Inclusion of an anti-drain valve in viscous fan clutches
A viscous fluid clutch assembly used in automobiles, SUVs, and trucks minimizes flow back of the cooling fluid from the reservoir towards the working chamber of the clutch when the vehicle is at rest and avoids excessive fan noise, wasted power and fuel inefficiency when a cold automobile engine is started. The clutch utilizes a discharge channel extending from the periphery of the working chamber to the reservoir and a specially designed ball check valve at the entrance to the reservoir which is open or closed depending on operation of the vehicle. The ball check valve is fluidly connected to the working chamber of the fluid clutch by a preferred articulated discharge channel which starts at the working chamber of the fluid clutch and ends at the reservoir of the fluid clutch.
1. A viscous fluid clutch assembly comprising:
(a) a clutch plate having a central hub portion and an annular disk portion, the annular disk portion having concentric annular lands and grooves formed on a surface thereof, the clutch plate being rotatably driven by an input shaft;
(b) a housing assembly rotatably mounted on the input shaft and comprising a housing and a cover, the cover having an inner surface having corresponding annular lands and grooves adjacent the annular lands and grooves on the clutch plate and extending from an inner edge to an outer edge, and a hydraulic dam having sidewalls proximate the outer edge of the annular lands;
(c) a shear zone disposed between the corresponding lands and grooves of the clutch plate and the cover which interleave to form the shear zone;
(d) a partition plate mounted internally in the housing assembly between the cover and the clutch plate for dividing an interior of the housing assembly into a fluid reservoir in the cover and a working chamber, wherein the shear zone is disposed in the working chamber;
(e) openings provided in the partition plate for transferring fluid between the working chamber and the fluid reservoir;
(f) a rotatable control arm disposed in the interior of the housing assembly adjacent the partition plate for opening or closing the openings in the partition plate;
(g) control means for controlling the rotatable control arm based on the temperature of the ambient air surrounding the housing;
(h) a discharge channel provided in the cover at a periphery of the shear zone and adjacent the hydraulic dam, the dam sidewalls contacting the fluid exiting the shear zone and altering the flow of fluid exiting the shear zone from tangential to axial; the discharge channel comprising a first section having a first end in fluid communication with the periphery of the shear zone and a second end, and a second section having a first end in fluid communication with the fluid reservoir and a second end; the second end of the first section and second end of the second section being fluidly connected, and the first section being disposed at an acute angle relative to the second section; and
(i) a check ball valve provided at the first end of the second section of the discharge channel, wherein the check ball valve and the first end of the second section of the discharge channel are directly connected, the check ball valve includes a ball movable to a closed position blocking the discharge passage to prevent migration of fluid from the reservoir into the discharge channel, whereby the ball is movable by gravity or centrifugal force, and the check ball valve further includes a check valve housing which is rectangular and integrally formed with the inner surface of the cover and comprises three sides, a base, and an open side at the first end of the second section of the discharge channel, wherein the ball is contained in the check valve housing by the three sides and base thereof and the partition plate with sufficient tolerances to allow free travel of the ball to the closed position and to an open position.
2. The viscous fluid clutch assembly of claim 1 wherein the check valve housing is sized so that the ball travels only about half of the ball's diameter and at rest the ball falls by gravity to close the first end of the second section of the discharge channel, and during operation centrifugal forces caused by rotation of the housing assembly forces the ball away from the center of the housing assembly so the ball covers the first end of the second section of the discharge channel, and fluid pressure in the return channel overcomes the centrifugal forces exerted on the ball to modulate the position of the ball with respect to the first end of the second section of the discharge channel allowing the fluid to flow from the working chamber to the reservoir.