Electro-hydraulic proportional valve is the core control valve in many hydraulic systems used in agricultural and engineering machinery. To address the problem related to the large throttling losses and poor stability typically associated with these valves, here, the beneficial effects of a triangular groove structure on the related hydraulic response are studied. A mathematical model of the pressure compensation system based on the power-bond graph method is introduced, and the AMESim software is used to simulate its response. The results show that the triangular groove structure increases the jet angle and effectively compensates for the hydrodynamic force. The steady-state differential pressure at the valve port of the new pressure compensation structure was 0.65 MPa. Furthermore, experimental results show that the pressure difference at the main valve port is 0.73 MPa, and that the response time is less than 0.2 s. It is concluded that the new compensation structure has good pressure compensation response characteristics.

Electrohydraulic proportional valve is the core control valve of hydraulic systems used in agricultural and engineering machinery. Its performance determines the reliability, stability, accuracy, and green energy savings of the entire hydraulic system. The performance of the electrohydraulic proportional valve directly affects the quality and efficiency of the entire operation [

In recent years, electrohydraulic proportional valves and their pressure compensation technologies have rapidly developed. Rexroth and Eaton developed supporting technologies and products to satisfy various system requirements [

Therefore, in this study, an electrohydraulic proportional control valve was selected as the research object, and an advanced international reversing valve was selected as the reference object [

The pressure compensation system of an electrohydraulic proportional valve consists of a pressure compensation valve, spring, main valve, and various oil passages. The structure of the pressure compensation valve is illustrated in

The working principle of the pressure compensation system is that, when the valve is in operation, the hydraulic oil from the pressure port flows into the pressure compensation valve spool through the thin-walled hole to reach the installation valve seat. Subsequently, the spool is pushed to the left toward the position where the thin-walled hole is closed. The pressure compensation valve port and thin-walled hole opens, and a portion of the hydraulic oil input from the pressure port flows into the main valve cavity. Thus, the load pressure and main valve orifice exhibit a logical relationship. The remaining hydraulic oil flows through the thin-walled hole into the pressure cavity formed by the right end of the pressure compensation valve spool and the installed valve seat and participates in the stress of the pressure compensation valve spool. After a certain period, the pressure-compensating valve spool reaches a balanced state.

A mathematical model is derived from the aforementioned power-bond diagram. The generalized displacement of element C and generalized momentum of element I in this system are considered as the state variables, which were set as X_{i} (i = 1, 2, 3, 4, 5, 6), expressed as follows:

According to the above expressions, the state equation can be deduced as follows:

Each parameter in the formula is defined as follows:

Sf——Input source,

Calculation of the pressure compensation valve port liquid resistance.

The valve port of the pressure compensation valve is similar to the nonlinear liquid resistance and is expressed as follows:

In the formula

Calculation of the liquid guide during the process, from the small hole on the left side to the installed valve seat through the valve spool interior.

During this process, oil passes through thin-walled holes 1, 2, and 3. The liquid guide of the thin-walled holes is given as follows:

The following can be determined using the orifice flow formula:

Each parameter in the formula is defined follows:

Via calculation, it is known that

Each parameter in the formula is defined as follows:

Calculation of the liquid guide during the process, from the small hole on the right side to the installed valve seat through the valve spool interior.

Similar to

Each parameter in the formula is defined as follows:

Calculation of fluid power on the pressure compensation valve spool.

The steady-state flow force can be expressed using the valve port flow and flow rate formulas as follows:

Each parameter in the formula is defined as follows:

The pressure compensation valve orifice was of the triangular groove type. The two orifices are arranged symmetrically; therefore, the flow area is:

Therefore,

Each parameter in the formula is defined as follows:

An improved valve core structure was designed, as shown in

The simulation results showed that the triangular groove structure can produce a flow component in the negative direction. This part of the liquid impacts the liquid flow in the positive direction, such that the flow angle of the liquid flow at the outlet increases; that is, the jet angle increases. The structure effectively compensates for the hydrodynamic force.

The simulation model of the pressure compensation system in the electrohydraulic proportional control valve of agricultural and engineering machinery is shown in

The simulation parameters of the model are set as shown in

Serial number | Parameter | Numerical value | Unit |
---|---|---|---|

1 | Pressure compensation valve spring rate | 22 | |

2 | Pressure compensation valve spring preload | 454 | |

3 | Pressure compensation valve spool viscous damping coefficient | 6.32 | |

4 | Pressure compensation valve damping length | 0.006 | |

5 | Equivalent mass of pressure compensation valve spool | 0.2 | |

6 | Control cavity orifice diameter | 1.8 | |

7 | Oil supply flow | 200 | |

8 | Load pressure | 29 |

Influence of spring stiffness on compensation characteristics.

The spring stiffness comparison values were 20,000, 25,000, and 30,000 N/m. The simulation duration was set to 0.2 s.

From

The spring preload affects the dynamic response and steady-state characteristics of the pressure compensation system of an electrohydraulic proportional valve. Within a certain range, the performance of the pressure compensation system can be improved by increasing spring stiffness. For the existing pressure compensation system model, the spring stiffness was set to 30,000 N/m.

Influence of the spring preload on the compensation characteristics.

The comparison values of the spring preloads were 456, 471, and 486 N. The simulation duration was set as 0.2 s. The simulation results are shown in

With the other parameters of the system remaining constant, increasing the spring preload of the pressure compensation valve within a certain range improves the stability of the pressure difference of the pressure compensation system, and the response characteristics of the output flow. It also improves the electrohydraulic pressure-compensation characteristic index of the proportional valve. For the current pressure compensation system model, a spring preload of 471 N is ideal.

Influence of viscous friction coefficient on compensation characteristics.

The viscous friction coefficients in the dynamic simulation model were set as 0.5, 1.5, and 2.5 s⋅N⁄m, while other system parameters remained unchanged. The system pressure, load pressure, and simulation duration were 30, 29, and 0.2 s, respectively. The response curves for different viscous friction coefficients were obtained and are presented in

The magnitude of the viscous friction coefficient is a key factor affecting the dynamic response and steady-state characteristics of the pressure compensation system of the electrohydraulic proportional valve. Within a certain range, increasing or decreasing the viscous friction coefficient improved the performance of the pressure compensation system. Thus, in the design and manufacturing process, designers should pay special attention to the indirect control of the viscous friction coefficient. In the existing pressure compensation system model, the viscous friction coefficient was set to 2.5 s⋅N/m.

An electrohydraulic proportional-valve hydraulic system test platform was built to verify the accuracy of the mathematical model and simulation results of the pressure compensation system of the electrohydraulic proportional valve, as shown in

The system pressure was set to 30 MPa, and the loading pressure of the load-proportional relief valve was set to 29 MPa. A step signal with an amplitude of 8 V is applied to the proportional controller. The output flow response, spool displacement response, and main valve port differential pressure-response curves were obtained experimentally, as shown in

As shown in

A comparison of the response curves of the test and simulation show that the simulation model built in this study accurately simulates the dynamic characteristics of the actual pressure compensation system.

The influence of the triangular groove shape of the valve core on the hydrodynamic response characteristics was analyzed using FLUENT software. The results showed that the triangular groove structure could produce a flow component in the negative direction. This part of the liquid flow reversely impacts the liquid flowing in the positive direction, thereby increasing the flow angle of the liquid at the outlet and jet angle. This structure effectively compensated for the hydrodynamic force and reduced pressure loss along the path.

The simulation models of the pressure compensation systems were built using AMESIM software. The influence of the pressure compensation valve spring preload, spring stiffness, and viscous damping coefficient on the pressure compensation characteristics was studied. The final spring preload, spring rate, and viscous damping coefficient were 471 N, 30000 N/m, and 2.5 s⋅N/m, respectively. A comparison of the load-step changes for the two systems showed that the response times of both systems were similar. The maximum fluctuations of the new pressure compensation system were 0.54 L/min, 0.017, and 0.006 MPa, with improved stability. In other words, its pressure compensation characteristics were better than those of the reverse valve.

A test platform was built to evaluate the electrohydraulic proportional valve. The results showed that the pressure difference at the main valve port was approximately 0.73 MPa, and the response time was approximately 0.2 s. The test and simulation curves were consistent, which verifies the accuracy of the mathematical and simulation models. An experimental analysis of different working conditions proved that the electrohydraulic proportional valve has good pressure-compensation performance and can replace similar products.

I would like to thank my tutor, R.L., for his support and guidance. I would also like to express my gratitude to my coworkers for their support and understanding, without which I would have never completed my research. I would also like to especially thank my family and friends, who listened to my frustrations and believed in me, sometimes more than I believed in myself.

This research was funded by the 2020

The authors declare that they have no conflicts of interest to report regarding the present study.

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