A VARIABLE ORIFICE DAMPING MECHANISM FOR A RECIPROCATING PISTON-CYLINDER PUMP

Digital Displacement pumps (DDP) are variable displacement radial piston pumps. Each cylinder comprises of a solenoid operated low pressure check valve and a passive high pressure check valve. Variable displacement is achieved by altering the number of active cylinders, and the fraction of displacement of which the active cylinders produce. DDP has been demonstrated to be quieter and possess a significantly less tonal sound quality than traditional variable displacement axial piston swashplate pumps[1]. However, as the industry continues to trend towards battery electric driven excavators, the existing masking noise produced by conventional diesel combustion engines will cease to exist. Consequently, the hydraulic system will be the most significant noise source on the machine, driving the need to further refine pump Noise, Vibration & Harshness (NVH) performance. Passive check valves produce a characteristic in-cylinder pressure overshoot as upstream pressure has to be sufficient to overcome downstream pressure forces, plus resistive spring and damping forces responsible for holding the valve in place. Within a DDP, the transient nature of a pressure overshoot is very effective at exciting several different high frequency responses of the pump, most noticeably fluid-borne noise, and consequently radiated noise. This paper presents a method for incorporating a damping mechanism within a piston which reduces pressure overshoot, allowing an investigation into the relationship between pressure overshoot, fluid-borne noise and radiated noise. Modelling methodology is presented demonstrating a reduction in pressurisation rate and overshoot during the pumping cycle. Several key design variables are shown to give a large range in tuning scope. Initial test results are presented, demonstrating good model correlation and improvement in NVH performance.