This invention relates to an oil-bath wheel spindle and hub assembly that is especially suitable for use on boat trailers. Specifically, the invention relates to an improved oil-bath wheel spindle and hub assembly which pressurizes the inside of the hub when the assembly is submerged in water during launching or loading the boat.
Generally, wheel spindle and hub assemblies are of two types utilizing either grease or oil as the lubricating medium. An oil-bath hub and spindle is normally comprised of a spindle, two or more bearings for rotatably supporting a hub, a hub, and an oil seal on both the inboard and outboard end of the hub. A lubricant receiving cavity is formed by the spindle, the hub, and the inner and outer seals.
In oil-bath spindles, the lubricant receiving cavity is filled with oil to a level sufficient to lubricate the spindle/hub assembly. In operation, a sufficient quantity of oil must remain in this cavity at all times. Because preventing oil loss is an important concern in an oil-bath hub and spindle assembly, the lubricant receiving cavity must be sealed at all times. Accordingly, the seals in an oil-bath spindle assembly must maintain a near airtight seal to prevent oil leakage.
Wheel spindles used on boat trailers are unique in that they are periodically intentionally submerged in water. To avoid corrosion, however, water must be prevented from entering into the hub and spindle assembly. The seals of the hub and spindle assembly must keep the lubricant in, and water and foreign particles out of the lubricant chamber.
The operation of a boat trailer over the road causes the hub and spindle assembly to become hot. As a result, the air in the lubricant receiving cavity expands as the spindle assembly becomes heated. This heating increases the pressure of air in the cavity, and in prior art devices can cause hot air to bleed through the seals. When the boat trailer is then backed into cold water to launch a boat, the spindle assembly is rapidly cooled. This rapid cooling then creates a reduced pressure inside the lubricant receiving cavity in both the ordinary grease filled hub and oil lubricated hub. As a result, water and foreign particles may be drawn through the oil seals and into the lubricant receiving cavity. Any water and foreign particles entering the lubricant receiving cavity shortens the spindle assembly's life span by causing rust and abrasion inside the spindle assembly.
Once the seals lose air tight integrity, oil or grease leakage is likely to result and the leaking seal must be replaced in the ordinary hubs. Failure by the operator to recognize this oil leakage, can result in a sufficient loss of oil or grease from the lubricant receiving cavity to increase friction causing subsequent failure of the spindle assembly.
Efforts have been made to eliminate the problems associated with immersing a hot spindle assembly in cold water, by the use of inflatable seals, venting tubes and air compressors. Examples of these efforts are found in U.S. Pat. Nos. 3,330,563; 4,557,526 and 4,489,998. These efforts have created some additional difficulties of their own.
Spindle assemblies utilizing inflatable seals such as disclosed in U.S. Pat. No. 3,330,563, or air compressors such as disclosed in U.S. Pat. No. 4,489,988, are pressurized from an external source. This adds to both the initial costs and the maintenance costs of a boat trailer using either system.
In systems employing inflatable seals, pressurized air comes from either a tank or air compressor. Pressurized air tanks must be periodically recharged or replaced and these systems must be manually actuated on and off by the boater or the seal will fail. As the pressurized air in a tank runs out, the effectiveness of the inflatable seal system decreases. Failure by the trailer operator to replace or recharge an expended tank results in such an inflatable seal system becoming ineffective. In addition, hub and spindle assemblies utilizing air compressors or inflatable seals employing air compressors require periodic maintenance to keep functioning properly. In many cases, the trailer owner will lack the knowledge necessary to maintain the system. This will further add to the cost of the system, as the owner will be required to pay someone else to maintain the system or allow the system will become inoperative.
Spindle assemblies utilizing a venting tube system such as disclosed in U.S. Pat. No. 4,557,526, contain one or more venting tubes that to function properly must extend upwardly to a height above the depth of the water in which the trailer is submerged. As a result, the trailer owner or manufacturer must anticipate the maximum depth to which the trailer will ever be submerged. As a consequence, the venting tubes tend to be very long, which exposes the tube to being bent, cut, crimped and otherwise damaged. If the seal fails, the chamber will have water drawn inside due to the unrestricted air flow through the venting tube.
Another manner of lubricating a spindle assembly is to use grease instead of an oil-bath. One such system is disclosed in Everett, U.S. Pat. No. 4,262,978, wherein there is described a grease spindle assembly in which the lubricant cavity includes a passageway which vents the lubricating medium. Grease is injected into the spindle assembly at the outboard end, until it completely fills the lubricating cavity. As more grease is injected, the grease pushes through the cavity, and from there flows through the spindle assembly until it exits from the spindle through the vent passageway. The passageway allows the grease to push any air trapped in the lubricant cavity through the passageway to the atmosphere.
As the grease-filled bearing assembly is used, grease must be regularly added and it will be continually moved through the assembly out the passageway to the atmosphere. If grease is constantly forced through the bearing assembly, a grease dam at the end of the passageway will close any opening to the atmosphere. This grease dam, if maintained, will prevent water and silt from entering the bearing assembly when the grease-filled wheel spindle is submerged in water. The grease spindle assembly can continually drip grease, however, which causes damage to both pavement and the environment, and unless constantly maintained the water seal is lost.
With a grease-filled bearing assembly the amount of air present in the lubricant cavity is minimized. If the lubricant cavity is totally filled with grease, there is little or no pressure change when a hot spindle assembly is immersed in cold water. Therefore, a grease-filled, grease-receiving cavity protects the spindle seals by minimizing pressure changes in the cavity. Because of the higher viscosity of grease relative to oil, however, the bearing pre-load adjustment must be lower than that for oil. As is known to those skilled in the art, lower bearing pre-load leads to shortened bearing and seal life.
With the oil-filled hub and spindle assembly of the present invention, these limitations of a grease-filled spindle assembly are overcome. In addition to allowing higher bearing preload, the oil-filled hub and spindle assembly has a much longer maintenance free life. A once a year check to "top off" the oil in the hub-spindle chamber is all that is required to insure against entry of water and dirt, and to prevent the destruction of the bearing. In this manner, the oil-filled hub and spindle of the present invention needs extremely little maintenance.