Created on:2021-06-17 09:36

Main parameters and commonness of hydraulic motor

1.7.9 dynamic characteristics

The dynamic characteristics of the hydraulic device (hydraulic power mechanism), which is composed of hydraulic control elements, hydraulic executive elements and load, determine the performance of the hydraulic control system to a great extent. There are two kinds of power machinery composed of hydraulic motors: valve controlled hydraulic motor system and pump controlled hydraulic motor system.

(l) It is used in small and medium-sized hydraulic system with high response speed and low power loss. The principle of a typical valve controlled hydraulic motor speed control system is shown in Figure e (a), and figure e (b) is a functional block diagram. The system is used to control the speed of the load and make it change according to the law given by the command signal. The shaft of the speed measuring motor 4 is connected with the load shaft to detect the speed of the load shaft. The difference (error signal) between the detected speed signal W and the command signal is amplified by the servo amplifier 1. The generated current controls the spool position of the electro-hydraulic servo valve 2. The electro-hydraulic servo valve outputs pressure oil to drive and control the rotation of the hydraulic motor 3 and the load.

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(2) Pump controlled hydraulic motor system is based on the principle of volume speed regulation, so it has high efficiency but slow response speed, and is mostly used in high-power system. The principle of a typical pump controlled hydraulic motor system is shown in Fig. f (a), and Fig. f (b) is a functional block diagram. The bidirectional variable hydraulic pump 5, the bidirectional quantitative hydraulic motor 6, the safety relief valve group 7 and the oil supplement check valve group 8 form a closed oil circuit. The speed of the bidirectional quantitative hydraulic motor 6 is regulated by changing the displacement of the bidirectional variable hydraulic pump 5. The displacement adjustment of the variable displacement pump is realized by the displacement adjustment of the valve controlled electro-hydraulic servo mechanism (often attached to the variable displacement pump) composed of electro-hydraulic servo valve 2 and double rod hydraulic cylinder 3. A speed measuring motor (speed sensor) 9 is arranged between the load and the command mechanism to form a closed-loop speed control loop. When the command signal is input, the pressure oil of the control hydraulic source supplies oil to the double rod hydraulic cylinder 3 through the electro-hydraulic servo valve 2, so that the variable mechanism of the variable displacement pump driven by the hydraulic cylinder can work in a certain position; the output speed ∞ of the hydraulic motor is detected by the speed measuring motor and converted into a feedback signal, and compared with the input command signal, the deviation signal is obtained to control the opening of the valve port of the electro-hydraulic servo valve, so as to realize the control Make the displacement of the variable displacement mechanism of the variable displacement pump keep near the set value, and finally ensure that the bidirectional quantitative hydraulic motor 6 works near the desired speed value. The position sensor 4 constitutes an internal feedback link to improve the control accuracy of the system.

The electro-hydraulic speed servo control system is widely used in prime mover speed regulation, machine tool feed drag and antenna, radar, turret attitude tracking and other technical fields.

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