What is a retarder?

A retarder is an innovative braking system. It reduces speed by providing mechanical or electrical resistance to the movement of the wheels. The retarder for a truck is designed to offer additional braking power, easing the load on conventional brakes. This can be particularly useful when descending steep slopes or braking at high speeds. In addition, it reduces wear and prevents brake overheating, which we’ll discuss later.

How does a retarder work?

A retarder is mounted on the gearbox. Inside the retarder, two discs with opposing propeller-like ribs are immersed in oil. When you engage the retarder, the pressure on this oil increases. As a result, the discs work against each other. The higher the pressure, the greater the braking power and the more the temperature rises.

The benefits of using a retarder on trucks

Using a retarder offers several advantages for trucks. As mentioned earlier, retarders help reduce the strain on the brakes. Retarders distribute braking power and relieve conventional brakes, reducing wear and extending the lifespan of the brakes. This saves on long-term costs. Additionally, a retarder improves safety by providing extra braking power. On steep hills, conventional brakes can quickly overheat, as the vehicle’s weight demands significant braking force.

Retarder vs. engine brake

Before we continue discussing retarders, let’s first clarify the difference between a retarder and an engine brake. An engine brake, often called a Jake Brake, uses exhaust gases to build up backpressure in the cylinders. A retarder, on the other hand, slows down the driveline.

Different types of retarders

Trucks and other heavy vehicles each serve their unique purpose when transporting goods. As a result, there is not just one type of retarder but several that are suited to the type of vehicle and load being carried. Here are the different types of retarders:

Hydrodynamic retarder

The hydrodynamic retarder uses fluid (usually oil) to generate braking power. This is integrated into the truck’s braking system. They provide effective deceleration at higher speeds and are especially useful when descending steep slopes. Here’s how it works: when the driver presses the brake pedal, oil is pumped through the retarder. This results in friction and resistance. The resistance that is created slows down the rotation of the wheels, thus reducing the speed of the vehicle. An example of a hydrodynamic retarder is the Voith retarder.

The intarder

A specific type of hydrodynamic retarder is the intarder. An intarder is integrated into the gearbox, hence the name "in"tarder. It is more compact and takes up less space in the driveline. These are often found in modern trucks equipped with automatic or automated transmissions.

Electromagnetic retarder

An electromagnetic retarder operates through magnetic resistance. It consists of a stator and a rotor that are located in the driveline. When the driver presses the brake pedal, electric current is sent through the stator, creating a magnetic field. This magnetic field exerts resistance on the rotor, slowing the rotation of the wheels and, in turn, the vehicle. Electromagnetic retarders are particularly suitable for city traffic and lower speeds. An example of an electromagnetic retarder is the Telma retarder. Telma induction braking systems consist of a fixed stator and a pair of rotors attached to the drive shaft to make them spin.

Electrodynamic retarders

An electrodynamic retarder uses electrical energy to resist the movement of the wheels. It works on the same principle as induction. When the driver presses the brake pedal, an induction system converts the vehicle's kinetic energy into electrical energy. This electrical energy is then converted into resistance, which slows the wheels. Electrodynamic retarders are efficient and easy to maintain.