Hybrid Transaxle Chain Final Drive Axial Length Reduction
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Solution Overview
Problem
In hybrid transaxles, the limited space within the engine compartment poses a challenge for efficiently arranging components such as planetary gear sets, sprockets, and differentials to optimize power transmission and minimize axial length, particularly in front wheel drive and all wheel drive vehicles.
Innovation Solution
The arrangement includes a power split planetary gear set with a sun gear connected to a motor, a carrier connected to an input shaft, and a ring gear fixedly coupled to a sprocket, along with a bevel gear differential that allows for a compact design by minimizing the axial length of electrical machines and optimizing torque multiplication through specific gear ratios and configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the transaxle uses a conventional arrangement with the engine crankshaft rotating about an axis offset from the axle axis, then the power transmission path is established, but the axial length of the transaxle increases and space in the engine compartment is consumed
Solution Approach 1:
The patent combines the final drive differential and the electric machine support functions into a single integrated housing structure. The differential carrier is directly coupled to the second sprocket, and the electric machines are mounted on the transaxle housing, eliminating the need for separate mounting structures and reducing overall axial length.
Solution Approach 2:
The patent transitions from an offset crankshaft arrangement to a centrally aligned crankshaft arrangement where the crankshaft rotation axis is aligned with the transaxle centerline. This dimensional repositioning allows for more efficient space utilization and reduced axial length in the transaxle assembly.
2Length of moving object
If the transaxle uses a compact arrangement to reduce axial length, then space efficiency is improved, but the ability to accommodate larger diameter electric machines is limited
Solution Approach 1:
The patent segments the electric machine functions into two separate machines (first and second electric machines) with distinct mounting locations. The first electric machine is coupled to the first sprocket while the second electric machine is coupled to the second sprocket, allowing each machine to be optimally sized for its specific function while maintaining overall compactness.
Solution Approach 2:
The patent provides different mounting environments for the two electric machines based on their functional requirements. The first electric machine is mounted in a location optimized for its power generation function, while the second electric machine is mounted to optimize torque delivery to the differential, allowing each machine to have appropriate diameter for its specific role.
3Productivity
If the transaxle uses a complex gear arrangement to optimize power transmission, then power transmission efficiency is improved, but the device complexity increases
Solution Approach 1:
The transaxle housing serves multiple functions simultaneously: it supports the differential carrier, mounts the electric machines, provides structural alignment for the gear train, and acts as the outer protective enclosure. This multi-functionality reduces the number of separate components needed and simplifies the overall device complexity.
Solution Approach 2:
The differential carrier is directly coupled to the second sprocket, creating a self-aligning power transmission path that eliminates the need for additional alignment mechanisms or intermediate support structures. The gear train and sprockets are arranged to automatically maintain proper meshing and alignment through the inherent geometry of the power flow path.
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 configuration enables the use of larger diameter electric machines, reduces the overall axial length of the transaxle, and provides efficient power transmission while allowing for more space in narrow engine compartments, enhancing performance and versatility in various vehicle types.
Implementation Method 1
a planetary gear set divides the mechanical power generated by the internal combustion engine into two power flow paths
Implementation Method 2
A second electric machine drives the drive wheels. This second machine is typically referred to as a traction motor although it may be capable of converting mechanical power into electrical power
Implementation Method 3
The differential may be a bevel gear differential having left and right beveled side gears coupled to left and right half shafts and meshing with beveled planet gears
Data Source
AI summary
A power-split hybrid transaxle uses a chain-only final drive. In addition to transferring power from the primary axis to the differential axis, the chain provides about a 2.5:1 torque multiplication. Eliminating the planetary final drive gear set traditionally associated with a chain axis transfer reduces that axial length of the transaxle and provides more space for a power take-off unit.