What Is a Pump Coupler?

A hydraulic coupling, also known as a hydraulic coupling, is a hydraulic transmission that is used to connect a power source (usually an engine or a motor) with a working machine and transfer torque by the change of the fluid momentum moment.

Chinese name: Hydraulic Coupler

Foreign name: Fluid Coupling
Advantages: Smooth start, reduced impact, etc.

Working principle of hydraulic coupler

Hydraulic coupling is a kind of non-rigid coupling with liquid as working medium. The pump impeller and the turbine of the hydraulic coupling (see figure) form a closed working cavity that can circulate the liquid. The pump impeller is mounted on the input shaft and the turbine is mounted on the output shaft. The two wheels are semi-circular rings with many blades arranged in a radial direction. They are arranged opposite to each other and do not touch each other. There is a gap of 3mm to 4mm in the middle, and a ring-shaped working wheel is formed. The driving wheel is called a pump wheel, the driven wheel is called a turbine, and the pump wheel and the turbine are both called working wheels. After the pump wheel and the turbine are assembled, an annular cavity is formed, which is filled with working oil.

The pump wheel is usually driven by an internal combustion engine or a motor, and the blades drive the oil. Under the action of centrifugal force, these oils are thrown toward the edge of the pump wheel blades. Because the radius of the pump wheel and the turbine are equal, the speed of the pump wheel is greater than the speed of the turbine. At this time, the hydraulic pressure at the outer edge of the pump wheel blade is greater than the hydraulic pressure at the outer edge of the turbine blade. Due to the pressure difference liquid impacts the turbine blade, when it is sufficient to overcome the external resistance, the turbine starts to rotate, that is, the kinetic energy is transmitted to the turbine, so that the turbine and the pump Rotate in the same direction. After the kinetic energy of the oil drops, it flows from the blade edge of the turbine back to the pump wheel, forming a circulation loop, and its flow path is like a circular spiral line connected end to end. Hydrodynamic couplers rely on the interaction of liquid with the blades of pump wheels and turbines to generate changes in momentum moments to transmit torque. When ignoring the wind loss and other mechanical losses during the impeller rotation, its output (turbine) torque is equal to the input (pump) torque.

Structure diagram

Classification of hydraulic couplers

According to different uses, hydraulic couplers are divided into ordinary type hydraulic couplers, moment-limiting type hydraulic couplers and speed regulating type hydraulic couplers. The torque-limiting hydraulic coupler is mainly used for starting protection and shock protection, position compensation and energy buffering of the motor reducer; the speed-adjusting hydraulic coupler is mainly used for adjusting the input-output speed ratio, and other functions It is basically the same as the moment-limited hydraulic coupler.

According to the number of working chambers, hydraulic couplers are divided into single working chamber hydraulic couplers, dual working chamber hydraulic couplers and multi-working chamber hydraulic couplers. According to the different blades, the hydraulic couplers are divided into radial blade hydraulic couplers, inclined blade hydraulic couplers and rotary blade hydraulic couplers.

Advantages and disadvantages of hydraulic coupling

Advantages of fluid coupling

(1) With flexible transmission automatic adaptation function.

(2) It has the functions of reducing shock and isolating torsional vibration.

(3) It has the function of improving the starting capability of the power machine and starting it with or without load.

(4) Overload protection function to protect the motor and working machine from damage when the external load is overloaded.

(5) It has the functions of coordinating the sequential start of multi-power machines, equalizing the load, and smooth running.

(6) Flexible brake deceleration function (refers to hydraulic retarder and stalled damping hydraulic coupler).

(7) It has the function of making the machine start slowly and delay, and it can start the large inertia machinery smoothly.

(8) Strong adaptability to the environment, can work in cold, humid, dusty, explosion-proof environments.

(9) An inexpensive cage motor can be used instead of an expensive winding motor.

(10) No pollution to the environment.

(11) The transmitted power is proportional to the square of the input speed. When the input speed is high, the energy capacity is large and the performance-price ratio is high.

(12) With stepless speed regulation function, the speed-adjusting hydraulic coupler can change the output torque and output speed by adjusting the filling volume of the working chamber during operation under the condition that the input speed is constant.

(13) With clutch function, speed-regulating and clutch-type hydraulic couplings can start or brake the working machine without stopping the motor.

(14) It has the function of expanding the working range of the stable operation of the power machine.

(15) With power saving effect, it can reduce the starting current and duration of the motor, reduce the impact on the power grid, reduce the installed capacity of the motor, it is difficult to start the machine with large inertia, and apply torque limiting hydraulic couplers and centrifugal machinery to adjust the speed The hydraulic coupling has significant energy saving effect.

(16) Except bearings and oil seals, there is no direct mechanical friction, low failure rate and long service life.

(17) The structure is simple, the operation and maintenance are simple, no particularly complicated technology is needed, and the maintenance cost is low.

(18) High performance-price ratio, low price, low initial investment and short payback period.

Disadvantages of fluid coupling

(1) There is always a slip rate and slip power loss. The rated efficiency of the torque-limiting hydraulic coupler is approximately 0.96. The relative operating efficiency of the speed-adjusting hydraulic coupler and the centrifugal machine is between 0.85 and 0.97. .

(2) The output speed is always lower than the input speed, and the output speed cannot be as accurate and constant as the gear transmission.

(3) The speed-adjusting hydraulic coupler requires an additional cooling system, which increases investment costs and operating costs.

(4) The floor space is large, and a certain space needs to be occupied between the power machine and the working machine.

(5) The speed adjustment range is relatively narrow. The speed adjustment range for matching with centrifugal machinery is 1 ~ 1/5, and the speed adjustment range for matching with constant torque machinery is 1 ~ 1/3.

(6) No torque change function.

(7) The ability to transfer power is directly proportional to the square of its input speed. When the input speed is too low, the size of the coupler increases and the cost performance ratio decreases.

Application field of fluid coupling

Hydraulic Coupler Car

Hydrodynamic couplings were used in early automotive semi-automatic transmissions and automatic transmissions. The pump wheel of the hydraulic coupling is connected to the flywheel of the engine, and the power is transmitted from the engine crankshaft. In some cases, the coupler is strictly a part of the flywheel. In this case, the hydraulic coupler is also called a hydraulic flywheel. The turbine is connected to the input shaft of the transmission. Liquid circulates between the pump wheel and the turbine, so that torque is transmitted from the engine to the transmission, driving the vehicle forward. In this respect, the hydraulic coupling acts very much like a mechanical clutch in a manual transmission. Because the hydraulic coupling cannot change the torque, it has been replaced by a torque converter.