Drum Brake Shoe Overlap Structure for Cam Load Distribution
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Solution Overview
Problem
Cam-actuated vehicle drum brakes experience increased stresses and potential component failure due to twisting forces from cams, leading to reduced operational reliability and service life, especially in commercial vehicles where wheel brake cylinders are not present to distribute these forces.
Innovation Solution
The brake shoe design incorporates a web plate with a projection that covers and is supported by the lining plate's end face, creating an overlapping area to distribute forces from the cam, reducing material stress and preventing failure by keeping stresses within the elastic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cam-operated drum brakes are used in commercial vehicles, then robust design and low susceptibility to failure are achieved, but increased stress on brake shoes occurs due to shear forces from cam rotation
Solution Approach 1:
The brake shoe is divided into two separate plates: a lining plate that carries the brake lining and a web plate that receives the cam force. This segmentation allows each component to be optimized for its specific function, with the web plate designed to handle the shear forces from cam rotation independently from the lining plate.
Solution Approach 2:
A projection is added to the web plate that acts as an intermediary element, extending into the lining plate to create an overlapping area. This projection serves as a force transfer mechanism that distributes the cam-induced shear forces across the overlapping region, preventing stress concentration at the cam-side end section.
2Productivity
If cam rotation generates shear forces on brake shoes, then braking function is achieved, but component failure risk increases due to excessive material stress
Solution Approach 1:
The force transfer is extended from a single-point contact at the cam-side end section into a distributed area through the projection overlapping the lining plate. This dimensional extension from point to area allows the shear forces to be distributed across multiple material bonds, reducing the stress intensity at any single location.
Solution Approach 2:
The brake shoe combines two metal plates (lining plate and web plate) with different functional requirements into a composite structure. The web plate is optimized for mechanical strength to withstand cam forces, while the lining plate is optimized for friction characteristics. The projection creates a composite joint that leverages the strengths of both materials.
3Strength
If web plate and lining plate are connected by welding, then structural integrity is achieved, but manufacturing complexity and potential weak points increase
Solution Approach 1:
The projection is designed to create an overlapping area that pre-distributes the forces before they reach the connection points between the web plate and lining plate. This preliminary force distribution reduces the stress demands on the welding joints, allowing for simpler welding procedures and fewer critical weld points while maintaining structural integrity.
Data Source
Figure 1
Figure 2~2a
Figure 3~3a
AI summary
A brake shoe of a cam-operated vehicle drum brake, comprising a lining plate (1) which is semicircularly curved and carries a brake lining on an outer side, comprising a web plate (2) which is arranged on an inner side of the lining plate (1) and is connected to it, wherein in a main section lining plate (1) and web plate (2) form a T-section, wherein the brake shoe has a bearing-side end section with which the brake shoe is supported on a bearing bolt and wherein the brake shoe has a cam-side end section onto which a pressure force can be applied by a brake cam. The web plate (2) has a projection at the cam-side end section, which covers a cam-side end face (1.3) of the covering plate (1) at least partially in an overlapping surface (7) and is supported on the overlapping surface (7) on the cam-side end face (1.3) of the covering plate (1).