WO2001069067A1

WO2001069067A1 - Method for operating an internal combustion engine

Info

Publication number: WO2001069067A1
Application number: PCT/DE2001/000347
Authority: WO
Inventors: Hansjoerg Bochum
Original assignee: Robert Bosch Gmbh
Priority date: 2000-03-11
Filing date: 2001-01-30
Publication date: 2001-09-20
Also published as: DE10012024A1; KR20020081425A; EP1266134A1; JP2003528243A

Abstract

The invention relates to a method for operating an internal combustion engine, especially a direct injection internal combustion engine. According to the invention, fuel is delivered by at least one pump (3, 7) into a pressure accumulator (8) out of which fuel is injected into a combustion chamber via an injection valve (10), whereby the open period (t_i) of the injection valve (10) is calculated according to the accumulated pressure (p_r) prevailing in the pressure accumulator (8). The aim of the invention is to be able to determine, with the greatest possible precision, the quantity of fuel to be injected, especially in the case of dramatic pressure fluctuations of the accumulated pressure (p_r). To this end, the invention provides that an estimated pressure value (p_r_est) is calculated from at least two measured pressure values and is used as the accumulated pressure (p_r) prevailing in the pressure accumulator (8) in order to calculate the open period (t_i) of the injection valve (10) in the case that the sum of the gradients (dp_r_syn) of the curve of the accumulated pressure exceeds a predetermined threshold value.

Description

Method for operating an internal combustion engine

State of the art

The present invention relates to a method for operating an internal combustion engine, in particular a direct-injection internal combustion engine, in which fuel is pumped into a pressure accumulator by at least one pump and the fuel is injected from the pressure accumulator into a combustion chamber via an injection valve, the opening duration of the injection valve depending is calculated from the accumulator pressure prevailing in the pressure accumulator. The invention also relates to an internal combustion engine, in particular a direct-injection internal combustion engine, with - a pressure accumulator, at least one pump for delivering fuel to the pressure accumulator, a combustion chamber, an injection valve for injecting fuel from the pressure accumulator into the combustion chamber, and a control unit for calculating the opening duration of the injection valve as a function of the accumulator pressure prevailing in the pressure accumulator. _S inally, the present invention also relates to a control apparatus for such a machine Brennkraf.

A _V out and a machine at the outset Brennkraf mentioned type are known from DE 195 48 278. There, a method for regulating the accumulator pressure in a pressure accumulator of a Co mon-rail injection system (CR system) is described. In such CR systems, the opening duration of the injection valves is calculated as a function of the quantity of fuel to be injected and of the accumulator pressure prevailing in the pressure accumulator. The accumulator pressure prevailing in the pressure accumulator must be included in the calculation of the opening duration, since the flow through the injection valves is dependent on the accumulator pressure. The accumulator pressure is recorded synchronously with the speed. The pressure control takes place in a fixed time grid. For pressure control, the accumulator pressure recorded in synchronism with the speed is sampled in a synchronous manner.

In the method for operating an internal combustion engine known from the prior art, it is disadvantageous that the opening duration of the injection valves does not depend on a storage pressure prevailing in the pressure accumulator at the time of the injection, but rather in

Dependence on pressure values measured before the injection is calculated. In stationary operation, where there is only a slight change in the storage pressure over time, the age of the measured pressure values has little effect on the calculated opening time of the

Injectors. With a dynamic pressure curve of the accumulator pressure, however, there can be relatively large differences between the pressure values used for the calculation of the opening duration and measured before the injection and the pressure value actually prevailing in the pressure accumulator during the injection. If the pressure rises dynamically, the storage pressure during injection is higher than the previously measured pressure value. As a result, the flow through the injection valves and ultimately the fuel mass injected into the combustion chambers is actually greater than is calculated; the engine runs in the transition to rich. Accordingly, the internal combustion engine runs in the transition to lean with a dynamic pressure drop.

It is known from the subsequently published patent application DE 198 57 971 not to calculate the opening times of the injection valves on the basis of pressure values measured before the injection, but rather to use future at least two measured pressure values to calculate a future pressure value, more precisely an estimated pressure value for the time when the injection begins determine and then use this estimated pressure value as the basis for calculating the opening duration of the injection valves.

Object of the invention

The present invention has for its object to reduce errors in the fuel mass injected into the combustion chambers in an internal combustion engine, thereby improving the emission behavior, noise and fuel consumption of the internal combustion engine.

To achieve this object, the invention proposes, starting from the method for operating an internal combustion engine of the type mentioned at the outset, that an estimated pressure value is calculated from at least two measured pressure values and is used as the storage pressure prevailing in the pressure accumulator for calculating the opening duration of the injection valve, if the Amount of the gradient of the

Memory pressure history exceeds a predetermined threshold.

According to the invention it is therefore proposed to operate the internal combustion engine in a stationary mode and in a dynamic mode

Operation with a slowly changing over time Accumulator pressure to calculate the opening times of the injection valves in a manner known per se on the basis of measured accumulator pressure values.

With a faster changing memory pressure, i. H. If the amount of the gradient of the accumulator pressure curve exceeds a predeterminable threshold value, the calculation of the opening times of the injection valves does not use a relatively old pressure value measured before the injection, but rather a current, estimated pressure value for the period of time during the injection. The estimated pressure value is calculated on the basis of at least two measured pressure values. With the present invention, dynamic pressure changes in the storage pressure can also be taken into account. Corresponding opening times of the injection valves can be calculated and the fuel mass to be injected into the combustion chambers can be measured particularly precisely even in the event of dynamic pressure changes. The method according to the invention leads to an improvement in the emission behavior, the noise level and the fuel consumption of the internal combustion engine.

As already mentioned, the estimated pressure value is only used to calculate the opening times of the injection valves if the gradient of the accumulator pressure curve exceeds a predetermined threshold value, i. H. if the accumulator pressure curve exceeds a certain dynamic. The gradient shows the direction of the greatest pressure change in the storage pressure curve. The amount of the gradient reflects the amount of the maximum pressure change.

According to an advantageous development of the present invention, it is proposed that the estimated pressure value characterizes an average storage pressure between the beginning and the end of the injection. The mean accumulator pressure can be a value between the accumulator pressure at the beginning and the accumulator pressure at the end of the injection. It is preferably the accumulator pressure that lies exactly in the middle between the accumulator pressure at the beginning and the accumulator pressure at the end of the injection. Alternatively, the mean accumulator pressure is the accumulator pressure that prevails in the pressure accumulator at a point in time exactly between the start of injection and the end of injection. As a result, errors in the fuel aces injected into the combustion chambers can be reduced particularly well.

According to a preferred embodiment of the present invention, it is proposed that a compensation function be placed by measured pressure values and the estimated one

Pressure value is calculated using the compensation function. A first-order compensation polynomial is advantageously placed through the measured pressure values. If the expected injection start or a point in time between the start of injection and the end of injection is inserted into the compensation function or into the compensation polynomial, a relatively precise estimated pressure value is obtained for the point in time of the start of injection or for a point in time between the start of injection and the end of injection. An equalization polynomial of the first order can be put through two measured pressure values without a great amount of computing time and with a small storage space requirement and provides an estimated pressure value with sufficient accuracy.

According to another advantageous development of the present invention, it is proposed that the measured pressure values be recorded over several injection cycles. In this way, short-term pressure fluctuations in the pressure accumulator can be dealt with, which results in a particularly smooth running of the internal combustion engine is made possible.

In the event of a dynamic pressure increase in the pressure accumulator, the opening times of the injection valves calculated using the method according to the invention are smaller than the opening times calculated on the basis of pressure values measured before the injection. Likewise, in the case of a dynamic pressure drop, the opening times calculated using the method according to the invention are greater than the opening times calculated on the basis of pressure values measured before the injection. In particular, in the case of very strong pressure fluctuations in the pressure accumulator, on the one hand the difference between the opening times calculated using the method according to the invention and the difference calculated on the basis of pressure values measured before the injection

On the other hand, in order not to allow opening times to become too large, according to a preferred embodiment of the present invention, it is further proposed that the estimated pressure value be multiplied by a reduction factor which is <1 before it is considered to be that in the

The accumulator pressure prevailing in the pressure accumulator is used to calculate the opening duration of the injection valve.

Of particular importance is the implementation of the method according to the invention in the form of a control element which is provided for a control unit of an internal combustion engine, in particular a direct injection internal combustion engine. In this case, a program is stored on the control element, which is executable on a computing device, in particular on a microprocessor, of the control device and is suitable for executing the method according to the invention. In this case, the invention is implemented by a program stored on the control element, so that this control element provided with the program does the same in the same way

Invention represents how the method for carrying it out the program is suitable. In particular, an electrical storage medium can be used as the control element, for example a read-only memory (ROM) or a flash memory.

As a further solution to the object of the present invention, it is proposed, starting from the internal combustion engine of the type mentioned at the outset, that the control unit calculates an estimated pressure value from at least two measured pressure values and uses the estimated pressure value as the storage pressure prevailing in the pressure accumulator if the amount of the gradient of the accumulator pressure curve exceeds a predeterminable threshold value.

According to an advantageous development of the present invention, it is proposed that the pressure accumulator is designed as a high-pressure accumulator of a Co mon-Rail (CR) fuel injection system and the injection valve as a high-pressure injection valve. In internal combustion engines with a CR injection system in particular, it is advantageous to determine the opening times of the

To calculate high pressure injectors in the event of dynamic pressure fluctuations in the accumulator pressure on the basis of estimated pressure values which characterize the accumulator pressure during the injection.

Finally, as yet another solution to the problem of the present invention, starting from the control device of the type mentioned at the beginning, it is proposed that the

The control unit calculates an estimated pressure value from at least two measured pressure values and attracts the estimated pressure value than the pressure prevailing in the accumulator reservoir pressure, if the amount exceeds the gradient of the _S peicherdruckverlaufs a predeterminable threshold value. drawings

Further features, possible applications and advantages of the invention result from the following description of an embodiment of the invention, which is shown in the drawings. All of the described or illustrated features, alone or in any combination, form the subject matter of the invention, regardless of their summary in the patent claims or their dependency, and regardless of their wording or representation in the description or in the drawings. Show it:

Figure 1 shows a fuel supply system of an internal combustion engine according to the invention;

Figure 2 is a procedural diagram of an inventive

Method according to a preferred

Embodiment and

Figure 3 shows a dynamic pressure curve of the

Storage pressure in an accumulator

Internal combustion engine.

In FIG. 1, a fuel supply system of an internal combustion engine according to the invention with high-pressure injection is designated in its entirety with reference number 1. The fuel supply system 1 is usually referred to as a common rail (CR) fuel injection system.

The reference numeral 2 designates a fuel reservoir which is connected to a prefeed pump 3. From the pre-feed pump 3, the fuel passes through a line 4 to a metering valve 5. The line 4 is via a low pressure relief valve 6 with the Fuel tank 2 in connection. The metering valve 5 is connected to a high-pressure accumulator 8 via a high-pressure pump 7. The high-pressure accumulator 8 is designed as a high-pressure accumulator line (rail). The high-pressure accumulator 8 is connected to high-pressure injection valves 10 (so-called injectors) via fuel lines 9. The high-pressure accumulator 8 is connected to the fuel tank 2 via a pressure relief valve 11. The metering valve 5 can be controlled by means of a coil 12.

The area of the fuel injection system 1 between the outlet of the high pressure pump 7 and the inlet of the pressure relief valve 11 is referred to as the high pressure area. The pressure in the high pressure area is detected by means of a sensor 13. The area of the fuel injection system 1 between the

Fuel reservoir 2 and the high pressure pump 7 is referred to as the low pressure area.

With 14 a control unit of the internal combustion engine is designated, which also controls the fuel supply system 1. The control unit 14 acts on the high-pressure injection valves 10 with control signals A and controls the coil 12 of the intake valve 5. For this purpose, the output signal P_r of the pressure sensor 13 and various output signals n from further sensors 15, such as a speed sensor, are evaluated.

The controller 14 comprises a filter 16, which the

Output signal P_r of the pressure sensor 13 is fed. The filter 16 applies a filtered pressure value P r of the pressure sensor 13 to a quantity calculation device 17 and a summation point 18. The output signal P_soll of a setpoint specification device 19 is present at a second input of the summation point 18. This processes the Output signals n of the further sensors 15 and the output signal Q_n of the quantity calculation device 17.

The quantity calculation device 17 applies control signals A to the high-pressure injection valves 10 and the setpoint specification device 19 to the signal Q_n, which corresponds to the quantity of fuel to be injected into the combustion chambers of the internal combustion engine. The output signal of the summation point 18 is applied to a pressure regulator 20, which in turn controls the coil 12 of the metering valve 5.

The Kraf material supply device 1 works as follows: First, fuel is delivered from the fuel tank 2 by the pre-feed pump 3. As soon as the pressure in the low-pressure area rises to impermissibly high values, the low-pressure relief valve 6 opens and releases the connection between the outlet of the prefeed pump 3 and the fuel tank 2.

The high-pressure feed pump 7 delivers the fuel from the low-pressure area to the high-pressure area. The high pressure pump 7 builds up a high pressure in the high pressure accumulator 8. Usually, pressure values of approximately 30 to 200 bar are achieved in a fuel supply system for a spark-ignition internal combustion engine and pressure values of approximately 1000 to 2000 bar in a high-pressure accumulator 8 in a self-igniting internal combustion engine. Via the high-pressure injection valves 10, the fuel can be metered under high pressure to the individual combustion chambers in the cylinders of the internal combustion engine.

The pressure in the high pressure area can be regulated by the metering valve 5. Depending on the voltage applied to the coil 12 or on the current flowing through the coil 12, the metering valve 5 supplies different delivery rates of the high-pressure pump 7 Available.

Additional actuators can also be used to regulate the accumulator pressure p_r in the high pressure range. As an alternative to metering valve 5, these are one in the

Flow adjustable electric pre-feed pump or a pressure relief valve, which can also be controlled by means of a coil.

The control signals A for the high-pressure injection valves 10 are dependent on the accumulator pressure p_r and on the fuel quantity Q_n to be injected. The fuel mass to be injected is set via the opening period t_i of the high-pressure injection valves 10. Since the flow through the open injectors 10 from the

Storage pressure p_r depends in the high pressure accumulator 8, this must be included in the calculation of the opening period t_i. The control signals A are calculated depending on the speed with a variable time interval. The time interval between the individual calculations depends on the speed n of the internal combustion engine. The control signal for the metering valve 5 in the pressure regulator 20 is calculated in a fixed time cycle. This time cycle is selected so that the pressure regulator 20 can immediately react to changing setpoints p_soll and the new setpoint p_soll is set as quickly as possible.

According to the prior art, the opening period of the high-pressure injection valves, ie the control signal A, is calculated directly from measured pressure values p_r. Since the injection can theoretically take place at relatively early points in time (for example at 340 ° before top dead center (TDC ^{) of} the ignition phase), the opening duration of the high-pressure injection valves 10 calculated for an injection must already be before this early

Available at the time. However, this means that in the case of a relatively late injection (for example at 240 ° before ignition TDC) the calculated opening time t_i for the high-pressure injection valves 10 took place on the basis of relatively old measured pressure values p_r.

The calculation of the opening time t_i

High-pressure injection valves 10 as a function of relatively old, previously measured pressure values p_r have hardly any effects in the stationary operation of the internal combustion engine. However, the pressure in the high-pressure accumulator 8 can fluctuate greatly. The pressure fluctuations are caused by the injection on the one hand and by the pressure build-up in the high pressure area on the other hand. In the case of such dynamic pressure fluctuations, the measured pressure value used for calculating the opening duration t_i deviates in part greatly from the accumulator pressure actually prevailing in the high-pressure accumulator 8 at the time of the injection.

In order to be injected into the combustion chambers of the internal combustion engine via the high-pressure injection valves 10

To be able to determine fuel mass as precisely as possible, it is proposed according to the present invention to calculate the opening duration t_i of the high-pressure injection valves 10 on the basis of an estimated pressure value of the storage pressure prevailing in the high-pressure accumulator 8 at the time of the injection. A flow chart of the method according to the invention is shown in FIG. 2. The method begins in a function block 30. In a subsequent function block 31, the current accumulator pressure p_r_act prevailing in the high-pressure accumulator 8 is measured and stored in a accumulator 32. In a function block 33, a previously measured old pressure value p_r_ist_alt is taken from the memory 32. The gradient of the accumulator pressure curve dp_r_syn is then formed in a function block 34, in which the old accumulator pressure value p_r_is the current one Storage pressure value p_r_ist_alt is subtracted. A query block 35 then checks whether the magnitude of the gradient dp_r_syn exceeds a predetermined threshold value. The magnitude of the gradient of the accumulator pressure curve exceeds the predetermined threshold if the accumulator pressure p_r in the high-pressure accumulator 8 changes relatively quickly. In this case, an estimated pressure value p_r_est is calculated in a function block 36. The opening duration t_i of the high-pressure injection valves 10 is then calculated in a function block 37 as a function of the estimated pressure value p_r_est.

In the present exemplary embodiment, a first-order compensation polynomial is set by means of two measured pressure values p_r and the estimated pressure value p_r_est is calculated on the basis of the compensation line. The estimated pressure value p_r_est can characterize a storage pressure p_r at the beginning of the injection, as is described in detail in DE 198 57 971, to which reference is expressly made here. In this case, the estimated pressure value p_r_est is calculated using the following equation (see FIG. 3):

w_esb_x p_r_est = ρ_r_ist + dp_r_syn, w_syn

where for a 4-stroke internal combustion engine:

720 ° w syn

number of cylinders

and w_esb_x is the angle at the start of injection.

In the present exemplary embodiment, the estimated pressure value p_r_est characterizes a storage pressure p_r in the Middle of the injection, ie between the beginning and the

End of injection, at an angle w_esm_x. In this

In this case, the estimated pressure value p_r_est is calculated using the following equations:

w_esm_x p_r_est = p_r_ist + dp_r_syn, w_syn

where w_esm_x is the angle in the middle of the injection and

w_esm_x = w_esb_x + angle {0, 5 • t_i}

the following applies to a 4-stroke internal combustion engine:

Angle {0.5- t__i} = 0.006

with the speed n of the internal combustion engine and the opening duration t_i, which corresponds to the injection duration.

If the amount of the gradient of the accumulator pressure curve is below the threshold value, i.e. in the cases in which the internal combustion engine is operated in the area of stationary operation, the opening time t_i of the high-pressure injection valves 10 is calculated directly from the measured pressure values p_r_ist in a function block 38 in a manner known per se from DE 195 48 278. Finally, the calculated opening time t_i of the high-pressure injection valves 10 is output in a function block 39. The method according to the invention is ended in a function block 40.

Claims

Expectations

1. Method for operating an internal combustion engine, in particular a direct-injection internal combustion engine, in which fuel is pumped by at least one pump (3, 7) into a pressure accumulator (8) and the fuel from the pressure accumulator (8) via an injection valve (10) into a combustion chamber is injected, the opening duration (t_i) of the injection valve (10) being calculated as a function of the accumulator pressure (p_r) prevailing in the pressure accumulator (8), characterized in that an estimated pressure value (p_r_act, p_r_act_alt) is at least ( p__r_est) is calculated and used as the accumulator pressure (p_r) prevailing in the pressure accumulator (8) to calculate the opening duration (t_i) of the injection valve (10) if the magnitude of the gradient (dp_r_syn) of the accumulator pressure curve exceeds a predetermined threshold value.

2. The method according to claim 1, characterized in that an average storage pressure (p_r) between the beginning and the end of the injection is characterized by the estimated pressure value (p_r_est).

3. The method according to claim 1 or 2, characterized in that a compensation function is placed by the measured pressure values and the estimated pressure value (p_r_est) is calculated using the compensation function.

4. The method according to claim 3, characterized in that a first order compensation polynomial is placed by the measured pressure values.

5. The method according to any one of claims 1 to 4, characterized in that the measured pressure values are recorded over several injection cycles.

6. The method according to any one of claims 1 to 5, characterized in that the estimated pressure value (p_r_est) is multiplied by a reduction factor which is <1 before it is used as the storage pressure in the pressure accumulator (8) for calculating the opening duration ( t_i) of the injection valve (10) is used.

7. Control element, in particular read-only memory (ROM) or flash memory, for a control device (14) of an internal combustion engine, in particular a direct-injection internal combustion engine, on which a program is stored, which is stored on a computing device, in particular on a

Microprocessor, the control unit (14) is executable and suitable for executing a method according to one of the preceding claims.

8. Internal combustion engine, in particular direct-injection internal combustion engine, with a pressure accumulator (8), at least one pump (3, 7) for conveying

Fuel in the pressure accumulator (8), - a combustion chamber, an injection valve (10) for injecting the

Prevailing fuel from the pressure accumulator (8) into the combustion chamber and a control unit _S (14) for calculating the opening duration (ti) ^{of the} injection valve (10) in response to the pressure in the accumulator (8) Storage pressure (p_r), characterized in that the control unit (14) calculates an estimated pressure value (p_r_est) from at least two measured pressure values and the estimated pressure value (p_r_est) as that prevailing in the pressure accumulator (8)

Storage pressure uses if the amount of the gradient of the storage pressure curve exceeds a predetermined threshold.

9. Internal combustion engine according to claim 8, characterized in that the pressure accumulator (8) as a high-pressure accumulator of a common rail (CR) -

Fuel injection system and the injection valve (10) is designed as a high-pressure injection valve.

10. Control device (14) for an internal combustion engine, in particular for a direct-injection internal combustion engine, with a pressure accumulator (8), - at least one pump (3, 7) for conveying

Fuel in the pressure accumulator (8), a combustion chamber, an injection valve (10) for injecting the

Fuel from the pressure accumulator (8) into the combustion chamber and the control unit (14) for calculating the opening duration (t_i) of the injection valve (10) as a function of the accumulator pressure (p_r) prevailing in the pressure accumulator (8), characterized in that the control unit (14) calculates an estimated pressure value (p r_est) from at least two measured pressure values and uses the estimated pressure value (p__r_est) as the accumulator pressure prevailing in the pressure accumulator (8) if the magnitude of the gradient of the accumulator pressure curve exceeds a predetermined threshold value.