This invention relates to a motor vehicle hub assembly and in particular to a hub assembly having an anti-lock brake system (ABS) exciter ring with a seal mounted to the exciter ring.
In recent years, anti-lock brake systems are being found on an increasing number of passenger motor vehicles, including light duty trucks. The ABS detects wheel rotation and acts to relieve braking force applied to the vehicle's wheels to prevent a lock-up condition from occurring. Wheel brake locking is undesirable since it can result in longer stopping distances and directional instability of the vehicle. The most advanced ABS designs employ a sensor at each wheel subject to ABS control. The sensors detect wheel rotation using various technologies including slotted disc light sensor devices, inductive pick-ups, Hall effect devices, variable reluctance sensors, etc. Signals from the wheel rotation sensors are fed into an ABS computer which modulates the braking force.
Present sensors typically use some type of exciter ring, slotted disc, or other component that rotates relative to the sensor in response to wheel rotation. Hereinafter, the term "exciter ring" will be used to refer to any such device. Due to packaging constraints involving the hub, rotor and brake caliper, the exciter ring is usually pressed on the end of the hub. This location is adjacent to the inner bearing and an oil seal. The outer race of the inner bearing, the oil seal and the exciter ring are all press-fit assemblies that can cause distortion in the hub and in the pressed on components. The distortion causes assembly problems, part-to-part variation and dimensional instability in the hub assembly. The part-to-part variation and dimensional instability can be of particular concern because many ABS sensors require that a very precise clearance be maintained between the exciter ring and the sensor during wheel rotation. In addition, dimensional tolerances affect the metal-to-metal contact between the oil seal and the hub which must be a close fit to prevent grease leakage and ingress of contaminants into the bearing. Accordingly, it is an object of the present invention to provide a hub assembly that avoids or reduces the distortion caused by multiple press-fits in one area of the hub.
The hub assembly of the present invention includes an exciter ring which, when press-fit over the end of the hub, forms a cylindrical inner surface extending beyond the end of the hub. The oil seal assembly is press-fit into the inner surface of the exciter ring. Several advantages follow from mounting the oil seal assembly in the exciter ring rather than the hub member. One advantage is that one of the three press fits on the hub has now been removed from the hub itself and placed on the exciter ring. Another advantage is that the pilot diameter for the exciter ring has now been moved to a location radially outward from the inner bearing such that there is additional support for the hub, reducing distortion caused by the press-fit of the exciter ring. These two advantages work to reduce the distortion found in previous hub assemblies.
Yet another advantage of mounting the oil seal to the exciter ring is the absence of the seal mounting surface in the hub. Less material is required to cast the hub, thus reducing the hub weight and there is no longer a need for machining of a seal diameter on the hub. This improves productivity and reduces the part cost. In the illustrated embodiment of the present invention, the exciter ring is made by a powder metal manufacturing process. As a result, there is no machining required to produce a seal mounting diameter. With reduced distortion of the hub assembly components, the dimensional accuracy will be improved, resulting in improved ABS functioning due to reduced variation between assemblies.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.