Patent Application
20090050112
This application claims priority to German application number 10 2007 040 122.3 filed Aug. 24, 2008, the contents of which are hereby incorporated by reference in its entirety.
The invention relates to a method and a device for controlling a pump connected to a fuel rail in an internal combustion engine.
In general in an internal combustion engine, fuel is supplied from the tank to the supply line of a downstream high-pressure pump by means of a fuel pump. The high-pressure pump supplies the fuel into a reservoir or a fuel rail. This fuel supply unit may preferably be controllable in such a way that only the amount of fuel that is actually required is supplied and there is no unnecessary pump output. In internal combustion engines with high-pressure direct injection, a high-pressure fuel pump must supply fuel to the reservoir or the fuel rail. The fuel supply device, consisting of a low-pressure pump and the high-pressure pump, is designed to supply only the amount of fuel that is actually required according to the injection quantity and the fuel pressure level.
The fuel mass can be influenced by design-specific actuators that are subject to a time lag. In engines with stroke change-over, a very rapid change in the air mass in the cylinder is caused by the change-over of the valve stroke characteristic curve. Due to this altered air mass, the injection mass must also be altered accordingly, which in turn requires a very rapid adjustment of the actuation of the delivery rate of the fuel pump.
In the prior art, fuel was previously firstly injected in motor vehicles by means of an injector. For this, a suitable quantity of fuel for the next stroke is supplied by a pump when the system is to change to the next stroke for example. However, this does not take into consideration that, for example, the pump provides the quantity of fuel with a certain delay so that the quantity of fuel may in some circumstances be pumped into an associated fuel rail too early or too late. Furthermore, too much or too little fuel may as a result thus be injected by the injectors for example, resulting in a subsequent adjustment of the supposedly insufficient quantity of fuel, even though the correct quantity of fuel had been determined beforehand, but was provided too early or too late.
A method and a device can be provided with which the control of the pump output of a pump that is connected to a fuel rail can be improved.
According to an embodiment, a method for controlling a pump that is connected to a fuel rail of an internal combustion engine in order to provide a predetermined quantity of fuel to the fuel rail for a predetermined operating state, may comprise the steps: a) Determining whether a process occurs to switch the internal combustion engine into a next predetermined operating state, b) Determining a pump output of the pump if the process for switching the internal combustion engine into a predetermined operating state was detected, wherein the pump output of the pump is selected so that the predetermined quantity of fuel for the operating state is provided, and c) Actuating the pump so that the pump provides the predetermined quantity of fuel when the predetermined operating state is achieved.
According to a further embodiment, the pump can be actuated for instance as a function of a time lag of the switch into the predetermined operating state and a time lag of the fuel system or a time lag of the pump. According to a further embodiment, the pump can be actuated in such a way that, taking into consideration a time lag of the pump, the pump has pumped the predetermined quantity of fuel into the rail at the end of a time lag in the switch into the predetermined operating state. According to a further embodiment, the detection of a signal can be used to determine whether a process for switching the internal combustion engine into a predetermined operating state is taking place for example, wherein the predetermined operating state is a stroke change-over to a next stroke and the process for switching the internal combustion engine into the next stroke is detected using a signal for stroke change-over for example. According to a further embodiment, the pump output of the pump can be determined as a function of the air mass change, the injection fuel mass change and/or the absolute injection fuel mass. According to a further embodiment, the pump can be a high-pressure pump or a low-pressure pump.
According to another embodiment, a device for controlling a pump that is connected to a fuel rail of an internal combustion engine in order to provide a predetermined quantity of fuel to the fuel rail for a predetermined operating state, may comprise: a detecting device for detecting a process according to which the internal combustion engine is switched into a predetermined operating state, a device for determining a pump output of the pump when the detecting device detects the process for switching the internal combustion engine into a predetermined operating state, wherein the pump output of the pump is selected such that the pump provides the predetermined quantity of fuel for the predetermined operating state, and a control device for actuating the pump in such a way that the pump provides the predetermined quantity of fuel when the predetermined operating state is achieved.
According to a further embodiment, the device for determining the pump output of the pump may take into consideration the air mass change, the injection fuel mass change and/or the absolute injection fuel mass in the predetermined operating state for the determination of the pump output for the predetermined quantity of fuel. According to a further embodiment, the control device may actuate the pump for example as a function of a time lag of a switching process into the predetermined operating state and a time lag of the fuel system or a time lag of the pump. According to a further embodiment, the control device can be configured in such a way that it actuates the pump so that the pump has pumped the predetermined quantity of fuel into the rail at the end of the time lag of the switching process into the predetermined operating state, taking consideration of the time lag of the pump. According to a further embodiment, the predetermined operating state may be for example a stroke change-over to a next stroke and the detecting device detects the process according to which the internal combustion engine is switched into the predetermined operating state using a signal, for example a signal for the stroke change-over.
The invention will now be described in more detail with reference to various embodiments in the accompanying drawings, in which;
According to various embodiments, actuating a pump that is connected to a fuel rail of an internal combustion engine can be provided in such a way that a predetermined quantity of fuel in the fuel rail can be provided for a predetermined operating state if this operating state occurs. For this, it is first determined whether a process occurs according to which the internal combustion engine is switched into a predetermined operating state. If the process for switching the internal combustion engine into the predetermined operating state is detected, a pump output of the pump is also determined, whereby the pump output is selected such that the predetermined quantity of fuel can be made available for the operating state. Furthermore, the pump is actuated in such a way that the pump provides the predetermined quantity of fuel when the predetermined operating state is reached.
This may have the advantage that the pump output of a pump is determined beforehand so that a predetermined quantity of fuel can be provided for a predetermined operating state and namely when this operating state is actually reached, for example when, for a stroke change-over, the valve changes to the next stroke, said stroke being a predetermined operating state. In contrast to this, in conventional systems the appropriate quantity of fuel cannot be provided reliably for the next stroke, for example at a stroke change-over. However, the “anticipatory” actuation of the pump according to various embodiments is however able to guarantee that the appropriate quantity of fuel can be made available at the correct time in the next stroke and that the formation of emissions can thus be reduced for example.
In a further embodiment, the process for switching the internal combustion engine into a predetermined operating state can be detected, for example using at least one signal for switching into the predetermined operating state. The predetermined operating state can be a stroke change-over into a next stroke for example and the process can be recorded using a signal for stroke change-over. The stroke change-over is a case where a particularly large air mass change can occur and where the provision of a suitable quantity of fuel is particularly important when the change-over process into the next stroke is completed, because the optimum combustion can be achieved in this way and no unnecessary pump output is required.
In another embodiment, time lags are taken into consideration for the actuation of the pumps in order to ensure that the pump only provides the desired predetermined quantity of fuel when the predetermined operating state, for example the change-over to the next stroke, is actually completed. To this end, the pump is actuated subject to a time lag of the predetermined operating state and a time lag of the fuel system or a time lag of the pump, for example.
In a further embodiment, the pump is actuated in such a way that, allowing for the time lag of the pump, the pump has pumped the predetermined quantity of fuel into the rail at the end of the time lag of the predetermined operating state, for example the stroke change-over. In this way, it is possible to ensure that the required quantity of fuel is not supplied in the rail too early or too late, but at the correct time when the switch to the predetermined operating state has been completed.
In a further embodiment, the pump output of the pump is determined as a function of the air mass change, the injection fuel mass change and/or the absolute injection fuel mass. This may have the advantage that these variables or parameters are normally known, for example for a stroke change from a small stroke to a large stroke and vice versa, and it is therefore easy to determine the required quantity of fuel and thus also the pump output of the pump.
According to a further embodiment, the pump can be a high-pressure pump or a low-pressure pump, as used in internal combustion engines or vehicles.
For the change-over of a valve stroke characteristic curve in an engine of a vehicle, the change-over does not usually occur immediately, but only after a certain time delay after actuators of a stroke change-over are actuated.
By means of the upstream signal for the change-over of the valve stroke characteristic curve or the signal for the stroke change-over and based on the knowledge of the time lags, the pump actuation can, in accordance with an embodiment, react more quickly to a subsequent air mass change and thus finally also to a fuel mass change by means of an appropriate control device, such as an ECU 26. This process can also be used to predict a controlled low-pressure fuel pump.
The fuel is supplied from the high-pressure fuel pump 20 into the rail 12 and introduced into a cylinder space (not shown) by injection valves 22. An additional non-return valve 23 can be provided in the line between the high-pressure fuel pump 20 and the rail 12 for example. The non-return valve 23 prevents the fuel from escaping from the rail 12 back towards the high-pressure fuel pump 20. In order to regulate the actuation of the actuating element of the high-pressure fuel pump 20 for supplying fuel into the rail 12, the fuel system 10 uses the signal from a fuel pressure sensor 24 for feedback.
The injection mass of the injectors or the injection valves 22 is primarily used to determine the quantity of fuel to be supplied. Deviations of the actual fuel pressure from the nominal fuel pressure are balanced out by increased or reduced supply from the high-pressure fuel pump 20. The high-pressure fuel pump 20 is affected by time delays in this respect, i.e. the pumped mass cannot be supplied by the pump 20 immediately, but only with a certain time delay, the time lag of the high-pressure fuel pump 20.
In normal operation (stationary), this does not generally present a problem. However, in operating states with a very high injection mass change, the fuel pressure can no longer track the nominal value quickly enough. An unfavorable operating state of this kind occurs primarily when there is a change-over of the valve stroke characteristic curve or a stroke change-over from a small to a large stroke and vice versa for example, because this results in a very high air mass change. However, this air mass change does not occur immediately after the actuation of the stroke change-over, but follows the actuation with a defined time delay, i.e. a time lag t2 of the stroke change-over.
The various embodiments now use the knowledge of this delay or the time lag t2 of the stroke change-over and the time lag t1 of the fuel system in order to regulate the request for a greater or smaller pump output MFP of the high-pressure fuel pump 20 at the correct time and thus to provide a suitable quantity of fuel at the correct time for a new stroke. In other words, when the signal for a stroke change-over, for example from a small stroke to a large stroke, occurs and is detected in a control device 26, as shown in
This now means that when the time lag t2 of the stroke change-over has passed and the system is switching to the new stroke, i.e. to the larger stroke shown in
The various embodiments therefore may have the advantage that the high-pressure fuel pump 20 can be actuated beforehand in such a way that a suitable quantity of fuel for the new stroke can be provided at the correct time at the change-over to the new stroke. In contrast to this, the time-delayed reaction of the pump and, for example, the time-delayed stroke change-over process are not considered in the prior art, which means that even though a suitable quantity of fuel can be provided, this may be too early or too late for example. This has the consequence that too little fuel is supplied, for example, because it has been provided too early. This can now cause the fuel quantity to be subsequently adjusted and, for example, increased because the false assumption is made that the fuel quantity was previously too low. According to various embodiments, however, the appropriate quantity of fuel and the associated pump output MFP are determined for the new stroke in advance and the quantity of fuel is supplied to the fuel rail at the correct time, so that incorrect readjustment of the fuel quantity, as in the prior art, can be prevented. In doing so, the various embodiments take consideration of the time lag of the stroke change-over t2 and the pump 20, so that when the system changes to the next stroke the correct quantity of fuel for this can be reliably provided at the correct time.
The quantity of fuel pumped for each stroke is calculated using the following formula for example. As an alternative to the fuel injection mass MFF, the air mass MAF can also be used for example.
MFP: Mass fuel pump
MFFact
MFFnext
According to the above formula, the quantity of fuel pumped MFP is equal to the injection fuel mass MFP=MFFact
The various embodiments may be advantageous in that a greater regulation quality of the fuel pressure can be achieved in the ways mentioned above. Furthermore, emissions limits are easier to comply with, or may even be reduced.
Furthermore, the invention is not restricted to the embodiment of a fuel system as shown in
Furthermore, the invention is not restricted to the stroke change-over as a predetermined operating state, but can be applied to a variety of operating states for which the required quantity of fuel is essentially known beforehand in order to calculate an associated pump output.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 040 122.3 | Aug 2007 | DE | national |
