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This study was conducted to evaluate the effect of surface finish on spur gear power losses under jet lubrication. Four different surface finish combinations were tested: (i) hard ground surface pair, (ii) chemically polished surface pair, (iii) super honed surface pair and (iv) hard ground against chemically polished surface pair. The test was conducted at 432 different operating condition combinations of speed, torque, lubricant type and inlet temperature. An FZG back-to-back set up was used to conduct the test. Surface roughness inspections were carried out at regular intervals to monitor any changes in surface roughness characteristics. The measured power losses were resolved into spin (load independent) and mechanical (load dependent) power losses. The relation between both losses and various operating conditions were explored. As expected, spin power loss did not vary with variation in surface finish. Mechanical power loss increased with increase in speed and torque. Various surface roughness and operating parameters such as BAC curves and lambda ratio were calculated for each surface finish combination to study their correlation to power losses measured. For smoother surfaces, an increase in temperature decreased power loss as the viscosity of the lubricant decreased and hence rolling friction losses dominating the mechanical power loss decreased. However, for rougher surfaces sliding friction losses seemed to be dominant due to high amounts of asperity contact. Thus, more cases of higher power loss at high temperatures were observed for rougher surfaces.
Abstract: Gear and transmission efficiency is one of the major issues in the automotive and aerospace industries. Both fuel economy and emission characteristics of vehicles are influenced by the efficiency of the drive trains and transmissions. The literature on gear efficiency is limited to few models. Accuracy of these models was not demonstrated, mainly due to the lack of experimental data, especially under high-speed conditions. Recent experiments by Chase [1] and Petry-Johnson [2] provided an extensive set of experimental data on efficiency for unity-ratio, precision spur gears operating at high- power conditions, representing racing applications. This experimental database was instrumental in validating the efficiency model of Xu, et al [3] for spur gears. This study presents experiments with the aim of extending this jet-lubricated spur gear efficiency database to non-unity ratio, production quality gear pairs having various surface treatments and operating with different lubricants under typical passenger vehicle conditions. As a separate study, it also provides a complete spin loss database for unity-ratio gears operating under dip-lubricated conditions. Direct comparisons between the two lubrication methods are also presented. Lastly, details of a design study for development of a test machine for efficiency measurements for helical gears is presented.
Abstract: An experimental investigation of high-speed spur gear efficiency was conducted for both jet-lubricated, dry sump conditions and dip-lubricated conditions. Inspection methodologies were developed for the documentation of gear surface roughness and wear after each test. An experimental test matrix including gears of two different modules and surface roughness levels operating under jet-lubrication conditions with four different gear lubricants was developed to quantify the influence of these parameters on load- dependent (mechanical) and load-independent (spin) power losses. The spur gear efficiency test machine was modified for dip-lubricated load independent power loss measurements, allowing direct comparison to jet-lubricated conditions using the same test fixtures. An experimental test matrix including unity ratio gears of different module and face width operating in an oil bath of four different levels for a range of rotational speed and oil viscosity was developed. The influence of rotational speed, oil viscosity, oil bath level, and rotational direction on load independent power loss was quantified.
Abstract: In this study, the influence of various engineered surface treatments on the contact fatigue behavior of spur gear pairs was investigated, focusing on pitting life. A number of standard gear durability test machines were furbished and sets of specially designed spur gear test specimens were procured to execute a test matrix that includes gears having various surface treatments. Typical hobbed-shaved surfaces were considered to represent the baseline surface treatment and their pitting lives were compared to lives of gears having (i) chemically polished, (ii) shot-peened and plastic honed, and (iii) chemically polished and CrN coated surfaces. Pitting life of each variation was quantified at several stress levels by using a set of predetermined failure criteria, and test and inspection procedures. The data for each variation was processed statistically and compared to data from other surface variations. The results indicate that chemically polishing increases the pitting life of spur gears nearly three times over the life of the baseline hobbed-shaved gears. It was also observed that the shot-peened and plastic honed gears did not deliver any tangible pitting life improvements over the baseline conditions. Finally, a slight increase in pitting life was observed over chemically polished gears with the application of the CrN coating.
This work describes an experimental investigation with the aim to evaluate and establish wire spark erosion machining (WSEM) as a viable alternative for high quality miniature gear manufacturing. External spur type miniature brass (ASTM 858) gears with 12 teeth, 9.8 mm outside diameter and 5 mm face width were manufactured by WSEM. The research work was accomplished in four distinct experimental stages viz., preliminary, pilot, main and confirmation. The aim, scope and findings of each stage are progressively presented and discussed. In essence, the investigation found that it was possible to manufacture miniature gears to high quality by using WSEM. Gears up to DIN 5 quality with a good surface finish (1.2 μm average roughness) and satisfactory surface integrity were achieved. The results suggest that WSEM should be considered a viable alternative to conventional miniature gear manufacturing techniques and that in some instances it may even be superior. This work will prove useful to researchers and professionals in the field of miniature and micro-scale manufacturing and machining.
An experimental investigation of spur gear efficiency is conducted under various jet-lubricated and dip-lubricated conditions. A test methodology is developed to measure load-independent (spin) and load-dependent (mechanical) losses to a gearbox containing a single spur gear pair. An experimental test matrix is defined to study the influence that the lubrication method has on these losses. The test matrix includes two dip-lubricated conditions that vary in submersion level of the gear pair, and four jet-lubricated conditions that vary in the gear mesh target location and velocity of the oil. Results indicate that the spin power losses are impacted by the lubrication method significantly while the mechanical losses are not influenced. An investigation of spur gear contact fatigue is conducted under several lubrication schemes from the efficiency study. A test methodology is developed to evaluate variations in tooth geometry due to surface wear, roughness, and pitting life. Pitting lives under each lubrication method are analyzed statistically to quantify any meaningful differences in gear pitting life. Results indicate that contact fatigue lives from jet-lubricated tests are as high as dip-lubricated ones as long as jet velocities are sufficient.
Noise and vibration performance of a gear system is critical in any industry. Vibrations caused by the excitations at the gear meshes propagate to the transmission housing to cause noise, while also increasing gear tooth stresses to degrade durability. As such, gear engineers must seek gear designs that are nominally quiet with low vibration amplitudes. tudes. They must also ensure that this nominal performance is robust in the presence of various manufacturing errors. This thesis research aims at an experimental investigation of the influence of one type of manufacturing error, namely random tooth spacing errors, on the vibratory responses of spur and helical gear pairs. For this purpose, families of spur and helical gear test specimens having intentionally induced, tightly controlled random spacing error sequences are fabricated. These specimens are paired and assembled in various ways to achieve different sequences of composite spacing errors. Static and dynamic motion transmission error measurements from these tests are compared to the baseline case of “no error” gear to quantify the impact of random spacing errors on the dynamic response. These comparisons show that there is a significant, quantifiable impact of random spacing errors on both spur and helical gear dynamics. In general, vibration amplitudes of gear pairs having random spacing errors are higher than those of the corresponding no-error gear pairs. In the frequency domain, gears having random spacing errors exhibit broad-band spectra with significant non-mesh harmonics, pointing to potential noise quality issues.
Abstract: In this study, an experimental investigation is performed to investigate the impact of various gear errors on transmission error and root fillet stresses. A test set-up is devised to operate a pair of spur gears under loaded, low-speed conditions. Two measurement systems; one an optical encoder-based transmission error measurement system and the other a multi-channel strain measurement system, are developed and implemented with the test set-up. A set of test gears having various types and tightly-controlled magnitudes of manufacturing errors are designed and procured. These errors include indexing errors of different tooth sequences, pitch line run-out errors and lead wobble errors. An extensive test matrix is executed to quantify the impact of these errors on the loaded static transmission error and the root stresses of the spur gears. At the end, the same test conditions are simulated by using a recent feature of gear analysis model (LDP) to assess the accuracy of its predictions.
This paper complements recent investigations [Handschuh et al. (2014), Talbot et al. (2016)] of the influences of tooth indexing errors on dynamic factors of spur gears by presenting data on changes to the dynamic transmission error. An experimental study is performed using an accelerometer-based dynamic transmission error measurement system incorporated into a high-speed gear tester to establish baseline dynamic behavior of gears having negligible indexing errors, and to characterize changes to this baseline due to application of tightly-controlled intentional indexing errors. Spur gears having different forms of indexing errors are paired with a gear having negligible indexing error. Dynamic transmission error of gear pairs under these error conditions is measured and examined in both time and frequency domains to quantify the transient effects induced by these indexing errors. These measurements are then compared against the baseline, no error condition, as a means to quantify the dynamic vibratory behavior induced due to the tooth indexing errors. These comparisons between measurements indicate clearly that the baseline dynamic response, dominated by well-defined resonance peaks and mesh harmonics, are complemented by non-mesh orders of transmission error due the transient behavior induced by indexing errors. In addition, the tooth (or teeth) having indexing error imparts transient effects which dominate the vibratory response of the system for significantly more mesh cycles than the teeth having errors are in contact. For this reason, along with the results presented in Talbot et al. (2016), it was concluded that spur gears containing indexing errors exhibit significant deviations from nominal behavior, at both a system and time-domain level.