Hydropneumatic machine tool with cushioning

A machine tool which operates with a hydropneumatic pressure intensifier whose step piston is braked hydraulically in particular towards the end of its stroke by forcing hydraulic fluid from a braking cavity formed during the stoke via a choke point.

BACKGROUND OF THE INVENTION 
The invention is based on a hydraulic machine tool as generically defined 
by the preamble to the main claim. In a known machine tool of this generic 
type (German Patent 43 01 983), the work stroke of the work piston is 
braked by causing the step of greatest diameter, namely of the work 
piston, that serves the purpose of the rapid traverses to strike the 
bottom of the corresponding pneumatic work chamber; there is a damping 
disk on the face of the work piston, but it accomplishes only slight 
damping. 
Machine tools of this generic type are intrinsically high-speed, 
energy-saving pneumatic systems, with which a hydraulic system is 
integrated, by means of which latter, after a desired forward stroke in 
the working direction, a power stroke with very high adjusting force is 
attainable. Although only pneumatic connections to outside the housing of 
the machine tool are available, the pressure intensification is 
accomplished with the aid of the hydraulics. As a result, hydraulic 
chambers along with pneumatic chambers move in the piston stroke 
direction, which involves the not-inconsiderable problem of sealing the 
one off from the other. Air that gets into the hydraulic fluid leads to 
undesired compressibility of the oil; oil leaking out of the hydraulic 
portion can cause functional failures. 
Damping the work stroke, and sometimes the return stroke as well, remains a 
problem in such machine tools, which use hydropneumatic pressure 
intensification. Especially whenever a sheet-metal connection, for 
instance, is to be made via a suitable tool, and upon idling the step 
piston, pounds into one of its terminal positions with full force, the 
result cannot only be considerable noise but also attendant damage. Even 
though this is an old, widespread problem in such machine tools, aside 
from the aforementioned elastic disk no damping that in particular is also 
adjustable to the weight or mass of the tool has yet been found. 
OBJECT AND SUMMARY OF THE INVENTION 
The machine tool of the invention as defined by the characteristics of the 
main claim has the advantage over the prior art that depending on the 
cross section of the choke point or throttle restriction, more or less 
major damping is attainable, especially toward the end of the work stroke, 
and this cross section at the throttle restriction can be adapted to the 
masses involved. For this damping, the hydraulic fluid can be used, with 
which the remaining hydropneumatic pressure intensifier also functions. 
The seals, which already have high quality, between the pneumatic chamber 
and the hydraulic chamber also serve to seal off the annular chamber, so 
that one additional expensive seal is not needed. The invention can 
already be achieved in a very simple way and highly effectively in such 
machine tools, which overcomes the prejudices of the professional field. 
It is admittedly known in work cylinders to damp the terminal position of 
the work piston hydraulically or pneumatically, but this known provision 
does not involve step pistons having the problems discussed above. 
In an advantageous feature of the invention, the step piston positively 
displaces fluid out of the annular chamber through a throttle restriction 
at least toward the end of the return stroke and in order to brake its 
return stroke motion. In this way, both the forward motion and the return 
motion of the step piston and thus the lower dead center range and the 
upper dead center range of the tool are damped in the reciprocating 
motion; the additional piston collar, disposed on the step piston and 
serving to damp the work stroke, accomplishes the return stroke damping 
with its annular face remote from the annular face used for the work 
stroke. 
In a further advantageous feature of the invention, the annular chamber, on 
at least one of its end portions, has a taper, which corresponds to the 
diameter of the piston collar and into which the piston collar plunges 
toward the end of the stroke and positively displaces the fluid volume, 
enclosed in this braking cavity or braking chamber, through the throttle 
restriction. As a result, only toward the end of the work stroke or return 
stroke is the reciprocating motion braked or damped. Instead of this, it 
is also possible to brake the entire reciprocating motion, in that the 
piston collar to a greater or lesser extent seals off from the cylinder 
wall, or the annular chambers located on both sides of the piston collar 
communicate with one another via a throttle conduit. 
In a further advantageous feature of the invention, the annular chamber can 
be made to communicate with the work chamber during the work stroke and/or 
the return stroke. In this way, depending on the control, the hydraulic 
fluid can flow unthrottled from the annular chamber to the work chamber, 
unless braking is to be done just at that time. As a result, the 
replenishment of hydraulic oil via the extra replenishing devices always 
provided for the purpose at the same time serves to provide hydraulic 
damping. However, the annular chamber may also be completely separate from 
the work chamber and may be located at some other point of the step 
piston, for instance in the region of the piston rod. 
In a further advantageous feature of the invention, the play defined 
between the piston collar and the annular chamber wall of the annular 
chamber acts as the throttle restriction. In the case of a taper in the 
end portions of the annular chamber, the damping naturally is operative 
only in those regions. 
In a further advantageous feature of the invention, a relief conduit 
branches off from the braking chamber (from the volume enclosed), in which 
conduit there is a control element for controlling the passage of fluid. 
The relief conduit can again discharge according to the invention into the 
annular chamber. Thus the relief conduit can also lead from one braking 
chamber to the other, and the braking chamber are each activated in 
alternation, and it is also possible for two control elements to be 
disposed in the relief conduit, one for the one braking chamber and the 
other for the other braking chamber, which are then in action in 
alternation. 
In a further advantageous feature of the invention, a bypass conduit, 
connecting the braking chamber to the storage chamber, is present, with a 
check valve that blocks in the direction of the storage chamber. Such a 
bypass bypasses the point at which the plunger piston separates the work 
chamber and the storage chamber from one another in order during the rapid 
traverse stroke to achieve rapid filling of the work chamber. As a result, 
in the invention, at the beginning of the rapid traverse stroke, fast 
replenishment of the work chamber, specifically via the braking chamber, 
is attained in the work stroke direction. 
In a further advantageous feature of the invention, a bypass conduit, 
connecting the annular chamber to the work chamber, is present, with a 
check valve that blocks in the direction of the work chamber. 
Advantageously, this bypass conduit extends within the work piston. Via 
the check valve, a pressure equilibrium is attained when the step piston 
moves away from its terminal position, or in other words before the return 
stroke begins. 
In a further advantageous feature of the invention, a short-circuit 
conduit, connecting the annular chamber to the work chamber, is disposed 
in the work piston, the orifice of the short-circuit conduit being present 
on the piston collar and the short-circuit conduit is closed, at least 
partially, toward the end of the work stroke, by the taper in the annular 
chamber. This short-circuit conduit also serves as an overflow bore to 
equalize volume as the step piston moves out of its outset position, or in 
other words at the beginning of the work stroke. 
In a further feature of the invention, which is also claimed on its own, 
the storage chamber is disposed in a storage cylinder and is defined via a 
storage piston, which is loaded with low pressure (pneumatically or 
spring) in order to generate a storage pressure on the side remote from 
the storage chamber; the center axis of the storage cylinder is disposed 
parallel to but spaced apart from that of the work piston; and the storage 
chamber and work chamber are accommodated inside a common tool housing. It 
is admittedly known, in a welding tool that operates with a hydropneumatic 
pressure intensifier, to dispose a hydraulic reservoir outside the tool 
housing and to connect it to the work chamber of the tool via a hydraulic 
line (U.S. Pat. No. 3,875,365). However, such an arrangement is usable in 
practical terms only for machine tools installed in stationary fashion. 
In a feature of the invention that is advantageous in this respect, a 
helical spring serves to generate the low pressure. This has the advantage 
that the hydraulic oil is always at a low pressure that is sufficient to 
ventilate the hydraulic region. When pneumatics are used for relieving the 
piston of the reservoir, which reservoir is normally switched off during 
the return stroke, with the disadvantage that in that case ventilation of 
the hydraulic region cannot be done. 
In another feature of the invention in this respect, a control rod 
protruding to outside the storage cylinder is disposed on the storage 
piston and has a longitudinal conduit (control bore), leading to the 
storage chamber, the end of which conduit remote from the storage chamber 
discharges into a control chamber that is closed from the outside but is 
visible from the outside. As a result, the actual oil level can be 
ascertained visually at any time, and during all the work steps, namely 
for the rapid traverse stroke, the work stroke, and the return stroke. 
In a further feature of the invention in this respect, the control chamber 
is disposed in a transparent (glass or plastic) control bush (screwed 
nipple) secured to the end of the control rod. This control bush may be of 
glass or plastic. In each case, this makes it very simple for the operator 
of the machine tool to see whether the oil is low. 
In a further advantageous feature of the invention, the control chamber can 
be ventilated to the outside via a ventilating device. This ventilation 
device may advantageously be a bore, which can be conceived of as a 
continuation of the longitudinal conduit all the way through the control 
chamber. 
In a further advantageous feature of the invention, the hydraulic 
communication between the storage chamber and work chamber is embodied as 
a transverse bore, which is disposed in the tool housing, is accessible 
from outside the tool housing, and can be used for oil replenishment. 
Depending on the location of the machine tool, this bore may also be used 
for ventilation. 
In a further advantageous feature of the invention, the plunger piston is 
disposed coaxially with the work piston and is actuatable via a pneumatic 
piston counter to the force of a restoring force. Especially whenever the 
storage chamber is disposed not around the plunger piston but rather 
parallel to and spaced apart from it, the work cylinder that receives the 
pneumatic piston of the plunger piston can be shortened, making it 
possible to shorten the total structural length of the machine tool. 
In a further, alternative feature of the invention, the pressure generator 
has a storage chamber disposed coaxially with the plunger piston, the 
common longitudinal axis being disposed parallel to that of the step 
piston, having a pressure conduit connecting the pressure generator to the 
work chamber, wherein after the work stroke has ended and after a 
corresponding replenishing flow of fluid out of the storage chamber into 
the work chamber, the plunger piston blocks the pressure conduit, after 
which upon a further stroke of the plunger piston a high pressure can be 
generated in the work chamber. In principle, such an arrangement is known 
(German Patent 43 01 983).

DETAILED DESCRIPTION 
All three exemplary embodiments function as stroke-controlled machine 
tools, each with a hydropneumatic pressure intensifier. With such a 
pressure intensifier, compressed air is used for a rapid traverse, namely 
for the approach of the tool to the workpiece, while conversely for the 
actual work stroke, a hydraulic high pressure is generated via a piston 
likewise driven by compressed air, and by means of this high pressure the 
tool is actuated. 
For the sake of simplicity, in the ensuing description the same two-digit 
reference numerals are used for equivalent parts, and these same reference 
numerals for the first and second variant of the first exemplary 
embodiment in FIGS. 2 and 3 are each raised by 100, while for the second 
and third exemplary embodiments they are raised by 200 to 300. 
In the first exemplary embodiment shown in FIG. 1, there is a step piston 
1, whose individual steps are formed by a work piston 2, a drive piston 3, 
and a piston rod 4. The work piston 2 functions in a work cylinder 5, 
which is part of the tool housing 6 and which is adjoined by a cylinder 
barrel 7, in which the drive piston 3 functions and on which, on the side 
remote from the work cylinder 5, a cylinder head 8 is disposed, in whose 
central bore the piston rod 4 is supported. The drive piston 3 can be 
acted upon on both sides by compressed air in a known manner, as a result 
of which a rapid traverse of this step piston in both reciprocation 
directions is effected. 
Coaxially to the step piston 1, a plunger piston 9 is shown in the upper 
part of the machine tool; it is drivable by means of a pneumatic piston 11 
and is shown with two different diameters in longitudinal halves in the 
drawing; naturally, each diameter effects a different positive 
displacement of oil per unit of reciprocation. The pneumatic piston 11 
operates in a cylinder barrel 12, which is mounted on the tool housing 6 
and is closed off by a cylinder head 13. Via this cylinder head 13, the 
compressed air is also delivered to actuate the pneumatic piston 11, the 
adjustment being effected counter to a restoring force, which by way of 
example may be controlled compressed air or may be a helical spring. The 
plunger piston 9 plunges with its free end into a chamber 14, which, 
communicates with a work chamber 16, located below a ring seal 15 secured 
in a step bore 6' in the housing 6, so that the plunger piston 9 in its 
reciprocating motion and on passing through the ring seal 15 divides the 
chamber 14 from the chamber 16 and in accordance with its cross-sectional 
area generates a corresponding hydraulic high pressure in the work chamber 
16. The piston 11 and plunger piston 9 function as a pressure generator 
for the work chamber 16. 
The chamber 14 communicates, via a transverse bore 17 extending in the 
housing 6, with a storage chamber 18, which is disposed substantially in a 
pneumatic cylinder 19 and is defined at the top by a storage piston 21. 
The storage piston 21 is urged in the direction of the storage chamber 18 
by a helical spring 22, which is supported, on the side remote from the 
storage piston 21, on a cylinder head 23 of the pneumatic cylinder 19. A 
control rod 24 toward the outside of the cylinder head 23 and passing 
through it is disposed on the storage piston, and in the control rod there 
is a control bore 25 that passes through the entire control rod in the 
longitudinal direction and discharges into a control chamber 26. The 
control chamber 26 is disposed above all in a screwed nipple 27, which 
comprises transparent material such as plastic or glass, so that it is 
possible to see from outside whether air has gotten into the hydraulic 
oil. Ventilation can be done if needed via a ventilation bore 28. To 
protect the observer, a transparent guard tube 29 is slipped onto the 
upper end of the cylinder head 23 coaxially around the control rod 24. 
A piston collar 31 is disposed on the jacket face of the work piston 2, and 
an annular groove 32 is present in the work cylinder 5, forming an annular 
chamber 33 toward the work piston 2 and having tapers 34 on both of its 
ends, the tapers corresponding to the diameter of the piston collar 31, as 
shown on a larger scale in FIG. 2. As soon as the piston collar 31, toward 
the end of its forward stroke or return stroke, plunges into this taper 
34, it defines a braking chamber, here identified by reference numeral 35. 
The volume of fluid enclosed in this braking chamber is positively 
displaced via a throttle restriction, as described in detail in 
conjunction with FIG. 2. In the exemplary embodiment shown in FIG. 1, the 
plunger piston 9 is disposed coaxially with the step piston 1, and the 
storage piston 21 is disposed parallel to the axes of the storage piston 9 
and step piston 1, but spaced apart from them. According to the invention, 
a bypass 40, shown only in dashed lines, may be disposed between the work 
chamber 16 and the storage chamber 17, 18, in which bypass, via a check 
valve, a flow is possible only in the direction toward the work chamber 
16, while conversely the flow from the work chamber 16 to the storage 
chamber 17, 18 is blocked. 
In the variant of this first exemplary embodiment, shown in FIG. 2, the 
pressure generator that has the plunger piston 109 is disposed parallel to 
the axis of the step piston 1, and the storage chamber 118 is disposed 
coaxially with the plunger piston 109. This creates a relatively large 
work chamber 116, namely between the ring seal 115, into which the plunger 
piston 109 plunges to generate the work pressure, and the upper face end 
of the work piston 102. Although this enlarges the "idle space" in the 
work chamber, nevertheless it has the disadvantage that the pressure 
generator is disposed next to the work cylinder in a space-saving way. 
As shown on the enlarged scale in FIG. 2, the work piston 102 has a head 
part 36, which is connected to the remainder of the work piston 102 by 
screws 37 and in which bypass conduits 38 and 39 are disposed that connect 
the respective braking chamber 35 to the work chamber 116 (in FIG. 1, the 
work chamber 16). Check valves 41, which allow a flow only in the 
direction of the braking chamber 35, are disposed in these bypass conduits 
38, 39, in the region of the orifice toward the work chamber 116. 
Accordingly, as soon as the piston collar 31 plunges into the taper 34 of 
the annular groove 32 and thus defines the respective braking chamber 35, 
no further hydraulic fluid can flow out of this braking chamber 35 into 
the work chamber via these bypass conduits 38, 39. In the drawing, the 
work piston 102 assumes its upper outset position, or in other words its 
position before the onset of the rapid traverse stroke. As soon as the 
work piston 102, via its drive piston 3, is driven pneumatically downward 
via its rapid traverse, hydraulic oil can flow out of the work chamber 116 
into the braking chamber to replenish it, via the bypass conduit 38 or the 
check valve 41 located there, so that in this respect there is no 
hindrance to the drive. As soon as the piston collar 31 has then emerged 
again from the taper 34, a hydraulic communication is established between 
the annular chamber 33 and the work chamber 116, so that the piston collar 
31 is freely movable. As soon as the end of the rapid traverse stroke is 
reached, the subsequently driven plunger piston 109 plunges through the 
ring seal 115 into the work chamber 116 and actuates the work piston 102 
via a corresponding hydraulic high pressure. The action of the 
hydropneumatic pressure intensifier is obtained by the cross-sectional 
difference of the plunger piston 109, of relatively small cross section, 
and the work piston 102 of relatively large cross section. As soon as the 
piston collar 31 then plunges into the lower taper 34, toward the end of 
the work stroke, a braking chamber 35 is formed there. Although the bypass 
conduit 39 branches off from this braking chamber 35, in this direction of 
reciprocation the communication with the work chamber 116 is blocked by 
the check valve 41. Not until the return stroke of the work piston 102 
begins again can hydraulic oil flow into this braking chamber, via the 
check valve 41 and the bypass conduit 39, so as to hinder the rapid 
traverse return stroke accomplished via the drive piston 3. Not until the 
piston collar 31 plunges into the upper taper 34 again is a braking 
chamber 35 formed again there. 
As shown both in FIG. 1 and in the variant of FIG. 2, one relief conduit 42 
and 43 branches off from each of the braking chambers 35 and discharges 
into the annular chamber 33. One throttle valve 44 is disposed in each of 
these relief conduits. Thus as soon as a suitable pressure arises in the 
braking chambers 35 as a result of the piston collar 33, the trapped 
hydraulic fluid is positively displaced back into the annular chamber 33 
upon the upper terminal stroke via the relief conduit 32 and upon the 
lower terminal stroke via the relief conduit 43 and in each case via the 
respective throttle valve 44. Because of this throttling action, damping, 
corresponding to the throttling cross section, of the remaining stroke of 
the work piston 102 is effected. The throttle valve 44 is adjustable in 
cross section, so that this braking or damping action can be adapted to 
the particular tool or to its function. An additional control action can 
be attained by means of a short-circuit conduit 45, which connects the 
annular chamber 33 to the work chamber 116 (16), and whose orifice toward 
the annular chamber 33 is disposed on the jacket face of the piston collar 
31 and is not blocked until after a certain plunging stroke of this piston 
collar 31 into the taper 34. Since this short-circuit bore 35 is 
independent of the braking chamber 35, it has no influence on braking, but 
does have the advantage that when the work piston 102 moves away from the 
upper dead center position shown, in this rapid traverse, a rapid 
equalization of volume can be effected between the annular chamber 33 and 
the work chamber 116. 
FIG. 3 shows a further variant of this first exemplary embodiment, which 
largely corresponds to that of FIG. 2 and is different only in that an 
annular gap is present between the piston collar 31 and the taper 34, by 
means of which gap the desired, but invariable throttling action arises, 
in that hydraulic fluid is positively displaced out of the braking chamber 
35 into the annular chamber 33 upon each reciprocating motion. For some 
uses of the machine tool of the invention, such an invariable but 
nevertheless effected damping of the work piston 102 suffices. Otherwise, 
the variant shown here functions like that of FIG. 2, especially as to the 
short-circuit conduit 45. 
In the second exemplary embodiment shown in FIG. 4, the braking device 
according to the invention is shifted into the region of the piston rod 
104. The other words, such as the work piston 2, plunger piston 9 and 
drive piston 3, are substantially equivalent to the variant of the first 
exemplary embodiment as shown in FIG. 1. This is also true of their 
function. The storage chamber 218, conversely, here is disposed with its 
center axis cross to the axis of the step piston 201, but this has no 
effect on the function of this second exemplary embodiment. The control 
rod 104 here has a piston collar 46, which is movable back and forth in an 
annular chamber 47 of the cylinder barrel 107 and which in the various 
terminal stroke positions defines braking chambers 49 by means of tapers 
48 of the annular chamber 47. Each of these braking chambers 49 have 
respective relief conduits 51, which may for instance communicate with one 
another but in which a throttle device is disposed. The advantage of this 
second exemplary embodiment is above all that the region of the work 
piston, with its alternating hydraulic high pressures, is not touched, and 
that such a damping device can be mounted onto a machine tool in a kind of 
building block system, where only the cylinder barrel 107 or control rod 
104 is correspondingly embodied differently. 
In the third exemplary embodiment, shown in FIG. 5, the braking or damping 
device acts over the entire stroke of the step piston 301. The work piston 
302 is radially sealed off by ring seals 52 toward its work cylinder 305, 
so that the resultant annular chamber 53 acts as a braking chamber, as 
soon as the hydraulic fluid present in this annular chamber 53 is 
throttled via a control conduit 54 and a corresponding device. Otherwise, 
the machine tool functions as described for the first exemplary 
embodiment. 
All the characteristics that can be learned from the specification, claims 
and drawing may be essential to one another but individually and in 
arbitrary combinations with one another. 
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List of Reference Numerals 
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1, 101, 201, 301 Step piston 
2, 202, 302 Work piston 
3 Drive piston 
4, 104 Piston rod 
5, 305 Work cylinder 
6, 106 Tool housing 
7, 107 Cylinder barrel 
8 Cylinder head 
9, 109 Plunger piston 
10 
11 Pneumatic piston 
12 Cylinder barrel 
13 Cylinder head 
14 Chamber 
15, 115 Ring seal 
16, 116 Work chamber 
17 Transverse bore 
18, 118, 218 Storage chamber 
19 Pneumatic cylinder 
20 
21 Storage chamber 
22 Helical spring 
23 Cylinder head 
24 Control rod 
25 Control bore 
26 Control chamber 
27 Screwed nipple 
28 Ventilation bore 
29 Guard tube 
30 
31 Piston collar 
32 Annular groove 
33 Annular chamber 
34 Taper 
35 Braking chamber 
36 Head part 
37 Screws 
38 Bypass conduits 
39 Bypass conduits 
40 Bypass conduits 
41 Check valve 
42 Relief conduit 
43 Relief conduit 
44 Throttle valve 
45 Short-circuit conduit 
46 Piston collar 
47 Annular chamber 
48 Tapers 
49 Braking chamber 
50 
51 Relief conduit 
52 Ring seals 
53 Annular chamber 
54 Control conduit 
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