Abstract:
A device for delivery of flowable media, especially of lubricants, includes a pump ( 1 ) driven by a motor and forming a component of a line system. At least one heating element ( 21 ) activated by energy supply is located outside of the housing ( 3 ) of the pump ( 1 ) in a position enabling heat transfer to the housing ( 3 ).

Description:
FIELD OF THE INVENTION 
   The present invention relates to a means or device for delivery of flowable media, especially of lubricants, with a pump which can be driven by a motor and which forms a component of a line system. 
   BACKGROUND OF THE INVENTION 
   In known means of this type, under certain unfavorable operating conditions the danger exists that malfunctions, for example, a drop of delivery output, pump overload, or even its failure will occur. These difficulties can occur especially when overly low oil temperatures occur as lubricating oils are being delivered in a lubricant circuit. These operating states prevail, for example, during cold running phases of certain systems, or occur in wind power plants under winter conditions that can last over longer time intervals. The corresponding strong increase in the viscosity of the lubricating oils to be delivered leads at least to a reduction of the delivery output, resulting in danger to the assigned machinery system, or in less favorable cases leads to overloading or even failure of the pump. This situation in turn entails corresponding subsequent damage to the pertinent system. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a means or device for delivering flowable media, especially lubricants, with operating reliability ensured even when very low temperatures of the line system and the medium to be delivered prevail. 
   This object is basically achieved by a means or device where heat transfer to the pump housing from the outside is provided. If necessary, a direct temperature increase can take place in the critical, i.e., fault-susceptible area of the line system, specifically directly on the pump. The heating of the pump housing also leads to a corresponding temperature increase of the delivered medium. This heating of the delivered medium causes a corresponding temperature increase of the entire pertinent line system, including an increase of a possible overly low oil temperature in a lubricant circuit. 
   In especially advantageous exemplary embodiments, at least one heating element is in the form of a self-regulating electrical resistance element with a positive temperature coefficient, for example, in the form of a PTC heating element. Commercially available PTC heating elements include doped polycrystalline ceramic with barium titanate as the base material. These PTC elements ensure rapid heat-up, have good self-regulation behavior, and thus, have a long service life, since there is no danger of overheating due to the self-regulating properties. The use of such PTC elements is also especially advantageous because these elements can automatically maintain a desired temperature level, without control means or temperature sensors being necessary. 
   Preferably, the housing of the pump has more than one flat outside wall section, to each of which one PTC element is assigned. 
   Preferably, the PTC heating elements are assigned to those outside wall sections of the housing that are spatially adjacent to the inside displacement elements of the pump. This piston arrangement leads to especially effective and prompt heat-up in the desired region which is critical against insufficient temperatures. 
   In exemplary embodiments in which on the pump housing fluid input and output define the start and end of the inner pump flow path and in which displacement elements are placed at the same height or coaxial with the input and output on end walls of the pump housing, preferably with the PTC heating element on the side walls joining the end walls and placed at the height of the fluid input and output. This placement yields especially specific heat-up in the area of the inner flow path of the pump. 
   In advantageous exemplary embodiments, the carrier for the PTC heating elements is an aluminum sheet adjoining the pertinent outside wall sections for heat transfer. The outer side of that sheet adjoins the PTC heating elements made in a flat construction. This support of the PTC heating elements ensures especially good heat transfer to the pump housing. 
   In this connection, the carrier can be made U-shaped with U-legs extending parallel to one another to form one collar of the two opposing outside side wall sections of the pump housing. On the outside of each U-leg, one PTC heating element is provided. 
   The PTC heating elements for their part can be held in contact with the U-legs by an enclosure attached to the outside of the U-legs and made from highly heat-conductive metallic material. 
   The efficiency of the means or device is especially good when the pump housing is surrounded with heat-insulating jacketing, leaving its pump shaft and fluid input and output exposed. Heat losses to the vicinity are then for the most part prevented. This jacketing, with the housing being, for example, cast round, prevents not only heat exit to the outside, but also forms protective jacketing preventing direct access to the PTC heating elements. 
   Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
       FIG. 1  is a perspective view of a pump according to one exemplary embodiment of the present invention; 
       FIG. 2  is a front elevational view, looking at the end wall of the pump housing, with its components surrounding the side walls being shown cutaway or in section; 
       FIG. 3  is a perspective view of part of a carrier forming the collar of the side walls of the pump housing with PTC heating elements located on its outside and their electrical connecting means; 
       FIG. 4  is a side elevational view of the carrier part of  FIG. 3 ; 
       FIG. 5  is a front elevational view of the carrier part of  FIG. 3 ; 
       FIG. 6  is a bottom plan view drawn roughly in actual size of a metallic enclosure with a PTC heating element of flat construction held in it; and 
       FIG. 7  is a side elevational view in section of the metallic enclosure taken along line VII-VII of  FIG. 6 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2  show a pump  1 , with a pump housing  3  which has a fluid input or inlet  9  provided with a connecting flange  7  on the front end wall. Diametrically opposite fluid input  9  on the rear wall (not shown) in the figures a corresponding fluid output or outlet  10  is placed at the same height (coaxially aligned) with the fluid input (inlet)  9 . Within the flow path of the pump  1  between the fluid input  9  and fluid output (outlet), a gear pair forms the displacement elements, i.e., the pump  1  is an outside gear pump with a drive shaft  11  located on the top of the housing. As is best shown in  FIG. 1 , the pump housing  3  is surrounded with heat-insulating jacket  13 , leaving exposed the areas of the fluid input  9 , of the housing top with the drive shaft  11 , and of the area of the fluid output (not shown). Jacket  13  can be a cast or foamed jacket. 
     FIG. 2  shows the part of the jacket  13  including the side walls  15  of the pump housing  3  extending between the end or front wall  5  and the rear wall. In a vertically cut representation between the side walls  15  and the jacket  13  a U-shaped carrier  17  is provided. 
     FIGS. 3 to 5  show the carrier  17  in greater detail. The carrier  17  is shaped from aluminum sheet, and has two U-legs  19  intended to make contact with the side walls  15  of the pump housing  3  and defining or extending in planes parallel to one another. A PTC element unit  21  shown schematically in  FIGS. 3 to 5  is attached to the outside of each U-leg  19 . U-legs  19  of carrier  17  are connected by a crosspiece  23  enclosing the bottom of the pump housing  3 . An electrical connecting means or connector  25  is provided on crosspiece  23  for supplying electrical power to PTC heating elements of PTC element units  21 . 
     FIGS. 6 and 7  show details of the PTC element units  21 . Each of the element units  21  is provided with its own PTC element  29  in the form of a flat cuboid. The PTC element  29  is located in an enclosure  31  made in the form of a round disk of metal with good heat conductivity and provided with profiling. The enclosure  31  has central profile  33  forming a receiving channel  37  in which the PTC element  29  is fixed by a heat-resistant adhesive film strip  39 , in the exemplary embodiment a Kapton® strip. The bottom  35  of the enclosure  31  is intended for contact with the pertinent U-leg  19 . On either side of the receiving channel  37 , profiles  41  of low height with a round mounting hole  43  and an oblong hole  45  are provided for forming a screw connection between the enclosure  31  and the pertinent U leg  19 . Carrier  17  mounts PTC heating elements  29  at the height of the fluid input  9  and the fluid out output. 
   Connecting wires  27  intended for power supply of the PTC element  29  are connected in the manner conventional for PTC elements  29  to the flat metal electrodes provided thereon. In the end area bordering the PTC element  29 , the connecting wires  27  are surrounded by a silicone insulating tube  47 . Moreover the transition area between the end of the connecting wires  27  provided with the insulating tube  47  can be sealed with rubber in the area bordering the PTC element  29 . 
   The enclosure  31  attached to the pertinent U-leg  19  of the carrier  17  forms a heat conducting plate for transfer of the heat generated by the PTC element  29  to the aluminum sheet of the pertinent U-leg  19  adjoining the pertinent side wall  15  of the pump housing  3  as a heat transfer agent. This thermal coupling makes it possible using the self-regulating characteristic of the PTC heating element  29  to maintain the desired temperature during changing operating states on the pump housing  3 , without the need for control electronics for this purpose. 
   The present invention is described above using the example of an outside gear pump, but can be used likewise in pumps of a different design, for example, for inside gear pumps, screw pumps, vane cell pumps, radial piston pumps or in pumps with a different operating principle. In any case, it is advantageous to attach the pertinent PTC heating elements to the respective pump housing in a position such that there is good thermal coupling to the pertinent inner displacement elements. While the present invention is explained using one example in which two element units  21  with one contained PTC element  29  each are used, there could be a different number of PTC elements  29 , and other designs different from the flat execution can be used, for example, PTC elements with a round or rectangular cartridge shape. 
   While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.