EP2217795B1 - Fuel injection system for an internal combustion engine, comprising a hydrocarbon injector - Google Patents

Description

State of the art

Internal combustion engines that operate according to the diesel process increasingly have a particulate filter in the exhaust gas system because of increasingly stringent exhaust gas regulations. Usually, these particulate filters are regenerated by the control of the internal combustion engine triggers afterinjections at the arranged in the combustion chamber injectors, so that in the hot exhaust gases is still unburned fuel which oxidizes in the exhaust pipe and thereby provides the heat required to trigger a regeneration of the particulate filter.

These post-injections are often not effective, so it is already known to provide so-called HC injectors in the exhaust system. These HC injectors inject fuel upstream of the particulate filter (s) into the exhaust pipe, thereby allowing better control of the regeneration of the particulate filter.

Out US 2007/0227126 A1 For example, a fuel injection system is known that has a delivery pump that delivers fuel from a tank to a high pressure pump. The high-pressure pump delivers the fuel to a high-pressure accumulator which is followed by several injectors. There is shown a regeneration system for a particulate filter having an injector to which fuel is supplied by the feed pump from the tank via a controllable valve.

In order to achieve the finest possible atomization of the fuel injected by the HC injectors, operating pressures of 7 to 10 bar (relative pressure) are desirable. The required fuel circuit is relatively expensive because of the not inconsiderable injection pressure and is only rarely needed. Thus, typically about every 500 to 1,000 km, corresponding to an operating time of in some cases well over 10 hours, a regeneration of the particulate filter required, this regeneration takes only about 10 to 20 minutes. Only during this short period of time is the HC injector active. Therefore, the operating time of the HC injector and the upstream pump is only a fraction of the total operating time of the internal combustion engine.

Disclosure of the invention

The invention has for its object to provide a fuel injection system with an HC injector, which is optimized in terms of efficiency and cost.

This object is achieved in a fuel injection system of an internal combustion engine having a low pressure region and a high pressure region, wherein in the low pressure region a prefeed pump is provided which promotes fuel from a fuel tank to a high pressure pump, and wherein in the high pressure region, a high pressure pump is provided, which are under high pressure Fuel to a common rail or at least one injector promotes, thereby solved, that the low-pressure region comprises at least one HC injector and that the at least one HC injector injects fuel upstream of one or more particulate filter in the exhaust aftertreatment device of the internal combustion engine.

Due to the invention claimed integration of the HC injector in the low pressure region of the fuel injection system can account for a separate fuel pump for the HC injector. Rather, the already existing feed pump is used if necessary for the promotion of fuel in the HC injector. This results in a simplification of the fuel injection system and the production costs are significantly lower. In addition, there is the advantage that no further fuel pump is required, whereby the weight and consequent fuel consumption and the CO2 emission of a vehicle equipped with the fuel injection system vehicle are low.

Inventive embodiments of the fuel injection system provide that the feed pump is designed as an electrically driven fuel pump or as a mechanically driven fuel pump. Alternatively, it is also possible that in addition to the mechanically driven feed pump, a switchable additional fuel pump is still provided.

This usually electrically powered switchable additional fuel pump is usually to do so, when starting the engine to achieve the fastest possible pressure build-up. Furthermore, this additional fuel pump can be used to refill the fuel injection system after a Tankleerfahrt. As soon as the internal combustion engine has started and the mechanically driven delivery pump builds up sufficient pressure, the additional fuel pump is switched off again. According to the invention, the additional fuel pump can now be switched on while the internal combustion engine is running, so that a two-stage pressure increase takes place in the low-pressure region of the fuel injection system. The first pressure increase is effected by the additional fuel pump, while the mechanically driven feed pump arranged downstream thereof effects a further pressure increase. Characterized the pressure on the pressure side of the prefeed pump is briefly and selectively increased during this particular mode of operation, so that a sufficiently high pressure for injecting fuel through the HC injector in the low pressure region is present. Since the electrically switchable additional fuel pump anyway has very low operating times, the additional short stress of about 10 to 20 minutes for regeneration readily possible and requires no additional measures to increase the robustness and life of the already existing additional fuel pump.

Alternatively, it is possible to connect the at least one HC injector to a fuel supply line or an interior of the high-pressure fuel pump. Of course, it is also possible to connect the at least one HC injector to a return line.

Since it is endeavored in normal operation to keep the delivery pressure of the prefeed pump and thus the pressure in the low-pressure region of the fuel injection system as low as possible, in a further advantageous embodiment of the invention between the interior of the high-pressure fuel pump and the return line, a pressure control valve is arranged. With the help of this pressure control valve, the operating pressure of the low pressure region of the internal combustion engine is regulated in normal operation. In addition, according to the invention, it is possible for a short time to increase the pressure in the low-pressure region of the fuel injection system by suitable control of the pressure regulating valve so that a sufficiently high pressure is available to inject fuel with the HC injector into the exhaust gas aftertreatment device of the internal combustion engine.

The pressure control valve may, for example, the pressure in the fuel inlet on the suction side the prefeed pump are controlled. By briefly increasing the delivery rate of the prefeed pump and the pressure in the low pressure region increases according to the characteristic of the pressure control valve.

The above object is also achieved by a method for operating a fuel injection system having a low-pressure region and a high-pressure region, wherein in the low-pressure region, a prefeed pump is provided which promotes fuel from a fuel tank to a high-pressure pump, and wherein in the high-pressure region, a high-pressure pump is provided at high pressure fuel in a common rail or at least one injector promotes, wherein at least one HC injector is connected to the low pressure region and wherein the at least one HC injector injects fuel upstream of one or more particulate filter in an exhaust pipe of the internal combustion engine, if necessary , is achieved in that during the injection of fuel through the HC injector, the pressure in the low pressure region of the fuel injection system is raised.

This ensures that a sufficiently high injection pressure for the HC injector is available for the injection of fuel into an exhaust pipe of the internal combustion engine. In normal operation of the internal combustion engine, that is, when no fuel is injected through the HC injector, the pressure in the low pressure region of the fuel injection system can be lowered again to the normal level. As a result, inter alia, the pre-feed pump is relieved, the heating of the fuel is reduced and the overall efficiency of the fuel injection system is increased.

In addition, the prefeed pump does not need to be designed for a steady-state pressure equal to the injection pressure of the HC injector. It is sufficient if the prefeed pump can provide the injection pressure of the HC injector for a short time, that is to say a few minutes. As a result, the prefeed pump can be designed to be less expensive and smaller.

The invention claimed temporary increase in pressure in the low pressure range can be done in an electrically driven feed pump by increasing the drive voltage of the same or in a pressure-controlled electrically driven pump by increasing the setpoint of the pressure.

Alternatively, it is also possible that in addition to the prefeed pump upstream, an electrically driven additional fuel pump is provided and that the temporary pressure increase in the low pressure region is carried out by temporarily switching on the additional fuel pump in addition to the prefeed pump. As a result, a two-stage pressure increase in the low-pressure region of the fuel injection system is possible with simple means, wherein the sum of both pressure increases must be so large that the injection pressure of the HC injector is achieved.

It is possible that one or more of the following return amounts flows through the switchable throttle: The return amount of the pump housing with or without flowing through the bearings of the drive shaft fuel, in addition, even the leakage amount from the injectors can flow through the switchable throttle ,

Further advantages and advantageous embodiments of the invention are the following drawings, the description and the claims removable. All of the features disclosed in the drawing, the description and the claims can be essential to the invention both individually and in any combination with one another.

Brief description of the drawings

Figuren 1 bis 4

Ausführungsbeispiele erfindungsgemäßer Kraftstoffeinspritzsysteme.

Show it:

FIGS. 1 to 4

Embodiments of fuel injection systems according to the invention.

Embodiments of the invention

FIG. 1 shows a first embodiment of a fuel injection system according to the invention in a block diagram representation.

The fuel injection system comprises, inter alia, a high-pressure fuel pump 1, a tank 3, a pressure sensor 4, an electrically driven prefeed pump 5, a fuel filter 7, a rail 9 and a pressure relief valve 11. The injectors connected to the rail 9 are in FIG. 1 not shown.

The pressure limiting valve 11 opens into a return line 13, in which the leakage quantities of the injectors, not shown, are discharged. The return line 13 opens in this embodiment in the tank 3 and drives there a jet pump 10 at.

Inside the high-pressure fuel pump 1 may optionally be arranged a temperature sensor T. The high-pressure fuel pump 1 is hydraulically connected to the tank 3 via a fuel inlet 15, the filter 7 and the prefeed pump 5. Downstream of the prefeed pump 5, an HC injector 16 is connected to the fuel inlet 15. If necessary, fuel can be injected into an exhaust pipe (not shown) of the internal combustion engine with the HC injector 16. The targeted injection of fuel into the exhaust pipe at a location upstream of a particulate filter, the regeneration of the particulate filter can be triggered.

The fuel inlet 15 connects a delivery side of the prefeed pump 5 with an interior 17 of the pump housing of the high-pressure pump 1, so that the entire delivery flow of the prefeed pump 5 passes into the interior 17. A connecting line 18 provides a hydraulic connection between the interior 17 of the pump housing on the one hand and a Metering unit 19 and the return line 13 on the other hand forth. Between the connecting line 18 and the return line 13, a pressure regulating valve 20 is arranged.

The metering unit 19 serves to control the amount of fuel sucked by pump elements 21 of the high-pressure fuel pump 1 and thus also the delivery rate thereof. For this purpose, the suction sides of the pump elements 21 are hydraulically connected via a distribution line 23 to the output of the metering unit 19.

The pump elements 21 consist essentially of suction valves 25, high-pressure side check valves 27 and a piston 29 which oscillates in a cylinder bore (without reference numeral). The pistons 29 of the pump elements 21 are driven by roller tappets 31 of cams 33 of a drive shaft 35. The pump elements 21 convey fuel under high pressure via a high-pressure line 34 into the rail 9.

The cams 33 are part of a drive shaft 35, which is rotatably mounted on both sides of the cam 33 in a first bearing and in a second bearing in a pump housing (not shown). The drive shaft 35 is arranged in the interior 17 of the pump housing. The bearings of the drive shaft 35 are forcibly traversed by a partial flow of the fuel flowing from the fuel inlet 15 into the interior 17 of the pump housing fuel and are in the block diagram according to FIG. 1 shown as throttle points. The first camp has in FIG. 1 the reference numeral 39, while the second bearing has been provided with the reference numeral 41.

At the in FIG. 1 illustrated first embodiment of a high-pressure fuel pump according to the invention, the pressure control valve 20 downstream of the interior 17 of the high-pressure fuel pump 1 is arranged. The pressure control valve 20 comprises a control piston 55, which is acted upon by a spring 56 in the closing direction and a leakage line 57th

By the arrangement of the pressure control valve 20 downstream of the interior 17 prevails in the interior 17 almost the same pressure as on the pressure side of the feed pump 5. In general, the pressure on the pressure side of the prefeed pump 5 and thus of the interior 17 is about 3 to 6 bar.

This pressure prevailing in the interior 17 leads among other things to the fact that fuel is pressed through the bearings 39 and 41. Since the first bearing 39 and the second bearing 41 are generally formed as sliding bearings, formed by the forced flow through the bearings 39 and 41 in the bearings 39 and / or 41, a hydrodynamic lubricating wedge. As a result, the load capacity of the first bearing 39 and the second bearing 41 increases considerably and at the same time the heat dissipation from the first bearing 39 and the second bearing 41 is improved.

The arrangement of the pressure regulating valve 20 in the connecting line 18 has in the normal operation of the fuel injection system, inter alia, the advantage that the delivery height of the prefeed pump can be reduced. However, this also means that the normal operating pressure in the low-pressure region of the Kralftstoffeinspritzsystems is not sufficient to operate an HC injector. Namely, when the pressure with which the fuel is injected from the HC injector 16 into the exhaust gas aftertreatment device of the internal combustion engine is too low, the fuel is not sufficiently finely atomized, and thereby the complete combustion of the injected fuel is not ensured. With incomplete combustion, the emission values of the internal combustion engine deteriorate, which is undesirable.

According to the invention, the pressure in the low-pressure region of the fuel injection system can now be increased simultaneously with the injection of fuel through the HC injector 16. This can be done by increasing the supply voltage of the electrically driven feed pump 5 so that it runs at a higher speed and as a result the delivery pressure increases to the desired value.

Alternatively, it is also possible to increase the operating pressure via a pressure control. This requires on the delivery side of the prefeed pump 5, a pressure sensor 4, which is connected via signal lines, not shown, with a pressure regulator. In normal operation, the pre-feed pump 5 is used as a setpoint _to the pressure p in the low pressure range is about 3 - 5 bar set. Now, if fuel is to be injected by the HC injector, the target value is p _to the pressure controller for a short time to a value of about 7 - increases bar 10th The prefeed pump is driven Consequently, 5 of the pressure regulator so that the desired nominal pressure p is set _to the low-pressure region.

As the regeneration of a particulate filter and the required injection of fuel in an exhaust pipe of the internal combustion engine through the HC injector lasts only about 10 - 20 min and is also rarely required, the prefeed pump 5 can be operated above the nominal point for these short operating times, without being damaged or their life is drastically reduced. Thus, the fuel injection system according to the invention can be realized without additional investment in a reinforced pump, which has an advantageous effect on its economy.

In order to prevent the increased pressure built up for the HC injection in the low-pressure region from being dissipated again via the bearings 39, 41, it can be provided that in the connection of the flows of at least one of the bearings 39, 41 with the return line 13, a flow-limiting element 42 is arranged. It can also be provided that the processes of both bearings 39, 41 are first brought together and then connected together with the return line 13, in which case only one flow-limiting element 42 is required for both bearings 39, 41. The flow-limiting element 42 may be formed, for example, as a throttle point. Alternatively, the flow-limiting element 42 may also be designed as a switchable throttle, for example in the form of an electrically or hydraulically actuated valve. Furthermore, the flow-limiting element 42 may also be designed as a pressure-holding valve, which opens at a certain pressure and then causes a pressure increase according to the valve characteristic. Particularly advantageous in combination with the flow-limiting element 42 when the pressure control valve 20 has a progressive spring characteristic. In this way, the most constant possible pressure in the low pressure range in normal operation, ie without HC injection, can be achieved, while the highest possible pressure increase in the low pressure region is achieved with increase in flow in the low pressure range for HC injection. The spring of the pressure regulating valve 20 is designed so that its spring stiffness increases with increasing opening stroke.

In FIG. 2 is shown a further embodiment of a fuel injection system according to the invention. In this embodiment, the prefeed pump 5 is mechanically driven. It is often coupled directly to the drive shaft 35 of the high-pressure pump 1. Because of this rigid coupling of the pressure build-up at the start of the engine, in which the speeds are naturally very low, relatively slow vonstatten. To remedy this deficiency is upstream of the Pre-feed pump 5 an electrically driven switchable additional fuel pump 43 is provided. This additional fluid pump 43 is usually operated only during the start of the internal combustion engine, so that a faster pressure build-up in the fuel injection system is possible. According to the invention, it is now provided that this additional fuel pump is operated simultaneously and hydraulically in series with the prefeed pump 5, even when the internal combustion engine is running, when fuel is to be injected through the HC injector 16. For then add the delivery levels of additional fuel pump 43 and feed pump 5 to a value that is sufficiently large to ensure the fine atomization of the fuel through the HC injector.

On the suction side of the prefeed pump, a suction throttle 45 is provided, which ensures that the flow rate of the prefeed pump 5 is limited, especially at high speeds

The mechanically driven prefeed pump 5 of the second exemplary embodiment can be designed as a vane cell pump, as an internal gear pump, in particular as a gerotor pump, or as an external gear pump. These pumps have a gap between the rotating components and the pump housing that causes leakage losses. This gap is in FIG. 2 represented by the symbol of a throttle (see reference numeral 49). The leaked through the gap leakage amount is discharged through a leakage line 51. The leakage line 51 opens into the line (without reference numeral), which supplies the flowing through the first bearing 39 amount of fuel to the return line 13.

At the in FIG. 2 1, the HC injector 16 is supplied with fuel from the interior 17 of the high-pressure fuel pump 1 and is arranged downstream of the priming pump 5, so that it is acted upon by the delivery pressure of the prefeed pump 5. Switching on the additional fuel pump 43 causes - depending on the speed of the high pressure pump 1 and the power of the additional fuel pump 43 - a pressure increase in the interior 17 and thus also at the HC injector sixteenth

In FIG. 3 a fuel injection system is shown, in which a mechanically driven prefeed pump 5 is provided, wherein in the inlet to the prefeed pump 5, a switchable throttle 50 is arranged. The switchable throttle 50 may be an electrically operated valve analogously to the embodiment according to FIG. 7 or hydraulically actuated. In the hydraulic control of the switchable throttle 50, the pressure drop resulting from the flow to the HC injector 16 can be utilized. Upstream of the mechanically driven feed pump 5 can analogously to the execution according to FIG. 2 an additional fuel pump 43 may be provided. If an increased pressure in the low-pressure region is required for the HC injection, then the switchable throttle 50 is set to a larger flow cross-section, so that the delivery rate of the prefeed pump 5 is increased, which in turn leads to pressure increase in the low pressure region.

Figure 4 shows an embodiment of the hydraulic control of the switchable Diossel 50th

If the control of the switchable Diassel 50 takes place hydraulically, one uses the resulting pressure drop at a throttle point 61. This throttle point 61 is arranged in a supply line (without reference numeral) of the HC injector 16. This means that a pressure drop occurs at the throttle point as soon as the HC injector 16 injects fuel. Via control lines, of which a first upstream of the throttle and the other downstream of the throttle body 61 is connected, the switchable throttle 50 is actuated hydraulically.

Claims (13)

1. Fuel injection system of an internal combustion engine, having a low-pressure region and a high-pressure region, wherein in the low-pressure region there is provided a predelivery pump (5) which delivers fuel from a fuel tank (3) to a high-pressure pump (1), and wherein in the high-pressure region there is provided a high-pressure pump (1) which has a drive shaft rotatably mounted in an interior space (17) and by means of at least one bearing (39, 41) and which delivers highly pressurized fuel to a common rail (9) or to at least one injection valve, wherein the interior space (17) of the high-pressure pump (1) is part of the low-pressure region, and the low-pressure region comprises at least one HC injector (16) which injects fuel on demand from the low-pressure region, and downstream of the predelivery pump (5), into an exhaust-gas treatment device of the internal combustion engine, characterized in that the pressure in the low-pressure region is raised, by means of an increase of the supply flow rate to the low-pressure region, during the injection of fuel by the HC injector into the exhaust-gas treatment device.
2. Fuel injection system according to Claim 1, characterized in that the predelivery pump (5) is in the form of an electrically driven fuel pump.
3. Fuel injection system according to Claim 1, characterized in that the predelivery pump (5) is in the form of a mechanically driven fuel pump, in particular of a fuel pump driven directly by the fuel high-pressure pump (1).
4. Fuel injection system according to Claim 3, characterized in that a switchable throttle (50) is provided upstream of the predelivery pump (5).
5. Fuel injection system according to Claim 3, characterized in that an electrically driven, activatable auxiliary fuel pump (43) is provided in addition to the mechanically driven predelivery pump (5).
6. Fuel injection system according to one of the preceding claims, characterized in that the at least one HC injector (16) is connected to a fuel supply line (15) or to an interior space (17) of the high-pressure fuel pump (1).
7. Fuel injection system according to one of Claims 1 to 6, characterized in that the at least one HC injector (16) is connected to the return line (13).
8. Fuel injection system according to Claim 4, characterized in that the switchable throttle (50) is electrically or hydraulically switched.
9. Fuel injection system according to one of the preceding claims, characterized in that a throughflow limiting element (42) is provided in a connection of the at least one bearing (39, 41) to the return line (13).
10. Method for operating a fuel injection system, having a low-pressure region and a high-pressure region, wherein in the low-pressure region there is provided a predelivery pump (5) which delivers fuel from a fuel tank (3) to a high-pressure pump (1), and wherein in the high-pressure region there is provided a high-pressure pump (1) which delivers highly pressurized fuel to a common rail (9) or to at least one injection valve, wherein to the low-pressure region there is connected at least one HC injector (16), and wherein the at least one HC injector (16) injects fuel on demand into an exhaust pipe of the internal combustion engine upstream of one or more particle filters, characterized in that the pressure in the low-pressure region is raised, by means of an increase of the supply flow rate to the low-pressure region, during the injection of fuel by the HC injector (16) into the exhaust pipe.
11. Method according to Claim 10, characterized in that the predelivery pump (5) is electrically driven, and in that the pressure increase in the low-pressure region is realized by means of an increase in the activation voltage of the predelivery pump (5).
12. Method according to either of Claims 10 and 11, characterized in that the predelivery pump (5) is controlled by a pressure regulator, and in that the pressure increase in the low-pressure region is realized by means of an increase in the setpoint value (p_soll) of the pressure.
13. Method according to either of Claims 10 and 11, characterized in that, in addition to the predelivery pump (5), there is provided an electrically driven auxiliary fuel pump (43) which is arranged upstream of the predelivery pump (5), and in that the pressure increase in the low-pressure region is realized by means of the activation of the auxiliary fuel pump (43) in addition to the predelivery pump (5).

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