Analysis and Optimization of Clutch Actuator on Automated Manual Transmission System

This paper presents dynamic analysis, control simulation, and optimization for a clutch actuator on Automated Manual Transmission (AMT). The main object is to optimize a clutch actuator, both in mechanical component and control component, to be able to drive clutch faster and more stable. Using Matlab Simulink, both dynamic model and control model are integrated into a unit. According to the integrated model and using optimization technique, the clutch actuator is modified to capable of disengage/engage clutch faster and more stable in a real case. On the other hand, in order to obtain more information about the affection of clutch control while shifting, the dynamic model of powertrain from engine to vehicle loading is created in the Matlab Simulink program to perform a complete simulation from part control to vehicle dynamic. INTRODUCTION Automated Manual Transmission (AMT) is prevailing in recent years. Vehicles from high quality sports cars like BMW M3, Ferrari 355, etc., to general sedans like Opel Corsa, Renault Twingo, etc. have introduced such system. It uses auto clutch and shifting actuator to simulate Manual Transmission (MT) as an auto transmission system (Figure 1). Due to the low cost and high efficiency of manual transmission, AMT can either have a lower cost and higher efficiency comparing to traditional Automated Transmission (AT), which uses torque converter and planetary gear box for shifting. Figure 1 Automated Manual Transmission (AMT) However, the main disadvantage of AMT, which leads to a worse competitiveness comparing to AT, is comfort. AMT, like MT, needs a complete power interruption to provide a chance for synchronizer to actuate to shift gear ratio. Such interruption, not likely occur on AT, always causes uncomfortable accelerations and jerks. The uncomfortableness is mainly dominated by the control of clutch. It can be apparently experienced by a novice driver of MT car. To have a more comfortable shifting process, a faster clutch motion which can lead to a shorter shifting time and less power interruption and a more stable clutch control which can lead to a more comfortable reacceleration while clutch is engaging are required. There are many strategies to deal with such problem, such as Double Clutch Transmission (DCT), [1], [2], etc., and torque tracking strategy [3]. Identically, both these methods require a fast and reliable auto clutch system. An approach to optimize a clutch actuator and its control according to the design requirements is proposed in this paper. The main object of this paper is to optimize a clutch actuator and its controller to drive clutch faster and more stable. Besides, in order to completely understand the dynamic character while shifting, a modular simulation program which integrated engine, clutch, gear box, vehicle loading, and control of each component is created. Researchers can obtain information of vehicle dynamic response with different Throttle Position (TPS) control, clutch control, and gear ratio control, which can help to develop shifting strategy, clutch control strategies, and TPS control strategy. Using Matlab Simulink, dynamic problems, control problems, and optimizations are integrated into a unit with modules to provide efficient computation, simultaneous analysis, and easy of modification. For dynamic module of the clutch system, a detailed dynamic model of the clutch actuator is created using free body analyses, and a black box model of the clutch is created according to experiments data and curve fitting methods. For control module, PID control strategy is used to control the clutch actuator. Ziegler-Nichols (Z-N) and Internal Model Control (IMC) control turning algorithms [4] are used at initial to design the controller parameters. With the combined model of clutch module, clutch actuator module, and controller module, dimensions of some mechanical parts of the clutch actuator are optimized to perform a faster actuating speed, and control parameters are optimized to give more stable clutch travel control. The optimization result is practiced on a real model and is verified to have a faster shifting speed. For the complete powertrain simulation program, engine module, gear box module, and vehicle loading module are also created by experiments data and free body analyses. Combined with the clutch actuator module and clutch module, shifting process simulations with different TPS control, clutch control, gear ration control, and driving condition are presented in the final part of this paper. DYNAMIC MODEL Vehicle dynamic models in this paper are mainly separated into two parts: clutch system and powertrain. Cultch system is the main objective of this paper which is to be optimized for faster actuating speed and more stable control. Dynamic model of the clutch system is to be created as detailed as possible by free body analysis. For other components of the powertrain, the models are mainly created by experiments data and simplified free body analysis, which also perform a well input-output relation. With the modular programming, such models can easily be modified to be more detailed if any of these components are to be studied more completely in the future. For the assumption of the model creation, since rigid body assumption is well approximated in most cases on vehicle [5], all components, besides springs, are considered as rigid bodies for simplification. CLUTCH SYSTEM Clutch actuator Structure of the clutch actuator is shown in Figure 2. Figure 2 Structure of Clutch Actuator The clutch actuator is mainly driven by a DC motor, through a couple of worm shaft and worm gear to magnify torque and serve as self-lock structure, to drive a linkage to move the clutch lever and to control the clutch position. A pre-deformed assist spring is assembled to assist clutch disengaging. According to “law of motor” and KVL analysis [6], model of the DC motor is created. And by free body analysis of each part of the clutch actuator, the dynamic model of the clutch actuator is created. Combining the DC motor module and mechanical parts modules, clutch actuator module is created (Figure 3).