EP1448895A1

EP1448895A1 - Rotary piston pump

Info

Publication number: EP1448895A1
Application number: EP02787733A
Authority: EP
Inventors: Peter Schnabl; Paul Schnabl
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-11-20
Filing date: 2002-11-19
Publication date: 2004-08-25
Also published as: DE10156835C1; US20050019195A1; WO2003044372A1; DE10164813A1; DE10164813B4; JP2005509801A; AU2002352059A1

Abstract

The invention relates to a rotary piston pump comprising a housing (10), an annular piston (18) in the form of a tubular segment, which is connected to a shaft (22) in a rotationally fixed manner and which is guided rotationally and displaceably in an annular chamber (28,10) of the housing, said chamber being coaxial with the shaft (22). The rotary piston pump also comprises at least one inlet and one outlet which are configured in the housing in such a way that the inlet or outlet on the annular chamber side are located inside an axial area of a surface area of the annular chamber, said surface area being determined by the maximum axial distance of the wave troughs of the end surfaces that face each other. The invention is characterized in that the annular piston has control pockets which are open toward its axial end surface, said control pockets controlling the inlets and outlets, wherein the characteristics of the control pockets (38) and the inlets and outlets are selected in such a way that maximum volume flow of the medium to conveyed is enabled by the inlet (40) when the piston performs a stroke between the top and bottom dead center and by the outlet (56) when the piston performs a stroke between the bottom and top dead center.

Description

Rotary pump

The invention relates to a rotary lobe pump with a housing, an annular piston in the form of a tubular section which is connected in a rotationally fixed manner to a shaft which can be rotated in the housing and is rotatably and axially displaceably guided in an annular space of the housing which is coaxial to the shaft, the axially facing one another End surfaces of the annular space and the annular piston are designed as shaft surfaces with axially parallel amplitude and with at least one wave crest and a wave trough, and each with at least one inlet and one outlet channel, which are formed in the housing such that the inlet and outlet openings on the annulus side are within an axial area of an annular space surface, which is determined by the maximum axial distance of the mutually facing end faces.

Such a rotary lobe pump is known from DE 199 53 168 A. In the known rotary lobe pump, the inlet and outlet openings are controlled by the contour of the shaft surface of the annular piston. It has been shown that the opening cross-sections have to be made relatively small in order to be able to control the inlet and outlet of the medium to be pumped without additional control elements such as check valves. Furthermore, it has been shown that the changes in the opening cross section take place only relatively slowly due to the combined lifting and rotating movement of the piston, viewed over the angle of rotation of the piston. This prevents an optimal filling of the annular space at higher speeds due to the increasing throttle effect on the inlet side. Another disadvantage is that the inlet and outlet channels cannot be separated from one another at bottom dead center. Without an additional check valve, the medium to be pumped therefore flows back through the bottom dead center from the outlet-side high-pressure region into the inlet region, which is approximately at atmospheric pressure, during the passage of the annular piston. The above-mentioned phenomena affect the delivery capacity of the rotary lobe pump or require measures that make the structure of the rotary lobe pump more complicated.

The invention has for its object to design a rotary lobe pump of the type mentioned while maintaining the simplest possible structure so that the delivery rate of the pump can be increased significantly.

This object is achieved in that the annular piston to the axial end face of the annular space has open control pockets for controlling the inlet and outlet openings and that the position, shape and size of the control pockets and the inlet and outlet openings are chosen so that the inlet opening with a piston movement between the top and bottom dead center and the outlet opening with a piston movement between the bottom dead center and the top dead center allow a maximum volume flow of the medium to be conveyed.

Due to the design, only a certain angle of rotation of the ring piston is available for the release of the inlet or outlet opening. By providing the control pockets, it is possible to optimize the control of the opening cross section in the sense that as large a part of the opening cross section as possible Inlet openings are open during as large a part of the available rotation angle of the piston as possible in order to achieve a maximum volume flow of the medium to be conveyed into the annular space. So while the contour of the wave surfaces of the annular space and the piston are selected with a view to an optimal harmonic movement of the piston, the volume flow of the medium to be conveyed through the inlet and outlet openings can be optimized by the choice of the shape and the position of the control pockets. In addition, the position and shape of the control pockets can ensure that, during the passage of the annular piston through bottom dead center, ie when the end face of the annular piston has its maximum axial distance from the end face of the annular space facing it, a sealing of inlet openings and outlet openings is ensured against each other so that no medium can overflow. The use of additional valves for this is not necessary.

The control pockets preferably have at least approximately axially parallel control edges, the pocket bottom following at least approximately the contour of the shaft surface section lying between the control edges when viewed in the circumferential direction of the annular piston. This configuration of the control pockets ensures that the change in the opening cross section per angular path of the annular piston becomes maximum, so that the time available for the inflow and outflow of the medium to be conveyed is optimally used. For the same purpose it is proposed that the inlet opening has an axially parallel front and rear edge (based on the direction of rotation) and that the upper edge of the inlet opening close to the wave surface of the annular space is shaped such that it is approximately congruent with the contour of the shaft surface of the annular piston when the rear control edge of a control pocket reaches the front edge of the inlet opening, ie the inlet opening is closed. This shape of the inlet opening also takes into account that the annular piston not only performs a rotary movement but also an axial movement. The lower edge of the inlet opening, which is remote from the wave surface of the annular space, preferably follows at least approximately the path of movement of the front lower corner of a control pocket during the movement of the annular piston from top dead center to bottom dead center. In order to optimally use the angle of rotation or the period of time available for the inflow of the medium to be conveyed, it is expedient for a wave surface shape with two wave peaks and two wave troughs if the width of the inlet opening measured in the circumferential direction of the piston and the width of the control pockets are so coordinated with one another that the inlet opening over the complete Hu of the ring piston between the top dead center and bottom dead center is open.

Controlling the cross section of the outlet opening is less critical to the overall volume flow rate than controlling the cross section of the inlet opening. Preferably, however, the outlet opening is also designed so that its rear edge is directed at least approximately axially parallel, that a first portion of the upper edge of the outlet opening adjoining the rear edge of the outlet opening is directed parallel to the shaft surface of the annular piston when the front control edge of a control pocket faces the rear edge reached the outlet opening, and that a second section of the upper edge adjoining the first section of the outlet opening follows the contour of the edge of the control pocket when the annular piston has reached top dead center.

When using a rotary lobe pump of the type mentioned above, it may be desirable to be able to change the delivery volume of the pump at a constant speed or, conversely, to be able to keep the delivery volume constant while the speed of the ring piston is constantly changing. The latter case occurs, for example, when such a rotary lobe pump is used in the motor vehicle sector if the pump is driven directly by the vehicle engine, the speed of which is constantly changing during operation, without a change in the delivery volume of the pump being desired at the same time.

In order to solve this problem in the simplest possible way, it is proposed according to the invention that two annular space / annular piston arrangements are arranged coaxially to one another so that the pistons arranged on the same shaft move together between the end faces of the two annular spaces so that the two annular spaces have one fluid connection lying radially inside the annular piston are in communication with each other and that the radially inner wall of each annular space is formed by the outer surface of a control sleeve, which are arranged in the housing in a rotationally fixed but axially displaceable manner so that by means of a control drive they move between an axially inner position in which they block the fluid connection, and an axially outer position that at least partially releases the fluid connection is adjustable.

This solution makes it possible to control the delivery volume of the pump by pumping a more or less large portion of the volume back and forth between the two annular spaces, i.e. is not released to the outside of the pump. If the fluid connection is blocked by the control sleeves, the pump delivers its maximum delivery volume. If, on the other hand, the cross section of the fluid connection is opened more or less, less or more fluid is released from the pump to the outside. The opening cross section of the fluid connection can be selected so that no medium is released to the outside when the fluid connection is opened to the maximum, i.e. the pump does not deliver anything. If, for example, the pump is driven by a motor vehicle engine, the speed of which changes very frequently during operation, the axial displacement of the control sleeves can react very quickly and sensitively to such a change in speed and in this way the delivery volume of the pump can be kept constant despite the changing speed become.

The control sleeves are expediently continuously adjustable between their axially inner and outer end positions. In principle, the axially inner end of the control sleeves can serve as the control edge on the control sleeves. However, in order to take account of the axial movement of the annular piston during one revolution, it is expedient if the control sleeves have at least one control slot directed parallel to the axis, which enables the opening or control of the fluid connection independently of the axial movement of the annular piston. In the solution described above, the outlet and inlet openings are expediently formed in the respective radially outer wall of the annular spaces in order to ensure that the pump is as simple as possible. You can in the two ring pistons are known to be combined to form a one-piece double piston.

In order to ensure that the rotary lobe pump according to the invention runs smoothly and with little wear and tear required for high speeds, the annular piston should perform a harmonic oscillating movement in the axial direction. This means that the vertex of the piston contour, i.e. the summit of a wave mountain - viewed in one development - the function

y = A - cos x (1)

follows, where y denotes the axial stroke of the piston and x the angle of rotation of the piston. In order to achieve the goal set above, it is proposed according to the invention that the contour of the wave surface of the annular space - viewed in one development - in that of the functions

y = cos x (2)

and

y = cos

included area, the contours of the two sliding shaft surfaces are selected so that the shaft surfaces are continuous at least in the area in which they are brought together or touch each other when the piston rotates. While it seems obvious at first glance to design both mutually facing wave surfaces as pure sine surfaces, practice shows that with such a solution the piston can never rotate smoothly and uniformly. When the top dead center was reached, the two wave surfaces would be in full contact with one another. In order to move the piston further from this position, a special force and therefore a sudden change in the acceleration is required. Which in turn means that the piston not only runs extremely rough, but is also exposed to high wear. In the solution described above, this is minimized in that the contours of the shaft surfaces touch each other only at one point, which also moves back and forth when the ring piston rotates around the respective apex of the piston contour.

In the equations (2) and (3) given above, the amplitude factor A was set = 1 for the sake of simplicity. A can of course have a larger or smaller value.

In practice, after determining the contour of the wave surface of the annulus, the piston contour is determined so that the harmonic movement of the piston results. The contours of the two sliding shaft surfaces are expediently coordinated with one another in such a way that in the most wear-critical area, when the vertex of the piston contour sweeps over the vertex of the contour of the shaft surface of the annular space, the sum of the wear of the surfaces brought together is as small as possible, as will be described later is explained in more detail.

In a modified embodiment of the invention, the rotary lobe pump is designed such that a rolling element, for example a roller, a ball or a cone with a rotary axis directed radially to the piston axis, is mounted in the shaft surface of the annular piston in the region of the apex of a wave crest, wherein the contour of the shaft surface of the annulus is selected so that - viewed in one development - the bearing center of the rolling element runs on a curve given by the function y = A ^• cos x and the point of contact between the annular piston and the end face of the annulus is always on the piston rotation Rolling circumference lies. This means that the annular piston is not slidably guided on the shaft surface of the annular space or stator, but rather rolls with the roller on the shaft surface of the annular space or stator while it rotates about its axis. This solution can be particularly advantageous if the rotary lobe pump is used to pump non-lubricatable liquid media or gaseous substances shall be. This results in an improved wear behavior, since the relative movement between the ring piston and the stator is essentially absorbed by the bearing of the rolling element. Instead of the ring piston, the respective rolling element can also be mounted in the stator shaft surface.

The condition described above for the shape of the wave surface contour of the annular space is met by a line whose distance from the function y = A ^• cos x describing the path curve of the bearing center of the rolling element is equal to the rolling element radius in each point. In this case it is ensured that the axial movement of the ring piston corresponds to a harmonic oscillation.

It also applies to the modified embodiment that A can have any value in the formula y = A ^• cos x.

Further features and advantages of the invention will become apparent from the following description, which explains the invention with reference to exemplary embodiments in conjunction with the accompanying drawings. Show it:

1 is a schematic section containing the axis through a rotary lobe pump according to the invention,

Fig. 2 is a perspective view of the between the end faces of the

Rotary piston lying in the annular spaces of the rotary lobe pump shown in FIG. 1 without the housing,

3 shows a section along III-III in FIG. 1,

Fig. 4 is a schematic representation of the between the end faces of the

Annularly lying rotary pistons with the schematically illustrated inlet openings in 10 different rotary angle positions of the piston between 0 ° and 90 °, each by 10 °, 5 shows a representation of the rotary pistons corresponding to FIG. 4 with the schematically represented outlet openings in 10 rotary angle positions of the piston between 90 ° and 180 °, each different by 10 °,

6 corresponding to FIGS. 4 and 5 schematic representations of the

Rotary or ring pistons in various angular positions to explain the regulation of the delivery volume, the control sleeves being shown in an axially outer position,

7 shows a representation corresponding to FIG. 6 with the control sleeves in an axially central position,

Fig. 8 is a graph showing the shape of the contour of the

Wave surfaces of the annular piston and the associated annular space and

Fig. 9 is a graph showing the shape of the contour of the

Wave surfaces of the annular piston and the associated annular space in a modified embodiment of the invention.

Fig. 1 shows in a section containing the axis in schematic form a rotary lobe pump according to the invention with a cylindrical housing 10, the cylindrical bore 12 is closed by an end piece 14 and 16, respectively. In the space enclosed between the end pieces 14 and 16, a tubular annular piston 18 is mounted, which is connected via a linear bearing 20 in a rotationally fixed but axially displaceable manner to a shaft 22 which passes through the end piece 16 coaxially to the cylindrical housing 10. The ring piston 20 has at its axial ends a shaft surface 24 with which it is guided on a shaft surface 26 formed on the end piece 14 and 16, respectively. The rotary lobe pump described so far is explained in more detail in DE 199 53 168 A1. For the basic function of this pump, reference is made to this document. In the solution shown in FIG. 1, the annular space 28 lying between the shaft surface 26 of the first end piece 14 and the shaft surface 24 of the annular piston 18 facing it and the annular space lying between the shaft surface 26 of the lower end piece 16 and the shaft surface 24 of the ring piston 18 facing it Annulus 30 connected to one another by one or more axially parallel channels 32, which are indicated by dashed lines in FIG. 1. These channels form a fluid connection between the two annular spaces 28 and 30. In the upper end piece 14, a first control sleeve 34 is arranged in a rotationally fixed but axially displaceable manner, which forms the radially inner boundary wall of the annular space 28. A second control sleeve 36 is arranged in the end piece 16 in a rotationally fixed but axially displaceable manner, which forms the radially inner boundary wall of the annular space 30. Both control sleeves 34 and 36 can be adjusted axially by an actuator (not shown) in the direction of the double arrows shown in order to block the channels 32, ie the fluid connection between the annular spaces 28 and 30 or to open them more or less. The function of these control sleeves 34 and 36 will be explained in more detail later with reference to FIGS. 6 and 7.

In Figures 2 and 3 it can be seen that open control pockets 38 are formed in the annular piston to the respective shaft surface, which serve to control the inflow of the medium to be conveyed, and the outflow of the medium from the annular spaces 28 and 30 and their shape and interaction with the inlet and outlet openings will now be explained in more detail with reference to FIGS. 4 and 5.

4, the inlet openings 40 are shown, which represent the mouth of an inlet channel in the bore 12 of the housing 10. The respective inlet opening 40 has - with respect to the direction of rotation of the annular piston 18 - a front edge 42 and a rear edge 44, which are each parallel to the axis of the annular piston 18. The lower edge 46 and the upper edge 48 of an inlet opening are approximately parallel to the contour of the shaft surface 24 of the annular piston 18 when it is in its 90 ° position, as will be explained later. The control pockets 38 also each have a front edge 50 and a rear edge 52, which run parallel to the axis of the annular piston. The pocket 38 is open to the wave surface 24. The pocket bottom 54 runs approximately parallel to the contour of the wave surface 24 between the edges 50 and 52.

In the following, only the upper part of the double-piston pump shown in FIG. 4 is considered. At 0 °, the annular piston 18 is at its top dead center. In this position, the front edge 50 of the control pockets 38 is congruent with the rear edge 44 of the inlet opening 40. This means that the entire height of the inlet opening is available for changing the cross-section when the annular piston 18 leaves top dead center and moves in the direction of arrow A into the 10 ° Position rotates. In the further course of the rotation, the lower front corner of the control pocket 38 approximately follows the inclined lower edge 46 of the inlet opening 40, since the annular piston 18 also moves axially downward with the rotation. The entire cross section of the inlet opening 40 is available between 30 ° and 60 ° for the inflow of the medium. From 70 °, the rear edge 52 of the control pocket 38 slides over the inlet opening 40. At the transition from 80 ° to bottom dead center to 90 °, the entire height of the inlet opening is crossed again by the final piston edge. Due to the axially approximately the same length of the opening edges, approximately the same values of the change in cross section result during the opening and closing process. At 90 °, i.e. at the bottom dead center, the inlet opening 40 is closed. The upper oblique edge of the inlet opening is approximately congruent with the contour of the shaft surface of the piston, which specifies the maximum upper position of the edge 48 of the inlet opening. The width of the inlet opening and the arc length of the control pocket are coordinated with one another such that the opening duration of the inlet opening extends over the total stroke of the annular piston 18 between the top dead center and the bottom dead center, i.e. extends over the angle of rotation of 90 °. This part of the piston movement thus corresponds to the suction stroke in the upper annular space 28, which is thereby filled with the medium to be conveyed.

When the annular piston 18 moves from its bottom dead center (90 °) back to top dead center (180 °), the sucked-in fluid is now expelled again. This is shown in FIG. 5. 5 shows the contour of the outlet opening 56. The contour of the outlet opening results from the structural specifications that were made on the inlet side. At 90 ° (bottom dead center), the outlet opening 56 is still closed. The rear edge 58 of the outlet opening 56 runs parallel to the axis of the rotary piston 18 and is congruent with the front edge 50 of the control pocket 38. A first section 60 of the upper edge of the outlet opening 56 runs approximately parallel to the shaft surface 24 in this area. If the piston is moved from the bottom dead center in the direction of the 100 ° position, this results in a maximum change in the opening cross section. The axially parallel extension of the opening to the center is determined by the depth of the control pocket or by the minimum size of the resulting opening cross-section required in accordance with the performance requirements of the pump. The outlet opening 56 has its maximum opening cross-section between approximately 120 ° and 140 °. Then the outlet opening begins to close again. In the 180 ° position, ie top dead center, the outlet opening is completely closed. It can be seen that the second section 62 of the upper opening edge of the outlet opening 56 is adapted to the course of the lower edge 54 of the control pocket 38.

It can be seen that in FIGS. 4 and 5 the processes with respect to the lower annular space 30 are each shifted by 90 °. In the 0 ° position in FIG. 4, the lower inlet opening has just been closed and the discharge of the fluid from the annular space 30 explained with reference to FIG. 5 begins, while in FIG. 5 fluid is again sucked into the lower annular space 30.

6 and 7, it will now be explained how the flow of the fluid conveyed by the pump can be regulated with the aid of the control sleeves 34 and 36 shown in FIG. 1. 6 shows the ring piston in different rotational positions, the control sleeves always being maximally axially extended. In this position the effective volume flow rate is practically zero. The pump does not deliver any fluid. In contrast, when the control sleeves are retracted to the maximum, the pump delivers the maximum volume and thus behaves like the already known rotary lobe pump without this regulation by the control sleeves. Fig. 7 shows the pump with the control sleeves in a middle position. In Fig. 7 two superimposed representations of the pump belong together. The upper illustration shows the relevant function of the upper annulus or the upper chamber and the lower illustration shows the relevant function of the lower chamber. At top dead center (FIG. 7, right representation), the axially parallel front edge 50 of the control pocket 38 is congruent with the rear edge of an axially parallel slot 64, which is formed in the control sleeve 34. The upper chamber 28 is still closed inwards, ie towards the connecting channels 32. The lower chamber 30, on the other hand, is connected to the channels 32 by a cross-hatched cross section. When the piston is rotated by 10 ° (FIG. 7, second illustration from the right), the annular piston 18 releases an opening cross section to the inside. In this phase, fluid flows into the upper chamber 28, the fluid volume displaced from the lower chamber escapes into the interior of the pump and flows through the connecting channels 32 into the upper chamber 28 without pressure.

At approximately 50 ° after top dead center (FIG. 7, middle), the lower chamber 30 is closed. The remaining stroke volume is compressed in the outlet duct in the housing 10. The upper chamber 28 is still open to the inside. Since the connection to the lower chamber 30 is interrupted, the remaining intake volume is supplied from the inlet duct. This state continues with further piston rotation up to 80 ° after top dead center and 90 ° after top dead center. Then the process is repeated only with the reversal of the bars from the upper to the lower chamber.

In the position of the control sleeves 34 and 36 shown in FIG. 6, the processes explained with reference to FIG. 7 are repeated with the difference that the opening of the lower chamber remains inward during its entire compression stroke, so that the fluid contained therein is conveyed without pressure to the upper chamber 28 located in the intake stroke. With this setting of the control sleeves 34 and 36, the complete fluid volume changes between the upper and the lower chamber. Fluid does not flow to the pump nor is fluid released from the pump. The control sleeves are not shown in their fully inserted position. In this inner end position there is no opening inwards in the compression phase, so that the entire stroke volume is conveyed to the outlet. The suction chamber (corresponding to the upper chamber in FIGS. 6 and 7) is open to the inside, but sucks the entire fluid volume from the inlet, since there is no other possibility.

In the described embodiment, the control sleeves 34 and 36 are arranged in a rotationally fixed manner and can only be moved axially. This can be ensured, for example, via a vertical guide groove, which is not shown. Under certain circumstances, however, it can prove to be advantageous to superimpose a rotary movement on the pure axial movement in order to achieve a correspondingly desired operating behavior. This combined rotary-stroke movement can be achieved, for example, by a helical groove in the respective control sleeve, in which a pin connected to the respective part 14 or 16 engages.

The cross section of the connecting channels 32 is to be selected so that a practically throttle-free change of the fluid volume between the two chambers is ensured at the maximum speed of the pump. To adjust the control sleeves 34 and 36, a servomotor can be used on both sides, which converts the input signal (speed or volume flow or system pressure or combinations of these three variables) into a corresponding stroke position of the control sleeves. This allows the pump delivery volume to be regulated continuously, for example, to keep it constant at a variable speed.

A major advantage over known variable displacement pumps is that the control sleeves 34, 36 are adjusted without back pressure. This means that the adjustment can be carried out with relatively little energy and in a relatively short time, since the masses to be moved are very small.

The shape of the wave surfaces 24 and 26 will now be explained in more detail with reference to FIG. 8. The aim is to ensure a harmonious kinematic movement of the ring piston 18 when pumping. The contours of the to determine mutually sliding shaft surfaces 24 and 26 of the annular piston (rotor) and the end pieces 14 and 16 of the housing 10 (stator) so that this sequence of movements is ensured.

A harmonic kinematic sequence of motion of the piston exists if the translatory speed component of the piston is the basic equation of the speed of the harmonic oscillation

v = A ^• ω ^• cos (ω- 1)

Fulfills. This definition refers to an embodiment in which the piston performs a simple sine wave during one revolution. However, the derived relationships are equally valid for a double oscillation if the angular relationship "ω ^• t" is replaced by "2 ^• ω ^• t" on the time axis.

The derivation of the formulas reflects the conditions on the outer surface of the piston. However, this is not a prerequisite for the validity of the formulas. It is important that the derived relationships with regard to the kinematic process can be equally applied and applied to the entire diameter of the piston.

The development of the piston contour results in a function curve according to the equation

f (x) = y = A ^• cos (x)

A harmonious kinematic movement sequence with regard to the piston stroke is only given if the vertex 1 (FIG. 8) of the piston runs on the function y = cos x when the piston rotates. A can have any value, but is set = 1 for the sake of simplicity. Since the piston not only • rotates (progression of the contour in the x direction) but also moves axially (movement of the piston in the y direction), the sequence of positions of the piston contour is determined by a family of curves with the equation f (x, 0 = y = cos ( ^χ -c) - (1 - cos (c))

described. Since the piston is guided by the corresponding stator surface, it can only realize this sequence of movements from the top dead center position if the stator contour describes the envelope of the family of curves. The envelope equation is

, cos + 1. cos + 1 y = cos (x - arccos - - -) + - - -

As can be seen in FIG. 8, the envelope intersects the straight line y = -1 (bottom dead center axis) at an angle of 45 °. In the case shown, the stator curve at 180 ° must therefore have a peak with an angle of 90 ° (-45 ° - + 45 °) if the bottom dead center is to be y = -1 and φ = π = 180 °.

On the other hand, the piston must have a peak at its maximum (= apex at φ = 0 in FIG. 8) if the stator contour were designed according to the function f (x) = cos (x) and the piston over the total stroke of y = + 1 to y = -1 should perform a harmonic linear movement.

For reasons of smooth, smooth running and optimized wear behavior, tips on the stator or piston cannot be accepted. It is therefore advisable to choose a stator curve that lies between the two extremes, namely the function y = cos (x) (curve B in FIG. 8) and the function of the envelope (curve C in FIG. 8). An actual realistic stator curve is shown in FIG. 8 in the area enclosed by curves B and C and labeled D. It represents the envelope for the movement of the actual rotor curve E. In FIG. 8, the movement of a piston with the contour E is represented by a family of curves 1 to 9. The piston moves with ^• its apex 1 on curve B, which is represented by the function y = cos x. The apex passes through the various layers 1 to 9. The respective contact points of the rotor contour are at the apex the stator contour shown, characterized by the points V to 9 'on the envelope D.

At top dead center (x = 0), vertex 1 and touch point Y are identical. In the further course, the contact point leads, which with this design reaches a maximum in pos. 6-6 ^' (φ = π / 2). From φ = π / 2bis φ = π, the leading rises and in φ = π = 180 ° the apex and the point of contact coincide again.

The curve or contour E of the piston is therefore below or at most on the curve y = cos (x) and its shape is derived from the stator curve D such that the apex 1 on the curve y = cos (x ) lies and at the same time there is a contact point to the stator curve.

The choice of the two associated curves E and D is preferably such that in the most wear-critical area, when the vertex of the piston contour passes the vertex of the contour of the wave surface of the annular space, the sum of the wear of the surfaces brought together is as small as possible. In this area around φ = 180 ° the contact point has its lowest angular velocity, i.e. the point of contact moves comparatively slowly both on the apex of the rotor or the piston contour and on the apex of the stator. In addition, the opposite curvature behavior has a negative impact on the surface pressure. A shift of curve D from the position shown in FIG. 8 towards curve C means less wear on the piston at the expense of the stator, a shift of curve D towards curve B means less wear on the stator at the expense of the piston.

The assignment of the contours can be exchanged between the piston and the stator.

FIG. 9 relates to the modified embodiment described above, in which the annular piston represented by the contour line F of its shaft surface does not slide on the stator shaft surface represented by curve G, but on - -

this is guided by means of a roller 66. The roller 66 is mounted in a slot, not shown, formed in the shaft surface of the annular piston, so as to be freely rotatable about an axis of rotation directed radially with respect to the piston axis, which is designated by the bearing center 68.

In order to achieve a harmonious axial movement of the rotary piston, the bearing center 68 must run on a trajectory H when the annular piston rotates, which is described by the function y = A ^■ cos x. Provided that the roller 66 always touches the stator shaft surface when the piston rotates, this harmonic axial movement of the annular piston is obtained when the piston rotates when the contour G runs parallel to the curve H at a distance from the roller radius R. Each point of the contour line G is therefore on a normal to the curve y = cos (x) at a distance R.

The exact course of the piston contour F is not critical as long as it is ensured that the contour is withdrawn to such an extent that it cannot touch the stator contour G during a piston revolution.

Like FIG. 8, FIG. 9 always shows the curves with the factor A = 1. It goes without saying that this factor can assume any values.

The above statements have also been explained with reference to developments which always show the outermost lateral surface of the rotary body shown. In practice it has to be taken into account that the shaft surfaces and also the roller 66 (rolling elements) have a finite radial extension (in relation to the piston axis). However, this does not fundamentally change the conditions described.

Claims

Expectations

Rotary lobe pump with a housing (10), an annular piston (18) in the form of a pipe section, which is non-rotatably connected to a shaft (22) rotatable in the housing (10) and in an annular space (28) co-axial with the shaft (22), 30) of the housing is rotatably and axially displaceably guided, the mutually facing axial end faces (26, 24) of the annular space (28, 30) and the annular piston (18) being designed as wave surfaces with axially parallel amplitude and with at least one wave crest and a wave trough , and each with at least one inlet and one outlet channel, which are designed in the housing (10) in such a way that the inlet and outlet openings (40, 56) on the annular space side lie within an axial region of an annular space surface which is determined by the maximum axial distance of the mutually facing end surfaces (24, 26), characterized in that the annular piston (18) has control pockets (38) open towards the axial end surface (26) of the annular space (28, 30) for controlling the inlet and outlet openings (40 , 56) and that the position, shape and size of the control pockets (38) and the inlet and outlet openings (40, 56) are selected so that the inlet opening (40) during a piston movement between the top and bottom dead center and the The outlet opening (56) enables a maximum volume flow of the medium to be conveyed when the piston moves between the bottom and top dead center.

:. Rotary lobe pump according to claim 1, characterized in that the control pockets (38) have at least approximately axially parallel control edges (50, 52) and that the pocket bottom (54) at least approximately corresponds to the contour of the - viewed in the circumferential direction of the annular piston (18) - between the control edges ( 50, 52) lying wave surface section follows.

i. Rotary lobe pump according to claim 1 or 2, characterized in that the inlet opening (40) has an axially parallel front and rear edge (42, 44) (relative to the direction of rotation A) and that the upper edge (48) close to the shaft surface of the annular space (28). ) the inlet opening (40) is shaped like this, that it is approximately congruent with the contour of the shaft surface (24) of the annular piston (18) when the rear control edge (52) of a control pocket (38) reaches the front edge (42) of the inlet opening (40).

4. Rotary lobe pump according to claim 3, characterized in that the lower edge (46) of the inlet opening (40) remote from the shaft surface (26) of the annular space (28) is at least approximately the path of movement of the front lower corner of a control pocket (38) during the movement of the Piston (18) follows from top dead center to bottom dead center.

5. Rotary lobe pump according to one of claims 1 to 4, characterized in that the width of the inlet opening (40) measured in the circumferential direction of the annular piston (18) and the width of the control pockets (38) are coordinated with one another in such a way that the inlet opening (40) over the complete stroke of the ring piston (18) is open between top and bottom dead center.

6. Rotary lobe pump according to one of claims 1 to 5, characterized in that the rear edge (58) of the outlet opening (56) is directed at least approximately axially parallel, that a first section (60) adjoining the rear edge (58) of the outlet opening (56) the upper edge of the outlet opening (56) is directed parallel to the shaft surface (24) of the annular piston (18) when the front control edge (50) of a control pocket (38) reaches the rear edge (58) of the outlet opening (56), and that a The second section (62) of the upper edge of the outlet opening (56) adjoining the first section (60) follows the contour of the control pocket edge when the annular piston has reached top dead center.

7. Rotary lobe pump in particular according to one of claims 1 to 6, characterized in that two annular space / annular piston arrangements are arranged co-axially to one another in such a way that the pistons arranged on the same shaft (22) are located together between the end surfaces (26) of the two annular spaces ( 28, 30) move so that the two annular spaces (28, 30) over a fluid connection (32) lying radially within the annular pistons are connected to one another and that the radially inner wall of each annular space (28, 30) is formed by the outer surface of a control sleeve (34, 36) which is rotationally fixed but axially in the housing (10). are displaceably arranged so that they can be adjusted by means of a control drive between an axially inner position in which they block the fluid connection (32) and an axially outer position which at least partially releases the fluid connection.

8. Rotary lobe pump according to claim 7, characterized in that the control sleeves (34, 36) are continuously adjustable between their axially inner and outer end positions.

9. Rotary lobe pump according to claim 7 or 8, characterized in that the control sleeves (34, 36) have at least one control slot (64) directed parallel to the axis.

10. Rotary lobe pump according to one of claims 1 to 9, characterized in that the inlet and outlet openings (40, 56) are formed in the respective radially outer wall of the annular spaces (28, 30).

11. Rotary lobe pump according to one of claims 1 to 10, characterized in that the annular pistons form a one-piece double piston (18).

12. Rotary lobe pump in particular according to one of claims 1 to 11, characterized in that under the condition that during a piston rotation the apex of the piston contour (E) - viewed in a development - follows the function y = cos x, where y is the axial stroke of the piston and x denote the angle of rotation of the piston, the contour (D) of the shaft surface (26) of the annular space (28) - viewed in a development - in that of the functions

, , cosx + 1 . cosx + 1 y = cos x and y = cos (x - arccos ) + enclosed area, the contours (E, D) of the two shaft surfaces (24, 26) sliding against one another being selected so that the shaft surfaces (24, 26) at least in the area in which they are guided against one another or touch each other during piston rotation , are continuous.

13. Rotary lobe pump according to claim 12, characterized in that the contours (E, D) of the two sliding shaft surfaces (24, 26) are selected so that in the most wear-critical area, when the apex of the piston contour sweeps over the apex of the contour of the ridged surface of the annular space , the total amount of wear on the surfaces connected to one another is as low as possible.

14. Rotary lobe pump in particular according to one of claims 1 to 11, characterized in that in the shaft surface (F) of the annular piston in the area of the apex of a wave crest, a rolling body (66) which projects beyond the shaft surface (F) and has an axis of rotation directed radially to the piston axis is mounted and that the contour (G) of the shaft surface of the annular space is chosen so that - viewed in a development - the bearing center (68) of the rolling element (66) runs on a curve (H) given by the function Yy = A • cos x and the point of contact between the annular piston and the end surface of the annular space is always on the rolling element circumference during a piston revolution.

15. Rotary lobe pump according to claim 14, characterized in that the contour (G) of the shaft surface of the annular space is given by a line whose distance from the function describing the trajectory (H) of the bearing center (68) of the rolling element (66) is y = A ^• cos x is equal to the rolling element radius (R) at every point.