Multifunctional lubricating fluid

This application is a National Phase Entry of International Application No. PCT/FR2007/001729, filed Oct. 19, 2007, which claims priority to European Patent Application No. EP 06291645.7, filed Oct. 24, 2006, both of which are incorporated herein by reference.

The present invention relates to multifunctional lubricating fluids for use in the various mechanisms of motor vehicles, in particular in the engine, the transmission or the hydraulic circuit. More precisely, the invention relates to a single fluid that can be used directly in several types of applications, in particular in the various mechanisms of motor vehicles such as engines, transmission devices (gearboxes and transfer boxes), hydraulic circuits and other ancillary mechanisms without any need for modification; in other words, the composition of this fluid is directly suitable for the various types of use in question.

At present every motor vehicle uses a variety of monofunctional lubricating fluids, each fulfilling different functions, for example engine oils, gearbox oils, hydraulic oils etc. The formulation of a monofunctional oil consists conventionally of a mixture of mineral, semi-synthetic or synthetic base oils, a package of performance additives, and optionally a viscosity improving polymer and a pour point improver. When a monofunctional lubricating oil is in service in a mechanism, the constant shear to which the viscosity improving polymer is subjected leads to a decrease in viscosity of the oil. The extent and rate of this decrease in viscosity depend on the nature and amount of viscosity improving polymer used.

Now, the shear rates to which the lubricant is subjected differ from one mechanism to another. For example, the high-pressure hydraulic circuits operating the lifting mechanisms produce more shear than the gearboxes, and they in turn produce more shear than the engines. If a monofunctional oil is used in a mechanism other than that for which it has been formulated, its viscosity may move away from the value required for optimum functioning of said mechanism. Formulations of multifunctional oils for engine, gearbox and hydraulic circuit are already marketed under the names TOTAL Multi TP, FINA Penta, ELF Noria. Their design is based on an appropriate choice of viscosity improving polymer and the amount incorporated.

The varying level of shear stability of the viscosity improving polymer incorporated in these multifunctional oils for engine, gearbox and hydraulic circuit will determine the respective levels of viscosity attained by this oil in each mechanism. If we use a viscosity improving polymer that is very sensitive to shear, the viscosity will drop very rapidly, even in those mechanisms having a low shear rate: it will drop below the minimum viscosities required in the engine and the gearbox. Conversely, if we use a polymer with a very high shear stability, the viscosity will remain high for a very long time even in those mechanisms having a high shear rate: it will take a very long time before the viscosity reaches in the best case a low enough value, as required for example in the hydraulic circuits. This can cause persistent cold starting problems for the lifting mechanisms operated by the hydraulic circuit.

If the behaviour of the polymer is intermediate, the adjustment parameters allowing simultaneous fulfilment of the 3 constraints of minimum viscosities in engine and gearbox, and maximum viscosity in the hydraulic system, are the amount and nature of the viscosity improving polymer used. Most of the multifunctional oils currently in use are based on this principle. We therefore end up with compromises that exceed the limits of capacity for use of the existing multifunctional oils in three mechanisms at the same time. Thus, the existing formulations of multifunctional oils do not allow them to simultaneously reach the performance levels expected in the various target mechanisms. Moreover, the performance levels are also not achieved in particular with respect to the high-temperature stability in the engines and the transmission and the cold starting of the hydraulics.

There is therefore a need for a single fluid whose performance is suitable for lubricating various mechanisms of a vehicle at the same time. In particular, there is a need for a single fluid that can be used for all three applications: engine, transmission and hydraulic circuit. There is also a need for the performance of this same single fluid to be adapted for good high-temperature stability in the engine and transmission and for cold starting of the hydraulics. In fact, having a single fluid available for lubricating various mechanisms of a vehicle, relative to the use of several monofunctional oils, offers advantages in particular in terms of ease of maintenance and storage, servicing of the vehicle or of a fleet of vehicles, packaging and logistics. This is true in particular for the large fleets of public service vehicles, which are often used on isolated sites and are subject to severe weather conditions, without adequate storage equipment.

Thus, the invention provides a lubricating composition comprising at least one oil of groups I to V and a mixture of at least two polymers having a difference in permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100° C. of at least 25, and having a viscosity profile such that

(a) at 100° C. after the Bosch-30 cycles test according to standard CEC-L-14-A-93 the viscosity of the final lubricating composition is greater than 9.0 cSt, preferably in the range from 9.0 to 12.0 cSt for an oil initially of grade 30, or else the viscosity of the final lubricating composition is greater than 12.0 cSt, preferably in the range from 12.0 to 15.0 cSt for an oil initially of grade 40, and

(b) at 100° C. after the KRL-20 hours test according to standard CEC-L-45-A-99 the viscosity of the lubricating composition is greater than 8.5 cSt, preferably in the range from 8.5 to 11.0 cSt for an oil initially of grade 30 or 40, and

(c) at 40° C. after the KRL-3 hours test, according to standard CEC-L-45-A-99 with the test duration reduced to 3 hours, the viscosity of the lubricating composition is less than 51 cSt, preferably in the range from 41 to 51 cSt for an oil initially of grade 30 or 40.

This formulation of multifunctional lubricant can be used for simultaneously lubricating various mechanisms of a motor vehicle. More particularly, this single lubricant is used for simultaneously lubricating at least three mechanisms, namely the engine, the gearbox and the hydraulic circuit, as it offers a viscosity profile adapted to the conditions of use required in each target mechanism. For simultaneously lubricating the various target mechanisms of a motor vehicle, this single lubricant incorporates a mixture of polymers having different shear stabilities.

The nature and the respective amount of the different types of polymers are determined in such a way that the lubricating composition incorporating this mixture adapts very rapidly to the conditions of use required in each target mechanism, owing to its viscosity profile. Thus, the lubricating composition includes at least 50 wt. %, based on the weight of the final composition, of at least one oil selected from the oils of groups I to V and at least 5%, preferably from 5 to 40%, or more preferably 5 to 15 wt. % based on the weight of the final composition, of a mixture comprising at least two different polymers of type “A”, “B”, or “C”, the polymers of the mixture differing from one another in that they belong to a separate range of permanent shear stability index (PSSI) such that:

the polymers of type “A” have a permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100° C., less than or equal to 40,

the polymers of type “B” have a permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100° C., between 40 and 65 exclusive;

the polymers of type “C” have a permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100° C., greater than or equal to 65;

said composition in which at least two polymers have a difference in PSSI measured after the standardized KRL 20 hours test at 100° C., of at least 25.