Mundo Automotriz La Revista No. 207 Junio 2013

artÍcUlo tÉcnico
Before engine control units, air/
fuel mixture, ignition timing, and
idle speed were mechanically set
and dynamically controlled by
mechanical and pneumatic means.
Once more fully developed, electronic valve operation will yield even more benefits.
Cylinder deactivation, for instance, could be made much more fuel efficient if the intake
valve could be opened on every downstroke and the exhaust valve opened on every
upstroke of deactivated cylinder. Another event more significant advancement will be the
elimination of the convention throttle. When a car is run at part throttle, this interruption
in the airflow causes excess vacuum, which causes the engine to use up valuable energy
acting as a vacuum pump. BMW attempted to get around this on their V-10 powered M5,
which had individual throttle butterflies for each cylinder, placed just before the intake valves.
With electronic valve operation, it will be possible to control engine speed by regulation valve
lift. At part throttle, when less air and gas are needed, the valve lift would not be as great. Full
throttle is achieved with the gas pedal is depressed, sending an electronic signal to the ECU,
which in turn regulates the lift of each valve event, and opens at all the way up.
PROgRAMMAblE ECUS
A special category of ECUs are those which are programmable. These units do not have
a fixed behavior and can be reprogrammed by the user. Programmable ECUs are required
where significant aftermarket modifications have been made to a vehicle´s engine. Examples
include adding or changing of a turbocharger, adding or changing of an intercooler,
changing of the exhaust system or a conversion to run on alternative fuel. As a consequence
of these changes, the old ECU may not provide appropriate control for the new configuration.
In these situations, a programmable ECU can be wired in. These can be programmed/
mapped with a laptop connected using a serial or USB cable, while the engine is running.
The programmable ECU may control the amount of fuel to be injected into each cylinder.
This varies depending on the engine´s rpm and the position of the accelerator pedal. The
engine tuner can adjust this by bringing up a spreadsheet-like page on the laptop where
each cell represents an intersection between a specific rpm value and an accelerator pedal
position. IN this cell a number corresponding to the amount of fuel to be injected is entered.
The spreadsheet is often referred to as a fuel table or fuel map.
By modifying these values while monitoring the exhausts using a wide band lambda probe
to see if the engine runs rich or lean, the tuner can find the optimal amount of fuel to inject
to the engine at every different combination of rpm and the throttle position. This process is
often carried out at a dynamometer, giving the tuner a controlled environment to work in. An
engine dynamometer gives a more precise calibration for racing applications. Tuners often
utilize a chassis dynamometer for street and other high performance applications.
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