VR6 Engine — Design Description (VW Sharan 1)

This section examines the 6-cylinder engine, first installed in 1991 in the Volkswagen Passat, called the VR6, which has significant differences from the usual engine design concept "Volkswagen" or "Audi". Engine in the company "Volkswagen" was given the name "AAA" but is more commonly known as the VR6. Its six cylinders are arranged in a V-shape at an angle of 15°, as opposed to traditional V-shaped engines which have an angle of 60° or 90°. The VR6 engine was so compact that it allowed both banks of cylinders to be covered by a single common head, as opposed to a conventional V-shaped engine. As a result, the VR6 engine is shorter in length than an in-line engine and narrower in width than a conventional V-shaped 6-cylinder engine. (Fig. 15) shows a schematic of the three types of 6-cylinder engines, and shows the basis on which the VR6 engine was developed.

With such an acute angle of the cylinders (15°), problems with uneven rotation of the crankshaft of the VR6 engine do not arise, it runs as smoothly as an in-line engine. The engine has two camshafts that control twelve vertically arranged valves (2 per cylinder). Both overhead camshafts are housed in an aluminum cylinder head. The camshaft for cylinders 1, 3 and 5 is mounted on four bearings, and the camshaft for cylinders 2, 4 and 6 is mounted on three bearings. The cylinder head surface is ground where the sealing gasket is installed. The combustion chambers are angled to match the V-shaped design of the engine.





Forged crankshaft rotates on seven main bearings and is equipped with twelve counterweights and one torsional vibration damper, which allows it to rotate without radial runout. The crankshaft journals for each cylinder bank are offset by 22°. Relatively long connecting rods (164 mm) connect the crankshaft to lightweight pistons with two compression piston rings and one oil-deflecting ring. Most of the engines developed by the company in recent years "Volkswagen" engines, the camshaft is driven by a toothed belt. However, in the VR6 engine, the two camshafts are driven by one common double-row chain (Fig. 16), which is driven by an intermediate shaft sprocket connected by a single-row chain to the crankshaft gear.

Two tensioners with shoes (unattended) provide the required chain tension, and self-adjusting hydraulic tappets drive the valves. The design of the drive mechanism made it possible to make the cylinder head more compact.

Special attention was paid to the supply of the air-fuel mixture during the design, since in one cylinder head the combustible mixture had to be provided to two rows of cylinders. The engine was designed with transverse scavenging - the intake ports are located on one side, and the exhaust ports on the other, and the combustible mixture in it had to enter simultaneously into 3 cylinders on each side of the engine, and the intake pipes had to be of equal length.


To solve this problem, the air intake housing was mounted on top of the cylinder head, from which each cylinder has its own separate intake pipe. Three pipes go directly to the cylinders at the front of the engine, and the other three pipes run above the engine and connect to the cylinders at the back of the engine. Each intake pipe is equipped with an injector, and the spark plugs are located on the outside of the cylinders.

[The original text can be found at: www.VWmanual.ru]

Despite the fact that the designers tried to make the intake pipes as equal in length as possible, there is still a difference in the compression rate of the two cylinder banks. However, this difference is reduced to nothing thanks to the Motronic fuel injection system produced by Bosch, which regulates the injection and ignition modes depending on the engine load and operating conditions. The electronic control unit (ECU) determines the amount of fuel injected into the cylinders and the exact ignition advance thanks to the information received in the form of electrical signals from the sensors, namely: data on the temperature, position and rotation speed of the crankshaft, the flow rate of air entering the engine, the compression ratio, the advance angle. The Motronic injection system is equipped with a knock sensor in each cylinder bank, which allows the ECU to precisely coordinate the injection and ignition control for the cylinders in each bank and, accordingly, synchronize the compression moments.



Today for "Volkswagen" it is almost common practice to install a neutralizer and an oxygen sensor on your car, which provide feedback. The sensor monitors the oxygen concentration in the exhaust gases, and the ECU uses its signals to maintain the air/fuel ratio that ensures the most efficient operation of the neutralizer. The general appearance of the VR6 engine assembly is shown in (Fig. 17).

Attention! In order to provide the engine with a good air-fuel mixture under other normal conditions, unleaded gasoline with an octane rating of at least 95 must be used.