Hydraulic Relief Pressure Control via Engine Torque Feedback
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Solution Overview
Problem
Existing hydraulic control systems for work machines like hydraulic shovels face challenges in accurately controlling circuit pressure due to variations in engine output and pump efficiency, making it difficult to manage relief pressures and protect hydraulic equipment effectively.
Innovation Solution
A hydraulic control system with a variable displacement hydraulic pump, a relief valve, and a relief pressure control mechanism that includes a pump pressure detection means, engine torque detection means, and a control means to regulate the pump flow rate and set a target engine torque to maintain a preset target relief pressure, allowing for accurate management of relief pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the set pressure of the relief valve is adjusted to control circuit pressure accurately, then relief pressure control improves, but readjustment is required after mounting which increases complexity and time consumption
Solution Approach 1:
The control system automatically detects actual relief pressure and engine torque, then self-adjusts the target relief pressure setting based on detected individual differences. This eliminates manual readjustment while maintaining accurate pressure control specific to each machine's characteristics.
Solution Approach 2:
The system continuously monitors actual relief pressure and engine torque during operation, using this feedback to automatically adjust the target relief pressure. This closed-loop control ensures accurate pressure management without requiring manual intervention after mounting.
2Measurement precision
If manual readjustment of the relief valve is performed after mounting, then pressure control accuracy improves, but time and operational complexity increase
Solution Approach 1:
The system performs preliminary detection of individual differences in engine output and pump efficiency during initial operation, then automatically sets appropriate target relief pressure values. This preliminary characterization eliminates the need for time-consuming manual readjustment procedures.
Solution Approach 2:
The control system automatically detects and adapts to each machine's specific characteristics without requiring operator intervention for adjustment, thereby eliminating time loss while maintaining pressure control accuracy.
3Device complexity
If a fixed target relief pressure is used, then system simplicity is maintained, but individual differences in engine output and pump efficiency cause inaccurate pressure control
Solution Approach 1:
The target relief pressure is transformed from a fixed value to a dynamic parameter that automatically adapts to each machine's characteristics. The system detects individual differences and adjusts the target pressure dynamically, maintaining both simplicity and accuracy.
Solution Approach 2:
The control system changes the target relief pressure parameter based on detected individual differences in engine torque and pump performance. This parameter adaptation maintains pressure control accuracy while preserving system simplicity through automatic adjustment.
4Reliability
If the relief valve is designed with override characteristic, then pressure relief function is achieved, but upstream pressure rises with increased flow rate making accurate control difficult
Solution Approach 1:
The system continuously detects actual relief pressure and engine torque, using this feedback to adjust the target relief pressure compensation amount. This compensates for the override characteristic effect and maintains precise pressure control despite varying flow rates.
Solution Approach 2:
The control system dynamically changes the target relief pressure parameter based on detected engine torque and actual pressure conditions, compensating for override characteristic effects and maintaining accurate pressure control across different operating conditions.
Data Source
AI summary
PROBLEM: To enable accurately controlling and managing by means of software, a relief pressure of a pump oil passage supplied with a discharge oil of a hydraulic pump. SOLUTION: There are provided a target engine torque setting/calibration unit (19) during relief configured to detect an engine torque in a state where a pump flow rate is regulated so that a detected pressure value of a pump oil passage (2) during the relief reaches a target relief pressure (LPt), and to set and calibrate the detected engine torque as a target engine torque (LTt) during relief, and a control unit (20) during relief configured to control a pump flow rate so that the detected value of the engine torque reaches the target engine torque (LTt) during the relief.