Clutches

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 due to 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.

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Abstract—The engineering technology for automotive systems is currently edging toward improving fuel economy. Transmission is one of the major parts to determine overall energy efficiency. The goal of this paper is to investigate the feasibility of a new clutch actuator in order to ...

Take-up judder is the first rigid body torsional mode of the clutch system, which occurs during clutch engagement. This phenomenon is induced by stick-slip oscillations at the friction lining interfaces between the clutch disc and flywheel, and the pressure plate. The phenomenon is influenced by the clutch lining friction characteristics, the topography of the mating-sliding surfaces and the operational conditions during the engagement process.
Therefore, the interfacial characteristics are affected by contact pressure, interfacial slip speed and surface temperature. Take-up judder causes driver and vehicle occupant discomfort, as well as gradual wear of contacting surfaces. The response frequency of the system is reported to be in the range 5-20Hz, depending on the clutch system and vehicle inertia. In this paper the measured interfacial friction characteristics together with clamp load variation (contact pressure) under different surface temperatures are included in a multidegree of freedom dynamic analysis to obtain torsional vibrations of the system, pertaining to take-up judder conditions. Such an in-depth investigation has not hitherto been reported in literature. The paper shows that take-up judder is omnipresent under all clutch engagement conditions, but its poignancy is most evident at cold surface temperatures. It is also shown that the transient judder response has a broader spectral content that is generally acknowledged.

Automotive clutches are prone to rigid body torsional vibrations during engagement, a phenomenon referred to as take-up judder. This is also accompanied by fore and aft vehicle motions. Aside from driver behaviour in sudden release of clutch pedal (resulting in loss of clamp load), and type and state of friction lining material, the interfacial slip speed and contact temperature can significantly affect the propensity of clutch to judder. The ability to accurately predict the judder phenomenon relies significantly on the determination of operational frictional characteristics of the clutch lining material. This is dependent upon contact pressure, temperature and interfacial slip speed. The current study investigates the ability to predict clutch judder vibration with the degree of complexity of the torsional dynamics model. For this purpose, the results from a four and nine degrees of freedom dynamics models are compared and discussed. Subsequently, the predictions are compared with the acquired data from an automotive driveline test rig. It is shown that the complexity of the dynamic model, intended for the study of a clutch system, can be as important as the thermo-mechanical and frictional properties of the clutch friction lining material.

Clutches are commonly utilised in passenger type and off-road
heavy-duty vehicles to disconnect the engine from the driveline and
other parasitic loads. In off-road heavy-duty vehicles, along with fuel
efficiency start-up functionality at extended ambient conditions, such
as low temperature and intake absolute pressure are crucial. Off-road
vehicle manufacturers can overcome the parasitic loads in these
conditions by oversizing the engine. Caterpillar Inc. as the pioneer in
off-road technology has developed a novel clutch design to allow for
engine downsizing while vehicle’s performance is not affected. The
tribological behaviour of the clutch will be crucial to start
engagement promptly and reach the maximum clutch capacity in the
shortest possible time and smoothest way in terms of dynamics. A
multi-body dynamics model of the clutch system is developed in
MSC ADAMS. The flywheel is introducing the same speed and
torque as the engine (represents the engine input to the clutch). The
hydraulic pressure is applied behind the piston to initiate the
engagement. The angular motion of the plates is supported by friction
torque between the plates and friction linings. The conjunctions
between paper-based linings and steel plates are designed to be dry.
Friction (the most significant tribological feature of the linings in
torque transmission) is measured in a pin-on-disc tribometer and
mapped into the dynamics model in MSC ADAMS. The pin-on-disc
tribometer is able to capture the variation of friction coefficient with
contact pressure and sliding velocity. The surface topography is
obtained experimentally to examine the consistency of surface
properties. The normal pressure and tribology of the contacting
components determines the engagement time, clutch capacity and
dynamic behaviour of the clutch.

The frictional performance of the clutch mating surfaces varies transiently during clutch engagement. The friction characteristics depend on the clamp load, relative slip speed of the mating surfaces and  the generated contact temperature. These operating conditions affect the characteristics and lead to clutch take-up judder during engagement. To study this phenomenon as well as issues relating to clutch wear, it is essential to evaluate the friction lining characteristics. This paper replicates the clutch conditions through careful experimentation with a fully instrumented pin-on-disc tribometer. It is shown that the kinetic coefficient of friction for the clutch friction lining material in contact with  the sinusoidal wavy and rough surface of pressure plate decreases with rising contact temperature and increasing slip speed.

Control of the dry clutch engagement process for automotive application is considered. A linear quadratic state feedback controller is obtained by solving a finite time horizon optimal control problem. The engine torque and the load torque are assumed as known disturbances. The control signal consists of a feedforward and a feedback component and it guarantees fast engagement, minimum slipping losses and comfortable lock-up. The critical standing start operating conditions are considered. Numerical results show the good performance of the closed loop system

This paper presents the development of a model-based estimator to provide real-time information about important, but unmeasurable, operating variables in stepped automatic transmissions. Specifically, model-based estimation of the transmission output shaft torque and the clutch pressure for each clutch involved in the gear shifting process is presented. Knowledge of clutch pressures and output shaft torque can be used for online diagnostics or development of closed-loop control in order to improve shift quality. In the approach described here, only speed measurements are used, viz, transmission input and output speeds and the wheel speed. The estimation technique used in this paper is based on the sliding mode observer. The performance of the estimation scheme is evaluated by simulation. Analysis of the accuracy and robustness of the proposed schemes is also presented.

A Clutch is a machine member used to connect the driving shaft to a driven shaft, so that the driven shaft may be started or stopped at will, without stopping the driving shaft. A clutch thus provides an interruptible connection between two rotating shafts. The present used material for friction disc is Grey Cast Iron, Sintered Iron, Kevlar, Aluminium Metal Matrix Composite etc. In this thesis analysis is performed using C45 and Sialons materials. These materials are considered due to their Specific Properties. In this thesis C45 and Sialons materials are taken. A single plate clutch is designed and modeled using SpaceClaim in Ansys software. Static analysis is done on the clutch to determine stresses and deformations using materials Grey Cast Iron, Sintered Iron, Kevlar, Aluminium Metal Matrix Composite, C45 and Sialons. Analysis is done in Ansys. Theoretical calculations are also done to determine stresses.