GB2170863A

GB2170863A - Rotary positive displacement pump or motor

Info

Publication number: GB2170863A
Application number: GB08503065A
Authority: GB
Inventors: Michael Charles Broad
Original assignee: HEAD ENGINEERING Ltd
Current assignee: HEAD ENGINEERING Ltd
Priority date: 1985-02-07
Filing date: 1985-02-07
Publication date: 1986-08-13
Also published as: GB8503065D0

Abstract

A rotating positive displacement pump or motor having two or more rotating rotors of constant section in the direction of the rotational axis wherein the rotors 1 are formed (e.g. by casting, moulding or extrusion) into a preformed shape parts of which are subsequently machined to produce surfaces 5 and 7 which in use effect sealing between co-operating parts of the rotors and between the rotors and the peripheral housing 9 while leaving unmachined areas 3, 10 and 11 not involved in the sealing function. <IMAGE>

Description

SPECIFICATION Rotating positive displacement pump or motor This invention relates to rotating positive displacement pumps or motors of the Rootes type.

The rotors for such pumps or motors are generally of complex profiles to form an effective seal between each other and between each and the peripheral housing. Different profiles perform various functions to achieve higher pressures, higher efficiency or smooth flow rates or the like. In general the rotors are machined all over from castings or from solid blocks of material. In some cases the rotors are formed by a process such as a plastic moulding.

The manufacture of these profiles is complex and involves greater accuracy in the places which perform a sealing function while not requiring such accuracy in other places not performing a sealing function.

According to the present invention there is provided a rotating positive displacement pump or motor of the Rootes type having two or more rotating rotors of constant section in the direction of the rotational axis having tips at the lobe extremities to run close to a housing to form an effective seal without contact and which rotors are shaped to intermesh with similar proximity to each other to effect sealing without contact, being maintained in non-contacting relative position by two or more gears coaxially fixed on the shafts of said rotors and meshing with each other, characterised in that the rotors are made from a preformed shape which due to insufficient accuracy of the preforming technique is subsequently machined with the accuracy required to effect sealing between co-operating parts of the rotors and between said rotors and the peripheral housing while leaving unmachined those areas not involved in the sealing function, but whose accuracy nevertheless is sufficient for defining the boundaries necessary to effect positive displacement.

In some embodiments of the invention the preformed shape is provided by the extrusion method normally associated with aluminium alloys or alternatively is provided by moulding methods normally associated with plastic materials.

In a modification the preformed shape may be provided by molten metal casting techniques where that method is accurate enough for the non-machined surfaces and may include shell moulding, investment casting, lost wax processes and the like.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a sectional view of a single rotor in the preformed shape Figure 2 is a sectional view of a single rotor in accordance with the invention showing where the co-operating and sealing portions have been machined to a greater accuracy to obtain necessary sealing clearances.

Figure 3 is a sectional view of a pair of rotors in accordance withthe invention showing the machined portions co-operating with each other and their mutually enclosing housing.

Referring to Fig. 2, the particular rotor shape chosen to depict the invention has three lobes 1 mutually equi-spaced and based on external curves 2 and internal curves 3 generated with reference to the pitch circle diameter 4. These curves represent the true position for exact contact of the lobes of one rotor with its cooperating second rotor. In order to both avoid contact and yet form an effective seal against excessive leakage of the fluid or gas the portions of the lobes which perform this sealing are machined to give surfaces at 5 where the surface profile lies inside the true position curve with a close tolerance. Similarly the lobe tip 6 is machined to provide a surface profile 7 which lies with close tolerance inside curve 8 which is the true position of the enclosing housing 9.In a similar way the enclosing housing 9 is machined to lie outside the true position of curve 8 to avoid contact. It is not essential that curves 8 and 2 are coincident at the lobe tip on the centre line.

The remaining parts of the rotor profile on the rotor lobe flanks 10 and at the internal portions between rotor lobes 11 may be allowed to vary by a larger tolerance sufficient to permit preforming techniques which cannot hold the accuracy of machined parts of the rotor profile.

1. A rotating positive displacement pump or motor of the Rootes type having two or more rotating rotors of constant section in the direction of the rotational axis having tips at the lobe extremities to run close to a housing to form an effective seal without contact and which rotors are shaped to intermesh with similar proximity to each other to effect sealing without contact, being maintained in noncontacting relative position by two or more gears coaxially fixed on the shafts of said rotors and meshing with each other, characterised in that the rotors are made from a preformed shape which due to insufficient accuracy of the preforming technique is subsequently machined with the accuracy required to effect sealing between co-operating parts of the rotors and between said rotors and the peripheral housing while leaving unmachined those areas not involved in the sealing function, but whose accuracy is nevertheless sufficient for defining the boundaries necessary to effect positive displacement.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Rotating positive displacement pump or motor This invention relates to rotating positive displacement pumps or motors of the Rootes type. The rotors for such pumps or motors are generally of complex profiles to form an effective seal between each other and between each and the peripheral housing. Different profiles perform various functions to achieve higher pressures, higher efficiency or smooth flow rates or the like. In general the rotors are machined all over from castings or from solid blocks of material. In some cases the rotors are formed by a process such as a plastic moulding. The manufacture of these profiles is complex and involves greater accuracy in the places which perform a sealing function while not requiring such accuracy in other places not performing a sealing function. According to the present invention there is provided a rotating positive displacement pump or motor of the Rootes type having two or more rotating rotors of constant section in the direction of the rotational axis having tips at the lobe extremities to run close to a housing to form an effective seal without contact and which rotors are shaped to intermesh with similar proximity to each other to effect sealing without contact, being maintained in non-contacting relative position by two or more gears coaxially fixed on the shafts of said rotors and meshing with each other, characterised in that the rotors are made from a preformed shape which due to insufficient accuracy of the preforming technique is subsequently machined with the accuracy required to effect sealing between co-operating parts of the rotors and between said rotors and the peripheral housing while leaving unmachined those areas not involved in the sealing function, but whose accuracy nevertheless is sufficient for defining the boundaries necessary to effect positive displacement. In some embodiments of the invention the preformed shape is provided by the extrusion method normally associated with aluminium alloys or alternatively is provided by moulding methods normally associated with plastic materials. In a modification the preformed shape may be provided by molten metal casting techniques where that method is accurate enough for the non-machined surfaces and may include shell moulding, investment casting, lost wax processes and the like. A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a sectional view of a single rotor in the preformed shape Figure 2 is a sectional view of a single rotor in accordance with the invention showing where the co-operating and sealing portions have been machined to a greater accuracy to obtain necessary sealing clearances. Figure 3 is a sectional view of a pair of rotors in accordance withthe invention showing the machined portions co-operating with each other and their mutually enclosing housing. Referring to Fig. 2, the particular rotor shape chosen to depict the invention has three lobes 1 mutually equi-spaced and based on external curves 2 and internal curves 3 generated with reference to the pitch circle diameter 4. These curves represent the true position for exact contact of the lobes of one rotor with its cooperating second rotor. In order to both avoid contact and yet form an effective seal against excessive leakage of the fluid or gas the portions of the lobes which perform this sealing are machined to give surfaces at 5 where the surface profile lies inside the true position curve with a close tolerance. Similarly the lobe tip 6 is machined to provide a surface profile 7 which lies with close tolerance inside curve 8 which is the true position of the enclosing housing 9.In a similar way the enclosing housing 9 is machined to lie outside the true position of curve 8 to avoid contact. It is not essential that curves 8 and 2 are coincident at the lobe tip on the centre line. The remaining parts of the rotor profile on the rotor lobe flanks 10 and at the internal portions between rotor lobes 11 may be allowed to vary by a larger tolerance sufficient to permit preforming techniques which cannot hold the accuracy of machined parts of the rotor profile. CLAIMS

2. A rotating positive displacement pump or motor as in Claim 1, wherein the preformed shape is formed by extrusion.

3. A rotating positive displacement pump or motor as in Claim 1, wherein the preformed shape is formed from a plastic moulding.

4. A rotating positive displacement pump or motor as in Claim 1, wherein the preformed shape is a metal casting.

5. A rotating positive displacement pump or motor substantially as described herein with reference to Figs. 1-3 of the accompanying drawing.