On the turbocharger of a car engine, there is a small cylinder. One end of it is connected to the compressor of the supercharger through a gas pipe, and the other end is a tie rod, which is connected to the turbine. connected to a small valve. Many people don't know what it is used for. In fact, it is the wastegate device on the turbocharger.
Why design such a waste gas bypass device? As we all know, the working principle of a turbocharger is to use the exhaust gas from the engine to push the turbine to rotate, and then drive the compressor to rotate, increasing the amount of air intake for the engine, which can greatly increase the engine power without changing the engine displacement. . Generally speaking, the more exhaust gas and the greater the exhaust gas pressure, the faster the turbine rotates, the stronger the supercharging effect of the engine, and the more violent the engine works; and the more violent the engine works, the more exhaust gas is produced, and the exhaust gas The pressure will increase, thus forming an "infinite loop". If this continues, the engine speed will become higher and higher (speeding phenomenon), and eventually it will become uncontrollable and cause damage to the engine. This phenomenon is called "overboost" of the engine.
In order to avoid the occurrence of "over-pressurization", a waste gas bypass device is designed on the turbocharger, which consists of a control air chamber, a tie rod, a waste gas bypass valve, etc., among which The control air chamber is the core component. It is a pneumatic cylinder composed of a diaphragm and a spring. One end is connected to the compressor of the supercharger. The pressure above the diaphragm is equal to the pressure in the compressor. The other end is connected to the exhaust gas. The valve is connected.
When the boost pressure in the compressor exceeds a predetermined value, the air pressure pushes the diaphragm to compress the spring, pushing the pull rod outward, opening the wastegate valve, and guiding part of the exhaust gas no longer to pass through the turbine, but Directly enter the exhaust pipe from the bypass valve installed in front of the turbine, which can reduce the quantity and pressure of exhaust gas that drives the turbine to rotate, thereby reducing the turbine speed, reducing the boost pressure, and avoiding engine problems caused by "over-pressurization" Speeding phenomenon. When the compressor pressure drops to a certain value, the pressure above the diaphragm is not enough to overcome the elastic force of the spring, and the spring will rebound, driving the connecting rod to close the bypass valve, and all the exhaust gas will push the turbine to run, and the boost pressure will increase again. Until the next time the bypass valve opens. As the cycle proceeds in this way, the engine's boost pressure is controlled at a fixed value.
There are two control methods for this waste gas bypass device. One is mechanical (vacuum) control, usually used in truck diesel engines; the other is electronic control, usually used in passenger car gasoline engines. superior. No matter which one, the principle is the same. The electronic control just adds a solenoid valve to the pipeline. By controlling the opening pressure of the bypass valve, the engine output power can be changed. For example, on a turbocharged gasoline engine of a passenger car, changing the opening timing of the solenoid valve can change the opening pressure of the bypass valve. The later the opening timing of the solenoid valve, the greater the boost pressure and the higher the engine power. This is actually how the high and low power adjustments of many engines are done. On the engine external characteristic curve, the speed at which the torque curve begins to decrease is the timing for the bypass valve to open.
The failure rate of this waste gas bypass device is very low, and failures are generally caused by human damage. What must be known is that the spring preload pressure in the bypass valve control air chamber is set and verified on special equipment, and the user cannot adjust or change it at will. If we try to lift the tie rod directly with our hands when transporting the supercharger, it will cause the tie rod to bend and deform, which will affect the opening timing of the bypass valve. If the connection between the tie rod and the bypass valve is disconnected, the bypass valve will lose control and remain open, and the engine will suffer from insufficient power and reduced power due to insufficient boost pressure. In addition, if the air pipe that controls the air chamber is broken or leaks, the bypass valve will not be able to open, and the engine will be overcharged. Of course, today's engines have an overspeed protection mechanism, which will cut off the oil when the speed exceeds a certain speed to prevent the engine speed from excessively increasing. However, ultra-high speeds and excessive boost pressure will still damage the engine.
This article comes from the author of Autohome Chejiahao and does not represent the views and positions of Autohome.