Identifying Dynamic Characteristics of the Traction Motor Housing for the Noise Reduction of the Electric Vehicle

Transcription

1 EVS28 KINTEX, Korea, May 3-6, 2015 Identifying Dynamic Characteristics of the Traction Motor Housing for the Noise Reduction of the Electric Vehicle Jongchan Park 1, Seungyong Park 1 Electric Power Engineering Team, HyundaiMobis, 17-2, 240 Beon- Gil,Mabuk-Ro, Giheung-Gu, Yongin-Si, Gyeonggi-Do, , Korea, jcp@mobis.co.kr

2 Introduction Global warming, CO 2, and Fossil FUEL Global warming issues with CO 2 emission by cars and rapidly diminishing fossil fuel have forced car manufacturers to develop more environmentally friendly and fossil fuel free cars. In order to meet this demand, there have been comprehensive researches on electric cars mainly in that electric vehicles have zero CO 2 emission and can enhance fuel efficiency using regenerative braking in which they recover kinetic energy and charge battery during deceleration and stop 1), 2). Main issues in developing Electric vehicles are performance and efficiency such as increasing efficiency of traction motor and extending EV range along with cooling problems and reliability of the electric parts and battery on severe environments. Trucks and cars account for 79% of the transportation related GHG emissions Source: National Aeronautics and Space Administration Goddard Institute for Space Studies 1. Y. Gao, L. Chen, M. Ehsani, Investigation of the Effectiveness of Regenerative Braking for EV and HEV., SAE Paper F.A. Wyczalk, Regenerative Braking Concepts for Electric Vehicle-A Primer, SAE

3 Introduction Nonlinearity In structural dynamics, typical sources of nonlinearities (3) are: - Geometric nonlinearity results when a structure undergoes large displacements and arises from the potential energy. - Inertia nonlinearity derives from nonlinear terms containing velocities and/or accelerations in the equations of motions, and takes its sources in the kinetic energy of the system. - Nonlinear material behaviors may be observed when the constitutive law relating stresses and strains is nonlinear. - Damping dissipation is essentially a nonlinear and still not fully modeled and understood phenomenon. The modal damping assumption is not necessarily the most appropriate representation of the physical reality, and its widespread use is to be attributed to its mathematical convenience. Dry friction effects (bodies in contact, sliding with respect to each other) and hysteretic damping are examples of nonlinear damping. - Nonlinearity may also results due to boundary conditions ( for examples, free surfaces in fluids, vibro-impacts due to loose joints or contacts with rigid constraints, clearances, imperfectly bonded elastic bodies), or certain external nonlinear body forces. Clearance and vibro-impact nonlinearity possesses non-smooth force-deflection characteristics and generally requires a special treatment compared with other types of nonlinearities. Among those various sources of nonlinearity, friction and contact boundary condition were studied in this research. 3. G. Kerschen, K. Worden, A. F. Vakakis, J. Golinval, Past, present and future of nonlinear system identification in structural dynamics, Mechanical Systems and Signal Processing, 20 (2006)

4 Noise Problem of EV In the view of NVH, electric vehicles are known as more silent than conventional vehicles because they remove combustion engines which are the main source of the noise and vibration of vehicles. However, in practical development processes noise issues on electric vehicles are more complicated. Quieter environments in a passenger cabin using electric motors for traction of the car instead of combustion engines make passengers feel uncomfortable to moderate noise. Vehicle Noise Sources - fuel explosion/muffler noise/ - shifting shock/crank pulsation - wind noise/tire noise - electric components Vehicle Sound for Pedestrians (VSP) - Quieter road noise of EV Publicity workshop in Japan, where visually-impaired had to raise their hands as soon as they heard the approaching car. Augustus 2009, [4]. 4

5 Road noise of Electric vehicle Physically, noise is a complex stimulus made of several 36 th 40 th 44 th 48 th mechanical vibrations or pressure fluctuations that are disseminated in elastic means. The auditory representation of a sound depends on specific physical parameters, namely frequency, period, and amplitude. Vehicle noise measured at the driver s ear point shows higher noise in low frequency, however test drivers feel annoyance at the circled region not boxed area even though physical level of noise of boxed area is much higher. Vehicle noise at diver s ear 5

6 Tacho1 (T1) rpm db(a) Pa Identification of the annoyance Among the various noise components, harmonic orders in the boxed area region are the 36 th, 40 th, 44 th and 48 th orders, which are the expected order components in Table 1. All the components boxed region B corresponds to electromagnetic origins. Interesting phenomena are founded in Fig. 5(b) which is the order slices of 36 th, 40 th, 44 th and 48 th noise. As the rpm goes higher, 48 th, 44 th, 40 th and 36 th noise peaks appear in turn with increasing rpm around 4,000rpm and 8,000rpm th 44 th 40 th 36 th Dynamo test AutoPower mic : 측면 :S (A) WF 576 [ rpm] Harmonic Order EMF EMF where : EMF EMF N SS S R S R, N N N respectively excitation P number of P P number of pole Freqeuncy rpm 60 excitation fron stator slot RS SS RS from rotor slot stator slot and rotor slot, Table 1 Parts Slot number Excitation orders Hz mic : 측면 :S (CH4) Traction motor noise Stator th, 36 th, 40 th Rotor th, 44 th, 48 th 6

7 db(a) Pa db(a) Pa Identification of the noise source order cuts of 36 th, 40 th, 44 th and 48 th noise. As the rpm goes higher, 48 th, 44 th, 40 th and 36 th noise peaks appear in turn with increasing rpm around 4,000rpm and 8,000rpm. Curv e Max rpm @ rpm db(a) Order mic : 측면 :S (A) _LMFC#1_ 1 Order mic : 측면 :S (A) _LMFC#1_ 1 Order mic : 측면 :S (A) _LMFC#1_ 1 Order mic : 측면 :S (A) _LMFC#1_ 1 48 th : 2959Hz Curv e Max rpm @ rpm db(a) @ rpm db(a) @ rpm db(a) @ rpm db(a) rpm Order Frequency 44 th : 40 th : 36 th : 3,006Hz 3,006Hz 3,006Hz 6,800rpm 7,400rpm 8,800rpm - 6,800/60*44= 4,986Hz Not depend on the rpm increase. - 7,400/60*40= 4,933Hz Contributions of Structural resonance. - 8,800/60*36= 5,279Hz 7

8 db/1 [(m/s2)/n] db/1 [(m/s2)/n] db/1 [(m/s2)/n] Pa db(a) Pa db(a) Contributions of structural resonance Overall level mic : 측면 :S (A) _LMFC#1_ 1 Traction motor noise and structural resonance Curv e Max rpm Order mic : 측면 :S (A) _LMFC#1_ 1 Order mic : 측면 :S (A) _LMFC#1_ 1 Order mic : 측면 :S (A) _LMFC#1_ 1 Order mic : 측면 :S (A) _LMFC#1_ @ rpm db(a) Curv e Max rpm @ rpm db(a) @ rpm db(a) @ rpm db(a) @ rpm db(a) rpm Frequency Traces: 1/1 Compressed Frequency [Hz] ( x E3 ) Frequency Traces: 1/1 Compressed Frequency [Hz] ( x E3 ) Frequency Traces: 1/1 Compressed Frequency [Hz] ( x E3 ) Sample #1 Sample #2 Sample #3 Noise from structural resonance at around 5kHz 8

9 Structure of traction motor Structural layout of the traction motor for EVs are presented. Housing is a framework of the motor. Stators which generate an electric field and front and rear covers which support rotors are assembled into the housing. For the case of the given traction motor the housing has two layer, inner and outer housing. Inner housing is fitted into the heated outer housing, which assigns some designed interference fit when it cooled as shown in the figures. After assembling, both end of the housing is welded together. There are cooling channels between the outer and inner housing for the cooling of the motor. Cooling channels are needed to cool out the heat generated in the stator coil. The existence of the cooling channel for almost all traction motors means a cavity in the frame. It makes the structure week and more vulnerable to NVH Problems. However, in almost all cases of the engineering applications efficiency and reliability performance is prior to noise. In electrical design reduction of electrical losses by cooling the stator is essential to improve the efficiency of the motor. Inner housing stator rotor Outer housing 5. Lee J. H., Ha M.J., S. Kang, Park Y. J, Thermal Analysis of Electric Vehicle Motor Using CFD, KSME,

10 Identification of the structural dynamics Noise reduction according to design modification of housing : Noise reduction was achieved by design modification of the interference fit of the inner and outer hosing of the traction motor( clearance modification) : Base model(design parameter A) and modified model (design parameter B) shows different noise but convectional FRF comparison cannot explain the noise response and design change. Need to assess dynamic characteristics of the housing for nonlinear structure : contact nonlinear 10

11 FRF K_d FRF and Dynamic Stiffness Frequency response function(frf) and Dynamic stiffness(k-d) of the system using conventional modal test cannot explain dynamic characteristics of the system which contribute noise reduction. Nonlinearity of the interference fit assemble of the inner and outer housing caused the complexity. 1.E+10 30dB 30dB 소음개선 K-D 1.E+09 Param A Param B - Parameter A - Parameter B Frequency [Hz] Frequency response function(frf) 1.E Hz Dynamic stiffness(k-d) Contact nonlinearity of the housing makes difficult to identify dynamic characteristics of the housing structure 11

12 Coherence- Nonlinearity of the press-fitted structure Coherence of the impact force Frequency [Hz] Interference fit assembly of the housing contributes strong contact nonlinearity, which makes it difficult to identify dynamic characteristics of the structure. In modal test, Impact forces are strongly influenced by the stiffness of the structure including the contact status of the test structure. 15dB 15dB Auto-Spectrum of the impact force 12

13 Auto-Power-Spectrum characteristics Dynamic characteristics of impulsive force of the test influenced by hammer tips according to the hammer tip choices, which phenomenon can be used to identify the assembly integrity Impact Excitation - Hammer Tip Selection Hammer & tips 6. SEM Experimental Techniques - October 1998 by Peter Avitabile 13

14 APS db [N 2 ] Auto-Power-Spectrum of impact force Representation of dynamic characteristics of assembled structures using APS of impact force : APS can be used to compare integrity of the assembly of Structures which show strong nonlinearity. For the given system over of correlation coefficient is required. Input Force APS dB # 소음양호한주신작한주신작 2 Auto-power-spectrum y = E-07x E-05x E+00 R 2 = E-01 Parameter A Parameter B y = E-07x E-03x E+00 R 2 = E-01 R 2 : Correlation Coefficient y = E-07x E-03x E+00 R 2 = E y = E-07x E-03x E+00 R 2 = E Hz

15 Conclusions Assessment of the dynamic characteristics of the traction motor housing is presented. Comparison analysis of the vehicle and traction motor noise spectrum illustrated that electromagnetic harmonic orders of the induction motor are directly related with the tonal noise. Modal test results of the traction motor showed that resonances of the traction motor frame coincide with the frequency range of tonal noise. Based on the simple idea that impact forces of modal tests are highly af fected on the condition of the hammer tip, Auto Power Spectrum of the impact forces are used to assess the assembling condition and dynamic characteristics of the system, especially, damping of the system.