An Injection Pump is a device that pumps diesel (as fuel) into a diesel engine cylinder. Traditionally, the injection pump is driven indirectly from the crankshaft by a gear, chain or toothed belt (often timing belt) which also drives the camshaft. It spins at a half-speed crankshaft in a conventional four-stroke diesel engine. The timing is such that the fuel is only slightly injected before the center dies from the compression step of the cylinder. The same thing happens to the pump belt on the gasoline engine to be driven directly from the camshaft. In some systems the injection pressure can be as high as 200 MPa (30,000 PSI).
Video Injection pump
Security
Because the need for positive injection into highly pressurized environments, the pumps develop substantial pressure - typically 15,000 psi (100 MPa) or more in newer systems. This is a good reason to be careful when working on a diesel system; Fuel coming out of this kind of pressure can easily penetrate skin and clothing, and is injected into tissues with serious medical consequences to ensure amputation.
Maps Injection pump
Construction
The earlier diesel pumps use an in-line layout with a series of cam-operated cam cylinders in line, somewhat like miniature inline engines. The piston has a constant stroke volume, and the injection volume (ie, throttling) is controlled by turning the cylinder against the cut-off port parallel to the helical slot in the cylinder. When all cylinders are rotated at once, they simultaneously vary their injection volume to produce more or less power from the engine. The inline pump still finds advantages on large multi-cylinder engines such as on trucks, factory construction, static machinery and agricultural vehicles.
For use on cars and light trucks, rotary pumps or distributor pumps are developed. It uses a single injection cylinder that is driven from the axial cam plate, which injects into individual fuel lines through a rotary distribution valve. Then incarnations such as Bosch VE pumps vary the injection time with crankshaft speed to allow for greater force at high crank speeds, and run smoother, more economical at slower crankshaft rotation. Some variants of VE have a pressure-based system that allows increased injection volume beyond normal to allow engines equipped with turbochargers or superchargers to develop more power under push conditions.
All injection pumps combine the governor to cut off the fuel supply if the crankshaft rpm endangers the engine - heavy moving diesel parts do not tolerate excessive speed well, and catastrophic damage can occur if over-revved. Machines that are not well maintained and worn can consume their lubricating oil through an outdated and 'run away' engine tub ventilation system, causing an increase in engine speed until the engine destroys itself. This is because most diesel engines only regulate their speed with fuel supply control and do not have throttle valves to control the air intake.
New type
Mechanical pumps are gradually phased out to comply with international emissions directives, and to improve performance and economy. From the 1990s the transition stage between full electronic controls was a pump that used an electronic control unit to control some functions of the rotary pump but still mechanically regulated and powered by the engine. The first four-and five-cylinder VW/Audi TDI engine pioneered this pump before switching to the Injector Unit. These pumps are used to provide better injection control and refinement for car diesel engines because they are transformed from indirect injection into a much more efficient but less subtle direct injection engine in the 1990s. The ECU can even vary the damping of the hydraulic engine cradle to assist the refinement. BOSCH VP30 VP37 VP44 is an example of a pump. Since then there has been a widespread change for common rail diesel systems and direct injection systems of electronic units. This allows for higher pressures to be developed, and for smoother injection volume control, and some injection stages compared to mechanical systems.
See also
- Injector unit
References
Source of the article : Wikipedia
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