Fiat introduced modern computer controlled Common Rail technology back in 1997. Due to financial problems they sold the technology to Bosch. Back in March at the Geneva Motor Show in Switzerland they debuted a technology just as important (perhaps more important). Its called Multiair
This technology might silence the gas versus diesel debate because having this much control over the intake valves does some neat things. For one depending on control strategies one could choose to run many different types of fuels and compression or spark ignition. The debate will now be hydrogen versus electricity. This technology is big for Internal combustion engines.
A 60% reduction in NOx thanks to internal exhaust gas recirculation (IEGR). Basically some exhaust is left in the cylinder which displaces oxygen which gives the nitrogen in the air nothing to bond to.
FIAT POWERTRAIN TECHNOLOGIES S.p.A. Fiat Group Automobiles SpA
www.fptpowertrain.com
MULTIAIR: THE ULTIMATE AIR MANAGEMENT STRATEGY
Multiair is the new electro-hydraulic system of engine
valves for dynamic and direct control of air and combustion,
cylinder by cylinder and stroke by stroke
Thanks to a direct control of the air through the intake
engine valves without using the throttle, Multiair helps reducing
fuel consumption; pollutant emissions are likewise reduced
through combustion control
Multiair is a versatile technology, easily applicable to all
gasoline engines and with future potential developments also for
Diesel engines
BENEFITS
FUEL CONSUMPTION AND EMISSIONS REDUCTION
INCREASE OF BOTH MAX POWER AND TORQUE
ENHANCED PERFORMANCE AND FUN TO DRIVE
The Fiat Multiair Technology: some history
In the last decade, the development of the Common Rail technology for Diesel
engines marked a breakthrough in the passenger car market. To be
competitive also in the field of gasoline engines, Fiat Group decided to follow
the same approach and focus on breakthrough technologies. The aim was to
provide customers with substantial benefits in terms of fuel economy and funto-
drive while maintaining the engine intrinsic comfort characteristics, based
on a smooth combustion process and on light structures and components.
The key parameter to control Diesel engine combustion and therefore
performance, emissions and fuel consumption is the quantity and
characteristics of the fuel injected into cylinders. That is the reason why the
Common Rail electronic Diesel fuel injection system was such a fundamental
breakthrough in Direct Injection Diesel engine technology.
The key parameter to control gasoline engine combustion, and therefore
performance, emissions and fuel consumption, is the quantity and
characteristics of the fresh air charge in the cylinders. In conventional gasoline
engines the air mass trapped in the cylinders is controlled by keeping the
intake valves opening constant and adjusting upstream pressure through a
throttle valve. One of the drawbacks of this simple conventional mechanical
control is that the engine wastes about 10% of the input energy in pumping the
air charge from a lower intake pressure to the atmospheric exhaust pressure.
A fundamental breakthrough in air mass control, and therefore in gasoline
engine technology, is based on direct air charge metering at the cylinder inlet
ports by means of an advanced electronic actuation and control of the intake
valves, while maintaining a constant natural upstream pressure.
Research on this key technology started in the 80’s, when engine electronic
control technologies reached the stage of mature technologies.
At the beginning world-wide research efforts were focused on the
electromagnetic actuation concept, following which valve opening and closing
is obtained by alternatively energizing upper and lower magnets with an
armature connected to the valve. This actuating principle had the intrinsic
appeal of maximum flexibility and dynamic response in valve control, but
despite a decade of significant development efforts the main drawbacks of the
concept - its being intrinsically not fail-safe and its high energy absorption -
could not be fully overcome.
At this point most automotive companies fell back on the development of the
simpler, robust and well-known electromechanical concepts, based on the
valve lift variation through dedicated mechanisms, usually combined with cam
phasers to allow control of both valve lift and phase. The main limitation of
these systems is low flexibility in valve opening schedules and a much lower
dynamic response; for example all the cylinders of an engine bank are
actuated simultaneously thereby excluding any cylinder selective actions.
Many similar electromechanical valve control systems were then introduced
over the past decade.
In the mid 90’s Fiat Group research efforts switched to electro-hydraulic
actuation, leveraging on the know-how gained during the Common Rail
development. The goal was to reach the desired flexibility of valve opening
schedule air mass control on a cylinder-by-cylinder and stroke-by-stroke basis.
The electro-hydraulic variable valve actuation technology developed by Fiat
was selected for its relative simplicity, low power requirements, intrinsic fail
safe nature and low cost potential.
The Fiat Multiair Technology: how it works
The operating principle of the system, applied to intake valves, is the following:
a piston, moved by a mechanical intake cam lobe, is connected to the intake
valve through a hydraulic chamber, which is controlled by a normally open
on/off Solenoid Valve.
When the Solenoid Valve is closed, the oil in the hydraulic chamber behaves
like a solid body and transmits to the intake valves the lift schedule imposed
by the mechanical intake cam. When the solenoid valve is open, the hydraulic
chamber and the intake valves are de-coupled; the intake valves do not follow
the intake cam anymore and close under the valve spring action. The final part
of the valve closing stroke is controlled by a dedicated hydraulic brake, to
ensure a soft and regular landing phase in any engine operating conditions.
Through Solenoid Valve opening and closing time control, a wide range of
optimum intake valve opening schedules can be easily obtained.
For maximum power, the Solenoid Valve is always closed and full valve
opening is achieved following completely the mechanical cam, which was
specifically designed to maximize power at high engine speed (long opening
time).
For low-rpm Torque, the Solenoid Valve is opened near the end of the cam
profile, leading to early intake valve closing. This eliminates unwanted
backflow into the manifold and maximizes the air mass trapped in the
cylinders.
In engine part load, the Solenoid Valve is opened earlier causing partial valve
openings to control the trapped air mass as a function of the required torque.
Alternatively the intake valves can be partially opened by closing the Solenoid
Valve once the mechanical cam action has already started. In this case the air
stream into the cylinder is faster and results in higher in-cylinder turbulence.
The last two actuation modes can be combined in the same intake stroke,
generating a so-called “Multilift” mode, that enhances turbulence and
combustion rate at very low loads.
The Multiair Technology Benefits
The Multiair Technology potential benefits for gasoline engines exploited so
far can be summarized as follows:
• Maximum Power is increased by up to 10% thanks to the adoption of a
power-oriented mechanical cam profile
• Low-rpm Torque is improved by up to 15% through early intake valve
closing strategies that maximize the air mass trapped in the cylinders.
• Elimination of pumping losses brings a 10% reduction of Fuel
Consumption and CO2 emissions, both in Naturally Aspirated and
Turbocharged engines with the same displacement
• Multiair Turbocharged and downsized engines can achieve up to 25%
Fuel Economy improvement over conventional Naturally Aspirated
engines with the same level of performance
• Optimum valve control strategies during engine warm-up and internal
Exhaust Gas Recirculation, realized by reopening the intake valves
during the exhaust stroke, result in emissions reduction ranging from 40%
for HC / CO to 60% for NOx
• Constant upstream air pressure, atmospheric for Naturally Aspirated and
higher for Turbocharged engines, together with the extremely fast air
mass control, cylinder-by-cylinder and stroke-by-stroke, result in a
superior dynamic engine response
Application of the Multiair Technology to FPT Engines
The first world-wide application of the Multiair technology will be the Fire
1400cc 16V Naturally Aspirated and Turbocharged engines.
The second application is a new Small Gasoline Engine (SGE - 900cc Twincylinder)
where cylinder head design has been specifically optimized for the
Multiair actuator integration. Here again, there will be both a Naturally
Aspirated and a Turbocharged version. A specific Turbocharged engine
version will be bi-fuel (gasoline- CNG).
Thanks to radical downsizing, the Turbocharged Small Gasoline Engine
achieves Diesel-like CO2 emission levels, which are further reduced in its
Natural Gas version with CO2 emissions lower than 80 g/km in many vehicle
applications.
Further Potential of the Multiair Technology
All breakthrough technologies open a new world of further potential benefits,
which are usually not fully exploited in the first generation, in order to minimize
industrial risk.
The Common Rail technology, a Fiat worldwide premiere in 1997, paved the
way to more than a decade of further technological evolutions such as
“Multijet” for multiple injections, Small Diesel Engines and the very recent
Modular Injection technology, soon to be launched on the market.
Similarly, the Multiair technology, a Fiat worldwide premiere in 2009, will pave
the way to a wave of further technological evolutions for gasoline engines:
• Integration of the Multiair Direct air mass control with Direct gasoline
Injection to further improve transient response and fuel economy.
• Introduction of more advanced multiple valve opening strategies to further
reduce emissions.
• Innovative engine-Turbocharger matching to control trapped air mass
through combination of optimum boost pressure and valve opening
strategies.
While electronic gasoline fuel injection developed in the 70’s and Common
Rail developed in the 90’s were fuel specific breakthrough technologies, the
Multiair Electronic Valve Control technology can be applied to all internal
combustion engines whatever fuel they burn.
Multiair, initially developed for Spark Ignition engines burning light fuel ranging
from gasoline to Natural Gas and hydrogen, has wide potential also for Diesel
engine emissions reduction.
Intrinsic NOx reduction of up to 60% can be obtained by internal Exhaust Gas
Recirculation (iEGR) realized with intake valves reopening during the exhaust
stroke, while optimal valve control strategies during cold start and warm-up
bring up to 40% HC and CO reduction of emissions. Further substantial
reduction comes from the more efficient management and regeneration of the
Diesel Particulate Filter and NOx Storage Catalyst, thanks to the highly
dynamic air mass flow control during transient engine operation.
Diesel engine performance improvement is similar to that of the gasoline
engine and is based on the same physical principles. Instead, fuel
consumption benefits are limited to few percentage points because of the low
pumping losses of Diesel engines, one of the reasons of their superior fuel
economy.
In the future, powertrain technical evolution might benefit from a progressive
unification of gasoline and Diesel engines architectures.
A Multiair engine cylinder head can be therefore conceived and developed,
where both combustion systems can be fully optimized without compromises.
Moreover the Multiair electro-hydraulic actuator is physically the same, with
minor machining differences, while internal subcomponents are all carry over
from the Fire and SGE applications.