In the production and use of construction machinery, mobile machinery and other equipment, how to stably transfer the engine power to the auxiliary devices is a problem. If you are a device engineer or manufacturer, reading this comprehensive article on power take-off will be helpful to you.
What is the Power Take-Off？
The power take-off is a mechanical power output device installed on the engine or the transmission system. It can transfer the power from the transmission or the engine to another device or machine that does not have its own power source.
How does the Power Take-Off Work?
The power take-off is mainly composed of a protective housing, a transmission gear set, a clutch or meshing sleeve, input and output shafts, control mechanisms, and bearings.
The housing is used to support and protect the internal transmission components. The gear set is responsible for power transmission and speed conversion. The clutch or the meshing sleeve is the component that controls the interruption or continuation of power.
The power take-off is connected to the power output end of the engine or gearbox through the input shaft and obtains continuous power from the power source.
When the control mechanism triggers the engagement action, the clutch or the meshing sleeve drives the transmission gear set to mesh, thereby stably transmitting the torque and speed from the power source to the output shaft, and then driving external hydraulic pumps, working machinery, and other equipment to operate.
When the control mechanism triggers the disengagement action, the clutch or the meshing sleeve disconnects the transmission connection, the gear set stops meshing, and the external power transmission path is immediately cut off, causing the output shaft to stop power output.
Types of Power Take Off
According to the Installation Location
Front-Mounted Power Take-off
The front-mounted power take-off is installed at the front end of the engine and directly obtains power from the engine crankshaft. The front-mounted power take off belongs to the full power output type and can obtain the maximum torque of the engine. Its power transmission has no intermediate loss, and the output power can reach 80% – 95% of the engine power.
The front-mounted power take-off is suitable for heavy-duty specialized equipment with extremely high power requirements, such as the water pump system of large fire trucks and the mixing drum drive of concrete mixer trucks.
Due to the direct linkage between the front mounted power take-off and the engine, you must consider lubrication and heat dissipation issues. You need to install forced lubrication and cooling devices under long-term high load conditions.
Side-Mounted Power Take-Off
The side-mounted power take-off is currently the most widely used type. It is installed on the take-off port on the side of the gearbox and achieves power extraction by meshing with the intermediate shaft gears of the gearbox.
The side-mounted power take-off belongs to the partial power output type. Its output power is usually 30%-60% of the rated power of the engine. The side mounted power take-off has a compact structure. It is easy to install and maintain, and does not occupy the transmission shaft space at the rear of the vehicle.
It is widely used on various specialized vehicles such as dump trucks, garbage trucks, and aerial work vehicles.
Rear-Mounted Power Take-Off
The rear-mounted power take-off device is installed at the rear end of the gearbox. It usually obtains power from the rear end of the gearbox’s intermediate shaft or the rear end of the second shaft. The rear-mounted power take-off device belongs to the high-power output type. The output power can reach 70% to 90% of the engine’s rated power.
The rear-mounted power take-off has high structural strength, adopts rigid connections, and has smooth power transmission. It can withstand the impact of heavy-load operations and has a small influence on the vehicle’s driving condition during operation.
The rear-mounted power take off is commonly used in heavy cranes for driving hydraulic lifting devices, large flatbed trucks for driving hydraulic loading and unloading devices, and high-power hydraulic pump stations, etc.
Bottom-Mounted Power Take-off
The bottom-mounted power take-off is usually installed at the bottom or lower part of the gearbox. Its output power is usually 20% -50% of the rated power of the engine. This installation method is relatively concealed and can avoid external collisions during operation.
The bottom-mounted power take-off is suitable for light vehicles and small construction machinery, such as light trucks, small loaders, etc. However, due to the low installation position, you need to take measures to prevent vibration and dust.
According to the Control Method
Independent Power Take-Off
The independent power take-off unit is controlled independently of the vehicle’s transmission system. It has its own clutch control mechanism. The operator can control the start and stop of the power take-off at any time during the driving, parking, or shifting process of the vehicle through buttons and handles inside the cab.
The independent power take-off is suitable for working conditions that require precise control of the output, such as combine harvesters, seeders, etc. However, the structure of the independent power take-off is complex and requires a dedicated control module.
Non-Independent Power Take-Off
The non-independent power take-off does not have an independent clutch and control mechanism. Its power output is fully linked with the vehicle’s main clutch and gearbox. When depressing the clutch to shift gears or start moving, the power output will be temporarily interrupted.
The non-independent power take-off system is simple in structure and has a low cost. It is widely used in engineering vehicles that perform intermittent operations.
Live Power Take-Off
The live power take-off can also achieve flexible power transmission through a two-stage clutch. The operator can partially press the clutch to stop the vehicle from moving forward while keeping the power take-off running. The power take-off will only stop power output when the clutch is fully depressed.
It is suitable for working conditions that require a brief stop of the vehicle but maintain external operation, such as mowing and baling.
According to the Driving Method
Mechanical Power Take-Off
The mechanical power take-off is the most basic type. It achieves the engagement and disengagement of the power take-off through the pull rod and the shift fork. The mechanical power take-off devices have a simple structure and high reliability.
However, its operation is difficult and requires manual control of the meshing force by the operator to avoid problems such as gear impact and skipping teeth.
Pneumatic Power Take-Off
The pneumatic power take-off uses the vehicle’s own compressed air system as the power source. It controls the flow of air into the cylinder inside the power take-off through an electromagnetic valve. The compressed air pushes the piston, which in turn drives the clutch gear to mesh.
The advantage of pneumatic control lies in its fast response speed and ease of operation. It is suitable for trucks or engineering vehicles that require remote or in-cab operation of power take-off.
Hydraulic Power Take-Off
The hydraulic power take-off is powered by the on-board hydraulic system. The pressure oil generated by the hydraulic pump is directed to the piston or hydraulic cylinder, causing the internal clutch or friction plate to be pressed or released, thereby achieving the connection or disconnection of the power.
The hydraulic control method can handle a very high starting torque. At the moment of engagement, the buffering effect of the hydraulic oil protects the entire transmission chain from being damaged by intense vibrations.
The hydraulic power take-off is suitable for heavy-duty and high-precision equipment, such as hydraulic cranes, aerial work platforms, and large-scale mining machinery, etc.
Electric Power Take-Off
The electric power take-off mainly operates by using direct current to drive the internal electromagnetic coils or small actuators. It has a simple structure, easy installation, and convenient operation.
The electric power take-off can be easily connected to the vehicle’s electronic control system and achieve automatic control. It is very suitable for use in light commercial vehicles, electric sanitation vehicles, automated material conveying vehicles, etc.
The Application of Power Take-Off
Engineering Machinery
The dump truck drives the hydraulic pump through the power take-off to generate high-pressure oil, which drives the hydraulic cylinder to lift and unload the cargo box.
The concrete mixer truck uses a power take-off to continuously drive the mixing drum to rotate, preventing the concrete from solidifying during transportation.
The vehicle-mounted crane transport vehicle uses the power take-off device to drive the hydraulic pump, providing power for the extension, rotation and lifting of the vehicle-mounted crane.
Agricultural Machinery
The tractor transmits power to various supporting agricultural tools such as rotary tillers, seeders, harvesters, sprinkler irrigation equipment, etc., through power take-off, achieving various operations such as land plowing, sowing, harvesting, irrigation, etc.
Under these conditions, the power take-off can provide a stable rotational speed, making sure the agricultural machinery maintains a consistent working frequency.
Municipal Affairs and Sanitation
The garbage compression vehicle uses the power take-off to draw power from the gearbox and then drives the compression mechanism and the discharge device to achieve the compression, storage and discharge of garbage.
High-pressure cleaning vehicles usually have large water tanks. They are driven by the power take-off to power the high-pressure pump, maintaining a stable spraying pressure while the vehicle is moving at a low speed, and completing cleaning tasks for road surfaces, guardrails and other facilities.
The suction truck adopts a side-mounted power take-off to drive the suction pump to generate negative pressure, achieving the extraction and storage of sewage and pollutants.
Material Transportation
The oil tanker uses the power take-off to drive the oil discharge pump for liquid transportation. The bulk cement transport vehicle uses a power take-off to drive an air compressor and blows the powder material into the storage bin through a pneumatic unloading system.
The refrigerated truck drives the refrigeration compressor through a power take-off to keep a constant temperature environment during the transportation of fresh food and pharmaceuticals. A refrigerated truck equipped with an electronic power take-off can achieve more precise temperature control and lower fuel consumption.
Special Vehicle
The fire truck obtains power from the engine through the power takeoff to drive the fire pump to operate, achieving a high-pressure water supply or foam transmission.
In a tow truck, the power take-off drives the hydraulic winch, providing a huge pulling force for towing the faulty vehicle.
The high-altitude rescue vehicle uses a power take-off to drive the hydraulic lifting system, which drives the rescue platform to lift smoothly and achieve high-altitude rescue operations.
How to Choose A Power Take-Off?
Clarify the Requirements of the Assignment
Before choosing a power take-off, you first need to clarify what type of work your device will perform. For example, if you drive a hydraulic pump intermittently for a short period of time, the requirements for heat resistance and wear resistance of the power take-off will not be very high.
If you are pumping materials for a long time or continuously driving hydraulic devices, you need to choose a power take-off that can withstand high heat and adapt to continuous working loads.
Match the Output Specifications of the Engine or Transmission
The power take-off must be matched with the parameters of the engine or gearbox, such as speed, torque, output shaft size, etc. When making the selection, you should carefully check the input speed range of the power take-off to make sure that it is consistent with the driving equipment.
In addition, you need to verify the installation holes and bolt types on the gearbox to make sure that the power take-off unit can be safely and firmly installed onto your vehicle or machinery.
Consider the Installation Location
You need to consider the installation space for the vehicle or equipment. Different installation positions, such as side-mounted, front-mounted, and bottom-mounted will affect the selection of the shape and size of the power take-off.
You should consider whether there will be interference between the power take-off and other components during assembly, and reserve sufficient installation space.
Due to the different installation positions, it may also affect the direction of the power take-off output shaft and the routing of the piping. You need to plan the layout of the hydraulic pipelines and the electrical control wiring in advance.
Confirm the Output Interface
There are various forms of output interfaces for power take-off, such as flange interfaces, keyway output, or spline output. You need to confirm whether the shape, size, and standard of the output end of the power take-off are compatible with the driven equipment such as hydraulic pumps and mechanical accessories.
If the power take-off output interface does not match the device, you will need to equip an additional adapter. This will increase the complexity of the system and may also bring vibration risks.
FAQs
What are the Common Causes and Solutions for the Fracture of the Power Output Shaft of the Power Take-Off?
The common causes of power take-off output shaft fracture include long-term overload of the load, poor gear meshing, abnormal operation of the secondary clutch, and aging and damage of the transmission shaft or connecting sleeve.
You need to first check whether there are any cracks on the broken shaft, the condition of the gears, and the status of the auxiliary clutch. If the shaft breaks or the gears are severely worn, you should replace these parts in time. If it is a problem with the clutch, you will need to adjust or replace the clutch.
Are There Any Details to Pay Attention to when Installing the Power Take-Off in Conjunction with the Hydraulic Pump?
First, you must make sure that the axial and angular alignment between the power take-off output shaft and the input end of the hydraulic pump is accurate. Poor alignment can lead to vibration and increased bearing load, thereby shortening the lifespan of the power take-off and pump.
Secondly, you need to confirm that the maximum output torque of the power take-off is consistent with the demand of the hydraulic pump to avoid overloading. For heavy-duty hydraulic pumps, you should use support brackets to prevent the pump’s own weight and vibration from causing lateral forces on the power take-off housing and output shaft.
Why is Gear Clearance Important when Installing A Power Take-Off?
Gear clearance refers to the small gap between the driving gear of the power take-off and the gearbox gear when they mesh. If the clearance is too small, severe wear and high-frequency screaming will occur during operation. And in severe cases, the gearbox gears may be damaged. If the clearance is too large, it will lead to an increase in impact load.
Why does the Power Take-Off Make Abnormal Noise or Vibration, and How Can It Be Resolved?
Abnormal noise or vibration in the power take-off is usually caused by poor alignment between the power take-off and the output shaft of the gearbox during installation. You can check and re-adjust the installation position of the power take-off.
If the overlap length between the inner and outer tubes of the power transmission shaft of the clutch is insufficient, it will cause severe oscillation during operation. You need to check and adjust the length of the transmission shaft to a suitable range.
Why should the Power Take-Off Avoid Excessive Angles When Attaching Equipment?
When the transmission shaft angle between the power take-off and the driven equipment is too large, obvious lateral forces and vibrations will be generated during the rotation process. This will accelerate the wear of components such as bearings, couplings and oil seals.
What should be Noted When the Power Take-Off is Not Used for A Long Time？
If the power take-off does not operate for a period of time, it is recommended to disconnect the power take-off first. Clean the surface of the power take-off and lubricate the output shaft and easily worn parts with rust prevention to avoid corrosion caused by residual moisture or pollutants.
You also need to inspect the condition of the output shaft guard and the seals to prevent leakage or meshing difficulties when it is used again next time. Regularly starting the power take-off can maintain lubrication and prevent lubricating oil from settling or drying up due to long-term inactivity.
Final Thoughts
The power take-off makes a single power source drive multiple additional operational equipment, improving the on-site operational capabilities of engineering machinery, agricultural machinery, and other equipment. If you want to learn more and need a good power take-off, please feel free to contact us.
