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The Rexroth Hydraulic Flywheel HFW concept is especially suitable for mobile working machines with cyclic recurring travel or working motions (e.g. road roller, excavator). Rexroth HFW can be integrated in an already existing hydraulic system. It consists of reliable standard components from the Rexroth product portfolio: axial piston variable pump A10VO series 31, HFW valve block, BODAS controller and accumulator. Currently, the Rexroth A10VO is the only available variable pump which offers overcenter operation in open circuit. The heart of the Rexroth HFW consists of the controller and the patented software.


At conventional drive concepts, the required diesel engine speed follows too slowly the command value of the pilot control device in driving and working situations with high performance demand. An engine lugging is the consequence. Considering road rollers, this situation appears while accelerating the working machine and activation of the vibration drive at the same time. Using the Hydraulic Flywheel HFW drive concept, the speed changes are recognized by the Rexroth BODAS controller at short notice. Via a signal, the stored energy will be fed back into the drive train. The installation of a Rexroth axial piston variable pump A10VO size 28 and an accumulator with 20 liters volume means that about 25 kilowatts are additionally available for the period of three seconds. Instead of using a diesel engine with 80 kilowatts, a combustion engine below the statutory TIER 4 legislation (56 kW) can be installed without negative effects on the performance of the mobile working machine. Furthermore, expensive and technical complex exhaust gas after-treatment systems can be avoided.


Overspeed protection of the combustion engine

The electronics of the Rexroth Hydraulic Flywheel HFW monitors the speed of the combustion engine and detects speed increases (e.g. moving downhill). In this situation, the Rexroth axial piston variable pump A10VO series 31 pumps oil under pressure into the accumulator. If it is filled, the high-pressure relief valve of the valve block limits the further surplus energy. This results in an additional supporting torque at the diesel engine which protects the engine from overspeeding (hydraulic braking).

Fuel savings through Rexroth Hydraulic Start-Stop HSS

The same components installed for the Rexroth HFW, can also be used to realize the Hydraulic Start-Stop HSS in mobile working machines which is also developed by Bosch Rexroth. In order to save fuel, HSS switches the diesel engine off during standstill phases. The engine is restarted automatically as soon as the driver moves the steering unit, the joystick or the accelerator pedal.


Supply of further auxiliaries

The Rexroth axial piston variable pump A10VO series 31 which is installed for the Rexroth HWF drive concept can also supply further auxiliaries, such as fan drives. This is possible in periods in which neither the boost nor the braking or accumulator charging function is used. Thus, no investments in additional hydraulic components are necessary.