Torque Transmissibility Assessment for Automotive Dry-Clutch Engagement

Abstract

Dry clutches are widely used in conventional and innovative automotive drivelines and represent a key element for automated manual transmissions (AMTs). In practical applications, it is fundamental to model the clutch behavior through its torque transmissibility characteristic, i.e., the relationship between the throwout bearing position (or the pressure applied by the clutch actuator) and the torque transmitted through the clutch during the engagement phase. In this paper, a new model for the torque transmissibility of dry clutches is proposed. It is analyzed how the transmissibility characteristic depends on: friction pads geometry, cushion spring compression, cushion spring load, and slip-speed-dependent friction. Corresponding functions are suitably composed determining the torque transmissibility expression. An experimental procedure for tuning the characteristic parameters is presented. The clutch-torque transmissibility model is tested on a detailed cosimulation model with a typical AMT controller

Dry Dual Clutch Torque Model with Temperature and Slip Speed Effects

“…In this scenario the maximum torque which can be transmitted by the clutch depends on the static friction coefficient μ s and on the pressure plate force F pp which corresponds to the diaphragm spring elastic force [3]. A typical expression for the maximum frictional torque for the closed clutch is given as in [3,9] T max f c = nμ s R eq F pp (1) where R eq is the equivalent radius of the contact surface and n is the number of contact surfaces which generate the friction torques, assumed equals on both sides. The clutch is said to be locked up when there is no slip between the flywheel and the clutch disk.…”

“…where R μ is the equivalent friction radius and F fc is the flat spring elastic force [3]. The torque dependencies on the slip speed ω fc = ω f − ω c , on the flat spring compression u fs and on the clutch temperature will be investigated in the next section.…”

“…By considering the dependencies described above, the expression of the equivalent friction radius proposed in [3] and used in (2) can be generalized as follows…”

“…Unfortunately, it is quite difficult to provide an on-board measurement of this torque and then the use of torque estimators is the typical solution adopted in practice, for both dry and wet clutches [1,2]. Several phenomena and components influence the torque in a dry dual clutch transmission (DDCT), such as friction, transmission kinematics [3], friction facing wear and diaphragm spring fatigue [4], pressure [5] and, overall, temperature and slip speed between the clutch disk and the flywheel. Some models proposed in the literature are based on the inversion of the driveline dynamic model [6,7], but the robustness of this solution depends on the availability of the system parameters and on clutch disk acceleration and engine torque measurements.…”

“…Some models proposed in the literature are based on the inversion of the driveline dynamic model [6,7], but the robustness of this solution depends on the availability of the system parameters and on clutch disk acceleration and engine torque measurements. In any case, the engagement controllers are typically equipped with a characteristic that describes the friction phenomena by providing the torque transmitted by the clutch as a function of the throwout bearing force [8] or the throwout bearing position [3,9].…”