Telescoping Spline Shaft Torque Transmission
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Solution Overview
Problem
The increasing demand for high-output electric power steering devices requires higher torque transmission, which necessitates an increase in the pitch circle diameter and consequently the outside diameter of the steering shaft, leading to interference issues during mounting and compromised performance.
Innovation Solution
A steering spline telescoping shaft with an inner and outer tubular shaft spline-fitted for axial sliding, featuring modified spline profiles with an addendum modification coefficient (0.4 < e < 1.1) to increase tooth depth and contact area without size increase, allowing for high torque transmission while maintaining strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the pitch circle diameter is increased to transmit higher torque, then the torque transmission capability is improved, but the outside diameter of the steering shaft must be increased which causes interference with other parts during mounting
Solution Approach 1:
The invention changes the spline profile parameters by introducing an addendum modification coefficient (e) that ranges from 0.3 to 1.2. This modifies the tooth depth and contact area of the splines, allowing the same outside diameter to transmit higher torque through optimized gear engagement geometry rather than increasing size
Solution Approach 2:
The invention applies a resin film coating on the spline surfaces to enhance the torque transmission capability. The composite structure of metal splines with resin film coating provides increased friction and better torque transmission without requiring an increase in the outside diameter
2Strength
If the outside diameter is increased to ensure steering shaft strength, then the strength is improved, but the mounting performance deteriorates due to interference with other parts
Solution Approach 1:
The invention optimizes the spline profile parameters including the addendum modification coefficient and tooth depth ratios to maximize strength utilization within the existing outside diameter constraints, eliminating the need to increase diameter for strength reasons
Solution Approach 2:
The telescopic structure with inner and outer shafts nested together allows the steering shaft to maintain high strength through the spline connection while keeping the overall outside diameter compact for easy mounting in vehicle spaces
3Power
If a resin film is provided on the spline surface and the profile is modified, then the contact area and torque transmission are improved, but the manufacturing complexity increases
Solution Approach 1:
The spline profile modification uses standard gear design parameters (addendum modification coefficient within 0.3-1.2 range) that can be implemented using conventional gear manufacturing processes, minimizing the increase in manufacturing complexity
Solution Approach 2:
The resin film acts as an intermediary layer that enhances torque transmission through increased friction and contact area. The film can be applied through conventional coating processes, adding minimal manufacturing complexity while significantly improving power transmission
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 modified spline design enhances the steering shaft's ability to transmit high torque with increased strength without size expansion, ensuring effective mounting and performance by increasing the contact area between splines.
Implementation Method 1
a resin film is provided on a surface of at least either of the female spline and the male spline
Data Source
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AI summary
A spline telescoping shaft includes an inner shaft including a male spline and a tubular outer shaft including a female spline. A resin film is provided on a surface of at least either of both the splines. An addendum modification coefficient e, the number of teeth Z, a module m, a reference pitch circle diameter PCD, a tip circle diameter d1 and a root circle diameter d2 of the male spline and a tip circle diameter D1 and a root circle diameter D2 of the female spline have relations expressed by expressions (1) to (8). m(Z+4)>d1>m(Z+2) ... (1), mZ>d2>m(Z-1) ... (2), m(Z+4)>D2>m(Z+2) ... (3), mZ>D1>m(Z-1) ... (4), D2>d1 ... (5), D1 >d2 ... (6), PCD=mZ ... (7), and 0.4<e<1.1 ... (8)