Variable Camshaft Phaser with Wrap Spring Locking
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Solution Overview
Problem
Variable valve timing systems in internal combustion engines face challenges in preventing unwanted back-driving, which can lead to unplanned gear rotations and reduced engine performance due to torque pulses from intake and exhaust valves.
Innovation Solution
A variable camshaft timing phaser mechanism incorporating a sprocket, planetary gear assembly, and a wrap spring, where the wrap spring expands or contracts to lock the gear assembly, preventing relative rotation between the sprocket and camshaft during back-driving, thus maintaining the camshaft's angular position and preventing unwanted advancements or retardations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a planetary gear assembly is used to enable variable camshaft timing adjustment, then the ability to advance or retard valve timing is improved, but the risk of unwanted back-driving and unplanned gear rotations increases
Solution Approach 1:
The wrap spring, which experiences expansion exertion during back-driving, is utilized to generate a locking force that prevents unwanted gear rotations. The harmful back-driving torque is converted into a beneficial locking action through the wrap spring's expansion, which increases frictional forces to lock the planetary gear assembly and prevent unplanned camshaft rotation.
Solution Approach 2:
The wrap spring is pre-positioned and pre-loaded in the planetary gear assembly to be ready to engage when back-driving occurs. The spring is arranged to automatically expand and create locking friction forces before unwanted gear rotations can occur, preventing the instability issue before it manifests.
2Reliability
If the wrap spring is designed to expand during back-driving to prevent gear rotation, then reliability is improved, but frictional losses increase
Solution Approach 1:
The wrap spring's frictional locking force is dynamic rather than static - it remains engaged but flexible during normal operation, allowing minimal friction when the spring is not actively expanding. During back-driving, the spring dynamically expands to increase friction only when needed, then returns to a lower-friction state once the locking function is achieved, optimizing the balance between reliability and energy loss.
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 minimizes frictional losses and prevents unplanned gear rotations during back-driving, enhancing engine performance by maintaining the desired camshaft position and reducing the risk of unwanted valve timing adjustments.
Implementation Method 1
The wrap spring experiences expansion exertion and prevents relative rotation between the sprocket and the engine camshaft to preclude advancing or retarding engine valve opening and closing
Implementation Method 2
The wrap spring has a pair of ends and is interrelated with the sun gear in a way to cause abutment with one of the ends and expansion or contraction exertions of the wrap spring
Data Source
AI summary
An engine variable camshaft timing phaser (10) includes a sprocket (12) and a planetary gear assembly (14). The sprocket (12) receives rotational drive input from an engine crankshaft. The planetary gear assembly (14) includes two or more ring gears (26, 28), multiple planet gears (24), a sun gear (22), and a wrap spring (76). One of the ring gears (26, 28) receives rotational drive input from the sprocket (12) and one of the ring gears (26, 28) transmits rotational drive output to an engine camshaft. The sun gear (22) engages with the planet gears (24). The wrap spring (76) experiences expansion and contraction exertions to permit advancing and retarding engine valve opening and closing, and to prevent advancing and retarding engine valve opening and closing.