Framed Impeller

Abstract

An impeller with a rotor carrying a set of fan blades has a circular duct of streamlined profile surrounding the rotor blades, the latter having their tips interconnected by a ring received with small clearance in an annular groove on the inner duct periphery so that this periphery is flush with the inner ring surface. Elastic inserts in the gap between the ring and the duct may be used to minimize or eliminate the intervening clearance.

Description

Our present invention relates to an impeller, such as a blower or fan, for circulating air or some other ambient fluid.

The intensity of a flow generated by such an impeller can be enhanced by channeling this flow through a short duct or shroud of air-foil cross-section presenting a streamlined profile to the fluid stream, this duct framing the rotor of the impeller whose blades terminate at a short distance from the inner duct periphery. The duct has the dual purpose of concentrating the flow by converging in the direction of fluid passage and of minimizing turbulence in a zone surrounding the rotor blades with resulting increase in operating efficiency. The latter function, of course, calls for a minimum spacing between the blade tips and the stationary duct, yet a certain tolerance must always be maintained to allow for unavoidable eccentricities of the rotor mounting with reference to the duct axis.

Attempts to minimize this tolerance by interconnecting the free ends of the blades with the aid of a concentric ring inside the duct have not solved the problem. Though such a ring reinforces the rotor structure, it does not eliminate existing eccentricities and requires, therefore, a certain radial spacing from the duct in order to prevent contact between the two relatively rotating bodies. Moreover, the presence of such a ring diminishes the effectiveness of the rotor, by reducing the cross-sectional area of the channel swept by the blades, and creates added discontinuities giving rise to further turbulence.

Thus, our invention aims at providing an improved impeller of the framed-rotor type wherein peripheral turbulence is effectively suppressed with avoidance of the aforestated drawbacks.

A more particular object is to provide a combination of a flow-guiding duct with a ring-reinforced rotor enabling the utilization of the entire cross-sectional area of the flow channel defined by the duct for the generation of forced circulation or thrust.

These objects are realized, in accordance with our present invention, by providing the inner duct periphery with an annular groove receiving, with small clearance, a ring interconnecting the free ends of the blades, the ring preferably having a substantially flat inner peripheral surface flush with the inner duct periphery so as to form part of a channel wall free from major discontinuities.

In the simplest case, the ring may be a relatively thin ferrule of cylindrical shape somewhat smaller than the relative shallow groove. In a more sophisticated arrangement, designed to throttle the fluid flow through the meandering gap between the ring and the groove wall, this gap may be further reduced or eliminated with the aid of preferably elastic sealing means in actual or potential contact with the rigid ring. The latter may be formed with one or more outwardly directed radial flanges which, in co-operation with an insert or filler interleaved therewith, lengthen the flow path around the rotor periphery and which could also be used to shield a set of swivel heads in the ring facilitating an adjustment of the blade pitch.

The problem of fitting the blade ring in the groove of the duct may be solved in various ways, as by making the duct in several axially or peripherally adjoining sections or by molding the duct directly about the rotor. If the ring is a sufficiently deformable ferrule, it could also be snapped into the groove of an integrally constructed duct.

The above and other features of our invention will be described in detail with reference to the accompanying drawing in which:

FIG. 1 is an axial view, partly in section, of an impeller embodying our invention;

FIG. 2 is a face view of the impeller shown in FIG. 1;

FIG. 3 is a fragmentary sectional view taken on the line III -- III of FIG. 2 but drawn to a larger scale;

FIGS. 4 and 5 show, on a still larger scale, modifications of the assembly illustrated in FIG. 3;

FIGS. 6 and 7 are enlarged views generally similar to FIG. 3, showing further modifications; and

FIGS. 8 and 9 are views similar to part of FIG. 5, illustrating yet other variants.

In FIGS. 1-3 we have shown an impeller which may be used as an air screw on an aircraft not further illustrated and which comprises a motor 1 driving a streamlined hub 2 of a rotor having several (here four) propeller blades 3 radiating from that hub. The free ends of these blades are interconnected by a ring 4 in the form of a thin ferrule received within an annular groove 8 on the inner peripheral surface 7 of a duct or shroud 5 of streamlined cross-section. Duct 5 is supported by struts 6 on the stationary engine housing of motor 1.

As best seen in FIG. 3, the inner peripheral surface 4a of ring 4 is flush with the inwardly convex surface 7 of duct 5 so as to define therewith a substantially continuous channel wall. The circular edges 10 of ring 4 are closely spaced from similar edges 9 of a sheet-metal sheath 5a which envelops the body of duct 5 and extends slightly past the sides of groove 8.

The thrust of the propeller shown in FIGS. 1-3 is somewhat diminished by an equalizing flow passing through the narrow gap between edges 9 and 10 from the high-pressure region behind the rotor blades 3 to the low-pressure region ahead of these blades. This bypass path can be blocked, as shown in FIG. 4, by the provision of a seal generally designated 11. Seal 11 comprises a pair of strips 12, 13, of rubber or other elastomeric material, mounted on a pair of shoulders 5', 5" which are formed by the projecting edges of sheath 5a inside groove 8 so as to bear upon the outer peripheral surface of ring 4. FIG. 4 also shows a screw 24 serving to fasten this ring to a corresponding blade 3.

In FIG. 5 we have illustrated a modified ring 4' of U-profile formed with two radial flanges 14, 15 received in the groove 8. Sealing strips 16 and 17, similar to those of the preceding embodiment, bear upon the outer surfaces of these flanges at locations spaced radially outwardly from the supporting shoulders 5' ,5".

According to FIG. 6, the flanged ring 4' co-operates with a tripartite insert, also preferably of elastic material, consisting of three labyrinth sections 18, 18' and 18" axially separated by narrow gaps which receive the ring flanges 14 and 15.

As shown in FIG. 7, an elastic filler 19 of polyurethane foam or other cellular material forms similar annular recesses 19a, 19b to accommodate the flanges 14 and 15.

FIGS. 8 and 9 illustrate the possibility of using a flanged ring 4' as a journal bearing for the rotor blades 3 whose pitch can be controlled from within the hub 2 (FIG. 1), by conventional means not shown, and which terminate in studs 20 (FIG. 8) or 20' (FIG. 9) received in respective sockets 22, 23. These sockets may be formed by individual bosses, as in FIG. 8, or by a continuous hollow ridge, as in FIG. 9, with interposition of bearing sleeves 25, 25' around the studs. FIG. 9 shows the bearing sleeve 25' as a spherically convex bushing 21 on stud 20'. Antifriction layers (e.g. of Teflon), not shown, may be inserted between these bearing sleeves and the coacting stud surfaces.

Claims

We claim:

1. An impeller for the circulation of an ambient fluid, comprising a rotor with a set of blades radiating from an axis; a circular duct of airfoil cross-section fixedly centered on said axis, said duct having an inner periphery provided with an annular groove and lined with a sheet-metal sheath projecting beyond the edges of said groove to form a pair of annular shoulders within said groove; a ring centered on said axis and interconnecting said blades, said ring projecting radially into said groove with small axial clearance from said shoulders; and sealing means in said groove bridgeing said axial clearance, said sealing means including a pair of elastic annular strips mounted in said groove on said shoulders and extending therefrom into contact with said ring.

2. An impeller as defined in claim 1 wherein said ring has a substantially flat inner peripheral surface flush with the inner periphery of said sheath.

3. An impeller as defined in claim 1 wherein said ring is provided with two outwardly directed radial flanges confronting said shoulders, said strips bearing upon said flanges at locations spaced radially outwardly from said sheath.