A rotary piston internal combustion engine

Abstract

A rotary piston internal combustion engine including an engine housing 10 having an internal surface defining a cavity 200, the engine housing having an end wall 22 and a side wall 24, the internal su

Description

FIELD The present invention relates to rotary piston internal combustion engines. More particularly, the invention relates to rotary piston internal combustion engines having a configuration which provides for improved efficiency. BACKGROUND It is known that rotary piston internal combustion engines, such as the Wankel engine, include an oval-like epitrochoidal cavity formed within the engine housing, a rotary piston and an output shaft. The rotary piston has a substantially triangular shape with convex arcuate flanks. Apex seals are located at the three apices of the rotary piston. During operation, the apex seals maintain physical contact with an internal surface of the housing, thereby forming three working chambers. The cavity is in communication with intake and exhaust ports, the intake port supplying a gas or fluid fuel to the cavity and the exhaust port venting exhaust gases to atmosphere after combustion has occurred in the working chambers. Combustion of the fuel causes expansion of combustion gases resulting in increased pressure in the working chambers, thereby resulting in rotation of the rotary piston relative to the engine housing. It is a non-exclusive object of the present invention to overcome or at least substantially alleviate one or more of the problems associated with the prior art. BRIEF DESCRIPTION OF THE INVENTION According to a first aspect of the invention, there is provided a rotary piston internal combustion engine including: an engine housing having an internal surface defining a cavity, the engine housing having an end wall and a side wall, the internal surface including at least a portion of the end wall and at least a portion of the side wall; an output shaft extending through the cavity, the output shaft configured to rotate relative to the engine housing about an axis for transmitting power to parts to be operated; a rotary piston mounted eccentrically on the output shaft; an intake port and an exhaust port each in communication with the cavity; an outlet port in communication with the cavity; and a valve movable between a first position in which the outlet port is generally sealed, and a second position in which the outlet port is open; wherein, when the valve is in the first position, a surface thereof lies in the same plane as a part of the internal surface adjacent the outlet port to form a substantially continuous surface. Optionally, the rotary piston may be a multi-Iobed trochoidal rotary piston having multiple apices each in engagement with the side wall, the rotary piston and the engine housing forming multiple working chambers including a first working chamber, wherein, in use, the first working chamber completes a four-stage cycle of intake, compression, expansion and exhaust for each revolution of the rotary piston. Optionally, in use, during at least a part of the intake stage, the outlet port and the intake port may be in communication with the first working chamber. Optionally, in use, during at least a part of the compression stage, the outlet port may be in communication with the first working chamber. Optionally, in use, during the compression stage, a gas or fluid may be maintained within the first working chamber when the valve is in the first position, and at least a portion of a gas or fluid in the first working chamber may pass through the outlet port when the valve is in the second position. Optionally, the internal surface may be a two lobed epitrochoid including a top lobe and a bottom lobe. Optionally, the outlet port may provided on or in the top lobe. Optionally, the intake port may be provided on or in the top lobe. Optionally, the exhaust port may be provided on or in the bottom lobe. Optionally, the outlet port may provided on or in the side wall. Optionally, the outlet port may be provided on or in the end wall. Optionally, the valve may be configured to move to an intermediate position between the first position and the second position. Optionally, the engine housing may include a first lateral side and a second lateral side. Optionally, the outlet port may be provided on the first lateral side. Optionally, the intake port may be provided on or in the first lateral side. Optionally, the outlet port may be in communication with the atmosphere. The rotary piston internal combustion engine may optionally further include a fuel injector configured to dispense fuel directly into the cavity. Optionally, the fuel injector is provided on the second lateral side. Optionally, the outlet port may be in communication with a portion of the intake port which is upstream of the cavity. The rotary piston internal combustion engine may further include a fuel injector configured to dispense fuel into the upstream portion of the intake port. Optionally, the rotary piston may include at least one sea. During rotation of the rotary piston the or each seal may be engageable with the surface of the valve when the valve is in the first position. Optionally, the at least one seal may be an apex seal configured to engage with the side wall. Optionally, the at least one seal may be an end seal configured to engage with the end wall. Optionally, the outlet port may have a first cross-sectional area through which a gas and / or fluid can pass, and the valve may be configured to alter the cross-sectional area of the outlet port from a first cross-sectional area to a second cross-sectional area as the valve moves between the first and second positions. Optionally, the valve may be configured to move away from the cavity when the valve moves from the first position to the second position. The rotary piston internal combustion engine may further include a plurality of outlet ports, each outlet port may be in communication with the cavity. Optionally, at least one outlet port may be provided on the side wall and / or at least one outlet port may be provided on the end wall. The rotary piston internal combustion engine may further include a plurality of valves, each valve being configured to move between the first position and the second position relative to a corresponding outlet port of the plurality of outlet ports. Optionally, the rotary piston internal combustion engine may not include a throttle. According to a second aspect of the invention, there is provided a vehicle or a device comprising a rotary piston internal combustion engine according to any preceding claim. The vehicle or the device may further include an engine control unit which is configured to move the valve between the first position and the second position. Optionally, the vehicle or the device may not include a throttle. BRIEF DESCRIPTION OF THE FIGURES In order that the present disclosure may be more readily understood, embodiments thereof will now be described, byway of example only, with reference to the accompanying drawings, in which: FIGURE 1 is a cross-sectional view of a rotary piston internal combustion engine having an outlet port provided on a side wall; FIGURE 2 is a cross-sectional view of a rotary piston internal combustion engine having an outlet port provided on an end wall; FIGURE 3 is a cross-sectional view of a rotary piston internal combustion engine having outlet ports provided on a side wall and an end wall; FIGURE 4 is a cross-sectional view of a rotary piston internal combustion engine whereby the first working chamber is in an intake stage; FIGURE 5 is a cross-sectional view of a rotary piston internal combustion engine whereby the first working chamber is entering the compression stage; FIGURE 6 is a cross-sectional view of a rotary piston internal combustion engine whereby the first working chamber is progressing through the compression stage; FIGURE 7 is a cross-sectional view of a portion of a rotary piston internal combustion engine whereby the valve is in a second position; FIGURE 8 is a cross-sectional view of a portion of a rotary piston internal combustion engine whereby the valve is in a first position; FIGURE 9 is a cross-sectional view of a portion of a rotary piston internal combustion engine utilising Direct Injection; FIGURE 10 is a cross-sectional view of a portion of a rotary piston internal combustion engine utilising Port Fuel Injection; and FIGURE 11 is a plan view of an unmanned aerial vehicle having a rotary piston internal combustion engine and an engine control unit (ECU). DETAILED DESCRIPTION OF THE DISCLOSURE Referring to the figures, there is provided a rotary piston internal combustion engine 1, or engine 1, in accordance with the present disclosure. The engine 1 includes an engine housing 10 configured to accommodate at least an output shaft 12 and a rotary piston 16. The engine 1 may include multiple engine housings 10, each containing any or all of the features described hereafter. The engine housing 10 includes an internal surface 100 which defines a cavity 200. The engine housing 10 includes an end wall 22 and a side wall 24. In embodiments, the engine housing 10 may include two end walls 22, each end wall 22 positioned on opposite ends of the side wall 24, such that the two end walls 22 and the side wall 24 generally surrounding or enclosing the cavity 200. In some embodiments, one or both end walls 22 may be formed integrally with the side wall 24, or may be formed as separate parts which may be connected to the side wall 24 in ways known in the art. The example embodiments shown in the figures show one end wall 22, as the figures are cross-sectional views of the engine 1. It should be appreciated that in each embodiment, the engine 1 may have two end walls 22, and that references to the end wall 22 may refer to any end wall 22 of the engine housing 10. The internal surface 100 of the engine housing 10 includes at least a portion of the end wall 22 and at least a portion of the side wall 24. As shown in Figures 1 to 10, at least a part of the end wall 22 may be oriented generally orthogonally to at least a part of the side wall 24. The engine 1 includes an intake port 102 and an exhaust port 104, wherein the intake port 102 may be configured to supply a gas or fluid to the cavity 200. It should be understood that the gas or fluid may be air, an air-fuel mixture or any other fluid or gas suitable for operating the engine 1. The exhaust port 104 may be configured to release exhaust gases, for example, to the atmosphere. The engine 1 also includes an outlet port 60 and a valve 70. The engine 1 may form a part of a vehicle or device which requires power to be transmitted from the engine 1 to another part of the vehicle or device. The vehicle may be a car, a motorcycle, an aircraft (such as an unmanned aerial vehicle), jet skis or a snowmobile. The device may be a powertool, such as a chainsaw. The skilled person would readily understand that the vehicle may be any suitable vehicle, and the device may be any suitable device. The output shaft 12 extends through the engine housing 10 and through the cavity 200, and is rotatable relative to the engine housing 10 and within the cavity 200 about an axis X for transmitting power to parts to be operated during use of the engine 1. The axis X may be oriented generally orthogonally to at least a part of the end wall 22 and may be generally parallel to at least a part of the side wall 24. The rotary piston 16 is mounted eccentrically to the output shaft 12, with methods of mounting the rotary piston 16 to the output shaft 12 known in the art. In embodiments, the rotary piston 16 may be a multi-lobed trochoidal rotary piston 16 having multiple flanks 161 and multiple apices 162, with each apices 162 generally engaging with, or being in close proximity to, the side wall 24. In some embodiments of the disclosure, the rotary piston 16 may be a three-lobed trochoidal rotary piston having three flanks 161 and three apices 162, each apex 162 in general engagement with the side wall 24. The rotary piston 16 further includes two end faces 164, with each end face 164 generally surrounded by the flanks 161 and apices 162. In embodiments, the end faces 164 are generally triangular in shape. It should be understood that in other embodiments of the disclosure, the rotary piston 16 may have more than three lobes. The rotary piston 16 may further include a plurality of seals 163, 165. At least one of these seals 163, 165 may be an apex seal 163 located at an apex 162 of the rotary piston 16, with the apex seal 163 configured to maintain constant physical contact with the internal surface 100 of the engine housing 10, and in particular the side wall 24 of the housing 10. At least one of the seals 163, 165 may be an end seal 165 located on an end face 164 of the rotary piston 16. The end seal 165 is configured to maintain constant physical contact with the internal surface 100 of the engine housing 10, and in particular, an end wall 22 of the housing 10. The side wall 24 of the engine housing 10 may be epitrochoidal in shape. In embodiments, the shape of the side wall 24 may be a two-lobed epitrochoid. The shape of the side wall 24 may, at least in part, be configured based on the shape of the rotary piston 16 of the engine 1. In the example embodiments of the disclosure, the side wall 24 forming part of the internal surface 100 is shaped as a two-lobed epitrochoid which is suitable for use with a three-lobed trochoidal rotary piston 16. The skilled person would readily appreciate that a trochoidal rotary having a differing number of lobes would require a suitable shape of the side wall 24. The two-lobed trochoidal internal surface 100 includes a top lobe 110 and a bottom lobe 120, with the top lobe 110 generally located above the axis X of the output shaft 12 and the bottom lobe 120 generally located below the axis X of the output shaft 12. It should be understand that “top” and “bottom” are used with reference to the orientation of the engine 1 shown in the figures. The peripheral shape of the part of the end wall 24 forming a part of the internal surface 100, as shown in the figures, is also a two-lobed-epitrochoidal when viewed from the front. The engine housing 10 may include a first lateral side 10a, and a second lateral side 10b generally opposite the first lateral side 10a. With reference to the figures and the specific orientation of the engine 1 shown, the first lateral side 10a may be a left-hand side of the engine housing 10 and the second lateral side 10b may be a right-hand side of the engine housing 10. The first lateral side 10a of the engine housing 10 may be considered to be the parts of the housing 10 generally positioned to the left of the axis X, and the second lateral side 10b of the engine housing 10 may be considered to be the parts of the housing 10 generally positioned to the right of the axis X. In embodiments of the disclosure with athree-lobed trochoidal rotary piston 16, such as those shown in the figures, as the rotary piston 16 is driven, the output shaft 12 rotates about the axis X. For every full revolution of the rotary piston 16, the output shaft 12 undergoes three full revolutions. As such, power can be transmitted to the parts of the vehicle or device to be operated, e.g., to a transmission, a wheel axis, a rotor blade, etc. In embodiments, the rotary piston 16 rotates in a clockwise direction. The engagement of the apices 162, 164 and seals 163, 165 of rotary piston 16 with the internal surface 100 of the engine housing 10 form a plurality of working chambers, with the number of working chambers defined by the number of lobes of the rotary piston 16. Each working chamber is generally sealed relative to the remaining working chambers. In embodiments, the rotary piston 16 is a three-lobed trochoidal rotary piston 16 which in conjunction with the internal surface 100 forms three working chambers including a first working chamber 50a, a second working chamber 50b and a third working chamber 50c. As would be appreciated by the skilled person, each working chamber 50a, 50b, 50c completes a four-stage cycle, known as the Otto Cycle. The four-stage cycle includes an intake stage, a compression stage, an expansion stage and an exhaust stage for each revolution of the rotary piston 16. The order of, the functions, and the effects of each of the four stages are readily understood by the skilled person. The intake port 102 may be configured to supply gas or liquid to the cavity 200, and it is in communication with each working chamber 50a, 50b, 50c during a part of the cycle undergone by the working chambers 50a, 50b, 50c. The intake port 102 may be provided on the top lobe 110 of the internal surface 100 and may be in communication with each working chamber 50a, 50b, 50c during at least a part of the intake stage of each working chamber 50a, 50b, 50c. As shown in the figures, the intake port 102 may be provided on the first lateral side 10a of the engine housing 10. The intake port 102 may be provided either on the side wall 24, as shown in the figures, or alternatively may be on the end wall 22. In some embodiments of the disclosure, the engine 1 may include multiple intake ports 102, either provided on the same wall 22, 24 or on different walls 22, 24. The exhaust port 104 may be configured to release exhaust gases, for example, to the atmosphere or other parts of the vehicle or device to which the engine 1 forms a part of, and it is in communication with each working chamber 50a, 50b, 50c during a part of the cycle undergone by each working chamber 50a, 50b, 50c. The exhaust port 104 may be provided on the bottom lobe 120 of the internal surface 100 and may be in communication with each working chamber 50a, 50b, 50c during at least a part of the exhaust stage of each working chamber 50a, 50b, 50c. As shown in the figures, the intake port 104 may be provided on the first lateral side 10a ofthe engine housing 10. The exhaust port 104 may be provided either on the side wall 24, as shown in the figures, or alternatively may be on the end wall 22. In some embodiments of the disclosure, the engine 1 may include multiple exhaust ports 104, either provided on the same wall 22, 24 or on different walls 22, 24. As such, the intake port 102 and exhaust port 104 are positioned relative to each other, and relative to the engine housing 10, based on their purpose within the four-stage cycle undergone by the rotary piston 16. With reference to the figures, the intake port 102 may be provided relatively above the exhaust port 104. The engine 1 includes an outlet port 60 and a valve 70, as shown in the figures. Where appropriate, the operation of the outlet port 60 and valve 70 will be described with reference to the first working chamber 50a. However, it should be understood that the operation of the outlet port 60 and the valve 70 is the same for each of the working chambers 50a, 50b, 50c. The outlet port 60 is in communication with the cavity 200 and is in communication with each working chamber 50a, 50b, 50c during a part of the cycle undergone by each working chamber 50a, 50b, 50c. The outlet port 60 is configured to release a desired amount of gas or fluid from each working chamber 50a, 50b, 50c during a part of the cycle. At least a part of the outlet port 60 is provided as an aperture 601 which extends through a wall 22, 24 of the engine housing 10 and through the internal surface 100. The aperture 601 of the outlet port 60 may be provided in any appropriate shape. For example, in Figure 2 the perimeter of the aperture 601 of the outlet port 60 is shown as generally triangular, generally resembling a Reuleaux triangle. It should be understood that in other embodiments, the aperture 601 of the outlet port 60 may be formed as any other appropriate shape as required, such as, but not limited to, generally circular, elliptical, triangular, square, rectangular or any appropriate regular polygon or irregular polygon. The outlet port 60 may include, or be connected to, other parts such as conduits, manifolds or other passages which enable the gas or fluid to be released to and transported to a desired location. Depending on the configuration of the engine 1, the gas or fluid may be released to the atmosphere, to another part of the engine 1, to parts connected to the engine 1, or to other parts of the vehicle or device to which the engine 1 forms a part of. The outlet port 60 may be provided on the top lobe 110 of the internal surface 100 of the engine housing 10, and may be provided on the side wall 24 or the end wall 22. In some embodiments of the disclosure, the engine 1 may include a plurality of outlet ports 60, each of which is in communication with the cavity 200. The plurality of the outlet ports 60 may be provided on the same wall 22, 24, or at least one may be provided on the end wall 22 and at least one may be provided on the side wall 24, as shown in Figure 3 for example. The outlet port 60 may be generally provided on the first lateral side 10a of the engine housing 10, and as such may be on the same lateral side of the engine housing 10 as the intake port 102 and the exhaust port 104. As shown in the figures, at least a part of the outlet port 60 may be located generally above both the intake port 102 and the exhaust port 104, or in other words, the intake port 102 may be positioned generally between at least a part of the outlet port 60 and the exhaust port 104. In some embodiments of the disclosure, the entirety of the aperture 601 of the outlet port 60 may be positioned generally above the intake port 102. In other embodiments of the disclosure, only a part of the aperture 601 may be positioned generally above the intake port 102, with other parts being generally inline with the intake port 102. In other embodiments of the disclosure, it is also envisaged that the aperture 601 of the outlet port 60 may be inline with the intake port 102. It should be understood that “above” is used with reference to the orientation of the engine 1 as shown in the figures, for example, with the top lobe 110 being located “above” the bottom lobe 120. The location of the outlet port 60 and the aperture 601 relative to intake port 102 and exhaust port 104 may also be described with reference to the clockwise rotation of the rotary piston 16, when the engine 1 is in the orientation shown in the figures. For instance, if one of the apices 162 of the rotary piston 16 is rotating through the bottom lobe 120 and subsequently into and through the top lobe 110, the apex 162 will first move past the exhaust port 104. Following this, the apex 162 will move generally towards the intake port 102 and the outlet port 60. During continued rotation of the rotary piston 16, the apex 162 will move past the intake port 102, but will not entirely move past the outlet port 60. Accordingly, whilst the intake port 102 has now been completely passed by the apex 162, at least a part of the aperture 601 of the outlet port 60 has not been passed by the apex 162. Subsequently, during continued rotation, the apex 162 will pass the outlet port 60. As such, relative to rotation of the rotary piston 16, the intake port 102 may be considered to be between the exhaust port 104 and the outlet port 60. With reference to the cycle undergone by the rotary piston 16 described above, the outlet port 60 is in communication with the first working chamber 50a during at least a part of the intake stage, as shown in Figure 4. Therefore, during the intake stage, both the outlet port 60 and the intake port 102 are in communication with the first working chamber 50a. During this part of the cycle, the outlet port 60 generally does not function to release gas or fluid from the working chamber 50a as the expansion of the volume of the first working chamber 50a causes gas or fluid, signified by a dashed arrow in Figure 4, to be drawn into the first working chamber 50a, as is typical of an intake stage of an engine 1 which does not include an outlet port 60. As the first working chamber 50a progresses to the compression stage, following the intake stage, the first working chamber 50a reaches a rotational position, as shown in Figure 5, whereby the intake port 102 is no longer in communication with it. At this stage, due to the isolation of the intake port 102 from the first working chamber 50a, the gas or fluid in the first working chamber 50a may be compressed as the rotary piston 16 continues to rotate, as is known in the art. However, during at least a part of the compression stage of the first working chamber 50a, the outlet port 60 is in communication with the first working chamber 50a. Accordingly, a portion of the gas or fluid drawn into the first working chamber 50a during the preceding intake stage may be released through the outlet port 60 during the compression stage. As such, the amount of gas or fluid present in the first working chamber 50a may be different relative to the amount of gas or fluid present in the first working chamber 50a in an engine which does not include an outlet port 60. As shown in Figure 6, the first working chamber 50a will subsequently progress through the compression stage until the outlet port 60 is no longer in communication with the first working chamber 50a. At this point, no gas or fluid will be released through the outlet port 60, and the remaining gas or fluid be maintained in the first working chamber 50a to be compressed. Following the compression stage, the first working chamber 50a will subsequently move to the expansion stage, whereby a spark plug 19, or plurality of spark plugs 19, may communicate with the first working chamber 50a and operate to combust the gas or fluid in the first working chamber 50a. The flow rate of gas or fluid, or any other appropriate gas or fluid released through the outlet port 60 may be determined, at least in part, by the location of the outlet port 60 relative to the intake port 102 and the timing at which the outlet port 60 should be isolated from the first working chamber 50a during the compression stage. The flow rate of gas or fluid released through the outlet port 60 may also be determined by at least the cross-sectional area A, or effective cross-sectional area A, of the aperture 601 of the outlet port 60. In other words, the location of the outlet port 60 and the cross-sectional area A of the aperture 601 of the outlet port 60 may be, at least in part, selected based on the relative location of the intake port 102, the timing at which the outlet port 60 should be isolated from the first working chamber 50a during the compression stage and the desired flow rate of gas or fluid to be released through the outlet port 60. The engine 1 also include a valve 70 which is configured to move relative to the outlet port 60. In particular, the valve 70 is configured to be movable between a first position and a second position. In the first position, a part of the valve 70 generally seals the outlet port 60 from the cavity 200, and in turn generally seals the outlet port 60 from the working chambers 50a, 50b, 50c. As such, when the valve 70 is in the first position, the outlet port 60 does not function to release gas or fluid from the first working chamber 50a during the compression stage, and operationally the engine 1 performs as though no outlet port 60 is present. In the second position, the outlet port 60 is generally open, and as such, gas or fluid may be released from the first working chamber 50a during at least a part of the compression stage as described above. The valve 70 may be controlled by an ECU (Engine Control Unit) 300 that may be provided as part of the vehicle or device of which the engine 1 is a part of. The ECU 300 may be connected to a suitable actuator which is capable of moving the valve 70 between the first and second positions. As the valve 70 generally seals the outlet port 60 when the valve is in its first position, the configuration of the valve 70 may be at least partly determined by the configuration of the outlet port 60. At least a part of the valve 70 should be of a size and shape that corresponds to the size and shape of a part of the outlet port 60, such as the aperture 601 of the outlet port 60. As shown in Figure 8, the valve 70 may have a surface 701 that faces generally inwards towards the cavity 200 when the valve 70 is in the first position. The surface 701, or at least the part of the surface 701 which is to seal the aperture 601, may be of generally the same shape and size (i.e., cross-sectional area) as a part of the outlet port 60, such as the aperture 601 as described above. Additionally, the valve 70 may include a seal which is configured to engage with a part of the outlet port 60 to enhance the ability of the valve 70 to prevent the passage of gas or fluid through the outlet port 60 when the valve is in the first position. In embodiments of the disclosure which include a plurality of outlet ports 60, the engine 1 may also include a plurality of valves 70, with each valve moveable between the first and second position relative to a corresponding outlet port 60 of the plurality of outlet ports 60. In some embodiments, each valve 70 may be independently moveable such that each outlet port 60 can be sealed and opened independently, so that the amount of gas or fluid which is released from the first working chamber 50a during the compression stage may be further adjusted and controlled. When the valve 70 is in the first position, the surface 701 of the valve 70 lies in the same plane as a part of the internal surface 100. In particular, the surface 701 lies in the same plane as a part of the internal surface 100 which is adjacent (i.e., which surrounds) the outlet port 60 to form a substantially continuous surface. Therefore, when the outlet port 60 is provided on the end wall 22, as shown in Figure 2, the surface 701 of the valve 70 forms a substantially continuous surface with the part of the internal surface 100 on the end wall 22 which is adjacent (i.e., surrounds) the outlet port 60, and the surface 701 and the part of the internal surface 100 lie on the same generally flat plane. However, when the outlet port 60 is provided on the side wall 24, as shown in Figure 1, the surface 701 of the valve 70 forms a substantially continuous surface with the part of the internal surface 100 on the side wall 24 which is adjacent (i.e., surrounds) the outlet port 60, and the surface 701 and the part of the internal surface 100 lie on the same generally curved plane. In other words, when the valve 70 is in the first position the surface 701 of the valve 70 continues the trochoidal shape of the side wall 24 over the outlet port 60. Therefore, it should be understood that “plane” may refer to any flat plane or any curved plane. As a result, when the valve 70 is in the first position, the surface 701 of the valve 70 is completely flush with the internal surface 100 and ensures that the seals 163, 165 of the rotary piston 16 are able to engage with the surface 701 and maintain the isolation of the working chambers 50a, 50b, 50c from each other as the seals 163, 165 pass over the surface 701. Movement of the valve 70 to the second position enables the outlet port 60 to be generally opened. The valve 70 is moveable relative to the outlet port 60. In some embodiments of the disclosure, the valve 70, or at least a part of the valve 70, may be movable towards and away from the aperture 601 of the outlet port 60, such that the part of the valve 70 does not move into the cavity 200 and collide with the rotary piston 16 during the piston’s rotation. For example, at least a part of the valve 70 may move linearly away and towards the aperture 601. In other examples, at least a part of the valve 70 may be hingeably or pivotably moveable away and towards the aperture 601 of the outlet port 60. In other embodiments of the disclosure, at least a part of the valve 70 may be slidably, pivotably or rotationally moveable relative to the outlet port 60 across the aperture 601. For example, a part of the valve 70 may operate similarly to a shutter valve, with multiple parts which slide and / or rotate relative to the aperture 601. In other examples, the valve 70 may rotate or pivot about a fixed-point relative to the aperture. Therefore, the valve 70 can be formed in any appropriate way which enables these forms of relative movement. During movement of the valve 70 between the first and second positions, the valve 70 may be moveable to an intermediate position. If the valve 70 is continuously moveable between the first and second positions (i.e., does not move solely in fixed increments), the intermediate position may be any position between the first and second position. If the valve 70 moves incrementally between the first and second positions, the intermediate position may be any incremental position between the first and second positions. Accordingly, when the valve 70 moves between the first and second positions, the cross-sectional area A of the aperture 601 of the outlet port 60 may be altered from a first cross-sectional area A1 to a second cross-sectional area A2. It should be understood that the cross-sectional area A, the first cross-sectional area A1 and second cross-sectional area A2, may refer to a physical cross-sectional area (i.e., a geometric cross-sectional area). In other instances, the cross-sectional area A, the first cross-sectional area A1 and second cross-sectional area A2, may refer to an effective cross-sectional area (i.e., relative to rate of gas or fluid which can flow through the aperture 601). Therefore, in embodiments, use of the term cross-sectional area may refer to a physical cross-sectional area or an effective cross-sectional area corresponding to the configuration of the valve 70 and I or outlet port 60. Thus, the amount of gas or fluid which can pass through the outlet port 60 may be altered. This enables the position of the valve 70 to be determined based on the performance requirements of the engine 1 during use. For example, in some embodiments, the outlet port 60 may have a first cross-sectional area A1 as shown in Figure 6, which may correspond to a cross-sectional area of the aperture 601 of the outlet port 60 equivalent to when no valve 70 is present and as such the first cross-sectional area A1 may be a maximum cross-sectional area. Depending on the configuration of the valve 70, the first-cross sectional area A1 may also correspond to a cross-sectional equivalent to when the valve 70 is in the second position, which may be equivalent to the maximum cross-sectional area, or may be a relatively smaller cross-sectional area than the maximum cross-sectional area described above but may be the maximum possible. This may be the case for a valve 70 which never completely reveals or exposes the entire aperture 601 of the outlet port 60. When the valve 70 moves from the second position, the cross-sectional area A of the outlet port 601 may be altered from a first cross-sectional area A1 to a second cross-sectional area A2. The second cross-sectional area may be relatively smaller than the first cross-sectional area A1, and may therefore be used to adjust or otherwise control the amount of gas or fluid which is able to pass through the outlet port 60. The second cross-sectional area A2 may be reached when the valve 70 is in an intermediate position or when the valve is 70 is in the first position, as shown in Figure 7. In some embodiments of the disclosure, when the valve 70 is in an intermediate position, the second cross-sectional area A2 may be of a non-zero value, whereas when the valve 70 is in the first position, the second cross-sectional area may be zero, as shown in Figure 8. In the above, it should be understood that the cross-sectional area A, the first cross-sectional area A1 and the second cross-sectional area A2 may refer to a physical cross-sectional area of the aperture 601 of the outlet port 60. In some embodiments, the change in the cross-sectional area may be due to a change in the geometric / numerical area of the aperture 601 from one value to another value, such that the actual size and area of the aperture 601 is altered. In one non-limiting example, if the valve 70 resembles a shutter valve, the movement of the valve 70 between positions may result in a change of the geometric / numerical value of the cross-sectional area A of the aperture 601. In other embodiments, the cross-sectional area may refer to an effective cross-sectional area in which the physical cross-sectional area of the aperture 601 is not altered, or is negligibly altered, but whereby parts of the valve 70 restrict the flow of a gas or fluid through the outlet port 60 due to the location of the valve 70 relative to a part of the outlet port 60. In one non-limiting example, if the valve 70 resembles a poppet valve, the movement of the valve 70 between positions may not alter the numerical value of the cross-sectional area A of the aperture 601, but a change in position of the valve 70 relative to the aperture 601, and I or relative to other parts of the outlet port 60 or parts to which the outlet port 60 is connected to may result in the change of the rate of flow of a gas or fluid (i.e., by changing the volumetric flow rate I mass flow rate) through the outlet port 60 without altering the physical cross-sectional area A of the aperture 601. In embodiments of the disclosure, the engine 1 may include at least one fuel injector 18 configured to dispense fuel to a part of the engine. In some embodiments of the disclosure, the fuel injector 18 may be configured to dispense fuel directly into a cavity 200, and therefore directly into a working chamber 50a, 50b, 50c when it is accessible by the fuel injector 18. In such embodiments of the disclosure, the fuel injector 18 may inject fuel into the working chamber 50a, 50b, 50c during the compression stage of said working chamber 50a, 50b, 50c. As shown in Figure 9, the fuel injector 18 may be provided on the top lobe 110 and second lateral side 10b of the engine housing 10 and generally opposite the intake port 102 and outlet port 60. This method of fuel dispensation is known as Direct Injection (DI) in the art. In these embodiments of the disclosure, the outlet port 60 may be in communication with the atmosphere, and release the gas or fluid in the first working chamber 50a to the atmosphere. This may occur before fuel is injected into the air in the first working chamber 50a, and as such releases air to the atmosphere, or it may occur once fuel has been injected into the air, and as such releases an air-fuel mixture into the atmosphere. Alternatively the outlet port 60 may be in communication with, and may release the gas or fluid into, a part of the vehicle or device to which the engine 1 is connected. In alternative embodiments, the fuel injector 18 may be configured to dispense fuel into a portion of the intake port 102 or larger intake assembly which is upstream (i.e., upstream portion 1002) from the cavity 200 and working chambers 50a, 50b, 50c, meaning that the fuel is injected into air in the intake port 102 before the air is drawn directly into the cavity 200. As such, the fuel injector 18 is not directly in communication with the cavity 200. This method of fuel dispensation is known as Port Fuel Injection (PFI) in the art. In these embodiments, the outlet port 60 may be in communication with a portion 1002 of the intake port 102 or the larger intake assembly which is upstream from the cavity 200 and working chambers 50a, 50b, 50c, and may release at least a part of the gas or fluid, which may be an airfuel mixture, in the first working chamber 50a to the upstream portion 1002, as shown in Figure 10. As such, the air-fuel mixture may be recirculated back through the intake port 102 and into the cavity 200, or it may be circulated to other parts upstream of the cavity 200 and may be utilised for other purposes. In some embodiments, such as the embodiment shown in Figure 10, the outlet port 60 may only be in communication with the upstream portion 1002, meaning that all of the airfuel mixture released from the first working chamber 50a is recirculated back to the upstream portion 1002. In other embodiments, the outlet port 60 may not be only in communication with the upstream portion 1002, but may also be in communication with the atmosphere, other parts of the engine 1, or other parts of the vehicle or device to which the engine 1 forms a part of. When utilising either DI or PFI methods of fuel dispensation, the valve 70 may be used to selectively open and close the outlet port 60 such that the gas or fluid in a working chamber 50a, 50b, 50c may be released from the working chamber 50a, 50b, 50c or maintained in the working chamber 50a, 50b, 50c as necessary based on changing performance requirements and operational modes of the vehicle or device to which the engine 1 forms a part of. In use of engine 1, embodiments of the outlet port 60 and valve 70 described above may be used in conjunction to alter the amount of a certain gas or fluid in a working chamber 50a, 50b, 50c before it reaches the expansion stage. In the example of an engine 1 which utilises air and fuel for combustion, the outlet port 60 may be used to reduce the amount of air in a working chamber 50a, 50b, 50c, and the valve 70 may be used to selectively control when this reduction is needed and to what extent. For example, the valve 70 may be controlled to be in the first position when the engine 1 is experiencing high load conditions, and may be controlled to move to the second position or an intermediate position when the engine 1 is experiencing relatively low load conditions. In this way, use of the valve 70 with the outlet port 60 may dispense with the requirement to use or include a throttle, meaning that the intake assembly may be simplified, and the pumping losses associated with using a throttle to alter the air being drawn into a rotary piston internal combustion engine may be reduced as the amount of air in a working chamber 50a, 50b, 50c may be altered after the intake stage. Therefore, in some embodiments, the engine 1, or the vehicle or device to which the engine 1 forms a part of, may not include a throttle. In other embodiments, the valve 70 and outlet port 60 may be used in addition to, or in conjunction with, a throttle, which may provide greater control over the overall power output of the engine 1. For example, during certain loading conditions the throttle alone may be used to control the engine 1, and during other loading conditions the valve 70 and outlet port 60 may be used in conjunction with, in addition to, or instead of the throttle to further control the engine 1. As a result, the efficiency of the engine 1 may be improved due to the ability to control the amount of air in the working chambers 50a, 50b, 50c in response to the conditions experienced by the engine before they undergo the expansion stage without sacrificing power output. Use of the outlet port 60 and valve 70 alters the characteristics of the compression stage of the cycle, and therefore may be considered to represent a modification to the traditional Otto Cycle under which a rotary piston internal combustion engine operates, with the modified four-stage cycle being analogous to the Atkinson cycle used with other types of combustion engines such as reciprocating engines. Additionally, as the valve 70 may be independent controlled by an ECU and moved by an actuator, the valve 70 does not need to be driven by the output shaft 12, meaning the valve does not introduce any additional frictional losses. Also, whilst the outlet port 60 is open, the cavity 200 may be vented to atmosphere and thus cooled. In one example, the vehicle or device of which the engine 1 forms a part of may be an unmanned aerial vehicle, such as a quadcopter 1000 which may include an ECU 300 in addition to the engine 1, as shown in Figure 11. The valve 70 of the engine 1 may be held in the first position, such that the outlet port 60 is generally sealed, when the engine 1 is experiencing high load conditions during take-off and landing manoeuvres, and may be moved to the second position or intermediate position when the engine 1 is experiencing relatively lower load conditions such as cruising. When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. The invention may also broadly consist in the parts, elements, steps, examples and / or features referred to or indicated in the specification individually or collectively in any and all combinations of two or more said parts, elements, steps, examples and / or features. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiment(s) described herein. Protection may be sought for any features disclosed in any one or more published documents referenced herein in combination with the present disclosure. Although certain example embodiments of the disclosure have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and / or to encompass equivalents.

Claims

1. A rotary piston internal combustion engine including:an engine housing having an internal surface defining a cavity, the engine housing having an end wall and a side wall, the internal surface including at least a portion of the end wall and at least a portion of the side wall;an output shaft extending through the cavity, the output shaft configured to rotate relative to the engine housing about an axis for transmitting power to parts to be operated;a rotary piston mounted eccentrically on the output shaft;an intake port and an exhaust port each in communication with the cavity;an outlet port in communication with the cavity; anda valve movable between a first position in which the outlet port is generally sealed, and a second position in which the outlet port is open;wherein, when the valve is in the first position, a surface thereof lies in the same plane as a part of the internal surface adjacent the outlet port to form a substantially continuous surface.

2. A rotary piston internal combustion engine according to claim 1, wherein the rotary piston is a multi-lobed trochoidal rotary piston having multiple apices each in engagement with the side wall, the rotary piston and the engine housing forming multipie working chambers including a first working chamber, wherein, in use, the first working chamber completes a four-stage cycle of intake, compression, expansion and exhaust for each revolution of the rotary piston.

3. A rotary piston internal combustion engine according to claim 2, wherein, in use, during at least a part of the intake stage, the outlet port and the intake port are in communication with the first working chamber.

4. A rotary piston internal combustion engine according to claim 2 or claim 3, wherein, in use, during at least a part of the compression stage, the outlet port is in communication with the first working chamber.

5. A rotary piston internal combustion engine according to any of claims 2 to 4, wherein, in use, during the compression stage, gas or fluid is maintained within the first working chamber when the valve is in the first position, and wherein at least a portion of a gas or fluid in the first working chamber may pass through the outlet port when the valve is in the second position.

6. A rotary piston internal combustion engine according to any preceding claim, wherein the internal surface is a two lobed epitrochoid including a top lobe and a bottom lobe, and wherein the outlet port is provided on the top lobe.

7. A rotary piston internal combustion engine according to claim 6, wherein the intake port is provided on or in the top lobe and / or the exhaust port is provided on or in the bottom lobe.

8. A rotary piston internal combustion engine according to any preceding claim, wherein the outlet port is provided on or in the side wall.

9. A rotary piston internal combustion engine according to any of claims 1 to 8, wherein the outlet port is provided on or in the end wall.

10. A rotary piston internal combustion engine according to any preceding claim, wherein the valve is configured to move to an intermediate position between the first position and the second position.

11. A rotary piston internal combustion engine according to any preceding claim, wherein the engine housing includes a first lateral side and a second lateral side, optionally wherein the outlet port and the intake port are provided on or in the first lateral side.

12. A rotary piston internal combustion engine according to any preceding claim, wherein the outlet port is in communication with the atmosphere.

13. A rotary piston internal combustion engine according any preceding claim, further including a fuel injector configured to dispense fuel directly into the cavity.

14. A rotary piston internal combustion engine according to claim 13, when dependent directly or indirectly on claim 11, wherein the fuel injector is provided on or in the second lateral side.

15. A rotary piston internal combustion engine according to any of claims 1 to 12, wherein the outlet port is in communication with a portion of the intake port which is upstream of the cavity.

16. A rotary piston internal combustion engine according to claim 15, further including a fuel injector configured to dispense fuel into the upstream portion of the intake port.

17. A rotary piston internal combustion engine according to any preceding claim, wherein the rotary piston includes at least one seal, and wherein during rotation of the rotary piston the or each seal is engageable with the surface of the valve when the valve is in the first position.

18. A rotary piston internal combustion engine according to claim 17, wherein the at least one seal is an apex seal configured to engage with the side wall.

19. A rotary piston internal combustion engine according to claim 17, wherein the at least one seal is an end seal configured to engage with the end wall.

20. A rotary piston internal combustion engine according to any preceding claim, wherein the outlet port has a first cross-sectional area through which a gas and / or fluid can pass, and wherein the valve is configured to alter the cross-sectional area of the outlet port from a first cross-sectional area to a second cross-sectional area as the valve moves between the first and second positions.

21. A rotary piston internal combustion engine according to any preceding claim, wherein the valve is configured to move away from the cavity when the valve moves from the first position to the second position.

22. A rotary piston internal combustion engine according to any preceding claim, further including a plurality of outlet ports, each outlet port in communication with the cavity, optionally wherein at least one outlet port is provided on the side wall and at least one outlet port is provided on the end wall.

23. A rotary piston internal combustion engine according to claim 22, further including a plurality of valves, each valve being configured to move between the first and the second position relative to a corresponding outlet port of the plurality of outlet ports.

24. A vehicle or a device comprising a rotary piston internal combustion engine according to any preceding claim.

25. A vehicle or a device according to claim 24 further including an engine control unit which is configured to move the valve between the first position and the second position.

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