Engine management sy stems Scuola di D ottorato di Ri cerca 2010 - Road vehicl e and engine engineering science 1 THE ENGINE MA NAGEMENT SYSTEM FOR GASOL I NE AND DI ESEL ENGINES References Automotive Handbook –R. Bos ch/SAE Gasoline-engin e management –R. Bosch/SAE Diesel-engin e management –R. Bosch/SAE
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Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
The engine management system ensures that the driver request is implemented;
for example, i t converts the accelerat ion/decelerat ion requests into a
correspon ding engine outpu t .
During its evolution electronic engine control progressively increases the number
of engine subsystems it manages and kind of tasks it performs. This development
is necessary to provide the needed accuracy and adaptability in order to minimise
exhaust emiss ions and fue l consumpt ion , provide opt im al dr iveabi l i ty for alloperating condition, minimise evaporat ive emission (gasoline engines) and
provide system diagnos is when malfunctions occur.
In order to meet these objectives the control system has been organised in
different functions. Each function manages a specific engine activity and is in
charge to accomplish some definite target. The engine operating conditions are
supervised by a finite state machine that defines the engine states and manages
the transition between these states.In the next slides a brief description of objectives, functions, components and
engine modes of the controls, both for Spark ignition engines and for Diesel
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
Exhaust EmissionsThe engine exhaust consists of products from the combustion of the air and fuel mixture. Under perfect
combustion conditions the hydrocarbons would combine in a thermal reaction with oxygen in the air to form
carbon dioxide (CO2) and water (H2O). Unfortunately perfect combustion does not occur and in addition toCO2 and water, carbon mon oxide (CO), oxides of nit rogen (NOX) and hydrocarbon (HC) occur in the
exhaust as a result of combustion reaction. Additives and impurities in the fuel also generate minute
quantities of pollutants such as lead oxides, lead halogenides and sulphur oxides. In diesel engines there
is also an appreciable amount of soot created. In Europe and United States the level of pollution, in terms
of HC, CO, NOX and, for diesel engines, particulates emitted in a vehicle’s exhaust, is regulated by law.
Fuel consumption A lot of different factors are working in partnership to make of central importance fuel economy:
The need of a better and more rational use of energetic resources to reach a sustainable growth
The fuel price increase and its market consequence
the legislation requirements both in Europe and in USA
The electronic engine control system provides the fuel metering and ignition timing precision required to
minimise fuel consumption.
Driveability Another requirement of the electronic engine control system is to provide acceptable driv eabil i ty under
al l operat ing co ndit ions . No stalls, hesitations or other objectionable roughness should occur under
vehicle operation. Driveability is influenced by almost every operation of the control system and, unlike
exhaust emissions or fuel economy, is not easily measured. Other factors that influence driveability are
the idle speed control, EGR control and evaporative emissions control.
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science
Evaporative Emissions (Gasoline engine only)Hydrocarbon (HC) emissions in the form of fuel vapours escaping from the v ehicle are closely regulated.
The prime source of these emissions is the fuel tank. Due to ambient heating of the fuel and the return ofunused hot fuel from the engine, fuel vapours are generated in the tank. The evaporative emission control
system (EECS) is used to control the evaporative HC emissions. The fuel vapours are rotated to the
intake manifold via the EECS and they are burned in the combustion process. The quantity of fuel vapours
delivered to the intake manifold must be metered such that exhaust emissions and driveability are not
adversely effected. The metering is provide by a purge control whose function is controlled by the
electronic control unit.
System DiagnosticsThe purpose of system diagnostics is to provide a warning to the driver when the contro l sy stem
determines a malfunct ion of a component or a system and to assist the service technician in identify
and correct the failure. To the driver the engine may appear to be operating correctly, but excessive
amounts of pollutants may be emitted. The ECU determines a malfunction has occurred when a sensor
signal, received during normal engine operation or during a system test, indicates there is a problem. For
critical operations such as fuel metering and ignition control, if a required sensor input is faulty, a substitute
value may be used by the ECU so that the engine will continue to operate.Starting from 2001 (Euro3) the European On Bord Diagnosis (EOBD) statutes require that, when a failure
occur in a system critical for exhaust emissions, the malfunctioning indicator lamp (MIL), visible to the
driver, must be illumined. Information on the failure is stored in the ECU. A service technician can retrieve
the information on the failure on the ECU and correct the problem.
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The key s ensors
Load sensor (Mass Flowmeters) – Mass flowmeters operate according to the hot-wire or
hot-film principle without any moving mechanical part inside the unit. The closed-loopcont ro l c i rcu i t in the meter’s hou sing mainta ins a cons tant temp erature di f ferent ia l
between a f ine plat inum wire or th in - fi lm resistor and the passing air stream. The
current required for heating provides an extremely precise, albeit nonlinear, index of air-mass
flow rate; the ECU converts the signal into linear form. Due to its closed-loop design, this air-
mass meter can monitor flow variations in the millisecond range.
Oxygen sensor – The fuel metering system of spark ignition engine employs the
exhaust-gas residual-oxy gen content as measured by the lamb da oxygen senso r to
regulate very precisely the air /fuel mixtu re for com bus t ion to the value lambd a = 1
(stoichiometric combustion). The oxygen sensor is a solid electrolyte made of ZrO ceramic
material that becomes electrically conductive for oxygen ions at temperature higher than
300°C. A galvanic charge is generated at the sensor terminals, which are design as porous
platinum thick-film electrodes and coated with a ceramic spinel layer: the voltage varies tothe greatest extend at the lambda value of 1.
Engine speed sensor – Generally a Magnet ic Speed Senso r detects wh en r ing g ear
teeth, or other ferrous p roject ions, pass the t ip of the senso r. Electrical impulses are
produced by the sensor’s internal coil and sent to the speed control unit. The signal from the
magnetic speed sensor, teeth per second (Hz.), is directly proportional to engine speed.
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The modern gasoline engine management system integrates both engine andignition control: the microprocessor continuously monitors the engine and vehicle
parameters measured by the sensors and calcu lates in real t ime :
the torque requested by the dr iver through the accelerator pedal,
the necessary f resh air ch arge to be introduced into the cylinders by actuating
a proper throttle angle,
the corresponding fuel delivery amoun t to guarantee a stoichiometric mixtureratio by actuating a definite opening time of the injectors
the adequate ign i t ion t iming (ignition angle in respect to the TDC) by
interrupting the primary winding of the ignition coil
In th e ECU there are loaded two necessary inform at ion packages :
the con tro l strategies for every engine operation mode, that are engineered
according to project targets,
and the cal ibrat ion data , mapped vs engine load and speed, temperatures,
and others parameters, that are specific value for any engine –vehicle application.
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Cranking - During engine cranking, the goals are
to get the engine started with the minimal amount or delay
and to minimize the exhaust emissions (during crank the catalyst is cold and its efficiency is very low).
To accomplish a rapid and robust start fuel must be delivered that meets the requirements for starting
for any com binat ions of engine coolant and amb ient temp eratures . For a cold engine, an increase
in the commanded A/F ratio is required due to poor fuel vaporization and “wall wetting” , which decrease
the amount of usable fuel. Wall wetting is the condensation of some of the vaporized fuel on the cold
metal surfaces in the intake port and combustion chamber. It is critical that fuel does not wet the spark
plugs, which can reduce the effectiveness of the spark plug and prevent the plug from firing.
Warm-Up - During the warm-up phase, there are three conflicting objectives:
keep the engine operating smoothly (i.e. no stalls or driveability problems),
increase exhaust temperature to quickly achieve operational temperature for catalyst (light-off) andlambda sensor so that close-loop control can begin operating,
and keep exhaust emissions and fuel consumption to a minimum.
The best method for achieving these objectives is very dependent on the specific application.
If the engine is still cold, fuel enrichment will be required to keep the engine running smoothly due,
again, to poor fuel vaporization and wall welling effects. The amount of enrichment is dependent on
engine temperature and is a correction factor to the injector pulse width.
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Cut-off - During deceleration, such as coasting or braking, there is no torque
requirement. Therefore, the fuel may be shut off until either an increase in throttle angle isdetected or the engine speed falls to a speed slightly above idle rpm. During the
development of the fuel cut-off strategy, the advantage of reduced emission and fuel
consumption must be balanced against driveability requirements. The use of fuel cut off
may change the perceived amount of engine braking felt by the driver. In addition, care
must be taken to avoid a “bump” feel when entering and when exiting the fuel cut off mode,
due to change in torque.
Idling - The objectives of the engine control system during idle are:
Provide a balance between the engine torque produced and the changing engine loads,
thus achieving a consistent idle speed even with various load changes due to accessories
(i.e. air conditioning, power steering, and electric loads) being turned on and off and during
engagement of the automatic transmission. In addition, the idle control must be able tocompensate for long-term changes in engine load, such as the reduction in engine friction
that occurs with engine break-in.
Provide the lowest idle speed that allows smooth running to achieve the lowest exhaust
emissions and fuel consumption (up to 30 percent of a vehicle fuel consumption in city
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 18
Normal - This mode practically cover the greatest part of engine operative range. When
the engine work in steady state condi t ion (i.e. without sensible variation of load and
speed) the learning phase of the auto-adaptative strategies is activated. During transition
such as acceleration or deceleration, the objective of the engine control system is to
provide a smooth transition from one engine operating condition to another (i.e., no
hesitations, stalls, bumps, or other objectionable driveability concerns), and keep exhaust
emissions and fuel consumption to a minimum.
Accelerat ion Enr ichment: When an increase in engine load and throttle angle occurs, a
corresponding increase in fuel mixture richness is required to compensate for increasedwell wetting. The sudden increase in air results in a lean mixture that must be corrected
swiftly to obtain good transitional response. The rate of change of engine load and throttle
angle are used to determine the quantity of fuel during acceleration enrichment. The
amount of fuel must be enough to provide desired performance, but not so much as to
degrade exhaust emission and fuel economy. During acceleration enrichment, the ignition
timing is set to the maximum torque without knocking.
Decelerat ion Enleanment : During deceleration the problem with well wetting is inversethan in acceleration; this means that at the end of the deceleration is possible to have a rich
mixture. If the deceleration is such that where is no torque requirement the mode becomes
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 20
Engine and vehicle speed limitation
Using the inputs of engine rpm and vehicle speed to the electronic control unit thresholds
can be establish for limiting these variables with fuel cut-off. When the maximum speed is
achieved the fuel injectors are shut off. When the speed decreases below the threshold
fuel injection resumes. These operation must be done with some caution in order to avoid
poor driveability. The rpm limitation function is used to protect the engine from overrun.
The rpm limitation is obtained through fuel modulation
Evaporative emission control system
A vapour ventilation line exits the fuel tank and enters the fuel vapour canister. The
canister consist of an active charcoal element which absorbs the vapour and allows only
air to escape to the atmosphere. Only a certain volume of fuel vapour can be contained
by the canister. The vapours in the canister must therefore be purged from and burned by
the engine so that the canister can continue to store vapours as they are generated. Toaccomplish these, another line leads from the charcoal canister to the intake manifold.
Included in this line is the canister purge solenoid valve.
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Knock cont ro l (Gasoline Engines)
Engine knock occurs when the ignition timing is advanced too far the operating condition
and causes, during the flames propagation, uncontrolled spontaneously combustion in the
end-gas that can lead to engine damage, depending on the severity and frequency.
Unfortunately, the igni t ion t iming for opt im isat ion of torque, fuel economy and
exhaust emiss ions is in c lose p rox imi ty to the ign i t ion t iming that resu l ts in eng ine
knock . As the ignition timing that results in engine knock depends from a lot of factors,such as air/fuel ratio, fuel quality, engine load, and variation in compression ratio, is not
possible to put in the ignition timing table values that are safe with respect to the knock
without penalise the engine performance. To avoid this, knock sensor (one or more) is
installed on the engine block to detect knocking. Knock sensors are usua l ly
accelerat ion sensors that provide an electr ic signal , proport ion al to the engine
vibrat ion, to the electronic co ntro l un i t . From this signal, the ECU control algorithmdetermines which cylinder or cylinders are knocking. Ignition time is retarded for those
cylinder until the knock is no longer detected. The ignition timing is then advanced again
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Turbocharger boost pressure control - The exhaust turbocharger consists of a
compressor and an exhaust turbine arranged on a common shaft. Energy from the exhaust
gas is converted to rotational energy by the exhaust turbine, which then drives the
compressor. The compressed air leaves the compressor and passes through the air cooler,
throttle valve, intake manifold, and into the cylinders. In o rder to ach ieve near co nstant air
charge pressure over a wide rpm range, the turboch arger uses a circui t that al lows
for the bypass of the exhaust gas away from the exhaust turbine throug h a valve
(wastegate) opening at a specif ied air charge press ure.
In the most modern turbocharged engines, by controlling the wastegate with a pulse-wide
modulated solenoid valve, di f ferent w astegate opening pressure can be sp eci f ied,depending o n the engine operat ive cond i t ions. Therefore, only the level of air charged
pressure required is developed. The electronic control unit uses information on engine load
from either manifold pressure or the air meter and rpm and throttle position. From these
information, a data table is referenced and the proper boost pressure (actually a duty cycle
of the control valve) is determined. On systems using manifold pressure sensor, a close-
loop control system can be developed to compare the specified value with the measured
value.
The boost p ressure cont ro l sys tem is u sua l ly used in c omb ination w i th the knock
contro l for turbocharged engines. When the ignition timing is retarded due to knock, an
increase in already high exhaust temperatures of turbocharged engines occurs. To
counteract the temperature increase, the boost pressure is reduced when the ignition timing
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 23
Torque based contro l
The torque of common S.I. engines is pr imari ly inf luenced b y the throt t le , contro l l ing the
mass air f low and therefore also the amoun t of fresh air f lowing into the comb ust ion c hamber.In addition to this, other variables are influencing the relative variation of the engine torque: ignition
timing, air/fuel ratio, deactivation of injection of certain cylinders, boost pressure control for
turbocharged engines, EGR, variable valve timing/lift and variable manifold. But there are other
torque-influencing control functions that affect engine torque as idle speed control, cruise control,
traction control, transmission control, etc.: all these additional functions drastically increased the
complexity of the complete system over the past years.
Since many “torque” interactions occur simultaneously, priorities must be established. However,
since the interactions take place in the individual functions, it’s not easy to observe the effects on theoverall system. If torque-relevant control values are directly called up by one of the systems or
subsystems, the various interactions influence each other. This requires a complex data calibration
of the various ECU’s installed in the vehicle. Between the subsystems themselves there are also
strong interdependencies of the parameters to be calibrated.
The most new strategy that introduced the clutch torque as central intermediate value became the
decisive step for solving this situation. Based on these physical values, all demands can be
coordinated, before the optimal conversion to the respective engine control values takes place(criteria such as emissions, fuel economy and protection of components).
With the torque based approach to a sys tem architecture of an engine contro l system, al l
demands whic h can be formu lated as torque or eff ic iency are def ined, based o n these
phys ical v alues. This means that interfaces within single functions as well as between (sub)
systems, are defined as torques or efficiencies, enabling a transparent and simplified system
architecture.
In the next figure a Bosch example of the torque based system is represented.
Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 30
Diesel engine management system - Comm on rai l
The common ra i l system's principal feature is that injection pressure is independent ofengine speed and injected fuel quantity, this is not the case of the previous Diesel fuel
systems.
The funct ion of pressu re generat ion and fuel in ject ion are separated b y an
accumula tor vo lum e. This volume is essential to the correct operation of the system
and is made up of the common fuel rail, the fuel lines and the injectors themselves.
The pressure is generated by a high p ressure plung er pump . For passenger cars
application, the desired rail pressure is regulated by a pressure-control valve mounted
on the high pressure side of the pump or the rail.
The system pressure generated by the high-pressure pump and regulated by a
pressure-control circuit is applied to the injector.
The injector is th e core of the system b y ensurin g correct fuel del ivery into the
combust ion chamber . At a precisely defined instant the control unit transmits an
activation signal to the injector solenoid to initiate fuel delivery. The injected fuel
quant i ty is def ined by the in jector opening t im e and the sys tem pressure.
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Comm on rai l Diesel in jector (solenoid-valve type)
Start of injection and injected fuel quantity are set by electrical activation.
The injection point is set by the angle/time system of electronic Diesel control.
The fuel is sent from the high-pressure port via an inlet passage to the nozzle and via the
inlet restrictor into the valve control chamber.
The valve control chamber is connected by the outlet restrictor, which can be opened bya solenoid valve, to the fuel return.
When closed, the outlet restrictor overcomes the hydraulic force acting on the valve plunger
opposing the force acting on the pressure shoulder of the nozzle needle. As a result, the
nozzle needle is pressed into its seat and seal off the high pressure passage to engine
chamber tight. The nozzle spring closes the injector when the engine is not running and
there is no pressure in the rail. The outlet restrictor is opened when the solenoid valve isactivated. The inlet restrictor prevents a complete pressure compensation in such a way
that the pressure in valve control chamber and thus the hydraulic force acting on the valve
control plunger decrease. The nozzle needle opens as soon as hydraulic force drops below
that acting on the pressure shoulder of the nozzle needle. Fuel is now admitted through the
injection orifices into the engine combustion chambers