Patent Publication Number: US-2010119398-A1

Title: Gerotor Pump

Description:
The present invention relates to gerotor oil pumps. 
     Gerotor pumps are used in a wide range of applications, such as automotive oil pumps as well as in farm tractor hydraulic circuits. The present invention may therefore be used to particular advantage, though not exclusively, in the manufacture of farm tractors, to which the following description refers purely by way of example. 
     Known gerotor pumps normally comprise a pump body closed by a cover. The pump body in turn comprises a cavity for housing: an outer rotor having an outer surface which slides on the cavity surface, and an inner surface with lobes projecting inwards of the outer rotor; and an inner rotor fitted to a drive shaft and with lobes which mesh with the lobes on the outer rotor. Up to a certain thickness of the rotors, no serious vibration of the pump is noticeable. To increase pump flow, however, the thickness of the rotors must necessarily be increased, thus resulting, in the case of very thick rotors, in a considerable increase in vibration and therefore in the noise level of the pump. 
     The present invention is designed to eliminate these drawbacks by cutting the inner rotor (and possibly also the outer rotor) into at least two portions along a plane perpendicular to its axis of rotation. This provides for a surprisingly drastic reduction in the noise level of the pump. Further improvements have been achieved by offsetting the resulting two inner rotors by a given angle. The rotors may be more than two in number, and may be of the same or different thicknesses. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A number of preferred, non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows an exploded view of a first embodiment of a gerotor pump in accordance with the present invention; 
         FIG. 2  shows a pump body forming part of the  FIG. 1  pump; 
         FIG. 3  shows a cover of the  FIG. 1  pump; 
         FIG. 4  shows a negative (i.e. “solid” for “hollow”) view of the  FIG. 1  pump; 
         FIG. 5  shows an exploded view of parts of a second embodiment of a gerotor pump in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Gerotor pump  10  comprises a pump body  11  and a cover  12  which “pack” together a number of parts described below. 
     Said parts comprise a first outer rotor  13 ; a first inner rotor  14 ; an annular partition disk  15 ; a second inner rotor  16 ; a second outer rotor  17 ; and a drive shaft  18  rotated by a motor (not shown) and having a longitudinal axis (AX) which is also the axis of rotation of drive shaft  18 . 
     Pump body  11  (which is later closed by cover  12 ) has a cavity (CV) for housing first and second outer and inner rotors  13 ,  14 ,  16 ,  17  and an annular partition disk  15 . 
     The first outer rotor  13  has an outer surface (SUP 1 ) that slides on the inner surface (SUP 2 ) of cavity (CV); first outer rotor  13  also has an inner surface (SUP 3 ) with a first number of lobes (LB 1 ) projecting inwards of first outer rotor  13 , First inner rotor  14  is fitted to drive shaft  18  of axis (AX) by means of a central through hole (FP 1 ); first inner rotor  14  also has a second number of (outwardly-projecting) lobes (LB 2 ) which, in use, mesh with lobes (LB 1 ) of first outer rotor  13 . An annular partition disk  15  has a central through hole (FP 2 ) also fitted through, in use, with drive shaft  18 ; partition disk  15  is fixed to first outer rotor  13  by pins (GR), each of which is inserted inside a respective seat (SD 1 ) formed in a front face of first outer rotor  13 , and inside a respective seat (SD 2 ) formed in partition disk  15 . It should be noted that assembly of partition disk  15  to first outer rotor  13  is made possible by partition disk  15  being larger in diameter than first inner rotor  14 , that pins (GR) are three in number and spaced 120° apart in the example shown, and that, without departing from the scope of the present invention, partition disk  15  may be fixed to second outer rotor  17  as opposed to first outer rotor  13 . 
     Second inner rotor  16  is fitted to drive shaft  18  of axis (AX) by means of a central through hole (FP 3 ), and having a third number of outer lobes (LB 3 ). Second outer rotor  17  has an outer surface (SUP 4 ) that slides on the inner surface (SUP 2 ) of cavity (CV). Second outer rotor  17  also has an inner surface (SUP 5 ) with a fourth number of lobes (LB 4 ) projecting inwards of second outer rotor  17 ; and lobes (LB 3 ) of second inner rotor  16  mesh, in use, with lobes (LB 4 ) of second outer rotor  17 . 
     It should be pointed out that, whereas the two inner rotors  14 ,  16  are fitted to drive shaft  18 , both disk  15  and the two outer rotors  13 ,  17  are mounted idly on drive shaft  18 . The outside diameters of disk  15  and the two outer rotors  13 ,  17  are substantially equal to the diameter of cavity (CV) of pump body  11 . 
     One aspect of the present invention therefore lies in cutting an inner rotor and an outer rotor each into two parts along a plane (ψ) substantially perpendicular to the axis (AX) of drive shaft  18  ( FIG. 1 ). 
     It should also be pointed out that the system would work equally well with two inner rotors and only one outer rotor, and even without the partition disk. 
     The two inner rotors  14 ,  16  can be mounted offset with respect to each other by an angle (not shown) formed between a lobe (LB 2 ) of a first lobed portion ( 14 ) and a lobe (LB 3 ) of a second lobed portion ( 16 ). 
     In one particular case, the offset angle may be such that at least one lobe (LB 2 ) of inner rotor  14  corresponds to a gap between two adjacent lobes (LB 3 ) of inner rotor  16 . 
     Offsetting inner rotors  14  and  16  is advantageously assisted using a drive shaft  18  with longitudinal grooves (not shown in  FIG. 1 ) which mate with like grooves (not shown) in the walls of respective central through holes (FP 1 ), (FP 3 ) of inner rotors  14 ,  16 . 
     If a partition disk  15  is provided, when pump  10  is fully assembled, parts  13 ,  14 ,  15 ,  16 ,  17  are packed together between the end (FND) of cavity (CV) of pump body  11  and cover  12 , which is tightened onto pump body  11  by four screws (VT); and parts  13 ,  14 ,  15 ,  16 ,  17  are all fitted through with drive shaft  18 , the ends  18 A,  18 B of which are supported by bearings (BR 1 ), (BR 2 ) housed respectively inside a seat (ALL 1 ) in the end (FND) of cavity (CV), and a seat (ALL 2 ) inside cover  12 . 
     When all the parts are assembled between pump body  11  and cover  12 , partition disk  15  forms a first pumping chamber (PP 1 ) and a second pumping chamber (PP 2 ). 
     More specifically, first pumping chamber (PP 1 ) is defined at one end by end (FND) of cavity (CV), and at the other end by a first face (FFC 1 ) of partition disk  15 , and houses first outer rotor  13 , first inner rotor  14 , and a first portion of drive shaft  18 . 
     Second pumping chamber (PP 2 ) is defined at one end by the end of cover  12 , and at the other end by a second face (FFC 2 ) of partition disk  15 , and houses second inner rotor  16 , second outer rotor  17 , and a second portion of drive shaft  18 . 
     The two pumping chambers (PP 1 ), (PP 2 ) are isolated hydraulically, as stated, by partition disk  15 . 
     As shown in  FIGS. 1 ,  2 ,  3  and  4 , whereas a common intake conduit (CND 1 ) is provided for both pumping chambers (PP 1 ), (PP 2 ), two delivery conduits (CND 2 ) and (CND 3 ) are provided, one for each pumping chamber (PP 1 ), (PP 2 ). 
     More specifically, intake conduit (CND 1 ) branches off into a first portion (PZ 1 ) ( FIG. 4 ) on the pump body  11  side, and a second portion (PZ 2 ) on the cover  12  side. In other words, a first delivery conduit (CND 2 ) is formed in pump body  11 , and a second delivery conduit (CND 3 ) in cover  12 . 
     As shown in  FIG. 4 , the delivery conduits (CND 2 ), (CND 3 ) may be connected by an inner channel (TB) connected to a further inner return channel (CND 4 ) which may be parallel-connected to a relief valve (VVM). 
     An intermediate conduit (CND 5 ) connects inner return channel (CND 4 ) hydraulically to intake conduit (CND 1 ). 
     As is known, when delivery exceeds a given pressure, relief valve (VVM) opens, and oil flows along intermediate conduit (CND 5 ) back into intake conduit (CND 1 ). 
     In the second embodiment in  FIG. 5 , partition disk  15  is replaced by a contoured disk  150 , again located between the two pumping chambers (PP 1 ), (PP 2 ). In the  FIG. 5  embodiment, contoured disk  150  has a first intake opening  152  and a second delivery opening  151  hydraulically connecting the two pumping chambers (PP 1 ), (PP 2 ). Contoured disk  150  also has a through hole (FP 4 ) fitted through, in use, with drive shaft  18 . 
     In other embodiments, not shown, of the present invention, the two faces (FFC 3 ) and (FFC 4 ) of contoured disk  150  may have grooves and/or slits and/or dead cavities by which to produce preferential paths and/or variations in speed and pressure in the oil flow inside the two pumping chambers (PP 1 ), (PP 2 ). 
     Each end point (P1), (P2) of second opening  152  of contoured disk  150  has a projection (EL 1 ), (EL 2 ). The two projections (EL 1 ), (EL 2 ) are fixed to the wall of cavity (CV) ( FIG. 1 ) in pump body  11  ( FIG. 1 ). 
     In the second embodiment in  FIG. 5 , contoured disk  150  must obviously be fixed to the wall of cavity (CV) to prevent the contoured disk from rotating, and to ensure correct positioning of first intake opening  152  and second delivery opening  151 . 
     The main advantage of the gerotor pump according to the present invention is that of providing a pump with extremely thick lobed rotors (and therefore high flow) while at the same time reducing vibration and the noise level of the pump. In fact, as stated, the present invention was conceived precisely to eliminate these drawbacks, by cutting the inner rotor (and possibly also the outer rotor) into at least two portions along a plane perpendicular to the axis of rotation of the inner rotor. So doing has proved to bring about a surprisingly drastic reduction in the noise level of the pump. Further improvements have been achieved by offsetting the two inner rotors by a given angle.