Transmission mechanism including shift drum and actuator unit which are coaxially disposed
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Solution Overview
Problem
In straddle vehicles like motorcycles, the existing linkage mechanisms between the actuator and shift drum are complex and prone to weight increase when reinforced, due to the need to avoid interference with the actuator, and the gear position sensor's axial placement complicates the power transmission route.
Innovation Solution
A configuration where the actuator unit is positioned inwardly of the transmission case with a drive shaft having the same rotational axis as the shift drum, allowing a straight power transmission route and eliminating the need for reinforcement, while the gear position sensor's detection axis is parallel to the shift drum's axis, hidden by the actuator unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the linkage mechanism is disposed to avoid the actuator, then the actuator does not interfere with the linkage mechanism, but the linkage mechanism becomes complicated
Solution Approach 1:
The actuator is integrated with the linkage mechanism such that the actuator shaft and shift drum share the same rotational axis. This merging eliminates the need for separate linkage components and their associated linkages, directly resolving the contradiction by simplifying the mechanism while maintaining interference-free operation.
Solution Approach 2:
The actuator is repositioned from a lateral arrangement to a coaxial arrangement along the rotational axis of the shift drum. This dimensional change allows the actuator and linkage to occupy the same radial space without interference, eliminating the need for complex avoidance linkages.
2Reliability
If reinforcement is provided to improve the durability of the linkage mechanism, then the durability is improved, but the weight of the vehicle is increased
Solution Approach 1:
The actuator shaft is directly coupled to the shift drum, eliminating intermediate linkage components that would require reinforcement. This direct coupling reduces the overall mass of the shifting mechanism while maintaining durability through the simplified load path.
Solution Approach 2:
The complex linkage mechanism is extracted and replaced with a direct coaxial coupling. This removal of unnecessary components reduces weight while the direct connection improves durability by eliminating potential failure points in the linkage.
3Measurement precision
If the gear position sensor is disposed on the axis of the shift drum, then the sensor can detect the rotation angle accurately, but the power transmission route becomes complicated
Solution Approach 1:
The gear position sensor is repositioned from a coaxial location to a lateral position where its detection axis is parallel to but offset from the shift drum axis. This dimensional change allows the sensor to accurately detect rotation angle while the power transmission route passes cleanly through the center without interference.
Solution Approach 2:
The actuator unit serves as an intermediary structure that houses both the power transmission components and the gear position sensor. This arrangement allows the sensor to be positioned away from the main power transmission path while still accurately measuring the rotation angle of the shift drum.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A straddle vehicle (1) includes: a shift drum (23) that makes a shift change of a transmission (12) including a plurality of gear trains (17); a transmission case (14) enclosing the shift drum (23), the transmission case (14) including a side wall portion (14a, 14b) provided with an insertion hole (H1, H2) into which an end portion (23b, 23c) of the shift drum (23) is inserted; and an actuator unit (30) secured to an outer surface of the side wall portion (14a, 14b), the actuator unit (30) including a drive shaft (30d) that outputs drive power to rotate the shift drum (23), the drive shaft (30d) having the same rotational axis (X) as the shift drum (23) and being connected to the shift drum (23) on the rotational axis (X).