# Energy-Saving Design Method for Hydraulic Press Drive System with Multi Motor-Pumps

• Haihong Huang
• Xiang Zou
• Lei Li
• Xinyu Li
• Zhifeng Liu
Regular Paper

## Abstract

Large energy consumption caused by the pump unloading, as well as the low energy efficiency of the motor, is a serious problem for hydraulic presses especially for the press with multi motor-pumps. By analyzing the energy dissipation characteristic of hydraulic press drive system which is composed of several motor-pumps used to provide energy, an energy-saving design method is developed to reduce the energy loss of the drive system. In this method, pumps are selected from the pump set by minimizing the proposed idling index to reduce the energy loss of motor-pumps in the unloading state. The index is defined as the sum of the product of the unloaded flow and the unloaded time for each stage in a working cycle of the hydraulic press. Then, the motors are selected from the motor set to drive the selected pumps correspondingly by ensuring that the load rate of all the motors is within a setting range for high energy efficiency in as many stages as possible. The method was applied to a 2000-ton rapid sheet tension hydraulic press, and results indicate that 26.97% of energy can be saved in a working cycle.

## Keywords

Energy-saving Drive system Multi motor-pumps Hydraulic press Idling index

## List of Symbols

Pin

Input power of the drive system

ηi

Energy efficiency of motor-pump i accessed to hydraulic circuit

ηpump(p)

Energy efficiency of pump

β

Ratio of output power to rated power of a motor

ηmotor(β)

Energy efficiency of motor

Δpj

Pressure loss of hydraulic circuit in working stage j

U

Sum of the product of the unloaded flow and the unloaded time in each stage of the hydraulic press in a working cycle

Zij

State of motor-pump i in stage j

$$q_{i}^{\rm u}$$

qk(pj)

Flow of pump k in the pump set when it works at the pressure of pj

ak

Number of selected pump k

PN i

Rated power of the selected motor i

qi(pj)

Flow of the selected variable pump i at the pressure of pj

Pi(pj)

Output power of selected variable pump i in stage j

ηpumpi(pj)

Energy efficiency of selected pump i when its working pressure is pj

ηmotori(pj)

Energy efficiency of selected motor i in stage j

βi(pj)

Load rate of selected motor i in stage j

Ein

Total energy consumption of the original drive system in a working cycle

$$E_{\text{in}}^{\prime }$$

Total energy consumption of the designed drive system in a working cycle

Ei(pj)

Output power of motor-pump i accessed to hydraulic circuit in stage j

ηi(pj)

Energy efficiency of motor-pump i accessed to hydraulic circuit in stage j

nj

Number of motor-pumps which are in the unloading state in stage j

ΔE

Energy consumption reduction

$$P_{\text{N}}^{\prime }$$

Installed power of the designed drive system

η

Energy efficiency of the original drive system

$$\eta^{\prime }$$

Energy efficiency of the designed drive system

ERR

Energy consumption reduction rate

EIR

Energy efficiency increment rate

PRR

Installed power reduction rate

## Notes

### Acknowledgements

The work is financially supported by the National Natural Science Foundation of China under Grant nos. 51722502 and 51635010, the International Cooperation and Exchange of the National Science Foundation of China Grant no. 51561125002.

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© Korean Society for Precision Engineering 2019

## Authors and Affiliations

• Haihong Huang
• 1
Email author
• Xiang Zou
• 1
• Lei Li
• 1
• Xinyu Li
• 1
• Zhifeng Liu
• 1
1. 1.School of Mechanical EngineeringHefei University of TechnologyHefeiPeople’s Republic of China