# Comparative Energy Analysis of a Load Sensing System and a Zonal Hydraulics for a 9-Tonne Excavator

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## Abstract

**:**

^{©}environment. This mathematical model was modified with electric components for simulating a zonal hydraulics excavator and compared with a conventional load sensing (LS) machine. The energy efficiencies of both the LS circuit and the new solution were evaluated for typical duty cycles, pointing out the obtainable energy efficiency improvements, which were mainly due to the absence of the directional valves and pressure compensators. The results also point out the effect of the pipe losses when the circuit layout requires the pipe for connecting the pump with the actuator; moreover, the effect of a diesel engine downsizing on the energy saving was evaluated.

## 1. Introduction

_{2}emissions produced by construction machinery. Subsequently, the cut in greenhouse gases production by excavators can lead to a significant reduction in the world CO

_{2}emission level. Work by Aalto university research group in [21,22] demonstrated that an EHA-type system enables up to 50% reduction in energy consumption compared to conventional low-cost Load Sensing valve-controlled system. This work was conducted with 1-tonne excavator test case.

^{©}environment. The excavator model is based on a lumped parameter approach that, in the hydraulic version, includes the following models: diesel engine, pump, directional flow control valves, hydraulic lines and kinematics of the front equipment. The standard LS excavator model was validated with experimental activities carried out on the excavator and on the single components, with the engine fuel consumption and many parameters measured during typical duty cycles. Other modelling approaches that can be found in literature [23,24,25,26,27] focus on more detailed aspects, while the followed approach permits the simulation of the components with computational run times suitable for circuit simulations [28]. The validated mathematical model of the standard hydraulic excavator [29,30,31,32,33,34,35,36,37] was modified and used for investigating new layout configurations based on zonal hydraulics.

## 2. Standard Hydraulic Excavator Mathematical Model

^{®}software; following a short description of the main features of the implemented sub-models is reported. For a detailed explanation refer to our earlier publication [34].

#### 2.1. Pump Model

#### 2.2. LS Flow Sharing Valve Block Model

^{©}environment.

#### 2.3. Hydraulic Cylinder Model

_{HC}, is calculated considering both the pressure and frictional forces, F

_{F}, in Equation (4). While the frictional force is defined by Equation (5), where the Coulomb friction force, F

_{C}, and the viscous friction coefficient, k

_{V}, were defined according to experimental results in [28]:

#### 2.4. Turret Motor Model

#### 2.5. Hydraulic Pipe Losses Model

_{L}was experimentally defined for each i

^{th}hydraulic line of interest.

#### 2.6. Excavator Kinematic Model

#### 2.6.1. Front Equipment

_{1}, y

_{1}) and (x

_{2}, y

_{2}) are the pivot joint coordinates relative to body 1 and 2. The masses of boom and arm incorporate the masses of the cylinder actuators. The centrifugal forces and the Coriolis forces acting on the bodies when the turret rotates have been neglected.

#### 2.6.2. Turret

#### 2.7. Internal Combustion Engine Model

## 3. Standard Excavator—Experimental Study

_{p}); pump outlet pressure (p

_{1}); actuators pressures (p

_{5}÷ p

_{22}); turret angular velocity (n

_{s}); hydraulic actuators linear positions (y

_{1}÷ y

_{3}); valves main spool positions (LVDT1 ÷ LVDT6).

_{IN}) and the influence of the driver on fuel consumption (${\overline{s}}_{mf}$), were defined for each working cycle with a 95% confidence level, Equation (10).

## 4. Zonal Hydraulics—DDH Solutions

^{©}environment. A simple map-based model has been considered for the simulation, which is obtained from previous experimental study.

^{©}.

#### 4.1. Operator Model

#### 4.2. Electric Components

^{©}environment.

#### 4.3. Battery

## 5. Results

^{©}environment.

## 6. Discussion

^{©}environment with a validated excavator mathematical model based on a standard LS system as reference. Two DDH configurations were considered: the first one with pipes, leaving the pumps in the turret, and a second one without pipes, assuming the location of the pumps close to the cylinders.

## 7. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Nomenclature

Abbreviation | Definition | |

BSFC | Brake Specific Fuel Consumption | |

DS | ICE downsizing | |

DDH | Direct Driven Hydraulics | |

ICE | Internal Combustion Engine | |

JCMAS | Japan Construction Machinery Association Standard | |

LS | Load Sensing | |

Symbol | Definition | Unit |

B | Fluid Bulk Modulus | (Pa) |

b_{t} | Turret Viscous Friction Coefficient | (N·m/(rad/s)) |

bx, by | Contact Damping Coefficient | (N/(m/s)) |

d_{p} | Actuator Piston Diameter | (m) |

e_{y} | Actuator Position Error | (m) |

I_{t} | Turret Moment of Inertia | (kg·m^{2})] |

k_{x}, k_{y} | Contact Stiffness Coefficient | (N/m) |

p | Pressure | (Pa) |

Q | Flow Rate | (m^{3}/s) |

${\overline{s}}_{mf}$ | Standard Deviation of the Mean | (kg) |

U_{IN} | Instrument Uncertainty | (kg) |

U_{C95} | Combined Standard Uncertainty | (kg) |

Tt | Torque turret | (N·m) |

TCt | Turret Coulomb Friction Torque | (N·m) |

T | Hydraulic Machine Torque | (N·m) |

V | Volume | (m^{3}) |

ϑ | Angular Position | (rad) |

µ | Fluid Dynamic Viscosity | (Pa·s) |

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**Figure 1.**Standard excavator hydraulic circuit with installed sensors for testing [34].

**Figure 7.**Actuator response to reference position of duty digging cycle: simulations results (

**a**) boom, (

**b**) arm, (

**c**) bucket.

Working Cycle | U_{C95} [%] | $\frac{\mathit{m}{\mathit{f}}_{\mathit{S}\mathit{I}\mathit{M}}-\mathit{m}{\mathit{f}}_{\mathit{E}\mathit{X}\mathit{P}}}{\mathit{m}{\mathit{f}}_{\mathit{E}\mathit{X}\mathit{P}}}$ [%] |
---|---|---|

Trench Digging | ±3.6 | −0.3 |

Grading | ±8.0 | −1.8 |

Component | Parameter | Value |
---|---|---|

Electric motor | Voltage [V] | 400 |

Max speed [r/min] | 4000 | |

Moment of inertia [kg/m^{2}] | 0.049 | |

Generator | Min speed [r/min] | 1000 |

Rated speed [r/min] | 2200 | |

Voltage [V] | 400 | |

Battery | Specific Energy [Wh/kg] | 130 |

Specific power [W/kg] | 2000 | |

Power [kW] | 50 | |

Mass [kg] | 25 |

Solutions | Mechanical Energy (kJ/Cycle) | Mechanical Energy Saving (%) | ||
---|---|---|---|---|

Digging | Grading | Digging | Grading | |

LS | 393.6 | 72.1 | / | / |

DDH with pipes | 185.3 | 15.7 | −54.0 | −78.3 |

DDH without pipes | 96.2 | 12.2 | −75.5 | −83.1 |

Solutions | Fuel Consumption (g/Cycle) | Fuel Saving (%) | ||
---|---|---|---|---|

Digging | Grading | Digging | Grading | |

LS | 34.5 | 10.5 | / | / |

DDH with pipes | 28.2 | 8.6 | −18.2 | −18.2 |

DDH without pipes | 24.1 | 8.6 | −30.1 | −19.7 |

DDH (DS) with pipes | 23.8 | 7.3 | −31.1 | −31.0 |

DDH (DS) without pipes | 17.0 | 5.9 | −50.8 | −43.6 |

**Table 5.**Mechanical energy supplied by diesel engine (for DDH solutions the diesel engine is connected to the generator).

Solutions | Mechanical Energy (kJ/Cycle) | Mechanical Energy Saving (%) | ||
---|---|---|---|---|

Digging | Grading | Digging | Grading | |

LS | 393.6 | 72.1 | / | / |

DDH with pipes | 245.8 | 26.9 | −37.5 | −62.8 |

DDH without pipes | 148.5 | 23.0 | −62.3 | −68.1 |

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**MDPI and ACS Style**

Casoli, P.; Scolari, F.; Minav, T.; Rundo, M. Comparative Energy Analysis of a Load Sensing System and a Zonal Hydraulics for a 9-Tonne Excavator. *Actuators* **2020**, *9*, 39.
https://doi.org/10.3390/act9020039

**AMA Style**

Casoli P, Scolari F, Minav T, Rundo M. Comparative Energy Analysis of a Load Sensing System and a Zonal Hydraulics for a 9-Tonne Excavator. *Actuators*. 2020; 9(2):39.
https://doi.org/10.3390/act9020039

**Chicago/Turabian Style**

Casoli, Paolo, Fabio Scolari, Tatiana Minav, and Massimo Rundo. 2020. "Comparative Energy Analysis of a Load Sensing System and a Zonal Hydraulics for a 9-Tonne Excavator" *Actuators* 9, no. 2: 39.
https://doi.org/10.3390/act9020039