ROTARY PISTON ENGINE

Abstract: A rotary piston engine (10) is described, with a housing (12), with two shafts (18, 20) running on bearings therein and coupled by a wheel gearing, with the shafts bearing two rotary pistons (28, 30) that can be put into counter-rotational motion in the housing by admission of a compressed medium, which motion can be used for the drive via one of the shafts. The two rotary pistons (28, 30) contact each other and the housing wall (32) under elastic pressure and like said housing wall they comprise extruded sections. The compressed air intake and outlet are arranged and designed in such a manner that as small a dead space as possible is formed. By means of this structure leakage losses are avoided, so that the engine has a good efficiency and can be used in particular as a swivel actuator with an actuating stroke of 360 DEG .

Description: ROTARY PrSTON ENGINE Description Technical Field This invention refers generally to a rotary piston machine, and more specifically to a rotary piston engine of the type given in the preamble of claim 1. Background Art A rotary piston engine of this sort is known from DE 38 10 498 Al , which will be described in greater detail below. A rotary piston engine or, more generally, a rotary piston machine represents the inverse of a rotary piston compressor (Meiers Lexikon der Technik und der angewandten Naturwissenshaften, 1969, p. 624). Rotary piston compressors have the advantage over reciprocating piston compressors of the elimination of valves and crank drive, but the disadvantage of relatively high leakage losses. A rotary piston compressor with two shafts constitutes the so-called Roots blower with two rotary pistons that have a lemniscate shape and are af¬ fixed to two shafts coupled by equal-size toothed gears and rotating in oppo¬ site directions when one shaft is driven. In this manner, without touching each other or the housing wall, the pistons convey a volume of gas contained be¬ tween the pistons and the housing wall from the suction to the compression side. In the inverse of such a rotary piston compressor, that is in the rotary pis¬ ton engine mentioned above, a rotary motion occurs when compressed air is admitted to the rotary pistons, which change their effective area during the rotation. This rotary motion can be transferred through a wheel gearing to the output shaft and used here for example to drive a boring spindle. This known case involves a pneumatic tool in which the aforementioned high leakaae losses can readily be tolerated. A rotary piston engine of this type has a poor efficiency by nature and because of its leakage losses could not be used for example as a swivel actuator, which should have precise positioning capabili¬ ties. Furthermore, in a known rotary piston engine of this kind it is not easily pos¬ sible to adjust the nominal output to the requirement. The aforementioned leakage losses are not only caused by the minimal seal¬ ing gaps between the rotary pistons and the housing wall. They also have their origin in a dead space that is formed when the rotary pistons assume positions in which, together with each other and with the housing wall, they delimit the smallest possible volume that their design allows, opposite the compressed medium inlet and outlet. A dead space is the space in which compressed medium that can not be further compressed or displaced is still present. The less the rotary pistons in the aforementioned position are capable of closing off the compressed medium inlet and/or outlet, the larger is the effective dead space. In the rotary piston engine known from the DE 38 10 498 Al already mentioned above, an air intake port is provided as the compressed medium inlet, and air outlet orifices are provided as the compressed medium outlet. However, the DE 38 10 498 Al does not reveal how these are designed and where they are disposed. In this known rotary piston engine the inner wall of the housing has a figure-eight cross section formed by two intersecting cylinders, as is also known in a similarly constructed blower from the US 24 92 935, Figure 1 . The intake port and the outlet port of this blower comprise large bores such as those also known from the DE-A 12 55 848 and the EP 0 209 788 A2. Such bores, opening unhindered into an intake or outlet conduit respectively, virtually incorporate the interior of the conduit into the dead space, i.e. they more or less cause leakage losses, since the rotary pistons in the given position can not ade¬ quately seal off the interior of the housing from the interior of the conduit. If the rotary pistons could properly seal off the intake port and the outlet port for the compressed medium, this would also lower consumption of the compressed medium thanks to lower losses due to less leakage. Moreover, another negative effect of a poor sealing of the intake and the outlet ports for the compressed medium by the rotary piston is that such an engine is very loud in operation. Disclosure of the Invention The object of the invention is to design a rotary piston engine of the type given in the preamble of claim 1 such that leakage losses and a large dead space are avoided while a simple engine structure is maintained, and the engine can also be employed as a swivel actuator. This object is fulfilled in accordance with the invention by the features of claim 1 . The problems with leakage that exist in the state of the art are lessened in ac¬ cordance with the invention first of all in that the rotary pistons and the housing are each designed as extruded section parts. An extruded section promotes tightness, since it maintains its sturdy shape in operation. Secondly, the leak¬ age problems are alleviated in that in the rotary piston engine according to the invention the rotary pistons roll directly off one another under elastic pres¬ sure and in sealing contact with each other on the one hand, and they are under elastic pressure and in sealed gliding contact with the housing on the other hand. Thirdly, the leakage problems are reduced in that in the housing, which on the inside comprises two intersecting cylinders, the narrow intake slot is located in the area of the constriction of the figure-eight formed by the inter¬ secting cylinders. Due to the narrowness of the intake slot and due to its posi¬ tion a dead space of minimal volume results when the two rotary pistons are in the given position. Furthermore, the wide outlet slot is disposed in one of the cylinders directly adjacent to the constricted portion of the figure-eight. It is therefore possible for the rotary piston moving in this cylinder to completely close off the outlet slot. At this moment there is virtually no further compressed medium loss at all, since a uniform pressure predominates throughout the entire interior of the engine, due to the fact that the rotary piston completely closes off the outlet slot. A pressure difference delta P occurs only after the rotary piston has opened the outlet slot again. Finally, this construction of the rotary piston engine according to the invention makes it possible to use the engine as a swivel actuator as well, since the leakage problems are avoided according to the invention in the manner described above. As a swivel actua¬ tor the engine according to the invention can pivot a flap or the like in a swiveling range of 360° in one direction of rotation, which is the most favorable configuration with this particular position and orientation of the outlet slot. The swiveling can also take place in the other direction of rotation, albeit with a somewhat poorer efficiency. Since the high leakage losses that appear in the state of the art are avoided in the rotary piston engine according to the inven¬ tion, this rotary piston engine is substantially more efficient and can be better controlled. Advantageous embodiments of the invention form the subject matter of the subclaims. If in a further embodiment of the invention the or each rotary piston that is elas- tically deformable at least on its surface is provided with an elastic coating, the same advantages result as in the aforementioned embodiment of the inven¬ tion. However, production becomes easier and the form stability is improved when the or each rotary piston is merely elastically deformable on its surface. If in a further embodiment of the invention the or each rotary piston that is elas¬ tically deformable at least on its surface consists of an elastomer, at least the rotary pistons can be produced particularly easily. If in a further embodiment of the invention the housing wall is provided with an elastic coating, then one rotary piston can be non-elastically produced and/or made with no elastic coating, without affecting the efficiency of the rotary pis ¬ ton engine according to the invention. For example, both rotary pistons can be produced as metallic extruded sec¬ tions that are subsequently provided with an elastic coating. In a further em¬ bodiment of the invention the rotary pistons can be made of any material that can be extruded. Thus, for instance, one or both of the two rotary pistons can also be extruded from an elastomer such as carbon ceramics. In a further embodiment of the invention the housing can consist of fiber glass reinforced plastic or of metal. The output of the rotary piston engine can be selected by selection of the length of the extruded sections. Thus engines with any output can be produced merely by choosing the appropriate length of the rotary pistons and of the housing, or by axially joining standard sections of the rotary pistons and of the housing. If in a further embodiment of the invention one or both rotary pistons are de¬ signed as hollow sections, the structure of the rotary piston engine according to the invention is particularly economical in terms of material and weight. Brief Description of the Drawings Embodiments of the invention are described in greater detail below with refer¬ ence to the drawings. Fig. 1 shows a longitudinal section of a rotary piston engine according to the invention, Fig. 2 shows a cross section of the rotary piston engine through line 11-11 in Fig. 1 Best Mode of Carrying Out the Invention A rotary piston engine designated as a whole as 10 in Figs. 1 and 2 has a sub¬ stantially rectangular housing 12 that is closed at its two ends by covers 14 and 16. The covers 14 and 16 are removably secured to the housing by screws or the like not shown here. Two shafts 18 and 20 are arranged in the housing 12 and rotate in bearings provided in the covers 14, 16, as Fig. 1 clearly shows. Further details of the bearings are of no interest here with regard to the inven¬ tion. At their ends viewed on the right in Fig. 1 the shafts 18, 20 are coupled by α wheel gearing labeled as a whole with 22. The wheel gearing 22 here com¬ prises two equal-size meshing toothed gears 24, 26, as Fig. 1 also clearly re¬ veals. The toothed gears 24, 26 are wedged onto the associated ends of the shafts 18 and 20, respectively. At its end shown on the left in Fig. 1 the shaft 20 extends out of the housing to form the driven shaft of the rotary piston engine 10. The shaft 18 bears a rotary piston 28, and the shaft 20 bears a rotary piston 30. The rotary pistons 28, 30 are in contact with one another and with the inner housing wall 32. The rotary piston engine 10 is operated with a compressed medium, namely compressed air in the embodiment represented here. The compressed air is fed to the rotary piston engine 10 via an inlet passageway 34 designed as a bore and reaches the interior of the engine via an intake slot 36 extending the entire axial length of the housing wall 32, where it applies pres¬ sure to the rotary pistons 28, 30 in a known manner, thereby causing them to rotate. The rotary pistons 28, 30 alter their effective area while rotating, result¬ ing in a rotating movement that is transmitted to the output shaft via the wheel gearing 22. The compressed air that has done the work finally passes into an outlet passageway 40 likewise designed as a bore via a wider outlet slot 38 likewise extending the entire axial length of the housing wall 32. Leakage losses could occur due to a dead space that is formed when the ro¬ tary pistons 28, 30 assume positions in which, together with each other and with the housing wall 32, they delimit the smallest possible volume that their design allows, opposite the intake slot 36 and the outlet slot 38. The inner wall 32 of the housing 12 has a figure-eight-shaped cross section formed by two intersect¬ ing cylinders. The intake slot 36 is disposed in the area of the constriction of the figure-eight formed by the intersecting cylinders. Due to the narrowness of the slot 36 and due to its position and orientation, a dead space of minimal vol¬ ume is formed when the rotary pistons 28, 30 are in the given position in which they delimit the smallest volume. The outlet slot 38 is located in one of the cylinders, directly adjacent to the constriction of the figure-eight, as is shown in Fig. 2. It is therefore possible for the rotary piston 28 to completely close off the outlet slot 38. The rotary pistons 28, 30 are under elastic pressure in sealing contact with each other and with the housing wall 32. Various designs of the rotary pistons and the inner housing wall 32 are possible for this and will now be dealt with in de¬ tail. In the embodiment shown in the drawings both rotary pistons are elastically deformable, whereas the inner housing wall 32 is not. The rotary pistons 28, 30 are constantly in mutual and sealed rolling contact with each other and are for the most part constantly in sealed gliding contact with the housing wall 32. The rotary piston 28 is made elastically deformable in the embodiment shown in that it consists entirely of an elastomer. The rotary piston 30 is made elasti¬ cally deformable in that it is a rigid section itself that bears an elastic coating 42 on its exterior. The two rotary pistons 28, 30 are each designed as extruded sections. However, after being produced by extrusion, the rotary piston 30 is provided with the elastic coating 42 on its exterior. The coating 42 can be applied by spraying. The housing 12 in the embodiment shown consists of a light metal such as aluminum or of a fiber glass reinforced plastic. The core of the rotary piston 30 can also be made of fiber glass reinforced plastic; its exterior then additionally has the elastic plastic coating 42. The coating could also simply be an elastic sheath (not shown) held at a dis¬ tance from the rotary piston or from the housing wall by a fluid. The fluid would yield when elastic pressure is exerted. A further embodiment would consist in making both of the rotary pistons 28, 30 out of an elastomer such as carbon ceramics or both out of a rigid material and in the latter case providing the exteriors of both with an elastic coating such as the coating 42 or the aforementioned sheath. In yet another embodiment one rotary piston is rigid and the other one is pro¬ vided with a plastic coating or made of an elastomer, and in addition the housing wall 32 is provided with an elastic coating 44 to produce a seal be¬ tween the latter rotary piston and the housing wall 32, as the reference number 44 merely hints at in Fig. 2. A preferred field of application of the rotary piston engine is its use as a swivel actuator with a positioning stroke of 360° and with a very high degree of posi¬ tioning accuracy. A particular advantage of the embodiment of the rotary piston engine 10 de¬ scribed here with two elastically deformable rotary pistons - irrespective of whether the pistons themselves are elastically deformable or whether one of them and the housing or both rotary pistons are provided with an elastic coat¬ ing or are elastically designed - is that no lubricant is required between the ro¬ tary pistons on the one hand and between the rotary pistons and the housing on the other. The elastic coating of the rotary piston or pistons and/or of the housing wall 32 can namely be of Teflon, for example, which renders any lubri¬ cant superfluous. Hollow sections can be considered for the extruded sections for the rotary pis¬ tons 28, 30, as Fig. 2 hints at with the example of the rotary piston 28. The nominal output that the rotary piston engine 10 is to deliver can be se¬ lected in a simple manner by selection of the appropriate length of the ex¬ truded sections (rotary pistons and housing). For this purpose several housing sections and several rotary piston sections can be axially joined, as Fig. 1 shows, to adapt the length of the rotary piston engine 10 to the output required. The rotary piston engine 10 offers the possibility of simply selecting the output by selecting the length of the rotary pistons and of the housing, since the intake slot 36 and the outlet slot 38 each extend over the entire axial length of the housing 12 and are thus open at both ends of the housing. The axial closure of these slots 36, 38 is made by the covers 14, 16. If, instead of the intake slot 36 and the outlet slot 38, a rotary piston engine had large radially extending bores, as is provided in the state of the art described above, it could not have a housing designed as a simple extruded section. The rotary piston engine described here, or to be more exact the rotary piston machine described here can be used inversely as a charger to charge internal combustion engines, i.e. as a compressor for the precompression of the com¬ bustion air or of the air/fuel mixture, to enhance the performance of internal combustion engines. In this case the rotary piston machine is mechanically driven by the internal combustion engine or by an exhaust turbine. To be sure, this use of the rotary piston machine is known in principle from the US 24 92 935 already mentioned above. However, the design of the machine according to the invention permits a far better efficiency and is particularly well suited for use as a charger in diesel engines of ceramic material.

Claims: Claims 1. A rotary piston engine with a housing (12) having a compressed medium intake (36) and a compressed medium outlet (38) and with an inner wall (32) having a figure-eight cross section formed by two intersecting cylinders, with two shafts (18, 20) rotating in bearings in the housing (12) and coupled by a wheel gearing (22), and with a first and a second rotary piston (28, 30) having a lemniscate-shaped cross section and being secured to the shafts (18, 20) and further being put into rotary motion in the housing (12) by admission of a com¬ pressed medium, said rotary motion being usable for the drive via the one or the other shaft (20), characterized in that the housing (12) is an extruded section, the rotary pistons (28, 30) are extruded sections the rotary pistons (28, 30) contact each other and the housing wall (32) under elastic pressure, the compressed medium intake is a narrow slot (36) extending the length of the inner housing wall (32) and opening into the interior of the housing in the plane of the constriction of the figure-eight, and the compressed medium outlet is a slot (38) that is wider than the narrow slot (36) and leads from the interior of the housing (12) in one of the two cylinders, directly adjacent to the constriction of the figure-eight. 2. The rotary piston engine according to claim 1 , characterized in that at least the first rotary piston (28, 30) and the housing wail (32) are elastically deform¬ able at least on their surfaces. 3. The rotary piston engine according to claim 2, characterized in that at least the two rotary pistons (28, 30) are designed to be elastically deformable at least on their surfaces. 4. The rotary piston engine according to claim 2 or 3, characteπzed in that the or each rotary piston (28, 30) that is elastically deformable at least on the sur¬ face is provided with an elastic coating (42). 5. The rotary piston engine according to claim 2 or 3, characteπzed in that the or each rotary piston (28, 30) that is elastically deformable at least on the sur¬ face consists of an elastomer. 6. The rotary piston engine according to any of claims l to 5, characteπzed in that the housing wall (32) is provided with an elastic coating (44). 7. The rotary piston engine according to any of claims 1 to 6, characteπzed in that the housing ( 12) consists of fiber glass reinforced plastic or of metal. 8. The rotary piston engine according to any of claims 1 to 7, characterized in that one or both rotary pistons (28, 30) are designed as hollow sections. 9. The rotary piston engine according to claim 2, characterized in that the second rotary piston (30) consists of a rigid matenal. 10. The rotary piston engine according to claim 8, characterized in that one or both rotary pistons (28, 30) consist of an elastomer such as carbon ceramics.

Inventors: GRAU JOERG, POESCHL GUENTER, STOLL KURT, GRAU, JOERG, POESCHL, GUENTER, STOLL, KURT
Applicants: FESTO KG, GRAU JOERG, POESCHL GUENTER, STOLL KURT, GRAU, JOERG, POESCHL, GUENTER, STOLL, KURT
Application year: 1997
Main classification: F01C1
IPC codes: F01C1