Numerical and Experimental Investigation of Temperature Distribution for Dry-Clutches

The temperature rise of the engaging clutch during shifting depends heavily on the transmitted torque. Precisely estimating the clutch temperature not only improves clutch control but also the optimal design of the clutch. However, the contact surface of the friction lining is closed, and the surface temperature is often difficult to measure accurately. In this study, a theoretical model of a two-dimensional transient temperature field for the friction disc has been established. In the radial and axial directions under different launching conditions, the temperature field of a friction disc is investigated. Four stages of clutch engagement have been determined, and finite-element analysis has been used to study the temperature field of a single clutch and to determine its duration.Then, the latest internationally developed distributed optical fiber sensing technology is used to perform measurement tests on the designed dry clutch friction characteristic test rig. The distributed fiber-optic temperature measurement technology can accomplish accurate temperature measurement with fast response speed and can acquire temperature value on different radii of friction discs with high spatial resolution. Such temperature sensing technology is very suitable for clutch working conditions. By analyzing the simulation and experimental results of temperature variation of different radii, different working conditions and different components, an important reference is provided for the establishment of the clutch temperature model and the optimization of the clutch heat dissipation structure design.

The optimization of friction disc gear-shaping process aiming at residual stress and machining deformation

Friction disc is the key part of the frictional clutch. But there is a lack of in-depth studies on the effect of the cutting parameters on residual stress and machining deformation. In this study, the simulation model for friction disc gear shaping was established and the effect of the typical cutting parameters on surface residual stress and machining deformation was studied. Based on the study’s results, the optimization experiment of friction disc gear shaping was carried out and a method was proposed to reduce machining deformation and to improve the fatigue life. Applying the proposed method, the residual stress on the tooth bottom increased from −122.50 to −371.33 MPa, an increase of 203.13% that increases the fatigue life greatly. Meanwhile, the front and bottom face deformation of the outer ring as well as the deformation of the front and bottom tooth tip can be decreased effectively. This study can provide technical support for improving the comprehensive performance of the friction disc and transmission system.

A Dynamic Investigation of the Impact Failure Analysis of the Friction Plate in a Planetary Transmission System

A clear understanding of both vibrations and the impact forces of planetary transmission systems is very helpful for decreasing impact failures of their friction discs and preventing serious accidents of the system. This study presents a multibody dynamic (MBD) investigation based on a commercial MBD software to predict the vibrations and impact forces of the friction disc in a planetary transmission system. In the MBD model, the radial clearance of the planet bearing is formulated, as well as the backlash between the outer gear teeth of the ring and friction disc teeth. However, the previous works in the literature only considered single radial clearance or backlash. The influences of the radial clearance of the planet bearing and backlash between the outer gear teeth of the ring and friction disc teeth on the vibrations and impact forces of the friction disc in the planetary transmission system are studied. The results give that a smaller radial clearance and backlash can be useful for decreasing both the vibrations and impact forces of the friction disc in the planetary transmission system. The MBD method can be applied to predict the vibrations and impact forces in the planetary transmission system as well.

Experimental investigation of friction disc temperature field under cooling fluid

The temperature field of the wet clutch is an important factor that influences the vehicle transmission performance. In order to predict and prolong the service life of the wet clutch, a test bench is built, and an accelerated life test is carried out based on the actual working conditions. Then, according to the variation of the friction coefficient and the maximum radial temperature difference, the sliding temperature field is analyzed in different periods. By introducing four evaluation indexes, a temperature field evaluation system is established and verified. With the help of this evaluation system, the temperature fields during running-in and unstable stages are compared, and the thermal failure mechanism of the friction disc is analyzed. In the stable stage, the influence of rotational speed, oil pressure and lubricant flow on the temperature field are investigated. The results of this study can guide the design and control of the friction components in the wet clutch.

Tribo-Brake Characteristics between Brake Disc and Brake Shoe during Emergency Braking of Deep Coal Mine Hoist with the High Speed and Heavy Load

The friction wear and thermal fatigue cracking of the brake shoe and friction-induced self-excited vibration (frictional flutter) of the disc brake can easily occur during emergency braking of a deep coal mine hoist with at high speed and with a heavy load. Therefore, tribo-brake characteristics between the brake disc and brake shoe during emergency braking of a deep coal mine hoist are investigated in the present study. Scaled parameters of the disc brake of a deep coal mine hoist are determined by employing the similarity principle. Friction tests between friction disc and brake shoe are carried out to obtain the coefficient of friction in the case of high speed and large specific pressure between the friction disc and brake shoe. Coupled thermo-mechanical finite element analyses of the brake disc and brake shoe are established to investigate temperature and stress fields of the brake disc and brake shoe during emergency braking, which is validated by the engineering failure case. Effects of braking parameters on flutter characteristics between the brake disc and brake shoe are explored by employing a double-degrees-of-freedom vibration mechanism model. The results show that the maximum temperature, equivalent Von Mises stress and contact pressure are all located at the average friction radii of contact surfaces of the brake disc and brake shoe during emergency braking. The cage crashing accident in the case of high speed and heavy load in a typical coal mine shows crack marks and discontinuous burn marks at central locations of brake shoe and brake disc surfaces, respectively, which indicates frictional flutter characteristics between brake disc and brake shoe. During emergency braking, flutter time duration decreases with increasing initial braking speed and damping parameter; the flutter amplitude and frequency of the disc brake increases with increasing normal braking load and stiffness, respectively.

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.