GB2391909A

GB2391909A - Rotary combustion engine

Info

Publication number: GB2391909A
Application number: GB0218839A
Authority: GB
Inventors: David Leslie Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-08-14
Filing date: 2002-08-14
Publication date: 2004-02-18
Also published as: GB0218839D0

Abstract

A rotary combustion engine 10 comprises a housing 12, a first rotor 14 mounted for rotation about a first axis 16, and a second smaller rotor 20 mounted for rotation about a second axis. The axes 16,22 are parallel. An inlet port 26 is provided for supplying air to the first rotor 14, and a further inlet port 28 is provided for supplying air to the second rotor 20. Each rotor 14,20 is provided with five respective lobes 30,32, which are eqiangularly spaced. Five respective combustion chambers 34,36 are formed between the lobes 30,32. The rotors 14,20 are arranged to counter-rotate in mesh, with the lobes 30 of the first rotor 14 passing through the combustion chambers 36 of the second rotor 20, and the lobes 32 of the second rotor 20 passing through the combustion chambers 34 of the first rotor 14, as the rotors rotate.

Description

239 1 909

Title: Engine The present invention relates to an ertgine, and more particularly to a rotary combustion engine.

A conventional rotary combustion engine, one design of which is known as a Wankel engine, comprises a biangular shapedrotor, which is mounted for movement within ahousing, shaped as 5 an epitrochoid. The rotor has three convex faces, each of which acts in the manner of apiston. The convex faces aredishedattheircentres, thusincreasingthevolumeofthecombustionchamber, i.e. the capacity of the engine. Blades mounted at the vertices of the rotor, malice a seal with the housing, and each blade moves in continuous contact with the housing. Internal gear teeth cut into the centre of one side of the rotor mate with a gear attached to the housing, which determines the 10 path of movement ofthe rotor.

An output shaft, which extends through the centre ofthe rotorhas an eccentric cam which is caused to rotate by the movement of the rotor. The cam and output shaft rotate three times for every rotation ofthe rotor. The Wankel engine operates on a four stroke cycle, known as the Otto cycle, which includes intake, compression, power and exhaust strokes. Each face ofthe rotor completes 15 all four strokes in a single rotation ofthe rotor. Therefore, for everyrotationoftherotor, there are three power strokes, ie for each rotation of the output shaft Were is one power stroke.

An alternative design of rotary combustion engine has been proposed in published patent application GB 1,198,625 in the name of John Wilmott Marshall. In this design, a male rotor having four circumferential equiangularly-spaced lobes and a female rotor having eight 20 equiangularly-spaced recesses are mounted about parallel axes in mesh. The rotors counter-rotate and air is suppliedto therecesses ofthe female rotor, followedby aninjectionoffuel. As aTecess ofthe female rotor comes into mesh with a lobe ofthe male rotor, the fueVair mixture in the recess is compressed and ignited. During combustion, the gases expand into the female recess, and act partially against one flank of the lobe of the male rotor.

It is believed to be a disadvantage of this design that although there is a net force acting in the driving direction of both rotors, there is a net reverse force acting on the female rotor, which significantlyincreases the stresses in the gearing ofthe rotors. This isbecausethe part of each female recess which forms a combustion chamberatthe positionjust past the point of mesh, has 5 a greaterradial surface area component in the rearward direction, than in the forward direction, due to the position of the male lobe in the recess.

Rotary engines are advantageous when compared to conventional piston engines, because they have fewermovingparts, eachrotorcontinuouslyrevolves and is easilybalanced, end thus rotary; engines are more reliable. However, rotary engines typically consume more fuel for a given power 10 output than piston engines, due to a low thermodynamic efficiency caused partly by low compression ratio.

It is therefore an obj ect of the invention to provide a rotary combustion engine with an increased compressionratio, which has ahigherthermodynamic efficiency, andis consequentlymore fuel efficient. 15 According to the present invention there is provided a rotary combustion engine comprising a housing having at least two inlet ports and at least two exhaust ports, a first rotor mounted for rotation about a first axis in a first part ofthe housing, and a second rotor mounted for counter-

rotation about a second axis in asecondpart ofthehousing, apluralityofcircumferentially spaced robes provided about the first rotor, and aplalityofcircumferentiallyspaced robes provided about 20 the second rotor, the lobes ofthe first rotor being arranged in mesh with the lobes ofthe second rotor, end means for maintaining the angularposition ofthe first rotor relative to the angularposition ofthe second rotor es the rotors rotate, apluralityofcircumferentiallyspaced combustion chambers formed about the periphery of each rotor in spaces between the lobes, in use, an air and fiael i mixture which is present in a chamber ofthe firstrotorbeing compressed as the chamber moves 25 into mesh with an associated lobe of the second rotor, the compressed air and fuel mixture expanding into a smaller chamber ofthe second rotor, and being further compressed as the smaller chamber moves into mesh with an associated lobe of the first rotor, expansion due to combustion

occurring es the smaller chamber andassociater.llobemovebeyondthepoint of mesh,to one side of a plane lying on the axes of the first and second rotors.

It is an advantage ofthe invention that due to the two stages of compression, a high compression ratio is achieved, which increases the thermodynamic efficiency of the engine. It is a further 5 advantage ofthe engine that due to the movement of partially compressed air/fuel mixture from the chamber ofthe first rotor into a smaller chamberofthe secondrotor, rruxing or squish ofthe air/fuel mixture is Unproved, which also increases the thermodynamic efficiency ofthe engine. Hence it is believed that the engine is more fuel efficient than prior designs of rotary engine.

Preferably the expansion due to combustion acts firstly to drive the second rotor. During 10 combustion, it is preferable that the expansion gases move into a combustion chamber ofthe first rotor, and continue to act by driving the first rotor.

It is a yet further advantageoftheinventionthatmovement of expansion gases from combustion chambers ofthe secondrotorinto respective combustion chambers ofthe firstrotorutilises all available work from each combustion, which again improves thermodynarnc efficiency and filet 15 consumption of the engine.

The combustion chambers are preferably sealedbyblade-like seals, analogous withpiston rings, whicharepositioned et the leadingperipheral edge of each lobe. The seals maysealbetweenthe respective rotors andtheirparts ofthehousing, es well asbetweentherotorswhenthe seals liein the plane on the axes of the first and second rotors.

20 Preferably the means for maintairung the angular position of the first rotor relative to the angular positionofthe secondrotor as the rotors rotate is apair of meshing gears mounted on the axes of the first and second rotors.

The invention will now be describedbywayofexample onlywith reference to the accompanying drawings, in which; Fig 1 shows a diagrammatic crosssectional view through the casing and rotors of an engine in accordance with the invention; 5 Fig 2 shows an exploded perspective view ofthe engine of Fig 1 together with an optional ducting; and Figs 3 to 10 show diagrammatic cross-sectional views through the casing and rotors of the engine of Fig 1, with the rotors in different positions in the Otto internal combustion engine cycle.

10 Referring firstly to Fig 1, a rotary combustion engine Is indicated generally at 10 and comprises a housing 12 haying a first rotor 14mountedforrotation about a first axis 16 inafirstpaTt 18 ofthe housing 12, and a second smaller rotor 20 mounted for rotation about a second axis 22 in a second part24Ofthe housing 12. The axes 16,22 areparallel. Aninletport26isprovidedinthefirstpart 18 ofthe housing, through which airis supplied to the first rotor 14, andaturthermletport28 is 15 provided in the second part of the housing, through which air is supplied to the second rotor 20.

Each rotor 14,20 is provided with five respective lobes 30,32, which are eqiangularly spaced about the circumference of each rotor. Five respective combustion chambers 34,36 are also circumferentially spaced about the rotors 14,20, and are formedbetween the lobes 30,32. The 20 rotors 14,20 are arranged to counter-rotatein mesh, with the lobes 30 ofthe first rotor 14passing through the combustion chambers 36 ofthe second rotor 20, and the lobes 32 ofthe second rotor 20 passing through the combustion chambers 34 ofthe first rotor 14, as the rotors rotate. Blade like seals 38, which are analogous to piston rings, are positioned at the leading peripheral edge of each lobe 30,32, and seal between the respective rotors 14,20 and theirparts 18,24 ofthe housing 25 12, as well as between the rotors when the seals lie in the plane lying on the axes 16,22 of both rotors.

The lobes 30 each have a flat across theirperipheraltip indicated at 66. This flattening prevents sealing ofthe chambers 36 into two halves at the point of mesh, as shown, and allows compressed air/fuel mixture in a combustioncharnber36 ofthe secondrotor 20 to move from theupperpart ofthe chamberthrough to the lowerpart ofthe chamber,priorto combustion. This movement of 5 air/fuelmixture is important for the smoothNnning ofthe engine, since it ensuresthatexpansiondue to combustion occurs below the plane lying on the axes 16,22 of the rotors 14,20.

The first rotor 14 rotates anticlockwise, when the engine is running, in the direction of arrow A as viewed, and the second rotor 20 rotates clockwise, in the direction of arrow B as viewed. The rotors 14,20 are mounted at the ends of shafts 44,46, which can be seen in Fig 2. Meshing gears 10 40,42, are mounted on the other ends of the respective shafts 44, 46 and maintain the angular position of the first rotor 14 relative to the angular position of the second rotor 20 as the rotors rotate. Referring back to Figure 1, a pair of exhaust ports 48,50 are provided in the lower part of the housing 12, as viewed, one ofthe exhaustports 48 communicating with the second part 24 ofthe 15 housing and the other exhaust port 5 0 conununicating with the first part 18 of the housing. The exhaustports 48,50 are channelled towards a common exhaust outlet 52. Fuel injectors 54,56 are provided in the upperpart ofthe housing 12 as viewed, the injector 54 enabling fuel to be injected into the combustion chambers 34 ofthe firstrotor 14, end theinjector 56 enabling fuel to beinjected into the combustionchambers 36 ofthe secondrotor20. Sparkplugs or glow plugs 20 (not shown) maybe provided in the end ofthe housing 12 inthepositions indicated at 58 and 60, where ignition takes place.

Refernngbackto Figure 2, a ducting 62 canoptionallybe arranged around the outside ofthe casing 12, which directs air through the inlet ports 26,28 and encloses the exhaust outlet 52. The ducting 62 can be pressurised with air if scavenging of air through the inlet ports is not sufficient.

25 The operation ofthe engine 10 will now be described with reference to Figures 3 to 10. The fuel injectors 54,56 are not shown in these Figures, since fuel air mixture can optionallybe supplied

directly through the inletports26,28. For ease of description air/fuelmixturewill be described

as supplied together, but in practice it is expected that the fuel will be injected into the combustion chambers 34,36 by the injectors 54,56, positioned after the air intakes.

In Figure 3 air fuel mixture is being supplied to the combustion chamber 34a, arid is alreadypresent 5 in combustion chambers 34b and 34c of the first rotor 14. Combustion has been completed in chamber 34d and the chamber 34e has just moved past the exhaust port 50. Air fuel mixture is present in the combustion chambers 36a and 36b, and ignition is occurring in chamber 36c.

Emission gases are being exhausted from chamber 36d through the exhaust port 38 and the chamber 36e is moving towards the inletport28. The lobe 30c ofthe first rotor 14 is in mesh with l O the chamber 36c of the second rotor 20, and hence, compression in the chamber 36c is at a maximum, prior to combustion.

Referring now to Figure 4, the rotors 14,20 have moved through 5 degrees beyond the point of mesh to one side ofthe plane lying on the axes 16,22 ofthe first and second rotors 14,20 and expansion due to combustion is occurring in the combustion chamber 36c. The forces due to 15 expansion on the end ofthe lobe 30c and the base ofthe combustion chamber 36c are almost negligible, and hence, substantiallyall ofthe work done in expansion is directed radiallytowards the lobe 36d, in the driving direction ofthe engine. The lobe 32c ofthe srnalIerrotor20 is moving into the combustion chamber34c ofthe first rotor 14, causing compression ofthe air fuel mixture present in the chamber 34c. In Figure 5, the rotors 14, 20 have moved through a furler 5 degrees, 2 combustion in the chamber 36c ofthe second rotor 20 is more advanced, as is compression in the chamber 34c of the first rotor 14.

After a further 15 degrees of rotation, as shown in Figure 6, the combustion chamber 36c ofthe second rotor 20 has opened into one end ofthe combustion chamber 34c ofthe first rotor 14. The shape ofthe combustion chamber 36c is such that the forces acting on the walls ofthe chamber 25 against the rotor 20 cancel each other out at this point due to its symmetry, and hence, no net driving force is applied to the rotor 20. However, an end face of the lobe 30c ofthe first rotor 14 is presented in the chamber 36c, and any firtherexpansionin the chamber acts onthis end face in

the driving direction of the engine, thus utilising any further available work from combustion.

Compression is further advanced in the chamber 34c. Air/fuel mixture is being supplied to the chamber 36e through the inlet port 28 and emission gases are being exhausted from the chamber 34d through the exhaust port 50.

5 Referring now to Figure 7, the rotors 14, 20 have moved through a further 10 degrees. The chamber 34c of the first rotor 14 has moved into communication with the chamber 36b of the second rotor 20. Hence, air/fuel mixture compressed in the chamber 34c, expands into the chamber36b. In Figure 8, the lobe 30b ofthe firstrotor 14 isbeginningto rnoveinto the chamber 36b ofthe second rotor 20, and the combined air/fuel mixture ofthe chambers 34c and 36b are l O beginning to be further compressed. The movement ofthe partially compressed air/ffiel mixture from the chamber34c into the chamber36b increases the mixing orsquish ofthe air/fuelmixture, which results in an increase in the thermodynamic efficiency of the engine.

Referring now to Figure 9, the rotors 14, 20 have moved through a further 10 degrees.

Compression in the chamber 36b is significantly advanced, and emission gases present in the 15 chamber 36c arebeing exhausted through the exhaust port 48. Air/fuel mixture is beginning to be supplied to the chamber 34e, and air/fuel mixture is present in the chamber 36e. Any further expansion which is occurring in the chamber 34c acts on the radial face at the end of the chamber against the lobe 30c in the driving direction.

Finally, in Figure 10, the rotors 14,20 have moved through a further 10 degrees. The lobe 3 Ob 20 is moving into mesh withe chamber 36b, end hence, compression ofthe air/fuel mixture in the chamber 36b is approaching amaximum. Whentherotormoves through a further 10 degrees, the rotors will have moved through approximately one fifth of a complete rotation and ignition in the chamber 36b will take place, followed by combustion. For every rotation ofthe rotors 14, 20 there are five power strokes, and it is believed that the overall compression ratio of the engine 25 resulting from the dual compression is around 12:1, i.e., sufficient for compression ignition.

Itcanbeseenthatduringthe operation ofthe engine 10, the exhaust gases are exhausted from the chambers 34 ofthe first rotor 14 through the exhaust port 50, and from the chambers 36 ofthe second rotor 20 through the exhaust port 48 alternately. For example, in Figure 3, the chamber 3 6d ofthe second rotor 20 is being exhausted, and subsequently in Figure 6 the chamber 34d of 5 the first rotor 14 is being exhausted. It is believed that this alternation of combustion chambers connected to exhaust, assists in exhaust scavenging, which improved the volumetric efficiency of the engine.

The embodiment of engine 10 shown and described, is only one example of an engine fallingwithin the intended scope of the invention. In an alternative embodiment (not shown), each rotor has six I O lobes, and an associated six combustion chambers formed between the lobes. This gives a compression ratio of approximately 7: 1, which is typical of a spark ignition petrol driven engine.

Other embodiments of engine may have fewer lobes arid combustion chambers formed about the rotors. For example, and engine having two lobes on each rotor may have a combustion ratio as high as 30:1, which could be run using low grade fuels, such as vegetable oils. For compression 15 ignition to take place, i.e. in order to run an engine on diesel fuel without a spark, typically a compression ratio of greater than 11:1 is required.

Claims

1. A rotary combustion engine comprising a housing having at least two inlet ports and at least two exhaust ports, a first rotor mounted for rotation about a first axis in a first part of the housing, and a second rotormounted for counter-rotation about a second axis in a second 5 part ofthe housing, apluralityofcircumferentiallyspaced robes provided aboutthe first rotor, and a plurality of circumferentially spaced lobes provided about the second rotor, the lobes ofthe firstrotorbeing arranged inmeshwith the lobes ofthe second rotor, and means for maintaining the angularposition ofthe first rotor relative to the angularposition of the second rotor as the rotors rotate, a plurality of circumferentially spaced combustion 10 chambers formed about the periphery of each rotor in spaces between the lobes, in use, an air and fuel mixture which is present in a chamber of the first rotor being compressed as the chamber moves into mesh with an associated lobe of the second rotor, the compressed air and fuel mixture expanding into a smaller chamber ofthe second rotor, and being furler compressed as the smaller chamber moves into mesh with an associated lobe 15 of the first rotor, expansion due to combustion occurring as the smaller chamber and associated lobe move beyond the point of mesh, to one side of a plane lying on the axes of the first and second rotors.

2. A rotary combustion engine as claimed in claim 1 in which We expansion due to combustion acts firstly to drive the second rotor.

2 0

3. A rotary combustion engine as claimed in claim 2 in which the expansion due to combustion continues to act by driving the first rotor.

4. A rotary combustion engine as claimed in anypreceding claim inwhich the combustion chambers are sealed by blade-like seals, which are positioned at the leading peripheral 25 edge of each lobe.