Tappet Guide Member Segmentation for Disc Brake Machining
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Solution Overview
Problem
Existing force transmission devices in air actuated disc brakes, such as those used in heavy vehicles, face challenges with complex and costly machining of trilobular surfaces, sealing issues, and high material costs due to complex shapes and corrosion concerns, particularly in the ELSA2 series brakes.
Innovation Solution
A force transmission device with a guide member and piston featuring a cylindrical sliding surface and anti-rotation formation, allowing simpler machining and sealing, along with a separate gear portion for rotary motion transmission, formed from lower strength materials, and a cover plate with journal bearings for improved manufacturing and sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If trilobular surfaces are used in the piston and guide member, then anti-rotation function is achieved, but machining complexity and cost increase
Solution Approach 1:
The anti-rotation formation is segmented into two separate components: a recess in the guide member and a complementary projection on the piston. This segmentation allows both components to be manufactured using simple cylindrical machining, eliminating the need for complex trilobular surface machining while maintaining the anti-rotation function through the interlocking recess-projection geometry.
2Stability of the object's composition
If trilobular surfaces are used in the piston, then anti-rotation function is achieved, but sealing cost increases
Solution Approach 1:
The sealing function is separated from the anti-rotation function. The piston features a simple cylindrical outer sliding surface that interfaces with a cylindrical guide form, allowing the use of conventional circular sealing elements. The anti-rotation function is achieved separately through the recess-projection formation, eliminating the need for expensive seals against trilobular surfaces.
3Strength
If the piston housing is formed from aluminium casting with trilobular machinings, then structural integrity is maintained, but manufacturing cost increases
Solution Approach 1:
The guide member is segmented into two functional zones: a cylindrical guide form for the piston sliding surface and a separate anti-rotation recess. This allows the guide member to be manufactured using simple cylindrical machining processes on aluminium casting, eliminating costly trilobular machinings while maintaining structural integrity through the reinforced recess-projection anti-rotation mechanism.
4Device complexity
If the piston housing acts as a cover plate for the rotor side, then component count is reduced, but corrosion resistance requires additional treatment
Solution Approach 1:
The piston housing is designed with differentiated local qualities: the inner surface featuring a cylindrical guide form with high precision for piston movement, and the outer rotor-side surface requiring corrosion resistance. This local quality differentiation allows targeted corrosion protection treatments only on the exposed outer surfaces, while the critical inner cylindrical surfaces maintain their precision machining without additional treatment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces manufacturing costs, simplifies the machining process, and enhances sealing efficiency while maintaining reliable operation and wear compensation in disc brake systems.
Implementation Method 1
a piston comprising a complementary generally cylindrical outer sliding surface slideable within the guide member
Implementation Method 2
an anti-rotation formation is provided between the guide member and the piston, the formation comprising a recess extending generally parallel to the first axis and a complementary projection
Implementation Method 3
arranged to cause the piston to extend to maintain a substantially constant running clearance in response to wear of the friction element
Data Source
Figure 1
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AI summary
A tappet comprising: a shaft portion for transmission of a thrust loading from an actuating member to a piston of a disc brake; and a gear portion for transmission of rotary motion to the shaft; wherein the gear portion is formed as a separate piece from the shaft portion.