WO2010129970A2

WO2010129970A2 - Air motor

Info

Publication number: WO2010129970A2
Application number: PCT/ZA2010/000021
Authority: WO
Inventors: Hubertus Helmuth Von Moltke
Original assignee: Cheetah Technologies (Pty) Ltd
Priority date: 2009-05-07
Filing date: 2010-05-07
Publication date: 2010-11-11
Also published as: WO2010129970A3

Abstract

A rotor for an air motor which has a body in which are formed slots which accommodate respective movable sealing vanes and wherein an air path is formed in the body to a volume in each slot which is partly enclosed by the respective vane.

Description

AIR MOTOR

BACKGROUND OF THE INVENTION

[0001] This invention relates to an air driven motor.

[0002] Motors which are driven by means of compressed air are in widespread use particularly in situations in which the use of electricity is not suitable nor advisable, for example for safety reasons.

[0003] In order to limit the use of compressed air and to reduce the size of an air motor it is desirable for optimum use to be made of the energy contained in the compressed air. Thus, the efficiency of an air driven motor should be as high as possible. To achieve this objective the effects of friction should be limited. This improves the power output of the motor and reduces wear in components of the motor such as the vanes, cylinder and rotor.

[0004] An air driven motor includes a rotor which is rotatable about an axis which is offset relatively to a central axis of a cylinder. A sealing action between the rotor and an inner wall of the cylinder is achieved by making use of sliding vanes, which are carried by the rotor. With rotation of the rotor the vanes move outwardly and then inwardly with an action which is matched to the positions of an air inlet port and an exhaust port.

[0005] The rotor is typically located between opposing end plates which are engaged with the cylinder. In one type of construction a thin oil film on an inner surface of each end plate provides a floating-type bearing support for the rotor which restricts axial movement of the rotor relatively to the cylinder. The rotor is axially positioned by means of a bearing. [0006] As a consequence of these constructional features it is necessary to displace the rotor blades outwardly, relative to the rotor, when the motor is started. This is done by introducing air into appropriate cavities. Generally similar considerations also apply to a motor which has a non-floating rotor.

[0007] The applicant has now determined that the type of construction referred to decreases efficiency of the air driven motor and, accordingly, it is an object of the present invention to provide a rotor, and an air motor which makes use of the rotor, with increased efficiency.

SUMMARY OF INVENTION

[0008] The invention provides, in the first instance, a rotor for an air motor which includes a circular, cylindrical body with a circumferential outer surface which is formed with a plurality of slots, wherein each slot extends from the outer surface into the body, and wherein the body has at least one formation which places the slots in air communication with one another.

[0009] The body may have opposed ends which extend at a right angle to a central longitudinal axis of the body and the formation may comprise a groove in at least one end.

[0010] Preferably the rotor has at least two of the formations and at least one formation, for example in the form of a groove, is provided in each respective end of the body.

[0011] Each formation may extend from a region near or at a base of each slot.

[0012] The invention further extends to an air motor which includes a cylinder in which is formed a chamber, and a rotor of the aforementioned kind which is mounted for rotation in the chamber and which includes a plurality of sealing vanes, each vane being engaged with a respective slot and being slidable relative to the slot upon rotation of the rotor with a protruding end of the vane in sealing engagement with an inner wall of the cylinder which bounds the chamber.

[0013] The invention also provides an air motor which includes a cylinder in which is formed a chamber, a rotor which is mounted for rotation inside the chamber and which includes a body with a circular, cylindrical circumferential surface, opposed first and second ends and a plurality of slots, wherein each slot extends into the body from the circumferential surface, has a mouth at the circumferential surface and a base within the body, and a plurality of sealing vanes which are respectively engaged with the slots, each vane including an outer edge which opposes a wall of the chamber and an inner edge, inside the slot, which opposes the base of the slot and which partly bounds a volume, inside the slot, which varies in size upon rotation of the rotor, and wherein the body has at least one formation which forms an air path which is in communication with each of the volumes.

[0014] The air motor may have a floating rotor or a non-floating rotor.

[0015] The formation may be in one of the first and second ends. Preferably each of the ends of the body carries a respective formation. The shape and size of each formation may vary according to requirement. Each formation may be a shallow groove which extends on a closed path, for example of circular outline, in a respective end.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention is further described by way of example with reference to the accompanying drawings in which:

Figure 1 is an end view of a rotor positioned inside a cylinder of an air motor, according to the invention; Figure 2 shows the rotor in perspective;

Figure 3 is a perspective view of the motor; and

Figure 4 is similar to Figure 2 and illustrates a non-floating rotor according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

[0017] Figures 1 to 3 of the accompanying drawings illustrate components of an air motor 10 which includes a cylinder 12 and a floating rotor 14. The cylinder and rotor are made from appropriate materials. The cylinder has a body 16 which has a circular outer surface 18 and through which extends a chamber 20 in the form of a cylindrical bore. The bore is offset relative to a central axis of the outer surface 18 and hence the thickness of a wall 24 of the body varies from a maximum value 22A, at what is referred to as a critical location, to a minimum value 22B diametrically opposed to the critical location. An input port 30 is formed through the wall 24. In use compressed air is introduced into the chamber 20 through this port. A port 32 is used to exhaust air from the chamber. The construction thus far is substantially conventional and for this reason has not been fully detailed.

[0018] The rotor 14 includes a circular cylindrical body 40 with an outer surface 42 and opposed first and second ends 44 and 46 respectively. The rotor is positioned to run on an axle (not shown) which is located in a passage with a central axis 48 which is off-centre relative to a central longitudinal axis 50 of the chamber (cylindrical bore) in the cylinder. End plates (not shown) which are fixed to the cylinder using appropriate techniques support the axle and precisely position the rotor inside the chamber. Thin oil films respectively between each end 44 and 46 and opposing inner surfaces of the end plates, act as floating bearings for the rotor. These aspects are generally known in the art and hence are not further described herein. [0019] The rotor is formed with a number of slots 60. In this instance there are five slots but this is exemplary only. Each slot extends from the outer surface 42 of the rotor inwardly into the body. The slots are not axially directed i.e. they do not extend directly towards the central axis 48. The angle of each slot, i.e. its orientation relative to a tangent on the outer surface 42, is determined taking into account various factors and operational requirements. Each slot has a mouth 64 and a base 66 within the body. The slots are identical in size. A respective sealing vane 70 is located in each slot. Each slot is sized so that the corresponding vane can be pushed fully into the slot with an outer end 72 of the vane then substantially in line with the outer surface 42. The slots are inclined so that the vanes extend generally in the direction of rotation of the rotor, marked R, in Figure 1 , in use of the motor.

[0020] As indicated in the preamble of the specification when an air motor of the aforementioned kind is used it is necessary to displace the vanes outwardly at the time the motor is put to use. This is done by introducing air into the slots, using a suitable technique, so that the vanes are forced outwardly. Air is then supplied to the chamber through the input port 30 and the rotor is thereby caused to move in the direction R. The air is contained in five volumes of variable size on an under side of the rotor. Each volume is located between projecting portions o a pair of adjacent vanes and opposing surfaces of an inner wall of the chamber and an outer wall of the rotor between the respective pair of vanes. The rotor turns and ultimately brings the air in each volume to the exhaust port at which point the energy in the air in the corresponding volume has been extracted and the spent air is then exhausted to atmosphere.

[0021] The applicant has determined that, within each slot, a small volume 80 is formed between a base 82 of the slot and an opposing end 84 of a vane. This volume varies in size due to the aforementioned operational reasons. As the oil films and the end plates effectively seal the volume 80 the air inside the volume is repeatedly compressed, as a vane is moved into a slot, and then allowed to expand, when the rotor rotates and the vanes are moved outwardly, mostly due to centrifugal action. An air motor can move at a considerable rotational speed e.g. 6000 rpm and the aforementioned action (i.e. of repeatedly compressing a small volume of air, within each slot, and then allowing the compressed air to expand) reduces the efficiency of operation of the air motor for energy from air introduced through the input port must be used for at least part of the compression process.

[0022] To address this factor at least one of the ends 44 and 46 of the rotor is formed with a small air passage 90 which extends to a region, for each slot, which is at or close to the base 82. The air passage may vary in shape and size but, preferably, is in the form of a shallow circular groove (as shown). In this way the respective volumes 80, defined by the various slots and vanes, are placed in air communication with each other. Preferably a respective air passage is formed in each end.

[0023] In use of the rotor, as a vane in one slot is being forced deeper into the slot the air in the corresponding volume 80 is compressed as the volume is reduced in size. However, in at least one other slot the corresponding vane is being moved outwardly and the corresponding volume 80 is increased in size. Thus air which is being pressurized in a volume of reducing size is allowed to move through the air passage 90 to at least one volume which is being increased in size. The pressure of the air trapped in the various slots is thereby substantially equalized for the air can flow freely between the volumes without material differential pressures occurring. At least part, if not all, of the energy which is required, in a conventional rotor, to compress the air at the base of each slot is thus not consumed and, in use, a motor which incorporates a rotor of the described kind exhibits an increased efficiency of operation. This manifests itself in an extended lifetime for components in the motor exhibit reduced effects of wear.

[0024] The principles of the invention can be applied with equal effect to a non- floating rotor. Figure 4 shows a rotor 14A which is similar in all material respects to the rotor 14 shown in Figure 1. For this reason like parts are designated by like reference numerals and the construction of the rotor is not further described. The rotor 14A is however supported on a shaft 96 which restrains the rotor against movement, relative to a cylinder (not shown) in an axial direction. Reliance is not placed on oil films at ends of the body 40 of the rotor to provide a floating bearing.

Claims

βCLAIMS

1. A rotor for an air motor which includes a circular, cylindrical body with a circumferential outer surface which is formed with a plurality of slots, wherein each slot extends from the outer surface into the body, and wherein the body has at least one formation which places the slots in air communication with one another.

2. A rotor according to claim 1 wherein the body has opposed ends which extend at a right angle to a central longitudinal axis of the body and the formation comprises at least one groove in one end.

3. A rotor according to claim 1 wherein the body has opposed ends which extend at a right angle to a central longitudinal axis of the body and at least one of the formations is positioned in each respective end of the body.

4. An air motor which includes a cylinder in which is formed a chamber and a rotor according to claim 1 which is mounted for rotation in the chamber and which includes a plurality of sealing vanes, each vane being engaged with a respective slot and being slidable relative to the slot upon rotation of the rotor with a protruding end of the vane in sealing engagement with an inner wall of the cylinder which bounds the chamber.

5. An air motor which includes a cylinder in which is formed a chamber, a rotor which is mounted for rotation inside the chamber and which includes a body with a circumferential surface, opposed first and second ends and a plurality of slots, wherein each slot extends into the body from the circumferential surface, has a mouth at the circumferential surface and a base within the body, and a plurality of sealing vanes which are respectively engaged with the slots, each vane including an outer edge which opposes a wall of the chamber and an inner edge, inside the slot, which opposes the base of the slot and which partly bounds a volume, inside the slot, which varies in size upon rotation of the rotor, and wherein the body has at least one formation which forms an air path which is in communication with each of the volumes.

6. An air motor according to claim 5 wherein at least one of the formations, in the form of a shallow groove which interconnects the slots, is provided in each respective end of the body of the rotor.