Spring guide rail with several centering fingers

The spring guide rail has several centering fingers and a bottom rail and is made out of a one-piece sheet metal strip into which substantially rectangular recesses are punched so that a ladder-type structure is formed with a pair of longitudinal bars being interconnected by cross bars. By repeated bending operations around given longitudinal axes the two parts of the bottom rail are formed by the longitudinal bars and the centering fingers are formed by the cross bars. Between the sections of the cross bars folded to face each other there is a space and in the bottom rail area projections are arranged which ensure the spacing between the opposite parts of the bottom rail. Thus, a simple and stable spring guide rail with a safe guidance is provided for the vane lifting springs.

BACKGROUND OF THE INVENTION 
The present invention relates to a spring guide rail with several centering 
fingers and a bottom rail for the guidance of the vane lifting springs and 
for the stroke limitation of the vanes of a rotary vane-type machine. The 
spring guide rail is shaped from a one-piece sheet metal strip, into which 
strip recesses of an essentially rectangular shape are punched so as to 
form a ladder-type structure with two longitudinal bars and with cross 
bars. From this ladder-type structure the spring guide rail is formed by 
means of repeated folding operations around longitudinal axes of the 
ladder-type structure, with the longitudinal bars of the ladder-type 
structure forming the two parts of the bottom rail and the cross bars 
forming the centering fingers. 
In rotary vane-type machines, radially outwardly directed guide grooves are 
provided in a rotor and working vanes are arranged in these grooves. 
Compression springs supporting themselves at the bottom of the groove 
press the working vanes radially outwardly against a cam curve surrounding 
the rotor. The compression springs are arranged on the centering fingers 
of a spring guide rail so that the centering fingers penetrate the 
interior of the compression springs. The spring guide rail supports itself 
at the bottom of the groove by means of a bottom rail. The spring guide 
rail further limits the inward movement of the working vane by means of a 
mechanical stop. 
A spring guide rail of the type referred to above is known from the German 
Patent DE-OS 1,653,923. In the spring guide rail disclosed therein the 
cross bar sections folded to face each other to form the centering fingers 
rest against each other. It is a disadvantage that the centering fingers 
have a rectangular transverse cross-section since an insufficient guide 
for the compression springs is provided thereby due to the circularity of 
the interior space of the compression springs. The centering fingers, and 
thus the spring guides further may easily be deformed upon the abutting 
action of the vane which will lead to operational disturbances up to total 
failure of the machine. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a simple and stable 
spring guide rail which will ensure a reliable guidance of the compression 
springs. 
A feature of the present invention is the provision of a method of 
manufacturing a spring guide rail including a bottom rail and a plurality 
of centering fingers for guidance of vane lifting springs and for limiting 
this stroke of vanes of a rotary vane-type machine comprising the steps of 
providing a one-piece rectangular sheet metal strip; punching a plurality 
of essentially rectangular-shaped recesses in the strip to form a 
ladder-type structure having two spaced longitudinal bars and a plurality 
of parallel cross bars interconnecting the two longitudinal bars; folding 
the ladder-type structure about a first longitudinal axis equally spaced 
from and between the two longitudinal bars to provide each of the 
plurality of centering fingers by sections of each of the plurality of 
cross bars facing each other with a space therebetween; folding a first of 
the two longitudinal bars about a second longitudinal axis disposed at the 
junction of one end of the plurality of cross bars and the one of the two 
longitudinal bars to extend outward from the one end of the plurality of 
cross bars to provide a first part of the bottom rail; folding a second of 
the two longitudinal bars about a third longitudinal axis disposed at the 
junction of the other end of the plurality of cross bars and the other of 
the two longitudinal bars to extend outward from the other end of the 
plurality of cross bars to provide a second part of the bottom rail; and 
forming a plurality of projections on at least one of the two longitudinal 
bars to maintain the space between the sections of each of the plurality 
of cross bars forming each of the plurality of centering fingers. An even 
and stable guidance of the vane lifting springs will be achieved due to 
the space between the opposingly folded sections of the cross bars forming 
the centering fingers. The projections arranged at the bottom rail ensure 
that the space will be maintained even during operation. 
A further feature of the invention provides that the projections project 
into the interior space of the punched recesses of the punched component. 
After the folding or rather the bending operation the projections will 
rest at the respective opposite part of the bottom rail. 
It will be expedient to arrange the projections on only one part of the 
total length of the shorter rectangular side of the recess. 
It will be favorable in terms of manufacture to arrange the projections on 
only one of the shorter rectangular sides of the recess. This does also 
apply to the arrangement of the projections on one of the two longitudinal 
bars and on each of the shorter rectangular sides of the recess. 
If the cross-section of the cross bars is enlarged where they pass over 
into the longitudinal bars, the finished bent spring guide rail will have 
a greater flexural strength and thus a greater resistance to deformation 
in the area where the centering fingers pass over into the bottom rail. 
In the middle, the cross-section of the cross bars is expediently 
diminished by means of neckings so that the assembly part will have a 
transition region of smaller cross-section at the upper end of the 
centering fingers. 
A particularly advantageous embodiment provides that the areas of the 
opposingly folded sections of the cross bars, along which the vane lifting 
springs are guided, are rounded off. This will improve the guidance. Sharp 
edges causing damages to the vane lifting springs do not exist any longer. 
It will be advantageous in terms of manufacture to produce the rounded-off 
areas by plastic deformation before the folding operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The spring guide rail has several centering fingers 1. At their lower ends, 
as seen in FIGS. 1 and 2, there are two parts 2 and 3 of a bottom rail 4 
which is common to all the centering fingers 1. At their upper ends the 
centering fingers have a transition region 5 of smaller cross-section and 
at their lower ends, near the transition into the bottom rail 4, they have 
a transition region 6 of larger cross-section. The centering fingers 1 are 
formed by sheet metal strip sections 7 and 8 folded to face each other and 
spaced with respect to each other. This results in an essentially square 
transverse cross-section of the centering fingers 1. The longitudinally 
extending edges 9 through 12 of the centering fingers 1 are rounded off 
for the purpose of improved guidance and durability of the vane lifting 
springs. The parts 2 and 3 of the bottom rail 4 are partially rounded off 
at their lower ends. 
FIG. 3 represents the developed view of the spring guide rail. Punched into 
a sheet metal strip are essentially rectangular recesses 20, thus 
resulting in a ladder-type structure with two longitudinal bars 21 and 22 
and several cross bars 23 interconnecting bars 21 and 22. In the middle of 
the cross bars there are neckings 24 and 25 which in the finished bent 
part form the transition region 5 of smaller cross-section at the upper 
end of the centering fingers 1. 
The cross-section of the cross bars 23 is enlarged where they pass over 
into the longitudinal bars 21 and 22 so that this transition region 6 of 
the assembly has an increased resistance to deformation. 
The mutual spacing of the cross bar sections 7 and 8 folded to face each 
other will be ensured by projections 30 (FIG. 2) in the area of the bottom 
rail 4. As shown in FIG. 3, projections 30 project into the punched recess 
20. Th projections 30 are each arranged on only one of the short sides of 
the punched rectangular recesses 20. 
The sheet metal part whose developed view is represented in FIG. 3 is bent 
along the dash-dotted line 40 by 180.degree., thus the sections 7 and 8 of 
each cross bar 23 lie opposite each other in a spaced relationship. Along 
the dash-dotted line 42, 43 a bending by 90.degree. is effected so that 
the parts 2 and 3 of the bottom rail 4 point outwards and the respective 
projection 30 bridges and maintains the space between the sections 7 and 8 
folded to face each other. 
While we have described above the principles of our invention in connection 
with specific apparatus, it is to be clearly understood that this 
description is made only by way of example and not as a limitation to the 
scope of our invention as set forth in the objects thereof and in the 
accompanying claims.