Powertrain control strategies achieving high performance and better shift control depend critically on the available measurements taken directly from the sensors. For Dual Clutch Transmission (DCT), the clutch friction forces are very important to improve the shift quality. So the estimations are needed to be able to set up the shift control on the powertrain system. For better shift comfort, accurate information for the dual clutch transmission should be available to control the clutch pressure. Furthermore, torque sensors for rotating shafts cannot be used on production vehicles since they are expensive and enduring in the environment of the automotive system.This paper presents an Improved Proportional Integral (IPI) observer for estimation of the unknown forces acting on the clutch during shift processes as well as the non measured states. The estimated unknown forces can be used for the closed-loop control of the dual clutch transmission for better shift quality. The IPI observer is improved to include also nonlinear known inputs. The observer was tested on experimental data obtained with a GETRAG dual clutch transmission in a BMW M3 with a petrol engine and yielded satisfactory results.