Planetary Gear Unit Research Articles

The model and design of a Spring-Embedded Planetary Dual-Motor Actuator to reduce energy losses

The electrification of many mobile applications such as wearable robots has led to the need for carrying batteries to store electrical energy. However, low-efficient actuators require larger batteries that have to be carried along, which limits the range and performance of such devices. In addition, collaborating with robots require safe cobots and actuators. To address this challenge, parallel and series elastic actuators have been adopted in many applications to increase safety and energy efficiency. Meanwhile, some industries, including the automotive industry, have put much research effort into dual motor actuation to decrease the energy consumption of the overall drivetrain.In this paper, we introduce a Spring-Embedded Planetary Dual-Motor Actuator (SEP-DMA) which combines both technologies using a planetary gear unit and a spring. We derive and validate a dynamic model for all possible configurations and discuss their operating modes, including active and passive actuation. To demonstrate the potential of the actuator, we compare it with a traditional stiff actuator consisting of a gearbox and electric motor. The former shows a 40% decrease in the overall energy consumption for a standard task of lifting and oscillating a mass.

Simulation Study on the Tribological Characteristics in the Meshing Contact in the Context of the Load Carrying Capacity Calculation of Internal Gears with Unbalanced Sliding Conditions

Planetary gearboxes are characterized by a high power density and a compact design with coaxial in- and output. Consequently, planetary gear units are frequently used in many practical applications, e.g. in wind energy and industrial transmission systems as well as in automotive applications such as automatic transmissions. As a result of the scaling-up of the required system power, the risk of flank damages increased during the last decade. Certain damage types, such as pitting and micropitting, occur predominantly in contact areas of negative specific sliding on the tooth flank surface. Unlike external gears, internal gears offer the possibility of positioning the pitch point C outside of the active profile. Depending on the gear design, this allows a complete avoidance of negative specific sliding either on the planet or on the ring gear. In contrast, the corresponding gear is subjected to negative specific sliding only. It can be assumed that the lifetime regarding flank damages of each meshing partner can be affected by different positions of the pitch point and the resulting differences in the specific sliding, which allows an optimization of the full gear system, taking into account e.g. the load carrying capacity reserves for different material pairings. It is to be noted that such gear designs are already part of some practical applications.However, the existing analytical approaches within standardized load carrying capacity calculation methods are typically based on investigations considering external gears with balanced sliding conditions. Systematic results on internal gear designs with pitch point positioned outside of the active profile are not available.Within this paper, extended theoretical studies on the tribological characteristics of different internal gear designs are presented. Therefore, a reference geometry with balanced sliding conditions is compared to internal gears with pitch point below respectively above the active profile. The focus of the studies is the analysis of the lubricant film thickness and the contact temperature in the meshing contact. Referring to this, a high-order TEHL contact simulation model was used. The results of the numerical analysis with the FZG calculation software TriboMesh are compared to different analytical approaches in the context of the calculation of load carrying capacity to derive recommendations for the design of internal gears.

Analyzing the Internal Part Condition on the Planetary Gear unit with Conditioning Monitoring Method at Cement Factory Horizontal Milling Station

Predictive maintenance is currently preferred over reactive maintenance because it’s very effective in reducing the costs incurred for unplanned breakdown stalling of a machine or equipment while production is running. In a production process at a Cement factory, the Milling station process is very important and becomes the main process. So, if something goes wrong in this process, the production line can be stopped, and the losses due to this are very big. Condition monitoring is a significant part of predictive maintenance because the application of condition monitoring allows the scheduled maintenance and precautions to be taken to prevent further failures and possible unplanned downtimes at a later date. By measuring the value of the vibration level, we can know whether the bearings and gear teeth on the machine are suitable for use or not. Based on this analysis, we can conclude that there is no sign of defect both on bearing in each gear teeth and the gear teeth inside the gearbox.

Power-Flow and Mechanical Efficiency Computation in Two-Degrees-of-Freedom Planetary Gear Units: New Compact Formulas

The mechanical efficiency is a computed value for comparing the performance of the multi degrees-of-freedom geared transmissions of hybrid vehicles. Most of the current methods for estimating gear trains mechanical efficiency require the decomposition of gear transmissions in basic structural elements or planetary gear units (PGU). These are two degrees-of-freedom components whose mechanical efficiency has a deep influence on the overall device. The authors (E.L.E., E.P.) already evidenced that, under certain kinematic conditions, the classic Radzimovsky’s formulas, widely accepted for computing the mechanical efficiency of PGUs, are not adequate. In this paper, more general and reliable formulas for computing the mechanical efficiency are deduced. The proposed formulas herein, exploiting the concept of potential or virtual power, evidence the dependency between kinematics and efficiency. A numerical example compares our results with previous work on the subject.

Design and Manufacturing Strategy of a Back-to-Back Test Rig for Investigation of Ultra High Cycle Fatigue Strength Regarding Tooth Root Strength in Aerospace Applications

Geared turbofans increase the efficiency of aircraft engines. By decoupling the fan and low- ressure turbine, both components can be operated at their optimum speed. Due to the high number of flight hours and the high turbine speeds of n > 10,000 rpm, the number of load cycles at the gear teeth of the planetary gear unit is significantly higher than the conventional fatigue strength of gear teeth. The planetary gears under fully reversed bending load are particularly susceptible to tooth root fractures. Pulsator test rigs are not suitable for testing tooth root load capacity under fully reversed bending load. The concept of a modified 3-shaft backto-back test rig was set up to cope with this challenge. A back-to-back test rig consists of a test and reference gearbox, which are connected by shafts to form a closed power circuit. In order to perform the investigation efficiently, the test rig is operated at a speed of n > 12,000 rpm with a recirculating power of P > 5 MW. This performance class results in special requirements for the test rig design. The roller bearing arrangements normally used for back-to-back test rigs no longer offer sufficient load carrying capacity, so that a changeover to journal bearings is necessary. This leads to high power losses of the bearings of P ≈ 200 kW and oil quantities of Q ≈ 450 l/min on the cooling and bearing lubrication side. The journal bearings of the gearboxes have a decisive disadvantage. Starting under load is not possible. Therefore, a hydraulic load unit was designed which allows load application at operating speed. In the reference gearbox, this unit shifts two helical gears on a spline shaft, which are slanted in opposite directions, towards each other, so that a torsional load is generated in the test gearbox by means of a closed power circuit. The two displaceable helical gears represent the greatest challenge from a manufacturing point of view. In order to achieve an even load distribution on both gears, they must be manufactured very precisely to each other and to the spline profile. In the report, the focus is set on the double helical reference gearbox including the axial load unit. Besides the design of the components the requirements regarding manufacturing are analysed and possible manufacturing chains are discussed.

Condition monitoring indicators for pitting detection in planetary gear units

Condition monitoring indicators for pitting detection in planetary gear units

Dynamical model of HEV with two planetary gear units and its application to optimization of energy consumption

A hybrid electric vehicle (HEV) that uses multiple planetary gear units with clutches as transmission system is advanced for the powertrain performance, because the operation of the clutches can lead to distinct operating modes, and the induced possible operating modes provide additional freedom to deal with the energy optimal control problem. Under each operating mode, the powertrain mechanical system has specific dynamical behavior. In order to develop model-based optimization schemes that can tackle the transient operations of the vehicle, exact dynamical modeling is investigated focusing on a hybrid powertrain system that uses a two-planetary-gear transmission box with two clutches. It shows that according to the states of the two clutches, the powertrain system has the power-split mode, parallel mode and the electric vehicle (EV) mode. Finally, an analysis for the calculation of the desired driving torque and its application to the dynamic programming (DP)-based energy management indicate the significance of the developed exact dynamical models.

The development of realia for the planetary gear unit to improve students’ understanding on the basics of automatic transmission

This study aims to design and develop a real model of a planetary gear unit providing three kinds of simulation for the basic configurations of the planetary gear unit in which one component member is locked, two members are held together, and two input members works. This is a research and development (R&D) to develop a realia of the planetary gear unit for the learning of automatic transmission basics. The realia is expected to demonstrate how the configurations in which one component member is locked, two members are held together, and two input members moves. This study was carried out through ten stages, namely analyzing potentials and problems, needs analysis, product design, focus group discussion, product development, pilot study (small-scale field test), product revision, large-scale field test, product revision, and final product. The data were collected by questionnaires and were analyzed quantitatively. The product of this study is learning media in the form of realia made of acrylic so that the components are clearly visible and the work of basic configurations of the three gears in the planetary gear unit is easy to understand. These basic arangements can be operationalized on the learning media by applying brakes to the ring, carrier, and sun gears and applying cluthes between the sun and carrier gears, the sun and ring gears, and the carrier and ring gears. Evaluated from its performance, the realia of the planetary gear unit can work well. The shaft can rotate well though some friction generated, the clutch and brake can work on its function, as well as the constituent gears can rotate as its real version does. This is reinforced by the responses from the material and media experts that reveal the product meets the very feasible category.

Development and Assessment of Planetary Gear Unit for Experimental Prototype of Vertical Axis Wind Turbine

Abstract The theoretical calculation for development of planetary gear unit of wind turbine (WT) and its experimental tests are presented in the paper. Development of experimental prototypes from composite materials is essential to determine capability of element and its impact on feature. Two experimental scale prototypes of planetary gear unit for WT were developed for such purposes. Hall transducer, servomechanisms and optical tachometers were used to obtain results, comparison analysis of theoretical and actual data was performed as well as quality assessment of experimental prototypes of planetary gear unit. After kinematic and load analysis as well as control of rotation frequency, it is possible to declare that the unit is able to operate at designated quality. Theoretical calculations and test results obtained are used for industrial WT prototype development.

Dynamic energy management for a novel hybrid electric system based on driving pattern recognition

This paper focuses on the dynamic energy management for Hybrid Electric Vehicles (HEV) based on driving pattern recognition. The hybrid electric system studied in this paper includes a one-way clutch, a multi-plate clutch and a planetary gear unit as the power coupling device in the architecture. The powertrain efficiency model is established by integrating the component level models for the engine, the battery and the Integrated Starter/Generator (ISG). The powertrain system efficiency has been analyzed at each operation mode, including electric driving mode, driving and charging mode, engine driving mode and hybrid driving mode. The mode switching schedule of HEV system has been designed based on static system efficiency. Adaptive control for hybrid electric vehicles under random driving cycles with battery life and fuel consumption as the main considerations has been optimized by particle swarm optimization algorithm (PSO). Furthermore, driving pattern recognition based on twenty typical reference cycles has been implemented using cluster analysis. Finally, the dynamic energy management strategy for the hybrid electric vehicle has been proposed based on driving pattern recognition. The simulation model of the HEV powertrain system has been established on Matlab/Simulink platform. Two energy management strategies under random driving condition have both been implemented in the study, one is knowledge-based and the other is based on driving pattern recognition. The model simulation results have validated the control strategy for the hybrid electric vehicle in this study in terms of drive pattern recognition and energy management optimization.

Efficiency Study of a Dual-Motor Coupling EV Powertrain

A novel dual-motor coupling powertrain (DMCP) with speed and torque coupling is proposed. In this powertrain, a planetary gear unit couples the speed of two motors, and another shaft-fixed gear unit couples the torque of two motors. By means of integrated control, the electric motors, synchronizer, and clutches, the DMCP can operate in four modes to satisfy the demands of different running conditions, thereby improving the energy utilization efficiency. In this paper, the operating principles of the DMCP in various modes are analyzed, and the instantaneous overall efficiency is optimized based on the vehicle longitudinal kinetic theory. Moreover, this paper formulates the optimal mode shift strategy and the power split strategy of the DMCP, and a detailed dual-motor electric vehicle (EV) model is developed in the MATLAB/Simulink environment. The simulation result indicates that, compared with the normal single-motor two-speed powertrain, the DMCP can effectively improve the energy utilization efficiency of the EV and extends the EV's driving range.

Design of 2-speed transmission for electric commercial vehicle

As environmental and economic interests increase, the need for eco-friendly vehicle such as an electric vehicle (EV) has increased rapidly. Various research of enhancing EV powertrain efficiency and relibility have been studied. In this study, 2-speed shift gears mechanism is designed by using simpson type planetary gear train. This transmission has two planetary gear unit. Gear position is determinded by which ring gear is fixed. Internal components of the transmission are designed for satisfying the required specification of EV. We analyze gear strength, gear mesh efficiency, and transmission efficiency. By manufacturing the transmission prototype and performing some experiments, we verify the application suitability of this transmission.

Latest technologies and modern guidelines on gear units

There are different configurations and designs available for gear units. The selection of correct design and arrangement of a gear unit for an industrial application to obtain an optimum performance, reliability, and efficiency based on machinery specific conditions and requirements presents challenges to mechanical engineers. Optimum design, manufacturing and configuration of gear units for industrial trains and packages are addressed. Practical notes on conventional gear units, planetary gear units, gear unit reliability and possible failure modes are discussed. Latest technologies and new achievements for gear units are also addressed. A case study for gear units of a fuel gas compressor in a power plant is presented.

Reliability for design of planetary gear drive units

Gear drive units are important components of technical systems (TS) and need to be of high quality. Planetary gear units are very compact and efficient mechanical power transformers, but further increase of operating quality level requires the application and development of the new design methodology. The subject of this contribution is presentation of Reliability for design as the new approach of reliability modelling suitable for the new design methodology application, especially for planetary gear units using various kinds of experimental and exploitation data. The methodology follows V-model for TS design which is in this work adapted for gear units design and for presentation of the new methodology based on property based design, axiomatic design and robust design methodology. To this end, the procedure for total reliability of TS decomposition, and methodology for elementary reliability for design of structure components calculation is developed and presented. The reliability for design is established in reverse form of reliability for maintenance which presents common perception of the “reliability” term. This approach is intended to provide further increase of planetary gear unit’s quality and efficient usability of gear unit component resources. The design directions are oriented to providing equal level of elementary reliability of components.

A Study on Optimum Calculation of Partial Transmission Ratios of Coupled Planetary Gear Sets

This paper introduces a new and effective study on optimum calculation of the partial ratios of coupled planetary gear sets for getting minimum radial size of the gear sets. In the paper, basing on moment equilibrium condition of a mechanic system including two row planetary gear units and their regular resistance condition, an effective model for determining the partial ratios of coupled planetary gear sets was proposed. Especially, by giving this explicit model, the partial ratios can be calculated accurately and simply.

On increasing the accuracy of combined errors estimation in satellite planetary gear units

On increasing the accuracy of combined errors estimation in satellite planetary gear units

Classification and analysis of electric-powered lateral torque-vectoring differentials

An electric-powered lateral torque-vectoring differential utilizes the output torque of an electric motor for generating the torque difference between the right and the left wheels. Compared with conventional torque-vectoring differentials which utilize the slipping clutch or brake for torque vectoring, electric-powered lateral torque-vectoring differentials have advantages, namely the response and the control accuracy of the torque difference. However, an electric-powered lateral torque-vectoring differential is complex as it is composed of a single electric motor and some planetary gear units; therefore it is difficult to understand its mechanism and characteristics. This paper describes the classification and analysis of electric-powered lateral torque-vectoring differentials. Electric-powered lateral torque-vectoring differentials are studied using the velocity diagram which is utilized for analysis of the conventional torque-vectoring differentials. The analysis shows that the simplest electric-powered lateral torque-vectoring differential is a mechanism of five elements with two degrees of freedom; the mechanism is composed of a single electric motor, one differential gear unit and two planetary gear units; the gear ratios of the planetary gear units are equal to each other. The simplest mechanisms are classified into nine kinds and these have two differences in their characteristics, namely the torque amplification factor between the electric motor and the vectoring torque, and the revolution speeds of one rotational element. Finally, the best mechanism is evaluated from the differences of the characteristics.

Modeling and Control of a Flux-Modulated Compound-Structure Permanent-Magnet Synchronous Machine for Hybrid Electric Vehicles

The compound-structure permanent-magnet synchronous machine (CS-PMSM), comprising a double rotor machine (DRM) and a permanent-magnet (PM) motor, is a promising electronic-continuously variable transmission (e-CVT) concept for hybrid electric vehicles (HEVs). By CS-PMSM, independent speed and torque control of the vehicle engine is realized without a planetary gear unit. However, the slip rings and brushes of the conventional CS-PMSM are considered a major drawback for vehicle application. In this paper, a brushless flux-modulated CS-PMSM is investigated. The operating principle and basic working modes of the CS-PMSM are discussed. Mathematical models of the CS-PMSM system are given, and joint control of the two integrated machines is proposed. As one rotor of the DRM is mechanically connected with the rotor of the PM motor, special rotor position detection and torque allocation methods are required. Simulation is carried out by Matlab/Simulink, and the feasibility of the control system is proven. Considering the complexity of the controller, a single digital signal processor (DSP) is used to perform the interconnected control of dual machines instead of two separate ones, and a typical hardware implementation is proposed.

Optimization of an 80 kW Radial-Radial Flux Compound-Structure Permanent-Magnet Synchronous Machine Used for HEVs

Compound-structure permanent-magnet synchronous machine (CS-PMSM), which is composed of a stator machine (SM) and a double-rotor machine (DRM), is a new power-split concept for hybrid electric vehicles (HEVs). To compare the CS-PMSM system with Toyota Prius based on the planetary gear unit, an 80 kW radial-radial flux prototype machine is designed. Fractional slots are employed for SM and DRM and the slot openings and pole-arc embraces of the two machines are optimized to decrease torque fluctuation. As the outer rotor is the structural and magnetic common part of SM and DRM, the magnetic circuits of the two machines are coupled. To obtain the thinner outer rotor and to decrease magnetic saturation of the outer rotor during machine design, the influences of the thickness and pole-arc embraces of permanent magnets on magnetic coupling are investigated by finite-element method. The magnetic field in the outer rotor may reach saturation, due to the impact of armature reaction on the flux distribution in the outer rotor. Under the condition of armature reaction, the flux distribution and electromagnetic torque are analyzed.

Fundamentals of the design of chain planetary reduction gear units with fine-module toothed chains

Fundamentals of the design of chain planetary reduction gear units with fine-module toothed chains