High performance non-zinc, zero phosphorus engine oils for internal combustion engines

Abstract

A substantially zinc and phosphorous free lubricating oil meeting engine performance requirements contain an additive system containing metal detergents, at least one borated ashless dispersant, at least an amine antioxidant and a trinuclear molybdenum compound. The lubricant contains a minimum of 120 ppm boron and a minimum of 80 ppm molybdenum.

Description

This application claims the benefit of U.S. Ser. No. 60/497,234 filed Aug. 22, 2003.

FIELD OF INVENTION

The present invention is concerned broadly with lubricating compositions and more specifically with lubricating compositions for internal combustion engines that are substantially free of phosphorous and zinc.

BACKGROUND OF INVENTION

Contemporary engine oil technology uses zinc dithiophosphates (ZDTP) or more specifically zinc dialkyldithiophosphate (ZDDP) for corrosion, oxidation and wear protection and metallic detergents for engine cleanliness. These additives are rich in sulfur, phosphorous and ash content, and play a critical role in meeting severe engine performance requirements. Unfortunately phosphorous tends to deactivate the catalysts typically employed for control of hydrocarbon emissions from the engine. Volatile sulfur is harmful to the catalysts used to control NO_x emissions; and, zinc contributes to plugging engine exhaust particulate filters. Although sulfur emissions can be reduced by formulating lubricant compositions using low sulfur base oils as much as two thirds of the sulfur and almost all of the phosphorous present in engine oils is due to the use of ZDTP or ZDDP. Thus, there is a need for low sulfur containing engine oils that are substantially free of zinc and phosphorous and yet which do not adversely effect engine performance. Indeed there is a further need for low sulfur, non-phosphorous, non-zinc engine oils that are particularly suitable for use with low sulfur (<350 ppm) fuels. The present invention provides for these and other needs.

SUMMARY OF INVENTION

In one aspect, the present invention is directed toward a lubricating composition having low levels of sulfur, preferably below about 2000 ppm sulfur, and substantially no zinc or phosphorous, the composition comprising:

• • (a) a major amount of a base oil of lubricating viscosity; and
  • (b) an additive system comprising
    • (i) a metal detergent or mixture of metal detergents;
    • (ii) an ashless dispersant or mixture of dispersants, at least one of which is a borated ashless dispersant;
    • (iii) an ashless aminic antioxidant or mixture of antioxidants containing at least an aminic antioxidant; and
    • (iv) an oil soluble, phosphorous free, trinuclear molybdenum compound.
  • (c) with the proviso that the composition has a minimum of 120 ppm boron and a minimum of 80 ppm molybdenum.

Another aspect of the present invention is directed toward a low sulfur containing lubricant composition which is substantially zinc and phosphorous free that is particular suitable for use in engines combusting low sulfur fuels, the composition comprising a major amount of a low sulfur base oil, preferably below about 300 ppm sulfur and an additive system comprising a combination of a metal detergent or mixture of metal detergents, at least a borated ashless dispersant, an ashless antioxidant or mixture of antioxidants containing at least an aminic antioxidant, and an oil soluble, phosphorous free, trinuclear molybdenum compound, the composition having a B:Mo:N ratio in the range of about 3:5:7 to about 5:1:18.

The lubricants of the invention are especially useful with fuels containing below about 350 ppm sulfur.

These and other aspects of the invention will become apparent from the detailed description which follows.

DETAILED DESCRIPTION OF INVENTION

The lubricating compositions of the present invention will comprise a major amount of a base oil of lubricating viscosity and a minor but effective amount of a specific combination of dispersants, antioxidants, detergents and antiwear agents which do not contain zinc and phosphorous. Thus the compositions do not include zinc and phosphorous containing additives and as such are substantially free of zinc and phosphorous.

The base oils of the present invention will have less than about 300 ppm sulfur. Thus suitable base oils include highly refined Groups II and III base oils as well as Groups IV and V oils and mixtures thereof. Preferred are Groups III, IV and V base oils.

The additive system of the invention includes a metal detergent or mixture of metal detergents, such as alkaline metal detergents. Useful alkaline metal detergents are selected from calcium and magnesium sulfonates, phenates and salicylates and mixtures thereof.

The amount of metal detergent will constitute about 1.5 to about 6.0 wt % based on the total weight of the composition. Preferably the detergent will be a mixture of alkaline metal sulfonates, and phenates and salicylates in the weight ratio of about 25:75:0 to 0:20:80.

The additive system includes a borated ashless dispersant or a mixture of a borated ashless dispersant and non-borated ashless dispersants. In general, sufficient borated dispersants will be used to provide the composition with a minimum of 120 ppm boron. Useful borated dispersants include sulfur and phosphorous free borated succinimides and succinic acid esters. Preferred borated dispersants are derivatives of polyisobutylene substituted with succinic anhydride and reacted with polyethylene amines, polyoxyethylene amines and polyolamines (PIBSA/PAM). Useful non-borated ashless dispersants include sulfur and phosphorous free succinimides, carboxylic acid amides, hydrocarbyl polyamines and the like. Preferred non-borated dispersants are based on 600 molecular weight PIB to 2800 molecular weight PIB as exemplified by Lubrizol 6461, Lubrizol 6418, Hitec 646, Oloa 13000, ADX 222 and the like.

In the practice of the invention it is preferred to use a mixture of borated and non-borated ashless dispersants in the weight ratio of 1:9 to 9:1. In any event, the total amount of ashless dispersant used in the composition is in the range of about 2.0 wt % to about 12.0 wt % based on the total weight of the composition.

The additive system of the invention includes an ashless aminic antioxidant or mixture of antioxidants containing at least an aminic antioxidant. Useful aminic antioxidants include alkylated diphenyl amine, alkylated phenylenediamine, alkylated phenyl alpha-naphthylamine and alkylated quinoline.

In addition to the aminic antioxidant supplementary antioxidants may be employed. These include hindered phenols, hindered bisphenols, sulfurized phenols, sulfurized olefins, dithiocarbamates, phenothiazines and the like.

Typically antioxidants used in the present invention will be a mixture of non-borated phenolic and amine antioxidants. The weight ratio of phenol to amine is in the range of 1.0:9.0 to 9.0:1.0. The preferred antioxidant is a mixture of hindered phenols and alkylated diphenylamines. It also is preferred that the antioxidant be present in an amount ranging from about 0.25 wt % to 2.5 wt %, based on the total weight of the composition.

The composition of the invention includes an oil soluble, phosphorous free trinuclear molybdenum compound. Such compounds may be represented by the formula Mo₃S_kL_nQ_z where the L are independently selected ligands having organo groups with a sufficient number of carbon atoms to render the compound soluble or dispersible in the oil, n is from 1 to 4, k varies from 4 through 7, Q is selected from the group of neutral electron donating compounds such as water, amines, alcohols, and ethers, and z ranges from 0 to 5 and includes non-stoichiometric values. At least 21 total carbon atoms should be present among all the ligands' organo groups, such as at least 25, at least 30, or at least 35 carbon atoms. The preferred ligands are dialkyl dithiocarbamates. In general, sufficient trinuclear molybdenum compound is used to provide the composition with a minimum of 80 ppm molybdenum. Thus, trinuclear compound typical is present in about 0.05 wt % to about 1.50 wt %, based on the total weight of the composition.

Importantly, the compositions of the invention are formulated to have a B:Mo:N ratio in the range of about 3:5:7 to about 5:1:18.

The compositions of the invention optionally may include other additives typically used in formulating engine oils such as antifoamants, seal swell agents, viscosity index improvers and the like.

The invention will be further illustrated by the following examples.

EXAMPLE 1

A series of engine lubricants were formulated having the compositions set forth in Table 1. Oil 1 included for comparative purposes had a sulfur content of 3080 ppm and a phosphorous content of 960 ppm. Oils 2 and 3 were substantially zinc and phosphorous free and had sulfur levels of 1161 and 1483 ppm respectively.

	TABLE 1
	Oil 1	Oil 2	Oil 3
	Synthetics	Synthetics	Synthetics
	Component	Viscosity Grade
Formulation	Chemistry	0W-40	0W-30	5W-30
Mixed Ashless	Borated & non-	8	8	8
Dispersants	borated PIB
	succinimide/ester
Mixed	Ca/Mg sulfonate/	3.35	4.3	4.3
Detergents	phenate/salicylate
ZDDP	Zinc	1.0	0	0
	dithiophosphates
Mixed	Phenolic &	1.0	1.5	1.5
Antioxidants	Aminic
	antioxidants
Mixed Friction	Moly Trimer &	0.46	0.35	0.35
Modifiers	ashless friction
	modifiers
Mixed	Silicone & non-	3.02	2.0	2.0
Defoamants/seal	silicone
swell agent/VI
improvers
Base Oil	Group IV/V	Bal.	Bal.	Bal.
Ash (D874)	Wt %	0.96	0.99	1.05
Zn	Ppm	1000	<5	<5
Mo	Ppm	0	180	170
B	Ppm	180	540	545
N	Ppm (calculated)	1049	1494	1494
P	Ppm	960	<5	<5
S (D2622-1)	Ppm	3080	1161	1483

These oils were then subjected to the engine performance tests listed in Table 2. The results of these tests are also provided in that table.

	TABLE 2
	Oil 1	Oil 2	Oil 3
	Engine Oil Type
	Synthetics	Synthetics	Synthetics
	Viscosity Grades
	PAO,	PAO,	Group III,
	0W-40	0W-30	5W-30
	Special Remark
Test	Test	Normal	Low S,	Low S,
Method	Measurement	S/P/Ash	Zn/P free	Zn/P free
HFRR1	Ave. Friction	0.125	0.12	0.123
0.7 Kg/60 Hz/	% Ave. Film	0	96.5	81.4
0.5 mm/	Scar X/Y (mm)	0.3/0.7	.3/0.7	0.267/0.667
60 min./75° C.	Calc. Scar Area	0.165	0.165	0.14
Set One	(mm2)
HFRR1	Ave. Friction	0.096	0.089	0.096
0.5 Kg/60 Hz/	% Ave. Film	4.66	90.8	95.7
1.0 mm/	Scar X/Y (mm)	0.3/1.28	0.3/1.23	0.28/1.2
60 min./100° C.	Calc. Scar Area	0.302	0.291	0.267
Set Two	(mm2)
Four-Ball Wear	WSD (mm)	0.47	0.40	0.38
40 Kg/1800 rpm/	K Factor
30 min./200° F.	(×10E−8)
PDSC2
Ramping @	Onset Temp	236	258.1	251.7
10° C. C/min.	(° C.)
Isothermal @	Time (min.)	10.8	16.9	16.6
220° C.
Hot Tube Test	1 = clean,	3	1	1
16 hr./288° C.	9 = dirty
Sequence IVA
Cam Nose		56.9	6.7
wear (Micron)
Total Wear		305	43.8
(Micron)
1HFRR = High Frequency Reciprocating Rig
2PDSC = Pressure Differential Scanning Calorine Tray

The High Frequency Reciprocating Rig (HFRR) test results indicate that oils 2 and 3 can lower the average friction by 1-4% in condition set one and 0-7% in condition set two. Similarly, oils 2 and 3 can also increase film formation via electric contact potential (ECP) measurements from 81-96% (versus 0% of oil 1) in condition set one and 91-96% (vs. 5% of oil 1) in condition set two. Furthermore, the calculated scar area (from the multiply of X-axis) of oil 1 is larger than the scar area of oils 2 and 3 (0-18% larger in condition set one and 4-13% larger in condition set two). Clearly, these results indicate the low sulfur, phosphorus/zinc free oils protect the metal surface from wear by forming stronger films, lowering frictional force and significantly reducing wear better than normal S/P oil 1. These results are correlated with Four-ball wear results very well. As the data indicated, a reduction of wear scar diameter (WSD) from 0.467 mm (oil 1) to 0.403 mm (oil 2) is 14% and a reduction from 0.467 mm (oil 1) to 0.383 mm (oil 3) is 18%.

As illustrated in Table 2, very good antioxidancy is achieved with the low sulfur, zinc/phosphorus free oils of the invention. As shown in Pressure Differential Scanning Calorimetry (PDSC), the onset temperature of oil 2 and oil 3 is 16-22 degrees higher than the result of oil 1 (ramping method). Since oxidation rates generally double with about 10° C. increase in temperature, these results can be translated into about 220% to 340% better in terms of control of viscosity or acid number increases or any other comparable measurements for control of oxidation. With the isothermal PDSC method, the oxidation resistance time is about 6 minutes longer (55% better) than the result of oil 1.

Sequence IVA testing is a very critical engine test that is used to assess anti-wear performance of engine oils. As demonstrated in oil 2, a low sulfur, phosphorus/zinc free oil, passes Sequence IVA engine test (cam wear and piston cleanliness) while oil 1 with normal sulfur/phosphorus/ash levels, fails. Reduction in cam nose wear can be as great as 88% reduction when compared oil 2 to oil 1 (6.7 vs. 56.9) and the reduction in total wear is equally outstanding (86% reduction from 305 micron to 44 micron).

EXAMPLE 2

A series of zinc and phosphorus free engine lubricants were formulated having the compositions set forth in Table 3. Oil 1 had a boron content of 93 ppm and molybdenum content of 190 ppm whereas oils 2 had a boron content of 540 ppm and molybdenum content of 180 ppm. Oil 3 was free of molybdenum, but had a similar boron content to oil 2 (550 ppm). These oils were then subjected to the same engine performance tests (Sequence IVA) set forth in Example 1 and the results of these tests are provided in Table 3.

The Sequence IVA test results indicated that oil 2 meets wear requirements (<120 micron) while oil 1 could not. Oil 3 also failed the engine test as molybdenum friction modifiers were removed from the formulation. Clearly, the boron-molybdenum synergism is needed in order to achieve a satisfactory engine performance. Either the high boron alone or a combination of low boron and high molybdenum is not sufficient to meet the engine requirements.

	TABLE 3
	Oil 1	Oil 2	Oil 3
	Synthetics	Synthetics	Synthetics
	Component	Viscosity Grade
Formulation	Chemistry	0W-30	0W-30	0W-30
Mixed Ashless	Borated & non-	8	8	8
Dispersants	borated PIB
	succinimide/
	ester and/or
	functionalized
	olefin copolymers
Mixed	Ca/Mg sulfonate/	4.3	4.3	4.3
Detergents	phenate/salicylate
Mixed	Phenolic &	1.5	1.5	1.5
Antioxidants	Aminic
	antioxidants
Mixed Friction	Moly Trimer	0.35	0.35	0.35
Modifiers	& ashless
Defoamants/seal	Silicone &	2.0	2.0	2.0
swell agent/VI	non-silicone
improvers
ZDDP	Zinc	0	0	0
	dithiophosphates
Base Oil	PAO/Group V	Bal.	Bal.	Bal.
Ash (D874)	Wt %	0.99	0.99
Zn	Ppm	<5	<5	<5
Mo	Ppm	190	180	<0.5
B	Ppm	93	540	550
N	Ppm (Calculated)	878	1494	1453
P	Ppm	<5	<5	<5
Sequence IVA		289	44	134
7-Point Total
Wear (Micron)

Claims

1. A lubricating oil composition having less than about 2000 ppm sulfur and substantially free of zinc and phosphorus comprising:

(a) a major amount of a base oil of lubricating viscosity; and

(b) an effective amount of an additive system comprising: (i) a metal detergent or mixture of metal detergents; (ii) an ashless dispersant or mixture of dispersants, at least one of which is a borated ashless dispersant; (iii) an ashless aminic antioxidant or mixture of antioxidants containing at least an aminic antioxidant; and (iv) an oil soluble, phosphorous free, trinuclear molybdenum compound.

(c) with the proviso that the composition have a minimum of 120 ppm boron and a minimum of 80 ppm molybdenum.

2. The composition of claim 1 wherein the composition has a B:Mo:N ratio in the range of about 3:5:7 to about 5:1:18.

3. The composition of claim 2 wherein the additive system includes a mixture of alkaline metal detergents selected from the group consisting of calcium and magnesium sulfonates, phenates, salicylates and mixtures thereof in the amount of about 1.5 to about 6.0 wt % based on the total weight of the composition.

4. The composition of claim 3 including a mixture of borated and non-borated dispersants in the weight ratio of 1:9 to 9:1 and wherein the total amount of ashless dispersant is in the range of about 2.0 wt % to about 12.0 wt % based on the total weight of the composition.

5. The composition of claim 4 includes a mixture of phenolic and amine antioxidants in the weight ratio of about 1.0:9.0 to about 9.0:1.6 and wherein the total amount is in the range of about 0.25 wt % to about 2.5 wt % based on the total weight of the composition and wherein the trinuclear molybdenum compound is present in an amount of from about 0.05 wt % to about 1.50 wt %, based on the total weight of the composition.

6. In the lubrication of an engine combusting a fuel containing below about 350 ppm sulfur, the improvement wherein the engine is lubricated with a composition comprising:

(a) a major amount of a base oil of lubricating viscosity; and

(b) an effective amount of an additive system comprising, (i) a metal detergent or mixture of metal detergents; (ii) an ashless dispersant or mixture of dispersants, at least one of which is a borated ashless dispersant; (iii) an ashless aminic antioxidant or mixture of antioxidants containing at least an aminic antioxidant; and (iv) an oil soluble, phosphorous free, trinuclear molybdenum compound.

(c) with the proviso that the composition have a minimum of 120 ppm boron and a minimum of 80 ppm molybdenum.

7. The improvement of claim 6 wherein the composition has a B:Mo:N ratio in the range of about 3:5:7 to about 5:1:18.

8. The improvement of claim 7 wherein the additive system includes a mixture of alkaline metal detergents selected from the group consisting of calcium and magnesium sulfonates, phenates, salicylates and mixtures thereof in the amount of about 1.5 to about 6.0 wt % based on the total weight of the composition.

9. The improvement of claim 8 wherein including a mixture of borated and non-borated dispersants in the weight ratio of 1:9 to 9:1 and wherein the total amount of ashless dispersant is in the range of about 2.0 wt % to about 12.0 wt % based on the total weight of the composition.

10. The improvement of claim 9 wherein includes a mixture of phenolic and amine antioxidants in the weight ratio of about 1.0:9.0 to about 9.0:1.6 and wherein the total amount is in the range of about 0.25 wt % to about 2.5 wt % based on the total weight of the composition and wherein the trinuclear molybdenum compound is present in an amount of from about 0.05 wt % to about 1.50 wt %, based on the total weight of the composition.