Note: Descriptions are shown in the official language in which they were submitted.
1 327054
The present invention relates to a plunger piston system
used, for example, to support and guide the pneumatic spring
bellows of an air suspension axle of a commercial vehicle or the
like, with a plunger piston that has a cylindrical plunger piston
skirt with a bottom foot region for a connection with an air
spring bearing arm and an upper plunger piston edge that adjoins
the plunger piston skirt and which becomes, radially in an inward
direction, a trough section that has a trough base that
incorporates an opening for the passage of a bolt for a force-fit
connection with a base of the air spring bellows, which forms a
trough to accommodate the convex base of the air spring bellows,
there being a supporting body in the inner space that is
surrounded by the plunger piston casing, the lower foot area of
said supporting body resting on the lower ~oot area of the
plunger piston.
More and more frequently, commercial vehicles are being
equipped with air spring systems to increase the level of comfort
provided by the springs, to take advantage of the ride height
adjustment and height control, in order to ensure optimal
distribution of axle loads by means o~ compensation lines in
multi-axle units~ and to protect the surface of the road. Axles
with air springing within multi-axle aggregates can be raised in
a simple manner by auxiliary systems in order to protect the
tires.
Pneumatic springs can transfer only vertical forces. Other
chassis elements are required in order to absorb all the other
!
.~ 5' 1 327054
forces and moments. The known air suspension systems comprise
primarily an air spring bellows that frequently incorporate a
rubber buffer as a stop, a plunger piston, and a bearing arm that
is, in its turn, mounted on or under the vehicle. The air spring
bellows are in the form o~ a rotationally symmetrical rubber sack
that can be filled with air and that is connected to the vehicle
frame by means of a steel plate that is fastened at the top as a
force transfer element. A round steel base that can support the
rubber buffer inside the air spring is clamped or vulcanized to
the bottom. The convex underside of the base is a form fit in a
correspondingly concave upper trough of the plunger piston and is
securely bolted to said piston.
In the usual steel version, the plunger piston is a
rotationally symmetrical deep-drawn or extruded part, the surface
o~ which is provided with corrosion protection. Its skirt, which
is essentially cylindrical, is shaped so as to be slightly
conical to the outside and then flanged inward in a semi-circle.
Holes in the flanged edge facilitate connection to the plate-
shaped end of the air spring bearing arm. In the upper section,
the plunger piston skirt maXes the transformation through an
essent~ally semi-circular edge into a truncated conical trough
with a level bottom, this serving to accommodate the convex
trough of the air spring bellows. The base of the trough
incorporates at least one drilled hole through which a screw bolt
can be passed to form a friction fit connection between the
plunger piston and the air spring bellows. ~hen under
4 ~ ~ 327054
compression, the base of the air filled spring bellows is a
friction fit in the trough of the plunger piston, whereas the
side wall of the essentially cylindrical air spring bellows is
slipped over the upper edge of the plunger piston and the
essentially cylindrical plunger piston skirt. The plunger piston
can move so deep into the air spring bellows that the rubber
buffer in the air spring bellows is clamped between the upper
steel plate and the plunger piston of the air spring bellows,
foxming a stop by so doing. In such cases, shock loads exert a
significant amount of stress directly on the surface of the
trough base.
Because they are made of metal, such plunger pistons are
relatively heavy and costly. Furthermore, metal plunger pistons
can corrode in their rolling region after prolonged periods o
use, and this can lead to increased wear of the rubber sack. For
this reason, attempts have been made to develop a plunger piston
of glass-fibre reinforced plastic, so as to reduce weight and
production costs, as well as to increase the useful life of the
entire air spring bellows, as a result of the smooth and non-
corrosion-free surface of the plunger piston. In this regard,
the outer shape of the plunger piston is similar to that of the
embodiment that is of steel. However, the edge near the foot is
not flanged, but its cross-s~ction is approximately trapezoidal
so as to ensure improved seating on the bearing arm plate.
Perpendicular to the foot edge at most four rîbs that are offset
by 90- relative to each other extend along the inner surface Or
'
5 1 1 327054
the skirt up to the upper edge of the plunger piston. In their
lower section, the rein~orcing ribs incorporate threaded holes or
threaded inserts of metal, these being used for the bolted
connection to the bearing arm plate.
In a ~urther emhodiment of a plunger piston of glass-fibre
reinforced plastic, it has been proposed to incorporate a
plurality of reinforcing ribs internally in the area of the upper
rounded transition from the plunger piston sXirt to the truncated
conical troughO In the event o~ shock stresses, however, at the
upper s~op, breaks still occur at the transition from the plunger
piston sXirt to the truncated conical trough. On the other hand,
it has also been seen that the base of the trough has been torn
out on rebound, because the efective tensile force is
transferred through the screw head and, optionally, a washer,
from the air spring bellows directly to the trough base of the
plunger piston. Besides these functional disadvantages, because
of the numerous ribs, this embodiment of the plunger piston is
almost as heavy as the steel version. Furthermore, the tool
costs associated with the production oP such embodiments of
:
plunger pistons are extremely high.
~ In still another embodiment of a plunger piston of glass
'! fibre reinforced plastic, a pipe stub is moulded into the
interior of the piston, starting concentrically from the trough
~ base; this pipe stub extends downward to the supporting arm plate
s and rests on said plate when subjected to a load. The object of
thin pipe stub was to transfer the shocks from the baee of the
:`
i
,: !
,~
:,
6 ~ 1 32705~
trough to the ~earing arm plate and to remove the load ~rom the
edge area of the plunger piston. However, the disadvantage vf
this embodiment is that in the production process that is used,
the reinforcing glass fibres do not get into the lower third of
the pipe stub, so that it fails under elevated shock stresses.
In addition, the dimensions of the pipe stub make it difficult to
install the supporting arm plate on a parabolic link, which is
necessary under some circumstances, if it should be n~cessary for
structural reasons to install it in this way instead of on the
supporting arm. For this reason, an area on the bottom edge of
the short pipe has been subsequently notched, which of course
further reduces the supporting effect.
GB-PS 1 231 766 describes a damped pneumatic spring with a
main and an secondary chamber, these being connected by an
opening in the partition wall that separates them. The main
chamber is formed by an air spring ~ellows, the base of which is
connected with the base plate o~ the plunger piston that forms
the second chamber that is closed up to the connection with the
~irst chamber. The upper base plate of the plunger piston welded
to the lower cover plate through a pipe-like member. The plunger
pi~ton wall is formed in part from a wall section that i5 sharply
curved and adjacent to the upper base plate, and in part from a
flange area that slopes upwards from the lower cover plate. If
this plunger piston system is to be used for supportiny and
guiding an air spring bellows incorporated in an air-sprung axle
of a commercial vehicle or the like, the plunger piston and the
7 ~ 1 32705~
pipe-like element must have extraordinarily thick walls in order
to b~ able to withstand the stresses to which they are subjected.
Because of its construction, this known plunger piston
arrangement is very heavy and entails very high production costs.
Proceeding from this, it is the task of the present
invention to develop a plunger piston system of the
a~orementioned kind, of glass ~igure reinforced plastic or
similar composite ~aterial, which even in extreme cases can
absorb all the compressive and tensile forces that occur during
the compression and rebound of the air suspension axles of a
commercial vehicle without incurring any damage, which can
provide for the smooth sliding of the air spring bellows when
describing the spring excursion, without the air spring bellows
becoming pinched, which also permits installation on a parabolic
link, and which can be manufactured in a cost-effective manner.
According to the present invention, this problem has been
solved essentially in that the plunger piston and the supporting
body are o~ plastic, preferably glass fibre reinforoed plastic or
composite material; in that the plunger piston is pot-shaped with
an essentially cylindrical casing; that the supporting body is
formed as a separate part of essentially truncated conical shape
:
with a diameter that grows smaller from the lower foot area to
the base of the trough of the plunger piston; and in that the
upper base plate of the supporting body lies against the under
id~ o~ the trough base of the plungQr piston.
.,
:`
, '
i
1 32705~
In this manner, the previous one-piece plunger piston, which
was a costly design, has been replaced by a two-part version,
both parts of which perform specific tasks, such that the outer
plunger piston essentially manages the usual guiding o~ the air
spring bellows during compres~ion and rebound, whereas a
truncated-conical one that is bolted with the outer plunger
piston to the lower convex air spring bellows plate essentially
absorbs the compressive and tensile forces that can be especially
damaging at the upper stop or during total rebound. Because of
the fact that the upper base plate of the supporting body is
adjacent to the under side of the plunger piston base plate,
both plates are strong enough, because of their sandwich
construction, with regard to the tensile stresses that result
from sudden and total rebound. The outer lower edge of the
supporting body that is positioned in the inside space of the
plunger piston lies in the foot area of the plunger piston skirt
so as to provide radial and axial to stabilize this edge area.
Despite its simple rotationally symmetrical shape and the very
simple construction method used as compared to the prior art, the
solution according to the present invention exhibits ~ar greater
serviceability than embodiments known from the prior art. The
supporting function is particularly effective because the foot
area of the supporting body is braced upward or outwards,
respectively, on the lower foot araa of the plunger piston.
Ef~ective savings of materials and effective absorption of the
compressive and tensile forces is achieved, in particular, in
~U 1 327054
that the supporting body is of ~ssentially truncated c~nical
shape, with a diameter that grows smaller from the lower foot
area to the base o~ the trough of the plunger piston.
It is preferred that khe supporting body be so configured as
to be rotationally symmetrical and are axranged to be coaxial
with the plunger piston, so that the forces involved are absorbed
uniformly around the perimeter
One specific embodiment of the present invention provides
that the plunger piston incorporates reinforcing ribs that are
oriented radially inwards and are distributed uniformly about the
periphery of the plunger piston, there being depressions in the
face ends of these to accommodated bolts for connection to the
air spring bearer; and that in its foot area the supporting body
is form-fitted at the foot region of the reinforcing ribs.
According to another feature of the present invention, the
supporting body and one preferably circular stop rib that is
incorporated at its bottom edge can be snapped in the manner of a
snap lock into at least a plurality of detent recesses that are
distributed around the periphery of the foot area of the plunger
pis~on skirt. Thus, the separate components, i.e., plunger
piston and supporting member, form a structural and functional
unit.
The notched recesses can preferably be incorporated in the
foot region of the reinforcing ribs.
During simple assembly, this snap-in function is achieved in
that the detent recesses are undercut, as viewed from below,
1 3 2 7 0 5 4
i.e., from the side from which the supporting member is
introduced into the interior space o~ the piston.
In addition, the notched recesses can incorporate a lead-in
slope so as to facilitate assembly.
Furthermore, if the notched recesses form an upper stop edge
for the preferably circular stop rib of the supporting member,
there i8 a greater likelihood o~ the supporting member being
supported on the plunger piston.
For the sake of simplicity during the joint assembly of the
supporting body and the plunger piston, the base plate of the
supporting body can incorporate an opening that is coaxial with
the opening within the trough base of the plunger piston, so as
to a~low passage of a bolt for the common force-fit connection
with the base of the air spring bellows.
Another feature of the invention is that the base plate of
the supporting body incorporates central reinforcement,
optionally with radial ribs and a circular ridge. This enhances
the absorption of the tensile for~es that, during rebound, act
through the central bolted connection between the air spring
bellows and the plunqer system or the supporting body,
respectively, on the base plate of the plunger piston or the base
plate o~ the supporting body, respectively.
Good conditions for the transfer of ~orces can be provided
if the upper side of the base plate is supported by an annular
area that surrounds ieS opening on the underside of the trough
11 rr ~ 327054
base of the plunger piston that is, in any case, level in this
annular area.
It is particularly advantageous if a shallow hollow space so
that encloses the opening is left free between the underside oE
the trough base and the upper side of the base plate, the base
plate being configured in the area of this hollow space that it
aompresses under the action o~ the bolt. This can be aahieved,
for example, in that the base plate of the supporting body is
sllghtly curved downward relative to the essentially flat base o~
the trough of the plunger piston. If the plunger piston and the
supporting body are connected to each other and to a rubber stop
by means of a bolt that passes through the openings provided at
this location, and a rubber buffer, for example, then the base
plate can be easily compressed. Kowever, if the bolt is screwed
firmly home to the stop, the base plate will remain flexible in
the area of the space. Although the parts are clamped together
by this, the air spring bellows with the hole pattern for
attachment in the upper steel plate and the air connection can be
rotated radially ralative to the plunger piston. This results in
considerable simplification of construction and assembly because
it becomes easier to adapt to the specific characteristi¢s of a
particular vehicle without any need to loosen and then tighten
all the parts involved.
An additional guarantee against the base plate of the
supporting body b~ing torn out when under tension is achieved if
the under sida of the base plate of the supporting body is
1 327054
transformed throuyh an arc with a large radius to the inner
surface of the conical casing of the supporting body.
The ~nnular cross-sectional sur~ace of the casing of the
supporting body is preferably equal at every level of the
truncated cone, so that the greatest possible transfer of
compressive and tensile forces is achieved for very low material
costs.
Essentially, this can be accomplished in that the inside
surface of the casing of the supporking member is more sharply
inclined relative to the vertical than the outer surface of the
supporting body casing.
In addition, the present invention proposes that for reasons
of production technology, the skirt of the plunger piston is
inclined less relative to the vertical for a considerable part of
its length and widens out conically in a wide-radius arc in its
lower foot area. This widening of the lower area of th~ plunger
piston increases the e~fective area of the air spring bellows if
the plunger piston plunges in by a corresponding amount. This
avoids violent impact against the rubber buffer (as can happen
during total deflectton).
In addition to the reinforcing ribs~ the plunger piston can
also incorporate inwardly oriented stif~ening ribs tha.
preferably extend to the complete height of the plunger piston
skirt, the inside contour of these being matched to the contour
of the outer surface of the supporting body casing. This makes
it possible to achieve not only an additional enhancement of the
~ 1 32705~
13
resistance moment of the plunger piston skirt, but also of its
support on the supporting body. The stif~ening ribs can be
arranged as a continuation of the reinforcing ribs or can be
arranged between the reinforcing ribs, preferably symmetrically,
around the periphery. If, for all practical purposes, they
extend to the total height of the plunger piston skirt, the width
of the stiffening ribs also fills the interior space between the
plunger piston skirt and the trough section as far as the trough
base, so that the upper, rounded edge of the plunger piston is
also relieved. Of course, it is also possible that, instead of
or in addition to this, the supporting body has stiffening ribs
that are oriented radially outwards, and these can extend as far
as the skirt of the plunger piston.
In a further embodiment of the presant invention the
supporting body can incorporate reinforcing ribs that project
radially outward and are distributed around the periphery o~ the
supportin~-body casing, there being depressions in the faces of
these to accommodate bolts for the csnnection with the air spring
bearer, the foot area of the plunger piston being a shape-locking
fit on the foot area of the reinforcing ribs. The stiffening
ribs do not have to extend to the full height of the supporting
body, o t~at it is possible to achieve a further effective
saving of materials, particularly in the case of larga plunger
pistons.
As another alternative, it can also be arranged that the
base plate of the supporting body is configured so as to be
'
14 ~ 1 327054
concave and rest with a middle, flat annular area that
immediately surrounds its opening on the underside of the base of
the trough of the plunger piston. This results in a favourable
flow of forces when the plunger piston is under tensile stresses,
particularly in the case of large plunger pistons.
Additional objectives, features, advantages and application
possibilities for the present invention are ~et out in the
following descrip~ion of embodiments shown in the drawings
appended hereto. All of the feature described and or shown,
either singly or in any combination, con~titute the object o~ the
present invention, regardless of tha wording of the claims or
references thereto. The drawings show the following:
Figure 1: A vertical cross~section of a complete air spring
bellows with a plunger piston formed as a deep-
drawn sheet me~al body as in the prior art.
Figure 2a: A section as seen ~rom the direction A in Figure
2b of a plunger piston system according to the
present invention.
Figure 2~: A vertical cross-section on the section line BB in
figure 2a.
Figure 2c: A detail enlargement as in section C in figure 2b.
Figur2s
3a to 4b: Diagrams as in fiyures 2a and 2b for two other
embodiments of the present invention.
The air spring shown in figure 1 incorporates an air spring
bellows 24 in the form of an air-filled, rotationally symmetrical
15' 1 32705~
rubber sack, which is to be connected through an upper flanged
steel plate 17, as a force transfer element, to a vehicle frame
(not shown herein). A convex, circular steel base is vulcanized
onto the underside of the air spring bellows24, and this supports
a rubber buffer as a stop inside the air spring bellows 24. The
underside of the base 23 is convex and is a form fit in a
correspondingly convex shaped upper trough base of a plunger
piston 1 and is bolted to this to form a force fit by means of a
bolt 22. Th~ plunger piston 1 is a pot-shaped rotationally
symmetrical deep-drawn part that is of steel. The essentially
cylindrical plunger piston skirt 9 is shaped so as to be slightly
conical to the outside and is then flanged in a semicircular
shape to the inside. Drilled hol~s in the flanged edge enable
connection to the plate-shaped end of an air spring bearing arm
(not shown herein).
The plunger piston system according to the present invention
and ~hown in figures 2a to 2c is intended for use with an air
spring bellows system 17, 23 ~24, 25 that is configured in
essentially the same way. The outer, pot-shaped plunger piston 1
incorporates four reinforcing ribs 2 that are displaced by 90
relative to each other, that are oriented inwards, and extend to
the whole height of the plunger piston skirt 9. In the foot area
3 of the reinforcing ribs 2 there are reces~es 4 to accommodate
threaded bolts (not shown harein) for connection with a bearer
arm plate (no~ shown herein~. At the top, the essentially
cylindrical plunger piston skirt 9 makes a transition to becom- a
16 ~ l 327054
rounded plunger piston edge 6 that is essentially semicircular in
cross-section, to which inclined inwards an essentially truncated
conical trough section 7 is connected to an essentially flat
trough base 8 to form an essentially truncated conical trough 27
in which the convex base 23 can be accommodated by a form fit.
The plunger piston skirt 9 has a smaller inclination (e.g.,
approximately 1) relative to the perpendicular S and widens out
in its lower foot area S outwards in the shape of a cone in an
arc 10 of a greater radius (e.g., approximately lO0 mm).
A hollow, truncated conical suppoxting body 11 is positioned
within the plunger piston 1. Its annular foot region 12 has on
its outer side a stop rib 13 that is, for example, circular and
can engage in corresponding detent recesses 14 on tha inner side
of the foot areas 3 of the four reinforcing ribs 2. To this end,
as viewed from below, the detent recesses 14 incorporate a lead-
in slope 29 that makes the transition to become a undercut 34 to
which in turn a stop edge 30 for the upper side of the stop rib
13 is adjacent at the top. Because of this detent and snap
connaction 13, 14, the two parts, i.e., the plunger piston and
the supporting body ll can be connected ri~idly but releasably by
a shape fit and support each other upwards and to the outside in
the foot areas 3, 12.
The slop~ of the inner surface 15 of the supporting body
ca~ing 33 is greater than the slope of the outer surface 16 to
the point that the annular cross-~ectional area F of tha
' 1 32705~
17
supporting body 11 remains constant at every level of the
truncated conical supporting body 11.
The upper base plate 18 which the supporting body aasing 33
becomes, abuts by its upper side 35, which i8 ~lat in an annular
area, against a similarly flat annular area of the underside 28
of the trough base 8 of the plunger piston 1. The base plate 18
incorporates an opening 19 that is coaxial to the opening 20 in
the trough base 8; a boIt 22 (not shown herein) that i5 used to
connect the two parts 1, 11 of the two-part plunger piston system
with the base 23 of the air spring bellows 24 can be passed
through this opening. The base plate 18 is configured so as to
be concave and resilient in the area of the opening 19, so that a
shallow space 36 remains free in the direction of the trough base
8: this space decreases somewhat when the bolt 22 is tightened in
the rubber buffer 25 as far as the base~ Because o~ the flat
annular contact between the outer plunger piston 1 and the
supporting body 11 that is arranged within this inside space 27,
the trouqh 26 that is enclosed by the trough section 7 form a
sort of double cone in the upper area of the outer plunger piston
1 and the supporting body 11.
In order to enhance the absorption of tensile forces that
act during rebound on the plunger piston system through the
above-described central bolt attachment between the air spring
bellows 24 and the plunger piston 1 or the supporting body 11,
respectively, on the trough base 8 or the base plate 18,
respectively, the latter has a reinforcement 31 in its central
18 132705~
area. The underside 32 of the bas-e plate 18 makes a transition
,f~ in an arc 2~ of relatively large radius to become the inner
sur~ace 15 of the truncated conical supporting body casing 33.
The ensures the highest degree o~ protection against the base
plate 18 tearing out when subjected to tensile loads.
Figures 3a and 3b show another embodiment of a ~lunger
piston 1, in this case without the supporting body 2, as viewed
from the direction A in figure 3b or on the section line B-B in
figure 3a, respectively. In this case, the plunger piston 1
incorporates additional stiffening ribs 37 that are distributed
symmetrically to the reinforcing ribs 2 around the periphery,
there sti~fening ribs are oriented radially inwards, and each of
them ~ills, to its whole width, the space between the plunger
piston skirt 9 and the trough section 7, and contribute to
increasing the moment of resistance of the plunger piston 1. The
inner shape 38 of the stiffening ribs 37 is matched to the shape
of the outer contour of the outer surface 16 of the supporting
body 33 so that the plunger piston 1 can rest on the outer
periphery of the supporting body 11 through the stiffening ribs
37. In this case, the depressions 4 are not threaded, as is the
case in the embodiment shown in figure 2 a to c. In this case,
self-tapping screws are used to produce the connection to the
bearer arm plate.
In the embodiment o~ the plunger piston system shown in
figures 4a and 4b, in place of the plunger piston 1 the
supporting body ll incorporate~ reinforcing ribs 39 thàt are
19 ~ 1 327054
distributed about the periphery of the supporting body casing 33
and which project radially outwards, and in which there are face
end depressions 40 to accommodate bolts to produce the connection
with the air spring bearer. The foot area 5 of the plunger
piston 1 abuts to form a shape-locking fit on the foot area 41 of
the reinfor~ing ribs. Seating thereon i~ enhanced by the
external pressure that is exerted by the air spring bellows 24
when it rolls over [bei dessen Ueberollen ~sic)--Tr.)~ The
plunger piston 1 and the supporting body 11 are only connected to
each other in the area of the trough base 8 and of the base
plate 17, so as to be releasable, during assembly on the base ~3
of the air spring bellows 24. In this case, the base plate 18 of
the supporting body 11 is configurPd so as to be slightly concave
so that it rests with a centre annular area that surrounds its
opening on the underside 28 of the trough base 8 of tha plunger
piston 1. The supporting body casing 33 is widened and extended
beyond the base plate 18 to form a supporting ring 41. This
supporting ring 41 lies with its face surface in an outer annul~r
area on the underside 28 of the trough base 8. Of course, here,
too, it is possible that the plunger piston skirt ~, like the
embodiment shown in figures 3a and 3b, be provided with
stiffening ribs 37 that are oriented radially inwards.
