EP1450036A1

EP1450036A1 - Metering device and method for setting a spring preload

Info

Publication number: EP1450036A1
Application number: EP03003849A
Authority: EP
Inventors: Gianbattista Fischetti
Original assignee: Siemens VDO Automotive SpA
Current assignee: Continental Automotive Italy SpA
Priority date: 2003-02-20
Filing date: 2003-02-20
Publication date: 2004-08-25
Anticipated expiration: 2023-02-20
Also published as: EP1450036B1; DE60310362D1; DE60310362T2

Abstract

The invention relates to a metering device for dosing pressurized fluids, particularly an injection valve (10) for a fuel injection system in an internal combustion engine, comprising a housing (12) having an end part provided with an outlet passage (14) terminating with a metering opening, an axially moveable valve needle (16) passing through the outlet passage (14), and controlling opening and closing of the metering opening, the valve needle (16) having a lower portion inside the outlet passage (14), with a lower end controlling the opening and closing of the metering opening, and having an upper portion with an upper end (18) cooperating with an actuator assembly to displace the valve needle (16) from the closing position, and spring means (20) for urging the valve needle (16) in the closing position. A blocking means (24,28; 32; 48) is arranged at and secured to the upper portion of the valve needle (16) to block the spring means (20) in a working position, thereby providing a predetermined spring preload.

Description

The present invention relates to a metering device for dosing pressurized fluids, particularly an injection valve for a fuel injection system in an internal combustion engine. The metering device is of the type which comprises a housing having an end part provided with an outlet passage terminating with a metering opening, an axially moveable valve needle passing through the outlet passage, and controlling opening and closing of the metering opening, the valve needle having a lower portion inside the outlet passage, with a lower end controlling the opening and closing of the metering opening, and having an upper portion with an upper end cooperating with an actuator assembly to displace the needle from the closing position, and further comprises a spring means for urging the valve needle in the closing position. The invention further relates to a method for setting a spring preload in such a metering device.
An injection valve of the above mentioned type is disclosed in the European Patent application EP 1 046 809 A2. For these injectors the preload of the biasing spring of the valve body has to be set at some point in the assembly process. Presently, the setting is achieved by first assembling the valve body subgroup, then measuring the initial spring preload and, if the spring preload is found to be out of tolerance, introducing a metallic spacer between the spring itself and its seat on the valve body in order to confer an increased stiffness and thus an increased preload to the spring. The spring preload is then measured again and, if its value is still out of tolerance, the procedure is repeated. Such an iterative sequence is, however, time consuming and expensive and may not be adapted to the mass production in a factory.
In view of the foregoing, it is an object of the present invention to improve the setting procedure for the biasing spring preload in a metering device of the above mentioned type.
This object is achieved by a metering device with the features of appended claim 1, and by the method for setting a spring preload in a metering device of independent claim 14. Advantageous embodiments of the invention are disclosed in the dependent claims.
According to the invention, in a metering device of the type mentioned above, a blocking means is arranged at and secured to the upper portion of the valve needle to block the spring means in a working position, thereby providing a predetermined spring preload.
In a first set of advantageous embodiments of the invention, the upper portion of the valve needle comprises a screwed part to which the blocking means is secured.
The blocking means is preferably formed by a spring washer and a threaded keeper nut, the threaded keeper nut engaging with the screwed part of the valve needle to secure an axial position of the spring washer along the valve needle, thereby blocking the spring means in the working position. This solution provides an excellent push-out load to failure ratio and allows for a flexible load setting.
In a preferred embodiment of the invention, the keeper nut has a conical shape and the spring washer has a corresponding conical central bore receiving and engaging with the conical keeper nut. The cone angle of the keeper nut and the central bore of the spring washer has advantageously a value between 10° and 25°, and more preferably a value of about 15°.
Alternatively, the blocking means may be formed by a spring washer with a collar, where the collar is crimped to the screwed part of the valve needle. This solution has as advantages, that it is well suited for automation, that it provides a good load value, allows for a flexible load setting and requires only little tooling investments.
In any of the above embodiments, the screwed part of the valve needle may have a pitch between about 0,1 mm and about 0,5 mm, preferably between about 0,2 mm and about 0,4 mm.
The screwed part preferably has a plurality of teeth, each having a lower tooth angle and an upper tooth angle. The lower and upper tooth angle are between about 30° and about 45°. In a particularly preferred embodiment, the lower and upper tooth angle are both about 30°. In another particularly preferred embodiment, the lower tooth angle is about 30° and the upper tooth angle is about 45°, thereby forming a saw tooth shape.
In a second set of advantageous embodiments the blocking means is formed by a spring washer laser welded to the upper portion of the valve needle, thereby blocking the spring means in its working position. In this set of embodiments, the upper portion of the valve needle need not be screwed. While requiring a higher tooling investment compared to the previously mentioned embodiments, laser welding can easily be adapted to automation for a high series production.
Preferably, the spring washer is secured to the valve needle by a plurality of laser spots. While any number of welding spots and also the use of a continuous welding line is possible, the plurality of laser welds consists preferably of 3, 4, 6 or 8 welding spots, equally spaced along the circumference of the valve needle.
In any of the embodiments described above, the spring washer is advantageously made of stainless steel, preferably it is made of SS 304, SS 316, SS 430 FR or SS 416 P70. Particularly good results have been obtained with washers made of stainless steel 316 or 416 P70.
According to the invention, in a method for setting a spring preload in any of the metering devices described above, a variable external preload force is applied to a top surface of at least one part of the blocking means during the assembly process of the metering device, the external preload force is measured, and the blocking means is secured to the upper portion of the valve needle to block the spring means in a working position, when a predetermined spring preload is reached.
In case that the blocking means is formed by a spring washer with a central bore and a fitting threaded keeper nut, and the upper portion of the valve needle comprises a screwed part, it is preferred that the external preload force is applied to a top surface of the spring washer, and that the keeper nut is screwed on the screwed part of the valve needle to engage with the with the spring washer, when the predetermined spring preload is reached.
If the blocking means is formed by a spring washer with a collar and the upper portion of the valve needle comprises a screwed part, it is preferred that the external preload force is applied to a top surface of the spring washer, and that the collar is crimped to the screwed part of the valve needle, when the predetermined spring preload is reached.
The collar is advantageously crimped to the valve needle using a punch having two parallel sharp teeth as a crimping tool.
In another preferred case, where the blocking means is formed by a spring washer, the external preload force is applied to a top surface of the spring washer, and the spring washer is laser welded to the upper portion of the valve needle, when the predetermined spring preload is reached.
The advantages gained by the technical features of the invention include

a very compact process sequence where the preload force is applied and measured in a single assembly step;
an increased load capacity of the components;
the preload force may be set directly, without using additional pieces such as metallic spacers; and
the assembly process is more compatible with high volumes production.

The invention, both its construction an its method of operation together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein

Figure 1: is a perspective view of a partly assembled valve body of an injector according to a first embodiment of the invention;
Figure 2: shows cross-sectional views of the spring washer in Fig. 2(a) and the threaded keeper nut in Fig. 2(b), which together form the blocking means of Fig. 1;
Figure 3: is a perspective view as in Fig. 1 of a partly assembled valve body of an injector according to another embodiment of the invention;
Figure 4: is a schematic side view of the spring washer with a collar forming the blocking means of Fig. 3;
Figure 5: shows a crimping tool as may be used for crimping the spring washer of Fig. 3 and 4 to the valve needle;
Figure 6: shows a detailed view of the screwed part of the valve needle in the embodiment of Fig. 3;
Figure 7: is a perspective view of the upper part of a valve needle and a laser welded blocking means according to a further embodiment of the invention;
Figure 8: shows a cross-section of the spring washer forming the blocking means of Fig. 7; and
Figure 9: shows a flowchart illustrating an embodiment of the method in accordance with the invention.

Figure 1 illustrates a first embodiment of the invention. The injection valve 10 for direct-injection gasoline engines shown comprises a housing 12 having an end part provided with an outlet passage 14 terminating with a metering opening (not shown), and an axially moveable valve needle 16 passing through the outlet passage 14.
The valve needle 16 has a lower portion inside the outlet passage 14, a lower end of which controls the opening and closing of the metering opening. The upper portion of the valve needle 16 terminates in an upper end 18, which cooperates with an actuator assembly (not shown) to displace the needle 16 from its closing position.
In response to an excitation voltage, the axial length of the actuator assembly increases and this extension is transmitted to the valve needle 16. The valve needle 16 depresses a biasing spring 20 and lifts from its seat to start the injection of pressurized gasoline in the engine cylinder. Upon termination of the excitation voltage, the length of the actuator assembly decreases to its normal value and the biasing spring 20 pushes the valve needle 16 back in its closing position.
Figure 1 shows the injection valve in a partially assembled state during the assembly process. The housing 12, the spring 20 and the blocking means 24, 28 described below are partially cut away for clarity.
The upper portion of the valve needle 16 is provided with a screwed part 22. A spring washer 24 is put on the valve needle 16 and brought into contacts with the biasing spring 20. To set the preload force of the biasing spring 20, an external preload force 26 is applied to the top surface of the spring washer 24 and the external preload force is measured with a dynamometric device, i.e. a load cell. When a preload force within the required tolerance range is reached, a threaded keeper nut 28 is screwed on the screwed part 22 of the valve needle 16, blocking the spring washer 24 and the working position of the biasing spring 20. Only a single step is required to apply and measure the preload force. Compared to prior art processes, the assembly process is thus significantly simplified.
Figure 2 shows cross-sectional views of the spring washer 24 (Fig. 2(a)) and the threaded keeper nut 28 (Fig. 2(b)). The spring washer 24 is provided with a conical central bore 30 and the keeper nut 28 has a corresponding conical outer shape. Both cones have the same cone angle α. In the embodiment shown, α = 15°.
A second embodiment of the invention is illustrated in Figs. 3 and 4. The valve needle 16 is provided with a screwed part 22 having a plurality of teeth 36. A spring washer 32 with a collar 34 made of stainless steel SS 316 is put on the upper part of the valve needle. An external preload force 26 is applied to the top surface of the spring washer 32 and in the same step, the preload force is measured with a load cell. When the spring reaches its required preload length, the collar 34 is crimped to the screwed part 22 as indicated by the arrows 38.
To perform an effective crimping operation, a punch 40 with two sharp teeth 42, such as shown in Fig. 5 may be used.
Figure 6 illustrates the structure of the screwed part 22 according to a preferred embodiment of the injector valve in detail. Each of the plurality of teeth 36 has a lower tooth angle 44 and an upper tooth angle 46, which are selected to lie between about 30° and about 45°. In the embodiment shown, the lower tooth angle 44 and the upper tooth angle 46 are chosen to be 30°.
A still further embodiment of the invention is illustrated in Figs 7 and 8. Figure 7 is a perspective view of the upper part of a valve needle 16, on which a spring washer 48 is put. The spring washer 48 rests on a helical spring, which is omitted from Fig. 7. An external preload force 26 is applied to the top surface of the spring washer 48 and in the same step, the preload force is measured with a load cell. When the spring reaches its required preload length, the spring washer 48 is laser welded to the upper portion of the valve needle 16, thereby blocking the working position of the spring biasing 20. The spring washer may be continuously welded or, preferably, be secured to the valve needle 16 by a plurality, such as 3, 4, 6 or 8 welding spots 50, which are equally spaced along the circumference of the valve needle 16.
Figure 8 shows a cross-sectional view of the spring washer 48, and illustrates a raised section 52 on the upper surface, which contains all of the laser welded spots 50.
Figure 9 shows a flowchart illustrating an embodiment of the method in accordance with the invention. The illustrated method starts in step S1. In step S2 a variable external preload is applied to the upper surface of the blocking means. The applied preload is measured in step S3. In step S4 it is checked whether the predetermined spring preload is reached. If this is not the case, the method returns to step S2 and a different external preload force is applied. If it is determined in step S4 that the predetermined spring preload is reached, the method continues to step S5. In step S5 the blocking means are secured to the upper portion of the valve needle to block the spring means in a working position. The securing may be done by screwing a keeper nut, by crimping a collar of the blocking means, or by laser welding. The method depicted in figure 9 ends in step S6.
The features disclosed in the foregoing description, in the drawings, and in the claims may alone as well as in any possible combination be important for the realization of the invention.

Claims

A metering device for dosing pressurized fluids, particularly an injection valve for a fuel injection system in an internal combustion engine, comprising

a housing (12) having an end part provided with an outlet passage (14) terminating with a metering opening,

an axially moveable valve needle (16) passing through the outlet passage (14), and controlling opening and closing of the metering opening,

the valve needle (16) having a lower portion inside the outlet passage (14), with a lower end controlling the opening and closing of the metering opening, and having an upper portion with an upper end (18) cooperating with an actuator assembly to displace the valve needle (16) from the closing position, and

spring means (20) for urging the valve needle (16) in the closing position,

characterized in that
a blocking means (24,28; 32; 48) is arranged at and secured to the upper portion of the valve needle (16) to block the spring means (20) in a working position, thereby providing a predetermined spring preload.
The metering device according to claim 1,
characterized in that
the upper portion of the valve needle (16) comprises a screwed part (22) to which the blocking means (24,28; 32) is secured.
The metering device according to claim 2,
characterized in that
the blocking means is formed by a spring washer (24) and a threaded keeper nut (28), the threaded keeper nut (28) engaging with the screwed part (22) of the valve needle (16) to secure an axial position of the spring washer (24) along the valve needle (16), thereby blocking the spring means (20) in its working position.
The metering device according to claim 3,
characterized in that
the keeper nut (28) has a conical shape and the spring washer (24) has a corresponding conical central bore (30) receiving and engaging with the conical keeper nut (28).
The metering device according to claim 4,
characterized in that
the cone angle α of the keeper nut (28) and the central bore (30) of the spring washer (24) has a value between 10° and 25°, preferably a value of about 15°.
The metering device according to claim 2,
characterized in that
the blocking means is formed by a spring washer (32) with a collar (34), the collar (34) being crimped to the screwed part (22) of the valve needle (16).
The metering device according to any of claims 2 to 6,
characterized in that
the screwed part (22) of the valve needle (16) has a pitch between about 0,1 mm and about 0,5 mm, preferably between about 0,2 mm and about 0,4 mm.
The metering device according to any of claims 2 to 7,
characterized in that
the screwed part (22) of the valve needle (16) has teeth (36) with a lower tooth angle (44) and an upper tooth angle (46), wherein the lower and upper tooth angle are between about 30° and about 45°.
The metering device according to claim 8,
characterized in that
the lower and upper tooth angle (44, 46) are both about 30°.
The metering device according to claim 8,
characterized in that
the lower tooth angle (44) is about 30° and the upper tooth angle (46) is about 45°, thereby forming a saw tooth shape.
The metering device according to claim 1,
characterized in that
the blocking means is formed by a spring washer (48) laser welded to the upper portion of the valve needle (16), thereby blocking the spring means (20) in its working position.
The metering device according to claim 11,
characterized in that
the spring washer (48) is secured to the valve needle by a plurality of laser spots (50) consisting of 3, 4, 6 or 8 welding spots, equally spaced along the circumference of the valve needle (16).
The metering device according to any claims 3 to 12,
characterized in that
the spring washer (24; 32; 48) is made of stainless steel, preferably that the spring washer (24; 32; 48) is made of SS 304, SS 316, SS 430 FR or SS 416 P70.
A method for setting a spring preload in a metering device according to any of the preceding claims, wherein

a variable external preload force is applied to a top surface of at least one part of the blocking means (24,28; 32; 48) during the assembly process of the metering device,

the external preload force is measured, and

the blocking means (24,28; 32; 48) is secured to the upper portion of the valve needle (16) to block the spring means (20) in a working position, when a predetermined spring preload is reached.
The method according to claim 14, wherein the blocking means is formed by a spring washer (24) with a central bore and a fitting threaded keeper nut (28), and the upper portion of the valve needle (16) comprises a screwed part (22),
characterized in that
the external preload force is applied to a top surface of the spring washer (24), and the keeper nut (28) is screwed on the screwed part (22) of the valve needle (16) to engage with the spring washer (24), when the predetermined spring preload is reached.
The method according to claim 14, wherein the blocking means is formed by a spring washer (32) with a collar (34) and the upper portion of the valve needle comprises a screwed part (22),
characterized in that
the external preload force is applied to a top surface of the spring washer (32), and the collar (34) is crimped to the screwed part (22) of the valve needle (16), when the predetermined spring preload is reached.
The method according to claim 16,
characterized in that
the collar (34) is crimped to the valve needle (16) using a punch having two parallel sharp teeth (42) as a crimping tool.
The method according to claim 14, wherein the blocking means is formed by a spring washer (24; 32; 48),
characterized in that
the external preload force is applied to a top surface of the spring washer (48), and the spring washer (48) is laser welded to the upper portion of the valve needle (16), when the predetermined spring preload is reached.