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Fiat 875 cc two cylinder TwinAir engine featuring Multiair technology

MultiAir or Multiair is a hydraulically actuated variable valve timing (VVT) and variable valve lift (VVL) engine technology enabling "cylinder by cylinder, stroke by stroke"[1] control of intake air directly via a gasoline engine's inlet valves. Developed by Fiat Powertrain Technologies, the technology addresses a primary engine inefficiency: pumping losses caused by restricting intake passage by the throttle plate that regulates air feeding the cylinders.[2]

Fiat S.p.A., now known as Stellantis, launched MultiAir in 2009, employing a proprietary electro-hydraulic system to precisely control air intake without a throttle valve[3] to increase engine power and torque, reduce fuel consumption, reduce emissions, and improve engine operation, offering "a more controllable flow of air during the combustion cycle in comparison with mechanical VVT systems."[4] The technology allows engines to be lighter and smaller while reducing pump losses. It can be adapted to existing engines by replacing the camshaft with the MultiAir system, thus requiring a new head only.

MultiAir was licensed to the Schaeffler Group in 2011, which also markets the system as Uniair.[5] Schaeffler began supplying Uniair systems in 2017 to Jaguar Land Rover, branded as Ingenium technology.[6]

Compatible with both naturally aspirated and forced-induction engines, MultiAir technology was patented by Fiat in 2002 and was launched at the 2009 Geneva Motor Show in the Alfa Romeo MiTo.[7] 1.4 L MultiAir engines for global markets are manufactured in Termoli, Italy at the Fiat Powertrain Technologies factory and the FCA's Dundee Engine Plant (formerly of Global Engine Alliance's GEMA manufacturing branch), with critical systems manufactured and assembled by Schaeffler Group.[5]

In 2010, the 1.4 L MultiAir engine won the International Engine of the Year[8] as well as Popular Science's Best of What's New.[1] In the same year, the Fiat SGE engine (0.9 L turbocharged and 1.0 L naturally aspirated TwinAir units), also using MultiAir technology, was launched in the Fiat 500. It is produced in Bielsko-Biała, Poland. It was named Best New Engine in 2011.[9]

Both FIRE and SGE units are equipped with MultiAir and use indirect fuel injection.

The GME (Hurricane) and GSE (FireFly) MultiAir II engines, which use direct fuel injection, were first made available in 2016.

Technology

[edit]

How it works
"The MultiAir system is elegantly simple. An electrohydraulic actuator, a high-response, electronically activated solenoid—controls the pressure applied to hydraulic fluid (engine oil drawn from the sump) that fills a thin passageway that connects the intake valves and the camshaft. The solenoid valve regulates the amount of oil pumped by the cam action to either the valve or a bypass reservoir.

When pressurized, the hydraulic line behaves like a solid body and transmits the lift schedule imparted by the intake cam directly to the intake valve. When the solenoid is disengaged, a spring takes over valve actuation duties.

This electrohydraulic link allows independent operation of the two components, which enables near real-time control over the valve lift profiles, said Bernard. Whereas a closed solenoid normally transmits the pressure generated by the camshaft’s intake profile to the valve, an open solenoid breaks the hydraulic link between cam and valve, decoupling their operations."[10]
Society of Automotive Engineering, 2010

For variable valve lift, competing technologies (e.g., Honda's VTEC and BMW's Valvetronic) use electromechanical concepts, achieving valve lift variation via dedicated mechanisms; it can also be combined with camshaft phasers to allow control of both valve lift and phase. In contrast, MultiAir uses managed hydraulic fluid to provide variable valve control.

Control of a MultiAir engine's intake valves works via a valve tappet (cam follower), moved by a mechanical intake cam, which is connected to the intake valve through a hydraulic chamber, controlled by a normally open on/off solenoid valve.[11] The system allows optimum timing of intake valve operation.

MultiAir technology can increase power (up to 10%) and torque (up to 15%), as well as reduce consumption levels (up to 10%) and emissions of CO2 (up to 10%), particulates (up to 40%) and NOx (up to 60%)[3][7] when compared to a traditional petrol engine. The system also provides smoother cold weather operation, greater torque delivery, and no engine shake at shut-off.[12]

Development

[edit]

Research on critical related technologies started in the 1980s when engine electronic control reached market maturity. MultiAir was developed over ten years at Fiat's Centro Ricerche Fiat (CRF) in Orbassano outside Turin,[13] after a five-year delay during Fiat's 2000-2005 partnership with General Motors.[14] The vice president of Fiat Powertrain Research & Development, Rinaldo Rinolfi, led the team who developed the technology at a cost of over $100 million.[15]

Other systems

[edit]

More advanced, fully camless valvetrain systems are under development but are not yet production-ready.[16] The Valvetronic system used by BMW allows the valve timing and lift to be varied, but not the cam profile. The ability to vary the latter is characteristic of camless and the MultiAir systems.

Applications

[edit]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

MultiAir

View on Grokipedia
from Grokipedia
MultiAir is an innovative electro-hydraulic variable valve actuation (VVA) technology developed by Powertrain Technologies (now part of ) that enables fully flexible, cylinder-by-cylinder control of valve lift, duration, and timing in internal engines, replacing the conventional plate to minimize pumping losses. Patented by in 2002 and first introduced in production vehicles at the 2009 Motor Show, it uses a hydraulic system with electronically controlled solenoids to decouple the valves from the , allowing the engine to dynamically adjust air for optimal efficiency across all operating conditions. The system's operation relies on a "lost motion" principle, where hydraulic fluid transmits or blocks camshaft motion to the valves: when the solenoid is closed, full cam lift is applied; when open, the valve partially or fully closes under spring pressure, enabling multi-lift profiles even within a single cycle. This design achieves notable performance gains, including up to a 10% increase in maximum power, 15% improvement in low-end torque, and 10% reduction in fuel consumption relative to equivalent conventional engines, while also lowering CO2 emissions by enhancing combustion control. Initially debuted in the 1.4-liter turbocharged powering the MiTo and later the , MultiAir has been integrated into a range of engines from 1.4 to 2.4 liters across brands, including , , , , and Lancia models such as the 2010 , 2013 , 2014 , and 2015 . Compatible with both naturally aspirated and turbocharged configurations, the technology has earned multiple awards, including the 2010 in the 1.0-1.4 liter category, underscoring its impact on advancing and drivability.

Development History

Invention and Research

Fiat Group's research into innovative valve actuation systems began in the mid-1990s, shifting focus to electro-hydraulic mechanisms that built upon the company's established expertise in high-pressure fuel injection from the Common Rail diesel technology. This effort, centered at the Centro Ricerche Fiat (CRF) in Orbassano near Turin, Italy, represented a strategic push to revitalize gasoline engines amid growing demands for better efficiency and lower emissions. The system emerged as the key outcome of this decade-long program, which originated from foundational work on variable inlet valve control patented by CRF engineers Massimiliano Maira and Francesco Richard in the late 1990s. Led by Dr. Rinaldo Rinolfi, Vice President of Research & Development, the initiative emphasized replacing rigid mechanical camshafts with flexible electro-hydraulic actuation to minimize pumping losses—the energy wasted in throttling intake air—which can account for up to 10% of fuel consumption in conventional engines. Intensive development accelerated in the early , with the program requiring an investment exceeding 100 million euros over approximately three years of final engineering and testing phases. Early prototypes, integrated into test vehicles like the with 1.6-liter and larger JTS engines, underwent rigorous evaluation starting around 2003 to confirm the viability of direct air management on a cylinder-by-cylinder basis. A major hurdle was attaining precise control of valve lift and timing at elevated engine speeds reaching 7,000 RPM, where hydraulic response times must synchronize with rapid cycles to avoid performance lags or . Additionally, ensuring long-term involved overcoming thermal stresses from hot engine oils and , which could degrade hydraulic seals and actuators under prolonged high-load operation. These advancements positioned MultiAir as a cost-effective alternative to more complex fully camless or hybrid solutions, prioritizing reliability for .

Patenting and Launch

Fiat filed a in 2002 (ITTO20020569A1) for the electro-hydraulic variable actuation method central to the system, which received European protection (EP1377400 family). This protected the innovative approach to control, enabling to advance toward commercialization after years of research at its Centro Ricerche facility. The legal protection was crucial for safeguarding the technology's amid growing interest in advanced management systems. The MultiAir system received its world premiere at the 2009 Motor Show, where it was demonstrated as an integral part of the 1.4L family. Developed by Powertrain Technologies, the debut showcased the system's compatibility with both naturally aspirated and turbocharged variants, positioning it as a breakthrough in air management for gasoline engines. The event marked the transition from prototype to production-ready technology, drawing significant attention from the . Production of the original MultiAir system commenced in 2010, with the serving as the first commercial vehicle to incorporate it. This rollout extended to other models in the Group lineup shortly thereafter, establishing MultiAir as a key feature in compact engines. Key milestones leading to launch included a collaboration with Magneti Marelli for production and rigorous testing phases spanning 2007 to 2009, which validated the system's reliability under diverse operating conditions.

Evolution to MultiAir II

The second-generation MultiAir system, known as MultiAir II, was first introduced in 2013 on the and later in 2015 on models such as the 500X crossover, debuting at the with a 1.4-liter turbocharged engine delivering 140 horsepower. This evolution built upon the original electro-hydraulic variable valve actuation by incorporating a fully variable valve-lift mechanism that uses an oil column to replace the traditional mechanical camshaft-to-valve linkage, enabling precise control of valve and duration. The design reduces pumping losses compared to conventional throttling, resulting in improved and dynamic engine response across operating conditions. Key enhancements in MultiAir II included extended inlet valve opening for greater internal exhaust-gas recirculation, which contributed to fuel economy gains of up to 7.5% while boosting power by up to 10% and torque by up to 15%. It achieved seamless integration with direct and turbocharging, as demonstrated in the 1.4-liter MultiAir II paired with a six-speed for optimized combustion and reduced CO2 emissions. The system's MultiLift mode, which allows multiple valve lifts per intake stroke, was expanded to provide finer control over air quantity and charge motion, enhancing tumble in the for more efficient burning and lower emissions. Following 2020, MultiAir technology adapted to electrification trends through its application in hybrid powertrains, such as the 2022 , where a 1.3-liter turbocharged MultiAir engine (180 horsepower) combines with an and six-speed to deliver balanced performance and efficiency. By 2025, the third-generation MultiAir III appeared in hybrids like the and , featuring advanced valve control for even broader operational range and quicker response in mild-hybrid configurations. The third-generation MultiAir III, introduced in 2025, features advanced electro-hydraulic controls optimized for mild-hybrid systems, enabling quicker response and broader efficiency in engines like the 1.2-liter three-cylinder unit in and hybrids. These developments reflect ongoing refinements to address hybrid and downsized engine demands, though no dedicated hydrogen-compatible variants have been commercialized as of late 2025 amid broader shifts away from pursuits.

Technical Principles

Operating Mechanism

MultiAir employs an electro-hydraulic lost-motion system that utilizes engine oil as the to decouple the mechanical motion of the intake from the actuation of the intake valves, allowing for precise, independent control of each valve's timing and lift. In this setup, a connected to the pushes against the oil-filled chamber above the valve stem, transmitting the cam's motion only when the fluid path is maintained; any "lost motion" occurs when the fluid is redirected, effectively shortening the transmission path and reducing valve displacement. The core of the control lies in the electromagnetic integrated into the hydraulic circuit for each . This is normally closed, enabling full transmission of the camshaft's motion to achieve maximum lift when no intervention is needed. To achieve partial lift or complete deactivation, the is pulsed open at specific points during the stroke, allowing the to bypass the chamber and flow to a low-pressure accumulator; this decouples the , permitting it to close early under spring pressure while the cam continues its full profile. By modulating the timing, duration, and of these pulses—controlled by the engine's —the system can generate complex profiles, including multiple partial openings to optimize air charge motion. The lost motion volume is adjusted hydraulically via pulsing, altering the fluid displacement and thus the effective lift transmitted to the , based on the incompressibility of the oil. Detailed calibration of and timing ensures stable operation across engine speeds, with the ECU compensating for oil temperature and pressure variations to maintain accuracy. Valve lift profiles in MultiAir vary continuously from 0 mm (full deactivation, where the valve remains closed throughout the cycle) to full cam lift transmission, with corresponding variable duration. This variability arises from the adjustable lost motion within the hydraulic system, where the volume of displaced oil determines the effective shortening of the actuator path.

Key Components and Modes

The MultiAir system features several primary components that enable its electro-hydraulic variable valve actuation. Central to the design is the End Pivot Element (EPE), which incorporates a hydraulic chamber filled with engine oil to transmit motion from the camshaft to the intake valves. This chamber acts as a rigid linkage when pressurized, allowing precise control over valve lift and timing. Complementing the EPE is a high-speed solenoid valve, which regulates oil flow into and out of the hydraulic chamber. An accumulator maintains stable hydraulic pressure within the system to minimize energy losses and ensure consistent performance across engine cycles. The system's operational modes leverage these components for flexible engine management, with the (ECU) providing real-time adjustments based on input, engine load, and RPM. This integration eliminates the need for a traditional body, as actuation directly controls air intake volume. One key mode is , which achieves high air-fuel ratios by modulating lift to optimize air mass and promote efficient stratified . Another is Multi Lift, where the enables multiple partial lifts within a single intake stroke, varying lift heights to fine-tune torque delivery and enhance charge motion for better stability. Early Intake Valve Closing (EIVC) serves as the primary mode for load control, where the opens during the intake stroke to release hydraulic pressure, closing the valves prematurely and trapping a controlled amount of air to reduce pumping losses. The ECU orchestrates transitions between these modes—EIVC for part-load efficiency, Multi Lift for mid-range torque, and for low-load operation—on a cylinder-by-cylinder and stroke-by-stroke basis, ensuring seamless adaptation to driving conditions. The following describes the original MultiAir system.

Performance Benefits

Fuel Efficiency and Power Output

MultiAir technology achieves significant improvements in fuel efficiency primarily through the elimination of throttling losses, allowing for more precise control of air intake and reducing the wasted in pumping air through a restricted body. This results in up to 10% better fuel economy in both naturally aspirated and turbocharged configurations compared to conventional engines with fixed and throttle-based load control. For instance, the 1.4-liter MultiAir engine in the delivers EPA-rated fuel economy of 31 mpg city and 38 mpg highway with a , representing an approximate 10-15% improvement over equivalent throttle-controlled engines of similar displacement. In terms of power output, enhances performance by optimizing lift and duration to improve across the operating range, yielding up to 10% higher peak power and 15% greater at low speeds. This allows for better low-end responsiveness without sacrificing high-RPM output; for example, the naturally aspirated 1.4-liter produces 105 horsepower while providing approximately 130 Nm of available from low RPMs through advanced strategies. Such gains enable up to 10% peak power boosts by maximizing air charge during full-load conditions. The reduction in pumping losses is fundamentally captured by the thermodynamic work integral over the intake process: ΔW=∫P dV\Delta W = \int P \, dV where PP is pressure and dVdV is the change in volume, contrasting the higher work required in throttle-restricted cycles against the lower work in direct valve-controlled cycles. This difference minimizes dissipation, contributing to the observed efficiency benefits in modes. Testing under standardized cycles demonstrates 10-25% lower CO2 emissions for MultiAir-equipped engines, directly tied to the fuel economy improvements from reduced pumping work.

Emissions and Environmental Impact

MultiAir technology significantly reduces () emissions, achieving up to 60% lower levels compared to conventional engines, primarily through internal enabled by precise valve control in operation. This capability allows for optimized that minimizes formation without compromising performance. Additionally, the system lowers (CO2) emissions by up to 10% via elimination of throttling losses and improved overall efficiency. The technology also cuts unburnt hydrocarbons (HC) and (CO) emissions by up to 40%, particularly during engine warm-up and through enhanced air-fuel mixture control via . In representative tests, HC emissions have been observed to decrease substantially, helping engines meet stringent limits such as 0.1 g/km for HC under Euro 6 standards. These reductions stem from better combustion completeness, which can be conceptually linked to improved η = 1 - (exhaust losses / intake energy), where minimized exhaust losses enhance energy utilization. MultiAir has played a key role in enabling compliance with Euro 5 and Euro 6 emission standards in vehicle models, such as the , where engines achieved CO2 outputs as low as 129 g/km while meeting regulatory thresholds for pollutants. Post-2020 adaptations, including integration with hybrid powertrains like the 1.3L turbo in the (as of 2025 models), support preparations for Euro 7 requirements by further optimizing emissions through electrified operation.

Comparisons with Other Technologies

Electro-Mechanical Variable Valve Systems

Electro-mechanical variable valve systems represent an alternative approach to hydraulic technologies like , employing electric actuators and mechanical linkages to vary valve lift and timing without traditional throttle bodies. These systems aim to reduce pumping losses by precisely controlling , but they often introduce added complexity through moving parts driven by electric motors. One prominent example is BMW's , introduced in 2001 on the 316ti compact model. This camshaft-based system uses an eccentric shaft adjusted by an to enable continuous variable intake valve lift, ranging from minimal to full opening, in conjunction with the variable timing system. It achieves efficiency gains of up to 10-12% in fuel consumption compared to conventional throttled engines by largely eliminating intake restrictions, though some residual throttling may occur under certain conditions. However, the design requires complex mechanics, including additional levers, springs, and the eccentric shaft assembly, which increase system intricacy and potential failure points. In contrast to MultiAir's hydraulic actuation, relies on mechanical linkages, resulting in higher overall weight from the extra components and potentially slower response times at low engine RPM due to inertial effects in the linkage system. This mechanical dependency can limit dynamic adjustments compared to fluid-based systems, particularly during transient load changes. Another electro-mechanical innovation is FreeValve, developed by and publicly demonstrated in 2016 through a prototype engine. The system employs electro-hydraulic-pneumatic actuators integrated with electronic controls to provide fully independent operation of each and exhaust , allowing infinite variability in lift, duration, and timing without a . While this offers superior flexibility for optimizing performance across operating conditions, it faces challenges including higher manufacturing costs from the sophisticated actuators and sensors, as well as reliability concerns related to electronic dependency and lack of mechanical fail-safes, hindering widespread production adoption. Overall, electro-mechanical systems like Valvetronic deliver fuel savings of 8-12% over traditional designs, falling short of MultiAir's potential 15% reduction in some applications, partly due to incomplete elimination of throttling losses and added mechanical friction.

Hydraulic and Mechanical Alternatives

Hydraulic and mechanical alternatives to MultiAir's electro-hydraulic approach primarily rely on traditional camshaft-driven systems with limited variability, often incorporating hydraulic or mechanical elements for adjustment but without the full continuous control offered by solenoid-actuated hydraulics. These technologies contrast with MultiAir by maintaining fixed or discrete cam profiles, leading to compromises in flexibility for valve lift and duration. One prominent mechanical example is Honda's Variable Valve Timing and Lift Electronic Control (), which debuted in 1989 on the Integra model. VTEC operates by mechanically switching between two distinct intake cam profiles—a low-lift profile for everyday efficiency and a high-lift profile for high-rpm performance—using a hydraulic pin actuated by oil pressure under electronic control. This switch typically occurs around 4,500-5,500 rpm, enabling a significant power increase, such as achieving 100 horsepower per liter in its initial 1.6-liter application at 7,600 rpm. However, VTEC's fixed lift options per profile limit its adaptability across the full engine speed range, as it cannot vary lift continuously or independently per . Hydraulic systems, such as Toyota's Variable Valve Timing-intelligent (), introduced in 1996, focus on adjusting phasing rather than lift. uses engine oil pressure, controlled by solenoids, to rotate the relative to its drive sprocket, advancing or retarding timing by up to 40-60 degrees for optimized performance at different speeds. This achieves fuel efficiency gains of around 10%, as seen in early implementations like the 1ZZ-FE engine, without altering lift, which remains dictated by the fixed cam lobe profile. The system's reliance on oil flow for actuation introduces inherent delays, with response times typically ranging from 50-200 milliseconds for events, slower than fully electronic overrides. Mechanical systems like introduce additional valvetrain inertia from extra rocker arms and cam followers, which can elevate dynamic loads significantly at high speeds—potentially by 25-33% in rocker arm forces when ratios or components increase—necessitating stronger springs and components to prevent valve float. Pure hydraulic approaches, while reducing some mechanical complexity, suffer from oil pressure-dependent lag, often 50-200 milliseconds in solenoid-actuated VVT setups, limiting rapid adjustments during transient engine conditions. Modern evolutions, such as Honda's i-VTEC introduced in the early 2000s, build on the original by adding continuous variable cam timing via electronically controlled oil actuators integrated with the mechanical cam-switching core. For instance, i-VTEC in the 2002 RSX combines VTEC's discrete lift changes with VTC for broader timing adjustments, improving both power (up to 200 hp) and efficiency while retaining the underlying mechanical structure. This hybrid enhancement provides more refined control than pure mechanical systems but still contrasts with MultiAir's complete electronic dominance over hydraulic valve actuation, as i-VTEC cannot fully decouple valves from cam profiles.

Vehicle Applications

Fiat Group Implementations

MultiAir technology made its debut in the Group with the 2010 , where it was paired with the 1.4-liter to deliver 105 horsepower and fuel economy of up to 35 mpg on the highway under European testing cycles. This implementation marked the first production application of the system in a , offering improved responsiveness and efficiency for urban driving. The base model with this engine achieved 0-60 mph acceleration in approximately 9.5 seconds, balancing everyday usability with agile handling. In 2012, the Abarth 500 performance model incorporated technology in its 1.4-liter turbocharged . adopted for sporty tuning in the 2013 Giulietta, featuring a turbocharged 1.4-liter version producing 170 horsepower, which enhanced throttle response and power delivery for dynamic driving characteristics. The also integrated the technology in its 2011 model with a 1.4-liter outputting 140 horsepower, providing a refined balance of performance and comfort in the premium segment. MultiAir evolved to the second generation (MultiAir II) for further refinements in efficiency and control, as seen in later Group applications.

Chrysler and Broader Adoption

Following the 2009 alliance between and , MultiAir technology was rapidly integrated into 's powertrain lineup to enhance fuel efficiency and performance across various models. The technology debuted in with the 2011 , utilizing a 1.4-liter FIRE engine equipped with MultiAir, which delivered 100 horsepower and 95 lb.-ft. of torque while achieving up to 10% improvements in power, fuel economy, and emissions compared to conventional engines. This marked the first mass-production application of MultiAir in the region, with plans to extend it to 's World Engine four-cylinder and Pentastar V-6 families. Chrysler expanded MultiAir adoption through the second-generation MultiAir II system, introduced in 2013 on the 2.4-liter Tigershark inline-four engine. This electro-hydraulic setup provided infinite variability in intake valve lift and duration, debuting in the GT and , where it offered refined power delivery and reduced emissions without sacrificing drivability. The 2.4-liter variant, producing 184 horsepower and 173 lb.-ft. of , became a staple in compact and midsize vehicles, including the sedan from 2015 onward, contributing to EPA ratings of up to 36 mpg highway in some configurations. Broader adoption within the portfolio (formerly ) extended MultiAir to , , and other brands, solidifying its role in over a dozen models by the mid-2010s. Notable implementations included the and Compass with the 1.4-liter MultiAir II turbo engine (160 horsepower), the Jeep Cherokee's 2.4-liter option, and the Dodge Hornet's 1.3-liter turbo variant (as of 2025), emphasizing lightweight efficiency for SUVs and crossovers. Despite its nature, MultiAir has not seen licensing or adoption outside , remaining a core technology for the group's gasoline engines focused on emissions compliance and performance.

References

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