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Engine management systems Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 1 THE ENGINE MANAGEMENT SYSTEM FOR GASOLINE.

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Presentation on theme: "Engine management systems Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 1 THE ENGINE MANAGEMENT SYSTEM FOR GASOLINE."— Presentation transcript:

1 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 1 THE ENGINE MANAGEMENT SYSTEM FOR GASOLINE AND DIESEL ENGINES References Automotive Handbook – R. Bosch/SAE Gasoline-engine management – R. Bosch/SAE Diesel-engine management – R.Bosch/SAE

2 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science The engine management system ensures that the driver request is implemented; for example, it converts the acceleration/deceleration requests into a corresponding engine output. 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 emissions and fuel consumption, provide optimal driveability for all operating condition, minimise evaporative emission (gasoline engines) and provide system diagnosis 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 engine, is performed. The engine management system

3 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science Exhaust Emissions The 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 (CO 2 ) and water (H 2 O). Unfortunately perfect combustion does not occur and in addition to CO 2 and water, carbon monoxide (CO), oxides of nitrogen (NO X ) 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, NO X and, for diesel engines, particulates emitted in a vehicles 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 driveability under all operating conditions. 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.

4 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science Evaporative Emissions (Gasoline engine only) Hydrocarbon (HC) emissions in the form of fuel vapours escaping from the vehicle are closely regulated. The prime source of these emissions is the fuel tank. Due to ambient heating of the fuel and the return of unused 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 Diagnostics The purpose of system diagnostics is to provide a warning to the driver when the control system determines a malfunction 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.

5 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 5 ECU SENSORS ACTUATORS From and towards other vehicle systems control The engine control system includes: sensors for the detection of the engine operating modes electronic control unit (ECU) which elaborates the signal values supplied by the sensor, according to defined control strategies and algorithms, and defines the actions to be delivered to the actuators actuators which have the task to actuate the defined commands System layout

6 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 6 The key sensors 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-loop control circuit in the meters housing maintains a constant temperature differential between a fine platinum wire or thin-film 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-oxygen content as measured by the lambda oxygen sensor to regulate very precisely the air/fuel mixture for combustion to the value lambda = 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 to the greatest extend at the lambda value of 1. Engine speed sensor – Generally a Magnetic Speed Sensor detects when ring gear teeth, or other ferrous projections, pass the tip of the sensor. Electrical impulses are produced by the sensors 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.

7 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 7 Hot-wire Air Flow Meter Last generation Bosch Source

8 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 8 Plug-in sensor housing Hybrid-section cover Measuring channel cover Sensor chip (CMF) Carrier plate Hybrid SHF O-ring Temperature sensor Hot-wire Air Flow Meter Bosch Source

9 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 9 Nernst Type Oxygen Sensors Thimble typePlanar type Exhaust gas P O 2 Air Exhaust gas P O 2 Sensing cell Reference air duct Heater ZrO 2 - Ceramic Electrodes Porous protective layer Insulation USUS In 4F4F RT P O 2 U reg Sensor characteristic curve Normalized A / F ratio Sensor voltage = Bosch Source

10 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 10 Thimble type ZrO 2 oxygen sensor LSH25 Oxygen content sensor (Lambda sensor) Bosch Source

11 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 11 Gasoline injector – The fuel injector essentially consist of a valve housing with solenoid coil and electric connections, a valve seat with spray- orifice disk and a moving valve needle with solenoid armature. When the coil is de-energized, the spring and the force resulting from the fuel pressure press the valve needle against the valve seat to seal the fuel supply system from the intake manifold. When the coil is energized, it generates a magnetic field which pulls in the armature and lifts the valve needle off of its seat to allow fuel to flow through the fuel injector. The ignition coil – It is a energy-charged high-voltage source similar to a transformer. Energy is supplied by the vehicle electrical system during the dwell period or charging time. At the moment of ignition, which at the same time is the end of the charging time, the energy is then transferred with the required high voltage and sparking energy to the spark plug. The ignition coil comprises two coils that are magnetically linked by an iron core. The key actuators

12 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 12 The gasoline injector The gasoline engine control system Fuel rail ECU Servo throttle body Pressure regulator Injector Knock sensor Bosch Source

13 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science ME 7 Motronic Components (Evoluted gasoline management system ) Bosch Source

14 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science MOTRONIC - Torque Guided Engine Management Systems M7 System Overview with OBD and RLFS Bosch Source

15 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 15 The modern gasoline engine management system integrates both engine and ignition control: the microprocessor continuously monitors the engine and vehicle parameters measured by the sensors and calculates in real time: the torque requested by the driver through the accelerator pedal, the necessary fresh air charge to be introduced into the cylinders by actuating a proper throttle angle, the corresponding fuel delivery amount to guarantee a stoichiometric mixture ratio by actuating a definite opening time of the injectors the adequate ignition timing (ignition angle in respect to the TDC) by interrupting the primary winding of the ignition coil In the ECU there are loaded two necessary information packages: the control strategies for every engine operation mode, that are engineered according to project targets, and the calibration data, mapped vs engine load and speed, temperatures, and others parameters, that are specific value for any engine –vehicle application. The control strategies

16 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 16 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 combinations of engine coolant and ambient temperatures. 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) and lambda 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. The control strategies

17 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 17 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 is detected 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 to compensate 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 driving occurs during idling). The control strategies

18 Engine management systems Scuola di Dottorato di Ricerca 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 condition (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. Acceleration Enrichment:When an increase in engine load and throttle angle occurs, a corresponding increase in fuel mixture richness is required to compensate for increased well 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. Deceleration Enleanment:During deceleration the problem with well wetting is inverse than 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 cut-off. The control strategies

19 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 19 Elektronische Zündungssteuerung mit Klopfregelung Motronic Klopfsensor-Signal ohne KlopfenKlopfsensor-Signal mit Klopfen Knock (acceleration) sensor Bosch Source

20 Engine management systems Scuola di Dottorato di Ricerca 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. To accomplish these, another line leads from the charcoal canister to the intake manifold. Included in this line is the canister purge solenoid valve. The control strategies

21 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 21 Knock control (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 ignition timing for optimisation of torque, fuel economy and exhaust emissions is in close proximity to the ignition timing that results in engine 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 usually acceleration sensors that provide an electric signal, proportional to the engine vibration, to the electronic control unit. From this signal, the ECU control algorithm determines 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 until knocking is detected The control strategies

22 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 22 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 order to achieve near constant air charge pressure over a wide rpm range, the turbocharger uses a circuit that allows for the bypass of the exhaust gas away from the exhaust turbine through a valve (wastegate) opening at a specified air charge pressure. In the most modern turbocharged engines, by controlling the wastegate with a pulse-wide modulated solenoid valve, different wastegate opening pressure can be specified, depending on the engine operative conditions. 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 pressure control system is usually used in combination with the knock control 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 is retarded past a predetermined threshold. The control strategies

23 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 23 Torque based control The torque of common S.I. engines is primarily influenced by the throttle, controlling the mass airflow and therefore also the amount of fresh air flowing into the combustion chamber. 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, its not easy to observe the effects on the overall 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 ECUs 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 system architecture of an engine control system, all demands which can be formulated as torque or efficiency are defined, based on these physical values. 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. The control strategies

24 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science MOTRONIC - Torque Guided Engine Management Systems Torque Based System Structure for PFI Systems w/o ETC Ind. fuel cut-off Torque demand coordinator Idle speed actuator Ignition timing Injection time Waste gate control Coordination of torque and efficiency demands Realization of desired torque Torque conversion Torque External Torque Demands Vehicle dynamic control Driveability Internal Torque Demands Engine start-up Idle speed control Engine speed limitation Engine protection Efficiency Demands Engine start-up Catalyst heating Idle speed control Efficiency Engine Driver Throttle angle Calculation of drivers request Current cylinder charge & engine speed Calculation of drivers request Current cylinder charge & engine speed Calculation of drivers request Current cylinder charge & engine speed Calculation of drivers request Current cylinder charge & engine speed Calculation of drivers request Bosch Source

25 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 25 UNIJET 2000 ECU Electronic Control Unit with Advanced Injector Drivers From Pilot Injection... TDC+60°-60° PILOTMAIN COMBUSTIO N RATE FUELLING … to Sequential Multiple Injections TDC+60°-60° PILOTPREMAINAFTER COMBUSTIO N RATE FUELLING POST Multiple Injection: From UNIJET to MULTIJET CRF Source

26 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 26 MOTRONIC - Torque Guided Engine Management Systems Fuel Injection Concepts for S.I. Engines Port Fuel InjectionGasoline Direct Injection Mixture transport over the intake stroke Mixture transport by charge motion and piston geometry Bosch Source

27 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 27 BMW 3.0l twin turbo direct injection gasoline engine

28 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 28

29 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 29 Diesel engine management system - Common rail In the Diesel engine the combustion torque is generated in the power cycle and is determined by the following variables if the excess air is sufficient: the supplied fuel mass, the start of combustion determined by the start of injection the injection/combustion process In addition, the maximum speed torque is limited by: smoke emission the cylinder pressure the temperature load of different components and the mechanical load of the drive train The primary function of engine management is to adjust the torque generated by the engine or, in some applications, to adjust a specific engine speed within the permitted operating range (i.e. idling). The control of exhaust emission and noise is performed by engine management by changing the following varaibles: cylinder charge exhaust gas recirculation rate (charge dilution) charge motion (intake swirl) start of injection injection pressure rate of discharge curve control (pilot injection, divided fuel injection, etc)

30 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 30 Diesel engine management system - Common rail The common rail system's principal feature is that injection pressure is independent of engine speed and injected fuel quantity, this is not the case of the previous Diesel fuel systems. The function of pressure generation and fuel injection are separated by an accumulator volume. 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 pressure plunger 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 the core of the system by ensuring correct fuel delivery into the combustion chamber. At a precisely defined instant the control unit transmits an activation signal to the injector solenoid to initiate fuel delivery. The injected fuel quantity is defined by the injector opening time and the system pressure.

31 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science Strictly confidential | DS/SGF | 07/04/2005 | © Robert Bosch GmbH reserves all rights even in the event of industrial property rights. We reserve all rights of disposal such as copying and passing on to third parties. System overview Common Rail Source: DS/EAC5 Sr e © Robert Bosch GmbH reserves all rights even in event of industrial rights. We reserve all rights of disposal such as copying and passing on third parties other sensors Tank Control unit High pressure pump CPx other actuators Prefilter Fuel filter high pressure backflow pressure Pressure regulating valve DRV Tank Electrical presupply pump EKP Injector (1...n) Metering unit ZME Rail pressure sensor RDS4 EKP pressure Rail (LWR) electrical lines Engine speed (crank) Engine speed (cam) Accelerator pedal return line pressure Throttle (1x) 0.85 Throttle (1x/injector) 0.85 mm Throttle Diesel Systems Bosch Source

32 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 32 Laser Welded Rail Low pressure fitting connection to system backflow ECU RDS4 ECU Engine Fixation Rail Body Throttles (optional) High pressure fitting pipe connection to injectors pipe connection to pump DRV Rail Pressure sensor Pressure Regulator Valve Diesel Systems Bosch Source

33 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 33 CRS2.2 - High Pressure Pump (1600 bar) CP1H CP3 Diesel Systems Bosch Source

34 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 34 Common rail Diesel injector (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 by a 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 is activated. 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 The key actuators

35 Engine management systems Scuola di Dottorato di Ricerca Road vehicle and engine engineering science 35 LINIETTORE DEL COMMON RAIL Bosch Source


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