Abstract
Numerical calculations of high speed solenoid valves (HSV) are performed to understand the effects of the driving current and structural parameters on electromagnetic energy conversion in HSV. The results show that the driving current plays a prominent role on the capability of electromagnetic energy conversion. The changes in the electromagnetic force are determined by the total magnetic reluctance and the range of the driving current. For large driving currents, the capability of electromagnetic energy conversion is not significantly influenced by the driving current and is only slightly affected by the working air-gap. The larger the driving current becomes, the smaller the increase of the electromagnetic force is with an increasing of the working air-gap. Within a certain range of driving currents, the armature thickness has positive effects on the capability of electromagnetic energy conversion, but the effects are not significant at large driving currents. At different driving currents, the effect of the number of coil turns on the electromagnetic force is mostly determined by the effects of the coil turns on the total magnetic flux and the total magnetic reluctance.
Keywords
Introduction
High pressure common rail systems have been applied widely because of their characteristics, such as their injection pressures independent of engine speed, injection timing, and flexible injection strategies. Engines that are equipped with high pressure common rail systems could potentially realize the design goals of high combustion efficiency and low emissions [1, 2, 3, 4]. Injectors are key parts of high pressure common rail systems and directly affect the fluctuations of the fuel injection, the gas-liquid two-phase flow characteristics of the high pressure fuel in nozzles, the fuel atomization characteristics and the quality of gas/oil mixture [5, 6, 7, 8, 9]. HSVs are core control components of common rail injectors. The high dynamic response of HSVs can improve the control accuracy of the cycle’s fuel injection quantity and timing.
Although both the electromagnetic characteristics and the armature’s mass determine the dynamic response of an HSV, the former have a more significant impact. Numerous studies have investigated the static electromagnetic characteristics of HSVs. Sun et al. [10], Topcu et al. [11], and Jaber [12] analyzed the effects of the driving current on the electromagnetic force of HSVs and found that the driving current has a significant influence on the electromagnetic energy conversion. Cheng et al. [13] studied the effects of Fe-based soft magnetic material on the magnetic field distribution and found that the material magnetism significantly affects the electromagnetic force of the HSV. Wang et al [14] experimentally determined that Al-Fe-based soft magnetic material could significantly reduce the material’s magnetic reluctance and consequently improve the efficiency of electromagnetic energy conversion. Liu et al. [15] presented a 3D simulation and analyzed the magnetic-field distribution of a solenoid valve with different airgaps and contact surfaces, and eventually determined the optimum airgap and optimum shape of the contact surface. Miller et al. [16] studied the effects of the number of coil turns on the electromagnetic force of a fast pneumatic brake actuator, and Liu et al. [17] performed numerical calculations and determined the effects of the structural parameters on the static electromagnetic force of a solenoid valve applied in an electronic unit pump.
Based on the changes between the electromagnetic force and structural parameters, scholars have used several optimization algorithms to calculate the optimum structure of HSVs. Liu et al. [18] adopted CloudPSO for the structural design of a direct action solenoid valve. Shin et al. [19] used the response surface methodology to optimize the dynamic response of a high-speed solenoid valve based on ANSYS. Sefkat [20] set up two optimization criteria of volume minimization and energy consumption minimization and used them to optimize the parameters of HSVs. Lu et al. [21] optimized the time interval between the injections of HSVs based on an injection control strategy.
These previous studies showed that the static electromagnetic characteristics of an HSV are closely related to its structure and control parameters and especially to its driving current. A small driving current will lead to a lower electromagnetic force and will be unable to lift an armature, and a large driving current may cause an electromagnetic valve to reach magnetic saturation and thus reduce the efficiency of the electromagnetic energy conversion [10, 11, 12]. However, systematic and in-depth investigations of the effects of the driving current coupled with the structural parameters are rare. To provide valuable information about electromagnetic energy conversion in HSVs, a systematic investigation was conducted, and the effects of the driving current and essential structural parameters on the static electromagnetic force were numerically studied and analyzed.
Description of models and methodology
Numerical model and calculation setup
Most previous studies of electromagnetic energy conversion have been based on 3D computational fluid dynamics (CFD) software [13, 17, 18, 19], which requires both sophisticated computer configurations and long computation times. These disadvantages are more significant in the detailed design phase of HSVs because of the large number of calculations. In addition, the working process of the HSV in a common rail injector involves nonlinear transient coupling between electromagnetism, mechanism and hydraulic power, and it is difficult for 3D CFDs to perform these transient coupled computations. In studying high pressure common rails, most scholars first modelled a one-dimensional electromagnetic submodel and then coupled it into a one-dimensional mathematical model of a high pressure common rail system [22, 23, 24]. Therefore, the electromagnetic model of HSVs is very important. In this investiga- tion, based upon the principle of electromagnetic coupling, a mathematical model of HSVs that considers the phenomenon of electromagnetic saturation is deduced based upon the principle of electromagnetic coupling, and the effects of the electromagnetic energy conversion are studied. Figure 1 shows the structural diagram of an HSV for a common rail injector. The HSV is comprised of an iron core, a coil, and an armature.
The structural schematic of the HSV.
The relationship between the total magnetic flux and the total magnetic reluctance in an HSV can be written as
Where
The total magnetic reluctance
Where
where
The average magnetic circuit length and corresponding effective cross-sectional area of each part can be expressed as follows.
Finally, the electromagnetic force of the HSV can be expressed as
The test bench of electromagnetic force for HSVs.
To test and validate the accuracy of the electromagnetic model, a test bench is used to measure the static electromagnetic force (Fig. 2). The iron core of the HSV is placed at the free end of the bench, and the armature and force sensor are fixed at the fixed end. The height of the free end is adjusted to keep the axes of the iron core and the armature at the same horizontal level. The value of the working air-gap of the HSV can be changed by adjusting the distance between the free end and the fixed end. The driving current of the HSV is controlled by a power amplifier. The current is measured using a current probe. The armature will be attracted towards the iron core when the coil is energized. A force sensor generates a weak voltage signal, which passes through a high-precision amplifier to denote the value of the electromagnetic force in the axial direction. Table 1 shows the specifications of the main sensors. By changing the air-gap and the driving current, the data of static electromagnetic force were measured on the test bench. Subsequently, the static electromagnetic characteristics of the HSV were obtained.
The specifications of main sensors
The specifications of main sensors
The detailed settings of the one-dimensional calculation
Table 2 shows the detailed structural parameters of the HSV, and Fig. 3 shows the B-H curve of the soft magnetic material. The electromagnetic forces at different driving currents are calculated by combining Eqs (1)–(15) and the B-H curve.
The B-H curve of the iron core and armature.
Comparison between simulated and experimental results of the electromagnetic force at different air-gaps: (a) air-gap of 0.1 mm; (b) air-gap of 0.12 mm.
Influence of the driving current on the electromagnetic force increment at different working air-gaps.
Influence of driving current on total magnetic reluctance at different working air-gaps.
Figure 4 shows comparisons between the simulated and experimental results of the electromagnetic force at various driving currents and working air gaps. For working air-gaps of 0.1 mm and 0.12 mm, the simulated and experimental results are consistent at different driving currents. These results demonstrate that the proposed electromagnetic model of the HSV is reasonable and can be used to predict the electromagnetic force of an HSV with acceptable accuracy. Therefore, based on the validated electromagnetic model of the electromagnetic force, the effects of the structural parameters on the electromagnetic energy conversion are studied at different driving currents.
Influence of the driving current
The effects of the driving current
Figure 6 shows that when
Figure 6 also shows that when
Influence of the working air-gap
Figure 7 shows that at different values of
Influence of 
Influence of 
Influence of 
Influence of 
At different values of
The working air-gap has direct effects on the air-gap’s magnetic reluctance as well as the magnetic reluctance of the soft magnetic material in the HSV. In the case of constant structural parameters, the air-gap’s magnetic reluctance increases linearly with an increase of the working air-gap regardless of the value of
Figure 10 clearly shows that at different values of
Influence of 
An increment of the armature thickness
Influence of 
Influence of 
Influence of 
Influence of 
Influence of 
Figure 13 shows that at different values of
Figure 15 shows that at different values of
At different values of
Figure 16 shows that with an increasing of
Conclusions
A numerical method is used to analyse the effects of the structural parameters of an HSV on its capability of electromagnetic energy conversion at different currents. The main conclusions are as follows:
The driving current plays a prominent role in the electromagnetic force of an HSV. Changes in the electromagnetic force with the driving current are determined by the ranges of the total magnetic reluctance and driving current. If the driving current is small, it is the main factor that changes the electromagnetic force. However, if the driving current is large, although the increase of the total magnetic flux is the main factor in the increase of the electromagnetic force, an increase of the total magnetic reluctance enhances the reduction of the electromagnetic force, which gradually weakens the effects of the driving current on the capability of electromagnetic energy conversion. The electromagnetic force will reduce with an increase of the working air-gap, and the reduction will decrease with increases of the driving current. For the case of a large driving current, the efficiency of electromagnetic energy conversion is slightly influenced by the working air-gap. Changes in the working air-gap can influence the air-gap’s magnetic reluctance as well as the magnetic reluctance of the soft magnetic material. The effects of the armature thickness on the electromagnetic energy conversion of the HSV are determined by the driving current. Within a certain range of driving currents, an increase of the armature thickness increases the capability of electromagnetic energy conversion. However, in the case of a large driving current, the armature thickness plays a minor role in the capability of electromagnetic energy conversion. The electromagnetic force will increase with an increasing in the number of coil turns, but its growth is determined by the driving current. The effects of the number of coil turns on the electromagnetic force at different driving currents are primarily determined by the effects of the coil turns on the total magnetic flux and the total magnetic reluctance.
Footnotes
Acknowledgments
This work is supported by the National Natural Science Foundation of China (Grant No: 51475100), the Natural Science Foundation of Heilongjiang Province of China (Grant No: LC201422), the China Scholarship Council (Grant No: 201506685031), the Fundamental Research Funds for the Central Universities (Grant No: HEUCFM170302).
