Fuel injection nozzle

A fuel injection nozzle of the type which includes an outwardly opening valve needle of a valve group and an inner longitudinal bore connecting the valve group with a fuel inlet to the nozzle. The longitudinal bore includes a narrow section between two larger sections, the two larger sections being thus decoupled from pressure variations in either section.

BACKGROUND OF THE INVENTION 
The invention relates to a fuel injection nozzle having an outwardly 
opening valve at one end and a longitudinal bore connected to the valve 
end with a pressure line. Fuel is supplied to the longitudinal bore from 
the pressure line. The fuel flows through the longitudinal bore and is 
discharged from the nozzle by the valve. 
In fuel injection nozzles of this type, which open outwardly and are used 
especially for low pressure injection, a chatter of the valve needle is 
preferred during operation in neutral gear or under low partial load, in 
order to obtain thereby a good concentration of the fuel on the one hand 
and an orderly sequence of injection on the other, independently of the 
load and the rpm. However, in the known fuel injection nozzles of the type 
noted above, over-oscillation associated with the chattering easily 
occurs, which leads to an uneven sequence of injection from stroke to 
stroke as well as to a possible interruption of the injection process and 
also to premature injections or after-injections. 
Chattering typically refers to the characteristic noise produced by the 
nozzle valve during opening or closing. In the context of the present 
invention it also refers to the harmonic oscillations which the valve 
experiences when it is opened. This meaning is illustrated in FIGS. 1 and 
2, which are discussed herein after. 
OBJECT AND SUMMARY OF THE INVENTION 
It is an object of the invention to improve the noted type of fuel 
injection nozzle so that the over-oscillations and their associated 
effects are avoided. 
This object is achieved by partitioning the inner longitudinal bore of the 
nozzle to include a narrow section between two larger sections, the two 
larger sections being thus decoupled from pressure variations in either 
section. 
The fuel injection nozzle according to the present invention has the 
advantage that, especially in neutral gear, small over-oscillations occur 
which do not lead to excessive oscillations. Therefore the injection 
sequence is smooth, especially in neutral gear and the lower area of 
partial load, and no premature injections or after-injections occur. The 
injection process is almost uninterrupted, i.e., there is either no 
contact or only minimal seating contact between the needle and the valve 
seat during injection. The invention is especially advantageous with a 
valve needle group having a long valve needle with only one guidance area 
on the side opposite the injection side and where it is comparatively 
difficult to obtain a favorable chattering effect. 
The invention will be better understood and further objects and advantages 
thereof will become more apparent from the ensuing detailed description of 
a preferred embodiment taken in conjunction with the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The fuel injection nozzle of the invention as shown in FIG. 3 comprises a 
nozzle holder 1 in which an inner longitudinal bore 2 is defined. The bore 
2 consists of several sections including an inlet 3, by way of which the 
fuel is brought to a valve group 4. The fuel is delivered to the inlet 3 
by a pressure line, not shown. The fuel flows through the valve group 4 
through which the fuel is injected into the combustion engine, also not 
shown. 
The valve group 4 consists of a nozzle body 5, which is fastened to the 
nozzle holder 1 by means of a cap screw 6 of a valve needle 7. The valve 
needle 7 is partly guided in a bore 8 of the nozzle body 5 which forms an 
extension of the bore 2 of the nozzle holder 1. The valve needle 7 is 
biased in the closing direction by means of a closing spring 9, which 
stresses, by means of a spring plate 10, the head 11 of the valve needle 7 
relative to the seat 12 of the nozzle body. A collar 13 is disposed on the 
shaft of the valve needle 7, which serves as a guide in the bore 8. 
By way of radial bores 14 the fuel flows from the longitudinal bore 2 of 
the nozzle holder 1 into the annular chamber 15 formed by the valve needle 
7 and the bore 8. Valve groups of this kind with only short guide collars 
have no great tendency to chatter, but they do, on the other hand, have 
other important advantages for injection. 
In order to obtain the desired chattering, the inner longitudinal bore 2 is 
provided with sections of differing diameters. The middle section 16 has 
been embodied as relatively narrow and thereby acts as a throttle. By 
means of the throttle section 16, section 17, disposed toward the inlet 3, 
is decoupled from section 18, through which the flow proceeds after 
passing the throttle section 16 so that pressure line oscillations in 
section 17 are not carried over into section 18. This results in a certain 
control over the oscillations in section 18 to such an extent that there 
only occurs a reflection of the discharged pressure resulting from valve 
chatter oscillations in section 18 because of throttle 16, and only the 
desired small over-oscillation is produced. On the other hand, pressure 
waves coming from the area of the pressure line, through the throttle 16 
are muffled so no excess oscillations occur. 
It appears to be especially advantageous for there to be a ratio of the 
diameters of the three sections, that is, of sections 17, 16 and 18, from 
approximately 7:4:10. For section 18 a ratio of diameter to length of 1:8 
up to 10 appears to be advantageous. 
The foregoing relates to a preferred exemplary embodiment of the invention, 
it being understood that other embodiments and variants thereof are 
possible within the spirit and scope of the invention, the latter being 
defined by the appended claims.