Patent Publication Number: US-8979518-B2

Title: Hydraulic toothed wheel machine

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2010/001163, filed Feb. 25, 2010, which claims the benefit of priority to application Ser. No. DE 10 2009 012 853.0, filed Mar. 12, 2009 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a hydraulic toothed wheel machine. 
     EP 1 291 526 A2 shows a toothed wheel machine having a housing in which two intermeshing toothed wheels supported in bearing bushes or bearing bodies are arranged, the housing being closed at the ends by a first and a second housing cover respectively. The helically toothed wheels are each supported in a sliding manner axially by two axial surfaces between the bearing bodies and radially by respective bearing shafts accommodated in the bearing bodies. During the operation of the toothed wheel machine, hydraulic and mechanical forces act on the toothed wheels along the same toothed wheel longitudinal axis in each case. To ensure that the first bearing body, which lies in the direction of action of the forces, is not pushed beyond the axial surfaces of the toothed wheels, between the toothed wheels and the first housing cover, and that only a small sliding gap occurs between the toothed wheels and the second bearing body, a counter-force is applied to the toothed wheels and to the first bearing body. This counter-force is larger than the hydraulic and mechanical forces, with the result that the first bearing body is pressed against the toothed wheels, the toothed wheels are pressed against the second bearing body, and the second bearing body is pressed against the second housing cover. All the resultant forces on the bearing bodies and the toothed wheels thus act in the direction of the second housing cover. 
     The counter-force on the toothed wheels is applied via pistons acting on the bearing shafts. The pistons are accommodated in a sliding manner, approximately coaxially with respect to the toothed wheel longitudinal axis, in an intermediate cover arranged between the first housing cover and the housing and rest by means of a first piston end face against a shaft end face of the bearing shafts which faces in the direction of the first housing cover and are each subjected to pressure by way of a second piston end face. The counter-force is applied to the first bearing body by way of a pressure field formed between the bearing body and the intermediate cover. 
     The disadvantage with this solution is that the entire assembly of bearing bodies and toothed wheels is pressed onto the second housing cover of the toothed wheel machine, with the result that the second housing cover and the housing are subjected to very high and uneven loads. Moreover, the pressing together of the toothed wheels and the bearing bodies results in very high wear between the axial surfaces of the toothed wheels and the bearing bodies. 
     SUMMARY 
     It is the object of the present disclosure to provide a hydraulic toothed wheel machine in which machine elements, in particular housing covers and housings, are subjected to little force and which is subject to minimal wear. 
     This object is achieved by a hydraulic toothed wheel machine in accordance with the features set forth below. 
     According to the disclosure, a toothed wheel machine has a housing for accommodating two intermeshing toothed wheels, in particular helically toothed wheels, which are supported in a sliding manner axially by axial surfaces between bearing bodies accommodated in the housing and radially by respective bearing shafts accommodated in the bearing bodies. During the operation of the toothed wheel machine, an axial force component of a force resulting from hydraulic and mechanical forces acts on each toothed wheel in the same axial direction. A counter-force against the respective axial force component is then applied to the toothed wheels and/or bearing shafts, the magnitude of said counter-force being equal to or less than that of the respective axial force component. 
     This solution has the advantage that the toothed wheels of the toothed wheel machine are each pressed against the bearing body lying in the direction of action of the axial force component by an axial force component reduced by the counter-force, with the result that there is a reduction in the sliding friction between the toothed wheels and the bearing body and the other bearing body, the one which does not lie in the direction of action of the axial force component, is not subjected to load. The axial force components reduced by the counter-forces can then be provided as axial-gap compensation for a sliding gap between the toothed wheels and the bearing bodies lying in the direction of action of the resultant force. Axial-gap compensation for a sliding gap between the toothed wheels and the bearing bodies that do not lie in the direction of action of the axial force component can be employed independently of the axial force components. It is furthermore possible, by means of the counter-force, to reduce loading due to the axial force component on the housing cover and the housing. 
     The toothed wheels of the toothed wheel machine are preferably helically toothed. 
     It is advantageous if the first bearing body, which lies in the direction of the effective axial force component, is pressed against a housing cover of the housing mechanically by way of the toothed wheels and/or hydraulically by way of a pressure force. 
     To make the second bearing body press lightly on the toothed wheels, a hydraulic pressure is applied to the bearing body at an end face facing away from the toothed wheels. 
     The counter-force acting on the toothed wheels and/or bearing shafts is preferably a hydraulic pressure force and/or a mechanical force. 
     It is advantageous if the counter-force acts on at least one toothed wheel by means of a pressure field between at least one toothed wheel and the first bearing body. A pressure pocket can simply be introduced into that axial surface of the at least one toothed wheel which faces the first bearing body in order to delimit the pressure field. 
     The axial surface of one toothed wheel consists of tooth faces and of an annular surface, and the pressure pocket is preferably an annular groove introduced into the annular surface and running approximately concentrically around a longitudinal axis of the corresponding toothed wheel. To enlarge the pressure field and hence the area of application of the hydraulic pressure, the annular groove can be enlarged by tooth pocket sections introduced into the tooth faces of the toothed wheel. 
     As a further development of the disclosure, the annular groove is introduced into that axial surface of the driving toothed wheel which faces the first bearing body, and the annular groove together with the tooth pocket sections is introduced into that axial surface of the driving toothed wheel which faces the first bearing body since the axial force component on the driving toothed wheel is larger than that on the driven toothed wheel. 
     It is expedient if the pockets are in pressure-medium communication with a high pressure of the toothed wheel machine. 
     A pressure field can be introduced into that end face of the second bearing body which faces away from the toothed wheels, and this can be brought about by pressing the second bearing body lightly against the toothed wheels. 
     It is advantageous if that end face of the second bearing body which faces away from the toothed wheels has introduced into it a first pressure groove, running concentrically all the way round a first bearing eye, and a second pressure groove, spanning a partial circle around a second bearing eye. The pressure grooves are then in pressure-medium communication with the high pressure of the toothed wheel machine via a pressure-medium port. 
     In a preferred embodiment of the toothed wheel machine, for each bearing shaft there is a piston supported in an axially movable manner in the housing cover of the housing, approximately coaxially with respect to the toothed wheel longitudinal axis, for applying force to the bearing shafts. The respective piston is arranged so as to rest approximately, by means of a first piston end face, against a shaft end face of the bearing shaft which faces in the direction of the axial force component, and has pressure applied to it by way of a second piston end face. The piston is a simple means of applying the mechanical counter-force to the bearing shafts. 
     For application of pressure, the second piston end faces are connected to the high pressure of the toothed wheel machine. The pressure force acting on the bearing shafts can be determined by means of the piston end face diameter. 
     Other advantageous developments of the hydraulic toothed wheel machine in accordance with the disclosure is set forth below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred illustrative embodiments of an disclosure are explained in greater detail below with reference to schematic drawings. In the drawings: 
         FIG. 1  shows a simplified illustration of a toothed wheel machine according to one illustrative embodiment in a longitudinal section; 
         FIG. 2  shows a simplified illustration of an assembly of bearing bodies and toothed wheels of the toothed wheel machine from  FIG. 1 , in a side view; 
         FIG. 3  shows a plan view of the toothed wheels of a second illustrative embodiment; and 
         FIG. 4  shows a plan view of a bearing body of a third illustrative embodiment of the toothed wheels. 
     
    
    
     DETAILED DESCRIPTION  
       FIG. 1  shows a hydraulic machine, embodied as a toothed wheel machine  1 , according to one illustrative embodiment in a longitudinal section. This machine has a machine housing  2 , which is closed by means of two housing covers  4  and  6 . Housing cover  6  of the toothed wheel machine  1 , which is on the right in  FIG. 1 , is penetrated by a first bearing shaft  8 , on which a first toothed wheel  10  is arranged within the machine housing  2 . The first toothed wheel  10  is in engagement with a second toothed wheel  12  by way of helical toothing  14 , toothed wheel  12  being arranged on a second bearing shaft  16  for conjoint rotation therewith. The first and second bearing shafts  8  and  16  are each guided in two plain bearings  18 ,  20  and  22 ,  24  respectively. The plain bearings  20 ,  24  on the right in  FIG. 1  are accommodated in a bearing body  26 , and the plain bearings  18 ,  22  on the left in  FIG. 1  are accommodated in a bearing body  28 . The toothed wheels  10  and  12  are each supported in a sliding manner in the axial direction by respective first axial surfaces  30  and  32  on the second bearing body  26  (on the right) and by respective second axial surfaces  34  and  36  on the first bearing body  28  (on the left). To reduce friction, sliding surfaces between the toothed wheels  10 ,  12  and the bearing bodies  26 ,  28  can be provided with an antifriction coating, such as MoS 2 , graphite or PTFE. Respective end faces  38  and  40  of the bearing bodies  26  and  28  face the housing covers  6  and  4 . 
     The housing covers  4 ,  6  are aligned on the machine housing  2  by means of centering pins  42 . A housing seal  44  is arranged between the housing covers  4  and  6  and the machine housing  2 . Respective axial seals  46  are furthermore inserted into the end faces  38  and  40  of the bearing bodies  26  and  28  to separate a high-pressure zone from a low-pressure zone of the toothed wheel machine  1 . A radial shaft seal ring  48  seals off the first bearing shaft  8  where it passes through the housing cover  6  on the right in  FIG. 1 . 
     Hydraulic and mechanical forces arise during the operation of the toothed wheel machine  1 , this being illustrated schematically in detail in  FIG. 2  below. 
       FIG. 2  shows a simplified illustration, in side view, of an assembly of toothed wheels  10  and  12  and bearing bodies  26  and  28  in order to illustrate the hydraulic and mechanical forces that arise during operation in the toothed wheel machine  1  from  FIG. 1 . A force component of a hydraulic force acts in the same axial direction on both toothed wheels  10 ,  12 , toward the left in  FIG. 2 . In addition, a driving toothed wheel, which is the upper toothed wheel  10  in  FIG. 2 , is acted upon by a mechanical force component of a mechanical force in the direction of action of the hydraulic force component, and a driven toothed wheel, which is the lower toothed wheel  12  in  FIG. 2 , is acted upon by a mechanical force component counter to the direction of action of the hydraulic force component. The hydraulic and mechanical force components each produce a resultant axial force component  47 ,  49  in the same direction (to the left in  FIG. 2 ) on the toothed wheels  10 ,  12 , although there is a difference in magnitude. 
     The toothed wheels  10  and  12  subjected to axial force components  47 ,  49  are each supported by axial surfaces  34  and  36 , respectively, on the bearing body  28  on the left in  FIG. 2 . The right-hand bearing body  26  is not subject to the axial force components acting on the toothed wheels  10 ,  12 . To reduce wear between the toothed wheels  10 ,  12  and the bearing body  28  on the left in  FIG. 2 , a counter-force is applied to the toothed wheels, this being indicated by dashed arrows in  FIG. 2 . 
     In  FIG. 1 , two cylindrical pistons  70 ,  72  are guided in an axially movable manner in housing cover  4 . These have different diameters, with the upper piston in  FIG. 1  having the larger diameter. The first piston  70  is arranged approximately coaxially with respect to the upper bearing shaft  8  in  FIG. 1 , and the second piston  72  is arranged approximately coaxially with respect to the lower bearing shaft  16 . The respective pistons  70  and  72  rest by means of piston end faces  74  and  76  against shaft end faces  78  and  80  of the bearing shafts  8  and  16 , said shaft end faces facing in the direction of the axial force component  49  in  FIG. 2 . A hydraulic pressure is applied to the pistons  70  and  72  via further piston end faces  82  and  84 , and the pistons transmit this pressure axially to the bearing shafts  8  and  16  as a counter-force. To apply pressure to the piston end faces  82 ,  84 , a pressure chamber  86  is provided, said pressure chamber being delimited by housing cover  4  and another housing cover, which is not shown. The pressure field is in pressure-medium communication with the high pressure of the toothed wheel machine  1 . 
     The mechanical counter-force acting on the bearing shafts  8 ,  16  is determined by means of the piston diameter of the pistons  70 ,  72  and the level of pressure in the pressure chamber  86 . Since the magnitude of the axial force components  47 ,  49  shown in  FIG. 2  is different, the respective mechanical counter-force should likewise be different. As already described, the upper piston  70  in  FIG. 1  has a larger diameter than the lower piston  72 , with the result that the lower piston has a larger pressure application area and hence that a higher pressure force is transmitted as a counter-force to bearing shaft  8  via piston  70  if the pistons  70 ,  72  are acted upon by an equal pressure, as is the case in the illustrative embodiment. It would also be conceivable for the pistons  70 ,  72  to have an equal piston diameter and to be acted upon with different pressures or, in the case of different piston diameters, by different pressure levels. The counter-forces are smaller than the axial forces  47 ,  49 , with the result that the toothed wheels  10 ,  12  are pressed against bearing body  28 , and the latter is pressed against housing cover  4 , by a resultant force. 
     Owing to the mechanical counter-force applied to the toothed wheels  10 ,  12  via the bearing shafts  8 ,  16 , the remainder of the axial force is introduced into the housing  2 , while bypassing bearing body  28 . 
       FIG. 3  shows a plan view of the axial surfaces  34 ,  36  of the toothed wheels  10 ,  12  of another illustrative embodiment, and an explanation of how a hydraulic counter-force is applied to the toothed wheels  10 ,  12  will be given below. The helical toothing  14  is clearly visible in  FIG. 3 . To apply a hydraulic counter-force to the respective axial force component  49  in  FIG. 2  by application of pressure to the toothed wheels  10 ,  12 , respective pressure pockets  50 ,  52  are introduced into each of the axial surfaces  34  and  36  of the toothed wheels  10  and  12 . Together with the first bearing body  28  from  FIG. 1 , the pressure pockets  50 ,  52  each delimit a pressure field which is in pressure-medium communication with the high pressure of the toothed wheel machine  1 . The pressure pocket  52  in toothed wheel  12  is designed as an annular groove  52  which is introduced around the axial surface  36  between the tooth end faces  53  of the teeth  54  of toothed wheel  12  and an outer circumferential surface of bearing shaft  16 . In addition to an annular groove corresponding to pressure pocket  52 , the pressure pocket  50  in toothed wheel  10  has tooth pocket sections  56  introduced into the tooth end faces  53 , pressure pocket  50  thus being introduced into the axial surface  34  over a large area and being larger in extent than pressure pocket  52 . Pressure pocket  50  is then delimited radially by a wall  58  running around the periphery of toothed wheel  14 . 
     In the case of the driving toothed wheel  10 , the axial force component  47  acting is greater than in the case of the driven toothed wheel  12 , see  FIG. 2 . By means of the pressure pocket  50  with a larger area than pressure pocket  52 , a larger pressure application area for the high pressure of the toothed wheel machine  1  is created on toothed wheel  10  and, as a result, a higher counter-force acts on toothed wheel  10  than on toothed wheel  12 , in accordance with the larger axial force component  47 . 
     As already explained, the counter-forces applied to toothed wheels  10 ,  12  via pressure pockets  50  and  52  are less than or equal to the respective axial force components  47 ,  49  in  FIG. 2 . This reduces the sliding friction between the toothed wheels  10 ,  12  and bearing body  28 , thereby minimizing wear. The counter-force thus acts as a means of compensating axial force on the toothed wheels  10 ,  12 . The resultant forces arising from the axial force components  47 ,  49  and the counter-forces then serve for axial-gap compensation of the sliding gap between toothed wheels  10 ,  12  and bearing body  28  (provided the resultant force is not zero). No measures for compensating an axial gap between the toothed wheels  10 ,  12  and the bearing bodies  26 ,  28  are necessary at that end face of bearing body  28  which faces housing cover  4  and, as a result, production is very simple here and does not require any major outlay on machining. 
     The bearing body  26  on the right in  FIG. 1  is not acted upon by any resultant force from the axial force components and the counter-forces. The sliding gap between the toothed wheels  10 ,  12  and bearing body  26  is compensated for in a conventional manner, independently of the axial force components and counter-forces between the toothed wheels  10 ,  12  and bearing body  28 . 
       FIG. 4  shows the end face  39  of a spectacle-shaped bearing body  28 , situated on the left in  FIG. 1 , of a third illustrative embodiment, said end face facing the toothed wheels  10 ,  12  from  FIG. 1 . Bearing body  28  can be of two-part design, as illustrated in  FIG. 4 . A first, annular pressure groove  62  is introduced into the end face  39  of bearing body  28 , running around a bearing eye  60  at the top in  FIG. 4 . A second pressure groove  64  is formed substantially in the high pressure zone of the toothed wheel machine  1 , spanning a partial circle around the lower bearing eye  66  of bearing body  28 . The pressure grooves  62 ,  64  are in pressure-medium communication with the high pressure of the toothed wheel machine  1  via radial grooves  68 . Pressure groove  62  forms a first pressure field, and pressure groove  64  forms a second pressure field, which is smaller than the first pressure field. Here too, therefore, the axial forces  47 ,  49  of different magnitudes are counteracted by counter-forces of different magnitude. 
     In the case of the illustrative embodiments shown in  FIGS. 3 and 4 , axial-force compensation between the toothed wheels  10 ,  12  and bearing body  28  is thus implemented with very little outlay in terms of apparatus. For example, there is no need for additional components, and this leads to low production costs. The internal hydraulic forces of the toothed wheel machine  1  can be used directly for axial-force compensation, thereby enabling said forces to be linked directly to the operating conditions of the toothed wheel machine  1 . Here, bearing body  28  rests against cover  4  under the action of the entire axial force. 
     The operation of the axial-gap and axial-force compensation explained above is independent of the construction of the bearing elements used and can therefore be employed for all components suitable for axial sealing of toothed wheel machines. The same applies also to the type of toothing and the parameters thereof. Such axial-gap and axial-force compensation can be employed both in external and internal toothed wheel machines. 
     The toothed wheel machine can be used as a gear pump or motor. 
     The disclosure is of a toothed wheel machine having a housing for accommodating two intermeshing toothed wheels. These are supported in a sliding manner axially by axial surfaces between bearing bodies accommodated in the housing and radially by respective bearing shafts accommodated in the bearing bodies. During the operation of the toothed wheel machine, an axial force component of a force resulting from hydraulic and mechanical forces arising during operation acts on each toothed wheel in the same axial direction. A counter-force against the respective axial force component is then applied to the toothed wheels and/or bearing shafts, the magnitude of said counter-force being equal to or less than that of the respective axial force component.