View of the engine 1.8 / 2.0 l 16V front right. The numbers indicate:
1 - generator;
2 - throttle valve with intake manifold;
3 - ignition module DIS;
4 - cylinder head cover;
5 - front cover of the toothed belt;
6 - servo pump;
7 - tension roller of the V-ribbed belt;
8 - belt pulley of the crankshaft;
9 - oil filter.
The advantages of the four-valve principle are obvious: in a round cylinder, it is impossible to increase the circumference of the valves in any way. Soon they collide with each other, while at the same time there is unused space on the right and left. But here four small circles can be placed relatively elegantly and thereby achieve a larger cross-section of the opening in total.
Why four valve technology?
One of the main problems of a four-stroke engine is to fill the cylinders on the intake stroke with a sufficient amount of air-fuel mixture. The problem grows with increasing engine speed, as valve opening time is getting shorter and shorter. Engineers talk about discovery losses. To counteract them, choose the maximum diameter of the valves, because. only in this way more mixture can flow. But this desire is limited by the diameter of the combustion chamber. Here lies the main idea of the four-valve technology: four small circles add up to a larger area compared to two large ones - relative to the same size of the combustion chamber.
Advantages of four-valve technology
Hardly any car manufacturer will dare to make expensive investments in their models, if this would not simultaneously lead to numerous advantages. And they do exist with four-valve technology:
- Four valves provide increased throughput for the combustible mixture and exhaust gases. «Freer breathing» has a positive effect on engine power and, consequently, on fuel consumption. For example, a four-valve engine has approximately 8% lower specific fuel consumption compared to a two-valve engine.
- Four-valve engines have smaller valves and therefore have less mass set in motion, resulting in faster response of the valve train. A nice side effect: less stiff springs are needed to close the valves.
- Smaller valves are cooled by their seats better during closing than larger valves. This leads to a reduction in thermal problems.
- Four-valve engines are less sensitive to knock combustion due to the conditions in the combustion chambers. They withstand a compression ratio increased by 1-5 points.
- The spark plug can be placed optimally in the center of the combustion chamber in a four-valve engine. Next, we describe the differences from the eight-valve engine.
Cylinder head
Doubling the number of valves led to a completely new design of the cylinder head, cast from aluminum.
Shown here is a 1.6L 16V engine with the following components:
1 - air conditioner compressor;
2 - servo pump;
3 - belt pulley of the crankshaft;
4 - V-ribbed belt;
5 - generator;
6 - intake manifold;
7 - ignition module DIS;
8 - dipstick for measuring the oil level;
9 - manual transmission;
10 - oil filter;
11 - lambda probe;
12 - exhaust manifold.
Left: front view of a 8-valve engine with a displacement of 1.6 liters:
1 - tension roller of the toothed belt;
2 - water pump;
3 - toothed belt;
4 - camshaft pulley;
5 - toothed belt drive pulley.
Right: front side of the 16V engine with a displacement of 1.8 / 2.0 liters:
1 - tension roller of the toothed belt;
2 - water pump;
3 - right guide roller;
4 - toothed belt;
5 - intake camshaft;
6 - final camshaft;
7 - left guide roller;
8 - toothed belt drive pulley.
In the combustion chambers, the intake and exhaust valves are suspended with a slight inclination to the axis of the cylinders. The spark plug is in the center. This creates equal length combustion paths in all directions. This creates the prerequisites for rapid and clean combustion of the combustible mixture.
A number of inlet valves are located on the engine at the rear in the direction of travel. In the manufacture of the exhaust valves located in front, a lot of effort was required, because. their hollow rods are filled with sodium. This liquid metal is thrown back and forth during operation. It can absorb the heat of the valve disc and lead it through the valve guide to the rod to the cylinder head.
Camshafts
Two camshafts are needed to actuate the two rows of valves. They rotate in journal bearings - five bearings on the exhaust camshaft and five on the intake camshaft. To save weight, both shafts are hollow.
The crankshaft drives both camshafts via a toothed belt. The front camshaft drives the exhaust valves, while the rear camshaft drives the intake valves. Both shafts rotate in the same direction.
Valve control
The valves are controlled by camshafts with the shortest transmission path - unlike the eight-valve engine - without intermediate pendulum levers. Inverted cup-like hydraulic tappets and both valve springs are fitted onto the valve stem as shown in the illustration below.
Noteworthy is the minimum bulge of the bottoms of the pushers, the inclination of the working surface of the cam that is not noticeable to the eye and the offset of 2 mm between the cam and the pusher. Due to this, the pushers, when the engine is running, receive a moment of impulse, which is transmitted to the valves. This eliminates wear on tappets and valve seats and achieves optimum tightness between valve and seat.
Toothed belt
As already mentioned, it directly drives both camshafts. Toothed rubber belt reinforced with steel wire is not subject to wear and runs silently. In addition, the toothed belt is not subject to maintenance, as the automatic tension roller ensures its constant tension.
Valve actuation by means of a hydraulic pusher in a 16V engine: oil under high pressure is depicted in dark color. One tone lighter is the amount of oil not needed to operate the valve. The numbers indicate the following details:
1 - camshaft cam;
2 - reservoir with oil;
3 - check valve;
4 - oil supply;
5 - high-pressure chamber;
6 - valve stem;
7 - clamping spring;
8 - cylinder;
9 - piston;
10 - hydraulic pusher.
In the engine lubrication system are important (shown on 8 valve engine):
1 - oil pump;
2 - oil filter;
3 - pressure control valve;
4 - oil pressure switch;
5 - camshaft and valve clearance adjuster.
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