1. Field of the Invention
The present invention relates to a method for optimizing fuel injection in operating an internal combustion engine.
2. Description of Related Art
Internal combustion engines are known commercially, for example, where gasoline is injected by injectors directly into the particular combustion chambers. Injectors of this kind come equipped with a valve needle that is actuated by an electromagnetic actuating device, for example. Various methods are known for calculating an optimal, exact quantity of injected fuel whereby, inter alia, control information for the injectors, such as start of control, control duration and/or end of control are ascertained. The more accurately this information is available, the more precisely can a metering of the control and/or regulating device be controlled; to this end, it also being necessary to consider delay times during valve needle opening and closing.
It is, therefore, an object of the present invention to further refine a method of the type mentioned at the outset that will further optimize fuel injection via the injectors.
An opening delay time of the injector is ascertained using the method according to the present invention. Individual, mutually deviating inaccuracies in the valve elements, in a valve seat, and also potentially in a solenoid armature are taken into consideration that lead to tolerance deviations for the opening delay time. In the context of the method of the present invention, the basic design of the injectors actuated by the electromagnetic actuating device is not particularly significant, i.e., the valve elements may be both fixedly connected to the solenoid armature, or they may include a solenoid armature that has a certain axial clearance from the valve element.
A valve opening time encompasses a control duration, minus the opening delay time, and (upon completion of the control duration) a closing time. Thus, purely mathematically, it holds that:
Valve opening time=control duration−opening delay time+closing time (1)
The idea underlying the present invention is to ascertain that control duration at which a lifting movement of the valve element is exactly no longer possible or is exactly not yet possible, and the valve thereby remains closed. Thus, there is no valve opening time and no closing time. Transposing the above mentioned formula for this case reduces the formula purely mathematically to:
Opening delay time=control duration (2)
In this case, this means that the thus ascertained control duration corresponds to that opening delay time which, in the simplest case, may be regarded as constant independently of the actual control duration during driving operation.
The closing of the injector may be readily determined using various known methods, for example with the aid of sensors and/or by analyzing electrical or electromagnetic parameters. Some of these are already implemented in the control and regulation of the injectors. Thus, this does not constitute an additional cost factor.
The method according to the present invention is particularly effective when the control duration is successively reduced until the very moment when a closing of the injector is no longer ascertainable, or when the control duration is successively increased until the very moment when a closing of the injector is ascertainable, and in that the opening delay time for the injector is determined from the time from the start of control until the closing for the last time, respectively the closing for the first time. To reduce the determination time, a greater jump in time to near the critical point may be executed in a first step of the method, and the critical control duration may be subsequently approached in small steps in which the lifting and closing movement of the valve element is only just recognized again, respectively is only just not yet recognized. In the process, it may be taken into account that the closing may not be diagnosable in the case of a minimal opening of the valve element, with the result that the diagnosed control duration deviates from a precise value. In this case, empirically determined adaptation values, for example from a test field, may be used to correct the ascertained control duration value accordingly, for example in the control and/or regulating device. It is also conceivable to approach the critical control duration from both sides and to subsequently derive the precise, critical control time from both ascertained values in accordance with a predefined algorithm (for example, by mean value generation).
The method of the present invention provides for the electrical operating variable to be a time derivative (gradient) of a voltage of a solenoid coil of the electromagnetic actuating device, and for a closing of the injector to be inferred from a minimum of the gradient. In response to the valve element making contact in a valve seat of the injector, the decaying voltage of the electromagnetic actuating device is influenced by a change in the mutual inductance induced by the change in the valve element movement, resulting in a saddle-like voltage curve in which the point of inflection of the curve corresponds to the point of contact of the valve element. To reliably recognize the contact making of the valve element, the time derivative (gradient) of the voltage curve is advantageous since the saddle-like curve is transformed into a readily diagnosable minimum. Upon completion of the control time, merely the first occurring minimum is to be considered since further minima may be subsequently produced, for example, by bouncing of the valve element or of the armature. Alternatively or additionally, the contact making of the valve element may be recognized by a second derivative of the function which has a zero value upon closing of the valve element. The voltage curve may be readily derived in the control and/or regulating device and at a low cost.
To obtain reliable opening time-delay values at any time and to recognize a drift, respectively a wear-induced aging of the injector, the process is repeated (for example, each time following a specific operating time or a specific number of operating cycles) during operation of the internal combustion engine.
It is also advantageous that the method may be implemented during an internal combustion engine operation employing multipoint injections, the control duration then being varied merely for one single point injection and being essentially compensated in a torque-neutral and/or exhaust gas-neutral manner by variations in the control duration of at least one other single point injection. This means that the method does not interfere with the operation of the internal combustion engine.
Moreover, the method may be carried out during an overrun condition of the internal combustion engine under retarded ignition timing conditions. Here the advantage is derived, for example, that a fuel pressure may be freely varied as needed to determine the pressure dependency of the opening delay time. The duration of injection may be gradually increased from the state in which the injector is definitely not opening to the first opening thereof. Thus, any adverse effect on the exhaust gas is minimal. If a retarded ignition timing is assigned to the control, the injected fuel is essentially combusted in a torque-neutral manner. This measure as well serves to ensure that the normal operation of the internal combustion engine is not hindered by the method.
The knowledge of the exact opening delay time makes it possible to consider the same when controlling and/or regulating the injector. The fuel metering and the entire control and/or regulation of the fuel injection may be hereby further refined (in this regard, compare formula (1)). Ascertaining the opening delay time for all injectors of an internal combustion engine reduces the variance in the injection quantity from one injector to another, thereby economizing fuel and ensuring greater uniformity of the internal combustion engine operation.
It is also provided that the method be implemented for different fuel pressures and that a characteristic map be generated from the results of the method. This may used, for example, for a regulated or controlled operation of the fuel injectors.
In
In principle, injector 18a functions in the following manner: Injector 18a is shown in
The characteristic curve of control current I in the top diagram shows an initially rapid rise (compare reference numeral 40), which is then kept constant for a certain time period, and then drops more or less by half (compare reference numeral 42). This current level is maintained until the end of control duration ti. The end of control duration ti is characterized in that current I is switched off (compare reference numeral 44).
In the bottom diagram, it is discernible that valve needle 28 of injector 18a lifts off following the beginning of the control only after a certain opening delay time t1 (compare reference numeral 46). If valve needle 28 has reached its maximum displacement, it suffices to use less control current 1 to maintain this level. If control current 1 is switched off, valve needle 28 is lowered again into valve seat 32, however, likewise after a delay (compare reference numeral 48). The time interval from the switching off of control current 1 until complete closing is defined as closing time tab of valve needle 28. The entire valve opening time is characterized by Top. Thus, purely mathematically, it holds that:
Top=ti−t11+tab
In
If the two zero values are substituted into the above mentioned formula for defining valve opening duration Top, then, for the case that control duration ti is so short that valve needle 28 has only just no longer lifted off, the result after transposing the formula is:
Control duration ti=opening delay time t11
This means that the principle of successive shortening of the control duration may be applied to ascertain opening delay time t11. A precise knowledge of opening delay time t11 makes it possible to refine the control and regulation of injectors 18a through 18d and, as a result, the entire fuel-injection process.
One possible method for determining opening delay time t11 is shown in
The point of departure is a normal vehicle operation featuring control duration ti (reference numeral 100) predefined by control and regulating device 22. Subsequently thereto, control and regulating device 22 checks in step 110 whether the external conditions of internal combustion engine 10 permit a shortening of control duration ti for at least one injector 18, without the vehicle operation of internal combustion engine 10 being adversely affected. This would be the case during an overrun condition, for example. If this is possible, control duration ti is shortened for selected injector 18 in step 120. At the same time, the first derivative of voltage curve UM is calculated for assigned solenoid coil 26. If a minimum 50 is recognized in the characteristic curve of the first derivative (reference numeral 130), control duration ti is reduced further (branch to step 120). If a minimum is no longer recognized, critical control duration t1 is reached. In this case, opening delay time t11 is calculated in step 140 from the difference between the start and the end of control. Correction factors may possibly be included in the calculation as well. In step 150, measured injector 18 is characterized in the control and regulating device, making it possible to select another injector 18 for the next measuring cycle.
Number | Date | Country | Kind |
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10 2009 027 311 | Jun 2009 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2010/057647 | 6/1/2010 | WO | 00 | 3/9/2012 |
Publishing Document | Publishing Date | Country | Kind |
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WO2011/000650 | 1/6/2011 | WO | A |
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