Servo-Assisted Gearbox Shifting with Spring Play
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Solution Overview
Problem
In commercial vehicles with cab-over designs, the long distance between the transmission and driver's seat complicates precise gear shifting due to lengthy and sometimes tight shift linkages, and existing servo-assistance devices face issues with ambiguous lever positioning and increased manual shifting forces, especially with high friction systems.
Innovation Solution
A servo-assistance device with a control rod and piston rod arrangement that includes a radially positioned spring element allowing play in both directions of actuation, reducing the triggering force by opening the valve before the spring element is compressed, and utilizing elastic elements to support the manual shifting force, ensuring clear lever positioning even in high-friction systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the spring element is positioned to engage the piston rod early in the actuation stroke, then the triggering force increases, but the valve opening force is insufficient to overcome the spring force
Solution Approach 1:
The valve is designed to open before the spring element engages the piston rod, allowing the valve to actuate the servo-assistance device in advance. This preliminary action ensures that the servo-assistance force is generated before the high spring force engages, making the system easier to operate without requiring excessive triggering force
2Force
If the spring element is positioned to engage the piston rod late in the actuation stroke, then the triggering force decreases, but the valve remains open too long causing ambiguous lever positioning
Solution Approach 1:
The spring element is designed with controlled engagement timing that dynamically adapts to the actuation stroke. The spring engages the piston rod at an optimized point during the stroke, allowing the valve to close promptly after actuation. This dynamic timing ensures precise lever positioning in detented positions while maintaining low triggering force throughout the motion range
3Measurement precision
If the spring force is increased to improve lever positioning, then the triggering force increases significantly, but the valve opening becomes difficult
Solution Approach 1:
The servo-assistance device acts as an intermediary between the manual shifting force and the transmission shifting mechanism. The servo mechanism amplifies the manual force applied to the control rod, allowing the operator to overcome high spring forces and achieve precise lever positioning without directly applying excessive force. The servo-assistance device mediates the force transmission, making the system both precise and easy to operate
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 reduces the triggering force required for shifting, enhances shifting comfort, and ensures precise positioning of the shift lever, addressing the issues of ambiguous positioning and increased manual effort in existing systems, particularly in high-friction scenarios.
Implementation Method 1
at least one spring element (40), which is arranged on the control rod (20) and radially inside the piston rod (22)
Implementation Method 2
A valve (54) is present in the servo-assistance device, which valve comprises actuating pistons (38, 58) and valve slides (36, 56) arranged on the control rod (20)
Data Source
Figure 1
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AI summary
The invention relates to a servo-assisted device (10) for a switching arrangement (11) on a motor vehicle gearbox, comprising a control rod (20), on which a manual switching force for assistance acts, a piston rod (22) and at least one spring element (40), arranged on the control rod (20) and radially within the piston rod (22). According to the invention, the spring element (40) is arranged on the control rod (20) such that in one or both operating directions of the control rod (20) a play (50, 52) is provided between the spring element (40) and the piston rod (22).