Patent Publication Number: US-8118573-B2

Title: Piston pump with at least one piston element

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2005/056773 filed on Dec. 14, 2005. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a piston pump with at least one piston element, which can be driven by a drive unit and is situated in a longitudinally moving fashion inside a housing. 
     2. Description of the Prior Art 
     WO 01/81761 A1 has disclosed a piston pump with two piston elements that can be driven by a drive unit and are situated in a longitudinally moving fashion inside a housing. Together with a housing, the piston elements each define a respective pressure chamber whose volume varies as a function of a piston movement. The pressure chambers are connected to both the suction side or a suction region and the pressure side or a delivery side of the piston pump; during a suction stroke of the piston elements, hydraulic fluid is drawn into the relevant pressure chamber, which is characterized by a steady volume increase, and during a delivery stroke of the piston element, hydraulic fluid is conveyed in the direction of the delivery side from the pressure chamber, which is then characterized by a steady volume decrease. In addition, the delivery side of the piston pump is respectively connected to a working piston chamber of a compensation piston unit whose compensation piston is likewise moved by the drive unit, back and forth in the longitudinal direction in the housing, between a top dead center and a bottom dead center. 
     In order to smooth a pressure pulsation on the delivery side of the piston pump, the piston element and the compensation piston unit corresponding to it are respectively phase shifted in relation to each other by 180° so that the compensation piston of the compensation piston unit is situated in its bottom dead center when the corresponding piston element is situated in its top dead center. 
     In addition, the compensation pistons are embodied as stepped in order to smooth a suction-side pressure pulsation of the two-piston pump in comparison to conventional two-piston pumps not equipped with compensation pistons. This is based on the knowledge that the suction-side delivery characteristic of a piston pump can be smoothed through the use of a so-called step-piston pump essentially to the same degree as the pressure-side delivery characteristic can be smoothed by the combination of the pump piston elements with the compensation pistons. 
     It is disadvantageous, however, that the piston rod, which cooperates with a cam of the drive unit, limits the effective area of the stepped compensation pistons used to smooth the suction-side pressure pulsations, in such a way that a desired smoothing of the suction-side pressure pulsation cannot be achieved to the extent desired. 
     SUMMARY AND ADVANTAGES OF THE INVENTION 
     The piston pump according to the invention is provided with at least one piston element, which can be driven by a drive unit and is situated in a longitudinally moving fashion inside a housing, and with a first pressure chamber that is delimited by the piston element and at least one component affixed to the housing, which first pressure chamber can be connected via an inlet valve device to a suction side of the piston pump, and can be brought into an operative connection with a delivery side of the piston pump via an outlet valve device. In addition, a compensation piston unit that can also be driven by the drive unit is provided, whose working piston chamber communicates with the delivery side. A stroke volume of the first pressure chamber is twice the stroke volume of the compensation piston unit. 
     The suction-side pressure pulsation of the piston pump according to the invention is improved in comparison to a one-piston pump known from the prior art because a second pressure chamber that is connected to the suction region of the piston pump and operationally connected to the first pressure chamber during a suction stroke of the piston element is provided, which is delimited by the piston element and at least one component affixed to the housing and whose volume varies by half the stroke volume of the first pressure chamber as a function of a movement of the piston element. The volume of the second pressure chamber expands during a delivery stroke of the piston element that decreases the volume of the first pressure chamber and contracts during a suction stroke of the piston element that increases the volume of the first pressure chamber. 
     As a result, by contrast with a conventional piston pump in which the stroke volume of the first pressure chamber is completely drawn out of the suction region during the suction stroke of the piston element, in the piston pump according to the invention, the stroke volume of the first pressure chamber is drawn out of the suction region halfway during the suction phase of the first pressure chamber and halfway during the delivery phase of the first pressure chamber. The half stroke volume drawn out of the suction region during the delivery phase of the piston pump according to the invention is first conveyed into the second pressure chamber and, during the suction stroke of the piston element in which the volume of the second pressure chamber is reduced by half the stroke volume of the first pressure chamber, is conveyed into the first pressure chamber. 
     The above-described functionality of the second pressure chamber results Trom the placement of the second pressure chamber between the suction region of the piston pump and the first pressure chamber and from the inverse volume changes of the two pressure chambers as a function of the movement of the piston element. 
     The second pressure chamber thus constitutes an intermediate storage space, which can be filled during the delivery phase of the first pressure chamber and is emptied during the suction phase of the first pressure chamber due to its volume reduction, discharging half the stroke volume of the first pressure chamber into said first pressure chamber. The rest of the portion of hydraulic fluid required to completely fill the first pressure chamber is drawn from the suction region of the piston pump during the suction phase of the first pressure chamber. In a simple fashion, this procedure leads to a reduction in the fluid friction in the suction region, which in turn achieves a reduced generation of noise during operation of a piston pump. 
     Other advantages and advantages embodiments of the subject according to the invention are disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred example of piston pumps embodied according to the invention is explained in detail in the subsequent description, taken with the accompanying drawing, in which: 
         FIG. 1  shows a schematic longitudinal section through piston pumps according to the invention; 
         FIG. 2  shows a very schematic partial view of a drive unit of the piston pumps according to  FIG. 1 ; and 
         FIG. 3  shows a suction-side pressure pulsation curve of one of the piston pumps according to  FIG. 1  in comparison to a piston pump that only aspirates during the suction stroke of the piston element. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows the longitudinal section through two piston pumps  1 A,  1 B. Each pump is embodied in the form of one-piston, pump with a piston element  4 A,  4 B, that can be driven by a drive unit  2  and is situated in a longitudinally moving fashion inside a housing  3 . The piston pumps  1 A,  1 B have basically the same design, which is why the description of the piston pumps  1 A and  1 B below refers to only one of the piston pumps  1 A or  1 B and in the drawings, parts that are the same have been provided with the same reference numerals, combined with the letter A or B. 
     The two pistons pumps  1 A and  1 B are each associated with a respective compensation piston unit  6 A,  6 B, while a working piston chamber  6 A —K  or  6 B —K  of the compensation piston unit  6 A,  6 B is connected to a respective delivery side  7 A,  7 B of the piston pumps  1 A,  1 B. 
     The piston element  4 A of the piston pump  1 A, together with two insert elements  8 A,  9 A affixed to the housing, delimits a first pressure chamber  10 A, which can be connected via an outlet valve device  11 A to the delivery side  7 A of the piston pump  1 A. In addition, the first pressure chamber  10 A can be connected via an inlet valve device  13 A to a suction region  12 A of the piston pump  1 A; the inlet valve device  13 A closes the first pressure chamber  10 A off from the suction region  12 A during the delivery stroke of the piston element  4 A and during a compression stroke that reduces the volume of the first pressure chamber  10 A. 
     The outlet valve device  11 A, which in the present case is embodied with a spherical sealing element  5 A spring-loaded in the closing direction of the outlet valve device  11 A, operates in such a way that during a delivery stroke of the piston element  4 A, once a defined pressure value in the first pressure chamber  10 A is achieved, the outlet valve device  11 A lifts away from the insert element  9 A and hydraulic fluid contained in the first pressure chamber  10 A is conveyed toward the delivery side  7 A of the piston pump  1 A. 
     At the same time, the inlet valve device  13 A, which is embodied with a disk-like sealing element  14 A, is closed so that during the delivery stroke of the piston element  4 A, the connection is interrupted between the first pressure chamber  10  and the suction region  12 A. 
     The piston elements  4 A and  4 B of the piston pumps  1 A and  1 B and the corresponding compensation piston units  6 A and  6 B rest with their respective end surfaces oriented toward the drive unit  2  against one of two cam elements  2 A,  2 B that are affixed to a drive shaft  2 C of the drive unit  2  in such a way as to prevent them from rotating in relation to it. The two cam elements  2 A and  2 B are embodied with the same eccentricity and, in the manner shown in detail in  FIG. 2 , are positioned offset from each other around the circumference of the drive shaft  2 C so that the compensation piston units  6 A and  6 B operationally connected to the cam element  2 B are each triggered by the drive unit  2  with a timing that is phase-shifted by 180° from the respective corresponding piston element  4 A or  4 B. As a result, the compensation piston elements  61 A and  61 B of the compensation piston units  6 A,  6 B are each moved toward their respective bottom dead center while the corresponding piston element  4 A or  4 B is moved toward its top dead center. 
     The effective areas of the compensation piston elements  61 A,  61 B and their stroke paths in the present case are dimensioned so that the volume of the delivery side  7 A or  7 B in the region of a compensation piston unit  6 A or  6 B is increased by half the stroke volume of the first pressure chamber  10 A or  10 B of the piston pump  1 A or  1 B during the delivery phase of the piston pump  1 A or  1 B and is also increased by half the stroke volume of the first pressure chamber  10 A or  10 B during the suction phase of the piston pump  1 A or  1 B. 
     As a result, both during the delivery phase and during the suction phase of a piston pump  1 A or  1 B, the delivery side  7 A or  7 B of a piston pump  1 A or  1 B is acted on with half the stroke volume of the first pressure chamber  10 A or  10 B of the piston pump  1 A or  1 B, by means of which a significantly smoother pressure pulsation on the delivery side  7 A or  7 B is achieved in comparison to a conventional piston pump embodied in the form of one-piston pump. 
     In addition, in a region oriented toward the suction region  12 A, the piston element  4 A is embodied as stepped in such a way that between the piston element  4 A and the housing  3 , a second pressure chamber  15 A is embodied, which is connected to the suction region  12 A and whose volume varies by half the stroke volume of the first pressure chamber  10 A as a function of a movement of the piston element  4 A. In this connection, the volume of the second pressure chamber  15 A expands during a delivery stroke of the piston element  4 A that decreases the volume of the first pressure chamber  10 A and contracts during a suction stroke of the piston element  4 A that increases the volume of the first pressure chamber  10 A. 
     The second pressure chamber  15 A is situated between the housing  3  and an outer circumferential surface of the piston element  4 A, which is embodied in the form of a hollow deep-drawn component. In addition, the second pressure chamber  15 A is connected to an inner chamber  17 A of the piston element  4 A via at least one bore or opening  16 A in the circumferential surface of the piston element  4 A so that the first pressure chamber  10 A is fluidically connected to the second pressure chamber  15 A when the inlet valve device  13 A is open. 
     The dimensioning and the above-described placement of the second pressure chamber  15 A achieve the fact that both during a compression stroke and during a suction stroke of the piston element  4 A, half the stroke volume of the piston pump  1 A or first pressure chamber  10 A is conveyed from the suction side toward the first pressure chamber  10 A. During the suction stroke of the piston element  4 A, the other half of the stroke volume to be conveyed from the second pressure chamber  15 A toward the first pressure chamber  10 A is used to completely fill the first pressure chamber  10 A because of its volume reduction. As a result, in the vicinity of the suction region  12 A, a pressure pulsation occurs that essentially corresponds to that of a two-piston pump. 
     This means that with both the compensation piston units  6 A and  6 B and the second pressure chambers  15 A and  15 B, it is possible on both the suction side and the delivery side to achieve the pressure pulsation of a two-piston pump by means of a piston pump embodied as a one-piston pump, i.e. without a second pump element actually being present. This advantageously reduces manufacturing costs. In addition, it is possible to use intrinsically known one-piston pumps that are embodied with a relatively low degree of complexity in the suction-side connection region to the second pressure chamber. 
     In addition, in comparison to conventional two-piston pumps, an improved pressure build-up dynamic is also achieved since one-piston pumps are essentially designed with larger suction cross-sections and larger inlet cross-sections. 
     Also, the working piston chamber  6 A_K of the compensation piston unit  6 A is connected to a master cylinder  19 A of a vehicle brake system that is not shown in detail, in order to convey hydraulic fluid in the direction of the master cylinder  19  of the brake system in certain operating states of an ABS or ESP system. 
     In order to improve driving comfort, the connection between the working piston chamber  6 A_K of the compensation piston unit  6 A and the master cylinder  19  as well as a connection between the working piston chamber  6 B_K of the compensation piston unit  6 B and the master cylinder  19  are each embodied with a check valve  20 A,  20 B in order to deaden or ideally, to completely eliminate, a pressure pulsation in the master cylinder  19  originating from the compensation piston units  6 A and  6 B. 
     Two curves of a pressure pulsation on the delivery side  15 A and  15 B of the piston pump  1 A and  1 B are shown in  FIG. 3 . The dashed line P 1  shows the curve of the pressure pulsation of a piston pump that is embodied in the form of a one-piston pump and is operated without an above-described compensation piston unit  6 A or  6 B on the delivery side. The pressure pulsation graphically depicted by the curve P 2  in  FIG. 3  occurs on the delivery side  7 A or  7 B of the piston pump  1 A or  1 B when it is operated with a compensation piston unit  6 A or  6 B in the system described above. 
     It is clear from the comparison of the two curves the P 1  and P 2  that the use of the piston pump  1 A or  1 B embodied according to the invention achieves a pressure pulsation that is flatter and smoothed over an operating cycle of the piston pump  1 A and  1 B and essentially results in a reduced operating noise due to reduced fluid friction. 
     The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.