Patent Application
20120179388
The present invention relates generally to fans, and more specifically to a system for determining that a fan is starting to fail, before an actual failure.
Computing systems generate heat during operation, and typically rely on high speed fans for cooling. Without the cooling support of a fan, the system is likely to fail. The mechanical reliability of a high speed fan is dependent on the reliability of a bearing assembly of the fan. Bearing wear accelerates with grease degradation and volatilization of the oil base. As the grease thermally degrades or loses its oil base due to thermal volatilization, bearing wear increases which eventually results in the failure of the fan. Some systems detect actual fan failures and automatically activate a redundant fan or increase the speed of the remaining fans. However, when these remedies are not effective or unavailable, the system enters an over temperature state and eventually throttles processor speed (to reduce power consumption) or simply powers down. Because computing systems and their speed of operation are important, it is important to detect a potential failure of a fan before the actual failure and replace the fan before the computer system is adversely affected.
Fan life is typically determined empirically by the fan manufacturer by subjecting multiple fans of the same type to accelerated aging conditions. An end-of-life value is then derived based on statistical treatment of the test data. A certain number of fans, however, will fail before the calculated end-of-life. A noisy fan or a slow-down in fan speed may indicate an impending fan failure. These indications, however, may not be noticed by an operator or provide sufficient time in which to replace the fan before it completely fails.
Existing methods for detecting grease degradation include the Kinematic Viscosity test, the Acid Number test, the Infrared test, and the Inductive coupled plasma spectroscopy test in which tests a technician periodically tests these properties of the grease using laboratory test equipment. These existing methods, however, require removing the grease from a device in order to perform the tests. Additionally, these tests require a larger sample size of grease than is typically found in a fan bearing. Thus, these tests are not well suited for determining grease degradation in a fan bearing.
Known microchips capable of detecting organic and inorganic gases are commonly used to control indoor air quality and to monitor for pollution. The chips rely on a chemo-sensitive polymer layer which absorbs volatile organic compounds (VOCs) or inorganic compounds in the gas. Sensors integrated into the chip detect gases in the air, and generate an analog signal representative of the level of the gases that was detected. The CMOS single-chip gas detection system as described in the IEEE Journal of Solid-State Circuits in December of 2002 is one example of a currently known gas detector chip.
A smoke detector is a known microchip for detecting gasses. As a compound burns, or erodes, it produces smoke. The smoke detector generates an alarm when it detects the smoke.
The present invention resides in a system, program product and method for early detection of fan degradation by monitoring grease degradation in a fan bearing assembly.
In a first embodiment of the present invention, a sensor detects a gas emitted from grease in the fan. A concentration level of the emitted gas is indicative of grease degradation. Circuitry coupled to the sensor compares the level of the detected gas to a predetermined level. An alert apparatus coupled to the circuitry generates an alert after the circuitry determines that the level of the detected gas exceeds the predetermined level.
In a second embodiment of the present invention, program instructions receive from the sensor data representative of detected gas emitted from grease in the fan. The concentration level of emitted gas is indicative of grease degradation. Program instructions compare the level of the detected gas to a predetermined level, and generate an alert responsive to the level of the detected gas exceeding the predetermined level.
The present invention will now be described in detail with reference to the Figures.
As illustrated in
Referring again to
As the grease begins to degrade, as evidenced by increased friction of the bearing and resultant increased temperature of the grease and emission of the gas, the fan nears its end-of-life. Accordingly, the gas-detecting fan failure detection device 26 notifies a user of a potential fan failure. The user may then proactively replace the fan, before complete failure of the fan, to avoid costly system down time.
In one embodiment of the present invention, gas sensor 28 comprises a silicon chip with a chemo-sensitive polymer layer tailored for specific VOCs or inorganic gases for a specific grease formulation. The chip is positioned in the airflow of the fan. VOCs or inorganic gases generated from the grease in the fan bearing will be carried by the air stream flowing from the fan to the chip. As the VOCs or inorganic gases pass over the chip, the VOCs or inorganic gases interact with the chemo-sensitive polymer layer of the chip. As the chip detects VOCs or inorganic gases, the chip generates an analog signal corresponding to the concentration level of VOCs or inorganic gases. The concentration level of the VOCs or inorganic gases and the generated signal correspond directly to the level of breakdown of the grease. The concentration level of VOCs or inorganic gases also indicates the rate of mass loss of the grease, i.e. the rate at which the existing amount of grease is being lost due to the excess friction and excess heat. For an embodiment of the present invention where the data analyzer function 30 is implemented with circuitry, the gas sensor 28 outputs an analog signal corresponding to the concentration level of VOCs or inorganic gases to the data analyzer function 30 for processing. (For another embodiment of the present invention described later where the data analyzer function 30 is implemented in software executed by the computer system, the gas sensor 28 also converts the analog signal to digital measurement data using a known analog to digital converter circuit, and transmits, by wire or wireless, the digital measurement data to the data analyzer function 30 for processing.)
Fan failure detection device 26 also comprises the data analyzer function 30, implemented as an application specific integrated circuit (“ASIC”) in one embodiment of the present invention, for processing the digital data generated by gas sensor 28. In this ASIC embodiment of the present invention, the data analyzer function 30 is implemented in circuitry, optionally with some of the function implemented by program code stored on a read only memory or other storage device and executed by a processor in the ASIC. Data analyzer function 30 compares the level of VOCs or inorganic gases to the known thermogravimetric response of the grease in the fan bearing to determine the current level of degradation of the grease and rate of mass loss of the grease.
Data analyzer function 30 makes the comparison by comparing the analog signal output from the gas detector to a series of predetermined reference voltages. Each of the reference voltages corresponds to a predetermined level of grease breakdown, predetermined rate of mass loss of the grease and/or predetermined amount of consumed life of the fan. The correlation of each reference voltage to the predetermined level of grease breakdown, predetermined rate of mass loss of the grease and/or predetermined amount of consumed life of the fan was previously determined through experimentation/test. Thus, in this embodiment of the present invention, the known thermogravimetric response of the grease is represented by the series of predetermined reference voltages and corresponding outputs of the data analyzer function 30, i.e. whether or not the data analyzer function 30 triggers an alarm.
Alternately, data analyzer function 30 makes the comparison by supplying the represented signal to three linear or nonlinear amplifiers whose outputs indicate the level of grease breakdown, rate of mass loss of the grease and amount of consumed life of the fan, respectively. The linearity or nonlineararity of each of these amplifiers was designed based on the known thermogravimetric response of the grease. Alternately, data analyzer function 30 makes this comparison by converting the output signal to a digital signal and comparing the represented signal output from the gas detector to a table which in one column lists a series of reference levels and in another column lists the corresponding level of grease breakdown, rate of mass loss of the grease and amount of consumed life of the fan as was previously determined through experimentation/test. The table also correlates the predetermined level of grease breakdown, predetermined rate of mass loss of the grease and/or predetermined amount of consumed life of the fan correlation of each reference voltage to the predicted end-of-life of the grease. Alternately, data analyzer function 30 extrapolates the current rate of mass loss linearly to a predetermined failure level to determine the time until end-of-life of the grease, and in turn the time until end-of-life of the fan.
Data analyzer function 30 then signals alerting apparatus/alarm 32 to notify an operator of computer 60 via audible alarm and/or flashing light and display, etc. that fan 24 is showing early signs of failure and indicates the predicted date of failure of fan 24. Alternately, alerting apparatus 32 can communicate to computer 60 the early signs of failure and the predicted date of failure of fan 24, and in response, computer 60 can notify the operator via the computer monitor, e-mail, text message, etc.
In the foregoing embodiment, fan failure detection device 26 is housed in a module supplied with electric power. The module includes the gas sensor 28, data analyzer function 30, and alert apparatus 32.
In a specific embodiment of the present invention, a compound is added to grease 27 of fan bearing 25 for the purpose of generating one or more predetermined gases which gas sensor 28 can detect. The compound is selected such that the degradation temperature of the added compound is lower then the degradation temperature of the grease so the predetermined gas triggers the gas sensor 28 before the grease begins to substantially degrade. This will allow sufficient time, for example, one month, to notify a user to take corrective action. Similarly, the degradation temperature of the added compound which is selected is not excessively low to prevent the predetermined gas from triggering a false alarm with gas sensor 28, i.e. before the grease begins to substantially degrade. Grease 27 typically begins to degrade at 225-250° C. Operating temperature of a fan is typically less then 70° C. Thus, adding a compound having a degradation temperature of 100-200° C. improves the ability to detect grease degradation. For example, a compound that begins to degrade at 150° C. is added to grease 27 that begins to significantly degrade at 225° C. At 150° C., the compound in the grease 27 emits the predetermined gas, triggering the gas sensor.
In one embodiment, azodicarbonamide is added to known grease 27 such as Kluber GLY 32, KluberQuiet BQ 72-72, or Multemp SRL/Multemp SB-M. By way of example, the ratio is 1% azodicarbonamide to 99% of this grease. Azodicarbonamide is a yellow, odorless crystalline powder that decomposes at 200° C. with evolution of nitrogen, carbon monoxide, carbon dioxide, and ammonia gases. For those greases that begin to degrade at temperatures lower than 200° C., the decomposition temperature of azodicaronamide can be lowered to 170° C. by use of activation agents or oxidizers such as ZnO. Additionally, incorporation of a synergist, such as urea at a ratio of 1% urea to 100% azodicarbonamide, to the azodicarbonamide lowers the decomposition temperature even further.
Ammonia gas is generally not present in the ambient atmosphere so presence of ammonia can be linked to breakdown of the grease. Ammonia can be detected using ammonia sensors such as solid state gas sensors, conducting polymer gas sensors, mixed oxide gas sensors, amperometric gas sensors, and catalytic field-effect devices.
By way of example, ammonia sensors are implemented as a silicon microchip. One such silicon chip is a TGS 826 manufactured by Figaro USA Inc. In this embodiment of the present invention, gas sensor 28 includes this type of chip and the thresholds for the data analyzer function 30 are set to levels corresponding to early breakdown of the grease and therefore, early breakdown of the fan, with sufficient advance notice, such as one month. This chip can detect small levels of ammonia gas, such as 1 PPM in the ambient atmosphere. Thus, very small levels of ammonia-emitting compound are needed in the grease formulation. Other compounds generally known to one skilled in the art may also be added to the grease formulation to release ammonia or other pre-determined gases, that can be detected by gas sensor 28, and release these gases at temperatures occurring during early breakdown of the grease.
Data analyzer function 30 and alert apparatus 32 can alternately be implemented as computer instructions stored on a hard drive of computer 60 and executed by a processor 52 via a RAM 56 of computer 60, according to another embodiment of the present invention. In this example, the digital data output from gas sensor 28 is input to computer 60 for processing via a wired or wireless connection.
Next, at decision step 48, data analyzer program 70 compares the predicted end-of-life to a predetermined threshold, such as one month, to determine whether the predicted end-of-life of the fan is less than a predefined date. If it is determined at decision step 48 that the predicted end-of-life of the fan is not less than the predefined value, fan failure detection device 26 continues to monitor and process gasses off-gassed from the fan but does not activate the alarm. However, if it is determined at decision step 48 that the predicted end-of-life of the fan is less than the predefined value, data analyzer program 70 notifies alert program 80 which in turn alerts a user of a failing fan at step 50.
Referring now to
Typically the computer-readable tangible storage device 66 is a magnetic disk storage device either internally installed in the computer 60 as a hard drive or externally accessible by computer 60. Alternately, the computer-readable tangible storage device 66 is a semiconductor storage device, such as flash memory, or any other computer-readable tangible device that can store and contain a computer program and other forms of data.
Data analyzer program 70 and alert program 80 can be loaded into server 60, via reader 62, from a portable computer-readable tangible storage device 72 such as a CD-ROM, DVD, memory stick, magnetic tape, or other forms of magnetic or optical disk or semiconductor storage device. Alternately, data analyzer program 70 and alert program 80 can be downloaded to computer 60 from the Internet or other network via network adapter card 68, for example, comprising copper wires, optical fibers, wireless transmission, routers, firewalls, switches, gateway computers, and/or edge servers.
Computer 60 includes display driver 64 for interfacing with external display 74. Computer 60 also includes keyboard 76 and mouse 78 for interfacing with computer 60.
The description above has been presented for illustration purposes only. It is not intended to be an exhaustive description of the possible embodiments. One of ordinary skill in the art will understand that other combinations and embodiments are possible. Accordingly, the above description is intended to embrace all such possible embodiments that fall within the scope of the appended claims.
