Adjustable Metering Servovalve Deformable Shim Design

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Solution Overview

Problem

Existing servovalves for fuel injectors face issues with rigid shims causing deformation and loosening of components, leading to inaccurate adjustments and reliability concerns due to machining tolerances and axial thrusts, which affect the precision and durability of the fuel metering system.

Innovation Solution

An adjustable metering servovalve using a deformable annular adjustment shim with elastic properties, allowing for precise adjustment of the armature travel and reducing the risk of deformation, combined with a balanced open/close element design to minimize axial loads and prevent loosening, utilizing a torque-screwed ring nut for stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If rigid adjustment shims are used to define armature travel, then adjustment precision is improved, but the polar surface of the core is damaged or deformed

Engineering Contradiction:

Improvearmature travel adjustment precisionVSAvoiddamage or deformation of polar surface

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent changes the material parameter of the adjustment shim from rigid to elastic. The elastic shim can be deformed elastically under compression to provide precise adjustment of the magnetic gap and armature travel, while its elastic nature prevents it from damaging the soft polar surface of the core, thus resolving the contradiction between adjustment precision and prevention of surface damage.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If rigid adjustment shims are used, then discrete variations of travel are obtained, but machining tolerances limit precision to 5 μm

Engineering Contradiction:

Improvediscrete variation capabilityVSAvoidtravel adjustment precision

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent makes the adjustment shim elastic rather than rigid, allowing it to be compressed to a desired thickness and maintain that dimension through elastic recovery. This dynamic elastic property enables continuous or finer adjustment of the magnetic gap, overcoming the discrete 5 μm limitation imposed by rigid shims and machining tolerances.

Inventive Principle:

Principle #15Dynamics

3Speed

If the armature travel is arrested against a fixed element, then promptness of response is optimized, but the rigid shim deforms the polar surface

Engineering Contradiction:

Improveresponse promptnessVSAvoiddeformation of polar surface

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent changes the material parameter of the arrest element from rigid to elastic. The elastic shim maintains the armature's arrested position against the core to optimize response promptness, while its elastic properties prevent permanent deformation of the polar surface, thus resolving the contradiction between speed and surface integrity.

Inventive Principle:

Principle #35Parameter changes

4Reliability

If high pre-loading spring force is used to overcome fuel pressure, then valve closing reliability is improved, but axial thrust increases causing loosening

Engineering Contradiction:

Improvevalve closing reliabilityVSAvoidaxial thrust

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

The patent introduces a balanced open/close element design that acts as an intermediary to distribute and balance the axial thrust forces. This design reduces the net axial thrust on the core and fastening components while maintaining sufficient spring force for reliable valve closing, thus preventing loosening due to vibrations and thermal gradients.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution provides high reliability and cost-effectiveness by enabling precise adjustment of the armature travel with reduced risk of deformation and loosening, ensuring accurate fuel metering and maintaining coaxiality with the sealing seat, even under thermal and mechanical stresses.

Implementation Method 1

the adjustment shim (48) is designed to undergo flexural or compressive elastic deformation but is of adequate stiffness

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Implementation Method 2

an electromagnet (15) designed to control a notched-disk armature (16)

Methodology Applied

Scientific EffectElectromagnetic actuation: Electromagnet

Implementation Method 3

a helical compression spring (22), pre-loaded so as to exert an action of thrust on the armature (16)

Methodology Applied

Scientific EffectSpring force: Spring

Data Source

PatentUS7458529B2Adjustable metering servovalve for a fuel injector

Publication Date: 2008.12.02 CENTRO RICERCHE FIAT SCPA

AI summary

The metering servovalve (7) comprises a valve body (8, 30), an open/close element (45) and an electromagnet (15), and is housed in a casing (2) of the injector (1). The electromagnet (15) actuates a mobile armature (16) for a travel defined by a polar surface (19) of the core (18) of the electromagnet (15). This latter is fixed in the casing (2) by means of a threaded ring nut (40), with the interposition of at least one deformable adjustment shim (48). The ring nut (40) is screwed with a pre-set tightening torque on a thread (46) of the casing (2) so as to bring about an elastic deformation of the adjustment shim (48) and to prevent accidental unscrewing of the ring nut (40). The adjustment shim (48) is constituted by a metal ring with a cross section having a shape chosen between L, C, S, Z, and Σ.