WO2003016678A1

WO2003016678A1 - Wankel rotary machine

Info

Publication number: WO2003016678A1
Application number: PCT/GB2002/003748
Authority: WO
Inventors: Bryan Nigel Victor Parsons
Original assignee: Bryan Nigel Victor Parsons
Priority date: 2001-08-15
Filing date: 2002-08-14
Publication date: 2003-02-27
Also published as: GB0119886D0

Abstract

A rotary machine which comprises: a machine casing (25); a drive shaft mounted for rotation within the said casing; an eccentric (15) attached to the drive shaft and parallel to the axis of rotation of the drive shaft (10); a rotor (20), mounted for rotation on the said eccentric constrained to rotate in the same direction as the drive shaft performing one revolution to three revolutions of the drive shaft; a housing with a profile (28) constructed from a diametrically divided circle in which the two halves are displaced apart perpendicular to the line of division and the ends joined, tangentially, by two equal parallel lines to form a smooth closed curve; so that in operation the path traced by a point attached to the said rotor closely approximates to the housing profile.

Description

ANKEL ROTARY MACHINE

The present invention relates to a rotary machine and in particular to a machine that can be adapted to form a pump or an internal combustion engine. This invention seeks to provide a geometry which is simple to machine using conventional high volume manufacturing techniques.

According to one aspect of the current invention a rotary machine comprises: a machine casing; a drive shaft mounted for rotation within the said casing; an eccentric attached to the drive shaft and parallel to the axis of rotation of the drive shaft; a rotor, mounted for rotation on the said eccentric constrained to rotate in the same direction as the drive shaft performing one revolution to three revolutions of the drive shaft; a housing with a profile constructed from a diametrically divided circle in which the two halves are displaced apart perpendicular to the line of division and the ends joined, tangentially, by two equal parallel lines to form a smooth closed curve; so that in operation the path traced by a point attached to the said rotor closely approximates to the housing profile.

Preferably the proportions of the housing profile are related to the eccentricity, being the distance between the axis of the drive shaft and the axis of the eccentric, and the describing radius, being the distance of the point on the rotor from the rotor centre, so that the distance between the centres of the semicircular arcs is equal to four times the eccentricity and the radius of the semicircular arcs is substantially 7.2 times the eccentricity for the condition when the describing radius is substantially 8.2 times the eccentricity.

In practice the cooperation of the rotor and the housing profile might entail an offset due to the point on the rotor having physical dimensions, so that a pin on the rotor of a given radius would engage with a inner profile offset by the said given radius. The radius of the circular arcs would increase by the said given radius, as would the parallel distance apart of the two lines, however the distance between centres of the two semicircular arcs would remain equal to four times the eccentricity.

Preferably for use as a pump or an engine the inner profile would be formed into an internal surface cooperating with three symmetric extremities on a substantially triangular rotor. The pump or engine would be substantially of constant cross section across the depth of the machine and be fitted with end plates to form a cavity. A sliding seal is made between the said end plates and the rotor edges. The said cavity is divided into three chambers by the interaction of the three symmetric extremities of the rotor. As the drive shaft rotates, the rotor rotates at one third of the drive shaft speed, whilst the centre of the rotor moves in a circular path, due to the action of the eccentric. The volume of the said chambers varies in capacity and this variation is used in the internal combustion engine or pump. A porting arrangement in the inner profile cooperates with the motion of the rotor to control the admission and extraction of the working fluid.

According to a further aspect of the invention, the interaction of the three extremities of the rotor with the inner profile can be utilised to drive the rotor at the required speed of rotation, being one revolution for three revolutions of the drive shaft. Preferably, the three extremities of the rotor would be fitted with pivoting bearing pads with a surface curvature equal to that of the semicircular arcs of the said inner profile.

Preferably, these bearing pads would be spring biased to ensure that hydrodynamic lubrication is generated for the direction of rotation. Preferably, the bearing pads would provide part of the sealing mechanism. Preferably, the bearing pads would be radially located so that centrifugal force would not increase the contact force between the pads and the inner profile (28).

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings, in which:-

Figure la is a side schematic of the mechanism in the form of a four stroke engine in accordance with the present invention, and figure lb illustrates the geometric profile of the of the casing;

Figure 2a-2f is a series of elevations showing the progression of the engine through its phases of operation from Figure 1;

Figure 3a to 3d illustrate the construction and operation of the tip seals;

Figure 4a-4d shows an orthographic projection with a isometric view for the rotor;

Figure 5a-5d shows an orthographic projection with a isometric view for the casing;

Figure 6a-6d shows an orthographic projection with a isometric view for the drive shaft;

Figure 7a & 7b show an plan view and an isometric view for an assembly of the rotor, drive shaft and the casing with one end plate attached;

Figure 8a-8d shows an orthographic projection with a isometric view for the end plate;

Figure 9a-9d shows an orthographic projection with a isometric view for the tip seal; Figure 10a- lOd shows an orthographic projection with a transparent isometric view for the tip seal with radial constraint and bias spring;

Figure 11 a- lid shows an orthographic projection with a isometric view for the tip seal constraint;

The mechanism illustrated in figure la depicts the invention as schematic section of a four stroke internal combustion engine, in which the drive shaft (10) is located centrally to the inner profile (28) of the case (25) and is attached to an eccentric (15). The rotor (20) is of generally triangular shape with flanks that are circular arcs centred on the opposite apex with threefold rotational symmetry, is mounted, at its centre, on the eccentric (15) via rotational bearing. The apex tips (19a, 19b &19c) follow the inner profile (28) of the case (25) when the drive shaft (10) and the rotor (20) rotate, such that the drive shaft (10) rotates at three times the speed of the rotor (20). The proportions of the rotor (20) are chosen so that the distance between the centre of the rotor (20) and the apex tips (19a, 19b &19c) is a factor of 8.2 times the distance between the centres of the drive shaft (10) and the eccentric (15). A seal is formed at the apex tips (19a, 19b &19c) to the inner profile (28) of the case (25) so that three separate areas are formed (12a, 12b &12c) bounded by the flanks of the rotor (20) and the inner profile (28) of the case (25). The size of these areas (12a, 12b &12c) varies as the drive shaft rotates, so that when the plan section has depth and the end faces are sealed, the areas (12a, 12b &12c) represent the working chambers of the engine. The admission and exhaust of gas, from the working chambers, is controlled by the exhaust port (24) and the inlet port (26) and the apex tips (19a, 19b &19c). The ignition of the flammable gasses in the engine is achieved with a spark plug situated in the ignition aperture (22) in the engine case (25). Figure lb demonstrates the geometric construction of the inner profile (28) of the engine case (25) showing the exhaust port (24), the admission port (26), the ignition aperture (22), the drive shaft (10) and the attached eccentric (15). The inner profile (28) comprises two semicircular sections (14a & 14b) interconnected by two equal tangential straight sections (16a & 16b). The centres of the semicircles (14a & 14b) lie on the diameter D of a circle centred on the centre of the drive shaft (10). The diameter D is equal to four times the eccentricity E of the eccentric (15) on drive shaft (10). The two straight sections (16a & 16b) are parallel offset from diameter D by the radius R of the semicircular sections (14a & 14b), so that the length of F is equal to D. The value of R is 8.2 times the value of the eccentricity E, which is also equivalent to 2.05 times the Diameter D. The semicircular sections (14a & 14b) and the straight line sections (16a & 16b) combine to form the inner profile (28) as a continuous curve with no discontinuity in gradient.

Figure 2a through 2f show the components depicted in figure la through a cycle of operation as the drive shaft (10) rotates through increments of sixty degrees. Starting at figure 2a, the first chamber area (12a) is at a maximum, representing the start of the exhaust stroke, and the exhaust port (24) is uncovered, whilst the ignition aperture is about to be masked by the rotor tip (19a). Progressing to Figure 2b the first chamber area (12a) has reduced and the ignition aperture (26) has left the defined area 12a. The first chamber area (12a) continues to reduce for positions shown in figure 2c and 2d. Figure 2e shows the first chamber area (12a) close to its minimum value, with the admission port uncovered. Figure 2f shows the inlet phase just started and the first chamber area (12a) is increasing. Continuing the cycle the first chamber area (12a) corresponds to the second chamber area (12b) shown in figure 2a. The second chamber area (12b) can be followed in sequence from figures 2a to 2f as a continuation of the cycle. The second chamber area (12b) expands from figure 2a to 2d and this represents the completion of the inlet stroke. Figure 2e shows the inlet port closed for the second chamber area (12b) and this represents the start of the compression phase. The compression phase continues in figure 2f at which point the second chamber area corresponds to third chamber area (12c) shown in figure 2a. The cycle can be followed to completion from the third chamber area (12c) from figures 2a to 2f. The third chamber area (12c) is shown just prior to ignition in figure 2b where the ignition aperture (22) has just entered the third chamber area (12c). Figure 2c shows the start of the expansion phase for the third chamber area (12c), which can be followed through to completion in figures 2d to 2f. It is clear that the chamber areas (12a, 12b &12c) cyclically vary and follow each other, the phases of operation remaining equidistant and each chamber completes two cycles of area size for three rotations of the drive shaft (10).

Figure 3a to 3c illustrate the sealing system for the chambers and the method of rotor position control. The rotor tip seals (18a, 18b & 18c) are shaped from two convex cylindrical surfaces, an outer surface of radius R equivalent to the semicircular section of the inner profile (28), and an inner radius matched to a pocket at the apex of the rotor and centred at the describing radius, being 8.2 times the eccentricity E of the drive shaft (10) and the eccentric. The outer surface (49) passes through the centre of the inner surface (42) to ensure that there is minimal induced turning moment in the rotor tip seal from frictional drag due to contact of the seal with the inner profile (28). The rotor tip seal (18) is pivotally located within the cylindrical pocket at the rotor apex and is spring biased to twist the seal so that the trailing edge of the seal is in contact inner profile (28). On rotation of the drive shaft (10) the tip seal slide against the inner profile (28) inclined with trailing contact to provide favourable conditions for hydrodynamic lubrication, as in the manner of a tilting pad bearing. Figure 3b shows the rotor (20) displaced by a small angle A about the eccentric centre compared to the nominal position. One tip seal (18a) has flattened out against the inner profile (28) whilst the other two tip seals (18b & 18c) have twisted in the trailing direction to maintain the gas seal. The forces acting on the rotor to accelerate or decelerate the motion or combat out of balance gas forces or friction will act through the tip seals, the heaviest loaded seal will twist and conform with the inner profile (28) to provide a good mechanical connection. There are always two seals in contact with the circular section of the inner profile (28). The sealing for each chamber is completed by face seals (17) attached to the rotor which link the tip seals at the rotor corners and seal to the end plates of the engine. Each chamber (12a-c) is sealed by the combination of the two side seals abutting the two tip seals associated with the chamber.

An important feature of the design, illustrated in figure 3d, is related to the ability of the tip seals (18) to close an aperture (41) in the inner profile (28), particularly the ignition aperture (22). When the tip seal (18a) engages with the circular portions of the inner profile (28) it has full face contact so that, provided that the aperture (41) has shorter circumferential dimensions than the face width of the tip seal (18), the aperture (41) will be completely isolated for some period during the passing of the tip seal (18) over the aperture (41). With tip seals that have line contact with the profile of the housing, considerable leakage between adjacent working chambers is probable, as the tip seal passes over the ignition aperture.

Figure 4a shows a plan view of the rotor with elevations shown in figures 4b & 4c and an isometric view in figure 4d. The circular groove (32) at the apex of the rotor corresponds to the cylindrical radius of the tip seal (18). The flanks (34) are centred on the centres of the circular grooves (32). The dimensions of the rotor (20) depend on the eccentricity E of the eccentric (15) on the drive shaft (10) so that the describing radius DR, being the distance from the centre of the rotor (15) to the centre of the circular grooves (32), is equal to the eccentricity E multiplied by 8.2, i.e.:

DR = S.2x E (1)

The flank radius FR (34) is related to the describing radius DR so that:

FR = DRxj3 (2)

which when equation 2 is combined with equation 1 yields the flank radius FR in terms of the eccentricity E:

FR = 14.2xE (3)

A small offset is made to this value to provide running clearance.

Figure 5 illustrates the three dimensional aspect of the housing with the inner profile (28), the inlet (26) and exhaust (24) ports and the ignition aperture (22).

Figure 6 illustrates the three dimensional aspects of the drive shaft (10) and the eccentric (15), as a one piece construction.

Figure 7 illustrates the three dimensional aspects of the engine partly built up with only one end plate so that the internal assembly can be seen.

Figure 8 illustrates the three dimensional aspects of the end plate showing the simple construction. The engine requires two such end plates.

Figure 9 illustrates the three dimensional aspects of the tip seal (18). Figure 10 illustrates the three dimensional aspects of the tip seal with restraint system and spring bias system. The modified tip seal (38) has a recess (39) machined into each end. Part of the profile of the recess (39) is circular and centred on the pivot radius (42). A retaining strap (36) engages with this internal face of the recess to prevent the modified tip seal (38) from leaving the rotor groove (32). A spring (37) is inserted in the recess (39) to bias the angle of the modified tip seal (38) in the required direction, trailing the direction of motion.

Figure 11 shows a three dimensional representation of the retaining strap (36). The inner surface (51) and the outer surface (52) are concentric and correspond to the centre of the modified seal (38). The eyelet (53) is used to attach the restraining strap (36) to the rotor (20).

An important aspect of the design is the relative ease of manufacture, particularly of the inner profile (28). The machining of this inner profile (28) can be achieved using a circular cutter, of radius equal to R the radius of the circular portions of the inner profile (28), moved linearly between the centres of the circular portions of the inner profile (28). This could be a simple milling operation achieved by the linear traverse of the bed. The rotor is similarly simple to machine being defined by simple circular arcs in plan.

Alterations can be made to the design without departing from the present invention. For example the inner profile is described as the internal surface formed from two semicircles and two straight lines. This might be reconfigured as an external surface of similar shape on a rotor cooperating with a housing having three fixed sealing points.

Claims

1. A rotary machine comprising: a machine casing; a drive shaft mounted for rotation within the said casing; an eccentric attached to the drive shaft and parallel to the axis of rotation of the drive shaft; a rotor, mounted for rotation on the said eccentric constrained to rotate in the same direction as the drive shaft performing one revolution to three revolutions of the drive shaft; a housing with a profile constructed from a diametrically divided circle in which the two halves are displaced apart perpendicular to the line of division and the ends joined, tangentially, by two equal parallel lines to form a smooth closed curve; so that in operation the path traced by a point attached to the said rotor closely approximates to the housing profile.

2. A rotary machine as in claim 1 in which the separation of the centres of the circles comprising the housing profile is equal to four times the eccentricity of the eccentric on the drive shaft.

3. A rotary machine as in claims 1 and 2, in which the radius of the circles, comprising the housing profile, is substantially equal to 7.2 times the eccentricity.

4. A rotary machine as in claims 1 ,2 and 3 in which the point on the rotor is circular and has a finite diameter, so that the profile of the housing is offset by the radius of the point, so that the radius of the circles, comprising the housing profile, is substantially equal to 7.2 times the eccentricity plus the offset radius.

5. A rotary machine as in claims 1 to 4 in which the describing radius of the rotor, being the distance between the centre of the rotor and the defining point, is related to the eccentricity, being the distance between the centre of the eccentric and the centre of the drive shaft, and is equal to 8.2 times the eccentricity.

6. A rotary machine as in claims 1 to 5 wherein the rotor is formed with three rotationally symmetric apexes corresponding to the defining radius.

7. A rotary machine as in claims 1 to 6 wherein the rotor is formed with three rotationally symmetric apexes corresponding to the defining radius in which the radius profile of the rotor is formed from circular arcs centred on the apexes and substantially equal in radius to the distance between adjacent apexes.

8. A rotary machine as in claims 1 to7 in which the housing profile is formed into an internal surface cooperating with three symmetric extremities on the rotor, so that the interaction of the three extremities of the rotor with the housing profile can be utilised to drive the rotor at the required speed of rotation, being one revolution for three revolutions of the drive shaft.

9. A rotary machine as in claims 1 to 8 wherein the three extremities of the rotor are fitted with pivoting bearing pads with a bearing surface curvature equal to that of the semicircular arcs.

10. A rotary machine as in claims 1 to 9 wherein the bearing pads are spring biased to ensure that hydrodynamic lubrication is generated for the direction of rotation.

11. A rotary machine as in claims 1 to 10 wherein the bearing pads maintain close contact with the said housing profile by pivoting to prevent gas leakage across the bearing pads.

12. A rotary machine as in claims 1 to 11 configured as an Internal Combustion Engine in accordance with the accompanying drawings 1 to 7