Closed Loop Operation

Closed loop operation simply means that the ECU is making air/fuel ratio corrections based on oxygen sensor information. Although the ECU can calculate injection duration very accurately without using information from the oxygen sensor, closed loop control brings the air/fuel ratio within the extremely narrow operating parameters of the three-way catalyst (TWC).

The oxygen sensor monitors the oxygen concentrations in the exhaust stream and outputs a voltage signal to the ECU. This signal allows the eCu to determine whether the air/fuel ratio is leaner or richer than the theoretical value necessary for the best catalyst conversion efficiency.

• Exhaust oxygen sensor voltage signal above 1/2 volt indicates an air/fuel ratio richer than stoichiometry. 'Me ECU will reduce fuel injection duration to correct this condition.

• Exhaust oxygen sensor voltage signal below 1/2 volt indicates an air/fuel ratio leaner than stoichiometry. The ECU will increase fuel injection duration to correct this condition.

• During normal closed loop operation, the oxygen sensor signal rapidly switches between these two conditions (at a rate of more than eight times in ten seconds at 2500 rpm). Small injection duration corrections take place each time the signal voltage switches from high to low and back again.

The closed loop correction coefficient ranges from 0.8 to 1.2 (that is, +20% from the basic fuel calculation). If the air/fuel ratio goes out of the ECU's range of correction, the ECU will typically set a diagnostic code and return to open loop operation.

In a closed loop control system, the command corrects the condition.

• Oxygen sensor monitors exhaust condition

• ECU commands injectors to correct condition

• Oxygen sensor indicates correction accuracy

• ECU again commands injectors to correct condition

High (Rich)

Voltage of Oxygen Sensor Signal

■5V

o

h

f

)

w

LJ

Low (Lean

Injection Volume

+ |

"I

s

r\1

--

Decreased Increased

Engine Open Loop Operation
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Responses

  • amira
    Why Toyota open loop closed loop?
    2 years ago

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