Numerical Simulation Study on Braking Performance of a New Eddy Current-Hydrodynamic Hybrid Retarder
1. Introduction
To further improve the power density of the retarder at full speed and ensure the safety of vehicle deceleration, a new eddy current-hydrodynamic hybrid retarder (ECHHR) is proposed. The electromagnetic field distribution, flow field velocity, and flow field pressure distribution inside the ECHHR are analyzed by the finite element analysis method, and the braking characteristics of the ECHHR under different working conditions are obtained by experiments.
2. Structure and Working Principles
The blades of the stator and rotor form a working chamber of hydraulic braking. Since the left and right structures of the ECHHR are symmetrical, two hydraulic retarders are formed. When the hydraulic braking of the ECHHR starts to work, the oil enters the hydraulic working chamber through the upper oil circuit. As the rotor rotates, the rotating rotor blade drives the oil in the hydraulic working chamber to undergo centrifugal acceleration movement. At the same time, the high-speed moving oil impacts the stator blades, and the rotor blades are also impacted by the oil, thereby hindering the rotation of the rotor. In this process, the oil constantly flows into the hydraulic working chamber from the liquid inlet, through the lower oil circuit, and finally discharges to the radiator from the liquid outlet so as to dissipate the heat energy converted by the rotating mechanical energy of the rotor. The rotor and stator connections are made of highly conductive magnet materials. When the excitation coils are excited with direct current (DC), a magnetic field generated by the excitation coils is closed via the left side of the rotor, the left air gap, the stator connections, the right air gap, and the right side of the rotor. The rotor rotating with the transmission shaft cuts the magnetic line of force generated by the tooth-shaped salient pole of the stator connections to generate eddy current. The magnetic field generated by the eddy current interacts with the magnetic field generated by the excitation coils to produce a braking torque. In this process, the heat generated at a certain depth on the radial surface of the rotor is taken away by the circulating oil of the shared hydraulic retarder, thus reducing the heat decay of the eddy current braking torque.
3. Theory Foundation
3.1. Hydraulic Brake
where α is the filling rate; λ is the moment coefficient; ρ is the fluid density; n is the rotor speed; and D is the cyclic circle equivalent diameter. It can be seen from the above formula that the torque of the hydraulic braking part can be achieved by controlling the fluid filling rate adjustment, and the fluid filling rate is affected by the inlet flow and outlet pressure.
3.2. Eddy Current Brake
where μ is the relative permeability of the rotor.
where t is the time.
where σ is the rotor conductivity.
4. Finite Element Analysis
4.1. Analysis of Eddy Current Characteristics
4.2. Analysis of Hydraulic Braking Characteristics
4.3. Hydroelectric Composite Torque
5. Test Bench
5.1. Bench Test System and ECHHR Prototype
5.2. Hydraulic Braking Torque Performance
Due to the fact that the torque of hydraulic braking is only divided into one gear control, the solenoid valve set at the outlet only has the function of opening and closing, and the outlet pressure is mainly achieved by adjusting the opening of the valve. Therefore, no control group of outlet pressure is set in this test scheme. On the other hand, a high-power centrifugal pump was used to simulate the vehicle-based mechanical pump, with a maximum working flow rate of 5.5 L/s. However, the working flow of the centrifugal pump is related to the load water resistance; the greater the load, the greater the pump water pressure, but the flow will be sharply reduced. Hence, the centrifugal pump cannot accurately control the flow. Therefore, under other unchanged conditions, this experiment controls the inlet pressure of the ECHHR by adding a pressure regulating valve at the outlet of the water pump and collects experimental data by comparing the simulation calculation results. In the experiment, it is assumed that the inlet pressure remains basically constant.
5.3. Eddy Current Braking Torque Performance
5.4. Composite Braking Torque Performance
5.5. Comparative Analysis of Hydraulic Braking Theory and Experimental Results
It is speculated that the following reasons may be the cause: in the low-speed section, the actual flow field may form an incomplete turbulence state, and the realizable turbulence model selected in this paper is more suitable to simulate the high-speed rotating turbulent flow field, so the error in the low-speed section is formed.
5.6. No-Load Torque Characteristics
5.7. Comparative Analysis of Eddy Current Braking Theory and Experimental Results
6. Discussion
The experimental results have proven the feasibility and rationality of the design scheme proposed in this paper, but they also indicate that there are certain shortcomings in the theoretical analysis and there are certain deviations in the experimental results. Compared with conventional hydraulic retarders, the hydraulic braking capacity of EHHR is reduced, but it can be used as a supplement to electromagnetic braking at low speeds. At high speeds, its braking torque and speed increase in a quadratic relationship, ensuring the braking performance of the retarder at high speeds. Considering that hydraulic braking only plays an auxiliary role at low speeds and mainly plays a main role at speeds above 1000 r/min, referring to the trial design experience of a straight blade hydraulic retarder, the braking performance at high speeds can be improved by reducing the size of the retarder’s working fluid outlet or increasing outlet control in the future.
The steady-state and transient electromagnetic fields of the electromagnetic braking part of ECHHR were simulated and analyzed, and the electromagnetic field distribution and braking torque values under different conditions of the retarder were obtained. The effectiveness of finite element analysis was verified via experiments. The research results have shown that via integrated structural design, the eddy current braking characteristics of the retarder have not been unreasonable or weakened. However, as this test only verifies the feasibility of the scheme, it is relatively simple and does not monitor the temperature and pressure in real time during the test. Therefore, the above test results cannot be verified via magnetic fluid thermal coupling. However, the conclusion drawn from coupling analysis infers the reason for the deviation, providing a theoretical basis for subsequent improvement.
7. Conclusions
A new ECHHR was proposed, and finite element analysis models of its eddy current and hydraulic braking were established. The electromagnetic field distribution, flow field velocity, and flow field pressure distribution of the ECHHR were analyzed. The relationship curves between eddy current braking torque under different excitation currents and hydraulic braking torque under different filling rates and velocities were obtained. The superior braking performance of the ECHHR in the full speed range was verified via finite element analysis and experiment methods.
Author Contributions
Methodology, F.W. and W.G.; software, W.G. and J.L.; writing—original draft preparation, F.W. and W.G.; writing—review and editing, J.L. and F.W.; validation, J.L. and F.W.; data curation, W.G. and F.W. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by the Scientific and technological breakthroughs Project in Anyang City, grant number [2023C01GX041], and the Doctoral Start-up Funding of Anyang Institute of Technology, grant number [40076212].
Data Availability Statement
Data are contained within the article.
Conflicts of Interest
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
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Figure 1.
(a) Overall cross-sectional view of the ECHHR. (b) Sectional view of stator connection of the ECHHR.
Figure 1.
(a) Overall cross-sectional view of the ECHHR. (b) Sectional view of stator connection of the ECHHR.
Figure 2.
Finite element simulation model of electromagnetic field of the ECHHR.
Figure 2.
Finite element simulation model of electromagnetic field of the ECHHR.
Figure 3.
The partial finite element analysis model.
Figure 3.
The partial finite element analysis model.
Figure 4.
(a) Magnetic field vector diagram. (b) Magnetic dense cloud diagram.
Figure 4.
(a) Magnetic field vector diagram. (b) Magnetic dense cloud diagram.
Figure 5.
Periodic static air gap magnetic density under different excitation currents.
Figure 5.
Periodic static air gap magnetic density under different excitation currents.
Figure 6.
Curve of eddy current braking torque under different excitation currents.
Figure 6.
Curve of eddy current braking torque under different excitation currents.
Figure 7.
CFD simulation model of flow field of ECHHR.
Figure 7.
CFD simulation model of flow field of ECHHR.
Figure 8.
Velocity vector diagram of flow field: (a) Rotor. (b) Stator.
Figure 8.
Velocity vector diagram of flow field: (a) Rotor. (b) Stator.
Figure 9.
Cloud chart of flow field pressure: (a) Rotor blade. (b) Stator blade.
Figure 9.
Cloud chart of flow field pressure: (a) Rotor blade. (b) Stator blade.
Figure 10.
Curve of hydraulic braking torque changing with fluid filling rate.
Figure 10.
Curve of hydraulic braking torque changing with fluid filling rate.
Figure 11.
Comparison curve of hydraulic brake, eddy current brake torque, and hydraulic electric composite brake torque.
Figure 11.
Comparison curve of hydraulic brake, eddy current brake torque, and hydraulic electric composite brake torque.
Figure 12.
Schematic diagram of the test bench.
Figure 12.
Schematic diagram of the test bench.
Figure 13.
ECHHR prototype.
Figure 13.
ECHHR prototype.
Figure 14.
Brake torque curves of different inlet pressure.
Figure 14.
Brake torque curves of different inlet pressure.
Figure 15.
Eddy current braking torque variation curve with rotational speed.
Figure 15.
Eddy current braking torque variation curve with rotational speed.
Figure 16.
Curve of composite braking torque variation with rotational speed.
Figure 16.
Curve of composite braking torque variation with rotational speed.
Figure 17.
Comparison of hydraulic braking torque test results with theoretical results.
Figure 17.
Comparison of hydraulic braking torque test results with theoretical results.
Figure 18.
No-load torque of the ECHHR.
Figure 18.
No-load torque of the ECHHR.
Figure 19.
Comparison of eddy current braking torque test results with theoretical results.
Figure 19.
Comparison of eddy current braking torque test results with theoretical results.
Table 1.
Design parameters of ECHHR.
Table 1.
Design parameters of ECHHR.
Parameters | Value/Model |
---|---|
Outer diameter of stator/mm | 490 |
Inner diameter of stator/mm | 200 |
Outer diameter of rotor/mm | 440 |
Inner diameter of rotor/mm | 224 |
Axial length of one side stator/mm | 45 |
Axial length of rotor/mm | 80 |
Thickness of stator connection/mm | 25 |
Stator material | Aluminum |
Rotor material | 10CrMo |
Material of stator connection | 10CrMo |
Excitation coils | Copper |
ECHHR quality/kg | 165 |
Table 2.
Geometric parameters of model.
Table 2.
Geometric parameters of model.
Parameter | Stator Impeller | Rotor Impeller |
---|---|---|
Circular outer diameter/mm | 427 | 410 |
Inside diameter of circular circle/mm | 290 | 290 |
Number of blades | 27 | 28 |
Blade thickness | 4.5 | 4.5 |
Table 3.
Boundary condition setting.
Table 3.
Boundary condition setting.
Item | Parameter |
---|---|
Analysis type | Transient |
Solution type | Based on pressure |
Turbulence model | Realizable k-ε |
Import boundary | 2.1 kg/s (Flow), 3 × 105 pa (Pressure) |
Exit boundary | 3.5 × 105 pa (Pressure) |
Stator and rotor domain | sliding mesh |
Time step | 0.005 |
Time step | 200 |
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