Friday, November 30, 2001

General Motors will soon begin equipping its large trucks and sport utility vehicles with innovative “displacement on demand” engines.

They can boost the fuel economy of these vehicles by about 8 percent, using the Environmental Protection Agency testing procedure, and up to 25 percent in certain real-world driving conditions. The engines will start appearing in 2004 as part of GM’s Vortec V-8 engine family.

Both customers and the environment will benefit from the engines’ improved fuel economy and lower emissions. In addition, GM’s loyal truck buyers won’t have to sacrifice superior engine performance and power to go farther on a tank of gas.

“Displacement on demand will allow us to maintain a leadership position well into the future,” said Sam Winegarden, GM Powertrain chief engineer of Vortec V-8 engines.

“Moreover, the technology will enhance fuel economy without compromising performance or the ability to carry heavy loads. And because there is no degradation in emissions, this technology will improve overall emissions to the extent that less fuel is consumed.”

Made possible by General Motors’ eMotion software and hardware, displacement on demand saves fuel by using only half of the engine’s cylinders during most normal driving conditions. The system automatically and seamlessly reactivates the other cylinders when the driver needs the engine’s full capabilities for brisk acceleration or load carrying.

Displacement on demand is a good example of the evolution of an engine technology GM pioneered 20 years ago. In 1981, GM introduced a cylinder-deactivation system that was a huge failure mainly because the mechanically controlled transmissions and limited computer power of the time were simply not up to the job.

Today’s engine computer is a 32-bit device (versus 8-bit) with an internal clock that is 25 times faster, has 50 times the computing power and 100 times the memory of the 1981 controller. Electronic throttle control and electronically controlled transmissions are now available, all proven technologies that allow seamless displacement on demand operation. Together these devices permit precise engine torque control at all times and provide more accurate information to the transmission for shift-point selection and actuator control settings.

With displacement on demand, the powertrain control system determines load conditions based on inputs from vehicle sensors.

When loads are light, the control system automatically closes both intake and exhaust valves for half of the cylinders, thus cutting off the air and fuel supply to those cylinders.

The valves are reopened to provide all-cylinder operation when the driver needs it for brisk acceleration or for hauling heavy loads.

Sensors tell the system what the engine is doing at any point in its cycle: for example, which cylinder has just fired and where the valve train is located at that particular point. The system interprets the information in order to control complex functions such as fuel injection, electronic spark control and electronic throttle control.

The sequential reactivation of cylinders to increase engine output happens so quickly that there is an immediate, undetectable increase in available engine output.

A special lifter, developed by Eaton Corp., is designed so that one section can collapse, or telescope, into the other section. The two sections can be either coupled to or uncoupled from each other by using the engine’s oil pressure.

The activated state of the special lifters is the default mode and the engine is always started on eight cylinders. In V-4 mode, every other cylinder, in the firing order, is deactivated.

In a V-8 engine, this means the process would affect the outer two cylinders on one bank and the inner two cylinders on the opposite bank. The cylinder deactivation-reactivation operation is accomplished in a fraction of a second, making the transition seamless and not apparent to the driver.

GM initially plans to produce more than 150,000 of these fuel-efficient V-8s in the first year. Production will then be increased over the next several years to nearly 1.5 million units in 2007.


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