Niagara Gazette

March 14, 2014

TOM'S CORNER: A cylinder deactivation technology update

By Tom Torbjornsen
Niagara Gazette

Niagara Gazette — Cylinder deactivation is used by carmakers to increase fuel efficiency & lower tailpipe emissions. The system selectively cancels cylinders while driving under light load, thus increasing fuel mileage. Cylinders are activated only when needed to pull or haul. There’s no real impact on drivers other than the need to maintain good maintenance. Additionally, tend to lit check engine lights immediately to stay the “domino theory” in your performance system. Additionally:

• Motorists might think that they have to do something to activate it. This is not true; the system operates without input from the driver. Motorists might be ill advised that the technology prematurely wears engines out. This is not true. Finally, Motorists might be jaded on the technology due the GM’s failed use of cylinder deactivation in the late 70s to early 80s. No need to be concerned about systems today, technology has been improved to the degree that it operates seamlessly due to greatly improved computerized engine management systems.

• Technicians/repair shops working on the systems need to have knowledge, tools, and database information necessary to diagnose & repair them.

• The technology reduces tailpipe emissions that contribute to air pollution & quality.

 How it works

Systems shut down fuel supply and close the valves of the cylinders not being used. There are two ways that valve control is accomplished: (1) control of rocker arms electro-hydraulically-mechanically or (2) collapsing valve lifters via oil pressure control through the Engine Control Module. When the valves close, the remaining exhaust gas from the previous combustion explosion in the deactivated cylinders acts as a cushion, bouncing the piston back down after it travels to Top Dead Center on compression and exhaust strokes. This action aids in keeping the crankshaft rotating despite the deactivated cylinders and causes no undue stress or pressure on the engine. Fuel, ignition, lifter collapse, and/or rocker arm control are all managed via microprocessors.

 Two designs available

The technology is available for 4, 6, 8 or 12 cylinder engines. Systems can deactivate up to ½ of engines’ cylinders.

1. Pushrod engines: in pushrod engines cylinder deactivation is achieved by bleeding off oil pressure to the lifters of the valves in the cylinder/s to be cancelled. This stops mechanical manipulation of the valves, leaving them closed.

2. Overhead cam engines: on engines where the valves are opened and closed by overhead camshafts, engine designers use a split rocker arm for each valve. One rocker arm rides on cam lobes and mechanically manipulates nothing, while the other rocker opens & closes the valve. When the cylinder is to be cancelled, oil control to a pin locking the two rockers together releases the pin causing the valve-actuating rocker to sit without being moved, thus closing the valves. The other rocker simply rides on the cam lobe manipulating nothing.

 Benefits of cylinder deactivation

Engines using the technology offer greater fuel efficiency. Carmakers claim an average of up to 20% fuel economy. The EPA did a study on this and came up with 7.5% savings overall.

Cadillac’s attempt at cylinder deactivation in 1981

When OPEC flexed their collective muscle on North America on the late 70s thru early 80s limiting oil production, GM, in an effort to lead the field in fuel economy decided to introduce a new engine management system called the “Cadillac 8-6-4. This system was touted by Cadillac to deliver 20% or more fuel savings.

The problem with Cadillac’s 8-6-4 cylinder deactivation system

When Cadillac tried cylinder deactivation in 1981, the concept was very unreliable because computer systems were primitive and unable to manage engine controls necessary to attain seamless operation. Today’s sophisticated computer systems powerfully and seamlessly control all elements of cylinder deactivation.

 Cylinder deactivation systems available today

What companies offer the technology? What are their unique “brand names” for it? See below:

• Mercedes-Benz’s system is called Active Cylinder Control (ACC) and is offered on their V8 and V12 engines. These engines are pushrod engines, hence the system employs the use of split rocker arms linked by a pin, that when the cylinder is deactivated, is actuated via oil control by way of the Engine Control Module.

• Chrysler Group’s system is called Multiple Displacement System. Its offered on Chrysler’s 5.7-liter HEMI V8 engine. When in operation (speeds below 30MPH and engine RPM 3000 or less) the system bleeds off oil pressure in the hydraulic lifters allowing the valves to stay closed by virtue of valve spring tension. When the engine demand exceeds the specified operation environment, the system restores the cancelled cylinder operation.

• GM’s system is called either Displacement On Demand or Active Fuel Management. Offered on GM’s V6 & V8 engines, the system closes valves via hydraulic lifter oil control. Upon demand, the lifters are pumped up once again asserting valve control.

• Honda’s system is called Variable Cylinder management. The system is offered on only their J-Series overhead cam V6. When activated, the system deactivates an entire bank of cylinders reducing engine output to 3 cylinders. Upon the need, the cylinders are energized once again, restoring full V6 engine power.

• Volkswagen’s system is called Active Cylinder Technology. The system uses as its foundation, a 4-cylinder engine; this is a first. Previously cylinder deactivation was only reserved for use in 6, 8, & 12 cylinder engines. When in operation, it shuts down number 2 & 3 cylinders. The system operates at low speeds, when pulling power becomes necessary, the engine returns to 4 cylinder operation with one press of the gas pedal.

Well, there’s your cylinder deactivation system update!

‘Til next time ... Keep Rollin’

"America's Car Show" with Tom Torbjornsen airs 7:30 p.m. Wednesday, 9 a.m. Thursday and 11 a.m. Saturday on WBBZ-TV.