EP1568874B1 - Method and apparatus for controlling the volume flow in a fuel injection system of an internal combustion engine - Google Patents

Description

The invention is based on a method or a device for controlling the volume flow in a common rail injection system of an internal combustion engine according to the independent claims 1 and 8. It is already known that in injection systems in which the fuel is injected directly into a cylinder of an internal combustion engine, the rail pressure is controlled by Absteuerung in the high pressure region with a pressure control valve. By contrast, the load-point-dependent volume flow is controlled by a volume flow control valve. The controller is designed so that the high-pressure pump delivers only the current need for fuel as possible. With this procedure should be achieved, on the one hand, the power consumption of the high-pressure pump is kept low. On the other hand, the fuel return amount and thereby introduced into the low pressure range amount of heat is minimized.

To control the volume flow valve, a two-dimensional pilot control map is used, which is guided by the injection quantity and the engine speed. In this pilot control map, the injection quantity and the engine speed form a measure of the current volume flow requirement, which corresponds to a specific load for the internal combustion engine. Due to component variations, it is necessary to additionally provide a map with adaptation values for the control of the volume flow control valve. In particular, since the volume flow requirement can increase due to wear-induced higher internal leaks over the lifetime of the system. The previously used adaptation map is only dependent on the rail pressure. Thus, in addition to the pilot control map, the one-dimensional adaptation map is used to control the flow control valve.

If the pilot control map (eg due to wear-induced higher volumetric flow requirement) is too low, the behavior of the rail pressure regulator (high positive control deviation, since the amount is insufficient to maintain the pressure) triggers an adaptation of the volumetric flow control valve actuation value until the quantity is sufficient again ,

This adaptation value has hitherto been stored as a function of the rail pressure and used at each load point which is driven at this pressure. The volume flow control valve is thus always controlled with the pre-control value plus the adaptation value.

The assignment of the load point and the rail pressure is not unique. One and the same pressure is used at different load points. This can result in the adaptation value being used without reason at a load point because the same rail pressure is traveled at this load point as at another load point at which the adaptation took place.

The consequence is that, for example, instead of the correct adaptation value, a wrong, too high adaptation value is read from the characteristic curve and thus too much fuel is provided. The pressure-dependent control thus leads in the cases mentioned to promote a wrong amount of fuel.

The invention is based on the object to improve the control of the flow control valve so that as possible only the required amount of fuel is provided. This object is achieved with the features of the independent claims 1 and 8.

In the inventive method for controlling the load-point-dependent volume flow in a fuel injection system of an internal combustion engine with the characterizing Features of the independent claims 1 and 8, the advantage is that for determining the valve position of the flow control valve in addition to the pilot control map, a two-dimensional adaptation map is used. It is considered to be particularly advantageous that in the two-dimensional adaptation characteristic map the adaptation values for the volume flow control valve are predefined as a function of two operating parameters of the internal combustion engine.

The measures listed in the dependent claims advantageous refinements and improvements of the independent claims 1 and 8 are given. It is considered to be particularly advantageous that in the adaptation characteristic map the adaptation values for the valve position can be formed as a function of two of the following four operating parameters: injection quantity, engine torque, engine speed and load. In the case of these possible combinations of two operating parameters, adaptation values which are adapted to the respective load point result in an advantageous manner.

A particularly favorable solution is also seen in the fact that the adaptation values are stored in an adaptation characteristic map which reproduces the adaptation values as a function of the two operating parameters engine speed and injection quantity. Because with these two operating parameters can be a one-time adaptation value for the flow control valve specify.

It is further provided to use the same operating parameters for the axes of the characteristic map both in the pilot control map and in the adaptation map. This procedure simplifies the control of the volume flow control valve, since the two operating parameters are already used for the pilot control map and thus a match of the load points is given.

Since the stored values do not always correspond to the current load point in the adaptation map, it is provided that interpolation takes place between two stored, adjacent values of the adaptation map.

Preferably, a linear interpolation of the adaptation values is carried out, for which the known algorithms can be used.

In a further preferred embodiment, the values of the adoption map are adjusted during operation of the injection system. Preferably, the values of the adaptation characteristic field are changed when the controlled variable of the regulator of the pressure regulating valve exceeds or falls below a defined threshold.

The device is advantageously applicable to a diesel, gasoline or gas engine.

Figur 1

zeigt in schematischer Darstellung den Hochdruckteil eines Common Rail Einspritzsystems,

Figur 2

zeigt ein zweidimensionales Vorsteuerkennfeld nach dem Stand der Technik,

Figur 3

zeigt ein Ausführungsbeispiel der Erfindung mit einem zweidimensionales Adaptionskennfeld und

Figur 4

zeigt ein Blockschaltbild einer erfindungsgemäßen Vorrichtung.

An embodiment of the invention is illustrated in the drawing and is explained in more detail in the following drawings.

FIG. 1

shows a schematic representation of the high pressure part of a common rail injection system,

FIG. 2

shows a two-dimensional pilot control map according to the prior art,

FIG. 3

shows an embodiment of the invention with a two-dimensional adaptation map and

FIG. 4

shows a block diagram of a device according to the invention.

In FIG. 1 is shown in a schematic representation of substantially the high-pressure part of a common rail injection system, which is usable for an internal combustion engine, such as a diesel, gasoline or gas engine. It shows the components that provide the fuel in the rail under high pressure for the injectors.

The fuel is first of a (in FIG. 1 not shown tank) via a fuel inlet A of a fuel feed pump 1 is supplied. The fuel feed pump 1 is connected via its output to the input of a controllable volume flow control valve VCV. In order to regulate the admission pressure, an admission pressure control valve 5 is connected in parallel to the fuel advance pump, via which excess fuel can be returned to the low pressure area. Furthermore, the output of the volume flow control valve VCV is connected to a high-pressure pump 8, which generates a very high fuel pressure in the rail, depending on the application example, 800 ... 2000 bar. To generate the high rail pressure, the high-pressure pump 8 has three displacement units 3. Furthermore, a flushing / lubricating valve 6 is installed in the inlet region of the high-pressure pump 8, via which the fuel feed pump 1 flushes and lubricates the high-pressure pump 8 with fuel.

At the high pressure outlet of the high pressure pump 8, a high pressure control valve PCV is arranged. The high-pressure control valve PCV preferably controls the high fuel pressure in the rail by means of a PI controller. On the output side, a gap filter 7 is connected downstream of the high-pressure control valve PCV in order to filter out solid suspended particles in the fuel before the fuel is fed via a high-pressure connection B to a downstream fuel reservoir with injectors connected thereto. In front of the inlet of the high-pressure control valve PCV, a branch for a fuel return C is provided in order to return excess fuel back into the low-pressure region.

FIG. 2 shows a known two-dimensional pilot map, which is used to control the flow control valve VCV use.

In the representation of the pilot control map according to FIG. 2 the engine speed N is plotted on the X axis and the injection quantity MF (mass of fuel) is plotted on the Y axis. The pilot control value for the volume flow control valve VCV is then read for a current speed N and a load-dependent predetermined injection quantity MF on the Z axis as a percentage value (% value) of the pulse width modulated signal with which the volume flow control valve is controlled. The pilot control characteristic initially serves for the volumetric flow control valve VCV as a presetting value, which can still be adapted with the aid of an adaptation value in order to obtain an exact valve position depending on the actual parameters of the injection system.

Alternatively, the pilot control value can also be stored as a table. Depending on the engine speed N and the injection quantity MF, the characteristic values are also indicated in the table as percentages from the maximum opening angle of the volume flow control valve VCV.

The valve position of the volume flow control valve VCV is controlled by means of a pulse width modulation (PWM values). In order to achieve an adaptation of the valve position, an adaptation value from the adaptation characteristic field is added to the pilot control value of the pilot control map to determine the PWM value for a current operating point.

According to the invention, it is proposed to design the adaptation map in two dimensions as a function of two operating parameters.

FIG. 3 shows an embodiment of the adaptation map according to the invention. Here are the operating parameters Injection amount MF and the engine speed N used. The adaptation map thus has - in this special case - the same axes as the pilot control map of FIG. 2 , The speed X is plotted on the X axis and the injection quantity MF on the Y axis. The adaptation value A can then be read on the Z axis as a percentage value from the maximum opening angle of the volume flow control valve VCV.

In an alternative embodiment of the invention, it is provided that the adaptation values are stored in the adaptation characteristic field as a function of in each case two of the following operating parameters: the injection quantity MF, the engine torque, the engine speed N and / or the load TQI. In each case two of these parameters can be used to produce an exact assignment of the adaptation value to the load of the internal combustion engine via the two-dimensional adaptation characteristic field. It is thus avoided that the high-pressure pump is promoted too much or too little fuel in the fuel tank of the internal combustion engine by an incorrect opening angle of the flow control valve VCV. The control according to the invention advantageously compensates for manufacturing tolerances of the individual components of the injection system of the internal combustion engine.

For the determination of the adaptation values, it is further provided that the values of the adaptation characteristic field are preferably linearly interpolated. As a result, intermediate values can also be determined with a simple linear regression, so that the adaptation values are determined more accurately.

According to the invention, it is further provided that the adaptation values for the individual load points in the two-dimensional adaptation characteristic field are continuously adapted, so that an automatic adaptation results for the volume flow control valve VCV. This results in an exact load point-dependent adaptation to the toleranced built-in components, which also works independently of their aging and wear.

To adapt the adaptation values of the adaptation characteristic field, the controlled variable of the PI regulator of the pressure regulating valve is monitored by a control unit. If the controlled variable of the PI controller exceeds a defined threshold, the control unit enters a corresponding adaptation value into the adaptation characteristic field for the present operating point in accordance with the parameters of the axis of the adaptation characteristic field. He adaptation value is selected so that when controlling the volume flow control valve VCV with the pilot value from the pilot map and the adaptation value from the adaptation map so much fuel is conveyed into the fuel tank that the control variable of the PI controller again gets below the threshold. The adaptation value is lowered or increased, for example, when the threshold for the controller value is exceeded or undershot by a specified value or a specified percentage.

The optimum adaptation to the required fuel quantity ensures that the low-pressure system becomes insensitive to the heat input via the fuel return system. The return system can therefore be connected in the vicinity, or directly to the high-pressure pump, since the fuel is no longer heated.

A further advantage is also seen in the fact that the control quality is improved in particular in injection methods with a multiple injection, since the pressure fluctuations in the rail are minimized due to a wrong or unstable valve position.

FIG. 4 shows an embodiment of the invention with a device for controlling the load-point-dependent volume flow in a common rail injection system. It has a program-controlled control unit 10, which is provided with a program memory 11, a memory 12 for a first pilot control map for the pressure control valve and a second pilot control map for the flow control valve and is connected to a memory 13 for an adaptation map. The control unit 10 executes a program which controls or controls the connected components fuel feed pump 1, high-pressure pump 8, high-pressure control valve PCV and the volume flow control valve VCV, etc. It is provided that a PI controller 9 controls the high-pressure control valve PCV according to the predetermined first pilot control map. In addition, the PI controller 9 is connected to the control unit 10 and reports the current control value of the high-pressure control valve to the control unit 10. The control unit 10 is connected to sensors that detect the operating parameters, in particular the speed, the injection quantity, the engine torque and the load. The volume flow control valve VCV is controlled in its valve position by means of the second pilot control map and the two-dimensional Adaptionskennfeldes so that the exact amount of fuel required for each current load point is provided. By this load point-dependent control of the volume flow control valve VCV is achieved in an advantageous manner that the fuel return amount is minimized and thus in particular a heating of the fuel in the tank is avoided. Furthermore, it is achieved that the high-pressure pump, which is driven by a toothed belt or a mechanical clutch, absorbs less energy and thus reduces the power consumption of the high-pressure pump. The result is a high engine performance and / or a reduced fuel consumption.

Claims (10)

1. Method for controlling the volumetric flow in a common rail injection system in an internal combustion engine, the rail pressure being produced by means of a high pressure pump (8) and being set in the rail by a regulatable high pressure regulation valve (PCV) and the volumetric flow being determined by the valve position of a controllable volumetric flow regulation valve (VCV), which is controlled by means of a precontrol characteristic field and an adaptation characteristic field as a function of an operating parameter of the internal combustion engine, characterised in that the adaptation characteristic field is configured as two-dimensional, the adaptation values for the valve position being predefined in the adaptation characteristic field as a function of two operating parameters of the internal combustion engine.
2. Method according to claim 1, characterised in that in the adaptation characteristic field the adaptation values for the valve position are determined as a function of two of the following operating parameters respectively:

   the mass of fuel (MF),

   the engine speed (N) and/or

   the engine torque or load (TQI).
3. Method according to claim 1 or 2, characterised in that the adaptation values are stored in the adaptation characteristic field with the operating parameters engine speed (N) and mass of fuel (MF).
4. Method according to claim 3, characterised in that the adaptation characteristic field has the same parameter axes as the precontrol characteristic field.
5. Method according to one of the preceding claims, characterised in that a current adaptation value is interpolated from adjacent values of the adaptation characteristic field.
6. Method according to claim 5, characterised in that the interpolation is linear.
7. Method according to one of claims 1 to 6, characterised in that the adaptation values of the adaptation characteristic field are adjusted as a function of the regulation value of the regulator (9) of the high pressure regulation valve (PCV).
8. Device for controlling the load-point-dependent volumetric flow in a common rail injection system in an internal combustion engine, with a high pressure pump (8), a regulatable high pressure regulation valve (PCV), a controllable volumetric flow regulation valve (VCV), a programmable control unit (10) and a storage unit (13) according to one of the preceding claims, characterised in that a two-dimensional adaptation characteristic field for the volumetric flow regulation valve (VCV) is stored in the storage unit (13) and that the control unit controls the valve position of the volumetric flow regulation valve (VCV) as a function of a precontrol characteristic field and the adaptation characteristic field as a function of two operating parameters of the internal combustion engine.
9. Device according to claim 8, characterised in that the adaptation values are stored in the adaptation characteristic field as a function of the speed (N) of the internal combustion engine and the mass of fuel (MF).
10. Device according to one of claims 8 or 9, characterised in that the control unit (10) detects a regulation value of the regulator (9) of the high pressure regulation valve (PCV) and, if said value exceeds or is below comparison thresholds, reduces or increases the adaptation value in the adaptation characteristic field.

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