DE102012207744A1 - Method for operating fuel system of internal combustion engine mounted in e.g. motor vehicle, involves pulsing electrically driven fuel pump, periodically, in manner of pulse width modulation, by a relay and connecting to power supply - Google Patents

Abstract

The fuel system (10) is comprised of at least one electrically driven fuel pump (16). The electrically driven fuel pump is periodically pulsed in the manner of pulse width modulation, by a relay (40) and is connected to the power supply (48). The duty ratio of the pulse width modulation is controlled and/or regulated, in dependence on the quantity of fuel to be pumped. The frequency of pulse width modulation is in the range of 1-100 Hz, preferably 10 Hertz. Independent claims are included for the following: (1) a control and/or regulating device for internal combustion engine; and (2) a computer program having instructions executed in control and/or regulating device of internal combustion engine.

Description

State of the art

The invention relates to a method according to the preamble of claim 1, and a control and / or regulating device and a computer program according to the independent claims.

From the market known fuel systems for internal combustion engines, which include at least one electrically driven fuel delivery pump. In particular, this is a prefeed pump of the fuel system, which promotes fuel to a downstream high-pressure pump. In a previously known embodiment of the fuel system, an excess flow rate of the electrically driven fuel delivery pump can be conveyed back into a fuel tank by means of an overflow valve.

Disclosure of the invention

The problem underlying the invention is achieved by a method according to claim 1, and by a control and / or regulating device and a computer program according to the independent claims. Advantageous developments are specified in subclaims. Features which are important for the invention can also be found in the following description and in the drawings, wherein the features, both alone and in different combinations, can be important for the invention, without being explicitly referred to again.

The invention has the advantage that a delivery rate of an electrically driven fuel delivery pump for a fuel system of an internal combustion engine can be controlled or regulated by means of clocking a relay. In particular, in an error case, if the fuel system promotes, for example because of a defective metering device or a clamping overflow valve too much fuel, the capacity of the electrically driven fuel pump can be controlled reduced. As a result, the overall availability of the internal combustion engine can be increased without the need for additional components such as a semiconductor-equipped output stage, which saves costs.

The invention relates to a method for operating the fuel system for the internal combustion engine, wherein the fuel system comprises at least one electrically driven fuel delivery pump. In the present case, an "electric fuel delivery pump" is understood as meaning a combination of a DC motor and a mechanical pump coupled thereto. In this case, the electric fuel pump is periodically clocked by means of a relay in the manner of a pulse width modulation to an operating voltage or to a ground potential. The operating voltage is, for example, the voltage of a vehicle battery. The relay may be a comparatively simple and inexpensive "standard relay" which is generally already present and used to permanently connect an electrical connection of the fuel delivery pump to the operating voltage or to the ground potential during operation of the internal combustion engine.

Among other things, the invention makes use of the fact that the fuel feed pump has a mechanical inertia and the other elements of the fuel system have a type of hydraulic inertia. Thereby, the resulting flow rate can be relatively constant even if the timing of the relay is due to its design with a comparatively low frequency and a smoothing of the current is not possible due to the inductance of the fuel pump alone. Essentially, the fuel system of the invention behaves as if the fuel delivery pump were each driven with an equivalent "analog" voltage.

In particular, it is provided that a pulse duty factor of the pulse width modulation is controlled and / or regulated as a function of a quantity of fuel to be delivered. As a result, the delivery rate of the fuel delivery pump can be changed in a simple manner and controlled over a comparatively wide speed range. This is done, for example, using a computer program. Additional components are generally not required.

It is further provided that a frequency of the pulse width modulation is 1 hertz to 100 hertz, preferably in about 10 hertz. A frequency on the order of 10 hertz represents a particularly suitable compromise for switching a standard relay commonly used for the electrically driven fuel delivery pump. On the one hand, this switching frequency is low enough that the relay can switch smoothly. On the other hand, this switching frequency is high enough to keep short-term fluctuations in the capacity small.

The invention is particularly useful when the duty cycle is controlled and / or controlled in response to a mean fuel pressure in a high pressure accumulator ("rail"), the fuel pressure being averaged over at least one period of the pulse width modulation. Thereby, the method according to the invention can be used to a downstream of the electrically driven fuel delivery pump arranged high-pressure pump to control the amount of fuel supplied in dependence on the fuel pressure. The averaging of the fuel pressure over at least one period of the pulse width modulation allows a particularly stable and precise control. A metering device, for example a quantity control valve or an adjustable throttle upstream of the high-pressure pump, is not absolutely necessary in this case.

An embodiment of the method provides that the electric fuel delivery pump is a prefeed pump in the fuel system. The delivery rate of the pre-feed pump is - compared to the high-pressure pump - low. Accordingly, the electric power of the fuel delivery pump is comparatively low, so that it can be operated particularly well clocked by means of the relay. Generally, a relay is a cost effective and common means for switching an electric fuel delivery pump.

A further embodiment of the invention provides that in a first operating state, the electric fuel pump is continuously switched by means of the relay to the operating voltage, and that in a second operating state, the electric fuel pump is switched by the relay periodically clocked in the type of pulse width modulation to the operating voltage , The first operating state is preferably a normal operation of the fuel system, that is, assumed to be faultless. In this case, the relay is not clocked, so that the electric fuel pump promotes constantly. The mechanical and electrical fatigue strength of the relay is thus correspondingly large. The setting of the effective amount of fuel delivered takes place in this operating state via other means.

By contrast, the second operating state is an emergency operating state of the fuel system in which a device (metering device, quantity control valve, overflow valve) of the fuel system, which controls an amount of fuel to be delivered in the first operating state, essentially no longer controls or no longer controls the fuel quantity to be delivered can control. Nevertheless, thanks to the invention, the fuel system and the internal combustion engine can continue to be operated. At the same time, a warning signal can be sent to an operator of the internal combustion engine or to a motorist, as a result of which, for example, a return of the motor vehicle is possible or a workshop can be reached. In general, therefore, a short-term shutdown of the internal combustion engine is not required and thus a further journey possible.

It is conceivable to carry out the method according to the invention also in the first operating state. This results in comparatively great cost advantages, since a metering device or a quantity control valve can be dispensed with because of the regulation according to the invention of the prefeed pump. In this case, the relay should have a corresponding mechanical and electrical fatigue strength.

The method can be carried out in a particularly simple and cost-effective manner by means of a control and / or regulating device for the internal combustion engine, preferably using a computer program. Additional components are generally dispensable, thereby saving costs.

Hereinafter, exemplary embodiments of the invention will be explained with reference to the drawings. In the drawing show:

1 a schematic representation of a fuel system for an internal combustion engine;

2 a first time chart for operating a fuel delivery pump;

3 a second time chart for operating the fuel delivery pump; and

4 a flowchart for a method for operating the fuel system according to 1 ,

The same reference numerals are used for functionally equivalent elements and sizes in all figures, even in different embodiments.

1 shows a fuel system 10 for a (not shown) internal combustion engine in a simplified representation. From a fuel tank 12 will fuel through a suction line 14 , By means of a direct current driven by DC fuel pump 16 (Pre-feed pump), via a low pressure line 18 , and about one of an electromagnetic actuator 20 actuatable quantity control valve 22 ("Metering device") of a high pressure pump - hereinafter as a piston pump 24 designated - supplied. Downstream is the piston pump 24 via a high pressure line 26 to a high-pressure accumulator 28 ("Common rail") connected. At the high-pressure accumulator 28 is a pressure sensor 29 arranged, which in the high-pressure accumulator 28 can determine prevailing fuel pressure. Other elements, such as valves of the piston pump 24 , are in the 1 not drawn.

The electromagnetic actuator 20 is controlled by a control and / or regulating device 30 controlled, which is a data store 32 as well as a computer program 34 includes. Via electrical lines 36 respectively. 38 respectively. 39 is the control and / or regulating device 30 with the quantity control valve 22 or a relay 40 or the pressure sensor 29 connected.

The relay 40 includes a magnetic coil 42 , which by means of an anchor, not shown, a switching contact 44 can operate. The magnetic coil 42 is with a connection to a ground potential 46 and with another connection to the electrical line 38 connected. The switching contact 44 is with a connection to an operating voltage 48 and with another connection to a first port 50 the fuel pump 16 connected. A second connection 52 the fuel pump 16 is present at the ground potential 46 connected. Between the electric wire 38 and the ground potential 46 is a drive voltage 54 of the relay 40 , and between the terminals 50 and 52 is a pump voltage 56 the fuel pump 16 ,

In a non-illustrated - functionally equivalent - another embodiment of the fuel system 10 is the connection 50 permanently with the operating voltage 48 connected and the switching contact 44 of the relay 40 is in the electrical line between the connection 52 and the ground potential 46 connected. In an alternative embodiment of the quantity control valve (not shown) 22 this is as a unit with the piston pump 24 educated. For example, the quantity control valve 22 a forced openable inlet valve of the piston pump 24 be.

In operation of the fuel system 10 promotes the electrically driven fuel delivery pump 16 Fuel from the fuel tank 12 in the low pressure line 18 , The quantity control valve controls 22 the one working space 25 the piston pump 24 amount of fuel supplied. The quantity control valve 22 can be closed and opened depending on a particular need for fuel. The fuel is for example gasoline or diesel fuel.

A fuel pressure in the high-pressure accumulator 28 comes with the pressure sensor 29 determined and a fuel pressure corresponding signal is via the line 39 to the control and / or regulating device 30 transmitted. The control and / or regulating device 30 is herein programmed to form a closed loop to control the fuel pressure to a set point. For this purpose, in a first operating state ("normal operation"), the electromagnetic actuator 20 controlled accordingly.

In a second operating state (error case, eg. Failure of the actuator 20 by breakage of the electric wire 36 ) becomes the relay 40 periodically clocked in the manner of a pulse width modulation 59 (see the 2 ) to the operating voltage 48 connected. At this time, the fuel pressure in the high-pressure accumulator becomes 28 over at least one period 61 (see the 2 ) of the pulse width modulation 59 averaged. In the present case, the control loop comprises one by means of electronic components and / or by means of the computer program 34 executed PID controller (PID means: proportional, integral, differential).

The frequency of the pulse width modulation is 59 present in about 10 hertz. Thus, the switching contact 44 periodically closed and opened at this frequency. This gives a mean voltage or current at the first terminal 50 , which correspond to a duty cycle 60 (see the 2 ) of the pulse width modulation 59 smaller than the operating voltage 48 or a maximum operating current of the fuel delivery pump 16 ,

2 shows a first timing diagram for the operation of the fuel delivery pump 16 , An upper curve in the drawing represents a fuel delivery 58 over a time t. Two lower curves in the drawing represent a pulse width modulation 59 for controlling the fuel feed pump 16 A curve drawn with a wide line width represents the pump voltage 56 and a thin line drawn curve represents the associated drive voltage 54 of the relay 40 dar. The pulse width modulation 59 has, as already mentioned above, a duty cycle 60 and a period 61 on.

The drive voltage 54 and the pump voltage 56 are shown in the drawing with a comparatively coarse quantization in relation to the time t and the respective amplitude. In fact, these are "analog" voltages. The pump voltage 56 has at each pulse a steep rise to a respective maximum value, which is approximately the operating voltage 48 equivalent. After the end of the respective pulse, the pump voltage drops 56 approximately in accordance with an exponential function decreases rapidly and is almost reduced to zero until the beginning of each subsequent pulse. Because of the comparatively low frequency of the pulse width modulation 59 is the timing of the pump voltage 56 clearly visible.

It can be seen that despite the comparatively low frequency of the pulse width modulation 59 of 10 hertz, a substantially constant fuel delivery 58 over time t yields. This is possible in particular because of the mechanical inertia of the fuel delivery pump 16 and the hydraulic inertia of the fuel system 10 all in all. The fuel delivery rate 58 associated curve is noticeably smoothed. In the present case, the fuel delivery amount 58 in about 20 percent of a possible full production.

3 shows a second time chart for operation of the fuel delivery pump 16 , A lower curve in the drawing represents the duty cycle 60 the pump voltage 56 Here is the duty cycle 60 for experimental purposes, steadily decreasing over time t, with a progressively smaller average pump voltage 56 results.

One in the drawing of 3 upper curve shows the to the duty cycle 60 respective associated fuel delivery 58 , It can be seen that the fuel delivery 58 with decreasing duty cycle 60 decreases steadily and thus results in a clear relationship between the two curves. The length of the in the 3 shown time interval is approximately one hundred times the length of in the 2 shown time interval. Thus, those in the 3 visible short-term fluctuations in the fuel flow 58 to the fluctuations of the fuel flow 58 in the 2 comparable.

4 shows a simplified flowchart for a method for operating the fuel system 10 , In a starting block 62 starts in the 4 represented procedure, for example by means of the computer program 34 can be processed.

In a following block 64 becomes the relay 40 constantly to the operating voltage 48 switched, provided that - not shown in the figures - internal combustion engine is in operation. In a query block 66 it is checked whether one by means of the quantity control valve 22 performed control of the fuel pressure in the high-pressure accumulator 28 is rated as error-free. If applicable, this will indicate normal operation of the fuel system 10 closed and to the beginning of the block 64 Branched back.

If inapplicable, it will indicate a malfunction of the fuel system 10 closed. In this operating state, the quantity control valve 22 essentially no longer control the amount of fuel to be delivered. For example, the quantity control valve 22 defective or the electromagnetic actuator 20 is de-energized (contact error or "connector drop") and the flow control valve 22 thus permanently quite or comparatively wide open. Then, an emergency operation for the fuel system will follow 10 carried out by means of clocking the relay 40 an alternative control of the fuel pressure in the high-pressure accumulator 28 he follows.

This is done in a following block 68 by means of the pressure sensor 29 the currently in the high-pressure accumulator 28 prevailing fuel pressure is determined and compared with a target value. In a following block 70 when the current fuel pressure is below the set point, the duty cycle is established 60 increased by a difference value. If the current fuel pressure is above the setpoint, on the other hand, the duty cycle 60 reduced by a difference value. The thus determined regulation of the fuel delivery 58 takes place here by means of a PID controller. Depending on whether the regulation is carried out digitally or analogously, the said difference value is finite or negligibly small.

In a following block 72 may be a single entry in a fault memory of the control and / or regulating device 30 carried out, and it is complementarily issued a warning, for example, on the dashboard of a motor vehicle. Thereafter, the procedure returns to the input of the query block 66 ,

The method also makes it possible - unlike the procedure described above - the regulation of the fuel pump 16 by clocking the relay 40 or by means of the blocks 68 . 70 and 72 even in normal operation of the fuel system 10 perform. Here is the quantity control valve 22 possibly dispensable.

Claims (9)

Method for operating a fuel system ( 10 ) for an internal combustion engine, wherein the fuel system ( 10 ) at least one electrically driven fuel delivery pump ( 16 ), characterized in that the electric fuel pump ( 16 ) by means of a relay ( 40 ) is periodically clocked in the manner of a pulse width modulation ( 59 ) to an operating voltage ( 48 ) is switched. Method according to claim 1, characterized in that a duty cycle ( 60 ) of the pulse width modulation ( 59 ) depending on an amount of fuel to be delivered ( 58 ) is controlled and / or regulated. Method according to Claim 1 or 2, characterized in that a frequency of the pulse width modulation ( 59 ) Is 1 hertz to 100 hertz, preferably about 10 hertz. A method according to claim 2 or 3, characterized in that the control and / or the regulation of the duty cycle ( 60 ) in response to a mean fuel pressure in a high-pressure accumulator ( 28 ) takes place, the fuel pressure over at least one period ( 61 ) of the pulse width modulation ( 59 ) is averaged. Method according to at least one of the preceding claims, characterized in that the electric fuel feed pump ( 16 ) a prefeed pump in the fuel system ( 10 ). Method according to at least one of the preceding claims, characterized in that in a first operating state the electric fuel feed pump ( 16 ) by means of the relay ( 40 ) permanently to the operating voltage ( 48 ) is switched, and that in a second operating state, the electric fuel pump ( 16 ) by means of the relay ( 40 ) periodically clocked in the type of pulse width modulation ( 59 ) to the operating voltage ( 48 ) is switched. Method according to Claim 6, characterized in that the second operating state is an emergency operating state of the fuel system ( 10 ) in which a device ( 22 ) of the fuel system ( 10 ), which in the first operating state, an amount of fuel to be pumped ( 58 ) controls the amount of fuel to be delivered ( 58 ) essentially no longer controls or can no longer control. Control and / or regulating device ( 30 ) for an internal combustion engine, characterized in that it is adapted to carry out a method according to one of claims 1 to 7. Computer program ( 34 ) for a control and / or regulating device ( 30 ), characterized in that it is programmed to perform a method according to any one of claims 1 to 7.

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