NVH Technologies and Challenges on Electric Powertrain

<div class="section abstract"><div class="htmlview paragraph">The Environmental Protection Agency (EPA) requirement for 54.5mpg by 2025 to reduce greenhouse gases has pushed the industry to look for alternative fuels to run vehicles. Electricity is of those green energies that can help auto industry to achieve those strict requirements. However, the electric or hybrid-electric vehicles brought new challenges into science and engineering world including the Noise and Vibration issues which are usually tied up with both airborne and structural noises. The electromagnetic force plays a significant role in acoustic noise radiation in the electric motor which is an air-gap radial Maxwell force.</div><div class="htmlview paragraph">This paper describes an innovative approach to model the physics of noise radiated by the electric motor. In order to compute the sound power level radiated by electric motor, the dynamic response of the structure is obtained by decomposing the electromagnetic force integrated with the Finite Element (FE) modelling of stator structure as an equivalent cylinder subjected to several sinusoidal distributed loads. Moreover, the modal response through Frequency Response Function (FRF) which is characterized by spatial orders is experimentally identified by measurement through the acoustic test. In the next step, an acoustic FE/BE model is used by taking the vibration velocity into account as a boundary condition for calculation of the vibrating structure radiation and the radiated sound pressure. Finally, the noise radiated by electric motor is identified through the FE simulation and confirmed by experimental measurement. This methodology gives rise to a fundamental understanding of how the electric motor as a noise and vibration subsystem behaves.</div></div>

<div class="htmlview paragraph">Low frequency torsional vibrations can be a significant source of objectionable vehicle vibrations and in-vehicle boom, especially with changes in engine operation required for improved fuel economy. These changes include lower torque converter lock-up speeds and cylinder deactivation.</div> <div class="htmlview paragraph">This paper has two objectives: <ol class="list nostyle"> <li class="list-item"><span class="li-label">1)</span><div class="htmlview paragraph">Examine the effect of increased torsional vibrations on vehicle NVH performance and ways to improve this performance early in the program using test and simulation techniques. The important design parameters affecting vehicle NVH performance will be identified, and the trade-offs required to produce an optimized design will be examined. Also, the relationship between torsional vibrations and mount excursions, will be examined.</div></li> <li class="list-item"><span class="li-label">2)</span><div class="htmlview paragraph">Investigate the ability of simulation techniques to predict and improve torsional vibration NVH performance. Evaluate the accuracy of the analytical models by comparison to test results.</div></li> </ol> </div> <div class="htmlview paragraph">A simple model is presented which gives fairly accurate results and can be included in a full vehicle finite element model to calculate vehicle level NVH responses. A procedure to calculate the loads to be applied to the model is also presented.</div>

<div class="htmlview paragraph">It is desirable for engines to produce high torque in lower speed ranges. Such conditions are encountered when vehicles climb gradients. Two techniques are compared in this paper along with their merits and demerits to improve torque of a CI engine for lower speeds.</div> <div class="htmlview paragraph">The first method increases swirl at lower speed whereas the second method uses a combined charging system to improve airflow rates.</div> <div class="htmlview paragraph">Matching of Turbocharging equipment with diesel engine throughout the operating speed range has also been discussed in this paper. Combining both methods, provides excellent torque characteristics at lower speeds without increase in smoke and other emissions. This improves driveability of the vehicles.</div>

<div class="section abstract"><div class="htmlview paragraph">The increasing trend toward electric and hybrid-electric vehicles (HEVs) has created unique challenges for NVH development and refinement. Traditionally, characterization of in-vehicle powertrain noise and vibration has been assessed through standard operating conditions such as fixed gear engine speed sweeps at varied loads. Given the multiple modes of operation which typically exist for HEVs, characterization and source-path analysis of these vehicles can be more complicated than conventional vehicles.</div><div class="htmlview paragraph">In-vehicle NVH assessment of an HEV powertrain requires testing under multiple operating conditions for identification and characterization of the various issues which may be experienced by the driver. Generally, it is necessary to assess issues related to IC engine operation and electric motor operation (running simultaneously with and independent of the IC engine), under both motoring and regeneration conditions. Additionally, mode transitions, including IC engine start/stop must be assessed.</div><div class="htmlview paragraph">An analysis is presented here, which explores the differences in NVH performance of multiple HEVs currently available in the US-market. Measurements were conducted on these vehicles to assess noise and vibration at the powertrain-level and vehicle interior. Two of the vehicles included in this investigation were then chosen for a more in-depth comparative analysis. The analysis of these two vehicles included assessment of source level excitations and vehicle NVH sensitivities, in the context of boundary conditions driven by their hybrid system architectures.</div><div class="htmlview paragraph">Based on the powertrain and vehicle NVH performance assessments, methods were explored for developing powertrain level NVH targets. For the initial phase of this target cascading process, the analysis was limited to full load (IC engine operational) and part load (EV-only) modes. Based on in-vehicle performance, and vehicle sensitivity information, test procedures and targets were defined for powertrain radiated noise and mount vibration content.</div></div>

<div class="section abstract"><div class="htmlview paragraph">NVH predictions have gained importance since last few decades due to increased focus on ride comfort as competitive advantage within cost target. Hence, NVH CAE has become integral part of product development process for early issue identification and solutions. To make NVH simulation robust, continuous improvement is required in existing CAE processes.</div><div class="htmlview paragraph">In automobile powertrains, components are connected with each other through fasteners. Gaskets are sandwiched at periphery between two mating components, while the components are bolted together with required torque. Gaskets are used to prevent leakage of oil and gases into the atmosphere while operation. NVH CAE modeling practices globally are evolved with considering gaskets as one of the less important modelled components. However, these practices miss to consider its effects considerably on NVH performance.</div><div class="htmlview paragraph">Scope of this paper is to address the gaps present in the existing powertrain modeling techniques with the introduction of gasket. First the impact of gasket inclusion is studied at the experimental level. Then modified CAE modeling process is proposed with modal correlations perspective.</div></div>

<div class="section abstract"><div class="htmlview paragraph">While designing the exhaust system of passenger car on one hand there is stringent emission regulations, packaging constraints, high NVH performance requirement. On the other hand with lightweight vehicle design there is tremendous pressure on weight reduction of exhaust system while keep the same NVH performance levels. Exhaust system consist of muffler, bellows, pipes and hangers. For muffler design both acoustic (transmission loss, pass-by noise, tail pipe noise etc.) and non-acoustic (backpressure) parameters needs to be considered.</div><div class="htmlview paragraph">In the current paper, methodology for muffler design optimization using 1D acoustic simulation software is presented. The baseline exhaust design consist of two mufflers; main muffler and post muffler. Simulation methodology is developed to optimize main muffler design in order to eliminate post muffler requirement while achieving the same performance of baseline exhaust design. For this purpose a DOE study is conducted by varying primary muffler internal pipe dimensions, baffle location, perforation etc. to achieve transmission loss (TL) and backpressure (BP) of the baseline design.</div><div class="htmlview paragraph">Based on simulation study a physical prototype is made for optimized exhaust design consisting of only main muffler (with modified design compared to baseline main muffler). Transmission loss and backpressure is measured physically and confirmed that the optimized exhaust design is able to deliver the same NVH performance as that of the baseline exhaust design. Furthermore, a vehicle level physical test is conducted to compare the pass-by noise for optimized exhaust design and compared with baseline exhaust design. It is observed that the optimized exhaust design with one muffler is able to maintain the same pass-by noise level as that of the baseline exhaust design with two mufflers.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Honda has developed the 2018 model CLARITY PLUG-IN HYBRID. Honda’s new plug-in hybrid is a midsize sedan and shares a body platform with the CLARITY FUEL CELL and the CLARITY ELECTRIC. The vehicle’s electric powertrain boosts driving performance as an electric vehicle (EV) over Honda’s previous plug-in hybrid.</div><div class="htmlview paragraph">The CLARITY PLUG-IN HYBRID’s electric powertrain consists of a traction motor and generator built into the transmission, a Power Control Unit (PCU) positioned above the transmission, an Intelligent Power Unit (IPU) fitted under the floor, and an onboard charger fitted below the rear trunk.</div><div class="htmlview paragraph">The PCU integrates an inverter that drives the traction motor, an inverter that drives the generator, and a DC-DC converter to boost battery voltage (referred to as a “Voltage Control Unit (VCU)” below). The VCU employs an interleaved circuit configuration and a coupled inductor and realizes approximately three times the rated continuous power and approximately three times the power density of a standard unit employed in a hybrid vehicle.</div><div class="htmlview paragraph">The IPU contains 17 kWh high-capacity battery modules and a 12 V DC-DC converter. A coolant-cooling method has been adopted to respond to the increased power of the battery, boosting cooling performance. The battery modules are positioned below the front and rear seats, and the high-voltage wiring is positioned between the modules, in the center of the vehicle. This layout has made it possible to fit the IPU below the floor of the vehicle, helping to enable the realization of a spacious and comfortable cabin seating five passengers, as well as a useful amount of trunk space.</div><div class="htmlview paragraph">The use of a high-power VCU and a high-capacity IPU has made it possible to realize EV operation in the high-speed range with no need to start the engine, giving the vehicle an adequate all-electric range (AER) for everyday use. During hybrid operation, increasing both the VCU power and the battery power helps ensure quietness while also allowing the engine to be downsized from 2.0 to 1.5 liters. The developed electric powertrain realizes a long AER of 47 miles and extremely quiet hybrid operation with a high level of fuel economy at 42 mpg.</div></div>

<div class="htmlview paragraph">As the community is becoming more and more aware and conscious of the pollution problems caused by the internal combustion engine and its use in transportation, we are now seeing the first projects and prototypes regarding hybrid and electrically-powered vehicles.</div> <div class="htmlview paragraph">One of the main problems witnessed by engineers has been that of the relatively low operating range provided by the storage batteries available on the market today, and so, recovering the energy that is inevitably lost during braking is of primary importance.</div> <div class="htmlview paragraph">The concept of regenerative braking is fairly simple as it consists in making the electric motors function as generators.</div> <div class="htmlview paragraph">In many of today's applications we find two indipendent controls for the operation of the hydraulic brake and for the activation of regenerative braking. The choice on which braking mode to use, or in which sequence the two modes are to be used is left to the driver who, at the onset of braking, is forced to make mental considerations in order to activate the two braking modes in the right sequence. Furthermore, the driver must not forget to disable the regenerative function at the end of each stop.</div> <div class="htmlview paragraph">BREMBO has designed a braking system in which a single control, that is, the brake pedal, activates and disables in the right sequence the two different braking modes, thus allowing:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">to maximize energy recovery by the electric motors each time the driver steps on the brake pedal;</div> </li> <li class="list-item"> <div class="htmlview paragraph">the hydraulic brake to be used in addition to regenerative braking when the latter is not enough to produce the required deceleration.</div> </li> </ul> </div> <div class="htmlview paragraph">The proposed braking system is lightweight and versatile. It can be adapted to the different powertrain configurations seen on various electric vehicles.</div>

<div class="section abstract"><div class="htmlview paragraph">Over recent years, NVH refinement of engine is becoming increasingly important in buying decision and can significantly give competitive edge to the vehicle in market place. This paper deals with the development phase of a prototype engine in which a specific testing activity was carried out to improve the overall NVH behavior of the powertrain. In order to explain the optimization process in detail, a case study was described in this paper.</div><div class="htmlview paragraph">First, NVH targets of the engine were set via benchmark tests on existing competitive products. Then series of baseline tests, such as 1M sound pressure level test and noise source identification, were performed on the engine. Test results indicated that an obvious breathing vibration mode exist near the intake manifold, which radiates high level noise.</div><div class="htmlview paragraph">In order to achieve the NVH targets, a correlation validation was performed to find out the main reason that caused the vibration of intake manifold. And then its structure was optimized through CAE analysis to change its modal frequencies.</div><div class="htmlview paragraph">After the optimization work, the NVH performance of the engine was significantly improved.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Hybridization of vehicle drive train is an important step to increase energy security, reduce crude oil import, improvement of air quality and GHG reduction. Heavy traffic congestion poses a great challenge in improvement of fuel economy. Nowadays urban climatic condition forces the passenger to keep air-conditioning (AC) on; thus further decreasing the fuel economy. In a typical urban drive; the vehicle commutes with low speed forcing IC Engine to run in its low efficiency operational points. Further it is characterized by frequent start-stop and crawling. It has been observed that the power consumption for AC is comparable to that required for the vehicle propulsion. Hence the AC on condition with propelling vehicle demands higher power from engine creating a challenge for fuel economy improvement. It is observed in literature and simulation exercises that the fuel economy sharply falls with AC on condition in urban drive cycle and worsens in frequent start-stop and city traffic crawling. A study is required to study the improvement of fuel economy in a hybrid vehicle with AC on condition. Most of the work published in literature focuses on improvement in fuel economy with hybridization without air-conditioning operational.</div><div class="htmlview paragraph">The paper describes the techniques to improve fuel economy of a hybrid electric vehicle with AC on condition for a typical urban and city traffic crawling conditions. The hybrid configuration selected for study is a parallel hybrid with dual AC clutch which enables the drive of AC compressor by electric motor or IC Engine. Different hybrid control strategies for AC control, with compressor driven by IC engine alone; electric motor alone and blend of both were simulated for fuel economy on various city and city traffic drive cycles. The AC compressor drive control was based on vehicle speed; gradient requirement; Battery SOC; idle start-stop conditions and gear engaged. The control strategy parameters for IC Engine shut-off at different battery SOC levels; torque split quantity from both electric motor and IC engine for vehicle propulsion and AC compressor load sharing by electric motor and IC engine, based on battery SOC and vehicle demand were optimized to achieve maximum fuel economy. An improvement of 25-30 % in fuel economy was achieved with optimized AC control over the conventional vehicle in all city traffic conditions. All the simulations were done without downsizing the AC compressor; thus providing the same comfort to the passenger as experienced in conventional vehicles.</div><div class="htmlview paragraph">Thus it has been found out that optimized control of Dual clutch AC in hybrid vehicle plays a significant role in fuel economy improvement. The enhanced performance of the hybrid vehicle is achieved with keeping the AC capacity at par with the conventional vehicle.</div></div>

<div class="htmlview paragraph">Cycle-resolved numerical and experimental analyses were carried out to study the dynamics of an automotive diesel injection system with a distributor-type pump during transient control phases. The investigation had the following main objectives: to assess a flexible and efficient simulation program of high-pressure fuel-injection systems in unsteady operating conditions; to examine the system response to rapid load or speed variations, regardless of the control device which may cause them. The program, based on a fast implicit numerical algorithm with second-order accuracy, was an extension of the computational code NAIS which had been previously developed and validated for stationary operating conditions. The experiments were made on a test bench usually used by industry to evaluate diesel injection equipment.</div> <div class="htmlview paragraph">A nonlinear system numerical model with two degrees of freedom, developed for the pump speed-governor, was set up and included in a library containing a variety of system component models so as to give a modular structure to the NAIS code. Comparison between computed and measured static characteristics of the governor was made in order to assess the model of this system component.</div> <div class="htmlview paragraph">Experimental tests were carried out by rapidly moving the pump control lever from its idle position to the full-load position at two constant pump speeds, in the low and high-speed range, respectively. During these transient operations pressure time-histories were gauged and simulated cycle-by-cycle in the pumping chamber and at the distribution-pipe ends. In-cycle fuel-injected quantities were also measured and computed. Results were compared and discussed.</div> <div class="htmlview paragraph">The dynamic system behavior under assigned transient load or speed phases was then theoretically analyzed by computing local-pressure, needle-lift and injection-rate time histories. Besides, experimental steady-state distributions of the injection rate and injection pressure, that is the pressure in the sac chamber, were compared to the simulation results during an acceleration phase at full load.</div>

<div class="section abstract"><div class="htmlview paragraph">Hybridization is a promising way to further reduce the CO<sub>2</sub> emissions of passenger vehicles. However, high engine efficiencies and the reduction of engine load, due to torque assists by an electric motor, cause a decrease of exhaust gas temperature levels. This leads to an increased time to catalyst light-off, resulting in an overall lower efficiency of the exhaust aftertreatment system (ATS). Especially in low load driving conditions, at cold ambient temperatures and on short distance drives, the tailpipe pollutant emissions are severely impacted by these low ATS efficiency levels.</div><div class="htmlview paragraph">To ensure lowest emissions under all driving conditions, catalyst heating methods must be used. In conventional vehicles, internal combustion engine measures (e.g. usage of a dedicated combustion mode for late combustion) can be applied. A hybrid system with an electrically heated catalyst (EHC) enables further methods such as the increase of engine load by the electric motor or electric catalyst heating. Since these methods result either directly or indirectly in additional fuel consumption there is a conflict of objectives between a fast catalyst heat-up and the reduction of fuel consumption.</div><div class="htmlview paragraph">This trade-off is addressed by an energy and emission management, which controls the split of the propulsion power between the combustion engine and electric motor, the electric catalyst heating and the selection of the combustion mode. Such a management system, based on offline-optimized rules, is presented in this paper. The results for different driving cycles are compared to those from a conventional non-hybrid vehicle in a detailed simulation framework, for a 48V P0 Diesel hybrid including an exhaust aftertreatment system with EHC. With the help of the EHC the NO<sub>x</sub> level was reduced significantly especially during city and short distance drives. On the WLTC a CO<sub>2</sub> saving of 7 % was achieved, maintaining the same NO<sub>x</sub> emissions level.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The motor generator unit installed on the turbocharger shaft (MGU-H) provides a fundamental contribution to the amazing performances and efficiency of the last Formula 1 power units. The excess of exhaust gas energy - normally dumped through the waste-gate - can be converted into electric energy and used to push the car, by means of a second motor generator unit installed on the engine crankshaft (MGU-K).</div><div class="htmlview paragraph">The goal of this paper is to assess pros and cons of the MGU-H technology when applied to a family of engines of different displacement, installed on a typical passenger car. The influence of engine size and cylinders layout is investigated, under the same set of hypotheses, considering both transient and steady engine operations.</div><div class="htmlview paragraph">The baseline engine is a commercial 2.0 L, SI, 4-cylinder in-line, rated at 200 HP at 4500-5000 rpm. The study considers the following other SI configurations: a) 1.5L, 3-cylinder in-line, 150 HP; b) 3.0L, V6, 300 HP; c) 4.0L, V8, 400 HP; d) 6.0L, V12, 600 HP. It is assumed that all the 5 engines have the same unit displacement and the same maximum load, expressed in terms of brake mean effective pressure as a function of rotational speed.</div><div class="htmlview paragraph">The study is carried out using an experimentally calibrated GT-Power model of the baseline engine, and considering the same class C vehicle. A Matlab/Simulink model is also developed for the analysis of the WLTP driving cycle.</div><div class="htmlview paragraph">The study demonstrates that the MGU-H technology can be conveniently applied to all the considered engines. The maximum advantage in terms of fuel saving on a driving cycle is obtained on the smallest. However, in the V6, V8 and V12 configurations, the installation of one electric turbocharger instead of two, strongly simplifies the engine layout, and it allows the designer to find some space for additional powertrain components, such as electric motors, battery packs, etc. Moreover, the elimination of the turbo-lag problem, gives the designer much more freedom, enabling the adoption of more fuel efficient engine settings.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Hybrid electric vehicle (HEVs) represents a promising approach to reduce vehicle fuel consumption and exhaust emissions. However, due to the electric motor (EM) assistance, the engine load could be reduced and intermittent operation of engine is realizable in HEVs powertrain system. Consequently, the HEV powertrain heating-up process and engine fuel consumption will be changed accordingly.</div><div class="htmlview paragraph">Therefore, the influences of the EM power and battery capacity on the hybrid powertrain heating-up process and the engine fuel consumption will be analyzed, and 2 methods for optimizing the heating-up process by applying the auxiliary heaters (AHs) and the modification of the energy management strategy are represented.</div><div class="htmlview paragraph">The application of AHs can improve engine efficiency during heating-up; the controlling of the power flow from the AHs to the ICE cooling system is of special important. Accordingly, a thermal and energy management strategy (TEMS) is introduced in this paper to find a balance between fuel consumption and heating-up.</div><div class="htmlview paragraph">The TEMS is based on model predictive control (MPC) and dynamic programming (DP). MPC analyzes the forthcoming vehicle speed profile, calculates the power requirement and controls the AH accordingly. A cost function is then formulated based on the battery SOC and other driving conditions. DP solves the objective function and optimizes the power distribution between electric motor and engine.</div><div class="htmlview paragraph">The effects of the two methods are demonstrated by simulation in Matlab/Simulink. Simulation results are compared to demonstrate the optimized heating-up process.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The noise performance of fully electric vehicles is essential to ensure that they gain market acceptance. This can be a challenge for several reasons. Firstly, there is no masking from the internal combustion engine. Next, there is pressure to move to cost-efficient motor designs such as Switched Reluctance Motors, which have worse vibro-acoustic behaviour than their Permanent Magnet counterparts. Finally, power-dense, higher speed motors run closer fundamental frequency to the structural resonances of the system [<span class="xref">1</span>]. Experience has shown that this challenge is frequently not met. Reputable suppliers have designed and developed their “quiet” subsystems to state of the art levels, only to discover that the assembled E-powertrain is unacceptably noisy.</div><div class="htmlview paragraph">The paper describes the process and arising results for the noise simulation of the complete powertrain. The dynamic properties are efficiently modelled as a complete system and subjected to motor excitation (torque ripple, electro-magnetic forces and rotor imbalance). Innovation in this project comes from the speed of the modelling and analysis, so that analysis and data interpretation comes early enough in a project to be effective in reducing the noise problems. This contrasts with the approach of simulating problems that have already occurred in testing.</div><div class="htmlview paragraph">Actions to reduce the motor noise are explained and identified. System dynamic response identifies the operating points in which different excitation mechanisms are most problematic and steps are taken to reduce the dynamic response. Also, problematic conditions can be identified where innovative motor control algorithms are necessary.</div></div>