Abstract:
A hydraulic unit for industrial trucks, comprising a motor pump unit which is directly attached to a tank, a reflux filter which has an elongate filter casing for a filtering element adapted to be introduced into the tank through an opening, a hose coupling, and an outlet opening, wherein the filtering element is disposed in the flow path between the hose coupling and the outlet opening, a reflux hose between the motor pump unit and the hose coupling, and a closure for the reflux filter, wherein the reflux hose extends within the tank and the hose coupling is disposed within the tank.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     Industrial trucks are provided with a hydraulic unit to lift loads by the use of a load-carrying means. The unit comprises a driving motor, mostly an electric motor, and a pump driven by the motor as well as a valve assembly. In the simplest case, an easy-action lift cylinder is actuated with a check valve being responsible for holding the load whereas the load is lowered by releasing a return path to the tank from the valve assembly, e.g. via the unblockable check valve.  
         [0004]     It has become known already to combine the motor, pump, and valve assembly as a unit within a common casing and to place the casing directly onto a hydraulic tank from which the pump draws in a hydraulic medium. Further, it has been known to feed the flow-back medium not straight to the tank, but route it through a so-called reflux filter during the lowering operation.  
         [0005]     Further, it has been known to configure a reflux filter such as to introduce an elongate filter casing (a bell), which contains a filtering element, into the hydraulic tank through an opening. A hose extends from the valve assembly of the hydraulic unit to a hose coupling of the filter casing, either through the tank lid which closes the sealing of the opening or even through a lateral coupling which is formed with a casing which, in turn, is fixed to the tank above the opening. However, a reflux filter of this type has some drawbacks. Possible leaks result because of the externally located couplings of the hose between the hydraulic unit and reflux filter. Furthermore, the reflux hose requires to be disconnected to change the filter. At least two sealing rings are necessary to provide a seal between the reflux hose and the tank or filter casing. Moreover, the known reflux filter necessitates a relative large number of individual components.  
         [0006]     It is the object of the invention to provide a hydraulic unit for industrial trucks in which the above-mentioned drawbacks are not encountered and which reduces the constructional and handling effort.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     In the invention, the reflux hose is located within the tank. A tube coupling is provided on the filter casing within the tank.  
         [0008]     The provision of such a filtering device merely requires three components, i.e. a filter casing, a lid, and a filtering element. However, this applies only when a hose coupling socket is integrally formed with the filter casing, according to an aspect of the invention.  
         [0009]     A further advantage is that it is unnecessary to disconnect the reflux hose for a filter change. There is merely a need to unscrew the tank lid from a threaded socket of the tank in order to remove the filtering element. If there is a leak in the area of the reflux hose, the hydraulic medium enters the tank and does not get into the surroundings. Merely a simple O-ring gasket is required to achieve a seal between the tank and filter. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0010]     The invention will be described in more detail below with reference to the embodiments shown in the drawings.  
         [0011]      FIG. 1  shows a perspective view of a hydraulic unit of the invention.  
         [0012]      FIG. 2  shows a side view of the hydraulic unit of  FIG. 1 .  
         [0013]      FIG. 3  shows a side view of the hydraulic unit of  FIG. 1  that is offset by 90°.  
         [0014]      FIG. 4  shows a section through a reflux filter of the hydraulic unit of FIGS.  1  to  3 .  
         [0015]      FIG. 5  shows a perspective view of the filter casing of the reflux filter of  FIG. 4 .  
         [0016]      FIG. 6  shows a section through another embodiment of a reflux filter.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     While this invention may be embodied in many different forms, there are described in detail herein a specific preferred embodiment of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated  
         [0018]     In FIGS.  1  to  3 , a compact hydraulic unit  10  is shown with a motor pump unit  12 , which have a common casing. The casing of the motor pump unit  12  has fastened thereto a valve casing  14  via which the motor pump unit  12  is mounted on the upper side of a hydraulic tank  16 . A solenoid valve  18  is attached to the valve casing  14 . The hydraulic unit described, for example, serves for actuating a lift cylinder in an industrial truck (not shown). When the motor of the motor pump unit  12  is turned on the hydraulic medium will be delivered to the lift cylinder from the tank  16 . The valve assembly has provided therein a check valve which prevents the hydraulic medium from flowing back and maintains the lift cylinder in the position assumed. Upon actuation of the valve  18 , the hydraulic medium will flow back from the lift cylinder, namely through a hose  20  which is shown in phantom lines in  FIGS. 2 and 3 . The hose is located within the tank  16  and leads to a filtering device  22  which will be explained in more detail with reference to  FIGS. 4 and 5 .  
         [0019]     The filtering device depicted in  FIG. 4 , which defines a so-called reflux filter, has a filter casing  24  which includes an elongate sleeve portion  26  at the upper end of which a radial flange  28  is formed. A couping socket  30 , in turn, is formed on the flange  28 . The filter casing  24  is integrally formed from a plastic material. The socket  30  allows to recognize some part of the reflux tube  20  at  32 .  
         [0020]     The sleeve portion  26  is partially closed in part at the lower end at  34 , an upwardly facing annular cylindrical lug  36  being formed in the area of a central lower opening. An annular cylindrical filter cartridge  38  is located within the filter casing  24  with the central passage  38   a  of the filter cartridge housing the cylindrical lug  36  and the lower end of the cartridge  38  abutting on the closed bottom portion  34 . The upper end of the cartridge has a diameter which is somewhat larger than the inside diameter of the sleeve portion  26 .  
         [0021]      FIG. 4  also allows to recognize a threaded socket  40  which is formed at the upper side of the tank  16  (also see FIGS.  1  to  3 ). A tank lid  42  is screwed onto the threaded socket  40 , an O-ring  44  being disposed between the tank lid  42  and socket  40  or the outside of the flange  28  to bring about a seal with regard to the tank, lid, and reflux filter in this area. A space  46  is defined between the inside of the lid  42  and the upper side of the filter casing  24  or filter cartridge  38 . The hydraulic medium which flows into the reflux filter  22  through the reflux hose  20  and coupling socket  30  (see the arrow) is capable of flowing through the space  46  and into the annular space  48  between the filter cartridge  38  and the inside wall of the socket portion  26  and, thence, into the passage  38   a  of the filter cartridge  38  (see the arrow). As can be recognized in  FIG. 4  the outside diameter of the cartridge  38  is smaller than the inside diameter of the socket portion  26 .  
         [0022]     The reflux filter  22  shown in the Figures only has 3 components, i.e. the tank lid  42 , the filter casing  24 , and the filter cartridge  38 . Therefore, its manufacture proves to involve particularly little effort. A change of the filter cartridge  38  merely makes it necessary to unscrew the tank lid  42 .  
         [0023]     If a leak should occur at the coupling points of the reflux hose  20  or the hose should become brittle as such the medium will not flow to the outside, but remain inside the tank  16 .  
         [0024]     Referring to the embodiment of  FIG. 1 , it should be added that the passage  38   a , at its upper end, is blocked by a check valve  50  from the space  46 . The valve solely opens at a predetermined pressure in the space  46 . The oil will then flow back to the tank in a non-filtered condition.  
         [0025]     Referring to  FIG. 5 , it should be mentioned that the underside of the radial flange  28  has formed thereon two projections  52 ,  54  which interact with matching recesses (not shown) of the threaded socket  28 . This helps achieve that the casing  24 , when in a predetermined rotational position, be inserted into the socket  28  and, hence, the tank  16 .  
         [0026]     In an alternative embodiment of  FIG. 6 , components like those of the embodiment of  FIG. 4  are given like reference numbers to which an index “a” is added. Identical components are not denoted with an additional index.  
         [0027]     It can be appreciated in  FIG. 6  that a coupling socket  30   a  is configured for a hose, which is not shown, at the lower end of the sleeve-like filter casing  24   a . The oil flowing back through the hose gets into the space  48  between the filter cartridge  38  and the associated inside wall of the casing  24   a  and, thence, flows into the passage  38   b  through the filter cartridge and, thence, flows downwards again as is shown by the arrows shown in the drawing.  
         [0028]     It is also conceivable to form the hose coupling socket laterally to the wall of the casing  24   a.    
         [0029]     In  FIG. 6 , a socket  40   a  is passed into the interior of the tank  18   a . It has a female thread to receive the male thread of the lid  42   a . The socket  40   a  has a radially inwardly directed flange at the lower end onto which a radial flange of the casing  24   a  is deposited. The upper end of the filter casing  24   a  has positioned thereon a closure  60  which closes the passage  38   b  and filter cartridge  38  towards the top. It can be provided with a throttle opening or a valve, which is not shown in detail, in the area of the passage  38   b  to correspond to the action of the valve  50  of  FIG. 4 .  
         [0030]     The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims.  
         [0031]     Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim  1  should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below.  
         [0032]     This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.