Miss the delicious piles of effortless, unrestricted torque produced by an American V-8? Thank you to the 1975 law passed by Congress requiring corporate average fuel efficiency. Beginning in 1978, the law established minimum fuel economy requirements for new cars, and by 1985, those requirements had doubled to 27.5 mpg. The Energy Independence and Security Act of 2007, which required automakers to provide a combined average fuel economy of 35 mpg for all automobiles and trucks by 2020, wasn’t enough to kill the V-8, however.
Manufacturers are responding by employing every technical gimmick available to meet the standard. Many are switching out V-8 engines for forced-induction V-6 or straight-6 engines, and some choose cylinder deactivation, which turns off some engine cylinders while the engine isn’t running hard to save gasoline. It’s also not a novel concept, like so many things in the auto industry.
The Boston-built 1905 Sturtevant is the first known automobile to use cylinder deactivationa name you’ve probably never heard before. By turning off one of the magnetos and raising the exhaust valves of three of the Sturtevant’s six cylinders, the driver could stop power to those engines.
The 1917 Enger Twin-Unit Twelve’s introduction brought the idea back into focus. An unusual feature of this vehicle’s 60-degree V-12 engine was a cylinder deactivation lever on the steering column that was used to close the intake manifold while keeping the exhaust valves on the left side of the engine block open. In tests on the Indianapolis Motor Speedway, the manufacturer claimed that this enabled the vehicle to return 35 mpg. However, the company’s downfall was caused by financial issues and the unexpected suicide of company founder Frank Enger.
The second OPEC oil embargo in 1979 was when the idea first surfaced again. Executives at Cadillac, seller of the 221-inch long Fleetwood, had a problem as Americans waited in line for rationed amounts of gasoline while listening to Abba, Barry Manilow, and Led Zeppelin. How could it satisfy the passion of land yachts among Americans while also providing higher fuel efficiency?
To improve fuel economy, the business started by reducing the size of its 7.0-liter V-8 engine to 6.0 liters and adding throttle-body fuel injection. The L61, as it was known, wasn’t fuel-efficient enough. Engineers then had a thought. Cars don’t always need eight cylinders to maintain speed, such as while cruising along the interstate. Why then do we keep them all going?
The L62 engine was developed by General Motors engineer Chris Meagher in collaboration with automotive supplier Eaton Corporation. Similar to the L61, the L62 had a displacement of 6.0 liters, but it had automated cylinder deactivation when not in use, which reduced its power and fuel consumption to that of a 4.5-liter V-6 or a 3.0-liter V-4. To determine whether to deactivate two or four cylinders by disengaging the appropriate rocker arms and closing the intake and exhaust valves on two or four cylinders, the system used engine speed, EGR (exhaust gas recirculation) position, intake manifold air pressure, coolant temperature, exhaust, and air pump operation. Cadillac predicted increases in fuel efficiency of up to 30% when traveling on the highway.
With the exception of the Seville, which received an Oldsmobile-sourced diesel V-8, the new engine became standard on all Cadillac models since the manufacturer was so confident in it. The manufacturer advised purchasers to “sit behind the wheel of a V-8-6-4 Cadillac to discover firsthand what a wonderful advancement it actually is” in a 12-page salesman’s pocket brochure outlining the new engine.
But once they did, issues started to arise. The technology worked well, but as driving circumstances swiftly changed, the microprocessors raced to activate, deactivate, and then reactivate cylinders, causing the automobile to hesitate, buck, and stall. Dealers deactivated the system on their clients’ cars, putting them in V-8 mode indefinitely as GM released 13 updates, none of which were successful. After just one year, GM discontinued the engine, but work on cylinder deactivation continued at GM, Eaton, and other manufacturers. Despite this, not a single technology made it into production.
By the turn of the century, as petrol prices began to rise once more, automakers sought to safeguard the pickup trucks and SUVs that were generating enormous profits. Meagher, who is currently GM’s associate chief engineer for small-block engines, proposed bringing back the concept of cylinder deactivation systems to GM.
“We were aware that we would have to focus on truck fuel economy. Meagher stated in a 2006 Automotive News interview that his team began asking itself, “How can we do that?” “You immediately return to the notion of using the engine simply for what you require as opposed to what it is capable of.
Surprisingly, GM Powertrain Chief Tom Stephens approved of the proposal with one condition: the new system had to function flawlessly. GM was able to successfully introduce Displacement on Demand on its mid-size SUVs in 2005 because to time and advances in computing capacity. When the system debuted on the redesigned Chevrolet Tahoe, GMC Yukon, Chevrolet Impala SS, and Pontiac Grand Prix GXP a year later (as early 2007 models), it was given the new name Active Fuel Management. Even the C7 Corvette can now travel the highway at 30 mpg with four active cylinders.
GM was six months behind Chrysler, which had been working on the similar concept since the 1990s. Cylinder deactivation systems were also being developed by Mercedes-Benz, Honda, and Toyota, but none of them had the same negative reputation as Cadillac’s 1981 attempt.
Which automobiles include cylinder deactivation?
When an internal combustion engine’s full power is not needed, cylinder deactivation devices selectively turn off part of the cylinders to increase fuel efficiency and lower CO2 emissions. Low power needs for the engine prevent it from operating at its best efficiency. The amount of air entering the throttle is little, and it is harder to get air into the cylinders. In addition to requiring extra energy to overcome the internal vacuum, the cylinders don’t fill up entirely with air. The combustion pressure is lowered when there is less air in the cylinder. Pumping loss is the term used to describe this circumstance, which can dramatically lower the engine’s efficiency.
By closing the intake and exhaust valves and turning off the fuel injection for a specific cylinder, cylinder deactivation effectively reduces the displacement of the engine. The compressed gases are forced back down by the pistons in the deactivated cylinders, resulting in zero net work being done. By running at a higher combustion pressure, the remaining cylinders make up for the loss in power brought on by the inactive cylinders. As a result, the throttle valve is more open for a given load on the engine, enabling the cylinder mean effective pressure to be closer to the ideal level and raising the engine’s efficiency.
The U.S. Corporate Average Fuel Economy (CAFE) rules forced automakers to find innovative solutions to improve the fuel efficiency of their vehicles. The 1981 Cadillac lineup featured the first production cars to use cylinder deactivation for better fuel economy. For an existing six liter pushrod V8 engine, GM created a new fuel management system they named “Modular Displacement” in collaboration with Eaton Corporation. According to engine load, a mechanism known as the “V-8-6-4” could switch the number of cylinders running from eight to six to four. The engine control module, or ECM, chose how many cylinders to turn off and was responsible for controlling cylinder deactivation.
By moving solenoids under the control of the ECM, cylinders could be turned off by causing the valve rocker arms to separate from the corresponding pushrods. The valves for those cylinders would remain closed because they were no longer receiving mechanical lift from the camshaft as a result of their separation from the pushrods. The early kind of electronic fuel injection known as “throttle body injection,” which supplies fuel to all cylinders from a single spot in the throttle body, was used to power the V-8-6-4. The ECM lowered the amount of gasoline injected when cylinders were deactivated, however this system did not allow for fuel to be cut to certain cylinders. According to general consensus, the system had drivability issues caused by the ECM’s limited computing capabilities and the lack of precise fuel control provided by throttle body injection.
Soon after, Mitsubishi introduced “Modulated Displacement,” a type of cylinder deactivation. Mitsubishi created a four cylinder engine that could shut down two of its cylinders using the same concepts as Cadillac’s design. The public did not favor either design, and cylinder deactivation remained unpopular for a while.
The concept of cylinder deactivation has been revived today by businesses like Mercedes-Benz, Chrysler Group, General Motors (GM), Honda, and Volkswagen, along with fresh concepts like variable valve timing and variable compression.
The pushrod design or the overhead cam design are the two types of camshaft layouts now used in engines. The cylinder deactivation mechanism stops feeding fuel into the deactivated cylinders and closes the intake and exhaust valves for both designs. The ECM is in charge of all cylinder deactivation components. The ECM decides when to start cylinder deactivation based on data it receives from a number of sensors. Vehicle speed, engine speed, engine load, and throttle position are typically deciding variables.
Cylinder deactivation is now used by Chrysler and GM in a few V6 and V8 pushrod engines. Both businesses employ a unique kind of hydraulic lifter to stop the deactivated cylinders’ intake and exhaust valve activation. This stops certain pushrods and their associated valves from being affected by the lifting motion produced by the spinning camshaft.
The plunger in a cylinder that touches and tracks the up-and-down action of the cam lobe is an analogy for hydraulic lifters. The lift is transferred from the camshaft to the pushrod and then to the valve by the plunger, which is located inside the top of the cylinder (or lifter body). Because the lifter body is filled with oil, the plunger typically doesn’t move inside of it.
The plunger is permitted to collapse into the lifter body in the particular hydraulic lifters used for cylinder deactivation, preventing the cam lobe’s lifting motion from reaching the valves. This is accomplished by allowing high pressure oil to enter the lifter body. This releases a locking pin, allowing the plunger to collapse. An electronic solenoid that is under the control of the ECM is used to turn on and off the delivery of high pressure oil. As long as the valves are not being forced open by the camshaft, they will remain closed thanks to valve springs.
Recently, cylinder deactivation has been implemented in a variety of OHC engines, from four cylinders to V12s, including Mercedes, Honda, and Volkswagen.
Honda and Mercedes employ comparable systems. Mercedes and Honda’s systems, like those used in Chrysler and GM pushrod engines, rely on solenoids that regulate high pressure oil flow in response to an ECM command. The OHC systems from these two manufacturers, as opposed to pushrod systems, use unique rocker arms to regulate the movement of valves in deactivated cylinders. There are two distinct rocker arms that sit next to one other and share the same fulcrum for each valve in a cylinder that can be disabled. Like a typical rocker, one of these rockers is constantly in contact with the camshaft. The valve is continuously in contact with the second rocker.
Two intake valve lobes are used in newer models of Honda’s all-aluminum SOHC 60-degree V6 engine, enabling the company’s i-VTEC technology at both low and high RPMs. The intake valves of these cylinders can be closed by a third zero-lift lobe that is solely connected to the back bank, thus turning them off.
In normal operation, a pin prevents the two rockers from moving independently. As a result, the lift that the camshaft imparts on the first rocker is transferred to the second rocker, opening the valve. The ECM activates the electronic solenoids in cylinder-deactivation mode, allowing high pressure oil to release the pin holding the two rocker arms together. As a result, the two arms now move independently of one another: the first rocker keeps moving in the direction of the cam, but this motion is not transferred to the second rocker; as a result, the valve remains closed due to the force of the valve spring.
Volkswagen employs a totally distinct methodology. The camshafts they utilize are unique multi-piece designs with short portions that fit over the main shaft like sleeves. These sleeves have a spiral-shaped slot carved into them and two different lobe profiles that can be used by one valve. When cylinders are to be deactivated, a pin that is located above the camshaft on an electromagnetic actuator descends and fits into the spiral groove on the revolving cam sleeve. The sleeve moves to the left or right as it travels with the pin along the spiral groove.
A lobe profile on the sleeve that resembles a typical cam lobe will be followed by the valve rocker during normal operation. When cylinder deactivation mode is engaged, the sleeve is moved axially, and the valve rocker then starts to follow the second lobe profile, which is totally spherical and has no cam form at alla lobe with “zero-lift.” The corresponding valve remains closed because the rocker continues to be in constant contact with the cam sleeve but is now following a lobe that generates no lift.
Although manufacturers now offer systems claiming efficiency increases as high as 20%, the U.S. Dept. of Energy believes that cylinder deactivation systems increase fuel efficiency by roughly 7.5 percent. The Honda Odyssey, Accord, and Pilot, Volkswagen Polo BlueGT, Lamborghini Aventador LP 700-4, Audi A1, A3, and A8 L, as well as Chevrolet (GM) Impala, Suburban, Silverado, Tahoe, Caprice, Camaro, and Corvette Stingray, all have cylinder deactivation options.
Dynamic Skip Fire is a technique created by a firm called Tula Technologies. This system continuously analyzes the torque needs on the engine and decides whether or not to fire each cylinder at each firing opportunity, as opposed to turning off a predefined group of cylinders. Tula Technologies has received significant investment from General Motors, and the automaker has said that this technology might be used in upcoming models.