Reversible double-throw air motor

Details Reversible double-throw air motor Reversible double-throw air motor

2000-04-17

2001-04-17

Denion, Thomas (Department: 3748)

Rotary expansible chamber devices

Miscellaneous

C418S268000

Reexamination Certificate

active

06217306

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates generally to pneumatically powered hand tools and more specifically to a motor for use with such tools.
BACKGROUND OF THE INVENTION
Various pneumatic impulse tools, such as impact wrenches, are powered by reversible rotary vane pneumatic motors. Such motors are required to have a large stall torque in both forward and reverse directions. It is advantageous for such motors to be relatively small in size, since they are generally hand-held by an operator.
Most previously known reversible air motors are changed from forward to reverse operation by rerouting the inlet (pressure) and outlet (exhaust) paths at a location remote from the motor package, such as by shuttle spool valves or rotary valves. Such reversing arrangements take up valuable space, making the tool larger, complicate the construction in terms of adding parts and requiring additional labor for assembly, thus increasing the manufacturing cost, and creating tortuous air flow paths, thus reducing efficiency.
Kettner U.S. Pat. No. 4,822,264 (1989) describes and shows a rotary vane air motor in which the supply and exhaust passages leading to and from the cylinder chambers are reversed by changing the rotational position of a rotary valve plate that is positioned between a fixed distributor mounted within the motor casing on a proximal side of the valve plate and a fixed cylinder member on the distal side of the valve plate. Although the design of Kettner's motor improves on some prior art reversible rotary vane motors in terms of size, it has some shortcomings. The distributor has two pressure ports located diametrically opposite each other, each of which is flanked on either side by an exhaust port. The exhaust ports are located very close to the pressure ports, thus presenting an opportunity for blowby of pressure air at the interface between the distributor and the valve plate. That possibility is exacerbated by the fact that the rotatable valve plate interfaces on opposite sides with fixed members with sliding fits. Thus, small tolerance variations can lead to large leaks and reduced efficiency. The position of the valve plate is maintained by a spring/ball detent, and avoiding the risk of an unintended rotation of the valve plate during handling of a tool equipped with the motor requires that the detent be quite strong, which detracts from a desirable facility of reversal by the user. If the valve plate is rotated inadvertently from a desired position during handling, there is no assurance that it will be moved to the proper position during operation of the tool, and the motor performance may be compromised, resulting in a defective operation, such as a low torque on a fastener. The motor/reversal package of the Kettner motor has five main parts—a housing; a cylinder member; a rotor assembly; a distributor; and a valve plate, each of relatively complicated design and calling for precision manufacture to minimize leaks.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a reversible double-throw air motor having a large torque and high rotational acceleration in both forward and reverse operation at slow motor speeds. A further object is to provide such a motor in which the motor package, including the reversing feature, is small in size. Still another object is to make the motor of relatively simple construction with a minimum number of main components, thus reducing the costs for parts and assembly labor. It is also an objective to make the motor easy to use, reliable in operation, durable, and readily cared for.
The foregoing objects can be attained, in accordance with an embodiment of the present invention, by a reversible double-throw air motor having a housing that includes a cavity defined by a peripheral wall and spaced-apart proximal and distal end walls. A tubular cylinder member is mounted in the housing cavity for rotation between a forward position and a reverse position and has an inner surface defining a hole of uniform oblong cross section along its length and having a lengthwise center axis. The inner surface has first, second, third, and fourth quadrants defined by the intersections with the inner surface of mutually perpendicular planes that include the center axis, one of which planes intersects the cylinder inner surface at diametrically opposite bottom dead center lines and the other of which planes intersects the cylinder inner surface at top dead center lines. A rotor is mounted in the housing for rotation about the cylinder center axis and has a circular cylindrical body portion received within the cylinder hole, the peripheral surface of the body portion being in close radial clearance with the inner surface of the cylinder member hole at the bottom dead center lines. The peripheral surface of the rotor, surfaces of the cavity end walls, and the cylinder inner surface define two crescent-shaped chambers. A plurality of circumferentially spaced-apart vanes carried by the rotor body portion for radial displacement toward and away from the cylinder axis and engaging the cylinder inner surface and the cavity end walls divide the two crescent-shaped chambers into a plurality of variable volume rotating working subchambers.
During each revolution of a given vane with the rotor, that vane makes two complete excursions between a bottom dead center position, the position in which the vane is located radially inwardly of one of the two bottom dead center lines of the cylinder inner surface, and a top dead center position, in which the vane is located radially inwardly of one of the two top dead center lines of the cylinder inner surface. During an initial part of each outward excursion, pressurized air is supplied to the cylinder quadrant traversed by the vane. When the next following vane passes bottom dead center, the pressurized air upstream of the vane in question is trapped in the subchamber between the two vanes but continues to expand as the volume in the subchamber increases due to continued outward excursion of the vane in question. When the vane in question passes the top dead center line at the end of the quadrant, the subchamber is opened to exhaust, thus creating a large pressure difference across the next following vane, which has pressurized air trapped in the subchamber behind it. The difference in the pressures in the adjacent subchambers imposes force on the vanes, thus imparting rotational torque to the rotor.
The present invention provides for reversing the direction of operation of the motor by rotating the cylinder between forward and reverse positions relative to pressure and exhaust ports of unique configurations in the proximal end wall of the cavity that receives the cylinder member and by transfer passages and associated ports in the cylinder wall. For purposes of explaining the invention, the four quadrants of the cylinder inner surface are given the numbers one to four, one and three being opposite each other, two being between one and three on one side of the inner surface, and four being between three and one on the other side of the inner surface and the numbers running consecutively in the clockwise direction with respect to the proximal end of the cylinder member. The following is the arrangement of passages and ports:
Exhaust passages in the housing open at a pair of diametrically opposite, circumferentially elongated exhaust ports in the proximal end wall of the cavity. The exhaust ports are positioned and configured to open exclusively to portions of the two crescent-shaped chambers radially inwardly of the second and fourth quadrants, respectively, of the cylinder inner surface when the cylinder member is in the forward position and to open exclusively to portions of the two crescent-shaped chambers radially inwardly of the first and third quadrants, respectively, of the cylinder inner surface when the cylinder member is in the reverse position.
Pressure passages in the housing open at a pair of diametrically opposite pressure ports in the proximal end wall of the cavity radial

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