Abstract:
The invention concerns an external gear hydraulic pump including a pump body housing rotating pinions that mutually engage. Located on opposite sides of the body are a cover and a support, forming an outlet manifold for high pressure fluid. Acoustic insulation elements damp the vibrations produced by the pinions. The acoustic insulation elements acoustically decouple the pump body from the support.

Description:
FIELD OF THE INVENTION 
     The invention relates to an external gear hydraulic pump arrangement comprising a pump body including a working chamber housing two rotating pinions that mutually engage, and, on either side of the body, a cover and a support forming an outlet manifold for the high pressure fluid, as well as acoustic insulation to damp the vibrations produced by the pinions. 
     BACKGROUND 
     The arrangements of this type which are known provide, as acoustic insulation, an envelope made of a heavy elastomer that encloses the pump. The arrangements provided for such an acoustic insulation envelope considerably raise the manufacturing cost and increase the size of the pump, although, particularly in the automobile industry, the desire is to reduce the space needed for installing pumps. 
     The purpose of the invention is to overcome these disadvantages. 
     SUMMARY OF THE INVENTION 
     To achieve this purpose, according to the invention the acoustic insulation means comprises elements for acoustically decoupling the pump body from its support. 
     According to a characteristic of the invention, the pump support includes two distinct pieces, one of which is integrally connected to the pump body while the other constitutes a manifold comprising the outlet for the high pressure fluid, and the two pieces are coupled via the interposition of acoustic insulation without physical contact that allows transmission of vibrations. 
     According to another characteristic of the invention, the support body comprises a face separated from the bearing face of the manifold by an acoustic insulation sheet. 
     According to another characteristic of the invention, the sheet is an elastomeric material. 
     According to another characteristic of the invention, the sheet is a multilayered sheet comprising a layer made of metal, and elastomer layers attached to the metal layer, on both sides. 
     According to another characteristic of the invention, the elastomer layers have different thicknesses. 
     According to another characteristic of the invention, the elastomer is a nitrile rubber. 
     According to another characteristic of the invention, the support body comprises connectors projecting from a bearing face, the manifold comprises reception recesses for the connectors and complementary in shape, so that a clearance remains between the facing surfaces of the connectors and the recesses, and the acoustic insulation elements are located on the facing surfaces. 
     According to another characteristic of the invention, the acoustic insulation elements are O-rings. 
     According to another characteristic of the invention, at least one reinforcement ring is provided next to an O-ring, to avoid extrusion when the O-ring is located between media at different pressures. 
     According to another characteristic of the invention, the support body comprises a threaded connector that extends through a recess passing through the manifold, and coupling of the manifold to the support body is effected by a nut and a ring of an acoustically insulating material interposed between the nut and the supporting surface of the manifold. 
     According to another characteristic of the invention, the manifold is coupled on the support body by a plurality of screws that are anchored in the support body and which have heads bearing against the manifold via washers of an acoustically insulating material. 
     According to another characteristic of the invention, the pump body is integrally connected to the support body by bolts that are screwed into the support body. 
     According to another characteristic of the invention, the support body comprises a projecting connector that delimits a space for the passage of high pressure fluid, that opens in an opening of a peripheral surface, and the acoustic insulation elements are respectively located above and below the opening and also constitute sealing elements. The sealing element that is located below the opening, prevents the possibility of high pressure fluid reaching an area under the connector, to ensure a balanced position of a front body in the manifold. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING FIGURES 
       The invention, as well as other purposes, characteristics, details and advantage thereof, will become clearer during the course of the explanatory description below that is made in reference to the schematic drawings, which are given solely as an example illustrating an embodiment of the invention, and in which 
         FIGS. 1 and 2  are two different oblique views of an external gear hydraulic pump arrangement according to the invention, 
         FIG. 3  is a top view of the pump, in the direction of the arrow III of  FIG. 1 , 
         FIG. 4  is a cross section along the line IV-IV of  FIG. 3  in a plane parallel to the axis of the pump, 
         FIG. 5  is a cross section similar to  FIG. 4 , but along line V-V of  FIG. 3 , 
         FIG. 6  is an oblique view of the front support body of the pump, in the direction of the arrow VI of  FIG. 4 , 
         FIG. 7  is an oblique view of the lower face of the front support body in the direction of the arrow VII of  FIG. 4 ; 
         FIG. 8  is an oblique view of the manifold including an acoustic decoupling element, 
         FIG. 9  is an oblique view of the lower face of another embodiment of the pump support, 
         FIG. 10  is a view of the detail circled at X in  FIG. 4 , and 
         FIG. 11  is a view of the detail marked XI in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     According to the figures, the external gear hydraulic pump arrangement according to the invention comprises a pump body  1  in which is housed, in a known manner, two pinions, of which one is marked  2  and is visible in  FIG. 4 , a pump cover  3 , and a pump support  4 , where the latter are attached to end surfaces of the body on both sides of the body. 
     The assembly of the cover  3 , the body  1 , and the support  4  is ensured by four bolts  6  having heads  7  bearing against the cover and ends engaged in the threaded holes  8  in the support, as shown in  FIGS. 4 and 5 . In these figures, one can also see that the pinion  2  is provided with a rotating drive shaft  10  with a drive end  1  that is accessible through an opening  12  in the free lower face  13  of the pump support. A sealing joint  14  is interposed between the shaft  10  of the pinion and the support. 
     According to the invention, the pump support  4  includes two pieces, i.e., a front support piece  16 , on a free face  19  of which the pump body  1  is fixed, and a back support body, called manifold  17 , having a free face constituting the lower face  13  of the pump. 
       FIGS. 6 and 7  are oblique views and, in particular, they illustrate the upper bearing face  19  of the pump body  1  and the lower face  20  on which the manifold  17  is mounted, respectively.  FIG. 6  clearly shows the threaded holes  8  with which the assembly bolts  6  are threadedly engaged, a bore  22  for the passage of the pinion driving shaft  10 , and a space  23 , which is part of the outlet path for the high pressure fluid. The space  23  communicates at a first end with the high pressure outlet of the working chamber (not shown) which accommodates the pinion  3 . The space  23  communicates at a second end with a passage  25  located in a cylindrical connector  26  that projects from the lower face  20  of the front body  16  and is closed at its free end. As one can see in  FIGS. 4 and 5 , this passage  25 , which extends axially into the connector  26 , communicates through a diametric passage  27  with the high pressure outlet orifice  29  of the manifold  17 .  FIG. 7  shows that a threaded cylindrical connector  31  projects from the lower face  20  of the body  16 , next to the connector  26 . This threaded connector  31  is intended to receive a nut  32 , for fixing the base  17  to the body  16  inside the central opening  39  in the free external face of the manifold. This bolt  32  bears against a support surface of the manifold via a ring or a washer  33  made of an acoustically insulating material and interposed between the nut and the supporting surface. 
     The manifold  17  comprises a contact surface  35  for the front body  16 , and around this face, a cylindrical external wall  36 , which projects beyond the bearing face  35  and has a free front face  37 , serves as support face for the placement of a reservoir, not shown, which is known and which delimits, with the internal space of the manifold, the volume that contains the low pressure fluid sucked in by the pump. A central recess  39  for receiving the connector  31  of the front support body  16  as well as a cylindrical recess  40  for receiving the channel connector of the high pressure outlet  26  of the front body are located in the bearing face  35 . The opening of the high pressure outlet  29 , which is produced in the peripheral surface of the manifold, is in communication with the recess  40 . 
     According to another characteristic of the invention, the front pump body  16  is fixed to the manifold  17 , without any direct contact between these two pieces that could allow the transmission of vibrations, produced by the pulses generated by engagement of the pinions, by the front body  16  to the manifold  17 . The manifold is thus completely decoupled from the source of the vibrations. For this purpose, an element that is advantageously in the shape of a sheet  42  and made of an acoustically insulating material is interposed between the lower face  20  of the body  16  and the bearing face  35  of the manifold ( FIG. 8 ). The decoupling requires the presence of clearances, as shown at  41  in  FIG. 11 , between the faces of the recesses  39  and  40  of the manifold and the peripheral surfaces of the connectors  31  and  26 , respectively, that are engaged in the recesses. To the extent that the connector  26  comprises a diametric passage  27  for conveying high pressure fluid to the high pressure outlet  29  of the manifold, O-rings  44 ,  45  are located above and below the diametric passage  27 . Another O-ring  46  is located between the central connector  31  and the recess  39  of the manifold. The O-rings are arranged in appropriate peripheral grooves or channels of the two connectors. The O-rings have the double function of serving as sealing and as acoustic insulation means. The seal  45  below the diametric passage  27  prevents high pressure fluid from reaching the area under the connector  26  and expelling the fluid from the housing upward. The seal thus ensures a perfect equilibration without the need to provide means for fixing the connector of the recess. 
     The decoupling sheet  42  can be a sheet made of elastomer, for example, with a thickness of 1 mm and a Shore hardness of 60-70. The sheet could also have a multilayered structure comprising a central layer, for example, made of steel, or at least one layer made of an elastomer, for example, nitrile, adhered to each surface of the central layer made of steel. The two elastomer layers can have different thicknesses for damping different frequency ranges. With regard to the nitrile, this material is particularly appropriate since it has good properties of acoustic insulation and a high resistance to creep. Naturally, the acoustic decoupling means can be made of any other appropriate material. 
     With regard to the sealing O-rings  44 ,  45  between the connector  26  of the front body  16  and the recess  40  of the manifold, to prevent these seals from deforming under the action of the high pressure fluid due to an extrusion effect, it is possible to place in the grooves  46 , on each side of the seal, but at least on the low pressure side, a bracing ring  47 , as shown in  FIG. 11 . 
     To complete the description, it is noted that seals  48  are placed between the contacting surfaces of the pump body and the front support body  16 . 
       FIG. 9  shows another possibility for fixation of the front body  16  to the manifold  17 . Instead of ensuring the tightening of the manifold against the body with the help of the nut, one can also provide, for example, four screws  49  that are intended to engage appropriately threaded holes in the body  16 , with the interposition of acoustically insulating washers  50  between each screw head and the corresponding supporting surface of the manifold. 
     According to yet another characteristic of the invention, one could use the outlet connector of the high pressure liquid  26  as a centering device in place of one of the two traditional centering pins. 
     It is apparent from the description of the invention, which is given as an example, that the means intended to prevent the transmission of vibrations generated by the pump do not further increase the size of the pump and are inexpensive, while ensuring an effective acoustic decoupling, starting at frequencies of 5 kHz and even lower, while the known enclosure insulation takes up much space and its effectiveness is significantly above 10 kHz. It should be noted that in spite of the interposition of the acoustic insulation elements between the support body  16  and the manifold  17 , the axial alignment and the correct positioning of the pieces are ensured and stable.