In-wheel Motor Radial Downsizing via 3D Shaft Arrangement
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Solution Overview
Problem
The existing in-wheel motor drive devices with parallel shaft gear speed reducers face challenges in downsizing, leading to increased weight, reduced strength of suspension parts, and degradation in vehicle motion performance due to inter-axis distance limitations between the output shaft and intermediate shaft, which affects the radial downsizing and mounting to the suspension device.
Innovation Solution
The configuration includes a parallel shaft gear speed reducer with input, intermediate, and output shafts supported by rolling bearings, where at least two rolling bearings on one side are positioned to prevent bearing width overlap in the axial direction, allowing for radial downsizing and improved mountability by eliminating mutual dependency between gear and bearing requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the parallel shaft gear speed reducer is used to reduce the size of the in-wheel motor drive device, then the device size is reduced, but the inter-axis distance between the output shaft and intermediate shaft cannot be optimized, leading to increased weight and reduced strength of suspension parts
Solution Approach 1:
The patent changes the arrangement from a conventional single-plane configuration to a three-dimensional spatial arrangement where the intermediate shaft is positioned at a different height than the input and output shafts. This vertical dimensionality change allows optimization of the inter-axis distance without increasing the overall radial footprint of the device, thereby reducing size while maintaining proper bearing and gear specifications that prevent weight increase.
2Volume of moving object
If the parallel shaft gear speed reducer is downsized in the radial direction, then the radial size is reduced, but the mounting space for the suspension device is insufficient
Solution Approach 1:
By positioning the intermediate shaft at a different vertical level than the input and output shafts, the patent creates unused vertical space within the radial envelope. This dimensional reorganization provides adequate mounting space for suspension device attachment points while maintaining a compact radial footprint, resolving the contradiction between radial downsizing and mounting space requirements.
Solution Approach 2:
The patent segments the functional components (input shaft, intermediate shaft, output shaft) into different vertical levels within the speed reducer assembly. This segmentation allows each component to be optimally positioned for its specific function while creating distributed space throughout the volume for suspension mounting, rather than concentrating all components in a single plane that would block mounting access.
3Reliability
If the inter-axis distance is determined based on bearing requirements, then the bearing function is ensured, but the gear function is compromised and sufficient downsizing cannot be achieved
Solution Approach 1:
The patent resolves the conflict between bearing requirements and gear requirements by introducing a vertical dimension to the shaft arrangement. The intermediate shaft is positioned at a different height, allowing the inter-axis distances to be independently optimized for both bearing load capacity and gear meshing requirements without compromising either function. This spatial separation enables proper bearing specifications while maintaining compact overall dimensions for downsizing.
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 achieves radial downsizing of the in-wheel motor drive device, enhancing motion performance and mountability to the vehicle while optimizing gear and bearing specifications for improved design freedom and reduced unsprung weight.
Implementation Method 1
the input shaft, the intermediate shaft, and the output shaft are supported at respective both end portions by rolling bearings so as to be rotatable
Data Source
AI summary
An in-wheel motor drive device includes an electric motor section, a speed reducer section, a wheel bearing section, and a casing. The speed reducer section includes a speed-reduction structure using a parallel shaft gear. The parallel shaft gear includes an input shaft, which is coupled to the electric motor section, an input gear, at least one intermediate shaft including input-side and output-side intermediate gears, an output shaft, which is coupled to the wheel bearing section, and a final output gear. The input, intermediate, and output shafts are supported by rolling bearings to be rotatable. At least two rolling bearings configured to support the intermediate and output shafts on an out-board side and two rolling bearings configured to support the intermediate and output shafts on an in-board side are arranged at positions at which respective bearing widths are prevented from being superimposed with each other in an axial direction.