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Honda’s new Thai-built Accord V6 -- to be launched in Australia in February
2008 -- will combine three engines under one bonnet.
No, it doesn’t actually come with thirteen cylinders, but the new 3.5-litre,
200kW-plus SOHC Accord V6 will feature Honda’s unique, high-tech Variable
Cylinder Management (VCM), allowing the car to run on six, four or three
cylinders depending on road speed and load conditions.
Once launched, the Accord will be the only car in the Large Car Segment to
have the advanced Variable Cylinder Management technology.
The key benefits are fuel savings and lower emissions. Customers from America
report that their V6-powered Accords achieve four-cylinder-like fuel
consumption.
The engine runs with the full six cylinders during acceleration or under high
load, and seamlessly switches to four or three cylinders for cruising or
low-speed running. The change between cylinder modes is seamless and is not
obvious to the driver.
It’s the automotive equivalent of having your cake and eating it too.
Honda will release further details of the exciting new Accord range closer to
the launch date.
How VCM works
During start-up, acceleration or when climbing hills - any time high power
output is required - the engine operates on all six cylinders. During moderate
speed cruising and at low engine loads, the system operates just one bank of
three cylinders. For moderate acceleration, higher-speed cruising and mild
hills, the engine operates on four cylinders.
With three operating modes, the VCM system can finely tailor the working
displacement of the engine to match the driving requirements from moment to
moment. Since the system automatically closes both the intake and exhaust valves
of the cylinders that are not used, pumping losses associated with intake and
exhaust are eliminated and fuel economy gets a further boost. The VCM system
combines maximum performance and maximum fuel economy - two characteristics that
don't typically coexist in conventional engines.
VCM deactivates specific cylinders by using the VTEC (Variable Valve-Timing
and Lift Electronic Control) system to close the intake and exhaust valves while
simultaneously the Powertrain Control Module cuts fuel to those cylinders. When
operating on three cylinders, the rear cylinder bank is shut down. When running
on four cylinders, the left and centre cylinders of the front bank operate, and
the right and centre cylinders of the rear bank operate.
The spark plugs continue to fire in inactive cylinders to minimize plug
temperature loss and prevent fouling induced from incomplete combustion during
cylinder re-activation.
The system is electronically controlled, and uses special integrated spool
valves that do double duty as rocker-shaft holders in the cylinder heads. Based
on commands from the system's electronic control unit, the spool valves
selectively direct oil pressure to the rocker arms for specific cylinders. This
oil pressure in turn drives synchronizing pistons that connect and disconnect
the rocker arms.
The VCM system monitors throttle position, vehicle speed, engine speed,
automatic-transmission gear selection and other factors to determine the correct
cylinder activation scheme for the operating conditions. In addition, the system
determines whether engine oil pressure is suitable for VCM switching and whether
catalytic-converter temperature will remain in the proper range. To smooth the
transition between activating or deactivating cylinders, the system adjusts
ignition timing, drive-by-wire throttle position and turns the torque converter
lock-up on and off. As a result, the transition between three-, four-, and
six-cylinder operation is unnoticeable.
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