# Dimensionless Energy Conversion Characteristics of an Air-Powered Hydraulic Vehicle
## 5 Simulation and Experimental Study on a HP Transformer  
### Experimental Verification of the Mathematical Model  
To verify the dimensionless mathematical model, a compressed air-powered hydraulic system was set up. Its schematic structure can refer to Figure 3. The compressed air, charged from the air source, flowed through a regulator (IR3010-03 BG, SMC, Tokyo, Japan), and its pressure was reduced to a fixed value (about 0.6 MPa). When the compressed air was supplied to the Hydropneumatic transformer (SWB-100D-5, SIWELL Supercharger Technology, Suzhou, China), pressurized hydraulic oil was output from the HP transformer. In order to stabilize the output pressure of the HP transformer, an accumulator (GXQA-0.35/25-L-A, AOQI, Guangdong, China) and a relief valve (DBDS6P1X/315, Rexroth, Lohr am Main, Germany) were installed in the downstream of the compressed air-powered hydraulic system. A pressure sensor (AK-4B, 701, Beijing, China), a data acquisition card (USB4711, Advantech, Taipei, Taiwan) and a computer (X430, Lenovo, Beijing, China) were utilized to measure the output pressure of the HP transformer.  
A dedicated test bench for the HP transformer, as shown in Figure 4, was designed and built to measure the output pressure of the HP transformer.  
According to previous study [17], because the temperature of the compressed air is almost same as the atmospheric temperature, so the influence of the temperature on the working characteristics  
Figure 4: Dedicated test bench for the HP transformer.  
Figure 3: Schematic structure of the HP transformer: (1) Regulator; (2) HP transformer; (3) Accumulator; (4) Silencer; (5) Tank; (6) Data acquisition card; (7) Pressure sensor; (8) Computer; (9) Relief valve.  
of a pneumatic booster can be neglected. As the structure and working principle of the pneumatic booster like the structure and working principle of the HP transformer, in this study, the working process of the HP transformer is considered to be an isothermal process.  
In simulation and experimental study on the HP transformer, the values of the dimensionless area of the hydraulic chamber and dimensionless output oil pressure were set to 0.25 and 2.92. As the output pressure of the HP transformer can be acquired with a pressure sensor, which is more precise and cheaper than a hydraulic flow sensor. Figure 5 depicts the simulation and experimental output hydraulic pressure characteristics.  
As shown in Figure 5, it is clear that the simulation results are consistent with the experimental results, and that verifies the mathematical model above. However, there are two differences between the simulation results and the experimental results: (1) The dimensionless output pressure in the  
Figure 5: Simulation and experimental contrast curves. (**a**) Simulation and experimental curves of the dimensionless output hydraulic pressure; (**b**) Simulation and experimental curves of the dimensionless flow.  
experiment results increases more sluggishly than the dimensionless output pressure in the simulation results; (2) There is a fluctuation in the dimensionless output pressure of the HP transformer, when the dimensionless output pressure gets to its top.  
The main reasons for the differences are listed as follows. In the experiment, the accumulator absorbed the fluctuation of the dimensionless output pressure, which slowed down the increase of the dimensionless output pressure of the HP transformer. Moreover, the opening size of the relief valve was regulated according to the output pressure of the HP transformer. With a decrease in the output pressure of the HP transformer, the opening size of the relief valve got smaller, then the output pressure of the HP transformer rose accordingly.