The ZF-Intarder is a hydrodynamically operating hydraulic retarder. It is integrated into the transmission at the output end and shares its oil supply with the transmission.
This is how the Intarder works:
Inside the Intarder, the blade wheels of the rotor and stator are facing each other. The rotor is connected to the transmission's output shaft via a step-up gear (i = 1:2). It is propelled by the step-up gear with twice the speed of the transmission output.
When actuating the Intarder, oil flows into the retarder chamber. The rotor accelerates the oil and triggers its gyration. In the course of flowing through the chamber, the oil gets to the stationary blades of the stator where its flow is re-directed and led back to the rotor. As a result of the rotor blade circulation, torque is generated which counteracts the rotor's direction of motion. This brake torque is transferred back to the transmission output via the step-up gear and thus, to the driveline. The vehicle is decelerated.
The braking energy created in the process is converted into heat energy which is dissipated to the vehicle engine’s cooling circuit via the heat exchanger.
During braking, the oil, from which braking energy is derived, passes between the Intarder and heat exchanger (short distances).
If the Intarder is switched off, the hydraulic pump directs the oil from the transmission directly through the Intarder's heat exchanger. This avoids peaks in transmission temperature and, on average, a considerably lower oil temperature is attained. All in all, this leads to reduced oil aging. The individual components' lifetime is positively influenced.
A special feature of the Intarder is its heating function:
During the commercial vehicle’s start phase, the coolant heats up more quickly than the transmission oil. Here, the cooling cycle or better the temperature exchange cycle is reversed: Now, the engine coolant's heat is transferred to the cooler transmission oil. The transmission oil reaches its operating temperature more quickly and the entire system operates more swiftly in the optimum temperature and efficiency range.
Once the transmission oil’s operating temperature is reached, the temperature exchange mode is set back to the normal cooling mode. The transmission oil passes the heat - generated by the Intarder during braking - back to the coolant.