EP1556609B1 - Method for operating a common rail fuel injection system for internal combustion engines - Google Patents

Abstract

Disclosed is a method for operating a fuel injection system. According to said method, the conveying behavior of the high-pressure fuel pump can be homogenized during idling or partial load operation, which has a positive effect on the smoothness of operation and the regulating quality of the pressure in the common rail.

Description

State of the art

The invention relates to a method for operating a fuel injection system of an internal combustion engine, with a high-pressure fuel pump, the high-pressure fuel pump having a plurality of pump elements, arranged with a suction side of the high-pressure fuel pump metering valve, wherein the sucked by the pump elements amount of fuel is controlled or controllable by the metering valve, with a common -Rail and with a pressure control valve and wherein the pressure in the common rail is controlled by the pressure regulating valve.

The flow control of high-pressure fuel pumps is of considerable importance for the overall efficiency of the fuel injection system and thus for the Fuel consumption of the internal combustion engine. In addition, a high-pressure fuel pump whose delivery rate only to a limited extent have controllable larger design reserves, which increases the cost of the high-pressure fuel pump.

From the prior art, it is known to limit the amount of fuel sucked by the pump elements by a metering valve on the suction side of the pump elements and thus to limit the delivery rate of the high-pressure fuel pump. The pressure in the common rail is regulated by a pressure regulating valve, which is usually arranged on the common rail, or by a metering valve.

If the high-pressure fuel pump has a plurality of pump elements and the delivery rate of the high-pressure fuel pump is greatly reduced by the metering valve, there is an unequal distribution of the delivery rate to the pump elements (see EP 1 195 514 A ). For example, of three pump elements, only two pump elements can make a significant contribution to fuel delivery, while a third pump element is de facto out of service. This effect is undesirable because it leads to increased pressure fluctuations in the common rail and also the power required to drive the high-pressure fuel pump is also subject to strong fluctuations. These power fluctuations as well as the mentioned pressure fluctuations in the common rail to a non-circular running of the engine in the partial load range, especially at idle.

The inventive method provides that the amount of fuel flowing through the metering valve is detected, the theoretical delivery volume of the high-pressure fuel pump is detected or calculated, and the pressure regulating valve, when the delivered amount of fuel is less than a predetermined minimum delivery, is so controlled that a defined leakage occurs.

Advantages of the invention

By the method according to the invention can be increased in the critical for the synchronization of the engine part load ranges with a degree of filling of the pump elements, for example less than 30% of this degree of filling that a defined leakage at the pressure control valve of the common rail is set. By increasing the degree of filling of the pump elements, the difference between the flow rates of the individual pump elements is reduced, which has a positive effect in a more constant pressure in the common rail and an improved concentricity of the internal combustion engine.

The inventive method is applicable to various types of high-pressure fuel pumps and requires in particular no high-pressure fuel pump with an integrated in the delivery chamber of the pump elements spring of the suction valve of the pump elements. For this reason, the method according to the invention makes no special demands on the high-pressure fuel pump or the fuel injection system.

In addition, the inventive method requires no additional data, but can on the basis of the data processed by a control unit of a fuel injection system anyway data, such as speed of the internal combustion engine, flow rate through the metering valve and more. For this reason, no additional sensors need to be installed on the internal combustion engine or the fuel injection system, which also contributes to the cost reduction.

It has been shown in measurements that with the aid of the method according to the invention, a synchronization of the internal combustion engine could be achieved at idle, which corresponds approximately to that of a radial piston pump whose Saugventilfedern are arranged in the delivery chamber of the pump elements. This mechanically relatively complex design has, as is due to the necessarily increased dead space volume, a poorer efficiency than a high-pressure fuel pump in which the Saugventilfedern are not arranged in the pumping chamber. Since the method according to the invention allows the high-pressure fuel pump to be used without suction-valve springs in the delivery chamber, the use of the method according to the invention leads to an improvement in the efficiency of the fuel injection system of 10% points in all operating ranges and over the entire service life of the fuel injection system.

The predetermined limit value can be freely selected according to the requirements of the fuel injection system. The predetermined limit value can also be stored as a map in the control unit of the internal combustion engine. It has proved to be advantageous if the limit value is selected such that it amounts to approximately 30% of the theoretical delivery rate of the high-pressure fuel pump.

It is particularly easy to set a defined leakage at the pressure control valve when the closing force of the Pressure control valve, in particular a designed as a seat valve pressure control valve is reduced so far that the desired leakage occurs at the pressure control valve.

The closing force of the pressure regulating valve can be controlled, for example, by changing the ratio between the time intervals in which the pressure regulating valve is de-energized and the time intervals in which the pressure regulating valve is energized.

It is advantageous if the control of the pressure control valve in response to a target pressure in the common rail and a speed at which the high-pressure fuel pump is driven takes place.

In order to avoid that inadmissible operating conditions occur in the fuel injection system, in a further advantageous embodiment of the method according to the invention, this is only applied if the fuel quantity delivered by the high-pressure fuel pump is greater than the fuel quantity consumed by the injectors. If this condition is not met, leakage at the pressure regulator would result in undersupply of the injectors, which should be avoided at all costs.

The control of the pressure regulating valve for setting a defined leakage can be adjusted via a controller and / or via one or more maps.

The method according to the invention can also be implemented in the form of a computer program, in particular a computer program that can be stored on a storage medium, or a control unit for a fuel injection system of an internal combustion engine.

Further advantages and advantageous embodiments of the invention are the following drawings, the description and the claims removable.

drawing

Fig. 1:

eine schematische Darstellung eines Kraftstoffeinspritzsystems zur Durchführung des erfindungsgemäßen Verfahrens;

Fig. 2:

eine stark vereinfachte Darstellung eines Pumpenelements mit einer im Förderraum befindlichen Saugventilfeder;

Fig. 3:

eine Mengenbilanz eines Kraftstoffeinspritzsystems in Abhängigkeit der Drehzahl der Brennkraftmaschine;

Fig. 4:

den Druckverlauf im Rail bzw. das Förderverhalten der Kraftstoffhochdruckpumpe ohne Anwendung des erfindungsgemäßen Verfahrens;

Fig. 5:

den Druckverlauf im Common-Rail, sowie Förderverhalten der Kraftstoffhochdruckpumpe ohne Anwendung des erfindungsgemäßen Verfahrens;

Fig. 6:

den Druckverlauf im Rail bzw. das Förderverhalten einer Kraftstoffhochdruckpumpe bei Anwendung des erfindungsgemäßen Verfahrens;

Fig. 7:

den Druckverlauf im Common-Rail sowie das Förderverhalten der Kraftstoffhochdruckpumpe bei Anwendung des erfindungsgemäßen Verfahrens und

Fig. 8:

Ein Ablaufdiagramm einer Variante des erfindungsgemäßen Verfahrens.

Show it:

Fig. 1:

a schematic representation of a fuel injection system for carrying out the method according to the invention;

Fig. 2:

a greatly simplified representation of a pump element with a suction valve spring located in the pump chamber;

3:

a mass balance of a fuel injection system as a function of the speed of the internal combustion engine;

4:

the pressure curve in the rail or the delivery behavior of the high-pressure fuel pump without application of the method according to the invention;

Fig. 5:

the pressure curve in the common rail, and conveying behavior of the high-pressure fuel pump without application of the method according to the invention;

Fig. 6:

the pressure curve in the rail or the delivery behavior of a high-pressure fuel pump when using the method according to the invention;

Fig. 7:

the pressure curve in the common rail and the Delivery behavior of the high-pressure fuel pump when using the method and

Fig. 8:

A flowchart of a variant of the method according to the invention.

Description of the embodiments

1 shows a common rail injection system according to the prior art is shown schematically. The injection system described in Fig. 1 serves to explain the problem underlying the invention, but the invention is not limited to injection systems of this type. The high-pressure lines of the fuel injection system are shown in FIG. 1 with thick lines, while the low-pressure areas of the fuel injection system are shown with thin lines.

A prefeed pump 1 sucks fuel from a tank 5, not shown, via a feed line 3. This is the fuel in one. Prefilter 7 and a filter filtered with water 9.

The prefeed pump 1 may be formed as a gear pump and has a first pressure relief valve 11. On the suction side, the prefeed pump is throttled by a first throttle 13. A pressure side 15 of the prefeed pump 1 supplies a high-pressure fuel pump 17 with fuel.

The high-pressure fuel pump 17 is designed as a radial piston pump with three pump elements 19 and drives the prefeed pump 1 at. Alternatively, the prefeed pump 1 can also be driven electrically, for example. On the suction side of the pump elements 19 a suction valve 21 is ever provided.

On the pressure side of the pump elements 19 each have a check valve 23 is provided, which prevents the high-pressure fuel, which was funded by the pump elements 19 in a common rail 25, can flow back into the pump elements 19.

The common rail 25 supplies one or more injectors, not shown in FIG. 1, via a high-pressure line 27 with fuel. The pressure control valve 51 also prevents unacceptably high pressures in the high pressure region of the fuel system. Via the return line 29 and a leakage line 31, the leakage and the control amounts of the injector or not shown, are returned to the tank 5. For pressure control, an unillustrated rail pressure sensor is required, which is usually arranged on the common rail 25.

The high-pressure fuel pump 17 is supplied by the feed pump 1 on the one hand with fuel for the pump elements 19 and on the other hand with fuel for lubrication. The amount of fuel which serves to lubricate the high-pressure fuel pump 17 is controlled via a first control valve 35 and a second throttle 37.

The prefeed pump 1 also supplies the pump elements 19 with fuel via a distribution line 45. To control the delivery rate of the high-pressure fuel pump 17, a metering valve 47 is provided between the pressure side 15 of the prefeed pump 1 and the distribution line 45. The metering valve 47 is a flow control valve, which is actuated by a control unit, not shown, of the fuel injection system. The pump elements 19 are thus throttled via the metering valve 47 on the suction side.

In push mode, i. For example, in a downhill driving of a motor vehicle, no fuel should flow into the pump elements 19 and no fuel from the injectors, not shown, are injected into the combustion chambers of the internal combustion engine. Since the metering valve 47 has manufacturing and functional condition in the closed state, a leakage amount that flows into the distribution line 45 would build up without appropriate remedial measures on the suction side of the pump elements 19, a pressure that is so great that the pump elements during the intake stroke, the suction valves 21 open and suck in fuel. This would mean that the pressure in the common rail 25 increases inadmissible.

To prevent this, a third throttle 49 is provided, which is also referred to below as the zero-feed throttle. By the zero-feed throttle 49, the fuel from the distribution line 45 can flow into the crankcase of the high-pressure fuel pump 17 and used there for lubrication of the high-pressure fuel pump 17. Due to the outflow of fuel through the zero-feed throttle 49 of the above-mentioned pressure build-up in the distribution line 45 during coasting due to the leakage of the closed metering valve 47 is prevented.

The pressure in the common rail 25 can be regulated both via a pressure regulating valve 51, which can also be designed as a flow control valve, and a metering valve 47. The pressure control valve 51 and the metering valve 47 are also controlled by the control unit, not shown.

In Fig. 2, two embodiments of Pump elements 19 of a high-pressure fuel pump 17 shown schematically.

In Fig. 2a, a pump element 19, consisting essentially of a cylinder bore 53, an oscillating in the cylinder bore 53 pump piston 55 and a suction valve 21, shown greatly simplified. A check valve 23 (see Fig. 1) is not shown, although it is necessary for the function of the pump element 19.

In the embodiment according to FIG. 2 a, a suction valve spring 57 of the suction valve 21 is arranged outside a delivery space 59 bounded by the cylinder bore 53 and the pump piston 55. In this design, the dead volume of the delivery chamber 59 can be kept very small, which has a positive effect on the efficiency of the high-pressure fuel pump 17. However, in a high-pressure fuel pump 17, which consists of several pump elements 19 shown in FIG. 2a, the delivery behavior of the individual pump elements in the partial load range is very different, which leads to undesirable pressure fluctuations in the common rail and unequal power consumption of the high-pressure fuel pump.

In Fig. 2b, another embodiment of a pump element 19 is shown, the performance in the part load range compared to the embodiment of FIG. 2a is significantly improved.

In the embodiment according to FIG. 2b, the suction valve spring 57 is supported on the pump piston 55. In this type, the dead volume of the delivery chamber 59 is necessarily much larger than that in the Embodiment of FIG. 2a, which has a negative effect in a poorer efficiency of the high-pressure fuel pump. However, in a high-pressure fuel pump 17, which consists of several pump elements 19 shown in FIG. 2b, the delivery behavior of the individual pump elements in the partial load range is almost equal, so that the pressure fluctuations in the common rail are low and the power consumption of the high-pressure fuel pump 17 is very uniform.

With the method according to the invention, it is possible, for example, to operate high-pressure fuel pumps 17 with pump elements 19 according to the exemplary embodiment of FIG. 2 a such that their delivery behavior corresponds to the pump elements according to FIG. 2 b without sacrificing efficiency.

In Fig. 3 is a mass balance of a fuel injection system, which consists essentially of the injectors as consumers and a high-pressure fuel pump as a conveyor, shown. The fuel injection system is operated as known in the art.

In this embodiment, the high-pressure fuel pump 17 pump elements 19 according to the embodiment of FIG. 2a, ie the Saugventilfeder 57 is disposed outside of the delivery chamber 59. In Fig. 3, the delivery rate 61 in liters / hour over twice the speed n of the high-pressure fuel pump 17 (see Fig. 1) is shown. A line designated m _{HDP, theor} in Fig. 3 shows the theoretical flow rate of the _{high-pressure} fuel pump. The theoretical flow rate m _{HDP, theor} increases linearly with the speed.

Below the line m _{HDP, theor} is the maximum _{delivery of the high-pressure} fuel pump, taking into account leaks, wear and other more registered. This maximum delivery rate is designated in FIG. 3 by the reference number 63.

In Fig. 3, the fuel demand of the internal combustion engine as a function of the rotational speed under the assumption of a specific load condition simplified as line 65 registered. However, since the injectors which inject the fuel into the combustion chambers of the internal combustion engine leak and require a control amount for opening and closing the nozzle needles, the actual fuel consumption of the injectors is greater than the fuel demand of the internal combustion engine. The high-pressure fuel pump must satisfy the actual fuel requirements of the injectors. Therefore, the actual fuel demand of the injectors is equal to the effective flow rate m _{HDP, eff of} the high- _pressure fuel pump. The line m _{HDP, eff} is at all speeds above the line 65, which represents the fuel consumption of the internal combustion engine.

If, for example, at a speed of the internal combustion engine of 1,500 l / min, corresponding to a speed of the high-pressure pump of 750 l / min at a gear ratio i = ½, the actual flow rate m _{HDP, eff is} less than an applicable minimum flow m _min (or m _limit ) In the method according to the invention, the pressure regulating valve 51 is actuated such that a defined leakage occurs at the pressure regulating valve 51. The minimum delivery rate m _MIN may, for example, be 30% of the theoretical delivery rate m _HDP . _theor .

This leakage increases the flow rate of the high-pressure fuel pump and thus the degree of filling of the pump elements 19 of the high-pressure fuel pump 17. In Fig. 3, the maximum permissible for this operating point leakage at the pressure control valve 51 is represented by a double arrow 67.

The minimum delivery m _min depends on the operating behavior of the high-pressure pump 17 and can therefore be stored, for example, in a characteristic curve or a characteristic field. The determination of the operating point-dependent minimum delivery rate m _Min can be made by measurements or calculations.

Of course, when using the method according to the invention, it must be ensured that the delivery rate m _{HDP, eff} * _, which is composed of the fuel consumption of the injectors m _{HDP, eff} plus the operating point-dependent leakage 67, is in no case greater than the maximum delivery rate 63 high-pressure fuel pump.

From Fig. 3 it is clear that in the speed ranges of the internal combustion engine between 1000 revolutions and 2000 revolutions, corresponding to a rotational speed of the high- _pressure fuel pump 17 from 500 to 1000 / min, the distance in the vertical direction of the line m _{HDP, eff} and the line 63 relatively large is. Therefore, in this speed range, in which the equal promotion of the pump elements 19 of the high-pressure fuel pump 17 is relatively poor without application of the method according to the invention, a relatively large leakage 67 can be adjusted at the high pressure valve 51 and thus the desired DC delivery of the pump elements 19 by the inventive method can be realized easily and without additional construction costs.

When the pressure regulating valve 51 has a spherical valve member which is pressed by a magnet armature in a valve seat to close the pressure regulating valve 51 (not shown in Fig. 1), the leakage 67 can be adjusted by the ratio of the time intervals within which the magnet armature of the pressure regulating valve 51 is energized, at the intervals within which the armature is de-energized, is changed accordingly. In other types of pressure control valves 51, the desired defined leakage 67 can be adjusted by a correspondingly different control of the pressure control valve 51.

In Fig. 4, the pressure profile in the common rail 25 of a radial piston pump with three pump elements 19 is shown without application of the method according to the invention. In FIG. 4, one revolution of the high-pressure fuel pump 17 is delimited by two vertical lines. It can clearly be seen that of the three pump elements only two pump elements make a significant contribution to the total delivery of the high-pressure fuel pump. These contributions are designated in FIG. 4 by I and II. By contrast, the contribution III of the third pump element is negligibly small. 4 shows a fuel injection system according to the prior art without the use of the method according to the invention.

In Fig. 5, the same fuel injection system without application of the method according to the invention is shown in diagram form. In Fig. 5 is over the time the volume flow m _Zumess through the metering valve 47 (s. Fig. 1).

A line 69 indicates the duty cycle on the pressure regulating valve 51. The duty cycle is a measure of the closing force with which the valve member of the pressure regulating valve 51 is pressed against its sealing seat.

Another line shows the desired value of the pressure p _desired in the common rail 25. Both the desired value p _setpoint and the duty cycle 69 are constant in time in FIG. A line 73 shows the measured actual pressure in the common rail. From Fig. 5 it is clear that both the flowing through the metering valve 47 amount of fuel m _meter and the pressure 73 in the common rail 25 are subject to relatively strong temporal variations.

In Fig. 6, the pressure curve of the high-pressure fuel pump of the same fuel injection system as in Fig. 4, but with application of the method according to the invention, is shown. It is clear from this illustration that the delivery rate of the high-pressure fuel pump 17 has been increased to such an extent by the defined leakage at the pressure regulating valve 51 that all three pump elements make an approximately equal contribution to the total delivery rate of the high-pressure fuel pump 17 (see FIGS. 1, II and III in FIG ).

In Fig. 7, both the effects of the application of the method _according to the invention on the fuel injection system, in particular the _delivery rate of the _high -pressure fuel pump m _meter , as well as the actual pressure 73 in the common rail 25 are clearly visible. From the comparison of Figs. 5 and 7 it is clear that the duty cycle 69 has been lowered by the application of the method according to the invention and consequently the amount of _{metering delivered by the high-pressure} fuel _pump clearly has risen. The differences between the maximum and the minimum of the _delivery m _meter has been significantly reduced by the application of the method _according to the invention. This has a homogenization of the drive power requirement of the high-pressure fuel pump 17 result, which has a positive effect on the smoothness of the internal combustion engine.

The control quality of the actual pressure 73 in the common rail 25 has also been greatly improved by the use of the method according to the invention. This can be seen from the comparison of FIGS. 7 and 5 from the fact that the differences between maximum value and minimum value are reduced.

By applying the method according to the invention, the differences in rail pressure between maximum and minimum could be reduced from 38 bar to 24 bar for a fuel injection system investigated. In this case, no change in the fuel injection system is required for the application of the method according to the invention; only the software in the control unit has to be adapted accordingly.

FIG. 8 shows a flow diagram of an exemplary embodiment of the method according to the invention. In a first step, the metering valve 47 and the pressure regulating valve 51 are activated in such a way that a predetermined desired value is established in the common rail 25. For example, a characteristic curve is used to store a minimum delivery rate m _min or a minimum percentage filling of the pump, depending on the engine or pump speed. This is multiplied by the theoretical delivery volume m _{HDP, theor of} the _{high-pressure} fuel pump 17, for example, and subsequently the result is deducted from the actual _delivery rate m _{Hdp, eff of} the pump. The Volume flow difference is converted for example via a controller or via one or more maps in a control variable for the pressure control valve 51. If the actual flow rate m _{HDP, eff} of the high-pressure fuel pump 17 is smaller than the applied minimum delivery rate _min , the manipulated variable or the duty cycle at the pressure regulating valve is correspondingly reduced. Corresponding to the manipulated variable change at the pressure regulating valve 51 and consequently the change in the leakage at the pressure regulating valve 51, the pressure in the common rail 25 will change. The increase in leakage at the pressure control valve 51 or the pressure change in the common rail 25 is compensated by the metering valve 47 is further compensated via the manipulated variable of the metering valve 47. If the current delivery rate of the high-pressure fuel pump 17 is greater than the applied minimum delivery rate m _min , then the pressure regulating valve 51 remains or is closed.

The control of the pressure control valve 51, for example, depending on the manipulated variable of the metering valve, the target pressure in the common rail 25 and a speed, pump or engine speed with which the high-pressure fuel pump 17 is driven, take place.

Claims (12)

1. Method for operating a fuel injection system of an internal combustion engine, with a high-pressure fuel pump (17), the high-pressure fuel pump (17) having a plurality of pump elements (19), with a metering valve (47) arranged on the suction side of the high-pressure fuel pump (17), the fuel quantity sucked in by the pump elements (19) being controllable or regulatable by means of the metering valve (47), with a common rail (25) and with a pressure-regulating valve (51), the pressure in the common rail (25) being controlled or regulated by means of the pressure-regulating valve (51), characterized by the following method steps:

   - detection or calculation of the feed quantity (m_HDP,eff) conveyed by the high-pressure fuel pump (17),

   - activation of the pressure-regulating valve (51) when the feed quantity (m_HDP,eff) is lower than a predetermined limit value (m_lim), so that a defined leakage occurs at the pressure-regulating valve (51),

   - activation of the metering valve (47) such that a predetermined desired pressure (p_des) is established in the common rail.
2. Method according to Claim 1, characterized in that the limit value (m_lim) is freely selectable.
3. Method according to Claim 1 or 2, characterized in that the closing force of the pressure-regulating valve (51) is reduced to an extent such that the required defined leakage occurs at the pressure-regulating valve (51).
4. Method according to Claim 3, characterized in that the closing force of the pressure-regulating valve (51) is controlled by a change in the ratio between the time intervals in which the pressure-regulating valve (51) is dead and the time intervals in which the pressure-regulating valve (51) is live.
5. Method according to one of the preceding claims, characterized in that the activation of the pressure-regulating valve (51) takes place as a function of a desired pressure in the common rail (25) and of a rotational speed at which the high-pressure fuel pump (17) is driven or of the engine rotational speed.
6. Method according to one of the preceding claims, characterized in that the method is employed only when the current feed quantity (m_HDP,eff) of the high-pressure fuel pump (17) is lower than the applied limit value (m_lim).
7. Method according to one of the preceding claims, characterized in that the activation of the pressure-regulating valve (51) is stored in one or more characteristic maps.
8. Method according to one of the preceding claims, characterized in that the activation of the pressure-regulating valve (51) takes place by means of a controller.
9. Method according to one of the preceding claims, characterized in that the feed quantity (m_HDP,eff) of the high-pressure fuel pump (17) is determined from the fuel quantity flowing through the metering valve (47).
10. Computer program, characterized in that it carries out a method according to one of the preceding claims when it is executed on a control apparatus for operating a fuel injection system of an internal combustion engine.
11. Computer program according to Claim 10, characterized in that it can be stored on a storage medium.
12. Control apparatus for a fuel injection system of an internal combustion engine, characterized in that it is designed for carrying out a method according to one of Claims 1 to 8.

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