A retarder is an additional supporting braking mechanism to service brakes or foundation brakes. Foundation brakes are the ones fitted in the wheels and high power vehicles and vehicles that run in gradients need to have additional braking force in comparison to them. Foundation brakes tends to heat up when used continuously and tend to give us over a period of time. Retarders serve to slow vehicles, or maintain a steady speed while travelling down a hill, and help prevent the vehicle from “running away” by accelerating down the hill. They are not usually capable of bringing vehicles to a standstill, as their effectiveness diminishes as vehicle speed lowers. They are usually used as an additional “assistance” to slow vehicles, with the final braking done by a conventional friction braking system. With the use of retarders, the service life of foundation brakes, here in this case brakes pads and brake liners increases 2 to 4 times. They are potential life savers and will supplement foundation brakes largely.
Retarders can be actuated by a supplementary switch integrated in the combo switch in steering wheel / foot pedal and can also be completely integrated by an ECU along with other braking systems like exhaust brakes, engine brakes.
Also there are lot of features available in the retarders:
- By setting a speed, retarders ensures that the truck or bus doesn’t exceed the particular speed. This is called as downhill retardation and is most useful when driving down hill. All we need to do is set a max speed and when ever the vehicles reaches the set speed retarder acts in coordination with braking ECU and ensures the vehicle doesn’t cross the speed.
- Partial braking as a feature can be used just to slow the vehicle a bit. This is a handy feature can be used in traffic condition, that doesn’t require full braking and requires deceleration may be negotiate a turn or to slow in view of oncoming traffic.
Retarders are primarily two types, Hydrodynamic retarders and Electromagnetic retarders.