Oil Pump Compression Stroke Cavitation Noise Reduction
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Solution Overview
Problem
Existing oil pumps in automatic transmissions experience cavitation noise and erosion due to vaporization of hydraulic oil at high speeds, leading to insufficient discharge and increased noise and vibration, with existing solutions inadequately addressing noise reduction.
Innovation Solution
Incorporating a compression stroke between intake and discharge strokes with a specific rotation angle range (21 to 27 degrees) to gradually eliminate cavitation and prevent erosion, while using a shallow groove to manage pressure at low revolutions and suppress excessive pressure increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rotor rotates at high speed to increase productivity, then the oil pump discharge amount increases, but cavitation occurs causing erosion and noise
Solution Approach 1:
The patent applies preliminary action by introducing a compression stroke before the discharge stroke. During this compression stroke, hydraulic oil is supplied in advance to the space part through a pressure reducing shallow groove, gradually increasing the internal pressure before the space communicates with the discharge port. This preliminary pressure build-up prevents sudden cavitation elimination and reduces erosion and noise while maintaining high-speed operation capability
2Object-affected harmful factors
If hydraulic oil is supplied from the delivery port to increase the internal pressure of the space part, then erosion is reduced, but cavitation noise remains inadequate suppressed
Solution Approach 1:
The patent segments the discharge process into two distinct strokes: a compression stroke for gradual pressure build-up and cavitation elimination, followed by a discharge stroke for oil delivery. This segmentation allows the compression stroke to handle pressure management and cavitation reduction separately from the discharge function, enabling optimized control of both erosion and noise through the pressure reducing shallow groove mechanism
3Object-affected harmful factors
If the internal pressure of the space part is increased to eliminate cavitation, then erosion is reduced, but fuel economy decreases due to excessive pressure increase
Solution Approach 1:
The patent applies parameter changes by controlling the pressure build-up rate through the pressure reducing shallow groove during the compression stroke. By regulating the cross-sectional area and geometry of this groove, the system achieves optimal balance between eliminating cavitation (reducing erosion) and controlling pressure increase (maintaining fuel economy). The groove design parameters are specifically optimized to prevent excessive pressure buildup while ensuring adequate cavitation elimination
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 approach effectively reduces cavitation noise to a level that does not cause driver discomfort, disperses cavitation over time to prevent erosion, and maintains fuel economy by controlling internal pressure, resulting in suppressed noise and reduced erosion risks.
Implementation Method 1
when the rotor rotates at high speed, a negative pressure on the intake port side of the space becomes partially lower than a saturated vapor pressure of the hydraulic oil. As a consequence, the hydraulic oil vaporizes and causes cavitation (air bubbles) in the space.
Implementation Method 2
a pressure reducing shallow groove D for supplying hydraulic oil from a delivery port 5 is formed in a space part (gap part) S
Data Source
AI summary
An oil pump having an inner rotor with of external teeth; an outer rotor that is eccentrically provided and has internal teeth that mesh with the inner rotor external teeth, and an oil pump body that accommodates the outer and inner rotors. By rotationally driving the inner rotor to increase and decrease a space between the internal and the external teeth, an intake stroke suctions hydraulic oil from the oil pump body and a discharge stroke discharges the suctioned hydraulic oil to a discharge port formed in the oil pump body. Between the intake and discharge strokes, a confinement stroke cuts off the suctioned hydraulic oil and confines the suctioned hydraulic oil in the space, and a compression stroke reduces the space and compresses the confined hydraulic oil. Further, an interval is set between a finish end portion of the intake port of the oil pump body and a start end portion of the discharge port such that a rotation angle of the inner rotor during the compression stroke is 21 to 27 degrees.