Motors having an air-gap jacket in particular for central heating accelerators and other like applications

Jan. 11, 1966 j. _L. g. drouard 3,229,130

MOTORS HAVING AN AIR-GAP JACKET IN PARTICULAR FOR CENTRAL

HEATING ACCELERATORS AND OTHER LIKE APPLICATIONS

Filed Jan. 25, 1963 2 Sheets-Sheet 1 < w*·

0) iE

<img file="US3229130A_D0001.tif" />

<img file="US3229130A_D0002.tif" />

Jan. 11, 1966 j. _L. g. drouard 3,229,130

MOTORS HAVING AN AIR-GAP JACKET IN PARTICULAR FOR CENTRAL

HEATING ACCELERATORS AND OTHER LIKE APPLICATIONS

Filed Jan. 25, 1963 2 Sheets-Sheet 2

<img file="US3229130A_D0003.tif" />

<img file="US3229130A_D0004.tif" />

<img file="US3229130A_D0005.tif" />

United States Patent Office

3,229,130

Patented Jan. 11, 1966

3,229,130

MOTORS HAVING AN AIR-GAP JACKET IN PARTICULAR FOR CENTRAL HEATING ACCELERATORS AND OTHER LIKE APPLICATIONS

Jean Louis Georges Drouard, Paris, France, assignor to Moteurs Drouard, Paris, France, a French corporation

Filed Jan. 25,1963, Ser. No. 253,867

Claims priority, application France, Feb. 2, 1962, 886,814

Claims. (CI. 310—54)

In the electric motors for driving water circulating pumps, for example in central heating pipes, there is employed for the purpose of preventing leakages an “air-gap jacket” constituted by a generally cylindrical wall composed of a non-magnetic material which is disposed in the air gap and encloses the rotor; this permits circulating the water within this jacket in a hydraulic circuit having merely static joints. Thus the rotor of the motor is immersed in the hydraulic circuit water which serves to lubricate the bearings and evacuates, by its circulation, a part of the heat generated in the motor in the form of losses.

However, this system has numerous drawbacks principally due to the fact that the water of the circuit often contains dirt, such as rust from the radiators, grains of foundry sand, asbestos waste, and calcareous deposits. These impurities become incrusted in the bearings owing to the circulation of the water and the bearings and the corresponding shaft portions are put rapidly out of use. These impurities furthermore have a tendency to become lodged in the air gap and are liable to block the rotor. In order to avoid this drawback it is necessary to make the air gap of large size, but this diminishes the electrical performances of the motor. This drawback is aggravated by the fact that the jacket must have sufficient thickness in order to possess minimum strength as concerns both the assembly and disassembly of the jacket and the resistance thereof to the pressures prevailing in the hydraulic circuit, above all in superheated water installations. The electrical performances are still more diminished in that the thickness of the jacket is added to the mechanical air gap. Further, although the jacket is of a non-magnetic metal, losses nonetheless occur therein, these losses being due to the eddy currents which rapidly increase with the thickness of the jacket.

The object of the invention is to provide an electric motor having an air-gap jacket in particular of utility in central heating accelerators and other like fluid circulating applications having the aforementioned drawbacks, such as circuits for circulating chemical products, oil for burners, and nuclear station circuits, this electric motor comprising a number of devices of known type which are so combined as to avoid the aforementioned drawbacks inherent in the present state of the art.

In the motor according to the invention, the air-gap jacket defines two cavities, one of which comprises the rotor and the other the stator and the winding, the part of the inner cavity opposed to the pump communicates with the exterior only by way of a vent and the part of the inner cavity adjacent the pump communicates with the fluid driven by the pump through a filter having such dimensional characteristics as to filter the fluid in the course of the first filling of said inner cavity while insuring the equilibrium of the pressures on both sides of said filter and on both sides of the bearing sleeve for the shaft of the motor, practically no circulation of fluid therefore occurring between said inner cavity and the exterior, the air gap and the thickness of the jacket being on account of the purity of the fluid reduced to the minimum values corresponding to the conditions of mechanical manufacture, the jacket being stiffened at its ends by flanges co20 operating with toric sealing elements mounted on the bearings and the case being provided, in contradistinction to the usual practice in this art, with cooling fins.

According to another feature of the invention, in order that these fins evacuate the maximum amount of heat to the surrounding air, this heat being generated to the extent of about 30% in the heads of the windings, a thermic contact is provided between the winding and the case by replacing the air filling the stator cavity by a solid powdered material which is a better heat conductor than air, such as quartz, silica or the like, the whole being, if desired, subjected to a special impregnation for both mechanical and thermic reasons.

It will be clear that these features permit avoiding that the bearings and the air gap become soiled by foreign bodies and insure an equilibrium of the pressures on both sides of the bearings by thus eliminating the circulation of the water in the bearings, an evacuation of the heat losses which is not obtained by a permanent flow of the fluid through the motor but through the medium of the case provided with fins, and a reduced air gap, made possible by the purity of the fluid, being put to use for the purpose of reducing the thickness of the jacket in thus improving the performances of the motor, the use of such a jacket being made possible by the use of special sealing means; in the event that the circulating fluid is a liquid a vent is provided for the evacuation of the gases which, owing to the fact that the liquid does not circulate, have a tendency to accumulate in the motor.

According to other features of the invention, if the motor has a jacket of diameter D, the single mechanical air gap does not exceed a value given in millimetres by the expression

0.2 mm.-|-D/500 in which D is expressed in millimetres and the thickness of the jacket does not exceed D/200.

The toric sealing means are disposed in recesses formed in the cylindrical faces of the bearings.

Said vent communicates with a de-gassing chamber with which communicates a blind hole formed in the end of the shaft of the motor opposed to the pump, this hole communicating with the inner cavity of the jacket by way of radial holes.

These features provide a motor which is sure in operation, which is improved as concerns electrical performances, lighter, relatively cheap and has a small overall size.

Further features and advantages of the invention will be apparent from the ensuing description, with reference to the accompanying drawings to which the invention is in no way limited.

In the drawings:

FIG. 1 is a longitudinal sectional view of the motor according to the invention:

FIG. 1A shows a modification of a detail of the jacket.

FIG. 2 is a sectional view of the air-gap jacket.

FIG. 3 is a sectional view of the forward bearing of the motor, and

FIG. 4 is a sectional view of the rear bearing of the motor.

FIG. 1 shows a stator 1 having a winding 2 and an air-gap jacket 3 having a generally circular tubular shape which fits in the bore of the stator. Rotative within this jacket is a rotor 4 mounted on a shaft 5, there being a clearance or air gap 6 between the stator and rotor. The shaft is supported by a rear bearing 7 and a forward bearing 8 provided with their sleeves 9 and 10 respectively. The rear bearing is provided with a closing cap 11 defining between the cap and the shaft a chamber 12 performing the function of a de-gassing chamber with

3,229,130 ³ which communicates an axial blind hole 13 formed in the shaft of the motor, this hole communicating with the inner space of the motor by way of radial holes 14.

Preferably the inner wall of the bearing 8 is heat insulated by means of a heat insulator.

Fluidtightness between the stator and rotor is obtained by means of toric sealing elements 15, 16 mounted in grooves 17, 18 formed in the cylindrical outer faces 19 and 20 of the bearings, as explained hereinafter.

The forward bearing has a filter 21.

The air-gap jacket 3 (FIGS. 1 and 2) is composed of very thin stainless steel sheet, for example 0.2 mm. thick for a diameter of 40 mm. In order to insure that this jacket has suitable rigidity, it is provided at its ends with an outwardly extending flange 22 and an inwardly extending flange 23. These flanges also permit the easy disassembly of the jacket and the removal of the rear sealing element 15.

The inner flange 23 is formed by a forming over of the end of the wall of the jacket 3 which can be formed over at 90° as shown in FIG. 1; preferably it is formed over at 180° as shown in FIG. 1A, which affords an improved stiffening of the jacket.

The filter 21 (FIG. 3) is constituted, for example, of a sintered metal pellet maintained in a chamber 24 formed in the bearing 8 forward of a chamber 25. The latter enables the fluid to flow to the interior of the motor through apertures 26 which communicate with a recess 27.

The section of the filter 21 and its porosity are so calculated that the pressure drop across the filter is less than that resulting from the clearance between the bearing sleeve 9 and the rotor shaft. The filter 21, the chamber 24, the apertures 26 and the recess 27 are arranged as shown in the drawings and insure the maximum passage of fluid and thus permit satisfying the aforementioned condition. The fluid in the annular clearance between the bearing sleeve 9 and the shaft 5 is consequently fed round the rear of the bearing so as to ensure the lubrication. It is therefore a fluid devoid of dirt which performs this function. The same of course is true in respect of the rear bearing sleeve 10. This lubrication by means of a filtered fluid precludes any premature wear of the bearing sleeves.

The forward bearing 8 furthermore carries a fixed abutment 28 which contacts a moving abutment 29 connected to the rotor when, owing to the axial thrust of the pump, the rotor is biased in the direction of arrow F (FIG. 1).

This abutment 28 and the bearing sleeves are preferably composed of a conglomeration of sintered bronze encased in a mass of polytetrafluorethylene (known under the trade name of “Teflon”), which permits an accidental operation in the dry condition.

FIG. 4 represents the detail of the rear bearing 7 and shows how it is possible to combine the known assembly of the sealing element 15 with the air-gap jacket 3 having the formed-over inner flange 23.

Provided forward of the groove 17, which serves as a housing for the sealing element 15, is a cylindrical portion 30 of short length. This cylindrical portion precludes any damage to the sealing element when assembling and prevents it from becoming pulled off inwardly of motor under the effect of the lateral thrust. The diameter of this cylindrical portion is so calculated that the expansion of the sealing element is within the values indicated by the manufacturer whereas the diameter in the bottom of the groove 17 is within normal seal assembly limits. Forward of this cylindrical portion 30 there is a frustoconical portion 31 on which the sealing element is applied without any force being necessary. When assembling the motor, by pushing the sealing element with a tube which is an easy slide fit in the air-gap jacket, the end of this tube (not shown) urges the sealing element over the cylindrical portion. As the sealing element is clamped between the air-gap jacket and the bearing it is compressed and even slightly raises the end of the jacket, but as the deformation of the latter re5 mains within the elastic limit range, when the sealing element finds its correct place in the groove 17 the jacket resumes its initial shape and even exerts a clamping action necessary for perfect fluidtightness.

The shaft 5 carries at the rear (FIG. 1) a shoulder 10 32 through the medium of which it abuts against the face of the rear bearing 7 when the motor is stationary and the static pressure of the fluid, on the turbine of the pump urges the rotor rearwardly; this shoulder 32 thus performs the function of a valve.

It will be observed that the rear bearing is provided with a bleeder 33 which can be automatic or otherwise and puts the chamber 12 in communication with the atmosphere.

This machine is surrounded by a case 34 provided with 20 outer cooling fins 35 which are shown in FIG. 1 to be circular but which could be longitudinal. This case further comprises inner cooling fins 36. All these surfaces are painted a dark colour.

The motor operates in a reliable manner under the 25 following conditions.

Owing to the filter 21 the fluid enters the motor but prevents entry of impurities although the same pressure is established on both sides of the filter without there being circulation of fluid inside the motor.

The fact that the liquid does not circulate in the motor diminishes the supply of heat from the liquid being circulated by the pump. This is an important advantage owing to the constantly increasing operational temperatures permissible in present-day heating; these temper35 atures systematically or accidentally reach for example 120° C.

The inner wall of the bearing 8 can be insulated by means of a heat insulator.

The losses of the rotor are evacuated through the me40 dium of the air-gap jacket and stator. The main obstacle to the heat flux is the air gap. The certainty that no impurity can enter the latter permits reducing it so far as mechanical construction permits, for example down to a value 0.2 mm. -f-D/500, in which D is the diameter of the 45 jacket. Further, the small value of the thickness of the air-gap jacket facilitates this evacuation of heat. The losses of the stator (and those transmitted thermically by the rotor) are easily evacuated owing to provision of the outer and inner fins on the case, the inner fins 36 more 50 particularly contributing to the evacuation of the heat generated by the heads of the windings.

These inner and outer fins also perform the function of a heat exchanger in the event that the blocking of the pump results in the motor operating under full load, the 55 windings carrying the short-circuit current. It should moreover be mentioned that this action is combined with that of the small air gap rendered possible owing to the very conception of the motor, the power wasted in the form of losses in short circuiting being the smaller as the air 60 gap is smaller.

When the rotor rotates, the fluid containing occluded gases within the jacket is subjected to centrifugal force. As the molecules of the liquid are much heavier than the molecules of gas the latter remain in the vicinity of the ⁶⁵ shaft and are discharged through the holes 14 and 13, the chamber 12 and the bleeder 33.

Thus, owing to the combination of the means described hereinbefore there is obtained a motor which operates under optimum conditions of reliability whether this motor be rotating or blocked by an accidental cause.

Although specific embodiments of the invention have been described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claims.

3,229,130