Jaguar unveiled its all-new direct-injection 5.0-L V8 gasoline engine in supercharged and naturally aspirated forms at the 2009 North American International Auto Show in Detroit. Designed in-house by Jaguar, the new AJ-V8 Gen III replaces the 4.2-L AJ-V8 to power the XF, XK, and next-generation XJ.
Malcolm Sandford, Jaguar’s Chief Engineer-Engines, said the only carryover components from the previous V8 are the exhaust tappets and cylinder-head bolts. "Everything else is new, with much of the design driven by the need to repackage. To achieve the efficiency required, we have bundled together several advanced technologies—and we are very pleased with the result."
The announcement of the new V8 came only days after Jaguar revealed its equally new AJ-V6D diesel, described in the January print edition of AEI. There are physical similarities in the appearance of both engines, said Sandford, demonstrating the synergy achieved in Jaguar’s core design philosophy for its new generation engines.
The gasoline engine comes with two output levels: 375 kW (503 hp) with 625 N·m (461 lb·ft) for the supercharged version, which is standard in the new XFR and XKR models; and 283 kW (380 hp) with 515 N·m (380 lb·ft) for the naturally aspirated version. The new engine is 64 mm (2.5 in) shorter in supercharged form and 11 mm (0.4 in) lower in normally aspirated form. To achieve this, every component was analyzed to reach the most efficient, practical package solution and also to meet the requirements of Design Director Ian Callum and his team, for cars with low, rounded noses. The two versions of the engine have 85% commonality.
Sandford emphasized the development focus that had been placed on achieving a very smooth and consistent power delivery. And while many aspects of the new V8 are significant, there are some elements that are particularly so, notably the Eaton supercharger design, and its optimization, and the spray-guided direct-injection system.
The supercharger is a Roots-type Twin Vortex Series, which, with an increased number of vanes (four instead of three) and with higher helix angle, is some 20% more efficient than that used on the outgoing 4.2-L engine, said Sandford. The air intake has been redesigned, giving a more direct airflow path and reducing flow losses by some 30%. Overall, the new supercharger application uses less energy to produce 375 kW on the 5.0-L V8 than the previous engine used to produce 228 kW (306 hp).
The direct fuel-injection system uses centrally mounted Bosch six-hole injectors; Jaguar believes it to be an industry first in that configuration. Fuel-injection pressure is 150 bar (2.2 ksi). Enhanced droplet control and vaporization create a homogeneous mixture to improve combustion, and charge cooling improves volumetric efficiency and knock limits. Cold-start fueling is reduced by up to 80%. A coil-on-plug system is used. The supercharged engine’s compression ratio is 9.5:1 vs. the naturally aspirated’s 11.5:1, which demonstrates convergence with Jaguar’s new V6 diesel engine, which has a compression ratio of 16:1 for both its power levels.
Initial design work for the new engine started in 2002. It was decided that a new aluminum high-pressure die-cast block would be essential. Deep skirted, cross-bolted, and with an integrated front chain case—all of which provide added stiffness—it is 2 kg (4.4 lb) lighter than the previous V8 block.
The cylinder-head casting uses recycled, non-heat-treated aluminum alloy. Each head incorporates two overhead camshafts with four valves per cylinder positioned slightly asymmetrically around the cylinder bore. The inlet cam is at a different height to the exhaust to find an additional 21 mm (0.8 in) needed to package the camshaft-profile-switching technology employed on the normally aspirated variant to boost low-speed torque and improve fuel efficiency.
"We strived to save every fraction of a degree to reduce angles and minimize engine width," said Sandford. The graded, direct-acting exhaust tappets facilitate adjustment of valve clearances. Although bore and stroke are larger than the outgoing V8, the engine is slightly undersquare.
Radiated sound from the cylinder block is reduced by some 4 dB compared to the previous engine, which means more than halved engine noise—a significant achievement in a premium luxury car such as a Jaguar.
A variable orifice oil separator and twin positive crankcase ventilation valves are integrated into the cam cover. This reduces oil pull-over by some 50%, a critical factor in the elimination of intake valve deposits in direct-injection engines, which, unlike conventional port-injected engines, do not have the cleansing effect of fuel sprayed onto the valves.
A reverse flow cooling system is fitted, explained Sandford: "By passing chilled coolant directly into the cylinder heads, we achieve improved knock sensitivity and better control of temperatures." The reverse flow and a large V-mounted heat exchanger also help achieve fast warm-up for oil (by about 30%) and the cabin heater (about 60%).
Lightweight cast pistons are used by both versions of the engine and have a low-friction solid-film lubricant on their skirts. The central injection configuration has helped achieve a flat piston and supports good thermal efficiency. Main bearing and cranktrain friction levels are low, the latter ahead of Jaguar’s main competitors, said Sandford. He added that every aspect of the engine’s design had been benchmarked and the design team’s philosophy throughout had been "pay attention to detail."
That included relatively low-tech subsystems such as the oil pump. A newly designed and patented pressure relief valve was developed with oil pressure controlled via a combination of oil gallery and pump outlet pressure. Energy saving is achieved thanks to reduced pump friction losses during warm-up and steady-state conditions, and it provides improved oil pressure control during start-up.
The new V8 has "fully independent, long-range" cam-torque-actuated variable-cam timing of both inlet and exhaust valves, giving enhanced exhaust gas recirculation for improved part-load efficiency. Sandford stated that the new engine is the first application of a new technology inlet and exhaust variable camshaft timing system supplied by BorgWarner. It is activated by torque generated by the valvetrain moving the phaser, not the oil pressure, and brings high response rates of better than 250 degrees/s, with enhanced performance feel and emissions control.
Service intervals have been upped to 24,000 km (15,000 mi) and an electronic dipstick replaces the conventional type.
Jaguar has paid particular attention to sound quality of the new gasoline engines with a semi-active valve exhaust muffler and an intake feedback tube. Sound engineers have worked to eliminate supercharger whine, although opinions are split about its appropriateness in a luxury sporting sedan. But Sandford has firm views: "I do not like supercharger whine. It is an inelegant result of poor machinery not doing what it should—so we have taken it out."
Not all may agree with his views, but it is one of the influential pluses of having the job title Chief Engineer-Engines.