GB2314120A

GB2314120A - I.c. engine outwardly opening fuel injection valve with adjustable stroke limiter

Info

Publication number: GB2314120A
Application number: GB9709910A
Authority: GB
Inventors: Detlev Potz; Guenter Lewentz; Uwe Gordon
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1996-06-11
Filing date: 1997-05-15
Publication date: 1997-12-17
Anticipated expiration: 2017-05-15
Also published as: ITMI971151A1; ITMI971151A0; DE19623211A1; JPH1054325A; GB2314120B; IT1293141B1; GB9709910D0

Description

1 2314120 Fuel ilpjection valve for internal combustio

Background art

The invention proceeds from a fuel injection valve for internal combustion engines according to the preamble of claim 1. Such a fuel injection valve known from DE-OS 43 40 883 A I comprises a valve body having an axial bore, in which is guided a piston-like valve element which, for control of an injection cross section, is displaceable by the high fuel pressure in an outward direction counter to the action of a closing spring. Said valve element at its combustion chamber end has a closing head, which projects from the bore of the valve body, forms a valve closure element and has, disposed at its side directed towards the valve body, a valve-sealing surface by means of which the closing head cooperates with a valve seat surface disposed at the end face of the valve body directed towards the combustion chamber. Furthermore, at least one injection opening is provided on the valve element at the level of the closing head and emanates from a pressure chamber formed between the valve element and the bore. In the closed position of the valve element the outlet operuing of the injection opening is covered by the valve body and is only released in the course of the outwardly directed opening stroke of the valve element as a result of its emergence from the bore. With its end remote from the combustion chamber and the closm'g head, the valve element projects into a spring chamber formed in a retaining body, which is axially braced with the valve body. At its stem end remote from the combustion chamber, the valve element has a spring cup, the closing spring being clamped Mi between said spring cup and a housing-fixed stop lying adjacent to the valve body.

Fuel injection occurs upon commencement of the supply of highpressure fuel into the pressure chamber of the injection valve, the high pressure of the fuel loading the valve element in opening direction and lifting itoutwardly 2 oll the valve seat counter to the restoring force of the closing spring. After just a short opening stroke travel of the valve element, the injection opening is opened so that the fuel is injected into the combustion chamber of the internal combustion engine being supplied. The maximum opening stroke movement of the valve element is delimited by the application of a step of the valve element stem against a housing-fixed stop, the position of which may be utilized to adjust the maximum opening stroke. For optimum fuel injection, the known fuel injection valve may be provided with a plurality of injection opemings, preferably two, which lie one above the other in an axial direction of the valve element and are successively openable in the course of the outwardly directed opening stroke of the valve element. In said case, it is particularly advantageous in specific operating states to open only the bottom row of injection openings so that only 50% of the opening cross section is used for fliel injection, with the result that in the partial load range of the internal combustion engine, given an identical injection quantity, the injection period may be prolonged. In the known injection valve, however, such a partial opening of the injection cross section may be achieved only in an unsatisfactory and poorly reproducible manner owing to the fixed stroke stop of the valve element. Here, a particular drawback is that the stroke stop in the known injection valve is not accessible from the outside without removing the injection valve.

From DE-OS 43 32 124 a fuel injection valve of the outwardly opening type is known, in which the maximum opening stroke of the valve element is controllable by means of a variable opening stroke stop, the adjustable stroke stop there being formed in a constructionally very costly manner by a piezoactor. Besides their high manufacturing and assembly costs, such piezoactors have the drawback that they take up a great deal of room and require a relatively complex power supply and drive circuit. Piezoactors are moreover extremely sensitive to heat so that their use on the thermally stressed fuel injection valves is possible only with additional thermal expansion compensating devices, 3 which additionally increases the complexity and hence the cost of such stroke stops.

Advantages of the invention In contrast, the fuel injection valve according to the invention for internal combustion engines having the characterizing features of claim 1 has the advantage that, with constructionally simple means, an adjustable stop for the maximuni opening stroke travel of the valve element is formed, which additionally damps the hard impact of the valve element on the stroke stop. Said adjustable stop takes the form of a hydraulically displaceable piston, of which one end face forms the stroke stop face cooperating with the valve element and the other end face delimits a working chamber. Said working chamber may, via a pressure line, be filled with and relieved of a hydraulic fluid which is preferably formed by the fuel of the internal combustion engine. The pressure 'm the working chamber is relatively low (around 5 - 10 bar) but is sufficient to keep the piston applied by its stroke stop face against an upper stop. Said upper stop is at a specific distance from the stop face on the valve element in closed position, said distance defining a first opening stroke travel of the valve element corresponding to the emergence of the bottom, combustion chamber-side row of injection holes from the bore of the valve body, in which case preferably 50% of the total injection cross section is opened. The extent of opening of the injection cross section during a half stroke of the valve element may be varied by means of the number of injection openings in a row of injection holes.

In said case, it is easily possible by closing the pressure line to deluinit the opening stroke travel at the level of said first upper stop, with the volume enclosed m the working chamber then acting as an oil pressure spring. To ensure that the necessary oil pressure, which holds the valve element fast in the case of partial stroke, builds up afterjust a short compression stroke of the piston, a small total capacity of the working chamber and in the pressure fine is required. The piston therefore preferably takes the form of a step piston, the annular end 4 face of which delimits the working chamber. The pressure line, up to the control valve, is preferably designed as short as possible and with a small cross section.

When the total opening stroke travel of the valve element is to be completed, the pressure line remains open so that the opening forces on the valve element, which are very much greater than the working pressure of the pressure medium. acting upon the piston, displace the valve element jointly with the piston as far as a lower stop. Said lower stop, which is preferably formed by the delimitation of the working chamber remote from the piston, corresponds to a valve element opening stroke position, in which the second upper row of injection holes has also emerged from the bore of the valve body, with the result that 100% of the opening cross section of the injection valve is then open. The working point at which 50% or 100% of the opening cross section of the injection valve is opened, is freely selectable in the engine characteristic map through suitable control of the control valve 'm the pressure line, the control valve preferably taking the form of a two/two-way solenoid valve. Control of the valve element stroke stop is possible independently of the injection pressure, load or speed. A single control valve may be used for all of the injection valves although it is also possible for a separate control valve to be associated with each injection valve.

The working pressure of the hydraulic fluid may be built up by means of a separate pmnp although it is also possible to utilize the initial delivery pressure at the fuel injection purrip. Upon actuation of the hydraulic stroke stop for 50% opening stroke or injection cross section, the control valve is controlled between the injection cycles in such a way that the oil volume in the working chamber is topped up again in order to compensate losses through leakage and guarantee a constant stroke stop.

The fuel injection valve according to the invention may be integrated into a pump-line-nozzle injection system although it is also possible to use it in common-rail injection systems, which have the advantage of a free choice of injection Mi the overall characteristic map of the internal combustion engine.

Use of the hydraulically adjustable stroke stop has the added advantage of damping the impact of the valve element on the stop, thereby reducing the stressing of components.

The fuel injection valve according to the invention having the adjustable stroke stop flirther has the advantage that it takes up no more space than conventional injection valves with the result that it may be retro- fitted in existing internal combustion engines.

Further advantages and advantageous refinements of the subject matter of the invention are indicated in the description, the drawings and the claims.

Drawings Two embodiments of the fuel injection valve for internal combustion engines according to the invention are illustrated in the drawings and explained in detail in the following description.

Of the drawings, Figure 1 shows a longitudinal section through a first embodiment of the fuel injection valve which is installed in a puniplinenozzle injection system. Figure 2 an enlarged cutout from Figure 1 along the line 11 in the region of the injection openings, Figure 3 a diagrammatic view of the control of the hydraulic flow into the working chamber of the stroke stop piston and Figures 4 to 4B a second embodiment, in which the fuel injection valve is integrated into a common-rail injection system.

Description of the embodiments

The first embodiment of the fuel injection valve according to the invention, which is shown mi longitudinal section in Figure 1, comprises a valve body 1, of which the bottom, free end projects into the combustion chamber of the i.c. engine to be supplied and the top end face 3 remote firom, the combustion chamber is braced by means of a clanipmg nut 5 axially against a valve-holding body 7. The valve body 1 has an axial through-bore 9, in which a piston-like valve element 11 is guided 'm an axially displaceable manner. At its bottom end 6 directed towards the combustion chamber, the valve element 11 has a closing head 13 projecting from the bore 9 and forming a valve closure element which, as is shown in an enlarged manner in Figure 2, has at its side directed towards the valve body 1 a valve-sealing surface 15, by means of which it cooperates with a valve seat surface 17 disposed at the side of the valve body 1 directed towards the combustion chamber. The valve-sealing surface 15 and valve seat surface 17, which produce a sealing cross section, are preferably conical, the cone angle of the two contact surfaces 15, 17 differing slightly from one another so as to produce a defined sealing edge. Formed between the valve element 11 and the wall of the bore 9 is an annular pressure chamber 19, which is delimited at the combustion chamber side by an annular shoulder 21 of a piston slide valve 22, which is formed by a widening of the diameter of the valve element 11 and verges into the closing head 13. Leading off from the annular shoulder 21 are injection openings 23, which initially take the form of longitudinal bores 23A, from which transverse bores 23 B then lead off at the level of the closing head 13. The outlet openings 25 of the injection openings 23 at the wall of the valve element 11 are disposed in such a way that in the closed position of the valve element 11, they are covered by the bore wall 9 of the valve body 1 and are opened only in the course of the outwardly directed opening stroke of the valve element 11 as a result of their emergence from the bore 9. Furthermore, preferably two rows of injection hole rows are provided, which are disposed one above the other in an axial direction of the valve element 11 and are successively openable.

For supplying the fliel which is under high pressure, an injection line 27 axially penetrating the valve-holding body 7 and the valve body 1 opens into the pressure chamber 19, the other end of said injection fine being connected, mi the first embodiment, in a manner not shown in detail to a high-pressure fuel PUMP.

The valve element 11 projects with its combustion chamber-remote stem into a spring chamber 29, which is provided in the preferably two-part 7 holding body 7 and in which a closing spring 31 supported in a fixed manner relative to the housing is disposed, which acts via a spring cup 33 fastened to the valve element stem in closing direction upon the valve element 11 and presses the latter with its valve-sealing surface 15 against the valve seat 17.

For delimiting the outwardly directed opening stroke movement of the valve element 11, the valve element stem 11 is ftu-ther provided with an annular step 35 in the form of a ring land, of which the annular surface directed towards the combustion chamber forms a stop face which cooperates with an adjustable stroke stop face 3 7. Said stroke stop face 3 7 is advantageously formed by the end face, remote from the combustion chamber, of a hydraulically displaceable piston 39. Said piston 39, which in the embodiment takes the form of a step piston, is guided in an axially displaceable manner on the valve element 11 and at the diameter transition its annular end face 41 remote from the stroke stop face 37 delimits a hydraulic working chamber 43. The working chamber 43 is delimited at the opposite end to the annular end face 41 of the piston 39 by the wall of a bore step 45 which simultaneously delimits the maximum opening stroke travel of the valve element 11. The fits between the lateral surfaces of the piston 39 and the wall of the bore guiding said piston are designed in such a way that, while providing ease of sliding, the leakage flow is reduced to a minimum. In its staffing position, the piston 39 lies with its stroke stop face J37 against a fixed step formed, in the embodiment, by an intermediate disk 47, which is clamped in between the two parts of the valve-holding body 7 and the axial extension of which is the means whereby the dimension of the first stroke stage of the valve element 11 up to contact with the piston 39 may be adjusted.

Control of the hydraulic stroke stop piston 39 is effected by filling and relieving the working chamber 43, to which end a pressure line 49 opens into the working chamber 43. said pressure line, as Figure 3 reveals, being connected to a feed pump 50 which delivers the pressure medium from a pressure medium reservoir, preferably the fuel tank 5 1. The pressure line 49 may be opened and 8 closed by means of a control valve in the form of a two/two-way solenoid valve, a common control valve 53 for all of the injection valves being provided in the described embodiment.

The first embodiment of the fuel injection valve according to the invention, which is shown in Figure 1, operates in the followmig manner.

In the closed position of the injection valve, the closing spring 3 1 holds the valve element 11 with its valve-sealing surface 15 applied against the valve seat 17, the outlet openmigs 25 of the injection openings 23 are closed and the hydraulically adjustable stroke stop piston 39 has been displaced by the pressure in the working chamber 43 so that its stroke stop face 37 is applied against the intermediate disk 47.

With the start of injection, the highly pressurized fuel periodically delivered by a high-pressure fuel pump passes through the injection line 27 into the pressure chamber 19, where it loads the valve element 11 in opening direction at the annular shoulder 2 1. Once a specific injection pressure has been reached in the pressure chamber 19, the fuel pressure acting in opeming direction upon the valve element 11 exceeds the restoring force of the closing spring 3 1 and the valve element 11 lifts in an outward direction off the valve seat 17. After just a short idle stroke of the valve element 11 in opening direction, the outlet openings 25 of the bottom, combustion chanber-side row of injection holes are uncovered so that the fuel passes in an unthrottled manner for injection into the combustion chamber. After completion of said first opeming stroke phase h I corresponding to the opening of the bottom row of injection holes, the annular step 35 of the valve element 11 comes into contact with the stroke stop face 37 of the piston 39. A finiher opening stroke movement of the valve element may then be ellected only by a simultaneous displacement of the piston 39. When the top row of injection holes is also to be opened, the pressure line 49 is opened by the control valve 53 so that the high pressure forces acting upon the valve element 11 displace the valve element 11 and the piston 39 further until the piston 39 is applied by its 9 annular end face 41 against the bore step 45. Said second stroke travel h2, from application of the valve element step 3 5 against the piston 3 9 up to application of the piston 39 against the step 45, corresponds to complete opening of the top row of outlet openings 25 of the injection openings 23.

When only some (preferably 50%) of the injection cross section of the injection valve is to be opened, the pressure fine 49 is closed by the electrically operated control valve 53 so that the pressure medium situated in the working chamber 43 cannot be displaced. Consequently, the enclosed volume acts like an oil spring and blocks the valve element 11 by means of the piston 3 9 in an intermediate position, in which only the bottom row of outlet openings 25 of the injection openings 23 is opened.

The end of injection is initiated by termination of the supply of highpressure fuel at the high-pressure pump, with the result that the pressure 'm the pressure chamber 19 drops back down below the injection pressure and the closing spring 3 1 once more displaces the valve element 11 so that it is applied against the valve seat 17. The only unilaterally effective application of the piston 39 against the valve element 11 guarantees that the closmig stroke movement of the valve element 11 is effected quickly and is not delayed by a possible low pressure mi the working chamber 43. The time between two injections is sufficient for the working chamber 433 to be completely refilled with fuel.

The second embodiment of the fuel injection valve according to the invention, which is shown in Figures 4, 4a and 4B, differs from the first embodiment in the nature of its injection system, which here takes the form of a common-rail injection system.

In the second embodiment, via the injection line 27 the pressure chamber 19 is constantly acted upon by high pressure from a high-pressure fuel store 6 1, from which all of the in. ection lines of the Midividual injection valves branch off. Further provided is a control line 633, which branches off from the injection Ime 27 and is connected by an annular gap between the piston 39 and the valve element 11 to a restoring chamber 65 at the valve element 11. Said restoring chamber 65 is delimited by the annular end face of a sleeve 67, which at its other end is supported against the annular step 35, here formed by a snap ring, of the valve element 11 so that the high pressure in the restoring chamber 65 loads the valve element 11 in closing direction and blocks it hydraulically. From the control line 63, a relieving line 69 for relieving the restoring chamber 65 also branches off into a relief chamber, which is not shown in detail. For controlling the pressure relief of the restoring chamber 65, a control valve 71 preferably in the form of an electrically controlled two/two-way valve is inserted into the relieving line 69. Throttle points 73 are moreover provided in the branch lines of the control line 63 to the injection line 27 and the relieving line 69.

Hydraulic control of the stroke stop piston 39 is effected as mi the first embodiment, the opening of the pressure line 49 into the working chamber 43 being shown in the sectional views of Figures 4A and 4B. The second embodiment shown in Figure 4 operates in the following manner.

In the closed state of the injection valve, the control valve 71 in the relieving fine 69 is, as Figure 4 reveals, switched in such a way that the outlet into the low-pressure chamber is closed. As a result, the restoring chamber 65 loading the valve element 11 in closing direction is full of the high-pressure fuel of the high-pressure store 61 and keeps the valve element 11 jointly with the closing spring 31 applied against the valve seat 17 counter to the opening pressure force present in the pressure chamber 19.

Injection at the injection valve is effected by switching the control valve 71 over into its let-through state so that the high pressure in the restoring chamber 65 may be relieved via the control line 63 and the relieving fine 69 into the low-pressure chamber, e.g. the fuel tank, which is not shown in detail. As a result of the pressure drop in the restoring chamber 65, the closing force on the valve element 11 drops below the opening pressure acting in the pressure chamber 19 in opening direction upon the valve element 11 and the valve element 11 is displaced outwards from the valve seat 17 so that the injection openings 23, as in Figure 2, are released. The characteristic of the opening stroke movement of the valve element 11 may be adjusted by means of the throttle 73 in the relieving Imie 69.

As in the first embodiment, the maximum opening stroke of the valve element 11 is adjustable by hydraulically blocking or relieving the working chamber 43, control of the working chamber 43 being effected, as in the first embodiment by means of the control valve 53 in the pressure line 49. In the second embodiment also. two stroke stop positions may be adjusted for the valve element 11 in such a way that, in a first stop position, only the bottom row of injection holes (50% injection cross section) is opened while, in the second stop position, all of the rows of injection holes emerge from being covered by the valve body 1 (100% injection cross section).

The high-pressure injection at the injection valve is initiated by once more switching over the control valve 71 in the relieving line 69, the closure of the relieving line 69 again leading to a build-up 'm the restoring chamber 65 of a high pressure, which together with the force of the closing spring 33 1 displaces the valve element 11 so that its valvesealing surface 15 is reapplied against the valve seat 17.

The second embodiment described mi Figure 4 has the advantage of a completely free choice of injection point. period and quantity in the characteristic map of the i.c. engine being supplied, given a variable injection cross section of the injection valve.

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Claims

1. Fuel injection valve for internal combustion engines having a valve element (11), which is guided in an axially displaceable manner in a bore (9) of a valve body (1) and at the combustion chamber end of which at least two injection openings (23) are provided, which lie one above the other in an axial direction of the valve element (11), are connected by inlet channels to a pressure chamber (19) formed between the valve element (11) and the bore (9) and the outlet openings (25) of which in the closed position of the valve element (11) are covered by the wall of the bore (9) and in the course of the outwardly directed opening stroke of the valve element (11) are successively released into the combustion chamber of the i.c. engine, as well as having a stop which delimits the maximum opening stroke of the valve element (11), characterized in that the stop delimiting the maximum opening stroke of the valve element (11) is adjustable and is provided on a displaceable piston (39), of which one end face forms a stroke stop face (37) for the valve element (11) and the other end face (41) remote from the stroke stop face (37) takes the form of a thrust face which delimits a closable hydraulic working chamber (43).

2. Fuel injection valve according to claim 1, characterized in that the piston (39) is disposed coaxially relative to the valve element (11), preferably so as to slide axially thereon.

3. Fuel injection valve according to claim 1, characterized in that the piston (39) takes the form of a step piston, of which the larger end face forms the stroke stop face (3 7) and the annular end face (4 1) 13 formed at the cross-sectional transition forms the thrust face (41) delimiting the working chamber (43), the piston (39) sliding with its peripheral surfaces sealingly in a pilot bore in the housing.

4. Fuel injection valve according to claim 1, characterized in that provided on the stem of the valve element (11) is a ring land (35), of which the annular end face directed towards the combustion chamber forms a stop face, by means of which the valve element (11) cooperates with the stroke stop face (37) on the piston (39).

5. Fuel injection valve according to claim 1, characterized in that a fixed upper stop (47) is provided, against which the piston (39) in starting position is applied by its stroke stop face (37) and the design of which is a means of ad usting the opening stroke travel of j the valve element (11) up to application of the latter against the stroke stop face (37) of the piston (39), and that a fixed lower stop (45) is provided, which delimits the maximum possible stroke travel of the piston (339).

6. Fuel injection valve according to claim 1, characterized in that the working chamber (43) may be filIed with and relieved of a hydraulic pressure medium. preferably fuel, by means of a pressure line (49), the pressure Iffle (49) being connected to a pressure medium reservoir (5 1) and being closable by means of a control valve (53).

7. Fuel injection valve according to claim 6, characterized Mi that the control valve (53) takes the form of a two/two-way valve.

14

8. Fuel injection valve according to claim 1, characterized in that a plurality of outlet openings (25) of the injection openings (23) are provided in a common radial plane of the valve element (11), which outlet openings 'm each case form one of preferably two rows of injection holes situated axially one above the other, a defined stroke stop position of the piston (39) being associated with each opened row of injection holes.

9. Fuel injection valve according to claim 1, characterized in that the valve element (11) at its combustion chamber end comprises a piston slide valve (22), which is guided sealingly in the bore (9) and with its combustion chamber-remote annular end face (21) delimits the pressure chamber (19) in the bore (9), the inlet channels of the injection openings (23) taking the form of axial blind holes in the piston slide valve (22), which emanate from the annular end face (2 1) and from which radial bores lead towards the lateral surface of the piston slide valve and open out at the outlet openings (25).

10. Fuel injection valve according to claim 9, characterized in that adjoining the piston slide valve (22) at the combustion chamber end is a closing head (13) projecting from the bore (9) and forming a valve closure element, which at its side directed towards the valve body (1) has a valve-sealing surface (15), by means of which it cooperates with a valve seat surface (17) disposed at the combustion chamber side of the valve body (1).

11. Fuel injection valve according to claim 1, characterized in that the pressure chamber (19) in the valve body (1) is connected by an injection line (27) to a high-pressure fuel store (6 1).

is

12. Fuel injection valve according to claim 11, characterized in that a restoring chamber (65) loading the valve element (11) at least indirectly in closing direction is provided, which may be filled with and relieved of high-pressure fuel by means of a control line (63) branching off from the injection line (27), a relieving line (69), which is openable and closable by means of a control valve (71), branching off from the control line (63).

13. Fuel injection valve according to claim 12, characterized 'm that the control valve (7 1) takes the form of a two/two-way valve.

14. Fuel injection valve according to claim 12, characterized in that the control fine (63) in each of its connections to the injection line (27) and the relieving line (69) has a throttle point (73).

15. Either of the fuel injection valves substantially as heremibefore described with reference to the accompanying drawings.