Multi-Speed Transfer Case Sun Gear Dynamics
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Solution Overview
Problem
Existing multi-speed transfer cases in motor vehicle powertrains face challenges in reducing noise, vibration, and harshness (NVH) while providing efficient torque transmission across different drive modes, particularly with high under drive ratios that limit vehicle speed in four-wheel-drive low range mode.
Innovation Solution
A motor vehicle transfer case design featuring a planetary gear set with a ring gear, pinion assembly, and sun gear that allows for spur gears in two-wheel drive and four-wheel-drive high range modes, and selectively fixes the sun gear against rotation in low range mode, reducing NVH and providing a lower under drive ratio for increased speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If helical gears are used in the planetary gear set, then noise, vibration, and harshness are reduced, but the under drive ratio becomes high which limits vehicle speed in four-wheel-drive low range mode
Solution Approach 1:
The patent applies dynamics by making the sun gear selectively connectable and disconnectable from the carrier through a clutch mechanism. In 2WD and 4WD high range modes, the sun gear rotates with the carrier providing direct drive. In 4WD low range mode, the clutch disconnects the sun gear from the carrier, allowing it to be held stationary while pinion gears rotate around it, creating a reduced ratio gear reduction that increases vehicle speed while maintaining torque multiplication.
Solution Approach 2:
The patent changes the operational parameters of the planetary gear set by selectively altering which components are connected or disconnected. The clutch mechanism enables parameter changes in the gear ratio by switching between two operational states: direct drive (sun gear connected to carrier) and reduced ratio drive (sun gear disconnected and held stationary), thereby optimizing both NVH characteristics and vehicle speed across different driving modes.
2Power
If the sun gear is connected to the carrier for direct drive, then torque transmission is efficient in two-wheel drive and four-wheel-drive high range modes, but the gear set generates more noise and vibration
Solution Approach 1:
The clutch mechanism dynamically switches the connection state of the sun gear to the carrier based on driving mode requirements. In 2WD and 4WD high range modes, the clutch engages connecting the sun gear to the carrier for efficient direct torque transmission. In 4WD low range mode, the clutch disengages allowing the sun gear to be held stationary, creating gear reduction that reduces noise and vibration while maintaining power transmission capability.
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
This design results in reduced noise, improved robustness, and increased vehicle speed in four-wheel-drive low range mode, enabling faster off-road performance compared to traditional transfer cases.
Implementation Method 1
a pinion assembly connected to the output and including pinion gears in mesh with the ring gear and a carrier to carry the pinion gears
Implementation Method 2
a planetary gear set between the input and the output. The gear set includes a ring gear connected to the input, and a pinion assembly connected to the output and including pinion gears in mesh with the ring gear
Data Source
AI summary
A transfer case of a motor vehicle drivetrain includes a planetary gear set including a ring gear to receive input torque, and a pinion assembly having pinion gears in mesh with the ring gear and a carrier to carry the pinion gears and transmit output torque. A sun gear is in mesh with the pinion gears, is selectively connectable to the carrier and rotatable therewith in a two-wheel drive mode and in a four-wheel-drive high range mode, and is selectively fixable against rotational motion in a four-wheel drive low range mode.