Rear Axle Electric Drive Layout for Low Unsprung Mass
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric drives for vehicles, particularly commercial vehicles, face challenges in achieving a compact, efficient, and low-complexity design that allows for both steerable and drivable axles, while minimizing unsprung mass and maximizing battery storage capacity.
Innovation Solution
The electric drive is arranged transversely behind the second axle with a housing connected to the vehicle frame, incorporating two coaxial planetary gear sets and an angular drive for torque deflection, allowing for a compact design and efficient torque transmission, while the housing is not fixed to the axle, reducing unsprung mass and enabling larger battery capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the electric drive is arranged longitudinally in the vehicle, then the torque transmission path is simplified, but the vehicle longitudinal space is consumed and the battery storage capacity is reduced
Solution Approach 1:
The patent transitions from a longitudinal arrangement to a transverse arrangement of the electric drive behind the rear axle. This dimensional change allows the torque transmission path to be redirected via bevel gears, achieving both compact space utilization and adequate battery storage capacity while maintaining drivability.
2Device complexity
If the housing of the electric drive is fixed to the axle, then the torque transmission is simplified, but the unsprung mass increases and drivability deteriorates
Solution Approach 1:
The patent segments the vehicle into sprung and unsprung masses by fixing the electric drive housing to the vehicle body rather than the axle. This separation allows the heavy electric drive components to be part of the sprung mass, improving drivability while the torque transmission is achieved through a cardan shaft connecting the two segments.
3Volume of moving object
If a transverse electric drive arrangement is implemented, then the battery storage capacity is maximized, but the torque must be redirected requiring additional components
Solution Approach 1:
The patent introduces a cardan shaft as an intermediary component to transmit torque from the transverse electric drive to the longitudinally oriented rear axle. This mediator enables the transverse arrangement that maximizes battery space while maintaining efficient torque transmission through proven mechanical components.
4Power
If multi-stage planetary gears are used, then the transmission ratio is increased, but the device complexity and length increase
Solution Approach 1:
The patent merges two single-stage planetary gear sets into a compact multi-stage configuration where the output of the first planetary gear directly drives the second planetary gear. This integrated design achieves high transmission ratios while minimizing overall length and complexity by eliminating intermediate shafts and bearings.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a motor vehicle (10) comprising a steerable first axle (12), a steerable second axle (20), an electric drive (26) for driving the second axle (20), and a traction battery (28), by means of which the electric drive (26) can be supplied with electric energy stored in the traction battery (28). The electric drive (26) has a housing (28); an electric motor (30) which has a stator (32) and a rotor (34) that can be rotated about a rotor axis (38) relative to the stator (32) and relative to the housing (28); and a first planetary gear set (42) which is arranged coaxially to the rotor axis (38) and which has a first element, a second element, and a third element.