Brakes – Elements – Shoes
Reexamination Certificate
1999-10-25
2001-12-11
Oberleitner, Robert J. (Department: 3613)
Brakes
Elements
Shoes
Reexamination Certificate
active
06328143
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to vehicle type braking equipment and, more particularly, this invention relates to a composition type brake shoe member for use in a railway type vehicle brake system and, even still more specifically, the invention relates to the development of a new type brake shoe and brake shoe friction material that accomplishes both the required braking levels and applies a substantially solid type friction modifier film on the wheel and transfers a portion of that film to the rail creating a substantially optimum friction level between the wheel and rail.
BACKGROUND OF THE INVENTION
Many railroad locomotives and cars use wheel tread braking which provides the braking efforts required by forcing a brake shoe formed with a composition friction material against the tread of the steel wheel. Brake shoe engagement with the wheel tread produces friction that dissipates energy of momentum in the form of heat. In order for such braking to be effective, however, wheel rotation is required. The adhesion due to the friction between the wheel tread and rail tends to maintain such wheel rotation as the brake shoe engages the wheel tread during a braking operation.
Excessive wheel wear and brake shoe change outs have been found to be cyclically high during the winter season. One theory attributes this, at least in part, to the more pronounced cleaning effect that the brake shoe has on the wheel as the result of higher moisture contact during wintertime. In that such cleaning action tends to increase the contact friction; or adhesion between the wheel and rail, increased contact stresses are created in the wheel. Such contact stresses being especially high during the guiding and steering action of the wheel set, particularly, when encountering track curvature.
The combination of braking effort through friction between the brake shoe and wheel tread surface and the adhesion between the wheel and rail translates into thermal and contact stresses of the wheel, which often result in wheel damage. High thermal and contact stresses are known to initiate microcracks in the wheel tread, eventually leading to a defect condition known as shelling.
Another common result of high friction levels between the wheel and the top of the rail is that the wheel tends to rub harder against the rail in the flange area of the wheel and the gage face area of the rail. This has typically been measured as the angle of attack of the wheel to rail and as the lateral force of the wheel against the rail, or as the ratio of the lateral force to the vertical force of the wheel to the rail (L/V ratio). The angle of attack and lateral forces or L/V ratio are prevalent at all times and tend to be higher in cornering cases.
Lowering the top of rail adhesion levels reduces the angle of attack and lateral forces. The effect of reducing these adhesion levels has the benefit of reducing train drag thereby increasing fuel/energy efficiency and reducing wheel tread and flange wear thereby increasing wheel life and reducing gage face rail wear thereby increasing rail life.
Another related problem encountered by some railroads is wheel sliding, which results in wheel tread flat spots. Such flat spots have a deleterious effect on equipment, lading, and passenger comfort due to the high vibration and noise produced by these flat spots. Flat spots due to wheel sliding also lead to wheel defects known as spalling. Repairing such a damaged wheel requires removal of the wheel and subsequent machining of the wheel tread to remove the flat spot or spall defect area.
It has been known to provide a friction modifier material directly to the railway vehicle wheel tread or flange to affect the coefficient of friction therebetween. Examples of such prior art devices can be found in U.S. Pat. Nos. 5,308,516 and 5,173,204, both of which are incorporated by reference herein. Generally, these provide a lubricant composition which can be formed into a solid product, which can be applied directly to the wheel tread or flange, such as by an attachment mechanism which positions the lubricant product immediately adjacent the railway vehicle wheel for periodic applications to the tread and/or flange.
It would be quite advantageous to the railroad industry if a single unit, a brake shoe, in particular, would not only provide the necessary friction between the brake shoe and wheel for satisfactory braking but also provide desirable friction modifiers to optimize the wheel/rail friction interface at the same time.
SUMMARY OF THE INVENTION
The present invention provides a friction management brake shoe adapted to engage the tread of a wheel of a railway vehicle via which the railway vehicle is guidably supported on a railed track. The friction management brake shoe comprises a brake lining affixed to a baking plate, such brake lining has a braking surface engageable with the wheel tread of a wheel of a railway vehicle. The brake lining includes a first friction composition material formed with at least one of a solid high positive friction modifier and a solid very high positive friction modifier which establish an optimum positive friction level between the wheel tread and the railed track.
OBJECTS OF THE INVENTION
It is, therefore, one of the primary objects of the present invention to formulate a compound which provides satisfactory braking while simultaneously transferring a friction modifying material to the wheel.
It is still another object of the present invention to provide a brake shoe which will extend the useful service life of a railroad wheel.
Yet another object of the present invention is to provide a brake shoe which will apply a solid friction modifier film to the wheel and rail.
An additional object of the present invention is to provide a brake shoe which will reduce energy consumption.
Another object of the present invention is to provide a brake shoe which will reduce rail wear.
Still another object of the present invention is to provide a brake shoe which will reduce noise created at the rail/wheel interface by reducing stick slip oscillation.
In addition to the various objects and advantages of the present invention which have been described in some specific detail above, various additional objects and advantages of the present invention will become much more readily apparent to those persons who are particularly skilled in the relevant brake shoe friction art from the following more detailed description of such invention, particularly, when such detailed description is taken in conjuction with the attached drawing Figures and with the appended claims.
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Chiddick Kelvin
Formolo Joseph F.
Shute Bruce W.
Buchanan Ingersoll P.C.
Nguyen Xuan Lan
Oberleitner Robert J.
Westinghouse Air Brake Technologies Corporation
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