Gearbox Efficiency Research Articles

CFD analysis on the oil flow of a gear stage with guide plate

Gearbox housing geometry and oil guide plates strongly influence gearbox oil flow and interaction of oil with machine elements. Guided oil flow can increase gearbox efficiency and improve heat management. Recent research studies have demonstrated the potential of Computational Fluid Dynamics (CFD) simulations to predict the gearbox oil flow and no-load losses. Thereby, the influence of housing geometry and guide plates has rarely been addressed. This study focuses on a CFD analysis on the oil flow of a dip lubricated spur gear stage with a guide plate. Grid-based CFD models with different simulation setups were confronted and evaluated. Results show that the selection of the simulation setup with respect to the acceleration ramp and mesh size needs to address the considered object of investigation and the desired depth of information. An appropriate simulation setup shows great accordance with recordings of the oil distribution by a high-speed camera. A detailed analysis of the simulation results identified the contribution of different gear surface zones to the no-load gear loss torque. For the considered guide plate a strong interaction of oil flow and loss torque due to pressure forces on the tooth flank surface zones and due to shear forces on the front and tip circle surface zones of the gears was determined.

End-to-end efficiency quantification of an autonomous underwater vehicle propulsion system

Increasing demand for versatile and long-endurance autonomous underwater vehicles puts significant design pressure on all aspects of AUV design and operation, including that of the propulsive system. The present study discusses testing of a thruster unit and several propellers developed to propel a hybrid glider/flight-style underwater vehicle. Due to the AUV being required to operate at largely different speeds and thrust levels between the two configurations, the propulsive subsystem needs to be capable of remaining efficient and effective across a wide range of operating conditions. Thus, the current results focus on quantifying all of the factors affecting the drive train, ranging from open-water performance of the propeller up to electro-mechanical efficiency of the magnetic coupling and geared electric motor. It is shown that, depending on the required operating point, total efficiency of the vehicle is primarily affected by non-linear low Reynolds number effects, sudden drop of gearbox efficiency at low revolutions and applied torques, as well as blade deformation, aside of the baseline propeller efficiency.

Estimation of the Performance Aging of the Vestas V52 Wind Turbine through Comparative Test Case Analysis

It is a common sense expectation that the efficiency of wind turbines should decline with age, similarly to what happens with most technical systems. Due to the complexity of this kind of machine and the environmental conditions to which it is subjected, it is far from obvious how to reliably estimate the impact of aging. In this work, the aging of five Vestas V52 wind turbines is analyzed. The test cases belong to two different sites: one is at the Dundalk Institute of Technology in Ireland, and four are sited in an industrial wind farm in a mountainous area in Italy. Innovative data analysis techniques are employed: the general idea consists of considering appropriate operation curves depending on the working control region of the wind turbines. When the wind turbine operates at fixed pitch and variable rotational speed, the generator speed-power curve is studied; for higher wind speed, when the rotational speed has saturated and the blade pitch is variable, the blade pitch-power curve is considered. The operation curves of interest are studied through the binning method and through a support vector regression with a Gaussian kernel. The wind turbine test cases are analyzed vertically (each in its own history) and horizontally, by comparing the behavior at the two sites for the given wind turbine age. The main result of this study is that an evident effect of aging is the worsening of generator efficiency: progressively, less power is extracted for the given generator rotational speed. Nevertheless, this effect is observed to be lower for the wind turbines in Italy (order of −1.5% at 12 years of age with respect to seven years of age) with respect to the Dundalk wind turbine, which shows a sharp decline at 12 years of age (−8.8%). One wind turbine sited in Italy underwent a generator replacement in 2018: through the use of the same kind of data analysis methods, it was possible to observe that an average performance recovery of the order of 2% occurs after the component replacement. It also arises that for all the test cases, a slight aging effect is visible for higher wind speed, which can likely be interpreted as due to declining gearbox efficiency. In general, it is confirmed that the aging of wind turbines is strongly dependent on the history of each machine, and it is likely confirmed that the technology development mitigates the effect of aging.

Enhanced efficiency prediction of an electrified off-highway vehicle transmission utilizing machine learning methods

The increasingly noticeable effects of climate change require action to reduce greenhouse gas emissions. In the transport sector, the increase in electromobility is an important tool for reducing CO2 emissions. In order to meet the essential requirements, a particularly detailed system knowledge, for example on energy efficiency in the powertrain, is needed for the development and improvement of electric vehicles.The present work contributes to this by mapping the efficiency of a planetary gearbox for an electric vehicle. The mapping is done by experimental modelling with machine learning methods based on a standard efficiency description. The data necessary for the neural network training is generated by efficiency experiments on the powertrain test rig. For suitable results the data was pre-processed by applying relevant low-pass filters. A comparison of the Bayesian-Regularization algorithm, the Levenberg-Marquardt algorithm and the scaled-conjugate-gradient algorithm for training exhibited the strengths and weaknesses of the individual algorithms for the efficiency mapping. By comparing each algorithms performance metrics, the one matching the requirements best is chosen for the efficiency mapping.The result is a continuous function that determines the efficiency based on speed- and torque-inputs. Based on a key performance indicator, statistical validation by evaluating the standard deviations is used to ensure the quality of the results. In this paper the suitable algorithm for the given use case was determined. It can be applied for further research due to the significant results shown.

Thermal Modeling of the FZG Test Rig: Application to Starved Lubrication Conditions

During their lifetime, gears may undergo starved lubrication operating conditions. Starvation has an impact on friction between gears and leads to modified gearbox efficiency. In this article, lubricant starvation tests on an FZG test rig adapted to this condition are presented. Gears were equipped with an embedded thermocouple sensor to measure their operating bulk temperature. An experimental method to isolate the test box power loss of the FZG machine is proposed. A thermal model of this test rig draws up the power loss distribution into the test box for a nominal condition of lubrication. A numerical method based on experimental results is proposed to estimate gear power loss variation during lubricant starvation.

Bilateral Drive Gear—A Highly Backdrivable Reduction Gearbox for Robotic Actuators

For safety purposes, cooperative robots are installed with an actuator composed of a low-power servo motor, a reduction gearbox, and a torque sensor. When cooperative robots make contact with humans or the environment, they must detect the contact force with a force sensor, a contact sensor, or a joint torque sensor. Equipping these sensors increases the cost and size of the application, but can be avoided under sufficient backdrivability of the actuator. To this end, we propose a method that maximizes the power transmission efficiency of the 3K planetary reduction gearbox and develop a prototype of the backdrivable reduction gearbox called the bilateral drive gear. For this maximization, the profile shift coefficients and the number of teeth are decided under some conditions. The forward- and backward-driving efficiencies of the prototype gearbox were 89.0% and 85.3%, respectively, and the reverse-drive starting torque was 0.020 N $\cdot$ m. The drive efficiency of the same gearbox with uncorrected teeth is 68.5%. The forward-driving efficiency was 20.5% higher than the nonoptimized one. We confirmed that prototype gearboxes with different gear ratios are easily backdrivable by hand.

Investigation on Influence of Circumferential Velocity and Lubrication Oil Grades on Scuffing and Thermal Efficiency of Gearbox

Lubrication oil grades plays major role in reducing the friction to prevent scuffing in gears. Gears transmit power through rolling/sliding contacts between teeth, which must operate reliably for designed life with reduced friction so that there will be minimum wear. Lubrication of tooth contacts, both as a means of minimizing scuffing and as a means of reducing friction due to sliding, is therefore of crucial importance. The circumferential velocity of high speed gearboxes and oil grades plays major role in thermal efficiency of gearboxes. In gearboxes with oil sumps, churning losses contribute for significant portion of the total power loss. Present empirical approaches for examining the churning losses are often limited to certain constraints and operating conditions. Furthermore, they do not provide any information about the oil distribution in the gearbox. In order to overcome these shortcomings, we investigated a steel mill gearbox failure with analytical tools and simulations with the help of renowned software packages and predicted the thermal behavior of the gearbox as function of oil grade and circumferential velocity, also validated later at application.

Determination of Optimum Working Parameters for Multiple Response Characteristics of Worm Gear Box

The reason for this task is to optimize the multiple response of single start worm gear using three working parameters to improve its performance. As the input torque and lubricant heating time are the most effective responses of worm gear box to reduce the no-load dependent losses, they are taken as the response parameters in this research. Taguchi Grey Relational Analysis (GRA) is the method used to determine the influence of type of lubricant, volume of lubricant and speed of worm gear on multiple responses (input torque & lubricant heating time) of worm gear. The specific test rig is developed based on direct torque measurement technique to measure the input torque and lubricant heating time of worm gear box. Experimental results have shown that the input torque and lubricant heating time can be improved effectively through Taguchi-Grey Relational Analysis. The result is validated using the Confirmation Test. ANOVA determines the important of parameters. It has been found that the type of lubricant and speed of worm gear are influential parameters for worm gear performance. By selecting these parameters, efficiency of the worm gearbox can be increased.

Effect of bearing thermally induced preload on the efficiency of automotive manual transmission under RDE

In order to calculate the efficiency of an automotive manual transmission, taking into consideration the effect of its most power consuming components – gears and bearings – as well as the interactions between them is of high importance. In this paper, a dynamic model has been developed which can predict the frictional losses of a complete gearbox as a system and, thus, its efficiency. The effect of temperature on bearing preload is also considered and taken into account from a system perspective identifying its effect on the bearings frictional losses (as well as the overall efficiency). The operating conditions used are snapshots of the Real Driving Emissions driving cycle, which is a standard metric for automotive manufacturers. Results show that doubling the temperature can lead to 120% increase of the bearing losses and up to 140% increase of the total transmission losses. The effect of the variation of operating conditions (velocity and torque) is also taken into account. The novelty of this paper lays in the development of a dynamic model which takes into account the performance of a complete gearbox under transient operating conditions, as well as the interaction among its main components and the ability to make changes on the influencing factors of transmission efficiency so that their effect on the complete gearbox efficiency can be tracked. This has not been yet reported in the relevant literature which mainly focuses on the influencing factors of transmission power loss and efficiency experimental measurements under various operating conditions for gear pairs instead of complete gearboxes.

Efficiency of Worm Gear Drives Under Transient Operating Conditions

Abstract In oil-lubricated worm gears, all moving components cause power losses during operation. These losses depend, among other things, on the viscosity of the lubricant used, which in turn is determined by the temperature present in the gearbox. The dependency between the temperature and the power dissipation is mutual, and they influence each other. For the analysis of gearboxes under transient conditions, the relationship among operating conditions, power dissipation, and temperature must be considered. In this paper, a method for the analysis of these interrelationships is presented, which is based on the combination of tribological simulation and thermal networks. With the developed calculation model, the gearbox efficiency and the temperature over time can be estimated for arbitrary load cases. The calculation results are compared with measurements on a real gearbox.

Non-regulatory parameters effect on consumption and emissions from a diesel-powered van over the WLTC

The effect of various non-regulatory parameters on a vehicle’s performance and emissions is investigated in this study, i.e. road grade, presence of crosswinds, surface wetness, tire pressure and use of the vehicle’s auxiliary systems. The vehicle under study is a diesel-powered turbocharged light commercial vehicle, running on the WLTC 3–2 cycle; comparison with the NEDC is also provided. The results derive from a computational code based on an engine-mapping approach applying experimentally derived correction coefficients accounting for transient operation. The engine code is coupled to a vehicle model that calculates the main longitudinal dynamic parameters (tire rolling resistance, aerodynamic performance, gearbox efficiency) on a fundamental basis. Soot and nitrogen monoxide are the examined pollutants, with fuel and energy consumption and CO2 emissions computed and discussed too. From the parameters examined, road grade was found to have the greatest impact on emissions (CO2: +116.8%, NO: +107.2%, Soot: +100.7%, for the maximum road grade examined of 8%), followed by wind speed (CO2: +38.9%, NO: +33.6%, Soot: +12%, for the maximum wind speed examined of 80 km/h). Auxiliary power demand can have a considerable effect, mostly on fuel consumption/CO2 emissions (+13.7% for maximum auxiliary power demand of 5000 W); the impact of tire inflation pressure and surface wetness is comparably smaller. Among the two driving cycles, the WLTC proved to be more ‘sensitive’ to road load changes, due to the broader speed range encompassed and its highly transient nature, compared to the softer NEDC.

Fault diagnosis model of the variable torque pumping unit well based on the power-displacement diagram

This work proposes a new method of diagnosing the variable torque pumping unit well, by analysing the eigenvalue of power-displacement diagram. Considering the actual angular velocity, the unbalanced weight of structure and the efficiency of motor and gearbox, the relationship between the polished rod load and the input power of motor are derived by analysing the internal relation between the polished rod load, the output shaft torque of the gearbox, the output shaft power of motor and the input power of motor. Then, the conversion model of the power-displacement diagram based on the dynamometer card is derived. By transforming the dynamometer card in typical working condition into the corresponding power-displacement diagram, 11 power-displacement diagrams in typical working conditions are established. By extracting the grayscale statistical eigenvalues from typical power-displacement diagrams, a working condition diagnosis model of oil well is established based on the grey correlation analysis. The test of 5 wells in the oilfield shows the average relative error of average normalized power of up and down stroke between the measured power-displacement diagram and the calculated power-displacement diagram are 6.31% and 5.83%, and the average fitting coefficient is 0.91. This shows that this model has a good accuracy, and it also proves the reliability of the typical power-displacement diagram. According to the test of 80 wells in the oilfield, the accuracy of diagnosis results based on the measured power-displacement diagram is 93.3%. This shows that the model has high accuracy and practicability, and can provide technical support for intelligent diagnosis and production optimization decision in production system of variable torque pumping unit well.

The cycloidal gearbox efficiency for different types of bearings—Sleeves vs. needle bearings

A comparative study of a cycloidal gearbox working with a different kind of bearings is presented in the article. Two kinds of the bearings used in the cycloidal gearbox are taken into consideration: sleeves and needle bearings. The theoretical efficiency calculation for both types of the bearing was compared with experimental results. The experiment was performed on a one-stage cycloidal gearbox designed, calculated, and manufactured during the research. The test was made under different working conditions, input speeds, and the braking torques. The results show an increase in the efficiency for the needle bearings compared to sleeves. The value of the efficiency is strictly connected with the braking torque of the gearbox as well as with the velocity. The article shows a very good correlation between calculated efficiency and the efficiency determined during the tests.

Analysis of the efficiency of wind turbine gearboxes using the temperature variable

The aim of this paper is to evaluate how lubricant selection affects gearbox efficiency and overall energy production by analysing real data from wind farms, monitored and controlled by a Supervisory Control and Data Acquisition (SCADA system). The turbines analysed worked with two or more oil types for the same amount of hours, which allowed to establish relations between the active power curves and wind velocity; oil temperature inside gearboxes and wind velocity; and oil temperature inside gearboxes and active power production. The results of this study evidenced a direct relation between oil characteristics and energy efficiency i.e. gearboxes working with mineral oil perform better then gearboxes working with synthetic oils. Those differences can be significant in terms of active power production. Also, it was observed oil degradation as function of temperature increase, with changes on viscosity, which reveals that temperature behaviour along the active power curve is strongly related to oil’ characteristics.

Active control of planetary gearbox vibration using phase-exact and narrowband simultaneous equations adaptation without explicitly identified secondary path models

Abstract So far only model-based approaches have been proposed for active control of planetary gearbox vibration. However their performance depends strongly on the quality of the used models. To overcome this problem a novel algorithm which is based upon the narrowband simultaneous equations adaptation is proposed. It requires no offline identified secondary path model and belongs to the class of direct adaptive feedforward control algorithms. The investigation reveals that a phase-exact implementation in which an incremental encoder is used to generate synthetical reference signals is required. No feedback between algorithm output and reference measurement occurs. Performance and robustness of the proposed algorithm is compared to the common model-based FxLMS algorithm in simulation and experiment. It achieves comparable convergence speeds and vibration reductions. However in contrast to FxLMS it is able to compensate for changes in the secondary path. A test rig for small planetary gearboxes is presented. Internal forces caused by gear meshing can be measured. In one of the experiments 112 vibration orders are controlled with a mean reduction of 72%. The proposed active vibration control setup consumes 22 W of electric power and thereby degrades the planetary gearbox efficiency by only 0.2% for the experimentally examined operating point.

Torque loss in FZG-A10 gears lubricated with axle oils

Abstract FZG type A spur gears, lubricated with axle gear oils with high EP properties, were tested in an FZG back-to-back test rig, and their torque loss was measured for wide ranges of the input torque and speed. Several models of the load-independent and load-dependent losses of the gearbox components (gears, rolling bearings and seals), were combined into a global power loss model for the prediction of the gearbox efficiency. The average friction coefficient of the meshing gears was derived from the experimental results. A satisfactory correlation between experimental power loss measurements and the generated simulation results is observed under different operating conditions. Several aspects are discussed such as gear loss factor, friction coefficient and the influence of oil formulations.

A novel shift control concept for multi-speed electric vehicles

Abstract This paper proposes a novel synchronizer ‘Harpoon-Shift’ aiming at improving the comfort and efficiency of gearbox, meanwhile, simplifying the shifting control strategy for multi-speed electric vehicles. It will overcome one of the biggest shortcomings of traditional synchronizer system with frictional cone clutch. Experiment is established to investigate the torque and speed responses during the engagement of gears pairs. Then, based on previous testing results, the relationship of the peak torque and minimum speed difference to implement gear shifting with various spring coefficients is investigated. In addition, a mathematical model of the Harpoon-Shift system is developed to simulate the engagement process. The simulation results of system transient responses are validated against the data measured on testing rig. The model is then improved to study the impact of the rotating inertia, speed and speed difference on the torsional vibration and required time of engagement. Both of the simulation and experimental results show the significant improvement of proposed synchronizer to conventional cone clutch synchronizer.

Experimental study of electric vehicle gearbox efficiency

This paper presents an experimental analysis of the overall efficiency of the gearbox for an electric vehicle with a Dual Motor Drive System (DMDS) propulsion system. The efficiency was measured in the powertrain testbed where the gearbox was placed between two dynamometers. The main aim of the experiment was to get relevant values of an overall efficiency as a function of input speed and torque. All these measured values of the gearbox efficiency are included in graphs and efficiency maps. Tests were run with two different amounts of oil charge. The experiment confirmed the expected high values of the overall mechanical gearbox efficiency. The results can be used further for advanced simulations and other electric vehicle experiments.

Fault Tolerant Control of Internal Faults in Wind Turbine: Case Study of Gearbox Efficiency Decrease

This paper presents a method to control the rotor speed of wind turbines in presence of gearbox efficiency fault. This kind of faults happens due to lack of lubrication. It affects the dynamic of the principal shaft and thus the rotor speed. The principle of the fault tolerant control is to find a bloc that equalizes the dynamics of the healthy and faulty situations. The effectiveness decrease impacts on not only the dynamics but also the steady state value of the rotor speed. The last reason makes it mandatory to add an integral term on the steady state error to cancel the residual between the measured and operating point rotor speed. The convergence of the method is proven with respect to the rotor parameters and its effectiveness is evaluated through the rotor speed.

General modelling method of power losses in transmission with parameter identification

There is rarely a general or standard method to calculate the overall efficiency of a complete vehicle gearbox. This paper aims to develop such method which can possibly be applied to different types of transmissions in a flexible way and provide a platform to compare several different products from different OEMs or suppliers in parallel. A number of standards and publications concerning the calculation of power losses specifically for one transmission component such as gears, roller bearings or specific phenomenon like oil churning are available in the literature. Different models from these sources are compared, selected and combined to obtain the resulting efficiency map of a complete gearbox system. This paper presents the calculation of such a combined efficiency map of a transmission for an electric vehicle through either the standard models (ISO14179) for industry transmissions or this new joint overall model. The comparisons of available experimental data and calculations show that the result of the joint overall model has a better proximity to the test results. Nevertheless, the uncertainties in the input parameters of the model strongly affect the calculated power loss and the resulting efficiency of the gearbox. Parameter studies are conducted to determine the most influential parameters in the joint overall model. Several selected parameters are identified through experimental overall efficiency maps by classic parameter identification method and algorithm. On the one hand, a much better proximity is achieved. On the other hand, the identified parameters indicate the optimization potential of the component losses for benchmarking of transmissions.