Volvo retarder is small but beautifully formed
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The Volvo VR3250 hydraulic compact retarder certainly lives up to its name, adding just 23mm to the overall length of the transmission, and around 100kg to the weight. The system, which is designed to work in conjunction with the standard exhaust brake, is compatible with all FM and FH models, but initial RHD application is expected to be mainly on FM? and FM10 models.
It should become available in the next couple of months, but it cannot be used with the Volvo Engine Brake (VEB), which is expected to remain the favoured choice on the 12-litre models.
The retarder works in a similar way to an automatic gearbox's torque converter. When retardation is required air pressure forces oil into the unit, creating drag which slows the vehicle.
The retarder has an oil-to-water heat exchanger plumbed into the engine's cooling system, which uses the largest available radiator Maximum retardation, when fitted to a typical FH12 at 40 tonnes and used in conjunction with the exhaust brake, is around 600kW at 90km/h and 2.300rpm. This level depends on cool oil and is available for around 20 seconds, after which it drops back to around 400kW at 2,300rpm.
Operation of the retarder system is by a column-mounted stalk which passes the message on to the retarder's electronic control unit (RECU). This takes into account the various data such as engine and road speed and vehicle weight
and requests braking effort in variable proportions from the retarder and exhaust brake as appropriate. The stalk has five operating positions—A, 1, 2, 3 and 4: A, for Automatic, links with the normal cruise control to provide downhill cruise control.
With normal cruise control and position A selected, retardation will automatically start when road speed rises to a predetermined level above cruising speed. By default, this level is 7km/h but can be changed to anything from 4 to 15km/h. The electronics then provide enough retarding effort to maintain the desired speed.
On the road in an FH12 460 4x2, again running at 40 tonnes, the system quite simply did what it said on the box. A motorway route around Bavaria provided a suitably hilly challenge, but the downhill cruise control just got on with the job without any fuss, maintaining speed even on quite steep descents for considerable distances. Combine the retarder with Ceartronic and the driver's major tasks will be steering and listening to the radio...