FR2684108A1 - NEW GREASE, ESPECIALLY FOR USE IN HOMOCINETIC JOINTS. - Google Patents

Abstract

The present invention relates to a new grease intended particularly to be used in Hooke's joints in order to improve the NVH characteristics of said joints. According to the invention, the grease is comprised, expressed in weight % : 3 to 90 %, and preferably 40 to 70 % of a base oil; 2 to 80 %, and preferably 10 to 50 % of a thickening agent comprised of a dispersion of clay in oil; 0.5 to 10 %, and preferably 3 to 7 % of at least one organic molybdenum compound; 0 to 10 %, and preferably 1 to 5 % of at least one organic zinc compound; and 0 to 10 % of at least one conventional additive for grease.

Description

New Grease intended in particular to be used in constant velocity joints.

 The present invention relates to a new grease intended in particular for the lubrication of constant velocity joints, although many other applications of this grease can be envisaged.

 It is known that most of the transmissions used in cars have constant velocity joints. This use has been generalized in particular in lateral transmissions for all types of cars: front-wheel drive, propulsion or 4-wheel drive.

The seals used can be classified into two large families, depending on whether they are fixed or sliding, and they can be produced using different technologies; the two main ones being:
* the so-called ball technology
* the so-called tripod technology
All these seals nevertheless have at least one point in common: they all include internal members intended to ensure load transfers between elements in relative motion.

 During these load transfers, frictional forces appear which can be of different types depending on who there is rolling contact, sliding or combination of the two.

 These forces combine with one another in arrangements which depend in particular on the kinematics and the geometric characteristics of the seals and the resulting torsor is transmitted to the vehicle components to which the seals are connected.

The existence of these friction forces can be at the origin of two harmful phenomena: - The generation of mechanical losses in the joints with for
consequences: The wear of the constituents, temperatures of
high operating times which shorten the service life or
performance and higher fuel consumption; - the appearance of incompatible acoustic or vibrational phenomena
tibles with the comfort requirements of modern vehicles.

It is therefore natural to seek to reduce as much as possible the internal friction at the joints, and this can be obtained - either by favoring the rolling movements over the
sliding movements but in this other area
design constraints related to capacity or cost which
the result is to limit the possibilities of evolution, - either by reducing the sliding forces by the interposition
a lubricating film with appropriate characteristics. This
advantage of providing a solution
tion simple to implement, applicable directly on
existing mechanisms, without calling into question the consti
internal kills.

 In recent years, we have sought to develop new greases whose properties make it possible to improve the characteristics of these seals, in particular with regard to noise, vibrations and driving comfort of the vehicles on which they are mounted. These characteristics are generally designated by the expression "NVH" (Noise Vibrations-Harshness).

 Generally speaking, a CV joint grease consists of a base oil, a thickening agent and various additives which give it certain specific properties.

 In document FR-2,592,891, it is shown that greases comprising a urea-type thickener and a friction-modifying agent consisting of an organic compound of molybdenum possibly associated with an organic compound of zinc or lead reduce the axial forces generated by the joint in your constant velocity constant velocity transmissions and absorb vibrations due to the engine, thereby preventing vehicle vibrations.

 EP-O 435 745 has also been proposed a grease comprising a base oil, a urea-based thickening agent and an additive system essentially consisting of organic compounds of molybdenum and zinc as well as copolymers of ethylene and alpha-olefins having a molecular weight between 300 and 4000.

 The greases described in these previous documents have the drawback, however, of using, as thickening agent, a product derived from urea, the processing and use of which may prove to be dangerous.

 The present invention therefore aims to solve the technical problem consisting in the supply of a new grease in particular for constant velocity joints which has properties at least comparable to those of the abovementioned greases, and which does not incorporate a thickening agent derived from urea or lead additive.

The solution according to the present invention, to solve this problem consists of a grease characterized in that it comprises, expressed in weight percent - 3 to 90%, and preferably 40 to 70%, of a base oil; - 2 to 80%, and preferably 10 to 50%, of a thickening agent
consisting of a dispersion of clay in oil; - 0.5 to 10%, and preferably 3 to 7%, of at least one compound
organic molybdenum; - 0 to 10%, and preferably 1 to 5%, of at least one compound
organic zinc; and - 0 to 10% of at least one conventional grease additive.

A currently preferred fat comprises, expressed in weight percent: - 45 to 60% base oil; - 35 to 45% of a thickening agent consisting of a dispersion
clay in Oil; - 4 to 6% of at least one organic compound of molybdenum; - 2 to 4% of at least one organic zinc compound; and - 0 to 7% of at least one conventional grease additive.

 It has been discovered, and this forms the basis of the present invention, that such greases make it possible to considerably improve the NVH characteristics of constant velocity joints.

 Particularly advantageous results have been obtained when the base oil comprises from 5 to 100%, and preferably from 80 to 100% by weight of ester oils, and in particular of esters of olefin-dicarboxylic acid copolymers.

 Such greases have been found to be at least equivalent from the point of view of the NVH characteristics of the grease seals specifically developed for this application and in particular described in the aforementioned documents of the state of the art.

According to a particular characteristic of the invention,
The aforementioned thickening agent consists of a dispersion at 25% by weight in bentonite hydrocarbon oil made hydrophobic by treatment with quaternary ammonium chlorides.

 According to another particular characteristic, the organic compound of molybdenum is chosen from the group formed by the dialkyl-dithiophosphates of molybdenum, the dialkyl-dithiocarbamates of molybdenum, the diaryl-dithiophosphates of molybdenum, and the organic compound of zinc is chosen from the group formed by zinc dialkyl dithiophosphates, zinc diaryl dithiophosphates, and zinc dialkyl dithiocarbamates.

 In accordance with the present invention, the base oil can be a mineral or synthetic oil, such as, for example, an alkyl benzene oil, a poly-olefin oil, an ester oil or a mixture in any proportion of these oils.

 Advantageously, an oil comprising from 5 to 100% by weight, and preferably from 80 to 100% of synthetic ester oils, will be chosen as the base oil.

 Among the ester oils which are particularly suitable for the preparation of a grease in accordance with the invention, mention may be made of butyl esters of olefin-dicarboxylic acid 4- / unsaturated copolymers. Such esters are commercially available. According to a currently preferred embodiment of the invention, an oil consisting mainly of these esters will be used as base oil.

 The amount of base oil present in a grease according to the invention can vary within a wide limit taking into account the nature of the thickening agent and the finished consistency of the grease. In general, the base oil will represent 3 to 90% by weight of the fat, preferably 40 to 70% and more preferably 45 to 60%. About 50% seems optimal.

 In accordance with the present invention, the thickening agent generally consists of a dispersion of clay in oil.

 This oil can be a mineral or synthetic oil of varied nature. Preferably a good hydrocarbon oil will be used.

 The clay consists of aluminosilicates made hydrophobic by treatment with amine salts preferably.

 The amounts of clay and oil will be chosen according to the viscosity grade and the desired consistency of the grease.

 In a currently preferred embodiment, the thickening agent consists of a 25% by weight dispersion in bentonite hydrocarbon oil treated with quaternary ammonium chlorides. This product is in the form of a gel, and will be designated below as a clay gel.

 The organic molybdenum compound used to prepare a fat in accordance with the invention is generally chosen from the group formed by molybdenum dialkyl-dithiophosphates, molybdenum dialkyl-dithiocarbamates, molybdenum diaryl-dithiophosphates.

These compounds are widely described in the literature to which a person skilled in the art may refer. A grease according to the invention can incorporate one or more molybdenum compounds in a weight concentration generally understood
between 0.5 and 10%, preferably between 3 and 7% and still
preferably 4 to 6%.

Used under these conditions, the organic compound of
molybdenum performs the function of friction reducer, agent
anti-wear, extreme pressure agent and antioxidant agent.

Likewise, an organic zinc compound used for the
preparation of a grease according to the invention is generally chosen
in the group formed by zinc dialkyl-dithiophosphates and
zinc diaryl dithiophosphates and dialkyl dithiocarbamates
zinc.

These compounds are also widely described in the
literature.

A grease according to the invention incorporates one or more
several organic zinc compounds in percent
weight, generally between 0 and 10%, preferably between
1 and 5% and more preferably between 2 and 4%.

Used under these conditions, the organic zinc compound
acts as an extreme pressure agent and antioxidant.

A grease according to the present invention may occur
tually contain up to 10% by weight of one or more additives
conventional tifs for grease as in particular an agent
antioxidant, antiwear agent, dispersing agent, agent
anti-rust, a viscosity stabilizing agent or a
coloring agent.

The grease according to the present invention can be
easily prepared using conventional conventional equipment
nant a kneader and a homogenizer.

 The fat obtained must have a NLGI consistency grade of the order of 000 to 3, and preferably from 0 to 2, and a viscosity at 400C of between 2.10-6m2 / s and 6.8.10 m2 / s, preferably between 32.10-6m2 / s and 6.8.10-4m2 / s and more preferably between 68.10 6m2 / s and 3.20.10-4m2 / s.

The present invention will be illustrated by the example not
following limitative.

In this example, the proportions are given in
percent weight, unless otherwise indicated.

 Two greases were prepared in accordance with the present invention (designated respectively X and Y) in a conventional installation comprising a mixer with coaxial movements and a homogenizer, by mixing the following constituents, in the proportions indicated below in percent by weight.

Composition: XY
Clay gel 39, - 42
Base oil
Mineral oil - 50
Butyl ester 53, - - olefin-unsaturated olefin-dicarboxylic acid copolymer commercially available.

Organic molybdenum compound 5 5
Organic zinc compound 3 3
The characteristics of the greases thus obtained are grouped in table I below in comparison with those of a conventional grease for constant velocity joint referenced
AT.

TABLE I
Characteristics Methods Typical values
XYA
NLGI ISO 2137 grade 1 1 2
Penetration at 25 0C - worked 60 shots ASTM D217 330 325 280
Penetration at -300C NF T 60-171 250 110 160
OC ASTM D2265>280> 280 270
Extreme Pressure Test / Anti-wear / Anti-friction - 4 balls weld test, ASTM D2596 315 315 250
Welding load, kg - Falex test
breaking load, N ASTM D3233 7500> 11 100 4900 - 4 wear ball test, ASTM D2266 0.50 0.45 0.50
cavity diameter, mm - SRV friction test, oscillations
counter ball - Coefficient of friction 0.07 0.09 0.15
As shown in Table I, the friction coefficient (measured using an SRV-Optimol machine) is significantly reduced with an advantage for grease comprising an ester base oil.

 The "NVH" performances of the grease designated X were evaluated and compared to those of conventional grease for constant velocity joints (designated A).

There is shown in perspective in Figure 1, a fixed seal of the type called tripod. The internal friction forces are combined so as to reveal, among other components, a
Moment M2, located perpendicular to the joint breaking plane.

 FIG. 2 represents the evolution of the torque M2 as a function of the breaking angle.

 The amplitude of this moment varies 6 times during a revolution of the joint.

 This alternative component thus generates excitations which are transmitted to the wheel hub, then to the passenger compartment where they produce annoying acoustic phenomena.

 Figure 3 illustrates the acoustic materialization of this phenomenon. It represents the evolution during the slow acceleration of a vehicle of the noise level in the passenger compartment for harmonic 6 of the frequency of rotation of the wheel.

 FIG. 4 also gives the results of the measurements of the mechanical losses appearing in a joint and their evolution as a function of the angularity of the joint.

 All of these results show that the greases according to the invention are at least equivalent from the point of view of N.V.H. with state-of-the-art fats.

Claims (9)

 1. Grease, in particular for constant velocity joints, characterized in that it comprises, expressed in weight percent - 3 to 90%, and preferably 40 to 70%, of a base oil; - 2 to 80%, and preferably 10 to 50%, of a thickening agent  consisting of a dispersion of clay in oil; - 0.5 to 10%, and preferably 3 to 7%, of at least one compound  organic molybdenum; - 0 to 10%, and preferably 1 to 5%, of at least one compound  organic zinc; and - 0 to 10% of at least one conventional grease additive.  2. Grease according to claim 1, characterized in that it comprises, expressed in weight percent: - 45 to 60 Z of base oil; - 35 to 45% of a thickening agent consisting of a dispersion  clay in oil; - 4 to 6% of at least one organic compound of molybdenum; - 2 to 4 Z of at least one organic zinc compound; and - 0 to 7% of at least one conventional grease additive.  3. Grease according to claim 1 or 2, characterized in that the aforementioned base oil comprises from 5 to 100% by weight, and preferably from 80 to 100%, of ester oils.  4. Grease according to claim 3, characterized in that the abovementioned ester oils are butyl esters of olefin-dicarboxylic acid copolymers.  5. Grease according to any one of claims 1 to 4, characterized in that the aforementioned thickening agent consists of a dispersion in oil, of clay treated with amine salts.  6. Grease according to claim 5, characterized in that the aforementioned thickening agent is a dispersion at 25 Z by weight in hydrocarbon oil, of bentonite treated with quaternary ammonium chlorides.  7. Grease according to any one of claims 1 to 6, characterized in that the abovementioned molybdenum compound is chosen from the group formed by molybdenum dialkyl-dithiophosphates, molybdenum dialkyl-dithiocarbamates, molybdenum diaryl-dithiophosphates .  8. Fat according to any one of claims 1 to 7, characterized in that the zinc compound is chosen from the group formed by zinc dialkyl dithiophosphates, zinc diaryldithiophosphates and zinc dialkyl dithiocarbamates.  9. Use of the grease according to any one of claims 1 to 8, for the lubrication of constant velocity joints.