Hydraulic Pump Torque Control for Excavator Swing Start
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Solution Overview
Problem
Hydraulic excavators experience energy inefficiency and reduced work efficiency during swing operations due to excessive energy loss through relief valves and insufficient flow rates, particularly during start-up and transition to constant speed, which affects both independent and combined swing operations.
Innovation Solution
The pump control unit dynamically adjusts the maximum absorption torque of hydraulic pumps based on delivery pressure, reducing energy loss by decreasing torque during high-pressure conditions and increasing it as pressure decreases, while redistributing torque between pumps to ensure adequate flow rates for swing motors and other actuators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the delivery flow rate of the hydraulic pump is excessively high during swing start, then the swing motor can overcome the heavy inertia load, but energy loss increases due to hydraulic fluid escaping from the relief valve
Solution Approach 1:
The pump control unit dynamically adjusts the displacement volume of the hydraulic pump during swing operations. During swing start, the displacement volume is reduced to limit delivery flow rate and prevent excessive energy loss through the relief valve. As the swing accelerates and relief stops, the displacement volume is increased to maintain adequate flow rate for achieving constant swing speed. This dynamic adjustment resolves the contradiction between providing sufficient flow for acceleration and preventing energy waste through relief.
Solution Approach 2:
The control unit changes the operating parameters of the hydraulic pump based on swing conditions. By adjusting the displacement volume parameter in response to delivery pressure and swing speed, the system optimizes the balance between providing enough flow to overcome inertia and limiting flow to prevent relief valve energy loss. This parameter change enables the system to adapt to different phases of swing operation.
2Loss of energy
If the delivery flow rate of the hydraulic pump is excessively low during swing acceleration, then energy loss is reduced, but the swing motor is unable to smoothly achieve constant speed due to insufficient flow rate
Solution Approach 1:
The system dynamically adjusts the pump displacement volume based on real-time swing conditions. During the acceleration phase when relief valve operation causes energy loss, the displacement is reduced. When the swing approaches constant speed and relief stops, the displacement is increased to ensure sufficient flow rate reaches the swing motor. This dynamic control resolves the contradiction between minimizing energy loss and maintaining productivity.
Solution Approach 2:
The pump control unit uses feedback from delivery pressure sensors and swing speed signals to adjust pump displacement. When delivery pressure indicates relief valve operation, the control unit reduces displacement to minimize energy loss. When pressure stabilizes and swing speed increases, the control unit increases displacement to maintain adequate flow for constant speed operation. This feedback mechanism enables the system to automatically optimize the balance between energy efficiency and work performance.
3Power
If total horsepower control is used to reduce pump displacement during swing start, then maximum absorption torque is maintained, but delivery flow rate becomes higher than required causing relief valve energy loss
Solution Approach 1:
The control unit modifies the displacement volume parameter of the hydraulic pump based on swing phase detection. During swing start when delivery pressure reaches maximum (relief pressure), the displacement is reduced below what total horsepower control would dictate, specifically limiting flow rate to prevent relief valve energy loss. This parameter change allows the system to prioritize energy efficiency over maximum torque utilization during the initial swing phase.
Solution Approach 2:
The system transitions from a static total horsepower control approach to a dynamic control strategy that adjusts displacement based on real-time swing conditions. During swing start, the displacement is dynamically reduced to limit flow and prevent relief valve operation. As swing accelerates and relief stops, displacement is dynamically increased to maintain adequate flow. This dynamic adjustment resolves the contradiction between maintaining maximum absorption torque and preventing energy loss.
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 approach enhances energy efficiency and work efficiency by minimizing energy loss during swing start-ups and maintaining required flow rates for smooth constant speed operations, improving both independent and combined swing operations.
Implementation Method 1
the delivery pressure of the second hydraulic pump rises sharply to reach the maximum pressure (relief pressure) determined by a relief valve
Implementation Method 2
a delivery flow rate of the hydraulic pump is excessively high at this time, the energy loss increases
Implementation Method 3
energy loss is produced by a hydraulic fluid escaping from the relief valve
Data Source
Figure 1
Figure 2
Figure 3
AI summary
During a swing start, a pump torque calculating section associated with pump delivery pressure 43, a pump torque calculating section associated with swing operation pressure 44, and a maximum value selecting section 45 of a controller 38 performs control to change a maximum absorption torque of a second hydraulic pump 3 between Tb and Tc in accordance with a delivery pressure of the second hydraulic pump 3. In a combined swing operation combining swing with other motion, a subtraction section 47 performs a calculation to subtract a maximum absorption torque Tp2 of the second hydraulic pump 3 from a total pump torque Tr0 and control to thereby distribute an amount of torque reduced in the second hydraulic pump 3 to a first hydraulic pump 2 associated with an actuator other than a swing motor 7. An energy loss due to relief during the swing start can thereby be reduced to improve energy efficiency. Further, a required flow rate can be supplied to the swing motor during a process of transiting to a constant speed following the swing start, thus achieving a smooth shift to a constant speed swing. Improved combined work operability and work efficiency can therefore be achieved.