Browse Topic: Wet disc clutches
High-speed wet clutches may experience dynamic instability between the friction plates, leading to rattling vibrations and a significant increase in drag torque. This study employs a homogeneous flow model to characterize the gas-liquid two-phase flow within a high-speed clutch. It establishes a dynamic model for the angular oscillation of friction plates. Finite-element numerical simulations and stability analyses were conducted. The results indicate that as the clutch speed difference increases, the density and viscosity of the two-phase flow decrease rapidly, leading to a sharp reduction in fluid stiffness and damping. Consequently, the friction plates become more susceptible to angular oscillation. The stability of angular oscillation is determined by two key parameters: dimensionless comprehensive stiffness and critical frequency ratio. Higher dimensionless comprehensive stiffness and a lower critical frequency ratio enhance oscillation stability. Numerical evaluations of various groove types reveal that as rotational speed and friction plate clearance increase, the fluid stiffness coefficient, damping coefficient, dimensionless comprehensive stiffness, and critical moment of inertia all decrease, thereby reducing angular oscillation stability. Among the tested groove geometries, enclosed grooves and spiral grooves exhibit superior stability due to their strong hydrodynamic effects, yielding the highest dimensionless comprehensive stiffness. The critical frequency ratio for the self-excited angular oscillation of friction plates is approximately 0.5, termed the half-frequency oscillation characteristic. Experimental data validate the proposed angular oscillation model and its frequency response, providing a theoretical foundation for performance prediction and stability optimization in high-speed clutch design.
As a newly designed hybrid transmission, DHT (Dedicated Hybrid Transmission) owns the advantages of compact structure, multi-modes and excellent comprehensive performance. Compared with the traditional add-on hybrid transmission with one single motor, DHT uses one independent generator for engine starting and speed adjusting which can be largely improve the driving performance in the mode changing process. Based on the series-parallel DHT with wet clutch for power coupling, this paper firstly analyses the power coupling clutch device functionalities from the power flow viewpoint under normal and limp home condition. And for the changing process from series to parallel mode, a clutch coordination control strategy is designed by combining generator fast speed adjusting with clutch accurately pressure controlling to fulfill the fast driver intension response and clutch protection. And target torques of power sources are designed by a model-based method and two PID closed-loop algorithms are designed for controlling the clutch pressure accurately. Such strategy and algorithms are verified with vehicle test and the results show that the strategy can quickly complete the mode changing and driver intension changing with vehicle jerk within ± 10 m/s3, improving the driving pleasure with prolonging the clutch lifetime.
This SAE Recommended Practice is intended as the definition of a standard test, which may be subject to frequent change to keep pace with experience and technical advances. This should be kept in mind when considering its use. The specific purpose of this SAE Recommended Practice is to define a procedure to determine intrinsic properties of friction materials such as compressive modulus and rebound/recovery time at specific fatigue test pressures. Results from this test will both independently characterize the friction material and serve as input to the compression fatigue test. NOTE: If this test is intended to determine the rebound interval for the compression fatigue test, then the maximum test pressure (Pmax) in this procedure must be selected with future fatigue testing levels in mind. It is important that the rebound time is sufficient at the maximum apply pressure to allow the matieral to rebound back to its original thickness. Standard reporting processes are recommended. This procedure is intended for use by both suppliers and end users of wet friction materials. The only variables selected by the supplier or user of the friction system are: a Friction material. b Fluid. c Maximum load. d Fatigue test cycle requirements. These variables must be clearly identified when reporting the results of this test. Data shall not be reported as having been obtained using this procedure if any test parameters or system hardware described in this document are changed or deviated from in any way (other than the variables described above).
Accurate determination of driveshaft torque is desired for robust control, calibration, and diagnosis of propulsion system behaviors. The real-time knowledge of driveshaft torque is also valuable for vehicle motion controls. However, online identification of driveshaft torque is difficult during transient drive conditions because of its coupling with vehicle mass, road grade, and drive resistance as well as the presence of numerous noise factors. A physical torque sensor such as a strain-gauge or magneto-elastic type is considered impractical for volume production vehicles because of packaging requirements, unit cost, and manufacturing investment. This paper describes a novel online method, referred to as Virtual Torque Sensor (VTS), for estimating driveshaft torque based on Machine-Learning (ML) approach. VTS maps a signal from Inertial Measurement Unit (IMU) and vehicle speed to driveshaft torque. The unique advantage is that VTS does not explicitly rely on the first principles unlike other estimation methods. A robust mapping framework implicitly accounts for road grade, while compensating the effects of vehicle mass and drive resistance. Mapping coefficients are automatically and adaptively learned during selective drive conditions and continuously updated by means of Kalman filtering. VTS is implemented in a test vehicle with a P2 hybrid electric propulsion system for the assessment of robustness and sensitivity to drive conditions. The accurate estimate of driveshaft torque from VTS is utilized to determine the characteristics of a wet clutch which is employed for cranking an internal combustion engine during EV-HEV mode transition. VTS demonstrates a ML-based data-driven solution to the accurate determination of driveshaft torque and wet clutch behaviors. VTS framework can be readily extended to broader applications, including battery electric vehicle, with additional capabilities such as wheel torque estimation during braking and steering.
Advanced features in automotive systems often necessitate the management of complex interactions between subsystems. Existing control strategies are designed for certain levels of robustness, however their performance can unexpectedly deteriorate in the presence of significant uncertainties, resulting in undesirable system behaviors. This limitation is further amplified in systems with complex nonlinear dynamics. Hydro-mechanical clutch actuators are among those systems whose behaviors are highly sensitive to variations in subsystem characteristics and operating environments. In a P2 hybrid propulsion system, a wet clutch is utilized for cranking the engine during an EV-HEV mode switching event. It is critical that the hydro-mechanical clutch actuator is stroked as quickly and as consistently as possible despite the existence of uncertainties. Thus, the quantification of uncertainties on clutch actuator behaviors is important for enabling smooth EV-HEV transitions. In this paper, a predictive hydro-mechanical clutch actuator model is first presented. The equations of motion of the actuator piston include a parametric representation of squeeze film and friction material compression for damping and stiffness effects. The hydraulic line dynamics is modeled with a series of lumped volumes connected through orifices. Clutch torque is computed based on the Coulomb friction assumption. The model behaviors are qualitatively validated with experimental vehicle data. Monte Carlo simulations are conducted to investigate the effects of uncertainties in the input signal, bulk modulus of the fluid, piston seal friction, and piston damping. The mean behavior of piston pressure changes considerably when the presence of uncertainty is accounted for, which significantly affects the piston motion and clutch torque predictions. The results demonstrate that uncertainty quantification offers valuable insights into system behaviors that are not obtainable through conventional deterministic analyses. This knowledge of the uncertainty propagation can in turn help improve system performance through uncertainty-aware control and hardware design.
Multi-speed transmissions can improve power and economy performance of battery electric vehicles (BEVs), thus becoming an inevitable trend in automotive industry. A two-speed dedicated electric transmission (2DET), which can realize switching of two gear ratios through two wet clutches, is explained firstly. Secondly, 2DET is developed and a prototype is assembled in a BEV of Beijing Electric Vehicle Co. Ltd. (BJEV). Thirdly, the differences of new European driving cycle (NEDC) and China light duty vehicle test cycle passenger (CLTC-P) are compared. Fourthly, the parameters of battery cell are tested and a simulation model of the whole vehicle with 2DET is built. Finally, vehicle economy performance under NEDC and CLTC-P is simulated, and the results are validated in bench tests. Comparison shows that the economy simulation results match the test results, and the vehicle economy under CLTC-P is better than NEDC, with an increase of 1.16%.
Hybrid powertrains have become many original equipment manufacturers (OEMs)’ choice to meet ever-stringent fuel consumption regulations. A P2 powertrain technology is widely adopted by automotive OEMs to reuse existing engines and transmission production capacity and reduce investment. A standalone P2 module of an integrated e-motor with an engine decoupling wet clutch is developed and applied in a transverse-mounted P2 hybrid powertrain system. A P2 hybrid powertrain controller has been developed to test and validate the P2 module and control strategy. This P2 powertrain system with a decoupling clutch capable of slipping control enables the vehicle launch or low-speed drive in engine direct-drive mode. A control algorithm that controls the clutch slipping to transmit the desired cranking torque from P2 e-motor to fast-start the engine during the drive mode change from Electric drive to Parallel drive has been developed and validated. The proposed engine slip-start with clutch pressure control has achieved robust results of a fast and smooth transition from the electric to hybrid mode.
This paper develops a lumped-parameter multi-plates wet clutch Offset Compound Gear (OCG) transmission dynamics and its thermal model for dual-speed rotorcraft applications with an active clutch slip-speed control. This model includes the Reynolds equation for the clutch oil film thickness, the clutch thermal model, the clutch transferred torques (viscous and asperity torque) and the clutch disengagement model. The wet clutch/OCG transmission system is implemented in Matlab® Simulink™ to manage the upshift clutch temperature rise, which is a main issue need to handle for a dual-speed helicopter transmission. Here, the clutch temperature rise is treated by injecting a certain amount of coolant during engagement so that the temperature rise for the wet clutch is much lower than that of an dry clutch. In order to transfer a required torque using the available power, the sizing of the wet clutch could be evaluated via the developed wet clutch/OCG transmission model. This study shows that the temperature rise drops as the wet clutch oil flow rate increases adding extra weights compared with the dry clutch. The simulation also captures a phenomenon that a larger clutch engagement pressure might be required for the wet clutch to transfer the same torque since the wet clutch oil viscosity drops as the oil temperature increases during the clutch engagement.
In the present article, structural spring characteristics of two different Belleville springs are analyzed to overcome a failure issue in an automatic shift transmission clutch system. The spring design is evaluated through explicit dynamics analysis by finite element modelling and validated by DIN 2093 standard. Automatic shift transmissions that are used in off-highway vehicles are employed with multi-plate wet clutch system to actuate the planetary gears. These clutches are actuated through automatic transmission fluid that are supplied through flow channels. The clutch piston is moved axially by fluid pressure against the clutch pack and Belleville spring thereby transfers torque. Meanwhile, the clutch piston is retracted by the spring force once the fluid pressure is cut off. The spring is designed in such a way that during the energizing mechanism, positive spring stiffness is maintained. It is noticed that the clutch function is obstructed as the spring is inverted to other side due to unstable negative stiffness characteristic. It stalls the function of clutch system and automatic shift transmission thereby vehicle becomes inoperable. The present study compares two different spring characteristics required to suit the clutch design for proper function of transmission system.
This paper focuses on modeling of the heavy-duty vehicle drivetrain with automatic transmission by using dual clutch scheme. The planetary gear set in the automatic transmission is complicated structure and difficult to understand. The advantage of the dual clutch scheme is that it can be used to represent the complex planetary gear set intuitively, which is a great help to understand the gear shifting process. It is also suitable for being used in the controller due to its low order. Some conditions are required to convert the planetary gear set to the dual clutch model. The heavy-duty vehicle driveline can be converted to the dual clutch model due to its heavy engine and vehicle inertia. This paper also proposes system parameter estimation methods to represent the driveline model. The main parameters are lumped inertia, lumped gear efficiency, output shaft compliance and friction coefficient of clutches. First, a method for estimating lumped inertia and lumped gear efficiency is proposed using WLSE (Weighted Least Square Estimation) when gear is engaged. Second, resonance frequency of the system is obtained from the lock-up oscillation data occurring at the end of the gear shifting. The output shaft compliance is calculated by analyzing resonance frequency of the system. Third, the slip and friction coefficients of the clutch over time are calculated in the inertia phase. Using those data, the relationship between the dynamic friction coefficients and slip of the wet clutch can be obtained. Finally, a simulation is constructed to verify the accuracy of the proposed dual clutch model and the estimated system parameters. Simulation result is compared with experimental data.
This study aims to solve the problem of impact in a parallel hybrid electric system based on the continuously variable transmission (CVT) during switching from pure electric mode to engine-driven, power-generating mode. Taking into account the torque response characteristics of the engine and motor and the dynamic characteristics of the wet clutch hydraulic control system, the mode switching process is divided into six stages, namely, pure electric mode, wet-clutch free travel, engine start-up, engine speed synchronization, clutch combination, and engine intervention drive. A coordination control strategy is developed based on the model predictive control algorithm to ensure smooth mode switching. The effectiveness of the control algorithm is verified using Matlab/Simulink and the AMESim co-simulation platform. Results show that with the mode switching coordination control strategy, the components of the system work harmoniously. The maximum impact is reduced by 52.0% at the speed synchronization stage and by 84.3% at the clutch coupling stage compared with the uncoordinated control situation.
A wet clutch model is required in automotive propulsion system simulations for enabling robust design and control development. It commonly assumes Coulomb friction for simplicity, even though it does not represent the physics of hydrodynamic torque transfer. In practice, the Coulomb friction coefficient is treated as a tuning parameter in simulations to match vehicle data for targeted conditions. The simulations tend to deviate from actual behaviors for different drive conditions unless the friction coefficient is adjusted repeatedly. Alternatively, a complex hydrodynamic model, coupled with a surface contact model, is utilized to enhance the fidelity of system simulations for broader conditions. The theory of elastic asperity deformation is conventionally employed to model clutch surface contact. However, recent examination of friction material shows that the elastic modulus of surface fibers significantly exceeds the contact load, implying no deformation of fibers. This article investigates the friction material contact mechanics through numerical simulations. A surface model is constructed based on microscopic examination of material topography and properties. An FEM simulation is conducted to examine the interactions between surface fibers and the surrounding medium under loaded conditions. The change in real contact area with respect to nominal surface pressure correlates qualitatively the simulations and experiments. The numerical study provides insight into frictional material contact mechanics that is not directly observable. It also supports the assumptions behind an empirical fiber contact model that was recently introduced to enhance hydrodynamic clutch models.
The wet clutch system (WCS) is a complex combination of friction plates, separator plates and fluid (lubricant). The basic function of the WCS is to transfer torque under various operating conditions such as slipping, shifting, start/launch and/or torque converter clutch (TCC) operation. Under these conditions the slope of the coefficient of friction (ÎĽ or COF) versus slip speed (ÎĽ-v) curve must be positive to prevent shudder of the WCS, a highly undesirable condition in the lubricated friction system. An extended durability duty cycle test procedure is required to evaluate the WCS during which the ÎĽ-v curve is monitored for a negative slope, a condition indicating the potential for shudder. The friction plates, separator plates, and lubricant must be tested together and remain together during the test to be properly evaluated as a WCS. This paper describes a new test procedure which builds on the basics of the SAE J2964 - Low Speed Continuous Slip ÎĽPVT Procedure [1] by adding a durability duty cycle to age the WCS. The test includes measurement of the ÎĽ-v curve at several intervals during the test (before break-in, after break-in, and after each 12-hour aging segment of testing). The aging segments are run at a specific continuous slip speed and constant power condition. The lubricant temperature is also controlled and the plate interface temperatures are measured. The dÎĽ/dv slope is calculated at different speed intervals and graphed to indicate when the slope changes from positive to negative. A negative dÎĽ/dv slope can indicate a potential for shudder in the WCS. This new procedure can be used to compare the performance of different friction material and lubricant chemistry combinations by analyzing the resulting dÎĽ/dv change over time. It can also assess the effect of changes in the groove pattern design, friction and separator plate surface finish and separator plate materials on the dÎĽ/dv slope.
Engine start while driving is one of the most typical and frequent work conditions for hybrid vehicles. Engine start has very significant impact on the driving comfort. Engine start, especially a dynamical engine start, have high control requirements regarding control time, torque output and riding comfort. In some hybrid transmissions such as P2, engine is cranked and synchronized through wet clutch slipping. Because clutch pressure control has time-varying delay and estimation precision of engine torque by ECU (Engine Control Unit) is poor, conventional PID controller is unable to meet the high requirements of control quality. A new control algorithm is proposed in this paper to cope with all these challenges. The new control algorithm is based on LADRC (Linear Active Disturbance Rejection Controller) and is improved through combination with Smith predictor and Adaline network. LADRC is adopted to reduce negative effects of poor precision of engine torque. Smith predictor is introduced to compensate the time delay of clutch torque. In addition, the time-varying delay can be estimated by Adaline network and parameters of Smith predictor can also be adaptive adjusted.
The dual clutch transmission is one of the possible choices for electric vehicle drivelines. The basic principle and control mode of shifting of wet dual clutch transmission are introduced, and the dynamic process of shifting of wet double clutch transmission is studied. Combined with the dynamic model of the wet clutch engagement process, the difference between the dynamic characteristics of the dual clutch transmission modeling using the Coulomb friction model and the dual-clutch transmission model using the average flow model and the micro-convex contact theory is analyzed. The shift control strategy of the dual clutch transmission proposes a correction method to improve the shifting smoothness. Studies have shown that the torque response of the wet clutch has significant hysteresis, and the improved control algorithm can significantly improve the shifting smoothness of the wet dual clutch transmission. Based on the dynamic model of the wet clutch, the torque interruption of the shift control strategy of the dual clutch transmission is studied, and the method of improving the shift smoothness by the correction of the shift control strategy is proposed.
The objective of this glossary is to establish uniform definitions of parts and terminology for engine cooling systems.
The objective of this glossary is to establish uniform definitions of parts and terminology for engine cooling systems.
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