Patent Application
20070235008
Needle-spring locking device in accordance with the invention relates to-pump-injectors and to conventional injectors of fuel supply systems for internal combustion engines, specifically for diesels.
In order to ensure greater fuel efficiency and lower exhaust smoke and particulate matter (PM) emission, the maximum and medium injection pressures in modern diesels are constantly increased. By now, commonly used injection pressures have reached 1600-2000 Bar, and in the near future they will reach 2500 Bar and more. The increase of the maximum and medium injection pressures is facilitated by the increase in the nozzle needle lift and closing pressures (pressures causing the needle to start its travel upward and reverse, to travel downward and seat on the nozzle's cone). The latter is also especially important for lowering exhaust smoke emission, in particular (PM), because by increasing the force on the nozzles needle, the needle closes faster, resulting sharp EOI (nd Of Injection), thus reducing the quantity of the fuel injected into the combustion chamber under low pressure at the final phase of the injection.
In modern diesels, needle-spring locking devices are most frequently used, with a cylindrical helical spring usually disposed in a central cavity formed in the pump-injector) body. The diameter of such cavities in actual diesels does not exceed 12-14 mm, because larger diameters would not allow for disposing and sealing the joint surfaces between the high-pressure channel delivering the fuel from under-plunger cavity, and the high-pressure channel of the nozzle body. According to a common formula, the maximum force that can be created by a cylindrical helical spring equals Fmax=τπd3/8D(Kgf), where τ—is maximum allowed torsion stress, d—diameter of the spring wire, D—average diameter of the spring coil. If we assume that for a cyclically working spring τ=3,000 kg/cm2, and minimum permissible ratio D/d=3 (based on the manufacturing considerations), the formula above can be reduced to: Fmax=44D2 kgf. Considering the dimensions of the cavity where the spring is disposed (see above) and granted that D/d=3, the permissible values for the average spring diameter will be D=0.9-1.05 cm. According to the formula above, the maximum spring force in the state-f-the-art diesels is Fmax=36+48 kgf. In modem high-speed diesels, the diameter of the nozzle needle is usually 0.6 cm and the needle cross-section differential coefficient is 0.65 (the ratio of the difference between the area of the needle cross-section and the area bounded by the circumference of the bearing edge of the needle cone to the needle cross-section area). In this case (granted that Fmax=50 kgf), the fuel pressure during the needle's travel upward will be about 400 kgf/cm2, and the fuel pressure in the beginning of the closing of the needle will be 280 kgf/cm2, which is not enough, considering the maximum injection pressures specified above (2000-2500 Bar and higher).
In order to significantly increase the lift and closing pressures of the proposed nozzle needle, the needle locking spring is disposed in the central cavity of the body around the outer surface of the plunger bushing and is connected to the needle via a transverse cross-arm disposed in the plunger bushing. In this case, the average diameter of the needle spring can reach 2-2.2 cm, and the spring force according to the above formula will constitute about 180-220 kgf. The nozzle lift pressure will then be about 1200 kgf/cm2 (if the needle diameter is 0.6 cm), and the nozzle closing pressure will be about 650-800 kgf/cm2, which better suits said maximum injection pressures (2000 kgf/cm2 and higher).
It should be noted that high lift and closing pressures of the nozzle (900 and 600 kgf/cm2 respectively) could be achieved in the proposed device even if the needle diameter is increased to 0.8 cm (corresponding to the cavity diameter of 2.5 cm) as is common in high-power diesels.
Needle-spring locking device in accordance with the invention is implemented in the design environment comprising a pumping plunger moving inside a bushing driven by a cam or hydro mechanical piston mechanism. The plunger bushing has an upper cylindrical part in which the plunger is moving and a lower larger diameter part with a precision face adjacent to the precision face of the nozzle, the pump-injector body being pressed to the nozzle body along said surfaces by a tightening nut. The subject of the invention also consists of the said lower part of the bushing that. has an aperture located above the precision face perpendicularly to the bushing axis (or centerline), and an axial opening adjoining the centre of said aperture to which the face of the nozzle needle is exposed. As mentioned above, a helical spring is mounted around the outer surface of the upper part of the plunger's bushing, one face of said spring pressed against said body, and its second face pressed against the edge surfaces of the cross-arm installed in said aperture of the lower part of the bushing. The central part of the cross-arm is pressed against the face of the nozzle needle. Said cross-arm and the spring interact via a washer installed between said cross-arm and the bearing face of the spring. The cross-arm has a spherical form at the contact areas with said washer and the face of the nozzle needle.
To illustrate the proposed device,
The pump-injector operates as follows:
Driving mechanism 1 forcing plunger 4 installed in bushing 2, and plunger 4 blocking filling channel 5 in body 3, the fuel in cavity 8 is exposed via channel 6 in bushing 2 and channel 7 in the nozzle body into chamber 9 of nozzle body 10. The sealing of channels 6 and 7 is achieved by surface precision joint 11 between pump-injector and nozzle bodies, pressed together by nut 12. Due to the action of the fuel on differential cross section 13 of nozzle needle 14, needle 14 that presses with its pin 16 on transverse cross-arm 15 disposed in cylindrical aperture of the bushing, travels upward overcoming the force of spring 17, arranged around the outer surface of said plunger bushing, whose lower face is set against the outer edges 18 of said cross-arm 15. At the end of the needle working stroke when the pressure in chamber 9 falls, the needle due to the action of spring 17 acting on the needle through cross-arm 15, seats on the cone of the nozzle body. To achieve high contact force between the cross arm 15 and the nozzle needle, while eliminating lateral forces to act on the needle, washer 19 is used. The edges of cross-arm 15 and central section 20, contacting pin 16 of needle 14, have a spherical surface. As has already been mentioned, transverse cross-arm 15 is disposed in the aperture of bushing 2, said aperture being perpendicular to the bushing axis, and radial channel 21 being made in the bushing for pin 16 of needle 14, contacting said cross-arm, said channel being connected with the center of said cylindrical channel. Driving mechanism 1 of plunger 4 can be made as a cam or hydraulically driven piston.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms -without departing from the spirit or essential attributes thereof The present embodiments are therefore to be considered in all respect as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
In the above embodiment shown in
The spring locking device of the nozzle needle according to the invention, as mentioned above, can be used in diesel pump-injectors, by both methods, either the plunger being driven by a cam, or the plunger being forced by a hydraulically driven piston. This device is especially efficient in a pump-injector for high-power diesels where high injection pressures of 2000 Bar and higher are used (for reasons mentioned above). The proposed locking device can also be used in conventional injectors of said diesels.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL04/00658 | 7/20/2004 | WO | 1/22/2007 |
