Method for starting operation of an internal combustion engine, internal combustion engine, vehicle and control unit

Abstract

The present invention relates to a method for starting the operation of an internal combustion engine (1), wherein the method comprises the following steps: providing pressurized gas in an intake duct (3) when the internal combustion engine (1) is not running; opening an intake valve (25) in the first cylinder (2a) while keeping the exhaust valve (24) of the first cylinder (2a) closed, so as to allow the pressurized gas to enter the first cylinder (2a) and press onto the corresponding piston (21), thereby moving the corresponding piston (21) and rotating the crankshaft (23); supplying fuel to at least one of the cylinders (2a, 2b) whose corresponding piston has performed or is performing a compression step, so as to ignite the fuel and start the operation of the engine (1). In the method, pressurized gas is provided by: closing an intake duct (3) upstream of an EGR duct (5) and closing an exhaust duct (4) downstream of the EGR duct (5) so as to form a closed recirculation loop including the EGR duct (5) for the gas contained in the closed recirculation loop; and, while keeping an intake valve (25) closed, operating a controllable gas feeding device (9) arranged in the closed recirculation loop, wherein the gas feeding device (9) is configured to feed gas from its inlet (9a) to its outlet (9b), and wherein the gas feeding device (9) is operated so that the pressure of the gas contained in the closed recirculation loop increases in the intake duct (3) and decreases in the exhaust duct (4).

Description

Technical Field

[0001] The invention relates generally to a method for starting operation of an internal combustion engine, and to an engine suitable for use in this method.

[0002] The invention is generally applicable to heavy vehicles such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not limited to this particular vehicle but may also be used in other vehicles, marine vessels and stationary applications. Background Art

[0003] An internal combustion engine is provided with a piston connected to a crankshaft and arranged to reciprocate in a corresponding cylinder, and starting of the internal combustion engine involves rotating the crankshaft and injecting or supplying fuel to the cylinder in some other way at a suitable time point (i.e., when the corresponding piston is at or near the top dead center (TDC) position after having performed the compression stroke). The rotation of the crankshaft (crankshaft starting) is usually achieved by operating an electric motor. Such electric starter motors are relatively expensive and increase weight, and the old idea of ​​starting the engine by compressed air has recently attracted some interest, namely: using a pneumatic system, which includes compressed air stored in an accumulator, wherein the pressurized air is fed to the cylinder via an intake valve and is used to press onto and move the piston so as to rotate the crankshaft, and the piston has been set in a suitable position (after TDC, but before the bottom dead center BDC) before the introduction of the pressurized air. However, conventional pneumatic starting systems require additional equipment and additional space, and improved starting systems and methods are desired.

[0004] DE102015216126 discloses an engine equipped with an electrically drivable turbocompressor arranged in an intake duct, wherein the compressor can be used to pneumatically position a piston before starting and start the engine without using, for example, a compressed air accumulator. However, the turbocompressor is designed for large air flows, so that for the very small air flows used before and during engine starting, the electrically drivable turbocompressor would require considerable drive power.

[0005] Therefore, there remains a need for improved starting systems and methods for internal combustion engines. Summary of the invention

[0006] An object of the present invention is to provide a method for starting the operation of an internal combustion engine which is more effective than known methods. This object is achieved by the method described below. Other objects are, for example, to provide an internal combustion engine suitable for the method and a vehicle provided with such an engine.

[0007] The present invention relates to a method for starting operation of an internal combustion engine, wherein the engine comprises: a group of one or more cylinders, each cylinder in the group being provided with an intake valve and an exhaust valve and a piston, the intake valve and the exhaust valve being arranged to regulate the flow of gas into and out of the cylinder, respectively, the piston being arranged to move back and forth in the cylinder; a crankshaft operatively connected to each piston so as to rotate when the piston moves back and forth in the corresponding cylinder; a fuel supply system arranged to supply fuel to the cylinder; an intake duct arranged to feed intake air to the cylinder; an exhaust duct arranged to feed exhaust gas away from the cylinder; and an exhaust gas recirculation (EGR) system comprising an EGR conduit arranged to connect the exhaust duct and the intake duct so as to allow recirculation of exhaust gas through the cylinder during operation of the engine,

[0008] The method comprises the following steps: providing pressurized gas in an intake duct when the internal combustion engine is not running; opening an intake valve in a first cylinder while keeping an exhaust valve of the first cylinder closed so as to allow pressurized gas to enter the first cylinder and be pressed onto a corresponding piston, thereby moving the corresponding piston and rotating the crankshaft; and supplying fuel to at least one of the cylinders whose corresponding piston has performed or is performing a compression step so as to ignite the fuel and start the operation of the engine.

[0009] In the method of the present invention, pressurized gas is provided by: closing an intake duct upstream of an EGR duct and closing an exhaust duct downstream of the EGR duct so as to form a closed recirculation loop, the closed recirculation loop comprising an EGR duct for the gas contained in the closed recirculation loop; and operating a controllable gas feeding device arranged in the closed recirculation loop while keeping an intake valve closed, wherein the gas feeding device is configured to feed gas from its inlet to its outlet, and wherein the gas feeding device is operated such that the pressure of the gas contained in the closed recirculation loop increases in the intake duct and decreases in the exhaust duct.

[0010] In addition to being able to avoid expensive electric starters and bulky systems with accumulators for pressurized air, the method of the present invention not only increases the pressure on the intake side as in DE102015216126, but also significantly reduces the pressure on the exhaust side, which means that it provides a higher pressure difference on the engine / cylinder. In turn, this provides a more efficient blow-start procedure. In addition, by using the gas / air contained in the closed recirculation loop and recirculating the gas instead of feeding outside air through the engine, a higher temperature of the pressurized gas will result, especially in cold (winter) conditions. The increased gas / air temperature is conducive to the strong autoignition of the fuel, so this is a significant advantage for diesel engines.

[0011] In principle, the engine can have any number of cylinders, for example a single cylinder or six cylinders (the latter being considered as a typical example), and if there are multiple cylinders, it is possible to select which cylinder or cylinders are used for the rotation of the crankshaft before ignition and which cylinder is used for the first fuel ignition.

[0012] When the engine is turned off or in an early step before the actual starting method is started, a selected cylinder may have been set in a suitable starting position, and this selected cylinder will then receive the first "load" of pressurized gas. In another example, sensors are used to determine the position of all cylinders so that when the engine is about to be started, one of the cylinders that is in the right position (or close to the right position and only requires slight crankshaft adjustments to obtain the right position) is selected as the first cylinder to receive pressurized gas in this particular starting procedure. During the starting process, pressurized gas can be fed to one or some selected cylinders or all cylinders.

[0013] At least in theory, the engine can be started, i.e. the fuel in one of the cylinders can be ignited, only after one stroke caused by the pressurized gas. That is, while the piston in the first cylinder performs an intake stroke caused by the pressurized gas (i.e. over a crankshaft angle CA of 180°), the other piston in the second cylinder can perform a compression stroke, and then the fuel can be introduced and ignited in the second cylinder. However, in many cases, it is appropriate to accelerate the crankshaft during some revolutions before supplying and igniting the fuel.

[0014] If the engine is provided with a variable valve actuation (VVA) system (for at least one of the cylinders), the pressurized gas can be introduced in a two-stroke manner, i.e., the intake valve opens each time the piston passes its TDC, and closes each time the piston passes its BDC (and the exhaust valve remains closed when the intake valve opens, and vice versa). When the engine is started, the operation of the valves switches to conventional four-stroke operation. In the absence of VVA, pressurized gas can be introduced into the cylinder during the normal intake stroke of the four-stroke cycle. The present disclosure is primarily directed to four-stroke engines.

[0015] Forming a closed recirculation loop means that the gases contained in the loop (i.e. a mixture of air and some previously generated exhaust gas) are prevented from escaping through the closed intake and exhaust ducts, but are allowed to recirculate: from the cylinder through the exhaust valve (when open), into and through the upstream part of the exhaust duct, into and through the EGR duct, into and through the downstream part of the intake duct, and back into the cylinder through the intake valve (when open).

[0016] In this starting method, the inlet of the gas feed device is directed toward the exhaust valve and the outlet is directed toward the intake valve in order to increase the gas pressure in the intake duct.

[0017] A gas feed device of an appropriately selected type (e.g. a positive displacement machine in the form of a Roots blower) is installed at an appropriate location (e.g. in the EGR duct) where it can be used for purposes other than engine blow-start, e.g. for feeding EGR into the high-pressure intake system, and if the use of such a gas feed device has been contemplated or even installed in the engine, then no additional hardware may be required to carry out the method.

[0018] Positive displacement machines, such as Roots blowers, produce one flow per revolution without internal compression and are therefore more efficient than compressors in the methods described herein. Positive displacement machines are generally reversible and can produce similar flows in either direction. By reversing the gas feed device / positive displacement machine (i.e., driving it in the opposite direction), the gas in the closed recirculation loop can be made to flow in the opposite direction (by passing the pressurized gas into the cylinder through the exhaust pipe and letting the expanded gas leave through the intake valve), thereby rotating the crankshaft backward. This is very useful in the case where it is desired to rotate the crankshaft slightly backward rather than forward when the piston is set in a suitable starting position, such as when there is a load connected to the engine / crankshaft via a transmission.

[0019] The fuel supply system is typically a fuel injection system, in which fuel (eg diesel) is injected into at least one cylinder.

[0020] In an embodiment, the method comprises the step of opening an EGR valve arranged to control the flow through the EGR duct. If the engine is provided with such a valve, it must be opened to allow gas to flow in said closed recirculation loop. However, the gas feed arrangement may also function as an EGR valve, and in this case there may be no separate EGR valve that must be opened.

[0021] In one embodiment, the intake duct is closed by closing an intake throttle valve arranged in the intake duct upstream of the EGR conduit.Many internal combustion engines are already equipped with an intake throttle valve suitable for this purpose.

[0022] In one embodiment, the exhaust duct is closed by closing an exhaust duct valve arranged in the exhaust duct downstream of the EGR duct. The exhaust duct valve may be, for example, a closed loop butterfly (CLB) valve or an engine brake (which are known per se). If such a unit is arranged in the exhaust duct, the exhaust duct valve may be arranged upstream or downstream of the turbocharger turbine.

[0023] In one embodiment, the gas feed arrangement is arranged in an EGR duct. The gas feed arrangement can then be used as an EGR valve as described above during normal operation of the engine, but can also be used as an EGR pump, which is particularly useful for providing EGR flow in engine systems operating with very high air pressures on the intake side.

[0024] In one embodiment, the gas feed device is a volumetric machine configured to move gas from its inlet to its outlet by capturing a fixed amount of gas and forcing the captured amount of gas from its inlet to its outlet. This means, for example, that the gas feed device, unlike a conventional compressor, is configured to act as a closed valve when not in operation. Preferably, the volumetric machine is a rotary Roots-type blower having a pair of rotating members provided with meshing lobes. Roots blowers are well suited for this application, although screw compressors or similar devices may also be used.

[0025] In one embodiment, the method includes the step of opening an exhaust valve in the first cylinder when the piston of the first cylinder has reached a bottom dead center (BDC) position to allow the now expanding pressurized gas to exit the first cylinder. Although this step may not be necessary for starting the engine, it is useful to reduce the work of moving the piston of the first cylinder back toward and past a top dead center (TDC) position.

[0026] In an embodiment, the method comprises the steps of continuing to feed pressurized gas into the group of cylinders while opening and closing the corresponding intake and exhaust valves until the crankshaft reaches a threshold rotational speed; wherein when the speed threshold is reached, the step of supplying fuel to at least one of the cylinders is performed. This is preferably in a manner that the crankshaft is accelerated during a few revolutions before the fuel is supplied and ignited.

[0027] In one embodiment, the engine is provided with a system for variable control of intake and exhaust valves, wherein the step of continuing to feed pressurized gas into the group of cylinders while opening and closing the intake and exhaust valves comprises: opening the intake valve of the first cylinder or the second cylinder during at least a portion of a crankshaft angle (CA) range of about 0-180°, and keeping the same intake valve closed at about 180-360°, wherein the piston in the same cylinder is at the top dead center (TDC) position at 0° and 360° CA and at the bottom dead center (BDC) position at 180° CA; and, opening the exhaust valve of the same cylinder during at least a portion of a crankshaft angle (CA) range of about 180-360°, and keeping the same exhaust valve closed at about 0-180° CA. This is the two-stroke approach further described above. The crankshaft ranges given above are approximate and also cover minor adjustments that may be suitable for a particular engine. For example, the first range may be, for example, 0-190° or -5°-185°.

[0028] In one embodiment, the step of supplying fuel to at least one of the cylinders is followed by the step of confirming whether ignition of the fuel has occurred and whether the engine has started to run, and if not, interrupting the supply of fuel, or if "yes", opening the intake and exhaust ducts in order to open the closed recirculation loop and allow the engine to run normally. The step of interrupting the supply of fuel is usually followed by a return to the step of feeding pressurized gas into the group of cylinders while opening and closing the intake and exhaust valves, because this step is usually the step before the step of supplying fuel to at least one of the cylinders is performed. A new attempt to ignite the fuel can be made later. Therefore, the step of supplying fuel during the starting method is usually only temporarily interrupted.

[0029] In one embodiment, the step of confirming whether the fuel ignition has occurred and whether the engine has started to run comprises: determining whether the crankshaft rotation speed has increased above a threshold value due to the step of supplying fuel. Speed ​​sensors for this purpose are known per se. It can be noted that if it is determined that the crankshaft rotation speed has increased above a threshold value due to the step of supplying fuel, it is confirmed that the fuel ignition has occurred and the engine has started to run; there is no need to confirm the fuel ignition and the engine running separately.

[0030] In one embodiment, the step of opening the intake and exhaust ducts in order to open the closed recirculation loop and allow normal engine operation comprises setting an operating drive level / power of the gas feed arrangement to a level desired during engine operation, which desired level may depend on a desired level of EGR flow if the gas feed arrangement is arranged as an EGR pump in an EGR duct.

[0031] In one embodiment, the engine is provided with a turbocharger arrangement comprising a turbocharger turbine operably connected to a turbocharger compressor, wherein the turbocharger compressor is arranged in an intake duct, wherein the turbocharger turbine is arranged in an exhaust duct to drive the turbocharger compressor, and wherein an EGR conduit is connected to the intake duct downstream of the turbocharger compressor and to the exhaust duct upstream of the turbocharger turbine. Such an EGR system is generally denoted as high pressure (HP) EGR. Although the method of the present disclosure may also be used for an engine provided with a low pressure (LP) EGR system, wherein the EGR conduit connects upstream of the turbo compressor and downstream of the turbine turbine, the HP EGR system reduces the volume of gas to be pressurized, and it obviates the need to swirl the compressor and turbine with recirculated gas, which would require a higher power gas feed arrangement.

[0032] In one embodiment, the step of opening the intake valve in the first cylinder is performed when the piston in the first cylinder is in a position where it has passed the top dead center (TDC) position but has not passed the bottom dead center (BDC) position. This means that the piston is in a suitable starting position where it can be pushed towards BDC (consistent with a normal expansion stroke) by the pressurized air. The engine can be configured to set a certain cylinder or one of the cylinders in such a suitable starting position when shut down, so that the certain cylinder or at least one of the cylinders can form the "first cylinder" used in the starting method. This is also described further above.

[0033] The present invention also relates to an internal combustion engine, which comprises: a group of cylinders consisting of one or more cylinders, each cylinder in the group is provided with an intake valve and an exhaust valve and a piston, the intake valve and the exhaust valve are arranged to respectively regulate the gas flow in and out of the cylinder, and the piston moves back and forth in the cylinder; the engine also comprises: a crankshaft, which is operably connected to each piston so as to rotate when the piston moves back and forth in the corresponding cylinder; a fuel supply system, which is arranged to supply fuel to the cylinder; an intake duct, which is arranged to feed intake air to the cylinder; an exhaust duct, which is arranged to feed exhaust gas away from the cylinder; an exhaust gas recirculation (EGR) system, which EGR system comprises an EGR conduit, which is arranged to connect the exhaust duct and the intake duct, so as to to allow recirculation of exhaust gas through the cylinders during engine operation; an intake throttle valve, which is arranged in the intake duct upstream of the EGR duct; an exhaust duct valve, which is arranged in the exhaust duct downstream of the EGR duct; a controllable gas feeding device, which is arranged in a closed recirculation loop, which includes the EGR duct and is formed by closing the intake throttle valve and the exhaust duct valve, wherein the gas feeding device is configured to feed gas from its inlet to its outlet, and wherein the gas feeding device is configured so that: the gas feeding device is operated so that the pressure of the gas contained in the closed recirculation loop increases in the intake duct and decreases in the exhaust duct; a control unit, which is configured to control the starting and operation of the engine.

[0034] In one embodiment, the control unit is configured to perform the steps of the method according to the above description.

[0035] In one embodiment, the gas feed arrangement is arranged in an EGR duct. The gas feed arrangement can then be used as an EGR valve as described above during normal engine operation, but can also be used as an EGR pump, which is particularly useful for providing EGR flow in engine systems operating with very high air pressures on the intake side, such as when using a high-efficiency turbocharging system.

[0036] In one embodiment, the gas feeding device is a volumetric machine configured to move gas from an inlet to an outlet by capturing a fixed amount of gas and forcing the captured amount of gas from its inlet to its outlet.

[0037] In one embodiment, the positive displacement machine is a rotary Roots-type blower having a pair of rotating members with meshing lobes.

[0038] In one embodiment, the engine is provided with a system for variable control of the intake and exhaust valves.

[0039] In one embodiment, the engine is provided with a turbocharger arrangement comprising a turbocharger turbine operatively connected to a turbocharger compressor, wherein the turbocharger compressor is arranged in an intake duct, wherein the turbocharger turbine is arranged in an exhaust duct to drive the turbocharger compressor, and wherein the EGR duct is connected to the intake duct downstream of the turbocharger compressor and to the exhaust duct upstream of the turbocharger turbine.

[0040] In one embodiment, the engine comprises a variable drive unit arranged to drive the gas feed means.Preferably, the variable drive unit is an electric motor, but it may alternatively be driven by hydraulic, pneumatic or mechanical means.

[0041] In an embodiment, the control unit is configured to control the drive unit so as to control the gas flow through the volumetric machine.

[0042] In an embodiment, the gas feeding arrangement comprises at least one rotating member operatively connected to a drive unit, wherein the control unit is configured to control a rotation speed of the rotating member.

[0043] The invention also relates to a vehicle comprising an internal combustion engine according to the above.

[0044] The present invention also relates to:

[0045] - a computer program comprising program code components for executing the steps of the above method when said program is run on a computer;

[0046] - a computer-readable medium carrying a computer program, the computer program comprising program code components for executing the steps of the above method when the program product is run on a computer; and

[0047] - a control unit for controlling an internal combustion engine according to the above,

[0048] The control unit is configured to perform the steps of the method according to the above description.

[0049] Further advantages and advantageous features of the invention are disclosed in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] With reference to the accompanying drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0051] In these figures:

[0052] Figure 1A truck is shown which is provided with an internal combustion engine according to an embodiment of the invention.

[0053] Figure 2 Shows Figure 1 Schematic diagram of an internal combustion engine.

[0054] Figure 3 Shows Figure 2 one of the cylinders of the engine, whose piston is operatively connected to the crankshaft, and Figure 3 Some other components are also shown.

[0055] Figure 4 Shows the formation Figure 2 Schematic diagram of the gas feed arrangement of a part of the engine.

[0056] Figure 5 A flow chart showing an embodiment of the method of the present invention is shown. DETAILED DESCRIPTION

[0057] Figure 1 A truck 100 is shown which is provided with an internal combustion engine 1 according to an embodiment of the invention.

[0058] Figure 2 Shows Figure 1 a schematic diagram of an internal combustion engine, and Figure 3-Figure 4 Some details of the engine 1 are shown, namely the cylinder 2a with its associated components ( Figure 3 ) and gas feeding device 9( Figure 4 ).

[0059] like Figure 2-4 As shown, the exemplary internal combustion engine 1 includes six similar cylinders 2a, 2b, wherein each cylinder is provided with an intake valve 25 and an exhaust valve 24 and a piston 21, wherein the intake valve 25 and the exhaust valve 24 are arranged to regulate the gas flow in and out of the cylinder respectively, and the piston 21 is arranged to move back and forth in the cylinder (see Figure 3 ).

[0060] The engine 1 also includes a crankshaft 23, which is operatively connected to each piston 21 via a connecting rod 22 so as to rotate when the piston moves back and forth in the corresponding cylinder 2a, 2b. A fuel supply system 26 in the form of a fuel injection system is arranged to supply fuel to the cylinders 2a, 2b by injecting fuel into each of the cylinders 2a, 2b.

[0061] The intake duct 3 is arranged to feed intake air to the cylinders 2a, 2b and the exhaust duct 4 is arranged to feed exhaust gas away from the cylinders 2a, 2b during operation of the engine 1. The engine 1 is also provided with an exhaust gas recirculation (EGR) system comprising an EGR conduit 5 arranged to connect the exhaust duct 4 and the intake duct 3 so as to allow recirculation of exhaust gas through the cylinders 2a, 2b during operation of the engine 1.

[0062] An intake throttle valve 11 is arranged in the intake duct 3 upstream of the EGR duct 5 , and an exhaust duct valve 12 in the form of a closed loop butterfly (CLB) valve is arranged in the exhaust duct 4 downstream of the EGR duct 5 .

[0063] The engine 1 is also provided with a turbocharger arrangement, which includes a turbocharger turbine 8b, which is operatively connected to a turbocharger compressor 8a via a shaft. The turbocharger compressor 8a is arranged in the intake duct 3, and the turbocharger turbine 8b is arranged in the exhaust duct 4 to drive the turbocharger compressor 8a. Figure 2 As can be seen in FIG. 8 , the EGR duct 5 is connected to the intake duct 3 downstream of the turbocharger compressor 8 a and to the exhaust duct 4 upstream of the turbocharger turbine 8 b .

[0064] An air cooler 6 is arranged in the intake duct 3 between the turbocharger compressor 8a and the intake throttle valve 11, and an EGR cooler 7 is arranged in the EGR conduit 5. Furthermore, an exhaust bypass valve 14 is arranged to allow a portion of the exhaust gas to bypass the turbocharger turbine 8b.

[0065] The engine 1 is also provided with a system (not shown) for variable control of the intake and exhaust valves 25, 24, which allows the valves 25, 24 to be opened and closed independently of the rotational position of the crankshaft 23. Such systems are generally referred to as variable valve actuation (VVA) and are known per se.

[0066] A controllable gas feed device 9 is arranged in the EGR duct 5 (downstream of the EGR cooler 7). The gas feed device 9 is a positive displacement machine of the Roots blower type, having a pair of rotating members 91, 92 provided with meshing lobes 91a, 91b, 92a, 92b, and configured to feed gas from its inlet 9a to the outlet 9b by capturing a fixed amount of gas and forcing the captured amount of gas from the inlet 9a to the outlet 9b (see Figure 4 ).

[0067] A controllable and variable drive unit 16 in the form of an electric motor is arranged to drive the gas feed arrangement 9 in order to control the gas flow through the gas feed arrangement 9. The rotating members 91, 92 are operatively connected to the drive unit 16 and, by controlling the rotation speed of the drive unit 16, the rotation speed of the rotating members 91, 92 and the gas flow through the gas feed arrangement 9 can be controlled.

[0068] During normal four-stroke operation of the engine 1 , the gas feed arrangement 9 acts as an EGR pump for feeding exhaust gas through the EGR duct 5 and also as an EGR valve.

[0069] By closing the intake throttle valve 11 and the exhaust pipe valve 12, a closed recirculation loop can be formed, which includes the EGR duct 5, the downstream part of the intake pipe 3 and the upstream part of the exhaust pipe 4 (see Figure 2 ). The gases contained in these tubes and in the various spaces forming part of this closed loop can thus be recirculated in this loop using the gas feed device 9 (assuming that the valves 24, 25 are at least occasionally open). During start-up of the engine 1 (and also during normal operation of the engine 1), the gas feed device 9 is driven to pump gases from the exhaust duct 4 to the intake duct 3. When the closed recirculation loop is formed and the intake valve 25 is closed, this causes the pressure of the gases contained in the closed recirculation loop to increase in the intake duct 3 and to decrease in the exhaust duct 4.

[0070] The engine is further provided with a control unit or control circuit 18, which is configured to receive control signals from various sensors, such as speed sensors for the crankshaft 23 and the rotating members 91, 92 of the gas feed arrangement 9 and a large number of other sensors, and to send control signals and control controllable components of the engine 1, thereby controlling the starting and operation of the engine 1. The control unit 18 is for example arranged to control said drive unit 16, the valves 24, 25, the intake duct valves 11 and the exhaust duct valves 12 and the fuel injection system 26. Engine control units, sensors etc. are well known per se.

[0071] According to the principles of the present invention, optional components are Figure 2 However, in practice, it is preferred to include these components to achieve high engine efficiency.

[0072] Figure 3 It is not intended to illustrate any particular moment of the method of the present disclosure, but rather to illustrate the general components and main functions of the cylinder 2a, piston 21, crankshaft 23 and valves 24, 25. Figure 3In the embodiment, valves 24, 25 are both closed and piston 21 has passed its BDC closest to crankshaft 23 and is moving toward its TDC closest to valves 24, 25. Therefore, Figure 3 can be considered as a representation of the compression stroke during normal operation of the engine 1. In order to set the piston 21 in the appropriate position for starting by feeding pressurized gas through the intake duct 3 and into the cylinder 2a via the intake valve 25 (when open), the crankshaft 23 will need to be rotated by approximately 180° so that the piston 21 is positioned some angle after its TDC.

[0073] Figure 5 A flow chart of an embodiment of a method for starting operation of an internal combustion engine 1 is shown. Figure 5 As shown, the exemplary method includes the following steps:

[0074] S1 - When the internal combustion engine 1 is not running, pressurized gas is provided in the intake duct 3; this is done in the following way:

[0075] - S2 - closing the intake duct 3 upstream of the EGR duct 5 (by closing the intake throttle valve 11 ) and closing the exhaust duct 4 downstream of the EGR duct 5 (by closing the exhaust duct valve 12 ) to form a closed recirculation loop including the EGR duct 5 for the gases contained in said closed recirculation loop; and

[0076] - S3 - operating a controllable gas feeding device 9 arranged in the closed recirculation loop (by means of a drive unit 16) while keeping the intake valve 25 closed, wherein the gas feeding device 9 is configured to feed gas from its inlet 9a to its outlet 9b, and wherein the gas feeding device 9 is operated such that the pressure of the gas contained in the closed recirculation loop increases in the intake duct 3 and decreases in the exhaust duct 4 (i.e. the gas contained in the closed recirculation loop is pumped from the exhaust duct 4 to the intake duct 3);

[0077] S4 - opening the intake valve 25 in the first cylinder 2a while keeping the exhaust valve 24 of the first cylinder 2a closed, so as to allow pressurized gas to enter the first cylinder 2a, press onto the corresponding piston 21, and thus move the corresponding piston 21 and rotate the crankshaft (23);

[0078] S5—when the piston 21 of the first cylinder 2a has reached the BDC position, the exhaust valve 24 in the first cylinder 2a is opened to allow the now expanded pressurized gas to leave the first cylinder 2a;

[0079] S6 - Continue to feed pressurized gas into at least some of the cylinders 2a, 2b while opening and closing the corresponding intake valves 25 and exhaust valves 24 (to achieve the two-stroke introduction of pressurized gas discussed further above), which is done by:

[0080] - S7 - opening the intake valve 25 of the first cylinder 2a or the second cylinder 2b during at least a portion of the crankshaft 23 angular (CA) range of 0-180° and keeping the same intake valve 25 closed at 180-360°, wherein the piston 21 in the same cylinder is in the TDC position at 0° and 360° CA and in the BDC position at 180° CA, and

[0081] - S8 - opening the exhaust valve 24 of the same cylinder during at least a portion of the crankshaft angle (CA) range of 180-360° and keeping the same exhaust valve 24 closed during 0-180° CA;

[0082] S9—determine whether the crankshaft 23 has reached a first threshold rotational speed; and when so:

[0083] - S10 - supplying fuel to at least one of the cylinders 2a, 2b in which the corresponding piston has performed or is performing a compression step, in order to (at least attempt to) ignite the fuel and start the operation of the engine 1,

[0084] S11 - confirming whether fuel ignition actually occurs and whether the engine 1 has actually started running by determining whether the rotation speed of the crankshaft 23 has increased above a second threshold value as a result of step S10 of supplying fuel, and:

[0085] - If not, then S12 - interrupt the fuel supply and return to step S6, or

[0086] If yes, then S13 - opening the intake duct 25 and the exhaust duct 24 (ie opening the intake duct valve 11 and the exhaust duct valve 12) in order to open the closed recirculation loop and allow the engine 1 to operate normally.

[0087] Step S13 can usually be supplemented by, for example, the following steps:

[0088] S14 - setting the operating drive level / power of the gas feed arrangement 9 to the level desired during operation of the engine 1, and

[0089] S15—Control the intake valve 25 and the exhaust valve 24 in the normal four-stroke mode.

[0090] The above method may be preceded by a step of setting the piston 21 in the first cylinder 2a to a position where it has passed its TDC position but has not yet passed its BDC position so as to be set in a position suitable for the starting method. This step may already be performed when the engine 1 is shut down (the crankshaft 23 may be controlled to stop at a certain angle). Instead of setting the piston in a certain position, this preceding step may include selecting one of the cylinders as the "first" cylinder, in which the piston is already in a suitable position (for many cylinders, one of the pistons is likely to have been set in a position that is at least sufficiently suitable when the engine is shut down without any special control, so any adjustment of the piston position may not be required).

[0091] The order of the above steps should not be interpreted too strictly. For example, if several cylinders are involved, step S4 may have been performed not only on the first cylinder, but also on another cylinder before step S5 is performed on the first cylinder. And step S6 is a repetition of steps S4 and S5, but (in this example) for several cylinders.

[0092] In a simple form, the method may comprise only steps S1-S4 and S10. However, in many applications it is useful to accelerate the rotational speed of the crankshaft 23 with steps S5-S8 (or at least S5-S6 if a two-stroke solution is not used) and also to check in S9 whether its speed is sufficient before introducing fuel into the cylinders in step S10. It is also useful to verify whether the engine 1 has actually started, as proposed in step S11. These optional method steps are Figure 5 Indicated by dotted line.

[0093] It should be understood that the present invention is not limited to the embodiments described above and shown in the drawings; on the contrary, those skilled in the art will recognize that many modifications and variations are possible within the scope of the appended claims.

Claims

1. A method for starting operation of an internal combustion engine (1), wherein: The internal combustion engine (1) comprises: - a group of one or more cylinders, each cylinder in the group being provided with an intake valve (25) and an exhaust valve (24) and a piston (21), the intake valve (25) and the exhaust valve (24) being arranged to regulate the flow of gas into and out of the cylinder respectively, the piston (21) being arranged to move back and forth in the cylinder; - a crankshaft (23) operatively connected to each piston (21) so as to rotate as the piston moves back and forth within the corresponding cylinder; - a fuel supply system (26) arranged to supply fuel to the cylinders; - an intake duct (3) arranged to feed intake air to the cylinder; - an exhaust duct (4) arranged to feed exhaust gas away from the cylinder; and - an exhaust gas recirculation system comprising an EGR duct (5) arranged to connect the exhaust duct (4) and the intake duct (3) so as to allow recirculation of exhaust gas through the cylinders during operation of the internal combustion engine (1); Wherein, the method comprises the following steps: - Step S1: providing pressurized gas in the intake duct (3) when the internal combustion engine (1) is not running; - Step S4: opening the intake valve (25) in the first cylinder (2a) while keeping the exhaust valve (24) of the first cylinder (2a) closed, so as to allow the pressurized gas to enter the first cylinder (2a) and press onto the corresponding piston (21), thereby moving the corresponding piston (21) and rotating the crankshaft (23); - step S10: supplying fuel to at least one of the cylinders in which the corresponding piston has performed or is performing a compression step, so as to ignite the fuel and start the operation of the internal combustion engine (1), It is characterized in that The pressurized gas is provided by: - Step S2: closing the intake duct (3) upstream of the EGR duct (5) and closing the exhaust duct (4) downstream of the EGR duct (5) so as to form a closed recirculation loop including the EGR duct (5), the EGR duct (5) being intended for the gases contained in the closed recirculation loop; - Step S3: operating a controllable gas feeding device (9) arranged in the closed recirculation loop while keeping the air intake valve (25) closed, wherein the controllable gas feeding device (9) is configured to feed gas from an inlet (9a) of the controllable gas feeding device to an outlet (9b) of the controllable gas feeding device, and wherein the controllable gas feeding device (9) is operated such that the pressure of the gas contained in the closed recirculation loop increases in the air intake duct (3) and decreases in the air exhaust duct (4).

2. The method according to claim 1, wherein: The method comprises the step of opening an EGR valve, the EGR valve being arranged to control flow through the EGR conduit (5).

3. The method according to claim 1 or 2, wherein: The intake duct (3) is closed by closing an intake throttle valve (11) arranged in the intake duct (3) upstream of the EGR conduit (5).

4. The method according to claim 1 or 2, wherein: The exhaust duct (4) is closed by closing an exhaust duct valve (12) arranged in the exhaust duct (4) downstream of the EGR conduit (5).

5. The method according to claim 1 or 2, wherein: The controllable gas feed device (9) is arranged in the EGR duct (5).

6. The method according to claim 1 or 2, wherein: The controllable gas feed device (9) is a volumetric machine configured to move gas from an inlet to an outlet by capturing a fixed amount of gas and forcing the captured amount of gas from the inlet of the volumetric machine to the outlet of the volumetric machine.

7. The method according to claim 6, wherein: The positive displacement machine is a rotary Roots-type blower having a pair of rotating members provided with engaging lobes.

8. The method according to claim 1 or 2, wherein: The method comprises the following steps: - Step S5: When the piston (21) of the first cylinder (2a) has reached the bottom dead center position, opening the exhaust valve (24) in the first cylinder (2a) to allow the now expanded pressurized gas to leave the first cylinder (2a).

9. The method according to claim 8, wherein: Step S5 is followed by the following steps: - continuing to feed pressurized gas into the group of cylinders while opening and closing the corresponding intake valves (25) and exhaust valves (24) until the crankshaft (23) reaches a first threshold rotational speed; wherein, when the first threshold rotational speed has been reached, the step of supplying fuel to at least one of the cylinders is performed.

10. The method according to claim 9, wherein: The internal combustion engine (1) is provided with a system for variable control of the intake valve and the exhaust valve, the group of cylinders comprising more than one cylinder, wherein the step of continuing to feed pressurized gas into the group of cylinders while opening and closing the corresponding intake valve (25) and exhaust valve (24) comprises: - step S7: opening the intake valve (25) of the first cylinder (2a) or the second cylinder (2b) during at least a portion of the crankshaft angle range of 0-180°, and keeping the same intake valve (25) closed during 180-360°, wherein the piston (21) in the same cylinder is in the top dead center position at 0° and 360° crankshaft angles, and in the bottom dead center position at 180° crankshaft angle, and - Step S8: opening the exhaust valve (24) of the same cylinder during at least a portion of the crankshaft angle range of 180-360° and keeping the same exhaust valve (24) closed during the crankshaft angle range of 0-180°.

11. The method according to claim 1 or 2, wherein: The step of supplying fuel to at least one of the cylinders is followed by the following steps: - confirming that fuel ignition has occurred and that the internal combustion engine (1) has started to run, and - If not, interrupt the fuel supply, or - If yes, opening the intake duct (3) and the exhaust duct (4) in order to open the closed recirculation loop and allow the internal combustion engine (1) to operate normally.

12. The method according to claim 11, wherein: The step of confirming whether fuel ignition has occurred and whether the internal combustion engine (1) has started to run comprises: - determining whether the rotational speed of the crankshaft (23) has increased above a second threshold value as a result of the step of supplying fuel.

13. The method according to claim 11, wherein: The steps of opening the intake duct (3) and the exhaust duct (4) in order to open the closed recirculation loop and allow the internal combustion engine (1) to operate normally include: - Step S14: Setting the operating drive level / power of the controllable gas feed device (9) to a level desired during operation of the internal combustion engine (1).

14. The method according to claim 1 or 2, wherein: The internal combustion engine (1) is provided with a turbocharger device, the turbocharger device comprising a turbocharger turbine (8b) operatively connected to a turbocharger compressor (8a), wherein the turbocharger compressor (8a) is arranged in the intake duct (3), wherein the turbocharger turbine (8b) is arranged in the exhaust duct (4) to drive the turbocharger compressor (8a), and wherein the EGR duct (5) is connected to the intake duct (3) downstream of the turbocharger compressor (8a) and to the exhaust duct (4) upstream of the turbocharger turbine (8b).

15. The method according to claim 1 or 2, wherein: When the piston (21) in the first cylinder (2a) is at a position having passed the top dead center position but not yet passed the bottom dead center position, a step of opening the intake valve (25) in the first cylinder (2a) is performed.

16. An internal combustion engine (1), comprising: - a group of one or more cylinders, each cylinder in the group being provided with an intake valve (25) and an exhaust valve (24) and a piston (21), the intake valve (25) and the exhaust valve (24) being arranged to regulate the flow of gas into and out of the cylinder respectively, the piston (21) being arranged to move back and forth in the cylinder; The internal combustion engine (1) further comprises: - a crankshaft (23) operatively connected to each piston (21) so as to rotate as the piston moves back and forth within the corresponding cylinder; - a fuel supply system (26) arranged to supply fuel to the cylinders; - an intake duct (3) arranged to feed intake air to the cylinder; - an exhaust duct (4) arranged to feed exhaust gas away from the cylinder; - an exhaust gas recirculation system comprising an EGR duct (5) arranged to connect the exhaust duct (4) and the intake duct (3) so as to allow recirculation of exhaust gas through the cylinders during operation of the internal combustion engine (1); - an air intake throttle valve (11), which is arranged in the air intake duct (3) upstream of the EGR duct (5); - an exhaust duct valve (12) arranged in the exhaust duct (4) downstream of the EGR duct (5); - a controllable gas feed device (9), the controllable gas feed device (9) being arranged in a closed recirculation loop including the EGR duct (5), wherein each of the intake throttle valve (11) and the exhaust duct valve (12) is configured to be closable, and wherein the closed recirculation loop is formed by closing the intake throttle valve (11) and the exhaust duct valve (12), wherein the controllable gas feed device (9) is configured to feed gas from an inlet (9a) of the controllable gas feed device to an outlet (9b) of the controllable gas feed device, and wherein the controllable gas feed device (9) is configured such that: the controllable gas feed device is operated so that the pressure of the gas contained in the closed recirculation loop increases in the intake duct (3) and decreases in the exhaust duct (4); and - a control unit (18) configured to control the starting and operation of the internal combustion engine (1), Wherein, the control unit (18) is configured to perform the steps of the method according to any one of claims 1-15.

17. An internal combustion engine (1) according to claim 16, wherein: The controllable gas feed device (9) is arranged in the EGR duct (5).

18. An internal combustion engine (1) according to any one of claims 16-17, wherein: The controllable gas feed device (9) is a volumetric machine configured to move gas from an inlet to an outlet by capturing a fixed amount of gas and forcing the captured amount of gas from the inlet of the volumetric machine to the outlet of the volumetric machine.

19. The internal combustion engine (1) according to claim 18, wherein: The positive displacement machine is a rotary Roots-type blower having a pair of rotating members provided with engaging lobes.

20. An internal combustion engine (1) according to any one of claims 16-17, wherein The internal combustion engine is provided with a system for variable control of the intake valve and the exhaust valve.

21. An internal combustion engine (1) according to any one of claims 16-17, wherein: The internal combustion engine is provided with a turbocharger arrangement, the turbocharger arrangement comprising a turbocharger turbine (8b) operatively connected to a turbocharger compressor (8a), wherein the turbocharger compressor (8a) is arranged in the intake duct (3), wherein the turbocharger turbine (8b) is arranged in the exhaust duct to drive the turbocharger compressor (8a), and wherein the EGR duct (5) is connected to the intake duct (3) downstream of the turbocharger compressor (8a) and to the exhaust duct (4) upstream of the turbocharger turbine (8b).

22. An internal combustion engine (1) according to any one of claims 16-17, wherein: The internal combustion engine comprises a variable drive unit (16) arranged to drive the controllable gas feed arrangement (9).

23. An internal combustion engine (1) according to claim 22, wherein: The control unit (18) is configured to control the variable drive unit (16) so as to control the gas flow through the controllable gas feeding device (9).

24. An internal combustion engine (1) according to claim 23, wherein: The controllable gas feeding device (9) comprises at least one rotating member operatively connected to the variable drive unit (16), wherein the control unit (18) is configured to control the rotation speed of the rotating member.

25. A vehicle comprising an internal combustion engine (1) according to any one of claims 16-24.

26. A control unit (18) for controlling an internal combustion engine (1) according to any one of claims 16-24, the control unit (18) being configured to perform the steps of the method according to any one of claims 1-15.

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