Bumpless mode switch of independent metering fluid power system for mobile machinery

Abstract The independent metering system is an alternative to the conventional valve control system, which operates by decoupling the meter-in and meter-out orifices. This system can improve the energy saving performance by flow recuperation or regeneration. The transfers between normal, recuperation, or regeneration hydraulic circuits require the mode switch control. The current switch approaches always employ the discrete switch in terms of the load force and the actuator velocity. Nevertheless, there are two problems with the use of the discrete switch: (1) an unstable switch and (2) an unsmooth switch. To solve the two problems, this paper proposes a bumpless mode switch approach for independent metering systems, which contains the dynamic dwell-time switch and a bidirectional latent tracking loop. The former one aims to solve the instability switch by transforming the fast switch to a slow switch such that the transient instabilities dissipate within a sufficiently long time. To precisely obtain the dwell time, a boundary value solution of dwell time based on the multi-Lyapunov function (MLF) is innovatively designed for the mode switch of the independent metering system, which is able to guarantee the stability of switch instant and simultaneously decrease the influence of the dwell time to the system response. The latter one of the strategy aims to solve the unsmooth switch by eliminating the discontinuities of the control signals of the valves. An extension is designed to make the latent tracking design also suitable to the bidirectional mode switch in the independent metering system. The proposed strategy is verified by a mini-excavator. The comparison results show that the instability during switch instant is eliminated and the transitions of the cylinder velocity between two modes are smoother. Meanwhile, the hysteresis of the mode switch caused by the dwell time is greatly decreased. In comparison to the conventional valve control system, an independent metering system could save energy without reducing the motion control performance using the proposed bumpless mode switch strategy.

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