GB2086479A - Rotary engines - Google Patents

Abstract

An internal-combustion engine comprises a casing (11) having a cylindrical bore (12) housing an eccentric rotor (13) with sliding radial vanes, or "plungers", (15). The rotor body may be cut away to provide differential areas on the plungers exposed to the gases within combustion chambers between the rotor body, the casing and the plungers. The rotor is mounted on a stationary hollow shaft (16) having a fuel-admission port (17) therein communicating sequentially with chambers (26, 27, 28) beneath the plungers, the fuel being expelled from these chambers through ports (23, 24, 25) into the combustion chambers by the plungers at appropriate points in the working cycle. The casing may be furnished with air-inlet and exhaust ports (29, 30) and ignition means (generally diametrically-opposite thereto). <IMAGE>

Description

SPECIFICATION A rotary engine The present invention relates to a rotary engine for producing motive power from combustible fuels.

Rotarngines, of course, known as such, the most widely known being the Wankel engine which employs an epitrochoidal cylinder with an eccentric trochoidal piston. Such known engines have experienced considerable problems, both in the manufacture ofthetrochoid and epitrochoidal forms, and also, particularly after a certain period of use, in maintaining the seal at the edges of the rotary piston between this and the epitrochoidal cylinder.

The present invention seeks to provide a rotary engine in which at least some of the disadvantages of such known engines are overcome, in part by designing the engine to employ largely circular or cylindrical components, avoiding the use of trochoidal and epitrochoidal shapes. The present invention also seeks to provide a construction in which the edge sealing problem previously of such serious proportions in the known engines can at least be minimised if not entirely eliminated.

According to the present invention a rotary engine comprises a substantially circular casing housing an eccentric rotor having a plurality of radial or generally radial bores therein, the bores housing respective radially or generally radially displaceable plungers, the rotor being mounted on a hollow shaft having at least one opening therein, the rotor having ports therein for the transfer of fuel from the interior of the shaft to chambers defined by the casing, the rotor and each pair of adjacent plungers.

The structure of the engine according to the present invention resembles, in many respects, the structure of a rotary pump, but various additional ports and fuel transfer arrangements have been introduced in order to allow the use of the construction as an engine. In particular, one of the modifications is to provide for the said ports to communicate between the aforesaid chambers and further chambers defined in the said radial or at least generally radial bores between the plungers therein and the stationary hollow shaft.This allows fuel transferred from the interior of the stationary hollow shaft into the said further chambers to be compressed as the plunger in question moves from the greatest extension point in the cycle towards its greatest retraction point, these points being diametrically opposite to one another and in line with a line joining the centre of the circular housing with the centre of the circular rotor which is eccentrically mounted therein.

The said fuel transfer ports require to have valves therein for ensuring the transfer fuel in the right direction from the said further chambers to the said chambers. Such valves may be operated to open and close at predetermined points in the cycle of the engine, or may be unidirectional valves operated by the appropriate differences in pressure on either side thereof in order to effect the required transfer, the unidirectional valves preventing reverse transfer of -fluids when the pressure differences are in the reverse direction thereby obtaining et,fectively automatic control of the fuel transfer.

To facilitate such fuel transfer the rotor and the rotary shaft are preferably provided with operirings which, together, comprise a rotary slide valve tor transfer of fuel from the interior of the hollow shaft to the said further chambers at appropriate parts Otc the cycle of the engine.

The circular components of the engine may hav any desired axial extent and this is a convenient way of controlling the capacity of the enginewithoufl requiring substantial modifications to the external diameters of the components. In this way a single engine casing can be used to provide engines otE different capacity simply by varying the axial dimen- sions of the cylindrical bore therein and those of thé ' rotor and plungers carried thereby. The plungers may be of any suitable form, although for an engine having any substantial axial extent these are preferably in the form of flat plates lying substantially in radial planes with respect to the axis of the rotor.The outer edges (that is the axially extending edges) of the plungers must form a seal with the inner cylindrical surface of the casing and this can be effected by means of a correspondingly shaped end face, with perhaps an extended trailing edge to increase the surface contact or alternatively one or a plurality of linear sacrificial seals may be inserted into longitudinal grooves in the end faces of the plungers, such seals being, again preferably, resiliently biased outwardly into contact with the inner wall of the cylinder. Such seals would correspond in many respects to the currently conventional substantially circular piston ring seals which are effectively resi lientiy biased into contact with the surface of the cylindrical bore in which the piston moves by virtue of their intrinsic resilience.Such sacrificial seals have considerable advantages in terms of extending the anticipated service life of an engine by replacement thereof.

A rotary engine formed as an embodiment of the present invention may be a compression ignition engine (Diesel cycle) or may be a spark ignition engine (Otto cycle), or alternatively any other known cycle for a heat engine, such as a Carnot cycle may be employed.

For an engine equipped as a spark-ignition engine it is necessary to provide spark-ignition means suitably timed to fire when the engine is at the appropriate points in its cycle, and it is envisaged that such spark-ignition means would be located in the quadrant defined at one end by the intersection with the casing of the line joining the centre of the cylindrical bore within the casing and the centre of the rotor at the end thereof corresponding to the point of maximum retraction of the plungers.

For increasing the differential piston effect upon firing of the fuel the rotor is preferably cut-away in each region on one side of respective plungers, this cut-away portion also serving to enlarge the com bustion chamber and determine the compression ratio.

It is also necessary to introduce combustion air into the combustion chambers defined by the casing, the rotor and adjacent plungers, and this can be effe'cted separately from the introduction of fuel by mraans of ports and/or openings in the casing. Likewi.se exhaust of the combustion products is achieved by suitawported openings in the casing.Circula tion of air through the engine can be improved by ,oroviding an auxiliary blower, either separately driven or driven from the engine itself, whereby to introduce air under pressure into the combustion chamber at the same time as the exhaust port is open thereby creating a "buffer" to ensure that all thre exhaust gases are discharged through the exhaust port and, at the same time, increasing the compression ratio ofthe engine.The particular shaping of the combustion chambers, being relatively long and narrow in the direction of the intended displacement of the plungers, has considerable advantages from the point of view of controlling turbulence and the flame front of the combustion mixture among other things by determining the point or points at which fuel is introduced into the chamber so that suitable variations in the mixture strength throughoutthe combustion chamber can be achieved readily. For example, immediately around the spark point it is desirable to have a fuel-rich mixture, with the mixture strength decreasing away from this point along the combustion chamber in order to obtain the most efficient combustion rate and generate the greatest pressure from a given charge in the combustion chamber.

One embodiment of the present invention will now be more particularly described, by way of example with reference to the accompanying drawing, the single figure of which is a schematic axial sectional view of an engine formed in accordance with the principles of the present invention.

Referring now to the drawing the engine shown comprises a casing, generally indicated 11 having a cylindrical bore 12 therein. The centre of the casing 11 is indicated 0. Eccentrically spaced from the centre 0 is the centre Pofa rotor 13, again of circular form but having three radial bores 14a, 14b, 14c therein. Within the bores 14 are housed respective slidable plungers 15, individually indicated 15a, 15b, 1 sic in correspondingly identified bores 14. The plungers 15 are in the form of generally flat plates the thickness of which corresponds, with a sliding fit, to the circumferential dimension of the bores 14 in the rotor 13, which bores are, of course, of corresponding rectangular cross-sectional form.

The rotor 13 is mounted on a stationary cylindrical shaft 16 having an elongate opening 17 therein. This opening is located at an angle of approximately 110 with respect to the line joining the two centres 0 and P of the casing and the rotor respectively taken from the point where this line intersects the casing 12 at the point nearest the centre P of the rotor.

As shown in the drawing the radially outer ends of the plungers 15 are formed as plain seals and have arcuately curved surfaces corresponding in radius to that of the casing bore 12. To increase the area of surface contact between the radially outer ends of the plungers 15 and the inner surface of the cylinder bore 12 the plungers are extended circumferentially as shown by the circumferential projections 18 at the radially outer ends thereof. Alternatively, as discus sed above, sacrificial linear seals in axially extending grooves in the ends of the plungers 15 may be provided instead of the plain bearings indicated.Such seals may not be necessary, however, because the amount of wear anticipated during an extended service life of the engine is not likely to exceed several tens of thousandths of an inch, whereas the radial dimension ofthe plunger would be several inches and since the contact between the plunger and the bore surface is maintained largely by centrifugal force during operation of the engine anywhere in the plunger and/or the cylinder bore will be accommodated by displacement of the plungers.

The point around the circumference of the casing intersected by the line joining the centres 0 and P will be identified as point A at the end ofthediame- ter where the point P is nearest the bore 12, and the diametrically oppositely intersecting point of this diameter line will be indicated by the reference B.

The plungers 15 define three combustion chambers between the bore 12 and the radially outermost surface of the rotor 13. The combustion chambers are indicated by the reference numerals 19,20 and 21. The shape of the combustion chambers is variable in dependence on the instantaneous position of the rotor and each combustion chamber will go through a cycle of variation in dimensions and shape corresponding to that experienced by the other two chambers so that the shape of each chamber as shown in the drawing represents the shape of the upper chambers at corresponding positions in the cycle. The combustion chambers are modified in shape by the provision in the rotor 13 of three cutaway portions 22 which ensure that, in each chamber, the trailing face of the plunger is larger than the leading face thereof, the direction of rotation of rotor 13 being clockwise.

Also formed within the rotor 13 are three fuel transfer ports 23,24,25 leading from respective combustion chambers 19,20,21 to chambers formed in the radial bores 14 between the plungers 15 and the hollow central shaft 16. These fuel transfer chambers are identified with the reference numerals 26,27 and 28 respectively.

Finally, in the outer casing 11 there are located two transfer ports 30,29 the former of which serves as an exhaust port and the latter of which as an induction port which can be fed with air under pressure from a blower (not shown) which may either be separately driven (for example by an electric motor) or may be driven from the engine itself, the power take off being derived from a shaft connected to the rotor 13.

It is to be noted that the rotor 13 rotates about a fixed axis defined by the centre P and consequently there is no power loss upon transmission from the piston to the shaft as there is in the case of the transmission from a trochoidal piston to the sun wheel on which it is mounted in the case of the Wankel engine.

The engine described above operates as follows: rotation of the rotor 13 causes the plungers 15 to be displaced radially within the bores 14 during each rotation; that is, upon each rotation of the rotor 13 a plunger starts from a point of maximum retraction within the associated bore 14 (which occurs at point A of this casing) extends gradually to a point of maximum extension (at point B ofthe casing) and again retracts to a point of maximum retraction. Correspondingly the combustion chambers increase in size from a minimum when the two defining plungers 15 are equiangularly spaced about the pointA ofthe casing, to a maximum when the two defining plungers are equiangularly spaced about the point B of the casing.

The combustion chamber 19 is, in the position shown in the drawing, in a compression phase during which, upon continued rotation of the rotor 13, it will reduce in size, compressing the gases contained therein, and at the same time, since the plunger 1 sic will be experiencing a retraction during this stage the fuel transfer chamber 26 will be compressed causing fuel to be transferred through the port 23 into the combustion chamber 19.Fuel within the combustion chamber 19 spreads out from the mouth of the port 23 in both directions, but the richest mixture will be in the vicinity of the mouth of the port 23 and this is chosen to be at a point midway between the two defining plungers 15a, 15e so that when this point reaches a coincidence with the point A of the casing 11 the mixture can be fired by a suitable spark-ignition device (not shown) or, in the case of a compression-ignition engine, will reach its maximum compression and will therefore ignite spontaneously.

The combustion chamber 20 is in the expansion stage, the mixture therein having been fired as it was symmetrically located about the point A of the casing. In this stage the gases within the chamber are being burnt, expanding rapidly and because the area of the plunger 15b exposed to the action ofthe expanding gases is substantially greater than the area of the plunger 15a exposed within this chamber the rotor 13 is urged to turn clockwise.At this point the plunger 15a is retracted within the bore 14a to such an extent that it cuts off communication between the fuel transfer port 24 and the fuel transfer chamber 27 whereas the plunger 15b is approaching its region of maximum extension and the fuel transfer chamber 28 is in communication via the fuel transfer port 25 with the combustion chamber 21 which, having reached its maximum expansion is now in communication with the exhaust port 30 and the combustion products will therefore have largely exhausted therethrough. The remaining exhaust gases can be encouraged to discharge through the exhaust port 30 by maintaining an over-atmospheric pressure at the port 29 by means of the blower (not shown) referred to above.The excess pressure does not require to be great since although substantial pressures are generated within the combustion chambers upon ignition of the fuel-air mixture therein, this rapidly discharges through the exhaust port 30 during the period of time when the leading plunger defining that particular combustion chamber is traversing between the exhaust port 30 and the induction port 29. The pressure within the combustion chamber 21 is thus only slightly above atmospheric pressure. At the same time the pressure within the fuel transfer chamber 28 will be somewhat below atmospheric pressure and, in the position illustrated in the drawing, this chamber is in communication with the interior of the hollow stationary shaft 16 through the port 17 thereof thereby allowing fuel contained within the hollow shaft 16 to be drawn into the chamber 28.A unidirectional valve 25a, schematically illustrated in the drawing, prevents the reverse flow of gases from the combustion chamber 21 where they are at above atmospheric pressure, to the fuel transfer chamber 28 where a sub-atmospheric pressure prevails. The fuel transfer ports 23 and 24 are likewise provided with unidirectional valves 23a, 24a.

The arcuate distance between the position of the leading plunger of a combustion chamber when ignition isfirstinitiated, and the position this plunger occupies when the exhaust port 28 is first exposed to the combustion chamber is in the region of 1200; this permits the maximum utilisation of the power stroke of the engine.

Fuel within the interior of the hollow shaft 16 may be in gaseous or vapour form, or may alternatively be in liquid form in which case the fuel transfer ports 23,24,25 would be provided with atomisers at the outlet ends thereof for spraying the fuel and vapourising it as it is discharged into the relevant combustion chamber. Such an atomisercould at the same time serve, or at least be constructed in order to enable it to serve, as the unidirectional valve preventing reverse flow along the fuel transfer port.

Engines formed as embodiments of the present invention have significant advantages in terms of avoidance of reciprocating parts thereby obtaining a very smooth generation of motive power, and are also particularly adapted for use with combustible fuels other than liquid fuels (that is fuel gases) since fuel transfer within the engine and mixture with the combustion air takes place entirely within the combustion chambers although, if necessary, additional combustion air may be introduced into the fuel prior to its introduction, or during its stay, within the interior of the stationary hollow shaft 16.

It is envisaged that engines formed as embodiments of the present invention will find particular applicability in the case of small motor units for driving equipment such as hand held machinery as weli as motors formed as propulsion units for agricultural and industrial machines, auxiliary engines for boats, outboard engines and the like which are all particularly susceptible to the problem of vibration previously encountered with reciprocating piston engines. In particular it is envisaged that an engine formed as an embodiment of the present invention could be formed as an interchangeable unit to fit a range of powered domestic, agricultural or horticultural implements, thereby economising on cost. A simple interconnector to the output shaft would be provided to allow interchanging to be effected quickly and easily.

The outer casing 11 may further be provided with a transfer port 40, indicated in broken outline in the drawing, leading from a point mid-way along the region where combustion takes place to a point closely adjacent the spark plug. This permits the transfer of hot combustion products, possibly still burning, to the space 19 from the space 20 as the plunger 15a passes the location ofthe outlet In this way ignition could proceed automatically with the hot gases from the previous power stroke being used to ignite the chargeforthe next.

Claims (15)

1. A rotary engine comprising a substantiallycir- cuiar casing having a substantially cylindrical inner surface housing an eccentric rotor having a plurality of radial or generally radial bores therein along which respective radially displaceable plungers are slidable, the rotor being mounted on a hollow shaft for rotation about an axis which is eccentric with respect to the axis of the cylindrical inner surface of the casing, the hollow shaft having at least one opening and, the rotor having ports therein for the transfer of fuel from the interior of the shaft to chambers defined by the casing, the rotor, and each pair of adjacent plungers.

2. A rotary engine as claimed in Claim 1, in which the said ports communicate between the aforesaid chambers and further chambers defined in the said radial or at least generally radial bores between the plungers therein and the hollow shaft.

3. A rotary engine as claimed in Claim 1 or Claim 2, in which the said hollow shaft is stationary within the engine casing and the rotor turns with respect thereto

4. A rotary engine as claimed in Claim 1, Claim 2, or Claim 3, in which the said fuel transfer ports have valves therein for ensuring transfer of fuel from the said further chambers to the said chambers, and for preventing a reverse flow of such fuel.

5. A rotary engine as claimed in any of Claims 1 to 4, in which the said plungers have part-cylindrical radially outer end surfaces engaging the cylindrical inner surface of the engine casing.

6. A rotary engine as claimed in Claim 4 or Claim 5, in which the said valves in the fuel transfer ports are unidirectional valves.

7. A rotary engine as claimed in any of Claims 1 to 6, in which the rotor and the rotary shaft have openings, which, together comprise a rotary slide valve forthetransfer of fuel to the said ports at appropriate parts of the cycle of operation of the engine.

8. A rotary engine as claimed in any preceding Claim, in which there are seals at the radially outer ends of the plungers for forming a sliding seal between the plunger and the inner cylindrical surface of the engine casing.

9. A rotary engine as claimed in Claim 8, in which the said seals are linear sacrificial seals.

10. A rotary engine as claimed in Claim 8 or Claim 9, in which the seals are spring biased outwardly.

11. A rotary engine as claimed in any preceding Claim, in which the radially outermost ends of the plungers are circumferentially enlarged to provide an extended bearing surface.

12. A rotary engine as claimed in any preceding Claim, in which there is provided a transfer port opening through the cylindrical inner surface of the engine casing and putting into communication that part of the chamber where combustion is initiated with a point further around the circumference in the direction of travel of the plungers.

13. A rotary engine as claimed in any preceding Claim, in which there are provided spark generating means for initiating combustion at a predetermined point around the circumference of the inner cylindrical surface of the engine casing.

14. A rotary engine as claimed in any preceding Claim, in which the engine casing is provided with a plurality of radial walls separating the cylindrical chamber into a plurality of axially separated compartments each housing a respective rotor and associated set of plungers.

15. A rotary engine substantially as hereinbefore described with reference to the accompanying drawing.