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VR6 engine

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The VR6 engine is an internal combustion engine configuration, consisting of six cylinders. It was developed by the German automotive industry concern, Volkswagen Group in the late 1980s, and evolutions of the original variant are still produced by them today.

It is similar to a 'Vee' engine, but with the 'rows' of cylinders offset and tilted from each other by an angle of either 10.6 degrees (°) or 15° - instead of the more common 45°, 60°, or 90° as found on conventional Vee engines.

DescriptionEdit

The name VR6 comes from a combination of V engine (German: V-motor), and the German word "Reihenmotor" (meaning "row engine" or straight engine) - and so is described as a "Vee-Row" engine.

This engine configuration can also be described as a "staggered six", in keeping with the geometry of the Lancia Fulvia staggered-four, developed in the late 1950s (a continuation of Lancia's design practice dating back to the 1920s). Staggered engines are an amenable further development, with both uneven cylinder numbers, and with staggered-bank Vee configurations.

The VR6 was specifically designed for transverse engine installations in front-wheel drive vehicles. By using the narrow angle of 15° between the two 'rows' in the VR6 engine, it was possible to install a six-cylinder engine within the existing Volkswagen Group four-cylinder-model engine bays. A wider V6 engine of conventional Vee design would have required lengthening existing vehicles to provide enough crumple zone between the front of the vehicle and the engine, and between the engine and the passenger cell. The VR6 is able to use the firing order of a straight-six engine (aka inline-six) engine and, as a result, it is nearly as smooth as an inline-six.

The narrow angle between cylinders allows the use of just one 'cylinder bank', and one cylinder head - whereas conventional Vee engines have two cylinder banks and require two separate cylinder heads. As a result of using just one cylinder head, it also allows just two overhead camshafts to drive all of the valves. This simplifies engine construction, and reduces costs. In early 12 valve VR6 engines, there are two overhead camshafts with six cam lobes on each. The forward camshaft has three intake valve lobes and three exhaust valve lobes to control the frontmost three cylinders. The rear camshaft is designed the same way, but controls the rearmost three cylinders instead. The operating principle of this design is most similar to a single overhead camshaft (SOHC) design. Later 24 valve VR6 engines still had two overhead camshafts, but now with 12 cam lobes each. However, the operation of the camshafts in the 24 valve engine is different to that of the earlier 12 valve engine, in that the front camshaft only operates the intake valves, and the rear camshaft only operates the exhaust valves. The operating principle of this design is most similar to a double overhead camshaft (DOHC) design.

There are several different variants of the VR6 engine. The original VR6 engine displaced 2.8 litres and featured a 12 valve design (two valves per cylinder). These engines produced a DIN-rated motive power output of 128 kilowatts (174 PS; 172 bhp), and 240 newton metres (177 ft·lbf) of torque.

Detailed specificationsEdit

The original VR6 engine features a one-piece grey cast iron crankcase and cylinder block, and one lightweight aluminium alloy crossflow cylinder head, with two valves per cylinder, operated by chain-driven overhead camshafts. All fuel and ignition requirements of the VR6 engine are controlled by Bosch Motronic engine control unit (ECU). This engine management system features an air mass sensor, dual knock sensors for cylinder-selective ignition knock regulation, and Lambda regulation for the air/fuel mixture. Exhaust gases are channeled through a three-way catalytic converter.

Volkswagen Group identifies the original VR6 by the "AAA" engine ID code. It operates on the four-stroke cycle, has an engine displacement of 2.8 litres, although some European engines had a displacement of 2.9 litres (this variant identified by the "ABV" engine ID code). The cylinder bore diameter is 81.0 millimetres (3.19 in), and the piston stroke is 90.0 millimetres (3.54 in). The "Vee" angle is 15°, and the compression ratio (CR) is 10:1.

The drop-forged steel, six-throw crankshaft runs in seven main bearings. The connecting rod bearing journals are offset 22° to one another. Two overhead camshafts (OHCs) operate the automatic hydraulic valve lifters which, in turn, open and close the 39.0 millimetres (1.54 in) intake valves and 34.3 millimetres (1.35 in) exhaust valves. Since the two 'rows' of pistons and cylinders share a single cylinder head and head gasket, the piston crown (or top surface) is tilted. Since the piston rings are better not tilted, and will only work when perpendicular to the cylinder bore, the firewall has a varying height, leading to unequal thermal stresses and a heavier piston. Intake and exhaust valves need different camshafts to vary valve overlap (they may be coaxial like in some 90° V8). To minimise the number of camshafts, both rows share their camshafts (like some 90° V8). Then due to the geometry, half of the valve stems are very long, which may be a problem in high revving race engine applications. The intake and exhaust ports pass closely within the cylinder head; this then heats the intake air/fuel mixture before it is ignited by the spark plug, which limits the amount of timing advance that can be used due to an increased possibility of pre-detonation of the air/fuel mixture and has the effect of reducing the power. This also cools the exhaust gasses, which hampers the operation of the catalytic converter. In the road car production engine, a single plane exhaust manifold gasket is used, and therefore half of the ports have to be very long, leading to increased heat insertion into the manifold, requiring a heavier manifold, and an otherwise unnecessary turn in the intake manifold. Since the cylinder pitch is decreased a bit too much (as compared to an inline-six), the longer ports on the four-valve version are squeezed into a standing rectangular cross section, and do not have the typical and more ideal lying elliptical or half moon cross section. In road car applications, the intake and exhaust ports are typically bent, and the different port lengths can easily be compensated. An exception is the W engine derivative of the VR6, where every second intake port has a notable chicane.

Because of the cylinder arrangement in the VR6 - with two rows of combustion chambers within the same cylinder head, the intake ports between the two rows of cylinders are of varying lengths. Depending on the specific generation of VR6, the difference in intake port length is compensated in the intake manifold, the camshaft overlap and lift profile, or a combination thereof. In the original VR6, each port is 420 millimetres (16.5 in) long. Exhaust gases are channeled from two 3-branch cast iron exhaust manifolds (one dedicated to three cylinders) into a sheathed Y-pipe. From there, they are channeled into a single flow pipe, before passing over the heated oxygen sensor, and then to the catalytic converter.

The fuel injectors, operated by the Bosch Motronic engine control unit (ECU) system, are mounted behind the bend of the intake manifolds. Besides being the optimum location for fuel injection, this location also helps shield the injectors during a frontal impact. The water pump housing is cast integral with the cylinder block. VR6 engines also use an additional auxiliary electric pump to circulate the engine coolant whilst the engine is running, and also during the cooling fan 'after-run' cycle, in addition to the belt-driven main water pump.

A replaceable oil filter cartridge element is used on the VR6 engine. The sump-mounted oil pump is driven via an intermediate shaft. An oil pressure control valve is integrated in the pump.

The one-piece cylinder block and crankcase is made from pearlitic grey cast iron with microalloyed steel (microalloy). The two rows of three cylinders are arranged at a 15° axial angle from the crankshaft. The cylinder bores are 81.0 millimetres (3.19 in) in diameter, with a spacing of 65 millimetres (2.6 in) between cylinders. They are staggered, but overlap along the length of the engine block - to allow the engine to be shorter and more compact than conventional V6 engines.

The centerline of the cylinders are also offset from the centerline of the crankshaft by 12.5 millimetres (0.49 in). To accommodate the offset cylinder placement and narrow "Vee" design, the connecting rod bearing journals are offset 22° to each other. This also allows the use of a 120° firing interval between cylinders. The firing order is: 1, 5, 3, 6, 2, 4.

History and evolutionEdit

The Volkswagen Group VR6 engine was introduced in Europe by Volkswagen Passenger Cars in 1991, in the Passat and Corrado; and in North America the following year. The Passat, Passat Variant (estate/wagon), and US-specification Corrado used the original 2.8 litre design; the European-specification Corrado and the 4WD Passat Syncro received a 2.9 litre version with 140 kilowatts (190 PS; 188 bhp). This version also had a free flowing 6 centimetres (2.4 in) (2.5 in) catalytic converter, sharper camshafts, 4 bars (58 psi) fuel pressure regulator, enlarged inlet manifold, and larger throttle body.

The 2.9 litre engine, as destined for the Corrado, was originally designed to benefit from a dual-tract variable-length inlet manifold - called the VSR (German: "Variables SaugRohr"), and made by Pieronberg for Volkswagen Motorsport. This gave extra low-down torque, but was deleted before production on cost grounds, and was instead offered as an aftermarket option. This design was later sold to Schrick, who redesigned it and offered it as the Schrick VGI ("Variable Geometry Intake").

In 1992, with the introduction of the Volkswagen Golf Mk3, a six-cylinder engine was available for the first time in a lower-midsize segment hatchback in Europe. North America waited until 1994 to received this engine; at the same time, the European model started to use the 2.9 litre in the VR6 Syncro model. The corresponding Vento/Jetta VR6 versions appeared in the same years.


Volkswagen Group removed a cylinder from the VR6 in 1997 to create the VR5 (aka 'V5'), the second block to use an uneven number of cylinders in a Vee design after the Honda V3 triples of MotoGP fame. This version, which had a 2.3 litre capacity, was capable of 110 kilowatts (150 PS; 148 bhp), and had a maximum torque of 210 newton metres (155 ft·lbf). It was introduced in the Passat in 1997, and the Golf and Bora in 1999.

Further modifications were added to the design in 1999, with the introduction of the 24-valve 2.8 litre VR6. This engine produced 150 kilowatts (204 PS; 201 bhp), and 265 newton metres (195 ft·lbf) of torque. The new version was not available in the Passat (as it was incompatible with the then-current generation's longitudinal engine layout), but was introduced as the range-topper in the Golf and Bora for European markets. The VR6 name was dropped as a commercial designation, and the 4WD system (now renamed 4motion) became standard on the V6 (VR6) in Europe. The corresponding multi-valve V5 was only released in 2001, with a 20 PS power increase, to 125 kilowatts (170 PS; 168 bhp). The multi-valve V6 (VR6) was introduced in North America in 2001 aboard the T4 Eurovan, producing 150 kilowatts (204 PS; 201 bhp), and in the GTI in 2002 (where it retained the VR6 name).

In 1999, an updated 12-valve VR6 model was released for the North American market A4-platform Golf Mk4/GTI/Jetta product line. This new VR6 improved performance via updated camshafts, variable geometry intake manifold, an increased compression ratio of 10.5:1, and updated emissions equipment. Motive power increased to 130 kilowatts (177 PS; 174 bhp) at 5,800 revolutions per minute (rpm), while torque increased to 245 newton metres (181 ft·lbf) at 3,200 rpm. This engine option was available from 1999.5—2002, when it was replaced by the 24-valve engine.

In 2001, the VR6 was enlarged to 3.2 litres, to create a limited-production, high performance, 168 kilowatts (228 PS; 225 bhp) version of the New Beetle called Beetle RSi. The Beetle RSi was the first production vehicle to use the 3.2 litre VR6. This engine was later used in the Mk4 Golf R32, and was also introduced in the original Audi TT. According to Volkswagen Group, this variant produced 184 kilowatts (250 PS; 247 bhp) and 320 newton metres (236 ft·lbf) of torque in TT trim, and 177 kilowatts (241 PS; 237 bhp) in R32 trim. Although it was rated at the same power as the European version, the North American R32 featured a larger Audi TT mass airflow sensor (3" in diameter, compared to 2.75"), and a different airbox which should have given the same 184 kilowatts (250 PS; 247 bhp) output of the Audi, without taking the harsher government decreed emissions restrictions into account.

The 3.2 litre was then used as a range-topper in the original Audi A3 and TT.

The 3.2 VR6 continued being used to power the R32, in the all-new Mk5 Golf R32.

In 2005, the European market version of Volkswagen's sixth generation Passat, now with a transverse engine layout, went on sale with a revised version of the 3.2 litre VR6 as its top-spec engine. For North America, the Passat received a new 3.6 litre VR6 with a narrower 10.6  cylinder angle, producing 206 kilowatts (280 PS; 276 bhp). These revised 3.2 and 3.6 feature Fuel Stratified Injection (FSI). This new 3.2 FSI VR6 develops 184 kilowatts (250 PS; 247 bhp) at 6,250 rpm, and 330 newton metres (243 ft·lbf)at 3,000 rpm.[1] The introduction of the Passat VR6 also marked the first time a VR6 powered vehicle was made available in North America before Europe.

The new Passat R36, available from early 2008, received an uprated version of the 3.6 FSI VR6 engine, with 220 kilowatts (299 PS; 295 bhp) at 6,600 rpm and 350 newton metres (258 ft·lbf) at 2,400 rpm, standard 4motion four-wheel drive, and standard Direct-Shift Gearbox (DSG).[2]

UsageEdit

VR6Edit

The VR6 engine was used by Volkswagen Passenger Cars in:


The VR6 is also used in other Volkswagen Group products, namely:

VR5Edit

The VR5 was used by in the following Volkswagen Group products:

Other applications of "VR" technologyEdit

Volkswagen Group has also developed a series of engines which use 'narrow angle' designs mated together at 72 degrees. For example, two imaginary VR6 engines mated together at 72 degrees result in a W12 engine configuration, which is significantly shorter than a conventional V12 engine, but only marginally wider. W8 engine and W16 engine designs were developed in a similar fashion. The W8 uses two imaginary four-cylinder VR engines mated together, and the W16 uses two imaginary eight-cylinder VR banks.

Though Volkswagen Group describes these compound VR engines as being of W configuration, it is more correct to describe them as staggered-bank V configuration engines, in keeping with the staggered-straight VR geometry.

See alsoEdit

Template:VR6 engine Template:Volkswagen Group brands

Piston engine configurations
This box: view  talk  edit
Type BourkeControlled combustionDelticOrbitalPistonPistonless (Wankel) •
RadialRotarySingleSplit cycleStelzerTschudi
Inline types H · U · Square four · VR · Opposed · X
Stroke cycles Two-stroke cycleFour-stroke cycleSix-stroke cycle
Straight Single · 2 · 3 · 4 · 5 · 6 · 8 · 10 · 12 · 14
Flat 2 · 4 · 6 · 8 · 10 · 12 · 16
V 4 · 5 · 6 · 8 · 10 · 12 · 16 · 20 · 24
W 8 · 12 · 16 · 18
Valves Cylinder head portingCorlissSlideManifoldMultiPistonPoppet
SleeveRotary valveVariable valve timingCamless
Mechanisms CamConnecting rodCrankCrank substituteCrankshaft
Scotch YokeSwashplateRhombic drive
Linkages EvansPeaucellier–LipkinSector straight-lineWatt's (parallel)
Other HemiRecuperatorTurbo-compounding

ReferencesEdit

  1. "The Passat (sales brochure) - 3.2 FSI VR6" (PDF). Volkswagen Group United Kingdom Limited. Volkswagen.co.uk. 1 December 2008. pp. 14,18,24. http://cdn.volkswagen.co.uk/assets/common/pdf/brochures/passat-saloon-brochure.pdf. Retrieved 31 July 2009. 
  2. "The Passat (sales brochure) - 3.6 FSI VR6" (PDF). Volkswagen Group United Kingdom Limited. Volkswagen.co.uk. 1 December 2008. pp. 11,12,14,19,24. http://cdn.volkswagen.co.uk/assets/common/pdf/brochures/passat-saloon-brochure.pdf. Retrieved 31 July 2009. 

External linksEdit

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