The empact CVT : dynamics and control of an electromechanically actuated CVT

The large ratio coverage of a CVT and the possibility to choose the engine speed in a wide range independently of the vehicle speed enables the ICE to operate at more fuel economic operating points, making the vehicle potentially more fuel efficient. Unfortunately, because the energy dissipation of the CVT itself is higher than that of a manual transmission, this efficiency improvement is partly lost. The main power losses in the CVT are due to the inefficient hydraulic actuation system and the excessive clamping forces used to prevent the belt from excessive slippage. Direct control of the slip can significantly increase the efficiency. Due to the low actuation stiffness at low hydraulic pressures, the hydraulically actuated CVT is not well suited for slip control. The Empact CVT, developed at the TU/e, is an electromechanically actuated pushbelt type CVT, which has a high stiffness at low clamping forces and is suitable for slip control. This system reduces the steady-state losses, which are dominantly present in a hydraulic system. The goals of this research are to achieve optimal efficiency of this system, to obtain good tracking performance and to prevent the pushbelt from slipping excessively. These objectives are experimentally validated at a Empact prototype, which is tested at a test rig and implemented in an Audi A3 2.0 FSI. The Empact CVT uses two servomotors to actuate the moveable pulley sheaves. To decouple the rotation of the input and output shaft from the servomotor rotations, a double epicyclic set is used at each shaft. The system is designed, such that one (primary) actuator accounts for the ratio changes and one (secondary) actuator sets the clamping forces in the variator. To optimally use the efficiency potential of the Empact system, the slip in the variator must be controlled. In this way, the clamping forces reduce to small values, thereby reducing the friction forces in the gears, spindles and bearings. Efficiency improvements of up to 20 [%] can then be reached at partial load (during 75 [%] of the duration of the FTP72 cycle) compared to a conventionally controlled CK2 147 transmission and efficiency gains of up to 10 [%] compared to an optimally, slip controlled CK2. To gain insight in the physical behavior of the Empact CVT, a multi-body model of the system has been developed, which incorporates a dynamical description of all major components of the test setup. Results show a realistic behavior of the system for both stationary and transient situations. Although this nonlinear simulation model gives a basis for control design and yields a realistic description of the closed loop system, for the actual control design an approximate, linear plant model that describes the frequency domain behavior of the system is estimated. These linearized descriptions are obtained from the simulation model using approximate realization from pulse response data. An iterative model identification and control design procedure is used, such that the plant is estimated in closed loop. In this way, the uncertainty in the frequency range of importance for the design of the controllers is reduced, which leads to less conservative control designs. Parallel to the identification and control design with the simulation model, this procedure is also applied for the test setup. Due to high measurement noise and excessive friction in the system, the quality of the approximated plants at the test setup is relatively low. The time responses are however comparable to the results from the simulation model. An important constraint for the controlled system is that slip cannot be controlled under all operating conditions. At low variator speeds and low loads, the slip controller must be switched off. A decentralized control structure is chosen. Pairing of the in- and outputs is primarily based on the mechanical design of the Empact CVT and are supported by a interaction analysis. The controllers are designed using a sequential loop closing procedure, in which the slip loop is closed last, such that stability of other loops is guaranteed independent of the switching of the slip controller. Using manual loop-shaping, decentralized lead-lag controllers are designed. Nominal stability and performance can be guaranteed. To obtain robust performance, gain scheduling of the slip controller is implemented. Resulting closed loop bandwidth is 8-10 [Hz] for both the ratio and slip control loops. Because the slip dynamics is not well defined at low or zero variator speeds, the slip controller is partly switched off below 2 [km/h]. Both the simulation model and the experimental setup show very good results for disturbance rejection and tracking performance. Torque disturbances of up to 100 [Nm], applied at the secondary variator shaft, can be suppressed within 0.2 [sec] for all ratios. The ratio tracking error is very small compared to conventional CVT systems. Experimental evaluation of the Empact CVT at the test rig showed that the average power consumption of the Empact CVT on the FTP72 cycle is 155 [W], whereas conventional hydraulically actuated CVTs consume over 400 [W] on the average at this drive cycle. Efficiencies of 90 [%], which is close to the maximum efficiency of the Empact CVT, are reached during these experiments. Evaluation of the Empact CVT in an Audi A3 2.0 FSI shows similar performance. Overall, an efficiency improvement of up to 10 [%] is obtained with the Empact CVT compared to a comparable size hydraulically actuated CVT

Analytical one parameter method for PID motion controller settings

In this paper analytical expressions for PID-controllers settings for electromechanical motion systems are presented. It will be shown that by an adequate frequency domain oriented parametrization, the parameters of a PID-controller are analytically dependent on one variable only, the cross-over frequency of the open loop transfer function. Analytical expressions are derived that relate the cross-over frequency clearly to the performance criteria for the closed loop system. In this paper the latter is shown in detail for servo problems. The effectiveness of the outlined approach is demonstrated by experimental results that were obtained from a two DOF tilting mirror system

Improving Energy Efficiency and Motion Control in Load-Carrying Applications using Self-Contained Cylinders

Because of an increasing focus on environmental impact, including CO2 emissions and fluid spill pollution, inefficient hydraulic systems are being replaced by more environmentally friendly alternatives in several industries. For instance, in some offshore applications that have multiple diesel generators continuously running to produce electricity, all hydraulic rotating actuators supplied from a central hydraulic power unit have been replaced with AC induction motors containing a variable frequency drive and gearbox. However, hydraulic linear actuators are still needed in most load-carrying applications mainly because of their high reliability associated with external impact shocks. Moreover, their force capacity is higher than that of their linear electromechanical counterparts. Valve-controlled linear actuators (cylinders) supplied from a centralized hydraulic power unit are standard in offshore load-carrying applications. In addition to the advantages mentioned above of hydraulic linear actuators, they have, nevertheless, a number of important drawbacks, which include: 1) a high level of energy consumption due to significant power losses caused by flow throttling in both the pipelines and valves, 2) reduced motion performance due to the influence of load-holding valves, 3) high CO2 emissions and fuel costs related to the diesel generator that supplies electricity to the hydraulic power unit, 4) significant potential for hydraulic fluid leakage because of many leakage points, 5) demanding efforts with respect to installation and maintenance, as well as 6) costly piping due to the centralized hydraulic power supply. The work presented in this dissertation and the appended papers are devoted to replacing inefficient hydraulic linear actuation systems traditionally used in offshore load-carrying applications with more environmentally friendly solutions. Two alternative technologies are identified, namely electro-mechanical and electro-hydraulic self-contained cylinders. The feasibility of replacing conventional valve-controlled cylinders with self-contained cylinder concepts is investigated in two relevant case studies.publishedVersio

Identification of Two-Mass Mechanical Systems Using Torque Excitation: Design and Experimental Evaluation

This paper deals with methods for parameter estimation of two-mass mechanical systems in electric drives. Estimates of mechanical parameters are needed in the start-up of a drive for automatic tuning of model-based speed and position controllers. A discrete-time output error (OE) model is applied to parameter estimation. The resulting pulse-transfer function is transformed into a continuous-time transfer function, and parameters of the two-mass system model are analytically solved from the coefficients of this transfer function. An open-loop identification setup and two closed-speed-loop identification setups (direct and indirect) are designed and experimentally compared. The experiments are carried out at nonzero speed to reduce the effect of nonlinear friction phenomena on the parameter estimates. According to results, all three identification setups are applicable for the parameter estimation of two-mass mechanical systems.Peer reviewe

Online identification of a two-mass system in frequency domain using a Kalman filter

Some of the most widely recognized online parameter estimation techniques used in different servomechanism are the extended Kalman filter (EKF) and recursive least squares (RLS) methods. Without loss of generality, these methods are based on a prior knowledge of the model structure of the system to be identified, and thus, they can be regarded as parametric identification methods. This paper proposes an on-line non-parametric frequency response identification routine that is based on a fixed-coefficient Kalman filter, which is configured to perform like a Fourier transform. The approach exploits the knowledge of the excitation signal by updating the Kalman filter gains with the known time-varying frequency of chirp signal. The experimental results demonstrate the effectiveness of the proposed online identification method to estimate a non-parametric model of the closed loop controlled servomechanism in a selected band of frequencies

Modeling and control of a modular iron bird

This paper describes the control architecture and the control laws of a new concept of Modular Iron Bird aimed at reproducing flight loads to test mobile aerodynamic control surface actuators for small and medium size aircraft and Unmanned Aerial Vehicles. The iron bird control system must guarantee the actuation of counteracting forces. On one side, a hydraulic actuator simulates the hinge moments acting on the mobile surface due to aerodynamic and inertial effects during flight; on the other side, the actuator to be tested applies an active hinge moment to control the angular position of the same surface. Reference aerodynamic and inertial loads are generated by a flight simulation module to reproduce more realistic conditions arising during operations. The design of the control action is based on a dynamic model of the hydraulic plant used to generate loads. This system is controlled using a Proportional Integral Derivative control algorithm tuned with an optimization algorithm taking into account the closed loop dynamics of the actuator under testing, uncertainties and disturbances in the controlled plant. Numerical simulations are presented to show the effectiveness of the proposed architecture and control laws

Diesel Engine

Diesel engines, also known as CI engines, possess a wide field of applications as energy converters because of their higher efficiency. However, diesel engines are a major source of NOX and particulate matter (PM) emissions. Because of its importance, five chapters in this book have been devoted to the formulation and control of these pollutants. The world is currently experiencing an oil crisis. Gaseous fuels like natural gas, pure hydrogen gas, biomass-based and coke-based syngas can be considered as alternative fuels for diesel engines. Their combustion and exhaust emissions characteristics are described in this book. Reliable early detection of malfunction and failure of any parts in diesel engines can save the engine from failing completely and save high repair cost. Tools are discussed in this book to detect common failure modes of diesel engine that can detect early signs of failure

Development of the UMAC-based control system with application to 5-axis ultraprecision micromilling machines

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Increasing demands from end users in the fields of optics, defence, automotive, medical, aerospace, etc. for high precision 3D miniaturized components and microstructures from a range of materials have driven the development in micro and nano machining and changed the manufacturing realm. Conventional manufacturing processes such as chemical etching and LIGA are found unfavourable or limited due to production time required and have led mechanical micro machining to grow further. Mechanical micro machining is an ideal method to produce high accuracy micro components and micro milling is the most flexible enabling process and is thus able to generate a wider variety of complex micro components and microstructures. Ultraprecision micromilling machine tools are required so as to meet the accuracy, surface finish and geometrical complexity of components and parts. Typical manufacturing requirements are high dimensional accuracy being better than 1 micron, flatness and roundness better than 50 nm and surface finish ranging between 10 and 50 nm. Manufacture of high precision components and parts require very intricate material removal procedure. There are five key components that include machine tools, cutting tools, material properties, operation variables and environmental conditions, which constitute in manufacturing high quality components and parts. End users assess the performance of a machine tool based on the dimensional accuracy and surface quality of machined parts including the machining time. In this thesis, the emphasis is on the design and development of a control system for a 5-axis bench-type ultraprecision micromilling machine- Ultra-Mill. On the one hand, the developed control system is able to offer high motion and positioning accuracy, dynamic stiffness and thermal stability for motion control, which are essential for achieving the machining accuracy and surface finish desired. On the other hand, the control system is able to undertake in-process inspection and condition monitoring of the machine tool and process. The control of multi-axis precision machines with high-speed and high-accuracy motions and positioning are desirable to manufacture components with high accuracy and complex features to increase productivity and maintain machine stability, etc. The development of the control system has focused on fast, accurate and robust positioning requirements at the machine system design stage. Apart from the mechanical design, the performance of the entire precision systems is greatly dependent on diverse electrical and electronics subsystems, controllers, drive instruments, feedback devices, inspection and monitoring system and software. There are some variables that dynamically alter the system behaviour and sensitivity to disturbance that are not ignorable in the micro and nano machining realm. In this research, a structured framework has been developed and integrated to aid the design and development of the control system. The framework includes critically reviewing the state of the art of ultraprecision machining tools, understanding the control system technologies involved, highlighting the advantages and disadvantages of various control system methods for ultraprecision machines, understanding what is required by end-users and formulating what actually makes a machine tool be an ultraprecision machine particularly from the control system perspective. In the design and development stage, the possession of mechatronic know-how is essential as the design and development of the Ultra-Mill is a multidisciplinary field. Simulation and modelling tool such as Matlab/Simulink is used to model the most suitable control system design. The developed control system was validated through machining trials to observe the achievable accuracy, experiments and testing of subsystems individually (slide system, tooling system, monitoring system, etc.). This thesis has successfully demonstrated the design and development of the control system for a 5-axis ultraprecision machine tool- Ultra-Mill, with high performance characteristics, fast, accurate, precise, etc. for motion and positioning, high dynamic stiffness, robustness and thermal stability, whereby was provided and maintained by the control system

Development of a general purpose airborne simulator

Variable stability system development for General Purpose Airborne Simulator /GPAS