NO142405B - LUBRICANT MIXTURE FOR USE IN THE TURTLE BOX - Google Patents

Description

This invention relates to lubricant mixtures and

their use for the lubrication of motor vehicle crankcases, more particularly lubricant compositions having a base material comprising a liquid polyol ester and a liquid synthetic hydrocarbon.

The use of various diesters, polyesters and complex esters as lubricating oils is well known in the field applicable here and is described in several patents, e.g. U.S. Patents 2,723,286, 2,743,234 and 2,575,196. Fats and oils occurring in nature, predominantly glyceride esters, have been used as lubricants in fle-

re centuries. In recent times, synthetic esters or synthetic ester mixtures prepared from various combinations of mono- and polyfunctional acids and alcohols have been developed for use as lubricants.

Synthetic esters have been used extensively as lubricants for turbines, but they have been little used in piston engines. The reason why they are not accepted as a lubricant for pistons has mainly been the esters' harmful effect on the elastomeric seals used in piston engines, namely excessive swelling of the seals.

By "swelling" is meant the amount of volume in percent by which elastomeric seals expand after contact with and after being exposed to lubricants when an engine is in operation. Insufficient or inappropriately strong swelling causes the seals to lose their ability to retain and limit or contain the engine's fluids, so that leaks occur which cause heavy oil consumption.

A controlled or controlled swelling of seals therefore one of the most important characteristic features of a crankcase lubricant. It is important that the lubricant used can ensure controlled swelling for the engine's elastomeric seals, a swelling that is sufficient to prevent lubricant leakage.

The base material included in the lubricant mixture according to the invention has been shown to have excellent properties with respect to elastomeric seals, particularly those known under the trade name "Buna-N" (a copolymer of butadiene and acrylonitrile).

Although the ability not to cause excessive or insufficient swelling of elastomeric material is a valuable feature, lubricant mixtures used in reciprocating internal combustion engines, hereinafter referred to as reciprocating engines, must possess other special properties in order to satisfactorily to meet the special requirements placed on lubricants for engines of the aforementioned type.

It is essential that these lubricants have sufficient lubricity to be used under harsh operating conditions. They must also be stable with regard to oxidation and heat and must be able to resist rust, sludge and varnish formation. The viscosity must be such that the lubricant can be used over a wide temperature range, i.e. have suitable viscosity at high temperature, low viscosity at low temperature and little viscosity change at varying temperature. The pour point of the lubricant must be low. The volatility of the lubricant must be low at the high temperatures encountered during operation, i.e. selective vaporization or volatilization of any component of the lubricant must not occur at the high temperatures encountered during operation.

The great advances in vehicles powered by piston engines have led to piston engine equipment being used in parts of the world where the temperature conditions are very harsh.

higher than the temperature conditions usually expected in areas with a more temperate climate and which are also more densely populated. It is required that engine oils must be sufficiently liquid at temperatures as low as -54°C, so that the engine can be started and still have such volatile properties that evaporation is prevented even if the oil is exposed for a long time to temperatures approaching 180°C.

Combining these properties with compatibility with a variety of elastomers is a difficult undertaking when it comes to an operating fluid. The base material is usually combined with various additives designed to improve certain characteristic properties that a lubricant must have. In order to achieve this, the starting material must be able to be combined with additives.

Compatibility with additives is defined as the additive's ability to dissolve or disperse homogeneously in the base material and is a measure of the additive's ability to avoid clouding, flocculation or precipitation from the base material fluid.

Petroleum lubricants, which until now have been almost exclusively used in piston engines, cannot usually satisfy the high and low temperature requirements set today. Petroleum oils can e.g. is modified by adding the kerosene to ensure starting at low temperature, but when this modification with respect to low temperature is carried out, the lubricant becomes too volatile to be used at high rpm and high temperature. Conversely, petroleum oil can be modified to ensure good behavior at high temperatures, but such oil mixtures usually become too viscous at low temperatures, so that they do not perform sufficiently well in cold weather.

Conventional synthetic esters which are usually used for the lubrication of turbine engines can provide certain improved properties compared to petroleum oils for reciprocating engines, but have largely been judged to be unsuitable for use as reciprocating lubricants. This is due to their unduly high volatility and unsatisfactory viscosity properties at high temperatures. More importantly, these fluids tend to affect such elastomers used as seals in vehicle engines so that these swell too strongly, which can result in loss of lubricant as a result of leakage past the engine's seals.

It is therefore surprising that the lubricant mixture according to the invention not only satisfies the strict requirements set for lubricants for lubricating engine crankcases, but is even in many respects better than what is required.

The base material included in the lubricant mixture according to the invention comprises a mixture of 2, possibly 3 components. These are: (1) a trimethylolpropane ester or a polytrimethylolpropane ester of an aliphatic hydrocarbon carboxylic acid with an average chain length of 4-12 carbon atoms, (2) an oligomer selected from the group consisting of octene/decene, mixed decene, and mixtures thereof, wherein the lubricant mixture provides 2-12% swelling of a butadiene/acrylonitrile elastomer seal and the viscosity of the lubricant mixture at 99°C is 3-20 cS; and optionally (3) 0.5-3% by weight zinc dithiophosphate, 0.1-3% by weight phenyl-a-naphthylamine and 0.005-0.1% by weight benzotriazole.

The aliphatic hydrocarbon carboxylic acids included in component (1) preferably have average chain lengths between 5 and 9 carbon atoms. Straight-chain acids are preferred, although branched acids can also be used, especially those which have no more than 2 carbon atoms in side chains.

When synthesizing polyol esters, smaller amounts of dibasic acids can be used as crosslinking agents. The alkyl portion of the dibasic acid has from 4 to 12 carbon atoms. Particularly preferred dibasic acids include adipic, azelaic, isophthalic acid and mixtures thereof. In terms of cross-linking, this also includes dimeric and trimer acids and their mixtures.

Among the polyols, trimethylolpropane is particularly suitable for use in engines with spark ignition.

It is particularly preferred that the polyol ester be a trimethylol-propane triester because of its superior compatibility with additives.

For use in a diesel engine where an ester with a higher viscosity is desired, an ester of a polyol with a higher molecular weight should be used, preferably a condensed polyol, such as ditrimethylolethane, ditrimethylolpropane, dipentaerythritol, tripentaerythritol and mixtures thereof.

As ditrimethylolpropane tetraester has very good compatibility with additives, it is particularly preferred that this tetraester is used as a polyol ester for use in diesel engines.

As regards component (2), i.e. the oligomer, it is preferred to use an α-olefin oligomer, with a preferred chain length of 10 carbon atoms, because this ensures better viscosity and temperature properties as well as lower volatility.

The components of the ester-oligomeric base material are mixed

in quantities which may cause the seals to swell sufficiently. In this invention, a swelling of from 2 to 12% is considered to be a sufficient degree of swelling, with a swelling of 6-9% being preferred for an elastomer such as "Buna-N" which is often used in crankcases in motor vehicles.

Another important property is viscosity. The lubricant mixture must have an acceptable viscosity range that liquefies at temperatures as low as -54°C, so that the engine can be started, but retains sufficient film strength for adequate lubrication at operating temperatures that can approach 180°C.

The acceptable viscosity of the lubricant composition base material may vary from 3 to 20 cS at 99°C and preferably from 4 to 12 cS at 99°C.

The lubricant mixture must also have such volatility properties that noticeable evaporation is avoided when it is exposed for longer periods to temperatures above approx. 180°C.

The most effective mixtures of polyol esters and α-olefin oligomers, where the control of the elastomer seal's swelling is of primary importance, is a mixture where the ratio between components (1) and (2) varies from 20:80 to 70:30, measured in parts by weight . The preferred ratio is between 30:70 and 65:35, preferably from 50:50 to 60:40, also measured by weight. The following table illustrates a controlled swelling of a seal in contact with a typical α-olefin oligomer/polyol ester mixture.

For use in diesel engines, a polyol ester with a higher viscosity will make an excellent base material, e.g. a ditrimethylolpropane tetraester mixed with α-olefin oligomers.

Such a base material is excellent with regard to viscosity and controlled swelling of the seal.

The system according to the invention with a base material of polyol ester and synthetic hydrocarbon oligomer has been shown to have excellent properties with respect to compatibility with additives and without adverse effect on the engine's elastomeric seals. Typical additives for the ester/oligomer mixture usually include such additives that increase or impart to the system such properties as better resistance to corrosion, resistance to wear, high load carrying capacity, good lubricity, properties that improve the viscosity index, washability, dispersing ability, ability to resist metal deactivation and good anti-foam properties.

Of particular importance is that dispersing additives and cleaning or washing additives are compatible and active or effective together with the base material mixture. The reason for this is that acid exhaust gases from the engine can leak past the engine's piston rings and contaminate the lubricant in the crankcase. The two last-mentioned additives prevent corrosion and rust on the engine's bearings and constitute necessary additions to the base material because they neutralize, dissolve and disperse these contaminants and likewise the breakdown products from oxidation of the fluid.

The following examples shall indicate different lubricant mixtures containing base material in the form of ester oligomers. If no denominations are given, all parts and shares are by weight.

Example 1

A lubricant mixture with the following composition was prepared and tested according to "The Coordinating Research Council's (CRC)L-38 test", also known as "Method 3405" in "Federal Test Method Standard Number 791a".

LUBRICANT COMPOSITION

CRC L-38 is used to evaluate lubricating oils with regard to resistance to oxidation, corrosion, sludge formation and varnish formation when the oil is exposed to high temperatures during operation. The procedure involves continuous operation of a single cylinder in a CLR oil test engine at constant speed, air/fuel ratio and fuel conditions for a period of 40 hours following a start-up or rest period of 1 hour. Before each run, the engine is cleaned very thoroughly, and measurements are taken of the relevant parts of the engine, and a new piston with piston rings and new bearing cups for the connecting rod or piston rod are inserted.

Operating data is as follows:

After the test run, the machine was dismantled, and the behavior of the oil during the test was judged by visual inspection of the engine for deposits, by measuring the weight loss of the copper-lead bearing liners, by comparing inspection data on samples of used oil taken at intervals with corresponding data on fresh oil.

Test results appear in the table below:

Test results

Assessment of the 40 hour test with regard to the oxidation of the oil in the crankcase.

Weight loss in the warehouse in mg

For this test, a maximum weight loss of 40 mg is permitted. This test causes a strong corrosion stress on the piston rod's bearings. With lubricants based on esters, i.e. where an ester forms the base material, the test will show failure in the form of an unduly large weight loss in the bearings which is then above the permitted 40 mg. The trial result of 33.3 mg weight loss is considered acceptable and indicative that a fluid will not cause undue

similar to heavy bearing wear during operation in an engine.

ASSESSMENT OF DEPOSITS IN THE ENGINE

It concerns an inspection with regard to the unit where the degree of cleanliness is assessed with numbers from 0 to 10.0. The last-mentioned number means that the engine is clean. Varnish indicates the lubricating oil's tendency to break down and manifests itself in a shellac-like glaze that has formed on the metal parts.

OIL ANALYSIS

Example 2

A lubricant composition identical to the composition of Example 1 was subjected to continuous high wear and high temperature testing performed on a 1970 Oldsmobile, 8 cylinder engine with a displacement of approx. 7 1. The duration of the test was 64 hours, and the criterion for the test is that the viscosity after 40 hours must not increase more than 400% and that the cam lifter wear is a maximum of less than 0.0508 mm and less than 0.025 mm in average wear. This test is called the 1970 General Motors "MS" Lubricant Evaluation: Sequence IIIC.

The results of the engine test appear in the table below: Viscosity increase:

Note: 12% increase in viscosity after 40 hours indicates excellent fluid stability. The maximum allowed value is 400%.

Assessment of sludge formation

Sludge and varnish deposits in the critical areas were

a very small amount considering the very hard test. As a comparison, it can be mentioned that lubricants based on mineral oils would tend to form much larger amounts of sludge and varnish deposits under equivalent conditions.

Assessment of the contact surfaces of the oil rings:

The inspection of the seals showed that they were in very good condition

and without any trace of decomposition. The seals retained their compliance, flexibility and dimensional integrity, and no leakage was visible.

Example 3

A lubricant composition identical to that examined in Example 1 was subjected to an evaluation method especially considering conditions during short trips in typical winter climate conditions of the northern part of the Midwest of the USA. The conditions for this investigation were very useful for the assessment of the motor oils' properties with regard to rusting, as the test conditions promoted rust formation in the engine's critical parts. This test is called 1971 General Motors Lubricant Evaluation: Sequence IIC. The test was conducted on a 1971 Oldsmobile with an 8-cylinder engine of 7 1 cylinder displacement.

Before each run, the engine was completely disassembled, cleaned with solvent, measured and assembled to exact specification. The engine was then installed on a test stand equipped with the necessary devices for measuring speed, load, temperature and other operating conditions. The engine ran continuously for 28 hours at moderate rpm^partially heated coolant in the jacket and rich air/fuel mixture. The results appear in the table below:

Immediately after this 28-hour operating period, the engine was operated for two hours under the same conditions except for the following changes:

The engine was then stopped for 30 minutes to change the carburettor, check the oil level, change the spark plugs and adjust the cooling system for the rocker arm cover (camshaft cover). Then, without draining the oil from the engine, it was operated for two hours under the following conditions (high temperatures).

SURVEY

After the test was completed, the engine was completely disassembled and treated for rusting using the prescribed procedure according to the "Coordinating Research Council (CRC)". A rating of 10.0 means that the part is completely clean. The following parts were examined and rated: (1) Rust - (CRC) Manual No. 7. Motor rust rating as an average of the five parts mentioned below:

Valve lifter rods

Valve lifter pistons

Valve lifter balls

Oil pump relief valve

Push rods

(2) Others: Jamming of the oil pump relief valve and jamming of the valve lifter piston.

SUMMARY OF THE TEST RESULTS

Note: The assessment grade of 8.4 on average is taken into account

as acceptable for this harsh rust-accelerating test.

The achieved average of 8.6 is particularly noticeable for the lifters, pistons, balls, pistons of the relief valves, as all dis-

see parts work within tight tolerances.

Inspection of the seals showed that these were in good condition

condition and without signs of degradation. They retained their elasticity and dimensional integrity and no leakage was visible. Resul-

the result of the experiment shows that this is a lubricant for crankcases that is well suited to harsh operating conditions in terms of wear and temperature.

Example 4

A lubricant mixture identical to the mixture according to

example 1 was subjected to the so-called Ford Sequence VC test;

This test is set up to assess the lubricant's ability to control and disperse harmful pollutants, such as acidic exhaust gases, especially with carbon, highly oxidized oxidation pro-

ducts etc. These contaminants cause the formation of sludge and varnish and are considered to have the easiest time to act when the engine is exposed to

is tested for various intermittently occurring cycles, such as idling, idling, mid-speed operation, high-speed operation and stalling.

The experiment was carried out on an 8-cylinder Ford engine with a cylinder volume of 5.25 1. The experiment includes four successive

successive operation cycles, each lasting four hours. During each cycle, the engine is subjected to separate idling periods, operating periods

oder at medium speed and operating periods at high rpm.

After 4 operating cycles are completed, the engine is stopped for 8 hours, after which the entire operation is repeated. The total test duration amounts to 192 operating hours.

After the test, the engine is completely dismantled, inspected and assessed. The results are as follows:

(Rating 10.0 means clean)

Note: The results show that the lubricant is able to disperse harmful contaminants and keep the engine in clean operating condition, so that good operating behavior is ensured even under difficult conditions. Inspection of the seals showed that they were in good condition, with no signs of degradation. There was no leakage, and the seals retained their elasticity and dimensional integrity.

Claims (4)

1. Lubricant composition, comprising a base material comprising a mixture of (1) a trimethylolpropane ester or a polytrimethylolpropane ester of an aliphatic hydrocarbon carboxylic acid having an average chain length of 4-12 carbon atoms, (2) an oligomer selected from the group consisting of octene /decene, mixed decene, as well as mixtures thereof, the lubricant mixture providing 2-12% swelling of a butadiene/acrylonitrile elastomer seal and the viscosity of the lubricant mixture at 99°C being 3-20 cS; and optionally (3) 0.5-3% by weight zinc dithiophosphate, 0.1-3% by weight phenyl-a-naphthylamine and 0.005-1% by weight benzotriazole, characterized in that the components (1) and (2) are present in a ratio of from 20:80 to 70:30 parts by weight. 2. Lubricant mixture as stated in claim 1, characterized in that the ratio between components (1) and (2) is from 30:70 to 65:35, preferably from 50:50 to 60:40. 3. Lubricant mixture as stated in claim 1, characterized in that component (1) is trimethylol<p>propane triheptanoate. 4. Application of lubricant mixture as stated in claims 1-3, for the lubrication of a crankcase for motor vehicles.