Hydraulic Tractor Speed and Steering Control
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Solution Overview
Problem
Hydrostatically steered windrowers face limitations in transport speed due to instability at high speeds, with complex motor displacement control and braking systems that result in unpredictable shifting characteristics and steering deviations, especially in dual path applications.
Innovation Solution
A hydraulically driven tractor with continuously variable hydraulic pumps and motors, allowing for step-less displacement control and independent steering, enabling symmetric or differential ground speed adjustments for improved stability and braking without affecting steering control, and incorporating separate steering signals for manual and automatic control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If hydrostatic propulsion system with variable displacement pump and motor is used, then torque and speed can be varied between high torque/low speed and low torque/high speed modes, but the system complexity increases due to discrete step control and unpredictable shifting characteristics
Solution Approach 1:
The patent applies dynamics by making the motor displacement continuously variable rather than discrete. The motor displacement control system allows smooth transition between high torque/low speed and low torque/high speed modes without fixed steps, eliminating unpredictable shifting characteristics while maintaining adaptability. This is achieved through a control system that continuously adjusts motor displacement based on operating conditions rather than predetermined discrete positions.
Solution Approach 2:
The patent replaces mechanical discrete step control mechanisms with an electronic control system that provides continuous variable displacement control. Instead of mechanical linkages and discrete positioning mechanisms, an electronic controller receives operator input and continuously modulates motor displacement, eliminating the complexity of mechanical step control while maintaining torque and speed adaptability.
2Ease of operation
If fixed gearbox ratio is used in dual path hydrostatic system, then wheel speed synchronization is simplified, but the vehicle cannot achieve both high torque/low speed working operations and low torque/high speed transportation efficiently
Solution Approach 1:
The patent applies dynamics by making the gearbox ratio variable rather than fixed. The dual path hydrostatic system incorporates a variable ratio gearbox that can continuously change transmission ratios to accommodate both high torque/low speed working operations and low torque/high speed transportation. This dynamic ratio adjustment maintains wheel speed synchronization while providing operational mode flexibility, eliminating the need to choose between fixed ratio limitations.
Solution Approach 2:
The patent changes the transmission ratio parameter from fixed to variable. The variable ratio gearbox allows the system to optimize the transmission ratio based on operational requirements - using lower ratios for high torque working operations and higher ratios for high speed transportation. This parameter change enables the system to achieve both synchronization simplicity and operational versatility simultaneously.
3Speed
If higher vehicle speeds are achieved, then transport efficiency improves, but stability deteriorates due to cab forward configuration with driven wheels ahead of castor wheels
Solution Approach 1:
The patent applies the counterweight principle by positioning the heavy engine at the rear of the vehicle, behind the castor wheels. This rearward weight placement creates a counterbalancing effect that offsets the instability caused by the cab-forward configuration with driven wheels ahead of the castor wheels. The rear engine weight acts as a counterweight that improves overall vehicle stability during high-speed transportation, allowing the vehicle to achieve higher speeds without sacrificing stability.
4Measurement precision
If independent braking is applied to each wheel in dual path system, then braking control precision is improved, but steering control becomes unpredictable due to differential braking effects
Solution Approach 1:
The patent merges the braking control of left and right wheels by linking the braking systems together. Instead of completely independent braking controls that cause unpredictable steering deviations, the braking systems are coordinated so that braking forces are applied in a balanced manner. This merging of braking controls maintains precision while ensuring that differential braking effects do not interfere with steering control, keeping steering behavior predictable during braking operations.
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 allows for higher vehicle speeds while maintaining stability and precise steering, reducing the complexity of braking and shifting, and enabling efficient operation in both working and transport modes.
Implementation Method 1
a first and a second hydraulic pump each driven by the engine for generating a source of hydraulic fluid under pressure
Implementation Method 2
the first driven wheel including a first hydraulic drive motor for driving the first wheel and the second driven wheel including a second hydraulic drive motor for driving the second wheel
Data Source
AI summary
A tractor has hydraulically driven wheels at a cab end and castor wheels at an engine end. Each driven wheels is driven by a hydraulic motor with a continuous adjustment of the motor displacement, with the motor being driven by a pump also having continuous displacement. The motor displacement is controlled by an electronic controller in response to stroking of the speed control lever to manage the displacement to provide required drive torques at different points in the stroke. There is provided an automatic steering system having a guidance controller arranged to receive GPS position information which controls the steering by differentially adjusting the displacement of the motors so that the automatic steering is independent of the manual steering which controls the pumps.