Hydraulic machine of axial-piston design

Abstract

A hydraulic axial-piston machine achieves a control cut-off by an additional control edge of a control valve of an actuating mechanism for swiveling a swash plate.

Claims

1. A hydraulic axial piston machine, comprising: a cylindrical drum defining a plurality of cylinder bores; a plurality of pistons, each of which is guided in a respective cylinder bore of the plurality of cylinder bores, the plurality of pistons each defining a working chamber and being supported on a swash plate having an adjustable swivel angle; an actuating device including (i) an actuating cylinder configured to adjust the swivel angle of the swash plate so as to adjust a displacement of the hydraulic axial piston machine and (ii) an actuating valve having a proportionally adjustable control piston, the actuating cylinder defining an actuation chamber configured to be connected to high or low pressure via the control piston, the control piston having a first control edge, a second control edge, a third control edge, and an fourth control edge; and a measuring spring configured for forcibly feeding back the swivel angle to the control piston, wherein, in a control cut-off position of the control piston: a first pilot oil connection between the actuation chamber and the low pressure is opened by the first control edge; a second pilot oil connection between the actuation chamber and the high pressure is closed by the second control edge; and a third pilot oil connection between the actuation chamber and the low pressure is closed by the third control edge, the third pilot oil connection being different from the first pilot oil connection.

2. The hydraulic axial piston machine according to claim 1, wherein: the actuating valve is configured to be adjusted by a proportional solenoid; a tappet submerges into a solenoid chamber into which a tappet-side end portion of the control piston also projects, the tappet-side end portion of the control piston being biased by the measuring spring into a position in which the tappet-side end portion bears against the tappet; and the solenoid chamber is permanently fluidly connected to the actuation chamber through a first portion of the first pilot oil connection, and the first control edge controls a second portion of the first pilot oil connection that connects the low pressure to the solenoid chamber so as to open and close the first pilot oil connection.

3. The hydraulic axial piston machine according to claim 2, wherein the actuating valve further comprises a control valve housing in which the control piston is arranged, and the control valve housing defines a connecting duct via which the solenoid chamber is permanently connected to the actuation chamber.

4. The hydraulic axial piston machine according to claim 1, further comprising a non-return valve configured to connect the actuating chamber to the high pressure, bypassing the second pilot oil connection, in order to prioritize inward swivel of the swash plate.

5. The hydraulic axial piston machine according to claim 4, wherein the non-return valve is arranged coaxially with the actuating valve.

6. The hydraulic axial piston machine according to claim 4, wherein: the measuring spring has a first side supported on the actuating cylinder and a second side supported on a valve body of the non-return valve, which is pre-tensioned against the control piston and together with the control piston forms the non-return valve, and an internal bore, in which the high pressure acts when the non-return valve is open, is defined in the control piston.

7. The hydraulic axial piston machine according to claim 1, wherein the actuating cylinder has a cupped configuration, the measuring spring is accommodated in the actuating cylinder, and a valve body is guided in the actuating cylinder.

8. The hydraulic axial piston machine according to claim 7, wherein an axial length of the valve body and guidance of the valve body in the actuating cylinder are optimized for tilting stability.

9. The hydraulic axial piston machine according to claim 1, wherein: the actuating valve further comprises a control valve housing in which the control piston is arranged; the actuating valve has a low-pressure connection connected to the low pressure, a working connection, and a pressure connection connected to the high pressure; and the control valve housing defines two intersecting radial ducts assigned to the working connection, and the control valve housing defines at least one further duct, which forms a fourth pilot oil connection that connects the actuation chamber and the working connection.

10. The hydraulic axial piston machine according to claim 1, further comprising: a proportional solenoid configured to adjust a position of the control piston, wherein, when the proportional solenoid is not energized, the control piston is moved into a control cut-off position.

11. The hydraulic axial piston machine according to claim 10, wherein, in a first energized state of the proportional solenoid, the first pilot oil connection is closed, the second pilot oil connection is open, and the third pilot oil connection is closed.

12. The hydraulic axial piston machine according to claim 11, wherein, in a second energized state of the proportional solenoid, the first pilot oil connection is closed, the second pilot oil connection is closed, and the third pilot oil connection is open.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred exemplary embodiments of the disclosure are explained in more detail below with reference to schematic drawings, of which:

(2) FIG. 1 shows a sectional representation of a hydraulic motor according to the disclosure, with electro-proportionally acting actuating device,

(3) FIGS. 2a, 2b show sectional representations of a first exemplary embodiment of an actuating device of the hydraulic motor in FIG. 1 with control cut-off,

(4) FIGS. 3a to 3c show the actuating valve in FIG. 2 in the position for control cut-off in various sectional representations,

(5) FIG. 3d shows a switch symbol of the actuating device,

(6) FIG. 4a shows a partial representation of an actuating device to illustrate a tilting of the valve body of the non-return valve,

(7) FIG. 4b shows an exemplary embodiment in which such tilting is prevented by the design and

(8) FIG. 5 shows an actuating valve without control cut-off and the corresponding switch symbol.

DETAILED DESCRIPTION

(9) The hydraulic machine according to the disclosure is explained below with reference to the example of a hydraulic motor. In principle the design features described can also be implemented in a hydraulic pump, preferably making the adjustments described below.

(10) FIG. 1 shows a longitudinal section through a hydraulic motor 1 of axial-piston design. This comprises a housing 2 and a housing cover 4, in which a motor shaft 8, which serves to drive a fan wheel, for example, is supported by way of a shaft bearing 6. The motor shaft 8 is rotationally fixed to a cylindrical drum 10, in which a plurality of pistons 12 is displaceably guided. These together with the cylindrical drum each define a working chamber 14, which by way of a control disk 16 connected to the housing 2 can be connected to high pressure or low pressure according to the rotational position of the cylindrical drum 10. The foot-side end portions of the pistons 12 remote from the respective working chamber 14 are each connected to a slide shoe 18 in the manner of a ball-and-socket joint. These slide shoes 18 bear on a slide surface of a swash plate 20, which is pivotally supported in the housing 2, so that as the cylindrical drum 10 rotates the pistons 12 perform a piston stroke according to the swivel angle of the swash plate 20. A return spring 22 acts on the swash plate 20 in the direction of its maximum swivel angle shown. This return spring 22 is on the one hand supported on an end wall of the housing 2 and on the other acts on the swash plate 20 at a radial distance from the shaft axis. The swash plate 20 is adjusted against the force of the return spring 22 by means of an actuating device 24, which basically comprises an actuating cylinder 26 and an actuating valve 28. The minimum swivel angle of the swash plate 20 is defined by a stop 30 adjustably arranged in the housing. Accordingly, in the position of the swash plate 20 shown, at the maximum swivel angle the hydraulic motor 1 is set to the maximum displacement, whilst with the swash plate 20 swiveled in (bearing on the stop 30) the minimum displacement is set.

(11) A non-return valve 31, which serves to prioritize the inward swiveling process for rapid adjustment of the hydraulic motor 1 in the direction of the minimum displacement, is integrated into the actuating device 24. The actuating valve 28 is proportionally adjustable by means of a proportional solenoid 32, so that accordingly the swivel angle and therefore also the displacement of the hydraulic motor 1 is adjustable in proportion to the energizing of the proportional solenoid 32.

(12) Details of the actuating device 24 are explained with reference to FIGS. 2 to 4. FIG. 2a shows an enlarged longitudinal section of the actuating device 28, the actuating device 28 in the view according to FIG. 2a being rotated through 180 about the radial axis, so that accordingly the proportional solenoid 32 is located on the left.

(13) As explained, the actuating device 28 basically comprises the actuating cylinder 26, the electro-proportionally adjustable actuating valve 28 and the non-return valve 31. The complete actuating device 24 is of cartridge-shaped design for fitting into a mount 34 (FIG. 1) of the housing 2. The actuating cylinder 26 has a cupped actuating piston 36, which is guided so that it is axially displaceable in the mount 34 of the housing 2 and acts by way of a type of ball-and-socket joint 38 (FIG. 1) on the swash plate 20. The actuating piston 36 together with the mount 34 and an actuating valve housing 40 defines an actuation chamber 42 which, as is explained in more detail below, can be connected to high pressure or low pressure by way of the actual actuating valve 28, in order to adjust the swash plate 20 through displacement of the actuating piston 36.

(14) The actuating valve 28 accordingly comprises a low-pressure connection T, a working connection A and high-pressure connection P. The latter is connected to the high-pressure side of the hydraulic motor, whilst the low-pressure connection T has a fluid connection to the tank or a fluid connection can be established via a pressure-regulating valve. The working connection A or its diagonal P-duct is connected to the actuation chamber 42 via two ducts 44, 45, yet to be explained in more detail below, only one duct 44 being indicated by dashed lines in the representation according to FIG. 2a. Accordingly the pressure set on the working connection A is also present in the actuation chamber 42.

(15) The actuating valve housing 40 has a valve bore 46, in which a control piston 48 is adjustably guided in an axial direction. This control piston 48 has two control grooves 50, 52, between which a control flange remains, which forms two control edges 54, 56. The second annular end face of the left-hand control groove 50 in FIG. 2a forms a further control edge 58, which serves as a control cut-off. The right-hand control groove 52 forms a further control edge 78. This will be explored in more detail below.

(16) The right-hand end portion of the control piston 48 in FIG. 2a extends into the interior of the actuating piston 36 and therefore into the actuation chamber 42. This end portion is provided with a taper 60, on which a valve body 62 tightly bears. This bearing contact is brought about by a measuring spring 61, which on the one hand is supported on the head of the actuating piston 36 and on the other acts on an annular shoulder of the valve body 62. In this bearing contact position the taper 60 submerges into a fabricated opening of the valve body 62, which forms a valve seat 64 of the non-return valve 31. The control piston 48 is formed with a bore 66, which opens out in the area of the valve seat 64 on the one hand and, via a radial bore portion, in the base of the left-hand control groove 50 in FIG. 2a on the other, and therefore forms a pilot oil connection 83 to the T-connection or its T-duct.

(17) According to FIG. 2a the proportional solenoid 32 is attached at the end face to the actuating valve housing 40, a tappet 68 at the end face bearing on the left-hand end portion of the control piston 48 in FIG. 2a, so that the control piston 48 can be adjusted via the tappet 68 according to the energizing of the proportional solenoid 32. The control piston 48 is biased into its bearing contact position against the tappet 68 by the measuring spring 61, and from the start of the control by a spring 70 supported at the end face on a housing shoulder, this spring 70 acting on a spring abutment 72 of the control piston 48.

(18) In the relative position represented in FIG. 2a the regular position 48 is situated in its regular position, which occurs when an equilibrium of forces prevails between the actuating forces applied by the proportional solenoid 32 and the opposing force resulting from the adjustment of the swash plate 20.

(19) The three connections T, A, P are each formed by radial ducts of the actuating valve housing 40, the working connection A being formed by two intersecting radial ducts, one of which runs perpendicular to the drawing plane in FIG. 2a (see also FIG. 3c). In the regular position shown the two middle control edges 54, 56 have a zero overlap with the radial bores of the working connection A, so that a pilot oil connection 83 to the low-pressure connection T or the pilot oil connection 82 to the high-pressure connection P is closed. In principle, however, a positive or negative overlap may also be selected in the regular position.

(20) In the regular position represented the pressure at the working connection A also acts, via the duct 44 and the further duct 45 not represented in FIG. 2a (see FIG. 3c), in the actuation chamber 42. The internal connection in the valve via the ducts 44 and 45 of the working connection A to the actuation chamber 42 means that such a connection through the pump housing can be dispensed with. In this position the low pressure, which is tapped via the internal bore 66 and the control groove 50, acts in the area of the valve seat 64.

(21) The spring 70 is arranged as a compression spring in a solenoid chamber 74, which is connected via a connecting duct 76, visible in FIG. 2b, to the actuation chamber 42, so that the same control pressure is present in both chambers 74, 42. This FIG. 2b shows a section through the actuating device 28, the sectional plane of which is offset by 45 in relation to that of FIG. 2a, that is to say it runs obliquely to the drawing plane in FIG. 2a.

(22) In the representation according to FIGS. 3a to 3c the control edge 58 of the control groove 50 opens the pilot oil connection 81 between the low-pressure connection and the solenoid chamber 74 when the proportional solenoid 32 is not energized, so that the low pressure prevails in this chamber. This is relayed via the connecting duct 76 also to the actuation chamber 42the actuating valve is in the control cut-off mode. In this case the pilot oil connection 82 between the working connection A and the high-pressure connection P is closed. By way of illustration, the actuating device 24 in FIGS. 3a to 3c is represented in this control cut-off position in three different sections. Here FIG. 3a shows a section corresponding to FIG. 2a. The representation according to FIG. 3b corresponds to that according to FIG. 2b, that is to say the sectional plane runs offset by approximately 45 to that in FIG. 3a. FIG. 3c finally shows a sectional profile which is offset by 90 in relation to that in FIGS. 3a, 2a, that is to say this sectional plane runs perpendicular to the drawing plane in the latter representations.

(23) It can be seen from the representation in FIG. 3a that in the control cut-off position the control edge 58 of the control piston 48 has opened the pilot oil connection 81 between the solenoid chamber 74 and the low-pressure duct connected to the low-pressure connection T. The pilot oil connection 82 between the connections A, P is closed by the outer control edge 78 of the control groove 52. The connecting duct 76, via which, as already explained, the solenoid chamber 74 is connected to the actuation chamber 42, can be seen in the section according to FIG. 3b.

(24) The two ducts 44, 45 referred to at the outset, via which the actuation chamber 42 is connected to the working connection A, or more precisely to the two intersecting radial A-ducts, can be seen in the section according to FIG. 3c. Accordingly, in the control cut-off position the low pressure is also present at the working connection A.

(25) In control cut-off the pump swivels out to the maximum swivel angle, for example in the event of a control signal loss.

(26) For example, should a pressure control be superimposed on the EK control previously described, which is an EP control with a cut-off position of the actuating valve, the interconnection ensues in such a way that the pressure regulator (not shown here) has priority over the electro-proportional adjustment. When the pressure regulator responds the tank connection T can then be connected to high pressure or load pressure via the pressure regulator, so that accordingly a pressure can also be built up in the actuation chamber 42 substantially regardless of the position of the control piston, 48, and the pump swivels back. In this case the non-return valve 31 described is operative. As explained, the pressure in the tank duct is tapped via the internal bore 66 of the control piston 48 and therefore acts on the valve body 62 in the opening direction. On activation of the pressure control a comparatively low actuating pressure (swash plate 20 swiveled) still prevails in the actuation chamber 42, so that the valve body 62 lifts off due to the pressure differential and pilot oil flows from the tank duct via the internal bore 66 and the opened non-return valve 31 into the actuation chamber 42, so that the actuating pressure in the latter is increased and the swash plate 20 accordingly swivels in and this inward swiveling movement is therefore prioritized. In the case of so-called DRS valves this high pressure may correspond to a relatively high control pressure, a load pressure or the like.

(27) With the non-return valve 31 opened, a control pressure is therefore admitted to the actuation chamber, bypassing the cross-sections opened by the control edges 52, 56.

(28) To illustrate this, the switch symbol of the actuating device 24 previously described, with the control cut-off, is shown in FIG. 3d. As explained above, the actuating device is biased by the return spring 22 and the measuring spring 61 towards the basic position shown, which corresponds to the control cut-off position. Through energizing of the proportional solenoid 32 a connection can then be made to high pressure in the A positions and to low pressure on further displacement into the b positions, so that pilot oil is delivered or drained off, in order to adjust the swivel angle. With an equilibrium of forces the regular position represented in FIG. 2a is adopted. According to the circuit diagram in FIG. 3d the spring 70 appears to be situated in the actuation chamber 42. It is located outside the actuation chamber, however, as can be seen from FIGS. 3a to 3c.

(29) The superimposed pressure control allows a pressure to operate on the tank connection T which via the internal bore 68 then acts on the non-return valve 31, so that the valve body 62 lifts off and pilot oil can swivel directly into the actuation chamber 42, bypassing the control cross sections of the actuating valve 28.

(30) FIG. 4a shows a problem which can occur with such an actuating device 24 having a non-return valve 31. Greatly simplified, this represents a part of the actuating device 24 with the control piston 48, the valve body 62 and the actuating piston 36, which is operatively connected to the swash plate 20 by the ball-and-socket joint 38. As explained, the valve body 62 of the non-return valve 31 also serves as spring plate for the measuring spring 61. As is shown in FIG. 4a, it may happen under unfavorable operating conditions (swivel angle, position of the control piston etc.) that the valve body 62 (in other words the spring plate of the measuring spring 61) tilts. This tilting may lead to damaging of elements of the actuating device 24, in particular the actuating piston 36, the valve body 62 and/or the control piston 48. Such short spring plates are used in axial piston pumps, for example, as are described in the publication DE 199 49 169.

(31) Compared to this known design the valve body 62 (see FIG. 4b) is designed with a significantly greater axial length, the piston skirt of the actuating piston 36 also being extended in order reliably to prevent such a tilting in all switching positions. The fact that the outside diameter of the valve body 62 and the inside diameter of the actuating piston 36 are adapted for optimum guidance and tilting safeguards likewise contributes to this.

(32) FIG. 5 shows a variant of the exemplary embodiment previously described, without control cut-off. The basic construction corresponds to the exemplary embodiment previously described, the only basic difference being that the control edge 58 does not serve to open a pilot oil connection between the tank duct and the solenoid chamber 74. The control groove 50 is therefore shorter than in the exemplary embodiment previously described. The actuating device 24 is again shown in the regular position of the actuating piston 36, in which the control edges 54, 56 control the pilot oil connection of the A-duct to the T-duct or to the P-duct. The circuit diagram is again drawn in at the bottom of FIG. 5. According to this circuit diagram the spring 70 again appears to be situated in the actuating chamber 42. It is located outside the actuating chamber, however, as can be seen from FIGS. 3a to 3c. When the proportional solenoid 32 is not energized, the actuating valve 28 is situated in its basic position shown, in which the pilot oil connection between the working connection A and the high-pressure connection P is opened, so that the high pressure acts in the actuating chamber 42the swash plate 20 swivels in. When the proportional solenoid 32 is energized the actuating chamber 42 is connected to the low-pressure connection T, so that the pump accordingly swivels out.

(33) In principle the designs described above can be used both in hydraulic motors and in hydraulic pumps, only minor adaptations being necessary. For example, the working point in the case of hydraulic motors according to the disclosure is selected so that a larger opening cross section is provided for swiveling the swash plate 20 of the hydraulic motor 1 out. This shifting of the working point makes it possible to use a solenoid having a shorter stroke and hence a greater force, without adversely affecting the swivel time. To compensate for this shifting of the working point the stiffness of the return spring 22 can be correspondingly increased. The control cut-off described is effective both in pumps and in motors. A further advantage of the solution according to the disclosure is that the connecting duct 76 for connecting the solenoid chamber 74 and the actuating chamber 42 and the two ducts 44, 45 are laid into the actuating valve housing 40.

(34) Another difference when using the design according to the disclosure in a hydraulic pump compared to use in a hydraulic motor is that the measuring spring 61 in a hydraulic pump is designed with a somewhat reduced spring characteristic. If, for example, a spring force of, say, 40N is necessary in the case of a hydraulic motor, the measuring spring 61 would be set to approximately 30N for use as a hydraulic pump. A corresponding adjustment should then also be made to the proportional solenoid. In principle, therefore, the control piston 48 is more strongly tensioned in motor operation due to the somewhat stronger proportional solenoid 32 and the stronger measuring spring 61. This modification can basically also be used to advantage in a hydraulic pump.

(35) In principle the actuating valve may be designed as a mounted valve for external attachment, or as a cartridge valve, in the manner previously described.

(36) It is naturally possible, by means of an overriding control, also to regulate the torque or the pressure of the motor electronically by controlling the swivel angle of the swash plate, as described above, provided that these variables are registered and evaluated by the system.

(37) A hydraulic motor of axial-piston design is disclosed, in which a swivel angle of swash plate is electro-proportionally adjustable.

LIST OF REFERENCE NUMERALS

(38) 1 hydraulic motor 2 housing 4 cover 6 shaft bearing 8 motor shaft 10 cylindrical drum 12 piston 13 cylinder bore 14 working chamber 16 control disk 18 slide shoe 20 swash plate 22 return spring 24 actuating device 26 actuating cylinder 28 actuating valve 30 stop 31 non-return valve 32 proportional solenoid 34 mount 36 actuating piston 38 ball-and-socket joint 40 actuating valve housing 42 actuation chamber 44 duct 45 duct 46 valve bore 48 control piston 50 control groove 52 control groove 54 control edge 56 control edge 58 control edge 60 taper 61 measuring spring 62 valve body 64 valve seat 66 internal bore 68 tappet 70 spring 72 spring abutment 74 solenoid chamber 76 connecting duct 78 control edge