US3486494A

US3486494A - Fuel injector

Info

Publication number: US3486494A
Application number: US705191A
Authority: US
Inventors: Alexander Dreisin
Original assignee: Allis Chalmers Corp
Current assignee: Deutz Allis Corp
Priority date: 1968-02-13
Filing date: 1968-02-13
Publication date: 1969-12-30
Anticipated expiration: 1986-12-30
Also published as: JPS4938769B1; DE1907316A1

Description

Dec. 30, 1969 A. DREISIN FUEL INJECTOR Filed Feb. 13. 1968 United States Patent US. Cl. 123139 Claims ABSTRACT OF THE DISCLOSURE A hydraulically controlled fuel injector for use in an internal combustion engine.

This invention relates to fuel injection and .more particularly to a hydraulically controlled fuel injector which controls the timing and quantity of fuel injected in an internal combustion engine.

A unit injector is a well known device used to supply fuel in highly atomized state to the combustion chamber of an internal combustion engine. It is actuated by means of a cam which is driven from the engine usually through a gear train. The cam motion is transmitted through a mechanical linkage to a reciprocating plunger in the unit injector. During the pumping stroke fuel is displaced by the plunger and fed to the nozzle usually arranged coaxially in the same housing and opening through spray orifices into the combustion chamber.

Two principal types of unit injectors are used today which include the mechanically controlled unit injector having a control device which senses engine speed and throttle position and is connected to each unit injector by mechanical linkages. Movement of these linkages is transmitted to the unit injector plunger and varies its effective stroke. This construction has the disadvantages of mechanical connection between the control devices such as governors and individual injectors which increases in complexity with the increasing number of engine cylinders. This induces friction into the control system which requires higher control forces from the governor and is in need of maintenance because a change in the relative position on these mechanical linkages can disturb the output balance of the individual injectors. In addition, injection timing is fiXed in relation to engine cycle.

The second type of unit injector in use is actuated mechanically by a cam in a manner similar to the first type described above. However, fuel quality for each injection is premetered separately at low pressure by a measuring device and is preloaded into the injector pump ing chamber preceding each pumping stroke.

This system does not require mechanical control linkages, but has the disadvantage of injecting the fuel from an intermediate portion of the plunger stroke all the way down to the top of the cam lift or to the bottom of the plunger stroke.

It is well known to the person skilled in the art that such injection has inherent disadvantages. Mainly the end portion of the injection occurs at a decreasing plunger velocity which adversely affects the atomization of the fuel and subsequently the quality of combustion. Another disadvantage common with the first type is that this system also has a fixed injection timing.

Since the modern engine speeds are increasing, it becomes more and more necessary to change the relative timing between fuel injection and the engine combustion cycle. At low speeds the optimum position of injection start can be close to the engine top dead center, at the end of the compression stroke. As the engine speed in- 3,486,494 Patented Dec. 30, 1969 "ice creases the engine crankshaft turns through a larger angle during'the time required to prepare the injected fuel for combination. This preparation time consists essentially of the time required to preheat and partially evaporate the injected droplets of fuel and the time needed to accomplish the so-called preflame oxidation reactions. As an example, this period might be on the order of two crankshaft degrees at 600 engine r.p.m., and 12 crankshaft degrees at 3,000 engine r.p.m. For optimum conditions throughout the speed range, injection timing therefore. shall be advanced by about 10 crankshaft degrees in respect to the engine top dead center.

This invention provides a hydraulically controlled unit injector which eliminates the disadvantages of the conventional systems without adding to the overall system complexity. A unit injector is used which is mechanically driven'by an engine through a cam which imparts reciprocal motion to a plunger in the bore of the injector housing. A supply pump supplies pressurized fuel which flows through the injector for cooling during the periods at which the injector is not in the injection phase. During the. period that the plunger is moving downwardly within the bore defining the high pressure chamber a hydraulic pressure signal is initiated by a control unit which controls the pressure in the fuel lines in the injector. A control valve operates in response to the pressure signal from the control unit. The control unit operation provides the timing at which the control valve closes thereby causing pressurized fuel from the high pressure chamber to be injected through the unit injector nozzle. At the end of the phase of injection the control valve is caused to open in response to another pressure signal which in turn spills high pressure fuel through the control valve and terminates injection. The supply pump, control unit, and control valve are a relatively simple means whereby the timing and quantity of fuel injected into the combustion chamber may be controlled within a very limited angular rotation of the engine crankshaft. Reference may be=had to a copending application, Ser. No. 705,176, filed Feb. 13, 1968, of the same inventor for a more specific illustration and description of the control unit.

It is an object of this invention to provide a hydraulically controlled fuel injector.

It is another object of this invention to provide a mechanically actuated hydraulically controlled fuel injector for an internal combustion engine.

It is a further object of this invention to provide a mechanically actuated unit injector having speed and load responsive hydraulic means to control timing and quant ity of fuel injected into a combustion chamber of an internal combustion engine.

The objects of this invention accomplished by the use bf a unit injector which is mechanically actuated for reciprocal movement of a plunger in a housing defining a high pressure chamber. A fuel line supply pump pressurizes fuel which flows through the injector to cool the nozzle and the injector assembly when the unit is not injecting fuel. The pressurized fuel flows through the unit injector and through a control valve in the injector which is biased in open position.

A hydraulic signal is transmitted from a control unit to the control valve which reduces the pressure on one side of the valve causing the pressure on the opposite side of the valve to bias the valve to a closed position thereby initiating injection. Injection continues until such time as pressure is restored on the low pressure side of the valve at which time the spring and pressure on the spring side of the valve will bias the valve to an open position. When the valve is biased to an open position the high pressure fuel from the high pressure chamber is spilled through the drain manifold and injection is terminated.

The distribution of the pressure signals is controlled by a control unit intermediate the supply pump and the control valve which transmits the timed signals for initiating and terminating injection to the unit injectors of the various cylinders.

The preferred embodiment of this invention will be described in the following paragraphs and described in the attached drawings.

FIG. 1 illustrates a cross section view of the unit injector.

FIG. 2 illustrates a fragmentary cross section view taken on line IIII of FIG. 1.

FIG. 3 is a schematic diagram of the hydraulic system and the injectors.

Referring to the drawings, FIG. 3 illustrates the com plete fuel injection system. The fuel tank 1 is connected by a conduit 2 through fuel filters to the supply pump 3. The supply pump 3 develops a steady flow of fuel at a pressure of approximately 50 to 100 pounds per square inch. The pressurized fuel is supplied to a control unit 4 which is driven synchronously or directly proportionately with the engine speed. The control unit has a fuel line return 5 under substantially ambient pressure which returns the excess fuel back to the tank 1. In addition the control unit is connected with the individual supply lines 6 to the respective injector 7. These lines are subject alternately to the supply pressure or to the ambient pressure as will be further explained.

After passing through the injector the fuel issues fro the drain lines 8 to the drain manifold 9 through a relief valve 10 and back to the tank by the valve return line 11. The engine 100 drives a plurality of

cams

101, 102, and 103 through the gearbox 104. Likewise the engine 100 is connected through the gearbox 105 and gear 106 to drive the control unit 4. The gearbox 104 on the engine 100 controls the reciprocating movement of the individual plungers in each of the plurality of injectors 7 which provide the actuating force to operate the injectors. The control unit 4 which is driven through the gearbox 105 has means built within the control unit 4 to permit timing changes of the pressure signals transmitted to the injectors. Changing the phasing of the pressure signal in relation to the engine cycle, alters injection timing. Changing duration of the pressure pulse controls fuel quantity injected. Timing changes are speed responsive. Quantity changes are responsive to speed changes and to changes of throttle position.

The unit injector 7 illustrated in FIG. 3 is shown in cross section in FIG. 1. The injector 7 is operated by engine 100 through the cam as shown which imparts a reciprocating motion of the plunger 12 which is closely fitted into the bore of the housing 13. During the interval between injections, fuel under supply pressure is furnished by the supply line 6 and fills the control spring chamber 14 shown in FIGS. 1 and 2. From there it passes through passage 15 in housing 13 and through the inlet 16 into the injection pumping chamber 17. The fuel then flows through the passage 18 into the gallery 19 surrounding the nozzle differential valve 20 and continues its flow through the

passages

21 and 22 to the control annulus 23 which surrounds a control valve 24. Control valve 24 is formed with radial slots 25. Fuel flow continues from the annulus 23 through the slots 25 into the inside of the control valve and through the clearance between the control valve and the stem of the adjusting screw 26. It then passes unobstructed through passage 27 to the drain line 8 into the drain manifold 9. The circuit is completed through the pressure relief valve 10 which is set at approximately 50 to 100 pounds per square inch and through the valve drain line 11 back to the fuel tank. The exact pressure is not critical in the fuel circuit however the pressure should be maintained reasonably constant.

From the above flow path description it is clear that the pressure in the drain line 8 and manifold 9 is of the same order as in the supply line 6. A small difference will only be induced by resistance to flow of the passages inside the unit injectors which are arranged in parallel. In the first approximation and for simplicity of further explanation we can assume that the pressure in the lines 8 and the manifold line is equal to the supply pressure furnished by the pump 3 and the control unit 4.

The operation of the injector and the hydraulic system will be described in the following paragraphs.

At the beginning of the cam stroke plunger 12 starts its pumping motion. At this time the fuel flows in the manner described above through the pumping chamber to the nozzle, cools the nozzle in its passage and is returned to the tank. During its pumping movement the edge 28 of the plunger 12 will override the inlet port 16 and will close it. Past this point the advancing plunger still displaces the fuel in the injector which flows as previously through the control valve 24 to the drain manifold. At the appropriate time in relation to the engine cycle, control unit 4 relieves the fuel pressure in the supply line 6 leading to the particular injector. Pressure in this line is relieved to ambient pressure.

Let us consider more in detail the behavior of the control valve 24. Prior to the start of injection it was subject to essentially the same pressure on its upward and lower faces. Its lower face on the side of control spring chamber 14 was subjected to the supply pressure arriving through the line 6. Its upper face on the side of the adjusting screw 26 was subjected to the same pressure diminished only by the resistance to fuel flow through the passages in the unit injectors. Control spring 29 exerts a. force which is approximately equal to /2 the axial force exerted on the valve by the supply pressure. As long as the supply pressure in the spring chamber 14 persists, the sum of the forces of the spring and the hydraulic pressure, force the control valve in the direction of the adjusting screw 26. The valve is stopped by the pin 30 which is located across the stem of the adjusting screw 26 and protrudes through the openings in the control valve skirt. When hydraulic pressure is eliminated in spring chamber 14, :the force of the spring 29 is overcome by the hydraulic force which is acting on the valve from the side of the adjusting screw 26. Although the supply pressure from the supply pump 3 is cut 01f by the control unit, pressure is also being developed by the downward movement of the plunger which in turn is transmitted to the annulus 23 which assists in closing the valve 24.

As the control valve moves against the spring, slots 25 override the edge of the annulus 23. This stops the flow of fuel from the nozzle passage 22. The continuing movement of the plunger 12 now compresses the fuel trapped in the chamber 17 and nozzle passages 18 through 22. When the opening pressure of the needle 20 is exceeded the nozzle opens in a conventional manner and the injection takes place. To terminate injection pressure has to be reestablished in the spring chamber 14. At that moment the hydraulic forces of the spring chamber will balance the hydraulic forces on the opposite side of the valve and the spring will shuttle the valve to an open position. Reopening of the valve slots will establish communication to the return manifold which will drop the pressure in the unit injector below the closing pressure of the nozzle. Accordingly the injection is terminated at this point.

The described unit injector can be controlled by dropping the supply pressure to ambient pressure or dropping the pressure substantially which initiates the injection and reestablishing the supply pressure which terminates injection. Varying the phasing of these events in relation to the engine will vary the injection timing. Varying the time interval between relief of supply pressure and establishing of supply pressure will change the portion of the plunger stroke during which time the fuel is trapped in the injector and, therefore, will change the fuel quantity injected through the nozzle. Duration of no pressure interval therefore determines the active plunger stroke of the injector.

It is understood that even if this interval repeats with absolute accuracy from one injection to the next and from one unit injector to the other, slight variations may be introduced into the quantities injected. This is undesirable because it will induce variation in the level of performance from one engine cylinder to another. These variations will be due to manufacturing tolerances which are impossible to eliminate completely. One of the factors, for example, is a variation of the valve movement required to close the relief slots 25. If, due to manufacturing tolerances, one of the injectors has a shorter stroke to close the valve, injection will commence sooner. If the same valve requires a longer stroke to reopen, injection will terminate later. Both factors will cause the injected quantity to be higher. Another factor in influencing the movement of the valve opening and closing is the force of the spring 29. For a given valve to reopen: a stronger spring will accelerate the valve quicker than a weaker spring which would tend to advance valve reopening and in turn will shorten duration of injection.

The valve as illustrated however has built in provisions which will allow a convenient way to adjust the valve stroke required for valve closing and valve reopening and to adjust the force of the spring 29. As shown in FIG. 2 total valve stroke is limited by the difference in diameter of the cross pin 30 and the hole arranged in the skirt of the valve. By holding these two features within close manufacturing tolerances the total valve stroke can be made very closely alike in all valves.

Pin 30 is placed into the stem of adjusting screw 26. By threading the screw 26 in or out valve stroke to close can be varied and adjusted conveniently while the injector is in operation on a test fixture.

Spring 29 is enclosed in the spring cap 31. By screwing this cap in or out the length of the spring 29 can be varied changing the spring force upon the valve. The two adjustments described make it possible to adjust the fuel delivery of each injector in such a way that when a calibrated pulse is received from the control unit, an equal amount of fuel is injected by the injector. By a calibrated pulse it is meant the complete event of supply pressure relief and, after a repeatable interval, reestablishment of pressure.

The preferred embodiment of this invention has been illustrated and described and the scope of this invention will be defined by the attached claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A fuel injector comprising a housing defining a fuel injection pumping chamber, a plunger reciprocating in said housing for pressurizing fuel in said injection pumping chamber, means defining an injection nozzle for injection of fuel in a combustion chamber, a nozzle valve in said nozzle for controlling the discharge of fuel through said nozzle, means defining passage means communicating with said nozzle valve and said injection pumping chamber, a control valve normally biased to an open position having a chamber on one side of said control valve adapted for receiving pressurized fuel from a fuel supply and pressure signals from a control unit, said chamber communicating and supplying fuel to said injection pumping chamber, means defining return passage means in communication with said nozzle valve through the other side of said control valve for returning pressurized fuel from the nozzle to the fuel supply when said control valve is open and tending to bias said valve to a closed position, said control valve closing and opening in response to pressure changes in said valve chamber to thereby respectively initiate and terminate fuel injection.

2. A fuel injection system comprising a fuel injector including a housing defining an injection pumping chamber, a plunger reciprocating in said housing for pressurizing fuel in said injection pumping chamber, means defining an injection nozzle adapted for injecting fuel in a combustion chamber, means defining passage means communicating with said injection pumping chamber and said nozzle, a valve in said nozzle for controlling the discharge of fuel from said nozzle, an injection control valve normally biased to an open position having a chamber On one side of said control valve adapted for receiving pressurized fuel from a fuel supply, said chamber communicating and supplying fuel to said injection pumping chamber, means defining return passage means communicating with said nozzle valve and connected through the other side of said control valve for returning fuel through said control valve when said valve is open and tending to bias said control valve to a closed position, an engine for actuating said plunger, a control unit connected to said chamber of said control valve and operated by said engine, a fuel supply connected to a fuel supply pump in communication and supplying pressurized fuel to said control unit, return conduit means connected to the other side of said control valve including a pressure relief valve for returning fuel to said fuel supply and maintaining a constant pressure in said return conduit means at said control valve, said control unit changing the pressure in said valve chamber of said control valve causing said valve to close during the interval when said plunger is actuated thereby initiating injection and restoring normal pressure in said valve chamber of said control valve causing said valve to open and termmating injection.

3. A fuel injector as set forth in claim 1 wherein said control valve includes a spring in said chamber normally biasing said control valve to an open position.

4. A fuel injector as set forth in claim 1 wherein said control valve includes means defining a cylindrical opening having an annular recess in communication with the return passage means, a reciprocating sleeve controlling fuel return through said annular recess and said return passage means to close said control valve when the pressure is decreased in said control valve chamber to thereby initiate fuel injection.

5. A fuel injector as set forth in claim 1 wherein said control valve includes a valve element and means for adjustably positioning said valve element to control the movement of the valve element required to close said control valve.

6. A fuel injector as set forth in claim 1 wherein said control valve includes a valve element normally biased to an open position by a spring, means adjustably controlling the compressive force on said spring to control the response of said valve for opening and closing to initiate and terminate injection.

7. A fuel injector as set forth in claim 1 wherein said valve includes means defining a cylindrical opening and an annular recess in communication with the return passage means in said injector, a spring bias plunger normally biased to an open position with means for adjusting the extent movement of said plunger required to open said valve and means for adjusting the spring tension biasing said valve to a normally open position.

8. A fuel injector as set forth in claim 1 wherein said control valve includes a spring chamber including a spring normally biasing said valve to an open position, mean-s adjustably controlling the spring force biasing said valve to an open position, means adjusting the movement of a valve element required to close said valve and thereby adjust control valve response for initiation and termination of injection.

9. A fuel injector as 'set forth in claim 2 wherein the plunger actuating mechanism and the control unit are synchronously operated from said engine and said con- 7 trol unit includes means to advance or retard initiation and termination of injection and to control the duration of injection by controlling the pressure signals transmitted to said control valve.

10. A fuel injector as set forth in claim 2 wherein said control unit controls timing of the pressure signals transmitted to said control valve in response to engine speed and duration of the pressure signals in response to engine speed and load requirements.

References Cited UNITED STATES PATENTS LAURENCE M. GOODRIDGE, Primary Examiner US. Cl. X.R.