Impact of water contamination and system design on wet clutch tribological performance

Wet clutches are lubricated machine components which utilize friction to transfer torque and thus establish connection between shafts rotating at different speeds. They are used in automatic transmission as shifting device or lockup clutch. As well as cooling the contacting surfaces, the lubrication provides controlled friction, smooth performance and long life. Because of this advantage, wet clutches are applicable for heavy duty vehicles (e.g. construction equipment, tractors) to handle high power. However, like any other tribological system, wet clutch performance is dependent on several factors concerning operating conditions, system design etc. As a friction generating machine component, the degradation of the lubricant and the contacting clutch surfaces are continuous process and the friction behavior also changes consequently with the progression of the system deterioration and that directly influences the clutch performance. So, to investigate the clutch influencing factors and fundamental understanding of the interaction mechanism is of great interest. Though wet clutches were immensely studied earlier to investigate different issues, there was lack of clear understanding and knowledge concerning water contamination problem and the system design parameters. The main aim of this thesis is to experimentally evaluate and explain the impact of water contamination and to verify different system design parameters’ influence on wet clutch tribological performance. The study focused on the wet clutches in automatic transmissions. Initially the thesis reviews the state of the art in wet clutch research, discusses the motivation for the current research aim and clarifies the goals of the investigation. Later the details of the experimental method and findings are discussed in this thesis. Since evaluating the friction behaviour in desired environment is the key requirement, an automated wet clutch test rig was utilized to carry out the friction test where operating conditions (slip time, oil temperature, contact pressure/load, sliding speed) can be controlled and the output torque, contact temperature etc. can monitored. This suitable test equipment was designed for standard paper based friction plate and steel separator plate lubricated with automatic transmission fluid. Instead of using a multiple clutch plate configuration, as in real applications, a single friction and reaction plate arrangement is considered to simplify the analyses.In the first part of the thesis the effect of water contamination on wet clutch tribological performances is experimentally investigated. The study reveals that both the friction reliability and the friction-velocity relation are influenced by the change in the friction behaviour for a water contaminated lubricant. It is shown that the friction level increased for the addition of water in the system. This is not a desirable clutch frictional behaviour for maintaining frictional stability. The increase of friction for added water is influenced by the water amount but not by the water exposure time. Then the study is continued for longer test to evaluate the ageing of the friction interfaces and the lubricant. Though water does not show any long term effect on water contaminated ATF as it is seen in case of friction interfaces, the short term effect in the surface active additives is observed in the current research. This finding also supported the investigation on the water contaminated friction interface degradation and the effect of water on additive adsorption of the contacting surfaces. It was found that the addition of water in ATF intensifies the mean friction coefficient, but in the long run the loss of friction much faster and high, which can in fact degrade the clutch life faster as well. Two simplified ATF was also analysed along with the commercial fully formulated ATF for investigating the water impact to get a simple and comprehensive overview of the consequence. In the second part of this thesis, the influence of the clutch’s output shaft’s stiffness and inertia on the clutch system‘s friction reliability is experimentally evaluated. Test results show that the change in the clutch frictional behaviour with time and degradation can largely influence by the choice of these design factors. This can provide different outcome concerning clutch frictional performance and shudder sensitivity. Shudder tendency is seen to be increased for decreased torsion shaft stiffness. High frictional losses and clutch degradation are observed for systems with less inertia.Godkänd; 2014; 20140811 (nowfat); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Nowshir Fatima Ämne: Maskinelement/Machine Elements Avhandling: Impact of Water Contamination and System Design on Wet Clutch Tribological Performance Opponent: Dr Amaya Igartua, Fundacion Tekniker, Procesos de Fabricacion, Eibar, Spanien Ordförande: Professor Pär Marklund, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Fredag den 24 oktober 2014, kl. 10.00 Plats: E231, Luleå tekniska universite

Wet clutch friction reliability : influence of water contamination and system design

Wet clutches are machine components using friction to transfer torque and providing interruptible connection between rotating shafts in different automobile applications including automatic transmissions. Like any friction generating machine components, wet clutches are susceptible to continuous wear and degradation during sliding. This regular deterioration process as well as the choice of operating conditions, ultimately change the overall system performance during operation due to resultant change in the system parameters. The first part of this thesis summarizes some of the notable studies on the wet clutch tribological performance and clarifies goals of the investigation.Previously, plenty of experimental studies on wet clutches have been reported but still some effects regarding the water contamination problem and the influence of mechanical design factors are not covered thoroughly. The thesis aims to experimentally analyse these two different aspects for improving wet clutch performance regarding frictional characteristics and reliability. These two investigations are focused on wet clutches in automatic transmission applications. For evaluating friction behaviour during a long clutch engagement period, suitable test equipment is designed where standard paper based friction plates and steel separator plates are tested with commercially available ATF. To investigate a clutch operated in a controlled environment is one of main the research objectives. The vital concern while designing the test rig is to monitor the clutch parameters for achieving the desired operating conditions for individual tests. Instead of using a multiple clutch plate configuration, as in real applications, a single friction and reaction plate arrangement is considered to simplify the analyses.An experimental study on wet clutch frictional behaviour under water contaminated lubrication condition reveals the change in the friction level for a water contaminated lubricant. It was shown that the friction level increased for the addition of water in the system. This is not a desirable clutch frictional behaviour for maintaining frictional stability. The increase of friction for added water was influenced by the water amount but not by the water exposure time. The test results also showed a higher change in the separator plate's roughness parameter (Ra) for water contaminated systems compared to an uncontaminated wet clutch. In the second part of this thesis, the influence of the clutch’s output shaft’s stiffness and inertia on the clutch system‘s friction reliability is experimentally evaluated. Test results show that the choice of these design factors can provide different outcome concerning clutch frictional performance and shudder sensitivity. Shudder tendency is seen to be increased for decreased torsion shaft stiffness. High frictional losses and clutch degradation are observed for systems with less inertia.Godkänd; 2012; 20120813 (nowfat); LICENTIATSEMINARIUM Examinator: Professor Roland Larsson, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Donald McCarthy, Volvo Tid: Fredag den 14 september 2012 kl 10.00 Plats: D770, Luleå tekniska universite

Impact of water contamination and system design on wet clutch tribological performance

Wet clutches are lubricated machine components which utilize friction to transfer torque and thus establish connection between shafts rotating at different speeds. They are used in automatic transmission as shifting device or lockup clutch. As well as cooling the contacting surfaces, the lubrication provides controlled friction, smooth performance and long life. Because of this advantage, wet clutches are applicable for heavy duty vehicles (e.g. construction equipment, tractors) to handle high power. However, like any other tribological system, wet clutch performance is dependent on several factors concerning operating conditions, system design etc. As a friction generating machine component, the degradation of the lubricant and the contacting clutch surfaces are continuous process and the friction behavior also changes consequently with the progression of the system deterioration and that directly influences the clutch performance. So, to investigate the clutch influencing factors and fundamental understanding of the interaction mechanism is of great interest. Though wet clutches were immensely studied earlier to investigate different issues, there was lack of clear understanding and knowledge concerning water contamination problem and the system design parameters. The main aim of this thesis is to experimentally evaluate and explain the impact of water contamination and to verify different system design parameters’ influence on wet clutch tribological performance. The study focused on the wet clutches in automatic transmissions. Initially the thesis reviews the state of the art in wet clutch research, discusses the motivation for the current research aim and clarifies the goals of the investigation. Later the details of the experimental method and findings are discussed in this thesis. Since evaluating the friction behaviour in desired environment is the key requirement, an automated wet clutch test rig was utilized to carry out the friction test where operating conditions (slip time, oil temperature, contact pressure/load, sliding speed) can be controlled and the output torque, contact temperature etc. can monitored. This suitable test equipment was designed for standard paper based friction plate and steel separator plate lubricated with automatic transmission fluid. Instead of using a multiple clutch plate configuration, as in real applications, a single friction and reaction plate arrangement is considered to simplify the analyses.In the first part of the thesis the effect of water contamination on wet clutch tribological performances is experimentally investigated. The study reveals that both the friction reliability and the friction-velocity relation are influenced by the change in the friction behaviour for a water contaminated lubricant. It is shown that the friction level increased for the addition of water in the system. This is not a desirable clutch frictional behaviour for maintaining frictional stability. The increase of friction for added water is influenced by the water amount but not by the water exposure time. Then the study is continued for longer test to evaluate the ageing of the friction interfaces and the lubricant. Though water does not show any long term effect on water contaminated ATF as it is seen in case of friction interfaces, the short term effect in the surface active additives is observed in the current research. This finding also supported the investigation on the water contaminated friction interface degradation and the effect of water on additive adsorption of the contacting surfaces. It was found that the addition of water in ATF intensifies the mean friction coefficient, but in the long run the loss of friction much faster and high, which can in fact degrade the clutch life faster as well. Two simplified ATF was also analysed along with the commercial fully formulated ATF for investigating the water impact to get a simple and comprehensive overview of the consequence. In the second part of this thesis, the influence of the clutch’s output shaft’s stiffness and inertia on the clutch system‘s friction reliability is experimentally evaluated. Test results show that the change in the clutch frictional behaviour with time and degradation can largely influence by the choice of these design factors. This can provide different outcome concerning clutch frictional performance and shudder sensitivity. Shudder tendency is seen to be increased for decreased torsion shaft stiffness. High frictional losses and clutch degradation are observed for systems with less inertia.Godkänd; 2014; 20140811 (nowfat); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Nowshir Fatima Ämne: Maskinelement/Machine Elements Avhandling: Impact of Water Contamination and System Design on Wet Clutch Tribological Performance Opponent: Dr Amaya Igartua, Fundacion Tekniker, Procesos de Fabricacion, Eibar, Spanien Ordförande: Professor Pär Marklund, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Fredag den 24 oktober 2014, kl. 10.00 Plats: E231, Luleå tekniska universite

Study on the wet clutch friction interfaces for humid lubrication condition

The friction influencing parameters also influence the wet clutch sliding surface conditions. The tribofilm formations as well as the chemical and mechanical degradation for frictional interfaces can be different for the choice of the lubricant conditions. The present investigations revealed the effects of water contamination in automatic transmission fluid (ATF) not only on the frictional performance, but also on the friction interfaces. The surface profiles of the tested separator plates, the EDS-SEM (Scanning Electron Microscopy-Energy-dispersive X-ray spectroscopy) analysis of the friction interfaces and optical microscopy for the used friction liners showed the difference in surface morphology, adsorption of additive elements, permeability and porosity for a humid clutch environment.Godkänd; 2013; 20130415 (nowfat

Adsorption of ATF additives on wet clutch friction interfaces under water contaminated lubricant conditions

Stable friction and positive slope of friction-speed is the typical criterion for a good clutch performance. Lubricated friction interfaces used for wet clutches produces different friction behavior depending on the lubricant conditions. Usually the lubricant conditions vary for different automatic transmission fluid (ATF) formulations implying e.g. water contamination and these conditions might influence the deterioration of the clutch plates. The aim of this paper is to verify additive adsorption on friction interfaces and ageing of the friction material in wet clutch system for a water contaminated commercial ATF (DEXRON® VI). Standard clutch plates are employed in an automated wet clutch test rig to evaluate the friction characteristics of the tested lubricant. For controlled test conditions (speed, contact pressure, oil temperature) and specific number of test cycles, the mean friction coefficient and the friction vs. speed relations are monitored during sliding test. The resultant tribofilms on the tested friction interface surfaces are characterized by means of Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM- EDS), Attenuated Total Reflectance -Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS analysis). The spectroscopic techniques were used to analyse adsorbed additives on friction interfaces and made it possible to correlate measured data to the specific friction behavior obtained after water contamination of the ATF.Godkänd; 2014; 20140616 (nowfat

Degradation mechanism of water contaminated automatic transmission fluid (ATF) in wet clutch system

Godkänd; 2013; 20140214 (andbra)</p