Section of the hydraulic valve lifter: 1 - camshaft cam; 2 - storage chamber; 3 - check valve; 4 - channel for supplying oil to the pusher; 5 - high pressure chamber; 6 - pusher; 7 - cylinder; 8 - valve clearance compensation spring; 9 - valve stem
Design
The hydraulic pusher consists of two main moving parts: the pusher itself 6 (see picture), which simultaneously serves as a plunger during operation, and cylinder 7.
Under the pressure of spring 8, the plunger and cylinder move away from each other, due to which the gap between the camshaft cam and the end of the valve stem is selected.
The filling and locking of the high pressure chamber 5 is ensured by the check valve 3.
Operating principle
Starting valve lift
At the moment the camshaft cam hits the valve stem, the check valve supports the chamber and the pressure in it increases. An increase in pressure does not compress the volume occupied by the oil in the pressure chamber. The pusher thus works as a rigid body.
Valve lift moment
The camshaft cam presses the pusher with force, which leads to a significant increase in pressure in the pusher cavity. A small amount of oil is ejected through leaks between the cylinder and the plunger, which leads to compression of the hydraulic pusher by a maximum of C. 10 mm. Such compression is structurally necessary for running in the pushers even if the distance between the camshaft cam and the end of the pusher is reduced.
Valve clearance compensation
The camshaft cam does not press on the tappet, and the pressure in the high pressure chamber drops. The spring separates the plunger and the cylinder, thereby compensating for the gap between the cam and the end of the valve stem.
At this point, the check valve opens, some oil enters the high pressure chamber. This quantity corresponds to the directly compensated gap.
Note. Noisy operation of the valve train actuator after starting the engine is normal. This is due to the fact that when the engine is stopped, part of the oil flows out of the cavity of the pushers. When the engine starts, the high pressure chamber refills and the noise stops. The filling of the high pressure chamber continues until the engine has warmed up to operating temperature.
The design of the lubrication circuit of the cylinder head prevents the complete removal of oil from the channels after the engine is stopped. This ensures that oil is supplied to the tappets immediately after the engine is started and the noise in the valve train drive stops as soon as possible.
The work of hydraulic pushers at the time of starting the engine
After the engine stops, oil drains from the channels coming from the oil pump, and the channels for supplying oil to the pushers remain filled with oil. In order to prevent air from entering under the action of oil pressure into the cavity of the pusher at the time of starting the engine, there are ventilation holes in the channels for supplying oil to the pushers, which provide automatic purging of the pusher cavity. In addition, the vent hole allows you to reduce the pressure of the oil entering the pushers.
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