EP0071655B1 - Pneumatically powered hydraulic pump - Google Patents

Abstract

1. Pneumatically actuated hydraulic pump (1) including a double acting actuator piston (9) adapted to be alternately pressurized via a switch valve (14) for actuating hydraulic pump elements (19), a valve spool (30) mounted in said switch valve (14) for displacement between two operative positions by the action of a selector control pressure derived from the pressure acting on said actuator piston (9) so as to connect in each of its operative positions a connecting passage (25 or 26) to a pressurized air supply passage, and another connecting passage (26 or 25) to a return passage (28 or 29), said return passages (28, 29) being disposed approximately in the same radial planes as said connecting passages (25, 26), as referred to the longitudinal axis of said valve spool, characterized in that a coaxial reduced-diameter auxiliary piston (41) is associated with each end face of said valve spool (30), each said auxiliary piston being sealedly slidable in the switch valve housing (15) and adapted to have its end facing away from said valve spool (30) acted upon by said selector control pressure, in that one of two annular chambers (39) is disposed between sealed guide means (38) for each auxiliary piston (41) and the respective end face (32) of said valve spool (30), the pressurized air being permitted to leak into said annular chambers, and in that a restricted venting channel (46) is formed between the end face (32) of said valve spool (30) closing the connection between the pressurized air supply passage (24) and the associated return passage (28, 29) and said return passage (28, 29).

Description

The invention relates to a pneumatically operated hydraulic pump, with a double-acting working piston, which can be acted upon alternately via a directional control valve, for actuating hydraulic pump elements, with a spool valve in the directional control valve, which is derived from the pressurization of the working piston and can be displaced between two working positions Connects compressed air connection and another supply connection with a return connection, the return connections being located in approximately the same radial planes - with respect to the longitudinal piston axis - as the supply connections.

In a known, pneumatically operated hydraulic pump (DE-U 7919602 and DE-A 2915096) the two ends of the spool are used in the directional control valve for the pilot pressure. The pilot pressure effective area corresponds to the cross-sectional area of the spool. A circumferential annular groove is formed in the piston valve for connecting a supply connection to the associated return connection. When the compressed air is released from the working piston into the return port, it applies the prevailing pressure to the two flanks of the annular groove. Since the flank surfaces are equal in size, there is no reaction force for the spool. To reverse the spool from one working position to the other working position, the pilot pressure is derived from the pressure on one side of the working piston and is guided to one end of the spool so that it moves to its other working position, in which it applied the pressure to the previous one Side of the working piston and creates a passage from the pressure supply to the other side of the working piston. The pilot pressure is reduced after the spool has moved to its new working position above the spool. It has now been shown in practice that, in particular when the pneumatically actuated hydraulic pump works against a hydraulic pressure accumulator, an equilibrium state is gradually reached between the pneumatically actuated working piston and the hydraulic pumping element which is just delivering. The reciprocating movement of the working piston slows down more and more as it approaches this state of equilibrium until the working piston finally comes to a standstill. Often, the working piston is in the equilibrium position from one end position, and the piston slide then creeps, so to speak, from one working position towards the other working position. It has now been found that the spool does not come completely into the new working position, but sticks shortly beforehand in an intermediate position in which the connection between the still pressurized working space on one side of the working piston and the return connection has not yet been established. If the back pressure on the hydraulic pump element then decreases, for example because pressure medium is withdrawn from the pressure accumulator, the spool should now move completely into its new working position in order to release the compressed air from one side of the working piston and pressurize the other side. However, the spool remains in this intermediate position and does not leave it even when the back pressure of the hydraulic pump element is completely reduced. It is obvious that such a pump cannot be used when reliable delivery is important, for example when keeping a hydraulic press closed or the like.

The invention has for its object to improve a pneumatically operated hydraulic pump of the type mentioned in such a way that it starts reliably again when its piston remains motionless for a long time in the state of equilibrium.

The object is achieved according to the invention in that the piston slide is assigned a coaxial auxiliary piston of smaller diameter on the end face, which is guided in a displaceably sealed manner in the directional control valve housing and can be acted upon with pilot pressure at its end facing away from the piston slide, that between the sealing guides for the auxiliary piston and one of two annular chambers is arranged at the respective end face of the piston valve, whereby the compressed air can leak into these annular chambers and a throttled ventilation channel is formed between the front end of the piston valve which blocks the connection from the compressed air connection to the associated return connection and the return connection.

It has surprisingly been found that with such a design of the pneumatically actuated hydraulic pump, the piston slide immediately gives up its previously explained intermediate position even after a long standstill with simultaneous standstill of the working piston when the back pressure on the working piston decreases and the state of equilibrium is released. The spool is reliably moved from this intermediate position to the new working position because the compressed air from the previously loaded side of the working piston can leak through the spool and builds up in front of the front end of the spool, since it prevents free flow through the return port, which has not yet been released becomes. In the annular chamber between the sealing guide for the auxiliary piston and the front end of the spool, this leaking compressed air presses on the front end of the spool with an effective area that the Area difference between the cross section of the spool and the cross section of the auxiliary piston corresponds. A force is created that moves the spool slightly towards its new working position, so that suddenly a small passage from the supply connection into this annular chamber and at the same time from the annular chamber to the return connection is free. The compressed air then flows in quickly and expands in the annular chamber, creating a new force impulse for the piston valve, which ultimately pushes it completely into its new working position. Since, of course, an annular chamber of the same type is filled with compressed air at the opposite end of the piston valve, which forms an air cushion that would initially oppose the piston valve movement, the throttled ventilation channels are provided which degrade this air cushion into the return connection.

It is advantageous if the auxiliary pistons are formed in one piece with the piston slide or are attached to the front ends of the piston slide. As an alternative to this, however, an embodiment is favorable in which the auxiliary pistons are formed separately from the piston slide and can be alternately placed against the respective end face at pilot pressure. The last-mentioned embodiment is cheaper in terms of production technology and with regard to the mounting of the directional control valve.

Also important is another feature according to which each auxiliary piston can be displaced in a through bore of a guide sleeve fixed in the piston slide bore, which separates a pilot pressure chamber from the aforementioned chamber, which is delimited by the respective end face and the guide sleeve. A cylindrical through piston slide bore can be provided in the housing of the directional control valve, into which the two guide sleeves are screwed after the piston slide has been inserted, before the auxiliary pistons are to be inserted into the through holes of the guide sleeves. This also has advantages in terms of manufacture and assembly.

In order that the formation of a harmful pressure cushion in each of the annular chambers is avoided, it is also important that the ventilation channels are formed in the piston slide. This also eliminates drilling work in the housing of the directional control valve.

A particularly expedient embodiment of the subject matter of the invention is characterized in that each venting channel is formed by at least one worn-off jacket area of the piston valve, which extends in the longitudinal direction from the free front end of the piston valve to the jacket area which is in a working position in front of the return connection. To do this, it is sufficient to grind or mill off the piston valve casing in the specified longitudinal extent range.

As an alternative to this, each ventilation duct can also be designed as a housing bore leading from the annular chamber to the return connection. It is only important that the venting channel vents the chamber when this ring chamber itself is shut off from the return port by the position of the piston valve.

Finally, it is still important that - with respect to the longitudinal axis of the spool - the supply connections from the front end of the spool can be released slightly ahead of the associated return connection. This measure leads to the effect that the deliberate leakage of the compressed air from the supply connection into the annular chamber and the associated pressure impulse for the piston valve are brought about in a targeted manner. This can be accomplished either by slightly displacing the mouth of each feed connection with respect to the mouth of the associated return connection or by customary bevels or notches on the spool or in the area of the feed connection.

An embodiment of the invention is explained below with reference to the drawing.

• Fig. 1 eine schematische Schnittansicht einer pneumatisch betätigten Hydraulikpumpe in einem Hydraulikbehälter,
• Fig. 2 einen Axialschnitt durch das in Fig. 1 als Block dargestellte Wegesteuerventil,
• Fig. 3 einen um 90° gedrehten Schnitt der Ebene 111-111 von Fig. 2, und
• Fig. 4 einen um 90° nach unten gedrehten Horizontalschnitt durch das Wegesteuerventil von Fig. 2, und zwar in einer die Kolbenschieberlängsachse aufweisenden Horizontalebene.

Show it:

• 1 is a schematic sectional view of a pneumatically operated hydraulic pump in a hydraulic tank,
• 2 shows an axial section through the directional control valve shown as a block in FIG. 1,
• 3 shows a section of the plane 111-111 of FIG. 2 rotated through 90 °, and
• Fig. 4 is a horizontal section rotated by 90 ° down through the directional control valve of Fig. 2, in a horizontal plane having the piston slide longitudinal axis.

In the unit shown in Fig. 1, a pneumatically operated hydraulic pump 1 is arranged in a trough-shaped container 2. It is surrounded on all sides by hydraulic fluid 4. The container is closed with a lid 3. A compressed air supply line 5 leads to the pneumatic part of the pump, while a return line 6 leads away from it and out of the container. A hydraulic pressure line leads from the hydraulic part of the pump 1 to a consumer, not shown, e.g. a hydraulic accumulator.

The hydraulic pump 1 consists of a cylinder liner 18, which is closed at both ends by cylinder bottoms 7, so that a closed cylinder space 8 is created therein. Between the cylinder bottoms 7, a double-acting pneumatic working piston 9 is slidably mounted, which is equipped with ring seals 10 on the circumference. A transverse bore 11 passes through the working piston 9. The working piston 9 also has a continuous piston rod 12 or two piston rod stubs which are sealed by the cylinder bottoms 7 and seals 13 and project displaceably outwards.

To act on the working piston, a directional control valve 14 is placed astride the cylinder liner 18; Via the directional control valve 14, compressed air is fed from the compressed air supply line 5 alternately via supply connections 20 and 21 to a piston side of the working piston 9. The used compressed air is led to the return line 6 via return connections 28, 29 which can be seen in detail from FIGS. 2 to 4. Small flow channels 23 in the cylinder liner 18 serve to tap pilot pressure. The directional control valve 14 is actuated with this pilot pressure. The flow channels 23 are run over by the ring seals 10 of the working piston 9 in such a way that its position causes the directional control valve to be reversed and the partial cylinders to be acted upon properly.

On the outside of the cylinder bottoms 7, a support part 27 is fastened with clamping screws, to each of which a hydraulic pump element 19 is fastened. Each pump element 19 has a pressure valve, not shown, and a suction valve, as well as a plunger 34, which is provided with a collar 35 at the free end and is thus pressed by a spring 33 against the free end of the piston rod 12, designated 22.

The hydraulic pump 1 works as follows:

In the position shown in FIG. 1, the compressed air comes from the supply line 5 and the supply connection 21 to the left side of the working piston 9 and shifts it to the right. The compressed air located on the right side of the piston is pressed through the supply connection 20 and the directional control valve into the return line 6. When it moved to the right, the working piston 9 caused an ejection stroke for hydraulic fluid via the piston rod 12 in the right pump element 19. In the left pump element 19, however, the spring 33 has brought about a suction stroke and tracked the plunger 34 of the movement of the piston rod 12.

When the working piston 9 has reached its outermost right position, its left ring seal 10 runs over the flow channel so that the pilot pressure 14 reaches the directional control valve 14. In the directional control valve 14, a piston slide 30 is now reversed so that the supply connection 20 is connected to the compressed air line 5. Thereupon, the working piston 9 is again shifted to the left. Then the pump element on the right in FIG. 1 operates in the suction cycle, while the left pump element works in the pressure cycle.

The directional control valve 14 has a cuboid housing 15, which is attached directly to the cylinder liner 18 via an intermediate layer 16. The housing 15 is penetrated in the longitudinal direction by a cylindrical piston slide bore 17. A compressed air connection 24, which is connected to the compressed air supply line 5, leads to the piston slide bore 17 in the central plane of symmetry of the housing 15. Supply connections 25 and 26 are assigned opposite the compressed air connection 24, but offset laterally thereto, to which the supply connections 20 and 21 connect to the respective piston sides. In the same radial planes as the feed connections 25, 26 there are in each case paired return connections 28 and 29, which lead to the return line 6 in a manner not shown. The return connections 28 and 29 cut the piston slide bore on the outside (see FIGS. 3 and 4). In the piston slide bore 17, the piston slide 30 is guided so as to be longitudinally displaceable and has a vertically continuous elongated hole 31 and flat end faces 32. The ends of the housing bore 17 are sealed by locking screws 36 which delimit pilot pressure chambers 37 inside the housing. The pilot pressure chambers 37 are on the other hand delimited by guide sleeves 38, each of which is provided with a seal 40 and fixed in the piston slide bore 17. An annular chamber 39 is formed between the inner end face of each guide sleeve 38 and the end face 32 of the piston valve facing it. In each guide sleeve 38, an auxiliary piston 41 is guided in a sealed, displaceable manner, the outer end of which protrudes into the pilot pressure chamber 37, while its inner end can be placed against an end 32 of the piston slide 30. In the housing 15, a pin 42 is also provided, which protrudes into the elongated hole 31 and both secures the piston slide 30 and causes a stroke limitation. Housing bores 43 and 44 lead from the flow channels 23 to the pilot pressure chambers 37. Plugs 45 close auxiliary bores in the housing, which are not highlighted, and which belong to the feed connections 25 and 26. From each annular chamber 39, a throttled ventilation duct 46 leads to a return connection 28, 29. These ventilation ducts 46 (FIG. 2, 3) are formed by lateral abrasion on the jacket of the piston slide 30, these removals extending from the respective front end of the piston valve to the jacket region extend with which the spool 30 is in a working position in front of the return ports 28, 29.

4 shows a variant in the formation of a ventilation channel 46 ', this being designed as a housing bore from the annular chamber 39 to the return connection 28 (indicated by dashed lines).

• Der Arbeitskolben 9 hat mit seiner Ringdichtung 10 soeben den Strömungskanal 23 überfahren. Zuvor hat die in Fig. rechte Ringdichtung den rechten Strömungskanal 23 überfahren, so dass die bis dahin mit Vorsteuerdruck beaufschlagte, rechte Vorsteuerdruckkammer 37 in die Querbohrung 11 hinein entlüftet wurde. Über das Langloch 31 steht der Druckluftanschluss 24 unmittelbar mit dem Zuführanschluss 25 in Verbindung. Gleichzeitig steht der Zuführanschluss 26 über Ringkammer 39 mit den Rücklaufanschlüssen 29 in Verbindung. Da die Druckluft von der linken Seite des Arbeitskolbens 9 über den Strömungskanal 23 nun in die Vorsteuerdruckkammer 37 gelangt, wird der Hilfskolben 41 nach rechts verschoben, wobei er den Kolbenschieber 30 aus der dargestellten linken Arbeitsstellung nach rechts verschiebt. Sobald das rechte Stirnende 32 den Zuführanschluss 26 abgedeckt hat, wird das dann in der Ringkammer 39 entstehende Luftpolster über den rechten, gedrosselten Entlüftungskanal 46 weiterhin in die Rücklaufanschlüsse 29 abgebaut. Der Kolbenschieber kann bis in seine rechte Arbeitsstellung verfahren, wo er durch den Stift 42 abgefangen wird.

The directional control valve works as follows:

• The working piston 9 has just passed over the flow channel 23 with its ring seal 10. Prior to this, the right ring seal in FIG. 1 passed over the right flow channel 23, so that the right pilot pressure chamber 37, which had previously been supplied with pilot pressure, was vented into the transverse bore 11. The compressed air connection 24 is via the elongated hole 31 indirectly in connection with the feed connection 25. At the same time, the feed connection 26 is connected to the return connections 29 via the annular chamber 39. Since the compressed air now reaches the pilot pressure chamber 37 from the left side of the working piston 9 via the flow channel 23, the auxiliary piston 41 is shifted to the right, whereby the piston slide 30 is shifted to the right from the left working position shown. As soon as the right front end 32 has covered the supply connection 26, the air cushion which then arises in the annular chamber 39 is further broken down into the return connections 29 via the right, throttled ventilation duct 46. The piston slide can move into its right working position, where it is intercepted by the pin 42.

During this displacement movement of the piston slide, the supply connection 25 is first shut off and at the same time the supply connection 26 is separated from the return connections 29. Subsequently, the left end 32 of the piston slide releases the connection from the supply connection 25 to the annular chamber 39 and from this to the return connections. At the same time, a connection is established from the compressed air connection 24 via the elongated hole 31 to the supply connection 26. The working piston 9 is reversed. As long as the back pressure from the pump elements 19 is still lower than the force generated by the working piston depending on the level of the pressure of the compressed air, the working piston moves back and forth in cycles.

With increasing back pressure of the hydraulic pump elements, the pump approaches an equilibrium state in which the force of the working piston is finally canceled by the counterforce of a pump element. When this equilibrium state is approached, the reciprocating movement of the working piston slows down until it finally stops. The last work cycle of the working piston runs at a speed that is almost imperceptible to the human eye. The state of equilibrium can occur when the working piston is in a position, and this is often the case in which the left-hand ring seal 10 (see FIG. 2) has not yet passed over the flow channel 23. Accordingly, sufficient pilot pressure cannot build up in the pilot pressure chamber 37 and would be able to move the piston slide fully into its right-hand working position via the auxiliary piston 41. Rather, it is shown that the flow channel 23 is only subjected to very low pressure, which pressure then only leads to the piston slide being shifted to the right until it finally stops in an intermediate position in which its left end face 32 just barely feeds the connection 25 does not release. The working piston and the piston slide 30 now remain in these positions as long as the state of equilibrium continues. It cannot be avoided that the compressed air on the left side of the working piston 9 begins to leak into the left annular chamber 39. As a result of a pressure build-up in the left-hand annular chamber 39, a force component results on the end face 32 which only slightly displaces the piston slide 30 in the direction of its new working position. As a result, the flow connection from the supply connection 25 to the left-hand annular chamber 39 is increased still further, the throttled ventilation duct 46 and a small passage to the return connection 28 also being cleared at the same time. The compressed air then flowing into the annular chamber 39, however, expands after the throttled inflow before it flows out into the return connection 28. This slight expansion is sufficient to completely push the piston slide 30 out of its intermediate position into the new working position. The right side of the working piston 9 is then connected to the compressed air supply line 5, while the left side is fully connected to the return line. If the state of equilibrium then continues, there is no further movement of the working piston 9, but the piston slide is in the correct working position, in which the directional control valve comes into operation again with its correct function when the hydraulic counterpressure on the working piston decreases.

This effect of the pressure pulse in the annular chambers 39 also occurs reliably when the auxiliary pistons are formed in one piece with the piston slide. It is only important that the cross-sectional area of the auxiliary pistons is smaller than the effective area of the piston slide in the annular chamber 39, and that a throttled ventilation line leads out of the annular chambers 39, which breaks down the air cushions, which have the desired effect of the relatively weak pressure pulses or that of them Could compensate pressure impulses on the spool.

Finally, it should also be pointed out that the front ends 32 of the piston slide release the feed ports 25, 26 in advance of the return ports. For this purpose, either small bevels are provided at the mouths of the feed connections, or a small offset is provided between each feed connection and its opposite return connection - with respect to the longitudinal axis of the slide.

Claims (7)

1. Pneumatically actuated hydraulic pump (1) including a double acting actuator piston (9) adapted to be alternately pressurized via a switch valve (14) for actuating hydraulic pump elements (19), a valve spool (30) mounted in said switch valve (14) for displacement between two operative positions by the action of a selector control pressure derived from the pressure acting on said actuator piston (9) so as to connect in each of its operative positions a connecting passage (25 or 26) to a pressurized air suply passage, and another connecting passage (26 or 25) to a return passage (28 or 29), said return passages (28, 29) being disposed approximately in the same radial planes as said connecting passages (25, 26), as referred to the longitudinal axis of said valve spool, characterized in that a coaxial reduced-diameter auxiliary piston (41) is associated with each end face of said valve spool (30), each said auxiliary piston being sealedly slidable in the switch valve housing (15) and adapted to have its end facing away from said valve spool (30) acted upon by said selector control pressure, in that one of two annular chambers (39) is disposed between sealed guide means (38) for each auxiliary piston (41) and the respective end face (32) of said valve spool (30), the pressurized air being permitted to leak into said annular chambers, and in that a restricted venting channel (46) is formed between the end face (32) of said valve spool (30) closing the connection between the pressurized air supply passage (24) and the associated return passage (28, 29) and said return passage (28, 29).

2. A pneumatically actuated hydraulic pump according to claim 1, characterized in that said auxiliary pistons (41) are integrally formed with said valve spool (30) or secured to the end faces (32) of said valve spool (30).

3. A pneumatically actuated hydraulic pump according to claim 1, characterized in that said auxiliary pistons (41) are formed separately from said valve spool (30) and adapted to be alternately engaged with respective end faces (32) thereof by the action of the selector control pressure acting thereon.

4. A pneumatically actuated hydraulic pump according to any of claims 1 to 3, characterized in that said venting channels (46) are formed in the valve spool (30).

5. A pneumatically actuated hydraulic pump according to claim 1, characterized in that said venting channel (46) is formed by at least one cut-away peripheral portion of said valve spool (30) extending from the end face (32) of said valve spool (30) in a longitudinal direction to a location facing the return passage (28, 29) in one operative position.

6. A pneumatically actuated hydraulic pump according to claim 1, characterized in that said venting channel (46') is formed as a housing bore extending from said annular chamber (39) to said return passage (28, 29).

7. A pneumatically actuated hydraulic pump according to any of claims 1 to 6, characterized in that - with reference to the longitudinal axis of said valve spool - the connecting passages (25, 26) are adapted to be uncovered by the end face (32) said valve spool (30) at a slightly advanced timing with respect to the associated return passage (28, 29).

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