Title:
High efficiency hydraulic oils
Kind Code:
A1


Abstract:
Methods for achieving favorable efficiency properties are disclosed including methods for blending a lubricant composition and lubricant compositions. In one embodiment, the method comprises the steps of obtaining at least one base stock and at obtaining at least one base stock chosen to have a favorable air release properties, obtaining at least one additive, blending at least one base stock and at least one additive to achieve a favorable effective bulk modulus through air release property, bulk modulus, and using a relationship between density and bulk modulus.



Inventors:
Wright, Kelli H. (Bordentown, NJ, US)
Holt, David G. L. (Medford, NJ, US)
Galiano-roth, Angela (Mullica Hill, NJ, US)
Carey, James T. (Medford, NJ, US)
Webster, Martin N. (Pennington, NJ, US)
Application Number:
12/009234
Publication Date:
07/24/2008
Filing Date:
01/17/2008
Primary Class:
Other Classes:
508/110, 508/421, 508/463
International Classes:
C10M125/04; C10M105/34; C10M137/04; C10M169/04
View Patent Images:



Primary Examiner:
HINES, LATOSHA D
Attorney, Agent or Firm:
ExxonMobil Research and Engineering Company (Annandale, NJ, US)
Claims:
What is claimed is:

1. A hydraulic lubricating oil, comprising a) at least one base stock; b) at least one additive; c) wherein the base stock has a density at 15.6° C. of greater than 0.9 and a ASTM D-3427 air release of less than 1.25 percent air at 1 minute.

2. The lubricating oil of claim 1 wherein the base stock has an ASTM D-3427 air release of less than 1 percent air at 1 minute.

3. The lubricating oil of claim 1 wherein the base stock has an ASTM D-3427 air release of less than 0.6 percent air at 1 minute.

4. The lubricating oil of claim 1 wherein the base stock has a bulk modulus of greater than 215,000 at 34.47 MPa (5,000 PSI).

5. The lubricating oil of claim 1 wherein at least one base stock is chosen from the group consisting of PAOs, Group III, GTL, aromatic esters, polyol esters, alkylated aromatics, phosphate esters, and any combinations thereof.

6. The lubricating oil of claim 1 wherein the lubricating oil has an ASTM D-3427 air release of less than 2 percent air at 1 minute.

7. The lubricating oil of claim 1 wherein the lubricating oil has an ASTM D-3427 air release of less than 1 percent air at 1 minute.

8. The lubricating oil of claim 1 wherein the lubricating oil has a Bulk Modulus greater than 195,000 at 34.47 MPa (5,000 PSI).

9. The lubricating oil of claim 1 wherein the lubricating oil has a density greater than 0.9.

10. The lubricating oil of claim 1 wherein at least one base stock is an ester and the ester comprises at least 20 percent of the hydraulic oil.

11. The lubricating oil of claim 1 wherein the base stock has air release properties better than equation:
Y=0.025X−0.55 Wherein: Y=Percent air at 1 minute using ASTM D-3427 at 50° C. X=Kinematic Viscosity at 40° C. in cST.

12. A method of improving hydraulic efficiency in a system comprising a) determining a favorable hydraulic efficiency requirement of the system. b) obtaining a hydraulic oil to achieve a favorable hydraulic efficiency property using a relationship between the hydraulic oil's density, and bulk modulus to obtain a high bulk modulus hydraulic oil. c) lubricating the system with the lubricant.

13. The method of claim 12 further comprising choosing a hydraulic oil with favorable air release properties wherein the base stock has air release properties greater than equation:
Y=0.025X−0.27 Wherein: Y=Percent air at 1 minute using ASTM D-3427 at 50° C. X=Kinematic Viscosity at 40° C. in cST

14. The method of claim 12 wherein the density is chosen to be greater than 0.8 at 15.6° C. and the ASTM D-3427 air release is chosen to be less than 1.25 percent air at 1 minute.

15. The method of claim 12 further comprising choosing a hydraulic oil with at least one base stock from the group consisting of consisting of PAOs, Group III, GTL, aromatic esters, polyol esters, alkylated aromatics, phosphate esters, and any combinations thereof with favorable air release properties.

16. The method of claim 12 wherein at least one base stock is an ester and the ester comprises at least 20 percent of the hydraulic oil.

17. A method of formulating a lubricating oil with favorable hydraulic efficiency comprising: a) obtaining at least one base stock chosen to have a favorable air release properties; b) obtaining at least one additive; c) blending at least one base stock and at least one additive to achieve a favorable bulk modulus and air release property using a relationship between density and bulk modulus.

18. The lubricating oil of claim 17 wherein the base stock has an ASTM D-3427 air release of less than 0.6 percent air at 1 minute.

19. The lubricating oil of claim 17 wherein the base stock has a bulk modulus of greater than 215,000 at 34.47 MPa (5,000 PSI).

20. The lubricating oil of claim 17 wherein at least one base stock is chosen form the group consisting of PAOs, Group III, GTL, aromatic esters, polyol esters, alkylated aromatics, phosphate esters, and any combinations thereof.

21. The lubricating oil of claim 17 wherein the lubricating oil has an ASTM D-3427 air release of less than 2 percent air at 1 minute.

22. The lubricating oil of claim 17 wherein the lubricating oil has an ASTM D-3427 air release of less than 1 percent air at 1 minute.

23. The lubricating oil of claim 17 wherein the lubricating oil has a bulk modulus greater than 195,000 at 34.47 MPa (5,000 PSI).

24. The lubricating oil of claim 17 wherein the base stock has air release properties better than equation:
Y=0.025X−0.55 Wherein: Y=Percent air at 1 minute using ASTM D-3427 at 50° C. X=Kinematic Viscosity at 40° C. in cST.

25. The lubricating oil of claim 17 wherein the base stock has air release properties better than equation:
Y=0.025X−0.27 Wherein: Y=Percent air at 1 minute using ASTM D-3427 at 50° C. X=Kinematic Viscosity at 40° C. in cST

Description:

CROSS-REFERENCE TO RELATED APPLICATION:

Non Provisional Application based on U.S. Ser. No. 60/881,420 filed Jan. 19, 2007.

This application claims priority of Provisional Application 60/881,420 filed Jan. 19, 2007.

BACKGROUND

The art or formulating lubricating oil compositions has become more complex as a result of increased government and user environmental standards and increased user performance requirements. Overall hydraulic system efficiency is defined by mechanical efficiency and volumetric efficiency contributions. Mechanical efficiency includes factors such as energy lost in the form of friction and heat in areas of contacting metal surfaces such as, pumps and actuators. Volumetric efficiency is related to how much work is done by the pressurized fluid. Lubricants with a high effective bulk modulus (“βe”) will have greater volumetric efficiency that those with low βe.

The effective bulk modulus of a fluid, βe is a calculated value that takes into account 1) the static bulk modulus of the fluid, which is a function of temperature and pressure and can be obtained through ASTM D6793, and 2) the air release properties of the lubricant, which can be assessed via ASTM D3427. The general equation for system effective bulk modulus is listed as follows:

1βe=VIVe1βI+VaVe1βa+1βc,

where βe is effective bulk modulus of the system, Ve is the effective volume within the system, V1 is the volume of liquid, β1 is the bulk modulus of the liquid, Va is the volume of air, βa is the bulk modulus of air, and βc is the bulk modulud of the container. See Manring, N. D. Hydraulic Control Systems, pp.5-25, John Wiley & Sons, Inc., 2005.

In designing a fluid, the portions of βe that can be controlled are the bulk modulus of the fluid and the volume of the air present in the pressurized system. Air entrainment is often a function of system design and maintenance, but the rate of entrained air release can be modified in one fluid versus another to achieve the most favorable effective bulk modulus for a particular system.

Air entrainment is a small amount of air in the form of extremely small bubbles (generally less than 1 mm in diameter) dispersed throughout the bulk of the oil. Agitation of lubricating oil with air in equipment, such as bearings, couplings, gears, pumps, and oil return lines, may produce a dispersion of finely divided air bubbles in the oil. If the residence time in the reservoir is too short to allow the air bubbles to rise to the oil surface, a mixture of air and oil will circulate through the lubricating oil system. This may result in an inability to maintain oil pressure (particularly with centrifugal pumps), incomplete oil films in bearings and gears, and poor hydraulic system performance or failure.

Air entrainment is treated differently than foam, and is most often a completely separate problem. A partial list of potential effects of air entrainment include: pump cavitation; spongy, erratic operation of hydraulics, loss of precision control, vibrations, oil oxidation, component wear due to reduced lubricant viscosity, equipment shut down when low oil pressure switches trip, “micro-dieseling” due to ignition of the bubble sheath at the high temperatures generated by compressed air bubbles, safety problems in turbines if overspeed devices do not react quickly enough, and loss of head in centrifugal pumps.

One commonly used method to measure air release properties of petroleum oils is ASTM D-3427. This test method measures air content via density at given time intervals following aeration at temperatures specified by viscosity grade. Air release performance is reported either in air content at various time intervals or the time required for the air entrained in the oil to reduce in volume to either 0.1% or 0.2% is recorded as the air release time. Typically, for hydraulic oil and for purposes of this application, all air release measurements are performed at 50° C.

Most solutions to the air entrainment problem have been to redesign the reservoir or choose additives not likely to cause aeration issues. There is a need to create new understanding of both the base stocks and additives to achieve favorable air release properties and reduce aeration issues.

Higher efficiency fluids that can do more work done per unit volume will assist in energy/fuel savings and potentially allow for cooler operation and optimized system design. Accordingly, there is a need for higher efficiency fluids with higher βe and this invention satisfies that need.

SUMMARY

A novel lubricant formulation is disclosed. In one embodiment the novel lubricant formulation comprises at least one base stock and at least one additive, wherein the base stock has a density at 15.6° C. of greater than 0.9 and a ASTM D-3427 air release of less than 1.25 percent air at 1 minute.

In a second embodiment, a method of achieving favorable efficiency properties in a system is disclosed. The method comprises determining a favorable hydraulic efficiency requirement of the system, obtaining a hydraulic oil to achieve a favorable hydraulic efficiency property using a relationship between the hydraulic oil's density and bulk modulus to obtain a high bulk modulus hydraulic oil, and lubricating the system with the lubricant.

In a third embodiment a method for blending a novel formulation is also disclosed. The method comprises obtaining at least one base stock chosen to have a favorable air release properties, obtaining at least one additive, blending at least one base stock and at least one additive to achieve a favorable βe using a relationship between density and bulk modulus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing air release properties as graphed versus density for different base oils in the 41.4-50.6 cSt at 40° C. range.

FIG. 2 is a graph showing air release graphed vs. isothermal secant bulk modulus at 34.47 MPA (5,000 PSI) and 60° C.

FIG. 3 is a graph of density with bulk modulus data.

FIG. 4 is a graph that illustrates several line profiles for air release as a function of viscosity grade.

DETAILED DESCRIPTION

We have discovered that certain base stocks provide system efficiency gains versus a Group I or Group II hydraulic oil formulation. These base stocks providing favorable efficiency gains include GTL base stocks, PAO blends, Esters and PAG Fluids. Table 1 details base oils and the improvements versus Group I/II base oils in terms of achieving a βe and thus, volumetric efficiency, improvement. In a further embodiment of this discovery, a novel combination of base stocks densities and bulk modulus provide unexpected favorable improvements in efficiency.

TABLE 1
Fluid TypePhysical Property (vs. Gr I/II)
GTL Base OilsMore Favorable Air Release
PAO BlendsMore Favorable Air Release
Select EstersHigher β1, More favorable air release
PAG FluidsHigher β1

The overwhelming majority of hydraulic oil sold on the market is either Group I or Group II. Typically, hydraulic oils range in viscosity from 10 cST, Kv40° C. to 150 cST, Kv40° C. and provide the ability to perform work. While there are small volumes of other base stocks commercially sold, they are marketed for niche applications, such as biodegradable and fire resistance and there are no claims to efficiency gains. Original equipment manufacturers are now considering moving to higher system pressures where fluids that contribute to efficiency will be more important in the future.

In one embodiment, suitable lubricant base stocks include PAOs, Group III, GTL, Aromatic Esters, Polyol Esters, Alkylated Aromatics, Phosphate Esters, and any combinations thereof. In a preferred embodiment, the lubricant comprises an ester base stock of at least 20 percent of the composition and more preferably at least 40 percent of the composition. FIG. 1 is a graph showing air release properties as graphed versus density for different base oils in the 41.4-50.6 cSt at 40C. range. As shown in FIG. 1, the most favorable base stocks exhibit high density and favorable air release properties. We have discovered the preferred range 2 for base stocks have an ASTM D3427 air release of less than 1.25 minutes. A more preferred range 3 would be a density of 0.85 and an ASTM D-3427 air release of less than 1 minute. The most preferred range 4 would be a density of greater than 0.9 and an ASTM D3427 air release of less than 0.5 minutes.

FIG. 2 is a graph showing air release graphed vs. isothermal secant bulk modulus at 34.47 MPA (5,000 PSI) and 60° C. As shown in FIG. 2, the most favorable base stocks exhibit favorable air release properties and high bulk modulus. We have discovered the preferred range 12 for base stocks have an ASTM D-3427 air release of less than 1.25 minutes and a bulk modulus of greater than 195,000. A more preferred range 13 would be a bulk modulus of greater than 205,000 and an ASTM D-3427 air release of less than 1 minute. The most preferred range 14 would be a bulk modulus of greater than 215,000 and an ASTM D-3427 air release of less than 0.5 minutes.

In another embodiment, a method of formulating a high efficiency hydraulic fluid is disclosed. This method may work through consideration of System design and fluid density, bulk modulus, and air release properties.

The most favorable method is dependant on whether the system entrains air during normal operations. For systems incurring minimal to no air entrainment, base stocks with high bulk modulus are selected, as the volume of air will be negligible in the expression for βe. The bulk modulus is predicted through the general linear increase of bulk modulus with density. FIG. 3 is a graph of density with bulk modulus data. This figure illustrates the general relationship of higher density equals higher bulk modulus. The most preferred range 31 has a density of greater than 0.9 and a bulk modulus of greater than 215,000.

For systems that entrain air during normal operation, fluids with good air release properties are selected, with high bulk modulus and high density being in the most Preferred range of FIGS. 1 and 2. However, lower bulk modulus and density may be acceptable as a preferred range with air release properties defined as acceptable as shown in FIGS. 1 and 2.

There are not as many data points on the bulk modulus graph because the ASTM D6793 method is not as common and more difficult to obtain. Therefore, using density to predict bulk modulus is an effective tool in selecting a fluid belonging to the most preferred, more preferred, and preferred ranges.

The air release performance of base stocks follows the pattern of light viscosities are better than heavy viscosities which are better than ultra heavy viscosity components. In others words, light viscosities exhibit the best performance whereas the ultra heavy viscosity components exhibit the worst air release properties.

We have created formulas for determining favorable air release ranges that are dependant on viscosity. FIG. 4 is a graph that illustrates several line profiles for air release as a function of viscosity grade. This graph shows viscosity ranges from ISO VG 32 through ISO VG 100. Line 41 represents the most preferred ranges of air release of base stocks based on viscosity with the favorable properties being the region 43 at or below the line. Line 42 represents the preferred ranges of base stocks with the favorable properties being the region 44 at or below the line. The lines are also represented by the equations 3 through 6 discussed below.

We have also created equations for determining the preferred and most preferred air release properties of fully formulated lubricating oils. The effects of additives on air release are discussed in more detail below. Line 41 is represented by equation 3 and equation 4 represents the corresponding preferred fully formulated air release properties or line 45. Line 42 is represented by Equation 5 and equation 6 is the corresponding most preferred air release properties of fully formulated oils or line 46.


Y=0.025X−0.53 Eq. 3

  • Wherein:
  • Y=Percent air at 1 minute using ASTM D-3427 (50C.)
  • X=Kinematic Viscosity at 40° C. in cST.


Y=0.025X−0.27 Eq. 4

  • Wherein:
  • Y=Percent air at 1 minute using ASTM D-3427
  • X=Kinematic Viscosity at 40° C. in cST.


Y=0.038X−0.53 Eq. 5

  • Wherein:
  • Y=Percent air at 1 minute using ASTM D-3427
  • X=Kinematic Viscosity at 40° C. in cST.


Y=0.038X−0.17 Eq. 6

  • Wherein:
  • Y=Percent air at 1 minute using ASTM D-3427
  • X=Kinematic Viscosity at 40° C. in cST.

Base Stocks

Groups I, II, III, IV and V are broad categories of base oil stocks developed and defined by the American Petroleum Institute (API Publication 1509; www.API.org) to create guidelines for lubricant base oils. Group I base stocks generally have a viscosity index of between about 80 to 120 and contain greater than about 0.03% sulfur and/or less than about 90% saturates. Group II base stocks generally have a viscosity index of between about 80 to 120, and contain less than or equal to about 0.03% sulfur and greater than or equal to about 90% saturates. Group III stock generally has a viscosity index greater than about 120 and contains less than or equal to about 0.03% sulfur and greater than about 90% saturates. Group IV includes polyalphaolefins (PAO). Group V base stocks include base stocks not included in Groups I-IV. Table 3 summarizes properties of each of these five groups.

TABLE 3
Base Stock Properties
SaturatesSulfurViscosity Index
Group I<90% and/or>0.03% and≧80 and <120
Group II≧90% and≦0.03% and≧80 and <120
Group III≧90% and≦0.03% and≧120
Group IVPolyalphaolefins (PAO)
Group VAll other base oil stocks not included in Groups
I, II, III, or IV

In a preferred embodiment, the base stocks include at least one base stock of synthetic oils and most preferably include at least one base stock of API group IV Poly Alpha Olefins. Synthetic oil for purposes of this application shall include all oils that are not naturally occurring mineral oils. Naturally occurring mineral oils are often referred to as API Group I oils.

Gas to liquid (GTL) base stocks can also be preferentially used with the components of this invention as a portion or all of the base stocks used to formulate the finished lubricant. We have discovered, favorable improvement when the components of this invention are added to lubricating systems comprising primarily Group II, Group III and/or GTL base stocks compared to lesser quantities of alternate fluids.

GTL materials are materials that are derived via one or more synthesis, combination, transformation, rearrangement, and/or degradation/deconstructive processes from gaseous carbon-containing compounds, hydrogen-containing compounds, and/or elements as feedstocks such as hydrogen, carbon dioxide, carbon monoxide, water, methane, ethane, ethylene, acetylene, propane, propylene, propyne, butane, butylenes, and butynes. GTL base stocks and base oils are GTL materials of lubricating viscosity that are generally derived from hydrocarbons, for example waxy synthesized hydrocarbons, that are themselves derived from simpler gaseous carbon-containing compounds, hydrogen-containing compounds and/or elements as feedstocks. GTL base stock(s) include oils boiling in the lube oil boiling range separated/fractionated from GTL materials such as by, for example, distillation or thermal diffusion, and subsequently subjected to well-known catalytic or solvent dewaxing processes to produce lube oils of reduced/low pour point; wax isomerates, comprising, for example, hydroisomerized or isodewaxed synthesized hydrocarbons; hydro-isomerized or isodewaxed Fischer-Tropsch (“F-T”) material (i.e., hydrocarbons, waxy hydrocarbons, waxes and possible analogous oxygenates); preferably hydroisomerized or isodewaxed F-T hydrocarbons or hydroisomerized or isodewaxed F-T waxes, hydroisomerized or isodewaxed synthesized waxes, or mixtures thereof.

GTL base stock(s) derived from GTL materials, especially, hydroisomerized/isodewaxed F-T material derived base stock(s), and other hydroisomerized/isodewaxed wax derived base stock(s) are characterized typically as having kinematic viscosities at 100° C. of from about 2 mm2/s to about 50 mm2/s, preferably from about 3 mm2/s to about 50 mm2/s, more preferably from about 3.5 mm2/s to about 30 mm2/s, as exemplified by a GTL base stock derived by the isodewaxing of F-T wax, which has a kinematic viscosity of about 4 mm2/s at 100° C. and a viscosity index of about 130 or greater. The term GTL base oil/base stock and/or wax isomerate base oil/base stock as used herein and in the claims is to be understood as embracing individual fractions of GTL base stock/base oil or wax isomerate base stock/base oil as recovered in the production process, mixtures of two or more GTL base stocks/base oil fractions and/or wax isomerate base stocks/base oil fractions, as well as mixtures of one or two or more low viscosity GTL base stock(s)/base oil fraction(s) and/or wax isomerate base stock(s)/base oil fraction(s) with one, two or more high viscosity GTL base stock(s)/base oil fraction(s) and/or wax isomerate base stock(s)/base oil fraction(s) to produce a bi-modal blend wherein the blend exhibits a viscosity within the aforesaid recited range. Reference herein to Kinematic Viscosity refers to a measurement made by ASTM method D445.

GTL base stocks and base oils derived from GTL materials, especially hydroisomerized/isodewaxed F-T material derived base stock(s), and other hydroisomerized/isodewaxed wax-derived base stock(s), such as wax hydroisomerates/isodewaxates, which can be used as base stock components of this invention are further characterized typically as having pour points of about −5° C. or lower, preferably about −10° C. or lower, more preferably about −15° C. or lower, still more preferably about −20° C. or lower, and under some conditions may have advantageous pour points of about −25° C. or lower, with useful pour points of about −30° C. to about −40° C. or lower. If necessary, a separate dewaxing step may be practiced to achieve the desired pour point. References herein to pour point refer to measurement made by ASTM D97 and similar automated versions.

The GTL base stock(s) derived from GTL materials, especially hydroisomerized/isodewaxed F-T material derived base stock(s), and other hydroisomerized/isodewaxed wax-derived base stock(s) which are base stock components which can be used in this invention are also characterized typically as having viscosity indices of 80 or greater, preferably 100 or greater, and more preferably 120 or greater. Additionally, in certain particular instances, viscosity index of these base stocks may be preferably 130 or greater, more preferably 135 or greater, and even more preferably 140 or greater. For example, GTL base stock(s) that derive from GTL materials preferably F-T materials especially F-T wax generally have a viscosity index of 130 or greater. References herein to viscosity index refer to ASTM method D2270.

In addition, the GTL base stock(s) are typically highly paraffinic of greater than 90 percent saturates) and may contain mixtures of monocycloparaffins and multicycloparaffins in combination with non-cyclic isoparaffins. The ratio of the naphthenic (i.e., cycloparaffin) content in such combinations varies with the catalyst and temperature used. Further, GTL base stocks and base oils typically have very low sulfur and nitrogen content, generally containing less than about 10 ppm, and more typically less than about 5 ppm of each of these elements. The sulfur and nitrogen content of GTL base stock and base oil obtained by the hydroisomerization/isodewaxing of F-T material, especially F-T wax is essentially nil.

In a preferred embodiment, the GTL base stock(s) comprises paraffinic materials that consist predominantly of non-cyclic isoparaffins and only minor amounts of cycloparaffins. These GTL base stock(s) typically comprise paraffinic materials that consist of greater than 60 wt % non-cyclic isoparaffins, preferably greater than 80 wt % non-cyclic isoparaffins, more preferably greater than 85 wt % non-cyclic isoparaffins, and most preferably greater than 90 wt % non-cyclic isoparaffins.

Useful compositions of GTL base stock(s), hydroisomerized or isodewaxed F-T material derived base stock(s), and wax-derived hydroisomerized/isodewaxed base stock(s), such as wax isomerates/isodewaxates, are recited in U.S. Pat. Nos. 6,080,301; 6,090,989, and 6,165,949 for example.

Additives

The additives include various commercially available industrial oil components and packages, which may include antiwear, antioxidant, defoamant, demulsifier, detergent, dispersant, metal passivation, and rust inhibition additive chemistries to deliver desired performance.

The preferred ashless antioxidants are hindered phenols and arylamines. Typical examples are butylated/octylated/styrenated/nonylated/dodecylated diphenylamines, 4,4′-methylene bis-(2,6-di-tert-butylphenol), 2,6-di-tert-butyl-p-cresol, octylated phenyl-alpha-naphthylamine, alkyl ester of 3,5-di-tert-butyl-4-hydroxy-phenyl propionic acid, and many others. Sulfur-containing antioxidants, such as sulfur linked hindered phenols and thiol esters can also be used.

Suitable dispersants include borated and non-borated succinimides, succinic acid-esters and amides, alkylphenol-polyamine coupled Mannich adducts, other related components and any combination thereof. In some embodiments, it can often be advantageous to use mixtures of such above described dispersants and other related dispersants. Examples include additives that are borated, those that are primarily of higher molecular weight, those that consist of primarily mono-succinimide, bis-succinimide, or mixtures of above, those made with different amines, those that are end-capped, dispersants wherein the back-bone is derived from polymerization of branched olefins such as polyisobutylene or from polymers such as other polyolefins other than polyisobutylene, such as ethylene, propylene, butene, similar dispersants and any combination thereof. The averaged molecular weight of the hydrocarbon backbone of most dispersants, including polyisobutylene, is in the range from 1000 to 6000, preferably from 1500 to 3000 and most preferably around 2200.

Suitable detergents include but are not limited to calcium phenates, calcium sulfonates, calcium salicylates, magnesium phenates, magnesium sulfonates, magnesium salicylates, metal carbonates, related components including borated detergents, and any combination thereof. The detergents can be neutral, mildly overbased, or highly overbased. Metal detergents have been chosen from alkali or alkaline earth calcium or magnesium phenates, sulfonates, salicylates, carbonates and similar components.

Inhibitors and antirust additives may be used as needed. Seal swell control components and defoamants may be used with the mixtures of this invention. Suitable defoamants include polydimethyl siloxane and polymacrylates.

Various antiwear and/or friction modifiers may also be utilized. Examples include but are not limited to alkylated dithiocarbamates, alkyl phosphate esters, aryl phosphate esters, thiophosphates, amine phosphates, and dithiophosphates, alkylated phosphonate esters, aliphatic succinimides, molybdenum compounds, acid amides, and any combination thereof.

Additives in hydraulic fluids generally comprise less than 10 weight percent of the fully formulated fluid. As such, the density contributions and therefore bulk modulus contributions of additives are assumed to be negligible in the approximations of β1. Performance additives can impact air release and in general, they are either air release neutral or detract from the air release properties of the base fluid. As such, additives should be selected (type and quantity) such that they meet basic performance characteristics while having minimal negative impact upon air release.

EXAMPLES

As an example we blended two unadditized fluids for comparison with commerciality available fluids. As shown in Table 4, the inventive example embodiments have higher densities, higher bulk modulus and better air release than the prior art commercially available base stocks.

TABLE 4
Prior ArtInvention
Example 1Example 2Example 3Example 4
Base OilGroup 1PAO w/ <20%PAO blendPolyol Ester
diester co-basew/60% aromaticco-base
stockester co-basestock
stock
Density.8766.8395.9114.918
Bulk Modulus217000204292228000 (est. based227000
(5000 psi, 60 C.)upon density of
blend and of
similar blends)
Air Release (% air2.28.58.78.45
at 1 min)