An overview of the various control func-tions which are possible with the EDC con-trol units is given in Table 1. Fig. 1 opposite shows the sequence of fuel-injection calcula-tions with all funccalcula-tions, a number of which are special options. These can be activated in the ECU by the workshop when retrofit equipment is installed.
In order that the engine can run with opti-mal combustion under all operating condi-tions, the ECU calculates exactly the right injected fuel quantity for all conditions.
Here, a number of parameters must be taken into account. On a number of solenoid-valve-controlled distributor pumps, the sol-enoid valves for injected fuel quantity and start of injection are triggered by a separate pump ECU (PSG).
68 Electronic diesel control Fuel-injection control
Table 1
1 Only control-sleeve in-line injection pumps
2 Passenger cars only 3 Commercial vehicles
only
EDC variants for road vehicles: Overview of functions
1
Fuel-injection syst em In-line injection pumps
PE
Helix-controlled distributor injection pumps
VE-EDC
Solenoid-valve-controlled distributor injection pumps VE-M, VR-M
Unit Injector System and Unit Pump System UIS, UPS
Common Rail System
CR
Function
Injected-fuel-quantity limitation
External torque intervention 3
Vehicle-speed limitation 3
Vehicle-speed control
(Cruise Control)
Altitude compensation
Boost-pressure control
Idle-speed control
Intermediate-speed control 3
Active surge damping 2
BIPcontrol – – –
Intake-tract switch-off – – 2
Electronic immobilizer 2
Controlled pilot injection – – 2
Glow control 2 2
A/C switch-off 2
Auxiliary coolant heating 2 –
Cylinder-balance control 2
Control of injected fuel
quantity compensation 2 –
Fan (blower) triggering –
EGR control 2 2
Start-of-injection control
with sensor 1, 3 – –
Cylinder shutoff – – 3 3 3
Electronic diesel control Fuel-injection control 69
Accelerator-pedal sensor (driver input) Inputs
Calculations
Triggering
Vehicle-speed controller (Cruise Control), vehicle-speed limiter
Inputs from other systems (e.g. ABS, TCS, ESP)
CAN
Start Switch
Drive mode Start quantity
Fuel-quantity metering (pump map)
Timing-device
triggering Solenoid-valve
triggering Pump ECU
triggering Control of start of injection,
and/or start of delivery
Selection of the required injected fuel quantity External torque intervention
Injected-fuel-quantity limit +/
-+ + Idle-speed controller,
or controller for injected-fuel-quantity compensation
Active surge damper Smooth-running controller
Calculation of fuel-injection process in the ECU
1
æ N M K 1 7 5 5 E
Start quantity
For starting, the injected fuel quantity is cal-culated as a function of coolant temperature and cranking speed. Start-quantity signals are generated from the moment the starting switch is turned (Fig. 1, switch in “Start” po-sition) until a given minimum engine speed is reached.
The driver cannot influence the start quantity.
Drive mode
When the vehicle is being driven normally, the injected fuel quantity is a function of the accelerator-pedal setting (accelerator-pedal sensor) and of the engine speed (Fig. 1, switch in “Drive” position). Calculation depends upon maps which also take other influences into account (e.g. fuel and intake-air temperature). This permits best-possible alignment of the engine’s output to the dri-ver’s wishes.
Idle-speed control
The function of idle speed control (LLR) is to regulate a specific setpoint speed at idle when the accelerator pedal is not operated.
This can vary depending on the engine’s par-ticular operating mode. For instance, with the engine cold, the idle speed is usually set higher than when it is hot. There are further instances when the idle speed is held some-what higher. For instance, when the vehicle’s electrical-system voltage is too low, when the air-conditioning system is switched on, or when the vehicle is freewheeling. When the vehicle is driven in stop-and-go traffic, to-gether with stops at traffic lights, the engine runs a lot of the time at idle. Considerations concerning emissions and fuel consumption dictate, therefore, that idle speed should be kept as low as possible. This, of course, is a disadvantage with respect to smooth-run-ning and pulling away.
When adjusting the stipulated idle speed, the idle-speed control must cope with heav-ily fluctuating requirements. The input
power needed by the engine-driven auxiliary equipment varies considerably.
At low electrical-system voltages, for in-stance, the alternator consumes far more power than it does when the voltages are higher. In addition, the power demands from the A/C compressor, the steering pump, and the high-pressure generation for the diesel injection system must all be taken into account. Added to these external load moments is the engine’s internal friction torque which is highly dependent on engine temperature, and must also be compensated for by the idle-speed control.
In order to regulate the desired idle speed, the controller continues to adapt the in- jected fuel quantity until the actual engine
speed corresponds to the desired idle speed.
Maximum-rpm control
The maximum-rpm control ensures that the engine does not run at excessive speeds.
To avoid damage to the engine, the engine manufacturer stipulates a permissible maxi-mum speed which may only be exceeded for a very brief period.
Above the rated-power operating point, the maximum-speed governor reduces the injected fuel quantity continuously, until just above the maximum-speed point when
fuel-injection stops completely. In order to prevent engine surge, a ramp function is used to ensure that the drop-off in fuel injection is not too abrupt. This is all the more difficult to implement, the closer the nominal performance point and maximum engine speed are to each other.
70 Electronic diesel control Fuel-injection control
Intermediate-speed control
Intermediate-speed control (ZDR) is used on commercial vehicles and light-duty trucks with power take-offs, e.g.crane), or for special vehicles (e.g. ambulances with a power generator). With the control in oper-ation, the engine is regulated to a load-inde-pendent intermediate speed.
With the vehicle stationary, the intermedi-ate-speed control is activated via the cruise-control operator unit. A fixed rotational speed can be called up from the data store at the push of a button. In addition, this opera-tor unit can be used for preselecting specific engine speeds. The intermediate-speed con-trol is also applied on passenger cars with automated transmissions (e.g. Tiptronic) to control the engine speed during gearshifts.
Vehicle-speed controller (cruise control)
Cruise control allows the vehicle to be dri-ven at a constant speed. It controls the vehi-cle speed to the speed selected by the driver without him/her needing to press the accel-erator pedal. The driver can set the required speed either by operating a lever or by press-ing buttons on the steerpress-ing wheel. The in- jected fuel quantity is either increased or
decreased until the desired (set) speed is reached.
On some cruise-control applications, the ve-hicle can be accelerated beyond the current set speed by pressing the accelerator pedal.
As soon as the accelerator pedal is released, cruise control regulates the speed back down to the previously set speed.
If the driver depresses the clutch or brake pedal while cruise control is activated, con-trol is terminated. On some applications, the control can be switched off by the accelera-tor pedal.
If cruise control has been switched off, the driver only needs to shift the lever to the restore position to reselect the last speed setting.
The operator controls can also be used for a step-by-step change of the selected speed.
Vehicle-speed limiter Variable limitation
Vehicle-speed limitation (FGB, also called the limiter) limits the maximum speed to a set value, even if the driver continues to depress the accelerator pedal. On very quiet vehicles, where the engine can hardly be heard, this is a particular help for the driver who can no longer exceed speed limits inad-vertently.
The vehicle-speed limiter keeps the injected fuel quantity down to a limit corresponding to the selected maximum speed. It can be deactivated by pressing the lever or depress-ing the kickdown switch. In order to reselect the last speed setting, the driver only needs to press the lever to the restore position.
The operator controls can also be used for a step-by-step change of the selected speed.
Fixed limitation
In a number of countries, fixed maximum speeds are mandatory for certain classes of vehicles (for instance, for heavy trucks). Ve-hicle manufacturers also limit the maximum speeds of their heavy vehicles by installing a fixed speed limit which cannot be deacti-vated.
In the case of special vehicles, the driver can also select from a range of fixed, pro-grammed speed limits (for instance, when workers are standing on the platform of a garbage truck).
Electronic diesel control Fuel-injection control 71
Active-surge damping
Sudden engine-torque changes excite the ve-hicle’s drivetrain, which, as a result, goes into bucking oscillation. These oscillations are perceived by the vehicle’s occupants as un-pleasant periodic changes in acceleration (Fig. 2, a). The function of the active-surge damper (ARD) is to reduce these changes in acceleration (b).
Two different methods are used:
In case of sudden changes in the torque required by the driver (through the accel-erator pedal), a precisely matched filter function reduces drivetrain excitation (1).
The speed signals are used to detect drive-train oscillations which are then damped by an active control. In order to counter-act the drivetrain oscillations (2), the active control reduces the injected fuel quantity when rotational speed increases, and increases it when speed drops.
Smooth-running control (SRC)/
Control of injected-fuel-quantity compensation (MAR)
Presuming a constant injection duration, not all of the engine’s cylinders generate the same torque. This can be due to differences in cylinder-head sealing, as well as differ-ences in cylinder friction, and hydraulic-injection components. These differences in torque output lead to rough engine running and an increase in exhaust-gas emissions.
Smooth-running control (LRR) or fuel-balancing control (MAR) have the function of detecting these differences based on the resulting fluctuations in engine speed, and to compensate by adjusting the injected fuel quantity in the cylinder affected. Here, the rotational speed at a given cylinder after in- jection is compared to a mean speed. If the
particular cylinder’s speed is too low, the in- jected fuel quantity is increased; if it is too
high, the fuel quantity is reduced (Fig. 3).
72 Electronic diesel control Fuel-injection control
Fig. 2
a Without active-surge damper
b With active-surge damper
1 Filter function 2 Active correction
Timet
I n j e c t e d f u e l q u a n t i t y E n g i n e s p e e d n
800
20
12
0 1
1+2 b
a b a
2 s 25
1,000
rpm
mm3
1 2 Example of active-surge damper (ARD)
2
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Actual speed:
Cyl. 1 Cyl. 2 Cyl. 3 Cyl. 4 800
rpm 790 820 790
Injected fuel
quantity = + +
Desired (setpoint) speed:800 rpm Example of smooth-running control (LRR)
3
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Smooth-running control is a convenience feature. Its primary object is to ensure that the engine runs smoothly at near-idle. The injected-fuel-quantity compensation func-tion is aimed at not only improving comfort at idle, but also at reducing exhaust-gas emissions in the medium-speed ranges by ensuring identical injected fuel quantities for all cylinders.
On commercial vehicles, smooth-running control is also known as the AZG (adaptive cylinder equalization).
Injected-fuel-quantity limit
There are a number of reasons why the fuel quantity actually required by the driver, or that which is physically possible, should not always be injected. The injection of such fuel quantities could have the following effects:
Excessive exhaust-gas emissions
Excessive soot
Mechanical overloading due to high torque or excessive engine speed
Thermal overloading due to excessive temperatures of the exhaust gas, coolant, oil, or turbocharger
Thermal overloading of the solenoid valves if they are triggered too long To avoid these negative effects, a number of input variables (for instance, intake-air quantity, engine speed, and coolant temper-ature) are used to generate this limitation figure. The result is that the maximum in- jected fuel quantity is limited and with it the
maximum torque.
Engine-brake function
When a truck’s engine brake is applied, the injected fuel quantity is either reduced to zero, or the idle fuel quantity is injected. For this purpose, the ECU detects the position of the engine-brake switch.
Altitude compensation
Atmospheric pressure drops as altitude in-creases so that the cylinder is charged with less combustion air. This means that the in- jected fuel quantity must be reduced
accord-ingly, otherwise excessive soot will be emitted.
In order that the injected fuel quantity can be reduced at high altitudes, the atmospheric pressure is measured by the ambient-pressure sensor in the ECU. This reduces the injected fuel quantity at higher elevations. Atmos-pheric pressure also has an effect on boost-pressure control and torque limitation.
Cylinder shutoff
If less torque is required at high engine speeds, very little fuel needs to be injected.
As an alternative, cylinder shutoff can be applied to reduce torque. Here, half of the injectors are switched off (commercial-vehi-cle UIS, UPS, and CRS). The remaining in- jectors then inject correspondingly more
fuel which can be metered with even higher precision.
When the injectors are switched on and off, special software algorithms ensure smooth transitions without noticeable torque changes.
Electronic diesel control Fuel-injection control 73
Injector delivery compensation
New functions are added to common-rail (CR) and UIS/UPS systems to enhance the high precision of the fuel-injection system further, and ensure them for the service life of the vehicle.
With injector delivery compensation (IMA), a mass of measuring data is detected for each injector during the injector manu-facturing process. The data is then affixed to the injector in the form of a data-matrix code. With piezo-inline injectors, data on lift response is included. This data is transferred to the ECU during vehicle production.
While the engine is running, these values are used to compensate for deviations in metering and switching response.
Zero delivery calibration
The reliable mastery of small pre-injection events for the service life of the vehicle is vitally important to achieve the required level of comfort (through reduced noise) and exhaust-gas emission targets. There must be some form of compensation for fuel-quantity drifts in the injectors. For this reason, a small quantity of fuel is injected in one cylinder in overrun conditions in second- and third-generation CR systems.
The wheel-speed sensor detects the resulting torque increase as a minor dynamic change in engine speed. This increase in torque, which remains imperceptible to the driver, is clearly linked to the injected fuel quantity.
The process is then repeated for all cylinders and at various operating points. A teach-in algorithm detects minor changes in pre-injection quantity and corrects the injector triggering period accordingly for all pre-injection events.
Average delivery adaption
The deviation of the actually injected fuel quantity from the setpoint value is required to adapt exhaust-gas recirculation and charge-air pressure correctly. The average delivery adaption (MMA), therefore deter-mines the average value of the injected fuel quantity for all cylinders from the signals re-ceived from the lambda oxygen sensor and the air-mass sensor. Correction values are then calculated from the setpoint and actual values (see “Lambda closed-loop control for passenger-car diesel engines”).
The MMA teach-in function ensures a constant level of favorable exhaust-gas emis-sion values in the lower part-load range for the service life of the vehicle.
Pressure-wave correction
Injection events trigger pressure waves in the line between the nozzle and the fuel rail in all CR systems. These pressure pulses affect systematically the injected fuel quantity of later injection events (pre-injection/main injection/secondary injection) within a combustion cycle. The deviations of later injection events are dependent on the fuel quantity previously injected, the time inter-val between injection events, rail pressure, and fuel temperature. The control unit can calculate a correction factor by including these parameters in suitable compensation algorithms.
However, extremely high application re-sources are required for this correction func-tion. The benefit is the possibility of flexibly adjusting the interval between pre-injection and main injection, for example, in order to optimize combustion.
74 Electronic diesel control Fuel-injection control
Electronic control unit Injector delivery compensation 75
Fig. 1
Curves of various injectors as a function of rail pressure.
IMA reduces curve spread.
EMI Injected-fuel-quantity indicator
Fig. 2
Calculation of injector triggering period based on setpoint quantity, rail pressure, and correction values
Fig. 3
Schematic of process chain from injector delivery compensation at Bosch through to end-of-line programming at the vehicle manufac-turer’s plant
Injector delivery compensation
Functional description
Injector delivery compensation (IMA) is a soft-ware function to make fuel quantity metering more precise and increase injector efficiency on the engine. The feature has the function of correcting injected fuel quantity to the setpoint value over the entire program map individually for every injector in a CR system. This re-duces system tolerances and exhaust-gas emission spread. The compensation values required for IMA represent the difference from the setpoint value of each factory test point, and are inscribed on each injector in encoded form.
The entire engine environment is corrected by means of a correction program map that uses compensation values to calculate a cor-rection quantity. At the end of the line of the car assembly plant, the EDC compensation values belonging to the injectors fitted and their cylinder assignment are programmed in the electronic control unit using EOL program-ming. The compensation values are also re-programmed when an injector is replaced at the customer service workshop.
Necessity for this function
The technical resources required for a further restriction of the manufacturing tolerances for injectors rise exponentially and appear to be financially unprofitable. IMA is a viable solution to increase efficiency, enhance the metering precision of fuel quantity injected in the en-gine, and reduce exhaust-gas emissions.
Measured values in testing
The end-of-line test measures every injector at several points that are representative for the spread of the particular injector type. Devia-tions from setpoint values at these points (compensation values) are calculated and then inscribed on the injector head.
I n
EMI characteristic curve without IMA
with IMA data
E
Fitting the injector
Process chain
Injection time
Flash EPROM compensation program map
For all injectors of identical type Setpoint quantityQ
Cylinder 1
Cylinder 2 Cylinder 3 Cylinder 4
∆Q
Rail pressure p
Plaintext code Data matrix code
EEPROM
Considering the matrix in the injection calculation
æ S M K 2 0 0 0 E