GB2524527A

GB2524527A - Cooled rotary engine rotor

Info

Publication number: GB2524527A
Application number: GB1405353.2A
Authority: GB
Inventors: Gilo Cardozo
Original assignee: Gilo Industries Research Ltd
Current assignee: Gilo Industries Research Ltd
Priority date: 2014-03-25
Filing date: 2014-03-25
Publication date: 2015-09-30
Also published as: GB201405353D0

Abstract

A rotor for a rotary engine comprising an external surface 14 extending between parallel end faces 12, having three apexes 18 and being defined by three flanks 40 each extending between two apexes and having a leading portion 42 and a trailing portion 44 defined by the direction of rotation of the rotor, wherein in the proximity of each apex each adjacent leading and trailing portion has an internal surface 32, 34 together defining walls of a cooling channel 30 extending between the end faces, multiple fins 50 extending in to each cooling channel from the internal surface of each leading portion but not trailing portion. Preferably, the remaining part of each channel is defined by the outer surface of a ring gear 22 or eccentric bearing 20. The fin arrangement allows for a higher rate of heat removal from the leading portions providing a more even heat profile along the whole of the flank.

Description

COOLED ROTARY ENGINE ROTOR

Field

This invention relates to rotary internal combustion engines. In particular, this invention relates to a rotor for a rotary internal combustion engine.

s Background

In a number of applications rotary internal combustion engines (for example, the Wankel layout) provide an attractive alternative to the more commonly utilised reciprocating piston engine, for example for use in light aircraft.

In a rotary engine a rotor is mounted eccentrically on an output shaft. The rotor is geared to the housing such that rotation of the output shaft causes eccentric rotation of the rotor, and vice versa. For example, a Wankel engine uses a three-sided (approximately triangular) rotor within an epitrochoidal chamber of a housing.

In the case of a Wankel engine, the three faces of the rotor combine with the housing to form three rotating combustion chambers that vary in size as the rotor rotates in the housing. In turn, each of the rotating combustion chambers moves through a cycle of intake, compression, combustion and exhaust.

Cooling of a rotary engine can present challenges. Reciprocating piston engines are typically either air cooled through the crankcase, cylinder block and heads, or water cooled by water flow paths in the cylinder block. Oil supplied to the crank shaft may also assist with cooling.

Although similar water cooling systems can be implemented for a rotary engine, cooling of the output shaft and gearing linking that shaft to the rotor is inefficient as those components are far removed from the cooling medium. Furthermore, the gears and bearings in the interior of the rotor must be lubricated, which makes circulating cooling media in that area difficult.

There is therefore a requirement for improving the cooling of rotary internal combustion engines.

The embodiments described below are not limited to implementations that solve any or all of the disadvantages of known cooling systems.

Summary

According to an aspect of the invention there is provided a rotor for mounting on an engine output shaft and in a housing of a rotary internal combustion engine, the rotor comprising an external surface that extends between parallel end faces of the rotor and has three apexes.

The external surface is defined by three flanks of the rotor in which each flank extends between two of the three apexes and has a leading portion and a trailing portion defined by the direction of rotation of the rotor. At each apex the leading portion of one of the flanks is adjacent to and joins the trailing portion of the neighbouring flank and in the proximity of each apex each of the adjacent leading and trailing portions has an internal surface which together define a cooling channel that extends between the end faces and in which cooling gas flows through the rotor when in use. The leading portion of each flank has a plurality of fins extending from its internal surface into the corresponding cooling channel while the trailing portion of each flank is smooth and has no fins.

In this way heat may be removed from hotter part of the flank in a more effective manner since each of the flanks of the rotor present a varied temperature profile across the flank during engine use. Removal of heat at a higher rate from the leading portions of the flanks than from the adjacent trailing portions allows a more even heat profile along the whole of the flank. Thus, heat is more effectively transferred into the coolant flowing in the cooling channel from the hotter part of the combustion face/flank. The Applicant has found that the claimed cooling system may increase the longevity of the rotor by approximately twenty percent. The life of the rotor is increased and maintenance intervals thus can be lengthened.

The following are optional features which may be additionally included in any compatible combination or independently of other optional features.

The rotor may include, immediately adjacent each apex, an additional fin projecting from the junction of the internal surfaces of the respective adjacent leading and trailing portions into the corresponding cooling channel. As the apex area, where the additional fin is located, also gets hot due to sealing friction against the housing, in addition to the heat generated by the combustion process, the heat may be more effectively removed through the addaional fin located directly under the apex.

The rotor may be installed/assembled into a rotary internal combustion engine comprising housing and mounted on an eccentric shaft in the housing.

The fins may project in a substantially perpendicular direction from the internal surface of the respective leading portion of each flank.

The fins may project in an angled direction relative to the internal surface of the respective leading portion of each flank and the fins are angled towards the internal surface of the adjacent trailing portion.

The additional fins may be substantially parallel to the fins projecting from the internal surface of the respective leading portion of each flank.

The fins may be straight fins which run the entire extent of the cooling channel. The straight fins may be cross-cut at regular intervals. The fins may comprise cylindrical pins. The choice s of fin shape may increase their surface area and increase heat transfer efficiency.

The rotor may further comprise a ring gear for meshing with a timing gear mounted on the housing and a circular eccentric bearing for mounting on an eccentric lobe of the engine shaft wherein the radially outer surfaces of the ring gear and/or the eccentric bearing define the remaining part of each cooling channel.

The distal end of the fins may define a clearance gap between the fins and the ring gear and/or eccentric bearing.

The end faces of the rotor may have a central recess so asto ensure a clearance from the housing.

The parallel end faces may include a groove on each flank to receive a face seal for sealing against the housing of the engine.

Each apex may include a groove extending between the parallel end faces of the rotor for receiving an apex seal for sealing against the housing of the engine. The flanks may define identical convex and bowed shaped combustion faces.

The preferred features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the invention.

Brief Description of the Drawings

Embodiments of the invention will be described, by way of example, with reference to the following drawings, in which: Figure 1 shows a cross-section through the housing of a rotary engine incorporating and showing a rotor according to the invention; and Figure 2 shows a detailed end elevation view of a rotor according to the invention.

Common reference numerals are used throughout the figures to indicate similar features.

Detailed Description

Embodiments of the present invention are described below by way of example only. These examples represent the best ways of putting the invention into practice that are currently known to the Applicant although they are not the only ways in which this could be achieved.

The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.

Figure 1 shows the basic arrangement for a rotary engine 100 incorporating a rotor 10 according to the present invention. With the exception of the arrangements discussed below the engine is conventional and its operation will therefore be apparent to the person skilled in io the art. Accordingly, for clarity, not every component of the engine is shown or described. The rotary engine comprises a housing 110 through which the cross-section of Figure 1 is drawn.

The housing 110 has an epitrochoidal shaped chamber 120 in which the rotor 10 is mounted.

The chamber 120 of the housing 110 has inlet 130 and outlet 140 ports that allow the intake of a fuel-air mixture and exhaustion of the combusted gases during operation of the engine 100. In this instance, two spark plugs 150 are shown and provide forthe ignition of the compressed fuel-air mixture. Other plug arrangements are conceivable.

The rotor 10 rides on an eccentric lobe 161 of an engine output shaft 160 through which the power output generated by the engine is transmitted. The axis of rotation of the engine shaft 160 substantially coincides with the axis through the centre of the circular timing gear 170.

Referring to Figure 2 in addition to Figure 1, the rotor 10 has two parallel end faces 12 that interface with two complementary parallel surfaces of the chamber 120 within the housing 110 when the rotor lois installed in the engine 100. The rotor 10 has an external surface 14 which extends between the end faces 12. The external surtace 14 is divided into three identical combustion faces 16. The external surface 14 has three apexes 18 or tips. Each combustion face 16 is bordered by two of the three apexes 18 and the two end faces 12.

The combustion faces 16 are bowed in a convex shape. When looking from end-on, or perpendicular to an end face 12, each of the combustion faces 16 show a symmetrical curve extending between two of the three apexes 18. The faces 16 form, in concert with the chamber 120, three individual combustion chambers orvolumes within the housing. These chambers rotate with the rotor and, in-turn, compress, combust and exhaust the fuel-air mixture drawn into each individual chamber as it passes the intake port 130. Each chamber is, during rotation, continually sealed against the epitrochoidal shaped part of the chamber by the apexes 18 of the rotor 10. The combustion faces 16 may include a pocket to increase the volume of fuel-air mixture that can be drawn into the engine, compressed and com busted.

In the centre of the rotor 10, a circular bearing 20 is provided on which the rotor is mounted to the eccentric lobe 161 of the output shaft 160 when installed in the engine 10. When in use, the rotor 10 exerts a force on the eccentric lobe 161 and so generates torque in the output shaft 160. The axis of the circular bearing 20 is coincident with the centre axis of the rotor 10 about which it rotates.

A ring gear 22 is also provided in the centre of the rotor 10. The ring gear 22 ensures that, under the forces exerted by the combusted gases on the combustion faces 14, the rotor 10 follows the correct rotational path inside the chamber 120 and sets the rotation speed of the rotor relative to that of the output shaft. The ring gear 22 engages the timing gear 170 io mounted on the housing. In this example, the ring gear 22 is coaxial with the circular bearing 20.

Each of the end faces 12 of the rotor may include a central recess into the end face 12. The recess ensures that there is a clearance between the central components pad of the rotor 10 and the two complementary parallel surfaces of the chamber 120.

is Each of the combustion faces 16 is defined by one of three flanks 40 of the rotor 10. Each of the flanks 40 joins the other two flanks 40 at one of the two apexes 18 between which it extends. Each of the flanks 40 may be described as neighbouring the other two flanks 40.

One of those neighbouring flanks 40 may be further described as preceding the flank 40 in question and the other trailing the flank 40 in question, as defined by the direction of rotation of the rotor when in use.

Each flank 40 has a leading portion 42 and a trailing portion 44 as defined by the direction of rotation of the rotor 10 when in use. The leading portion 42 of each flank 40 joins the trailing portion 44 of the neighbouring flank 40 at the corresponding apex 18. Thus, in the region of each apex 18 of the rotor 10, the leading portion 42 of the corresponding flank 40 is adjacent the trailing portion 44 of the neighbouring flank 40.

When the engine 100 is operating and the hot gases are acting on the combustion faces 16 of the rotor 10 the flanks 40 get very hot. To cool the rotor 10 in the engine 100, cooling gas is passed through the interior of the rotor 10, substantially in parallel with the engine shaft 160.

Openings (not illustrated) are provided in the flat side of the chamber 120 to allow cooling gas to flow through the rotor 10. To this end the rotor 10 is provided with cooling channels 30 in the vicinity of each apex 18. Each of the three cooling channels 30 passes through the rotor allowing coolant to flow from one side to the other of the rotor 10 and remove heat therefrom. For this reason the channels 30 extend through the entire extent, or thickness, of the rotor 10 between the end faces 12. Because the channels 30 are inside the line of the exterior surface 14 (looking end-on to the rotor 10) and the end face 12 seals, a flow path is provided for the coolant without interfering with the sealing of the rotor 10 against the flat sides of the chamber 120.

Each of the cooling channels 30 is partially defined by internal surfaces 32,34 of the corresponding adjacent leading 42 and trailing portions 44 of the relevant flanks 40. The s remaining part of the surface of the cooling channels 30 may be defined by the radially outer surfaces of the either of, or both of, the ring gear 22 or circular bearing 20. Alternatively, the cooling channels 30 may have another wall which completes the enclosure of the cooling channel 30.

The internal surface 32 of each of the leading portions 42 of each flank 40 has a plurality of io fins 50 that project into the corresponding cooling channel 30. The fins 50 provide a large cooling surface area within the corresponding cooling channel 30. In contrast, the internal surface 34 of each of the trailing portion 44 of each flank 49 is and has no fins. There may however be small protrusions, such as bumps or dimples, provided on the trailing portion 44 internal surface 44. The small protrusions may increase turbulence in the coolant for example.

is Since there are no fins or protrusions on the adjacent trailing portion 44 internal surface 34 of the neighbouring flank 40, only the fins 50 protruding from each leading portion 42 internal surface 32 occupy the volume/space of the corresponding cooling channel 30. Because the available cooling surface area for the leading portion 42 of each face is maximised by this fin arrangement, there is a larger heat transfer potential from the leading portion 42 than from the trailing portion 44 of each flank 40. In other words heat may be drawn from the leading portions 42 at a faster rate than from the trailing portions 44 of the flanks 40.

As cooling gas flow through the cooling channels 30, heat is radiated and conducted from the fin surfaces into that gas, thereby cooling the fins 50 and rotor 10. As the fins 50 are arranged within each cooling channel 30 to provide greater conduction of heat from the leading portion 42 of each flank 40, the extension of the fin 50 from what is a hotter region of the flanks 40 maximises heat conducting from that hot region into the fins 50 and therefore into coolant flowing in the channel 30.

Additional fins 51 are also shown in Figure 2, each of which projects from the respective junctions of adjacent leading 42 and trailing portions 44 of neighbouring flanks 40. Each of the additional fins 51 projects into the corresponding cooling channel 30 from a position immediately adjacent the corresponding apex 15. The location of the additional fins 51 may be alternately described as being substantially under the corresponding apex 15. Thus, each of the apex 15 regions may be cooled at a higher rate than the trailing portion 44 of each flank 40.

As shown, the fins 40 may project in a substantially perpendicular direction from the internal surface 32 of the leading portion 44. Alternatively, the fins 40 may be inclined at an angle to the internal surface 32, for example, by tilting towards the adjacent trailing portion 44 internal surface 34. The fins 50 may have a crooked or bent profile for example. The optional additional fins 51 may be oriented so as to be parallel with the other tins 50 provided on the leading portion 42 internal surface 32.

The fins 50, Slmay be straight fins that cover the full extent of, or run the entire length of, the respective cooling channel 30. Alternatively, the fins 50, 51 may be cross-cut at regular intervals to increase their surface area and efficiency. Such cross-cutting may be possible io before the insertion ot the ring gear 22 and/or bearing 20 into the rotor 10 body and adjacent the fins 50, 51. This may be particularly possible with fins 50, 51 that have been manufactured by extrusion with the rotor 10 flanks 40. Alternatively, the fins 50, 51 may be provided by cylindrical pins that protrude from the leading portion 42 internal surface 32 at the appropriate desired angles.

A gap is shown in Figure 3 between the far ends ot the tins 50, 51 and the ring gear 22 and/or bearing 20. This gap allows sound assembly of the rotor 10 when these components are inserted into position. However, in an alternative embodiment the fins may be integral with leading portion 42 of each flank 40 and the ring gear 22 and/or bearing 20. Such an arrangement may provide preferable heat transfer profiles.

Each of the apexes 18 includes a slot 60 that extends between the two end faces 12. The slots 60 are able to receive an apex seal inserted into them. This may be a simple metal strip forming the apex seal. A groove 62 is also provided on the end faces 12 along each flank 40.

The groove accepts the insertion of a face seal that seals the combustion chambers against the sides of the housing 110 chamber 120.

It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments Any range or device value given herein may be extended or altered without losing the effect sought, as will be apparent to the skilled person.

Any reference to an' item refers to one or more of those items. The term comprising' is used herein to mean including the method blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

It will be understood that the above description ot a preterred embodiment is given by way ot example only and that various modifications may be made by those skilled in the art.

Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention.

S

Claims

Claims 1. A rotor for mounting on an engine output shaft and in a housing of a rotary internal combustion engine, the rotor comprising an external surface that extends between parallel end faces of the rotor and has three s apexes, where the external surface is defined by three flanks of the rotor in which each flank extends between two of the three apexes and has a leading portion and a trailing portion defined by the direction of rotation of the rotor, where at each apex the leading portion of one of the flanks is adjacent to and joins the trailing portion of the neighbouring flank, and in the proximity of each apex each of the adjacent leading and trailing portions has an internal surface which together define walls of a cooling channel that extends between the end faces and in which cooling gas flows through the rotor when in use, wherein the leading portion of each flank has a plurality of fins extending from its internal surface into the corresponding cooling channel while the trailing portion of each flank has no fins.
2. A rotor according to claim 1 wherein the fins project in a substantially perpendicular direction from the internal surface of the respective leading portion of each flank.
3. A rotor according to claim 1 wherein the fins project in an angled direction relative to the internal surface of the respective leading portion of each flank and the fins are angled towards the internal surface of the adjacent trailing portion.
4. A rotor according to any preceding claim where the rotor includes, directly adjacent each apex, an additional fin projecting from the junction of the internal surfaces of the respective adjacent leading and trailing portions into the corresponding cooling channel.
5. A rotor according to claim 4 wherein each additional fin is substantially parallel to the fins projecting from the internal surface of the respective leading portion of each flank.
6. A rotor according to any preceding claim wherein the fins are straight fins which run the entire extent of the cooling channel.
7. A rotor according to claim 6 wherein the straight fins are cross-cut at regular intervals.
B. A rotor according to any of claims ito 5 wherein the fins comprise cylindrical pins.
9. A rotor according to any preceding claim where the rotor further comprises a ring gear for meshing with a timing gear mounted on the housing and a circular eccentric bearing for mounting on an eccentric lobe of the engine output shaft wherein the radially outer s surfaces of the ring gear and/or the eccentric bearing define the remaining part of each cooling channel.
10. A rotor according to claim 9 wherein the distal end of the fins define a clearance gap between the fins and the ring gear and/or eccentric bearing.
11. A rotor according to any preceding claim wherein the end faces of the rotor have a io central recess so as to ensure a clearance from the housing.
12. A rotor according to any preceding claim wherein the parallel end faces include a groove on each flank to receive a face seal for sealing against the housing of the engine.
13. A rotor according to any preceding claim wherein each apex includes a groove extending between the parallel end faces of the rotor for receiving an apex seal for sealing against the housing of the engine.
14. A rotor according to any preceding claim wherein the flanks define identical convex and bowed shaped combustion faces.
15. A rotary internal combustion engine comprising a housing and a rotor mounted on an eccentric output shaft in the housing wherein the rotor is a rotor according to any preceding claim.
16. A rotor for a rotary internal combustion engine substantially as described herein with reference to the accompanying figures.