Measuring and testing – Instrument casing
Reexamination Certificate
2001-02-20
2003-05-13
Noland, Thomas P. (Department: 2856)
Measuring and testing
Instrument casing
C073S637000, C073S494000, C073S866500
Reexamination Certificate
active
06561024
ABSTRACT:
BACKGROUND OF THE INVENTION
Measuring the rotational speed of a shaft is a need for many customers of hydraulic/hydrostatic pumps and motors. One method of doing this is to affix a ring to the shaft, or something rotating with a constant ratio to shaft, that has several equally spaced magnetic poles. A Hall Effect sensor can then be placed in proximity to the magnetic ring. The Hall Effect sensor can detect the rate at which the magnetic poles pass by, providing enough information to calculate the rotational speed of the shaft. The applications of this technology are many, including engine speed and ground speed. A challenge that exists when assembling the hydraulic/hydrostatic pump or motor is to accurately and consistently place the sensor at the correct location, related to the magnetic ring. If the sensor is too close, it may come in contact with the ring during operation due to shaft deflection, tolerance issues, or other reasons. This may cause damage to the sensor, the magnetic ring, or both parts. If the sensor is placed further away, the magnetic field created by each pole on the magnetic ring will be weaker, reducing the Hall Effect and making the sensor less accurate, especially at high rotational speed. If the sensor is to work correctly, therefore, correct placement is crucial
In most applications, the Hall Effect sensor is placed in a threaded housing, then screwed into the pump or motor's external housing until the desired clearance is reached. Unfortunately, this assembly procedure is a blind operation, meaning that it is impossible to directly measure the clearance. One way to establish the correct distance is to screw in the sensor until it touches the magnetic ring, then unscrew it a defined number of rotations (based on thread pitch). This process relies heavily on operator knowledge and skill.
It is therefore a principal object of this invention to provide a method and means of creating a clearance or free space between two parts under blind assembly conditions.
A further object of the invention is to provide a method and means of creating a clearance or free space between two parts under blind assembly conditions which is fast and accurate to implement.
These and other objects will be apparent to those skilled in the art.
SUMMARY OF THE INVENTION
A method for creating a finite clearance space between two parts under blind assembly conditions involves threading an elongated sensor into a housing containing the part to be sensed by first placing a spacer element on an operative surface of the sensor wherein the spacer element has a radial thickness equal to the finite clearance space. The sensor is screwed unto the housing in a radial direction towards the operative surface of the sensor until the spacer element engages the operative surface, thereby specifically locating the operative surface a precise radial distance from the operative surface.
To resolve the placement issue, this invention applies a material to the end of the sensor that has thickness equaling the optimum distance between the magnetic ring and the sensor. With this insert, operators are no longer required to unscrew the sensor to establish an acceptance distance. The sensor can simply be screwed in until the applied material (spacer) touches the item being sensed. The spacer is not a functional part of the sensor, so if it contacts the ring during operation, causing part or all of it to wear away, there are no adverse consequences.
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Noland Thomas P.
Sauer-Danfoss Inc.
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