Electric Work Vehicle Hydrostatic Drive Train Switching
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Solution Overview
Problem
Existing work vehicles equipped with hydrostatic transmission drive trains cannot switch seamlessly between four-wheel drive and two-wheel drive configurations while moving, due to insufficient responsiveness of the hydrostatic pump and internal combustion engine, leading to sudden variations in hydraulic fluid flow.
Innovation Solution
The implementation of an electric work vehicle with a hydrostatic drive train that includes an electric motor, a hydrostatic pump, and drive units with variable displacement hydrostatic motors, along with a switching device and control unit that manage the engine displacement and electric motor speed to control hydraulic fluid flow smoothly during configuration switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If switching between four-wheel drive and two-wheel drive configurations is performed, then the work vehicle can achieve both high tractive effort and high forward speeds, but the switching cannot be carried out while the vehicle is moving due to sudden variation in hydraulic fluid flow rate
Solution Approach 1:
The patent applies dynamics by making the hydrostatic pump's displacement variable rather than fixed. The control unit dynamically adjusts the pump's displacement in response to switching commands, enabling smooth transition between drive configurations while moving. This resolves the contradiction by allowing configuration switching during motion through continuous adjustment of hydraulic flow rate.
Solution Approach 2:
The patent changes the parameter of pump displacement from fixed to variable. By controlling the pump's displacement parameter dynamically based on the desired drive configuration, the system can smoothly adjust hydraulic fluid flow rate during switching operations, eliminating sudden variations and enabling switching while the vehicle is moving.
2Power
If the hydrostatic pump and internal combustion engine are used, then the system can provide hydraulic power, but the responsiveness is insufficient to control sudden variations in hydraulic fluid flow rate during configuration switching
Solution Approach 1:
The patent replaces the internal combustion engine with an electric motor that has superior responsiveness. The electric motor can rapidly adjust its speed to control the hydrostatic pump's output, providing the necessary response speed to handle sudden changes in hydraulic fluid flow rate during configuration switching while maintaining adequate power output.
3Force
If the total engine displacement is increased for high tractive effort, then the vehicle can achieve significant pulling force, but the forward speed decreases
Solution Approach 1:
The patent applies dynamics by making the drive unit displacement variable rather than fixed. The control unit dynamically adjusts the pump's displacement based on the selected drive configuration, enabling the system to provide high tractive effort when needed while maintaining the capability for high forward speeds, thus resolving the contradiction between force and speed.
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
Enables smooth and dynamic switching between high-tractive-force, low-speed and low-tractive-force, high-speed hydrostatic configurations while the vehicle is moving, optimizing performance based on speed and operational requirements.
Implementation Method 1
a hydrostatic pump driven by the electric motor... at least one hydrostatic motor for rotational driving of the at least two drive wheels
Implementation Method 2
at least one hydrostatic motor for rotational driving of the at least two drive wheels
Data Source
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AI summary
The invention relates to a work vehicle comprising an electrical power source 10, a hydrostatic drivetrain, a switching device 20, and a control unit 25. The hydrostatic drivetrain comprises an electric motor 9 powered by the electrical power source 10, a hydrostatic pump 11 driven by the electric motor 9, the hydrostatic pump 11 having a continuously variable pump displacement, drive wheels 8F, 8R, and at least one hydrostatic motor 13F, 13R with a fixed motor displacement. The switching device 20 is configured to selectively switch the drive displacement between at least one slow-moving drive and one fast-moving drive of the work vehicle. The control unit 25 is configured to drive the rotational speed of the electric motor 9 in response to a switching of the drive displacement.