Progressive Spring Rate Isolator for Engine Vibration
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Solution Overview
Problem
Existing isolators fail to effectively isolate driven accessories from torsional vibrations and high torque transfer during key start events and in Belt-Assisted Start (BAS) drive systems, where traditional isolators do not perform optimally.
Innovation Solution
The isolator design includes a shaft adapter, a rotary drive member, and a torsion spring with a torque limiting surface, where the torsion spring has a varying spring rate based on angular movement, allowing for efficient vibration isolation and torque transfer management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional isolator with constant spring rate is used, then the structure is simple and easy to manufacture, but it cannot effectively isolate torsional vibrations during resonance and high torque transfer events
Solution Approach 1:
The isolator employs a progressive spring rate mechanism where the spring stiffness changes dynamically based on the angular displacement from neutral position. Within a selected angular range, the spring rate remains below a first threshold to provide soft isolation for normal vibrations. Beyond this range, the spring rate progressively increases above the first threshold to handle high torque events, achieving adaptive vibration isolation without complex active control systems.
Solution Approach 2:
The patent changes the physical parameter of spring rate from a constant value to a variable value that depends on angular position. By designing the torsion spring with specific geometric features (such as variable coil spacing or progressive unwinding characteristics), the spring rate transitions from a low value during normal operation to a progressively higher value during large angular excursions, effectively addressing both vibration isolation and high torque transfer requirements.
2Reliability
If a progressive spring rate isolator is implemented, then vibration isolation during resonance is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The torsion spring is designed with non-uniform geometric properties along its length. Specific portions of the spring (such as individual coils or sections) have different spacing, diameters, or cross-sectional areas to create the progressive spring rate effect. This local variation in geometry allows the spring to exhibit different stiffness characteristics in different regions of operation, achieving the desired progressive rate while maintaining manufacturability through focused precision requirements on critical sections only.
3Adaptability or versatility
If the isolator is designed for Belt-Assisted Start systems, then it can handle torque reversal and bidirectional operation, but the device complexity increases compared to unidirectional isolators
Solution Approach 1:
The isolator is designed to perform multiple functions within a single device structure. It provides vibration isolation during normal engine operation, handles torque reversal during Belt-Assisted Start events, and manages high torque transfer during key start events. The progressive spring rate mechanism and symmetric design allow the isolator to function effectively in both directions of torque application, eliminating the need for separate isolators for different operating modes.
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 isolator effectively isolates torsional vibrations and manages torque transfer efficiently during engine start and BAS operations, ensuring reliable performance and reduced wear.
Implementation Method 1
a torsion spring that is positioned to transfer torque between the shaft adapter and the rotary drive member
Implementation Method 2
The spacing between the torque limiting surface and each coil is selected such that, during operation, the torsion spring has a spring rate that is below a first spring rate during relative movement between the shaft adapter and the rotary drive member within a selected angular range from a neutral position, and has a spring rate that increases progressively above the first spring rate during relative movement between the shaft adapter and the rotary drive member beyond the selected angular range from the neutral position
Data Source
AI summary
In an non-limiting embodiment, an isolator is provided for isolating a device driven by an engine via an endless drive member. The isolator includes a shaft adapter that is connectable with a shaft of the device, a rotary drive member that is engageable with the endless drive member, a torsion spring that is positioned to transfer torque between the shaft adapter and the rotary drive member, and a torque limiting surface. The torsion spring has a first helical end, a second helical end and a plurality of coils between the first and second helical ends. The torque limiting surface has a selected non-zero spacing from the coils. The spacing between the torque limiting surface and each coil is selected such that, during operation, the torsion spring has a spring rate that is below a first spring rate during relative movement between the shaft adapter and the rotary drive member within a selected angular range from a neutral position, and has a spring rate that increases progressively above the first spring rate during relative movement between the shaft adapter and the rotary drive member beyond the selected angular range from the neutral position.