SUBARU BOXER DIESEL: Features & Benefits Low vibrations and noise - The movements of the horizontally-opposed pistons work in unison to effectively cancel out the second harmonic vibration (vibration at double the frequency of the engine’s revolution) that causes discomfort in drivers. Thanks to this structural advantage, the SUBARU BOXER DIESEL does not need balancer shafts which are commonly used in conventional in-line and V-type engines. The compactly designed crankshaft sandwiched by the highly rigid cylinder blocks helps minimizing an uncomfortable noise and vibration up to high rpm’s. Superior engine response and good fuel economy - No need for balancer shafts leads to low rotational inertia and friction within the engine itself. The result is exceptional accelerator response and good fuel economy. Contribution to the handling performance - The bore pitch has been shortened and the left and right blocks holding the crankshaft provide a highly rigid design compared to the conventional in-line engines, which has also allowed use of an aluminium alloy cylinder block for weight savings. - In addition to the low centre of gravity provided by the structure of the Horizontally-Opposed Engine, the placement of the turbocharger unit at the lower part of the engine functions to maintain a low centre of gravity for the diesel engine, which tends to be quite heavy in weight. - These engine features contribute to excellent handling performance. SUBARU BOXER DIESEL: Mechanisms 1. Cylinder block - Cylinder block An aluminium alloy cylinder block has been used to maximise the potential of the highly rigid Horizontally-Opposed Engine layout. To obtain ideal diesel combustion, the stroke was extended by 11 mm and the bore was shortened by 6 mm compared to the SUBARU BOXER four-cylinder 2.0-litre petrol engine (EJ20). The bore pitch has been shortened to 98.4 mm, which is similar to that of SUBARU BOXER 6-cylinder petrol engine (EZ30), while the petrol engine (EJ20) has 113.0 mm. This has led to a 61.3 mm reduction in engine block length for even more compact design. Semi-closed deck: The block design uses the semi-closed deck type that has proven its durability in the turbocharged petrol models. This increases rigidity around the head gasket mating areas. Metal matrix composite journal: All 5 main bearings (journals) in the cylinder block incorporate metal matrix composite journals (which are inserted during the casting process), resulting in superior levels of quietness due to high rigidity and similarity in thermal expansion ratio to that of crankshaft. Extra cooling channels: Cooling slits have been given between the cylinder bores to operate as water cooling channels, thus improving cooling performance. - Pistons High strength materials have been used to withstand the high combustion pressures of the diesel engine. Cooling channels within the pistons have been incorporated, with engine oil squirted via oil jets, which enhances piston cooling. - Connecting rods The large ends of the connecting rods feature an asymmetrical profile, which increases precision during assembly and in roundness of the surface connecting the crankpin for reduced friction. It has also contributed to minimizing the rotational path, thus allowing an extended piston stroke inside the compact cylinder block. - Crankshaft The high strength crankshafts have undergone surface treatment to withstand the high combustion pressures that are found in a diesel engine. Since the Horizontally-Opposed engine layout allows for shorter journal pitch, high rigidity is maintained in a diesel engine that is dramatically lighter in weight than conventional in-line engines. 2. Valve system / intake and exhaust system - Cylinder head High strength cylinder heads have been used to withstand the high combustion pressures. Roller rocker arms: compact and low friction end pivot type roller rocker arms have been used in combination with the double overhead cam (DOHC) system. Valve System: The diameter of the intake valves have been optimised for enhanced breathing performance and swirl ratios, resulting in improved combustion efficiency. - Intake ports The combination of an intake swirl pot system and optimised intake valve diameter results in ample swirl performance. - Cam Drive System A highly durable chain system has been used to drive the camshaft to handle the variations in torque produced by the diesel engine. 3. Common rail system A common rail system has been used for fuel delivery for better performance. The fuel is pressurised to 180 MPa before being fed into the common rail. - Solenoid injectors Specially designed injectors have been used. A shorter overall length of the injector has contributed to maintain overall engine width as that of the regular petrol engine despite the longer piston stroke. 4. Turbocharger A variable nozzle type turbocharger has been specially designed to deliver ample turbocharged performance across the entire engine range. The turbocharger itself has been positioned under the engine and mounted directly to the catalytic converters for increased environmental friendliness. Response has been improved while also helping to lower the centre of gravity. 5. Exhaust The exhaust system has been fine tuned for use with the diesel engine. 6. Exhaust Emission Control System A closed-type of diesel particulate filter (DPF) has been adopted for the exhaust emission control system of the Impreza in order to further enhance environmental friendliness. The DPF has been positioned together with the turbo charger at the lower part of the engine. This not only improves exhaust gas purification performance, but also helps keeping the centre of gravity low, thus further enhancing the superb handling performance of the symmetrical AWD. This system complies with European EURO 4 exhaust gas regulations. - Oxidation catalytic converter The catalytic converter separates un-burnt fuel into water and carbon dioxide. The unit has been made compact enough to be activated soon after the engine has been started. If the temperature rises to 300°C under certain driving conditions, the oxidation catalytic converter generates NO2, which oxidises collected diesel particulates inside the DPF. - Closed Diesel Particulate Filter (DPF) The adoption of a closed DPF functions to improve engine combustion efficiency and reduce particulate matter (PM) in the exhaust in order to further enhance environmental friendliness. The closed DPF features a honeycomb shaped filter made of silicon carbide. The filter channels are blocked on alternating ends of each side and there are also microscopic pores on the inner filter wall, thereby functioning to effectively collect the PM as the exhaust gas passes through these microscopic pores. The collected PM is combusted inside of the filter, which reaches 600°C and higher depending on operating conditions, and repeatedly regenerated, processed, and emitted as exhaust. Conversely, if the internal filter temperature is low with a continuous load operation, the temperature within the layers is controlled to cause combustion of the PM, which is then repeatedly generated, processed, and emitted as exhaust. - EGR (Exhaust Gas Recirculation) system An EGR system has been used to comply with European EURO 4 exhaust gas regulations. The cooled exhaust gas is fed back into the combustion chamber to lower the combustion temperature and reduce NOx emissions. 7. Engine mounting system A liquid-filled engine mounting system has been employed for even less vibration and better handling performance.