Part-synthetic, aviation piston engine lubricant

Details Part-synthetic, aviation piston engine lubricant Part-synthetic, aviation piston engine lubricant

1999-09-21

2001-02-20

Johnson, Jerry D. (Department: 1764)

Solid anti-friction devices, materials therefor, lubricant or se

Lubricants or separants for moving solid surfaces and...

Heterocyclic ring compound; a heterocyclic ring is one...

C508S280000, C508S291000, C508S294000

Reexamination Certificate

active

06191078

ABSTRACT:

FIELD OF INVENTION
The present invention relates to a lubricating composition for aviation piston engines. More particularly the present invention is directed toward a part synthetic aviation piston engine lubricant.
BACKGROUND OF INVENTION
Lubricating oils have been used in internal combustion engines, power transmission components, shock absorbers, power steering devices and the like. Crank case lubricants, i.e., oils for internal combustion engines, are formulated to perform a number of functions. The most important of these is to reduce friction on and wear of the engines pistons, valves, rings and the like. Engine oils also are formulated to protect metal surfaces against rust and corrosion, to provide oxidation stability, minimize deposits, and to flush out contaminants.
The performance of lubricant oils is a function of the additive composition they contain. The most common types of additives are: antiwear agents, extreme pressure (EP) agents, antifoams, antioxidants, detergents, dispersants, viscosity-index improvers, rust inhibitors, corrosion inhibitors, friction modifiers, and pour point depressants.
Unfortunately the effectiveness of any combination of additives cannot be predicted because of factors such as physical and chemical compatibility, for example. Also, while a given lube additive may contribute to the enhancement of one property of the lubricant composition often it has a negative impact on another property of the lubricant composition.
Among the many additives that are used in automotive engine lubricants are zinc compounds such as zinc dialkyldithiophosphate, molybdenum compounds such as molybdenum dithiocarbamate, calcium salts such as calcium sulfonate and borated compounds such as borated hydrocarbon-substituted succinic acid compounds. Because these additives produce ash deposits when used in internal combustion engines, they cannot be used in aviation piston engine lubricant compositions. Thus, one object of the present invention is to provide a lubricating composition for aviation piston engines that does not contain ash forming additives.
Another object of this invention is to provide a lubricating oil for aviation piston engines that has enhanced oxidative and thermal stability with sufficient solvency for fuel degradation products thereby reducing undesirable engine deposits.
Additional objects and advantages will be set forth in or will be obvious from the discussion of the invention.
SUMMARY OF INVENTION
In accordance with the invention there is provided an aviation piston engine lubricant having no metal-containing additive content, the lubricant comprising:
(a) a base oil consisting essentially of a mixture of
(i) at least about 50 wt % based on the total weight of the lubricant of one or more mineral oils having a viscosity in the range of about 5 cSt to about 25 cSt at 100° C.;
(ii) about 15 to about 40 wt % based on the total weight of the lubricant of a polyalpha olefin fluid having a viscosity in the range of about 4 cSt to about 40 cSt at 100° C.;
(b) at least about 3 wt % based on the total weight of the lubricant of an ashless polyisobutylene succinic anhydride/polyamine (PIBSA/PAM) dispersant; and
(c) an effective amount of one or more of ashless additives selected from the group consisting of antiwear agents, extreme pressure agents, metal passivators and antioxidants.
In another embodiment, the lubricant of the present invention includes a sufficient amount of a viscosity improver (VI) to provide the lubricant with a multi-grade viscosity.
Other embodiments will be apparent from the detailed description which follows.
DETAILED DESCRIPTION OF THE INVENTION
A. The Base Oil
Mineral Oil Basestock
The mineral oil basestock used in the base oil may be selected from any of the natural mineral oils of API Groups I, II, III or mixtures of these used in lubricating oils for spark-ignited engines. Preferably, the mineral basestock is a Group I basestock or basestock blend having the properties shown in Table 1.
An especially preferred basestocks comprise a mixture of a solvent extracted mineral oil and solvent extracted bright stock. Typically these are combined in amounts such as those shown in Table 1 to meet preselected viscosity grades.
Typically the mineral oil basestock will comprise at least 50 wt % of the lubricant, for example from about 50 to about 75 wt % and preferably 60 to 75 wt %.
(ii) The Polyalpha Olefin Fluid
The polyalpha olefin (PAO) fluid used in the base oil may be selected from any of the olefin oligomer oils used in lubricants. In general the PAO will have a viscosity at 100° C. in the range of about 4 cSt to about 40 cSt and preferably about 4 cSt to about 10 cSt. Preferably the polyalpha olefin is one having the properties shown in Table 2.
TABLE 1
Mineral Basestock
Solvent
Solvent
Solvent
Solvent
Mineral Basestock Blends
Extracted
Extracted
Extracted
Extracted
For SAE
For SAE
For SAE
150N
325N
600N
Bright Stock
10W-50
15W-50
20W-50
Composition
S150N (wt %)
60
S600N (wt %)
40
90
55
Bright Stock (wt %)
10
45
Kinematic Viscosity
(ASTMD445)
@ 100° C., cSt
5.0-5.4
8.1-8.6
11.7-12.5
30-33
7.1
13.2
18.1
@ 40° C., cSt
29-31
62-67
110-116
440-500
49
128.5
207
Pour Point (ASTM D97), ° C.
−9
−9
−9
−9
−9
−9
−9
Specific Gravity @
0.868-0.878
0.872-0.884
0.879-0.890
0.893-0.908
0.877
0.886
0.890
(15.6/15.6° C.)
TABLE 2
POLYALPHA OLEFIN
Properties
PAO-4
PAO-6
PAO-8
PAO-10
PAO-40
Kinematic Viscosity
(ASTM D445)
@ 100° C., cSt
 4.0
 6.0
 8.0
10.0
40.0
@ 40° C., cSt
17.0
31.5
46.5
62.5
39.5
@ −40° C., cSt
2500
8000
19000
32000
—
Pour Point
−70    
−68    
−63    
−53    
−34    
(ASTM D97), ° C.
Specific Gravity
0.820
0.830
0.835
0.840
0.840
@ (15.6/15.6° C.)
Typically the PAO will comprise from about 15 to about 40 wt % of the lubricant and preferably from about 20 to about 30 wt %.
B. The Ashless Dispersant
The lubricant composition also includes at least about 3 wt % based on the total weight of the lubricant of a polyisobutylene-succinic anhydride/polyamine (PIBSA/PAM) ashless dispersant. Preferably the lubricant contains 3 wt % to about 6 wt % and more preferably 4 wt % of the PIBSA/PAM.
PIBSA/PAM dispersants are polyamino alkenyl or alkyl succinimides which are the reaction product of an alkenyl- or alkyl-substituted succinic anhydride and a polyalkenyl polyamine. The aliphatic substituted succinic acids or anhydrides are those materials bearing aliphatic groups containing from 20 to 200 carbons, preferably 20 to 100 carbons, most preferably 50 to 70 carbons, the aliphatic group, consequently being of from about 280 to 2800 molecular weight most preferably about 700 to 1000 molecular weight wherein the aliphatic substituent are usually olefin homopolymers or copolymers, e.g. homopolymers or copolymers, of ethylene, propylene butylene, isobutylene, etc. Thus, a typical aliphatic substituted succinic acid or anhydride is polyisobutylene succinic acid or anhydride (PIBSA) wherein the polyisobutylene moiety ranges from about 280 to 2800 molecular weight, most preferably about 700 to 1000 molecular weight.
The polyalkenyl polyamine (PAM) portion of the dispersant molecule may be composed of varying alkene type and oligomer chain length. Tetraethylene pentamine is commonly used in this synthesis.
The ashless dispersant would be available from additive suppliers typically at 50% active ingredient concentration, with the remainder being a low viscosity mineral oil.
The ashless dispersant can also provide strong protection against rust. To accomplish that some level of weak acidity (measured by ASTM D664) is desirable.
The ashless dispersant (after dilution) should have a nitrogen concentration of 1% to 2.2%, preferably 1.4 to 1.8%, most preferably around 1.6%. The acid number (ASTM D664-Buffer B end-point) should be from 4 to 9, preferably from 5 to 8.
C. Ashless A

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