Clutch Engagement Research Articles

Optimizing thermal performance of a dry rigid clutch by varying groove pattern and friction material

A precise calculation of temperature distribution is necessary to avoid the heat fluctuation in clutch facing and this also acts as an aid during a clutch design to achieve improved heat transfer. This article presents a systematic way to design and analyze the thermal characteristics of a clutch facing during clutch engagement assuming uniform wear rate between the contact surfaces. Finite Element Analysis (FEA) has been used to study the effect of groove patterns on the thermal characteristics of a dry friction clutch disc, followed by a comparative analysis between the organic and inorganic materials. The clutches with different groove configurations are designed using SOLIDWORKS 2020 while the thermal simulations are carried out using ANSYS 2020 R2. In this research, the optimal design for better thermal stability is accomplished by considering different configurations and materials for the clutch facing. The acquired temperature results for each configuration depict that the heat dissipated by convection through the friction material can be regulated by altering the groove pattern and area. It is found that organic based friction linings are exhibiting about 30% lower temperatures than inorganic linings.

Architecture Modeling and Test of Tractor Power Shift Transmission

Architecture modeling, simulation, and test verification are performed to meet the requirements of multi-domain modeling and simulation of tractor power shift transmission (PST). The principles of architecture modeling and high level architecture (HLA) are analyzed, and the PST architecture modeling connotation and simulation system structure are studied. Then the dynamic principles of PST mechanical, hydraulic and control subsystems are analyzed in the preparation phase, sliding friction phase and holding phase of clutch engagement. To build the PST system simulation model, the simulation models and components of the three subsystems are established, and the object and interaction classes of the simulation object model (SOM) for each component are defined. After that, the parameter mapping relationship between the components is analyzed, the interfaces between the simulation components and HLA are encapsulated, and the simulation component running sequence is analyzed. Finally, the PST clutch engagement law under tractor shift conditions is simulated and tested. The relative error and correlation coefficient between the simulated and test data of shift solenoid valve drive current are used as indexes to evaluate the PST system simulation model. The results show that the simulated drive current curves are consistent with the test ones. The maximum error between the simulated and test shift time appears at the third gear downshift point, with a value of 7.89%, and the minimum correlation coefficient value between the simulated and the test drive current at all shift points is 0.92, which indicate that the PST system simulation model is effective and accurate.

Simulation of Design Factors of a Clutch Pack for Power-Shift Transmission for an Agricultural Tractor.

The objective of this study is the simulation of the most affected design factors and variables of the clutch pack for the power-shift transmission (PST) of a tractor based measured data. The simulation model, the mathematical model of sliding velocity, a moment of inertia, and clutch engagement pressure of clutch pack were developed using the powertrain and configurations of the real PST tractor. In this study, the sensor fusion method was used to precisely measure the proportional valve pressure by test bench, which was applied to the simulation model. The clutch engagement times were found 1.20 s at all temperatures for determined factors. The engagement pressures have a significant difference at various temperatures (25 to 100 °C) of the hydraulic oils after the 1.20 s but the most affected factors were satisfied with the simulation conditions that ensure the clutch engagement on time. Finally, this sensor fusion method is believed to be helpful in realizing precision agriculture through minimization of power loss and maximum energy efficiency of tractors.

Decoupling internal model control for the robust engagement of clutches

Research on the robustness of clutch engagement control is attracting considerable interest because of its wide applications in advanced powertrains. Internal model control (IMC) is advantageous because it can handle model errors and external disturbances with light computational loads. However, during clutch engagement, two control inputs (engine output torque and clutch transmitted torque) and two system outputs (driving speed and the driven part of the clutch) are coupled; moreover, the two reference inputs are considerably different. A method for directly decoupling and stabilizing multi-input multi-output systems controlled by a two-degree-of-freedom (2DOF) IMC is proposed based on the construction of V-canonical matrices. The proposed method allows simple expressions for the control algorithm to be obtained without computing an inverse matrix that is used conventionally. Two filters, considering both the reference inputs and system characteristics, are independently designed considering the decoupling operation. The simulation results show that the proposed decoupling 2DOF IMC gains a considerably less tracking error and better robustness to model error and disturbance compared to classical 2DOF IMC and model predictive control. The performance is validated via dynamometer experiments.

Upshift optimization control of dedicated hybrid transmission with P2 configuration

Based on the traditional automatic transmission, Dedicated Hybrid Transmission (DHT) with P2 configuration is developed by replacing hydraulic torque converter with a wet electronically controlled clutch and a driving motor. The paper proposed a coordinated control strategy of the upshift process for the P2 configuration parallel hybrid vehicle equipped with DHT to ensure the shift quality. Firstly, considering the meshing transmission loss, the dynamics modelling of DHT shifting process was built by Lagrange method, and the model parameters were identified by bench test; Secondly, taking no jerk as the constraint and minimum slipping work as the optimisation goal, the forward discrete dynamic programming was used to solve the optimal control law of the transmission torque of the shifting clutch and the input shaft torque of transmission. Besides, for the hybrid operation mode, further considering the influence of the motor, engine and main clutch, two coordinated control strategies of the main clutch engagement and slipping were proposed. The simulation results show that the two coordinated control strategies can achieve small jerk and slipping work, ensure smoothness in the course of gear shift. And by the method of slipping control of the main clutch, the shifting time can be shortened.

Design, fabrication, modelling and analyses of a movable speed bump-based mechanical energy harvester (MEH) for application on road

In this paper, a novel mechanical energy harvester (MEH) based on a movable speed bump, which is integrated to a rack and gear mechanism with a combination of one-way clutches, is designed, fabricated and tested for application on the road. The device is capable of harvesting the kinetic energy that the decelerating vehicles dissipate in the form of vibrations during impact with the speed bump on the road, not only under loaded but also restoration conditions. The proposed harvester consists of four modules including energy input, transmission, energy conversion and storage. The up-down input motion of the bump is converted into bidirectional rotation by the transmission module, which is further transformed into unidirectional rotation of generator shaft by the continuous engagement and disengagement of one-way clutches. The mechanical energy is converted into electrical power by a DC generator that can be stored in batteries after rectification and used to light up the LED bulbs as electrical load. The operation of the MEH was modelled and simulation study was conducted in Solidworks and Autodesk Inventor to investigate and validate the dynamic response of the mechanism. A prototype was fabricated to determine the feasibility of the design and tests were performed to evaluate the output power from the MEH. A peak output power of 11.99 W and a peak voltage of 20.57 V was achieved at an excitation speed of 120 mm/s and applied force of 150 N. The experimental results were compared with the simulation and were found lying within accordance with each other at similar loading conditions. The proposed device would be able to power road lights, traffic cameras and signals which makes it suitable for application on the road, at the exit of the toll plaza and remote suburbs.

Performance analysis and tank test validation of a hybrid ocean wave-current energy converter with a single power takeoff

This paper introduces a hybrid ocean wave-current energy converter (HWCEC) that harvests energy from ocean waves and current simultaneously with a single power takeoff. The wave energy is extracted through relative heaving motion between a floating buoy and a submerged second body, while the current energy is extracted using a marine current turbine. Energy from both sources is integrated by a hybrid power takeoff whose concept is based on a mechanical motion rectifier. The hybrid power takeoff with two one-way clutches converts bidirectional, up-and-down motion from the waves into unidirectional rotation of the generator. Meanwhile a third one-way clutch couples the turbine with the same generator. The wave and current can simultaneously or separately drive the same generator through different engagement and disengagement statuses of the one-way clutches. Time-domain simulation is conducted with hydrodynamic coefficients obtained from computational fluid dynamics analysis and the boundary element method. Tank tests were conducted for an HWCEC under a co-existing wave and current inputs. For comparison, separate baseline tests of a turbine and a two-body point absorber, each acting in isolation, are conducted. Experimental results validate the dynamic modeling and show that an HWCEC can increase the output power with a range between 24 and 89% over either current turbine and wave energy converter acting individually, and it can reduce by up to 70% the peak-to-average power ratio compared with the wave energy converter on the tested conditions.

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.

Temperature Analysis of Wet Clutch Surfaces During Clutch Engagement Processes Based on Friction Pad Patterns

Temperature distributions of wet clutch contact during engagement and disengagement processes are investigated considering lubricant flow behaviors in the gap between the friction pad and steel separator. Frictional heat generated by wet clutch contact in repeated operational modes that simulates high thermal endurance performance of a wet clutch system is modeled. This study applies CFD analysis to the lubricant convective flows that remove most of the frictional heat with respect to groove patterns on the frictional pad surface. Based on fluid flow analysis between the friction pad gap and the steel separator that includes the effects of pattern shapes on the friction pad, frictional heat, convective cooling behaviors and temperature distributions are computed with the repeated modes of varying sliding velocities and applied loads. The cooled frictional heat is investigated considering the convective flows in the gap of friction pad and separator. Frictional temperature variations on a wet clutch surface are computed for the effects of groove pattern shapes on the friction pad, waffle, and radial-arc types for better cooling effects. It is expected that the computational results will provide design methods for higher heat resistance durability and stable frictional torque transfer and effective cooling performance in wet clutch systems.

Influence of single and dual mass flywheel usage in IC engines on clutch dynamics

The dual mass flywheel especially used in diesel engines has a structure in which the single- mass flywheel is divided into two parts and these two parts are combined with a curved helical spring. The flywheel is a part that reduces the speed fluctuations in the crankshaft of the internal combustion engines. In addition to this function, the dual mass flywheel dampens the torsional vibrations better than the clutch disc springs thanks to the spring system found in its structure. There are no torsional springs in the disc of the clutch system where dual mass flywheel is used. The dual mass flywheel is used with a rigid clutch disc without torsion springs. From this point of view, it is thought that the clutch dynamics of both systems are different. For this purpose, mathematical models of both systems were formed. The obtained models were solved after the appropriate transformations. As a result, it was seen the clutch engagement times are almost same in both systems. However in the clutch system where the dual mass flywheel is used the clutching process is performed more smoothly.

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.

Automotive vehicle clutch engagement characteristics for different types of force trajectories

Vehicle driveline of automobile, which transmit engine energy to the wheels, is complex system with nonlinear behavior. In manual transmission clutch engagement performance depends upon driver’s skill and is significantly affected by traj ectory of clutch force during engagement process. In this work different types of clutch force trajectories are analyzed based on engagement performance which can be incorporated in automated manual clutch system. A driveline of a vehicle is modeled using multi body dynamics software and simulation were carried out for different type of force trajectories i.e. linear, parabolic and spline, which is followed by clutch force during engagement. The results of simulation were used to analyze the quality of clutch engagement and vehicle performance by looking into clutch lock-up phase and vehicle launch. The clutch lock time and clutch lock speed for various types of trajectories were calculated and compared. These results were also compared with analytical results reported by researchers. The results would be useful in selecting appropriate type of clutch actuating force trajectories for automation of clutch system of automobiles.

Optimal control of a novel cutter head driving system for tunnel boring machine

The cutter head of a tunnel boring machine may be trapped in extremely adverse geological environments, which requires a large enough driving torque to get rid of the trapped condition. In this paper, a novel driving scheme is proposed to improve the driving performance of the tunnel boring machine cutter head without increasing the installation power. First, the hydro-viscous clutch is introduced to achieve the soft start of the cutter head by the flexible effect of viscous oil film. Then, the flywheel is employed as the energy storage element to provide sufficient torque during the hydro-viscous clutch engagement, which assists the cutter head to get rid of the trapped condition. Moreover, an optimal state feedback control law based on a linear quadratic regulator is designed by compromising system impact and hydro-viscous clutch friction loss to optimize the hydro-viscous clutch engagement process and achieve favorable driving performance of the cutter head. Finally, numerical simulations are conducted to validate the effectiveness of the proposed driving technology.

Zero overshoot speed controller with active damping for improving engine clutch engagement performance

This paper proposes an enhanced speed control algorithm that synchronizes the rotation speeds of the engine and the drive motor at the engine start to improve the engagement performance of the engine clutch in a parallel hybrid vehicle. The zero overshoot with active damping speed controller proposed in this paper has an active damping control structure that is robust against load variations and a control structure that does not include a zero in the control response. This feature has the advantage of reducing the engine clutch engagement time as much as possible to improve the acceleration response of parallel hybrid vehicles and to minimize the energy wasted to maintain heavy engine rotation. The proposed algorithm has been validated through simulation using Matlab and through a vehicle test.

DCTF Flow Distribution Design in Clutch Packs of wet DCTs

Wet clutch pads require temperature control on contact surface because increased frictional heat abruptly decreases friction coefficient, and eventually, the desired torque transfer becomes difficult to control. Generation of frictional heat is inevitable during clutch engagement, but the frictional heat should be cooled by the convective flow of DCTF for the stable torque transfer capacity in the wet clutch pack. Two-phase DCTF flow behavior was investigated inside the entire cavity space of a wet clutch pack, and detailed flow patterns were computed using CFD analysis. Particularly, outer clutch pack of the DCT, which has severe thermal duty, was studied with respect to DCTF flow rate distribution through the gaps of the clutch pads. Hydrodynamic pressures, velocity fields of DCTF flow, and volume fractions of the DCTF fluid in the wet clutch pack were computed, and evenly distributed flows through the gaps of outer clutch pads to combat unbalanced thermal durability among the clutch pads were achieved by optimizing the design of hub shell outlets. Using computational results, DCTF velocity fields and the volume of fluid (VOF) were compared and they will lead to the well-distributed flow design against the abnormal local frictional temperature rises without unnecessary additional oil pump power.

Variation mechanism of the friction torque in a Cu-based wet clutch affected by operating parameters

A comprehensive thermodynamic model is proposed to investigate the variation mechanism of friction torque in a Cu-based wet clutch affected by the operating parameters, which is verified by the bench test. The results show that the variation of friction torque is composed of three stages: preparation stage A, stable growth stage B and exponential growth stage C. Moreover, increasing the relative speed can reduce the growth rate of friction torque, so as to decrease its peak value; contrarily, increasing the applied pressure can effectively offset the decline of the friction torque slope caused by the rise of relative speed. Therefore, the relative speed and applied pressure should be reasonably matched to ensure a smooth and safe clutch engagement.

Efficient Mode Transition Control for Parallel Hybrid Electric Vehicle With Adaptive Dual-Loop Control Framework

Mode transition control problem in a hybrid powertrain has always been a central concern, because many complicated transient dynamics are involved in this process, such as engine-start, clutch engagement, and actuator control, etc. Especially for a parallel hybrid electric vehicle (HEV), the drivability problem during mode transition process is significant yet challenging to solve. In this paper, a new efficient mode transition control method with adaptive dual-loop control framework is proposed for the clutch engagement in a parallel HEV. Firstly, the expected clutch engaging speed can be calculated by two approaches, optimization method via particle swarm optimization algorithm, and practical method by compromising the transient vehicle jerk and the clutch slipping power, respectively. Utilizing the integral transformation, the demand clutch position trajectory for the inner loop can be obtained. Considering the uncertainties and the backlash in the clutch actuator system, an adaptive state feedback controller is designed in the inner loop. Simulation and experimental results show that the proposed control method can effectively improve the HEV drivability while taking clutch actuator uncertainties into consideration. Furthermore, compared with the control method commonly used in practice, the time of mode transition process can be shortened and vehicle jerk can be controlled within an acceptable range using the proposed method.

Study on the Influence Factors Upon the Propensity to Stick-Slip Phenomenon During Vehicle Start-Up Process

The vibration caused by the friction characteristic of the clutch during the vehicle start-up process has an impact on driveline torsional oscillation. This results in the occurrence of the stick-slip phenomenon which in turn aggravates the torsional oscillation. In this study, the dynamic model of the wet clutch was built and the self-excited vibration and stick-slip phenomenon during clutch engagement were theoretically analyzed and numerically simulated. The vehicle start-up driveline model was then built with consideration of the stiffness of the shafts, the time-varying mesh stiffness of the gear set, and system damping. The start-up process of the vehicle was simulated through the adoption of a constant engine speed control strategy, and the influence of the control and structure parameters on the stick-slip phenomenon during the vehicle start-up process was investigated. The results showed that increasing the relative speed threshold value of the constant engine speed control decreases the likelihood of the occurrence of the clutch stick-slip action, and the shaft stiffness, system damping, and inertia of each component also affect the stick-slip phenomenon during vehicle start-up.

Two-Layer Structure Control of an Automatic Mechanical Transmission Clutch During Hill Start for Heavy-Duty Vehicles

The engagement control of an automatic mechanical transmission (AMT) clutch during the hill start of a heavy-duty vehicle has a significant impact on the comfort, safety and service life of the vehicle. However, the control effect of a traditional control strategy can be easily affected by interference (clutch wear, temperature). Therefore, this paper proposes a two-layer structure control strategy based on an AMT clutch automatic actuator with the clutch engagement speed as the control target. First, the clutch automatic actuator is designed and the governing characteristics of the diesel engine and the control characteristics of the solenoid valve are studied. Second, a logic threshold control method and PID control method are adopted in the proposed two-layer structure control method. Moreover, the robustness of the proposed control algorithm is validated by a co-simulation platform (TruckSim, MATLAB/Simulink). Finally, experimental research under different slopes (13% and 22%) is carried out to verify the simulation results. The experimental results prove that compared with a single-layer control strategy, the two-layer control strategy proposed in this paper can shorten the start time by more than 10%, and reduce the vehicle start-up jerking by approximately 20%, which significantly improves the performance of the vehicle in the hill start process.

Modeling and analysis of engagement behavior of one-way clutch with a variable rectangular cross-section torsional spring

This article presents a study on the transient dynamic responses of engagement process of one-way clutch using variable rectangular cross-section torsional spring, which is usually installed on the end of engine for preventing torque being transmitted back. A 2-degree-of-freedom torsional dynamic model is proposed in this article to study the engagement process of clutch under two conditions. Due to the variation of parameters, the torque transfer of the wrap–spring clutch during engagement is described by a multi-parameter equation. The torque transmitted by clutch during engagement process has been described by two phases, spring expanding and spring locking. Physical parameters of spring determining the torque during expanding are discussed. To verify the model, a dynamic experiment on clutch engagement is conducted.