Automatic Data Acquisition and Control of an Engine Test ... - ADAI

Automatic Data Acquisition and Control of an Engine Test BenchM. C. Gameiro da Silva, M. L. O. .S. Mateus, Luís M. V. SerranoDEM – FCTUCUniversidade de Coimbra – Polo II3030 CoimbraAbstractIt is presented the software and the system developed to perform the automatic data acqusition andcontrol of an engine test bench installed in ADAI, an interface laboratory of the Mechanical EngineeringDepartment of the Universidade de Coimbra.KeywordsMotor, testing, test engines, engines.IntroductionOn the combustion engines tests it is necessarily to impose some different workingsituations defined by two variables, the velocity of rotation of the engine and theabsorbed torque on dynamometer. The different test parameters are defined with thetime evaluations required for this two values, where are naturally verified the transitionphase witch duration tend to be minimized. This way, its ease to conclude that therealization of engines tests will be much more effective and improved when donethrough an automated system allowing the data acquisition and the control of theengines test process.The need to register a great number of parameter, the presence of high frequencyphenomenon, where the acquisition frequency need to be very high, does not allow thatthe values read and register could be done by the operator, also the fact that in thechanging of step on the process, it was imposed the simultaneous and multiple actions,all these additional reasons justifies the option for the automated system in the controland data acquisition.

The primordial objective of this work was the development of an software and itsposterior implementation in an experimental installation involving an engine test bench,allowing the control of the engines tests and the data acquisition and saving.Selection of the equiment to installThis installation is composed by an hydraulic dynamometer Schenck, modelD230-1. The engine test bench has several measurement systems, such as the fuelconsumption AVL Dynamic Fuel Meter 733, the Blow-by meter, AVL 437 and a groupof sensors for thermo and pressure measurements. On the control room attached to thatone were the engine test bench is, there are a box where we find the reading andcontrolling units associated to the measurement systems already mentioned. In eachthere are one analog output for every signals, since that was necessary to allow theautomation of the process.The dynamometer control system allows, in alternative, several kinds ofoperation: -constant resistant torque, constant rotational velocity, or keeping aproportional relation with between these two variables. One of the steps of operationtests is defined with the control of the two variables, so there was the need to get oneanother way to control beyond that one on the dynamometer, imposing the value of theanother parameter that was not controlled by the initial system. This led us to projectand construct one control system acting on the accelerator.Both the controllers allow the definition off the operation conditions throughpotentiometers placed on the front of the box panel, or in alternative, through an electricsignal. In this last option, the control off the evaluation off the tests can be done usingthe automated system, sending the right signals according to the changing of action, thissignals transport the information about the correct values for the operation of the engineand dynamometer, compelling the changing of the rotational velocity and the resistanttorque, making possible the desired operation line.From the computer, through acquisition board output ports, analog signals weresend proportional to the wonted values of rotational velocity and resistant torque anddigital signals were also send to the dynamometer controller making the changing oftype of operation (constant torque, constant velocity, or else.)The engine accelerator controller has a system based on a comparing circuit usingan electrical signal proportional to the instantaneous rotational velocity that is read inthe sensor installed and another signal generated from the wanted value of the rotational

velocity. The difference of this two velocity values generates another proportionalsignal, using an appropriate circuit, which is send to an step engine mechanicallyconnected to the engine accelerator. This circuit allows the correction of the engineoperation directly on the rotational velocity, since the generated signal is proportional tothe difference of the real and wonted signals, and this will act on the engine making theappropriate acceleration or deceleration.This controller has in fact an important particularity since the speed of theactuation is proportional to the difference between the real value and the wonted value,given that the impulse frequency witch is send to the step engine is proportional, in eachinstant, to the error tension.BALANÇA FUEL DECOMBUSTÍVEL CONSUMPTIONMETERBLOW-BYBanco Test deEnsaios RoomENGINEFREIOThermo Sensores detemperaturaSensorsSensores dePressurepressãoSensorsDINAMOMETERSala Control deControlo Room456058,750008MÓVEL COM CONTROLADORESControllers E MOSTRADORES and Displays BoxPLACA DE AQUISIÇÃOACQUISITION BOARDdas1600 DAS 1600Fig.1 – Scheme of the Electric Circuit Implemented

This behavior of the controller allows an adequate response from the tested engine,since, this way, we can obtain a much more stable operation, avoiding oscillatorybehaviors.StepEngineVelocitySensorF1 8 7 22 2 3 4AmplifierComparationCircuitVVVV FConverserFFig. 2 – Representative scheme of the controller circuit for the rotational velocity of theengine.Development of the softwareFor the development of the program it was necessary to use an appropriatelanguage that could make some pre-established functions through a proper code. Thechoice was the Test Point language, since the kind of program developed and the typeof actions to make. This is an interesting tool when associated to the data acquisitionand variable control, given that it was easy to use some communication tools since theseveral parameter were already defined.This way, the developed program named “SABEM”, initializes with apresentation window that, passing a few seconds, allows the appearance of a secondwindow named “Definições do Motor”(fig 3). This window presents two squares onwitch it could be written the several parameters of the engine and the admissible limitvalues for the engine correct operation. These last values will be used on the program toestablish the value limits for the actuation of the system in the alarm situations. In thiswindow it could be find two buttons that tend to help on the filing the engine data placessince that gives the possibility to save and open files with these data. In this window itis possible to find four large buttons that allows the selection of the type of cycle

imposed to the engine (Europe cycle, performance cycle, calibration routine and smoothcycle). The engine data can be used in identification and security functions, since theycould be saved with the several test data acquired identifying that files and also theycould be used to establish limit situations witch could be used to trigger securityoperations including the end of the tests. The referred engine data could in future,according to the needs, be more expanded.Fig. 3 – Opening Window of the Program SABEMAfter the cycle choice, it appears the principal window presented in figure 4,where it is possible to see the several operation parameters such as the severaltemperatures and pressures, the torque, velocity, power, test duration, real time, stepnumber and its duration, and control required values for rotational velocity and resistanttorque. Beside the displayed values it could also be seen four buttons that may give thestart to another four situations. The button for return (“Voltar”) that make possible toreturn to the previous window for some changing in the engine data, the start button(“Iniciar”), witch allows the beginning of the control and acquisition cycle. The othertwo buttons could be used to end the cycle (Fim Ensaio) and to see the graphicevaluation of the test by choosing the first button of the column (Gráficos).

The choice for the button INICIAR, serves to begin the test cycle or cycles,leading to a serial actions witch are time controlled, imposing to the engine and to thedynamometer the proper operation according to the proceedings of the test legislation.Besides that, allows the monitorization of the several values corresponding to thedifferent variables, allows the visualization of the test parameters used for control, andalso allows the data save for the mean values of all the variables correspondent to eachstep in each cycle.Fig. 4 – Data Input for Engine Values WindowPresentation and Discussion of the resultsIt has been done two tests under the same conditions, the only difference was thatone was operator controlled and the other was controlled by the automated system. Thisresults are visible in figure 5, where it can be seen the time evaluations for both controlsignals rotational speed ant torque resistant, as well as the desired evaluation lines forthese two variables. It is clear the improvements made by the automated system, giventhat the following of the control lines were much more perfect in this case.The developed system shows clearly that it can improve the time response sincethe duration between the imposed value and the consequent response of the engineoperation is lesser than in the case of the operator controller system. This is moreevident in the most exigent step changes, witch correspond to the 6, 7 and 8, where

some errors occurred and the shrinking on the duration of the last step was substantialdue fundamentally to the errors while running the 6º step.100908070605040302010Delay on the executionof the changing of steps.ManuallyEnsaio ControloControlManualTest ResultsError on the execution ofthe more critical steps.0-100 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 3900Tem Operation po de ensaio Time [s]vel_imp [rps] bin_imp [N.m] vel_real [rps] bin_real [N.m]Ensaio Automated Controlo Control Automatizado Test Results1009080706050403020100-100 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 3900Operation Tempo de Time ensaio [s] [s]vel_imp [rps] bin_imp [N.m] vel_real [rps] bin_real [N.m]Fig. 4.8 – Graphic representation of the response differences of the same engine underthe same imposed cycle with two different control types one automated and another made byoperator.

The previous experience, with the execution of several cycles manually controlledshows that its is impossible to execute the test in the same way, given the need tocontrol the tests making the changes in the operation and the simultaneous registrationof al the data corresponding to the variables, all this in a small lap of time, makesimpossible the task to do all this properly in the right time without mistakes.ConclusionsImproves on the execution of the tests and on the precision of the imposed cyclewere evident, when the automated system were used. The liability and quality of theresults were also a clear sign of success since there was a minor possibility in makingerrors and there was a great increase in the repeatability on the execution of the severalcycles.It will be possible in the near future, to develop the present work, expanding thepossibilities of this program making possible the execution of other cycles. It will bedesirable the increase of the system capacities using more signals to acquire and to acton the dynamometer controller and on the security equipments raising the possibilitiesof all the process.Bibliography1- Michael Plint and Anthony Martyr– “Engine Testing, theory and practice”, second edition(1999) – Butterworth-Heinemann. ISBN:07506402192- Richard Stone – “Introduction to Internal Combustion Engines”, second edition (1992) –MacMillan Press Lda. ISBN:033355083-83- John B. Heywood – “Internal Combustion Engine Fundamentals”, (1988) – MacGraw-Hill. ISBN:00710049984- M. C. Gameiro da Silva, Mário L. S. Mateus, Luís M. V. Serrano – “Instalação de umBanco de Ensaio de Motores de Combustão Interna” – 1ª National Conference ofMechanical Engineering College of the Engineers Order – Porto19975- Luís M. V. Serrano – “Desenvolvimento de um Sistema Automático para o Controlo e aAquisição de Dados de um Banco de Ensaio de Motores de Combustão Interna” – MasterTeases, Coimbra 20006- M. C. Gameiro da Silva, Mário L. S. Mateus, Luís M. V. Serrano – “Desenvolvimento deum Sistema Automático para o Controlo e a Aquisição de Dados de um Banco de Ensaiode Motores de Combustão Interna” – 2ª National Conference of Mechanical EngineeringCollege of the Engineers Order – Coimbra 2000