Variable Displacement Hydraulic Drive for Adjustable Actuator Torque
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Solution Overview
Problem
Conventional hydraulic drive apparatuses have a fixed displacement pump, limiting the ability to change the speed reduction ratio of the hydraulic actuator even when the rotational speed and torque of the electric motor are constant, making it difficult to adjust thrust or torque as needed.
Innovation Solution
A hydraulic drive apparatus with a variable displacement pump and a control device that adjusts the pump's volume based on pressure differences between supply/discharge lines, allowing for a changeable speed reduction ratio by tilting the swash plate in response to pressure differences, and using a control device for precise position feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed displacement pump is used, then the structure is simple and reliable, but the speed reduction ratio cannot be changed even when motor speed and torque are constant
Solution Approach 1:
The pump structure is made dynamic by introducing a swash plate that can change its tilt angle. The tilt angle of the swash plate directly determines the displacement volume of the pump, allowing the speed reduction ratio to be adjusted dynamically while maintaining a relatively simple overall pump structure. This resolves the contradiction by enabling adaptability through a single dynamic element rather than complex reconfiguration.
2Speed
If the pump displacement is decreased to increase speed reduction ratio, then the hydraulic actuator speed decreases, but the thrust or torque capability is reduced
Solution Approach 1:
The invention changes the physical parameter of pump displacement volume dynamically by adjusting the swash plate tilt angle. By varying this parameter, the system can achieve different combinations of speed reduction ratio and force multiplication, allowing optimization of both speed and thrust/torque characteristics according to operational requirements without the trade-off being as severe as in fixed displacement systems.
3Adaptability or versatility
If a variable displacement pump with swash plate is used, then the speed reduction ratio becomes adjustable, but the device complexity increases
Solution Approach 1:
The swash plate mechanism is designed to be self-regulating or easily controllable through hydraulic pressure differentials. The pump's own operating conditions (pressure, flow) can influence the swash plate angle, or it can be controlled by simple hydraulic signals, avoiding the need for complex external control systems. This minimizes the increase in overall device complexity while maintaining variable displacement functionality.
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
Enables adjustable speed reduction ratio for the hydraulic actuator even with constant electric motor speed and torque, allowing for precise control of thrust or torque, suitable for applications like humanoid or industrial robots.
Implementation Method 1
a pump configured such that a volume of the pump decreases in accordance with increase in a pressure difference between the first supply/discharge line and the second supply/discharge line
Implementation Method 2
the pressure of the supply/discharge line at the hydraulic oil supply side to the hydraulic actuator is higher, and the pressure of the supply/discharge line at the hydraulic liquid discharge side from the hydraulic actuator is lower
Data Source
AI summary
A hydraulic drive apparatus includes: an electric motor; a variable displacement pump driven by the electric motor, the pump including a pair of pump ports whose delivery side and suction side are switched with each other in accordance with a rotation direction of the electric motor; a hydraulic actuator connected to the pair of pump ports by a first supply/discharge line and a second supply/discharge line; and a control device that controls the electric motor based on an actuator position command value for the hydraulic actuator. The pump is configured such that a volume of the pump decreases in accordance with increase in a pressure difference between the first supply/discharge line and the second supply/discharge line.