Electronic Diesel Control

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Electronic Diesel Control ( EDC ; German " electronic diesel control ") describes a system from Bosch that consists of sensors, logic (electronic hardware and software in a control unit) and actuators. To simplify matters, the system is described as an engine control unit for diesel engines . Typical names are EDC15, EDC16 and EDC17. The numbers describe the respective generation. Other important manufacturers of such engine control units are u. a. Continental , Delphi and Denso , but their products are not necessarily listed under a comparable name.

The EDC is used for engines in vehicle construction, construction machinery, rail and water vehicles as well as for mobile units (pumps, power generators).

Bosch brought EDC onto the market in 1986; the system was first used in the M21 engine of the BMW E28 524td .

Mode of action

EDC control unit logic part
EDC control unit power section

An EDC describes an electronic engine control unit for controlling the fuel injection quantity in a diesel engine. Injection quantities and distribution determine the torque in this engine and are controlled by electronically adjustable (in the construction machinery sector also mechanical) high-pressure pumps or electronically switchable injectors. The task of the EDC is to calculate the time profile of the fuel injection into the combustion chamber and to ensure this via the control of the pump and injection valves.

A modern diesel injection system, such as common rail injection , is only possible because of the many degrees of freedom afforded by EDC. Due to its complexity, it would be very expensive to implement without EDC.

The central component is a powerful microcontroller with analog / digital inputs / outputs. A large number of electronic peripheral systems process the signals from and to the diesel engine.

The software plays a very important role in the EDC, as it takes on very complex dimensions due to the increasing requirements of the exhaust gas limit values . A large number of functions are required for on-board diagnosis (OBD) in order to be able to monitor the diesel engine in the event of service. Many convenience functions have also been added because they were only made possible by EDC and are now standard, especially in diesel cars.

The electronic control of the injection system results in the following advantages:

  • Stricter exhaust emission limits can be monitored and adhered to over a long period of time, and the emission range of the various vehicles of one type can be narrowed
  • Lower engine noise, smoother running (important in cars, not important for construction machines)
  • Better responsiveness
  • Problem-free equipping of motor vehicles with comfort functions, for example with cruise control
  • Simplified adaptation of an engine type to different applications (e.g. truck, ship, stationary engine).

In a motor vehicle, the EDC is one of the most powerful and complex control devices. Here, not only are many input and output signals processed according to the speed and the number of cylinders , but this must also be done in real time . The heart of the hardware is a microcontroller with flash memory on which software runs that can be several megabytes in size.

Further functions of the control unit are:

  • Communication with other control units via CAN bus , LIN , PSI5 or other interfaces
  • Self-diagnosis of the control unit: Detect and save errors
  • Diagnosis of sensors and actuators: Detect and save errors
  • Monitoring of engine operating conditions and safety shutdown
  • Controlling the exhaust system with particle filter and catalytic converter
  • Diagnostic interface via communication protocol e.g. B. KWP2000

Functionally, EDC control units for cars and commercial vehicles differ only slightly at first glance, but a closer look reveals some differences:

feature Car Commercial vehicles, industrial engines
Battery voltage (actual on-board voltage during operation approx. 20% higher): 12 volts 12 or 24 volts
Idle regulator Smooth running with low fuel consumption Particularly large and powerful software part. Enables loaded 40-tonne trucks to idle in top gear, as well as increased idling speed for work machines.
Flash level Few flash levels for OEMs and authorized workshops, e.g. B. End-Of-Line and software update Like a car. Additional flash level for different OEMs, e.g. B. Parameter changes / software updates for engines OEM, parameter changes for chassis builders OEM, parameter changes for special bodies OEM, etc.
ECU generation life Due to the frequent generation leaps in hardware, the software was also constantly being redeveloped. In the future, new architectures such as AUTOSAR should make the software more independent of the hardware. Software is being further developed for existing hardware for a longer period and errors are eliminated.
Calculated service life ten years > 10 years (application-specific)
Optimization target operating behavior Best overall coordination, especially of power, torque, consumption, smoothness, exhaust gas, noise, service life Low operating costs, especially due to low consumption, inexpensive maintenance, long service life

Functions of the EDC

The EDC offers numerous functions that may be included depending on the drive and type of injection. These functions are described in more detail here, as they are also contained in a similar form in competing injection systems and generally describe the state of the art in diesel control.

If corrections are made according to maps, these maps are usually based on the temperatures of the engine, intake air and fuel.

Functions of a motor control with EDC (as of version 16):

  • Start quantity : control of the fuel quantity of tempering to idle speed. The regulation is autonomous, i. i.e., it ignores the accelerator pedal position.
  • Driving operation control: Control according to the accelerator pedal position, corrected with speed and according to the map.
  • Idle speed : Autonomously variable control according to loads such as air conditioning, electrical auxiliary consumers (rear window heating, air heating), battery charge level, power steering. In this operating range, very small amounts of fuel must be metered very precisely in order to achieve a smooth idling.
  • Limitation : Quantity reduction above the nominal speed down to 0 when the maximum permissible engine speed is reached.
  • Intermediate speed control (ZDR): trucks with power take- offs (e.g. cranes, dump trucks, refrigerated boxes or typical municipal vehicles) keep the speed at a specified value, regardless of the load.
  • Cruise control : engine control at constant speed. In contrast to the ZDR, the engine control also compensates for gear changes in automatic transmissions .
  • Driving speed limitation : Prevents exceeding a specified driving speed. This specification can be variable (e.g. adjustable limit for winter tires of a low speed class) or fixed (e.g. legal maximum speed of trucks)
  • Jerk damping (cars only): By quickly stepping on or releasing the accelerator pedal (rapid load changes) the driver can stimulate the engine and vehicle to vibrate ( bonanza effect ). The jerk damping smoothes out rapid torque changes and detects vibrations in the drive train , which are then actively dampened.
  • Quantity compensation (MAR) : Differences between the cylinders in compression, friction or in the injection components mean that the same injection quantities and times lead to different torques in the work cycle. The EDC measures the speed / acceleration in the work cycle and compares it with the other cylinders in order to adjust the amount of fuel. This function is also referred to as "Adaptive cylinder equalization" (AZG) and "Smooth Running Control" (SRC).
  • Limitation quantity : This function cuts off the maximum torque, for example, if mechanical components are not designed for the possible maximum torque of the motor (particularly applies to gearboxes, drive shafts ) or if there is a risk of thermal overload or excessive emissions. In the torque diagram, the effect of this function can be seen in the fact that there is no “torque peak”, but instead the torque reaches a horizontal plateau from a certain speed and from there drops again at a higher speed.
  • Engine brake : On trucks, the function for parking the vehicle or in conjunction with the exhaust flap brake ( engine dust brake ) to increase the engine braking effect.
  • Altitude correction : Compensates for the falling air pressure when driving in mountains. Naturally aspirated engines have a greater need for regulation than turbo engines.
  • Injector calibration : In the case of piezo injectors , the accuracy of the injection is improved via the operating voltage of the injector, provided that the data was measured during the manufacture of the injector and transferred to the engine control unit. In the case of an engine overhaul, this means that the assignment of injectors to their cylinders must be retained or recalibrated.
  • Zero quantity calibration : In common rail systems in particular, multiple injections in one work cycle are common. An aging-related drift of the quantities is avoided in that small injections take place in overrun mode at different operating points and for all cylinders and the change in speed is evaluated.
  • Average quantity adjustment (MMA): Corrects aging-related drift in exhaust gas recirculation, lambda control (if available) and boost pressure.
  • Pressure wave correction : At high injection pressures , pressure waves occur in the high pressure part of the fuel system , which worsen the control accuracy between the individual injections in a work cycle. The pressure wave correction also makes it possible to dynamically shift the distance between pilot and main injection.
  • Regeneration : If, for example, a higher exhaust gas temperature is required for the regeneration of the soot particle filter , the EDC conditions the engine accordingly.
  • Increment angle correction : Corrects inaccuracies in the speed sensor in order to better hit the optimal injection point, from which UIS (pump-nozzle systems) in particular benefit.
  • Injection start control : While in the 1980s the car driver still operated the injection start adjuster manually for the cold start, today this is determined according to maps. The control also compensates age-related drift in the switching times of solenoid valves.
  • BIP control : In the case of solenoid valves (especially UIS, UIP, see next section), the current curve at the solenoid valve is recognized and evaluated in order to compensate for the age-related drift here as well.
  • Shutdown : In older diesel vehicles, there was only a mechanical or electrical shutdown (currentless solenoid valve in the injection pump does not allow pressure to build up). In principle, however, the engine could continue to run, especially if it sucked in its own engine oil due to a defect. The engine could only be switched off with a manual gearbox, automatic vehicles would idle and the engine destroyed itself. Due to this behavior of a diesel engine, a shut-off flap or intake manifold flap is usually installed to prevent oil vapors from "shaking off" when switching off and continuing to run should. It is controlled accordingly and thus throttles the amount of air drawn in. This means that it can also be used to increase the EGR rate by introducing the returned exhaust gas behind the intake manifold flap.
If a lambda probe is installed, the EDC checks for undesired combustion and opens the exhaust gas recirculation valve so that the combustion in its own combustion products is extinguished. The lambda probe in the diesel engine determines the oxygen content in the exhaust gas and is used to regulate exhaust gas recirculation and to limit smoke in full load operation.
  • External torque intervention : reaction to requests from other control units in the vehicle that need support from the engine management system. This includes, for example, the automatic transmission (reduce shift jerk by reducing the torque), support of the ESP (see there) during control interventions in borderline situations such as emergency / full braking (in commercial vehicles, the engine is also fired so that the axle does not block on ice).

Other functions that can be controlled are the immobilizer , exhaust gas recirculation , glow time control (via its own control unit), control of fans, control of the additional coolant heating, switching of intake ducts (swirl control with several intake valves), boost pressure regulation, switching off the air conditioning system (strong acceleration) and cylinder deactivation.

In some cases, such functions can also be activated retrospectively on delivered vehicles, provided that additional components have been retrofitted (e.g. steering column stalk for cruise control) or are not required.

Injection pump systems

The injection systems with which the EDC works are diverse, which results from the wide range of applications of the diesel engine. In particular, common rail systems (dominant in passenger cars), distributor and in- line injection pumps , pump-nozzle systems with separate pumps and combined units.

Mechanical injection pumps with electronic support offer advantages when reliability and a mechanical fall-back level (emergency operation) are required.

Pump-nozzle systems are served by the EDC in various designs. With the “Unit Pump System” (UIP), the pump is separated from the nozzle, for example as a plug-in pump on an underlying camshaft that is connected to the nozzle in the cylinder head via a high-pressure line. Combined units are referred to as “Unit Injector System” (UIS) and are directly actuated, for example, with an overhead camshaft (especially in VW Group diesel engines from the mid-1990s, phasing out from 2010).

Considerable differences in detail result from the use of magnetic or piezo injectors. The differences include the electronics in the control unit as well as extensive software functions for controlling or correcting the injectors.

  • Timing of the injectors
  • Power supply for controlling the injectors
  • Various corrections and correction functions (temperature, voltage supply, drift, ...)

Many other tasks of the control unit are largely independent of the injection system.

Sensors & actuators

Electronic sensors:

  • Engine speed sensor + camshaft sensor as phase sensor
  • Intake air temperature sensor
  • Intake air mass flow sensor
  • Atmospheric pressure sensor (ambient pressure)
  • Boost pressure sensor at the turbocharger outlet
  • Rail pressure sensor in the high pressure system for common rail injections
  • Broadband lambda probe
  • Exhaust gas temperature sensors on the turbocharger and the lambda probes
  • Differential pressure sensor on the diesel particulate filter
  • Fuel temperature sensor
  • Coolant temperature sensor
  • Pedal encoder
  • Clutch pedal switch
  • Brake pedal switch
  • Control slide travel potentiometer in older injection systems
  • Needle motion sensor on the first injector in distributor pump systems
  • Cylinder pressure sensor for pressure-controlled combustion processes

Electric actuators:

  • Cylinder-specific control of the injectors in the common rail engine
  • Servomotor or magnetic drive for boost pressure control
  • Bypass flaps with multiple turbochargers
  • Actuator for the turbine guide vanes on VTG turbochargers
  • Throttle valve to support exhaust gas recirculation and, among other things, to interrupt the air supply for gentle engine shutdown
  • Valve for exhaust gas recirculation
  • Quantity control valve for the flow rate control of the high pressure pump in the common rail engine
  • Pressure control valve in the common rail engine
  • Fuel shutoff valve
  • Quantity control unit for moving the control slide
  • Injection adjuster solenoid valve (start of injection)
  • Glow plugs (possibly via additional control unit)
  • Motor fan (possibly via additional control unit)
  • Actuators for camshaft adjustment

literature

  • Konrad Reif (Ed.), " Diesel engine management at a glance - including exhaust technology ", Bosch Fachinformation Automobil, 2nd edition 2014, Springer Fachmedien Wiesbaden, ISBN 978-3-658-06554-6
  • Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Automotive pocket book. 25th edition, Friedr. Vieweg & Sohn Verlag, Wiesbaden, 2003, ISBN 3-528-23876-3
  • Robert Bosch (Ed.): Autoelectronics Autoelectronics. 5th completely revised and expanded edition. Vieweg & Sohn Verlag, Wiesbaden 2007, ISBN 978-3-528-23872-8
  • Kai Borgeest: Electronics in vehicle technology. 1st edition, Friedr. Vieweg & Sohn Verlag, Wiesbaden, 2007, ISBN 978-3-8348-0207-1

Individual evidence

  1. ↑ a b c See section "Electronic diesel control" in Konrad Reif (Ed.), " Overview of diesel engine management - including exhaust technology "
  2. ^ Brian Long: Zero Carbon Car: Green Technology and the Automotive Industry, Crowood, 2013, ISBN 9781847975140 .