Reversible gerotor pump having magnetic attraction between the rotor and the reversing ring

A reversible gerotor-type pump having an angularly moveable reversing ring rotatably supporting an internally toothed rotor which in turn cooperates with an externally toothed gear received within the rotor and rotatable therewith about an axis parallel to but spaced from the axis of rotation of the rotor, and, magnet means magnetically attracting the rotor towards the reversing ring so as to provide drag between the rotor and the reversing ring at least at the commencement of rotation of the rotor relative to the reversing ring.

This invention relates to reversible gear pumps of the kind often referred 
to as reversible gerotor pumps. 
Reversible gerotor pumps are well known, and include an externally toothed 
gear surrounded by, and meshing with, an internally toothed rotor. The 
gear and rotor rotate together in the same direction about spaced parallel 
axes, and the gear generally has one fewer teeth than the meshing form on 
the inner surface of the rotor. The shaping of the tooth forms on the gear 
and the rotor is such that as the two rotate together, the shaping, and 
number of teeth, together with the eccentricity of the rotation axes of 
the gear and the rotor produce a pumping action. 
It is well known that if the direction of rotation of the gear and rotor is 
reversed then the pumping action is reversed in that the pump inlet 
becomes a pump outlet and vice versa. It is also well known that if the 
eccentricity of the axes of the gear and rotor is reversed then again the 
pumping flow is correspondingly reversed. This knowledge has been made use 
of in a number of reversible gerotor pump constructions in which reversal 
of rotation of the gear and rotor is accompanied by reversal of the 
eccentricity so that irrespective of the change in rotation direction the 
pumping flow direction stays the same, and the pump inlet remains an inlet 
while the pump outlet remains an outlet. 
Conventionally eccentricity reversal is achieved by movement of a reversing 
ring within which the rotor of the pump is mounted. The reversing ring is 
mounted for rotation about an axis co-extensive with the axis of the gear 
of the pump and has an eccentrically positioned cylindrical bore within 
which the cylindrical outer surface of the pump rotor is received. Thus 
the angular position of the reversing ring determines the eccentricity of 
the rotor relative to the gear and moving the ring relative to the rotor 
through 180.degree. reverses the eccentricity of the rotor relative to the 
gear. Conventionally frictional drag between the rotor and the reversing 
ring moves the reversing ring when reversal of the rotation of the rotor 
takes place, an outer housing providing abutments cooperating with the 
reversing ring to limit the movement of the reversing ring to 180.degree.. 
There are many variations of such arrangements, and three different 
examples are illustrated respectively in U.S. Pat. Nos. 4,171,192, 
4,200,427 and 4,222,719. 
It will be recognised that where the supply of liquid from the pump is 
crucial, as can be the case where the pump is pumping lubricating oil to a 
critical, high speed, component such as an electrical generator of an 
aircraft gas turbine engine, then any delay in pumping could be 
disastrous. The three patents mentioned above disclose different ways of 
ensuring that there is sufficient drag between the rotor and the reversing 
ring to ensure that the reversing ring is driven against its appropriate 
abutment immediately the rotor commences rotation. Such solutions to 
augmenting the drag between the rotor and the reversing ring may well be 
suitable for non-critical applications, but since each involves the 
provision of a friction enhancing device linking the rotor to the 
reversing ring then each carries with it the risk of wear of the sliding 
interface, and the risk of fracture of the friction enhancing component. 
Such wear and/or fracture can be extremely disadvantageous in that it may 
result in the loss of drag between the rotor and the reversing ring so 
that the reversing ring is not driven immediately against its abutment 
when rotation of the rotor commences, and thus there can be a delay in the 
supply of liquid from the pump. Moreover, wear and/or fracture can give 
rise to contaminants in the liquid flow from the pump and contaminants 
which could, conceivably, prevent appropriate movement of the reversing 
ring relative to the outer housing. 
It is an object of the present invention to provide, in a simple and 
convenient form, a reversible gerotor type pump in which the 
aforementioned difficulties are minimised or obviated. 
In accordance with the present invention there is provided a reversible 
gerotor-type pump having an angularly moveable reversing ring rotatably 
supporting an internally toothed rotor which in turn cooperates with an 
externally toothed gear received within the rotor and rotatable therewith 
about an axis parallel to but spaced from the axis of rotation of the 
rotor, and, magnet means magnetically attracting the rotor towards the 
reversing ring so as to provide drag between the rotor and the reversing 
ring at least at the commencement of rotation of the rotor relative to the 
reversing ring. 
Preferably said magnet means comprises a region of said reversing ring 
which has been treated to render it magnetic. 
Alternatively said magnet means comprises an insert of permanent magnet 
material received in a pocket in the face of the reversing ring presented 
to the rotor. 
As a further alternative said magnet means comprises an insert of permanent 
magnet material received in a pocket in the face of the rotor presented to 
the reversing ring. 
Desirably where said magnet means is an insert of permanent magnet material 
then said insert is set fractionally below the cylindrical surface of the 
reversing ring or the rotor so as not to be in rubbing contact with the 
rotor or reversing ring.

Referring first to FIG. 1 of the accompanying drawings it can be seen that 
the reversible gerotor-type pump is generally of conventional form 
comprising a circular-cylindrical reversing ring 12 rotatably supported 
within a fixed pump housing 11. The housing 11 and reversing ring 12 
incorporate stop means 13 of any convenient form limiting rotational 
movement of the ring 12 in the housing 11 to an angular movement of 
180.degree.. 
The ring 12 has a circular cylindrical bore 14 the axis of which is 
parallel to, but offset from, the axis of rotation of the ring 12 in the 
housing 11. Thus the bore 14 is eccentric in relation to rotation of the 
ring 12. 
The ring 12 is formed from a wear-resistant, ferromagnetic material and 
rotatably receives a circular-cylindrical pump rotor 15 formed from a 
similar material. The outer cylindrical surface of the rotor 15 is a 
close, sliding fit within the cylindrical bore 14 of the ring 12, and the 
interface of the rotor 15 and ring 12 is lubricated in use. In the 
preferred embodiment the pump is an oil pump, and thus a supply taken from 
the output of the pump can be directed to the interface of the rotor 15 
and ring 12 for lubrication purposes. 
The rotor 15 is shaped internally to define a gear-form having five 
equiangularly spaced recesses 16. Positioned within the rotor 15 is a gear 
17 having four equi-angularly spaced lobes 18. 
The gear 17 is keyed to a shaft 19 having its rotational axis co-extensive 
with the rotational axis of the ring 12. The rotor 15 is driven for 
rotation with the shaft 19 but of course rotates about an axis eccentric 
to the axis of the shaft 19 and gear 17. 
As is well understood the progression of the lobes 18 of the gear 17 from 
recess 16 to recess 16 as the gear and rotor rotate together, produces in 
conjunction with the shaping of the gear 17 and the internal gear form of 
the rotor 15, displacement of liquid filling the space between the gear 17 
and the internal gear form of the rotor 15, from an outlet (not shown) of 
the pump, while drawing liquid from a supply into the rotor 15 through a 
corresponding pump inlet (not shown). 
As is conventional, reversal of the rotation direction of the rotor and 
gear pumps the liquid in the opposite direction so that the inlet of the 
pump becomes an outlet, and the outlet of the pump becomes an inlet. 
Similarly, reversal of the eccentricity of the arrangement, by rotating 
the ring 12 through 180.degree., also reverses the pumping action, and so 
if it is desired to maintain the pumping direction unchanged, while 
reversing the direction of rotation of the gear 17 and rotor 15, then the 
reversing ring 12 must be rotated through 180.degree.. 
In known gerotor-type pumps the movement of the reversing ring 12 between 
its alternative 180.degree. abutment positions is generated by drag 
between the rotor 15 and the ring 12. Thus if the rotor 15 rotates in a 
clockwise direction the ring 12 is dragged with the rotor in a clockwise 
direction until the appropriate abutments are operative to prevent further 
movement of the ring 12 whereupon the rotor rotates relative to the ring. 
Similarly rotation of the rotor 15 in the opposite direction drags the 
ring 12 in the opposite direction through 180.degree. until the abutments 
13 are effective to stop further rotation of the ring. 
Where the supply of fluid from the pump is critical, it is essential that 
the initial movement of the rotor 15 in either direction either drives the 
ring 12 to its appropriate abutment position, or ensures that the ring 12 
is in that position. However, frictional drag between the rotor 15 and the 
ring 12 may be ineffective if the interface between the ring 12 and rotor 
15 is well lubricated, but alternatively in the event that there is high 
friction between the rotor 15 and the ring 12 then in use this will 
rapidly give rise to wear reducing the drag, and risking the introduction 
of particles of metal from the rotor 15 and/or the ring 12 into the oil 
supply. Such contaminants may have a disastrous effect on the equipment 
supplied with liquid by the pump, and could also find their way into the 
interface between the ring 12 and the housing 11 thus preventing movement 
of the ring relative to the housing. 
In FIG. 1 a region 21 of the ring 12 has been treated to render it 
magnetic. Thus in the static condition of the rotor the magnetic 
attraction of the ring 12 to the rotor will minimise the clearance between 
the ring and the rotor, thereby ensuring that when the rotor commences 
rotation there is sufficient drag between the rotor and the ring for the 
ring 12 to move with the rotor until it is arrested by the respective 
abutment arrangement 13. Thereafter, as the rotor 15 rotates within the 
ring the film of lubricant between the rotor 15 and the ring, which was 
displaced or thinned by the magnetic attraction pulling the ring and the 
rotor together, will be restored thus centering the rotor 15 within the 
bore 14 of the ring 12 and minimising wear between the ring and the rotor. 
Viscous drag within the oil film between the ring and the rotor will 
ensure that the ring remains driven against the respective abutment 13. 
In FIG. 1 the magnetic region 21 is an integral region of the ring 12 the 
material of which has been rendered magnetic by appropriate treatment. In 
FIG. 2 the magnetic attraction between the ring 12 and the rotor 15 is 
provided by an insert of permanent magnet material 22 received in a pocket 
in the wall of the bore 14 of the ring 12. FIG. 3 illustrates an 
alternative arrangement in which the magnetic means attracting the ring 12 
to the rotor 14 is defined by an insert 23 of permanent magnet material 
housed in a pocket in the outer surface of the rotor 15. 
Where permanent magnet material inserts are utilized, as illustrated in 
FIGS. 2 and 3, it will be recognised that the inserts will be permanently 
bonded into their respective pockets by a suitable adhesive material, or 
some form of mechanical fixing arrangement. Various permanent magnet 
materials would be suitable, but rare-earth materials are preferred. For 
example, a cobalt-samarium material might be used. It is recognised that 
permanent magnet materials are generally rather brittle, and thus to avoid 
the risk of permanent magnet material being abraded from the inserts 22, 
23 when the rotor 15 rotates relative to the ring 12, it is desirable to 
recess the inserts 22, 23 fractionally below the cylindrical surface of 
the ring 12 or rotor 15 so that a gap 25 exists and there is no contact 
between the insert and the opposite component during relative rotation. 
The degree of drag may be adjusted by varying the magnetic attraction 
between the rotor 15 and the ring 12, and this can be achieved by 
adjusting the dimensions of the gap 25. 
Reversible gerotor-type pumps of the kind described above with reference to 
FIGS. 1, 2 and 3 are particularly useful in supplying cooling/lubricating 
lubricating oil to aircraft gas turbine engine electrical generators. Each 
generator may incorporate a gerotor-type pump, the rotor 15 and gear 17 of 
which rotor with the shaft of the generator. Each engine may drive a pair 
of generators, and because of mounting requirements the two generators of 
the engine may be required to rotate in opposite directions. It will be 
understood that gerotor-type pumps of the kind described above with 
reference to FIGS. 1 to 3 can be used in either of the two generators 
without modification since they will accommodate rotation of the rotor in 
either direction, and in each case the ring 12 will be driven against the 
correct abutments 13 by the rotation of the respective rotor and 
thereafter the rotor will rotate within each respective ring in a very low 
friction relationship by virtue of the restoration of the oil film 
disrupted by the magnetic attraction when the rotor and ring are 
stationary.