EP3114340B1

EP3114340B1 - Method for controlling an internal combustion engine

Info

Publication number: EP3114340B1
Application number: EP15758594.4A
Authority: EP
Inventors: Eric Olofsson; Henrik Skog; Niklas Philipson; Andreas Dahl; Michael VALLINDER; Niclas Gunnarsson
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2014-03-07
Filing date: 2015-02-26
Publication date: 2022-07-06
Anticipated expiration: 2035-02-26
Also published as: EP3114340A1; WO2015133961A1; EP3114340A4

Description

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to an internal combustion, a vehicle that comprises such an internal combustion engine, and a method to control an internal combustion engine according to the appended claims.
In some operating modes, such as at a low load and a low engine speed in internal combustion engines of four-stroke and diesel type, it is desirable to shut off the fuel supply to some of the internal combustion engine's cylinders, with the objective of reducing the fuel consumption and thus reducing the environmental impact. The engine's aftertreatment system for exhausts will, however, be cooled by the air passing through those cylinders where the fuel supply has been shut off. The cooling down of the aftertreatment system arises because inlet air, which is supplied to the deactivated cylinders through the inlet valves, passes through the cylinders' combustion chambers, and further through the exhaust valves with no combustion. As a result, the temperature of the inlet air will remain relatively low as it is transported further to the after-treatment system, which results in the inlet air cooling down the aftertreatment system.
In order for the after-treatment system to be able to after-treat the internal combustion engine's exhausts in a satisfactory manner, and thus to reduce emissions in the exhausts, the after-treatment system must achieve an operating temperature in the range of 300-600 °C.
One problem that also arises when one or several cylinders are deactivated, and the other cylinders are activated through compression, fuel supply and expansion, is that vibrations arise in the internal combustion engine as a consequence of reduced frequency of ignition pulses in the engine and that torque pulses from the pressure in the deactivated cylinders become lower. At cylinder deactivation of, for example, 3 of 6 cylinders in a six cylinder engine, vibrations arise to the order of 1.5, which is perceived as disrupting by the driver and passengers in a vehicle operated by the internal combustion engine. If only the fuel is throttled to the deactivated cylinders, no change in the mass flow or exhaust temperature is achieved. This applies provided that fuel to the active cylinders is doubled, that is to say the load for the engine is kept constant.
In order to reduce the mass flow and increase the exhaust temperature, the exhaust and inlet valves may be closed in deactivated cylinders. The pressure in the deactivated cylinders then gives rise to a torque pulse per revolution per cylinder, until the pressure becomes so low in these cylinders that no significant torque is obtained from the compression pressure. The pressure in deactivated cylinders becomes low because of leakage in the cylinder. This leads to even greater vibration problems, and oil may be sucked up from the crank house, as a negative pressure in the lower part of the stroke arises in the deactivated cylinders after a certain time following deactivation.
The vibrations may be reduced if either the exhaust or the inlet valves are kept closed, and the active valves constitute both the exhaust and inlet opening. Torque pulses will then be obtained from the compression/expansion pressure in the deactivated cylinders. This results in largely the same vibration problem as only shutting off the fuel to the deactivated cylinders. Additionally, a nearly halved mass flow to the exhaust after-treatment results.
The compression/expansion pressure in the deactivated cylinders reduces vibrations, since they partly cancel orders on a lower level than the ignition frequency. Ignition frequency, as used herein, means ignition frequency without cylinder deactivation.
By controlling the exhaust or inlet valves in the deactivated cylinders, so that they are kept closed, the engine's after treatment system for exhausts will not be cooled down, since no air is supplied to the deactivated cylinders, and no air is forwarded to the engine's after treatment system from the deactivated cylinders.
The deactivation with closed exhaust or inlet valves may also apply while driving a vehicle in the event of such load cases, wherein the exhaust temperature becomes so low that the exhaust treatment system cools to such an extent that it falls below the critical temperature, where its conversion ceases wholly or partly. Accordingly, this prevents exhausts from passing through the exhaust treatment system completely untreated during a part of the vehicle's driving cycle.
In order to try and avoid cooling of the aftertreatment system while trying to equalize the vibrations, a zero flow of air through the deactivated cylinders may be created. Thus, air will be prevented from passing through the deactivated cylinders, and further to the aftertreatment system. Accordingly, the aftertreatment system will not be cooled. The zero flow must be achieved efficiently, so that pressure pulses, noise and mechanical stress is minimised or eliminated.
The document US 6431154 B1 shows how the air flow is reduced through deactivation of cylinders in an internal combustion engine, with the objective of avoiding emissions and vibrations.
US 2009/013669 A1 discloses a method of operating an engine. The method comprises discontinuing combustion in the cylinder during a plurality of cycles of the engine.
US 2004/168655 A1 discloses a control device for a spark-ignition engine. More particularly, the invention pertains to a device for controlling combustion state in individual cylinders to improve fuel economy and characteristics of emissions in a multicylinder engine.
US 2005/022755 A1 discloses a control device for a spark ignition engine and in more detail relates to a device that controls the combustion condition in the cylinders of a multi-cylinder engine in order to improve fuel consumption and reduce emissions.

SUMMARY OF THE INVENTION

Despite prior art solutions, there is a need to further develop an internal combustion engine, in which vibrations are equalized as a result of the deactivation of cylinders. There is also a need to further develop an internal combustion engine, which saves fuel through deactivation of one or several cylinders, and in which the internal combustion engine's cooling of the exhaust treatment system is avoided at deactivation of one or several cylinders, and wherein an effective zero flow of gases through the deactivated cylinders is achieved.
The primary objective of the invention is to provide an internal combustion engine, in which vibrations are effectively equalized as a consequence of the deactivation of cylinders.
Another objective of the invention is to avoid that oil may be sucked up from the crankcase, where a negative pressure arises at the lower part of the stroke in the deactivated cylinders, after a certain time following deactivation.
Another objective of the present invention is thus to provide an internal combustion engine, which saves fuel through deactivation of one or several cylinders.
These objectives are achieved with an internal combustion engine , not claimed, of the type specified at the beginning.
Such an internal combustion engine will save fuel, avoid cooling of the exhaust treatment system, and ensure that vibrations at a low load and at low engine speeds are effectively equalized. By ensuring that no air is supplied to the exhaust system from the first cylinder, while the first cylinder is supplied with a first fuel volume and the second cylinder is supplied with a second fuel volume, the pressure in the first cylinder will increase in relation to the pressure in the second cylinder. Thus, the pressure in the first and the second cylinders will be adapted to pressure levels which substantially correspond to each other. Accordingly, the vibrations will be effectively equalized. According to one embodiment of the invention, the second fuel volume is larger than the first fuel volume. Thus, a pressure increase is obtained in the first cylinder, which, in relation to the pressure in the second cylinder, is advantageous for the objective of reducing vibrations.
At cylinder deactivation of, for example, 3 of 6 cylinders in a straight six cylinder engine, vibrations to the order of 1.5 arise. With the invention, the vibrations are altered to the order of 3 by increasing the pressure in the cylinders, from which no air is supplied to the exhaust system, that is to say in those cylinders through which a zero flow prevails from the inlet side to the exhaust side. In order to minimise excitation to the order of 1.5, the sum of the torque pulses obtained from the pressure in the cylinders must not contain the order of 1.5. In order to achieve this, the differences between the torque pulses from the deactivated and the active cylinders, respectively, are reduced by reducing the compression pressure in the active cylinders, while the pressure in the deactivated cylinders is increased. The magnitude of the cylinder pressure reduction required in the active cylinders becomes load-dependent, and is advantageously controlled in such a way that vibrations for idling load are compensated. The torque pulses from the active cylinders are a function of the lever constituted by the crank rod, the crankshaft web of the crankshaft and the crankshaft angle, as well as the cylinder pressure. The size of the lever is fixed by the geometry of the crank rod and the crankshaft web, and may not be impacted, which is why the cylinder pressure is used to optimise the torque pulses. The area around 25 degrees before and after the piston's top dead centre is particularly important, since the combination of a high cylinder pressure and a lever results in high torque.
According to one embodiment not claimed. the control device is arranged to control the internal combustion engine in such a way that the air mass sucked into the second, active cylinder decreases in relation to the air mass sucked into the first cylinder. By controlling the internal combustion engine in order to decrease the air mass sucked into those cylinders, in which a throughput of gases from the inlet side to the exhaust side occurs, in relation to the air mass sucked into the first cylinder, the difference in torque pulses between the first and the second cylinder decreases. The invention is especially efficient for equalizing the low frequency vibrations arising at idling of the engine.
The magnitude of the cylinder pressure reduction required in those cylinders, in which a throughput of gases from the inlet side to the exhaust side occurs, is load dependent and advantageously controlled in such a way that vibrations for idling is prioritised. The torque pulses from the cylinders are a function of the lever constituted by the crank rod, the crankshaft web of the crankshaft and the crankshaft angle, as well as the cylinder pressure. The size of the lever is fixed by the geometry of the crank rod and the crankshaft web, and may not be impacted, which is why the cylinder pressure is used to optimise the torque pulses. The area around 25 degrees before and after the piston's top dead centre is, as stated, particularly important, since the combination of a high cylinder pressure and lever results in high torque.
According to one embodiment not claimed, two inlet valves and two exhaust valves are arranged in each cylinder. In such an internal 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, and their filling and emptying.
According to another embodiment not claimed, two first and two second valve control means are arranged in the internal combustion engine. An efficient control of the valves is thus obtained. Preferably the valve control means consist of camshafts, but it is possible to use other types of valve control means, for example hydraulic, pneumatic or electric valve control means.
According to another embodiment not claimed, the internal combustion engine is a diesel engine.
Since the diesel engine operates with compression ignition, the cylinders, combustion chamber, pistons and valves may be adapted, at the same time as control of the valve times and a suitable geometry of the components interacting in the engine is 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. A vehicle with such an internal combustion engine will save fuel, avoid that cooling of the exhaust treatment system occurs, and ensure that vibrations are effectively equalized. The comfort level for the individuals travelling in the vehicle improves, since the vibrations in the vehicle decrease.
The above objectives are achieved also with a method to control an internal combustion engine of the type specified at the beginning.
The method entails that fuel is saved, cooling of the exhaust treatment system is avoided, and vibrations are effectively equalized.
According to the invention, two inlet valves and two exhaust valves per cylinder are controlled by the respective valve control means. In such a internal combustion engine the application of the invention may be very efficient, since the number of valves per cylinder impacts the flow of air through the cylinders, and their filling and emptying.
According to another embodiment, the internal combustion engine is operated with diesel. Since an engine fuelled by diesel operates with compression ignition, the cylinders, combustion chamber, pistons and valves may be designed at the same time as control of the valve times and a suitable geometry of the components interacting in the engine is provided, so that a functioning interaction between pistons and valves is achieved.
Since substantially no negative pressure develops in the deactivated cylinders, no oil pumping from the crankcase to the combustion chamber in the cylinders, above the pistons, occurs.
According to the invention, the internal 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 valve control means, which in turn is operated by the crankshaft. At the respective valve control means there is a control device, which controls the valve control means, and thus the opening and closing times of the valves. The control device is preferably connected to a control unit, which controls the control device to a state adapted to the internal combustion engine's operating mode. The control device also controls a fuel injection device, delivering fuel to the cylinders.
When the engine and the vehicle according to the present invention are set in an operating mode, wherein there is a risk of the exhaust treatment system cooling, and wherein fuel must be saved, the inlet valves and the exhaust valves will be controlled in those cylinders, through which a zero flow from the inlet side to the exhaust side must prevail, so that no air is supplied to the exhaust system from these cylinders when the pistons move backwards and forwards in said cylinders. At the same time, the control device will control the fuel pump, so that it supplies a first fuel volume to those cylinders through which a zero flow from the inlet side to the exhaust side must prevail during the expansion stroke of said cylinders, and so that it ensures that a second fuel volume is supplied to those cylinders in which a throughput of gases from the inlet side to the exhaust side occurs during the expansion stroke of said cylinders. Preferably the second fuel volume is greater than the first fuel volume, resulting in an effective vibration reduction in the internal combustion engine. However, under certain operating conditions another volume allocation between the first and the second fuel volume is possible. For example, they may be of equal size, or the first fuel volume may be larger than the second fuel volume.
According to the invention, one of the first inlet valves is controlled to open at a bottom dead centre for the piston in the first cylinder, between an expansion stroke and an exhaust stroke, and to close at a top dead centre for the piston in the first cylinder, between the exhaust stroke and an inlet stroke, while the second of the first inlet valves is controlled to open when one of the first inlet valves closes, and to close at the bottom dead centre, between the inlet stroke and a compression stroke, and the first exhaust valves are controlled in such a way that they remain closed during all the strokes of the engine.
According to another embodiment not part of the invention, one of the first exhaust valves is controlled to open at a bottom dead centre for the piston in the first cylinder, between an expansion stroke and an exhaust stroke, and to close at a top dead centre for the piston in the first cylinder, between the exhaust stroke and an inlet stroke, while the second of the first exhaust valves is controlled to open when one of the first exhaust valves closes, and to close at the bottom dead centre, between the inlet stroke and a compression stroke, and the first inlet valves are controlled in such a way that they remain closed during all the strokes of the engine.
The internal combustion engine according to the invention preferably has separate valve control means for the inlet and exhaust valves. In one operating mode of the internal combustion engine, corresponding to normal load, the control device is controlled in such a way that the exhaust valves open at the bottom dead centre for completion of the expansion stroke, and so that they close at the top dead centre to begin the inlet stroke, and in such a way that the inlet valves open at the top dead centre when the inlet stroke begins, and close at the bottom dead centre when the compression stroke begins.
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 an internal combustion engine according to the present invention,
Fig. 2 is a top view of a schematically displayed internal combustion engine according to the present invention,
Fig. 3 is a cross section view through the line II-II in Fig. 2,
Fig. 4a-d show a diagram of the torque in the cylinders of an internal combustion engine according to the present invention,
Fig. 5 shows a diagram of the pressure in a cylinder of an internal combustion engine according to the present invention, and
Fig. 6 shows a flow chart of a method to control an internal combustion engine according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 shows a vehicle 1 in a schematic side view, which vehicle 1 is equipped with an internal combustion engine 2 according to the present invention. The internal combustion engine 2 is preferably a diesel engine. The vehicle 1 is also equipped with a gearbox 4 connected to an internal combustion engine 2, driving the driving wheels 6 of the vehicle 1 via the gearbox 4, and a propeller shaft 8.
The internal combustion engine 2 according to the invention will be described below with reference to Figs. 2 and 3. Fig. 2 shows a schematic top view of a straight internal combustion engine 2 of four-stroke type. The embodiment relates to a diesel engine fuelled by diesel fuel. The internal combustion engine 2 comprises at least one first and one second cylinder C1, C4. The internal combustion engine 2, according to the embodiment in Fig. 2 comprises six cylinders C1 - C6, arranged in a row, where one piston P1 - P6 is arranged in each cylinder C1 - C6 of the engine 2.
At least one first inlet valve 18 is arranged in the first cylinder C1, which first inlet valve 18 is connected to an inlet system 20. At least one exhaust valve 24 arranged in the first cylinder C1, which first exhaust valve 24 is connected to an exhaust system 26. At least one second inlet valve 19 is arranged in the second cylinder C4, which second inlet valve 19 is connected to the inlet system 20. At least one second exhaust valve 25 is arranged in the second cylinder C4, which second exhaust valve 25 is connected to the exhaust system 26. The inlet and exhaust valves are similarly arranged in the other cylinders C2, C3, C5, C6.
Preferably, two inlet valves 18, 19 and two exhaust valves 24 are arranged in each cylinder C1 - C6, where each inlet valve 18, 19 is connected with the inlet system 20, and each exhaust valve 24, 25 is connected with the exhaust system 26. According to one embodiment, a damper 23 may be arranged in the inlet system 20, which damper 23 may be set so that it limits the air supply to the cylinders C4 - C6 of the engine 2.
Fig. 3 shows a cross section view of the internal combustion engine 2 through the line II-II in Fig. 2. The piston P1 is connected via a crank rod 14 to a crankshaft 16, which at rotation moves the piston P1 forwards and backwards in the cylinder C1. At least one first valve control means, in the form of a first camshaft 22, is arranged to control the first and the second inlet valves 18, 19. At least one second valve control means, in the form of a second camshaft 28, is arranged to control the first and the second exhaust valves 24, 25. According to the embodiment displayed, the valve control means consist of camshafts 22, 28, but it is possible to use other types of valve control means, for example hydraulic, pneumatic or electric valve control means.
The crankshaft 16 is arranged to control each camshaft 22, 28. At least one control device 34 is arranged between the crankshaft 16 and each camshaft 22, 28, in order to control the first inlet valve 18 and the first exhaust valve 24, in such a way that no air is supplied to the exhaust system 26 from the first cylinder C1, when the first piston P1 moves backwards and forwards in the first cylinder C1. Accordingly, a zero flow through the first cylinder C1 may be created.
The control device 34 is also arranged to control the internal combustion engine 2 in such a way that the air mass sucked into the second cylinder C4 decreases in relation to the air mass sucked into the first cylinder C1. In an operating mode of the internal combustion engine 2, corresponding to a normal state, the control device 34 is controlled in such a way that the exhaust valves 24, 25 open at the bottom dead centre BDC for completion of the expansion stroke, and so that they close at the top dead centre TDC to begin the inlet stroke, and in such a way that the inlet valves 18, 19 open at the top dead centre TDC when the inlet stroke begins, and close at the bottom dead centre when the compression stroke begins.
Depending on the type of internal combustion engine 2, the two first 22 and two second camshafts 28 may be arranged in the internal combustion engine 2. This is advantageous if the engine 2 is of V-type.
A camshaft control 30 is arranged in the internal combustion engine 2 according to the present invention. The crankshaft 16 controls each camshaft 22, 28 via a camshaft transmission 32. At least one control device 34 is arranged between the crankshaft 16 and each camshaft 22, 28, so that the valves may be controlled to a state where the exhaust valves 18, 19, 24, 25 are controlled in such a way that no air is supplied to the exhaust system 26 when the pistons P1 - P3 move forwards and backwards in each of the cylinders C1 - C3. Preferably, a control 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 unit 36 impacts the control devices 34, which adjust the opening and closing times of the valves 18, 19, 24, 25 in relation to the crankshaft's 16 angular position.
A fuel pump 41 is connected to an injection device 43, arranged in each cylinder C1 - C6 for injection of fuel into the cylinder C1 - C6.
Fig. 4 a-d show graphs of torque as a function of the crankshaft angle in an internal combustion engine 2 with six cylinders C1 - C6. The Y-axis represents the torque T from the cylinders C1 - C6. The X-axis represents the crank angle state ϕ of the crankshaft 16, and thus the movement of the piston P1. Each positive torque pulse in Fig. 4a represents an expansion for each cylinder C1 - C6. Each negative torque pulse represents the compression for each cylinder C1 - C6.
Fig. 4b three of the engine's six cylinders have been deactivated by no fuel being supplied to the cylinders C1 - C3, while the remaining three cylinders C4 -C6 are still activated and operate the engine's 2 crankshaft 16. All the valves in the three deactivated cylinders C1 - C3 are closed, and the cylinders C1 - C3 have successively been emptied of air. One problem that arises when one or several cylinders C1 - C3 are deactivated, and the other cylinders C4 - C6 are activated and operate the crankshaft 16 of the engine 2, is that vibrations arise in the internal combustion engine 2 as a consequence of a reduced frequency of expansions in the engine 2, so that no torque pulses are obtained from the pressure in the deactivated cylinders C1 - C3.
Fig. 4c the vibrations have been reduced to some extent by control of the internal combustion engine 2, so that a zero flow of air is created over the deactivated cylinders C1 - C3, so that the air enclosed in the deactivated cylinders C1 - C3 will be compressed or expanded. Thus, the order of 1.5 is reduced in favour of the order of 3. Fig. 4c shows, however, that the positive torque pulse in the active cylinders C4 - C6 is higher than the positive torque pulse, which builds up in the deactivated cylinders C1 - C3. This torque difference will cause vibrations in the engine 2, which become particularly disruptive when the engine 2 is operated at idling speed. The vibrations are generated through lateral forces on the pistons P1 - P3 and the cylinder C1 - C3, and in the bearings for the crankshaft 16.
By controlling, according to the invention, the inlet valves and the exhaust valves in those cylinders, through which a zero flow from the inlet side to the exhaust side prevails, in such a way that no air is supplied to the exhaust system from said cylinders when the pistons move backwards and forwards in said cylinders, while the fuel pump 41 is controlled to supply a first fuel volume to those cylinders through which a zero flow from the inlet side to the exhaust side must prevail during the expansion stroke of said cylinders, and also by ensuring that a second fuel volume is supplied to those cylinders, in which a throughput of gases from the inlet side to the exhaust side occurs during the expansion stroke of said cylinders, the pressure in the cylinders C1 - C3 will increase and be adapted to a pressure level, which substantially corresponds to the pressure in the cylinders C4 - C6, as illustrated by the graph in Fig. 4d. Accordingly, the vibrations will be effectively equalized. The ratio between the first and the second fuel volume may vary, depending on the internal combustion engine's and the vehicle's operating mode. The first and the second fuel volume may be substantially of equal size.
According to one embodiment, the air mass sucked into the active cylinders C4 - C6 is reduced in relation to the air mass sucked into the deactivated cylinders C1 - C3. Thus, the pressure in the cylinders C4 - C6 will decrease and be adapted to a pressure level, which substantially corresponds to the pressure in the cylinders C1 - C3, which entails additional equalization of the vibrations.
At the cylinder deactivation of for example 3 of 6 cylinders C1 -C3 in the straight six cylinder engine in the example embodiment above, vibrations to the order of 1.5 arise. With the invention, the vibrations are reduced to the order of 3, by maintaining the compression and expansion pressure in the deactivated cylinders C1 - C3. By controlling the internal combustion engine 2 in such a way that the air mass sucked into the active cylinders C4 - C6 decreases in relation to the air mass sucked into the deactivated cylinders C1 - C3, the mass flow of air to the active cylinders C4 - C6 decreases. According to one embodiment, the inlet valves 19 in the active cylinders C4 - C6 are controlled to reduce the air volume sucked into the active cylinders C4 - C6. This is achieved through controlling the inlet valves 19 in the active cylinders C4-C6 to close before or after the time when the inlet valves 19 close at normal operation of the internal combustion engine 2.
The graphs in Fig. 4 represent a internal combustion engine 2 of four-stroke type, which entails that the crankshaft 16, and therefore each piston P1, will have moved the equivalent of 720° when all four strokes have been completed.
Fig. 5 shows graphs of cylinder pressure as a function of the crankshaft angle of a internal combustion engine 2. The Y-axis represents the pressure p in the cylinder C1 and in the cylinder C4. The X-axis represents the crankshaft angle ϕ of the crankshaft 16, and accordingly the piston's P1 position in the cylinder. The graph A in Fig 5 shows how the pressure in the deactivated cylinder C1 varies with the crankshaft angle ϕ of the crankshaft 16. The graph B shows how the pressure in the active cylinder C4 varies with the crankshaft angle ϕ of the crankshaft 16. The graph C shows how air mass caught - and therefore the pressure - in the active cylinder C4 has been reduced, and varies with the crankshaft angle ϕ of the crankshaft 16. The additional pressure increase arising after the top dead centre TDC for the graphs B and C is attributable to the expansion at the combustion of fuel.
In order to completely eliminate excitation of vibrations to the order of 1.5, the pressure in all the cylinders C1 - C6 must be identical. In order to achieve this to the extent possible, the inlet valves and the exhaust valves in the cylinders C1 -C3, through which a zero flow from the inlet side to the exhaust side prevails, are controlled in such a way that no air is supplied to the exhaust system from said cylinders, when the pistons move backwards and forwards in these cylinders C1 - C3. At the same time, the fuel pump 41 is controlled to supply a first fuel volume to the cylinders C1 - C3 during the expansion stroke of these cylinders. A second fuel volume is also supplied to the cylinders C4 - C6 during the expansion stroke of these cylinders. Thus, the pressure in the cylinders C1 - C3 will increase, and be adapted to a pressure level that substantially corresponds to the pressure in the cylinders C4 - C6. Accordingly, the vibrations will be effectively equalized. If the first and the second fuel volumes are of equal size, there is a substantially complete elimination of the order of 1.5.
One alternative way of reducing torque differences between active and deactivated cylinders is to reduce air mass caught in the active cylinders. The graph C shows, as described above, how air mass caught - and therefore the pressure - in the active cylinder C4 has been reduced, and varies with the crankshaft angle ϕ of the crankshaft 16. The magnitude of the cylinder pressure reduction required in the active cylinders C4 - C6 becomes load-dependent, and is advantageously controlled in such a way that vibrations for idling load are prioritised. The torque additions from the cylinders C1 - C6 are a function of the lever constituted by the crank rod 14, the crankshaft web of the crankshaft 16 and the crankshaft angle, as well as the cylinder pressure. The size of the lever is fixed by the geometry of the crank rod 14 and the crankshaft web, and may not be impacted, and accordingly the cylinder pressure is used to optimise the torque additions. The area around 25 degrees before and after the piston's top dead centre TDC is particularly important, since the combination of a high cylinder pressure and a lever results in high torque. According to one embodiment, the second inlet valves are controlled to reduce the air volume sucked into the active cylinders C4 -C6. This is achieved through controlling the inlet valves 19 in the cylinders C4- C6 to close before or after the time when the inlet valves 19 close at normal operation of the internal combustion engine 2.
According to one embodiment, the inlet valves 19 in the cylinders C4 - C6 are controlled to close in the interval corresponding to 10 crankshaft degrees before the bottom dead centre BDC to 40° after the bottom dead centre BDC, preferably 15 crankshaft degrees after the bottom dead centre BDC.
According to another embodiment, the inlet valves 19 in the cylinders C4 - C6 are controlled to close in the interval corresponding to 40° after the bottom dead centre BDC to 90° after the bottom dead centre BDC, preferably 60 crankshaft degrees after the bottom dead centre BDC.
According to a third embodiment, the damper 23, arranged in the inlet system 20, is used. By setting the damper 23 so that it limits the air supply to the active cylinders C4 - C6 of the engine 2, the air volume sucked into the active cylinders C4 - C6 will decrease. The damper 23 may be used in combination with the control of the inlet valves 19 to the cylinders C4 - C6.
In order to control the inlet valves 18 and the exhaust valves 24 of the cylinders C1 - C3 in such a way that no air is supplied to the exhaust system 26 from the cylinders C1 -C3 when the pistons P1 - P3 move backwards and forwards in the cylinders C1 - C3, according to a first embodiment, the inlet valves in the cylinders C1 - C3 are controlled to open during the exhaust stroke and the inlet stroke, while the exhaust valves in the cylinders C1 - C3 are controlled to a closed state during all the strokes.
According to a second embodiment not part of the invention, the exhaust valves in the cylinders C1 - C3 are controlled to open during an exhaust stroke and an inlet stroke, while the inlet valves in the cylinders C1 - C3 are controlled to a closed state during all the strokes. Therefore the resulting flow to the exhaust system 26 will be zero. Accordingly, the exhaust temperature increases drastically as does, consequently, the conversion degree in the exhaust purification. Since substantially no negative pressure develops in the cylinders C1 - C3, no oil pumping from the crankcase to the cylinders C1 - C3 takes place, which reduces the oil consumption. In this context, it should be pointed out that, when fuel is supplied to the deactivated cylinders C1 - C3 while a zero flow of air is generated in these cylinders, a combustion of the supplied fuel in the deactivated cylinders arises. Therefore the graph A in Fig. 5 will change because of the pressure change from the combustion of the fuel in the deactivated cylinders C1 -C3. The method to control the internal combustion engine 2 according to the present invention will be described below jointly with the flow chart in Fig. 6, which method comprises the steps:

a) to control the first inlet valve 18 and the first exhaust valve 24, in such a way that no air is supplied to the exhaust system 26 from the first cylinder, when the first piston P1 moves backwards and forwards in the first cylinder C1,
b) to supply a first fuel volume to the first cylinder C1 during the expansion stroke of the first cylinder C1, and
c) to supply a second fuel volume to the second cylinder C4 during the expansion stroke of the second cylinder C4.

Preferably, the second fuel volume is larger than the first fuel volume.
The method also comprises the additional step:
e) to reduce the air mass sucked into the second cylinder C4, in relation to the air mass sucked into the first cylinder C1.
In step d) the second inlet valve 19 is preferably controlled to reduce the air volume sucked into the second cylinder C4.
The second inlet valve 19 is controlled to close before or after the point in time for closing the second inlet valve 19 at normal operation of the internal combustion engine 2.
Preferably, the second inlet valve 19 is controlled to close in the interval corresponding to 10 crankshaft degrees before the bottom dead centre BDC to 40° after the bottom dead centre BDC, preferably 15 crankshaft degrees after the bottom dead centre BDC.
According to an alternative embodiment, the second inlet valve 19 is controlled to close in the interval corresponding to 40° after the bottom dead centre BDC to 90° after the bottom dead centre BDC, preferably 60 crankshaft degrees after the bottom dead centre BDC.
According to one embodiment not part of the invention the first inlet valve 18 is controlled in step a) to open during an exhaust stroke and an inlet stroke, while the first exhaust valve 24 is controlled to a closed state during all strokes.
According to an alternative embodiment not part of the invention, the first exhaust valve 24 is controlled in step a) to open during an exhaust stroke and an inlet stroke, while the first inlet valve 18 is controlled to a closed state during all strokes.
The fuel supplied in steps b) and c) is preferably diesel fuel.
The method also comprises the additional step:
e) to control two inlet valves 18, 19 and two exhaust valves 24, 25 for each cylinder C1, C4 with the respective camshafts 22, 28.
According to the invention one of the first inlet valves 18 is controlled in step e) to open at a bottom dead centre for the piston P1 in the first cylinder C1, between an expansion stroke and an exhaust stroke, and to close at a top dead centre for the piston P1 in the first cylinder C1, between the exhaust stroke and an inlet stroke, while the second of the first inlet valves 18 is controlled to open when one of the first inlet valves 18 closes, and to close at the bottom dead centre BDC, between the inlet stroke and a compression stroke, and the first exhaust valves 24 are controlled in such a way that they remain closed during all the strokes of the engine 2.
According to an alternative embodiment not part of the invention, one of the first exhaust valves 24 is controlled in step e) to open at a bottom dead centre BDC for the piston P1 in the first cylinder C1, between an expansion stroke and an exhaust stroke, and to close at a top dead centre TDC for the piston P1 in the first cylinder C1, between the exhaust stroke and an inlet stroke, while the second of the first exhaust valves 24 is controlled to open when one of the first exhaust valves 24 closes, and to close at the bottom dead centre BDC, between the inlet stroke and a compression stroke, and the first inlet valves 18 are controlled in such a way that they remain closed during all the strokes of the engine 2.
The method may comprise the additional step: f) to control the respective valves 18, 19, 24, 25 with two first and two second camshafts 22, 28.

Claims

Method to control a four stroke internal combustion engine, which internal combustion engine (2) comprises,
- at least one first and one second cylinder (C1, C4);

- a first piston (P1), arranged in the first cylinder (C1);

- a second piston (P4), arranged in the second cylinder (C4);

- two first inlet valves (18), arranged in the first cylinder (C1), which first inlet valves (18) are connected to an inlet system (20);

- two first exhaust valves (24), arranged in the first cylinder (C)1, which first exhaust valves (24) are connected to an exhaust system (26);

- two second inlet valves (19), arranged in the second cylinder (C4), which second inlet valves (19) are connected to the inlet system (20);

- two second exhaust valves (25), arranged in the second cylinder (C4), which second exhaust valves (25) are connected to the exhaust system (26);

- at least one first valve control means (22), which controls the first and the second inlet valves (18, 19);

- at least one second valve control means (28), which controls the first and the second exhaust valves (24, 25); and

- a crankshaft (16), controlling each valve control means (22, 28), wherein the method comprises the following steps:
a) controlling the first inlet valve (18) and the first exhaust valve (24), so that no air is supplied to the exhaust system (26) from the first cylinder when the first piston (P1) moves backwards and forwards in the first cylinder (C1),

b) supplying a first fuel volume to the first cylinder (C1) during the expansion stroke of the first cylinder (C1),

c) supplying a second fuel volume to the second cylinder (C4) during the expansion stroke of the second cylinder (C4), and

d) reducing the air mass sucked into the second cylinder (C4) in relation to the air mass sucked into the first cylinder (C1),

characterised in that, in step e):
- controlling one of the first inlet valves (18) to open at a bottom dead centre (BDC) for the piston (P1) in the first cylinder (C1), between an expansion stroke and an exhaust stroke, and to close at a top dead centre (TDC) for the piston (P1) in the first cylinder (C1), between an exhaust stroke and an inlet stroke,

- controlling the second of the first inlet valves (18) to open when the one of the first inlet valves (18) closes, and to close at the bottom dead centre (BDC), between the inlet stroke and a compression stroke, and

- controlling the first exhaust valves (24), so that they remain closed during all the strokes of the engine (2).
Method according to claim 1, characterised in that the second fuel volume is greater than the first fuel volume.
Method according to any of claims 1 - 2, characterised in that in step d) the second inlet valve (19) is controlled to reduce the air mass sucked into the second cylinder (C4).
Method according to claim 3, characterised in that the second inlet valve (19) is controlled to close before or after the time when the second inlet valve (19) closes at normal operation of the internal combustion engine (2).
Method according to claim 3, characterised in that the second inlet valve (19) is controlled to close in the interval corresponding to 10 crankshaft degrees before the bottom dead centre BDC to 40° after the bottom dead centre BDC.
Method according to claim 3, characterised in that the second inlet valve (19) is controlled to close in the interval corresponding to 40° after the bottom dead centre BDC to 90° after the bottom dead centre BDC.