Zvonko Herold

Dry clutch control based on electromechanical actuator position feedback loop

The paper presents identification and control of an experimental dry clutch actuated by a geared dc motor and ball-ramp mechanism. The identification results are used to describe the multi-dimensional clutch friction coefficient characteristic. The proposed clutch torque control system is based on closed-loop actuator position control and the identified friction coefficient curves. In order to compensate for a clutch pack thermal expansion effect, which affects the torque control accuracy, the control strategy is extended with feedforward or feedback path that outputs a position reference additive signal. The torque control strategy is verified experimentally within a clutch slip speed control system.

Experimental identification of dynamic tire friction potential on ice surfaces

Recently, it has been shown that the tire–ice friction is characterized by a significant dynamic potential for abrupt increases of wheel torque. With the aim to gain insight into the dynamic tire friction potential features and to provide a comprehensive set of experimental data for model validation, a detailed experimental investigation of the dynamic potential has been presented in this article. The experimental data have been collected by using an experimental electrical vehicle with an in-wheel motor. Influence of the following operating parameters has been analyzed: rate of change of applied wheel torque, time for which the tire stands still on ice before applying the abrupt transient, initial vehicle speed, and initial tire force. In order to check a possible correlation between the dynamic potential and the rubber–ice friction dynamics, an experimental analysis based on a pin-on-disc tribometer has also been presented.

Modeling of electromagnetic circuit of a magnetorheological fluid clutch

The steady-state and transient accuracy of magnetorheological fluid (MRF) clutch torque control is affected by the magnetic hysteresis and eddy current lag. The paper presents a nonlinear analytical model of the MRF clutch electromagnetic circuit dynamics. The model includes two state variables describing the combined solenoid and eddy current dynamics, and the dynamics induced by the magnetic hysteresis effect. The overall nonlinear model is experimentally validated under the clutch current-control conditions. It is demonstrated that the use of second state variable for magnetic hysteresis significantly improves the modeling accuracy when compared to the more traditional first-order linear model.

An in-wheel motor-based tyre test vehicle

An experimental three-wheel electrical vehicle has been developed in order to provide a platform for experimental verifications of advanced tyre friction models, estimators and controllers. The vehicle comprises a high-torque permanent-magnet synchronous motor built in the front wheel and precise incremental encoders for the front- and rear-wheel speed measurements. The paper presents a description of the vehicle and gives characteristic experimental procedures and results related to motor static and dynamic behaviour. Experimental results on tyre friction identification are also presented.

Modelling of electromechanically actuated active differential wet-clutch dynamics

The paper presents a lumped-parameter dynamic model of an electromechanically actuated wet clutch found in an active limited slip differential. The bond graph modelling technique is used to describe the multi-physical clutch system including the clutch actuator dynamics, the axial dynamics with the fluid film squeeze effect, the thermal dynamics, and the torque development dynamics with a multi-functional clutch friction coefficient static characteristic. Different variants of the individual subsystem models are considered, ranging from first-principle models to simplified and numerically more efficient models. The proposed models are parameterized and thoroughly validated on the basis of the experimental data collected by using an active differential and clutch test rig. The modelling results are used for the purpose of analysis of the clutch steady state and transient behaviour under various operating modes.

Design of Test Rigs for a Dry Dual Clutch and its Electromechanical Actuator

Dual Clutch Transmissions with dry electromechanically actuated clutches have emerged on the market recently. In order to provide their favorable operation in terms of the clutch torque control, it is very important to have a good knowledge on the system behavior related to the actuator dynamics, the dry friction coefficient behavior, and the thermal dynamics. This paper describes two test rigs developed to support the research work on a dry dual clutch with a leverbased electromechanical actuation system. The first test rig (actuation system test rig) provides a basis for a comprehensive multi-step identification of the actuation system parameters and characterization of the overall system behavior. This test rig includes a modified dual clutch assembly including a built-in sensor for the purpose of direct normal force measurement. The second test rig (transmission test rig) is aimed at providing support for more comprehensive characterization of the actuation system under realistic operating conditions and characterization of the clutch torque transfer dynamics/friction coefficient behavior, thermal dynamics, and wear. Both test rigs are computer controlled and include measurements of all main system variables. Functionality of the test rigs is demonstrated by characteristic experimental results.

Experimental Characterization and Modeling of Dry Dual Clutch Wear

Clutch wear is dominantly manifested as the reduction of friction plate thickness. For dry dual clutch with positioncontrolled electromechanical actuators this affects the accuracy of normal force control because of the increased clutch clearance. In order to compensate for the wear, dry dual clutch is equipped with wear compensation mechanism. The paper presents results of experimental characterization and mathematical modeling of two clutch wear related effects. The first one is the decrease of clutch friction plate thickness (i.e. increase of clutch clearance) which is described using friction material wear rate experimentally characterized using a pin-on-disc type tribometer test rig. The second wear related effect, namely the influence of the clutch wear compensation mechanism activation at various stages of clutch wear on main clutch characteristics, was experimentally characterized using a clutch test rig which incorporates entire clutch with related bell housing. Finally, the previously proposed and experimentally validated physical clutch model, which was focused on the clutch actuator and axial dynamics, is extended to capture both wear related effects as a further step towards a more comprehensive overall clutch dynamics model.

Modeling and Experimental Validation of Active Limited Slip Differential Clutch Dynamics

This paper deals with modeling of an Active Limited Slip Differential (ALSD) which comprises a wet clutch actuated by an electromechanical mechatronic system consisting of a DC motor and ball-ramp mechanism. The structure of the proposed ALSD model is divided in two subsystems: (i) clutch axial force development model and (ii) clutch torque development model. The former includes DC motor dynamics; gear box kinematics and backlash; ball-ramp mechanism kinematics, friction, and compliance; fluid squeeze speed dynamics; and clutch pack axial compliance and damping. The latter includes structural compliance and inertias, as well as dynamic friction effects. Each submodel has a pure physical structure. This facilitates model parameterization through a series of relatively simple experimental procedures, which are also described in the paper. The final model has been validated under various operating conditions by using an ALSD test rig. The validation results point to a good modeling accuracy.Copyright

Modeling of dry dual-clutch axial dynamics:

A dynamic model of an automotive dry dual clutch is proposed and experimentally validated for a wide range of operating conditions, including those related to the thermal expansion effects and the wear effects. The bond graph method is used to derive the model and to analyze its simplification. The main model maps, which relate to the stress–strain curves of key clutch assembly components, are identified by using a custom-made manual press rig. The clutch coefficient of friction is described as a function of the temperature, the slip speed, and the normal force, which is determined from the tribometer characterization data. A lumped-parameter third-order thermal dynamics model is proposed and experimentally identified, in order to predict accurately the pressure plate and the flywheel friction interface temperatures. The overall clutch model, including an electromechanical actuator submodel, is validated against experimental data collected on a custom-made clutch test rig.

Normal force control for a pin-on-disk tribometer including active or passive suppression of vertical vibrations

This paper presents the design of a computer-controlled pin-on-disk tribometer for friction characterization of various sliding pairs. The pin-on-disk setup comprises two high-bandwidth servomotors for the control of the rotating disk and the normal load-related spindle drive, as well as a high-precision tri-axial piezoelectric force sensor for normal and tangential forces measurement. Since the spindle drive system is characterized by notable compliance effects, the normal force cascade control system is designed with the aim of vertical vibrations active damping. In order to account for notable unevenness of the rotating disk surface and related high-level perturbations in the specimen normal force, the normal force control system is extended with a feedforward compensator of the disk unevenness disturbance, and, in particular, a dedicated leaf spring suspension system is designed. The effectiveness of the proposed system of vertical vibrations damping is verified experimentally.