DE102016200716A1 - Method and device for controlling a fuel metering system of an internal combustion engine - Google Patents

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 feed pump and a high-pressure pump, which is the start signal of the internal combustion engine, the drive signal of the feed pump is increased, and at least one characteristic feature of the pressure in a high-pressure region is determined.

Description

State of the art

The invention relates to a device and a method according to the preamble of the independent claims.

From the DE 198 53 823 A1 a method for controlling a fuel metering system of an internal combustion engine is known. The fuel metering system includes a delivery pump and a high pressure pump. The feed pump delivers the fuel from a fuel tank via a low pressure area to the high pressure pump. The high-pressure pump delivers the fuel into a high-pressure region, which in particular comprises a so-called rail. From the rail, the fuel reaches the injectors of the individual combustion chambers of the internal combustion engine.

In today's systems used in series, the fuel metering system consists of a low pressure and a high pressure system. The low-pressure system consists essentially of the feed pump. The high pressure system basically consists of a high pressure pump and a pressure sensor. In this case, preferably pre-controlled low-pressure systems are used, which have to get along for cost reasons without pressure sensor in the low pressure system. In these systems, it is necessary to use a pilot control for the feed pump, since there is no pressure information of a pressure sensor. This pressure and / or flow-dependent pilot control is faulty for reasons of different tolerances, in particular the feed pump and other boundary conditions and thus does not provide exactly the desired low pressure available.

However, the high-pressure pump supplied by the low-pressure system requires, for reasons of strength, wear and functional reasons, a certain admission pressure, which in some cases must be well above the vapor pressure of the fuel used. To avoid any pressure drops, the tolerances in the feedforward control must be maintained. This leads in the series on average to increased admission pressure values. Since the low pressure generation by the feed pump requires energy of the electrical system, this method is not optimal with regard to the fuel consumption of the vehicle due to the tolerance reserve.

The inventive method with the features of the independent claim has the advantage that the specimen tolerances balanced and thus a significant energy savings can be effected.

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 feed pump in a low-pressure system and a high-pressure pump in a high-pressure system, a drive signal of the feed pump is abruptly increased when starting the internal combustion engine that at least one characteristic feature of Pressure is determined in a high pressure area.

As a result, the feed pump installed in the vehicle can be characterized very simply and accurately and the drive signal of the feed pump can be corrected in a simple manner.

Particularly advantageous features for the characterization of the feed pump according to the invention, the sizes duration of the pressure rise, the maximum gradient of the pressure rise and / or the absolute pressure difference were detected. These features are easy to determine and depend heavily on the characteristics of the feed pump. Only one or more of these features can be used

It is particularly advantageous if the triggering signal is set to a base value at the beginning and is increased in steps starting from this base value. The underlying value is chosen so that there is just a slight increase in pressure in the high-pressure system.

The measures listed in the dependent claims advantageous refinements and improvements of the independent claim device are possible.

In a further aspect, the invention relates to a new program code together with processing instructions for creating a computer program executable on a control unit, in particular source code with compilation and / or linking instructions, the program code giving the computer program for carrying out all the steps of one of the described methods, if he the processing instructions is converted into an executable computer program, that is in particular compiled and / or linked. This program code can be given in particular by source code, which can be downloaded for example from a server on the Internet.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. Show it:

1 the essential elements of a fuel delivery system,

2 various sizes applied over time and

3 a flowchart illustrating the procedure of the invention.

Embodiments of the invention

In the 1 the essential elements of a fuel metering system are shown. In the 1 is with 100 denotes a feed pump. This promotes fuel from a reservoir 110 via a check valve 115 and a low pressure line to a high pressure pump 120 , The high pressure pump 120 builds pressure in a high pressure area. The high-pressure area comprises in particular a pressure accumulator, which also serves as a rail 130 is designated. In the high-pressure region is also a pressure sensor 140 arranged. From the rail 130 the fuel passes through the injectors 150 in the combustion chambers of the internal combustion engine. The pressure build-up by the high-pressure pump 120 , the opening and closing of the injectors 150 and the power output of the feed pump 100 is through a control unit 160 controlled. This controller 160 also evaluates the output of the pressure sensor 140 out.

The area between the feed pump 100 and the high pressure pump 120 is referred to as a low pressure area. This low pressure area is via a pressure relief valve 170 with the reservoir 110 connected. Due to the included check valve 115 a once built pressure is maintained in the low pressure line. Due to leakage effects, a slight pressure reduction can occur.

Preferably, the feed pump is electrically driven and by the controller 160 subjected to a pulse width modulated signal. The delivery pump builds in the low pressure range from a certain fuel pressure. If this exceeds a certain value, then the pressure relief valve gives 170 the connection to the fuel tank 110 free. This is done primarily against the background that in certain operating conditions no unwanted pressure build-up in the low pressure area. This is the case, for example, when switching off the internal combustion engine, in which due to the heating of the fuel, the pressure in the low-pressure region can rise sharply.

The high pressure pump 120 builds in the rail 130 a correspondingly necessary for the injection pressure. The from the high pressure pump 120 Promoted fuel quantity and thus the pressure in the rail can be controlled by appropriate control of the high-pressure pump by the control unit 160 be set.

In the control unit, a map is implemented in which is deposited depending on various operating parameters, a duty cycle, with which the feed pump 100 is to be controlled so that the corresponding amount of fuel required is promoted or to build a corresponding pressure in the low pressure range. In the characteristic diagram, the drive signal, in particular the duty cycle, is stored at least as a function of the desired amount of fuel to be delivered and the target pressure to be set in the low-pressure region. In advantageous embodiments, further input variables for the characteristic diagram can be provided.

Due to tolerances promote different copies of otherwise identical feed pumps with the same drive signals different flow rates. These are also called specimen distribution. According to the invention, it is now provided that the tolerance of the feed pump is determined or estimated by means of an adaptation or a characterization method. With knowledge of the tolerance, this means the knowledge of whether the feed pump delivers more or less pressure or flow than a nominal pump, the control of the feed pump is optimized accordingly, without the pump must be controlled with a larger lead. Due to the improved feedforward control of the feed pump better compliance with the desired target pressure in the low-pressure circuit is possible, at the same time lower driving power, compared with the purely pre-controlled system.

This method of characterization and tolerance detection is performed as follows. When cold starting the engine, the feed pump 100 usually driven either when opening the door or at the latest when starting the engine for a few seconds. This is commonly referred to as a feed pump flow. A cold start occurs when the engine has been switched off for a longer period of time and the pressure in the low pressure range and in the high pressure range has been reduced to a minimum. The opening of the door is preferably detected by a door contact switch. The starting of the internal combustion engine is detected by means of the so-called. Terminal 15, which indicates that the ignition is turned on. This control is carried out before or at the start to provide the necessary low pressure quickly and already before the engine is spinning for the high-pressure start. After the feed pump feed, the pressure in the low pressure circuit is also controlled without activation of the feed pump via the non-return valve contained at the feed pump outlet 115 largely maintained (less possibly possibly existing leakage).

In the method according to the invention, the pressure at the beginning of the pressure build-up is not immediately raised to a maximum value but increased slowly over stages. For this, the feed pump 100 , which is usually infinitely variable in the flow rate via a PWM control, controlled by a special step-shaped duty cycle. As a result, the pressure in the high-pressure region will also rise in a manner similar to that in the low-pressure region. This increase in the high pressure range can be detected with the rail pressure sensor in the high pressure range. The pressure in the fuel system increases stepwise in a characteristic manner, whereby the dynamics of the low-pressure system plays a major role. Due to the pressure storage capability and depending on the boundary conditions, the fuel system has characteristic dynamic properties. The boundary conditions are determined essentially by the variables temperature, elastic modulus, flexibility of the fuel system by rubber lines. By evaluating the dynamic pressure increase in the step-shaped pressure increase differences in the capacity of the pump are detected.

During the development phase, measurements are carried out with a nominal delivery pump and with boundary-layer delivery pumps for the evaluation. Their dynamic values for the test drive are stored in the memory of the control unit. In the characterization measurement during the flow of the feed pump then the currently determined dynamic characteristics are compared with those stored in the memory. From this it is found out by a comparison, which tolerance position has the existing in the vehicle copy of the feed pump. Accordingly, a correction of the drive signal of the feed pump. Preferably, the pilot control value of the feed pump is corrected accordingly. For example, the output signal of the map is increased or decreased by a corresponding value. However, it can also be provided that the values of the characteristic map are changed accordingly.

The determination of the characteristic features, which are also referred to below as characteristic values, is now carried out as follows. The method is essentially divided into two parts, first the duty cycle TVb of the zero promotion is determined. This is necessary in order to give the jump of the duty cycle completely to the system in the later procedure. Only when the duty cycle TVb of the zero promotion is exceeded, the delivery pump begins to promote. This duty cycle TVb of zero promotion is also referred to below as the basic value TVB. If the jump is switched on at a smaller duty cycle, part of the jump in this area is lost without promotion and falsifies the result of the characterization. Subsequently, after a waiting time, the jump DTV is given to the duty cycle. This means that the duty cycle is increased in steps by the value DTV. As a result, the pressure in the low-pressure region and the rail pressure in the high-pressure region rise in a characteristic manner. After a waiting period, when a steady state of the rail pressure is reached, three characteristics, which are also referred to as characteristic features, are calculated.

In the 2a is the drive signal TV and in 2 B the pressure P in the high pressure region over time t applied. At the time t0, the drive starts according to the method according to the invention. Until the time t1, the drive signal is increased to the value TVb. This drive signal ensures that the feed pump delivers fuel. As a result, the pressure in the high-pressure region increases to the value PS0.

After a waiting time, which is such that a stable state is reached and the pressure P has reached the value PS0 safely in the high-pressure region, the drive signal is increased in steps of the value DTV to the value TVS at the instant ts. As a result, the pressure P increases to the value PS90. This value is reached at time t2. At time t3, the duty cycle is increased to its maximum value TVM. This causes the pressure P to reach its maximum value PS100 by time t4.

The course of the sizes is in 2 only applied qualitatively.

As characteristic features, the following quantities are determined. The first feature is a purely temporal feature. As the first feature, the period of time required for the pressure rise to rise from the time ts of the start of the step change of the drive signal from the output pressure PS0 to a certain pressure value is determined. Preferably, the first feature used is the time required for the pressure to rise to the value PS90. Thus, this feature corresponds to the difference between the two times t2-ts.

The second feature corresponds to the maximum gradient dp / dt that pressure builds up during the jump. It is determined at a defined interval during the duty cycle jump. In the 2 this characteristic would correspond to the relationship between DP and t2-ts. In the case of a real pressure curve, the pressure in this interval is to be differentiated over the time t and the maximum value of the derivative of the pressure profile to be used as the second characteristic feature.

The third feature corresponds to the absolute pressure difference DP between the value before the applied jump PS0 and the steady-state pressure value PS100 after the jump. Alternatively, the pressure value PS90 can be used.

The features are subsequently further processed individually or together to determine the tolerance position of the feed pump by comparison with the stored in the control unit characteristics for the nominal feed pump, the worst-case feed pump and the best-case feed pump. This corrects the pilot control of the feed pump for the following time. These values will be used until the next valid characterization measurement. If the characteristic features correspond to a worst-case feed pump, the duty cycle is increased by a specific value. If the characteristic features correspond to a best-case feed pump, the duty cycle is reduced by a specific value. By doing so, it is achieved that the item used in the vehicle is accurately supplied with the drive signal required to deliver a desired amount of fuel at a desired pressure.

The stronger the delivery pump is conveyed, the faster the pressure will rise compared to the nominal delivery pump. This is reflected in a decrease of the first feature. That is, the time until reaching the pressure value PS90 becomes smaller. The maximum pressure gradient, which corresponds to the second feature, however, is greater, since the higher pressure of the feed pump, the high pressure is reached faster. The same is true of the third feature. The more efficient feed pump also makes the maximum pressure PS100 a bit bigger. Correspondingly, the behavior of the worst-case delivery pump is reversed, which causes a slower and somewhat lower pressure build-up with lower gradients due to the less efficient delivery.

An exemplary flowchart for the method is shown in FIG 3 shown.

With step 300 begins the procedure. A query 305 Checks whether a feed pump flow is to take place. It is checked whether the driver wants to start the vehicle soon. This is detected, for example, by means of a door contact. If this is not the case, the query is again 305 , If a flow of the feed pump is detected, the query checks 310 whether a minimum time has elapsed since the last operation of the internal combustion engine. This query ensures that the pressure in the low pressure range and in the high pressure range has dropped to the ambient pressure. If this time condition has not yet been met, it is done in step 370 the normal control of the feed pump.

Recognizes the query 310 that the time condition is met, so in step 315 the delivery pump with the minimum duty cycle TV0 driven, in which it is ensured that the feed pump is not yet promoted. Then in step 320 the associated pressure value PS0 is determined, which is set in the high-pressure range during this activation of the feed pump.

In step 325 the drive signal TV of the feed pump is increased. The subsequent query 330 checks whether an increase in pressure is recognizable. If this is not the case, then step again 325 , If this is the case, then the value of the current duty cycle in step 335 stored as duty cycle TVb of zero promotion

In step 340 Wait for a wait until a stable pressure value has been set. Preferably, a fixed time is awaited. Then in step 345 the duty cycle is increased by the jump value DTV. In the subsequent step 350 Wait for a wait until a stable pressure value has been set. Again, preferably a fixed time is awaited.

In the subsequent step 355 the characteristic features are determined. In the following step 360 the determination of the correction values, which are used to control the feed pump, takes place.

Then in step 370 the normal control of the feed pump is carried out using the determined correction values. In step 380 the procedure ends.

The proposed method has been described for a feed pump with conventionally commutated motors, which are usually driven by a variable duty cycle PWM signal. In this case, the current through the feed pump and thus the approximate speed of the electric motor is provided on the duty cycle. However, the method is equally suitable for electrically commutated electric motors, so-called BLDC motors. These are controlled via a speed specification. The proposed method now works analogously when the controlled ramp and the jump in the control now instead of the duty cycle with a predetermined speed and performs the evaluation for the tolerance detection equivalent on the speed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19853823 A1 [0002]

Claims (8)

Method for controlling a fuel metering system of an internal combustion engine, wherein the fuel metering system comprises a delivery pump ( 100 ) in a low pressure area and a high pressure pump ( 120 ) comprises that at the start of the internal combustion engine, a drive signal (TV) of the feed pump is increased in a jump, that at least one characteristic feature of the pressure in a high-pressure region is determined. A method according to claim 1, characterized in that at least one of the values duration of the pressure rise, a maximum gradient of the pressure rise (dP / dt) and or an absolute pressure difference (DP) is used as a feature. A method according to claim 1, characterized in that the drive signal is initially set to a base value (TVb) and is increased starting from this base value. Method according to one of the preceding claims, characterized in that the drive signal of the feed pump is corrected on the basis of the at least one characteristic feature. Computer program adapted to carry out all the steps of one of the methods according to one of Claims 1 to 5. Machine-readable storage medium on which the computer program according to claim 6 is stored. A controller adapted to perform all the steps of one of the methods of any one of claims 1 to 5. Program code along with processing instructions for creating a computer program executable on a controller, the program code providing the computer program of claim 6 when converted into an executable computer program according to the processing instructions.

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