EP1950400A1

EP1950400A1 - Arrangement and method for switching off a combustion engine

Info

Publication number: EP1950400A1
Application number: EP07100960A
Authority: EP
Inventors: Kim KYLSTRÖM; Jens Svensson; Ulf Carlsson; Mats Hägg
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2007-01-23
Filing date: 2007-01-23
Publication date: 2008-07-30
Anticipated expiration: 2027-01-23
Also published as: ATE454547T1; EP1950400B1; DE602007004184D1

Abstract

The present invention relates to an arrangement and a method for switching off an engine (1) with a fuel injection system which comprises having injection means (8) for injecting the pressurised fuel in an accumulator tank into the respective combustion spaces of the engine, and a control unit (9) for executing a first switch-off process (A) of the engine which results in fiiel at an overpressure remaining in the tank after the engine has stopped. The method comprises the step of executing a second switch-off process (B) by stopping the supply of fuel to the tank while the injection means are activated so that the engine runs for a final period until a fuel pressure in the tank has decreased to a predetermined pressure level or the fuel in the tank is consumed to such an extent that no overpressure remains in the tank.

Description

BACKGROUND TO THE INVENTION

The present invention relates to an arrangement and a method for switching off a combustion engine according to the preambles of claims 1 and 11.
A so-called "Common Rail" system is commonly used to make fuel injection possible at very high pressure in the combustion spaces of a diesel engine. A Common Rail system comprises a high-pressure pump which pumps fuel at very high pressure to an accumulator tank (the "Common Rail"). The pressure in the accumulator tank during operation may be within the range 250 to 2200 bar. The fuel in the accumulator tank is intended to be distributed to all the cylinders of the combustion engine. Fuel from the accumulator tank is injected into the combustion spaces of the respective cylinders by electronic injectors which can open and close very quickly. An electronic control unit substantially continuously calculates the amount of fuel to be supplied to the respective cylinders on the basis of information about various engine parameters, e.g. the combustion engine's load and speed. The electronic control unit also receives information from a pressure sensor concerning the prevailing pressure in the accumulator tank. On the basis of knowing the pressure in the accumulator tank, the electronic control unit controls the opening times of the electronic injectors so that the calculated amount of fuel is supplied with good accuracy to the combustion spaces of the respective cylinders.
Certain Common Rail systems, however, are very dense. In such cases the high pressure in the accumulator tank may continue for a relatively long time after the combustion engine is switched off. This is inherently desirable in making it possible to start the engine without the pressure having to be built up again before doing so. When servicing or repair work has to be carried out on the fuel injection system and parts have to be removed, there is therefore a risk that the accumulator tank may contain fuel at a very high pressure which may spurt out in an uncontrolled manner.
Such work on the fuel injection system has therefore always to be performed with great caution during an initial stage.

SUMMARY OF THE INVENTION

The object of the present invention is to decrease the possibility of accidents and unnecessary dirtying when servicing or repair work has to be carried out on a combustion engine provided with a common-rail injection system.
The invention relates to an arrangement for switching off a combustion engine, whereby the combustion engine is provided with a fuel injection system which comprises a fuel line for supplying fuel to the combustion engine, a fuel pump adapted to transport fuel in the fuel line, a high-pressure pump adapted to pressurise the fuel in the fuel line, an accumulator tank adapted to receive and store fuel from the high-pressure pump at high pressure, a pressure sensor for sensing a fuel pressure in the accumulator tank, injection means adapted to inject the pressurised fuel situated in the accumulator tank into the respective combustion spaces of the combustion engine, a start/stop means adapted to initiate the starting and switching off of the combustion engine, and a control unit for executing a first switch-off process of the combustion engine when such a process is initiated by the start/stop means, which first switch-off process results in fuel at an overpressure remaining in the accumulator tank after the combustion engine has stopped. The arrangement also comprises means adapted to make it possible to execute a second switch-off process of the combustion engine by being adapted to stop the supply of fuel to the accumulator tank while at the same time the injection means are activated so that the combustion engine will run for a final period of operation until the fuel pressure in the accumulator tank has decreased to a predetermined pressure level or the fuel in the accumulator tank is consumed to such an extent that substantially no overpressure remains in the accumulator tank after the combustion engine has stopped. Hereby is achieved that the pressure of the fuel in the accumulator tank in a safe and convenient way may be decreased to an acceptable pressure level for performing servicing or repair work without the risk of fuel spurting out in an uncontrolled manner from the fuel injection system when dismantling the combustion engine.
The means adapted to make it possible to execute the second switch-off process may in one embodiment of the arrangement be adapted to, when the combustion engine has stopped, determine if the fuel pressure in the accumulator tank has decreased to at least the predetermined pressure level, and, if the fuel pressure in the accumulator tank is above the predetermined pressure level, cause injection of fuel from the accumulator tank in at least one of the combustion spaces without running the combustion engine. Hereby an additional function for securing that the pressure level in the accumulator tank has decreased to an acceptable pressure level in case the engine for some reason, such as a seized engine, has stopped before the acceptable pressure level has been reached.
The means adapted to make it possible to execute the second switch-off process may in one embodiment of the arrangement be adapted to, when the combustion engine has stopped, stop the injection of fuel into the at least one of the combustion spaces while the combustion engine is not running when the fuel pressure in the accumulator tank has reached the predetermined pressure level. Hereby is achieved that an unnecessary amount of fuel does not have to be wasted by injecting it into the cylinders without being combusted if the predetermined pressure level is set as acceptable even if it is higher than the atmospheric pressure.
The means adapted to make it possible to execute the second switch-off process may in one embodiment of the arrangement be adapted to, before the stopping of the fuel supply to the accumulator tank, check if the combustion engine is running, and cause injection of fuel from the accumulator tank into at least one of the combustion spaces without running the combustion engine if the combustion engine is not running. Hereby is achieved that the combustion engine does not have to be running in order to decrease the fuel pressure in the accumulator tank. This is particularly important in those cases when the person making the repair, before initiating the second switch-off process, already knows that the combustion engine cannot or should not be started in order to not cause any extra damage to the combustion engine.
In one embodiment of the arrangement, the means comprises the control unit and a diagnostic tool by which it is possible to communicate with the control unit and initiate the second switch-off process. With such a diagnostic tool it is possible to programme an existing control unit so that it switches off the combustion engine by the alternative switch-off process instead of the ordinary switch-off process.
The diagnostic tool may comprise a computer program with information about how to execute the second switch-off process. This will make it easy for the diagnostic tool to inform the control unit about how to execute the alternative switch-off process without having to install a new computer program in the control unit. Alternatively, the control unit may already comprise a computer program with information about how to execute the second switch-off process, thereby making it possible to use the diagnostic tool for selecting the switch-off process of the combustion engine to be executed by the control unit. It is therefore possible by a simple choice to select the switch-off process which the control unit is to execute. In another embodiment of the latter alternative, the diagnostic tool is only used for initiating the second switch-off process.
The means adapted to make it possible to execute the second switch-off process may in one embodiment of the arrangement comprise the start/stop means for initiating the second switch-off process. This may be in addition or as an alternative to the initiation of the second switch-off process through the diagnostic tool.
The control unit may be adapted to stop the supply of fuel to the accumulator by halting the operation of the fuel pump and/or the high-pressure pump. If either of these components stops, no further fuel can be supplied to the accumulator tank.
Thee control unit may be adapted to run the combustion engine at an ordinary idling speed or a somewhat increased idling speed during said final period of operation. A somewhat higher speed will ensure that the overpressure in the accumulator tank is substantially completely eliminated before the combustion engine stops.
The invention also relates to a method for switching off a combustion engine, whereby the combustion engine is provided with a fuel injection system which comprises a fuel line for supplying fuel to the combustion engine, a fuel pump adapted to transport fuel in the fuel line, a high-pressure pump adapted to pressurize the fuel in the fuel line, an accumulator tank adapted to receive and store fuel from the high-pressure pump at high pressure, a pressure sensor for sensing a fuel pressure in the accumulator tank, injection means adapted to inject the pressurised fuel situated in the accumulator tank into the respective combustion spaces of the combustion engine , a start/stop means adapted to initiate the starting and switching off of the combustion engine, and a control unit for executing a first switch-off process of the combustion engine which results in fuel at an overpressure remaining in the accumulator tank after the combustion engine has stopped. The method comprises the step of executing a second switch-off process of the combustion engine by stopping the supply of fuel to the accumulator tank while at the same time the injection means are activated so that the combustion engine runs for a final period of operation until a fuel pressure in the accumulator tank has decreased to a predetermined pressure level or the fuel in the accumulator tank is consumed to such an extent that substantially no overpressure remains in the accumulator tank after the combustion engine has stopped.
The method may comprise the steps when the combustion engine has stopped:

determining if the fuel pressure in the accumulator tank has decreased to at least the predetermined pressure level, and
injecting fuel from the accumulator tank in at least one of the combustion spaces without running the combustion engine if the fuel pressure in the accumulator tank is above the predetermined pressure level.

The method may comprise the step of stopping the injection of fuel into the at least one of the combustion spaces while the engine is not running when the fuel pressure in the accumulator tank has reached the predetermined pressure level.
The method may comprise the following step before the stopping of the fuel supply to the accumulator tank:

checking if the combustion engine is running, and injecting fuel from the accumulator tank into at least one of the combustion spaces without running the combustion engine if the combustion engine is not running.

The method may comprise the step of using a diagnostic tool for communicating with the control unit and initiating the second switch-off process.
The method may comprise the step of using the start/stop means for initiating commencement of the alternative switch-off process.
The method may comprise the step of stopping the supply of fuel to the accumulator by halting the operation of the fuel pump and/or the high-pressure pump.
The method may comprise the step of running the combustion engine at an ordinary idling speed or a slightly increased idling speed during said final period of operation.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described below by way of examples with reference to the attached drawings, in which:

Fig. 1 depicts an arrangement which makes possible an alternative switch-off process of a combustion engine,
Fig. 2 depicts a flowchart illustrating a method for executing an alternative switch-off process of a combustion engine, and
Fig. 3 depicts a flowchart illustrating an embodiment of a method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

While the invention covers various embodiments, some embodiments of the invention are shown in the drawings and will hereinafter be described in detail. However, it is to be understood that the specific description and drawings are not intended to limit the invention to the specific forms disclosed. On the contrary, it is intended that the scope of the claimed invention includes all embodiments thereof falling within the spirit and scope of the invention as expressed in the appended claims as well as their equivalents.
Fig. 1 depicts a fuel injection system for a combustion engine 1 in the form of a schematically represented diesel engine. The fuel injection system and the diesel engine are with advantage fitted to a heavy vehicle, such as a truck or bus. The fuel injection system is a so-called Common Rail system and comprises a fuel line 2 for supply of fuel from a fuel tank 3 to the cylinders of the diesel engine. A fuel pump 4 is arranged in the fuel line 2 to convey fuel from the fuel tank 3 via a filter 5 to a high-pressure pump 6. The high-pressure pump 6 is adapted to pressurising the fuel so that it enters at high pressure an accumulator tank 7 which takes the form of a so-called Common Rail. The high fuel pressure in the accumulator tank 7 constitutes a power source making it possible for fuel to be injected at high pressure into the respective cylinders of the diesel engine. To control the injection of the fuel, an injection means 8 is arranged in each of the connections between the accumulator tank 7 and the respective cylinders of the diesel engine. When an injection means 8 is in an open state, it injects fuel at high pressure into the cylinder concerned. A control unit 9 in the form of an electronic control unit (ECU) is adapted to control the operation of the fuel pump 4, the high-pressure pump 6 and the injection means 8. A pressure sensor 7a is fitted in the accumulator tank 7 to detect the prevailing pressure therein and to send to the control unit 9 a signal conveying information about the pressure values detected. A schematically depicted start/stop means 10 in the form of an ignition switch of the engine is connected to the control unit 9.
The start/stop means 10 is adapted to send a signal to the control unit 9 when the diesel engine is to be started. The control unit 9 thereupon activates the fuel pump 4 and the high-pressure pump 6 so that fuel at high pressure is fed to the accumulator tank 7. The control unit 9 activates at the same time the injection means 8 so that fuel at high pressure is injected into the respective cylinders of the diesel engine from the common accumulator tank 7. During operation of the diesel engine, the control unit 9 substantially continuously receives control signals concerning engine parameters such as, for example, the diesel engine's load and speed. On the basis of that information, the control unit 9 calculates the amount of fuel to be supplied to the cylinders of the diesel engine. The control unit 9 receives at the same time information from the pressure sensor 7a about the instantaneous pressure in the accumulator tank 7. Knowing the desired amount of fuel and the pressure in the accumulator tank 7 enables the control unit 9 to adjust the opening times of the respective injection means 8 so that an optimum amount of fuel is supplied to each of the cylinders of the diesel engine at a correct time.
The control unit 9 also has the function of stopping the diesel engine when it receives information from the start/stop means 10 that the diesel engine is to be switched off. To this end, the control unit 9 comprises a computer program product 9a in the form of e.g. a flash memory, an EPROM, an EEPROM and a ROM which stored thereon has a first computer program for switching off the diesel engine by a first, ordinary switch-off process A. During such an ordinary switch-off process A, the control unit 9 substantially immediately halts the operation of the fuel pump 4, the high-pressure pump 6 and the injection means 8 so that the diesel engine stops substantially immediately. The ordinary switch-off process A results, however, in residual high pressure in the accumulator tank 7 when the diesel engine has stopped. As many fuel injection systems are very dense, such overpressure of fuel will remain in the accumulator tank 7 for a relatively long time after the diesel engine has been switched off. It is therefore often difficult to perform servicing and repair work on this kind of fuel injection system.
In contrast, the present invention uses an arrangement which makes it possible to execute a second, alternative switch-off process B of the diesel engine whereby substantially no fuel at an overpressure remains in the accumulator tank 7 after the diesel engine has stopped. The arrangement comprises the existing control unit 9 and a diagnostic tool 11 which may conventionally comprise a portable computer connectable to the control unit 9 by a suitable connection cable, either directly or via a vehicle internal computer network and comprising software for communication with at least some of the ECUs in the vehicle in order to diagnose certain systems/components in the vehicle. The diagnostic tool 11 comprises software 11a which makes it possible to communicate with the control unit 9. It is possible by means of the diagnostic tool 11 to adjust the control which is exercised by the control unit 9 over various components of a vehicle. Furthermore, as is known to a person skilled in the art, the diagnostic tool 11 also comprises means for displaying instructions, hints or suggestions to e.g. the workshop personnel. It is according to the invention possible by means of the diagnostic tool 11 to replace the ordinary switch-off process A of the diesel engine conducted by the control unit 9 by at least one alternative switch-off process B whereby there will be substantially no residual overpressure in the accumulator tank 7 after the diesel engine has stopped. When the diesel engine has been switched off by such an alternative switch-off process B, repair work can be performed on the fuel injection system without the risks which an overpressurised accumulator tank 7 entails.
Using the diagnostic tool 11, which will usually be connected to the vehicle internal computer network during servicing or repair work, results in substantially no extra components having to be supplied or fitted to the vehicle in order to provide the possibility of switching off the diesel engine by the alternative switch-off process B. The extra cost arising from the alternative switch-off facility B will therefore be substantially negligible. The diagnostic tool 11 may comprise a computer program 11b containing information about how to execute the alternative switch-off process B. Alternatively or in addition thereto, the control unit 9 may already comprise a second computer program 9b stored on the computer program product or another storing unit in the control unit 9 for causing the control unit 9 to start the alternative switch-off process B. In the latter case the diagnostic tool 11 need only be used for selecting switch-off process A or B of the diesel engine 1 or means for initiation of the alternative switch-off process B.
Fig. 2 depicts a general example of a method using the alternative switch-off process B. At step S1, the diagnostic tool 11 is connected by a connection cable to the control unit 9. At step S2, a written suggestion is displayed on a screen of the diagnostic tool. The suggestion may be to advice the reader to start the diesel engine via the start/stop means 10 or any other means enabled by the vehicle or diagnostic tool 11. The suggestion may or may not be followed by the person/persons using the diagnostic tool 11. The person/persons performing the service or repair work may for instance already know that the condition of an engine in a particular case may be such that it is unwise to start the revolutions of the engine or that the engine is not be able to run although the start/stop means 10 is affected. In a third step S3 a manual activation of the alternative switch-off process B is initiated through the diagnostic tool 11. The alternative switch-off process B is in this embodiment activated whether or not the diesel engine is actually running. In a fourth step S4 the alternative switch-off process B is run and an embodiment of the alternative switch-off process will be explained more in detail below in conjunction with Fig.3. In a fifth step S5, servicing or repair work may be performed on the fuel injection system without the risks which a pressurised accumulator tank 7 entails.
Fig 3 schematically shows an embodiment of the fourth step S4. Once the alternative switch of process B has been initiated in order to decrease the pressure in the accumulator tank 7 it is in a first substep S41 determined if the engine is running. This may be determined by the control unit 9 by checking the values received from an engine speed sensor (not shown). A second substep S42 follows, if it is determined that the engine is running a second substep S42 follows, else a third substep S43 follows.
In the second substep S42, the control unit 9 switches off the diesel engine by stopping the supply of fuel to the accumulator tank 7 by halting the operation of the fuel pump 4 and the high-pressure pump 6. When either of these pumps 4, 6 stops, no further fuel will be supplied to the accumulator tank 7. The control unit 9 initiates at the same time continued activation of the injection means 8 so that the diesel engine continues to run for a final period using the existing fuel in the accumulator tank 7. The overpressure of fuel in the accumulator tank 7 will therefore decrease progressively as the fuel is consumed. During this substep S42 the diesel engine may be run at idling speed or slightly above idling speed to ensure that the overpressure in the accumulator tank 7 is completely eliminated or at a predetermined pressure level considered acceptable for service and repair work on the fuel injection system. In the shown embodiment the diesel engine is run until the combustion processes in the cylinders stop due to lack of fuel. A fourth step S44 follows after the second substep S42.
In the third substep S43, at least one of the injection means 8 is opened so that fuel from the accumulator tank is allowed to flow into the corresponding cylinder/cylinders in order to decrease the pressure in the accumulator tank 7. At the same time the pressure in the accumulator tank 7 is monitored by the control unit 9. As soon as the overpressure in the accumulator tank 7 is completely eliminated or the predetermined pressure level is reached, the opened injection means 8 are closed in order to not dump any more fuel into the cylinders than necessary. Alternatively, instead of or in addition to monitoring the pressure, the injection means 8 may be opened for an empirically determined time or a calculated period dependent on the pressure in the accumulator tank 7 when the fourth step S4 is started. The fourth step S4 is ended after the third substep S43. Since the engine is not running, i.e. the speed of the diesel engine is zero, during the third substep S43, e.g. the high pressure pump 6 does not supply any fuel to the accumulator tank 7 since the high pressure pump 6 is driven by the diesel engine.
In the fourth substep S44, it is checked if the pressure in the accumulator tank 7 is or lower than the predetermined pressure level. If the pressure has reached the predetermined pressure level during the second substep S42 the fourth step S4 ends. However, if the predetermined pressure has not been reached, the third substep S43 is executed after the fourth substep S44. The third substep S43 in combination with the fourth substep S44 make certain that the pressure is not more than the predetermined pressure level in case the diesel engine would stop before the predetermined pressure level is reached.
The second computer program 9b may in an alternative embodiment of the second substep S42 cause the control unit 9 to continuously monitor the pressure in the accumulator tank 7 through the pressure sensor 7a and interrupt the running of the diesel engine if the pressure in the accumulator tank 7 has reached the predetermined pressure level, although the combustion processes in the cylinders have not yet stopped due to lack of injected fuel.
In an alternative embodiment of the invention the diagnostic tool 11 is not needed for performing the second switch-off process B. The second switch-off process B may in this embodiment be initiated by a push button in the vehicle or by setting the start/stop means 10 in a certain position provided that the control unit 9 comprises the second computer program 9b.

Claims

An arrangement for switching off a combustion engine (1), whereby the combustion engine (1) is provided with a fuel injection system which comprises a fuel line (2) for supplying fuel to the combustion engine (1), a fuel pump (4) adapted to transport fuel in the fuel line (2), a high-pressure pump (6) adapted to pressurise the fuel in the fuel line (2), an accumulator tank (7) adapted to receive and store fuel from the high-pressure pump (6) at high pressure, a pressure sensor (7a) for sensing a fuel pressure in the accumulator tank (7), injection means (8) adapted to inject the pressurised fuel situated in the accumulator tank (7) into the respective combustion spaces of the combustion engine (1), a start/stop means (10) adapted to initiate the starting and switching off of the combustion engine (1), and a control unit (9) for executing a first switch-off process (A) of the combustion engine when such a process is initiated by the start/stop means (10), which first switch-off process (A) results in fuel at an overpressure remaining in the accumulator tank (7) after the combustion engine (1) has stopped, characterised in that the arrangement comprises means adapted to make it possible to execute a second switch-off process (B) of the combustion engine (1) by being adapted to stop the supply of fuel to the accumulator tank (7) while at the same time the injection means (8) are activated so that the combustion engine (1) will run for a final period of operation until the fuel pressure in the accumulator tank (7) has decreased to a predetermined pressure level or the fuel in the accumulator tank (7) is consumed to such an extent that substantially no overpressure remains in the accumulator tank (7) after the combustion engine has stopped.
An arrangement according to claim 1 characterised in that, when the combustion engine (1) has stopped, the means adapted to make it possible to execute the second switch-off process (B) is adapted to determine if the fuel pressure in the accumulator tank (7) has decreased to at least the predetermined pressure level, and, if the fuel pressure in the accumulator tank (7) is above the predetermined pressure level, cause injection of fuel from the accumulator tank (7) in at least one of the combustion spaces without running the combustion engine (1).
An arrangement according to claim 2, characterised in that the means adapted to make it possible to execute the second switch-off process (B) is adapted to stop the injection of fuel into the at least one of the combustion spaces while the combustion engine (1) is not running when the fuel pressure in the accumulator tank (7) has reached the predetermined pressure level.
A method according to any one of claims 1-3, characterised in that the means adapted to make it possible to execute the second switch-off process (B) is adapted to, before the stopping of the fuel supply to the accumulator tank (7), check if the combustion engine (1) is running, and cause injection of fuel from the accumulator tank (7) into at least one of the combustion spaces without running the combustion engine (1) if the combustion engine (1) is not running.
An arrangement according to any one of claims 1-4, characterised in that said means comprises the control unit (9) and a diagnostic tool (11) by which it is possible to communicate with the control unit (9) and initiate the second switch-off process (B).
An arrangement according to claim 5, characterised in that the diagnostic tool (11) comprises a computer program (11b) with information about how to execute the second switch-off process (B).
An arrangement according to claim 5, characterised in that the control unit (9) comprises a computer program (9b) with information about how to execute the second switch-off process (B).
An arrangement according to any one of claims 1-4, characterised in that said means comprises the start/stop means (10) for initiating the second switch-off process (B).
An arrangement according to any one of claims 1-8, characterised in that the control unit (9) is adapted to stop the supply of fuel to the accumulator (7) by halting the operation of the fuel pump (4) and/or the high-pressure pump (6).
An arrangement according to any one of claims 1-9, characterised in that the control unit (9) is adapted to run the combustion engine (1) at an ordinary idling speed or a somewhat increased idling speed during said final period of operation.
A method for switching off a combustion engine (1), whereby the combustion engine (1) is provided with a fuel injection system which comprises a fuel line (2) for supplying fuel to the combustion engine (1), a fuel pump (4) adapted to transport fuel in the fuel line (2), a high-pressure pump (6) adapted to pressurize the fuel in the fuel line (2), an accumulator tank (7) adapted to receive and store fuel from the high-pressure pump (6) at high pressure, a pressure sensor (7a) for sensing a fuel pressure in the accumulator tank (7), injection means (8) adapted to inject the pressurised fuel situated in the accumulator tank (7) into the respective combustion spaces of the combustion engine (1), a start/stop means (10) adapted to initiate the starting and switching off of the combustion engine (1), and a control unit (9) for executing a first switch-off process (A) of the combustion engine (1) which results in fuel at an overpressure remaining in the accumulator tank (7) after the combustion engine (1) has stopped, characterised in that the method comprises the step of executing a second switch-off process (B) of the combustion engine (1) by stopping the supply of fuel to the accumulator tank (7) while at the same time the injection means (8) are activated so that the combustion engine (1) runs for a final period of operation until a fuel pressure in the accumulator tank (7) has decreased to a predetermined pressure level or the fuel in the accumulator tank (7) is consumed to such an extent that substantially no overpressure remains in the accumulator tank (7) after the combustion engine(1) has stopped.
A method according to claim 11, characterised by the following steps when the combustion engine has stopped:
determining if the fuel pressure in the accumulator tank (7) has decreased to at least the predetermined pressure level, and

injecting fuel from the accumulator tank (7) in at least one of the combustion spaces without running the combustion engine (1) if the fuel pressure in the accumulator tank (7) is above the predetermined pressure level.
A method according to claim 12, characterised by the step of stopping the injection of fuel into the at least one of the combustion spaces while the engine is not running when the fuel pressure in the accumulator tank (7) has reached the predetermined pressure level.
A method according to any one of claims 11-13, characterised by the following step before the stopping of the fuel supply to the accumulator tank (7):
checking if the combustion engine (1) is running, and injecting fuel from the accumulator tank (7) into at least one of the combustion spaces without running the combustion engine (1) if the combustion engine (1) is not running.
A method according to any one of claims 11-14, characterised by the step of using a diagnostic tool (11) for communicating with the control unit (9) and initiating the second switch-off process (B).
A method according to any one of claims 11-14, characterised by the step of using the start/stop means (10) for initiating commencement of the alternative switch-off process (B).
A method according to any one of claims 11-16, characterised by the step of stopping the supply of fuel to the accumulator (7) by halting the operation of the fuel pump (4) and/or the high-pressure pump (6).
A method according to claim any one of claims 11-17, characterised by the step of running the combustion engine (1) at an ordinary idling speed or a slightly increased idling speed during said final period of operation.