The Automotive Engine Controller (ECU) is the most complex and powerful computer in the car. It includes 9 modules including power supply, MPU, communication link, discrete input, frequency input, analog input, switching output, PWM output and frequency output. Understanding these modules and the projects to be tested has certain guiding significance for the (China) test engineers to participate in the test of automotive ECUs, and also helps design engineers to fully consider the design problems of automotive engine controllers from the test point of view.
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The engine electronic control unit, also known as the engine controller (ECU), was born in the 1970s. At the time, due to the oil crisis, people were looking for a way to improve fuel economy, and they wanted to find a way to make the engine run in cleaner and less polluted conditions. Engineers at the time used a mechanical device called a fuel dispenser to control spark timing and a carburetor to control fuel mixing. This mechanical system has poor adjustment capabilities. Microprocessors were born in the 1970s, a technology that enables complex, high-speed operations required to control spark timing and fuel mixing. In the early 1980s ECU became a standard part of most vehicles. The ECU is a computer designed to solve specific problems. Often the ECU is the most complex and powerful computer in a car.
Vehicles usually contain more than one electronic control module (ECM). The ECU is an electronic control module responsible for engine control functions. Its main purpose is to provide closed-loop control of the fuel and ignition system in the engine to improve fuel economy and reduce gas pollutants generated by the engine.
Why test the ECU?
Testing is often considered a job that does not add value. This is true in an ideal world, because in an ideal world, the production process never produces defects, the system design is never flawed, the software is always running normally, there is never a customer return, and the quality of the products and raw materials is zero. Tests are unnecessary because there are no faults. But the world is not perfect, so testing is required to achieve measurable, repeatable, and traceable minimum quality standards. Quality is indeed valuable, although its value cannot be directly measured.
The need for testing is also reflected in other aspects. Automakers have their own quality requirements and standards (such as QS-9000) as well as long-term tracking and regulatory requirements. Automakers typically require component suppliers to test components before sending them to a B&A assembly where the components are assembled into a complete vehicle. The B&A factory is a labor-intensive factory. Car rework is unacceptable due to component failure of the supplier, which can cause significant losses. The supplier contract usually includes a fine clause related to component defects caused by the supplier.
ECU manufacturers need to prove that their products meet customer specifications, which needs to be achieved through DV (design verification) testing. Manufacturers also need to prove that their production process can produce the product correctly, which needs to be achieved by PV (production verification). Quality standards usually require a quality assessment of a certain percentage of ECUs to ensure that the production process is free of defects. This quality assessment is performed through continuous consistency (small design verification) testing.
Test system developers face challenges
As mentioned earlier, testing is often considered a work that does not add value, although testing is an important means of improving the quality of each stage of the production process. This situation puts tremendous pressure on test organizations to ensure that the test process is robust, comprehensive, fast and cost-effective.
The test system must be stable. The test system must be able to run around the clock. Most automotive component suppliers have high-volume production lines that can be costly to stop production. JIT (punctual) production does not allow for wholesale shipments, delays in delivery or a shortage of quantities. Errors can result in production downtime, as required by quality control procedures and processes. For these reasons, test equipment must be reliable and accurate.
The scope of the test must be comprehensive. The test system should be tested as wide as possible and the test must be accurate. The test system should prevent defects downstream of the production process as much as possible. In general, the more problems that occur downstream, the higher the cost of repair.
The test system must run fast. High-volume production requires that each stage of the production process cannot be slower than the slowest process. The testing process should not be a bottleneck, especially when testing is considered to be work that does not add value. The test system should be faster than the slowest upstream process.
The test system must be cost effective. Test system designers must compare performance and cost. The cost of a test system is not just the price of its purchase. Test systems generate other significant short-term costs such as equipment, training, maintenance, upgrades, support, and connectivity. The long-term cost of a test system is less obvious, depending on parameters such as development time, flexibility, scalability, reusability, modularity, and portability. These factors are directly related to the software and hardware used in the test system.
In addition to these points, test system designers must complete the design within a limited budget and in a shorter period of time. It is getting harder and harder to develop new products, the life cycle of products is getting shorter and shorter, and new rules, technologies and customer needs are constantly emerging. Faced with this, test system designers must find a way to develop a system that meets both current and future needs.
How does the ECU work?
Simply put, the ECU works by controlling fuel mix (air-to-fuel ratio) and spark timing (ignition advance and duration) based on feedback from sensors connected to the engine. The control of fuel mixing and ignition timing is quite complicated. The ECU needs to acquire data from multiple sensors to achieve optimal control of the system. The ECU needs to know the ground speed, engine speed, crankshaft position, air quality (oxygen content), engine temperature, engine load (such as when the air conditioner (A/C) is turned on), throttle position, throttle change rate, shift gear, exhaust emissions, and many more. As we have already mentioned, the ECU is a computer for solving specific problems. Computers often cannot interact directly with the analog world. It is therefore necessary to use a signal conditioning/data acquisition interface to convert the analog signal from the sensor into a digital signal that the computer can understand. In order to control the fuel system and the ignition system, digital signals must be converted to analog signals.
ECU function module
The ECU contains the following functional modules: 1. Power - Digital and analog (power supply for analog sensors). 2. MPU - microprocessor and memory (usually flash and RAM). 3. Communication link - (eg CAN bus). 4. Discrete Input - On/Off Input. 5. Frequency input - Encoder type signal (crankshaft or vehicle speed). 6. Analog Input - Feedback signal from the sensor. 7. Switch output - On/Off type output. 8. PWM output - frequency conversion and duty cycle (eg injector or igniter). 9. Frequency Output - Constant duty cycle (eg stepper motor - idle speed control).
Figure 1 shows a typical input/output block diagram of the ECU. The boxes list the types of excitation and measurement equipment provided by NI and the connection to the load and instrument.
The power supply to the ECU is a DC-DC converter. The battery voltage is converted to a voltage suitable for the MPU and other digital circuits. In some cases, the ECU provides a voltage source for the analog sensor. In this case, the ECU provides one or more analog supply voltages (derived from the battery voltage). Typical tests include:
Switch Check - Check for shorts or open circuits between power and ground.
Power Load Test - If the ECU is an analog power supply, verify the supply voltage under maximum load conditions.
Power Supply Noise Test - If the ECU is using an analog power supply, check the output noise level.
Sleep Current - Check the current on VBATT when the ignition key is in the "off" position.
Wake-up current - Check the current on VBATT when the ignition key is in the "on" position.
The MPU contains the processor and memory components. In most cases, flash storage applications (sometimes called application code) are used. A calibration lookup table is included in the application software. These tables set the optimal fuel mix and ignition timing parameters based on the input feedback. With flash you can reprogram the ECU at any time. In some cases, the application software includes a specific test mode for production testing. Typical tests include:
RAM test - usually for some form of writing and reading.
Flash Test - Check the manufacturer/product number and verify the sum.
"Watchdog" timer test.
Download the application software and/or embedded test code to the flash memory.
Production testing usually uses one or more of the following methods:
The application code includes a built-in test branch for external control of the ECU.
Download the test code to the flash memory. The test code can test all inputs and outputs.
Download code related to the test (such as downloading only the code used to read the analog input).
The ECU has a communication link to the outside world. There are many types of ECU protocols and standards, and new protocols and standards emerge every few years. Communication links have multiple functions. One of the most important functions is to meet the requirements for on-board diagnostics (OBD). OBD detects faults in the vehicle exhaust system. The ECU monitors exhaust emissions; when the exhaust emissions exceed the allowable standards, the ECU records the data for use by technicians. The technician acquires data over the communication link and can use other diagnostic tools connected to the communication link to locate the faulty component. Today's vehicles typically use more than one ECM (ABS, body control, telematics, etc.), which are typically connected together via a communication link. In order to function properly, the ECU may require status information of an electronic or mechanical system that is not related to the engine. Similarly, other ECMs also require status information from the ECU to ensure proper operation.
ECU testing is usually done through frequent communication link inputs/outputs. Since communication with the ECU takes up 30% to 40% of the actual test time, the equipment used for the communication link has a large impact on system performance. The throughput time of the device (such as converting RS-232 to CAN or converting CAN to RS-232) can affect the overall performance of the test system. The range of choices will be limited depending on the agreement. But when making a choice, you should still make a comparison to find the fastest solution.
A simple example can illustrate the impact of your choices. Suppose you have a Vehicle Communication Interface (VCI) device that converts RS-232 to CAN. If the RS-232 side of the VCI device is operating at 9600 baud and 1 bit per baud, the transfer rate on the RS-232 side is 9.6 kbps.
Here is 11 bytes or 88 bits. It takes 9.17 ms to transfer data at 9600 kbps. This time does not seem to be long, but it is necessary to know that during the test of the ECU device, 200 or more pieces of information are usually transmitted, and it takes 1.83 seconds to transmit only 200 pieces of information in one direction. Of course, the information usually follows the command/response protocol, so the actual time to transmit 200 messages is 2 Ã— 1.83 seconds, or 3.66 seconds. This does not include conversion of data from RS-232 to CAN, conversion from CAN to RS-232, and other latency for the ECU or test system controller to process the data. If you choose a VCI device with an operating speed of 18.2 kbps on the RS-232 side, you can reduce the test time by 1.83 seconds. In the case where the test code or application code must be downloaded to the ECU, selecting a slow device will have a greater impact.
Discrete (or switch) inputs monitor the switching status of various components and accessories in the car. The most important discrete input is the ignition switch. The ECU needs to know the position of the ignition switch (start, run, shut down, assist) to determine when and how to control the fuel and ignition system. Other discrete or switch inputs include parking switches, brake switches, and A/C switches.
In an ECU test system, a load/excitation module, typically consisting of a general purpose and/or matrix relay, connects a test source (VBATT, BATT_GND, DAC, DIO) to a discrete input on the ECU. Typical tests include:
Move 1/0 - For Move 1, first set all discrete inputs to 0, then switch the input from high to low, one at a time. Moving 0 is the opposite.
The mode test (such as 0xAA, 0x55) reads the status of the ECU.
Connect each input to VBATT and read the status of the ECU.
Connect each input to BATT_GND to read the status of the ECU.
Test under open circuit conditions.
Frequency inputs are typically used to monitor test speed (such as vehicle speed) or speed and position (such as crankshaft) sensors. The most important feedback signal for the ECU is the crankshaft signal. In some engine applications, both crankshaft and cam signals are used to provide speed (speed) and position (crank angle) information to the ECU. The crankshaft and cam sensors can be either variable reluctance type (VAR) sensors or infrared sensors (IR). Both types of sensors produce encoder signals that the ECU uses to determine fuel and ignition output parameters.
Typical frequency tests include:
The ECU frequency input is driven with a signal having a variable amplitude and/or frequency and/or duty cycle.
Perform an open circuit test on the input.
Test with VBATT and / or BATT_GND shorted to the input.
The analog input monitors a large number of sensors in the car. There are many types of sensors, each of which is conditioned by the ECU. Temperature (engine temperature), pressure (MAP-pool absolute), flow (EGR), and air quality (oxygen) are part of the ECU feedback loop.
Typical analog input tests include:
Open circuit - no source or load connected to the input.
Shorted to VBATT and / or BATT_GND.
Analog-to-digital linear conversion (such as 5 and 95% of the input signal of the range is tested).
The switching output, sometimes referred to as a discrete output, is typically a small current driver (<2 A). The signals used to control the travel control clutch and fuel pump are the switch outputs. Sometimes it is divided into a large current driver and a small current driver according to whether the switching output supplies reference power to other components in the system or reference ground. These output-driven loads can be either resistive loads (such as checking engine lights) or reactive loads (such as pneumatic solenoid valves).
Pulse width modulation (PWM) output
The PWM output is the most complex of the ECU outputs. In the PWM output, the injection and ignition (or EST-engine ignition timing) output may be the most computationally complex. The main factors determining the timing, frequency and duty cycle of the injection and ignition output are the crankshaft speed (speed) and position (crank angle, 0 to 360 degrees). Other factors used to determine fuel and ignition parameters are vehicle speed (mph), throttle position (acceleration, deceleration, constant), EGR (exhaust gas recirculation), engine temperature, manifold pressure, fuel temperature/pressure, and the like. Simply put, the engine application code uses all of these feedbacks to perform some calculations, then finds and selects the best fuel mix and spark timing (spark advance and lag) in the calibration table to optimize engine performance. In general, the PWM output drives inductive loads such as ignition coils and injector solenoids. Most loads are less than 5A, but some loads, such as ignition coils, can range from 5 to 20A depending on the engine design.
Typical tests include:
Voh = VBATT Â±0.5 VDC, Vol = BATT_GND Â±0.5 VDC.
The clamp voltage/flyback voltage is mostly <100 V and the retrace voltage of the ignition coil is up to 450 V.
Output leakage current.
Short the output to VBATT and / or BATT_GND Â· Switching time, rise time / fall time, duty cycle, frequency.
Timing/synchronization between crankshaft position and injection/ignition/EST (eg delay relative to the rising or falling edge of TDC).
Current to voltage ratio (eg Vsat-voltage at I=500 mA).
The frequency output is typically a constant frequency and/or duty cycle output. They are often used to control stepper devices. An example of a frequency output is ISC, the idle speed control, which adjusts the air flow into the fuel system to change the idle speed.
ECU test software
Software is a major component of the test system. There are usually two types of software to use:
Application Development Environment (ADE) - used to write test code.
Test executive - used to manage test sequences.
The choice of ADE is very important because it has a major impact on the long-term and short-term costs of the system. Test execution procedures also have an impact on costs. Any test application needs to use some type of ADE to create test code. ADE has a direct impact on development time and therefore has a direct impact on the cost of the system. When choosing an ADE, consider the cost, ease of use, and the tools and libraries it contains. In addition, the availability of additional software or software packages from ADE vendors or third-party software vendors is also a factor to consider. The standard libraries and add-on software provided with the ADE usually determine how much code must be written. In general, the less code a developer needs to write, the shorter the software development time and the lower the development cost.
Traditionally test code and test executives have to be combined. Every time a test program needs to be developed for a new product, the developer must either write a new test executive or import the test executive code from the old product into the test code for the new product. If you need to change the code in the Test Executor section because of the requirements of the new product, you must either modify the system that uses the test Execution program or write its own test executive for the new product. This often results in multiple versions of the same test executive, increasing the cost of software maintenance and software documentation.
Commercial off-the-shelf (COTS) test execution procedures have emerged on the market today. With the COTS test executive, test system developers simply focus on the test code without worrying about the test executive. TestStand is one of the best COTS test executives on the market, it can be connected to test code in almost all ADEs and integrates seamlessly with code generated with LabVIEW and LabWindows/CVI.
In addition, NI offers CAN (Controller Area Network) devices for a variety of platforms, such as PCI, PXI, and PCMCIA, which can be used in almost any automotive test application that requires a CAN interface.
Summary of this article
The ECU is a complex electronic device with versatile inputs and outputs. Test engineers face many challenges when designing and developing systems for ECU testing. The combination of computer-based measurement equipment (such as PXI) and virtual instrumentation provides an ideal hardware and software platform for ECU test applications, enabling system developers to develop test systems that meet today's and tomorrow's needs.
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