The Engine unit Management Systems Engineering Essay

Engine management system handles the engine motor in response to both engine unit and vehicle inputs. Today's automobile EMS consists of a microprocessor based electronic control device and (ECU) and a big number of electronic and electromechanical detectors and actuators. Sensors are the devices which monitor the engine unit and detect parameters like crank angle, engine acceleration and lambda values etc. ECU can determine the ignition timing, amount of gas and other parameters to keep an engine unit running utilizing the input values which can be determined from the inputs from the sensors. Based on all those calculations ECU (Electronic Control Device) control all the actuators to obtain best possible engine motor operation in terms of fuel ingestion, performance, exhaust gas emissions and generating smoothness.

Fig. 1. 1 popular mechanics (1997) online image

Sensors that can be found in an average unit installation (Fig. 1. 1) are the following with their transmission type (analogue or digital).

Crankshaft position (digital)

It uses inductive pickup technology. It can determine the positioning of crankshaft producing an analogue transmission which is then signal-conditioned by using a high-gain amplifier to create pulses of constant voltage. These pulses can be produced on every degree of crank position.

Camshaft position (digital)

Camshaft position sensor works together crankshaft position sensor. Camshaft position sensor tells the ECU which stroke number one piston is on so that it is aware of which cylinder to flame or inject gasoline into. The crank position sensor can only send a sign sharing with the ECU that number 1 piston is at TDC but it can't inform it which heart stroke could be compression or exhaust.

Combined information from both these detectors is called crankshaft timing information which is utilized to control the following

Ignition timing

Ignition coil on time

Start of injection

Throttle position (analogue)

Throttle position is provided by the potentiometer which suggests to the engine management system the load being demanded by driver. This immediate knowledge of throttle transients allows to employ a technique for managing fuelling changes during transients. Small changes in throttle position have a sizable influence on the ventilation. When throttle starts off to open, an idle rate control valve allows an air flow to bypass the throttle dish to provide idle speed control.

Air stream rate (analogue)

Air stream rate is assessed by pivoting a truck with potentiometer or by a hot line probe, which is more prevalent due to its fast response (5ms compared with 35ms for the vane). (Rock and Ball 2004)

Air mass circulation is assessed by keeping the line at a regular heat range above the air temp and measuring the power that is dissipated by the line. This air flow rate can be used for determining the amount of gas to be injected and determining the engine unit operating point.

Inlet manifold overall pressure (analogue)

The inlet manifold pressure is measured by way of a piezo-resistive transducer which consists of a silicone diaphragm that has strain gauges etched onto its areas.

The engine quickness, air temperatures and manifold definite pressure allow estimating mass circulation rate in to the engine, which when weighed against air mass circulation rate be able to presume the amount of exhaust gas recirculation.

Air temps and Coolant temperatures (Analogue)

Temperatures are assessed by thermistors which coupled with measurements taken by other detectors help out with the estimation of mass circulation rate into the engine.

Lambda Sensor (Digital or Analogue)

The ECU tries to maintain, normally, a certain air-fuel percentage by interpreting the information it gains from the air sensor. The primary goal is a bargain between power, gasoline market, and emissions, and in most cases is achieved by an air-fuel-ratio near to stoichiometric.

Knock detector (analogue)

A knock sensor can be an accelerometer which senses engine motor structural vibrations. In the commencement of knock, accelerometer detects it and slows down the ignition, in doing this averting damage to the engine.

Advantage of knock detector is that it provides a safety advantage which usually could be obtained insurance firms less compression ratio or completely retarded ignition.

Waste-gate control sensor

In addition to above mentioned sensors, in a turbocharged engine unit a waste-gate control is also used for minimizing turbo lag. Additional gain is that it can help to limit the maximum cylinder pressure. Waste-gate is an easy flap valve built-in the turbine casing.

Boost pressure in sensed with help of inlet manifold pressure sensor, when it goes up above a certain level, some of the exhaust stream is permitted to bypass the turbine. It stops the turbine over speeding and restricts the boost pressure from the compressor.

Working of ECU

Control of fuel mixture

An engine unit control product (ECU) determines the amount of petrol to inject predicated on a number of parameters. In case the throttle pedal is pressed further down, this will open the throttle body and allow more air to be taken into the engine motor. The ECU will inject more fuel regarding to how much air is passing into the engine unit. If the engine has not heated up yet, more gas will be injected (producing the engine to run slightly 'abundant' before engine unit warms up).

Control of ignition timing

A spark ignition engine takes a spark to start combustion in the combustion chamber. An ECU can change the precise timing of the spark called ignition timing to provide better vitality and economy. When the ECU picks up knock, it'll delay the timing of the spark to prevent this. Another, more common source, cause, of knock/ping is functioning the engine motor in too low of any RPM range for the "work" dependence on the moment. The ECU managing an automatic transmitting would simply downshift the transmission if this were the cause of knock/ping.

Control of idle speed

The engine motor RPM is watched by the crankshaft position sensor which performs, the burkha role in the engine unit timing functions for energy injection, spark situations, and valve timing. Idle velocity is controlled by the programmable throttle stop or an idle air bypass control stepper motor. Effective idle swiftness control must foresee the engine load at idle.

A full authority throttle control system enable you to control idle rate, provide cruise control functions and top swiftness limitation.

Control of adjustable valve timing

In machines having variable valve timing, the ECU control buttons enough time in the engine cycle of which the valves open up. The valves are usually opened faster at higher velocity than at lower quickness. This can enhance the move of air into the cylinder, increasing ability and market.

B: Methods used by an EMS to calculate spark progress and fuel injection number for given engine motor conditions - using Open up LOOP Control.

Open loop control systems count on the parameter (e. g. , ignition timing) being set on the basis of stored information (in ECU's ROM), with the particular ignition timing being determined on the basis of measurements such as manifold pressure, engine unit velocity and coolant heat (Stone and Ball 2004).

Electronic control unit (ECU) handles air-fuel ratio via an electronic fuel shot system (EFI). Fig1. 2 shows a basic Electronic fuel treatment system. EFI handles the quantity of fuel injected into each cylinder by handling 'on time' period of the injectors. These injectors are solenoid comprising a spray nozzle and a solenoid-operated plunger that are linked to each cylinder.

Fig1. 2 Injection system petrol delivery (Smith, J. H 2002)

Fuel pressure in the delivery pipe is kept frequent by a fuel pressure regulator which has fuel constantly streaming around it when turned on.

According to (Smith, J. H 2002) Solenoid handled petrol injectors have starting and concluding times of between 0. 5 and 1 ms. Considering an engine working swiftness of 6000 rpm where the trend period is 10ms this gives an adequate control range of between 1 and 10ms for the injector on-time.

Two types of EFI control systems are commonly in use. Key source signals to both systems are engine quickness and intake air mass. The way intake air mass is obtained instructs apart the two types of EFI system; speed-density EFI and mass air-flow EFI.

Speed-density EFI

Since the essential fuel injection beginning period is straight related to mass of air streaming into the engine unit, air-fuel proportion must be maintained constant in steady-state procedure. The mass of ventilation relates to the manifold complete pressure (MAP) by the equation

Where

: Displacement of the cylinder,

: Volumetric efficiency

: Manifold absolute pressure,

R: Constant

: Absorption air temperature

As is a non-linear function of engine speed and exclusive to a particular engine design, combined with intake air heat a look-up desk is used to create a basic injector starting time which includes values for all those combinations of engine swiftness and MAP. (Smith, J. H 2002)

Mass air-flow EFI

Contrary to speed-density EFI quantity of air drawn in to the engine on each intake heart stroke is assessed by an air-flow sensor (AFS) in this system. Some types of suggestions AFS are flap-type, Karman vortex and hot-wire.

When air-flow is immediately measured this way, it automatically compensates factors like variant in volumetric efficiency and in engine motor displacement anticipated to speed and internal deposits.

Ignition timing

Primary sensors to control the spark progress or ignition timing are Crank angle (engine position or TDC position), air-flow in to the engine and throttle demand. Mapped ignition timing data is stored in ECU's read only storage area (ROM) which includes values for all the variable treatment pulse length and engine speed. The circuitry determines which cylinder needs petrol and exactly how much, starts the essential injector to provide it, then causes a spark at the right minute to burn up it. (Heisler, H. 1999)

C: Describe how this is modified to Shut LOOP control using sensor information from a lambda (air) sensor.

Closed loop control systems rely on measuring the result of an parameter that has been varied, to regulate the parameter to a goal value. Both types of EFI mentioned recently could be improved upon with the addition of a lambda sensor to determine a stoichiometric procedure however a far more complicated exhaust gas air sensor must measure air-fuel ratio (Natural stone and Ball 2004).

Basically, either speed-density or mass air flow could be used for EFI control, but if the engine is usually to be controlled accurately around its stoichiometric or chemically perfect point when a three-way catalyst is usually to be used, it is vital to use a feedback system integrating such a sensor to preserve an air-fuel proportion within 1%. This is only possible with closed-loop control coupled with speed-density or mass air-flow EFI. (Smith, J. H 2002).

Composition of inducted air-fuel mixture and the timing of ignition spark are the primary factors which control the combustion process and so the current economic climate and performance of the engine motor and also the quantity of contaminants in its exhaust.

Lambda sensors are used in such a way that determine if the mixture is rich or weakened, a control system is necessary making the air-fuel ratio closed down to stoichiometric i. e. 14. 7:1 (chemically perfect). This opinions control system can only just be utilized only following the engine has heated up because lambda sensors only work close to the temperature of approximately 300 C (572 F). Through the use of an electrical warming element in the centre of the sensor this warm-up time can be reduced (to 20-30 s). (Rock and Ball 2004).

The exhaust gas oxygen sensor is made up of a set of lambda sensors, made of three tiers of zirconia. All tiers are warmed and the most notable two tiers have platinum electrodes and electro-mechanical associations. The fig. 1. 3 shows a Universal exhaust gas air (UEGO) sensor. It offers an electrical opinions signal indicating if the mix is above or below the stoichiometric.

When weak mixture is present focus gradient between exhaust gas and dimension cavity will make the air to diffuse through gas consumption and electric current in the pumping cell will be proportional to the air focus in the exhaust gas. With there's a rich mixture, partial products of combustion (CO, Hydrocarbons) will be oxidized triggering more to diffuse through the porous absorption. In end result current will usually stay proportional to the exhaust gas mix.

Fig. 1. 3. (Natural stone and Ball 2004)

(a) Composition, (b) operation

D: Describe how control can be prolonged using sensor information from a knock sensor.

A knock sensor can be an accelerometer which senses engine unit structural vibrations. On the commencement of knock, accelerometer detects it and decreases the ignition, in doing this averting harm to the engine. Combustion knock causes the engine to vibrate anticipated to cylinder pressure oscillation.

Knock detector contains a mass installed on a spring and coil, with a method of detecting movements on the mass or make in the springtime. Fig. 1. 4 shows an average piezo-electric knock detector. It is convenient to combine spring and coil and sensing component which is done by mounting a mass over a piezo-electric crystal.

It is fixed on the engine unit where a good vibrational signal is found, which is located by undertaking exams on the engine. As the sign is seen for a particular time period, the knocking cylinder can be identified and ignition timing can be postponed selectively.

Fig. 1. 4 a piezo-electric knock detector. (Turner and Austin 2000)

Piezo-electric crystal comes with an good thing about high stiffness so it is better to design a transducer with high natural consistency; disadvantage is the fact it produces electric powered fee proportional to acceleration which needs to be amplified by an impedance amplifier to give a voltage transmission.

Knock detector detects the structural vibrations at a specific frequency and if it corresponds to the natural regularity of the transducer, the resonance provides dynamic amplification and transducers give an improved signal-to-noise percentage.

Advantage of knock detector is that it offers a safety border which in any other case could be obtained insurance firms less compression ratio or completely retarded ignition.

E: Discuss the huge benefits and issues of EMS control regarding Wide-band lambda sensors.

Normal lambda sensors used in most vehicles are stoichiometric plus they only reveal if the air/fuel ratio is abundant or slim i. e. they have binary output. However they don't identify how abundant or how trim the proportion is. Their output indication could be vertically on either side of stoichiometric proportion 14. 7:1.

As emission benchmarks have become tighter for vehicle, much advancement is being manufactured in the emission control and correct signal measurement is required for this function. Recent advancements are made ad a fresh more complicated sensor is employed nowadays called wide-band lambda sensor which can gauge the actual lambda prices (Olley, P. 2010). Wide-band lambda sensor informs the ECU of a variety of air petrol rations from 9:1 to air.

Wide-band lambda detectors are way more superior than their predecessors. In these kinds of receptors exhaust gas oxygen levels sit in a closed chamber of air within the sensor rather than outside air. There is also a fitted home heating component within those heats up the sensor quicker from a frosty start.

According to (CDX global online) Current through the water heater is controlled by the ECU. This enables the right operating temperature to be continually maintained. A minute chamber within the sensor has usage of the exhaust gas. This sensor works by using a sound state pump to include or remove oxygen from the exhaust gas chamber. The computer controls the current moving through the pump so the output is at stoichiometric. Current moving in one route through the pump offers oxygen whilst current in the contrary direction removes oxygen. The worthiness and course of current required to do this symbolizes the amount of air in the exhaust gas. This allows the ECU to regulate the amount of fuel delivered and keep maintaining correct emission levels.

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