Leo: 九月 2011

Engine Elwctronic Control Systems Off-Car Practical

Sensors:
Note:the term TPS can mean either throttle position sensor or throttle position switch

Throttle Position Sensor(potentiometer)
Potentiometer type sensors are composed of variable resistors that have a slide contact,
which changes its position as the throttle butterfly moves.
A voltage is supplied to the sensor by the E.C.U. As the throttle position changes, the
output voltage from the sensor changes, this in turn is recognised and a comparison made
by the E.C.U to its memory. These sensors are adjusted by loosening the sensor mounting
screws. (It is critical that you follow the manufacturer’s set-up procedure)

For example:
The idle position is recognised by the lowest voltage reading through the sensor but in
contrast, the maximum power signal is recognised by the highest reading at the full throttle
position of the sensor travel. It is important that both signals are correct.

Checking the Throttle Position Sensor

What type of TPS is this?
We used Switch typle Throttle Position Sensor

Explain its internal operation and why your voltage changes
A throttle position sensor gives very important information to the ECU .The ECU uses that data to give the driver more or less engine power when it be needed, also drivers can experience bad or faulty TPS when engine is running rough or not giving enough power. The internal operation of the TPS switch have contacts, the middle one is moved by groves that moves between the two outer contacts, the middle contact always stay on idle pin when throttle is opend less than 1.5° it will send a voltage to the ECU so that knows its on idle . When the throttle is opened less than 70° no voltage is sent,when the throttle is opened more than 70° the middle contact comes into contact with the power switch contact sending another voltage to the ECU to let it know the engine needs more fuel.

Now connect a Power Supply to your sensor and test the voltage output at different throttle angles.
NOTE: Always use a 5V supply
Throttle angle Voltage out put
   0 0.37v
   20    1.18v
   40 1.95v
   60 2.78v
   80 3.9v
   90 4.4v

Now plot your findings on a graph

Things that can happen if yous throttle position is in bad condition:
car's engine stalling when driving
surge in car's speed when driving
Idle surging of the carwhat happens when the throttle position sensor bad or faulty.
The computer would get the wrong information the engine malfunction indicator light will be on. The fuel economy of the car drops drastically.

Throttle Position Switch

There is an idle position signal that is used mainly for fuel cut-off control and ignition timing corrections. The power signal is created at full throttle and is used for increasing fuel injection volume which in turn increases engine power output. Note there is no switching at part throttle.

Throttle position switch detects throttle position at idle or full throttle by using switch contacts that are connected or disconnected as throttle position changes.

This type of switch can have two or three contact positions and is usually checked and adjusted using a multi-meter.

Adjustment is made by loosening the mounting screws and rotating the switch assembly.

On - Off type throttle position switches can have:

Two position (three pin) or

Three position (four pin).

Testing the throttle position switch

The TPS signal is very important to ensure smooth and economic engine running and the TPS is made to be adjusted to ensure optimum operation.

The condition of the contacts inside the switch is the first test, and should be checked for high resistance in both the idle and full throttle position.

Place the ohm meter across the E and IDL pins and with the throttle shut, check for continuity.(0.1Ω)

Place the ohm meter across the E and PSW pins and check for continuity when the throttle is wide open.(0.2Ω）

Plot your finding on the graph

Explain the internal operation of this sensor and why the resistance changes

In switch type TPS sensor there is a two contact points inside the throttle.There is a arm in the middle inside it, that makes the connections at two points. One point is for close postion and other for wide open (WOT) At Idle, throttle is closed and the resistance is infinite and when it starts open, the resistace at once jump to 0.1 ohms with any variations in between. In other way around, when it closing down from its fully open postion, the resistance jumps to infinite.

Manifold Absolute Pressure (MAP)

Wire up a map (manifold absolute pressure) sensor with a 5 V feed and earth. Measure

the return voltage from the third wire.

Using a mity-vac apply vacuum to the map sensor. Plot the voltage return in relation to the vacuum applied.

Explain the internal operation of this sensor and why the output voltage changes

The sensor consists of a piezoresistive silicon chip an integrated circuit. A perfect vacuum is applied to the other side when pressure in te intake manifold changes the silicon chip flex's causing changes in it's resistance. The varying resistance of the sensor causes a change in signal voltage at the PIM terminal.

Air flow/mass sensor (MAF)

A mass air flow sensor is used to find out the mass of air entering a fuel-injected internal combustion engine. The air mass information is necessary for the ECU to balance and deliver the correct fuel mass to the engine. Air changes its density as it expands and contracts with temperature and pressure. In automotive applications, air density varies with the ambient temperature, altitude and use of forced induction and this is an ideal application for a mass sensor.

Vane or flap air flow sensor/meter (AFM)

checking sensor operation.

Vane type air flow meters:

As previously mentioned it is important that manufacture's specifications be used when testing sensor operation.

The sensor can be checked with an Ohm meter,testing individual circuits for variable resistance in reponse to air vane movement.

However it is more accurate to check the voltage output signal on the vehicle by back probing the multi-plug with the ignition on.

The sensor is normally a reliable component but it can be dameged by engine backfire or moisture and condensation on the resistor strip.

The sensor is made as an unserviceable item, and should be replaced as a unit if faults are diagnosed. The settings of the spring tension are preset during manufacture.

If obvious signs of tampering with the sealed cover are evident it is possible that the cause of faults may be traced back to this source.

An air flow meter also known as an air consumption meter, is a device that measures how much air is flowing through a tube. It does not measure the volume of the air passing through the tube, it measures the actual speed of the air flowing through the device in a defined time segment. Thus air flow meters are simply an application of mass flow meters for a special medium. Typically, mass air flow measurements are expressed in the units of kilograms per hour.

An air flow meter is used in some automobiles to measure the quantity of air going into the internal combustion engine. All modern electronically controlled diesel engines use air flow meter, as it is the only possible means of determining the air intake for them. In the case of a petrol engine, the (ECU) then calculates how much fuel is needed to inject into the cylinder ports. In the diesel engine, the ECU meters the fuel through the injectors into the engines cylinders during the compression stroke.

Explain its internal operation and why your voltage changes:

When the amount of air intake changes the vane will move This vane changes the resistance and voltage when the vane is closes, the resistance value is the highest with highest signal voltage. When the vane is fully opens the resistance value is the lowest with the lowest voltage.

CTS (Coolant Temperature Sensor)

THw (Thermistor water)

ECT (Engine Coolant Temperature)

Suspend the engine coolant temperture sensor in a container of water.

Explain the internal operation of the sensor?

The internal operation of the negative temperature coefficient sensor is when the temperature goes up the resistance goes down . Thermistor gets a decrease in electrical resistance when subjected to an increase in body temp .

Knock sensor

A knock sensor is a knob-like part that is linked to the car's engine. As the name implies, it senses knocks in the engine. Wells Manufacturing, a company that produces knock sensors, likens the sound of an engine knock to marbles against metal.
A knock sensor is important to a car's fuel efficiency. It helps the car balance its timing and fuel-to-air mix, which optimizes the amount of power to the engine.

One of the purposes of a knock sensor is to monitor the performance of the engine. If there is a problem, the knock sensor will send a signal to the ECU

Knock sensors also protect car parts from the damaging effects of engine knock. When a knock sensor is bad, it can't regulate the engine properly. The car vibrates and it sounds like there is something banging up against the car's cylinder. The knocking action can destroy the pistons, rods, valves, gaskets and plugs.

Connect the knock sensor up to an oscilloscope

Gently tap the end of the knock sensor and observe the waveform

Draw the waveform on the graph below

Explan why we are reading a voltage from this sensor when we are not supplying a voltage to it

The tap knocking produes centain voltage around 10mv whithout supplying voltage. The sensor being small electrical device that the properties of produes at voltage when subjectes to kinetic-engery.

Wiring up ignition systems

Wire up an ignition module using a function generator to trigger the module.

Have a coil and spark plug in the circuit so the spark plug can fire

Check with your tutor taht you have done it correctly

Draw a wiring diagram of how you wired the circuit.