Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reexamination Certificate
2001-03-06
2002-12-24
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S166000, C384S448000, C029S894000
Reexamination Certificate
active
06498475
ABSTRACT:
BACKGROUND
A) Field of the Invention
This invention relates generally to a rotational velocity sensor ring and method for forming the ring.
The invention is particularly applicable to and will be described with reference to a rotational velocity sensor ring for use in a speed sensor package mounted on a wheel bearing spindle of a vehicle for anti-lock and like purposes. However, those skilled in the art will recognize that the invention has broader application and can be applied in any number of industrial and non-vehicular applications in which the rotational movement of an object is to be detected.
B) Incorporation by Reference
The following patents are incorporated by reference herein and made a part hereof so that details related to wheel bearings, wheel bearing spindles and sensors used with sensor rings which are conventionally well known in the art need not be described in detail in the specification of this patent.
1) U.S. Pat. No. 5,696,442, issued Dec. 19, 1997 to Foster, et al., entitled “ROTATIONAL VELOCITY SENSOR RING APPARATUS AND METHOD”.
2) U.S. Pat. No. 5,111,138, issued May 5, 1992 to Kramer, entitled “SPEED SENSOR HAVING A CLOSED MAGNETIC FLUX PATH FOR SENSING SPEED FROM AN AXIAL FACE OF A ROTATING MEMBER”.
3) U.S. Pat. No. 5,010,290, issued Apr. 23, 1991 to Foster, entitled “EASILY INSTALLED WHEEL BEARING SENSOR PACKAGE”.
4) U.S. Pat. No. 4,988,220, issued Jan. 29, 1991 to Christiansen et al., entitled “SERVICABLE WHEEL SPEED SENSOR ASSEMBLY”.
5) U.S. Pat. No. 4,795,278, issued Jan. 3, 1989 to Hayashi, entitled “BEARING ASSEMBLY”.
The material incorporated by reference herein does not, per se, form the present invention.
C) Prior Art
In a known manner of sensing rotational velocity of a rotating body, a sensor ring, also known as an encoder ring, exciter ring or tone ring, is mounted so that it rotates with the rotating body. A variable inductance or variable reluctance sensor is mounted concentrically around the sensor ring or, alternatively, proximate to one portion of the exterior of the sensor ring. The sensor is fixedly mounted and does not rotate with the sensor ring. The sensor includes circuitry configured to provide an output signal that varies with the rotational velocity of the sensor ring. Typically, as the rotational velocity of the sensor ring increases, the frequency of the output signal increases.
One known type of sensor ring comprises a machined or pressed metal ring with extending teeth substantially equally spaced around the outside perimeter of the ring. The sensor is configured so that when the ring is in certain positions, each tooth lines up with one or more poles of the sensor. When the ring is then turned from that position so that the teeth are no longer directly aligned with the pole, the sensor detects a change in inductance or reluctance of the magnetic circuit including the sensor poles and the sensor ring. It is through detecting such changes in inductance or reluctance that rotational velocity sensors operate.
For the most part, sensor rings have been formed from powdered metal sintered into a desired shape. Certain metals in the composites are selected for their magnetic properties. However, the prior art has recognized that plain carbon steels, (i.e., sheet metal stock or plain carbon steel with alloying elements for enhanced magnetic properties), has superior ferro-magnetic properties and does function, if properly formed, as rotational sensor rings. Plain carbon steel sensor rings have been fabricated in a variety of ways which can be generally classified or grouped in several categories.
One category can be explained as forming fingers on a rotating hub such as shown in U.S. Pat. No. 5,080,500, issued Jan. 14, 1992, which are difficult to handle in mass manufacturing and tend not to be durable. Accordingly, the fingers are strengthened by being bent back onto one another and formed into a ring such as shown in my prior '442 patent cited above or interlocked together to form two hubs forming “windows” such as shown, for example, in U.S. Pat. No. 4,940,937, issued Jul. 10, 1990, which is generally not desirable.
Another category forms windows on a hub such as shown in the '138 patent and U.S. Pat. No. 5,166,611, issued Nov. 24, 1992. In the '278 patent, the windows are formed on a hub or on a hub which is formed as a cup or in one embodiment, a hub with a “V” shaped cross-section. The “windows” are formed between the ends or edges of the hub. In practice, it is difficult to form the shapes depicted from a blank without distorting the cylindrical hub and the windows.
Another type of sensor ring is shown in pictorial representation in prior art
FIGS. 1A and 1B
. This design has proven itself to be commercially durable, extremely rigid, and produces acceptable sensor signals. It is a variation of a design illustrated in the second embodiment disclosed in the '442 patent. The sensor is produced from a stamped blank in which the hub
1
is drawn and a stepped “U” shaped sensor portion
2
as shown in prior art
FIG. 1B
is formed radially outward of hub
1
. The outer leg
3
of the “U” is corrugated or formed with sine shaped undulations
3
as best shown in FIG.
1
B. Undulations
3
have peaks
4
and valleys
5
which correspond to the “windows” discussed above. The sensor pickup head detects the changes in the magnetic flux density which is caused by the peaks and valleys and then detects the rotational velocity of the sensor ring.
All of the sensor rings discussed are functional and several have been commercially implemented. Each, however, have drawbacks and can be improved. For example, finger designs are suspect of being bent or distorted not only in use but simply in the handling and storing of a large number of rings inevitably occurring in the manufacturing process of a bearing assembly. Window designs are preferred for reasons discussed below but are difficult to accurately produce from a stamped blank with minimal forming steps. Variations in the window edges cause accuracy error in the sensor signal and may require revised sensor design and/or cause mounting restrictions. Corrugated sensor rings give limits to sensor sensitivity due to lack of sharp edges which tend to provide better flux changes.
SUMMARY OF THE INVENTION
Accordingly, it is one of the main objects of the invention to provide an improved sensor ring which can be formed from a metal blank of minimal mass while producing improved magnetic performance.
This object along with other features of the invention is achieved in a method of manufacturing a rotational velocity sensor ring which includes the steps of forming a flat ring-shaped blank from a sheet of ferro-magnetic metal stock and drawing a cylindrical hub portion from the radially inner portion of the ring blank so that the blank has an L-shaped, cross-sectional configuration with an annular sensor portion extending radially outward from the hub portion. In the drawn blank, a plurality of substantially identical, circumferentially spaced windows are punched in the sensor portion with each window having an inner edge adjacent to but spaced radially outward from the hub portion and an outer edge adjacent to and spaced radially inwardly from the outside edge of the sensor portion. Importantly, the sensor portion is bent along an imaginary bend circle adjacent the windows' inner edges in the direction of the hub so that the blank now has a U-shaped, cross-sectional configuration while simultaneously forming an undulation in the sensor portion of the blank between the peripheral outer end of the sensor portion and the outer edge of each window whereby a symmetrically uniform sensor portion of the sensor ring is formed into a rigid structure from a blank with less metal or mass than that of the prior art.
In accordance with another important feature of the invention, the depth of the undulations formed in the bending step are precisely controlled to produce a sensor portion in the form of a substantially symmetrical cylinder or, alternatively, a substantially symmetrical f
Foster David Alden
Kalb Karl Edward
Kreh Larry R
Delphi Technologies Inc.
Kinder Darrell
Lefkowitz Edward
McBain Scott A.
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