In the continuous operation of equipment such as conveyor belts and mixers, hydraulic gear motors provide stable and constant driving support. Want to have a deeper understanding of hydraulic gear motors? This article will contain everything you want to know.
What is the Hydraulic Gear Motor?
The hydraulic gear motor is an actuating element in a hydraulic transmission system. It can convert the hydraulic energy provided by the hydraulic pump into mechanical energy to drive the load to work.
Key Components of the Hydraulic Gear Motor
Shell
The housing of the hydraulic gear motor serves as the framework of the entire device. It can fix the internal gears and bearings in the correct position and withstand working pressure and external loads.
The shell also needs to be equipped with a properly designed installation flange and oil passage channel to facilitate system connection and heat dissipation. The processing accuracy and rigidity of the shell will affect the sealing performance of the cavity and the fit of the parts.
Gear
The gear is the core moving component in the motor. Whether it is an external meshing, internal meshing or epicyclic structure, it achieves rotation by generating torque through the tooth surfaces and closing the working chamber.
Axis and Bearing
The output shaft is capable of transmitting the torque generated internally to the external load. Bearings provide low-friction support for the output shaft and gears, and can withstand radial and certain axial forces.
Depending on factors such as rotational speed and load, you can choose different types of bearings such as ball bearings, needle bearings, or tapered roller bearings. Appropriate bearings and good lubrication channels can reduce mechanical wear and extend the service life of the motor.
Flow Distribution Structure
The inlet and outlet oil ports of the hydraulic gear motor are designed symmetrically. This makes that the motor can rotate in both directions. Additionally, the hydraulic gear motor is equipped with a separate oil drain port. It drains the leaked oil from the bearing area promptly to prevent excessive pressure.
Seals
The sealing component can prevent the leakage of hydraulic oil and block the entry of external contaminants. It includes shaft seals, O-rings, end cover gaskets, etc. Sealing failure is one of the main causes of internal leakage in the motor, decreased efficiency and contamination of the oil. So you should pay attention to the selection and installation accuracy of the seal.
Working Principle of the Hydraulic Gear Motor
When the high-pressure oil enters the sealed chamber through the inlet, it will fill the space between the gear teeth. Due to the characteristics of the gear meshing points, the pressure area on the oil inlet side of the tooth surface is much larger than that on the oil outlet side.
This creates a pressure difference. Then, the driving and driven gears are rotated in the opposite direction, and the hydraulic energy is converted into mechanical energy for the rotation of the gears.
When the gear rotates, the volume between the teeth on the inlet side increases to absorb oil. continuously. The volume reduction on the oil outlet side pushes the oil towards the return port and discharges it. This completes the oil suction and discharge cycle.
As long as the oil supply is continuous, the gears will rotate stably and drive the external load through the output shaft.
Types of Hydraulic Gear Motors
External Gear Motor
The external gear motor is a high-speed hydraulic motor. It can be applied in high-pressure hydraulic circuits with a requirement of 200 bar. Its basic structure is similar to that of an external meshing gear pump. It is mainly composed of a driving gear connected to the output shaft and an idler gear that meshes with each other.
To meet the requirements of high-speed operation and long service life, the lubrication and bearing design of the external gear motor are very important. A small portion of the high-pressure oil will be directed and diverted for lubricating the gear surfaces and the bearings. This forms a stable lubricating film, reducing the contact and wear between metals.
Internal Gear Motor
The internal gear motor is usually used in medium-pressure applications. It is composed of a smaller external gear and a larger internal gear. The small external gear serves as the driving wheel. Through internal meshing transmission with the large internal gear, it forms a continuous sealed working chamber.
This meshing method avoids the problem of tooth tip interference in external gear motors. During operation, the gear contact becomes smoother and enhancing the overall operational stability significantly.
The working noise is also reduced by 10-15 decibels compared to external gear motors. It is suitable for industrial environments with high requirements for noise reduction.
The structure of the internal gear motor is simple and compact. It is easy to integrate into equipment with limited space. It is compatible with hydraulic oils of different viscosity ranges and can adapt to special fluid media. You can use internal gear motors in food, beverage, and chemical processing scenarios.
Epicyclic Gear Motor
The epicyclic gear motor is also known as the orbital gear motor or the gear ring motor. It is a low-speed high-torque motor. The core structure of this motor consists of a rotor and a stator.
The rotor is usually a gear with teeth on its outer surface. It rotates around its own axis and rolls along the inner wall of the stator under hydraulic drive. It is just like planetary motion. The stator is a fixed component, and its inner ring gear has one more tooth than the rotor.
With the planetary motion of the rotor, its tooth surface continuously meshes with the stator tooth surface and forms a series of periodic changes in the sealed cavity. This process converts hydraulic energy into mechanical energy.
This special structure enables the motor to maintain torque stability even at low speeds, without the crawling phenomenon that is common in ordinary motors. It can provide stable power for your mining equipment, ship deck machinery and heavy transportation systems.
Some Terms Related to Hydraulic Gear Motors
Hydraulic Gear Motor Displacement
The displacement of a motor refers to the volume of hydraulic oil required or discharged for each revolution of the motor output shaft. When choosing a hydraulic gear motor, the displacement is one of the factors you must take into consideration.
A larger displacement means that at the same pressure, the motor can push more liquid with each rotation. This usually results in a higher torque output and a lower rotational speed. You can use it to drive devices with heavy loads and low speeds.
The small-displacement motors are designed for high rotational speeds and are suitable for applications with light loads and high speeds.
Hydraulic Gear Motor Efficiency
The efficiency of a hydraulic gear motor is a measure of its ability to convert the input hydraulic energy into mechanical energy. It is usually determined by two key indicators: volumetric efficiency (ηₙ) and mechanical efficiency (ηₘ).
Volumetric Efficiency
It is the ratio of the actual output flow of the motor to the displacement under the ideal condition of no leakage. It reflects the extent of flow loss caused by internal leakage in the hydraulic gear motor.
There is an essential clearance between the gears of the gear motor and the housing. A small portion of the high-pressure oil did not participate in the work process but instead leaked directly to the low-pressure area.
A higher volumetric efficiency means that the motor has good internal sealing and can maintain a higher speed at the same flow rate.
Mechanical Efficiency
It is the ratio of the actual output torque to the theoretical output torque. Mechanical efficiency reflects the extent of torque loss caused by friction in the motor. These friction losses mainly come from the moving parts such as gear meshing, bearings, and shaft seals. A hydraulic gear motor with high mechanical efficiency can output a greater actual torque under the same working pressure.
Hydraulic Gear Motor Torque
The torque of a hydraulic gear motor refers to the rotational force that the output shaft can provide. It depends on the system’s hydraulic pressure and the displacement of the motor.
Under the same system pressure, if your motor has a large displacement, then the torque output will be strong. When the displacement remains constant, the higher the system working pressure is, the greater the torque will be.
It is very important for you to understand the meaning of torque and evaluate torque output reasonably in system design and equipment selection. The appropriate torque can ensure that your equipment can start and operate continuously under the expected load.
Advantages of Hydraulic Gear Motors
Simple and Compact Structure
Compared with hydraulic piston motors or hydraulic vane motors, hydraulic gear motors have a simpler structure and fewer internal components. This design makes it have a smaller overall size and a lighter weight.
If your equipment has limited space or you have a high demand for lightweight, a hydraulic gear motor is a good choice.
Strong Adaptability
The transmission method based on gear meshing is not sensitive to tiny impurities in the oil. The hydraulic gear motor has strong anti-contamination ability and has relatively low requirements for the cleanliness of hydraulic oil.
You can apply it in harsh working environments such as construction, mining and agriculture. It doesn’t require frequent replacement of oil and filters. It can help you reduce the cost of consumables and also prevent stuck faults caused by contamination.
Respond Promptly
The rotational inertia of the gear motor is small, and its start-up and direction-changing response speed is very fast. This makes it very suitable for situations that require high-frequency start stop.
For example, you can use it in the material pushing mechanism of automated production lines and the cleaning brush drive of small sanitation vehicles. Combined with modern control systems, it can achieve precise control of flow and direction.
Economically Applicable
The manufacturing cost and maintenance cost of hydraulic gear motors are relatively low. It offers a cost-effective option for budget-sensitive projects. At the same time, the technology of hydraulic gear motors has become very mature, which ensures the reliable operation of your equipment.
The Difference between a Hydraulic Gear Pump and a Hydraulic Gear Motor
Core Function
The essential difference between hydraulic gear pumps and motors is that the direction of energy conversion is completely opposite. This determines the role positioning of the two in the hydraulic system directly.
- The hydraulic gear pump is the power source of the hydraulic system. It is driven by a motor or an engine and converts the input mechanical energy into hydraulic energy. Its function is to output oil with a certain pressure and flow rate, providing power for the entire system.
- The hydraulic gear motor is the actuating component of the system. Its function is the opposite of that of a pump. It receives the high-pressure oil liquid output by the pump and converts the hydraulic energy of the oil into mechanical energy. Then, it outputs torque and rotational speed, which are used to drive the external load to rotate and do work.
Structure
Oil Port
- The inlet and return oil ports of the hydraulic gear motor are usually designed symmetrically and have the same size. It can rotate in both forward and backward directions.
- Gear pumps are generally of one-way rotation, and the suction chamber of such pumps is prone to forming a local vacuum. To enhance the oil absorption efficiency and prevent cavitation failures, the oil intake port is usually larger while the oil outlet port is smaller.
Oli Drain Port
- Gear motors usually have separate oil drain ports. This is because there is back pressure when the motor returns oil, and the inlet and outlet chambers will be interchanged during forward and reverse rotation. Separate leakage can prevent the shaft seal from being damaged by the high-pressure oil.
- The gear pump has no drain port. The leaked oil from the gear pump is usually directed to the oil suction chamber.
Bearing
- The speed of the gear pump is stable and high, and ordinary needle roller bearings can meet the requirements.
- The gear motor has a wide speed range and is prone to lack lubrication at low speeds. Therefore, rolling bearings are more commonly used.
Performance
When you are choosing hydraulic gear motors and gear pumps, the priorities of the performance factors to be considered will be different.
- When choosing a gear motor, you might pay more attention to the starting torque and the minimum stable speed. The starting torque must reach more than 70% of the rated torque in order to start the heavy load from a standstill. The lower minimum speed means smoother operation and avoids crawling at low speeds.
- Hydraulic gear pumps focus on self-priming capability and volumetric efficiency. Self-priming capability ensures that pressure can be quickly established when there is no oil. Volumetric efficiency affects the energy consumption of the system.
Application
- Hydraulic gear pumps are mainly used as the power source of hydraulic systems. It is widely used in the oil supply process of low and medium pressure systems. For example, you can use it in auxiliary oil circuits of construction machinery, hydraulic clamping devices of industrial equipment, and other scenarios.
- The hydraulic gear motors focus on the driving section. For example, you can use it for continuous conveying on conveyor belts and driving fans.
Can a Gear Pump be used as a Hydraulic Gear Motor?
From the above description, you will find that the principles of hydraulic gear motors and hydraulic gear pumps are reversible. However, in practical applications, the two cannot be used interchangeably!
If a gear pump is used as a motor, it will fail to drive the load due to the lack of starting torque and the unsuitable design of the suction port.
On the contrary, if the gear motor is used as a pump, it will result in insufficient oil supply to the system due to poor self-priming ability and low volumetric efficiency.
The Application of Hydraulic Gear Motors
Engineering Machinery
Hydraulic gear motors are suitable for the auxiliary drive systems of small and medium-sized equipment. The vibrating wheels of the road roller, the rotating mechanism of the small excavator, and the bucket flipping device of the loader all commonly employ hydraulic gear motors.
Hydraulic gear motors have strong anti pollution capabilities and can withstand the pollution of hydraulic oil caused by dust and sediment on construction sites. You don’t need to replace the filter element frequently.
The simplicity of the structure makes maintenance easier. Even in remote construction sites, you can quickly complete the replacement of seals or gears.
Agricultural Machinery
The outdoor operation scenarios of agricultural machinery have very high requirements for the durability and stability of the motors.
In the cutting table drive of the harvester and the lifting system of the orchard picking platform, hydraulic gear motors can adapt to high and low temperature fluctuations in the field. And it is not sensitive to the straw shreds and soil mixed with hydraulic oil in agricultural operations, which can reduce the failure rate.
In addition, the hydraulic gear motor is compact in size. It can be easily integrated into the compact body layout of agricultural machinery.
Industrial Automation
Hydraulic gear motors are commonly used for the drive of conveyor belts in assembly lines, the feeding mechanism of packaging machinery, and the power output of fans and pumps. Its startup response time is only 0.1 seconds. It can accurately cooperate with sensor signals to achieve rapid start-stop and transportation of materials.
Its rotational speed range is wide (600 – 3000 rpm). You can adjust the hydraulic oil flow to adapt to different conveying speeds, which meet the production requirements for your various-sized products.
Special Vehicle
Hydraulic gear motors can be used in the brush drive of sanitation cleaning vehicles and the auxiliary power system of electric sightseeing vehicles. Its compact structure can be adapted to the limited installation space of vehicles. At the same time, its light weight can reduce the energy consumption of the vehicle.
Special Working Conditions
Emulsified liquid is usually used as the working medium underground in coal mines. In such explosion-proof situations, synchronous gear motors and non-circular epicyclic gear motors are applied to handheld drilling rigs and other equipment. They have low rotational speed and high output torque, which can directly drive the load.
FAQ
Why does the Hydraulic Gear Motor sometimes Shake after being repaired, Disassembled and then Restarted?
If you do not thoroughly clean the outside, seal it poorly, or loosen the joints, it is easy for air to enter the system. The air mixed into the hydraulic oil will form bubbles or cavitation and this will cause fluctuations in flow and pressure as well as uneven lubrication. Then, it will lead to unstable motor speed, shaking, noise and other phenomena
Can the Hydraulic Gear Motor Operate for a Short Period of Time without Oil?
It is absolutely not allowed. Even an oil-free operation within 10 seconds may cause irreversible damage.
The lubrication of gears and bearings relies on the oil film formed by the oil. When running in an oil-free state, dry friction will occur instantly, and the gear tooth surface will be quickly scratched. The bearing raceways can also be worn out due to direct metal contact.
This kind of damage may initially only result in a decrease in efficiency. However, in the later stage, there may be severe leakage.
At this point, your maintenance costs will increase. Therefore, before starting, you must confirm that the oil has filled the interior of the motor.
What are the Specific Requirements for Installing the Oil Drain Pipe of the Hydraulic Gear Motor?
The oil discharge pipe must be led back to the oil tank separately and cannot be shared with the system’s return oil pipe. You need to ensure that the drain pipe is unobstructed to avoid an increase in back pressure caused by pipeline blockage, small size, or excessive bending.
Target Hydraulics: Your Reliable Hydraulic Gear Motor Manufacturer
Target Hydraulics is dedicated to providing you with high-efficiency, stable and durable hydraulic gear motors. We offer professional customised services. We can design and manufacture hydraulic gear motors according to your specific needs. This will make a perfect fit for your system. Welcome to contact us!
