Bi-directional Overrunning Clutch Indexing Mechanism
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Solution Overview
Problem
Existing four-wheel drive systems require manual engagement and disengagement of secondary drive shafts, lack efficient torque distribution, and suffer from issues like tire scrubbing and twitchiness during turns due to locking differentials, and require complex and costly hydraulic systems in limited slip differentials.
Innovation Solution
A bi-directional overrunning clutch assembly with an electromagnetic system that indexes a roll cage relative to a clutch housing, allowing for automatic engagement and disengagement of secondary driven shafts, providing four-wheel drive capability and engine braking, while maintaining independent half shaft operation for improved traction and cornering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a locking differential is used to transfer torque to both wheels, then traction is improved, but the half shafts cannot rotate at different speeds causing tire scrubbing and twitchiness during turns
Solution Approach 1:
The clutch assembly dynamically transitions between locked and unlocked states based on operational conditions. The roll cage can be indexed to different positions where it either constrains the hubs together (locked state for traction) or allows independent rotation (unlocked state for turning), resolving the contradiction between maintaining traction and allowing differential rotation during turns
2Reliability
If a hydraulic limited slip differential is used to transfer torque, then traction is improved, but the system complexity and cost increase due to expensive fluids and complex pumping systems
Solution Approach 1:
The patent replaces complex hydraulic systems with a mechanically-operated clutch assembly. The roll cage indexing mechanism uses mechanical components (springs, detents, cam surfaces) to achieve the same torque transfer function, eliminating the need for hydraulic fluids, pumps, and associated control systems while maintaining limited-slip differential functionality
3Device complexity
If manual engagement of secondary drive shafts is used, then system simplicity is maintained, but the vehicle must stop to engage/disengage causing loss of time and productivity
Solution Approach 1:
The clutch assembly is automatically engaged and disengaged based on vehicle operational conditions without requiring operator intervention. The indexing mechanism responds to torque demands and speed differentials, self-regulating the engagement state to maintain four-wheel drive capability when needed while allowing two-wheel drive operation when appropriate, eliminating the need to stop the vehicle for engagement changes
4Force
If the roll cage indexing mechanism uses friction members and spring pressure, then engagement force is improved, but the friction generates heat requiring auxiliary cooling
Solution Approach 1:
The patent extracts and eliminates the auxiliary cooling system by designing the indexing mechanism to minimize friction-based heat generation. The engagement force is achieved through mechanical indexing and geometric constraints rather than continuous friction, removing the need for additional cooling components and reducing overall system complexity
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
Enables seamless switching between two-wheel and four-wheel drive modes, improves traction by engaging secondary driven shafts as needed, and provides engine braking without locking the half shafts, reducing tire scrubbing and twitchiness, and eliminates the need for costly hydraulic systems.
Implementation Method 1
an electromagnetic system (120) for indexing the roll cage (54) relative to the clutch housing (46). The electromagnetic system includes first and second indexing devices for indexing the roll cage
Implementation Method 2
at least one friction member which is in contact with the roll cage and the hub such that, during operation, the friction member generates friction forces between the roll cage and the hub which cause the roll cage to turn with the hub
Data Source
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AI summary
A bi-directional overrunning clutch assembly for engaging secondary driven shafts in a four wheel drive vehicle. The assembly includes a differential housing with a pinion input gear rotatably disposed within it that is engaged to a drive shaft. A bi-directional overrunning clutch housing is engaged to the pinion gear. A roll cage assembly is located inside the clutch housing. A pair of hubs are positioned within the roll cage assembly and connected to the secondary driven shafts. An electromagnetic system controls indexes the roll cage in a first direction relative to the clutch housing using a first indexing device for coupling the secondary drive shaft to the secondary driven axles when four wheel drive is needed, and in an opposite direction using a second indexing device when an engine braking condition is needed. A spring assembly is preferably used to bias the roll cage back to a neutral position.