Lubricating oil composition

1. A lubricating oil composition comprising the below-described additive components dissolved or dispersed in a base oil;

1) an overbased sulfurized alkylphenol calcium salt having a TBN of 200 to 300 mgKOH/g, in an amount of 0.06 to 0.25 wt. % in terms of a calcium content;

(2) an overbased alkylsalicylic acid calcium salt having a base ratio of 1.8 to 2.5 and one hydrocarbyl group of 14 to 18 carbon atoms, the base ratio being expressed in terms of a calcium content in an overbase portion per a calcium content in a soap portion, in an amount, of 0.05 to 0.7 wt. % in terms of a calcium content;

(3) an overbased alkylsalicylic acid calcium salt having a base ratio of 4.2 to 5.8 and one hydrocarbyl group of 20 to 28 carbon atoms, the base ratio being expressed in terms of a calcium content in an overbase portion per a calcium content in a soap portion, in an amount of 0.19 to 1.05 wt. % in terms of a calcium content;

(4) a borated ashless dispersant in an amount of 0.005 to 0.06 wt. % in terms of a nitrogen content and 0.001 to 0.02 wt. % in terms of a boron content; and

(5) a zinc dihydrocarbyldithiophosphate in an amount of 0.01 to 0.1 wt. % in terms of a phosphorus content.

2. The lubricating oil composition, of claim 1 , which has a TBN of 20 to 60 mgKOH/g.

3. The lubricating, oil composition of claim 1 , in which the overbased alkylsalicylic acid calcium salt of (2) has a TBN of 120 to 220 mgKOH/g.

4. The lubricating oil composition of claim 1 , in which the overbased alkylsalicylic acid calcium salt of (3) has a TBN 230 to 340 mgKOH/g.

5. The lubricating oil composition of claim 1 , in which the borated ashless dispersant is a succinimide compound containing a boron atom in a molecular structure thereof.

6. The lubricating oil composition of claim 1 , in which the zinc dihydrocarbyldithiophosphate is a primary zinc dihydrocarbyldithiophosphate.

7. A lubricating oil composition comprising the below-described additive components dissolved or dispersed in a base oil:

(1) an overbased sulfurized alkylphenol calcium salt having a TBN of 200 to 300 mgKOH/g, in an amount of 0.06 to 0.40 wt. % in terms of a calcium content;

(2) an overbased alkylsalicylic acid calcium salt having a base ratio of 1.8 to 2.5 and one hydrocarbyl group of 14 to 18 carbon atoms, the base ratio being expressed in terms of a calcium content in an overbase portion per a calcium content in a soap portion, in an amount of 0.05 to 0.5 wt. % in terms of a calcium content;

(3) an overbased alkylsalicylic acid calcium salt having a base ratio of 3.6 to 4.5 and one hydrocarbyl group of 20 to 28 carbon atoms, the base ratio being expressed in terms of a calcium content in an overbase portion per a calcium content in a soap portion, in an amount of 0.08 to 1.55 wt. % in terms of a calcium content;

(4) an overbased alkylsalicylic acid calcium salt having a base ratio of 7.7 to 8.7 and one hydrocarbyl group of 20 to 28 carbon atoms, the base ratio being expressed in terms of a calcium content of an overbase portion per a calcium content of a soap portion, in an amount of 0.1 to 0.7 wt. % in terms of a calcium content;

(5) a borated ashless dispersant in an amount of 0.005 to 0.06 wt. % in terms of a nitrogen content and 0.001 to 0.02 wt. % in terms of a boron content; and

(6) a zinc dihydrocarbyldithiophosphate in an amount of 0.01 to 0.1 wt. % in terms of a phosphorus content.

8. The lubricating oil composition of claim 7 , which has a TBN of 20 to 60 mgKOH/g.

9. The lubricating oil composition of claim 7 , in which the overbased alkylsalicylic acid calcium salt of (2) has a TBN of 120 to 220 mgKOH/g.

10. The lubricating oil composition of claim 7 , in which the overbased alkylsalicylic acid calcium salt of (3) has a TBN 200 to 270 mgKOH/g.

11. The lubricating oil composition of claim 7 , in which the overbased alkylsalicylic acid calcium salt of (4) has a TBN 280 to 350 mgKOH/g.

12. The lubricating oil composition of claim 7 , in which the borated ashless dispersant is a succinimide compound containing a boron atom in a molecular structure thereof.

13. The lubricating oil composition of claim 7 , in which the zinc dihydrocarbyldithiophosphate is a primary zinc dihydrocarbyldithiophosphate.

14. A method for reducing top ring piston wear of a four stroke trunk piston engine comprising operating said engine with the lubricating oil composition of claim 1 .

15. A method for reducing top ring piston wear of a four stroke trunk piston engine comprising operating said engine with the lubricating oil composition of claim 7 .