Abstract:
The invention relates to a reciprocating pump comprising a drive shaft ( 2 ) that is mounted in a housing ( 1 ) and that has a freely definable and in exceptional cases sinusoidal control curve ( 5 ). A transmission element ( 6 ) that is connected to a piston ( 4 ) penetrates the control curve ( 5 ). The transmission element ( 6 ) is guided in an elongated guide section ( 7 ) of the housing ( 1 ). The displacement directions of the piston ( 4 ) run parallel to the rotational axis of the drive shaft ( 2 ). The reciprocating pump is extremely compact and is particularly suitable for use as a fuel pump in a motor vehicle.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a reciprocating pump with at least one piston arranged axially displaceably in a casing, with a rotatably mounted drive shaft for driving the piston, with an inlet channel and with an outlet channel. The invention relates, furthermore, to an advantageous use of the reciprocating pump.  
         [0002]     The reciprocating pumps known from practice mostly have as drive shaft a crankshaft connected to the piston via a connecting rod. The inlet channel and the outlet channel each have valves. The valves may be positively controlled via a camshaft or have a spring element and be controlled via the pressure generated in the casing by the piston. A very high feed volume at a high feed pressure can be generated by means of an intended diameter and stroke travel of the piston and rotational speed of the drive shaft. The known reciprocating pump has the disadvantage that it has a very large construction space and a highly complicated construction.  
         [0003]     To simplify the construction of the reciprocating pump, it is known, for example from DE 0 855 488, to drive the piston via a compensating drive. The pressure feed is achieved by means of the actual movement of the piston. A regulating control pressure piston executes a combined rotational and reciprocating movement and has a control groove on its outer surface area. This reciprocating pump has the disadvantage that it is of likewise highly complicated construction and is suitable only for low feed quantities.  
         [0004]     The problem on which the invention is based is to design a reciprocating pump of the type initially mentioned in such a way that it is constructed in a particularly simple and compact way and makes it possible to have high feed capacity at a high feed pressure. Furthermore, advantageous use of the reciprocating pump is to be provided.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0005]     The first mentioned problem is achieved, according to the invention, in that the drive shaft has a control curve with at least one upper reversal point and one lower reversal point, in that the piston is guided in the control curve, and in that a transmission element extends from the piston through an elongated guide in the casing into the control curve.  
         [0006]     As a result of this configuration, the direction of movement of the piston can be arranged parallel to the drive shaft, thus allowing a particularly compact construction of the reciprocating pump. In the simplest instance, the control curve is configured sinusoidally over the circumference of the shaft and has in each case an upper and a lower reversal point. In the event of a rotation of the drive shaft over 180°, the piston is consequently moved in one direction, and, in the event of rotation over the next 180°, the piston is moved in the opposite direction. By virtue of this configuration of the control curve, the piston is driven in the same way as the piston connected to the crankshaft via the connecting rod. The feed pump according to the invention therefore has a high feed volume at a high feed pressure. A connecting rod mounted on the piston and mounted on the drive shaft is avoided by virtue of the invention. The reciprocating pump according to the invention therefore requires particularly few components to be mounted and consequently has a very simple construction. Preferably, the direction of movement of the piston is arranged parallel to the axis of rotation of the drive shaft. The piston of the reciprocating pump according to the invention may be sealed off with respect to the casing, for example, via sealing rings or via a diaphragm.  
         [0007]     According to an advantageous development of the invention, a rotation of the transmission element can be prevented in a simple way if the transmission element is led through an elongated guide in the casing.  
         [0008]     The reciprocating pump according to the invention requires only a single control curve for a plurality of pistons if a plurality of pistons are arranged concentrically with respect to the drive shaft.  
         [0009]     The inlet channel could be arranged, for example, in the casing and have a control valve or be controlled by the movement of the piston. However, according to an advantageous development of the invention, the reciprocating pump according to the invention has a particularly compact configuration when the inlet channel passes through the piston and has a nonreturn valve. The outlet channel preferably has a nonreturn valve in the casing in the same way as known reciprocating pumps.  
         [0010]     The reciprocating pump according to the invention has a particularly low axial construction height if the nonreturn valve of the inlet channel and/or a nonreturn valve of the outlet channel are/is designed as a diaphragm valve.  
         [0011]     A contribution is made to a reduction in the radial dimensions of the reciprocating pump according to the invention when the nonreturn valve of the inlet channel and/or the nonreturn valve of the outlet channel have/has a valve body guided longitudinally displaceably and located opposite a valve seat. To assist the movements, the valve body may be prestressed relative to the valve seat by a spring element. In an instance which is particularly simple in structural terms, the valve bodies can be controlled, even without spring force, by the pressure in the casing.  
         [0012]     According to another advantageous development of the invention, the manufacture of the piston requires a particularly low outlay if a recess provided in the piston for receiving the transmission element has a peripheral groove. The peripheral groove may in this case, for example, be of rectangular or trapezoidal design or have a segment of a circle.  
         [0013]     The piston could, for example, be manufactured in one piece with a transmission element. However, according to another advantageous development of the invention, the piston can be manufactured particularly simply, without radially projecting components, when the piston has a pocket, shaped correspondingly to the transmission element, for receiving a part region of the transmission element. By virtue of this configuration, the piston is secured against rotation, and the connection between transmission element and piston can be mounted, for example, hydrostatically. A further advantage of this configuration is that, by means of the pocket, a surface support of the transmission element can be achieved, in contrast to the recess being designed as a peripheral groove. The reciprocating pump according to the invention consequently has particularly low wear. The pocket may be designed, for example, as a cylindrical bore or a conical bore or have a form of a spherical cap corresponding to the transmission element. Furthermore, the transmission element can be pressed into the pocket, and consequently a relative movement of the piston with respect to the transmission element can be avoided. This leads to a further reduction in the wear of the reciprocating pump according to the invention.  
         [0014]     The reciprocating pump according to the invention can be composed of particularly cost-effective components if the transmission element is designed as a ball. Preferably, in this case, the control curve of a cross section is designed as a partial circle.  
         [0015]     According to another advantageous development of the invention, a rotation of the transmission element can be reliably avoided if the transmission element is designed as a rotationally symmetrical sliding block. The control curve preferably has in this case a rectangular or trapezoidal cross section.  
         [0016]     The reciprocating pump according to the invention has a particularly simple structural configuration when the guide in the casing is arranged on a straight line connecting the axes of symmetry of the piston and of the drive shaft.  
         [0017]     According to another advantageous development of the invention, the transmission element can be provided with particularly large dimensions, without this contributing to increasing the radial dimensions of the reciprocating pump according to the invention, if the guide in the casing is arranged outside the straight line connecting the axes of symmetry of the piston and of the drive shaft.  
         [0018]     According to another advantageous development of the invention, a play of the transmission element in the guide of the casing or in the control curve can be compensated in a simple way if lateral bearing faces of the guide of the transmission element in the casing and/or of the control curve are prestressed relative to one another. As a result, the transmission element is guided particularly accurately, and therefore wear is kept particularly low.  
         [0019]     According to another advantageous development of the invention, the control curve can have a particularly long configuration if the drive shaft has, in the region of the piston, a rim surrounding the piston at least partially radially on the outside and the control curve is arranged on the rim radially on the inside. The drive shaft consequently surrounds the piston.  
         [0020]     The control curve, of particularly long configuration, is subject to particularly low wear.  
         [0021]     The contribution to a further reduction in the wear of the control curve is made when the piston is arranged between two control curves one radially surrounding the other concentrically.  
         [0022]     According to another advantageous development of the invention, the drive shaft can be operated at a particularly low rotational speed if the control curve has a plurality of upper and lower reversal points over the circumference of the drive shaft.  
         [0023]     The intake and ejection of the medium to be fed require, as a rule, a different energy consumption. According to another advantageous development of the invention, different torques on the drive shaft can be avoided in a simple way if the control curve has during an intake stroke at least one curve function other than during an ejection stroke. This contributes to a reduction in vibrations of the reciprocating pump according to the invention. The control curve and consequently the intended sequence of movement of the piston over the angle of rotation of the drive shaft are freely definable by virtue of the invention.  
         [0024]     The control curve may be composed of even a plurality of curve functions. The piston can therefore move according to the equations x=(m+r) and m=360°−r, x being a number of strokes per drive shaft revolution, m being the angular range of the drive shaft during the upward movement of the piston, and r being the angular range of the drive shaft during a downward movement of the piston. At x=1, m=240° and r=120°, the piston is moved upward to the upper reversal point in the event of a rotation of the drive shaft through 240° and is moved downward to the lower reversal point during the subsequent rotation of the drive shaft through 120°.  
         [0025]     The second-mentioned problem, to be precise the determination of an advantageous use of the reciprocating pump, is solved, according to the invention, by use as a fuel pump in a structural unit with a motor for driving the drive shaft.  
         [0026]     In fuel pumps of present-day motor vehicles, there is the problem, even when the fuel is hot, of generating a high feed pressure and a high feed volume. In motor vehicles with particularly high-power internal combustion engines, therefore, two feed units with fuel pumps designed, for example, as side channel pumps or as gerotor pumps are often employed.  
         [0027]     These feed units therefore also require two electric motors for driving the fuel pumps. By virtue of the invention, a plurality of pistons can be operated simultaneously by a single drive shaft, thus leading to a particularly simple construction of the feed unit. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     The invention permits numerous embodiments. To make it even clearer, several of these are illustrated in the drawing and are described below. In the drawing:  
         [0029]      FIG. 1  shows a longitudinal section through a reciprocating pump according to the invention.  
         [0030]      FIG. 2  shows a sectional illustration through the reciprocating pump from  FIG. 1  along the line II-II.  
         [0031]      FIG. 3  shows a sectional illustration through a further embodiment of the reciprocating pump according to the invention.  
         [0032]      FIG. 4  shows diagrammatically a longitudinal section through a further embodiment of the reciprocating pump according to the invention.  
         [0033]      FIG. 5  shows diagrammatically a longitudinal section through a further embodiment of the reciprocating pump according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]      FIG. 1  shows a longitudinal section through a fuel pump with a drive shaft  2  mounted in a casing  1 . The casing  1  has a cylindrical bore  3  with a piston  4  guided axially movably therein. The drive shaft  2  has a control curve  5  for receiving a part region of a transmission element  6 . The transmission element  6  passes through an elongated guide  7  arranged parallel to the axis of rotation of the drive shaft  2 , located in the casing  1  and projecting into a recess  8  of the piston  4 , said recess being designed as a peripheral groove. An inlet channel  9  passes through the piston  4 . An outlet channel  10  is arranged in the casing  1 .  
         [0035]     Valves  11 ,  12  designed as nonreturn valves and having valve bodies  17 ,  18  prestressed relative to valve seats  15 ,  16  by spring elements  13 ,  14  are arranged in each case in the inlet channel  9  and the outlet channel  10 .  
         [0036]     The control curve  5  has an upper reversal point  19  and a lower reversal point  20 . The piston  4  is illustrated in the drawing at the upper reversal point  19 . In the event of a rotation of the drive shaft  2 , the transmission element  6  slides to the control curve  5  and into the guide  7  of the casing  1  and at the same time displaces the piston  4  away from the outlet channel  10 . In this case, the valve  12  in the outlet channel  10  closes. This gives rise to a vacuum in the space delimited by the piston  4  and the casing  1 , with the result that the valve  11  in the inlet channel  9  opens and a medium to be fed is sucked in. The valve  11  in the inlet channel  9  closes at the lower reversal point  20 . When the drive shaft  2  is rotated further beyond the lower reversal point  20 , this gives rise, in the space delimited by the piston  4  and the casing  1 , to a pressure which presses the valve body  18  of the valve  12  in the outlet channel  10  away from the valve seat  16 . The medium to be fed is consequently ejected through the outlet channel  10 .  
         [0037]      FIG. 2  shows, in a sectional illustration through the reciprocating pump from  FIG. 1  along the line II-II, that overall three pistons  4 ,  4 ′,  4 ″ are arranged in the casing  1  concentrically around the drive shaft  2 . The casing  1  is consequently designed as a cylinder support and guides a plurality of pistons  4 ,  4 ′,  4 ″. Of course, even more than three pistons  4 ,  4 ′,  4 ″ may be arranged in the casing  1 . Each of the pistons  4 ,  4 ′,  4 ″ is connected to the single control curve  5  of the drive shaft  2  via a transmission element  6 ,  6 ′,  6 ″. The guides  7 ,  7 ′,  7 ″ for the transmission elements  6 ,  6 ′,  6 ″ are designed as bores. Axes of symmetry of the drive shaft  2 , of the piston  4 ,  4 ′,  4 ″and of the guides  7 ,  7 ′,  7 ″ are arranged in each case on a straight line.  
         [0038]      FIG. 3  shows a further embodiment of the reciprocating pump in a sectional illustration, which differs from that of  FIG. 2 , above all, in that the axes of symmetry of the guides  7 ,  7 ′,  7 ″ are arranged outside straight lines running from the axes of symmetry of the driving shaft  2  and the pistons  4 ,  4 ′,  4 ″. Furthermore, bearing faces  21  of the guides  7 ,  7 ′,  7 ″, said bearing faces bearing against the transmission elements  6 ,  6 ′,  6 ″, are arranged on tension elements  23  prestressed by spring elements  22 . The transmission elements  6 ,  6 ′,  6 ″ are consequently prestressed in the guides  7 ,  7 ′,  7 ″.  
         [0039]      FIG. 4  shows diagrammatically a longitudinal section through a further embodiment of the reciprocating pump, in which a drive shaft  24  has a rim  26  surrounding a piston  25  radially on the outside. A control curve  27  is arranged on the radial inner side. A casing  28  arranged radially within the rim  26  has a cylindrical bore  29  for guiding a piston  25 . A  20  transmission element  30  is pressed in a recess  31 , designed as a pocket, of the piston  35  and passes through the casing  28  in the region of a guide  32  running parallel to the axis of rotation of the drive shaft  24  and penetrates into the control curve  27 . The control curve  27  has a rectangular cross section. As in the embodiment according to  FIGS. 1 and 2 , here too a plurality of pistons  25  may be arranged concentrically about the axis of rotation of the drive shaft  24 . An inlet channel  33  and an outlet channel  34  are arranged, in each case with valves  35 ,  36  designed as nonreturn valves, in the casing  28 .  
         [0040]      FIG. 5  shows a further embodiment of the reciprocating pump, in which a drive shaft  37  has a shaft stub  38  with a first control curve  40  and a rim  39  concentrically surrounding the shaft stub  38  and having a second control curve  41 .  
         [0041]     Between the shaft stub  38  and the rim  39 , a piston  42  is guided axially displaceably in a bore  43  of a casing  44 . Transmission elements  45 ,  46  guided in the control curves  40 ,  41  pass in each case through elongated guides  47 ,  48  in the casing  44  and project into a recess  49 ,  50  of the piston  42 , said recess being designed as a pocket. In the casing  44 , an inlet channel  51  and an outlet channel  52  with valves  53 ,  54  designed as diaphragm valves are arranged.  
         [0042]     The valves  53 ,  54  have a resiliently elastic diaphragm  57 ,  58  prestressed towards valve seats  55 ,  56 . The control curves  40 ,  41  in each case have a trapezoidal cross section. A bearing face of the radially outer control curve  41  is arranged on a tension element  60 . The tension element  60  is screwed to the casing  44  and is prestressed against the latter by cup springs  61 . Similarly, of course, the control curve  40  of the shaft stub  38  may also be provided with a prestressed bearing face or the shaft stub  38  is prestressed axially with respect to the radially outer control curve  41 .