Pistons, connecting rods, cylinders
In the upper third of each piston, three piston rings are resiliently inserted in the corresponding grooves. They, shock-absorbing, put pressure on the cylinder wall. Both upper piston rings keep combustion chamber gases from flowing down into the crankcase, while the lower oil scraper piston ring prevents excessive crankcase lubricant from entering the combustion chamber. The cylinders, in which the pistons move up and down, are located in the cast-iron engine block. The inner walls of the cylinders are cross-cut. The cylinder walls must not be perfectly smooth, otherwise the oil needed for lubrication will not be able to adhere to them. When repairing the engine, the working surfaces of the cylinders can be ground up to two times.
Crankshaft
The task of the crankshaft is to convert the rectilinear movement of the pistons moving up and down in the cylinder into rotational motion.
Connecting rods leading to the pistons - connecting rods - act on the crankshaft, they are located on the connecting rod journals of the crankshaft. Counterweights are placed opposite the crankpins to prevent excessive vibration.
6-cylinder engine in section:
1 - inlet gas pipeline;
2 - a package of ignition coils;
3 - toothed belt;
4 - V-ribbed belt;
5 - a pulley with a damper on the crankshaft;
6 - oil pump;
7 - inlet pipe of the oil pump;
8 - crankshaft;
9 - connecting rod;
10 - piston;
11 — hydraulic pushers;
12 - valve;
13 - camshaft.
Valve actuation by means of a hydraulic tappet: pressurized oil is indicated in red. Light red indicates the amount of oil not needed to actuate the valves. The numbers mean:
1 - camshaft eccentric;
2 - oil reservoir;
3 - check valve;
4 - oil inflow;
5 - high pressure chamber;
6 - valve stem;
7 - compression spring;
8 - cylinder;
9 - piston;
10 - hydraulic pusher.
To prevent deflection of the crankshaft during operation, it is located in a 4-cylinder engine on five, and in a 5-cylinder engine on six bearings - main journals. Each «knee», located on the connecting rod, thus, on the right and left is supported by the bearing. The 6-cylinder engine is different: for space reasons, the two connecting rods are always located between the two main bearings. Thus, such an engine has a total of 4 main main bearings.
Behind the direction of motion on the crankshaft is a disk with a ring gear for the starter gear. This is the flywheel, on which the clutch is mounted and thereby communicates with the gearbox, or the driven disk, to which the automatic transmission torque converter is attached. A toothed belt drive gear is installed at the front end of the crankshaft.
Cylinder head and camshaft
The cylinder head in a certain sense represents the upper boundary of the combustion chambers. At the very top of the cylinder head is the camshaft. With his eccentrics, he forces the valves to open and close at certain positions of the pistons. Thus, it determines the valve timing. The camshaft drive drives the crankshaft via a toothed belt.
But the valve drive does not occur directly through the camshaft. An intermediate instance is the so-called poppet pushers. Each such poppet pusher is put on the valve stem.
Hydraulic pushers
The already mentioned poppet hydraulic tappets have a built-in hydraulic adjustment of the valve clearance. This device makes it possible to eliminate the valve clearance control required earlier: the valve drive works with the clearances set by the manufacturer and ensures flawless operation throughout the life of the engine.
Note: An engine with hydraulic tappets may produce loud rattling noises when it is first started after a long period of standstill. Don't worry: after a short time, this sound disappears and the valve actuator runs silently again. If one of the hydraulic tappets knocks for a long time even when the engine is warm, then it must be checked.
Action of hydraulic pushers
When the valve is closed, oil from the engine lubrication system flows through the annular groove into the poppet. After passing the check valve in the tappet, the lubricant enters the still empty high-pressure chamber and fills it completely. In addition, the spring presses the poppet to the camshaft.
If the camshaft now turns and its eccentric presses on the poppet, then the pressure in the chamber increases. The non-return valve closes the inlet so that no more oil can escape. Since the oil is incompressible, a rigid connection is established between the poppet and the cylinder. That is, the valve can be pushed down by the force of the cam.
After closing the valve, a small gap occurs due to oil leakage, which, however, is immediately balanced by a compression spring, which pushes the poppet upwards. Oil rushes back into the increased volume of the high-pressure chamber with the check valve open. This makes the hydraulic tappet ready for the next valve actuation.
The figure shows the passage of a toothed belt in a 6-cylinder engine. The numbers indicate:
1 — a pulley of the pump of a cooling liquid;
2 - tension roller;
3 - toothed pulley of the crankshaft belt;
4 - guide roller.
Toothed belt
The crankshaft-driven toothed belt is an almost silent camshaft drive element. Toothed rubber belt reinforced with steel wire, the belt runs without wear, in addition, the rubber compound of the toothed belt provides dry lubrication of the pulleys. In addition to the camshaft, the toothed belt also drives the coolant pump on models with 5- and 6-cylinder engines. On models with 4-cylinder engines, the belt additionally drives the intermediate shaft, which in turn drives the oil pump and distributor.
Cylinder head gasket
The gasket between the cylinder block and the cylinder head provides isolation from each other of the combustion chambers and channels for coolant and oil. At the same time, it must withstand extreme fluctuations in temperature and pressure.
Visitor comments