Traditional power self-salvation analysis fuel injection technology

On the issue of how to improve fuel economy, engineers have tried everything. The most direct one is to change the structure or control logic of the fuel injection system. Their goal is only one, and it is based on meeting the driving demand. As far as possible to save fuel, how to save money and increase expenditure is indeed the art.

If you often look at our technical articles, then you will certainly be familiar with my writing routines. Yes, this time it is the same. I will first talk to you about some theoretical knowledge about fuel injection. Finally, I will focus on fuel injection. Those who say that maintenance, of course, will expose the little tricks of the shopkeepers.

This article will describe fuel injection in the context of the gasoline engine's EFI system. As for the earlier carburetor and mechanical injection system, it will not be introduced. In my opinion, although old, but the old fuel injection technology is not necessarily inferior to the electronic control of the jet technology, but for most users, obviously these things are more visible and tangible Concerned.

● How did gasoline get from the rear to the front?

This problem must be discussed based on an engine with a front-mounted engine. Most of the fuel tanks of such vehicles will be placed near the bottom of the trunk. Of course, for a rear-mounted or mid-engined vehicle, It would be more appropriate to change the question to “How does gasoline get from the front to the rear?” Anyway, what we must discuss first is the issue of gasoline transportation. In fact, this is very simple. The petrol pump is the key to the problem, but have you paid attention to some details?

☆ Where does the "click" come from?

Before you turn the ignition switch, petrol will stay quietly in the tank, with little fluctuation. After turning on the power supply, many people noticed a "click" from the rear of the car. Some people with a lot of spirits were not concerned about this, but this voice would surely attract those who thought carefully. After many observations, they also found out that when the power supply was turned on, the “click” sound lasted only about 2 seconds and then disappeared. Perhaps you already know that this "click" sound is sent by the petrol pump hidden in the fuel tank. Then why does it sound when it is turned on, not when it is started?

☆ Gasoline pressure determines the starting quality If the gasoline cannot be supplied to the cylinder of the engine in time, the start-up time will inevitably be longer, and even more than one ignition can complete the engine start-up process. The oil pressure in the fuel system pipeline is an important condition for the normal start of the engine. After the power is turned on by the ignition switch, the gasoline pump starts to work, and the pressure inside the fuel system is established during the period between the time the power is turned on and the time it is started. In order to prepare for fuel supply during the start-up process. With the continuous improvement of car configuration, more and more models are equipped with a key to start the function, although the one-button start function will still follow the principle of first ignition after power, but from the driver's operating habits, this The time difference between the two steps is basically negligible (if the brake pedal is not applied, the engine is only switched on without starting the engine, and most people are used to pressing the start button while pressing the brake pedal. ) However, the starting quality of the engine has not been compromised. Why?

- For vehicles equipped with a one-touch start-up function, the time difference is still the key to establishing oil pressure.

It takes time for the petrol pump to establish the oil pressure for the fuel system to start normally. However, due to the upgrade of the configuration, the driver's operating mode changes, but the engineer still squeezes out the time for the establishment of the oil pressure. Occurs when the owner presses the door unlock button or pulls the door open (most cars equipped with a one-button start feature also have a keyless entry function. Therefore, opening the door will also induce gasoline pump work, and different brands will There are different control logics. This way, before the ignition switch is pressed, the oil pressure in the fuel system line is already established.

☆ When starting, shouldn't it stop at the power block for a while and wait for the meter's self-test light to go out before starting?

This problem will be mentioned by the friends around you. Some friends with positive answers will view this issue from the perspective of car electrical protection. However, some friends think that it is not necessary to care too much about it. In their view, one key is provided. Vehicles with a start-up function seldom delay time in the process of power-on. If you look at this issue from the point of view of establishing oil pressure, it is better to wait for a period of time, and at least wait until the “click” sounds stop before starting, so as to ensure the start quality.

●What happens when the petrol pump HOLD fails?

Under normal circumstances, after the flameout, the oil pressure in the fuel system pipeline will not be immediately drained, but will be maintained for a period of time by using the pressure-maintaining capacity of the petrol pump. This is the key to restarting the engine after a short period of flameout. Because, from the driver's operating habits, most drivers will directly turn the ignition switch to the starter, if the fuel pressure in the fuel system pipeline at this time does not meet the start-up standard, so as to affect the owner's use Car feel. With this "impression" to the 4S shop inspection, in addition to the routine testing of gasoline pressure steps (testing gasoline pressure under different operating conditions), one of the most important test items is to look at the pressure in the fuel system piping after the flameout. Capacity, if within a certain period of time, the oil pressure value falls beyond the standard range, it can prove that the petrol pump's pressure holding capacity is reduced, and if the owner wants to completely improve this "defect", he can consider replacing the petrol pump.

The decrease in pressure holding capacity not only affects the start after a short flameout, but also relates to the performance of the cold car start. For example, you are turning on the power (turning the ignition switch to turn on the power or remotely opening the door, triggering the start of the petrol pump After work, the owner may not start the engine immediately. Because the petrol pump's pressure-keeping capacity is insufficient, even if the gasoline pressure that meets the start conditions has been established before, when the car starts the engine, the gasoline in the tubing cannot be fully satisfied. Required by the engine, resulting in reduced start-up quality.

• How is the gasoline delivered to the engine distributed? (For ease of understanding, the following are four-cylinder engines as an example)

During the start-up and operation of the engine, a steady stream of gasoline is pumped out of the tank by a petrol pump and sent to the rails after being filtered by the filter core. Wait, what does it mean to use multiple injections in the configuration form? Is there a single point? What is the difference between multiple points and single points?

☆What is a single shot?

The so-called "point" refers to the fact that there are several fuel injection points, that "single point" is undoubtedly only a fuel injection point, you can also understand that there is an injector, the injector is located in front of the throttle, driving When the user depresses the accelerator pedal, the flap of the throttle valve opens, and the engine computer determines the opening time of the injector according to the signal collected by the relevant sensor. The injected fuel enters the intake manifold through the throttle, and then, each cylinder All of them need to be taken (gasoline will be sucked into the cylinder when the intake valve is open). This type of injection is obviously too extensive in control, and the fuel economy is necessarily poor. Therefore, it will not be replaced by multiple injections.

"Because there are few pictures about single-point jet technology, we have to find pictures on textbooks to illustrate the difference in structure between single-point jets and multiple jets."

The emergence of any new thing has its own reason for existence. Single point EFI is no exception. It is the product of the evolution of the carburetor era to the era of EFI. Due to the low production cost, the manufacturer hopes to build the foundation of the original carburetor engine. The completion of the transformation of the fuel injection system, to be over-completed, they have launched multi-point EFI.

☆Manipulator self-salvation (multi-point injection)

Multi-point injection has been undergoing multiple developments since its inception, from the initial simultaneous injection to sequential injection. Since many people believe that manifold injection has developed into a bottleneck, coupled with the promotion of in-cylinder direct injection technology on gasoline engines, The injection of tube was very much replaced. However, in the future technological advancement, we saw it again and we could not help but lament it.

The structure of simultaneous injection of multiple injections allowed each cylinder to have its own fuel injector. There has been a qualitative leap in the control of fuel injection. However, in the early stages of development, they did not perform well. This structural advantage is fully realized. Due to the single control logic, the engine computer cannot accurately calculate which cylinder needs fuel injection. Therefore, the engine computer will issue a fuel injection instruction every time the crankshaft rotates 360°. The injectors simultaneously perform the fuel injection action. That is, in order to meet the fuel injection requirements of a single cylinder, the gasoline injected into other cylinders is wasted, which is bound to be detrimental to fuel economy, and elimination is only a matter of time.

The control logic of the fuel injection system was upgraded shortly after the packet injection. After the improvement, the four fuel injectors were divided into two groups, that is, one set of each crankshaft rotation (2). Fuel injection nozzles have doubled fuel economy, but this has not been accepted by people.

- Sequential injection manifold injection has been developed so far that it can accurately control the fuel injection of each injector according to the working process of the cylinder and the rhythm of the timing of gas distribution. We call it sequential injection. When many manufacturers are switching to more advanced direct injection technology, Nissan still hopes to make more contributions in the field of manifold injection. The 2011 1.6-liter HR16 model equipped by Trent uses the DIS dual-nozzle. In terms of technology, the accuracy of the fuel injection control is higher than that of a traditional one-cylinder injection nozzle.

Advantages of the direct injection system in the cylinder: lean combustion can be achieved, fuel economy can be improved, higher compression ratio can be allowed, and engine power can be increased.

The emergence of direct fuel injection systems has brought new opportunities for the development of multi-point injections. Its significance is that it can make a drop of fuel more dispersed to increase its combustion efficiency. Prior to this, multi-point manifold injections also tried to In this regard, the method used is better. The method adopted is to open more holes in the injector head to enhance its atomization capability. However, under the premise of limited fuel pressure, The method quickly developed into a bottleneck.

The installation position of the high-pressure pump components and injectors is different in structure between the direct-injection system and the manifold injection. If you want to understand the direct-injection system directly, you can divide the system into high and low pressure parts. The low-pressure part is the same as the manifold injection system. It is also the petrol pump that pulls the gasoline out of the tank and sends it to the engine after being filtered by the filter core. At this time, the pressure inside the tubing is almost the same as that of the manifold injection system. The quality change occurs after the high pressure pump. It can push gasoline pressure to hundreds or even higher (three to forty times the fuel pressure of the manifold injection system), and then the fuel will pass through the fuel rails to the nozzles belonging to each cylinder, only waiting for the engine computer to sound. In the instant, oil droplets, the diameter of which is equivalent to only one tenth of the diameter of the hair, will be injected directly into the cylinder. The high-pressure oil pump is usually driven by a camshaft, and a double-headed or three-headed cam is pressurised inside (such as "No. 9 cam" of the Ford ECOBOOST series engine).

-- It took its short-term hybrid injection When the fuel pressure was raised to 100 Bar or even higher, a new era of fuel injection came, but engineers did not abandon the traditional injection method due to the gradual maturity of new technologies. In their opinion, manifold injections still have great value.

â—‹ Toyota's hybrid injection technology was developed as early as 1998. SZ and NZ engines equipped with Toyota D4 technology first appeared on the Japanese market. Several years later, they were replaced by GR series engines. The 3GR-FSE 3.0L engine used D4 direct injection technology. Only one set of injectors extends into the cylinder to achieve homogeneous combustion.

The 2GR-FSE engine is equipped with a more advanced D4-S technology. In addition to a group of injectors extending into the cylinder, it also has a conventional intake manifold injector. At low load conditions, the manifold injectors inject fuel during the intake stroke, the mixture enters the cylinder, and then the cylinder injection nozzles are injected with the compression stroke to achieve stratified combustion; at high load conditions, In-cylinder direct injection is only performed during the compression stroke. This will increase engine power and economy.

The advantage of this design is that the oil and gas mixing can be more complete, that is, the engine computer will actively switch the fuel supply mode according to the load of the engine and the operating conditions, and at the same time, the high compression ratio of 11.8 can further enhance the mixing and combustion of oil and gas. Efficiency, to achieve even more outstanding power and fuel consumption performance. This is also the key factor that 2GR-FSE won Ward's top ten engine for three consecutive years.

â—‹ The stratified combustion technology used by Audi's hybrid injection system in-cylinder direct injection system achieves lean combustion. Compared with ordinary combustion technology, its advantage is that it allows the mixture to have a higher air/fuel ratio (less fuel). , more air) to complete the combustion, improve fuel efficiency, however, this combustion technology will also have certain side effects, in the lean combustion (excess oxygen) operating conditions, the excess oxygen in the cylinder and the nitrogen retained in the cylinder memory is more likely to occur The strong reaction resulted in the formation of nitrogen oxides, which had a very bad impact on tailpipe emissions. Prior to this, improving the capacity of catalytic converters was an important way to remedy this drawback, which was followed by an increase in manufacturing costs. This was not worth the loss. The technology has been divided into tasteless areas in the eyes of some people. But such voices did not shake the engineers' determination to continue to develop stratified combustion technology. The most important issue they faced is how to fundamentally solve the disadvantages of stratified combustion technology. From the current point of view, it is a good idea to join a manifold injection system. The program, which is designed for low load conditions of the engine, improves the quality of the exhaust gas and the operating pressure of the three-way catalytic converter.

● How is the fuel injection adjusted?

For different operating conditions, the engine computer will control the injection quantity of each cylinder. For example, in the cool car stage, the mixture will be enriched, and as the engine temperature warms up, the fuel and air in the mixture The proportion gradually moves towards the best condition (the fuel injection amount gradually decreases) until the engine idle speed falls back to the normal range.

In the normal driving process, the driver controls the acceleration of the vehicle through the accelerator pedal, that is, the deeper the accelerator pedal is, the faster the vehicle speed will be. In an ideal state, the pedal cadence will directly affect the vehicle's acceleration time. Among these, it is natural to rely on intake, fuel injection, ignition and other auxiliary components in order to make the engine output a higher power, as to how the vehicle's acceleration response, but also depends on the gearbox mood. Since the subject of this article is jetting, then it is still a case in point. How does the amount of fuel injection increase?

The manifold injection system first talks about manifold injection. The gasoline pump installed in the fuel tank will adjust its own working state within a certain range as the engine speed changes, thus changing the oil supply pressure. In general, it It will be proportional to the engine speed. Of course, the discussion here does not include the factory-set fuel cutoff speed.

The amount of fuel injection is related to the internal valve needle opening time and the pressure in the fuel rail. It can be understood that under the same gasoline pressure conditions, the longer the valve needle is opened, the more gasoline will be injected. Then the amount of fuel injected becomes less, and if the pressure in the rail rises, then the amount of gasoline injected by the injector will be more in unit time. The injector valve needle opening/closing and the petrol pump operating status are adjusted by the engine computer.

- In-cylinder direct injection system In-cylinder direct injection is also in the low-pressure stage, and the high-pressure part is entirely controlled by the high-pressure oil pump. This type of high-pressure oil pump is a plunger type structure and is driven by a dedicated cam on the camshaft. Seeing this, you may have doubts that since the cam is used to drive, the piston pump pressurization process cannot be adjusted according to the engine speed. Even if the engine computer can control the opening and closing time of the injector nozzle To control the amount of fuel injected, it is clear that such controls have certain limitations. Indeed, the angle of the cam is not adjustable, and it is impossible to switch the cam with different angles like Audi's AVS technology to achieve the purpose of adjusting the stroke of the plunger pump. Therefore, the plunger pump itself cannot perform the task of adjusting the gasoline pressure. After thinking about this problem, you will definitely go over and think about it. In fact, if you pay attention to the figure, you will understand.

There is a harness connector on the high-pressure pump housing, which is connected with an electronic control valve, which can adjust the gasoline pressure. Of course, here is more of the atomization effect of fuel injection into the cylinder. Considering that during the acceleration process, higher gasoline pressure can also help the injector to emit more gasoline, which imposes a considerable demand on the execution capability of the injector, because under such pressure, The valve needle's operating frequency and stability are critical. Because of this, the injectors used in the direct injection system of the cylinder are very different from those used for manifold injection.

When should I clean the injector?

If you ask a 4S shop service advisor, most of the time, they will use the mileage as a basis to suggest that you are in the cleaning time. So, you dubiously signed the repairs on the maintenance slip, but also specifically The phrase "I want to be quick, I'll be in a hurry." Do you not know that this sentence is about their hearts and minds. What do they think?

What happens if the injector is dirty? Naturally, it will be blocked. The consequence of this is that gasoline cannot be ejected from the nozzle at a normal flow rate. This obviously can affect the working condition of the engine, but the owner seems to be unaware of this. why?

The oxygen sensor installed on the exhaust pipe will monitor the quality of the exhaust gas in real time. The engine computer can use it as the basis to calculate the concentration of the mixture. When the mixture is too lean, the engine computer will increase the valve opening time to the nozzle. In order to compensate for the impact of insufficient flow, the response is to increase the value of the injection pulse width in the data. Using this feature, we can determine the cleanliness of the nozzle by the injection pulse width. Engage mileage to determine whether to clean the injector.

Finally, returning to the above question, why did service consultants like to hear customers complain about their rush? The cleaning time determines the quality of the cleaning. According to the normal process, the person responsible for construction must use a whole bottle of syrup for cleaning to calculate a complete maintenance operation, but this will take a short time, and the workshop will be The position is limited. Only after the maintenance vehicle is handed over to the customer as soon as possible can the next customer be welcomed. Therefore, if the customer is worried about the time it takes to clean the injector, this will surely result in multiple parties. Satisfaction, if you want to ask if I am likely to be “pulled” to the shop after the car is not cleaned, it will be handed over to the owner. I advise you how long it will be.

Edit summary:

The injection method of the engine is the art of the door. From the purely mechanical structure of the injection system to the electronically controlled fuel injection system, the efficiency is gradually improved after multiple evolutions, until it reaches a bottleneck in the stage of manifold injection, followed by technology. The breakthrough has fueled a new era for fuel injection, and in the technical foresight of the fuel injection system, you will find that the manifold injection that is about to be reformed again appears in the injection system and also plays an important role in optimizing the exhaust quality. The role of this multi-tasking life course is indeed worth studying. After understanding it, it will surely help future car owners.