LL-NEW “4N1” DIESEL ENGINE
- Low Impact -
Just as ambitious and innovative as its all-new C- and D-Segment “Project Global” flexible architecture, MMC now introduces “4N1”: an all-new family of all-aluminum, double overhead camshaft (DOHC), 16v 4-cylinder common rail, direct injection, “low impact” Euro 5* Diesel engines.
Jointly developed by Mitsubishi Motors Corporation and Mitsubishi Heavy Industries, Ltd. (MHI), these engines will be made available in two displacements and featured in Europe in the following models:
- ASX (1.8 liter “4N13”),
- Lancer Sports Sedan & Sportback (1.8 liter “4N13”),
- Outlander (2.2 liter “4N14”)
Originally announced in June 20th, 2006 – and previewed first with Concept-cX in September 2007 (1.8 liter) and confirmed with Concept-ZT in October 2007 (2.2 liter) – this new family of high tech Diesel engines will allow Mitsubishi Motors 1) to better respond to future market trends*, 2) to keep mastering its own technology - Diesel in this case and 3) to reduce its dependence on outside partners, whether in terms of supply or development.
MIVEC + Diesel = World First
The latest of a long Diesel tradition at Mitsubishi Блокирано back to 1931 – with “450AD”, the first Diesel engine to be developed in Japan for use in motor vehicles – this “4N1” family is the recipient of a number of proprietary innovative engine technologies, including those learned from the development of MMC’s recent “4B1” family of petrol engines, as well as high-efficiency combustion characteristics that stem from the application of MMC’s and MHI’s own analytic technology.
* Whilst it will of course meet Euro-5, it will also have enough built-in flexibility for Euro-6 and beyond as well as other emission requirements outside of the EU, if needed (“Tier 2 Bin 5” in the US and “Post New Long Term” in Japan)
Of all, the main technological highlight is Mitsubishi’s proprietary MIVEC variable valve timing system - a world first for passenger car Diesel engines – allowing MMC engineers to reach their goal of the lowest possible compression ratio and all it implies in customer benefits.
Fresh approach
Of strategic importance in Europe against high profile competitors in a very competitive segment, the smooth running “4N1” Mitsubishi Diesel MIVEC engine is the result of an innovative approach to Diesel questions as applied to high efficiency lightweight / passenger car applications.
Prompted by strategic sales & marketing needs in the European market, Mitsubishi engineers had to face two very contrasted realities:
On the one hand, a proven know-how in petrol engine development whether for instance with the tiny but highly efficient 3-cylinder 660 cc MIVEC engine of the Japanese market “i” or at the other end of the spectrum, with the mighty 295 ps 4-cylinder 2.0l MIVEC engine of Lancer Evolution.
On the other hand and heritage notwithstanding, an area - Diesel engines - where their most recent developments were mostly related to the very specific requirements of heavy-duty 4x4s such as Pajero/Montero/Shogun or L200.
Unencumbered with in-house engineering conventions and/or traditions, they turned this challenge into an opportunity, starting off with a clean sheet and a few simple questions: “Can our know-how in petrol engine technology be applied to Diesel powertrains ? Knowing the specifics of this technology, why can’t we still make a Diesel engine as close as possible to a petrol engine ? Can petrol engine technologies contribute to a new generation of low environmental impact Diesel engines ?”
The answer to these questions became “4N1”: a compact and lightweight family of motors delivering high-performance, excellent fuel mileage and emission levels and with much in-built development potential.
During this innovative development, MHI provided – amongst others - engineering expertise gained through experience in industrial and marine Diesel engines, as well as in gas turbine technologies. In particular, MHI engineers were given specific assignments in the areas of casting flow (aluminum cylinder block), heat transfers (cylinder head) and combustion, using “Computational Fluid Dynamics” (CFD) technology. As a reminder, CFD is a sophisticated tool used in the aeronautical industry whose purpose is to model and analyze various dynamic (thermo-dynamic in this case) configurations prior to any real life testing. As such, CFD allows for reduced development time and investment while increasing the accuracy of the design.
Going light, going low
Going back to some Diesel basics, a Diesel engine uses the heat of compression to initiate ignition to burn the fuel which is injected into the combustion chamber during the final stage of compression.
Because of the very high compression ratio this process requires, Diesel engines have the highest thermal efficiency of any regular internal engine, itself leading to lower fuel consumption and logically, lower emissions and esp. CO2.
However, in order to withstand the operating pressure caused by the high compression ratio and the large amounts of torque generated to the crankshaft, Diesel engines needs heavier, stronger parts making them heavier than petrol equivalents.
So, the logical solution to reduce the forces at play within the block is to lower the compression ratio.
In turn, this would allow for a lighter structure, not dissimilar to that of a petrol engine: something Mitsubishi engineers decided to apply to “4N1” engine and a key feature to understand “4N1”, distinguished with the very low (for a Diesel engine) compression ratio, the lowest of any current passenger car Diesel engine in the market:
14.9:1 for the 1.8 liter “4N13” (ASX and New Lancer)
14.9:1 for the 2.2 liter “4N14” (Outlander).
This record low ratio was one of the main objectives of MMC and MHI engineers in order to (eventually) achieve an excellent level of NVH, low emissions, long lasting reliability, smooth running and enjoyable driving performance, whether with a displacement of 1.8 or 2.2 liter.
Therefore, sharing its basics architecture with MMC’s recent “4B1” petrol engines - but nonetheless the result of a specific Diesel development - “4N1” features – amongst others:
a lightweight cylinder block. Made of die cast aluminum, this unit is lighter by about 10 kg compared to a cast iron block. It can sustain the high temperatures and massive forces at play within a Diesel engine, thanks to an elaborate CAD/CAM – supported design process conducted together with MHI which also contributed to a significant improvement in casting quality.
Atop, MMC engineers have selected the same concept of a plastic cylinder head cover as for “4B1”. Developed by Mahle for MMC, this component is 50% lighter (1 kg vs about 2 kg for a comparable aluminum item) with additional benefits in terms of fuel efficiency and stable driving.
This similarity of architecture with MMC’s petrol engine family offered some obvious benefits, whether in terms of development time (about 3 years between the first engineering studies and the April 2010 start of production) or cost savings through the use of common production tooling at MMC’s Shiga engine plant.
Furthermore, going for a “square” configuration with nearly equal bore & stroke means shorter & lighter connecting rods & pistons and therefore less weight. More so, with our smaller displacement (1.8 liter in this case)…
Obviously, all this weight saving is good for fuel economy and therefore emissions, but also for dynamics since there is less weight over the front end.
“MIVEC” valve timing
Going for a lighter structure allows for a low compression ratio, but how to retain enough compression to initiate ignition ? Enters MIVEC...
Just as i-MiEV became a reality through the development of its awarded “MiEV OS” operating system, 4N1’s existence owes a lot to the implementation of another Mitsubishi Motors proprietary technology: MIVEC (or “Mitsubishi Innovative Valve timing Electronic Control system”): previously “restricted” to heavy-duty Diesel truck engines, this is a world first for lightweight/passenger car Diesel engines
At the time of “4N1” original development, MIVEC was the best possible enabler to achieve the low compression ratio targeted by MMC and MHI engineers, itself the trigger for this engine’s architectural and dynamic performance.
Applied to the intake valve train for this Diesel application, MIVEC varies the timing, lift and duration of the valves opening by using two different cam profiles.
The idea is to better manage the air intake flow for a greater efficiency and power, over a wider range of engine speed, even with such a low compression ratio and of course, better economy and lower emissions.
This especially true for Diesel engines where the range of engine speed is more limited than in petrol engines. More so with low compression Diesel engines not only to offset the loss of compression vs. traditional engines but also when dealing with:
cold starting,
combustion stability and the related NVH issues.
In these two instances, MIVEC comes handy:
advancing the closing timing of the intake valves for an improved effective compression ratio,
reducing the lift of the one intake valve for a stronger swirl – to improve mixing and combustion, control of the in-cylinder temperature at the end of compression - to avoid the creation of too much NOx and also, control of the flows within the cylinder.
In addition…
As of today, MIVEC is still the key enabler of 4N1’s performance but it is not the only one.
Managing the air intake flow is one thing, getting to the right combustion characteristics is another one and there comes into the picture a succession of items:
The shape of the combustion chamber is one, in order to burn the mixture as completely as possible but also avoid excessive temperatures and therefore creation of NOx. In the case of 4N1, Mitsubishi’s engineers decided to go for a shallow dish at the upper part of the piston and a narrow cavity entrance for better fuel economy and combustion robustness.
The injection process is another item. For their new Diesel engine, they went for:
- a very high 2,000 bar pressure common rail system - than the more frequent 1,800 bar - to create a better atomization of the injected Diesel fuel,
- an optimized three-stage injection sequence:
-> pilot injection,
-> pre-injection,
-> main injection.
Quiet
If 4N1 is light and can operate efficiently with its low 14.9:1 compression ratio, how can it be kept quiet and vibration-free, away from the traditional Diesel clatter ?
In a nutshell, 3 separate areas have been explored:
Compression ratio: with 14.9:1, it is obvious that such a low level of stress contribute a lot to the overall NVH performance, esp. vibrations.
Combustion: thanks to the combination of MIVEC + shallow combustion chambers + multi-stage injection + 2,000 bar common rail pressure + sophisticated electronic control, Diesel clatter – which is basically combustion noise - has been reduced a lot.
As an illustration, the first pilot injection shot of Diesel fuel into the chamber initiates the combustion but also reduces the explosiveness the vibrations this may cause.
Offset crankshaft: to minimize the side force created by the pistons, the crankshaft is offset by 15 mm to reduce CO2 emissions whilst generating a higher output and reducing NVH for smoother operation at all engine speeds. Thanks to Computer Aided Movement Simulation, the cylinder off-set structure was optimized, leading to a decrease of 20% of piston related friction-loss, with further benefits in terms of fuel economy.
Real-life
A true engineering achievement, 4N1 offers real driving pleasure from a more efficient and cleaner Diesel engine than its competitors, esp. considering its smaller displacement.
Taking the example of ASX vs. Qashqai (data as of Aug. 2010):
ASX 1.8 DiD 2WD Qashqai 2.0 dCi 2WD
(6-speed M/T) (6-speed M/T)
Displacement 1,798 cc 1,995 cc
Output 150 ps @ 4,000 rpm 150 ps @ 4,000 rpm
Specific Output 83.4 ps/l 75.2 ps/l
Torque 300 Nm @ 2000-3000 rpm 320 Nm @ 2,000 rpm
CO2 145 g/km (ClearTec) 167 g/km
Also, when compared to the existing Lancer 2.0 DiD, the benefits of “4N1” are just as clear - even taking the 200 cc smaller displacement:
Lancer Sportback 1.8 DiD “4N13” Lancer Sportback 2.0 DiD
(6-speed M/T) (6-speed M/T)
Displacement 1,798 cc 1,968 cc
Output 150 ps @ 4,000 rpm 140 ps @ 4,000 rpm
Torque 300 Nm @ 2000-3000 rpm 310 Nm @ 1,750 rpm
CO2 139 g/km (ClearTec) 163 g/km
Both figures and actual driving experience also tells another part of 4N1’s story: that of a Diesel engine whose behavior is not too dissimilar to that of a petrol engine. More so at higher engine speeds, where Diesel engines are usually not as good as their petrol counterparts.
No surprise of course, knowing MMC’s experience in petrol engine technology…
No surprise either, knowing the relation existing between 4N13 and the latest generation of MMC’s petrol engines…
No surprise, knowing the palette of technologies selected by MMC’s engineers to compose this character:
MIVEC and the possibilities it offers in terms of air flow management: in full-load, the very good level of power output and torque is achieved thanks to both 1) the high lift of intake valves and 2) the application of a broad operating valve angle at a high speed mode.
An intake port whose design is similar to that of a petrol engine.
A variable geometry (VG) turbo-charger – in this case, MHI’s own TF035 - featuring a new wide-range compressor vane allow higher charge efficiency in high speed driving.
As a reminder, VG technology aims at searching for the optimum aspect ratio at both low and high speed , itself a guarantee of efficiency, esp. in the areas of exhaust emissions and response (absence of lag, etc,…).
In the case of MMC’s “4N1”, the adoption of an 8-vane design of the aluminum compressor wheel (vs. 12 for a conventional type) was meant to expand the operating range of the compressor and therefore supercharging efficiency.
In parallel, the variable capacity of the turbine translates into high acceleration response and optimum boost pressure across the engine speed range to deliver dynamic performance and low emissions.
ClearTec
Depending upon markets and models, the environmental performance of Mitsubishi’s new “4N1” engines can be further enhanced with the adoption of a full ClearTec low CO2 package.
Similar in concept to the one already fitted to Colt, it includes:
“Automatic Stop & Go” system
Electric power steering
Generation Control System (i.e. regenerative braking)
Low resistance tires
Closed flow particulate filter
Low viscosity oil
etc,…
A family of engines
Originally announced in 2006 as a “2.0 liter class” engine, “4N1” offers a lot of potential either with different displacements or outputs, beyond the original 150ps “4N13” 1.8 liter variant fitted to ASX and Lancer.
Next in line will be “4N14”, a larger 2,268 cc (86.0mm x 97.6mm) derivative, meant to power the bigger Outlander as well as other (large) Mitsubishi vehicles in the future:
Lancer Sportback 1.8 DiD “4N13” Outlander 2.2 DiD “4N14”
(6-speed M/T) (6-speed M/T)
Displacement 1,798 cc 2,268 cc
Output 150 ps @ 4,000 rpm 177 ps @ 3,500 rpm
Torque 300 Nm @ 2000-3000 rpm 380 Nm @2000-3000 rpm
CO2 139 g/km (ClearTec) 155 g/km (2WD ClearTec)
In the case of Outlander, it should be noted that the existing 156ps 2.2 DiD (PSA-sourced engine) will remain, fitted with Mitsubishi Motors’ twin clutch TC-SST gearbox and sold alongside the more powerful 177 ps “4N14” 6 M/T variant.
Originally announced in 2006 as a “2.0 liter class” engine, “4N1” offers a lot of potential either with different displacements or outputs, such as the 116ps / 300 Nm “low power” version to be made available at a later stage in selected markets for both Lancer and ASX.
At launch and whatever the displacement, “4N1” will only be offered with a 6-speed manual gearbox. However, depending on market feedback, Mitsubishi Motors may expand its product offering with one of its own automatic solutions.
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