Electric Motor Torque Control for Fast Hydraulic Pump Response
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Solution Overview
Problem
Existing hydraulic systems in construction machines suffer from slow response times and latency issues due to slow communication interfaces and PLC processing delays, which affect machine handling accuracy and can lead to undesired over-steering.
Innovation Solution
A control unit that directly converts load pressure into target drive torque for an electric drive motor, bypassing slow feedback loops, allowing for faster and more energy-efficient control of hydraulic systems by using a look-up table or analytical relationships to map load pressure to torque, and incorporating feedback for calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If control messaging via CAN bus and PLC processing is used, then system reliability is maintained, but control response time increases and bandwidth is limited
Solution Approach 1:
The patent extracts the critical control function from the slow PLC/CAN bus system and implements it directly in the motor controller's microprocessor. This allows the torque control to bypass the slow communication interface and respond immediately to load pressure changes, achieving millisecond-level response times while maintaining system reliability through the distributed control architecture.
Solution Approach 2:
The control system is segmented into two parts: time-critical torque control handled by the motor controller's microprocessor, and higher-level system management handled by the PLC. This segmentation allows fast local responses without compromising overall system coordination and reliability.
2Productivity
If feedback loops are used for motor control, then system stability is improved, but control bandwidth is reduced and latency increases
Solution Approach 1:
The system pre-calculates the relationship between load pressure and required torque using a lookup table stored in the motor controller's memory. When load pressure changes, the controller immediately retrieves the corresponding torque value from the pre-computed table, eliminating the need for real-time iterative calculations and reducing control latency while maintaining accuracy.
Solution Approach 2:
The patent replaces the traditional mechanical-hydraulic feedback loop with an electronic control system that directly measures load pressure and converts it to torque commands. This substitution eliminates mechanical delays and enables faster electronic response, achieving high control bandwidth without the latency inherent in mechanical feedback systems.
3Speed
If direct torque control is implemented, then responsiveness to load changes is improved, but energy efficiency may be compromised without proper pressure margin management
Solution Approach 1:
The system continuously monitors actual pump output pressure and compares it with the target pressure derived from load pressure plus margin. This feedback loop allows the controller to adjust motor torque in real-time, ensuring the motor only consumes the energy necessary to maintain the required pressure margin, thereby achieving both responsiveness and energy efficiency.
Solution Approach 2:
The control system dynamically adjusts the pressure margin based on operating conditions. During transient load changes, a larger margin ensures rapid response, while during steady-state operation, the margin is reduced to minimize energy consumption. This dynamic adjustment optimizes the trade-off between responsiveness and energy efficiency.
Data Source
AI summary
A control unit (150) for controlling a hydraulic system on a construction machine (100), where the hydraulic system comprises a hydraulic pump arrangement with an electric drive motor configured to drive a hydraulic pump at a controllable drive torque, wherein the control unit (150) is arranged to obtain a load pressure of at least one actuator in the hydraulic system, to convert the obtained load pressure into a corresponding torque, and to control the electric drive motor to generate the torque.