WO2003067074A1

WO2003067074A1 - Method and device for controlling a control valve of a pump-nozzle unit

Info

Publication number: WO2003067074A1
Application number: PCT/DE2003/000298
Authority: WO
Inventors: Maximilian Kronberger
Original assignee: Volkswagen Mechatronic Gmbh & Co. Kg
Priority date: 2002-02-07
Filing date: 2003-02-03
Publication date: 2003-08-14
Also published as: DE50305256D1; EP1472455A1; EP1472455B1

Abstract

The invention relates to a method and device (80) for controlling the control valve (22) of a pump-nozzle unit. The positional accuracy of the valve lifts is increased by means of an automatic control, especially an adaptive automatic control, in order to avoid high pressure gradients at low engine speeds during the shut-off of the valve.

Description

description

Method and device for controlling a control valve of a pump-nozzle unit

The invention relates to a method and a device for controlling a control valve of a pump-nozzle unit, wherein the control valve has at least one movable element which can be moved into a first end position for closing the control valve and into a second end position for fully opening the control valve is.

Pump-nozzle units are used to supply fuel into a combustion chamber of an internal combustion engine. This can be, for example, a pump-nozzle unit with a control and / or controllable fuel pump, a fuel injection nozzle which has a nozzle needle which can be moved back and forth between a closed position and an open position, a first pressure chamber which is separated from the fuel pump can be filled with fuel under a first pressure, a second pressure chamber, with fuel under a second pressure exerting a closing force on the nozzle needle in the second pressure chamber, and a third pressure chamber which communicates with the first pressure chamber, in the third Pressure chamber under a third pressure fuel exerts an opening force on the nozzle needle.

Pump-nozzle units are used in particular in connection with pressure-controlled injection systems. An essential feature of a pressure-controlled injection system is that the fuel injection nozzle opens as soon as an opening force, which is at least influenced by the currently prevailing pressures, is exerted on the nozzle needle. Such pressure-controlled injection systems are used for fuel metering, fuel conditioning, shaping the injection process and sealing the fuel supply against the combustion chamber of the internal combustion engine. With pressure controlled Injection systems can be controlled in an advantageous manner the course of the volume flow over time during the injection. This can have a positive impact on the performance, fuel consumption and pollutant emissions of the engine.

In pump-nozzle units, the fuel pump and the fuel injection nozzle are generally designed as an integrated component. For each combustion chamber of the internal combustion engine, at least one pump-nozzle unit is provided, which is usually installed in the cylinder head. The fuel pump typically comprises a fuel pump piston that can be moved back and forth in a fuel pump cylinder and is driven either directly by a tappet or indirectly by rocker arm of a camshaft of the internal combustion engine. The section of the fuel pump cylinder which usually forms the first pressure chamber can be connected to a low-pressure fuel region via a control valve, fuel being drawn into the first pressure chamber from the low-pressure fuel region when the control valve is open, and into the fuel chamber from the first pressure chamber when the control valve is still open. Low pressure area is pushed back. As soon as the control valve is closed, the fuel pump piston compresses the fuel in the first pressure chamber and thus builds up pressure. It is known to provide the control valve in the form of a solenoid valve. However, solenoid valves usually have a relatively long response time, which is due in particular to the fact that the magnet armature of a solenoid valve cannot be accelerated as quickly as desired due to the inertia forces which are dependent on its mass. Furthermore, the build-up of the magnetic field to generate the attraction force requires time. A pump-nozzle unit equipped with a solenoid valve is known for example from EP 0 277 939 B1. In order to avoid the problems caused by the use of solenoid valves, it is also known to equip pump-nozzle units with a control valve that is operated piezoelectrically. Such a Pu pe nozzle unit is known for example from DE 198 35 494 AI.

In order to introduce an additional pre-injection quantity and / or an additional post-injection quantity into the combustion chamber in addition to a main injection quantity during an injection process, it is also known to trigger a plurality of injection pulses which follow one another in short time intervals during an injection cycle.

Optimal combustion processes, for example in the case of direct-injection diesel engines, require this flexible design of the injection process with multiple injection, for example pre-injection, main injection and post-injection. At higher speeds, a very quick closing and opening of the control valve over its entire stroke is necessary for this purpose, with correspondingly high pressure gradients. Such high pressure gradients are often undesirable, especially at low speeds, since they trigger pressure fluctuations. The decay time of these pressure fluctuations influences the maximum number and accuracy of the control processes within a sequence of multiple injections. The low pressure level of the

Fuel supply to pump-nozzle systems favors low fuel consumption, but often increases the tendency to cavitation. Higher pressure gradients increase this tendency, which increases engine noise.

Control valves in the form of solenoid valves generally only have stable stroke positions when fully open and when closed. These stable positions are usually determined by mechanical stops. The stroke curve over time depends on the resulting force curve from magnetic, hydraulic and frictional forces. For control valves in the form of solenoid valves, there are approaches that to reduce through a step-like stroke. However, such stepped stroke profiles show, in principle, strong stochastic and specimen-specific variations in the case of solenoid valves. Furthermore, the respective duration of the partial stroke phases is strictly limited.

Control valves in the form of piezo valves enable a relatively stable control of partial strokes, with practically no disturbing time limit. However, the positioning accuracy that can be achieved is considered critical, since, for example, with a total stroke of 200 μm, a positional accuracy of the valve part strokes of, for example, +/- 5 μm is considered necessary to avoid undesirable side effects in the course of the injection.

The invention is based on the object of developing the generic methods and devices in such a way that control valve part strokes with improved positional accuracy can be achieved, in particular in order to be able to avoid high pressure gradients at lower engine speeds.

This object is solved by the features of the independent claims.

Advantageous refinements and developments of the invention result from the dependent claims.

The method according to the invention for controlling a control valve of a pump-nozzle unit builds on the generic prior art in that a control, in particular an adaptive control, is used at least temporarily to set at least one intermediate position of the at least one movable element. With this solution, valve partial strokes with a high degree of positional accuracy are achieved, which leads, for example, to an improvement in noise and exhaust gas emissions and in the torque curve of the engine. It is particularly advantageous if the method according to the invention provides that at least one intermediate position is set for a predetermined period of time when the at least one movable element for opening the control valve is moved from the second end position into the first end position. By setting one or more defined intermediate positions for one or more predetermined periods of time, the opening process of the control valve can be slowed down in a targeted and defined manner, for example in order to avoid high pressure gradients at lower engine speeds.

It is preferably further provided that the control valve is actuated by electrical actuation of an actuator for the at least one movable element. The type of actuator defines the type of control valve, for example solenoid valve or piezo valve.

With regard to the actual regulation, it is preferred that the manipulated variable of the regulation is an electrical quantity with which the actuator is electrically actuated. In the case of a piezo valve, the electrical variable can be the control voltage of the piezo element, for example.

In preferred embodiments of the method according to the invention, it is further provided that the controlled variable of the control is a resultant force and / or a resultant force curve as a result of a pressure within at least one area of the control valve, in particular a pressure and / or pressure curve within the control valve when it is opened of the at least one area. If it is a piezo valve, the at least one area can be, for example, the fuel-filled space in front of the piezo element and / or a control chamber, an increase in pressure occurring there causing an increase in the pressure force on the piezo ceramic, for example via a piston or the like , The result of this is that the pressure and / or the pressure profile within the at least one area of the control valve is detected via a piezo element.

In this context, it is preferably further provided that the piezo element is part of the actuator or forms it.

In particularly preferred embodiments of the method according to the invention, it is further provided that the pressure and / or pressure curve detected during a current opening process of the control valve within the at least one area of the control valve for the current opening process and / or for at least one subsequent opening process is included in the control, in particular in the form of offset values of at least one electrical variable with which the actuator is controlled. For example, an increase in the pressure force on a piezoceramic can be evaluated by an electrical variable measured on the piezo element. During the current injection process, preferably at the latest from the next injection process, the desired partial stroke positions can then be achieved by superimposing corresponding offset values on the value of the piezo control variable available at the time of evaluation. The target partial stroke positions can assume different values within a multiple control.

The device according to the invention for controlling a control valve of a pump-nozzle unit is based on the generic state of the art in that it carries out a regulation, in particular an adaptive regulation, at least temporarily to set at least one intermediate position of the at least one movable element , This results in the advantages explained in connection with the method according to the invention in the same or similar manner, half to avoid repetition, reference is made to the corresponding statements.

The same applies mutatis mutandis to the following preferred embodiments of the device according to the invention, reference also being made to the corresponding statements in connection with the method according to the invention with regard to the advantages achievable by these embodiments.

It is also provided in advantageous embodiments of the device according to the invention that it sets the at least one intermediate position for a predetermined period of time when the at least one movable element for opening the control valve is moved from the second end position into the first end position.

Furthermore, embodiments of the device according to the invention are considered to be advantageous in which it is provided that it controls the control valve by electrically controlling an actuator for the at least one movable element.

In this case, it is preferred for the device according to the invention that, to carry out the control, it uses an electrical variable as the manipulated variable with which it electrically controls the actuator.

Similar to the method according to the invention, it is preferably also provided in the device according to the invention that it uses a resultant force and / or a resultant force curve as a control variable of the regulation as a result of a pressure within at least one area of the control valve, in particular one that occurs when the control valve opens Pressure and / or pressure curve within the at least one area. In this context in particular, preferred developments of the device according to the invention provide that the pressure and / or the pressure profile within the at least one area of the control valve is detected via a piezo element.

It is further preferred that the piezo element is part of the actuator or forms it.

It is also preferred for the device according to the invention that it includes, in particular, the pressure and / or pressure curve detected during a current opening process of the control valve within the at least one area of the control valve for the current opening process and / or for at least one subsequent opening process in the form of offset values of at least one electrical variable with which it controls the actuator.

The invention is based on the knowledge that the noise and exhaust emissions and the torque curve of an internal combustion engine can be improved if a control is used to increase the positional accuracy of partial strokes of the control valve of a pump-nozzle unit.

The invention will now be described with reference to the accompanying

Drawings exemplified using preferred embodiments.

Show it:

FIG. 1 shows a schematic embodiment of a pump-nozzle unit with or with which the method according to the invention or the device according to the invention can be used; Figure 2 is a schematic partial sectional view of a control valve which can be used with the pump-nozzle unit of Figure 1; and

FIG. 3 shows a flow chart which illustrates an embodiment of the method according to the invention.

Figure 1 shows schematically a pump-nozzle unit. The pump-nozzle unit shown for supplying fuel 10 into a combustion chamber 12 of an internal combustion engine has a fuel pump 14-22. A fuel pump piston 14 can be moved back and forth in a fuel pump cylinder 16. The fuel pump piston 14 is driven directly or indirectly via a camshaft, not shown, of the internal combustion engine. The compression space of the fuel pump cylinder 16 forms a first pressure space 28. The first pressure space 28 is connected via a fuel line 20 to the control valve 22 to be controlled according to the invention. The control valve 22 serves to either close the fuel line 20 or to connect it to a low-pressure fuel region 18 from which fuel 10 can be drawn. In the open rest position of the control valve 22, fuel 10 is drawn from the low-pressure fuel region 18 into the first pressure chamber 28 when the fuel pump piston 14 moves upward in relation to FIG. 1.

If the control valve 22 is still in its open rest position when the fuel pump piston 14 moves downward in relation to FIG. 1, fuel 10 previously drawn into the first pressure chamber 28 can be pressed back into the low-pressure fuel region 18. With a suitable control of the control valve 22 closes, this is the fuel line 20. This compresses the sucked into the first pressure chamber 28, fuel 10 at a downwardly directed movement of the fuel pump plunger 14, whereby a first pressure p is produced in the first pressure chamber 28 _28th The pump-nozzle unit shown also comprises a total of 24 Fuel injection nozzle which has a nozzle needle 46 which can be moved back and forth between a closed position and an open position. In relation to the illustration in FIG. 1, a pressure pin 26 can in particular exert a downward force on the nozzle needle 46. At the upper end of the push pin 26, a shim 40 is provided, which is guided in a second pressure chamber 30, wherein in the second pressure chamber 30 at a second pressure p ₃ o standing fuel 10 via the pressure pin 26 has a relative lung to the representation of Figure 1 downward closing force exerts on the end face 45 of the nozzle needle 46. A further closing force, likewise directed downward, is exerted by a first spring 36 on the pressure pin 26 and thus on the nozzle needle 46, the first spring 36 being arranged in the second pressure chamber 30 and having its rear end supported on the adjusting disk 40 , A section of the nozzle needle 46 having a shoulder 44 is surrounded by a third pressure chamber 32, which communicates with the first pressure chamber 28 via a connecting line 42. Depending on the throttling action of the connecting line 42 and possibly other throttling devices (not shown), a third pressure p _{32 is} built up in the third pressure chamber 32 as a function of the first pressure p ₂₈ prevailing in the first pressure chamber 28. The fuel 10, which is under the third pressure p ₃₂ in the third pressure chamber 32, exerts an opening force on the nozzle needle 46 which is directed upward in relation to the illustration in FIG. The nozzle needle 46 assumes its open position as long as a difference between the opening force caused by the third pressure p ₃₂ and the sum of the closing force generated by the second pressure p ₃₀ and the closing force generated by the first spring 36 exceeds a predetermined value. The nozzle opening pressure can thus be influenced via the second pressure p ₃₀ in the second pressure chamber 30. In order to limit and maintain the second pressure p ₃₀ in the second pressure chamber 30 to suitable values, for example, a pressure limiting and maintaining valve 34 can be located between the first pressure chamber 28 and the second pressure chamber 30 may be provided. The control valve 22 is controlled by an embodiment of the device 80 according to the invention for controlling the control valve 22, in particular in such a way that the method according to the invention results.

FIG. 2 shows a schematic partial sectional view of a control valve 22 which can be used with the pump-nozzle unit according to FIG. 1. The control valve 22 shown has a movable element 48 in the form of a valve needle, which can be moved into the first end position shown for closing the control valve 22 and into a second end position for fully opening the control valve 22, which is shifted to the right in relation to the illustration , When the valve needle 48 is in its illustrated first end position, a valve plate 64 provided on the valve needle 48 interacts with a valve seat 62 on the housing side. As a result, the low-pressure fuel region 18 is closed off from a high-pressure chamber 38, which is connected to the fuel line 20 shown in FIG. 1. The control valve 22 shown in FIG. 2 is a piezo valve which has a piezo element 76. With suitable activation of the piezo element 76, this exerts a force on a pressure piece 54 via an end face 78. The pressure piece 54 in turn transmits the force generated by the piezo element 76 to a first lever 56 and a second lever 58, the first lever 56 and the second lever 58 being provided to effect a force transmission. The first lever 56 and the second lever 58 rest against a second axial end surface 72 of the valve needle 48 in order to transmit the translated force generated by the piezo element 76 to the valve needle 48. The translated force generated by the suitably controlled piezo element 76, which acts on the valve needle 48, is greater than an opposite force, which is generated by a second spring 66 and is exerted on a first axial end face 70 of the valve needle 48 via a spring pressure piece 68. The fuel Low-pressure area 18 is connected to a control chamber 50, which is also connected via a compensating bore 52 to an actuator chamber 74 located in front of the piezo element. This actuator chamber 74 is connected to a return 60 via which fuel can flow back from the actuator chamber 74.

When the control valve 22 begins to open (generally at the point in time at which fuel injection into the combustion chamber has ended "end of delivery"), a pressure rise occurs in the control chamber 50 by connecting it to the high-pressure chamber 38. The bore 52 guides this pressure increase approximately at the speed of sound into the actuator space 74 filled with fuel in front of the piezo element 76, which causes an increase in the pressure force on the piezo ceramic. The pressure rise occurring in the actuator space 76 also acts via the valve needle 48, which is designed as a piston, with the force transmission of the levers 56 and 58 as an additional force via the pressure piece 54 on the end face 78 of the piezo element 76. The resultant of these forces in this embodiment represents the controlled variable Regulation according to the invention. The resultant is evaluated by means of an electrical variable, for example the voltage, measured on the piezo element 76 at this time. This procedure can be used both when the valve needle 48 is moved to its second end position to open the control valve completely (total stroke) and when the valve needle 48 is to assume an intermediate position (partial stroke). During the current injection process, preferably at the latest from the next injection process, the desired partial stroke positions are achieved by superimposing corresponding offset values on the control variable of the control (for example the piezo voltage) present at the time of evaluation (= fuel-feeding). It should be noted that the target partial stroke positions can assume different values within a multiple control. If the valve needle 48 has one or more intermediate positions, the position of which is regulated according to the invention, is moved to the second end position, there is a slower opening of the valve. In this way, undesirable high pressure gradients can be at least reduced, for example, at lower engine speeds.

FIG. 3 shows a flow diagram which illustrates an embodiment of the method according to the invention. The embodiment of the method according to the invention shown in FIG. 3, which can be applied to the piezo element 76 of FIG. 2, begins at step SI. Then, in step S2, an external voltage is applied to the piezo element 76 in order to close the control valve 22. As soon as the fuel delivery end is reached, the process continues in step S3. In step S3, the external voltage is removed or reduced from the piezo element 76 in order to open the control valve 22. The resulting force is then detected via an electrical variable on the piezo element 76, for example via the voltage applied to the piezo element 76. The detected force or the detected force is then in step S4

Force curve in the actuator chamber 74 compared with a target force or a target force curve. Furthermore, a new value for the external voltage is determined, for example by suitably setting offset values. If the method according to the invention is not intended to end in step S5, a branch is made back to step S2. Otherwise, the method ends in step S6.

The invention can be summarized as follows: The invention relates to a method and a device 80 for controlling the control valve 22 of a pump-nozzle unit. In particular in order to avoid high pressure gradients during valve deactivation at low engine speeds, the positional accuracy of valve part strokes is improved by a control, in particular an adaptive control. The features of the invention disclosed in the above description, in the drawings and in the claims can be essential for realizing the invention both individually and in any combination.

Claims

claims

1. A method for controlling a control valve (22) of a pump-nozzle unit, wherein the control valve (22) has at least one movable element (48) for closing the control valve (22) in a first end position and for completely opening the control valve (22) can be moved into a second end position, characterized in that a control, in particular an adaptive control, is used at least temporarily to set at least one intermediate position of the at least one movable element (48).

2. The method according to claim 1, so that the at least one intermediate position is set for a predetermined period of time when the at least one movable element (48) for opening the control valve (22) is moved from the second end position into the first end position.

3. The method according to claim 1 or 2, d a d u r c h g e k e n e z e i c h n e t that the control valve (22) is controlled by electrical control of an actuator (76) for the at least one movable element (48).

4. The method of claim 3, d a d u.r c h g e k e n n z e i c h n e t that the manipulated variable of the control is an electrical variable with which the actuator (76) is electrically controlled.

5. The method according to any one of the preceding claims, characterized in that the controlled variable of the control a resulting force and / or a resulting force curve as a result of a pressure within at least one area of the control valve is, in particular a pressure and / or pressure curve occurring when the control valve opens within the at least one area.

6. The method as claimed in claim 5, so that the pressure and / or the pressure profile within the at least one area (50, 74) of the control valve (22) is detected via a piezo element (76).

7. The method according to claim 6, so that the piezo element (76) is part of the actuator or forms it.

8. The method according to any one of claims 3 to 7, characterized in that the pressure and / or pressure curve detected during a current opening process of the control valve (22) within the at least one region (50, 74) of the control valve (22) for the current opening process and / or is included in the control for at least one subsequent opening process, in particular in the form of offset values of at least one electrical variable with which the actuator (76) is controlled.

9. Device for controlling a control valve (22) of a pump-nozzle unit, wherein the control valve (22) has at least one movable element (48), which for closing the control valve (22) into a first end position and for complete Opening the control valve (22) in a second end position is characterized in that it performs regulation, in particular adaptive regulation, at least temporarily to set at least one intermediate position of the at least one movable element (48).

10. The device according to claim 9, so that it sets the at least one intermediate position for a predetermined period of time when the at least one movable element (48) for opening the control valve (22) is moved from the second end position into the first end position.

11. The apparatus of claim 9 or 10, d a d u r c h g e k e n e z e i c h n e t that it controls the control valve (22) by electrical control of an actuator (76) for the at least one movable element (48).

12. The device according to claim 11, so that it uses an electrical variable as a manipulated variable for carrying out the control, with which it electrically controls the actuator (76).

13. Device according to one of claims 9 to 12, characterized in that it uses a resultant force and / or a resultant force curve as a control variable of the regulation as a result of a pressure within at least one area (50, 74) of the control valve (22), in particular a pressure and / or pressure curve occurring when the control valve (22) is opened within the at least one area (50, 74).

14. The device as claimed in claim 13, so that the pressure and / or the pressure profile within the at least one region (50, 74) of the control valve (22) is detected via a piezo element (76).

15. The apparatus according to claim 14, characterized in that the piezo element (76) is part of the actuator or forms it.

16. Device according to one of claims 11 to 15, characterized in that it detects the pressure and / or pressure profile detected during the current opening process of the control valve (22) within the at least one region (50, 74) of the control valve (22) for the current opening process and / or for at least one subsequent opening process in the control, in particular in the form of offset values of at least one electrical variable with which it controls the actuator (76).