DK155757B - Fuel injector for diesel motor that runs on gas - Google Patents

Abstract

The injector has a valve part (19) which under actuation of a lock spring (21) lies against a seat in the injector's housing and thereby blocks a canal (20) which connects the injector's fuel input (8) with one or more nozzle holes in the foremost end of the injector. On supply of pressurized servo oil to a chamber (26), which is bordered at the rear by a surface on the valve part (19), this is aired from its seat, whereby the gas injection begins. In a second chamber (22), which stands freely connected with the gas duct (20), the gas pressure works against a backwards-facing face of a piston (24), which is in power transmission connection with the valve part (19), preferably in one piece with this. The valve part is thereby in operation constantly worked against its closed position of a power exerted by gas pressure, which supplies spring power and thereby makes it possible to have a reduction of the spring's dimensions and/or tension level. In the event of a broken spring the closure of the valve is assured by the gas pressure, when the servo oil pressure falls.<IMAGE>

Description

DK 155757 B

BACKGROUND OF THE INVENTION The invention relates to a fuel injector for a gas-powered diesel engine of the type having an elongated housing with a pressure gas supply and a duct between the supply and one or more nozzle holes in the front end of the engine cylinder combustion chamber. the injector, which gas duct is controlled by a valve body cooperating with a seat in the injector housing, which is actuated in the direction towards the seat by a biased closing spring and in the opposite direction by a periodic disk applied to the servo oil.

Diesel engines that can run on gas as fuel include: interesting as propulsion machinery in gas tankers, especially for the transport of liquefied natural gas (LNG), since the amount of gas which inevitably evaporates from the cargo can be utilized with high efficiency in the diesel engine. However, the type of motor can also advantageously be used in stationary systems, including as a driving force for electric generators.

Regardless of the scope of the engine, it is a natural requirement that the risk of gas explosions in the engine itself is prevented as far as possible already by virtue of the engine design. A severe explosion can occur especially if the gas valve body of a cylinder injector gets stuck in fully or partially open position, so that during a working cycle substantially more gas is injected than corresponding to the amount of oxygen present in the cylinder. The amount of unburned gas, which then flows out of the cylinder mixed with the hot combustion gases, can be expected to ignite spontaneously or elsewhere in the exhaust system, where it comes into contact with free oxygen, such as e.g. is found in the exhaust gas from another, normally functioning cylinder. Especially if the ignition occurs in an exhaust receiver, a momentary pressure rise of pronounced explosive nature can occur, 35 which can lead to serious injury.

In order to prevent the situation described, it is desirable to provide the valve with a spring,

DK 155757 B

2, which can produce a high closing force, while the corresponding stresses in the spring material are so relatively low that there is only minimal risk of fatigue failure.

However, this desire often clashes with the limited space conditions in the engine cylinder covers1, especially in long-flush engines, where the exhaust valve in the center of the cylinder cover takes up a significant portion of the available planar area.

The invention aims to provide an injector 10 which combines a small space requirement with a high degree of assurance that the gas valve always closes completely and at the predetermined time of the duty cycle.

For this purpose, it is peculiar to the invention that in the injector housing a 15 chamber is formed which is in permanent flow communication with the gas duct and which is axially in front towards the nozzle holes is tightly bounded by a displaceable actuating piston in force transfer connection with the valve body. .

Hereby it is obtained that during normal operation of the engine the valve body is constantly influenced in the closing direction by two cooperating forces, partly from the closing spring and partly from the relatively high pressure, often about 200 bar, which constantly prevails in the supply system connected to the injector gas supply and thus in injector gas duct. As a result, the closure spring can be sized according to a lower biasing force and / or lower internal stresses, resulting in smaller spring dimensions and / or increased safety against fatigue breakage by the 30 highly oscillating stresses to which a valve spring is subjected. Furthermore, the valve closure at the moment when the servo oil pressure acting in the opening direction ceases is ensured even in the event of a spring break. The invention thus provides, among other things, a convenient supplement to such safety measures as closing a stop valve and thereby interrupting

DK 155757 B

the gas supply to a cylinder's injector or injectors in the event of an abnormally high gas flow, but which, on the other hand, cannot prevent at least a portion of the gas quantity located on the downstream side of the closed stop valve from seeping into the engine cylinder.

In a constructively simple and therefore usually preferred embodiment of the invention, the actuating plunger is formed as part of the rear end of the body facing the fuel supply towards the fuel supply. However, it will be appreciated that the above-described beneficial effects are also achieved by a separate actuating piston in - directly or indirectly - abutment against a backward face of the valve body.

According to the invention, the closure spring can be built into the chamber between a wall fixed in the housing and the back of the actuating piston facing the fuel inlet, and the chamber can then be formed in the part of the injector which projects outside the engine cylinder when mounted. The embodiment is particularly convenient when the space conditions make it desirable to minimize the outside diameter of the front part of the injector housing which is inside the cylinder cover, for example in long-flush central exhaust valve engines and multiple injectors distributed along the combustion chamber perimeter.

The invention will now be explained in more detail with reference to the somewhat schematic drawing, in which FIG. 1 is a longitudinal section, taken along line I-I of FIG.

3, through a first embodiment of the injector according to the invention mounted in a cylinder cover; FIG. 2 is a larger scale section of the top or rear of the injector, along line II-II of FIG. 3, FIG. 3 is a top plan view of the injector, and FIG. 4 shows a section on an even larger scale through the front part of a slightly modified embodiment of the invention.

DK 155757 B

4

The FIG. 1-3 illustrated fuel injector has an elongated housing comprising a slender front portion 1 which is fully accommodated in the engine cylinder cover 2, a center portion 3 of somewhat larger diameter, and a 5 head 4 with through holes 5, see FIG. 3, for mounting bolts for securing the injector to the cylinder cover. A central screw 6 fixed in the head 4 is designed for connecting a high-pressure line from a source, e.g. a conventional Bosch-type fuel pump 10 for periodically delivering metered quantities of pilot oil to the injector.

In the head 4 is also provided an approach 7 for control or servo oil for opening the later described gas valve in the injector and a corresponding approach 8 for connecting a normally constant open line for supplying high pressure gas from a suitable source for blowing into the engine cylinder when the gas valve in the injector is open.

An atomizer 9, which projects from the front 20 end of the housing 1 into the combustion chamber 10 of the engine cylinder, has two sets of nozzle holes 11 and 12 for injection of pilot oil and gas, respectively. The nozzle holes 11 and 12 are perpendicular to each other in pairs and are fed from a central hole 13 common to all holes 11, respectively, in a spindle guide 14, to whose front end surface the nebulizer 9 is attached, and separate inclined bores 15 through the spindle guide 14. In FIG. 1, it will be understood that the aforementioned bolts passing through the holes 5 in the head 4 hold the front portion 1 of the injector housing tightly against an inner surface of the cylinder cover 2, while the spindle guide 14 is axially fixed to a chest. in the injector housing via an elongated pressure sleeve 16, a flange on an inner slide guide 17 and a spring guide 18, which abuts against the screw 6 at the top.

The spindle guide 14 is formed on its exterior with a tapered valve seat which cooperates with a counterbalance.

DK 155757B

a conical seat surface on the lower te end of a tubular valve body 19 which is guided above and below, respectively, on the pressure bushing 16 and on the spindle guide 14. Between a valve body 19 and the inside of the front part 1 of the injector housing, a passage or channel 20 is defined. for the flow of gas from the inlet 8 via longitudinal and transverse bores in the housing parts 3 and 4, see fig. 2, to the valve seat at the end of the valve body 19. In the closed position 10 of the valve body 19, its tapered seat surface blocks the connection from the channel 20 further through the bores 15 to the nozzle holes 12. The valve body is held in the closing position by a coil spring 21 mounted in a housing part 3. and the pressure bush 16 delimited chamber 22, with the top 15 supporting a flange 23 on the upper end of the pressure bush 16, while the bottom supporting a corresponding flange 24 on the upper end of the valve body 19.

As shown in FIG. 2, the chamber 22 is gas tightly delimited at its upper and lower ends, with in the flanges 23 and 24 suitable sealing rings for abutment against the chamber wall. Furthermore, the chamber is openly connected through a transverse bore 25 with the aforementioned system of bores connecting the gas supply 25 to the duct 20. As a result, the chamber 22 has the same pressure as in the gas inlet 8 and this pressure affects the flange. 24 and thus the valve body 19 in the direction of the valve seat of the spindle guide 14 with a force which supplements the force of the closing spring 21.

When, during a work cycle, the valve body 19 is to be lifted from its seat to thereby initiate the gas supply into the combustion chamber 10, a servo oil is supplied under a suitable high pressure, e.g. about 500 bar, to the approach 7, which through a second set of longitudinal and 35 transverse bores in the housing parts 3 and 4 is in flow communication with a small annular chamber 26 under the

DK 155757 B

6 of the body flange 24. In the embodiment shown here, it is provided that the servo oil is supplied from a Bosch-type dosing pump and, having regard to this, a pressure limiting valve 27 is fitted in the injector head 4, whose spring-loaded valve body 28 is set to to open and thereby relieve the pressure in the annulus 26 when the pressure has reached the value necessary to lift the valve body 19 and keep it lifted until the delivery of the metering pump is interrupted.

Alternatively, if the servool pressure in the chamber 26 were provided by valve controlled opening of a connection from an oil reservoir at the required pressure, the restriction valve would be unnecessary, since the flow of oil from the reservoir to the chamber 26 would then cease by itself when the valve body 19 was lifted. maximum for impact against the pressure bushing 16.

The pilot oil, which in a known manner is to be injected into the combustion chamber 10 through the nozzle holes 11 immediately before or at the same time as the injection of gas 20 begins, can, as initially mentioned, be delivered from a Bosch-type dosing pump to the screw 6. From here the oil flows through the hollow spring guide. 18 and a flush passage in a vent slider 29 for an annulus 30 between the slider 29 and a central 25 pressure tube 31. The lower end of the pressure tube 31 guides the valve body 32 of the actual pilot oil valve, which is previously formed with a seat surface cooperating with a valve seat about the bore 13 at the bottom of the spindle guide 14.

During the periods between the deliveries of the pilot oil pump, the vent slider 29 occupies the position shown, where it, under the influence of a relatively weak spring 34, blocks the passage of the oil forward from the chamber 30. In these periods, in known manner, e.g. As described in EP-A1-0 052 937, a continuous circulation of oil takes place at pre-pump pressure through the oil pump up to 7

DK 155757B

injektortilgangen. 6 and back to the suction side of the pre-pump via a transverse bore in the spring guide 18, which is blocked by the slider 29 as it increases with increasing oil pressure and releases a further passage of the oil from the chamber 30 to 5 a corresponding annulus 35 in front of the valve body 32.

As the pressure herein overcomes the biasing force of the closing spring 33, the pilot oil flows on to the bore 13 and out through the nozzle holes 11.

In FIG. 2 and 3, there is also seen an approach 36 in the head 10 4, through which a suitable sealing and lubricating oil can be supplied at a suitable pressure, which is distributed through bores in the head 4 and the housing part 3 to the inner and outer sliding surfaces of the valve body 19.

In FIG. 4 are those components which functionally correspond to those of FIG. 1-3, with the same reference numeral plus 100. Between the two embodiments, there is the constructive difference that the pilot oil-valve valve bar 132 is extended in front of its tapered seat surface by a tubular slide 141 which has a relatively tight fit. in the nebulizer 109, and as in the shown position, where the two tapered seat faces are facing one another, the nozzle holes 111. Lock the inner cavity 142 of the slider in flow communication with a ring chamber 143 located on the downstream side of the tapered seat faces via recesses 144 in the sliding wall. .

It will be seen that the addition of the slider 141, which projects in the closing position a short distance past the nozzle holes 111, causes these holes during the closing movement to be blocked at a time when the valve memory 132 has not yet fully closed, so that there is still a connection between chambers 143 and 135 and thence further backward towards the oil pump. Therefore, the termination of the oil injection takes place at a time when the oil pressure is relatively high, which reduces the risk of undesirable post-drip, in addition to

Claims (4)

1. Fuel injector for a gas-powered diesel engine of the type having an elongated housing (1, 3, 4) with a gas supply pressure (8) and a duct between the supply and one or more nozzle holes (12) in the forward end of the injector facing the engine cylinder combustion chamber (10), which gas channel is controlled by a valve body (19) cooperating with a seat in the injector housing, which is actuated towards the seat 15 by a prestressed closing spring (21) and in the opposite direction of a periodically applied servo oil pressure, characterized in that a chamber (22) is provided which is in permanent flow communication with the gas duct and which in the axial direction advances towards the nozzle holes 20 is tightly bounded by a displaceable actuating piston (24 ) in power transmission with the valve body (19). Fuel injector according to claim 1, characterized in that the actuating piston (24) is formed as part of the rear end of the valve body (19) towards the fuel inlet. Fuel injector according to claim 1 or 2, characterized in that the closing spring (21) is built into the chamber (22) between a wall 30 (23) fixed in the housing and the actuating piston (24) facing the back of the fuel supply. Fuel injector according to claim 3, characterized in that the chamber (22) is formed in the part (3) of the injector which projects in the mounted state outside the engine cylinder 35.