Flow-optimised vane pump

Abstract

The invention relates to a vane pump for conveying liquids, in particular viscous oils, which vane pump includes: a rotor having sliding slots in which movable vanes are held and can be countersunk in relation to a rotor radius (r); a pump housing including a pump chamber, which encloses the rotor; and an inlet and an outlet, which open into the pump chamber at at least one end face of the rotor; radial elevations protruding, with respect to the sliding slots, over the circumference of the rotor, which elevations form a rotor radius (r) on either side of the vanes that can be countersunk, and radial pockets being recessed, relative to the rotor radius (r), between the radial elevations. Within the radial elevations, recesses are formed on the at least one end face of the rotor at which the inlet and the outlet open, which recesses provide rotating anticipatory control geometry for reducing pressure spikes in the vane cells.

Claims

1. A vane pump for conveying liquids, comprising: a rotor having sliding slits into which slidable vanes are accommodated and retractable with respect to a rotational axis of the rotor; a pump housing having a pump chamber encompassing the rotor and an inner contour comprising a hollow cylinder that is excentric with respect to the rotational axis of the rotor or has at least a radial raising with respect to the rotational axis of the rotor such that vane cells that respectively take up a revolving partial volume of the pump chamber between two adjacent vanes pass through a volume increase and a volume decrease as a function of the inner contour of the pump chamber; and an inlet in a rotational angle range of the volume increase and an outlet in the rotational angle range of the volume decrease which each open at least towards a face side of the rotor into the pump chamber; wherein across the circumference of the rotor, radial raisings protruding from the rotor towards the sliding slits form a rotor radius to each side of the retractable vanes, and, between the radial raisings, radial pockets are recessed with respect to the rotational axis of the rotor; wherein within the radial raisings at at least one face side of the rotor, to which the inlet and the outlet open, a recess is formed.

2. The vane pump according to claim 1, wherein the recesses comprise, in a radial direction of the rotor, at least two adjacent radial portions that differ from one another with reference to a depth of the recesses with respect to the surface of the at least one face side of the rotor.

3. The vane pump according to claim 1, wherein a radial portion of the recesses which is located further inwards in a radial direction of the rotor comprises a larger depth, and an adjacent radial portion of the recesses which is located further outwards in a radial direction of the rotor comprises a smaller depth.

4. The vane pump according to claim 1, wherein a contour of the recesses or of a portion of the recesses extending in a radial direction is constant along the circumferential direction of the rotor.

5. The vane pump according to claim 1, wherein the recesses or a portion of the recesses extending in a radial direction form a groove having an oblong, v-shaped or u-shaped contour.

6. The vane pump according to claim 1, wherein a distance between a mouth of the inlet and a mouth of the outlet into the pump chamber essentially corresponds to the distance between two vanes.

7. A hydraulic pump for generating a constant pressure for hydraulic actuators or drives comprising a vane pump according to claim 1.

8. The hydraulic pump according to claim 7, further comprising: a volumetrically variable pump geometry, wherein a distance is settable between the rotor radius (r) and the inner contour of the hollow cylinder that is excentric to the rotor axis or the radial raising of the pump chamber by means of an actuator.

9. The hydraulic pump according to claim 7, wherein the hydraulic pump is a drive source in a hydraulic steering assistance system for vehicles.

Description

(1) The invention will be explained hereinafter with the aid of exemplified embodiments and with reference to the accompanying drawings, in which:

(2) FIG. 1 shows an open plan view of a volumetrically adjustable vane pump according to a first embodiment of the invention;

(3) FIG. 2 shows a perspective view of a rotor having a recess according to the first embodiment of the invention;

(4) FIG. 3 shows a perspective view of a rotor having a face-side recess according to a second embodiment of the invention;

(5) FIG. 4 shows a virtual view of a simulation of a normalized pressure progression in the pump chamber during a volume closure of a vane cell between the outlet and inlet;

(6) FIG. 5 shows a virtual view of a simulation of a normalized flow progression which results according to the pressure progression of FIG. 6; and

(7) FIG. 6 shows a graph of a normalized initial pump pressure in dependence upon a rotational angle of the rotor for a vane pump in accordance with the invention and a conventional vane pump.

(8) The structure of the vane pump in accordance with the invention will be described hereinafter with reference to FIGS. 1 to 3.

(9) FIG. 1 shows a view of an open pump housing 1 of a volumetrically adjustable vane pump, from which a pump cover has been removed. In order to be able to set the conveyed volume flow independently of a rotational speed of the pump, the pump has a variable pump geometry which is adjusted by means of a displacement between two housing parts.

(10) An outer housing part 1a forms a main part of the pump housing 1 and accommodates an inlet 5, an outlet 6 and an actuator 7 with a return spring 70 therein. Furthermore, a rotor 2 is mounted in a rotatable manner on the outer housing part 1a and so the rotor 2 and the outer housing part 1a define a fixed component in relation to the adjustment movement of the variable pump geometry. A lifting ring 1b which comprises the pump chamber 10 is accommodated together with a guide ring 13 arranged coaxially with respect thereto as an inner housing part in a displaceable manner in the outer housing part 1a, and thus forms a movable component in relation to the adjustment movement of the variable pump geometry.

(11) The lifting ring 1b forms a chamber wall of the pump chamber 10 in the form of a hollow cylinder. An inner contour 12 of the cylindrical pump chamber 10 extends excentrically in relation to the rotor 2, wherein a measure of the excentricity or a distance of the centre points of the pump chamber 10 and of the rotor 2 are set in dependence upon a linear displacement of the lifting ring 1b with respect to the outer housing part 1a. The adjustment movement is performed by actuating an actuator 7 which is not explained further and which generates an actuating force along the adjustment path and in so doing pretensions the return spring 70 for a reversible actuating movement.

(12) The guide ring 13 is arranged on both sides with respect to the axial ends of the rotor 2 and concentrically with respect to the inner contour 12 of the pump chamber 10. The guide ring 13 is fixedly connected to the lifting ring 1b and so it always has the same excentricity as the pump chamber 10 with respect to the rotor 2 in any position of the adjustment path. The same arrangement of a guide ring 13 is provided on the opposite axial side, not illustrated, of the rotor 2.

(13) The rotor 2 has sliding slits 23, in which radially oriented blocking vanes 3 are accommodated in a displaceably mounted manner. A radial extension of the blocking vanes 3 corresponds to a distance between the guide ring 13 and the inner contour 12 of the pump chamber 10 and so the inner ends of the blocking vanes 3 slide on the guide ring 13, and the outer ends of the blocking vanes 3 slide in the inner contour 12 of the pump chamber 10 while the blocking vanes 3 are guided through the pump chamber 10 by means of a rotation of the rotor 2 on a circular path. Moreover, since the guide ring 13 and the inner contour 12 extend excentrically with respect to the rotor 2, the blocking vanes 3 also slide in the radial direction in and out of the sliding slits 23. The blocking vanes 3 are completely retractable with respect to a rotor radius r in the sliding slits 23.

(14) A maximum flow being conveyed by the pump is achieved if the lifting ring 1b is displaced together with the guide ring 13 to a maximum excentricity with respect to the rotor 2 and so the inner contour 12 almost comes into contact with a rotor radius r of the rotor 2. In such a position, a maximum volume change of the vane cells between the blocking vanes 3 is achieved during a rotor revolution of 180° in the pump chamber 10. In contrast thereto, a minimum flow being conveyed by the pump is achieved if along the adjustment path a position is taken up, at which essentially there is no longer any excentricity, i.e. a centre point of the rotor 2 and a centre point of the guide ring 13 are arranged coaxially and so the revolving vane cells within the pump chamber 10 do not undergo any volume change.

(15) In an upper region of FIG. 1, in each case a crescent-shaped depression which forms a mouth of the outlet 6 into the pump chamber 10 extends in the face-side chamber wall of the pump chamber 10 at both axial ends of the rotor 2. Substantially axially symmetrical thereto, in a lower region of FIG. 1, in each case a crescent-shaped depression which forms a mouth of the inlet 5 into the pump chamber 10 extends likewise at the two axial ends of the rotor 2. In conjunction with the indicated anticlockwise rotational direction of the rotor 2, a volume of the vane cells decreases in the upper rotational angle range and increases in a lower rotational angle range, whereby a displacement and intake procedure is effected between the revolving vane cells and the outlet 6 or inlet 5.

(16) A distance c is provided between an end of an opening contour of the crescent-shaped mouth of the outlet 6 and a start of an opening contour of the crescent-shaped mouth of the inlet 5 in relation to the rotational direction. Within a revolution distance of the distance c, the face-side chamber wall is in sliding contact with the blocking vanes 3 and a face surface 22 of the rotor 2.

(17) Furthermore, the rotor 2 has on the circumference radial raisings 21 which taper towards the sliding slits 23 and define the rotor radius r of the rotor 2 at the sliding slits 23. Between the radial raisings 21, radial pockets 20 are recessed in the rotor radius r and form a clearance volume which promotes a flow behaviour and sealing of the effective working volume outside the rotor radius r in the vane cell.

(18) If the rotor 2 rotates and the vane cells between the blocking vanes 3 are guided in a revolving manner through the pump chamber 10, the volume of the vane cells increases in the rotational angle range of the crescent-shaped mouth of the inlet 5 and so the medium being conveyed or hydraulic oil is drawn into the pump chamber 10 as long as there is a connection between the vane cell and inlet 5. In the subsequent rotational angle range of the crescent-shaped mouth of the outlet 6, the volume of the vane cells decreases and so the hydraulic oil is displaced or urged out as long as there is a connection between the vane cell and outlet 6. In a rotational angle of the distance c lying between the mouth of the outlet 6 and the mouth of the inlet 5, the volume of the vane cells is closed because in the meantime there is no connection to the inlet 5 or to the outlet 6.

(19) If the leading blocking vane 3 of a vane cell passes through the distance c and the trailing blocking vane 3 of this vane cell moves towards the end of an opening contour of the crescent-shaped mouth of the outlet 6, a circumferential slope of the corresponding radial raising 21 initially reaches an edge at the end of an opening contour of the crescent-shaped mouth of the outlet 6 in the face-side chamber wall of the pump chamber 10. At this point in time, a connection cross-section, through which the decreasing volume of the vane cell upstream of the trailing blocking vane 3 is urged out of the pump chamber 10 to the outlet 6, is considerably reduced or already substantially closed if a setting position of the pump chamber is located on the adjustment path at an end position with respect to the rotor radius r. Subsequently, the blocking vane 3 passes beyond the end of the opening contour of the crescent-shaped mouth of the outlet 6 and completely closes a connection between the vane cell and the outlet 6. Shortly after this or essentially at the same time, the leading blocking vane 3 passes beyond an edge at the beginning of an opening contour of the crescent-shaped mouth of the inlet 5 in the face-side chamber wall of the pump chamber 10 and the closed volume of the vane cell is then opened with respect to the inlet 5. The short-term closure of the volume of the vane cell ensures a constant barrier between the crescent-shaped mouths of the inlet 5 and outlet 6 in order to preclude a hydraulic short-circuit between the inlet 5 and the outlet 6.

(20) FIG. 2 shows a recess 4 according to a first embodiment of the invention. The recess 4 extends on a face side of the rotor 2 starting from a radial pocket 20 over the radially protruding cross-section of a radial raising 21. The recess 4 is subdivided into a radially outer portion 40 and a radially inner portion 41 which differ from one another by virtue of a different depth of the recess 4. The face-side surfaces both of the inner portion 41 and the outer portion 40 of the recess 4 are recessed with respect to a radially further inwardly lying face surface 22 of the rotor 2.

(21) If a blocking vane 3 moves towards an edge at the end of the opening contour of the crescent-shaped mouth of the outlet 6, wherein the blocking vane is inserted or retracted in the sliding slit 23 and the upstream circumferential slope of the radial raising 21 has already passed beyond the edge at the end of the opening contour, substantially no opening cross-section, through which the medium being conveyed or hydraulic oil can escape during the further volume reduction, remains at the circumference of the rotor 2. However, a small opening cross-section still remains on the face-side through the recessed surfaces of the recess 4 to the chamber wall of the pump chamber 10, whereby hydraulic oil is able to escape at a later stage before the trailing blocking vane 3 passes beyond the end of the edge of the opening contour of the crescent-shaped mouth of the outlet 6 and finally breaks a connection between the volume of the vane cell and the outlet 6. Therefore, shortly before the volume closure of the vane cells, an extended equalising flow is permitted through the recesses 4 in the face surface of the rotor 2, said flow limiting or reducing a pressure increase in the vane cells.

(22) Within the recess 4, the inner portion 41 with the larger depth assumes the function of a channel which feeds hydraulic oil from the clearance volume of the radial pocket 20. The outer portion 40 with the smaller depth produces a defined flow resistance by reducing the size of the flow cross-section in a radial exit direction. Therefore, on the basis of the depth of the outer portion 40 and the geometry of the recess 4 it is possible to select a flow resistance to prevent a potential leakage flow which can occur for a short time through the vane cells by reason of distance c which is as short as possible and a pressure difference between the inlet 5 and the outlet 6.

(23) FIG. 3 shows a recess 4 according to a second embodiment of the invention. The second embodiment differs from the first embodiment by virtue of the inner portion 42 of the recess 4. Instead of the oblong or U-shaped contour of the inner portion 41 of the recess 4 of the first embodiment, the inner portion 42 of the recess 4 of the second embodiment has a V-shaped contour. Therefore, the recess 4 of the second embodiment forms a flatter graduation between the inner portion 42 and the outer portion 40, thus resulting in a larger flow cross-section. The graduation of the recess 4 according to the first embodiment or the second embodiment and the depth can be selected in a suitable manner e.g. in dependence upon a viscosity of the designated medium being conveyed or the hydraulic oil.

(24) FIG. 4 shows, as a result of a virtual simulation of the pump operation, a pressure progression of the vane cells in the pump chamber 10 with reference to differently denoted regions.

(25) On the left-hand side in FIG. 4, a pump geometry without the recesses 4 is simulated. The illustrated volumes of the vane cells correspond, in relation to the opening contours, sketched thereover, of the crescent-shaped mouths of the inlet 5 and the outlet 6, to the same rotational angle position of the rotor 2 as in FIGS. 1 and 2. From the simulation, it is evident that a pressure peak passes through a vane cell in the bottom left position which travels the distance between the mouths of the inlet 5 and the outlet 6 while the volume of the vane cell is closed. If the vane cell moves further in an anticlockwise direction, it passes into a rotational angle range of the inlet 5, in which a negative pressure prevails in the vane cell until a volume increase ends at a position opposite the region of the pressure peak. Subsequently, by reason of a volume decrease a pressure increase begins in the vane cell which ends shortly before a volume closure in the described pressure peak.

(26) On the right-hand side of FIG. 4, the simulation shows an inventive pump geometry with recesses 4 in the face sides of the radial raisings 21 of the rotor 2. As can be seen in the perspective view of the hollow spaces in the pump chamber 10, the volumes of the vane cells fill the free spaces of the recesses 4 on both sides with respect to the blocking vanes 3 on the face-side. During the progression of the rotor rotation over time, the filled free spaces represent, in conjunction with the opening contours of the crescent-shaped mouths of the inlet 5 and the outlet 6, an extension of an opening cross-section for an equalising flow. As shown in the illustration, the virtual simulation for the pump geometry with the recesses 4 as illustrated on the right-hand side brings about a substantial reduction in the pressure peak to a level which corresponds substantially to that of the displacement phase which has been previously passed through and in which there is a complete opening to the mouth of the outlet 6.

(27) FIG. 5 shows a distribution of the pressure-equalising flow from a vane cell shortly before the volume closure, wherein the rotational angle position again corresponds to that of FIGS. 1 and 4. The size and length of the illustrated vector arrows corresponds to a flow rate or a volume flow per unit area of the flow cross-section.

(28) In the left-hand illustration which relates to a pump geometry without the recesses 4, the vector arrows in the centre of the illustration which emerge at the edge of the opening contour of the mouth of the outlet 6 are very much larger than the vector arrows in an upper region of the illustration which represent a flow of the urging-out phase of the subsequent vane cell. This high flow rate results from the small opening cross-section which remains in an overlap of the radial raising 21 with the opening contour of the mouth of the outlet 6.

(29) In contrast thereto, the right-hand illustration of the pump geometry with the recesses 4 illustrates the larger remaining opening cross-section between the vane cell and the outlet 6 after the radial raising 21 has already partially passed the opening contour of the mouth of the outlet 6. The upwards pointing vector arrows show that the flow rate in the critical range is still greater than that in the displacement phase of the subsequent vane cell. However, when comparing the left-hand illustration and the right-hand illustration, it can be stated that a reduction in the increase in the flow rate is achieved by the recesses 4.

(30) FIG. 6 shows a graph of an output-side conveyance pressure of the pump in dependence upon a rotational angle of the rotor 2. A broken line indicates a pressure progression for a pump geometry without the recesses 4 and a solid line indicates the pressure progression of an inventive pump geometry with recesses 4. The pressure progression and a resulting distribution of the flow rate which have been explained with FIGS. 4 and 5 propagate to the outlet 6 of the pump and accordingly produce a fluctuation in the output-side conveyance pressure of the pumps. In comparison with a conveyance pressure which is normalized to the average value and in FIG. 6 is 1.00 [−], a pressure fluctuation having a difference value of 0.23 [−] occurs in the case of a conventional rotor 2 each time a vane cell is passed, whereas the pressure fluctuation is lowered by the inventive pump geometry with recesses 4 to a pressure fluctuation having a difference value of 0.19 [−].

(31) Apart from the illustrated and described embodiments, the vane pump for utilising the invention can likewise have a different pump housing 1. For example, the pump housing 1 can have different kinematics for the purpose of volumetric adjustment, in which between an inner contour of the pump chamber 10 and the rotor 2 a pivoting movement follows instead of a linear displacement, as is known from other types of variable pumps. Furthermore, the pump chamber 10 can have an inner contour 12 other than that of an excentric hollow cylinder. For example, the inner contour 12 of the pump chamber 10 can have at least one cam-shaped raising with respect to the rotor radius r.