Variable Drive Return to Neutral Mechanism Hysteresis Reduction
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Solution Overview
Problem
Variable drive apparatus, such as hydraulic systems, face hysteresis issues due to machining tolerances in scissors-style return to neutral (RTN) mechanisms, leading to delayed responsiveness and potential vehicle creep, making it difficult to achieve and maintain a reproducible neutral setting.
Innovation Solution
The introduction of a speed adjustment assembly with an RTN mechanism that includes a neutral lockdown plate, control arm, rotatable return plate or arm, and bias springs, which are strategically positioned to minimize hysteresis and allow for differing return forces in forward and reverse directions, enabling a lighter return force in the predominant direction of operation and the option to eliminate one return force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If scissors-style RTN mechanisms are used, then flexibility in applying RTN mechanism is improved, but hysteresis increases due to cumulative machining tolerances
Solution Approach 1:
The RTN mechanism is divided into separate functional components: a control arm directly coupled to the control shaft, a return arm with a return surface, and a separate RTN member with a contact surface. This segmentation allows each component to be precisely manufactured and assembled to minimize cumulative tolerances, thereby reducing hysteresis while maintaining design flexibility.
Solution Approach 2:
A spring is introduced as an intermediary element between the control arm and return arm, providing a controlled return force that compensates for minor tolerance variations. The spring acts as a mediator that ensures consistent neutral positioning while allowing the rigid components to maintain their precise geometric relationships.
2Ease of operation
If control arm has free play before contacting scissor return arm, then ease of operation is improved, but neutral setting reproducibility worsens
Solution Approach 1:
The mechanism transitions from a static rigid linkage to a dynamic system where the spring provides a progressive return force. The spring allows initial free play for ease of operation, then progressively engages to ensure precise neutral positioning, adapting its stiffness characteristic to the operational phase.
Solution Approach 2:
The spring rate and pre-load are carefully selected to provide adequate free play during normal operation while ensuring sufficient return force to eliminate backlash and achieve reproducible neutral settings. The geometric parameters of the contact surfaces are also optimized to minimize hysteresis.
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 solution minimizes hysteresis and associated effects, improving vehicle responsiveness and reducing operator fatigue by providing precise control over the return to neutral position, ensuring predictable vehicle operation and flexibility in RTN mechanism design.
Implementation Method 1
a pair of springs to bias the control shaft back to a neutral position from either a forward or reverse rotation
Data Source
AI summary
A return to neutral (RTN) mechanism for a variable drive apparatus having a rotatable control shaft is provided. The RTN mechanism incorporates a neutral lockdown plate secured to the housing of the variable drive apparatus and disposed about the rotatable control shaft, a control arm fixed to the control shaft to impart rotation thereto, a single, rotatable return arm piloted upon a protective cover, and a pair of springs to bias the control shaft back to a neutral position from either a forward or reverse rotation.