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VR6 engine

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

Description

The name VR6 comes from a combination of V engine (German: V-Motor) and the German word "Reihenmotor" (straight engine). The combination of the two can be roughly translated as "inline V6 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. 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 in existing Volkswagen models. 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. In addition, the VR6 is able to use the firing interval of an inline-6 engine. As a result, it is nearly as smooth as an inline-6.

The narrow angle between cylinder banks also allows just two camshafts to drive all of the valves, and a single cylinder head to be used. This simplifies engine construction and reduces costs. In early (12 valve) VR6 engines, one camshaft is used per bank of cylinders. This is most similar to the operation of a SOHC V6 engine. However, later (24 valve) VR6 engines use two camshafts, the right bank camshaft operates the right bank exhaust valves and the left bank intake valves, the left bank camshaft operates the left bank exhaust valves and the right bank intake valves. This is most similar to a DOHC Inline-6 engine.

There are several different variants of the VR6 engine. The original VR6 engine displaced 2.8 L and featured a 12 valve design. These engines produced 174 PS (128 kW/172 hp) and 240 N·m (177 ft·lbf) of torque.


History

The VR6 engine was introduced in Europe in 1991 in the Passat and Corrado, and in North America the following year. The Passat, Passat Variant wagon and US-spec Corrado used the original 2.8 L design, while the Euro-spec Corrado and the 4WD Passat Syncro received a 2.9 L version with 190 PS (140 kW/187 hp). This version also had a free flowing 6 cm (2.5 in) catalytic converter, enlarged inlet manifold and larger throttle body.

The 2.9 L 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 VW 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 Golf's third generation, 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 L in the VR6 Syncro model. The corresponding Vento/Jetta VR6 versions appeared in the same years.

In 1997, VW removed a cylinder from the VR6, creating the VR5, 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 L capacity, was capable of 150 PS (110 kW/148 hp) and had a maximum torque of 210 N·m (154 ft·lbf). It was introduced in the Passat in 1997, and later in the Golf and Bora in 1999.

For 1999, VW added further modifications to the design, with the introduction of the 24-valve 2.8 L VR6. This engine produced 204 PS (150 kW/201 hp) and 265 N·m (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, and the 4WD system (4Motion) was now standard on the V6 in Europe. The corresponding multivalve V5 was only released in 2001, with a 20 PS power increase, to 170 PS (125 kW/168 hp). The multivalve V6 was introduced in North America in 2001 aboard the Eurovan producing 201 bhp and in the GTI in 2002 (where it retained the VR6 name).

In 1999, VW also released an updated 12-valve VR6 model for the North American market A4-chassis Golf/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. Power increased to 174 hp @ 5800 RPM while torque increased to 181 ft·lbf @ 3200 RPM. This engine option was available from 1999.5-2002 when it was replaced by the 24-valve engine.

In 2003, the VR6 was enlarged to 3.2 L to create a limited-production, high performance version of the Golf called R32. It was also introduced in the Audi TT. According to Volkswagen, this variant produced 250 PS (184 kW/247 hp) and 320 N·m (236 ft·lbf) of torque in TT trim and 241 PS(177 kW/238 hp) in R32 trim. Although it was rated at the same power as the European version, the North American R32 featured a larger mass airflow sensor (3" in diameter compared to 2.75"), and the airbox differed as well.

The 3.2 was then used as a range-topper in the Audi A3 and TT or as an entry level version in the VW Touareg and Porsche Cayenne, although the version used in the Cayenne features modifications to the head as well as the intake and timing systems.

In 2005, the European market version of Volkswagen's sixth generation Passat went on sale with a revised version of the 3.2 L VR6 as its top-spec motor. For North America, the Passat received a new 3.6 L VR6 with a narrower 10.6 degree cylinder angle, producing 280 PS (206 kW/276 hp). The 3.2 and 3.6 feature Fuel Stratified Injection. The introduction of the Passat VR6 also marked the first time a VR6 powered vehicle was made available in North America before Europe. The Audi Q7 and restyled VW Touareg received the 3.6 L engine in late 2006, along with the Porsche Cayenne for 2008..

The 3.2 VR6 is also being used to power the new MK V Golf R32. The Passat will receive an R36 variant, with 300 PS (221 kW/295 hp), standard four wheel drive and optional DSG gearbox, in mid 2007.


Technical information and engine specifications

The engine features a cast-iron crankcase, one light 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 management. 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.

Internally, Volkswagen identifies the VR6 by the "AAA" engine code. It is a four-stroke, internal combustion engine with 2.8 L of displacement, though some European engines had 2.9 L of displacement (this variant identified by the "ABV" engine code). The bore diameter is 81.0 mm with a 90.0 mm stroke. 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 journals are offset 22° to one another. Overhead camshafts (one for each bank of cylinders) operate the hydraulic valve lifters which, in turn, open and close the 39.0 mm intake valves and 34.3 mm exhaust valves. Because of the special VR6 cylinder arrangement with two rows of combustion chambers in the same cylinder head, the intake runners between the two cylinder banks are of varying lengths.

Depending on the specific generation of VR6, the difference in intake runner length is compensated in the overhead intake manifold, the camshaft overlap & lift profile, or a combination thereof.

In the original VR6, each runner is 420 mm long. Exhaust gases are channeled from two 3-branch cast-iron exhaust manifolds (one dedicated to three exhaust ports) 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 the intermediate shaft. Fuel injectors of the Bosch Engine Management 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 engine crankcase. In addition to the belt-driven water pump, VR6 engine will use an auxiliary electric pump to circulate water while the engine is running and during the cooling fan after-run cycle.

In the interest of environmental friendliness, a replaceable oil filter cartridge 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 crankcase is made from Perlitic gray cast iron with micro-alloy. Two banks of three cylinders are arranged at a 15° axial angle from the crankshaft. The cylinder bores are 81 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 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.

Usage

The VR6 was used by Volkswagen in:

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

The Porsche Cayenne, which shares its chassis with the VW Touareg, also uses the 3.2 L VR6 as its base engine.

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


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 VR6 engines mated together at 72 degrees result in a W12 configuration, which is significantly shorter than a V12 engine, but only marginally wider. W8 and W16 designs were developed in a similar fashion. The W8 uses two four-cylinder VR engines mated together, and the W16 uses two eight-cylinder VR banks.

Though Volkswagen 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

External links

Piston engine configurations
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V 2, 4, 5, 6, 8, 10, 12, 16, 20, 24
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