Patent Publication Number: US-2017350913-A1

Title: Suspension System

Description:
RELATED APPLICATION DATA 
     This application claims priority to U.S. Provisional Application No. 62/345,265 filed on Jun. 3, 2016, and titled “Suspension System,” which is incorporated herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to Health and Usage Monitoring Systems (HUMS) in high vibration environments. In particular, the present invention is directed to a suspension system for HUMS. 
     BACKGROUND 
     Data collected and processed by HUMS can be used to reduce unscheduled maintenance, improve reliability, and facilitate an overall improvement in safety for rotorcraft (helicopters) as well as fixed wing aircraft or ground vehicles. 
     At a high level, HUMS incorporate sensors to perform: mechanical diagnostics of rotating equipment; rotor track and balance to trim and balance the main rotor (for a helicopter); regime recognition, which determines the state of the aircraft, allowing the HUMS to take acquisitions when the vehicle is in nominal (straight and level) regimes, thereby reducing variance mechanical diagnostics analysis and allowing a damage factor to be applied based on time spent in specific regimes; and structural health monitoring to ensure structural integrity of vehicle frames/bulkheads. 
     The information collected by the HUMS interrelates to improve performance. For example, regime recognition improves structural health monitoring by allowing correlation of vehicle loads induced by a regime to the measured fatigue by structural health monitoring. Regime recognition is also used by rotor track and balance, in that a helicopter manufacturer establishes flight regimes in which rotor track and balance data is collected, such as, but not limited to, a ground regime, a hover regime, 90 knot regime, and a 120 knot regime. 
     Additional data collected during operation of the vehicle can include monitoring the performance of the operator (e.g., the pilot or driver of the vehicle). For the helicopter community, this data monitoring is commonly known as helicopter flight data monitoring. Flight data monitoring is the systematic, pro-active, and non-punitive use of digital flight data from routine helicopter operations to improve aviation safety. Flight data monitoring programs assist operators to identify, quantify, assess, and address operational risks, by allowing for the identification of areas of concern and allowing for remedial measures to be taken. The United States Federal Aviation Administration has issued a new rule for Helicopter Air Ambulance, Commercial Helicopter, and Part 91 Helicopter Operations that includes a fixture requirement for flight data monitoring capability in air ambulances. 
     Both flight data monitoring and regime recognition function require vehicle state data, such as velocities, accelerations, altitude, rates, and time. For HUMS installed on fixed-wing or rotorcraft, this data is usually derived by interfacing with the vehicle&#39;s flight control system or altitude heading reference system. This interface requires a significant number of connections (i.e., wires) and a junction box to interface with existing avionics. Additionally, it requires writing custom software to convert the vehicle data into engineering units that can be used by HUMS for, e.g., flight data monitoring and regime recognition analysis. 
     In a more modern HUMS, to reduce weight and cost of implementing the regime recognition and flight data monitoring function, a HUMS may have an integrated microelectromechanical systems base inertial measurement unit and global positioning system (GPS) receiver. These components allow the HUMS to have the capability of a fully global navigation satellite system and thus fall access to all data related to aircraft velocity, accelerations, heading, altitude, position, and time without the need for connections to other vehicle systems and hardware. 
     Weight reduction is achieved by removing the additional wiring and the junction box needed to interface with other vehicle systems and hardware, which also reduces reapplication costs by eliminating the need to update or implement an interface control (between the junction box and the vehicle hardware) for different configurations of vehicle hardware. 
     An advantage of integrating GPS into the inertial measurement unit is that having the GPS update position and velocity states allows for a lower cost microelectromechanical systems base inertial measurement unit to have the performance capabilities of a much more expensive, navigational grade inertial measurement unit. 
     The environment in which a HUMS is installed can have very high vibration levels. High vibration levels can cause higher than normal failure rates of electronic components included with the HUMS. More problematically, high vibration levels can saturate the accelerometers used in an inertial measurement unit, thus rendering them grossly inaccurate or inoperable. An inertial measurement unit typically has three orthogonally oriented accelerometers, typically with a range of +/−18 g&#39;s of acceleration, which are constructed so as to measure vehicle body accelerations at relatively low frequencies (e.g., from about 0 to about 10 Hz). 
     Rotating equipment on vehicles with HUMS often generate vibration synchronous with a shaft with velocities of 0.5 to 1.0 inches per second. The relationship between shaft rotations in inches per second and g&#39;s can be determined by the following: 
       g=0.0162*shaft rotation in inches per second*frequency  Eq. 1
 
     For low frequency shafts, such as a main rotor of a helicopter, which has a frequency of about 5 Hz, a shaft rotation of 1 inch per second generates 0.081 g&#39;s of acceleration. However, the input shaft of the main gearbox of a helicopter may have a shaft rate of 268 Hz and include a 22 tooth input pinion, resulting in a gear mesh frequency of 5896 Hz (268 Hz*22) and a 2 nd  harmonic frequency of 11,792 Hz. Even with moderately low vibration, the main gearbox can cause accelerations of 10 to 100&#39;s of g&#39;s in the frequency domain. Further exacerbating the vibrations generated in these environments is that the measured, time domain acceleration is the superposition of all shaft, gear, and bearing vibration within a gearbox, which is composed of many shafts and gears. 
       FIG. 1  is a graph  100  of acceleration versus time and presents 0.02 seconds of data acquired at 97656 samples per second by an accelerometer proximate a HUMS on a commercial rotorcraft during normal operation. As can be seen, the time domain vibration is on the order of +/−100 g&#39;s.  FIG. 2  is another graph, graph  200 , of acceleration versus frequency acquired by an accelerometer proximate a HUMS on a commercial rotorcraft. As can be seen, there are a number of gear mesh tones that individually contribute 8 or more g&#39;s of acceleration (at around 3000 Hz, 4100 Hz, 4500 Hz, and 10,000 Hz), In one example, the 14 g&#39;s of acceleration at 3000 Hz is from a velocity of 0.3 inches per second. The levels of vibration shown in  FIGS. 1 and 2  would reduce the reliability of the HUMS and will saturate the inertial measurement unit, rendering the inertial measurement unit inoperable. In order to improve reliability of the HUMS and to allow for continued operation of the inertial measurement unit, the vibration and shock experienced by the HUMS and the inertial measurement unit needs to be reduced. 
     It is known that a way to reduced vibration and shock is to shock mount equipment. And while there are examples of avionics that are shock mounted, these mounts are external to the equipment package containing the avionics. External shock mounts, however, add to the weight, complexity, and expense of the installation of avionics. In addition, there is not always sufficient space to externally shock mount the equipment package. Therefore, there is a need for an improved system for reducing excessive vibration and shock experienced by avionics that is light and does not add to the total volume of the equipment package. 
     SUMMARY OF THE DISCLOSURE 
     A suspension system for a vehicle including a health and usage monitoring system subject to shock and vibration is provided including an enclosure attached to the vehicle, an electronics board within the enclosure and having a plurality of health and usage monitoring system components, including an inertial measurement unit, and a plurality of elastomer standoffs coupling the electronics board to the enclosure. Each of the plurality of elastomer standoffs has a loss factor of between about 0.7 and about 1.0 and includes a vibration reducer having a stiffness of between about 20.0 and 30.0 lbs/in, an engagement member having a top mounted to the vibration reducer, and a receiver including an insert having an aperture, wherein the insert is mounted substantially within the vibration reducer. 
     In another embodiment, an elastomer standoff for reducing vibration experienced by components, including an inertial measurement unit, of a health and usage monitoring system on a vehicle is provided including a vibration reducer having a stiffness of between about 20.0 and 30.0 lbs/in, an engagement member having a top molded into the vibration reducer, the engagement member configured to couple the vibration reducer to an enclosure of the health and usage monitoring system, and a receiver including an insert having an aperture, wherein the insert is mounted substantially within the vibration reducer and configured to couple the vibration reducer to an electronics board of the health and usage monitoring system, wherein the elastomer standoff has a loss factor of between about 0.7 and about 1.0 such that, when the receiver is attached to an electronics board of the health and usage monitoring system and the engagement member is attached to an enclosure of the health and usage monitoring system, energy of vibrations transmitted to the electronics board and the inertial measurement unit is limited to about +/−0.5 g&#39;s when the vehicle is in operation. 
     In another embodiment, a suspension system for a health and usage monitoring system on a vehicle is provided including an enclosure for the health and usage monitoring system, the enclosure attached to the vehicle, an electronics board within the enclosure and including an inertial measurement unit, and a plurality of elastomer standoffs coupling the electronics board to the enclosure, wherein each of the plurality of elastomer standoffs has a loss factor of between about 0.7 and about 1.0. Each of the plurality of elastomer standoffs includes a vibration reducer having a stiffness of between about 20.0 and 30.0 lbs/in, an engagement member having a top mounted to the vibration reducer, and a receiver including an insert having an aperture, wherein the insert is mounted substantially within the vibration reducer, wherein when the receiver of each of the plurality or elastomer standoffs is attached to the electronics board and the engagement member of each of the plurality of elastomer standoffs is attached to the enclosure, energy of vibrations transmitted through the enclosure to the inertial measurement unit is limited to about +/−0.5 g&#39;s when the vehicle is in operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
         FIG. 1  is a graph of acceleration versus time for a prior art HUMS experiencing vibration; 
         FIG. 2  is a graph of acceleration versus frequency for a prior art HUMS experiencing vibration; 
         FIG. 3  is a graph of transmissibility versus frequency for a suspension system according to an embodiment of the present invention; 
         FIG. 4  is a graph of acceleration versus time for a suspension system according to an embodiment of the present invention; 
         FIG. 5  is a cross-sectional plan view of an elastomer standoff according to an embodiment of the present invention; 
         FIG. 6  is an exposed plan view of a HUMS system including a suspension system according to an embodiment of the present invention; and 
         FIG. 6A  is a plan view of the HUMS system including a suspension system according to an embodiment of the present invention of  FIG. 6  along section  6 A- 6 A. 
     
    
    
     DESCRIPTION OF THE DISCLOSURE 
     A suspension system according to the present disclosure significantly reduces the impact of vibration on HUMS components and diminishes the possibility of inertial measurement unit saturation. In an exemplary embodiment, the suspension system includes an enclosure with a plurality of elastomer standoffs designed and configured to reduce shock and vibration to internal HUMS components. The elastomer standoffs&#39; vibration responses, as disclosed herein, are tuned so that vibration above 20 Hz is attenuated and thus the impact of high vibration levels associated with a gearbox on the HUMS or inertial measurement unit is reduced. 
     Elastomeric standoffs provide isolation to reduce the transmission of energy from the HUMS packaging (e.g., box, case, or enclosure), which is attached to the aircraft or vehicle, to the electronics board and inertial measurement unit. In an exemplary embodiment, the suspension system has a natural frequency (f n ) that is dependent on the stiffness of the elastomeric material and the sprung mass of the electronics board on which the inertial measurement unit is mounted. The natural frequency is calculated as: 
         f   n =3.13 √{square root over (K/W)}   Eq.
 
     where K is the stiffness of the standoff in pounds per inch and W is the weight of the electronics board. 
     The elastomeric material of the standoffs is designed to employ hysteretic damping so as to dissipate absorbed energy (i.e., shocks and vibrations) as low-grade heat. A loss factor can be used to quantify the level of hysteretic damping of any given elastomeric material. The loss factor is the ratio of energy dissipated from the system to the energy stored in the system for every oscillation. At resonance, the loss factor, η, is 2ζ, where ζ is the damping ratio. Examples of typical loss factors for elastomeric materials include η=0.4 for Butyl Rubber and η=1.0 for Isodamp® C-1002 (made by Aearo EAR Specialty Composites of Indianapolis, Ind.). 
     The ability of a system to reduce the impact of vibration and shock, such as the suspension system discussed herein, is determined by the transmissibility of the system, which is the ratio of the energy going into the system to the energy coming out of the system. The transmissibility (T) is determined using Equation 3: 
     
       
         
           
             
               
                 
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     where A out  is the energy that goes out of the system, A m  is the energy that comes into the system, f d  is the driving frequency, and f a  is the natural frequency. 
     In an exemplary embodiment, an elastomeric standoff designed and configured according to the present disclosure has a stiffness of about 23 lbs/in. Thus, for a HUMS electronics board with weight of about 0.5 lbs, the f n , natural frequency would be about 21 Hz. Using an elastomeric material with loss factor of around 0.8 would result in the suspension system having a transfer function  300 , which is shown in  FIG. 3  on a graph of transmissibility of the suspension system versus frequency of the driving frequency (i.e., the vibrations emanating from the gearbox, etc.). In this scenario, the suspension system would have a bandwidth (3 dB loss, or 50% energy) of about 46 Hz (location  304  on function  300 ). 
       FIG. 4  shows a graph  400  of acceleration versus time and represents the vibration measured on an electronics board in a HUMS, including an inertial measurement unit, on a rotorcraft (at a similar placement as the accelerometer that measured the data used to produce the graph shown in  FIG. 1 ), when including an embodiment of the suspension system discussed herein. As can be seen, the vibration signature transmitted to the HUMS electronics and inertial measurement unit is about +/−0.5 g&#39;s, substantially less than the +/−100 g&#39;s measured without the suspension system and is well within the acceptable limits of the inertial measurement unit. This low vibration level will enhance the reliability of the HUMS electronics. 
       FIG. 5  shows a cross-section of an exemplary elastomer standoff  500  according to an embodiment of the present disclosure. At a high level, the elastomer standoff includes an engagement member  504 , a vibration reducer  508 , and a receiver  512 . Engagement member  504  is designed and configured to couple the elastomer standoff  500  to an enclosure containing a HUMS. As shown in  FIG. 5 , engagement member  504  has a first end  516  and a top  520 . In the embodiment shown in  FIG. 5 , first end  516  is threaded for fastening to the enclosure; however other types of fastening mechanisms and/or methodologies could be used, such as, but not limited to, snap fit connectors, press rating, etc. 
     Top  520  is coupled to vibration reducer  508 . In an exemplary embodiment, engagement member  504  is coupled to vibration reducer  508  using a molding process wherein top  520  is joined to the bottom of vibration reducer  508 . 
     Vibration reducer  508  is an elastomeric material that has a loss factor of between about 0.7 and 0.9. In an exemplary embodiment, vibration reducer  508  has a loss factor of about 0.8. In another exemplary embodiment, vibration reducer  508  has a stiffness of between about 20.0 and 30.0 lbs/in. In an exemplary embodiment, vibration reducer  508  has a stiffness of about 23.0 lbs./in. 
     As shown in  FIG. 5 , vibration reducer  508  is cylindrical in shape; however, other shapes may be used so as to conveniently attach to or be included within the HUMS enclosure. 
     Receiver  512  is sized and configured to couple elastomer standoff  500  to a HUMS electronics board. In the embodiment shown in  FIG. 5 , receiver  512  includes an insert  524  including an aperture  528  that has receiving threads. In alternative embodiments, receiver  512  can be configured to receive other types of fasters or connectors. As with engagement member  504 , receiver  512  is preferably molded into vibration reducer  508 . 
     Engagement member  504  and receiver  512  are, in an exemplary embodiment, made of a metal, such as aluminum, but other materials could be used such as plastics (e.g., Coolpoly® E2 (a product of Celanese Corporation headquartered in Dallas, Tex.), Polycarbonate). As the elastomer standoff is designed to reduce vibration and shock to the HUMS, creating a durable connection between the HUMS electronics board and the enclosure can be an important consideration depending on the environment into which the HUMS is to be placed. 
     In an exemplary embodiment of elastomer standoff  500 , vibration reducer  508  may have a diameter of about 0.28 inches and have a length (in a direction between the HUMS electronics board and the HUMS enclosure) of about 0.32 inches, with engagement member  504  being a male machine screw having a length of about 0.20 inches and receiver  512  having a female mounting thread depth of about 0.11 inches. 
       FIGS. 6 and 6A  show an exemplary HUMS system  600  that includes an electronics card  604 , an inertial measurement unit  608 , and a USB  612  within an enclosure  616 . Four elastomer standoff&#39;s  620  (e.g.,  620   a,    620   b,    620   c,  and  620   d ) couple enclosure  616  to electronics card  604 , thereby reducing the amount of vibration transmitted from external sources to electronics card  604  and its components. 
     Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.