scholarly journals Integrated Thermal and Dynamic Analysis of Dry Automotive Clutch Linings

2019 ◽  
Vol 9 (20) ◽  
pp. 4287 ◽  
Author(s):  
Theofilos Gkinis ◽  
Ramin Rahmani ◽  
Homer Rahnejat
Keyword(s):  
Thermal Performance ◽  
Pressure Profile ◽  
Rear Wheel ◽  
Operating Conditions ◽  
Contact Heat ◽  
Stick Slip ◽  
Powertrain System ◽  
Clutch Engagement ◽  
Lining Material ◽  
System Temperature

Optimum operation of clutch systems is dictated by their dynamic as well as thermal performance. Both of these aspects are closely related to the interfacial frictional characteristics of the clutch lining material, which also affects the noise, vibration and harshness response of the entire vehicular powertrain system. Severe operating conditions such as interfacial clutch slip and increased contact pressures occur during clutch engagement, leading to generation of contact heat, and higher clutch system temperature. Therefore, any undesired oscillatory responses, generated during clutch engagement, such as take-up judder phenomenon can exacerbate generated heat due to stick-slip motion. The paper presents an integrated thermal, and 9-DOF dynamic model of a rear wheel drive light truck powertrain system. The model also includes experimentally measured clutch lining frictional variations with interfacial slip speed, non-linear contact pressure profile and generated surface flash temperature. It is shown that severe torsional oscillations known as take-up judder lead to an increased overall clutch temperature. It also shows that ageing of clutch lining material alters its dynamic and thermal performance.

Dynamic analysis of vehicle start-up judder based on elasto-plastic friction model and dry clutch maneuvering characteristic

2018 ◽  
Vol 233 (2) ◽  
pp. 455-469 ◽  
Author(s):  
Renfei Yuan ◽  
Guangqiang Wu
Keyword(s):  
Friction Model ◽  
Step Response ◽  
Negative Slope ◽  
Stick Slip ◽  
Clamp Force ◽  
Powertrain System ◽  
Start Up ◽  
Clutch Engagement ◽  
Engagement Process ◽  
Dry Clutch

This paper presents a detailed investigation of the dry clutch engagement process, and vehicle start-up judder phenomenon that could result in the deterioration of vehicle ride comfort. Elasto-plastic friction model is elaborated through the slider-pulley system, which shows some friction characteristics such as presliding, stick-slip motion, Stribeck effects, etc., and applied to dry clutch. The axial compression characteristics of three elastic parts, which include diaphragm spring, cushion spring, and link strip have been taken into consideration, and nonlinear relationship between the release bearing travel and the clutch clamp force is also established. The powertrain system model of front-engine and front-wheel-drive vehicle equipped with manual transmission is set up to recreate the start-up judder phenomenon in the numerical simulation and analyze its mechanism. The sudden transfer of the engine torque during the clutch engagement process results in the initial judder, which can be supposed as the step response of system and is initially weakened due to the damping of the powertrain system. Then the judder gradually strengthens and gets in the most severe vibrance when the clutch is about to get in to the fully engaged state, which is related to the frictional characteristics that forms a closed-loop positive feedback system, as well as the frequent state transitions between sliding state and engaged state. The positive slope of Stribeck effect as well as the reduction of absolute value of negative slope can both effectively suppress the start-up judder, and the apparent judder occurs only if the negative slope is outside of a certain range, instead of in all of the range. In addition, the fluctuation of clutch clamp force can aggravate the start-up judder, in which a more chaotic oscillation is emerged.

Experimental Exploration of Schallamach Waves and Self-Excitation in a Belt-Drive System

2018 ◽  
Author(s):  
Yingdan Wu ◽  
Michael Varenberg ◽  
Michael J. Leamy
Keyword(s):  
Angular Velocity ◽  
Dynamic Behavior ◽  
Oscillation Amplitude ◽  
Operating Conditions ◽  
Drive System ◽  
Belt Drive ◽  
Stick Slip ◽  
Stick Slip Motion ◽  
System Inertia ◽  
Slip Motion

We study the dynamic behavior of a belt-drive system to explore the effect of operating conditions and system moment of inertia on the generation of waves of detachment (i.e., Schallamach waves) at the belt-pulley interface. A self-excitation phenomenon is reported in which frictional fluctuations serve as harmonic forcing of the pulley, leading to angular velocity oscillations which grow in time. This behavior depends strongly on operating conditions (torque transmitted and pulley speed) and system inertia, and differs between the driver and driven pulleys. A larger net torque applied to the pulley generally yields more remarkable stick-slip oscillations with higher amplitude and lower frequency. Higher driving speeds accelerate the occurrence of stick-slip motion, but have little influence on the oscillation amplitude. Contrary to our expectations, the introduction of flywheels to increase system inertia amplified the frictional disturbances, and hence the pulley oscillations. This does, however, suggest a way of facilitating their study, which may be useful in follow-on research.

scholarly journals Thermal Performance and Efficiency of a Mineral Oil Immersed Server Over Varied Environmental Operating Conditions

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Richard Eiland ◽  
John Edward Fernandes ◽  
Marianna Vallejo ◽  
Ashwin Siddarth ◽  
Dereje Agonafer ◽  
...  
Keyword(s):  
Flow Rate ◽  
Thermal Performance ◽  
Data Center ◽  
Mineral Oil ◽  
Operating Conditions ◽  
Published Data ◽  
Inlet Temperature ◽  
Air Cooling ◽  
Bulk Fluid ◽  
Oil Immersion

Complete immersion of servers in dielectric mineral oil has recently become a promising technique for minimizing cooling energy consumption in data centers. However, a lack of sufficient published data and long-term documentation of oil immersion cooling performance make most data center operators hesitant to apply these approaches to their mission critical facilities. In this study, a single server was fully submerged horizontally in mineral oil. Experiments were conducted to observe the effects of varying the volumetric flow rate and oil inlet temperature on thermal performance and power consumption of the server. Specifically, temperature measurements of the central processing units (CPUs), motherboard (MB) components, and bulk fluid were recorded at steady-state conditions. These results provide an initial bounding envelope of environmental conditions suitable for an oil immersion data center. Comparing with results from baseline tests performed with traditional air cooling, the technology shows a 34.4% reduction in the thermal resistance of the system. Overall, the cooling loop was able to achieve partial power usage effectiveness (pPUECooling) values as low as 1.03. This server level study provides a preview of possible facility energy savings by utilizing high temperature, low flow rate oil for cooling. A discussion on additional opportunities for optimization of information technology (IT) hardware and implementation of oil cooling is also included.

Influence of Flow Structure on Shaped Hole Film Cooling Performance

2010 ◽  
Author(s):  
Benoit Laveau ◽  
Reza S. Abhari
Keyword(s):  
Flow Structure ◽  
Thermal Performance ◽  
Turbine Blades ◽  
Density Ratio ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Infrared Measurements ◽  
Cylindrical Holes ◽  
Shaped Hole ◽  
Adiabatic Effectiveness

Shaped holes are used on modern turbine blades for their higher performance and greater lateral coolant spreading compared to classic streamwise angled holes. This study incorporates measurements and observations from a shaped hole geometry undertaken at ETH Zurich in which a row of laterally expanded diffusely shaped holes is compared to the classic row of streamwise round holes. Infrared measurements provide high-resolution data of the adiabatic effectiveness and three dimensional velocity measurements are carried out through stereoscopic Particle Image Velocimetry. Both experiments are run for similar operating conditions allowing a comparison to be made between the flow structure and the thermal performance. The adiabatic effectiveness is seen to be higher for shaped holes compared to cylindrical holes: in particular the laterally averaged values are higher due to a larger lateral spreading of the coolant. The work presented here shows the first results on the limited influence of the density ratio on the thermal performance. The performance is also influenced by the vortical structure. The typical counter-rotating vortex pair which is completed by another pair of anti-kidney vortices is observed with their strength being clearly reduced compared to the example with cylindrical holes. The doubled structure and the reduced strength change the behavior of the jet, explaining the higher performance of a jet with shaped holes. The vertical motion leading to lift-off is reduced, so the jet remains close to the surface even at high blowing rates. The goal of this article is to present data for the thermal performance and flow field of shaped holes and then explain the relationship between the two.

scholarly journals Vehicle Sideslip Angle Estimation Based on Tire Model Adaptation

Electronics ◽  
2019 ◽  
Vol 8 (2) ◽  
pp. 199 ◽  
Author(s):  
Kanwar Bharat Singh
Keyword(s):  
Experimental Tests ◽  
Estimation Algorithm ◽  
Rear Wheel ◽  
Stability Control ◽  
Operating Conditions ◽  
Successful Implementation ◽  
Tire Model ◽  
Sideslip Angle ◽  
Wheel Drive ◽  
Sideslip Estimation

Information about the vehicle sideslip angle is crucial for the successful implementation of advanced stability control systems. In production vehicles, sideslip angle is difficult to measure within the desired accuracy level because of high costs and other associated impracticalities. This paper presents a novel framework for estimation of the vehicle sideslip angle. The proposed algorithm utilizes an adaptive tire model in conjunction with a model-based observer. The proposed adaptive tire model is capable of coping with changes to the tire operating conditions. More specifically, extensions have been made to Pacejka's Magic Formula expressions for the tire cornering stiffness and peak grip level. These model extensions account for variations in the tire inflation pressure, load, tread depth and temperature. The vehicle sideslip estimation algorithm is evaluated through experimental tests done on a rear wheel drive (RWD) vehicle. Detailed experimental results show that the developed system can reliably estimate the vehicle sideslip angle during both steady state and transient maneuvers.

scholarly journals Cooling Performance of Arrays of Vibrating Cantilevers

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Mark Kimber ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Vibration Amplitude ◽  
Past Research ◽  
Resonant Mode ◽  
Operating Conditions ◽  
Infrared Thermal Imaging ◽  
Practical Applications ◽  
Wide Range ◽  
Piezoelectric Fans

Piezoelectric fans are vibrating cantilevers actuated by a piezoelectric material and can provide heat transfer enhancement while consuming little power. Past research has focused on feasibility and performance characterization of a single fan, while arrays of such fans, which have important practical applications, have not been widely studied. This paper investigates the heat transfer achieved using arrays of cantilevers vibrating in their first resonant mode. This is accomplished by determining the local convection coefficients due to the two piezoelectric fans mounted near a constant heat flux surface using infrared thermal imaging. The heat transfer performance is quantified over a wide range of operating conditions, including vibration amplitude (7.5–10 mm), distance from heat source (0.01–2 times the fan amplitude), and pitch between fans (0.5–4 times the amplitude). The convection patterns observed are strongly dependent on the fan pitch, with the behavior resembling a single fan for small fan pitch and two isolated fans at a large pitch. The area-averaged thermal performance of the fan array is superior to that of a single fan, and correlations are developed to describe this enhancement in terms of the governing parameters. The best thermal performance is obtained when the fan pitch is 1.5 times its vibration amplitude.

Copper-Carbon Nanotube Micropillars for Passive Thermal Management of High Heat Flux Electronic Devices

2020 ◽  
Author(s):  
Gerardo Rojo ◽  
Jeff Darabi
Keyword(s):  
Thermal Management ◽  
Thermal Performance ◽  
Computational Study ◽  
Copper Substrate ◽  
Heat Removal ◽  
Cost Effective ◽  
High Heat ◽  
Operating Conditions ◽  
High Heat Flux ◽  
Micropillar Array

Abstract Miniaturization of electronic products and a consequent rapid increase in power density of advanced microprocessors and electronic components have created a need for improved cooling techniques to efficiently remove heat from such devices. Traditional air-cooled heat sinks have been utilized for several decades as the most cost-effective cooling technique for electronic cooling applications. However, the existing thermal management solutions are unable to maintain the temperature of the next generation of complex electronic systems within acceptable limits without adding considerable weight and complexity. This paper reports a microstructured wick for application in passive thermal management systems such as heat pipes and vapor chambers. The wick structure consists of mushroom-like composite copper-carbon nanotubes (Cu-CNT) micropillars. The small spacing between micropillar heads provides a higher capillary pressure whereas the large spacing between the base of micropillars provides a higher permeability for liquid flow. The micropillar array was fabricated on a copper substrate using an electroplating technique. The micropillar array was then tested in a controlled environment to experimentally measure its thermal performance under several operating conditions. A heat removal capability of 80 W/cm2 was demonstrated at a wall superheat of 15° C. In addition, a computational study was performed using ANSYS Fluent to predict the thermal performance of the micropillar array. Model predictions were compared with the experimental results and good agreement was obtained.

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