Split Ring Planetary Drive Travel End Stop
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Solution Overview
Problem
In variable cam timing systems, particularly in electric phasers, stopping the travel of planetary gears relative to each other can cause binding, and existing solutions struggle to effectively limit the carrier travel to prevent over-rotation, which can lead to torque issues and inefficient engine control.
Innovation Solution
A split ring planetary drive system with a travel end stop mechanism, such as a deadbolt, snap ring, pivoting pawl, or linear acting pin, that engages and disengages with the planet carrier to precisely control the rotation, allowing for accurate phase adjustments between the camshaft and crankshaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the travel of the planetary drive is limited by stopping one ring gear relative to the other, then the phase angle adjustment is achieved, but the planet gears bind due to over-running
Solution Approach 1:
A travel end stop is introduced as an intermediary component between the planet carrier and the first ring gear. This end stop acts as a mediator that selectively engages to prevent over-travel of the planet carrier while allowing free rotation during normal operation, thus avoiding direct binding between the ring gears and planet gears.
Solution Approach 2:
The travel end stop is designed to be dynamically engageable and disengageable based on the position of the planet carrier. It transitions between a non-engaged state during normal rotation and an engaged state when the carrier reaches the predetermined travel limit, providing dynamic control rather than static constraint.
2Ease of operation
If the carrier travel is limited to stop phaser travel at specific stops, then the phase adjustment is controlled, but the carrier rotation is restricted which affects phaser travel
Solution Approach 1:
The travel end stop provides partial limitation of carrier travel by allowing the carrier to rotate freely during most of the phaser operation and only intervening when the predetermined travel limit is reached. This partial action achieves the necessary phase control without excessively restricting carrier rotation throughout the entire operation.
3Reliability
If the motor torque is increased to prevent planet gear binding, then the gear binding is resolved, but the motor size and complexity increase
Solution Approach 1:
The travel end stop serves as a mechanical intermediary that prevents planet gear binding by limiting carrier over-travel, eliminating the need to increase motor torque. This mechanical intervention is simpler and more reliable than relying on increased motor power to prevent binding.
Data Source
AI summary
A split ring planetary drive with at least one travel end stop received in at least one pocket of a first ring gear. The travel end stop is moveable between a first stop position in which as the planetary drive rotates in a direction the travel end stop engages the stop on the planet carrier, preventing further rotation of the split ring planetary drive in the direction, and a second position in which the travel end stop does not engage the stop on the planet carrier. The travel end stop may be a deadbolt, a snap ring or pivoting pawl.