DE102020205775A1 - Comparing the flow rates of injection valves of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for comparing the flow rates (Qstat) of at least two injection valves (14) of an internal combustion engine (2), the at least two injection valves (14) being supplied with fuel (5) from a high-pressure reservoir (8) and the method comprises: (A) operating a feed pump (6) in order to set the fuel pressure (p) in the high-pressure reservoir (8) to a predetermined value; (B) turn off the feed pump (6) after the predetermined fuel pressure (p) has been reached in the high-pressure reservoir (8); (C) to carry out at least one injection process each with at least two injection valves (14) one after the other; (D) to measure the pressure drop (Δp) caused by the at least one injection process in the high-pressure reservoir (8); (E) from the pressure drop (Δp) measured for each injection process, to determine a measure (M) for the flow rate (Qstat) through the respective injection valve (14); and (F) to compare the dimensions (M) of the flow rate (Qstat) measured for the at least two injection valves (14) with one another.

Description

The invention relates to a method for comparing the flow rates of injection valves of an internal combustion engine. The invention also relates to an injection system for an internal combustion engine, which is designed to carry out such a method, and to a motor vehicle with an internal combustion engine and such an injection system.

State of the art

Injection systems with injection valves are used in internal combustion engines (internal combustion engines) to deliver fuel from a tank into the combustion chambers of the internal combustion engine.

The static flow rate Qstat, i.e. the fuel volume Qstat = V / t flowing through an open injection valve per unit of time, is a characteristic variable of an injection valve. Variations in the static flow rate Qstat, as can be caused, for example, by component tolerances and / or deposits in the injection valve, can lead to malfunctions or even failure of the internal combustion engine. For troubleshooting and prevention, there is therefore a need to compare the static flow rates Qstat of the injection valves of an internal combustion engine.

It is therefore an object of the invention to enable a reliable, quick and convenient comparison of the static flow rates Qstat of the injection valves of an internal combustion engine.

Disclosure of the invention

1. (A) eine Förderpumpe zu betreiben, um den Kraftstoffdruck im Hochdruckreservoir auf einen vorgegebenen Wert einzustellen;
2. (B) die Förderpumpe abzustellen, nachdem der vorgegebene Kraftstoffdruck im Hochdruckreservoir erreicht worden ist;
3. (C) nacheinander mit wenigstens zwei der Einspritzventile jeweils wenigstens einen Einspritzvorgang durchzuführen;
4. (D) den von dem wenigstens einen Einspritzvorgang im Hochdruckreservoir verursachten Druckabfall zu messen;
5. (E) aus dem für den wenigstens einen Einspritzvorgang gemessenen Druckabfall ein Maß für die Durchflussmenge, die während des wenigstens einen Einspritzvorgangs durch das wenigstens eine Einspritzventil geströmt ist, zu bestimmen; und
6. (F) die für die verschiedenen Einspritzventile gemessenen Maße der Durchflussmengen miteinander zu vergleichen.

According to one embodiment of the invention, a method for comparing the flow rates of at least two injection valves of an internal combustion engine, in which the injection valves are supplied with fuel from a high-pressure reservoir,

1. (A) operate a feed pump to set the fuel pressure in the high pressure reservoir to a predetermined value;
2. (B) turn off the feed pump after the predetermined fuel pressure has been reached in the high pressure reservoir;
3. (C) to carry out at least one injection process in succession with at least two of the injection valves;
4. (D) measuring the pressure drop caused by the at least one injection process in the high-pressure reservoir;
5. (E) from the pressure drop measured for the at least one injection process, to determine a measure of the flow rate which has flowed through the at least one injection valve during the at least one injection process; and
6. (F) compare the measurements of the flow rates measured for the various injectors with one another.

• (A) eine Förderpumpe zu betreiben, um den Kraftstoffdruck im Hochdruckreservoir auf einen vorgegebenen Wert einzustellen;
• (C) nacheinander mit wenigstens zwei der Einspritzventile jeweils wenigstens einen Einspritzvorgang durchzuführen, wobei jeder Einspritzvorgang wenigstens einen verbrennungswirksamen Haupteinspritzvorgang (HE) und wenigstens einen nicht verbrennungswirksamen Nacheinspritzvorgang (NE) umfasst;
• (D) die von den Einspritzvorgängen im Hochdruckreservoir verursachten Druckabfälle zu messen; dabei können entweder nur die durch die Nacheinspritzvorgänge (NE) verursachte Druckabfälle oder die von den Haupteinspritzvorgängen (HE) und den Nacheinspritzvorgängen (NE) gemeinsam im Hochdruckreservoir verursachten Druckabfälle gemessen werden;
• (E) aus den für die Einspritzvorgänge gemessenen Druckabfällen ein Maß für die Durchflussmenge, die während der Einspritzvorgänge durch das wenigstens eine Einspritzventil geströmt ist, zu bestimmen; und
• (F) die für die verschiedenen Einspritzventile gemessenen Maße der Durchflussmenge miteinander zu vergleichen.

In a further exemplary embodiment of the invention, a method for comparing the flow rates of at least two injection valves of an internal combustion engine, in which the injection valves are supplied with fuel from a high-pressure reservoir,

• (A) operate a feed pump to set the fuel pressure in the high pressure reservoir to a predetermined value;
• (C) to carry out at least one injection process in succession with at least two of the injection valves, each injection process comprising at least one main injection process (HE) that affects combustion and at least one post-injection process (NE) that does not affect combustion;
• (D) measure the pressure drops caused by the injections in the high pressure reservoir; either only the pressure drops caused by the post-injection processes (NE) or the pressure drops caused jointly in the high-pressure reservoir by the main injection processes (HE) and the post-injection processes (NE) can be measured;
• (E) from the pressure drops measured for the injection processes, to determine a measure of the flow rate which has flowed through the at least one injection valve during the injection processes; and
• (F) compare the measurements of the flow rate measured for the various injectors with one another.

An injection process can also include several main injection processes (HE) and / or several post-injection processes (NE).

Optionally, the feed pump can also be switched off in a method in which each injection process comprises at least one combustion-effective main injection process (HE) and at least one non-combustion-effective post-injection process (NE) after a predetermined fuel pressure has been reached in the high-pressure reservoir.

Embodiments of the invention also include an injection system for an internal combustion engine, in particular for an internal combustion engine in a motor vehicle. Such an injection system comprises: at least two injection valves which are designed to inject fuel into a combustion chamber of the internal combustion engine during operation; a high-pressure reservoir which is designed to store fuel under increased pressure and to make it available to the injection valves; a feed pump which is designed to feed fuel into the high-pressure reservoir; a pressure sensor which is designed to measure the fuel pressure (“system pressure”) in the high-pressure reservoir; and a control device which is designed to receive at least one measurement signal from the pressure sensor and to control the feed pump and the injection valves. The control device is designed to carry out a method according to an exemplary embodiment of the invention in a diagnostic mode in order to compare the flow rates of at least two injection valves with one another.

A method according to the invention and an injection system according to the invention make it possible to compare the flow rates through the injection valves of an internal combustion engine with high accuracy without the injection valves having to be removed from the internal combustion engine. The flow rates through the injection valves can be compared with one another, especially when the internal combustion engine is running, i.e. under real operating conditions.

With a method according to the invention, in particular the flow rates of three or more injection valves can be compared in order to reliably identify possible outliers.

A method according to the invention and an injection system according to the invention therefore enable rapid and inexpensive diagnosis in a workshop. A method according to the invention can also be used in vehicle production at the end of the line in order to check the built-in injection valves and to prevent the delivery of vehicles and / or internal combustion engines with faulty injection valves.

In one embodiment, the method comprises repeating steps (C) and (D) several times and determining the measure for the flow rate from a sum, from an integral over time or from an average value of the pressure drops measured several times. In this way, the accuracy and the reliability of the measurement results can be improved.

In one embodiment, the method comprises measuring the fuel pressure in the high pressure reservoir and taking into account the current fuel pressure in the high pressure reservoir when determining the measure for the flow rate from the pressure drops measured for the individual injection processes, for example by means of a correction factor. In this way, the quality and reliability of the method can be improved, since changes in the fuel pressure in the high-pressure reservoir caused by the injection processes are recognized and compensated for.

In one embodiment, the method includes monitoring the fuel pressure in the high pressure reservoir and operating the feed pump in order to set the fuel pressure in the high pressure reservoir back to the specified value as soon as the fuel pressure in the high pressure reservoir falls below a specified limit value, for example a limit value of 200 bar.

By refilling the high-pressure reservoir with fuel in order to set the fuel pressure in the high-pressure reservoir back to the specified value, the number of repeatable injection processes, the results of which can be averaged or integrated, can be increased even further. As a result, the accuracy and the reliability of the measurement results can be improved even further.

In one embodiment, the defined fuel pressure that is set in the fuel reservoir is the maximum fuel pressure of the injection system, for example a fuel pressure of 350 bar. The accuracy of the measurement results increases with the fuel pressure in the fuel reservoir. It is therefore advantageous to set as high a fuel pressure as possible in the fuel reservoir, which is as close as possible to the maximum permissible fuel pressure in the fuel reservoir.

In one embodiment, the injection quantity for each injection process is greater than the injection quantity required in the respective operating state of the internal combustion engine. The drop in fuel pressure in the fuel reservoir caused by each injection process can be increased by an increased injection quantity. A larger pressure drop in the fuel reservoir can be measured more easily and / or with better accuracy, in particular a smaller relative error. The accuracy and reliability of the measurement results can therefore be improved by increasing the injection amount.

In one embodiment, the method of delivering the content of the at least one combustion chamber into which fuel has been injected from the at least one combustion chamber, the proportion of fuel in the from the to determine at least one combustion chamber conveyed content and to determine the flow rate of the injection valves from the proportion of fuel thus determined. In this way, the flow rate of the injection valves can be determined independently of the pressure drop in the high-pressure reservoir. This makes it possible to improve the accuracy and reliability of the method.

In one embodiment, the method comprises determining the proportion of fuel in the content conveyed from the combustion chamber using a lambda probe, in particular using a broadband lambda probe. Lambda sensors, such as those used in motor vehicles to regulate exhaust gas cleaning, are also well suited, due to their sensitivity to hydrocarbons (HC sensitivity), to determine the proportion of fuel in an air-fuel mixture delivered from the combustion chamber.

In one embodiment, the method comprises moving the pistons of the internal combustion engine with the aid of an electric motor, in particular an electric starter motor, in order to convey the contents of the at least one combustion chamber out of the at least one combustion chamber, while the injection system and the ignition of the internal combustion engine are deactivated. In this way, the content of the at least one combustion chamber can be conveyed out of the at least one combustion chamber without an additional conveying device having to be provided. The pistons can in particular be moved by rotating a crankshaft of the internal combustion engine, which is mechanically connected to the pistons of the internal combustion engine.

Embodiments of the invention also include a motor vehicle with an internal combustion engine and an injection system which is designed according to an embodiment of the invention.

In one embodiment, the motor vehicle has an exhaust gas line which is in fluid connection with the at least one combustion chamber of the internal combustion engine and a lambda probe arranged in the exhaust gas line. In such an embodiment, the control device is designed to evaluate a signal provided by the lambda probe in order to determine the flow rate of the injection valves.

In one embodiment, the motor vehicle has an electric motor, in particular an electric starter, which is designed to rotate a crankshaft of the internal combustion engine, which is mechanically connected to the pistons of the internal combustion engine, in order to convey the contents of at least one combustion chamber to the lambda probe in the exhaust system.

Figure list

• 1 shows a schematic view of a motor vehicle with an internal combustion engine and an injection system according to the invention.
• 2 shows a flowchart that illustrates the sequence of a method according to the invention for determining the static flow rate of at least one injection valve.
• 3 shows an example of the course of the combustion pressure in a combustion chamber of an internal combustion engine and the course of the pressure in the high-pressure reservoir as a function of the angle of rotation of the crankshaft of the internal combustion engine.
• 4th shows a flowchart that illustrates the sequence of a further method according to the invention for determining the static flow rate of at least one injection valve.
• 5 shows schematically the course of a signal supplied by a lambda probe for leakage-free and leakage-prone injection valves.

Figure description

An exemplary embodiment of the invention is described below with reference to the accompanying figures.

1 shows a schematic view of a motor vehicle 1 with an internal combustion engine (“internal combustion engine”) 2 and an injection system according to the invention 3 .

The injection system 3 includes a feed pump 6th , which is formed, fluid fuel 5 from a fuel tank 4th to be removed and fed to a high pressure reservoir (“high pressure rail”) 8 under increased pressure.

The feed pump 6th can be a prefeed pump 6a and a main feed pump 6b and filters (not shown) formed by the feed pump 6th pumped fuel 5 to clean. The feed pump 6th can also include control valves (not shown) that allow the delivery rate and delivery pressure of the feed pump 6th adjust.

Several injection valves (“fuel injectors”) 14, which are designed to deliver fuel 5 in combustion chambers ("cylinders") 12 des Internal combustion engine 2 are to be injected fluidly in such a way with the high pressure reservoir 8th connected to that from the high pressure reservoir 8th with fuel 5 are supplied.

At / in the high pressure reservoir 8th is a pressure sensor 10 provided, which is designed to control the fuel pressure in the high-pressure reservoir 8th to measure and to provide a corresponding measurement signal.

Movable in the combustion chambers 12th arranged pistons 13th are mechanical with a crankshaft 24 connected. The crankshaft 24 can be powered by an electric motor (starter motor 22nd ) are driven to the pistons 13th , especially for starting the internal combustion engine 2 , inside the combustion chambers 12th to move.

The combustion chambers 12th are with an exhaust line 18th connected, which makes it possible to remove combustion gases from the combustion chambers 12th to dissipate. Between the combustion chambers 12th and the exhaust system 18th are in the 1 Exhaust valves, not shown, are arranged, which are opened in a targeted manner in order to remove combustion exhaust gases from the respective combustion chamber 12th in the exhaust system 18th to dissipate.

In the exhaust system 18th can use a lambda probe 20th be arranged.

Lambda sensors 20th are oxygen partial pressure sensors with a cross sensitivity to hydrocarbons (HC).

Lambda sensors 20th are particularly suitable for determining the oxygen content in combustion exhaust gases, from which conclusions can be drawn with regard to the operation of an internal combustion engine 2 the amount of fuel burned can be drawn.

Due to the HC cross-sensitivity, lambda sensors are 20th also suitable to determine whether air is released without combustion, in particular by operating the electric motor 22nd , from the combustion chambers 12th is promoted with fuel 5 is mixed.

With a simple lambda probe 20th the combustion air ratio λ can only be determined in a very narrow range of values around λ = 1. A broadband lambda probe 20th is a variant of a simple lambda probe 20th that are specially designed for use in internal combustion engines 2 with direct fuel injection has been developed. Broadband lambda probes 20th can be used reliably in a value range of λ = 0.8 and higher.

The injection system 3 comprises a control device 16 going through in the 1 electrical line (not shown) or wirelessly with the feed pump 6th , the pressure sensor 10 and the injectors 14th is connected and designed, measurement signals from the pressure sensor 10 to receive and the feed pump 6th and the injectors 14th to control the operation of the internal combustion engine 2 to enable. Is in the vehicle 1 a lambda probe 20th is present, the control device is 16 also with the lambda probe 20th connected as it is in the 1 is shown.

In an injection system according to the invention, the control device is 16 designed to be operated selectively in a diagnostic mode in order to determine the static flow rate Qstat through at least one of the injection valves 14th to determine.

The sequence of a method according to the invention for determining the static flow rate Qstat is shown in FIG 2 illustrated flowchart.

First of all (step 100 ) becomes the feed pump 6th operated to the fuel pressure p ("system pressure") in the high pressure reservoir 8th set to a predetermined value pnenn, for example a value of pnenn = 350 bar. Since the accuracy of the method increases with increasing fuel pressure p, the fuel pressure p can in particular be adjusted to the maximum possible fuel pressure of the injection system 3 can be set.

After the fuel pressure p in the high pressure reservoir 8th has reached the specified value, we control the feed pump 6th turned off (step 200 ).

In the next step 300 is with at least one of the injectors 14th carried out at least one injection process, and by the at least one injection process in the high pressure reservoir 8th The pressure drop caused by Δp is determined by the pressure sensor 10 measured.

Becomes the pressure drop Δp for each of the injectors 14th repeatedly, ie for several injection processes, is measured in step 350 an averaging of the for the respective injection valve 14th measured pressure drops .DELTA.p carried out, or the measured pressure drops .DELTA.p are added or integrated over time t.

The static injection quantity Qstat of an injector 14th is proportional to the pressure drop Δp in the high pressure reservoir 8th and inversely proportional to the open time Δt of the injection valve 14th : $${\text{Q}}_{\text{stat}}\sim \Delta \text{p /}\Delta \text{t}.$$

Therefore, from the measured pressure drop Δp in the high pressure reservoir 8th and the known open time Δt of the injection valve 14th a measure M for the static injection quantity Qstat of each injection valve 14th which is proportional to the static injection quantity Qstat (M ~ Qstat).

The fuel pressure p in the high pressure reservoir 8th is measured and can be taken into account when determining the dimension M for the static injection quantity Qstat to avoid falsification of the measurement results resulting from changes in the fuel pressure p in the high-pressure reservoir 8th may arise to avoid.

In addition, the fuel pressure p in the high pressure reservoir 8th compared with a predetermined limit value (minimum value) pmin (step 400 ).

Is the measured fuel pressure p in the high pressure reservoir 8th is greater than a predetermined limit value pmin of, for example, 200 bar, the method is repeated, that is, an injection process with at least one of the injection valves is repeated 14th carried out and thereby in the high pressure reservoir 8th The resulting pressure drop Δp is measured.

If it falls below that in the high pressure reservoir 8th measured fuel pressure p the predetermined limit value pmin is in step 500 checked whether at least a predetermined number nmin of injection processes has been carried out.

If at least a predetermined number nmin of injection processes has been carried out for each of the injection valves, the averaged, summed or integrated measures M for the injection quantities Qstat are for each of the injection valves 14th output separately (step 600 ).

In particular, the dimensions M for the injection quantities Qstat of the injection valves 14th compared with one another and / or differences between the dimensions M of the injection quantities Qstat of the individual injection valves 14th are displayed.

If the specified number nmin of injection processes has not yet been reached, the feed pump is activated 6th operated again (step 550 ) to determine the fuel pressure p in the high pressure reservoir 8th to increase again to the specified value p _rated.

Measured values of pressure drops Δp that are measured while the feed pump is running 6th is operated, are not taken into account in the averaging or summation / integration, ie the summation / integration or averaging is for the period in which the feed pump 6th is being operated, stopped as the during operation of the feed pump 6th recorded measured values would falsify the results.

To the pressure drop Δp in the high pressure reservoir 8th The injection process can increase the accuracy of the measurement results even further 300 comprise at least one combustion-effective main injection process (HE) and at least one non-combustion-effective post-injection process (NE). The at least one non-combustion-effective post-injection process (NE) is carried out after the at least one main injection process (HE). An injection process can also comprise several main injection processes (HE) and / or several post-injection processes (NE).

In a post-injection process (NE), there is an exhaust stroke of the respective combustion chamber 12th additional fuel 5 into the combustion chamber 12th injected. The amount of fuel injected in a post-injection process (NE) does not take part in the combustion and can therefore be significantly greater than that at the respective operating point of the internal combustion engine 2 required amount of fuel. The purpose of injecting a larger amount of fuel is to create a larger pressure drop Δp in the high-pressure reservoir 8th to effect the one with the pressure sensor 10 is easily measurable.

In the following evaluation, either only that of the at least one post-injection process (NE) in the high-pressure reservoir can be used 8th caused pressure drop Δp _{N or the greater pressure drop Δp = Δp H} + Δp _N caused jointly by the at least one main injection process (HE) and the at least one post-injection process (NE) can be taken into account.

_{If only the pressure drop Δp N} caused by the at least one post-injection process (NE) is taken into account and the point in time of the at least one post-injection process (NE) at a sufficiently large distance from the last preceding pump stroke of the feed pump 6th selected, the pressure drop Δp in the high pressure reservoir is selected 8th not from the feed pump during the at least one post-injection process (NE) 6th influenced. In this case, the feed pump can therefore be dispensed with 6th switch off before the injection process.

Carrying out at least one post-injection process (NE) and switching off the feed pump 6th can also be combined in one method, in particular if the at least one post-injection process (NE) is not at a sufficiently large time interval from the last preceding pump stroke of the feed pump 6th can be carried out.

3 shows an example of the course of the combustion pressure in a combustion chamber 12th of the internal combustion engine (solid line) and the fuel pressure p in the high pressure reservoir 8th (dashed line) as a function of the angle of rotation θ of the crankshaft of the internal combustion engine 2 .

In the lower area of the 3 a main injection process HE and a post-injection process NE are plotted. The ignition point is marked with "OT".

_{The pressure drops Δp H} and Δp _H caused by the main injection process HE and post-injection process NE, which add up to the total pressure drop Δp = Δp _H + Δp _N , are shown in FIG 3 good to see.

It can also be seen that the main injection process HE takes place before the ignition time OT and the post-injection process NE takes place after the ignition time OT.

Embodiments of the invention make it possible to determine the static flow rates Qstat of injection valves 14th of an internal combustion engine 2 easy to compare with each other. In particular, they enable the static flow rates Qstat of injection valves 14th to compare with each other without the injectors 14th from the internal combustion engine 2 to expand.

4th shows a flowchart that illustrates the sequence of a further method according to the invention for determining the static flow rate of at least one injection valve.

In a first step 50 of the 4th illustrated procedure is the vehicle 1 preconditioned to the lambda probe 20th to bring into an operational state. This can in particular include the internal combustion engine 2 to start and then so long to operate, for example in idle or at a speed higher than idle, until an optimal operating temperature of the internal combustion engine 2 and / or the lambda probe 20th is reached.

As soon as the internal combustion engine 2 and the lambda probe 20th are preconditioned, the internal combustion engine 2 switched off (step 60 ). The readiness for operation and measurement of the lambda probe 20th is also after switching off the internal combustion engine 2 maintain.

The steps 100 to 500 correspond to those related to the 2 described steps of the procedure described there. A new description is therefore dispensed with at this point.

The feed pump 6th is usually mechanical with the crankshaft 24 of the internal combustion engine 2 coupled. Will the crankshaft 24 in step 550 , for example by operating the electric motor (starter) 22nd , turned to the feed pump 6th to drive and so the pressure in the high pressure reservoir 8th to increase (again), this will simultaneously increase the pistons 13th of the internal combustion engine 2 emotional. The ignition and the injection system 3 of the internal combustion engine 2 remain disabled, leaving no fuel 5 into the combustion chambers 12th is injected and the internal combustion engine 2 does not start.

Moving the pistons 13th of the internal combustion engine 2 when the ignition is switched off, the contents (volume) of the combustion chambers 12th one after the other into the exhaust system 18th be promoted and at the lambda probe arranged there 20th stream past.

Due to the sensitivity of the lambda probe 20th for hydrocarbons (HC sensitivity) can be obtained from the oxygen sensor 20th The signals supplied show the proportion of fuel in the content of each combustion chamber 12th can be determined (step 555 ).

The assignment of the lambda probe 20th delivered signals to the individual combustion chambers 12th can be over the time t or over one of a rotation angle sensor 26th detected rotation angle θ of the crankshaft 24 respectively.

5 shows schematically the course of one of the lambda probe 20th delivered signal 30th as a function of time t or as a function of the angle of rotation θ of the crankshaft 24 .

The content of a combustion chamber 12th with a leak-free injector 14th essentially comprises pure air (“fresh air”). The "fresh air" causes a strong first increase 31 of the lambda probe 20th delivered signal 30th . The content of a combustion chamber 12th with a leaked injection valve 14th contains an air-fuel mixture. This causes a significantly weaker first rise 32 of the lambda probe 20th delivered signal 30th .

In the event that the contents of a combustion chamber 12th with a leaked injection valve 14th according to the contents of a combustion chamber 12th with a leak-free injector 14th from the lambda probe 20th is detected, causes the air-fuel mixture in the contents of the combustion chamber 12th with the leaked injection valve 14th a weakening 33 of the already existing increase in the course of the time of the lambda probe 20th delivered signal 30th . In extreme cases, there can even be a plateau 33 in the measurement signal 30th to be observed.

If the fuel content determined in this way exceeds the content of a combustion chamber 12th a predetermined limit value can indicate a leak in the injection valve 14th are closed to the respective combustion chamber 12th assigned.

In order to establish the same initial conditions for iterations over several cylinders or for repetitive measurements for averaging, the internal combustion engine 2 started with the ignition activated (step 560 ) to in the combustion chambers 12th burn remaining fuel.

In a following step 600 the measurement results are output as it was previously in connection with the 3 has been described. As an alternative or in addition to that, based on the pressure drop in the high-pressure reservoir 8th certain results also by evaluating the signals from the lambda probe 20th determined results are output.

By comparing the results determined in different ways, conclusions can be drawn about the reliability and accuracy of the measurement results.

The procedure can then apply to the fuel injectors 14th another combustion chamber 12th and / or for other operating points of the internal combustion engine 2 , especially for other pressures p in the high pressure reservoir 8th be repeated.

If it is not necessary and / or desired, the pressure in the high pressure reservoir 8th it is advantageous to use the crankshaft to carry out the lambda measurement 24 of the internal combustion engine 2 to rotate to the contents of the combustion chambers 12th in the exhaust system 18th to promote without the feed pump 6th to operate. This way you can reduce the load on the electric motor 22nd and thus also the energy consumption of the electric motor 22nd be reduced.

Theoretically, this can be achieved by mechanically decoupling the feed pump 6th from the crankshaft 24 respectively. Such a mechanical decoupling of the feed pump 6th from the crankshaft 24 however, is the case with most vehicles 1 not provided.

As an alternative to mechanical decoupling, the supply of fuel can be used 5 to the feed pump 6th reduced or completely interrupted. The feed pump 6th is in this case still from the crankshaft 24 driven, but does less work due to the reduced fuel supply and thus creates less load on the crankshaft 24 .

In order to ensure comparability of the measurements, it should be specified whether the fuel supply to the feed pump 6th normal, reduced, or interrupted while measurements are being taken.

Also the speed of the electric motor 22nd during measurements should be given.

Claims (15)

Method for comparing the flow rates (Q _stat ) of at least two injection valves (14) which are designed to inject fuel (5) into at least one combustion chamber (12) of an internal combustion engine (2), wherein the at least two injection valves (14) consist of one High-pressure reservoir (8) are supplied with fuel (5) and wherein the method comprises: (A) operating a feed pump (6) in order to set the fuel pressure (p) in the high-pressure reservoir (8) to a predetermined value (p _nom ); (B) turn off the feed pump (6) after the predetermined fuel _{pressure (p nom} ) has been reached in the high pressure reservoir (8); (C) to carry out at least one injection process in each case with at least two injection valves (14) one after the other; (D) to measure the pressure drop (Δp) caused by the at least one injection process in the high-pressure reservoir (8); _{(E) to determine a measure (M) for the flow rate (Q stat} ) through the respective injection valve (14) from the pressure drop (Δp) measured for the at least one injection process; and (F) to compare the dimensions (M) of the flow rate (Q _stat ) measured for the at least two injection valves (14) with one another. A method for comparing the flow rates (Q _stat ) of at least two injection valves (14) of an internal combustion engine (2), the at least two injection valves (14) being supplied with fuel (5) from a high-pressure reservoir (8), and the method comprising: ( A) to operate a feed pump (6) in order to set the fuel pressure (p) in the high-pressure reservoir (8) to a predetermined value (p _nom ); (C) sequentially to carry out at least one injection process with at least two of the injection valves (14), each injection process comprising at least one main injection process (HE) with a combustion effect and at least one post-injection process (NE) not effective in combustion; (D) to measure the pressure drops (Δp) caused by the injection processes in the high-pressure reservoir (8); (E) from the measured pressure drops (Δp) to determine dimensions (M) for the flow rates (Q _stat ) through the injection valves (14); and (F) to compare the dimensions (M) of the flow rate (Q _stat ) measured for the injection valves (14) with one another. Procedure according to Claim 2 , where the measure (M) for the flow rate (Q _stat ) either only from the pressure drop (Δp) caused by the at least one post-injection process (NE) or from the at least one main injection process (HE) and the at least one post-injection process (NE) jointly caused in the high pressure reservoir (8) pressure drop (Δp) is determined. Procedure according to Claim 2 or 3 , the method comprising switching off the feed pump (6) in an additional step (B) after the predetermined fuel _{pressure (p nom} ) has been set in the high-pressure reservoir (8). Procedure according to Claim 1 or 4th , the method comprising monitoring the fuel pressure (p) in the high-pressure reservoir (8) and operating the feed pump (6) in order to set the fuel pressure (p) in the high-pressure reservoir (8) back to the predetermined value as soon as the fuel pressure (p ) in the high pressure reservoir (8) falls _{below a predetermined limit value (p min} ). The method according to any one of the preceding claims, wherein the method comprises repeating steps (C) and (D) several times and the measure (M) for the flow rate (Q _stat ) through each of the injection valves (14) from a sum of one To be determined integrally or from an average value of the pressure drops (Δp) measured for the respective injection valve (14). Method according to one of the preceding claims, wherein the defined fuel pressure (p _nom ) is the maximum fuel pressure (p _max ) of the injection system (3). Method according to one of the preceding claims, wherein the injection quantity of each injection event for which the pressure drop (Δp) is measured is greater than the injection quantity required in the respective operating state of the internal combustion engine (2). Method according to one of the preceding claims, wherein the method additionally comprises conveying the content of the at least one combustion chamber (12) into which fuel (5) has been injected from the at least one combustion chamber (12), the proportion of fuel (5) ) to determine in the content conveyed from the at least one combustion chamber (12) and from this to determine the flow rate (Q _stat ) of the injection valves (14). Procedure according to Claim 9 wherein the method comprises using a lambda probe (20) in order to determine the proportion of fuel (5) in the content conveyed from the at least one combustion chamber (12). Procedure according to Claim 9 or 10 , the method comprising moving the piston (13) of the internal combustion engine (2) with the aid of an electric motor (22) in order to convey the contents of the at least one combustion chamber (12) out of the at least one combustion chamber (12), the method in particular comprises rotating a crankshaft (24) of the internal combustion engine (2) in order to move the pistons (13) of the internal combustion engine (2). Injection system (3) for an internal combustion engine (2), in particular for an internal combustion engine (2) in a motor vehicle (1), the injection system (3) comprising: at least two injection valves (14) which are designed to deliver fuel (5) during operation to inject into at least one combustion chamber (12) of the internal combustion engine (2); a high-pressure reservoir (8) which is designed to store fuel (5) under increased pressure (p) and to make it available to the injection valves (14); a feed pump (6) which is designed to feed fuel (5) into the high-pressure reservoir (8); a pressure sensor (10) which is designed to measure the fuel pressure (p) in the high-pressure reservoir (8); a control device (16), which is designed to receive a measurement signal from the pressure sensor (10) and to control the feed pump (6) and the injection valves (14), wherein the control device (16) is designed, in a diagnostic mode, a method according to a of the Claims 1 to 8th perform in order to compare the flow rate (Q _stat ) of at least two of the injection valves (14) with one another. Motor vehicle (1) with an internal combustion engine (2) and an injection system (3) Claim 12 . Motor vehicle (1) according to Claim 13 , which additionally has an exhaust gas line (18) which is in fluid connection with the at least one combustion chamber (12) of the internal combustion engine (2), and a lambda probe (20) arranged in the exhaust gas line (18), the control device (16) being designed to evaluate a signal (30) provided by the lambda probe (20) in order to determine the flow rate (Q _stat ) of the injection valves (14). Motor vehicle (1) according to Claim 13 or 14th with an electric motor (22) which is designed to rotate a crankshaft (24) of the internal combustion engine (2) in order to convey the contents of at least one combustion chamber (12) into the exhaust gas line (18).

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