Displacement

The volume of space through which the piston moves from top dead center to bottom dead center is called the cylinder displacement. If the engine has several cylinders, the sum of the working volumes of all the cylinders is called the engine displacement.

Torque

Torque is the force that rotates an object. The engine torque refers to the torque output from the crankshaft side of the engine. In the condition of fixed power, it is inversely proportional to the engine speed. The faster the speed, the smaller the torque, and vice versa, it reflects the load capacity of the car within a certain range.

Compression ratio

That is, the degree to which the engine mixture gas is compressed is represented by the ratio of the total volume of the cylinder before compression to the volume of the compressed cylinder (ie, the volume of the combustion chamber). Compression ratio has a lot to do with the performance of the engine. Usually the low pressure compression ratio refers to a compression ratio of 10 or less and a high compression ratio of 10 or more. Relatively speaking, the higher the compression ratio, the greater the power of the engine, but the inside of the engine. Process, combustion accuracy and oil quality requirements are also higher.

Multi-point EFI

The EFI system of an automobile engine is generally composed of three parts: a fuel injection circuit, a sensor group, and an electronic control unit. If the injector is installed in the original carburetor position, ie the entire engine has only one petrol injection point, this is a single-point EFI; if the injector is installed on the intake pipe of each cylinder, ie the injection of gasoline is from multiple places (At least one injection point per cylinder) is injected into the cylinder, which is the multi-point EFI.

Multi-valve

Most of the traditional engines are one intake valve and one exhaust valve per cylinder. This two-valve gas distribution mechanism is relatively simple and the manufacturing cost is low. For an ordinary engine whose output power is not so high, it can obtain comparatively good results. Satisfactory engine output power and torque performance. Large-displacement, high-power engines use multi-valve technology. The simplest multi-valve technology is the three-valve structure, which is based on an intake valve and a two-valve structure. In recent years, most of the cars newly developed by major automobile companies in the world have adopted the four-valve structure. In the four-valve gas distribution mechanism, each cylinder has two intake valves and two exhaust valves. The four-valve structure can greatly improve the efficiency of the engine's intake and exhaust, and most of the new cars use four-valve technology.

Overhead camshaft (OHC)

The camshaft mounting position of the engine has three forms: lower, center, and top. Due to the high speed of the car engine, the rpm can reach more than 5,000 rpm. In order to ensure the intake and exhaust efficiency, the intake valve and the exhaust valve are used in the inverted form, namely the overhead valve device, which can be applied to the camshaft. The three installation forms. However, if a lower-mounted or mid-mounted camshaft is used, because the distance between the valve and the camshaft is relatively long, auxiliary components such as a valve lifter and a tappet are required, resulting in a large number of valve transmission mechanisms, a complicated structure, and a large engine volume. It is also easy to produce noise at high speeds, but it can be changed by using an overhead camshaft. Therefore, modern sedan engines generally use an overhead camshaft, which is arranged above the engine, shortens the distance between the camshaft and the valve, omits the tappet and tappet of the valve, and simplifies the camshaft to the valve. The transmission mechanism between them will make the structure of the engine more compact. More importantly, this installation method can reduce the reciprocating quality of the entire system and improve the transmission efficiency. According to the number of camshafts, it can be classified into two types: single overhead camshaft (SOHC) and double overhead camshaft (DOHC). As the mid- to high-class sedan engine is generally a multi-valve and V-cylinder arrangement, dual camshafts are required. The intake and exhaust valves are controlled separately, so dual overhead camshafts are used by many brand-name engines.

Variable valve timing

The crankshaft rotates the camshaft via a toothed transmission, so that when the valve is actuated to open and close, it will form a certain correspondence relationship with the rotation angle of the crankshaft. The flow of gas will change with the speed of the engine's operation. How can the cylinder achieve good air intake efficiency at different speeds? For this reason, the valve opening and closing time must be changed. The camshaft can be made to rotate at a small angle through the oil pressure device installed at the front end of the camshaft so that the intake valve can be opened early when the rotation speed increases.

Variable length intake manifold

In order to maintain a smooth intake efficiency at high and low engine speeds, how to fabricate a suitable intake line has become an important issue. By setting the valve in the intake pipe, the intake pipe is changed to a short, two-path path to satisfy the need for a high flow rate and high kinetic energy flow when the engine is operating at a high rotation speed; and to supply the engine with an appropriate flow of air at a low rotation speed. . This allows the engine to achieve greater horsepower at high speeds and better fuel economy at lower speeds.

EGR - Exhaust gas recirculation

The engine control computer controls the engine speed, load (throttle opening), temperature, intake air flow, and exhaust temperature so that a small part of the exhaust gas enters the intake system and mixes with the mixed gas before entering the cylinder for combustion. A small part of the exhaust gas enters the cylinder to participate in the combustion of the mixture, which reduces the temperature in the cylinder during combustion because NOx (nitrogen oxides) is generated under conditions of high temperature and oxygen enrichment, so that the generation of NOx is suppressed and the exhaust gas is reduced. The NOx content. However, excessive exhaust gas participation in the recirculation will affect the ignition and performance of the mixture, which will affect the engine's dynamic performance, especially when the engine is idle, at low speed, at low load, and when the engine is cold, the recirculated exhaust gas will significantly affect the engine. performance. Therefore, when the engine is at idle, low speed, low load, and cold, the computer-controlled exhaust gas does not participate in the recirculation to prevent the engine performance from being affected; when the engine exceeds a certain speed, load, and reaches a certain temperature, the computer controls only a small portion. Exhaust gas participates in recirculation, and the amount of exhaust gas participating in the recirculation varies depending on engine speed, load, temperature, and exhaust gas temperature to achieve the lowest NOx in the exhaust gas.

Three-way catalytic converter

It is the most important external purifying device installed in the exhaust system of an automobile. It can convert harmful gases such as CO, HC and NOx emitted from automobile exhaust into non-harmful carbon dioxide, water and nitrogen through oxidation and reduction. Because this kind of catalytic converter can convert the three main harmful substances in the exhaust gas into non-hazardous substances at the same time, it is called ternary. The working principle of the three-way catalytic converter is that when a high-temperature automotive exhaust passes through the purification device, the purifying agent in the three-way catalytic converter will enhance the activity of the three gases of CO, HC, and NOx, and promote a certain oxidation-reduction chemical reaction. Among them, CO is oxidized to a colorless, non-toxic carbon dioxide gas at high temperatures; HC compounds are oxidized to water and carbon dioxide at high temperatures; NOx is reduced to nitrogen and oxygen. The three harmful gases become harmless gases, so that the automobile exhaust can be purified.

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