Flow Amplifiers in Hydrostatic Steering 2002-01-1358
In hydrostatic steering systems, occasionally, the need arises of exerting large forces as, for example, is the case in steering actuators of articulated dumpers (see Fig. 1) or in rudder actuation on ships. Consequently, linear motors with large bore diameters are required not to exceed system operational pressure limits. Such actuators, whose travel is dependent on the specific application, absorb a quite large flow rate (up to 400 L/min) to respond, within an appropriate time frame, to steering commands. The flow rate, generated by a properly sized feed unit, cannot in full be handled by the hydro-steering (see Fig. 2), as this,
beside other aspects, would necessarily imply too large an orbital motor. A feasible solution to the problem is grounded on the coupling of a compact hydro-steering, governing only what can be regarded as a control flow, with a flow amplifier capable of multiplying that flow by a nominally constant factor and of delivering control and power flows to the steering actuators.
In this framework the paper considers a commercial flow amplifier1, embodying a priority valve, used in applications where the flow rate handled by a standard hydro-steering is inadequate in providing sufficient actuator velocities. This is the case in a class of articulated dumpers where priority is granted to steering and excess flow is diverted to a secondary user (lift dump actuator).
The amplifier, detailed in its constitutive components, functions and peculiarities, is analysed in depth and its modelling, developed within the AMESim® simulation environment, allows to establish its amplification factor, and how this becomes influenced by the control flow rate (yielded by the hydro steering) and by varying loads on steering cylinders.
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