Measuring and testing – Speed – velocity – or acceleration – Magnetic speed measuring or mechanical speed measuring with...
Reexamination Certificate
1998-09-18
2001-07-03
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Magnetic speed measuring or mechanical speed measuring with...
C324S174000, C324S207150
Reexamination Certificate
active
06253614
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a sensor for detecting the angular velocity of a rotating element, and more particularly, to a speed sensor for use in a vehicle anti-lock braking system or transmission. Specifically, the invention relates to a new seal that protects the internal components of a sensor from exposure to external environmental elements, as well as a new method for applying the seal to a sensor.
BACKGROUND OF THE INVENTION
It is known in the art to mount a speed sensor in the transmission or in the bearing or wheel end assembly of a vehicle such as a truck or an automobile. The sensor measures the angular velocity of a rotating element within the transmission or bearing assembly. Typically, sensors of this type utilize variable reluctance, a form of electromagnetic sensing, generally known and understood by those skilled in the art. Such sensors are used in transmissions to assist in electronic shifting and in vehicle anti-lock braking (ABS) systems to detect wheel speed.
Generally, sensors of this type include a coil mounted on a bobbin which is inserted into a housing. A wheel speed sensor for use in an ABS application typically is connected or bolted into a hub assembly which is located by a brake, usually a front brake, of a vehicle. A tone wheel rotates with or around an axle, typically a front axle, and induces a voltage signal within the wheel speed sensor. The wheel sensor communicates with an on-board controller or computer of the vehicle when any of the vehicle's four wheels lock-up in a panic breaking situation. The sensor sends a voltage signal to the computer and the computer determines if a correct voltage signal has been sent. Based on the signal received, if the computer determines that any of the wheels of the vehicle has locked-up, the vehicle computer automatically takes over and controls the vehicle braking system, pumping each brake for a safer controlled, skid-free stop.
The environment in which sensors of this type are subjected can be extremely harsh and, as a result, the sensors must be capable of withstanding a significant amount of repeated temperature variations over a wide range of temperatures (thermal cycling), intense vibration and exposure to corrosive elements. One such wheel speed sensor is described in commonly assigned U.S. Pat. No. 5,629,618, which is hereby incorporated by reference. In the '618 Patent, a wheel speed sensor is described such that in order to seal the sensor from the environment, a bobbin is connected to a housing and the combination is overmolded with an injected molded plastic cover, i.e., an overmold, to provide a molded seal between the bobbin and the housing.
SUMMARY OF THE INVENTION
Speed sensors can be of many different shapes and sizes. The overall configuration of a speed sensor is largely dependant on the type and make of vehicle in which the speed sensor will be placed.
One problem with known sensors is that if the bobbin and the housing do not form a mechanical seal between one another, the potential exists for water or other outside influences to flow into the interior of the speed sensor and damage the coil. The '618 Patent describes a speed sensor having a housing that provides a sealed environment for a bobbin and a coil.
Another problem, similar to the problem described above, is that if an overmold does not provide a proper seal between a housing and a bobbin/terminal area, water or other contaminants can leak into the interior of the speed sensor and damage the coil or other internal components. Without a mechanical bond or seal between the overmold and the housing, there is not a hermetic seal, i.e., airtight and impervious to external influences. Further, the extreme temperatures and other external influences to which the sensor is subjected can cause additional degradation of the seal.
One solution to the problems described above is to use an O-ring external seal between an overmold and a cooperating housing. Another solution to this problem is to use an externally applied ultraviolet cured glue to seal a housing to a surface of an overmold. However, both of these solutions require speed sensor assemblies that are relatively large in shape. For example, if an external O-ring is used, the overmold must be of sufficient size to allow for the placement of the O-ring between the overmold and the housing. The diameter of the overmold near the location where an O-ring is positioned must be about 5.5 mm greater than the diameter of the housing, or 2.75 mm per side, in order to provide sufficient space for an externally applied O-ring. In the case of externally applied ultraviolet cured glue, the surface upon which the glue is dispensed must be large enough to accommodate the applied glue. Similar to the requirements necessary for use of an external O-ring, the surfaces upon which externally applied glue is applied require a total of about 5.5 mm of space available to which glue may be applied. The diameter of an overmold according to the present invention is only about 3.5 mm larger than the diameter of the housing near that location where a conventional O-ring or externally applied ultraviolet glue would be used. Also the diameter of the overmold of the present invention is offset in its relationship to the housing by about 0.9 mm near the location where a conventional O-ring or externally applied ultraviolet glue might be considered. Thus, these prior sealing techniques are not capable of use in a speed sensor of the present invention.
There are other problems with these prior art techniques that prevent widespread use of such prior sealing means in all applications. The O-ring sealing technique requires an extremely detailed and complex injection molding fixture in order to provide an annular grove in the overmold for placement of an O-ring between the housing and the overmold to seal the connecting surfaces of these two pieces. Once molded, further assembly is required wherein the O-ring must be installed in the annular groove after the injection molding process. This additional assembly adds delay and cost to the overall manufacturing process.
When using the externally applied ultraviolet cured glue sealing technique, the part receiving the glue must have two edges large enough for the glue to rest upon. Not all speed sensors are designed to include these two edges or even large enough edges. As noted, the overall configuration of a speed sensor is largely dependent on the type and make of vehicle in which the speed sensor will be placed. Moreover, it has been observed that externally applied ultraviolet cured glue is susceptible to thermal breakdown as a result of the harsh environments to which the sensors are subjected. Another problem with externally applied ultraviolet cured glue is that the shape of such an applied glue is only controlled by the applicator. If not properly or evenly applied, the glue may cure leaving a gap between the parts to be sealed. Also, an uneven glue application may create a glue seal that is thin at various locations around the sealed part thereby leaving a weak seal point. In such situations, water or some other contaminant may find its way to the core of the speed sensor and short out the electrical function of the sensor.
Thus, what is needed is a speed sensor assembly that provides a sealed environment to isolate the internal components of the sensor from detrimental external forces. What is further needed is a new seal that seals between a housing and an overmold of a speed sensor, and yet is capable of use in a speed sensor of all different sizes and shapes. In other words, what is needed is a seal means that does not require a speed sensor to be of a particular size and shape such as those needed for conventional sealing techniques. What is also needed is a new method of applying an ultraviolet cured glue to a speed sensor that eliminates application problems of conventional glue sealing techniques.
The solution to providing a speed sensor assembly that seals and protects the internal parts of the speed sensor from harsh
Schneider Gary P.
Steinauer Timothy J.
Kwok Helen
Michael & Best & Friedrich LLP
SSI Technologies, Inc.
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