Patent Publication Number: US-10781814-B2

Title: Piston pump comprising a piston with a profiled front face

Description:
BACKGROUND OF THE INVENTION 
     The invention starts from a piston pump. 
     Currently known piston pumps operate on the following principle: the piston, which is arranged and can be moved in a cylinder, is moved in the direction of an armature plate arranged on the rear side of the cylinder, e.g. by means of a magnetic field produced by a solenoid. During this process, a fluid, e.g. a fuel, is drawn via an inlet valve into a compression chamber, which is arranged between the inlet valve in the cylinder bottom and the piston. If the magnetic field is switched off, a spring, for example, which is arranged between the piston and the armature plate, pushes the piston back in the direction of the initial position and, in the process, compresses the fluid and pushes it out of the compression chamber via an outlet valve. 
     In many embodiments of the piston pump, especially in piston pumps with simultaneous inflow and outflow, there is the problem that there is a volume region in the compression chamber itself or directly adjoining the compression chamber in which the fluid present therein cannot be compressed or displaced or cannot be adequately compressed or displaced by the piston movement. This volume region is referred to as the dead volume. The size of the dead volume affects the efficiency of the piston pump. 
     SUMMARY OF THE INVENTION 
     The piston pump according to the invention is designed to reduce the dead space volume and thus to increase the efficiency of the piston pump. 
     For this purpose, it is envisaged according to the invention that the piston has, on its side facing a channel, a region which can be made to enter into the channel. In particular, this region is made to enter into the channel at least temporarily during a pump cycle. Typically, the channel is arranged fluidically between the compression chamber and the outlet valve, especially if the outlet valve and the inlet valve of the piston pump are arranged coaxially with one another. In particular, the channel is arranged directly upstream of the outlet valve and typically has a smaller diameter than a compression region at a distance from the outlet valve. By virtue of the region, the piston has a section which is designed to enter the channel, particularly during the compression phase or displacement phase of the pump cycle, and to compress or displace the fluid present there. As a result, the dead volume of the piston pump is reduced and the efficiency of the piston pump is increased. 
     In an advantageous development, it is envisaged that the outlet valve, the channel and the piston with the region are arranged along a common axis. The axis preferably lies in the direction of movement of the piston. This ensures that the piston pump has a particularly high efficiency since, during the compression phase, when the fluid leaves the compression chamber through the outlet valve, the fluid can flow in the same direction in which the piston is moving to leave the compression chamber. 
     It has proven advantageous if the region is formed as a projection on the end face of the piston which faces the channel. The piston itself can have a geometry which is matched, in particular optimized, to the geometry of the compression chamber, while the region or projection is matched or optimized to the geometry of the channel, in particular having the same geometry, e.g. cross section and/or length and/or diameter. In this context, “optimized” means that the piston is configured in such a way in relation to the compression chamber that, on the one hand, the piston pump has a high effective cross section and, on the other hand, the piston has low wear—caused by friction with the side walls of the compression chamber for example—and thus a long life. 
     For example, the region or the projection can have a cylindrical, conical or cuboidal geometry. The projection is preferably formed as an annular shoulder on the piston end face. 
     In a preferred development, the region or projection has a length M which is not less than 5% of the length L of the channel, in particular not less than 25% of the length of the channel and/or not greater than 95% of the length L of the channel. The length M of the region or projection is the distance from the end face of the piston, on which the region or projection is arranged, perpendicularly as far as the end face of the region or projection which faces the channel. This ensures that the region has a sufficiently great length M to effectively reduce the dead volume in the channel. 
     In addition or as an alternative, it is envisaged that the region or projection has at least an entry depth T into the channel, wherein the entry depth T is at least 5% of the length L of the channel, in particular at least 15% of the length L of the channel and/or not greater than 95% of the length L of the channel. This ensures that the region has a sufficiently great entry depth T to effectively reduce the dead volume in the channel, even if the region or projection cannot enter the channel with its complete length M. 
     The channel preferably has a smaller diameter than the compression chamber. The diameter of the channel corresponds to at least 5% and/or at most 30% of the diameter of the compression chamber. 
     In an advantageous embodiment, it is envisaged that the region is a boss. The boss is formed during the production of the piston by machining in a turning process, in accordance with DIN 6785. Normally, the boss is removed from the piston end face to ensure that the piston has a smooth end face. The boss is a suitable means of reducing the dead volume. In addition, there is also the effect that it is possible to dispense with the working step of removing the boss from the piston during the production of the piston and the piston pump and thus that the production of the piston pump is simplified. 
     In principle, the region or projection can advantageously be formed integrally with the piston, e.g. in the form of the boss, or as a multi-part assembly with the piston. In the case of a multi-part design, the region is connected materially, e.g. by means of welding, to the piston. 
     In the case of the integral configuration, there is the advantage that there is no need for an extra material joint between the region and the piston. Fundamentally, additional joints can always be weak points in mechanically stressed components. 
     The multi-part configuration provides the advantage that the region can be produced independently of the piston. Depending on the intended use and configuration of the piston pump, the piston can be combined with a corresponding region matched to the channel and the intended purpose. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 a  and 1 b    show a first example of a piston pump according to the invention 
         FIGS. 2 a  and 2 b    show a second example of a piston pump according to the invention 
     
    
    
     DETAILED DESCRIPTION 
     Two illustrative embodiments of the piston pump  1  according to the invention are shown in  FIG. 1  and  FIG. 2 . The two illustrative embodiments differ in the precise configuration of the region  20  arranged on the end face  12  of the piston  6  which faces the channel  15 . Part a) of each of the two figures shows a schematic illustration of a piston pump  1 , wherein the basic construction of the piston pump  1  is the same in both illustrative embodiments. Part b) of each of the two figures shows an enlargement of the region X marked by a circle in part a) of the figures. 
     The basic construction of the piston pump  1  is described below. The piston pump  1  has a housing  2 , an armature plate  3  and, for example, a solenoid  5  or solenoid set arranged in the housing  2 . A cylinder  4  is arranged in the solenoid  5 . A movable piston  6  is, in turn, arranged in the cylinder  4 . The magnetic field produced by the solenoid  5  moves the piston  6  in the direction of the armature plate  3 . On its side facing the piston  6 , the armature plate  3  has a stop, against which the piston  6  strikes when the solenoid  5  is energized, i.e. when the magnetic field is switched on. The side of the piston  6  which faces the armature plate  3  is referred to as the piston rear side  10 . The surface by means of which the piston rear side  10  touches the stop of the armature plate  3  when the magnetic field is switched on is referred to as the contact surface. The end face  14  of the piston  6  situated opposite the piston rear side  10  is also referred to as the piston front side. 
     A piston spring  7  is arranged between the piston  6  and the armature plate  3 . The piston spring  7  is fixed on the side thereof facing the armature plate  3  by a spring holder  8 . The piston spring  7  can be arranged partially or completely within the piston  6  or in a cavity arranged in the piston  6 . The piston rear side  10  has an opening, through which the piston spring  7  projects from the piston. The piston spring  7  is compressed owing to the movement of the piston in the direction of the armature plate  3 . After the magnetic field is switched off, the piston spring  7  pushes the piston  6  back in the opposite direction. 
     An inlet valve  11  and an outlet valve  12  are furthermore arranged in the cylinder  4 , in particular in the cylinder bottom. The cylinder  4  is delimited by the armature plate  3  on one side and by the cylinder bottom on the opposite side. A compression chamber  9  is arranged within the cylinder  4 . The compression chamber  9  is delimited by the cylinder walls, the inlet valve  11  and the piston  6 . 
     The inlet valve  11  and/or the outlet valve  12  can be designed as Belleville springs. The inlet valve  11  and the outlet valve  12  and thus also the inlet and the outlet are arranged on the same side of the cylinder  4  or of the compression chamber  9 . The compression chamber  9  is arranged fluidically between the inlet valve  11  and the outlet valve  12 . A valve body  13  is arranged between the inlet valve  11  and the outlet valve  12 . A channel  15  is formed within the valve body  13 . Typically, the length of the channel  15  corresponds to the length of the valve body  13 . The outlet valve  12  is connected to the compression chamber  9  by means of the channel  15 , thus allowing the fluid to flow from the compression chamber  9  to the outlet valve  12  via the channel  15 . 
     Fuel lines, via which a fuel is drawn into the compression chamber  9  within the cylinder  4  from a tank through the inlet valve  11  owing to the vacuum, are not shown. The vacuum in the cylinder  6  or in the compression chamber  9  is produced by the movement of the piston  6  in the direction of the armature plate  3 . The fuel is forced from the piston  6  to an injection valve via further fuel lines and the outlet valve  12 . 
     In the first illustrative embodiment, which is shown in  FIG. 1 , the region  20  is designed as a cylindrical protrusion. The region  20  has a length M of 93% of the length L of the channel  15 . The entry depth T of the region  20  in the channel  15  is 90% of the length L of the channel  15 . The fact that the diameter of the region  20  is matched to the diameter of the channel  15 , i.e. the difference between the two diameters of the region  20  and the channel  15  is less than 10% of the diameter of the channel  15 , ensures that the dead volume in the channel  15  is effectively minimized and, at the same time, as little friction as possible is produced between the region and the channel wall. 
     In the second illustrative embodiment, which is shown in  FIG. 2 , the region is designed as a boss. The boss has a length M of 15% of the length L of the channel and an entry depth T of 11.5% of the length L of the channel.