Tribodynamics of hydraulic actuated clutch system for engine-downsizing in heavy duty off-highway vehicles

Engine downsizing is desired for modern heavy-duty vehicles to enhance fuel economy and reduce emissions. However, the smaller engines usually cannot overcome the parasitic loads during engine start-up. A new clutch system is designed to disconnect the downsized engine from the parasitic losses prior to the idling speed. A multi-scale, multi-physics model is developed to study the clutch system. Multi-body dynamics is used to study the combined translational–rotational motions of the clutch components. A micro-scale contact model is incorporated to represent the frictional characteristics of the sliding surfaces. Although the clutch is designed for dry contact operation, leakage of actuating hydraulic fluid can affect the interfacial frictional characteristics. These are integrated into the multi-body dynamic analysis through tribometric studies of partially wetted surfaces using fresh and shear-degraded lubricants. Multi-scale simulations include sensitivity analysis of key operating parameters, such as contact pressure. This multi-physics approach is not hitherto reported in the literature. The study shows the importance of adhesion in dry clutch engagement, enabling full torque capacity. The same is also noted for any leakage of significantly shear-degraded lubricant into the clutch interfaces. However, the ingression of fresh lubricant into the contact is found to reduce the clutch torque capacity

Heat generation and transfer in automotive dry clutch engagement

Dynamic behaviour of automotive dry clutches depends on the frictional characteristics of the contact between the friction lining material, the flywheel, and the pressure plate during the clutch engagement process. During engagement due to high interfacial slip and relatively high contact pressures, generated friction gives rise to contact heat, which affects the material behaviour and the associated frictional characteristics. In practice excess interfacial slipping and generated heat during torque transmission can result in wear of the lining, thermal distortion of the friction disc, and reduced useful life of the clutch. This paper provides measurement of friction lining characteristics for dry clutches for new and worn state under representative operating conditions pertaining to interfacial slipping during clutch engagement, applied contact pressures, and generated temperatures. An analytical thermal partitioning network model of the clutch assembly, incorporating the flywheel, friction lining, and the pressure plate is presented, based upon the principle of conservation of energy. The results of the analysis show a higher coefficient of friction for the new lining material which reduces the extent of interfacial slipping during clutch engagement, thus reducing the frictional power loss and generated interfacial heating. The generated heat is removed less efficiently from worn lining. This might be affected by different factors observed such as the reduced lining thickness and the reduction of density of the material but mainly because of poorer thermal conductivity due to the depletion of copper particles in its microstructure as the result of wear. The study integrates frictional characteristics, microstructural composition, mechanisms of heat generation, effect of lining wear, and heat transfer in a fundamental manner, an approach not hitherto reported in literature

Heat generation and transfer in automotive dry clutch engagement

Dynamic behaviour of automotive dry clutches depends on the frictional characteristics of the contact between the friction lining material, the flywheel and the pressure plate during the clutch engagement process. During engagement due to high interfacial slip and relatively high contact pressures, generated friction gives rise to contact heat, which affects the material behaviour and the associated frictional characteristics. In practice excess interfacial slipping and generated heat during torque transmission can result in wear of the lining, thermal distortion of the friction disc, and reduced useful life of the clutch. This paper provides measurement of friction lining characteristics for dry clutches for new and worn state under representative operating conditions pertaining to interfacial slipping during clutch engagement, applied contact pressures, and generated temperatures. An analytical thermal partitioning network model of the clutch assembly, incorporating the flywheel, friction lining, and the pressure plate is presented, based upon the principle of conservation of energy. The results of the analysis show a higher coefficient of friction for the new lining material which reduces the extent of interfacial slipping during clutch engagement, thus reducing the frictional power loss and generated interfacial heating. The generated heat is removed less efficiently from worn lining. This might be affected by different factors observed such as the reduced lining thickness and the reduction of density of the material but mainly because of poorer thermal conductivity due to the depletion of copper particles in its microstructure as the result of wear. The study integrates frictional characteristics, microstructural composition, mechanisms of heat generation, effect of lining wear and heat transfer in a fundamental manner, an approach not hitherto reported in literature

Steam bottoming cycle for an adiabatic diesel engine

Steam bottoming cycles using adiabatic diesel engine exhaust heat which projected substantial performance and economic benefits for long haul trucks were studied. Steam cycle and system component variables, system cost, size and performance were analyzed. An 811 K/6.90 MPa state of the art reciprocating expander steam system with a monotube boiler and radiator core condenser was selected for preliminary design. The costs of the diesel with bottoming system (TC/B) and a NASA specified turbocompound adiabatic diesel with aftercooling with the same total output were compared, the annual fuel savings less the added maintenance cost was determined to cover the increase initial cost of the TC/B system in a payback period of 2.3 years. Steam bottoming system freeze protection strategies were developed, technological advances required for improved system reliability are considered and the cost and performance of advanced systes are evaluated

Tribological And Dynamical Study Of An Automotive Transmission System

The transmission system is critical for automotive and heavy duty equipment due to its prominent role in the powertrain system, which is often challenged with degraded torque capacity and harsh dynamic response. Simulation-guided design can provide appropriate guidelines to resolve these problems with virtual analyses. In current study, the tribological and dynamical study of an automatic transmission is performed at two levels: a wet clutch and powertrain. In this dissertation, tribological study is performed for a wet clutch based on the thermohydrodynamic (THD) analysis that takes the following factors into account. • The groove effect (depth, area, and pattern) is investigated for lubrication analysis; • The elastic-plastic asperity contact model is used to predict the contact pressure; • The heat transfer during the entire cycle of engagement from slip to lock to detachment is covered; • The engagement time and the temperature profile are predicted for torque and thermal analysis. With large engagement cycles, the friction lining of a wet clutch is worn off due to the material degradation at high load/temperature condition. By relating the wear behavior with the mechanism of thermal degradation and thermomechanical degradation, a physics-based wear model is proposed for the first time to analyze the wear process in a wet clutch. The predicted wear rate falls within nearly 95% confidence interval of the test results. Discrepancies of simulation are primarily due to limited availability of input data and model assumptions. Therefore, an uncertainty quantification analysis of the wear model is performed using the Monte Carlo simulations. In addition, a comprehensive parametric analysis of the clutch wear is considered with various factors, including groove design (waffle pattern shows the minimum wear), material properties and operational configurations (rotational speed plays the most influential role). The dynamics of transmission directly affects the performance of the powertrain. The coupling effects of the key transmission components are examined. Of particular interests are the stick-slip behavior of the wet clutch and backlash of the gear train. Through simulation of the powertrain, the main source and the pattern of vibration propagation in the driveline are examined. Major vibration is observed during inappropriate clutch engagement

An analysis of kinetic energy recovery systems and their potential for contemporary internal combustion engine powered vehicles

The Internal Combustion Engine has played an incomprehensible role in contemporary society ever since its invention. Oil shortages will almost certainly eventually lead towards a search for propulsion from renewable sources, but for the time being there is no sign of any significant alternative for everyday transport. Any product that offers a fuel economy improvement is of benefit to both the individual and the environment. As vehicles speed up, they convert stored energy into kinetic energy. As the mass or velocity increases, the kinetic energy will also increase. It is for this reason that light commercial vehicles on our roads have so much kinetic energy when travelling at speed. The concept of being able to recover this energy when braking is the foundation for regenerative braking or Kinetic Energy Recovery. The energy captured is then stored to be used in the future: in most cases it is converted back into kinetic energy to bring the vehicle back to speed. The technology is particularly effective in drive cycles consisting of frequent stop-start driving. This project seeks to investigate the feasibility of a mechanical Kinetic Energy Recovery System for implementation via a retrofit on existing light commercial vehicles. In order to be effective, the system must be cost effective and easy to implement. The objective was to design a system able to be fitted to a large number of vehicle platforms and with a reasonable payback period. A literature review was carried out to discern the most appropriate system for light commercial vehicles. Existing systems were analysed and their benefit was appraised from a retrofit stance. A flywheel system was chosen due to its recent success in F1 and its very high energy density amongst other factors. A system was designed to be fitted to a representative vehicle, with potential to be fitted to other platforms. The theory of operation, driveline configuration and attachment options were developed. The system was modelled in Creo and a Matlab code was developed to calculate the potential fuel savings under different circumstances using drive cycles. The dissertation found that the technology was conceptually viable. A vehicle of mass 2680kg with load would save $0.91 per 100km (6.9$1.64 per 100km (7.6% saving). The total cost of the system was found to be $2680. The repayment period ranged from 5-8years to a best case scenario of 3-4 years

Conception d’un embrayage de dérivation du couple à courants de Foucault pour les transmissions manuelles automatisées sans interruption de couple dans les véhicules à motorisation électrique ou hybride

Les voitures électriques ont peu d’énergie embarquée pour se mouvoir comparativement aux véhicules thermiques. Il est donc important d’optimiser l’efficacité de la chaîne de traction pour maximiser la distance parcourue entre les recharges. Ces voitures utilisent un ratio simple pour coupler le moteur aux roues de la voiture. Le remplacement du ratio simple par une transmission à plusieurs vitesses dans une voiture électrique améliore l’efficacité du système de propulsion. Cependant, l’introduction d’une transmission à plusieurs ratios ne doit pas seulement améliorer l’efficacité énergétique pour recevoir l’acceptabilité du marché. Elle doit aussi offrir un confort de conduite similaire au ratio simple. L’ajout d’un embrayage de déviation du couple à la transmission manuelle permet de réduire ou d’éliminer les interruptions de celui-ci lors du passage des ratios. Cependant, les technologies d’embrayages à friction secs et humides ne sont pas bien adaptées à cette tâche de déviation du couple cependant. D’abord, l’embrayage est ouvert la majeure partie du temps ce qui fait en sorte qu’un embrayage humide aurait de grandes pertes visqueuses. Ensuite, les moteurs électriques tournent rapidement (11 000 révolutions par minute). Cela fait en sorte que l’embrayage dissipe de grandes quantités de chaleur pour ralentir le moteur avant l’engagement du prochain ratio. Un embrayage sec ne contient pas d’huile pour aider à l’extraction de la chaleur et ses bandes de friction s’usent rapidement sous ces conditions. Ce travail de maîtrise propose d’utiliser un embrayage électromagnétique plutôt qu’un embrayage à friction pour dévier le couple moteur. La démarche de conception d’un tel embrayage est présentée. Premièrement, un modèle analytique simple sert à déterminer les dimensions physiques de l’embrayage pour qu’il développe un certain couple électromagnétique. Ce requis provient des spécifications techniques d’une plateforme véhiculaire électrique disponible à l’Université de Sherbrooke (Projet Phoebus). Deuxièmement, des études par éléments finis des champs magnétiques de l’embrayage servent à valider que l’embrayage produit le niveau de couple désiré. L’embrayage est finalement testé dans une transmission manuelle automatisée installée sur un banc de test dynamométrique. Des changements de ratios sans interruption de couple démontrent la viabilité de l’embrayage à courants de Foucault en tant qu’embrayage de déviation du couple

Two-Speed Gearbox Dynamic Simulation Predictions and Test Validation

Dynamic simulations and experimental validation tests were performed on a two-stage, two-speed gearbox as part of the drive system research activities of the NASA Fundamental Aeronautics Subsonics Rotary Wing Project. The gearbox was driven by two electromagnetic motors and had two electromagnetic, multi-disk clutches to control output speed. A dynamic model of the system was created which included a direct current electric motor with proportional-integral-derivative (PID) speed control, a two-speed gearbox with dual electromagnetically actuated clutches, and an eddy current dynamometer. A six degree-of-freedom model of the gearbox accounted for the system torsional dynamics and included gear, clutch, shaft, and load inertias as well as shaft flexibilities and a dry clutch stick-slip friction model. Experimental validation tests were performed on the gearbox in the NASA Glenn gear noise test facility. Gearbox output speed and torque as well as drive motor speed and current were compared to those from the analytical predictions. The experiments correlate very well with the predictions, thus validating the dynamic simulation methodologies