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Transcript of Automotive Electronics
Automotive electronicsUse of electronics in automobile To improve fuel economy To reduce exhaust emission
Current trend in automobile1. Electronic engine control for minimizing exhaust emissions and maximizing fuel economy 2. Instrumentation for measuring vehicle performance parameters and for diagnosis of on-board system malfunctions 3. Driveline control 4. Vehicle motion control 5. Safety and convenience 6. Entertainment/communication/navigation
AUTOMOBILE PHYSICAL CONFIGURATION
These systems include the following: 1. Engine 2. Drivetrain (transmission, differential, axle) 3. Suspension 4. Steering 5. Brakes 6. Instrumentation 7. Electrical/electronic 8. Motion control 9. Safety 10. Comfort/convenience 11. Entertainment/communication/navigation
The 4-Stroke Cycle
Intake Manifold and Fuel Metering
Spark Plug Configuration
Schematic of the Ignition Circuit
Spark Pulse Generation
Shock Absorber Assembly
Power Power is a measurement of an engines ability to perform useful work. Brake power, which is measured with an engine dynamometer, is the actual power developed by the engine minus losses due to internal friction. BSFC BSFC is a measurement of an engines fuel economy. It is the ratio of fuel flow to the brake power output of the engine BSFC = rf/pb Torque Engine torque is the twisting action produced on the crankshaft by the cylinder pressure pushing on the piston during the power stroke.
Volumetric Efficiency Volumetric efficiency actually describes how well the engine functions as an air pump, drawing air and fuel into the various cylinders. It depends on various engine design parameters such as piston size, piston stroke, and number of cylinders and is strongly influenced by camshaft design. Thermal Efficiency Thermal efficiency expresses the mechanical energy that is delivered to the vehicle relative to the energy content of the fuel. Calibration The definition of engine calibration is the setting of the air/fuel ratio and ignition timing for the engine.
ELECTRONIC ENGINE CONTROL
Inputs to Controllers 1.Throttle position sensor (TPS) 2. Mass air flow rate (MAF) 3. Engine temperature (coolant temperature) (CT) 4. Engine speed (RPM) and angular position 5. Exhaust gas recirculation (EGR) valve position 6. Exhaust gas oxygen (EGO) concentration Outputs from
Outputs from Controllers 1. Fuel metering control 2. Ignition control 3. Ignition timing 4. Exhaust gas recirculation control
Electronic Distributor less Ignition System
Sensors and actuatorsSensors: Sensors provide measurements of important plant variables in a format suitable for the digital microcontroller. Ex:Throttle position sensor (TPS), directly regulates the air flow into the engine, thereby controlling output power. Autuators:Actuators are electrically operated devices that regulate inputs to the plant that directly control its output. Ex: Fuel injectors are electrically driven actuators that regulate the flow of fuel into an engine for engine control applications.
TYPES OF SENSORS 1. Mass air flow (MAF) rate 2. Exhaust gas oxygen concentration (possibly heated) 3. Throttle plate angular position 4. Crankshaft angular position/RPM 5. Coolant temperature 6. Intake air temperature 7. Manifold absolute pressure (MAP) 8. Differential exhaust gas pressure 9. Vehicle speed 10. Transmission gear selector position
AIR FLOW RATE SENSOR
In the MAF, the hot-wire, or sensing, element is replaced by a hot-film structure (Thermister) mounted on a substrate. On the air inlet side is mounted a honeycomb flow straightener that smooths the air flow. The film element is electrically heated to a constant temperature above that of the inlet air.
The Wheatstone bridge consists of three fixed resistors R1, R2, and R3 and a hot-film element having resistance RHW. With no air flow the resistors R1, R2, and R3 are chosen such that voltage va and vb are equal (i.e., the bridge is said to be balanced). As air flows across the hot film, heat is carried away from the film by the moving air. The amount of heat carried away varies in proportion to the mass flow rate of the air. The heat lost by the film to the air tends to cause the resistance of the film to vary, which un balances the bridge circuit, thereby producing an input voltage to the amplifier The output of the amplifier is connected to the bridge circuit and provides the power for this circuit. The amplified voltage changes the resistance in such a way as to maintain a fixed hotfilm temperature relative to the inlet temperature.
voltage-to-frequency (v/f ) converter is used to convert the analog voltage in to digital signal This circuit is a variable-frequency oscillator whose frequency f is proportional to the input voltage (in this case, the amplifier output voltage). The variable-frequency output voltage (vf ) is applied through an electronic gate, which is essentially an electrically operated switch. Control circuitry (also part of the sensor solid-state electronics) repeatedly closes the switch for a fixed interval t. Then it opens it for another fixed interval. During the first interval the variable-frequency signal from the v/f circuit is connected to the binary counter (BC) B=ft B = BC count f = frequency of v/f t = duration of closure of electronic gate After the engine controller reads the count, the BC is reset to zero to be ready for the next sample
Indirect Measurement of Mass Air Flow (speed-density method)This method computes an estimate of mass air flow from measurements of manifold absolute pressure (MAP), RPM, and inlet air temperature.
Strain Gauge MAP Sensor Manifold pressure applied to the diaphragm causes it to deflect. The resistance of the sensing resistors changes in proportion to the applied manifold pressure by a phenomenon that is known as piezoresistivity.
The resistors in the strain gauge MAP sensor are connected in a wheatstone bridge circuit. Output voltage of the circuit varies as the resistance varies in response to manifold pressure variations.
ENGINE CRANKSHAFT ANGULAR POSITION SENSOR
Crankshaft angular position is an important variable in automotive control systems, particularly for controlling ignition timing and fuel injection timing.
The crankshaft angular position is the angle between the reference line and the mark on the flywheel .Imagine that the flywheel is rotated so that the mark is directly on the reference line. This is an angular position of zero degrees. For our purposes, assume that this angular position corresponds to the No. 1 cylinder at TDC (top dead center). As the crankshaft rotates, this angle increases from zero to 360 in one revolution. one full engine cycle from intake through exhaust requires two complete revolutions of the crankshaft. That is, one complete engine cycle corresponds to the crankshaft angular position going from zero to 720. During each cycle, it is important to measure the crankshaft position with reference to TDC for each cylinder. This information is used by the electronic engine controller to set ignition timing and, in most cases, to set the fuel injector pulse timing.
TYPES MECHANICAL Magnetic Reluctance Position Sensor Hall-Effect Position Sensor OPTICAL Optical Crankshaft Position Sensor
MAGNETIC RELUCTANCE POSITION SENSOR In the magnetic reluctance position sensor, a coil wrapped around the magnet senses the changing intensity of the magnetic field as the tabs of a ferrous disk pass between the poles of the magnet.
The voltage generated by the magnetic reluctance position sensor is determined by the strength of the magnetic flux. When a tab on the steel disk passes through the gap, the flow of the magnetic flux changes significantly.
The reluctance of a magnetic circuit is inversely proportional to the magnetic permeability of the material along the path. The magnetic permeability of steel is a few thousand times larger than air; therefore, the reluctance of steel is much lower than air. Note that when one of the tabs of the steel disk is located between the pole pieces of the magnet, a large part of the gap between the pole pieces is filled by the steel. Since the steel has a lower reluctance than air, the flow of magnetic flux increases to a relatively large value. when a tab is not between the magnet pole pieces, the gap is filled by air only. This creates a high-reluctance circuit for which the magnetic flux is relatively small. Thus, the magnitude of the magnetic flux that flows through the magnetic circuit depends on the position of the tab, which, in turn, depends on the crankshaft angular position.
Output Voltage Waveform From The Magnetic Reluctance Position Sensor CoilThe voltage induced in the sensing coil varies with the rate of change of the magnetic flux. When the tab is centered between the poles of the magnet, the voltage is zero because the flux is not changing coil voltage, Vo, begins to increase from zero as a tab begins to pass between the pole pieces, reaches a maximum, then falls to zero when the tab is exactly between the pole pieces . (Note that although the value of magnetic flux is maximum at this point, the rate of change of magnetic flux is zero; therefore, the induced voltage in the sensing coil is zero.) Then it increases with the opposite polarity, reaches a maximum, and falls to zero as the tab passes out of the gap between the pole pieces
Disadvantages: Lack of output when the engine isnt running.
Hall-Effect Position SensorThe Hall element is a thin slab of semiconductor material that is placed between the magnets so it can sense the magn