Force Sensor for Tractor Hitch Control with Conical Stress Distribution
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Solution Overview
Problem
Existing force sensors in electrohydraulic control systems face challenges with vibration susceptibility and non-linear signal output due to clamping methods, and require improved fatigue strength and sensitivity for sustained operation.
Innovation Solution
A force sensor design featuring a cylindrical part with a central force introduction section, conical sections for stress distribution, and a rigid measuring rod with a conical shape and shoulders for secure fitting, combined with a Hall sensor and evaluation electronics for accurate signal conversion and protection, optimized through finite element simulation and NC machine production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the measuring rod is clamped in on one side, then the device complexity is reduced, but the measuring rod becomes susceptible to vibrations and the fatigue strength decreases
Solution Approach 1:
The cylindrical housing is divided into three functional sections: a first abutment section, a second abutment section, and a force introduction section between them. The measuring rod is clamped between the two abutment sections, creating segmented support points that reduce vibration susceptibility while maintaining structural integrity.
Solution Approach 2:
The conical sections with decreasing wall thickness are designed to distribute stresses beforehand, preventing stress concentration at the clamping locations. This prior stress distribution cushioning increases the fatigue strength of the measuring rod and housing structure.
2Reliability
If the measuring rod is clamped in on both sides, then the vibration susceptibility is reduced, but the output signal becomes highly nonlinear
Solution Approach 1:
The cylindrical housing has non-uniform wall thickness with conical sections that create local quality variations. The wall thickness decreases toward the force introduction section, optimizing the stress distribution and deformation characteristics to achieve linear signal output while maintaining vibration resistance.
Solution Approach 2:
The wall thickness parameter of the cylindrical housing is varied axially, creating conical sections with decreasing thickness. This parameter change optimizes the mechanical properties to achieve both vibration resistance and linear signal output simultaneously.
3Measurement precision
If a taper is provided on the outer cylindrical housing, then the rotationally symmetrical taper reduces resistance torque and increases sensitivity, but the shape is not optimal for stress distribution
Solution Approach 1:
The wall thickness parameter is changed axially to create conical sections with decreasing thickness toward the force introduction section. This optimized parameter variation achieves better stress distribution and fatigue strength while maintaining the sensitivity benefits of the tapered shape.
Solution Approach 2:
The design transitions from a simple rotational taper to a more complex three-dimensional shape with varying wall thickness in the axial direction. This dimensional complexity allows simultaneous optimization of sensitivity and fatigue strength.
4Force
If the force introduction section is made solid and non-deformable, then the force application is improved, but the overall deformation of the sensor is reduced
Solution Approach 1:
The cylindrical housing has different local qualities: the abutment sections have greater wall thickness for force application and support, while the force introduction section has decreased wall thickness to allow controlled deformation for measurement. This local quality variation resolves the contradiction between force application and measurable deformation.
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 enhances resonant frequency, reduces signal interference, increases fatigue strength, and achieves a linear output signal with high sensitivity and reproducibility, allowing for efficient integration into higher-order control systems.
Implementation Method 1
A Hall sensor detects a position change of the measuring rod in relation to a plane radial to the longitudinal axis of the cylindrical sleeve
Implementation Method 2
the measuring principle of the detection of the position as a result of a change in the air gap of a measuring coil through which alternating current flows
Implementation Method 3
The deformation of the cylindrical sleeve follows the bending line according to the mechanical bending of a double-mounted flat beam as a result of a single force acting in the center
Data Source
AI summary
A force sensor is suitable for an electrohydraulic hitch control system of an agricultural tractor. The force sensor has an outer cylindrical part with a bore and a measuring rod fixed on one side in the bore. A central section of the cylindrical part is provided as force introduction section. Two outer sections of the cylinder part are removed equally far axially from the center of the force introduction section and are provided as abutment sections. The measuring rod is clamped in an area of the force introduction section.