Overview: Alfa Romeo Mito Multijet II and Multiair
The Fiat Group’s Multiair and Multijet engine technologies define the Company’s current thinking for conventional power units.
Multiair is the name given by Fiat to directly-fuelled petrol engines that use a variable valve lift arrangement, rather than a butterfly valve, to control the quantity and speed of air entering the combustion chamber.
Multijet II is the latest incarnation of Fiat’s common-rail diesel family. Like the Multiair engines, the Multijet II units meet Euro 5 emissions limits.
The new Multijet II power unit is finding its way into other cars inside and outside the Fiat Group, including the G.M. Corsa and Fiat 500. Headline outputs of 95PS at 4000rpm and 200Nm and 1500rpm are distinctly impressive. In the Alfa, this engine manages a European CO2 result of 112g/km.
The Alfa Romeo Mito powered by the MultiJet II diesel is known as the 1.3 JTDM-2. It’s available in three trim levels: Turismo, Lusso and Veloce.
It is normal for a common-rail engine to inject five or six separate injection pulses. This allows for greater control of the rate at which the fuel burns, and thus the temperature and pressure in the combustion chamber. In particular, a small initial injection pulse raises the temperature in the combustion chamber which might at first be too cool to burn a more substantial quantity of fuel. While it is hard to imagine a combustion chamber ever becoming ‘cool’ in an engine that’s running, the metals from which the head, pistons and liners are made conduct heat away very quickly; the cooler the combustion chamber walls, the greater the ‘quenching’ effect they have on the combustion process, and the less effective the engine is at burning its fuel completely. So multiple-pulse injection is very useful in controlling the combustion process.
Despite using balanced solenoids rather than the increasingly prevalent piezo crystals, Fiat has managed to fit eight injection pulses into each combustion cycle.
Alfa Romeo Mito JTDM-2.
The Multijet’s balanced solenoid arrangement is used to apply what Fiat calls ‘Injection Rate Shaping’ (IRS), in which two consecutive injection pulses are deployed with zero hydraulic dwell. This is claimed to improve combustion at higher loads.
A significant feature of this engine — or, rather, of its control systems — is that it comes with am automated stop-start device. A particulate filter is also fitted. The turbocharger features a variable geometry primary turbine: a vane alters the angle at which exhaust gases enter the turbine, balancing boost against back-pressure.
Other aspects of the Mito Multijet are familiar from earlier cars. Suspension is unremarkable, with McPherson struts at the front and a C-section torsion beam, trailing arms and helical springs at the rear. The rear suspension bushes are slotted, providing variable stiffness for attaching the torsion beam to the bodyshell. Brakes are ventilated front and solid rear discs, with floating calipers at both ends.
Fiat Group Multijet II 1248cc, 95PS. Click here for a detail view.
Coilover dampers are used. The damper units are fitted with a spring between the outer pipe and inner pushrod. Then spring is secured to the upper end of the damper tube, and it acts during rebound (unload) rather than load. The damper’s spring acts in parallel to the main suspension spring.
The length of the internal damper spring determines the point at which it begins to take effect. Under normal driving conditions, the springs will not come into play; but during brisk driving, the damper springs will begin to work, increasing roll stiffness.
When lateral acceleration is high, a car with coilover dampers resists roll more effectively than its spring- and anti-roll bar rates would normally allow; when cornering loads are lower, the damper coilover springs do not cut in, and the suspension set-up feels softer.
When the damper coilover springs begin to take effect in a bend, only the inner (unloaded) wheel’s damper springs are working — by stretching. The outer (loaded) wheel dampers work conventionally, remaining compressed.
Under these conditions, the roll-resistance is asymmetrical. This affects the car’s dynamics in a bend in two ways: first, the outer wheels sit more firmly on the road to promote tyre grip (and thus the transmissible lateral forces); and the roll centres are lower for greater stability.
Mito 1.3 JTDM-2
Bore / stroke
69.6 / 82
PS / rpm
95 / 4000
Nm / rpm
200 / 1500
Urban MPG (l/100km)
Fiat’s new 1.4-litre Multiair engine made its international debut in the Mito late last year. In Britain it is initially offered in two outputs: 135PS and 170PS. Both variants are turbocharged. An atmospheric 105PS version is available in other territories.
In Fiat’s view, the key to optimising performance, fuel efficiency and emissions in a petrol engine is to take the most precise possible control of the quantity and dynamics of the air drawn into the cylinders. A familiar way of approaching this is by using variable valve timing: typically, timing of the intake valves (and often the exhaust valves as well) is continually adjustable over a range of around 40 degrees.
Fiat Group Multiair 1368cc, 135PS. Click here for more detail (slow page).
Fiat’s Multiair system controls the air charge at the cylinder inlet ports by controlling valve lift as well as timing. An electro-hydraulic actuation and control system is used, with five operating parameters: valve timing and lift are adjusted according to engine speeds and loads.
MultiAir engines use a single camshaft, with three lobes allocated to each cylinder. The first two control the two exhaust valves in the conventional way. The third lobe defines the maximum possible lift and opening duration of the two inlet valves. It also acts on a small piston that sends engine oil through pressurised hydraulic channels to additional pistons located just above the inlet valves.
Each cylinder has an associated solenoid valve, controlled by the Magneti Marelli ECU engine management system. The valve can be opened at any point during the inlet valve’s movement to bleed off oil from the pressurised channel. Varying the oil flow controls the opening and closing of the intake valves between the extremes mechanically defined by the shape of the camshaft lobe.
The Multiair system can even open the inlet valve twice in one intake stroke. This régime is used at low speeds and loads, creating more swirl.
When the solenoid valve is closed, the oil in the hydraulic chamber couples the cam lobe directly with the intake valves, and valve opening follows the cam lobe profile. When the solenoid valve is open, the hydraulic chamber and the intake valves are decoupled; the valves no longer follow the cam profile. The result is that all aspects of the operation of the intake valves can be controlled electronically, by opening and closing the solenoid valve for each cylinder. In the case of the intake valves at least, the camshaft has become little more than a hydraulic pump.
Fiat claims that Multiair is a landmark technology, though such claims are two-a-penny. In this case, though, we totally agree: this system, or variants of it, has the potential to be widely adopted in the future. Its significance in managing gas-flow in the combustion chamber is huge. Only by using colossal solenoids to control the valves directly could greater control be achieved, and the electrical demands of such a system would be hard to meet.
The Multiair system’s relevance is not solely to Otto cycle engines — like the Fiat’s — in which the fuel is drawn into the cylinder with the charge air on the intake stroke. Fiat’s technique also applies to the increasingly common breed of directly fuelled petrol engines and to diesels. With these engines, the dynamics of the charge air alone will be affected by the intake valve’s behaviour, but charge air dynamics are hugely important, irrespective of the injection pressures in use. The Multiair system is potentially of great value in improving combustion performance across the spectrum of piston engine design.
Multiair operating strategies
Different strategies, or operating models, are used according to driving conditions.
Full lift is used for for maximum power. The solenoid valve remains closed, the cam profile is followed, and full valve opening is achieved.
EIVC (Early Intake Valve Closing) is aimed at achieving good torque at low engine speeds. 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 maximises the air mass trapped in the cylinders.
LIVO (Late Intake Valve Opening): with the power unit on part-load, the solenoid valve is open momentarily at the beginning of the valve lift phase, delaying the opening of the valve. Partial valve openings control the trapped air mass according to the required torque.
Under partial load, the intake valves can be partially opened by closing the Solenoid Valve once the mechanical cam action has already started. Here, the air stream into the cylinder is faster and results in higher in-cylinder turbulence, but power output is limited. This régime is used at at engine start and idle.
Multiple valve opening can be used to enhance turbulence and combustion rate at very low loads. Here, a multi-lift cycle is used This improves fuel economy and emissions in urban driving.
In comparison with Fiat’s previous 120PS turbocharged 1.4-litre engine, the new 135PS Multiair unit produces 10 per cent. less CO2, uses less fuel, delivers more power and — according to Fiat — suffers less turbo lag.
The Mito’s new Multiair engines are based on the Fiat Group’s familiar ‘FIRE’ (Fully Integrated Robotised Engine) block. The Multiair top-end is self-contained and designed to be fitted to the existing, unmodified block.
The most powerful form of 1.4-litre Multiair engine presently available delivers 170PS. In the Mito range it is fitted solely to the Cloverleaf model. Its specific power output of 124PS/l is the highest value ever achieved for a production Alfa Romeo engine.
Any other business: Alfa Romeo Mito
As you would expect, the Mito range features some interesting gadgetry. The Cloverleaf has an active suspension system, which adjusts damping rates according to driving conditions; an automatic stop-start system is fitted to all models, to reduce fuel consumption in urban conditions; and Alfa Romeo’s ‘DNA’ allows the driver to adjust various electronically-controlled parts of the car according to his mood.
DNA communicates with the engine, brakes, steering, suspension (on the Cloverleaf model), and the automated transmission if this is fitted. It offers three modes — or perhaps ‘moods’ — ‘Normal’, ‘Dynamic’ and ‘All weather’.
Dynamic mode: VDC and ASR are less intrusive; the power steering has less assistance; DST gives tandard braking control, coordinated with the anti-lock system; greater control of lateral acceleration is provided, with oversteer correction by means of a slight pressure through the steering wheel to encourage the driver to steer in the correct direction; the engine management system is set to provide a more rapid response to the throttle; and on Cloverleaf cars, the ‘Synaptic Damping Control’ provides firm damping settings.
Normal mode: VDC and ASR are at their standard settings; power streering weight is normal; DST provides standard braking control, coordinated with the ABS; control of lateral acceleration is at a ‘normal’ level; oversteer correction, as is the case in Dynamic mode, provides a slight pressure through the steering wheel to encourage the driver to steer in the correct direction; the engine responds less avidly to throttle inputs, helping the driver to drive smoothly; and Cloverleaf models provide slightly softer damping than was on offer in Dynamic mode.
All weather mode: VDC is more intrusive while ASR is less so. The power steering offers normal assistance; DST provides standard braking control, coordinated with VDC; control of lateral acceleration is standard; oversteer correction is the same as with the other modes; throttle response and — on Cloverleaf models — damper settings are normal.
Jargon and TLAs
VDC (Vehicle Dynamic Control) is Alfa Romeo’s version of ESP (Electronic Stability Program). It’s a system that activates under extreme conditions when vehicle’s stability is deemed to be at risk, helping the driver to control the car. It is permanently engaged.
ASR (Anti Slip Regulation) is an integral part of VDC. It is intended to optimise traction at any speed with the aid of the brakes and throttle. The system computes the degree of slip on the basis of wheel revolutions calculated by the ABS sensors, and activates two different control systems — braking and engine power — to restore grip.
CBC (Cornering Brake Control) is really a function of the car’s anti-lock braking system. It comes into play when the driver brakes heavily in a corner. Brake pressure is modulated on each wheel individually to maintain vehicle stability, minimising any understeer or oversteer behaviour.
DST (Dynamic Steering Torque) sets out to improve safety through the driver’s ability to handle the car. The electric power steering generates torque at the steering wheel, automatically making corrections to the steering angle; it is intended to ensure that the VDC system activates unobtrusively.
The Mito comes with Alfa Romeo’s Electronic Q2 limited slip differential as a standard fitting. When the driver accelerates in a bend, the inner (unloaded) driven wheel is braked to increase traction on the loaded outer wheel. The result is that torque is distributed more effectively to the driving wheel with the greater level of traction.
For the benefit of anyone too young to remember what mechanical limited slip differentials are, they are final drive units that restrict the extent to which torque can be lost through a single wheel spinning as a result of poor traction — for example, under power with lock applied or on a surface with uneven traction. Because the difference between the rates of rotation of the two driving wheels is mechanically limited, the tendency of one wheel to slip results in torque being transferred away from the spinning wheel to the wheel with greater grip. Limited slip differentials were quite common when most cars were driven by their rear wheels and performance models were particularly prone to spin an inside rear wheel on bends.
Alfa Romeo’s stop-start system is much like anyone else’s. Whenever the car is stationary and idling in neutral, the engine is automatically shut off. It restarts automatically when the clutch pedal is depressed. The stop-start system can be deactivated by the driver.
Twin clutch gearbox: TCT
From spring 2010, the 135PS version of the Mito Lusso and Veloce will be available with Fiat’s twin-clutch automated gearbox. Dry clutch plates are used; as usual with these transmissions, the TCT can be used like a conventional automatic or controlled manually by means of a shift lever or steering wheel paddles.
The mechaniocal arrangement is familiar. One clutch controls the ‘odd’ gears (first, third, fifth) and reverse, while the other controls the ‘even’ gears. This allows gears to be changed very quickly without interrupting the power flow from the engine to the transmission.
The TCT gearbox has a higher torque capacity than the six-speed manual unit, allowing the 135PS engine to run with a more generous engine management map: the result is 230Nm instead of the 206Nm that’s available with the standard manual gearbox.
Alfa Romeo is crowing about the Mito Cloverleaf’s performance and fuel economy figures, and they’re certainly a tribute to the efficacy of the Multiair system. Outputs of 170PS, 230-250Nm (depending on the driver’s chosen driving mode) and 139g/km of CO2.
A new active suspension system adjusts the dampers, altering damping rates according to the prevailing driving conditions. The system was developed jointly by Alfa Romeo and Magneti Marelli and uses five accelerometers, located on the front two dampers, rear centre and rear bulkheads. Each shock damper is controlled independently; the damping rate is increased when necessary by the movement of oil into a chamber inside the damper or softened by allowing the oil to escape. As you would expect, the four electronically controlled dampers, five accelerometers and an electronic control unit talk to the Mito’s other on-board electronic systems.
The Cloverleaf’s 170PS engine comes attached to a C635 six-speed manual gearbox, developed by Fiat Powertrain and manufactured at the Verrone factory in Italy. The new gearbox features a very short action. The C635 is the first of a family of manual transmissions set to be deployed in a wide range of vehicles.
Alfa Romeo Multiair
1.4 MPI 105PS ‡
1.4 TB 135PS
1.4 TB 170PS
Bore / stroke
72 / 84
72 / 84
72 / 84
PS / rpm
105 / 6500
135 / 5000
170 / 5500
Nm / rpm
130 / 4000
180 / 1750 206 / 1750†
230 / 2500 250 / 2500*
Urban MPG (l/100km)
‡ Not U.K.
† In Sport mode, manual transmission; 230Nm with TCT gearbox.
* In sport mode.