DE10351507A1 - Process for operating a fuel system of an internal combustion engine, especially with direct fuel injection, comprises performing conveying strokes using a differential piston of pressure-generating device during start phase of the engine - Google Patents

Abstract

Process for operating a fuel system (10) of an internal combustion engine, especially with direct fuel injection, comprises performing a number of conveying strokes using a differential piston (30) of a pressure-generating device (26) during a start phase of the engine. An independent claim is also included for a fuel system for an internal combustion engine, especially with direct fuel injection.

Description

The Invention relates first a method for operating a fuel system of an internal combustion engine, especially with direct fuel injection, in which the fuel from a high-pressure pump, mechanically from the internal combustion engine is driven, is conveyed to a high pressure area, and at least while a starting phase of the internal combustion engine, a pressure generating device, which a differential piston, at least indirectly with a Fuel tank connected low pressure chamber, and one with the high pressure area connected high pressure chamber, the high pressure area with pressure applied.

object The present invention also relates to a fuel system for an internal combustion engine. especially with direct fuel injection, with an electric supply pump, with a high-pressure pump, which mechanically from the internal combustion engine is driven and promotes a high-pressure area, and with a pressure generating device, which a differential piston, a low-pressure chamber, and a High pressure chamber, wherein the low pressure chamber at least temporarily connected to the output of the feed pump and the High pressure chamber is connected to the high pressure area.

A method of the type mentioned is from the EP 11 67 744 A1 known. There it is described that an electric prefeed pump delivers the fuel to a mechanically driven by the internal combustion engine high-pressure pump. This promotes further in a fuel rail to which a plurality of fuel injectors are connected. The fuel is stored under normal pressure in the fuel rail under high pressure. Since the mechanical high-pressure fuel pump can not yet compress the fuel to the desired extent at the start of the internal combustion engine, is in the EP 11 67 744 A1 proposed to connect the fuel rail with a pressure generating device which operates with a differential piston. A low-pressure chamber of the differential piston is connected to the outlet of the electric prefeed pump. As a result, in the low-pressure chamber of the pressure-generating device, as soon as the electric prefeed pump begins to deliver, a pressure builds up, which acts on the differential piston and thus leads to a pressurization of the fuel rail. This is intended to improve the starting behavior of the internal combustion engine, in particular in the case of a cold internal combustion engine.

The The present invention has the object, a method and a fuel system of the aforementioned type so that the internal combustion engine even more reliable can be started and consumes less fuel. In addition, should improves the emission behavior of the internal combustion engine at startup become.

These Task is characterized by a method of the type mentioned by solved, that at least during a start phase of the internal combustion engine of the differential piston of the Pressure generating device executes a plurality of delivery strokes.

Around in a fuel system to solve the object mentioned, is proposed that the pressure generating device is designed such that at least during a start phase can perform a plurality of delivery strokes.

Advantages of invention

thanks the measures according to the invention is an elevated one Pressure in the high-pressure area not only immediately at the beginning of the starting phase to disposal, but while the entire starting phase, even if it lasts longer. This may be required, for example, with very cold internal combustion engine be. The reason for that is that of the fuel injectors injected Fuel is continuously nachgefördert of the pressure generating device. This thus works not only as a pressure generating device, but as a pump.

by virtue of during the the entire starting phase of the internal combustion engine present increased pressure at the same time sufficient capacity can while the entire starting phase a comparatively high injection pressure be maintained at the fuel injectors, so that the injected fuel is very well atomized. This allows the during the amount to be injected in the starting phase can be reduced. All this reduces fuel consumption during the starting phase of the internal combustion engine and improves their emission behavior. Especially with internal combustion engines with fuel direct injection, and here again in particular in internal combustion engines, which as Fuel can use gasoline, thanks to the measures according to the invention independently from the temperature of the internal combustion engine, a start of the internal combustion engine be carried out with layered mixture. Possibly even a direct start of the internal combustion engine is possible. Alles this reduces the fuel consumption and the emissions of the internal combustion engine during the Startup.

Regarding the Advantages of the fuel system according to the invention is based on the above advantages of the method according to the invention directed.

advantageous Further developments of the invention are specified in subclaims.

First, will proposed that the differential piston of the pressure generator against a conveying direction is biased, and that the low pressure chamber during the Starting phase of the internal combustion engine alternately with an outlet and an inlet of an electric feed pump is connected. A such prefeed pump is already present on many fuel systems at the inlet the high-pressure pump, which of the internal combustion engine mechanically is already providing an increased pressure level to be able to. The delivery rate such an electric feed pump is, however, many times higher as the output, the while the starting phase of the internal combustion engine is needed. In the case proposed here inventive method will this excess flow of the electric prefeed pump for the Drive the pressure generator used. Thanks to these measures can the advantages of the invention achieved without significant additional costs.

Advantageous is also when the promotion of fuel through the pressure generator from the pressure in High pressure range depends. That is the consideration basis, that then, if in the high pressure area one for a economic and low-emission start sufficient pressure exists a promotion of fuel through the pressure generator or not is required to the full extent. In this training will be on the one hand increases the life of the pressure generating device, and at the start of the engine are by the operation of the pressure generator caused noises avoided.

there is possible, too, that the promotion of Fuel by the pressure generator from the speed a crankshaft of the internal combustion engine depends. This training is in turn the consideration underlying that, if the crankshaft with a sufficient Speed rotates, mechanically driven by the internal combustion engine High pressure pump sufficient pressure and a sufficient flow rate to disposal can make. This also makes unnecessary operation of the pressure generating device avoided, which extends their life.

at an advantageous embodiment of the fuel system according to the invention It is proposed that the high pressure chamber via a high pressure chamber opening check valve with the outlet of the pre-feed pump connected is. Such a check valve thus forms an inlet or suction valve for the pressure generating device.

Further can be provided that the differential piston of the pressure generating device against a conveying direction is biased, and that between the low-pressure chamber and the outlet the pre-feed pump a valve device is arranged which a 3/2-way valve or includes two 2/2-way valves. With such switching valves is an alternating connection of the low pressure chamber of the pressure generating device with the outlet of the pre-feed pump easy and inexpensive realizable.

proposed is further, that between the high pressure chamber and the high pressure area check valve is arranged, which blocks to the high pressure chamber. This prevents the pressure in the high pressure area due to leaks decreases in the area of the pressure generating device. This measure will Overall, the efficiency of the fuel system according to the invention increases.

Further it is advantageous if the differential piston of the pressure generating device is designed so that during operation of the pressure in the high-pressure chamber approximately ten times as high as in the low pressure chamber. Usual prefeed pumps provide a feed pressure of about 4 bar. This leads the embodiment of the invention a delivery pressure of 40 bar, with which the pressure generating device the high pressure area applied. Such a pressure allows a very good fuel treatment while the start of the internal combustion engine. This is a sure start low emissions possible. At the same time, at a delivery stroke the differential piston of the pressure generating device still a so sufficient amount of fuel promoted that sustaining of the raised Pressure in the high pressure area during the entire starting phase is ensured.

A further advantageous embodiment of the fuel system according to the invention is characterized in that in the high-pressure region, a pressure control valve is arranged, which over a return line with the outlet of the pre-feed pump is connected, and that the low pressure chamber of the pressure generator with the return line is connectable. This allows for short flow paths and use Any existing components, what the manufacturing cost of the fuel system according to the invention lowers.

drawing

following will be a particularly preferred embodiment of the present invention Invention explained in more detail with reference to the accompanying drawings. In show the drawing:

1 a schematic representation of a fuel system with an electric feed pump, a mechanical high pressure pump, and a pressure generating device; and

2 a flowchart for operating the fuel system of 1 ,

description of the embodiment

A fuel system carries in 1 Overall, the reference number 10 , It belongs to an internal combustion engine, which in 1 not shown in detail.

The fuel system 10 includes a fuel reservoir 12 in which gas is stored. An electrically driven prefeed pump 14 promotes the fuel from the reservoir 12 via a low pressure line 15 to a mechanically driven by the internal combustion engine high-pressure pump 16 , The pre-feed pump 14 During normal operation, the fuel is compressed to a pressure of approximately 4 bar. This in the low pressure line 15 Ruling pressure is controlled by a pressure regulator 17 adjusted, whose inlet with the low-pressure line 15 and its outlet with the inlet of the feed pump 14 connected is.

The high pressure pump 16 compresses the fuel further to a pressure of a few hundred bar and conveys it into a high pressure line 18 leading to a fuel manifold 20 leads. The pressure prevailing in this can be controlled by a pressure control valve 21 be adjusted, which via a return line 23 with the low pressure line 15 connected is. To the fuel manifold 20 are a total of four fuel injectors 22 connected to each of the fuel in a directly associated combustion chamber 24 inject. The fuel system 10 So belongs to an internal combustion engine with gasoline direct injection.

The fuel system 10 further comprises a pressure generating device 26 , This consists among other things of a housing 28 in which a stepped differential piston 30 is guided in a sliding manner. A section 32 of the differential piston 30 has a larger diameter than a section 34 , The projecting boundary of the section 32 with larger diameter limits a low pressure chamber 36 whereas the exposed area of the section 34 a high pressure chamber 38 limited. Between the section 32 and the housing 28 is in a spring room 40 a compression spring 42 braced. This is the differential piston 30 to the low pressure chamber 36 biased towards.

The low pressure chamber 36 is with a 3/2 solenoid valve 44 connected. In one of its switching position 46 becomes the low pressure chamber 36 over a line 48 with the reservoir 12 or the inlet of the feed pump 14 connected. In a switching position 50 is the low pressure chamber 36 with the return line 23 and thus ultimately via the low pressure line 15 with the outlet of the pre-feed pump 14 connected. A leakage channel 52 leads from the spring chamber 40 to the line 48 ,

The high pressure chamber 38 is via a check valve 54 leading to the high pressure chamber 38 locks out with the high pressure line 18 connected. The high pressure chamber 38 is also a check valve 56 leading to the high pressure chamber 38 opens, with the return line 23 , and thus ultimately on the low pressure line 15 also with the outlet of the pre-feed pump 14 connected.

The operation of the fuel system 10 is total of a control and regulating device 58 controlled or regulated, which, for example, with the pressure control valve 21 with which the pressure in the fuel manifold 20 is set, and the solenoid valve 44 , with which the operation of the pressure generating device 26 is controlled connected.

In normal operation of the internal combustion engine is the solenoid valve 44 closed, that is, it is in the de-energized switching position 46 , However, when the internal combustion engine is to be started, a procedure is followed, which is now with reference to 2 is explained. The method is a computer program in a memory 60 of the control and regulating device 58 stored.

After a starting block 62 will be in a block 64 queried whether a start bit B_Start is set. If this is not the case, this means that the internal combustion engine should not be started. In this case, in the block 66 a bit B_DKP set to zero, which means that the pressure generator 26 should not promote fuel. The solenoid valve 44 is therefore in its closed currentless switching position 46 ,

Is the answer in the block 64 however, "yes", so the start bit B_Start is set, is in the block 68 a bit B_EKP set. As a result, the prefeed pump 14 set in motion, and subsequently it is building in the low pressure line 15 and in the return line 23 a pressure of about 4 bar. In the block 70 a query is made as to whether a pressure pr is greater than a limit value G1. The pressure pr is the pressure of the fuel in the fuel rail 20 , He is going through an in 1 Sensor not shown detected.

Is the answer in the block 70 "yes", becomes the block 66 jumped and bit B_DKP set to zero: when the pressure in the fuel rail 20 is sufficiently high, is an operation of the pressure generating device 26 not mandatory. The same applies if a rotational speed N of a crankshaft of the internal combustion engine is above a limit value G2. This is in a block 72 queried.

Is the answer in the two blocks 70 and 72 each "no", is in the block 74 the bit B_DKP too 1 set. This means that first the solenoid valve 44 energized and in its switching position 50 is brought. In this is the low pressure chamber 36 with the return line 23 connected. The pressure in the low pressure chamber 36 therefore also increases to that in the return line 23 prevailing pressure of 4 bar. This will cause the differential piston 30 against the force of the compression spring 42 in 1 moved up, and in the high pressure chamber 38 enclosed fuel is compressed.

As that area of the section 32 of the differential piston 30 which the low pressure chamber 36 limited, ten times larger than the area of the section 34 which the high pressure chamber 38 limited, can during the movement of the differential piston 30 the pressure in the high pressure chamber 38 ten times that in the low-pressure chamber 36 increasing pressure. This opens the check valve 54 and the gas under a pressure of about 40 bar flows out of the high pressure chamber 38 in the high pressure line 18 and further into the fuel manifold 20 , Now the solenoid valve 44 back to its de-energized switching position 46 brought in the low pressure chamber 36 over the line 48 with the reservoir 12 and thus basically connected to ambient pressure. Due to the compression spring 42 now becomes the differential piston 30 again in the direction of low pressure chamber 36 pressed. This reduces the pressure in the high-pressure chamber 38 abruptly, causing the check valve 54 closes and the check valve 56 opens. In the high pressure chamber 38 can therefore from the return line 23 Fuel (with the pre-feed pressure of about 4 bar) in the high-pressure chamber 38 flow. Now the solenoid valve 44 back to its energized switching position 50 brought, with the technical consequences already described above.

By alternating activation of the solenoid valve 44 becomes the low pressure chamber 36 the pressure generating device 26 alternating with the low pressure line 15 (Ambient pressure) or with the outlet of the feed pump 14 (Pre-feed pressure) connected. The pressure generating device 26 Therefore, successively performs a plurality of delivery strokes, through the gasoline at a pressure of about 40 bar in the high-pressure line 18 and further into the fuel manifold 20 is pressed. The pressure generating device 26 So it works as a differential piston pump, and indeed completely independent of the current performance of the mechanically driven high-pressure pump 16 ,

Because in the fuel manifold 20 soon after the start of the conveying activity of the pressure generating device 26 a pressure of about 40 bar is applied, the fuel from the fuel injectors 22 atomized comparatively well, so that even with a cold internal combustion engine only comparatively little fuel in the combustion chambers 24 must be injected. For a safe cold start of the internal combustion engine so it is sufficient, compared to warm engine approximately twice the amount of fuel in the combustion chambers 24 inject. This amount of fuel can easily from the pre-feed pump 14 and also from the pressure generator 26 into the fuel rail 20 be nachgetrördert so that even with continuous injection of fuel through the fuel injectors 22 into the fuel rail 20 the pressure in the fuel rail 20 does not collapse.

In addition, the mechanically driven high-pressure pump begins 16 Fuel in the fuel rail 20 as soon as the starter sets the crankshaft of the internal combustion engine in rotation. The pressure generating device 26 Therefore, in any case, only that difference in the fuel rail must 20 promote which between the fuel injectors 22 retrieved and currently from the high pressure pump 16 eligible fuel quantity is.

Once the pressure pr in the fuel rail 20 the limit value G1 or the rotational speed N of the crankshaft exceeds the limit value G2 (blocks 70 and 72 ), is in the block 66 the solenoid valve 44 in its de-energized switching position 46 brought and so the promotion of fuel through the pressure generator 26 completed. The program ends in an endblock 76 ,

Claims (10)

Method for operating a fuel system ( 10 ) of an internal combustion engine, in particular with direct fuel injection, wherein the force substance from a high-pressure pump ( 16 ), which is mechanically driven by the internal combustion engine, in a high-pressure region ( 18 ) is conveyed, and in which at least during a starting phase of the internal combustion engine, a pressure generating device ( 26 ), which a differential piston ( 30 ), at least indirectly with a fuel tank ( 12 ) connected low-pressure chamber ( 36 ), and one with the high pressure area ( 18 ) connected high-pressure chamber ( 38 ), the high pressure area ( 18 ) is pressurized, characterized in that at least during a starting phase of the internal combustion engine, the differential piston 30 the pressure generator ( 26 ) performs a plurality of delivery strokes. Method according to claim 1, characterized in that the differential piston ( 30 ) of the pressure generating device ( 26 ) is biased against a conveying direction, and that the low-pressure chamber ( 36 ) during the starting phase of the internal combustion engine alternately with an outlet and an inlet of an electric prefeed pump ( 14 ) is connected. Method according to one of the preceding claims, characterized in that the delivery of fuel through the pressure generating device ( 26 ) from the pressure (pr) in the high-pressure region ( 18 ) depends. Method according to one of the preceding claims, characterized in that the delivery of fuel through the pressure generating device ( 26 ) depends on the rotational speed (N) of a crankshaft of the internal combustion engine. Fuel system ( 10 ) for an internal combustion engine, in particular with direct fuel injection, with an electric prefeed pump ( 14 ), with a high-pressure pump ( 16 ), which is mechanically driven by the internal combustion engine and to a high pressure area ( 18 ), and with a pressure generating device ( 26 ), which a differential piston ( 30 ), a low pressure chamber ( 36 ), and a high pressure chamber ( 38 ), wherein the low pressure chamber ( 36 ) at least temporarily with the output of the feed pump ( 14 ) and the high pressure chamber ( 38 ) with the high pressure area ( 18 ), characterized in that the pressure generating device ( 26 ) is designed so that the differential piston ( 30 ) can perform a plurality of delivery strokes at least during a starting phase. Fuel system ( 10 ) according to claim 5, characterized in that the high pressure chamber ( 38 ) via a to the high pressure chamber ( 38 ) opening check valve ( 56 ) with the outlet of the pre-feed pump ( 14 ) connected is. Fuel system ( 10 ) according to one of claims 5 or 6, characterized in that the differential piston ( 30 ) of the pressure generating device ( 26 ) is biased against a conveying direction, and that between the low-pressure chamber ( 36 ) and the outlet of the feed pump ( 14 ) a valve device is arranged, which is a 3/2-way valve ( 44 ) or two 2/2-way valves. Fuel system ( 10 ) according to one of claims 5 or 6, characterized in that between the high-pressure chamber ( 38 ) and the high pressure area ( 18 ) a check valve ( 54 ), which leads to the high-pressure chamber ( 38 ) locks out. Fuel system ( 10 ) according to one of claims 5 to 8, characterized in that the differential piston ( 30 ) of the pressure generating device ( 26 ) is designed so that during operation of the delivery pressure in the high-pressure chamber ( 38 ) is about ten times as high as in the low pressure chamber ( 36 ). Fuel system ( 10 ) according to any one of claims 5 to 9, characterized in that in the high-pressure area ( 18 ) a pressure control valve ( 21 ), which via a return line ( 23 ) with the outlet of the pre-feed pump ( 14 ), and that the low-pressure chamber ( 36 ) of the pressure generating device ( 26 ) with the return line ( 23 ) is connectable.