VR6 engine

Schematic 'top view' of a 15° VR6 engine

VR6 engines, and the later VR5 variants, are a family of internal combustion engines, characterised by a narrow-angle (10.5° or 15°) V engine configuration. Developed by the Volkswagen Group in the late 1980s, evolutions of these engines are still produced by them.

When containing six cylinders, a VR-engine's cylinder block consists of two cylinder banks (left: 1-3-5; right: 2-4-6) while there is only a single cylinder head covering both rows of cylinders.

Description

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

Cylinder block arrangements
Left: I4, Center: V6, Right: VR6
A V6 engine has two separate cylinder heads, while the VR6 uses one, like an inline engine

The name VR6 comes from a combination of V engine (German: V-Motor), and the German word "Reihenmotor" (meaning "inline engine" or "straight engine") - and so is described as a "Vee-Inline engine" (VR-Motor). It shares a common cylinder head for the two offset banks of cylinders. It has a specific sound that is unique and different than either inline or "V" engines. The engine is currently in use in a variety of VW models, one such example is the Volkswagen Passat NMS.^[1]

This engine configuration was also adopted for the Horex VR6 Motorbike.

The Volkswagen VR6 was specifically designed for transverse engine installations in front-wheel drive vehicles. The narrow angle of 15° between the two 'rows' in the VR6 engine is a more compact size than a wider angle V6 design. This made it possible for Volkswagen to install six-cylinder engines in existing four-cylinder cars. The wider configuration of a wider angle V6 engine would have required an extensive redesign of the vehicles to enlarge the engine compartment. The VR6 is also able to use the firing order of a straight-six engine.

The narrow angle between cylinders allows the use of just one cylinder head - whereas wider angle Vee engines require two separate cylinder heads, one for each cylinder bank. The VR6 arrangement needs two overhead camshafts to drive all the valves, regardless of whether the engine has two valves per cylinder, or four per cylinder. This simplifies engine construction and reduces costs. In early VR6 engines with 12 valves (two per cylinder) two overhead camshafts were used. The forward camshaft (in the transversely mounted engine) has six cam lobes to control the three intake and three exhaust valves of the front cylinder bank, without using rockers. The rear camshaft is designed the same way, but controls the rear cylinder bank. The operating principle of this design is comparable to a single overhead camshaft (SOHC) design with intake and exhaust valves of one bank driven by one camshaft. The later VR6 engine designs with 24 valves (four per cylinder) had two overhead camshafts as well, however with a slight change of operation principle: In the 24 valve engine all intake valves are operated by the front camshaft (with the aid of rockers), while all the exhaust valves are operated by the rear camshaft (again with rockers). This operating principle is more akin to a double overhead camshaft (DOHC) design, with one camshaft for intake valves, and one for exhaust valves.

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 power output of 128 kW (174 PS; 172 bhp), and 240 N⋅m (177 lbf⋅ft) of torque.

Detailed specifications

Schematic cross-section of the VR6 engine.
Note the "twin SOHC" design.

Volkswagen Group identifies the original VR6 by the chassis "AAA" engine ID code. It operates on the four-stroke cycle, and has an engine displacement of 2.8 litres. The 2.8 VR6 cylinder bore diameter is 81.0 millimetres (3.19 in), and the piston stroke is 90.0 millimetres (3.54 in), although some European engines had a displacement of 2.9 litres (this variant identified by the "ABV" engine ID code). The 2.9 VR6 bore diameter is 82.0 millimetres (3.23 in), and the stroke is 90.0 millimetres (3.54 in). The "Vee" angle is 15°, and the compression ratio (CR) is 10:1.^[2]

The drop-forged steel six-throw crankshaft runs in seven main bearings; unlike the majority of wide angle V6 engines which have only four main bearings. The connecting rod bearing journals are offset 22° to one another.^[3] Two overhead camshafts (OHCs) operate the automatic hydraulic valve lifters which, in turn, open and close the 39.0 mm (1.54 in) intake and 34.3 mm (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. Intake and exhaust valves need different camshafts to vary valve overlap (they may be coaxial like in some 90° V8).

Schematic diagram showing the differences in port lengths between a V6 and VR6 using 12-valves

Schematic diagram showing the differences in port lengths between a V6 and VR6 using 24-valves

Because of the cylinder arrangement in the VR6 - with two rows of combustion chambers within the same cylinder head, the intake and exhaust ports between the two rows of cylinders are of varying lengths. Without compensation, these varying port lengths would result in the two rows of cylinders producing different amounts of power at a particular engine RPM. Depending on the specific generation of VR6, the difference in port lengths are compensated for by specific tuning of the intake manifold, the camshaft overlap and lift profile, or a combination thereof. The fuel injectors, operated by the Bosch Motronic engine control unit (ECU) system, are mounted behind the bend of the intake manifolds. VR6 engines also use an auxiliary electric pump to circulate the engine coolant while the engine is running, and also during the cooling fan 'after-run' cycle, in addition to the belt-driven main water pump.

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.^[4] The firing order is: 1, 5, 3, 6, 2, 4.^[5]

History and evolution

A European-spec 'ABV' 2.9 litre VR6 in a Volkswagen Corrado

The Volkswagen Group VR6 engine was introduced in Europe by Volkswagen in 1991, in the Passat and Corrado; and in North America the following year. The Passat, Passat Variant (estate/wagon), and U.S.-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 kW (190 PS; 188 bhp). This version also had a free flowing 6 cm (2.4 in) catalytic converter, sharper camshafts, 4-bar (58 psi) fuel pressure regulator, enlarged inlet manifold, and larger throttle body. It was also sold to Mercedes Benz for use in their vans, and designated as M104.900.

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 Pierburg 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 receive 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 kW (150 PS; 148 bhp), and had a maximum torque of 210 N⋅m (155 lb⋅ft). 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 kW (204 PS; 201 bhp), and 265 N⋅m (195 lbf⋅ft) 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 under engine codes AQP and AUE from 1999. 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 (15 kW; 20 hp) power increase, to 125 kW (170 PS; 168 bhp). The multi-valve V6 (VR6) was introduced in North America in 2001 aboard the T4 Eurovan, producing 150 kW (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. Power increased to 130 kW (177 PS; 174 bhp) at 5,800 rpm, while torque increased to 245 N⋅m (181 lbf⋅ft) at 3,200 rpm. This engine option was available from 1999.5—2002, when it was replaced by the revised 24-valve engine producing more power and torque, engine code BDF, at the same time as the European market also introduced this revised engine.

In 2001, the VR6 was enlarged to 3.2 litres, to create a limited-production, high-performance, 168 kW (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 24-valve VR6 engine. This engine was later used in the Mk4 Golf R32, and was also introduced in the original Audi TT. According to Volkswagen Group, these variants produced 184 kW (250 PS; 247 bhp) in TT trim (engine ID code: BHE), and 177 kW (241 PS; 237 bhp) in R32 trim (engine ID code: BFH/BML).

The then range-topping 3.2-litre VR6 was later used in the current Audi A3 and the 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 degree cylinder angle, producing 206 kW (280 PS; 276 bhp). These revised 3.2 and 3.6 feature Fuel Stratified Injection (FSI). This new 3.2 FSI VR6 develops 184 kW (250 PS; 247 bhp) at 6,250 rpm, and 330 N⋅m (243 lbf⋅ft) at 3,000 rpm.^[6] The 3.2 VR6 engine was recently used by professional drifter Wojciech Gozdziewicz from Poland, who swapped his original BMW engine out of the car in favor of the VW power plant.^[7] The introduction of the Passat VR6 also marked the first time a VR6 powered vehicle was made available in North America before Europe.

The Passat R36, available from early 2008, received an uprated version of the 3.6 FSI VR6 engine, with 220 kW (299 PS; 295 bhp) at 6,600 rpm and 350 N⋅m (258 lbf⋅ft) at 2,400 rpm, standard 4motion four-wheel drive, and standard Direct-Shift Gearbox (DSG).^[8]

The first generation Porsche Cayenne base model is powered by a 3.2-liter VR6 engine producing 250 hp (186 kW; 250 bhp); modifications in the exhaust manifold allow power to peak at 6700 rpm. This is the same 3.2-liter motor found in the Volkswagen Touareg and Volkswagen R32.

Usage

Other applications of "VR" technology

Volkswagen Group has also developed a series of compound VR engines referred to as "W engines", which resemble two narrow angle VR cylinder blocks mated together at 72 degrees. Typically, these W engines are significantly shorter but only marginally wider than their conventional V engine counterparts. For example, the W12 engine configuration is conceptually similar to two VR6 blocks mated together at 72 degrees. Likewise, W8 engine and W16 engine designs follow the same concept. The W8 resembles two four-cylinder "VR4" blocks arranged in a V configuration. The W16 resembles two eight-cylinder "VR8" blocks arranged in a V configuration, or two W8 blocks places end-to-end.

See also

• Lancia's V4 engines were the first narrow-angle V-engines in series-production automobiles, starting in 1922.

References

External links

Wikimedia Commons has media related to Volkswagen VR6 engine.

• Volkswagen’s VR6 engine
• VW's new 496bhp 3.0-litre VR6 engine
• Slow death of Volkswagen's VR6
• VW Is Cooking Up A VR6-Powered Arteon R With Over 400bhp
• Video by Engineering Explained on YouTube