Brakes – Operators – Spring
Reexamination Certificate
1999-09-13
2001-07-03
Schwartz, Christopher P. (Department: 3613)
Brakes
Operators
Spring
Reexamination Certificate
active
06253886
ABSTRACT:
The present invention relates to a combined spring and service brake cylinder the service brake cylinder piston rod of which is adapted to be linked to a brake rigging via a slack adjuster housed at least in part in said piston rod, the free end, remote from said service brake piston, of which is adapted to be operated on by the spring brake piston rod which is linked to said spring brake piston by a linkage having a reversible thread which is locked in rotation and possibly adapted to be unlocked.
FR-A-2,492,330 discloses a pressurised fluid and spring brake cylinder comprising a service brake piston operated by fluid pressure and a spring brake piston which is kept in the released position by a release fluid pressure and which is able to transmit all or part of the spring reaction force to the service brake piston rod, downstream of a slack adjuster.
Such combined brake cylinders which operate as an adjustable fluid service brake and a non-adjustable parking or immobilizing brake, using one or more springs, has the advantage of allowing the spring brake to utilise the service brake rigging slack adjuster and the spring brake to be manually set to a released position (if it was previously in its braking position) or to an inactive position, by using a handle to act on activation locking means. In another embodiment (FR-A-2,366,967) this locking means makes it possible to automatically maintain the spring brake in an inactive position (which removes the risk of superimposing the service and spring brakes one over the other which in general leads to wheel lock and skidding) and to only activate it when proceeding to a release of the spring brake, intended to return the spring brake to its position where it is ready to operate, which for example is achieved by using the service brake braking pressure, this in order to avoid an unintentional initiation of a spring brake application without the driver being aware of it, notably in railroad braking.
One disadvantage of such combined brake cylinders clearly resides in their mechanical complexity and, consequently, in their cost. These two negative consequences are further aggravated by the fact that, for a given service brake bore diameter, springs having differing reaction forces are necessarily, as a function of the parking or immobilizing braking forces required, depending on whether the parking brake is for example applied to one or several brake discs on an axle and on whether, for an immobilizing brake, wheel-to-rail adhesion at a standstill that is higher than the maximum adhesion employed for braking is accepted practise or not.
The spring system of spring brake cylinders is in general constituted, for reasons of compactness and cost, by one single helical spring having several turns which are designed to come almost into touching contact when the spring brake is fully released. As a result of this single spring embodiment, when it is desired to modify the elastic reaction forces significantly, it is generally required, not only to modify the spring packing washers, but also to modify the diameter of the cylindrical wire of the helical springs, which considerably increases the cost of obtaining a different embodiment of spring brake cylinders.
Moreover, in the case mentioned above where the braking pressure and/or a pressure which is a function of the braking pressure (for example, the general brake operating pressure via a pressure reduction system) is used for ensuring release of the spring brake, preventing the forces of the service brake and immobilizing brake from being superimposed, the pneumatic brake releasing cross-section must frequently be increased compared to the cross-section of the service brake, which complicates the provision of a combined brake cylinder of the “spring+service” type.
There is thus a need to diversify and increase power of the spring and spring brake piston portion of a spring brake of this type, employed notably for railroad braking using compressed air which are usually produced in relatively small manufacturing runs and frequently in numbers of less than a hundred.
To achieve this, according to the invention, the brake cylinder comprises:
a service brake cylinder,
a service brake piston mounted in the service brake cylinder and integral with a service brake piston rod,
a spring brake cylinder mounted coaxially on the service brake cylinder,
a spring brake annular piston mounted in the said spring brake cylinder and on said service brake piston rod, for transmitting a spring brake braking force to the latter,
a plurality of springs arranged around said service brake piston, between said spring brake piston and an abutment surface integral with the assembly formed from said service brake cylinder and said spring brake cylinder assembled coaxially.
A slack adjustment member is fitted between said service brake piston rod and a brake rigging head. The spring brake piston is axially linked to said service brake piston rod via a linkage having a reversible thread able to be locked or unlocked in rotation. The abutment surface for springs is provided on an annular base interposed by means of its periphery, and keyed to prevent rotation, between the said service brake cylinder and said spring brake cylinder.
According to another embodiment, the springs are helical springs which bear axially, each one of said springs of said plurality is arranged at at least one end in a cavity of a generally cylindrical shape, for example formed in the said spring brake piston or around a central abutment.
The cavities formed in the spring brake piston are concentrically distributed with respect to the spring brake piston axis, and equally distributed on a circle of the periphery of the said spring brake piston. At least a part of the plurality of helical springs is constituted by a main helical spring inside the internal cylindrical space of which a supplementary helical spring is housed.
The spring brake piston contains a number N of cavities, and a number P of springs, with P≦N, are then mounted, each one in a cavity of the spring brake piston between the base of the said cavity and said abutment surface, in an arrangement such that the resultant of the axial forces in the springs is substantially directed along the axis of the service brake piston rod.
For a given diameter of the spring brake and service brake piston, the combined cylinder can thus be constituted by a modular axial assembly of:
a service brake cylinder with its piston and piston rod fitted with the slack adjuster;
an annular abutment base, at one side, springs for of the spring brake cylinder and, at the other side, a service brake piston recall spring, the service brake piston rod passing through this annular base;
a spring brake cylinder, through the base of which the service brake piston rod passes surrounded by the spring brake piston rod, this spring brake cylinder comprising, in a bore, a standard spring brake piston which is annularly sealed as regards the spring brake release fluid acting on one side of said spring brake piston, and which is provided at the other side thereof, in the annular space available between the two annular sealing zones, with an even number of cavities, of generally cylindrical shape, for receiving at least one end portion of a helical spring or concentric helical springs, these cavities having substantially the same shape and same size, being evenly and concentrically distributed with respect to the axis of the spring brake piston;
an even number of main helical springs, of an outside diameter slightly less than the diameter of the cylindrically-shaped cavities, this even number being equal to or less than the number of cavities, each one of said helical springs being interposed, by means of its generally annular flat ends, between the base of one of said cavities, and a corresponding abutment location provided on said annular base and delimited by at least one lateral abutment;
at least one keying means for to prevent rotation, between said spring brake piston and annular base, such as a pin that sim
Beauvois Damien
Brugait Jean-Louis
Goncalves Claudino
Bartz C. T.
SAB WABCO S.A.
Schwartz Christopher P.
Townsend and Townsend / and Crew LLP
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