What Is a Hydraulic Manifold?

The intake stroke of a four-stroke engine of a modern automobile sucks in the mixed vapor within a very limited time. At the same time, due to the needs of the structure and working principle, the air must pass through the barriers such as air filters, throttles, and intake valves. Entering the cylinder, both the limited time and the road blockage make the pressure in the intake pipe lower than the outside atmospheric pressure. The difference between the intake pressure in the intake pipe and the outside atmospheric pressure is called the engine intake manifold vacuum degree P.

Chinese name: Manifold vacuum
Foreign name: Manifold Vacuum
Function: Mechanical work, signal

Production site: Intake manifold
control method: Structural design
Features: Reliable and convenient

Manifold vacuum manifold vacuum introduction

With the development of China's car industry and the influx of foreign advanced vehicles, we find that many rubber hoses are arranged vertically and horizontally on the engines of modern automobiles, and one end of most hoses is directly connected to the engine intake manifold. These hoses vacuum out the engine intake manifold and perform two functions: to perform mechanical work; and to sense the transmission of engine load signals.

Manifold vacuum engine intake manifold vacuum does mechanical work

Engine intake manifold vacuum does not consume engine energy. As far as the engine structure is concerned, no special preparation equipment is needed, so it is the most convenient and cheapest power. Because it doesn't require processing equipment, it also has another advantage: reliability. Modern automobiles use a large number of automatic control devices and power-assist devices. Because the engine intake manifold vacuum has the advantages of convenience, cheapness, and reliability described above, it is widely used. These vacuum devices can be divided into two categories: actuators of control devices and boosters.

Vacuum motor schematic

The simplest actuator is the "vacuum motor" shown in Figure 1. When the vacuum is turned on, a pressure difference occurs on both sides of the diaphragm. This pressure difference overcomes the elastic force of the spring, and the diaphragm lever is pulled to cause the valve to rotate.

In addition, the manifold vacuum can also be used as an actuator of an automatic vehicle speed control system. In order to alleviate the fatigue caused by the long-term depression of the accelerator pedal while driving a car for long distance driving, almost all modern cars are equipped with an automatic speed control system.The driver can set the speed to a certain value, and then leave the car to stabilize automatically. Drive at speed without having to step on the accelerator. Most of these mechanisms use vacuum as power because it is safer and more reliable than other types of power (and devices). The source of vacuum is generally the engine intake manifold vacuum, and some vehicles are equipped with small electric vacuum pumps to generate vacuum in order to be more reliable. As shown in the figure below, the schematic diagram of the vacuum vehicle speed control system. In the figure, the engine intake manifold vacuum is drawn to the converter. The converter adjusts the actual vacuum according to the speed fluctuation of the vehicle, and then sends it to the actuator. The actuator pulls the throttle to automatically stabilize it. Speed.

Figure 2 Schematic diagram of air intake constant temperature control

Manifold vacuum engine intake manifold vacuum is used for pressure regulation and pressure sensing

The degree of vacuum in the intake manifold of the engine itself is an important sign of engine load, so it is also considered as the "load" signal of the engine.

Some electronic gasoline injection engines eliminate the air flow sensor, and only use a "load sensor" to sense the vacuum of the engine intake manifold, which reflects the intake air flow. This device simplifies the sensing device of the electronic gasoline injection system and gives a simple feeling.

The electronic fuel injection cycle fuel injection quantity is controlled by controlling the length of the nozzle opening time pulse. In order to ensure the precise control of the injection quantity, the pressure difference before and after the nozzle must be stable, that is, the pressure of the gasoline and the engine are required. The pressure difference of the intake manifold is a fixed value, so the engine intake manifold vacuum is used as a signal of the oil pressure regulator, so that the injection pressure is always maintained at a fixed value higher than the intake pipe pressure.

Because the engine intake manifold vacuum objectively reflects the engine load, it can replace the throttle position sensor and become a signal of the automatic transmission. This signal, together with the vehicle speed signal, becomes the two fundamentals of the automatic transmission control system.

Numerical characteristics of manifold vacuum degree

P Stability of manifold vacuum P (vacuum degree)

P is formed by the combined action of the cylinders when they alternately charge air. Obviously, it is normal that the P reading has a regular and small fluctuation. The more the number of cylinders, the better the stability of the P reading; as the engine speed n increases, the P reading becomes more stable.

P Typical value of P at manifold vacuum idle

Under normal idle speed of the engine in good technical condition, the typical value of P should be stable at 60 70kPa, the specific size depends on the idle speed. In stable engine operating conditions, the P value during idling conditions is large and stable, and has a strong comparability. At the same time, it is more sensitive to the causes of P abnormalities. Therefore, the P value under idle conditions is one of the important diagnostic parameters for P fault diagnosis of the engine.

P Typical value of P in manifold vacuum rapid acceleration and rapid deceleration conditions

From P = f (, n), is constant, n increases, P increases; n is constant, increases, P decreases; as long as one of the two parameters and n is fixed, P can be measured or observed Another parameter changes the size or follow-up. But the difficulty of operation is that and n are positively related and cannot be separated. Fortunately, according to the principle of inertia of the object, by stepping on the accelerator quickly, it can be considered that and n are close to separation instantaneously, and the size or following of the change of P with and n can be read or observed Sex. ^[1]