Hydraulic Drive:
Hydraulic drive uses hydraulic oil as the working medium. Through the power component (oil pump), it converts the mechanical energy of the prime mover into hydraulic pressure energy. This energy is then transmitted through control components and, with the help of execution components (cylinders or hydraulic motors), it converts pressure energy back into mechanical energy to drive loads for linear or rotary motion. By remotely manipulating control components and adjusting flow rates, the force and speed of the execution components can be set.
When external disturbances affect this system, the output of the execution component typically deviates from its original set value, resulting in a certain error.
Hydraulic Control:
Similar to hydraulic drive, the system includes power components, control components, and execution components, also transmitting power through hydraulic fluid.
The difference is that hydraulic control features a feedback mechanism. The feedback device compares the output of the execution component (displacement, speed, force, etc.) with the input (which can vary or be constant). The deviation from this comparison is used to control the system, allowing the output of the execution component to change or remain constant in accordance with the input.
This forms a closed-loop hydraulic transmission system, also known as a hydraulic tracking system or hydraulic servo system.
In hydraulic transmission systems, on/off or logical control components are used primarily to maintain the stability of the set value or simply to change direction, also referred to as constant value and sequence control components.
Hydraulic control systems utilize servo control components that incorporate feedback structures and are controlled electrically, offering high control precision and response speed, with pressures and flows that often vary continuously. The output power can also be amplified.
Proportional Control:
Proportional control is a hybrid of the two types mentioned above. The proportional control valve is a new type of electro-hydraulic control component developed from on/off control components and servo control components. It possesses features of both types and is used in situations where manual on/off control is inadequate but does not require the stringent contamination control standards of hydraulic systems with servo valves.
Advantages and Disadvantages of Hydraulic Transmission Systems:
Among the four major types of transmission methods (mechanical, electrical, hydraulic, and pneumatic), no single power transmission method is perfect. However, hydraulic transmission has several significant advantages:
- Structural Advantages: It boasts superior power output per unit weight and size compared to other transmission methods. Hydraulic transmission devices are smaller, lighter, have low inertia, and feature compact structures with flexible layouts.
- Performance: Speed, torque, and power can be infinitely adjusted, offering quick response times and allowing for rapid direction changes and speed variations. The speed range can reach from 100:1 to 2000:1, with good action responsiveness. Control and adjustments are relatively simple, facilitating easy operation and integration with electrical controls and CPUs for automation.
- Maintenance: Components have good self-lubrication, making overload protection and pressure maintenance achievable. They are also easy to standardize and generalize.
- Reliability: All equipment utilizing hydraulic technology has high safety and reliability.
- Economic Efficiency: Hydraulic technology is highly adaptable and flexible, allowing for easy adjustments in production processes. The manufacturing cost of hydraulic components is relatively low, providing strong adaptability.
- Integration with New Technologies: Hydraulic systems can easily integrate with new technologies like microcomputer control, forming an integrated system of “mechanical-electrical-hydraulic-optical,” which has become a trend in global development, facilitating digitization.
Disadvantages of Hydraulic Transmission:
Every system has its drawbacks, and hydraulic transmission is no exception:
- Leakage: Due to unavoidable relative motion between surfaces, leakage occurs. Since hydraulic oil is not absolutely incompressible and tubing can deform elastically, hydraulic transmission cannot achieve strict transmission ratios, making it unsuitable for applications like threading in machine tools.
- Efficiency Losses: During fluid flow, there are losses due to friction, local losses, and leakage, resulting in lower transmission efficiency, especially over long distances.
- Temperature Sensitivity: Hydraulic systems can encounter difficulties under high or low temperature conditions.
- Precision Requirements: To prevent oil leakage and meet certain performance requirements, hydraulic components need to be manufactured with high precision, which complicates use and maintenance.
- Fault Diagnosis Challenges: Troubleshooting is difficult, particularly in units where hydraulic technology is not widely adopted, which can hinder the further promotion and application of hydraulic technology. Repair of hydraulic equipment often relies on experience, and training hydraulic technicians can be time-consuming.