2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:42
Retarder. What it is, not everyone understands only from 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 slow down the dynamics of any process. In the field of mechanical engineering, a retarder is a device that is installed on vehicles in order to slow down the speed of their movement without participation or with partial use of the main braking systems.
Where does the retarder come in handy?
The need to use retarders is due to the fact that under conditions of prolonged loads on the main braking system, the reliability and efficiency of the latter are significantly reduced, which has a negative impact on safety. As a rule, this applies to heavy trucks and road trains that move in conditions of constant ups and downs on mountain roads.
Let's consider a real situation that helps to understand what a retarder is for. When driving down a slope, the driver must constantly brake to maintainconstant speed. Such a prolonged load on the friction brake system leads to its overheating and premature wear. In the first case, precious flight time is spent on letting the brakes cool down, in the second, the cost of repair and maintenance of the car increases.
The need to find an additional source of slowdown was also influenced by the fact that every year the carrying capacity and speed of trucks increased. For example, to stop a road train from a speed of 80 km/h, it will take 4 times more braking force than to stop it from 40 km/h. It's hard not to agree that having and knowing how to use a retarder makes the driver feel much more confident and calm.
From the history of the retarder
The most significant representative in the history of the invention of the retarder is the German company Voith. Attempts to apply the idea of a retarder have been made by the company since the second quarter of the last century, and it received its first order for development in the late 50s from a major manufacturer of railway locomotives. After the successful completion of the project in 1961, Voith created a separate division of its own, which to this day specializes exclusively in the production of retarders.
Seven years later, Voith develops the first retarders for wheeled vehicles for the founder of Setra. In this way, Setra sought to significantly improve the safety of passenger transportation with its buses. The new development from Voith lived up to expectations and began to gain popularity among other car manufacturers. By the end of the last century, drivers of heavy vehicles had not only a general idea of what a retarder on trucks and buses was, but also actively used the unit in their daily work.
Variety of moderators
Retarders include both engine braking and exhaust brake. However, the term "retarder" is more often applied 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. Primary are located before the checkpoint, and secondary - after. Primary retarders have one significant drawback. At the moment of gear shifting, it does not interact with the transmission, and the braking force on the wheels disappears. According to the principle of operation, retarders are divided into hydrodynamic and electrodynamic.
Hydrodynamic retarders
More often than others, a hydrodynamic retarder can be found on heavy vehicles. What it is and how it works, it will be easier to understand for those who are familiar with the automatic transmission device. The operation of a hydrodynamic retarder is based on the principle of a fluid coupling. Structurally, the unit consists of two wheels with propeller blades located in a common housing in front of each other. One of the wheels is rigidly fixed inside, and the second, whichcoupled with the vehicle shaft, has the ability to rotate.
When the retarder is turned on, the space between the blades is filled with liquid. The centrifugal force that occurs during the rotation of the rotor tends to displace it outward, while the stator impeller prevents this process and has a reciprocal slowing effect. In the off state, when there is no liquid in the moderator housing, the blades rotate freely and practically do not interact.
In most cases, oil is used as the working fluid. In some units, the oil supply is autonomous, and in some it is associated with the transmission lubrication system. During the operation of the retarder, a significant amount of heat is generated. According to the law of conservation of energy, the traction moment that the retarder absorbs is converted into heat, which increases the temperature of the working fluid. Therefore, for efficient heat transfer, the retarder is connected to the circuit of the main engine cooling system.
Electrodynamic retarder. What is it?
An electrodynamic retarder works on a similar principle. 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 liquid in electrodynamic moderators is played by a magnetic field. After turning on the retarder, the current from the battery is supplied to the electrical stator windings, formingmagnetic field in which the rotor rotates. The resulting eddy currents create fields opposite to those generated by the stator, and the rotor acquires a decelerating moment.
As with hydrodynamic moderators, a significant amount of heat is released during operation. Overheating in such units leads to a decrease in efficiency and its complete failure. The use of liquid cooling in electrodynamic retarders is difficult for obvious reasons. 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 that, when rotated, create an air flow that dissipates the generated heat. Also, electrodynamic retarders are equipped with a current limiting system in case of overheating.
Intarder and Aquatarder
The types of moderators listed above are basic. On their basis, designers create new types of retarders, which can rather be called improved classical models. ZF, the European market leader in the production of parts and transmission parts, for example, built a retarder inside the gearbox and called this unit 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 aquatarder - a retarder, which is installed in front of the engine and uses antifreeze as a working fluid. Such a retarderthe principle of operation of which does not differ from any other hydrodynamic device, it no longer needs forced cooling, which significantly simplifies its design and reduces the curb weight.
