Research and Analysis on dynamic characteristics o

Research and Analysis on the dynamic characteristics of electrorheological fluid engine mount

preface

automotive powertrain mount system refers to the system composed of elastic mount elements between powertrain (including engine, clutch, transmission, etc.) and frame/chassis. The vibration of engine powertrain is transmitted to the body/frame through this system, and the vibration caused by uneven road surface is also transmitted to the engine through this system, Therefore, the performance design of the system directly affects the NVH performance of the whole vehicle

in order to improve the vibration in the car, a large number of mounting systems are used in the car powertrain. An ideal power 1 spindle and its drive system spindle (1) is composed of Panasonic exchange electromechanical (2) and pwmc pulse width speed regulation control system. The rated torque of the electromechanical system is 9.545n · m, the pulse width speed regulation range is 10 (2) 000r/min, stepless constant torque, and the high-speed accuracy is 1% The maximum power of the electromechanical system is about 1.5KW. The upper mounting system of the main shaft (1) and electromechanical (2) should have the following characteristics: (1) in the low-frequency range of 5 ~ 20Hz, in order to effectively attenuate the low-frequency and large amplitude vibration caused by uneven road surface and uneven engine idle gas pressure, it needs to have the characteristics of high stiffness and large damping; (2) In the frequency band above 20Hz, in order to reduce the noise in the vehicle and improve the handling stability of the vehicle, it is necessary to have the characteristics of low stiffness and small damping. The traditional passive mount has been difficult to meet the requirements of vehicle vibration isolation performance. In order to achieve good vibration isolation effect, the research has not only been limited to rubber mounts and passive hydraulic mounts, but also new mounting systems such as electrorheological hydraulic mounts have emerged

1 Characteristics of electrorheological fluid

electrorheological fluid is a complex fluid composed of dielectric particles and insulating liquid. For most electrorheological fluids, when there is no external electric field, its viscosity is low, which shows the mechanical properties of Newtonian fluids; When the applied electric field is applied, the mechanical properties of the fluid change significantly, and the electrorheological fluid turns into viscoplastic. Only when the shear stress is greater than the yield stress, the liquid will flow, and the liquid presents the yield stress τ y. The liquid at this time is a Bingham fluid, and its performance is shown in Figure 1

the equation conforms to B ngham model

where τ Is shear stress; τ Y E) is the shear yield stress caused by electric field; η Is the dynamic viscosity of electrorheological fluid; γ Is the shear rate

under the action of electric field, er liquid can be converted between liquid and viscoplastic body. Its conversion process is continuous, and the response is very sensitive. Generally, its response time is ms level, and the conversion between liquid and solid is reversible, and the energy required to control the phase transition is also very small. Electrorheological technology refers to the application of electrorheological effect in engineering practice. It is now widely used in automotive engineering, aerospace, mechanical engineering and other fields. In automotive engineering, it is mainly used in clutch, suspension system, engine mount, etc

2 establishment of electrorheological fluid mount model

2.1 structural composition of electrorheological fluid mount

electrorheological fluid mount is an engine mount with good dynamic characteristics, and its body structure is shown in Figure 2

(1) the upper cavity of the charged rheological fluid composed of the elastic element (rubber shell) is the elastic element of the mounting system. When it bears the effect of external excitation force, it can deform and change the volume of the upper cavity, so that the electrorheological fluid can be discharged through the damping hole. If the damping hole of the upper cavity is unobstructed, the stiffness of the vibration isolation device is mainly determined by the stiffness of the rubber elastic element; If the damping hole is completely blocked, because the ER fluid in the upper cavity is incompressible, the elastic element and the liquid form a new composite elastic element with greater stiffness. Obviously, by changing the strength of the electric field, the viscosity of the liquid in the suspension can be changed, and then the damping and dynamic stiffness can be affected. As the electric field increases, the damping and dynamic stiffness increase

(2) damping holes are opened on the diaphragm between the upper and lower cavities. The holes are generally clearance channels with rectangular cross-section. The two sides of the channel are used as cathode and anode to form a uniform electric field, and the other two sides are insulators. The flow of ER fluid in the damping hole is a gap flow parallel to the plane. When there is only one damping hole on the diaphragm, the damping force of the electrorheological fluid mount can be steplessly adjusted by changing the intensity of the electric field; When there are multiple damping channels on the clapboard, the electric field can be used to control the combination of each channel to form multiple different damping forces, so that the electrorheological fluid mount can obtain multiple different natural frequencies. The latter is relatively simple in the control of the electric field, which does not need stepless adjustment, but only needs switching control

(3) the inferior chamber is composed of an elastic bottom membrane. Using its own elasticity, the elastic bottom membrane can change its shape and volume to bear the flow in the upper and lower cavities and the change of the liquid capacity of the upper and lower cavities caused by the deformation of the components in the aerospace field and the manufacturing industry of high-speed and high-density power components due to the elasticity of rubber

(4) the rigid lower shell is wrapped outside the elastic membrane, which is filled with air so that the elastic membrane can expand and contract freely

(5) high voltage electric field and high voltage applied to the positive and negative electrodes on the damping channel

2.2 mechanical model of electrorheological fluid mount

mechanical model of electrorheological fluid mount the structure of electrorheological fluid mount is relatively complex, and the simplified and abstract model is shown in Figure 3

according to the characteristics of electrorheological fluid, its viscosity can be obtained as

where η A is the viscosity of electrorheological fluid. It can be concluded that the damping force of the liquid flowing through the damping hole is

, where l and B are the depth and width of the damping hole respectively, h is the gap distance of the electrode, and Qi T) is the liquid flow of the damping hole

according to the momentum equation and continuity equation of incompressible fluid, it can be concluded that in the formula

Kr BR is the stiffness and damping coefficient of the rubber main spring respectively, AR is the equivalent piston area of the rubber main spring, C1 and C2 are the volume flexibility of the upper and lower liquid chambers respectively, and P1 and P2 are the liquid pressure in the upper and lower liquid chambers respectively

from this model, it can be seen that the force transmitted to the vehicle body through the electrorheological fluid mount has two parts: one part is transmitted through the rubber main spring; The other part is produced by the pressure of the liquid in the upper and lower liquid chambers. Therefore, the calculation formula of the support reaction force at the fixed end of the suspension is

by controlling the electric field of the damping channel, the viscosity of the ER fluid can be changed, so as to change the size of the generated damping force and achieve the effect of absorbing vibration

3 simulation and test results

according to the mechanical model and the model mentioned in the literature, after setting the relevant parameters, use ADAMS software to simulate the dynamic characteristics of the system. When the tensile strength of carbon fiber (T800 grade) is ≥ 5.8gpa without electric field, the dynamic stiffness and response lag angle change curve of the system are shown in the dotted lines in Figure 4 and figure 5. It can be seen from the figure that when the electric field is not applied to the electrorheological hydraulic mount, its dynamic characteristics are similar to the traditional passive hydraulic mount

the dynamic characteristic test of electrorheological fluid mount was carried out on the instron8800 servo hydraulic vibration test bench. The electrorheological fluid materials used in the test can refer to the laboratory's special papers on electrorheological fluids with low electrical stress. During the test, connect both ends of the suspension with the test bench, and then apply a displacement excitation XF (T) =x0sin at one end ω t. XF (T) is the displacement excitation, x0 is the displacement excitation amplitude, and the other end is fixed on the test bench. Record the signal x (T) of the displacement sensor at the moving end and the signal f (T) of the force sensor at the fixed end to obtain the dynamic stiffness and hysteresis angle at a certain frequency. The solid lines in Figure 4 and figure 5 are the corresponding curves measured in the test without electric field

by comparing the dynamic stiffness and lag angle curves of the hydraulic mount calculated by simulation and tested by experiment, it can be seen that the two are relatively consistent, which verifies the correctness of the model. An ideal mount needs the dynamic characteristics of high stiffness and large damping at low frequency and low stiffness and small damping at high frequency. For the electrorheological fluid mount, the characteristics of the electrorheological fluid can be adjusted by controlling the electric field between the electrodes of the damping hole, so as to change the peak value and frequency of the dynamic stiffness and hysteresis angle curve of the mount. The dotted lines in Fig. 6 and Fig. 7 are the simulation results of the dynamic stiffness and hysteresis angle of the ER suspension after the electric field is applied. The solid line is the measured curve after the corresponding electric field is applied

4 Conclusion

(1) the dynamic model of electrorheological fluid mount is established and simulated in ADAMS. The correctness of the model is verified by comparing with the experimental results

(2) the simulation model established in this paper can well predict the dynamic characteristics of the mount, and can optimize its performance by changing some parameters when designing the hydraulic mount, so as to shorten the product development cycle and improve the product design quality

(3) the simulation results show that the electrorheological fluid mount with damping adjustment ability can effectively isolate the transmission of engine vibration to the frame and the transmission of road roughness excitation to the engine, and improve the NVH performance of the whole vehicle. (end)