Search Results (103)

This paper presents a stochastic regression model for predicting the coefficient of friction (COF) in automotive dry clutches with organic linings. The influence of temperature, normal load, and slip speed on COF behaviour is investigated based on a large set of clutch wear-characterization data, collected using a custom-designed disc-on-disc tribometer that replicates realistic clutch-engagement cycles. The proposed model calculates both the expected value and standard deviation of the COF. The COF expectation model takes temperature, normal load, and slip speed as inputs, and it has a cubic polynomial form selected through a feature-selection method. The COF standard deviation model is fed by the same three inputs or alternatively the COF expectation input, and it is parameterized using the maximum likelihood method. The overall model is validated on an independent characterization dataset and an additional dataset gained through separate experiments designed to mimic real driving conditions. Full article

As critical actuating components in vehicular transmission systems, wet clutches exhibit strongly nonlinear thermal responses in their friction pairs during engagement operations. Although existing temperature prediction models achieve high-accuracy prediction performance, their practical application remains constrained by significant limitations such as high computational costs and time consumption. This study proposes an Optuna-LSTM temperature prediction model for wet clutch friction pairs, developed through the integration of long short-term memory (LSTM) deep learning theory with finite element method generated training datasets under diverse operating conditions. By synergistically combining the automated hyperparameter optimization library (Optuna) framework and early stopping mechanisms, the model enables dynamic temperature prediction of friction pairs. Experimental results indicate that the proposed model achieves prediction metrics of Root Mean Squared Error (RMSE) of 1.42 °C, Mean Absolute Error (MAE) of 1.09 °C, Coefficient of Determination (R²) of 0.9930, and Mean Absolute Percentage Error (MAPE) of 0.72% with a prediction duration of 60 ms. These findings confirm that the Optuna-LSTM model enables both accurate and rapid temperature prediction for friction pairs, providing an efficient solution for thermal management in wet clutch systems. Full article

Thermal gradients induced by friction frequently trigger buckling deformation of the friction elements, especially in heavy-duty helicopters. Nevertheless, the subsequent influence of such post-buckling deformation on transient thermal characteristics during helicopter successive shifting remains insufficiently addressed in existing research. In the present work, a gap model for friction pairs with conical separate discs is first proposed. Subsequently, a comprehensive thermal-fluid-dynamic model incorporating spline friction, split springs, and time-varying thermal parameters is developed to investigate the transient thermal characteristics of wet clutches with conical separate discs in successive shifting. A corresponding qualitative analysis is performed to explore the transient thermal response and influence mechanisms of operating parameters, including shifting interval, rotation speed and control oil pressure. The results indicate that a rise in the control oil pressure from 1.5 MPa to 1.9 MPa facilitates a 42.65% increase in the maximum radial temperature gradient and augments the maximum axial temperature gradient by 24.35%. Meanwhile, an increase in rotation speed accelerates heat dissipation but compromises the uniformity of the temperature field. Additionally, extended shifting intervals under inadequate heat dissipation exacerbates thermal buildup, driving a persistent and significant escalation in the temperature of friction elements. The conclusions can provide a theoretical basis for the optimal design, condition monitoring, and fault diagnosis of aviation clutches. Full article

Two-speed transmissions can improve battery electric vehicle (BEV) drivetrain efficiency. However, the additional losses caused by shifting actuators offset these efficiency gains. Particularly hydraulic actuated wet-running multi-plate clutches, which enable powershifts, typically require rotary feedthroughs. Commonly used rectangular sealing rings (RSR) demand continuous hydraulic power due to leakage and cause friction torque. This leads to high RSR temperatures, especially at high angular velocities of electric machines. This article introduces a two-speed BEV transmission concept using wet-running multi-plate clutches actuated via a rotating 5/3-way valve that can shut off, i.e., lock up the actuating pressure directly in the rotating system. Consequently, the rotary feedthrough is depressurized and contactless gap seals are usable. This reduces supply pressure requirements and minimizes hydraulic and friction losses while retaining powershift capability. Component-level tests evaluate leakage, pressure shut off, actuator dynamics and power consumption. Results show that actuating pressure in a shut-off clutch is maintained for longer than 60 min and electrical actuator power consumption is less than 20 W. During overlapping gearshifts, gap seal leakage is less than 1 L/min at 10 bar and sufficient pressure dynamics are achieved. These findings confirm the feasibility of the proposed actuator for multi-plate clutches in two-speed BEV transmissions. Full article

The optimization of clutch engagement strategies is of great significance for improving vehicle power performance, fuel economy, and driving comfort. Traditional control strategies are difficult to adapt to complex working conditions and lack coordinated optimization of fuel and clutch. This paper proposes a multi-objective optimization method for clutch engagement strategies based on the Deep Deterministic Policy Gradient (DDPG) algorithm. A simulation environment is constructed, which includes a vehicle longitudinal dynamics model, clutch state switching logic, and a reinforcement learning agent. A multi-dimensional state space and action space are designed, and a composite reward function combining power performance, fuel economy, and comfort is developed to achieve multi-objective optimization of the fuel–clutch coordination curve. Experimental results show that the optimized engagement strategy significantly reduces sliding friction power (by 94.07%), power interruption speed (by 8.75%), and jerk (with a maximum reduction of 35.6%), while the average fuel consumption per distance is reduced by 0.39%. Through weight sensitivity analysis, it is found that when the weight of fuel economy is 0.3 and the weight of power performance is 0.5 (Scheme P5E3), the optimal balance among multiple objectives can be achieved. This study provides a new theoretical framework and engineering practice reference for the intelligent control of clutches. Full article

Oil film cavitation in the friction pairs of wet clutches significantly compromises transmission stability and component durability. This study investigates the cavitation evolution across three microtexture types—hexahedral, cylindrical, and hemispherical—with texture ratios ranging from 3.205% to 12.917% and a constant depth of 0.0564 mm, under a 6000 rpm operating condition. A finite element model of the oil film was established to analyze the cavitation volume fraction, pressure field, and gas-phase mass transfer rate. The numerical simulations were complemented by visualization experiments, where high-speed imaging (550–1050 rpm) captured the cavitation bubble dynamics, and the transmitted torque was measured. The results indicate that microtexture parameters profoundly influence cavitation intensity. Hemispherical textures with a 6.41% texture ratio yielded the highest cavitation volume fraction (0.020215), substantially exceeding that of hexahedral textures (0.0015197). Cavitation initiates within the texture dimples, with hemispherical geometries facilitating its diffusion into non-textured regions. A threshold effect of the texture ratio was identified, where cavitation intensity peaks at 6.41% but diminishes at 12.917%, attributable to flow homogenization. Optimized designs can effectively suppress cavitation: either increasing the texture depth or adopting a high texture ratio (>45%) with hexahedral or cylindrical geometries reduces the pressure drop in low-pressure zones by over 30%. Experimental validation confirmed that an increased texture ratio reduces torque by 20%, correlating with the shrinkage of the oil film at the outer diameter. High-speed imaging revealed a periodic cavitation evolution, with the collapse of sheet-to-cloud cavitation occupying 15.2% of the cycle, which aligns with the simulated peak in mass transfer at t = 0.003 s. In conclusion, cavitation can be effectively controlled by optimizing the texture ratio, depth, and geometry to maintain a stable oil film pressure gradient. This study provides a theoretical foundation for the microtexture design of wet clutches, thereby enhancing their reliability in power-shift applications. Full article

This paper introduces innovative approaches to the design of railway point machines, with particular emphasis on the implementation of multi-component AlNiCoFe alloys, classified as semi-hard magnetic materials. A comprehensive review of existing mechanisms for mechanical force transmission—from the electric motor to the throwing bar—was conducted. The inherent limitations of conventional dry friction clutches, commonly used in current point machine designs, are critically analyzed. Furthermore, the feasibility of employing multi-component AlNiCoFe alloys as functional materials in hysteresis magnetic clutches is examined, with a view toward enhancing the reliability and performance of railway point actuation systems. A review of diagnostic methods for railway point machines was conducted to evaluate the potential application of a novel magnetic torque limiter as a means to eliminate maintenance activities typically required for systems utilizing dry friction clutches. Experimental research was performed on AlNiCoFe alloys employed as the hysteresis layer in the proposed torque limiter. Microstructural and compositional analyses were carried out using scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) to determine the crystallographic structure, chemical composition, and selected physical properties of the tested materials. The hysteresis loops of the tested materials were measured using a Vibrating Sample Magnetometer (VSM) over a wide temperature range. A prototype magnetic clutch, functioning as a torque limiter in a railway point machine, was developed and presented. The operational characteristics—specifically the throwing force as a function of time—were recorded for a railway point machine equipped with an electromechanical module incorporating the new magnetic torque limiter. The advantages of the proposed solution in terms of force transmission and overall system performance in railway point machine design were analyzed and discussed. Full article

This study investigates the flow field and temperature field characteristics of a certain type of aerospace tail-thrust clutch friction plate under engagement conditions. A thermo–fluid–solid coupled convective heat transfer model was established based on the velocity distribution of lubricating oil within the groove cavities. The model was applied to analyze the surface temperature distribution of a single friction pair (friction plate and steel plate) under different operating parameters. The results reveal that both the inlet temperature and flow rate of the lubricating oil have a mitigating effect on temperature rise. However, due to the geometric constraints of the groove structure, the maximum wetted area and the actual inflow are inherently limited. Consequently, the temperature evolution during engagement is more significantly influenced by rotational speed and applied pressure. In particular, once these parameters exceed certain critical values, the surface temperature exhibits a sharp increase. Furthermore, the optimization of lubricating flow is constrained by friction materials. A higher flow rate does not necessarily yield greater lubrication benefits; instead, the optimal flow rate solution tailored to the friction pair should be pursued. This work provides theoretical insights into parameter control for aerospace tail-thrust clutches in practical operation. Full article

Friction pairs in heavy-duty power-shift tractor wet clutches operate under complex conditions, making them vulnerable to damage and reducing reliability. Optimizing their tribological performance requires a trade-off between a high coefficient of friction (COF) for torque transmission and a low temperature rise ($∆T$) to prevent thermal damage. Surface texturing is an effective method for improving the tribological performance of friction pairs. This study simulated the friction of wet clutch pairs via pin-on-disk tests and designed micro-textures on the pin surface to enhance tribological performance. Based on the experimental data, a Gaussian Process Regression (GPR) surrogate model was developed to accurately predict COF and $∆T$ as a function of the clutch’s operating and micro-texture’s geometric parameters. A Multi-Objective Particle Swarm Optimization (MOPSO) algorithm was then employed to obtain the optimal set of solutions. The obtained pareto front clearly revealed the COF–temperature rise trade-off. From the optimal solution set, optimal micro-texture parameters for two typical operating conditions of different clutches were extracted. Compared with the untextured surface, the optimal solutions increased COF by 2.6%/1.2% and reduced $∆T$ by 39.2%/12.1%. Relative to neighboring experimental points, COF further increased by 11.3%/2.7% and $∆T$ decreased by 16.6%/1.7%. This work establishes a method for balancing the frictional and thermal performance of friction pairs. Full article

The aviation wet clutch, as an indispensable component in helicopters, is particularly vulnerable to performance deterioration due to temperature rises, especially in high-power-density and high-torque conditions. Consequently, a comprehensive thermal-fluid-dynamic model, coupled with a dynamic model considering the spline friction and split spring and a thermal model considering the heat transfer parameters in friction pair gaps, was proposed in this work. The effects of operating parameters on the transient thermal behaviors of friction discs were investigated. A rise in rotation speed from 2000 rpm to 2400 rpm facilitates a 10.1% increase in the maximum temperature of the friction discs. An increase in control oil pressure from 1.5 MPa to 1.9 MPa rises the maximum temperature of the friction disc by 19.4%. Moreover, increased lubrication oil flow not only depresses the maximum temperature of the friction disc by 14.5% but also significantly narrows the temperature gradient by 16.7% and improves the temperature field uniformity. Therefore, reasonably increasing lubricant oil flow and decreasing control oil pressure can effectively reduce temperature rises and improve the temperature field uniformity. These results contribute to designing and developing optimal control strategies to enhance the comprehensive performance of helicopter transmission. Full article

Under no-load conditions, the wet clutch of vehicles generates drag torque across a wide speed range, which increases power loss in the transmission system and significantly impacts its efficiency and reliability. To address the clutch drag issue over a wide speed range, this study first establishes a low-speed drag torque model that simultaneously considers the viscous friction effects in both the complete oil film region and the oil film rupture zone of the friction pair clearance. Subsequently, by solving the fluid-structure interaction dynamics model of the friction plates, the collision force between high-speed friction pairs and the resulting friction torque are determined, forming a method for calculating high-speed collision-induced drag torque. Building on this, a unified drag torque model for wet clutches across a wide speed range is developed, integrating both viscous and collision-induced drag torques. The validity of the wide-speed-range drag torque model is verified through experiments. The results indicate that as oil temperature and friction pair clearance increase, the drag torque decreases and the rotational speed corresponding to the peak drag torque is reduced, while the onset of collision phenomena occurs earlier. Conversely, with an increase in oil supply flow rate, the drag torque rises and the rotational speed corresponding to the peak drag torque increases, but the onset of collision phenomena is delayed. Finally, with the optimization objectives of minimizing the peak drag torque in the low-speed range and the total drag torque at the maximum speed in the high-speed range, an optimization design model for the surface grooves of the clutch friction plates is constructed. An optimized groove pattern is obtained, and its effectiveness in suppressing drag torque across a wide speed range is experimentally validated. Full article

Wet clutches are extensively employed in automotive transmission systems due to their benefits of smooth shift and stable operation. However, existing methodologies have not yet thoroughly analyzed the real-time dynamic temperature distribution of wet clutches, and the heating and heat transfer mechanisms during the sliding friction process of friction pairs remain underexplored. To address these gaps, this study proposes a real-time dynamic temperature prediction model for wet clutches and investigates the heat generation and transfer mechanisms in the friction pair sliding process. Specifically, the heat production and exchange dynamics of the wet clutch friction pair are systematically analyzed, followed by an examination of the real-time temperature variation of the separator plate under both high-slip and low-slip speed conditions. In the numerical simulations, the predicted temperature values from the proposed model demonstrate excellent agreement with experimental measurements, with dynamic peak temperature discrepancies remaining within ±2 °C. Furthermore, the validated temperature evolution laws are corroborated by experimental results obtained from a dedicated wet clutch performance test rig, thereby providing comprehensive empirical verification of the proposed real-time dynamic temperature prediction framework for wet clutch separator plates. In summary, the model can accurately capture the temperature variation characteristics of wet clutches under different operating conditions, providing a reliable basis for real-time thermal management of transmission systems. It holds significant practical value for optimizing cooling system design, extending clutch service life, and ensuring shifting quality in vehicles. Full article

In the tail rotor transmission system of a high-speed helicopter, the timely supply of lubricating oil to the wet friction clutch during frequent starts and stops has a significant impact on the performance of the transmission system. The oil flow requirements of clutches vary across different operational stages, posing a challenge for traditional centrifugal oil supply methods to meet the demand for flow regulation under such dynamic conditions. This paper proposes a novel two-stage centrifugal oil supply structure capable of achieving superior flow control during various clutch operating phases. An experimentally validated two-phase oil–gas CFD model was established to analyze the effects of operational parameters, such as rotational speed and oil supply pressure difference, as well as structural parameters, on oil supply performance. To enhance oil supply flow rate and efficiency under high-speed conditions (rated speed of 4800 rpm and 85% speed) at a common supply pressure (0.45 MPa), while reducing the pressure at the input shaft interface, key structural parameters were determined and optimized using a combined approach of Taguchi orthogonal experiments and response surface methodology. The results demonstrate that the optimized structure achieves a 142.8% increase in the weighted oil supply flow rate, an 11.1% improvement in oil supply efficiency, and a 7.5% reduction in pressure at the input shaft interface. Full article

This study addresses the thermal hazards that arise during the initial engagement stage of wet clutches, where rapid heat generation within the transient lubricating film may cause premature film rupture, torque instability, and accelerated wear. To overcome these challenges, a coupled thermo–fluid model was developed to capture oil film flow, heat transfer, and viscous torque behavior under varying groove structures. A novelty of this work is the first integration of computational fluid dynamics (CFD) with response surface methodology (RSM) to systematically reveal how groove geometry—cross-sectional shape, number, and inclination angle—collectively influences peak temperature and viscous torque during the lubricating film stage. Simulation results show that spiral semi-circular grooves provide superior thermal management, reducing the peak friction plate temperature to 75.5 °C, while the optimized design obtained via RSM (groove depth of 0.89 mm, 19 grooves, and a 5.28° inclination angle) further lowers the maximum temperature to 68.2 °C and sustains torque transmission above 18.5 N·m. These findings demonstrate that rational groove design, guided by multi-objective optimization, can mitigate thermal risks while maintaining torque stability, offering new insights for the high-performance design of wet clutches. Full article

The paper presents an experimentally validated regression model for dry clutch friction lining wear, accounting for the influence of clutch temperature, initial slip speed, torque, and closing time. The experimental data have been collected by using a custom-designed disk-on-disk computer-controlled tribometer and conducting repetitive real operation-like clutch closing cycles for different levels of the above operating parameters. The model is designed to be cycle-wise, predicting cumulative worn volume expectation and standard deviation after each closing cycle. It is organized around three distinctive submodels, which provide predictions of: (i) wear rate expectation, (ii) wear rate variance, and (iii) elevated wear rate during run-in operation. Finally, the wear rate expectation and variance submodels and the overall, cumulative worn volume model are validated on independent experimental datasets. The main novelty of the presented research lies in the development of stochastic multi-input cycle-wise dry cutch wear model for clutch design and monitoring applications. Full article