BRAKE SHOE WITH A BRAKE LINING HAVING SPATIALLY VARYING THERMAL MATERIAL PROPERTIES

Abstract

The invention relates to a brake shoe for a drum brake system, the brake shoe having a length configured to extend in a circumferential direction of a brake drum of the drum brake system, and a width configured to extend in an axial direction of the brake drum, wherein the brake shoe has spatially varying thermal properties along its length, in particular a change in heat capacity and/or a change in thermal expansion coefficient and/or a change in thermal conductivity. The invention also relates to a drum brake system having a brake shoe of the above-mentioned type.

Claims

1. A brake shoe for a drum brake system, the brake shoe having a length configured to extend in a circumferential direction of a brake drum of the drum brake system, and a width configured to extend in an axial direction of the brake drum, wherein the brake shoe has spatially varying thermal properties along its length, in particular a change in heat capacity and/or a change in thermal expansion coefficient and/or a change in thermal conductivity.

2. The brake shoe according to claim 1, having a leading side and a trailing side, wherein the heat capacity and/or the thermal conductivity and/or the thermal expansion coefficient increases from the leading side of the brake shoe to the trailing side.

3. The brake shoe according to claim 1, comprising at least two segments, with different thermal properties from one another, in particular with different heat capacity and/or different thermal expansion coefficient and/or different thermal conductivity from one another.

4. The brake shoe according to claim 3, wherein the at least two segments are provided in a brake lining and/or in a lining holder of the at least one brake shoe.

5. The brake shoe according to claim 3, comprise a first segment being a leading segment, and a second segment adjacent to the first segment, wherein the heat capacity and/or the thermal expansion coefficient and/or the thermal conductivity in the first segment is at least 5 % less than the heat capacity and/or the thermal expansion coefficient and/or the thermal conductivity in the second segment.

6. The brake shoe according to claim 1, wherein the at least three segments are provided in a brake lining and/or in a lining holder of the at least one brake shoe.

7. The brake shoe according to claim 6, wherein the at least three segments are provided in a brake lining and/or in a lining holder of the at least one brake shoe.

8. The brake shoe according to claim 6, comprise a first segment being a leading segment, and a second segment adjacent to the first segment, wherein the heat capacity and/or the thermal expansion coefficient and/or the thermal conductivity in the first segment is at least 5 % less than the heat capacity and/or the thermal expansion coefficient and/or the thermal conductivity in the second segment.

9. The brake shoe according to claim 8, comprising a third segment adjacent to the second segment, wherein the heat capacity and/or the thermal expansion coefficient and/or the thermal conductivity in the third segment is at least 5 % more than the heat capacity and/or the thermal expansion coefficient and/or the thermal conductivity in the second segment.

10. The brake shoe according to claim 1, wherein the spatially varying thermal properties are provided in a brake lining of the brake shoe, the brake lining having: a heat capacity that is in a range from 5 J/(Kg*K) to 20 J/(Kg*K), the heat capacity of the brake lining varying by at least 10 % along the length of the brake shoe, and/or a volumetric thermal expansion coefficient that is in a range from 100*E-061/K to 300*E-061/K, the volumetric thermal expansion coefficient of the brake lining varying by at least 10 % along the length of the brake shoe, and/or a thermal conductivity that is in a range from 0.1 W/(m*K) to 0.8 W/(m*K), the thermal conductivity of the brake lining varying by at least 10 % along the length of the brake shoe.

11. The brake shoe according to claim 1, wherein the spatially varying thermal properties are provided in a lining holder of the brake shoe, the lining holder comprising steel and/or cast iron.

12. The brake shoe according to claim 1, wherein the spatially varying thermal properties are provided in a lining holder of the brake shoe, the lining holder having: a heat capacity that is in a range from 280 J/(Kg*K) to 420 J/(Kg*K), the heat capacity of the lining holder varying by at least 10 % along the length of the brake shoe, and/or a volumetric thermal expansion coefficient that is in a range from 24*E-061/K to 36*E-061/K, the volumetric thermal expansion coefficient of the lining holder varying by at least 10 %along the length of the brake shoe, and/or a thermal conductivity that is in a range from 8 W/(m*K) to 18 W/(m*K), the thermal conductivity of the lining holder varying by at least 10 % along the length of the brake shoe.

13. The brake shoe according to claim 1, wherein the brake shoe has a spatially varying friction coefficient along its length.

14. A drum brake system for a vehicle, having a brake drum, a leading brake shoe and a trailing brake shoe, wherein at least one of the leading brake shoe and the trailing brake shoe, is a brake shoe according to claim 1, in particular both the leading brake shoe and the trailing brake shoe are brake shoes according to any of the preceding claims .

15. The drum brake system according to claim 14, wherein the change in heat capacity and/or the change in thermal expansion coefficient and/or the change in thermal conductivity of the leading brake shoe is greater than the change in heat capacity and/or the change in thermal expansion coefficient and/or the change in thermal conductivity of the trailing brake shoe.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0033] The invention will now be explained in an exemplary fashion with reference to the appended figures. Therein,

[0034] FIG. 1 shows a drum brake system with two brake shoes and a pressure distribution along a length of the brake shoes,

[0035] FIG. 2 shows a non-uniform pressure distribution according to the state of the art,

[0036] FIG. 3 shows a uniform pressure distribution,

[0037] FIG. 4 shows two brake shoes of a drum brake system, each brake shoe having three segments,

[0038] FIG. 5 shows two brake shoes of a drum brake system, each brake shoe having two segments provided in a brake lining,

[0039] FIG. 6 shows two brake shoes of a drum brake system, each brake shoe having three segments provided in a brake lining,

[0040] FIG. 7 shows two brake shoes of a drum brake system, each brake shoe having four segments provided in a brake lining,

[0041] FIG. 8 shows two brake shoes of a drum brake system, each brake shoe having two segments provided in a brake lining and in a lining holder,

[0042] FIG. 9 shows two brake shoes of a drum brake system, each brake shoe having three segments provided in a brake lining and in a lining holder, and

[0043] FIG. 10 shows two brake shoes of a drum brake system, each brake shoe having three segments provided in a lining holder.

DETAILED DESCRIPTION

[0044] FIG. 1 schematically shows a drum brake system for a vehicle. The drum brake system has a brake drum 40 with a main rotating direction 41 (indicated by an arrow), which corresponds to the vehicle moving in a forward direction. The drum brake system has a back plate assembly with two brake shoes 1, 2. The brake shoes 1, 2 each have a brake lining 11, 21, made of a friction material, and a lining holder 12, 22, made for instance of cast metal or steel. The brake shoes 1, 2 each have a pivot axis 13, 23 at the bottom, where they are pivotably connected to a back plate, and there is an actuator 30 provided near the top of the brake shoes, configured for pressing the brake shoes 1, 2 outward and against the brake drum 40 for braking. Accordingly, and in view of the main rotating direction 41 of the brake drum, the brake shoe 1 on the right is a leading brake shoe 1, and the brake shoe 2 on the left is a trailing brake shoe.

[0045] In FIG. 1, a brake force distribution F1 for the leading brake shoe 1, and a brake force distribution F2 for the trailing brake shoe 2 is indicated by way of arrows, longer arrows indicating higher brake force, and shorter arrows indicating lower brake force. For both brake shoes 1, 2 the brake force decreases from the leading edge to the trailing edge. Moreover, brake force of the trailing brake shoe 2 is less than brake force at the leading brake shoe 1. These distributions are due to the mechanical setup of the drum brake and may for instance result in less than optimal stopping power and uneven heating and wear.

[0046] Turning to FIGS. 2 and 3, a typical uneven force distribution is shown in FIG. 2, and an even pressure distribution is shown in FIG. 3. It is an object of the invention, to enable a more evenly distributed brake force, i.e., go from the force distribution of FIG. 2 towards the force distribution of FIG. 3.

[0047] This may be accomplished by providing the brake system with brake shoes as shown and explained in either of the following figures.

[0048] FIG. 4 shows an embodiment of a pair of brake shoes 1, 2, aimed at establishing a more evenly distributed brake force.

[0049] The brake shoes 1, 2 each have a brake lining 11, 21, made of a friction material, and a lining holder 12, 22, made for instance of cast metal or steel. Each of the brake shoes 1, 2 has a length configured to extend in a circumferential direction of the brake drum 40 of the drum brake system, and a width configured to extend in an axial direction of the brake drum 40.

[0050] Both brake shoes 1, 2 have spatially varying thermal properties along their length, wherein their heat capacity and thermal expansion coefficient and thermal conductivity changes from their leading side to their trailing side.

[0051] Specifically, for the leading brake shoe 1 and for the trailing brake shoe 2, the heat capacity and the thermal conductivity and the thermal expansion coefficient increases from the leading side of the respective brake shoe 1, 2 towards its trailing side. I.e., for the leading brake shoe 1 on the right, the leading side is at the top, and the parameters increase from top to bottom, and for the trailing brake shoe 2 on the left, the leading side is at the bottom, and the parameters increase from bottom to top.

[0052] The idea is to match the thermal properties at the different positions to meet a target of relatively constant friction values along with the total circumference of the drum.

[0053] In a drum brake system for a vehicle, for instance as shown in FIG. 1, the leading brake shoe 1 and the trailing brake shoe 2 of FIG. 4 may be provided.

[0054] The change in heat capacity and/or the change in thermal expansion coefficient and/or the change in thermal conductivity of the leading brake shoe 1 is greater than the change in heat capacity and/or the change in thermal expansion coefficient and/or the change in thermal conductivity of the trailing brake shoe 2, as will be explained further here below.

[0055] Each of the leading brake shoe 1 and the trailing brake shoe 2 comprises three segments S11, S12, S13; S21, S22, S23, with different thermal properties from one another, in particular with different heat capacity and different thermal expansion coefficient and different thermal conductivity from one another.

[0056] The segments S11, S12, S13; S21, S22, S23 are provided in the linings 11, 21.

[0057] The leading brake shoe 1 has a first segment S11 which constitutes a leading segment, a second segment S12 which constitutes a central segment, and a third segment S13 which constitutes a trailing segment. In the second segment S12, the central segment, the brake lining 11 has a heat capacity with a nominal value that is in a range from 5 J/(Kg*K) to 20 J/(Kg*K), for instance between 7 J/(Kg*K) and 17 J/(Kg*K), and a volumetric thermal expansion coefficient with a nominal value that is in a range from 100*E-06 1/K to 300*E-061/K, for instance between 130*E-061/K to 270*E-061/K, and a thermal conductivity with a nominal value that is in a range from 0.1 W/(m*K) to 0.8 W/(m*K), for instance between 0.2 W/(m*K) and 0.7 W/(m*K). Values are in each case given at 20° C. In the first segment S11 of the leading brake shoe 1, the brake lining 11 exhibits, for each of heat capacity, thermal expansion coefficient and thermal conductivity, a nominal value that is reduced by 10 to 20 % as compared to that of the central second segment S12. In the third segment S13, the trailing segment of the leading brake shoe 1, the brake lining 11 exhibits, for each of heat capacity, thermal expansion coefficient and thermal conductivity, a nominal value that is increased by 10 to 20 % as compared to that of the central second segment S12.

[0058] In the case of the trailing brake shoe 2, there is also a first segment S21 which constitutes a leading segment, a second segment S22 which constitutes a central segment, and a third segment S23 which constitutes a trailing segment. In the second segment S22, the central segment, the brake lining 21 has a heat capacity with a nominal value that is in a range from 5 J/(Kg*K) to 20 J/(Kg*K), for instance between 7 J/(Kg*K) and 17 J/(Kg*K), and a volumetric thermal expansion coefficient with a nominal value that is in a range from 100*E-061/K to 300*E-061/K, for instance between 130*E-061/K to 270*E-061/K, and a thermal conductivity with a nominal value that is in a range from 0.1 W/(m*K) to 0.8 W/(m*K), for instance between 0.2 W/(m*K) and 0.7 W/(m*K). Values are in each case given at 20° C. In the first segment S21 of the trailing brake shoe 2, the brake lining 21 exhibits, for each of heat capacity, thermal expansion coefficient and thermal conductivity, a nominal value that is reduced by 5 to 20 % as compared to that of the central second segment S22. In particular, the reduction may be less than the reduction between segments S11 and S12 of the leading brake shoe 1. In the third segment S23, the trailing segment of the trailing brake shoe 2, the brake lining 21 exhibits, for each of heat capacity, thermal expansion coefficient and thermal conductivity, a nominal value that is increased by 10 to 25 % as compared to that of the central second segment S22. In particular, this increase may be larger than the increase between segments S12 and S13 of the leading brake shoe 1.

[0059] The friction materials which form the linings consist of a number of different substances, which affect friction, adhesion and thermal properties. The composition of these substances is changed from one segment to the next, to achieve the above-identified target values, leading to a homogeneous brake force and temperature distribution over the total length of both linings 11, 21.

[0060] In the brake shoes 1, 2 a spatially varying friction coefficient along their lengths may additionally be provided.

[0061] FIG. 5 shows a pair of brake shoes 1, 2, comprising a leading brake shoe 1 and a trailing brake shoe 2. Each of the brake shoes 1, 2 has two segments S11, S12; S21, S22, in each case provided in the lining 11, 21. For each of the brake shoes 1, 2, the heat capacity and/or the thermal expansion coefficient and/or the thermal conductivity of the trailing segment S12, S22 is by at least 20 % higher than in the leading segment S11, S21.

[0062] FIG. 6 shows a pair of brake shoes 1, 2, comprising a leading brake shoe 1 and a trailing brake shoe 2. Each of the brake shoes 1, 2 has three segments S11, S12, S13; S21, S22, S23, in each case provided in the lining 11, 21. For each of the brake shoes 1, 2, the heat capacity and/or the thermal expansion coefficient and/or the thermal conductivity increases from the respective leading segment S11, S21 to the respective central segment S12, S22 by at least 10 %, and then increases again, from the respective central segment S12, S22 to the respective trailing segment S13, S23, by another at least 10 %.

[0063] FIG. 7 shows a pair of brake shoes 1, 2, comprising a leading brake shoe 1 and a trailing brake shoe 2. Each of the brake shoes 1, 2 has four segments S11, S12, S13, S14; S21, S22, S23, S24 in each case provided in the lining 11, 21. For each of the brake shoes 1, 2, the heat capacity and/or the thermal expansion coefficient and/or the thermal conductivity increases from the respective first, leading segment S11, S21 to the respective second segment S12, S22 by at least 5 %, and then increases again, from the respective second segment S12, S22 to the respective third segment S13, S23, by another at least 5 %, and then increases again from the respective third segment S13, S23 to the respective fourth, trailing segment S14, S24, by another at least 5 %.

[0064] FIGS. 8 and 9 relate to embodiments of brake shoes, wherein spatially varying thermal properties are provided in a lining holder 12, 22 of the brake shoe 1, 2, the lining holder 12, 22 comprising steel and/or cast iron. Therein, varying thermal properties are also provided in the linings 11, 21. In these cases, a combination of modifications in both lining and lining holder is advantageously exploited to achieve the desired goal.

[0065] Referring to both FIGS. 8 and 9, the lining holders 12, 22 have a heat capacity that is in a range from 280 J/(Kg*K) to 420 J/(Kg*K), and a volumetric thermal expansion coefficient that is in a range from 24*E-061/K to 36*E-06⅟K, and a thermal conductivity that is in a range from 8 W/(m*K) to 18 W/(m*K). In particular, segments S11, S12; S21, S22, (and S13, S23, in the case of FIG. 9) are provided in the lining holders 12, 22, wherein the heat capacity, volumetric thermal expansion coefficient and thermal conductivity of the lining holders 12, 22 varies from one segment to the next, each of these parameters increasing by at least 10 % over the length of the brake shoe 1, 2, from the leading segments S11, S21, to the trailing segments S12, S22 or S13, S23. To this end, the lining holders 12, 22 comprise varying material compositions in the various segments, wherein heat capacity, volumetric thermal expansion coefficient and thermal conductivity are tuned by changing the constituents or their concentration from one segment to the next.

[0066] In the case of FIG. 8, there are, in each brake shoe 1, 2, two segments S11, S12, S21, S22 provided in both the brake lining 11, 21 and the lining holder 12, 22. Varying heat capacity, volumetric thermal expansion coefficient and thermal conductivity are provided in both the brake linings 11, 21 and the lining holders 12, 22.

[0067] In the case of FIG. 9, there are, in each brake shoe 1, 2, three segments S11, S12, S13, S21, S22, S23 provided in both the brake lining 11, 21 and the lining holder 12, 22. Varying heat capacity, volumetric thermal expansion coefficient and thermal conductivity are provided in both the brake linings 11, 21 and the lining holders 12, 22.

[0068] FIG. 10 shows a pair of brake shoes 1, 2, wherein spatially varying thermal properties are provided in a lining holder 12, 22 of the brake shoes 1, 2, the lining holder 12, 22 comprising steel and/or cast iron. Therein, the heat capacity, volumetric thermal expansion coefficient and thermal conductivity of the lining holders 12, 22 increases by at least 10 % from the respective leading segments S11, S21 to the respective central segments S12, S22, and then increases again by at least 10%, to the respective trailing segments S13, S23. The linings 11, 21 may be provided with constant material properties throughout.