Exhaust System; Three-Way Catalyst; Oxygen Sensor - Kubota WG1605-G-E3 Workshop Manual

WG1605-G-E3,WG1605-L-E3,WG1605-GL-E3, WSM

5. EXHAUST SYSTEM

[1] THREE-WAY CATALYST

[2] OXYGEN SENSOR

A three-way catalyst is a catalyst that oxidizes HC to
CO and H O and also CO to CO
2 2
same time reduces NOx to N
ratio.
The main basic component of an exhaust gas
purification system that uses a three-way catalyst is
feedback control of air-fuel ratio by means of an oxygen
sensor for the purpose of maximizing the emission
purification efficiency characteristic with reference to the
intake air-fuel ratio of the three-way catalyst.
(1) Catalytic Converter
An Oxygen sensor is an essential element of a
feedback control of air-fuel ratio. The sensor has a
mechanism in which a zirconia tube, which is a solid
electrolyte, is exposed into the exhaust gas and the
outside of a zirconia tube to an exhaust gas, the inside
to an atmosphere with a known oxygen concentration
respectively. Any difference produced between the two
sides of the zirconia tube causes electromotive force to
be generated. Oxygen sensor should be installed at the
catalyst inlet and outlet each.
[Pre-Catalyst Oxygen Sensor]
When the air-fuel ratio is rich, HC, CO, H
with the oxygen (O
2
This causes a significant reduction of the concentration
of the remaining oxygen, which considerably increases
the ratio of it to the concentration of oxygen contained in
the atmosphere inside, increasing the electromotive
force. When the air-fuel ratio is lean, the process is the
other way around, resulting in a significant drop in the
electromotive force near the stoichiometric ratio. That is,
the feedback control functions as electronic control that
reduces the air-fuel ratio when it is judged to be on the
rich side based on the electromotive force and increases
the ratio when it is on the lean side.
[Post-Catalyst Oxygen Sensor]
A post-catalyst oxygen sensor provides information
that can be used 1) to diagnose how efficiently a catalyst
is using the available oxygen to react and 2) to adjust or
trim pre-catalyst equivalence ratio (air-fuel ratio) to a
desired level to optimize catalyst conversion efficiency.
1-M18
respectively and at the
2
near the stoichiometric
2
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, etc. react
2
) that remains in the exhaust gas.
9Y1210661ENM0024US0
KiSC issued 01, 2012 A
ENGINE