A description of system control

Way back in the ?early to mid 80,s the motor trade started to see engine management systems  control at this stage i might just interject and say i speak from a vauxhall point of view.so here goes
The motor industry is under going  a dramatic change in its approach to problem solving .
When i first started work  on a petrol engine all you were involved with was spark  / ignition and fuel
now you are thinking about is there spark yes or no can the imobiliser see the engine controller if not then & so forth.

OBD GENERATION 1





In order to have greater control of fueling to achieve emission standards .
microprocessor control systems were developed by :-
bosch
ac-delco
ford   -

 To name but a few, these systems all differed in one way or other but  they all controlled the fueling by acting on information supplied by various sensors.

 input signals involved








engine speed + crank angle
engine load
water temperature
air temperature
air mass or quantity
Camshaft sensor (only used for sequential injection on multivalve engines)
in some cases  vehicle speed.

The control unit  takes all these input signals and calculates the following :-

output signals








Ignition output and advance to drive the coil into collapse condition to create a spark at the correct time
injection pulse to drive the injector/s open for the correct length of time (pulse width or dwell)
 

At the same time the ECU is looking at a mapped reference if at any time it see,s anything that it objects to, the management warning light will be illuminated to warn the driver at which point the engine may go into limp home mode and start running roughly  this would depend on the particular fault that had occurred.

If  after the engine cools down and the ECU still see,s a fault the engine may not start at all (fault dependant)
 
 
 

with onward  development  of engine control systems (closed loop operation) was introduced to bring even greater control  to fueling requirements , engines running correctly will conform to something called  stoichiometry which is an air/fuel ratio of  14.7:1 to achieve this an oxygen sensor is placed in the exhaust system in front of an item called a catalyictic convertor for more information  on CATS refer to   Bath university.

and also see Eurocats
below you will see an oxygen(o2 sensor) this is yet an other input signal
 
 

This o2 sensor is at the heart of the closed loop operation, it looks at exhaust gas passing over it  when it see,s o2 it generates a small ac voltage which the ecu uses to modify injection pulse width to conform to stoichiometry see below the curve of stoichiometry with kind permission of the spx corp. (bear diagnostics)
defunked in the uk as of 29/3/2k1
 
 
 
 
 


 
 
 
 
 
 
 
 
 
 
 

O2 = OXYGEN

                                                                                                                                    CO2                                                                                                                                       CO = CARBON  MONOXIDE
                                                                                                                                   HYDRO CARBONS
                                                                                                                                    HC IS ALSO KNOWN AS UNBURNT FUEL
An other name for stoichiometry is lambda 1
And thus the O2 sensor often gets called  the lambda sensor.
 
 

The air we breath consists of 20% O2 therefore on a four cylinder engine each cylinder will receive 5% thats the theory .
however in reality  even an engine that is brand spanking new will never ever have complete burn properties and as a result you can expect to see up to 2% O2 residue in exhaust gas analysis
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