Multi-mode Transaxle Drive System with Selective Axle Disconnect
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional all-wheel drive (AWD) systems in vehicles with transaxles face inefficiencies and component wear when only one axle is driven, as they are designed to handle higher torques, leading to unnecessary power loss and increased NVH (noise, vibration, and harshness), and require oversized components to accommodate both 'high' and 'low' range operations.
Innovation Solution
The system introduces selective disconnection of front and rear axles, incorporating three-position dog clutches and planetary gearsets with adjustable reduction ratios to allow for efficient operation of either axle independently, reducing driveline loading and enabling smaller component sizing for normal operations, while maintaining 'low' range capability for off-road use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the PTU's hypoid gearset, propshaft, and rear drive assembly are sized to accommodate higher operating torques for low range operation, then off-road performance and towing capacity are improved, but fuel efficiency deteriorates and NVH increases during normal high range operation due to unnecessary power loss and component wear
Solution Approach 1:
The system dynamically switches between high range and low range modes using a selectable reduction hub that engages or disengages the planetary gear set. During normal operation, the reduction hub disengages the planetary gears, creating a direct drive path that eliminates unnecessary power loss through oversized components. When low range is needed, the reduction hub engages the planetary gear set to provide torque multiplication, allowing the system to adapt its mechanical configuration based on operating conditions.
Solution Approach 2:
The drivetrain is segmented into distinct functional sections with independent control. The selectable reduction hub acts as a disconnect mechanism that can isolate the planetary gear set from the power flow during high range operation. This segmentation allows the oversized hypoid gearset and propshaft to be physically decoupled from the power transmission path when their enhanced torque capacity is not needed, eliminating energy losses associated with driving these components in normal operation.
2Force
If the planetary gear set is engaged to provide low range torque multiplication, then off-road performance is improved, but fuel consumption increases during normal road operation
Solution Approach 1:
The selectable reduction hub provides dynamic reconfiguration of the drivetrain by engaging or disengaging the planetary gear set based on operating conditions. During normal road operation, the hub disengages the planetary gears, creating a direct drive path that eliminates the energy losses associated with power transmission through the reduction gearing. When off-road conditions require low range torque multiplication, the hub engages the planetary gear set, allowing the system to optimize its mechanical advantage for high-torque applications.
3Adaptability or versatility
If all driveline components are continuously engaged to maintain AWD capability, then vehicle towing capacity is improved, but component wear and power loss increase during normal operation
Solution Approach 1:
The drivetrain incorporates a selectable reduction hub that segments the power flow path, allowing the planetary gear set to be isolated from the driveline during normal operation. This disengagement prevents unnecessary wear on the planetary gears and related components when their torque multiplication function is not required. The system maintains the capability to engage these components when towing or off-road conditions demand enhanced torque capacity, thus preserving component lifespan while retaining versatility.
4Ease of operation
If the reduction hub disconnects the front differential and PTU from the engine during neutral condition, then vehicle towing is facilitated, but the system complexity increases due to additional clutch mechanisms
Solution Approach 1:
The selectable reduction hub merges multiple functions into a single integrated component. It simultaneously controls the engagement/disengagement of the planetary gear set and coordinates the operation of the front and rear clutches to achieve neutral condition for towing. This consolidation reduces the number of separate control mechanisms needed while maintaining the capability to disconnect both front and rear driveline components from the engine, facilitating towing operations without requiring overly complex independent control systems for each disconnect function.
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 enhances fuel efficiency, reduces perceived NVH, and extends component lifespan by allowing the driveline components to operate under lower torque conditions when only the front axle is powered, while maintaining off-road performance and towing capacity.
Implementation Method 1
a first planetary gearset having a first ring gear grounded to the first housing, a first sun gear permanently coupled for rotation with the first input shaft, and a set of first planet gears supported by a first planetary carrier
Data Source
AI summary
A vehicle drive system capable of selectively providing all-wheel drive and single-driven-axle modes includes a front drive unit having a planetary gearset with a grounded ring gear and a sun gear driven by the transaxle's drive spool via an input shaft, and a differential selectively coupled by a dog clutch to one of the sun gear or the planetary carrier, or neither of them, to thereby selectively provide both an available low range and a front axle disconnect. The front drive unit further defines a power take-off unit with a clutch selectively coupling the input shaft to a propshaft. The rear drive unit includes a planetary gearset with a grounded ring gear, a sun gear driven by the propshaft, and a differential selectively coupled by a dog clutch to one of the sun gear or the planetary carrier, or neither of them, to thereby likewise selectively provide both an available low range and a rear axle disconnect.