Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic compound containing boron
Reexamination Certificate
2002-03-15
2003-12-09
Howard, Jaqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic compound containing boron
C508S196000, C508S294000, C508S433000, C508S438000, C508S441000, C508S442000
Reexamination Certificate
active
06660695
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a composition and a method of improving the properties of power transmitting fluids, particularly to obtaining power transmission fluids of improved anti-shudder durability.
Transmissions used in passenger cars and heavy duty vehicles continue to become more sophisticated in design as vehicle technology advances. These design changes result from the need to improve vehicle operability, reliability, and fuel economy. Vehicle manufacturers worldwide are increasing vehicle warrantee periods and service intervals on their vehicles. This means that the transmission and the transmission fluid must be designed to operate reliably without maintenance for longer periods of time. In the case of the fluid, this means longer drain intervals. To improve vehicle operability, especially at low temperature, manufacturers have imposed strict requirements for fluid viscosity at −40° C. To cope with longer drain intervals and more severe operating conditions, manufacturers have increased the requirements for fluid oxidation resistance, required less change in viscosity with vehicle mileage (improved shear stability) and increased the amount of wear protection that the fluid must provide for the transmission. To improve the fuel economy of the vehicle and reduce energy loss, manufacturers employ continuously slipping clutches either as wet starting clutches or as a torque converter clutch. These devices require very precise control of fluid frictional properties.
One method of improving overall vehicle fuel economy used by transmission designers is to build into the torque converter a clutch mechanism capable of “locking” the torque converter. “Locking” refers to eliminating relative motion between the driving and driven members of the torque converter so that no energy is lost in the fluid coupling. These “locking” or “lock-up” clutches are very effective at capturing lost energy at high road speeds; however, when they are used at low speeds vehicle operation is rough and engine vibration is transmitted through the drive train. Rough operation and engine vibration are not acceptable to drivers.
The higher the percentage of time that the vehicle can be operated with the torque converter clutch engaged, the more fuel efficient the vehicle becomes. A second generation of torque converter clutches have been developed which operate in a “slipping” or “continuously sliding mode”. These devices have a number of names, but are commonly referred to as continuously slipping torque converter clutches. The difference between these devices and lock-up clutches is that they allow some relative motion between the driving and driven members of the torque converter, normally at relative speeds of 10 to 100 rpm. This slow rate of slipping allows for improved vehicle performance as the slipping clutch acts as a vibration damper. Whereas the “lock-up” type clutch could only be used at road speeds above approximately 50 mph, the “slipping” type clutches can be used at speeds as low as 25 mph, thereby capturing significantly more lost energy. It is this feature that makes these devices very attractive to vehicle manufacturers.
A second method of reducing energy loss in the engine—transmission coupling is to use a wet starting clutch. These wet starting clutches resemble shifting clutches but are made to handle the entire energy of the vehicle. Therefore they tend to be physically larger than shifting clutches. However, just as with the torque converter clutch they are continuously slipped to improve overall vehicle driveability and ride feel.
It is well known that improving friction durability of power transmission fluids can be accomplished by the selection of the appropriate types of friction modifiers. However, we have found that the combination of friction modifier and anti-wear agent is the most critical factor in improving friction durability. Selection of the correct anti-wear agent is as important as the selection of the correct friction modifier system.
Due to the efficacy of continuously slipping clutches they are fitted to all types of transmissions. Continuously slipping torque converter clutches and wet starting clutches are routinely used with conventional automatic transmissions, continuously variable transmissions (CVTs), and manual transmissions. Continuously slipping clutches impose very exacting friction requirements on power transmission fluids used with them. The fluid must have a very good friction versus velocity relationship, i.e., friction must always increase with increasing speed. If friction decreases with increasing speed, a self-exciting vibrational state can be set up in the driveline. This phenomenon is commonly called “stick-slip” or “dynamic frictional vibration” and manifests itself as “shudder” or low speed vibration in the vehicle. Clutch shudder is very objectionable to the driver. A fluid which allows the vehicle to operate without vibration or shudder is said to have good “anti-shudder” characteristics. Not only must the fluid have an excellent friction versus velocity relationship when it is new, but the fluid must retain those frictional characteristics over the lifetime of the fluid, which can be the lifetime of the transmission. The longevity of the anti-shudder performance in the vehicle is commonly referred to as “anti-shudder durability”. It is this aspect of fluid frictional performance that this invention addresses.
Control of fluid viscosity is also critical to transmissions with hydraulic operating systems, such as conventional automatic transmissions, continuously variable transmissions and automated manual transmissions. Changes in fluid viscosity caused by shearing or oxidation of polymeric thickeners is detrimental to good transmission operation. Therefore when polymeric viscosity modifiers are used, they should be shear stable materials.
We have now found that a combination of anti-wear agents and calcium detergents when used with known friction modifiers produce fluids of significantly improved anti-shudder durability. These fluids are particularly suited for use as CVT fluids since they do not adversely effect the steel-on-steel coefficient of friction developed by the fluid in CVT variators.
SUMMARY OF THE INVENTION
The present invention is a power transmission fluid comprising:
(1) a major amount of a lubricating oil; and
(2) an effective amount of a performance enhancing anti-shudder additive combination comprising:
(a) an organic phosphate having the structure: R
1
—X
2
—P(:X
1
)(R
2
X
3
)—X—R
5
where R
1
, and R
2
may independently be substituted or unsubstituted alkyl, aryl, alkylaryl or cycloalkyl having 1 to 24 carbon atoms and X, X
1
, X
2
and X
3
may independently be sulfur or oxygen. R
1
, and R
2
may also contain substituent hetero atoms, in addition to carbon and hydrogen, such as chlorine, sulfur, oxygen or nitrogen; wherein R
5
is derived from a reactive olefin and can be either −CH
2
—CHR—C(:O)O—R
6
; —CH
2
—CR
7
HR
8
; or R
9
—OC(:O)CH
2
—CH—C(:O)O—R
10
where R is H or the same as R
1
R
6
, R
7
, R
9
and R
10
are the same as R
1
and R
8
is a phenyl or alkyl or alkenyl substituted phenyl moiety, the moiety having from 6 to 30 carbon atoms;
(b) a calcium detergent; and
(c) a friction modifier.
Further embodiments of this invention are a continuously variable transmission or an automatic transmission apparatus containing the fluids of this invention, a method for lubricating such apparatus using the fluids of this invention and the novel additive combination of (a), (b) and (c) above.
DETAILED DESCRIPTION OF THE INVENTION
Lubricating a continuously variable transmission equipped with a steel push belt or chain drive variator and a slipping clutch system is not a simple matter. It presents a unique problem of providing high steel-on-steel friction for the variator and excellent paper-on-steel friction for the slipping clutch. Added to these requirements is the need for the fluid to provide a positive d&mgr;/dV over a wide range of operating temperatures. Therefore, the
Richard Katherine M.
Watts Raymond F.
Howard Jaqueline V.
Infineum International Ltd.
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