Hydraulic motor

                                                                 Hydraulic motor

Hydraulic motor is an executive component of hydraulic system. It converts the hydraulic pressure energy provided by hydraulic pump into the mechanical energy (torque and speed) of its output shaft. Liquid is a medium that transmits force and motion.
Hydraulic motor, also known as oil motor, is mainly used in injection molding machinery, ships, hoists, engineering machinery, construction machinery, coal mining machinery, mining machinery, metallurgical machinery, marine machinery, petrochemical industry, port machinery, etc

purpose
Hydraulic motor
Hydraulic motors, also known as oil motors, are mainly used in injection molding machinery, ships, hoists, engineering machinery, construction machinery, coal mining machinery, mining machinery, metallurgical machinery, marine machinery, petrochemical industry, port machinery, etc.
Boring machine boring machine
High speed motor gear motor has the advantages of small volume, light weight, simple structure, good manufacturability, insensitive to oil pollution, impact resistance and small inertia. Disadvantages include large torque pulsation, low efficiency, small starting torque (only 60% - 70% of rated torque) and poor low-speed stability.
characteristic
From the point of view of energy conversion, hydraulic pump and hydraulic motor are reversible hydraulic components. Inputting working fluid to any kind of hydraulic pump can turn it into the working condition of hydraulic motor; Conversely, when the main shaft of the hydraulic motor rotates driven by external torque, it can also be changed to the working condition of the hydraulic pump. Because they have the same basic structural elements - closed and periodically variable volume and corresponding oil distribution mechanism.
However, due to the different working conditions of hydraulic motor and hydraulic pump, there are still many differences between the same type of hydraulic motor and hydraulic pump. Firstly, the hydraulic motor should be able to forward and reverse, so its internal structure is required to be symmetrical; The speed range of hydraulic motor needs to be large enough, especially for its minimum stable speed. Therefore, it usually adopts rolling bearing or hydrostatic sliding bearing; Secondly, because the hydraulic motor works under the condition of input pressure oil, it does not have to have self-priming capacity, but it needs a certain initial sealing to provide the necessary starting torque. Due to these differences, the hydraulic motor and hydraulic pump are similar in structure, but they can not work reversibly.
classification
Hydraulic motors can be divided into gear type, blade type, plunger type and other types according to their structural types. According to the rated speed of hydraulic motor, it can be divided into high-speed and low-speed. Those with rated speed higher than 500r / min belong to high-speed hydraulic motor, and those with rated speed lower than 500r / min belong to low-speed hydraulic motor. The basic types of high-speed hydraulic motors include gear type, screw type, blade type and axial plunger type. Their main characteristics are high speed, small moment of inertia, easy to start and brake, and high sensitivity of regulation (speed regulation and commutation). Usually, the output torque of high-speed hydraulic motor is small, so it is also called high-speed small torque hydraulic motor. The basic type of low-speed hydraulic motor is radial plunger type. In addition, there are low-speed structural types in axial plunger type, blade type and gear type. The main characteristics of low-speed hydraulic motor are large displacement, large volume and low speed (sometimes up to a few revolutions per minute or even a few tenths of a revolution), so it can be directly connected with the working mechanism; No reduction device is needed, which greatly simplifies the transmission mechanism. Generally, the output torque of low-speed hydraulic motor is large, so it is also called low-speed high torque hydraulic motor.
radial piston motor 
Axial piston motor
Inclined shaft plunger motor
Swashplate plunger motor
Low speed hydraulic motor
radial piston motor 
The connecting rod hydraulic motor has the advantages of simple structure, reliable operation, many varieties and specifications and low price. Its disadvantages are large volume and weight and large torque pulsation.
Connecting rod less hydraulic motor
Swing cylinder hydraulic motor
Roller type hydraulic motor
Axial piston motor
Double swashplate plunger motor
Axial ball plug motor
Motor blade
Gear hydraulic motor
structural style
Vane type
Due to the action of pressure oil, the unbalanced force makes the rotor produce torque. The output torque of vane hydraulic motor is related to the displacement of hydraulic motor and the pressure difference between the inlet and outlet of hydraulic motor, and its speed is determined by the flow of input hydraulic motor. Since hydraulic motors generally require positive and negative rotation, the blades of vane hydraulic motors should be placed radially. In order to ensure that the blade root is always filled with pressure oil, a check valve shall be set on the path between the return and pressure oil chamber and the blade root. In order to ensure that the blade hydraulic motor can start normally after the pressure oil is filled, the blade top must be in close contact with the inner surface of the stator to ensure good sealing. Therefore, a pre tightening spring shall be set at the blade root. The vane hydraulic motor has the advantages of small volume, small moment of inertia and sensitive action. It can be used in occasions with high commutation frequency; However, the leakage is large and unstable at low speed. Therefore, vane hydraulic motors are generally used in occasions with high speed, small torque and sensitive action requirements.
Radial plunger type
Radial plunger hydraulic motor
Working principle: when the pressure oil enters the bottom of the plunger in the cylinder through the window of the fixed oil distribution shaft 4, the plunger extends outwards and firmly bears against the inner wall of the stator, because there is an eccentric distance between the stator and the cylinder block. At the contact between the plunger and the stator, the reaction force of the stator to the plunger is. The force can be divided into and two components. When the oil pressure acting on the bottom of the plunger is p, the diameter of the plunger is D, and the included angle between the force and is x, the force generates a torque on the cylinder block to rotate the cylinder block. The cylinder block then outputs torque and speed through the transmission shaft connected to the end face.
In the case of torque generated by a plunger analyzed above, because there are several plungers acting in the oil pressure area, the torque generated on these plungers rotates the cylinder block and outputs torque. Radial piston hydraulic motors are mostly used in the case of low speed and high torque.
1. Single acting connecting rod radial piston motor
The appearance of the single acting connecting rod radial piston motor is Pentagram shaped. The motor is composed of shell, crankshaft, port shaft, connecting rod, plunger, eccentric wheel and other parts.
Advantages: simple structure and reliable operation.
Disadvantages: large volume, large weight, rotation and torsion pulsation, poor low-speed stability.
2. Multi action internal curve plunger motor
The motor is composed of a flow distribution shaft, a cylinder block, a plunger, a cross beam, a roller, a stator and an output shaft. The displacement of this motor is twice that of a single stroke motor. Equivalent to 21 plungers. As the number of equivalent plungers increases, the output torque increases and the torque pulsation rate decreases under the same working pressure. Sometimes the motor is made into multi row plunger, the number of plunger is more, the output torque is further increased, and the torque pulsation rate is further reduced. Therefore, the motor can be made into a large displacement and can run smoothly at a very low speed. Since the motor needs two-way rotation, the blade slots are arranged radially.
3. Plunger type high-speed hydraulic motor
Plunger type high-speed hydraulic motors are generally axial.
Axial piston motor
Except for valve type flow distribution, other forms of axial piston pump can be used as hydraulic motor in principle, that is, axial piston pump and axial piston motor are reversible. The working principle of the axial piston motor is that the oil distribution plate and swashplate are fixed, and the motor shaft is connected with the cylinder block and rotates together. When the pressure oil enters the plunger hole of the cylinder block through the window of the oil distribution plate, the plunger extends under the action of the pressure oil and is close to the swashplate. The swashplate generates a normal reaction force P to the plunger, which can be divided into axial component force and vertical component force Q. Q is balanced with the hydraulic pressure on the plunger, and Q causes the plunger to produce a torque to the center of the cylinder block, driving the motor shaft to rotate counterclockwise. The instantaneous total torque produced by axial piston motor is pulsating. If the input direction of motor pressure oil is changed, the motor shaft rotates clockwise. The change of swashplate inclination a, that is, the change of displacement, affects not only the torque of the motor, but also its speed and steering. The greater the inclination angle of the swashplate, the greater the torque and the lower the speed.
Axial piston motor
Except for valve type flow distribution, other forms of axial piston pump can be used as hydraulic motor in principle, that is, axial piston pump and axial piston motor are reversible. The working principle of the axial piston motor is that the oil distribution plate and swashplate are fixed, and the motor shaft is connected with the cylinder block and rotates together. When the pressure oil enters the plunger hole of the cylinder block through the window of the oil distribution plate, the plunger extends under the action of the pressure oil and is close to the swashplate. The swashplate generates a normal reaction force P to the plunger, which can be divided into axial component force and vertical component force Q. Q is balanced with the hydraulic pressure on the plunger, and Q causes the plunger to produce a torque to the center of the cylinder block, driving the motor shaft to rotate counterclockwise. The instantaneous total torque produced by axial piston motor is pulsating. If the input direction of motor pressure oil is changed, the motor shaft rotates clockwise. The change of swashplate inclination a, that is, the change of displacement, affects not only the torque of the motor, but also its speed and steering. The greater the inclination angle of the swashplate, the greater the torque and the lower the speed.
Gear motor
In the structure of gear motor, in order to meet the requirements of forward and reverse rotation, the oil inlet and outlet are equal and symmetrical, and there is a separate oil outlet to lead the leaked oil from the bearing out of the shell; In order to reduce the starting friction torque, rolling bearings are used; In order to reduce torque ripple, the number of teeth of gear hydraulic motor is more than that of pump.
The gear hydraulic motor has poor dry sealing, low volumetric efficiency, high input oil pressure and large torque. And the instantaneous speed and torque change with the position of the meshing point, so the gear hydraulic motor is only suitable for the occasion of high speed and small torque. It is generally used in engineering machinery, agricultural machinery and mechanical equipment with low requirements for torque uniformity.
High speed motor
Motors with rated speed higher than 500r / min belong to high-speed motors. The basic forms of high-speed motor include gear type, blade type and axial plunger type. They are mainly characterized by high speed and small moment of inertia, which is convenient for starting, braking, speed regulation and reversing.
Low speed motor
Hydraulic motors with rotational speed lower than 500r / min belong to low-speed hydraulic motors. Its basic form is radial plunger type. The main characteristics of low-speed hydraulic motor are: large displacement, large volume and low speed. It can be directly connected with the working mechanism without reducer, which greatly simplifies the transmission mechanism. The output torque of low-speed hydraulic motor is large, up to thousands to tens of thousands of nm. Therefore, it is also called low-speed high torque hydraulic motor.
case
Motor blade
Compared with other types of motors, vane motor has the advantages of compact structure, small outline size, low noise and long service life. Its inertia is smaller than that of plunger motor, but its anti pollution ability is worse than that of gear motor, and the speed can not be too high. Generally, it works below 200R / min. The blade motor is unstable when the load changes or at low speed due to large leakage.
orbit motor 
In the late 1950s, the initial low-speed high torque hydraulic motor was developed from a stator and rotor component of the oil pump, which was composed of an internal gear ring and a matching gear or rotor. The inner gear ring is fixedly connected with the shell, and the oil entering from the oil port pushes the rotor around a central point. This slowly rotating rotor drives the output through the spline shaft to become a cycloidal hydraulic motor. After the initial cycloid motor came out, another concept of motor began to form after decades of evolution. The motor is equipped with rollers in the built-in ring gear. The motor with roller can provide high starting and running torque, the roller reduces friction, thus improving efficiency, and the output shaft can produce stable output even at very low speed. By changing the direction of input and output flow, the motor can quickly reverse, and produce equivalent torque in both directions. Each series of motors have various displacement options to meet the requirements of various speeds and torques.
main parameter 
Hydraulic motor
1. Working pressure and rated pressure
Working pressure: the actual pressure of the input motor oil, which depends on the load of the motor.
The difference between the inlet pressure and the outlet pressure of the motor is called the differential pressure of the motor.
Rated pressure: the maximum pressure for continuous normal operation of the motor according to the test standard.
2. Displacement and flow
Displacement: the volume of liquid input required for each revolution of the hydraulic motor without considering leakage. Vm (m3/rad)
Flow: the flow without leakage is called theoretical flow qmt, and the leakage flow is considered as actual flow QM.
3. Volumetric efficiency and speed
Volumetric efficiency η MV: ratio of actual input flow to theoretical input flow.
4. Torque and mechanical efficiency
Regardless of the loss of the motor, its output power is equal to the input power.
Actual torque T: torque loss due to actual mechanical loss of motor Δ T. Make it smaller than the theoretical torque TT, that is, the mechanical efficiency of the motor η Mm: equal to the ratio of the actual output torque of the motor to the theoretical output torque
5. Power and overall efficiency
The actual input power of the motor is PQM and the actual output power is t ω。
Total motor efficiency η M: The ratio of actual output power to actual input power
Hydraulic motor circuit
There are two circuits of hydraulic motor: hydraulic motor series circuit and hydraulic motor braking circuit, and these two circuits can be classified at the next level
One of the series circuits of hydraulic motors: connect three hydraulic motors in series with each other, and use a directional valve to control their start, stop and steering. The flow of the three motors is basically the same. When their displacement is the same, the speed of each motor is basically the same. It is required that the oil supply pressure of the hydraulic pump is high, and the flow of the pump can be small. It is generally used in the occasion of light load and high speed.
Hydraulic motor series circuit 2: each reversing valve in this circuit controls a motor. Each motor can act alone or at the same time, and the steering of each motor is also arbitrary. The oil supply pressure of the hydraulic pump is the sum of the working pressure difference of each motor, which is suitable for high-speed and small torque occasions.
One of the parallel circuits of hydraulic motors: two hydraulic motors are controlled by their respective directional valves and speed regulating valves, which can operate simultaneously and independently, regulate speed respectively, and keep the speed basically unchanged. However, with throttling speed regulation, the power loss is large. The two motors have their own working pressure difference, and their speed depends on the flow they pass through.
Hydraulic motor parallel circuit 2: the shafts of the two hydraulic motors are rigidly connected together. When the change-over valve 3 is in the left position, motor 2 can only idle with motor 1, and only motor 1 outputs torque. If the output torque of motor 1 cannot meet the load requirements, place valve 3 in the right position. At this time, although the torque increases, the speed should be reduced accordingly.
Hydraulic motor series parallel circuit: when solenoid valve 1 is energized, hydraulic motors 2 and 3 are connected in series. When solenoid valve 1 is powered off, motors 2 and 3 are connected in parallel. When the two motors are connected in series through the same flow, the speed is higher than that when they are connected in parallel. When they are connected in parallel, the working pressure difference of the two motors is the same, but the speed is lower.
repair
Hydraulic motor maintenance refers to the fault diagnosis and maintenance of hydraulic motor, hydraulic components, hydraulic equipment and hydraulic system.