EP2357354B1 - Hydraulic system and fuel injection system for a combustion engine - Google Patents

Description

State of the art

The invention relates to a fuel injection system for an internal combustion engine with a hydraulic system according to the preamble of claim 1.

Such a hydraulic system is from the DE 10 2007 010 495 A1 the applicant known. In the known, designed as a fuel injection system for an internal combustion engine hydraulic system, it may be provided in a variant that a high-pressure pump delivers fuel into a fuel reservoir, which in turn is coupled to a pressure booster, the fuel with further pressure increase in a second high-pressure accumulator, in particular as so-called rail is formed promotes. Here, the pressure boosting device is equipped with a pressure piston acting for two compression chambers, so that a continuous delivery of the fuel can be done in the second high-pressure accumulator.

Such fuel injection systems having a pressure boosting device are used in particular at higher system pressures (in this case, system pressures higher than 3000 bar) are used for efficiency and strength reasons. With regard to the pressure reduction, the known systems of this kind are usually designed in such a way that the pressure is reduced via the injectors of the fuel injection system, which are subject to leakage. In other words, this means that the pressure reduction rate depends on the leakage quantities of the injectors. There are operating conditions of an internal combustion engine or of a fuel injection system in which relatively high pressure reduction rates are desired are. On the one hand, for safety reasons, especially after switching off the engine and on the other hand for reasons of comfort, since in a change from large to small load, the relatively high pressure should be adjusted lower partly for reasons of noise. If this does not happen, the part load has a relatively high noise level. On the other hand, for system efficiency reasons, the injectors are designed for the lowest possible leakage, so that it becomes increasingly difficult to achieve a sufficiently high pressure reduction rate under the operating conditions mentioned.

From the DE 44 01 083 A1 In addition, a hydraulic system is known with a high-pressure accumulator, as well as from DE 10 2007 062 176 A1 , From the DE 10 2008 011 677 A1 Furthermore, a test device for a fuel injection system is known, which also includes a high-pressure accumulator.

Disclosure of the invention

Based on the illustrated prior art, the invention has the object, a fuel injection system for an internal combustion engine with a hydraulic system according to the invention according to the preamble of claim 1 such that an increased pressure reduction speed can be achieved. This object is achieved in a hydraulic system with the features of claim 1. The invention is based on the idea, by a pressure reduction device which is coupled to the second high-pressure accumulator, specifically and quickly to allow the desired pressure reduction. The pressure reduction thus happens mainly not via the or with the second high-pressure accumulator coupled consumers, but via the (separate) pressure reducing device. Therefore, the at least one consumer can be optimized or minimized with regard to its leakage. The pressure medium is fuel and the at least one consumer is an injector for injecting fuel into a combustion chamber of the internal combustion engine. As an internal combustion engine in particular self-igniting internal combustion engines (diesel engines) are provided in commercial vehicles or passenger vehicles. In addition, the pressure reduction device is arranged between the two high-pressure accumulators and leads from the second high-pressure accumulator flowing back into the first high-pressure accumulator. Such an arrangement has the advantage the efficiency of the overall system is relatively high, since the recirculated fuel only has to be brought to the pressure level of the second high-pressure accumulator by the pressure boosting device once again from the pressure level of the first high-pressure accumulator.

Advantageous developments of the fuel injection system according to the invention for an internal combustion engine are specified in the further claims. All combinations of at least two of the features disclosed in the claims, the description and / or the figures fall within the scope of the invention.

In order to allow a relatively simple construction of the pressure reducing device, which also ensures a particularly safe operation, it is provided in a constructive embodiment of the invention that the pressure reducing device is designed as a switchable between two positions overflow.

In a further embodiment of the invention, it is proposed that the pressure reduction device opens the outflow of the fuel from the second high pressure accumulator when a certain pressure ratio between the two high pressure accumulators is exceeded. Such a design has the advantage that an overload or too high pressure in the second high-pressure accumulator can be avoided.

In particular, it is provided that the first high pressure accumulator is coupled to a pressure control valve, which is connected to a low pressure region is. Thus, the pressure in the first high pressure accumulator is determined by the pressure regulating valve, so that the pressure in the first high pressure accumulator also can not exceed a certain value.

It is particularly preferred in this case that the pressure regulating valve is formed by a control device of the motor vehicle electrically controlled. A pressure reduction can therefore be achieved in a particularly simple manner that the control unit controls the pressure control valve, which then lowers the pressure in the first high pressure accumulator, whereupon the ratio between the pressure in the second high pressure accumulator and the pressure in the first high pressure accumulator increases, which in turn has the consequence in that the pressure in the second high-pressure accumulator is reduced in the desired manner via the pressure reduction device.

In a further embodiment of the invention, it is also provided that two, in particular identically designed pressure amplification devices are provided, which are independently controllable. Such a design has the advantage that it operates particularly reliably or, in the event of a malfunction in a pressure-increasing device, the pressure can be maintained at least at a certain level by means of the second pressure-increasing device.

Fig. 1

ein erfindungsgemäßes, als Kraftstoffeinspritzsystem ausgebildetes Hydrauliksystem unter Verwendung einer Druckreduzierungseinrichtung in einer schematischen Darstellung.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawing. This shows in

Fig. 1

an inventive, designed as a fuel injection system hydraulic system using a pressure reducing device in a schematic representation.

In the Fig. 1 a hydraulic system 1 designed as a fuel injection system 10 is shown. The fuel injection system 10 is used in particular in a self-igniting internal combustion engine 2, in particular a diesel engine, which has a plurality, for example six, of consumers designed as injectors 3 for injecting fuel into the combustion chambers of the internal combustion engine 2.

Such, known per se fuel injection system 10 has (among other components, not shown for clarity, such as a fuel filter, a water separator, etc., which are usually present in practice, but are not required for understanding the invention) a fuel tank 11th on, is conveyed from the fuel by means of a high-pressure feed pump 12 in a first high-pressure accumulator 13. By means of such, known from practice high-pressure feed pump 12, for example, a pressure of 1500 bar is generated in the first high-pressure accumulator 13.

The first high pressure accumulator 13 is equipped with an electrically controllable pressure control valve 14, which allows a backflow of fuel from the first high pressure accumulator 13 into the fuel tank 11 when a certain pressure in the first high pressure accumulator 13 is exceeded. The pressure control valve 14 is connected to a control device, not shown, of the motor vehicle and electrically controlled by this, the e.g. at certain operating conditions, e.g. the shutdown of the internal combustion engine 2 or at a partial load operation of the internal combustion engine 2, the pressure in the first high pressure accumulator 13 down regulates.

The first high-pressure accumulator 13 is coupled to two pressure-increasing devices 17, 18 which are of identical design but can be operated independently of one another and are not shown in detail in the drawing. The two pressure increasing devices 17, 18 are each coupled to a 3/2-control valve 19, 20. The two outputs of the pressure increasing devices 17, 18 are in turn connected to a second high-pressure accumulator 22 for the fuel. The second high-pressure accumulator 22 is designed as a so-called rail and has a pressure sensor 23. From the second high-pressure accumulator 22 in each case a line 24 goes to each of the injectors 3. Furthermore, each injector 3 has a return line 16, which connects the injector 3 to the low pressure region 5 of the fuel injection system 1 and the unneeded fuel is returned to the fuel tank 11.

According to the invention, it is provided that the two high-pressure accumulators 13 and 22 are coupled to one another with a pressure reduction device 25. Here, the pressure reduction device 25 is designed in particular as a mechanically operating, in particular spring-loaded differential pressure overflow valve 26. The differential pressure overflow valve 26 has a connection line 27, via which, for example, leakage losses of the differential pressure overflow valve 26 can be diverted into a low-pressure region 5 of the fuel injection system 10. The low-pressure region 5 is in turn connected to the fuel tank 11. Furthermore, a connection 28 is provided in the differential pressure overflow valve 26, which allows the discharge of the differential pressure overflow valve 26, a drainage of fuel from the second high pressure accumulator 22 into the first high pressure accumulator 13.

The first pressure boosting device 17 has check valves 30, 31 which prevent a backflow of fuel from the second high-pressure accumulator 22 into the first pressure increasing device 17 or from the first pressure increasing device 17 into the first high-pressure accumulator 13. Likewise, the second pressure increasing device 18 check valves 33, 34, which prevents a backflow of fuel from the second high pressure accumulator 22 in the second pressure increasing means 18 and of the second pressure increasing means 18 in the first high pressure accumulator 13.

In the in the Fig. 1 illustrated position of the two 3/2-control valves 19, 20, the control valve 20 is shown in the actuated position, in which the associated second pressure increasing means 18 is thus in the delivery phase of their cycle. The pressure increasing device 18 in this case conveys a fuel quantity as a function of its geometric transmission ratio from the first high-pressure accumulator 13 into the second high-pressure accumulator 22.

The control valve 19, however, is shown in the unactuated position, in which the associated pressure booster 17 is in the filling phase of its cycle. Thanks to the spring force, it fills the high-pressure chamber of the pressure-increasing device 17 with fuel via the non-return valve 30 and returns to its initial state after complete filling, in which all volumes are at system pressure level.

If now a pressure reduction is desired, the two pressure boosting devices 17, 18 are not actuated, wherein the two check valves 31, 34 are in their closed position. Since no or only a very small leakage occurs at the injectors 3, initially only a slight pressure reduction occurs in the second high-pressure accumulator 22. The differential pressure relief valve 26 is closed due to its geometric pressure area ratio and the spring action (1st position). If the pressure in the first high-pressure accumulator 13 is now reduced by means of the pressure regulating valve 14 as a result of control via the control unit, the closing force at the differential pressure overflow valve 26 is also reduced and it can open (2nd position). Now, the pressure in the second high pressure accumulator 22 is reduced, since fuel from the second high pressure accumulator 22 via the connection 28 in the first high pressure accumulator 13 can flow. Thus, as desired, the pressure in the second high-pressure accumulator 22 is lowered relatively quickly.

To rebuild the pressure in the second high pressure accumulator 22, the pressure control valve 14 must be closed again, wherein the pressure in the first high pressure accumulator 13 due to the promotion by means of the high pressure feed pump 12 increases again. In this case, the pressure increases until the force acting on the Differenzdrucküberströmventil 26 compressive force closes this and thus the connection between the two high-pressure accumulators 13, 22. Here, there is always a nearly identical pressure ratio between the pressures in the two high-pressure accumulators 13, 22 a because only the pressure area ratio at the differential pressure spill valve 26 determines the pressure levels. Thus, the gear ratios of the activated pressure increasing means 17, 18 determine the pressure ratio between the two high pressure accumulators 13, 22 and the differential pressure spill valve 26 by the pressure area ratio of the pressure ratio between the high pressure accumulators 13,22 in the pressure reduction. In this case, the pressure area ratio of the differential pressure overflow valve 26 must be greater than the transmission ratios of the activated pressure increasing devices 17, 18, otherwise the differential pressure overflow valve 26 would also open during the delivery phase of the pressure increasing devices 17, 18, which adversely affects the efficiency.

Claims (7)

1. Fuel injection system (10; 10a) for an internal combustion engine (2), having a hydraulic system (1), having a pump device (12), which is connected to a first high-pressure accumulator (13) and which delivers pressure medium into the first high-pressure accumulator (13) with an increase in pressure, having at least one pressure-boosting device (17, 18), which is coupled to the first high-pressure accumulator (13) and which delivers the pressure medium situated in the first high-pressure accumulator (13) into a second high-pressure accumulator (22) with a further increase in pressure, wherein at least one consumer (3) is supplied with pressure medium from the second high-pressure accumulator (22), wherein, between the two high-pressure accumulators (13, 22), at least one valve device (31, 34) is coupled to the at least one pressure-boosting device (17, 18), which at least one valve device prevents an outflow of pressure medium from the second high-pressure accumulator (22) in the direction of the at least one pressure-boosting device (17, 18), wherein the second high-pressure accumulator (22) is coupled to a pressure-reducing device (25; 25a) by means of which pressure medium can flow out of the second high-pressure accumulator (22) such that the pressure in the second high-pressure accumulator (22) is reduced, wherein the pressure medium is fuel and the at least one consumer is an injector (3) for injecting fuel into a combustion chamber of the internal combustion engine (2),
   characterized
   in that the pressure-reducing device (25) is arranged between the two high-pressure accumulators (13, 22) and discharges fuel flowing back from the second high-pressure accumulator (22) into the first high-pressure accumulator (13) .
2. Fuel injection system according to Claim 1,
   characterized
   in that the pressure-reducing device (25; 25a) is formed as an overflow valve (26) which is switchable between two positions.
3. Fuel injection system according to either of Claims 1 and 2,
   characterized
   in that the pressure-reducing device (25; 25a) opens up the outflow of the fuel from the second high-pressure accumulator (22) in the event of a certain pressure ratio between the two high-pressure accumulators (13, 22) being exceeded.
4. Fuel injection system according to Claim 3,
   characterized
   in that the first high-pressure accumulator (13) is coupled to a pressure regulating valve (14) which, in an open position, effects a return flow of fuel into the low-pressure region (5).
5. Fuel injection system according to Claim 4,
   characterized
   in that the pressure regulating valve (14) is electrically actuatable by a control device of a motor vehicle.
6. Fuel injection system according to one of Claims 2 to 5,
   characterized
   in that the overflow valve (26) is designed as a mechanically operating, in particular springloaded valve.
7. Fuel injection system according to one of Claims 1 to 6,
   characterized
   in that two pressure-boosting devices (17, 18) are provided which are in particular of identical design and which are actuatable independently of one another.

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