Air springs

An air spring comprises a substantially tapered flexible air sleeve, a piston connected to the small-diameter portion of the air sleeve, and an end cap connected to the large-diameter portion of the air sleeve. In this air spring after the inflation, the length of freely deformable portion of the air sleeve is longest at a position in its peripheral direction and shortest at a position opposite to the longest position in radial direction and is gradually changed between the longest position and the shortest position.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an air spring using a substantially tapered 
flexible air sleeve. More particularly it relates to an air spring capable 
of sufficiently reducing friction and effectively preventing the 
occurrence of wrinkles in a turned-up portion of the air sleeve when it is 
applied to a structure of changing a deflection angle between axis of 
piston and axis of end cap in expansion and contraction operation. 
2. Related Art Statement 
As the conventionally known diaphragm type air spring, there is a structure 
that a straight-type air sleeve 1 having uniform inner and outer diameters 
over its whole length is airtightly connected at its end portions to a 
piston 2 and an end cap 3, respectively, as shown in FIG. 6a. 
In the air spring using such a straight-type air sleeve 1, however, the 
distance of elastic hysteresis loop in a direction of minor axis becomes 
fairly long as shown in a load-displacement curve of FIG. 6b and hence the 
distance between intersections of hysteresis loop and load axis or 
friction is large. For instance, when this air spring is applied to an 
automotive vehicle, if vibrations having an amplitude of about .+-.10 mm 
are transmitted thereto, these vibrations can not effectively be absorbed 
by the air spring, so that the ride comfortability on the vehicle is 
considerably damaged. 
Recently, in order to sufficiently reduce the friction in the air spring 
and ensure the large relative stroke of the piston 2 to the end cap 3, 
there has been proposed an air spring that an air sleeve 4 having a 
substantially tapered from as sectionally shown in FIG. 7 is airtightly 
connected at its small-diameter end portion 4a to the piston 2 and at its 
large-diameter end portion 4b to the end cap 3. Also, the gauge of the air 
sleeve 4 in uniformly thinned to, for example, about 2 mm for more 
reducing the friction. 
For instance, when the above air spring is mounted to an automotive vehicle 
at a posture shown in FIG. 6a, or when the air spring is used to align the 
axis of the piston 2 and the axis of the end cap 3 on a common line, 
friction is reduced to improve the ride comfortability on the vehicle and 
also vibrations having a small amplitude as well as vibrations having a 
large amplitude are sufficiently absorbed. 
In these conventional air springs, however, when the air spring is applied 
to cross the axis of the piston 2 and the axis of the end cap 3 with each 
other at a deflection angle .delta. under a service load by fixing the 
piston 2 and the end cap 3 to an unsprung member 5 and a sprung member 6 
in a vehicle. The unsprung member 5 and the sprung member 6 gradually 
extend toward the side direction of the vehicle as shown in FIG. 8. There 
is still a problem that when the air spring is deformed in a direction of 
increasing the deflection angle or in the expansion direction under a load 
larger than the service load, many wrinkles 7 are always produced in a 
turned-up portion of the air sleeve 4 as shown by a phantom line to lower 
the durability of the air sleeve 4. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the invention to advantageously solve the 
aforementioned problems of the conventional techniques and to provide an 
air spring capable of sufficiently reducing the friction under a service 
stroke of the air spring and producing no wrinkles in the air sleeve even 
at the increase of deflection angle between the axis of the piston and the 
axis of the end cap. 
According to the invention, there is the provision of an air spring 
comprising a flexible air sleeve of a substantially tapered form as a 
whole, a piston airtightly connected to the small-diameter end portion of 
the air sleeve at its inwardly turned-up state and an end cap airtightly 
connected to the large-diameter end portion of the air sleeve, 
characterized in that the axial lines of the piston and the end cap 
connected to the air sleeve are aligned with each other, and a length of a 
freely deformable portion in the air sleeve at an internal pressure filled 
posture, for example, a length of connected portion of the air sleeve 
extending between the piston and the end cap is longest at a position in 
the peripheral direction of the air sleeve and shortest at a position 
opposite to the longest position in the radial direction and gradually 
changes between the longest position and the shortest position. 
Moreover, the difference in the length of the freely deformable portion of 
the air sleeve can properly be selected in accordance with the deflection 
angle between the axis of the piston and the axis of the end cap at the 
application state of the air spring or at the operation state of the air 
spring under a service stroke. 
In the air spring according to the invention, when the air sleeve is curved 
in any direction, the position showing the longest length of the freely 
deformable portion of the air sleeve locates outside the curve, while the 
position showing the shortest length of the freely deformable portion 
locates inside the curve, so that the air sleeve is subjected to an 
approximately uniform external tension force in the lengthwise direction 
based on the internal pressure filled in the air spring even at any 
positions in the peripheral direction at the applied state of the air 
spring or use state under the service stroke. This is also true when the 
air spring is deformed in a direction of increasing the deflection angle 
between the axis of the piston and the axis of the end cap. Even in the 
latter case, there no fear of generating cramp, wrinkle or the like in the 
turned-up portion of the air sleeve due to the fact that external tension 
force acting to the turned-up portion is non-uniform the peripheral 
direction and consequently the durability of the air sleeve is 
considerably enhanced. 
Furthermore, the air sleeve is shaped into a substantially tapered form as 
a whole and preferably, the gauge thereof is sufficiently thinned, whereby 
the friction under the service stroke of the air spring can sufficiently 
be reduced to effectively improve the ride comfortability on the vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 is sectionally shown a first embodiment of the air spring 
according to the invention, wherein numeral 11 is a flexible air sleeve 
having a substantially tapered form as a whole. The air sleeve 11 is 
airtightly connected at its small-diameter end portion to a piston 12 
under an inwardly turned state on one hand, and at its large-diameter end 
portion to an filled in the inside of the air sleeve 11 under a proper 
pressure to form an air spring 14. 
In the illustrated air spring 14, the length of freely deformable portion 
of the air sleeve 11 at the connected state of the air sleeve to the 
piston 12 and the end cap 13, i.e. the connecting length of the air sleeve 
extending between the piston 12 and the end cap 13 is made longest at a 
position in the peripheral direction thereof and shortest at a position 
opposite to the longest position in the radial direction and is gradually 
changed between the longest position and the shortest position. Thus, the 
bottom face 12a of the piston 12 is maintained in parallel with the top 
face 13a of the end cap 13 to align the axes of the piston and end cap 
with each other. At a posture when the air spring is inflated under an 
internal pressure as shown in FIG. 1, the length of the longest position 
of the freely deformable portion in the air sleeve 11 is L.sub.1 
proportional to the original length and the length of the shortest 
position is L.sub.2 proportional to the original length, and the length 
between both the positions is gradually changed from one of the positions 
to the other. 
When the piston 12 and the end cap 13 in the air spring 14 are fixed to an 
unsprung member 15 and a sprung member 16 in a vehicle wherein the 
unsprung member 15 and the sprung member 16 are gradually enlarged in the 
side direction as shown in FIG. 2, respectively, if oscillation motion is 
caused in a vertical plane of the unsprung member 15, the piston 12 
enables to move on a curved axial line X--X of the air sleeve 11. In such 
an application state of the air spring 14, the lengths of the air sleeve 
11 connected to the piston 12 and the end cap 13 are frequently L.sub.11 
longer than the length L.sub.1 at the outside of the curve and L.sub.22 
shorter than the length L2 at the inside of the curve as compared with the 
case of FIG. 1. 
In this case, the difference between the lengths L.sub.1 and L.sub.2 of the 
freely deformable portion of the air sleeve 11 as shown in FIG. 1 can 
properly be selected in accordance with the degree of the curve at the 
mounted state of the air spring 14 as shown in FIG. 2. Therefore, when the 
lengths L.sub.1 and L.sub.2 are sufficiently and properly selected, the 
air spring 14 can be mounted onto the vehicle without hardly changing 
these lengths. 
In FIGS. 3a to 3c are shown various embodiments of the air sleeve 11 
applicable for use in the air spring 14. The air sleeve 11 of FIG. 3a has 
a substantially tapered form as a whole and is previously curved in a 
predetermined form, whose axial line X.sub.1 --X.sub.1 preferably matches 
with the curved axial line X--X of the air sleeve 11 at the mounted state 
of the air spring 14. Furthermore, in the air sleeve 11 extending from the 
small-diameter end portion connected to the piston 12 to the 
large-diameter end portion connected to the end cap 13, the longest length 
l.sub.1 is outside the curve and the shortest length l.sub.2 is inside the 
curve. 
FIG. 3b shows another embodiment of the air sleeve 11, which has a 
substantially tapered form as a whole likewise the case of FIG. 3a, but 
the center axis Y--Y thereof is straight and the elongated line of the 
small-diameter end portion slantly intersects with the center axis Y--Y. 
Even in the air sleeve 11 of FIG. 3b, the longest length of the portion 
connecting to the piston 12 and end cap 13 is made l.sub.1 and the 
shortest length thereof is made l.sub.2, whereby the freely deformable 
lengths L.sub.1 and L.sub.2 as shown in FIG. 1 can be obtained when the 
air sleeve 11 is connected to the piston 12 and the end cap 13 and then 
inflated under a given internal pressure. Furthermore, when such an air 
spring is applied to the vehicle as shown in FIG. 2, the lengths inside 
and outside the curve are substantially the same as in FIG. 2 at a curved 
state of the central axis of the air spring itself and hence the central 
axis of the air sleeve 11. 
FIG. 3c shows the other embodiment of the air sleeve, which is 
substantially the same as the air sleeve 4 of FIG. 7 and produces an air 
spring similar to the case of using the air sleeve 11 of FIG. 3b by using 
particular clamping members. 
That is, the large-diameter end portion of the air sleeve 11 is fixed to 
the end cap 13 through a belt 17 having an equal width over a whole 
periphery as shown by a phantom line in FIG. 3c, while the small-diameter 
end portion thereof is fixed to the piston 12 through a belt 18 having a 
gradually changed width in circumferential direction, whereby the length 
of the air sleeve 11 connecting to the piston 12 and the end cap 13 is 
l.sub.1 at the longest position and l.sub.2 at the shortest position and 
the central axis thereof is substantially curved likewise the case of FIG. 
2, whereby the lengths inside and outside the curve are the same as in 
FIG. 2. 
According to the air spring 14 of the above structure, since the flexible 
air sleeve 11 is shaped into a substantially tapered form as a whole, when 
vibrations are transmitted to this air spring, the friction can be reduced 
to sufficiently improve the ride comfortability on the vehicle 
irrespective of large and small amplitudes of vibrations. 
Furthermore, the lengths of the air sleeve 11 connected to the piston 12 
and the end cap 13 are longest (L.sub.1) at a position in the peripheral 
direction and shortest (L.sub.2) at a position opposite to the longest 
position in radial direction in the posture of air spring shown in FIG. 1, 
and are gradually changed between the longest position and the shortest 
position. Thus the tensile stress acting to the air sleeve 11 in the 
longitudinal direction can substantially be uniformized over a whole in 
circumferential direction at the application state of the air spring 14 as 
shown in FIG. 2 and under a service stroke thereof. Therefore, even if the 
thickness of the air sleeve 11 is very thin, the occurrence of cramp, 
wrinkle or the like in the turned-up portion of the air sleeve can 
completely be prevented at the above state. Furthermore, even when the air 
spring 14 is deformed in a direction of increasing the deflection angle 
between the axis of the piston and the axis of the end cap, the tensile 
stress acting to the turned-up portion of the air sleeve 11 can 
sufficiently be uniformized in circumferential direction to effectively 
prevent the occurrence of cramp and wrinkle. 
In FIG. 4 sectionally illustrates another embodiment of the air spring 
according to the invention, which produces the function and effect similar 
to the aforementioned embodiment by using the same air sleeve 11 as in 
FIG. 7 and a special piston 12 for this air sleeve 11. 
In the embodiment of FIG. 4, a belt-like protrusion 12b projecting outward 
in radial direction is arranged in the portion of the piston 12 connecting 
to the air sleeve 11 as shown in FIG. 4b. The projecting amount of the 
belt-like protrusion 12b in radial direction is made minimum at a position 
of the piston 12 in the peripheral direction and maximum at a position 
opposite to the minimum position in radial direction. Thus, the freely 
deformable portion in the air sleeve 11 has a longest length L.sub.1 at 
the minimum projecting position of the protrusion 12b and a shortest 
length L.sub.2 at the maximum projecting position. That is, in this 
embodiment, the portion of the air sleeve riding on the shoulder part of 
the protrusion 12b can not substantially deform except for a special case 
that the piston 12 and the end cap 13 are extremely separated from each 
other so as not to cause the slackening of the air sleeve 11. Hence, even 
when the air sleeve itself is symmetrical with respect to the axial line 
as shown in FIG. 7, if the air spring is inflated under a given internal 
pressure as shown in FIG. 4a, the length of the freely deformable portion 
of the air sleeve becomes shorter by a length corresponding to the length 
of the air sleeve located on the shoulder part of the belt-like protrusion 
12b at the outwardly projecting position of the piston 12 as compared with 
the length at the non-projecting position of the piston. Therefore, when 
this air spring 14 is applied so that the maximum projecting position of 
the belt-like protrusion 12b locates inside the curve of the air sleeve 11 
and the minimum projecting position locates outside thereof as shown in 
FIG. 5, the tensile stress acting to the turned-up portion of the air 
sleeve 11 can sufficiently be uniformized in the circumferential direction 
likewise the aforementioned case and consequently the occurrence of cramp, 
wrinkle and the like can effectively be prevented. 
Moreover, the amount of the belt-like protrusion 12b projecting outward 
from the piston in radial direction may be changed into an ellipsoidal 
form in the circumferential direction in accordance with the use 
conditions and the like as shown in FIG. 4c. 
Although the invention has been described with respect to the illustrated 
embodiments, it is a matter of course that the air spring according to the 
invention may be applied to a case of increasing the deflection angle 
between the axis of the piston and the axis of the end cap when the piston 
and the end cap displace in a direction of approaching to each other. 
As mentioned above, according to the invention, the axial lines of the 
piston and the end cap connected to the air sleeve are aligned to each 
other, while the length of the freely deformable portion of the air sleeve 
at the posture inflated under internal pressure is longest at a position 
in the peripheral direction and shortest at a position opposite to the 
longest position in radial direction and is gradually changed between the 
longest position and the shortest position. Thus even when the air spring 
is deformed in a direction of increasing the deflection angle between the 
axis of the piston and the axis of the end cap, or even if the gauge of 
the air sleeve is thin, the occurrence of cramp, wrinkle and the like in 
the turned-up portion of the air sleeve can effectively be prevented and 
the durability of the air sleeve can considerably be improved. 
Furthermore, the air sleeve is shaped into a substantially tapered form as 
a whole, whereby the friction of the air spring can be reduced to 
sufficiently absorb vibrations.