Gasoline fuel is not only highly combustible,
it also evaporates easily. The fumes – which contain benzene – pose a health
hazard when inhaled and in combination with sunlight and exhaust gases they can
cause photochemical smog which is a concern in large cities. This is why modern
gasoline cars have a system onboard to minimize hydrocarbon emissions.
A canister filled with
activated carbon is used to collect all fumes from the tank. Of course the
canister with the cumulated hydrocarbon (HC) needs to be flushed or purged from
time to time. The air content, rich in HC, is fed forward to the intake
manifold and flows into the combustion chambers where it gets burnt. This
system has greatly reduced evaporative HC emissions.
However, two challenges begin
to threaten this success story: Firstly, the legislation on evaporative HC
emission is set to become much stricter around the world over the next four to
five years. Secondly, purging the HC canister is currently done by using the
vacuum that is generated in the intake manifold of a gasoline engine during
part-load operation by so-called throttling. In highly efficient gasoline cars
there is less or no vacuum available, though, because throttling is inefficient
and is avoided wherever possible. In a gasoline mild hybrid car the engine may
not be running at up to 20 per cent of the driving time, so no vacuum either.
“Continental has developed an
electrified solution to further reduce HC evaporative emissions”, said Klaus
Hau, head of the Business Unit Sensors & Actuators in the Continental
Division Powertrain. “For the first time the Active Purge Pump makes canister
purging available independent from engine operation point and vacuum
availability. With the Active Purge Pump vehicle manufacturers will be in a
much better position to meet oncoming HC emission legislation,” said Hau. First
SOP is planned for end of 2019.
From Active Purge Pump to Active Purge System
Put very simply, the
efficiency of modern gasoline cars is partly based on running the engine in the
most efficient part of its map whenever possible – or not to run it all, for
instance, in a hybrid car. Throttling in particular is avoided as the engine’s
thermodynamic efficiency is reduced by throttle losses. This is increasingly
unacceptable because environmental concerns and economic considerations
unanimously advocate lower fuel consumption.
“The need for higher engine
efficiency is beginning to make vacuum a rarity in gasoline cars. As a result
it is becoming more difficult to flush the HC canister because often the
boundary conditions will not allow this”, said Stefan Grüneis, product manager
for Continental exhaust and emissions actuators.
The Active Purge Pump (APP) is
not dependent on vacuum. Instead it actively pulls the HC-laden air from the
canister. The pump used for this action is a very compact and light-weight
radial pump, driven by a highly efficient brushless DC motor. “The biggest
benefit of the APP is that we can use it on demand, and activate it any time
when it is necessary”, said Grüneis. “This makes the APP a perfect match for
turbocharged engines which are run at higher loads more often, de-throttled
engines, start-stop and hybrid powertrains with long engine-off periods.”
Then again, actively purging
the canister is only the core function of the new solution. Additional software
modules and some additional hardware (like valves) will make further functions
available. Among these are a high-performance leak detection and a measurement
of the HC content in the purged air. “Additional functions like these make the
pump the core of an Active Purge System (APS). For instance, determining the HC
concentration in the purge air is needed to adapt the amount of fuel injection
during part load or idling”, Grüneis explained.
Tank leak detection, on the
other hand, is currently a stand-alone system which has to be integrated
separately. Making this part of an Active Purge System built around the
existing Active Purge Pump is more efficient. To support the trend to higher
system integration levels, the required APP and APS functional content can be
flexibly combined from hardware and software components.
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