Shock Absorber Damping Piston for Constant End-Stroke Braking
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Solution Overview
Problem
Existing shock absorbers with progressive damping characteristics experience jerky braking due to high velocity forces, leading to unpredictable vehicle handling and the risk of uneven wheel adhesion, and often require precise tolerances to avoid locking issues.
Innovation Solution
A shock absorber design featuring a damping medium-filled damping cylinder with a main piston and a damping piston that generates a substantially constant counter-force throughout the stroke by using flow limiters to minimize pressure drop variations, allowing radial movement and reducing leakage flow, thus avoiding a geometrically over-defined system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a second piston with a shim stack is used to create progressive damping, then the damping force increases with velocity, but the braking becomes jerky and vehicle handling becomes unpredictable
Solution Approach 1:
The invention changes the parameter relationship between damping force and velocity from a progressive (increasing) relationship to a substantially constant relationship. This is achieved by designing the second piston with a specific geometry where the opening area of the flow limiters is substantially equal to the cross-sectional area of the piston rod, causing the pressure drop across the piston to remain constant throughout the stroke, thereby providing predictable damping force.
Solution Approach 2:
The invention uses a second piston with outside diameter smaller than the inside diameter of the cup, creating a deliberate gap that allows controlled leakage flow. This partial engagement design prevents the geometrically over-defined system from locking while still providing the desired damping effect without excessive force variations.
2Reliability
If the second piston outside diameter is significantly smaller than the cup inside diameter to avoid locking, then the system avoids geometric over-definition, but leakage flow reduces the braking function and creates progressive damping characteristics
Solution Approach 1:
The invention optimizes the parameter relationship between the second piston outside diameter and cup inside diameter. Rather than making the piston significantly smaller, the invention uses a specific size relationship where the piston outside diameter is smaller than the cup inside diameter but not excessively so, and combines this with specific flow limiter geometry to achieve constant pressure drop, thereby maintaining effective braking function while preventing locking.
3Force
If a shim stack is used to create progressive damping, then the damping force increases with velocity, but the force increases sharply per unit time when the second piston engages at high velocity
Solution Approach 1:
The invention fundamentally changes the force-velocity parameter relationship from progressive to constant. By designing the flow limiters with opening areas substantially equal to the piston rod cross-sectional area, the pressure drop across the second piston remains constant throughout the stroke, eliminating the sharp force increases that occur with velocity in conventional progressive damping systems.
4Force
If the second piston has outside diameter equal to cup inside diameter for precise control, then the braking function is maximized, but the system becomes geometrically over-defined and may lock or require extremely precise tolerances
Solution Approach 1:
The invention deliberately uses a second piston with outside diameter smaller than the cup inside diameter, creating a controlled gap rather than a tight fit. This partial engagement approach prevents the system from becoming geometrically over-defined, eliminating locking issues and reducing tolerance requirements while maintaining effective braking function through the controlled leakage flow and flow limiter geometry.
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
The design provides gentle braking at the limit position, maintaining a consistent damping force with velocity changes, enhancing vehicle handling and stability without the need for precise tolerances, and minimizing the risk of bottoming.
Implementation Method 1
The through-ducts are defined in a direction of flow by flow limiters, which produce a restriction of the damping medium flow
Implementation Method 2
the restriction of the damping medium flow varies minimally with increased flow, that is to say it produces low lifting heights of the first flow limiter even in the case of relatively large flows. This results in small variations in the pressure drop over the first flow limiters as the flow varies
Implementation Method 3
The opening force is generated when the pressure in the cup acts on the opening area of the shim stack
Implementation Method 4
a damping medium-filled damping cylinder divided into two damping chambers
Data Source
Figure 1a~1b
Figure 2a~2d
Figure 3a~3c
AI summary
The invention relates to an arrangement in a vehicle shock absorber (1) for generating an additional counter-force (F2) acting counter to the direction of movement in the limit position (s) (R1) of a movement /stroke between the parts (4, 2) of the shock absorber moving relative to one another, and to a shock absorber (1) comprising such an arrangement. The shock absorber in both cases substantially comprises a damping medium-filled damping cylinder (2), divided into two damping chambers (Cl, C2 ), by a main piston (5), axially moveable relative to the damping cylinder (2) and attached to a piston rod (4). Also arranged around the piston rod (4) is a second piston/damping piston (5), which contains one or more first and second through-ducts (9, 10), which are defined by first and second flow-limiting devices (11, 12), preferably consisting of multiple thin first washers. The damping piston (5) is intended to slide in a restricting space (6) located in the damping cylinder (2), and having an inside diameter smaller than the inside diameter of the damping cylinder. The additional counter- force counter (F2) is substantially constant throughout the entire stroke in order to create gentle braking of the damping movement.