EP1511928A1

EP1511928A1 - Method and device for measuring and regulating the closing and opening period of a piezo control valve

Info

Publication number: EP1511928A1
Application number: EP03756964A
Authority: EP
Inventors: Harald Schmidt; Harald Gegenfurtner; Walter Schrod; Richard Pirkl
Original assignee: Volkswagen Mechatronic GmbH and Co KG
Current assignee: Continental Mechatronic Germany GmbH and Co KG
Priority date: 2002-06-11
Filing date: 2003-06-03
Publication date: 2005-03-09
Also published as: DE10225911B3; WO2003104633A1

Abstract

The invention relates to a method and a device for measuring the time period required by the valve needle (50) of a control valve (21) of a piezo unit injector system to move from a first end position (64) into a second end position (65). According to the invention, the time period is determined in accordance with the voltage (u (t)) that is applied to the control valve (21) and/or the applied current (i (t)) and the actuating signal is generated at a time, which guarantees that the pressure in the control valve (21) during the measurement substantially corresponds to the pressure in the low-pressure fuel region (31).

Description

description

Method and device for measuring and regulating the closing and opening times of a piezo control valve

The invention relates to a method and a device for measuring the length of time that a valve needle of a piezo control valve needs to move from a first end position to a second end position. Piezo control valves are used in piezo pump-nozzle units

(PPE) used for fuel quantity metering in internal combustion engines. Such a PPE is already known from DE 100 38 995 A1. With this PPE, the pump and nozzle form one unit. The pump is operated either directly via a tappet or indirectly via a rocker arm from an engine camshaft. The piezo control valve is controlled via an actuation unit in such a way that it is fully open in a first end position and completely closed in a second end position. When the control valve is open, the fuel is pressed back into the low-pressure fuel area by the pump piston via the piezo control valve during the piston stroke. If the control valve closes, the pump piston cannot push the fuel back into the low-pressure fuel range. The fuel is compressed, which leads to an increase in pressure in the high-pressure area of the pump unit. If the pressure in the pump unit exceeds the opening pressure of the injection nozzle, fuel is injected into the combustion chamber of the internal combustion engine. The closing time of the control valve thus determines the time of the fuel injection and the closing time the injection quantity.

The actuation unit of the PPE consists of a piezo actuator. The expansion of the piezo actuator is proportional to the am Piezo actuator applied voltage (u (t)) and / or the applied current (i (t)). In order that the injection quantity spread is as small as possible, the piezo actuator must be as precise as possible to set the start, duration and end of the injection process by means of a precisely defined voltage (u (t)) and / or a precisely defined current (i (t)) can be controlled. Wear, aging processes and temperature changes lead to changed closing and opening times of the piezo control valve, as a result of which precise fuel injection quantity control can no longer be guaranteed.

DE 199 10 388 C2 discloses a method for checking that a capacitive actuator is functioning properly. The actuator is checked by comparing the duration of the actuator actuation with the duration of the control signal which is responsible for the actuator actuation. The correct functioning of the actuator is assumed if the measured duration of the actuation of the actuator lies within a range determined by the duration of the control signal.

The invention is based on the object of realizing a method and a device which precisely determine the actual closing and opening times of the control valve. The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are characterized in the subclaims.

The invention is characterized in that the measurement of the actual closing and opening times of the control valve, in

Depending on the voltage applied to the control valve (u (t)) and / or the applied current (i (t)), is carried out within the time interval in which the pressure in the control valve largely corresponds to the pressure of the low pressure range. As a result, the very strong pressure surges caused by the hydraulics, which occur when the valve needle is closed or opened quickly, can be avoided. This has a positive effect on the closing and opening behavior of the valve needle. In particular, a sputtering valve needle stroke caused by the pressure surges is avoided, as a result of which the closing or opening times of the control valve can be determined more precisely.

An advantageous embodiment of the invention provides for the measurement of the time for moving the valve needle, from one end position to the other end position, on the running engine, within the time span within which the camshaft relates to the pump piston of the injection nozzle or to the corresponding one Transmission links, located within their base circle. During this time, the pump piston of the pump unit remains in its upper end position, the pressure in the control valve thus approximately corresponds to the pressure in the low-pressure fuel range.

A further advantageous embodiment of the invention provides for measuring the time period for moving the valve needle from one end position to the other end position with the camshaft stationary (engine off). In this case, the pump piston does not perform a stroke and it is ensured that moving the valve needle does not lead to pressure surges within the control valve.

The invention is explained in more detail below with reference to the drawings. 1 shows a schematic illustration of a PPE; FIG. 2 shows a piezo control unit for the PPE shown in FIG. 1; Figure 3 is a schematic representation of the camshaft and the rocker arm for actuating the pump piston of the PPE;

Figure 4 is a graph illustrating the course of the piezo voltage (u (t)), the piezo current (i (t)) and the valve needle stroke (h (t)) for a closing process of the control valve; 5 shows a further graph showing the course of the piezo voltage (u (t)), the piezo current (i (t)), the valve needle stroke (h (t)) and the piezo charge (g (t)), in particular for an opening process of the Control valve, illustrated; Figure 6 is a schematic representation of a flow chart for controlling the closing time of a control valve.

Figure 1 shows schematically a PPE. The PPE shown is used to supply fuel into the combustion chamber of an internal combustion engine. The PPE has a pump unit 1 which is used to build up the injection pressure. The compressed fuel is injected into the combustion chamber of the internal combustion engine via an injection nozzle 10. Furthermore, the PPE has a piezo control unit 20 with a control valve 21 and an externally controllable actuation unit 22. The actuation unit 22 is designed as a piezoelectric actuator and is connected to the control unit 40, which contains an evaluation unit 41 and a control unit 42. The pump unit 1, the injection nozzle 10 and the piezo control unit 20 preferably form a unit.

The pump unit 1 is driven directly or as shown via a rocker arm 3 by the camshaft 2. The pump chamber 5 is connected to the control valve via a bypass bore 30. til 21, the piezo control unit 20 connected. When the control valve 21 is open, a free flow between the low-pressure fuel region 31 and the pump chamber 5 is ensured. In the suction stroke of the pump piston 4, fuel can be drawn into the pump chamber 5 from the low pressure region 31, through the control valve 21 and the bypass bore 30. If the control valve 21 remains open, the fuel is pressed back into the low-pressure fuel part 31 during the subsequent delivery stroke of the pump piston 4 without the fuel being compressed.

If the control valve 21, before or during the delivery stroke of the pump piston 4, is closed via the externally controllable actuating unit 22, the fuel in the pump chamber 5 is compressed. If the pressure in the pump chamber 5 exceeds the opening pressure of the injection nozzle 10, the injection nozzle opens and fuel becomes available injected into the combustion chamber of the internal combustion engine.

FIG. 2 shows a schematic representation of a section through a piezo control unit 20 which can be used with a PPE according to FIG. 1. The piezo control unit

20 has a valve needle 50 which can be moved between a first and a second end position. In the first end position 64 of the valve needle 50, indicated by the dashed lines, the control valve 21 is completely open and there is a connection between the low-pressure fuel area 31 and the high-pressure fuel area 52. In the second end position 65, this is shown by the solid lines, is the control valve

21 completely closed. The valve needle 50 is located in the valve seat 51 on the housing side and separates the low-pressure fuel area 31 from the high-pressure fuel area 52. which is connected to the pump chamber 5 via the bypass bore 30.

The first end position can also be the position at which the control valve 21 is completely closed. The second end position then corresponds to the position in which the control valve 21 is fully open. The measurement of the closing or opening time of the control valve 21 then takes place analogously to the description in the exemplary embodiments. The valve needle 50 is actuated via a piezo actuator 55. If the piezo actuator 55 is charged electrically, it expands and transmits a force to the pressure piece 57 via the end face 56. The pressure piece 57 stands with a first lever 58 and a second lever 59 in contact. The force that is transmitted from the piezo actuator 55 to the pressure piece 57 is amplified via the levers 58 and 59 and transmitted to a first axial end surface 70 of the valve needle 50. If the force generated by the piezo actuator 55, transmitted via the pressure piece 57 and amplified by the levers 58 and 59, is greater than a counterforce which is exerted by a spring 71, via a spring end piece 72, on a second axial end face 73 of the valve needle 50 is transmitted, the valve needle 50 is pressed into the valve seat 51. The low-pressure fuel region 31 is connected to the control chamber 60, which is connected to the actuator chamber 62 via a compensating bore 61. The actuator chamber 62 is in turn connected to the return 63, via which the fuel can flow from the actuator chamber 60 back into the low-pressure fuel region 31.

FIG. 3 shows a schematic illustration of an exemplary embodiment for actuating the PPE according to FIG. 1. The pump piston 4 is actuated via the camshaft 2 of an internal combustion engine. With each revolution of the camshaft 2, the cam 81 of the camshaft 2 actuates a rocker arm 82. The rocker arm 82 transmits and amplifies due to its

Leverage the force from the camshaft 2 to a transmission member 83 which in turn is in contact with the pump piston 4. Depending on the position of the cam 81 relative to the rocker arm 82, the pump piston 4 is in a suction stroke, a delivery stroke, or it remains in its upper starting position between the end of the suction stroke and the beginning of the delivery stroke. The pump piston 4 carries out a delivery stroke as long as the contact point 84, between the rocker arm 82 and the camshaft 2, is in the area of the cam start AN. If the contact point 84 is in the area of the cam run AB, the pump piston 4 performs a suction stroke. During the time interval in which the contact point 84 lies in the area of the base circle G, the pump piston 4 remains in its upper starting position. In this time interval, the pressure between the high-pressure fuel area and the low-pressure fuel area is equalized and the valve needle 50 can be moved back and forth between the two end positions without pressure surges being generated in the process. The time interval is therefore particularly well suited for measuring the closing and opening times of the control valve 21.

FIG. 4 shows a graph which illustrates the course of the piezo voltage (u (t)), the piezo current (i (t)) and the valve needle stroke (h (t)) for a closing process of the control valve 21. At the time t _S oN, an actuating signal is set, for example in the form of a normalization pulse SON, which gives the command to close the control valve 21. The valve needle 50 moves between the time t _S0N and the time t _c from the first end position 64 to the second end position 65. The time interval between t _S0N and t _c thus corresponds exactly to the length of time that the control valve 21, from the control _command to complete closing required. When reaching the second end position 65, at time t _c , is determined by the

Impact of the valve needle 50, in the valve seat 51, suddenly generates a counterforce. The counterforce is passed on to the piezo actuator 55 by the mechanical coupling of the valve needle 50, via the levers 58 and 59 and the pressure piece 57, and has the effect that charge carriers are induced which appear as discontinuities in the course of the piezo voltage (u (t ) ) to make noticable. The discontinuity in the voltage curve can be determined particularly easily via the time derivative of the piezo voltage (u '(t)). An electrical circuit which includes a differentiator with a subsequent threshold value detection is suitable for detecting the discontinuity in the voltage curve.

Figure 5 shows a graph showing the course of the piezo voltage (u (t)), the piezo current (i (t)) and the valve needle stroke (h (t)) and the piezo charge (q (t)), in particular for an opening process of the Control valve 21 illustrates. At time t _E 0N, an actuating signal is set, for example in the form of a normalization pulse EON, which gives the command to open control valve 21. The valve needle 50 moves between the times t _E oN and the time t ₀ from the second end position 65 to the first end position 64. The time interval between t _E0 N and t ₀ thus corresponds exactly to the time that the control valve 21 receives from the control command needed until fully opened. During the opening process, the piezo actuator 55 is discharged and moves very quickly back to its starting position defined for the opening state. The valve needle ^'50 and with it coupled mechanical components can DEM piezo actuator 55 is not follow-positively and meet as a result of the already present in its initial position piezo actuator 55. The impact induces a charge in the piezo actuator 55 as a pulse in the voltage and / or current curve. The discontinuity can be determined in a simple manner, for example by a simple threshold value detection.

FIG. 6 shows a schematic illustration of a flow chart for regulating the closing time of the control valve 21. The regulating device includes the sensor 90, the control unit 40, which has an evaluation unit 41 and a control unit 42, and the actuation unit 22. The entire program flow for regulating the valve closing time and the

Setpoints are stored in control unit 40. The evaluation of the variables recorded during the program run takes place in the evaluation unit 41. The control unit 42 generates the necessary control signals for moving the valve needle 50. The intervals in which the closing time measurements are to be carried out can, for example, at once, at the beginning of a new operating cycle will set.

As soon as the program for regulating the valve closing time starts, a measurement is first carried out in a first step SO, which determines whether the camshaft 2 is stationary or whether it is rotating. When the camshaft 2 is stationary, the pressure in the control valve 21 and in the injector 10, regardless of the camshaft position and the position of the pump piston 4, largely corresponds to the pressure of the low-pressure fuel region 31 and the closing process of the control valve 21 can, as described later from step S3a, be performed.

If the camshaft 2 rotates, the sensor 90 first determines in a step S1 in which position P _IST the camshaft 2 is currently. For example, a camshaft speed sensor can be used as sensor 90 for this purpose. Alternatively, a position sensor can also be used. In a step S2, the current position P _IST with a stored position P _START compared. In the PSTART position, the camshaft 2 is located within its base circle G with respect to the pump piston 4, preferably in the vicinity of the cam outlet AB. At this point in time, the pump piston 4 is in its upper starting position and the pressure in the control valve 21 and in the injection nozzle 10 largely corresponds to the pressure of the low-pressure fuel region 31. If P _{IST is} equal to P _START , the measurement of the valve _{closing time} begins. The closing process of the control valve 21 is initiated in step S3a, in which a normalization pulse SON is set, by which the actuating unit 22 is controlled. The time tso_./ of the control is stored in step S3b, and the piezo actuator 55 is activated in step S3c and / or S3X, with the piezo voltage UPIE _ZO and / or the piezo current i _P ι _E - zo or the control _energy E _PIEZ0 applied. A charge is thereby generated in the piezo actuator 55, as a result of which the piezo actuator 55 expands. The expansion of the piezo actuator 55 causes the valve needle 50 to begin moving from its first end position 64 to its second end position 65.

If the valve needle 50 hits the valve seat 51, a force is transmitted to the piezo actuator 55 by the mechanical coupling of the valve needle 50 to the piezo actuator 55. The sudden action of force on the piezo actuator 55 when the valve needle 50 strikes the valve seat 51 has the effect that a charge is suddenly induced in the piezo actuator 55 that is proportional to the force acting. Since the force is proportional to the piezo voltage u _P ι _EZ o and proportional to the integral of the piezo current | ip _IEZO , an abrupt change in the charge, which is equivalent to reaching the valve needle in the valve seat, can be done directly on the basis of the derivative of the piezo voltage u 'PIEZO and / or the piezo current i _P ι__ _Z o can be recognized. For this purpose, during the closing process of the control valve 21, in a step S4, the derivation of the piezo voltage u ' _P ι _{EZ0 is} formed and in a step S5 or S5' the curve of the derived piezo voltage u ' _P ι _EZ o or the curve of the piezo current i _P ι _EZ0 with a threshold value u Compare _SC HWEL or iscHWEL. If the derived voltage U ' _PΪ EZO or the current i _P ι _EZ o exceeds the corresponding threshold values u' SCHWELL / or isc _HEL , the program recognizes that the control valve 21 is closed. The time t _c at which the threshold value is exceeded and which corresponds to the closing time of the control valve 21 is recorded and stored in a further step S6. In a step S7, the ACTUAL closing time t _v _ιsτ is calculated from the subtraction of the control time t _S0N from the closing time t _c . And from the ACTUAL closing time t _v _ιsτ and a predetermined target closing time t _v _so _LL , the closing time difference Δt is calculated in a further step S8 by subtracting the actual closing time tv_ιsτ from the target closing time t _v _soLL. From the closing time difference Δt _v , it can then be determined in a further step S9 whether the piezo voltage u _P ι _EZ0 and / or the piezo current i _P ι _EZ0 or the control _energy E _PIEZ0 with which the piezo actuator 55 has been applied is too high or is selected too low. If Δt _v > 0, the actual closing time t _v _ιsτ is shorter than the desired closing time t _v _soLL, ie the piezo voltage u _P ι _EZ0 and / or the piezo current i _P iEzo or the control energy E _PIEZ0 are too high and become too high one last

Step SlO decreased. If Δt _v <0, the actual closing time t _v _ιsτ is greater than the desired closing time t _v _so _LL, ie the piezo voltage u _P ι _E zo and / or the piezo current ipι _EZ o or the control _energy E _P ι _EZ0 are too low and SlO are increased in a last step. With the readjustment of the piezo voltage u _PIEZ0 and / or the piezo current i _P ι _EZ0 or the control _energy E _PIEZ0 , the program run ended and the valve closing time can be measured again.

Claims

claims

1. A method for measuring a period of time that the valve needle (50) of a control valve (21) of a piezo-pump-nozzle unit, taking into account the response time of the control valve (21) to from a first end position (64) to a second End position (65) to arrive at

the time duration is determined as a function of the voltage (u (t)) applied to the control valve (21) and / or the applied current (i (t)),

- An actuating signal is generated for moving the control valve (21) from the first (64) to the second end position (65) and

- The control signal is generated at a time at which it is ensured that the pressure in the control valve (21) and in the injection nozzle (10) largely corresponds to the pressure of the low-pressure fuel region (31) during the measurement.

2. The method according to claim 1, characterized in that the measurement of the duration of the running engine takes place within the period in which the camshaft (2) based on the pump piston (4) of the injection nozzle (10) or the corresponding transmission elements within their base circle ( G) is located.

3. The method according to any one of the preceding claims, that the measurement of the time is carried out with the camshaft (2) stationary.

4. The method according to any one of the preceding claims, characterized in that reaching the first (64) or second end position

(65) based on at least one discontinuity in the course of the

Voltage (u (t)) and / or the current (i (t)) is detected.

5. The method according to any one of the preceding claims, characterized in that the detection of the first or second end position (64), (65) on the basis of at least one pulse in the course of the voltage (u (t)) and / or the current (i (t)) takes place.

6. Device for measuring a period of time that the valve needle (50) of a control valve (21) of a piezo-pump-nozzle unit takes into account, taking into account the response time of the control valve (21), from a first end position (64) to a second To reach the end position (65), the device comprising a control unit (40) with the following components:

- an evaluation unit (41) which determines the duration as a function of the voltage (u (t)) applied to the control valve (21) and / or the applied current (i (t)),

- And a control unit (42), which generates the control signal, for moving the control valve (21) from the first end position (64) to the second end position (65) and generates the control signal at a time in which it is ensured that the pressure in the control valve (21) and in the injection nozzle (10) largely corresponds to the pressure of the low-pressure fuel region (31) during the measurement.

7. The device according to claim 6, characterized in that that the evaluation unit (41) includes a circuit u, which is evaluated by evaluating the voltage (u (t)) and / or the current

(i (t)) the detection of at least one discontinuity or a pulse in the course of the voltage (u (t)) and / or the

Current (i (t)) includes.