In order to improve material service life under a fatigue and corrosion coupling environment, a high-velocity oxygen fuel (HVOF) Cr₃C₂–NiCr coating with a bonding layer was prepared. The objective was to obtain the optimum bonding layer for the HVOF Cr₃C₂–NiCr coating, which included a laser cladding (LC) Ni625 layer, extreme high-speed laser material deposition (EHLA) Ni625 layer and HVOF NiCr layer. Fatigue properties of the samples with various bonding layers were investigated by means of a four-point bending fatigue test. Electrochemical impedance spectroscopy (EIS) and the salt spray test were executed after the bending fatigue test to simulate the interactive effect of fatigue and corrosion atmosphere. Failure surfaces were characterized by scanning electron microscopy (SEM) and an energy-dispersive spectrometer (EDS) to indicate the details of corrosion products. Corrosive behaviors of samples were adequately demonstrated according to the results, which included the curves of potentiostatic polarization, impedance magnitude and phase degree, and corrosion products. The result showed that the cycles of perforative cracking for the sample with the EHLA Ni625 bonding layer was almost three times than that of the sample with the HVOF NiCr layer. The magnitude of EIS reduced from ~10⁵ to ~10³ for the sample after BFT. Eventually, the main improvement mechanism of the HVOF Cr₃C₂–NiCr coating with the EHLA Ni625 bonding layer was attributed to the grain refinement of the bonding layer and performed a good level of metallurgical bonding with the substrate.

The bulk modulus of the gas-containing hydraulic oil is an important indicator reflecting its compressibility, directly affecting the stability, accuracy, rapidity, and reliability of the fluid transmission system. In the time-varying system with high speed and pressure, since the gas release rate differs from the gas dissolution rate, there exists a large difference between the static and dynamic values of the bulk modulus of hydraulic oil. Therefore, it is necessary to research the dynamic bulk modulus of the gas-containing hydraulic oil. Based on the improvement of Henry’s law and gas-polytropic-process equation, a modified model of dynamic bulk modulus of the gas-containing hydraulic oil was proposed. Through the analysis of parameter influence, the influence of initial gas content and pressure on the dynamic bulk modulus of the gas-containing hydraulic oil during compression and expansion was discussed. Comparing the modified model and the Zhou model with the experimental results, the goodness of fit between the Zhou model and the experimental results during compression and expansion was 0.9936 and 0.9864, respectively. And the goodness of fit between the modified model and the experimental results during compression and expansion was 0.9937 and 0.9936, respectively. The prediction precision of the dynamic bulk modulus was improved while verifying the accuracy of the modified model. This research can provide a reference for optimizing the theoretical model of the dynamic bulk modulus of the gas-containing hydraulic oil.

Diamond-like carbon (DLC) and fluorinated diamond-like carbon (F-DLC) films were deposited via pulsed cathodic arc deposition on pretreated nitrile butadiene rubber (NBR) and polyurethane (PU) rubber substrates. Both DLC and F-DLC films showed a more than 50% decrease in coefficients of friction compared to uncoated NBR and PU rubber substrates. The incorporation of fluorine was found to have little influence on the film coefficient of friction. However, a decrease in film wettability was overserved in the F-DLC films compared to the DLC films.

As a new type of hydraulic system, the independent valve control system (IMCS) has higher flexibility compared with the traditional four-side slide valve control system. The independent metering control system (IMCS) is divided into four quadrant modes, based on the speed and load of the actuator. The traditional control methods always use a discrete control strategy to realize the switching between different modes based on mode recognition. However, the spool signals frequently switch, and the actuator operating pressure and speed are not stable when the IMCS is switched between different modes. To solve the above problems, this paper proposes a continuous control strategy for the IMCS. Based on the fuzzy control principle, the variable universe fuzzy controller (VUFC) was designed. The controller contains 49 fuzzy rules, and the output of the controller at any time is calculated by the weighted sum of several fuzzy rules. The VUFC divides the system into 49 rules, which are activated by multiple modes at any time to achieve a smooth transition between different modes. The VUFC was verified in a 37 ton excavator model and compared with the traditional independent metering meter-out (IM_MO) control strategy. The results showed that the VUFC significantly improved the frequent switching of the spool signals, and the running speed and pressure stability of the hydraulic cylinder were significantly improved. At the same time, the response speed of the hydraulic cylinder became faster at the start of the system. The VUFC can realize the continuous control of the IMCS and improve the operating performance of excavators.

In order to improve the energy efficiency and dynamic of negative control swing systems of excavators, this paper proposes a technical scheme of adding two PRVs (pressure reducing valves) to main valve pilot control circuit, which can adjust main value opening arbitrarily according to the working condition. A pump-value compound control strategy was formulated to regulate the system power flow. During swing motor acceleration, main pump and the two PRVs are controlled to match system supply flow with motor demand flow, thereby reducing motor overflow and shortening system response time. During swing motor braking, the channel from motor to tank is opened to release hydraulic brake pressure by controlling PRVs before swing speed reduces to zero, which prevents the motor from reversing and oscillating. A simulation model of 37-ton excavator was established, and the control strategy was simulated. The original and optimized performance of the swing system were compared and analyzed, and results show that the application of new scheme with the compound control strategy can reduce overflow and increase braking stability of the swing system. In addition, system response and speed control performance are also improved when excavator performs a single-swing action.