If the engine is compared to the “heart” of the car, then the “brain” of the car should be ECU. What is ECU? How does ECU work? This paper analyzes in detail.
What is ECU? ECU has two full names, namely engine control unit and electronic control unit. It is not difficult to see that the former is “engine control unit” and the latter is “electronic control unit”. These are two concepts that are easily confused. Today, we will mainly analyze “engine control unit”.
The appearance of ECU
Before 1967, the supply system of gasoline engine was supplied by carburetor, which is completely different from the principle of today’s EFI engine. Carburetor uses the pressure difference before and after the throttle to absorb oil, which not only can not accurately control the fuel supply, but also restricts the improvement of vehicle power performance and environmental performance. Bosch and other enterprises have developed electronic fuel injection systems. The earliest Bosch electronic fuel injection system is d-jetronic, and later developed k-jetronic and L-jetronic. After the intervention of electronic technology, Bosch has developed many sets of electronic fuel injection systems, among which Ke jetronic is widely used today, although the trade names of various enterprises are different, But they are similar in structure.
The working characteristic of EFI system lies in “quantitative and timing” injection of fuel, how much fuel the engine needs and when to inject it, which has a direct relationship with the engine speed, air flow and so on. In addition, it also involves various parameters such as water temperature, oil pressure and so on. How to deal with so many parameters and issue injection instructions to the injection system? This requires the intervention of the engine control unit, ECU came into being.
Working principle of ECU
ECU is composed of microprocessor, memory, I / O interface, analog-to-digital converter, shaping, driving and other integrated circuits, just like ordinary single-chip microcomputer. The function of ECU is to calculate the driving condition of the vehicle through various sensors, so as to control the ignition, air-fuel ratio, idle speed, exhaust gas recirculation and other parameters of the engine. The working temperature is – 40 ~ 80 degrees, and it can also withstand large vibration, so the probability of ECU damage is very small. In addition, ECU has the function of fault self diagnosis and protection. When the system has a fault, it can automatically record the fault code in the memory and use protective measures to read the replacement program from the above inherent program to maintain the operation of the engine, so that the car can drive to the repair shop.
How does ECU work? In short, it is a general’s commanding process: “thinking”, “commanding”, and finally “confirming”.
“Reconnaissance” is completed by sensors, which are responsible for “reconnaissance” of the whole engine. On one engine, there are dozens of sensors large and small. Throttle opening sensor, crankshaft speed sensor, oxygen sensor, crankshaft position sensor, camshaft position sensor, intake temperature sensor, water temperature sensor and knock sensor are the most basic sensors in a car engine. Sensors are everywhere. They are responsible for collecting relevant information and sending it to ECU in the form of electrical signal. After the analog-to-digital converter A / D becomes a digital signal, ECU can judge the working state of the engine at this time through calculation, which is the “thinking” process of ECU.
What is the standard of “thinking” process? The computer certainly can’t have the thought, what this needs is the ROM storage procedure. This is equivalent to a software, when the data is transferred to ECU, the ROM program has the data to compare with the collected signal, from which ECU can get the adjustment method. This program is the soul of ECU, which is based on a large number of experimental data, and often needs bench test and road test. Usually, the refitting company changes the ECU program by rewriting or revising the ROM program to change the calculation criteria of ECU.
Let’s take a closer look at this process
The amount of fuel supply is calculated according to the injection time of the fuel injector. The fuel supply computer (ECU) calculates the required fuel supply time by using the originally set fuel supply program according to the air flow, engine speed and the compensation signals provided by each sensor. The fuel supply program can be represented by graphics.
The fuel injection time calculated by ECU is the sum of “basic injection time”, “compensation injection time” and “invalid injection time”, the unit is microseconds (MS), 1ms = 0.001 seconds. Among them, the amount of gasoline injected by the nozzle in unit time is determined by the diameter of the nozzle itself and the injection pressure.
1. Basic injection time
The basic injection time is determined by the amount of intake air (here weight) and engine speed. When you step on the accelerator pedal, what you control is the opening angle of the throttle valve. The larger the opening is, the larger the air intake is. The fuel supply computer calculates the required fuel supply and the relative injection time according to the air intake measured by the air flow meter and the engine speed at that time and the preset fuel supply program.
2. Compensating injection time
Compensation injection is also known as “speed up”. It detects the working condition and load of the engine at that time by various sensors, transmits the signal to the computer (ECU), and calculates the additional fuel supply required to maintain the stable and smooth operation of the engine. The setting of compensation injection program is a complex work, and it varies from vehicle to vehicle.
Generally speaking, the compensation injection program has the following items: cold start compensation, warm up compensation, idle start compensation, high temperature compensation, acceleration compensation, high speed / high load compensation, theoretical air-to-natural ratio feedback compensation, fuel cut-off control.
3. Invalid injection time
There is a delay time from the coil power on to the full injection, which is called “on delay”, and there is also a delay time from the coil power off to the complete stop of injection, which is called “off delay”.
Since the opening delay time is greater than the closing delay time, the actual fuel supply will be less than the required amount, and the opening delay time minus the closing delay time is called “invalid injection time”. In order to get the correct fuel supply quantity, the invalid injection time must be included, that is to say, after the fuel supply quantity is calculated, the invalid injection time must be added, and the fuel quantity ejected will be the same as expected. Therefore, the invalid injection time can also be regarded as a compensation injection.
Of course, ECU is not immutable. Another function of memory is like the “black box” of an airplane, which can record the data of a car’s driving. Usually, many ECUs have the “learning” ability. Under normal circumstances, the memory will keep recording the data of your driving, becoming the learning program of ECU, providing the best control state to adapt to your driving habits, This program is also called adaptive program. But because it is stored in the memory, just like the error code, once the battery is removed and the power supply is lost, all the data will be lost. ECU can continuously learn the driver’s driving style from the data recorded in memory, so as to be more humanized. Of course, in case of failure, you can also read the information from the memory, so as to make support for maintenance.
After “thinking”, the next step for ECU is to “command”. Controlled by ECU is the injector, which is responsible for adjusting the injection quantity and injection time, and the gasoline pump is responsible for supplying oil to it; The ignition controller and ignition coil are controlled by ECU. After that, ECU needs to receive data again to confirm the end of a closed-loop control.
With the development of automotive technology, ECU is shouldering more and more responsibilities. Variable valve timing technologies such as i-vtec need to add additional camshaft position sensors and convert the camshaft phase through ECU calculation. In particular, continuous variable valve timing systems such as BMW double VANOS need ECU to make precise calculation to control its phase and valve lift. At present, ECU is used not only in engine but also in many other places on some medium and high-class cars. For example, anti lock braking system, four-wheel drive system, active suspension system, air bag system and automatic transmission all need separate control system. More and more ECU appear in the car, and many devices added to the car need ECU management. However, the traditional “engine control unit” can not meet the development of the times, and has become a module of the vehicle control system. Therefore, today we prefer to call ECU “electronic control unit”, that is, electronic control system. With the improvement of car electronic automation, ECU will be more and more, and the circuit will be more and more complex. In order to simplify the circuit and reduce the cost, the information transmission between multiple ECUs on the vehicle needs to adopt a technology called multiplex communication network, which forms the ECU of the whole vehicle into a network system, namely can data bus. The can will be mentioned later.
1. Feasibility of ECU modification
ECU manufacturers are international multinational enterprises, such as Bosch, Siemens, mm. The products are sold all over the world. Due to the differences of gasoline quality, temperature, atmospheric pressure, humidity and engine form in each country, ECU program software must be set according to the conditions of each country. Because modern cars have to adapt to all kinds of weather, environment (such as plateau, desert, severe cold and inferior gasoline) and different requirements of various drivers, At the same time, it also needs to ensure that it can still drive freely in this complex situation and pass the strict exhaust emission and fuel consumption standards. Therefore, in most cases, the program in the original ECU is the best compromise that meets many conditions, so that it will not be acclimatized. Therefore, a lot of space is reserved for modification in the design. In addition, when automobile brand manufacturers adjust engine parameters, they generally consider that the engine can be used normally even in the worst environment or in the state of long-term maintenance. That is to say, vehicle manufacturers always set the engine output in the most conservative way. Therefore, car owners only need to ensure that the car is maintained regularly, You can get more output and extraordinary driving pleasure by re adjusting the engine parameters.
Take the air-fuel ratio (AFR) as an example, the original programmer may adjust the AFR of some driving conditions (such as driving at constant speed) to a lean point (i.e. less fuel and more gas) to reduce the fuel consumption, so as to pass the fuel consumption test standards of some countries and have a new look. In other times, the AFR of the original ECU is mostly set at the above-mentioned 1:14.7, Because this is the easiest proportion to meet the exhaust standard. However, for most engines, the AFR that can generate the maximum power is in the range of rich mixture (i.e. more oil and less gas). Similarly, in order to broaden the vehicle’s fuel adaptability (different grades of fuel in different regions), the ignition advance angle set by the original factory can generally adapt to the lower grade fuel (the engine’s output power is different at different ignition advance angles). That is to say, the ignition advance angle of your current engine may not match the fuel of your current grade best, If we can modify the original program to the power performance, we can increase the horsepower by about 5-8%, and some turbo cars can even achieve 15%.
2. How to modify ECU
When designing an engine, the ECU chip Refitting Factory has recorded the original fuel supply program on Rom. this program is usually the product of compromise of fuel consumption, pollution, running smoothness and other conditions, and can not be changed. Because it can not be changed, if you want to change the fuel supply program, you must change to another mode of ROM. Usually, the professional Refitting Factory will supply the refitting computer chips of different models. When refitting, the chip of the original computer should be removed first (usually the ROM of the original computer is directly soldered on the circuit board), an IC block should be soldered on (in this way, it can be easily replaced in the future), and then the refitting chip should be inserted. In this way, the fuel supply procedure is still fixed. It is only a modification to the original procedure. One of the most important is to delay or even cancel the fuel cut-off control time in the compensation injection procedure.
It should be noted that each kind of chip for refitting has its set applicable conditions (that is, the degree of refitting). When refitting, you must select a chip similar to the refitting condition of your car in order to get the best effect, otherwise it may backfire. The only way to select chips is to seek consulting from experienced refitting factories. A chip is a fuel supply program. Smart readers will think: if two or three chips are installed, what will the result be? Yes, there used to be a Refitting Factory in China that installed two or three chips with different fuel supply modes on the same circuit board at the same time. The driver can select the required fuel supply mode at will by connecting an external switch to the in car switch, just like switching the P, e and s gears of the automatic transmission, so as to meet the needs of different situations of car owners.
ECU computer programming is a more professional one in ECU system modification. Haltec computer is the most familiar one in domestic modification field. Through this computer, the owner can set the best fuel supply program according to the modification degree of his car’s engine and the measurement of the air-fuel ratio meter. That is to say, the basic injection program and each compensation injection program mentioned above can be changed arbitrarily by using the laptop. The biggest difference between the new chip and the new one is that when the engine is changed or refitted in the future, if the original fuel supply program is not applicable, it can be solved immediately through the modification of the program. After computer programming, the fuel supply program of the original car will be abandoned, but the higher level computer can retain all the sensor functions of the original car, that is to say, all kinds of fuel supply compensation programs can operate normally, and can also be changed, without sacrificing the smoothness and practicability of operation for obtaining high performance.
The biggest difficulty of refitting programmable ECU is not the installation, but the setting and optimization of fuel supply program. This often requires experience and equipment, through continuous testing to achieve. At present, the practice of the refitting plant is to select a basic mode as the basis, and then gradually correct it through actual operation and testing until it is satisfied.
3. Several common problems in the process of refitting ECU
Maybe because the function and working principle of ECU are “invisible” different from other mechanical systems. In addition, most repair garages and even 4S shops don’t understand and can’t repair or solve the problems caused by ECU, so the mystery of ECU is formed. Now let’s talk about several common problems in the process of brushing ECU
1) Original ECU or brand new ECU
If it is a general refit in civil, I prefer to refit it with original ECU. Because the function of the original ECU is very strong, and its program is developed through the long-term data accumulation and countless tests of the manufacturer’s engineers, it can protect the engine under any circumstances, and there will be no fault code, warning light, and rejection problems when other systems such as ABS, anti-skid and anti-theft system work together, I won’t delete some important functions of the car. On the other hand, the cost of modification is relatively low.
2) The modification degree and adjustment style of ECU
From the perspective of performance modification, ECU modification is an indispensable link. ECU can help the engine perform the best mechanical function, but it can not exceed the limit allowed by the original design. For example, when some professional teams develop the engine of racing car, they first design the matching of mechanical parts such as camshaft, piston and connecting rod, and first determine the compression ratio and maximum speed of the engine, and then consider the ECU problem. Because there is no strong engine, ECU again “capable” is just in vain. Therefore, for the ECU program adjustment mode, unless it is used in racing cars, it generally does not focus on the maximum horsepower when digging the full throttle. More attention will be paid to the acceleration ability and throttle response of the car at low and medium speed, because for civil cars, it is very rare to drive with full throttle and maximum speed. Therefore, the focus is on the speed range of 2000rpm-4000rpm, acceleration force and throttle response under half throttle condition, rather than striving for two more horsepower at 7000rpm. In these places, try to make the horsepower and torque curves smooth and gradual, so that the driver will feel that the throttle is particularly sensitive and obedient, and the power is abundant. The number of maximum horsepower may attract attention in the propaganda, but in the actual environment, no one likes to drive a car with poor acceleration. Therefore, it is not necessary to achieve the power level comparable to that of competitive vehicles for general road refitting vehicles. The correct cognitive concept should be whether this kind of refitting products can meet the practical needs of players in addition to the improvement of power output value on the premise of not damaging vehicle safety at all! This includes: smooth start, medium and high range extension and smoothness, as well as re acceleration ability and so on. At the same time, the trend of the test data and curve chart of the horsepower engine, as well as the actual sensory experience of the owner, play an important basis to verify the quality of the product and modification effect!
3) Will ECU upgrade affect the service life and safety of the car
Many people may have such doubts about whether the ECU upgrade will affect the service life and safety of the car. In fact, there is no need to worry about it. Brushing the ECU only makes a comprehensive optimization on the data of the car’s driving computer, not to blindly pursue the improvement of a certain index and give full play to the full capacity of the engine. His optimization is built on the basis of ensuring the economy and safety of the service life. It will reserve the absolutely safe use space for the car and bring the most comfortable operation space for the car engine. But there is another situation. Because of the relationship between the cost and the technical level, some car fans will take the second place and install some accessories commonly known as “secondary air intake” or “fuel supplement” to increase the amount of fuel and air into the engine. These accessories actually “cheat” the ECU by bypassing the original sensor or changing the voltage of the sensor, It can change the air-fuel ratio into the engine without knowing it, and improve the power performance of the engine under some conditions. This kind of incomplete modification method will bring other side effects, and even may cause safety problems. Although the orthodox modification method has high cost, it can avoid many bad sequelae.
4) Difference between streetcar and racing car in ECU setting
ECU settings are generally divided into two types, one is streetcar, the other is racing car. For a racing car, because the factors such as the fuel used, the venue and the driver are well regulated, the computer setting focuses on how to deal with the changing weather, temperature and other environmental factors at any time. Street cars are much more complicated. There is no limit on driving time, and the fuel will change. Even if high-quality fuel is used, the fuel consumption of different gas stations will be different. Compared with racing cars, streetcar refitting needs to consider more safety factors, so the computer settings should be reserved. After comprehensive consideration of the driving style and vehicle characteristics of the vehicle owner, it can be set. And even the same situation, the same car, there will be changes, so using the same data to set is not necessarily the best.
5) Several points should be paid attention to when brushing ECU
Many car owners only consider how much horsepower there is, but don’t pay attention to torque, which is often encountered. In fact, the car should not be too numb to blindly pursue horsepower. Before refitting, you should be clear about the purpose of the car and the car owner’s driving habits.
For refitting shop owners, when retrofitting ECU, it is recommended not only pay attention to fuel injection time, but also pay attention to whether the fuel supply is enough. In fact, we should also pay attention to the arrangement of ignition time, because the advance angle of ignition time is extremely important. And the hardware installed on the car, we must first understand its characteristics, so that when changing the ECU to cooperate, we can make it play the best effect.
In addition, if the engine uses a high angle camshaft, because it will change the valve opening and closing time, it is even more difficult to adapt the program, so it needs more accurate calculation and adjustment. Whether the performance of the modified parts can be fully played depends on the adjustment of ECU, but it is very difficult to change the characteristics of the engine by changing the ECU data.
4. Future trend of vehicle control
We might as well count by fingers, how many systems need to be controlled. Automatic transmission, ABS system, car entertainment audio-visual system, four-wheel drive torque distribution system, active suspension system, airbag + seat belt system, etc. So many systems have their own sensors and processors for independent calculation, so the water in the well doesn’t break the river… However, the automatic transmission and the engine need to cooperate, for example, the engine’s oil collection is needed in the shifting process, and the gearbox’s kickdown downshift is needed in the big foot throttle… Under various states, they need to share a lot of data, For example, the crankshaft speed of the engine, automatic transmission, to re-establish a set of sensors will cause a waste of cost, but also unrealistic. The best way is to share data between the transmission and the engine ECU, which gives birth to the information network system between ECUs – can data bus. The same can data bus is also used in chassis electronic equipment, such as 4WD torque distribution system and ABS, which share many sensor parameters of chassis.
With the development of can data bus, all control systems must be integrated. There is a saying that the future ECU will be a powerful computer system, which will integrate the engine, automatic transmission, ABS system, on-board entertainment audio-visual system, four-wheel drive torque distribution system, active suspension system, airbag + seat belt system and all other components that need to be managed. We can enjoy the car audio-visual system, play PC game and receive GPS signals, Even a cup holder will be under the management of ECU.
What’s more interesting is that in the future, ECU might build a set of open interactive software, such as windows operating system, and then install a bunch of engine management system, transmission management system, ABS system, etc. at that time, the engine “ECU” management system was just a software that could be updated in real time. You can choose version 1.1, You can also choose version 2.0. Of course, you also need to install a firewall to prevent hackers.