Variable displacement
Encyclopedia
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. Many automobile manufacturers have adopted this technology as of 2005, although the concept has existed for some time prior.
of an internal combustion engine
during light-load operation. In typical light-load driving the driver uses only around 30 percent of an engine’s maximum power. In these conditions, the throttle
valve is nearly closed, and the engine needs to work to draw air. This causes an inefficiency known as pumping loss. Some large capacity engines need to be throttled so much at light load that the cylinder pressure at top dead centre is approximately half that of a small 4-cylinder engine. Low cylinder pressure means low fuel efficiency. The use of cylinder deactivation at light load means there are fewer cylinders drawing air from the intake manifold
, which works to increase its fluid (air) pressure. Operation without variable displacement is wasteful because fuel is continuously pumped into each cylinder and combusted even though maximum performance is not required. By shutting down half of an engine's cylinders, the amount of fuel being consumed is much less. Between reducing the pumping losses, which increases pressure in each operating cylinder, and decreasing the amount of fuel being pumped into the cylinders, fuel consumption can be reduced by 8 to 25 percent in highway conditions.
Cylinder deactivation is achieved by keeping the intake and exhaust valves closed for a particular cylinder. By keeping the intake and exhaust valves closed, it creates an "air spring" in the combustion chamber
– the trapped exhaust gases (kept from the previous charge burn) are compressed during the piston’s upstroke and push down on the piston during its downstroke. The compression and decompression of the trapped exhaust gases have an equalising effect – overall, there is virtually no extra load on the engine. In the latest breed of cylinder deactivation systems, the engine management system is also used to cut fuel delivery to the disabled cylinders. The transition between normal engine operation and cylinder deactivation is also smoothed, using changes in ignition timing
, cam
timing and throttle position (thanks to electronic throttle control
). In most instances, cylinder deactivation is applied to relatively large displacement engines that are particularly inefficient at light load. In the case of a V12
, up to 6 cylinders can be disabled.
Two issues to overcome with all variable-displacement systems are the unbalanced cooling and vibration of variable-displacement engines.
, developed in the late 19th century. These single-cylinder stationary engine
s had a centrifugal governor
that cut the cylinder out of operation so long as the engine was operating above a set speed, typically by holding the exhaust valve open.
, were re-attempted in 1981 on Cadillac
's ill-fated L62 "V8-6-4" engine. The technology was made a standard feature on all Cadillac models except Seville
. Cadillac, in conjunction with Eaton Corporation
, developed the innovative V-8-6-4 system which used the industry's first engine control unit
to switch the engine from 8- to 6- to 4-cylinder operation depending on the amount of power needed. The original multi-displacement system turned off opposite pairs of cylinders, allowing the engine to have three different configurations and displacements. But the system was troublesome, and a rash of unpredictable failures led to the technology being quickly retired.
developed its own variable displacement in the form of MD (Modulated Displacement) which proved that the technology, first used in Mitsubishi's 1.4 L 4G12
straight-4
engine, can function successfully. Because Cadillac's system proved to be a failure and a four-cylinder engine was used, Mitsubishi hailed their own as a world first. The technology was later used in Mitsubishi's V6 engines. Mitsubishi's effort was also short-lived, mainly because of a lack of response from car buyers.
In 1993, a year after Mitsubishi developed its own variable valve timing
technology, the MIVEC
-MD variant was introduced. The revived MD technology was now in its second generation with improved electronic engine controls enabling the switch from 4 to 2 cylinders to be made almost imperceptibly. In MD mode, the MIVEC engine utilizes only two of its four cylinders, which reduces significantly the energy wasted due to pumping losses. In addition, power loss due to engine friction is also reduced. Depending on conditions, the MIVEC-MD system can reduce fuel consumption by 10–20 percent; although some of this gain is from the variable valve timing system, not from the variable-displacement feature. Modulated Displacement was dropped around 1996.
experimented with their Multi-Displacement System
V12
in the late 1990s. It was not widely deployed until the 2004 DaimlerChrysler
Hemi. Other systems appeared in 2005 from GM (Active Fuel Management
in the Generation IV small-block
) and Honda
(Variable Cylinder Management
on the J family
engines). Honda's system works by deactivating a bank of cylinders, while the Chrysler Hemi shuts off every other cylinder in the firing order.
There are currently two main types of cylinder deactivation used today, depending on the type of engine. The first is for the pushrod design which uses solenoids to alter the oil pressure delivered to the lifters. In their collapsed state, the lifters are unable to elevate their companion pushrods under the valve rocker arms, resulting in valves that cannot be actuated and remain closed. The second is used for overhead cam engines, and uses a pair of locked-together rocker arms that are employed for each valve. One rocker follows the cam profile, while the other actuates the valve. When a cylinder is deactivated, solenoid-controlled oil pressure releases a locking pin between the two rocker arms. While one arm still follows the camshaft, the unlocked arm remains motionless and unable to activate the valve. .
Although the attempts to use variable-displacement technology failed in the past, automakers have been able to overcome the problems that occurred using new advancements in computers. With computers this fast cylinder deactivation and reactivation occur almost instantly.
After the price of oil surged in 2008, consumers were looking for a more fuel efficient car without sacrificing peak power. This has led many manufacturers to put variable-displacement controls into their cars, especially those with V8s installed.
It is also possible to alter the engine's displacement by shortening or lengthening the stroke of the pistons, thereby changing the actual cylinder displacement, rather than simply deactivating and sealing off cylinders. There are no production vehicles that use this design, however.
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...
engine technology that allows the engine displacement
Engine displacement
Engine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top dead centre to bottom dead centre . It is commonly specified in cubic centimeters , litres , or cubic inches...
to change, usually by deactivating cylinders
Cylinder (engine)
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...
, for improved 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....
. The technology is primarily used in large, multi-cylinder engines. Many automobile manufacturers have adopted this technology as of 2005, although the concept has existed for some time prior.
Theory of operation
Cylinder deactivation is used to reduce the fuel consumption and emissionsMotor vehicle emissions
Motor vehicle emissions are composed of the by-products that comes out of the exhaust systems or other emissions such as gasoline evaporation...
of an internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
during light-load operation. In typical light-load driving the driver uses only around 30 percent of an engine’s maximum power. In these conditions, the throttle
Throttle
A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases , but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which...
valve is nearly closed, and the engine needs to work to draw air. This causes an inefficiency known as pumping loss. Some large capacity engines need to be throttled so much at light load that the cylinder pressure at top dead centre is approximately half that of a small 4-cylinder engine. Low cylinder pressure means low fuel efficiency. The use of cylinder deactivation at light load means there are fewer cylinders drawing air from the intake manifold
Manifold
In mathematics , a manifold is a topological space that on a small enough scale resembles the Euclidean space of a specific dimension, called the dimension of the manifold....
, which works to increase its fluid (air) pressure. Operation without variable displacement is wasteful because fuel is continuously pumped into each cylinder and combusted even though maximum performance is not required. By shutting down half of an engine's cylinders, the amount of fuel being consumed is much less. Between reducing the pumping losses, which increases pressure in each operating cylinder, and decreasing the amount of fuel being pumped into the cylinders, fuel consumption can be reduced by 8 to 25 percent in highway conditions.
Cylinder deactivation is achieved by keeping the intake and exhaust valves closed for a particular cylinder. By keeping the intake and exhaust valves closed, it creates an "air spring" in the combustion chamber
Combustion chamber
A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...
– the trapped exhaust gases (kept from the previous charge burn) are compressed during the piston’s upstroke and push down on the piston during its downstroke. The compression and decompression of the trapped exhaust gases have an equalising effect – overall, there is virtually no extra load on the engine. In the latest breed of cylinder deactivation systems, the engine management system is also used to cut fuel delivery to the disabled cylinders. The transition between normal engine operation and cylinder deactivation is also smoothed, using changes in ignition timing
Ignition timing
Ignition timing, in a spark ignition internal combustion engine , is the process of setting the angle relative to piston position and crankshaft angular velocity that a spark will occur in the combustion chamber near the end of the compression stroke...
, cam
Cam
A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path...
timing and throttle position (thanks to electronic throttle control
Electronic throttle control
Electronic throttle control is an automobile technology which severs the mechanical link between the accelerator pedal and the throttle. Most automobiles already use a throttle position sensor to provide input to traction control, antilock brakes, fuel injection, and other systems, but use a...
). In most instances, cylinder deactivation is applied to relatively large displacement engines that are particularly inefficient at light load. In the case of a V12
V12 engine
A V12 engine is a V engine with 12 cylinders mounted on the crankcase in two banks of six cylinders, usually but not always at a 60° angle to each other, with all 12 pistons driving a common crankshaft....
, up to 6 cylinders can be disabled.
Two issues to overcome with all variable-displacement systems are the unbalanced cooling and vibration of variable-displacement engines.
History
The oldest engine technological predecessor for the variable-displacement engine is the hit and miss engineHit and miss engine
A hit-and-miss engine is a type of four-stroke internal combustion engine that was conceived in the late 19th century and was produced by various companies from the 1890s through approximately the 1930s. The name comes from the method of speed control that is implemented on these engines...
, developed in the late 19th century. These single-cylinder stationary engine
Stationary engine
A stationary engine is an engine whose framework does not move. It is normally used not to propel a vehicle but to drive a piece of immobile equipment such as a pump or power tool. They may be powered by steam; or oil-burning or internal combustion engines....
s had a centrifugal governor
Centrifugal governor
A centrifugal governor is a specific type of governor that controls the speed of an engine by regulating the amount of fuel admitted, so as to maintain a near constant speed whatever the load or fuel supply conditions...
that cut the cylinder out of operation so long as the engine was operating above a set speed, typically by holding the exhaust valve open.
Cadillac L62 V8-6-4
First experiments with multiple-cylinder engines during WWIIWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, were re-attempted in 1981 on Cadillac
Cadillac
Cadillac is an American luxury vehicle marque owned by General Motors . Cadillac vehicles are sold in over 50 countries and territories, but mostly in North America. Cadillac is currently the second oldest American automobile manufacturer behind fellow GM marque Buick and is among the oldest...
's ill-fated L62 "V8-6-4" engine. The technology was made a standard feature on all Cadillac models except Seville
Cadillac Seville
The Cadillac Seville is a luxury-type car that was manufactured by the Cadillac division of American automaker General Motors from 1975 to 2004, as a smaller-sized top-of-the-line Cadillac...
. Cadillac, in conjunction with Eaton Corporation
Eaton Corporation
Eaton Corporation is a global diversified power management company with 2010 sales of $13.7 billion. The company is a leading provider of electrical components and systems for power quality, distribution and control; hydraulics components, systems and services for industrial and mobile equipment;...
, developed the innovative V-8-6-4 system which used the industry's first engine control unit
Engine control unit
An engine control unit is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running...
to switch the engine from 8- to 6- to 4-cylinder operation depending on the amount of power needed. The original multi-displacement system turned off opposite pairs of cylinders, allowing the engine to have three different configurations and displacements. But the system was troublesome, and a rash of unpredictable failures led to the technology being quickly retired.
Mitsubishi MD
One year later, in 1982 MitsubishiMitsubishi Motors
is a multinational automaker headquartered in Minato, Tokyo. In 2009 it was the fifth-largest Japan-based automaker and the 17th-largest in the world measured by production...
developed its own variable displacement in the form of MD (Modulated Displacement) which proved that the technology, first used in Mitsubishi's 1.4 L 4G12
Mitsubishi Orion engine
The Mitsubishi Orion or 4G1 engine is series of straight-4 internal combustion engines introduced by Mitsubishi Motors in the 1970s, along with the Astron, Sirius, and Saturn. It was introduced in the Colt and Colt-derived models in 1978...
straight-4
Straight-4
The inline-four engine or straight-four engine is an internal combustion engine with all four cylinders mounted in a straight line, or plane along the crankcase. The single bank of cylinders may be oriented in either a vertical or an inclined plane with all the pistons driving a common crankshaft....
engine, can function successfully. Because Cadillac's system proved to be a failure and a four-cylinder engine was used, Mitsubishi hailed their own as a world first. The technology was later used in Mitsubishi's V6 engines. Mitsubishi's effort was also short-lived, mainly because of a lack of response from car buyers.
In 1993, a year after Mitsubishi developed its own variable valve timing
Variable valve timing
In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...
technology, the MIVEC
MIVEC
MIVEC is the brand name of a variable valve timing engine technology developed by Mitsubishi Motors...
-MD variant was introduced. The revived MD technology was now in its second generation with improved electronic engine controls enabling the switch from 4 to 2 cylinders to be made almost imperceptibly. In MD mode, the MIVEC engine utilizes only two of its four cylinders, which reduces significantly the energy wasted due to pumping losses. In addition, power loss due to engine friction is also reduced. Depending on conditions, the MIVEC-MD system can reduce fuel consumption by 10–20 percent; although some of this gain is from the variable valve timing system, not from the variable-displacement feature. Modulated Displacement was dropped around 1996.
Aftermarket systems
A number of companies have developed aftermarket cylinder deactivation systems, with varying degrees of success. The 1979 EPA evaluation of the Automotive Cylinder Deactivation System (ACDS), which allowed eight-cylinder engines to be run on four cylinders, found that carbon monoxide and nitrogen oxide emissions were increased beyond the legal limits of the emission standards then in force. While fuel economy was increased, acceleration was seriously compromised, and the loss of engine vacuum led to a dangerous loss of braking assist when the system was in four-cylinder mode. In addition to these issues, while the company proposed a hydraulically controlled system that could be switched from within the car, the version they implemented had to be manually changed in the engine compartment using hand tools.Present
No automaker attempted the same trick again until Mercedes-BenzMercedes-Benz
Mercedes-Benz is a German manufacturer of automobiles, buses, coaches, and trucks. Mercedes-Benz is a division of its parent company, Daimler AG...
experimented with their Multi-Displacement System
Multi-Displacement System
Chrysler's Multi-Displacement System is an automobile engine variable displacement technology. It debuted in 2004 on the 5.7 L modern Hemi V8...
V12
V12 engine
A V12 engine is a V engine with 12 cylinders mounted on the crankcase in two banks of six cylinders, usually but not always at a 60° angle to each other, with all 12 pistons driving a common crankshaft....
in the late 1990s. It was not widely deployed until the 2004 DaimlerChrysler
DaimlerChrysler
Daimler AG is a German car corporation. By unit sales, it is the thirteenth-largest car manufacturer and second-largest truck manufacturer in the world. In addition to automobiles, Daimler manufactures buses and provides financial services through its Daimler Financial Services arm...
Hemi. Other systems appeared in 2005 from GM (Active Fuel Management
Active Fuel Management
Active Fuel Management 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...
in the Generation IV small-block
GM LS engine
The GM LS engine family is an engine design intended as the only V-8 engine used in General Motors' line of rear-wheel-drive cars and trucks. The LS series was a "clean sheet" design with little in common with the classic Chevrolet small block V8...
) and Honda
Honda
is 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...
(Variable Cylinder Management
Variable Cylinder Management
Variable 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...
on the J family
Honda J engine
The J-series was Honda's second V6 engine family, introduced in 1996. It is a 60° V6 – Honda's existing C-series was a 90° engine. The J-series was designed for transverse mounting. It has a shorter bore spacing , shorter connecting rods, and a special smaller crankshaft than the C-series for...
engines). Honda's system works by deactivating a bank of cylinders, while the Chrysler Hemi shuts off every other cylinder in the firing order.
There are currently two main types of cylinder deactivation used today, depending on the type of engine. The first is for the pushrod design which uses solenoids to alter the oil pressure delivered to the lifters. In their collapsed state, the lifters are unable to elevate their companion pushrods under the valve rocker arms, resulting in valves that cannot be actuated and remain closed. The second is used for overhead cam engines, and uses a pair of locked-together rocker arms that are employed for each valve. One rocker follows the cam profile, while the other actuates the valve. When a cylinder is deactivated, solenoid-controlled oil pressure releases a locking pin between the two rocker arms. While one arm still follows the camshaft, the unlocked arm remains motionless and unable to activate the valve. .
Although the attempts to use variable-displacement technology failed in the past, automakers have been able to overcome the problems that occurred using new advancements in computers. With computers this fast cylinder deactivation and reactivation occur almost instantly.
After the price of oil surged in 2008, consumers were looking for a more fuel efficient car without sacrificing peak power. This has led many manufacturers to put variable-displacement controls into their cars, especially those with V8s installed.
It is also possible to alter the engine's displacement by shortening or lengthening the stroke of the pistons, thereby changing the actual cylinder displacement, rather than simply deactivating and sealing off cylinders. There are no production vehicles that use this design, however.
Variable-displacement technologies
- General Motors V8-6-4 (Cadillac)
- General Motors Cadillac SixteenCadillac SixteenThe 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...
(Cadillac) - General Motors Active Fuel ManagementActive Fuel ManagementActive Fuel Management 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...
- DaimlerChryslerDaimlerChryslerDaimler AG is a German car corporation. By unit sales, it is the thirteenth-largest car manufacturer and second-largest truck manufacturer in the world. In addition to automobiles, Daimler manufactures buses and provides financial services through its Daimler Financial Services arm...
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) (for Chrysler) - DaimlerChryslerDaimlerChryslerDaimler AG is a German car corporation. By unit sales, it is the thirteenth-largest car manufacturer and second-largest truck manufacturer in the world. In addition to automobiles, Daimler manufactures buses and provides financial services through its Daimler Financial Services arm...
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) (for Mercedes-BenzMercedes-BenzMercedes-Benz is a German manufacturer of automobiles, buses, coaches, and trucks. Mercedes-Benz is a division of its parent company, Daimler AG...
) - 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...
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)