EP0071655A1 - 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 actuated 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 in the directional control valve which can be displaced between two working positions by pilot pressure derived from the pressurization of the working piston. which connects a supply connection to the pressure supply and another supply connection to a return connection in each working position, the return connections lying 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-GM 7 919 602 and DE-OS 2 915 096) 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 connection, it acts on the two flanks of the annular groove with the prevailing pressure. Since the flank surfaces are of equal size, there is no reaction force for the piston slide. 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 guided to one end of the spool, so that it moves to its other working position, in which it applies pressure to the one previously 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 pump element which is just conveying. The reciprocating movement of the working piston slows down Approaching this state of equilibrium is increasing 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 hangs 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 piston slide would now have to move completely into its new working position in order to release the compressed air from one side of the working piston and to apply pressure to the other side. The piston slide 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 is the. Object of the 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 in that the spool is assigned a coaxial auxiliary piston of smaller diameter on the end face, which is guided in a sealed manner in the directional control valve housing and is displaceably guided at the end facing away from the spool can be acted upon by pilot pressure, and that a throttled venting channel is formed between the front end of the spool valve, which shuts off the connection from the feed connection to the associated return connection, and the return connection.

It has surprisingly been found that, with such a design of the pneumatically operated hydraulic pump, the piston slide, even after a long standstill with simultaneous standstill of the working piston, immediately gives up its previously explained intermediate position when the back pressure on the working piston drops 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 can leak through from the previously applied side of the working piston and builds up in front of the front end of the spool, since it is prevented from flowing freely into the return port, which has not yet been released. Between the sealing guide for the auxiliary piston and the front end of the piston slide there is an annular chamber in which this leaking compressed air presses on the front end of the piston slide with an active surface which corresponds to the area difference between the cross section of the piston slide and the cross section of the auxiliary piston. There is a force 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 pulse for the piston valve, which finally pushes it completely into its new working position. Since, of course, there is an annular chamber of the same type at the opposite end of the piston valve, which is filled with compressed air, which forms an air cushion that initially prevents the piston valve movement still opposed, the throttled ventilation channels are provided, which break down this air cushion into the return connection.

According to the invention, 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 space 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 according to the invention 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 useful embodiment of the subject of the invention is characterized in that everyone Venting channel is formed by at least one worn 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 the piston valve casing in the specified longitudinal extent.

As an alternative to this, each ventilation channel can also be designed as a housing bore leading from the chamber to the return connection. It is only important that the venting channel vents the chamber when this 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 piston axis - the feed connections from the front end of the piston valve can be released slightly in advance 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 chamber and the pressure pulse associated therewith 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 piston slide 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 III-III 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,
• Fig. 3 is a 90 ° rotated section of the plane III-III of Fig. 2, 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 40 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 formed 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 is from the Compressed air supply line 5 is alternately supplied with compressed air 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 22 are run over by the ring seals 10 of the working piston 9 in such a way that their position causes the reversal of the directional control valve and the correct loading of the partial cylinder spaces.

On the outside of the cylinder bottoms 7, a carrier 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 26.

• In der in Fig. 1 gezeigten Stellung gelangt die Druckluft aus der Zuführleitung 5 und den Zuführanschluß 21 auf die linke Seite des Arbeitskolbens 9 und verschiebt diesen nach rechts. Die auf der rechten Seite des Kolbens befindliche Druckluft wird durch den Zuführanschluß 20 und das Wegesteuerventil in die Rücklaufleitung 6 gepreßt. Bei seiner Bewegung nach rechts hat der Arbeitskolben 9 über die Kolbenstange 12 im rechten Pumpelement 19 einen Ausstoßtakt für Hydraulikflüssigkeit bewirkt. In dem linken Pumpelement 19 hat hingegen die Feder 33 einen Saughub bewirkt und den Tauchkolben 34 der Bewegung der Kolbenstange 12 nachgeführt.

The hydraulic pump 1 works as follows:

• In the position shown in Fig. 1, the compressed air from the feed line 5 and the feed port 21 reaches 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 feed 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 extreme right position, its left ring seal 10 runs over the flow channel, so that it reaches the directional control valve 14 as a result of this pilot pressure. In the directional control valve 14, a piston slide 30 is now reversed so that the compressed air connection 20 is connected to the compressed air supply 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 to the compressed air connection 24 opposite, but laterally offset, to which the 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 each cut the housing bore on the outside (see FIGS. 3 and 4). In the housing bore 17, the piston slide 30 is guided so as to be longitudinally displaceably sealed and has a vertically continuous elongated hole 31 and flat end faces 32. The ends of the housing bore 17 are sealed by screw plugs 36 which delimit pilot pressure chambers 37 inside the housing. The pilot pressure chambers 37, on the other hand, are delimited by guide sleeves 38, each of which is provided with a seal 40 and fixed in the housing bore 17. Between the inner end of each guide sleeve 38 and an annular chamber 39 is formed on the end 32 of the spool that faces this end. 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 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 connecting channels 23 to the pilot 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 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 removals on the jacket of the piston slide 30, these removals extending from the respective front end of the piston slide 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 chamber 39 to the return connection 28 (indicated by dashed lines).

• Der Arbeitskolben 9 hat mit seiner Ringdichtung 10 soeben den Kanal 23 überfahren. Zuvor hat die in Fig. 2 rechte Ringdichtung den rechten Anschluß 23 überfahren, so daß die bis dahin mit Vorsteuerdruck beaufschlagte, rechte Steuerkammer 37 in die Bohrung 11 hinein entlüftet wurde. Über das Langloch 31 steht der Druckanschluß 24 unmittelbar mit dem Zuführanschluß 25 in Verbindung. Gleichzeitig steht der Zuführanschluß 26 über die Ringkammer 39 mit den Rücklaufanschlüssen 29 in Verbindung. Da die Druckluft von der linken Seite des Arbeitskolbens 9 über den Kanal 23 nun in die Steuerkammer 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 Kammer 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 run over the channel 23 with its ring seal 10. Before that, the right ring seal in FIG. 2 passed over the right connection 23, so that the right control chamber 37, which had been acted upon by pilot pressure up to that point, was vented into the bore 11. The pressure connection 24 is connected directly to the feed connection 25 via the elongated hole 31. At the same time, the feed connection 26 protrudes the annular chamber 39 with the return ports 29 in connection. Since the compressed air now passes from the left side of the working piston 9 via the channel 23 into the control chamber 37, the auxiliary piston 41 is shifted to the right, whereby it moves the piston slide 30 from the left working position shown to the right. As soon as the right front end 32 has covered the feed connection 26, the air cushion which then arises in the 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 valve, the feed connection 25 is first shut off and at the same time the feed connection 26 is separated from the return connections 29. Subsequently, the left end 32 of the spool releases the connection from the feed port 25 to the annular chamber 39 and from there to the return ports. At the same time, a connection is established from the pressure connection 24 via the elongated hole 31 to the feed 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 equilibrium state 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 channel 23. Accordingly, sufficient pilot pressure cannot build up in the control pressure chamber 37, which would be able to move the piston slide fully into its right-hand working position via the auxiliary piston 41. Rather, it turns out that the 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 annular chamber 39 is further enlarged, the throttled ventilation duct 46 and a small passage to the return ducts 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 pressure supply 5, while the left side is fully connected to the return. If the state of equilibrium then continues, there is no further movement of the working piston 9, however the spool is in the correct working position, in which the directional control valve starts operating again with its correct function when the hydraulic back pressure 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 spool in the chamber 39, and that a throttled vent line leads out of the chambers 39, which breaks down the air cushions, which have the desired effect of the relatively weak pressure impulses or by them Could compensate pressure impulses on the spool.

Finally, it should be pointed out that the front ends 32 of the piston slide release the feed ports 25, 26 leading to 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 (8)

1.Pneumatically operated hydraulic pump, with a double-acting working piston, which can be acted upon alternately via a directional control valve, for operating hydraulic pump elements, with a spool valve in the directional control valve, which can be displaced between two working positions by the pilot pressure being derived from the pressurization of the working piston, which in each working position has a supply connection with the pressure supply and connects another feed connection with a return connection, the return connections in approximately the same radial planes - with respect to the longitudinal piston axis - as the Zu Guide connections are located, characterized in that the piston spool (30) is assigned a coaxial auxiliary piston (41) with a smaller diameter on the end face, which is guided displaceably in a sealed manner in the directional control valve housing and can be acted upon by pilot pressure at the end facing away from the piston spool, and that between each of which A throttled ventilation channel (46, 46 ') is formed from the supply connection to the front end of the spool valve (30) which shuts off the associated return connection and the return connection. 2. Pneumatically operated hydraulic pump according to claim 1, characterized in that the auxiliary pistons with the piston slide (30) are integrally formed or attached to the front ends of the piston slide. 3. Pneumatically operated hydraulic pump according to claim 1, characterized in that the auxiliary pistons (41) from the piston slide (30) are formed separately and can be applied alternately against the respective end face (32) when the pilot pressure is applied. 4. Pneumatically operated hydraulic pump according to one of claims 1 to 3, characterized in that each auxiliary piston (41) is displaceable in a through bore of a guide sleeve (38) fixed in the piston slide bore (17), which has a pilot pressure chamber (37) from a chamber ( 39) separates, which is limited by the respective end face (32) and the guide sleeve. 5. Pneumatically operated hydraulic pump according to one of claims 1 to 4, characterized in that the ventilation channels (46) are formed in the piston valve (30). 6. Pneumatically operated hydraulic pump according to claim 4, characterized in that the ventilation channel (46) is formed by at least one worn-off jacket area of the piston valve (30), which extends from the front end (32) of the piston valve (30) in the longitudinal direction to the jacket area , which is in a working position in front of the return connection (28, 29). 7. Pneumatically operated hydraulic pump according to claim 4, characterized in that the ventilation channel (26 ') is formed as a housing bore leading from the chamber (39) to the return. 8. Pneumatically operated hydraulic pump according to one of claims 1 to 7, characterized in that - based on the longitudinal piston axis - the feed connections (25, 26) from the front end (32) of the piston valve (30) each slightly leading to the associated return port (28, 29th ) can be released.

Images