Introduction to the working principle, components, application scope, and other aspects of hydraulic transmission systems

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​Hydraulic transmission refers to a type of transmission that uses a liquid as the working medium for energy transfer and control. Hydraulic transmission systems are a type of transmission method that utilizes the kinetic energy of liquids for energy conversion; examples include hydraulic couplings and torque converters. Hydraulic transmission is a type of transmission that uses the pressure energy of liquids for energy conversion. The use of hydraulic drive technology in machinery can simplify its structure, reduce its weight, lower material consumption, decrease manufacturing costs, ease the workload, and improve both efficiency and reliability. Hydraulic transmission systems are widely used in vehicles, construction machinery, and other types of machinery, especially in cars (such as automatic transmissions, hydraulic steering systems, braking systems, etc.), and have become an essential part of automobiles. Next, the editor from Xianji Network will introduce to you the working principle, components, application areas, advantages, disadvantages of hydraulic transmission systems, their use in machine tool equipment, as well as common faults and their solutions. Working principle of hydraulic transmission systems: In actual operation, hydraulic transmission systems rely primarily on the function of hydraulic pumps to function. Utilizing the functions of a prime mover, mechanical energy is converted into hydraulic pressure energy, enabling efficient energy transfer. Under the action of internal pipes and control valves in the system, components such as motors and hydraulic cylinders are used to convert the pressure energy of the liquid into mechanical energy, thereby enabling the system to rotate or move back and forth in a linear motion. When performing system control tasks and transferring energy, a liquid medium in the hydraulic transmission system is required to function, and the system’s unique transmission pathways ensure its high level of efficiency. Components of a hydraulic transmission system: 1. Power element. The power element is the hydraulic pump, which converts the mechanical energy supplied by the prime mover into pressure energy of the liquid medium. Its function is to provide pressurized oil for the hydraulic system; it serves as the power source of the system. 2. Actuators: Actuators refer to hydraulic cylinders or hydraulic motors, which are devices that convert hydraulic energy into mechanical energy. Their function is to generate force and speed (or torque and rotational speed) under the push of pressurized oil, thereby driving the working components. 3. Control elements: Control elements include various types of valves, such as relief valves, throttle valves, directional control valves, etc. The function of such components is to control the pressure, flow rate, and direction of fluid in the hydraulic system, so as to ensure that the actuating elements carry out their intended tasks. 4. Auxiliary components: Auxiliary components include fuel tanks, fuel pipes, filters, as well as various indicators and control instruments. Their role is to provide the necessary conditions for the system to function properly and to facilitate monitoring and control. 5. Working medium: The working medium is the transmission fluid, commonly referred to as hydraulic oil. A hydraulic system transfers motion and power through a working medium. Applications of hydraulic transmission systems: 1. Hydraulic systems for general industrial use, such as plastic processing machinery (injection molding machines), pressure machinery (forging presses), heavy machinery (scrap metal compacting machines), machine tools (fully automatic hexagonal lathes, surface grinders), etc ； 2. Hydraulic systems for mobile machinery: construction machinery (excavators), lifting equipment (truck cranes), construction equipment (pile drivers), agricultural machinery (combine harvesters), automobiles (steering gears, shock absorbers), etc ； 3. Hydraulic systems for the steel industry: metallurgical machinery (rolling mills), lifting devices (elevators), roll adjustment devices, etc ； 4. Hydraulic systems for civil engineering: floodgate and dam devices (tidal protection barriers), riverbed elevation devices, bridge control mechanisms, and mining machinery (drill machines), etc ； 5. Hydraulic systems for power plants, turbines (speed control devices), etc ； 6. Hydraulic systems for special applications: control devices for giant antennas, measuring buoys, retraction/extension mechanisms for aircraft landing gears and rudder control devices, lifting rotating stages, etc ； 7. Hydraulic systems for ships: deck lifting machinery (winches), bow doors, bulkhead valves, stern thrusters, etc ； 8. **Industrial hydraulic systems for artillery control devices, ship stabilizers, aircraft simulation, etc.** Advantages of hydraulic transmission systems: 1. Hydraulic transmission can generate high thrust or high torque, enabling low-speed movement with large loads, which is a significant advantage over other transmission methods. 2. Hydraulic transmission enables seamless variable speed control with a wide range of speed adjustments, and the speed can be changed during the operation of the system. 3. Under the same power conditions, hydraulic transmission systems are small in size, light in weight, and compact in structure. Hydraulic components can be connected by pipes or through integrated connections; their layout and installation offer great flexibility, enabling the creation of complex systems that are difficult to assemble using other transmission methods. 4. Hydraulic transmission enables the movement of the actuator elements to be very uniform and stable, eliminating any shock when the moving parts change direction. Moreover, due to its fast response speed, frequent commutation can be achieved. 5. It is simple to operate, easy to adjust and control, and suitable for automation. Especially when used in combination with machinery and electricity, it can easily implement complex automatic working cycles. 6. The hydraulic system facilitates overload protection, ensuring safe and reliable operation. Since the moving parts in various hydraulic components operate in oil, they can be self-lubricated; therefore, these components have a long service life. 7. Hydraulic components are easy to serialize, standardize, and generalize, facilitating their design, manufacturing, maintenance, and widespread use. Disadvantages of hydraulic transmission systems: 1. Oil leakage and the compressibility of the fluid can affect the accuracy of the movement of the actuating elements, thus preventing the achievement of a precise transmission ratio. 2. It is relatively sensitive to changes in oil temperature and should not operate under very high or very low temperature conditions. 3. The energy losses (leakage loss, overflow loss, throttling loss, friction loss, etc.) are significant, the transmission efficiency is low, and it is not suitable for long-distance transmission. 4. When the system malfunctions, it is difficult to identify the cause. In summary, the advantages of hydraulic transmission are major and prominent, while its disadvantages will be gradually overcome with the advancement of science and technology; the development prospects for hydraulic transmission technology are very promising. Applications of hydraulic drive systems in machine tool equipment 1. Drive mechanisms for feed motions: Hydraulic drive is predominantly used for the feed motions of the grinding wheel head and worktable in grinders ； Tool holders or turret tool holders for lathes, hexagonal lathes, and automatic lathes ； The feed motion of worktables in milling machines, planing machines, and combined machine tools is also achieved through hydraulic drive. Some of these components require fast movement, while others require slow movement. Some require both fast movement and slow movement. Most of these applications require a wide speed control range, as well as stepless speed adjustment during operation ； Some require continuous feeding, while others require intermittent feeding ； Some require a constant speed under varying loads, while others demand good commutation performance, and so on. All of these requirements can be met using hydraulic drive. 2. For the transmission devices that enable reciprocating motion in machines such as planers, shaper machines, or slotting machines – namely the worktable of planers – hydraulic drive can be utilized, as these devices require high-speed reciprocating linear motion, along with low impact during direction changes, short direction-changing times, and low energy consumption. 3. The profiling operation on lathes, milling machines, and planers can be carried out using hydraulic servo systems. Its precision can reach 0.01–0.02 mm. Furthermore, this system can also be used for the shaping wheel correction device on grinders. 4. Auxiliary devices on machine tools, such as clamping devices, gearbox speed control mechanisms, devices for eliminating gaps in screw nuts, balancing mechanisms for vertically moving components, indexing devices, devices for loading and unloading workpieces and tools, and workpiece conveying systems, benefit from the use of hydraulic drive systems, as this helps to simplify the structure of the machine tool and increase its level of automation. 5. By using hydrostatic support for bearings, guide rails, lead screw-nut mechanisms, etc., in heavy-duty machine tools, high-speed machine tools, and high-precision machine tools, the operational stability and motion accuracy can be improved. Common faults and troubleshooting in hydraulic transmission systems. I. Low system flow rate. 1. Main causes of low flow rate in hydraulic transmission systems: ① Poor operability of control valves ； ②There is air in the return pipe, and the liquid level is above the specified limit ； ③The hydraulic pump has an unsatisfactory rotation speed, incorrect steering, poor overall performance, and signs of wear ； ④Damage to sealing or hydraulic components ； ⑤The accumulator pressure is low; oil suction is not smooth; the fluid level in the tank does not reach the standard level, etc. 2. Handling method: ① Replace or repair the damaged components ； ②To verify the functionality of the accumulator and the sealing effectiveness of the system, rigorous testing must be conducted on the hydraulic pump and prime mover; ③ replace any hydraulic pumps that do not meet quality standards ； ④Ensure proper addition of fluid to reduce the viscosity of the hydraulic oil, keeping the oil suction pipes unobstructed. II. Lack or insufficiency of system pressure
1. Main reasons for the lack or insufficiency of system pressure in a hydraulic transmission system:
① The hydraulic pump has insufficient power, its rotational speed does not meet requirements, or the direction of rotation of the hydraulic pump is incorrect ； ②Spool jamming causes unloading ； ③Oil temperature is outside the specified range, oil suction is not smooth, and the liquid level does not meet the specified standards ； ④Improper sealing leads to leaks and component damage ； ⑤After the relief valve is opened, the damping hole becomes blocked, the spring fails to function as intended, and it is not possible to close the valve core. 2. Handling method: ① It is necessary to inspect the power source of the hydraulic transmission system, and thoroughly clean the cooling system/oil suction pipe and damping orifices ； ②Replace the spring and add hydraulic oil ； ③Ensure the proper operation of the valve element inside the valve body, and repair or replace any faulty components ； ④Test the sealing integrity of connections at pipes, valves, pumps, and other components in the system; replace sealing parts to improve the sealing effect ； ⑤Repair and adjust the system housing and valve spools. III. System leakage faults 1. Main reasons for leakage faults in the hydraulic system: ① An improper oil level in the tank, which leads to leakage between the oil in the tank and the water in the cooler ； ②The operating pressure of the system auxiliary/hydraulic components remains consistently below the system pressure ； ③The screw fastening at the flange/plate connection area is poor, resulting in inadequate sealing ； ④Loose or detached joint positions, etc. 2. Methods for handling leakage faults: ① The pressure of the system components’ housings should be adjusted to remain within the allowable pressure range of the oil seal, in order to improve the overall sealing performance ； ②Disassemble and repair the faulty part ； ③Reduce the hydraulic pressure below the level of the pre-tension force in order to strengthen the connected joint. IV. Vibration in the hydraulic transmission system 1. The main causes of system vibration faults are: ① Impact forces exist in the moving components, the damping during direction changes is low, and the motor coupling and the hydraulic pump are not synchronized ； ②The distance between the oil return pipe and the oil suction pipe is inappropriate; the pipes are not stable, and they are small in diameter and long in length ； ③The gears and tooth shapes used in the operation of the hydraulic pump are not precise enough, resulting in misalignment issues ； ④The spring at the relief valve area has lost its functionality, and the valve seat and valve element are not properly aligned ； ⑤The hydraulic pump does not draw in oil properly; air gets into the pump, the plunger or blades get stuck, and the parts are severely worn out ； ⑥There is a clogging issue with the hydraulic oil, and the oil level is not at the standard level ； ⑦It could also be due to a jammed valve core inside the valve body, or improper welding of the electromagnet. 2. Methods for dealing with vibration faults: ① Install buffer devices to ensure that the motor shaft and hydraulic pump are concentric, keeping the deviation within 0.1 mm, thereby ensuring stable operation of the motor ； ②Clean promptly, cleaning the valve body, damping holes, and filters to ensure the unobstructed flow in the damping holes ； ③Replace the spring to ensure welding quality, thereby maintaining the distance between the valve seat and the valve core at an optimal level ； ④Increase the diameter of the system pipes, secure them properly, and control the distance between the pipes ； ⑤Set the position of the oil suction pipe appropriately, replace worn parts, and ensure that the height difference between the oil suction port of the hydraulic pump and the mouth of the oil suction pipe is within 50 cm.