Master Cylinder Piston Rod Joint for Compact Pull-Out Resistance
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Solution Overview
Problem
Conventional master cylinders for hydraulic clutch actuation in vehicles face challenges in securely assembling and compactly designing the piston rod connection, particularly in handling tensile forces without damaging the connection, while avoiding space-consuming fastening methods like gluing or welding.
Innovation Solution
A master cylinder design featuring a form-fit connection between the piston rod and piston, where the piston rod has a ball head accommodated in a recess with an undercut insert part, which is secured by a snap-on connection, allowing direct transmission of compressive forces and reinforcement of the connection under tensile forces, with a stop end contacting the cylinder housing to prevent tensile forces from affecting the form-fitting connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an insert part with a combined force fit/positive fit connection is used to articulate the piston rod on the piston, then the connection can withstand compressive forces well, but the connection requires a certain axial space and may be damaged or loosened by tensile forces
Solution Approach 1:
The connection is segmented into two functional zones: the first region (undercut) handles compressive forces while the second region (stop end) handles tensile forces. This segmentation allows each region to be optimized for its specific force type, reducing the overall axial space required while maintaining strength against both compressive and tensile loads.
2Reliability
If the insert part protrudes with a stop end to contact the piston and keep tensile forces away from the positive connection, then the connection is protected from tensile damage, but the device requires more axial space
Solution Approach 1:
The connection geometry is designed to dynamically adapt to the applied load direction. Under compressive forces, the ball head contacts the first region; under tensile forces, the stop end contacts the piston. This dynamic load path selection protects the positive connection from tensile damage while minimizing the axial space required compared to a static design that would need to accommodate both force types simultaneously.
3Strength
If conventional fastening methods like gluing or welding are used to secure the piston rod, then the connection strength is increased, but the assembly complexity and space requirements increase
Solution Approach 1:
The patent replaces chemical (gluing) or thermal (welding) fastening methods with a purely mechanical solution using an undercut and stop end geometry. This mechanical interlocking system achieves comparable or superior connection strength while dramatically simplifying assembly - the insert part can be directly pressed into the piston recess without additional fastening steps, reducing both assembly complexity and space requirements.
Data Source
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AI summary
A master cylinder (10) has a cylinder housing (12) in which a piston (14) that can be moved between a piston rest position and a piston actuation position by means of a piston rod (18) variably delimits a pressure chamber (16). The ball head in the recess lies directly against the piston in a highly compact manner such that pressure forces (D) applied via the piston rod can be constantly transmitted directly to the piston. Furthermore, the formfitting connection is located between the undercut and the stop end of the insert part such that tensile forces (Z) applied via the piston rod reinforce the formfitting connection in a piston actuation position in order to ensure a high degree of pull-out reliability.