US3302047A

US3302047A - Fan assembly for high-torque application

Info

Publication number: US3302047A
Application number: US420935A
Authority: US
Inventors: Harold O Short
Original assignee: Black and Decker Manufacturing Co
Current assignee: Black and Decker Corp
Priority date: 1964-12-24
Filing date: 1964-12-24
Publication date: 1967-01-31
Anticipated expiration: 1984-01-31

Description

Jan. 31, 1967 H ,5 3,302,047 FAN ASSEMBLY FOR HIGH-TORQUE APPLICATION Original Filed Nov. 27, 1963 I 2 Sheets-Sheet l i g |||l||||||||||l||||||||||||||- numnmumumnnm V I '8 Illlllllllllllflllllllllllllllllllllllllllllllllllllllllllmm; ||||||||||||||I||||||||||||lq! v 4!. x lllllllllllllllllllllllllllll- I nmnmnunmmmuui i =||lllllllllllllllllllllllll|l= INVENTU) HAROLD 0. SHORT BY m /f ATTORNI-i'r' Jan. 31, 1967 H 0. SHORT 3,302,047

FAN ASSEMBLY FOR HIGH-TORQUE APPLICATION Original Filed Nov. 27, 1965 I 2 Sheets-Sheet z NVENTOR HAROLD 0. SHORT ATTORNEY United States Patent C) 3,302,047 FAN ASSEMBLY FOR HIGH-TORQUE APPLICATION Harold 0. Short, Towson, Md., assignor to The Black and Decker Manufacturing Company, Towson, Md., a corporation of Maryland Continuation of application Ser. No. 326,569, Nov. 27, 1963. This application Dec. 24, 1964, Ser. No. 420,935 2 Claims. (Cl. 310-60) The present application constitutes a continuation of application Ser. No. 326,569, filed November 27, 1963, and now abandoned.

The invention relates to a fan assembly suitable for use in conjunction with relatively high-speed high-torque electrically operated machine tools and the like, as for example, to a fan assembly used in a high-torque portable electric tool where performance, portability, convenience,

and reliability are all important criteria.

One such tool is a portable electric hammer-drill used for masonry drilling operations. In the hammer-drill, an embodiment of which is illustrated in the Short Patent 3,119,274 assigned to the assignee of the present invention, the tool bit is constantly rotated at a continuous r.p.m., while the shank of the tool bit experiences intermittent hammer impacting or ratcheting in the order of 15,000 to 20,000 blows per minute. The hammer-drill is powered by a relatively high-speed high-torque electric motor which requires adequate cooling supplied by means of a fan assembly mounted upon the armature shaft of the motor. The cooling fan assembly usually draws cooling air in through a number of inlet openings disposed in the rear of the motor housing, and the cooling air passes through the motor and is discharged through exhaust openings located forwardly of the motor housing.

The fan assembly comprises a blade portion secured to a hub portion, and the hub portion of the assembly, in turn, is slidably fitted over and keyed (or otherwise secured) to the armature driving shaft of the motor for rotation in unison. Various designs and constructions of fan assemblies have been resorted to in the prior art, especially in the design of fan assemblies which are intended to be used in the relatively severe environments herein contemplated.

For example, the prior art has resorted to a stakedover or peened-over design, wherein a peripheral portion of one of the members, such as the hub member, is lanced or peened over by means of a plurality of circumferentially spaced staking tools, so as to retain the center section of the blade portion (or vane member) against an annular shoulder formed on the hub portion of the fan assembly. This construction, however, is generally unsatisfactory; the peened-over portions of metal tend to spring back, resulting in a loose and unreliable connection, one that does not hold up well over extended periods of usage under severe requirements.

The .deficiency of the peened-over design and construction is especially pronounced in high-speed heavily loaded applications, such as are encountered in high-torque portable electric tools, where the armature speeds range from 20,000 to 30,000 rpm. In this speed range, the centrifugal forces and other forces acting on the fan assembly become appreciable, especially where the fan assembly is unbalanced, and thus stresses and vibrations are created which tend to rupture the connection between the blade portion and the hub portion of the fan assembly. Moreover, in tools such as the aforementioned hammer-drill, shock and vibrational forces arise from the inherent ratcheting function of the machine itself, and these forces further tend to rupture the connection between the blade portion and the hub portion of the fan assembly.

Another means resorted to in the prior art comprises a spun-over hub; this involves a spinning operation in which the blade portion and the hub portion are chucked within a lathe or suitable power-operated machine, and a stationary tool engages the hub portion and spins out a peripheral portion of the hub portion over the center section of the blade portion. However, the spun-over hub suffers from the same serious defects as the stacked-over or peened-over design. The connection between the blade portion and the hub portion is not secure, not permanent, and not sufficiently reliable for the intended application.

A further means resorted to in the prior art comprises a drawn hub; this involves a drawing operation in which the substantially fiat center section, sometimes referred to as the dish portion of the blade, is drawn out and then turned at right angles to itself to form an integral, yet relatively inexpensive hub, which in turn is pressed over a spindle, such as an armature shaft. Experience has found, however, that this drawing operation results in a relatively thin wall section at the right-angle bend, and this creates an inherent weakness in the structure. Moreover, the subsequent press-fitting of the drawn-out hub portion of the fan assembly has not been particularly reliable; for example, the drawn hub tends to creep along the spindle during the operation of the tool, and in general, is totally unsatisfactory for the relatively severe environments herein contemplated.

The prior art has also resorted to a riveted construction; but riveting, besides being somewhat awkward, time consuming and expensive, does not provide a reliable joint that will accommodate itself to stresses, forces, and random vibrations encountered in high-torque applications.

The prior art has alsoresorted to a brazed construction in which the blade portion is brazed to the hub portion of the fan assembly. Experience with this method, however, has shown that the heat generated during the brazing operation tends to distort the blade, so that a subsequent straightening and/or a reaming operation is required, which is time-consuming and hence expensive. Moreover, a brazing operation, even when brazing steel to steel, sets up certain changes in the character or metallurgy of the material, with the result that minute cracks tend to form around the braze line on out to the blades or vanes; and thus a latent structural defect is introduced, which is of course, undesirable. This is especially serious in high-torque tools which may experience an 0ccasional stalling of the tool. This may occur if the tool bit, such as a masonry drill, hangs up in the work, and the momentary stoppage of the tool bit results in relatively high stall-torques which are imparted to the motor and to the other components of the tool. The stall torques, to date, are instrumental in precipitating a rupture in a brazed fan assembly, especially if there is a crack or latent defect in the assembly. Moreover, in portable electric tools, and in other applications, size, weight, and portability are important considerations, and obviously, the use of lighter materials, such as aluminum, is recommended. For example, the concurrent use of an aluminum blade member brazed to an aluminum hub member has been attempted, but generally abandoned, due to the difiiculties and technical problems encountered in brazing aluminum to aluminum. Ideally, the blade portion should be made from a lightweight material, such as aluminum, for less overall weight and hence less centrifugal force, while the hub portion should be made from a material, such as steel, for strength and rigidity; but it has not been commercially practical, nor econom- 3 ically feasible, in the art, to date, to braze or to weld different materials together, such as aluminum to steel.

Accordingly, it is an object of the present invention to alleviate the aforementioned deficiencies of the prior art by providing a reliable, yet inexpensive, fan assembly, one which is capable of meeting the relatively severe en- Vi'r'onmental conditions imposed by high-speed high-torque portable electric tools and those devices involving interrnittent relatively high stall torques, and especially those in which relatively severe shock and vibrational forces are experienced by the fan assembly in the normal usage of the tool.

It is another object of the present invention to provide a fan assembly having an axially loaded resilient m'ember, such as a cone-type of lock washer, for axially retaining the blade portion of the assembly against a shoulder on the hub portion.

It is yet another object of the present invention to provide a fan assembly whose blade portion may move or index circumferentially in relation to its hub portion, yet still be retained axially, whenever the motor driving shaft (upon which the hub is mounted) is momentarily stopped due to a high stall-torque experienced by the tool.

It is a further object of the present invention to provide a fan assembly which does not require the material of its blade portion to be matched to the material of it hub portion.

It is a still further object of the present invention to facilitate the use of universal hub members for various sizes and types of blade members, thereby substantially minimizing the inventory problems otherwise associated with stocking a large variety of completed fan assemblies.

In accordance with the broad teachings of the present invention, a fan assembly is herein illustrated and described which is ideally suited for use in a high-speed high-torque portable electric tool; this fan assembly comprises a hub portion, a blade portion, the two portions of the assembly being at least partially telescoped with respect to each other, and means including an axially loaded annular resilient member having a frustro-conical cross-section for axially retaining the blade portion to the hub portion of the assembly, whereby the blade portion of the assembly may index circumferentially in relation to its hub portion, yet still be retained axially, whenever the tool experiences a stall-torque of a certain magnitude.

In accordance with the more specific teachings of the present invention, there is herein illustrated and described, in combination with a high-speed high-torque portable electric tool, a fan assembly comprising a hub portion having an annular shoulder, a blade portion having a center section seated against the shoulder, and a conetype of lock washer axially pressed against the other side of the center section of the blade portion, the washer being disposed concavely with respect to the blade portion of the assembly, such that the outer periphery of the washer is disposed against the exposed face of the blade portion, and such that the inner circular periphery of the washer is axially spaced from the blade portion, but has a forced or interference fit substantially all the way around with respect to the hub portion of the assembly.

These and other objects of the present invention will become apparent from a reading of the following specification, taken in conjunction with the enclosed drawings, in which:

FIGURE 1 is an elevational view of a relatively hightorque portable electric tool, in this case a hammer-drill, in which the teachings of the present invention have been especially well combined, the view showing part of the motor housing broken away to illustrate the fan assembly;

FIGURE 2 is an enlarged longitudinal section of the motor housing portion of FIGURE 1, the improved fan assembly being illustrated generally in relation to the motor;

FIGURE 3 is a section view taken transversely of FIGURE 2, and showing (in detail) the preferred fan assembly mounted upon the armature driving shaft of the tool motor;

FIGURE 4 is a transverse section taken along the lines 44 of FIGURE 2, enlarged over the scale of FIGURE 3, and showing the manner in which the blade portion of the fan assembly is secured to the hub portion of the assembly; i

' FIGURE 5 is an exploded view of the fan assembly of FIGURE 4, showing from left to right, the preferred type of retaining member, in this case a cone-type of lock washer, the substantially fiat center section of the blade (or vane) portion of the fan assembly, a relatively thin flexible washer that may be ttsed on one side or the blade portion, and the hub portion of the assembly, with the hub portion having the annular shoulder against the center section of the blade portion is seated and axially retained by means of the axially loaded lock washer;

FIGURE 6 is an enlarged fragmentary sectional iew, corresponding substantially to a portion of FIGURE 4,- but showing the initial position in which the preferred cone-type of lock Washer is disposed upon the hub;

FIGURE 7 is a fragmentary sectional view, corresponding substantially to that of FIGURE 6, but showing how the preferred cone-type of lock washer is axially loaded or pressed in the direction of the shoulder on the hub, such that the inner circular periphery of the washer bites into the cylindrical surface of the hub and acquires a forced or interference fit substantially all the way around the hub, thereby axially retaining the blade portion against the shoulder on the hub portion of the assembly, yet allowing the blade portion to index circumferentially with respect to the hub portion whenever the tool experiences a stall-torque of a predetermined magnitude.

FIGURE 8 is a first modification, showing the use of an axially loaded split retaining ring in conjunction with the preferred cone-type of lock washer; and

FIGURE 9 is a second modification in which the outer circular periphery of the lock washer is beveled or chamfered to insure that its outer periphery will not bite into the flat central section of the blade portion of the fan assembly.

With reference to FIGURES 1 and 2, there is illustrated a portable electric hammer-drill 10 which is indicative of the relatively high-speed high-torque devices with which the fan assembly of the present invention is combined. The hammer-drill 10 may be adjusted for either a drill position or a hammer-drill position. In the drill position of the tool, the output spindle rotates at approximately 1000 rpm, while the armature driving shaft rotates at approximately 22,000 rpm. In the hammer-drill position of the tool, the output spindle (in addition to being rotated constantly) experiences a series of intermittent repeated impacts or hammer blows in the order of 15,000 to 20,000 blows per minute. In this latter position, the tool is Well adapted for masonry drilling operations in concrete and other materials; and especially under these conditions, the tool bit tends to hang up? upon infrequent occasions, thereby momentarily stopping the electric motor and resulting in relatively high stall-torques of various magnitudes. In the prior art, and without the benefit of the combined teachings of the present invention, these stall-torques have been sufficient to rupture the brazed bond between the fan portion and the hub portion of the fan assembly.

With this in mind, the hammer-drill 10 generally comprises a motor housing 11; an end handle 12 provided with a manually controlled electric switch 13; a gear case 14 forwardly of the motor housing; an impact housing 15 forwardly of the gear case, the mechanical components Within the impact housing 15 (and their cooperation with one another) forming no part of the present invention, but being detailed more specifically in the Short Patent 3,119,274 issued January 28, 1964, and assigned to the assignee of the present invention; an adjusting collar a to switch from the drill position to the hammer-drill position, and vice versa; a tool bit 16 suitably chucked in the output spindle in the impact housingta workpiece, such as a block of masonry 17, engaged by the tool bit; an electric motor 18 in the motor housing, the motor having an armature driving shaft 18a; inlet air openings 19a in the rear portion of the motor housing; exhaust air openings 1% forwardly of the motor housing; and a fan assembly 26 mounted upon the armature driving shaft for drawing cooling air in through the inlet openings and discharging it through the exhaust openings.

With reference to FIGURES 3-8, the fan assembly 20 is illustrated in greater detail. The fan assembly 20 comprises a blade portion 21, sometimes referred to as a vane portion and having a substantially fiat center section 22, and the assembly further comprises a hub portion 23 which receives the blade portion of the fan assembly. The hub portion 23 is generally cylindrical and has a first annular ledge 24, see FIGURES 4 and 5, and an annular shoulder 25 in the nature of a peripheral flange extends radially from the ledge. The hub portion 23 is further provided with a second annular ledge 26 (comprising a smooth cylindrical surface of reduced diameter) which is formed on the side of the first ledge which is opposite from the shoulder 25. Preferably, a fillet 27 is provided between the first and second

annular ledges

24, 26, and an annular chamfered edge 28 is provided anteriorly of the second annular ledge 26. Moreover, the hub portion 23 is further provided with a bore 29 so that the fan assembly 20, when completed, may be pressfitted, keyed, or otherwise secured, over the armature driving shaft 18a of the motor 18, with the hub portion 23 being disposed against a shoulder 30 on the motor shaft, as shown in FIGURE 2. The center section 22 of the blade portion 21 has a circular opening 31 formed therein which is in registry with, and complementary to, the first annular ledge 24 of the hub portion 23; and the blade portion 21' is' seated on the first annular ledge 24 of the hub portion 23, with one side of the center section 22 of the blade portion being disposed flush against the annular shoulder 25 of the hub portion, as shown in FIGURE 6. Preferably, but not necessarily, a relatively thin washer 32, such as a Mylar washer, is disposed between the center section 22 (of the blade portion 21) and the annular shoulder 25 of the hub portion 23, so as to compensate for any surface irregularities that may occur, either on the blade portion or on the hub portion.

An annular resilient member 33, preferably comprising a cone-type of lock washer having a substantially frustroconical cross section. see FIGURE 5, is seated on the hub portion 23 axially of the blade portion 21 such that the outer circular periphery 34 of the washer 33 is disposed against the exposed face of the center section 22 of the blade portion, see FIGURE 4, and such that the inner circular periphery 35 of the washer has a slide fit (or preferably a slight interference fit) with respect to the second annular ledge 26 of the hub portion 23. This assembly is then received within a suitable jig or fixtures (not shown) so that a conventional ram member, which may be power-operated, axially presses the cone-type of lock washer 33 in the direction of the annular shoulder 25 on the hub portion 23, so as to axially retain the blade portion 21 to the hub portion 23.

In the assembly, and as shown more clearly in FIG- URE 7, the inner circular periphery 35 of the washer 33 bites into the second annular ledge 26 of the hub portion 23 and acquires a forced or interference fit with respect to the hub portion 23, as denoted generally as at 36. In one embodiment, the washer 33 is axially loaded to the extent of approximately 500 pounds. Moreover, the washer 33 is not flattened completely, but rather, is concavely disposed and is axially spaced by a slight amount with respect to the fillet 27 of the hub portion 23; and

6 it will be appreciated that in FIGURES 6 and 7, certain dimensions have been exaggerated for ease of understanding. 7

With reference to FIGURE 8, there is illustrated a modification in which the second annular ledge 26 of the hub portion 23 is provided with an external annular groove 37; and a split retaining ring 38 is axially pressed over the hub portion until it drops into the groove 37. The ring 38 engages the exposed portion of the cone-type of lock washer 33 and further presses it against the center section 22 of the blade portion 21 for the purpose of further retention.

In FIGURE 9, a second modification (constituting a preferred embodiment) is illustrated. Here, the outer circular periphery 34 of the retaining washer 33 is beveled or chamfered, as at 39, to insure that the washer 33 will not scratch or bite into the flat center section 22 of the blade portion 21 of the completed fan assembly 20.

In the preferred embodiment, the washer 33 is first blanked out as a disc, then cupped into its frustroconical form, and then its center is blanked out to provide for the annular form of the washer. Experience has found that if the washer is first blanked out completely and then cupped, that its central aperture becomes somewhat egg shaped and hence detracts from the ability of the washer to acquire an interference fit substantially all the way around the hub portion of the assembly.

In the drawings, and more particularly in the cross hatching thereof, the blade portion 21 has been illustrated as molded from a suitable plastic, while the hub portion 23 has been illustrated as machined from a suitable metal. This demonstrates that-unlike the conventional brazing technique heretofore widely resorted to in the prior art the teachings of the present invention eliminate the necessity for the matching of materials between the blade portion and the hub portion of the completed fan assembly. Instead, all types of materials, matched or mismatched, may be used. For example, a plastic blade portion may be used on a metal hub portion, or an aluminum blade portion on a steel hub, etc. Yet the connection between the blade portion and its hub portion is secure and reliable for usage even in the critical high-torque vibratory applications heretofore described.

In these environments, the connection between the blade portion and the hub portion remains secure and readily accommodates a variety of centrifugal forces, stresses, and shock and vibrational forces. The blade portion of the assembly is retained axially, yet at the high stall-torques occasionally encountered by the tool, the blade portion of the assembly may rotate or index circurnferentially with respect to its cooperating hub portion, thereby precluding fan assembly breakage and insurin-g subsequent adequate cooling for the motor. This has heretofore been a problem in the prior art machine tools which employed brazed fan assemblies.

Moreover, the speed and simplicity with which the completed fan assembly may be fabricated-together with its inherent low cost and its use of readily available components-renders the teachings of the present invention sound, acceptable, and commercially practical for this environment and for a variety of other critical applications.

Obviously, many modifications may be made without departing from the basic spirit of the present invention; and accordingly, within the scope of the appended claims, the invention may be practiced other than has been specifically described herein.

I claim:

1. In combination with a relatively high-speed hightorque electrically operated machine of the type experiencing occasional relatively high stalltorques and comprising a motor housing, a motor in the motor housing, a driving shaft on the motor, and air inlet and exhaust openings in the motor housing: a cooling fan assembly for the motor for drawing cooling air in through the inlet 7 openings and discharging the cooling air through the exhaust openings, said fan assembly comprising:

(A) a hub portion having a central aperture for receiving said motor driving shaft;

(B) means for mounting said hub portion to said motor driving shaft of said machine for rotation in unison;

- (C) a shoulder on said hub portion;

(D) a blade portion having an apertured central section seated upon said hub portion and disposed against said shoulder; and

(B) an annular retaining member having a frustroconical cross-section concavely disposed with respect to said blade portion and seated with an interference fit upon said hub portion axially of said blade portion;

,(F) whereby said blade portion is retained axially said hu'b portion;

(G) whereby any necessity for selecting the material of said blade portion for compatibility with the material of said hub portion, is eliminated; and

(H) whereby said blade portion may index circumferentially with respect to said hub portion whenever the machine experiences a stall-torque of a predetermined magnitude, thereby precluding fan assembly breakage and insuring subsequent adequate cooling for the motor.

2. In combination with a relatively high-speed hightorque electrically operated machine of the type experiencing occasional relatively high stall-torques and comprising a motor housing, a motor in the motor housing, a driving shaft on the motor, and air inlet and exhaust openings in the motor housing: a cooling fan assembly for the motor for drawing cooling air in through the inlet openings and discharging the cooling air through the exhaust openings, said fan assembly comprising:

(C) said hub portion having a first annular ledge and an annular shoulder extending radially from said first annular ledge; I

(D) a blade portion having a substantially fiat central section with a circular opening formed therein;

(B) said blade portion being received over said hub portion in registry with said first annular ledge, whereby one side of said central section of said blade portion is disposed substantially flush against said annular shoulder of said hub portion;

(F) said hub portion further having a second annular ledge of reduced diameter than said first annular ledge, said second annular ledge being disposed on the side of said blade portion which is opposite from said annular shoulder; and a (G) an annular resilient retaining member seated with an interference fit upon said second annular ledge of said hub portion and bearing axially against the exposed side of said central section of said blade portion;

(H) whereby said blade portion is retained axially on said hub portion; and

(1) whereby said blade portion may index circumferentially with respect to said hub portion whenever the machine experiences a stall-torque of a predetermined magnitude, thereby precluding fan assembly breakage and insuring subsequent adequate cooling for the motor.

References Cited by the Examiner UNITED STATES PATENTS 1,411,126 3/1922 Page 170135.75 2,156,047 4/1939 Arnold 170-173 X 2,653,459 9/1953 Morrill 170-173 X FOREIGN PATENTS 551,444 6/ 1932 Germany.

MILTON O. HIRSHFIELD, Primary Examiner. DAVID X. SLINEY, Examiner.

Claims

1. IN COMBINATION WITH A RELATIVELY HIGH-SPEED HIGHTORQUE ELECTRICALLY OPERATED MACHINE OF THE TYPE EXPERIENCING OCCASIONAL RELATIVELY HIGH STALL-TORQUES AND COMPRISING A MOTOR HOUSING, A MOTOR IN THE MOTOR HOUSING, A DRIVING SHAFT ON THE MOTOR, AND AIR INLET AND EXHAUST OPENINGS IN THE MOTOR HOUSING: A COOLING FAN ASSEMBLY FOR THE MOTOR FOR DRAWING COOLING AIR IN THROUGH THE INLET OPENINGS AND DISCHARGING THE COOLING AIR THROUGH THE EXHAUST OPENINGS, SAID FAN ASSEMBLY COMPRISING: (A) A HUB PORTION HAVING A CENTRAL APERTURE FOR RECEIVING SAID MOTOR DRIVING SHAFT; (B) MEANS FOR MOUNTING SAID HUB PORTION OF SAID MOTOR DRIVING SHAFT OF SAID MACHINE FOR ROTATION IN UNISON; (C) A SHOULDER ON SAID HUB PORTION; (D) A BLADE PORTION HAVING AN APERTURE CENTRAL SECTION SEATED UPON SAID HUB PORTION AND DISPOSED AGAINST SAID SHOULDER; AND