Hydraulic drive system

Hydraulic transmission, hydraulic transmission, which are used for stepped or stepless speed-torque conversion.

Hydrodynamic hydraulic gearbox operate at low pressure and high amount of oil and allow a compact design. Hydrostatic hydraulic gearbox operate at very high oil pressures and low oil quantity and allow a spatial separation of input and output.

4.1 Road vehicles 4.1.1 Hydrostatic transmissions
4.1.2 Hydrodynamic transmissions
4.1.3 retarder

4.2.1 drive
4.2.2 brake

4.3.1 drive
4.3.2 brake

History

At the turn of the 20th century, stood in front of the shipbuilding problem to underpin the high speed of the steam turbine at high performance to a low speed, as it is necessary for a good efficiency of the propeller. Suitable gear drives for high performance could not be made . A solution is the hydraulic transmission: a centrifugal pump sucks from a reservoir fluid, it accelerates, and outputs it through a pipe system to the next turbine. In the turbine, the flow energy of the fluid is converted into mechanical rotation. Exiting the turbine fluid flows back into the reservoir. The separate arrangement of pump and turbine brings considerable losses by friction of the fluid on the pipe walls, internal friction of the liquid as well as entrance and exit losses. By combining all of the components, the majority of these losses can be avoided.

Hydrostatic transmissions

A hydrostatic transmission is known in the art to connect a hydraulic pump to one or more hydraulic motors. Such transmissions can have a up to several meters large distance between the pump and motor part, can be done because the resulting high pressures no stall (as in the hydrodynamic transmission ). By continuously adjusting the oil flow between the hydraulic pump and hydraulic motor, for example, by delivery or absorbing volume change can be continuously adjusted the translation.

As long as the angle between the disk and the ring is connected to the pistons 0 °, there will be no promotion. Bent to the side of the piston or the disc ( depending on the design ) to the side, so contact the pistons during the rotation caused by the oblique position of the disc or of the ring with the plunger on the bending inner side further into the pump housing and on the other side of. This results in a pressure and a suction side, which are separated by a type of the cylinder head. Thus, the pump starts to discharge upon rotation. The pump is connected through pressure lines with the similarly constructed hydraulic motor again ( that is, a rotational movement ) into the hydraulic power (pressure, volume flow rate) into a mechanical energy. By changing the bending angle and bending direction on the pump flow rate and direction, and thus translation and direction can be controlled.

Hydrodynamic Transmission

Fluid coupling

In hydrodynamic gear pump and turbine are combined in a housing. The pump sits directly on the shaft and is enclosed by the turbine. The pump draws oil to the shaft and throws it to the outside directly into the turbine blades. For a fluid coupling those named already includes all necessary parts. The oil is sucked by the pump and accelerated outward. The pulse is transmitted to the turbine wheel, then bounces off the oil from the housing, and runs back in to the pump or to the oil sump.

The fluid coupling does not convert the torque, it only couples. There occurs a slip, which is converted into heat energy.

Torque converter

In order to achieve a torque conversion, in the case a guide unit is integrated. It consists essentially of the blades for collecting the discharged from the turbine oil. The oil from the turbine has a radial component of motion by inertia and a tangential component of motion by the rotation speed of the turbine. The distributor directs to the oil and accelerates it toward the pump. For this purpose, it is still, it is supported usually via a freewheel. The oil enters with a residual kinetic energy back into the pump. With this arrangement, a speed-torque conversion can be achieved up to a maximum of 1:5. The efficiency drops with decreasing or increasing speed ratio from strong, which is why most of converter lock-up clutches are used in automotive transmissions, turning off the slip and thus greatly improve the efficiency.

Applications

Road vehicles

Flow transmissions are used in road vehicles, especially in the field of automatic transmissions and in commercial vehicles.

Hydrostatic transmissions

Hydrostatic transmissions are mainly used for auxiliary drives with low power or traction drives for construction machinery ( excavators ), trucks and farm equipment (eg combine). Pump and hydraulic motors can be arranged separately at cheaper place here. One drawback is the poor efficiency, which is why they are not often used in modern tractors. Exceptions are power-split transmission, in which only a part of the drive power is transmitted hydrostatically.

Hydrodynamic transmissions

Hydrodynamic transmissions are to be found in automatic transmissions and replace there the clutch ( fluid coupling ) or the entire transmission ( torque converter ). There are also mixed types between mechanical and hydrodynamic gear type, such as the differential converter gear ( DIWA ) the manufacturer Voith, in which the engine power is transmitted at the same time partly mechanically and hydrodynamically in part, with the proportion of the two types of transmission with the speed varies ( when starting high proportion of hydrodynamic transmission, with increasing power, increasing proportion of the mechanical power transmission ).

Retarder

In buses and other heavy vehicles a retarder is often installed as virtually wear -free brake to reduce the wear of the friction brakes and to increase the security by a second, independent braking system. A retarder is a special design of the hydraulic coupling, in which the turbine is fixed. The entire kinetic energy of the impeller is converted into heat and the hydraulic medium (in vehicles usually oil) discharged, which must be cooled.

Rail vehicles

Drive

Hydrodynamic power transmission is in powerful diesel locomotives in addition to the diesel-electric power transmission one of two possible power transmission methods, as purely mechanical (switching ) gear for the transmission of such high drive outputs are not available. The hydrodynamic power transmission offers considerable advantages over diesel-electric variant has the advantage of saving weight, which is paid for by a lower acceleration. An example of a locomotive with hydraulic power transmission is the Class 218 of Deutsche Bahn AG.

Brake

In the field of railway engineering (also H- brake) in use for the term hydrodynamic retarder brake. The operation is the same retarder used in road vehicles, but the components must be carried out according to performance in order to raise the required braking forces; in the construction of Kühlanlangen of equipped with a hydrodynamic brake drive vehicles, the large quantity of heat must be considered. Known vehicles with hydrodynamic brake are eg the locomotives of the series 218 or the railcars of Class 612 of Deutsche Bahn AG.

Industry

In industry as a starting fluid couplings, as a rule coupling for variable speed control and a brake (retarder ) are used. The operating medium mostly mineral oil or water is used.

Drive

For smooth acceleration of large masses such as crushers Turbo couplings are used with constant fill. By slowly developing circulatory flow between pump and turbine as a result of accelerating resource after starting the engine is the same gently accelerated to rated speed. However, there is always a slip between the driving and driven machine. If a variable speed adjustment required during operation, a fluid coupling comes with variable capacity ( turbo coupling ) are used. Here the coupling fill can, for example, changed by a scoop tube and thus the transmission of torque or the speed can be controlled. For fast processing machinery such as compressors or feedwater pumps are geared variable couplings, turbo couplings with upstream or downstream transmission in the same housing used. With Mechanical Variable Speed Drives stepless speed control on propulsion engines with a power up to 80 MW possible.

Brake

Industrial retarder with variable capacity are used for example as a test bed brakes.

Hydraulics Axial piston pump Manual transmission Retarder (mechanical engineering) Viscous coupling unit

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