Hydraulic Torque Feedback Circuit for Excavator Pump Control
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Solution Overview
Problem
Current hydraulic drive systems for construction machines, such as hydraulic excavators, face challenges in performing total torque control with high precision, especially when one hydraulic pump is under torque control and the other is under load sensing control, leading to inefficient use of prime mover output torque and potential engine stall.
Innovation Solution
A hydraulic drive system with two variable displacement pumps, where one pump includes a torque control unit and the other a load sensing control unit, utilizes a torque feedback circuit to precisely detect and simulate the absorption torque of the second hydraulic pump, allowing for precise total torque control through a purely hydraulic structure and feedback mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a constant set pressure is used in the pressure reducing valve for total torque control, then the rated output torque of the prime mover can be efficiently utilized when one pump operates at maximum torque, but the absorption torque control becomes imprecise when the other pump operates below maximum torque
Solution Approach 1:
The patent applies dynamics by making the set pressure of the pressure reducing valve variable rather than constant. The set pressure is made to vary in accordance with the delivery pressure of the second hydraulic pump, allowing the system to adapt to different operating conditions. This dynamic adjustment enables precise total torque control whether the second pump operates at maximum torque or below maximum torque, resolving the contradiction between efficient torque utilization and control precision.
2Speed
If the delivery pressure of the second hydraulic pump is directly led to the regulator of the first hydraulic pump, then the total torque control response is fast, but the control precision deteriorates when the second pump is under load sensing control
Solution Approach 1:
The patent introduces an intermediary element - the pressure reducing valve with variable set pressure - between the delivery pressure of the second hydraulic pump and the regulator of the first hydraulic pump. This intermediary processes the delivery pressure signal and adjusts it according to the actual absorption torque of the second pump, providing both fast response and precise control. The intermediary transforms the raw pressure signal into an accurate torque representation that accounts for load sensing control conditions.
3Device complexity
If a purely hydraulic structure is used for torque feedback, then the system complexity is reduced, but achieving high precision torque detection becomes difficult
Solution Approach 1:
The patent employs pneumatic and hydraulic principles to create a torque feedback circuit that uses fluid pressure to represent and transmit torque information. The pressure reducing valve with variable set pressure, fed by the delivery pressure of the second pump, generates a feedback pressure that accurately reflects the absorption torque. This purely hydraulic approach achieves high precision torque detection without requiring complex electronic sensors or computational systems, maintaining simplicity while ensuring accuracy.
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 efficient utilization of prime mover output torque and prevents engine stall by accurately controlling the displacement of both hydraulic pumps, ensuring precise total torque control even when pumps operate under different control modes.
Implementation Method 1
a torque feedback circuit which is supplied with the delivery pressure of the second hydraulic pump and the load sensing drive pressure, modifies the delivery pressure of the second hydraulic pump to achieve a characteristic simulating the absorption torque
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
The object is to make it possible to efficiently utilize rated output torque of the prime mover by performing total torque control with high precision through precise detection of absorption torque of the other hydraulic pump by use of a purely hydraulic structure and feedback of the absorption torque to the one hydraulic pump's side. For this purpose, the hydraulic drive system is equipped with: a torque feedback circuit 112v which is supplied with delivery pressure of a main pump 202 and load sensing drive pressure, modifies the delivery pressure of the main pump 202 to achieve a characteristic simulating the absorption torque of the main pump 202, and outputs the modified pressure; and a torque feedback piston 112f which is supplied with output pressure of the torque feedback circuit and controls displacement of a main pump 102 so as to decrease the displacement of the main pump 102 and thereby decrease maximum torque T12max as the output pressure increases. The torque feedback circuit 112v includes first and second variable pressure reducing valves 112g and 112q.