With the development of modern industry, hydraulic transmission has been used more and more. Compared with mechanical transmission, hydraulic transmission is a new technology. In the early stage, water was used as the transmission medium, and the modern hydraulic transmission was driven by the booming oil industry.
At present, the hydraulic technology has made great progress in achieving the requirements of high pressure, high speed, high power, high efficiency, low noise, durability, high integration, miniaturization, intelligence, etc., and has made many new achievements in improving the proportional control, servo control, digital control and other technologies. In addition, there are more and more remarkable achievements in the development research of hydraulic components and hydraulic system, such as computer-aided design, computer simulation and optimization, and computer control.
This paper mainly studies the application of hydraulic drive in the elevator. For the elevator, the advantages of hydraulic drive are mainly as follows:
1. Under the same volume, the hydraulic device can generate more power than the electrical device. Under the same power, the volume and mass of the hydraulic device is small, that is, its power density is large and its structure is compact.
2. The hydraulic device works stably. Because of the small mass and inertia, quick reaction, the hydraulic device is easy to realize quick start, braking and frequent reversing.
3. The hydraulic device can realize stepless speed regulation in a large range, and it can also adjust speed in the operation process.
4. Hydraulic transmission is easy to adjust or control the liquid pressure, flow or flow direction. Especially in the case of high automation, when hydraulic control is combined with electrical control, electronic control or pneumatic control, the whole transmission device can achieve very complex sequential action, and also can easily achieve remote control and automation.
5. The hydraulic device is easy to realize overload protection.
6. The hydraulic components have been standardized, serialized and generalized, and the design, manufacture and use of the hydraulic system are relatively convenient.
7. Using hydraulic transmission to realize linear motion is much simpler than mechanical transmission.
Chapter I basis for design of hydraulic transmission system of elevator
(1) the overall layout and process requirements of the lift, including the type of lift movement completed by the use of hydraulic drive, the type and model of possible hydraulic actuator proposed in the mechanical design, the locations of the actuator and the size range of its space, the required automation degree, etc.
(2) the working cycle of the lift, the movement mode of the actuator (moving, rotating or swinging), and the completed working range.
(3) the moving speed, speed regulating range, working stroke, load property and change range of the hydraulic actuator.
(4) the action sequence and interlock requirements of each part of the lift, as well as the working environment and floor area of each part, etc.
(5) the working performance of the hydraulic system, such as the requirements of working stability, reliability, reversing accuracy, dwell time, impulse output, etc.
(6) other requirements, such as pollution, corrosiveness, flammability, quality, overall dimension and economy of hydraulic device, etc.
Chapter 2 steps of designing hydraulic transmission system
1. It is the basis for designing the hydraulic transmission system to make clear the working requirements for the hydraulic transmission system, which is put forward by the user department in the form of technical specification.
2. Draw up the hydraulic transmission system diagram. (1) select the hydraulic actuator reasonably according to the movement form of the working parts; (2) list the possible basic circuits according to the performance requirements and action sequence of the working parts. At this time, we should pay attention to the selection of appropriate speed regulation scheme, speed change scheme, and determine safety measures and unloading measures to ensure the completion of automatic working cycle and sequential action and reliability.
After the hydraulic transmission scheme is drawn up, the formal schematic diagram shall be drawn according to the graphic symbols specified in the national standards. The drawing shall be marked with the model and specification of each hydraulic component, the action cycle diagram of the executive component and the action cycle table of the electrical component, and the list of standard (or general) components and auxiliary components.
3. Calculate the main parameters of the hydraulic system and select the hydraulic components. (1) calculate the main parameters of the hydraulic cylinder; (2) calculate the flow required by the hydraulic cylinder and select the hydraulic pump; (3) select the oil pipe; (4) select the component specification; (5) calculate the actual working pressure of the system; (6) calculate the power and select the motor; (7) calculate the heating and tank volume;
4. Check the necessary hydraulic system.
5. Structure design of hydraulic device.
6. Draw the working drawing of hydraulic system and prepare technical documents.
Chapter three problems in designing hydraulic transmission system
1. When combining basic circuits, pay attention to prevent mutual interference between circuits to ensure normal working cycle.
2. Improve the working efficiency of the system and prevent the system from overheating. For example, if the power is small, the throttling speed regulating system can be used; if the power is large, the volume speed regulating system is preferred; if the pump can be unloaded in time when the brake is frequently stopped; if the fuel consumption rate of the system varies greatly in each working cycle, the high efficiency circuits such as accumulator or pressure compensation variable pump should be considered.
3. To prevent hydraulic shock, for the system with high pressure and large flow, the hydraulic reversing valve should be used instead of the electromagnetic reversing valve to slow down the reversing speed; the accumulator or buffer circuit should be used to eliminate the hydraulic shock.
4. On the premise of satisfying the working cycle and productivity, the system should be simple as much as possible. The more complex the system is, the more opportunities for failure will be. The system shall be safe and reliable, and the actuator for lifting the weight by vertical movement shall be provided with a balance circuit; the actuator with strict sequence action requirements shall be provided with a sequence action circuit of stroke control. In addition, there should be interlock device and some safety measures.
5. Try to achieve standardized and serial design and reduce the design of special parts.
Chapter IV problems to be noticed when using hydraulic system
1) the user shall understand the working principle of the hydraulic system, be familiar with various operations and adjust the position and rotation direction of the handle.
2) before start-up, check whether the adjustment handles and hand wheels on the system have been moved by irrelevant personnel, whether the positions of electrical switch and travel switch are normal, and whether the installation of tools on the main engine is correct and firm, and then wipe the exposed parts of guide rail and piston rod before start-up.
3) when starting up, start the hydraulic pump for controlling the oil circuit first. When there is no special hydraulic pump for controlling the oil circuit, directly start the main hydraulic pump.
4) the hydraulic oil shall be inspected and replaced regularly. For the hydraulic equipment newly put into use, the oil tank shall be cleaned and replaced about 3 months after use. After that, clean and change oil every six months to one year.
5) pay attention to the oil at any time during operation, and the oil temperature in the oil tank shall not exceed 60 ℃ during normal operation. If the oil temperature is too high, try to cool it and use hydraulic oil with high viscosity. When the temperature is too low, preheating shall be carried out, or intermittent operation shall be carried out before operation, so that the oil temperature will gradually rise, and then it will enter into the formal operation state.
6) check the oil level to ensure that the system has enough oil.
7) the system with exhaust device shall be vented, and the system without exhaust device shall be reciprocated for many times, so as to discharge gas naturally.
8) the oil tank shall be capped and sealed, and the air filter shall be set at the vent hole on the oil tank to prevent the invasion of dirt and moisture. The oil should be filtered to make the oil clean.
9) coarse and fine filters shall be configured in the system as required, and the filters shall be checked, cleaned and replaced frequently.
10) for the adjustment of pressure control elements, generally, first adjust the system pressure control valve - overflow valve, open the valve when the pressure is zero, and gradually increase the pressure to reach the specified pressure value; then adjust the pressure control valve of each circuit in turn. The regulating pressure of the safety relief valve of the main oil circuit hydraulic pump is generally greater than 10% - 25% of the working pressure required by the actuator. The pressure valve of the fast-moving hydraulic pump, whose adjustment pressure is generally 10% - 20% higher than the required pressure. If unloading pressure is used to supply control oil circuit and lubricating oil circuit, the pressure shall be kept within the range of 0.3-0.6mpa. The regulating pressure of pressure relay shall be generally 0.3-0.5mpa lower than the oil supply pressure.
11) the flow control valve shall be adjusted from small flow to large flow, and shall be adjusted gradually. The flow control valve of synchronous motion actuator shall be adjusted at the same time to ensure the smoothness of motion.
Chapter V causes of working parts crawling and troubleshooting
1) because of the high compressibility of air, when the liquid containing bubbles reaches the high pressure area and is compressed violently, the volume of oil will become smaller and the working parts will crawl.
Measures to be taken: exhaust device shall be set at the high place of system circuit to remove air.
2) because the friction resistance between the relative moving parts is too large or the friction resistance changes, the working parts will crawl when moving.
Measures to be taken: there are certain requirements for the form and position tolerance and surface roughness of hydraulic cylinder, piston, piston rod and other parts; and the cleanness of hydraulic system and hydraulic oil shall be ensured to prevent dirt from entering the surface of relative moving parts, so as to increase friction resistance.
3) the surface of moving parts is poorly lubricated, forming dry friction or semi friction, which is also easy to cause crawling.
Measures to be taken: frequently check the lubrication between surfaces of parts with relative motion to keep them in good condition.
4) if the sealing and centering of the piston and piston rod of the hydraulic cylinder are not good, it will also creep.
Measures to be taken: the load shall be removed to make the hydraulic cylinder act independently. After the friction resistance is measured, the centering shall be corrected.
5) creeping due to serious leakage of hydraulic cylinder.
Measures: reduce leakage loss or increase the capacity of hydraulic pump.
6) during the working process, due to the change of load, the oil supply of the system will fluctuate, causing the working parts to crawl.
Measures to be taken: pay attention to the selection of speed control valve with stable performance under small flow, and try not to connect the hose between the hydraulic cylinder and speed control valve, otherwise it will cause large deformation of the hose and creep phenomenon.
-This article comes from the love hydraulic forum, original address: http://www.iyeya.cn/thread-4913-1-1.html
