How the engine and gearbox work

Excerpt from: http://club.autohome.com.cn/bbs/thread-c-172-10864192-1.html###

First, a general diagram: This is the structure of the car's power system, the following question is around this diagram to explain:

Engine

first, the basic theory

The simplest way for a petrol engine to convert the energy of gasoline into kinetic energy to drive a car is through the engine
Internal combustion of gasoline to obtain kinetic energy. Therefore, the automobile engine is the internal combustion engine----combustion inside the engine occurs.

There are two points to be aware of:
1. There are other types of internal combustion engines, such as diesel engines, gas turbines, each with its advantages and disadvantages.
2. There are also external combustion machines. The steam engine used in the early days of trains and ships is a typical external combustion machine. Fuel
(coal, wood, oil) burns the outside of the engine to produce steam, and then steam enters the engine to generate
Force. The efficiency of the internal combustion engine is much higher than that of the external combustion machine, and it is smaller than that of the same power. Therefore, modern cars do not use steam engines.
By contrast, an internal combustion engine is more efficient than a gas turbine, cheaper than an electric vehicle, and easily added to fuel. These advantages enable most modern cars to use reciprocating internal combustion engines.

second, combustion is the key

The car's engine generally uses 4 strokes. (Mazda's rotor engine is not discussed here, car pictorial has been introduced)

4 strokes are: intake, compression, combustion, exhaust. Complete these 4 processes, the engine completes a cycle (2 turns).

Understanding 4 Strokes

Piston, which is connected by a piston rod and a crankshaft, the process is as follows

1. The piston starts at the top, the intake valve opens, the piston moves downward, and the gas mixture is inhaled.
2. The piston moves toward the top to compress the gas mixture, making the explosion more powerful.
3. When the piston reaches the top, the spark plugs emit sparks to ignite the gas mixture, and the explosion causes the piston to move downward again.
4. The piston reaches the bottom, the vent valve opens, the piston moves upwards, and the exhaust gas is discharged from the cylinder by the exhaust pipe.
Note: The final movement of the internal combustion engine is rotational, and the linear reciprocating movement of the piston is eventually converted from the crankshaft to the rotation to drive the car tires.

third, cylinder number

The core part of the engine is the cylinder, the piston in the cylinder reciprocating movement, described above is a single cylinder movement process, and the actual application of the engine is a plurality of cylinders (4, 6, 8 cylinder is more common). We usually classify the engine by the way the cylinders are arranged: inline, V or horizontal alignment (and now, of course, the VW Group's W-type, which is actually two V).
Different arrangement of the engine in the smoothness, manufacturing costs and the shape of the advantages and disadvantages of each, equipped with the corresponding car.

Iv.. Displacement

Mixing gas compression and combustion in the combustion chamber, piston reciprocating movement, you can see the combustion chamber volume changes, the maximum and minimum value of the difference is the displacement, with liters (l) or ml (cc) to measure. The displacement of the car is usually between 1.5l~4.0l. The displacement of the 0.5l,4 cylinder per cylinder is 2.0L, if the V-type arrangement of 6 cylinders, that is V6 3.0 liters. In general, displacement indicates the size of the engine's power.

So more power can be gained by increasing the number of cylinders or increasing the volume of each cylinder's combustion chamber.

v. Other parts of the engine

Camshaft controls the opening and closing of intake valves and exhaust valves
Spark plugs spark sparks to ignite oil and gas mixtures, causing explosions to occur. Sparks must be released at the right time.
The valve inlet and outlet valves are opened at the appropriate time to inhale the gas mixture and exhaust gas. In compression and
When burning, both valves are closed to ensure that the combustion chamber is sealed.
The piston rings are sealed in the cylinder wall and piston:
1. Prevents oil and gas mixtures and exhaust gases from leaking into the lube tank during compression and combustion.
2. Prevents lubricant from entering the cylinder to burn.
Most "engine oil" cars are because the engines are too old: piston rings are no longer sealed (exhaust pipe
Blue smoke)
The piston rods are connected to the Pistons and crankshafts, allowing the Pistons and crankshafts to maintain their respective motions.
The lubricating oil tank surrounds the crankshaft with a considerable amount of oil.

General engine appearance

The following is the focus of the common cylinder structure of different engines

Inline 4 cylinders (A3 is such a structure)

V6 (medium and high-grade sedan)

Horizontal alignment (e.g. Subaru's leopard)

Gearbox

First, the role of the gearbox

The physical characteristics of the engine determine the existence of the gearbox. First of all, any engine has its peak speed, second, the maximum engine power and maximum torque in a certain speed zone. For example, the maximum power of the engine appears at 5500 rpm. The gearbox can produce a different speed ratio between the engine and the wheel during the car's driving, and shifting can make the engine work in its optimal dynamic performance state. Ideally, the gearbox should have a flexible speed ratio. The stepless transmission (CVT) has this characteristic, which can better exert the power performance of the engine.

(1) CVT

The stepless gearbox has a continuous speed ratio. It has not been heavily equipped with cars because of its price, size and reliability. Now, the improved design makes the use of CVT more common.
Domestic Audi 2.8 CVT

(2) This is a manual gearbox.

Mercedes-Benz C-Class sport Coupe 6-speed manual gearbox
The gearbox is connected to the engine through the clutch so that the input shaft of the gearbox can be synchronized with the engine.

Generally 5-speed, parameters are for reference only
A 5-gear gearbox provides 5 different variable-speed ratios, resulting in a poor rotational speed between the input shaft and the output shaft. See table below:

Second, the simple transmission model

To better understand how the gearbox works, let's look at a simple model of a 2-speed gearbox to see how the parts fit together:

• The input shaft (green) is connected through the clutch and the engine, and the shaft and the gear above are a part.

• Shafts and gears (red) are called intermediate shafts. They rotate together. The shaft (green) rotates through the meshing gear to drive the middle shaft, at which point the middle axle can transmit the engine's power.

• The shaft (yellow) is a spline shaft that connects directly to the drive shaft and drives the car through the differential. The wheel rotates with the spline shaft.

• The gears (blue) rotate freely on the spline shaft. When the engine stops, but the vehicle is still in motion, the Gears (blue) and the intermediate shafts are stationary, while the spline shaft rotates with the wheels.

• The gears (blue) and spline shafts are connected by a sleeve that rotates with the spline axis, and can also slide freely around the spline shaft to engage the gear (blue).


When 1 gears are attached, the sleeve engages with the right gear (blue). See:

, the input shaft (green) drives the intermediate shaft, the middle shaft drives the right gear (blue), and the gear is connected to the spline shaft through the sleeve and transmits energy to the drive shaft. At the same time, the left side of the gear (blue) is also rotating, but because there is no meshing with the sleeve, so it does not affect the spline shaft.

When the sleeve is in the middle of the two gears (shown in the first picture), the gearbox is in the neutral position. All two gears rotate freely on the spline axis, and the speed is determined by the ratio of gear to gear (blue) between the middle shaft.

Third, the real gearbox (A3 transmission principle is also the case)

Today, the 5-speed manual gearbox application is already common, and the following is its model.

The shift lever is connected with three shift forks through three connecting rods, see

There is a rotation point in the middle of the shift lever, and when you dial in 1, you actually push the connecting rod and shift fork in the opposite direction.

When you move the shift lever around, you are actually choosing a different shift fork (different sockets), or selecting a different gear (blue) when moving back and forth.

Four, reverse gear

Reverse gears are achieved by means of an intermediate gear (purple). , the gears (blue) always turn in the opposite direction of the other Gears (blue). Therefore, in the process of car forward, it is impossible to put into reverse gear, the sleeve teeth and gears (blue) can not mesh, but will produce a lot of noise.

Five, synchronous device

Synchronization is caused by a friction contact between the teeth on the sleeve and the Gears (blue) before meshing, see

The conical protrusion of the gear (blue) is just the tapered notch that snaps into the sleeve, and the friction between the two makes the sleeve and gear (blue) synchronous, the outer slide of the sleeve, and the gear mesh.

How the engine and gearbox work