Fuel injection systems have been used on vehicles for many years. The earliest ones were purely mechanical. As technology advanced, electronic fuel injection systems became more popular. Early mechanical and electronic fuel injection systems did not use feedback controls. As emissions became more of a concern, feedback controls were adapted to both types of fuel injection systems.

燃油喷射系统已经在汽车上运用了许多年。最早期的喷射系统都是机械式的。随着技术的进步，电子燃油喷射系统逐渐得到普及。早期机械式和电子式燃油喷射系统都没有采用反馈控制。由于排放问题越来越得到重视，反馈控制在这两种系统中都得到了应用。

Both mechanical and electronic fuel injection system can be found on gasoline engines. Diesel engines are most commonly found with mechanical type systems, although the newest generation of these engines have been using electronic fuel injection (EFI)

汽油发动机使用机械式或电子式燃油喷射系统。柴油机通常使用机械式燃油喷射系统，但是最新一代的柴油发动机也已经在使用电子式燃油喷射系统了。

5.1  Basic theory  

EFI uses solenoid valves called injectors to meter fuel delivery. Most vehicles today use 1 injector per cylinder. When the solenoid is energized, fuel sprays out into the valve port. Fuel is delivered to the injector by a high-pressure electric pump at around 40 psi. Fuel delivery is controlled by the injectors which are cycled by the computer. The computer produces a signal to open the injectors for a certain length of time depending on engine conditions relayed by sensors. The longer that the injector is open, the more fuel is injected. As engine load and rpm are increased, the injector open times are increased to match increasing airflow. This computer output signal is called the injector pulse width. The longer the pulse width, the more fuel is injected.

电子式燃油喷射系统使用被称作喷油器的电磁阀来控制喷油量。今天大多数汽车1个气缸使用1个喷油器。电磁阀一上电，燃油就被喷射至电磁阀口。高压电动燃油泵以大约40psi的压力将燃油送到喷油器。喷油量是由喷油器控制的，而喷油器的开启和关闭又是被计算机控制的。计算机根据传感器送来的工况信号，向喷油器发送开启以及开启持续时间的信号。喷油器打开时间越长，喷出的燃油越多。随着发动机负载和转速的增加，喷油器打开的时间也

要增加来匹配进气量的增加。计算机输出信号被称作喷油器脉冲宽度。脉冲宽度越大，喷出的燃油越多。

5.2 Engine Requirements 

Stand spark ignited, 4 stroke engines require that the correct proportion of fuel be mixed with the incoming air for efficient operation. This proportion is in the range of 13 parts air to 1 part fuel for best power, 15 to 1 for best emission and 17 to 1 for best economy. Most modern engines aim for a ratio of around 14.7 to 1 for the majority of cruising and medium power conditions. This is the chemically correct ratio which results in the lowest average emissions and reasonable power. A rich condition is characterized by an excess of fuel, and a lean condition is characterized by an excess of air or lack of fuel.

标准四冲程点火式发动机为了获得高的效率，要求合适的空燃比。为了获得最佳动力性，空燃比是13比1，为了获得最佳排放，空燃比是15比1，为了获得最佳经济性，空燃比是17比1。大多数现代发动机在大多数巡航工况和适中的动力性条件下，空燃比控制目标为14.7比1。这是化学分析上适当的空燃比，可以获得最低的平均排放和适当的动力性。燃烧浓工况意味着燃料过多，稀工况意味着空气过量或燃料不足。

As rpm is increased, up to a point, airflow also increases and fuel flow must increase to match it. As the throttle is opened at a given rpm, airflow increases to a certain point and again, fuel flow must follow airflow.

当发动机转速上升到某一点，空气进气量也随之上升，此时进油量也必须对应随之上升。在某一发动机转速下，当节气门打开，空气进气量上升到某一数值下，同样进油量必须跟随空气进气量。

5.3  fuel system   

EFI fuel system consists of a tank, pump, fuel rail,, regulator,  out an excess of fuel injectors and return line. Fuel is drawn from the tank by the pump which steps up pressure to around to 40 psi. Fuel pressure is controlled by the fuel pressure regulator located on one end of the fuel rail by bleeding fuel back to the tank through the return line. The pump always puts out an excess of fuel so large quantities are returned back to the tank during idle and low speed conditions and less as engine demand increases. The fuel rail is essentially a tubular fuel manifold designed to carry fuel to the injectors as well as hold them in place on the intake manifold. The injectors are usually sealed with O-rings on each end. One end has the fuel entering from the rail and the other end spigots into the manifold. The injector has a 2 pin electrical plug to carry switching current to the solenoid winding. When energized, the solenoid core is pulled back which pulls back a sealing pintle, disc or ball, allowing fuel to spray out in a fine, conical pattern,

电子喷油系统由油箱、油泵、油轨、调节器、喷油嘴和回油管路组成。燃油由油泵从油箱吸出，并被加压到大约40psi。油压通过位于油轨一端的燃油调节器控制。燃油调节器将燃油通过回油管路放回到油箱实现对油压的控制。油泵总是泵出过多的燃油。因此，空转或低速工况下，多余的燃油就返回到邮箱。随着发动机负载的增加，返回邮箱的燃油减小。油轨实际上就是油路歧管，用来将燃油送到喷油嘴，同时把燃油存在进油歧管内。通常使用O型环把喷油嘴的两端密封。喷油嘴一端与油轨相连，另一端与歧管采用连接管接合。喷油嘴有一个两脚电子开关来承载电磁线圈的开关电流。当电磁线圈上电，衔铁吸回，带动密封轴、密封盘或密封球，从而使得燃油细密呈圆锥形喷出。

5.4 Air metering and measurement 

The amount of air entering the engine is controlled by a conventional butterfly valve on most engines located in a throttle body assembly.

一般大多数发动机使用一个蝶形阀来控制进入到发动机的空气。这个阀位于节气门体总成上。

Airflow measurement is by one of two basic methods: Mass Airflow and speed Density. The mass airflow method uses either a spring loaded flap attached to a potentiometer or a heated mire mounted in front of the throttle body to sense actual airflow. The position of the flap or amount of current required to keep the wire heated to a certain temperature is relayed to the computer as a voltage signal. A certain voltage equals a certain airflow rate.

发动机进气量的测量有两种基本方法：空气流量计和速度密度法。空气流量计法使用与电位计相连的弹簧接片或位于节气门体总成前端的热线来测量实际空气流量。弹簧接片的位置或保持热线在一定温度下所需的电流被转换为电压信号传给计算机。一定的电压信号对应着一定的空气进气速率。

The speed density system uses a solid state pressure transducer to measure the pressure in the intake manifold with rpm and air temperature to indirectly determine airflow. Again, a certain pressure relates to a certain voltage which is relayed to the computer.

速度密度系统使用晶体管压力传感器测量进气歧管的压力，并联合发动机转速和空气温度来间接确定进气量。同样，一定的压力对应着一定的电压信号，然后被传给电脑。

5.5.1RPM    

Most systems measure rpm off of the ignition coil tachometer pulse or crank triggered magnetic/Hall effect sensors. Rpm is considered a primary input signal on all EFI systems. Most systems generate an injection pulse for every tach pulse so as rpm is increased, the frequency of injection pulses is also increased.

发动机转速  大多数燃油喷射系统实用点火线圈转速计脉冲或曲轴触发磁场/霍尔效应传感器来测量发动机转速。发动机转速是所有燃油喷射系统最重要的一个输入信号。大多数系统对每一个测速脉冲信号产生一个喷射脉冲信号。因此，随着发动机转速的增长，喷射脉冲信号频率也随着增长。

5.5.2 airflow  

On mass airflow type system, this input is also considered a primary input signal. X amount of air requires Y amount of fuel. As rpm and throttle opening is increased, airflow increases to a point

空气进气量  对于空气流量计系统，空气进气量也是一个非常重要的输入信号。X份的空气要求Y份的燃油。随着发动机转速和节气门开度的增加，空气进气量也随之增加到一个数值点上。

5.5.3Manifold Pressure 

 On speed density type systems, this input is essential when combined with the rpm signal to calculate airflow. As the throttle is opened, the manifold pressure increases which will require more fuel.

歧管压力  对于速度密度式系统，歧管压力非常重要，它需要和联合发动机转速信号来计算空气进气量。当节气门打开，歧管压力增加，这就需要更多燃油。

5.5.4 Throttle Position 

This input is a secondary input on most systems. It is required mainly for acceleration enrichment when the throttle is rapidly opened. By looking at the rate of change of throttle blade angle, the computer can determine how quickly the throttle is being opened and can supply the extra fuel required momentarily to alleviate the lean condition. Throttle position is measured by a potentiometer attached to the throttle shaft.

节气门位置 节气门位置信号对于大多数系统是个较为次要的信号。它主要是用于当节气门被快速打开时，加快燃油浓工况的过程。通过观测节气门叶片角度的变化率，计算机可以判断节气门以多快的速度打开，从而瞬时间提供过量的燃油来减轻较稀的工况。节气门位置是用于节气门轴相连的一个电位计来测量。

5.5.5Water Temperature  

 Water temperature is a secondary input required mainly to ensure proper starting and warm-up of the engine. When the engine is cold, the air to fuel ratio must be very rich to enable enough fuel to vaporize for proper starting. The computer increases the injector pulse width to supply extra fuel when cold and tapers this fuel off as the water temperature increases. Once the water warms past 120 degrees or so, the computer does not need to add any extra fuel.

水温 水温信号也是一个次要输入信号，主要用来保证发动机适当启动和热机。当发动机处于冷态，为了保证发动机较好的启动，空燃比必须变得很浓，来确保足量的燃油被蒸发。冷态时，计算机增加喷油嘴脉冲宽度来提供额外的燃油，并随着水温的升高逐步减少额外的燃油喷射。当水温超过大约120度，计算机不再提供额外的燃油喷射信号。

5.5.6 Air Temperature 

This is a secondary input required especially on speed density systems. The sensor is usually mounted in the intake manifold or air filter area. As the air temperature drops, its density increases. Dense air requires more fuel. As the temperature of the inducted air increases, the computer reduces the pulse width to compensate for lower density. Mass airflow systems are not critically affected by operation without air  temperature sensor because the airflow meter is already measuring the air mass entering the engine.

空气温度 对于速度密度式系统，空气温度信号是一个次要的输入信号。这个传感器一般位于进气歧管或者空气滤清器区域。当空气温度下降，空气密度上升。空气密度越大，所要求的燃油越多。随着进气温度的上升，计算机减小喷油嘴的脉冲宽度来补偿密度的降低。由于空气流量计已经测量了进入发动机的进气量，空气流量计系统严格意义上无需温度传感器。

5.6  oxygen sensor 

This sensor is employed in closed loop systems to modify the basic pulse width after the fact. It is mounted into the exhaust manifold area. By looking at the oxygen content of the exhaust gases after combustion, the computer can determine if the air/fuel ratio is too rich or too lean for optimum combustion and adjust the next few injections accordingly. This sensor is primarily employed for emission control and to a lesser degree, fuel economy. For the lowest average emission, the air/fuel ratio must be kept around 14.7 to 1.

氧气传感器被用在闭环系统来根据实际情况调整基本脉冲宽度。它位于排气歧管区域。通过检测燃烧后排放的废气中氧气的含量，计算机能判断出对于最佳燃烧而言，空燃比是否过浓或过稀，从而调整接下来喷油量。氧气传感器首先被用来排放控制，其次用于燃油经济性控制。对于最低的平均排放，空燃比必须要控制在14.7：1左右。

Under full throttle conditions, this sensor is ignored by the computer so that the engine can produce more power. This is called open loop mode and the computer is supplying the injector pulse width from tables based on all of the other sensors inputs.Once throttle opening and rpm are reduced to cruising conditions, most systems will jump back into the closed loop mode where they will stay for a large portion of the time on most street driven applications.

当节气门全开状态下，氧气传感器的输入被计算机忽略，从而使得发动机产生更大的功率。这被称作开环模式。此时，计算机根据其他传感器的输入信号基于数据表提供喷油嘴脉冲宽度。一旦节气门开度和发动机转速减小到巡航状态，大多数系统会再回到闭环控制模式。对于大多数街道驾驶的情况，系统主要采用闭环控制模式。

5.7  basic operation  

As explained in the Basic Theory section, the computer processes all of the voltage signals from the various sensors to determine the engine operation conditions at the moment and delivers the appropriate pulse width to the injectors. If engine airflow increases by 10%, the pulse width is also increased by about 10% to keep the air/fuel ratio constant. If the rpm is doubles from 2000 to 4000 rpm, the number of injections are also doubled to double the fuel flow.

正如基本理论一节中所介绍的，计算机处理来自不同传感器的所有电压信号来判断发动机所处的实时工况，并向喷油嘴发送适当的脉冲宽度。如果发动机进气量增加了10%，脉冲宽度也要相应的增加大约10%来保证空燃比恒定。如果发动机转速从2000转/分变为4000转/分，喷油脉冲个数也要翻倍来匹配翻倍的空气进气量。

The computer looks at the changes in sensor inputs every few milliseconds in order to be ready to modify the pulse width if any parameter changes.

每隔几微秒，计算机就要观察传感器输入的变化，从而调整脉冲宽度，以适应参数的变化。

5  exercise

1 The injection pump in the jerk pump system is used to time, meter and pressurize the fuel. This is the most common and utilized system. The plungers are driven by a camshaft that is designed to control the injection characteristics of the engine.

高压燃油喷射泵系统中的喷油泵用来给燃油分配，测量和施加压力。它是最普遍使用的系统。活塞由凸轮轴驱动，设计用来控制发动机的喷油特性。

2Compared to gasoline engines, diesel have a number of important advantages. One is fuel economy. Diesel engines are unthrottled, so pumping losses are reduced. This improves breathing efficiency for more fuel-efficient operation. Diesel engines also run much leaner air/fuel ratio than their gasoline counterparts, and have much higher compression ratios which improves thermal efficiency and helps squeeze even more power out of every drop of fuel.

与汽油机相比，柴油机具有许多重要的优势，其中之一就是燃油经济性。柴油机没有节气门，从而减小了泵的能量损失。这为更有效的运行改善了发动机呼吸效率。柴油机与汽油机相比，可以运行在更稀的空燃比下，有更高的压缩比，从而提高了热效率，有助于从燃油上更多地获取能量。

3The injection systems that delivers fuel to a diesel engine operates at much higher pressure than a gasoline: as much as 17400 psi for traditional pump, line and injector systems up to 23500 psi for common rail system, compared to 35 to 90 psi for most gasoline EFI system. The fuel is also sprayed directly into the combustion chamber rather than into the intake port.

     给柴油机送燃油的喷射系统工作油压要比汽油机高出许多。传统柴油机泵的优雅达到17400 psi，一般的喷油泵-高压油管-喷油器系统可以高达23500psi，而大多数汽油电子喷射系统只有35到90psi。对于柴油机，燃油并不是喷射到进油口，而是直接喷射到燃烧室内部。

4  Diesel engines have no ignition system, so there are no spark plug, plug wire or distributor to cause problems. The fuel is ignited by the heat of compression and controlled by injection timing. For cold starting, diesels use a glow plug system as an additional heat source to aid in the combustion process until the engine is running and generating its own heat.

柴油机没有点火系统，因此也就没有可能引发问题的火花塞、火花塞线圈或分电器。柴油被压缩产生的热量点燃，并由喷射时间加以控制。对于冷机启动，柴油机使用电热塞来作为额外的热源，从而给燃烧提供帮助，直至发动机运转，可以产生自己的热量。

5 The HEUI System develops injection pressures as high as 18000-24000 psi, by applying high-pressure oil to the top of an intensifier piston. By varying the oil pressure, injection rate can be controlled independently of the crank or cam. Thus injection timing, rates, and pressures are no longer dependent on camshaft position, speed or cam ramp velocity. This is all controlled by a solenoid-actuated valve that determines when high-pressure oil is applied to the piston.

HEUI系统（美国卡特匹勒公司的电控中压共轨式喷油系统）通过将高压油施加在强化过的活塞上部，可以产生高达18000至24000psi的喷射油压。通过改变油压，可以独立于曲柄或凸轮来控制喷射频率。因此，喷射的时间，频率和压力都不再依赖于凸轮轴位置，车速或凸轮斜面速率。这些都可以通过一个电磁作动阀进行能够控制，这个阀决定了向活塞施加高压油的时间。