C O V E R S T O R Y DIESEL ENGINES
THE NEW 3-CYL ENGINE FROM VW’s MODULAR DIESEL ENGINE SYSTEM With its new three-cylinder diesel engine, Volkswagen has created a universal basis for application in the small vehicle segments of the Group. This slimming down of the engine range and integration into the modular diesel architecture has succeeded in significantly reducing production effort and costs compared to the previous multi-engine strategy. Development was focused on cutting CO2 emissions, and all versions of the Polo equipped with the new engine also comply with the Euro VI emissions standard.
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AUTHORS
DIPL.-ING. FRIEDRICH EICHLER is Head of Engine Development at Volkswagen AG in Wolfsburg (Germany).
DIPL.-ING. JÖRN KAHRSTEDT is Head of Diesel Engine Development at Volkswagen AG in Wolfsburg (Germany).
DR.-ING. EKKEHARD POTT is Head of Commercial Vehicle and Small Diesel Engine Development at Volkswagen AG in Wolfsburg (Germany).
OBJECTIVES
Volkswagen’s modular diesel engine system (MDB) was designed from the concept phase to incorporate a range of cylinder numbers. The line-up is thus being expanded with a reduced-displacement three-cylinder unit. The main area of application for this is in the Volkswagen Group’s smaller vehicle platforms. The specification document for the new threecylinder TDI engine is focused particularly on the technical and economic requirements for using diesel engines in small vehicle classes: :: Compatibility with all of the group's transverse platforms; :: Significant reduction in CO2 emissions and weight compared with preceding engine; :: Raising the specific power and torque compared with the previous engine and thus the potential for slimming down the engine line-up; :: Cost reduction through part sharing from the modular diesel engine system and through flexible production and assembly on existing equipment; and :: Fulfilment of Euro VI emission standards.
MAJOR ELEMENTS OF THE NEW THREE-CYLINDER ENGINE FAMILY DIPL.-ING. (FH) HENRIK BEDDIES is Project Manager of Diesel Engine Development at Volkswagen AG in Wolfsburg (Germany).
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Following introduction of the four-cylinder variants of the modular diesel engine system [1, 2] in 2012, the diesel range is now being expanded downwards with the new three-cylinder engine in three power outputs ranging from 55 kW (74 hp) to 77 kW (103 hp) and a common displacement of 1.4 l, ➊. In its first application in the new Polo, the engine has been able to replace the 1.2 l three-cylinder TDI and the 1.6 l four-cylinder TDI engines entirely [3, 4]. In view of the expanded performance spectrum and the elements familiar from the four-cylinder engines in the modular diesel engine system, development work on the new three-cylinder engine is able to call on extensive previous experience. While the crankcase, cylinder head and valve drive, turbocharging assembly and powertrain had to be reconfigured specifically for the three-cylinder layout, it was possible either to carry over or optimise
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C O V E R S T O R Y DIESEL ENGINES
1.4 l, 55 kW, EURO 6
1422 cm
DISPLACEMENT
3
1.4 l, 66 kW, EURO 6
1422 cm
3
1.4 l, 75 kW, EURO 6
1422 cm 3
79.5/95.5 mm
79.5/95.5 mm
79.5/95.5 mm
88 mm
88 mm
88 mm
16.1
16.1
16.1
RATED POWER
55 kW at 3000-3750 rpm
66 kW at 2750-3250 rpm
77 kW at 3500-3750 rpm
MAX. TORQUE
210 Nm at 1500-2000 rpm
230 Nm at 1500-2500 rpm
250 Nm at 1750-2500 rpm
132 kg
132 kg
132 kg
BORE/STROKE CYLINDER SPACING COMPRESSION RATIO
WEIGHT (DIN 70020-GZ)
❶ Technical data for the new three-cylinder TDI engine
existing assemblies for the ancillary drive and timing gear, as well as on both the hot and cold side of the engine, ➋.
CRANKCASE
The development objective of a weightreduced and acoustically optimised crankcase was achieved through realisation of the following points: :: Designing the crankcase in aluminium with material-appropriate adaptations; :: Dedicated coolant circuit for rapid component warm-up;
:: Integration of thermal management measures; :: Placement of the threads for the cylinder-head fasteners beneath the water jacket; :: Optimisation of the untreated and clean oil circuits to reduce flow losses; and :: Extension of the oil-return and blow-by channels to the oil-sump parting line. The crankcase, which for the first time in the modular diesel engine system is made from gravity-die-cast AlSiCu3 alloy, makes a major contribution to weight reduction, ➌. The cylinder sur-
faces are thermal-interference-fit thinwall liners made from GJL 250. Compared with the preceding engine, just changing the material of the crankcase achieved a weight reduction of 11 kg. In order to allow for the use of aluminium, the crankshaft bearing cover alignment was widened and the thread chamfer for the bearing cover screws raised. Further stress reduction in the bearing seats was achieved by calculating optimised relief grooves. As a result, the new engine is 11 kg lighter than a comparable grey cast iron three-cylinder and no less than 27 kg lighter than the 1.6 l TDI engine.
❷ Modules with synergies and new modules
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head can be produced extremely economically on the same production line as the four-cylinder unit.
CHARGE-AIR COOLING
❸ Crankcase
BALANCER SHAFT, CRANKSHAFT DRIVE AND OIL SUMP
A balancer shaft rotating at engine speed in the opposite direction to the crankshaft is used to balance out the free moments of inertia. To reduce friction, the balancer shaft is integrated into a combination module consisting of the oil and vacuum pumps, ➍. This combined module is driven by a singlespeed 1:1 gear drive with an acoustically-optimised tooth profile. The crankshaft’s rotational moment of inertia is minimised via optimised mass balancing, incorporating the vibration damper and flywheel. This also reduces the weight of the crankshaft. The oil and vacuum pumps were carried over as components from the fourcylinder TDI engine. Oil supply is via a vane-type pump with a regulated volumetric flow rate. In addition, a magnetic valve (controlled by mapping specifically for three-cylinder engines) can be used to switch between low-pressure and highpressure operation. The two-part oil sump features a strengthened pressure-die-cast aluminium upper part that helps to stiffen the engine/ transmission assembly. The lower section of the sump is made from sheet metal. Its special contours and higher ductility compared with cast components result in greater safety under contact with the road surface or foreign objects.
MDB. The valve-gear components were all carried over one-to-one. The cooling concept with the newly introduced thermal management was also integrated, with a two-part water jacket as its basis. The straight symmetrical layout of the valve star means that the intake and exhaust valves are respectively aligned. The parallel valve positioning and an intake channel arrangement optimised for minimum pressure loss leads to a higher degree of cylinder fill. The desired swirl level is assured by seat swirl chamfers with targeted adaptations to the port geometry, as well as an adjustable intake manifold. The coolant circuit in the cylinder head facilitates needs-based adaptation of the intake and exhaust ports to suit further possible power and emissions requirements. The conceptual carry-over of the vertical intake flange from the four-cylinder engine, as well as its drilling and fastening concept, means that the new cylinder
Like all engines in the modular diesel engine system, the new three-cylinder also has a water-cooled intercooler, ➏. In contrast to the four-cylinder engines, incorporation into the Volkswagen Group’s smaller vehicle platforms means that the intercooler had to be positioned on the transmission side of the cylinder head. The radiator block of the intercooler is made from a total of seven horizontally stacked flat aluminium tubes. Turbulence elements between, and indentations inside the tubes, lead to a considerable improvement in heat transfer from the charge air to the coolant. The plastic air boxes are crimped together with the cooler package.
COUPLED LOW-PRESSURE AND HIGH-PRESSURE EGR
The layout of the exhaust-gas aftertreatment with NOx storage catalyst, DFP and dual-circuit exhaust gas recirculation is the same as that of the four-cylinder Euro VI engine [5]. The cooled low-pressure EGR system (LP EGR) on the exhaust side is thus enhanced by a non-cooled highpressure EGR system (HD EGR) with a valve on the transmission side. Because the intercooler is located at the side of the engine for packaging reasons, the arrange-
CYLINDER HEAD
The cylinder head, ➎, too, is derived from the four-cylinder engine family of the autotechreview
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❹ Combination module
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C O V E R S T O R Y DIESEL ENGINES
❺ Cylinder head
ment differs from that of the four-cylinder Euro VI engine with the HD EGR feed positioned after the intercooler but before the intake manifold.
INJECTION SYSTEM
A strategic development objective for the entire modular diesel engine system was the fundamental compatibility of injections systems from a range of different providers with all engines in the modular diesel engine system, regardless of cylinder number. The new three-cylinder TDI engine features the injection system called DFS 1.20 from Delphi with 2,000 bar of system pressure and seven-hole nozzles with a flow rate of 500 mm3/60 s at 100 bar test pressure. Reduction in the leakage rate at the DFI 1.20 solenoid valve injector has led to CO2 benefits in fuel metering. A number of adjustments to the
injectors, such as the use of a more powerful magnet coil and optimisation of the needle seat, have further increased robustness for use in global markets. Appearing here for the first time is the so-called Cylinder Counter Pressure Compensation (CCP) software function, which contributes to an additional improvement in injection precision at relatively low cylinder back pressures and in regeneration cycles. Combined with the aforementioned layout of the port geometry and valve arrangement in the cylinder head, the measures cited above lead to a significant reduction of untreated emissions from the 1.4 l engine compared with the preceding 1.2 l model.
FRICTION
A significant reduction in frictional
losses is particularly important, when it comes to meeting the extremely stringent restrictions on CO2 emissions in the geographical operating regions for a three-cylinder diesel engine, and plays a major role in the achievement of fuel consumption targets. Starting with the 1.2 l TDI three-cylinder engine, the increase in displacement to 1.4 l was achieved by lengthening the stroke from 80.5 mm to the 95.5 mm familiar from the 2 l four-cylinder TDI engine. Systematic optimisation of the piston assembly in respect of piston clearance, ring tension and ring contour more than compensated for the disadvantages of the less optimum stroke/ con-rod ratio. A further reduction of the external drive power is achieved via modifications to the timing gear, resulting from a reduction in the number of toothed-belt guides and pulleys, as well as a friction-optimised high-pressure pump. Modified camshaft bearings in the new, one-piece, modular camshaft mounting frame reduce losses in the valve gear. The integration of the balancer shaft with the oil and vacuum pumps into a compact combined module negates the need for a separate drive for the balancer shaft. The regulated oil pump incorporated into this module is specific to three-cylinder application, which also reduces the power required to drive it. The water pump with a variable volumetric flow rate enables not just shorter warm-up times for the cooling system, but also makes it possible to reduce to a minimum the power consumption of the pump, when running. A comparison of total engine drag shows that the measures cited led to an improvement of around 20 % compared with the preceding, lower-displacement version of the three-cylinder engine, ➐.
NVH ANALYSIS
❻ Charge-air assembly
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The new three-cylinder TDI engine heralds the first application of an aluminium crankcase for the entry-level engines in Volkswagen’s modular diesel engine system. The new crankcase material meant that the objectives set for acoustic comfort necessitated intensive development work to ensure sufficient casing stiffness and to avoid any loss of acoustic comfort that www.autotechreview.com
might impact the customer. Further activities for minimising noise generation concentrated on the drive for the balancer shaft and the timing gear. Extensive experimental structural analysis was carried out and measures for improvement of casing stiffness developed and implemented to ensure the lowest possible noise emissions from the crankcase, despite the change of material to aluminium. Using NVH calculations, an optimum distribution of ribs is achieved on both the inside and outside of the casing. The noise-emitting surface of the crankcase is thus beneficially divided into several smaller, unevenly sized surfaces. The tooth geometry and number of teeth were optimised as a result of investigations carried out on the balancer-shaft drive. The outcome effectively prevents
the generation of disruptive tonal and pulsating sound. Modifications to the timing gear in respect of tensioner positioning and the aforementioned changes to the roller arrangement also have a positive impact on acoustics. Beyond this, an extensive package of measures has reduced the emission of airborne and structure-borne noise and improved vibration dampening. In particular, intensive adaptation work was carried out on the engine mounts and the dual-mass flywheel to guarantee good decoupling of the body shell and transmission from the engine across the entire frequency spectrum. To reduce noise emission in the engine bay, there is also an oil-sump baffle, an acoustically effective design cover and an engine-mounted air-filter box with extensive acoustic opti-
misation. Taken together, all of the measures achieve highly effective damping of airborne noise from the driveline across the entire rev range, ➑.
POWER AND TORQUE
The new 1.4 l three-cylinder TDI engine marks a significant upward expansion in the power on offer within the three-cylinder segment, ➒. While the preceding engine was offered only with an output of approximately 74 hp, the range now consists of three variants up to a maximum of close to 103 hp with a peak torque of up to 250 Nm. The ideal torque range, with more than 90 % of maximum torque, is available across a broad rev range as of 1,500 rpm in all engine versions. The performance benefits of the new 1.4 l engine are particularly evident in the 74 hp version. At 210 Nm, the maximum torque exceeds that of its predecessor by 30 Nm and is reached considerably earlier at just 1,500 rpm. This variant with the lowest output has undergone an increase in torque disproportionate to displacement of more than 30 % at the frequently used lowest end of the rev range, which is particularly relevant to pulling away.
PERFORMANCE AND FUEL CONSUMPTION
❼ Comparison of engine drag at 1600 rpm and 90 °C oil temperature (schematic; overall improvement around 20 %)
❽ Sound output with and without engine-related acoustic measures autotechreview
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Intensive refinement work on flow paths, charge cycling and the combustion process in the new three-cylinder engine has resulted in improved turbocharger response and high-torque power delivery in every power variant. In the new Polo, this led to an improvement in the elasticity figures for all the diesel engines, combined with a decrease in fuel consumption compared with the equally powered predecessor. Performance optimisations in the 74 hp power variant are particularly notable. The 66 kW (88 hp) version marks Volkswagen’s first use of a three-cylinder TDI engine in combination with its wellknown seven-speed DSG dual-clutch transmission. The shift programme is designed for a very low-revving driving style and, alongside the vehicle-based fuel-consumption measures (BlueMotion Technology), is a key factor in the CO2
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C O V E R S T O R Y DIESEL ENGINES
three-cylinder engine fulfils the Euro VI emissions standard and, due to its modular structure, can be adapted to comply with further emissions legislation. With the new three-cylinder TDI engine, Volkswagen has created a universal basis for application across the Group's small vehicle segments. By establishing the MDB, slimming down the engine programme and incorporating it into the modular diesel engine system, effort and cost have been reduced significantly compared with the previous engine ranges. The objectives set for the new engine and laid out at the beginning of this article have thus been fulfilled in their entirety. REFERENCES
❾ Power and torque curves for the 55 kW, 66 kW and 77 kW versions of the new 1.4-l three-cylinder engine (EA288) versus the preceding engine with 55 kW (EA189)
decrease of 19 g/km compared with its preceding four-cylinder engine variant. Despite the greater demands set by emissions legislation and increased comfort expectations, all the engine variants with manual transmissions also boast significantly lower CO2 emissions than the outgoing versions, ❿.
CONCLUSION
Within the scope of the Volkswagen brand’s engine strategy, the modular diesel engine system (MDB) has been enhanced with a new, universally applicable three-cylinder engine. The focal points
of the development process were a considerable weight reduction compared with the preceding engine, combined with exceptionally low fuel consumption and improved performance. As it currently stands, the new engine has been developed for an output range of 74 to 103 hp, thus enabling it to replace four-cylinder engines with low specific power. It marks the first use of a pressure die-cast aluminium crankcase optimised for stiffness and weight. The extremely compact design makes it particularly suitable for use in the Volkswagen Group’s small vehicle platforms, where there are high demands for especially low CO2 emissions. The new
55 kW
66 kW
BlueMotion
77 kW
With DSG
Acceleration [s] : 0-80 km/h
8.6
8.6
7.4
7.4
6.9
: 0-100 km/h
10.9
10.9
9.9
12.9
12.9
Elasticity 80-120 km/h [s] : 4 th gear
12.0
12.0
9.5
–
9.0
: 5 th gear
15.5
15.0
13.0
–
12.5
Top speed [km/h] : 5 th gear
173
178
184
184
194
CO2 emissions [g/km]
88*
82
88
92
90
*Without start/stop = 94 g/km
❿ Fuel consumption and performance data for the new Polo
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[1] Neußer, H.-J.; Kahrstedt, J.; Jelden, H.; Engler, H.-J.; Dorenkamp, R.; Jauns-Seyfried, S.; Krause, A.: The New Modular TDI Generation from Volkswagen. 33rd International Vienna Motor Symposium, 2012 [2] Neußer, H.-J.; Kahrstedt, J.; Jelden, H.; Dorenkamp, R.; Düsterdiek, T.: The Euro 6 Engines from Volkswagen’s Modular Diesel Engine System – Innovative Close-to-engine Exhaust Gas Treatment for Further Reduction of NOx and CO2. 34th International Vienna Motor Symposium, 2013 [3] Rudolph, F.; Hadler, J.; Engler, H.-J.; Krause, A.; Lensch-Franzen, C.: The New 1.2-l TDI from Volkswagen – Innovation with 3 Cylinders for Extremely Low Fuel Consumption. 31st International Vienna Motor Symposium, 2010 [4] Rudolph, F.; Hadler, J.; Engler, H.-J.; Krause, A.; Stamm, M.: The New 1.6-l TDI Engine from Volkswagen. 30th International Vienna Motor Symposium, 2009 [5] Neußer, H.-J.; Kahrstedt, J.; Dorenkamp, R.; Jelden, H.: The Euro 6 Engines from the Volkswagen Modular Diesel Engine System. In: MTZ 74 (2013), No. 6
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