Bearings, as an important basic component of contemporary mechanical equipment, play the role of supporting and transmitting power, and are the guarantee for the smooth operation of machinery. With the continuous increase of the bearing speed, a series of problems caused by the high-speed operation of the bearing, such as increased friction and heat generation of the bearing, reduced fatigue life, slippage of the cage and rolling elements, damage to the rolling surface and instability of the cage, have been brought about. It will directly affect the working performance and life of the spindle-bearing system. In particular, the sharp increase in frictional heat generation will lead to an abnormal increase in the operating temperature of high-speed rotating bearings. Therefore, temperature is considered to be the most important parameter affecting the life and performance of high-speed rotating bearing components.
Different temperature measurement and testing methods are selected based on factors such as range accuracy, sensitivity, life, size, cost, reliability and measurement feasibility required to measure bearing temperature. The temperature measurement methods of high-speed rotating bearings mainly include thermocouple temperature measurement method, infrared radiation temperature measurement method, fiber grating sensor temperature measurement method, and LC electronic oscillation temperature measurement method.
1 Thermocouple temperature measurement
Thermocouple temperature measurement method is a contact temperature measurement method that uses the principle of thermoelectric effect to convert temperature signals into thermoelectromotive force signals. Thermocouple has the advantages of simple structure, high temperature measurement accuracy, convenient remote measurement and control, and low price. It is a widely used temperature measurement method in the field of bearing temperature measurement. However, the thermocouple temperature measurement method belongs to the point temperature measurement method, which cannot reflect the change of the regional temperature distribution, and has certain limitations.
RADIL et al.” conducted a study on the internal temperature distribution of radial air bearings.
experimental research. By arranging 9 K-type heat numbers in the center and edge of the bearing, it is often chosen as a functional couple for observing the condition monitoring of high-speed rotating bearings, local temperature parameters of the bearing under different rotational speeds and load conditions. Measurements were made to estimate axial and circumferential temperature gradients. Both rotational speed and radial load are important factors that affect the temperature increase caused by bearing frictional heat, and the influence of rotational speed is more obvious.
CLAVATSIII121 has studied a method for monitoring the temperature of the bearing oil film, using thermocouples to measure the temperature of the back of the bearing bushing and the bushing,
As shown in Figure 1. After A/D conversion, the measured temperature is displayed by the relevant data acquisition and analysis software, so as to realize the real-time monitoring of the thrust sliding bearing.
Figure 1 Installation of thermocouples
Figure 2 Connection of thermocouples on bearings
AIIMAD et al. used 12 thermocouples to measure the influence of the oil supply position of the oil tank on the bearing temperature distribution under different radial loads and speeds. The results show that when the oil supply position of the oil tank is located in the convergence section near the minimum film thickness, the bearing temperature distribution There is a decreasing trend.
TARAWNEH et al. used K-type thermocouples to conduct 70 temperature test experiments on the bearing working process with inner and outer ring defects. The results show that bearings with considerable size defects cannot be detected when they are healthy and without defects, and the current detection methods that use bearings to monitor temperature status cannot be detected, and the current detection methods that use bearings to monitor temperature status are insufficient.
Based on a K-type thermocouple, CRISTEA et al. determined the circumferential and axial temperature distributions of the lubricating film in the bearing groove during the process of starting from a static state to a thermally stable operating state under low-load steady-state conditions. The bearing oil film pressure field builds up faster than the temperature field. In the region with the lowest oil film pressure, the pressure field builds up faster than the temperature field. In the region with the lowest oil film pressure, the performance was experimentally studied. 15 thermocouples were installed to measure the performance of bearing oil and an experimental study was carried out. Fifteen thermocouples were installed to measure the temperature distribution of the bearing oil film. The test results show that the cooling circuit used in the pad body has a great influence on the performance of the bearing. The use of water cooling device can greatly reduce the oil film temperature of the bearing, thereby greatly improving the efficiency and life of the bearing.
In order to measure the performance of the rocket engine turbopump bearing under the use of gas coolant, KAKUD0 et al. used thermocouples to test the bearing temperature under different bearing speed, thrust load, and coolant flow conditions. Bearing temperature increases rapidly with increasing rotational speed and thrust load. Under higher flow conditions, bearing temperatures remain low.
2 Infrared radiation thermometry
Infrared radiation thermometry is based on the fact that all objects with a temperature higher than thermodynamic zero have the characteristics of radiating energy outward in the form of electromagnetic waves. Based on the temperature effect of infrared light, the infrared light is converted into a digital signal using Planck’s distribution law. Way. The infrared radiation temperature measurement method is safe, fast, reliable and convenient, and belongs to the non-contact temperature measurement method, which can obtain the dynamic change characteristics of the bearing temperature during the operation of the bearing.
Based on the infrared radiation temperature measurement technology, YUSIIA et al. proposed and designed an experimental bench for measuring the surface temperature of the rotating shaft during the friction heating of non-lubricated bearings. The bearing temperature measurement error did not exceed 2.6%.
“Wang et al.” used an infrared thermal imager to measure the inner surface temperature of the bushing of transparent bearings, and studied the effect of rotational speed and axial position on the inner surface temperature of the bushing. The results showed that the inner surface temperature of the bushing and the dynamic pressure of the screw oil wedge The temperature rise of the bearing increases with the increase of the rotational speed. The temperature around the oil return hole is higher. The higher the rotational speed, the higher the maximum temperature and temperature rise of the inner surface of the bushing.
According to the slot position and slot size of the bearing, CIHEN et al. integrated the infrared temperature sensor and vibration signal sensor into the bearing body, which can meet the requirements of miniaturization and low power consumption, as shown in Figure 3. The sensor module is bonded with epoxy resin On the monitoring bearing, the probe of the infrared temperature measuring sensor is aimed at the inner ring of the bearing to measure the temperature of the inner ring of the bearing, so as to realize the real-time intelligent monitoring of the running state of the bearing.
Figure 3 Integration of bearings and sensors
3 Fiber Bragg Grating Sensor Thermometry
The fiber grating sensor temperature measurement method uses the photosensitive characteristics of the fiber material to make the refractive index of the fiber become permanent periodic or aperiodic along the axial direction. It has small size, light weight, no electromagnetic interference, high sensitivity, corrosion resistance, long transmission distance, etc. Features.
DREYER et al. “give a fiber Bragg grating temperature sensor for quasi-distributed temperature measurement of hydro-generator bearings in hydropower plants. Compared with the P100 platinum thermistor sensor, the fiber Bragg grating sensor is used in calibration experiments. The maximum error of temperature measurement in the 12-h test of the device is 1.0C, which is more in line with the requirements of the temperature monitoring of the hydro-generator bearing.
LIU et al. used a quasi-distributed fiber Bragg grating sensor to experimentally measure the steady-state and transient temperature distribution of the thrust sliding bearing bush. The experimental results show that the fiber Bragg grating temperature sensor has good accuracy and stability in measuring the temperature distribution of the bearing bush. Compared with the thermocouple temperature measurement results, the temperature measurement error of the fiber Bragg grating sensor is less than 2C.
According to the structural characteristics of the double-row tapered roller bearing, ZIIOU et al.4 arranged 15 fiber Bragg grating sensors in the circumferential, axial and radial directions of the bearing, as shown in Figure 4, to achieve multi-point temperature detection in the inner and outer rings of the bearing. real-time measurement. The circumferential, axial and radial temperature differences of the bearing are affected by its rotational speed and external load. The impact of the rotational speed on the bearing temperature rise is more than that of the external load, and the impact of the rotational speed on the bearing temperature rise is more obvious than that of the external load. . The average temperature of the inner ring of the bearing is higher than that of the outer ring. For heavy-duty or high-speed bearings, it is necessary to pay attention to the circumferential temperature of the fixed bearing rings.
LIU proposed a multi-point quasi-distributed sensing method based on embedded fiber Bragg grating sensors, and measured the temperature field of the bearing outer ring under three different working conditions: idling, axial uploading and radial cutting force. The experimental results show that the temperature measurement error between the fiber grating and the thermocouple is within 10%. This quasi-distributed sensing method can be well applied to the measurement of the temperature field distribution of the spindle bearing.
4 LC electronic oscillation thermometry
The LC electronic oscillation temperature measurement method is a temperature measurement method that converts the measured temperature into the resonant frequency of the LC resonant circuit through the LC sensor composed of all passive components and temperature-sensitive materials. This temperature measurement method no longer relies on various line signals, and can be applied to bearing temperature measurement in complex and harsh working environments.
NICKEL et al. “Use frequency modulation of an LC electronic oscillator to measure the roller temperature in tapered roller bearings. The study confirmed that the temperature reached by the bearing element is more sensitive to the bearing operating conditions than the housing temperature. JIOSII et al.” On this basis , Developed two temperature telemeters for bearing temperature measurement, namely battery-powered and remote-powered, and demonstrated their effectiveness as bearing condition monitoring instruments. Experiments show that cage temperature responds very quickly to tribological changes. Cage temperature is a good monitoring parameter for determining the temperature state of rolling bearings.
IIENAO et al. 19-01 presented a batteryless wireless sensing technology based on Colpitts oscillator for monitoring the temperature of the bearing cage. The installation of the sensor is shown in Figure 5. A small antenna is attached to the output of the oscillator, and the radiated electromagnetic signal is detected by a nearby receiver. The temperature measurement circuit has the characteristics of small size, low power consumption, wide dynamic range and low cost.
Figure 5 Installation of temperature sensor on ball bearing
DRANEY2 presents a bearing temperature sensor based on LC electronic oscillation sensing method, which has the characteristics of miniaturization, low power consumption, and can withstand higher temperature. Capable of operating at temperatures as high as 300C, it can be used for monitoring to determine bearing health in harsh environments such as turbine engines.
“SIHIIDI et al.” proposed a wireless temperature sensor based on LC oscillator circuit for multi-point temperature health monitoring of bearing cages. Using a passive dual-sensor design, as shown in Figure 6, each sensor can be calibrated to 90C. This sensor concept can be extended to include more than two LC oscillating circuits, enabling more local temperature detection. On this basis, IHIIDI et al. called the development-a wireless temperature and vibration sensor for real-time monitoring of bearing conditions, able to utilize inductive coupling simultaneously
Measure temperature and vibration characteristics of bearing cages. The measurement of bearing cage temperature from 209C to 90C was achieved from 1280 r/min to 3 250 r/min.
Figure 6 Installation of the LC temperature sensor on the bearing
In addition, CUPTA et al.2 proposed a wireless temperature sensor for bearing condition monitoring. The sensor is a combination of a ring-shaped permanent samarium cobalt magnet and a Hall-effect sensor that detects the temperature of the bearing due to changes in the magnetic field caused by temperature changes. The installation position of the sensor on the bearing is shown in the figure
7 is shown. At a speed of 1 500 r/min and a load of 100 to 150 pounds
dynamic testing. The magnet temperature sensor is rated for operating temperature
The temperature can reach 150C, and the expected service life is more than 10 000 h.
Figure 7 Mounting of Magnetic Field and Hall Effect Sensors on Bearings
(1) The thermocouple temperature measurement method is relatively mature, the structure is simple, and the temperature measurement accuracy is
High, convenient for remote measurement and control, low price, and should be used in the field of bearing temperature measurement.
widely used. But thermal: The temperature measurement of the galvanic couple can only reflect the temperature of the monitoring point, not the temperature of the monitoring point.
The regional temperature distribution of the bearing is studied, and the dynamic temperature measurement of the thermocouple
The measurement accuracy is not high.
(2) Infrared radiation thermometry, as a non-contact temperature measurement method, can
Reflect the temperature distribution of the bearing, and can monitor the dynamic characteristics. but infrared
Radiation thermometry is susceptible to interference from ambient background radiation, resulting in temperature measurement.
The measurement accuracy is not high, and the bearing infrared temperature measurement results need to be compensated
(3) The fiber grating sensor temperature measurement method, as a temperature measurement method of passive sensitive components, has the advantages of small size, light weight, large measurement range, and high sensitivity. In the harsh environment of high temperature and high rotation speed, the bearing temperature is expensive. , The reliability of bearing temperature measurement in harsh environments with high temperature and high rotational speed needs to be further verified.
(4) (4 LC electronic oscillation temperature measurement method is based on the characteristics of passive devices, and can be applied to the measurement of bearing temperature in harsh working environments, but further breakthroughs are needed for the accurate measurement of bearing temperature in the environment of ultra-high rotation speed.
(5) The development of accurate measurement technology for bearing temperature under ultra-high-speed rotation conditions such as aero-engines will be one of the key research directions in the field of bearing temperature measurement. One of the research directions of the recent breakthrough in CdTe quantum dots temperature transfer. The recent CdTe quantum dot temperature sensor is theoretically not limited by the bearing speed, and has been successfully applied to the temperature monitoring of the bearing under the ultra-high rotation speed of 15000 r/min. Has good development potential.