Variable Valve Timing Spool Reduces Hysteresis
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Solution Overview
Problem
Conventional variable valve timing devices experience unstable response characteristics due to high hysteresis and stick-slip phenomena caused by irregular sliding resistance, which affects the control valve's performance.
Innovation Solution
The design incorporates a biasing device with a movable member and resilient members that generate restoring forces, allowing the spool to move with reduced resistance by switching between summed and single restoring forces at boundary positions, thereby stabilizing the spool's movement and reducing hysteresis and stick-slip occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the movable member is supported from the radial outside by the sleeve, then the spool can move relative to the movable member without contact in the second region, but this causes small movement resistance and hysteresis that adversely affects response characteristic
Solution Approach 1:
The movable member acts as an intermediary between the spool and the sleeve. In the first region, the movable member engages with the spool to move together, providing controlled support. In the second region, the movable member rests on the sleeve while allowing the spool to move relative to it, reducing direct contact and movement resistance. This intermediary structure resolves the contradiction by providing support where needed while minimizing friction where motion is required.
2Stability of the object's composition
If the movable member engages with the spool in the first region, then the spool receives sliding resistance from the movable member contacting the sleeve, but this increases movement resistance and hysteresis
Solution Approach 1:
The system transitions from a static support structure to a dynamic one where the movable member can switch between two states: engaged with the spool in the first region to provide stability, and resting on the sleeve in the second region to reduce friction. This dynamic adaptability allows the system to optimize between stability and low resistance based on the operational region, resolving the contradiction.
3Force
If the second restoring force pushes the movable member axially, then the movable member may receive side force in the radial direction and be pushed onto the sleeve, but this increases sliding resistance and hysteresis
Solution Approach 1:
The support structure provides different qualities of support in different axial regions. In the first region, the movable member is supported to allow engagement with the spool and application of restoring forces. In the second region, the support configuration changes to allow the movable member to rest on the sleeve with minimal interference, reducing side forces and sliding resistance. This local differentiation resolves the contradiction between force application and response characteristic.
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 approach results in a variable valve timing device with improved stability and consistent response characteristics by minimizing hysteresis and stick-slip, enhancing the control valve's performance and reliability.
Implementation Method 1
The first resilient member generates a first restoring force that axially urges the spool in both the first region and the second region
Implementation Method 2
The second resilient member generates a second restoring force that axially urges the movable member in both the first region and the second region
Data Source
AI summary
A variable valve timing device includes a control valve for switching fluid communication among ports. The control valve includes a sleeve, a spool, a movable member, and resilient members. A first resilient member pushes the spool in both of the regions. A second resilient member acts on the spool via the movable member engaged with the spool in an advancing region. In a lock region, the movable member rests on the sleeve to enable the spool to move freely from the second resilient member. As a result, force acting on the spool can be restricted in the lock region. The movable member is supported from a radial inside by the spool and is radially distanced from the sleeve. As a result, it is possible to reduce a sliding resistance acting on the movable member.