However, enthusiasts who like to do everything themselves, including experienced motorists, these achievements are more likely to bring some disappointment. Here it is hardly possible to put your hand.
The electronically loaded engine management unit, which is located in the battery compartment, constantly calculates the amount of fuel injected and the injection timing for each combustion process based on a large amount of data. Quite understandable electromechanical equipment has turned into a complex engine control device based on computer technology. This device is multivariate programmable, uses fault memory data, and detects faults using a self-diagnostic system.
Location: The engine control unit is located next to other electronic components in the electronics box, which is located on the left side of the battery section. The illustration shows the ASN six-cylinder engine control unit as an example.
Since the data for the petrol injection system are also of great importance when calculating the ignition timing, the control unit also takes over the regulation of the ignition timing. In case of Motronic engine control (Bosch) or Simos (Siemens) it is no longer possible to separate the injection system and the ignition system from each other. Despite this, for clarity, we describe the components of the ignition system in a separate chapter.
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Functional system of the Motronic system. The control device processes a large number of signals. In some cases, if the sensors fail, emergency programs begin to operate. However, if, for example, the speed sensor fails, the engine is switched off.
With the help of a comprehensive electronic engine management system, low fuel consumption can be optimally achieved while maintaining strict limit values for the exhaust gas composition. To do this, the control device must receive accurate data on the current mode of operation of the engine. When a carburetor was used, the only controlled variable was reduced pressure in the intake manifold. In the case of a central electronic engine management system, sensors located on and around the engine provide data on engine temperature, coolant and intake air, air density, exhaust gas composition, engine load and shaft speed.
Since the computing device has all the necessary information, additional tasks are assigned to it:
- speed control,
- exhaust gas composition regulation,
- management of the evaporating fuel regeneration system,
- antiknock regulation,
- control of the exhaust gas recirculation system,
- turbocharger control, since turbocharging is used,
- intake manifold switching control and camshaft adjustment.
Continuous improvement
In addition, the electronic digital engine control device interacts with other vehicle systems. Together with the automatic transmission control unit, the electronic engine management system, which is constantly being improved and offers new features, ensures smooth gear changes. This is achieved by slightly reducing the speed when changing gears. The electronic digital engine control also communicates with the anti-lock and traction control systems.
Gasoline direct injection
The last step in the development of engine management systems is internal mixture formation, that is, fuel injection directly into the combustion chamber. So far, systems are mainly used, in which the formation of the mixture occurs outside the combustion chamber. However, since the end of summer 2001, when the 2.0l FSI engine began to be installed, a new trend has emerged in the development of the Audi A4. This engine is equipped with an FSI gasoline direct injection system.
The economic and ecological function of the engine management system, which is to ensure a reduction in fuel consumption and the content of harmful substances in the exhaust gases, as well as a good engine run, is most clearly manifested in the FSI engine. Electronic control using technically advanced injection pumps allows for each engine mode to dose the correct amount of injected fuel and set the appropriate start of injection.
Electronic control device
The computing and switching device of the engine management system, based on the signals that come from the sensors, calculates the control signals for the actuators, that is, for the ignition coil, injectors, etc. The control device is in a metal case, inside the case there is a printed circuit board with electronic components. This small inconspicuous block is located at the edge of the engine compartment, on the left side of the battery section.
The digital circuits of the control device are powered by a voltage regulator. The control device includes final stages, which provide sufficient power for direct connection of actuators. A protection circuit protects these final stages from short circuits to the ground and destruction due to electrical overload.
Audi A4 engines are mainly controlled by electronic systems manufactured by Bosch. The ALT motor is equipped with an ME 7, AVJ control (turbocharged) - ME 7.5, and the six-cylinder ASN engine - the control unit ME 7.1. In a two-valve four-cylinder engine (type ALZ) control is assigned to the Simos 3.4 electronic device.
The aforementioned diagnostic function allows you to determine the faults that may occur in some final stages and, if necessary, disable the faulty output. Information about the fault is stored in a memory device. This information can be read in a specialized workshop using a special device. Faults are recorded in the form of a printout of digital codes, these codes are processed in specialized workshops.
Switching system on a single CAN bus
Conventional switching systems in a car differ in that each signal corresponds to a separate wire. The huge increase in communication between electronic components in modern motor control systems makes it difficult to use older switching systems. For some time now, it has become difficult to understand the intricacies of conventional cable harnesses.
The switching system developed specifically for cars on a single CAN bus made it possible to solve the problem. The electronic control devices must have a serial CAN interface, this interface allows them to be connected to each other via the appropriate data bus.
In a vehicle, CAN performs three important functions:
- pairing of control devices with each other,
- ensuring the operation of body electronics and ensuring comfort (Multiplex),
- provision of mobile communications.
The International Organization for Standardization provides for the use of CAN in vehicles as a standard. This standard is valid for data exchange rates greater than 125 kbps, in addition, there are two more protocols for data rates less than 125 kbps.
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