Dry Clutch Engagement Research Articles

The Optimization and Control of the Engagement Pressure for a Helicopter Dry Clutch

The engagement quality of a helicopter dry clutch has a significant impact on the service life and overall flight performance of the helicopter. The engagement oil pressure is an important factor affecting the clutch engagement quality. Firstly, a nonlinear input–output dynamic model for the dry clutch is developed to investigate the optimization and control of dry clutch engagement pressure in this paper. Secondly, to efficiently obtain the optimal pressure curve, an optimal method combining the developed dynamic model with the state feedback gain of a linear quadratic optimization regulator (LQR) solver is proposed. Thirdly, considering that hydraulic actuators may struggle with tracking certain pressure curves, a hydraulic actuator for accurately tracking pressure curves based on fuzzy PID is proposed. The simulation results indicate that the developed hydraulic actuator exhibits an excellent tracking performance. Moreover, compared with linear and segmented pressure curves, the optimal pressure curve derived from the proposed method significantly reduces jerk, friction work, and engagement duration, resulting in improved helicopter dry clutch engagement quality.

Tribo-thermal simulation study of AMT dry clutch assembly under the continuous sliding grinding condition

Electronic Mechanical Transmission (AMT) is an automatic transmission device that combines hydraulic automatic transmission (AT) with manual transmission (MT). AMT has the advantages of automatic transmission as well as high efficiency, low cost, simple structure, and easy manufacture in the traditional manual transmission system. In dry clutch engagement, the wear of the engagement surface should be minimized to achieve good performance. It is necessary to control some influencing factors during its use. When the car starts, the flywheel and driven disc in the clutch change from a separation state to a full engagement state. When joining, due to the increase in speed of the driven disc, relative sliding occurs between the drive and driven parts, which causes the temperature of the friction surface to rise. If the temperature is too high, the wear of friction plates will be increased, which will reduce the service life and working stability of the clutch. In this study, the coupling field transient analysis of the clutch under continuous sliding wear conditions is carried out, and the clutch temperature change and heat generated by friction are obtained by simulation calculation under the use of simulated clutch holding for 1s. Based on the results of the simulation, the factors that may affect the friction heat generation of the clutch are analyzed.

Characterization of the Thermal Behavior of a Complex Composite (Clutch Facing) Combining Digital Image Stereo Correlation and Numerical Approach.

Car clutch facings are complex fiber-reinforced composites. The coefficient of thermal expansion (CTE) of the composite is one of the main thermal properties, which affects dry clutch engagement process due to heat associated with friction. In the case of clutch facing, which only exists in its final form as a non-planar annular disc, it is difficult to define an elementary representative volume. The objective of this work was to develop a method for identifying the CTE distributions on the entire part. A device allowing measuring the strain fields by digital image correlation (DIC) under homogeneous thermal loading (up to 300 °C) was developed. The experimental results highlight the heterogeneity and the orthotropic nature of the material behavior and the influence of the angle between the fibers on the CTE. To take into account that the measured strain fields are related to the CTE, but also to the shape of the part, different approaches to identify the CTE were considered: direct measurements, classical laminate theory (CLT) and finite element method updating (FEMU). Only the FEMU allows an accurate identification of the CTE distributions. Nevertheless, the CLT respects the orders of magnitude and remains a useful tool for the design of clutches.

Control of Pneumatic Actuator for Automated Mechanical Transmission Dry Friction Clutch Base on the Pulse Width Modulation Signal

To ensure quality of dry friction clutch engagement in automated mechanical transmission during vehicle starting-up and maneuvering the control range of clutch actuator has to be maximum wide. It depends on the consistency of the clutch actuator geometric parameters with the electrical characteristics of the used solenoid valves, the output stage of the controller and the PWM control signal frequency. In addition to precision electronic control the driver must be able to “manually” operate the dry friction clutch in emergency. That is why friction clutch must have two independent control circuits. The original automated drive with a duplicate pneumohydraulic circuit for the friction clutch is presented in the paper, as well as the research results of the PWM frequency influence on operating range of the clutch pneumatic actuator. The research was based on the analysis of semi-natural experiment for assessing the functional performance of the designed automated mechatronic control system for the truck mechanical transmission. Ecomat R360 controllers were used as a hardware base of the test bench information control system. The developed software for the controller with one-parameter feedback on the clutch release lever movement allows to provide the PWM signal of varying duty ratio to the proportional solenoid valve of the automated drive. A graphical representation of the research results was performed with visualization possibilities of CoDeSys V2.3. During the semi-natural experiment, the polynomial dependence between variation of the clutch actuator control range and the generated PWM signal frequency in the range up to 400 Hz was revealed as well as practical recommendations on the choice of the optimum PWM signal frequency are also given in activity. The research results can be used in an adaptive control algorithm for automated mechanical transmission of trucks and road trains to ensure precise control of the clutch actuator in the starting-up and maneuvering processes.

The performance of Cu-based friction material in dry clutch engagement

An enhanced Cu-based friction material was prepared by the powder metallurgy techniques and proposed for use in the dry clutch system. The friction characteristics and wear rate of this friction material sliding against 65Mn steel are obtained using Universal Material Tester-5. The friction pairs were subjected to two operating variables, which are sliding speed and temperature. The effect of these variables during the engagement process of the friction pairs is investigated. Knowing the normal applied force and dimension of the clutch disc, the dynamic friction coefficient was translated to friction torque capacity with time. It was found that instability can be excited at low operational conditions when the resulting friction coefficient is high. At 25 ℃, the dynamic friction torque oscillates with time likewise at 400 ℃. Generally, a more stable friction torque is obtained when the sliding speed is varied compared to varying the temperatures. Moreover, the influence of the operating temperatures and sliding speeds on thermal buckling and thermoelastic instability of the friction disc is the second consideration in this work. The onset of thermoelastic instability occurs when the sliding speed exceeded 200 r/min and the results for the growth rate of hot spots were found to agree well with the critical speed of the system. Also, thermal buckling was highly dependent on the temperature difference between the inner and outer radius of the friction disc.

Noise, vibration and harshness during dry clutch engagement oscillations

Determining the root causes of various noise, vibration and harshness phenomena in modern automotive drivetrains is a critical task for industry, since noise, vibration and harshness issues often result in worsened driving experience. The aim of the current research is to investigate the dynamics during dry clutch engagement and the associated – often problematic – oscillations. This paper reports the development and partial validation of numerical models to study dry clutch behaviour. The models are used to investigate the influence of clutch and throttle actuation on the occurrence of unwanted clutch oscillations. The dynamic coefficient of friction between the clutch interacting surfaces was measured using a pin-on-disc rig under different slip speeds and contact pressure conditions, which are representative of a typical clutch engagement manoeuvre. The paper highlights the occurrence of instability issues in clutch dynamics (disc radial mode) as potential generators of aggressive noise, vibration and harshness, particularly during two different clutch pedal actuations. Such analysis has not hitherto been reported in the open literature.

Thermal Compensation Control Strategy in Automated Dry Clutch Engagement Dynamics and Launch Manoeuvre

Repeated engagements in dry clutch systems could yield remarkable increase of clutch disk temperature. In dry clutch based transmissions like Automated Manual Transmissions and Dual Clutch Transmissions the overheating leads to poor control of gearshift quality due to unpredictable and fast change of frictional characteristic. Even permanent damage of clutch facings may occur. Under this light, this paper focusing on thermal effects to improve control performances and prevent uncomfortable engagements. To this aim, detailed analyses of dry clutch architecture have been carried out to understand the main phenomena which affect the clutch torque transmissibility. Moreover, a lumped thermal model has been developed to predict both the disk surface and cushion spring temperature in real-time environment. To validate the proposed thermal model, a non-linear least squares method has been used by comparing simulations with finite element results. A control strategy based on model predictive control and thermal compensation effects has been proposed to simulate vehicle launch manoeuvres in flat and up-hill road conditions with low and high initial clutch temperature as well. Finally, the proposed control approach has been compared with classic PI control strategy to prove its effectiveness.

Detailed Modeling and Experimental Assessments of Automotive Dry Clutch Engagement

The characteristics of the clutch engagement process would have significant influences on the torque transmissibility and operation comfort. However, some crucial components are simplified in many previous literature, which would cause imprecision. Therefore, it is important to build a detailed mathematical model of these components and inspect the whole process of clutch engagement. In order to improve the torque transmissibility and achieve better pedal releasing comfort, solutions based on the modeling of the clutch cover assembly and the friction disc assembly, the analysis of the clamping force and the releasing characteristics of the release bearing are proposed in this paper. Furthermore, models of the crucial components such as the diaphragm spring, which connects the straps and cushion plate, are built and the corresponding mechanical properties are analyzed. Based on the manufacturing tolerance, the life cycle, and the wear properties, diaphragm spring correction formula is proposed by referring to Almen-Laszlo method. On the system level, the whole engagement process is divided into four stages because of the differences between the engaging and disengaging processes, which would affect the pedal releasing comfort in the manual transmission system and the shifting quality in the automated transmission system. To demonstrate the effectiveness of the proposed method, detailed mathematic models are built and the corresponding experiments are conducted.

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

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.

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.

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.

Joint structure for the real-time estimation and control of automotive dry clutch engagement

In this paper, real-time identification of the dry-clutch torque characteristics model in automotive systems is investigated. The proposed algorithm focused to provide the direct capability to update the clutch torque characteristics model by using engine speed and torque as measurable signals in real-time, within a multiple model predictive control loop. First, the clutch torque is estimated with some uncertainty. Then, it is proposed a new trust-region based identification approach which is robust enough to cover this uncertainty. The aim of the MPC controller is to ensure a comfortable lockup by avoiding engine stall and reasonable engagement time. The effectiveness and performance of the approach are demonstrated through the real-time model simulations in various conditions.

Multiple Constrained MPC Design for Automotive Dry Clutch Engagement

In this paper, a multiple model predictive controller (MPC) is proposed for the management of passenger car start up through dry clutch in automated manual transmission. Based on a high-order dynamic model of powertrain system, the feedback controllers are designed by using the crankshaft angular speed and the clutch disk angular speed as measured variables. Moreover, the MPC is developed to comply with constrains both on the input and on the output. The aim of the controller is to ensure a comfortable lockup and to avoid the stall of the engine as well as to reduce the engagement time. Numerical results show the good performance of the MPC with constrains in overcoming critical operating conditions. Comparisons with similar state-of-the-art works are also shown.

Optimal control of dry clutch engagement based on the driver’s starting intentions

This paper explores the association between the driver’s starting intentions and control of dry clutch engagement during the vehicle launch in order to develop an intelligent automated mechanical transmission system. The optimal engagement laws are deduced by finding a compromise between the friction loss, the shock intensity, the engine torque and the engine angular acceleration, based upon the extremum value theorem. The optimal parameters of clutch engagement are adjusted for the value of the shock intensity. The driver’s starting intentions, which can be divided into three patterns, namely fast starting, medium-speed starting and slow starting, are associated with optimal control of clutch engagement according to fuzzy control theory. It is demonstrated that optimal control of dry clutch engagement can reflect the driver’s starting intentions correctly. The obtained optimal accelerator opening has more advantages than the actual accelerator opening, which can be adopted as the ideal input of the vehicle with an intelligent automated mechanical transmission system.

Observer-Based Optimal Control of Dry Clutch Engagement

Conventionally the control of dry clutch's engagement during a standing start in AMT vehicles is assured by look-up tables whose values are carefully chosen to produce a smooth synchronisation at the expense of a long slipping time. This article proposes, instead, a two phase approach: a first open-loop look-up table phase aiming to reduce the slipping time and a second observer-based optimal control phase assuring the engagement comfort. Particular attention has been given to the details of the on-line implementation on a Clio AMT prototype. Experimental results show both a close match between the predicted and the actual trajectories and a high level of comfort.

LURCH AVOIDANCE STRATEGY AND ITS IMPLEMENTATION IN AMT VEHICLES

Conventionally the control of dry clutch's engagement during a standing start in AMT vehicles is assured by look-up tables whose values are carefully chosen to produce a smooth synchronisation at the expense of a long slipping time. This article proposes, instead, a two phase approach: a first open-loop lookup table phase aiming to reduce the slipping time and a second observer-based optimal control phase assuring the engagement comfort. Particular attention has been given to the details of the on-line implementation on a Clio AMT prototype. Experimental results show both a close match between the predicted and the actual trajectories and a high level of comfort.

A Control Strategy on Starting up of Vehicle with Automatic Manual Transmissions (AMT)*

Recently, starting control takes an important role in the automatic manual transmission systems; clutch engagement control is the key of it. In order to improve the starting performance of AMT vehicle, clutch dynamic response must be control during the slipping phase. Therefore, this paper puts forward a control strategy for the dry clutch engagement process, considered as a finite time optimal control problem. The main idea of this strategy is to obtain a linear quadratic state feedback controller by solving the optimal control problem. The performance obtained with the proposed controller are compared with those achievable by means of a classical open loop control strategy. Moreover, different starting operating conditions are used to test the controller performance. Numerical simulations shows the good performance obtained by the proposed controller, which guarantees fast engagement, minimize the slip losses, reduce the fuel consumption and improve in the shift quality.

Optimizing the thermal properties of clutch facings

The tribological contact under sliding situation taking place in the friction surfaces during dry clutch engagement process is strongly affected by heat transfer occurring in the clutch system. Heat is produced due to dissipation mechanisms of mechanical work which is developed by the frictional forces acting in the contact paths yielding the interfacial temperature to increase. The magnitude of temperature rise depends to a large extent on the thermal properties of clutch facings fitting the friction disk. This paper gives a modeling of the thermal properties of general organic clutch facings which are manufactured according to the scatter wound procedure. Starting from the material formulation, the rule of mixtures approach is used to determine the local thermal properties for an elementary yarn segment embedded in a matrix shell taken to be a representative volume element. Then, estimates for the thermal properties of the whole facing are obtained through a homogenization technique where global averaging over the facing surface of the directional contributions set by these individual segments are performed. Optimization of the facing thermal properties is conducted after that with regard to material formulation of the clutch facings and key parameters of the fabrication process.

OPTIMAL TRACKING FOR AUTOMOTIVE DRY CLUTCH ENGAGEMENT

Based on a state space dynamic model of a typical automotive driveline, a new control technique for the dry clutch engagement process is proposed. The feedback controller is designed following an optimal control approach by using the crankshaft speed and the clutch disk speed as state variables: a tracking problem is formulated and solved by using the engine torque and the clutch torque as control variables. The controller guarantees fast engagement, minimum slipping losses and comfortable lock-up. The critical standing start operating conditions are considered. Numerical results show the good performance obtained with the proposed controller.

Optimal Piecewise-Linear Control of Dry Clutch Engagement

This paper proposes a novel piecewise linear feedback control strategy for the dry clutch engagement process. Based on a dynamic model of the powertrain system, the controller is designed by minimizing a quadratic performance index subject to constraints on the normal force, normal force derivative, and engine speed. The resulting model predictive controller is shown to consist of a piecewise linear feedback control and can be tuned so that fast engagement, small friction losses and smooth lock-up are achieved. Numerical results show the good performance of the closed-loop system.