Speed Reducer with 120-Degree Gear Meshing
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Solution Overview
Problem
Conventional differential/oscillating type speed reducers with three externally-toothed gears experience increased rotational loss and durability issues due to sliding movement of gears relative to pin teeth, and challenges in downsizing while maintaining performance and strength.
Innovation Solution
A speed reducer design with a crankshaft featuring three eccentric portions and a connection portion between them, where each externally-toothed gear is meshed with pin teeth at a 120-degree angle, reducing sliding and enhancing load distribution, and a bearing system that evenly supports rollers to prevent wobbling and misalignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If three externally-toothed gears are arranged with 180-degree meshing engagement range, then the load on each pin tooth is reduced, but the gears slide relative to pin teeth causing increased rotational loss
Solution Approach 1:
The patent changes the meshing engagement angle parameter from the conventional 180 degrees to 120 degrees. This parameter modification allows the externally-toothed gears to rotate smoothly around the pin teeth without sliding, eliminating rotational loss while maintaining balanced load distribution across all three gears through the optimized angular configuration.
2Volume of moving object
If the crankshaft diameter is reduced for downsizing, then the speed reducer size is reduced, but the strength and flexibility are compromised
Solution Approach 1:
The patent employs composite material construction for the crankshaft, combining materials with complementary properties to achieve both reduced weight and maintained strength. This allows downsizing of the speed reducer while preserving the mechanical strength and flexibility required for reliable operation under load.
Solution Approach 2:
The crankshaft is designed with non-uniform cross-sectional properties, featuring varying wall thicknesses and reinforcement in critical stress zones. This local quality optimization allows the overall diameter to be reduced while maintaining sufficient strength where needed, achieving downsizing without compromising structural integrity.
3Power
If three externally-toothed gears are used with 180-degree engagement, then the speed reduction ratio is achieved, but the bearing structure becomes complex and difficult to assemble
Solution Approach 1:
The patent integrates the bearing support structure with the crankshaft body, merging previously separate components into a unified structure. This simplification reduces the number of parts, eliminates complex assembly procedures, and maintains the necessary support for the three externally-toothed gears operating at 120-degree intervals.
Solution Approach 2:
The bearing structure is designed to perform multiple functions simultaneously: supporting the three eccentric portions, guiding the externally-toothed gears, and providing precision alignment. This multi-functionality reduces the need for separate specialized components, simplifying the overall bearing system while maintaining the required speed reduction performance.
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 minimizes rotational loss, enhances durability by reducing sliding between gears and pin teeth, and allows for a smaller diameter while maintaining strength and flexibility in speed reduction ratios.
Implementation Method 1
a bearing (49b) to be fitted on the intermediate eccentric portion (248e), the bearing (49b) comprising a plurality of rollers (50) and a retainer (51)
Implementation Method 2
each externally-toothed gear (44a, 44b, 44c) is in meshing engagement with the pin teeth (31)
Implementation Method 3
three eccentric portions (48a, 48b, 48c) arranged to have a phase difference of 120 degrees with respect to each other
Data Source
Figure 1
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AI summary
Disclosed is a speed reducer which comprises a crankshaft adapted to be rotated in conjunction with a drive unit, a first eccentric portion provided on the crankshaft, a second eccentric portion provided on the crankshaft, a third eccentric portion provided on the crankshaft, a first externally-toothed gear adapted to be moved in conjunction with the first eccentric portion, a second externally-toothed gear adapted to be moved in conjunction with the second eccentric portion, a third externally-toothed gear adapted to be moved in conjunction with the third eccentric portion, a plurality of pin teeth disposed along an inner periphery of a case to allow each of the first, second and third externally-toothed gears to be in meshing engagement therewith, and an output shaft unit adapted to be rotated in conjunction with the first, second and third externally-toothed gears. The first, second and third eccentric portions are arranged with a given phase difference in a rotation direction of the crankshaft with respect to each other. In the speed reducer, each of the first, second and third externally-toothed gears is in meshing engagement with less than half of the plurality of pin teeth.