DE202005003868U1 - hydraulic power unit - Google Patents

Abstract

hydraulic power unit (1), in particular for Pallet truck, with a housing (2), with a pump piston acting on hydraulic medium in a pump chamber (3), with an actuator (4) for the pump piston (3), with a reciprocating piston (5) and with a pressure chamber.

Description

The The invention relates to a hydraulic unit, in particular a hydraulic unit for pallet trucks, with a housing, with a pump piston acting on hydraulic medium in a pump chamber, with an actuating element for the Pump piston, with a reciprocating piston and with a pressure chamber. The pump piston is with the help of the actuator in a filled with hydraulic medium Pump room moves. By this pumping stroke is hydraulic medium of the Pump space pumped into a, a reciprocating piston associated pressure chamber, whereby displaces the reciprocating piston can and raise a load. In general, the pump piston is over a Spring moved back to its original position, being at this backward movement of the pump piston in its initial position hydraulic medium from a Tank space is sucked into the pump room.

advantageous Embodiments are specified in the subclaims.

According to one first execution is provided with advantage that all, visible from the outside, Components of the hydraulic unit are made of stainless steel. In particular, when the hydraulic unit installed in a pallet truck it is advantageous if the whole, externally visible, Components of the fork lift truck are made of stainless steel. The formed according to the invention Hydraulic unit is particularly suitable for use in work areas, where with aggressive media, like acids or bases is worked. It has been observed that conventional Hydraulic power units through use in food or chemical Industry wear much faster than in other areas turned on hydraulic units. This is due to the fact that the usual made of cast aluminum or coated cast iron hydraulic units through contact with lactic acids, Meat juice, pickling salt, Cleaners, etc. much faster corrode, which ultimately leads to premature failure of the hydraulic units. According to the embodiment of the invention is get a durable hydraulic power unit, which is largely immune to the usual is used for coming, aggressive media.

According to one further execution a hydraulic unit is provided with advantage that the actuating element is designed as a pivot lever, wherein the housing stops for limiting the pivoting movement are provided of the pivot lever in both directions. When using the Hydraulic power units on a pallet truck are at the pivot lever usually around the drawbar of the fork lift truck. So far, it was common only to limit the pivoting movement of the pivot lever upwards in its initial position to provide a stop on the housing. The pivoting movement the swing lever down was in the prior art by limited that the pump piston during its pump stroke against the ground or pushed a stop inside the pump room. There were enormous forces on the power-transmission Components of the hydraulic unit, resulting in increased wear would have. Due to the inventive design the hydraulic unit is the pivoting movement of the pivot lever in both directions by stops on the housing limited, which absorb the forces occurring at the stop of the pivot lever. The pump piston, the pump cylinder and the pump chamber are by the Stop of the pivot lever in both Maximalauslenkungen not charged.

According to one further embodiment of the invention is provided with advantage that the actuating element is designed as a pivot lever and that the pivot axis below of the force introduction point is arranged in the pump piston. hereby is achieved with advantage that the introduction of force in the pump piston pulling and not as usual oppressively he follows. Due to the inventive design of the hydraulic unit, it is possible the pump cylinder, which leads the pump piston axially, longer form than in known Hydraulic units. As a result, in the pivoting of the Swing lever necessarily occurring, on the pump piston acting, lateral forces distributed on a larger guide surface. One Another advantage of the embodiment according to the invention is that the transverse forces resulting from the pulling force are lower as oppressive Force introduction into the pump piston.

In an embodiment of the invention is advantageously provided that the introduction of force from the pivot lever into the pump piston via a driver part, wherein the driver part is articulated on the pivot lever, that it is pivotable relative to the pivot lever. The driver member rests on the pump piston and is movable relative to this. Upon actuation of the pivot lever, an axial force component is exerted on the pump piston by the driver part, with the driver part making a rocking motion on the pump piston by the pivoting movement of the pivot lever. In one possible embodiment, the driver part is substantially U-shaped, wherein the driver part is articulated with the parallel legs on the pivot lever and wherein the driver part rests with the underside connecting the parallel legs on the pump piston. According to a further improved embodiment, the driver part is circumferentially be tig closed, so for example tubular designed to provide even better lateral protection, especially against aggressive substances and forces. The pivot axis of the driver part is spaced and parallel to the arranged below the force introduction point in the pump piston pivot axis of the pivot lever.

In order to the driver part on the pump piston as possible without friction can be moved, is provided with advantage that the driver part on a ball arranged at the top of the pump piston activity the swing lever rolls, preferably the introduction of force into the pump piston over the ball takes place. The driver part performs on actuation of the pivot lever a Rocking motion on the arranged on the top of the pump piston Ball, wherein the force application point migrates on the spherical surface. The ball is advantageously pressed into the pump piston. With advantage is in the driver part a recess for receiving and positioning the Mitnehmerteils provided on the ball.

Thereby, that the pivot axis of the pivot lever below the force application point is arranged in the pump piston, can be provided with advantage that protrudes out of the case Section of the pump piston, or at least the end portion of the pump piston, is disposed within the pivot lever, so at least two, preferably three or four peripheral sides of the pivot lever is surrounded. If the pivot lever, for example, a U-shaped cross-section has, so the pump piston protrudes with advantage between the two parallel leg of the pivot lever. Due to the inventive design becomes the pump piston and / or the driver part against external influences protected.

According to one further execution of the hydraulic unit, the hydraulic unit has a lowering control valve with a valve core, wherein in the valve core. a, preferably axial, hydraulic medium channel and at least one, in the hydraulic medium channel opening out, Supply channel is provided, via the supply channel hydraulic medium from the pressure chamber into the valve chamber and into a tank room flow away can. The supply channel opens in one over at least a part of the circumference of the valve insert extending groove, wherein the groove cross-section in the circumferential direction with increasing distance from the mouth of the Supply channel decreases. The valve insert is of one surrounded under pressure by deformable throttle ring. It can be provided that the cross-section increases in the circumferential direction Distance from the mouth of the Supply channel decreases linearly.

Of the the valve insert at height the circumferential groove surrounding throttle ring settles with the hydraulic fluid channel open due to the pressure prevailing in the pressure chamber to the circumferential groove or to the edge of the circumferential groove. The application behavior is proportional to the height the pressure in the pressure chamber. The latter depends on the size of the the lifting piston acting load. This means that the bigger the Load is that acts on the reciprocating piston, the greater the pressure in the pressure chamber and the bigger starting from the mouth opening the Nutstrecke covered by the throttle ring in the circumferential direction. There the groove cross-section in the circumferential direction with increasing distance from the Mouth opening decreases, is the flow area for Pressure medium through the groove at a larger load accordingly lower than at a smaller load, since the throttle ring at lower load the groove just over covers a small circumferential distance and there the groove cross-sectional area is larger. The outflowing Hydraulic medium volume flow and thus the lowering speed of Lifting piston is therefore dependent from the size of the up the lifting piston acting load. The regulation of the lowering speed is done over the length the throttle section (covered by the throttle ring groove route) and on the Cross sectional area the groove (inflow area of Hydraulic medium in the partially covered by the throttle ring circumferential groove).

In Embodiment of the invention is provided with advantage that at least two, in particular opposite, supply channels are provided, where not several, but only one supply channel opens into a groove. It goes the groove is not over the entire scope, but only over part of the scope, especially about the half of the scope. In this expedient development the invention will immediately one of the two supply channels Completely closed by the throttle ring and the outflow takes place, depending on the size of the the load acting on the reciprocating piston, only through a supply channel in the, preferably axially extending, hydraulic medium channel within of the valve insert.

It is advantageous if the groove cross section formed in approximately V-shaped is, wherein the groove depth with increasing distance from the mouth opening in the circumferential direction decreases. A V-shaped training the groove cross-section has the advantage that a disproportionate cross-sectional area removal with given increasing distance from the mouth opening is.

In order to fully cover the groove over the entire width is provided with advantage that the width of the throttle ring, at least in Be rich of the groove is such that it covers these with axial reserve.

Farther it is appropriate that at least one supply channel formed as a radial transverse bore is that, if the hydraulic medium channel within the valve core axially, to this an angle of 90 °.

at The valve insert is advantageously a component with at least on both sides of the groove of circular cross-section, wherein the Throttle ring in the undeformed state has a circular cross-section and wherein the inner diameter of the throttle ring is larger as the outer diameter the valve core at both groove edges, so that the throttle ring is radially spaced from the valve insert in the undeformed state.

In Embodiment of the invention is provided with advantage that the Groove to two opposite Sides of at least one orifice in the circumferential direction runs, especially on every page about about ¼ of the Scope. If according to an advantageous Design only a mouth opening in a groove opens, extends this groove about in this way half the circumference of the valve core.

It is appropriate if at least one supply channel and the hydraulic medium channel as inflow for hydraulic medium during pumping into the pressure chamber.

With Advantage is the hydraulic medium channel in the outflow direction by means of a check valve, in particular Ball valve sealable. If the reciprocating piston to be lowered, so must first the check valve be opened against a spring force, allowing hydraulic fluid in the closing direction of the check valve from the pressure room over the groove, at least one supply channel and the hydraulic medium channel can drain into a tank room.

It is advantageous to form the throttle ring of plastic, since such a throttle ring with larger tolerances can be made. To the desired application behavior to the To achieve the groove in a metal throttle ring would have to be minimized Manufacturing tolerances are met.

According to one further execution the hydraulic unit has a switching device for switching between two different power input surfaces of the Pump piston on, causing the hydraulic unit between quick lift and normal lift is switchable. In fast-stroke mode, the force from the pump piston by means of a larger effective area registered in the hydraulic medium in the pump chamber as in the normal stroke mode, whereby in fast-stroke mode, more hydraulic medium is displaced during a pumping stroke, as with the same pump stroke in Normalhubmodus.

The Switching device comprises a ring piston chamber, which partially is limited by the pump piston. Furthermore, one, preferably centric, Provided connection between the piston ring space and the pump space, sealed by means of a spring-loaded switching valve is. The hydraulic medium can be exceeded when a switching pressure is exceeded in the pump room against the closing direction of the changeover valve flow into the ring piston space. The switching pressure can for example about the choice of the spring of the changeover valve can be varied. Reached the pressure in the pump chamber does not change the switching pressure, the switching valve remains closed. Upon reaching the switching pressure can hydraulic medium from the pump chamber into the ring piston space, creating a pressure balance between the piston ring space and pump space is produced. As the hydraulic medium in the piston ring space, the force input surface of the pump piston partially behind flows, becomes at a pressure equilibrium between piston ring space and pump space the effective force input surface reduced, whereby the force input then only over one smaller force entry area into the pump room.

in the The prior art has the problem that hydraulic medium at Reaching the switching pressure in one not, or only partially filled with hydraulic medium Ring piston chamber flows. To have to So usually several pump strokes accomplished be about the piston ring space over Fill the changeover valve with hydraulic fluid. Therefore, according to a advantageous embodiment provided that a connecting line between the piston ring space and a tank space exists in the direction Tank space sealed by a check valve is, and that hydraulic medium in a pumping stroke through the connecting line, against the closing direction the check valve, is sucked from the tank space in the piston ring space. The ring piston chamber is thereby filled at any time with hydraulic medium, thereby Upon reaching the switching pressure in the pump room immediately a pressure increase in Ring piston space is reached.

In order to enable a movement of the pump piston in its initial position with filled piston ring space, a Abströmmöglichkeit for hydraulic medium from the piston ring chamber must be created because the drain is blocked via the connecting line to the tank space due to the check valve. An embodiment of the hydraulic unit therefore provides that the annular gap formed between the pump piston and the pump chamber wall a provided on the circumference of the pump piston, axially displaceable annular seal is sealable. If the pressure in the pump chamber is higher than the pressure in the piston ring chamber, the ring sealing device is moved by the hydraulic medium into an axial position in which it seals the annular gap. If the pressure in the piston ring space is higher than in the pressure chamber, the ring seal is displaced by the hydraulic medium into an axial position, in which a flow of hydraulic medium from the piston ring space into the pressure chamber is possible. The ring seal receives over the axial displaceability a double function. On the one hand, it seals off the annular gap during the pumping process and additionally allows outflow of hydraulic medium from the annular piston space into the pump chamber during a movement of the pump piston back into its starting position. The ring seal thus acts as a check valve. In order for the ring seal to bear better against at least one sealing surface, at least one spring element, preferably a corrugated spring ring arranged axially between the ring seal and the securing ring, can be provided.

With Advantage is the ring seal between two axial stops axially displaceable, with an axial stop, for example, as an annular shoulder of the ring piston and the opposite Axial stop can be designed as a locking ring.

Around the inflow volume flow to increase from the piston ring space in the direction of the pump chamber, are advantageous radially behind the ring seal in the pump piston axially extending flow grooves brought in. These must Of course can not be incorporated in the pump piston, but can also, for example, in be introduced the ring seal.

It is provided with advantage that the pump piston at least two Having sections of mutually different diameter, the pump piston exclusively is axially guided with the portion with the smaller diameter. So far, it was common the pump piston both at its larger diameter, as well axially to guide at its smaller diameter, wherein the smaller diameter in a pump cylinder and the larger diameter led to the wall of the pump room was. According to the embodiment of the invention of the hydraulic unit, it is now possible, the pump piston exclusively in the pump cylinder to lead axially and seal the pump piston only marginally opposite the Pumpraumwandung. Thus, leaks, assembly, and wear problems due to a production-related offset between the pump room wall and pump cylinder avoided.

According to one advantageous embodiment has the switching valve between the piston ring space and pump space a Federkraftbeaufschlagten Umschaltstößel, wherein the Umschaltstößel against the Spring force in one, opposite the annular piston space sealed, low-pressure space is displaced. The pressure in the low pressure chamber is always lower than the switching pressure. The switching pressure can be selected by selecting the spring acting on the changeover plunger be determined. By this configuration of the hydraulic unit is not the Umschaltstößel Completely surrounded by hydraulic fluid. For hydraulic units from the state In engineering, the changeover plunger is completely off Enclosed hydraulic medium, whereby acting on the Umschaltstößel Spring force can not be permanently compensated. At acquaintances Hydraulic power units must therefore over the entire pump stroke first Spring force overcome are, since the spring is always striving, the connection between the piston ring space and pump room to close.

ever after how big the across from the low pressure space sealed cross-sectional area of the Umschaltstößels in relationship to the cross-sectional area of the changeover plunger or the cross-sectional area one connected to the Umschaltstößel Selected sealing elements is to which the hydraulic medium located in the pump chamber a compressive force exerts can the spring force completely or partially compensated upon reaching the switching pressure. From a complete Compensation of the spring force at the switching time is followed by a jerky one Switchover. Therefore, one strives that the opposite of the Low-pressure chamber sealed cross-sectional area of the Umschaltstößels smaller is as the cross-sectional area of the changeover plunger or one connected to the Umschaltstößel Sealing element, on the hydraulic medium in the pump chamber when the changeover valve is closed, d. H. exerts a compressive force. The product from the sealed cross-sectional area of the Umschaltstößels and the pressure in the pump chamber acts on the Umschaltstößel acting Spring force with open Reversing valve against. The force on the changeover plunger due Any pressure in the low-pressure space can usually be neglected. So meet the opposite the low pressure space sealed cross-sectional area of the Umschaltstößels the Cross sectional area of Umschaltstößels, on the hydraulic medium in the pump chamber exerts a compressive force is the Spring force suddenly fully compensated in the switchover time, which makes it a jerky switching behavior of quick lift comes on normal lift. It is better if the sealed cross-sectional area is smaller is as the cross-sectional area of the Umschaltstößels or the sealing element on which a pressure force acts. In this version there there is a transition area, in which the spring force is not completely canceled, resulting in a softer switching behavior results.

In Embodiment of the invention is provided with advantage that the Maximum pressure in low-pressure chamber with the switching valve closed so big is that that of a medium in low pressure medium, preferably Gas, pressure applied to the changeover plunger smaller but rectified than acting on the Umschaltstößel Spring force.

According to one Embodiment of the invention, the low-pressure space is connected to the atmosphere. Here you can however, soiling and unwanted chemical substances get into the low-pressure space, which is not enough for a variant Stainless steel leads to corrosion problems.

Based the drawing, the different versions are explained in detail.

there demonstrate:

1 a side view of a hydraulic unit,

2 a side view of a hydraulic unit,

3 a section through a valve plane of a hydraulic unit,

4 a cross section through a lowering control valve of a hydraulic unit,

5 a section through a pumping device of a hydraulic unit and

6 a section through a hydraulic unit.

In the figures and the following description were for the same Components or components with the same function identical reference numerals used.

That in the 1 and 2 illustrated hydraulic unit 1 is particularly suitable for use in pallet trucks. However, the scope is not limited to this. The hydraulic unit has a housing 2 on, which is made of stainless steel. From the housing protrudes a pump piston 3 out, with a designed as a pivot lever actuator 4 in one in the housing 2 located pump space can be moved. Furthermore, the hydraulic unit 1 one out of the case 2 standing up out, parallel to the pump piston 3 arranged, reciprocating 5 on, which is assigned a arranged in the housing pressure chamber. By increasing the pressure in the pressure chamber of the reciprocating piston is moved out of the housing.

All externally visible components of the hydraulic unit 1 like the housing, the actuator 4 and the pump piston 3 and the reciprocating piston 5 are made of stainless steel and therefore largely corrosion-resistant.

The actuator 4 is by means of a bolt 6 so hinged to the housing, that the pivot axis 7 of the actuating element 4 below the force application point 8th is arranged in the pump piston.

The trained as a pivot lever actuator 4 can from the in 1 drawn with a thick line starting position around the pivot axis 7 to a maximum tilt angle of 70 ° in an in 1 dashed end position can be pivoted. On the case 2 are two stops 9 and 10 for limiting the pivoting movement of the actuating element 4 provided in both directions. The stop 9 defines the starting position and the stop 10 defines the end position of the 70 ° swivel range of the actuator 4 , The actuator 4 lies with a first mating surface 11 in the starting position at the stop 9 and in the end position with a second counter surface 12 at the stop 10 of the actuating element 4 at. The forces occurring in the abutment of the actuating element on the attacks are from the actuating element 4 and the housing 2 added.

On the actuator 4 is at a distance from the pivot axis 7 a driver part 13 articulated, wherein the driver part 13 around a pivot axis 14 relative to the actuator 4 is pivotable. Here is the pivot axis 14 parallel to the pivot axis 7 of the actuating element 4 arranged and rotates upon actuation of the actuating element 4 around. The driver part 13 lies on a pump piston 3 rotatably pressed ball 15 up and over the ball 15 an axial force component in the pump piston 3 initiate. The driver part 13 has a sleeve-shaped peripheral wall 16 and one fixed to the peripheral wall 16 connected lid 17 on. In the lid 17 is a depression, not shown, for guiding the driver part 13 on the ball 15 brought in. When pivoting the actuating element 4 around the pivot axis 7 leads the driver part 13 in relation to the pump piston 3 a kind of rocking motion.

The force is introduced into the pump piston in the illustrated hydraulic unit 1 astringent. When pivoting the actuating element 4 around its pivot axis 7 pushes the rotatable with the actuator 4 connected driver part 13 with the bottom of its lid 17 on the ball 15 the pump piston 3 , whereby this in moved in the pump room. As a result, hydraulic fluid from the pump chamber in a on the reciprocating piston 5 displaced acting pressure chamber, causing the lifting piston lifts. The return of the pump piston 3 into its starting position via an in 1 not shown coil spring.

By laying the pivot axis 7 of the actuating element under the force introduction point and the resulting, pulling force introduction, it is possible, the space gained at the top by an elongated pump cylinder 3 and thus to exploit an extended guidance of the pump piston by extending the pump cylinder, whereby the wear of the hydraulic unit 1 is significantly reduced. The arrangement in the starting position and the end position of the actuating element of the driver part 13 on the pump piston 3 transferred transverse forces compared to other arrangements reduced.

As in particular in 2 It can be seen, that is from the housing 2 outstanding section of the pump piston 3 as well as the driver unit 13 within the actuator 4 arranged. In the specific embodiment, this means that said components between two side surfaces of the actuating element formed as a pivot lever 4 arranged and are protected against lateral force.

In 3 is a control valve 18 , a lowering valve 19 and an overpressure safety valve 20 in a hydraulic power unit 1 shown. The control valve 18 is via a shifter 21 actuated. With the help of the shift lever 21 and the control valve 18 can be switched between the three operating states pumping position, neutral or driving position and lowering position. In 3 the operating state pumping position is shown.

About a line 22 is the control valve 18 connected to the pump space not shown in this figure. A sealing element 23 seals a passage opening 24 starting in an annulus 25 with coil spring 26 opens, with the annulus 25 with an in 3 not shown tank space for hydraulic medium is connected. Will in this operating position of the pump piston 3 over the actuator 4 operated, so flows over the line 22 Hydraulic fluid in a valve chamber 27 and from there against the closing direction of a check valve 28 with valve ball 29 through a hydraulic medium channel 30 in a valve core 31 the lowering control valve 19 to two opposite supply channels 32 and 33 and through this further into an in 3 not shown, acting on the reciprocating pressure chamber.

In the lowering position, not shown, presses a countersink 34 of the control valve 18 against the valve ball 29 the check valve 28 so that hydraulic medium from the pressure chamber via the supply channels 32 and 33 as well as the now opened hydraulic medium channel 30 in the valve room 27 and from there over the in the lowered position of the sealing element 23 unsealed passage opening 24 in the annulus 25 and from there into the tank room can flow.

In the neutral or driving position, the countersink pushes 34 not against the valve ball 29 the check valve 28 so that the hydraulic medium channel 30 within the valve core 31 remains closed. However, in the neutral position, the through hole is 24 not from the sealing element 23 sealed, allowing a possible actuation of the actuator 4 and thus the pump piston 3 only leads to a hydraulic medium flow from the pump chamber into the tank space. A lifting of the reciprocating piston is in this switching position of the control valve 18 avoided.

The lowering control valve 19 consists of the valve core 31 in the valve core 31 axially extending hydraulic medium channel 30 and the hydraulic medium channel 30 sealing check valve 28 consisting of a coil spring 35 and the valve ball 29 with guide pins 36 for the coil spring 35 , Furthermore, the lowering control valve comprises 18 two opposite and radial in the valve core 31 running supply channels 32 . 33 and a coaxial with the valve core 31 arranged throttle ring 37 and one over half the circumference of the valve core 31 running groove 38 ,

The supply channel 33 flows with its mouth opening 39 in the groove 38 , The cross-sectional area of the groove 38 is V-shaped. The groove depth and thus the groove cross-section increases on both sides of the mouth opening 39 in the circumferential direction with increasing distance to the mouth opening 39 from, with the groove to each side of the mouth opening 39 in the circumferential direction over ¼ of the circumference of the valve core 31 runs. One between valve insert 31 and a peripheral wall 40 formed annulus 41 is over a connecting line 42 in communication with the pressure room. How out 3 it can be seen, is the throttle ring 37 wider than the V-shaped, over half the circumference of the valve core 31 running groove 38 , Once over the shifter 21 the control valve 18 is moved into the lowering position, wherein the lowering ram 34 the check valve 28 opens, the hydraulic medium is anxious, from the pressure chamber via the connecting line 42 , the annulus 41 , the supply holes 32 and 33 and the hydraulic medium channel 30 to drain towards the tank room. The thereby on the throttle ring 37 acting pressure force leads to a deformation of the throttle ring 37 on the one hand sealing against the mouth opening 43 of the supply channel 32 applies and on the other hand sealing to both sides of the groove to the valve core 31 invests. The greater the load acting on the reciprocating piston, the greater the pressure acting on the throttle ring and the longer the distance of the groove covered by the throttle ring, in which the throttle ring sealingly engages the valve core over part of the circumference invests. Since the cross section of the groove 38 on both sides of the mouth 39 in the circumferential direction with increasing distance from the mouth opening 39 decreases, thereby reducing the available for the outflow of hydraulic fluid Nuteinströmquerschnitt. At the same time, the outflow path (sealed groove section up to the mouth opening) lengthens. As a result, the pressure losses occurring increase and the outflow volume decreases. The larger the pressure prevailing in the pressure chamber, the slower the hydraulic medium flows through the lowering control valve 19 the slower the load is lowered.

In the 5 and 6 are different sections represented by an inventive hydraulic unit.

In 5 is a switching device 44 to switch between fast and normal lift shown. Above the pump room 45 is a ring piston room 46 to recognize. In the pump room 45 protrudes in a pump cylinder 47 axially guided pump piston 3 into it. The pump piston 3 is by means of a coil spring 48 contrary to the direction of actuation in the in the 5 and 6 shown starting position moves, wherein the coil spring 48 on a shoulder 49 the pump cylinder 47 and a stopper disc 50 the pump piston is supported. On the top of the pump piston 3 is the ball 15 for rocking storage of a driver unit 13 or an actuator 4 for the pump piston 3 to recognize.

The ring piston chamber 46 goes down, ie towards the pump room through a section 51 the pump piston 3 limited to large diameter. If between ring piston chamber 46 and pump room 45 a pressure balance is established, becomes a part of the large force input surface 52 compensated, leaving only a smaller force input surface 53 on the hydraulic medium in the pump room 45 acts. So can between fast lift (large force input surface 52 ) and normal stroke (small force input surface 53 ) are switched.

The ring piston chamber 46 is via a connection line 54 that only in 5 it can be seen with the in 6 illustrated tank space 55 connected. In the connection line 54 there is a check valve 56 , which is the outflow of hydraulic medium from the piston ring space 46 over the connecting line 54 in the tank room 55 prevented. Every pump stroke of the pump piston 3 is via the connection line 54 Hydraulic medium from the tank room 55 in the ring piston space 46 sucked so that it is filled with hydraulic medium at all times.

So that the pump piston 3 must be moved back to its original position, must hydraulic medium from the piston ring space 46 be displaced. For this purpose is on the perimeter of the section 51 the pump piston 3 an axially displaceable ring seal 57 provided between two attacks, namely a shoulder 58 the pump piston 3 and a circlip 59 on the circumference of the pump piston 3 is axially displaceable. When the pressure in the pump room 45 higher than the pressure in the piston ring chamber 46 , becomes the ring seal 46 from the hydraulic medium against the shoulder 58 Pressed and sealed in this position, the annular gap 60 between pump piston 3 and peripheral wall 61 the pump room 45 from.

When the pressure in the piston ring chamber 46 is higher than in the pump room 45 , the ring seal is displaced axially in the direction of the circlip, whereby hydraulic medium from the piston ring space 46 in the pump room 45 can flow. Not shown are axial channels, in particular grooves, in the peripheral wall 62 the pump piston 3 radially behind the ring seal 57 , These channels increase the flow area. The ring seal 57 fulfilled by their axial mobility, the function of a check valve. Thus, it is possible to dispense with a separate check valve and a ring seal fixed on the circumference of the pump piston.

In 6 it can be seen that the switching device 44 a centric in the pump piston 3 arranged switching valve 63 includes. The changeover valve 63 closes a connection 64 between pump room 45 and ring piston space 46 , The changeover valve 63 is from a switchover plunger 65 and a thereto attached, designed here as a ball sealing element 66 educated. The changeover plunger 65 is from the power of a coil spring 67 subjected to, whereby the sealing element 66 against a sealing surface 68 at the connection 64 is pressed. Exceeds the pressure in the pump room 45 by actuation of the pump piston 3 a fixed switching pressure, the Umschaltstößel 65 moved upwards against the force of the coil spring, causing the connection 64 becomes free and hydraulic medium from the pump room 45 in the ring piston space 46 can flow, which in turn a pressure balance between the pump piston space 45 and ring piston space 46 will be produced. This leads to Umschal from the large force entry area 52 on the small force input surface 53 the pump piston 3 , The switching pressure essentially corresponds to the quotient of the changeover plunger 65 acting spring force and cross-sectional area 69 of the sealing element 66 to which a compressive force in the pump room 45 befindlichem hydraulic medium is applied. The changeover plunger 65 is against the spring force of the spring 67 in a low-pressure room 70 slidable, by means of gasket 71 opposite the ring piston chamber 46 is sealed. Here is the space by the spring 67 is arranged, part of the annulus 46 , The feather 67 is therefore surrounded by hydraulic medium.

In the embodiment shown, the low pressure space 70 filled with gas, in particular air at atmospheric pressure, and not connected to the atmosphere.

The opposite the low pressure room 70 sealed cross-sectional area 72 the Umschaltstößels 65 is smaller than the cross-sectional area 69 of the sealing element 66 , acts on the hydraulic medium located in the pump chamber with the check valve closed. As a result, a transition region is generated during the switching process by the spring force of the spring 67 is not completely canceled. Thus, there is no sudden complete compensation of the spring force of the spring 67 , which makes the switching softer. With further increasing pressure in the pump room 45 and thus also in the ring piston space 46 becomes the force of the coil spring 67 increasingly compensated, so that the spring force in the further course of the pumping process no longer needs to be overcome. As a result, less force must be expended for actuating the actuating element.

1

hydraulic power unit

2

casing

3

pump piston

4

actuator

5

reciprocating

6

bolt

7

swivel axis

8th

Force application point

9

attack

10

attack

11

first counter surface

12

second counter surface

13

driver part

14

swivel axis

15

Bullet

16

peripheral wall

17

cover

18

control valve

19

Senkregelventil

20

Overpressure safety valve

21

gear lever

22

management

23

sealing element

24

Through opening

25

annulus

26

coil spring

27

valve chamber

28

check valve

29

valve ball

30

Hydraulic medium channel

31

valve core

32

supply channel

33

supply channel

34

Senkstößel

35

coil spring

36

guide pins

37

throttle ring

38

groove

39

mouth

40

peripheral wall

41

annulus

42

connecting line

43

mouth

44

switchover

45

pump chamber

46

Ring piston chamber

47

pump cylinder

48

coil spring

49

shoulder

50

stop disc

51

Abschnitthubkolben with big diameter

52

large force introduction surface

53

small Force introduction surface

54

connecting line

55

tankage

56

check valve

57

ring seal

58

shoulder

59

circlip

60

annular gap

61

peripheral wall

62

peripheral wall

63

switching valve

64

connection

65

Umschaltstößel

66

sealing element

67

coil spring

68

Sealing surface (sealing edge)

69

Cross-sectional area

70

Low-pressure chamber

71

poetry

72

Cross-sectional area

Claims (27)

Hydraulic unit ( 1 ), in particular for pallet trucks, with a housing ( 2 ), with a pump piston acting on hydraulic medium in a pump chamber ( 3 ), with an actuating element ( 4 ) for the pump piston ( 3 ), with a reciprocating piston ( 5 ) as well as with a pressure room. Hydraulic unit according to claim 1, characterized in that at least the housing is made of stainless steel and preferably all visible from the outside, components ( 2 . 3 . 4 . 5 ), the hydraulic unit, are also made of stainless steel. Hydraulic unit according to one of the preceding claims, characterized in that the actuating element ( 4 ) is designed as a pivot lever, and that on the housing ( 2 ) Attacks ( 9 . 10 ) are provided for limiting the pivotal movement of the pivot lever in both directions. Hydraulic unit according to one of the preceding claims, characterized in that the actuating element ( 4 ) is designed as a pivot lever, and that the pivot axis ( 7 ) of the pivot lever below the force application point ( 8th ) in the pump piston ( 3 ) is arranged. Hydraulic unit according to claim 4, characterized in that on the pivot lever, a driver part ( 13 ) is articulated, which is rotatable relative to the pivot lever, and that of the driver part ( 13 ) upon actuation of the pivot lever an axial force component on the pump piston ( 3 ) is transferable and that the driver part ( 13 ) relative to the pump piston ( 3 ) is movable. Hydraulic unit according to claim 5, characterized in that the driver part ( 13 ) on a ball arranged on the top of the pump piston ( 15 ) slides upon actuation of the pivot lever, wherein preferably the introduction of force into the pump piston via the ball ( 15 ) he follows. Hydraulic unit according to one of claims 4 to 6, characterized in that the out of the housing ( 2 ) outstanding section of the pump piston ( 3 ) is arranged within the, in particular in cross section U-shaped or tubular, pivot lever. Hydraulic unit according to one of the preceding claims, characterized in that the hydraulic unit ( 1 ) a lowering control valve ( 19 ) with a valve core ( 31 ), wherein in the valve core ( 31 ), preferably axial, hydraulic medium channel ( 30 ) and at least one supply channel ( 32 . 33 ), which is connected to the hydraulic medium channel in such a way that via the supply channel ( 32 . 33 ) Hydraulic medium from the pressure chamber into the hydraulic medium channel ( 30 ) and that the supply channel ( 32 . 33 ) into at least a part of the circumference of the valve core ( 31 ) running groove ( 38 ), and that the groove cross-sectional area in the circumferential direction with increasing distance from the mouth opening ( 39 . 43 ) of the supply channel, and that the valve core ( 31 ) of a deformable throttle ring ( 37 ) is surrounded. Hydraulic unit according to claim 8, characterized in that at least two, in particular opposite, supply channels ( 32 . 33 ), whereby only one supply channel ( 32 ) into a groove ( 38 ) opens. Hydraulic unit according to one of claims 8 or 9, characterized in that the groove cross-sectional area is V-shaped, wherein the groove depth with increasing distance from the mouth opening ( 39 . 43 ) decreases in the circumferential direction, preferably linear. Hydraulic unit according to one of claims 8 to 10, characterized in that the width of the throttle ring ( 37 ), is dimensioned so that the groove ( 38 ) covered with axial reserve. Hydraulic unit according to one of claims 8 to 11, characterized in that at least one supply channel ( 32 . 33 ) is designed as a radial transverse bore. Hydraulic unit according to one of claims 8 to 12, characterized in that the cross section of the valve insert ( 31 ) on both sides of the groove ( 38 ) is circular, and that the throttle ring ( 37 ) in the non-deformed state has a circular cross-section, and that the inner diameter of the Dros selrings ( 37 ) is greater than the outer diameter of the valve core ( 31 ) at both edges of the groove ( 38 ). Hydraulic unit according to one of claims 8 to 13, that the groove ( 38 ) to two opposite sides of at least one, preferably only one, orifice ( 39 . 43 ) in the circumferential direction, in particular over a quarter of the circumference, runs. Hydraulic unit according to one of claims 8 to 14, characterized in that at least one supply channel ( 32 . 33 ) as well as the hydraulic medium channel ( 30 ) serve as inflow channel for hydraulic medium during the pumping process in the pressure chamber. Hydraulic unit according to one of claims 8 to 15, characterized in that the hydraulic medium channel ( 30 ) in the outflow direction by means of check valve ( 28 ), in particular ball valve, is sealable. Hydraulic unit according to Ansprü 8 to 16, characterized in that the throttle ring ( 37 ) consists of plastic. Hydraulic unit according to one of the preceding claims, characterized in that the hydraulic unit ( 1 ) a switching device ( 44 ) for switching, between two different power input surfaces ( 52 . 53 ) of the pump piston ( 3 ), whereby the hydraulic unit ( 1 ) is switchable between fast and normal lift, wherein the switching device ( 44 ) an annular piston space ( 46 ), which partially from the pump piston ( 3 ) and that one, preferably centric, compound ( 64 ) between the piston ring space ( 46 ) and the pump room ( 45 ), which by means of a switching valve ( 63 ) is sealed, and that hydraulic medium when a switching pressure in the pump chamber ( 45 ) counter to the closing direction of the switching valve ( 63 ) in the ring piston space ( 46 ) can flow. Hydraulic unit according to claim 18, characterized in that a connecting line ( 54 ) between the piston ring space ( 46 ) and a tank room ( 55 ) in the direction of the tank space by means of a check valve ( 56 ) is sealed, and that hydraulic medium during a pumping stroke through the connecting line ( 54 ), contrary to the closing direction of the check valve ( 56 ), from the tank room ( 55 ) in the ring piston space ( 46 ) is sucked. Hydraulic unit according to one of claims 18 or 19, characterized in that between pump piston ( 3 ) and pump room wall ( 62 ) an annular gap ( 60 ) is formed, and that an axially displaceable annular seal ( 57 ) on the circumference of the pump piston ( 3 ), which, when the pressure in the pump chamber ( 45 ) is higher than the pressure in the piston ring chamber ( 46 ), is displaced by the hydraulic medium into an axial position, in which the annular gap ( 60 ) and that the ring seal ( 57 ), when the pressure in the piston chamber ( 46 ) is higher than in the pump room ( 45 ), is displaced by the hydraulic medium into an axial position, in which a flow of hydraulic medium from the annular piston space ( 46 ) into the pump room ( 45 ) is possible. Hydraulic unit according to claim 20, characterized in that the annular seal ( 57 ) is axially displaceable between two axial stops. Hydraulic unit according to one of claims 20 or 21, characterized in that radially behind the ring seal ( 57 ) in the pump piston ( 3 ) At least one axially extending flow channel is introduced. Hydraulic unit according to one of claims 18 to 22, characterized in that the pump piston ( 3 ) has at least two sections of mutually different diameter, wherein the pump piston ( 3 ) is axially guided exclusively with the section with the smallest diameter. Hydraulic unit according to one of claims 18 to 23, characterized in that the switching valve ( 63 ) between ring piston space ( 46 ) and pump room ( 45 ) a spring-loaded Umschaltstößel ( 65 ), wherein the Umschaltstößel ( 65 ) against the spring force in one, with respect to the annular piston space ( 46 ) sealed, low-pressure space ( 70 ) is displaceable. Hydraulic unit according to claim 24, characterized in that the pressure in the low-pressure space ( 70 ) with the check valve closed ( 63 ) is so large that the one in the low-pressure chamber ( 70 ), preferably gas, on the Umschaltstößel ( 65 ) applied pressure force is smaller than that on the Umschaltstößel ( 65 ) acting spring force. Hydraulic unit according to one of claims 24 or 25, characterized in that the low pressure space ( 70 ) is connected to the atmosphere. Hydraulic unit according to one of claims 24 to 26, characterized in that the opposite to the low pressure space ( 70 ) sealed cross-sectional area ( 72 ) of the Umschaltstößels ( 65 ) is smaller than the cross-sectional area ( 69 ) of the Umschaltstößels, or one with the Umschaltstößel ( 65 ) cooperating sealing element ( 66 ), in the pump room ( 45 ) located hydraulic medium with closed reversing valve ( 63 ) acts.