Recently, we got some readers’ feedback, hoping that I can tell you about the manifold absolute pressure sensor, at the request of readers, today we will discuss this common car sensor in detail!
The Role of the MAP Sensor?
EFI engine using manifold absolute pressure sensor to detect the intake volume is called D-type injection system (speed density type). manifold absolute pressure sensor to detect air intake is not like the intake flow sensor as a direct detection, but the use of indirect detection, while it is also affected by many factors, and therefore in the detection and maintenance of many different from the amount of sensor into the airflow, the resulting failure also has its special characteristics.
Working principle of the MAP sensor
The intake pressure sensor detects the absolute pressure of the intake manifold behind the throttle and valve, which detects the change in absolute pressure in the manifold according to the engine speed and load, and then converted into a signal voltage sent to the electronic controller (ECU), the ECU based on the size of this signal voltage, control the size of the basic injection. There are many types of manifold absolute pressure sensors, such as varistor type and capacitor type. The piezoresistive type is widely used in D-type injection systems because of its fast response time, high detection accuracy, small size and flexible installation. The operating principle of piezoresistive intake pressure sensor. Strain resistors R1, R2, R3 and R4, which form a Wheatstone bridge, are bonded together with a silicon diaphragm. The higher the absolute pressure in the manifold, the greater the deformation of the silicon diaphragm, and thus the greater the change in resistance of the resistor R. That is, the mechanical change of the silicon diaphragm is transformed into an electrical signal, which is then amplified by the integrated circuit and output to the ECU.
Output characteristics of the MAP sensor
When the engine is working, with the change of throttle opening, the vacuum, absolute pressure and output signal characteristics curve in the intake manifold are changing. But what is the relationship between their changes? Is the output characteristic curve positive or negative? This problem is often not easy to understand, so some maintenance personnel in the work of a “can not eat” feeling. D-type injection system is to detect the absolute, pressure in the intake manifold behind the throttle. The back of the throttle reflects both the vacuum and the absolute pressure, so some people think that the vacuum and the absolute pressure is a concept, in fact, this understanding is one-sided. Under the condition of constant atmospheric pressure (standard atmospheric pressure is 101.3kPa), the higher the vacuum in the manifold, the lower the absolute pressure in the manifold is reflected, and the vacuum is equal to the difference between the atmospheric pressure minus the absolute pressure in the manifold. And the higher the absolute pressure inside the manifold, the lower the vacuum inside the manifold, and the absolute pressure inside the manifold is equal to the difference between the atmospheric pressure outside the manifold minus the vacuum. That is, the atmospheric pressure is equal to the sum of vacuum and absolute pressure.
After understanding the relationship between atmospheric pressure, vacuum and absolute pressure, the output characteristics of the MAP sensor are clear. In the engine work, the smaller the throttle opening, the larger the vacuum of the intake manifold, the smaller the absolute pressure in the manifold, the smaller the output signal voltage. The larger the throttle opening, the smaller the vacuum in the intake manifold, the larger the absolute pressure in the manifold, and the larger the output signal voltage. The output signal voltage is inversely proportional to the magnitude of the vacuum in the manifold (negative characteristic) and positively proportional to the magnitude of the absolute pressure in the manifold (positive characteristic).
Through the above introduction of the role of the MAP sensor in the car, I believe that the manifold absolute pressure sensor in the car parts have a detailed understanding. As a car repair engineer, or auto parts wholesaler, it is necessary to learn more product knowledge, to provide customers with professional services is the purpose of our auto parts people. Have you learned today? If you think this article can help you, please help forward to out, so that more people understand the auto parts knowledge!
