Longitudinal Displacement Unit Cage Stops and Springs
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Solution Overview
Problem
Existing longitudinal displacement units for driveshafts face issues with jamming and reduced torque transmission due to groove run-out, and require high spring forces for smooth operation, leading to potential component damage during rapid movements.
Innovation Solution
A longitudinal displacement unit with a sleeve-shaped cage guiding rolling contact members between shaft elements, featuring pressure springs that are unloaded during normal operation, and stops that engage only when maximum adjustment is reached to prevent damage and maintain smooth operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If groove run-out is provided to delimit ball travel, then cage movement is constrained, but jamming occurs and torque transmission is reduced
Solution Approach 1:
The harmful groove run-out is completely removed from the shaft elements. Instead, the cage is given a defined free displacement path with stops at the extremes, extracting the delimiting function from the grooves and placing it in the cage assembly with stops, thereby eliminating jamming while maintaining movement constraints
Solution Approach 2:
The rolling contact members (balls) are used as intermediaries that engage with the grooves during normal operation but are prevented from entering the groove run-out region by the stops. The stops act as intermediaries that block the balls before they can reach the harmful groove run-out area, preventing jamming while allowing normal torque transmission
2Reliability
If pressure springs are used to load cage toward central position, then cage is constrained to center, but high spring forces are required causing difficult smooth operation
Solution Approach 1:
The pressure springs are designed to provide only partial action - they are pre-compressed to provide a weak centering force during normal operation, but are allowed to become fully compressed when the cage reaches the end positions. This partial action provides enough centering tendency without requiring high continuous spring forces that would cause smooth operation difficulties
Solution Approach 2:
The spring force parameter is dynamically changed through the mechanism: during normal operation the springs provide a weak centering force, but at end positions the stops prevent further compression, effectively changing the force parameter from weak to infinite (hard stop). This parameter change allows smooth operation while maintaining cage positioning
3Reliability
If stops are provided to delimit cage travel, then component damage is prevented, but violent ball impact occurs during rapid movements
Solution Approach 1:
The pressure springs are positioned to compress beforehand as the cage approaches the end positions, providing a cushioning effect that absorbs the kinetic energy of rapid movements. The springs are pre-compressed during normal operation and continue compressing as the cage moves toward stops, cushioning the impact before the balls reach the stops and preventing violent impacts
4Reliability
If circumferential recess is provided to receive balls, then cage is constrained, but torque transmitting ability is reduced
Solution Approach 1:
The harmful circumferential recess is completely removed from the shaft elements. The cage constraint function is extracted and implemented through stops at the extreme positions rather than through a continuous circumferential recess, eliminating the torque transmission obstruction while maintaining cage constraint
Solution Approach 2:
The cage constraint is segmented into discrete stop positions at the extremes of the travel path, rather than using a continuous circumferential recess. This segmentation allows the balls to engage with grooves along the entire length of the shaft elements for torque transmission, while constraint is provided only at the necessary end positions
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 ensures low-friction operation within the normal adjustment range, dampens movement at end positions to prevent component damage, and avoids jamming by allowing rolling contact members to bypass potential run-out regions, thus enhancing the reliability and durability of the driveshaft system.
Implementation Method 1
The pressure springs are designed to provide only partial action - they are pre-compressed to provide a weak centering force during normal operation, but are allowed to become fully compressed when the cage reaches the end positions
Implementation Method 2
Within the normal operating range when the two shaft elements are adjusted relative to one another, the longitudinal displacement unit operates in a low-friction way because there exists a rolling contact friction only
Implementation Method 3
The stops act as intermediaries that block the balls before they can reach the harmful groove run-out area, preventing jamming while allowing normal torque transmission
Implementation Method 4
The pressure springs are positioned to compress beforehand as the cage approaches the end positions, providing a cushioning effect that absorbs the kinetic energy of rapid movements
Data Source
AI summary
A longitudinal displacement unit includes a first shaft element including an outer face having a plurality of first grooves and a second shaft element having a through-bore that receives the first shaft element. The second shaft element has a plurality of second grooves opposite the first plurality of grooves. A sleeve-shaped cage is disposed between the first shaft element and the second shaft element for guiding rolling contact members that engage the first plurality of grooves and the second plurality of grooves. The cage is provided with through-apertures that are circumferentially distributed, extend parallel to the longitudinal axis, and include longitudinal ends. Pressure springs are disposed within the through-apertures and are loaded between the longitudinal ends thereof. At least one stop is associated with one of the shaft elements, against which the pressure springs abut after having passed through a free displacement path of the cage between the two shaft elements, which free displacement path is not loaded by the pressure springs.