Patent Publication Number: US-10323551-B2

Title: Combustion engine, vehicle comprising the combustion engine and method for controlling the combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application (filed under 35 § U.S.C. 371) of PCT/SE2014/051441, filed Dec. 3, 2014 of the same title, which, in turn, claims priority to Swedish Application No. 1351445-0, filed Dec. 5, 2013 of the same title; the contents of each of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention pertains to control of a combustion engine. 
     BACKGROUND OF THE INVENTION 
     In connection with engine braking of a vehicle, the throttle and fuel supply to the combustion engine are shut off. When the air in the cylinders is compressed during the compression stroke, the pistons will, via the rods, exert a braking torque on the crankshaft, which during the engine brake process is operated by the vehicle&#39;s driving wheels via driving shafts, a propeller shaft and the transmission. Since the crankshaft is directly connected with the vehicle&#39;s driving wheels during the engine-braking process, the braking torque from pistons and rods, affecting the crankshaft, will therefore brake the vehicle during engine braking. 
     In order to reinforce the effect of the engine brake, the exhaust valves may be deactivated, so that they remain closed during the exhaust stroke. The air in the cylinders will thus be compressed also during the exhaust stroke, entailing that the braking torque from the pistons and rods, affecting the crankshaft, also arises during the exhaust stroke. 
     In order to utilize the braking energy in connection with engine braking, the pressure of the air compressed in the cylinders must be reduced at the end of each compression. This is carried out with a decompression device that controls the exhaust valves, so that they are opened at the end of the compression stroke and at the end of the expansion stroke. Therefore, the air compressed in the cylinders will leave the cylinder via the exhaust channels and further along through the exhaust system. The decompression device subsequently closes the exhaust valves, so that air may be sucked in through the inlet valves and an overpressure may be built up in the cylinders during the next compression. 
     When the exhaust valves are deactivated during the exhaust stroke, a very high pressure arises in the cylinders. When the subsequent inlet stroke is initiated, it is important that the high pressure in the cylinders has been reduced with the help of the decompression device before the inlet valves are opened. In the event the pressure in the cylinders exceeds a certain level as the inlet valves are opened, the inlet valves and the drivetrain connected to the inlet valves may fail, because of the substantial force which the inlet valves and its drivetrain must overcome in order to open the inlet valves in the cylinder. 
     In a combustion engine comprising several cylinders, it is possible to control the braking torque during engine braking, by controlling the deactivation of the exhaust valves and controlling the decompression device for each cylinder. For example, by deactivating the exhaust valves and activating the decompression device in half of the engine&#39;s cylinders, the braking torque will be halved. It is also possible to deactivate the exhaust valves in any number of the engine&#39;s cylinders. Control may thus be carried out in steps, wherein the number of controllable steps depends on the number of cylinders in the engine. 
     Under certain operating conditions in the vehicle, it would be desirable to carry out the control of the engine braking torque steplessly, in order thus to be able to engine-brake the vehicle comfortably. 
     Document WO 2004059131 shows a system for engine braking in a combustion engine, wherein an exhaust valve is opened on several occasions during engine braking. 
     Document WO 2012038195 pertains to an engine-braking system for a combustion engine, wherein the opening and closing of the exhaust valves is brought forward in time, following which an opening of the exhaust valves takes place after the closing, with the objective of increasing the engine brake effect. 
     Document U.S. Pat. No. 6,394,067 shows a combustion engine with double camshafts, wherein the opening of the exhaust valve is brought forward in time during engine braking. The exhaust valve is subsequently only partly closed, in order to be fully closed before it is opened to reduce the pressure in the cylinders. 
     Document U.S. Pat. No. 3,234,923 describes a method and an engine braking system for a combustion engine. A phase shift of a camshaft to control exhaust valves results in engine braking. The phase shift is approximately 160 degrees on the crankshaft, which entails that the exhaust valves are opened at a crankshaft position, corresponding to the exhaust valve opening achieved by the decompression device, as discussed above. 
     SUMMARY OF THE INVENTION 
     Despite prior art solutions, there is a need to further develop a combustion engine, efficiently engine braking a vehicle by using compression during the exhaust stroke, at the same time as the risk of engine failure is reduced. There is also a need for steplessly controlling the size of the braking torque during engine braking. 
     The objective of the present invention is thus to provide a combustion engine, which efficiently engine-brakes a vehicle by using compression during the exhaust stroke. 
     Another objective of the invention is to provide a combustion engine, for which the risk of engine failure is reduced, when engine braking is carried out by using compression during the exhaust stroke. 
     Another objective of the invention is to provide a combustion engine, in which the size of the braking torque may be controlled steplessly during engine braking. 
     These objectives are achieved with a combustion engine of the type specified at the beginning, which is characterized by the features specified in claim  1 . 
     In such a combustion engine, the risk of engine failure is reduced because the opening of the exhaust valves is phase-shifted instead of deactivated. At the same time, it is possible to control the braking torque by controlling the phase shift of the second camshaft, in order thus to control the second compression during the exhaust stroke. The size of the braking torque may thus be controlled steplessly during engine braking. 
     According to the invention, a decompression device is connected to the exhaust valves, which decompression device is adapted to open and close the exhaust valves in the transition area between an exhaust stroke and an inlet stroke, when the piston is at top dead center in the cylinder. By opening the exhaust valves in the transition area between an exhaust stroke and an inlet stroke, the pressure in the cylinders is reduced when the inlet valves are opened. The risk of engine failure is therefore reduced when engine-braking is carried out by using compression during the exhaust stroke. 
     According to one embodiment, the at least one phase-shifting device is also arranged between the crankshaft and the at least one first camshaft, in order to phase-shift the at least one first camshaft in relation to the crankshaft, to a position where the inlet valves are controlled in such a manner, that they open at a crank angle where the exhaust valves are closed with the decompression device. Phase-shifting of the inlet lifting during the engine braking entails that the pressure in the cylinder is reduced to a level, where the risk of the inlet valves and their drivetrain failing is reduced. At the same time, pressure pulses in the inlet pipe are avoided when the inlet valves open, which reduces the risk of noise arising in the combustion engine. 
     According to another embodiment, two inlet valves and two exhaust valves are arranged in each cylinder. In such a combustion engine the application of the invention will be very effective, since the number of valves per cylinder impacts the flow of air through the cylinders, which in turn impacts the adjustability of engine braking. 
     According to another embodiment, two first and two second camshafts are arranged in the combustion engine. Individual control of the inlet and exhaust valves is thus facilitated, impacting the adjustability of engine braking. 
     According to another embodiment, a phase-shifting device is arranged for each camshaft. By arranging a phase-shifting device for each camshaft, an effective phase shift of the camshafts may be achieved, increasing the adjustability of engine braking. 
     According to another embodiment, the combustion engine is a diesel engine. Since the diesel engine operates with compression ignition, cylinders, combustion chambers, pistons and valves may be adapted in such a way that a substantial phase shift of the camshafts, and thus the valve times, is achieved, while simultaneously a suitable geometry of the components interacting in the engine may be provided, so that a functioning interaction between pistons and valves is achieved. 
     The objectives specified above are also achieved with a vehicle of the type mentioned above, which is characterized by the features specified in claim  8 . In a vehicle with such a combustion engine, an effective engine-braking of the vehicle may be achieved by using, with the phase shift of the opening and closing times of the exhaust valves, compression during the exhaust stroke, while simultaneously the risk of engine failure is reduced when engine braking is carried out through the use of compression during the exhaust stroke. The size of the braking torque may be controlled steplessly during engine braking, meaning that the driving comfort is in-creased. 
     The above objectives are achieved also with a method to control a combustion engine of the type specified at the beginning, which is characterized by the features specified in claim  9 . 
     The method according to the present invention entails that the fuel supply to all the cylinders is closed, and that every second camshaft is phase-shifted in relation to the crankshaft, so that every second camshaft is phase-shifted to a state where the exhaust valves are controlled in such a way, that they are opened during the expansion stroke of the engine and closed during the exhaust stroke of the engine, in order to achieve engine braking through compression in the cylinders during the exhaust stroke. With such a method, the risk of engine failure is reduced, because the opening of the exhaust valves is phase-shifted instead of being deactivated. At the same time, it is possible to control the braking torque by controlling the phase shift of the second camshaft, in order thus to control the second compression during the exhaust stroke. 
     According to one embodiment, the at least one second camshaft is phase-shifted between −60° and −120° crankshaft degrees, preferably −90° crankshaft degrees. The at least one second camshaft will thus open early during the expansion stroke and initiate closing early during the exhaust stroke, with the objective of obtaining a compression during the exhaust stroke. The phase shift of the at least one second camshaft may be changed steplessly between 0 to −60 crankshaft degrees, according to some embodiments, and between 0 to −120 crankshaft degrees according to other embodiments. 
     According to another embodiment, the exhaust valves are opened and closed with a decompression device in the transition area between an exhaust stroke and an inlet stroke, where the piston is at a top dead center in the cylinder. By opening the exhaust valves in the transition area between an exhaust stroke and an inlet stroke, the pressure in the cylinders is reduced when the inlet valves are opened. Thus, the risk of engine failure is reduced when engine braking is carried out by using compression during the exhaust stroke. 
     According to another embodiment, the exhaust valves are opened with the decompression device 40°-80° crankshaft degrees, preferably 60° crankshaft degrees, before the top dead center between the exhaust stroke and the inlet stroke, and the exhaust valves are closed with the decompression device 40°-80° crankshaft degrees, preferably 60° crankshaft degrees, after the top dead center between the exhaust stroke and the inlet stroke. By opening the exhaust valves in the transition area between an exhaust stroke and an inlet stroke, the pressure in the cylinders is reduced when the inlet valves are opened. Thus, the risk of engine failure is reduced when engine braking is carried out by using compression during the exhaust stroke. 
     According to another embodiment, the decompression device is adapted to open and close the at least one exhaust valve in the transition area between an inlet stroke and an exhaust stroke, when the piston is at a top dead center in the cylinder. 
     According to another embodiment, two inlet valves and two exhaust valves per cylinder are controlled by the respective camshaft. In such a combustion engine the application of the invention will be very effective, since the number of valves per cylinder impacts the flow of air through the cylinders, which in turn impacts the adjustability of engine-braking. 
     According to another embodiment, each first camshaft is phase-shifted in relation to the crankshaft, so that each first camshaft is phase-shifted to a state where the inlet valves are controlled in such a way, that they are opened at a crankshaft angle where the exhaust valves are closed with the decompression device. Phase-shifting of the inlet lifting during the engine braking entails that the pressure in the cylinder is reduced to a level, where the risk of the inlet valves and their drivetrain failing is reduced. At the same time, pressure pulses in the inlet pipe are avoided when the inlet valves open, which reduces the risk of noise arising in the combustion engine. 
     According to another embodiment, the inlet valves are opened 20°-80° crankshaft degrees, preferably 50° crankshaft degrees, after the top dead center between the exhaust stroke and the inlet stroke. In such a phase shift the pressure in the cylinder is reduced to a level, which reduces the risk of the inlet valves and their drivetrain failing. At the same time, pressure pulses in the inlet pipe are avoided when the inlet valves open, which reduces the risk of noise arising in the combustion engine. The phase shift of the inlet valves may also be stepless according to some embodiments, e.g. between 0-20 crankshaft degrees, or 0-80 crankshaft degrees, after the top dead center between the exhaust stroke and the inlet stroke. 
     According to another embodiment, two exhaust valves per cylinder are controlled with the at least one second camshaft. In such a method the application of the invention will be very effective, since the number of valves per cylinder impacts the flow of air through the cylinders, which in turn impacts the adjustability of engine braking. 
     According to another embodiment, the combustion engine is operated with diesel. Since an engine operated with diesel works with compression ignition, cylinders, combustion chambers, pistons and valves may be designed in such a way, that a substantial phase-shifting of the camshafts, and thus the valve times, is achieved at the same time as a suitable geometry of the components interacting in the engine may be provided, so that a functioning interaction between pistons and valves is achieved. 
     Since substantially no negative pressure develops in the cylinders, no oil pumping from the crankcase to the cylinders occurs. 
     According to the invention, the combustion engine comprises a crankshaft, preferably a number of cylinders where each one has a forwards and backwards moving piston assembled inside, and is connected to the crankshaft for movement forwards and backwards, as well as a number of inlet and exhaust valves of disc type, in order to allow inlet air to come into the cylinders and to allow exhausts to leave the cylinders. 
     The inlet and exhaust valves are each controlled and operated by a camshaft, which in turn is operated by the crankshaft. Between the crankshaft and each camshaft, there is a phase-shifting device that controls the camshaft and thus the valves&#39; opening and closing times in relation to the crankshaft. The phase-shifting device is preferably connected to a control device, which controls the phase-shifting device into a position adapted to the combustion engine&#39;s operating mode. The control device also controls a fuel injection device, delivering fuel to the cylinders. 
     When engine braking is applied, and the vehicle according to the present invention thus decelerates in speed, the control device will close the flow of fuel to the cylinders and adjust the phase-shifting device for each camshaft, so that no fuel is injected into the cylinders and a compression is obtained during the exhaust stroke. 
     According to the invention, the combustion engine preferably has separate camshafts for inlet and exhaust valves. At an operating mode corresponding to normal load in the combustion engine, the phase-shifting device for the camshaft is controlled in such a way, that the exhaust valves open at the bottom dead center for termination of the expansion stroke, and the inlet valves open at the top dead center when the inlet stroke is initiated. 
     In the absence of throttle to the engine and instructions that engine braking must be activated, the control device will close the fuel supply to the engine&#39;s cylinders and adjust the phase-shifting device to the camshafts, so that a compression is obtained during the exhaust stroke. 
     Other advantages of the invention are set out in the detailed description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below is a description, as an example, of preferred embodiments of the invention with reference to the enclosed drawings, in which: 
         FIG. 1  is a side view of a schematically displayed vehicle, with a combustion engine according to the present invention, 
         FIG. 2  is a cross-sectional view of a schematically displayed combustion engine according to the present invention, 
         FIG. 3  shows a diagram of a phase shift of inlet and exhaust valves in a combustion engine according to the present invention, and 
         FIG. 4  shows a flow chart of a method to control a combustion engine according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
       FIG. 1  shows a schematic side view of a vehicle  1 , which vehicle  1  is equipped with a four-stroke combustion engine  2  according to the present invention. The combustion engine  2  is preferably a diesel engine. The vehicle  1  is also equipped with a gearbox  4  connected to a combustion engine  2 , driving the driving wheels  6  of the vehicle  1  via the gearbox  4 , and a propeller shaft  8 . 
       FIG. 2  shows a cross-sectional view of a combustion engine  2  according to the present invention. The combustion engine  2  comprises at least one cylinder  10 , with a piston  12  arranged in each cylinder  10 . The piston  12  is connected via a connecting rod  14  to a crankshaft  16 , which at rotation moves the piston  12  forwards and backwards in the cylinder  10 . At least one inlet valve  18  is arranged in each cylinder  10 , which inlet valve  18  is connected with an inlet system  20 . At least one first camshaft  22  controls each inlet valve  18 . At least one exhaust valve  24  is arranged in each cylinder  10 , which exhaust valve  24  is connected with an exhaust system  26 . Preferably, two inlet valves  18  and two exhaust valves  24  are arranged in each cylinder  10 . At least one second camshaft  28  controls at least one exhaust valve  24 . Depending on the type of combustion engine  2 , two first and two second camshafts  22 ,  28  may be arranged in the combustion engine  2 . This is advantageous if the engine  2  is of V-type. Preferably, the combustion engine has several cylinders. 
     A camshaft control  30  is arranged in the combustion engine  2  according to the present invention. The crankshaft  16  controls each camshaft  22 ,  28  via a camshaft transmission  32 . At least one phase-shifting device  34  is arranged between the crankshaft  16  and each camshaft  22 ,  28 , so that each camshaft  22 ,  28  may be phase-shifted to a desired angular position in relation to the angular position of the crankshaft. Preferably, a phase-shifting device  34  is arranged for each camshaft  22 ,  28 . A control device  36  receives signals from a number of different sensors (not shown), such as absolute pressure in the inlet manifold, charge air temperature, mass airflow, throttle position, engine speed, engine load. The control device  36  operates the phase-shifting devices  34 , which adjust the angle position of the camshafts  22 ,  28  in relation to the crankshaft  16 . A decompression device  37  is connected to the exhaust valves  24 , decompression device  37  is adapted to open and close the exhaust valves  24  in the transition area between an exhaust stroke and an inlet stroke, when the piston  12  is at top dead center in the cylinder  10 . By opening the exhaust valves  24  in the transition area between an exhaust stroke and an inlet stroke, the pressure in the cylinders  10  is reduced when the inlet valves  18  are opened. The risk of engine failure is therefore reduced when engine braking is carried out by using compression during the exhaust stroke. The decompression device  37  is connected to the control device  36 . 
       FIG. 3  shows a graph representing a phase shift of inlet and exhaust valves  18 ,  24  in a combustion engine  2  according to the present invention. The Y-axis represents the distance that the inlet and exhaust valves  18 ,  24  move. The X-axis represents the angular movement of the crankshaft  16 . The piston  12  moves between a top dead center, TDC, and a bottom dead center, BDC, in the cylinder  10 . At e.g. 0°, the piston  12  is at the top dead center, TDC, and at 180° the piston  12  is at the bottom dead center, BDC. The graph in  FIG. 3  represents a combustion engine  2  of four-stroke type, which entails that the crankshaft  16  and therefore the piston  12  will have moved 720° when all four strokes have been completed. 
     The curve A 1  represents the movement of the exhaust valve  24  in relation to the piston movement at normal load. The curve  11  represents the movement of the inlet valve  18  in relation to the piston movement at normal load.  FIG. 3  thus shows, through the curve A 1 , that the exhaust valve  24  at normal load opens at the end of the expansion stroke, i.e. at 120°, in order to release the exhausts to the exhaust and after-treatment system  38  during the exhaust stroke. The exhaust valve  24  then closes at the start of the inlet stroke, which occurs at 360°. Roughly at the same time, the inlet valve  18  opens, shown by the curve  11 , in order to let air into the cylinder  10 . The inlet valve  18  then closes at 590°, at which point the compression stroke is initiated. At 720°, corresponding to 0°, the expansion stroke is started. 
     The curve A 2  illustrates a situation where the engine  2 , and therefore the vehicle  1 , are decelerated through engine braking according to the present invention, wherein the phase-shifting device  34  for the second camshaft  28  has been adjusted, so that the exhaust valves  24  open and close earlier than what would be the case with normal load. At the same time, the fuel supply to one or several of the cylinders  10  of the engine  2  is closed or restricted, so that no fuel, or a limited volume of fuel is injected into one or several of the cylinders  10 . By phase-shifting the second camshaft  28  in relation to the crankshaft  16 , so that every second camshaft  28  is phase-shifted to a state, where the exhaust valves  24  are controlled in such a way that they are opened during the expansion stroke of the engine and closed during the exhaust stroke of the engine, engine braking is achieved through compression in the cylinders  10  during the exhaust stroke. Preferably, the second camshaft  22  is phase-shifted between −60° and −120° crankshaft degrees, preferably −90° crankshaft degrees. Engine braking is thus obtained, since compression arises in the cylinders  10  during both the compression stroke and the exhaust stroke. 
     In order to utilize the braking energy at engine braking, the pressure of the air compressed in the cylinders  10  must be reduced at the end of each compression. The exhaust valves  24  are therefore opened and closed with the decompression device  37  in the transition area between an exhaust stroke and an inlet stroke, when the piston  12  is at a top dead center in the cylinder  10 . The air compressed in the cylinders  10  will therefore leave the cylinders  10  through the exhaust channels and further along through the exhaust system. The decompression device  37  subsequently closes the exhaust valves  24 , so that air may be sucked in through the inlet valves  18 , and an overpressure may be built up in the cylinders  10  at the next compression. With the decompression device the exhaust valves  24  are opened 40°-80° crank-shaft degrees, preferably 60° crankshaft degrees, before the top dead center between the exhaust stroke and the inlet stroke, and the exhaust valves  24  are closed with the decompression device 40°-80°, preferably 60°, after the top dead center between the exhaust stroke and the inlet stroke. The opening and closing of the exhaust valves  24  with the decompression device  37  is shown by the curves D 1  in  FIG. 3 . 
       FIG. 3  and the curves D 1  thus show that the decompression device  37  may also open and close the exhaust valves  24  in the transition area between an inlet stroke and an exhaust stroke when the piston  12  is at a top dead center in the cylinder  10 . The air compressed in the cylinders  10  will therefore leave the cylinders  10  through the exhaust channels and further along through the exhaust system. With the decompression device, the exhaust valves  24  are opened 50°-90° crankshaft degrees, preferably 70° crankshaft degrees, before the top dead center between the inlet stroke and the exhaust stroke, and the exhaust valves  24  are closed with the decompression device 20°-60°, preferably 40°, after the top dead center between the inlet stroke and the exhaust stroke. 
     By opening the exhaust valves  24  in the transition area between an exhaust stroke and an inlet stroke, the pressure in the cylinders  10  is reduced when the inlet valves  18  are opened. Thus, the risk of engine failure reduced when engine braking is carried out by using compression during the exhaust stroke. In order to further reduce the risk of the inlet valves  18  opening at too high a pressure in the cylinders  10 , the first camshaft  22  is phase-shifted in relation to the crankshaft  16 , so that the first camshaft  22  is phase-shifted to a state, where the inlet valves  18  are controlled in such a way, that they are opened at a crankshaft degree where the exhaust valves  24  are closed with the decompression device. The first camshaft  22  is phase-shifted to a state where the inlet valves are opened 20°-80° crankshaft degrees, preferably 50° crankshaft degrees, after the top dead center between the exhaust stroke and the inlet stroke, as shown by the curve  12  in  FIG. 3 . Phase-shifting of the inlet lifting during the engine braking entails, that the pressure in the cylinders  10  is reduced to a level where the risk of the inlet valves  18  and their drivetrain failing is reduced. At the same time, pressure pulses in the inlet pipe are avoided when the inlet valves  18  open, which reduces the risk of noise arising in the combustion engine  2 . 
     The method to control the combustion engine  2  according to the present invention will be described below jointly with the flow chart in  FIG. 4 , which method comprises the steps: 
     a) to phase-shift every second camshaft  28  in relation to the crankshaft  16 , so that every second camshaft  28  is phase-shifted to a state, where the exhaust valves  24  are controlled in such a way, that they are opened during the expansion stroke of the engine and closed during the exhaust stroke of the engine, to achieve engine-braking through compression in the cylinders  10  during the exhaust stroke. 
     According to one embodiment of the invention, the at least one second camshaft  22  is phase-shifted in step a), representing −60° to −120° crankshaft degrees, preferably −90° crankshaft degrees. 
     The method also comprises the additional step: 
     b) to open and close the exhaust valves with the decompression device in the transition area between an exhaust stroke and an inlet stroke, where the piston  12  is at a top dead center in the cylinder  10 . 
     According to one embodiment of the invention, the phase shift of every second camshaft may be controlled in order to thus control the second compression during the exhaust stroke, for achieving stepless control of the size of the braking torque during engine braking. 
     According to one embodiment of the invention, in step b) the exhaust valves are opened with the decompression device 40°-80° crankshaft degrees, preferably 60° crankshaft degrees, before the top dead center between the exhaust stroke and the inlet stroke, and the exhaust valves are closed with the decompression device 40°-80°, preferably 60°, after the top dead center between the exhaust stroke and the inlet stroke. 
     The method also comprises the additional step: 
     c) to phase-shift each first camshaft  22  in relation to the crankshaft  16 , so that each first camshaft  22  is phase-shifted to a state, where the inlet valves  18  are controlled in such a way, that they are opened at a crankshaft angle where the exhaust valves are closed with the decompression device. 
     According to one embodiment of the invention, in step c) the inlet valves are opened 20°-80° crankshaft degrees, preferably 50° crankshaft degrees, after the top dead center between the exhaust stroke and the inlet stroke. 
     According to one embodiment of the invention, in step a) two exhaust valves  24  per cylinder are controlled 
     with the at least one second camshaft  28 . 
     According to one embodiment of the invention, in step a) each exhaust valve  24  is controlled with two second camshafts  28 . 
     According to one embodiment of the invention, every second camshaft  28  is phase-shifted in step a) with a phase-shifting device  34 , arranged for every second camshaft  28 . 
     According to one embodiment of the invention, the method before step a) comprises the additional step: 
     d) to close or reduce the fuel supply to at least one of the cylinders  10 . 
     According to one embodiment of the invention, the combustion engine  2  is powered with diesel fuel. 
     According to one embodiment of the invention, the method comprises the additional step: 
     e) to open and close the at least one exhaust valve  24  with a decompression device in the transition area between an inlet stroke and an exhaust stroke, when the piston  12  is at a top dead center in the cylinder  10 . 
     The components and features specified above may, within the framework of the invention, be combined between different embodiments specified.