Hybrid software takes control

  • 08-Sep-2009 02:13 EDT

General Motors' Larry Nitz noted that “selling” battery power using software to keep a V8 engine running longer in its four-cylinder mode, such as in the Chevrolet Tahoe Two Mode Hybrid (shown), can maximize fuel efficiency.

As engineers devise ways to get the most out of hybrid components and systems, control software is a vital element. These programs manage all aspects of a hybrid system, making decisions about batteries, power sources, and many other factors.

When electric motors enter the mix, software throughout the drivetrain is impacted. The software for hybrids moves to the top of the powertrain hierarchy.

“From an architectural perspective, the engine has always been the master,” said Larry Nitz, General Motors’ Executive Director for Hybrid Powertrains. “In the hybrid world, the hybrid system is the master. When and how the engine will start and stop is managed by the hybrid control manager. Movements of the throttle pedal are interpreted by the hybrid system.”

The programs handle a range of systems that extend beyond the powertrain. All of them have a single goal—to reduce gasoline consumption.

“Our Sentience program optimizes battery charging, air-conditioning usage, and other things, with control algorithms that optimize fuel efficiency,” said Roger Thornton, Global Hybrid & Electric Vehicles Group Director for Ricardo. “This system provides around 10% overall improvement in fuel consumption.”

As with hardware components, design teams are searching for ways to maximize their software efforts. At GM, one way they are doing that is to use software on a broad range of vehicles.

“When you get down to the software architecture, all of our hybrids use similar architectures,” Nitz said. “We do real-time optimization of losses; the system is constantly analyzing the operating points of the engine, transmission, and electric motors to minimize losses.”

Those losses are both mechanical and electrical. Constantly analyzing them helps maximize efficiency. For example, running internal-combustion engines at their sweet spot can trim fuel usage while enhancing system performance.

“Charging the battery while driving might not seem optimal, but if it lets the engine operate at higher efficiency, it can be a wise choice,” Nitz said. “You’re effectively buying energy cheaply.”

Other times, it can make sense to use batteries to augment the ICE. Nitz noted that “selling” battery power to keep a V8 engine running longer in its four-cylinder mode can maximize fuel efficiency.

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