Patent Publication Number: US-6714135-B2

Title: Collective head bearing monitor

Description:
FIELD OF THE INVENTION 
     The present invention relates to bearing monitors and, more particularly to, an improved bearing monitor that has a sensor and a processor attached to a rotating component of a system supported by the bearing. 
     BACKGROUND OF THE INVENTION 
     Bearings are commonly used to support rotating masses in many types of vehicles. Over the lifetime of the vehicle, bearings may endure hundreds of thousands or even millions of cycles. Eventually, bearings will fail because of repetitive cycles of stresses. Bearing failure can cause catastrophic results depending on when the bearing fails. Bearing failure in a collective head of a helicopter, for example, may cause the helicopter to crash if the bearing fails during flight. 
     Usually, however, bearings do not fail instantaneously. Cumulative wear gradually degrades bearing components, which may emit measurable indicators of imminent failure. It is known in the art that a worn bearing will emit vibrations in a frequency range at or above 1 KHz. Consequently, bearing monitors that trigger an alarm when a bearing emits frequencies in this range have been developed. These monitors usually have a sensing component to measure the frequency of a particular bearing and a processing component to analyze data sent from the sensing component. 
     Monitoring bearings in many vehicles is a relatively simple process because the bearing is fixed in the vehicle structure and the sensing component is mounted to or near the bearing. A signal from the sensing component is then sent to the processing component through wires or other direct connection. However, in aircraft having rotors, for example, the only structure available to mount a bearing monitor may be a rotating structure. 
     One solution that has been used to monitor bearings in rotating structures is mounting the sensing component on or near the bearing. The processing component receives the signal from the sensing component through a slip ring of the rotating structure. Although transmitting signals through the slip ring is common and usually effective, in the case of monitoring high frequencies above 1 KHz, undesirable noise generated by the rotating structure often degrades the signal from the sensing unit. Therefore, monitoring the bearing through the slip ring is unreliable and could be dangerous to the passengers and crew of the aircraft. 
     It would, therefore, be desirable to have an improved apparatus, method and system for monitoring bearings in rotating systems that does not require transmitting a signal through the slip ring. 
     SUMMARY OF THE INVENTION 
     The present invention is a bearing monitor that has a bearing sensor to monitor frequencies emitted by a bearing in a rotating component. The bearing sensor has an output to a processor. The processor is attached to the rotating component to process the output from the bearing sensor to output a digital or logical signal correlating to a condition of the bearing. 
     In one embodiment of the invention, a method of monitoring a bearing includes the step of sensing vibrations emitted by a bearing using a sensor mounted on a rotating component. The bearing sensor has an output. The method then includes the step of providing a processor attached to the rotating component to process the output from the bearing sensor to output a digital or logical signal. 
     In another embodiment of the invention, a system to monitor a bearing in a rotating component includes a housing that is attached to the rotating component. A bearing sensor attached to the housing monitors vibrations emitted by the bearing in the rotating component. The bearing sensor has an output. A processor attached to the rotating component processes the output from the bearing sensor outputs a digital or logical signal correlating to a bearing condition. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, including its features and advantages, reference is now made to the detailed description of the invention, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 is a perspective cut-away view of a bearing monitor that depicts an embodiment of the present invention; 
     FIG. 2 is perspective view of a collective head that depicts an embodiment of the present invention; 
     FIG. 3 is a cut-away view of a collective head that depicts an embodiment of the present invention; and 
     FIG. 4 is an electrical schematic diagram that depicts an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the making and using of various embodiments of the present invention is discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the invention. 
     In one embodiment of the invention, for example, a bearing monitor that monitors the condition of one or more bearings in a collective head of a rotor driven aircraft may be attached to the rotating collective head. Monitoring a collective head bearing using a conventional bearing monitor is not practical because conventional bearing monitors must be attached near the bearing. Typically, a conventional bearing monitor will be mounted on the stationary housing of the bearing or on the stationary structure in which the bearing is fixed. In the case of a collective head, the bearings are located internally, which precludes placement of a bearing monitor on or near the housing of the bearing. Although a conventional bearing monitor could be mounted to the collective head, the signal from the conventional monitor must be transmitted through the slip ring of the collective head. This transmission degrades the transmitted signal, which reduces or eliminates the reliability of a conventional bearing monitor. 
     Referring to FIG. 1, the bearing monitor  10  according to one embodiment of the present invention includes a sensor  12  and a processor  14 . Although including the processor in the bearing monitor  10  increases total mass, the mass of the bearing monitor  10  is a negligible addition to the rotating mass of the collective head. If required, the mass of the bearing monitor may be balanced about the axis of the collective head. 
     The sensor  12  may be a piezoelectric quartz accelerometer or other instrument to measure the vibrations of the bearing. Other methods and instruments to measure vibrations emitted by the bearing will be apparent to those having ordinary skill in the art. Because a failing bearing typically emits frequencies above 1 KHz, the sensor  12  may be adjusted to monitor frequencies in that range. Additional frequencies generated by the collective head, external forces such as wind speed and air resistance, or the engine may be filtered by circuitry within the processor  14 . 
     Information from the processor  14  may be transmitted from the processor  14  through the slip ring to a diagnostic system in the aircraft. This information may be transmitted using a 5-volt signal. Because the processor  14  is located in the rotating collective head, the signal from the sensor  12  is processed before being transmitted through the slip ring. The 5-volt signal is not degraded through the slip ring, as a raw signal from the sensor  12  would be. Consequently, processing the signal from the sensor  12  before it is transmitted from the rotating collective head is much more reliable than processing a signal that has been transmitted through the slip ring. 
     The processor  14  may be a printed circuit board or other electronic circuitry to monitor the output of the sensor  12 . The processor  14  controls the functions of the bearing monitor  10  and may also contain diagnostic circuitry. The processor  14  analyzes the signal from the sensor  12  and outputs a digital or logical signal correlation to bearing condition, which may include determining if the bearing should be replaced. For example, if the sensor  12  detects frequencies in a selected range for a specified period of time, the processor  14  may trip an indicator  16  on the bearing monitor  10  to alert maintenance personnel of the bearing condition. The indicator  16  may visually or audibly alert maintenance personnel and will remain in a tripped condition until reset. The processor  14  may also send an alarm signal to the cockpit of the aircraft to alert the flight crew of the bearing condition. 
     The bearing monitor  10  may have a test circuit  18  to manually test the function of the bearing monitor  10 . When activated by maintenance personnel, the test circuit  18  sends an artificially generated signal, which may simulate frequencies of a failing bearing, to the processor  14  for a specified period of time. If the bearing monitor  10  is working properly, the indicator  16  will trip because the generated signal is indicative of a failing bearing. If the indicator  16  fails to trip, the maintenance personnel may replace or repair the bearing monitor  10 . If the bearing monitor  10  is functioning properly, maintenance personnel may manually reset the indicator  16  to prepare the bearing monitor  10  for operation. 
     The bearing monitor  10  may also have a connector  20  to interface with the aircraft. The 5-volt signal may be transmitted from the processor  14  into the connector  20  and subsequently through the slip ring to a diagnostic system in the aircraft. Although the connector  20  typically connects the bearing monitor  10  to the aircraft using a wired connection, the connector  20  may also be connected to circuitry that transmits a wireless signal. The connector  20  may also provide connections to other circuitry within the bearing monitor  10 . For example, the connector may allow the flight crew to remotely activate the test circuit  18 . Additionally, the connector  20  may allow the flight crew to monitor the status of the processor  14  in the bearing monitor  10 . 
     The bearing monitor  10  may have a housing  22  that contains the sensor  12  and the processor  14  and provides mounting points for the indicator  16 , the test circuit  18  and the connector  20 . The housing  22  may provide a robust enclosure for the circuitry of the processor  14  and may also be weatherproof and waterproof. The indicator  16  may be mounted to the outside of the housing  22  so a tripped indicator  16  is conspicuous to an observer. A switch to activate the test circuit  18  may also be mounted on the outside of the housing  22  for easy access by maintenance personnel. The connector  20  is also mounted to the outside of the housing  22  so the bearing monitor  10  may be easily connected to other systems in the aircraft. The housing  22  may be made from a lightweight material such as carbon fiber or an aluminum alloy. Because the housing may be mounted directly to the collective head, a lightweight housing  22  is less likely to unbalance loads about the rotational axis of the collective head. 
     Referring now to FIGS. 2 and 3, a collective head  24  of an aircraft is depicted. The collective head  24  may be in the rotor of a helicopter or the rotors of a tilt-rotor aircraft. As depicted in FIG. 2, the bearing monitor  10  may be attached directly to the collective head  24  using bolts, screws or other fasteners known to those having ordinary skill in the art. As the aircraft engines rotate the rotors, the collective head  24  also rotates. In addition to the bearing monitor  10 , the collective head may also house or support electronic components and circuitry or mechanical linkages that aid sustained flight. 
     As depicted more clearly in FIG. 3, the collective head  24  has a bearing  26 . The bearing  26  is located within the collective head  24  and supports rotation of the collective head  24  about a shaft. As discussed above, mounting the bearing monitor  10  on the bearing  26  is impractical. Consequently, the bearing monitor  10  may be mounted in a location  27  on the collective head  24 . Location  27  is generally designated and not necessarily the only location that the bearing monitor  10  may be located. The bearing monitor  10  may be located at any point on the collective head  24  that will accommodate the size of the bearing monitor  10 . 
     As the bearing  26  wears and begins to fail, vibrations in the 5-20 KHz range are emitted from the bearing  26  and are transmitted through the collective head  24 . The sensor  12  in the bearing monitor  10  detects the vibrations and the processor  14  filters and analyzes the vibrations detected by the sensor  12 . The indicator  16  is tripped if the processor  14  determines that the bearing  26  is failing. The processor may also output the 5-volt signal through the connector  20  and through the slip ring to trip an alarm in the cockpit. 
     Referring now to FIG. 4, a schematic block diagram of the bearing monitor  10  is depicted. In this particular example, the sensor is a piezoelectric accelerometer  28 . Vibrations from the environment imparted to the accelerometer  28  are converted to an electrical signal, as will be apparent to those having ordinary skill in the art. Alternatively, activating the test circuit  18  may impart an electrical current to the accelerometer  28  to self-test the bearing monitor  10 . The electrical signal from the accelerometer  28  is transmitted to a bandpass filter  30  that filters frequencies in the electrical signal that do not fall within the selected frequency range. 
     The signal then passes through an AC/DC converter  32 , which converts the alternating current signal to a direct current signal. The direct current signal then passes to a comparator  34 . An adjustable trip level  36  may be imparted to the comparator  34 . The adjustable trip level  36  allows maintenance personnel to set a threshold of vibration required to trip the indicator  16 . For example, maintenance personnel may determine that when the bearing  26  has approximately thirty hours of service life remaining, the vibration from the bearing  26  is at a particular level. Maintenance personnel may then set the adjustable trip level  36  threshold at that particular vibration level. 
     The comparator  34  compares the filtered DC signal from the accelerometer  28  to the threshold. If the filtered DC signal exceeds the threshold, a timer  38  is activated. If the timer  38  detects that the threshold is exceeded for a set amount of time, fifteen seconds, for example, the indicator  16  is tripped and maintenance personnel are alerted that the bearing  26  requires maintenance. The timer  38  prevents the indicator  16  from being unnecessarily tripped if the accelerometer  28  detects intermittent vibration in the selected range. Consequently, vibration in this range that is not indicative of bearing wear does not falsely trigger the indicator  16 . 
     Whereas the invention has been shown and described in connection with the preferred embodiment thereof, it will be understood that many modifications, substitutions and additions may be made which are within the intended broad scope of the appended claims. There has therefore been shown and described an improved bearing monitor that accomplishes at least all of the above stated advantages.