WO1991014081A1

WO1991014081A1 - Engine stabiliser mechanism

Info

Publication number: WO1991014081A1
Application number: PCT/AU1991/000090
Authority: WO
Inventors: David Nicholas Buchhorn; George Kingsley Cureton; Joseph Scalzo; Marek Jacek Sykurski
Original assignee: Scalzo Automotive Research Ltd.
Priority date: 1990-03-14
Filing date: 1991-03-13
Publication date: 1991-09-19

Abstract

A rotary piston engine or pump (110) has a trochoidal piston (112) eccentrically mounted in a housing (111), defining at least two working chambers (118, 119) corresponding to the outer enclosing curve of the piston. The piston is rotatable about a crankpin (113) of a crankshaft (114) that is mounted in the housing for rotation about its axis (AA). The piston and crankshaft rotate oppositely at a relative speed determined by a stabilising gear system therebetween. The gear system includes a first gear (25) having a pitch circle radius (F) greater than the throw (E) of the crankpin rigidly mounted coaxially on a piston extension (112a) surrounding the crankpin (113), and a second gear (26) with which the first gear meshes. One of said first and second gears is an external gear while the other is an internal gear. The gear system also includes a drive train (27) to achieve the required speed ratio and direction of rotation of the piston and crankshaft.

Description

ENGINE STABILISER MECHANISM

The present invention relates to devices comprising a rotary piston engine or pump of trochoidal construction. Rotary piston engines or pumps of trochoidal construction, hereinafter referred to jointly as engines, have a housing and a trochoidal piston eccentrically mounted in the housing. The piston has the shape of a trochoid or of a curve inside and parallel to a trochoid and typically has the configuration of a cardioid, usually inflection-point-free. The housing defines a compartment defining n+1 working chambers, where n is the number of lobes of the piston, and having a configuration corresponding to the outer enclosing curve or outer envelope of the trochoid. In these engines, the number of revolutions and direction of rotation of a drive or driven shaft and of the piston have a specific relationship with respect to each other. Generally the piston is rotatable in the opposite direction to the shaft; with the piston movement being controlled, or stabilised, by guide gearing. Generally, there is used toothed wheel gearing in which an external gear having a smaller diameter engages with an internal toothed gear wheel having a larger diameter. Previous proposals have adopted an arrangement in which the larger gear wheel is rigidly connected to the housing and the smaller gear wheel is rigidly connected to the piston, such as disclosed in U.S. patent specification 3,410,254 issued 12 November 1968 to Franz Hϋf. In conventional proposals for such one lobe, two chamber engines, a ratio of the larger gear to the smaller gear is determined as 2:1 by design and the dimensions of the drive shaft are established. This necessitates use of a crankshaft having a relatively long crankpin with a stepped narrowing, with a resultant weakness at the crankpin, to an extent that it is not practical to construct a multi-piston engine.

In order to overcome the disadvantage of a stepped narrowing of the crankpin, other forms of piston stabilisation have been proposed. These utilise guide rods or sliders in conjunction with eccentrics fixed to the piston, such as proposed in US patent specifications 3,909,163 and 3,923,430 respectively issued 30 September 1975 and 21 February 1975 to Franz Hϋf. This type of stabilisation is required to transmit a substantial part of the engine torque but, because of a need for eccentrics of large diameter combined with sliding blocks on tracks or rods, frictional losses can be substantial.

The present invention is directed to providing a rotary piston engine or pump of trochoidal construction, having a gearing system for controlling or stabilising piston and crankshaft rotation which, in particular, obviates the constraint resulting from a stepped crankpin. For this purpose, the present invention principally is concerned with one lobe, two chamber engines or pumps. However, the invention also is applicable to engines or pumps having a piston with n lobes and n+1 chambers, where n is greater than one. In at least one form, the invention also enables use of a shorter crankpin than is typically required for one lobe, two chamber arrangements; and that one form is preferred where the invention is applied to such arrangements in which n is greater than one.

According to the invention, there is provided a rotary piston engine or pump having a housing and a trochoidal piston eccentrically mounted in the housing, the housing defining a compartment of at least two working chambers and having a configuration corresponding to the outer enclosing curve of the piston, wherein the piston is rotatable on a crankpin of a crankshaft which is mounted in the housing for rotation on an axis thereof, and wherein the piston and crankshaft are oppositely rotatable at a relative speed determined by a stabilising gear system therebetween, the stabilising gear system including a first gear mounted on the piston co-axially around the crankpin and movable with the piston, a second gear with which the first gear is in meshing engagement during opposite rotation of the piston and crankshaft, and a drive train operable between the second gear and the crankshaft, one of said first and second gears being an external gear and the other thereof being an internal gear, the first gear having a pitch circle radius F which exceeds the throw E of the crankpin and the second gear being movable relative to the housing. In a first form of the invention, the first gear is an external gear and the second gear is an internal gear. In that form, the first gear preferably is on an axial extension of the piston. In a first arrangement the internal, second gear has a fixed centreline about which it is rotatable, with rotation of the external, first gear. In a second arrangement the internal, second gear is constrained against rotation on its centreline by constraining means which enables or causes its orbital movement, with rotation of the first gear. In each case the internal, second gear is angularly movable relative to the housing, rather than being fixed to or in relation to the housing.

In the first arrangement, the second gear may have a pitch circle radius of F+E. The drive ratio between the first and second gears need not be 2:1 and preferably is less than 2:1. The second gear most preferably is rotatable by or with a drive train comprising a planetary gear drive, with such drive train providing a gear ratio relative to the crankshaft to produce a resultant 2:1 speed ratio between the piston and crankshaft in their rotation in opposite directions. The drive train preferably includes a ring gear, preferably an internal ring gear, co-axially rotatable with, and typically of larger pitch circle radius than, the second gear. The ring gear of the drive train and the second gear most preferably are provided on a common hub. The drive train preferably includes at least one planetary gear which is rotatable on a fixed axis laterally offset from the axis of the crankshaft and which meshes with the ring gear. Most preferably, there is a plurality of planetary gears substantially uniformly spaced around the crankshaft. In one arrangement, the or each planetary gear is rotatable on a pin or a respective pin fixed on or in relation to the engine casing. The or each planetary gear rotates with rotation of the second gear and the ring gear, and meshes with a sun gear fixed concentrically on the crankshaft.

In the second arrangement, the second gear most preferably has a 2:1 speed ratio relative to the first gear, while the second gear is orbitable about a centre directly opposite to that of the crankpin at a position determined by the size selected for the first gear. This orbital motion is achieved in one embodiment by an eccentric on the crankshaft in combination with stabilising cranks rotatable about fixed equidistant points on the engine casing around the periphery of the second gear. In an alternative embodiment, the orbiting motion is achieved by an eccentric on the crankshaft combined with a crankshaft driven, synchronised crank at a suitable distance from the centre of the crankshaft. In a further alternative embodiment, the orbiting motion is produced by the second gear being supported on two crankshaft driven synchronised cranks positioned at 180 degrees from each other. In a second form of the invention, the first gear is an internal gear and the second gear is an external gear; the first gear preferably being mounted within one side of the piston. With this form of the invention, the alternative first and second arrangements detailed for the first form are possible, although it is preferred that the second gear has a fixed centreline about which it is rotatable, with this being on the crankshaft axis.

In the second form of the invention, the internal first gear most conveniently is mounted within or at one side of the piston, concentrically around the crankpin, for rotation with the piston. The external second gear has its centre of rotation fixed on the crankshaft axis, within the first gear, with the offset centrelines of the first and second gears being equal to the throw of the crankpin. The drive train operable between the second gear and the crankshaft is such as to cause the second gear to rotate in the opposite direction to the crankshaft, and preferably is such as to achieve a 2:1 speed ratio between the piston and the crankshaft. The drive train preferably comprises an epicyclic gear system operable between the second gear and the crankshaft.

In one arrangement according to the second form of the invention, the epicyclic gear system comprises a ring gear concentrically mounted on and rotatable with the crankshaft, at least one planetary gear rotatable on a fixed axis laterally offset from the crankshaft and a sun gear journalled concentrically on the crankshaft. The piston and crankshaft, in that arrangement, are oppositely rotatable by driving engagement between the first and second gears and between the at least one planetary gear and both the ring gear and the sun gear, and by the sun gear being connected to and rotatable with the second gear.

In order that the present invention can be more fully understood, reference now is made to the accompanying drawings, in which:

Figure 1 is a schematic transverse cross-sectional view of a one lobe, two working chamber arrangement of the prior art for a rotary piston engine having a 1:1 epitrochoidal shape; Figure 2 is a schematic longitudinal cross-sectional view of the prior art engine, taken on line II-II of

Figure 1;

Figure 3 is a schematic longitudinal cross-sectional view of a rotary, single piston engine according to a first embodiment of the present invention;

Figure 4 is a schematic longitudinal cross-sectional view of a rotary, single piston engine according to a second embodiment of the present invention;

Figure 5 is a partial cross-sectional view taken along line V-V of Figure 4;

Figure 6 is a schematic longitudinal cross-sectional view through a rotary single piston engine according to a third embodiment of the present invention;

Figure 7 is a cross-sectional view taken along line VII-VII of Figure 6;

Figure 8 is a schematic longitudinal cross-sectional view through a two piston, rotary engine according to a fourth embodiment of the invention, based on the embodiment of the Figures 6 and 7; Figure 9 is a cross-sectional view taken along line IX- IX of Figure 8 ;

Figure 10 is a schematic longitudinal cross-sectional view of a rotary, single piston engine according to a fifth embodiment of the present invention; and

Figure 11 is a sectional view on line XI-XI of Figure 10, showing the gear mounting and position.

In the prior art arrangement of Figures 1 and 2, the engine 10 has an engine casing 11 in which rotary piston 12 is rotatably mounted on crankpin 13 which forms part of crankshaft 14 and has a throw of radius R. Crankshaft 14 is rotatably mounted in casing 11 via bearings 15; while piston 12 is rotatable on crankpin 13 by provision of bearing 16 therebetween. Piston 12 has a trochoidal configuration, while the interior surface 17 of casing 11 has a shape corresponding to the outer enclosing curve of the trochoid. Two working chambers 18,19 are defined between piston 12 and surface 17 of casing 11; with chamber 19 being occupied by piston 12 in the condition shown for engine 10. Piston 12 is movable between variable-volume chambers 18,19, with rotation of crankshaft 14, thereby varying the volume of the chambers. Sealing strips 20 located in casing 11 sealing bear against the peripheral face of piston 12, and isolate chambers 18,19 from each other.

Engine 10, in the form illustrated, is an internal combustion engine. A portion of each chamber 18,19 defines a respective combustion chamber 18a,19a in which a fuel/air mixture is alternately compressed by piston 12 and ignited by a respective spark plug 21. Fuel/air induction and combustion gas exhaust facilities have not been shown for simplicity of illustration.

Piston 12 is constrained to rotate in the opposite direction to crankshaft 14 but at the same speed. Thus the relative speed between piston 12 and crankshaft 14 is twice that of the crankshaft. This relative movement, or stabilisation, is achieved by 2:1 gear drive between a small gear 22, fixed to axial extension 12a of piston 12, and a larger internal gear 23 which is fixed to engine casing 11 and with which gear 22 meshes. However, for internal gear 23 to be fixed to engine casing 11, the 2:1 ratio means that gear 22. must have a pitch circle radius which does not protrude past the centreline A of crankshaft 14. This constraint necessitates crankpin 13 having an extension 13a which is within piston extension

12a and of much smaller diameter than the crankpin 13. As a consequence of that smaller diameter, the stiffness and torque transmitting capacity of crankshaft 14 is substantially reduced, to an extent such that coupling further pistons to provide a multi-piston engine is effectively precluded, and even the single piston engine is severely limited in its torque transmitting capacity.

Only brief comment is necessary in relation to the working of engine 10. With rotation of piston 12 in one direction on bearing 16, gear 22 also rotates in that one direction. The meshing engagement of gears 22,23 results in gear 22 being drawn around gear 23, but in the reverse direction. Crankpin 13 is drawn around centreline A with gear 22, such that crankshaft 14 rotates on centreline A in the reverse direction. One revolution of piston 12 results in one revolution of crankshaft 14 but, as the directions of rotation are opposite, the required 2:1 drive ratio is achieved.

Before turning to the embodiments of Figures 3 to 11, it first is to be noted that while each of these embodiments show engines, the overall structure of each (as with that of engine 10) is equally applicable to a pump. Clearly, the issue is simply whether rotation of a crankshaft is driven by rotation of a piston or vice versa. For this reason, but also for ease of illustration. Figures 3 to 11 do not show combustion chambers, spark plugs, fuel injectors or the like.

A second matter to be noted is that while, in each of the embodiments of Figures 3 to 11, there is shown a one lobe form of piston in a two chamber housing or casing, this is not to be understood as limiting on the invention. That is, the invention also is applicable to a piston with n lobes, rotatable in housing defining n+1 chambers, where n is greater than one. Thus, while each embodiment arises from seeking solutions to problems existing with one lobe, two chamber arrangements, they have broader application. However, for arrangements where n is greater than one, other solutions are available and there are some difficulties to be addressed in adapting the solutions of the present invention to those arrangements. However, in the latter regard, the embodiment of Figures 10 and 11 in particular offers promise.

Figure 3 illustrates an engine 110 in accordance with a first embodiment of the invention. In Figure 3, components of engine 110 corresponding to those of engine 10 of Figures 1 and 2 have the same reference numeral plus 100, and are referred to only in so far as is necessary for a full understanding. In essence engine 110 is a rotary piston engine having a gear stabiliser combined with an epicyclic gear. Trochoidal rotary piston 112 is rotatably mounted in crankpin 113 via bearing 116. Crankpin 113 has a throw E which, relative to centreline A of crankshaft 114, is determined by design, while the diameter of crankpin 113 also is determined by design but preferably is within the lateral extent of flanges 114a of crankshaft 114 to ensure rigid construction.

The requirement for rotation of piston 112 in the opposite direction to crankshaft 114, but at the same speed, is provided by gears 25 and 26 and epicyclic gear train 27 which overall provide the required 2:1 speed ratio between piston 112 and crankshaft 114. Gear 25, of pitch circle radius F with F>E, is fixed on extension 112a of piston 112; extension 112a being shown as portion of a separate component which is secured to and rotatable with piston 112. Gear 25 meshes with larger internal gear 26 of pitch circle radius (F+E) , with gear 26 being concentric with centreline A of crankshaft 114 and rotatably mounted on a bearing 28 fixed to engine casing 111. This arrangement of gears 25,26 produces a gear ratio of less than the required 2:1 speed ratio between piston 112 and crankshaft 114, and compensation must be provided. Compensation is provided by epicyclic gear train 27, which causes opposite rotation between gear 26 and, hence piston 112 on the one hand and crankshaft 114 on the other hand.

Gear train 27 includes a ring gear 29 which is attached to and runs concentrically with gear 26. In the arrangement illustrated, gears 26,29 are formed internally on a common hub 30 which is stepped so that gear 29 is of larger diameter than gear 26. However, a gear selection in which gears 26,29 have the same diameter can be used. Gear train 27 also includes a planetary gear 31 which meshes with gear 29 and is rotatably mounted, via a bearing 32, on a pin 33 fixed to engine casing 111 at a location laterally offset from centreline A. Train 27 further includes a central sun gear 34 which is fixed to and concentric with crankshaft 114 and with which the planetary gear 31 meshes.

As will be appreciated, gear 26 is rotatable in the same direction as piston 112 and gear 25, with ring gear 29 and planetary gear 31 also being caused to rotate in that direction. However, sun gear 34 and, hence, crankshaft 114 is caused to rotate in the opposite direction. The gear ratio between ring gear 29 and sun gear 34 is selected by design to produce the necessary compensation to achieve the required 2:1 speed ratio between rotation of piston 112 and crankshaft 114. Of course, with this overall rotation of piston 112 and crankshaft 114, crankpin 112 and hence gear 25 move around centreline A.

As can be appreciated from the arrangement of Figure 3, the diameter of crankshaft 114 throughout, including that at any part of crankpin 113, and also the throw E of crankpin 113, can be chosen as a matter of design rather than subject to the constraint of attaining the 2:1 piston to a crankshaft speed ratio. Crankshaft 114 thus can be designed throughout for torque transmitting capacity, enabling use of a crankshaft having an appropriate torque transmitting capacity. Indeed, that capacity can be such that the torque requirements of a multi-piston engine, based on the arrangement of Figure 3, can be accommodated. In such multi-piston engine, each piston most preferably is provided with a respective stabiliser comprising a gear train 27.

In the gear train 27 of engine 110 of Figure 3, only one planetary gear 31 is illustrated. However, there preferably is a plurality of uniformly spaced gears 31. Two diametrically opposed gears 31 can be used, although most preferably at least three gears 31 are provided at a uniform angular spacing around centreline A.

Figures 4 and 5 illustrate an engine 210 in accordance with a first embodiment of the invention. In Figures 4 and 5, components of engine 210 corresponding to those of engine 110 of Figure 3 have the same reference numeral plus 100, and are referred to only in so far as is necessary for a full understanding.

In essence, engine 210 is a rotary piston engine having a 2:1 gear stabiliser combined with an eccentric driven, orbiting large gear stabilised by peripheral cranks. As in Figure 3, trochoidal rotary piston 212 is rotatably mounted on crankpin 214 via bearing 216; crankpin 216 having a throw E relative to centreline A of crankshaft 214 and a diameter each chosen by design.

As in engine 110 of Figure 3, engine 210 of Figures 4 and 5 has a gear 125, of pitch circle radius F with F>E, fixed on extension 212a of piston 212. Around gear 125, there is provided an internal gear 36 with which gear 125 meshes. Gear 36 has a pitch circle radius twice that of gear 125 and has its centreline offset from the centreline of crankpin 213 and gear 125, around centreline A of crankshaft 214 by 180°. Thus, the rotational centre of gear 36 is at a distance of (F-E) , where E and F are as previously explained.

It is necessary to achieve correct stabilisation of trochoidal rotary piston 212, allowing for the 2:1 drive ratio between gears 125,36. For this stabilisation internal gear 36 is mounted so as to be orbitable around centreline A of crankshaft 214, via an eccentric 37 fixed to crankshaft 214, and at a pitch circle radius of (F-E). As shown, gear 36 is provided on an internal, peripheral wall of dished hub or cradle 38, with eccentric 37 being rotatable in hub 38 via a bearing 39 concentric with gear 36. Furthermore, hub 38 is constrained to orbital movement, without rotation, by at least three constraining systems 40 provided at locations spaced around gear 36.

Each system 40 has a secondary crankshaft 41 of which the ends 42,42a are journalled, via bearings 43, in engine casing 211. Each crankshaft 41 has a crankpin 44, with the axis of the crankpins being equidistance radially from, and uniformly spaced angularly around, the centreline of gear 36. Also, each crankpin 44 has a throw the same as that of eccentric 37, that is (F-E), and is at the same angular position relative to the axis of its crankshaft 41 as eccentric 37 is relative to centreline A of crankshaft 214. Moreover, each crankpin 44 is rotatable via a bearing 45 in a respective boss 46 of hub 38. Thus, the systems 40 constrain hub 38 to orbital movement in a circular path, without rotation. As a consequence, systems 40 allow internal gear 36 to be orbited in a circular path, as represented by orbital path C of Figure 5 for the centreline of gear 36. In its orbital movement, gear 36 is maintained in meshed engagement with gear 125,. while that movement results in rotation of eccentric 37 and hence, crankshaft 214.

As will be appreciated, rotation of piston 212 in one direction on bearing 216 rotates gear 125 in that direction. As a consequence, internal gear 36 and hence hub 38 is caused to orbit around gear 125, as allowed by systems 40; with the orbiting movement also being in that one direction. The orbiting movement of hub 38 results in rotation of eccentric 37 and hence crankshaft 214, with this rotation being in the reverse direction to piston 212. The previously indicated 2:1 drive ratio between gears 125,36 results in the required 2:1 relative speed ratio between piston 212 and crankshaft 214, given that the arrangement of engine 210 achieves one revolution of eccentric 37 during each non-rotational orbit of gear 36. Orbitable hub 38 and eccentric 37 contribute to engine balance, eliminating the need for or reducing the size of any necessary additional balance weight. Also, as with engine 110 of Figure 3, engine 210 achieves the required 2:1 relative speed ratio between piston 212 and crankshaft 214, without the need to observe the constraints applicable to engine 10 of Figures 1 and 2. That is, the diameter of crankshaft 214 throughout, including that of any part of crankpin 213, and also the throw E of crankpin 213, can be chosen as a matter of design. Thus, crankshaft 214 can be designed throughout for strength and torque transmitting capacity, such that a multi-piston engine can be based on the arrangement of Figures 4 and 5.

While a multi-piston engine based on engine 210 is not illustrated, a two piston engine for example readily will be able to be comprehended. Thus, in relation to that shown in Figures 4 and 5, a two piston engine can be provided by extending casing 211 and crankshaft 214 to the right-hand side of Figure 4, to accommodate the second piston 212 on a second crankpin 213. In such arrangement, secondary crankshafts 41 can be extended beyond their ends 42a and provided with additional crankpins 44 by which a second hub 48 is constrained for orbital movement. The second hub 48 would have a second internal gear 36 meshing with a gear 125 on the end of the second piston 212 facing first piston 212. The second crankpins 44 would have a different phase to those shown for the piston. However, while able to be provided, there would not need to be a second eccentric 37 and bearing 39 for the second hub 38. That is, the one eccentric 37 would suffice to achieve orbiting motion for the two internal gears 36. In addition, if the stabilising crankshafts 41 are located at a pitch circle radius outside the envelope of the pistons 212 and working chambers 218,219, the one eccentric 37 can suffice for an engine having more than two pistons 212, since secondary crankshafts 41 can be extended somewhat in the sense in which an overhead camshaft extends in a conventional reciprocating engine.

Engine 310 of Figures 6 and 7 is a rotary piston engine having a 2:1 gear stabiliser combined with an eccentric driven large gear stabilised by one crankshaft driven outrigger. Engine 310, in large part, is the same as engine 210 of Figures 4 and 5, and similar components therefore have the same reference numerals. Dealing with the arrangement by which engine 310 differs from engine 210, an internal gear 36 again is provided, but by a different form of orbitable hub 46 in which eccentric 37 is rotatable via bearing 39. In this instance orbiting, non-rotational motion of hub 46 is produced by the combined action of eccentric 37 and one constraining system 47 operable via a radially projecting arm 48 of hub 47.

System 47 comprises a secondary crankshaft 49 parallel to crankshaft 214 and having its opposed ends 50 rotatable in bearings 51 mounted in engine casing 211, in a similar manner to crankshafts 42 of engine 210. Crankshaft 49 has a crankpin 52 rotatable in a bearing 53 provided in the outer end of arm 48. Crankpin 52 has the same throw of (F-E) as eccentric 37, where F and E are as described for engine 210. Also, crankpin 52 is at the same angular position relative to the axis of crankshaft 49 as eccentric 37 is relative to centreline A of crankshaft 214. Crankshaft 49 is rotatable by a 1:1 speed ratio drive (not shown) , such as a belt drive, from crankshaft 214, and thus is synchronised to maintain a constant distance between the centreline of its crankpin 52 and the centre of eccentric 37.

Hub 46 thus is constrained so as to be orbitable, but non-rotational; as represented by orbital path D of Figure 7 for the centreline of gear 36 during its resultant orbital movement. Thus, with rotation of piston

212 and hence gear 125 in one direction, gear 36 and hence hub 46 is caused to orbit in the same direction. As a consequence, eccentric 37 and hence crankshaft 214 are caused to rotate but in the opposite direction. As in engine 210, gear 36 of engine 310 has a pitch circle radius twice that of gear 125, with its centreline offset from the centreline of crankpin 213, around the centreline

A of crankshaft 214, by 180°. Thus, again, there is achieved the required 2:1 speed ratio between piston 212 and crankshaft 214, providing the benefits specified for engines 110 and 210 in respect of torque transmitting capacity and multi-piston engine capability. That is, engine 310 is not subject to the design constraints and torque capacity limitations detailed in relation to prior art engine 10 .

Figures 8 and 9 illustrate a two-piston rotary engine 410, based on engine 310 of Figures 6 and 7, but having two crankshaft driven outrigger synchronised cranks. In Figures 8 and 9, parts corresponding to those of engine 310 are identified by the same reference numerals and, for brevity, description is limited to differences in structure.

In engine 410, a respective internal gear 36 for each piston 212 is provided on a modified form of hub 55 which does not have crankshaft 214 journalled therein, while the latter does not have an eccentric corresponding to eccentric 37 of engine 310. Rather, the orbiting motion of each hub 55 is stabilised by respective constraining systems 47, each operable via a respective one of two opposed, radially projecting arms 48 of hub 55. Each system 47 is of the form described above for system 47 of engine 310, with the crankpin 52 of each having the same throw of (F-E), where E is the throw of crankpin 213 and F is the pitch circle radius of gear 125, with F>E. Also, as shown, the angular position of each crankpin 52 relative to the centreline of its crankshaft 49 is the same.

A 1:1 speed ratio drive (not shown), such as a belt drive, is provided between crankshafts 49 and crankshaft 214, such that all crankshafts rotate in the same direction. Thus, on rotation of pistons 212 and hence gears 125 in one direction, gear 36 and hence hub 55 are caused to orbit in that one direction, under the stabilising influence of systems 47. Resultant orbital movement of arms 48 rotates secondary crankshafts 49, but with the latter rotating in the opposite direction to pistons 212. Rotation of crankshafts 49 rotates crankshaft 214, also in that opposite direction, due to the 1:1 speed drive therebetween. As in engine 310, gear 36 has a pitch circle radius twice that of gear 125, with its centreline offset from the centreline of crankpin 213, around the centreline A, by 180°. Thus, gears 125,36 provide a 2:1 drive ratio which, given the 1:1 ratio drive between crankshafts 49 and crankshaft 214, establishes the 2:1 speed ratio between pistons 212 and crankshaft 214. That speed ratio is achieved without necessary constraint on the cross-section of crankshaft 214 which, throughout, can be determined by design requirements consistent with the required torque transmitting capacity for engine 410.

The drive between crankshafts 49 and crankshaft 214 can be extended to enable provision of additional crankshafts 49, where required for stabilisation and support for additional hubs 55 and internal gears 36 in an engine having more than two pistons 212. As will be appreciated, a multi-piston engine necessitates selected phasing from one piston 212 to the next, as illustrated in Figure 8 in which the pistons 212 are 90° out of phase.

In engine 410, hubs 55 contribute to balancing of the engine. They can eliminate the need for or reduce the size of any necessary additional balance weight.

Engine 510 of Figures 10 and 11 is a rotary piston engine having gear stabilisation by means „ of an alternative system of epicyclic gearings. In so far as components of engine 510 are similar to those of engine 310 of Figures 6 and 7, they are identified by the same reference numerals plus 200.

Engine 510 of Figures 10 and 11 has a rotary piston 512 rotatably mounted on crankpin 513 of crankshaft 514, via bearing 516; crankpin 513 having a throw E relative to centreline A of crankshaft 514. In this instance, crankshaft 514 has two parts 514a,514b joined by an hydraulically assisted taper 60 between the crankpin 513 and flange 514c of completed crankshaft 514. Bolt 62, an extension of crankpin 513, provides an additional locking system and also assists during disassembly of the crankshaft 514. Hydraulic oil pressure is able to be supplied via an oil hole 63, which communicates with an oil groove 64 formed around and within flange 514c to separate slightly the taper in flange 514c to assist assembly and disassembly of the crankshaft 514.

Rotary piston 512 is suitably constructed, as indicated in Figure 11, so that its centre of mass is located at the centreline of bearing 516, and may be constructed of light metal such as aluminium. Piston 512 defines, in one side face, an annular recess 512a in which an internal, first gear 65 is mounted concentric to bearing 516 by a number of solid or spring roll pins 66. Gear 65 also allows for a groove 67 to house a circular oil seal (not shown). Additionally, a gear member 68, comprising a hub 69 and axially spaced external, second gear 70 and further external gear 71, is supported by a bearing 72 to the engine case 511, concentric with crankshaft 514. Gear 70 engages with internal gear 65 fixed to the inside of rotary piston 512.

An internal bearing 73, fixed to the inside bore of hub 69 of gear member 68, rotatably supports the crankshaft 514. By design, the relative sliding velocity between crankshaft 514 and bearing 73, is greater than two but less than three, and is a function of the relative sizes of gears 65 and 70. The diameters of crankpin 513, and the portion of crankshaft 514 which is rotatable within bearing 73, are designed to be as large as possible within the constraints of meshing gears 65 and 70. The 2:1 speed ratio between the rotary piston 512 and crankshaft 514, via meshing gears 65 and 70, is compensated by an epicyclic gear train 74 which includes a ring gear 75, a planetary gear 76 and also a central sun gear which comprises previously mentioned external gear 71 of gear member 68. Ring gear 75 is attached to crankshaft 514, via key 77 (or other fixing means), concentrically to the centreline A of crankshaft 514. Planetary gear 76, which meshes with gear 75, is rotatably mounted, via bearing 78, on a pin 79 fixed to a planet carrier 80, while carrier 80 is rigidly bolted to engine casing 511 such that gear 76 is at a location laterally offset from centreline A. Only a single planetary gear 76 is shown, although there preferably is a plurality of planetary gears 76 uniformly spaced around, and at the same pitch circle radius of pin 79, relative to centreline A. The or each planetary gear 76 meshes with central sun gear 71, while gear 71 is concentric with crankshaft 514.

As will be appreciated, ring gear 75 rotates with crankshaft 514 and, via the or each planetary gear 76, causes rotation of sun gear 71. The rotation of gear 71 causes rotation of piston 512, via gears 70 and 65, in the opposite direction to crankshaft 514. The overall speed ratio between the ring gear 75 and internal gear 65, must (for the one lobe piston 512 shown) be 2:1 in opposite rotation to one another, and the ratios of the respective gear trains are selected to achieve the required 2:1 ratio. Crankshaft 514 is rotatably supported and axially located by radial bearings 81,82. Also, crankshaft 514 is axially located by thrust bearings 83,84, respectively fixed to front and rear plates 85,86 of crankcase 511.

Balance weights are required to be attached to the crankshaft 514 to balance the mass of the rotary piston 512 and crankpin 513. On the output side of the crankshaft 514, a balance weight 87 is incorporated within the ring gear 75 and represents half of the total balance weight necessary to balance the engine 510. Balance weight 87 is located on the inner side of radial bearing 82. The other half of the balancing weight is provided by a weight 88 on flange 514c of crankshaft 514 at a position opposite to crankpin 513, and by an additional balance weight 89 incorporated into a drive pulley 90 bolted to the crankshaft 514. Weight 88 may be of a heavy metal, such as tungsten, and secured to flange 514a such as by electron beam welding. As can be appreciated from the construction of the engine 510 of Figures 10 and 11, the placement of internal gear 65 within piston 512 enables crankpin 513 to be short and enables crankshaft 514 to be rigid and with large journal diameters. Although the main support bearings 81,82 for crankshaft 514 are relatively widely spaced along axis A, the effective support bearings, where deflection of crankshaft 514 may occur at high engine speed, are bearing 81 and bearing 72 via bearing 73 in gear member 69. It is evident from the arrangement that close support of the rigid crankshaft 514 by these effective bearings allows high speed engine operation to be achieved. In addition, the balance weights 87 and 84 are located close to and inside bearings 82 and 81, respectively, assist in preventing deflection of crankshaft 514. The rigidity of crankshaft 514 also allows high torque transmitting capacity particularly necessary for multi-piston engines. In such multi-piston engine, each piston most preferably is provided with a respective stabiliser comprising of gear train 74 and gears 65 and 70. As indicated at the outset, the invention relates to both a rotary piston engine and a rotary pump. The description principally is directed to the invention as applicable to an engine, although its application to a pump readily will be understood. Thus, in the latter case, drive will be from the crankshaft to the piston (that is, to a rotor of the form of the piston). Also, the chambers defined by the housing and rotor will be adapted for flow of a fluid, rather than for combustion of a fuel/air mixture.

Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

Claims

CLAIMS :

1. A device comprising a rotary piston engine or pump, having a housing and a trochoidal piston eccentrically mounted in the housing, the housing defining a compartment of at least two working chambers and having a configuration corresponding to the outer enclosing curve of the piston, wherein the piston is rotatable on a crankpin of a crankshaft which is mounted in the housing for rotation on an axis thereof, and wherein the piston and crankshaft are oppositely rotatable at a relative speed determined by a stabilising gear system therebetween, the stabilising gear system including a first gear mounted on the piston co-axially around the crankpin and movable with the piston, a second gear with which the first gear is in meshing engagement during opposite rotation of the piston and crankshaft, and a drive train operable between the second gear and the crankshaft, one of said first and second gears being an external gear and the other thereof being an internal gear, the first gear having a pitch circle radius F which exceeds the throw E of the crankpin and the second gear being movable relative to the housing.

2. A device according to claim 1, wherein said first gear is an external gear and said second gear is an internal gear.

3. A device according to claim 2, wherein said internal second gear has a fixed centreline about which it is rotatable with rotation of the external first gear, said fixed centreline being on said crankshaft axis.

4. A device according to claim 3, wherein said internal second gear is rotatably mounted in a bearing which is fixed in relation to the housing, and said drive train comprises a ring gear co-axially rotatable with the second gear, at least one planetary gear rotatable on a fixed axis laterally offset from the crankshaft axis and a sun gear fixed concentrically on and rotatable with the crankshaft, the piston and crankshaft being oppositely rotatable by driving engagement between the first and second gears, between the ring gear and the at least one planetary gear and between the at least one planetary gear and the sun gear.

5. A device according to claim 4, wherein the internal second gear and the ring gear are mounted on a common hub, with the ring gear having a larger pitch circle radius than the second gear, and wherein there is a plurality of planetary gears uniformly spaced angularly around the crankshaft axis, each of said planetary gears being rotatable on a respective pin fixed in relation to the housing and each providing driving engagement between the ring gear and the sun gear.

6. A device according to claim 2, wherein said drive train constrains said internal second gear against rotation with rotation of the external first gear, the drive train being operable during rotation of the first gear to move said second gear orbitally.

7. A device according to claim 6, wherein drive train comprises an eccentric on the crankshaft, a hub in which the eccentric is journalled, and a plurality of stabilising cranks each rotatable on a respective fixed axis laterally offset from the crankshaft, each stabilising crank having a throw equal to and in phase with the eccentric and being coupled to the hub such that the hub is caused to orbit without rotation during rotation of the crankshaft, the second gear being mounted on the hub and thereby caused to orbit therewith, said stabilising cranks being spaced angularly around the crankshaft axis, each of said cranks being journalled for rotation on a respective axis fixed in relation to the housing, each of said cranks having a stabilising crankpin journalled in a respective boss of said hub.

8. A device according to claim 1 wherein said first gear is an internal gear and said second gear is an external gear.

9. A device according to claim 8, wherein said piston defines a recess in one side face thereof, with said first gear being mounted on the piston within said recess.

10. A device according to claim 8 or claim 9, wherein said crankpin has a length substantially equal to the axial width of the piston.

11. A device according to any one of claims 8 to 10, wherein said external second gear has a fixed centreline on which it is rotatable, with said fixed centreline being on said crankshaft axis.

12. A device according to any one of claims 8 to 11, wherein said drive train comprises an epicyclic gear system operable between the second gear and the crankshaft, said epicyclic gear system comprising a ring gear concentrically mounted on and rotatable with the crankshaft, at least one planetary gear rotatable on a fixed axis laterally offset from the crankshaft axis and a sun gear journalled concentrically on the crankshaft, the piston and crankshaft being oppositely rotatable by driving engagement between the first and second gears and between the at least one planetary gear and both the ring gear and the sun gear, and by the^' sun gear being connected to and rotatable with the second gear.

13. A device according to claim 12, wherein the external second gear and the sun gear are mounted on a common hub, with said hub being journalled on the crankshaft.

14. A device according to claim 13, wherein said hub is rotatable on the crankshaft in a first bearing fixed in relation to the housing, with support for the crankshaft adjacent to the crankpin being provided by said first bearing and a second bearing between the hub and the crankshaft.

15. A device according to any one of claims 12 to 14, wherein part of overall balance weight requirements for said device is provided by a weight on said ring gear at a location opposed to the mass of the piston and crankpin.

16. A device according to any one of claims 1 to 15, wherein said piston is a one lobe piston and said housing defines two working chambers, and wherein said drive train is operable to rotate said piston and crankshaft at a relative speed ratio of 2:1.

17. A device according to any one of claims 1 to 16, wherein said crankpin is of substantially uniform cross- section throughout its axial extent.