Piston-Cylinder Assembly With Nested Trailing Pistons

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Solution Overview

Problem

Conventional piston-cylinder assemblies for automatic transmission have an unnecessarily large axial length due to the radial protrusion of the main piston and the trailing piston thrust piece, which obstructs each other, limiting the compactness of the design.

Innovation Solution

The main piston and trailing pistons are adapted with geometrically matched recesses and thrust portions, allowing the trailing pistons to overlap axially within the main piston web, reducing the overall axial length by incorporating alternating arcuate thrust segments and pocket-shaped recesses, and utilizing a travel limiter to limit axial travel.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the main piston has a radial protrusion (piston web) and the trailing piston has a thrust portion, then the trailing piston can carry along the main piston in axial direction, but the axial length of the assembly becomes unnecessarily large due to the protrusion and thrust piece obstructing each other

Engineering Contradiction:

Improvetrailing piston carrying along main pistonVSAvoidaxial length of piston-cylinder assembly

Core Design Contradiction:

Ease of operationVSLength of moving object

Solution Approach 1:

The trailing piston is nested within the main piston by allowing the thrust portion of the trailing piston to dip into an axial recess of the piston web. This nesting arrangement enables the trailing piston to be partially contained within the radial protrusion of the main piston, significantly reducing the overall axial length of the assembly while maintaining the force transmission function.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

Instead of having the thrust portion of the trailing piston abut against the outer face of the piston web, the design inverts the arrangement by creating a recess in the piston web that accepts the thrust portion. This inversion allows the thrust portions to engage within the radial protrusion rather than from the outside, reducing axial length.

Inventive Principle:

Principle #13The other way round (Inversion)

2Length of moving object

If alternating arcuate thrust segments and pocket-shaped recesses are used, then compactness is improved, but manufacturing complexity increases

Engineering Contradiction:

Improveaxial length of assemblyVSAvoidmanufacturing of recesses and thrust segments

Core Design Contradiction:

Length of moving objectVSEase of manufacture

Solution Approach 1:

The thrust portions and recesses are segmented into alternating arcuate thrust segments and pocket-shaped recesses around the circumference of the main piston. This segmentation allows for compact radial arrangement while maintaining manufacturability through standard machining operations. The segmented design enables the trailing piston to engage at multiple points around the circumference, distributing loads and simplifying the engagement geometry.

Inventive Principle:

Principle #1Segmentation

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 design significantly reduces the overall axial length of the piston-cylinder assembly, saving material and weight, while maintaining functionality as a transmission actuator in automatic transmissions.

Implementation Method 1

a pressurized fluid can be applied to the main piston on both sides and to the trailing piston on one side

Methodology Applied

Scientific EffectFluid pressure: Pressure Increase

Implementation Method 2

the at least one trailing piston dragging along with the main piston by means of the thrust portion

Methodology Applied

Scientific EffectMechanical force transmission: Mechanical Force

Implementation Method 3

a travel limiter for limiting an axial travel range of the at least one trailing piston being arranged or formed on the cylindrical housing

Methodology Applied

Scientific EffectMechanical constraint: Physical Containment

Data Source

PatentUS11333242B2Piston-cylinder assembly

Publication Date: 2022.05.17 ZF CV SYST EURO BV

AI summary

A piston-cylinder assembly (1) has a cylindrical housing (3), with a main piston (2) and at least one trailing piston (11, 12). The trailing piston (11, 12) is axially guided on a cylindrical outer lateral face (38) of the main piston (2). The trailing piston (11, 12) has a thrust portion (13, 14) at one end near a piston web on the main piston, The thrust portion extends axially inward toward the piston web (10) A travel limiter (28) on the cylindrical housing limits a travel range of the trailing piston (11, 12) Under pressure, the trailing piston (11, 12) follows the main piston (2) until the trailing piston (11, 12) hits the travel limiter (28). The thrust portion (13, 14) of the trailing piston (11, 12) is shaped to fit into an associated recess (30, 31) in the piston web with a positive lock.