Abstract:
A metering pump, especially for feeding fuel to a vehicle heater, comprising a delivery plunger ( 50 ), which can be moved to and fro for delivering liquid medium, a guide sleeve ( 42 ), which partially accommodates the delivery plunger ( 50 ) and guides same for the reciprocating movement, wherein the guide sleeve ( 42 ) with an inner surface ( 46 ) thereof defines a pump ejection chamber ( 48 ) and it defines with an outer surface ( 60 ) thereof a channel arrangement ( 74 ) leading to the pump ejection chamber ( 48 ), wherein the guide sleeve ( 42 ) is carried in a carrier element ( 24 ) and is in contact with the carrier element ( 24 ) by its outer surface ( 60 ) essentially over the entire circumference in a first length area ( 58 ) and is located with its outer surface at a spaced location from the carrier element ( 24 ) in a second length area ( 64 ), wherein the channel arrangement ( 74 ) is provided between the carrier element ( 24 ) and the guide sleeve ( 42 ) in its second length area ( 64 ), is characterized in that in its second length area ( 64 ), the guide sleeve ( 42 ) has at least one support area ( 78, 80, 82, 84 ), with which it is supported in relation to the carrier element ( 24 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of priority under 35 U.S.C. § 119 of German Application DE 10 2004 002 245.3 filed Jan. 15, 2004, the entire contents of which are incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention pertains to a metering pump, with which, for example, liquid fuel can be delivered to a heater in a vehicle. 
   BACKGROUND OF THE INVENTION 
   Such metering pumps comprise, in general, a delivery plunger, which can be moved to and fro for delivering the liquid fuel and is accommodated and guided for this purpose, for example, in a guide sleeve. Due to its reciprocating movement, the plunger dips more or less deeply into the guide sleeve depending on its movement cycle. The liquid fuel is ejected in this manner from a pump ejection chamber, which is also defined by an inner surface of the guide sleeve, namely, when the delivery plunger is being moved in the direction in which the pump ejection chamber volume is minimized, or fuel can be taken up in the chamber, namely, when the delivery plunger is being moved in the direction in which the pump ejection chamber volume is maximized. 
   This guide sleeve is carried, in general, firmly in a carrier element, which may be part of a housing of the metering pump or in such a housing. To make it possible to guide the liquid fuel in the direction of the pump ejection chamber, a circumferential distance is present between an outer surface of the guide sleeve and the carrier element, which carries the guide sleeve per se, so that an annular flow space is formed. This leads in the direction of the pump ejection chamber. In another length area, the guide sleeve is in contact with the carrier element essentially over the entire circumferential area, so that stable mounting of the guide sleeve is ensured by press fit, on the hand, and, on the other hand, the annular channel area is axially defined and it is ensured that no liquid fuel can escape in the transition between the carrier element and the guide sleeve. To achieve the stable mounting of the guide sleeve, the latter must be made, in general, of a metallic material, so that this mounting is brought about in a comparatively short length area by the contact between the guide sleeve and the carrier element, while the annular intermediate space, in which there is no contact between the guide sleeve and the carrier element, is then formed in a longer section. This is also due to the fact that such guide sleeves are brought, in general, to the desired dimensions by a turning operation, so that, in principle, a rotationally symmetrical outer surface is obtained, as a consequence of which the load-bearing contact with the carrier element is present only in a predetermined length area. 
   SUMMARY OF THE INVENTION 
   The primary object of the present invention is to provide a metering pump which has improved operating characteristics along with a simplified and less expensive design. 
   This object is accomplished according to the present invention by a metering pump, especially for feeding fuel to a vehicle heater, comprising a delivery plunger, which can be moved to and fro to deliver liquid medium; a guide sleeve, which partially accommodates the delivery plunger and guides same for the reciprocating movement, wherein the guide sleeve with an inner surface thereof defines a pump ejection chamber and it defines with an outer surface thereof a channel arrangement leading to the pump ejection chamber, wherein the guide sleeve is carried in a carrier element and is in contact by its outer surface with the carrier element in a first length area essentially over the entire circumference and is located at a spaced location with its outer surface from the carrier element in a second length area, wherein the channel arrangement is provided between the carrier element and the guide sleeve in its second length area, wherein the guide sleeve has at least one support area in its second length area, with which said support area the guide sleeve is supported in relation to the carrier element. 
   Various advantageous aspects are obtained with the metering pump according to the present invention. Thus, the embodiment of the guide sleeve with at least one support section in the length area in which the guide sleeve also defines the channel arrangement makes it possible to achieve better distribution of the supporting or carrying action in relation to the carrier element over the length of the guide sleeve. This means that the length area in which there is essentially a full-area circumferential contact in relation to the carrier element is relieved of its support function, which is also significant for the correct functionality of the metering pump, because better distribution can be obtained over the entire length area of the guide sleeve. This in turn makes it possible not to manufacture the guide sleeve of metal, but, e.g., of a plastic. In case of the configuration known from the state of the art, the use of a guide sleeve made of plastic implies, in principle, the problem that if the carrying function is limited to a comparatively short length area, namely, the length area in which no annular channel is formed, there is a risk of tilting of the guide sleeve because of the markedly higher elasticity and flexibility of the plastic material compared with metallic material. However, this risk of tilting can also be prevented from occurring even when a plastic material is used due to the fact that additional supporting is provided in the metering pump according to the present invention in the length area that is also used to feed the fuel. On the other hand, the use of plastic material makes it possible to design the guide sleeve as is specified in the metering pump according to the present invention, i.e., with support sections in certain length areas, i.e., with a shape that is, in principle, not rotationally symmetrical, e.g., by manufacturing according to an injection molding method. Due to the possibility of using materials other than metal due to the preset shape, the material can in turn be selected such that the operating characteristics are improved, namely concerning the frictional characteristics between the delivery plunger movable to and fro and the guide sleeve. Especially low-friction plastics can be used here, so that the service life of a metering pump designed according to the present invention can be markedly increased. 
   Provisions may be made, for example, in the metering pump according to the present invention for the guide sleeve to have an outer surface that is set back in relation to the first length area in its second length area in at least one circumferential area. It is possible now, for example, to provide a support section projecting over the set-back outer surface in the area of the set-back outer surface. 
   To obtain a support function in the second length area as well, which approximately corresponds to the support in the first length area, it is proposed, furthermore, that the support section project over the set-back outer surface up to the level of the outer surface in the first length area. 
   To provide a transition between the channel arrangement and the pump ejection chamber, it is proposed that at least one passage opening leading to the pump ejection chamber be provided in the area in which the first length area adjoins the second length area. 
   To obtain the largest possible flow cross section in the area of the channel arrangement despite the possibility of also providing a support for the guide sleeve in relation to the carrier element in the second length area, it is proposed, furthermore, that a set-back outer surface be provided at two circumferential areas, which are located essentially opposite each other, in the second length area. 
   Furthermore, the metering pump according to the present invention may be designed such that the guide sleeve defines the pump ejection chamber essentially in its first length area and it defines the channel arrangement essentially in its second length area. 
   According to another aspect of the present invention, the guide sleeve in the metering pump may be designed such that in its second length area, the guide sleeve has an outer contour that corresponds to the outer contour of the guide sleeve in the first length area and is interrupted at at least one circumferential area by a depression, which is open toward the outside and forms the channel arrangement at least partially. 
   As was already mentioned above, it is a special aspect of the present invention that, especially also due to the design embodiment, the guide sleeve can be made of a plastic material, with the advantage that it is possible not only to use a material that is less expensive and can also be processed more easily and can be handled in an easier manufacturing process, but also to markedly improve the sliding properties during the guiding of the delivery plunger. 
   The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described below with reference to the drawings attached. In the drawings: 
       FIG. 1  is a longitudinal sectional view of a metering pump, cut along line I-I in  FIG. 2 ; 
       FIG. 2  is a cross-sectional view of the metering pump shown in  FIG. 1 , cut along line II-II in  FIG. 1 ; 
       FIG. 3  is an enlarged detail of III in  FIG. 2 ; and 
       FIG. 4  is a perspective view of a guide sleeve used in the metering pump according to  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings in particular, a metering pump designed according to the present invention is generally designated by  10  in  FIG. 1 . This metering pump  10  can be used to deliver liquid fuel from a tank provided in a motor vehicle in the direction of a heater, e.g., a parking heater or an auxiliary heater. 
   The metering pump  10  comprises a housing arrangement  12 , which is composed of a plurality of components. Thus, a housing end part  14  is provided, on which an inlet pipe connection  16 , which is to be connected with a flexible tube connection, is provided. Furthermore, a filter  18  is provided in the housing end part  14 . A housing outer wall  20  is rigidly connected with the housing end part  14  in the outer circumferential area, and the housing outer wall  20  is connected with another housing end part  22  at its other axial end area, axially being related to a longitudinal axis of the entire metering pump  10 . An elongated, sleeve-like carrier element  24  is carried at this additional housing end part  22  in the radially inner area, radially being again related to the longitudinal axis A. This sleeve-like carrier element  24  carries, in turn, a nonreturn discharge valve  26 , which comprises a part  28  providing essentially a valve seat and an outlet pipe connection  30  that can be connected with a flexible tube. A spring-pretensioned valve ball  32 , which prevents the liquid fuel being delivered into the outlet pipe connection  30  from flowing back, is seated on the valve. 
   An electromagnet coil designated generally by  34  is carried on the housing end part  14  and the carrier element  24 . The housing end part  14 , a coil carrier  36  of the electromagnet coil  34  and the carrier element  24  define a pump inlet chamber  38 , to which an inlet opening  40  provided in the housing end part  14  leads. 
   The carrier element  24 , which has, as can be recognized from  FIG. 2 , generally an annular cross section, carries with its inner surface a guide sleeve  42 . This guide sleeve  42 , which likewise has a generally annular cross section and will be described in detail below with reference to  FIGS. 3 and 4 , has an interior space  44 , which has, for example, a circular cross section. This interior space  44 , which is defined by an inner surface  46 , defines a pump ejection chamber  48  in cooperation with the part  28  of the valve arrangement  26  and is used, furthermore, to guide a delivery plunger  50  for moving to and fro in the direction of the longitudinal axis A. In its area not engaging the guide sleeve  42 , the delivery plunger  50  carries an armature  52 . Furthermore, the delivery plunger  50  is pretensioned by a pretensioning spring  54  such that it tends to move as far out of the interior space  44  of the guide sleeve  42  and to close the inlet opening  40  in the process with a sealing element  56 , which is carried, for example, at the armature. 
   The guide sleeve  42 , which is preferably made of a plastic material according to the principles of the present invention, is of an elongated shape and has essentially two length areas. The guide sleeve  42  is shaped in a first length area  58  such that the circumferential contour of an outer surface  60  of the guide sleeve corresponds to the circumferential contour of an inner surface  62  of the carrier element  24 . This inner surface  62  is provided, for example, with an essentially circular contour in the example being shown, so that the guide sleeve  42  is likewise made with a circular outer surface in the first length area  58 . Provisions may be made in this connection for the outside dimension of the guide sleeve  42  to have a certain oversize compared with the inner dimension of the carrier element  24  at least in this length area  58 , so that a press fit is provided, in particular, in this first length area  58  with the guide sleeve  42  inserted into the carrier element  24  and stable mounting of the guide sleeve  42  is thus ensured. 
   In a second length area  64 , the shape of the outer surface of the guide sleeve  42  differs from the shape of the inner surface  62  of the carrier element  24 . It is recognized especially in  FIG. 2  that the guide sleeve  42  is flattened at two circumferential areas located opposite each other, so that essentially flat, i.e., noncurved outer surface areas  70 ,  72  are formed. These outer surface areas  70 ,  72  are located at spaced locations from the inner surface  62  of the carrier element  24 , so that a channel arrangement  74  is created between the carrier element  24  and the guide sleeve  42  in this second length area  64 . This channel arrangement  74  joins the inlet chamber  38  and leads to passage openings  76 , which are provided in the outer surface areas  70 ,  72  in the adjoining area to the first length area  58  of the guide sleeve  42  and lead into the interior space  44 . The position of these openings  76  relative to the longitudinal extension of the guide sleeve  42  is selected to be such that when the delivery plunger  50  is maximally moved out of the guide sleeve  42 , the end of the delivery plunger still engaging the guide sleeve  42  does not cover the openings  76  any longer or it does so only incompletely. With the delivery plunger  50  dipping maximally into the guide sleeve  42 , i.e., in case of the minimum volume of the pump ejection chamber  58 , the delivery plunger  50  covers the openings  76 , so that a connection between the pump ejection chamber  48  and the channel arrangement  74  and consequently the pump inlet chamber  38  is now interrupted. 
   It is, furthermore, recognized from  FIGS. 3 and 4  that a support section  78 ,  80  is provided in each of the flattened surface areas  70 ,  72 . The support sections  78 ,  80  extend in the example being shown from the end area of the guide sleeve  42  located close to the inlet chamber  38  into the area in which a particular passage opening  76  is formed. The amount of projection of the support sections  78 ,  80  over the respective flattened surface area  70 ,  72  is selected to be such that these support sections  78 ,  80  extend radially approximately up to the level of the outer surface  60  in the first length area  58 , doing so in the circumferential area in which a corresponding support section  78 ,  80  will then also adjoin. 
   Thus, not only is a stable hold of the guide sleeve, which is secured against evading movements, achieved in the first length area  58  when the guide sleeve  42  is inserted into the carrier element  24 , but it is also ensured, despite the fact that the channel arrangement  74  is provided, that stable supporting is provided for the guide sleeve  42  in the second length area  64  as well in practically any direction, so that the guide sleeve  42  can nevertheless provide a stable guiding function for the delivery plunger  50  despite the fact that it can be made of a plastic material, which is considerably more flexible than a metallic material. 
   The function of the metering pump  10  according to the present invention will be described below. 
   If the delivery plunger  50  is in the position shown in  FIG. 1 , in which the volume of the pump ejection chamber  48  has its maximum, and the electromagnet arrangement  34  is then excited, the armature  52  moves together with the delivery plunger  50  in the direction in which the volume of the pump ejection chamber decreases. The delivery plunger  50  completely covers the openings  76  in the guide sleeve  42  already after a short delivery stroke, so that no fuel contained in the pump ejection chamber  48  at that point in time can be displaced back in the direction of the inlet chamber  38  via the openings  76 . During a subsequent further minimization of the volume of the pump ejection chamber  48 , the fuel contained therein is displaced through an outlet opening  84  of the part  28 , so that the valve ball  32  will also lift off from its valve seat and the fuel being delivered can be released via the outlet pipe connection  30  while overcoming the valve arrangement  26 . Liquid fuel is also drawn at the same time into the inlet chamber  38  during this delivery cycle due to the increase in the volume of the inlet chamber  38  due to the fact that the delivery plunger  50  dips more deeply into the guide sleeve  42 . 
   If the excitation of the electromagnet arrangement  34  is terminated after the minimum volume of the pump ejection chamber  48  had been reached, the delivery plunger  50  returns under the pretension in the direction of increasing pump ejection chamber volume and a vacuum is generated during this phase in this pump ejection chamber  48  as long as the openings  76  are still being covered by the delivery plunger  50 . At the same time, overpressure is generated in the inlet chamber  38  by the delivery plunger  50  moving out of the guide sleeve  42 . A certain percentage of the liquid fuel can now escape through the inlet opening  40 . However, as the escape via the inlet opening  40  is becoming increasingly difficult and the connection between the pump ejection chamber  48  and the inlet chamber  38  is released, the fuel is then displaced via the channel arrangement  74  into the pump ejection chamber  48 , so that another quantity of fuel is then delivered in the direction of the outlet pipe connection  30  during a subsequent reduction of the volume of the pump ejection chamber  48 . 
   Due to the use of a guide sleeve made of a plastic material, which can be optimized in terms of its sliding properties, on the one hand, and concerning the resistance to the medium to be delivered, on the other hand, the wear due to the frictional contact between the delivery plunger  50  and the guide sleeve  42  can be markedly reduced. Due to the fact that the guide sleeve  42  is also supported in the length area in which it defines the channel arrangement  74  together with the carrier element  24 , it is ensured at the same time that very stable mounting is nevertheless achieved if plastic material is used for this guide sleeve  42 . 
   It shall be pointed out that the shape of the guide sleeve  42  may, of course, be different in its second length area  64 . For example, splitting at an angle ratio other than 180° is possible. It is, of course, also possible to provide the channel arrangement  74  by groove-like depressions of a different shape, which are open radially outwardly and extend along the guide sleeve  42  to one or more of the openings  76 . The variant that can be recognized in  FIGS. 3 and 4  can ultimately also be interpreted such that an interruption of the outer surface  60  that otherwise corresponds to the shape in the first length area  58  is generated in certain circumferential areas in the second length area  64 , so that support of the guide sleeve  42  is achieved not only via the two support sections  78 ,  80 , but the guide sleeve is also supported in relation to the carrier element  24  in the circumferential areas  82 ,  84  located between the two surface areas  70 ,  72 , which are flattened and thus provide the groove-like depressions. In case of corresponding stability of the guide sleeve  42 , it would optionally be possible to ensure support only via such circumferential areas  82 ,  84 , which also act as support areas, and to do away with the support sections  78 ,  80 . 
   While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.