Abstract:
The instant invention relates to a thermally stable, friction, wear and degradation reducing transmission fluids for use in highly stressed power transmission systems. The transmission fluids of the instant invention have improved performance under extreme conditions and extend the life of automatic transmissions.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to lubricating compositions. In particular, the instant invention relates to a thermally stable, friction, wear and degradation reducing composition for use in highly stressed power transmission systems.  
         [0003]     2. Description of Related Art  
         [0004]     Motorized vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in increased engine wear and tear and reduced engine efficiency. Therefore, manually-shifted transmissions were the most popular for used in motor vehicles.  
         [0005]     With the advent of three- and four-speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity. These transmissions improved the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.  
         [0006]     Automatic transmissions comprise a myriad of mechanical parts which operate at close tolerances. Automatic transmissions typically require transmission fluid in order to function properly. The purpose of transmission fluid is to lubricate these close-fitting parts to reduce wear and keep down temperatures that are a result of friction. Achieving this function is complicated by the changing temperatures and pressures under which the transmission is operated. Transmission fluids are complex multifunctional fluids that serve to control heat dissipation, wear protection, lubrication, foam inhibition and shift quality. Typically, different types of automatic transmission fluids are used depending on the design and severity of application.  
         [0007]     Generally, transmission fluids are designed to meet specific manufacturer requirements. Delivery trucks and or car fleets are unusually hard on transmissions. Current automatic transmission fluid formulas address the automatic transmission needs primarily of passenger car motor vehicles. Medium duty trucks such as postal delivery vehicles have transmissions that are subject to constant stopping and starting of heavily loaded vehicles and a preponderance of low gear use and shifting per mile driven in comparison to normal usage. This creates a lubrication environment for early failure of the transmission due to high frictional heat and wear that causes thermal break down of the fluid and loss of adequate wear protection. This invention creates a thermally stable fluid for high temperature applications with lower volatility creating fluid stabilization, increased lubrication properties, high natural viscosity index for consistent hydrolytic lubrication coupled with improved resistance to low and high shear degradation. The transmission fluids of the instant invention demonstrate better film strength for extended lubrication along with maintaining excellent performance in low and high temperature climatic conditions.  
         [0008]     Constant and rapid start and stop activities in low gears coupled with a wide variety of climatic conditions leads to the breakdown of automatic transmission fluid. This type of severe use and subsequent breakdown of the fluid will result in premature failure of the transmission. Thus, it is an objective of this invention to create a unique transmission fluid composition to address specific lubrication requirements of highly stressed automatic transmissions. Further, this invention is designed to perform under extreme conditions and to extended the life of automatic transmissions.  
       SUMMARY OF THE INVENTION  
       [0009]     One embodiment of the invention is a unique transmission fluid for highly stressed automatic transmissions.  
         [0010]     Another embodiment of the invention is an improved thermally stable automatic transmission fluid with enhanced frictional properties to reduce wear of mechanical in heavily loaded transmissions  
         [0011]     A further embodiment of the invention is a transmission fluid comprising a specific TMP C8/C10 polyol ester, a unique amide containing friction modifier, a viscosity index (VI) improver, a corrosion inhibitor, an antioxidant, dispersants, a lubricating oil flow improver, anti-foam agents and anti-wear additives. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0012]      FIG. 1  illustrates a typical line pressure/temperature change during one cycle.  
         [0013]      FIG. 2  shows the permanent viscosity loss response of the two automatic transmission fluids used in these tests.  
         [0014]      FIG. 3  shows the line pressure consistency during operation over the test period for the ATC #3 dynamometer test.  
         [0015]      FIG. 4  shows the line pressure consistency during operation over the test period for the Jasper 4 dynamometer test  
         [0016]      FIG. 5  shows the generation of lead from babbit bearing wear with cycles of test. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     For simplicity and illustrative purposes, the principles of the present invention are described by referring to various exemplary embodiments thereof. Although the preferred embodiments of the invention are particularly disclosed herein, one of ordinary skill in the art will readily recognize that the same principles are equally applicable to, and can be implicated in other compositions and methods, and that any such variation would be within such modifications that do not part from the scope of the present invention. Before explaining the disclosed embodiments of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of any particular embodiment shown, since of course the invention is capable of other embodiments. The terminology used herein is for the purpose of description and not of limitation. Further, although certain methods are described with reference to certain steps that are presented herein in certain order, in many instances, these steps may be performed in any order as may be appreciated by one skilled in the art, and the methods are not limited to the particular arrangement of steps disclosed herein.  
         [0018]     It has long been determined that certain automatic transmissions, e.g. those found in delivery vehicles, are highly stressed due to rapid starting and stopping. This stress is exacerbated by the constant use of first and second gear. This type of use creates abnormal heat and wear conditions that require an automatic transmission fluid with superior resistance to thermal breakdown and enhanced lubrication characteristics. This invention was developed to address these deficiencies in normal automatic transmission fluids in addition to maintaining and or improving friction modification (i.e. shift quality), low temperature performance, seal compatibility, anti-wear, antifoam and overall fluid solubility. The composition of this invention addresses all of these performance shortcomings typical of automotive transmission fluids by coupling a unique composition of the following:  
                                                   A specific TMP C8/C10 polyol ester           Unique amide containing friction modifier           VI improver           Corrosion Inhibitor           Anti-oxidant           Corrosion inhibitor           Dispersants           Lubricating oil flow improver           Anti foam agents           Anti wear additive                      
 
       EXAMPLE 1  
       [0019]     One embodiment of the present invention comprises the a unique automatic transmission fluid for highly stressed automatic transmissions. Such an automatic transmission fluid could have the following components:  
                                                       V.I improver    1.0—4.0%           corrosion inhibitor   0.01—1.5%           oxidation inhibitor   0.01—1.5%           dispersants   0.01—5.0%           lubricating oil flow improver   0.01—1.5%           detergents and rust inhibitors   0.01—3.0%           anti-wear agent   0.001—0.01%           anti-foaming agent   0.001—0.01%           seal swellant    0.1—4.0%           friction modifiers   0.01—1.5%           lubricating oil    0.1—17.0%           neopolyol ester   balance                      
 
         [0020]     One of skill in the art will recognize that the above components can be replaced by substitute or equivalent components. For example, other synthetic oils that could be used include, but are not limited to, diesters, complex esters or a poly alcohol olefin. One of skill in the are would further recognize that changes in the ratios of components could affect solubility of the fluid, the frictional reducing characteristics of the fluid, foaming characteristics, flow characteristics especially at low temperatures, rusting, wearing characteristics, heat transfer characteristics and the propensity of the fluid to thermally degrade.  
       EXAMPLE 2  
       [0021]     The automatic transmission fluid of the present invention was tested through dynamometer tests of two automatic transmissions. The two transmission tests are identified as ATC #3, using an automatic transmission fluid in accordance with the present invention, and JASPER #4 using Dexron III ATF a high quality commercial automatic transmission fluid specified under the General Motors Dexron trademark and registration number. Evaluation of the automatic transmission test data clearly indicate the improved performance and durability of the transmission fluid of the instant invention.  
         [0022]     The dynamometer automatic transmission tests were designed to test the two competitive transmissions in a repetitive cycle reflecting the use to which the transmissions would be put in a special stop and go service. This service involves frequent shifting between first and second gears at relatively high engine speed and torque. A typical line pressure/temperature cycle taken from data obtained early in the test of the ATC #3 transmission/ATF is shown in  FIG. 1 .  
         [0023]     One cycle involves two relatively rapid sets of gearshifts from first to second gears with a brief pause between the first and second set of shifts. The temperature shown was taken from the fluid flowing out of the transmission to the cooler and, as evident, reaches over 300° F. as a result of this cycle. This is considered a rigorous test of both the automatic transmission and its fluid.  
         [0024]     One of the important properties of an automatic transmission fluid is viscosity and its maintenance during the operation of the transmission. Frequently, Viscosity Index Improvers (VI Improvers), very large, oil-soluble polymers, are blended into the base stock in small amounts to give better viscosity-temperature characteristics to the automatic transmission fluid. Unfortunately, these macromolecules are subject to temporary viscosity loss at the high shear rates encountered in the transmission and also permanent viscosity loss as a consequence of being ruptured under boundary lubrication conditions such as in gears.  FIG. 2  shows the permanent viscosity loss response of the two automatic transmission fluids used in these tests.  
         [0025]      FIG. 2  shows that the Jasper #4 automatic transmission fluid loses viscosity very rapidly at first but as the macromolecules of its VI Improver are sheared, fewer and fewer are left and the degradation slows somewhat. In the case of the ATC #3, there are fewer macromolecules necessary for the automatic transmission fluid of the present invention and the material shows much less initial shear degradation and less continuing degradation as well.  
         [0026]     The following analyses of the data generated by the dynamometer tests directly compares the performance of the two transmissions and their fluids in several important criteria:  
         [0027]     1. The consistency of the data generated by the number of cycles over the period of test.  
         [0028]     2. Control of transmission function as a consequence of transmission and/or fluid degradation, and, most important  
         [0029]     3. Wear and resultant durability of the transmission. As previously noted, the two transmission tests are identified as ATC #3, using an automatic transmission fluid in accordance with the present invention, and JASPER #4 using Dexron III ATF.  
         [0030]     The consistency of the transmission operation and the ability of the automatic transmission fluid to maintain its viscosity and friction modifying properties are critical to the smoothness of operation and the life of the transmission.  FIG. 3  shows the consistency of maintaining line pressure during operation over the test period for the ATC #3 dynamometer test. Over nearly 1000 cycles the pressure curves are virtually indistinguishable.  FIG. 3  shows the same data for the second transmission, Jasper #4. In this case, the data are markedly inconsistent indicating erratic control of the servomechanisms and coupling of the clutch plates.  
         [0031]     Other data gathered concerning transmission temperatures and speed shown similar differences.  
         [0032]     Samples of the automatic transmission fluids were taken periodically during the dynamometer tests and a number of these samples were analyzed for physical and chemical properties. One of these analyses was of the wear levels shown in the tests.  
         [0033]      FIG. 4  shows the lead wear rate during the tests. The two tests show considerably different levels of lead wear. Lead concentration in the Jasper #4 test at about 500 cycles was almost 400% greater than shown in the ATC #3 test at the same number of cycles.  
         [0034]     This comparatively high wear rate is considered a major factor in the failure of the Jasper #4 transmission at about 500 cycles. In contrast, the ATC #3 test was still functioning consistently as shown in  FIG. 3  until the test was terminated at about 1500 cycles.  
         [0035]     Overall, the combination of highly consistent performance in shift cycles and greater wear resistance of the transmission and the degradation resistance of the automatic transmission fluid of the present invention were considered to be the difference between the two sets of tests.  
         [0036]     The test data and indicate that the transmission and fluid used in the Jasper #4 test is inferior to the transmission and fluid used in the ATC #3 test. While the causes of this difference may be complex, the conclusion is clear.  
         [0037]     While the invention has been described with reference to certain exemplary embodiments thereof, those skilled in the art may make various modifications to the described embodiments of the invention without departing from the scope of the invention. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. In particular, although the present invention has been described by way of examples, a variety of compositions and methods would practice the inventive concepts described herein. Although the invention has been described and disclosed in various terms and certain embodiments, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved, especially as they fall within the breadth and scope of the claims here appended. Those skilled in the art will recognize that these and other variations are possible within the scope of the invention as defined in the following claims and their equivalents.