Fuel Nozzle Check Damper

Technical Field

This invention relates to a fuel injector for internal combustion engines, and more specif¬ ically, to such an injector wherein there is in¬ cluded a spring loaded injector valve.

Background Art

Internal combustion engines which operate on a diesel cycle, and a limited number of internal combustion engines which operate on different cycles, require a fuel injector which provides fuel to the combustion space at an appropriate time in the operating cycle. One type of fuel injector includes as principal elements a nozzle, an injector valve and a spring to urge the injector valve to a pos¬ ition closing the nozzle. Another type of injector utilizes fuel trapped above the injector valve and compressed as the valve opens to provide the force required to urge the nozzle to the closed position. In either case, a seat for the valve is located within the nozzle or tip of the injector such that only a very small volume of fuel exists downstream of the seat and upstream of the nozzle outlets .

When high pressure fuel is provided to the fuel injector from an engine fuel pump, the injector valve is forced to open and fuel is in¬ jected through the nozzle into the combustion space. When fuel pressure from the fuel pump drops, the injector valve is returned to its closed position by the injector valve spring or fuel trapped above the valve and injection of fuel to the combustion space is cut off.

Because the length- of the period of injec¬ tion is quite critical in maximizing performance and operating economy, the valve closing force is typic¬ ally high so as to effect rapid closing of the valve thereby providing the ability to closely control the length of the injection period by controlling the pressure of fuel supplied by the fuel pump. The high closing force thus causes the valve to engage the seat with a considerable impact. The impact can be of a magnitude that will create stresses and cause breakage of the nozzle tip through the mechanism of fatigue failure. Failure of the nozzle tip causes metal particles to drop into the combustion space which interfere with the smooth operation of the. engine. Also, since the injector valve seat is no longer present, the injector valve cannot stop fuel injection at the proper time. Fuel ^• therefore flows into the combustion space at all times, causing localized engine heating, fuel waste and increased hydrocarbon exhaust emissions.

Even if valve impact is not of a magnitude sufficient to cause nozzle tip breakage, or prior to failure of the nozzle tip, this impact may have det- •. rimental effects on engine performance. The impact can cause rebound of the injector valve from the valve seat, reopening the injector valve. Rebound will allow additional fuel to flow into the combus¬ tion space, resulting, to a lesser degree, in the above problems associated with nozzle tip breakage, and may allow combustion gas to enter the fuel injector.

Entry of combustion gas into the fuel injector will cause nozzle fouling and can result in the delay of delivery of fuel to the combus- tion space since at the beginning of the succeed¬ ing injection period these gases must be forced from the nozzle before fuel can be injected.

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Disclosure of the Invention

In one aspect of the present invention, there is provided in a fuel injector including a nozzle tip, an injector valve and means to urge the injector valve towards a closed position, means to slow the injector valve as it approaches the closed position, thereby reducing impact forces associated with valve closure.

Consequently, nozzle tip breakage is reduced or eliminated and valve rebound, with its attendant disadvantages, is eliminated.

Brief Description of Drawings

Fig. 1 is a vertical section of a fuel injector made according to one embodiment of the present invention;

Fig. 2 is an enlarged, fragmentary ver¬ tical section of the fuel injector;

Fig. 3 is a graph illustrating valve po¬ sition, stress on the fuel injector valve tip, and fuel pressure in the injector tip as typically found in a prior art fuel injector;

Fig. 4 is a- graph illustrating valve po¬ sition, stress on the fuel injector valve tip, and fuel pressure in the injector tip in a fuel injector made according to one embodiment of the present invention.

Best Mode for Carrying out the Invention

An exemplary embodiment of a fuel injec¬ tor made according to the invention is illustrated in Fig. 1 and is used in connection with an internal combustion engine (not shown) . The injector includes an elongated body 8 which receives fuel supplied to an inlet port 10 at one end of the body 8 and ultimately directs the fuel to a combustion space

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(not shown) through a nozzle in the form of fuel injector tip orifices 12 located at the opposite end of the body 8.

The fuel inlet port 10 is in fluid commun- ication with the orifices 12 through a fuel passage¬ way 14 located in a fuel line adapter 16, a fuel passage 18 extending through the main body of the fuel injector and a fuel chamber 20 which surrounds the lower portion of a fuel injector valve 22. At the correct point of the engine opera¬ ting cycle, high pressure fuel is supplied to the intake port 10 in a conventional fashion and is communicated to the fuel ^' chamber 20. The high pres¬ sure fuel in the fuel chamber 20 acts upon a piston surface 24' of the injector valve 22 which is slidably received in a bore 25 in the upper portion of the fuel injector tip 26. A slight clearance 27 (Fig. 2) is provided between a piston portion 24 of the injector valve 22 and the injector tip 26 so that a small amount of fuel may flow past the injector valve 22 and provide lubrication between the valve and the injector tip 26. This lubricating fuel flows into a spring chamber 28 having a lower end 29 and is ultimately returned to the fuel system through return ports 30. Thus, fuel in the chamber 28 will be at low pressure.

Because of the pressure difference be¬ tween fuel in the fuel chamber 20 and the spring chamber 28, the piston portion 24 and consequently, the injector valve 22, are urged upwardly.

The high pressure of fuel acting against the piston surface24' causes the compression of a return spring 32, until the end of a spring guide 34 contacts the lower surface of a spacer 36. As injector valve 22 moves upwardly, a valve tip 38 thereon separates from a valve seat 40 located in the injector tip 26, placing the

fuel chamber 20 in fluid communication with the injection tip orifices 12. Fuel from the fuel cham¬ ber 20 is thus expelled through the orifices 12 into the engine combustion chamber. As the pressure of the fuel in the supply line, and thus in the fuel chamber 20, decreases, the force caused by the fuel acting on the piston surface 24'of the injection valve 22 is reduced. When the magnitude of the upward force caused by the fuel decreases below the value of the downward force provided by the return spring 32 and trans¬ mitted to the injector valve 22 through a novel check damper 42 to be explained hereinafter and an injector valve shoulder 44, the injector valve 22 will begin to move in a downward direction to¬ wards the closed position as shown.

When the valve tip 38 once again contacts the valve seat 40, the injector valve 22 is in its closed position blocking the flow of fuel from the fuel chamber 20 through the orifices 12 and into the engine combustion chamber.

According to the present invention, the check damper 42 is a flat, thin circular spacer and has a close diametral fit with the inner surface of the spring chamber 28. The diametral clearance 45 between the check damper 42 and the inner sur¬ face of the spring chamber 28 is typically, though not limited to, .001".

Industrial Applicability in operation, when it is desired to supply fuel to the engine combustion area, high pressure fuel will be supplied to the intake port 10 in a conventional fashion and a small amount of fuel will flow past the piston portion 24 of the injector valve 22 and fill the spring chamber 28 including

the lower end 29, up to the level of the return ports 30.

As fuel pressure is conventionally relaxed by the fuel pump (not shown) , the spring 32 will overcome the force caused by the pressure of the fuel and the injector valve 22 will begin to move in a downwardly direction towards the closed posi¬ tion. Since the lower end 29 of the spring chamber 28 is filled with fuel, the injector valve 22 can close only as rapidly as fuel can escape past the check damper 42. By controlling the diametral clearance 45 between the check damper 42 and the inner surface of the spring chamber 28, the rate of fuel flow around the check damper 42, and there- fore the velocity of the injector valve 22, may be controlled.

It must be noted that although fuel may flow from the fuel chamber 20 past the injector valve 22 and into the lower end 29 of the spring chamber 28, reverse flow past the valve 22 will be negligible. Reverse fuel flow will be limited because the duration of the injector valve 22 closing stroke is extremely short.

It has been found that the diametral clearance of .001" provides the desired fuel flow rate around the check damper 42 and consequently, the desired injector valve 22 closing velocity. It must be noted, however, that suitable diametral clearance can only be determined in conjunction with other fuel injector parameters, in particular, the return spring's 28 spring rate, friction present between the piston portion 24 of the injector valve 22 and the bore 25 of the injector tip 26, fuel viscos¬ ity, and the mass of injector valve 22. The advantages of providing a fuel injector with the check damper 42 having a close diametral fit

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on the spring chamber 28 inner surface can readily be ascertained by a comparison of Figs. 3 and 4, the former illustrating valve position, the stress on the injector tip 26 and fuel pressure in the injector tip 26 of a prior art system without the check damper 42 and the latter illustrating the same characteristics of a fuel injector made accor¬ ding to one embodiment of the present invention. Referring to Fig. 3, the valve position versus time curve 48 shows that, in the typical fuel injector, after the injector valve 22 first closes at the indicated valve closing point 50, the valve will "bounce" or, in other words, reopen and reclose a number of times before finally firmly seating on the injector valve seat 40. These re¬ peated openings of the valve after initially con¬ tacting the valve seat 40 is detrimental to engine performance in that it allows additional fuel to enter the combustion space at an undesirable portion of the engine operating cycle thus increasing hydro¬ carbon exhaust emissions, increasing localized en¬ gine heating and wasting fuel.

As can be seen on the curve indicating stress on ^" the valve tip versus time 52, this "bounc- ing" action is also detrimental to the fuel injector unit itself. The stress curve 52 indicates that repeated openings and closing of the valve tip 38 cause a number of reversing stress cycles to be imposed upon the injector tip 26. Cyclical stresses of the type illustrated by stress curve 52 are known to cause component failure through the mech¬ anism of fatigue failure. It has been observed that cyclical loading eventually causes the portion of injector tip 26 around valve seat 40 to break off which allows direct, uncontrolled fluid commun¬ ication between fuel chamber 20 and the engine

combustion space. The result is that a very large amount of fuel flows into the combustion space whenever fuel is provided to the broken injector, greatly increasing fuel consumption, localized engine temperature and hydrocarbon emissions.

In a fuel injector made according to one embodiment of the present invention, as illustrated in Fig. 4, the problems of fuel waste, increased hydrocarbon exhaust emissions and injector tip breakage are greatly reduced.

As will be seen in the valve position versus time curve 54 of Fig. 4, reduced injector valve velocity allows the injector valve 22 to remain closed after initial contact with valve seat 40. As a result, fuel flow is positively cut off, thereby eliminating the problems associated with fuel leakage indicated above. Cyclical stresses on the injector tip are reduced, as shown in the stress versus time curve 56, thus extending the life of the injector tip 26 and preventing catas¬ trophic fuel loss.

While particular reference has been made to an injector which utilizes a spring 32 to effect closing of the valve 22, it will be recognized that the present invention is equally applicable to injectors which utilize other means, i.e. fuel trapped above the injector valve 22, to provide the required valve closing force.

Other aspects, objects and advantages of this invention may be obtained from a study of the drawings, the disclosure and the appended claims.

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