ZF-Intarder A safer way to brake

Slowing down a multi-ton truck, bus or train as it descends a steep gradient places major stresses on standard service brakes, which quickly wear out and may even stop working. The ZF-Intarder is the obvious answer.

The Intarder is so compact, it can be built into transmissions.

It's not only about how powerful the engines are. Commercial vehicles also need instant access to maximum braking force: just think of a fully-laden tour bus descending a steep mountain road. So truckers and bus drivers who can call on a hydrodynamic auxiliary brake like the ZF-Intarder are definitely operating on the safe side.

The Intarder auxiliary brake is so compact, it can be built into the transmission, where it not only provides additional support for engine braking, but also relieves stress on the main brake by as much as 90 percent – especially on lengthy downhill gradients. This means the main brake system stays cool and retains its full capacity for potential emergency braking. Vehicles fitted with an Intarder don’t suffer from the rapid brake wear or brake fade associated with prolonged braking stresses. The best way to discover how ZF’s comparatively small and lightweight (65 kilograms) retarder device actually performs its heavyweight duties is to take a look inside.

Powerful retarding effect

Oil flows into the Intarder, where it is acceleratedby the rotor in a swirling motion.

Inside the Intarder, two vane wheels are positioned opposite each other: one of them is a rapidly rotating rotor, connected to the transmission output shaft by gearwheels; the second is an immobile stator. When the auxiliary brake is actuated, an electronically controlled h­ydraulic pump transfers oil into the Intarder. The rotor accelerates the viscous liquid while simultaneously causing it to flow in a swirling motion. This forces the oil into the spaces between the stator’s stationary vanes, which deflect the oil back toward the rotor in such a way that the flow of returning oil strongly counteracts the rotor’s original direction of rotation. This creates a braking torque that is transferred to the transmission output shaft and from there to the driveline. This in turn has a powerful retarding effect on the heavy vehicle, despite the fact that neither the service brake nor engine braking have been applied.

The whole process happens very quickly, which means in one second at the very most. That’s enough time for the current, third generation of ZF-Intarders to generate a sustained braking torque of up to 4,000 Newton meters and a maximum braking force of 600 kilowatts – either automatically, or in one of five stages that can be selected by the driver. This means the Intarder can keep the forward momentum of any commercial vehicle effectively under control – even gearshifts don’t impede the braking effect. Similarly, other systems that are important for vehicle safety, such as ABS and ESP, remain fully active and unaffected.

This is how the Intarder works

Good for the environment

In view of the benefits, it’s hardly surprising that about one in three commercial vehicle transmissions is now equipped with an optional Intarder. ZF alone has shipped 800,000 of these transmission brakes since production started in 1992. Of these, 100,000 belong to the latest generation of products. The Intarder is making the transport industry safer already, and will continue to do so. At the same time, it is reducing the sector’s environmental impact: the 800,000 ZF-Intarders manufactured to date have helped avoid around 16,320 tons of brake dust for every million kilometers traveled.

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