High pressure unit fuel injector

Abstract: A fuel injector of the open nozzle type, which is capable of achieving SAC pressures (i.e. the pressure of the fuel in the injection chamber just in front of the injector spray holes) in excess of 30,000 psi during injection. The injector assembly (11) of the preferred embodiments includes a plunger assembly (7) having three plungers (9,11,13) arranged to form a hydraulic, variable timing fluid chamber between upper (13) and intermediate (11) plungers and an injection chamber below a lower plunger (9). To prevent leakage from the injection chamber, the fuel supply passage (31) is provided, along with the injection chamber, within a one-piece injector cup (5) and a predetermined minimum seal length, at commencement of injection, between a land portion (9b) of an injection plunger (9) and a wall surface defined by a bore (6) of the injector within which it reciprocates is coordinated to the dimensions of the bore below the land and a predetermined maximum solid fuel height for the injector to result in the minimum seal length being at least one-half of the maximum solid fuel height. To obtain an increase in SAC pressures under low speed operating conditions without exceeding pressure capabilities under high speed conditions, some embodiments have valve arrangements for draining timing fluid from the timing chamber whenever the pressure of the timing fluid therein exceeds a predetermined value.

Description: This invention relates to fuel injectors and in particular unit fuel injectors especially those of the type having an open nozzle and a reciprocating injection plunger that is mechanically actuated by an engine cam shaft. Such fuel injector is described in the generic part of claim 1. As the needs for higher levels of pollution control and increased fuel economy have called for substantially improved fuel supply systems, unit fuel injectors, of the initially mentioned type have been developed which are designed to provide a fuel injector of simplified design, thereby providing cost reductions, while at the same time providing reliable and precise control of independently variable fuel injection timing and quantity parameters, as is necessary from a fuel economy and emissions abatement standpoint. The following patents are representative of the prior art unit fuel injectors: US-Patents 4,471,909; 4,441,654; 4,420,116; 4,410,137; 4,410,138. All these injectors are having an open nozzle and a reciprocating injection plunger mechanically actuated by an engine cam shaft. Even though fuel injectors of the above noted type have proven to be very effective, reliable, and economical, impending further restrictions on the levels of hydrocarbons, nitrogen oxides, and particulate mass in vehicle emissions pose problems in attainment, particularly in a cost effective and fuel efficient manner. To avoid using expensive, hard to maintain after treatments like catalysts, requires dealing with the pollutants at the source, i. e., in the combustion space. This means increasing the efficiency of the combustion process which, in turn, means injection of the fuel at considerably higher pressures than have heretofore been attained, particularly during low speed operation. For example, in the above listed patents, the injection chamber is formed in an injector cup that constitutes the bottom-most element of a multipiece injector body and fuel is supplied to the injection chamber via a supply passage formed in another injector body element. In such an arrangement, clamped high pressure joints are present which limit the injection pressure capabilities of the fuel injector to SAC pressures (i.e., pressure of the fuel in the injection chamber just in front of the injector spray holes) to under 1.400 bar (20.000 psi). Furthermore, another pressure limitation is imposed by the fact that, in operation of such injection systems, injection commences (i.e., the plunger reaches the solid fuel height within the injection chamber) very shortly after a sealing portion of the plunger has blocked the supply port. As a result, the seal length of the plunger (i.e., the length of the sealing surface of the plunger below the fuel supply orifice), which is typically 0,4 mm, presents an interface which will leak if very high SAC pressure levels occur, such as those over 2.100 bar (30.000 psi). Also, the presence of the supply orifice in close proximity to the region of very high pressure cyclically creates stress risers that result in fatigue effects which shorten the life of the injector. In addition to the above-noted "open nozzle" unit fuel injectors, unit fuel injectors of a "closed nozzle" type exist which function on difference operational principles. US-Patent 4,463,901 represents a unit fuel injector having independently controlled timing and metering of this type which utilizes a plunger assembly having three plungers. Apart from the fact that the unit fuel injector as disclosed in this patent is not operational as an open nozzle system, it too would be subject to many of the same problems (such as leakage and dilation effects) as just described, if such a system were to be used with SAC pressures in excess of 2.100 bar (30.000 psi). In this regard, this patent discloses, as significant, the fact that it is able to achieve SAC pressures of approximately 1.100 or 1.200 bar (16.000 or 17.000 psi) in comparison to the SAC pressures achieved by more conventional injector designs of approximately 760 bar (11.000 psi). Now, an important factor to be taken into consideration in the pursuit of higher emission abatement, particularly that of particulant matter and nitrogen oxides in diesel engines, via increased injection pressures, is the question of how to deal with low speed operational conditions. That is, for a given injector, the peak SAC pressure occurring at engine speeds of 5.000 rpm are many times that occurring at 1.000 rpm. Thus, current systems which can only withstand peak SAC pressures of, for example, 830 bar (12.000 psi), at maximum engine speeds of 5.000 rpm have been forced to manage with SAC pressures at low speed (for example 1.000 to 2.000 rpm) of from 140 to 300 bar (2.000 - 4.500 psi). To attain even 600 bar (8.700 psi) at 1.000 rpm could dictate SAC pressures over 4.800 bar (70.000 psi) at 5.000 rpm (a pressure greater than anything sustainable by a fuel injector). Thus, for a fuel injector to be successful in increasing the peak SAC pressures achieved under low speed operating conditions, some provision must be made to prevent the peak SAC pressures occurring under high speed operation (for example, 3.000 to 5.000 rpm) from exceeding the pressures sustainable by the injector. The desirability of pressurizing the fuel to a substantial level in the low speed operation range without increasing the injection pressure more than necessary in the high speed operation range has been recognized in association with distributor type fuel injection systems having a single centralized high pressure pump and a distributor valve for metering and timing fuel flow from the pump to each fuel injection nozzle (e.g. US-Patent 4,544,097). In such systems, an approach taken for confining the injection pressure to a range lower than a predetermined value has taken the form of a valve member that is acted upon by the injection fuel pressure and which is constructed to relieve fuel pressure by diverting fuel to a lower pressure zone when the fuel pressure level to which the valve is exposed reaches a predetermined value. However, it should be appreciated that if this concept were applied to unit fuel injectors that are designed to operate with precisely metered quantities of fuel, any such bleeding off of fuel from the injection chamber via a fuel pressure responsive valve would make it impossible to maintain the desired precise fuel metering under any operating conditions wherein the relief valve is caused to open. Thus, there is a need for a means which can be utilized in association with unit fuel injectors to achieve pressurizing of the fuel to a substantial level in low speed operational ranges without undesirably elevating the injection pressure in the high speed operational ranges. Now, the prior art forming the exact starting point of the invention is disclosed in DE-A-3 224 769. Here means for permitting maximized injection chamber pressure under both low speed and high speed operating conditions are provided, those means comprising valve means for draining timing fluid from a timing chamber whenever the pressure of timing fluid in the timing chamber exceeds a predetermined value at the end of an injection stroke movement of the lower plunger. This valve means is activated at the very end of the injection stroke and even if designed to stay open until the pressure drops below a predetermined value the injection orifice was already closed by the valve needle under the bias force of the bias spring. With above described, prior art valve means only the residual pressure in the injection chamber can be defined. In view of the foregoing, it is the object of the present invention to provide a fuel injector, particularly a fuel injector of the open nozzle type, which is capable of achieving high SAC pressures not only under high speed but also and comparable in value under low speed operating conditions. This object is achieved with a fuel injector with the features of the generic part of claim 1 by realizing the features of the characterizing part of claim 1. The invention provides for valve means activated all the time during injection and being able to open during the injection stroke and not only at the end or near the end of the injection stroke. The inventive valve means serves to regulate the pressure in the collapsing hydraulic link so that the injection is always made at a pressure which is close to a preset maximum. Since the valve means is able to open whenever excessive pressure condition exist it will open even during the injection stroke if such situation occurs. Thus, with the invention, the valve means opens only at the end of the injection stroke until engine speed reaches a specific value, e.g. 3.000 rpm, at which value the valve means commences draining of the timing fluid during the injection stroke and only completes draining of the fluid at the end of the injection stroke. In result the inventive valve means is the means by which low speed pressures can be maximized at a level comparable to that achieved under high speed operating conditions. It does not maintain any particular pressure in either the timing chamber or the injection chamber but rather acts to prevent the maximum sustainable pressure from being exceeded. Further preferred features of an inventive fuel injector may be obtained from the dependent claims. Further, those features and advantages will become more obvious from the following description of a preferred embodiment of the fuel injector according to the invention. Figure 1 is a schematic cross-sectional view of a unit fuel injector, Figures 2a - 2d are cross-sectional views of the unit injector of Figure 1 operating in different phases, Figure 3 is a diagrammatic illustration of an electronically controlled fuel injection system incorporating fuel injectors in accordance with Figure 1, Figure 4 is a graph of SAC pressure verses crank angle for a fuel injector operating at various different speeds, Figure 5 is a view, similar to Figure 1, but illustrating a fuel injector in accordance with the present invention, Figure 6 is an enlarged view of the injector of Figure 5 in the area of the intermediate plunger, illustrating a timing fluid draining valve arrangement, Figure 7 is a view, similar to Figure 6, but illustrating a modified timing fluid draining valve arrangement, and Figure 8 is a graph of SAC pressure verses engine speed for conventional fuel injectors and fuel injectors in accordance with the present invention. Figure 1 illustrates an open nozzle unit fuel injector in general. In particular, Figure 1 shows a fuel injector designated generally by the reference numeral 1 which is intended to be received, in a conventional manner, within a recess contained in the head of an internal combustion engine (not shown). The body of the fuel injector 1 is formed of two sections, an injector barrel 3 and a one-piece injector cup 5. Extending axially through the fuel injector is a bore 6 within which is disposed a reciprocating plunger assembly generally designated as 7. The reciprocating plunger assembly 7 is comprised of three plungers. An injection plunger 9 is the lowermost plunger shown in Figure 1 and serially arranged above it are an intermediate plunger 11 and an upper plunger 13. A shim 23 is provided in intermediate plunger 11 and permits compensation for the accumulation of dimensional variations which will occur in manufacture in order to correctly position the plunger within the bore 6, as will be more fully described below. A compensating chamber 17 is formed below intermediate plunger 11. A spring 19 is disposed within compensating chamber 17 and is a coil spring through which the upper end 9d of the lower plunger 9 extends. An actuating member 21' engages the underside of upper end 9d of injection plunger 9 and the top end of spring 19. The lower end of spring 19 rests upon a seat 5a formed on the injector cup 5. In this way, the force of spring 19, via the actutor 21' serves to draw the injection plunger 9 upwardly into engagement with the compensating shim 23 of the intermediate plunger 11 and, thereby, forces the three plunger elements together, from completion of an injection cycle up until metering and timing has commenced for the next injection cycle. In this regard, it is noted that a plunger return spring 22 engages the upper end 13a of upper plunger 13 at one end and seats against the top of the injector barrel 3. Return spring 22 biases the upper plunger 13 so as to return it to an uppermost position within bore 6 as such is allowed by the injection cam 100 (Figure 3), which acts thereon via a rocker arm 105. In the first of four stages of each injection cycle, the upper plunger 13 has been retracted sufficiently by the return spring 22 so as to uncover a timing chamber fill passage 25 so that a hydraulic timing-fluid (such as fuel) will exert a pressure that will separate the intermediate plunger element 11 from the upper plunger element 13 by causing the compensating spring 19 to compress. The amount of separation of the upper plunger 13 from the intermediate plunger 11 is determined by the equilibrium between the spring force of spring 19 and the force produced by the timing fluid pressure acting on the area of intermediate plunger 11. The greater the separation between plungers 11 and 13, the greater the advance of injection timing. At the same time that the injection timing is being established by the feeding of timing fluid into the timing chamber 21, fuel for injection is caused to flow through an outlet feed orifice 33 of a fuel injector supply passage 31 into the upper portion 35 of injector cup 5 spring 19 having drawn plunger 9 upwardly a sufficient extent for the land portion 9b of plunger 9 to have been raised above feed orifice 33. The fuel then passes through a clearance space existing between an elongated lower portion 9a of injection plunger 9 and a lower portion 37 of injector cup 5, into injection chamber 41 adjacent the injection orifice openings 39 disposed at the bottom end of injection cup 5. During metering of injection fuel the injection chamber 41 will be partially filled with a precisely metered quantity of fuel in accordance with the known "pressure/time" principle whereby the amount of fuel actually metered is a function of the supply pressure and the total metering time that fuel flows through the feed orifice 33, which has carefully controlled hydraulic characteristics in order to produce the desired pressure/time metering capability. Figure 2a shows the above noted metering and timing stage. In the second stage, the injection stage, the cam 100 causes the upper plunger 13 to be driven down. As a result, timing fluid is forced back out through passage 25 until the timing port is closed by the leading edge of upper plunger 13. At this point, the timing fluid becomes trapped between plungers 11 and 13 forming a hydraulic link which causes all three plunger elements to move in unison toward the nozzle tip. As shown in Figure 2b, the land 9b of lower injection plunger 9 closes the outlet feed orifice 33 of injector supply passage 31 as it moves downwardly. However, the fuel previously metered into the injection chamber 41 does not begin to be pressurized until plunger 9 has moved into the injection chamber 41 sufficiently to occupy that part of the injection chamber's volume that was not filled with fuel. The distance measured from this point to the point where downward injection plunger travel is completed is termed the "solid fuel height" and determines the point in the plunger's travel when injection actually begins. In fuel injectors of the open nozzle type used up to this point, the solid fuel height has been reached at or close to the point at which the feed orifice of the supply passage has been closed by the injection plunger. However, such a characteristic is undesirable for use in injectors which seek to dramatically increase SAC pressures to levels well above those utilized in prior art injectors to over 2.100 bar. Firstly, because of the relatively short distance that fuel needs to leak, at the commencement of injection, from the solid fuel height level to the feed orifice, the degree of sealing produced by such prior art arrangements is insufficient to sustain SAC pressures at the level sought by the present invention without significant leakage occurring. Additionally, the presence of a high pressure chamber in virtually intersecting proximity to the feed orifice a 3.81 stress concentration factor typically caused by the intersecting drilling forming the supply passage. Both of these problems have been solved by ensuring that the minimum seal length, i.e., the axial distance between the orifice 31 and the leading edge 9e of land 9b, occurring at commencement of injection, is equal to a least one half of the solid fuel height. By maintaining such a minimum seal length relationship, not only can SAC pressures as high as 2.400 bar (35.000 psi) be maintained, but also the high pressure chamber will be displaced sufficiently away from the intersecting drilling forming the supply passage 31 that the stress concentration factor (which can lead to fatigue failure of the injector) is removed. Also, it is noted that the present construction enables high SAC pressures to be achieved, without leakage, and without requiring high clamping pressures as well. That is, in the past, the injection fuel supply passage was formed in the barrel element of the injector body not in the injector cup. Thus, an interface between the injector barrel part and the injector cup existed below the feed orifice, and the presence of such a clamped high pressure joint limited the injection pressure capabilities. Now, no such clamped high pressure joints are necessary since, due to the three plunger design it is practical to actually form the injection supply passage within the injector cup because it is possible to elongate the injector cup portion and shorten the injector body barrel portion and because the joint between the injector barrel 3 and injector cup 5 can be situated in a region of low pressure at chamber 17. In this regard, it is noted that, while it is possible for the one-piece injector cup to be made of a single piece of material, it is equally possible to form a one-piece cup via the permanent unification of separate metal components, such as by welding. However, the latter unification is less desirable due to the problems and expenses associated with producing a welded joint sufficient to sustain injector operating conditions. Additionally, it is noted that achievement of SAC pressures above 2.100 bar requires more than consideraton of the sealing capacity of the lower end of the injector at which metering and injection of the fuel occurs. That is, since the pressure for injection of the fuel is transmitted from the upper plunger 13 via the hydraulic timing arrangement to the lower plunger 9 and since, in conventional systems, the diameter of the plunger assembly acting upon the timing fluid is co-equal to that acting upon the fuel to be injected, attainment of SAC pressures in excess of 2.100 bar would require the timing chamber also to sustain such pressure levels. Likewise, a dramatic increase in the injector drive train mechanical loads would also occur and have to be compensated for. Such problems, however, are avoided since the elongated lower plunger 9 is made significantly smaller in diameter than the intermediate and upper plungers 11 and 13 (which are of the same diameter). Thus, the load to which the timing fluid is subjected, for example, can be much lower (one quarter of that in the ignition chamber) and thus much more easily sustained than the pressures to which the fuel in the injection chamber 41 are subjected. A lower timing fluid pressure also permits a large return force to be applied. Use of a separate smaller injection plunger 9, also, provides the advantage that there is no longer a requirement for precise concentricity of the portion of bore 6 within which plungers 11 and 13 reciprocate with respect to the lesser diameter lower portion within which plunger 9 is received. Injection ends sharply when the tip of the plunger element 9a contacts its seat in the nozzle tip as shown in Figure 2c. At this time, the overrun-stage is produced wherein the hydraulic link between plungers 11 and 13 is collapsed. That is, the timing chamber draining passage 27 is opened by the upper edge of intermediate plunger 11 passing below the top of the timing chamber draining passage, which occurs just before the plunger 9 seats in the nozzle tip. During this stage, plunger 13 continues to move downward forcing the timing fluid out from the timing chamber 21. In this regard, it is noted that the flow resistance of passage 27 is chosen to ensure that the pressure developed in the collapsing timing chamber 21, between plungers 11 and 13, is sufficient to hold injection plunger 9 tightly against its seat, preventing secondary injection. In this regard, it is again noted that the shim 23 provides a very simple means by which the accumulation of dimensional variations in the plungers can be compensated for in order to correctly control the point in the plunger travel at which the timing chamber drain passage 27 will open. Figure 2d shows the injector after all of the timing fluid has been drained so that the plungers 11 and 13 no longer are separated. At this point, the entire injection train, from the injection cam to the nozzle tip, is in solid mechanical contact. Initial adjustment of the injector, made during installation, provides the force necessary to prevent any after-injection, until the cycle is repeated, during the engine's next induction stroke. In both the overrun and scavenge stages (Figure 2c, 2d) scavenging of the system of gases and cooling of the injector is produced. In particular, when injection has ended by the plunger 9 seating in the nozzle tip, a relieved groove 9c in land portion 9b of the plunger 9 is brought into communication with fuel supply passage 31 so that fuel may pass through this groove 9c to an axially relieved portion 9f of land 9b, along which the fuel travels up into compensating chamber 17 and then out of the injector body via injector drain port 29. Figure 3 diagrammatically depicts an electronically controlled injection system for supplying the timing fluid and fuel to be injected. As shown, fuel is drawn from a reservoir 110 by a fuel pump 115. An electronic control unit ECU monitoring throttle position, and the output of sensors measuring such factors as engine temperature, emissions, and the like operates an electronically controlled fuel supply valve arrangement 120 which regulates the supplying of fuel to supply rails 125, 130 associated with a plurality of injectors of an engine, and also controls the pressure of the fluid in the timing rail 125 via an electronically actuated pressure controller arrangement 135. Turning now to Figure 4, the relationship between SAC pressure and crank angle, at increments of 1.000 rpm, between 1.000 and 5.000 rpm, for a small displacement, high speed diesel engine can be seen. As these results show, when peak SAC pressures at 276 - 345 bar (4.000 - 5.000 psi) are attained at 1.000 rpm, peak SAC pressures of between 2.330 - 2.400 bar (34.000 - 35.000 psi) are attained at 5.000 rpm. Thus, even with the ability of the present invention to sustain SAC pressures of 2.400 bar (35.000 psi), severe limitations are imposed on the SAC pressures that are achievable under low speed operating conditions. Furthermore, as noted initially, it has already been recognized that there is a need to produce a substantial increase in injection pressures during low speed operation for the purpose of controlling emissions but, further increases beyond that depicted in Figure 4 would exceed even the dramatically improved pressure sustaining capabilities of the fuel injector as described with reference to the Figure 1 construction of the present type. As also noted in the background portion of this application, in distributor type fuel injection systems, an approach has been taken whereby a relief valve is utilized to bleed fuel from the injection nozzle if injection fuel pressures exceed a predetermined value. Of course, such a system could not be utilized in a unit fuel injector, designed to inject precisely metered quantities of fuel, without adversely affecting the ability to control the amount of fuel injected under any operating conditions wherein such a valve would open. On the other hand, it has been found to be possible, to attain a substantial increase in SAC pressures in the low speed operational range (to near what had been the maximum under high speed operation conditions in more conventional injectors of this type) without exceeding the operational pressure capabilities of the injector in the high speed range. Figures 5 and 6 illustrate a version of the Figure 1 injector wherein common components bear the same reference numerals. Firstly, with reference to Figure 5, it can be seen that the injector barrel 3 differs from injector 3 of Figure 1 in that draining of the timing chamber 21 is occuring via at least one timing chamber draining passage 27 formed in intermediate plunger 7. Thus, in a manner to be described in greater detail below, the timing fluid is drained from the timing chamber 21 via the timing chamber draining passage means 27 in the intermediate piston 7 into the compensating chamber 17 and out via the injector drain portion 29. Accordingly, injector cup 5 is provided with a separate injector drain port 29a for the scavenging flow occurring during the overrun and scavenge stages described with reference to Figures 2c, d. However, it is noted that the addition of such a separate drain port 29a is purely optional for use in this embodiment, on the one hand, and may be added to the Figure 1 construction, optionally, on the other hand. The essential and inventive difference between the Figure 1 and Figure 5 injectors is the provision of valve means 43 (shown in greater detail in Figure 6) for controlling the draining of timing fluid from the timing chamber 21 via the passages 27. In particular, valve means 43 comprises a valve disc 45, which may be attached to or integral with actuating member 21'. The end 9d of plunger 9 is provided with an enlarged stop means 47 upon which the valve means 43 is carried so that it may execute a predetermined axial displacement x relative to stop means 47 in a direction away from intermediate plunger 11. Valve means 43 sealingly engages against a raised valve seat 11a formed on the facing lower side of intermediate plunger 11 under action of the compensation spring 19 during the timing and metering phase of Figure 2a. Metering of the fuel for injection and separation of the plungers 11, 13 for timing occurs in this embodiment in the same manner as described with regard to the embodiment of Figure 1. Likewise, the injection process begins in the same manner as described for Figure 1. In this case, the fuel in the timing fluid chamber 21 is trapped by the valve means 43, which is forced against the lower surface of plunger 11 by the spring 19. So long as injection pressure remains less than a preset value determined by spring 19, injection continues normally until it is ended sharply by the seating of plunger 9 in the nozzle tip. At this point, the pressure in timing fluid chamber, 21 rises to a level sufficient to unseat the valve means 43, thereby allowing the fuel to drain from timing chamber 21 via the timing chamber draining passages 27 to the drain portion 29 via the compensation chamber 17. Furthermore, the valve means 43 regulates the pressure in the hydraulic link formed by the timing chamber and plungers 13, 11 to prevent uncontrolled collapse and secondary injection. On the other hand, if during the injection cycle the injection pressure exceeds the preset value when the plunger 13 is still being driven toward the nozzle tip, the pressure in the the timing chamber between the plungers 11 and 13 will overcome the sealing pressure exerted by the compensating spring 19. thereby allowing fuel to escape from the hydraulic link to the drain port 29 via passages 27 . In this case, the valve means 43 serves to regulate the pressure in the collapsing hydraulic link so that the injection is completed at pressures which are close to the preset maximum. This pressure regulating action of the valve means 43 also ensures that the duration of injection is minimized and the injection ends sharply, without secondary injection. Apart from the above described factors, the remainder of injector 1 and the remainder of its injection cycle is the same as described with respect to Figure 1. Figure 7 shows a modified pressure regulating valve arrangement in accordance with the present invention. In this embodiment, the intermediate plunger 11 is hollow and has a single, central, draining passage in its top wall. Draining passage 27 communicates with a hollow interior space 11 a formed by the insertion of a plunger plug portion 11 b into a cup shaped plunger shell portion 11 c. In this case, the valve means for opening and closing the draining passage 27 comprises a valve disc 45 that is positioned for reciprocation within the chamber 11 a under action of three or more equi-angular spaced actuating pins 47 (only one of which is shown) that are carried on the end of plunger 9 by the actuating member 21' . The valve disc 45 is held in the illustrated closed position by the action of compensating spring 19 and it is shifted therefrom in the same manner and under the same conditions as described with respect to the embodiment of Figures 5 and 6. The axial extent of the relative displacement of valve disc 45 is limited to a predetermined value dictated by the distance between the underside of disc 45 and the top surface of plunger plug portion 11 b. Similarly, all other aspects of the construction and operation of an injector including this modified pressure regulating valve arrangement of Figure 7 correspond to that described above with respect to the other embodiments. It will be appreciated, also, that numerous other pressure regulating valve arrangements can be produced which will function in the same manner as those shown in Figures 5-7 for purposes of draining the timing fluid from the timing chamber when injection pressures above a predetermined value occur. Additionally, timing fluid draining valve means used as an injection pressure limiting mechanism in accordance with the present invention achieve several advantages even with respect to the injector of Figure 1. Firstly, the need for formation of a timing fluid drain passage in the barrel portion of the injector body is eliminated and thus the need for maintaining precise tolerances for the timing fluid draining passage is eliminated. Secondly, the shim 23 is no longer required for compensation of dimensional variations. Most importantly, is the fact that the use of a pressure regulating valve means in accordance with the present invention enables the maximum injection pressure to be limited to a preset value which permits the use of a faster injection cam lift than would be possible, for example, with the embodiment of Figure 1. Faster injection cam lift increases injection pressures of low engine speeds, while the pressure regulating valve means prevents excessive injection pressures at high engine speeds. Additionally, use of a spring that is compressed when the valve opens has the benefit that valve closing occurs at a higher pressure than valve opening and produces the desirable effect of causing more of the fuel to be injected at the end of the stroke when the fuel is burning best. Figure 8 shows a comparison between current fuel injectors, a fuel injector in accordance with Figure 1 and a fuel injector in accordance with the embodiments of Figures 5 - 7 in a plot of injection SAC pressure verses engine speed. In Figure 8, curve A represents current systems, curve B represents the Figure 1 system, and curve C represents embodiments in accordance with Figures 5 - 7. As can be seen, the Figure 1 system already attains a dramatic increase in SAC pressures relative to former systems. Furthermore, by use of the pressure regulating valve means in accordance with the present invention, SAC pressures below the maximum speed can be dramatically raised still further, without further increasing the maximum injection SAC pressures occuring.

Claims: A fuel injector for periodically injecting fuel of a variable quantity on a cycle to cycle basis as a function of the pressure of fuel supplied to the injector from a source of fuel and at a variable time during each cycle as a function of the pressure of a timing fluid supplied to the injector from a source of timing fluid, comprising: a) an injector body (5) containing a central bore (6) and an injector orifice (39) at the lower end of the body (5); b) a reciprocating plunger assembly including an upper plunger (13) and a lower plunger (9) mounted within said central bore (6) to define ba) a variable volume injection chamber (41) located between said lower plunger (9) and the lower end of said injector body (5) containing said injection orifice (39) said variable volume injection chamber (41) communicating during a portion of each injector cycle with the source of fuel (130), and bb) a variable volume timing chamber (21) located below said upper plunger (13), said timing chamber (21) communicating for a portion of each injector cycle with the source of timing fluid (125); characterized in that, c) means for permitting maximized injection pressures under low speed and high speed operating conditions without exceeding the operational pressure capabilities of the injector during high speed operation are provided, those means comprising valve means (43) for draining timing fluid from said timing chamber (21) through a timing chamber draining passage (27) whenever the pressure of timing fluid in said timing chamber (43) exceeds a predetermined value during an injection strike movement of the lower plunger (9) toward said injection orifice (39) as well as at the end of the injection stroke movement. A fuel injector according to claim 1, wherein said valve means (43) recloses at a closing pressure that is higher than said predetermined value. A fuel injector according to claim 1 or 2, further comprising an intermediate plunger (11) mounted for reciprocal movement within the central bore (6) between the upper and lower plungers (13, 9) with the timing chamber (21) provided between the upper and intermediate plungers (13, 11), and a biasing means (19), preferably in the form of a spring, mounted in the central bore (6) and acting upon the lower plunger (9) biasing the intermediate plunger (11) upwardly and controlling lifting of the lower plunger (9), and, preferably, controlling opening of the valve means (43). A fuel injector according to claim 3, wherein the biasing means (19) is located within a variable volume compensation chamber (17) located at the side of the intermediate plunger (11) opposite to the timing chamber (21). A fuel injector according to claim 3 or 4, wherein the valve means (43) acts to compress the biasing means (19) as it moves from a position closing the timing chamber draining passage (27 ) in response to the pressure of the timing fluid within the timing chamber (21). A fuel injector according to any of claims 3 to 5, wherein the timing chamber draining passage (27 ) comprises at least one passage (27 ) communicating the timing chamber (21) with a drain passage (29) in the injector body (5) via the compensating chamber (17). A fuel injector according to claim 6, wherein said at least one passage (27 ) is formed in the intermediate plunger (11) and wherein, preferably, the valve means (43) is disposed in the compensating chamber (17) or within the intermediate plunger (11). A fuel injector according to any of claims 1 to 7, wherein the valve means (43) is relatively displaceably mounted on an upper end of the lower plunger (9) for movement in directions parallel to the directions of the reciprocal movement of the plungers (9, 11, 13). A fuel injector according to claims 3 and 8, comprising stop means for limiting the extent of relative movement of the valve means (43), wherein, preferably, the stop means are carried by the lower plunger (9), and wherein, preferably, the passage means (27) comprises a plurality of passages (27 ) extending through the intermediate plunger (11) and the valve means (43) comprising a valve disc (45) that is sealingly engageable against the intermediate plunger (11) for closing the passages (27 ) under the action of the biasing means (19). A fuel injector according to claim 3 and, preferably, any of claims 4 to 8, wherein the valve means (43) comprises a valve disc (45 ) disposed within a valve chamber (11a) formed in the intermediate plunger (11), an actuating member (21') carried upon an upper end of the lower plunger (9), and connecting pins (47) extending from the actuating member (21'), through a bottom portion (11b) of the intermediate plunger (11), into engagement with the valve disc (45 ), the biasing means (19) acting upon the actuating member (47) in a direction for biasing valve disc (45 ) into a position sealingly closing a passage (27) extending from the timing chamber (21) to the valve chamber (11a). A fuel injector according to any of claims 1 to 10, wherein the injector body has a one-piece injector cup (5) containing the central bore (6) with a fuel supply passage (33) extending through an upper portion (35) of the injector cup (5) for communicating the central bore (6) with a supply of fuel (31), and the injection orifice (39) at the bottom of a lower portion (37) thereof, wherein the central bore (6) has a larger diameter in the upper portion (35) than in the lower portion (37), wherein the lower plunger (9) is provided with an elongated lower portion (9a) of a diameter corresponding to that of the central bore (6) in the lower portion (37), and a radially enlarged land (9b) above the lower portion (9a) of a diameter closely matched to that of the central bore (6) in the upper portion (35), and the plunger (9) being reciprocal within the central bore (6) from raised positions wherein the land portion (9b) is above the supply passage (33) for metering of fuel into the injection chamber (41), through intermediate positions wherein the land portion (9b) blocks metering of fuel from the supply passage (33) into the injection chamber (41), to a lowermost position at which the injection orifice (39) is closed by the bottom end of the lower portion (9a) of the injection plunger (9), wherein, for enabling injection chamber pressures in excess of 2.100 bar (30.000 psi) to be achieved during injection, a predetermined minimum seal length is attained, at commencement of injection, between a leading edge of the land portion (9b) and an outlet feed orifice of the supply passage (33), the minimum seal length being equal to at least one-half of a predetermined solid fuel height.

Inventors: PERR JULIUS P, PERR, JULIUS P.
Applicants: CUMMINS ENGINE CO INC, CUMMINS ENGINE COMPANY, INC.
Application year: 1987
Main classification: F02M59
IPC codes: F02M59, F02M57