Let me show you what the internal structure of the engine looks like?

The engine block of a modern automobile engine is mainly composed of the engine block, cylinder head, cylinder head cover, cylinder liner, main bearing cap and oil pan. The engine block is the support of the engine and the assembly base of the crankshaft connecting rod mechanism, valve mechanism and major parts of various engine systems. The cylinder head is used to close the top of the cylinder and form a combustion chamber together with the piston top and cylinder wall.

Airframe components

Cylinder head The cylinder head is used to seal the cylinder and form the combustion chamber. The cylinder head is cast with a water jacket, water inlet hole, water outlet hole, spark plug hole, bolt hole, combustion chamber, etc.

Cylinder head

Cylinder block The cylinder block is the main body of the engine. It connects each cylinder and the crankcase into one, and is the supporting frame for installing the piston, crankshaft and other parts and accessories.

Cylinder Block

Cylinder gasket The cylinder gasket is located between the cylinder head and the cylinder block. Its function is to fill the microscopic gaps between the cylinder block and the cylinder head to ensure good sealing at the joint surface, thereby ensuring the sealing of the combustion chamber and preventing air leakage in the cylinder and water leakage in the water jacket.

Cylinder head gasket

Piston-connecting rod assembly The piston-connecting rod assembly is the transmission part of the engine, which transmits the pressure of the combustion gas to the crankshaft, causing the crankshaft to rotate and output power. The piston-connecting rod assembly is mainly composed of pistons, piston rings, piston pins and connecting rods.

Piston connecting rod assembly

The main function of the piston is to bear the pressure of the combustion gas and transmit this force to the connecting rod through the piston pin to drive the crankshaft to rotate. In addition, the top of the piston, the cylinder head and the cylinder wall together form the combustion chamber. The piston is the part with the most severe working conditions in the engine. The gas force and reciprocating inertia force act on the piston.

piston

Connecting rod The connecting rod assembly includes connecting rod body, connecting rod cap, connecting rod bolt and connecting rod bearing. The function of the connecting rod assembly is to transmit the force borne by the piston to the crankshaft and convert the reciprocating motion of the piston into the rotational motion of the crankshaft. The small end of the connecting rod is connected to the piston pin and reciprocates with the piston; the big end of the connecting rod is connected to the crank pin and rotates with the crankshaft. Therefore, the connecting rod performs complex planar motion when the engine is working.

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Crankshaft flywheel assembly The crankshaft flywheel assembly includes a crankshaft, a flywheel, a torsional vibration damper, and a balance shaft. The function of the crankshaft flywheel assembly is to convert the reciprocating motion of the piston into the rotational motion of the crankshaft, output torque for the driving of the car and other mechanisms that require power; at the same time, it also stores energy to overcome the resistance of the non-power stroke and make the engine run smoothly.

Crankshaft flywheel assembly

The function of the crankshaft is to convert the gas force transmitted by the piston and connecting rod into torque to drive the vehicle's transmission system, the engine's valve mechanism and other auxiliary devices. The crankshaft works under the combined action of periodically changing gas force, inertia force and torque, and bears alternating bending and torsion loads.

Crankshaft

Crankshaft Terminology

Crankshaft installation position

Crankshaft installation position

Crankshaft Working Principle We all know that the piston in the cylinder moves up and down in a straight line, but how to convert the straight line motion into rotational motion in order to output the rotational force that drives the wheels forward? In fact, this has a lot to do with the structure of the crankshaft. The connecting rod shaft and the main shaft of the crankshaft are not on the same straight line, but are arranged oppositely.

Working principle of crankshaft This movement principle is actually very similar to pedaling a bicycle. The two feet are equivalent to two adjacent pistons, the pedals are equivalent to the connecting rod shaft, and the large flywheel in the middle is the main shaft of the crankshaft. When the left foot pushes down hard (the piston does work or inhales and moves downward), the right foot will be lifted up (the other piston compresses or exhausts and moves upward). This cycle repeats itself, and the linear motion is converted into rotational motion.

The valve mechanism mainly includes the timing gear system, camshaft, valve transmission components (valves, push rods, rocker arms, etc.). Its main function is to open and close the intake and exhaust valves of each cylinder in time according to the working conditions of the engine, so that the fresh mixed gas can fill the cylinder in time and the exhaust gas can be discharged from the cylinder in time.

Schematic diagram of valve train

Valve mechanism composition

Valve train types can be divided into bottom camshaft type and overhead camshaft type according to the position of the camshaft. Bottom camshaft type means that the camshaft is arranged at the bottom of the cylinder; overhead camshaft type means that the camshaft is arranged at the top of the cylinder. OHV (Overhead valve ) refers to the bottom camshaft of the overhead valve. OHC (Overhead camshaft) refers to the overhead camshaft. If there is only one camshaft on the top of the cylinder that is responsible for the opening and closing of the intake and exhaust valves at the same time, it is called a single overhead camshaft (SOHC).

Overhead valve engine If there are two camshafts at the top, responsible for the opening and closing of the intake valve and exhaust valve respectively, it is called double overhead camshaft (DOHC). Under DOHC, there are two camshafts, one can control the intake valve and the other can control the exhaust valve. This can increase the intake valve area, improve the shape of the combustion chamber, and increase the valve movement speed, which is very suitable for high-speed cars.

Double overhead camshaft

OHV vs SOHC

Valve timing Valve timing can be simply understood as the moment when the valve opens and closes. Theoretically, during the intake stroke, when the piston moves from the top dead center to the bottom dead center, the intake valve opens and the exhaust valve closes; during the exhaust stroke, when the piston moves from the bottom dead center to the top dead center, the intake valve closes and the exhaust valve opens.

Schematic diagram of valve timing The purpose of timing in actual engine operation is to increase the amount of air intake in the cylinder. The intake valve needs to be opened earlier and closed later. Similarly, in order to exhaust the exhaust gas in the cylinder more cleanly, the exhaust valve also needs to be opened earlier and closed later, so as to ensure the effective operation of the engine. Camshaft The camshaft is mainly responsible for the opening and closing of the intake and exhaust valves. The camshaft rotates continuously under the drive of the crankshaft, and the cam continuously presses down the valve, thereby realizing the function of controlling the opening and closing of the intake and exhaust valves.

Camshaft structure

Camshaft Terminology Valve The function of the valve is to input fuel into the engine and expel exhaust gas.

Valve components

Valve Terminology Valve Spring The function of the valve spring is to rely on the tension of its spring to quickly return the open valve to the closed position, and prevent the valve from creating a gap due to inertia during the movement of the engine, ensuring that the valve can fit tightly when closed, and also preventing the valve from breaking the seal due to bouncing during vibration.

Typical valve springs and related parts Valve seat inserts Valve seat inserts are the contact surface between the valve and the cylinder head. The valve and valve seat insert are used to seal the combustion chamber to regulate intake and exhaust.

Valve seat Valve clearance When the engine is cold and the valve is in the closed state, the clearance between the valve and the transmission part is called valve clearance. Figure (a) shows the adjustment of valve clearance by screws, and Figure (b) shows the adjustment of valve clearance by shims.

Valve clearance Hydraulic tappet The hydraulic tappet is mainly composed of the tappet body, plunger, ball plunger (push rod support), check valve, check valve spring and return spring. The unique internal structure design of the hydraulic tappet can automatically adjust the transmission clearance of the valve mechanism, transmit the cam lift change, and open and close the valve on time.

The working principle of hydraulic tappet is that when the cam is in the lifting stage, the cam compresses the plunger, the one-way valve is closed, and a small amount of oil in the high-pressure chamber leaks out from the clearance between the tappet body and the plunger according to the matching parts. At this time, the hydraulic tappet can be approximately regarded as an uncompressed rigid body. Under the support of the "rigid body", the intake and exhaust valves are opened. In the return stage of the cam, the force on the plunger is released, and the plunger resumes its rise under the action of the return spring. The valve automatically closes under the action of the valve spring, completing a working cycle and achieving the purpose of automatically adjusting the valve clearance. Rocker arm The rocker arm is a lever mechanism that presses the valve and is used to drive the valve to open and close.