Next-generation valve actuation for digital displacement machines

Abstract

A pump is the heart of a fluid-powered machine, which has a substantial impact on its efficiency. According to the state-of-the-art, the efficiency of a hydraulic excavator is about 16% due to a poor efficiency powertrain, combining a 40% efficient diesel engine and conventional hydraulic systems of between 30 and 40% efficiency. However, the efficiency of excavators can be significantly improved by using a Digital Displacement pump/motor (DDPM) instead of a conventional swash plate pump.

DDPM is a highly innovative hydraulic machine in which displacement and mode of operation are commanded by a dedicated computer by selective control of solenoid valves on a cycle-bycycle basis. Optimal control of the valves is essential. This thesis is about the new solenoid valve actuation design development, aiming to extend the DDPM application by maximising the precision and efficiency of the valve control.

The development and testing of the new design of the coil driver for Digital Displacement (DD) valves are described. The new design of the coil driver is based on a combination of a new "smart" gate driver technology and pseudo-H-bridge topology. It was demonstrated that the new design benefits from a significant reduction of energy dissipation by implementing synchronous rectification during slow decay and energy regeneration at a fast decay mode of operation (up to 12.25%), improving reliability and fault tolerance by implementing fast overcurrent protection, the cost and footprint reduction (up to 40%).

Described the development, implementation, and testing of a method that allows for reliable detection of the low-pressure valve (LPV) reopening event, which applies to all existing designs of DD modules. It was demonstrated that the method enables the closed-loop motoring technique to apply to new DDPMs, which improves the safety and stability of operation of the DD machine and provides its auto-adjustment over the life span and self-calibration, which, in turn, allows for its mass production.

Development, implementation and testing of a new method to allow stabilisation of the response time of a cyclically operating solenoid valve at the turn-on phase were described. It was proven experimentally that the method enables precise control of the LPV closing angle within the established supply voltage and solenoid coil circuit resistance ranges, which improves the stability of operation and increases the displacement of the DDPM. Also, the implementation of the method cancels a need for the front-end DC-DC converter of the DD controller, thus improving its efficiency, EMC performance, as well as reducing its cost and size.

Another new method to provide a sensorless diagnostic of the DD machine before its operation is described. The feasibility of the method was proven experimentally. Based on the method an algorithm that allows to determine the approximate level of the hydraulic fluid in the DD machine is proposed.

The test results from an electric powertrain demonstrator rig consisting of a DDPM DDP1X0, specifically designed for up to 30T excavators, powered by a high-efficiency Editron electric motor and controlled by the DDC15 controller based on the developed coil actuation design, are described and discussed. The test results demonstrate that the coil residual energy regenerating feature decreases the energy consumption of the DD controller by 10-11% at the pumping mode of operation. Up to 30% of displacement increment was demonstrated for the DDP1X0 by enabling the closed loop motoring mode of operation, which proportionally increases the developed torque, thus, leading to an increase in the regenerative efficiency of the DDPM. Also, it was proven that applying the valve response time stabilisation method allows for precise control of the DDPM displacement fraction at the static mode of operation.