The development of commercial vehicles in the field of transporting goods and goods has contributed to the faster supply of the market and, by extension, to meeting human needs. However, there was a need to reduce the delivery time of the loads, which required the vehicles to maintain a high average speed always within the framework of road safety.
However, the evolutionary path is not only about increasing power and horsepower to deal with difficult climbs or high tonnages, but also to control the vehicle's descent speed on a steep downhill.
Here, the auxiliary braking systems make their appearance, which ensure permanent and continuous deceleration when the vehicle is downhill (and not only) in order to avoid using the main brakes. Now, in modern trucks, 85-90% (!) of the total braking belongs to the auxiliary systems, while the brakes are only used to bring the vehicle to a complete stop.
The auxiliary or secondary braking systems are also called Retarders (=retarders) and are mainly distinguished: In the mechanical brake, the hydrodynamic retarder (known to us Retarder/Intarder) and the electromagnetic retarder (electrobrake).
So, for the next issues we will delve into the above systems through analyses, comparisons, reports and also from itineraries carried out for the purpose of TROXOI & TIR with the aim of the best possible impression of them.
USE OF MAIN BRAKES ON DOWNHILLS
During descent, various forces act that tend to increase the kinetic energy of the vehicle. The main force is the weight of the vehicle, which increases the acceleration as the angle of inclination of the road increases. On the contrary, the rolling resistance of the tires and the aerodynamics of the vehicle create a deceleration in the truck, which in any case is much less than the weight.
As is well known, trucks have two types of brakes: Drum and disc brakes. The similarity that these brakes have is that, the braking is done through the friction of the jaws on the drums or by the pads on the disc brakes. Since friction generates heat, during braking the vehicle's kinetic energy is converted into heat. The heat increases depending on the gross weight, the speed of the vehicle and the pressure exerted by the driver on the foot brake. As long as the heat is dissipated by the brakes, they continue to work. If the temperature exceeds certain limits then what motorists say "my brakes are on" happens, resulting in ineffective braking and uncontrollable descent.
Therefore, the driver must adjust his speed as much as necessary so that the heat developed in the brakes is small so that it has time to transfer heat to the environment. Naturally, speeds on steep downhills with a "full" truck did not exceed 30-40 km/h. This had the consequence of the delay at the place of delivery, reduction of the average speed, the strain and wear of the brakes, the fatigue of the driver, etc. For this reason, retarders were invented, putting an end to all these problems, thus relieving driver and vehicle congestion.
At this point, the importance of the Greek motorist before (but clearly also after) the appearance of the Retarders must be emphasized as Greece consists to a large extent of mountainous areas with sharp descents (Katara, Bralo-51, Kastania, Agia etc.) . Such routes required from the driver strictly professional driving with maturity and vigor while giving him rich experience.
ENGINE BRAKE
Downhill, the vehicle must ALWAYS be "in gear" ie the engine must always be connected to a gear so that a steady course is maintained through the differential and wheels. The braking induced in the drive line is due to the energy losses of the motor.
For this reason, it is extremely dangerous to put the vehicle in "Dead" as its use makes the truck uncontrollable. Exceptions are the new eco-roll, i-roll etc. systems, which make maximum use of the vehicle's kinetic energy in order to minimize fuel consumption by using "Dead" whenever necessary without the vehicle "stalling" mainly on the straights or in the end of some GPS assisted descents.
The braking caused by the engine when the driver leaves the "gas" pedal is due to the friction that exists in the moving parts and also to the leakage of energy during the compression phase as the engine "strains" to compress the air losing mechanical work.
Bearing in mind the above, it is enough to understand that the engine brake that we will analyze below is essentially a further development of the already existing engine brake. Analyzing the Retarders, it would be impossible not to mention the engine brake first, and specifically the flapper, as its use in trucks goes back several years, long before the appearance of the rest of the retarders.
