Module -2 ELECTRONIC DIESEL CONTROL (EDC)

Electronic control of a diesel engine allows fuel-injection parameters to be varied precisely for different conditions. This is the only means by which a modern diesel engine is able to satisfy the many demands placed upon it. The EDC (Electronic Diesel Control) system is subdivided into three areas, “Sensors and desired-value generators”, “Control unit”, and “Actuators”. System overview:

Requirements

Present-day development in the field of diesel technology is focused on lowering fuel consumption and exhaust-gas emissions (NOx, CO, HC, particulate), while increasing engine performance and torque. In recent years this has led to an increase in the popularity of the direct-injection (DI) diesel engine, which uses much higher fuel-injection pressures than indirect-injection (IDI) engines with whirl or pre chamber systems. Due to the more efficient mixture formation and the absence of flow-related losses between the whirl chamber/pre chamber and the main combustion chamber, the fuel consumption of direct-injection engines is 10...20% lower than that achieved by indirect-injection designs. In addition, diesel engine development has been influenced by the high levels of comfort and convenience demanded in modern cars. Noise levels, too, are subject to more and more stringent requirements. Demand of fuel-injection and engine-management systems

• High fuel-injection pressures

• Pre-injection and, where applicable, secondary injection

• Variation of injected fuel quantity, charge air pressure, and start of injection to suit operating conditions

• Temperature-dependent excess-fuel quantity for starting

• Control of idle speed independent of engine load • Controlled exhaust-gas recirculation (cars)

• Cruise control

• Tight tolerances for injection duration and injected fuel quantity, and maintenance of high precision over the service life of the system (long- term performance)

Operating concept

The injected fuel quantity is actually determined by a number of different influencing variables. They include:

• The vehicle response desired by the driver (accelerator-pedal position) • The engine operating status

• The engine temperature Interventions by other systems (e.g. TCS)

• The effect on exhaust-gas emission levels, etc.

Electronic diesel control allows data exchange with other electronic systems, such as the Traction Control System (TCS), Electronic Transmission Control (ETC), or Electronic Stability Program (ESP).

As a result, the engine management system can be integrated in the vehicle’s overall control system network, thereby enabling functions such as reduction of engine torque when the automatic transmission changes gear, regulation of engine torque to compensate for wheel spin, disabling of fuel injection by the engine immobilizer, etc. The EDC system is fully integrated in the vehicle’s diagnostic system. It meets all OBD (On-Board Diagnosis) and EOBD (European OBD) requirements.

System modules Electronic Diesel Control (EDC) is divided into three system modules (Fig. 1):

1. Sensors and set point generators detect operating conditions (e.g. engine speed) and set point values (e.g. switch position). They convert physical variables into electrical signals.

2. The electronic control unit processes data from the sensors and set point generators based on specific open- and closed-loop control algorithms. It controls the actuators by means of electrical output signals. In addition, the control unit acts as an interface to other systems and to the vehicle diagnostic system.

3. Actuators convert electrical output signals from the control unit into mechanical parameters (e.g. the solenoid valve for the fuelinjection system).

Data processing:

The main function of the Electronic Diesel Control (EDC) is to control the injected fuel quantity and the injection timing. The common-rail fuel-injection system also controls injection pressure. Furthermore, on all systems, the engine ECU controls a number of actuators. For all components to operate efficiently, the EDC functions must be precisely matched to every vehicle and every engine. This is the only way to optimize component interaction.

The control unit evaluates the signals sent by the sensors and limits them to the permitted voltage level. Some input signals are also checked for plausibility. Using these input data together with stored program maps, the microprocessor calculates injection timing and its duration. This information is then converted to a signal characteristic which is aligned to the engine’s piston strokes. This calculation program is termed the “ECU software”.

The required degree of accuracy together with the diesel engine’s outstanding dynamic response requires high-level computing power. The output signals trigger output stages that supply sufficient power for the actuators (e.g. high- pressure solenoid valves for the fuel-injection system, exhaust-gas recirculation positioners, and boost-pressure actuators). Apart from this, a number of other auxiliary-function components (e.g. glow relay and air- conditioning system) are triggered.

Faulty signal characteristics are detected by output-stage diagnostic functions for the solenoid valves. Furthermore, signals are exchanged with other systems in the vehicle via the interfaces. The engine ECU monitors the complete fuel- injection system as part of a safety strategy.

Data transmission to other systems (Data exchange with other systems)

Fuel-consumption signal The engine ECU (Fig. 1, 3) determines fuel consumption and sends this signal via CAN to the instrument cluster or a separate onboard computer (6), where the driver is informed of current fuel consumption and/or the range that can be covered with the remaining fuel in the tank. Older systems used Pulse- Width Modulation (PWM) for the fuel-consumption signal. Starter control The starter motor (8) can be triggered from the engine ECU. This ensures that the driver cannot operate the starter motor with the engine already running. The starter motor only turns long enough to allow the engine to reach a self- sustaining speed reliably. This function leads to a lighter, and thus lower- priced, starter motor. Glow control unit The glow control unit (GZS, 5) receives information from the engine ECU to control glow start and duration. It then triggers the glow plugs accordingly and monitors the glow process, and reports back to the engine ECU on any faults (diagnostic function). The pre glow indicator lamp is usually triggered from the engine ECU.

Electronic immobilizer To prevent unauthorized starting and drive off, the engine cannot be started before a special immobilizer (7) ECU removes the block from the engine ECU. The driver can signal the immobilizer ECU that he/she is authorized to use the vehicle, either by remote control or by means of the glow-plug and starter switch (“Ignition” key). The immobilizer ECU then removes the block on the engine ECU to allow engine start and normal operation. External torque intervention In the case of external torque intervention, the injected fuel quantity is influenced by another (external) ECU (for instance, for transmission- shift control, or TCS). This informs the engine ECU whether the engine torque is to be changed, and if so, by how much (this defines the injected fuel quantity). Alternator control By means of a standard serial interface, the EDC can control and monitor the alternator (9) remotely. The regulator voltage can be controlled, just the same as the complete alternator assembly can be switched off. In case of low battery power, for instance, the alternator’s charging curve can be improved by increasing the idle speed. It is also possible to perform simple alternator diagnosis through this interface. Air conditioner In order to maintain comfortable temperatures inside the vehicle when the ambient temperature is high, the air conditioner (A/C) cools down cabin air with the help of an A/C compressor (10). Depending on the engine and operating conditions, the A/C compressor may draw as much as 30% of the engine’s output power. Immediately the driver hits the accelerator pedal (in other words he/she wishes maximum torque), the compressor can be switched off briefly by the engine ECU to concentrate all of the engine’s power to the wheels. Since the compressor is only switched off very briefly, this has no noticeable effect on interior temperature.

Electronically controlled PE-EDC in line fuel injection pumps

ECU:

Digital technology furnishes an extensive array of options for open and closed- loop control of automotive electronic systems. A large number of parameters can be included in the process to support optimal operation of various systems. After receiving the electric signals transmitted by the sensors, the control unit processes these data in order to generate control signals for the actuators. The control program, the “software”, is stored in a special memory and implemented by a microcontroller. The control unit and its components are referred to as “hardware”. The EDC control unit contains all of the algorithms for open and closed-loop control needed to govern the engine- management processes

Operating conditions

The ECU is subjected to very high demands with respect to extreme ambient temperatures (during normal operation from –40°C to +60...+125°C), violent temperature fluctuations, resistance to the effects of such materials as oil and fuel, etc., surrounding dampness, and mechanical stresses such as engine vibrations.

Signal processing:

The control unit is the switching center governing all of the functions and sequences regulated by the engine-management system. The closed and open- loop control functions are executed in the microcontroller. The input signals from sensors and interfaces linking other systems (e.g., CAN bus) serve as the input parameters and are subjected to a further plausibility check in the computer. The ECU program supports generation of the output signals used to control the actuators.

The microcontroller is the ECU’s central component and controls its operative sequence. Apart from the CPU (Central Processing Unit), the microcontroller contains not only the input and output channels, but also timer units, RAMs, ROMs, serial interfaces, and further peripheral assemblies, all of which are integrated on a single microchip. Quartz-controlled timing is used for the microcontroller.

Program and data memory In order to carry out the computations, the microcontroller needs a program – the “software”. This is in the form of binary numerical values arranged in data records and stored in a program memory. These binary values are accessed by the CPU which interprets them as commands which it implements one after the other.

This program is stored in a Read-Only Memory (ROM, EPROM, or Flash- EPROM) which also contains variant-specific data (individual data, characteristic curves, and maps). This is non-variable data which cannot be changed during vehicle operation. It is used to regulate the program’s open and closed-loop control processes. The program memory can be integrated in the microcontroller and, depending upon the particular application, expanded by the addition of a separate component (e.g., by an external EPROM or a Flash-EPROM).

The peripheral components must communicate with it within the ECU:

ROM: Program memories can be in the form of a ROM (Read Only Memory). This is a memory whose contents have been defined permanently during manufacture and thereafter remain unalterable. The ROM installed in the microcontroller only has a restricted memory capacity, which means that an additional ROM is required in case of complicated applications. EPROM: The data on an EPROM (Erasable Programmable ROM) can be erased by subjecting the device to UV light. Fresh data can then be entered using a programming unit. The EPROM is usually in the form of a separate component, and is accessed by the CPU through the Address/Data-Bus.

Flash-EPROM (FEPROM): The Flash-EPROM is electrically erasable so that it becomes possible to reprogram the ECU in the service workshops without having to open it. In the process, the ECU is connected to the reprogramming unit through a serial interface. If the microcontroller is also equipped with a ROM, this contains the programming routines for the Flash programming. FlashEPROMs are available which, together with the microcontroller, are integrated on a single microchip its decisive advantages have helped the Flash- EPROM to largely supersede the conventional EPROM.

RAM: Instantaneous values are stored in the RAM (Random Access Memory) read/write memory. If complex applications are involved, the memory capacity of the RAM incorporated in the microcontroller is insufficient so that an additional RAM module becomes necessary. It is connected to the ECU through the Address/Data-Bus. When the ECU is switched off by turning the “ignition” key, the RAM loses its complete stock of data (volatile memory).

EEPROM :( also known as the E2PROM) as stated above, the RAM loses its information immediately its power supply is removed (e.g. when the “ignition switch” is turned to OFF). Data which must be retained, for instance the codes for the vehicle immobilizer and the fault-store data, must therefore be stored in a non-erasable (non-volatile) memory. The EEPROM is an electrically erasable EPROM in which (in contrast to the Flash EPROM) every single memory location can be erased individually. It has been designed for a large number of writing cycles, which means that the EEPROM can be used as a non- volatile read/write memory.

Applications of Sensors (EDC System blocks of Sensors): Safety concepts: Temperature sensors: Engine-temperature sensorThis is installed in the coolant circuit .The engine management uses its signal when calculating the engine temperature (measuring range –40…+130°C). Air-temperature sensorThis sensor is installed in the air-intake tract. Together with the signal from the boost-pressure sensor, its signal is applied in calculating the intake-air mass. Apart from this, desired values for the various control loops (e.g. EGR, boost-pressure control) can be adapted to the air temperature (measuring range –40…+120°C).

Engine-oil temperature sensorThe signal from this sensor is used in calculating the service interval (measuring range –40…+170°C).

Fuel-temperature sensorIs incorporated in the low-pressure stage of the diesel fuel circuit. The fuel temperature is used in calculating the precise injected fuel quantity (measuring range –40…+120°C).

Exhaust-gas temperature sensorThis sensor is mounted on the exhaust system at points which are particularly critical regarding temperature. It is applied in the closed-loop control of the systems used for exhaust-gas treatment. A platinum measuring resistor is usually used (measuring range –40…+1,000°C).

Micromechanical pressure sensors

Manifold-pressure or boost-pressure sensorThis sensor measures the absolute pressure in the intake manifold between the supercharger and the engine (typically 250kPa or 2.5 bar) and compares it with a reference vacuum, not with the ambient pressure. This enables the air mass to be precisely defined, and the boost pressure exactly controlled in accordance with engine requirements.

Atmospheric-pressure sensorThis sensor is also known as an ambient pressure sensor and is incorporated in the ECU or fitted in the engine compartment. Its signal is used for the altitude-dependent correction of the set point values for the control loops. For instance, for the exhaust-gas recirculation (EGR) and for the boost-pressure control. This enables the differing densities of the surrounding air to be taken into account. The atmospheric-pressure sensor measures absolute pressure (60...115kPa or 0.6...1.15 bar).

Oil and fuel-pressure sensor Oil-pressure sensors are installed in the oil filter and measure the oil’s absolute pressure. This information is needed so that engine loading can be determined as needed for the Service Display. The pressure range here is 50...1,000kPa or 0.5...10.0 bar. Due to its high resistance to media, the measuring element can also be used for pressure measurement in the fuel supply’s low-pressure stage. It is installed on or in the fuel filter. Its signal serves for the monitoring of the fuel- filter contamination (measuring range: 20... 400kPa or 0.2...4 bar).

Advantages of EDC

 No single system (for instance, boost pressure, fuel injection, pre-glow) has a direct effect on engine management. This enables the engine management to also take into account higher-level optimization criteria (Such as exhaust-gas emissions and fuel consumption) when processing External requirements, and thus control the engine in the most efficient Manner  Many of the functions which do not directly concern the engine management can be designed to function identically for diesel and gasoline engines.  Extensions to the system can be implemented quickly.