Background of the Invention

[0001] The present invention relates to an air motor, and in one particular example, an air motor capable of exploiting a low pressure differential in order to generate meaningful torque, as well as an electrical supply system employing an air motor for generating electrical power from compressed air.

Description of the Prior Art

[0002] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgement or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0003] Air motors use compressed air to generate movement. Air motors typically fall into three categories, namely linear, rotary vane and turbine motors.

[0004] In linear motors, compressed air is fed into a piston chamber to thereby pressurise the chamber and drive a piston. A return can be used to return the piston to a starting position when pressure in the piston chamber is released. Such piston motors are most commonly used in hydraulic systems.

[0005] Rotary vane motors use vanes mounted on a slotted rotor air to produce rotational motion. Air pumped through the motor pushes on the vanes creating the rotational motion of the central shaft. Rotation speeds can vary between 100 and 25,000 rpm depending on several factors which include the amount of air pressure at the motor inlet and the diameter of the housing. Vane-type air motors are often used to start large industrial diesel or natural gas engines.

[0006] Air turbine motors use compressed air to drive turbine blades mounted on a drive shaft, and these are typically used in applications requiring a high speed but low torque. [0007] Air motors have also been proposed which operate in a manner similar to combustion engines, replacing ignition of fuel with compressed air in order to drive pistons, which are then used to drive a crankshaft.

[0008] However, the above arrangements often require large air pressures and/or volumes of compressed air in order to generate meaningful torque, making these inefficient to operate in many situations.

Summary of the Present Invention

[0009] In one broad form, an aspect of the present invention seeks to provide an air motor including: a drive shaft; a rotor mounted on the drive shaft, the rotor including a drive surface; a plurality of piston assemblies, each piston assembly including: a piston housing; a piston mounted within the piston housing and configured to undergo reciprocal linear movement within the piston housing; a follower coupled to the piston, wherein the piston assemblies are mounted circumferentially spaced outwardly of the rotor and substantially radially orientated so that the follower engages the drive surface; and, a valve arrangement configured to be coupled to an air supply to pressurise and depressurise the piston housings to selectively actuate the pistons and thereby drive the rotor.

[0010] In one embodiment the follower is a roller rotatably mounted to a piston rod extending radially inwardly from the piston.

[0011] In one embodiment the drive surface has at least one of: an elliptical shape; a geometric stadium shape; and, a Reuleaux Triangular shape.

[0012] In one embodiment the rotor is an elliptical rotor, with the drive surface being formed from an outer edge of the rotor.

[0013] In one embodiment the rotor is a cylindrical or disc rotor.

[0014] In one embodiment the air motor includes a casing supporting the piston assemblies.

[0015] In one embodiment the plurality of piston assemblies includes at least one of: an odd number of piston assemblies; at least three piston assemblies; at least five piston assemblies; at least seven piston assemblies; at least nine piston assemblies; at least eleven piston assemblies; at least thirteen piston assemblies; and, at least fifteen piston assemblies.

[0016] In one embodiment the air motor includes multiple axially spaced piston assembly rings, each piston assembly ring including a plurality of piston assemblies.

[0017] In one embodiment the air motor includes a respective rotor for each piston assembly ring.

[0018] In one embodiment the air motor including n rotors and the rotors are rotationally offset by an angle of 360° In.

[0019] In one embodiment a motor output is depending on at least one of an eccentricity of the drive surface; a piston capacity; a piston diameter; a number of piston assemblies; and, an air pressure.

[0020] In one embodiment the air motor includes a controller configured to control the valve arrangement.

[0021] In one embodiment the controller includes an electronic processing device that electronically controls the valve arrangement.

[0022] In one embodiment the controller includes a mechanical timing arrangement driven by the drive shaft, which mechanically controls the valve arrangement.

[0023] In one embodiment the valve arrangement includes an inlet valve and an outlet valve for each piston assembly.

[0024] In one embodiment the air supply includes a supply of low pressure air.

[0025] In one broad form, an aspect of the present invention seeks to provide an electrical supply system including: an air motor including: a drive shaft; a rotor mounted on the drive shaft, the rotor including a substantially elliptical drive surface; a plurality of piston assemblies, each piston assembly including: a piston housing; a piston mounted within the piston housing and configured to undergo reciprocal linear movement within the piston housing; a follower coupled to the piston, wherein the piston assemblies are mounted circumferentially spaced outwardly of the rotor and substantially radially orientated so that the follower engages the drive surface; and, a valve arrangement configured to be coupled to an air supply to pressurise and depressurise the piston housings to selectively actuate the pistons and thereby drive the rotor; and, a generator coupled to the drive shaft of the air motor, the generator being configured to generate electrical power.

[0026] In one embodiment the electrical supply system includes: a renewable power supply; a compressor; and, an air storage tank, wherein the power supply is configured to drive the compressor and store pressurised air within the air storage tank, and wherein the air storage tank acts as an air supply for the air motor.

[0027] It will be appreciated that the broad forms of the invention and their respective features can be used in conjunction and/or independently, and reference to separate broad forms is not intended to be limiting. Furthermore, it will be appreciated that features of the method can be performed using the system or apparatus and that features of the system or apparatus can be implemented using the method.

Brief Description of the Drawings

[0028] Various examples and embodiments of the present invention will now be described with reference to the accompanying drawings, in which: -

[0029] Figure 1 A is a schematic perspective view of an example of an air motor;

[0030] Figure IB is a schematic cut-away side view of a piston assembly of the air motor of Figure 1A;

[0031] Figure 1C is a schematic end view of the air motor of Figure 1 A;

[0032] Figure ID is a schematic side view of the air motor of Figure 1 A;

[0033] Figure IE is a schematic cut-away view of the air motor of Figure 1 A along the line B- B' of Figure ID; [0034] Figure IF is a schematic cut-away view of the air motor of Figure 1 A along the line A- A' of Figure 1C;

[0035] Figure 2A is a schematic perspective view of the air motor of Figure 1A including a casing;

[0036] Figure 2B is a schematic perspective view of the air motor of Figure 2A with one end cap removed;

[0037] Figure 2C is a schematic end view of the air motor of Figure 2A with one end cap removed;

[0038] Figure 2D is a schematic side view of the air motor of Figure 2A with one end cap removed;

[0039] Figure 2E is a schematic cut-away view of the air motor of Figure 2A along the line D- D' of Figure 2D;

[0040] Figure 2F is a schematic cut-away view of the air motor of Figure 2A along the line C- C of Figure 2C;

[0041] Figure 3 A is a schematic perspective view of a further example of an air motor;

[0042] Figure 3B is a schematic perspective view of the air motor of Figure 3 A with the piston assemblies removed;

[0043] Figure 3C is a schematic cut-away side view of the air motor of Figure 3A with the piston assemblies removed;

[0044] Figure 3D is a schematic end view of the rotor arrangement of the air motor of Figure 3 A;

[0045] Figure 3E is a schematic side view of the rotor arrangement of the air motor of Figure 3A;

[0046] Figure 4 is a is a schematic end view of an alternative rotor arrangement; and, [0047] Figure 5 is a schematic diagram of an example of an electrical supply system using an air motor.

Detailed Description of the Preferred Embodiments

[0048] An example of an air motor will now be described with reference to Figures 1 A to IF.

[0049] In this example, the air motor 100 includes a drive shaft 110 and a rotor 120, mounted on the drive shaft 110, which includes a drive surface 121. In this example, the rotor is in the form of shortened cylinder, disc or plate, with the drive surface being an elliptical surface formed from an outer edge of the rotor. However, this is not essential and other suitable arrangements could be used, such as to provide a drive surface extending axially from an end of a circular disc rotor, or to use different shapes for the drive surface, such as geometric stadium shapes, Reuleaux Triangle, or the like, depending on ignition points required.

[0050] The air motor further includes a plurality of piston assemblies 130, each of which includes a piston housing 131, having a piston 132 movably mounted therein, and configured to undergo reciprocal linear movement within the piston housing. A follower 133, is coupled to the piston 132, with the piston assemblies 130 being mounted circumferentially spaced outwardly of the rotor 120 and substantially radially orientated so that the follower 133 engages the drive surface 121.

[0051] In one example, the piston housing 131 includes a threaded end portion 131.1 allowing the piston to be mounted to an air motor casing, as will be described in more detail below. The piston housing 131 may also include a port 134, allowing pressurised air to be supplied into the piston housing. In this regard, a valve arrangement (not shown) is provided that is configured to be coupled to an air supply to selectively pressurise and optionally depressurise the piston housings, to thereby selectively actuate the pistons 132. If the piston assemblies are actuated in sequence, the followers 133 engage the drive surface 121 and thereby drive the rotor 120, and hence drive shaft.

[0052] The above described arrangement can provide a number of benefits over traditional air motor arrangements. [0053] Firstly, the air motor 100 can employ a large number of piston assemblies 130 spaced around the rotor 120, so that each piston assembly 130 contributes to the overall torque generated by the motor 100. This allows the air motor 100 to generate a relatively large amount of torque, whilst only requiring a relatively small amount of force to be generated by each piston assembly 130.

[0054] Secondly, the cross sectional area of each piston effects the power generated by each piston for a given pressure of compressed air supplied to the piston, so that maximising the cross sectional area can increase the power generated by the motor for a given air pressure.

[0055] Thirdly, the extent of travel of each piston 132 is governed by the eccentricity of the drive surface. Selection of a suitable eccentricity can be used to control the torque and power generated, but also impacts on the volume of air used by the motor. Specifically, minimising the eccentricity reduces the travel of each piston and hence minimises the volume of air required by each piston, and hence reduces air usage by the motor as a whole.

[0056] Accordingly, it will be appreciated that the above arrangement, through use of suitable parameters, such as piston cross sectional area, drive surface eccentricity and number of piston assemblies, can be configured to provide a highly efficient air motor, which is capable of generating significant torque and power, whilst minimising the volume and pressure of air required.

[0057] As will be described in more detail below, this makes the air motor suitable for use with low pressure compressed air sources, which might for example, be generated using renewable energy sources.

[0058] These features and potential benefits make the motor suitable for use in a wide range of applications, including but not limited to propelling crafts or vehicles, driving machinery or pumps, or the like, as well as for use in driving generators for generating electricity, as will be described in more detail below.

[0059] A number of further features will now be described. [0060] In the current example, the follower is a roller 133 rotatably mounted to a piston rod 132.1 extending radially inwardly from the piston 132, although it will be appreciated that this is not essential and other suitable arrangements could be used.

[0061] In one example, the air motor includes a casing supporting the piston assemblies, and an example of this arrangement will now be described with reference to Figures 2A to 2F.

[0062] In this example, the casing includes two circular caps 241, 242 interconnected by a cylindrical ring 243. The caps 241, 242 include respective bearings 241.1, 242.1, which are used to support the drive shaft 110, with the rotor 120 being positioned between the caps 241, 242, and inwardly of the ring 243. The ring 243 includes a plurality of openings 243.1, which in use receive the threaded end portion 131.1 of the piston housing 131, to hold the piston assemblies relative to the rotor 120, whilst allowing the piston assemblies 130 to be easily attached to and removed from the ring 243 so that the piston assemblies to be easily removed and replaced as needed. The ring and caps are typically made of metal, although other suitable materials could be used.

[0063] Typically the plurality of piston assemblies includes an odd number of piston assemblies, which can help ensure even application of power to the rotor, whilst preventing motor seizure. The motor can include at least three piston assemblies, at least five piston assemblies, at least seven piston assemblies, at least nine piston assemblies, at least eleven piston assemblies, at least thirteen piston assemblies or at least fifteen piston assemblies.

[0064] In another example, the air motor includes multiple axially spaced piston assembly rings, each piston assembly ring including a plurality of piston assemblies, and an example of this will now be described with reference to Figures 3 A to 3E.

[0065] In this example, the casing includes four caps 341, 342, 344, 346 and intervening cylindrical rings 343, 345, 347. The caps 341, 342, 344, 346 again include respective bearings 341.1, 342.1, 344.1, 346.1, which are used to support the drive shaft 110. In this example, a respective rotor 320, 322, 324 is provided between the pairs of caps 341, 342; 342, 344; 344, 346, so that the rotors 320, 322, 324 are positioned between the caps 341, 342, 344, 346, inwardly of the cylindrical rings 343, 345, 347. Each ring 343, 345, 347 includes a plurality of openings, which in use receive the threaded end portion 131.1 of the piston housing 131, allowing the piston assemblies 130 to be secured to the cylindrical rings 343, 345, 347, and held in place relative to the rotors 320, 322, 324. Thus, in this example, a respective rotor for each ring 343, 345, 347, with the rotors being rotationally offset by 120° to help maintain motor balance.

[0066] However, it will be appreciated that other arrangements could be used, for example including a single rotor driven by piston assemblies in different rings, or by using a greater or lesser number of rotors, in which case if the air motor includes n rotors and the rotors are rotationally offset by an angle of 360° In.

[0067] As previously mentioned, the motor output is dependent on a range of factors, including but not limited to an eccentricity of the drive surface, a piston capacity, a piston diameter, a number of piston assemblies, a number of rotor assemblies, and an air pressure.

[0068] In one example, the piston assemblies have a length of about 200-300mm, 225-275mm and more typically about 250mm (excluding the threaded end portion 131.1), and a diameter of about 100-150mm, 112-138mm and more typically about 125mm. The rotor include a major axis diameter of 150-230mm, 175-205mm and more typically about 190mm, and an eccentricity of 0.95-0.85 and more typically about 0.9. However, these values are for the purpose of illustration only and other arrangements could be used, depending on the desired output characteristics and intended usage of the air motor.

[0069] In the above example, the rotors are elliptical, but this is not essential and other rotor shapes could be used depending on the preferred implementation. For example, the rotor could have a rounded triangular shape as shown by the rotor 420 in Figure 4. Other geometric shapes could also be used, including for example multiple rounded corners, depending on the number of ignition points desired.

[0070] The air motor typically further includes a controller configured to control the valve arrangement, and specifically to operate the valves with specific timing to thereby ensure optimum efficiency and power output is maintained. In this regard, the valve arrangement typically includes an inlet valve and an outlet valve for each piston assembly, with these being used to control the supply of pressurised air into the piston chamber, or release of air from the piston chamber, respectively. In use, the controller operates to control the relative timing of the opening closing of the inlet and outlet valves, for all of the piston assemblies, thereby ensuring the pistons are driven to thereby rotate the rotor(s).

[0071] In one example, the controller includes an electronic processing device that electronically controls the valve arrangement, although this is not essential and alternatively a mechanical timing arrangement driven by the drive shaft, can be used to mechanically control the valve arrangement.

[0072] It will be appreciated that such valve and controlling arrangements may be similar to those employed in combustion engines and these will not therefore be described in any further detail.

[0073] In one example, the air supply includes a supply of low pressure compressed air, and the air motor can be coupled to a generator, to thereby generate electricity from compressed air. In one particular example, this forms part of an electrical supply system optionally powered by renewable energy sources, such as solar and/or wind power, and an example of this will now be described with reference to Figure 5.

[0074] In this example, the electrical supply system 550 includes a power supply 551, a compressor 552 and an air storage tank 553. In use, the power supply 551 is configured to drive the compressor 552 and store pressurised air within the air storage tank 553. The air storage tank then acts as an air supply for the air motor 500, which is in turn used to drive a generator 554 and generate electricity.

[0075] Whilst the above arrangement results in energy losses in converting electrical power into compressed air and back again, the losses are relatively small. Furthermore, through suitable configuration, large amounts of energy can be stored as compressed air, whilst the air motor is highly efficient at converting even low air pressures back into electricity, meaning the ability to deliver power until the compressed air supply is entirely depleted.

[0076] This makes this arrangement suitable for providing continuous power from renewable power supplies, such as wind, solar, hydroelectric power supplies, kinetic energy recovery systems, or the like, allowing a power supply system of the above described form to act as a consistent supply of energy for distribution via a connected Virtual Power Plant (VPP) or as a stand-alone system in any location.

[0077] Additionally and/or alternatively, the renewable power supply could be replaced by an electrical grid connection, with this being used to store power off-peak and supply power during peak times, reducing peak loading costs, and even providing supply back to the grid for load balancing purposes. This can therefore be used to help maintain grid stability and/or operating frequencies. This can also be used to establish a micro-grid that is not subject to volatile market prices, and can provide base load power irrespective of demand.

[0078] In one example, the above described arrangement can be remotely controlled, using a suitable control arrangement, allowing release of stored energy either to the power grid or other loads, to be controlled from other locations, as needed, in real time.

[0079] The above described motor is also simply and easy to maintain, ensuring long term reliability, whilst, the piston assemblies can be simply screwed in or out, making these easy to replace. As a result the air motor and hence electrical supply system is suitable for use in remote locations.

[0080] It will also be appreciated that whilst the air motor has been described for use in generating electrical power, this is only one example application and this is not intended to be limiting. In particular, the arrangement is suitable for use in any scenario where rotational torque can be used, including but not limited to powering vehicles, such as cars, boats, or similar, direct water pumping, for irrigation or similar, or other applications as needed.

[0081] Throughout this specification and claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers. As used herein and unless otherwise stated, the term "approximately" means ±20%.

[0082] Persons skilled in the art will appreciate that numerous variations and modifications will become apparent. All such variations and modifications which become apparent to persons skilled in the art, should be considered to fall within the spirit and scope that the invention broadly appearing before described.