Hydraulic Auto-Tensioner Leak Gap Design for Idling Stop Stability
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Solution Overview
Problem
In idling stop vehicles, existing auto-tensioners cause excessive retraction of the cylinder and rod when the engine is restarted, leading to belt slippage and unstable engine starts due to the design's inability to manage the change in pulley configuration effectively.
Innovation Solution
The auto-tensioner employs a specific leak gap size that provides a leak down time of 0.65 seconds/mm or more under a 980 N load, utilizing viscous resistance to prevent excessive retraction and maintain stable belt tension, eliminating the need for a solenoid and reducing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the auto-tensioner uses a standard leak gap design, then the structure is simple and manufacturing is easy, but the cylinder and rod retract excessively when the engine is restarted after idling stop, causing belt slippage
Solution Approach 1:
The patent applies parameter changes by optimizing the leak gap dimensions to achieve a specific leak down time (0.65 seconds/mm or more under 980 N load). This parameter adjustment allows the hydraulic oil's viscous resistance to buffer excessive retraction forces during engine restart, preventing belt slippage while maintaining the simple structure of the auto-tensioner without requiring additional components like solenoids.
2Reliability
If the leak gap is made smaller to increase viscous resistance, then excessive retraction is prevented, but the manufacturing precision requirements increase and production becomes more difficult
Solution Approach 1:
The patent applies self-service by designing the leak gap to automatically provide the required viscous resistance through the natural properties of hydraulic oil. The optimized leak gap dimensions enable the system to self-regulate the retraction speed during engine restart without requiring external control mechanisms, achieving reliable belt tension stability while keeping manufacturing requirements reasonable.
3Reliability
If the solenoid is added to control the check valve, then excessive retraction can be prevented, but the manufacturing cost increases
Solution Approach 1:
The patent applies taking out by removing the solenoid component from the auto-tensioner system. Instead of using an active control mechanism, the invention extracts the control function and achieves it passively through optimized leak gap dimensions that utilize the viscous resistance of hydraulic oil to prevent excessive retraction during engine restart, thereby reducing manufacturing cost while maintaining engine start stability.
4Reliability
If the leak down time is increased to buffer retraction forces, then belt slippage is prevented, but the response time of the auto-tensioner to belt tension changes is reduced
Solution Approach 1:
The patent applies dynamics by optimizing the leak gap dimensions to achieve a balanced leak down time that provides sufficient viscous resistance during engine restart (preventing belt slippage) while maintaining adequate response speed for normal belt tension adjustments. The dynamic characteristic of the hydraulic oil flowing through the optimized leak gap allows the system to adapt to different operational conditions.
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 configuration ensures a stable engine start by preventing belt slippage and maintaining tension pulley position, while simplifying the auto-tensioner's structure and reducing manufacturing costs.
Implementation Method 1
the pushing-in force is buffered by hydraulic damping caused by viscous resistance of the hydraulic oil passing through the leak gap
Data Source
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AI summary
The object is to provide a hydraulic auto-tensioner which can stably start the engine of an idling stop vehicle and which can be manufactured at a low cost. A hydraulic auto-tensioner comprising a cylinder 17 filled with hydraulic oil therein, a rod 21 inserted in the cylinder 17, a plunger 22 provided at the bottom end of the rod 21, slidably fit in the inner diameter face of the cylinder 17, defining a leak gap 24 therebetween, defining a pressure chamber 25 therebelow and a reservoir chamber 26 thereabove and formed with a path 28 communicating the pressure chamber 25 with the reservoir chamber 26, the path 28 being provided with a check valve that closes the path 28 when the pressure in the pressure chamber 25 exceeds the pressure in the reservoir chamber 26, and a return spring 31 provided outside the cylinder 17 and biasing the cylinder 17 and the rod 21 in extending direction, wherein the size of the leak gap (24) is determined such that the leak down time when a load of 980 N is applied to the plunger (22) is 0.65 seconds/mm or over.