## 3 Results
### Lifting Energy and Efficiency  
This section presents the methodology and results related to the evaluation of the energy efficiency during the load lifting process in the electric forklift. Figure 8 provides a detailed overview of the energy conversion architecture involved in the lifting system, including the measurement points for voltage and current signals captured by the D&Q equipment, as well as the energy transformation stages--from the buck converter output to mechanical lifting via the electro-hydraulic system. The schematic highlights the flow of energy through main components such as the DC motor, hydraulic pump, piping, lifting cylinders, mast, and fork. This representation also clarifies the use of electrical power (voltage \(\times\) current) as a reliable indicator that integrates the net effect of all intermediate conversion efficiencies. The positioning of the sensing equipment ensures that measurements reflect the electrical input to the motor, which drives the entire lifting subsystem. Energy losses across the electro-hydraulic lifting system significantly affect the overall efficiency of the load-lifting process. The brushed DC motor used in the forklift typically exhibits moderate efficiency, ranging between 80 and 85%, meaning that most of the electrical input is successfully converted into mechanical energy to drive the hydraulic gear pump. However, the subsequent conversion of mechanical to hydraulic energy introduces further losses. Hydraulic gear pumps have an overall efficiency ranging from 60 to 90%, which depends on the operating pressure and speed. When operating at low pressure and low speed, a gear pump has an inefficient operation [9]. Once hydraulic energy is transmitted through the piping to the lifting cylinders, additional losses occur. Hydraulic cylinder efficiency can reach approximately 90% (particularly at operating speeds above 0.05 m/s), with losses due to friction in seals and guide elements. Finally, more significant mechanical losses take place in the mast assembly, including friction in sliding elements, the fork carriage, chains, bearings, and the dead weight of the fork structure itself. Combined, these losses contribute to a significant reduction in the total energy transferred from the electrical input to effective vertical lifting motion. The overall lifting efficiency, denoted  
Figure 7: LM power plots for the cases of (**a**) 800.5 kg, (**b**) 1002.5 kg, and (**c**) 1202.0 kg. as \(\eta_{\rm l}\), can be approximated by the product of the efficiencies at each stage of the energy conversion chain:  
\[\eta_{\rm l}\approx\eta_{\rm motor}\cdot\eta_{\rm hyd}\cdot\eta_{\rm cyl}\cdot \eta_{\rm mech} \tag{1}\]  
Here, \(\eta_{\rm motor}\) refers to the DC motor efficiency, \(\eta_{\rm hyd}\) accounts for losses in the hydraulic pump, piping, and valves, \(\eta_{\rm cyl}\) represents the efficiency of the lifting cylinder, and \(\eta_{\rm mech}\) corresponds to mechanical losses in the mast assembly. For aged equipment, assuming \(\eta_{\rm motor}=0.80\), \(\eta_{\rm hyd}=0.60\), \(\eta_{\rm cyl}=0.90\), and \(\eta_{\rm mech}=0.40\), the overall lifting efficiency is estimated as follows:  
\[\eta_{\rm l}\approx 0.80\times 0.60\times 0.90\times 0.40=0.1728 \tag{2}\]  
This implies that only about 17.3% of the electrical power input is ultimately converted into useful mechanical lifting work, with the remaining energy lost throughout the conversion chain. Now, considering the measured data, the lifting efficiency can be defined as the ratio between the potential energy of the load (\(E_{pl}\)) and the electrical energy consumed (\(E_{el}\)) during the lifting operation. The potential energy was computed using the classical mechanical expression:  
\[E_{pl}=m\cdot g\cdot h \tag{3}\]  
where \(m\) is the mass of the load (in kilograms), \(g=9.81\) m/s\({}^{2}\) is the gravitational acceleration, and \(h=2\) m is the lifting height, which remained constant in all tests.