Subaru CB engine

Subaru CB engine
CB18 in a Levorg (Oct 2020)
Overview
ManufacturerSubaru
Production2020–present
Layout
ConfigurationFlat-4
Displacement
  • 1.8 L (1,795 cm3)
Cylinder bore
  • 80.6 mm (3.17 in)
Piston stroke88 mm (3.46 in)
ValvetrainDOHC 4 valves x cyl. with AVCS
Compression ratio10.4:1
Combustion
TurbochargerYes
Fuel systemFuel injection
Fuel typePetrol/gasoline
Cooling systemWater-cooled
Output
Power output177 PS (130 kW; 175 hp)
Torque output300 N⋅m (221 lb⋅ft; 31 kg⋅m)
Chronology
PredecessorFB, FA (split diagonally)

The Subaru CB engine is a gasoline boxer-4 engine used in Subaru automobiles. It is the fourth generation of Subaru boxer engines, following the first (EA, 1966–94), second (EJ, 1989–2021), and third (FB/FA, 2010/2012–present) generations.

Overview

The CB engine was first introduced in August 2020 with the second-generation Levorg.[1][2] According to Subaru, CB stands for Concentration/Compact Boxer.[3] It is the fourth-generation boxer engine family from Subaru.[4] Compared to the preceding FB series, the CB is shorter; the bore pitch (centerline to centerline spacing between adjacent cylinders) has decreased from 113.0 to 98.6 mm (4.45 to 3.88 in) and the overall crank length has decreased from 350.5 to 315.9 mm (13.80 to 12.44 in).[5]

For the first time in a Subaru engine, the centerlines of the cylinder bores do not intersect with the crankshaft axis; instead, there is a crank offset of 8 mm (0.31 in). This offset reduces friction during the piston downstroke. Overall thermal efficiency is 40% due to the adoption of lean-burn combustion with an excess air ratio (λ) of 2.[5] The injector is positioned next to the spark plug in the center of the combustion chamber to ensure the lean mixture will ignite reliably. A small single-scroll turbocharger was equipped to maintain charge air volume and improve throttle response.[5]

The connecting rods in the CB engine are split horizontally,[3] like those in the second generation EJ engines.[5][6] The third generation FB/FA connecting rods are split diagonally[7] (also called an offset or asymmetrical connecting rod) to allow a longer piston stroke without increasing the width of the engine,[8] but the horizontally-split connecting rods are stronger.[3]

CB18

The first engine in the series is designated CB18, a 1.8 litre dual overhead cam 16-valve engine featuring dual AVCS with gasoline direct injection and a turbocharger.[9] Compared to the FB16 used in the previous generation of the Levorg, the CB18 offers decreased fuel consumption (16.6 km/L (39 mpg‑US) for the CB18 and 16.0 km/L (38 mpg‑US) for the FB16, both using the JC08 mode) and increased torque (300 N⋅m (31 kg⋅m; 220 lb⋅ft) for the CB18 and 250 N⋅m (25 kg⋅m; 180 lb⋅ft) for the FB16). In addition, the CB18 achieves its peak torque at a lower engine speed.[5] Engine weight of the CB18 has been reduced by 14.6 kg (32 lb) compared with the FB16.[5]

In October 2020, Subaru announced the CB18 also would be fitted to the top-of-the-line 'Sport' trim of the 5th generation Subaru Forester in the Japanese market; other models of the Forester are equipped with the mild hybrid FB20D e-BOXER.[10]

The CB18 engine is also fitted to the Subaru Legacy Outback for the Japanese market.[11][12]

In April 2022, Subaru had to suspend production of Forester, Outback and Levorg after it discovered a sensor in CB18 engine malfunctioned.[13]

CB18 specifications
  • Displacement: 1,795 cc (1.8 L) DOHC, turbocharged
  • Bore × stroke: 80.6 mm × 88 mm (3.17 in × 3.46 in)
  • Compression ratio: 10.4:1
  • Power: 177 PS (130 kW; 175 hp) at 5,200–5,600 RPM
  • Torque: 300 N⋅m (31 kg⋅m; 221 lb⋅ft) at 1,600–3,600 RPM
CB18 applications

References

  1. ^ Stocksdale, Joel (August 20, 2020). "Subaru Levorg, also known as the WRX's wagon cousin, revealed in production form". Autoblog. Retrieved 2 September 2020.
  2. ^ Lye, Gerard (August 21, 2020). "2020 Subaru Levorg officially debuts in Japan – SGP platform; new 1.8L turbo boxer engine and EyeSight X". paultan.org. Retrieved 2 September 2020.
  3. ^ a b c Tanikawa, Kiyoshi (August 28, 2020). "スバル、新開発水平対向エンジン「CB18型」の疑問点を確認 「EJ20時代の強度剛性思想を採用」" [Subaru answers questions about the newly developed boxer engine 'CB18': 'Adopts the strength and rigidity concept of the EJ20 era']. Car Watch (in Japanese). Retrieved 6 April 2021.
  4. ^ "テクノロジー：DRIVING | 水平対向エンジン" [Technology: Driving | Horizontally opposed engine] (in Japanese). Subaru of Japan. Retrieved 6 April 2021.
  5. ^ a b c d e f Tanikawa, Kiyoshi (August 27, 2020). "スバル、新型レヴォーグのCB18エンジンは熱効率40％ λ＝2のリーン燃焼やオフセットシリンダー採用" [Subaru's new Levorg CB18 engine uses lean combustion with a thermal efficiency of 40%, λ=2, and an offset cylinder]. Car Watch (in Japanese). Retrieved 6 April 2021.
  6. ^ "Connecting Rod — Subaru (12100AA201) [EJ22]". Subaru Parts. Retrieved 6 April 2021.
  7. ^ "Connecting Rod — Subaru (12100AA470) [FB25]". Subaru Parts. Retrieved 6 April 2021.
  8. ^ Colwell, K.C. (January 2011). "Examining Subaru's New FB-series Flat-Four". Car and Driver. Hearst Corporation. Retrieved 15 April 2011.
  9. ^ "スペック" [Specifications] (PDF). Subaru of Japan. Retrieved 2 September 2020.
  10. ^ "ＳＵＢＡＲＵ 「フォレスター」改良モデルを発表" [SUBARU 'Forester' improved model announced] (Press release) (in Japanese). Subaru Global Media. October 22, 2020. Retrieved 6 April 2021.
  11. ^ "SUBARU 新型「レガシィ アウトバック」を発表" [SUBARU announces new 'Legacy Outback'] (Press release) (in Japanese). Subaru Global Media. October 7, 2021. Retrieved 8 November 2021.
  12. ^ "Subaru Legacy Outback Main equipment list (Japanese)". Retrieved 9 September 2021.
  13. ^ "Subaru Suspends Shipment of Some Models Due to Engine Sensor Malfunction — Media". Reuters. 14 April 2022. Retrieved 15 April 2022.
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(Japanese: Subaru CB engine)