US1937891A - Brake shoe - Google Patents

Description

J. H. HUNT BRAKE SHOE Filed Aug. 26

Dec. 5, 1933.

, 1927 2 Sheets-Sheet l Am/ 5.421- mam/0 EQAGE M w n Dec. 5, 1933. HUNT 1,937,891

BRAKE SHOE Filed Aug. 26 1927 2 Sheets-Sheet 2 gnuw bom Patented Dec. 5, n 1933 1,937,891 BRAKE SHOE John H. Hunt, Detroit, Mich assignor to General Motors Corporation, Detroit, Mich), a corporation of Delaware Application August 2c, 1927. Serial No. 215,670

Claims.

Thisinvention relates to brakes and more particularly to an improvement in internal rigid shoe brakes for use on vehicles.

In providing brakes for vehicles it is customary 5 to employ a drum on the wheel or other rotating part. A band or shoe is used, usually with a fixed anchor, to engage the drum and check or stop the rotation of the movable part. When such a band is used on the outside of the drum it is .10 subject to rain, dust and dirt. Also the presence of an external band prevents the use of ribs which are frequently considered desirable to stiffen the drum and to radiate heat, These disadvantages and certain advantages inherent in internal brakes is the occasion fora preference for the internal type of brakes.

This invention, then, is concerned with internal brakesand with a rigid shoe for such a brake. In the rigid shoe brake the shoe is pivotally anchored adjacent one end and has acurved outer periphery corresponding in general to the inner periphery of the drum. Its other end is termed to be engaged by a cam or other equivalent means to force the shoe, usually against theresistance of a 2i retracting spring, against the drum.

It is well understood that as the drum is rotating, one direction of rotation. tends to swing the shoe about its pivot against the drum, and the opposite direction of rotation tends to swing the shoe awayfrom the drurn. The force by which the drum, if it rotates, tends to swing the shoe about its pivotal anchor against the drum is commonly known as self-actuation. It is well understood that the more the anchor for the shoe 35 ismoved away from the drum and toward the center of the drumthe greater the self-actuation will become. It is also known that the self-actuation varies falongthe arc of the shoe, being least at a point relatively near the anchor end. From 0 this point self-actuation rapidly increases toward theanchor end, and gradually increases from the samepoint toward the cam abutment end. It is necessary to prevent the self-actuating force from becoming so high that the shoe, when applied to the drum, shall become locked. To prevent such a result it is common practice to construct the shoe so that its lining shall not be carried to a point in the line joining the center of the drum and the anchor of the shoe. In constructing such shoestherefore the lining is carried from the point of least self-actuation only a short distance along the arc toward the anchor or heel end of the shoe. In the direction fromthe point of least actuation toward the cam end the lining is carried to a pointwellwithin the self locking range but it should not be carried so far that the average self-actuation of the whole shoe will render the shoe self locking.

It is possible to calculate the anchor and cam abutment positions and the length'of arc in a way to secure the desirable results of high selfactuation and the prevention of locking, and these results would be reliable if the shoe be suffioiently rigid to retain its form. Under the repeated applications of the brake, however, the outer portion of the beam of the shoe receives considerable heat from the frictional engagement of the lining with the drum, while the inner portion of the beam remains comparatively cool.

The greater expansion of the outer portion of n the beam as a result of this transmitted heat as compared with that of the inner portion of the beamcauses the shoe, as a Whole, to curl so that the heel portion engages the drum to the exclusion of the toe portion, when the brake is applied. Under these circumstances the selfactuation of the shoe as a whole isreduced, and the pedal pressure is relatively high. Also, and what is of more consequence, the lining at the heel portionis unduly worn. Thereafter, when the brake shoe cools, and the brake is applied, the toe portion engages the drum more effectively than the heel portion since the lining of the latter has been worn down. It is, therefore, the high actuation portion of the shoe which is en- 85 gaging the drum to the exclusion of the low actuation portion. This is very apt to result in a. grabbingbrake which looks the drum and permits skidding. V

It is specifically, then, an object of this invention to construct a brake shoe which shall have an advantageous self actuating factor, this to be obtained by a location of the anchor well inward from the drum periphery, and a drum engaging arc, the toe portion of which extends well 95 within the self locking range; and it is the purpose of the invention to so construct the shoe that under the eifects of temperatures as described above there will be no danger that the shoe will lock to the drum;

. In the accompanying drawings are shown sev eral forms of brake shoe in which my invention may be embodied. Each of these shoes is intended to be anchored within the drum at a point well within the periphery. of the drum and to have an arc carried well within the range of self-actuation. In each casethe shoe construction is such that the shoe is not to lock to the drum even under the extreme conditions arising from a high degree of heat.

In the drawings, Figure 1 shows a first form of the invention in side elevation.

Figure 2 illustrates a cross section on the line 22 of Figure 1.

Figure 2a is a similar cross section of a modified form of shoe.

Figure 3 is a side elevation of a modified form of brake shoe.

Figure 4 is a side elevation of still another modification.

Figure 5 illustrates in side elevation a further and comparatively simple form in which the invention may be embodied.

Referring first to Figure 1, numeral 5 represents a brake shoe as a whole. It includes a rigid part '7 having an eye 9 located at one end for engagement with an anchor pin. It will be seen that the eye 9 is located considerably within the arc of the peripheral portion of the shoe, the

purpose of this location being to secure a comparatively high degree of self-actuation, to thereby render the pedal pressure easy. Secured to the peripheral portion of the shoe as by rivets 11 there is a'plate 13 which extends considerably beyond the extreme portion 15 of the rigid shoe '7. This plate 13 has secured thereto by rivets or the like a lining member 17, the lining member being selected to have the desired coeflicient of friction when engaged with the drum. At the end of plate 13 remote from the anchor there is secured a plate 19, suitable fastening means 21 being employed. The plate 19 is doubly bent as at 23 to afford a flat sur face 25 to which is secured an abutment member 27 by suitable fastening means 29. It will be understood that the abutment member 2'? is tobe engaged by the cam or its equivalent in rotating the shoe as a whole about its pivotal point 9 with the anchor. It will be also observed that the plate 19 from its return bend is brought into engagement with the plate 13 but is spaced from the extreme point 15 of the rigid brake shoe. The construction shown in Figure 2a resembles that shown in 1 and 2 except that the material of the rigid shoe is Z-shaped as shown "'at 7 instead of being channel shaped as illustrated in Figure 2.

With a shoe of this kind, when the cam forces the shoe against the drum the relatively high self-actuation at the cam end of the shoe com- "bines with the relatively low actuation near the anchor end of the shoe to produce an average self -actuation sufiiciently high to render the pedal pressure comparatively easy. vShould the drum become highly heated from frictional engagement 1 with the lining and transmit its heat to the shoe, causing undue wear at the heel portion of the shoe and tend to make the shoe as a whole self locking as explained above, it will be understood that the yielding of the plate 13 beyond the tip 15 of the rigid shoe will take place and prevent the shoe becoming locked to the drum. In the construction of such a shoe it will be understood, of course, that the extreme point 15 of the rigid part of the shoe 7 is such that under no circumstances will the rigid part 7 be itself self locking. To make the construction and operation as clear as possible from the drawings, Fig. 1 has been m marked by a designating reference character a: and by suitable legends. This indicates that at some point beyond the end of rigid part 7 is point :1: toward the heel from which the applied forces never cause self-locking and toward the toe from which the shoe might lock except for the provision for yielding in the region marked m.

Another form of the invention is shown in Figure 3. In this form the rigid anchor portion, represented by numeral 31 is formed with the eye 33 for engagement with the anchor pin. The toe portion or cam abutment part 35 is in this case also a rigid member. Integral with or secured to the toe portion 35 is the plate 37. This plate 37 extends along the arc-shaped surface of part 31 85 and has secured thereto an angle plate 39. The angle plate 39 is formed with a slot 41 engaging a pin 43 carried by part 31, to thereby provide a limited sliding of part 37 relatively to part 31 to accommodate relative movement between the shoe members 35 and 31. The two shoe members 35 and 31 are also connected together by link means 45 pivoted to each of said shoe members on pins 47.

The operation of the shoe constructed as shown in Figure 3 is much the same as that shown in Figure 1. The yielding connection between the two parts 35 and 31 prevents under extreme conditions the locking of the shoe to the drum, and it does so with the shoe having an anchor point. 190 33 and a length of are selected to give normally a high self-actuation. There is also to be noted that the points e7 may be selected so as to increase the self-actuation of part 35 as desired. That is to say, if the points 47 are moved outwardly in a radial direction toward the periphery the self-actuation of shoe portion 35 is reduced, and if these points are moved inwardly the selfactuation may be increased. The self-actuation depends in part upon the radial position of its center of rotation. The shoe portion 31 may be considered as actuated by the mechanical force applied at the abutment end of shoe 35 together with whatever brake torque is developed by part. 35 owing to its own self-actuation about its pivotal connection 47 with the ri id shoe portion 31.

The form of the invention shown by Figure 4. operates in substantially the same way. In this form of the invention the shoe 19 has the eyev 51 for the anchor pin as before. In this case the 129 shoe is formed with an integral lining carrying flange 53. The lining 55 is shown as mounted on this flange. The shoe 49 is in this case unitary in construction from the anchor to the cam abut-j ment but is cut away from its inner beam portion 125 to a point adjacent the flange 53 as shown at 5'? in Figure 4. This cutaway portion, terminating at a point 59, is so chosen that the actuation factor of the anchor end of the shoe willbesuch as, under no circumstances, to cause self locking. 130 Any tendency of the toe end 61 of the shoe to cause trouble is prevented by the location of what' may be called its anchor point 59 well out toward the periphery of the shoe. In this case the anchor end of the shoe may be regarded as actuated by the mechanical force applied to the toe portion 61 together with whatever brake torque is developed in the toe portion 61, point 59 being consid-f ered as its anchor.

A very simple form in which the inventionmay 140 be embodied is illustrated in Figure 5. In. this. form of the invention a rigid shoe 63 is employed having an eye 65 for its anchor, chosen as'in the previous forms of the invention to give a desired self-actuation factor. The flange 67 carries the 5 usual lining 69. At the toe end of the shoe 71 is an abutment for engaging the cam, as willbe understood. From a point on the peripheryof the shoe adjacent the abutment plate 71 a slot'73 is cut into the material of the shoe 63and ex- 150 for a desired distance along the shoe. A shoe is thus produced having rigidity to a point '75 from its heel, the point I5 being selected such that the shoe shall be free from any danger of self locking up to that point 75. Beyond the point the shoe is in the self locking range but danger of self locking is prevented by the limited flexibility of the radially outer part of the tip portion between point '75 and the cam engaging abutment. this flexibility being produced by cutting slot 73 While the several forms described above are believed to be economical and convenient ways in which the invention is embodied they are understood to be illustrative of the invention and not to comprehend all the constructions in which the inventive idea may be carried out.

I claim: l l

1. A self-actuating shoe for internal brakes, said shoe having a rigid heel portion adapted to be pivotally anchored and having a peripheral are extended to a point adjacent but not within the self-locking range of actuation, and a toe portion yieldingly connected to the rigid heelportion.

2. A self-actuating shoe for internal brakes, said shoe having a heel portion and adjacent thereto an opening for an anchor pin and a yieldingly connected portion adjacent the cam engaging part, said yieldingly connected portion lying entirely within the self-locking range.

3. A self-actuating shoe for internalbrakes,

said shoe having an anchored rigid portion and a rigid toe portion adapted to be engaged by a brake-applying means, and means yieldingly connecting said portions, said heel portion extending along the arc'of the shoe to a point adjacent but not within the locking range of self-actuation.

4. A brake shoe having an anchored heel portion of dimensions such that its self-actuation is relatively low as to avoid locking, and an applying toe portion having a higher actuation factor and located entirely within the self -locking range, means yieldingly connecting said portions to movably associate the same to prevent locking of said shoe under extreme conditions.

5. A brake shoe comprising a heel portion and a toe portion, said toe portion being entirely within the self-locking range of the shoe, means connecting said portions and said connecting means being yieldable when the toe portion tends to lock as the result of a movement of the shoe as a whole about the anchor carrying the heel portion.

6. A shoe for engaging a drum having an anchor pin opening at one end and an abutment at its opposite end, said shoe having a toe portion at the abutment end, the last named end being sufficiently removed from the anchor to at times permit the shoe to lock,,and yielding means to prevent such locking of the shoe, said yielding means connecting the parts of said shoe and lying partly within said self-locking range.

7. A shoe for brakes having a rigid anchor part and a rigid abutment part, yielding means connecting said parts, said yielding means being so positioned and so related with respect to said parts and to the anchor pin position as to provide for inward yielding of the abutment part to prevent locking when the shoe tends to become locked to the drum.

8. A rigid shoe for internal brakes, said shoe having a slot adjacent the end remote from its anchor whereby said shoe is provided with a yielding tip to prevent locking, said slot being in the self-locking range of the shoe.

9. A brake shoe comprising two shoe parts integrally united by a yielding bridge, each part consisting of a lining carrying portion and an are shaped web, one web terminating in an actuating abutment and the other web having at its outer web an anchor pin abutment.

10. A shoe for brakes having a rigid anchor part and a rigid abutment part, link means pivotally connecting said parts, the arc of said anchor part being of such extent that the said part is not of itself self-locking.

JOHN H. HUNT.

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