Fuel injection nozzle valve and system incorporating such valve

Abstract

 Loss of valve opening pressure (VOP) attributed to wear of contacting portions in fuel injection nozzle valves (22) is limited due to provision of a valve tip (38) having a lower portion (38a) which repetitively engages only a lower portion (40a) of a valve seat (40). Advantageous wear of the engaging portions increases the seating area but reduces the effective differential area for fuel pressure to act against, thus reducing the need for increased pressure to open or unseat the valve (22). Increased clearance results in less wear between a reciprocating valve (36) and a cooperating guide (34) which also contributes to reduced VOP loss during the life of such nozzle valves (22).

Description

[0001] This invention relates generally to fuel injection nozzle valves,.

[0002] In general, fuel injection nozzle valves operate in response to high pressure fuel creating forces acting on differential areas of the valve causing rapid reciprocation of the valve. The rapid reciprocation causes intermittent seating and unseating of a tip of the valve with a valve seat which permits the fuel to be injected into an engine cylinder. Under the influence of such high pressure, this seating and unseating results in tip wear which is known to change the differential areas to the point where valve operating characteristics are changed undesirably. Also, the rapid reciprocation of the valve in a valve alignment guide causes detrimental wear between the valve and guide to add to the undesirable change in operating characteristics.

[0003] Parameters'which govern the desired operating characteristics of the valve, therefore, change through use of the valve. These parameters include a desired relationship between valve opening pressure (VOP) and valve closing pressure (VCP).

[0004] VOP results from high pressure fluid forces intermittently imposed on the valve and is required to cause the valve to lift or unseat and permit fuel injection. Over a period of time, wear at the tip and seat can cause a significant detrimental loss of VOP (VOP loss).

[0005] VCP results from forces acting on the valve and is required to cause the valve to seat and stop fuel injection. Conventional fuel injection nozzle valves become seated between the timing of the intermittently imposed high pressure fluid forces which lift the valve from the seat. Such seating is usually accomplished by a high rate spring matched with specific initial VOP parameters. Conventional fuel injection nozzle valves also have a relatively close fit between the valve and guide to limit leakage of fuel past the guide. Some fuel does leak past the guide and is usually returned to a fuel reservoir. The tight fit creates high friction forces which limit rapid valve closing resulting in poor injection. As the valve and guide wear, friction is reduced and VOP loss occurs due to the reduced friction. The spring then becomes unmatched with the specific intial VOP parameters. In addition, the desired relationship of VOP to VCP gradually deteriorates. Such deterioration results in inefficient fuel injection causing fuel waste, unduly high noxious exhaust emissions, and excessive exhaust smoke.

[0006] According to one aspect of the present invention a fuel injection nozzle valve comprising a housing having a conical valve seat of a first constant conical angle,(the seat including a lower portion, and a valve member reciprocable in the housing,is characterized in that the valve member has a conical tip of a second constant conical angle less than the first angle, the tip having a lower portion formed so as to contact only the lower portion of the valve seat. Thus only the lower portion of the valve. tip engages only:the lower portion of the valve seat, and effectively reduces limitations of the known prior art.

[0007] In another aspect of this invention a fuel injection nozzle valve comprising a housing having a valve guide of a first diameter separating a closed upper fluid cavity from a lower fluid cavity, and a conical valve seat; and a member valve reciprocable in the housing and having a conical tip engaging the seat is characterized in that the valve member has an enlarged diameter portion reciprocable in the guide, the enlarged diameter portion being of a second diameter less than first guide diameter, the guide and enlarged portion diameters defining a clearance therebetween sufficient for metering an amount of fluid between, the upper and lower cavities for maintaining relative fluid pressures in the cavities to avoid a hydraulic lock of the valve in the housing. The invention also includes a fuel system incorporating such valves.

[0008] One example of a valve constructed according to the present invention will now be described with reference to the accompanying drawings, in which:-

Figure 1 is a diagrammatic view of a fuel system embodying the present invention;

Figure 2 is a view illustrating an enlarged partial section of the nozzle valve tip and seat shown in Figure 1;

Figure 3 is a view illustrating another enlarged partial section of the nozzle valve tip and seat embodiment of Figure 2 further illustrating wear effects of the tip and seat;

Figure 4 is a view illustrating another enlarged partial section of the valve and guide embodiment of Figure 1;

Figure 5 is a view illustrating a graphic representation of guide clearance (dc) to trapped volume pressure relationships; and

Figure 6 is a view illustrating a graphic representation of test hours to valve opening pressure (VOP) relationship.

[0009] In Figure 1, a fuel system is generally design- _ated 10, and includes a reservoir 12. A well known fuel transfer pump 13 is connected via a conduit 14 for pumping fuel from reservoir 12 at a system pressure of about 30_-35 psi. The fuel is then passed through a known filter 16 in conduit 18 to a conventional high pressure fuel injection pump 20 which supplies the fuel at pressures ranging from about 2000 psi to about 15,000 psi and then to a fuel injection nozzle valve 22 via a conduit 24. It is preferred that a known reverse flow check valve 26 be provided between high pressure pump 20 and nozzle valve 22 to check against pressure waves which may oscillate between pump 20 and nozzle valve 22 as a result of rapidly created high pressure surges of fuel being pumped through nozzle valve 22 into an associated engine cylinder 23 at a rate of several times per second.

[0010] Nozzle valve 22 comprises a housing 28 having a fuel passage 30 for receiving fuel from pump 20 and for conducting the fuel to a cavity 32 formed in housing 28.

[0011] Housing 28 defines an upper cavity portion 32a and a lower cavity portion 32b and further defines a reduced diameter cylindrical guide 34 separating the upper and lower cavity portions 32a, 32b, respectively. Guide 34 has a diameter designated dg in Figure 4.

[0012] A valve member 36 is reciprocably disposed in cavity 32. An extended portion 36a of valve 36 extends into upper cavity portion 32a. Valve 36 includes a lower portion 36b having a tip 38 urged into engagement with a valve seat 40 formed in housing 28. Tip 38 is so urged by a resilient means such as a compression spring 42 disposed in upper cavity portion ₃2a. Upper and lower valve portions 36a, 36b, respectively, are separated by an enlarged diameter valve portion 36c which reciprocates within guide 34 and has a valve diameter designated dv in Figure 4.

[0013] The foregoing generally describes a conventional fuel injection nozzle. Clearance between the valve portion 36c and guide 34 is generally kept to a minimum. That is, valve portion 36c and guide 34 have a relatively tight fit to limit leakage of fuel from lower cavity 32b to upper cavity 32a. Such tight fit causes the problem of high frictional forces between the valve and guide which limit movement of valve portion 36c in guide 34. Such friction causes substantial wear which substantially changes the initial valve and guide diameters so that after prolonged hours of operation, the initial operating characteristics of the nozzle become.undesirably changed. Conventionally, fuel which does leak into upper cavity 32a is returned to the fuel reservoir.

[0014] This embodiment of the invention generally includes housing 28 provided with a guide 34 of a first diameter dg separating upper cavity 32a from lower cavity 32b. Valve 36 is provided with an enlarged diameter portion 36a reciprocable in guide 34 and having a second diameter dv, less than the guide diameter dg. The diameters dv, dg, define a clearance sufficient for passing fluid from the lower cavity 32b to the upper cavity 32a for metering relative fluid pressures in said cavities 32, 32b to avoid a hydraulic lock of valve 36 in housing 28. Fluid passing through the clearance forms a lubricating fluid film which assists in hydraulically aligning valve portion 36c in guide 34. The clearance varies depending on para-, meters of nozzle 22 relating to the diameter dg and length of guide 34, and the quantity and pressure of fluid volume trapped in upper cavity 32a.

[0015] Specifically, for example, this embodiment avoids conventional friction and wear problems by cooperatively forming valve diameter dv for reciprocating within guide diameter dg such that the initial diametral clearance.between the valve and guide (guide clearance dc) is expanded from the conventional tight fit (.00254 mm to .00381 mm) (.000100 inches to .000150 inches) to an initial diametral clearance range of from about .01143mm (.000450 inches) to about .01651mm (.000650 inches). That is dg minus dv = dc will preferably vary initially from about .01143mm (.000450 inches) to about .01651 mm (.000650 inches). Such expanded clearance permits passage or leakage of fuel from lower cavity 32b to upper cavity 32a. Due to the expanded diametral clearance, friction and thus wear are substantially reduced between guide 34 and valve portion 36c. Such leakage provides an advantageous lubricating hydraulic film of fluid in the expanded clearance between guide 34 and valve portion 36c. Fuel which leaks into cavity 32a is not returned to reservoir 12 since cavity 32a represents a trapped volume having no outlet except for a bleed screw 44 which is normally closed but may be selectively opened if desired. There is less wear between guide 34 and valve portion 36c as compared to previously known nozzles. Thus, the increased guide clearance of the present invention substantially reduces a change in VCP during the useful life of nozzle 22. Also, increased guide clearance provides an advantageous hydraulic film between guide 34 and valve portion 36c which permits valve 36 to self align resulting in a centered seating of tip 38 on seat 40 and reduced impact loads during seating of tip 38 on seat 40. In this example, the diameter dg of guide 34 is about 3.9878 mm, length of guide 34 is about 7.644 mm, the trapped volume quantity is about x 121.4mm³, and the peak trapped volume pressure is about 6 x 10⁶ N/m² (90₀ psi).

[0016] The graph of Figure 5 illustrates the basis for the preferred guide clearance range. The trapped volume of fuel which leaks into upper cavity portion 32a ultimately reaches a peak pressure Pt, that is, the highest pressure the trapped volume of fuel sees during an injection stroke of valve 36. This peak pressure, in addition to spring 42, acts on upper portion 36a of valve 36 on closing or seating of tip 38 against seat 40. Residual trapped volume. fuel pressure B is the average pressure between injections, of the fuel remaining in upper cavity 32a after seating of tip 38 against seat 40. From the Figure 5 graph, it is apparent that the peak pressure curve A has a substantially stable portion extending from a guide clearance of about 0.1143 mm (.000450 inches) to about .01651 mm (.000650 inches). The portion of the peak pressure curve wherein the guide clearance is greater than .01651 mm (.000650 inches) illustrates that peak pressure rises at a rate sufficient to eventually cause a hydraulic lock of valve 36 in housing 28. That is, if guide clearance is too great the value of the pressures in cavities 32a, 32b will converge and valve 36 will not reciprocate. Thus, the preferred guide clearance range of about .01143 mm (.000450 inches) to about .01651 mm (.000650 inches) permits the VCP to substantially stabilize resulting from a combination of forces acting on uppervalve portion 36a including forces exerted by spring 42 and forces exerted by trapped volume peak pressure in upper cavity 32a. These forces act across an area defined by the diameter dv of valve 36 at portion 36c. Also, in the preferred guide clearance range, residual pressure is substantially reduced which lowers VOP required to lift valve 36 for the next injection.

[0017] The present embodiment also uses wear advantageously to avoid detrimental VOP loss during the useful life - of nozzle 22. This is accomplished by providing seat 40 with preferably a constant conical angle sa and also providing tip 38 with a constant conical angle ta which is less than the angle sa, see Figure 2. It is preferred that angle ta be less than angle sa by a magnitude of from about 2.5 degrees to about 3.5 degrees. In this manner only a lower portion 38a of a tip 38 contacts only a lower portion 40a of seat 40. As a result, tip portion 38a and seat portion 40a have an interference fit and contact is made at an intial (solid line) diameter sd₁, see Figure 3. Through prolonged use of nozzle 22, numerous intermittent contacts between'tip 38 and seat 40 result in wear of both the tip and seat. Due to the preferred interference fit of the constant conical angles sa, ta, contact between tip 38 and seat 40 eventually occurs at a second (dotted line) diameter sd₂, greater than sd_l. The diameters sdl, sd₂, define areas of valve 36 at lower tip portion 38a. VOP acts across the area defined by dv - sd_l or sd₂ to open nozzle 22 for injecting fuel into the associated cylinder 23. The area defined by diameter dv of valve 36 at portion ₃6c and the areas defined by the diameters sd_l, sd₂ of valve 36 at tip portion 38a, are the differential areas affected by fuel pressure for causing valve 36 to reciprocate in housing 28 and provide fuel injection. It can be seen, therefore, that with an increase from diameter sd₁ to diameter sd₂, and with diameter dv and the force of spring 42 remaining substantially constant, the difference between the defined areas will be reduced and VOP loss can be reduced.

[0018] An advantage of providing contact between lower tip portion 38a and lower seat portion 40a is a resultant reduction in volume of a sac portion 46. It is well known that a small sac volume 46 is preferred and results in decreasing the emission of hydrocarbons into the atmosphere. Also, a desirable effect of small sac volume and a plurality of small orifices 48 is that some hydraulic damping occurs which aids in cushioning the tip to seat contact.

[0019] An added advantageous feature is demonstrated by the graph of Figure 6 which illustrates that conventional initial VOP (C) occurs at about 19.3 x 10⁶ _N/m² (2800 psi) and, during the life of the valve, for example at 1300 engine hours the VOP has been subtantially lowered to about 15.4 x 10⁶ N/m² (2230 psi). The present embodiment however, significantly reduces initial VOP (D) to about 17.2 x 10 N/m² (2500 psi) which only slightly lowers to about 16.1 x 10 Nl² (2330 psi) after 1300 engine hours. Thus, in the given example, the valve substantially reduces initial VOP and VOP loss when compared to a conventional valve. Lower initial VOP results in lower stress in the nozzle which reduces wear and deterioration of the fuel injection apparatus and system.

[0020] With the parts assembled as set forth above high pressure fuel enters cavity ₃₂ and flows to upper portion 32a and lower portion 32b of cavity 32. Pressure builds at a greater rate in lower portion 32b to about 2500 psi to eventually lift tip 38 from seat 40 and cause fuel to be injected into culinder 23. Increased clearance between guide 34 and valve portion 36c permits eventual stabilization of peak pressure to about '6 x 10⁶ N/m² in upper cavity portion 32a.

[0021] Prolonged use of nozzle 22 causes an area of tip 38 to seat 40 contact to increase as defined by a initial diameter sd₁ to an eventual diameter of sd₂, greater than sd_l'. Diameter dv of valve portion 36c remains substantially constant due to reduced wear between guide 34 and valve portion 36c. As a result, the difference between the areas defined by diameters dv and sd₂ is reduced and substantial VOP loss is avoided.

[0022] The foregoing has described a fuel injection nozzle which reduces detrimental wear between the valve and guide and advantageously utilizes wear between the tip and seat to reduce VOP loss during the life of the nozzle. It can be appreciated by those skilled in the art that the preferred guide clearance range and tip to seat angular relationship can be determined for various size nozzle valves according to the teachings of this invention.

Claims

1. A fuel injection nozzle valve (22) comprising a housing (28) having a conical valve seat (40) of a first constant conical angle (sa), the seat (40) including a lower portion (40a); and a valve member (36) reciprocable in the housing (281 characterized in that the valve member (36) has a conical tip (38) of a second constant conical angle (ta) less than the first angle (sa), the tip (38) having a lower portion (38a) formed so as to contact only the lower portion (40a) of the valve seat (40).

2. A valve according to claim 1, characterized in that the second angle (ta) is less than the first angle (sa) by a magnitude of from about 2.5 degrees to about 3.5 degrees.

3. A valve according to claim 1 or claim 2, wherein the valve member tip (38) is an interference contact fit with the valve seat (40).

4. A valve according to any of claims 1 to 3, wherein the housing includes a guide (34), the valve member (36) having an extended portion (36a) extending through the guide (34) and defining a diametral clearance between the valve member (36) and guide (34), the clearance being from about .01143 mm (.000450 inches) to about .01651 mm (.000650 inches).

5. A fuel injection nozzle valve (22) comprising a housing (28), having a valve guide (34) of a first diameter (dg) separating a closed upper fluid cavity (32a) from a lower fluid cavity (32b), and a conical valve seat (40); a member valve (36) reci^procable in the housing (28) and having a conical tip (38) engaging the seal, characterized in that the valve member (36) has an enlarged diameter portion (36a) reciprocable in the guide (34), the enlarged diameter portion (36a) being of a second diameter (dv) less than said first guide diameter (dg), the guide and enlarged portion diameters (dv, dg) defining a clearance therebetween sufficient for metering an amount of fluid between the upper (32a) and lower (32b) cavities for maintaining relative fluid pressures in the cavities (32a, 32b) to avoid a hydraulic lock of the valve (36) in the housing (28).

6. A valve according to claim 5, wherein the clearance is from about .01143 mm (.000450 inches) to about .01651 mm (.000650 inches).

7. A valve according to claim 5 or claim 6, wherein the conical seat (40) has a first conical-angle (sa) and includes a lower portion (40a); and wherein the conical tip (38) has a second constant conical angle (ta) less than the first angle (sa), the tip (38) having a lower portion (38a) having an interference fit with the lower seat portion (40a).

8. A valve according to claim 7, wherein the second angle (ta) is less than the first angle (sa) by a magnitude of from about 2.5 degrees to about 3.5 degrees.

9. A fuel system (10) comprising a fuel reservoir (12); a fuel transfer pump (13) for pumping fuel from the reservoir (12); a high pressure fuel pump (20) for pumping and greatly pressurizing the fuel from the fuel transfer pump(13) and aninjection nozzle valve (22) connected to receive the pressurized fuel from the high pressure fuel pump (20) the nozzle valve (22) being in accordance with any of claims 1 to 8.

10. A system (10) according to claim 9, including a fuel filter (16) connected between the fuel transfer pump (13) and the high pressure pump (20).

11. A system (10) according to claim 10, including a reverse flow check valve (26) connected between the high pressure pump (20) and the nozzle valve (22).

Drawing