GB2505522A

GB2505522A - Rotary pump or motor with lobed driving gears

Info

Publication number: GB2505522A
Application number: GB201215853A
Authority: GB
Inventors: John Leonard Stagg
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-09-04
Filing date: 2012-09-04
Publication date: 2014-03-05
Also published as: GB201215853D0

Abstract

A rotary pump or motor comprises two solid recessed rotors 1,2 in a Roots type arrangement. The rotors are coupled together by two non circular gears 7, 8 so that they rotate with cyclically relatively varying speed. In the illustrated embodiment, the rotors have three arms and recesses, and the gears have three lobes. One rotor 1 may be driven at a constant speed, and the other rotor 2 may be driven at a varying speed by the non circular gearing to provide the relative speed difference.

Description

ROTARY PUMP/MOTOR This invention relates to a device for use as a hydrostatic pump or motor.

Rotary fluid pumps commonly involve either a circular rotor revolving in a larger cylinder and having movable vanes that advance and retract to maintain contact with the cylinder wall, or two toothed rotors meshing with each other in an overlapping double bored cylinder so that fluid is transported around the periphery of the rotors to the outlet Both of these systems have disadvantages when required to deliver large volumes of fluid at high pressures. The first type of pump has a limit to the strength of the vanes when fully extended and the second type has a limit to the root strength of the gear elements when large tooth sizes are used.

Any attempt to use two solid rotors that are not of gear form has a fundamental requirement to form a seal between one rotor and the other before the latter breaks its seal with the former. This is only possible with conventional gear-driven rotors if the solid arms of the rotors are the same width as the gaps between the solid arms, if they are smaller than the gaps the seal cannot be ntaintained and if they are larger they will collide with the solid arms of the other rotor. Even if the widths are exactly the same as the gaps the edges of the rotors would have to be razor sharp with no allowance for radiusing or bevelling in order to maintain the seal between the two rotors. This, although theoretically possible, is in practice impossible to achieve and maintain.

To overcome this, the present invention uses two non-circular gears to dilve the two rotors such that the solid arms of the rotors can be narrower than the gaps between adjacent arms and still maintain a seal between the two rotors at all times- With reference to the accompanying drawings:-Page 1 shows a part-section side view with rotors connected to drive gears.

Page 2 shows a top view sectioned through the rotors. -Page 3 shows a top view sectioned through the gears, the teeth being drawn only in the area where meshing occurs.

Two identical and intermeshing rotors 1 & 2 are a close fit in a double bored casting 3. The space is sealed with a top cover plate 4 bolted to casting 3.

Drive shafts 5 & 6 fit through rotors 1 & 2 via bearings (not shown) in casting 3 and plate 4.

Two lobed gears 7 & B fit on the ends of shafts 5 & 6 which are splined at the rotors and gears but plain at the bearings. Drive shaft 5 continues beyond the sketch to a power source if the invention is used as a pump or to a load if used as a motor. Shaft 6 could end in a blind bearing in plate 4. The gears are enclosed in a pressed steel box fixed to casting 3 which is about two thirds filled with oil.

It can be seen from drawings 2/3 and 313 that the centres of the rotor arms line up with the lobes of the gears attached to them by the corresponding splined drive shafts. The gears mesh with each other such that the tooth at the shortest distance from the centre meshes with the tooth gap at the longest distance from the centre of the other gear. This ensures that the centres of the arms of the rotors correspond to the centres of the gaps between the arms of the other rotor and viceversa.

The action of the lobed gears has two related effects; firstly, when the rotors are positioned so that one rotor arm (for example, item No.1, drawing 2/3) is centrally located in the gap between two arms of the other rotor (item No.2), simple lever action causes one arm of No.2 rotor to move out of the way of No.1 rotors arm quicker than it would do if circular gears were used. Also, another arm of No.2 rotor moves in to take over the central sealing function quicker than with circular gears.

The second effect of the lobed gears action involves the length of the reference curve between the centre of the tooth gap at the lobe and the centre of the tooth at the shortest distance from the centre of the gear, an angular distance of 60 degrees for a 3 lobed gear.

In standard gears the diameter at which solid discs without teeth would rotate together using friction only is called the reference circle or sometimes the pitch circle as this is where the pitch of the teeth is established. With lobed gears it is a curve instead of a circle with the largest curvature at the lobe and therefore the halfway point between the apex of the lobe and the 60 degree angle is not 30 degrees but a few degrees less, the actual amount depending on the severity of the distortion of the gear from a circular shape. When the halfway points coincide, one of the rotor arms, which in the above example would be No.2 rotor has rotated slightly more than 30 degrees and it's leading edge has crossed the line between the two centres of rotation. At the same time the trailing edge of the other rotor arm (No.1) has rotated slightly less than 30 degrees and has not yet crossed the same line. The angular relationship of the two rotors at the halfway point is depicted in drawing 2/3 and that of the gears in drawing 3/3.

The shape of the gears depicted in the drawings has been exaggerated to illustrate the principle.

When used as a pump, rotor No.1 will rotate at constant angular velocity while rotor No.2 will rotate at varying angular velocity. When used as a motor, the load connected to shaft No.5 will cause the same effect.

The gears can be manufactured using existing numerically controlled industrial laser culling machines to a tolerance and finish more than adequate for this use, however gear finishing machines have been in use for a long time by manufacturers which run pairs or stacks of gears together under parafin in which powdered abrasive is suspended. The pairs of gears converge whilst running until the finished size is achieved, then separate and stop automatically.

Claims

CLAIMS.1. A rotary fluid pump/motor comprising two solid and recessed rotors in an overlapping double bored cylinder such that one rotor's arm extends into a recess in the other rotor forming a seal with it followed, after partial rotation, by the opposite situation which repeats at least once more during the course of each revolution during which the angular velocity of the rotors varies relative to each other.
2. A rotary pump/motor according to claim 1, in which the variation of angular velocity of the rotors is achieved by the use of non circular gears to drive the rotors.
3. A rotary pump/motor according to claim 1, which can consist of rotors with two or more arms connected to drive gears with the same number of lobes.
4. A rotary pump/motor according to claim 1, in which the two rotor and gear assemblies are identical and can function equally well in either direction.