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Cylinder Deactivation Reborn - Part 2

We take a look at the latest breed of cylinder deactivation systems....

By Michael Knowling

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At a glance...

  • Final of 2-part series
  • The latest cylinder deactivation systems
  • DaimlerChrysler (Mercedes, Chrysler and Jeep)
  • GM
  • Honda
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In the first part of this series we looked at the principle of cylinder deactivation and its first mass production application in the 1981 Cadillac. The old Cadillac system was successful in reducing fuel consumption but its driveability and reliability problems gave cylinder deactivation a poor reputation for many years.

In the second part of this series we’ll look at the latest wave of cylinder deactivation systems that have emerged from European, American and Japanese car companies.

DaimlerChrysler (Mercedes V12/V8)

DaimlerChrysler was the first company following Cadillac to apply cylinder deactivation to mass produced cars. The first Mercedes models to appear with cylinder deactivation were the European-spec 1999 CL600, S600 and CL500. These vehicles were powered by either a DOHC 6.0 litre V12 or DOHC 5.0 litre V8.

The Mercedes cylinder deactivation system, known as Active Cylinder Control (ACC), is quite unlike the system used in the 1981 Cadillac.

The Mercedes approach involves deactivating half of the engine’s cylinders - which means the V12 becomes a 6 cylinder and the V8 becomes a four. The Mercedes follows the common principle of keeping the intake and exhaust valves closed and preventing a fresh air-fuel charge entering the combustion chamber.

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The valves of each cylinder are kept closed using a pair of arms that replace the conventional engine’s roller-type rocker arm. One of these arms follows the cam profile while the second arm connects to the valves. During normal engine operation the two arms are joined by a locking pin. When cylinder deactivation is required, solenoid-controlled oil pressure is used to move the locking pin. This disengages the two arms and the valves remain in their closed position (due to valve spring tension).

But the biggest advancement in cylinder deactivation is the use of sophisticated electronic control.

The Mercedes uses a sequential fuel delivery system that cuts fuel to the cylinders that are deactivated. This prevents the driveability problems that were encountered in the throttle-body injected Cadillac. In addition, the use of electronic throttle control, valve timing, ignition timing and a variable intake manifold help give a seamless transition.

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Interestingly, Mercedes teamed with Eberspaecher to install an ECU-controlled valve in the exhaust system downstream of the cat converters. This valve is closed during 4 cylinder operation to preserve engine sound.

Mercedes says the system improves fuel economy by around 7 percent in city driving and up to 20 percent at a steady cruise. Power output for the 1999 5.0 litre V8 CL500 is 225kW while the 6.0 litre V12 CL600 and S600 makes a stomping 290kW.

DaimlerChrysler (HEMI V8)

Also released by DaimlerChrysler is the 5.7 litre HEMI V8 featuring cylinder deactivation. The system was introduced in the 2004 Chrysler 300C, Dodge Magnum, Dodge Charger, Jeep Grand Cherokee, Dodge Durango, Dodge Ram and Jeep Commander.

The DaimlerChrysler HEMI cylinder deactivation system is known as MDS (Multi-Displacement System). MDS involves disabling 4 of the HEMI’s 8 cylinders at road speeds above 30 km/h and with the engine spinning at less than 3000 rpm.

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The system works entirely differently to the Mercedes approach.

The HEMI uses a special set of lifters which are referred to as “lost motion devices”. To enable 4 cylinder operation, the lifters are fed oil at high pressure. This oil pressure (controlled by ECU operated solenoids) pushes on an internal locking pin that causes the lifter to collapse. Once the lifter collapses, the camshaft is disengaged from the pushrod and valve - and the cylinder is deactivated.

MDS can switch between 8 and 4 cylinder operation in just 40 milliseconds (0.040 seconds). Fuel is cut to the deactivated cylinders and the electronic-controlled throttle is used to maintain engine power during the transition.

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Interestingly, Chrysler (like Mercedes) teamed with Eberspaecher to design an exhaust system to maintain a V8-like rumble even when 4 cylinders are deactivated.

Power output varies depending on vehicle model and ranges from 240kW to 290kW. MDS is said to bring fuel consumption gains of around 10 – 20 percent.

GM V8 and V6

Displacement on Demand (DoD) is the name for GM’s latest cylinder deactivation system.

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After its association with the notorious 1981 Cadillac, GM waited until 2004 to re-release cylinder deactivation. The DoD system has been initially released in the GMC Envoy and TrailBlazer SUVs.

The Envoy and Trailblazer use a Vortec 5.3 litre Gen IV V8 (dubbed LH6). The engine runs on all 8 cylinders during start-up, idle and heavy acceleration but switches to 4 cylinder mode on light loads.

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Like the HEMI, the GM system employs specially developed hydraulic lifters (known as switching roller followers) for the intake and exhaust valves. The lifters can be collapsed by disengaging an internal locking pin. The locking pin is disengaged using solenoids to alter oil pressure fed into the lifter. When the locking pin is disengaged and the lifter collapses, the camshaft is isolated and the valves remain closed.

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A new 32-bit ECU orchestrates the valve deactivation solenoids, throttle control, ignition timing and sequential fuel delivery (which includes cutting fuel to cylinders which are deactivated). A pressure-operated valve in the muffler also serves to maintain a suitable exhaust note in V8 and 4 cylinder operating modes.

The Vortec 5.5 litre V8 with DoD generates 224kW at 5000 rpm and 449Nm at 4000 rpm. Average fuel consumption is improved by around 8 percent – up to 25 percent in some conditions.

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At the time of writing, GM is yet to release DoD technology in a selection of V6-powered mid-size passenger cars.

Honda V6

As far as we are aware, there’s only one mass produced Japanese engine that employs cylinder deactivation – the Honda J-series V6.

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For the 2005 model year, Honda introduced its Variable Cylinder Management (VCM) system to the 3.5 litre Odyssey and 3.0 litre Accord Hybrid. For the 2006 model year, VCM is also likely to appear in the Honda Pilot soft-roader.

Honda’s VCM system deactivates an entire bank of cylinders at light load – the engine switches from 6 to 3 cylinder operation. Road speed, rpm and throttle position are the major factors used determine when the engine switches to 3 cylinder mode.

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Deactivation of cylinders is achieved by releasing a synchroniser pin that normally interlocks the cam follower and rocker arms. The synchroniser pin is released using hydraulic pressure which is controlled by a dedicated solenoid. Once the synchroniser pin is released, the cam follower continues to move against the camshaft but the rocker arms and valves remain in a closed position.

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It is said that 3 cylinder operation remains smooth (though not quite as smooth as in 6 cylinder mode) and Honda has done a great job calibrating the electronic throttle system for a seamless transition. Actively controlled engine mounts are also employed to reduce the sensation of cylinder switching.

Interestingly, the VCM-equipped Odyssey and Accord Hybrid also feature an Active Noise Control (ANC) system that uses the audio system speakers to cancel undesirable engine boom during 3 cylinder operation. The ANC controller uses 2 microphones inside the cabin and generates an out-of-phase signal to cancel out the sound waves. ANC is not used during 6 cylinder operation.

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The J30 3.0 litre VCM engine of the Accord Hybrid generates 179kW (plus 12kW from its electric motor assist) and delivers 23 – 43 percent better fuel consumption than a conventional Accord V6.

The Odyssey’s J35 3.5 litre VCM engine puts out a considerable 190kW and returns fuel consumption around 11 – 12 percent better than the non-VCM version.

Conclusion

We recommend you familiarise yourself with the cylinder deactivation technologies – if fuel prices continue to surge, you can expect to see the deactivation concept take off in the next few years.

See Cylinder Deactivation Reborn – Part 1

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