What is a PTO and why it is needed
Every motorist knows perfectly well that the transmission in the car performs a key function. It is the transmission of torque from the engine. Through this connection, the wheels turn and the car moves.
So there is a direct correlation between the engine and the transmission. But it is not the only consumer in need of power transmission.
There are units and equipment that require their own source to perform their assigned functions. For these purposes, the internal combustion engine itself can be used. Only additionally used such a node as a power take-off box, or in abbreviated form KOM.
What is it
To begin with, it is necessary to understand the purpose of power take-off boxes and understand why they are used in the design of a car or other vehicle.
The example of the transmission and engine forces, which are transmitted to the drive wheels with minimal losses, was given for a reason. There are mechanisms and units on a car that need their own power source to be able to perform their assigned functions.
It in many respects gives understanding, for what the PTO is necessary and for what purposes it is intended. After all, putting another motor or electric motor under the hood makes no sense. The drive is the main engine of the vehicle.
This is what the so-called power takeoff box is for. It allows to connect the motor with additional consumers and transfer power flows from the main kinematic scheme. Depending on the specific type of transport, it can be provided from one to several such mechanisms.
KOM can be characterized as a mechanical classic gearbox. But its type and technical characteristics largely depend on what equipment is used to work in conjunction with it.
Depending on what load is provided for additional and attached equipment, the box can transfer up to 40% of the maximum parameters of the internal combustion engine power. As a result, an assembly designed for such tasks in the form of a PTO is structurally different.
There are also regulated standards for where the PTO is installed and how it is positioned.
Varieties
As you have already understood, the PTO is used on machines in order to transfer energy to additional equipment.
If you start from the driven mechanisms and the requirements for the device, there are different types of existing power takeoff boxes. They can differ from each other according to several principles:
- Number of stages. This determines the step between the available working mechanisms.
- Availability of reverse. Some units, such as pumps, imply rotation only in one direction. If it is a truck crane, then the KOM must work in two opposite directions.
- Transmission ratio. The change in angular speed and transmitted torque depends on this value.
- Number of shafts. It may be different, depending on the design of a particular box.
- The arrangement of the components that make up the box.
- A special control signal. It can be mechanical, with a lever or via the on-board computer.
When getting acquainted with the design of power take-off boxes, it is necessary to take into account the possible options of their location.
Basically the systems can be mounted at the following points:
- at the side of the machine’s gearbox;
- On the end face of the gearbox;
- in the gearbox crankcase;
- together with the transfer case.
KOM requires mandatory lubrication, which depends on the specifics of installation and the presence of its own oil reservoir in the design. Most often the lubrication is performed by the oil and crankcase of the main gearbox.
Sometimes the position of the final drive assembly is upright. In this case a pump is additionally used. This enables the lubricant to be supplied to the assembly.
All boxes used in machines can be divided into several subcategories. They can be:
- reversible;
- Gearless;
- dependent;
- independent.
Each variant requires a separate consideration for a better understanding of the essence and principle of operation of the device.
Reversible systems
Such KOMs have a gearbox, and the arrangement of the shafts here is longitudinal. The installation of such units is carried out in the lower side of the crankcase of the machine gearbox.
Here the power take-off is realized by the gearbox intermediate shaft pinion. It is in a state of permanent firm meshing with the block pinion, of which there are several in the scheme. Another pinion will be in mesh together with the intermediate pinion. The block gears themselves, as well as the intermediate pinion, are located on the axles. The latter are mounted directly on the crankcase of the gearbox.
Gearless gears
In addition to gearless gearboxes, which were discussed above, there are also gearless boxes, designed for power take-off. Their distinctive feature is the simplicity of design. They also have a single gear ratio.
To select the necessary power in this case, the transfer gearbox primary shaft is used, on the end of which special splines are provided. These types of boxes are mounted on the end of the transfer case crankcase at the top of the design.
The KOM shaft has the same splines on one end as the transfer case primary shaft. At the other end, a flange is installed to mount the drive shaft of the already additional automotive equipment.
To engage the transfer case, it is required to use the locking of the two shafts with a special carriage. The latter is moved by an actuating fork located on the rod. The stem has two fixed standard positions. In the left position, the PTO is in the active, i.e. working, position. The right position means that the reversing mechanism is switched off.
Changing the direction of rotation of the KOM shaft can be done by engaging the reverse gear on the vehicle’s gearbox.
If you study the design of the considered box, you can notice one important nuance. It is the use of a plunger pump. It is needed to lubricate the components of the body of the transmission and transfer case at the moment when the car is stationary, but the additional equipment is working. This prevents possible wear and tear due to lack of lubrication. The pump forcibly supplies oil to the components, thereby lubricating and cooling them.
The plunger-type pump itself is mounted in a casing located directly in the KOM cover lug. It consists of the plunger pump itself as well as the return, suction and the obligatory discharge valve.
To operate such a PTO, you use a lever directly connected to the rod and placed in the cab of the machine or other vehicle.
The operation of PTOs without a gearbox is now understood. Now it’s worth taking a look at two more varieties of units.
Dependent gearboxes
Here we are talking about the dependence on the clutch. Such devices are usually located on vehicles equipped with manual transmissions. Such systems are relevant when the attached additional equipment does not need to be switched on the fly, that is, during the movement of the vehicle.
Dependent transmissions have several major advantages:
- they have a low weight, which simplifies the work with them during repair and maintenance;
- the repair itself does not cause any difficulties with a certain level of knowledge;
- if the box is in the off state, such KOM does not additionally load the engine;
- the design is simple and reliable enough;
- they have a long service life;
- Maintenance requirements are minimal;
- high level of safety, since the PTO can not spontaneously start working while running.
The most striking example of machines where PTO is used are dump trucks.
Installation of PTOs is extremely simple. A special place is provided for this purpose. The hatch is dismantled beforehand. If the location will be upper, in addition in the scheme is used a pump.
With the dismantling work is also simple. In the case of removal it will not affect the work of the main gearbox in any way.
Independent transmissions
A distinctive feature of independent KOMs is that they can be installed on cars and vehicles with any type of gearbox, that is, with different transmissions.
The main advantage is the possibility of engaging the mechanism when the vehicle is moving or standing on the spot. Such KOMs are widespread on the domestic trucks KAMAZ.
It can be installed on the right or left side of the side hatch. There are also options when it is mounted at the end. This already depends on the specific model of the PTO. To implement an effective lubrication system, a pump is connected to the scheme.
To control the frequency of rotation of the shafts of the box, as well as the power transmitted to additional and attached necessary equipment, you can use the engine of the vehicle. Quite often there are machines, where the system of activation and deactivation of KOM is realized by hydraulic or electro-pneumatic principle. These boxes are actively used in vehicles equipped with automatic transmissions.
As you understand, KOM are not used on conventional passenger cars. These are solutions relevant for dump trucks, tank trucks, crane trucks, utility vehicles, etc.
During their operation, it is important to follow a few rules:
- periodically check the reliability of attachment;
- exclude the possibility of strong vibrations;
- to observe the sequence of switching on and off KOM;
- periodically check the condition of the lubricating fluid;
- periodically check the condition of the lubricating fluid; lubricate some components additionally according to the instructions;
- timely change oil in the gearbox.
All this is intended to prolong the service life of the unit. Initially it has an impressive service life. However, if the PTO is actively used and the rules of PTO usage are violated, the wear and tear may occur considerably earlier than the specified period.
What is a PTO and why it is needed
Every motorist knows perfectly well that the transmission in the car performs a key function. It is the transmission of torque from the engine. Through this connection, the wheels turn and the car moves.
So there is a direct correlation between the engine and the transmission. But it is not the only consumer in need of power transmission.
There are units and equipment that require their own source to perform their assigned functions. For these purposes, the internal combustion engine itself can be used. Only additionally used such a node as a power take-off box, or in abbreviated form KOM.
What is it
To begin with, it is necessary to understand the purpose of power take-off boxes and understand why they are used in the design of a car or other vehicle.
The example of the transmission and engine forces, which are transmitted to the drive wheels with minimal losses, was given for a reason. There are mechanisms and units on a car that need their own power source to be able to perform their assigned functions.
It in many respects gives understanding, for what the PTO is necessary and for what purposes it is intended. After all, putting another motor or electric motor under the hood makes no sense. The drive is the main engine of the vehicle.
This is what the so-called power takeoff box is for. It allows to connect the motor with additional consumers and transfer power flows from the main kinematic scheme. Depending on the specific type of transport, it can be provided from one to several such mechanisms.
KOM can be characterized as a mechanical classic gearbox. But its type and technical characteristics largely depend on what equipment is used to work in conjunction with it.
Depending on what load is provided for additional and attached equipment, the box can transfer up to 40% of the maximum parameters of the internal combustion engine power. As a result, an assembly designed for such tasks in the form of a PTO is structurally different.
There are also regulated standards for where the PTO is installed and how it is positioned.
How to use the PTO correctly
Considering the intensive loads on trucks, the PTO is subject to gradual wear and tear. In order to extend the life of this mechanism and ensure its smooth operation, it is necessary to follow several rules. Firstly, it is necessary to check the condition of the final driveshaft pinion. Secondly, you need to make sure that the mountings are secure before installing the KOM. Thirdly, when you turn on the box should strictly comply with the requirements of the manufacturer of this mechanism. In addition, you must constantly monitor the level of lubrication and be sure to lubricate all moving elements of the box.
Varieties
As you have already understood, the PTO is used on machines in order to transfer energy to additional equipment.
If you start from the driven mechanisms and the requirements for the device, there are different types of existing power takeoff boxes. They can differ from each other according to several principles:
- Number of stages. This determines the step between the available working mechanisms.
- Availability of reverse. Some units, such as pumps, imply rotation only in one direction. If it is a truck crane, then the KOM must work in two opposite directions.
- Transmission ratio. The change in angular speed and transmitted torque depends on this value.
- Number of shafts. It may be different, depending on the design of a particular box.
- The arrangement of the components that make up the box.
- A special control signal. It can be mechanical, with a lever or via the on-board computer.
When getting acquainted with the design of power take-off boxes, it is necessary to take into account the possible options of their location.
Instructions for Use.
Justify to the students the importance of the considered educational issue. Give the main points to be written down in the lecture notes.
Give concrete examples from the experience of operating the vehicles.
Pay attention to the correctness of the notes.
Teaching material, using the frames in Microsoft PowerPoint, schemes and posters.
Keep in touch with the class.
Control the quality of assimilation of educational material to produce a brief survey on the material set out.
Summarize the issue and proceed to the next educational issue.
Make conclusions on the material of the lesson, summarize the lesson, answer the students’ questions. Provide a task for independent work.
Reversible systems
Such KOMs have a gearbox, and the arrangement of the shafts here is longitudinal. The installation of such units is carried out in the lower side of the crankcase of the machine gearbox.
Here the power take-off is realized by the gearbox intermediate shaft pinion. It is in a state of permanent firm meshing with the block pinion, of which there are several in the scheme. Another pinion will be in mesh together with the intermediate pinion. The block gears themselves, as well as the intermediate pinion, are located on the axles. The latter are mounted directly on the crankcase of the gearbox.
PTO diagrams for the various cars
Fig. Schematic diagram of the power take-off box MAZ 5334 AC-8: 1 – Rubber diaphragm; 2 – spring; 3 – rod; 4 – body; 5 – shift fork; 6 – collar; 7 – spline shaft; 8 – flange; 9 – pin; 10 – pinion; 11 – parasite gears; 12 – primary converter tachometer; a – chamber
Fig. Schematic diagram of power takeoff box KCM-68B: 1 – gear shift rod; 2 – body; 3 – gear shift lever; 4 – fork switch KOM; 5 – gear (Z = 17); 6, 7, 10, 20 – bearing; 8 – clutch; 9 – secondary shaft; 11 – cover; 12 – oil seal; 13 – clutch flange; 14 – handle; 15 – shift fork; 16 – gear (Z = 41); 17 – roller bearing; 18 – engagement rod KOM; 19 – pinion shaft; 21 – primary shaft; 22 – gearbox primary shaft pinion; I – side clearance in meshing
Fig. PTO of CMK-10 crane (a) and its kinematic diagram (b): 1, 5 – flanges, 2 – bearing; 3, 4 – input and output shafts; 6 – body; 7 – ring gear; 8 – shift coupling; 9 – toothed ring gear; 10 – hub; 11 – pulley; 12 – fingers
Fig. PTO RK-5: 1 – gearbox PK-5-11A; 2 – axis RK-5-13; 3 – housing box PK-5-01; 4 – pump NCh10; 5 – pump shaft RK-5-16B; 6 – plug RK-5-26A; 7 – shifting shaft RK-5-21; 8 – shifting shaft RK-5-26; 9 – plug RK-5-27A; 10 – gearbox RK-5-14A; 11 – selection shaft RK-5-31A; 12 – gearbox RK-5-15A
Fig. Power take-off gearbox ZIL-131: 1 – stem of the gear fork; 2 and 23 – sleeves: 3 – sealing ring; 4 – engagement fork; 5 – ball lock; 6 – stem plug; 7 – rear bearing cover; 8 – ball bearing; 9 – gearbox engagement wheel; 10 – main shaft; 11 – gear axle of constant mesh; 12 – bearing washer; 13 – intermediate gear of constant mesh; 14 – gearwheel block axle; 15 – gearbox crankcase; 16 – gearwheel assembly; 17 – roller bearing; 18 – supporting washer; 19 – spacer ring; 20 – bearing cover gasket; 21 – front bearing cover; 22 – flange; 24 – supporting flange washer; 25 – fill plug; 26 – PTO engagement lever; 27 – drain plug; 28 – nut; 29 – lock nut; 30 – lever arm; 31 – gasket
Fig. Power take-off gearbox MAZ: 1 – intermediate gear; 2 – body; 3 – pinion, driven; 4 – plug; 5 – locking bolt; 6 – lock washer; 7 – axle; 8 – ball bearing; 9 – roller bearing; 10, 14 – cover; 11 – cup; 12 – spring; 15 – nut; 15 – air chamber; 16 – diaphragm; 17 – washer; 18 – thrust washer; 19, 23, 25 – gaskets; 20 – screw; 21 – gasket ring; 22 – rod; 24 – shaft
Fig. PTO from the transfer case (KOM-1) (for special equipment): 1 – crankcase; 2 – spacer sleeve; 3 and 20 – nuts; 4 and 18 – bearing caps; 5 – shaft; 6 and 23 – ball bearings; 7 – carriage; 8 – plug; 9 – manhole cover; 10 – guard; 11 – switch; 12 – switching chamber; 13 – diaphragm; 14 – spring; 15 – rod; 16 – gasket; 17 – adjusting washer; 19 – flange; 21 – spring washer; 22 and 28 – thrust washers; 24 – lock ring; 25 – toothed ring of permanent engagement; 26 – plug; 27 – axle; 29 – roller bearing; 30 – spacer ring; 31 – plugs; 32 – safety valve; 33 – lock bolt; 34 – locking plate
Fig. Schematic diagram of the electrical equipment PTO: 1 – switch on the control lamp PTO; 2 – solenoid air valve; 3 – three-terminal connecting plate; 4 – PTO switch; 5 – relay on the front axle; 6 – double-socket connector; 7 – switch; 8 – control lamp PTO; 9 – fuse for 20A
Gearless gears
In addition to gearless gearboxes, which were discussed above, there are also gearless boxes, designed for power take-off. Their distinctive feature is the simplicity of design. They also have a single gear ratio.
To select the necessary power in this case, the transfer gearbox primary shaft is used, on the end of which special splines are provided. These types of boxes are mounted on the end of the transfer case crankcase at the top of the design.
The KOM shaft has the same splines on one end as the transfer case primary shaft. At the other end, a flange is installed to mount the drive shaft of the already additional automotive equipment.
To engage the transfer case, it is required to use the locking of the two shafts with a special carriage. The latter is moved by an actuating fork located on the rod. The stem has two fixed standard positions. In the left position, the PTO is in the active, i.e. working, position. The right position means that the reversing mechanism is switched off.
Changing the direction of rotation of the KOM shaft can be done by engaging the reverse gear on the vehicle’s gearbox.
If you study the design of the considered box, you can notice one important nuance. It is the use of a plunger pump. It is needed to lubricate the components of the body of the transmission and transfer case at the moment when the car is stationary, but the additional equipment is working. This prevents possible wear and tear due to lack of lubrication. The pump forcibly supplies oil to the components, thereby lubricating and cooling them.
The plunger-type pump itself is mounted in a casing located directly in the KOM cover lug. It consists of the plunger pump itself as well as the return, suction and the obligatory discharge valve.
To operate such a PTO, you use a lever directly connected to the rod and placed in the cab of the machine or other vehicle.
Auxiliary clutch control actuator
Schematic diagram of an additional mechanical clutch control system on a tank truck
1 – clutch bearing; 2 – yoke; 3 – pedal; 4 – clutch; 5 – lock nut; 6 – small rod; 7 – rod; 8 – button; 9, 12, 18 – levers; 10 – latch; 11 – toothed sector; 13 – intermediate support; 14 – big rod; 15 – axis; 16 – intermediate rod; 17 – spring; 19 – roller
Additional control system of the clutch mechanism is designed to disconnect (turn on) the fire pump from the engine of the chassis. The figure shows the circuit diagram of the additional mechanical control system of the clutch of the fire tank truck (applied on the AC models 63B and 137A of early releases, PM-548 and some others).
There is a clutch lever 9 and a toothed sector 11 in the pump compartment of the fire truck. To disengage the clutch to press with your finger on the button 8, which through the rod 7 will withdraw from the engagement with a toothed sector latch 10, and the clutch lever to move to the position “on itself” and fix it in the extreme rear position (in the direction of the arrow). This will move a small rod 6, turning the lever 12 intermediate support 13 with simultaneous movement of a large rod 14, which is screwed on the coupling 4 with a slit. Further clutch acts through the axis 15 of the clutch pedal and intermediate linkage 16 to the lever 18 of the shaft 19 of the clutch. Fork 2 of the shaft acts on the release bearing 1, providing release of the clutch. When pressing the clutch pedal 3 in the driver’s cab, its lower axis moves freely through the slot in the clutch 4, without affecting the traction system of additional clutch control system. Return of the clutch pedal to its original position is due to the action of the return spring 17. Free movement of the clutch pedal is regulated by changing the position of the clutch 4, installed on the intermediate link. The value of the free stroke of the clutch pedal must comply with the lower limit of the range set by the chassis manufacturer. For example, if the car ZIL-131 the value of a free stroke of 35 … 50 mm for a tank truck on this chassis should be set the value of the free stroke of 35-40 mm (no more). With a larger value of free stroke due to the inevitable backlash of the drive will be incomplete disengagement of the clutch.
In order to adjust the clutch control system rod length it is necessary to put the clutch lever in the pump compartment to the extreme front fixed position, release the lock nut 5 of the big rod and set the required length of rods by turning the clutch coupling 4. When moving the clutch lever to the rearmost position, achieve such a position so that when pressing the clutch pedal its free movement was within the required value. When moving the clutch lever to the rearmost fixed position, the clutch must be completely disengaged so that with the engine running and the KOM engaged the PTO shaft to the pump does not rotate. After finishing the adjustment, tighten the locknuts.
Conclusion on the issue: for the convenience of work on fire trucks, there is an additional clutch drive.
Dependent gearboxes
Here we are talking about the dependence on the clutch. Such devices are usually located on vehicles equipped with manual transmissions. Such systems are relevant when the attached additional equipment does not need to be switched on the fly, that is, during the movement of the vehicle.
Dependent transmissions have several major advantages:
- they have a low weight, which simplifies the work with them during repair and maintenance;
- the repair itself does not cause any difficulties with a certain level of knowledge;
- if the box is in the off state, such KOM does not additionally load the engine;
- the design is simple and reliable enough;
- they have a long service life;
- Maintenance requirements are minimal;
- high level of safety, since the PTO can not spontaneously start working while running.
The most striking example of machines where PTO is used are dump trucks.
Installation of PTOs is extremely simple. A special place is provided for this purpose. The hatch is dismantled beforehand. If the location will be upper, in addition in the scheme is used a pump.
With the dismantling work is also simple. In the case of removal it will not affect the work of the main gearbox in any way.
