Clickthe blue text to follow Wangcai Powertrain
For more timely and valuable content, please follow our WeChatpublic account: wc_dk8
Source: Yilan Zhongche
Introduction
If we compare the engine to the “heart” of a car, then the ECU should be the “brain”. What is an ECU? How does it work? This article provides a detailed analysis.
What is an ECU? The ECU has two full names: Engine Control Unit and Electronic Control Unit. It is easy to see that the former refers to the “engine control unit” while the latter is the “electronic control unit”. These are two concepts that can be easily confused, and today we will primarily analyze the “Engine Control Unit”.
1. The Emergence of the ECU
Before 1967, the fuel supply system of gasoline engines was managed by carburetors, which is completely different from today’s electronic fuel injection engines. Carburetors use the pressure difference before and after the throttle to draw fuel, which not only fails to accurately control the fuel supply but also limits the improvement of vehicle performance and environmental protection. Companies like Bosch developed electronic fuel injection systems, with the earliest BOSCH electronic injection system being D-Jetronic, followed by K-Jetronic and L-Jetronic. After the introduction of electronic technology, BOSCH developed several electronic management fuel injection systems, among which KE-Jetronic is the widely adopted electronic injection technology today. Although the product names vary among companies, their structures are quite similar.The working characteristic of the electronic injection system is the “quantitative and timed” injection of fuel. The engine requires a certain amount of fuel to be injected at a specific moment, which is directly related to the engine’s speed, air flow, and various other parameters such as water temperature and oil pressure. How are so many parameters processed and how does the injection system receive the fuel injection commands? This is where the engine control unit comes into play, and thus the ECU was born.
2. The Working Principle of the ECU
Like a typical microcontroller, the ECU consists of a microprocessor, memory, input/output interfaces, analog-to-digital converters, and integrated circuits for shaping and driving. The ECU’s role is to calculate the vehicle’s operating conditions through various sensors, thereby controlling multiple parameters of the engine such as ignition, air-fuel ratio, idle speed, and exhaust gas recirculation. It operates within a temperature range of -40 to 80 degrees Celsius and can withstand significant vibrations, making the probability of ECU failure very low. Additionally, the ECU has self-diagnostic and protection functions; when a fault occurs, it can automatically record the fault code in memory and adopt protective measures by reading alternative programs from its inherent routines to maintain engine operation, allowing the vehicle to reach a repair shop.How does the ECU work? Simply put, it is a command process akin to that of a general: “thinking”, “commanding”, and ultimately “confirming”.The “reconnaissance” is performed by sensors, which are responsible for monitoring the entire engine. A single engine can have dozens of sensors, including throttle position sensors, crankshaft speed sensors, oxygen sensors, crankshaft position sensors, camshaft position sensors, intake temperature sensors, water temperature sensors, and knock sensors, which are the most basic sensors in a car engine. Sensors are ubiquitous; they collect relevant information and transmit it to the ECU in the form of electrical signals. After being converted into digital signals by the A/D converter, the ECU processes the data to determine the current operating state of the engine, which constitutes the “thinking” process of the ECU.What is the standard for this “thinking” process? Computers do not possess thoughts; they rely on programs stored in ROM. This is akin to software. When data is fed into the ECU, the ROM program compares the existing data with the collected signals to derive adjustment methods. This entire program is the soul of the ECU, and its development is based on extensive experimental data, often requiring bench tests and road trials to establish. Typically, when tuners modify ECU programs, they rewrite or revise the ROM program to change the ECU’s calculation criteria.Let us delve deeper into this process:The amount of fuel supplied is calculated based on the duration of the fuel injector’s injection time. The fuel computer (ECU) calculates the required fuel injection time based on air flow, engine speed, and compensation signals provided by various sensors, using the originally set fuel supply program, which can be represented graphically.The fuel injection time calculated by the ECU is the sum of the “basic injection time”, “compensation injection time”, and “ineffective injection time”, measured in microseconds (ms), where 1 ms = 0.001 seconds. The amount of gasoline injected by the injector in a unit time is determined by the size of the injector’s diameter and the injection pressure.1. Basic Injection TimeThe basic injection time is determined by the intake volume (referring to weight) and engine speed. When you press the accelerator pedal, you control the throttle opening angle; the larger the opening, the greater the intake volume. The fuel computer compares the intake volume measured by the air flow meter and the current engine speed with the pre-set fuel supply program to calculate the required fuel amount and corresponding injection time.2. Compensation Injection TimeCompensation injection, commonly referred to as “acceleration”, is determined by various sensors that detect the engine’s current operating conditions and load, sending signals to the computer (ECU) to calculate the additional fuel required to maintain stable and smooth engine operation. The setting of the compensation injection program is complex and varies by vehicle.Generally, the compensation injection program includes the following items: cold start compensation, warm-up compensation, idle restart compensation, high-temperature compensation, acceleration compensation, high RPM/high load compensation, theoretical air-fuel ratio feedback compensation, and fuel cut control.3. Ineffective Injection TimeThere is a delay time from when the injector is energized to when it fully injects fuel, known as “opening delay”, and there is also a delay time from when the coil is de-energized to when it completely stops injecting fuel, known as “closing delay”. Since the opening delay time is greater than the closing delay time, the actual fuel supply will be less than required. The difference between the opening delay time and the closing delay time is referred to as “ineffective injection time”. To obtain the correct fuel supply, the ineffective injection time must be accounted for, meaning that after calculating the fuel amount, the amount of fuel injected during the ineffective injection time must be added to match the desired amount. Therefore, ineffective injection time can also be considered a part of compensation injection.Of course, the ECU is not static; another function of the memory is akin to an airplane’s “black box”, capable of recording vehicle operation data. Many ECUs have a “learning” capability; under normal circumstances, the memory continuously records your driving data, forming the ECU’s learning program to provide optimal control states that adapt to your driving habits. This program is also called an adaptive program. However, since it is stored in memory, similar to error codes, if the battery is disconnected and power is lost, all data will be lost. The ECU can continuously learn from the recorded data to understand the driver’s driving style, making it more user-friendly. Of course, in the event of a fault, information can also be retrieved from the memory to assist in repairs.After completing the “thinking” process, the next step for the ECU is to “command”. The components controlled by the ECU include the fuel injectors, which adjust the fuel amount and timing, while the fuel pump is responsible for supplying fuel; the ignition controller and ignition coil are also controlled by the ECU for ignition timing, etc. After this, the ECU needs to receive data again to confirm the end of a closed-loop control.With the advancement of automotive technology today, the ECU is taking on more and more responsibilities. Technologies such as i-VTEC, which involve variable valve timing, require additional camshaft position sensors and calculations by the ECU to adjust the camshaft phase. Especially in systems like BMW’s Double-VANOS, which features continuously variable valve timing, the ECU must perform precise calculations to control its phase and valve lift. Currently, in some mid-to-high-end vehicles, ECUs are not only applied to engines but can also be found in many other areas. For example, anti-lock braking systems, four-wheel drive systems, active suspension systems, airbag systems, and automatic transmissions all require separate control systems. The increasing number of ECUs in vehicles means that many added devices require ECU management, and the traditional “Engine Control Unit” can no longer meet the demands of the times, becoming just one module of the overall vehicle control system. Therefore, today we prefer to refer to the ECU as the “Electrical Control Unit”, i.e., the electronic control system. With the increasing automation and electrification of vehicles, the number of ECUs will continue to rise, and the wiring will become increasingly complex. To simplify circuits and reduce costs, the information transfer between multiple ECUs in a vehicle will adopt a technology called multiplex communication network, forming a network system of the vehicle’s ECUs, known as the CAN data bus, which will be discussed later.
3. Upgrading the ECU
1. The Feasibility of ECU ModificationECU manufacturers are all international multinational companies, such as BOSCH, SIEMENS, MM, etc. Their products are sold worldwide. Due to differences in gasoline quality, temperature, atmospheric pressure, humidity, and engine types in different countries, the ECU program software must be set to meet the conditions of each country. Modern vehicles must adapt to various weather and environmental conditions (such as high altitudes, deserts, extreme cold, and poor-quality gasoline) and different driver requirements, while ensuring that they can operate smoothly and meet strict emissions and fuel consumption standards. Therefore, in most cases, the original ECU program is a compromise that meets many conditions to avoid incompatibility. Additionally, when manufacturers tune engine parameters, they generally consider that the engine should operate normally even in the worst conditions or when not maintained for long periods. This means that manufacturers always set engine output conservatively, so as long as the owner ensures regular maintenance, they can recalibrate engine parameters to achieve greater output and an extraordinary driving experience.For example, in terms of air-fuel ratio (AFR), the factory programmer may set the AFR to be leaner (less fuel, more air) in certain driving conditions (such as cruising) to reduce fuel consumption and pass fuel consumption tests in some countries. However, during other times, the factory ECU’s AFR is generally set at 1:14.7, as this is the easiest ratio to meet emissions standards. But for most engines, the AFR that produces maximum power is in a richer range (more fuel, less air). Similarly, to broaden the fuel adaptability of the vehicle (different fuel grades in different regions), the factory-set ignition advance angle is generally suitable for lower-grade fuels (the engine outputs different power at different ignition advance angles). This means that the current ignition advance angle of your engine may not be optimal for the fuel grade you are using. If the original program can be modified to favor performance, it can increase horsepower by about 5-8%, and some turbocharged vehicles can achieve up to 15%.2. Methods of ECU ModificationECU chip modification: When a manufacturer designs an engine, the originally set fuel supply program is burned into the ROM. This program is usually a product of compromise among fuel consumption, emissions, and smooth operation, and it is non-modifiable. Because it is non-modifiable, if you want to change the fuel supply program, you must use a different mode of ROM. Typically, professional tuning shops provide modified computer chips for various vehicle models. During modification, the original chip is removed (usually the factory fuel computer’s ROM is directly soldered onto the circuit board), an IC socket is soldered on (to facilitate future replacements), and the modified chip is inserted. The resulting fuel supply program remains fixed; it merely corrects the original program, with one important aspect being the ability to delay or even cancel the fuel cut control time in the compensation injection program.It is important to note that each modified chip has its set applicable conditions (i.e., the degree of modification). When modifying, you must choose a chip that closely matches your vehicle’s modification status to achieve the best results; otherwise, it may backfire. The selection of chips should only be done in consultation with experienced tuning shops. One chip corresponds to one fuel supply program, and smart readers may wonder: what if two or three are installed? Indeed, in the past, some tuning shops have installed two or three different fuel supply mode chips on the same circuit board, allowing the driver to switch between the desired fuel supply modes using an external switch, similar to switching between P, E, and S modes in an automatic transmission to meet different driver needs.ECU computer programming: This is a more specialized aspect of ECU modification, and the most familiar in the domestic tuning community is the HALTEC computer. With this computer, the owner can set the optimal fuel supply program according to the degree of modification of their engine, in conjunction with measurements from an air-fuel ratio meter, allowing for arbitrary changes to the basic injection program and various compensation injection programs using a laptop. Its greatest difference from chip modification, and its biggest advantage, is that if the engine undergoes further modifications later, and the original fuel supply program becomes incompatible, it can be immediately resolved through program adjustments. After programming, the original fuel supply program becomes obsolete, but higher-level computers can retain all the functions of the original vehicle’s sensors, meaning that various fuel compensation programs can still operate normally and can be modified without sacrificing smooth operation and practicality for higher performance.The greatest difficulty in modifying a programmable ECU does not lie in installation but in the setting and optimization of the fuel supply program. This often requires experience and instruments, and continuous testing to achieve satisfactory results. Currently, tuning shops typically select a basic mode as a foundation and then gradually adjust it through actual operation and testing until satisfied.3. Common Issues During ECU ModificationUnlike other mechanical systems, the functions and working principles of the ECU are “invisible”, and most auto repair shops, even 4S dealerships, do not understand or cannot repair or resolve ECU-related issues, creating a sense of mystery around the ECU. Below, we will discuss several common issues during ECU flashing.1) Use the original ECU or a brand new ECU?For general civilian modifications, I personally prefer using the original ECU for modifications. This is because the original ECU is very powerful, and its program has been developed through long-term data accumulation and countless tests by manufacturer engineers. It can protect the engine under any circumstances, and will not trigger fault codes or warning lights, nor will it cause conflicts with other systems like ABS, anti-skid, and anti-theft systems. Additionally, it will not delete important functions from the vehicle. On the other hand, the modification cost is relatively low.2) The degree of ECU modification and tuning styleFrom a performance modification perspective, ECU modification is an indispensable step. The ECU can help the engine achieve optimal mechanical functionality, but it cannot exceed the limits originally designed. For example, when professional racing teams develop racing engines, they first design the camshaft, pistons, connecting rods, and other mechanical components, determining the engine’s compression ratio and maximum RPM data before considering the ECU. Without a powerful engine, no matter how capable the ECU is, it is merely a waste of effort. Therefore, regarding the tuning methods for ECU programs, unless used for racing, the focus is generally not solely on extracting maximum horsepower at full throttle. More attention is paid to the vehicle’s acceleration capability and throttle response at low to mid RPMs, as civilian vehicles rarely operate at full throttle and maximum RPM. Thus, the emphasis is on achieving smooth and progressive horsepower and torque curves in the 2000-4000 RPM range and half-throttle conditions, rather than striving for the additional horsepower that may be gained at 7000 RPM. In these areas, the goal is to make the horsepower and torque curves as smooth and progressive as possible, so that drivers feel the throttle is particularly responsive and powerful. The maximum horsepower figure may attract attention in marketing, but in real-world conditions, no one enjoys driving a car that accelerates unsmoothly.3) Will ECU upgrades affect the vehicle’s lifespan and safety?Many people may have concerns about whether ECU upgrades will affect the vehicle’s lifespan and safety. In fact, there is no need to worry; flashing the ECU is merely a comprehensive optimization of the vehicle’s driving computer data, not an attempt to maximize a single performance indicator by unleashing the engine’s full capabilities. The optimization is conducted on the basis of ensuring longevity, economy, and safety, providing the vehicle with an absolutely safe operating margin and creating the most comfortable operating environment for the engine. However, in another scenario, due to cost and technical levels, some car enthusiasts may resort to installing components commonly referred to as “secondary air intake” or “fuel addition” to increase the amount of fuel and air entering the engine. These components essentially bypass the original sensors or alter sensor voltages to “deceive” the ECU, causing it to unknowingly change the air-fuel ratio entering the engine, improving engine performance under certain conditions. This incomplete modification approach can lead to other side effects and even potential safety issues, while the proper ECU modification method, although more costly, can avoid many adverse side effects.4) Differences in ECU settings between street cars and race carsECU settings are generally divided into two types: street cars and race cars. For race cars, since the fuel, track, and driver factors are predetermined, the focus of the computer settings is on how to respond to changing weather, temperature, and other environmental factors. Street cars, on the other hand, are much more complex, as there are no restrictions on driving time, and fuel quality can vary. Even if high-quality fuel is used, different gas stations may provide different qualities. Compared to race cars, street car modifications must consider safety factors, so the computer settings must retain some margin. After comprehensively considering the driver’s driving style and vehicle characteristics, the settings can be made. Moreover, even under the same conditions and with the same vehicle, variations can occur, so using the same data for settings may not yield the best results.5) Points to note when flashing the ECUMany car owners focus solely on horsepower without considering torque, which is a common occurrence. In fact, modifications should not be blindly focused on horsepower; before modifying, one should clearly understand the vehicle’s intended use and the owner’s driving habits.For tuning shops, when modifying the ECU, it is advisable not to focus solely on fuel injection timing but also to ensure that fuel supply is adequate. Attention should also be paid to the ignition timing arrangement, as the ignition advance angle is extremely important. Additionally, any hardware added to the vehicle must be understood in terms of its characteristics, so that the ECU can be adjusted accordingly to achieve optimal performance.Furthermore, if the engine uses a high-angle camshaft, it will alter the timing of the valve openings and closings, making programming adjustments even more challenging, requiring more precise calculations and tuning. The ability to fully utilize the performance of modified parts is entirely dependent on the ECU’s adjustments, but changing the engine’s characteristics through ECU data modification is a very difficult task.
4. Future Trends in Automotive Control
Let us count how many systems require control systems. Automatic transmissions, ABS systems, in-car entertainment systems, four-wheel drive torque distribution systems, active suspension systems, airbag + seatbelt systems, etc. So many systems have their own sensors and processors, performing separate calculations without interfering with each other. However, the automatic transmission and engine need to cooperate; for example, the engine needs to reduce power during gear shifts, and during full throttle, the transmission requires a kickdown to downshift. In various states, both need to share a large amount of data, such as the engine’s crankshaft speed. Establishing a new set of sensors for the automatic transmission would incur unnecessary costs and is impractical. The best solution is for the transmission and engine ECUs to share data, which has led to the emergence of an information network system between ECUs—the CAN data bus. The same CAN data bus is also used in chassis electronic devices, where the four-wheel drive torque distribution system and ABS share many chassis sensor parameters.The development of the CAN data bus will inevitably integrate all control systems. There is a saying that future ECUs will be powerful computer systems that integrate all components requiring management, including the engine, automatic transmission, ABS system, in-car entertainment system, four-wheel drive torque distribution system, active suspension system, airbag + seatbelt system, etc. We will be able to enjoy the car’s audio system, play PC games, receive GPS signals, and even a cup holder will be managed by the ECU.Interestingly, future ECUs may establish an open interactive software system, like the Windows operating system, on which various engine management systems, transmission management systems, ABS systems, etc., can be installed. At that time, the engine “ECU” management system will merely be a software that can be updated in real-time; you can choose version 1.1 or version 2.0. Of course, you will also need to install a firewall to prevent hackers from intruding.