DE102017113938A1 - Filter device for a hydraulic system - Google Patents

Abstract

Filter device for a hydraulic system, in particular on an industrial truck, comprising a filter element with a filter body and a valve element, wherein the valve element opens below a predetermined first system pressure bypassing the filter body first bypass channel for fluid flowing through the filter device and above a predetermined second system pressure a the filter body bypassing the second bypass passage for fluid flowing through the filter device, wherein the second system pressure is greater than the first system pressure.

Description

The invention relates to a filter device for a hydraulic system, which can be used in particular in an industrial truck.

Industrial trucks usually have a hydraulic system via which the load-bearing parts of the truck are controlled. About the hydraulic system, for example, a mast with a mast and connected to the mast load part can be controlled, for example, to lift loads or lower. For this purpose, the hydraulic system usually comprises a plurality of hydraulic cylinders acting on the mast, to which hydraulic fluid is supplied from a tank by means of a hydraulic unit. Via a valve arrangement, the hydraulic fluid is distributed to the cylinders or discharged from them. By actuating the hydraulic cylinder, a load located on the load part of the mast can be moved, for example lifted by means of a lifting cylinder. To lower the load hydraulic fluid is discharged from the lifting cylinder via the valve assembly and returned to the hydraulic tank.

Furthermore, such a hydraulic system generally comprises a filter with which impurities can be filtered out of the hydraulic fluid. These impurities may be, for example, particles formed by abrasion of material or even clumping of the hydraulic oil itself. The filter is usually a return filter, thus filtering the fluid returned in the hydraulic tank. Known return filters have the disadvantage that liquid flowing through the filter is exposed to a high flow resistance for the desired filter effect. Thus, recirculated liquid can escape only slowly from the hydraulic cylinder, which in turn has a slow load movement result. In particular, when lowering the load part or the mast without load thereon, this is disadvantageous, since without load usually only the weight of the mast or the load part displaces the hydraulic fluid from the hydraulic cylinder. Thus, lowering without load is particularly slow.

It is known to increase the lowering speed without load in that at low pressure in the hydraulic system, the return filter is bypassed. EP 2 236 453 B1 describes for this purpose a hydraulic lifting device with a hydraulic system comprising a return filter and a filter control valve upstream of the return filter. The filter control valve comprises a valve member which connects a filter input optionally with a first filter output or a second filter output or with both outputs. Via a spring, the valve member is biased in a first position in which the valve member at low system pressure in the filter control valve flowing liquid to the first valve outlet and thus passes over a bypass circuit to the hydraulic filter. With increasing system pressure, the valve member is displaced against the spring force of the spring, and thus the valve inlet connected to the second valve outlet, which is connected to the hydraulic filter. Such a complete bypass of the filter is technically complex and also requires a lot of space.

The invention is therefore based on the object to provide a filter device available that allows a shutdown of the filtration of the hydraulic fluid in several different pressure ranges.

The invention solves the problem by a filter device according to claim 1. Advantageous embodiments are the subject of the dependent claims, the description and the figures.

The filter device according to the invention for a hydraulic system, in particular on an industrial truck, comprises a filter element with a filter body and a valve element, wherein the valve element opens below a predetermined first system pressure bypassing the filter body first bypass channel for fluid flowing through the filter device and above a predetermined second system pressure a the filter body bypassing the second bypass channel for fluid flowing through the filter device opens, wherein the second system pressure is greater than the first system pressure.

The system pressure in the hydraulic system depends, among other things, on the permeability of the filter body and on the mass of the load. If, for example, the hydraulic system comprises a lifting device with a lifting frame and / or load part actuated by a lifting cylinder, a load located on the load part exerts a force on the hydraulic fluid in the hydraulic system via the lifting cylinder. For example, at a high load, the system pressure is higher than at a low load. Especially when there is no load on the load part, the system pressure is usually low. In order nevertheless to enable a rapid lowering of the load part of the lifting device without load, it is therefore provided to open a first bypass channel bypassing the filter body below the first system pressure. Thus, hydraulic fluid flowing through the filter device flows through the first bypass channel below the first system pressure. The first system pressure can thus be defined so that the first bypass channel opens when no load on the load part flies. Consequently, can be provided that the first system pressure is exceeded, if only the weight of the load part and / or the mast on the hydraulic system loads.

According to the invention, a second bypass channel is further provided, which is opened by the valve element when the system pressure is above a predetermined second system pressure. Thus, therefore, in a second, higher pressure range of the filter body of the filter element can be bypassed. Bypassing of the filter element allows for a faster flow rate of hydraulic fluid passing through the hydraulic system and thus faster movement of hydraulic cylinders connected to the hydraulic system. By bypassing the filter body even at high system pressures, above the second system pressure, the hydraulic system and thus the industrial truck can be used reliably even in the case of a filter heavily blocked by contaminants. The predetermined second system pressure is thus preferably chosen such that the hydraulic system only reaches such a pressure value when the permeability of the filter body has decreased (strongly).

The invention enables the bypassing of the filter body in two different, separate pressure areas. In particular, the filter body can thus be bypassed not only at a low system pressure, but also at a high system pressure. It can also be provided that, even if the first and / or the second bypass channel is open, fluid also continues to flow through the filter body itself and is thus filtered. However, since the bypass channels have a much lower flow resistance, in this case too, most of the fluid flow will flow through them.

According to a preferred embodiment, both bypass passages are closed above the first system pressure and below the second system pressure, so that fluid flowing through the filter device only flows through the filter body of the filter element. Thus, if the system assumes a pressure value that is between the first and second system pressures, the first bypass channel as well as the second bypass channel are closed to allow complete filtration of the fluid. Within this normal pressure range, the filter device allows reliable filtering of impurities from the fluid.

According to a further embodiment, it is provided that the first bypass channel is closed when the second bypass channel is open. Accordingly, therefore, the second bypass channel is closed when the first bypass channel is open. This ensures that the fluid always flows through only one of the bypass channels. As explained above, the bypass channels are controlled pressure-dependent. It can thus be provided that, below the first system pressure, the first bypass channel is opened and the second bypass channel is closed, while above the second system pressure, the second bypass channel is opened, but the first bypass channel is closed. In particular, at a pressure value between the first system pressure and the second system pressure, both bypass channels may be closed, as mentioned above.

According to a preferred embodiment, the filter element has a passageway extending along a longitudinal axis of the filter element and surrounded by the filter body, the filter element having a fluid inlet at one longitudinal end and a fluid outlet at the other longitudinal end, the fluid inlet and the fluid outlet via the fluid inlet Passage passage are interconnected, and wherein the valve element is disposed at the longitudinal end of the filter element, in which the fluid outlet is located. The filter element may, for example, have a cylindrical shape, wherein the filter body of the filter element may be formed in particular hollow cylindrical. Preferably, the filter element has a circular cylindrical shape. The passage channel may extend along the (hollow) cylinder longitudinal axis through the filter body. The filter element may further comprise, for example, a filter housing which carries the filter body. The filter element may have two opposite longitudinal ends, wherein at one longitudinal end of the filter element, a fluid inlet is provided through which fluid can enter the filter element, move along the passageway, and exit the filter element through a fluid outlet at the other longitudinal end of the filter element ,

At the fluid outlet end of the filter element, the valve element is arranged. Thus, liquid supplied to the filter element by a hydraulic system can flow through the fluid inlet into the passageway of the filter element. At a system pressure below the first predetermined system pressure, the first bypass passage is opened so that the fluid flowing through the filter element can exit the fluid outlet through the valve element. At least a small portion of this liquid flow can also penetrate in a direction substantially perpendicular to the longitudinal axis of the filter element in the filter body surrounding the passage channel and thus leak filtered on the other side of the filter body along the lateral surface of the cylindrical filter element again. At a system pressure that is between the first and the second system pressure value, are Preferably, both bypass channels of the valve element closed, so that no liquid flowing into the passage channel can leave the filter element via the fluid outlet. Instead, all liquid flows into the filter body and leaves the filter body again over the lateral surface of the cylindrical filter element. Above the second system pressure value, the valve element opens the second bypass channel and, in turn, allows the liquid flowing into the filter element via the fluid inlet to escape from the fluid outlet without being filtered out after passing through the passage channel. Again, however, is not excluded that at least a portion of the liquid also penetrates through the filter body to the outside. In principle, the first bypass channel and the second bypass channel thus do not necessarily completely bypass the filter body; at least one residual flow can also occur through the filter body.

According to this embodiment, the valve element is thus integrated directly into the filter element. In this embodiment of the filter device, no external valve technology is necessary to enable the pressure-based bypass control according to the invention. Instead of circumventing the filter element by additionally provided lines and switching valves, the fluid always flows through the filter element, with the bypass open, however, passing through the passage on the filter body. In particular, it is ensured by this design of the filter device that during fluid flow through one of the bypass channels no or at least hardly any impurities can be washed out of the filter body. This structure requires very little space and is also mounted with little effort. The entire filter device can already be stored pre-assembled and integrated into an existing hydraulic system. Thus, the filter device can be easily retrofitted. Also, the valve element can be designed to be retrofitted. Thus, a filter element having a passage channel can be supplemented with the valve element according to the invention, for example a possibly present maximum pressure valve at the outlet end of the valve element can be replaced by the valve element according to the invention.

According to a preferred embodiment, the valve element comprises a valve seat and a two-part valve member, wherein the two-part valve member comprises a first valve body having a passage opening as part of the first bypass channel and a second valve body adjustable relative to the first valve body, wherein below the first system pressure of the second valve body of spaced apart from the first valve body to open the first bypass passage extending through the passage opening, wherein above the first system pressure, the second valve body abuts against the first valve body to obstruct the passage opening and thus close the first bypass passage. The valve element may thus comprise a valve seat and a two-part valve member having a first and a second valve body. The second valve body can be adjusted relative to the first valve body and thus release or close a passage opening in the first valve body. The first valve body thus forms a seat for the second valve body. The adjustment of the second valve body relative to the first valve body takes place depending on the pressure. If the system pressure is below the first system pressure, then the second valve body is spaced from the first valve body. For example, the second valve body may be biased in this open position of the first bypass channel. At low pressure is thus opened by a spacing of the second and first valve body of the first bypass channel. If the system pressure in the hydraulic system now rises above the first system pressure, then the second valve body moves in the direction of the first valve body and thus closes the passage opening of the first valve body. For this purpose, the second valve body can in particular engage in the passage opening of the first valve body. This movement of the second valve body relative to the first valve body preferably takes place passively solely on the basis of the system pressure in the filter device. In a structurally simple way, such a pressure-controlled valve element can be provided.

As a seat for the first valve body, the valve seat of the valve element is used. Preferably, this valve seat comprises a seat opening as part of the second bypass channel, below the second system pressure, the first valve body rests against the valve seat to close the second bypass channel, wherein above the second system pressure, the first valve body is spaced from the seat opening together with the second valve body to open the second bypass passage extending through the seat opening. The first bypass channel is thus opened between the first valve body and the second valve body and the second bypass channel between the first valve body and the valve seat. In this case, the first valve body lies against the valve seat below the second system pressure and thus closes the second bypass channel. If the first system pressure has been exceeded, the second valve body is also in contact with the first valve body, so that accordingly also the first bypass channel is closed, as explained above. If the system pressure rises to a value above the second system pressure, the second bypass channel is opened by the first valve body lifts from the valve seat of the valve element. In this case, the second valve body is lifted together with the first valve body from the valve seat, wherein the first bypass channel remains closed. consequently If only the first bypass channel is open below the first system pressure, both bypass channels are closed between the first and the second system pressure, so that hydraulic fluid can only escape from the filter device via the filter body, and above the second system pressure the first bypass channel is closed, but the second bypass channel open. In particular, the first bypass channel may extend in this embodiment through the seat opening and through the passage opening, while the second bypass channel extends only through the seat opening. The passage opening and the seat opening can thereby be arranged in alignment one behind the other. This embodiment allows a particularly compact construction of the valve element. In particular, a movement of the valve body in this construction can passively be effected solely by the present system pressure. Preferably, the valve element is integrated with its valve seat and its two-part valve member in the manner described above in the filter element, that is arranged at the fluid outlet of the filter element. For example, the second valve body relative to the first valve body and the first valve body relative to the valve seat along the longitudinal axis of the filter element can be adjusted.

According to a further embodiment, the valve element is connected to a filter cover of the filter element, wherein the filter cover forms the valve seat of the valve element. Valve element and filter element can therefore be connected to one another via the filter cover, wherein the filter cover fulfills two functions. On the one hand it holds the filter body in the filter element, for example via a filter housing, and on the other hand it serves as a valve seat of the valve element, thus has the seat opening. This structure is particularly compact. Preferably, the filter cover is seated at a longitudinal end of the filter element at which the fluid outlet is located. The filter element thus preferably has a passageway extending along a longitudinal axis, through which the liquid can flow into the filter body and, in turn, can optionally leave the filter element via the valve element, as explained above.

Preferably, the valve element further comprises a guide rod on which the valve seat and the two-part valve member are mounted. This guide rod can protrude through the passage opening of the first valve body and through the seat opening and possibly also through the second valve body. In the above-explained movements of the second valve body relative to the first valve body and the first valve body together with the second valve body relative to the valve seat, the first valve body and in particular also the second valve body can move relative to the guide rod. However, it can also be provided that the second valve body is fixedly connected to the guide rod and is moved together with this relative to the first valve body. If the valve element is integrated into the filter element as described above, then the guide rod can protrude into the passage channel, in particular along the longitudinal axis of the filter element. Thus, the second valve body relative to the first valve body and the first valve body relative to the valve seat along the longitudinal axis of the filter element can be adjusted. In particular, the second valve body can move into the passage in the described switching operations. This also makes the filter device again more compact.

According to a preferred embodiment, the first valve body is biased relative to the valve seat in a closed position and / or the second valve body is biased relative to the first valve body in an open position. The bias of the first valve body in the closed position relative to the valve seat can be effected in particular by means of a first spring. The first spring can be arranged, for example, the guide rod enclosing between the valve seat and the first valve body. Likewise, the bias of the second valve body in the open position relative to the first valve body by means of a second spring. The second spring can be arranged, for example, the guide rod enclosing between the first valve body and the second valve body. By the bias of the second valve body in an open position is achieved that the valve element releases the first bypass channel in the pressureless state, in particular below the first predetermined system pressure. In this state, the second bypass channel is closed by the bias of the first valve body relative to the valve seat in a closed position. If the system pressure exceeds the first predetermined system pressure, the bias of the second valve body with respect to the first valve body is overcome and thus the first bypass channel is closed. If the second system pressure is also exceeded, the bias of the first valve body with respect to the valve seat is overcome, so that the second bypass channel is opened by lifting the first valve body from the valve seat. The first bypass channel remains closed in this case, in particular, the second valve body is lifted together with the first valve body from the valve seat. In particular, a completely passive regulation of the valve element via the system pressure can take place via this pretensioning with respect to the guide rod. The entire filter device can thus switch without electrical control in the manner according to the invention. By choosing suitable spring forces for the first spring or the second spring, the bypass channels can be adapted to desired pressure ranges.

According to a further embodiment, the guide rod extends through the seat opening of the valve seat and the passage opening of the first valve body, wherein the valve seat and the first valve body are mounted on the guide rod via radial webs. The guide rod may preferably project through the seat opening of the valve seat and the passage opening of the first valve body in the middle, in particular run along a longitudinal axis of the filter element, as mentioned above. The valve seat may thus have radial webs which extend from an inner edge of the seat opening into the seat opening and are in contact with the guide rod. Likewise, the first valve body may have radial webs which extend from an inner edge of the through hole into the through hole and are in contact with the guide rod. In this way, the first valve body and the valve seat can be mounted on the guide rod. Should a possibly provided filter cover of the filter element serve as a valve seat, as explained above, then the guide rod itself can be mounted on the valve seat. In particular, the guide rod can then be firmly connected to the valve seat, wherein a movement of the guide rod mounted on the valve body along the guide rod can be made relative to the valve seat. The projecting into the passage opening or seat opening radial webs are preferably dimensioned so that they impede a flow of liquid through the passage opening or the seat opening only to a small extent.

According to a preferred embodiment, the valve element for opening the first and / or second bypass channel is controlled solely by the present system pressure. As already mentioned, therefore, a control of the valve element can be done completely passive. In particular, therefore, the first valve body as well as the second valve body can be moved mechanically only in such a way that the first or second bypass channel are opened or closed merely because of the present system pressure. However, it can also be provided that, for example, only the second valve body or only the first valve body are passively controlled by the system pressure, while the respective other valve body is actively electrically controlled.

Thus, according to a further embodiment it can be provided that the valve element for opening the first and / or second bypass channel is electrically controllable, and the filter device comprises at least one pressure sensor for detecting the system pressure, wherein an active control of the valve element in response to one of the pressure sensor recorded system pressure takes place. It can therefore be provided that the system pressure present in the filter device is determined via a pressure sensor. The pressure sensor can be connected, for example, to a control device which opens or closes the first or second bypass channel as a function of the pressure values determined by the pressure sensor. It can also be provided, for example, that the movement of the second valve body relative to the first valve body is passive, while the movement of the first valve body relative to the valve seat is active. Thus, therefore, the first bypass channel can be closed or opened in a passive manner and the second bypass channel can be closed or opened in an active manner. A passive control is particularly simple, less error-prone and particularly easy to implement. An active control in turn has the advantage that the predetermined system pressures can also be changed and adjusted in retrospect.

The invention further relates to a hydraulic tank for an industrial truck, comprising a tank shell and a filter device according to the invention, wherein the filter device has an inlet opening for supplying fluid to the filter device and an outlet opening for the passage of fluid from the filter device into the tank shell, wherein the filter element of the filter device is arranged in the flow path of the fluid between the inlet opening and the outlet opening. The filter device according to the invention can thus be integrated in a hydraulic tank for a truck. Returned hydraulic fluid can be supplied to the filter device via the inlet opening. Depending on the switching state of the valve element, this supplied hydraulic fluid flows either through the filter element of the filter element, through the first bypass channel or through the second bypass channel. If the fluid flows through one of the bypass channels, it will flow unfiltered into the tank shell again. If the liquid flows through the filter body of the filter element, it also passes into the tank shell via the outer surface of the filter body, but in this case it is filtered. From the tank shell, the hydraulic fluid can again be guided via the hydraulic system to the desired hydraulic cylinders.

The invention also achieves the object by an industrial truck, in particular a forklift, comprising a filter device according to the invention or a hydraulic tank according to the invention.

• 1 die erfindungsgemäße Filtervorrichtung in einer Schnittansicht mit geöffnetem ersten Bypasskanal,
• 2 die erfindungsgemäße Filtervorrichtung in einer Schnittansicht mit geschlossenen Bypasskanälen,
• 3 die erfindungsgemäße Filtervorrichtung in einer Schnittansicht mit geöffnetem zweiten Bypasskanal,
• 4 einen Hydrauliktank für ein Flurförderzeug in einer Seitenansicht,
• 5 den Hydrauliktank aus 4 um 90° gedreht in einer Schnittansicht, und
• 6 ein Hydraulikschema eines Hydrauliksystems eines Flurförderzeugs.

The invention will be explained below with reference to figures. Show it:

• 1 the filter device according to the invention in a sectional view with opened first bypass channel,
• 2 the filter device according to the invention in a sectional view with closed bypass channels,
• 3 the filter device according to the invention in a sectional view with opened second bypass channel,
• 4 a hydraulic tank for a truck in a side view,
• 5 off the hydraulic tank 4 rotated by 90 ° in a sectional view, and
• 6 a hydraulic diagram of a hydraulic system of a truck.

Unless otherwise indicated, like reference characters designate like items.

The 1 to 3 show a filter device according to the invention 10 with a filter element 20 and a valve element 30 , The filter element 20 has a circular cylindrical shape and has a hollow cylindrical filter body 22 which is one along the longitudinal axis L the filter element extending passageway 24 surrounds. Furthermore, the filter element has 20 at one of its longitudinal ends via a fluid inlet 26 , in particular in 3 or in 5 and at its other longitudinal end via a fluid outlet 28 , The fluid inlet 26 of the filter element 20 is in the 1 and 2 not visible, because there the lower end of the filter device 10 not shown. The fluid inlet 26 and the fluid outlet 28 are over the passageway 24 connected with each other. At its outlet end has the filter element 20 also via a filter cover 29 with an opening for the fluid outlet 28 , At this filter cover 29 is the valve element 30 arranged. The valve element 30 So it is in the filter element 20 integrated. The valve element may in particular be retrofitted. The fluid outlet 28 is formed by through holes 42 and an annular gap-shaped opening 76 as explained below.

The valve element 30 includes a valve seat 32 which in the present case through the filter cover 29 of the filter element 20 is formed, and a two-part valve member 34 consisting of a first valve body 36 and a second valve body 38 , which has a guide rod 40 connected to each other. The first valve body 36 has a passage opening 42 on, by radial webs 44 extending from an inner wall of the first valve body 36 in the passage opening 42 in the direction of the guide rod 40 extend, is divided into several opening sections. The radial webs 44 stand with a center in the through hole 42 located bearing ring 46 in connection, over which the first filter body 36 on the guide rod 40 is movably mounted. The valve seat 32 has a seat opening 48 caused by radial webs 50 extending from an inner wall of the valve seat 32 in the seat opening 48 extend, is divided into several sections. The radial webs 50 open in the middle of the seat opening 48 in a ring element 52 over which the guide rod 40 to the valve seat 32 and thus on the filter cover 29 is fixed. The passage opening 42 and the seat opening 48 are arranged in alignment one behind the other. As in particular in 1 to recognize, corresponding to the passage opening 42 and the seat opening 48 such that the first valve body 36 or the valve seat 32 the opening 48 . 42 the other part is not obscured. The second valve body 38 has engaging elements 54 corresponding to the through hole 42 and the seat opening 48 are formed. About a storage section 56 is the second valve body 38 on the guide rod 40 movably mounted.

The filter device 10 is part of a hydraulic system, which continues via a tank shell 60 with an inlet pipe 61 for refilling the tank shell 60 with hydraulic fluid, one inside the inlet nozzle 61 arranged tank entrance 62 for the return of hydraulic fluid and a tank outlet 64 features. About the tank outlet 64 can by means of a pump 66 Hydraulic fluid from the tank shell 60 be pumped to one or more hydraulic cylinders, not shown. The tank shell 60 has a recording 68 for the filter device 10 , where the recording 68 after inserting the filter device 10 with a screw cap 70 can be closed. The lid 70 can be removed again according to the filter device 10 exchange. The fluid inlet 26 the filter device 10 is about an inlet opening 72 having hose connection with a hose 74 connected via the from the hydraulic system through the tank inlet 62 Returned hydraulic fluid of the tank shell 60 the filter device 10 can be supplied. The fluid outlet 28 is with an outlet opening 73 the filter device connected or forms this.

Is now hydraulic fluid from the hydraulic system through the input 62 back to the tank 60 returned, it runs over the hose 74 and the fluid inlet 26 in the filter device 10 , The liquid enters the passageway 24 of the filter element 20 and flows in the direction of the fluid outlet 28 of the filter element 20 , As long as the flow pressure does not exceed a first predetermined system pressure, the hydraulic fluid flows on the second valve body 38 past through the seat opening 48 as well as the passage opening 42 and thus passes through the fluid outlet 28 in the tank shell 60 , The second valve body 38 is here on the guide rod 40 biased into its open position, as in 1 shown. For this purpose, a spring, not shown, between the second valve body 38 and the first valve body 36 be arranged. The liquid thus flows along the in 1 shown arrow lines through the first bypass channel A , The first bypass channel A So runs past the second valve body 38 through the seat opening 48 of the valve seat 32 and the through hole 42 of the first valve body 36 , The first predetermined system pressure is preferably selected so that a controlled via the hydraulic circuit lifting cylinder allows a rapid lowering of a connected to the lifting cylinder load part without load. This can, for example, via a corresponding bias of the second valve body 38 be reached in the open position. The first valve body 36 is at this time in its closed position, in which it is biased. This bias can be done for example via a spring, not shown.

If the pressure now exceeds the first predetermined system pressure, it pushes through the passageway 24 flowing liquid flow the second valve body 38 along the guide bar 40 in the direction of the first valve body 36 , The engaging elements 54 penetrate into the seat opening 48 as well as the passage opening 44 and close both, as in 2 to recognize. The second valve body 38 is thus moved to its closed position. If the system pressure is above the first, but below the second system pressure, so no bypass channel is open and through the passageway 24 flowing hydraulic fluid leaves the filter device 10 instead over the filter body 22 , according to the in 2 illustrated arrow lines. In this case, complete filtering of the liquid takes place. After passing through the filter body 22 passes through the hydraulic fluid in 5 illustrated housing 21 the filter device 10 and enters the interior of the tank shell 60 one.

If the system pressure continues to increase, so that a second predetermined system pressure is exceeded, the pressure is applied to the two-part valve member 34 acting flow pressure so great that the first valve body 36 together with the second valve body 38 in the flow direction along the longitudinal axis L on the guide rod 40 is moved along. It is here by the bias of the first valve body 36 overcome force generated in its closed position and thus the second bypass channel B open, as in 3 shown. The second valve body 38 is also in this case by the flow pressure in the direction of the first valve body 36 pressed and closes its passage opening 42 complete with its engaging elements. The first bypass channel A is closed in this case. The seat opening 48 of the valve seat 32 However, it has a larger opening cross section than the through hole 44 so that - as in 3 seen - the liquid flow at high pressure in the second valve body 38 past the seat opening 48 can reach, according to the in 2 illustrated arrow lines. Because of the high pressure, the first valve body 36 from the valve seat 32 is lifted, forms an annular gap-shaped opening 76 through which the liquid flow, along an underside of the first filter body 36 and along an upper side of the valve seat 32 (or the filter cover 29 ), from the filter device 10 can escape. A movement of the second valve body 38 in the flow direction along the guide rod 40 is above the second system pressure through the ring element 52 of the valve seat 32 stopped.

Due to the special design of the valve element 30 allows the filter device according to the invention 10 consequently a bypass of the filter body 22 at low, but also at high pressure in the hydraulic system. At a normal pressure, ie a pressure value between the first and the second system pressure, hydraulic fluid flowing into the filter device flows exclusively through the filter body 22 , At system pressures below the first system pressure and above the second system pressure, the hydraulic fluid substantially flows only through the first and second bypass channels, as discussed above. Depending on the permeability of the filter and depending on the system pressure, however, at least a small part of the liquid flow can pass through the filter body to the outside, even when the bypass channels are open.

The valve element described in this embodiment is passively controlled solely by the present system pressure, as just explained. However, it is also conceivable that the valve element is electrically controlled. For this purpose, the second valve body 38 For example, firmly with the guide rod 40 be connected, wherein the guide rod together with the second valve body in the passageway 24 can be moved in or out of this. The first valve body 36 can continue to passively be controlled solely by the present system pressure in this case. In this case, the guide bar is 40 then not firmly with the ring element 52 of the valve seat 32 or the filter cover 29 connected.

In 6 is a hydraulic diagram for a truck with a filter device according to the invention shown. A lifting unit, not shown, of the truck can over the cylinder 100 and 102 be moved, the cylinder 100 one Lifting mast of the truck and the cylinder 102 on a connected to the mast load part, such as a fork acts. The hydraulic cylinder 100 So controls the mast lift, while hydraulic cylinder 102 controls the free lift. Hydraulic fluid gets out of the tank shell 60 over the pump 66 through a check valve 104 in the mast lifting cylinder 100 and / or in the Freihubzylinder 102 pumped. The mast lifting cylinder 100 this is an electrically actuated two-way proportional valve 106 upstream, which can be switched to a passage position, to an inflow and a return flow of hydraulic fluid to and from the Mast cylinder 100 to allow, and can be switched to a blocking position. The free-lift cylinder 102 is an electrically operated two-way valve 108 upstream, which in a passage position an inflow to the Freihubzylinder 102 and a return flow from the free-lifting cylinder 102 allows and locks in a blocking position these tributaries.

Will now be from one of the hydraulic cylinders 100 . 102 by a corresponding passage position of the valves 106 . 108 Discharged liquid, so it reaches the filter device 10 , The filter device 10 directs the hydraulic fluid in the manner described above either through the filter body, or through one of the two bypass channels back into the tank shell 60 , In addition, the filter device, a two-two-way valve 112 and / or a pressure control valve 114 be upstream.

LIST OF REFERENCE NUMBERS

10

filter means

20

filter element

22

filter body

24

Passageway

26

fluid inlet

28

fluid outlet

29

filter cover

30

valve element

32

valve seat

34

two-piece valve member

36

first valve body

38

second valve body

40

guide rod

42

Through opening

44

radial webs

46

bearing ring

48

seat opening

50

radial webs

52

ring element

54

engaging members

56

bearing section

60

tank shell

61

flowguide

62

tank input

64

tank outlet

66

pump

68

admission

70

screw

72

inlet port

73

outlet

74

tube

76

annular gap-shaped opening

100

mast lift cylinder

102

free lift cylinder

104

check valve

106

Two-way proportional valve

108

Two-way valve

112

Two two-way valve

114

Pressure control valve

A

first bypass channel

B

second bypass channel

L

longitudinal axis

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2236453 B1 [0004]

Claims (14)

Filter device for a hydraulic system, in particular on an industrial truck, comprising a filter element (20) with a filter body (22) and a valve element (30), wherein the valve element (30) has a first bypass channel bypassing the filter body (22) below a predetermined first system pressure ( A) opens for fluid flowing through the filter device (10) and above a predetermined second system pressure opens a second bypass channel (B) bypassing the filter body (22) for fluid flowing through the filter device (10), the second system pressure being greater than the first system pressure. Filter device after Claim 1 , characterized in that above the first system pressure and below the second system pressure both bypass channels (A, B) are closed, so that flowing through the filter device (10) flowing fluid only through the filter body (22) of the filter element (20). Filter device after Claim 1 or 2 , characterized in that the first bypass channel (A) is closed when the second bypass channel (B) is opened. Filter device according to one of the preceding claims, characterized in that the filter element (20) has a passage (24) extending along a longitudinal axis (L) of the filter element (20) and surrounded by the filter body (22), wherein the filter element (20) a fluid inlet (26) at one longitudinal end and a fluid outlet (28) at the other longitudinal end, the fluid inlet (26) and fluid outlet (28) communicating with each other via the passageway (24), and wherein the valve member (30 ) is disposed at the longitudinal end of the filter element (20) where the fluid outlet (28) is located. Filter device according to one of the preceding claims, characterized in that the valve element (20) comprises a valve seat (32) and a two-part valve member (34), wherein the two-part valve member (34) has a first valve body (36) with a through opening (42) as Part of the first bypass channel (A) and a relative to the first valve body (36) adjustable second valve body (38), wherein below the first system pressure, the second valve body (38) from the first valve body (36) is spaced around which opening the first bypass passage (A) extending through the passage opening (24), wherein above the first system pressure the second valve body (38) bears against the first valve body (36) in order to obstruct the passage opening (24) and thus the first bypass passage (A) to close. Filter device after Claim 5 characterized in that the valve seat (32) includes a seat opening (48) as part of the second bypass passage (B), wherein below the second system pressure, the first valve body (36) abuts the valve seat (32) to engage the second bypass passage (B ), wherein above the second system pressure, the first valve body (36) is spaced from the seat opening (48) together with the second valve body (38) to open the second bypass passage (B) extending through the seat opening (48). Filter device after Claim 5 or 6 characterized in that the valve element (30) is connected to a filter cover (29) of the filter element (20), the filter cover (29) forming the valve seat (32) of the valve element (30). Filter device according to one of Claims 5 to 7 , characterized in that the valve element (30) further comprises a guide rod (40) on which the valve seat (32) and the two-part valve member (34) are mounted. Filter device after Claim 8 , characterized in that the first valve body (36) opposite to the valve seat (32) is biased into a closed position, and / or that the second valve body (38) is biased towards the first valve body (36) in an open position. Filter device after Claim 8 or 9 , characterized in that the guide rod (40) through the seat opening (48) of the valve seat (32) and the passage opening (42) of the first valve body (36), wherein the valve seat (32) and the first valve body (36) via radial webs (44, 50) are mounted on the guide rod (40). Filter device according to one of the preceding claims, characterized in that the valve element (30) for opening the first and / or second bypass channel (A, B) is passively controlled solely by the present system pressure. Filter device according to one of Claims 1 to 10 , characterized in that the valve element (30) for opening the first and / or second bypass channel (A, B) is electrically controllable, and the filter device (10) comprises at least one pressure sensor for detecting the system pressure, wherein an active actuation of the valve element ( 30) in response to a detected by the pressure sensor system pressure. Hydraulic tank for a truck, comprising a tank shell (60) and a A filter device (10) according to any one of the preceding claims, wherein the filter device (10) has a port (72) for supplying fluid to the filter device (10) and an outlet port (73) for discharging fluid from the filter device (10) into the tank shell (60), wherein the filter element (20) of the filter device (10) in the flow path of the fluid between the port (72) and outlet port (73) is arranged. Industrial truck, in particular a forklift, comprising a filter device (10) according to one of Claims 1 to 12 or comprising a hydraulic tank according to Claim 13 ,

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