Abstract:
An internal gear pump for a slip-controlled hydraulic vehicle braking system includes a pinion, a ring gear, and a filler piece (sickle). The filler piece has an inner part extending in a curved manner in the peripheral direction and an outer part extending in a curved manner in the peripheral direction. The inner part and the outer part are interconnected in a hinged manner on the suction-sided ends. A leg spring is arranged between the inner and outer parts and is configured to separate the inner and outer parts and press against the tops of the teeth of the pinion and the tops of the teeth of the ring gear of the internal gear pump.

Description:
BACKGROUND 
     This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2011/051310, filed on Jan. 31, 2011, the disclosure of which is incorporated herein by reference in its entirety. 
     The disclosure relates to an internal gear pump for a hydraulic vehicle braking system having the features of the disclosure. Such internal gear pumps are used, instead of the piston pumps usually employed, in slip-controlled and/or externally powered vehicle braking systems and are often referred to, if not necessarily accurately, as return pumps. 
     Internal gear pumps are known. They comprise a pinion, that is, an externally toothed gear wheel, which is arranged in an internally toothed ring gear with which it meshes at a point on the circumference, or in a circumferential section. Through rotational driving of the pinion the ring gear is also driven in rotation and the internal gear pump delivers fluid in known fashion; in a hydraulic vehicle braking system it delivers brake fluid. 
     Opposite the circumferential section in which the pinion meshes with the ring gear, the internal gear pump has a crescent-shaped cavity between the pinion and the ring gear in which a filler piece is arranged. 
     The filler piece is normally pivoted about an axis parallel to the axis of the internal gear pump. Because of its curved shape, the filler piece is also referred to as a sickle, and internal gear pumps having such a filler piece are also referred to as sickle pumps. Tooth heads of the pinion bear against a concave inner side of the filler piece and tooth heads of the ring gear against a convex outer side of the filler piece. When the gear pump is driven, the tooth heads of the pinion and of the ring gear slide along the inner and outer sides of the filler piece respectively. The filler piece seals gaps between the pinion teeth and between the ring gear teeth along the circumference, so that fluid volumes are enclosed in the gaps between the teeth of the pinion and of the ring gear and are delivered by the rotational driving of the pinion and the ring gear from a pump inlet to a pump outlet. The pump inlet forms a suction side and the pump outlet a pressure side of the internal gear pump. 
     The patent DE 196 13 833 B4 discloses such an internal gear pump, the filler piece of which is divided in the circumferential direction and comprises an inner part referred to as the segment carrier and are outer part referred to as the segment. Leaf springs arranged between the inner part and the outer part press the inner part and the outer part radially apart and against the tooth heads of the pinion and of the ring gear in order to achieve a good abutment against the tooth heads and therefore a good sealing effect, which is a prerequisite for high efficiency of the internal gear pump. When the internal gear pump builds up a pressure during operation, this pressure acts on a gap or intervening space between the inner part and the outer part in a pressure-side region of the filler piece. In a central region an intermediate pressure acts on the intervening space between the inner part and the outer part, and in a suction-side region the suction pressure of the internal gear pump prevails in the intervening space between the inner part and the outer part. The pressure build-up during operation of the internal gear pump presses the inner part and the outer part of the filler piece of the known internal gear pump apart and against the tooth heads of the pinion and of the ring gear, additionally to the leaf springs, in order to improve the sealing effect. 
     The leaf springs arranged between the inner part and the outer part of the filler piece of the known internal gear pump are disposed transversely to the filler piece, that is, parallel to an axis of the internal gear pump. In order to achieve a significant spring travel, the springs must have a certain length, which determines a minimum width of the internal gear pump. 
     SUMMARY 
     The filler piece of the internal gear pump according to the disclosure has a leg spring the legs of which are disposed in the circumferential direction, although it is not critical that they lie exactly in the circumferential direction. The legs of the leg spring press the filler piece inwards against the tooth heads of the pinion and outwards against the tooth heads of the ring gear. An advantage of the disclosure is that a leg spring is sufficient to apply a force inwards and outwards to the filler piece over a major part of its length. A further advantage of the disclosure is that a width of the leg spring determines the (minimum) width of the internal gear pump, so that the disclosure makes possible a narrow internal gear pump. For a hydraulic vehicle braking system, the pinion and the ring gear have a width of, for example, approximately 2 mm. The disclosure makes possible narrower internal gear pumps the pinion and ring gear of which may have a width of 1 mm or less. A further advantage of the disclosure is simple assembly of the filler piece and installation thereof in the internal gear pump. The internal gear pump according to the disclosure has a high degree of fluid-tightness of the volumes enclosed between the teeth of the pinion and of the ring gear, and high volumetric efficiency. The leg spring of the internal gear pump according to the disclosure is, in particular, a leaf spring bent to form a U-shape, the legs of which are bent preferably in the same direction although not necessarily with the same curvature. However, a leg spring bent from wire or produced from solid material is also possible. The list is not definitive. 
     Advantageous configurations and developments of the disclosure are the subject matter of the dependent claims. 
     In a simple embodiment of the disclosure, the leg spring itself forms the filler piece, its outer leg bearing resiliently outwards against the tooth heads of the ring gear and its inner leg bearing resiliently inwards against the tooth heads of the pinion. 
     A yoke of the leg spring is preferably oriented towards an inlet, that is, a suction side of the internal gear pump. An application of pressure to the inner side of the leg spring from the pressure side of the internal gear pump is thereby achieved or at any rate made possible, pressing the legs of the leg spring, or the filler piece, inwards and outwards against the tooth heads of the pinion and of the ring gear. 
     The subject matter of the disclosure includes a multi-part filler piece comprising an inner part and outer part which are pressed apart and against the tooth heads of the pinion and of the ring gear by the leg spring arranged between them. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is explained in more detail below with reference to exemplary embodiments represented in the drawings. The two figures show two embodiments of internal gear pumps according to the disclosure in front views. 
     
    
    
     DETAILED DESCRIPTION 
     The internal gear pump  1  according to the disclosure represented in  FIG. 1  is provided as a hydropump or so-called return pump in a hydraulic vehicle braking system having slip control. It comprises a pinion  2 , that is, an externally toothed gear, which is arranged non-rotatably on a pump shaft  3 . The pinion  2  is arranged eccentrically in an internally toothed ring gear  4  which is received rotatably in a tubular pump housing  5 , although the pump housing may also have, for example, a polygonal configuration (not shown). Housing covers are omitted from the drawing so that the internal parts of the internal gear pump  1  are visible. The pinion  2  meshes with the ring gear  4  in a circumferential section; by rotational driving of the pinion  2  with the pump shaft  3  the ring gear  4  is also driven in rotation, so that the internal gear pump  1  delivers fluid, brake fluid in the exemplary embodiment represented, in a manner known per se. Opposite the circumferential section in which the pinion  2  meshes with the ring gear  4  the internal gear pump  1  has a crescent-shaped cavity  6  between the pinion  2  and the ring gear  4 . In the region of an end of the cavity  6  a bore opens paraxially into the cavity  6  as the pump inlet  7 , approximately opposite which a further bore opens into the cavity  6  as the pump outlet  8 . The pump inlet  7  may also be understood as the suction side and the pump outlet  8  as the pressure side of the internal gear pump  1 . A filler piece  9 , in the form of a leg spring  10  in  FIG. 1 , is arranged in the cavity  6 . In the embodiment of the disclosure which is represented and described, the leg spring  10  is a leaf spring bent to form a U-shape, the yoke  11  of which is located approximately centrally between the pump inlet  7  and the pump outlet  8 . The legs  12 ,  13  of the leg spring  10  are curved according to respective tip circles  22 ,  23  of the ring gear  4  and the pinion  2  and extend from the yoke  11  in the direction of the pump outlet  8 . The yoke  11  of the leg spring  10  is therefore oriented towards the pump inlet  7 . The legs  12 ,  13  bear resiliently with a pretension against heads of teeth  14  of the ring gear  4  and heads of teeth  15  of the pinion  2 . The legs  12 ,  13  of the leg spring  10  forming the filler piece  9  enclose fluid volumes in gaps between the teeth  14  and of the ring gear  4  and between the teeth  15  of the pinion  2 , so that driving of the pinion  2  and of the ring gear  4  in rotation causes fluid to be delivered from the pump inlet  7  to the pump outlet  8 . 
     For positional fixing, the leg spring  10  forming the filler piece  9  bears in the circumferential direction and in the direction of the pump inlet  7  against an abutment pin  16  which passes paraxially through the housing  5  and is received in blind bores in the housing covers (not shown) or in a housing front wall (not shown). In order to improve the support, the abutment pin  16  has a flattened portion  17  against which the yoke  11  of the leg spring  10  bears. 
     The leg spring  10  is open between the free ends  18  of the legs  12 ,  13 . The free ends  18  and the open end of the leg spring  10  are located in the region of the pump outlet  8 , that is, of the pressure side of the internal gear pump  1 . An intervening space  21  between the legs  12 ,  13  of the leg spring  10  is thereby charged with pressurized brake fluid during operation of the internal gear pump  1 , pressing the legs  12 ,  13  outwards additionally to the spring force of the leg spring  10  and thereby improving the abutment of the legs  12 ,  13  of the leg spring  10  against the heads of the teeth  14  of the ring gear  4  and of the teeth  15  of the pinion  2 . A sealing effect of the abutment of the legs  12 ,  13  against the heads of the teeth  14 ,  15  of the ring gear and of the pinion  2  is thereby improved with increasing delivery pressure of the internal gear pump  1 . This improves the efficiency of the internal gear pump  1 . 
     Like the internal gear pump  1  of  FIG. 1 , the internal gear pump  1  of  FIG. 2  comprises a pinion  2  which is arranged non-rotatably on a pump shaft  3  and eccentrically in a ring gear  4  with which it meshes in a circumferential section. The structure and functioning of the internal gear pump  1  of  FIG. 2  coincide to that extent with the structure and functioning of the internal gear pump  1  represented in  FIG. 1 . To avoid repetition, the explanations relating to  FIG. 1  are referred to in a supplementary manner in the explanation of  FIG. 2 . Like components are denoted by the same reference numerals in  FIGS. 1 and 2 . 
     In deviation from  FIG. 1 , the filler piece  9  in  FIG. 2  is of multi-part configuration, comprising an outer part  19  and an inner part  20  which extend in an arcuate manner in the circumferential direction and between which an intervening space  21  is located, which is also disposed in an arcuate manner in the circumferential direction and in which the leg spring  10  is arranged. Because of its curved overall shape the filler piece  9  may also be referred to as a sickle; its inner part  20  may also be referred to as the segment carrier and its outer part  19  as the segment. An outer side of the outer part  19  is curved in an arc of a circle conforming to the tip circle  22  of the ring gear  4 . An inner side of the inner part  20  has a concave curvature conforming to a tip circle  23  of the pinion  2 . Heads of the teeth  14  of the ring gear  4  bear sealingly against the outer side of the outer part  19  of the filler piece  9  and heads of the teeth  15  of the pinion  2  bear sealingly against the inner side of the inner part  20  of the filler piece  9 . The leg spring  10  arranged between the inner part  20  and the outer part  19  presses the inner part  20  and the outer part  19  apart and thereby presses the outer part  19  outwards in sealing abutment against the heads of the teeth  14  of the ring gear  4  and the inner part  20  inwards in sealing abutment against the heads of the teeth  15  of the pinion  2 . 
     In order to improve the sealing effect as the delivery pressure of the internal gear pump  1  rises, the intervening space  21  between the inner part  20  and the outer part  19  is charged with pressurized brake fluid from the pump outlet  8 . The pressurization presses the inner part  20  and the outer part  19  apart, additionally to the leg spring  10 , and increases the sealing effect at the heads of the teeth  15 ,  14  of the pinion  2  and the ring gear  4  as the delivery pressure of the internal gear pump  1  rises. The volumetric efficiency of the internal gear pump  1  is improved thereby. The pressure is applied through an open end of the intervening space  21  at the pump outlet  8  and/or through a pressure field  24 . The leg spring  10  is slightly narrower than the inner part  20  and the outer part  19  of the filler piece  9 . The pressure of the pump outlet  8  therefore also acts on a sealing element  30  and an adjustment element  31  which are arranged on a pump outlet side of the yoke  11  of the leg spring in the intervening space  21  between the inner part  20  and the outer part  21  of the filler piece  19  and are explained below. The pressure field  24  is a groove-shaped depression in an axial disk  25 . The pressure field  24  extends in the circumferential direction from the pump outlet  8  to a longitudinally central region of the intervening space  21  between the inner part  20  and the outer part  19  of the filler piece  9 . Axial disks  25  which seal against side faces of the ring gear  4  and the pinion  2  are arranged on both sides of the internal gear pump  1 . The axial disks  25  are located between the housing covers (not shown) on one side and the ring gear  4  and the pinion  2  on the other. 
     End faces  26  of the inner part  20  and of the outer part  19  facing towards the pump inlet  7  on the suction side are flat and are disposed approximately radially. They bear against the flattened portion  17  of the abutment pin  16 . The end faces  26  are located approximately at a center of the cavity  6  somewhat closer to the pump inlet  7  than to the pump outlet  8 . 
     In  FIG. 2  also, the yoke  11  of the leg spring  10  is oriented towards the suction side, that is, towards the pump inlet  7 , while the open end of the leg spring  10  and the free ends  18  of the legs  12 ,  13  of the leg spring  10  are oriented towards the pump outlet  8 . 
     At their ends on the suction side the inner part  20  and the outer part  19  are articulated to one another; for this purpose the inner part  20  has an outward projection  27  which engages in a recess  28  on the inner side of the outer part  19 . The inner part  20  is secured with a pin  29  which passes transversely through it close to its end on the suction side and is retained in the housing covers (not shown). The inner part  20  pivots about the pin  29 . 
     In the region of its end on the suction side the filler piece  9  is sealed with a sealing element  30  and an adjustment element  31 . In the embodiment of the disclosure represented, the sealing element  30  has a rectangular cross section and fits into the recess  28  of the outer part  19  in which the projection  27  of the inner part  20  also engages. The sealing element  30  extends transversely, that is paraxially, through the cavity  6  of the internal gear pump  1  and bears with its end faces sealingly against the axial disks  25 , which bear sealingly against the side faces of the pinion  2  and of the ring gear  4  and close the cavity  6  laterally. On the outside the sealing element  30  bears against an inner side of the outer part  19 , and on the inside against the projection  27  of the inner part  20 , in the direction of the suction side of the internal gear pump  1 . The sealing element  30  consists of a sealing material with very high resistance to extrusion. Resistance to extrusion means the resistance of the sealing element  30  to plastic deformation when subjected to high pressure, in particular, resistance to creeping of the sealing element  30  into a gap. The internal gear pump  1  can generate a pressure of up to  300  bar, which acts on the sealing element  30 ; the sealing element  30  must withstand this pressure. An elastomer does not withstand such a pressure; the sealing element  30  therefore consists, for example, of PTFE (polytetrafluoroethylene), the elasticity of which is, however, limited. For this reason the adjustment element  31 , the elasticity of which is greater than that of the sealing element  30 , is additionally provided. The adjustment element  31  consists, for example, of an elastomer such as EPDM (ethylene-propylene-diene rubber). The adjustment element  31  is cylindrical and is arranged radially inside the sealing element  30  in a channel (inside corner) on the outer side of the inner part  20  at the transition to the projection  27 . In this region there is no gap into which the adjustment element  31  could creep. The adjustment element  31  presses the sealing element  30  elastically outwards against the outer part  19 . The end faces of the adjustment element  31  bear sealingly against the axial disks  25  and its circumference bears against the outer side of the inner part  20  and against the projection  27 . The sealing element  30  and the adjustment element  31  jointly seal the filler piece  9  at its end on the suction side laterally with respect to the axial disks  25 , and seal the inner part  20  and the outer part  19  of the filler piece  9  with respect to one another.