Glow Plug Load Sensing Sleeve for Cylinder Pressure Measurement
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Solution Overview
Problem
Existing glow plugs with integrated load sensors face challenges such as exposure to high combustion chamber temperatures, mechanical interference, and complex assembly issues, leading to unreliable pressure measurements and compatibility problems with different engine types.
Innovation Solution
A glow plug design featuring a load sensing sleeve that extends around the peripheral metal tube of the heating rod, allowing axial translation and impermeability while minimizing thermal and mechanical interference, and enabling detection of shear stresses through axial compression and traction, thus improving sensitivity and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the load sensor is placed at the proximal extremity of the electrical power supply electrode outside the cylinder head, then radial space requirements are met, but measurement accuracy deteriorates due to deformation of the cylinder head and plug body
Solution Approach 1:
The load sensor is nested within the plug body structure, specifically positioned in the proximal zone of the receiving housing. The sensor is housed inside the plug body rather than outside, allowing it to be surrounded by the plug body structure which provides mechanical stability and reduces deformation effects during measurement.
Solution Approach 2:
A rigid connection element is introduced as an intermediary between the heating rod and the load sensor. This rigid element directly connects the distal extremity of the heating rod to the load sensor, eliminating the need for long kinematic linkages that would otherwise generate vibration modes and reduce measurement accuracy.
2Temperature
If the load sensor is housed inside the plug body, then thermal exposure to combustion chamber is reduced, but available space for sensor installation is reduced
Solution Approach 1:
The load sensor is oriented with its sensitive axis perpendicular to the principal axis of the heating rod. This dimensional reorientation allows the sensor to utilize radial space within the plug body rather than competing for axial space, effectively using a different spatial dimension to accommodate the sensor while maintaining thermal isolation.
Solution Approach 2:
The load sensor is nested within the proximal zone of the receiving housing, utilizing the internal volume of the plug body structure. The sensor is surrounded by the plug body which provides both thermal protection and structural support, efficiently using the available internal space.
3Reliability
If a rigid connection element directly connects the heating rod to the plug body, then vibration interference is reduced, but differential thermal expansion between materials increases
Solution Approach 1:
The rigid connection element is designed with specific dimensional parameters (length, cross-section) and material properties that are optimized to balance thermal expansion effects. The element's dimensions and material are selected to minimize the impact of differential thermal expansion while maintaining the rigidity needed for reliable signal transmission.
4Measurement precision
If the load sensor is positioned close to the heating rod for direct measurement, then measurement sensitivity is improved, but exposure to high temperatures and mechanical interference increases
Solution Approach 1:
The rigid connection element serves as a mediator that transmits mechanical forces from the heating rod to the load sensor while isolating the sensor from direct exposure to harmful conditions. The element acts as a force transmission medium that protects the sensor from thermal and mechanical interference while maintaining measurement sensitivity.
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 effectively isolates the load sensor from combustion chamber temperatures, reduces mechanical and thermal interference, and enhances sensitivity, enabling precise pressure measurement across various engine models and speeds, ensuring reliable operation and compatibility with both ceramic and metal heating rods.
Implementation Method 1
axial translation movements of the heating rod relative to the plug body generate axial compression and/or traction stresses in said load sensing sleeve
Implementation Method 2
a heating rod comprising a peripheral metal tube, and having an extremity, called the proximal extremity, which is equipped with an electrical power supply connection of the heating rod
Data Source
AI summary
A glow plug includes a heating rod (11), a plug body (13) having a receiving housing (14) of the heating rod, a mounting device (48) for mounting the heating rod, permitting axial translation movements of the heating rod relative to the plug body and ensuring impermeability between the heating rod and the plug body, a load sensing sleeve (17) which extends around the proximal portion (50) of the peripheral metal tube (59, 61) of the heating rod in the proximal zone (51) of the receiving housing, directly adjoining axially the mounting device (48) axially on the proximal side.