Self-pumping hydropneumatic spring strut with internal level regulation

A self-pumping hydropneumatic spring strut that continuously regulates the pressure in the low- and high-pressure work cavities of the work cylinder to control the height of the vehicle body during all vehicle operation situations. According to the present invention, a valve is provided between the high-pressure work cavity and the pump cylinder. The valve is movable axially within the pump cylinder and advantageously blocks a first nonreturn valve between the pump cylinder and the low-pressure work cavity when spring strut is caused to elongate, and unblocks this first nonreturn valve when the spring strut is caused to compress.

FIELD OF THE INVENTION 
The present invention relates to a self-pumping hydropneumatic spring strut 
with internal level regulation. 
BACKGROUND OF THE INVENTION 
German Patent No. DE-OS 44 16 641 discloses a vehicle spring strut having a 
work cylinder that is divided by a damping piston into a high-pressure 
work cavity and a low-pressure work cavity--both of which act upon the 
work cylinder. An oil pump formed by a pump rod and a hollow space defined 
in a piston rod is fastened to the base of the work cylinder. The 
movements of the vehicle axle and of the piston rod fastened thereto that 
are brought about by unevenness in the road surface, for example, actuate 
this oil pump which constantly delivers oil, controlled by valves, from 
the low-pressure work cavity into the high-pressure work cavity. The 
piston is accordingly caused to move out of the work cylinder (i.e., 
during a pulling stage) until the conical tip of the pump rod produces a 
fluid connection between the high-pressure cavity and the pump cylinder. 
The pressure compensation between the high-pressure cavity and the 
low-pressure cavity is effected via an outlet opening over which the 
piston passes as the piston is pushed out of the work cylinder. 
Initially, i.e. when the vehicle is stationary and the spring strut is not 
actuated, the pressure between the high-pressure work cavity and the 
low-pressure work cavity is equalized. Since the damping valves for the 
pushing (i.e. when the piston is caused to move into the work cylinder) 
and pulling stages likewise affect the pressure regulation between the 
high- and low-pressure work cavities, a sharp drop in pressure 
disadvantageously occurs in the high-pressure work cavity relative to the 
low-pressure work cavity during the downward movement of the work piston 
in the case of a high adjustment of the damping valve. When, in addition, 
the work piston moves over the regulating area defined by the conical tip 
of the pump rod, the damping medium can flow freely out of a low-pressure 
oil reservoir into the low-pressure work cavity and from there into the 
high-pressure work cavity. This causes an undesirable temporary height 
gain in the vehicle body. A clear disadvantage with respect to pressure 
regulation consists in that the excessively rapid drop in oil volume in 
the high-pressure work cavity can only be regulated gradually, that is, 
gradually returned to the low-pressure oil reservoir. 
SUMMARY OF THE INVENTION 
The present invention advantageously overcomes the above-mentioned 
shortcomings of the prior art in a novel an unobvious manner by providing 
a self-pumping hydropneumatic spring strut that continuously regulates the 
pressure in the low- and high-pressure work cavities of the work cylinder 
to control the height of the vehicle body during all vehicle operation 
situations. According to the present invention, a valve is provided 
between the high-pressure work cavity and the pump cylinder. The valve is 
movable axially within the pump cylinder and advantageously blocks a first 
nonreturn valve between the pump cylinder and the low-pressure work cavity 
when spring strut is caused to elongate, and unblocks this first nonreturn 
valve when the spring strut is caused to compress. 
The valve of the inventive spring strut is provided in the pump cylinder 
and is preferably constructed as an annular disk. The valve is arranged 
for axial movement on a cylindrical pin part of a pump rod that is 
provided with the work cylinder and that penetrates the pump cylinder as 
the piston rod moves in and out of the work cylinder. A first nonreturn 
valve provided in the work piston is configured to permit the one-way flow 
of liquid from the low-pressure work cavity into the pump cylinder. A 
second nonreturn valve provided in the piston is configured to permit the 
one-way flow of liquid out of the pump cylinder into the high-pressure 
work cavity. The valve is sized and shaped to block the flow of liquid 
through first nonreturn valve when the piston rod is caused to move out of 
the work cylinder. Conversely, when the piston rod is caused to move into 
the work cylinder, the valve does not block the first nonreturn valve 
thereby permitting the flow of fluid therethrough. The blocking and 
unblocking of the first nonreturn valve effects a pressure balance between 
the high- and low-pressure work cavities to control the height of the 
vehicle body during all vehicle operation situations. 
The tip of the pump rod is generally conically shaped and defines a 
regulating area over its length. As the work piston moves axially over the 
conical tip of the pump rod, a fluid channel is created between the 
high-pressure work cavity and the pump cylinder. The channel size 
increases as the spring strut elongates (i.e. as the piston rod moves out 
of the work cylinder) and decreases as the spring strut compresses (i.e. 
as the piston rod moves into the work cylinder). When the piston is caused 
to move into the work cylinder and out of the regulating area, the channel 
is fluidly sealed between the piston and the pump rod. 
A coil spring arranged coaxial with the cylindrical pin part biases the 
valve into contacting engagement with the work piston. When the piston rod 
is caused to move out of the work cylinder the valve moves axially along 
the pin part together with the work piston and piston rod, compressing the 
spring in the process, and the valve remains in position to block the 
first nonreturn valve. When the piston rod is caused to move into the work 
cylinder, a shoulder defined between the conical tip of the pump rod and 
the pin part arrests the axial movement of the valve, which is held in 
place by the spring. Consequently, the valve does not block the first 
nonreturn valve. At the approximate point where further axial movement of 
the valve is arrested, the piston is moving out of the regulating area and 
the channel between the high-pressure work cavity and pump cylinder is 
cut-off. 
In accordance with the present invention, the valve advantageously blocks 
the first nonreturn valve when the spring strut is operating with the work 
piston in the regulating area and when the piston rod is caused to move 
out of the work cylinder. Only when the piston rod and work piston are 
caused to move into the work cylinder beyond the regulating area is the 
first nonreturn valve unblocked and damping medium can flow from a 
low-pressure reservoir into the low-pressure cavity and then into the pump 
cylinder. 
The valve may alternatively be constructed as a cup-shaped structural 
component part. 
In an alternative embodiment, the high- and low-pressure reservoirs may 
define separate cavities peripherally disposed about the work cylinder. 
Other objects and features of the present invention will become apparent 
from the following detailed description considered in conjunction with the 
accompanying drawings. It is to be understood, however, that the drawings 
are designed solely for purposes of illustration and not as a definition 
of the limits of the invention, for which reference should be made to the 
appended claims.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
The present invention provides a novel vehicle spring strut or shock 
absorber that continuously regulates the pressure between two cavities 
defined with a work cylinder to maintain the position of the vehicle at a 
constant height while the vehicle encounters a variety of road and travel 
conditions. The terms spring strut and shock absorber are used 
interchangeably herein and are intended to denote a load-levelling part of 
a vehicle suspension system. 
Referring next to the drawings, FIGS. 1-4 depict a first embodiment of a 
self-pumping hydropneumatic spring strut 40 configured in accordance with 
the present invention. As shown in FIG. 1, the inventive spring strut 40 
comprises a work cylinder 2 which is divided by a work piston 6 having a 
circumferentially disposed piston seal 4 into a high-pressure work cavity 
21 and a low-pressure work cavity 22. The work piston 6 is carried by a 
piston rod 10 having a pump cylinder 9 defined therein. A pump rod 1 
having a generally conically shaped tip 42 that defines a regulating area 
7 having a length Y (see, e.g. FIG. 3) extends into the work cylinder 2 
and into the pump cylinder 9. A pin 28 is connected to the tip 42 of the 
pump rod 1. 
An annular valve 24 having a valve body 26 is disposed on the pin 28 and is 
movable coaxial therealong. The valve body 26 includes a first end face 32 
and an oppositely disposed second end face 34. A coil spring 27 is 
disposed coaxially on the pin 28 and contacts the second end face 34 so as 
to bias the first end face 32 of the valve body 26 into abutting 
engagement with a valve seat 38 defined in the pump cylinder 9 and with a 
shoulder 36 defined between the conical tip 42 and the pin 28. A constant 
passage 25 defined through the valve body 26 extends between the first and 
second end faces 32, 34 and fluidly connects the pump cylinder 9 with a 
regulating cavity 47 defined in the work piston 6. Depending on the 
position of the work piston 6 in the work cylinder 2, the regulating 
cavity 47 may be fluidly connected with the high-pressure work cavity 21, 
as described in more detail hereinbelow. 
The pump cylinder 9, valve 24 and spring 27 comprise a piston pump 70 that 
pumps oil within the inventive spring strut 40 as the strut 40 compresses 
and elongates. 
A first one-way or nonreturn valve 14 is included in the work piston 6 near 
the valve seat 38 and permits one-way fluid flow from the low-pressure 
work cavity 22 into the pump cylinder 9. A second one-way or nonreturn 
valve 5 is included in the work piston 6 near the regulating cavity 47 and 
permits one-way liquid flow from the regulating cavity 47 into the 
high-pressure work cavity 21. 
The high-pressure work cavity 21 is fluidly connected with a high-pressure 
reservoir 50 that is partly filled with a gas and partly filled with a 
dampening medium such, for example, as oil. The reservoir 50 is 
partitioned by a dividing piston 3 into a first high-pressure cavity 12 
containing the gas and a second high-pressure cavity 11 containing the 
oil. Alternatively, a resilient diaphragm may separate the cavities 11, 12 
in the reservoir 50. The high-pressure reservoir 50 is fluidly connected 
to the high-pressure work cavity 21 via a flow connection 30 including a 
damping valve 23. 
The low-pressure work cavity 22 is fluidly connected with a low-pressure 
reservoir 60 having a first low-pressure cavity 16 filled with a gas and a 
second low-pressure cavity 17 filled with a damping medium such, for 
example, as oil. The reservoir 60 is fluidly connected through a 
regulating openings 8, 19 to the low-pressure work cavity 22. 
The high- and low-pressure work cavities 21, 22 and the high- and 
low-pressure reservoirs 50, 60 cooperatively pressurize the work cylinder 
2 as the piston rod 10 is caused to move in and out of the work cylinder 
2, as described in more detail hereinbelow. 
The valve 24 is arranged on the pin 28 so as to be movable axially 
therealong and is held in a predetermined end position depicted in FIG. 1 
by the spring 27. As the work piston 6 is caused to move out of the work 
cylinder 2, the valve 24 is caused to move axially along the pin 28, 
compressing the spring 27, and the first nonreturn valve 14 remains 
blocked. Alternatively, when the work piston 6 is caused to move into the 
work cylinder 2, movement of the valve 24 is arrested by the shoulder 36 
such that the valve 24 remains in the position shown in FIG. 1 and the 
first nonreturn valve 14 is unblocked during a further axial movement of 
the work piston 6 in this direction, i.e. into the work cylinder 2 and 
towards the high-pressure work cavity 21. In addition, as the piston 6 is 
caused to move into the work cylinder 2 and past the regulating area 7, 
the channel 62 is fluidly closed due to a sealing engagement between the 
pump rod 1 and the work piston 6. 
If the work piston 6 is moved further out of the work cylinder 2, e.g., 
when the vehicle is unloaded, a short circuit is created between the 
low-pressure reservoir 60 and the high-pressure reservoir 50 (see, e.g. 
FIG. 4), when the regulating opening 8 is unblocked, so that the vehicle 
body is lowered again to the predetermined level. 
With every stroke of the work piston 6 in the work cylinder 2, a damping 
medium is delivered from the second low-pressure cavity 17 via the opening 
19 into the low-pressure work cavity 22 and then, via the first nonreturn 
valve 14, into the pump cylinder 9--provided that the valve 24 is not 
seated in the valve seat 38 and blocking the first nonreturn valve 14. As 
a result of the pumping movement of the pump rod 1 in the pump cylinder 9 
during each stroke of the work piston 6, the damping medium is conveyed 
from the pump cylinder 9 through the constant passage 25 into the 
high-pressure work cavity 21 via either the second nonreturn valve 5, for 
compression strokes, or via the bypass or channel 62 (see FIG. 4), for 
expansion or elongation strokes. Consequently, the high-pressure gas 
cavity 12 is simultaneously pretensioned via the opening 18. During 
elongation strokes, the work piston 6 moves out of the work cylinder 2 as 
the level of the vehicle body rises relative to the vehicle wheels until 
the piston 6 passes the conical tip 42 of the pump rod 1, i.e. until the 
piston 6 is positioned near the regulating area 7 (see, e.g. FIG. 3). Due 
to the generally conical shape of the regulating area 7 defined by the 
conical tip 42, a bypass or channel 62 (see, e.g. FIG. 4) is created 
between the high-pressure work cavity 21 and the pump cylinder 9 which 
permits the flow of fluid therebetween and which reduces or entirely 
eliminates the output of the piston pump 70. The bypass 62 necessarily 
extends through the constant passage 25 of the valve 24--the constant 
passage 25 being required in this embodiment due to the presence of the 
pin 28 which causes displacement of the fluid in the pump cylinder 9 as 
the piton rod 10 moves with the work cylinder 2. 
Referring next to FIGS. 2-4, the inventive spring strut 40 is there 
depicted: 1) in a compressed condition (FIG. 2), e.g. such as when the 
vehicle experiences a maximum load condition; 2) with the piston 6 located 
approximately at the regulating area 7 (FIG. 3); and 3); in an elongated 
condition (FIG. 4). Thus, FIGS. 2-4 depict three predetermined positions 
of the work piston 6. 
FIG. 2 depicts the inventive spring strut 40 at its shortest length. The 
work piston 6 moves along the pump rod 1 in a sealing manner (i.e. no 
fluid communication between the pump cylinder 9 and the high-pressure work 
cavity 21) and the area indicated by reference letter X defines a 
generally cylindrical area in which the greatest pump output is generated. 
When the work piston 6 is disposed as in FIG. 2, the valve 24 does not 
block the first nonreturn valve 14 and fluid communication is possible 
between the low- and high-pressure work cavities 22, 21 via the first and 
second nonreturn valves 14, 5 and the pump cylinder 9. 
FIG. 3 shows a position of the work piston 6 in which the work piston 6 is 
located approximately at the regulating area 7 of the pump rod 1--the 
regulating area extending along a length Y. When the work piston 6 is 
disposed thusly, a fluid connection is formed between the high-pressure 
work cavity 21 and the pump cylinder 9, via the constant passage 25 and 
the bypass 62. The first nonreturn valve 14 remains blocked by the valve 
24 and fluid communication between the low-pressure work cavity 22 and the 
pump cylinder 9 is prevented. 
FIG. 4 shows the embodiment form in which the piston rod 10 is moved 
farther out of the work cylinder 2. The valve 24 still blocks the 
nonreturn valve 14 while the spring 27 holds the valve 24 in contact with 
the valve seat 38 of the work piston 6 by corresponding reservoir 50 and 
the low-pressure reservoir 60 are peripherally defined about the work 
cylinder 2 and are separated from each other by an intermediate wall 15. 
While the valve 24 configure as a cup-shaped component part 29 has been 
described herein with respect to the embodiment depicted in FIG. 7, it 
will be obvious to persons skilled in the art that such description 
applies equally to the various embodiments depicted in FIGS. 1-6. 
Thus, while there have shown and described and pointed out fundamental 
novel features of the invention as applied to preferred embodiments 
thereof, it will be understood that various omissions and substitutions 
and changes in the form and details of the devices illustrated, and in 
their operation, may be made by those skilled in the art without departing 
from the spirit of the invention. For example, it is expressly intended 
that all combinations of those elements and/or method steps which perform 
substantially the same function in substantially the same way to achieve 
the same results are within the scope of the invention. It is the 
intention, therefore, to be limited only as indicated by the scope of the 
claims appended hereto.