Purpose, device, timing. Internal combustion engine: gas distribution mechanism

The gas distribution mechanism of the car is one of the most complex mechanisms in the engine design. The control of the intake and exhaust valves of the engine is entirely on the timing. The mechanism controls the process of filling the cylinders with a fuel-air mixture by timely opening the intake valve at the intake stroke. Also, the timing system controls the removal of exhaust gases from the internal combustion chamber - to do this, the exhaust valve opens at the exhaust stroke.

The device газораспределительного the mechanism

Details of the gas-distributing mechanism perform different functions:

• The camshaft opens and closes the valves.
• The drive mechanism drives the camshaft in motion at a certain speed.
• The valves close and open the inlet and outlet channels.

The main parts of the timing are the camshaft and valves. Cam, or distributing, the shaft is an element on which the cams are located. It is driven and rotated by bearings. At the time of the intake or exhaust stroke, the cams located on the shaft are pressed against the valve pushers during rotation.

The timing mechanism is located on the cylinder head. In the cylinder head there is a camshaft and bearings from it, rocker arms, valves and pushers of valves. The upper part of the head is closed with a valve cover, the installation of which is carried out using a special gasket.

Functioning of gas-distributing mechanism

The timing is fully synchronized with the ignition and fuel injection. Simply put, at the moment the gas pedal is depressed , a throttle opens to let in airflow into the intake manifold. As a result, a fuel-air mixture is formed. After that, the gas distribution mechanism starts working . The timing increases the throughput and exhausts the exhaust gases from the combustion chamber. For correct performance of this function, it is necessary that the frequency with which the inlet and outlet valve of the timing valve is opened is high.

The valves are actuated by the engine's camshaft. When the crankshaft speed is increased, the camshaft and the camshaft are quicker to rotate, which increases the valve opening and closing frequency. As a result, the engine speed and the return from the engine increase.

Combining the crankshaft and the camshaft allows the combustion engine to burn exactly the amount of air-fuel mixture that is necessary for the operation of the engine in this or that mode.

Features of drive timing, chain and belt

The pulley of the camshaft drive is outside the cylinder head. In order that no oil leakage occurs, an epiploon is placed on the shaft neck. The timing chain drives the entire timing mechanism and puts it on the driven sprocket or pulley on one side, and on the other hand transfers the force from the crankshaft.

The correct and unchanged position of the crankshaft and camshafts relative to each other depends on the belt drive of the valves. Even small deviations in position can cause the timing engine to fail.

The most reliable is considered to be a chain drive using a timing roller, but there are some problems with ensuring the necessary level of belt tension. The main problem faced by drivers and which is characteristic of the chain of the mechanism, is its breakage, which is often the cause of the bending of the valves.

Among the additional elements of the mechanism can be attributed the timing belt used for the belt tension. To the minuses of the chain drive of the gas distribution mechanism, in addition to the risk of breakage, also include a high noise level during operation and the need to change it every 50-60 thousand kilometers.

Valve mechanism

The design of the valve mechanism includes valve seats, guide bushings, valve rotation mechanism and other elements. The force from the camshaft is transmitted to the rod or to the intermediate link - rocker arm, or rocker.

It is often possible to meet the timing models, which require constant adjustment. Such designs have special washers and bolts, the rotation of which expose the necessary clearances. Sometimes the gaps are maintained in automatic mode: the adjustment of their position is made by hydraulic compensators.

Valve timing control

Modern engine models have undergone significant changes, having received new control systems, based on microprocessors - the so-called ECU. In the field of engine building, the main task was not only to increase capacity, but also to economize the output of power units.

Increase the performance of engines, while reducing fuel consumption, was only possible with the use of timing control systems. The engine with such systems not only consumes less fuel, but also does not lose power, due to which they began to be used everywhere in the production of cars.

The principle of operation of such systems is that they control the speed of rotation of the camshaft. In fact, the valves open slightly earlier due to the fact that the camshaft rotates in the direction of rotation. Actually, in modern engines, the camshaft no longer rotates relative to the crankshaft at a constant speed.

The main task remains to maximize the effective filling of the engine cylinders, depending on the selected mode of operation. Such systems monitor the state of the engine and correct the flow of the fuel mixture: for example, when idling, its volumes are reduced to a minimum, since large quantities of fuel are not required.

Timing gears

Depending on the design features of the car engine and gas distribution mechanism in particular the number of drives and their type can vary.

• Chain drive. A few earlier this drive was the most common, but even now it is used in the timing of the diesel. With this design, the camshaft is located in the cylinder head, and is driven by a chain driven from the gear. The minus of such a drive is a complicated process of changing the belt, since it is located inside the engine in order to ensure a constant lubrication.
• Gear drive. It was installed on the engines of tractors and some cars. Very reliable, but extremely difficult to maintain. The camshaft of this mechanism is below the cylinder block, so that the camshaft gear clings to the crankshaft gear. If the timing gear of this type was unusable, the engine was changed almost completely.
• Belt drive. The most popular type, it is installed on petrol power units in passenger cars.

Pros and cons of belt drive

The belt drive gained its popularity due to its advantages compared to similar types of drives.

• Despite the fact that the production of such structures is more difficult than chain construction, it is much cheaper.
• It does not require constant lubrication, due to which the drive was put on the outside of the power unit. The replacement and diagnosis of the timing system as a result of this greatly facilitated.
• Since in the belt drive metal parts do not interact with each other, as in the chain drive, the noise level during its operation has decreased several times.

Despite a large number of pluses, there is a belt drive and its minuses. The lifetime of the belt is several times lower than the chain, which causes frequent replacement. In the event of a belt break, it is very likely that the whole engine will have to be repaired.

Sequence of belt failure or loosening

In the event that the timing chain is torn, the noise level rises during engine operation. In general, such a nuisance does not cause something unworkable in terms of repair, in contrast to the timing belt. With the weakening of the belt and its leap over one tooth of the pinion, a slight disruption of the normal functioning of all systems and mechanisms occurs. As a result, it can provoke a reduction in engine power, increased vibration during operation, and difficulty starting. In the event that the belt jumped immediately through several teeth or even broke, the consequences can be most unpredictable.

The most harmless option is the collision of the piston and the valve. The impact force will be sufficient to bend the valve. Sometimes it is enough to bend the connecting rod or complete destruction of the piston.

One of the most serious failures of the car is the breakage of the timing belt. The engine in this case will either have to be overhauled, or completely changed.

Timing Belt Maintenance

The level of belt tension and its general condition is one of the most frequently checked factors during vehicle maintenance. The frequency of verification depends on the particular brand and model of the machine. Procedure for monitoring the timing belt tension: the motor is inspected, the protective cover from the belt is removed, after which the latter is checked for twisting. During this manipulation, it should not rotate more than 90 degrees Degrees. Otherwise, the belt is pulled using special equipment.

How often is the timing belt replaced?

Full replacement of the belt is made every 50-70 thousand kilometers of the car. It can be carried out more often in case of damage or the appearance of traces of stratification and cracks.

Depending on the type of timing, the complexity of the belt replacement procedure also changes. For today in cars two types of the mechanism газораспределения - with two (DOHC) or one (SOHC) camshafts are used.

Replacement of gas distribution mechanism

In order to replace the timing belt type SOHC, it is enough to have a new part and a set of screwdrivers and keys at hand.

First remove the protective cover from the belt. It is fixed either to latches or to bolts. After removing the cover, access to the belt opens.

Before weaken the belt, the timing markings on the camshaft gear and crankshaft are displayed. On the crankshaft, the marks are placed on the flywheel. The shaft is cranked until the timing marks on the body and on the flywheel coincide with each other. If all the marks coincide with each other, they begin to loosen and remove the strap.

To remove a belt from a gear wheel of a cranked shaft, it is necessary to dismantle a pulley of drive ГРМ. For this purpose, the car is lifted by a jack and the right wheel is removed from it, which gives access to the pulley bolt. On some of them there are special holes through which you can fix the crankshaft. If they are not, then the shaft is fixed in one place, installing a screwdriver into the crown of the flywheel and pushing it into the body. After that, the pulley is removed.

Access to the timing belt is fully open, and you can proceed with its removal and replacement. The new one puts on crankshaft gears, then clings to the water pump and puts on the camshaft gears. For the tensioning roller, the belt is turned on at the very last. After you can return all the items in place in the reverse order. It only remains to tighten the belt with a tensioner.

Before starting the engine, it is advisable to crank the crankshaft several times. Do this to check whether the marks match and after turning the shaft. Only after this the engine is started.

Features of the timing belt replacement procedure

On the car with the DOHC system, the timing belt is replaced a little differently. The very principle of changing parts is similar to the above, but access to it in such machines is more difficult, because there are bolted protective covers.

In the process of combining labels it is worth remembering that the camshafts in the mechanism are two, respectively, the labels on both must completely match.

In such cars, in addition to the guide roller, there is also a supporting roller. However, despite the presence of a second roller, the belt is wound behind the guide roller with the tensioner in the last turn.

After the new belt is installed, the labels are checked.

Simultaneously with the replacement of the belt, the rollers also change, since their service life is the same. It is also advisable to check the condition of the bearings of the liquid pump so that after the procedure for installing new timing components the failure of the pump is not an unpleasant surprise.