U.S. patent application number 11/804853 was filed with the patent office on 2007-12-13 for hydraulic unit and method for providing a pressurized hydraulic fluid.
This patent application is currently assigned to Richard Bergner Verbindungstechnik GmbH & Co. KG. Invention is credited to Christian Bohner, Klaus Dehlke, Gerd Hartrampf.
Application Number | 20070286740 11/804853 |
Document ID | / |
Family ID | 50845248 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070286740 |
Kind Code |
A1 |
Dehlke; Klaus ; et
al. |
December 13, 2007 |
Hydraulic unit and method for providing a pressurized hydraulic
fluid
Abstract
An hydraulic unit provides a pressurized hydraulic fluid at an
outlet. The unit has an electric motor and a pump operated by the
motor for generating pressure. A reservoir having a variable
compensation volume stores the hydraulic fluid primed by the pump
in a gas-free manner. The hydraulic fluid is especially pressurized
in order to safely and reliably guarantee that the hydraulic fluid
is gas-free. The inventive design allows for the safe and
operationally reliable use of the hydraulic unit even at high
acceleration values. The hydraulic unit is especially adapted for
use in an industrial robot.
Inventors: |
Dehlke; Klaus; (Windsbach,
DE) ; Bohner; Christian; (Burghaslach, DE) ;
Hartrampf; Gerd; (Abenberg, DE) |
Correspondence
Address: |
LERNER GREENBERG STEMER LLP
P O BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Assignee: |
Richard Bergner Verbindungstechnik
GmbH & Co. KG
|
Family ID: |
50845248 |
Appl. No.: |
11/804853 |
Filed: |
May 21, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP05/10208 |
Sep 21, 2005 |
|
|
|
11804853 |
May 21, 2007 |
|
|
|
Current U.S.
Class: |
417/53 ;
417/410.1 |
Current CPC
Class: |
B21J 15/14 20130101;
B21J 15/32 20130101; B21J 15/043 20130101; B25J 15/00 20130101;
F04B 49/16 20130101; B25J 9/14 20130101; F15B 1/265 20130101; B21J
15/142 20130101 |
Class at
Publication: |
417/053 ;
417/410.1 |
International
Class: |
F04B 17/04 20060101
F04B017/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2004 |
DE |
10 2004 056 046.3 |
Dec 16, 2004 |
DE |
10 2004 061 164.5 |
Sep 21, 2005 |
DE |
10 2005 023 099.7 |
Claims
1-20. (canceled)
21. An hydraulic unit for providing a pressurized hydraulic fluid
at an outlet, comprising: an electric motor; at least one pump for
pressure generation driven by said electric motor; a storage space
configured with a variable compensating volume; and an amount of
the hydraulic fluid enclosed free of gas in said storage space and
fluidically connected to a suction side of said at least one
pump.
22. The hydraulic unit according to claim 21, wherein the hydraulic
fluid is disposed in said storage space with an overpressure.
23. The hydraulic unit according to claim 22, wherein the
overpressure is approximately in a region of several 10.sup.5
Pa.
24. The hydraulic unit according to claim 23, wherein the
overpressure lies between 3 and 50.times.10.sup.5 Pa.
25. The hydraulic unit according to claim 21, wherein said storage
space includes a compensating wall displaceably mounted in form of
a piston and sealing against a stationary housing wall of said
storage space.
26. The hydraulic unit according to claim 25, wherein said
compensating wall is disposed to be subject to a counterforce.
27. The hydraulic unit according to claim 26, wherein said
compensating wall bounds a pressure space with a connection for a
pressure medium on an outside facing away from said storage
space.
28. The hydraulic unit according to claim 26, which comprises a
spring element disposed to generate the counterforce.
29. The hydraulic unit according to claim 28, wherein said spring
element is a securing spring.
30. The hydraulic unit according to claim 21, which comprises a
housing forming an inner housing space, and wherein said electric
motor and said pump are disposed in said inner housing space, and
said inner housing space forms said storage space filled with the
hydraulic fluid.
31. The hydraulic unit according to claim 30, which comprises a
function block disposed to close off said housing and formed with
the outlet, and wherein a plurality of hydraulic components are
integrated in said function block.
32. The hydraulic unit according to claim 31, wherein said function
block is configured for controlling and routing the hydraulic fluid
provided at the outlet.
33. The hydraulic unit according to claim 31, which comprises a
line connecting said pump to said function block, and wherein all
further hydraulic components following said pump are integrated in
said function block.
34. The hydraulic unit according to claim 21, wherein said pump is
one of at least two pumps for providing a low-pressure part stream
and a high-pressure part stream, respectively.
35. The hydraulic unit according to claim 34, wherein said pumps
are jointly driven by said electric motor.
36. The hydraulic unit according to claim 34, which comprises a
valve assembly configured to provide in each case only one part
stream at the outlet.
37. The hydraulic unit according to claim 36, wherein said valve
assembly is configured to enable switching one of the part streams
to pressureless in each case.
38. The hydraulic unit according to claim 21, wherein said electric
motor is a controlled motor for setting a predetermined profile of
the pressure of the hydraulic fluid at the outlet.
39. The hydraulic unit according to claim 21, wherein said electric
motor is a servomotor.
40. The hydraulic unit according to claim 21, which comprises a
connector for connection to a machine tool.
41. The hydraulic unit according to claim 40 connected, via said
connector, to a rivet setting appliance.
42. In combination with a machine part that is subject to
accelerations during operation, the hydraulic unit according to
claim 21 disposed on the machine part.
43. A method of providing a pressurized hydraulic fluid, which
comprises: providing an hydraulic unit and driving a pump of the
hydraulic unit for pressure generation with an electric motor;
supplying the pump with hydraulic fluid from a storage space having
a variable compensating volume, wherein the hydraulic fluid is
stored in the compensating volume free of gas.
Description
[0001] The invention relates to a hydraulic unit and a method for
providing a pressurized hydraulic fluid.
[0002] Hydraulic units are employed in the most diverse possible
technical sectors. In particular, the hydraulic unit is also used
in a machine tool which has to execute an axial movement with high
force during a machining operation. Such a machine tool is, for
example, a press or a punching machine, in which a hole is punched
out or a punching element punched in with the aid of an axially
displaceable ram.
[0003] The hydraulic unit serves, in particular, also in the sector
of riveting technology, for connection to a setting appliance for
setting a rivet, in particular a blind rivet. In the case of a
blind rivet, this is introduced, with its rivet sleeve in front,
from one side into a bore of two components to be connected, until
its setting head comes to lie on the upper component. In the rivet
sleeve, a rivet plug is arranged, which is drawn in the axial
direction with the aid of the setting appliance. In this case, the
rivet sleeve is deformed and forms a closing head, so that the
components to be connected are clamped between the closing head and
setting head. Where specific tensile force is overshot, the plug
tears off, and the operation of setting the blind rivet is
concluded. A continuous pressure build-up occurs during the setting
operation. In this case, first, under low pressures, comparatively
long axial strokes are executed. At the end of the setting
operation until the rivet plug is torn off, high deformation forces
and consequently high pressures must be provided, along with
comparatively low axial strokes. In order to achieve as short cycle
rates as possible, therefore, the hydraulic unit must be capable
both of executing long axial travels quickly and of applying very
high forces.
[0004] In process automation, in particular, for example, in the
automobile industry, efforts are aimed at a fully automated and
monitored blind rivet setting operation with the aid of an
industrial robot. In this case, however, there is a problem that
hydraulic lines have to be led from the fixed hydraulic unit to the
robot and along its robot arms to a rivet setting appliance
fastened to the robot hand. The routing of the hydraulic lines is
difficult under these circumstances. Particularly in confined
workspace situations, for example in body components of a motor
vehicle, there is the additional problem that only very little
space is available to the robot and there is the risk of chafing of
the hydraulic lines on sharp-edged components.
[0005] The object on which the invention is based is to specify a
compact hydraulic unit which can be employed, in particular, in
combination with an industrial robot. The object on which the
invention is based is, furthermore, to specify a method for
providing a pressurized hydraulic fluid.
[0006] The object relating to the hydraulic unit is achieved,
according to the invention, by means of the features of patent
claim 1. Accordingly, a hydraulic unit for providing a pressurized
hydraulic fluid is provided at an outlet of the unit which has an
electric motor and at least one pump for pressure generation,
operated via the electric motor and designed, in particular, as a
piston pump. In this case, for the hydraulic fluid sucked in by the
pump, a storage space with a variable compensating volume is
provided, in which the hydraulic fluid is stored free of gas.
[0007] The invention in this case proceeds from the consideration
that, because of the problems of routing the hydraulic lines along
the robot, it is advantageous for the hydraulic unit to be arranged
directly on the robot, in particular on the robot hand, so that no
hydraulic lines are routed via a movable robot axis. This presents
the problem, however, that, in a conventional hydraulic unit, air
or gas would pass into the hydraulic fluid on account of the
acceleration, so that a reliable and defined hydraulic actuation of
a machine tool, for example of a blind rivet setting head, would
not be possible.
[0008] Owing to the arrangement of the storage volume with a
variable compensating volume in which the hydraulic fluid is
arranged so as to be free of gas, the penetration of air into the
hydraulic fluid and the foaming of the latter are avoided. The
change in a hydraulic volume of the machine tool, occurring during
the operation of the machine tool, leads to a variation in the
compensating volume of the storage space. Here, therefore, in
contrast to conventional hydraulic units, no air is used for volume
compensation in the compensating volume. In the hydraulic unit
proposed here, therefore, rapid movements and, in particular,
abrupt accelerations, for example direction changes, do not lead to
a foaming of the hydraulic fluid.
[0009] The hydraulic unit proposed here is therefore arranged, in
particular, on machine parts which are accelerated during
operation. These are, in particular, the robot hand of an
industrial robot, crane or gripper devices, motor vehicles, in
particular motor trucks, and, for example, mobile entertainment
equipment for amusement parks. When an industrial robot is
concerned, accelerations of, for example, 20 times gravitational
acceleration and above may in this case occur. The mobile hydraulic
unit is capable of executing such high accelerations, without its
functioning capacity being impaired.
[0010] Expediently, in this case, the hydraulic fluid in the
storage space has an overpressure with respect to an ambient
pressure. Foaming is thereby reliably avoided. Preferably, this
overpressure is in the region of a few 10.sup.5 Pa, in particular
between 3 and 50.times.10.sup.5 Pa.
[0011] To form the variable compensating volume, according to an
expedient development a compensating wall of the storage space is
arranged displaceably in the manner of a piston and so as to be
sealed off with respect to a stationary housing wall of the storage
space. This design having the mechanically particularly rigid
compensating wall achieves a very robust construction. Moreover,
the preferred configuration as a piston has the advantage of a
simple construction. The pressure generation unit is therefore
designed in the manner of a piston storage space. Alternatively to
the mechanically rigid configuration, the compensating wall is
designed, for example, as an elastic diaphragm.
[0012] To generate the overpressure in the storage space, in this
case, the compensating wall can expediently be acted upon by a
counterforce or a counterpressure. For this purpose,
advantageously, on the outside facing away from the storage space a
pressure space is provided to which a pressure line can be
connected. The generation of the counterforce therefore takes
place, in particular, pneumatically or else hydraulically. In
principle, a mechanical application of the counter-pressure, for
example by means of a spring element, is also possible. By
contrast, the advantage of pneumatic or hydraulic pressure action
is that the magnitude of the counterpressure can be controlled in a
simple way. The pressure unit for generating the counterpressure is
therefore designed, in the case of pneumatic pressure generation,
in the manner of a media converter, that is to say converts
pneumatic pressure into hydraulic pressure. Preferably, in this
case, the pressure unit is designed in such a way that pressure
intensification is achieved.
[0013] In order, in particular, to ensure reliable operation, in
particular, for example, in the event of an interruption of the
pneumatic line for generating the counterpressure, in a preferred
version a securing spring is additionally provided for generating
the counterpressure. A securing spring is in this context to be
understood, in general, to mean an elastic element which exerts a
fixed elastic restoring force. Preferably, in this case, a spring
element in the actual sense, for example a compression spring, is
employed. Alternatively to the additional arrangement of the spring
element, this is provided instead of the pressure space.
[0014] In order to achieve as compact a construction of the
hydraulic unit as possible, the electric motor and the pump are
arranged in a housing of the unit, and the inner space surrounded
by the housing forms the storage space, that is to say is filled
with hydraulic fluid. The electric motor and the pump are therefore
arranged in the hydraulic fluid, in particular hydraulic oil. The
housing is sealed off, overall, hermetically relative to the
outside. By virtue of this configuration, a separate compensating
vessel is not required. Furthermore, there is no need for any
supply lines from the compensating vessel to a suction-intake side
of the pump.
[0015] Furthermore, with a view to as compact a construction as
possible, the housing is preferably closed by an, in particular,
end-face function block in which a plurality of hydraulic
components are integrated. Hydraulic components of this type are,
for example, hydraulic lines and valves. The function block
therefore forms a cover of the housing and consequently of the
unit. By the hydraulic components being integrated into the cover,
there is no need for a separate space requirement for these
components and the unit overall can have a very compact
construction.
[0016] Expediently, the function block is designed for controlling
and routing the hydraulic fluid provided at the outlet. For this
purpose, a multiplicity of lines and also hydraulic control
elements, such as valves, are arranged in the function block. The
function block therefore serves, for example, for shutting off or
releasing the pressurized hydraulic fluid generated by the
pump.
[0017] Preferably, the pressure side of the pump is connected via a
line to the function block. All further hydraulic components
following the pump on the pressure side are integrated in the
function block. By all the hydraulic function elements being
arranged within the function block, the construction of the
remaining unit is kept comparatively simple and robust.
[0018] According to a particularly preferred embodiment, at least
two pumps are provided for the provision, on the one hand, of a
low-pressure part stream and, on the other hand, of a high-pressure
part stream of the hydraulic fluid. A two-stage hydraulic unit is
thus provided. The advantage of this is that different pressure
stages are provided at a low energy outlay as a function of the
respective application. Different pressure requirements are
therefore served simply and in an energy-saving way. Particularly
in a blind rivet setting operation, there is no need for high
pressure to be provided at the commencement of the setting
operation.
[0019] Expediently, the at least two different pumps are actuated
jointly by the electric motor. A plurality of hydraulic part
streams of different pressures and/or of different feed quantities
are therefore generated via one and the same electric motor, so
that the most diverse possible pressure requirements can be
fulfilled by means of only one electric motor and therefore in a
highly space-saving way. Particularly in two-stage or multistage
machining operations in which different pressure requirements are
demanded within one operation, this embodiment is of particular
advantage. For example, long axial strokes must be executed at only
low pressure and short axial strokes at high pressure, as, for
example, in a blind rivet setting operation.
[0020] Expediently, in this case, the pumps are actuated jointly
via an eccentric shaft of the electric motor and are therefore
arranged approximately annularly around the eccentric shaft. The
pumps are therefore actuated directly by the electric motor,
without a gear being interposed. In the provision of two hydraulic
part streams, in this case, expediently a plurality of pumps are
provided for generating the low pressure part stream and a
plurality of pumps are provided for generating the high-pressure
part stream, a pump for the high-pressure part stream and a pump
for the low-pressure part stream preferably being alternately
adjacent to one another.
[0021] Preferably, furthermore, a valve arrangement for controlling
the at least two part streams is provided, which is designed in
such a way that in each case only one part stream is provided at
the outlet of the hydraulic unit. There is therefore no need for
any external control valves outside the unit for changing over from
one part stream to the other part stream, so that, overall, a
compact construction is achieved. The valve arrangement is in this
case designed, in particular, in such a way that an automatic
changeover between the part streams takes place as a function of
the current pressure requirement.
[0022] This valve arrangement is in this case integrated, in
particular, in the function block. Preferably, the valve
arrangement has a pressure switching valve which automatically
switches off the low-pressure part stream when a predeterminable
pressure of the hydraulic fluid provided at the outlet is
overshot.
[0023] In order to keep energy necessary for generating the
pressure as low as possible, furthermore, the valve arrangement is
preferably designed in such a way that in each case one of the part
streams can be switched to pressureless. There is therefore
provision, in particular, for in each case one of the part streams
to be pressureless during operation. The electric motor therefore
needs to build up pressure in only one part stream and can
therefore have a lower-power and compact design.
[0024] According to an expedient development, the electric motor is
controllable and, in particular, regulatable. The electric motor is
in this case started only as required, that is to say when there is
a pressure requirement. The pressure is therefore generated, only
as required, in an energy-saving way without a pressure
accumulator.
[0025] Preferably, in this case, the electric motor is regulated to
a constant rotational speed. A constant stream of hydraulic fluid
is thereby provided. In particular, in addition to this, the
electric motor is regulated to a constant torque, so that a
specific pressure, for example a limited maximum pressure, is
generated and maintained. Torque regulation is advantageous
particularly in the case of a 0-travel stroke, that it is to say,
for example, when, during the operation of setting a blind rivet, a
setting or forming force has to be maintained without or virtually
without a movement of the blind rivet.
[0026] The advantage of controlling the pressure via the electric
motor is to be seen, in particular, in that no pressurized
hydraulic fluid has to be stored. There is therefore no pressure
storage volume provided between the pump for generating the
pressure in the hydraulic fluid and the outlet. The generation of
pressure therefore takes place instantaneously, that is to say
without a buffer or the like, by the electric motor being started
up and controlled. The pressure is provided very quickly at the
outlet via the regulation of the electric motor.
[0027] The electric motor is expediently designed, in particular,
as a servomotor.
[0028] Furthermore, the object is achieved, according to the
invention, by means of a method for providing a pressurized
hydraulic fluid according to patent claim 20. The advantages and
preferred embodiments listed with regard to the hydraulic unit are
also to be applied accordingly to the method.
[0029] The hydraulic unit described here is distinguished, on the
one hand, by its mobility, that is to say the hydraulic unit can be
moved and accelerated very quickly, without its functioning
capacity being impaired, and is therefore functionable, in
particular, even independently of position. Owing to this property,
the hydraulic unit is suitable, in particular, for arrangement on
an industrial robot and there is, in particular, part of an
exchangeable robot hand. Owing to arrangement directly on the robot
hand, the hydraulic lines to the machine tool, for example a
setting tool, are reduced to the necessary minimum amount, so that
damage to these on account of the movements of the robot arms is
not to be feared.
[0030] Furthermore, by virtue of the compact configuration, even
confined workspaces are accessible.
[0031] The hydraulic unit described here is distinguished, on the
other hand, by its highly compact construction, at the same time
with the generation of very high pressures. Expediently, the
hydraulic unit has an approximately cylindrical housing which has a
length of only about 30-40 cm, with a diameter of about 12 cm. At
the same time, the hydraulic assembly is provided for the
provision, in particular, of the two pressure part streams, the
low-pressure part stream being provided, for example, for about
200.times.10.sup.5 Pa and the high-pressure part stream preferably
being provided for 500.times.10.sup.5 Pa. Even with an overall
construction space of 3000 to 10 000 ccm, therefore, a mobile
hydraulic unit is afforded which makes it possible to have two
hydraulic part streams with 100 to 300 bar and 300 to 700 bar
pressure. The overall volume of the hydraulic fluid within the
hydraulic unit in this case preferably amounts to only about 500
ml. The hydraulic unit is therefore distinguished by a high power
density along with the use of low energy. Since no pressure
limiting valves of any kind are provided and the hydraulic unit is
operated in switch-off mode, that is to say only when there is
actually a pressure requirement, only low energy losses occur and
the necessary use of energy is low. This makes it possible to use a
comparatively low-power and compact electric motor.
[0032] An exemplary embodiment of the invention is explained in
more detail below with reference to the drawings, in which, in each
case in diagrammatic illustrations:
[0033] FIG. 1 shows a longitudinal section through a hydraulic
unit,
[0034] FIG. 2 shows a view of the front end face, designed as a
function block, of the hydraulic unit,
[0035] FIG. 3 shows a view of the rear end face of the hydraulic
unit, and
[0036] FIG. 4 shows a hydraulic diagram of the hydraulic unit.
[0037] Identically acting parts are given the same reference
symbols in the figures.
[0038] The hydraulic unit 2 illustrated in FIGS. 1 to 3 has,
overall, an essentially cylindrical housing 4, the inner space of
which forms a storage space 5 for the hydraulic fluid and is sealed
off hermetically. The housing 4 is closed on its left end face by
means of a control or function block 6 designed in the manner of a
housing cover. On its right end face lying opposite the function
block 6, the hydraulic unit 2 has a compensating block 8 which
closes the housing 4 on the rear end face. A pressure generation
block 10 is arranged between these two blocks 6, 8. As is evident
from the figure, the individual housing components of the hydraulic
unit 2 are fastened to one another by means of screw connections.
At the parting planes or parting points of two components, which
are in each case in the form of metallic components, in each case
sealing elements 12 are provided, so that a hermetic sealing off of
the overall inner space 5 with respect to the surroundings is
achieved.
[0039] The pressure generation block 10 is formed essentially by a
suboil electric motor 14, designed as an alternating current
servomotor, and by a plurality of pumps 16 designed as piston
pumps. The electric motor 14 has a stator 14A with a stator winding
and a rotor 14B with a permanent magnet. Provided on the rotor 14B,
on its end face, is an eccentric shaft 18, the axis of which is
arranged so as to be offset radially with respect to the rotor axis
20. The pumps 16 arranged annularly around the eccentric shaft 18
are actuated alternately via the eccentric shaft 18. The piston of
the respective piston pump 16 is actuated via the eccentric shaft
18 for the suction intake and expulsion of the hydraulic oil. A
bearing 22 is arranged between the eccentric shaft 18 rotating
during operation and the stationary pumps 16.
[0040] Each of the pumps 16 is followed on the pressure side by a
pressure line 24 which leads to the function block 6. The pressure
line 24 is in this case formed by a duct worked into the housing
wall. The suction side of the pumps 16 is connected in each case to
the inner space 5 in which the hydraulic oil is located.
[0041] In the exemplary embodiment, six pumps 16 overall are
arranged annularly around the eccentric shaft 18, alternately
adjacent pumps 16 being provided for generating two different
pressures, to be precise a low pressure of the magnitude of about
200.times.10.sup.-5 Pa and a high pressure of the magnitude of
about 500.times.10.sup.-5 Pa.
[0042] The function block 6, designed as a solid metal cover, has a
thickness d which amounts, for example, to about 10% of the overall
length 1 of the hydraulic unit 2. A multiplicity of ducts for
forming hydraulic lines 28 and bores 30 for arranging hydraulic
valves are introduced into the function block 6, so that the
function block forms a valve block.
[0043] The arrangement of the individual hydraulic lines 28 and of
the bores 30 or the valves is also apparent, in particular, from
the end view according to FIG. 2, in which the hydraulic lines 28
and the bores 30 are illustrated by broken lines. As can be seen
from this, a multiplicity of bores 30 and consequently hydraulic
valves are provided. Of these, a directional seat valve 32A and a
pressure switching valve 32B can be seen in FIG. 1. Furthermore, on
the top side, a filling or top-up valve 32C is provided, via which
the storage space 5 can be filled. Moreover, a venting valve 32D is
arranged on the end face. A further orifice 34, which is open only
during filling with the hydraulic fluid, serves for pressure
compensation during filling.
[0044] All the hydraulic control elements are therefore integrated
in the function block 6. Via the function block 6, the hydraulic
oil provided at an outlet 36A, B (cf. FIG. 4) is controlled, that
is to say, via the function block 6, the hydraulic pressure at the
outlet 36A, B is controlled. Hydraulic control elements are no
longer required thereafter. Instead, a hydraulic line can be linked
directly to the outlet 36 and be connected to a corresponding
hydraulic inlet on a example a blind rivet setting tool 38
functioning of the function block 6 and the significance of the
individual valves are also apparent, in particular, from the
description of the hydraulic diagram according to FIG. 4.
[0045] The compensating block 8 comprises an annular or cylindrical
housing wall which is formed by the housing 4 and which forms a
cylinder 40 open to the inner space. A piston 42 forming a
compensating wall is arranged with an exact fit in this cylinder
40. The piston 42 is sealed off with respect to the inner wall of
the cylinder 40 by means of sealing elements 12 and is arranged so
as to be displaceable in the longitudinal direction in relation to
the cylinder 40. The piston 42 is designed as a hollow piston
which, like the cylinder 40, widens in a step-shaped manner, as
seen in cross section. The cavity of the piston 42 forms a pressure
space 44 which can be acted upon with a predeterminable pressure
via a pneumatic connection 46 (cf. FIG. 3). The pressure space 54
is delimited on the rear side by a fixed end wall 48 of the
housing. A securing spring 50 designed as a compression spring is
supported on the end wall 48 and exerts a pressure force on the
piston 42. The configuration illustrated affords a pressure
intensifier and media converter.
[0046] To operate the hydraulic unit 2, the inner space 5 is filled
completely with a hydraulic fluid, in particular hydraulic oil, so
that the electric motor 14 and, with it, the pumps 16 are mounted
in hydraulic oil. Complete venting takes place via the venting
valve 32D, so that the overall inner space 5 is free of gas and of
air. In order to maintain this reliably, a counterpressure of about
5-15.times.10.sup.-5 Pa is generated in the pressure space 44 via
the pressure compensating block 10 by the application of a
corresponding pneumatic pressure. The overall housing inner space 5
is therefore under an overpressure. Furthermore, filling level
monitoring, not described in any more detail here, is provided, so
that an automatic check of the hydraulic oil quantity is carried
out.
[0047] To provide the hydraulic fluid at the outlets 36A, B under
high pressure, the electric motor 14 is started, as required. That
is to say, the hydraulic pressure is generated only when there is
actually a requirement for this, that is to say when the blind
rivet is already introduced into the blind rivet hole and the
setting operation commences by drawing on the rivet plug. There is
no pressure vessel provided. The eccentric shaft 18 is set in
rotational movement via the electric motor 14, so that the
individual pumps 16 are actuated alternately and in rotation and in
each case convey a predefined quantity of hydraulic fluid into the
pressure line 24 and consequently to the function block 6.
[0048] Since the hydraulic quantities in the inner space 5 vary
during operation, the volume of the inner space 5 can be varied in
order to avoid the occurrence of gas bubbles in the hydraulic
fluid. The volume of the inner space 5 therefore forms a
compensating volume and the inner space 5 forms a storage space. To
vary the volume, the piston 42 moves automatically within the
cylinder 40 according to the respective current requirements.
[0049] The operation of the setting tool 38 via the hydraulic unit
2 may be gathered from the hydraulic diagram according to FIG. 4.
This illustration illustrates, on the right half of the figure, the
compensating block 8, following this the pressure generation block
10 and, again following this, the function block 6. The setting
tool 38 is acted upon by the pressurized hydraulic oil via two
outlets 36A, B and supply lines 52A, B.
[0050] The pumps 16 are arranged in the pressure generation block
10, in this case three of the pumps 16 being combined to form a
high-pressure part stream 54 and three further pumps 16 being
combined to form a low-pressure part stream 56. A plurality of
nonreturn valves 58 which in each case permit the throughflow of
the hydraulic oil in the direction of the arrow only may be
gathered from the hydraulic diagram. Furthermore, the pressure
switching valve 32B, already mentioned with regard to FIG. 1, two
controllable directional seat valves 33A, B and two safety valves
60A, B are arranged.
[0051] To start the riveting operation, the electric motor 14 is
switched on, so that a hydraulic pressure is provided both in the
high-pressure part stream 54 and in the low-pressure part stream
56. The high-pressure part stream 54 is routed via the safety
valves 60A and via the directional seat valves 33A which are
illustrated on the right half of the figure. The directional seat
valve 33A is in this case activated in such a way that the
throughflow for the high-pressure part stream 54 is opened as long
as a predeterminable pressure is not overshot at the outlets 36A,
B. With the directional seat valve 33A open, the high-pressure part
stream 54 issues immediately into the housing inner space 5, so
that no pressure build-up can occur on the high-pressure side and
the part stream 54 is switched to pressureless. The low-pressure
part stream 56 is fed via the nonreturn valve 58 and via the supply
line 52A to the setting tool 38. The latter has an axially
displaceable piston element 62 which, by being acted upon by the
low-pressure part stream 54, moves to the right at the commencement
of the setting operation. In this first phase of the setting
operation, comparatively long travels are covered at only low
pressures. An alignment of the blind rivet in the blind rivet hole
and a first forming take place in this phase.
[0052] To operation of forming the blind operation, the directional
seat valve 33A is activated and closed, so that the high pressure
at the outlet 36A to the supply line 52A builds up in succession in
the MS range. The pressure switching valve 32B is in this case
designed in such a way that it switches automatically at a
predetermined pressure, for example at a pressure of 80 bar, so
that the low-pressure part stream 54 is switched free to the inner
space 5 and is consequently switched to pressureless. The pressure
supply in this case takes place via the high-pressure part stream
54. Via the nonreturn valve 58 in the high-pressure part stream 54,
the latter is provided at the outlet 36 to the supply line 52A.
[0053] During the setting operation, the further directional seat
valve 33B, which is connected to the second supply line 52B via the
second outlet 36B, is in the state shown in FIG. 4. That is to say,
the supply line 52B is connected via the directional seat valve 33B
to the inner space 5 in the manner of a return line.
[0054] After the end of the setting operation, that is to say after
the rivet plug has been torn off, the high-pressure part stream 54
is switched to pressureless again due to the switching of the
directional seat valve 33A. Owing to the pressure drop caused
thereby, the pressure switching valve 32B switches on the
low-pressure part stream 56 automatically again.
[0055] For the restoring movement required after the setting
operation, the directional seat valve 33B is switched so that, as
illustrated, the part streams 54, 56 provided by the pumps 16, in
particular the low-pressure part stream 54, in this case prevail
both on the right side of the piston element 62 and on the left
side in exactly the same way. Owing to the selected larger
cross-sectional area on the right side of the piston element 62,
the latter is pushed to the left back into the initial position
again.
[0056] Moreover, for protective purposes, the high-pressure part
stream 54 is connected to the housing inner space 5 via the safety
valve 60A. This safety valve 60A switches, for example, when a
pressure of 400.times.10.sup.-5 Pa is overshot. The safety valve
60B, illustrated on the left, is provided for protecting the
pressure prevailing in the inner space 5. This safety valve 60B
switches, for example, when a pressure of 25.times.10.sup.5 Pa is
overshot.
LIST OF REFERENCE SYMBOLS
[0057] 2 Hydraulic unit [0058] 4 Housing [0059] 5 Inner space
[0060] 6 Function block [0061] 8 Compensating block [0062] 10
Pressure generation block [0063] 12 Sealing element [0064] 14
Electric motor [0065] 14A Stator [0066] 14B Rotor [0067] 16 Pump
[0068] 18 Eccentric shaft [0069] 20 Rotor axis [0070] 22 Ball
bearing [0071] 24 Pressure line [0072] 26 Suction line [0073] 28
Hydraulic line [0074] 30 Bore [0075] 33A, B Directional seat valve
[0076] 32B Pressure switching valve [0077] 32C Top-up valve [0078]
32D Venting valve [0079] 34 Orifice [0080] 36, 36A, B Outlet [0081]
38 Setting tool [0082] 40 Cylinder [0083] 42 Piston [0084] 44
Pressure space [0085] 46 Pneumatic connection [0086] 48 End wall
[0087] 50 Securing spring [0088] 52A Supply line [0089] 52B Supply
line [0090] 54 High-pressure part stream [0091] 56 Low-pressure
part stream [0092] 58 Nonreturn valve [0093] 60A, B Safety valve
[0094] 62 Piston element [0095] d Thickness [0096] 1 Overall
length
* * * * *