Retarder - what is it? Retarder - retarder

Retarder. What it is, not everyone understands only the name. Translated from English, this term literally means "retarder". It is used in various fields of science and industry to devices, aggregates or substances that inhibit the dynamics of the course of any process. In the field of engineering, a retarder is a device that is mounted on vehicles in order to slow the speed of their movement without participation or with partial use of the main braking systems.

Where is the retarder useful?

The need for the use of retarders is due to the fact that under conditions of long loads on the main brake system the reliability and efficiency of the latter significantly decrease, which has a negative impact on safety. As a rule, this applies to heavy trucks and road trains, which move in conditions of constant ascent and descent along mountain roads.

Consider the real situation, which helps to understand what the retarder is for. Moving down the slope, the driver has to constantly brake to maintain a constant speed. Such a prolonged load on the friction braking system leads to its overheating and premature wear. In the first case, precious time is spent to allow the brakes to cool down; in the second, the cost of repair and maintenance of the car is increased.

The need to search for an additional source of deceleration was also influenced by the fact that the carrying capacity and speed of trucks increased every year. For example, to stop the road train from a speed of 80 km / h, it takes 4 times more braking force, than for its stop from 40 km / h. It is difficult not to agree that, having at the disposal and knowing how to use the retarder, the driver feels much more confident and calmer.

From the history of retarder

The most significant representative in the history of the retarder invention is the German company Voith. Attempts to apply the idea of a retarder were undertaken by the company since the second quarter of the last century, and its first order for development, it received in the late 50's from a major manufacturer of railway locomotives. After the successful completion of the project in 1961, Voith creates its own separate unit, which to this day specializes exclusively in the release of retarders.

Seven years later, Voith designs the first decelerators for wheeled vehicles on the order of the founder of Setra. Thus, Setra sought to significantly improve the level of passenger transport safety with its buses. The new development from Voith met expectations and began to gain popularity among other automakers. By the end of the last century, drivers of heavy vehicles had not only a general idea of what a retarder was in trucks and buses, but also actively used the unit in their daily work.

A variety of moderators

Retarders include braking by the engine, and a mountain brake. However, the term "retarder" is applied more often to individual units that are mounted on the drive shafts of the engine or transmission. There are several types of retarders. Depending on the place of installation, they are divided into primary and secondary. The primary ones are located before the checkpoint, and the secondary ones are after. Primary retarders have one significant drawback. At the time of gear shifting, it does not interact with the transmission, and the braking force on the wheels disappears. According to the principle of work, retarders are divided into hydrodynamic and electrodynamic.

Hydrodynamic retarders

Most often on heavy vehicles, you can find a hydrodynamic retarder. What it is and how it works, it will be easier to understand those who are familiar with the automatic transmission device. The hydrodynamic retarder is based on the principle of hydraulic coupling. Structurally, the unit consists of two wheels with propeller blades located in a common hull facing each other. One of the wheels is rigidly fixed inside, and the second, which is coupled to the shaft of the vehicle, is able to rotate.

When the retarder is switched on, the space between the blades is filled with liquid. The centrifugal force generated by the rotation of the rotor tends to push it outward, while the stator impeller impedes this process and has a retarding retarding effect. In the off state, when there is no liquid in the retarder body, the blades rotate freely and practically do not interact.

In most cases, oil is used as a working fluid. In some units, the supply of oil is autonomous, and in some, it is associated with a transmission lubrication system. During the work of the retarder, a significant amount of heat is released. According to the law of conservation of energy, the traction torque that absorbs the retarder is converted to heat, which raises the temperature of the working fluid. Therefore, for effective heat exchange, the retarder is connected to the main cooling system of the engine.

Electrodynamic retarder. What it is?

By a similar principle, the electrodynamic retarder works. What it is and how it copes with its task can be understood by referring to the laws of electrodynamics. The device also has a rotor and a stator, and the braking torque is created as a result of their interaction. But the role of the liquid in the electrodynamic moderators is played by the magnetic field. After the retarder is switched on, the current from the battery goes to the electric windings of the stator, forming a magnetic field in which the rotor rotates. The resulting eddy currents create fields that are opposite to those generated by the stator, and the rotor acquires a deceleration torque.

As in hydrodynamic moderators, a significant amount of heat is released during operation. Overheating in these units leads to a decrease in efficiency and complete failure of it. The use of liquid cooling in electrodynamic retarders is, for obvious reasons, difficult. Therefore, the design of the device includes a number of elements that perform the function of protection against overheating. On the rotor wheel there are blades, which, when rotated, create an air flow dissipating the heat generated. Also, the electrodynamic retarders are equipped with a current limiting system in case of overheating.

Intarder and aquatander

The above types of moderators are basic. On their basis, designers create new types of retarders, which can rather be called improved classical models. The company ZF, the leader in the European market for the production of parts and parts of transmissions, for example, built a retarder brake inside the gearbox and named this node an intarder.

German Voith, in turn, is experimenting with the location of the retarder on the vehicle and the composition of the working fluid. One of the developments is an aquatard - retarder, which is installed in the front of the engine and uses antifreeze as a working fluid. Such a retarder, the principle of operation of which does not differ from any other hydrodynamic device, no longer requires forced cooling, which greatly simplifies its design and reduces the curb weight.