Planetary gear transmission systems or components – Electric or magnetic drive or control – Differential drive or control
Reexamination Certificate
1999-04-23
2001-05-29
Estremsky, Sherry (Department: 3681)
Planetary gear transmission systems or components
Electric or magnetic drive or control
Differential drive or control
Reexamination Certificate
active
06238316
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
This invention relates to an automotive speed sensing system used in such devices as speedometers, anti-locking brakes and traction control systems. More particularly, the invention relates to the use of a roll-formed tone wheel and sensing device within an axle system, particularly with respect to sensing the speed of a differential assembly.
b) Description of Related Art
There are numerous prior art axle assemblies that provide speed sensing mechanisms for a differential axle housing or axle. Typically, a toothed tone wheel is disposed on the rotating member and a magnetic sensor senses the rotational speed of the tone wheel teeth. Most sensing systems within a differential axle housing involve the placement of a stamped tone wheel at the ring gear flange of the differential assembly, or at a trunnion extending from and typically integral with the ring gear flange. Sensing systems attached to an axle shaft typically involve a powdered metal, or forged, tone wheel disposed on that shaft. Other tone wheel systems use sensing teeth that are integrally formed as part of the differential case during the casting process.
The manufacturing process associated with conventional stamped tone wheel systems results in substantial material waste, as will be appreciated by those skilled in the art.
Additional drawbacks related to the use of pressed rings containing teeth for registration with the pickup or sensing element, include the requirement of additional parts, extra tooling and machining, potential seating problems for the extra parts, and increased runout which causes transducer sensing problems.
The need therefore exists for a speed sensing system that reduces the substantial material waste associated with convention tone wheel systems, while maintaining the sensitivity and reliability of the system.
SUMMARY OF THE INVENTION
The invention presented and disclosed herewith provides a system wherein all of the aforenoted disadvantages of the prior art are either minimized or entirely eliminated. Significantly, the speed sensing differential mechanism of this invention is not subjected to the material waste associated with the stamped metal tone wheel.
In a preferred form, the speed sensing differential axle mechanism of the present invention provides a roll-formed tone wheel lightly pressed onto the differential case or axle, thereby providing an adequate run-out specification for the electrical gap between the sensor and the tone wheel teeth.
The tone wheel itself is roll-formed from a long steel sheet that is continuously passed through a suitable roll-forming die. Once the teeth are properly formed into the steel sheet, the sheet is cut to a proper length determined by the differential and axle specifications. The ends of the cut sheet having roll-formed teeth are then spot welded to form a toothed ring properly sized for placement on the differential case or axle assembly. In the preferred design, tabs formed on the inner side of the roll-formed tone wheel lock onto a turned diameter of the differential case and the wheel is held in place by the attachment of the ring gear.
A stationary electronic pickup element extends toward the teeth and is spaced therefrom by a gap of conventional dimensions. The pickup element extends from, and is secured in, a cover plate on the axle housing for ease of access and convenience.
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Estremsky Sherry
Liniak Berenato Longacre & White
Pang Roger
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