Hub Unit Planetary Gear Nesting for Axial Compactness
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Solution Overview
Problem
Existing hub units for heavy vehicles and work machines rely on internal combustion engines, which are inefficient and costly due to increasing energy prices and reduced oil access, necessitating a transition to electric machines that require compact and efficient torque and speed adaptation for wheel operation.
Innovation Solution
A hub unit with a series of planetary gears and a gear shifting device that allows for high and low gear shifting, enabling the electric machine to bypass one planetary gear for increased speed, featuring a sun gear as input and a planet carrier as output, and a compact axial design with the electric machine positioned inward and planetary gears arranged for optimal power transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple planetary gears are coupled in series between the electric machine and wheel hub, then torque and speed adaptation is improved, but the axial length of the hub unit increases
Solution Approach 1:
The planetary gears are arranged in a nested configuration where the second planetary gear is positioned inside the first planetary gear, and the third planetary gear is positioned inside the second planetary gear. This nesting allows multiple gear reductions to be achieved within a compact axial space, resolving the contradiction between achieving sufficient torque/speed adaptation and maintaining a compact axial length.
Solution Approach 2:
Instead of arranging planetary gears in series along the axial direction, the invention utilizes the radial dimension by positioning gears concentrically. The sun gear, planet gears, and ring gear are arranged radially, allowing multiple planetary gear stages to be coupled in a compact axial footprint while maintaining the required gear reduction ratio for torque and speed adaptation.
2Length of moving object
If the electric machine is positioned axially inwards of the planetary gears, then the hub unit becomes more compact in the axial direction, but the power transmission path becomes more complex
Solution Approach 1:
The planet carrier of the first planetary gear and the sun gear of the second planetary gear are merged into a single integrated component. This merging reduces the number of separate parts and simplifies the power transmission path, allowing the electric machine to be positioned axially inwards while maintaining a manageable transmission complexity.
3Device complexity
If the maximum rotation speed of the electric machine is limited to 4000 rpm, then the design is simplified, but the maximum speed of the machine is restricted to 10 km/h
Solution Approach 1:
The hub unit incorporates a gear shifting device that can dynamically change the gear ratio by disconnecting and reconnecting planetary gears. This allows the system to operate in different gear stages: at lower speeds, all planetary gears are engaged for high torque multiplication, while at higher speeds, some planetary gears are disconnected to reduce the overall gear ratio, enabling the electric machine to achieve higher vehicle speeds without exceeding its 4000 rpm rotation limit.
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 enhances the compactness of the hub unit in the axial direction, allows for efficient torque and speed adaptation, and increases the maximum speed of the machine by disconnecting one planetary gear, making it suitable for electric machine-driven work machines.
Implementation Method 1
The hub unit comprises at least two planetary gears (104, 106, 108) coupled in series between the electric machine (102) and a wheel hub (110)
Data Source
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AI summary
The invention relates to a hub unit (100) comprising an electric machine (102) adapted for driving a wheel. The hub unit (100) comprises at least two planetary gears (104, 106, 108) coupled in series between the electric machine (102) and a wheel hub (110), and a gear shifting device (112) for connecting and disconnecting, respectively, one of said planetary gears from being drivingly connected to the electric machine.