Hydrostatic Drive Pivot Control to Prevent Cavitation on Reversal
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Solution Overview
Problem
Cavitation occurs during reversing or decelerating of a hydrostatic drive due to rapid changes in fluid flow, potentially causing damage to the hydraulic system.
Innovation Solution
Implementing an electrohydraulic adjustment system with controlled pivoting angles and limited pivoting speeds for hydraulic machines to prevent cavitation by gradually adjusting displacement volumes and pressures, using electronic feedback to manage the transition between motor and pump operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the pivoting angle of the output-side hydraulic machine is rapidly changed to reverse or decelerate the drive, then the response time is improved, but cavitation occurs due to dynamic acceleration of the oil column
Solution Approach 1:
The control unit limits the pivoting speed of the swashplate in the adjustment phase before full reversal or deceleration is achieved. By pre-controlling the rate of change of the pivoting angle, the system prevents cavitation from occurring while still enabling the drive to respond to reversal commands in a timely manner.
Solution Approach 2:
The system dynamically adjusts the pivoting speed of the swashplate based on the current operating state. During the transition phase from motor operation to pump operation, the pivoting speed is constrained to prevent cavitation, while after the transition is complete, the system can operate at full dynamic performance.
2Productivity
If the displacement volume of the hydraulic machine is rapidly adjusted to change torque direction, then the control responsiveness is improved, but the cavitation risk increases
Solution Approach 1:
The control unit pre-regulates the displacement volume change rate during the transition phase. By limiting how quickly the displacement volume can be adjusted, the system prevents cavitation while maintaining responsive control capability for the overall operation.
Solution Approach 2:
The system changes the operating parameters (pivoting angle, displacement volume) in a controlled manner with regulated rates of change. This allows the hydraulic machine to transition between operating modes while maintaining parameters within safe limits that prevent cavitation.
3Productivity
If the fluid flow direction is quickly reversed to change torque direction, then the operational efficiency is improved, but damage to the hydraulic system may occur
Solution Approach 1:
The control unit implements preliminary control of the pivoting speed before the fluid flow direction reversal is completed. This pre-control measure ensures that the oil column acceleration remains within safe limits, preventing damage to the hydraulic system while enabling efficient operation.
Solution Approach 2:
The control unit acts as a cushioning mechanism by limiting the rate of change of the pivoting angle. This prevents sudden shocks and dynamic stresses that could damage the hydraulic system during flow direction reversal, while still allowing the system to achieve the desired operational changes efficiently.
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
Prevents cavitation by controlling pivoting speeds and pressures, ensuring stable operation during direction changes, thereby protecting the hydraulic system from damage.
Implementation Method 1
One phenomenon is cavitation. As the oil column in the suction line must be accelerated, this process must not be too dynamic. The cavitation at the suction port of the motor is dependent on the speed, pivoting angle, and pivoting speed.
Data Source
AI summary
A method for controlling a drive, which has a first hydraulic machine coupled to a drive machine and a second hydraulic machine coupled to an output to change one of the hydraulic machines from a pump operation to a motor operation and the other of the hydraulic machines from a motor operation to a pump operation includes controlling the pivoting angle of the other hydraulic machine so that the pivoting angle goes from a positive start pivoting angle to a negative target pivoting angle or from a negative start pivoting angle to a positive target pivoting angle. The control of the pivoting angle of the other hydraulic machine between the start pivoting angle and the target pivoting angle is limited such that the pivoting speed of the pivoting angle of the second hydraulic machine does not exceed a predefined value.