Some people say this is a three-cylinder car. What does this three-cylinder car mean?

Faced with more and more three-cylinder engines in the compact market, many friends who want to buy a car are at a loss. Today I will explain the problem of three-cylinder engine in detail. Before we begin, the professor wants to ask you a little question: Why do almost all brands flock to three-cylinder engines when consumers are so exclusive?

Cost, yes, compared with the four-cylinder engine, the three-cylinder engine reduces a whole set of intake and exhaust components and piston connecting rod structure, which has considerable advantages in cost. At the same time, there is a second reason for manufacturers to choose three cylinders, that is, the current "double integral policy" has forced almost all manufacturers to embark on the road of no return with three cylinders under heavy pressure.

The "double-integral policy" stipulates that the average fuel consumption per 100 kilometers of passenger cars from 20 18 to 2020 will be 6 liters, 5.5 liters and 5 liters respectively. The positive integral of that year can be carried forward, and the negative integral can be reduced to zero through the positive integral of affiliated enterprises or deducted from the positive integral of new energy vehicles.

Many people may wonder, can a three-cylinder engine save fuel? I'm afraid it's not from the manufacturer, right? Don't worry, because the three-cylinder machine still has many problems to explain to you, but the three-cylinder machine is really more fuel-efficient.

More fuel-efficient three-cylinder engine

In order to understand that a three-cylinder engine can save fuel, we need to find out the factors that affect automobile fuel consumption:

● Air resistance: wind resistance. For a car, its drag coefficient (Cd value) is determined by the body design. The lower the drag coefficient, the lower the fuel consumption at the same speed, while the faster the speed, the greater the drag and the higher the relative fuel consumption.

● Wheel rolling resistance: that is, tire resistance, which is related to tire width, tire model, temperature and weather.

● Curb quality: that is, vehicle weight, which is easy to understand. The heavier the car, the higher the fuel consumption.

● Internal friction of body system: here mainly refers to the power consumption generated by gearbox and transmission system.

● Engine thermal efficiency: refers to the ratio of engine efficiency to the total energy consumed by fuel, which is related to the technology of the engine itself.

It is obvious to all that automobile manufacturers and tire manufacturers have made gratifying breakthroughs in the first three tasks. The weight of the intermediate car with lightweight aluminum alloy can be reduced to about 1.5 tons, and the Cd value can generally be less than 0.30 after optimized wind resistance design. Among all kinds of tires, a special column is reserved for low rolling resistance economical tires.

Reducing vehicle fuel consumption, on the one hand, is to meet consumers' demand for daily low cost, on the other hand, it is also the constant oppression of policies. Where fuel consumption can be stolen, manufacturers are making various efforts. Now all manufacturers use three-cylinder engines, which is the best scheme with the lowest cost and the best effect at this stage.

The displacement of a three-cylinder engine is generally less than 1.5L, but now the turbocharging technology is mature. Under the condition of "stable working conditions", the rising power of three-cylinder turbocharged engines generally exceeds 80kW, and it may even exceed 100kW in the future, which means that the power of 1.0T small-displacement turbine engines is not inferior to that of traditional 1.5L and 6544.

The principle of reducing fuel consumption of three-cylinder small displacement engine is also very simple, mainly for the following reasons:

● Small displacement: At the same number of revolutions, the friction between the piston ring and the inner wall of the cylinder is small, reducing the internal friction of the engine.

● Reduce the number of three-cylinder kinematic pairs: Compared with the four-cylinder engine, the three-cylinder engine reduces a set of crank-connecting rod mechanism and piston cooling nozzle, and also reduces the friction work of camshaft bearings, tappets and other kinematic pairs.

● Volume weight loss: Weight loss directly affects fuel consumption, just like body weight loss; At the same time, the volume is reduced, and the heat dissipation of the engine cylinder will also be reduced, which is conducive to reducing fuel consumption.

Here you may ask, since reducing the number of cylinders can improve the efficiency of the engine, why not use a single-cylinder or double-cylinder engine?

Do you really think that car manufacturers don't want to? Believe me, they will do it if conditions permit, but there are two problems that are really difficult to overcome. The first is NVH. The NVH performance of three-cylinder engine is still unsatisfactory after the introduction of balanced shaft and other technologies, and single-cylinder and double-cylinder engines are more deadly in this respect.

Secondly, and most importantly, single-cylinder and double-cylinder cannot match the turbocharging technology well, because the exhaust continuity of single-cylinder and double-cylinder engines is insufficient.

One cycle of the engine is 720 degrees, that is, two revolutions. The normal exhaust cycle is 180 degrees. Assuming that the opening advance angle of the exhaust valve is 30 degrees and the closing lag angle is 30 degrees, the exhaust stroke is about 240 degrees. This means that the single-cylinder engine has 2/3 cycles (720-240=480 degrees) without exhaust pulse, while the double-cylinder engine has 1/3 cycles without exhaust pulse, which will lead to insufficient turbine pressure. Three-cylinder engines do not have this problem. 240+240+240 is exactly equal to 720 degrees, and the exhaust pulse can cover the whole engine cycle. Even if the opening advance angle and closing lag angle of the exhaust valve are not so large, it is enough to ensure the operation of the whole turbine system.

Four-cylinder engine matching turbine still needs to optimize the exhaust manifold design to avoid exhaust interference, while three-cylinder engine can perfectly avoid this problem.

Moreover, the three-cylinder turbocharging technology has accumulated a lot. The V6 twin-turbo engine with the ignition sequence of 1-5-3-6-2-4 is cut off in half, and its basic structure is exactly the same as that of the three-cylinder engine, which has been widely used in various medium and large cars and sports cars.

It is precisely because of the low technical threshold and low cost of three-cylinder engine that manufacturers are eager for this imperfect engine structure in order to reduce fuel consumption and meet regulatory requirements. However, it is undeniable that there are serious problems in the three-cylinder engine. In the next section, we will explain it in detail.

Congenital defects of three-cylinder engine

In Legend, the three-cylinder engine has various shortcomings, such as large vibration, loud noise, weak acceleration, short life and so on. But to some extent, I am really allergic to the three-cylinder machine.

The structure of a three-cylinder engine can be simply regarded as a semi-V6 engine. As we said in the last part, the performance of 1.0T three-cylinder turbocharged engine is higher than that of 1.5L naturally aspirated engine. And in the engine verification test, the three-cylinder engine, like the previous four-cylinder engine and six-cylinder engine, has to undergo endurance fatigue test and deep cold and hot impact test, and its calibration performance needs to be re-verified after the system test. The intensity of these tests far exceeds the load of daily vehicles, so there is no need to worry about the quality of the engine.

However, due to structural problems, the jitter of the three-cylinder engine affects the daily experience of the owner. Even though the manufacturers provide much more optimization for the jitter of the three-cylinder engine than the four-cylinder engine in the past, the three-cylinder engine with congenital deficiency is really "jitter".

The reason why the engine vibrates is that in an engine cycle (crankshaft rotates twice), the motion pairs (piston, crankshaft and connecting rod) in each cylinder are in different working states at different time nodes, and the force and torque of the system will vibrate at any time when it is unbalanced. From a mechanical point of view, there are four factors to be analyzed:

Low reciprocating inertia force

Low reciprocating moment of inertia

● Centrifugal inertial force

● Centrifugal inertia moment

If I start writing formulas, I believe everyone will start reading with a closed book, so let's take an intuitive look at this problem.

As can be seen from the figure, in an in-line four-cylinder engine, 1 cylinder is opposite to cylinder 4, and cylinder 2 is opposite to cylinder 3. The piston always moves twice with the same relative position, which balances the reciprocating inertia force. The moment of reciprocating inertial force acting on the crankshaft is just like two people with the same weight and size sitting on the seesaw, keeping the balance of reciprocating inertial force distance, and so is the inline six-cylinder engine.

However, the crank structure of the three groups of pistons of the three-cylinder engine is 120 degrees, and the three-piston structure looks unbalanced, but we can know through calculation that the reciprocating inertia force of the three-cylinder engine is dynamically balanced. On the crankshaft, the reciprocating moments of inertia generated by three groups of motion pairs are very chaotic, and their own structures can not be balanced at all. These chaotic moments need to be borne by the crankshaft, so irregular torsional vibration is produced.

To understand how serious the vibration of a three-cylinder engine is, we must first popularize some knowledge about 1, 2,3 ... the N-order vibration of the engine. In the stage of engine vibration optimization, engineers will sample and analyze the engine vibration wave, and then decompose the complex main vibration wave into independent vibrations in different frequency domains through the "Fourier transform" in traditional engineering. According to the different vibration frequencies, these periodic vibration waves can be divided into 0-order, 2-order ... n-order vibrations.

Because the vibration is caused by the structural imbalance of the system, whether it is 1 order vibration or second-order vibration, it is periodic. In the engineering test, it is found that the main vibration of the three-cylinder engine comes from the 1 order vibration with strong impact, the proportion of which is close to 80%, while the proportion of the second-order vibration is only 20%, which can be ignored compared with the vibration above the third order. Our common in-line four-cylinder engine has no 1 vibration, so the vibration degree is much less than that of three-cylinder engine.

Moreover, because the frequency of 1 order vibration is only half that of the second order vibration, the "impulse feeling" of vibration transmission is stronger, while the high-frequency vibration feeling is denser and the impact feeling is lower.

Although we often say that the in-line six-cylinder engine and the horizontally opposed oblique engine are completely balanced, there is no perfect balance when the engine really works. Due to the combustion impact in the cylinder, the total overturning moment of the system cannot be completely offset. Only by increasing the number of cylinders and balancing the ignition time can the impact of combustion impact be minimized.

Three-cylinder engine can do more work at a time under the same power output because of the small number of cylinders, which further intensifies the vibration. Due to such congenital defects, the three-cylinder engine does "shake" even more.

The jitter that cannot be eliminated can only be optimized.

Theoretically, as long as the main source of vibration can be determined, inertia balance can be achieved by designing the balance shaft, optimizing the dynamic balance of flywheel and crankshaft, and designing the eccentric piston. Many four-cylinder engines also have corresponding designs, but it is particularly difficult to completely balance the vibration of three-cylinder engines, and even no manufacturer will do so.

To solve the vibration problem perfectly, a three-cylinder engine needs four sets of balance shaft devices, which not only costs too much, but also loses the advantages in volume and weight, not to mention the corresponding friction resistance caused by the movement of each balance shaft, and finally the fuel consumption advantage of the four-cylinder engine will be exhausted.

Therefore, the vibration problem of three-cylinder engine is destined to be optimized, but not completely solved.

Fortunately, the automobile industry has accumulated a lot of technology after so many years of development. At present, the excellent three-cylinder engines on the market have come up with many optimization technologies worth learning:

● Balance shaft: It works synchronously with the engine through the structure of the rotating shaft to balance the periodic vibration of one order 1. Of course, the engine can achieve better balance effect by designing multiple groups of balance shafts, but due to objective reasons such as space and cost, usually only one balance shaft is designed for three-cylinder engines to balance 1 order vibration.

● Eccentric flywheel/crankshaft counterweight: reduce the eccentricity of the whole structure and eliminate centrifugal inertia force, thus reducing vibration.

● Intra-abdominal lightweight: through lightweight piston-connecting rod structure, unbalanced inertia force is reduced, thus reducing vibration.

● Eccentric piston: By adjusting the position of the center of mass of the piston, the imbalance problem in the piston movement can be balanced.

● Optimize ignition timing: By adjusting the ignition timing of the cylinder, unnecessary vibration can be reduced under the condition of ensuring combustion.

However, unlike in-cylinder direct injection and dual camshaft technologies, these technologies cannot be directly used. So even though many manufacturers in the market claim that they have made various optimizations, the engine performance is still unsatisfactory. Technology upgrading needs a lot of data precipitation, and system optimization also "affects the whole body". It is very difficult to optimize a three-cylinder engine because there are too many uncertain "X factors".

An interesting phenomenon can also be found by counting the customer complaints of various types of three-cylinder engines in the market, that is, the performance of jitter problem and the speed range with serious jitter are very different among different brands and models, which also shows that the performance of all three-cylinder engines can not be characterized only by "three cylinders".

Vibration optimization of three-cylinder engine is more like chassis tuning, which is quite metaphysical and requires deep technical precipitation and cost-free attempts by manufacturers. Therefore, there are indeed three-cylinder engines with acceptable vibration performance in my opinion, but for some brands of three-cylinder engines, I can only respect them and stay away silently.

So, does the three-cylinder engine have a future?

Through the above long explanation, we understand why the three-cylinder engine will shake, and where is the difficulty of the optimization of the three-cylinder engine shake. Since it is almost impossible to completely balance the three-cylinder engine itself, you may ask: Does the three-cylinder engine have a future?

To this, my answer is yes. First of all, there are indeed some three-cylinder models with good vibration performance on the market. In order to avoid advertising suspicion, the specific models will not be discussed, but the appearance of this part of the "high-quality" three-cylinder engine is enough to prove that the vibration problem of the three-cylinder engine is far from unbearable after the optimization.

Of course, the current objective situation is that NVH optimization of most three-cylinder engines and vehicles on the market needs to be improved.

The NVH performance that vehicles really convey to users includes the optimization of vehicle NVH. Manufacturers can further enhance the user experience by isolating the engine suspension and the overall vibration without completely solving the vibration of the three-cylinder engine, and if you can accept the inherent gap between the three-cylinder engine and the four-cylinder engine in vibration, you can also get a cheaper car purchase price.

Buick with three-cylinder engine

Yinglang (parameter | picture) model experienced a period of low sales, but eventually the sales rebounded rapidly after the terminal discount became larger. Last month, it reached the monthly sales level of 30,000 bicycles, ranking the top 5 in the total sales list of models.

The three-cylinder BMW model has a similar situation. The 1.5T three-cylinder of its B series engine is currently

X 1 (parameter | picture). Like other brands, people generally scoff at BMW with three-cylinder engine, but market statistics give completely different feedback. 85% of the sales of BMW 1 Series sedan comes from 1.5T three-cylinder engine.

Similarly, 80% of the sales of BMW's entry-level SUV X/KLOC-0 comes from its two-wheel drive 1.5T three-cylinder engine version. Even the most BMW-inspired 3-series model, the 3 18 model with three-cylinder engine has an excellent performance of selling more than 1,000 a month.

Simply adding up the sales of these three-cylinder BMW models, we can find that the monthly sales of three-cylinder BMW models are stable at more than 1 10,000 vehicles. A luxury brand is still like this. For some cheaper grocery shopping models, if the optimization of the three-cylinder engine can pass, my car purchase cost can be greatly reduced, so it is not bad to buy an optimized three-cylinder model.

We have always emphasized that the three-cylinder engine has the advantages of small size and light weight besides fuel saving. When combined with new energy technology, the use of three-cylinder engine is more conducive to vehicle lightweight and optimization of power system layout. At the same time, with the help of motor power, the idling jitter problem of the three-cylinder engine can be perfectly avoided, and the advantages of the three-cylinder engine can be maximized.

Of course, it is untenable to blindly believe in saving fuel with small displacement. Small-displacement turbine engines do have advantages in the test of the Ministry of Industry and Information Technology, but if you need to accelerate quickly, the deterioration of combustion conditions will make the small-displacement three-cylinder engine of small horse-drawn carts consume more fuel.