U.S. patent application number 13/737147 was filed with the patent office on 2013-07-11 for neutral setting device for an adjustable hydraulic machine.
This patent application is currently assigned to SAUER-DANFOSS GmbH & Co. OHG. The applicant listed for this patent is SAUER-DANFOSS GmbH & Co. OHG. Invention is credited to Peter BAHNA, Sebastian BUJNA, Peter CHEBLANA, Miroslav CHMATIL, Michael KNAZEK, Reinhardt THOMS.
Application Number | 20130174925 13/737147 |
Document ID | / |
Family ID | 48652631 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130174925 |
Kind Code |
A1 |
BAHNA; Peter ; et
al. |
July 11, 2013 |
NEUTRAL SETTING DEVICE FOR AN ADJUSTABLE HYDRAULIC MACHINE
Abstract
The invention relates to a neutral setting device of an
adjustable hydraulic machine, in particular the adjustment of the
neutral setting of a servo valve. The present invention relates in
particular to servo adjustment devices with mechanically adjustable
control pistons, wherein the necessary force can be applied
mechanically, electromagnetically, pneumatically or hydraulically.
The invention relates to a neutral setting device of an adjustable
hydraulic machine with a housing in which a mounted input shaft is
arranged, at which on one end a torque can be applied for turning
the input shaft around an axis. On a second end a cylindrical
extension is arranged eccentrically parallel to the axis. An
adjustable control piston for opening and closing hydraulic fluid
openings for application of pressure of a servo piston adjusts the
hydraulic machine with respect to its delivery volume.
Inventors: |
BAHNA; Peter; (Pruzina,
SK) ; BUJNA; Sebastian; (Dubnica nad Vahom, SK)
; CHEBLANA; Peter; (Nova Dubnica, SK) ; CHMATIL;
Miroslav; (Nova Dubnica, SK) ; KNAZEK; Michael;
(Nemsova, SK) ; THOMS; Reinhardt; (Holzbunge,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAUER-DANFOSS GmbH & Co. OHG; |
Nuemunster |
|
DE |
|
|
Assignee: |
SAUER-DANFOSS GmbH & Co.
OHG
Nuemunster
DE
|
Family ID: |
48652631 |
Appl. No.: |
13/737147 |
Filed: |
January 9, 2013 |
Current U.S.
Class: |
137/561R |
Current CPC
Class: |
Y10T 137/8593 20150401;
F15B 13/04 20130101; F04B 49/12 20130101 |
Class at
Publication: |
137/561.R |
International
Class: |
F04B 49/12 20060101
F04B049/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 9, 2012 |
DE |
10 2012 200 217.0 |
Claims
1. A neutral setting device (1) of an adjustable hydraulic machine
with a housing (2), in which are arranged: an input shaft (3)
mounted in the housing (2) with a first end (3a), at which a torque
can be applied for turning the input shaft (3) around an axis (23),
and a second end (3b), at which a cylindrical extension (25)
eccentrically parallel to the axis (23) is arranged, an adjustable
control piston (4) for opening and closing hydraulic fluid openings
for application of pressure of a servo piston (24), which adjusts
the hydraulic machine with respect to its delivery volume, a lever
(5), with a first end (5a) and a second end (5b) as well as with a
bearing position (5c) arranged between the two ends (5a, 5b), in
which the cylindrical extension (25) of the input shaft (3)
engages, wherein the first end (5a) of the lever (5) is connected
in an articulated manner to the control piston (4) and the second
end (5b) of the lever (5) is mounted in an articulated manner on a
position feedback device (6), which transfers the position of the
servo piston (24) to the lever (5), a sliding part (8), which
exhibits a planar face (8a) on one end, with which it is supported
against a planar flattened portion (7a) on the input shaft (3),
wherein the sliding part (8) is elastically prestressed
perpendicular to the axis (23) of the input shaft (3) and is held
by a guide element (10) in such a way that the sliding part (8) can
be moved perpendicular to the axis (23) of the input shaft (3)
relative to the guide element (10) and the planar face (8a) and the
planar flattened portion (7a) in neutral position of the control
piston (4) lie flat upon one another, characterized in that the
guide element (10) is supported vis-a-vis the housing (2) in such a
way that the guide element (10) can be rotated in circumferential
direction of the input shaft (3) relative to said shaft.
2. The neutral setting device (1) according to claim 1, in which
the guide element (10) through a setting screw (11) which is
arranged perpendicular to the direction of movement of the sliding
part (8) and perpendicular to the axis (23) of the input shaft (3)
and which supports the guide element with one end (11a) vis-a-vis
the housing (2) and engages in the guide element (10) in such a way
that the guide element (10) is rotatable by turning the setting
screw (11) in circumferential direction of the input shaft (3)
relative to said shaft.
3. The neutral setting device (1) according to claim 2, in which
the end (11a) of the setting screw (11) in engagement with the
guide element (10) is spherical and engages in a corresponding
recess (10a) on the guide element (10) and supports itself in a
groove (16) in the housing (2) which is constructed on an inside
wall (13) of the housing (2) parallel to the axis (23).
4. The neutral setting device (1) according to claim 1, in which
the guide element (10) exhibits a pot-like bore into which the
sliding part (8) is guided and upon whose floor area an elastic
element (9) is supported, which prestresses the planar face (8a) of
the sliding part (8) against the planar flattened portion (7a) on
the input shaft (3).
5. The neutral setting device (1) according to claim 1, in which
the planar flattened portion (7a) is constructed on the input shaft
(3) in a recess (7) of the input shaft (3).
6. The neutral setting device (1) according to claim 5, in which
the end of the sliding part (8) is constructed on the face (8a),
providing with the recess (7) in the input shaft (3) an axial guide
of the input shaft (3).
7. The neutral setting device (1) according to claim 1, in which
the input shaft (3) exhibits a circumferential groove (20) into
which the guide element (10) engages with fork shaped ends (10a,
10b), as a result of which the guide element (10) is connected to
the input shaft (3) in an axially fixed manner.
8. The neutral setting device (1) according to claim 1, in which
the sliding part (8) exhibits an elastically mounted ball (28) on
the end at which the planar face (8a) is constructed, said ball in
neutral position of the control piston snapping into a
corresponding recess (30) in the input shaft (3).
9. The neutral setting device (1) according to claim 1, in which
the hydraulic machine is integrated in a closed hydraulic
circuit.
10. The neutral setting device (1) according to claim 1, in which
the input shaft (3) can be rotated mechanically or
electromagnetically.
Description
[0001] The invention relates to a neutral setting device of an
adjustable hydraulic machine in accordance with the preamble of
Claim 1. The invention relates in particular to the adjustment of
the neutral setting of a servo valve. The invention relates in
particular to hydrostatic adjustment devices of hydraulic machines
in which case both the delivery volume and the delivery direction
are adjustable. The present invention relates in particular to
servo adjustment devices with mechanically adjustable control
pistons, wherein the forces necessary for this purpose can be
applied mechanically, electromagnetically, pneumatically or
hydraulically. A generic device is known from DE 41 25 706 C1,
whose features constitute the preamble of Claim 1.
[0002] Hydraulic servo valves are used in variable designs for the
adjustment of the delivery volume of hydraulic pumps. In the
process a servo piston is controlled via such a servo valve with
hydraulic fluid or has hydraulic pressure applied so that the servo
piston adjusts the actual adjustment device of the hydraulic
machine, such as for example the swash plate of an axial piston
machine. The invention can be used for servo valves of this type.
Additional fields of application are for example the control of
radial piston machines whose eccentricity is adjustable, or for
example bent axis pumps which can be modified in their power or
also delivery direction by deflection of a burden. Normally the
servo pistons which act on the adjustment devices of the hydraulic
machines are centered via springs in their zero position, as a
result of which in the case of balanced pressure conditions for
example on a double-sided servo piston, the delivery flow of the
hydraulic machine is zero. This is also known from the generic
device according to DE 41 25 706 C1, whose features constitute the
preamble of Claim 1.
[0003] The delivery volume zero corresponds to machine downtime,
i.e. the hydraulic machine neither receives power nor emits it.
This machine downtime is of safety significance and must therefore
be precisely definable by the servo valve device. The control
piston in the servo valve responsible for the pressures on the
servo piston controls the respective hydraulic pressures to the
servo piston or pistons via its control edge, which is why the
hydraulic neutral position of the control piston in the control
cylinder, thus its position for the machine downtime of the
hydraulic machine necessarily must be precisely adjustable.
[0004] However, in practice both the control piston in its diameter
and its control edges as well as the control cylinder in its
diameter and its corresponding control edges are subject to
tolerances in production, as a result of which the neutral position
of the control piston in the control cylinder usually deviates from
the constructive predefined central position or the geometrically
centered location. Thus if one wants to strictly geometrically
center the control piston of a servo valve in the control cylinder
of the servo valve, an asymmetrical application of pressure of for
example a two-sided servo piston cannot be ruled out. As a result
of this the servo piston moves and the adjustable hydraulic machine
would be outside of the zero position and machine downtime could
not be achieved. Hence a mechanism for neutral setting is necessary
to compensate the position error of the control piston in the
control cylinder caused by production tolerances so that the
hydraulic machine facilitates the zero position of the servo piston
in the hydraulic neutral position of the control piston and thus
machine downtime can be achieved.
[0005] By means of a neutral setting-adjustment it is ensured that
in the case of a reported position of the servo system in which the
hydraulic machine does not produce any delivery flow, no control
signal counteracting this state is generated in the servo valve.
Otherwise the setting of the control piston in the servo valve does
not match the setting of the servo piston in the adjustment device
for the hydraulic machine. In such a case machine downtime can
never be achieved, since one of the two pistons is always outside
of the hydraulic center. A neutral adjustment for the servo valve
has the task of centering the control piston in the servo valve in
the case of machine downtime in such a way in the control cylinder
that through suitable control edge overlaps with appropriate
control edge gaps no fluid flows or servo pressures arise that
would bring the servo piston of the adjustable hydraulic machine
out of balance against the spring forces.
[0006] Mechanically actuated servo valves are as a rule controlled
via Bowden cables or rod systems in order to regulate the delivery
volume of the adjustable hydraulic machine in both delivery
directions. This mechanical control should have the most equal
reaction possible for both delivery directions. As a result of this
the need arises for a symmetrical, that is equally great in both
delivery directions but respectively small dead band within which
the pump does not produce any delivery volume. Simultaneously the
maximum delivery volumes of the two delivery directions of the
adjustable hydraulic machine should be achieved in the case of an
equally great input signal. In particular for mechanical
adjustments this means that the deflection of the control device in
one direction should be precisely as great in amount as in the
other direction so that the delivery power generated by the
adjustable hydraulic machine or received by the adjustable
hydraulic machine is equally great for both delivery directions. In
particular a forward-reverse driving or a left-right pivoting is to
be thought of here, which should take place with the same power. In
a known design for a mechanical drive of a servo valve by means of
for example a Bowden cable or a rod system a torque acts on an
input shaft on the servo valve in order to turn said input shaft in
the one or other direction. For different reasons, in particular
for safety reasons and for reasons of user friendliness, this input
shaft must always autonomously strive to return to its neutral
position. By way of illustration the machine operator expects that
the deflected control lever autonomously swivels back to the
neutral position after being released. This can for example be
achieved by a permanently acting spring force in the servo
valve.
[0007] In the case of a design of such a neutral setting mechanism
known from DE 41 25 706 C1the input shaft, which can be turned
mechanically in two directions, exhibits a flattened portion upon
which a spring-loaded spring-loaded, guided sliding part acts. The
sliding part exhibits a likewise planar surface on the contact
surface between the flattened portion and the face of the sliding
part, as a result of which in the event of the turning of the input
shaft from the neutral position a lateral contact on the flattened
portion of the input shaft occurs. The outer axial force through
the spring action which acts on the sliding part generates an
aligning torque on the input shaft. This aligning torque attempts
to move the input shaft back to its neutral position in which the
two areas, that is the planar face of the sliding part and the
planar flattened portion on the input shaft lie flat or planar on
one another. In this planar, flat contact the spring action acts
directly in the direction of the axis of the input shaft, so that
no torque is generated by the spring action. Through the flat
contact of the sliding part on the flattened portion of the input
shaft, regardless of the direction of rotation of the shaft the
sliding part is shifted away from the axis of the input shaft, to
be precise always in the same direction against the springs. As a
result of that, torque acting in the one or other direction is
generated in the case of the deflection of the input shaft. If the
deflection torque on the input shaft is lower than the torque which
is generated by the shifted sliding part via the flattened portion
on the input shaft, the input shaft rotates by itself back to its
neutral position. For the setting/adjustment of the neutral
position of the servo valve the known design proposes shifting the
connecting lever which connects the input shaft to the control
piston beyond its eccentric relative to the position feedback
device. With this the control piston in the control cylinder
occupies a neutral position for the servo adjustment, regardless of
the position of the input shaft. The signal forwarded by the
position feedback of positioning the adjustment device of the
hydraulic machine is thus adapted to the control piston
position.
[0008] However, with this, since the neutral position of the servo
piston in the servo cylinder in most cases does not correspond to
the geometric center, the deflection capability of the control
piston in one direction is less than the deflection capability of
the control piston in the other direction, which in the two
delivery directions leads to differing delivery volumes. In the end
result this leads to an asymmetrically adjustable hydraulic
machine. The greater the position error to be corrected between the
servo valve, i.e. the control piston in the control cylinder and
the involved levers as well as the involved guides, the greater the
asymmetry between the input signal and the delivery flows in both
delivery directions. In the process there are different capacities
in the one or other delivery direction, since the maximum delivery
volumes of the hydraulic fluid which can be achieved in the one
delivery direction or other delivery direction are different.
[0009] The invention therefore addresses the problem of providing a
device for setting the neutral position of servo valves for
adjustable hydraulic machines which ensures the neutral position of
the control device in the event of machine downtime and in addition
guarantees a balance of the delivery volumes in both delivery
directions.
[0010] The problem addressed by the invention is solved with a
neutral setting device in accordance with the features from the
characterizing part of Claim 1 by having the guide element
supported against the housing in such a way that the guide element
is rotatable in the circumferential direction of the input shaft
relative to said input shaft. Preferred embodiments are specified
in the subsidiary claims dependent on Claim 1.
[0011] In order to obtain the balance of the servo valve with
respect to a potential dead band and the maximum delivery volume
regardless of the neutral setting, the input shaft, the sliding
part and the control piston must be aligned jointly and
simultaneously to the neutral setting, so that between the control
piston and control cylinder the necessary control edge overlaps or
the corresponding control edge gaps arise, so that an equally great
deflection capability of the input shaft on both sides is
retained.
[0012] In accordance with the invention this is achieved with a
neutral setting device of an adjustable hydraulic machine with a
housing, in which an input shaft is pivoted, at which on a first
end a torque can be applied for timing the shaft around its central
axis. The torque can for example be applied via a control lever.
The shaft is preferably arranged with a first end outside of the
housing, wherein its second end protrudes into the servo housing.
On the second end protruding into the servo valve housing a
cylindrical extension is arranged eccentrically to the central
axis, parallel to it, said extension being able to move in a
circular path with the input shaft. In the servo valve housing
there is further arranged an adjustable control piston which with
its control edges in cooperation with the control edges of a
control cylinder control the fluid openings to a servo piston, said
servo piston in turn setting the hydraulic machine with respect to
its delivery direction and/or delivery volume. A lever is arranged
for transfer of the deflections of the input shaft to the control
piston, said lever being connected in an articulated manner with
its end to the control piston and with its second end being mounted
in an articulated manner at the position feedback device, which
transfers the position of the servo piston to the lever. This
position is transferred then from the lever to the control piston.
Between the two ends of the lever a bearing position is provided
for the reception of the cylindrical extension of the shaft, via
which the lever can transfer the deflection of the input shaft to
the control piston.
[0013] Thus, in the event of the deflection of the input shaft the
cylindrical extension is moved on a circular path, as a result of
which the articulated, in particular rotatable lever mounted on the
bearing position likewise moves in a type of circular path, which
shifts the control piston in the control cylinder in the servo
valve housing. Through the shifting of the control piston in the
control cylinder the openings for hydraulic fluid are altered for
control of the servo piston, as a result of which the servo piston
is deflected in its position and the hydraulic machine is adjusted.
With the eccentric arrangement of the cylindrical extension on the
shaft a rotary deflection movement on the input shaft is converted
to a translational movement of the control piston, with which the
adjustable hydraulic machine can be controlled.
[0014] In addition a sliding part is arranged in the servo valve
housing, said sliding part being held elastically in a guide
element and being able to move perpendicular to the axis of the
input shaft. The sliding part is elastically mounted in the
direction of movement and exhibits on one end a planar face with
which the sliding part can be supported against a planar flattened
portion on the input shaft. In the process the support through the
elastic mounting is pre-stressed. The cooperation of the
flat/planar face of the sliding part with the flat flattened
portion, which is constructed on the input shaft, in this
connection acts in the same manner as is known from the initially
described exemplary embodiment from the prior art. The guide
element receives the other end of the sliding part and provides a
guide perpendicular to the axis of the input shaft for the sliding
part. The sliding part can be pushed away against an elastic force
from the shaft along this direction of movement or moved by this
elastic force to the shaft. If the shaft is turned, the flattened
portion of the shaft presses the sliding part against the spring
force for example into the guide element, as a result of which a
torque against the turning of the input shaft is generated by means
of the elastic force via the eccentric contact of the sliding part
on the input shaft caused by the turning of the input shaft. If the
deflection torque on the shaft is taken away, the aligning torque,
which is transferred via the sliding part to the shaft, causes said
shaft to return to its neutral position in which the two planar
areas lie flat upon one another.
[0015] In accordance with the invention the guide element for the
sliding part can be turned in circumferential direction of the
shaft, as a result of which the neutral position of the servo valve
can be adjusted. If the guide element is moved in circumferential
direction of the input shaft the face of the sliding part loses its
planar contact with the flattened portion on the shaft, as a result
of which due to the elastic force a torque acts on the shaft via
the sliding part and the shaft follows the movement of the guide
element. Simultaneously with this turning of the input shaft the
cylindrical journal, which is arranged eccentrically on the shaft,
is moved in a circular path, as a result of which in turn the
control piston in the control cylinder is adjusted. Thus a neutral
position adjustment of the control piston can be performed, wherein
a relative shifting of the control piston vis-a-vis the deflection
of the input shaft is prevented. With this the balance for the
deflection in both delivery directions is preserved, as a result of
which also the delivery maximums in both delivery directions remain
more or less the same. With this arrangement the control piston can
be adjusted in the neutral position important for machine safety,
in said neutral position which the adjustable hydraulic machine
does not show any delivery volumes, thus is in machine downtime.
Simultaneously the autonomously acting control signal feedback
system, which is constructed by the two planar areas of the sliding
part and the flattened portion on the input shaft, is in its
geometric zero position, in which no torque is exercised on the
input shaft. From this geometric zero position the input shaft can
now be deflected equally wide symmetrically in both directions, as
a result of which there are equally great maximums in delivery
volume for both delivery directions on the hydraulic machine.
[0016] Through the relative rotatability of the guide element and
thus of the sliding part guided within a common zero position
adjustment, i.e. neutral position adjustment for the servo valve is
achieved, in which the input shaft, the sliding part and the
control piston are aligned commonly and simultaneously. Thus
between the control piston and the servo valve housing, i.e.
control cylinder, the control edge overlap on both sides of the
control piston or corresponding control edge gaps necessary for
machine downtime arise, said control edge gaps guaranteeing a
symmetrical application of hydraulic pressure to the servo piston,
so that the servo piston does not change the zero position of the
adjustable hydraulic machine. According to the customary state of
the art in this connection it is possible to work with both
negative and positive control edge overlap as long as it is ensured
that in the event of required machine downtime the servo piston,
which as a rule can have hydraulic pressure applied on both sides,
is not shifted from its zero position and both sides have equally
great force applied. Thus the invention provides with simple and
cost-effective means a robust neutral position setting device which
in addition is extremely robust.
[0017] Through the independent rotatability of the guide element
relative to the input shaft in the event of neutral position
adjustment of the control piston in the servo valve the input shaft
can simultaneously be adapted to the adjusted neutral position, as
a result of which a symmetrical deflection of the input shaft
continues to be possible. This neutral position adjustment of the
control piston in the servo valve executed preferably during
machine downtime takes place by removing the planar face of the
sliding part by turning the guide part from the flat recess at the
input shaft and thus forcing the input shaft to turn around its
central axis, as a result of which the lever, which is moved via
the cylindrical pin on the shaft, adjusts the control piston. After
completion of the adjustment operation, i.e. after the resetting of
the zero position the input shaft is automatically carried along,
without imbalances in the servo valve.
[0018] In one preferred embodiment a setting screw, which is
arranged perpendicular to the axis of the input shaft and
perpendicular to the direction of movement of the sliding part in
the servo valve, engages on the guide element, as a result of which
by turning the setting screw via for example a threaded engagement
between guide element and setting screw the guide element can be
turned in circumferential direction of the input shaft. Depending
on the selection of the thread in the setting screw or in the guide
element a more or less precise adjustment can be achieved, wherein
the adjustment can be all the more exact, the finer the thread
is.
[0019] In a further preferred embodiment the setting screw exhibits
a spherical extension on its end in contact with the guide element
or is constructed nodular or spherical, and engages in a
corresponding indentation on a face of the guide element. Such an
indentation can likewise be spherically constructed or can also be
inserted into the guide element in the form of a trapezoid groove
or keyway. The course of the groove is then preferably arranged
parallel to the axis of the input shaft. The thread for tightening
or loosening the setting screw is then consequently preferably
constructed in the servo valve housing,through which the setting
screw penetrates. In the process the screw head of the setting
screw is accessible from outside the servo valve housing. This
likewise applies to the previously cited embodiment.
[0020] For both of the previously cited embodiments it applies that
the setting screw preferably supports itself on an inside wall of
the servo valve housing, as a result of which the guide element is
supported vis-a-vis the servo valve housing. Through the elastic
prestress between the guide element and sliding part an equally
great counter force acts on the setting screw, said force pressing
the setting screw on the inside wall of the servo valve housing. In
order to achieve a guiding of the setting mechanism, consisting of
the setting screw, guide element, sliding part and elastic element
in the direction of the axis of the input shaft, preferably a
groove or a threading is arranged on the inside wall at which the
setting screw is resting, in which said setting element is guided
in its axial direction.
[0021] Such a notch, groove or thread on the inside wall area of
the servo valve housing in this connection only has to be connected
sufficiently long that the empirically determining manufacturer
tolerances can be compensated by the adjustment range/swivel range
of the guide element arising from the adjustment range of the
setting screw. As a rule some clockwise and counterclockwise
angular degrees should be sufficient with respect to the axis of
the input shaft as a normal swivel range for the guide element.
[0022] As described above, the neutral position setting for the
control piston in the servo valve can take place by moving the
lever via the cylindrical extension on the input shaft by turning
the input shaft, wherein the lever is supported on the position
feedback device, which for this purpose thus forms a counter
bearing. If one proceeds from the zero position of the servo
piston, thus from machine downtime, in which the hydraulic machine
shows no delivery volume, imbalances on the basis of the
manufacturer tolerances in the entire adjustment system of the
hydraulic machine--servo piston, servo adjustment device, servo
valve and its components--can be corrected by turning the guide
element in the servo valve via a setting screw to the effect that
the inflows and outflows for servo adjustment of the hydraulic
machine are symmetrical and thus the machine can be kept idle. If
the hydraulic flows which flow through the openings between the
control piston and control cylinder in the servo valve are not
equally high for the respective delivery direction in the amount,
there would be an adjustment in the servo adjustment device, as a
result of which the hydraulic machine would be deflected from its
zero position. The present invention prevents this and in the
process preserves the balance of the servo valve in advantageous
manner.
[0023] In the case of adjusted neutral position of the servo valve,
as stated above, the openings for the application of pressure of a
servo adjustment device of a hydraulic machine are symmetrical,
i.e. the equal quantity of hydraulic fluid flows through the
respective inflows and outflows for the two delivery directions of
the hydraulic machine. In the process a positive control edge
overlap is also included, in which there is no hydraulic flow on
either of the two sides. With this a secure zero position of the
servo piston in the servo adjustment of the hydraulic machine can
be achieved, which in turn can be safely kept in machine
downtime.
[0024] The described implementation ensures that in the neutral
position the direction of movement of the sliding part, which often
also represents the common axis of guide element and sliding
part--for example if these are constructed as a
rotation-symmetrical body--always has an intersection with the axis
of the input shaft running at a right angle to it. In the process
the planar areas of the face of the sliding part and those of the
flattened portion, which for example is constructed in a recess on
the input shaft, lie flat upon one another. In a further preferred
arrangement of the elements in the servo valve the axis of the
position feedback device is likewise perpendicular to the common
axis of the guide element and of the sliding part. Depending on the
position of the guide element in circumferential direction of the
input shaft in the special case here an intersection arises between
the axis of the lever of the position feedback device and the
common axis of the guide element and the sliding part. In a
theoretical arrangement of the individual elements of the servo
valve, thus for example in the case of the theoretical design and
development of a servo valve this intersection of the position
feedback device could define the zero point of the servo valve with
the axis of the guide element and sliding part. From this zero
point the guide element can be adjusted clockwise or
counterclockwise in order in practice to compensate the production
tolerances of the individual parts and ultimately to shift or turn
the control piston to a position in which the inflows and outflows
on both sides of the control piston are symmetrically
constructed.
[0025] The position feedback device of an adjustable hydraulic
machine generally consists of a lever which is connected to the
adjustment device of a hydraulic machine, for example a swash plate
of a swash plate axial piston pump or for example to the bent axis
of a bent axis hydraulic motor and is carried along with the
respective deflection. Normally the position feedback device
exhibits a pin which protrudes into the servo valve and is mounted
in an articulated manner there in such a way that depending on the
position of the deflected hydraulic machine in the servo valve it
represents the position of the adjustment element of the hydraulic
machine. Simultaneously with the movement of the lever of the
position feedback device the lever of the servo valve is moved to
adjust the control piston, which in turn has an effect on the
position of the control piston in the servo valve. In the process
the cylindrical extension on the input shaft, which is arranged
eccentrically to the central axis of the input shaft, forms the hub
for the lever of the servo valve. If the input shaft of the servo
valve is turned, the position of the hub also changes, i.e. the
pivot bearing of the lever of the servo valve, as a result of which
the position of the control piston is changed. Such a position
change of the control piston results in a change in the openings to
the servo piston, as a result of which the position of the
hydraulic machine is changed.
[0026] In the case of the adjustable hydraulic machine the
adjustment range is usually limited due to structural presettings
or due to strived for optimal operating points so that likewise a
stroke limiter of the control piston is to be provided. In the case
of the inventive servo valve this can for example take place by
means of a stroke limiter, i.e. a movement limitation through a
stop between the guide element and the sliding part. If the sliding
part can no longer be pressed into the guide element due to the
stop, then the input shaft also cannot be turned any further. This
can be felt by the machine operator as a mechanical stop. Other
embodiments of a rotation stop in conventional manner with for
example a journal on the input shaft and a stop in the servo valve
housing are in this connection likewise conceivable.
[0027] In a further preferred embodiment the sliding part
simultaneously assumes an axial guiding of the input shaft by
having said sliding part engage in a groove in the input shaft,
wherein the areas adjacent to the planar face, which are preferably
aligned perpendicular to the axis of the input shaft, fix the input
shaft in its axial mobility. If the input shaft is not fixed in
axial direction, it can happen that the input shaft is pushed out
of the servo valve housing by the hydraulic pressure present in
said servo valve housing. To prevent this, for example in the prior
art the input shaft is fixed by a cover which is arranged outside
of the servo valve housing. In accordance with the invention the
axial securing of the input shaft can take place via the sliding
part or also via the guide element, which for example then
encompasses the input shaft in a peripheral groove. For this
purpose preferably fork-shaped extensions are constructed on the
guide element, which engage in a peripheral groove of the input
shaft. In this connection care is to be taken that the fork-shaped
extensions and the peripheral groove of the input shaft do not
hamper the rotatability of the input shaft. For both preferred
embodiments for axial fixation of the input shaft there is a
prerequisite that the guide element and the sliding part in the
servo valve housing are likewise fixed axially, i.e. in the
direction of the axis of the input shaft or can support themselves
against the servo valve housing. To this end for example a suitably
designed shoulder can be constructed in the servo valve housing.
The setting screw can also be seen as a further support in axial
direction, wherein here high forces cannot be transferred. To
prevent the input shaft from pressing into the servo valve housing,
a shaft shoulder can be provided on the first end of the input
shaft which prevents a shifting of the input shaft into the servo
valve housing.
[0028] In a further preferred embodiment the fork ends of the guide
element not only protrude into a peripheral groove on the input
shaft, but rather perpendicular to the axis of the input shaft they
are implemented so wide that they can likewise engage in a groove
which is arranged at the height of the peripheral groove of the
input shaft in the servo valve housing. With this the fork-shaped
extensions of the guide element engage both in the groove in the
input shaft and also in a groove in the servo valve housing and
thus serve both as a type of shaft retainer ring to prevent the
input shaft from either moving out of the valve housing or into the
servo valve housing. Such designed fork ends on the guide element
then make a shaft shoulder provided outside of the servo valve
housing, as described in the previous exemplary embodiment,
superfluous. Fork-shaped extensions, which simultaneously engage in
a groove in the input shaft and in a groove in the servo valve
housing secure the input shaft in its position so that it only
exhibits a degree of freedom, that of turning around its central
axis.
[0029] If the guide element is designed as previously described,
i.e. it encompasses the shaft in a peripheral groove of the shaft
and simultaneously engages in a groove or recesses in the servo
valve housing, the axial securing task of the sliding part can
likewise be omitted, as a result of which frictional forces, caused
by sliding the end of the sliding part with the planar face in or
out of the recess on the input shaft can be reduced. With this
there remains for the sliding part the purely radial direction of
movement for fixing the neutral position of the servo valve. With
the engagement of extensions of the guide element into the servo
valve housing the guide element can simultaneously be fixed in its
axial position with respect to the servo valve housing, as a result
of which axial forces, i.e. forces in the direction of the input
shaft are prevented. If the setting screw is designed with a
spherical end within the servo valve housing, and in the servo
valve housing on the inside wall, at which the spherical end of the
setting screw adjoins, and simultaneously the end of the guide
element in which the spherical end of the setting screw engages,
are designed nodular or friction optimized, excess contact
pressures can be prevented, which leads to an easily accessible
adjustability of the servo valve.
[0030] For an improvement of the surface feel with respect to the
zero position, i.e. neutral position of the servo valve, for
example a spring loaded ball can be provided on an adjacent surface
of the face of the sliding part in axial direction of the input
shaft, which snaps into a corresponding notch of an axial area of
the input shaft in the neutral position of the servo valve. Of
course this principle can also be reversed, so that the notch is
arranged in the sliding part and a spring loaded ball is provided
in the input shaft on an axial area. The development of a ball can
however also be provided on the face of the sliding part itself,
wherein a spherically constructed region of the face of the sliding
part engages in a corresponding recess of the input shaft, as soon
as the two planar areas lie flat upon one another.
[0031] With the present invention a simple, robust and
cost-effective possibility is created for providing a servo valve
for the adjustment of a hydraulic machine whose neutral position is
adjustable, and wherein the balance of the adjustment region of the
servo valve is preserved. In the following some exemplary
embodiments are shown as examples with the aid of drawings, said
exemplary embodiments however are not intended to restrict the
scope of protection of the present invention. The figures show the
following:
[0032] FIG. 1 shows a partially schematic representation of the
arrangement of a servo valve of an adjustable hydraulic machine
with a neutral position device in accordance with the
invention.
[0033] FIG. 2 shows a section through a servo valve in accordance
with the first exemplary embodiment.
[0034] FIG. 3 shows a sectional view of a second exemplary
embodiment.
[0035] FIG. 4 shows a detailed view of a third embodiment in a
partial section.
[0036] FIG. 5 shows an embodiment in accordance with FIG. 4 in
front view.
[0037] FIG. 6 shows a further exemplary embodiment in section
through the guide element.
[0038] FIG. 7 shows a further exemplary embodiment of the guide
element.
[0039] FIG. 1 shows a section in lateral view through a servo valve
1 with a neutral setting device according to the invention with a
servo valve housing 2, in which an input shaft 3 is pivoted. The
input shaft 3 is connected on its upper end 3a to a control lever
27 and can be swiveled via said lever by an operator in an angular
region around the axis 23. On the lower end 3b of the input shaft 3
a cylindrical extension 25 is constructed, said extension being
arranged eccentrically to the axis 23, but parallel to it. The
extension 25 engages in a recess in the lever 5 serving as a
bearing position 5c, whose first end 5a is mounted in an
articulated manner in the control piston 4 of the servo valve 1 and
is pivotably guided in a delimited angular region. The second end
5b of the lever 5 is connected to a lever 6 of a position feedback
device.
[0040] As schematically implied in FIG. 1, the servo valve 1 is
connected via pressure lines 24a, 24b to pressure cylinders 26a,
26b, said cylinders acting on a servo piston 24 of an adjustment
device of a hydraulic machine not shown in the figure. The position
of the first end 5a of the lever 5 determines the position of the
control piston and with this the pressure conditions prevailing n
the pressure lines 24a, 24b and thus the position of the servo
piston 24, which causes the actual adjustment of the hydraulic
machine. The supply of the servo valve 1 and the pressure lines
24a, 24b with pressure fluid, customarily hydraulic oil, takes
place via connections 28 on the servo valve 1, of which only one
connection 28 is shown in FIG. 1 by way of example.
[0041] The input shaft 3 exhibits a groove-like recess 7 in its
lower region, whose floor area is constructed as a planar flattened
portion 7a. In the recess 7 one end of a sliding part 8 is guided
in a sliding manner, said sliding part having a planar face 8a. The
end of the sliding part 8 is dimensioned in such a way that the
face 8a can come into positive contact with the flattened portion
7a of the input shaft 3, wherein this contact can extend to
complete, parallel contact of the two planar areas 7a and 8a. The
other end of the sliding part 8, shown here as a cylinder, is in
accordance with this exemplary embodiment mounted in sliding manner
in the interior of a guide element 10 and is pre-stressed vis-a-vis
this guide element 10 via the spring 9 in the direction of the axis
23 of the input shaft 3. On an outer face of the guide element 10
an inside taper 12 is constructed, which is in contact for example
with a spherical or nodular end 11a of the setting screw 11. This
end 11a supports itself in addition on a groove 14 on an inside
wall area 13 of the servo valve housing 2.
[0042] FIG. 2 shows a further section in top view through the servo
valve 1 in accordance with FIG. 1 in the height of the axis of the
setting screw 3, which is cut here at the height of the recess 7
and therefore appears in the shape of a half moon with the
flattened portion 7a. The flattened portion 7a is in full, areal
contact with the planar face 8a of the sliding part 8, which
corresponds to the neutral position of the adjustment device. Parts
of the guide element 10 formed as fork end 15 encompass the input
shaft 3 and are supported vis-a-vis said input shaft. With this a
lateral fixation of this end of the guide element 10 is given,
which however permits a swiveling around the axis 23 of the input
shaft 3. In the inside of the guide element 10 a spring 9 is shown,
which is constructed as a compression spring and presses the
sliding part 8 against the input shaft 3. The setting screw 11 is
longitudinally displaceably mounted in the housing 1 via a thread
and engages with its spherical constructed end 11a into the
indentation of the Inside taper 12 on the face of the guide 10. The
opposite side of the spherical end 11a of the setting screw 11 is
supported in the groove 14 in the servo valve housing 2 so that the
guide element 10 with the spring 9 and the sliding part 9 is
supported on both ends and the spring 9 can exert pressure on the
input shaft 3.
[0043] The setting of the neutral position of the operating device
27 of the hydraulic machine takes place via the setting screw 11 in
the following way: An adjustment of the setting screw 11, whose end
region protruding out of the servo valve housing 2 is formed for
the engagement of an adjustment tool, leads to a carrying along of
the guide element 10, since its Indentation in the face constructed
as an inside taper 12 from the spherical end 11a of the setting
screw 11 is positively and non-positively mounted. This causes a
swiveling of the sliding part 8 mounted in the guide element 10
with the planar face 8a vis-a-vis the input shaft 3. As a result
the input shaft 3 is likewise swiveled, since the face 8a raises
from the flattened portion 7a and generates a torque on the input
shaft 3. The swiveling of the input shaft 3 is transferred from the
cylindrical extension 25 on the lower end 3b of the input shaft 3
to the lever 5 for adjustment from its end 5a in the control piston
4. As a result of this the respective pressure in the pressure
lines 24a, 24b to the pressure cylinders 26a, 26b can be set
precisely. The swiveling of the input shaft 3 also shows itself on
the control lever 27, which is connected to the upper end of the
input shaft 3. This lever can be fixed in a desired position by
means of a detachable and lockable connection between the input
shaft 3 and the control lever 27 after the neutral setting of the
device. This e.g. makes possible an adjustment of the control lever
27 with respect to a scale on a control panel of the hydraulic
machine after the setting of the neutral position of the control
piston 4 of the servo valve 1 and with it of the servo piston
24.
[0044] In the operation of the hydraulic machine the control lever
24 can be swiveled by the operator from the neutral position, which
for example can be a central position, to a predefined direction.
The swivel angle in known manner predefines the desired reaction of
the hydraulic machine by having the control piston 4, which is
subsequently shifted, change the flow of the pressure fluid in the
pressure lines 24a, 24b, as a result of which the servo piston 24
(see FIG. 1) is shifted in one or the other direction. The shifting
of the servo piston 24 causes a change in direction and or of the
delivery quantity of the pressure fluid in the main circuit of the
hydraulic machine, which as a result causes the action desired by
the operation.
[0045] The swiveling of the input shaft 3 caused by the operator
via the control lever 27 also changes the contact of the flattened
portion 7a and of the planar face 8a of the sliding part 8. Instead
of contact over the entire area in the neutral position there is
only a linear contact on one side of the two areas 7a or 8a. Since
the force-transmitting contact line lies off center with respect to
the axis 23, the sliding part 8 compression loaded by the spring 9
exerts a torque on the input shaft 3. This torque has the tendency
of counteracting adjustments made by the operator and returns the
control lever to the neutral position. This reset force must
accordingly be overcome continuously by the operator. A release of
the control lever 27 leads to an automatic reset of the control
lever 27 and with that of the control piston 4 to the neutral
position, on the basis of the elastically pre-stressed sliding part
8.
[0046] In FIGS. 3 through 5 further similar examples of the
invention are shown in accordance with FIG. 2, wherein FIG. 3 shows
a cross-section, FIG. 4 shows a top view and FIG. 5 shows a lateral
view of details of the essential components for setting the neutral
position. These exemplary embodiments differ from the previously
described embodiments among other things in the deviating design of
the guide element 10 and its connection to the input shaft 3. The
same reference numbers are used in these and additional figures for
matching parts, as can be seen in FIGS. 1 and 2. In FIGS. 4 and 5
it can be seen that the end of the guide element 10 adjacent to the
input shaft 3 is constructed in the shape of a fork in the lower
region and for stabilization of its position encompasses a lower
part of the input shaft 3 in a cylindrical region 29 of lesser
diameter. The ends of the fork 15 extend over an imaginary center
plane of the input shaft, so that the guide element 10 is securely
guided even in the case of the swiveling of the input shaft 3. In
addition the ends of the fork 15 fix the input shaft 3 against an
axial shifting from the servo valve housing 2, which could take
place under the influence of the fluid pressures in the servo valve
housing 2. To this purpose said ends protrude on the one hand into
the region 29 with lower diameter of the input shaft 2 and on the
other hand support themselves in a correspondingly formed groove 16
(not shown) in the servo valve housing 2.The sliding part 8 is in
the case of this exemplary embodiment held in a longitudinally
displaceable manner in the cylindrical guide element 10 and is
pre-stressed by the spring 9 in the direction of the input shaft
3.
[0047] FIG. 6 shows a further constructive variant of the invention
in top view of a cross-section, in which the guide element 10 for
the sliding part 8 is arranged in its inside and the spring 9 is
arranged on the outside of these components. The front end of the
sliding part 8 with the planar face 8a is mounted here in a recess
in the form of a groove 16 (not shown) of the servo valve housing
2, surrounding a sub-region of the input shaft 3. The wall of the
groove 16 and the front end region of the sliding part 8 are formed
in such a way that a swiveling is possible, but a secure guiding of
the sliding part 8 perpendicular in the axis 23 of the input shaft
3 is always ensured. In accordance with the exemplary embodiment
according to FIG. 6 the front end of the sliding part 8 is
spherically formed and penetrates into the recess 7 in the input
shaft 3. The walls of the recess 7 stabilize in this connection
both the axial shifting of the sliding part 8 and that of the input
shaft 3, into whose groove-like recess 7 the sliding part 8
protrudes. The rear end of the sliding part 8 exhibits a bore in
which the guide element 10 is mounted in a sliding and
longitudinally displaceable manner. The guide element 10 and
sliding part 8 are braced against one another by the spring 9
arranged on the cylindrical outside of the sliding part 8. The
remaining arrangement and its operation correspond to the
previously described exemplary embodiments. In the event of the
turning of the input shaft 3 the spherically formed extension 30 of
the sliding part 8 remains in engagement with the recess 7, as a
result of which the axial fixation of both components is preserved
even in the case of the swiveling of the input shut 3.
[0048] FIG. 7 shows a further exemplary embodiment of the invention
in a top view in section. A detailed view is given of the essential
components for setting the position of the input shaft 3. The
figure shows a constructive variant of the arrangement according to
FIG. 6. The sliding part 8 exhibits a spherical or spherical
journal on its front side facing the input shaft 3, which engages
in a recess 7 in the input shaft 3 that is formed essentially
complementary to it. The front end of the sliding part is as a
result mounted and fixed in the input shaft 3. The front region of
the sliding part 8 surrounding the journal contains the flat planar
face 8a, which can be in contact with the flattened portion 7a with
the input shaft 3 in its peripheral region. This front region 8b of
the sliding part 8, which exhibits a greater width than the other
regions, is guided into a groove 14 in the servo valve housing 2not
shown here. This is analogous to the design described with the help
of FIG. 6 and likewise serves for axial securing of the relative
position of the sliding part 8 and input shaft 3 in the servo valve
housing 2.
LIST OF REFERENCE SYMBOLS
[0049] 1 Servo valve [0050] 2 Servo valve housing [0051] 3 Input
shaft [0052] 3a first end input shaft [0053] 3b second end input
shaft [0054] 4 Control piston [0055] 5 Lever [0056] 5a first end
lever [0057] 5b second end lever [0058] 5c Bearing position [0059]
6 Lever of a position feedback [0060] 7 Recess of the input shaft
[0061] 7a Flattened portion [0062] 8 Sliding part [0063] 8a planar
face [0064] 8b front region of the sliding part [0065] 9 Spring
[0066] 10 Guide element [0067] 11 Setting screw [0068] 11a End of
the setting screw [0069] 12 Inside taper [0070] 13 Inside wall area
of the servo valve housing [0071] 14 Groove in the servo valve
housing [0072] 15 Fork end [0073] 16 Groove in the servo valve
housing [0074] 17 Groove in the input shaft [0075] 23 Axis of the
input shaft [0076] 24 Servo piston [0077] 24a,b Servo-pressure line
[0078] 25 Cylindrical extension [0079] 26a,b Pressure cylinder
[0080] 27 Control lever [0081] 28 Opening [0082] 29 Region of
smaller diameter [0083] 30 Spherical Journal [0084] 31 Recess
* * * * *