Quantification of Diesel Engine Vibration Using Cylinder Deactivation for Exhaust Temperature Management and Recipe for Implementation in Commercial Vehicles
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Downloaded from SAE International by Audra Ziegefuss, Tuesday, May 21, 2019 2018-01-1284 Published 03 Apr 2018 Quantification of Diesel Engine Vibration Using Cylinder Deactivation for Exhaust Temperature Management and Recipe for Implementation in Commercial Vehicles Akibi Archer and James McCarthy Jr Eaton Corporation Citation: Archer, A. and McCarthy Jr, J., “Quantification of Diesel Engine Vibration Using Cylinder Deactivation for Exhaust Temperature Management and Recipe for Implementation in Commercial Vehicles,” SAE Technical Paper 2018-01-1284, 2018, doi:10.4271/2018-01-1284. Abstract vibration data in a dynamometer test cell. Three degrees of ommercial vehicles require continual improvements linear vibration and one degree of rotational vibration were in order to meet fuel emission standards, improve measured using accelerometers and rotational speed sensors. Cdiesel aftertreatment system performance and Historical data analysis showed that the remaining two rota- optimize vehicle fuel economy. Aftertreatment systems, used tional degrees of freedom were insignificant when considering to remove engine NOx, are temperature dependent. Variable driveline vibration. The engine was tested using a combination valve actuation in the form of cylinder deactivation (CDA) of deactivating two, three and four cylinders (of the six) up to has been shown to manage exhaust temperatures to the after- engine loads of approximately 4 bar BMEP in order to quantify treatment system during low load operation (i.e., under system vibration and resonance frequencies. These results 3-4 bar BMEP). During cylinder deactivation mode, a diesel were compared to driveline NVH standards to determine the engine can have higher vibration levels when compared to modes of operation that were acceptable over the engine speed normal six cylinder operation. The viability of CDA needs to and load operating range. A variable CDA implantation be implemented in a way to manage noise, vibration and strategy for operating the engine over transient engine opera- harshness (NVH) within acceptable ranges for today’s tion is recommended for this dynamometer operation. commercial vehicles and drivelines. A heavy duty diesel Additionally, a theory is provided for operating cylinder deac- engine (inline 6 cylinder) was instrumented to collect tivation in a commercial diesel vehicle. Introduction (CDA) is another type of VVA that has shown fuel economy here are increasing pressures to improve exhaust emis- improvement ranging from 2-12% [6, 7, 8, 9, 10, 11, 12, 13, 14] sions and fuel economy for commercial vehicles, agri- while typical gains are on the order of 5-6% [15, 16, 17, 18, 19]. Tcultural equipment and passenger cars. This paper There is a growing demand for improved fuel economy focuses on diesel technology applied to the heavy duty market while reducing tailpipe emissions which is driving development while the results are applicable to the medium duty market. of new engine and aftertreatment technologies. Aftertreatment Passenger car emissions in the United States have been systems are efficient for removing NOx as the exhaust and mandated to improve both fuel economy and CO2 reductions. catalyst temperatures reach 250 °C while these systems are less The mandates have increased the average fuel economy for efficient at lower temperatures. Exhaust thermal management passenger car and light trucks from 27.5 miles per gallon equiva- is a key technology area for improving aftertreatment NOx effi- lent (mpge) in 2008 to 35.5 mpge in 2016 [1]. The Environmental ciency while maintaining or improving engine fuel economy at Protection Agency (EPA) and the National Highway the same time. One VVA method to increase aftertreatment Transportation and Safety Administration extended the temperature is to use early exhaust valve opening (EEVO). improvement of fuel economy and greenhouse gases for EEVO test results on a medium duty diesel engine showed an passenger vehicle models in 2017 through 2025 [2]. These actions increase in exhaust temperature on the order of 30 to 80 °C with move the average required fleet wide fuel economy in 2025 in an associated fuel consumption increase of 15 to 23% [20, 21]. the range of 55.3 to 56.2 mpge for passenger cars, and 39.3 to Cylinder deactivation is another VVA means to increase 40.3 mpge for light trucks, resulting in a combined 48.7 to 49.7 exhaust temperature at low load operation while improving mpge [2]. Variable valve actuation (VVA) including variable fuel economy at the same time. Medium duty diesel results valve lift and early intake valve closing can be used in improve showed that CDA can be used to increase exhaust temperature fuel economy on the order of 3-4% [3, 4, 5]. Cylinder deactivation by 100 °C while reducing fuel consumption at unloaded and © 2018 Eaton Corporation. Downloaded from SAE International by Audra Ziegefuss, Tuesday, May 21, 2019 2 QUANTIFICATION OF DIESEL ENGINE VIBRATION USING CYLINDER DEACTIVATION lightly loaded engine conditions [22, 23] depending on engine once every two crank revolutions. This allows the calculation calibration. Additionally, VVA functions can be applied to of the engine firing order based on the number of cylinders the firing cylinders while other cylinders remain deactivated that are firing. Each cylinder firing once per two crank revolu- to yield even higher exhaust temperatures [24]. These VVA tions means that half of the cylinders are fired during one functions include variable valve lift, early intake valve closing, crank revolution. Therefore, for a 6 cylinder engine, the late intake valve closing and internal EGR. Later work showed dominant order of vibration is 3rd order, and for an 8 cylinder that reactivating the cylinders remains first fire ready for engine, the dominant order of vibration is 4th order, and so on. accurate combustion supporting operating an engine in CDA A six cylinder engine with appropriate CDA hardware mode for up to 20 minutes [25]. The torque requirements for can be operated with zero to six cylinders active. Different vehicle acceleration starting in CDA mode and transitioning active cylinder counts may be advantageous depending on to normal six cylinder operation are met for starting in half the engine operating state. Half engine CDA with three active engine CDA [26] along with one-third and two-thirds engine cylinders has been shown to offer reduced fuel consumption CDA [27]. Finally, exhaust temperatures have been shown to and increased exhaust gas temperature at low engine loads increase to active Diesel Particulate Filter (DPF) regeneration and speeds [23, 24, 25, 26, 27]. Half engine CDA with even temperatures above 550 °C utilizing CDA at road-load cruise firing interval can be implemented on inline six cylinder diesel conditions without fuel dosing in the tailpipe [28]. engines using two different schemas. One source of premature driveline component failures Figure 1a shows half engine operation with the front half can be attributed to driveline torsional vibration problems. of the engine inactive. Valves at cylinders 1, 2, and 3 remain Driveline torsional vibration problems are also often a source stationary, and fuel injection only occurs in cylinders 4, 5, of customer noise and vibration complaints in class 8 vehicles and 6. Combustion events occur in cylinders 4, 5, and 6 at [29]. Driveline components have a resonance frequency that 240° crank rotation intervals. Figure 1b shows half engine may align with the engine firing frequency at a point during operation with the rear half of the engine inactive. Valves at the drive cycle as the engine speed changes. When the engine cylinders 4, 5, and 6 remain stationary, and fuel injection only firing frequency aligns with a driveline resonance, the vibra- occurs in cylinders 1, 2, and 3. Combustion events occur in tion levels increase to a level that may damage driveline cylinders 1, 2, and 3 at 240° crank rotation intervals. During components. Vehicles using cylinder deactivation have a 3 cylinders firing (CF), the dominant order of torsional vibra- higher level of ignition force resulting in higher torque varia- tion is 1.5th order (half of the number of active cylinders). The tion. This higher torque variation with engines using cylinder engine firing frequency can be calculated by using equation 1. deactivation can cause unacceptable levels of noise and vibra- 1min tion performance [30]. Thus, engine vibration needs to be fred=*pm *O (1) managed while in CDA mode. Active engine mounts using 60 sec open and closed loop controls have been investigated as a Where Od is the dominant order and fe is the engine firing solution to manage noise and vibration performance for frequency. Therefore, at the limits of the speed range 600 and engines using cylinder deactivation (Shin, 2007) [31]. This paper focuses on engine vibration of an inline, six cylinder, heavy duty diesel engine for CDA at low load. The benefits of FIGURE 1 Half engine CDA for inline six cylinder engine operating CDA were quantified in terms of exhaust tempera- with (a) front half deactivated and (b) rear half deactivated. ture increase, fuel consumption, and friction from idle speeds of 800 rpm up to high speed conditions of 2100 rpm in previous works [32]. This work recommended operating half engine CDA below 3-4 bar BMEP over all engine speeds. Background The four stroke, inline six cylinder diesel engine is commonly used in medium and heavy duty commercial vehicles. The engine used in this study has four valves per cylinder; each cylinder has a pair of intake valves and a pair of exhaust valves. Valve pairs are each connected to a common rocker arm and connecting bridge. The crankshaft contains six independent journals arranged in such a way as to produce a 1-5-3-6-2-4 firing order with combustion events occurring at 120° crank rotation intervals. The firing frequency (Hz) can be calculated from the engine speed (rpm), by dividing the rpm by 60 since there are 60 rpm = 1 revolution per second, or 1 Hz.