Active Fuel Management
Encyclopedia
Active Fuel Management (formerly known as Displacement on Demand) is a trademarked name for the automobile
variable displacement
technology from General Motors. It allows a V6 or V8 engine to "turn off" half of the cylinders under light-load conditions to improve fuel economy
. Estimated performance on EPA
tests show a 5.5%-7.5% improvement in fuel economy.
GM's current Active Fuel Management technology uses a solenoid to deactivate the lifter
s on selected cylinders of a pushrod V-layout engine.
, rolling friction, and to operate accessories such as air conditioning
.
However, when a gasoline internal combustion engine is operating under less than full load, the effective compression ratio is much less than the measured compression ratio. Under light load, the throttle is not fully open, and the cylinders receive less than a full charge of air on each intake stroke. The pressure and temperature generated at combustion are therefore less than under full load, and the thermodynamic laws which apply to all heat engines dictate that the engine will then be operating at less than its maximum possible thermal efficiency
.
Thus, a high-powered, large-displacement engine is highly inefficient and wasteful when being used for normal driving conditions. This is the motivation for cylinder deactivation, to effectively spread the work load of the engine over fewer active cylinders which then operate under higher individual loads and therefore at higher efficiency.
is prevented from opening after the power stroke
and the exhaust gas
charge is retained in the cylinder and compressed during the exhaust stroke. Following the exhaust stroke, the intake
valve
is prevented from opening. The exhaust gas in the cylinder is expanded and compressed over and over again and acts like a gas spring. As multiple cylinders are shut off at a time (cylinders 1, 4, 6 and 7 for a V8), the power required for compression of the exhaust gas in one cylinder is countered by the decompression of retained exhaust gas in another. When more power is called for, the exhaust valve is reactivated and the old exhaust gas is expelled during the exhaust stroke. The intake valve is likewise reactivated and normal engine operation is resumed. The net effect of cylinder deactivation is an improvement in fuel economy and likewise a reduction in exhaust emissions. General Motors was the first to modify existing, production engines to enable cylinder deactivation, with the introduction of the Cadillac L62 "V8-6-4" in 1981.
control valve assembly integrated into the engine valley cover contains solenoid valves that provide a pressurized oil signal to specially designed hydraulic roller lifters provided by Eaton Corp. and Delphi. These lifters disable and re-enable exhaust and intake valve operation to deactivate and reactivate engine cylinders http://www.gm.com/company/onlygm/fuel/engine.html. Unlike the first generation system, only half of the cylinders can be deactivated. It is notable that the second generation system uses engine oil to hydraulically modulate engine valve function. As a result, the system is dependent upon the quality of the oil in the engine. As anti-foaming agents in engine oil are depleted, air may become entrained or dissolve in the oil, delaying the timing of hydraulic control signals. Similarly engine oil viscosity
and cleanliness is a factor. Use of the incorrect oil type, i.e. SAE 20W40 instead of SAE 5W20, or the failure to change engine oil at factory recommended intervals can also significantly impair system performance.
In 2001, GM showcased the 2002 Cadillac Cien
concept car
, which featured Northstar XV12 engine with Displacement on Demand. Later that year, GM debuted Opel Signum
² concept car in Frankfurt Auto Show, which uses the global XV8 engine with displacement on demand. In 2003, GM unveiled the Cadillac Sixteen
concept car at the Detroit Opera House, which featured an XV16 concept engine that can switch between 4, 8, and 16 cylinders.
On April 8, 2003, General Motors announced this technology (now called Active Fuel Management) to be commercially available on 2005 GMC Envoy
XL, Envoy XUV and Chevrolet TrailBlazer
EXT using optional Vortec 5300 V8 engine. GM also extended the technology on the new High Value LZ8 V6 engine in the Chevrolet Impala
and Monte Carlo
as well as the 5.3L V8 LS4 engine in the last generation Chevrolet Monte Carlo SS and Pontiac Grand Prix GXP. In both designs, half of the cylinders can be switched off under light loads.
On July 21, 2008, General Motors unveiled the production version of the 2010 Chevrolet Camaro
. The Camaro SS with an automatic transmission features the GM L99 engine, a development of the LS3 with Active Fuel Management which allowed it to run on four cylinders during light load conditions.
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
variable displacement
Variable displacement
Variable displacement is an automobile engine technology that allows the engine displacement to change, usually by deactivating cylinders, for improved fuel economy. The technology is primarily used in large, multi-cylinder engines...
technology from General Motors. It allows a V6 or V8 engine to "turn off" half of the cylinders under light-load conditions to improve fuel economy
Fuel economy in automobiles
Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....
. Estimated performance on EPA
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
tests show a 5.5%-7.5% improvement in fuel economy.
GM's current Active Fuel Management technology uses a solenoid to deactivate the lifter
Tappet
A tappet is the noise made by a worn cam follower, however the term is widely used to represent the cam follower itself. In mechanical engineering it is a projection which imparts a linear motion to some other component within an assembly...
s on selected cylinders of a pushrod V-layout engine.
Background
High-powered multi-cylinder internal combustion engines may be necessary to satisfy driver demands for quick acceleration and/or heavy towing capacity, but during daily use they are generally operated at power settings of less than 25%. For example, at freeway speeds, less than 40 hp (30 kW) are required to overcome aerodynamic dragDrag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
, rolling friction, and to operate accessories such as air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
.
However, when a gasoline internal combustion engine is operating under less than full load, the effective compression ratio is much less than the measured compression ratio. Under light load, the throttle is not fully open, and the cylinders receive less than a full charge of air on each intake stroke. The pressure and temperature generated at combustion are therefore less than under full load, and the thermodynamic laws which apply to all heat engines dictate that the engine will then be operating at less than its maximum possible thermal efficiency
Thermal efficiency
In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...
.
Thus, a high-powered, large-displacement engine is highly inefficient and wasteful when being used for normal driving conditions. This is the motivation for cylinder deactivation, to effectively spread the work load of the engine over fewer active cylinders which then operate under higher individual loads and therefore at higher efficiency.
The Pumping Loss
A so-called "pumping loss" is also cited as causing extra work for the engine to do under partial load conditions because the pistons have to work harder to suck in the fuel-air mixture when the throttle position results in low intake-manifold pressure. Under this scenario, deactivating some of the cylinders allows the remaining active ones to have less manifold vacuum to overcome during the intake stroke.How it's done
In order to deactivate a cylinder, the exhaust valveValve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
is prevented from opening after the power stroke
Power stroke
Power Stroke may refer to:In motoring:*Power stroke , the stroke of a cyclic motor which generates force*Ford Power Stroke engine, Ford diesel engineOther:*In baseball, a batter who hits for extra bases is said to have a power stroke...
and the exhaust gas
Exhaust gas
Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline/petrol, diesel fuel, fuel oil or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack or propelling nozzle.It often disperses...
charge is retained in the cylinder and compressed during the exhaust stroke. Following the exhaust stroke, the intake
Intake
An intake , or especially for aircraft inlet, is an air intake for an engine. Because the modern internal combustion engine is in essence a powerful air pump, like the exhaust system on an engine, the intake must be carefully engineered and tuned to provide the greatest efficiency and power...
valve
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
is prevented from opening. The exhaust gas in the cylinder is expanded and compressed over and over again and acts like a gas spring. As multiple cylinders are shut off at a time (cylinders 1, 4, 6 and 7 for a V8), the power required for compression of the exhaust gas in one cylinder is countered by the decompression of retained exhaust gas in another. When more power is called for, the exhaust valve is reactivated and the old exhaust gas is expelled during the exhaust stroke. The intake valve is likewise reactivated and normal engine operation is resumed. The net effect of cylinder deactivation is an improvement in fuel economy and likewise a reduction in exhaust emissions. General Motors was the first to modify existing, production engines to enable cylinder deactivation, with the introduction of the Cadillac L62 "V8-6-4" in 1981.
Second generation
In 2004, the electronics side was improved greatly with the introductions of Electronic Throttle Control, electronically controlled transmissions, and transient engine and transmission controls. In addition, computing power was vastly increased. A solenoidSolenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
control valve assembly integrated into the engine valley cover contains solenoid valves that provide a pressurized oil signal to specially designed hydraulic roller lifters provided by Eaton Corp. and Delphi. These lifters disable and re-enable exhaust and intake valve operation to deactivate and reactivate engine cylinders http://www.gm.com/company/onlygm/fuel/engine.html. Unlike the first generation system, only half of the cylinders can be deactivated. It is notable that the second generation system uses engine oil to hydraulically modulate engine valve function. As a result, the system is dependent upon the quality of the oil in the engine. As anti-foaming agents in engine oil are depleted, air may become entrained or dissolve in the oil, delaying the timing of hydraulic control signals. Similarly engine oil viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
and cleanliness is a factor. Use of the incorrect oil type, i.e. SAE 20W40 instead of SAE 5W20, or the failure to change engine oil at factory recommended intervals can also significantly impair system performance.
In 2001, GM showcased the 2002 Cadillac Cien
Cadillac Cien
The Cadillac Cien was a concept car created by Cadillac and unveiled at the 2002 Detroit Auto Show to celebrate Cadillac's 100th anniversary...
concept car
Concept car
A concept vehicle or show vehicle is a car made to showcase new styling and or new technology. They are often shown at motor shows to gauge customer reaction to new and radical designs which may or may not have a chance of being produced....
, which featured Northstar XV12 engine with Displacement on Demand. Later that year, GM debuted Opel Signum
Opel Signum
The Opel Signum was a large family car/executive hatchback engineered and manufactured by Opel in Germany between 2003 and 2008. It was almost exclusively sold in Europe. In the United Kingdom it was sold under the Vauxhall Signum nameplate...
² concept car in Frankfurt Auto Show, which uses the global XV8 engine with displacement on demand. In 2003, GM unveiled the Cadillac Sixteen
Cadillac Sixteen
The Cadillac Sixteen was a prototype of a stylish and high performance automobile first presented by Cadillac in 2003.The vehicle was equipped with a 32-valve V16 concept engine displacing 13.6 liters and was mated to a four-speed, electronically controlled, automatic transmission driving the rear...
concept car at the Detroit Opera House, which featured an XV16 concept engine that can switch between 4, 8, and 16 cylinders.
On April 8, 2003, General Motors announced this technology (now called Active Fuel Management) to be commercially available on 2005 GMC Envoy
GMC Envoy
The GMC Envoy is an SUV from the GMC marque of General Motors. It was introduced as a high-end version of the Jimmy for the 1998 model year, the same year the Jimmy was restyled...
XL, Envoy XUV and Chevrolet TrailBlazer
Chevrolet TrailBlazer
The Chevrolet TrailBlazer is a mid-size sport utility vehicle produced by the Chevrolet division of American automaker General Motors.On November 10th, 2011, General Motors officially revealed a second generation of the vehicle to be sold worldwide...
EXT using optional Vortec 5300 V8 engine. GM also extended the technology on the new High Value LZ8 V6 engine in the Chevrolet Impala
Chevrolet Impala
The Chevrolet Impala is a full-size automobile built by the Chevrolet division of General Motors introduced for the 1958 model year. Deriving its name from the southern African antelope, Chevrolet's most expensive passenger model through 1965 had become the best-selling automobile in the United...
and Monte Carlo
Chevrolet Monte Carlo
The Chevrolet Monte Carlo was an American-made two-door coupe introduced for model year 1970, and manufactured over six generations through model year 2007. It was marketed as a personal-luxury coupe through most of its history, with the last model version being classified as a full-sized coupe...
as well as the 5.3L V8 LS4 engine in the last generation Chevrolet Monte Carlo SS and Pontiac Grand Prix GXP. In both designs, half of the cylinders can be switched off under light loads.
On July 21, 2008, General Motors unveiled the production version of the 2010 Chevrolet Camaro
Fifth-generation Chevrolet Camaro
The fifth-generation Chevrolet Camaro is a pony car produced by General Motors and marketed under the Chevrolet brand. It is the fifth distinct generation of the Camaro to be produced since its original introduction in 1967...
. The Camaro SS with an automatic transmission features the GM L99 engine, a development of the LS3 with Active Fuel Management which allowed it to run on four cylinders during light load conditions.
See also
- Variable displacementVariable displacementVariable displacement is an automobile engine technology that allows the engine displacement to change, usually by deactivating cylinders, for improved fuel economy. The technology is primarily used in large, multi-cylinder engines...
- HondaHondais a Japanese public multinational corporation primarily known as a manufacturer of automobiles and motorcycles.Honda has been the world's largest motorcycle manufacturer since 1959, as well as the world's largest manufacturer of internal combustion engines measured by volume, producing more than...
's Variable Cylinder ManagementVariable Cylinder ManagementVariable Cylinder Management is Honda's term for a variable displacement technology. It uses the i-VTEC system to disable one bank of cylinders during specific driving conditions to save fuel. The 2008 Accord takes this a step further allowing the engine to go from 6 cylinders, down to 4, and...
(VCM) - ChryslerChryslerChrysler Group LLC is a multinational automaker headquartered in Auburn Hills, Michigan, USA. Chrysler was first organized as the Chrysler Corporation in 1925....
's Multi-Displacement SystemMulti-Displacement SystemChrysler's Multi-Displacement System is an automobile engine variable displacement technology. It debuted in 2004 on the 5.7 L modern Hemi V8...
(MDS) - Daimler AG's Active Cylinder ControlActive Cylinder ControlDaimler AG's Active Cylinder Control is a variable displacement technology. It debuted in 2001 on the 5.8 L V12 in the CL600 and S600...
(ACC) - Start-stop systemStart-stop systemIn automobiles, a start-stop system or stop-start system automatically shuts down and restarts the internal combustion engine to reduce the amount of time the engine spends idling, thereby improving fuel economy and reducing emissions...