WO2001021464A1

WO2001021464A1 - Offset drawhook system

Info

Publication number: WO2001021464A1
Application number: PCT/US2000/025758
Authority: WO
Inventors: Karl E. Serbousek
Original assignee: Thrall Car Manufacturing Company
Priority date: 1999-09-20
Filing date: 2000-09-20
Publication date: 2001-03-29
Also published as: AU3887101A

Abstract

An offset drawhook system that eliminates one or more of the pins that have been commonly employed in the past to link the components of offset drawhook systems. In the preferred system, draft loads (19) on the drawhook linkages (12) are transmitted to a shock absorbing plunger (16) and to a pivot bar by a lever (14), without pinned connections therebetween. The pivot bar acts as a fulcrum (18A) between the drawhook linkage and the plunger. The lever preferably engages in rolling contact with the drawhook linkage, plunger and pivot bar as the drawhook linkage moves between a retracted position and an extended position. The angular displacement of the lever changes the pivot point at which the lever pivots about the pivot bar, and also changes the point at which the lever arm engages the other components. The rolling contact reduces wear on the surfaces of the respective components, and also enables a mechanical advantage to be provided to the plunger (16) as draft loads on the drawhook linkage (12) increase.

Description

OFFSET DRAWHOOK SYSTEM

BACKGROUND OF THE INVENTION

The invention relates generally to railcars or wagons, and more particularly to an offset drawhook pivot.

Drawhook and buffer heights are standardized on the UK rail system. Normally, the draw gear is in line with the drawhook. If there is a need to have a wagon deck height below the drawhook level, an offset drawhook system can be used. The offset drawhook transfers the longitudinal drawhook load to the draw gear. In the past, the drawhook loads typically have been transmitted to a plunger by a lever which is pinned to the drawhook linkage and to the plunger. Figs. 1, 2 and 3 show a known offset drawhook system of this type.

SUMMARY OF THE INVENTION

The invention provides an offset drawhook system that eliminates one or more of the pins that have been employed in the past to link the components of offset drawhook systems. In the preferred system, draft loads on the drawhook linkage are transmitted to a shock-absorbing plunger and to a pivot bar by a lever, without pinned connections therebetween. The pivot bar acts as a fulcrum between the drawhook linkage and plunger. The lever preferably engages in rolling contact with the drawhook linkage, plunger, and pivot bar as the drawhook linkage moves between a retracted position and an extended position. The angular displacement of the lever changes the pivot point at which the lever pivots about the pivot bar, and also changes the point at which the lever arm engages the other components. The rolling contact reduces wear on the surfaces of the respective components, and also enables a mechanical advantage to be provided to the plunger as draft loads on the drawhook linkage increase, thereby reducing maximum loads on the plunger and other components of the assembly. To this end, the effective length of the lever arm between the drawhook linkage and the pivot bar decreases, and the effective length of the lever arm between the plunger and the pivot bar increases, as the drawhook is pulled toward its extended position. Thus, the shifting of the pivot point permits management of stresses developed in the lever arm and the plunger.

In the preferred embodiment, a top portion of the lever is engaged by the drawhook linkage, and a bottom portion of the lever is engaged by the plunger, with an intermediate portion of the lever engaged by the pivot bar. Each of the drawhook linkage, pivot bar and plunger preferably has a convex, arcuate surface engaging the lever to provide the rolling contact. To maintain the lever in position so that it does not drop through the assembly due to gravity, a retainer is preferably provided at the top of the lever to engage the top surface of the drawhook linkage and constrain the lever against downward displacement.

The invention thus provides an improved drawhook system in which the cost of one or more link pins may be eliminated, and wear may be reduced. The invention may further permit management of stresses developed in the lever and the plunger.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a plan view of an offset drawhook arrangement that is believed to be in the prior art. Fig. 2 is a side elevational view thereof.

Fig. 3 is an enlarged side elevational view thereof .

Fig. 4 is a schematic side elevational view of a drawhook arrangement in accordance with an embodiment of the invention.

Fig. 5 is a schematic perspective view thereof.

Fig. 6 is a schematic perspective view of the plunger thereof .

Fig. 7 is a schematic perspective view of the drawhook linkage thereof.

Fig. 8 is a schematic perspective view of the lever thereof .

Fig. 9 is a schematic perspective view of the lever and pivot bar thereof.

Fig. 10 is a schematic view similar to Fig. 4, with certain dimensions and geometric relationships indicated thereon.

Fig. 11 comprises tables of data illustrating the relationships between displacement and force on the plunger and drawhook in particular embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The invention is generally embodied in an offset drawhook system 10, shown in Figs. 4 through 10, comprising a drawhook linkage 12, a lever 14 extending from the drawhook linkage 12 to a plunger 16, and a pivot bar 18, preferably fixed, that acts as a rolling fulcrum for changing or shifting portions of the lever 14.

In the past, drawhook systems have typically employed pinned connections joining a drawhook, lever, and plunger. In the standard offset drawhook arrangement shown in Figs. 1 through 3, the drawhook is pivotally connected to a lever by a first pin, and the lever pivots about a second pin which is fixed relative to the frame of the wagon. A third pin pivotally connects the lever to a plunger. Each of the pinned connections represents a potential wear point in the system.

Referring to Figs. 4-10, the preferred embodiment of the invention eliminates the pinned connections. In the preferred system, draft loads on the drawhook linkage

(indicated by arrow 19 in Fig. 4) are transmitted to the plunger 16 and pivot bar 18 by the lever 14 by rolling contacts and without pinned connections therebetween. The pivot bar 18 acts as a fulcrum between the drawhook linkage

12 and the plunger 16.

The ends of the drawhook linkage, plunger and pivot bar in contact with lever 14 are preferably rounded, so that in operation, the lever 14 engages each of the drawhook linkage 12, pivot bar 18 and plunger 16 with a rolling contact as the drawhook linkage moves between a retracted position and an extended position. The rolling contact reduces wear on the surfaces of the respective components.

The preferred system is configured to provide a variable relationship between the force F_dh applied to the drawhook and the resultant force F_plng applied to the plunger. More specifically, the ratio F_dh/F_plng increases as F_dh increases. Thus, the system enables a mechanical advantage to be provided to the plunger as draft loads on the drawhook linkage increase, thereby reducing maximum loads on the plunger and other components of the assembly. To this end, the effective length of the lever arm between the drawhook linkage and the pivot bar decreases, and the effective length of the lever arm between the plunger and the pivot bar increases, as the drawhook is pulled toward its extended position. Due to the rolling contact discussed above, the variable relationship and change of mechanical advantage is continuous and smooth, and remains so throughout life of the system.

Referring to Fig. 4, the drawhook linkage 12 is displaced toward the right (see arrow 19) , and the plunger 16 displaced toward the left, with respect to the frame of the wagon, as the drawhook linkage 12 is displaced toward its extended position by draft loads. As mentioned, the pivot bar 18 is preferably fixed relative to the frame of the wagon. Plunger 16 is engaged by a compression spring 50 which reacts to resist loads applied to the plunger by the lever 14. In addition to the compression spring, a damping mechanism may be incorporated with the spring 50 to damp oscillations of the system.

In the preferred embodiment, a top portion of the lever is engaged by a surface 12a located in an opening 13 in the drawhook linkage, and a bottom portion of the lever is engaged by a surface 16a of the plunger, with an intermediate portion of the lever engaged by a surface 18a of the pivot bar 18. As can be seen in Fig. 4, opening 13 is formed in part by a second surface 12b. Preferably, the surface 12b is relieved or recessed at its end so as to avoid contact with lever 14, and preferably, surface 12b has a rounded convex shape. Each of the drawhook linkage, pivot bar and plunger has a convex, arcuate surface (see reference numerals 12a, 16a, 18a) engaging the external surface of the lever to provide low resistance rolling contact therewith. Preferably the lever has generally flat, opposed external surfaces 14a, 14b which cooperate to provide the rolling contact. The lever could also be curved or serpentine, if desired.

To maintain the lever in position so that it does not drop through the assembly due to gravity, a retainer 20 is preferably provided at the top of the lever to engage the top surface of the drawhook linkage. The retainer 20 may comprise a bar or pin or other elongated member having a transverse dimension greater than that of the opening 13 in the drawhook linkage 12.

The geometric relationships of the components of an offset drawhook system in accordance with a preferred embodiment of the invention are shown in Fig. 10, with dimensions indicated as follows:

RI = radius of surface on drawhook linkage that engages lever.

R2 = radius of convex surface on pivot bar 18 that engages lever 14.

XI = longitudinal dimension between the lever- engaging surface of drawhook linkage 12 and the lever- engaging surface of pivot bar 18. X2 = longitudinal dimension between lever- engaging surface of plunger 16 and lever-engaging surface of pivot bar 18.

Yl = transverse dimension between the point at which the lever 14 engages drawhook linkage 12 and point at which lever engages pivot bar 18.

Y2 = transverse dimension between points on plunger and pivot bar engaged by lever.

θ = inclination of lever arm relative to vertical.

Y1B = distance between longitudinal axis of drawhook linkage 12 and pivot bar 18.

Y2B = distance between longitudinal axis of pivot bar 18 and longitudinal axis of plunger 16.

The relationships between these parameters may be described as follows:

Depth R X2 = Y2B t nθ + — _r+ — ^l—- R cos θ COS θ

_Λ Depth R cos θ COS θ

71 = Y\B+ R_λ ύnθ + R₂ smθ

Relationships between the forces applied to and displacements of the drawhook linkage 12 and plunger 16 are set forth for two embodiments in respective charts shown in Fig. 11, wherein the displacements and forces are indicated as follows:

D_ d_dh = displacement of drawhook, in mm.

D_d_plng = displacement of plunger, in mm.

F_plng(kN) = force applied to plunger 16 by lever 14, in kN.

F_dh(kN) = force applied to drawhook linkage 12, in kN.

The linear dimensions in Fig. 11 are in millimeters .

The upper chart in Fig. 11 illustrates the relationships between displacements of the drawhook and plunger, and force on the plunger, in a static load situation, in response to the indicated force or draft load on the drawhook linkage 12. In the upper chart, the system is configured so that the angle of inclination of the lever θ is degrees in a zero load condition. A stop may be provided to constrain displacement of the drawhook linkage toward the left of Fig. 10 relative to the frame of the wagon so that θ may not exceed 30°.

The lower chart in Fig. 11 is similar to the upper chart of that Figure, but corresponds to a configuration in which the zero load position of the lever corresponds to θ = 20°.

The charts of Fig. 11 are set forth for purposes of example only, with respect to two particular embodiments. In other embodiments of the invention, the relationships between the various parameters may be different .

From the foregoing, it should be appreciated that the invention provides a novel and improved offset drawhook system in which the cost of one or more link pins may be eliminated, and in which wear may be reduced by substitution of rolling contact for at least some of the sliding contact that occurs in conventional offset drawhook systems. The invention also allows management of stresses developed in the lever, plunger and pivot bar by changing the geometric relationships between these components and the drawhook linkage when under load.

The drawings and the foregoing descriptions are not intended to represent the only forms of the invention in ^^'.rd to the details of its construction and manner of operation. Changes in form and in the proportion of parts, as well as the substitution of equivalents, are contemplated as circumstances may suggest or render expedient; and although specific terms have been employed, they are intended in a generic and descriptive sense only and not for the purposes of limitation, the scope of the invention being delineated by the following claims.

Claims

What is claimed:

1. An offset drawhook assembly comprising a drawhook linkage movable between a retracted position and an extended position, a plunger, a lever connecting the drawhook linkage to the plunger, and a pivot providing a fulcrum for the lever, characterized in that the drawhook linkage, plunger, lever and pivot are not pinned to one another.

2. The offset drawhook assembly of claim 1 wherein the drawhook linkage, plunger, lever and pivot each have respective external surfaces in contact with one another.

3. The offset drawhook assembly of claim 2 wherein th~ ^" .ternal surfaces drawhook linkage, plunger and pivot are rounded so as to be in rolling contact with said lever.

4. The offset drawhook assembly of claim 3 wherein said lever has a relatively flat surface at the point of contact with said drawhook linkage, plunger and pivot.

5. The offset drawhook assembly of claim 1 wherein a first lever arm is defined between said drawhook linkage and said pivot, and a second lever arm is defined between said plunger and said pivot, and wherein said first lever arm decreases in length and said second lever arm increases in length as said drawhook moves toward said extended position.

6. An offset drawhook assembly comprising a drawhook linkage movable between a retracted position and an extended position, a plunger, a lever connecting the drawhook linkage to the plunger, and a pivot providing a fulcrum for the lever, wherein a first lever arm is defined between said drawhook linkage and said pivot, and a second lever arm is defined between said plunger and said pivot, characterized in that said first lever arm decreases in length and said second lever arm increases in length as said drawhook moves toward said extended position.

7. The offset drawhook assembly of claim 6 characterized in that the drawhook linkage, plunger, lever and pivot are not pinned to one another.

8. An offset drawhook assembly in accordance with any of the preceding claims wherein said lever engages said drawhook Ή^¹ tge, plunger and pivot in rolling contact .