# Experimental Study of Drag Torque between Wet Clutch Discs
###### Abstract
However, their conclusions are based on the results obtained for rotational speed up to 4000 rpm. Similar research was led by [PERSON] et al. [6]. The two-disc system with open grooves has been designed and manufactured. The presented solution allowed us to identify the fluid flow pattern between the discs at the low-speed condition (240 rpm). The researchers also observed three types of flow patterns depending on the fluid flow rate and the plates clearance. They concluded that it is caused by the centrifugal force coupling effect, fluid shearing force and surface tension. Moreover, the change of single-phase fluid to air-liquid mixture flow is determined by insufficient flow supply. [PERSON] et al. [7] proposed the use of a three-dimensional model to simulate the operation of a disengaged wet clutch. Even though in the clearance between the rotating discs at higher speeds, a two-phase fluid flow is observed. The authors decided to use a single-phase model, which significantly reduced the time of numerical calculations. However, the results obtained from such a model are in line with the experimental tests only in terms of low rotational speeds for which the formation of an oil-air mixture does not occur. [PERSON] et al. [8] used continuity and Navier-Stokes equations taking into account the laminar flow. The model uses both the shear of the oil film and the air bubble content that causes the oil film to break. The simulations were compared with the experiment, and it can be noticed that the results accurately reflect the drag torque as a function of rotational speed, even for high relative speeds of the discs. This model is more complicated than the one described by [PERSON] et al. [7] but still its simplicity makes it suitable for online control and optimization. A mathematical model was also developed by [PERSON] et al. [9]. It allowed us to analyze the influence of various parameters on the drag torque in a disengaged clutch. The model was experimentally verified, and its novelty was that instead of the cavitation boundary condition which is commonly used in this type of simulation, the authors implemented an incipient reverse flow (Prandtl-Hopkins) condition to determine the moment of the oil film separation. The obtained results show that the assumed model of fluid film separation is in coincidence with the experimental measurements. [PERSON] et al. [10] made an attempt to simulate the drag torque in open wet clutches caused by the mechanical contact at high circumferential speed. The proposed solution takes into consideration a rigid-body impact model. The results demonstrate the advantage of this idea which is the possibility to predict the drag torque with high accuracy even at a high-speed range. Moreover, the calculations show that the drag torque increases with larger fluid flow. The influence of fluid flow on the heat exchange processes in the multidisc clutches was studied by [PERSON] et al. [11]. The research was performed for three different oil flows: 1, 2 and 3 L per minute for each single pair of plates. The simulation model and the test on the bench confirmed that the larger the lubrication flow, the slower the temperature rise of the clutch, and the faster the temperature rise of the oil. However, the influence of the oil flow on the drag torque between the rotating discs was not the subject of these studies. Another parameter that influences the drag torque of the disengaged clutches is the oil viscosity. [PERSON] et al. [12] investigated the influence of lubrication oil (ATF) temperature on disengaging dynamic characteristics through a comprehensive numerical model for the clutch disengaging process. The results presented in the conclusion indicate that the increase in oil temperature not only accelerates the change of the lubrication status between the discs but also leads to the decrease in friction torque and hydrodynamic torque. [PERSON] et al. [13] studied the influence of the clearance between the wet disc clutches on the drag torque.