Is the piston important to the engine? Why it matters.

Engine Piston Working Principle

It takes the pressure from the combustion gas at the top of the piston and passes the gas pressure through the piston pin to the connecting rod to drive the rotation of the crankshaft, which rotates and outputs power. The engine piston consists of a top, head and skirt. When the piston works, the combustion gas pressure acts on the top of the piston, and the piston pin reaction force acts on the pin seat hole in the head.

Working Process Of Piston Connecting Rod Group:

1. Air Intake Stroke
The piston moves from top to bottom TDC under the drive of the crankshaft. The exhaust valve closes and the intake valve opens. In the process of piston movement, the cylinder volume increases gradually, and a certain vacuum degree is formed in the cylinder. Air is drawn into the cylinder through the intake valve.
2. Compression Stroke
After the intake stroke, the crankshaft continues to drive the piston from BDC to TDC. At this point, the intake and exhaust valves are closed. As the piston moves the cylinder volume decreases, the mixture in the cylinder is compressed, and its pressure and temperature rise simultaneously.
3. ExpansionStroke
When the compression stroke is close to the end (about 20 degrees before the top dead center and injection advance Angle), fuel is injected into the nozzle, and fuel is injected while burning (diesel diffusion combustion). The volume of the combustion gas expands rapidly, and the pressure and temperature rise rapidly. Under the action of gas pressure, the piston moves from top TDC to bottom TDC and rotates the crankshaft through the connecting rod to do work. The intake and exhaust valves are still closed.
4. Exhaust Stroke
The exhaust stroke begins, the exhaust valve opens, the intake valve is still closed, and the crankshaft drives the piston to move from the bottom DEAD center to the top dead center through the connecting rod. At this time, the combustion gas (or waste gas) after expansion is discharged from the cylinder through the exhaust valve under its own residual pressure and the push of the piston. When the piston reaches TDC, the exhaust stroke ends and the exhaust valve closes.

Engine Piston Combustion Is Caused By What Reason

Causes of engine piston burning are:
1. The engine temperature is too high, causing the piston to boil.
2. The fuel injector pressure is too large, resulting in detonation combustion of the piston of the cylinder, resulting in combustion of the piston.
3. The clearance between the piston and the cylinder liner is too small.
4. The piston pin holes and the piston pins are tightly installed. The engine piston consists of a top, head and skirt. The position at which a piston burns, usually at the head or skirt of the piston.

As the top of the piston is directly in periodic contact with high temperature gas, the highest temperature of gas can reach more than 2500K, so the temperature of the piston is also very high, the temperature of the top of the piston can reach 600-700K. On the one hand, the high temperature reduces the mechanical strength of the piston material significantly, and on the other hand, it increases the thermal expansion of the piston, which is easy to destroy the coordination of the piston and its related parts.

It can be seen from the working conditions of the piston, in order to ensure the good operation characteristics of the engine, the piston alloy material properties have the following requirements: low density, low thermal expansion coefficient, good wear resistance, good mechanical properties, good thermal conductivity and good processing performance. For this reason, the piston material used in automobile engine is aluminum alloy, and the piston of individual automobile diesel engine is made of high grade cast iron or heat resistant steel.

Engine Piston Installation Method And Piston Ring

The installation method of engine piston is as follows:
1. First in the piston pin and the piston pin hole coated with oil, and then the piston and connecting rod with the piston pin connection, and installed on the piston pin spring;
2. Install piston rings and install each ring on the piston from bottom to top; When installing gas ring, pay attention to the direction of ring mouth and positive and negative side;
3. Mount the upper bearing bush and connecting rod together;
4. Clamp the piston ring with a special tool and tap the piston head with a wooden handle to load the piston connecting rod assembly.

Engine piston ring is a kind of metal elastic ring with large outward expansion deformation ability, gas ring and oil ring. The air ring is installed in the gap between the piston and the cylinder to prevent air leakage; The oil ring is installed in the cylinder wall, relying on the movement of gas and liquid pressure difference, scraping off the excess oil on the cylinder wall, avoiding the oil entering the combustion chamber, but also making the oil on the cylinder wall evenly distributed, improving lubrication.

Precautions For Installing Engine Pistons

1. Before installation, the parts must be cleaned, the clearance should be checked, and the technical identification should be carried out. Parts that do not meet technical requirements must be repaired or replaced.
2. The pit in the vortex chamber at the top of the piston and the lubricating oil hole at the small end of the connecting rod should be on the same side and must be upwards.
3. When replacing the new cylinder liner, the cylinder should be put into the mounting hole before installing the waterproof ring, and check the protruding height of the body to meet the requirements before formal installation.
4. Do not scratch the piston or break the piston ring when installing the piston ring. Chrome plated ring shall be installed in the first ring slot. If the inner edge of the second and third air rings has grooves, the grooves should be made upward; If the outer edge has grooves, the grooves shall be downward. The chamfering on the outer edge of the oil ring should be upward.
5. After use, the left and right main bearings shall not be replaced, and the upper and lower connecting rod tiles shall not be installed incorrectly. Connecting rod bush after pressing into the tile seat should have a certain tightness, and slightly higher than the tile seat plane.
6. The edge of the cylinder gasket should face the cylinder head, and the hole should be aligned with the hole of the body. When tightening the cylinder head nut, the diagonal cross nut should be evenly tightened according to the specified torque. Too loose easy to leak and burn out cylinder pad; Too tight easy to make cylinder cushion lose elasticity, resulting in bolts or screw hole slip. Replace with a new cylinder gasket and tighten the cylinder head nut again according to the regulations after working for 20 hours.

The Process Of Removing An Engine Piston

Disassembly process of the engine piston:
1. Check the assembly mark on the top of the piston before disassembly, or mark it yourself.
2. Turn the crankshaft to bring the piston to BDC.
3. Remove the connecting rod nut, take off the connecting rod cover and bearing, and place them in order.
4. Push out the piston connecting rod group using a rubber hammer or hammer wooden handle.
5. After removing the piston connecting rod group, reinstall the connecting rod cover, bolts, and nuts, and check the assembly mark of the connecting rod.
6. Remove the piston ring using the piston ring handling pliers.
7. Remove the piston, heat it to 60 ° C, and remove the piston pin.

Matters Needing Attention In Disassembly And Assembly Of Engine Piston

1. Before disassembly, remove external dust, carefully observe and remember the position and mark of each disassembly part.
2. Before pulling out the piston connecting rod group, the carbon step on the upper part of the cylinder liner must be scraped to avoid damage to the piston and piston ring.
3. When taking the piston connecting rod group, the rod can be directly pushed out. After the piston connecting rod group is drawn out, the connecting rod cover, tiles and connecting rod bolts should be reassembled in situ immediately.
4. When removing cylinder liner, use cylinder liner puller or wooden rod. Do not strike cylinder liner directly with metal rod.
5. The removed piston ring should be placed in order. Gaskets and paper pads should be properly kept.
6. If you need to remove the flywheel, use the flywheel puller. The two bolts in and out of the flywheel should be alternated. When removing the flywheel, do not remove the flywheel nut after it is loosened to prevent the flywheel from falling down and injuring people.

The collinear position of the engine piston and connecting rod is the dead point. When the transmission Angle on the follower is equal to zero, the effective turning moment of the driving force on the follower is zero, and this position is called the dead point position of the mechanism. That is, the collinear position of the follower and connecting rod in the mechanism is called the dead point position of the mechanism.

How Do Engine Pistons Divide Air Intake And Exhaust

The larger side of the piston pit is the intake. General intake valve corresponding to the pit are large.
Close to the inlet side is the intake valve, close to the exhaust is the exhaust valve, and generally the intake valve will be larger than the exhaust valve.
Engine piston intake stroke: the intake valve of the cylinder head is opened, the exhaust valve is closed, and the piston slides down from the top dead point to the bottom dead point. The volume in the cylinder gradually increases, and the pressure decreases -- lower than the atmospheric pressure outside. A mixture of fresh gasoline and air is then drawn into the cylinder through an open intake valve. Exhaust stroke: After the working stroke, due to inertia, the crankshaft continues to rotate, causing the piston to move upward from the bottom dead center. At this time the intake valve is still closed, and the exhaust valve is wide open, burning exhaust gas will be discharged through the exhaust valve to the outside. By the time the piston reaches the top dead center, most of the exhaust gas has been expelled. Then the exhaust valve closes, the intake valve opens, and the piston starts the cycle again by descending from the top dead center.

The farthest point at the top of the piston at the center of rotation of the crankshaft is called the top dead point, the nearest point is called the bottom dead point, and the distance from the top dead point to the bottom dead point is called the piston stroke. The piston passes through four strokes in the cylinder, namely the intake stroke, the compression stroke, the expansion stroke and the exhaust stroke. A cylinder completes a working cycle.

As the vehicle on the engine performance, fuel economy and environmental protection is more and more strict, and reliability requirements of piston has developed into a new set of lightweight high strength materials, profiled cylindrical composite surface, pin hole and so on many new technology in the integration of high technology content of products, to ensure that the piston heat resistance, abrasion resistance, steady guidance and good sealing function, reduce the engine mount Friction loss, reduce fuel consumption, noise and emissions.