US2401938A - Internal-expanding braking device - Google Patents

Description

June 11, 1946. w p KOCH 2,401,938

INTERNAL-EXPANDING BRAKING DEVICE Filed Aug. 3, 1943 2 Sheets-Sheet 1 INVENTOR ATTORNEY Patented June 11, 1946 2,401,938 INTERNAL-EXPANDING BRAKING DEVICE Wilfred Dell Koch, Troyeville, Johannesburg,

Transvaal, Union of South Africa Application August 3, 1943, Serial No. 497,188 in the Union of South Africa October 10, 1942 This invention relates to improvements in braking and clutching devices of the internalexpanding type and constitutes an'improvement in or development of the invention described in the specification of my earlier co-pending U. S. A.

3 Claims. (Cl. 183-78) patent application Serial No. 406,417, filed August 11, 1941, now U. S. Patent No. 2,334,935.

One of the advantages flowing from the application of this prior invention to' the two-shoe type of vehicle brake, was that, due to the anchoring pivot bolt being located some distance inwardly of the brake shoes, and circumferentially rearwardly of the common pivot-pin, application of the brake caused the lower or heel portions of the shoes to move towards the brake drum simultaneously with an outwardly expandin; movement of the top or toe portions thereof. This arrangement resulted in reducing the tendency of the self-energising shoe to cause snatching and consequent locking and skidding of the wheels at high speeds, but suffered from the disadvantages that at slow speeds greater brake pedal pressure was required for effective braking, and that the heel portions of the brake shoe linings tended to wear more quickly than the upper or toe portions thereof.

It is to be understood that the above remarks apply to the particular arrangement of the braking shoes as illustrated in the drawings of the aforesaid U. 8. Patent No. 2,334,935. On referring to Fig. 1 of these drawings it -will be seen that the anchorbolt is positioned at a consid erable circumferential distance away from the common pivot pin of the two shoes, and at a substantial distance to one side of the vertical centre line of the brake drum, whereby application of the brakes gave a preponderantly radial movement to the heel portions of the brake shoes.

According to one feature of the present invention the anchor bolt is positioned substantially close to and inwardly of the said common pivot pin of the brake shoes, so that application of the brake by outward expansion of the toe ends of the brake shoes by known mechanical or hydraulic means, imparts a simultaneous and similar outwardly expansive movement, as well as a slight outwardly radial movement to the heel ends of said shoes, whereby wear on the shoelinings is more evenly distributed and snatching by the selfenergising shoe is prevented.

According to a preferred arrangement for achieving this result, the axis of the anchor bolt is positoined on the rearwardside of a radial line passing through the axis of the brake drum cam-shaped automatically adjustable stop memand the axis of the aforementioned common pivot pin connecting the heelends ofthe brake shoes. The term "rearward being used in relation to the normal direction of rotation of the brake drum.

The presentinvention is also intended to include a simplified construction of brake having the above described features but in which the bers are dispensed with, and the usual manually adjustable eccentric stop members substituted therefor. An advantage of this form of the invention, besides simplicity, resides in its capability of being employed for the purpose of converting existing types of brakes, by the making of minor alterations thereto.

This simplified form of the invention may be preferred in cases where cheapness and-simplicity arethe main considerations.

A further feature of the invention resides in the substitution for the single tension brakewithdrawal spring of the aforesaid U. S. Patent No. 2,334,935, connecting the two top or toe ends of the brake shoes, of two tension springs, one of which connects the top or toe end of the rear or non-self-energlsing shoe to an anchoring point on the back plate of the brake drum arranged substantially horizontally in line therewith, while the other is connected between a point on the self-energising shoe intermediately'of its ends. and a point on said back plate adjacent the point to which the first mentioned spring is attached. By this provision a more rapid and even withdrawal of the brake shoes is secured on release of the brake pedal. It will be understood from the above description that, with the normal brake arrangement having the toe ends of the brake shoes above the wheel axis, the first-mentioned spring extends in a substantially horizontal direction while the second extends in a substantially vertical direction.

According to a modification of this feature, the spring connecting the toe ends of the shoes remains unchanged, as in the aforesaid U. S. Patent No. 2,334,935, but a second spring, arranged as above described is provided between an intermediate point of the self-energising brake shoe and an anchor point on the back plate.

According to yet a further feature of the invention, the friction washers which, as described in the aforesaid U. S. Patent No. 2,334,935, are pressed against the pivotally mounted cam shaped stop members by the compression springs threaded onto the stop pins, are feather-keyed to said stop pins so as to prevent rotation therepivot pin l.

sometimes disturbed by a slight easing backmovement owing to the reaction of a sprin against the rotational movement imparted to it by the stop member while being re-set.

To enable the invention to be more clearly understood and carried into practice, reference is now made tothe accompanying drawings, in

which like references denote like parts throughout the several views.

In the drawings:

Fig. 1 is a vertical section taken'through the drum of a brake assembly constructed and arranged according to the invention.

Fig. 2 is a similar view showing an alternative arrangement. I

Fig. 3 is a fragmentary sectional detail view to an enlarged scale, taken substantially on line III-III of Fig. 2.

Fig. 4 is a perspective view showing a friction washer and its stop pin in separated relationship, and

Fig. 51s a diagram showing relative positions of the anchor bolt and pivot'pin.

Referring to Fig. I ofthc drawings reference I denotes the axle of a vehicle wheel to which a brake drum 2 is secured in known manner, and for which the fixed back plate 8 forms a closure. Co-acting internally with the brake drum 2 is a rear brake shoe 5a and a front or self-energising brake shoe 6a,.both pivotally. connected together adjacent their heel ends by the common pivot pin 7. Outward expansion of the top or toe ends of the brake shoes for brake applying purposes, is

eifected by means of the usual hydraulic cylinder 8. The self-energising shoe to is pivotally mounted on the anchor bolt 13, which is located in-* wardly of the pivot pin 7, and a small angular distance rearwardly of a radial line it passing through the axes of the axle! and said common This angular distance G is of the order of 2 to 3 degrees as compared to about 30 degrees in the case of the illustrated modification of the invention of the aforesaid U. SLPatent No. 2,334,935. By this modified arrangement it will be apparent that an expansive or opening movement of the toe ends of the shoes to and in, will impart a simultaneous and substantially similar movement to the heel ends of said shoes due to the resulting rotational movement of the pivot pin 1 about the axis of-the anchor bolt l3, which thereby causes. an expansive movement of said heel ends. In addition, due to the axis of the anchor bolt is being on'the rearward side of the centre line I 4, a small simultaneous outward or substantially radial movement is imparted to these heel ends. These two movements result in a more efiective and even distribution of brake pressure on thedrum. 2 and consequent decrease in brake lining wear'and counteract any'tendency for the self-energising shoe 8a to snatch or bind, particularly at. high road speeds with the consequent heavy application of the brakes required for stopping or slowing down purposes.

The lever arms I50. and Ila operate to adjust the cam-shaped stop members Illa and Ila in the same manner as describedwith reference to the equivalent parts in the aforesaid U. 8. Patent No. 2,384,935.

5 The extent of the aforementioned outward or substantiallyradial movement-imparted tothe heel 4 ends of the shoes 5a and in, will depend upon the distance between the pivot pin I and the anchor bolt l3 as well as upon the aforesaid angular distance G. For normal purposes this distance will be from A to /3 of the distance between the pivot pin l and the axis of the axle l or center of the brake drum 2. I

A further feature of the present invention resides in the provision of two brake-withdrawal springs in place of the single spring 9 of the above referred to prior patent. In this case a horizontally disposed tension spring i6 is connected ad- 1 jacent the toe end of the rear brake shoe and to an anchor bracket ll fixed to the back plate 4,

while a. second substantially vertically disposed tension spring i8, is connected between the lever arm Ho and the aforesaid bracket ll. It will be noted that this point of connection is more or less midway between the ends of the shoe to. It has been found that this arrangement of the springs gives a positive, even and rapid withdrawal of the shoes on release of the brake-applying pedal or the like.

Figs. 2, 3 and 4, show further modifications in the invention, in which the automatically adjusted cam-shaped stop members Ma and Ma, are replaced by manually adjustable stop members 28 of the usual cam or eccentric type. This substitution results in the lever arms I50. and Ila being dispensed with, so that a simpler and cheaper construction of brake is provided.

In other respects the brake shoes 51) and 6b operate in a similar manner to their counterparts 8a and 6a of Fig. 1. A lug 2! is however provided as the connecting means for 'the lower end of. the spring i8.

According to another feature of the invention which is applicable to all modifications, an improved construction of friction washer 22a is substituted for the flat friction washer 22 of the aforesaid U. S. Patent No. 2,334,935. This friction washer 22a is provided with a flange 23 adapted to be a sliding fit on the hollow stop pin 24, and in addition is provided with a keyway 25 which is arranged to co-act with the feather key 26 onthe stop pin 26, so that said washer may move axially but is prevented from rotating. In the assembly shown in Fig. 3, the stop member 20 which is permanently attached to its fixing pin 21 is at all times in frictional contact with the washer 22a by reason of the compression spring 28. For adjusting purposes the nut 29 is loosened and the-fixing pin 2'! rotated-in the required dimotion by means of the flats 30 on the, end thereof, whereafter the nut 29 is tightened. to secure the stop member 20 in its new setting.

Fig. 5 shows diatically the diflerence between the present invention and the invention of the parent U. 5. Patent No. 2,334,935,

In the aforesaid U. S. Patent No. 2,334,935, the anchor bolt i3 is positioned at an angular distance A of preferably 44 degrees from the verthe order of 13 degrees. The radius R of the.

anchor bolt II from acentre 0 displaced as shown by an amount D of 92 of the diameter of the brake drum, is of the order of .3 of the diam eter of the brake drum, while the radius P of the pivot pin .1 from the true centre is or the order of .43 of the diameter of the brake. drum,

It is to be und erstoodthat these dimensions nomes refer to the normal size of brake drum as used on road motor vehicles.

The term rearward as used in this specification and in the appended claims has reference to the direction away from the front of the vehicle provided with the brake according to the invention.

What I claim is:

1. An improved brake of the internal-expand= ing type, comprising a brake drum, a backing plate therefor and two pivotally connected arcuate shoes co-acting with said brake drum over substantially equal effective areas and severally provided with a heel end and a toe end, a common pivot pin connecting the heel ends of said shoes, the said pivot pin being slightly rearwardly displaced with respect to the vertical axis of the drum, linings on said shoes, an anchor bolt on said backing plate, the pivoted end of one of said shoes being extended beyond the common pivot pin and being pivotally attached to said anchor bolt on the backing plate, an adjustable stop member arranged to locate each shoe in its retracted position with respect to the drum, the arrangement being such that, irrespective of the condition of wear of the shoe linings, a constant minimum clearance is main, tained between said linings and the brake drum by the normal application of the brake, said tioned substantially close to and inwardly of the ,common pivot pin of the shoes, the distance between the said anchor bolt and pivot pin being of the order of from /4 to A, of the distance between said pivot pin and the axis of the brake drum whereby application of the brake by outward expansion of the toe endsof the shoes imparts a simultaneous and similarly outwardly expansive movement as well as a slight outwardly substantially radial movement to the heel ends of said shoes, so that initial frictional contact with the brake drum takes place below the center line thereof, whereby wear on the shoe linings is more evenly distributed and snatching is prevented.

3. An, improved brake of the internal-expanding type, comprising a brake drum, a backing plate therefor and two plvotally connected arouate shoes co-acting with said brake drum over substantially equal effective areas and severally provided with a heel end and a toe end, a common pivot pin connecting the heel ends of said shoes, the said pivot {am being slightly rearwardly displaced with respect to the vertical axis the drum, linings on said shoes, an anchor bolt shoes on the rearward side of a radial line passing through the axis of the brake drum and the axis of the said common pivot pin, the rearward angular displacement oi the axis of the anchor bolt with respect to the axis of the common pivot pin being of the order of from to degrees, whereby application of the brake by outward expansion of the toe ends of the shoes imparts a simultaneous and similarly outwardly expansive movement as well as a slight outwardly substantially radial movement to the heel ends of said shoes, so that initial frictional contact with the brake drum takes place below the center line thereof, whereby wear on the shoe linings is more evenly distributed and snatching is prevented.

2. An improved brake oi the internal-expanding type, comprising a brake drum, a backing plate therefor and two pivotally connected arcuate shoes co aoting with said brake drum over substantially equal efiective areas and severally provided with a heel end and a toe end, a common pivot pin connecting the heel ends of said shoes, the said pivot pin being slightly rearwardly displaced with respect to the vertical axis of the drum, linings on said shoes, an anchor bolt on said backing plate, the pivoted end of one of said shoes being extended beyond the common pivot pin and being pivotally attached to said anchor bolt on the backing plate, an adjustable stop member arranged to locate each shoe in its retracted position with respect to the drum, the arrangement being such that, irrespective of the condition of wear of the shoe linings, a constant on said backing plate, the pivoted end of one of said shoes being extended beyond the common pivot pin and being pivotally attached to said anchor bolt on the backing plate, an adjustable stop member arranged to locate each shoe in its retracted position with respect to the drum, the arrangement being such that, irrespective of the condition oi wear of the shoe linings, a constant minimum clearance is maintained between said linings and the brake drum by the normal application of the brake, said anchor bolt being posi-' tioned substantially close to and inwardly of the common pivot pin of the shoes on the rearward side of a radial line passing through the axis of the brake drum and the axis of the said common pivot pin, the rearward angular displacement of the axis of the anchor bolt with respect to the axis of the common pivot pin being of the order of from 5 to 15 degrees, whereby application of the brake by outward expansion of the toe ends of the shoes imparts a simultaneous and similarly outwardly expansive movement as well as a slight outwardly substantially radial movement to the heel ends of said shoes, so that initial frictional contact with the brake drum takes place below the center line thereof, whereby wear on the shoe linings is more evenly distributed and snatching is prevented, a. tension spring connecting the toe end of the rear shoe to an anchoring point on the said backing plate arranged substantially horizontally in line with said end, and a second tension spring extending between a point on the other shoe intermediately of its ends and a point on said backing plate adjacent the point to which said first-mentioned spring is attached.

WILFRED DELL KOCH.

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