Working Principle Of Fuel Injection Pump

Oil suction process: the plunger is driven by the CAM of the camshaft. When the convex part of the CAM leaves the plunger, the plunger moves down under the action of the plunger spring. The volume of the oil chamber increases and the pressure decreases. When the radial oil inlet hole on the plunger sleeve is exposed, the fuel in the low pressure oil chamber flows into the pump chamber along the oil inlet hole.
Pump oil process: when the convex part of the CAM lifts the plunger, the volume in the pump chamber decreases, the pressure increases, and the fuel flows back to the low pressure oil chamber along the radial oil hole on the plunger sleeve; When the plunger goes up to completely plug the radial oil hole on the plunger sleeve, the pressure on the pump chamber increases rapidly; When the pressure overcomes the preload of the valve spring, the valve moves upward; When the pressure relief belt on the oil outlet valve leaves the seat, the high pressure diesel oil is pumped into the high pressure tubing and injected into the cylinder by the injector.
Oil return process: With the continued upward movement of the plunger, when the diagonal groove on the plunger is communicated with the radial oil hole on the plunger sleeve, the fuel in the pump chamber will pass through the axial oil channel on the plunger, and the oil hole on the inclined oil channel and the plunger sleeve will flow back to the low pressure oil chamber, and the pump oil will stop.
Take the plunger type injection pump as an example to see how the "pump" works:
Fuel injection pump to have a power source to operate, its lower camshaft is driven by the engine crankshaft gear.
The key part of the injection pump is the plunger, if the hospital common syringe analogy, then the mobile plug is called the plunger, the needle is called the plunger sleeve, assuming that the needle inside the installation of a spring against the plunger end, the other end of the plunger contact camshaft, when the camshaft rotation, the plunger will move up and down in the plunger sleeve once, This is the basic movement of the injection pump plunger.
The plunger and plunger sleeve are very precise parts. The plunger body has a inclined slot, the plunger sleeve has a small hole called suction, the suction is full of diesel, when the plunger inclined slot against the suction, diesel into the plunger sleeve, when the plunger is camshaft top to a certain height, the plunger inclined slot and suction staggered, suction inlet is closed, so that the diesel can not be inhaled and can not be pressed out, the plunger continues to rise when the pressure diesel, The diesel pressure to a certain extent will open the check valve and rush out into the fuel injection nozzle, and then enter the cylinder combustion chamber from the fuel injection nozzle.
It should be pointed out here that the diesel engine has an inlet pipe and a return pipe, and the inlet pipe is easy to understand, so what is the use of the return pipe? The original plunger discharged a certain amount of diesel oil each time, only a part of the injection into the cylinder, the rest is drained by the oil return hole, and use the increase or decrease of the amount of oil return to adjust the injection amount.
When the plunger rises to the "top dead center" and moves down, the plunger tilt slot will meet the suction inlet, and the diesel oil will be sucked into the plunger sleeve, and the above action will be repeated again. Each group of plunger system corresponds to a cylinder, and there are 4 groups of plunger systems in 4 cylinders, so the volume is relatively large and it is used in more than medium-sized cars. For example, diesel engines on buses and large trucks generally use in-line fuel injection pumps.
The fuel injection pump on the diesel engine of cars and light vehicles is generally distributed, which has the advantages of small volume, light weight, few parts and simple structure. It is pressurized with two sets of plunger systems (or one set of plunger systems), and diesel fuel is fed into each nozzle.
Its basic working principle is that there are two sets of opposite plungers installed in the impeller in the pump, the impeller is driven by the engine to rotate, the plunger also rotates, because the convex part of the CAM ring presses the plunger, so that the plunger plays the role of the pump to the impeller central oil feed hole pressure to send diesel, then sent out of the diesel filled with the distributor inlet, and then according to the order of the cylinder injection.
Because the number of operating revolutions of two sets of plunger systems (or one set of plunger systems) increases in proportion to the number of cylinders, the fuel injection pump is limited by the number of cylinders and the maximum speed.
With the development of diesel engine technology, there is a monomer fuel injection pump form (called monomer pump or pump nozzle), which is actually the above two types of fuel injection pump "broken into pieces", and the fuel injection of each cylinder of the engine is completed by its own independent injection unit (monomer pump or pump nozzle).
For the single pump, the injection pump and the nozzle are connected by a short high-pressure tubing, while for the pump nozzle, the injection pump and the nozzle are combined into one, mounted directly on the diesel cylinder head and driven by an overhead camshaft. Their biggest advantage is that they can reduce or eliminate the impact of pressure waves formed in the high-pressure tubing during the flow and injection of diesel oil. Because this pressure wave will prevent the injection system from matching well with the load and speed, and will increase with the length of the high pressure pipe.
Therefore, shorten the length of the high pressure tubing (the design idea of the fuel injection pump) or simply do not have the high pressure tubing (the design idea of the pump nozzle), reduce the high pressure volume between the plunger and the fuel injection nozzle, and the oil supply law can be obtained close to the CAM contour. Pump nozzles, in particular, have been applied to General Motors more than a decade ago, and now have precise control of electronic technology to improve their performance.