A gerotor hydraulic motor, hydraulic gerotor motor, gerotor motor, or low-speed, high-torque motor (LSHT motor) is a hydraulic actuator that uses the flow of hydraulic fluid to drive an internal gear train and produce torque. It is more suitable for low-speed, high-torque applications such as agricultural machinery, construction machinery, and forestry machinery (e.g., lawn mowers and sweepers) than standard high-speed motors. While compact, its internal structure encompasses multiple core components, each of which directly impacts the motor's performance and lifespan.
Accessories typically include: a gerotor front cover, a flat key shaft, lotus gears, oil inlet and outlet ports on the rear cover, bolts, O-rings to prevent oil leaks, sealing rings and oil seals, and a housing. Poocca Motor Manufacturers offer motor models including: 2000/4000/6000/8000/10000, OMR/OMP/OMH/OMS, TG/TB/TJ, and many more.
Detailed Explanation of the Main Components of a Hydraulic Gerotor Motor
Drive Shaft of an gerotor Motor
The drive shaft is the main output member that connects the motor to the external mechanical system. Located at the motor front, one end is connected to the internal gerotor gear set and the other end to the external load (e.g., wheel, capstan, conveyor belt, etc.) via a spline, keyway, or flange.
The drive shaft carries torque and also sustains heavy radial and axial loads. The drive shaft is therefore typically constructed of high-strength alloy steel, and some designs feature a hardened surface for improved wear resistance. For heavy-duty applications, a larger diameter shaft and double bearing support are used to prevent shaft bending or breakage in the event of overload conditions.
Gerotor/Geroler Set of a Hydraulic Motor
This is the "heart" of the gerotor motor, determining its basic operating principle and displacement. It consists of an inner rotor and an outer stator, separated by a tooth difference of one.
Gerotor structure: The inner rotor directly meshes with the outer stator, generating rotational motion through hydraulic oil pressure.
Geroler structure: Based on the Gerotor structure, multiple needle bearings (rollers) are added, positioned between the inner and outer gears. This effectively reduces friction and wear, making it suitable for applications requiring longer life and higher efficiency.
Hydraulic oil sequentially fills and discharges each tooth cavity, driving the rotor to eccentrically rotate and simultaneously driving the drive shaft to output mechanical energy.
Motor Distribution Valve System (Valve Mechanism)
There are two common distribution forms now:
Spool Valve: The distribution unit is incorporated within the drive shaft to create a compact structure.
Disc Valve: With a separate disc structure for oil distribution, the sealing performance and stability of this valve are enhanced, and it suits high-load and high-pressure application.
The sealing and precision of the distribution valve will have direct impacts on the starting pressure, efficiency, and noise of the motor.
Output Shaft Bearings
Bearings Position The Drive Shaft And Take Up Radial And Axial Load Forces. Different Gerotor Motor Designs Use Different Bearings:
Small motors use needle roller bearings or ball bearings for medium loads;
Large motors use tapered roller bearings for more loads and greater life.
The hydraulic fluid lubricates the bearings itself, so sealing and cleanliness are of vital concern. Bearing wear or contamination can very quickly lead to motor performance decline or shaft failure.
Motor Housing
The housing is the "skeleton" of the entire gerotor motor. Its internal structure integrates channels, oil passages, support surfaces, and sealing grooves. It performs the following functions:
Provides structural strength and prevents internal hydraulic oil leakage;
Directs high-pressure oil flow to designated locations;
Supports the internal gear train and bearings.
The housing is generally constructed of high-strength cast iron or steel, with some models utilizing aluminum alloy for weight reduction. The housing is rust-proofed and features a standard mounting flange for easy installation within the mechanical system.
End Cap
The end cap is located at the rear of the motor, primarily sealing off the entire system and protecting the internal oil distribution mechanism or bearings. Some high-performance motors also incorporate a pressure regulator or bypass valve within the end cap to provide additional control functionality.
The end cap often features a small vent or oil drain port for maintenance or oil return.
Seals and Gaskets
The hydraulic oil within a hydraulic gerotor motor is under high pressure, so seals must possess excellent pressure and wear resistance. Common seals include:
Drive shaft oil seal (prevents oil leakage from the output shaft);
O-ring (for static sealing);
Rubber gasket or combination seal (for the interface between the end cap and the housing).
Poor seals are one of the most common causes of hydraulic motor failure, often leading to internal leakage, reduced efficiency, and even system contamination.
Case Drain Port [Optional]
Some hydraulic gerotor motors are equipped with a case drain port, also known as an external drain port, to direct any leaking oil from the motor back to the reservoir. Although the amount of leakage is minimal, long-term accumulation can lead to excessive internal pressure, potentially damaging oil seals or bearings.
The case drain port is useful in the following situations:
High-speed operation;
High-pressure systems;
Systems that are installed at an elevation at which the oil is unable to flow back naturally.
The case drain port is usually connected during installation to the main oil return line of the system or a special oil return tank having a return line.
Finally, although the concept of a hydraulic gerotor motor's design is simple, each component has its vital role in providing high-pressure and high-load operation. The drive shaft delivers torque, the gerotor gearset converts hydraulic energy to mechanical energy, the flow control valve controls the direction and efficiency of the motor, and the case, bearings, and seals facilitate stable and extended operation of the entire system.
To buyers of hydraulic equipment, the inside construction of a gerotor motor is not only useful for model selection but also for servicing the equipment in the future and debugging. For example, where the application involves constant load fluctuation or extensive low-speed operation, Geroler roller configuration motors and oil drainage ports should be given high priority because of enhanced servicing life and stability.
If you wish to receive information about some of the models, structural arrangements, or recommendations for selecting a brand such as Poocca, Eaton, Danfoss, or Parker, let us know your request and we will provide you with the information you need.
