Wednesday 7 September 2011

Off-Car Practical

1. TPS (Throttle Position Sensors)
- Theory
Throttle Position Sensors : The sensors give the ECU information about the throttle positions with its resistance and voltage values which shows idling status and wide open throttle status. The ECU controls idle stability, proper acceleration and deceleration according to the acceleration pedal positions. There are two types of TPS which are called Potentiometer type sensors and On-Off switch type sensors.

- Procedure 
Potentiometer type sensors
A voltage(5v) is supplied to the sensor by the ECU. When the throttle position angle is changed, the output signal will also change.
I have tested a TPS with four terminals. Vcc(Voltage Constant Control), E2(Ground), IDL( Idle Switch) and VTA(Voltage Throttle Angle)
A 5v and earth of the power supply are connected sensor's Vcc and E2 each. Then, the VTA terminal is touched a red lead of a multimeter and another black lead connects the ground as well. When I change the throttle angle, the output voltage are changed. When the angle is bigger, the voltage goes up. At closed throttle, the IDL touches the red lead of a multimeter with at 0v and IDL signal flows through the ground. When the throttle opens, the IDL is disconnected with an open circuit and the IDL voltage goes up form 0v to high voltage(12v).

On-Off switch type sensors 
This sensors detect throttle position with its switching operation at idle and WOT.  
When the red lead of a multimeter is connected the IDL and the black lead is touched the earth with the idling status, the resistance value is at 0.8Ω. When the red lead is made contact with the PSW with the WOT status, the resistance value is also at 0.8Ω. 
When the throttle is closed, the earth connects IDL and it has certain resistance with digital signal representing. On the other hand, when the throttle is widely opened, the earth touches PSW and it also has certain resistance. As a result, when the engine is idling, the ECU knows that the throttle is closed from the resistance value. When the acceleration pedal is fully pushed, the ECU knows that the throttle is opened from its resistance value.

- Reflection
The TPS gives the ECU the position of an acceleration pedal, then the ECU controls fuel injection and the change of engine rpm and power. If the TPS is faulty, the idle would be operated with higher rpm due to wrong resistance and output voltages and the engine will not run properly.

2. MAP (Manifold Absolute Pressure Sensors)
- Theory
Manifold Absolute Pressure sensors : These sensors measure the intake manifold pressure and it gives the ECU information about the output signal. Then, the ECU controls the fuel injection and ignition timing from the MAP's data. The lower pressure(higher vacuum) of the intake manifold at idle produces low output voltage at around 0v in a MAP. On the other hand, the higher pressure(lower vacuum) in the intake manifold at WOT creates high output signal at just under 5v in the MAP. 
- Procedure
The 5 voltage is supplied the red lead of MAP and the black lead is touched the earth. After then, the green lead of the MAP connects the multimeter's red lead for measuring output voltage. Using a mity-vac apply vacuum to the MAP. When the low vacuum is applied to the MAP sensor, the output signal is high. when the vacuum increased, the the output voltage dropped.
The sensor consists of a piezoresistive silicon chip and integrated circuit(IC). A perfect vacuum is applied to one side of the silicon chip and manifold pressure applied to the other side. When pressure in the intake manifold changes, the silicon chip flexes causing a change in its resistance. The changing resistance means a change in signal voltage.
- Reflection
 The MAP sensor gives the ECU information about the measurement of an amount of intake air(manifold pressure), then the ECU controls fuel injection and ignition timing. So, the MAP sensor are a critical factor for operating engine. If the MAP sensor is faulty, the engine would not run, get rough idle and less power at acceleration. 
 3. CTS(Coolant Temperature Sensors)
- Theory
Coolant Temperature Sensor : The sensors give the ECU information about the coolant temperature with its resistance values. Then, the ECU controls the fuel injection, ignition timing, idling speed and automatic transmission timing. When the engine is cold at starting, the sensors will produce high resistance and this signal applies to the ECU and then the ECU orders rich mixture due to the condensation of the cold engine condition. As a result, the engine rpm goes up and when the coolant temperature is gradually warmed up with lower resistance, the engine rpm will gradually decreased until fully warm-up.
The ECU can calculate the temperature from sensor's signal. Two resistors in series must drop all the voltage across them. If the first resistor(sensor) is larger more voltage is dropped accross it and the A position value will be smaller. 
 NTC Thermistor (Negative Temperature Coefficient Thermistor)
When the temperature goes up, the resistance drops. The CTS uses a this type thermistor. 
 PTC Thermistor (Positive Temperature Coefficient Thermistor)
When the temperature goes up, the resistance also increases.     

- Procedure
The engine coolant temperature sensor suspends in a container of water. The water is heated up and check the temperature with a thermometer. Simultaneously, the two termials are connected the multimeter' two leads with the ohm range. When the water was gradually heated up, the resistance values are gradually dropped. Therefore, this sensor is a NTC type thermistor.  

- Reflection
CTS is also a crucial factor for operating engine. If the sensor is faulty, the engine would not run properly which means that the CTS is related to fuel injection, ignition timing , idling speed, cooling fan and referencing data of other systems.
 4. ATS(Air Temperature Sensors)
- Theory
Air Temperature Sensor : The sensors give the ECU information about the intake air temperature with its resistance values. Then, the ECU controls the fuel injection, ignition timing, idling speed. When the intake air is hot with less oxygen, the ECU controls less fuel injection and it can make the optimum combustion condition.
The ATS also uses a NTC type thermistor. When the air temperature is high, the resistance of a sensor decreases.

- Procedure
The two terminals of a sensor are connected the leads of a multimeter with ohm's range. Then, hot air is blown by a blow gun. The resistance values are changed. When the temperature increased, the resistance of the sensor dropped.
  

- Reflection
The air temperature sensor gives the ECU information about the measurement of air temperature, then the ECU controls fuel injection and ignition timing, idling speed for proper combustion with less emission. If the sensor is faulty, the engine would not run properly.


5. Thermo Fan Switch
- Theory
When the coolant is hot, it should be cool by the fan's operation and prevent over heating. So thermo fan switch controls on-off the fan's operation according to coolant temperature. Normally, two metals are contacted with the closed circuit when the coolant temperature is cold. However, when the engine is hot with load's conditions, the thermo fan switch has an open circuit with switch on then, the fan runs and when the coolant is cool again, the switch will be off. 


- Procedure
The one terminal of a sensor is connected the red lead of a multimeter and the black lead is touched an earth of sensor's body with ohm's range. Then, the water is heated up gradually. The resistance values are at 0Ω before 94℃ When the temperature reached at 94℃, the sensor changed an open circuit with infinite resistance.
This thermo fan switch turns on at 94℃ with open circuit. The fan operates with a relay which uses a closed relay. When the voltage is supplied the relay, the relay has an open circuit.
  - Reflection
The thermo fan switch turns on a fan when the coolant temperature reaches certain temperature at around 90℃ to 98℃. If the switch is faulty, the engine would be overheated because of no fan operation or the fan would run continuously when the engine is cool which causes fan's damage.

6. Knock Sensor
- Theory
The knock sensor detects engine detonation(knock) and this sensor produces the small voltage signal when the engine knock is produced. The signal is applied to the ECU and the ECU control the ignition timing for the optimum combustion. Engine knock occurs within a specific frequency range.

- Procedure
The one terminal of a knock sensor connects a positive lead of an oscilloscope and the body of the sensor is touched the earth of the oscilloscope. When the tap is produce the end of the knock sensor, I can see the waveform on the oscilloscope screen. 
The sensor being a small piezo-electrical device that has the properties of producing a voltage when subjected to kinetic energy(knock). The tap produces certain voltage at around 10mv without supply voltage.

- Reflection
I have tested a knock sensor which produce small voltage with its frequency from tap. The ECU receives these voltage and controls the ignition timing for the proper combustion. If the knock sensor is faulty, the ECU would not controls the ignition timing when the knock produced. The engine would be damaged under knock conditions, such as a higher engine temperature, high loads, and fully opened throttle with using high power.


7. Mass Air Flow Sensor
- Theory
The mass air flow sensor directly measures the amount of intake air when the air goes through between an air cleaner and a throttle body. The sensor gives the ECU information about the output signal. Then, the ECU controls the fuel injection and ignition timing from the MAF's data. It is critical that the sensor signal uses to determine injector's operation time. 


- Procedure
Vane type air flow meters

There are seven terminals in a vane type air flow meter. The sensor is checked resistance with using a multimeter and ohm range. E2(earth) connects a black lead of the multimeter and Vs is touched a red lead of the multimeter. When the vane moves, the resistance value changes. Using 5v power, a 5v is supplied Vb(source) and the voltage is measured between Vs and earth using voltage range of the multimeter. When vane is closed, the voltage is high at near 5v. When the vane angle increases, the output voltage drops.
  



When the amount of intake air changes with vane's movement, the resistance and voltage are also changed. When the vane closes, the resistance value is the highest with the highest signal(Vs). On the other hand, when the vane fully opens, the resistance value is the lowest with the lowest voltage. Therefore, the ECU knows the amount of intake air from the signal voltage changes.
- Reflection
I have tested a vane type air flow sensor which produces voltage between 0v and 5v. When I connected the terminals for measuring resistance and voltage, I had wrong results due to faulty connections. A Vc terminal should be touched the constant 5v and a Vs should be connected multimeter's red lead. So, I could check the voltage changes according to different vane angles.
 If the MAF sensor is faulty, the ECU would not controls the fuel injection and the ignition timing due to wrong signal. As a result, the idle would be unstable or turned off the engine. The acceleration would also be abnormal with less power.

8. Speed or Position Sensors
- Theory
 Speed (Crankshaft Position sensor) or Position(Camshaft Position Sensor) sensors give the ECU information about crankshaft speed(rpm) and cylinder positions. Therefore, the ECU controls the ignition timing and correct fuel injection according to engine speed and camshaft positions. 
Magnetic Distributor
This system uses magnetic principles coupled together with an inductor winding commonly known as the pickup winding. Magnetic inductive devices can be found in many shapes and forms. The single most important aspect of their operation is that they need some kind of movement between the conductor coil and the magnetic field. In a normal situation we would think of induction taking place by the moving of a conductor across a stationary magnetic field or conversely a moving magnetic field across a stationary conductor.
Hall-Effect SensorWhen a chip of semi conductor material carrying a signal current across it is exposed to a
magnetic field, a small voltage called the “Hall voltage” is generated between the chip edges at 90 degrees to the path taken by the signal current. When the window is opened, the current does not flow. On the other hand, when the window shutters, the current can flow through chip to magnet.

  The hall voltage is supplied to the non-inverting side of a non-inverting op-amp which will switch high, supplying a voltage to the base of the NPN transistor. The transistor turns on pulling the signal out line to ground. As the magnet is interrupted and shielded the voltage is switched off and on to ground creating a square wave.
Optical Distributor






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1 comment:

  1. A good start Kim, maybe more content on your 'reflection/faults' would be good

    ReplyDelete