Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2003-05-07
2004-06-15
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S495000, C417S228000
Reexamination Certificate
active
06748923
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an injection system for an internal combustion engine, according to the preamble of claim
1
, and to a method for regulating and/or bleeding an injection system for an internal combustion engine, according to the preamble of claim
9
.
Such injection systems for internal combustion engines conventionally have a pre-feed pump which feeds the fuel to be injected out of a fuel tank via a fuel line and transfers it to a high-pressure pump which generates the injection pressure necessary for injecting the fuel into the combustion spaces of the internal combustion engine. In the case of a common-rail injection system, the high-pressure pump is connected on the outlet side to a high-pressure accumulator, from which the injectors assigned to the individual combustion spaces of the internal combustion engine procure the fuel to be injected.
The known injection systems also make it possible to scavenge the high-pressure pump with the fuel to be injected, with the result that a lubrication and cooling of the high-pressure pump are brought about. For this purpose, a feed branches off, between the pre-feed pump and the high-pressure pump, from the fuel line connecting the pre-feed pump to the high-pressure pump and issuing on the outlet side into the casing of the high-pressure pump. Via the feed, part of the fuel conveyed by the pre-feed pump is branched off and used for scavenging the high-pressure pump. The fuel used for scavenging purposes is subsequently returned to the fuel tank via a fuel return line.
As a result of the scavenging of the high-pressure pump by the fuel stream branched off from the feed stream, however, when the internal combustion engine is started the pressure build-up on the intake side of the high-pressure pump is delayed or even prevented, so that the internal combustion engine starts only with a retard or not at all. A regulating valve is therefore arranged in the feed branching off between the pre-feed pump and the high-pressure pump, said regulating valve releasing the scavenging stream in the feed only when the fuel pressure necessary for operating the high-pressure pump is reached on the intake side of the high-pressure pump.
In the known injection systems, the pre-feed pump and the high-pressure pump are driven via a mechanical connection by the internal combustion engine of the common-rail system, so that the rotational speed of the pre-feed and the high-pressure pump is proportional to the engine rotational speed. Since the rotational speed of the high-pressure pump is a function of the engine rotational speed, at low engine rotational speeds, which occur, for example, during starting, the high-pressure pump conveys only a relatively low volume flow into the high-pressure accumulator. For a rapid start of the engine, however, a rapid pressure build-up in the high-pressure accumulator is necessary. It is therefore necessary for the entire injection system to be constantly filled completely with fuel and contain as far as possible no air bubbles or gas bubbles. However, by the fuel tank being emptied, due to maintenance work on the system or as a result of leaks, air may infiltrate into the system. In order to prevent a delayed pressure build-up during the starting operation due to the included air in the system, therefore, bleeding devices are provided.
Normally, for bleeding the injection system in this way, individual bleeding valves or throttles are installed, in addition to the regulating valve for the scavenging stream, in the feed in the low-pressure region between the pre-feed pump and the high-pressure pump. What is to be achieved thereby is that the air can be discharged via the bleeding valves or throttles and cannot pass into the displacement spaces of the high-pressure pump. When a throttle is used, on the one hand, it is necessary, for a rapid escape of air, that the throttle has a relatively large throughflow cross section. On the other hand, the selected size of the throughflow cross section of the throttle must be sufficiently small, so that as little fuel as possible can escape through the throttle. A satisfactory dimensioning of the throttle in terms of the size of the throughflow cross section is therefore difficult to achieve. By contrast, when nonreturn valves are used as a bleeding device, it is always necessary to build-up a specific pressure in the fuel line, in order to open the nonreturn valve and thus bleed the injection system. In this case, however, at low starting rotational speeds of the engine, problems arise with regard to the build-up of a corresponding pressure which is sufficient for opening the nonreturn valve. The bleeding of the injection system is therefore not always ensured.
Furthermore, it is known to install a bleeding valve, in which a closing body is guided in a guide of the bleeding valve. Between the guide and the closing body is provided a capillary gap, via which the air included in the system is discharged during the bleeding operation. After bleeding, the fuel flows into the capillary gap. In this case, due to the high flow resistance of the fuel in the capillary gap, the closing body is taken up, so that the bleeding valve is closed by the closing body. Where a wetted capillary gap is concerned, however, there is the problem that the closing body is moved into its sealing position even during bleeding and the air can no longer escape completely through the capillary gap. Sufficient bleeding of the injection system is consequently difficult to achieve.
SUMMARY OF THE INVENTION
The object on which the invention is based is therefore to provide an injection system which can be bled simply and reliably, a rapid pressure build-up in the high-pressure accumulator being ensured at the same time, and a method for regulating and/or bleeding such an injection system.
This object can be achieved by an injection system for an internal combustion engine, comprising a pre-feed pump, a high-pressure pump, a high-pressure accumulator and at least one injector, which are connected to one another via a fuel line, in order to convey fuel out of a fuel tank via the pre-feed pump and the high-pressure pump into the high-pressure accumulator and to inject said fuel out of the high-pressure accumulator via the injector into a combustion chamber of the internal combustion engine, a feed for the high-pressure pump, said feed being connected to the fuel line between the pre-feed pump and the high-pressure pump, in order to supply fuel for lubrication and cooling to the high-pressure pump, and a valve device connected to the feed, which regulates the fuel stream for lubricating and cooling the high-pressure pump and/or bleeds the injection system, wherein the valve device comprises at least one movably arranged actuator and a first and a second throttle device, the actuator being set as a function of a pressure of the fuel stream between the pre-feed pump and the high-pressure pump, in such a way that a first connection through the first throttle device to the high-pressure pump is released or the feed to the high-pressure pump is interrupted or a second connection through the second throttle device to the high-pressure pump is released.
The object can also be achieved by an injection system for an internal combustion engine, with a pre-feed pump, a high-pressure pump, and a high-pressure accumulator which are connected to one another via a fuel line, in order to convey fuel out of a fuel tank via the pre-feed pump and the high-pressure pump into the high-pressure accumulator, a feed for the high-pressure pump, said feed being connected to the fuel line between the pre-feed pump and the high-pressure pump, in order to supply fuel for lubrication and cooling to the high-pressure pump and to bleed the injection system, and a valve device connected to the feed, which regulates the fuel stream for lubricating and cooling the high-pressure pump and which bleeds the injection system, and wherein the valve device comprises at least one movably arranged actuator and a first and a seco
Grossner Thomas
Husslein Klaus
Klesse Christoph
Werner Martin
Zander Eckbert
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