Field of Invention

The invention relates generally to a pressure reducer (also called „expander") for rotary internal combustion engines, and more specifically, to a pressure reducer having intermeshing rotors.

Background Art

Rotary internal combustion engines take advantage of a cycle of distinct intake, compression, combustion-expansion and exhaust processes as in a four stroke cycle. Pressure reducers are used in the combustion cycle for expanding gases passing through the engine before they are exhausted.

The basic example of such an engine is the Wankel engine. In a modern version a stator is in the shape of a two-lobed epitrochoid and a rotor is a trochoid. This symmetrical trochoid rotor revolves on a large bearing on the crank arm of the crankshaft which is an eccentric on the driveshaft. The three tips of the trochoid rotor have tip seals. An internal gear on the rotor, concentric with the rotor bearing, constrains the rotor to a planetary motion about a sun gear, concentric with the crank shaft.

A later development of a rotary internal combustion engine is described in US 3, 724, 427. A plurality of segregated chambers are arranged in communicating relation with one another for compression, combustion and expansion of the gases. Each of the chambers comprise a rotary pump for example in the form of a pair of multi-lobed intermeshing rotors mounted on two parallel drive shafts within a housing. The rotors together with the housing establish chambers, the volume of which is changing when the rotors are rotating with in the housing, such that the changing volume can cause the expansion of the combustion gases. Such arrangements often are subject to a high level of wear, which impacts the expansion capacity of the engine.

Various other expanders have also been proposed in the prior art, such as for example disclosed in US 4,963,079 or US 5, 393, 209.

Description of the invention

It is an object of the invention to improve a pressure reducer for a rotary internal combustion engine, in particular to provide such a pressure reducer with a high expansion capacity and enlarged mechanical potential, which needs a small number of components, and has a long service-life.

These and other objects, which will appear from the description below, are achieved by a pressure reducer for a rotary internal combustion engines set forth in the appended independent claim. Preferred embodiments are defined in the dependent claims.

In particular the objects of this invention are realized by the following technical solutions. According to the invention a pressure reducer for a rotary internal combustion engine comprises a housing, which accommodates a first shaft and a second shaft running parallel to each other through the housing. Further the pressure reducer comprises a first rotor on the first shaft and a second rotor on the second shaft. The first rotor and the second rotor are configured in a meshing arrangement, when the first shaft and the second shaft rotate in counter direction to each other. To realize the meshing arrangement the first rotor comprises several radial extensions having non-circular convex shaped outer flanks, and the second rotor comprises several radial wings defining indentations in between two wings having a non-circular concave shaped surface. When in meshing into each other the extensions and indentations define a pressure expansion chamber in between themselves. The pressure expansion chamber is defined by a volume between a convex shaped flank of one of the extensions of the first rotor and a concave shaped surface of one of the indentations of the second rotor. The convex flank lies opposite of the convex surface, when the extensions reaches into the indentation. An outer tip of the radial extension abuts on the concave shaped surface of the indentation and an outer edge of the indentation, that means an edge of the wing, abuts on the convex shaped surface of the extension. The shapes of the convex flanks and the concave surfaces are realized such, that in rotation the indentation and extension contact each other simultaneously at only two distinct contact points at said outer tip of the extension on the concave shaped surface on the one end and at the outer edge of the indentation on the convex shaped flank of the extension on the other end.

The expansion of the pressure expansion chamber is used to reduce the pressure of gases trapped with in the chamber during the rotation of the to rotors within the housing. The pressure expansion provided by the pressure expansion chamber according to the invention guarantees a reliable pressure release of high efficiency due to the well-defined work space between the meshing rotors. However, not many parts are required to realize the pumping of the gases and the pressure reducer can be produced at low costs. In one embodiment of the pressure reducer according to the present invention the housing comprises an inlet opening culminating in an inlet chamber within the housing. The inlet chamber is defined by a convex flank of the first rotor, a concave surface of the second rotor and a first inner surface of the housing. In the area defining the inlet chamber the extension of the convex flank and the indentation of the concave surface are not yet in a meshing engagement . By rotation of the rotors the extension reaches into the indentation. By doing so the pressure expansion chamber is established and the gas present in the inlet chamber is trapped within the pressure expansion chamber.

On the opposite side of the inlet opening the housing comprises an outlet opening out of an outlet chamber defined within the housing. The outlet chamber is defined by a further convex flank of the first rotor, a further concave surface of the second rotor and a second inner surface of the housing. The second inner surface is opposing the first inner surface. The outlet chamber results from disengagement of the extension and the indentation that defined the pressure expansion chamber when the rotors keep rotating. Therefore the expanded gas from the pressure expansion chamber is released into the outlet chamber and out of the housing through the outlet opening .

In one embodiment of the pressure reducer according to the invention the housing has a first portion of at least half cylindrical shape for housing the first rotor and a second portion of at least half cylindrical shape for housing the second rotor. The first and the second portions are connected to realize the housing. Thus the housing has an elongated cross section with rounded opposite ends. In case the first and the second portions show a cylindrical shape for more than half of their circumference the housing will have a tapered or 8-like shape. The inner surface of the half cylindrical portions of the housing are flush with outer ends of the wings and the tips of the extensions, respectively. Thus, there is now bypass for the gas and the gas will be forced through the pressure expansion chambers created by the indentations and extensions during revolution of the rotors. According to a preferred embodiment of the pressure reducer according to the present invention the number of indentations on the second rotor is larger than the number of extensions on the first rotor. That means the rotors show a design, which results in an enhancement of the expansion efficiency. For example the second rotor comprises two wings resulting in two indentations with a concave surface and the first rotor comprises four, five, six or seven extensions resulting in an equal number of convex flanks. Alternatively the second rotor may have four wings with four indentations in between them and five, six or seven extensions. As a result of the asymmetric design of the rotors they will rotate with different velocity within the housing ensuring a complete expansion of the gas pumped by the pressure reducer. Preferably the abutting surfaces and flanks of the first and second rotor are lubricated to seal the pressure expansion chamber and enclose the gas in the chamber. For example an oil film on the convex flanks and the concave surfaces can be used as lubricant .

According to a further embodiment of the pressure reducer according to the present invention meshing toothed wheels are fixed on the first shaft and on the second shaft for synchronizing the revolting movement of the shafts. A first toothed wheel is fixed on the first shaft and a second toothed wheel is fixed on the second shaft engaging with the first toothed wheel. The interacting toothed wheels allow for a precise coordination of the rotors, which is important in particular in case the pressure reducer is set up with an asymmetric rotor design as described above.

According to a still further embodiment of the pressure reducer of the present invention the first shaft and the second shaft comprise means for reducing a pressure exerted on the shafts during operation of the rotary internal combustion engine, in particular means for reducing a mechanical pressure on the shafts. The means for reducing the pressure include for example ball bearings for the shafts, bearings having a low friction surface, like synthetic material bearings, or an enlargement of the bearing surface between the rotating shafts and stationary elements of the housing. Other means for reducing a pressure exerted on the first shaft and the second shaft during operation of the rotary internal combustion engine are possible.

A rotary internal combustion engine according to the present invention takes advantage of a pressure reducer as described above. A rotary internal combustion engine using such a pressure reducer has an enhanced pressure expansion after the combustion step of the engine cycle resulting in a high efficiency level of the engine. In a preferred embodiment of the rotary internal combustion engine the inlet chamber is connected to a combustion chamber of the engine to directly facilitate the expansion of the combustion gases. A preferred embodiment of a pressure reducer according to the present invention will be described in the accompanying drawings, which may explain the principles of the invention but shall not limit the scope of the invention. The drawings illustrate :

Appended drawings

Fig. 1 a schematic cross section of a pressure reducer according to the invention, and

Fig. 2 a three-dimensional view of the pressure reducer shown in figure 1. Description of a preferred example of the invention

Figure 1 shows a cross-sectional view of a pressure reducer according to the invention. The pressure reducer comprises a housing 1 with a first half cylindrically shaped portion 2 and a second half cylindrically shaped portion 3. The portions 2 and 3 of the housing 1 are connected, although in figure 1 they are depicted unconnected due to an inlet opening 4 into the housing and an outlet opening 5 out of the housing . The first half cylindrically shaped portion 2 of the housing 1 accommodates a first shaft 6 carrying a first rotor 7. The second half cylindrically shaped portion 3 accommodates a second shaft 8 carrying a second rotor 9. The shafts run parallel through the housing 1 and can be supported by bearings in opposing walls of the housing 1.

The first rotor 7 comprises several radial extensions or lobes 10. In the shown example the rotor 7 has four extensions 10. The extensions or lobes 10 have non-circular, elliptical or ovoidal, convex shaped outer flanks 11 extending from a central mounting hub of the rotor 7 on shaft 6, said elliptically shaped flanks 11 joining radially in to form an outer tip 12 of each extensions or lobes 10.

The second rotor 9 comprises several radial wings 13 extending from a central mounting hub of the second rotor 9 on shaft 8. In the shown example the rotor 9 has six radial wings 13. The wings 13 define indentations or grooves 14 between each other. The indentations or grooves 14 are designed with a non-circular, elliptical or ovoidal, concave shaped surface 15. The wings 13 terminate in edges 16 at their radially outer most points.

The first shaft 6 and the second shaft 8 are distanced in the housing 1 and the radial extensions 10 of the first rotor 7 and the indentations 14 of the second rotor 1 are respectively configured in such a way that said extensions 10 mesh in the indentations 14 in a non-mating fashion, i.e. the radius or curvature of the flanks 11 differ from that of the inner surface of the grooves or indentations 14, more specifically the radius or curvature of the flanks 11 is larger than that of the inner surface 15 of the grooves or indentations 14 such that, as represented in fig. 1, a pressure expansion chamber 17 is established upon meshing of an extension 10a in an indentation or groove 14a between a flank 11a of said extension 10a and the inner surface 15a of said indentation or groove 14a. Upon meshing, the outer tip 12a of the radial extension 10a abuts at a first point on the concave shaped surface 15a of the indentation 14a, while an outer edge 16a of the indentation 14a abuts at a second point different from said first point on the convex shaped flank 11a of the extension 10a, defining a croissant-shaped inner volume forming the expansion chamber 17 between said extension 10a of the first rotor 7 and concave surface 15a of the indentation 14a.

In rotation the tip 12a slides over the concave surface 15a of the indentation 14a and the edge 16a of the indentation 14a slides along the convex flank 11a, while the shafts 6 and 8 rotate in counter direction. At the beginning the tip 12a contacts the concave surface 15a shortly behind the edge 16a. With continuing rotation of the shafts, the tip 12a slides down the concave surface 15a. Simultaneously the edge 16a slides along the convex flank 11a from the tip 12a to the bottom of the flank. In other words, the outer flank 11a of an extension 10a of the first rotor 7 and the inner concave surface 15a of a corresponding indention 14a of the second rotor 9 are contacting each other simultaneously during a meshing engagement of the rotor 7, 9 at only two distinct contact points at said outer tip 12a of the radial extension 10a on the concave shaped surface 15a on the one end and at the outer edge 16a of the indentation 14a on the convex shaped flank 11a of the extension 10a on the other end. Thereby an expansion chamber 17 is permanently defined and arranged therebetween, the volume of which varies upon rotation of the rotors 7, 9 until disengagement of the extension 10a with the indentation 14a.

Accordingly, as opposed to prior art expanders, the meshing between rotors 7, 9 never results in either a continuous linear contact or a single contact point between mating surfaces of the extensions 10 of the first rotor 7 and corresponding indentations 14 of the second rotor 9. This specific configuration of the rotors 7, 9 of the pressure expander of the invention and relative movement in operation results in expanding the volume of the pressure expansion chamber 17 upon rotation in opposite directions of the rotors 7, 9. The inlet opening 4 of the housing 1 culminates in an inlet chamber 18, which is defined by a convex flank 11 of the first rotor 7, a concave surface 15 of the second rotor 9 and a first inner surface 19 of the housing. On the opposite side of the inlet opening 4, i.e. at the outlet opening 5 the housing 1 comprises an outlet chamber 20 defined by a convex flank 11 of the first rotor 7, a concave surface 15 of the second rotor 9 and a second inner surface 21 of the housing 1 on the opposite side of the first inner surface 19. In operation gas enters the inlet opening 4 into inlet chamber 18. The revolution of the shafts 7 and 9 moves the convex flank 11 towards the concave surface 15, which define the inlet chamber 18 towards each other until the tip 12 abuts on the concave surface 15 and traps the gas in the pressure expansion chamber 17. Continuing revolution enlarges the volume of the pressure expansion chamber 17 and the gas inside the chamber expands. Further rotation of the shafts 7 and 9 results in an opening of the pressure expansion chamber 17 and a release of the gas into the outlet chamber 20. From there the expanded gas can be emptied out of the housing 1 via the outlet opening 5. Continued rotation of the rotors 7 and 9 allows a constant gas flow through the housing and a continuous expansion of the gas. The inlet opening is connected to a rotary internal combustion engine (not shown) . The use of the pressure reducer as described for figure 1 facilitates the expansion of the combustion gas generated during the combustion cycle of the engine .

Figure 2 shows a three-dimensional semi-transparent view of the housing 1 of the pressure reducer according to the invention. The first shaft 6 carrying the first rotor 7 and the second shaft 8 carrying the second rotor 9 are supported in bearings 30. The inlet opening 4 of the housing 1 is located at the same axial position than the rotors 7 and 9. The housing accommodating the shafts 6 and 8 and the rotors 7 and 9 represents a compact construction unit for the rotary internal combustion engine that is made up of only a few parts and can be produced at low costs. Further the unit can be easily exchanged and/ or maintained.

As mentioned before the bearings 30 may comprise means for reducing a pressure exerted on the first shaft 6 and the second shaft 8 during operation of the rotary internal combustion engine. For example ball bearings may be arranged between the housing 1 and each of the shafts 6 and 8. Other means for reducing the pressure on the shafts are known to a person skilled in the art, like for example an advantageous static construction of the housing and the shafts. The pressure reducing means helps to decrease the pressure exerted on the shafts 6 and 8 during the process of expanding the volume of the pressure expansion chamber 17. Reference Signs used in the appended drawings

1 housing

2 first cylindrical portion

3 second cylindrical portion

4 inlet opening

5 outlet opening

6 first shaft

7 first rotor

8 second shaft

9 second rotor

10, 10a extension

11, 11a convex flank

12, 12a tip

13 wing

14, 14a indentation

15, 15a concave surface

16, 16a edge

17 pressure expansion chamber

18 inlet chamber

19 first inner surface

20 outlet chamber

21 second inner surface

30 bearing