Hydraulic Torque Feedback Circuit for Construction Machine Pump Control
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Solution Overview
Problem
Existing hydraulic drive systems for construction machines, particularly hydraulic excavators, face challenges in accurately performing total torque control when one hydraulic pump is not limited by torque control and is operating under load sensing control, leading to unnecessary reduction in absorption torque and inefficiency in utilizing the rated output torque of the prime mover.
Innovation Solution
A hydraulic drive system with two variable displacement pumps, where the absorption torque of one hydraulic pump is accurately detected and fed back to the other pump using a purely hydraulic torque feedback circuit, allowing for precise total torque control and effective utilization of the prime mover's output torque, while also enabling miniaturization of the pump control unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed set pressure is used in the pressure reduction valve for torque control, then the structure is simple, but the total torque control accuracy deteriorates when the second pump is not limited by torque control
Solution Approach 1:
The pressure reduction valve is replaced with a variable restrictor valve whose opening area dynamically changes based on the load sensing drive pressure. When the second pump operates under load sensing control (lower pressure), the restrictor valve opens wider to allow more flow, accurately reflecting the actual torque. When the second pump is torque-limited (higher pressure), the restrictor valve closes more, preventing excessive torque simulation. This dynamic adjustment resolves the contradiction by adapting the flow restriction to operating conditions.
Solution Approach 2:
The opening area of the restrictor valve is changed as a parameter in response to changes in load sensing drive pressure. This parameter change allows the system to transition from a fixed flow restriction (simple but inaccurate) to a variable flow restriction (complex but accurate). The restrictor valve's opening area becomes a dynamic parameter that correlates with the actual torque being absorbed by the second pump, enabling accurate total torque control across all operating conditions.
2Measurement precision
If the tilting angle of the second hydraulic pump is detected to perform total torque control, then the torque control accuracy is improved, but the device complexity increases
Solution Approach 1:
The mechanical detection method (tilt angle sensor) is replaced with a hydraulic detection method using a restrictor valve and pressure feedback. Instead of mechanically measuring the tilting angle of the second pump, the system uses the hydraulic pressure and flow characteristics through the restrictor valve to indirectly but accurately represent the torque. This substitution maintains torque control accuracy while significantly reducing device complexity by eliminating mechanical sensors and their associated wiring and signal processing.
Solution Approach 2:
The restrictor valve acts as an intermediary element that translates the operating state of the second pump into a proportional pressure signal. Rather than directly measuring tilting angle or torque with complex sensors, the restrictor valve mediates by creating a pressure drop that is proportional to the flow and pressure conditions, which in turn reflects the torque. This intermediary approach simplifies the measurement system while maintaining accuracy.
3Stability of the object's composition
If a pressure reduction valve with fixed set pressure is used, then the system is stable, but the energy utilization efficiency deteriorates
Solution Approach 1:
The static, fixed-pressure reduction valve is replaced with a dynamic restrictor valve whose flow restriction adapts to operating conditions. This dynamic system maintains stability through controlled feedback while improving energy utilization by allowing the first pump to absorb only the actual torque being used by the second pump, rather than unnecessarily reducing torque based on a fixed conservative estimate. The system remains stable because the restrictor valve's opening area changes smoothly in response to load sensing drive pressure.
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 accurate total torque control, efficient energy use, and reduced fuel consumption, enhancing the energy efficiency and practicality of construction machines by accurately simulating the absorption torque of the second hydraulic pump and adjusting the first pump's torque accordingly.
Implementation Method 1
a torque feedback circuit that receives the delivery pressure of the second hydraulic pump and the load sensing drive pressure and modifies the delivery pressure of the second hydraulic pump to provide a characteristic simulating the absorption torque of the second hydraulic pump and that outputs the modified pressure as a torque control pressure
Implementation Method 2
The torque feedback circuit includes a fixed restrictor, a variable restrictor valve located on a downstream side of the fixed restrictor, and a pressure limiting valve connected to a hydraulic line between the fixed restrictor and the variable restrictor valve
Implementation Method 3
a pressure limiting valve connected to a hydraulic line between the fixed restrictor and the variable restrictor valve to control the pressure in the hydraulic line such that the pressure does not increase beyond a pressure that initiates the control of the second torque control section
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
It is an object of the present invention to accurately detect the absorption torque of the other of two hydraulic pumps by a purely hydraulic structure and feed the absorption torque to one of the two hydraulic pumps, thereby to accurately perform a total torque control, effectively utilize a rated output torque of a prime mover, and enhance mountability. To achieve the object, there are provided: a torque feedback circuit 31 to which the delivery pressure of a first hydraulic pump 1a and a load sensing drive pressure are introduced, which modifies the delivery pressure of a second hydraulic pump 1b to provide a characteristic simulating the absorption torque of the second hydraulic pump 1b, and which outputs the modified pressure; and torque feedback pistons 32a, 32b to which the output pressure of the torque feedback circuit 31 is introduced, and which control the capacity of the first hydraulic pump 1a to decrease the capacity of the first hydraulic pump 1a and decrease a maximum torque T1max as the output pressure becomes higher. The torque feedback circuit 31 includes pressure dividing restrictor parts 34a, 34b, pressure dividing valves 35a, 35b, and relief valves 37a, 37b.