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In order to analyze the power torque characteristics of wet clutch produced under the disengaging state and reduce the drag torque of wet clutch, a flow rate equation under full film state was deduced based on the Navier-Stokes equations and a new equation calculated oil film equivalent radius was derived according to the relationship of oil flow r...
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Context 1
... wet clutch disengagement is shown in Fig.1. Under the actual conditions in disengaged wet clutch, we assume some conditions as follows. ...
Context 2
... to the above formula (10) (11), the sensitive coefficient and sensitivity could be calculated. The input parameters were summarized in Table 3. Figure 10: the sensitive coefficient and sensitivity of clutch parameters As shown in Figure 10, the sensitivity for the effect of clutch parameters on drag torque was calculated, the result was oil viscosity, friction couples size, gap thickness, friction couples number, oil flow rate, oil density according to the influence degree of design parameters on drag torque form high to low. ...
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Citations
... Hence, the model combines the partial drag torques caused by the shearing of the oil in the continuous and ruptured section and the mist in the ruptured section, see Figure 17b. The model developed by the authors of Ref. [54] is based on the equivalent radius approach and incorporates a non-uniform clearance distribution through a non-uniform coefficient. ...
Wet brakes and clutches are crucial drivetrain components widely used in many sectors. However, their drag losses can account for a considerable share of the overall drivetrain losses. Therefore, investigation of the drag loss behavior of wet brakes and clutches has been the subject of research since the 1970s. This paper aims to provide a comprehensive overview of existing knowledge of drag loss behavior and identify future research directions. To this end, a scoping review was conducted according to the PRISMA guideline. It was found that research mainly, but not only, focused on gaining a fundamental understanding of the drag loss generation process, investigating the integral drag loss behavior, analyzing the flow in the sub-millimeter gaps, and modeling and calculating the drag losses. The review summarizes the state of the art and may support researchers and engineers in developing low-loss wet brake and clutch systems. Several research gaps were identified and are provided.
... Under the assumption of steady, incompressible, laminar and symmetrical oil, the theoretical oil flow rate in the disc gap can be described along the radial direction. Li et al. [24] assume that there is always a full oil film between disc gaps, even when the actual oil flow rate is slower than the theoretical value. In this case, a factor named equivalent radius is employed in the model to indicate the full oil film area. ...
Energy transfer improvement and energy consumption reduction are getting more crucial in the automotive sector. As one of the essential elements directly influencing energy transfer in the powertrain system, transmission losses have been widely analyzed with both simulation and experimental approaches. For a better characterization of individual losses, this paper investigates and compares most of the available analytical models for further system implementation. Regarding laboratory experiments, an adaptive sampling strategy is presented and analyzed for various operating conditions. Compared to the traditional factorial design, the applied Gaussian Process Regression (GPR) delivers both estimations and their predictive variances in the entire experiment process. Besides, new measurement candidates can be determined with the prior information from GPR model. The analytical simulation and adaptive measurement are employed to investigate a seven-speed transmission. With both approaches, a detailed discussion about total transmission losses and individual loss mechanisms are performed under various operating conditions.
... Zhou et al. [7], in the analysis of two-speed dual clutches, improved the drag torque model of wet clutch by Yuan et al., and proposed a new method considering the equivalent radius of oil film contraction phenomenon. Li et al. [8], based on the relationship between inlet and outlet oil flow rate and volume, obtained a new equation for calculating the equivalent radius of oil film. In particular, the peak torque and the corresponding critical speed are also taken as two evaluation indexes. ...
Wet friction clutch is the key functional component of the high-speed helicopter variable-speed transmission system, which is used to change the power transmission path. In the engagement process of wet friction clutch, the driving/driven disc will produce drag torque under the shearing of lubricating oil, which reduces the transmission efficiency. This unnecessary drag torque reduces efficiency and increases clutch temperature. The temperature increase promotes the wear of gears and bearings and the aging deformation of friction plates, which leads to local wear and reduces the service life of the clutch. From the principle of wet friction clutch, the oil groove structure is directly related to the drag torque and the temperature rise of friction disc. It is very important for the long-distance flight and service life of high-speed helicopters to obtain the groove structure with low drag torque and low temperature rise. In order to solve this problem, taking the wet friction clutch of a high-speed helicopter as the research object, based on the radial and annular compound groove, the thermal-fluid-solid coupling simulation model of the wet friction clutch is established to obtained the flow characteristics and temperature field distribution of the lubricating oil in the friction disc oil groove, and to analyze the influence law of the oil groove structure parameters on the drag torque and temperature field. In order to improve the transmission efficiency and the service life of friction disc, Taguchi experiment and non-dominated neighborhood immune algorithm were used to optimize the structural parameters of the oil grooves. The comparison results show that the optimized structural can effectively reduce the drag torque and the temperature rise. This work can provide a theoretical reference for the structure design of a wet friction clutch.
... The causes of transmission losses at the machine element level can be separated into load-dependent and loadindependent loss sources [9] . This paper distinguishes between load-dependent gear losses [10][11][12][13][14][15] , load-independent gear losses [ [12] , [16][17][18][19][20][21][22] ], bearing losses [23][24][25][26][27] , seal losses [ [19] , [27] , [28] ] and clutch and synchronizer losses due to synchronization and oil shearing [29][30][31] . Numerous studies deal with the total losses of vehicle transmissions both automated and manual [32][33][34][35][36][37][38][39][40] . ...
... If there is a relative speed between the plates of released wet clutches, a torque loss due to oil shearing occurs [31] . This torque loss T LC in N ·m, which acts on both clutch halves, is calculated according to Eq. (21) . ...
In this paper, a new method for efficiency modeling of gear transmissions is presented and subsequently tested on a six-speed dual-clutch transmission in a passenger car application. The method is intended to support the evaluation and optimization of transmission concepts with regard to their loss behavior in early development stages and to identify the main causes of the losses. To allow for a fast conceptual assessment through short model execution time the method is used to build a rigid-body transmission model in MATLAB/Simscape, which takes the individual component torque losses into account. Compared to existing approaches, it is thus possible to transiently determine the motion and load conditions of the individual loss sources and to include them in the overall loss calculation. In addition to the evaluation at steady state operating conditions, the power losses of transmissions in driving cycles and in particular regarding gear shifts can thus be investigated. The validation of the simulation model shows good agreement with measurements carried out on a dynamometer in a wide operating range. For the case considered the results show that the majority of the transmission losses in vehicle operation lead back to the synchronization losses of the input clutches.
... The paper [14,15] has shown the expression of the torque of the lubricating oil film under the condition of ignoring the gap hi when the friction pair is fixed [15] (Traditional model): Z is the number of friction pairs; Rs (m) is the equivalent radius of contact oil film; μ (Pa·s) is the hydrodynamic viscosity of lubricating oil (μ=υρ); Δω (rad/s) is the relative angular velocity of the friction plate and the steel plate, Δω=2πΔn. Substituting the formula (17) into the formula (18), the expression of the drag torque with an uneven gap due to the bias of the friction pairs is obtained: ...
... Under the same simulation parameters in the reference [14,15], as shown in Table 1, the traditional model and the bias model are simulated in the 0.5L/min of the single pair lubrication flow and the Δn range of the speed difference is 0~2000r/min. The variation curves of the two models with torque simulation are shown in Fig 6: Figure 6. ...
... Lubricant pressure distribution along radial can be expressed as [14,15]: ...
A theoretical model of friction plate is established by using Resal theorem, and the inertia resistance of the friction plate is obtained from this theoretical model. Focusing on the bias phenomenon in friction pairs, a new model is investigated for analyzing the bias state under low speed difference considering about the gyro effect. As for the gap shrinkage under high speed difference, the negative pressure contraction model for the friction pairs is built by analyzing the oil film and the pressure between plates. Based on that, the influences of the inertia resistance of the friction plates for these two models are also discussed. Afterwards the gap dynamic change between friction pairs is investigated in the whole variation range of the relative speed. Finally, an improved model, considering the influence of the gap dynamic change between friction pairs, is proposed to simulate the drag torque. The results obtained from the simulation and test data indicate that, under the same lubrication condition, the drag torque in the wet multi-disk clutch increases at first and then decreases and finally increases with the rise of the rotational speed difference. Furthermore, the main factors influencing the drag torque are the bias of plates in the low speed difference (0∼1000r/min) and the gap shrinkage in the medium and high speed difference (>1000r/min) respectively. From the comparison between test data and the simulation results obtained from the improved model, the average relative error is only 6.34% at medium and high speed difference (>1000r/min), which can greatly improve the accuracy for the estimation of the drag torque in wet multi-disk clutch.
... The drawback of this mathematical model is that it cannot describe the drag torque accurately at high speeds. (Li et al., 2013) Unlike the surface tension model, this model describes the drag torque at high speeds accurately with the following conditions: -The transmission fluid is in steady-state. -The transmission fluid is an incompressible oil. ...
In the automatic transmission system of automobiles, clutches effectively contribute to fuel consumption. The internal resistance of transmission fluid between the clutch discs and plates causes a loss in power. In this work, efforts have been made to shed light on using programming skills to create a computer program that facilitates the calculation of this power loss, referred to drag torque. This paper is limited to reviewing different modeling techniques to calculate the drag torque in disengaged multi-disc wet clutches by using a computer program written in Python 3. For developing the graphical user interface of the program, Tkinter and Matplotlib libraries have been used. This computer program provides a fast way to enter and modify the numerical values of the necessary operating and geometrical parameters. After that, the processing using wet clutch mathematical models inside the black box is done by calculating the drag torque and revealing four required graphs.
... The onset of aeration and its evolution are dictated by the balance between the pressure gradient induced by the rotating disk in one direction and by the imposed pressure gradient to force the oil flow through the gap in the other direction. A number of investigators [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] have used analytical methods to study the pressure distribution in the gap. On the oil-air interface, most modeled its location by introducing the concept of "equivalent" radius with oil below that radius and air above. ...
... (3) needs to be modified. Li et al. [15] proposed that Eq. (3) be modified by replacing R out by R s ; that is, ...
... By weighting, it shows the effects of the errors on the predicted drag torque that affect the efficiency. Figure 6 shows predictions of C and drag torque from the model developed in this study and from experimental data for Transactions of the ASME configuration 2. Figure 7 shows comparison of drag torque for configuration 2 predicted by the model developed with experiment data from Ref. [18] and with results from models in the literature [12,15]. In Fig. 6(a), the maximum relative errors in predicting C 1 , C 2 , and C 3 are 5.11%, 1.79%, and 0.83%, respectively. ...
Computational fluid dynamics (CFD) has been unable to reliably predict aeration and drag torque in clutches. In this study, a CFD method was developed to reliably predict the onset of aeration and drag torque as a function of the clutch's rotational speed. This study showed that though the oil and air behave as if they are incompressible at steady-state, the formulation must account for the compressible nature of the gas and the unsteady processes that occur before reaching steady-state. This study also showed that the dynamic nature of the contact angle between the oil and the stationary disk must be accounted for to predict drag torque and aeration as a function of rotational speed, and a model of the dynamic-contact angle was developed.
... The onset of aeration and its evolution are dictated by the balance between the pressure gradient induced by the rotating disk in one direction and by the imposed pressure gradient to force the oil flow through the gap in the other direction. A number of investigators [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] have used analytical methods to study the pressure distribution in the gap. On the oil-air interface, most modeled its location by introducing the concept of "equivalent" radius with oil below that radius and air above. ...
... (3) needs to be modified. Li et al. [15] proposed that Eq. (3) be modified by replacing R out by R s ; that is, ...
... By weighting, it shows the effects of the errors on the predicted drag torque that affect the efficiency. Figure 6 shows predictions of C and drag torque from the model developed in this study and from experimental data for Transactions of the ASME configuration 2. Figure 7 shows comparison of drag torque for configuration 2 predicted by the model developed with experiment data from Ref. [18] and with results from models in the literature [12,15]. In Fig. 6(a), the maximum relative errors in predicting C 1 , C 2 , and C 3 are 5.11%, 1.79%, and 0.83%, respectively. ...
When a liquid is forced to flow radially outward in the gap between two coaxial, parallel annular disks—one rotating and one stationary—the liquid occupies the entire gap until the speed of the rotating disk reaches a critical value. Beyond that critical speed, gas from the outer radius starts to enter into the gap, a process referred to as aeration. The higher the rotational speed, the greater is the extent of penetration by the gas into the gap. The extent of gas penetration strongly affects the torque exerted between the two disks because of the large difference in the gas and liquid viscosities. In this study, a reduced-order model is developed to predict the onset of aeration, extent of gas penetration into the gap, and drag torque as a function of the disk's rotational speed, gap between disks, properties of the liquid, and mass flow rate of the liquid forced through the gap. The model developed was validated by comparing predictions with experimental data.
... Oerlikon Graziano SpA has developed an in-house mathematical model that estimates the transmission power loss contributions in steady-state conditions (see references [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] for the relevant literature on the topic). Based on the transmission design parameters, the model generates the transmission power loss maps as functions of the input torque, input speed, and operating temperatures of the transmission and clutch lubricant. ...
... Wet clutch churning power losses, P c,wc [27,28]. During the engaged gear operation of the DCT, either clutch (i.e., the disengaged one) is characterised by a slip condition. ...
The main benefits of dual clutch transmissions (DCTs) are: (i) a higher energy efficiency than automatic transmission systems with torque converters; and (ii) the capability to fill the torque gap during gear shifts to allow seamless longitudinal acceleration profiles. Therefore, DCTs are viable alternatives to automated manual transmissions (AMTs). For vehicles equipped with engines that can generate considerable torque, large clutch-slip energy losses occur during power-on gear shifts and, as a result, DCTs need wet clutches for effective heat dissipation. This requirement substantially reduces DCT efficiency because of the churning and ancillary power dissipations associated with the wet clutch pack. To the knowledge of the authors, this study is the first to analyse the detailed power loss contributions of a DCT with wet clutches, and their relative significance along a set of driving cycles. Based on these results, a novel hybridised AMT (HAMT) with a single dry clutch and an electric motor is proposed for the same vehicle. The HAMT architecture combines the high mechanical efficiency typical of AMTs with a single dry clutch, with the torque-fill capability and operational flexibility allowed by the electric motor. The measured efficiency maps of a case study DCT and HAMT are compared. This is then complemented by the analysis of the respective fuel consumption along the driving cycles, which is simulated with an experimentally validated vehicle model. In its internal combustion engine mode, the HAMT reduces fuel consumption by >9% with respect to the DCT.
... A lot of research discusses the mathematical model for the clutch drag torque. 14,19,20 In this study, an alternative shrinking model 14 was used to calculate the clutch drag torque as follows ...
In this study, a new sub-shift schedule was proposed for a hydro-mechanical transmission. To develop the sub-shift schedule, a network analysis was performed by considering the hydrostatic unit loss and mechanical component losses. In the new sub-shift schedule, the sub-shift gear can be selected with respect to the demanded wheel torque and vehicle speed, which provides improved system efficiency for the given vehicle operating condition. Since the sub-shift can only be carried out at a speed ratio where the off-going and on-coming clutch speeds are synchronized in the existing sub-shift control, a sub-shift control algorithm without the clutch speed synchronization was proposed to apply the new sub-shift schedule using the forward clutch pressure and hydrostatic unit stroke control. The performance of the sub-shift control algorithm without the clutch speed synchronization was evaluated by the simulation and experiment. It was found from the simulation and experimental results that the sub-shift can be achieved, showing an acceptable peak-to-peak torque variation in the driveshaft.
