Automobile Engineering-Why Oxygen Sensor O2 used in car

A rich mix results in fuel that is not burnt. ... Most car engines can determine how much fuel is expended in the O2 sensor. If your oxygen sensor fails to function properly, your engine management computer can not determine the air to fuel ratio.

The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust as the exhaust exits the engine. Monitoring oxygen levels in the exhaust is It causes the oxygen or less oxygen to rise.






















What the Home Mechanic Needs to Know about O2 Sensors?

Today's computerized engine control system rewards on inputs from a variety of sensors to regulate engine performance, emissions and other important functions. The sensors must provide accurate information other driveability problems, increased fuel consumption and emission failures

One of the sensors It's often referred to as the "O2" sensor because O2 is the chemical formula for oxygen (oxygen atoms are always traveling in pairs, never alone).

The first O2 sensor was introduced in 1976 on a Volvo 240. California vehicles got them in the 1980's when California's emission rules low emissions. Federal emission laws made O2 sensors virtually mandatory on all cars and light trucks built since 1981. And now that OBD-II regulations are here (many new ones), many vehicles are now equipped with multiple O2 sensors, some as many as four!
The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust as the exhaust exits the engine. Monitoring oxygen levels in the exhaust is It causes the oxygen or less oxygen to rise.

A lot of factors can affect the relative richness or leanness of the fuel mixture, including air temperature, engine coolant temperature, barometric pressure, throttle position, air flow and engine load. There are other sensors to monitor these factors, too, but the O2 sensor is the master monitor Consequently, any problems with the O2 sensor can throw the whole system out of whack.

Loops

The computer uses the oxygen sensor's input to regulate the fuel mixture, which is referred to as the fuel "feedback control loop." The computer takes its cues from the O2 sensor and responds by changing the fuel mixture. This produces a corresponding change in the O2 sensor reading. This is referred to as "closed loop" operation because the computer is using the O2 sensor's input to regulate the fuel mixture.

The result is a constant flip-flop back and forth from rich to lean which allows the catalytic converter to operate at peak efficiency while keeping the average overall fuel mixture in proper balance to minimize emissions. It's a complicated setup but it works.

When no signal is received from the O2 sensor, as is the case when a cold engine is first started (or the 02 sensor fails), the computer orders a fixed (unchanging) rich fuel mixture. This is referred to as "open loop" operation because no input is used from the O2 sensor to regulate the fuel mixture.
 
If the engine fails to go into closed loop when the O2 sensor reaches operating temperature, or drops out of closed loop because the O2 sensor's signal is lost, the engine will run too rich. A bad coolant sensor can also prevent the system from going into closed loop because the computer also considers engine coolant temperature when deciding whether or not to go in closed loop.
How it works


The O2 sensor works like a miniature generator and produces its own voltage when it gets hot. Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb. The bulb is coated on the outside with a porous layer of platinum. Inside the bulb are two strips of platinum that serve as electrodes or contacts.

The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors "breathe" through their wire connectors and have no vent hole.

It's hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). 
Venting the sensor through the wires instead of a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail. The difference in oxygen levels between the exhaust and outside air within the sensor causes voltage to flow through the ceramic bulb. The greater the difference, the higher the voltage reading.

An oxygen sensor will usually generate up to about 0.9 volts when the fuel mix is ​​rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor's output voltage will drop down to about 0.1 volts.  
When the air / fuel is balanced or at equilibrium point of about 14.7 to 1, the sensor will read around 0.45 volts. When the computer receives a rich signal (high voltage) from O2 sensor, it leans the fuel sensor's reading.  
When the O2 sensor reading goes (low voltage), the computer reverses again This continuous flip-flopping back and forth of the fuel system. The transition rate is the slowest on engines with feedback carburetors, typically once per second at 2500 rpm. 
Engines with throttle body injection are somewhat faster (2 to 3 times per second at 2500 rpm), while engines with multiport injection are the fastest (5 to 7 times per second at 2500 rpm) .The oxygen sensor should be hot (about 600 degrees or higher) before it is started to generate a voltage signal, so many oxygen sensors have a hot heating element inside the operating temperature.  
The heating element can also prevent the sensor from cooling off too much during prolonged idle, which would cause the system to revert to open loop.Heated O2 sensors are mostly used in newer vehicles and typically have 3 or 4 wires. Older single wire O2 sensors do not have heaters When replacing an O2 sensor, make sure it is the same type as the original (heated or unheated).
Sensor Replacement
Any O2 sensor that needs to be replaced But there are also benefits of replacing the O2 sensor periodically for preventive maintenance. Replacing a aging O2 sensor that has become sluggish can restore power efficiency, minimize exhaust emissions and prolong the life of the converter.

Unheated 1 or 2 wire wire O2 sensors on 1976 through early 1990s vehicles can be replaced by 30,000 to 50,000 miles Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications can be changed every 60,000 miles On OBDII equipped vehicles (1996 & amp; nbsp; up), a replacement interval of 100,000 miles is recommended.