JPS6157929B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas purification device that oxidizes HC and CO and refluxes NOx while maintaining the best fuel efficiency of an engine. Harmful components emitted from engines include HC, CO, and NOx, and HC and CO can be converted to harmless components by oxidizing them, and NOx can be converted to harmless components by reducing them.

For this purpose, a three-way catalyst is installed in the exhaust system,
An exhaust purification system that simultaneously oxidizes HC and CO and reduces NOx has been proposed.

In this case, the three-way catalyst combines oxidizing components ( _O2 gas) and reducing components (CO,
The catalyst will not be effective unless it contains just the right amount of reducing gas (HC, H2 _, etc.) to react with each other. Therefore, the total air-fuel ratio of the catalyst inflow gas must be accurately set to the stoichiometric air-fuel ratio (excess air ratio: 1). Must be.

To do this, either the mixture supplied to the engine has a stoichiometric air-fuel ratio, or the mixture supplied to the engine is rich and secondary air is introduced into the exhaust gas. This kept the air-fuel ratio at the stoichiometric ratio.

However, the fuel efficiency of the engine is best when a mixture that is slightly leaner than the stoichiometric air-fuel ratio is supplied, so supplying a mixture that is at or above the stoichiometric air-fuel ratio is not a good idea in terms of fuel efficiency. I can not say.

The present invention was made with attention to this point, and it is possible to operate the engine with a lean mixture,
By providing a device for removing oxygen components not involved in combustion from the exhaust gas, such as an oxygen removal device using a selective oxygen permeable substance, the total air-fuel ratio of the exhaust gas flowing into the three-way catalyst is approximately the stoichiometric air-fuel ratio. To provide an exhaust purification device that efficiently oxidizes HC and CO and reduces NOx while maintaining the best fuel efficiency of an engine.

Embodiments of the present invention will be described below based on the drawings.

In FIG. 1, 10 is the engine body;
As the fuel supply device 9, for example, a fuel injection valve that injects and supplies fuel to an intake port is attached.

The fuel supply device 9 controls the fuel supply amount corresponding to the intake air amount so that the engine intake air-fuel mixture becomes an air-fuel ratio thinner than the stoichiometric air-fuel ratio during steady operation, most preferably an air-fuel ratio in the best fuel efficiency range. be done.

An oxygen removal device 12 is provided in the exhaust passage 11 to remove oxygen components in the exhaust gas.

Downstream of the oxygen removal device 12, when the total air-fuel ratio of the exhaust gas flowing into the catalyst is the stoichiometric air-fuel ratio, HC, CO
A three-way catalyst device 13 that efficiently oxidizes NOx and reduces NOx is installed, and the exhaust gas after passing through this catalyst is passed through the oxygen removal device 12 again to the exhaust pipe 14.
flows out to.

The oxygen removal device 12 has a rectangular parallelepiped housing 16.
There are two inlets 17A and 18A and an outlet 17.
B, 18B are formed, and a diaphragm 1A made of a selective oxygen-permeable material, such as a solid electrolyte such as zirconia oxide shown in FIG. 2, is accommodated therein.

That is, porous electrodes A ₁ to A ₉ and C ₁ to C ₉ made of platinum (Pt), palladium (Pd, and rhodium (Rh)) as shown in Figure 3 are attached to both sides, and they are alternately spaced at predetermined intervals and widths. The diaphragm 1 which has been folded up with the same angle as the diaphragm 1 is tightly housed inside the housing 16.

In this case, the exhaust gas flowing in from the inlet 17A passes through the upstream chamber 21 divided by the diaphragm 1A and flows out only from the outlet 17B, and the exhaust gas flows from the other inlet 18A.
The upper and lower surfaces and both ends are sealed so that the exhaust gas flowing in from the diaphragm 1A passes through the downstream chamber 22 divided by the other surface of the diaphragm 1A, and flows out only from the outlet 18B.

The diaphragm 1 is formed of an oxygen ion conductive solid electrolyte, and when there is a difference in oxygen concentration on both sides, oxygen is moved from the side with a higher oxygen partial pressure to the side with a lower oxygen partial pressure.

Furthermore, an oxygen sensor 19 is provided downstream of the oxygen removal device 12 to detect the oxygen concentration in the exhaust gas flowing into the three-way catalyst 13.
Based on the output of 9, a control circuit (not shown) adjusts the minute voltage applied between the aforementioned opposing electrodes _A1 and _C1 , _A2 and _C2 ... _A9 and _C9 , and The conductivity of oxygen ions in the diaphragm 1A made of electrolyte is controlled.

Next, the effect will be explained.

In an oxygen removal device, the exhaust gas upstream of the catalyst is in contact with one side of the selective oxygen permeable diaphragm, and the exhaust gas downstream of the catalyst is in contact with the other side, and the oxygen component content (%) on both sides is
are the same, but the oxygen partial pressure is higher on the upstream side than on the downstream side due to the pressure difference based on the flow resistance in the catalyst section, so oxygen in the upstream exhaust gas moves through the diaphragm into the downstream exhaust gas. do.

In Fig. 3, a diaphragm 1 made of a solid electrolyte such as zirconia oxide (ZrO ₂ ) can cause a difference in the partial pressure of oxygen in the exhaust gas that comes into contact with both sides of the diaphragm 1. Assuming that the partial pressure is higher than that of the exhaust gas after passing through, oxygen ions flow from the electrodes A ₁ to _{A 9} side to the electrodes C ₁ to C ₉ side in the solid electrolyte.
O ^2- moves.

Therefore, the reaction O ₂ ÷ 4e ^- →2O ^2- progresses on the A electrode side and 2O ^2- → O ₂ +4e ^- on the C electrode side, and the electron e generated on the C electrode side moves to the A current side. , oxygen O ₂ taken in from the A electrode side moves to the C electrode side.

In this way, oxygen moves from the combustion exhaust gas of the lean mixture after passing through the catalyst to the exhaust gas after passing through the catalyst through the solid electrolyte diaphragm 1, and the total exhaust air-fuel ratio gradually approaches the stoichiometric air-fuel ratio. .

However, as can be seen from the configuration in FIG. 1, in reality, the exhaust gas discharged from the engine body 10 passes through the three-way catalyst device 13 and directly flows into the oxygen removal device 12, so the solid electrolyte partition wall 1
At first, there is almost no difference in the oxygen concentration on both sides of A.

In other words, the above assumption is based on the assumption that the exhaust gas after passing through the three-way catalyst contains almost no oxygen, so oxygen transfer is smooth, but the three-way catalyst To the extent that the oxygen components in the exhaust gas are consumed by the oxidation reaction of unburned HC and CO in step 13, the difference in oxygen concentration on both sides of the diaphragm 1A is small, and the reaction rate that causes the movement of oxygen is extremely small.

On the other hand, if a small voltage is applied from a control circuit between electrodes C ₁ to C ₉ and A ₁ to _{A 9} to force current to flow, oxygen uptake is forced and the reaction rate slows down. It increases significantly.

Therefore, by applying a minute voltage between the A and C electrodes and expanding the area of the diaphragm 1A made of solid electrolyte in a corrugated shape as shown in FIG. It is possible to sufficiently reduce the oxygen component in the exhaust gas before it enters the exhaust gas, so that the air-fuel ratio becomes approximately the stoichiometric air-fuel ratio.

In the three-way catalyst device 13, if the total air-fuel ratio of the inflowing exhaust gas is controlled to the stoichiometric air-fuel ratio (λ ₀ ≒ 14, 54), both the oxidation of HC and CO and the reduction of NOx can be efficiently performed. This can be done, and together with the dilution of the air-fuel mixture for the engine body 10, exhaust purification and fuel efficiency can be improved at the same time.

Figure 4 shows the changes in the characteristics of NOx emissions and fuel efficiency in relation to the air-fuel ratio (A/F) of the mixture and the exhaust gas recirculation rate (EGR rate). The dashed-dotted line indicates the stability limit of the engine, and the shaded area is the area where operation becomes difficult due to poor stability if the EGR rate is increased further or the air-fuel ratio is made leaner.

If the NO emission value is set as a target of 1.5g/PS・h, achieving this with EGR would be around point A in the figure due to the balance with fuel efficiency.

In this case, an oxidation catalyst is also installed to reduce HC and CO while supplying secondary air into the exhaust gas.

In the conventional three-way catalyst device, the supplied air-fuel mixture is limited to around the stoichiometric air-fuel ratio, so the area with the best fuel efficiency is around point B.

However, with a three-way catalyst, NO can be reduced to about 1/4, so emissions from the engine can be tolerated up to about 5g/PS/h.

In contrast, when the air-fuel ratio is diluted,
In the region where NO emissions are below 5g/PS・h, fuel efficiency is best around point C.

This point C has much better fuel efficiency than the other points A and B, so the fuel supply amount is adjusted so that the fuel supply device 9 obtains an air-fuel ratio near this point C. Through this control, the present invention can achieve significantly better fuel efficiency than conventional systems.

By the way, in the oxygen removal device 12, when rhodium (Rh) is added to the platinum electrodes _A1 to _A9 , it also functions as a catalyst, making it possible to reduce NOx and oxidize HC and CO.

In the region where the overall air-fuel ratio of the exhaust gas becomes almost the stoichiometric air-fuel ratio due to the movement of oxygen ions, the electrode area of the electrodes A ₁ to _{A 9} (electrodes on the downstream side with respect to the exhaust flow) that come into contact with this exhaust gas is reduced to a certain extent. By enlarging it, the three components mentioned above can be removed at the same time as oxygen is removed.

Therefore, the power consumption in the three-way catalyst device 12 is such that the voltage value is very small, so the load on the battery is not so great, and even if the applied current is not strictly controlled, the power consumption in the upstream exhaust gas will be reduced. As long as the concentration is zero, unless a high voltage is applied,
Since no oxygen is transferred and the air-fuel ratio freely reaches the theoretical value, feedback control using the oxygen sensor 19 is not necessarily required.

FIG. 5 shows the housing 16' of the oxygen removal device 12.
This is a modification of the solid electrolyte folded partition wall 1
A retention chamber 30 is formed at the rear of A, and an inlet 17A is formed.
The exhaust gas flowing into the upstream chamber 21 (see Figure 2) from the inlet 17A removes oxygen and oxidizes HC and CO.
It flows into the retention chamber 30 while undergoing a reduction reaction of NOx, and here it makes a U-turn and flows into the downstream chamber 22 and flows out from the outlet 18B.

Note that an oxygen sensor 19 may be attached to the retention chamber 30 to detect the oxygen concentration.

In this case, the three-way catalyst device 13 is removed, but it is also possible to do so if the catalytic action in the oxygen removal device 12 is sufficiently performed.

As explained above, the present invention removes excess oxygen contained in the exhaust gas before it flows into the three-way catalyst, so that the engine can be operated at the best fuel efficiency and the three-way catalyst can also function optimally. This has the effect of improving both fuel efficiency and exhaust performance.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the overall configuration of the present invention;
Figure 2 is a perspective view of the solid electrolyte diaphragm, Figure 3 is a partially enlarged sectional view of the solid electrolyte diaphragm, and Figure 4 is a diagram showing fuel efficiency.
An explanatory diagram showing the NO emission characteristics based on the air-fuel ratio and the exhaust gas recirculation rate, and FIG. 5 is a perspective view showing another example of the oxygen removal device. 1, 1A... Solid electrolyte diaphragm, 9... Fuel supply device, 10... Engine body, 12... Oxygen removal device, 13... Three-way catalyst device, 16... Housing, 17A, 18A... Inlet, 17B ,18B...
...Exit, 19...Oxygen sensor, 20...Control circuit (means), 21...Upstream side chamber, 22...Downstream side chamber.

Claims (1)

[Claims] 1 A fuel that supplies a mixture leaner than the stoichiometric air-fuel ratio to the engine in an internal combustion engine that has a three-way catalytic converter installed in the engine exhaust passage to simultaneously oxidize HC and CO in the exhaust gas and reduce NOx. The oxygen removing device is equipped with a supply device and an oxygen removing device installed in the upstream exhaust passage of the three-way catalyst device. 1. An exhaust gas purification device characterized in that the exhaust gas is configured to remove excess oxygen in the exhaust gas before the catalyst flows in by passing the exhaust gas after the catalyst flows into a downstream chamber.