Hydraulic Servo Drive Torque Limiting for Pump Protection
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Solution Overview
Problem
Hydraulic systems face limitations in utilizing the full range of mechanical load torque due to fixed maximum and minimum motor torque limits, which restrict performance and can lead to pump damage from negative torque reversal.
Innovation Solution
A dynamic limiting unit that adjusts motor torque based on real-time system variables, such as actual system pressure and motor speed, to prevent excessive load torque, allowing for highly dynamic motor torque generation without exceeding permissible limits, and includes a calculation unit to estimate load torque and a comparison unit to enforce torque thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed maximum and minimum motor torque limits are applied to prevent pump damage, then pump reliability is improved, but the servo drive performance and productivity are worsened due to restricted torque range
Solution Approach 1:
The patent implements dynamic torque limiting where the maximum and minimum torque thresholds are not fixed but adapt based on real-time system state variables including motor speed, actual system pressure, and estimated load torque. This allows the torque limits to change dynamically during operation, enabling higher productivity when conditions permit while maintaining pump protection when conditions require it.
Solution Approach 2:
The patent changes the parameter of torque limits from fixed constant values to variable values that depend on system state. The controlling device continuously adjusts the permissible torque range based on measured parameters like motor speed and system pressure, allowing the system to operate at the boundaries of safety rather than being constrained by conservative fixed limits.
2Speed
If negative electric motor torque is applied for rapid deceleration of the pump, then the speed response and productivity are improved, but the mechanical load torque may become negative causing pump destruction
Solution Approach 1:
The patent dynamically adjusts the minimum torque threshold based on motor speed. When the motor is decelerating, the system allows negative torque values but limits them to a dynamically calculated minimum threshold that prevents the load torque from becoming negative. This enables rapid deceleration while protecting the pump from reverse torque damage.
Solution Approach 2:
The system uses feedback from motor speed measurements and estimated load torque calculations to continuously adjust the permissible torque range. During deceleration phases, the feedback mechanism detects the changing system state and adjusts the minimum torque limit to allow negative torque for braking while preventing it from exceeding the threshold that would cause pump damage.
3Reliability
If fixed torque limits are specified to protect the pump, then pump reliability is improved, but the system adaptability and ease of operation are worsened due to inability to utilize full torque range
Solution Approach 1:
The patent transforms the static torque limiting approach into a dynamic one where the permissible torque range adapts to real-time system conditions. The system can utilize a wider torque range when conditions are favorable while automatically constraining torque when conditions require protection, providing both high adaptability and reliable pump protection.
Solution Approach 2:
The patent changes the torque limit parameters from fixed values to state-dependent variable values. The system continuously calculates permissible torque boundaries based on current motor speed, system pressure, and estimated load torque, allowing the torque range to expand or contract dynamically to match actual system needs and capabilities.
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 enables the hydraulic system to operate within a wider range of mechanical load torque, preventing pump damage and allowing for more dynamic pressure control, while ensuring that motor torque remains within safe limits, thus enhancing system performance and safety.
Implementation Method 1
a servo drive serves as the hydraulic generator... a combination of an electric motor and a pump, wherein the electric motor is supplied with motor current by an inverter
Implementation Method 2
the pump supplies a hydraulic volume flow, dependent on the supplied mechanical motor torque, of a supplied medium of the hydraulic load
Data Source
AI summary
To utilize and protect a mechanical load torque range of a servo drive in combination with a pump, a control unit is given a target system pressure as a reference variable and an actual system pressure as a control variable. An electric motor torque acting on a pump of the servo drive is specified by the control unit to an electric motor of the servo drive, a volume flow at the hydraulic load is generated by the pump, by which a mechanical load torque sets it at the electric motor and the actual system pressure is produced in the hydraulic load via the volume flow. A dynamic system variable of the hydraulic system is transmitted to the limiting unit. The limiting unit limits the motor torque transmitted by the control unit to the electric motor as a function of the value of the system variable.