1. Field of the Invention
The present invention relates, in general, to a method of adjusting the characteristics of a dry clutch used in an automated manual transmission (AMT) or a double clutch transmission (DCT), and more particularly, to a method of adjusting the transmission torque characteristics of a dry clutch with respect to the stroke of an actuator which actuates the dry clutch.
2. Description of Related Art
Semi-automatic transmissions, such as automated manual transmissions (AMTs) and double clutch transmissions (DCTs), are systems which automatically control a manual transmission mechanism. Unlike typical automatic transmissions (ATs) which use a torque converter and a wet multi-plate clutch, semi-automatic transmissions frequently use a dry clutch to transmit engine torque to a transmission mechanism.
The dry clutch is controlled by an actuator, which is generally controlled based on a T-S curve that presents variations in the transmission torque of the dry clutch with respect to the stroke of the actuator.
The dry clutch is characterized in that the transmission torque thereof significantly varies depending on a variety of factors, such as a single part tolerance of each element, a degree of wear due to the duration of use, thermal deformation at high temperature and a variation in the coefficient of friction of a disk. It is difficult to convert the transmission torque of the dry clutch into a preset form of data.
However, the dry clutch fails to properly reflect variations in the characteristics of the transmission torque when controlling the actuator. When the actuator is controlled insufficiently or excessively, the dry clutch may slip excessively or be subjected to impact. There is required a technique for accurately finding transmission torque characteristics of the dry clutch depending on the actuator stroke so as to be used for control over the actuator.
Therefore, in the vehicle, a T-S curve presenting the characteristics of transmission torque with respect to the stroke of the actuator of the dry clutch is adjusted by learning such that the present state of the dry clutch can be reflected as accurately as possible. FIG. 1 is graph illustrating a conventional method of adjusting a T-S curve by learning.
In FIG. 1, P02 to P11 are characteristic points that reflect the characteristics of the T-S curve. The characteristic points P02 to P11 can be changed by learning. For instance, when a learning point P is newly learned, the existing T-S curved is adjusted based on the new learning point. As shown in the figure, the characteristics points P08 and P09 that are most close to the learning point P are moved in the direction toward the learning point. At this time, the characteristics points P10 and P11 are also moved by applying the same amount of change thereto, such that the inclination of the section of the T-S curve to which these points belong can stay unchanged.
With respect to the learning point P, a uniform amount of change is given for upper torque components, and no amount of change is given for lower torque components. This is intended to maintain transmission characteristics defined by the spring stiffness of the dry clutch system.
When the T-S curve is adjusted by learning as above, the inclination of the section of the T-S curve including the characteristic points P06 and P07 and newly-moved point P08NEW is significantly changed. This shape of the T-S curve indicates that the required change of the stroke must be discontinuous along the section in the case in which the transmission torque is changed by a uniform amount. This discontinuous change of the stroke makes the control difficult and inaccurate. This consequently leads to uncomfortable feel when shifting.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.