GREASE COMPOSITION FOR A CONSTANT VELOCITY JOINT

Abstract: A grease composition for a constant velocity joint, characterised in that it contains from 0.05 to 30 percent by weight of sodium thiosulphate with respect to a base oil and urea-based thickener.

Description: GREASE COMPOSITION FOR A CONSTANT VELOCITY JOINT The present invention relates to grease compositions which are especially suitable for use in a constant velocity joint also referred to as CVJ. Grease lubrication of CVJ's is extremely harsh since it is carried out under conditions of friction under high surface pressures where slipping and rolling over in reciprocating movement are intermixed. The present invention relates to a grease composition for a constant velocity joint having an extremely long-lived durability and to prevent the occurrence of abnormal wear and flaking. CVJ' s in automobiles are employed in front-wheel drive vehicles and four-wheel drive vehicles, as well as rear-wheel drive vehicles, and demand tends to increase. As automobiles achieve higher speeds, higher outputs and lighter weights, CVJ's become smaller, whilst sustaining higher torques and being applied at higher speeds . Therefore, the grease must meet increasing performance specifications. CVJ's can be categorised as fixed joint or plunging joint depending on the mechanism. Conditions are extremely harsh for fixed joints since these are generally used for wheels and are employed at high angles and under high surface pressure. Usually, CVJ greases contain lithium soap as thickener and additives such as sulphur/phosphorus-based extreme pressure agents and molybdenum disulphide. Recently, urea-based greases containing various extreme pressure agents have become more common. These have outstanding heat-resisting properties. JP-A (Japanese Laid-Open Patent Application) H 6- 57284 (1994) discloses a grease composition for a constant velocity joint in which a urea grease contains, as essential constituents, (A) a molybdenum dialkyldithiocarbamide sulphide, (B) an extreme pressure additive comprising a specific zinc dithiophosphate compound, and (C) an epoxy-modified aliphatic acid ester or an epoxy-modified aliphatic acid glyceride. Further urea greases have been described in JP-B (Examined Japanese Patent Document) H 4-34590 (1992), JP- A H 6-57283 (1994), JP-A H 6-100878 (1994), JP-A H 7-197072 (1995) and JP-A H 8-41485 (1996), and US-A- 4,840,740, US-A-5,160,645 and US-A-5, 449, 471. These documents teach to add an organic molybdenum compound to a base grease together with yet other additives (such as zinc dithiophosphate) to reduce frictional wear and, as a result, prevent flaking. However, these compositions still suffer from flaking which stems from metal surface fatigue caused by roll-over slipping friction in complex reciprocating movements of the inner and outer wheel channels and balls as well as cages and balls in a CVJ mechanism. In US-A-4, 923, 625 grease compositions are described for use in cutting and grinding operations. The compositions contain a mixture of a metal thiosulfate and a metal phosphate to impart both extreme pressure and antiwear properties to a base lubricant. CVJ-producing manufacturers and grease-supplying manufacturers are trying to predict flaking in CVJ with the help of frictional wear tests such as the four-ball EP tests described in ASTM D2596. Where durability in CVJ' s is concerned appropriate greases cannot be selected using the test apparatuses mentioned above. This is thought to be due to the complexity of the lubrication conditions. Therefore, the performance in terms of the flaking life, state of wear and the like is evaluated using a bench test apparatus in which an actual CVJ is used. The fact that substances which exhibit outstanding results in general frictional wear tests do not necessarily prevent CVJ flaking or have long durability, makes it difficult to develop CVJ flaking prevention technology. The aim of the present invention is to provide a novel constant velocity joint grease composition whereby CVJ flaking can be prevented. It has been found that flaking is reduced in greases containing metal thiosulphate. The present invention relates to a grease composition for a constant velocity joint, which grease composition comprises base oil and urea-based thickener, and which composition further contains from 0.05 to 30% by weight of metal thiosulphate, based on weight of base oil and urea-based thickener. The present invention further relates to the use of a grease composition for lubricating a constant velocity joint, which grease composition comprises base oil and urea-based thickener, which composition further contains from 0.05 to 30% by weight of metal thiosulphate, based on weight of base oil and urea-based thickener. Furthermore, the present invention further relates to a constant velocity joint containing a grease composition comprising base oil and urea-based thickener, which grease composition further contains from 0.05 to 30% by weight of metal thiosulphate, based on weight of base oil and urea-based thickener and the use of metal thiosulphate for reducing flaking of a grease containing base oil and urea-based thickener. The base oil used in the present embodiment can be a mineral oil or a synthetic oil such as an ester oil, ether oil or hydrocarbon oil, or an oil mixed from these. Preferably, the base oil is a mineral oil. Any urea-based thickener can be used. Examples of urea-based thickeners include diurea, triurea and tetraurea. Further, it is also possible to use various thickeners containing urea compounds such as urea- urethane compounds and urea-i ido compounds. The metal thiosulphate used in the present invention, can contain any metal that is capable of forming a metal thiosulphate salt. Typical examples are lithium, sodium, potassium, manganese, calcium, barium, strontium, titanium, zirconium, cadmium, zinc, nickel, cobalt, copper, iron, magnesium, lead, tin, silver, or a mixture of these. A useful class of metal thiosulphate is represented by the following formula 0 (R S - S - 0) M 0 where R represents a hydrocarbon radical containing 1 to 30 carbon atoms, M is a metal capable of forming a metal thiosulphate salt and n is the valence of M. Examples of this class of metal thiosulphates are sodium ethyl thiosulphate, potassium benzyl thiosulphate and barium isoamyl thiosulphate. The compounds can be prepared by reacting an alkyl halide with sodium thiosulphate. Preferably, the metal thiosulphate used in the present invention is sodium thiosulphate. Most preferably, the sodium thiosulphate is Na 2 S 2 0 3 (anhydrous), Na 2 S 2 0 3 .5H 2 0 (pentahydrate) or a mixture of these. Further, it is possible to use commercial additives containing sodium thiosulphate, such as Desilube 88, Desilube Technology, Inc. USA. The amount of sodium thiosulphate added is from 0.05 to 30 percent by weight, and preferably from 0.2 to 20 percent by weight based on weight of base oil and urea- based thickener, more preferably 0.2 to 10% by weight, more preferably 0.2 to 8% by weight, most preferably 0.5 to 6% by weight. If the amount is less than 0.05 percent by weight, the flaking-preventing effect is insufficient. If the amount is more than 30 percent by weight, there is no further increase in the effect. The composition of the present invention can further contain one or more known additives such as phenol-based and amine-based antioxidants, organic molybdenum compounds, molybdenum disulphide, sulphur-modified fats and oils, sulphur-modified olefins, zinc dithiophosphate, thiophosphate, phosphite, phosphate, and polysulphide, and other such extreme pressure/anti- wear agents, polybutenes, polymethacrylates and other such viscosity enhancers. Greases according to the invention and comparative examples were obtained using the formulations shown in Table 1 and Table 2 by adding the additives to a base grease and processing in a three-roll mill. The compositions of the base greases are given below. The base oil was purified mineral oil with a viscosity at 100°C of 15mm 2 /S. I . Diurea grease A grease was obtained by reacting diphenylmethane- 4, ' -diisocyanate (295.2 g) and octylamine (304.8g) in a base oil (5,400 g) , and uniformly dispersing the resulting urea compound. The urea compound content was 10 percent by weight. II. Tetraurea grease A grease was obtained by reacting diphenylmethane- 4, 4' -diisocyanate (334.2 g) , stearylamine (345.6 g) and ethylenediamine (40.2 g) in a base oil (5,280 g) , and uniformly dispersing the resulting urea compound. The urea compound content was 12 percent by weight. III. Lithium soap grease A grease was obtained by dissolving lithium 12- hydroxystearate (540 g) in a base oil (5,460 g) , and uniformly dispersing. The lithium soap content was 9 percent by weight. The resulting greases were subjected to durability testing on mounts using actual CVJ's, and the degree of flaking was checked. Test conditions Rotational speed 1,400 rpm Load torque 294 N m Joint angle 6 deg Joint type Burfield joint Further, the fusion load (N) was determined using the four-ball EP test specified in ASTM D2596. The results are collated in Tables 1 to 4. It should be noted that, in the tables, *1 to 7 and ** are as follows. *1 Desilube 88 (trade mark, made by Desilube Technology Inc.) is an inorganic additive containing sodium thiosulphate. *2 Moliban A (trade mark, made by the Vanderbilt company) is molybdenum dithiocarbamate . *3 Sakura Lube 600 (trade mark, made by Asahi Denka) is molybdenum dithiocarbanate. *4 Sakura Lube 300 (trade mark, made by Asahi Denka) is molybdenum dithiophosphate. *5 Lubrizol 1395 (trade mark, made by the Lubrizol company) is zinc dithiophosphate. *6 Anguramoru 33 (trade mark, made by the Lubrizol company) is a sulphur-modified olefin. *7 Iruga Lube TPPT (trade mark, made by the Ciba-Geigy company) is triphenylphosphorothionate . **For the degree of flaking, the condition after 12,600,000 revolutions, and the condition after 25,200,000 revolutions of the CVJ was observed and evaluated as follows. 0 No flaking o Minor flaking Δ Moderate flaking x Extensive flaking TABLE 1 TABLE 2 TABLE 3 Embodiment Composition Base grease Diurea grease 93 wt% Tetraurea grease Lithium grease 97 97 97 Additives a 2 S 2 θ 3 (anhydrous) Na 2 S 2 0 3 5H 2 0 Desilube 88 *1 Moliban A *2 Sakura Lube 600 *3 Sakura Lube 300 *4 Lubrizol 1395 *5 Anguramoru 33 *6 Iruga Lube TPPT *7 Molybdenum disulphide Total 100 100 100 100 Test results Four-ball EP Fusion load (N) 6076 3920 6076 3087 test Degree of By 12,600,000 flaking * revolutions By 25,200,000 revolutions TABLE 4 Embodiment 5 6 7 8 Composition Base grease Diurea grease 96 96 wt Tetraurea grease 93 96 Lithium grease Additives a 2 S 2 θ 3 (anhydrous) Na 2 S 2 θ 3 .5H 2 0 Desilube 88 *1 Moliban A *2 5 Sakura Lube 600 *3 3 3 Sakura Lube 300 *4 3 Lubrizol 1395 *5 1 1 Anguramoru 33 *6 Iruga Lube TPPT *7 1 1 Molybdenum 1 disulphide Total 100 100 100 1O0 Test results Four-ball EP Fusion load (N) 2450 2450 3087 2450 test Degree of By 12, 600,000 Δ X X X flaking ** revolutions By 25,200,000 X - - - revolutions As is clear from the results shown in Tables 1 to , the grease composition for a constant velocity joint of the present invention has outstanding extreme pressure properties, and provides more effective flaking prevention properties than do conventional greases. This effect improves the durability of constant velocity joints .

Claims: C L A I M S 1. Grease composition for a constant velocity joint, which grease composition comprises base oil and urea- based thickener, and which composition further contains from 0.05 to 30% by weight of metal thiosulphate, based on weight of base oil and urea-based thickener. 2. Grease composition according to claim 1, in which grease composition the metal thiosulphate is sodium thiosulphate. 3. Use of a grease composition for lubricating a constant velocity joint, which grease composition comprises base oil and urea-based thickener, which composition further contains from 0.05 to 30% by weight of metal thiosulphate, based on weight of base oil and urea-based thickener. 4. Use of a grease composition according to claim 3, in which the metal thiosuphate is sodium thiosulphate. 5. Use of a grease composition according to claim 3 or 4, in which the grease composition contains from 0.2 to 20% by weight of metal thiosulphate. 6. Use of a grease composition according to any one of claims 3-5, in which the base oil is a mineral oil. 7. Constant velocity joint containing a grease composition comprising base oil and urea-based thickener, which grease composition further contains from 0.05 to 30% by weight of metal thiosulphate, based on weight of base oil and urea-based thickener. 8. Use of metal thiosulphate for reducing flaking of a grease containing base oil and urea-based thickener.

Inventors: MASUMORI RYUICHI, MUNAKATA TOMOO, OZAKI TAKAHIRO, YOSHIDA TSUTOMU, MASUMORI, RYUICHI, MUNAKATA, TOMOO, OZAKI, TAKAHIRO, YOSHIDA, TSUTOMU
Applicants: MASUMORI RYUICHI, MUNAKATA TOMOO, OZAKI TAKAHIRO, SHELL INT RESEARCH, YOSHIDA TSUTOMU, MASUMORI, RYUICHI, MUNAKATA, TOMOO, OZAKI, TAKAHIRO, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V., YOSHIDA, TSUTOMU
Application year: 1998
Main classification: C10M169
IPC codes: C10M169, C10N10, C10N30, C10N40, C10N50