Electro-mechanical friction clutch control using proportional derivative plus conditional integral controller

Abstract

Electro-Mechanical Friction Clutch (EMFC) is a clutch-by-wire system developed in Universiti Teknologi Malaysia (UTM) that uses a power screw mechanism for the engagement process. The mechanism provides self-lock capability that eliminates the requirement of continuous hydraulic pressure that leads to inefficiency during operation. Together with Electro-Mechanical Dual Acting Pulley Continuously Variable Transmission, an internal combustion engine (ICE) based powertrain efficiency improves significantly. However, its performance during vehicle start-stop, which is particularly critical during driving, has not been studied so far. Thus, the aim of this research was to simulate and experimentally validate the best controller for EMFC so that the start-stop condition can be executed smoothly and quickly for driving comfort. It was started by developing a mathematical model of the EMFC’s actuator. Next, axial movement of the actuator was studied in the model for closed loop system using Proportional Integral Derivative (PID) based control algorithm. Relay feedback and Ziegler-Nichols’s methods were utilized to tune the PID controller parameters. Based on the tuned parameters, various PID controller schemes such as Proportional (P), Proportional Integral (PI), PID and Proportional Derivative (PD) controllers were evaluated and the one with the best performance in terms of response time (Tr), percentage overshoot (PO), and steady state error (ESS) was determined. From the evaluation, PD controller showed the best overall performance in terms of Tr (1.3 s), PO (0.7%) and ESS (0.04 mm), hence it was selected as the reference. To further reduce the ESS, which is crucial for precise clutch engagement, conditional integral parameter was activated in the controller, hence, it became Proportional Derivative Plus Conditional Integral (PDPCI). As a result, the ESS was reduced to 1 µm while maintaining the Tr and PO. Subsequently, PD and PDPCI controller schemes were adopted for experimental work, to verify that they were safe to be implemented. Comparing the experimental results of the two controllers, PDPCI controller improved the EMFC performance against PD controller in terms of PO and ESS by 32.8% (1.8% against 2.7%) and 77.3% (0.05 mm against 0.22 mm), respectively. The PDPCI was selected as the EMFC controller for the vehicle testing. In the testing, axial movement of the EMFC’s actuator was controlled by the PDPCI controller to regulate the clutch engagement process. During the process, two clutch engagement strategies based on single-step-up (SSU) and double-step-up (DSU) inputs for the PDPCI controller were used. It was found that PDPCI using SSU input strategy makes the ICE stalled. PDPCI with DSU input strategy, on the contrary, shows a good EMFC engagement performance in terms of smooth engagement process with less than ±8 mm/s3 jerking, no ICE stalling and minimum engagement time of less than 4 seconds for the vehicle start-stop under low, medium and full throttle pedal opening. In conclusion, the best EMFC controller has been successfully simulated and validated experimentally. It was shown that these outcomes provide an important contribution towards achieving EMFC desired engagement performance during vehicle launching condition.