Abstract:
A control ring for controlling the flow of a pressure medium in a displacement pump is provided. The control extends along a first rotational axis, and includes a first and a second axial surface. The first axial surface has an interface section provided with at least a first and a second opening, which first and second openings are arc shaped and are separated by a first and a second land. The first land is provided with a first tapered groove extending from the first opening into the first land, and having its broader edge in a direction of the first opening and its tip in a direction of the second opening. The first tapered groove extends into the first land such that an angular distance between the first and second openings over the first land is different at different radial distances.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to European patent application number EP 14150744.2, filed Jan. 10, 2014, which is incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to displacements pumps and the control of a displacement pump, and especially to a control ring for a displacement pump. 
       BACKGROUND 
       [0003]    The displacement of a displacement pump stationary pressure chambers, such as a bent axis piston or gerotor pump, is commonly controlled through a control ring. The control ring is provided with openings in order to control the flow of pressure medium from the displacement pump. Typically, there are two openings, which are divided by an intermediate section, referred to as a land. 
         [0004]    When pistons/pressure chambers pass over the land between the high pressure and low pressure opening of a control ring, the pressure is decreasing/increasing rapidly due to the land blocking the pressure medium. When the opening has passed over the land and reaches the opening in the control ring a pressure spike/pressure dip causing vibration and noise occurs due to the large pressure differences. 
         [0005]    Pre-compression/pre-decompression and how it varies dependent of the position of the control ring. In a displacement pump with a control ring arranged for 100% displacement, the pressure rises slowly over the land. In a displacement pump with a control ring arranged for 0% displacement, the pressure rises very high over the land, causing high pressure differences between the outlet openings and the opening in the control ring to which it opens to. The standard solution of today is a compromise, in which the land is adapted such that it gives an ideal pre-compression in an intermediate position of the control ring. An obvious drawback to this solution is that in any other control position of the displacement pump, the pre-compression becomes to large/small, whereby the displacement pump still will have problems with pressure pulses and there from derived vibrations and disturbing noises. A displacement pump according to the prior art is disclosed in WO 12120094. 
       SUMMARY 
       [0006]    An object of the disclosure is to suggest a control ring and a displacement pump that minimizes the pressure pulses in a displacement pump with stationary pressure chambers. 
         [0007]    The disclosure is based upon the idea that the pre-compression/pre-decompression over the land can be varied, which in the present disclosure is achieved through that the size of the land is varied. According to the inventive solution the design of the land is such that by adjusting the position of the control ring the size of the land (i.e., the active land over which the pressure chamber passes) can be varied dependent of the position of the control ring. 
         [0008]    The disclosure can advantageously be applied to a control ring provided for controlling the flow of a pressure medium in displacement pump stationary pressure chambers. The control ring is centred about a first rotational axis about which it extends. The control ring is further provided with a first and a second axial surface. 
         [0009]    The first axial surface is provided with an interface section having at least a first and a second opening. The first and second openings are arc shaped and are separated by a first and a second intermediate section in the further text referred to as land. When the control ring is used within a displacement pump, one of the openings is a high pressure opening. The high pressure opening can be any of the two openings, and can also change dependent of which direction the displacement pump is driven in. 
         [0010]    According to the disclosure, a pre-compressions/pre-decompression is achieved in that the first land is provided with a tapered groove. The tapered groove extends from the first opening into the first land and having its broader edge in direction of the first opening and its tip in direction of the second opening. The tapered groove extends into the first land such that an angular distance between the first and second openings over the first land is different at different radial distances. 
         [0011]    By arranging a control ring according to the disclosure in a displacement pump with an offset between the first rotational axis and a second rotational axis (e.g., rotational axis of the displacement pump), the tapered groove will vary the length of the first land depending on in which rotational position the control ring is placed. This is explained in further detail in detailed description of the drawings. 
         [0012]    In one aspect of the disclosure the first tapered groove is arranged at an inner circumference of the first opening and the first land is provided with a second tapered groove, which is correspondently arranged as the first tapered groove at an outer circumference of the first opening. By providing the first land with two tapered grooves each directed from the first opening into the land and at the outer and the inner circumference respectively, the first land can be varied in both rotational directions of the control ring from the 100% displacement position. 
         [0013]    In one aspect of the disclosure the first land is provided with a third and fourth tapered groove, extending correspondently from the second opening, into the first land, as the first and second tapered grooves from the first opening. 
         [0014]    In a further aspect of the disclosure the second land is provided with a corresponding number of tapered grooves as the first land. By providing the first land with tapered grooves in all of its four corners a rotational weight balance of the control ring is easily facilitated. 
         [0015]    To achieve the first beneficial effect of the disclosure, i.e., enable a variable land and thereby avoid vibrations and disturbing noises due to high pressure spikes, only one tapered groove is needed. Above are combinations with one, two and four tapered grooves in one or both lands described. The disclosure does however not exclude any other not described number of tapered grooves. Any combination of one-four tapered grooves at one of the lands or both of the lands are possible and within the scope of the disclosure. 
         [0016]    In one aspect of the disclosure the tapered grooves are continuously tapered. In an alternative solution the tapered grooves are provided with a stepped tapered form. 
         [0017]    In one further aspect of the disclosure the first and the second opening are mouthing to a corresponding mouthing area provided at either of an inner and outer radial surface. 
         [0018]    The disclosure further concerns a pumping device comprising a pump unit provided with a control ring according to the disclosure. The pump unit is provided with a rear plate and axial outlets. The pump unit is centred about a rotational axis, further referred to as a second rotational axis. The axial outlets are provided at the rear plate rotational symmetrical about the second rotational axis. The rear plate is adapted to rotate about the second rotational axis. The control ring is adapted to abut against a rear plate such that by rotating the control ring a displacement of the pumping device can be changed between 100 and zero %. 
         [0019]    The control ring is centred about the first rotational axis, which in the pumping device is eccentric from the second rotational axis such that
       when the control ring is arranged for 100% displacement, the axial outlets passing over the first land is fully blocked by the first land ( 15 ,  215 ) during a first predetermined angular distance (a 1 ), and   when the control ring is positioned for 0% displacement the axial outlets passing over the first land ( 15 ,  215 ) are fully blocked by the first land during a second predetermined angular distance, wherein
 
the first predetermined angular distance is longer than the second predetermined angular distance.
       
 
         [0022]    The pumping device provided with the above control ring enables a variable land. Due to the eccentric arrangement of the control ring and that a first tapered groove is provided in the first land, the angular distance along which an axial outlet of the pumping unit passes over the first land and is fully covered by it can be varied dependent on the position of the control ring. 
         [0023]    When the control ring is positioned in a position for 100% displacement, the land is arranged between the high pressure and the low pressure chamber. In this position the pressure is raised minimal for each angular distance the axial outlets are moved over the land. Therefore it is desired that the axial outlets are block by the land sufficiently long to build up a pressure in the outlet opening passing over the land, which correlates with the pressure in the high pressure chamber. Hence, the length of the land is adjusted to achieve such a pressure rise in the outlet opening. Because the pressure thereby is essentially equal in the outlet opening as in the high pressure chamber, there will be no pressure spikes causing vibrations or noise as the outlet openings can start to deliver pressure medium into the high pressure chamber. 
         [0024]    When the control ring is positioned for 0% displacement, i.e., rotated 90 degrees from the 100% displacement position; the land is arranged in the middle of the high pressure chamber, where the pressure raises quickly with the angular distance the axial outlets are moved over the land. Therefore it is desired that the axial outlets are blocked by the land as short time as possible. Hence, the tapered groove in the first land is adjusted such that the axial outlet only is fully closed by the land during a very short angular distance, before it enters the high pressure chamber. 
         [0025]    Due to the eccentric arrangement of the control ring relative the pumping unit and the tapered grooves in the first land, the angular distance the land fully covers the axial outlets can be varied with the position of the control ring. The inclination of the tapered grooves is dependent of the offset of the second rotational axis from the first rotational axis. 
         [0026]    In a preferred embodiment, the control ring is provided with four tapered grooves in each of the two lands. One tapered groove is thereby provided in each corner of the land. By providing the tapered grooves in each corner of the two lands, a variable land can be achieved in all directions of rotation of the control ring. 
         [0027]    In one aspect of the disclosure the pumping unit is a gerotor pump unit. In another aspect of the disclosure, the pumping unit is an axial piston pump. 
         [0028]    It is preferred that the pumping unit and the control ring are arranged within the same housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    The present disclosure will now be described in detail with reference to the below drawings, wherein: 
           [0030]      FIG. 1  discloses a gerotor pump provided with a control ring according to the disclosure; 
           [0031]      FIGS. 2   a - e  disclose an embodiment of the control ring in a position of the control ring allowing 100% displacement; and 
           [0032]      FIGS. 3   a - d  disclose the interaction between the control ring and the axial outlet openings in a position of the control ring allowing 0% displacement. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    As required, detailed embodiments are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary and that various and alternative forms may be employed. The figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art. 
         [0034]      FIG. 1  discloses a displacement pump  200 , in which a control ring  210  according to the disclosure is provided. The displacement pump  200  is disclosed as a gerotor pump. The control ring  210  is however compatible with any displacement pump having stationary pressure chambers. The displacement pump  200  comprises a front and a back housing  101 ,  102 , a front and a rear plate  103 ,  104 , in between which a pumping unit  105  is arranged. The pumping unit  105  comprises a rotor set of an outer rotor  115  and an inner rotor  116 , whereby the inner rotor  116  is provided upon an eccentric shaft  106 . The pumping unit  105  is provided in between the front and the rear plate  103 ,  104 , wherein the rear plate  104  is provided with supply conduits  114  in order to connect the pressure chambers of the pumping unit  105  with an inlet and an outlet  108 ,  109  in the rear housing  102 . 
         [0035]    In the embodiment shown, the control ring  210  is provided in between the rear plate  104  and the rear housing  102 , such that it controls the flow of pressure medium between the inlet and the outlet  108 ,  109  and the pressure chambers of the pumping unit  105 . The control ring  210  could however be arranged directly against a pumping unit, independently if it is a gerotor, bend axis pump or another displacement pump with stationary pressure chambers. An actuator pin  107  is provided, which acts upon a gearing  207  of the control ring  210  in order to rotate the control ring  210  into different control positions. By rotating the control ring  210 , the displacement of the displacement pump  200  can be set between 0 and 100%. The control ring  210  is centred about a rotational axis ax 1 , which is eccentric to the centre axis ax 2  of the displacement pump  101 . In  FIG. 1 , the displacement pump  100  is provided with a control ring  210  disclosed in  FIGS. 2   a - e . The displacement pump  100  could however also be provided with a control ring  310  disclosed in  FIGS. 3   a - d.    
         [0036]    By turning the control ring  210  between 0 and 90 degrees the flow of the pressure medium from the displacement pump  200  can be controlled between  100  and zero % displacement. The control ring can be turned over 90 degrees, whereby the inlet and outlet  108 ,  109  change places, i.e., the flow direction becomes reverse, whereby the pumping unit  105  still rotates in the same direction. In the two embodiments of the control ring  210 ;  310  disclosed in  FIGS. 2   a - e  and  3   a - d  respectively, the variation in angular distance the axial openings  260 ;  360  travel over the lands  215 ,  216 ;  315 ,  316  is achieved for all turning angles of the control ring  210 ;  310 . 
         [0037]    The general function of the displacement pump  101  is known and will not be described further. With the control ring  210  according to the disclosure the displacement of the displacement pump  100  can be controlled by rotating the control ring  210  relative the rear plate  104  and thereby the pressure chambers of the pumping unit  105 . Due to the control ring  210  an angular distance that the axial outlets of the rear plate  104  passes over the land of the control ring and are fully blocked thereby, can be varied with the displacement of the pumping unit  105 . 
         [0038]      FIGS. 2   a - e  disclose a first embodiment of the control ring  210 . The control ring  210  has an inner diameter d and an outer diameter D, a first and a second axial surface  213 ,  214 , and an inner and an outer radial surface  211 ,  212 . The control ring  210  is centred about its rotational axis ax 1 . 
         [0039]    The first axial surface  213  is provided with an interface section  220  with a first and a second opening  221 ,  222 . The first and the second opening  221 ,  222  are separated with a first and a second intermediate sections, i.e., lands  215 ,  216 . The interface section  220  is adapted to connect to the pressure chambers of pumping unit  105  via the rear plate  104 . As can be seen in the  FIG. 1 , the first and the second opening  221 ,  222  are shaped as circular arcs and follow the circumference of the control ring  210 . It shall be noted that the control ring  210  could also be arranged directly against the pumping unit  105 ; this however is mostly suitable for a device with lower pressures. The first and the second opening  221 ,  222  are separated by a first and a second land  215 ,  216 . The first and the second opening  221 ,  222  are constructed by several smaller openings which all have a common upper space, such that the pressure in the whole opening  221 ,  222  is the same. 
         [0040]    In the embodiment disclosed in  FIGS. 2   a - e  the first and second openings  221 ,  222  of the control ring  210  are mouthing to the outer axial surface  212 , however at a different axial distance from the first axial surface  213 . The different axial distance of the mouthing is important in order to create two separate mouthing areas. A first, a second and a third seal ring  223 ,  224 ,  225  are thereby also provided at the outer radial surface  212 , in order to create mouthing spaces between the control ring  210  and the rear housing  102 . One of the inlet and outlet  108 ,  109  ( FIG. 1 ) is connected to a respective mouthing area/space between the seal rings  223 ,  224 ,  224 . 
         [0041]    Now, as can be seen in the Figures, the first and the second land  215 ,  216  are each provided with four tapered grooves  240 - 243 ,  244 - 247 . As can be seen, all the tapered grooves  240 - 247  extend from either of the first and second openings  221 ,  222  into either of the first and second lands  215 ,  216 . The broader edges of the tapered grooves  240 - 247  are directed towards the first or the second opening  221 ,  222  and the tips of the tapered grooves  240 - 247  are directed into the first or the second land. The tapered grooves  240 - 247  are further located in each corner of the first and the second land  215 ,  216 , such that they extend the first and second openings into the first and second lands. 
         [0042]    In  FIG. 2   b  the control ring  210  is disclosed with a cut out of the end plate  104  just where it abuts against the control ring  210 . The rear plate  104  is centered about the rotational axis ax 2  of the displacement pump  200 , whereby the control ring  210  is eccentric arranged relative the rear plate  104  and is centered about the rotational axis ax 1 . In the rear plate  104  the axial outlet openings  260  can be seen. At some point when the axial outlet openings  260  pass over the first and the second land  215 ,  216 , the axial outlet openings  260  are completely blocked by the first and the second land  215 ,  216  respectively. The blocking is necessary to avoid the high pressure chamber HP and the low pressure chamber LP to be connected. However, during the passing over the first and the second land  215 ,  216  respectively a pressure rise/pressure drop in the outlet openings  260  occurs, because of the blocking. 
         [0043]    The control ring  210  can be turned in order to change the displacement of the pumping device and thereby also change the position of the first and the second land  215 ,  216 . In 
         [0044]      FIG. 2   b , the control ring  210  is positioned such that the first land and the second land  115 ,  116  are positioned in between the high pressure chamber HP and the low pressure chamber LP of the pumping unit  105 . This position means that the displacement pump is controlled to deliver 100% displacement. At the transmission between the high pressure chamber HP and the low pressure chamber LP and vice verse, the pressure rises slowly. This means that a small pressure increase occurs for each angular distance α blocked outlet opening  260  travels over the first land  116  and a small pressure decrease occurs for each angular distance α blocked outlet opening  260  travels over the second land  216 . 
         [0045]    In  FIGS. 2   c - e  and  FIGS. 3   b - d  only one axial outlet  260  is illustrated together with the outlines for the rotational path for the axial outlets  260 , this to illustrate the movement of the axial outlets  260  over the first and the second land and function of the tapered grooves  240 - 247 . 
         [0046]    In  FIG. 2   c  the control ring  210  is in the same position as in  FIG. 2   b , i.e., 100% displacement. In  FIG. 2   c  the illustrated axial outlet  260  is in a position such that it just has become fully blocked by the first land  215 . In this position no pressure medium can be provided out from the illustrated axial outlet  260 . Further, in  FIG. 2   c , two different radial distances r 1 , r 2  from center axis ax 1  to the first land  215  of control ring are symbolically shown with arrows, whereby also two different angular distances ad 1 , ad 2  over the first land  215  are clearly visible. How the angular distance varies with the radial distance is dependent on shape of the tapered grooves  241 - 243 . The same applies for the second land  216 . 
         [0047]    In  FIG. 2   d  the control ring  210  is still in the same position as in  FIG. 2   c , however, the illustrated axial outlet  260  is in a position such that it is just about to open to the first opening  221 , i.e., not be fully blocked by the first land  215  anymore. The position of the axial outlet  260  in  FIG. 2   c  is shown with dashed lines. The axial outlet  260  has thereby moved as angular distance α between  FIG. 2   c  and  FIG. 2   d . The angular distance α is the angular distance the axial outlet  260  travels over the first land  215  and is fully blocked thereby, when the control ring  210  is positioned in a position for 100% displacement. It is preferred that the angular distance α is adapted such that the pressure increases in the axial outlets  260  during the movement over the first land  215  to the same pressure as in the first opening  221 . 
         [0048]    In the embodiment shown in  FIG. 2   d  the illustrated axial outlet  260  does not pass over the tapered grooves  240 - 243  in the first land  215 . However, for the disclosure, it is not important if the tapered grooves  240 - 243  are passed by the first land  215  or not. What is important is the angular distance the axial outlet  260  travels over the first land  215  and is fully blocked. The angular distance can be varied dependent on the position of the control ring  210  due to the control ring  210  is eccentric arranged relative the pumping unit  105  and the tapered shape of the tapered grooves  240 - 243 . 
         [0049]    The eccentric arrangement of the control ring  210  and the shape of the tapered grooves  240 - 243  are adapted such to each other that a change in position of the control ring  210  changes at which radial distance the axial outlets  260  are fully blocked by the tapered grooves  240 - 243  and are openeds to the first or second opening  221 ,  222  again. 
         [0050]    In  FIG. 2   e  the control ring  210  is arranged in a position for a 0% displacement. In this position the axial outlets  260  pass the longest distance over the tapered grooves  240 ,  242 , whereby the angular distance β that the axial outlets  260  are fully blocked by the first land  215  is the shortest than in any other position of the control ring  210 . In an ideal case the angular distance between the fully blocking of the axial outlets  260  and the reopening is zero, whereby no additional pressure will be able to be build up during the passing of the first land  215 . 
         [0051]    In the  FIGS. 2   a - e  only the first land  215  has been dealt with, and only the tapered grooves  240  and  242  are affected by the disclosed turning of the control ring  210 . However by turning the control ring  210  the same angular distance in an opposite direction as what is disclosed between  FIG. 2   d  and  e , the same effects are achieved with the tapered grooves  241  and  243 . 
         [0052]    Further the design of the second land  216  and its tapered grooves  244 - 247  is such that the axial outlets  260  are fully blocked the same axial distance over the second land  216  for one position of the control ring  210  as the axial outlets  260  are fully covered by the first land  215 . Hence, the second land  216  and its tapered grooves  244 - 247  are a mirroring of the first land  215  and its tapered grooves  240 - 243 . 
         [0053]    In  FIGS. 3   a - d  a second embodiment of the control ring  310  is disclosed. The control ring  310  differs from the control ring  210  in  FIGS. 2   a - e  in that it is provided with four tapered grooves  340 ,  341 ,  344  and  345 , instead of eight.  FIG. 3   a  discloses a perspective view of the control ring  310 .  FIGS. 3   b - d  show the control ring  310  and one axial outlet opening  360  and the travelling path of the outlet openings  360 . The description of  FIG. 2   c  and  FIG. 2   d  applies mutatis mutandis to  FIG. 3   b  and  FIG. 3   c  respectively and the description of  FIG. 2   e  applies mutatis mutandis to  FIG. 3   d . The numbering of the  FIGS. 3   a - d  corresponds to the numbering of the  FIGS. 2   a - e , whereby in  FIGS. 3   a - d  the numbering has the prefix 3 instead of 2 as in  FIGS. 2   a - e.    
         [0054]    Independent of which embodiment of the disclosure that is implemented, it is the relation between the shape of the tapered grooves  240 - 247 ;  340 ,  341 ,  344 ,  345  and the eccentricity of the control ring  210 ;  310  that determines the variation of the length of the first and the second land  215 ,  216 ;  315 ,  316 . Wherein the tapered grooves  240 - 247 ;  340 ,  341 ,  344 ,  345  and the eccentricity of the control ring  210 ;  310  is adapted such that a pressure in the axial outlets  260 ;  360  is adapted to a pressure in the one of the first and the second opening  221 ,  222 ;  321 ,  322  that the axial opening  260 ,  360  is open to next, i.e., that the pressure in the axial outlets  260 ;  360  is increased to the pressure of the high pressure opening when opened up to the high pressure opening and is decreased to the pressure of the low pressure opening when opened up to a low pressure opening. When implemented in a pumping device, the shape of the axial outlets  260 ;  360  of the pumping unit are adapted to the shape of the first and the second land  215 ,  216 ;  315 ,  316 , such to allow the difference in angular distance between closing and opening an axial outlet  260 ;  360  at different turning angles of the control ring  2160 ;  360 . 
         [0055]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.