US2145429A - Fuel injection system - Google Patents

Description

Jan. 31, 1939. R NELSON H FUEL INJECTION SY $TEM Filed July 22, 1936 2 Sheets-Sheet l Jan. 31, 1939. R E. NELSON FUEL INJECTION SYSTEM Filed July 22, 1936 2 Sheets-Sheet 2 .mawaavvdsm av /v17 Q Q Q 0 sansss Ho w/ '09 a d s97 0/ RWY INVENTOR W 6?.

Patented Jan. 31, 1939 UNITED squares PATENT OFFICE This invention relates to fuel injection in internal combustion engines. It operates on the wellknown principle of the hydraulic ram, which may be stated as follows: I

When a column of liquid confined by a duct is given a high velocity of flow along the duct and then abruptly brought to rest, pressure is generated, amounting for the more common liquids to about 60 pounds per square inch for each foot per second of extinguished velocity.

In previous attempts known to me to apply this principle to the problem of fuel injection, fuel in a duct has been brought to the required velocity by means of pressureat the upstream end of the duct supplied by a pump delivering from a suitable source. At the downstream end the fuel Was permitted to return to its source until the flow was stopped, more or-less abruptly, by the closing of an engine-operated valve.

In the present invention I prefer to employ for thes ame purpose a reciprocating engine-operated displacer. This displacer produces momentarily a substantial pressure at' the upstream end of the ram duct by its displacement of fuel there, preferably into an adjacent accumulator, and simultaneously yields downstream aspace to receive flow through the duct. When this space, which is limited in extent, becomes filled, thefiow into it is automatically terminated and the rapidly moving column of fuel brought to rest, except for a small amount of delivery at high pressure to the injection nozzle lasting the time required for one round trip of the flow-curtailing wave through the ram duct.

This method of terminating flow is clean and sharp, and permits of an exceptionally 'short length of ram duct, giving a correspondingly short injection wave. This is particularly advantageous in high-speed engines, especially in those employing high dispersion injection nozzles, since the nozzle opening may be made substantially greater than has heretofore been practicable. Not only does it become easier to obtain uniform dispersion of the spray but also the penetration of the short, intense discharge resulting isgreatly superior to that obtainable from smaller-opening relatively slow-discharging nozzles of similar design. I prefer to employ an outwardly-opening automatic poppet injection valve where the design of the engine will permit. I have found it feasible to tune such a valve to the period qLthe injection wave; so that the-valve swings/openand closed again just once during the incidence of the wave.

Other features and advantages of my invention may best be made apparent from a study of the following description'and of the drawings.

In the drawings, Figure I is a comprehensive view of a preferred embodiment of my invention, partly in section and partly in diagram. In Figure II the operation of the system is graphically analyzed to show the sequence of events.

In Fig. I the numeral I represents an engine cylinder and 2 its piston, which, incooperation with the cylinder head 3, form the combustion chamber 5 when the piston is near the top 'of its stroke, where it is shown. Conveniently built into the head 3 are the injection wave generator 4 and the injection valve 5. This valve is of the poppet type and forms, when open, an annular orifice directed to reach most of the air in the combustion space. The injection wave generator 4 is operated hydraulically in response to the engine cycle by a wave of pressure coming along the line 9 from the operating unit I, conveniently mounted on the engine I0 and itself operated by means of cams on the camshaft 80. The camshaft is engine-driven through the symbolically indicated drive 8, with which may be combined any one of the suitable well-known mechanisms for advancing the timing of operation automatically at high speeds of the engine.

The injection orifice is formed at 55 by the lifting of the valve head 52 from its seat 5| under the pressure of the injection wave. opening is determined by the elasticity of the slender valve stem 53, acting as a tension spring. The valve parts are centered at 54, where the stem is given an enlarged diameter for a short length to'fit into a guide bore in' the seat-piece 5|. Passages 56 in 5| give the fuel injection pressure access to the valve. threaded enlargement 51 at the inner end of the valve stem and the nut 582, the valve is secured to the automatic take-up plug 58l, which fits into the bore 584 in the head 3.

The bore 584 is closed by the cap 585, thus leaving a small space at 581. This space and the chamber 48, formed in the head 3, are kept filled with fuel. The plug 5Bl should -fit its bore 584 with slight looseness to permit adjustment flow past itself to allow the spring 586 to define the opening pressure of the injection valve, which pressure should be great enough to prevent opening of the valve exceptat the time of the generation of the injection wave. High momentary pressure in 48 occurs at the time of injection, as will be seen, and opposes movement of the f\ plug 58l under the increased stem stress when the injection valve is open.

The 'amount of By means of the.

H is the dlsplacer of the injection wave generator 4. This displacer is stepped in diameter and fits at 4 and 2 with a correspondingly stepped bore in the sleeve 43, which is set into the head 3 snugly at 43I and 432, securing the valve piece 5| and secured by the retainer 44. This retainer and the seatpiece 5I limit the travel of the displacer at 46 and 41 respectively. The ram column 42 is formed axially in the displacer, and is conveniently passed through longitudinally by the valve stem 53.

The displacer is operated on its active stroke by hydraulic pressure on the face 45 between the ends of different diameters. This, pressure comes along the line 9 from the operating unit 1. In turn the displacer forces fuel from the space at its end 46 into the fuel-filled chamber 48, and at the same time creates a space at its end 41 downstream of the ram column. Under the pressure built up in 48 by the upstream displacement, a flow develops in the ram column, and continues until the space at 41 created by the movement of the displacer becomes completely filled, at which time wave generation occurs.

The ram column 42, the passages 56 and the fuel compression chamber 48 are kept filled with fuel at a pressure which maybe conveniently about 150 lbs. per sq. inch by means of a supply system as follows:

Fuel from any convenient source such as a tank I is taken by the line ml to the pump I02, which may be an engine-driven gear-pump. This delivers into a stabilizing duct or reservoir I03. From this the tube I04, at least a part of which is of small section, goes to the chamber 48. From the chamber, preferably at its highest point, another tube I havinga length at similar small section leads to the second reservoir I06, the pressure in which is maintained at the desired average value by the loaded relief valve I 01, which discharges back through the line I08 to the source of fuel.

The pump I02 should be of suflicient capacity to deliver fuel in excess of that required for injection in order to maintain a net flow out of the chamber 48 through the tube I05, by which any air in 48 may be exhausted. At the time of compression in 48 by the. action of the displacer M the pressure in 48 will be high. The small tubes I04 and I05, since they resist by the inertia of their columns changes in flow, permit this high pressure momentarily but serve to discharge quickly any residual pressure at the end of the period of activity of the wave generator. As will be seen later, a reflected wave returns from the injection valve. This causes some surging from the ram column into the chamber 48, which the tubes, especially I 05, largely absorb.

The body of the operating unit, indicated by 1, is mounted conveniently on the engine to permit its camshaft 80 and its tappets H3 and 123 to be built into the engine. Into the body 1 is formed the chamber 10, which is filled with a suitable grade of lubricating oil. Threaded into the bottom of this chamber is the barrel 1I0, to which is fitted the plunger H I, operated by the cam 2 through the tappet H3 and returned by the spring 1I4. Between the chamber and the line 9 is the bore 13I, to which is fitted the plunger or release-displacer 13. This release-- displacer is enlarged on its bottom face to seat against the end 1200 of the barrel 120, which has its plunger assembly including the release plunger 12I, the cam 122, the tappet 123,. and the spring 124. A spring 132, held by the retainer 133, mg; the release-displacer toward its seat. A

small hole 130 is drilled in the face of the releasedisplacer to permit a limited degree of communication between its ends.

In operation the plunger 1 builds up a high pressure in 10 until the plunger 12I is advanced. This plunger unseats by hydraulic pressure or direct contact the release-displacer 13, which is then driven forcefully into the bore 13I for a short distance, transferring by its displacement the energy of the compression chamber to the line 9. The throttle valve 11, which may be manually operated or governor-controlled, regulates the-intensity of the outgoing wave as desired for control of the intensity of the injection wave and thus for control of the amount of fuel injected.

plunger 12 I. During this return, accompanied by return of the release-displacer, any deficiency in liquid in 10 will be made up by flow through the hole- 130. release-displacer to seat, and recedes somewhat farther until the time for its next lifting.

' In Fig. II the operating characteristics of the system are plotted for maximum usable engine speed and full injected charge. The curves are somewhat idealized and are intended to show only in a general way the actual conditions in the system to indicate the sequence of events. At the top of the chart the movements of several parts are plotted against time in degrees of crank angle to the same linear scale. The curves are numbered to correspond to the parts to which they refer. Pressure variations for a number of points in the system are similarly plotted below.

These pressures, given in thousands of pounds per square inch are, of course, not the only ones for which the system may be designed.

The membersof the system are in the position shown in Fig. I at about -70 degrees, or 70 degrees before top center, with the releasing plunger 12I still descending slowly. At about 66 degrees the cycle of operation of the system begins as the cam 1I2 starts to lift the plunger 1| I. As this advances the pressure in 10 rises proportionately. This compression continues until release at about 26 degrees.

The releasing plunger starts to rise at about 28 degrees but does not cause release until the volume swept on the previous return after closing 10 to govern, the release-displacer is rapidly accelerated, producing by its motion a'strong wave to go out along the line 9. At the same time the pressure in 10 will fall off rapidly, and-becomes negligible at about -17 degrees. The intensity of the outgoing wave reaches its maximum early and later falls off more slowly than does the pressure in the chamber, because of the momentum of the release-displacer.

At. about 21 degrees, depending upon the length of the operating line 9, the operating wave The plunger 12I finally permits the in every respect, the reverse of the opening.

reaches the displacer 4 I, which immediately starts to move in response to the pressure. This pressure, high at the start, falls off rapidly; most of the energy given the displacer comes during the first part of its motion. In the meantime the pressure in the fuel compression chamber 48 builds up, so that, during the later part of the movement of the displacer this pressure is dominant and brings the displacer to rest, in cooperation with the retainer 44 against which the displacer subsequently bears. While the displacer goes through its movement, the fuel in the ram column accumulates velocity of flow into the space at 41, which it fills completely at the time that the displacer 4| ends its motion. It is then, at about -l0 degrees, that the injection wave is generated, beginning at the downstream end of the column.

When the space at 41 has filled, the moving column of fuel in the ram column is forced to seek an outlet through the passages 56, which, however, being filled with stationary fuel, resist flow and force thedevelopment of a high pressure at 41. This pressure, suflicient to equalize the flow in ram-column and passages, travels in both directions in a wave with the velocity of sound. When this wave reaches the compression chamber 48 a wave of decompression to the pressure of the chamber 48 immediately begins to return along the column. The total time that the downstream end of the column is at high pressure is, then, that required for one round trip of a wave in the ram column. This is the period of the injection wave.

When the forward wave reaches the head 52 of the valve, it is, at first, almost totally reflected, since the valve is closed; sothat the pressure almost doubles. The valve opens rapidly, and continues to open as the pressure is partially relieved by the discharge through the injection orifice thus formed. At the same time the tension in the stem 53 is increasing. Under these changing conditions the valve is brought to rest and accelerated on its return motion, which is, As the valve nears its closed position the fuel pressure again builds up to its initial value. Just as the valve comes to rest the wave of pressure relief from arrives and the action ceases. The proportions of the valve stem and head necessary for this synchronism are best arrived at by experiment, although they may be calculatedreadily by assuming for the valve head simple harmonic motion for approximate results.

It will be obvious that this invention may be varied radically in design without departing from the spirit and scope of its application.

I claim as my invention:

1. In a fuel injection system, an hydraulic ram generator of injection pressure comprising a fuel filled duct, means for supplying fuel to this duct, a displacer having opposing abutments at opposite ends of said duct, engine-operated means for rapidly moving said displacer in a direction to increase the space available for fuel at one end of said duct while decreasing the space at the other or upstream end, an hydraulic accumulator adapted to receive at rising pressure the fuel so hydraulic accumulator at the upstream end of said duct, a fixed abutment adapted to limit the stroke of said displacer, and means for rapidly operating said displacercomprising a second hydraulic pressure accumulator, means for displacing liquid into said accumulator, an engine-operated valve adapted to release the pressure so produced, and a duct connecting said valve with the above-mentioned additional abutment of said displacer.

3. In a fuel injection system, an engine-operated hydraulic ram having as one of its elements 1 a fuel-filled duct, an outwardly-opening long-stem automatic poppet injection valve, a duct connecting said first-named duct at its downstream end with said injection valve,'the dynamic period oi. said injection valve as determined by the mass of its head and the elasticity ofdts stemibeing equal to the time required for sound to travel twice the length of said first-named duct.

ROBERT E. NELSON.

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