/ / Hydromechanical gearbox: operating principle and device

Hydromechanical gearbox: operating principle and device

Despite the growing popularity of cars withautomatic gearbox, the classic mechanics are still in high esteem among many drivers. It is more reliable than automatic transmission. But during operation the driver is constantly forced to work with the clutch pedal. This gives some inconvenience, especially in traffic. So there was a hydromechanical transmission. The principle of its work and the device will be considered in our today's article.


Those drivers who do not want to work withclutch, give preference to this particular transmission. Hydromechanical gearbox performs several functions at once. It combines the clutch and the classic box.

hydromechanical transmission principle of operation
The gearshift here is madeautomatically or semi-automatically. In the same way, the hydromechanical gearbox of the loader is arranged. While driving, the driver does not engage the clutch pedal. All you need is an accelerator and a brake.

About construction

Hydromechanical gearbox assemblypresupposes the presence of a hydraulic transformer. This element, depending on the design features, can be two-, three- and multi-shaft. Now manufacturers use a planetary automatic hydromechanical gearbox.

How does the CVT work?

On trucks and large buses more oftena multi-shaft transmission is used. To switch gears, multi-plate clutches are used here. For their work, lubrication is necessary. The oil of a hydromechanical gearbox differs significantly in consistence from "mechanics". In the latter case, it is more dense. In order to include the first and the back speed on hydromechanics, gear couplings are used. This design allows you to smoothly transfer torque from the flywheel to the wheels.


Now this is more common hydromechanical gearbox.

repair of a hydromechanical gearbox
It was used because of its compactsize and light weight. Another advantage of the planetary transmission is the long service life and the absence of noise during operation. But there are drawbacks to such a box. Due to the design features, this transmission is more expensive in production. It also has a low efficiency.

How the Planetary Transmission Works

Its algorithm of work is extremely simple.The gears are switched on the planetary hydromechanical transmission using friction clutches. Also, to smooth the blows when switching to a lower one, a special brake band is used. It is during the operation of the "brake" that the torque transmission force is reduced. But at the same time the switching speeds are smoother than the analogue ones.

At the heart of the planetary transmission is a hydraulic transformer. This element is located between the engine and the gearbox. GDF consists of several components:

  • The gear wheel.
  • Pump.
  • Turbine.

In the people this element is called a "bagel" because of its characteristic shape.

hydromechanical gearbox
When the engine is running, the pump impellerrotates together with the flywheel. The lubricant penetrates into the pump and then starts to rotate the turbine under the influence of centrifugal force. The oil from the last element penetrates into the reactor, which performs the function of smoothing the shocks and shocks, and also transmits the torque. Circulation of oil is carried out in a closed circle. The car's power increases with the rotation of the turbine wheel. The maximum torque is transmitted when the vehicle moves from the spot. In this case, the reactor is in a stationary state - it is kept by a clutch. When the car picks up speed, the turbine and pump rises. The coupling is wedged out and the reactor rotates with increasing speed. When the revolutions of the last element are maximum, the torque converter will enter the clutch operation state. So it will rotate at the same speed as the flywheel.

Features of the design of the planetary gearbox

Planetary hydromechanical gearboxconsists of the drive shaft on which the articulated gear is located. Also, there are satellites rotating on separate axes. These elements are meshed with the inner teeth of the box and the ring gear. Transmission of torque is due to the action of the brake band. She brakes the ring gear. As the car accelerates, their speed increases. The driven shaft, which perceives the transmission of the torque from the master, is engaged.

hydromechanical gearbox
How does GTP establish the required gear ratio? This action is automatic. When the wheel speed of the car grows, the oil pressure that goes from the pump to the turbine increases. Thus, the torque at the latter increases. Accordingly, the speed of the wheel and the speed of the machine are also growing.

About efficiency

As for the coefficient of efficiency, it is an order of magnitude lower than in the global PPC.

hydraulic transmission oil
Its maximum value is from 0.82 to 0.95. But with an average engine speed, this ratio does not exceed the mark of 0.75. This figure is increasing with increasing load on the torque converter.

Maintenance and repair of hydromechanical gearbox

When using this transmission, it is necessaryfollow the oil level. This fluid here is working. It is the oil that uses the turbines to transfer the torque. On mechanical boxes, it simply lubricates rubbing gears. Manufacturers recommend replacing the oil on hydromechanical boxes every 60 thousand kilometers. It is worth noting that in the design of such a checkpoint has its own filter. It also changes when this time is reached. Operation at a low level of oil threatens to stall and overheat the transmission.

automatic hydromechanical gearbox
Regarding repair, most often failshydraulic transformer. Symptom of failure is the impossibility of switching on one of the transmissions, the increased "tripping" time of the required speed. Also in this case, the mesh-oil intake is disassembled and cleaned and the spool valve is changed. If there are leaks, it is necessary to check the tightening torque of the bolts and the condition of the sealing elements. During operation, metal chips are formed on the filter. It clogs the mechanism and the oil pressure level drops. With increased loads, the resource of this cleaning element is reduced. In this case, it is recommended to change it once in 40 thousand kilometers.

How to extend the resource

To extend the service lifehydromechanical box, it is necessary to monitor the oil level. If it is insufficient, the box overheats. The operating temperature should not exceed 90 degrees. Modern cars are equipped with an oil pressure sensor. The control lamp caught fire, do not ignore it. In the future, this can provoke a breakdown of the torque converter.

hydromechanical gearbox forklift
Also, do not switch gears without squeezingbrake pedals. The box will take the whole blow, especially if you switch from the first to the rear without a preliminary braking. On the move, if this is a lingering descent, it is not recommended to include a "neutral". This also significantly reduces the life of the hydraulic transformer and the working couplings. In the rest it is necessary to adhere to the regulations for oil change and filters. The service life of this checkpoint is about 350 thousand kilometers.


So, we found out what thehydromechanical gearbox. As you can see, with proper maintenance it will be as reliable as mechanical. In this case, the driver does not have to constantly squeeze the clutch.