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In electric vehicle applications, the majority of the traction motors can be categorized as Permanent Magnet (PM) motors due to their outstanding performance. As indicated in the name, there are strong permanent magnets used inside the rotor of the motor, which interacts with the stator and causes strong magnetic pulling force during the assembly process. How to estimate this magnetic pulling force can be critical for manufacturing safety and efficiency. In this paper, a full 3D magnetostatic model has been proposed to calculate the baseline force using a dummy non-slotted cylinder stator and a simplified rotor for less meshing elements. Then, the full 360 deg model is simplified to a half-pole model based on motor symmetry to save the simulation time from 2 days to 2 hours. A rotor position sweep was conducted to find the maximum pulling force position. The result shows that the max pulling force happens when the rotor is 1% overlapping with the stator core.

Electric motor whine is a major NVH source for electric vehicles. Traditional mitigation methods focus on e-motor hardware optimization, which requires long development cycles and may not be easily modified when the hardware is built. This paper presents a control- and software-based strategy to reduce the most dominant motor order of an IPM motor for General Motors’ Ultium electric propulsion system, using the patented active Torque Ripple Cancellation (TRC) technology with harmonic current injection. TRC improves motor NVH directly at the source level by targeting the torque ripple excitations, which are caused by the electromagnetic harmonic forces due to current ripples. Such field forces are actively compensated by superposition of a phase-shifted force of the same spatial order by using of appropriate current.

Electric motor noise mitigation is a challenge in electric vehicles (EVs) due to the lack of engine masking noise. The design of the electric motor mounting configuration to the motor housing has significant impacts on the radiated noise of the drive unit. The stator can be bolted or interference-fit with the housing. A bolted stator creates motor whine and vibration excited by the motor torque ripple at certain torsional resonance frequencies. A stator with interference fit configuration stiffens the motor housing and pushes resonances to a higher frequency range, where masking noise levels are higher at faster vehicle speeds. However, this comes with additional cost and manufacturing process and may impact motor efficiency due to high stress on stators. In this paper, a thin sheet metal NVH ring is developed as a tunable stiffness device between the stator and the motor housing. It is pre-compressed and provides additional torsional rigidity to mitigate torsional excitations.

Pulse Width Modulation or PWM has been widely used in traction motor control for electric propulsion systems. The associated switching noise has become one of the major NVH concerns of electric vehicles (EVs). This paper presents a multi-disciplinary study to analyze and validate current ripple induced switching noise for EV applications. First, the root cause of the switching noise is identified as high frequency ripple components superimposed on the sinusoidal three-phase current waveforms, due to PWM switching. Measured phase currents correlate well with predictions based on an analytical method. Next, the realistic ripple currents are utilized to predict the electro-magnetic dynamic forces at both the motor pole pass orders and the switching frequency plus its harmonics. Special care is taken to ensure sufficient time step resolution to capture the ripple forces at varying motor speeds.

Electric motor is among the main sources of noise and vibration for electrified propulsion systems. This paper focuses on the electric motor rotor NVH optimization, which is identified as a key enabler to reduce the motor whine, and balances other performance such as motor torque and efficiency. First, conventional rotor NVH design technologies such as rotor skew and asymmetric rotor pole-to-pole design are discussed, along with their associated tradeoff including reduced motor torque and additional sideband orders. Next, a special notch feature is proposed on the rotor surface with one notch per pole at every q-axis. A DOE study leads to the optimal notch design which significantly reduces the dominant motor torque ripple order by up to 20 dB, with minimum impact to motor torque or loss. Further design studies are then performed to explore additional d-axis notches which are symmetrically located within the top layer magnet opening angles.

Electric motor whine is one of the main noise sources of hybrid and electric vehicles. This paper describes a comprehensive analytical and experimental investigation of permanent magnetic electric motor NVH designs focusing on the contribution from torque ripple (TR) and radial forces (RF). A design-of-experiment method is adopted to design and build candidate motors with (i) high TR and high RF; (ii) high TR and low RF; (iii) low TR and high RF and (iv) low TR and low RF. Four prototype motors are built and tested on motor fixtures to measure dynamic stator forces in radial, tangential and axial directions, track dominant motor orders, and estimate motor Operational Deflection Shapes (ODS). Finite-element based electromagnetic and NVH analyses are performed and correlated to test data. Both tests and analyses confirm reducing TR and RF improves motor NVH performance at dominant pole pass orders.

Electric motor whine is one of the main noise sources of electric vehicles (EVs). Without engine masking noise, high pitch tonal noise from electric motor can be highly annoying and raise sound quality issues for electrified propulsion systems. This paper describes a patented new technology that controls electric motor to actively mask annoying high-pitch tonal noise by (i) controlling electric motor to create complementary low order tones to enrich sound complexity and distract high pitch tones; (ii) controlling motor to generate random dithering noise to raise masking noise floor and reduce tone-to-noise ratio around tonal targets; (iii) combining complementary injection at low frequency and dithering at high frequency for enhanced masking. This new technology enables controlling masking noise level, frequency, order and bandwidth as a function of motor torque and speed for most effective masking.

With the emphasis of electrification in automotive industry, tremendous efforts are made to develop electric motors with high efficiency and power density, and reduce noise, vibration and harshness (NVH). A multiphysics simulation workflow is used to predict the eccentricity-induced noise for GM’s Bolt EV motor. Both static and dynamic eccentricities are investigated along with axial tilt. Analysis results show that these eccentricities play a critical role in the NVH behavior of the motor assembly. Transient electromagnetic (EM) analysis is performed first by extruding 2D stator and rotor sections to form 3D EM models. Sector model is duplicated to form full 360-degree model. Stator is split into three rotated sections to characterize stator skew, and the skew between two sections of rotor and magnets are also modelled. Sinusoidal current is applied and lumped-sum forces on each stator tooth are computed.

Electric motor whine is one of the main noise sources of hybrid and electric vehicles. Compared with permanent magnetic motors, characterization and prediction of traction induction motor is particularly challenging due to high computational costs to calculate the electro-magnetic (EM) forces as noise source, as well as motor slip and harmonic orders change at different torque/speed operating conditions. Historically, induction motor NVH is designed qualitatively by optimizing motor topology including rotor bar, pole number and slot counts etc. A new integrated electromagnetic and NVH analysis method is developed and successfully validated at all dominant motor orders for an automotive traction motor, which enables quantitative prediction of induction motor N&V performance in early design stage: First, a new equivalent rotor current method is used that significantly reduces the computational time required to calculate the EM force over transient responses.

Electric motor whine is one of the main noise sources of hybrid and electric vehicles. Motor air gap eccentricity due to propulsion system deflection, part tolerances and manufacturing variation is typically ignored in motor NVH design and analysis. Such eccentricity can be a dominant noise source by amplifying critical motor whine orders up to 10 dB, leading to poor NVH robustness. However, this problem cannot be explained by conventional method based on symmetric 2D approach. New 3D electromagnetic (EM) and NVH analyses are developed and validated to accurately predict air gap induced motor noise to enhance NVH robustness: First, a true 3D full 360-degree electric motor model is developed to model asymmetric air gap distribution along motor stack length. Predicted 3D EM forces are mapped to mechanical finite-element mesh over the cylindrical stator surface.

A multi-stage system level method is used to design, optimize and enhance electric motor NVH performance of General Motors’ Chevrolet Bolt battery electric vehicle (BEV). First, the rotor EM (electromagnetic) design optimizes magnet placement between adjacent poles asymmetrically, along with a pair of small slots stamped near the rotor outer surface to lower torque ripple and radial force. The size and placement of stator slot openings under each pole are optimized to lower torque ripple and radial force. Next, motor stator level FE (Finite Element) analysis and modal test correlation are performed to benchmark the orthotropic stator material properties and accurately predict modal results within 7% error below 2 kHz. Furthermore, tangential and radial EM forces are applied on motor-in-fixture subsystem FE model, which predicts surface vibration and pseudo sound power on the motor housing.

Competing linear, quasi-linear and non-linear hydraulic mount formulations of fixed and free decoupler types are comparatively evaluated for transient responses. First, features of the realistic excitation conditions are addressed. For instance, the mean load itself may vary with time, and several sinusoidal or transient excitations may be simultaneously present. Second, a multi-staged top chamber compliance model is proposed to capture asymmetric transient responses given step-up (-down) excitations. Third, implicit excitations introduced by the decoupler switching mechanism are identified at the odd harmonics of the explicit excitation frequency. Fourth, discontinuous model of bottom chamber compliance is proposed depending on the operating point(s) and/or dynamic loading. Some of the discrepancies observed between prior models and measurements can be explained using new models.

This paper comparatively evaluates measurement-based quasi-linear and true non-linear (mechanical and fluid type) models of hydraulic engine mounts and examines their dynamic effects within the context of a simplified half-vehicle system. A non-linear approximate model is also developed to provide improved insight into the decoupling effects. The proposed model is validated by comparing predictions with those from a “true” non-linear fluid model. When embedded into the vehicle system, hydraulic mount efficiently provides high amplitude-sensitive damping and tunes the engine bounce mode. Proposed model concepts could be effectively utilized to examine linear and non-linear vehicle responses in both time and frequency domains.

The major objectives of this study are to identify the source(s) of high frequency resonance(s), suggest a method to effectively estimate mount parameters and propose both linear and nonlinear models capable of predicting the high frequency characteristics. First, a lumped parameter linear model is derived and the resonances controlled by decoupler, fluid column and rubber element are examined. By using a simplified mechanical model, typical parameters are estimated from measured dynamic stiffness data. Estimations correlate well with experiments and provide quantitative evaluation of the physical parameters, some of which (such as the decoupler damping) are otherwise difficult to measure by using conventional experimental techniques. A nonlinear time domain model for a free decoupler mount is proposed to predict both the inertia track and decoupler resonances. Both nonlinear and linear models match well with high frequency measurements.

New procedures are proposed to estimate the amplitude-sensitive parameters of hydraulic engine mounts that typically exhibit many nonlinearities. The estimation is based on the premise that the analyst has access to limited dynamic stiffness test data (say up to 50 Hz), and the detailed laboratory work required for the nonlinear model development would be minimized. By using an analogous mechanical model, a 3rd/2nd type transfer function is suggested to curve-fit the empirical dynamic stiffness data. Key parameters (such as the inertia-augmented fluid damping and decoupler gap length) are approximated and the effects of some system nonlinearities (such as the vacuum-induced asymmetric chamber compliance) are quantified, leading to a quasi-linear model. For the sake of illustration, transient predictions for a free decoupler mount are made; simulations match well with measurements. Main simplifications and limitations of the method are briefly discussed.