Rotary piston engine and method for operating a rotary piston engine

Abstract

The invention relates to a rotary piston engine comprising a housing which forms an interior space, two rotary pistons which are arranged in the interior space, an inlet opening for introducing a fluid into the interior space, and an outlet opening for the fluid, which is located in the interior space on a side opposite the inlet opening. Each rotary piston comprises at least two sealing strips and at least two recesses on the outer circumference thereof, wherein the shapes of the recesses and the sealing strips are selected to engage the sealing strips of a respective rotary pistons in the recesses of the respective other rotary piston. In addition, the sealing strips are dimensioned in the radial direction to sealingly contact an inner wall of the housing. The invention also relates to a corresponding method for operating a rotary piston engine.

Claims

1. A rotary engine comprising: a housing defining an inner room, two rotary pistons arranged in the inner room, an inlet opening for letting a fluid into the inner room, and an outlet opening for the fluid defined at the inner room at a side opposite to the inlet opening, wherein each rotary piston comprises at least two sealing strips and at least two recesses at its outer circumference, wherein the sealing strips are sized to sealingly contact a housing inner surface in a radial direction, wherein the sealing strips are comprised of a deformable material, wherein each of the sealing strips comprises a fluid contact surface facing inflowing fluid when the respective rotary piston is at a rotation angle position at which said sealing strip contacts the housing inner surface, wherein the shapes of the recesses and the sealing strips are sealingly engaged with the sealing strips of each one of the rotary pistons with the recesses of the respective other rotary piston, and wherein the fluid contact surface of each sealing strip has a concave shape.

2. The rotary engine as defined in claim 1, wherein each of the sealing strips has a rear side which is opposite the fluid contact surface and which does not face inflowing fluid when the respective rotary piston is at a rotation angle position in which said sealing strip contacts the housing inner surface, and wherein the rear side has a convex shape.

3. The rotary engine as defined in claim 1, wherein each rotary piston comprises at its respective outer circumference slots for receiving and securing the sealing strips and wherein the sealing strips are formed as slot nuts for securely coupling with the slots of the respective rotary piston.

4. The rotary engine as defined in claim 3, wherein the slots are formed as T-slots and each of the slot nuts respectively comprises a laterally protruding shroud for engaging with one of the T-slots.

5. The rotary engine as defined in claim 1, wherein each rotary piston comprises two sealing strips at opposite angle positions at its outer circumference, and wherein each rotary piston comprises exactly two recesses arranged at the outer circumference at angle positions which are each offset by 90 relative to the angle positions of the two sealing strips.

6. The rotary engine as defined in claim 1, wherein the sealing strips are sized such that, and a housing inner surface is formed such that the sealing strips sealingly contact the housing inner surface within a rotary angle range of the rotary piston.

7. The rotary engine as defined in claim 1, wherein each rotary piston comprises a gear rim at its outer circumference, and the rotary pistons are arranged such that their gear rims mesh.

8. The rotary engine as defined in claim 7, wherein the sealing strips protrude from their respective rotary piston further outwards in a radial direction than the respective gear rim.

9. The rotary engine as defined in claim 7, wherein the sealing strips protrude from the respective gear rim by a radial distance which is between 5% and 30%, in particular between 10% and 25%, of a radius of the gear rim.

10. The rotary engine as defined in claim 1, wherein an end portion of each fluid contact surface has a concave shape.

11. A waste heat recovery system comprising: a working fluid circuit in which a fluid circulates, a heat exchanger in which heat can be transferred from a medium to the fluid in the working fluid circuit, wherein the working fluid circuit is formed as a thermodynamic cycle, in particular as an organic Rankine cycle, and comprises means for converting heat energy of the fluid into motion energy, wherein the working fluid circuit comprises a rotary engine as defined in claim 1, in which fluid flowing through undergoes a pressure reduction and thus causes rotation of the rotary pistons.

12. The waste heat recovery system as defined in claim 11, wherein a generator is provided and configured to convert rotational energy of the rotary engine into electrical energy.

13. The waste heat recovery system as defined in claim 11, wherein the waste heat recovery system is part of a vehicle, and wherein the heat exchanger is arranged to transfer heat from exhaust gas to the fluid.

14. A method for operating a rotary engine, the method comprising: introducing a fluid through an inlet opening into an inner room of a housing of the rotary engine, providing in the inner room two rotary pistons which are rotated by the fluid, wherein each rotary piston comprises at its outer circumference at least two sealing strips and at least two recesses, wherein the sealing strips are each sized in radial direction for sealingly contacting a housing inner surface, wherein the sealing strips are each comprised of a deformable material, wherein each of the sealing strips comprises a fluid contact surface facing inflowing fluid when the respective rotary piston is at a rotation angle position at which said sealing strip contacts the housing inner surface, wherein the shapes of the recesses and the sealing strips are sealingly engaged with the sealing strips of each one of the rotary pistons with the recesses of the respective other rotary piston, wherein the fluid coming from the inlet opening pushes against some of the sealing strips, whereby said sealing strips are pushed against the housing inner surface, and wherein the fluid contact surface of each sealing strip has a concave shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention are described below with reference to the attached schematic figures in which:

(2) FIG. 1 is a cross-section of an embodiment of a rotary engine of the invention, and

(3) FIG. 2 is an enlarged detail of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(4) Similar components and components with similar effects are generally indicated with the same reference signs throughout the figures.

(5) FIG. 1 shows schematically a cross-section of an embodiment of an inventive rotary engine 100. An enlarged detail thereof is shown in FIG. 2.

(6) The rotary engine 100 is powered by a fluid which flows through it, and serves for converting energy of the fluid into rotational energy. To this end, the rotary engine 100 comprises as important components two rotary pistons 20 and 30 which are arranged in an inner room 11 which is limited by a housing inner surface 12 of a housing 10.

(7) An inlet opening 13 which is not shown in more detail allows fluid to enter the inner room 11. The fluid may in principle be any liquid or also any gas or mixture of a liquid and gas.

(8) An outlet opening 15 is furthermore provided at the inner room 11. If the fluid flows from the inlet opening 13 through the inner room 11 to the outlet opening 15, it must pass both rotary pistons 20, 30, and has to rotate these. The reference signs 21 and 31 mark the rotation axes of the two rotary pistons 20 and 30. The rotation axes 21, 31 extend into the drawing plane.

(9) The design of the rotary pistons 20, 30 is decisive for an efficient functioning. The rotary pistons shall provide a sealing to each other and a sealing to the surrounding housing inner surface 12 so that the fluid cannot reach the outlet opening 15 if the rotary pistons 20, 30 do not move.

(10) Simultaneously, the rotary pistons 20, 30 should be easily rotated by the fluid, i.e., the rotary pistons 20, 30 should already rotate at low pressure.

(11) To this end, the two rotary pistons 20 and 30 comprise sealing strips 25, 26, 35, 36 at their respective outer surfaces. The outer surfaces may be regarded as the shell surfaces of substantially cylindrical rotary pistons 20, 30. The sealing strips 25, 26, 35, 36 extend preferably over the whole height of the inner room 11, wherein the height may refer to a direction of the rotation axes 21, 31.

(12) In some variants, the rotary piston 20 comprises at least two, preferably exactly two, sealing strips 25, 26. Similarly, the rotary piston 30 comprises at least two, preferably exactly two, sealing strips 35, 36. The sealing strips 25, 26, 35, 36 extend radially beyond the remaining outer circumference of the respective rotary piston 20, 30. In these variants, the sealing strips 25, 26, 35, 36 are preferably received in slots at the respective rotary piston 20, 30, and may preferably consist of a material different to the part of the rotary piston 20, 30 in which the slots are formed. The sealing strips 25, 26, 35, 36 consist of a deformable material, which may be, for example, rubber, resin or a plastic material. In this way the sealing strips 25, 26, 35, 36 may be slightly deformed by fluid flowing against it, and may thus be pressed against the housing inner surface 12. In this way a particularly good sealing to the housing inner surface 12 is achieved. In principle, the sealing strips 25, 26, 35, 36 may also consist of a rigid material, for example a metal. Alternatively or additionally the sealing strips 25, 26, 35, 36 may be received with some leeway in their respective slots, and thus the fluid pressure slightly tilts the sealing strips 25, 26, 35, 36. In this way the sealing strips 25, 26, 35, 36 may in principle also be pressed against the housing inner surface 12.

(13) The two rotary pistons 20, 30 are arranged in the inner room 11 such that they contact each other. In this way, a fluid flow between the rotary pistons is substantially excluded. The rotation axes 21 and 31 may be parallel to each other. However, also a tilt between the rotation axes 21, 31 is possible as long as a substantially sealing contact between the rotary pistons 20, 30 is ensured.

(14) To this end, the rotary pistons 20, 30 also each comprise a gear rim 23, 33 at the respective outer circumference, which gear rim is rigidly connected with the remainder of the corresponding rotary piston 20, 30. The two gear rims 23, 33 are sized and arranged to intermesh. Thereby the two gear rims 23, 33 rotate jointly and form hardly any free spaces between each other. It is thus hardly possible for fluid to flow between the two gear rims 23, 33.

(15) Furthermore, the rotary pistons 20 and 30 comprise recesses 27, 28 and 37, 38, respectively, at their respective outer circumference. The number of recesses 27, 28 of the first rotary piston 20 is equal to the number of sealing strips 35, 36 of the second rotary piston 30. Similarly, the number of recesses 37, 38 of the second rotary piston 30 is equal to the number of sealing strips 25, 26 of the first rotary piston 20. Furthermore the recesses 27, 28, 37, 38 and the sealing strips 25, 26, 35, 36 are arranged at the two rotary pistons 20, 30 such that the sealing strips 25, 26 of the first rotary piston 20 mate with the recesses 37, 38 of the second rotary piston 30 when the two rotary pistons 20 and 30 rotate. Similarly the sealing strips 35, 36 of the second rotary piston 30 mate with the recesses 27, 28 of the first rotary piston 20. To this end, a recess and a sealing strip may alternate in 90 separations at the outer circumference of each rotary piston 20, 30, for example. In other words, the two sealing strips 25, 26 are distanced from each other by an azimuth angle of 180 (i.e., an angle of 180 about the rotation axes 21). Also the two recesses 27, 28 are separated from each other by an azimuth angle of 180, and by an azimuth angle of 90 relative to the sealing strips 25, 26. This is analogously valid for the sealing strips 35, 36 and recesses 37, 38 of the other rotary piston 30. In general, also other angles are possible. Other azimuth angles result in particular when there are more than two sealing strips and two recesses per rotary piston 20, 30. Size and shape of the recesses are thus chosen such that the sealing strips may be received therein, in particular in a sealing manner.

(16) Similar to the gear rims 23, 33, also the sealing strips 25, 26 35, 36 provide together with the recesses 27, 28, 37, 38 that fluid can hardly pass between the two rotary pistons.

(17) Independent from a current rotary position, always one of the sealing strips 25, 26 35, 36 of each rotary piston 20, 30 shall provide a sealing to the housing inner surface 12. To this end a rotation angle is relevant over which one and the same sealing strip 25, 26 35, 36 causes a sealing to the housing inner surface 12. This rotation angle may be larger than 180, as shown in FIG. 1, and may for example be between 185 and 240. To this end, the housing wall 12 may have the shape of a segment of a circle at each rotary piston, wherein this shape forms a segment of a circle which is larger than 180 and thus forms more than a semi-circle.

(18) FIG. 2 shows in greater detail the reception of the sealing strips 25, 26 35, 36 in their corresponding slots. For example, for all sealing strips 25, 26 35, 36, the sealing strip 35 is shown in its cross-section. The sealing strip 35 may have the shape of a profile, i.e., it may have the same cross-section throughout its length (in particular in the direction of the rotation axis 31). As shown, the cross-sectional shape forms a slot nut. Towards the inner end of the sealing strip, a collar 35C is formed, which engages with a T-shaped recess/slot. This inhibits that the slot nut may inadvertently come loose out of the slot of the rotary piston in a radial direction. Inserting and removing the slot nut 35 is possible in the longitudinal direction, i.e., in the direction of the rotation axis 31. By forming slot nuts, the sealing strips can be easily secured. Furthermore, also replacement is facilitated. This is relevant as gradual abrasion of the sealing strips 25, 26, 35, 36 may occur and may thus make a replacement necessary due to the sealing contact with the housing inner surface 12.

(19) As shown in FIG. 1, the fluid in the inner room 11 pushes against the rotary pistons 20, 30 and those sealing strips 25, 35 that face the inlet opening 13 in the momentary rotary position of the rotary pistons 20, 30. This pressure causes rotation of the rotary pistons 20, 30 in the direction of the arrows shown in FIG. 1.

(20) For the rotation and in particular for the sealing effect of the sealing strips 25, 35, the shape of the sealing strips is important. This is explained in more detail with respect to FIG. 2, which shows a sealing strip 35 which protrudes radially from the gear rim 33. The sealing strip 35 has a point of maximal radial extension or an edge which extends into the paper plane (or in the direction of the rotation axis 31). Starting from this edge, the sealing strip 35 has a surface 35A or fluid contact surface 35A facing the incoming fluid (this is valid for rotation positions in which the sealing strip 35 contacts the housing inner surface 12). On the opposite side of said edge, the sealing strip 35 comprises another surface 35B which is referred to as a rear side 35B. The rear side 35B does not face the incoming fluid when the sealing strip 35 contacts the housing inner surface 12.

(21) The fluid contact surface 35A comprises a recess or a concave shape, whereas the rear side 35B has an outwardly curved or convex shape. In this way, the outer end of the sealing strip 35, i.e., the radially furthest extending part, is deformed transversely or approximately perpendicularly to the radial direction by the fluid flowing against it. The sealing strip 35 is thus pressed against the housing inner surface 12. In FIG. 2, the lower end of the sealing strip 35 is deformed approximately to the left and thus against the housing inner surface 12.

(22) Advantageously, in this way a particularly good sealing may be provided, without however causing unduly high friction between the sealing strips and the housing inner surface. Advantageously, already at a comparably low fluid pressure, the rotary pistons may thus be set in rotation. Also fluids at low pressure may thus be used for energy use.

(23) A possible application is the usage of exhaust waste heat of a combustion machine. For example, an internal combustion engine of a vehicle emits exhaust gases with heat that can, in principle, be used. The heat may be transferred with a heat exchanger to a fluid in a working fluid circuit. For instance, the working fluid may be compressed and then relaxed in a basically known Rankine cycle or organic Rankine cycle (ORC). Here, it passes an engine which generates a rotational movement with the energy of the fluid. The rotary engine according to the invention is used as such a motor. In particular with the exhaust waste heat, pressures are produced at which hitherto used motors have a rather low efficiency. In contrast, the rotary engine of the invention allows efficient usage of exhaust waste heat energy. The produced rotational energy may in principle be used in any manner. In particular, it may be converted into electrical energy, for example with a generator. The electrical energy may be fed in a board grid of the vehicle and/or may be stored in an electrochemical battery of another storage.

(24) In the above embodiment a specific shape of the sealing strips is used. However, it must be stressed that also with other shapes generally suitable sealing properties may be provided, and the invention is not limited to the (preferred) shape of the sealing strips shown in the figures. It may thus suffice if the fluid contact surface or the rear side is formed as described. The other side may, for example, be flat or shaped like the other side. It is also possible that the described shapes of the fluid contact surface and the rear side are only formed at an end portion of the sealing strips and not across the whole part that radially protrudes beyond the corresponding gear rim. It may generally suffice for sufficient sealing properties if the sealing strips are deformable or movable relative to the gear rim and are, in particular, not formed integrally with the gear rim.