Epicyclic Gear Drive System for Low-Floor Vehicle Torque Distribution
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Solution Overview
Problem
Existing systems for low-floor vehicles, such as urban buses, face challenges in minimizing unsprung mass and floor height due to complex and expensive electronic differentials, while also increasing space requirements and unsprung mass, especially in rear axle designs.
Innovation Solution
A drive system featuring electric motors mounted on the chassis frame with epicyclic gear trains and constant velocity joints, allowing for horizontal and vertical offset of components to reduce unsprung mass and floor height, and incorporating a rotation reversal mechanism to ensure consistent torque transmission to drive wheels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an electronic differential is used to manage torque distribution, then torque control flexibility is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the electronic differential with a purely mechanical torque distribution system using epicyclic gear trains. The mechanical arrangement of sun gears, planet gears, and ring gears naturally distributes torque between wheels based on their resistance to rotation, eliminating the need for electronic sensors, controllers, and actuators while maintaining adaptive torque control capabilities.
Solution Approach 2:
The mechanical differential system automatically distributes torque between the left and right wheels based on their individual wheel resistances. The epicyclic gear train self-regulates torque distribution without external control, with each wheel receiving appropriate torque based on its loading conditions, thereby eliminating the need for complex electronic management systems.
2Device complexity
If a traditional differential is placed at the center of the driving axle, then torque distribution is simplified, but floor height increases and unsprung mass increases
Solution Approach 1:
The patent segments the differential function from the traditional centralized axle arrangement and distributes it to individual wheel assemblies. Each wheel has its own epicyclic gear train that performs differential functions locally, eliminating the need for a large central differential housing and reducing the mass that must be accelerated and decelerated with each wheel movement.
Solution Approach 2:
The patent repositions the differential mechanism from a horizontal arrangement at the axle center to a vertical arrangement integrated into the wheel assembly. The epicyclic gear trains are positioned above the axle with the sun gear axis offset from the wheel axis, creating a compact three-dimensional configuration that reduces floor height while maintaining differential functionality.
3Length of stationary object
If speed reduction gears are distributed on each side near the wheels, then floor height is reduced, but unsprung mass increases
Solution Approach 1:
The patent merges the speed reduction gears with the differential mechanism into a single integrated epicyclic gear train assembly. The sun gear, planet gears, and ring gear simultaneously perform both speed reduction and torque distribution functions, eliminating the need for separate speed reduction gears on each side and reducing the total unsprung mass while maintaining the low floor height benefit.
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 system minimizes unsprung mass, reduces floor height, and optimizes torque and speed characteristics, enabling efficient power transmission while allowing for redundancy in motor operation and reduced service loss in case of failure, thus enhancing vehicle performance and service reliability.
Implementation Method 1
an epicyclic gear train driven by said input pinion via a gear set, said epicyclic gear train having a ring gear, a planet wheel carrier and a sun gear
Implementation Method 2
said half-shaft being provided at its ends with constant velocity joints
Data Source
AI summary
The invention relates to a system for driving the drive wheels (1) of a vehicle, comprising two sets of electric motors (2) and casings (3) (left and right). Each of the casings (3) comprises an input pinion (8) which rotates interdependently with the rotor of one of the electric motors (2) as well as with a set of gears (12) driving the ring gear (7) of a planetary gear set (4). The two planetary gear sets (4) are connected to one another by a connecting means (9) that rotates interdependently with each of the two sun gears (5) (inner planetaries). The planet carrier (6) of each of the planetary gear sets (4) rotates interdependently with a connecting means (11) of one of the drive wheels (1). The two planetary gear sets (4) perform a double differential function. The invention also relates to a method for controlling the electric motors (2) that allows the drive system to be used as a torque converter. The drive system can be fixed to the chassis frame of the vehicle. In addition, the two casings (3) can be located in the wheel cages (13). The connecting means (9) that rotates interdependently with the two sun gears (5) can be located inside the casing of the floor pan (14) of the vehicle. The two electric motors (2) can be located just behind the driven wheels (1).