[YesAuto Engine Technology] Since 1917, engineer Max Fritz developed the first BMW inline six-cylinder aero engine-BMW IIIa. Nearly a century of annual rings have been run over, from aero engines to car engines, from carburetors. When it comes to direct injection technology, and then from naturally aspirated to full implementation of turbocharging, the continuously evolving BMW engine has become a frequent visitor on the international engine award list. What we still see today is BMW’s adherence to the inline six-cylinder engine camp. . Today, we will not talk about the past historical feelings and merits. At the moment when the previous generation of N55 inline six engine will be replaced, let's rationally interpret BMW's latest B58 inline six engine to see where it is better than the N55?
● Why is it called B58?
The code-name of BMW's new-generation inline six-cylinder engine is B58 (hereinafter referred to as B58). After 2013, the original “N” prefix was changed to the “B” prefix. “5” and “8” respectively represent inline six. The meaning of cylinder and gasoline engine, and pioneered the concept of modular development of BMW engines.
● BMW 3.0T new-generation inline six-cylinder engine (B58) equipped models
BMW 7 Series 2016 740Li Exclusive Type
● Vehicles equipped with in-line six-cylinder engines
● Don’t talk about feelings, let’s talk about why BMW arranges six cylinders in a row?
Aside from the love festival of BMW and BMW fans for inline six-cylinder engines, and the technical accumulation and cost control advantages of developing inline six-cylinder engines for many years, what are the reasons for BMW to stick to inline six-cylinder engines?
□ From the perspective of ride comfort, inline six-cylinder engines are “naturally beautiful”
As we all know, the power output by the engine comes from the explosive work of the fuel mixture in each cylinder. However, if you want to get a continuous and smooth power source, you must make good use of the “violent tempers” of these cylinders, and rely on them to offset the imbalance. The specific method is to control the timing of their “fire”, that is, the ignition sequence. The in-line six-cylinder engine relies on its unique ignition sequence and arrangement, which achieves its unique smoothness among traditional automobile engines.
Generally speaking, an ordinary engine completes a working cycle with four strokes of intake, compression, work, and exhaust. The crankshaft of a single-cylinder engine rotates 720° and there is a work stroke, while for a six-cylinder engine, every time the crankshaft rotates There is one work stroke at 120°. The ignition sequence of an in-line six-cylinder engine is 1-5-3-6-2-4 or 1-4-2-6-3-5. The purpose of this setting is for the two symmetrical cylinders in the middle to move at the same pace. This suppresses the “rocker” vibration of the in-line engine. In addition, because the six cylinders are in two groups, the gas distribution phases of the three cylinders are exactly 120° apart, so that at any moment when the crankshaft rotates, the reciprocating inertial forces of the pistons are always in a state of canceling each other in all directions. This is Three-cylinder engines, four-cylinder engines and V6 engines cannot achieve. Therefore, the inline six-cylinder engine does not need to install a balance shaft .
□ Vertical layout that turns disadvantages into advantages
Obviously, compared to a four-cylinder engine or a V6 engine, the disadvantage of an in-line six-cylinder engine is that it is not compact enough. The straight-line cylinder bank increases the overall length of the engine, which affects the flexibility of the layout. Placing an inline six-cylinder engine horizontally can be very difficult, almost only Volvo has done so. For BMW models with longitudinal engines as the main engine, the longer engine does not only take up the negative impact of the car’s interior space. The longitudinally arranged inline six-cylinder engine extends more behind the front axle. To a certain extent, the counterweights of the front and rear axles are also optimized to improve the handling stability of the vehicle.
□ No need for a cylinder head
Compared with the V6 engine, because the six cylinders of the inline six-cylinder engine are arranged in a row, only one cylinder head is needed. For engines that use dual overhead camshafts (DOHC), it means eliminating two camshafts. On the one hand, the number of parts is reduced, the weight is reduced, and the engine structure is simplified; on the other hand, it also reduces the power loss caused by an additional set of valve trains.
Perhaps by installing balance shafts, three- and four-cylinder, V6 engines can also achieve good ride comfort; perhaps by optimizing the structural layout of the entire vehicle, other models can also achieve perfect front and rear axle weight distribution; perhaps through other improvements. It can keep the engine's fuel efficiency high, and BMW's choice is simple, that is, to continue to develop an inline six-cylinder engine. What improvements does the new B58 engine have on the basis of the N55? We will give the answer next.
● Compared with the current N55 inline six-cylinder engine, where is the B58 better?
Compared with the predecessor code-named N55, the new-generation inline six-cylinder engine B58 has improved the structure of the intake, exhaust and turbochargers. It adopts a water-cooled intercooler integrated on the intake manifold and is also optimized. Variable intake lift mechanism Valvetronic. In addition, the thermal management system of the entire engine has been upgraded, including the use of thermal management modules to control the temperature of the coolant, and the use of new processes to coat the cylinder wall with wear-resistant coatings, and so on. These innovations have improved the performance and fuel efficiency of the B58 engine.
□ Power increase 20Ps, torque increase 50N·m
It is also a 3.0T turbocharged engine, why the new B58 can increase the maximum power and torque so much? Especially in terms of torque, an increase of 50N·m. In addition to the factor of changing the compression ratio from 10.2:1 to 11:1, it is inseparable from the B58's reduced cylinder diameter and longer stroke design.
The B58 engine has not only changed the size of the cylinder, but also improved the treatment process of the cylinder wall. At present, most manufacturers use plasma thermal spraying technology to spray alloy carbide or other composite materials on the cylinder wall to improve the wear resistance and thermal conductivity of the cylinder wall. B58 adopts electric arc spraying method. In contrast, its process is more difficult, but the effect is better. It can make the cylinder wall have good wear resistance and reduce the power loss caused by friction to a certain extent.
In addition, carefully observe the torque characteristic curves of the two engines. You will find that when the engine speeds up, the torque of the B58 is smaller than that of the N55 at the beginning, but the slope of the torque curve of the B58 is larger, that is, the acceleration of the engine torque rises. Big. What makes them so different torque characteristics? The answer is that the B58 uses a smaller turbine.
□ How to make the engine “breath” better
In order to adapt to the engine's gas distribution requirements under different operating conditions, the new-generation inline six-cylinder engine B58 uses the same intake and exhaust dual variable timing system (VANOS) and variable valve lift technology (Valvetronic) as the N55. The difference is that the physical structure of the variable valve lift technology has been improved.
Generally speaking, the body structure, supercharging system and valve mechanism of the new-generation B58 engine have undergone certain changes, which are mainly reflected in the cylinder size setting, processing technology, turbine size, and valve variable lift mechanism. However, there is a prerequisite for these improved components to work, and that is to allow the cooling system to maintain normal operating temperatures for them.
□ How to prevent the engine from “fever”
The temperature generated by the combustion of the combustible mixture in the engine cylinder is very high. If the engine cannot be cooled normally, it will seriously affect the fuel economy and power of the engine, and even damage the engine. Of course, it is not that the lower the temperature, the better. Generally speaking, the best engine coolant working temperature is around 80-100°C. Therefore, when starting the vehicle in winter, the engine must be warmed up and maintained at the best working temperature. The new generation of B58 engine has made great efforts in the cooling system.
First of all, the B58's intercooler was changed from the original N55 air-cooled intercooler to a water-cooled one. The air-cooled intercooler uses the air “hit” from the front of the car to cool the supercharged intake air. Obviously, it will be affected by the speed of the car and cannot maintain the best cooling effect under any working conditions. The water-cooled intercooler is different. It uses the computer to actively control the flow rate of the circulating coolant to achieve the “on-call” cooling “service”.
In addition to cooling the air sucked in by the engine, complex temperature management of the entire engine body is required, which includes not only the temperature control of the six cylinders, oil, turbocharger and other components, but also the heat exchange of the air conditioning system The temperature of the device is controlled.
The thermostat that plays a great role in the cooling system is the thermostat. Compared with the traditional thermostat based on the principle of thermal expansion of paraffin, the new B58 engine relies on temperature sensors and electronically controlled rotary valves to form a thermal management module. Under the circumstances, the cooling system has been controlled more accurately and intelligently.
In addition, in terms of the water pump as the power source for driving the coolant circulation, the B58 has also made some changes compared to the N55. The cooling system of the N55 uses an electric water pump, while the B58 is equipped with two water pumps, one of which is a mechanical water pump. To drive the main cooling cycle of the engine, the other is an electric water pump, which is used to individually control the cooling of the turbocharger. The mechanical water pump is driven by the crankshaft of the engine, so the disadvantage is that the coolant cannot be circulated after the vehicle is turned off. Therefore, it can be said that the strategy adopted by BMW on the B58 engine is to choose a suitable cooling cycle method to cool different parts according to different working conditions.
● Using modular development method
This inline six-cylinder engine also reflects BMW’s future trend of modular production of engines. Based on a single-cylinder 0.5L displacement, it has expanded its research and development of three-cylinder, four-cylinder and six-cylinder engines because of this as a unit. The power output, fuel economy, and mechanical friction of each cylinder can be maintained in an ideal state. Compared with three and four-cylinder engines, this new inline six-cylinder engine may not be modular. The biggest difference is that the intercooler uses a water-cooled type with better performance.
From N55 to B58, in this era of rampant three-cylinder and four-cylinder engines, we can believe that in the future, BMW will still not let fans who love straight-six engines lose, and BMW will still inherit this engine form. Moreover, not only the improvement of the intake and exhaust system and the turbocharger, but also the optimization of the engine cooling system, we can see that on the basis of the N55, the B58 has once again squeezed out all aspects of the inline six-cylinder engine performance . In addition, it is very important that the modular design concept of BMW B series engines will also reduce the cost of engine development and manufacturing, and shorten the development cycle. In short, BMW's paranoia about inline six-cylinder engines is justified. In fact, how does the new-generation B58 inline six-cylinder engine perform? We still have to wait for the actual test drive of the model equipped with it before we can make a conclusion. (Auto House Text/Picture Xia Zhimeng)