Improving the Engagement Smoothness Through Multi-Variable Frictional Map in Automated Dry Clutch Control

Abstract

An Automated Manual Transmission (AMT) is directly derived from a manual one through the integration of actuators; then, development and production costs are generally lower than other automatic transmissions, while the reliability and durability are at highest level. For high class sport cars, vehicle dynamic performances and driving quality can be strongly improved with respect to automatic transmissions [1]. AMTs systems are generally constituted by a dry or wet clutch assembly and a multi-speed gearbox, both equipped with electro-mechanical or electro-hydraulic actuators, which are driven by a control unit, the transmission control unit (TCU). The operating modes of AMTs are usually two: semiautomatic or fully automatic. In both cases, after the gear shift command, the TCU manages the shifting steps according to current engine regime, driving conditions and selected program. In this transmission type the quality of the vehicle propulsion as perceived by the driver is largely dependent on the quality of the control strategies. Furthermore, sensitivity analyses on control schemes for AMTs have shown that uncertainties in clutch torque characteristic can severely affect the performance of the clutch engagement: modeling in detail the torque transmitted by the specific clutch architecture is a crucial issue in order to design robust engagement control strategies [2, 3 and 4]. This paper aims at investigating the engagement performance of an actuated dry clutch by taking into account the inference of the pressure on the facing materials and the sliding speed. In fact, according to literature outcomes [5], the friction coefficient after a first rising behavior with the sliding speed shows an asymptotic value for a typical clutch facing; the same material exhibits a nearly linear dependence of the friction coefficient on the pressure. The simulations consider: reduced-order dynamic system for simulation of passenger car driveline, control algorithm, experimental maps of the n-D clutch transmission characteristic, and gear shift maneuvers in different operating conditions. The outcome of this analysis could provide valuable issues for designers of automated clutches and control engineers to overcome the well known poor engagement performances of open loop motion strategy of the throwout bearing where cost reason and complexity don’t permit the use of displacement sensor.

Dry Dual Clutch Torque Model with Temperature and Slip Speed Effects

“…6c), the measured torques and the mod- Torque versus x to and θ c ( • C) parametrized respect to ω fc ; darker colors stand for higher slip speeds eled ones are still comparable, but the accuracy reduces and it seems there is even a qualitative change in the shape of the measured torque. It's not clear the reason of this effect which might be due to the pressure effect on the friction material or to the change in the slope of the flat spring characteristic, which in the proposed model it is not considered being temperature dependent, but that it is reasonable to assume as temperature influenced too [9,12].…”

“…The slope λ of u fs with respect to x to is unaffected by the temperature because it is determined by the diaphragm spring characteristic that is assumed to be temperature independent. The flat spring stiffness is assumed to be unaffected by the temperature too [12]. Later in this section it will be explained how the parameters λ, λ k , k = 0, 1, 2, and x to,max have been identified.…”

“…In [11] the authors investigated the temperature distributions in automotive dry clutch during single and repeated engagements under two different hypotheses: uniform pressure and uniform wear. In [12], under the assumptions that the friction coefficient is uniform along the whole contact surface, the clutch torque is assumed to be a function of the product between the friction coefficient and the clamping (or contact) force. In these papers, the temperature influence on the two functions is separately considered: the temperature influence on the friction is modeled by using experimental data from [13] while, in order to model the temperature influence on the contact force, a finite element analysis is used.…”

“…The friction facings temperature distribution is also dependent on the grooves shape [16], and in [17] it is shown that the thermal proprieties are also affected by some manufacturing process parameters. The temperature distributions are usually assumed to be uniform and average temperatures are considered in order to determine the torque characteristic [12,13].…”

Frictional Behaviour and Engagement Control in Dry Clutch Based Automotive Transmissions

“…Note that with this proposed terminology in ordinary engagement phases, the clutch is engaged before being closed [21]. Even though the torque transmitted through dry-clutch also influences and is influenced by driveline components and diaphragm spring, the frictional torque transmission model assumed in the present analysis is mainly based on cushion spring loading and dry friction phenomenon [22].…”