GB2036865A

GB2036865A - Fuel injector

Info

Publication number: GB2036865A
Application number: GB7942050A
Authority: GB
Original assignee: Ford Motor Co Ltd; Ford Motor Co
Current assignee: Ford Motor Co Ltd; Ford Motor Co
Priority date: 1978-12-07
Filing date: 1979-12-05
Publication date: 1980-07-02
Also published as: DE2946573C2; US4197996A; CA1125122A; JPS5851153B2; GB2036865B; JPS5578161A; DE2946573A1

Description

GB 2 036 865 A 1

SPECIFICATION

Fuel Injector Assembly This invention relates to fuel injector assemblies for internal combustion engines.

Electromagnetically actuated fuel injection valves or fuel injectors are known especially in diesel engine applications in which oil is injected usually at high pressures, into the combustion chamber of the engine This requires a high pressure pump and generally elaborate control means to regulate the fuel pressure to the injector for subsequent ejection.

For example, U S Patent Specification No.

2,332,909 discloses a fuel injector having a fuel 1 5 charging piston with differential areas subjected, respectively, to combustion chamber pressures and fuel pressures to inject a predetermined quantity of fuel into the combustion chamber at essentially a constant pressure level upon the excitation of a magnetic coil However, this device suffers from the disadvantages that it is not compact, a differential area piston is required, the piston structure is offset to one side of the injector and, therefore, not incorporated to be symmetrically arranged with respect to the injector; furthermore, there is no inlet check valve on the pressure source, reliance being made upon movement of the piston smaller diameter to cut off the fuel source prior to pressurization, and the fuel leak rate is high Furthermore, the fuel charge pressure is not determined by the spring and only one flow rate is possible since the piston cuts off the fuel to thereafter pressurize the fuel chamber.

According to the present invention, there is provided a fuel injector for an internal combustion engine comprising a housing having a fuel passage for conducting fuel to a fuel outlet orifice, a fuel flow control valve axially movable to block or permit fuel flow through the orifice, an electromagnet assembly within the housing including a coil and an armature secured to the valve, spring means urging the armature and valve to a first position closing the orifice, the valve being movable to a second position opening the orifice upon energization of the coil, a check valve for permitting an inflow of fuel into the housing and for permitting a buildup of pressure within the housing when the control valve is closed, a fuel pressure chamber communicating at one end with the passage end and at the other end with the space into which the orifice discharges, a fluid pressure responsive means in the charging chamber movable by pressure in the said space to pressurize the passage and means urging the fluid pressure means in a direction to increase fuel pressure in the passage.

By the use of a fuel reservoir that is pressurized to the level of the combustion chamber plus the force of a charging spring, the fuel pressure and combustion chamber pressures will be balanced permitting the fuel to be injected at a pressure level determined solely by the force of the spring.

Therefore, essentially a constant charge injection pressure is provided regardless of the increase in combustion chamber pressures above a predetermined level.

The preferred fuel injector assembly of the invention is compact in construction and utilizes balanced area fluid pressure actuated or responsive means in cooperation with a spring to provide essentially a constant fuel charge pressure for injection into the engine combustion chamber.

Preferably, the fuel injector assembly includes an electromagnet assembly having a movable armature formed on one end and constituting a valve member adapted to seat in a fuel outlet orifice or nozzle to block the same until energization of the magnetic coil withdraws the armature and valve; and annular fluid pressure means coaxially surrounding the fuel injection valve to be subjected to fuel pressure on one side and combustion chamber pressure on the opposite side with a spring biasing the fluid pressure means in a direction to increase fuel pressure, whereby opening of the injector valve effects a balance of pressures on opposite sides of the fluid pressure means to permit the force of the spring to inject the fuel into the combustion chamber at the force level of the spring.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the drawings, in which:- Figure 1 is a cross-sectional view of a fuel injector assembly embodying the invention; and, Figure 2 is a view similar to Figure 1 illustrating a modified embodiment of the invention.

Figure 1 shows a fuel injector assembly that includes a steel outer housing or shell 10 providing a hollow interior defining a central axially extending bore 12 Received within the housing is an electromagnet assembly that includes a conventional magnetic coil 14 mounted upon an annular spool 16 supported upon a soft iron magnetic core member 18 The core is axially aligned with an axially movable armature pintle or plunger 20 also partially received within the coil 14 Armature 20 and magnetic core 18 are biased apart by a spring 22 to define an air gap 26, the spring being seated in a recess 24 provided in the two members.

Energization or excitation of magnetic coil 14 causes an attraction of the armature 20 towards core 18 to close the gap 26, in a known manner.

The coil 14 is connected to a source of electrical energy by an adapter 28 sealingly secured to the left end (as seen in Figure 1) of the housing 10, by means not shown, and against magnetic core 18, as shown The adapter has a plug in socket 30 with an electrical connection 32 to coil 14 as shown The adapter also has a fuel inlet nipple 34 with a central passage 36.

Passage 36 is connected to bore 12 past a one- way check valve 38 and through a filter screen Check valve 38 is seated against a conically formed end of passage 36 by a spring 42 seated at its opposite end on a shoulder formed in an enlarged fuel inlet chamber 44 The fuel in GB 2 036 865 A 2 conduit 36 is supplied thereto from any suitable fuel pump having a pressure regulator for delivering the fuel at a pressure level of between 10-80 psi, for example.

The right hand side of a steel housing 10 has a fuel outlet orifice or nozzle 50 The nozzle is adapted to receive the pointed end 52 of a fuel injector control valve 54 that is formed integrally on one end of the armature plunger 20 The valve in this case is an inwardly opening valve, as indicated, and has a reduced diameter end portion defining between it and an internal diameter portion 56 of housing 10 a fuel flow chamber 58.

Chamber 58 communicates with the fuel in the bore 12 through a number of transverse openings 60.

Also provided in the housing is a toroidal-like recess 62 that surrounds the fuel injection control valve 54 It is connected to fuel chamber 58 at one end of recess 62 by the space 64 provided between an outer diameter of the armature plunger 20 and the internal diameter 56 of the housing Axially slidably mounted in the recess is an annular cup-shaped graphite ceramic type piston 66 that is essentially friction free to move easily in either direction in the recess An insulating disc 68 also serves as a seat for a charging spring 70 The recess 62 communicates at its rightward end, as seen in Figure 1, through an annular vent opening 72, to the pressure of the engine combustion chamber The injector 54 in this case would be adapted to be inserted into the combustion chamber of an engine for direct injection of fuel into the cylinder.

The embodiment of the invention shown in Figure 1 thus provides a compact fuel injection assembly construction that is electromagnetically actuated to provide essentially a constant charge pressure to the fuel injected into the engine and at a low pressure level that is essentially unaffected by the changes in combustion chamber pressure levels Its operation is as follows:- In the inexcited or unenergized state of magnetic coil 14, the armature spring 22 will separate the armature plunger 20 from the magnetic core 18 to seat the valve end 52 in the outlet orifice or nozzle 50 and block injection of fuel into the combustion chamber When the engine is operating on its intake or induction stroke, the combustion chamber pressures will be subatmospheric allowing the fuel pressure acting against the check valve 38 to unseat the same against the force of spring 42 and fill the central cavity or bore 12 This fuel flow will also fill the reservoir, i e the fuel charging portion 80 of recess 62 on the left side of piston 66 through connecting holes 60 and chamber 58 to move the piston rightwardly against the force of spring 70 until the fuel pressure in chamber 80 balances the force of spring 70 At this point, the inlet check valve 38 will close and the fuel will be trapped in the various cavities.

As soon as the engine rotates through the induction stroke and proceeds into the compression stroke, the build-up of combustion chamber pressure will be sensed through vent 72 against the right side of piston 66 and will move the piston leftwardly upon continued rise in the combustion chamber pressure until the fuel pressure in fuel charge chamber 80 equals the combustion chamber pressure level plus the force of spring 70 Assume now that coil 14 is energized or excited for a predetermined time interval to inject a predetermined quantity of fuel, such as 80 milliliters, for example into the combustion chamber The armature plunger 20 is moved leftwardly to close the airgap 24 and to open the valve Immediately, fuel will be injected to the nozzle 50 at a pressure level equal to that of the force of spring 70 since the differential pressure acting on the piston will be that due to the spring 70 The amount of travel of the piston 66 will be very small, such as 0025 inches, for example Therefore, the force of spring 70 will be decayed by only a very small amount, if any, resulting in an essentially-constant pressure fuel delivery As soon as the timed duration of injection is over, the magnetic coil 14 will be deenergized allowing spring 22 to again seat control valve 54 in the outlet orifice 50 Once again,upon decay of the combustion chamber pressure to a level below that of the force of spring 70, the inlet check valve 38 will open and refill or reprime the fuel passages, bores and recesses.

From the above, it will be seen that the piston 66 is subjected to equal pressure levels on opposite sides and that, therefore, the fuel is injected at a force level determined solely by that of the spring 70 and the inlet pressure level of the fuel.

Figure 2 shows an alternative construction for an outwardly opening control valve 54 A In this case, the positions of the magnetic core 18 A and the armature plunger 20 A are reversed since the armature plunger in this case will move in the direction opposite to that shown in Figure 1 A spring 22 A again biases the armature and core apart to provide the air gap 24 A The valve 54 A in this case has a semi-spherical surface 84 that is adapted to seat against a mating or conically formed surface 86 on the valve housing 1 OA The remaining parts and operation of the injector assembly shown in Figure 2 are the same as those in Figure 1 and, therefore, will not be repeated Again, excitation of the magnetic coil 14 moves open the valve 54 A causing a timed injection of fuel into the combustion chamber at a pressure level determined solely by the force of spring 70 A since the fluid pressure level on opposite sides of piston 66 A are balanced.

While the invention has been shown and described in its preferred embodiments, it will be clear to those skilled in the arts to which it pertains that many changes and modifications may be made thereto without departing from the scope of the invention For example, while the spring 70, 70 A has been illustrated as a compression spring located in the chamber to the right of piston member 66, 66 A in Figures 1 and 2, respectively, the spring could equally be i GB 2 036 865 A 3 located on the opposite side of piston 66, 66 A in the fuel charging chamber 80, 80 A so as not to subject the spring to the high temperatures of the combustion chamber In this case, the spring would be a tension spring to be stretched by the fuel pressure during the intake stroke, to provide an overall operation corresponding to that previously described.

Claims

1 A fuel injector for an internal combustion engine comprising a housing having a fuel passage for conducting fuel to a fuel outlet orifice, a fuel flow control valve axially movable to block or permit fuel flow through the orifice, an 1 5 electromagnet assembly within the housing including a coil and an armature secured to the valve, spring means urging the armature and valve to a first position closing the orifice, the valve being movable to a second position opening the orifice upon energization of the coil, a check valve for permitting an inflow of fuel into the housing and for permitting a buildup of pressure within the housing when the control valve is closed, a fuel pressure chamber communicating at one end with the passage end and at the other end with the space into which the orifice discharges, a fluid pressure responsive means in the charging chamber movable by pressure in the said space to pressurize the passage and means urging the fluid pressure means in a direction to increase fuel pressure in the passage.

2 A fuel injector according to Claim 1 wherein the fluid pressure means comprising a toroidal shaped piston surrounding the control valve.

3 A fuel injector according to Claim 1 or Claim 2 wherein the control valve has a needle-like shape to seat in the orifice.

4 A fuel injector according to any one of Claims 1 to 3 wherein the orifice includes a conical valve seat and the control valve comprises an outwardly opening valve having a semi- spherically shaped end adapted to seat on the valve seat.

A fuel injector according to any one of Claims 1 to 4 wherein the electromagnet assembly comprises a core axially aligned with the armature and spring means biasing the core and armature apart to define an air gap, the coil surrounding portions of the core and armature to effecting axial movement of the armature to close the gap when energised.

6 A fuel injector according to any one of Claims 1 to 5 wherein the control valve is inwardly opening.

7 A fuel injector according to any one of Claims 1 to 5 wherein the control valve is outwardly opening valve.

8 A fuel injector for an internal combustion engine substantially as herein before described and as illustrated in Figure 1 or 2 of the drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1980 Published by the Patent Office, Southampton Buildings, London, WC 2 A 1 AY, from which copies maybe obtained.