CN106988895B

CN106988895B - Method and device for controlling a fuel metering system of an internal combustion engine

Info

Publication number: CN106988895B
Application number: CN201710042326.4A
Authority: CN
Inventors: A.S.Z.施魏因斯贝格; B.希勒; H-F.施瓦茨; J.金佩尔; K.约斯
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2016-01-20
Filing date: 2017-01-20
Publication date: 2022-05-24
Anticipated expiration: 2037-01-20
Also published as: DE102016200716A1; CN106988895A

Abstract

The invention relates to a method for controlling a fuel metering system of an internal combustion engine, wherein the fuel metering system comprises a delivery pump and a high-pressure pump, wherein, when the internal combustion engine is started, an actuation signal of the delivery pump is increased, and at least one characteristic of the pressure in a high-pressure region is detected.

Description

Method and device for controlling a fuel metering system of an internal combustion engine

Technical Field

The invention proceeds from a device and a method according to the preambles of the independent claims.

Background

A method for controlling a fuel metering system of an internal combustion engine is known from DE 19853823 a 1. The fuel dosing system includes a transfer pump and a high pressure pump. The delivery pump delivers fuel from a fuel reservoir (vortatsbeh ä filter) through a low-pressure region to a high-pressure pump. The high-pressure pump delivers fuel into a high-pressure region, which in particular comprises a so-called rail. Fuel is passed from the rail to an injector (Injektor) of a single combustion chamber of the internal combustion engine.

In the systems used in mass production today, the fuel dosing system consists of a low pressure system and a high pressure system. The low-pressure system essentially consists of the delivery pump. The high-pressure system essentially consists of a high-pressure pump and a pressure sensor. In this case, a pre-controlled low-pressure system is preferably used, which for reasons of cost must also be used without a pressure sensor in the low-pressure system. In such a system, one should point out that: since no pressure information is available from the pressure sensor, a pre-control of the delivery pump is used. Due to, in particular, different tolerances of the delivery pump and other boundary conditions, this pre-control as a function of pressure and/or delivery quantity is disadvantageous and thus does not provide the desired low pressure precisely.

For reasons of strength, wear and functionality, the high-pressure pump fed by the low-pressure system necessarily requires a certain pre-pressure (Vordruck) which must be partially clearly above the vapor pressure (dampfdrive) of the fuel used. In order to avoid possible pressure underflows or pressures falling below the target value (druckuncerschritting), the tolerance must be preceded in the preliminary control (vorhalten). In mass production, this leads to a precompression value which is excessively increased on average. Since the low-voltage generation by the delivery pump requires energy from the vehicle electrical system, this method is not optimal for the fuel consumption of the vehicle due to tolerance pre-staging (Toleranzvorhalt).

Disclosure of Invention

The method according to the invention, which is characterized by the independent claims, accordingly has the following advantages: the sample tolerances (exemplar error zen) can be compared and thereby can lead to significant savings in energy.

According to the invention, in a method for controlling a fuel metering system of an internal combustion engine, in which the fuel metering system comprises a delivery pump in a low-pressure system and a high-pressure pump in a high-pressure system, when starting the internal combustion engine, a control signal of the delivery pump is increased in a jump shape (Sprungf) such that at least one characteristic-indicating characteristic of the pressure in the high-pressure region is detected.

Thereby, the characteristics of the delivery pump installed in the vehicle can be expressed very simply and accurately, and the manipulation signal of the delivery pump can be corrected in a simple manner.

A feature which is particularly advantageous for characterizing the delivery pump is that, according to the invention, the following quantities are identified: the duration of the pressure rise, the maximum gradient of the pressure rise, and/or the absolute pressure difference. These characteristics are easily determinable and strongly dependent on the characteristics of the delivery pump. Only one of these features may be used or a plurality of features may be used.

It is particularly advantageous if the control signal is initially set to a base value (baserest) and rises in a jump-like manner starting from this base value. The basic value is selected such that in the high-pressure system, only a small pressure increase takes place.

Advantageous modifications and improvements of the device specified in the independent claims are achieved by the measures cited in the dependent claims.

In a further aspect, the invention relates to a new program code with processing instructions for creating a computer program that can be run on a control device, in particular a source code with compilation instructions (compilierandrweiung) and/or chaining instructions (verlinkungsanweiung), wherein the program code results in a computer program for carrying out all the steps of one of the described methods, if the program code is transformed (in particular compiled and/or chained) into a computer program that can be run according to the processing instructions. In particular, such program code can be given by the following source code (Quellcode): the source code can be downloaded, for example, from a server in the internet.

Drawings

Embodiments of the invention are illustrated in the drawings and are further described in the following description. The figures show:

FIG. 1: basic elements of a fuel supply system (kraftstoffzu hrsystem);

FIG. 2: different quantities described in time; and

FIG. 3: a flow chart illustrating the setup scheme (Vorgehensweise) according to the present invention.

Detailed Description

The basic elements of a fuel metering system (kraft affzumessystem) are shown in fig. 1. In fig. 1, the transfer pump (a flipurple) is labeled 100. The delivery pump delivers fuel from a reservoir 110 via a non-return valve (rickschlagventil) 115 and a low-pressure line (niederdruckleitsung) to a high-pressure pump 120. The high pressure pump 120 builds pressure in a high pressure region. In particular, the high-pressure region includes a pressure store (druckpeicher), also referred to as Rail (Rail) 130. In addition, a pressure sensor 140 is arranged in the high-pressure region. From the rail 130 fuel is admitted to the combustion chamber of the engine through the injector 150. The pressure build-up of the power output of the delivery pump 100 by the high-pressure pump 120, the opening and closing of the injectors 150 is controlled by a control device 160. This control device 160 also analyses the output signal of the pressure sensor 140.

The region between the feed pump 100 and the high-pressure pump 120 is referred to as a low-pressure region. This low pressure region is connected to the reservoir 110 via a pressure-limiting valve 170. The pressure once built up is maintained in the low pressure conduit due to the inclusion of the check valve 115. A small pressure drop may occur due to a leakage effect (lockageeffekt).

The feed pump is preferably driven electrically and a pulse width modulated (pulsewidth modulated) signal is applied to the feed pump by the control device 160. The delivery pump amplifies a certain fuel pressure in the low-pressure region. If the fuel pressure exceeds a certain value, the pressure-limiting valve 170 opens a connection to the fuel reservoir 110. This is first of all carried out in the following context: in certain operating states, no unintentional pressure buildup takes place in the low-pressure region. This is the case, for example, when the internal combustion engine is switched off, in which case the pressure in the low-pressure region may rise sharply as a result of the heating of the fuel.

The high-pressure pump 120 builds up a pressure in the rail 130 which is accordingly required for injection. The quantity of fuel delivered by the high-pressure pump 120 and thus the pressure in the rail can be set by corresponding actuation of the high-pressure pump by the control device 160.

In the control device, a characteristic map (Kennfeld) is implemented in which a duty cycle (Tastverh ä ltnis) is stored (with which the delivery pump 100 is actuated) for delivering the respectively required fuel quantity or for building up a respective pressure in the low-pressure region as a function of the different operating characteristic values. In the integrated characteristic, the control signal, in particular the duty cycle, is stored at least as a function of the desired fuel quantity to be delivered and the target pressure to be set in the low-pressure region. In an advantageous embodiment, further input values (Eingangsgr) can also be provided for the characteristic map.

For reasons of tolerance, different samples of the same delivery pump generally deliver different delivery quantities with the same actuation signal. This is also called sample spreading (exemplar treeuung). Now, according to the invention, provision is made for: the tolerances of the delivery pump are determined or estimated by means of an adaptation method (adaptionverfahren) or a method of characterizing a property (charaktericerierrungsverfahren). With the aid of the knowledge of tolerances, which is relevant for the knowledge that the delivery pump delivers more or less pressure or delivery quantity than a nominal pump, the actuation of the delivery pump is optimized accordingly, without the pump having to be actuated with a larger advance. The improved pre-control of the delivery pump also enables the desired setpoint pressure in the low-pressure circuit (niederdruckreis) to be better complied with at the same time at lower operating powers than in a purely pre-controlled system.

This method for characterizing and tolerance acquisition (toleranzefassung) is carried out as follows. When the engine is cold started, the feed pump 100 is operated for a few seconds, typically when the vehicle door is opened or at the latest when the internal combustion engine is started. This is generally referred to as a transfer pump-pre-run (Frendrapump-Vorlauf). A cold start occurs if the engine has been shut down for a relatively long time before and the pressure in the low-pressure region and in the high-pressure region drops to a large extent. The opening of the vehicle door is preferably detected by a vehicle door contact switch (T ü rkaktschalter). The starting of the internal combustion engine is detected by means of a so-called pinch (Klemme) 15, which indicates that the ignition is switched on. The purpose of this control before or during start-up is: the necessary low pressure for high-pressure starting (Hochdruckstart) is provided quickly and already before full revolution (Durchdrehen) of the engine. After the pre-run of the delivery pump, the pressure in the low-pressure cycle is largely maintained (minus possible small amount of leakage) even without actuation of the delivery pump, by the inclusion of the check valve 115 at the delivery pump-outlet (foster pumpen-ausgarg).

In the method according to the invention, the pressure is not raised to a maximum immediately at the start of the build-up of pressure, but is raised slowly in steps. In this case, the delivery pump 100 (which can be adjusted steplessly in the delivery quantity by PWM control (PWM Ansteuerung)) is operated with a specific, stepped duty cycle profile (tastveh ä ltnisverlauf). The pressure in the high-pressure region then also rises in a similar manner to that in the low-pressure region. This rise in the high-pressure region can be detected by the rail pressure sensor in the high-pressure region. The pressure in the fuel system rises in a stepwise manner in a characteristic manner, wherein the dynamics (Dynamik) of the low-pressure system plays a significant role. By means of the pressure storage capacity and depending on the boundary conditions, the fuel system has a dynamic characteristic which characterizes it. The boundary condition is essentially determined by the following quantities: flexibility, temperature, modulus of elasticity of the fuel system through the rubber conduit. When the stepped pressure rises, a difference in the delivery capacity of the delivery pump is detected by evaluating the dynamic pressure rise.

For the analysis, in the development phase, the measurement is carried out with a nominally conveying pump and with a conveying pump at the boundary position (grenzlagig). In this case, for the test operation, their dynamic values are stored in a memory of the control device. During the pre-operation of the delivery pump, the characteristic value of the currently acquired dynamics is then compared with the characteristic value stored in the memory. Thus, by comparison, it was found that: the tolerance position (Toleranzlage) of the delivery pump for the sample present in the vehicle. The control signal of the delivery pump is corrected accordingly. The pre-control value (Vorsteuerwert) of the delivery pump is preferably adapted accordingly. For example, the output signal of the characteristic map is increased or decreased by a corresponding value. However, it can also be provided that the value of the characteristic map is changed accordingly.

The determination of the characteristic features (also referred to as characteristic values in the following) is currently carried out as follows. The method is basically divided into two parts, the duty cycle TVb of the null delivery (Nullf narderung) being acquired first. This is necessary in order to give the system the jump of the duty cycle also in the later method in its entirety. The delivery pump starts delivering only when the duty cycle TVb of the zero delivery is exceeded. This zero-fed duty cycle TVb is also referred to as base value TVb in the following. If the jump is switched in at a smaller duty cycle (aufschalten), part of the jump is lost in this region without being transmitted and the result of the signature (charaktersiering) is falsified. Next, after a period of latency (Wartezeit), the hopping DTV is given the duty cycle. This means that the duty cycle is increased in a step-like manner by the amplitude of the value DTV. The pressure in the low-pressure region and the rail pressure in the high-pressure region then rise in a characteristic manner. After a waiting time, if the ringing (eingeschwungen) state of the rail pressure is reached, three characteristic values (Kenngr Cb beta) are calculated, which are also referred to as characteristic-indicative characteristics.

The control signal TV is depicted in fig. 2a at a time t, and the pressure P in the high-pressure region is depicted in fig. 2b at a time t. At time t0, the operation of the method according to the invention begins. Until time t1, the control signal rises to the value TVb. In this control signal, it is ensured that: causing the transfer pump to transfer fuel. As a result, the pressure in the high-pressure region rises to the value PS 0.

After a waiting time (which is measured in such a way that a stable state is reached and the pressure P in the high-pressure region has definitely reached the value PS 0), the control signal is increased abruptly to the value TVS at the time ts by the amplitude of the value DTV. As a result, the pressure P rises to a value PS 90. This value is reached at time t 2. At time t3, the duty cycle rises to its maximum value TVM. This results in the pressure P reaching its maximum value PS100 up to time t 4.

The course of the variation of the quantities is depicted only qualitatively in fig. 2.

The next quantities are obtained as features indicative of the property. The first feature is a time-only feature. The following durations (Zeitdauer) were obtained as a first feature: the duration of the pressure increase is required in order to increase from the output pressure PS0 to a specific pressure value at the time of the start of the jump-shaped change of the control signal. Preferably, the following durations are used as a first characteristic: the pressure needs this duration in order to rise to the value PS 90. This feature therefore corresponds to the difference t2-ts between the two moments.

The second feature corresponds to the following maximum gradient dp/dt: the pressure build-up during the jump exhibits this maximum gradient. During the duty cycle-hopping it is determined in defined intervals. In FIG. 2, this feature corresponds to the ratio between DP and t 2-ts. During the actual pressure change, the pressure in this interval is differentiated over time t (differenzieren) and the maximum value of the derivative of the pressure change (Ableitung) is used as a characteristic of the second characteristic indicator.

The third characteristic corresponds to the pressure difference DP between the value before the engaged jump PS0 and the value of the already vibrated pressure PS100 after the jump. Alternatively, the pressure value PS90 can also be used.

The characteristics are then processed further individually or jointly in order to obtain a tolerance position of the delivery pump by comparison with the characteristic data (Kenndaten) stored in the control device for the nominal, worst-case, and best-case delivery pumps. This corrects the pre-control of the feed pump for a later time. These values are used until the next valid characterization measurement (charakterisiness Messung). If the characteristic-indicating characteristic corresponds to a worst-case delivery pump, the duty cycle is increased by a certain value. If the characteristic-indicating feature corresponds to a best-case delivery pump, the duty cycle is reduced by a certain value. This arrangement makes it possible to load the sample used in the vehicle exactly with the control signal (beaufschlagen) which is required in order to deliver the desired fuel quantity at the desired pressure.

The more intensively the delivery of the delivery pump proceeds, the faster the pressure rise compared to a nominal delivery pump. This is shown when the first characteristic decreases. That is, the duration until the pressure value PS90 is reached becomes smaller. Since the high pressure is reached more quickly by the more intensive delivery by the delivery pump, the maximum pressure gradient corresponding to the second characteristic conversely becomes greater. The third feature also reacts in the same way. The maximum pressure PS100 is also somewhat greater by the more efficient delivery pump. Correspondingly, the performance of the worst-case delivery pump is reversed, which, by virtue of the less efficient delivery, leads to a slower and slightly smaller pressure build-up with a smaller gradient.

An exemplary flow chart for the method is shown in fig. 3.

The setup protocol begins at step 300. Query (abbragage) 305 checks: whether the delivery pump should be pre-run. It is checked whether the driver wants to start the vehicle in a short time. This is recognized, for example, by means of a door contact. If this is not the case, the query is replayed 305. If a pre-run of the delivery pump is identified, query 310 checks for: whether a minimum time (Mindestzeit) has expired since the internal combustion engine was last operated. With the aid of this query, it is ensured that the pressure in the low-pressure region and in the high-pressure region drops to ambient pressure. If this time condition has not been met, then normal operation of the transfer pump is performed in step 370.

If the query 310 identifies that the time condition is met, then the delivery pump is commanded at a minimum duty cycle TV0 in step 315, at which it is ensured that the delivery pump has not delivered. Subsequently, in step 320, the associated pressure value PS0 is obtained, which is present in the high-pressure region during such a control of the delivery pump.

In step 325, the control signal TV of the delivery pump is increased. The subsequent query 330 checks: whether a pressure rise can be recognized. If this is not the case, step 325 is resumed. If this is the case, then the value of the current duty cycle is stored as the duty cycle for the null delivery TVb in step 335.

In step 340, a wait time is waited until a stable pressure value occurs. Preferably waiting a fixed period of time. Subsequently, in step 345, the duty cycle is increased by the magnitude of the skip value DTV. In a subsequent step 350, a waiting period is waited until a stable pressure value occurs. Here too, it is preferred to wait for a fixed period of time.

In a following step 355, the characteristic-indicative feature is obtained. In a subsequent step 360, a correction value (Korrekturwert) is obtained, which is used to actuate the delivery pump.

Subsequently, in step 370, normal operation of the delivery pump is performed using the correction value obtained. In step 380, the method ends.

The proposed method describes a delivery pump with a conventional commutation motor, which is generally actuated by a PWM signal with a variable duty cycle. In this case, the current through the delivery pump and thus the approximate rotational speed of the electric motor is set by the duty cycle. Of course, the method is also well suited for electrically commutated electric motors (elektrisch kommutierter elektromotors), so-called BLDC motors. The electronically commutated motor is controlled by a predetermined speed. The proposed method currently functions analogously if the controlled ramps and jumps in the actuation are not actuated with the duty cycle but rather currently with a predefined rotational speed, and the evaluation for tolerance recognition (toleranzekennung) is carried out equivalently with the rotational speed.

Claims

1. Method for controlling a fuel distribution system of an internal combustion engine, wherein the fuel distribution system comprises a delivery pump (100) in a low-pressure region and a high-pressure pump (120), the actuation signal (TV) of which is increased in a jump-shaped manner when starting the internal combustion engine, such that at least one characteristic-indicating characteristic of the pressure in the high-pressure region is detected,

wherein at least one of the following quantities is used as a characteristic: the duration of the pressure increase, the maximum gradient of the pressure increase (dP/dt) and/or the absolute pressure Difference (DP),

wherein the processing then continues individually or jointly for the characteristics in order to obtain a tolerance position of the delivery pump by comparison with the characteristic data stored in the control device for a nominal delivery pump, a worst-case delivery pump and a best-case delivery pump,

the controlled ramps and jumps in the control are controlled at a predetermined rotational speed, and the evaluation for tolerance detection is carried out equivalently via the rotational speed.

2. Method according to claim 1, characterized in that the control signal is initially set at a base value (TVb) and is increased starting from this base value.

3. Method according to any one of the preceding claims, characterized in that the control signal of the delivery pump is modified on the basis of the at least one characteristic-indicative feature.

4. A machine-readable storage medium on which a computer program is stored, the computer program being configured to carry out all the steps of one of the methods according to any one of claims 1 to 3.