Browse Topic: Transmission gears
The Army requires rotorcraft drive systems to operate for 30 minutes following a loss of lubrication event to make an emergency landing. Coatings research has shown great promise for loss of lubrication, but coating repeatability and quality control is a primary hurdle. The Army partnered with Acree Technologies via a Small Business Innovation Research (SBIR) effort to develop an optimized gear coating for loss of lubrication. The research culminated in a system level transmission experiment that maintained flight relevant torque and speed through a helicopter gearbox without oil for three hours. The authors decided to shutdown the experiment for inspection after three hours of operation without oil because the temperature and vibration signals maintained steady state conditions without signs of failure. Teardown analysis showed the transmission gear surfaces did not scuff, scanning electron microscope analysis showed coating remained on the gear teeth, and cross-sectional SEM analysis showed a measurable coating thickness remaining on the gear teeth after three-hours of operation without oil.
This study develops a one-dimensional (1D) model to enhance transmission efficiency by evaluating power losses within a transmission system. The model simulates power flow and identifies losses at various stages such as gear mesh, bearing, churning, and windage losses. Using ISO/TR 14179, which provides a method for calculating the thermal transmittable power of gear drives with an analytical heat balance model, the 1D model ensures accurate thermal capacity evaluation under standard conditions. A key advantage of this 1D model is its efficiency in saving time compared to more complex 3D modelling, making it particularly useful during the conceptual stage of transmission system development. This allows engineers to quickly assess and optimize transmission efficiency before committing to more detailed and time-consuming 3D simulations. To validate the model, experimental tests were conducted at various motor speeds (RPM) and torque values, using high-precision sensors and dynamometers to measure input and output power. The data obtained from experiments aligned well with the outcomes predicted by the model, showing average relative deviations of 2.63% for efficiency. This methodology offers critical insights for improving design and performance of transmission systems in automotive applications. The validated 1D model serves as a reliable tool for optimizing transmission efficiency, this contributes to the advancement of more efficient and environmentally sustainable vehicles. Recent research, including the 2023 U.S. Electric Vehicle Consideration (EVC) Study by J.D. Power, supports this trend, highlight the growing consumer interest in electric vehicles and the importance of addressing transmission efficiency to meet market demands. Additionally, the development of new transmission systems for hybrid vehicles emphasizes the need for innovative solutions to enhance system efficiency and performance.
Electric vehicle (EV) transmissions play a vital role in powering EVs by channeling energy from the electric motor to the wheels. Recently, the focus has shifted to multi-speed transmissions in the EV sector due to their potential to improve efficiency and performance. By utilizing various gear ratios, these transmissions enable the motor to function within its most efficient range across different speeds. Most of these transmissions need electric control unit (ECU) with software for optimal functionality and smoother gear shifting. These controllers incorporate controller area network (CAN) communication protocol to operate along with other ECUs. Thus validation of these transmissions is a challenge as they are clutch less, motor has to be controlled for speed matching and have electro mechanical systems replacing conventional systems for operation. This paper proposes a methodology to validate multispeed EV transmissions on a test bench. The validation setup consists of electric motor at the input of a two speed EV transmission and inertia at the output of the transmission to simulate vehicle along with control unit flashed with vehicle level software. Scripts based on C-language and panels are developed which use CAN database (dbc) file of the vehicle to communicate between electric motor, transmission and vehicle control unit. Using the panels the user either controls the gear shift actuation manually or automate the gear shifting process as per vehicle operating conditions for evaluating the gear shift process. Using the mentioned methodology various vehicle scenarios can be simulated and validated on test bench at early stages, thus providing important feedback in development stage for software refinement for optimal operation of the motor and transmission actuator during gear shift process. The developed scripts can be modified to match for other vehicle configurations.
Driver-in-the-Loop (DIL) simulators have become crucial tools across automotive, aerospace, and maritime industries in enabling the evaluation of design concepts, testing of critical scenarios and provision of effective training in virtual environments. With the diverse applications of DIL simulators highlighting their significance in vehicle dynamics assessment, Advanced Driver Assistance Systems (ADAS) and autonomous vehicle development, testing of complex control systems is crucial for vehicle safety. By examining the current landscape of DIL simulator use cases, this paper critically focuses on Virtual Validation of ADAS algorithms by testing of repeatable scenarios and effect on driver response time through virtual stimuli of acoustic and optical warnings generated during simulation. To receive appropriate feedback from the driver, industrial grade actuators were integrated with a real-time controller, a high-performance workstation and simulation software called Virtual Test Drive (VTD). By developing an integrated solution for acquiring driver response, creation of scenarios and evaluation of control systems, this paper focuses on virtual validation of systems in a time saving and cost-effective manner.
Model Based Design (MBD) uses mathematical modelling to create, test and refine systems in simulated environment, primarily applied in control system development. This paper discusses an approach to control gear shifting using shift logic on vehicle level for twin clutch transmission using prototype controller. Twin clutch transmission is a concept with two clutches, one at input end of the transmission called primary clutch and the other at output end of the transmission called secondary clutch. This concept is proposed to counter the challenges with conventional transmission which include increased gear shift time and effort in lower gears, potential rollback of vehicle in uphill condition and chance of missed shifts. The advantages of this concept include reduced gear shift effort and improved synchronizer life with potential for reducing the size of the synchro pack. This paper proposes a methodology to develop shift logic, integrate hardware with software, flashing and calibration on vehicle using prototype controller. The shift logic is implemented using state machines in ASCET. The state machine uses vehicle speed, accelerator pedal position, gear shifter input, shift maps and current gear to determine most optimal gear shift in real-time. This control logic is then converted into c-code and integrated with hardware using INTECRIO, which is a build environment where inputs and outputs are mapped accordingly for shift actuation. In the next step, .a2l and .cod files are generated, which are flashed onto rapid prototyping hardware from ETAS using INCA. The same is used to actuate shift solenoids of transmission to change the gear. Use of rapid prototyping hardware has significantly reduced the number of iterations required for integrating software with ECU from specific supplier, thus reducing overall development time. Final vehicle level calibration is done using INCA, followed by validation process to ensure optimal performance.
Gear noise is a common challenge that all gear manufacturers must contend with. In tractors, while it is often sufficiently low in intensity to not pose a significant issue, there are instances where gear whine may occur which is noticeable. In such cases, identifying the source and effectively addressing the problem can prove to be particularly difficult. This paper addresses the root cause analysis carried out for the evaluation of factors influencing whine noise behavior of Spiral bevel gear pair (SO2) in a tractor transmission system. Numerous publications have been published on gear noise of spiral bevel gear pair, too many to list here. However, once the gearbox assembled into the transmission, such models are of limited practical value. The work explained in this paper is a typical example offers avenues in correcting the issue using more limited means.
Bogie frame is a main skeleton and structural member in railway system which is carrying all the loads such as Suspensions, Axles, wheels, car body, Motor, Gear box etc. The frame is subjected an exceptional and service stresses in Vertical, Longitudinal, Lateral and twist directions throughout the service life which should be withstand for a life span of 30 years without failure. The purpose of this project is to determine the Structural integrity of the Metro rail bogie frame in consideration with EN13749 standard. This paper is the outcome of bench testing of metro rail bogie frame with the application of multiaxial loading in static and dynamic campaign through which stress data is collected with strain gauge sensors and correlated with the FEA results at initial design phase. This helps to verify and evaluate the design and validate the quality of metro rail frame as per the requirement specified in EN13749:2021 European standard in early design stages.
In heavy-duty tippers, where challenging conditions demand high torque, planet carriers play a crucial role by enabling efficient load distribution and torque transmission while supporting gear ratio and speed variation in space-constrained systems such as automatic transmissions, hybrid drivetrains, and electric vehicles. This paper focuses on the comprehensive durability performance assessment of planet carrier housing (PCH) using duty cycles derived from road load data acquisition (RLDA) measurements for a heavy-duty tipper gearbox development program. The existing Design Validation Plan (DVP) for the planet carrier considers first gear utilization of 10-15% at 40% vehicle overload, in line with historical data. However, recent trends in mining applications revealed vehicle overloads of 55-65%, leading to an increase in first gear utilization (25-35%). This shift presents challenges for original equipment manufacturer (OEM) to enhance design durability while incorporating additional safety margins to meet the demands of a competitive, cost-driven market. To address this discrepancy, road load data was collected on a heavy-duty tipper with 65% abusive overloads. Torque telemetry on the propeller shaft captured RLDA data, which was processed to generate a torque profile for the planet carrier. This profile was then used to define the duty cycle via torque rainflow matrices across various gear conditions. The data revealed a 35% first gear utilization, prompting a revision of the existing DVP using this field-reflective data. Using revised DVP, a comprehensive durability assessment of the planet carrier was conducted, considering the torque rainflow matrices for all gear operating conditions. The fatigue assessment included the effect of induction hardening using a boundary layer approach in the commercial fatigue solver FEMFAT. Critical locations in the planet carrier were identified and addressed through suitable design modifications to meet the fatigue damage targets of the revised DVP. The final prototype design was validated through physical testing, showing no failures and aligning well with simulation predictions.
Puddling is a crucial process in rice cultivation, involving the preparation of the soil in a flooded field to create a soft, muddy seedbed. There are two classifications for puddling: full cage and half cage. Full cage puddling involves replacing the rear wheels of the tractor with steel paddle wheels, which are used to till the rice paddies directly without any additional implement. In the half cage puddling, the rear wheels remain on the tractor, and a smaller cage or paddle wheel is attached to the outside. Considering the field size, the operator often releases the clutch very quickly after a speed or direction change. This generates torque spikes, which are harmful to Transmission Gears and Clutches. This can lead to gear teeth bending fatigue failure due to repeated higher bending stresses. In this paper, a study related to how to reduce overall product development time by simulating bending fatigue failure of gear in lab environment is presented. A systematic approach is used to understand the field application, data acquisition, Data analysis, new test stand development and replication of failure mode in lab environment. This approach resulted in significant time savings. Multiple design iterations with minimal variation can be executed. This eliminates dependency on field, environmental conditions, and different variabilities. Finally, it supports timely decision-making based on the outcomes.
This paper, explores the design and sizing of a planetary gear-based electronic continuously variable transmission (ECVT) for implementation of a parallel gas-electric hybrid helicopter propulsion system. The ECVT consists of a differential planetary gear transmission (PGT) and an electric motor/generator (MG) unit. The ECVT enables power-flow between engine, motor and helicopter main rotor. The parallel arrangement enables the main rotor speed to varied continuously based on the MG speed while the engine speed can remain constant. The performance benefits enabled by the main rotor speed variation capability are offset by the added weight penalties introduced by the ECVT system. By considering factors such a as gear tooth bending and contact stress, bearing loads, required motor torque, planetary gear kinematics and pitch-line velocity constraints, this paper conducts a minimum mass design study for several PGT / ECVT arrangements. Here, three different single stage PGT/ECVT arrangements are compared along with an improved two stage ECVT. The three single stage ECVT configurations can be summarized as; I) Sun-Engine / Carrier-Motor / Ring-Out, II) Sun-Engine / Ring-Motor / Carrier-Out, and III) Carrier-Engine / Sun-Motor / Ring-Out. Of these three types, it was found that type III was significantly lighter in weight compared with types I and II since type III would have the highest relative motor speed. When sized for a 3000 Hp engine-side power input at 6000 rpm, the minimum mass design for type III was on the order of 100 lbs compared to 400 lbs and 700 lbs respectively for types I and II. Despite the seemingly obvious advantage of design type III, it's drawback is that it is effectively a speed increasing stage with respect to the engine. To address this, a two-stage ECVT with compound planetary arrangement of Type III and II was designed which achieved an overall minimum weight of 219 lbs at the 3000 Hp level while providing 1:0.351 gear reduction form engine to output. The analysis tools developed and sizing results flowing from this study will provide a baseline for evaluating performance benefits and weight penalties introduced by parallel hybrid drive-systems for rotorcraft applications.
Gear whine has emerged as a significant challenge for electric vehicles (EVs) in the absence of engine masking noise. The demand from customers for premium EVs with high speed and high torque density introduces additional NVH risks. Conventional gear design strategies to reduce the pitch-line velocity and increase contact ratio may impact EV torque capacitor or its efficiency. Furthermore, microgeometry optimization has limited design space to reduce gear noise over a wide range of torque loads. This paper presents a comprehensive investigation into the optimization of transfer gear blanks in a single-speed two-stage FDW electric drive unit (EDU) with the objective of reducing both mass and noise. A detailed multi-body dynamics (MBD) model is constructed for the entire EDU system using a finite-element-based time-domain solver. This investigation focuses on the analysis and optimization of asymmetric gear blank design features with three-slot patterns. A design-of-experiment (DOE) methodology is employed to identify pivotal gear blank design parameters, including the blank thickness and slot angle. The radiated sound power and mount vibration responses from the EDU are predicted and correlated with test data. The time-varying stiffness at the meshing point gives rise to sidebands around the transfer gear orders, which are accurately captured using the MBD time-domain solver. The asymmetric gear blank stiffness changes the torsional vibration transfer path, necessitating microgeometry re-optimization to fully capture the NVH benefits. A case study is conducted based on the Ultium EDU, focusing on transfer gear blank design. It is demonstrated that a selected three-slotted gear blank design, in conjunction with optimized microgeometry, results in reduced mass and up to 10 dB lower gear noise for the electric drive unit system.
In addition to providing safety advantages, sound and vibration are being utilized to enhance the driver experience in Battery Electric Vehicles (BEVs). There's growing interest and investment in using both interior and exterior sounds for pedestrian safety, driver awareness, and unique brand recognition. Several automakers are also using audio to simulate virtual gear shifting of automatic and manual transmissions in BEVs. According to several automotive industry articles and market research, the audio enhancements alone, without the vibration that drivers are accustomed to when operating combustion engine vehicles, are not sufficient to meet the engagement, excitement, and emotion that driving enthusiasts expect. In this paper, we introduce the use of new automotive, high-force, compact, light-weight circular force generators for providing the vibration element that is lacking in BEVs. The technology was developed originally for vibration reduction/control in aerospace applications, has been recently tested in various vehicles, and demonstrates the effectiveness for providing a real haptic feel across the entire vehicle. Shaking the vehicle globally provides a unique capability for BEVs, including Hybrid Electric Vehicles and for helping to create a smooth transition between Gas and Electric power, for example. The technology can be used to generate and emulate high-performance, high power, combustion engine feel, including idle, engine run-up/acceleration, simulated gear shifts, and Advanced Driving Assistance and Systems (ADAS) haptic indicators. The optional and customizable vibration can also mask road vibration which becomes very noticeable in otherwise smooth BEVs and can provide the perfect supplement to existing audio enhancements and gear shifting features. Additionally, the paper describes how the force generating device can be packaged in a light weight, compact, low-power manner. The technology will be compared to other force generating methods, and discuss its pros and cons.
This paper describes an optimal control method utilizing a Linear Quadratic Regulator (LQR) to control the torque during the gear shift on a multispeed electrified transmission to optimize for clutch actuator durability and shift performance. The dynamic state-space model of the system has been obtained using System-Identification. An LQR controller is formulated to minimize driveline oscillations and transmission-input-torque using the model by manipulating the electrical torque applied by the traction motor at the transmission input. The LQR controller is implemented in a simulation framework wherein the impact of vehicle parameters on the shift quality metrics is also assessed. Subjective and objective requirements are considered in the tuning process for the LQR controller. The LQR controller is utilized to generate profiled torque table calibrations. These calibrations are then deployed onto a production ready Transmission Control Unit and experimentally validated on a Class-8 Heavy Duty vehicle retrofitted with an electrified multispeed transmission. Experimental validation is performed at multiple Gross-Combination-Vehicle Weight (GCVW) configurations. Significant reduction of clutch actuation effort, shift time while maintaining adherence to subjective and objective shift quality metrics has been demonstrated compared to traditional S-Shaped torque profiling.
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