1. A method for manufacturing an iron golf club head comprising a face portion having a backside portion, the iron golf club head made of metal material in which the head has a concave portion having a bottom surface and being surrounded by a convex portion in the backside portion of the face portion, at least the convex portion and the concave portion are formed integrally and at least a part of the bottom surface of the concave portion is a mirror surface; wherein the mirror surface is formed through plastic working of the bottom surface.
2. A method for manufacturing an iron golf club head according to claim 1, wherein the mirror surface is obtained through press working with a die having a surface roughness finer than the mirror surface for which treatment for making a mirror surface is to be performed.
3. A method for manufacturing an iron golf club head according to claim 2, wherein a die face with treatment for making a mirror surface applied is provided in the die of the backside of the head for forming an iron golf club, press working is performed with the die face and the die face of the movable die on the side of the face portion and the die face with treatment for making a mirror surface applied applies treatment for making a mirror surface on the backside portion, and
wherein a liner member is provided in the die face of the die of the backside of the head so as to be movable relative thereto forward and backward and the press working is performed on the bottom surface with the liner member to apply treatment for making a mirror surface on the backside portion.
4. A method for manufacturing an iron golf club head according to claim 1, wherein the mirror surface is formed on a part of the bottom portion and the mirror surface has a surface having a value no less than 400 GU in 20\xb0 according to JIS Z8741 which defines standards for glossiness of a mirror surface and measurement of glossiness.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
What is claimed is:
1. An air-fuel ratio control system for an internal combustion engine provided with a NOx trap catalyst disposed in an exhaust gas passageway and arranged to trap NOx in a first condition in which an air-fuel ratio of exhaust gas flowing to the NOx trap catalyst is lean and to release and reduce trapped NOx in a second condition in which the air-fuel ratio of exhaust gas flowing to the NOx trap catalyst is rich, said air-fuel ratio control system comprising:
a sensor for detecting an air-fuel ratio of exhaust gas in the exhaust gas passageway downstream of the NOx trap catalyst; and
a control circuit configured to
cause the engine to operate at a rich air-fuel ratio to accomplish a rich air-fuel ratio engine operation after an engine operation at a lean air-fuel ratio, and
continue the rich air-fuel ratio engine operation for a first duration even after said sensor has detected that the air-fuel ratio of exhaust gas is rich.
2. An air-fuel ratio control system as claimed in claim 1, wherein said control circuit is configured to set the first duration in accordance with a second duration of from a first time at which the rich air-fuel ratio engine operation is initiated to a second time at which said sensor detects that the air-fuel ratio of exhaust gas is rich.
3. An air-fuel ratio control system as claimed in claim 2, wherein said control circuit is configured to set the first duration by multiplying the second duration by a rate.
4. An air-fuel ratio control system as claimed in claim 1, wherein said control circuit is configured to gradually decrease a degree of enrichment of the air-fuel ratio for the first duration.
5. An air-fuel ratio control system as claimed in claim 1, wherein said control circuit is configured to set the first duration in accordance with a first value corresponding to a fuel injection amount for enriching the air-fuel ratio over a stoichiometric air-fuel ratio for the second duration.
6. An air-fuel ratio control system as claimed in claim 5, wherein said control circuit is configured to subtract a first accumulated value of the first value for the first duration from a second accumulated value of a second value obtained by multiplying the first value by a rate so as to obtain a subtracted value, and terminate the rich air-fuel ratio engine operation at a time when the subtracted value becomes lower than a threshold value.
7. An air-fuel ratio control system as claimed in claim 6, wherein said control circuit is configured to decrease the degree of the enrichment of the air-fuel ratio as the subtracted value decreases.
8. An air-fuel ratio control system as claimed in claim 1, wherein said control circuit is configured to decrease a degree of enrichment of the air-fuel ratio for the first duration relative to a degree of enrichment of the air-fuel ratio used before said sensor detects that the air-fuel ratio of exhaust gas is rich.
9. An air-fuel ratio control system as claimed in claim 1, wherein said control circuit is configured to accomplish the rich air-fuel ratio engine operation for the first duration by enriching an average air-fuel ratio in an air-fuel ratio feedback control.
10. An air-fuel ratio control system as claimed in claim 1, wherein said control circuit is configured to cause the engine to operate at a stoichiometric air-fuel ratio after termination of the rich air-fuel ratio engine operation for the first duration.
11. An air-fuel ratio control system for an internal combustion engine provided with a NOx trap catalyst disposed in an exhaust gas passageway and arranged to trap NOx in a first condition in which an air-fuel ratio of exhaust gas flowing to the NOx trap catalyst is lean and to release and reduce trapped NOx in a second condition in which the air-fuel ratio of exhaust gas flowing to the NOx trap catalyst is rich, said air-fuel ratio control system comprising:
means for detecting an air-fuel ratio of exhaust gas in the exhaust gas passageway downstream of the NOx trap catalyst;
means for causing the engine to operate at a rich air-fuel ratio to accomplish a rich air-fuel ratio engine operation after an engine operation at a lean air-fuel ratio; and
means for continuing the rich air-fuel ratio engine operation for a duration even after said detecting means has detected that the air-fuel ratio of exhaust gas is rich.
12. A method of controlling an air-fuel ratio in an internal combustion engine provided with a NOx trap catalyst disposed in an exhaust gas passageway and arranged to trap NOx in a first condition in which an air-fuel ratio of exhaust gas flowing to the NOx trap catalyst is lean and to release and reduce trapped NOx in a second condition in which the air-fuel ratio of exhaust gas flowing to the NOx trap catalyst is rich, said method comprising:
detecting an air-fuel ratio of exhaust gas in the exhaust gas passageway downstream of the NOx trap catalyst;
causing the engine to operate at a rich air-fuel ratio to accomplish a rich air-fuel ratio engine operation after an engine operation at a lean air-fuel ratio; and
continuing the rich air-fuel ratio engine operation for a duration even after the sensor has detected that the air-fuel ratio of exhaust gas is rich.