Faced with an aggressive deadline, and knowing they would need the flexibility to adapt requirements quickly, Eaton chose to apply Model-Based Design with MathWorks tools.
A team of Eaton engineers designed and simulated a model of the control scheme architecture with Simulink® software that included energy management, subsystems of the engine, the clutch, the battery, the motor, and other vehicle components.
“The beauty of model architecture in Simulink,” Carpenter says, “is that if any of the vehicle components change, we simply modify those blocks, and the overall system is not affected.”
They then created a plant model to simulate all the inputs and outputs that the hybrid control module would use to communicate with the real vehicle components. They used Simulink Coder™ to generate C code from the Simulink model and downloaded the code onto Simulink Real-Time™ for hardware-in-the-loop simulations.
“Essentially, we had a working vehicle on our PC, so whenever we wanted to adjust or make improvements, we could run a simulation in our PC environment,” Carpenter says.
Eaton used Simulink to enhance the model’s performance and Optimization Toolbox™ to determine the optimal emissions and fuel economy.
After validating their results on the PC against the actual I/O by running hardware-in-the-loop simulations, Eaton developed a prototype controller. They created one model, consisting of the Simulink architecture, the operating system, and the hardware abstraction layer (HAL), which includes the drivers on the chipset of the board. They developed an operating system to interface between the HAL coded in C and the Simulink model, using Stateflow® and Simulink Coder as a scheduler in the operating system.
Using Embedded Coder®, Eaton generated C code from the model and downloaded the code onto a Freescale™ MPC5xx microcontroller for real-time operation in the freight carrier’s ECU.
The Eaton prototype surpassed emission and fuel efficiency requirements during dynamometer testing.
With the competition won, Eaton began building 20 hybrid test vehicles in 2004. The vehicles have since been deployed in several cities across the United States for real-world testing by the freight carrier, which has more than 40,000 conventional delivery vehicles on the road. Plans are in place to introduce more hybrid test vehicles into the fleet over time.