The electronically controlled injector of the excavator is based on the electronic control signal sent by the electronic control unit. The electronic control injector uses the high pressure fuel in the common rail component to spray the human combustion chamber with the best injection timing, fuel injection and fuel injection rate.
Liebherr R934B excavator electronically controlled injector can be divided into two categories:
1 electrohydraulic injector
2 piezo lens type injector
The working principle of Liebherr R934B excavator electronically controlled injector:
1 electrohydraulic injector
The main components of the electro-hydraulic injector include fuel injector, thimble, solenoid valve, control plug and ball valve.
The fuel from the high-pressure joint is sent to the injection nozzle through the inlet channel, and is sent into the control room through the inlet throttle hole. The control room is connected to the oil return hole through the oil recovery hole opened by the solenoid valve.
When the solenoid valve is stationary, the throttle return hole is closed and the fluid pressure on the control is greater than the force acting on the pressure surface of the nozzle needle valve, so the nozzle needle valve is pressed on the seat surface without fuel into the combustor.
When the solenoid valve moves, the throttle hole is opened and the pressure in the control room is reduced. When the fluid pressure on the plug is less than the force acting on the pressure surface of the nozzle needle valve, the injection nozzle needle valve opens immediately and the fuel is sprayed into the combustion chamber through the injection hole. A hydraulic pressure amplification system realizes this indirect control of the needle valve. In this process, besides the fuel injected into the combustion chamber, there are additional so-called throttle holes that control the fuel through the control chamber into the back of the oil channel.
In addition to the amount of fuel injection and control oil, there is also the leakage of oil from the needle valve guide part and the piston guide part. The leakage of fuel and control fuel are reflued to the tank with the oil pipe (overflow valve, oil supply pump and pressure regulating valve also connected with the tubing).
2 piezo lens type injector
(1) the piezoelectric effect and its characteristics. When the crystal is deformed under the external force, the positive and negative charge will be produced on some of its corresponding crystal surfaces. This kind of polarization, which is caused by the deformation, is called the positive piezoelectric effect. Otherwise, if the electric field is applied on this kind of crystal, it produces not only the polarization but also the strain. Or stress, this is the reverse piezoelectric effect, also called the electrostrictive effect. The positive piezoelectric effect and the reverse piezoelectric effect are called the piezoelectric effect. Such crystals are called piezoelectric crystals. The piezoelectric sensors are mostly made of the positive piezoelectric effect of the piezoelectric materials, while the piezoelectric actuated high speed open valve is the reverse piezoelectric effect of the piezoelectric material. It should be made.
The strain of piezoelectric crystals is very small. It is commonly used mainly the stacking type piezoelectric crystal heap, that is, the piezoelectric crystals with multi-layer thickness and deformation are connected in series, and the piezoelectric reactor is connected in parallel. In the electronic control injection system of the engine, the practical application of the high speed switch valve of the piezoelectric crystal is often in the suitable multi-layer pressure. On the basis of the superposition of the electric sheet to form a piezoelectric reactor, the displacement of the piezoelectric actuator is further amplified by the hydraulic magnifying mechanism to meet the needs of the high speed switch valve.
The most obvious advantage of the piezo crystal type injector is that the most obvious advantage of the piezo crystal type injector is the quick response speed; the minimum fuel injection is smaller than the 1.5mm / stroke; the time interval between the pre injection and the main injection can be less than 100US; the injection rate is more flexible and adjustable; the change of the fuel injection and the ejection point of each cylinder is very small; the repetition precision is very high.
The structure and principle of piezo crystal type fuel injector: to be exact, the high speed switch of piezoelectric crystal driven by piezoelectric crystal should be used to control the high pressure common rail electronically controlled injector. The structure of the piezo crystal type injector is divided into two routes after the injection of the common rail oil tank into the injector: a route pipe enters the fuel tank of the injector and acts on the needle valve. On the cone surface, the other way is through the throttle hole to enter the oil cavity of the piston top 11..
1, 11- oil gun 2- small piston 3- common rail oil tank 4, 8- one-way valve 5- pipeline 6- piezoelectric crystal reactor 7- big piston 9, 10- channel 12- throttle 13- piston rod 14- return spring
Figure 1 Structure of a piezo crystal injector
When the piezoelectric stack is not energized, the check valve 4 is closed, the fuel in the oil chamber Il pushes the piston rod, the fuel injector is closed, and the injector does not spray fuel.
When the piezoelectric crystal stack is electrified, the piezoelectric crystal elongated and propels the fuel in the L of the large piston compression oil cavity, and then pushes the small piston. Because the area of the large piston and the small piston is larger than the dry L, the small piston displacement is magnified, and the small piston displacement pushes the steel ball in the one-way valve 4 away from the cone, forming a channel with a certain throttle section so that the oil cavity is made. The fuel in 11 passes through the channel 10, the one-way valve 4 and the channel 9 back to the tank. The upper part of the piston rod is unloaded and the needle valve is under the action of fuel pressure in the oil sump, to overcome the upward movement of the back spring force, thus opening the nozzle and spraying the fuel.
When the piezoelectric crystal stack is broken, the one-way valve 4 falls, the fuel pressure in the oil chamber 1 rises, the piston rod moves down and closes the injection nozzle. The one-way valve 8 is used to supplement the leaked fuel in the oil cavity L, so as to ensure the reliability of the nozzle.
