GB2472827A - Discharge control strategy for a piezoelectric fuel injector of an i.c. engine - Google Patents
Discharge control strategy for a piezoelectric fuel injector of an i.c. engine Download PDFInfo
- Publication number
- GB2472827A GB2472827A GB0914564A GB0914564A GB2472827A GB 2472827 A GB2472827 A GB 2472827A GB 0914564 A GB0914564 A GB 0914564A GB 0914564 A GB0914564 A GB 0914564A GB 2472827 A GB2472827 A GB 2472827A
- Authority
- GB
- United Kingdom
- Prior art keywords
- discharge
- piezoelectric actuator
- time
- setpoint
- engine
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000000446 fuel Substances 0.000 title claims abstract description 30
- 238000011217 control strategy Methods 0.000 title claims abstract description 15
- 238000002347 injection Methods 0.000 claims abstract description 26
- 239000007924 injection Substances 0.000 claims abstract description 26
- 238000000034 method Methods 0.000 claims abstract description 21
- 238000002485 combustion reaction Methods 0.000 claims abstract description 10
- 238000007599 discharging Methods 0.000 claims description 7
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 claims 1
- 230000006870 function Effects 0.000 description 10
- 230000001419 dependent effect Effects 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 230000032683 aging Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000010417 needlework Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/20—Output circuits, e.g. for controlling currents in command coils
- F02D41/2096—Output circuits, e.g. for controlling currents in command coils for controlling piezoelectric injectors
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/30—Controlling fuel injection
- F02D41/32—Controlling fuel injection of the low pressure type
- F02D41/34—Controlling fuel injection of the low pressure type with means for controlling injection timing or duration
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
- Fuel-Injection Apparatus (AREA)
Abstract
The invention relates a method for controlling a piezoelectric injector for metering fuel inside the cylinder of a combustion engine, wherein the injector comprises an injection needle operated by means of a piezoelectric actuator and wherein a discharge control strategy is applied to the piezoelectric actuator. The method comprises the following steps (i) calculate a discharge time setpoint (Ts) in function of at least an engine operating parameter, (ii) sample, during a fuel injection cycle, the discharge time (Tm) of the piezoelectric actuator, (iii) determine the difference between the discharge setpoint time (Ts) and the sampled discharge time (Tm) and (iv) use the difference between Ts and Tm to generate a correction index to be applied, during the next fuel injection cycle, to the discharge control strategy to discharge the piezoelectric actuator in order to minimize that difference.
Description
1TH0D FOR CONTROLLING THE DISCHARGE OF A PIEZOELECTRIC
INJECTOR
TECHNICAL FIELD
The present invention relates to a method for controlling a piezoelectric fuel injector for an internal combustion engine, in particular by controlling the discharge phase.
BACKGROUND OF THE INVENTION
The fuel injection system of internal combustion engine is provided, for each cylinder, with at least an injector comprising an injection needle allowing for the injection of fuel from a distribution pipe, known as rail, into the cylinder.
The injection needle works as a valve member opening and closing a valve seat.
The movement of the injection needle can be operated by means of a piezoelectric actuator comprising a stack of p�ezoelectric elements whose displacement is proportional to a voltage applied thereto.
Since the piezoelectric stack can be considered as an electric capacitor, the charge stored inside the piezoelectric stack and the voltage upper level reached are proportional to the applied current profile.
Hence to inject a predetermined quantity of fuel into the cylinder a voltage according to a predetermined current profile is applied to the stack of piezoelectric elements.
The applied voltage gives rise to an expansion of the piezoelectric elements which lift up the needle from its seat valve allowing the fuel to be injected into the combustion chamber.
In order to stop the fuel injection, the injector needle must be lift down in the seat valve and so the stack of piezoelectric elements must be discharged by applying a proper discharge current profile. The time between the start of discharge and the fully discharge of the piezoelectric injector, detected as zero voltage across the piezoelectric actuator, is called discharge time, and it's dependent on the charge previously stored inside the stack.
A drawback of piezoelectric actuators is that the charge quantity transferred to the piezoelectric elements, during a charging profile, can vary mainly in function of the aging and of the temperature of the piezoelectric elements. This situation is disclosed in Fig. 1 which shows the variation in the time of a charge transferred to the stack of piezoelectric element, during an injection cycle, where the same current profile has been applied.
In detail, in Fig. 1 three different charge curves are shown as a result of the same applied current profile. As can been noticed the discharge time Ti, T2, T3 for each curve is different.
The result is that for a given current profile the injection needle will be lowered at different values of time Ti, T2, or T3, and a different quantity of fuel will be injected in the combustion chamber.
A wrong injected quantity of fuel has effects on engine emission of polluting substances and on combustion noises.
This is particular relevant in multi-jet diesel i.c. engine where multiple small fuel quantity injection are required.
Aim of the present invention is to solve, or at least to positively reduce, the above mentioned drawbacks with a simple, rational and inexpensive solution.
The aim is attained by the characteristics of the invention as reported in independent claim 1. The dependent claims recite preferred and/or especially advantageous features of the invention.
DISCLOSURE OF THE INVENTION
The invention provides a method for controlling a piezoelectric injector for metering fuel inside the cylinder of a combustion engine, wherein the injector comprises an injection needle operated by means of a piezoelectric actuator and a discharge control strategy is applied to the piezoelectric actuator.
The method comprises the following steps: -to calculate a discharge setpoint time in function of an engine operating parameter, -to sample, during a fuel injection cycle, the discharge time of the piezoelectric actuator, -to determine the difference between the discharge setpoint time and the sampled discharge time, -use the difference between the discharge setpoint time and the sampled discharge time to generate a correction index to be applied, during the next fuel injection cycle, to the discharge control strategy to discharge the piezoelectric actuator.
According to the invention the engine operating parameter used to calculate the discharge setpoint time can be the engine temperature or the fuel pressure measured in the rail.
Alternative discharge control strategies can be used in the method according to the invention. All discharge control strategies provides that a current discharging profile is applied to the piezoelectric actuator.
A first embodiment of the invention provides that the discharge control strategy supplies a discharge current profile to the piezoelectric actuator up to its fully discharge. According to this control strategy the correction index is a correction value which is multiplied for the discharging current of the current discharging profile.
A second embodiment of the invention provides that the discharge control strategy supplies to the piezoelectric actuator a first discharge current profile up to a predetermined threshold value of voltage across the piezoelectric actuator and a second discharge current profile up to the fully discharge of the actuator. In this case the correction index is a correction voltage to be added to a free discharge threshold voltage during discharging of the piezoelectric actuator. The predetermined discharge voltage threshold is a predetermined value of the voltage across the piezoelectric actuator at which the closure (lift down) of the injection needle is guaranteed by shunting to ground the piezoelectric actuator.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of the charge pattern during an injection cycle according to the prior art; Figure 2 is a schematic illustration of a flow chart of the circuit allowing the method according to the invention; Figure 3 is a schematic illustration of the charge curve according to a first embodiment of the invention.
Figure 4 is a schematic illustration of a flow chart of a circuit allowing a second embodiment of the method according to the invention; Fig. 5 is a schematic illustration of the charge pattern according to a second embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Fig. 2 shows a piezoelectric injector 1 comprising an injection needle 2 operated by a piezoelectric actuator 3 which is electrically connected to a control circuit 4.
The control circuit 4 comprises a discharge circuit 5 which is able to apply a discharge control strategy to the piezoelectric actuator 3 in order to fully discharge it.
According to the present embodiment of the invention the discharge control strategy provide a discharge current profile to fully discharge the stack of piezoelectric elements.
The control circuit 4 comprises also a memory module 6 in which, as a map, discharge setpoint times are stored in function of an engine parameter.
The discharge setpoint times are values of time which guarantee the complete discharge of the piezoelectric elements and consequently the lift down of the injector needle in order to stop fuel delivery into the combustion chamber of the cylinder.
As reference engine parameter can be chosen the engine temperature or the fuel pressure measured in the rail.
A sampler circuit 7 is connected to the piezoelectric injector with the function of sampling, during a fuel injection cycle, the discharge time (Tm) of the piezoelectric actuator.
The sampled values of time are sent to an adder 8 with which is also connected the memory module 6 storing the setpoint times. The adder 8 calculates the difference (e) between the discharge setpoint time (Ts) and the sampled discharge time (Tm): e T s -Tm The difference (e) is supplied to a controller 9, for instance a P1 controller, which in function of the above named difference, generates a correction index, which is used as output signal of the controller 9, to correct the applied discharge current profile in the next injection cycle.
In detail, a multiplier 10 multiplies the correction index for the discharge current profile and supplies the corrected discharge current profile to the piezoelectric actuator 3 of the injector.
As illustrated in Fig. 3, thanks to the method of the invention it's possible to control the piezoelectric actuator 3 by controlling the discharge time since the discharge of the piezoelectric actuator 3 takes place within the discharge setpoint time (Ts) independently from the effective charge transferred to the piezoelectric actuator.
A second embodiment of a circuit implementing the method according to the invention is illustrated disclosed in Fig. 4.
In the disclosure of the second embodiment of the invention the components equal to those already disclosed in the first embodiment will be referred to with the same reference signs.
The second embodiment of the invention differs from the above described first embodiment mainly because a different discharge strategy is applied. According to the second embodiment of the invention the discharge strategy provide to supply to the piezoelectric actuator a first discharge current profile up to a predetermined threshold value of voltage across the piezoelectric actuator and a second discharge current profile up to the fully discharge of the actuator.
The discharge voltage threshold is a predetermined calculated value of the voltage across the piezoelectric actuator at the reaching of which the piezoelectric actuator is shunted to ground and completely discharge in few microseconds.
The threshold voltage value is calculated in function of an engine parameter such as the engine temperature or the fuel pressure in the rail.
Fig. 4 shows the piezoelectric injector 1 comprising an injection needle 2 operated by a piezoelectric actuator 3 which is electrically connected to a control circuit 11.
The control circuit 11 comprises a discharge circuit 12 which is able to apply the above disclosed discharge control strategy to the piezoelectric actuator 2 in order to fully discharge it.
The control circuit 11 comprises also the memory module 6, in which, as a table, discharge setpoint times are stored in function of an engine parameter.
The discharge setpoint. times are values of time which guarantee the complete discharge of the piezoelectric elements and consequently the lift down of the injector needle in order to stop fuel delivery into the combustion chamber of the cylinder. As reference engine parameter can be chosen the engine temperature or the fuel pressure measured in the rail.
Furthermore the control circuits comprises also a second memory module 13 in which are stored a predetermined threshold voltage values calculated in function of an engine parameter, such as the engine temperature and/or the fuel pressure in the rail.
A sampler circuit 7 is connected to the piezoelectric injector with the function of sampling, during a fuel injection cycle, the discharge time (Tm) of the piezoelectric actuator.
The sampled values of time are sent to the adder 8 with which is also connected the memory module 6 storing the setpoint times. The adder 8 calculates the difference (e) between the difference between the discharge setpoint time (Ts) and the sampled discharge time (Tm): (e) Ts-Tm The difference (e) is supplied to a controller 14, for instance a P1 controller, which in function of the above named difference, generates a correction threshold voltage, which is used as output signal of the controller 14, to correct, during the next injection cycle, the predetermined threshold voltage value stored in the second memory module 13.
In detail, a second adder 15 calculates a corrected threshold voltage by adding the correction threshold voltage to the predetermined threshold voltage. The variation of the voltage across the piezoelectric actuator is measured by a voltmeter and when the voltage across the piezoelectric actuator 3 reaches the value of the corrected threshold voltage the piezoelectric actuator 3 is shunted to ground and completely discharge in few microseconds by means of a usual circuit not shown.
As illustrated in Fig. 5, thanks to the method of the invention it's possible to control the piezoelectric actuator 2 by controlling the. discharge time since the discharge of the piezoelectric actuator 2 takes place within the discharge setpoint time (Ts) independently from the effective charge transferred to the piezoelectric actuator.
While the present invention has been described with respect to certain preferred embodiments and particular applications, it is understood that the description set forth herein above is to be taken by way of example and not of limitation. Those skilled in the art will recognize various modifications to the particular embodiments are within the scope of the appended claims. Therefore, it is intended that the invention not be limited to the disclosed embodiments, but that it has the full scope permitted by the language of the following claims.
Claims (9)
- CLAIMS1. A method for controlling a piezoelectric injector for metering fuel inside the cylinder of a combustion engine, wherein the injector comprises an injection needle operated by means of a piezoelectric actuator and wherein a discharge control strategy is applied to the piezoelectric actuator, the method comprises the following steps: -to calculate a discharge time setpoint (Ts) in function of at least an engine operating parameter, -to sample, during a fuel injection cycle, the discharge time (Tm) of the piezoelectric actuator, -to determine the difference between the discharge setpoint time (Ts)and the sampled discharge time (Tin), -use the difference between the discharge time setpoint and the sampled discharge time (Ts) to generate a correction index to be applied, during the next fuel injection cycle, to the discharge control strategy to discharge the piezoelectric actuator in order to minimize the difference between the discharge setpoint time (Tm) and the sampled discharge time (Ts).
- 2. Method according to claim 1, wherein the engine operating parameter used to calculate the discharge setpoint time (Ts) is the engine temperature.
- 3. Method according to claim 1, wherein the engine operating parameter used to calculate the discharge setpoint time (Ts) is the fuel pressure measured in the rail.
- 4. Method according to claim 1, wherein the discharge strategy comprises the step of applying to the piezoelectric actuator a discharge current profile.
- 5. Method according to claim 4, wherein the correction index is a correction value which is multiplied for the discharging current of a current discharging profile.
- 6. Method according to claim 4, wherein said discharge current profile comprises a first discharge current profile up to a predetermined threshold value of voltage across the piezoelectric actuator and a second discharge current profile up to the fully discharge of the actuator, the predetermined discharge threshold voltage being a predetermined value of the voltage across the piezoelectric actuator at the reaching of which the piezoelectric actuator is shunted to ground.
- 7. Method according to claim 6, wherein the correction index is a voltage value to be added to a free discharge threshold voltage during discharging of the piezoelectric actuator.
- 8. Method according to claim 6, wherein the predetermined threshold voltage value is calculated in function of an engine parameter such as the engine temperature or the fuel pressure in the rail.
- 9. Method according to claim 4, wherein the applying the correction index to the discharge current profile provides to multiply the correction index to the discharge current profile
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0914564A GB2472827A (en) | 2009-08-20 | 2009-08-20 | Discharge control strategy for a piezoelectric fuel injector of an i.c. engine |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0914564A GB2472827A (en) | 2009-08-20 | 2009-08-20 | Discharge control strategy for a piezoelectric fuel injector of an i.c. engine |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB0914564D0 GB0914564D0 (en) | 2009-09-30 |
| GB2472827A true GB2472827A (en) | 2011-02-23 |
Family
ID=41171666
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0914564A Withdrawn GB2472827A (en) | 2009-08-20 | 2009-08-20 | Discharge control strategy for a piezoelectric fuel injector of an i.c. engine |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2472827A (en) |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2005047682A1 (en) * | 2003-11-03 | 2005-05-26 | Daimlerchrysler Ag | Method for compensating for injector dispersions in injection valves |
| US20070018534A1 (en) * | 2005-07-22 | 2007-01-25 | Giacomo Sciortino | Method and apparatus for monitoring and evaluating operation of a piezoelectric actuator |
-
2009
- 2009-08-20 GB GB0914564A patent/GB2472827A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2005047682A1 (en) * | 2003-11-03 | 2005-05-26 | Daimlerchrysler Ag | Method for compensating for injector dispersions in injection valves |
| US20070018534A1 (en) * | 2005-07-22 | 2007-01-25 | Giacomo Sciortino | Method and apparatus for monitoring and evaluating operation of a piezoelectric actuator |
Also Published As
| Publication number | Publication date |
|---|---|
| GB0914564D0 (en) | 2009-09-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |