4 cylindres sur 16
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fred
- Messages : 112
- Enregistré le : ven. 20 sept. 2002, 15:29
4 cylindres sur 16
Comment c'est possible que le moteur 16 cylindres de la Cadillac Sixteen ne puisse tourner que sur 4 cylindres seulement ?
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Jonathan
- Site Admin
- Messages : 214
- Enregistré le : dim. 01 sept. 2002, 00:16
Voici un communiqué de la GM détaillant cette technique :
(désolé, c'est en anglais).
(désolé, c'est en anglais).
GM's 'Displacement On Demand' Technology To Provide Fuel Economy Benefits
PONTIAC, Mich. - General Motors plans to begin equipping its large trucks and sport-utility vehicles with innovative "Displacement-on-Demand" engines to boost the fuel economy of these vehicles by about 8 percent, based on an EPA testing procedure, and up to 25 percent in certain real-world driving conditions. The engines will debut in 2004 as part of GM's Vortec V8 engine family.
GM initially plans to produce more than 150,000 of these fuel-efficient V8s in the first year. Production will then be increased over the next several years to nearly 1.5 million units in 2007. Displacement on Demand will be featured in standard and optional Vortec engines in GM's large trucks and full-size sport-utility vehicles.
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.
Right now, GM leads the industry in truck fuel economy.
"Displacement on Demand will allow us to maintain that leadership position well into the future," said Sam Winegarden, GM Powertrain chief engineer of Vortec V8 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."
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.
"We have figured out a way to make our V8 engines work smarter," said Winegarden. "GM's new Vortec V8s will be able to deliver the same top-of-the-line performance with less effort, with less energy. That's the essence of efficiency."
The engine is always started on eight cylinders. But once the vehicle is moving, the powertrain control module activates Displacement on Demand.
While actual fuel economy gains depend on driving style, vehicle options and load-carrying conditions, the potential customer benefits are significant. For example, a full-size sport-utility vehicle with a current cruising range of more than 400 miles per tank of gasoline could gain as much as 100 miles per tank with Displacement on Demand, based on a 25 percent improvement in real-world testing done by GM Powertrain engineers.
That means a 2001 Chevrolet Silverado equipped with a Vortec V8 engine featuring Displacement on Demand could travel from Washington, D.C., to Cincinnati, Ohio - roughly 509 miles - on a single tank of gas. The cruising range of this vehicle today is 427 miles, about the distance from Washington, D.C., to Columbus, Ohio.
In addition, Displacement on Demand enables improved performance through relatively inexpensive increases in engine displacement. This gives GM a competitive advantage by being able to offer our customers more options.
"For example, within GM's Vortec overhead valve V8 engine family with available displacements from 4.8L to 6.0L, you can choose the larger displacements to gain performance improvements without fuel economy penalty and without increasing the external package," said Winegarden. "When you add our Displacement on Demand technology, you can actually run a larger displacement engine in V4 mode over a greater range of operating conditions than with the smaller displacement engine.
"So when customers choose performance driving, or must accelerate to avoid a hazard, or haul a trailer or carry heavy loads, they benefit from the increased engine capability. But when they are driving without a load, their vehicles will get fuel-economy benefits through the Displacement on Demand technology."
GM's overhead valve engines are particularly well suited for Displacement on Demand, Winegarden said. The engines have a flexible architecture that has been adapted for racing, for trucks and for passenger cars in markets worldwide. Displacement on Demand is an example of how GM has continuously improved the engine by adding new technology.
"With two valves per cylinder, only two actuators per cylinder are needed," Winegarden said. "The system is intelligently simple and compact.
"By contrast, while Displacement on Demand certainly has merit for overhead cam multi-valve engines, four valves per cylinder require four actuators per cylinder. Additionally, the electro-hydraulic (or other) control network must be packaged within the tight confines of the cylinder head assembly, adding both complexity and cost."
Although GM Powertrain will introduce Displacement on Demand on overhead valve V8 engines, other applications are being considered, including six-cylinder and four-cylinder engines, as well as overhead cam engines.
"We plan to leverage the lessons we learn on our initial applications to create opportunities across our global engine families," Winegarden said.
Displacement on Demand marks a dramatic evolution in this engine technology GM pioneered 20 years ago. In 1981, GM implemented a cylinder deactivation technology that was limited by a cable throttle, mechanically controlled transmission and a fraction of the computer power currently available.
Today's engine computer is a 32-bit machine (versus 8 bit) that has an internal clock that is roughly 25 times faster, 50 times the computing power and 100 times the memory of the 1981 controller. Electronic Throttle Control (ETC) 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 more accurate information used by the transmission for shift-point selection and actuator control settings.
Displacement on Demand is just one of several advanced powertrain technologies GM is developing to address fuel economy.
"Other promising powertrain technologies include continuously variable transmissions, direct injection-gasoline, port deactivation, manual transmission auto shift and variable valvetrain," Winegarden said. "GM also is continuing work on many alternate propulsion systems.
"GM's extensive research and development efforts in engine technologies are all geared towards making sure we meet, and exceed, the high expectations of the government, our customers and the general public."
General Motors (NYSE: GM), the world's largest vehicle manufacturer, designs, builds and markets cars and trucks worldwide. In 2000, GM earned $5 billion on sales of $183.3 billion. It employs about 386,000 people globally. More information on General Motors can be found at http://www.gm.com.
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Sidebar: Displacement on Demand in Action
In choosing a vehicle, most customers select a powertrain that will meet their needs in maximum operating conditions. Many truck buyers, for example, demand powerful V8 engines to handle the heavy load without sacrificing performance.
But when a vehicle equipped with such an engine is driven for routine transportation purposes - such as typical city driving - the engine operates at a small fraction of its capability at almost closed throttle conditions. This impaired volumetric efficiency causes poor fuel economy.
Displacement on Demand automatically turns off half of the cylinders during light-load operating conditions, enabling the working cylinders to achieve higher fuel efficiency through better thermal, pumping and mechanical efficiency.
To make the technology seamless to customers, GM is developing improvements in powertrain electronic control systems, intake and exhaust noise silencing, and powertrain mounts. Cost and complexity are minimized by modifying existing electronic and mechanical controls.
With Displacement on Demand, the vehicle's powertrain control module determines load conditions based on inputs from vehicle sensors. When loads are light, the control module 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 powertrain control module what the engine is doing at any point in its cycle - for example, which cylinder has fired and where the valvetrain is located at that particular point. The module interprets the information in order to control complex functions such as fuel injection, electronic spark control and electronic throttle control.
Using the same information already provided to the control module, Displacement on Demand adds algorithms to manage the cylinder deactivation and reactivation process. The powertrain control module monitors driver commands, several engine sensors and mathematical models to determine the right time in the engine cycle to initiate the process. It then controls spark advance, fuel injectors, electronic throttle and four valvetrain control solenoids in precise coordination to achieve seamless transition between V4 and V8 operation.
The sequential reactivation of cylinders to increase engine output happens so quickly that there is an immediate increase in engine output.
Displacement on Demand also leverages an existing oil pump system to provide hydraulic pressure to activate the system. The mechanical actuators are special hydraulic lifters, each with a spring-loaded locking pin that deactivates the cylinders. In normal operation, when the camshaft rotates against the hydraulic lifter, it opens and closes either an intake or exhaust valve.
The 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 or uncoupled to each other by means of the locking pin. When cylinder deactivation is initiated, hydraulic pressure is used to dislodge the locking pin and collapse the lifter, thus closing the valve. In reactivation mode, the removal of hydraulic pressure causes the locking pin to return to its latched position to restore the lifter's normal function.
The activated state of the special lifters is the default mode, and the engine is always started on eight cylinders.
In V4 mode, every other cylinder, in the firing order, is deactivated. In a V8 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 transparent to the driver.