Analysis on the Causes of Torsional Vibration in the Dual-mode Multi-Gear Power Transmission Mechanism of Hybrid Electric Vehicles

In order to analyze the causes and influencing factors of torsional vibration of the dual-mode multi-stage gear power transmission mechanism of hybrid electric vehicles, a vehicle dynamics model was established based on SIMPACK. By applying excitation to the dynamic model and setting the output channel, a torsional vibration simulation system is constructed.

Abstract: In order to analyze the causes and influencing factors of torsional vibration of the dual-mode multi-stage gear power transmission mechanism of hybrid electric vehicles, a vehicle dynamics model was established based on SIMPACK. By applying excitation to the dynamic model and setting the output channel, a torsional vibration simulation system is constructed. The torsional vibration simulation system is used to analyze the vibration mode of the multi-stage gear transmission mechanism, and the results are compared and verified with theoretical calculations and experimental results. The results of the mode shape analysis of the torsional vibration simulation system are consistent with the theoretically calculated natural frequency of the transmission system and the main noise frequency obtained from the noise experiment, which proves the correctness of the construction system. On this basis, the influence of target optimization parameters such as the damping and stiffness changes of the damping shock absorber on the torsional vibration generated by the multi-stage gear transmission mechanism is analyzed. The results show that adjusting the parameters of the torsional vibration damper within an appropriate range has a better attenuation effect on the partial torsional vibration of the multi-stage gear transmission mechanism.

1 Introduction

Due to the continuous decline of the world’s oil reserves, the development of new energy vehicles is now the direction of development. Hybrid electric vehicles are a reliable alternative form of existing automobiles. Because of their NVH (Noise, Vibration and Harshness) issues, which have a great impact on passengers’ ride comfort, they have received more and more attention from manufacturers and research institutions.

There are many noise sources of hybrid electric vehicles, and the abnormal torsional vibration of the multi-stage gear transmission mechanism is an important noise source. Since hybrid vehicles adopt a dual-mode driving mode of pure electric drive and hybrid drive, the torsional vibration characteristics of the gear transmission mechanism are more complicated than those of ordinary automobiles. When there is excitation of input torque at the engine end and the drive motor end, the problem of abnormal forced torsional vibration will occur in the multi-stage gear transmission mechanism. When the interference frequency of the external excitation is equal to any natural frequency of the system, the transmission power flow transmission system will have strong forced torsional resonance, and the load on the corresponding components will increase significantly, which will seriously damage the components of the transmission system. And cause torsional vibration and discomfort. Therefore, it is very important to study the influencing factors and elimination methods of torsional vibration.

Some studies have analyzed the vibration problem of the vehicle power system.

Yang Yuan et al. used the method of individual sound power and spectrum analysis to identify the meshing noise generated by the transmission gear as the main reason for the noise of the electric drive powertrain system.

Chang et al. used the experimental method to verify the engine torque fluctuation as the excitation source of the powertrain, and proved that the excitation generated by the engine torque fluctuation is one of the main excitation sources of the torsional vibration of the powertrain.

Yue et al. analyzed the dynamic characteristics of the hybrid power system and studied the vibration characteristics of the system. According to the above research, the engine or electric motor is an important source of excitation for the torsional vibration of the transmission system. In order to reduce the vibration and noise of the transmission mechanism, relevant measures need to be taken. The use of a damping shock absorber is an effective measure to attenuate torsional vibration. When there is excitation at the power input end of the car, the gear transmission mechanism is one of the main assemblies that produce vibration and noise.

Paul D et al. studied the instantaneous vibration caused by the active damping of the automobile transmission system and proposed an active control strategy, and compared its application effects on traditional cars and hybrid cars. Lin Xinhai et al. analyzed the main factors affecting gearbox vibration through a combination of modal test and bench test.

Tang et al. conducted theoretical analysis and experimental verification on the noise source of the planetary gear structure of hybrid electric vehicles. The common point of these methods is to analyze the torsional vibration characteristics of gears based on theoretical calculations. The theoretical calculation method requires the establishment of an accurate gear mathematical model, and the calculation results are more accurate. However, for more complex transmissions, the system has more degrees of freedom, the process of establishing a perfect model is more cumbersome, and it is more difficult to modify the model. Once the model is wrong, it is more troublesome to modify.

Using Adams and other multi-body dynamics software for dynamic model construction and analysis is more convenient and intuitive, and can simulate the transmission characteristics of torsional vibration of the transmission mechanism. However, this method is difficult to accurately describe the meshing parameters of the gear pair model, so the effect of gear dynamics analysis is poor. Some researchers have proposed alternative methods. Hong Qingquan et al. proposed a method to establish a virtual gear pair model in Adams. This method takes into account the moment of inertia, equivalent damping and equivalent stiffness of the gear, and obtains the results of the gear dynamics analysis. A certain effect.

Yu et al. also used this method to analyze the torsional vibration characteristics of the planetary gear mechanism of hybrid electric vehicles, which provided a reference for the noise reduction research of hybrid electric vehicles, but this method only approximates the equivalent damping and equivalent stiffness of torsion springs. Instead of gear meshing, it is impossible to establish physical and material characteristic parameters such as gear modification coefficient, Poisson’s ratio, elastic modulus, tooth surface friction factor, etc., especially unable to simulate the comprehensive elastic deformation of a single pair of gear teeth, gear coincidence degree, gear The time-varying parameters of the damping change during meshing and the comprehensive stiffness change during gear meshing. This makes the analysis of gear torsional vibration characteristics by the method of virtual gear pair model and the actual situation have a certain error. Constructing an accurate hybrid transmission system model through a suitable method and analyzing its vibration characteristics are very helpful for the optimization of the target parameters of the hybrid multi-stage gear transmission mechanism.

In this paper, a multi-body dynamics model of the hybrid power transmission system based on SIMPACK is constructed, an accurate gear model is established in SIMPACK, and the gear meshing force element is used to establish the gear connection. The torsional vibration simulation system is established based on the built model, and the torsional vibration characteristics of the hybrid power transmission system are studied, and the torsional vibration characteristic frequency of each component and the influence of key parameters on the torsional vibration are analyzed.

2 Establishment of torsional vibration simulation system

The establishment of the dynamic model in SIMPACK is based on the characteristics of the mass and component distribution of the prototype transmission system, and the torsional vibration modeling of the hybrid powertrain shown in Figure 1 is carried out by using the discrete modeling method of multi-degree-of-freedom concentrated mass.

The following simplification principles should be followed when modeling:

(1) The stiffness of the connecting shaft between two adjacent concentrated masses is regarded as the stiffness between the concentrated masses, that is, the moment of inertia of the shaft is evenly distributed to the adjacent concentrated masses.

(2) The front and rear damping shock absorbers are respectively connected with the engine and planet carrier, which can be simplified into damped torsion springs. To analyze the torsional vibration of the planetary gear train, it is the key to establish the dynamic model of each meshing gear pair. In SIMPACK, accurate gear models can be built. The parameters that need to be input when building a gear pair model are: gear meshing form (outer, inner, rack), number of teeth, modulus, normal pressure angle, tooth tip height and tooth root height, helix angle, taper angle, backlash, Tooth width, initial angle of engagement. Gear meshing adopts special gear force element. The gear force element considers the physical and material characteristics of gear meshing stiffness, damping, gear modification coefficient, Poisson’s ratio, elastic modulus, and tooth surface friction factor. The torsional vibration mechanics model of the complete vehicle driveline is shown in the figure. Among them, in addition to the MEEBS power synthesizer, it also includes a damping shock absorber, left and right drive axles, and a pair of left and right wheels. In this model, the damping shock absorber is simplified to a torsion spring, the gear adopts the gear model provided by SIMPACK, and other parts are regarded as rigid components.

Analysis on the Causes of Torsional Vibration in the Dual-mode Multi-Gear Power Transmission Mechanism of Hybrid Electric Vehicles

In order to obtain the natural frequency and frequency response characteristic curve, the torsional vibration simulation system can be established in SIMPACK according to the established dynamic model. The torsional vibration simulation system can analyze the natural frequency and frequency response in the frequency domain. The system can set free vibration excitation as input. The simulation system consists of 3 parts, as shown in the figure. The first part is the motivation element. The excitation force element adopts the sinusoidal force of unit amplitude, and the initial phase angle is 0. The excitation frequency range continues to grow. The range is 1~5000 Hz, and the number of calculation steps is 10000. Calculate the natural frequencies under pure electric working conditions and hybrid working conditions respectively. The second part is the input channel. According to the operating conditions of the hybrid power transmission system, it is required to input the excitation from the engine end or the motor end. The third part is the output channel. The output channels can be set on the components of the built model according to the analysis requirements. Corresponding to the input channel, the test directions of the output parameters are x, y, z directions and the corresponding axial torsion direction.

Analysis on the Causes of Torsional Vibration in the Dual-mode Multi-Gear Power Transmission Mechanism of Hybrid Electric Vehicles

3 Conclusion

SIMPACK is used to construct a torsional vibration simulation system based on the optimization of target parameters, and the following conclusions are obtained through analysis:

(1) The comparison of simulation, theoretical calculation and experimental results verifies the correctness of the constructed system. The analysis of the results shows that in the pure electric working condition, the noise frequency is mainly concentrated near the high-order frequency of 1715 Hz. The noise source mainly comes from the gears in the planetary row. In hybrid power conditions, the noise frequency is mainly concentrated in the low order of 0~30 Hz. The noise at the engine and flywheel is the main noise source.

(2) By analyzing the influence of the characteristic parameters of the torsional vibration damper on the torsional vibration characteristics, it can be seen that when the engine is used as the input excitation source, the damping and stiffness adjustment of the torsional vibration damper has a relatively obvious weakening effect on the low-frequency torsional vibration, and It has little effect on high-frequency torsional vibration. When the main motor is used as the input excitation source, the adjustment of damping will weaken the high-frequency torsional vibration to a certain extent, but has no effect on the low-frequency torsional vibration. The adjustment of stiffness has a certain weakening of low-frequency torsional vibration, but has little effect on high-frequency torsional vibration.

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