Automatic Transmission Gerotor Pump With Matched Thermal Expansion
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Solution Overview
Problem
Gerotor pumps in automotive applications face inefficiencies due to varying axial clearance between aluminum-based pump housings and steel gear sets caused by differing thermal expansion coefficients, leading to reduced volumetric efficiency and increased torque requirements across temperature ranges.
Innovation Solution
Using an aluminum-based material for both the housing and gear set, ensuring a consistent linear coefficient of thermal expansion, which maintains optimal axial clearance and reduces frictional forces across temperatures, thereby enhancing volumetric efficiency and reducing torque requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the axial clearance is reduced to improve volumetric efficiency, then liquid slip is reduced, but friction forces increase substantially at low temperatures
Solution Approach 1:
The patent changes the material parameter (coefficient of thermal expansion) of the housing from aluminum-based to steel-based to match the gear set material properties. This parameter change ensures that thermal expansion differences do not cause clearance variations across temperature ranges, allowing the axial clearance to be optimized for volumetric efficiency without causing excessive friction at low temperatures.
2Reliability
If the gear set is sized to ensure minimum axial clearance at low temperatures, then rotation is enabled, but axial clearance becomes excessively large at normal operating temperatures
Solution Approach 1:
The patent changes the thermal expansion parameter of the housing material to match the gear set material. By using steel-based housing instead of aluminum-based housing, the thermal expansion coefficients are matched, ensuring that the axial clearance remains consistent across the operating temperature range from -40°C to 160°C, thereby maintaining both rotation capability and volumetric efficiency.
3Weight of moving object
If aluminum-based housing is used to reduce weight, then pump weight decreases, but axial clearance varies with temperature due to different thermal expansion coefficients
Solution Approach 1:
The patent changes the material parameter (thermal expansion coefficient) of the housing from aluminum-based to steel-based to match the gear set material properties. This ensures that thermal expansion differences do not cause clearance variations across temperature ranges, maintaining manufacturing precision for axial clearance while accepting the trade-off of increased weight.
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 solution achieves a volumetric efficiency greater than 80% across a temperature range of -40°C to 160°C, minimizing torque requirements and optimizing pump operation without increasing power consumption.
Implementation Method 1
A linear coefficient of thermal expansion of the first aluminum-based material may be substantially the same as that of the second aluminum-based material
Data Source
AI summary
A hydraulic gerotor pump for an automatic transmission may comprise a housing and a gear set rotatably disposed within the housing. The gear set may comprise an inner gear and an outer gear having radially opposed intermeshing teeth that together define a plurality of circumferentially disposed variable volume pumping chambers therebetween. The housing may be made of a first aluminum-based material, and the inner gear and the outer gear of the gear set may be made of a second aluminum-based material. The linear coefficient of thermal expansion of the first aluminum-based material may be substantially the same as that of the second aluminum-based material.