Figure 114. Hydraulic valve lifter: 1 — rocker arm; 2 - retaining ring; 3 - washer; 4 — cap; 5 - push rod; 6 - guide bushing; 7 - ball guide channel; 8 - ball with a diameter of 4 mm; 9, 10 — pressure springs; 11 — ball bearing; 12 — valve spring plate; 13 — valve; a — oil chamber; b — working chamber; c — leak return channels; f — annular groove; h — oil channel
The task of hydraulic valve lifters is to compensate for the clearance in the valves, which changes as a result of thermal expansion and wear of the valve timing system components. The rocker arms are in constant contact with the camshaft, so the noise level from the valve mechanism is kept low. Hydraulic compensators are installed in the rocker arms and act on the valves through the ball seat 11 (figure 114). The hydraulic valve clearance compensation system consists of the following main elements:
- push rod 5 with oil chamber a and oil return channels with a check ball valve, parts 8, 9 and 10. The ball valve separates the oil chamber from the working chamber;
- guide sleeve 6 with working chamber b, pressure spring 9 and closing cap 4.
When the engine is stopped, if the compensator is under constant pressure from the camshaft cam, it can be completely unloaded (compressed). The oil squeezed out of the working chamber b flows into the oil chamber a through the annular gap - through the gap between the guide sleeve and the pressure rod. When the top of the cam comes off the rocker arm, the load is removed from the pressure rod 5. Spring 9 moves the rod upward until the rocker arm comes into contact with the cam. The vacuum created in the working chamber from the movement of the rod opens the ball valve, and oil can flow from the oil chamber into the working chamber. The ball valve closes as soon as the rocker arm rests against the cam, and the load on the push rod begins to increase. The oil in the working chamber now acts as a rigid hydraulic connection, which opens the corresponding valve.
When the engine is running, depending on the engine speed and the position of the cam, the pressure rod drops by an insignificant amount. The oil required for the operation of the compensators is supplied through an oil line running along the cylinder head and then through transverse channels leading to the rocker arm bearing supports. Next, from the bearing pillars, oil is supplied to the rocker shaft, and from it through channel h in the rocker arm to the corresponding compensator. Oil is supplied to the oil chamber through spline washer 3. The amount of oil in oil chamber a is always sufficient to fill the working chamber b in any operating mode of the engine. Excess oil and air inclusions (air bubbles in oil) can exit through the annular gap between washer 3 and the rocker arm. Oil squeezed out of the working chamber flows down the annular gap (along the ring channel) between the guide sleeve and the pressure rod and then through the return channels into the oil chamber. When dismantling hydraulic tappets, it is necessary to remember the following points:
- hydraulic tappets should always be stored in an upright position - with the open side facing up.
- after dismantling the hydraulic tappet (subsection 2.13.2) it should be marked with the cylinder number and the pusher well.