JPH06167215A - Catalyst warming up device for internal combustion engine - Google Patents

Abstract

PURPOSE:To keep NOx emission amount to the atmosphere within the target value and to. CONSTITUTION:A catalyst warming up device is provided with an upstream side lean NOx catalyst 5, which reduces NOx by utilizing HC and is provided in an engine exhaust passage 3, a downstream side catalyst 4, which at least has oxidation action and is provided in the engine exhaust passage 3, and a combustible material supply combustion means 6, 8, 9, which supply a combustible material between both of the catalysts in the engine exhaust passage 3 at least on an engine cool start so as to burn the combustible material by utilizing unburned oxygen in the engine combustion chamber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention supplies a combustible material such as hydrogen upstream of a catalytic converter in an exhaust passage and ignites it with a spark plug to burn it, thereby warming up the catalyst early when the engine is cold started. The present invention relates to a catalyst warm-up device for an internal combustion engine for activating it.

[0002]

2. Description of the Related Art Conventionally, in such a catalyst warm-up device, oxygen for burning hydrogen is required, and an air supply device is provided in addition to the hydrogen supply device. Japanese Patent Laid-Open No. Hei 4
In order to reduce the cost by omitting this air supply device, the No. 262086 adopts an internal combustion engine that enables lean combustion, and removes oxygen that is left unburned from the combustion chamber. Those used for hydrogen combustion have been proposed.

A three-way catalyst that is usually used for purifying exhaust gas is one that, when the catalyst is active, oxidizes carbon monoxide and hydrocarbon, which are harmful components in the exhaust gas, and reduces nitrogen oxide to purify it. . When the air-fuel mixture is near the stoichiometric air-fuel ratio, the aforementioned oxidation and reduction are carried out in a well-balanced manner, and good purification of harmful components is realized, but the leaner the air-fuel mixture, the more inactive the reducing action becomes, and the nitric oxide Has the drawback that it is discharged without being purified.

Therefore, in the exhaust system of a lean burn internal combustion engine,
In addition to the above-mentioned three-way catalyst, a lean NOx catalyst for purifying nitrogen oxide is provided. Since this lean NOx catalyst normally reduces nitrogen oxides by utilizing hydrocarbons in exhaust gas, it is arranged upstream of the three-way catalyst where a large amount of hydrocarbons are present in the exhaust gas.

[0005]

The above-mentioned conventional technique is to supply hydrogen to the upstream side of the lean NOx catalyst arranged upstream of the three-way catalyst to burn it at the cold start of the engine. As a result, the lean NOx catalyst is warmed up, and the nitrogen oxides are satisfactorily purified, and the amount of atmospheric release can be made equal to or less than the target value, but the combustion heat of hydrogen is absorbed by the lean NOx catalyst, so that it is downstream thereof. The located three-way catalyst could not be warmed up and some of the hydrocarbons were used in the lean NOx catalyst to purify the nitric oxide, but due to the small amount, hydrocarbons and A large amount of carbon oxide is released into the atmosphere. .

Therefore, an object of the present invention is to maintain at least the atmospheric emission amount of nitrogen oxides at this time in an internal combustion engine that executes lean combustion at the cold start of the engine, and, in comparison with the prior art, It is an object of the present invention to provide a combustible substance combustion type catalyst warm-up device for an internal combustion engine capable of reducing the amount of hydrocarbons and carbon monoxide released into the atmosphere at this time.

[0007]

A first catalyst warm-up device for an internal combustion engine according to the present invention is an upstream lean NOx provided in an engine exhaust passage for reducing nitrogen oxides by utilizing hydrocarbons.
A combustible material is supplied between the catalyst, a downstream catalyst provided in the engine exhaust passage having at least an oxidizing action, and at least both catalysts in the engine exhaust passage at the time of engine cold start, and unburned in the engine combustion chamber. And a combustible substance supply and combustion means for combusting using oxygen.

A second catalyst warm-up device for an internal combustion engine according to the present invention is the catalyst warm-up device for a first internal combustion engine as described above, further comprising upstream of the upstream lean NOx catalyst in the engine exhaust passage. A sub-catalyst having a capacity selected so as to at least purify hydrocarbons in exhaust gas having an oxidizing action even when the catalyst is activated, and supplying the combustible material upstream of the engine exhaust passage. It is characterized in that the combustion means supplies a combustible material and burns it by utilizing the unburned oxygen.

[0009]

In the above-described first catalyst warm-up device for an internal combustion engine, the combustible substance supply / combustion means uses at least the upstream lean NOx catalyst for reducing nitrogen oxides using hydrocarbons and at least an oxidizing action when the engine is cold-started. By supplying a combustible substance to the engine exhaust passage between the downstream side catalyst and the downstream side catalyst, the unburned oxygen in the engine combustion chamber is used for combustion, whereby the downstream side catalyst is warmed up and activated. It successfully purifies carbon oxides and significantly reduces their atmospheric emissions. On the other hand, nitric oxide is not generated much at the time of cold starting of the engine, and the amount of atmospheric release can be made equal to or less than the target value even by the lean NOx catalyst before warming up.

In the catalyst warm-up device for the second internal combustion engine described above, a sub-catalyst having at least an oxidizing action is further provided upstream of the upstream lean NOx catalyst, and a combustible material is supplied when the engine is cold started. The combustor supplies a combustible material upstream of the sub-catalyst and burns it using unburned oxygen in the engine combustion chamber, whereby the sub-catalyst is warmed up and activated.
This sub-catalyst is selected so that its capacity can purify hydrocarbons in the exhaust gas to some extent even when the catalyst is activated, so that the amount of hydrocarbons and carbon monoxide is purified to reduce atmospheric emissions. At the same time, the remaining hydrocarbons are supplied to the lean NOx catalyst located downstream thereof and utilized for the reduction of nitric oxide, so that the atmospheric emission amount thereof can be made equal to or less than the target value.

[0011]

FIG. 1 is an overall schematic view showing a first embodiment of a catalyst warm-up device for an internal combustion engine according to the present invention. In the figure, 1 is a lean burn engine, 2 is an intake passage, and 3 is an exhaust passage. The exhaust passage 3 has a three-way catalyst 4 and C upstream thereof.
A u / zeolite lean NOx catalyst 5 is arranged. Exhaust gas discharged from the combustion chamber due to lean combustion
Since the three-way catalyst 4 contains a large amount of unburned oxygen, the reducing action of the three-way catalyst 4 becomes inactive, and the nitrogen oxide cannot be sufficiently purified. Therefore, in the lean burn engine 1, in addition to the three-way catalyst 4, There is provided a lean NOx catalyst 5 which is in charge of purifying nitric oxide.

This lean NOx catalyst 5 reduces nitrogen oxides by utilizing the hydrocarbons in the exhaust gas, and has a sufficient reducing action unless there are several times as many hydrocarbons as nitrogen oxides by weight. Although not realized, the hydrocarbon actually used is only a fraction of nitric oxide. Therefore, the lean NOx catalyst 5 is arranged upstream of the three-way catalyst 4 in which a large amount of hydrocarbons are present in the exhaust gas, and the three-way catalyst 5 is still needed. The three-way catalyst 4 has a considerable difference in purification performance depending on its temperature, and since the purification performance is considerably low especially at low temperatures, early warm-up is required when the engine is cold started. It

A supply pipe 6a extending from the hydrogen generator 6
Is a three-way catalyst 4 and a lean NOx catalyst 5 via the control valve 7.
A spark plug 8 is arranged in the vicinity of this connection portion of the exhaust passage 3 and is connected to the spark plug 8. The control device 9 that controls the fuel injection amount of the engine 1 is also in charge of the opening / closing control of the control valve 7 and the ignition control of the spark plug 8, and the control device 9 includes sensors such as the cooling water temperature sensor 10 (not shown). No) is electrically connected.

The control device 9 controls the control valve 7 and the spark plug 8 based on the signal from the cooling water temperature sensor 10 and the ON signal of the starter switch (not shown) to detect that the engine is cold starting. Then, the control valve 7 is opened and the spark plug 8 is ignited. As a result, at this time, hydrogen is supplied to the exhaust passage 3 between the three-way catalyst 4 and the lean NOx catalyst 5, and is reliably ignited by the spark plug 8 together with unburned oxygen discharged by the lean combustion of the engine 1. The three-way catalyst 4 is warmed up early.

Since the conventional catalyst warm-up device carries out the combustion of hydrogen upstream of the lean NOx catalyst 5, the lean NOx catalyst 5 is warmed up and the nitrogen oxide is satisfactorily purified,
Although the amount of atmospheric release can be made equal to or less than the target value, the combustion heat of hydrogen is absorbed by the lean NOx catalyst 5, and the three-way catalyst 4 located downstream of the lean NOx catalyst 5 cannot be warmed up. And carbon monoxide was released into the atmosphere.

However, since the catalyst warm-up device of this embodiment executes the combustion of hydrogen between the lean NOx catalyst 5 and the three-way catalyst 4, the three-way catalyst 4 is warmed up early. It can clean hydrocarbons and carbon monoxide well and reduce their atmospheric emissions considerably. On the other hand, lean NO
The x-catalyst 5 is not warmed up so much, but the purification performance of this catalyst does not depend so much on the temperature, and since the combustion temperature is low at the cold start of the engine, the amount of nitrogen oxides generated is small and the catalyst is warmed up. Even with the previous lean NOx catalyst 5, the atmospheric emission amount can be made sufficiently lower than the target value.

FIG. 2 is a schematic view of an exhaust passage portion showing a second embodiment of the catalyst warm-up device for an internal combustion engine according to the present invention. Only the differences from the first embodiment will be described below. In the present embodiment, an auxiliary three-way catalyst 11 having a small capacity is further arranged upstream of the lean NOx catalyst 5 in the exhaust passage 3. The capacity of the sub-three-way catalyst 11 takes into consideration the amounts of hydrocarbons and nitrogen oxides contained in the exhaust gas when the engine is cold-started, and even when the catalyst is active, the lean NOx catalyst 5 located downstream thereof is oxidized. It is determined that only enough hydrocarbons to achieve a good reduction of nitrogen will pass unpurified.

The supply pipe 6a of the hydrogen generator 6 is connected upstream of the sub-three-way catalyst 11, and a spark plug 8 is arranged near this connection portion of the exhaust passage 3. Control valve 7 and spark plug 8
The control is executed in the same manner as in the first embodiment, and therefore, the combustion of hydrogen is realized upstream of the sub-three-way catalyst 11 when the engine is cold started.

As a result, the sub-three-way catalyst 11 is warmed up early, and in order to purify hydrocarbons and carbon monoxide in the exhaust gas flow to some extent, their atmospheric emission amounts are increased as compared with the conventional catalyst warming device. Can be reduced accordingly. Further, as for the nitric oxide reducing action in the lean NOx catalyst 5, since the hydrocarbons that are well realized are supplied without purification, the nitrogen oxide atmospheric release amount is equal to or less than the target value as in the first embodiment. Can be

In the present embodiment, since the capacity of the sub-three-way catalyst 11 is small, there is an advantage that the hydrogen required for warming up can be reduced, and by supplying the same amount of hydrogen as in the first embodiment, In addition to warming up the sub-three-way catalyst 11, it is possible to warm up the lean NOx catalyst downstream thereof to some extent, and the nitrogen oxides can be further purified by that amount as compared with the first embodiment.

The catalysts for reducing nitric oxide used in the first and second embodiments are not limited to those of Cu / zeolite type, and any catalysts that reduce nitric oxide using hydrocarbons can be used. Hydrogen and carbon monoxide oxidation catalyst,
It is obvious that the catalyst is not limited to the three-way catalyst, and any catalyst having at least an oxidizing action may be used.

It is also possible to use a combustible substance other than hydrogen as the combustible substance burned in the exhaust passage for warming up the catalyst.

[0023]

As described above, according to the catalyst warm-up device for an internal combustion engine according to the present invention, by setting the hydrogen combustion position in the exhaust passage between the upstream lean NOx catalyst and the downstream three-way catalyst, the It is possible to warm up the three-way catalyst whose purification performance deteriorates considerably at temperature early, and to effectively purify hydrocarbons and carbon monoxide when the engine is cold-started. Can be significantly reduced. On the other hand, the reduction of nitric oxide in the lean NOx catalyst is
At this time, since the amount of generated nitrogen oxide is small, the amount of atmospheric release can be made sufficiently lower than the target value even with the lean NOx catalyst before warming up. Further, in a configuration in which a sub-three-way catalyst is further provided upstream of the upstream lean NOx catalyst, the hydrogen combustion position in the exhaust passage is set to the upstream of the sub-three-way catalyst, so that the sub-three-way catalyst can be used at the engine cold start. Can be warmed up early to purify hydrocarbons and carbon monoxide to some extent, and correspondingly reduce their emission into the atmosphere. On the other hand, the reduction of nitric oxide in the lean NOx catalyst is
Since the capacity of the sub-three-way catalyst is determined so that hydrocarbons sufficient to achieve the reduction effect are supplied unpurified, the amount of nitrogen oxides released into the atmosphere is set to the target value or less. be able to.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram showing a first embodiment of a catalyst warm-up device for an internal combustion engine according to the present invention.

FIG. 2 is a schematic view of an exhaust passage portion showing a second embodiment of the catalyst warm-up device for an internal combustion engine according to the present invention.

[Explanation of symbols]

 1 ... Lean combustion engine 3 ... Exhaust passage 4 ... Three-way catalyst 5 ... Lean NOx catalyst 6 ... Hydrogen generator 7 ... Control valve 8 ... Spark plug 9 ... Control device 11 ... Sub-three way catalyst

Claims (2)

[Claims] 1. An upstream lean NOx catalyst provided in an engine exhaust passage for reducing nitrogen oxides using hydrocarbons,
A combustible substance is supplied between at least the downstream catalyst provided in the engine exhaust passage having an oxidizing action and the both catalysts in the engine exhaust passage at the time of engine cold start, and unburned oxygen in the engine combustion chamber is used. And a combustible substance supply and combustion means for combusting and burning the catalyst. 2. The lean N upstream of the engine exhaust passage.
Further, upstream of the Ox catalyst, there is further provided a sub-catalyst whose capacity is selected so that hydrocarbons in exhaust gas can be purified only to some extent even if the catalyst has an oxidizing action and the catalyst is activated. 2. The catalyst warm-up device for an internal combustion engine according to claim 1, wherein the combustible material supply / combustion means supplies combustible material upstream thereof to utilize the unburned oxygen for combustion.