Bimetal coil assembly for fan drive

A system and method of anchoring a bimetal coil member on a viscous clutch fan drive. An adjustable channeled retainer member together with a silicone or silicone-type material is used to anchor the free end of the bimetal coil member.

TECHNICAL FIELD

The present invention relates to bimetal coil viscous fan drives and more particularly on methods and systems for improving the attachment of the bimetal coil on the fan drive.

BACKGROUND OF THE INVENTION

There are many devices and systems in use today for operating a fan drive to aid in cooling a vehicle engine and/or engine fluids. Viscous fan drives are one of the most popular types in use today. The viscous fan drives can be operated, for example, by a bimetal mechanism, or an electromagnetic mechanism.

Bimetal viscous clutch drives provide an effective and cost efficient way to rotate a cooling fan and cool an engine. Often, however, the positioning and anchoring of bimetal coil members on such fan drives can cause engagement/disengagement repeatability concerns. Varying side loads and friction on the valve shafts connected to the bimetal coils can create repeatability issues.

Thus, there is a need for a method and system for improving the anchoring and anchoring of bimetal coil members on fan drives and thus improving the repeatability of the engagement and disengagement of the fan drives.

SUMMARY OF THE INVENTION

The present invention provides a system and method for satisfying that need. The present invention provides an improved way to position, secure and calibrate a bimetal coil member on a fan drive housing and improve the repeatability of the engagement and disengagement of the fan drive.

An adjustable retainer member on the housing is utilized to position and secure the outer free end of the bimetal coil member. The free end is anchored in place by a curable material, such as silicone. In this manner, the operation of the fan drive can be tested and calibrated, during and after production, and the position of the free end adjusted as needed to insure appropriate engagement and disengagement.

Other features, benefits and advantages of the present invention will become apparent from the following description of the invention in conjunction with the drawings and appended claims.

DESCRIPTION OF PREFERRED EMBODIMENTS

A bimetal viscous fan drive10is shown inFIG. 1. The fan drive includes a body member12and a cover member14that are affixed securely together to form a housing. A cooling fan20(shown in dashed lines) is attached to the body member12by fasteners22, such as bolts, positioned in openings24. The body member, cover member and cooling fan all rotate at fan speed.

A centrally positioned shaft member30is connected to the body member by bushing32. A clutch disk34is fixedly attached to the shaft member. A labyrinth36of grooves and lands is positioned on the radially outward portion of the clutch disk. This forms one-half of the viscous clutch mechanism positioned in the working chamber40. The shaft member30is also connected to a pulley member (not shown) which is attached to a belt member operated by a vehicle engine. The shaft member30, and clutch disk34rotate at input speed.

A fluid retainer plate member44is positioned in the central cavity between the body member and cover member. The retainer plate member44is positioned between a fluid reservoir chamber46and a fluid operating chamber48and has one or more openings or ports50therein for passage of fluid between chambers46and48.

A second labyrinth52of grooves and lands is positioned on the inside of the cover member14. This forms the second half of the viscous clutch mechanism positioned in the working chamber40.

A wiper member54is positioned in the small gap between the outer face of the clutch disk34and the opposing face of the internal cavity in the housing. It is typically positioned adjacent to the scavenge hole and typically on the same plane. The wiper member is used to pump out viscous fluid from the working chamber40and pass it into the fluid reservoir46. A scavenge channel (or passageway)60in the cover member14is utilized to convey the fluid from the working chamber to the fluid reservoir.

Mounted on the front face of the cover member is a bimetal coil member70. The bimetal coil member is attached by a shaft member72to a valve member74positioned on the fluid retainer plate member44. The valve member74is positioned adjacent opening50in the fluid retainer plate member and is mounted such that it can rotate (as shown by arrow78) to cover and uncover the opening50.

During use of the viscous clutch fan drive10, the bimetal coil member70heats up and deforms. This causes the valve member74to rotate and uncover or partially uncover the opening50. The more the temperature increases, the more the valve member74uncovers the opening. This causes a direct increase in the speed of the fan, since more of the viscous fluid is retained in the working chamber, and more viscous shear is formed. This causes the rotation of the fan20to increase.

In use, the shaft member72and valve member74can rotate as much as 10°-20°.

The bimetal coil member70has a circular coil shape, as is typical with conventional bimetal coils. This is shown more clearly inFIG. 2. The center of the coil member71is secured directly to the shaft member72by a fastener73or the like. The opposite end75of the bimetal coil member is anchored to the cover member14. An adjustable retainer member80is used for this purpose. The preferred embodiment of retainer member80is shown inFIG. 3.

In order for the bimetal viscous clutch fan drive to operate in an optimum manner, the bimetal coil member must be anchored at both ends. This allows the coil members to exert a rotational force on the shaft72and operate the valve member74. Rotation of the shaft member controls the point at which the viscously coupled fan drive engages and disengages, and this depends on the ambient air temperature.

A fixed bimetal coil attachment can cause inconsistency in the fan engagement and disengagement temperature. Varying amounts of side loads on the coil based on its connection to the rotatable shaft member can occur depending on production variability. Stated another way, the resulting varying amount of side loads and friction on the shaft connected to the central end of the bimetal coil can create engagement/disengagement repeatability issues. This, of course, is because the shaft's rotation dictates fan drive response. An unintended shift of only a few degrees in the rotation response can make a bimetal coil viscous fan drive defective.

Simply anchoring the free end of a bimetal coil member in silicone also is not optimal. Once the silicone cures, any further adjustment or calibration during or after production is prevented.

The retainer member80has a pair of slots (or “openings”)81and82in which fastener members84are positioned. The positions of the openings81and82allow adjustment of the retainer member on the fan drive housing and hence adjustment of the end75of the bimetal coil member70. Loosening of the fastener members84permits lateral adjustment of the position of the retainer member84on the housing.

The retainer member also has a pair of raised guide ridge members86and88forming a channel90. A pair of nubs or protrusions92and94are positioned in the channel90. The guide ridges and nubs are used to center and position the end75of the bimetal coil member in the channel90.

The retainer member80is preferably made of a lightweight metallic material, such as aluminum or zinc.

A setting material, preferably a silicone material100, is applied to the end75of the bimetal coil member in the channel90. The silicone can be positioned in the channel before the coil is positioned on the housing. The silicone material100is utilized to hold and anchor the bimetal coil member in place on the cover member. Also, since the silicone material has an extended setting (curing) time, the end of the bimetal coil can be repositioned during calibration as the silicone is cured. Preferably, the silicone is a UV curable silicone material and a UV light is used to cure and set the silicone in place when it is time to do so.

Also, with the present invention, once the silicone has cured, the retainer member80can be repositioned in order to further reposition the end of the bimetal coil. This allows the bimetal coil member to be calibrated and finally positioned and anchored after all tests and calibrations are concluded. This ensures that each viscous clutch fan drive is also able to be easily recalibrated as needed to respond at the specific desired temperature.

Once the first calibration testing is completed and the silicone is set, the bimetal fan drive member is retested. At that point, any inconsistencies can be corrected by adjusting the position of the retainer member80on the housing. For this purpose, a series of markings110can be provided on the retainer member and/or the housing (as shown inFIG. 2). This allows the retainer member to be adjusted one way or another (i.e. left or right) the number of markings corresponding to the amount of calibration is necessary. For example, each marking could be a change of several degree F., such as 5 or 10°.

Materials other than silicone could also be utilized to encapsulate, cover, and anchor the free end of the bimetal coil member, so long as the material has a curing time and adjustment function substantially the same as silicone. Silicone allows the free end to locate itself prior to finish of the curing process.