheel can experience a sudden loss of traction. During acceleration this can cause a dramatic increase in motor speed and needs to be handled safely. However, this safety behaviour cannot be physically reproduced on a dynamometer and is time consuming and difficult to reproduce on a test track. Since complex control algorithms for specific safety conditions like this need to be developed and verified, the testing needed to account for outlying operating conditions to satisfy the quality level required for a production model vehicle.

The challenge was to use automated testing to develop a new verification system that satisfied the control quality level required for the motor electronic control unit (ECU) in Subaru's XV Crosstrek Hybrid, and to create strenuous test conditions that are difficult to achieve using real machines.