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
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.
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.
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
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
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.
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
Interestingly, Chrysler (like Mercedes) teamed with Eberspaecher to design an
exhaust system to maintain a V8-like rumble even when 4 cylinders are
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
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.
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.
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
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.
At the time of writing, GM is yet to release DoD technology in a selection of
V6-powered mid-size passenger cars.
As far as we are aware, there’s only one mass produced Japanese engine that
employs cylinder deactivation – the Honda J-series V6.
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
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.
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.
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
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