The engine-management system is continu-ally being integrated more closely into the overall vehicle system. Through the CAN bus, vehicle dynamics systems such as TCS, and comfort and convenience systems such as cruise control, have a direct influence on theElectronicDieselControl (EDC). Apart from this, much of the information regis-tered and/or calculated in or by the engine management system must be passed on to other ECUs through the CAN bus.
In order to be able to incorporate the EDC even more efficiently in a functional alliance with other ECUs, and implement other changes rapidly and effectively, it was neces-sary to make far-reaching changes to the newest-generation controls. These changes resulted in the torque-controlled EDC which was introduced with the EDC16. The main feature is the changeover of the module interfaces to the parameters, as commonly encountered in practice in the vehicle.
Engine parameters
Essentially, an IC engine’s output can be de-fined using the three parameters: powerP , engine speedn , and torqueM .
For 2 diesel engines. Fig. 1 compares typi-cal curves of torque and power as a function of engine speed. Basically speaking, the fol-lowing equation applies:
P = 2 ·π· n · M
In other words, it suffices to use the torque as the reference (command) variable. Engine power then results from the above equation.
Since power output cannot be measured di-rectly, torque has turned out to be a suitable reference (command) variable for engine management.
Torque control
When accelerating, the driver uses the accel-erator pedal (sensor) to directly demand a
given torque from the engine. At the same time, but independent of the driver’s re-quirements, via the interfaces other vehicle systems submit torque demands resulting from the power requirements of the particu-lar component (e.g. air conditioner, alterna-tor). Using these torque-requirement inputs, the engine management calculates the out-put torque to be generated by the engine and controls the fuel-injection and air-sys-tem actuators accordingly. This method has the following advantages:
No single system (for instance, boost pres-sure, fuel injection, pre-glow) has a direct effect on engine management. This en-ables 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 di-rectly concern the engine management can be designed to function identically for diesel and gasoline engines.
Extensions to the system can be imple-mented quickly.
Electronic diesel control Torque-controlled EDC systems 81
Fig. 1
a Year of manufacture 1968
b Year of manufacture 1998
P o w e r o u t p u t
0 25 50 75 kW
T o r q u e
0 0
Engine speed 1,000 2,000 3,000 4,000 100
200 300 N·m
a b a b
rpm Example of the torque and power-output curves as a function of engine speed for two passenger-car diesel engines with approx. 2.2 l displacement
1
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Engine-management sequence
Fig. 2 shows (schematically) the processing of the setpoint inputs in the engine ECU. In order to be able to fulfill their assignments efficiently, the engine management’s control functions all require a wide range of sensor signals and information from other ECUs in the vehicle.
Propulsion torque
The driver’s input (that is, the signal from the accelerator-pedal sensor) is interpreted by the engine management as the request for a propulsive torque. The inputs from the cruise control and the vehicle speed limiter are processed in exactly the same manner.
Following this selection of the desired propulsive torque, should the situation arise, the vehicle-dynamics system (TCS, ESP) in-creases the desired torque value when there is the danger of wheel lockup and decreases it when the wheels show a tendency to spin.
Further external torque demands
The drivetrain’s torque adaptation must be taken into account (drivetrain transmission ratio). This is defined for the most part by the ratio of the particular gear, or by the torque-converter efficiency in the case of automatic transmissions. On vehicles with an auto-matic-gearbox, the transmission control stip-ulates the torque requirement during the ac-tual gear shift. Apart from reducing the load on the transmission,reduced torque at this point results in a comfortable, smooth gear shift. In addition,the torque required by other engine-powered units (for instance, air-conditioner compressor, alternator, servo pump) is determined. This torque require-ment is calculated either by the units them-selves or by the engine management.
Calculation is based on unit power and rotational speed, and the engine manage-ment adds up the various torque require-ments. The vehicle’s drivability remains unchanged despite varying requirements from the auxiliary units and changes in the engine’s operating state.
Internal torque demands
At this stage, the idle-speed control and the active surge damper intervene.
For instance, if demanded by the situa-tion, in order to prevent mechanical dam-age, or excessive smoke due to the injection of too much fuel, the torque limitation reduces the internal torque requirement.
In contrast to the previous engine-manage-ment systems, limitations are no longer only applied to the injected fuel-quantity, but in-stead, depending upon the required effects, also to the particular physical quantity in-volved.
The engine’s losses are also taken into account (e.g. friction, drive for the high-pressure pump). The torque represents the engine’s measurable effects to the outside.
The engine management, though, can only generate these effects in conjunction with the correct fuel injection together with the correct injection point, and the necessary marginal conditions as apply to the air-in-take system (e.g. boost pressure and EGR rate). The required injected fuel quantity is determined using the current combustion efficiency. The calculated fuel quantity is limited by a protective function (for in-stance, protection against overheating), and if necessary can be varied by smooth-running control (SRC). During engine start, the injected fuel quantity is not determined by external inputs such as those from the driver, but rather by the separate “start-quantity control” function.
Actuator triggering
Finally, the desired values for the injected fuel quantity are used to generate the trig-gering data for the injection pump and/or the injectors, and for defining the optimum operating point for the intake-air system.
82 Electronic diesel control Torque-controlled EDC systems
Electronic diesel control Torque-controlled EDC systems 83
Driver input: Selection of the
desired propulsion torque
Propulsion torque:
Further external torque demands - Accelerator-pedal
sensor
- Vehicle-speed control (cruise control)
- Vehicle-speed limitation
Intake-air system - Turbocharger - EGR ...
Injection system - Fuel-injection
pump - Injectors ...
Inputs:
Actuator triggering
- Boost pressure - EGR rate - ...
External inputs
Input:
- Start of delivery - Timing device - Rail pressure
- ... (depending on system) Input from the
vehicle-dynamics systems:
Drivetrain transm.
Input from the transmission ECU
Coordination of the drivetrain torque
Start quantity Engine loading due
to auxiliary units
Coordination of the propulsion torque - TCS
- ESP Data
exchange Sensor
signals
Internal sequences Data trans-mission possible through CAN
Fuel-quantity input
Start Drive
mode Engine efficiency
Fuel-quantity limit
Smooth-running control Internal torque requirements
Control of the engine torque (internal functions) Idle-speed control
Active-surge damping
Torque limitation
Engine-management sequence for torque-controlled diesel injection
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