Patent Application
20100231201
The invention relates to turbomachinery, and more particularly to driveshaft speed detection in turbomachinery.
In turbomachinery, it may be important to measure the speed of a driveshaft for the power compressor and the turbine with a high degree of accuracy. Due to the high temperatures, pressures and vibration of such machinery, the most ideal positioning of a driveshaft speed sensor is on the end of the driveshaft forward of the compressor impeller.
A shaft speed sensor assembly generally comprises a shaft speed exciter rotor mounted on the driveshaft and at least one shaft speed magnetic pickup or sensor proximate the exciter rotor. The exciter rotor generally comprises a cylindrical ferromagnetic member that has multiple teeth about its periphery to cause a change in the reluctance of the magnetic circuit for the magnetic sensor as the shaft rotates. Such an exciter may have excessive mass and volume for placement on the driveshaft forward of the compressor impeller in many applications.
Another type of shaft speed sensor for the shaft of an adjustable speed drive has used a cup member serving as an exciter rotor. The cup member retains one end of compression spring that rotates along with an inner output shaft. The cup member has multiple perforations about its periphery that cause the reluctance of the magnetic circuit of a proximate magnetic pickup or sensor to change as the cup member and output shaft rotates.
The invention generally comprises a speed sensor assembly that comprising: a driveshaft with a driveshaft axis, a sensing portion of the driveshaft having an axial bore along the driveshaft axis and multiple axial slots radially spaced around the sensing portion that penetrate the through the driveshaft into the axial bore; and at least one electromagnetic sensor with a magnetic circuit proximate the sensing portion of the driveshaft; wherein rotation of the driveshaft causes the slots in the sensing portion to sequentially pass through the magnetic circuit of the electromagnetic sensor, thereby causing a change in the reluctance of its magnetic circuit that induces the electromagnetic sensor to generate an output signal that is representative of the rotational speed of the driveshaft.
At least one electromagnetic sensor 14 is proximate the sensing portion 8 of the driveshaft 4. The electromagnetic sensor 14 has a magnetic circuit, such as formed by a magnetic pole piece 16, and an electric circuit, such as formed by electric coils 18. As the driveshaft 4 rotates about the driveshaft axis 6, the slots 12 cause periodic increases in the reluctance of the magnetic circuit of the electromagnetic sensor 14. The changes in reluctance of the magnetic circuit induce current in the electric circuit of the electromagnetic sensor 14 that generates an output signal representative of these periodic changes in reluctance proportional to the rotational speed of the driveshaft 4.
For instance, with six of the slots 12 as shown and a rotational speed of the driveshaft 4 of 20,000 revolutions per minute (rpm), the sensing portion 8 and sensor 14 combination will generate an output signal that has 2000 pulses per second in the time domain or a frequency of 2000 Hz in the frequency domain. Counting pulses may provide an accurate measurement of position as well, with more slots 12 providing a higher degree of position accuracy.
If the axial bore 10 extends the entire length of the driveshaft 4 as shown, the sensing portion 8 and electromagnetic sensor 14 may have any position between the ends of the driveshaft 4 as
When the sensing portion 8 is on one end of the driveshaft, it may in fact be a separate component that attaches to the driveshaft 4. The attachment may be by any convenient means, such as fastening by way of at least one fastener, such as a bolt, or by welding, such as by inertia welding.
The sensor assembly 2 may have multiple electromagnetic sensors 14 that surround the sensing portion 8 of the driveshaft 4.
The described embodiments of the invention are only some illustrative implementations of the invention wherein changes and substitutions of the various parts and arrangement thereof are within the scope of the invention as set forth in the attached claims.
The development of this invention involved government support under N00019-06-C-0081 awarded by the United States Navy. The government has certain rights in the invention.
