Control Electronics - Engine ECU - Part 1 - Engineering

What kind of computers do we carry with us every day?

To begin with, it is important to mention that the electronic control unit that controls the operation of the car engine is just one of a series of computers that we find in today's cars. In addition, modules for monitoring the airbag system, the so-called body control computers take care of the central locking, power windows, etc., there is also a computer that monitors the operation of the (electric) power steering, for the brake system (ABS, ESP etc.) takes care of special computers, automatic and semi-automatic transmissions have their own separate computer to control certain functions, there is also a cruise control unit, and we should not forget the seemingly "unimportant" computers of the control unit that take care of electric starters, air conditioning device, telephone, audio system, etc.

Engine Control Unit (ECU) for Competitive Car Engines (Magneti Marelli)

Many of these computers are interconnected, such as e.g. cruise control units (constant speed vehicle maintenance units) and engine control units, since cruise control determines how fast we will move, which in turn directly affects the engine management (fuel injection, etc.). In any case, every time you turn the engine start key (or push the switch), a dozen separate computers will come to life in the average car.

Let's say that some surveillance computers are sometimes connected, ie. they are in the same housing (this would, for example, be logical for the cruise control and engine control unit). But now we would complicate this topic too much to start a discussion of how many monitoring units work independently, and how many of them are integrated with some other systems. After all, it varies from manufacturer to manufacturer. In principle, we can say that one motherboard - represents one control computer (so now you disassemble the car and count all Motherboard and in doing so, lure all the insects that have lurked there, like this one from our opening image, which is comfortably housed on a micromechanical sensor whose structure is visible only under the microscope).

EDC16 - ECU diesel engine (Robert Bosch GmbH)

Electronic engine control unit, ECU, ECM, Central or whatever you like…

An electronic control module (ECU - Electronic Control Unit or ECM - Electronic Control Module) is in fact an impersonal metal or plastic box with a series of electrical connectors on the outside and extensions for mounting the box in the car, while the inside is filled with some chips. , printed circuit boards and other electronic wonders. The interior of the ECU actually looks like a small computer, which it actually is.

For comparison, let's just say how today's electronic car engine control unit (ECU) can have a 32-bit 40-MHz processor. This is, seemingly, almost ridiculous compared to the average PC, but it is necessary to take into account how the car ECU "deals" with specialized and much more efficient code (software). Thus, the average car ECU takes up less than 1 MB of memory, while the average computer's memory contains several GB of program code of all possible types.

The basis of ECU operation is based on processing input parameters coming from certain parts of the engine and sending data to some other components of the same, depending on the current driver's request (accelerator pedal pressure, gear…). The biggest part of the job that the ECU does is control the ignition timing and the amount of fuel delivered to the engine, monitoring the engine idling, controlling the VVT ​​system (variable camshaft system) and the like.

Significant input parameters

The data needed for "thinking" our Electronic Control Module (ECU) comes with the help of a series of sensors. On the crankshaft, at one end of it, a wheel resembling a gear is attached. What it is? An optical, or magnetic, sensor mounted next to that wheel sends a signal to the ECU each time a mark attached to that point passes in front of it. It is most often made in the form of an opening, a hole or a tooth on its rim. As the crankshaft rotates, this mark passes in front of a sensor that currently notifies the ECU. The ECU then measures the time that has elapsed between the two passes of the mark and thus calculates the crankshaft speed (number of engine revolutions per minute - rpm).

Crankshaft Position / Speed ​​Sensor (Adam Opel AG)

Engine speed is a basic parameter for calculating the ignition timing. The information thus processed is sent by the ECU to the ignition system, which then knows exactly when to spark plug. In theory, our crankshaft wheel could have only one tooth, while in practice it would be sufficient to fit only 2 such marks. However, this is only true for high-speed motors and where the rpm changes are relatively small (it is typical for motorcycle engines to only use two readings per crankshaft frequently, but these are higher-speed drive motors from 10.000 rpm).

The problem, in car engines, occurs primarily at startup. When you turn the key in the ignition switch, the engine spins at about 250 rpm, but that number jumps to 800 or more at the time of ignition of the first cylinder. Therefore, in practice, it is necessary to place far more marks on that wheel, which then really resembles a gear. Thus, e.g. some Opel engines in the ECOTEC series use 58 teeth, while others, this time with Ford propulsion engines of similar characteristics, have 36. In these two cases, the result is that the ECU receives Update engine speeds of 58 and 36 respectively for one revolution (360 °) of the crankshaft, which is quite sufficient. It should be noted here that when looking at these gears, you will notice that some gears are missing (in Opel 2, and in Ford 1). This is set as a reference point so that the ECU "knows" exactly where the crankshaft is at some point.

Intake air flow sensor (Robert Bosch GmbH)

Another important input parameter of the Electronic Computer Monitor (or "module") is the position of the butterfly on the intake system. As the position of the butterfly is directly related to how much the accelerator pedal is depressed, it depends on how much fuel the ECU will "approve" to the engine. And there, on the butterfly, is a sensor that sends its data to the ECU, from where it, processed, goes to the injection system. This, in turn, according to the obtained parameters determines how long the injection pulse will last, ie. how long the injectors will be open (remember the fuel injection story).

The third input parameter illustrated in our scheme is the data that comes from the lambda probe. (lambda is a sensor that measures the percentage of oxygen in the exhaust gas). But let's just say that this information is also crucial to the exact calculation that is done in the ECU, with the aim of maintaining the proper operation of the engine, ie. adjusting the proper ratio of fuel to air in the mixture.

From what has been stated so far, it can be seen that the structure of electronic engine management (Engine Management) consists of three basic groups, namely: input parameter sensors, the electronic control module (ECU) itself, and the system that controls the engine, and what information is needed they get it from the ECU for proper operation. Of course, there is also power to all components.

In the ECU housing

If we take a look inside the electronic control unit of a car engine, we will see three basic parts. These are CPU, ROM and RAM. We believe that it is not necessary to explain to anyone what these abbreviations, common in the computer world, mean, but… CPU (Central Processing Unit) is the main processor that recalculates the obtained input parameters using the program contained in it.

The first electronically controlled injection system, the D-Jetronic, for the production car was introduced in 1967. To the right is a modern such system, Motronic (Robert Bosch GmbH)

ROM (Read Only Memory) is a memory composed of one or more chips that contain data according to which the CPU synchronizes the data calculation. In other words, ROM is like a kind of book in which the doctor will find a description of the disease typical for some symptoms (input parameters), and in it he will find the recommended medicine for the same. Significantly, the CPU cannot change the parameters stored in the ROM memory. Therefore, some ECUs have a built-in removable chip called PROM (Programmable Read Only Memory) in which it is also not possible to change the data, but it can be replaced by a chip with stored different data. In this way, we can influence the "decisions" made by the CPU, and thus the operation of the motor.

The third version of this memory is called EEPROM (Electrically Erasable PROM) and is a memory chip that can be connected to computers and thus change the entered parameters ("map" of ignition and injection, etc.). RAM (Random Access Memory) is a memory chip that is active only when the engine is running. In other words, its data begins to be entered by starting the engine, and is erased by turning it off. RAM chips are used so that the CPU can write data obtained from input sensors, current calculations and similar information that is constantly changing. The CPU is constantly accessing RAM, deleting old and entering new data.

The last memory chip to describe is KAM (Keep Alive Memory) and it is one type of RAM. The CPU can also enter data into this chip, delete it and replace it with new ones, and it is special in that it "remembers" what is written as long as it is connected to the power source. KAM memories are primarily used to store "Trouble or Failure Codes", which is information that can be read (in service) with the help of a control computer and thus find out what problem the engine has detected sensors. Of course, KAM memory is erased by turning off the voltage, ie. by disconnecting the battery.

 

The OBD II 'diagnostic' connector is usually located under a cover, to the left of the steering wheel or on the center console

I want to know more!

Let's also say that the car is usually equipped with an OBD (today OBD II) connector. This connector (OBD - On-board diagnostics) is used to connect diagnostic devices in service workshops, which are used to check for errors stored in the KAM memory. And, if you are really interested in how "healthy" the engine of the car you are sitting in is, you can always play with one of the OBD applications for smartphones and tablets, which are most often connected to the OBD II connector via Bluetooth.

These applications are able to display the reported error codes (which by a manufacturer means, you can easily detect through the list Trouble codes available on the Internet), data from various sensors (temperature and oil pressure, coolant temperature, turbocharger speed, turbocharger pressure, etc.) or results from the ECU account (or one of the connected computers) such as current or average fuel consumption. Of course, we probably don't have to mention that you will perform such "games" at your own risk, because if you "burn" the integrated circuit of a control unit of your car, we will not be to blame for it!