Research and improvements on key characteristics of pilot-assisted counterbalance valve used in hydraulic luffing system

This paper reports the work principle of pilot-assisted counterbalance valve based on hydraulic-mechanical feedback principle , the mathematical modeling was built up. According to the load characteristics and application requirements of mobile crane luffing system, flow control characteristics, over-compensation feature, and influence of back-pressure on main flow were analyzed with AMESIM simulation. Aiming at the shortcomings of counterbalance valve, a segmented structure of pilot spool with pre-compensation port was proposed to improve fine-tuning performance. In order to improve the over-compensation characteristics, the key parameters were analyzed and optimized, and the method of using the gap throttling at the fast closing orifice to compensate feedback flow was proposed, to improve the anti-stall characteristics when the back-pressure rises, a back-pressure compensation structure was designed. The optimized valve was tested on a test bench and mobile crane, experiment results show that the optimized valve has good fine-tuning and proportional control characteristics, the over-compensation feature was greatly improved, compensation rate is greater than 70 %, the back-pressure compensation function was effective, the main flow will be lower under a higher back-pressure and the pilot control region is almost unchanged. • The pilot segmented structure was designed, the improved valve had a flow fine-tuning range. • The compensation rate can be increased to more than 70 %. • The main flow rate was almost unchanged under different back pressure .