2007 BMW Z4 Coupe

Higher fuel-injection pressure, up from 3.5 to 5 bar (51.4 to 73.5 lb/sq in.), results in an improved injection spray, helping reduce raw hydrocarbon emissions in a cold engine.

All-new engine electronics. The number of variables (inputs) feeding into the engine’s electronic management system has increased significantly; a completely new system was developed. Among many innovative details, the basic ignition and valve-timing functions are duplicated. The first part was optimized for fuel consumption and emissions; the second part was determined according to pure driving parameters. Depending upon how perfectly the engine is running at any time, control interpolates between the two strategies. Under ideal conditions, the engine always runs with its lowest fuel consumption. In case of poor fuel quality or unfavorable environmental conditions, the control parameters prioritize driveability.

Magnesium/aluminum composite construction

Although the direct customer benefits of this unique and pioneering construction are subtler than those of Valvetronic, this is an important innovation – a world’s first in modern times and exclusive to BMW.

Structurally, the new engine block consists of three major castings:
Bedplate (magnesium alloy ). This casting forms the lower portion of the block (crankcase), and is similar in concept to a construction element found in some racing engines – as well as the 500-hp V-10 engine that powers the BMW M5 and M6. The bedplate combines with the upper crankcase to form the outer shell of the cylinder block, resulting in an ultra-rigid engine structure.
Upper crankcase (magnesium alloy). Joining the bedplate at the level of the crankshaft (main) bearings, this too is a weight-saving casting. It is mounted onto the bedplate from above.
Insert (aluminum alloy). Forms the cylinders and their coolant passages. Whereas the previous engine has an aluminum block with cast-iron sleeves as the cylinders’ working surfaces, this insert is of silicon-impregnated aluminum (Alusil). Silicon particles are thus cast into the block; a “soft honing” machine removes just enough of the aluminum to leave the crystals as the ultra-hard cylinder surfaces. In this sense, the N52’s block construction resembles that of current BMW V-8 and V-12 engines, though these blocks are all-Alusil.

How it goes together. First, the aluminum insert is cast by conventional methods. Then, during a newly developed die-casting method, the magnesium upper shell shrinks onto the insert while cooling; structural rigidity and stability are ensured by interlocking ribs where the two castings meet.

In the next step, the upper crankcase, consisting of magnesium shell and aluminum insert, is mounted onto the magnesium bedplate from above. The sintered-steel main bearings’ lower halves are in place in the bedplate, the upper halves in the upper crankcase. After the bedplate and upper crankcase have been bolted together, a liquid sealing compound is injected into a groove on the contact surface between the two components. Special aluminum bolts are used to attach parts, such as the engine mounting brackets, to the magnesium/aluminum castings.

As in all BMW engines for decades, the cylinder head is of aluminum; however, the head of an inline 6-cylinder engine must be cast with great precision because its relatively great length implies relatively large contraction as it cools after casting. The casting process used here is called “lost-foam”; this process, which employs a polystyrene “dummy” of the head to form the mold into which the aluminum is poured, results in an extremely precise casting.

Other weight-saving materials. Though the magnesium/aluminum composite crankcase construction is the most sensational example, other materials and production innovations also help pare weight from the N52 engine. The second most productive material innovation was the adoption of hollow camshafts, which save a remarkable 2.6 lb. Beginning as steel tubes, the camshafts are shaped in a hydroforming procedure, subjected from the inside to a water pressure of 4000 bar (58,000 lb./sq in.) against outer forms to achieve the cam profiles. All this takes place in a cold state – nothing melts – and as a final step the cams are polished to a finish quality of 1/1000 mm.

The engine’s camshaft cover is of weight-saving magnesium. And the chain camshaft drive, a high-durability, low-maintenance feature of all current BMW engines, has an aluminum chain tensioner that also saves weight. Instead of being a separate casting, the camshaft drive’s housing is integrally cast into the magnesium structure, eliminating a production step and sealing components. As one final weight-reducing element, the exhaust headers’ flanges are formed from 2-mm-thick steel, significantly lighter than the 12-mm flanges used previously.

Electric water pump. A conventional engine water (coolant) pump is driven by a belt at a speed directly proportional to engine rpm. This innovation is electrically driven and electronically controlled according to the engine’s coolant and oil temperatures at any moment. Thus it runs only as much as needed, and in doing so consumes a maximum of 200 watts vs. up to 2 kilowatts (10 times as much) for a conventional pump. The electric pump has numerous tangible benefits:

• By requiring less power, contributes to the engine’s increased power output.
• Faster engine warmup, because it doesn’t circulate coolant when the engine is cold.
• By eliminating an external drive belt, makes the engine shorter.

Variable-volume oil pump. Conventional oil pumps, too, deliver oil in direct proportion to engine speed. To supply pressure to the VANOS system (which employs oil pressure to rotate the camshafts and thus vary valve timing) at all speeds and temperatures without excess capacity at high engine speeds, BMW engineers developed a new type of oil pump. By varying the output of its pump element according to engine oil pressure, this pump always delivers sufficient pressure to lubricate the engine and operate VANOS, yet never pumps more oil than is necessary. Thus it –

• Contributes to the engine’s increased power output, by requiring less power from the engine.
• Doesn’t require a bypass to divert excess flow, which can be up to 80% with a conventional pump. This also avoids possible excess oil temperatures and oil foaming.

Oil/coolant heat exchanger. Another feature that speeds engine warmup; during this phase of operation, it transfers heat from the coolant to the oil circuit. Under conditions of high engine power and high oil temperatures, it performs the reverse, transferring heat from the oil circuit to the coolant, from which the engine cooling system then removes excess heat.

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