Fig. 15. Schematic representation of the three types are used in the automotive six-cylinder engines: a - V-shaped 6-cylinder engine; b - Engine VR6; c - line engine
This section discusses the set for the first time in 1991 on the car Volkswagen Passat 6-cylinder engine under the name VR6, with significant differences from a conventional engine design concept ?«Volkswagen?» or ?«Audi?». The engine in the company ?«Volkswagen?» was named ?«AAA?», but he is better known as the VR6. Its six cylinders are arranged V-shaped at an angle of 15 ?° in contrast to conventional V-type engine having an angle of 60 ?° or 90 ?°. Engine VR6 become so compact that allow to cover both rows of cylinders a common head, unlike the conventional V-type engine. As a result, VR6 engine will get less in length than the row, and smaller in width than the conventional V-shaped 6-cylinder engine. In (Fig. 15)
schematically shows the three type 6-cylinder engines, and is seen on the basis of which the engine was designed VR6.
With this arrangement of cylinders acute angle (15 ?°) problems with uneven rotation of the crankshaft VR6 engine does not arise, it works exactly the same as the row. The engine has two camshafts, which control twelve vertically arranged valves (2 per cylinder). Both camshafts Overhead placed in an aluminum cylinder head. Camshaft 1, 3 and 5 of the four cylinders mounted on bearings and the camshaft 2, 4 and 6 of the cylinders - on three bearings. The surface of the cylinder head gasket installation site sanded. The combustion chambers are made at an angle to match the V-shaped design of the engine.
Fig. 16. The timing VR6 engine
rotates in seven main bearings and is equipped with twelve counterweights and a vibration damper, which allows it to rotate without radial runout. Crank pins for each row of cylinders are offset by 22 ?°. Relatively long connecting rods (164 mm) connected with a crankshaft light weight piston, the piston having two compression rings and one slinger ring. Most developed in recent years by the company ?«Volkswagen?» engines drive a camshaft timing belt. However, in the motor drive VR6 two camshafts made one common two-row chain (Fig. 16)
which is driven by a sprocket intermediate shaft connected to the single-row chain pinion of the crankshaft.
Two tensioner shoe (unattended) provides the desired chain tension, and Belleville self-adjusting hydraulic tappets driven valves. The design of the drive mechanism allowed us to make more compact cylinder head.
Particular attention was paid to the design of the supply air-fuel mixture, as a cylinder head gas mixture had to be provided with two rows of cylinders. The engine has been constructed with transverse blowing - inlets disposed on one side, and outlet channels on the other side, and the fuel mixture therein was exposed simultaneously to three cylinders on each side of the engine, and the intake pipes were to be of equal length.
To solve this problem, air intake housing installed at an upper portion of the cylinder head, from which each cylinder is its own separate inlet pipe. Three tubes go directly to the cylinders in front of the engine, and the other three tubes extend above the engine and connected to the cylinder on the rear side of the engine. Each inlet pipe is provided with a nozzle and a spark plug arranged at the outer side of the cylinder.
Despite the fact that the designers tried to make the inlet pipe as far as possible equal in length, yet there is a difference in the rate of compression in the two rows of cylinders. However, this difference is reduced to nothing, thanks produced by ?«Bosch?» fuel injection system ?«Motronic?», which regulates the operation of fuel injection and ignition timing according to engine load and the conditions of its operation. The electronic control unit (ECU) determines the amount injected to the cylinders of fuel and accurate spark advance thanks obtained as electrical information signals from the sensors, namely, temperature data, position and engine speed, flow to the engine of air compression ratio angle advance. Injection system ?«Motronic?» equipped with a knock sensor per row of cylinders, which allows the computer to coordinate precisely control fuel injection and ignition for the cylinder in each row and thus synchronize the compression points.
Fig. 17. General view of the VR6 engine assembly
Today, ?«Volkswagen?» is almost commonplace to install on their cars converter and oxygen sensor, which provide feedback. The sensor monitors the oxygen concentration in the exhaust gases, and computer signals its support for such an air / fuel ratio, which provides the most efficient operation of the neutralizer. A general view of the motor assembly VR6 represented by (Fig. 17).
In order to provide the engine with the other normal conditions of good air-fuel mixture to be used unleaded gasoline with an octane rating no lower than 95.