1 - leading half coupling (water pump drive), 2 - driven half coupling (fan blade fastening).
Operation of a viscous coupling
The coupling consists of a driven and a driving half coupling. The leading half coupling 1 is located inside the driven one and is driven by the water pump. The fan blades are attached to the driven half coupling 2. On both half couplings there are circular grooves that fit into each other with a small gap 3 filled with silicone liquid, which can flow into different areas of the coupling through the valve plate 4. The position of the valve 5 is regulated by a bimetallic spring 6.
The engine is cold
While the engine is not running, the fluid in the clutch flows into chambers A and B. After the engine starts, the fluid in chamber A causes the fan blades to rotate at a higher speed, which produces a characteristic sound. After a short period of time, all the liquid flows into chamber B (see picture), which leads to slippage of the half couplings, and the fan rotation speed decreases.
Slippage of half couplings (the engine is cold): 1 - leading half coupling (spins quickly), 2 - driven half coupling (rotates slowly), 3 - clearance in circular grooves, 4 - valve plate, 5 - control valve (closed), 6 - bimetallic spring, 7 - seals, 8 - ball bearing.
As the engine shaft speed increases, the degree of slippage of the half couplings increases, limiting the rotation speed of the fan blades.
The coupling halves move without slipping (the engine is warm, the control valve is open).
The engine is warmed up
At high ambient temperatures or when the vehicle is stationary with the engine running and warm, a bimetallic spring opens the control valve connecting chambers A and B of the clutch. Fluid from chamber B flows into chamber A, eliminating slippage between the clutch halves. The fan speed increases, improving engine cooling conditions.
Comments on this article