Drive Device Shaft Deflection Reduction via Bearing Inversion
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Solution Overview
Problem
In electric power steering systems, conventional motors with oil seals face challenges due to axial runout issues, leading to potential water intrusion and electrical failures when space constraints reduce the distance between bearings, compromising the watertight seal and causing rust or electrical shorts.
Innovation Solution
A drive device design with a stator and rotor configuration that includes a shaft with a reduced deflection amount at the seal location, utilizing a first bearing inside the shaft hole and a second bearing in a bearing box, along with a biasing member to minimize seal deformation and wear, ensuring effective water prevention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between the output end bearing and the opposite-side bearing is increased to reduce axial runout, then the watertight property of the oil seal is improved, but the axial space requirement increases, which may not be compatible with vehicular mounting restrictions
Solution Approach 1:
Instead of positioning the fulcrum at the opposite-side bearing (conventional design), the invention inverts the fulcrum position to be at the output end bearing. This allows the seal member to be positioned closer to the fulcrum, reducing shaft deflection at the seal location and improving watertight property without requiring increased axial distance between bearings.
Solution Approach 2:
The invention changes the parameter of fulcrum position from the opposite-side bearing to the output end bearing. This parameter change fundamentally alters the shaft deflection characteristics, allowing the seal member to maintain effective contact with the shaft even when the axial distance between bearings is reduced, thus resolving the contradiction between compact size and watertight reliability.
2Length of moving object
If the axial distance between bearings is decreased to meet mounting space restrictions, then the device compactness is improved, but the axial runout increases, causing deterioration of the oil seal's watertight property
Solution Approach 1:
The invention inverts the conventional fulcrum position arrangement. By placing the fulcrum at the output end bearing instead of the opposite-side bearing, the shaft deflection pattern is reversed, allowing the seal member to remain effective even when bearings are positioned closer together axially.
Solution Approach 2:
Changing the fulcrum position parameter from opposite-side bearing to output end bearing enables the system to achieve adequate seal performance with reduced axial distance between bearings, thus resolving the contradiction between compactness and reliability.
3Device complexity
If the seal member is positioned farther from the fulcrum to accommodate bearing spacing, then the bearing arrangement is simplified, but the shaft deflection at the seal location increases, causing excessive deformation and wear of the seal member
Solution Approach 1:
By inverting the fulcrum position to the output end bearing, the invention ensures that the seal member is positioned close to the fulcrum, minimizing shaft deflection and bending at the seal location. This maintains precise interference fit and reduces wear, even with simplified bearing arrangements.
Solution Approach 2:
The parameter change of fulcrum position to the output end bearing directly reduces the distance between the fulcrum and seal member, thereby minimizing shaft deflection and maintaining manufacturing precision of the seal fit without complicating the bearing arrangement.
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 design reduces deflection and interference fit issues, preventing water intrusion and maintaining the watertight seal, thus avoiding motor seizure and electrical failures in electric power steering systems.
Implementation Method 1
a biasing member housed in the bearing box, the biasing member biasing an outer race of the second bearing toward the output end
Implementation Method 2
the seal member being in sliding contact with an outer circumference of the shaft
Data Source
AI summary
A drive device includes a shaft rotatably supported by a first bearing and a second bearing. The first bearing is disposed in a shaft hole of an output frame end. The second bearing is disposed in a bearing box of an opposite-to-output frame end. An oil seal is fixed in the shaft hole and is closer to an output end than the first bearing is, and is in sliding contact with an outer circumference of the shaft. A biasing member is housed in the bearing box and biases an outer race of the second bearing toward the output end. Accordingly, a deflection amount and a bend amount of the shaft at the location where the oil seal is disposed may be reduced.