Flat Spiral Spring Tensioner With Wind-Up Limiting for Stable Belt Load
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Solution Overview
Problem
Existing belt tensioning systems with coil springs can experience excessive winding, leading to instability in the entrained transmission body due to a temporary drop in biasing force when a large load is applied, resulting in excessive slack.
Innovation Solution
A tensioner design featuring a movable section supported by a fixed section, a flat spiral spring with varying inter-plate friction forces, and a wind-up limiting section to prevent excessive winding, including a resistance force imparting section to counter radial contraction of the spring, ensuring stable operation by absorbing and attenuating vibrations through hysteresis characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the flat spiral spring is allowed to wind-up freely to absorb large loads, then the biasing force can be maintained, but the spring may wind-up excessively causing instability in the entrained transmission body
Solution Approach 1:
A wind-up limiting section is introduced as an intermediary component between the flat spiral spring and the movable section. This limiting section acts as a mediator that allows the spring to wind-up within safe limits while preventing excessive winding-up that would cause instability. The limiting section translates the spring's winding motion into linear displacement of the movable section, thereby controlling the spring's rotation while maintaining system stability.
Solution Approach 2:
The wind-up limiting section预先 (in advance) prevents the harmful effect of excessive winding-up by imposing a mechanical constraint before the spring can reach an unstable state. The limiting section is designed with a maximum wind-up angle that stops the spring from rotating beyond the safe threshold, thereby preemptively avoiding the instability problem before it occurs.
2Loss of energy
If the inter-plate friction force is increased to improve hysteresis characteristics, then energy absorption is enhanced, but the spring may not unwind properly under large biasing forces
Solution Approach 1:
The flat spiral spring is designed with non-uniform plate thickness, creating local quality variations along its structure. The plate thickness is greater at the inner radius and decreases toward the outer radius. This local variation in thickness creates different inter-plate friction forces at different radial positions, allowing the spring to maintain high hysteresis for energy absorption while ensuring sufficient biasing force transmission when needed.
Solution Approach 2:
The inter-plate friction force is controlled by changing the physical parameter of plate thickness distribution. By varying the thickness parameter radially, the friction characteristics are adjusted to achieve optimal balance between energy absorption (hysteresis) and force transmission capability. The friction-reducing polymer coating further modifies the friction parameter to prevent excessive resistance during unwinding.
3Reliability
If the coil spring is made stiffer to maintain tension, then the entrained transmission body remains stable, but vibrations cannot be effectively buffered
Solution Approach 1:
The flat spiral spring is designed to operate dynamically within a controlled range of motion. The wind-up limiting section allows the spring to dynamically adjust its winding angle based on the applied load, enabling the system to maintain stability through controlled deformation rather than rigid stiffness. The spring's dynamic response to varying loads provides both tension maintenance and vibration buffering.
Solution Approach 2:
The flat spiral spring with its hysteresis characteristics provides beforehand cushioning by absorbing vibrational energy through internal friction during normal operation. The non-uniform plate thickness creates progressive resistance to deformation, cushioning vibrations before they can propagate through the system while still maintaining adequate tension.
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 prevents instability in the entrained transmission body by managing the winding of the flat spiral spring, maintaining tension and reducing mechanical losses, thereby improving fuel efficiency and preventing abnormal shapes and noise.
Implementation Method 1
energy can be absorbed and attenuated by hysteresis characteristics due to the difference between the inter-plate friction force of the flat spiral spring in an unwind direction and a wind-up direction
Implementation Method 2
a flat spiral spring biasing the movable section so as to resist the tension member, the flat spiral spring unwinding in a state in which there is a small inter-plate friction force
Data Source
AI summary
A tensioner includes a movable section, a fixed section, a flat spiral spring, and a back-up spring. The movable section receives load from an entrained transmission body through a tension member. The fixed section supports the movable section so as to be capable of displacing. The flat spiral spring biases the movable section so as to resist the tension member. The flat spiral spring unwinds in a state in which there is a small inter-plate friction force in cases in which there is a large biasing force applied to the tension member to counter load acting from the tension member. The flat spiral spring winds-up in a state in which there is a large inter-plate friction force in cases in which there is a small biasing force applied to the tension member to counter load acting from the tension member. The back-up spring limits wind-up of the flat spiral spring.