Piezoelectric Rail Load Sensor for High-Frequency Detection

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Solution Overview

Problem

Existing rail load sensors are inaccurate due to temperature dependence and aging of elastic materials, and they fail to detect high rail loads and dynamic components with sufficient temporal resolution, requiring frequent replacements and higher costs.

Innovation Solution

A device using piezoelectric sensor elements that generate electric polarization charges proportional to the rail load, providing high accuracy and temperature independence, with a form-fit and force-fit connection for low-cost mounting and a service life matching that of the rail.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If elastic mass is used in the load sensor, then the sensor can detect rail load through deformation, but the elasticity strongly depends on temperature and ages rapidly leading to inaccuracy

Engineering Contradiction:

Improverail load detection accuracyVSAvoidtemperature dependence and aging

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces the mechanical elastic mass with a piezoelectric sensor element that converts mechanical stress directly into electrical signals. This substitution eliminates the temperature-dependent elastic deformation mechanism while maintaining the ability to detect rail load, thereby resolving the contradiction between measurement capability and environmental stability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention changes the detection parameter from mechanical deformation (which is temperature-sensitive) to piezoelectric charge generation (which is temperature-independent). By measuring the electrical charge produced by the piezoelectric element under stress rather than mechanical displacement, the system achieves accurate rail load detection without temperature dependence or aging effects.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If conventional load sensor is used, then it can detect rail load, but it fails to detect high rail loads up to 250 kN with sufficient temporal resolution

Engineering Contradiction:

Improvetemporal resolution of dynamic componentVSAvoiddetectable rail load magnitude

Core Design Contradiction:

Measurement precisionVSForce

Solution Approach 1:

The piezoelectric sensor element directly converts high mechanical forces into proportional electrical charges, enabling detection of forces up to 250 kN. The electrical signal generation mechanism has inherently higher temporal resolution compared to mechanical deformation measurement, allowing accurate capture of dynamic load components at high frequencies.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Duration of action of stationary object

If adhesive-mounted strain gauges are used, then they can detect rail load, but they require frequent replacement due to adhesive life cycle being less than rail service life

Engineering Contradiction:

Improveservice lifeVSAvoidadhesive durability

Core Design Contradiction:

Duration of action of stationary objectVSReliability

Solution Approach 1:

The patent replaces adhesive-mounted strain gauges with a piezoelectric sensor element that is mechanically integrated into the rail structure through a form-fit connection. This mechanical integration eliminates the adhesive layer, ensuring the sensor's service life matches the rail's service life of at least ten years without requiring replacement.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Reliability

If load sensor requires frequent replacement, then it may maintain functionality, but it increases cost and downtime

Engineering Contradiction:

Improvecontinuous operationVSAvoidreplacement frequency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

By replacing adhesive-mounted components with mechanically integrated piezoelectric sensors, the invention eliminates the need for frequent replacements. The form-fit connection ensures permanent installation that matches the rail's service life, thereby maintaining continuous operation without downtime associated with sensor replacement.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 device accurately detects both static and dynamic rail loads with high temporal resolution up to 100 kHz, maintaining accuracy and durability over a wide temperature range and extended service life, while being cost-effectively mounted on existing rails.

Implementation Method 1

said sensor comprises at least one piezoelectric sensor element, said piezoelectric sensor element generating electric polarization charges as the load signal

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11933687B2Device for detecting a rail load and method for mounting such device in a rail

Publication Date: 2024.03.19 KISTLER HLDG AG

AI summary

A device for detecting a rail load fits into a bore of a rail and includes a sensor that generates a load signal under an action of the rail load caused when rail vehicles with wheels travel on the rail and the wheels exert a load onto the rail. The load signal is a measure for the rail load. The sensor includes at least one piezoelectric sensor element that generates electric polarization charges as the load signal.