Retractable Key Mechanism for Gearbox Reverse Braking
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Solution Overview
Problem
Existing reverse gear braking systems in manual gearboxes with parallel shafts experience creaking issues due to speed differences between gears, and current solutions either require additional synchronizers or direct braking, which can be inefficient and generate additional forces during gear shifting.
Innovation Solution
A retractable key mechanism is introduced that radially engages and disengages from a forward gear dog, using guided tracks to drive the synchronizer fork, allowing for precise control and synchronization without relying on ramps or beading systems, thereby reducing drag and synchronization effort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a forward synchronizer is used to brake the input shaft before reverse gear engagement, then the grinding noise is reduced, but additional force is required to actuate the synchronizer during gear shifting
Solution Approach 1:
The synchronizer is actuated in advance during the first part of the reverse gear engagement travel, before the intermediate reverse gear engages with the secondary reverse gear. This preliminary braking action reduces the speed difference between gears, eliminating grinding noise while the gear teeth are not yet engaged, thus reducing the force required during the actual engagement phase
Solution Approach 2:
The reverse gear engagement process is divided into two distinct phases: the first part where the synchronizer is actuated for braking, and the second part where the gear engagement occurs. This segmentation allows the braking function to be separated from the engagement function, optimizing both noise reduction and shifting effort independently
2Object-affected harmful factors
If the primary shaft speed is reduced to no higher than 150 rpm before reverse gear engagement, then smooth engagement is achieved, but the braking system must handle high speed differences
Solution Approach 1:
The synchronizer performs preliminary braking of the input shaft before reverse gear engagement, reducing the primary shaft speed from idle (approximately 800 rpm) to below 150 rpm in advance. This preliminary action prepares the system for smooth engagement while managing the high speed difference through controlled, gradual deceleration
Solution Approach 2:
The synchronizer acts as an intermediary braking mechanism between the input shaft and the reverse gear engagement process. It mediates the speed difference by providing controlled friction braking, allowing the primary shaft to decelerate smoothly without requiring excessive braking force on the reverse gear shaft itself
Data Source
Figure 1A
Figure 1B~1C
Figure 1D~1E
AI summary
Device for braking of reversing in a parallel shaft gearbox, comprising a reversing shaft mounted in a gearbox housing and carrying an intermediate reversing pinion which continually meshes with a primary reversing pinion, and which can move between a disengaged position and a reversing position under the control of a forward dog (12) actuated by a shift finger (3) which is rotated with a selector shaft (2) to select a line of gears and moves in translation in a key (11) locked on the selector shaft (2) to engage a forward or reversing gear on a selected line of gears, characterized in that the finger (3) moves a cotter (13) mounted inside the key (11), radially engaged in a forward dog (12) which it drives on a first part of the reversing engagement course, and radially retracted towards the interior of the key on a second part of the reversing engagement course, where it retracts to the forward dog (12).