Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035 (2021) / Chapter Skim
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4 Internal Combustion Engine-Based Powertrain Technologies
4 Internal Combustion Engine-Based Powertrain Technologies
Pages 44-71
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From page 44... ...
This pathway approach allows technologies to be evaluated, including their potential contribution in specific system-level applications. For example, the benefit of cylinder deactivation is different for a downsized/boosted 4-cylinder engine than for a large displacement, naturally aspirated 8-cylinder engine and might therefore be prioritized differently for different applications.
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From page 45... ...
than modern naturally aspirated engines with gasoline direct injection. The result is a lower peak efficiency for downsized/boosted engines than that of a naturally aspirated engine, but more time spent operating in the higher efficiency region.
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From page 46... ...
to roller finger follower type. Numerous engine entries now use so-called dual fuel injection systems employing a combination of port and direct injection.
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From page 47... ...
Level 1 downsized/boosted engines tend to have CRs in the 10.0–10.5:1 range, lower than those in modern naturally aspirated engines with gasoline direct injection, which are typically at least 12:1. Based on data from Heywood (1988)
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From page 48... ...
This result is consistent with other studies showing that cooled EGR can offer BSFC improvements of at least 3%. Beyond LP-EGR as a technology to improve efficiency of GTDI engines, Stuhldreher and colleagues (2018)
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From page 49... ...
Some of those technologies are listed in Table 4.1. In summary, applying the Miller cycle concept in various ways to improve thermal efficiency of downsized/ boosted engines seems to be a significant focus going forward into 2025–2035.
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From page 50... ...
, present present present friction reduction, higher stroke/bore ratio • Includes other technologies: continuously variable valve duration, 350 psi direct injection Example: VW EA211 EVO 1.5 L GTDI Engine • Includes NHTSA technologies: VVT, SGDI, CEGR1 $250 $230 $230 2%–3% TURBO1, VTG, DEAC (cylinder deactivation of 2 cylinders) • Includes technologies from Stuhldreher et al.
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From page 51... ...
, Miller cycle, friction reduction • Includes other technologies: dual PFI/DI fuel injection Example: Nissan 2.0 L VC-Turbo Engine (Variable Compression Ratio) • Includes NHTSA technologies: VVT, SGDI, CEGR1 $250 $230 $230 2%–3% TURBO1, variable compression ratio (VCR)
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From page 52... ...
to allow for higher expansion ratios and therefore greater thermal efficiency, cooled EGR, friction reduction technologies, and the application of cylinder deactivation to already downsized 4- and even 3-cylinder engines. FINDING 4.3: By 2025, non-electrified internal combustion engines could implement technologies such as currently represented in 2020 by the advanced downsized/boosted engines described in Tables 4.1 and 4.2, which would offer improvements in efficiency of up to 5% over a current baseline downsized/boosted engine.
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From page 53... ...
Many strong hybrid powertrains currently use highly efficient naturally aspirated engines utilizing the Atkinson cycle made possible by hybrid electric synergies described in Section 4.5.2. Implementation will likely continue as these engines are lower in cost than boosted variants so can help defray hybridization cost.
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From page 54... ...
NOTE: The baseline engine represents an advanced naturally aspirated, unhybridized engine in 2020, which may represent typical naturally aspirated engines in 2025. The example fuel economy technology advancement above the baseline illustrates a "next step" technology that could be implemented in 2025–2035.
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From page 55... ...
The technical challenge for the diesel engine is the ability to meet stringent criteria emission standards, especially nitrogen oxides (NOx) and particulates, and to manage the cost associated with that challenge while maintaining a compelling fuel efficiency advantage versus improving spark ignition engines.
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From page 56... ...
CVTs will be particularly effective in a powertrain system using a high efficiency or Atkinson cycle naturally aspirated engine of higher displacement by keeping the engine in its most efficient operating points, reducing the benefit of additional engine technologies such as cylinder deactivation. Dual clutch transmissions (DCTs)
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From page 57... ...
By far, the most fuel-efficient gasoline-only vehicles in the U.S. fleet are strong hybrids.
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From page 58... ...
Strong hybrids represent the greatest potential to improve the fuel efficiency of gasoline-only powered vehicles. Even some of the 2020 vehicles that were previously mentioned as high performers in their base ICE form (Toyota Camry, RAV4, Ford Escape)
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From page 59... ...
Schematic diagrams of P0 mild hybrid, P2 mild or strong hybrid, PS strong hybrid, and series strong hybrid architectures are shown in Figure 4.4. The position of the electrical machine is often important to FIGURE 4.4 Basic mild and strong hybrid architectures including BISG P0, P2, PS, and Series.
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From page 60... ...
Along with their lower absolute costs than strong hybrids, 48 V MHEVs have relatively limited benefits. Since most applications to date use a belt-driven machine in a P0 configuration, the belt transfer capability limits the maximum motor and braking torque.
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From page 61... ...
Similar to stop-start systems, 48 V BISG hybridization could represent an evolutionary step in ICE powertrains because, while not capable of delivering the fuel efficiency benefit of strong hybridization, it can be "added-on" relatively simply and at lower cost. 4.5.1.2 Strong Hybrid Strong hybrids use a larger motor/generator and battery at higher voltage levels than mild hybrids and, as a result, can achieve much greater levels of braking regeneration and engine support, often including some degree of electric-only driving.
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From page 62... ...
However, since all engine energy is exposed to double conversion before reaching the wheels, this hybrid configuration has an efficiency disadvantage compared to other architectures. Alongside the proliferation of HEV offerings, automakers are offering configurations of many strong hybrid powertrains as plug-in hybrids with the addition of an onboard charger and an energy-type battery1 offering varying levels of electric-only range.
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From page 63... ...
Crossover 2020 ESCAPE FWD Intake/Exhaust, GDI 181 3298 46.01 Conventional: 41.166 42% –30% 1.5 L TC Hydraulic 241,387 Actuated VCT 2020 ESCAPE FWD Hydraulic MFI 200 3534 2020 is the 58.344 2.5 L NA HEV Actuated VCT first MY of the Escape Hybrid 2020 ESCAPE AWD Intake/Exhaust, GDI 181 3474 39.431 45% –31% 1.5 L TC Hydraulic Actuated VCT 2020 ESCAPE AWD Hydraulic MFI 200 3668 57.042 2.5 L NA HEV Actuated VCT Medium car 2020 CAMRY LE Intake and GDI 203 3296 48.46 Conventional: 43.451 65% –39% FWD 2.5 L NA exhaust 336,978 2020 CAMRY LE 208 3472 Hybrid: 26,043 71.781 FWD 2.5 L NA HEV 2020 CAMRY XLE 203 3391 42.669 47% –32% FWD 2.5 L NA 2020 CAMRY XLE 208 3572 62.929 FWD 2.5 L NA HEV NOTE: FWD = front-wheel drive; MFI = multipoint fuel injection; NA = naturally aspirated; TC = turbocharged. Switching to the hybrid version can also mean changes in valves, fuel injection, horsepower, weight, and footprint of the vehicle, all of which affect its final fuel economy.
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From page 64... ...
To date, automakers have offered the required engine performance of hybrids through the use of relatively low cost, naturally aspirated engines that achieve high efficiency by aggressively utilizing the Atkinson cycle with geometric CR up to 14:1. However, looking ahead, there are still significant opportunities to improve the overall powertrain system efficiency by further improving the ICE in a hybrid context.
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From page 65... ...
The PS hybrid architecture can approach this level with its CVT-like functionality. An engine operating in a series hybrid application that demonstrated up to 10% improvement in BSFC over a state-of-the-art downsized/boosted Miller cycle engine meeting all conventional application requirements was reported by VW (Brannys, 2019)
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From page 66... ...
4.5.3 Technology Cost and Effectiveness for Hybrid Vehicles Tables 4.6 and 4.7 below report estimated and projected cost and effectiveness values for representative PS and P2 strong hybrids of example vehicle classes. Cost estimates are provided for key components in 2025, 2030, and 2035.
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From page 67... ...
b Medium Car Engine Modificationsc Total: $55 Total: $50 Total: $50 Medium Car Naturally Aspirated • Electric water pump $55 $50 $50 Hybridization to PS Hybrid • Increased compression ratio No change No change No change Effectiveness 8-speed AT to eCVTd –$435 –$410 –$390 Average: –42% Motore $320 $290 $260 Range: –32% to –47% Generatore $140 $125 $115 Battery (1.0 kWh, Li-ion) f $550 $425 $330 Inverter/power electronicsg $490 $440 $310 Battery Monitoring, Safety, and $330 $315 $300 Thermal Management Systemsh ECU Upgradeh $45 $40 $40 High-Voltage Harnessh $130 $125 $120 Regenerative Brakesh $170 $165 $155 AC Modificationsh $170 $165 $155 DC/DC converter (1.1 kWh)
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From page 68... ...
b Medium Car Engine Modificationsc Total: $55 Total: $50 Total: $50 Medium Car Naturally Aspirated • Balance shaft deletion May be May be May be Hybridization to P2 Hybrid possible possible possible Effectiveness • Electric water pump $55 $50 $50 Average: –39% Transmission Modifications Total: –$5 Total: –$5 Total: –$5 Range: –33% to –44% 8-speed AT to 6-speed ATd –$55 –$50 –$50 Electric transmission pumpe $50 $45 $45 Motor f $240 $215 $195 Battery (1.5 kWh, Li-ion) g $825 $640 $495 Inverter/power electronicsh $315 $280 $175 Battery Monitoring, Safety, and $330 $315 $300 Thermal Management Systemsi ECU Upgradei $45 $40 $40 High-Voltage Harnessi $130 $125 $120 Regenerative Brakesi $170 $165 $155 AC Modificationsi $170 $165 $155 DC-DC converter (1.1 kWh)
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From page 69... ...
Many of the future developments of the internal combustion engine itself are focusing on the added efficiency potential of the engine when integrated into a hybrid system. FINDING 4.6: Mild hybrids, defined here as 48 V, represent a viable pathway to realize some of the same CO2 reduction benefits of hybridization described for strong hybrids, but at a lower overall cost.
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From page 70... ...
In the Mazda 2.0 L SkyActiv-X, three distinct combustion modes are utilized: lean air to fuel ratio SPCCI at light to moderate loads, lean exhaust gas to fuel ratio using cooled EGR at higher loads, and conventional spark ignition at full load. The technology is offered only in combination with Mazda's mild hybrid system.
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From page 71... ...
1988. Internal Combustion Engine Fundamentals.
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