DE102013204328A1 - Method for controlling a fuel injection system - Google Patents

Abstract

The invention relates to a method for controlling a fuel injection system of an internal combustion engine of a motor vehicle with a start-stop function, the fuel injection system comprising a high-pressure pump (10) which is supplied with fuel by a pre-feed pump (3), during a stop phase when a value falls below a Preselectable minimum pressure in a high-pressure accumulator (40) pressurized by the high-pressure pump (10) causes a motor shaft of the internal combustion engine to rotate at least one revolution, so that a cam (30) that is operatively connected to the motor shaft, by means of which the high-pressure pump (10 ) is drivable, is operated.

Description

The present invention relates to a method for controlling a fuel injection system of an internal combustion engine with start-stop function, wherein the fuel injection system comprises a high-pressure pump, which is supplied by a prefeed pump fuel.

State of the art

Internal combustion engines with so-called start-stop functions are already known from the prior art. Such internal combustion engines are usually switched off automatically at standstill to reduce fuel consumption or fuel savings by an injection suppression. To restart the internal combustion engine, a renewed start request is generated, for. Example, by a user of the internal combustion engine, so that an internal combustion engine associated starter is operated to perform a renewed cranking operation by starter.

In such internal combustion engines, restarting after a stop phase is generally dependent on the generated start request, so that the start time required for restarting to minimize comfort losses is to be kept as low as possible. Furthermore, each restart represents a load on the on-board power supply system and may lead to unwanted and subjectively perceived as unpleasant noises, which may occur especially in a required for restarting control of the feed pump of the internal combustion engine.

For the conventional start of an internal combustion engine in a hybrid vehicle, a torque reserve of the electric machine is required. This reduces the available torque for subsequent electric driving, which leads to the need for greater sizing of the electric machine. In order to avoid this, the so-called direct start, in which an injection or ignition takes place when the engine is stationary or the engine is rotating, is preferred in hybrid vehicles.

The prerequisite for a direct start is that the pressure in the high-pressure system does not fall below a minimum value. Due to leaks in the high-pressure system, for example via a pressure relief valve or an outlet valve of the high-pressure pump, sufficient pressure is only available for a limited time after a stop, so that after falling below the minimum pressure no direct start is possible.

Alternatively, it is attempted to develop common rail systems in a particularly dense design, so that fuel does not escape in the low pressure circuit, and the pressure in the high pressure accumulator can be maintained. However, this results in significantly higher demands on the tightness of the high-pressure pump, which leads to increased costs.

Also conceivable are additional devices for pressure build-up, such as controllable or intelligent memory, heating elements, additional pumps, etc. Also, such additional devices are associated with increased costs.

Disclosure of the invention

It is therefore an object of the present invention to provide a method and apparatus for restarting with a shortened starter life in a start-stop-function internal combustion engine after a stop phase, without increasing the manufacturing cost.

This object is achieved with a method for controlling a fuel injection system of an internal combustion engine having the features of patent claim 1.

In an internal combustion engine with start-stop function, the invention makes it possible to shorten the restart time after a stop phase.

In particular, according to the invention, a high-pressure start is simplified compared to conventional solutions. Under high pressure start (rail pressure> 20 bar, typically injection into the compression stroke) is understood here, when first the pressure in the high-pressure system is built up until an injection release threshold is exceeded. Then the injection and the start take place. In particular, repeat starts as direct starts, which represent a special embodiment of the high-pressure start, can also be carried out according to the invention. With such a start, injection and ignition are performed while the engine is stopped or rotating.

Overall, the starting times are shortened according to the invention, and the turning by a starter or an electric motor (especially in hybrid vehicles) can be completely eliminated, or at least done with significantly less torque.

According to the invention, a pressure build-up in the high-pressure system is provided in a simple manner even when the engine is switched off, so that a direct start is possible at any time. The invention can be used in both gasoline and diesel systems.

Disclosure of the invention

According to the invention a method with the features of independent claim 1 is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

With the present invention, it is easily possible to maintain a pressure in a high-pressure system of an internal combustion engine above a system pressure required for a direct start. According to the invention this can be realized without increased demands on the tightness of the high-pressure pump or additional devices for pressure build-up. According to the invention, during a stop phase, i. when the internal combustion engine is switched off, this sporadically, i. for example, during a braking operation or with low load, to rotate over one or a number of revolutions, which is operable via an operatively connected to the motor shaft cam, by means of which the high-pressure pump is driven, this can be actuated.

Advantageously, the at least one revolution by means of actuation of a clutch, via which a drive shaft of the motor vehicle with the motor shaft of the motor vehicle is coupled causes. With this, for example, it is easily possible to use a conventional vehicle clutch to rotate the motor shaft during operation of the vehicle to operate the high-pressure pump.

It is also conceivable that at least one revolution of the motor shaft by means of actuation of a clutch, via which a flywheel is coupled to the motor shaft to cause. As a result, it is also possible for engines which are designed with a flywheel to perform the actuation of the high-pressure pump according to the invention during a stop phase even when the motor vehicle is stationary.

Particularly advantageous is the application of the method according to the invention for controlling the internal combustion engine of a hybrid drive. In such a hybrid drive, which comprises an internal combustion engine and an electric motor, it is possible to make the electric motor smaller than conventional systems.

An arithmetic unit according to the invention, e.g. a control device of a motor vehicle is, in particular programmatically, configured to perform a method according to the invention.

The implementation of the method in the form of software is also advantageous, since this causes particularly low costs, in particular if an executing control device is still used for further tasks and therefore exists anyway. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

Brief description of the drawings

Hereinafter, an embodiment of the present invention will be explained in more detail with reference to the accompanying drawings. It shows

1 1 is a schematic representation of a fuel injection system of an internal combustion engine having a high-pressure pump, to which the method according to the invention can be applied,

2 a schematic representation of the drive train of an internal combustion engine, in which the inventive method is applicable, and

3 a schematic representation of various system parameters to illustrate a preferred embodiment of the method according to the invention.

Embodiment (s) of the invention

1 shows a schematic representation of a fuel injection system 1 an internal combustion engine 42 with a start-stop function. This includes a fuel tank 2 from which a prefeed pump 3 over a line 4 with a corresponding feed pressure fuel to one about a cam 30 driven high-pressure fuel pump 10 inflated. At the high pressure pump 10 is a low-pressure side a quantity control valve 20 intended. By means of the quantity control valve 20 is the flow rate of the high pressure pump 10 set. The cam 30 is from the internal combustion engine 42 driven, z. B. from an associated motor shaft and may also be part of this motor shaft. Such a motor shaft is in 2 explained in more detail and with 64 designated.

The high pressure pump 10 preferably has a delivery chamber with a check valve arranged on the input side. It compresses the fuel to a very high pressure and delivers it via a pipe 5 in a high-pressure accumulator 40 , in which the fuel is stored under very high pressure and which is also referred to as "rail" or "rail". At these are several injectors or injectors 41 connected, the fuel directly into them associated combustion chambers of the engine not shown in detail 42 inject. The internal combustion engine 42 serves z. B. to drive a motor vehicle.

The actual fuel pressure in the high-pressure accumulator 40 is from a pressure sensor 43 detected. Its signals are transmitted by the pressure sensor 43 to a control and regulating device 46 , the input side also with a temperature sensor 45 and one on the internal combustion engine 42 arranged speed sensor 44 connected is. On the output side is the control and regulating device 46 with the pre-feed pump 3 and the quantity control valve 20 connected.

The control and regulating device 46 implements the start-stop function of the internal combustion engine 42 and causes an injection suppression for automatically switching off the internal combustion engine 42 in a so-called "engine stop", ie at standstill of the internal combustion engine, in particular for consumption reduction or fuel economy. In a following on the shutdown stop phase of the internal combustion engine 42 can the prefeed pump 3 depending on operating parameters of the internal combustion engine 42 activated to accelerate the starting of the internal combustion engine 42 in a subsequent start-up phase.

In 2 is schematically the power transmission of an internal combustion engine (here also with 42 referred to) on a drive shaft 50 shown. As is known, the internal combustion engine drives a motor shaft 44 on which the motor shaft with a transmission input shaft 47 a gearbox 48 can couple or decouple. About the transmission 48 becomes a drive shaft 50 driven by the motor vehicle.

In a motor vehicle with start-stop function, it may also come during a movement of the vehicle to a shutdown of the internal combustion engine, so a stop phase. This turns the motor shaft 44 Not. By disengaged clutch 46 are also the motor shaft 44 and the transmission input shaft 47 decoupled from each other. It comes with a movement of the vehicle thus only to a rotation of the transmission input shaft 47 and the drive shaft 50 , According to a preferred embodiment of the method according to the invention is now provided during such movement of the vehicle with simultaneous stop phase of the internal combustion engine 42 the coupling 46 briefly engage, thereby rotating the motor shaft 44 to effect. On the motor shaft 64 is already referring to 1 described here but not shown cam 30 educated. Overall, it is thus caused by a movement of the vehicle rotation of the motor shaft 64 to a rotation of the cam 30 and thus an actuation of the high-pressure pump 40 ,

In 3 Various parameters measurable or occurring in connection with the method according to the invention are now plotted against time. This is a purely schematic representation. The abscissa denotes the time, the ordinate optionally the rail pressure p, the vehicle speed v or the engine speed n.

With 300 an engine speed provided by the engine is plotted against time. As can be seen, the internal combustion engine is in operation until a time t ₀ , and the engine speed 300 correspondingly positive. One with 310 designated rail pressure is constant during this time. The speed of the motor vehicle (with 320 is also positive.

If a stop process is initiated at time t ₀ , the engine speed decreases 300 within a short time to zero. Accordingly, there is a reduction in the rail pressure 310 and the speed 320 of the vehicle. At a time t ₁ , the rail pressure reaches with 312 designated pressure value p ₀ . This pressure value represents a minimum pressure which is in the high-pressure accumulator 40 (please refer 1 ) must be provided to allow a direct start of the internal combustion engine. According to the invention at time t ₁ , for example by coupling the reference to 2 Coupling, the drive shaft coupled to the motor shaft, so that the motor shaft is rotated a few times. In the example shown, this turning of the internal combustion engine takes place between the time t ₁ and a further time t ₂ . The engine speed 300 is therefore greater than zero during this time. It can be seen that in this case the rail pressure 310 again above the threshold 312 increases. If it comes now to a start request for the internal combustion engine at a time t ₃ 42 , a direct start can be carried out without time delay. As can readily be seen, increase the engine speed after a start request at time t ₃ 300 as well as the rail pressure 310 , After minimal, not noticeable to a driver, delay occurs at a time t ₄ to an acceleration of the motor vehicle.

Claims (7)

Method for controlling a fuel injection system of an internal combustion engine of a motor vehicle with start-stop function, wherein the fuel injection system comprises a high-pressure pump ( 10 ) supplied by a prefeed pump ( 3 ) Fuel is supplied, characterized in that during a stop phase falls below a preselectable minimum pressure in one of the high-pressure pump ( 10 ) pressurized high-pressure accumulator ( 40 ) causes an engine shaft of the internal combustion engine to execute at least one revolution, so that a cam ( 30 ), by means of which the high-pressure pump ( 10 ) is driven, is operated. A method according to claim 1, characterized in that the at least one revolution by means of actuation of a clutch ( 66 ), via which a drive shaft of the motor vehicle can be coupled to the motor shaft, is effected. A method according to claim 1, characterized in that the at least one revolution by means of actuation of a clutch, via which a flywheel of the motor vehicle is coupled to the motor shaft, is actuated. Method according to one of the preceding claims for controlling the internal combustion engine of a hybrid drive. Arithmetic unit which is adapted to carry out a method according to one of the preceding claims. Computer program with program code means which cause a computer unit to carry out a method according to one of claims 1 to 4 when executed on the computer, in particular according to claim 5. Machine-readable storage medium with a computer program stored thereon according to claim 6.

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