Valve Rotation Devices. Function

Function. Regular rotation of the valve is of critical importance to its perfect functioning. In this way, valve head temperatures are stabilized and leaks due to warping are avoided. Carbon deposits on the valve seat are prevented as well. Positive-action rotation devices are used in industrial engines, for example, wherever natural valve rotation is not sufficient.

Designs and Functioning. Valve rotators function according to one of two principles:
- Rotation during the valve opening stroke: The system comprises a round base featuring several oblong slots along its circumference. Mounted in each slot are a ball and a coil spring that forces the ball to the upper end of an inclined race. A flexible washer is located around the base’s center hub, and this is topped by a collar, Fig. 7-148.

Fig. 7-148. Valve rotation during the opening stroke

When the valve opens, the stroke is transferred to the collar (due to rising valve spring force), and the collar then flattens the flexible washer. This washer forces the balls in the slots to roll downward along the inclined races; the washer itself rolls downward on those balls. The contact with the balls causes the pressure exerted by the flexible washer on the hub to be reduced, causing slippage.

The collar and the flexible washer, however, are joined one with the other by friction, thus preventing rotation. When the rotator is located below, the relative rotation between the base and the unit formed by the collar and the flexible washer is transferred to the valve via the collar, valve spring, flexible washer, and keeper. When the valve closes, the flexible washer is relieved and the coil springs move the balls, which do not roll in this phase, back into their initial position at the top of the inclined races.

It is a known fact that when a coil spring is compressed, the two ends of the spring rotate in opposite directions, and, when relieved, the ends rotate back into their original position. This rotation effect is preserved; the balls are mounted in the slots in the base in such a way that when the valve opens, the rotator action and valve spring rotation are aggregated, while, when the valve closes, only the reverse rotation of the valve spring is effective. The difference between the two values gives the actual valve rotation angle per stroke.

- Rotation during the valve closing stroke: If at all possible, the rotator should be located at the top, since in this location its functioning is less likely to be affected by grime, Fig. 7-149.

Fig. 7-149. Valve rotation during the closing stroke

Rotator function here is the reverse of the situation where the valve is rotated during the opening stroke.

Either type may, in principle, be employed in the versions situated above or below. In high-speed engines, preference is given to location at the bottom to avoid increasing the masses in the valve train.

In the version at the top, the rotator replaces the spring collar. It is used in slow-running engines as well as when the version at the bottom cannot be used because of space limitations. What is important here is continuous valve rotation in dependency on engine speed.

Bibliography:
1) TRW Thompson GmbH & Co. KG. Handbuch. 7th edition, 1991.
2) R. Milbach. VentilscMden und ihre Ursache. TRW Thompson GmbH & Co. KG, 5th edition 1989.

 






Date added: 2024-05-12; views: 70;


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