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HIL Simulation System for Application of Electrical Diagnosis and OBD in Diesel Engines ECUs Ricardo Andrade Ranal Robson Alves Nascimento MWM International Motores
ABSTRACT In order to validate the strategies of software as well as help in the process of calibration of OBD (On-Board Diagnostic) was developed a test system and simulation Hardware-In-the-Loop (HIL) with the PXI hardware and VeriStand software of National Instruments. This system simulates sensor signals and actuators functions to the engine ECU (Electronic Control Unit), with the goal of making the electrical diagnosis calibration, enabling to run some tests on bench that could only be achieved in the field – in vehicles – or test benchs – dynamometers. With this system it is possible to optimize time and resources related to their tests, such as: Reducing the total calibration time; Basic Calibration of Diagnosis; Diagnosis calibration for different applications; Undefined repetition of test routines with complete control of variables; Development of other applications with the know-how obtained; Lower cost with allocation of resources in the engines development. The savings in the system deployment was 83% compared to commercial systems offered on the market.
INTRODUCTION Emissions of pollutant gases in the atmosphere from combustion engines, there are times, are a major concern of humankind to the environment. As a result, several initiatives have emerged in order to contain such issues as improvements in fuel injection control systems, increase fuel quality and the addition of after treatment systems. Since then, with the growing number of actions and technologies for controlling emissions, it also appears the need to normalize the parameters and requirements for these systems. Along with first on-board computers designed by automakers and without standardization, begin to emerge the first implementation of OBD to auto-diagnose simple problems of a vehicle. Later, with the recommendation of standards by SAE (Society of Automotive Engineers) and the pioneering implementation of CARB (California Air Resources Board) the OBD gains strength as system for monitoring the performance of some key components of engines, including those responsible for controlling emissions. Thus, the EPA (Environmental Protection Agency) adopt the OBD as mandatory for all vehicles sold in the USA, followed by the European Union and, more recently, the rest of the world. Today, electronic fuel injection systems have a relatively high level of complexity and, consequently, their strategies for OBD. Calibrating a infinity of conditions and possibilities of different types of sensors, actuators and control functions of an ECU can be an extremely slow and expensive. The allocation of human resources (engineers and technicians) and technical resources (equipment, test benches, test vehicles), besides to add costs to the project, are not always available when requested.
Figure 1 - Wiring diagram of an ECU and its complexity displayed by the various connected sensors and actuators.
Due to this scenario, solutions and simulation systems are increasingly employed in the automotive sector. Conduct tests and trials quickly, controlled and configurable, are difficult to achieve in real environments. It is clear that the simulation system needs to have good level of maturity for the tests have a significant representation. But since this issue is resolved, the reductions in development time of a project can be considerable. Based on these facts, this paper will discuss a case study where, by necessity of cost reduction with the allocation of resources in new projects and increased know-how of work teams, has developed a simulator HIL (Hardware In the Loop) to help expedite the process of OBD calibration for ECUs of diesel engines. The feasibility of this project was also possible due to the difference between the investment for the development of the HIL simulator and the purchase of a commercial system offered in the market. Such data are also part of this article.
THE HIL SIMULATOR REQUIREMENTS - From the beginning it was thought in some requirements that should be mandatory to meet the first and future demands of testing with HIL: Reliable - We cannot think of a system where there is no certainty of the integrity of the signals generated. It is necessary to ensure that everything is free from noise and interference that can compromise the tests. Expandable - the possibility of expanding the system for future demands should be so simple. Configurable - the system should be customizable in order to obtain full control over the configuration of the HIL. Compatible with modeling software - work with the softwares as the MatLab Simulink, GT Power, among others LabVIEW. Automatic tests - Run pre-programmed tests automatically. Tests through real data acquisition - Be able to work with real data of tests of engines or vehicles and play them in the simulation environment. Fault Insertion - Ready to work short-circuit failures with source or connections between wires without causing any damage to equipment. It's must have appropriate protection circuits.
Affordable - The systems offered on the market are extremely expensive and almost always have more features than are really necessary. Therefore, the customized solution must have a value more attractive. Easy to use - There is no point having a great simulation system if your use is extremely difficult. Users should focus on program and run the tests and not configure the simulator. In addition, some steps have been established for the implementation of the system: Run electrical diagnosis calibration system (open loop); Run system with partial models of motor (closed loop); Once matured, run system with complete and detailed models. CHOSEN PLATFORM - Among the various options market, the platform that best fits the requirements of the project was from National Instruments, using NI Veristand as the simulation software and NI PXI hardware to ensure accuracy, speed and reliability to the signals generated and recorded. NI VeriStand is a software environment for configuring test applications in real time. Being a software for the industry, NI VeriStand help in setting up mechanisms for real-time and parallel processing to perform tasks that include: Analog interfaces, digital communication buses and I/O based FPGA (Field-Programmable Gate Array); Startup and writing data to multiple files; Generation of stimuli in real time; Calculated channels; Alarm events and alarm response routines. NI VeriStand can also import control algorithms, simulation models and other tasks of NI LabVIEW software and thirdparty development environments. You can monitor and interact with these tasks using a user interface run-time editable includes many tools useful to force values, alarm monitoring, calibration of I/O and editing of stimulus profiles. In addition, no programming knowledge is required to use the NI VeriStand, it is designed to be customized and extended using a variety of modeling and programming environments. NI PXI (PCI EXtensions for Instrumentation) is a rugged PC that offers solutions for high performance and low cost deployment for measurement and automation systems. PXI combines the electrical bus Peripheral Component Interconnect (PCI) bus with the robust synchronization, such as mechanical modules of packaging Eurocard with the CompactPCI and adds specialized resources of software . PXI also adds mechanical, electrical and software tools that complement test and measurement systems, data acquisition and production applications. It is often applied in manufacturing test military and aerospace, machine monitoring, automotive and industrial tests.
ARCHITECTURE - The HIL simulation system was designed in two distinct parts: Software - an integrated simulation environment and programmable models where the engine subsystems works. It is a configurable and flexible platform for execution of different models according to demand tests. Hardware - composed of the following equipment:
Simetric Power Supply Engine ECU
Power Supplies
Notebook running Simulation Software (NI VeriStand) Break Out Box NI PXI
Ethernet
Real Time Control Unit
CAN
Signal Conditioning and Fault Insertion Unit
Engine Wiring Harness with Sensors and Actuators
Figure 2 - Architecture of the HIL simulator.
Computer - dimensioned so that run the simulation environment with the best performance; Real Time Control Unit - where the models and test programs are executed deterministically to provide a simulation as representative as possible. This module consists of an industrial computer running a real-time operating system, card with an FPGA chip (Field-Programmable Gate Array) cards and I/O analog and digital. Signal Conditioning Unit - This unit has I/O properly conditioned to the power drives (e.g. injectors), and the Fault Insertion Unit with its protected channels against short-circuits and electromagnetic interferences. Break Out Box - This "box" is responsible for the connection between the HIL simulated signals, the engine wiring harness and ECU. With this device you can switch the connections between the three units attached to it, besides using small terminals that provide access to measurements on each pin of the ECU. Break Out Box is the block that is changed according to the type of application or ECU that will be tested. Therefore, the amount of BOBs depends on the different types of applications that will be tested with the system.
Figure 3 - HIL simulator running on the lab bench.
Figure 4 - Development team working with the HIL simulator.
INVESTMENT VERSUS ECONOMY - For this comparison were made estimates hours of electrical diagnosis calibration (US$ 31,000) and OBD calibration (US$ 10,000). In these hours are included the costs of using test benches and travels with test vehicles that would be needed. As for the cost of the commercial system (US$ 363,000), were included the operation trainings and acquisition of some toolkits for the desired application. The amount invested in the HIL simulator development was US$ 69,000 with the platform and architecture earlier presented. Note that the savings generated by the HIL development in company was 83% compared to the costs that would be spent with another solution. Something very representative taking into account that the estimates were very conservative. Note: the dollar at the time of implementation of the project was quoted at R$ 1.80 (brazilian currency).
Figure 5 - Graph of investment for the HIL simulator development and the savings achieved.
ACHIEVED RESULTS - It's a little premature to comment results, because the system is in development and undergoing some improvements. However, several simulations have been carried out in the step of electrical diagnosis calibration and the estimated reduction in test time was 40% at 50%. With the maturing of the system the goal is to reduce these times by 80% or more.
CONCLUSION Besides the economy generated by the implementation of the HIL simulation system, it was found that there are other economies that are difficult to measure, considered "intangible". How much does a recall? It is known that in addition to high financial costs, the inconvenience caused by this type of intervention can profoundly affect the trust between suppliers and their customers. There is not estimate a value for this type of occurrence. How much does to predict a failure that would be difficult to predict in vehicle? With a simulation system where you have full control of the application, an ECU can be tested repeatedly to exhaustion or several ways by different types of tests. This offers the possibilities for the development team to test things that would be impractical or difficult to execute in real systems. How much is the know-how acquired by the development team? This is perhaps the most important question of the work presented. The information acquired by all project participants will be used in other applications, increasing the quality and speed in solving future problems. These facts raise the importance of developing this project with something that is impossible to measure, but has an inestimable cost to man: the knowledge.
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