Catalyst light-off method and device for direct injection engine

Claim 2

A catalyst light-off method for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber the method comprising: causing the injector to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device, and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher than the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and retarding the ignition point of the ignition device by a specified amount beyond a minimum spark advance for best torque (MBT) when the catalyst is in its unheated state.

Claim 3

A catalyst light-off method for a direct injection engine according to claim 1 , wherein the later injection cycle is performed during a compression stroke and the earlier injection cycle is performed during the intake stroke in the split injection conducted when the catalyst is in its unheated state, and wherein the later injection cycle is commenced before three-fourths of the period of the compression stroke elapses.

Claim 4

A catalyst light-off method for a direct injection engine according to claim 2 , wherein the amount of fuel injected in the earlier injection cycle is made equal to larger than the amount of fuel injected in the later injection cycle in the split injection conducted when the catalyst is in its unheated state, and wherein the ignition point is retarded to or beyond the top dead center of the compression stroke in a low-speed, low-load range.

Claim 5

A catalyst light-off method for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber the method comprising: causing the injector to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device, and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher than the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and retarding the ignition point of the ignition device by a specified amount beyond a minimum spark advance for best torque (MBT) when the catalyst is in its unheated state wherein the earlier injection cycle is performed during the intake stroke and the later injection cycle is performed during a middle portion of a compression stroke or later but before three-fourths of the period of the period of the compression stroke elapses in the split injection, the air-fuel ratio in the entire combustion chamber is set to fall within a range of 13 to 17, and the amount of fuel injected in the earlier injection cycle is set to fall within a range of about ⅕ to about ⅘ of the total amount of the injected fuel when the catalyst is in its unheated state, and wherein the ignition point of the ignition device is retarded to or beyond the top dead center of the compression stroke in a low-speed, low-load range excluding an idling speed range and a no-load range.

Claim 6

A catalyst light-off method for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber the method comprising: causing the injector to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device, and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher than the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and retarding the ignition point of the ignition device by a specified amount beyond a minimum spark advance for best torque (MBT) when the catalyst is in its unheated state wherein the earlier injection cycle is performed during the intake stroke and the later injection cycle is performed during a middle portion of a compression stroke or later but before three-fourths of the period of the period of the compression stroke elapses in the split injection, the air-fuel ratio in the entire combustion chamber is set to fall within a range of 13 to 17, and the amount of fuel injected in the earlier injection cycle is set to fall within a range of about ⅕ to about ⅘ of the total amount of the injected fuel when the catalyst is in its unheated state, and wherein the ignition point of the ignition device is retarded to or beyond the top dead center of the compression stroke in a low-speed, low-load range excluding an idling speed range and a no-load range.

Claim 7

A catalyst light-off method for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber the method comprising: causing the injector to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device, and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher than the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and retarding the ignition point of the ignition device by a specified amount beyond a minimum spark advance for best torque (MBT) when the catalyst is in its unheated state, wherein uniform combustion is made by causing the injector to inject the fuel during the intake stroke in a low-speed, low-load range when the catalyst is in its heated state in which its temperature is equal to or higher than its activation temperature, whereas the air-fuel ratio in the entire combustion chamber is set to fall within a range of 13 to 17, and the injector is caused to make the split injection including the earlier injection cycle performed during the intake stroke to injection about ⅕ to ⅘ of the total amount of the injected fuel and the later injection cycle performed during a middle portion of a compression stroke or later to inject the remainder of the total amount of the injected fuel in the low-speed, low-load range, wherein the earlier injection cycle produces a uniform and lean mixture in the combustion chamber and the later injection cycle creates unevenness in the mixture in the combustion chamber, forming mixture masses locally richer than other portions and scattering them in the combustion chamber, when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, and the ignition point of the ignition device is retarded compared to the ignition point set under the same engine speed and load conditions as when the catalyst is in its heated state.

Claim 8

A catalyst light-off method for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber the method comprising: causing the injector to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device, and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher than the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and retarding the ignition point of the ignition device by a specified amount beyond a minimum spark advance for best torque (MBT) when the catalyst is in its unheated state, wherein uniform combustion is made by causing the injector to inject the fuel during the intake stroke in a low-speed, low-load range when the catalyst is in its heated state in which its temperature is equal to or higher than its activation temperature, whereas the air-fuel ratio in the entire combustion chamber is set to fall within a range of 13 to 17, and the injector is caused to make the split injection including the earlier injection cycle performed during the intake stroke to injection about ⅕ to ⅘ of the total amount of the injected fuel and the later injection cycle performed during a middle portion of a compression stroke or later to inject the remainder of the total amount of the injected fuel in the low-speed, low-load range, wherein the earlier injection cycle produces a uniform and lean mixture in the combustion chamber and the later injection cycle creates unevenness in the mixture in the combustion chamber, forming mixture masses locally richer than other portions and scattering them in the combustion chamber, when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, and the ignition point of the ignition device is retarded compared to the ignition point set under the same engine speed and load conditions as when the catalyst is in its heated state.

Claim 9

A catalyst light-off device for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber, catalyst light-off device comprising: a temperature state identifier for judging the temperature state of the catalyst; a fuel injection controller for controlling fuel injection from the injector; and an ignition timing controller for controlling an ignition point of the ignition device; wherein the fuel injection controller controls the injector based on judgment results of the temperature state identifier to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device; and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and the ignition timing controller controls the ignition device in such a way that the ignition point is retarded by a specified amount beyond a minimum spark advance for best torque (MBT) when the split injection is conducted while the catalyst is in its unheated state.

Claim 10

A catalyst light-off device for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber, catalyst light-off device comprising: a temperature state identifier for judging the temperature state of the catalyst; a fuel injection controller for controlling fuel injection from the injector; and an ignition timing controller for controlling an ignition point of the ignition device; wherein the fuel injection controller controls the injector based on judgment results of the temperature state identifier to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device; and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and the ignition timing controller controls the ignition device in such a way that the ignition point is retarded by a specified amount beyond a minimum spark advance for best torque (MBT) when the split injection is conducted while the catalyst is in its unheated state.

Claim 11

A catalyst light-off device for a direct injection engine according to claim 6 , wherein the fuel injection controller controls the injector such that the later injection cycle is performed during a compression stroke and the earlier injection cycle is performed during the intake stroke in the split injection conducted when the catalyst is in its unheated state, and wherein the later injection cycle is commenced before three-fourths of the period of the compression stroke elapses.

Claim 12

A catalyst light-off device for a direct injection engine according to claim 7 , wherein the fuel injection controller makes the amount of fuel injected in the earlier injection cycle equal to larger than the amount of fuel injected in the later injection cycle, and the ignition timing controller retards the ignition point to or beyond the top dead center of the compression stroke in a low-speed, low-load range when the split injection is conducted while the catalyst is in its unheated state.

Claim 13

A catalyst light-off device for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber, catalyst light-off device comprising: a temperature state identifier for judging the temperature state of the catalyst; a fuel injection controller for controlling fuel injection from the injector; and an ignition timing controller for controlling an ignition point of the ignition device; wherein the fuel injection controller controls the injector based on judgment results of the temperature state identifier to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device; and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and the ignition timing controller controls the ignition device in such a way that the ignition point is retarded by a specified amount beyond a minimum spark advance for best torque (MBT) when the split injection is conducted while the catalyst is in its unheated state, wherein a piston which is fitted in a cylinder bore of the engine and forms a bottom side of the combustion chamber is a flat piston having no cavity for capturing a mixture for stratified charge formation, and the later injection cycle of the split injection cycle conducted when the catalyst is in its unheated state creates a condition in which mixture masses locally richer than other portions are scattered in the combustion chamber.

Claim 14

A catalyst light-off device for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber, catalyst light-off device comprising: a temperature state identifier for judging the temperature state of the catalyst; a fuel injection controller for controlling fuel injection from the injector; and an ignition timing controller for controlling an ignition point of the ignition device; wherein the fuel injection controller controls the injector based on judgment results of the temperature state identifier to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device; and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and the ignition timing controller controls the ignition device in such a way that the ignition point is retarded by a specified amount beyond a minimum spark advance for best torque (MBT) when the split injection is conducted while the catalyst is in its unheated state, wherein a piston which is fitted in a cylinder bore of the engine and forms a bottom side of the combustion chamber is a flat piston having no cavity for capturing a mixture for stratified charge formation, and the later injection cycle of the split injection cycle conducted when the catalyst is in its unheated state creates a condition in which mixture masses locally richer than other portions are scattered in the combustion chamber.

Claim 15

A catalyst light-off device for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber, catalyst light-off device comprising: a temperature state identifier for judging the temperature state of the catalyst; a fuel injection controller for controlling fuel injection from the injector; and an ignition timing controller for controlling an ignition point of the ignition device; wherein the fuel injection controller controls the injector based on judgment results of the temperature state identifier to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device; and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and the ignition timing controller controls the ignition device in such a way that the ignition point is retarded by a specified amount beyond a minimum spark advance for best torque (MBT) when the split injection is conducted while the catalyst is in its unheated state, wherein the fuel injection controller controls the injector based on judgment results of the temperature state identifier to perform the earlier injection cycle during the intake stroke and the later injection cycle during a middle portion of a compression stroke or later but before three-fourths of the period of the compression stroke elapses in the split injection, sets the air-fuel ratio in the entire combustion chamber to fall within a range of 13 to 17, and sets the amount of fuel injected in the earlier injection cycle to fall within a range of about ⅕ to about ⅘ of the total amount of the injected fuel when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, and the ignition timing controller retards the ignition point to or beyond the top dead center of the compression stroke in a low-speed, low-load range based on a temperature state of the catalyst and a load condition when the split injection is conducted while the catalyst is in its unheated state.

Claim 16

A catalyst light-off device for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber, catalyst light-off device comprising: a temperature state identifier for judging the temperature state of the catalyst; a fuel injection controller for controlling fuel injection from the injector; and an ignition timing controller for controlling an ignition point of the ignition device; wherein the fuel injection controller controls the injector based on judgment results of the temperature state identifier to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device; and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and the ignition timing controller controls the ignition device in such a way that the ignition point is retarded by a specified amount beyond a minimum spark advance for best torque (MBT) when the split injection is conducted while the catalyst is in its unheated state, wherein the fuel injection controller controls the injector based on judgment results of the temperature state identifier to perform the earlier injection cycle during the intake stroke and the later injection cycle during a middle portion of a compression stroke or later but before three-fourths of the period of the compression stroke elapses in the split injection, sets the air-fuel ratio in the entire combustion chamber to fall within a range of 13 to 17, and sets the amount of fuel injected in the earlier injection cycle to fall within a range of about ⅕ to about ⅘ of the total amount of the injected fuel when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, and the ignition timing controller retards the ignition point to or beyond the top dead center of the compression stroke in a low-speed, low-load range based on a temperature state of the catalyst and a load condition when the split injection is conducted while the catalyst is in its unheated state.

Claim 17

A catalyst light-off device for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber, catalyst light-off device comprising: a temperature state identifier for judging the temperature state of the catalyst; a fuel injection controller for controlling fuel injection from the injector; and an ignition timing controller for controlling an ignition point of the ignition device; wherein the fuel injection controller controls the injector based on judgment results of the temperature state identifier to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device; and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and the ignition timing controller controls the ignition device in such a way that the ignition point is retarded by a specified amount beyond a minimum spark advance for best torque (MBT) when the split injection is conducted while the catalyst is in its unheated state, wherein the fuel injection controller controls fuel injection based on a temperature state and a load condition in such a way that uniform combustion is made by causing the injector to inject the fuel during the intake stroke in a low-speed, low-load range when the catalyst is in its heated state in which its temperature is equal to or higher than its activation temperature, whereas the air-fuel ratio in the entire combustion chamber is set to fall within a range of 13 to 17, and the injector makes the split injection including the earlier injection cycle performed during the intake stroke to inject about ⅕ to about ⅘ of the total amount of the injected fuel and the later injection cycle performed during a middle portion of a compression stroke or later to inject the remainder of the total amount of the injected fuel in the low-speed, low-load range, wherein the earlier injection cycle produces a uniform and lean mixture in the combustion chamber and the later injection cycle creates unevenness in the mixture in the combustion chamber, forming mixture masses locally richer than other portions and scattering them in the combustion chamber, when the catalyst is in its unheated state in which its temperature is lower than its activation temperature; and the ignition timing controller controls the ignition device such that the ignition point of the engine is retarded compared to the ignition point set under the same engine speed and load conditions as when the catalyst is in its heated state, when the split injection is conducted while the catalyst is in its unheated state.

Claim 18

A catalyst light-off device for a direct injection engine having a catalyst provided in an exhaust passage for converting exhaust gases, an injector for injecting fuel directly into a combustion chamber and an ignition device for igniting a mixture in the combustion chamber, catalyst light-off device comprising: a temperature state identifier for judging the temperature state of the catalyst; a fuel injection controller for controlling fuel injection from the injector; and an ignition timing controller for controlling an ignition point of the ignition device; wherein the fuel injection controller controls the injector based on judgment results of the temperature state identifier to make at least two-step split injection during a period from an intake stroke to an ignition point when the catalyst is in its unheated state in which its temperature is lower than its activation temperature, the split injection including: a later injection cycle which produces a mixture mass having a plurality of richer mixture portions scattered substantially in the entirety of the combustion chamber to be ignited and burnt by said ignition device; and an earlier injection cycle which produces a lean mixture mass having an air-fuel ratio higher the stoichiometric air-fuel ratio by injecting fuel prior to the later injection cycle, wherein the lean mixture mass causes flame propagation by fuel injected in the later injection cycle and combustion thereof and causes main combustion during a main combustion period in which approximately 10% to 90% by mass of the injected fuel is burnt in a combustion process occurring in the combustion chamber; and the ignition timing controller controls the ignition device in such a way that the ignition point is retarded by a specified amount beyond a minimum spark advance for best torque (MBT) when the split injection is conducted while the catalyst is in its unheated state, wherein the fuel injection controller controls fuel injection based on a temperature state and a load condition in such a way that uniform combustion is made by causing the injector to inject the fuel during the intake stroke in a low-speed, low-load range when the catalyst is in its heated state in which its temperature is equal to or higher than its activation temperature, whereas the air-fuel ratio in the entire combustion chamber is set to fall within a range of 13 to 17, and the injector makes the split injection including the earlier injection cycle performed during the intake stroke to inject about ⅕ to about ⅘ of the total amount of the injected fuel and the later injection cycle performed during a middle portion of a compression stroke or later to inject the remainder of the total amount of the injected fuel in the low-speed, low-load range, wherein the earlier injection cycle produces a uniform and lean mixture in the combustion chamber and the later injection cycle creates unevenness in the mixture in the combustion chamber, forming mixture masses locally richer than other portions and scattering them in the combustion chamber, when the catalyst is in its unheated state in which its temperature is lower than its activation temperature; and the ignition timing controller controls the ignition device such that the ignition point of the engine is retarded compared to the ignition point set under the same engine speed and load conditions as when the catalyst is in its heated state, when the split injection is conducted while the catalyst is in its unheated state.