US3618472A

US3618472A - Device for adjusting the stroke volume in a swash plate axial piston motor or pump

Info

Publication number: US3618472A
Application number: US9641A
Authority: US
Inventors: Hans Knaak
Original assignee: Mannesmann Meer AG
Current assignee: Mannesmann Meer AG
Priority date: 1969-02-14
Filing date: 1970-02-09
Publication date: 1971-11-09
Anticipated expiration: 1988-11-09
Also published as: AT294584B; FR2032880A5; CH505988A; SE383020B; SE366802B

Abstract

THE TILTING ANGLE OF A SWASH PLATE IN A FLUID PUMP OF MOTOR IS ADJUSTED BY A PISTON ARTICULTED TO THE PLATE AND POSITION CONTROLLED BY A SERVO VALVE WHICH, IN TURN, IS OPERATED BY A PLUNGER COUPLED TO THE SWASH PLATE BY A SINGLE CONTROL LEVER. THE CONNECTING LEVER IS CONNECTED TO SWASH PLATE AND PLUNGER SO THAT ONE OF THE CONNECTING POINTS CAN UNDERGO DIMENSIONAL MOTION IN RELATION TO THE RESPECTIVE OTHER ONE.

Description

NOV. 9, 1971 KNAAK 3,618,472

DEVICE FOR ADJUSTING THE STROKE VOLUME IN A SWASH PLATE, AXIAL PISTON MOTOR OR PUMP Filed Feb. 9, 1970 2 Shoots-Shoot 1 Fig" 34 2a 41;, 40 44 In ventor 1 4 naal JyKZwM NOV. 9, 1971 H KNAAK 3,618,472

DEVICE FOR ADJUSTING THE STROKE VOLUME IN A SWASH PLATE, AXIAL PISTON MOTOR OR PUMP Filed Feb. 9, 1970 2 Sheets-Shoot 2 a H F Flg- 2 I 2 Inventor: H44; 1 /1446 @fiaa #4 6 United States Patent US. Cl. 91506 11 Claims ABSTRACT OF THE DISCLOSURE The tilting angle of a swash plate in a fluid pump or motor is adjusted by a piston articulated to the plate and position controlled by a servo valve which, in turn, is operated by a plunger coupled to theswash plate y a single control lever. The connecting lever is connected to swash plate and plunger so that one of the connecting points can undergo three dimensional motion in relation to the respective other one.

The present invention relates to control device for infinite adjustment of the stroke volume of swash plate fluid motors or pumps with axially operating pistons. The invention relates particularly to improvements in arrange ments of a control piston, of feedback servo valve, of a swash plate tilt angle adjuster, and of linkage between them as well as for the swash plate.

Upon varying the tilting angle of a swash plate, the point of connection thereof to the tilt control device outlines a circle. Thus, it has been found necessary to employ at least two coupled levers as linkage to take u this circular motion of adjustment. Aside from the construction being expensive, a plural member lever mechanism has the disadvantage that play in the several joints superimpose by addition, and the accuracy of adjustment deteriorates accordingly. This is hardly tolerable, as pump or motor adjustment requires usually great precision, otherwise erroneous motion components of significant magnitude are included in the drive and drive position output to be produced. The problem exists, therefore, to simplify the linkage between swash plate, adjusting mechanism, feedback structure and adjustment input, and particularly to reduce the number of levers, joints and linking points. Also, a compact design of the entire adjusting mechanism is highly desirable.

In accordance with one aspect of the invention in the preferred embodiment thereof, there is provided a control piston linked to the swash plate and position controlled by a servo valve, as the valve controls fluid passage to and from the piston chamber or cylinder of the control piston, in dependence upon position of a control plunger. The plunger is linked to the swash plate by means of a single control lever to obtain feedback which lever can pivotally move as if supported by an actual spherical bearing due to pivotability of the lever about an axis transverse to the axis of the control plunger in relation thereto and further due to the ability of the control plunger to turn in its valve chamber.

In order to provide a swash plate tilt angle adjustment input, an adjusting lever can be provided and articulated to the control lever, or an axially displaceable control rod can be provided on which is journalled an axially fixed connector which, in turn, is linked directly to the control lever by a ball and socket like joint. In the first embodiment, swash plate adjustment is initiated by a turning motion, in the second embodiment swash plate adjustment is initiated by a linear motion in the system to be transmitted upon the control lever. In the latter 3,618,472 Patented Nov. 9, 1971 case, the axial position of the connector on the control rod is fixed by a holding disk screwed to the connector, and having a collar sandwiched between them. The collar pertains to the control rod and defines relative axial position of the connector on the control rod. The precise axial position of the connector on the rod results from placement of suitable washers in relation to collar and connector.

During adjustment by means of turning an adjustment lever, the three-dimensional movement of the control lever is taken up by the pivot point in a ball-and-socket joint, the socket thereof together with the ball being disposed to permit displacement thereof in a fork and pertaining to the adjustment lever. However, the fork retains the pivot point established by the ball-and-socket joint.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject ma ter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a section view into a swash plate, axial piston fluid motor or pump improved in accordance with the invention;

FIG. 2 is a section view along lines I I of FIG. 1, showing details of a first embodiment of the invention;

FIG. 3 is a vertical section along lines II-II in FIG. 2, and

FIG. 4 can be regarded as a corresponding section view along lines II in FIG. 1 but showing a modified construction as to that section.

Proceeding now to the detailed description of the drawings, there is illustrated a housing 24 journalling a shaft 25 and including parallel operating pistons 27 which r ciprocate in cylinder barrels such as 26. A swash plate or tilting plate 1 is mounted on the shaft for rotation therewith. This fluid device can operate as pump or as motor. The tilting angle of swash plate 1 is adjusted by means of a control piston 2 displaceably disposed in a control cylinder or piston chamber 17. A piston rod 3 connects plate 1 to piston 2. Adjustment of the tilting angle serves for the adjustment of the stroke volume or piston displacement volume in the axial piston fluid motor or pump.

The control piston 2 is constructed as differential piston, A relatively small annular surface 4 of control piston 2 is permanently subjected to a particular hydrostatic pressure. The relatively large circular surface 5 on the other side of the piston is selectively subjected to the same pressure or is relieved upon depressurizing chamber 17. The position of piston 2 is determined at any instant by the balance of pressure forces acting on opposite ends of the piston and adjusting same.

In order to avoid dangerous transverse forces and in order to avoid tipping or undesired tilting of piston 2 the permissible angular deflection of piston rod 3 is maintained rather small. This feature is obtained by selecting a correspondingly large distance between bearing and support points of piston rod 3 on tilting plate 1 and in control piston 2, respectively. The connection and pivot point of piston rod 3 in control piston 2 is located in the range of piston guidance in the cylinder or chamber 17 (see particularly FIG. 2).

Swash plate 1 is tilted about pivot axis S by means of adjustment of control piston 2. Upon adjustment, the pivot and linking point and axis at the connection of swash plate 1 and rod 3 describes an arc on which there are shown three points, A, B and C, in representation of particular adjusting positions. Point A denotes the position of the connecting point for adjusting the axial piston-cylinder arrangement (27, 26) of the fluid pump or motor for maximum stroke volme. Upon retracting control piston 2, the rod-swash plate linking point is tilted to assume position B, and here the stroke volume of the pump or motor is zero, as in this position plate 1 is transverse, at right angles, to the axis of shaft 25. Further retracting of the control piston leads to position C corresponding to a phase shift by 180 of swash plate operation because inlet and outlet sides of the axial piston unit have been interchanged. In position C there is again maximum stroke volume for this mode of operation.

The adjustment of the swash plate 1 in accordance with the embodiments of FIGS. 2, 3 and 4 will be described in the folowing in greater detail. FIGS. 2 and 3 pertain to the same embodiment. FIG. 2 illustrates in particular a section view wherein the section plane coincides with the plane of operation of the control piston and of the servo valves. The linking point of piston rod and swash plate 1, however, can be tilted out of that plane.

Control fluid is provided through a channel 6 for control of the position of piston 2. That control fluid may be taken from the main fluid circuit or from the control circuit or any other suitable source or reservoir of pressurized fluid. The control fluid is fed from channel 6 to a ring channel 7 to act on piston face 4. Additionally, a duct 8 leads from ring channel 7 to a ring channel 9 of a servo valve. Ring channel 9 is, thus, under pressure of the control fluid. A second ring channel 10 is connected through a duct 11 to a venting outlet leading to the tank, i.e., the interior of housing 24 or to any other return path for the control fluid at zero pressure. Further fluid conduction is under control of the servo valve linking these ducts and channels with piston chamber 17. In particular, a ring chamber 19 may selectively be connected to channel 10 leading to the venting outlet, or chamber 19 may be connected to pressurized ring channel 9. Ring channel 19 is connected to piston chamber 17 via a duct 18. The selectivity of this connection depends on the position of a plunger 15.

In the illustrated position of swash plate 1 and of the various control elements the axial piston-cylinder arrangement of the motor or pump is adjusted for maximum stroke volume (position A). Swash plate 1 is connected to the control plunger of the servo valve by means of a single control lever 12. A roll joint 21 establishes articulation between plunger 15 and lever 12. An adjusting lever 23 is connected to lever 12 by a ball and socket joint estabishing pivot point D (see FIG. 3). As schematically indicated, lever 23 can be pivotally adjusted by suitable handle or control knob means, whereby a fork end of the lever 23 turns in a plane transverse to the plane of FIG. 3 and on an axis transverse to the plane of FIG. 2. As lever 23 turns lever 12 and the point D move in direction E (FIG. 2); control plunger 15 of the servo valve is shifted correspondingly to the right. This is true because the center of a slidably positioned ball of a ball and socket joint 13 serves as fixed reference point for pivoting. The ball of joint 13 pertains to a pin 14 as part of the linkage between swash plate 1 and lever 12.

As control plunger 15 moves to the right its control edge passes the control edge 16 of the valve cylinder establishing communication between

ring chambers

10 and 19, so that the cylinder and piston chamber 17 of the control piston (2)-cylinder arrangement is vented through outlet duct 11. The conduit path for venting runs particularly from chamber 17 via duct 18, ring channel 19 as now connected to ring channel 10, and from there to venting duct 11. Thus, chamber 17 depressurizes, and now the previously too low pressure force acting on annulus 4 of control piston 2 prevails and suffices to shift piston 2 to the right. Accordingly, the swash plate 1 is shifted in direction of point B (see FIG. 1). Concurrently, the center of the ball of ball and socket joint 13 is shifted to the right (FIG. 2). The pivot point D acts as fixed point so that double arm lever 12 pulls control plunger 15 of the servo valve to the left and back into its initial position.

The adjustment of swash plate 1 is terminated as soon as the control edge of plunger 15 is receded so that the control edge 16 of the servo valve chamber is blocked again. Now the stroke volume of the axial pistoncylinder arrangement is adjusted in accordance with the new position of pivot point D, and the position of the latter was adjusted by lever 23.

If adjusting lever 23 is actuated to pivot point D in direction of arrow F, control piston 15 is shifted to the left at first. Thereupon the control edge 20 of the valve chamber is opened. Now a flow path for pressurized control fluid is established, running from ring channel 9 across edge 20, ring channel 19, duct 18 to cylinder chamber 17 of the principle control piston 2. Hence, chamber 17 will be pressurized. As circular area 5 is about twice as large as annulus 4, pressure force on piston surface 5 soon prevails and shifts control piston 2 to the left. Accordingly, the swash plate 1 is tilted to move towards point A. By analogous feed back operation control piston 15 is shifted back to the right until closing control edge 20 (or until the piston 2 has assumed terminal position which limits the tilting angle of swash plate 1).

As was mentioned above, play and slack in a linkage and lever arrangement for returning the control piston is detrimental to the accuracy of the adjustment. For this reason, the arrangement as described operates with a single lever 12 and there are only two pivot joints, 13 and 21, thus, solving the aforementioned problem.

In order to compensate changes in length as between the end points of plunger 15 and piston rod 3 and resulting from the adjustment, ball and socket joint 13 is provided with a socket bore 22 for the ball. The ball on pin 14 can thus move back and forth in bore 22 of control lever 12. Furthermore, control lever 12 is linked to control piston 15 by means of roll joint 21 having fixed pivot point and axis in relation to both

elements

12 and 15. Moreover, the pivot axis in joint '21 is transverse to the axis of plunger 15.

During adjustment of the tilting angle of swash plate 1, pin 14 and the ball joint 13 outline a section of a circle around tilting axis S which circle is in a plane parallel to the direction of control motion of piston 2 and of plunger 15. Therefore, lever 12 undergoes a threedimensional motion which must be taken up by a spherical type bearing, so as to avoid locking. The spherical bearing is established in accordance with a feature of the invention, by permitting concurrent pivoting of control lever 12 about the longitudinal axis of bearing 21 as well as rotation of control plunger 15 in its cylinder about its axis. As the ball and socket joint linking levers 23 and 12 is slidably disposed in the fork of lever 23, the threedimensional motion of lever 12 is taken up by that linking point.

Turning now to the description of FIG. 4, there is illustrated a second example for the swash plate tilting control, using also a servo valve controlling a piston drive and being by itself controlled by a plunger 15. Again, the pressurized fluid required for operation of control piston 2 is fed into duct 6 to be passed on to ring channel 9 of the servo valve via duct 8. Ring channel 10 of the servo valve connects to the Zero pressure venting and discharge outlet of the system via duct 11.

The control plunger 15 is connected to control lever 12 by means of a fork 47 and by the roll joint 21. One end of lever 12 is connected to swash plate 1 by means of ball and socket joint 13 comprised of a ball on pin 14 which ball can turn and slide in socket 22 of lever '12. The other end of lever 12 is connected to a connecting piece or connector 29 by means of a ball and socket joint 48. The ball of that joint has a bore slidably receiving an end pin 28 of lever 12.

Connector 29 is journalled on a control rod 30 so that the connector can pivot about the longitudinal axis of the rod. The axial position of connector 2 9 on rod 30, in longitudinal direction thereon, is a fixed one. For this, control rod 30 is provided with a collar 31. One axial side of collar 31 faces the connector, while on the other side of the collar there is a holding disk 32. Disk 32 is connected to connector 29 by means of bolts 33, and a washer 34 is interposed to determine the precise axial distance between connector 29 and disk 32. The thickness of washer 34 is selected in accordance with the thickness of the sandwiched collar 31 so that the collar 31 can rotate within the space between

elements

29 and 32 at minimum axial play.

The control rod 30 is axially displaced by forces acting against the force of a spring 35. Pressurized fluid (control pressure) is fed either into a cylinder chamber 37 via a duct 36 to act on the front face of rod 30 or into a cylinder chamber 39 via a duct 38. Chamber 39 contains also the spring 35.

The front face of control rod 30 serves as piston upon which may act hydrostatic control pressure. Any particular pressure within a particular range produces a force capable of balancing spring 35 at a particular degree of spring compression. Control rod 30 has a central position if the two

chambers

37 and 39 are both pressure relieved. In the central position of rod 30 spring disk 40 bears against cylinder end face 41, while a second spring disk 42 bears against the front face of an adjustment or trimmer ring 43.

As chamber 37 is pressurized, a particular pressure therein will correspond to the then existing bias of spring 35 as threshold. Upon further increase of pressure in chamber 37 disk 40 recedes from cylinder end face 41, and rod 30 is shifted to the right and into the position illustrated in FIG. 4. The spring stroke increases with increasing spring force. Thus, the rod is displaced from central, neutral position for a distance which increases with increasing hydrostatic pressure in chamber 37. The cylinder chamber 39 is still depressurized at that point. On the other hand, if chamber 37 is discharged and depressurized, and if chamber 39 is pressurized instead, disk 42 will recede from the front face of adjusting ring 43, and the control rod is shifted to the left, out of the position illustrated in FIG. 4.

It should be mentioned that the particular mode of displacement of the rod to the left and to the right, to different adjusting positions, has been described here by way of example only, and other modes of motion control can be provided in principle. The displacement of the con; trol rod operates as adjustment of the tilting angle of swash plate 1 in the illustrated poition of control rod 30 the swash plate has a tilting angle corresponding to maximum piston displacement and stroke volume of the pistons 27 in cylinders 26 of the pump or motor. Again, the housing of the axial piston is denoted with 24, journalling drive or driven shaft 25. The adjusting operation in detail is as follows:

If the control rod 30 is shafted to the left, the center M of ball-and-socket joint 48 is likewise displaced to the left, in direction G. The center of ball-and-socket joint 13 is a fixed pivot point at that time, so that the control plunger 15 of the servo valve is shifted also to the left. Now the control edge of plunger 15 passes over control edge 44 of valve chamber 19 and opens a passage between

ring channels

19 and 10.

Cylinder chamber 17 is vented via duct 18, chamber 19, channel and duct 11. As the hydrostatic pressure in chamber 17 collapses, the force acting on relatively smaller annulus 4 prevails over any residual force on surface 5, and control piston 2 is shifted to the right. As a consequence, swash plate 1 is tilted to move towards point B. Concurrently, the center of ball-and-socket joint 13 is shifted to the right. The center M of ball-and-socket joint 48 defines a fixed pivot point here so that control plunger of the servo valve is returned to its initial position.

Accordingly, the passage via control edge 44 is blocked,

so is the communication between chamber 17 and the venting outlet. The adjustment of swash plate 1 to a new position of tilting is now completed. The axial piston arrangement of the fluid pump or motor has now been adjusted to assume a new stroke volume and corresponding to the displacement of control rod 30 from central position to the shaft.

As control rod 30 is shifted to the right, the center M of ball-and-socket joint 48 shifts in direction H. At first, control plunger 15 is likewise shifted to the right to open passage through control edge 45 between

ring channels

9 and 19. Accordingly, the pressure fluid fed to channel 9 (via 6), is conducted through channel 19 and duct 18 into chamber 17, so that full hydrostatic control pressure can build up therein.

As the circular area 5 of piston 2 is about twice as large as annular 4, force on surface 5 prevails and control piston 2 is shifted to the left. As a consequence, swash plate 1 is tilted in direction A until control edge 45 blocks again passage between

channels

6 and 19 or until piston 2 has reached terminal position, limiting the tiltingangle 0f swash plate 1 accordingly.

As stated above, doubly acting spring 35 places control rod 30 in central position whenever the two

chambers

37 and 39 are depressurized. This position must correspond to a stroke valve zero of the axial piston arrangement of this swash plate motor or pump. Accordingly, swash plate 1 must be adjusted to central position (B) at tilting angle zero for this control position of rod 30.

In order to trim adjustment position of swash plate 1 to obtain that central position control plunger 15 and fork 47 are provided with threading 46 to obtain relative positive adjustment between them. This may be a self-locking thread to prevent unintended position change.

It is repeated here that the play in any extensive linkage deteriorates accurately of adjustment as to transmission of linear control action. This problem is solved in the structure as aforedescribed, by connecting control rod 30 to the control lever 12 directly, by means of connector 29 and ball-and-socket joint 48. The control lever returns the control plunger 15 after initial actuation, as piston rod 30 pivots lever 12 about pivot point M.

During tilting of swash plate 1, pin 14 and, therefore, ball-and-socket joint 13 outlines a circle about tilting axis G. The resulting three-dimensional motion of the control lever 12 is taken up by a spherical bearing. Special bearing support is established by permitting concurring pivoting of lever 12 about the longitudinal axis of roll joint 21 and by permitting control plunger 15 to turn in the valve chamber. As the three-dimensional motion of lever 12 is also operative as longitudinal displacement between lever 12 and the pivot point 48, it is also necessary to permit such axial displacement as between lever end 28 and the ball of joint 48. Additionally, connector 29 can pivot about the longitudinal axis of rod 30, thus, compensating three-dimensional lever movement in cooperation and the universal joint like adjustment of ball-andsocket joint 48. The length compensation as between connector 29 and lever 12 results from shifting of lever end 28 in the ball of joint 48. As it can be seen further from FIG. 4, the connector turns in a plane transverse to the plane of tilting motion, the latter plane being transverse to axis S. This way, the compensatory turning of connector has practically no influence on the tilting.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

I claim:

1. A device for infinite adjustment of the stroke volume in a pressure fluid, swash plate, axial piston motor or pump, the swash plate coupled to a control piston for tilting the swash plate about a first axis, there being a servo valve controlling the Position of the piston, and being controlled by a plunger, the improvement comprising:

a control lever articulated to the swash plate and connected to the plunger by means permitting pivoting of the control lever relative to the plunger about an axis transverse to said first axis, the plunger disposed for rotation about its own axis; and

adjusting means linked to the control lever for pivoting the control lever about its point of articulation to the swash plate for changing the position of the plunger to obtain valve operation, and establishing a pivot point for the control lever upon resulting piston displacement whereby the plunger is returned to its previous position concurring with turning about its axis and change in angle relation to the control lever.

2. A device for infinite adjustment of the stroke volume in a pressure fluid, swash plate, axial piston motor or pump comprising:

a piston-cylinder arrangement, the piston thereof connected to the swash plate for adjusting the tilting angle thereof in dependence upon the relative position of the piston;

a servo valve, including a plunger, the servo valve controlling the fluid in the piston-cylinder arrangement;

a control lever for directly conecting the plunger to the swash plate for providing stabilizing feed back;

means for pivotally linking the swash plate to the control lever;

a roll joint pivotally linking the plunger to the control lever, for pivoting about an axis transverse to the axis of the plunger, the plunger permitted to turn in the servo valve chamber about its axis to obtain spherical bearing support for the lever; and adjusting means connected to the control lever to determine an initial position of the plunger for initiating adjusting of the swash plate tilt angle by the piston as controlled by the servo valve.

3. A device as in claim 2, the adjusting means coupled to the control lever for pivoting the control lever about a pivot point established by pivotally linking the swash plate to the control lever, and including means establishing a particular pivot point for the control lever upon change of the relative position of the piston, said established pivot point relatively movable to the axis of the roll joint transverse thereto upon pivoting of the control lever about said established pivot point.

4. A device as in claim 3, there being a ball and socket joint connecting the adjusting means to the control lever for establishing said particular pivot point and constructed to permit linear displacement of the particular pivot point in relation to the adjusting means of the lever.

5. A device as in claim 3, the control lever articulated to the swash plate by a ball and socket joint, the socket thereof permitting lateral displacement of the ball in a direction having an angle to the tilting plane of the swash plate.

6. Device as in claim 2, the adjusting means including an adjusting lever articulated to the control lever.

7. Device as in claim 6, there being a ball-and-socket joint for articulating the control lever to the adjusting lever and establishing a pivot point slidably disposed on the adjusting lever, for taking up three dimensional movement of the control lever upon change of tilting angle by operation of the control piston.

8. A device as in claim 7, the adjusting lever being a turning fork receiving and slidably positioning a ball and socket joint, the control lever connected to the ball thereof.

9. Device as in claim 2, the adjusting means including an axially movable control rod;

a connector journalled on the rod;

means inhibiting axial displacement of the connector on the rod; and

a ball-and-socket joint linking directly the connector with the control lever.

10. Device as in claim 9, the inhibiting means including a collar on the rod, a holding disk secured to the connector, the collar being disposed between the connector and the disk, there being at least one distance defining washer in between the connector and the disk.

11. Device as in claim 9, the ball of said joint having an aperture slidably receiving one end of the control lever for articulatedly linking the lever to the connector.

References Cited UNITED STATES PATENTS 2,578,561 12/1951 Lagardelle 91-506 3,139,006 6/1964 Budzich 91506 3,463,087 8/1969 Grant 91-506 CARLTON R. CROYLE, Primary Examiner J. J. VRABLIK, Assistant Examiner US. Cl. X.R. 417222