WO2007033861A1

WO2007033861A1 - Fuel injection apparatus

Info

Publication number: WO2007033861A1
Application number: PCT/EP2006/065129
Authority: WO
Inventors: Patrick Mattes; Wolfgang Stoecklein
Original assignee: Robert Bosch Gmbh
Priority date: 2005-09-20
Filing date: 2006-08-08
Publication date: 2007-03-29
Also published as: DE102005044830A1

Abstract

In a fuel injection apparatus (1) for internal combustion engines, having a piezoelectric actuator (23) which is provided for moving a movable valve part (43) of a control valve (20), which valve part (43) closes or opens an outlet of a control space (9) depending on its position, with a hydraulic coupler (25) being connected in between, wherein highly pressurized fuel can be fed to the control space (9) via an inlet restrictor (15) during operation, as a result of which the pressure in the control space (9) is influenced and the fuel injection is started and ended, there is provision according to the invention for the piezoelectric actuator (23) and the coupler (25) to be arranged in a space (actuator space 27) which is filled with highly pressurized fuel during operation, for the actuator space to have an inlet channel (29) for connection to a pressure accumulator for highly pressurized fuel, and for the coupler (25) to have a coupler body (35) which has guide bores (36, 37), in which two coupler plungers (38, 39) which delimit a coupler space (41) are guided in a sliding manner, wherein at least one guide gap which serves to fill the coupler space (41) is provided by the guide bores (36, 37) and at least one guide bore is connected to the actuator space (27).

Description

Fuel injector

State of the art

The invention relates to a fuel injection device according to the preamble of patent claim 1.

Based on the function of the known CRI3.0 Piezo CR injector developed by the Applicant (a fuel injection device for common rail vehicles (CR)), the following facts are defined as prior art:

Usually in CR systems, the rail is at a certain distance from the injector. As a result, pressure vibrations in the pipeline system are triggered by the injection. In piezo injectors, a certain bias of the ceramic must be provided by eg mechanical biasing elements, so that during operation of the actuator (piezo actuator) no tensile forces in the ceramic can occur, which would lead to the destruction of the actuator.

For the clearance compensation in the switching chain actuator switching valve hydraulic couplers are used. These require provision of increased pressure in the low pressure circuit. The switching valve influences the pressure in a control chamber and thereby the position of a valve piston (nozzle needle) of an injection nozzle and thus controls the injection of fuel into one during operation

Internal combustion engine. In the known device, the movable valve part of the switching valve opens against the rail pressure, that is, an I-valve (inwardly opening) is used.

Advantages of the invention

The fuel injection device according to the invention for internal combustion engines with the characterizing features of claim 1 has the advantage that the bias of the piezoelectric actuator is at least partially made hydraulically. Only a reduced additional mechanical actuator bias is necessary. Thereby, e.g. simple coil springs can be used for the preload, in contrast to usual coil springs. This results in a simpler structure than before.

It is also advantageous that only slight pressure oscillations are caused in the line system, since a large storage volume can be shown near the injection nozzle. Namely, it acts against the space surrounding the coupler and the piezo actuator, which forms, so to speak, an additional rail in the injector, against the formation of strong vibrations. In contrast, in known injectors, the near-nozzle storage volume in the injector is relatively small, which among other things is a cause of strong vibrations. Lower pressure oscillations at the nozzle in the invention cause less nozzle wear and higher injection efficiency.

The return of the injector no longer needs to be pressurized to ensure refilling of the coupler. The coupler is namely surrounded on its outside by the rail pressure and is filled by this quickly. This eliminates the usual return trail, and it is possible not particularly pressure-resistant return line.

If, in accordance with claim 2, it is ensured that the pressure in the coupler space can not fall or does not drop sharply, the coupler space is filled even faster.

If according to claim 3, the movable valve member is at least partially pressure balanced, the piezo-actuator is less heavily mechanically loaded, and it is possible to use a smaller piezoceramic.

Overall, there is a lesser constructive and manufacturing effort. The design can be displayed on the control side (actuator / coupler / switching valve) much easier and cheaper.

Further advantages and advantageous embodiments of the subject invention are the description, the drawings and claims removed.

drawing

Embodiments of the fuel injection device according to the invention are illustrated in the drawing and explained in more detail in the following description. Show it:

Fig. 1, the fuel injection device according to the invention in longitudinal section;

Fig. 2 shows a detail of a first modification of the device according to Fig. 1 in

Area of one of the coupler pistons of a hydraulic coupler; Fig. 3 shows a detail of a further modification of the device of Figure 1 in the region of the movable valve member (valve ball) of the control valve.

Fig. 4 is an enlarged detail of Figure 1 illustrating a required dimensioning of the lower coupler piston compared to the valve seat. and

5 shows graphs as a function of time for the case of the first modification (FIG. 2) with reference to FIG. 4.

Description of the embodiments

The figures are only for understanding important parts. The Fign. 1 to 4 are longitudinal sections, partially broken. In Fig. 1, the injection valve is shown partially schematized. In Fign. 2 or 3 modified, the Fig. 1 corresponding parts have an addition to the reference numeral.

In Fig. 1, a fuel injection device 1, a nozzle 2 (also known as injector), which is connected to a unit 3 and can be controlled by this. The nozzle 2 corresponds largely known devices. A valve piston (nozzle needle) 5 is controlled in its position by forces which are generated on its upper end face 7 by the pressure in a control chamber 9 and on a control surface 11. When the nozzle is open, a fuel is discharged through at least one injection port 13. The control chamber 9 is constantly filled with fuel under high pressure during operation via an inlet throttle 15 and then relieved of pressure via an outlet throttle 17 when the flow is released by a control valve 20. The control valve 20 is located in the embodiment in the unit 3. To actuate it serve a piezo actuator 23 and a hydraulic coupler 25. These are both contained in a designated here as the actuator chamber 27 space which is pressure-tight. The actuator chamber 27 has an inlet channel 29, the fuel is supplied under high pressure from a pressure accumulator or common rail (not shown) via a high pressure supply. Therefore In operation, the piezo actuator 23 and the hydraulic coupler 25 are surrounded by rail pressure. The fuel for the injection is removed from this actuator chamber 27 via a high-pressure passage 31 and passed through a further high-pressure passage 33 to previously mentioned components of the nozzle 2.

The hydraulic coupler 25 is also surrounded by rail pressure. The coupler 25 has a coupler body 35 with guide bores 36, 37 and two coupler pistons 38 slidably guided in the guide bores (connected to the piezo actuator 23) and 39 (for actuating the control valve 20). In the example, the coupler pistons 38 and 39 are arranged linearly one behind the other with the interposition of a coupler space 41. The guide bore 36 and the coupler piston 38 are each with its upper end to the actuator chamber 27 and therefore with the fuel under high pressure directly in communication. Since, in the example, an increase in the speed of the coupler piston 39 acting on the movable valve part 43 of the control valve 20 is desired in comparison to the other coupler piston 38, the diameters and thus the cross sections of the coupler pistons are suitably provided differently. A play between the guide bore 36 and the coupler piston 38 forms a guide gap and filling gap and allows a rapid filling of the coupler space 41 with fuel under high pressure. The pressure in the coupler chamber 41 presses the coupler piston 38 against the piezo actuator 23 and biases it mechanically to pressure. Thereby, a spring 53 provided for biasing the actuator 23 can be made weaker than heretofore. The control valve 20 opens with the rail pressure from the control chamber 9, it is therefore an A-valve, that is, outward opening. The movable valve member 43 is in the example a ball which is directly actuated by the coupler piston via a fixed thereto, a lateral tolerance compensation enabling actuator plate 45 and an annular seat 47 (valve seat) of a nozzle on the top adjoining plate-shaped element 49 of the unit 3 interacts. The seat 47 surrounds the upper end of a channel provided in the element 49, which is connected to the outlet throttle 17. The area 50 downstream of the control valve 20, in which the valve member 43 and the lower end of the lower coupler piston 39 are located, is connected to a return 51. The coupler body 35 is sealed at its lower end on the periphery, as indicated by "D" in Fig. 1, high-pressure-tight against the member 49 and the region 50. In the coupler chamber 41, a pressure level is set, which is (depending on the game of the coupler piston 38 and 39 in this receiving guide holes 36, 37 of the coupler body 35, and their guide lengths) between the rail pressure and return pressure level. Because of the game, the guide holes 36, 37 guide gaps. Through the games and the guide lengths, the said pressure level can be adjusted. Thus, at the appropriately set pressure level of the example on the lower coupler piston 39 in the idle state hydraulic forces, which keep the valve member 43 closed in the valve seat.

According to FIG. 4, 0 $ (the seat diameter is the diameter of the seat 47) and 0κ (diameter of the coupler piston 39) must be selected so that the control valve 20 does not open automatically due to the rail pressure acting on the valve part 43 from the control chamber. In the initial state of Fig. 1 (with the control valve disabled, no injection), the piezo actuator 23 is charged (it is supplied with an electrical voltage), that is, the actuator 23 is in the extended state. If an injection takes place, the electrical voltage at the actuator 23 is reduced, whereby the pressure in the coupler chamber 41 lowers, since the actuator 23 is shortened. If a certain pressure level in the coupler space 41 is reached, the control valve 20 opens. The valve closure is correspondingly reversed. The leakage amount escaped from the coupler space 41 during the injection is quickly filled up after the injection by the high rail pressure via one (36) of the guide bores. The control valve 20 is quasi pressure balanced in combination with the lower coupler piston 39. As a result, the size of the piezoceramic of the actuator 23 can be reduced compared to non-pressure compensated valves.

The properties of the fuel injection device 1 counteracting the above-mentioned vibrations can be varied by changing the available volume of the fuel chamber 27 for fuel. An enlargement of the actuator chamber 27 can have a similar effect as a reduction of the accommodated in the actuator chamber 27 elements. Fig. 2 shows a modified example. While in Fig. 1 leakage from the hydraulic coupler 25 enters the area 50 and thereby the pressure in the coupler chamber 41 decreases, Fig. 2 provides a remedy. In order to define the pressure in the hydraulic coupler 25 more accurately and to be independent of games of the coupler pistons 38, 39 'and thus tolerances, on the coupler piston 39' an additional extending at least a part of the circumference of the groove 55 together with a connecting channel 57 to substantially cylindrical outer side of the coupler body 35 'is provided. As a result, the coupler space 41 is surrounded on all sides by rail pressure, and in the coupler space 41 inevitably sets a rail pressure level, regardless of the leakage occurring. The coupler pressure (pressure in the coupler space 41) is independent of manufacturing tolerances, as well as of the diameters and guide lengths of the coupler piston 38, 39 '. The groove 55 is an annular groove in the example. The groove may instead of in the coupler piston 39 'or additionally in the guide bore 37' a. It does not necessarily have to be completely circular. The longitudinal displacement of the coupler piston is smaller than the width of the groove.

3, if necessary, a spring element 61, in the example a helical spring, is provided on the lower coupler piston 39 "to ensure, for example, a defined position of the coupler piston 39" at system startup.

4 shows enlarged the diameter of the lower piston 39 and the seat 47. When the force acting on the valve member 43 from the control chamber 9 maximum force is approximately equal to the force exerted by the lower coupler piston 39 downward force at maximum elongated piezoelectric actuator 23 (case a), the control valve 20 begins to open at the beginning of a reduction in the electrical voltage on the piezo-actuator 23, see Fig. 5. If the diameter of the lower coupler piston 39 in contrast significantly larger in the case b), the control valve 20 opens later (at lower voltage) and closes sooner than in case a). In FIG. 5, for the cases a) and b), the electrical actuator voltage U, the valve lift L, and the pressure P in the coupler space 41 are shown graphically as a function of time.

Claims

claims

A fuel injector (1) for internal combustion engines, comprising a piezo actuator (23) for moving a movable valve member (43) of a control valve (20) which, depending on its position, has an outflow

Control chamber (9) blocks or releases, with the interposition of a hydraulic coupler (25) is provided, wherein in operation the control chamber (9) via an inlet throttle (15) fuel can be supplied under high pressure, whereby the pressure in the control chamber (9) influenced and the fuel injection is started and stopped, characterized in that the piezo actuator (23) and the coupler (25) are arranged in a space filled with fuel under high pressure (actuator chamber 27), that the actuator chamber has an inlet channel ( 29) for connection to a pressure accumulator for fuel under high pressure, and that the

Coupler (25) has a coupler body (35) having guide bores (36, 37) in which two coupler pistons (38, 39) are slidably guided defining a coupler space (41), at least one for filling the coupler space (41 ) serving guide gap through the guide holes (36, 37) is provided and at least one guide bore with the

Aktorraum (27) is in communication.

2. Fuel injection device according to claim 1, characterized in that arranged on the outer wall and / or guide bore of the control valve (20) facing the coupler piston (39) at least at a portion of the circumference in a spaced-apart from the two ends of the guide bore area a groove (55) is connected via a connecting channel (57) with a high pressure area.

3. Fuel injection device according to claim 1 or 2, characterized in that in operation by the associated coupler piston (39) on the valve member (43) exerted force is at least approximately equal to the force exerted by the control chamber (9) forth on this force, so that the valve member (43) is at least approximately pressure balanced.