abs

What is abs (anti locking braking system)
Anti-Lock Braking System was designed originally for  aircraft's to shorten the braking distance on short run way like aircraft carriers. It is designed to stop the wheels of a car from locking up, this result in vehicle still having steer-ability when braking because the tires still have grip of the road. This in turn enables the vehicle slow down aswell as steer around the object.



How does ABS workABS controlls the pressure automatically in the braking system by increasing or decreasing it, a similar effect to the driver using cadence braking style this pressing the brake and letting go, repeating  pumping of the paddle.
Speed sensor mounted next to the cv joint, this measure if the wheel is locked and  fast or slow the wheel is moving compared to the other 3 wheels.
Then after gathering the result the control module and modulator unit controls the  valve in the hydraulic controls each brake line.
-need the alternater to be working 14.6v to be working or else the abs light somes on
-need the back brake light bulb to be working or the abs will come on aswell


Types of ABS 

1ch = only one sensor at on the back axel controlling RL and RR
3ch= only 1 sensor at the back axel but 2 at the front 
4ch= All 4 wheel has a sensor

Operational amplifier (OPAMP)

What is a OPAMP
OPAMP is an electronic circuit module  made up of components like transistors, resistors and diodes all into one. Originally, OPAMPS were named because they were used to model the basic mathematical operations add, subtract,integrate and differentiate in analogue computers.

Characteristics of an Ideal OP-AMP
The ideal op-amp has:
-open-loop gain infinite,
-infinite bandwidth
-Infinite input impedances so that no current is drawn
-Zero output impedance so that maximum current is transferred to the load.
-input offset zero
-No thermal drift.




Inverting op-amp
Vin goes to (-) inverting input

Calculate Vout
If Vin =14 ,R1/Rf=15000, Rin=180
the Rf(R1) resistor is counted as a minus
formula is Vout=Vin(-Rf/Rin) 


Vout=14(-15000/180)
Vout=-1166 use 1k2



Non-Inverting op-amp 
Vin going to (+) non inverting input

Calculate Vout
Vin=27, Rf=150000,Rin=390
In a non-inverting op-amp we have to add +1 to Rf/Rin
so Vout=Vin(1+Rf/Rin)
Vout=27(1+150000/390)
Vout=10411 use 10k

oxygen sensor part 2

What does a Oxygen Sensor do

The Oxygen sensor was design to tell the ECU when there is oxygen in the exhaust gas, so the ECU can adjust the mixture close to Lambda 1 (14.7:1) as well as the purpose to protect the catalytic converter (CAT).O2 sensors becomes unresponsive and slow to change voltage after a while,a slow or unresponsive O2 sensor will result in consuming more fuel and a lag in engine performance when accelerate. It is recommended to change them every 60,000-100,000km,some newer cars the engine check light will come on when they need changing. Oxygen Sensor is passive sensor which does not require power to run, most outputs its own voltage.Leaded fuel and non O2 sensor safe silicone gasket makers (If it smells like vinegar it's not O2 safe) will destroy the O2 Sensor.

How it works
Oxygen sensors need to be at 500-600 degrees for it to start working (when O2 sennsor is cold its open loop
when 02 sensor is hot n working its close loop).This is why some O2 sensor have 4 wires, they has a heater core to heat them up this brings them up to working condition as soon as possible so the car will function at its  properly.Some have a earth wire directly to EC to stop interference because the voltage is so small a earth wire is to be presise.
-If 02 sensor is not working it goes lean or stuck at a voltage.
-If a air leak in the exhaust pipe before the 02 sensor it  goes lean

0v lean
0.45 ideal voltage
0.9v rich


Types of O2 sensor
- Zirconia
switching type DC volt
-Wideband
5-7 wire  basicly 2 02 sensors together so 2 signal, 2 ground, 2 heaters and a ground

-Titania switching (narrow-band lambda)
Unlike the other 2 this does not create its own voltage instead it changes its resistance




Numbers of O2 sensor in a car.
-Newer cars have 2 O2 sensor, before the CAT (up stream) for the mixture lamda and after the cat (down stream) to make sure if the cat is working.
-V style engine have a O2 sensor per bank so a V12 would have 2 left and 2 right.

Multiplexing and CAN (Controller Area Network)

What is Multiplexing?
A Network
Instead of 1 ECU controlling everything, this system work by having lots of modules (Each module on the network is called a “Node”) all digital communication between modules is connected by a few wires, Modules are connected together in either series or parallel circuits.Signals from sensors and actuators are now manage by modules in different areas but still communicates with the main modules with high1, low1, +12v and ground.This system saves complications with a huge amoung of wires (If 2 wires are found twisted together DO NOT untwist them they are twisted together to cancel out EMI electro magnetic field interference).



Advantages of Multiplexing Network
-Many modules can share information with less wires
-Saves money (to share VSS info with different modules,
would require more wires for each module)
-Provides more features on vehicles
-Saves weight
-Less wires and connections to go bad.
-Easier to trace/replace wire.

Airbag

What is a airbag
Airbag (SRS=secondary restrict system (primary is seat belt) is a safety feature in a car to stop the driver/passenger from hitting their head against the wind screen,steering or dash board. Late vehicles comes with multiple airbag this includes curtain airbags for driver,front and back passenger

How it works

How it works is basically a explosion ( of nitrogen gas) happens in the bag and the bag holds the explosion inside this inflates the bag to acts as a force against the force of the driver/passengers moving forward. The curtain airbag works the same, it is hidden in the side pillar.There is capacitors inside the ECU to keep the air bag working  this is so that if something happens to the battery and you have a crash  the air bag still works (disconnect both wires positive and negative of battery the longer the better so the capacitor discharge if need to disable airbag
The passengers seat has a sensor so that the air bag  don't go off  if there's no one in the seat.

For the airbag to work all sensors must be trigger, 2 front shock sensors(normally open switch sensor) in series and 1 in the ECU,all 3 sensor has to close in series. Ones the sensor switch is close it cant be open you have to replace them.


2 Types of Air bag system
mechnical = dont have light
electrical = dash board light 7 seconds until the light goes off


To test airbag
Use a dummy resistor (eg usually2 oh use 2R2ohm not all air bag is 2 ohm ) connect to the wire ,connect the battery and  if  the dash light goes off then you know its the airbag that the fault
or swap the passenger with the driver. (don't ever use a multimeter to check the ohm of the airbag, the airbag will go off.)
yellow/orange colour of loom (not wire) for airbag

Scan tool

What is a scan tool
Scan tool is a electronic tool used to reads what the ECU see, its the cars " live data". We use this if the car check engine light is ON this tells us what the ECU think is wrong with the car so it makes it easier for us to know where to start looking for the fault. But not all faults can be seen by the ECU there for the scan tool  is limited to what it can do eg sometimes the ECU cannot read a faulty TPS so there will be no trouble code.



Example of live data problem
The car owner complains of a lack of power when cruising. The emission at idle look clean. During a road test with the scan tool  recorded the following data.What is wrong?

Predicted  that the fuel filter must have been plugged so the engine doesnt get enough fuel, as shown the O2 sensor reading lean, even though the injector is open for longer and the long term fuel trim i strying to richen up the fuel since the O2 is correctly shown the lean mixture. The clean emissions at idle tells us the O2 is probably works correctly , along with most of the rest of the system.

Manifold absolute pressure (MAP) sensor

What is a MAP sensor
This sensor is use to measure the amount of vacuum in the intake manifold because the amount of intake manifold vacuum is directly related to engine load. The ECU takes this infomation and use it to calculate the correct  amount of fuel to inject, when to ignite (ignition timing retard or advance) and other function.

How it works

In the MAP sensor there is a silicon chip mounted inside a reference chamber.One side of the chip is the reference pressure.This reference pressure is a calibrated pressure,on the otherside is the pressure to bo measured. The silicon chip changes  its resistance with the change in pressure. This change in resistance alters the voltage signal which tells the ECU there was a change in pressure.

http://media.photobucket.com/image/how%20do%20map%20sensor%20work%20inside/tzelenko/DSC00865.jpg

Stock map sensor can stand up to MAX 1 bar (15psi) boost

Metal Oxide Field Effect Transistors (MOSFET)

Transistors has at least 3 terminalsis. Voltage/Current to one pair of the terminal changes the current flowing through the other pair of terminals thus used for amplifying or switching electronic signals. 


Metal Oxide Field Effect Transistors (MOSFET)




















MOSFET
-low voltage gain
-high current gain
-very high input impedance
-high output impedance
-low noice generation
-fast switching time
-easily damage by static!!!(USE OF AN ANTI-STRAP IS RECOMMENDED)
-some require an input to turn it "OFF"
-voltage controlled device
-more expancive than BJT

2 Types of mosfet= 'N' channel and 'P' channel

Data sheet

The Linear De-rating Factor, tells you how many watts must be reduce as the temperature increase
example. If the device was operating at 55oC, what would be the max power the device could handle?

(temp needed to operate at) - (normal operating temp) = X
X x (linear derating factor) = Y
(Power Dissipation(PD) - Y = Z <-- this is now the max PD@TC=XoC

55 oC – 25 oC = 30
30 x 0.59 = 17.7
88 – 17.7 = 70.3W – This is now the max PD @ TC = 55 oC.

Bipolar Junction Transistor (BJT)

Transistors has at least 3 terminalsis. Voltage/Current to one pair of the terminal changes the current flowing through the other pair of terminals thus used for amplifying or switching electronic signals. 


Bipolar Junction Transistor (BJT)

Not Pointing iN (NPN)  Point iN Please (PNP) 

Bipolar
-high voltage gain
-low current gain
-low input impedance
-low output impedance
-medium noise generation
-medium switching time
-robust
-requires zero input to turn it "OFF"
-current controlled device
-cheap



BJT as a switch.
To work out RB in this type of circuit

Calculate the the resistor needed for Rb
If Vcc=14, VBB = 5 volts, Rc=150,Beta= 55, Vce= .5 volts


We first need to get Ic, this is done by dividing Vsupply (Vcc) by Rc, do not forget to minus Vce 
So:Ic= (Vs-Vce)/Rc
Then we use the beta formula : Ic=Beta x Ib,
 we to transpose this formula to get Ib
Once we have Ib we can use it to calculate Rb by dividing VBB by Ib, do not forget to minus Vbe :
Rb=(VBB-Vbe)/Ib


Ic=(14-0.5)/0.09
Ic=0.09A


Ib=0.09/55
Ib=0.00163A


Rb=(5-0.7)/0.00163
Rb=2638 use 2700




Fault finding a BJT