Series-Spring Isolator With Direction-Dependent Friction Damping
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Solution Overview
Problem
Existing isolators for engine accessory drives struggle to provide adequate damping in certain situations while minimizing damping in others, and they often have limited travel range which can be insufficient in some operating conditions.
Innovation Solution
The isolation device incorporates a dual helical compression spring arrangement with different spring rates and lengths, allowing for adjustable damping and travel range by sliding the springs along a friction surface during torque transfer, thereby generating varying frictional damping torques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frictional damping is provided in the isolator, then resonance is inhibited, but the isolator's primary function of reducing natural frequency is negatively affected
Solution Approach 1:
The isolator employs a dual-spring arrangement where springs can slide relative to each other along friction surfaces. This dynamic configuration allows the system to adjust damping characteristics based on operating conditions. During resonance conditions, the springs slide and generate frictional damping torque to inhibit resonance. During normal operation, the springs maintain optimal positioning to preserve natural frequency reduction performance without excessive damping.
Solution Approach 2:
The system changes the effective damping parameter by varying the relative position of springs along friction surfaces. The spring positions are not fixed but can adjust during operation, changing the frictional contact characteristics. This parameter change allows the system to provide high damping when needed (during resonance) and low damping during normal operation, resolving the contradiction between resonance inhibition and performance maintenance.
2Reliability
If increased damping is provided in the isolator, then resonance is better controlled, but damping cannot be maintained at high levels during all operating conditions
Solution Approach 1:
The dual-spring arrangement with friction surfaces creates a dynamic damping system. The springs can slide relative to each other, and their relative position changes based on the direction and magnitude of torque transfer. This dynamic behavior provides high damping during resonance conditions when springs engage friction surfaces, and reduced damping during normal operation, achieving adaptability across different operating conditions.
Solution Approach 2:
The isolator exhibits periodic engagement and disengagement of frictional damping during torque transfer cycles. As torque direction reverses during engine operation, the springs alternately engage and disengage from friction surfaces, providing periodic damping action. This periodic action ensures damping is available when resonance occurs while allowing low-damping operation during normal cycles, achieving both resonance control and adaptability.
3Productivity
If the isolator is designed with maximum travel, then it can accommodate large torque variations, but it requires larger space and may not be needed in all situations
Solution Approach 1:
The dual-spring arrangement allows one spring to be nested within or alongside the other spring. When the isolator experiences small torque variations, only one spring is actively engaged, providing the necessary travel. When large torque variations occur, both springs engage sequentially, effectively increasing the total travel capacity without requiring a proportionally larger overall structure. This nested configuration accommodates both small and large torque variations efficiently.
Solution Approach 2:
The isolation function is segmented into two separate spring elements working in series. Each spring can independently engage and disengage based on torque requirements. This segmentation allows the system to provide maximum travel when needed by engaging both springs, while maintaining a compact size by allowing one spring to remain inactive or nested during low-torque conditions, reducing the effective volume required.
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
This solution allows for increased damping in specific situations without constant high damping, and provides greater travel range when needed, effectively managing torque transfer and reducing resonance in engine accessory drives.
Implementation Method 1
Each of the first and second isolation springs is a helical compression spring having a length
Implementation Method 2
the first isolation spring transfers torque from the second isolation spring into a first one of the hub and the pulley and the second isolation spring transfers torque from the first isolation spring into a second one of the hub and the pulley
Data Source
AI summary
In one aspect, there is provided an isolation device, which includes a hub, a pulley and at least one isolation spring arrangement including first and second springs in series. The first spring rate is higher than the second spring rate. Initially during torque transfer from the first one to a second one of the hub and the pulley, the entire first isolation spring is slid along a friction surface towards the second one of the hub and the pulley during compression of the second isolation spring thereby generating a first frictional damping torque. During torque transfer the other way, at least a portion of the first isolation spring remains stationary relative to the friction surface, such that the first frictional damping torque is greater than the second frictional damping torque.