Patent Publication Number: US-6213729-B1

Title: Suction-throttled pump

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a suction-throttled pump comprising at least one displacement body for the delivery of a medium in accordance with the preamble of claim  1 . 
     Suction-throttled pumps are known. They are used in motor vehicles, for example, and operated at varying speeds. The flow of medium required by the pump consumer is limited. At high pump speeds, the delivery rate of the medium would be too high. Therefore, a throttle valve, also referred to as a suction control valve, is provided in the suction region of the pump, i.e. between the pump and a reservoir or tank, and limits the quantity of medium sucked in. If pumps of this type are used in connection with a liquid medium, for example hydraulic oil, the static pressure in the suction region of the pump can drop below atmospheric pressure, with the result that foam forms. The dynamic properties of the pump are permanently impaired by the foam-containing oil. Furthermore, a pump displacer, which delivers the medium, is not uniformly filled on account of the foam, resulting in a non-uniform delivery rate. Moreover, the operating noises of the pump increase considerably. 
     SUMMARY OF THE INVENTION 
     Therefore, the object of the invention is to provide a suction-throttled pump of the aforesaid type which does not have these disadvantages. 
     A suction-throttled pump with features including at least one displacement body movable in a working chamber for delivery of a fluid medium, a suction chamber, an inflow channel between the delivery chamber and the suction chamber, and a suction control valve for the inflow channel is proposed in order to achieve this object. The pump is characterized in that the suction control valve co-operates directly with an inflow channel opening into a working chamber of a displacement body and extending between a suction chamber and this working chamber. The suction control valve is arranged at the end of the inflow channel facing the suction chamber so that there is only a minimal volume of oil in which the static pressure can drop below atmospheric pressure. Even if foam forms here, the foam quantities are so small that in practice they no longer have a detrimental effect on the dynamic properties, the pumping behavior or the noise generation of the pump. 
     A preferred embodiment of the pump comprises a plurality of valve bodies each having an inflow channel opening into the suction chamber. The suction control valve is characterized by a valve body associated with all the inflow channels. This produces a very simple pump design with optimum operating behavior. 
     A further embodiment of the pump is characterized in that the suction control valve is adjustable, consequently, the working rate of the pump is easily controllable. 
     Another embodiment of the pump comprises a cylinder block in which the displacement body or bodies are arranged. The cylinder block is characterized by a groove having an annular surface into which the inflow channel or channels open. The valve body of the suction control valve co-operates with this annular surface. This produces a very simple, but effective design which is inexpensive to manufacture and is distinguished by the fact that no more than a very small quantity of foam-containing oil is produced. 
     Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a partial longitudinal section through a first embodiment of a pump; 
     FIG. 2 shows a view of the suction control valve of the pump shown in FIG. 1; 
     FIG. 3 shows a partial longitudinal section through a second embodiment of a pump; 
     FIG. 4 shows a cross-section through the pump shown in FIG. 3; 
     FIG. 5 shows a partial longitudinal section through a pump with a suction control valve modified in relation to FIG. 3, and 
     FIG. 6 shows a further embodiment of the invention comprised of an axial piston pump. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The suction-throttled pump according to the invention comprises at least one displacement body for the working of a medium. The structure of the pump is irrelevant to the inventive solution described here. Consequently, the pump may be designed as an axial or radial piston pump. It is also possible to form the pump as a gerotor pump. 
     The following is based, purely by way of example, on a radial piston pump comprising four displacement bodies and provided for the delivery of a liquid medium. 
     FIG. 1 shows a partial longitudinal section through the interior of a pump  1  formed as a radial piston pump and comprising a cylinder block  3  in which at least one, in this case a plurality of displacement bodies are movably mounted. An upper displacement body  5   a  and a lower displacement body  5   b  are shown in longitudinal section. The displacement bodies, designated in short in the following by the reference numeral  5 , are housed in bores  9   a ,  9   b  extending radially to a drive shaft  7  and designated in short in the following by the reference numeral  9 . The displacement bodies  5  are cylindrical and to a certain extent cup-shaped, i.e. hollow inside. The base  11   a ,  11   b — 11  in short in the following—faces the drive shaft  7 , and a resilient member, formed as a helical spring  13 , is inserted into the interior of the displacement bodies  5  and is supported on a cover  15  closing the radially outer end of the bore  9 . The space enclosed by the displacement bodies  5  and the covers  15  forms the working chamber  17   a ,  17   b , designated in short in the following by the reference numeral  17 . The base  11  of the displacement bodies  5  co-operates with a cam  19  provided on the drive shaft  7 , the center axis  21  of the cam  19  being offset in relation to the rotation axis  23  of the drive shaft  7  so that, on rotation of the drive shaft  7 , the displacement bodies  5  are forced back into the bores  9  against the force of the helical spring  13  by varying amounts. In the representation shown here, the upper displacement body  5   a  is at top dead center, i.e. in a position in which the base  11   a  is at the maximum distance from the rotation axis  23 . In contrast, the displacement body  5   b  is at bottom dead center, in which its base  11   b  is at its shortest distance from the rotation axis  23 . As a result of the reciprocating movement of the displacement bodies  5 , the working chamber  17  becomes alternately larger and smaller, resulting in suction of the medium to be delivered or expulsion thereof. 
     A feed channel  25   a , extending parallel with the rotation axis  23 , opens into the working chamber  17   a . In the same way, an inflow channel  25   b , extending parallel with the rotation axis  23 , is associated with the working chamber  17   b . The medium to be delivered can pass from a suction chamber  27  into the working chamber  17  via the inflow channel  25 . The suction chamber is formed here as an annular groove  29 , the base of which faces the displacement bodies  5  and forms an annular surface  31 . 
     An annular discharge chamber  26  communicates with working chambers  17   a  and  17   b  by way of respective discharge passages  28   a  and  28   b . Conventional one-way discharge valves in each passage (not shown) prevent backflow into the working chambers during the suction cycles. A discharge opening  30  communicates with discharge chamber  26 . 
     The inflow channels  25  communicating with the suction chambers  17  open into the suction chamber  27 . It can be seen from the drawing that a suction control valve  33  co-operates directly with the inflow channels  25  and comprises a valve body  35 . The latter can comprise a plurality of ring segments or be formed as a continuous annular disc which rests on the annular surface  31  and thereby controls all the inflow channels  25  opening into the suction chamber  27 . Valve openings, designated in short in the following as openings  37 , are provided in the valve body  35 , one opening  37  preferably being associated with each mouth of an inflow channel  25  and covering the mouth to a varying extent. 
     The suction control valve, arranged upstream of the working chamber  17  in the immediate vicinity thereof, is adjustable and co-operates with an operating device  39  which can produce a rotation movement of the disc-shaped valve body  35  so that the openings  37  cover the mouths of the inflow channels  25  opening into the suction chamber  27  to a varying extent. 
     FIG. 2 shows a view of the suction control valve  33 . The valve body  35 , formed as a continuous annular disc, is clearly identifiable and has four openings  37   a ,  37   b ,  37   c  and  37   d  designated in short in the following by the reference numeral  37 . FIG. 2 also shows that the pump  1  has four displacement bodies  5   a  to  5   d  which co-operate with the cam mounted on the drive shaft  7  and form variable working chambers  17 , into which the medium to be delivered passes via inflow channels  25   a  to  25   d . The mouths of the inflow channels  25  are shown as circles which can be covered by the valve body  35 , the openings  37  uncovering the mouths of the inflow channels  25  to a varying extent. A reciprocating movement—indicated by a double arrow—of the operating device  39 , of which only an operating rod is shown and which substantially executes a translatory movement extending in the horizontal direction, produces a reciprocating rotation movement of the valve body  35 —indicated by a double arrow—so that the openings  37  thereof uncover the mouths of the inflow channels  25  to a varying extent. The movably constructed valve body  35  thus forms an adjustable suction control valve  33 . 
     FIG. 3 shows a partial longitudinal section through a modified embodiment of a pump  10 . Parts corresponding to those in FIG. 1 are provided with the same reference numerals. In this respect, reference is made to the description relating to FIG.  1 . 
     In the following, only the differences between the pump  10  and the pump  1  described with reference to FIG. 1 will be considered: the cylinder block  3  of the pump  10  has an annular groove  29 ′ in which a suction control valve  33 ′ is arranged. The latter comprises a valve body  35 ′ formed as a cylindrical ring or at least comprising cylindrical ring segments. Openings  37 , also designated as valve openings, are provided in the valve body  35  and are associated with inflow channels  25 ′ a  and  25 ′ b  comprising a channel portion  41  extending parallel with the rotation axis  23  of the drive shaft  7 , and a channel portion  43  intersecting the channel portion  41 , but extending perpendicularly thereto. The medium to be delivered can pass from the groove  29 ′, forming the suction chamber  27 , into the working chambers  17  or  17   a ,  17   b  through the in effect angular inflow channels  25 . The base of the groove  29 ′ forms a cylindrical annular surface  31 ′ arranged concentrically with the rotation axis  23 , whereas the annular surface  31  shown in FIG. 1 lies in a plane perpendicular to the rotation axis  23 . The valve body  35 ′ rests on this annular surface  31 ′. In this case too, it co-operates with an operating device  39  so that the displaceably formed valve body  35 ′ can be adjusted. With a rotational reciprocating movement of the valve body  35 ′, the openings  37  thereof overlap the mouths of the inflow channels opening into the suction chamber  27 , or more precisely the mouths of their radially extending channel portions  43 . The suction control valve  33 ′ can thus control the working of the medium fed into the working chambers  17 ; in this case too, there are only very small residual quantities between the suction control valve  33 ′ and the working chambers  17 , and thus only extremely small quantities of foam can be formed. 
     FIG. 4 shows a cross-section through the pump  10  described with reference to FIG.  3 . Like parts are provided with like reference numerals; in this respect, reference is made to the description relating to FIGS. 3 and 1. 
     The representation in FIG. 4 shows the inflow channels  25 , or more particularly their channel portions  41   a  to  41   d  and  43   a  to  43   d  extending axially and radially respectively. The sectional representation also shows that the openings  37   a  to  37   d  cover the radially outer mouths of the radially extending channel portions  43   a  to  43   d  to a varying extent, a translatory movement of the adjusting device  39 —indicated by a double arrow—producing a rotational reciprocating movement of the valve body  35 ′, likewise indicated by a double arrow. 
     Finally, FIG. 5 shows a partial longitudinal section through a pump  10 , wherein the suction control valve  33 ″ has been modified in relation to the suction control valve  33 ′ shown in FIG. 3 in that an operating device  39 ′ does not produce a rotation movement of the valve body  35 ″, but a translatory reciprocating movement indicated by a double arrow both on the operating device  39 ′ and on the valve body  35 ″. In the case of a translatory movement, the valve body  35 ″ is not rotated, but pushed into the groove  29 ′ to a varying extent so that the valve body  35 ″ is displaced on the annular surface  31 ′ of the groove  29 ′ in a direction parallel with the rotation axis  23 . The mouths of the radially extending channel portions  43   a ,  43   b , etc. are covered to a varying extent by the openings  37   a ,  37   b , etc., thus producing a variable throttle cross-section. It should also be pointed out here that a translatory movement can also be superposed by a rotation movement in order to produce a variable throttle cross-section. 
     It can easily be seen that the suction control valve can also be provided in the region of the cover  15  if the radial piston pump  10 , described with reference to FIGS. 3 to  5 , is designed accordingly, in which case a suction chamber  27  extending round the outside,of the cylinder block  3  would be provided. However, for the operation of the suction control valve, it would also be ensured here that only a very small amount of oil forms between the working chamber  17  and the suction control valve and only extremely small quantities of foam can form. 
     FIG. 6 illustrates the application of the suction control valve described shown in FIG. 5 for use in connection with pumps having displacement bodies which extend not radially, but axially, i.e. parallel with the rotation axis  23 , thereby producing axial piston pumps  10 ′. These may also have a plurality of displacement bodies  5   a  and  5   b , reciprocating in respective bores  9   a  and  9   b . The axial reciprocal motion may be achieved by use of a conventional swash plate mechanism which cooperates with spherical projections  40   a  and  40   b  on displacement bodies  5   a  and  5   b , respectively. Naturally, it is possible to use a suction control valve of the type described here together with a gerotor pump. 
     In all cases, it can be seen that the pump is of very compact construction and that the suction control valve co-operates directly with the inflow channels opening into the working chambers. For the design of the suction control valve, it is possible for the valve body to co-operate with a plurality of mouths of the inflow channels, for example to use ring segments as valve bodies and preferably to construct these so as to be movable. However, the structure of the pumps is particularly simple if the valve body is formed as a continuous disc-shaped or cylindrical annular member. In this case, all the inflow channels can be controlled by one operating device. 
     The structure of the suction control valve described here produces particularly good dynamics of the pump, i.e. it responds very quickly to a change in the position of the valve body. Moreover, the working chambers are filled better and more uniformly, as there are only extremely small amounts of foam to affect the behavior of the pump. This also results in better and more uniform pump working. In addition, noise generation is substantially reduced. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.