VR6 engine

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The VR6 engine is an internal combustion engine configuration, consisting of six cylinders. It was developed and is produced by Volkswagen Group. It is similar to a V engine, but with the cylinders offset and tilted from each other by either 10.6° or 15°, instead of the more common 45°, 60°, or 90°.

Description

Three types of engine: a — straight engine, b — V engine, c — VR6 engine

The name VR6 comes from a combination of V engine (German: V-Motor), and the German word "Reihenmotor" (straight engine).

The 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 practise dating back to the 1920s). Staggered engines are an amenable further development, with both uneven cylinder numbers, and with staggered-bank V configurations.

The VR6 was specifically designed for transverse installation in front-wheel drive vehicles. By using the narrow 15° 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 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-6) engine and, as a result, it is nearly as smooth as an inline-6.

The narrow angle between cylinders allows the use of just one 'cylinder bank', and one cylinder head - whereas conventional V engines require two cylinder banks and 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, one overhead camshaft is used for all cylinders. This is similar to the operation of a single overhead camshaft (SOHC) V6 engine. Later 24-valve VR6 engines operate all of the exhaust valves with one camshaft, and operate all of the intake valves with another camshaft. This is similar to a double overhead camshaft (DOHC) inline-6 engine.

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 rated motive power output of 128 kilowatts (174 PS; 172 bhp), and 240 newton metres (177 ft·lbf) of torque.

Detailed specifications

The 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. Exhaust gases are channeled through a 3-way catalytic converter.

Volkswagen Group identifies the 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 mm, and the piston stroke is 90.0 mm. 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. Overhead camshafts operate the automatic hydraulic valve lifters which, in turn, open and close the 39.0 mm intake valves and 34.3 mm exhaust valves. Since the two 'rows' of pistons share a single seal,^{[clarification needed]} the surface of the piston is tilted. Since the piston rings are better not tilted, the firewall^{[clarification needed]} has a varying height leading to unequal thermal stresses and a heavier piston.^{[citation needed]} Intake and exhaust valves need a 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,^{[clarification needed]} which may be a problem in high revving race engine applications.^{[citation needed]} The intake and exhaust ports pass closely. This heats the intake, reducing the power, and cools the exhaust gasses, hampering the operation of the catalytic converter. In the road car production engine, a single plane exhaust manifold seal is used, and therefore half of the ports have to be very long,^{[clarification needed]} leading to increased heat insertion into the manifold and 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 a R6), the longer ports on the 4-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 street 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.^{[clarification needed]}

Because of the special VR6 cylinder arrangement with two rows of combustion chambers in 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 mm 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 before passing over the heated oxygen sensor, and then to the catalytic converter.

The oil pump driveshaft is driven by an intermediate shaft. Fuel injectors of 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.^{[citation needed]} The water pump housing is cast integral with the cylinder block. VR6 engines will use an auxiliary electric pump to circulate water while the engine is running, and during the cooling fan after-run cycle, in addition to the belt-driven water pump.

A replaceable oil filter cartridge element is used on the VR6 engine. The sump-mounted oil pump is driven via the 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). Two rows of three cylinders are arranged at a 15° axial angle from the crankshaft. The cylinder bores are 81.0 mm in diameter, with a spacing of 65 mm between cylinders. They are staggered 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 mm. 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

The 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 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 cm (2.5 in) catalytic converter, sharper camshafts, 4 bar 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. The 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 only received this engine in 1994; 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 first block to use an uneven number of cylinders in a V-design (other than 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.

VWAG added further modifications 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 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,^{[citation needed]} and the 4WD system (4motion) became standard on the V6 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 was introduced in North America in 2001 aboard the Eurovan producing 150 kilowatts (204 PS; 201 bhp), and in the GTI in 2002 (where it retained the VR6 name).

In 1999, VWAG also released an updated 12-valve VR6 model for the North American market A4-chassis 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 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 Beetle called Beetle RSi. The Beetle RSi was the first production vehicle to use the 3.2 litre VR6.^{[citation needed]} This engine was later used in the Mk4 Golf R32, and was also introduced in the 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.

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

In 2005, the European market version of Volkswagen's sixth generation Passat 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 degree cylinder angle, producing 206 kilowatts (280 PS; 276 bhp). The 3.2 and 3.6 feature Fuel Stratified Injection (FSI).^[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 3.2 VR6 (non-FSI) is also being used to power the Mk5 Golf R32, while the new Passat R36, available from early 2008, received a new version of the 3.6 litre engine, with 221 kilowatts (300 PS; 296 bhp), standard 4motion four-wheel drive, and standard Direct-Shift Gearbox (DSG).

Usage

The VR6 was used by Volkswagen Passenger Cars in:

• Volkswagen Golf Mk3, Mk4 and Mk5
• Volkswagen Passat (B3, B4, and B6 chassis)
• Volkswagen Vento/Volkswagen Jetta Mk3
• Volkswagen Bora/Volkswagen Jetta]] Mk4
• Volkswagen New Beetle
• Volkswagen Corrado
• Volkswagen Phaeton
• Volkswagen Transporter/Caravelle/Multivan T4 and T5
• Volkswagen Sharan/SEAT Alhambra/Ford Galaxy

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

• Audi A3 Mk2
• Audi TT both generations
• SEAT León
• Skoda Superb Mk2

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

• Volkswagen Golf Mk4
• Volkswagen Bora
• Volkswagen Passat (B5 chassis)
• Volkswagen New Beetle
• SEAT Toledo Mk2

Other applications of VR6 technology

Volkswagen 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 engined configuration, which is significantly shorter than a 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 also

Wikimedia Commons has media related to: VR6 engines

• List of Volkswagen Group petrol engines
• List of Volkswagen Group diesel engines
• List of discontinued Volkswagen Group petrol engines
• List of discontinued Volkswagen Group diesel engines
• List of North American Volkswagen engines
• Straight engine
• V engine
• W8 engine
• W12 engine
• W16 engine
• W18 engine

References

External links

• Volkswagen Group corporate website
• Volkswagen's VR6 and W-engines
• Sensors for Engine Management (PDF) - shows build dates for various VWAG engines