`
`
`
`AUTOMOTIVE .-
`
`HANDBOOK
`
`EDITION
`
`
`
`.
`Page 1 of? .
`
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`BMW1046 _'
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`BMW1046
`Page 1 of 9
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`

`

`Reproduction, duplication and translation
`of this publication, including excerpts
`therefrom, is only to ensue with our
`previous written consent and with parti(cid:173)
`culars of source. Illustrations, descrip(cid:173)
`tions, schematic diagrams and other data
`serve only for explanatory purposes and
`for presentation of the text. They cannot
`be used as the basis for design, installa(cid:173)
`tion, and scope of delivery. We undertake
`no liability for conformity of the contents
`with national or local regulations.
`We reserve the right to make changes.
`The brand names given in the contents
`serve only as examples and do not repre(cid:173)
`sent the classification or preference for a
`particular manufacturer. Trade marks are
`not identified as such.
`The following companie::; kindly placed
`picture matter, diagrams and other infor(cid:173)
`mative material at our disposal:
`Audi AG, lngolstadt;
`Bayerische Motoren Werke AG, Munich;
`Behr GmbH & Co, Stuttgart;
`Brose Fahrzeugteile GmbH & Co. KG,
`Coburg;
`Continental AG, Hannover;
`Eberspacher KG, EBlingen;
`Filterwerk Mann und Hummel,
`Ludwigsburg;
`Ford-Werke AG, Cologne;
`Aktiengesellschaft Kuhnle, Kopp und
`Kausch, Frankental;
`Mannesmann Kienzle GmbH,
`Villingen-Schwenningen;
`Mercedes-Benz AG, Stuttgart;
`Pierburg GmbH, Neuss;
`RWE Energia AG, Essen;
`Volkswagen AG, Wolfsburg;
`Zahnradfabrik Friedrichshafen AG,
`Friedrichshafen.
`Source of information for motor-vehicle
`specifications: Automobil Revue Katalog
`1995.
`
`Imprint
`
`Published by:
`© Robert Bosch GmbH, 1996
`Postfach 30 02 20
`D-70442 Stuttgart
`Automotive Equipment Business Sector,
`Department for Technical Information
`(KHNDT).
`Management: Dipl.-lng.(FH) Ulrich Adler.
`
`Editor in chief:
`Dipl.-lng.(FH) Horst Bauer.
`
`Editors:
`lng.(grad.) Arne Cypra,
`Dipl.-lng. (FH) Anton Beer,
`Dipl.-lng. Hans Bauer.
`
`Production management:
`Joachim Kaiser.
`
`Layout:
`Dipl.-lng.(FH) Ulrich Adler,
`Joachim Kaiser.
`
`Translation:
`Editor in chief:
`Peter Girling
`Translated by:
`lngenieurbi.iro fur Technische und
`Wissenschaftliche Obersetzungen
`Dr. W.-D. Haehl GmbH, Stuttgart
`Member of the ALPNET Services Group
`William D. Lyon
`
`Technical graphics:
`Bauer & Partner GmbH, Stuttgart.
`Design, front cover, front matter:
`Zweckwerbung, Kirchheim u.T., Germany
`Technische Publikation, Waiblingen
`
`Distribution, 4th Edition:
`SAE Society of Automotive Engineers
`400 Commonwealth Drive
`Warrendale, PA 15096-0001 U.S.A.
`ISBN 1-56091-918-3
`
`Printed in Germany.
`lmprime en Allemagne.
`
`4th Edition. October 1996.
`
`Editorial closing: 31.08.1996
`
`BMW1046
`Page 2 of 9
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`

`

`426 Charging systems
`
`The rotary-piston supercharger incor(cid:173)
`porates a rotary piston moving about an
`internal axis. The driven inner rotor (rotary
`piston) turns through an eccentric pattern
`in the cylindrical outer rotor. The rotor
`ratios for rotary-piston superchargers are
`either 2:3 or 3:4. The rotors turn around
`fixed axes without contacting each other
`or the housing. The eccentric motion
`makes it possible for the unit to ingest
`the maximum possible volume {cham(cid:173)
`ber I) for compression and discharge
`(chamber Ill). The internal compression is
`determined by the position of the outlet
`edge A.
`A ring and pinion gear with sealed
`grease lubrication synchronizes the mo(cid:173)
`tion of the inner and outer rotors. Perma(cid:173)
`nent lubrication is also employed for the
`roller bearings. Inner and outer rotors
`employ gap seals, and usually have some
`form of coating. Piston rings provide the
`seal between working chamber and gear
`case.
`Superchargers on
`IC engines are
`usually belt-driven (toothed or V-belt).
`The coupling is either direct (continuous
`engagement) or via clutch (e.g. , solenoid(cid:173)
`operated dutch, demand actuation). The
`step-up ratio may be constant, or it may
`vary according to engine speed.
`Mechanical positive-displacement su(cid:173)
`perchargers (MVL) must be substantially
`larger than their centrifugal counterparts
`(MKL) in order to produce a given mass
`flow. The mechanical positive-displace(cid:173)
`ment supercharger is generally applied to
`small and medium-displacement engines,
`
`Cross section of a rotary-piston
`supercharger
`1 Housing
`2 Outer rotor
`3 Inner rotor
`4 Outlet edge A
`5 Chamber Ill
`6 Chamber II
`?Chamber/
`
`1
`2
`
`where the ratio between charge volume
`and space requirements is acceptable.
`
`Exhaust-gas turbochargers
`The exhaust-gas turbocharger consists of
`two turbo elements, a turbine and a com(cid:173)
`pressor, which are installed on a single
`shaft. The turbine uses the energy of the
`exhaust-gas to drive the compressor. The
`compressor, in turn, draws in fresh air
`which it supplies to the cylinders in com(cid:173)
`pressed form. The air and the mass flow
`of the exhaust gases represent the only
`coupling between the engine and the
`compressor. Turbocharger speed does
`not depend upon engine speed, but is
`rather a function of the balance of drive
`energy between the turbine and the com(cid:173)
`pressor.
`Exhaust-gas turbochargers are used
`on engines in passenger cars, trucks and
`heavy-duty engines (marine and locomo(cid:173)
`tive power plants, stationary generators).
`The typical engine-performance curves
`for this type of application are illustrated in
`a compression graph (p. 427), valid for all
`displacements, in which the surge line se(cid:173)
`parates the stable operating range on its
`right from the instable range. It is obvious
`that the instable range presents no diffi(cid:173)
`culties provided that the correct tur(cid:173)
`bocharger is selected, as all of the points
`representing potential operating conditi(cid:173)
`ons lie either on the engine operating cur(cid:173)
`ves (full load) or below them (part-load
`operation).
`
`Boost-pressure regulation via exhaust-side
`boost-pressure control valve (wastegate)
`1 Engine, 2 Exhaust-gas turbocharger,
`3 Wastegate.
`
`BMW1046
`Page 3 of 9
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`

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`Charging systems 427
`
`Variable turbine geometry (schematic
`diagram)
`1 Turbine housing, 2 Adjusting ring,
`3 Control cams, 4 Adjustable guide blades,
`5 Guide blades with adjusting lever,
`6 Air intake.
`
`Truck exhaust-gas turbocharger with
`twin-flow turbine housing
`1 Compressor housing, 2 Compressor
`wheel, 3 Turbine housing, 4 Rotor,
`5 Bearing housing, 6 Incoming exhaust-gas,
`7 Exhaust-gas discharge, 8 Atmospheric air,
`9 Compressed fresh air, 1 O Oil supply,
`11 Oil return.
`
`1
`
`2
`
`5
`
`6
`
`require various
`Different applications
`configurations. However, all exhaust-gas
`turbochargers have practically the same
`major components: the turbocharger rotor
`and shaft assembly, which combine with
`the bearing housing to form the so-called
`core assembly, and the compressor hou(cid:173)
`sing. Other components such as turbine
`housing and control elements vary accor(cid:173)
`ding to the specific application.
`Piston rings are installed on both the
`exhaust and intake sides to seal off the
`bearing housing's oil chamber. In some
`special applications sealing is enhanced
`by trapped air or a compressor-side car(cid:173)
`bon axial face seal. Friction bearings are
`generally used, installed radially as either
`floating double plain bushings or statio(cid:173)
`nary plain-bearing bushings, while multi(cid:173)
`ple-wedge surface bushings provide axial
`support. The turbocharger is connected to
`the engine's lube-oil circuit for lubrication,
`with oil supply and return lines located
`between the compressor and turbine hou(cid:173)
`sings. No additional cooling arrange(cid:173)
`ments are provided for the bearing hou(cid:173)
`sing on standard units. The temperatures
`can be maintained below critical levels
`using devices such as a heat shield, and
`by thermally isolating the bearing housing
`from the hot turbine housing, supple(cid:173)
`mented by incorporating suitable design
`elements in the bearing housing itself.
`
`Compression graph with typical engine
`operation curves valid for all displacements
`
`4.0
`
`1u = 450m/s
`2u = 300m/s
`3u = 150m/s
`
`~3.5
`t3.0
`0
`~
`~ 2.5
`
`:5 i 2.0
`
`a..
`
`1.5
`
`1.0 C2::~~=----'------'--
`0.1
`0.2
`0.3
`0.4
`Mass-flow factor <p = VfD2a
`
`Water-cooled bearing housings are em(cid:173)
`ployed for exhaust-gas temperatures in
`excess of 850°C. The rear wall of the
`compressor seals the compressor side of
`the bearing housing.
`The housing of the radial compresor is
`generally made of cast aluminum. An air
`bypass valve can be integrated in the
`housing for special applications.
`Turbine housings differ substantially
`according to intended use. Casting ma(cid:173)
`terials for turbine housings range from
`GGG 40 to NiResist D5 (depending upon
`exhaust-gas temperature). Exhaust-gas
`turbochargers for trucks incorporate a
`
`BMW1046
`Page 4 of 9
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`

`

`simple adjustment of the blade angle. The
`blades, in turn, are swiveled to the desi(cid:173)
`red angles using adjusting cams, or direc(cid:173)
`tly via adjusting levers attached to the in(cid:173)
`dividual blades. The pneumatic actuator
`can operate with either vacuum or posi(cid:173)
`tive pressure. Microelectronic control sy(cid:173)
`stems can exploit the advantages of va(cid:173)
`riable turbine-blade geometry by provi(cid:173)
`ding optimal boost pressure throughout
`the engine's operating range.
`
`Pressure-wave superchargers
`The pressure-wave supercharger exploits
`the dynamic properties of gases, using
`pressure waves to convey energy from
`the exhaust-gas to the intake air. The
`energy exchange takes place within the
`cells of the rotor (cell-type wheel), which
`also depends upon an engine-driven belt
`for synchronization and maintenance of
`the pressure-wave exchange process.
`Inside the rotor, the actual energy(cid:173)
`exchange process proceeds at the speed
`of sound. This depends upon exhaust(cid:173)
`gas temperature, meaning that it is es(cid:173)
`sentially a function of engine torque, and
`
`Pressure-wave supercharger
`1 Engine, 2 Ce/I-type compressor wheel,
`3 Belt drive, 4 High-pressure exhaust-gas,
`5 Pressurized air, 6 Low-pressure air intake,
`7 Low-pressure exhaust outlet.
`
`428 Charging systems
`
`twin-flow turbine housing in which the
`two streams join just before reaching the
`impeller. This housing configuration is
`employed to achieve pulse turbochar(cid:173)
`ging, in which the pressure of the ex(cid:173)
`haust-gas is supplemented by its kinetic
`energy.
`In contrast, in the case of constant-pres(cid:173)
`sure turbocharging, only the pressure
`energy of the exhaust-gas is utilized, and
`single-flow turbine housings can be em(cid:173)
`ployed. This configuration has become
`especially popular for use in conjunction
`with water-cooled turbine housings on
`marine engines. The exhaust-gas turbo(cid:173)
`chargers on heavy-duty engines often in(cid:173)
`corporate a nozzle ring upstream from the
`turbine. The nozzle ring provides a parti(cid:173)
`cularly smooth and consistent stream to
`the impeller while allowing fine adjustment
`of the flow through the turbine.
`Exhaust-gas turbochargers for pas(cid:173)
`senger cars generally use single-flow tur(cid:173)
`bine housings. However, the car engine's
`wide rpm range means that some form
`of turbocharger governing mechanism is
`required if the boost pressure is to be
`maintained at a relatively constant level
`throughout the engine's operating range.
`Standard practice presently favors regu(cid:173)
`lating flow on the exhaust side, whereby
`a portion of the engine's exhaust gases
`is routed past the turbine (bypass) using
`a governing mechanism
`(waste-gate)
`which can be in the form of a valve or a
`flap.
`The wastegate is actuated pneumati(cid:173)
`cally. The necessary control pressure is
`tapped-off from the pressurized side of
`the turbocharger, making it possible to
`combine turbocharger and wastegate in a
`single unit.
`The available energy is exploited more
`efficiently by governing systems incor(cid:173)
`porating
`turbines with variable blade
`geometry. With this system, the turbine's
`flow resistance is modified continuously
`to achieve maximum utilization of the
`exhaust energy under all operating con(cid:173)
`ditions.
`Of all the potential designs, adjustable
`guide blades have achieved general
`acceptance, as they combine a wide con(cid:173)
`trol range with high efficiency levels.
`An adjusting ring is rotated to provide
`
`BMW1046
`Page 5 of 9
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`

`

`Charging systems 429
`
`not engine speed. Thus the pressure(cid:173)
`wave process is optimally tailored to
`only a single operating point if a con(cid:173)
`stant step-up ratio is employed between
`engine and supercharger. To get around
`this
`disadvantage,
`appropriately-de(cid:173)
`signed "pockets" can be incorporated in
`the forward part of the housings. These
`achieve high efficiency levels extending
`through a relatively large range of engine
`operating conditions and provide a good
`overall boost curve.
`The exchange of energy occurring
`within the rotor at the speed of sound
`ensures that the pressure-wave super(cid:173)
`charger responds rapidly to changes in
`engine demand, with the actual reaction
`times being determined by the charg(cid:173)
`ing processes in the air and exhaust
`tracts.
`The pressure-wave supercharger's
`rotor is driven by the engine's crankshaft
`via a belt assembly. The rotor's cell walls
`are irregularly spaced in order to reduce
`noise. The rotor turns within a cylindrical
`housing, with the fresh air and exhaust(cid:173)
`gas tracts feeding into the housing's
`
`respective ends. On one side are low(cid:173)
`pressure air intake and pressurized air,
`while the high-pressure exhaust and low(cid:173)
`pressure exhaust-gas outlet are located
`on the other side.
`The accompanying gas-flow and state
`diagrams
`illustrate the pressure-wave
`process in a basic "Comprex" at full load
`and moderate engine speed. Developing
`(or unrolling) rotor and housing converts
`the rotation to a translation. The state dia(cid:173)
`gram contains the boundary curves for
`the four housing openings in accordance
`with local conditions. The diagrams for
`the ideal no-loss process have been
`drawn-up with the assistance of the in(cid:173)
`trinsic characteristic process.
`The pressure-wave supercharger's
`rotor is over-mounted and is provided
`with permanent grease lubrication, with
`the bearing located on the unit's air side.
`The air housing is of aluminum, the gas
`housing of NiResist materials. The rotor
`with its axial blades and chambers is cast
`using the lost-wax method. A integral
`governing mechanism regulates boost
`pressure according to demand.
`
`Gas-flow diagram (a) and state diagram (b) for pressure-wave supercharger
`A Exhaust-gas outlet, B Exhaust-gas intake, C Air intake, D Air outlet, E Residual air, fresh air,
`F Direction of rotor rotation.
`
`a
`
`b
`
`-gt
`
`::::J
`0
`(/)
`
`D
`
`2
`
`Mach curves
`Particle paths
`
`5
`
`- Velocity
`-
`--- - Pressure
`
`BMW1046
`Page 6 of 9
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`

`

`474 Engine management (spark-ignition engines)
`
`can be adjusted by varying the pulse-duty
`factor. Other types of actuator, with only a
`single winding (single-coil operation), ge(cid:173)
`nerally act against the force of a counter(cid:173)
`spring, while the movement of the arma(cid:173)
`ture can be either rotary or lateral. Under
`zero current conditions, some actuators
`revert to a "limp-home aperture" which
`is just sufficient to allow the engine to con(cid:173)
`tinue running at a minimal idle speed. A
`special case is the step motor which
`moves by one increment (step) per con(cid:173)
`trol pulse. A gear-drive converts its rota(cid:173)
`tion into linear motion.
`
`Electronic throttle control
`(EGas or drive-by-wire)
`EGas departs from conventional mecha(cid:173)
`nical systems by replacing the Bowden
`cable or linkage with an ECU and electric
`motor for throttle-valve control. The sys(cid:173)
`tem can thus control and modify throttle
`valve aperture with reference to nume(cid:173)
`rous operating parameters, performing
`tasks such as torque reduction for elec(cid:173)
`tronic traction control (ASR).
`A travel sensor monitors the position of
`the accelerator pedal and transmits this
`information to the ECU. The ECU proces(cid:173)
`ses this travel-sensor signal along with
`data transmitted
`from other systems
`(such as ASR and Motronic) to calculate
`the control signal for the throttle actuator.
`A closed-loop control circuit ensures pre(cid:173)
`cise adjustment of the throttle angle in
`a process based on signals transmitted
`to the ECU from a potentiometer within
`the actuator.
`The ECU continuously monitors all
`components to ensure that the system is
`operating correctly. Because the ECU
`processor and all sensors have backup
`units iredundancy), the system can com(cid:173)
`pare the signal pairs to verify the monito(cid:173)
`ring processes.
`While some systems rely solely on an
`electrical connection between the accele(cid:173)
`rator pedal and the actuator, other avail(cid:173)
`able units
`incorporate a mechanical
`connection element (such as a Bowden
`cable). This permits "limp-home" should a
`malfunction cause the system to deac(cid:173)
`tivate the actuator.
`Because it regulates the throttle valve el-
`
`Electronic throttle control (ETC)
`1 Accelerator pedal, 2 Pedal-position
`sensor, 3 ECU with 3a microprocessor and
`3b data bus, 4 Throttle actuator.
`
`Engine
`management
`
`• 1 ~~ r'Yr'YI
`~ n:::::-a ~ ,i;J
`
`r - ·- -- - -- -- ·- -- -- --- '
`i
`. 3
`I
`.
`
`ABS/ASR
`
`ectronically, EGas can assume various
`functions to enhance driving safety, con(cid:173)
`venience and engine performance. The
`safety measures include both ASR and
`engine drag-torque control. The latter em(cid:173)
`ploys programmed throttle openings to re(cid:173)
`duce the drag torque induced by engine
`braking to uncritical levels for enhanced
`rear-wheel traction.
`Features for driving convenience and
`comfort include the cruise control ("Tem(cid:173)
`pomat") and the option of using EGas
`to reduce load-change reactions under
`transient conditions.
`The idle-charge control system, incor(cid:173)
`porating a separate actuator for the
`throttle bypass on systems without EGas,
`is an example of an engine-management
`function. Development now focuses on
`adapting EGas to enhance other aspects
`of engine performance (e.g., emissions
`and fuel economy).
`
`Electronic boost-pressure control
`With turbocharged engines the primary
`goal -
`to achieve the specified maxi(cid:173)
`mum performance levels -
`is joined by
`a second priority: providing effective
`boost at low rpm. The ultimate objective is
`to maximize efficiency levels. The means
`
`BMW1046
`Page 7 of 9
`
`

`

`Engine management (spark-ignition engines) 475
`
`to this end is to design the boost curve
`for rapid initial pressurization. Upon com(cid:173)
`pletion of this initial phase boost levels
`should even out to furnish consistently
`high torque throughout a maximum range
`of engine speeds and throttle positions.
`Exhaust-gas turbochargers with me(cid:173)
`chanical wastegates are severely limited
`in their ability to meet these requirements.
`In contrast, a properly designed turbo(cid:173)
`charger equipped with electronic boost
`control can combine virtually ideal boost
`progression characteristics
`throughout
`the entire rpm range with satisfactory
`control response during transitions. The
`boost pressure specifications for the va(cid:173)
`rious engine speeds and load factors are
`stored in program maps. Turbocharger
`and wastegate valve are designed to
`ensure that a sufficiently long control
`stroke is available, allowing a solenoid
`valve operating at a specific duty cycle to
`maintain the programmed boost pressure
`by continuously adjusting the wastegate-
`
`control valve to reflect instantaneous
`conditions. Potential sources of load data
`include intake-manifold pressure, intake(cid:173)
`air quantity and mass air flow.
`Boost-pressure control systems are al(cid:173)
`ways used together with knock control to
`obtain high specific engine outputs. This
`makes it possible to exploit the potential
`for advancing the timing without risking
`preignition damage.
`As soon as combustion knock is detec(cid:173)
`ted (e.g., owing to low-octane fuel), the
`system responds by reducing ignition ad(cid:173)
`vance.
`from
`turbo-charger
`the
`To prevent
`being exposed to excessive exhaust-gas
`temperatures, the system accompanies
`extreme reductions in advance angle by
`enrichening the mixture. If the pre-ignition
`tendency is still present at this point, the
`next step is to reduce the boost pressure.
`
`Combined knock and boost control
`1 Intake air, 2 Compressor, 3 Turbine, 4 To exhaust system, 5 Waste-gate control valve,
`6 Throttle-valve, 7 Throttle potentiometer, 8 Temperature sensor, 9 Knock sensor, 1 O Control valve,
`11 ECU. p 1 Pressure before compressor, p2 Boost pressure, p2 ' Intake-manifold pressure,
`p3 Exhaust back pressure, SK Knock-sensor signal, SR Engine-speed signal, TL Boost-air
`temperature, VA Exhaust-gas flow, VT Flow through turbine, Vw Flow through wastegate,
`a0 Throttle angle, a2 Ignition advance angle.
`
`11
`
`BMW1046
`Page 8 of 9
`
`

`

`nition engines)
`
`Knock control
`
`Function
`Internal-combustion engines are dama(cid:173)
`ged by combustion knock (see p. 366).
`Higher combustion ratios intended to im(cid:173)
`prove fuel economy and fluctuations in
`fuel quality both increase the engine's
`tendency to knock. Knock control serves
`to prevent preignition under all operating
`conditions. With high compression ratios,
`the knock limit is often within the ignition(cid:173)
`timing range for minimum fuel consump(cid:173)
`tion or later. Knock control makes it pos(cid:173)
`sible to design the engine for operation
`in this range without additional safety
`margins.
`
`Operation
`From a suitable installation location on
`the engine block, the knock sensor moni(cid:173)
`tors structure-borne noise, which it trans(cid:173)
`forms into an electrical signal suitable
`for transmission to the ECU. An evalua(cid:173)
`tion circuit in the ECU adjusts the ampli(cid:173)
`tude of the noise signal, adapting it for
`processing at both low or high engine
`speeds, and on quiet or loud engines. A
`"measuring window," synchronized to the
`crankshaft, and a band pass are used
`to filter out the data which characterize
`knocking. This information is then com(cid:173)
`pared with signals from knockless com-
`
`Knock control
`Control algorithm for ignition adjustments with
`a 4-cylinder engine.
`K, ... s knock in cylinders 1 ... 3.
`Cylinder 4: No knock.
`a Delay prior to ignition retard
`b Retardation, c Delay before return to original
`ignition point, d Spark advance.
`
`az
`"*, K1 K2 13 K1
`K3
`..I,
`~ ..1,-.Nl,..I,
`Cyl.
`4
`~
`~ 1-_-_-r t;---;-\-, r.._-__ -_--j""-."-.~---- ----- -::_ ~:--_-..r......,·
`y· ----
`-fi
`L--· - ••3-.r·
`/}~J-7--+i
`~
`,2
`b
`d
`·c .!? L-_,,....""'-+ .......................... ~.L.u. ........ ___.
`13421342
`Combustion cycles in
`individual cylinders -
`
`C
`
`-
`
`Engine management (spark-ignition engines) 455
`
`Knock sensor
`1 Seismic mass, 2 Potting compound,
`3 Piezoceramic element, 4 Contacts,
`5 Terminals.
`
`~ - --1
`...,... ___ 2
`
`transmitted to an annular piezoceramic
`disk. Here the oscillations induce alterna(cid:173)
`ting electrical surface voltages for trans(cid:173)
`mission to the ECU through a shielded
`wire.
`Two knock sensors may be required
`to monitor pre-ignition on engines with
`higher numbers of cylinders. These are
`then synchronized with the camshaft,
`allowing the system to correlate knock
`sensor signals with individual cylinders.
`
`Monitoring functions
`The driver must be informed of any failure
`in the knock-control system. The ECU
`therefore combines continuous sensor
`monitoring with self-test functions de(cid:173)
`signed to ensure correct response. In
`case of malfunction, it protects the engine
`by permanently retarding the ignition. A
`dashboard display provides notice in case
`of malfunction, or if the closed-loop con(cid:173)
`troller reaches the limits of its control
`range.
`
`bustion processes to determine whether
`preignition is present. The closed-loop
`control circuit uses actuators to adjust the
`engine and eliminate the knock. Ignition
`timing is an especially effective manipula(cid:173)
`ted variable, as it permits the most rapid
`corrections.
`When knock occurs, the ignition timing
`is retarded for a certain number of cycles,
`after which it gradually moves back to(cid:173)
`ward its original setting. The ability to re(cid:173)
`tard the timing for each cylinder individu(cid:173)
`ally is of major importance.
`The objective is to restrict the timing
`adjustment to the cylinders where knock
`is actually occurring, allowing the others
`to continue operating at their respective
`optima.
`
`Knock control in turbocharged
`engines
`With turbocharged engines, ignition-tim(cid:173)
`ing adjustments are joined by a second
`option: The boost/intake pressure can be
`employed as a manipulated variable. In
`the illustration, the knock sensor is instal(cid:173)
`led between cylinders 2 and 3 on the
`intake side. The ECU adapts the ignition
`while simultaneously activating the duty(cid:173)
`cycle solenoid, opening the exhaust-side
`wastegate to bypass the turbine. This
`reduces the boost pressure and with it
`the preignition tendency. The pressure
`sensor in the intake manifold provides
`load data.
`When used in combination with circuits
`to monitor throttle-valve position
`this
`system allows boost-pressure control
`capable of preventing excessive boost
`pressures under static operation while
`simultaneously reducing back-pressure
`for enhanced economy (see "boost-pres(cid:173)
`sure control" p. 426 and 475).
`
`Supplementary knock control
`It is quite easy to combine knock control
`with electronic ignition; this arrangement
`is frequently employed in Motronic sys(cid:173)
`tems (p. 481).
`
`Knock sensor
`The knock sensor is installed in a loca(cid:173)
`tion selected to provide optimum knock(cid:173)
`detection for all cylinders. The structure(cid:173)
`borne noise from the engine block is
`
`BMW1046
`Page 9 of 9
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