Heating system for catalytic converter

A heating system for a catalytic converter of a multi-cyclinder, spark-ignition engine is provided. Half of the cylinders of the engine, for example, the cylinder #2 and the cylinder #3, are operated on a rich gas mixture with an excess air ratio of 0.6 or less to produce a combustible gas mixture comprising hydrogen, carbon monoxide, and unburned fuel components, while the remaining half of the cylinders, for example, the cylinder #1 and the cylinder #4, are utilized as air blowers to which no fuel is fed. The flammable gas mixture produced from the combustible gas produced in the cylinder #2 and the cylinder #3 and the air supplied by the cylinder #1 and the cylinder #4 is burned in the combustor equipped with an ignition device which is installed upstream from the catalytic converter to provide heat energy to activate the catalyst. The system can rapidly heat and activate the catalyst without requiring a special fuel supply system and air blower.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a heating system used in a catalytic 
converter for a multi-cyclinder, spark-ignition engine, and more 
particularly to a heating system for a catalytic converter which rapidly 
heats and activates the catalyst during the warm-up period of an engine 
cold start without requiring a special fuel supply system and air blower 
for heating the catalyst. 
2. Discussion of the Background 
Various rapid heating systems for the catalysts in catalytic converters for 
exhaust gas from internal combustion engines have been proposed, 
accompanying the enforcement of regulations for exhaust gas. One of these 
systems has an exhaust gas combustor installed upstream from the catalyst. 
Fuel is injected into the combustor to generate heat energy to rapidly 
heat the catalyst. 
This conventional system requires a fuel supply unit with a fuel injector 
through which the fuel is fed to the exhaust gas combustor. In addition, a 
separate air blower is required to supply air to the exhaust gas 
combustor. The requirement for these units pose serious problems in terms 
of cost and reliability. 
The object of the present invention is to provide a heating system which 
can rapidly heat the catalyst in the catalytic converter without requiring 
a separate fuel supply unit and an air blower, thereby ensuring a 
less-polluting exhaust gas emission from internal combustion engines. 
SUMMARY OF THE INVENTION 
This object of the present invention is achieved by the provision of 
heating system for a catalytic converter comprising: 
a multi-cylinder, spark-ignition engine, 
a combustor provided with an ignition means which is installed downstream 
from the exhaust gas manifold of the engine and upstream from a catalytic 
converter, and 
a controller which controls the operation of the multi-cylinder, spark 
ignition engine so that, up to the point where the catalyst in the 
catalytic converter is sufficiently activated to convert the exhaust gas 
from the engine half of the cylinders are operated on a rich gas mixture 
with an excess air ratio of 0.6 or less to produce a combustible gas 
mixture comprising hydrogen, carbon monoxide, and unburned fuel components 
and the remaining half of the cylinders are operated to feed air, thereby 
producing a flammable gas mixture including said combustible gas mixture 
and the air, the flammable gas mixture being burned in said combustor to 
provide heat energy to activate the catalyst, and after the catalyst has 
been activated all cylinders are operated in a normal manner. 
Other objects, features and advantages of the invention will hereinafter 
become more readily apparent from the following description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
By means of the above-described heating system of the present invention 
half of the cylinders in a multi-cylinder, spark ignition engine are 
operated on a rich gas mixture with an excess air ratio of 0.6 or smaller 
to produce a combustible gas mixture comprising hydrogen, carbon monoxide, 
and unburned fuel components, while the remaining half of the cylinders 
are utilized as air blowers to which no fuel is fed. This operation 
ensures production of a flammable mixture in the combustor which is 
installed upstream from the catalytic converter for the exhaust gas. In 
this manner the catalyst is rapidly heated without requiring a separate 
fuel supply unit and air blowers. 
An embodiment of the present invention will be described with reference to 
FIG. 1 showing the construction of the heating system of the present 
invention. A multi-cylinder, spark ignition engine 1 has four cylinders, 
#1 to #4, which are indicated by the numeral 3. The cylinders have an 
air-intake manifold 2 to introduce air therein and fuel injectors 4 
through which fuel is injected. The exhaust gas exits the cylinders 
through an exhaust gas manifold 5 and is sent to a catalytic converter 6, 
where the noxious components in the exhaust gas are catalytically 
converted into clean gas. A temperature sensor 7 is installed in the 
catalytic converter which detects the temperature of the catalyst and 
transmits the detected temperature to the engine control unit 10 for 
controlling the operation of the fuel injectors 4. 
A combustor 8 equipped with an ignition means 9, such as a spark plug, is 
installed upstream from the catalytic converter 6. During the warm-up 
period after a cold start, the engine control unit 10 controls the fuel 
injectors 4 so that fuel is fed to half the cylinders, for example, the 
cylinder #2 and the cylinder #3 or the cylinder #1 and the cylinder #4, to 
produce a rich gas mixture with an excess air ratio of 0.6 or less, while 
no fuel is fed to the remaining cylinders, that is, the cylinder #1 and 
the cylinder #4 or the cylinder #2 and the cylinder #3. 
Illustrating the operation for the case where the fuel is fed to the 
cylinder #2 and the cylinder #3, and not to the cylinder #1 and the 
cylinder #4, as an example, the excess air ratio of a rich gas mixture in 
the cylinder #2 and the cylinder #3 is maintained at 0.6 or less, while 
the cylinder #1 and the cylinder #4 function as air blowers. 
A combustible gas mixture is produced in the cylinder #2 and the cylinder 
#3 by the combustion of the rich gas mixture and discharged to the exhaust 
gas manifold 5. The combustion gas mixture is then sent to the combustor 8 
which is located immediately below the exhaust gas manifold 5, where the 
combustible gas mixture is mixed with the air supplied by the cylinder #1 
and the cylinder #4 to produce a flammable mixture. This flammable mixture 
is ignited and burned in the combustor 8 by the ignition means 9 to 
produce heat energy which rapidly heats the catalyst in the catalyst 
converter 6. 
While the flammable mixture is burned in the combustor 8, the engine 
control unit controls the quantity of fuel supplied to the fuel injectors 
4 for the cylinder #2 and the cylinder #3 so that the excess air ratio of 
the flammable mixture in the combustor 8 is maintained preferably at 1.0 
or more. Emission of carbon monoxide and unburned fuel should be minimized 
by maintaining this oxidative atmosphere. 
The catalyst in the catalytic converter 6 has been confirmed by experiment 
to be rapidly heated to a temperature of 400.degree. C. within 20 seconds 
after a cold start. This temperature of the catalyst is measured by the 
temperature sensor 7 installed in the catalyst bed. Upon completion of 
rapid heating of the catalyst, the quantity of fuel supplied to the 
cylinder #2 and the cylinder #3 through the fuel injectors 4 is restored 
to the quantity for normal operation via instruction from the engine 
control unit 8 and, at the same time, the quantity of fuel for normal 
operation is also supplied to the cylinder #1 and the cylinder #4, which 
function as air blowers. 
In order to burn the flammable mixture in the combustor 8, the 
concentration of the combustible gas mixture comprising hydrogen, carbon 
monoxide, and unburned fuel components and the concentration of oxygen 
should be within a flammable limit. Experiments have proven that among 
hydrogen, carbon monoxide, and unburned fuel components the hydrogen has 
the broadest flammable limit, and thus the concentration of hydrogen is 
most important for igniting the gaseous mixture. It was found that the 
concentration of hydrogen in the flammable gas mixture should be about 5% 
or more and that of oxygen about 9% or more. 
The concentrations of hydrogen produced by the combustion of flammable 
mixture are about 10%, 15%, and 20% at the excess air ratios of 0.6, 0.5, 
and 0.4, respectively. If the combustible mixture with these hydrogen 
concentrations are diluted with air having an oxygen concentration of 
20.6%, the hydrogen concentrations are about 5%, 7.5%, and 10% at the 
excess air ratios of 0.6, 0.5, and 0.4, respectively, and the oxygen 
concentration is about 10.3%. These concentrations of both the hydrogen 
and oxygen are above the flammable limits mentioned above, and thus 
satisfy the conditions for ignition. 
Based on this analysis, by means of the present invention half of the 
cylinders of the multi-cylinder, spark ignition engine are operated on a 
rich gas mixture with an excess air ratio of 0.6 or less, and the 
remaining half of the cylinders are utilized as air blowers to which no 
fuel is fed. The exhaust gas from the first half the cylinders containing 
10% or more hydrogen is thereby diluted with the same volume of air to 
ensure production of a flammable mixture containing 5% or more hydrogen 
and 9% or more oxygen. 
As illustrated above, by means of the heating system of the present 
invention half of the cylinders of the multi-cylinder, spark ignition 
engine are operated on a rich gas mixture with an excess air ratio of 0.6 
or less to produce a combustible gas mixture comprising hydrogen, carbon 
monoxide, and unburned fuel components, while the remaining half of the 
cylinders are utilized as air blowers to which no fuel is fed. The 
flammable gas mixture produced from the combustible gas produced in half 
of the cylinders and the air supplied by the other half of the cylinders 
is burned in the combustor equipped with an ignition means which is 
installed upstream from the catalytic converter. This system can rapidly 
heat the catalyst during the warm-up period at a cold start without 
requiring a separate fuel supply unit and air blowers, and ensures the 
remarkable effects of low cost and high reliability. 
This application is based on Japanese patent application 333763/1994, filed 
on Dec. 19, 1994, which is incorporated herein by reference in its 
entirety. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that, within the scope of the appended claims, the invention 
may be practiced otherwise than as specifically described herein.