Abstract
The invention relates to a brake shoe for a drum brake and a drum brake that comprises a supporting unit and a lining unit, wherein the supporting unit comprises a bearing portion for pivotable support and an actuation portion, wherein the supporting unit comprises two supporting portions, wherein the center of the mean curvature of the first supporting portion is spaced apart from the center of the mean curvature of the second supporting portion.
Claims
1. A brake shoe for a drum brake, comprising: a supporting unit which comprises a bearing portion for pivotable support and an actuation portion; and a lining unit fixed at a convexly curved outer side of the supporting unit, wherein, when an actuation force smaller than a limiting force is applied to the actuation portion, the lining unit shows a braking effect in a first lining portion only, wherein, when an actuation force larger than the limiting force is applied, the lining unit shows a braking effect also in a second lining portion, and wherein a majority of the first lining portion is located adjacent one of the bearing portion and the actuation portion of the supporting unit, and a majority of the second lining portion is located adjacent the other of the bearing portion and the actuation portion of the supporting unit; wherein the supporting unit between the bearing portion and the actuation portion comprises a curved first supporting portion, and a curved second supporting portion; and wherein a center of a mean curvature of the first supporting portion at the convexly curved outer side is spaced apart from a center of a mean curvature of the second supporting portion at the convexly curved outer side.
2. The brake shoe of claim 1, wherein the distance of the centers relative to each other is in a relationship of within a range of from about 0.01 to about 0.15 to a mean radius of curvature of the first supporting portion.
3. The brake shoe of claim 2, wherein the distance of the centers relative 3 each other is in the ratio of within the range of 0.03 to 0.1 to the mean radius of the first supporting portion.
4. The brake shoe of claim 3, wherein the distance of the centers relative to each other is in the ratio of within the range of 0.05 to 0.07 to the mean radius of the first supporting portion.
5. The brake shoe of claim 1, wherein the first supporting portion spans a first angle of arc about the center of the mean curvature of the first supporting portion, wherein the second supporting portion spans a second angle of arc about the center of the mean curvature of the second supporting portion, and wherein the ratio of the first angle to the second angle of arc is in a range of from about 0.5 to about 3.
6. The brake shoe of claim 5, wherein the ratio of the first angle of arc to the second angle of arc is in the range of 0.7 to 2.
7. The brake shoe of claim 6, wherein the ratio of the first angle of arc to the second angle of arc is in the range of 0.9 to 1.3.
8. The brake shoe of claim 1, wherein in a decompressed state of the brake shoe a mean radius of curvature of the first supporting portion to a mean radius of curvature of the second supporting portion is in a ratio within a range of from about 0.8 to about 0.99.
9. The brake shoe of claim 8, wherein the ratio of the mean radius of curvature of the first supporting unit to the mean radius of curvature of the second supporting unit is within the range of 0.85 to 0.95.
10. The brake shoe of claim 9, wherein the ratio of the mean radius of curvature of the first supporting unit to the mean radius of curvature of the second supporting unit is within the range of 0.88 to 0.92.
11. The brake shoe of claim 5, wherein the first lining portion has a first thickness and the second lining portion has a second thickness, and wherein the first thickness is in a relationship of within a range of about 1.05 to about 4 to the second thickness.
12. The brake shoe of claim 11, wherein the relationship of the first thickness to the second thickness is within the range of 1.2 to 2.
13. The brake shoe of claim 12, wherein the relationship of the first thickness to the second thickness is 1.5.
14. The brake shoe of claim 1, wherein the supporting unit comprises at least one material weakness, which reduces the bending stiffness of the supporting unit.
15. The brake shoe for a drum brake of claim 1, wherein the majority of the first lining portion is located proximate the bearing portion of the supporting unit.
16. A brake shoe for a drum brake, comprising: a supporting unit which comprises a bearing portion for pivotable support and an actuation portion; and a lining unit fixed at a convexly curved outer side of the supporting unit, wherein, when an actuation force smaller than a limiting force is applied to the actuation portion, the lining unit shows a braking effect in a first lining portion only, wherein, when an actuation force larger than the limiting force is applied, the lining unit shows a braking effect also in a second lining portion, and wherein a majority of the first lining portion is located adjacent one of the bearing portion and the actuation portion of the supporting unit, and a majority of the second lining portion is located adjacent the other of the bearing portion and the actuation portion of the supporting unit; wherein the supporting unit between the bearing portion and the actuation portion comprises a curved first supporting portion, and a curved second supporting portion; and wherein a center of a mean curvature of the first supporting portion at the convexly curved outer side is spaced apart from a center of a mean curvature of the second supporting portion at the convexly curved outer side, and wherein the first lining portion comprises a material having a greater abrasion resistance than the second lining portion.
17. A brake shoe for a drum brake, comprising: a supporting unit which comprises a bearing portion for pivotable support and an actuation portion; and a lining unit fixed at a convexly curved outer side of the supporting unit, wherein, when an actuation force smaller than a limiting force is applied to the actuation portion, the lining unit shows a braking effect in a first lining portion only, wherein, when an actuation force larger than the limiting force is applied, the lining unit shows a braking effect also in a second lining portion, and wherein a majority of the first lining portion is located adjacent one of the bearing portion and the actuation portion of the supporting unit, and a majority of the second lining portion is located adjacent the other of the bearing portion and the actuation portion of the supporting unit; wherein the supporting unit between the bearing portion and the actuation portion comprises a curved first supporting portion, and a curved second supporting portion; and wherein a center of a mean curvature of the first supporting portion at the convexly curved outer side is spaced apart from a center of a mean curvature of the second supporting portion at the convexly curved outer side, and, wherein a coefficient of friction of the second lining portion is within the range of from about 1.1 to about 3 times a coefficient of friction of the first lining portion.
18. The brake shoe of claim 17, wherein the relationship of the coefficient of friction of the second lining portion to the coefficient of friction of the first lining portion is within the range of 1.15 to 2.
19. The brake shoe of claim 18, wherein the relationship of the coefficient of friction of the second lining portion to the coefficient of friction of the first lining portion is within the range of 1.3 to 1.7.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 a view of the drum brake of the invention in its first state,
(2) FIG. 2 a view of the drum brake of the invention in its second state,
(3) FIG. 3 a side view of a preferred embodiment of the brake shoe of the invention,
(4) FIG. 4 a first sectional view of a preferred embodiment of the brake shoe of the invention,
(5) FIG. 5 a second sectional view of a preferred embodiment of the brake shoe of the invention,
(6) FIG. 6 a view of a preferred embodiment of the actuation portion of the invention, and
(7) FIG. 7 a view of a preferred embodiment of the brake shoe of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(8) FIG. 1 shows a partially sectional view of the drum brake according to the invention in its first state. The drum brake has a brake drum 10 and a brake shoe 1, wherein the brake shoe 1 comprises a supporting unit 2 and a lining unit 4. The supporting unit 2 is a curved component, wherein the lining unit 4 is fixed at the convex outer surface A. Furthermore, the line of curvature K, in the outer surface A, runs between the bearing portion 23 and the actuation portion 24 of the supporting unit 2. The supporting unit 2 comprises a first supporting portion 21, which preferably is arranged adjacent to the bearing portion 23, and a second supporting portion 22, which preferably is arranged adjacent to the actuation portion 24. Alternatively preferably, it is possible to provide a plurality of supporting portions between the bearing portion 23 and the actuation portion 24. According to the invention, it is provided that the first supporting portion 21 has a curvature with a mean radius of curvature R.sub.1, wherein the mean radius of curvature R.sub.1 spans a circle segment with a first angle of the arc .sub.1. Analogously, the second supporting portion 22 has a curvature with a mean radius of curvature R.sub.2, wherein the mean radius of curvature R.sub.2 spans a circle segment with a second angle of the arc .sub.2. Preferably, the relationship of the first angle of the arc .sub.1 to the second angle of the arc .sub.2 is 0.5 to 3, wherein the Figure shows a particularly preferred range of 2 to 2.6. The center M.sub.1 of the mean curvature of the first supporting portion 21 is spaced apart from the center M.sub.2 of the mean radius of curvature of the second supporting portion 22 by a distance a. By differently curving the first and second supporting portions 21, 22 according to the invention it is achieved that the lining unit 4 comes into friction contact with the brake drum 10 at first only with its first lining portion 41 in the area of the first supporting portion 21, and only after the supporting unit 2 has been deflected or bent, also with the second lining portion 42 in the area of the second supporting portion 22 (cf. FIG. 2). Preferably, this behavior of the brake shoe 1 is supported and reinforced also by a bending stiffness of the supporting unit 2 varying between the bearing portion 23 and the actuation portion 24. In the Figure, there is shown the mean radius of curvature R.sub.1 of the curvature of the first supporting portion 21 and the mean radius of curvature R.sub.2 of the curvature of the second supporting portion 22, wherein, in the unstressed or unloaded state of the brake shoe 1 (not shown), the preferred relationship of the curvatures is 0.8 to 0.95. Preferably, the brake drum 10 rotates in the clockwise direction relative to the brake shoe 1, i.e. running towards the bearing portion 23 so as to make use of the self-servo effect of the drum brake. The first state of the drum brake is characterized in that an actuation force F is applied at the actuation portion 24, which is smaller than a limiting force F.sub.G, so that the brake shoe 1 and in particular the lining unit 4 comes to rest against the brake drum 10 in its first lining portion 41 only. In this context, the limiting force F.sub.G is to be understood as an abstract parameter, which results from the constructive design of the drum brake. It may also be defined as the value of the actuation force F, at which the brake shoe 1 only just rubs against the brake drum 10 in the first lining portion 41 thereof. When there is provided a plurality of lining portions 41, 42, 43 (cf. FIG. 7), there will consequently be a first limiting force F.sub.G, up to which only the first lining portion 41 rubs, a second limiting force F.sub.G, up to which only the first and the second lining portions 41, 42 rub, and so on. The transition between the lining portions 41, 42 may be stage-less in case leaps are to be avoided in the course of the brake force when the actuation force F increases continuously. As is shown in the Figure, the individual lining portions 41, 42 may also be clearly delimited against each other, by means of grooves, cavities or gaps between the lining portions 41, 42, for example.
(9) FIG. 2 shows the drum brake 10 shown in FIG. 1 in its second state. Here, the actuation force F applied at the actuation portion 24 is larger than the limiting force F.sub.G, and the supporting unit 2 of the brake shoe 1 is deformed such that the second lining portion 42 is forced or pushed against the inside of the brake drum 10. The deformation of the supporting unit 2 preferably also causes the mean radius of curvature R.sub.2 of the curvature of the second supporting portion 22 to be equal to the mean radius of curvature R.sub.1 of the first supporting portion 21. Further preferably, in the second state of the drum brake, the centers M.sub.1, M.sub.2 of the mean curvature of the first and second supporting portions 21, 22 are congruent. To put it differently, as the actuation force increases, the outer contour of the brake shoe 1 more and more adapts to the inner contour of the brake drum 10, wherein the size or magnitude of the friction surface between the lining surface 4 and the brake drum 10 increases.
(10) The embodiment of the brake shoe 1 of the invention shown in FIG. 3 comprises a supporting unit 2 and a lining unit 4. The supporting unit 2 is preferably designed such that it is arc-shaped or curved, wherein the lining unit 4 is arranged at the convex outer surface of the curvature. The supporting unit 2 comprises a bearing portion 23 and an actuation portion 24, wherein, in the preferred embodiment, which is shown, the bearing portion is a bore, for example, by means of which the supporting unit 2 may be pivotably mounted by means of a pin, for example. Furthermore, the supporting unit 2 comprises a first supporting portion 21 and a second supporting portion 22, wherein the first supporting portion 21 preferably has a lower bending stiffness than the second supporting portion 22. The lining unit 4 preferably in the area of the first supporting portion 21 comprises a first lining portion 41, and in the area of the second supporting portion 22 it comprises a second lining portion 42. Particularly preferably, as is shown, the thickness D of the lining unit in the area of the first lining portion is on average larger than in the area of the second lining portion 42.
(11) FIG. 4 shows the sectional view indicated by numeral II in FIG. 3 of a preferred embodiment of the brake shoe 1 according to the invention. The T-shaped design of the supporting unit 2, which comprises a lining plate 28 and a web plate 27, is clearly shown. In FIG. 4, the brake shoe is shown as a sectional view in the area of the first lining portion 41 or of the first supporting portion 21, respectively, and the lining unit 4 has a mean thickness D.sub.1 in this area. Preferably, the supporting unit 2 may also have a double-T-shaped cross-section, i.e. two parallel web plates 27, or be box-shaped, for example, wherein the web plate 27 is U-shaped and connected to the lining plate 28 with its distal ends.
(12) FIG. 5 shows the sectional view of the brake shoe indicated by numeral III in FIG. 3. The lining unit 4 is shown in sectional view in the second lining portion 42 or in the area of the second supporting portion 22, respectively, and has a thickness D.sub.2, which is smaller than the thickness D.sub.1 of the first lining portion 41 (cf. FIG. 2). Furthermore, it is apparent that the lining plate 28 of the supporting unit 2 in the area of the second supporting portion 22 has a larger thickness or material gauge than the lining plate 28 in the area of the first supporting portion 21. Consequently, the lining plate in the area of the second supporting portion 22 has a greater bending stiffness than the lining plate 28 in the area of the first supporting portion 21. The same applies to the web plate 27, which in the area of the second supporting portion 22, as is shown in FIG. 5, has a greater material gauge or wall gauge or plate thickness than in the area of the first supporting portion 21, as is shown in FIG. 4.
(13) FIG. 6 shows a preferred embodiment of the actuation portion 24. Preferably, the actuation portion 24 has a first engagement portion 241 and a second engagement portion 242, which are each formed two-dimensional or planar and which are pivoted relative to each other. Below the actuation portion 24, there is indicated an actuation element (without reference sign), which transmits an actuation force F to the actuation portion 24. The continuous lines in the Figure show how, in the first state of the drum brake, the actuation element transmits an actuation force F smaller than a limiting to F.sub.G to the first engagement portion 241. It becomes apparent that by diagonally arranging the first engagement portion 241 the resultant force acting on the supporting unit 2 has a force component directed towards the right. The dashed lines in FIG. 6 show the preferred position of the supporting unit 2 in the second state of the drum brake, wherein the actuation element acts on the second engagement portion 242. Preferably, the actuation force F is larger than the limiting force F.sub.G, wherein the force actually transmitted to the supporting unit 2 has another main direction than the actuation force transmitted to the supporting unit 2 in the first state of the drum brake. In this preferred embodiment, in the first state, a force is transmitted to the supporting unit 2, which force acts at least in certain areas along the circumferential direction of the supporting unit 2 or the brake drum 10 surrounding said supporting unit 2 (cf. FIGS. 1, 2). Preferably, the first lining portion (not shown in FIG. 6) in the first state of the drum brake is forced against the brake drum with an additional force. As a matter of course, the first engagement portion 241 and the second engagement portion 242 may also be formed rounded, wherein the transition between the two engagement portions may also be formed rounded. Preferably, the actuation portion 24 is adapted to the geometry of the actuation element in order to achieve an optimum transmission of force from the actuation element to the supporting unit 2.
(14) FIG. 7 shows a particularly preferred embodiment of the brake shoe 1 according to the invention. The brake shoe 1 preferably comprises a supporting unit 2 with three supporting portion 21, 22, 25. The supporting portion 21 adjacent to the bearing portion 23 has a mean curvature, the center M.sub.1 of which is preferably displaced relative to the centers M.sub.2 and M.sub.3 of the mean curvatures of the second supporting portion 22 and of the third supporting portion 25. By way of example the distance a of the center M.sub.1 from the center M.sub.2 is shown, which preferably is in a relationship of 0.01 to 0.2, more preferably 0.05 to 0.1, and particularly preferably 0.07 to 0.09 to the mean radius of curvature of the first supporting portion 21. Furthermore, two of the supporting portions 21, 22, 25 preferably have local material weaknesses 29, which influence the bending stiffness of the supporting unit 2 along the course of curvature between the bearing portion 23 and the actuation portion 24. Preferably, there are provided material weaknesses 29, as recess for example, also in the transitional area between two supporting portions 21, 22, 25 so that the supporting portions 21, 22, 25 may be easier pivoted relative to each other and it is possible to achieve that the brake shoe 1 rests optimally against the brake drum 10 (not shown) during different operational states of the brake. FIG. 7 shows also the preferred design of the lining portions 41, 42, 43, wherein they are made from different materials. Advantageously, the first lining portion 41 has a higher abrasion resistance than the second lining portion 42 and the third lining portion 43, wherein the third lining portion 43 in turn has the highest coefficient of friction of the lining portions 41, 42, 43. Thus, the brake and wear behavior of the brake shoe 1 for certain expected times of stress of the individual lining portions 41, 42, 43 may be optimized during operation and for the required brake forces. In the embodiment shown, all lining portions 41, 42, 43 have the same thickness. Alternatively, it could be preferred that the thickness D.sub.1 of the first lining portion 41 is larger than the thickness D.sub.2 of the second lining portion 42, and the latter in turn is larger than the thickness D.sub.3 of the third lining portion 43.
LIST OF REFERENCE SIGNS
(15) 2supporting unit 4lining unit 10brake drum 21first supporting portion 22second supporting portion 23bearing portion 24actuation portion 25third supporting portion 27web plate 28lining plate 29material weakness 41first lining portion 42second lining portion 43third lining portion 241first engagement portion 242second engagement portion Dthickness of the lining unit Aouter surface of the supporting unit adistance D.sub.1first thickness D.sub.2second thickness Factuation force F.sub.Glimiting force Kline of curvature M.sub.1, M.sub.2, M.sub.3center of the mean curvature Rdirection of rotation .sub.1, .sub.2first, second angle of the arc
