Drum-Cam Shift Actuator for Low-Torque Spline Alignment
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Solution Overview
Problem
Existing shift actuators for power transfer units in vehicles lack efficient mechanisms to transition between four-wheel drive and two-wheel drive settings, leading to inefficiencies in torque management and alignment of splines, which affects the vehicle's performance and reliability.
Innovation Solution
A shift actuator design that includes a motor-driven drum assembly with disconnect and range tracks, a fork rod, and position sensors, allowing for precise actuation positions and torque management through sloped portions, enabling smooth transitions between drive settings by building momentum and maintaining consistent axial positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional shift actuator mechanism is used, then the structure is simple, but the torque management is inefficient and spline alignment is poor
Solution Approach 1:
The drum cam uses curved tracks instead of straight mechanical linkages. The disconnect track and range track are formed as curved paths on the drum cam surface, allowing smooth rotational conversion to linear fork movement. This curvature enables gradual torque application and precise spline alignment through the oblique sloped portions of the tracks.
Solution Approach 2:
The mechanism transitions from static mechanical linkages to dynamic rotational motion. The drum cam rotates about an axis parallel to the fork rod, converting rotational motion into controlled linear movement of the disconnect and range forks. This dynamic approach allows momentum building and reduces initial torque requirements.
2Speed
If the motor directly drives the fork assembly, then the response is fast, but the initial torque load is too high
Solution Approach 1:
The drum cam's curved tracks prepare the fork assembly for movement before direct engagement. The oblique sloped portions of the tracks gradually guide the forks into position, allowing the motor to build momentum before the forks engage the splines. This preliminary action reduces the shock load and initial torque requirement.
Solution Approach 2:
The rotational motion of the drum cam creates periodic engagement cycles. The motor rotates the drum cam through specific angular positions where the curved tracks provide mechanical advantage, creating rhythmic torque application that reduces peak loads while maintaining shift speed.
3Productivity
If the fork assembly moves directly through the tracks, then the shifting is quick, but torque efficiency is low
Solution Approach 1:
The curved drum cam tracks optimize the mechanical advantage throughout the rotation cycle. The oblique sloped portions of the disconnect and range tracks are positioned to provide maximum torque efficiency at critical engagement points, allowing quick shifts while minimizing energy loss through optimized force vectors.
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 enhances torque efficiency, reduces the initial load on the motor, and ensures precise alignment of splines, improving vehicle performance and reliability by allowing for smooth transitions between drive settings.
Implementation Method 1
Rotation of the drum cam with the fork assembly in one of the actuating positions defines a low-torque area characterized by at least a portion of the fork assembly being maintained in a consistent axial position with respect to a drum. Rotation of the drum cam in the low-torque area builds momentum for operating the fork assembly through sloped portions of the disconnect track and the range track.
Data Source
AI summary
A shift actuator includes a motor that drives a drum assembly having a disconnect track and a range track. Operation of the motor rotates the drum assembly about a rotational axis. A fork rod is positioned parallel with the rotational axis. A disconnect fork is slidably coupled with the disconnect track and the fork rod. A range fork is slidably coupled with the range track and the fork rod. The disconnect track and the range track define a plurality of actuating positions of the disconnect fork and the range fork. The plurality of actuating positions are defined by corresponding flat portions of the disconnect track and the range track that maintain a position of the disconnect fork and the range fork, respectively, relative to the fork rod.