Device and method for determining the start of injection in a direct-injection internal combustion engine

Information

  • Patent Grant
  • 6553819
  • Patent Number
    6,553,819
  • Date Filed
    Tuesday, December 22, 1998
    25 years ago
  • Date Issued
    Tuesday, April 29, 2003
    21 years ago
Abstract
A device for determining a start of injection in a direct-injection internal combustion engine has a magnetoelastic pressure sensor disposed in an injection line leading to an injection valve which detects pressure changes in the injection line owing to an injection process of the injection valve by utilizing the magnetoelastic effect. The device also has an evaluation device that determines a dead time between an initiation of the injection process and the start of injection with the aid of the measurement signal of this magnetoelastic pressure sensor.
Description




BACKGROUND OF THE INVENTION




Field of the Invention




The invention relates to a device for determining the start of injection in a direct-injection internal combustion engine. It is important in a direct-injection internal combustion engine to know the exact start of injection in order to be able to make an optimum setting of the injection profile and thus also of the combustion behavior.




This holds, in particular, for the injection systems known under the designation of common rail systems in diesel engines and under the designation of high-pressure direct-injection systems in spark-ignition engines. In such systems a high-pressure pump is used to convey fuel from a fuel reservoir into a high-pressure accumulator via which the fuel is then present at injection valves which are disposed in the combustion chambers of the internal combustion engine. The processes of injecting into the combustion chambers of the internal combustion engine are initiated by applying current to the injection valves, the start of injection into the combustion chambers depends on the response delay of the injection valves and on the pressure present at the injection valves.




Various methods are already known in the prior art for determining the exact start of injection into the combustion chambers of the internal combustion engine after current has been applied to the injection valves, and in order to be able thereby to make an optimum setting of the injection profile and/or combustion profile in the combustion chamber. Thus, it has been proposed to fix the exact start of injection in accordance with the respective operating conditions of the internal combustion engine with the aid of a characteristic diagram stored in the control unit of the internal combustion engine. However, in this case it is necessary in advance for the characteristic diagram data to be determined either by simulation calculation or by experiment, something that is very expensive since it has to be performed separately for each type of injection system. Even after the characteristic diagram data have been matched to the respective type of injection system, strong deviations still frequently occur between the start of injection as determined from the characteristic diagram data and the actual start of injection into the combustion chamber. It is also the case in the prior art that pickups, which directly scan the stroking of the nozzle needle in the injection valve in order to avoid these disadvantages of an evaluation based on characteristic diagram data, are already known. However, these pickups are relatively complicated and expensive, since they have to be installed directly into the injection valves.




SUMMARY OF THE INVENTION




It is accordingly an object of the invention to provide a device and method for determining the start of injection in a direct-injection internal combustion engine which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which is distinguished by simple construction and high reliability and measuring accuracy.




With the foregoing and other objects in view there is provided, in accordance with the invention, in combination with a direct-injected internal combustion engine having an injection valve and an injection line connected to the injection valve, a device for determining a start of injection in the direct-injection internal combustion engine, including: a magnetoelastic pressure sensor disposed on the injection line connected to the injection valve, the magnetoelastic pressure sensor detecting a magnetoelastic effect caused by a pressure change in the injection line owing to an injection process of the injection valve and outputting a measurement signal for determining the start of injection.




The device according to the invention essentially has a pressure sensor which is disposed directly at the injection line to the injection valve and uses the magnetoelastic effect to detect the pressure change triggered by the injection process in the injection line. The measurement signal of the pressure sensor which indicates such a pressure change is temporally correlated in an evaluation unit for the purpose of initiating the injection process, in order to determine a dead time between the initiation of the injection process and the start of injection. The device according to the invention is distinguished by a simple and cost effective configuration which, in addition, can easily be integrated in any type of injection system. Furthermore, determining the start of injection requires only very simple detection and evaluation of the measured values.




It is advantageous, in particular, for the magnetoelastic pressure sensor to be constructed as a coil which is made from a ferromagnetic material and is wound around the injection line. The pressure sensor construction is particularly simple, robust and cost effective.




In accordance with an added feature of the invention, there is an evaluation device receiving and temporally correlating the measurement signal of the magnetoelastic pressure sensor with a drive signal output to the injection valve for initiating the injection process to determine a dead time between an initiation of the injection process and the start of injection.




In accordance with an additional feature of the invention, the magnetoelastic pressure sensor is formed of a ferromagnetic material.




In accordance with another feature of the invention, the magnetoelastic pressure sensor is formed of a nickel-iron alloy with a nickel component of 80%.




In accordance with a further added feature of the invention, the magnetoelastic pressure sensor has a coil wound around the injection line to detect a voltage induced by the pressure change in the injection line.




In accordance with a further additional feature of the invention, the magnetoelastic pressure sensor has a transformer with two coils detecting a voltage induced by the pressure change in the injection line.




In accordance with yet another feature of the invention, the evaluation device corrects an interference component generated by the drive signal of the injection valve in the measurement signal of the magnetoelastic pressure sensor resulting in a corrected measurement signal.




In accordance with another added feature of the invention, the evaluation device determines the measurement signal of the magnetoelastic pressure sensor by deriving a difference between an initial measurement signal and a signal picked up by the magnetoelastic pressure sensor in a time period between the drive signal of the injection valve and an instant of the start of injection that is yielded by a response delay of the injection valve.




In accordance with another additional feature of the invention, the evaluation unit compares an absolute value of the corrected measurement signal with a threshold value to determine the start of injection of the injection valve in an event of overshooting of the threshold value.




In accordance with a concomitant feature of the invention, the evaluation device indicates the start of injection of the injection valve only if an absolute value of a predetermined sequential number of sample points of the measurement signal overshoot the threshold value.




Other features which are considered as characteristic for the invention are set forth in the appended claims.




Although the invention is illustrated and described herein as embodied in a device and method for determining the start of injection in a direct-injection internal combustion engine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.











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




BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a diagrammatic block diagram of an injection system for an internal combustion engine having a device according to the invention;





FIGS. 2



a


-


2




d


are graphs of signal profiles during an injection process;





FIGS. 3



a


-


3




b


are graphs of interference signal compensations; and





FIG. 4

is a graph of dead times determined between a start of driving and a start of injection in an internal combustion engine.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to

FIG. 1

thereof, there is shown a fuel injection system for a direct-injection internal combustion engine, as it is used under the designation of a common rail system, above all in diesel engines. In the case of this injection system, fuel is sucked in from a fuel reservoir


10


via a fuel line


11


by a presupply pump


12


. The presupply pump


12


supplies the fuel via a fuel filter


13


to a high-pressure pump


15


which compresses the fuel and feeds it under high pressure into a high-pressure accumulator


17


.




In order to be able to set a volumetric flow of the high-pressure pump


15


into the high-pressure accumulator


17


as required in accordance with the respective operating conditions of the internal combustion engine, there is disposed in the fuel line


11


between the presupply pump


12


and the high-pressure pump


15


an additional suction throttling valve


14


with the aid of which a supply current to the high-pressure pump


15


can be regulated. The suction throttling valve


14


is addressed by a control unit


19


via a control line


22


.




In order to be able to set the pressure in the high-pressure accumulator


17


in accordance with the desired operating conditions of the internal combustion engine, a pressure regulating valve


16


is further connected into the fuel line


11


downstream of the high-pressure pump


15


. Via a fuel line


25


, the pressure regulating valve


16


directs superfluous fuel which is not required to maintain a desired pressure in the high-pressure accumulator


17


away into the fuel reservoir


10


, the retaining pressure of the pressure regulating valve


16


being set by the control unit


19


via a control line


24


. Furthermore, a pressure sensor


23


is provided for regulating the pressure in the high-pressure accumulator


17


. The pressure sensor


23


serves to detect the pressure prevailing instantaneously in the high-pressure accumulator


17


, on the basis of which the control unit


19


undertakes to regulate the pressure via the pressure regulating valve


16


in accordance with the desired operating conditions of the internal combustion engine.




Fuel pressures of 0 to 150 MPa can be produced in the high-pressure accumulator


17


with the aid of the pressure regulating devices represented. The fuel pressures are available via fuel injection lines


27


at injection valves


18


(only one being shown), which are disposed in the combustion chambers of the internal combustion engine (not shown). The injection valves


18


generally have an injection nozzle that is closed by a needle subjected to a spring force. The needle can be raised against the spring force by a needle stroke generator, which is actuated piezoelectrically, for example, in order in this way to open the injection valve and thus permit the fuel present at the injection valve to be injected into the combustion chamber of the internal combustion engine. The injection process is initiated by the control unit


19


, which is connected to the injection valves via control lines


26


. The leakage fuel further occurring in the injection valves


18


is led back into the fuel reservoir


10


via fuel lines


21


.




In order to be able to set the injection profile, and thus the combustion profile, in the combustion chamber of the internal combustion engine in an optimum fashion, it is important to know the exact start of injection of the fuel into the combustion chamber. The start of injection depends, on the one hand, on the response delay of the needle stroke generator in the injection valve or of the needle in the injection nozzle. Furthermore, the delay time between the driving of the injection valve and the start of injection rises with increasing fuel pressure in the high-pressure accumulator


17


and the fuel injection line


27


. The needle stroke generator must then open the needle in the injection nozzle against a higher pressure, and this lengthens the injection process and thus the dead time between driving and the start of injection.




In order to be able to determine exactly the dead time between the triggering of the injection valve


18


and the start of injection, and thus to permit optimization of the engine management, in accordance with the invention a pickup


30


is disposed in the fuel injection line


27


upstream of the injection valve


18


. As

FIG. 1

shows, the pickup


30


has a coil


29


that is wound around the injection line


27


and preferably has approximately 1000 turns. The coil


29


consists of a material that exhibits a magnetoelastic effect. Such materials are principally ferromagnets in which a mechanical stress, for example a pressure change, influences the permeability, there being an approximately linear relationship between the change in the permeability and the mechanical stress. Nickel-iron alloys are particularly suitable in this case, the nickel component preferably being 80%. Permeability changes of approximately 40% are achieved with such nickel-iron alloys in conjunction with mechanical stresses of 100 N/mm


2


. This change in permeability occurring in the case of ferromagnetic materials can be measured, for example, with the aid of a transformer-type configuration in which the mutual inductance of the two windings is influenced. However, it is also possible to detect the induced voltage by only one coil on the basis of the natural premagnetization of the ferromagnetic materials, as is carried out in the case of the pickup


30


in FIG.


1


. The use of only one coil permits a simple, robust and also cost effective pickup


30


, which also can easily be adapted to the respective spatial conditions in the direct-injection internal combustion engine.




The voltage induced in the coil


29


of the pickup


30


can be expressed by the following equation:










u
ind

=




3
/
8







λ
p



J
2


H



(


2


κ
u


+


3
/
8







λ
p


p


)

2



nAp





(
1
)













where λ


p


and κ


u


are constants which depend on the material used in the coil and reproduce the relative change in length between a completely non-magnetized or saturated state, and the anisotropy constant. J corresponds to the magnetic polarization of the material used, and n and A stand for the number of turns and the cross-sectional surface of the coil, respectively. H reproduces the magnetic field strength of the premagnetization that is produced by the natural premagnetization of the material used for the coil. However, as an alternative it is also possible to configure the pressure sensor in a way similar to a transformer with two windings, the second winding ensuring the premagnetization. Such a configuration would increase the sensitivity of the pickup


30


. Equation (1) further shows that the voltage u


ind


induced in the coil is a linear function of the temporal change in the pressure on the assumption of a stationary pressure operating point, that is to say p˜const.




When the control unit


19


addresses the injection valve


18


via a drive line


26


for initiating an injection process, the needle stroke generator opens the injection nozzle by raising the needle against the spring bias, and the fuel present via the injection line


27


is injected into the combustion chamber of the internal combustion engine. The start of injection of the fuel into the combustion chamber leads, however, to a pressure drop in the injection line


27


. In accordance with equation (1), the pressure drop induces a voltage in the coil


29


of the pickup


30


. The induced voltage is amplified via an amplifier


31


integrated in the pickup


30


, and applied on a measuring line


32


as a signal to the control unit


19


. The control unit


19


correlates the measurement signal of the pickup


30


with the,drive signal for the injection valve


18


, and can then determine the dead time between the start of driving and start of injection therefrom. However, instead of undertaking the evaluation in the control unit


19


of the internal combustion engine, it is also possible as an alternative to provide an independent evaluation unit which detects the measurement signal of the pickup


30


and the drive signal for the injection valve


18


, and calculates the dead time therefrom.





FIGS. 2



a


-


2




d


show the signal profile of an injection process with a piezoelectrically controlled injection valve.

FIG. 2



a


represents the drive voltage u(t), and

FIG. 2



b


represents the drive current i(t) of the piezoelectric injection valve.

FIG. 2



d


reproduces the voltage u


i


(t) induced in the coil


29


. Furthermore,

FIG. 2



c


shows the signal profile of a reference pressure sensor that has additionally been disposed in an experimental setup on the injection line


27


near the pickup


30


. This reference pressure sensor has been attached at the end of a spur line approximately 5 mm long, which has been branched off from the injection line


27


at a distance of approximately 2 cm upstream of the coil


29


. The signal profiles shown in

FIGS. 2



a


-


2




d


were sampled using a frequency of 2.5 MHz. The pressure in the high-pressure accumulator


17


was 100 MPa during the measurement process.





FIGS. 2



a


and


2




b


show the build up of the charge in the piezoelectric crystal of the injection valve at the start of driving by the control unit


19


at the positive current peak, and the degradation of the charge at the end of the drive by the negative current peak. The reference pressure sensor shows in

FIG. 2



c


the start of the pressure drop in the injection line


27


and thus the start of the injection into the combustion chamber via the injection valve approximately 150 μsec after the start of the drive shown in

FIGS. 2



a


and


2




b


. Finally, in

FIG. 2



c


the pressure drop in the signal of the reference pressure sensor is followed by decaying pressure fluctuations which are caused by the opening of the needle in the injection nozzle of the injection valve after the injection process on the injection line.




In addition to the induced voltage caused by the pressure change in the injection line


27


, the measurement signal, shown in

FIG. 2



d


, of the voltage induced in the coil


29


has an interference component which is produced by parasitics of the drive current for the injection valve. The voltage u


i


(t) induced in the coil


29


of the pickup


30


can therefore be represented by the following equation:








u




i


(


t


)=


u




i1


(


t


)+


u




i2


(


t


)  (2)






where u


i1


(t) reproduces the pressure change in the injection line, and u


i2


(t) the interference component of the drive signal.




In order to be able to carry out a reliable determination of the start of injection with the aid of the pickup


30


, it is therefore advantageous to separate the interference component from the signal shown in

FIG. 2



d


. Such a compensation of interference can be carried out as follows in accordance with a preferred embodiment of the invention: assuming that the parasitic of the drive current for the injection valve can be represented as an interference system S with a transfer function of G


St


(s), the interference component u


i2


(t) can be represented as a convolution of an impulse response g


St


(t) of the interference system S with a drive current i(t) in accordance with the equation








u




i2


(


t


)=


g




St


(


t


)*


i


(


t


)  (3)






In a known transfer function G


St


(s), the result for the voltage caused by the pressure change in the injection line is thus








u




i1


(


t


)=


u




i


(


t


)−


g




St


(


t


)*


i


(


t


)  (4).






Since the transfer function G


St


(s) is in general not known, the interference system S must be estimated. The following approach is suggested in this case: the transfer function can be determined by an identification algorithm for a time range in which the measured induced voltage u


i


(t) in the coil


29


is determined only by the interference component u


i2


(t) of the drive current, that is to say there are no pressure changes in the injection line


26


which cause voltage to be induced in the coil


29


. This is the case during the minimum dead time t


T,min


of the piezoelectric injection valve which arises as a result of the valve-specific response delay between starting to drive the valve at t


0


and the opening of the injection valve. The following equation holds for this:








t




1,min




=t




0




+t




T,min


  (5)






During the valve-specific minimum dead time, the interference system S can be identified and the time-discrete transfer function can be modulated with the aid of an autorecursive formulation and be identified from the drive current i(t) of the injection valve and the induced voltage u


i


(t) in the coil


29


in the time range [t


0


, t


1,min


].

FIGS. 3



a


and


3




b


show the result of this processing method,

FIG. 3



a


reproducing the induced voltage u


i


(t) as a noisy signal, and the reconstructed interference component u


i2


(t) as a smooth curve.

FIG. 3



b


shows the difference between the two signals and thus represents the voltage u


i1


(t) induced owing to the pressure change in the coil


29


, that is to say the actual useful information.




The interference signal compensation is preferably performed directly in the control unit


19


. The control unit


19


then determines the start of injection t


1


into the combustion chamber from the interference-signal-compensated voltage signal. As

FIG. 3



b


shows, the start of injection, which coincides with a pressure drop in the injection line


27


, causes a negative voltage in the interference-signal-compensated voltage profile of the coil


29


. In order to determine the start of injection, the control unit


19


compares the voltage profile, as compensated for interference signal, with a lower threshold value u


i,s


and displays the start of injection as soon as the voltage undershoots the threshold value.




Since, as represented in

FIGS. 3



a


-


3




b


, the voltage profile as compensated for interference signal is also overlaid by noise, there is the risk that the threshold value will already be undershot before the actual start of injection. In order to prevent the start of injection from being erroneously indicated in this case, the control unit


19


evaluates an undershooting of the threshold value at a specific sampling instant only when the threshold value is also undershot at a specific number of sampling instants following thereupon. It is also possible, as an alternative, to provide a low-pass filter in the pickup


30


or in the control unit


19


, by which transient radio-frequency noise components can be filtered out of the signal.




After establishing the start of injection t


1


, the control unit


19


determines the exact dead time of the injection valve by temporal correlation with the start of driving t


0


of the injection valve.

FIG. 4

represents the dead time t


T


for various fuel pressures in the high-pressure accumulator


17


. It is to be seen in this case that the dead time rises in the case of higher pressures, since the needle in the piezoelectric injection valve must be opened against higher pressures.




In accordance with the invention, it is therefore possible for the exact instant of injection into the combustion chamber of the internal combustion engine to be determined in a simple and reliable way by detecting a magnetoelastic effect which is caused-by a pressure change in the injection line owing to an injection process of the injection valve. The magnetoelastic pressure sensor in this case preferably includes a coil wound around the injection line, and thereby permits a simple, robust and cost effective measurement setup.



Claims
  • 1. In combination with a direct-injected internal combustion engine having an injection valve and an injection line connected to the injection valve, a device for determining a start of injection of a fuel in the direct-injection internal combustion engine, comprising:a pickup disposed on the injection line connected to the injection valve, said pickup detecting a magnetoelastic effect in the fuel caused by a pressure change in the injection line due to an injection process of the injection valve and outputting a measurement signal for determining the start of injection.
  • 2. The device according to claim 1, including an evaluation device receiving and temporally correlating said measurement signal of said pickup with a drive signal output to the injection valve for initiating the injection process to determine a dead time between an initiation of the injection process and the start of injection.
  • 3. The device according to claim 2, wherein said evaluation device corrects an interference component generated by the drive signal of the injection valve in the measurement signal of said pickup resulting in a corrected measurement signal.
  • 4. The device according to claim 3, wherein said evaluation device determines the measurement signal of said pickup by deriving a difference between an initial measurement signal and a signal picked up by said pickup in a time period between the drive signal of the injection valve and an instant of the start of injection that is yielded by a response delay of the injection valve.
  • 5. The device according to claim 3, wherein said evaluation unit compares an absolute value of said corrected measurement signal with a threshold value to determine the start of injection of the injection valve in an event of overshooting of the threshold value.
  • 6. The device according to claim 5, wherein said evaluation device indicates the start of injection of the injection valve only if an absolute value of a predetermined sequential number of sample points of the measurement signal overshoot the threshold value.
  • 7. The device according to claim 1, wherein said pickup is formed of a ferromagnetic material.
  • 8. The device according to claim 1, wherein said pickup is formed of a nickel-iron alloy with a nickel component of 80%.
  • 9. The device according to claim 1, wherein said pickup has a coil wound around the injection line to detect a voltage induced by the pressure change in the injection line.
  • 10. A method for determining a start of injection of a fuel in a direct-injection internal combustion engine, which comprises:a providing a pickup having a coil; placing the coil on an injection line connected to an injection valve; detecting with the coil a magnetoelastic effect in the fuel caused by a pressure change in the injection line due to an injection process of the injection valve; and outputting a measurement signal for determining a start of injection when a change in voltage in the coil has been detected.
  • 11. The method according to claim 10, which comprises:transmitting a drive signal from a control unit to the injection valve, the drive signal initiating the injection process: timing the drive signal; and temporally correlating the measurement signal of the pickup with the drive signal to determine a dead time between an initiation of the injection process and the start of injection with an evaluation device receiving the measurement signal.
  • 12. The method according to claim 10, which comprises forming the pickup from a ferromagnetic material.
  • 13. The method according to claim 10, which comprises forming the pickup from a nickel-iron alloy with a nickel component of 80%.
  • 14. The method according to claim 11, which comprises correcting with the evaluating device an interference component generated by the drive signal of the injection valve in the measurement signal of the pickup resulting in a corrected measurement signal.
  • 15. The method according to claim 14, which comprises determining with the evaluating device the measurement signal of the pickup by deriving a difference between an initial measurement signal and a signal picked up by the pickup in a time period between the drive signal of the injection valve and an instant of the start of injection that is yielded by a response delay of the injection valve.
  • 16. The method according to claim 14, which comprises comparing in the evaluating device an absolute value of the corrected measurement signal with a threshold value to determine the start of injection of the injection valve in an event of overshooting of the threshold value.
  • 17. The method according to claim 16, which comprises indicating with the evaluating device the start of injection of the injection valve only if an absolute value of a predetermined, sequential number of sample points of the measurement signal overshoot the threshold value.
  • 18. The method according to claim 10, which comprisesnot placing a second coil around the injection line; measuring a premagnetization of a second coil; forming a transformer from said first coil and said second coil; detecting a change in voltage in the first coil by comparing the voltage in the second coil.
  • 19. In combination with a direct-injected internal combustion engine having an injection valve and an injection line connected to the injection valve, a device for determining a start of injection of a fuel in the direct-injection internal combustion engine, comprising:a pickup disposed on the injection line connected to the injection valve, said pickup detecting a magnetoelastic effect in the fuel caused by a pressure change in the injection line due to an injection process of the injection valve and outputting a measurement signal for determining the start of injection, said pickup having a transformer with two coils detecting a voltage induced by the pressure change in the injection line, a first of said coils wound around said injection line to detect a voltage induced by a pressure change in the injection line, a second of said coils not wound around said injection line, said second coil determining a premagnetization of said coils.
Priority Claims (1)
Number Date Country Kind
197 57 293 Dec 1997 DE
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Number Name Date Kind
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4299124 Knapp et al. Nov 1981 A
4462368 Funada Jul 1984 A
4494507 Yasahura Jan 1985 A
4785771 Ibuki et al. Nov 1988 A
4989150 Tazawa Jan 1991 A
5535621 Glidewell et al. Jul 1996 A