SE542314C2

SE542314C2 - Method and system for stopping an internal combustion engine

Info

Publication number: SE542314C2
Application number: SE1651045A
Authority: SE
Inventors: Erik Höckerdal; Ola Stenlåås
Original assignee: Scania Cv Ab
Priority date: 2016-07-12
Filing date: 2016-07-12
Publication date: 2020-04-07
Also published as: WO2018013041A1; DE112017002863T5; SE1651045A1; BR112018075612A2

Abstract

The present invention relates to a method for stopping an internal combustion engine (101), said internal combustion engine (101) having at least one combustion chamber (209) and a crankshaft (112) being arranged to be propelled by said at least one combustion chamber (209), wherein intake of gas to said at least one combustion chamber (209) is controlled by at least one intake valve (211), and wherein evacuation of said at least one combustion chamber (209) is controlled by at least one exhaust valve (213). The method includes, when said internal combustion engine (101) is to be stopped:- turning off fuel injection,- with fuel injection turned off, controlling an intake valve (211) and/or an exhaust valve (213) of said at least one combustion chamber (209) such that, following compression in said at least one combustion chamber (209), pressure in said combustion chamber (209) is reduced to reduce a crankshaft (112) propelling power caused by gas expansion following said compression.

Description

METHOD AND SYSTEM FOR STOPPING AN INTERNAL COMBUSTION ENGINE Field of the invention The present invention relates to combustion processes, and in particular to a method and system for stopping an internal combustion engine. The present invention also relates to a vehicle, as well as a computer program and a computer program product that implement the method according to the invention.

Background of the invention With regard to vehicles in general, and at least to some extent heavy/commercial vehicles such as trucks, buses and the like, there is constantly ongoing research and development with regard to increasing fuel efficiency and reducing exhaust emissions.

This is often at least partly due to growing governmental concern in pollution and air quality, e.g. in urban areas, which has also led to the adoption of various emission standards and rules in many jurisdictions.

Undesired emission of substances can be reduced by reducing fuel consumption and/or through the use of aftertreatment (purifying) of exhaust gases emanating from combustion.

With regard to fuel consumption there are various ways of reducing such consumption, e.g. by controlling the combustion process. Furthermore, brake energy can be regenerated to electrical energy in electric hybrid vehicles. Other methods include improving use of energy, e.g. by reducing unnecessary braking. Fuel consumption may also be reduced using engine start/stop (a.k.a. stop/start) functionality, where the internal combustion engine is stopped when the vehicle is standing still, e.g. due to traffic lights, to be started again when the vehicle is to be set in motion to avoid fuel consumption when the vehicle is standing still.

Apart from fuel consumption and emissions, there may also be restrictions regarding the sound being produced by a vehicle in motion or when standing still, e.g. in city centres.

Summary of the invention It is an object of the present invention to provide a method and system for stopping an internal combustion engine that stops the internal combustion engine in a short period of time thereby reducing noise produced by the engine. This is achieved by a method according to claim 1.

According to the present invention, it is provided a method for stopping an internal combustion engine, said internal combustion engine having at least one combustion chamber and a crankshaft being arranged to be propelled by said at least one combustion chamber, wherein intake of air to said combustion chamber is controlled by at least one intake valve, and wherein evacuation of said combustion chamber is controlled by at least one exhaust valve. The method includes, when said internal combustion engine is to be stopped: - turning off fuel injection, - with fuel injection turned off, controlling an intake valve and/or an exhaust valve of said combustion chamber such that, following compression in said combustion chamber, pressure in said combustion chamber is reduced to reduce a crankshaft propelling power caused by gas expansion following said compression. With regard to the control of intake valve and/or exhaust valve to reduce compression this may be accomplished by phasing of at least one camshaft, or part thereof, to thereby control opening and/or closing of an intake valve and/or exhaust valve.

Start-stop systems, also known as stop-start systems, controlling internal combustion engines are becoming increasingly frequent as regulations regarding fuel economy and emissions are becoming stricter. Start-stop systems automatically, e.g. through the use of a vehicle control system, stops, i.e. turns off, and restarts the internal combustion engine in situations where the internal combustion engine is idling to reduce the amount of time spent idling to thereby reduce fuel consumption and emissions. In addition to fuel savings, start-stop functionality may also be beneficial from a noise restriction point of view, since noise produced by the internal combustion engine when running is essentially eliminated when the engine is stopped.

In fact, there may restrictions regarding noise levels that require the internal combustion engine to be turned off when the vehicle is standing still, e.g. in city centres, to fulfil noise restrictions. Also, in some instances it may be required to turn off the internal combustion engine when the vehicle is in motion and switch to electrical propulsion e.g. in city centres to fulfil noise regulations. According to the invention, it is provided a method for stopping the internal combustion engine in a short period of time so that the noise produced by the internal combustion engine is reduced by the reducing the time the internal combustion engine is running.

This is accomplished by turning off fuel injection, and, with fuel injection turned off, controlling an intake valve and/or an exhaust valve of a combustion chamber such that, following compression in said combustion chamber, pressure in the combustion chamber is reduced to reduce crankshaft propelling power caused by gas expansion following said compression.

In general, when stopping an internal combustion engine, valves are controlled in the same manner as when the internal combustion engine is running, where the engine is stopped by turning off fuel injection. According to the invention, valves are controlled differently when stopping the engine. In general, crankshaft rotation is subjected to a brake force when e.g. a piston reciprocating in the combustion chamber, or other means such as a rotor of a Wankel engine, acting in the combustion chamber compresses air provided during an intake phase. Following compression, however, a large part of the work produced during compression is returned as crankshaft motive force from the following gas expansion, e.g. by providing a crankshaft propelling force on a piston or other means in the combustion chamber, which occurs also when there is no combustion in the combustion chamber.

According to the invention, the compression still takes place, at least to a large extent, while the propelling force from gas expansion is reduced by reducing the pressure in the combustion chamber prior to or at the beginning of the following expansion stage. This is accomplished by opening an intake valve and/or exhaust valve at the end of compression stage and/or at the beginning of the following expansion stage. In this way, the stopping of the engine benefits from the crankshaft retarding force generated through compression, while the following crankshaft accelerating force from gas expansion is reduced or eliminated by allowing gas expansion through one or more valves instead of acting against e.g. a piston or other means in the combustion chamber. That is, pressure, and hence the crankshaft propelling power, is reduced in relation to the pressure, and crankshaft propelling power, obtained when valves are not opened at the end of compression stage or beginning of expansion stage.

Pressure may be reduced e.g. to atmospheric pressure, or some other suitable pressure being lower than the pressure being the result of the compression.

This substantially reduces the time it takes to stop the internal combustion engine, and thereby the noise produced when stopping the engine is also reduced since the time noise is produced is reduced. The invention is applicable to any internal combustion process involving a compression stage and following expansion stage.

The compression can be arranged to be reduced by changing an opening time of one or more intake valves and/or one or more exhaust valves of the combustion chamber. For example, an intake valve and/or an exhaust valve can be arranged to be opened during the last part of, or at the end of, the compression stage to thereby allow expansion by evacuation through the valve. Alternatively, an intake valve and/or an exhaust valve can be arranged to be opened at the beginning of the expansion stage that follows the compression stage. In this way, although the expansion may occur to some extent, a major portion of the expansion will still take place through the open valve. In this way, the force exerted on the means in the combustion chamber interacting with the crankshaft, such as e.g. a reciprocating piston, will be reduced and hence the propelling force provided to the crankshaft is also reduced.

According to embodiments of the invention, the intake valve and/or exhaust valve is maintained open from the end of the compression stage to the beginning of the exhaust stage.

According to embodiments of the invention, a valve may open first at the end of the compression stage, where a valve (the same or a different) is opened at the beginning of the following expansion stage, e.g. taking into consideration limitations regarding valve clearance when opening valves at/near top dead centre TDC of a piston.

The intake valve and/or exhaust valve may be controlled to reduce crankshaft propelling power caused by expansion following compression at least substantially until the speed of rotation of said crankshaft is reduced to zero, or at least until the speed of rotation of the crankshaft has been reduced to some suitable speed.

Furthermore, valves may be controlled in a conventional manner during the combustion cycle apart from the particular control to reduce the propelling effect from expansion. Hence, prior to said compression, the intake valve and/or exhaust valve of said combustion chamber may be opened for intake of gas (air), e.g. according to normal operation, to provide gas for compression to obtain the retarding force acting on the crankshaft where the propelling force is then reduced according to the above.

According to embodiments of the invention, pressurized air is provided to the combustion chamber to thereby increase compression and the retarding force.

According to embodiments of the invention, an intake valve of said combustion chamber is opened for intake of air for compression, and following compression of said intake of air, an exhaust valve of said combustion chamber is opened to reduce pressure in said combustion chamber to thereby reduce crankshaft propulsion by gas expansion.

In case the internal combustion engine operates according to a combustion cycle including a compression stroke followed by an expansion stroke, pressure may be reduced in said combustion chamber by opening an intake valve and/or an exhaust valve at the end of the compression stroke and/or at the beginning of the following expansion stroke. Hence the present invention may be used e.g. in two stroke or four stroke internal combustion engines. The invention is, however applicable also for internal combustion engines operating according to other principles such as Wankel engines.

The camshaft can be arranged to be phase shifted (phased), e.g. using phasers, to accomplish control of the valves according to the above. That is, a camshaft can be arranged to comprise a degree of freedom of rotation independent from the rotation of the crankshaft. For example, a camshaft may be designed to allow a phasing corresponding e.g. to any suitable number of crankshaft degrees in the interval 10-100 degrees, where the phasing can be arranged to be both retarding and advancing in relation to crankshaft rotation.

Other means may also be used, in the alternative, or in addition, to control the valves. For example, additional camshaft tappets may be utilised, where such tappets may be arranged to be selectively engageable. In this way additional valve openings may be achieved, and used to increase the retarding force in order to stop the engine in a shorter period of time.

Such additional valve openings may be arranged to be used e.g. only when stopping the internal combustion engine, and not during normal operation when the internal combustion engine is running. It is also contemplated that the valves may be controlled independently from the rotations of the crankshaft, e.g. through the use of suitable electrical / mechanical / pneumatical means or combinations thereof.

When the internal combustion engine is of a kind where a reciprocating member reciprocates in the combustion chamber the intake valve and/or exhaust may be arranged to be controlled in a variable dependence of the position of the reciprocating member in said combustion chamber, e.g. in relation to the position of the reciprocating member in relation to top dead centre TDC so that valves open and close in a desired manner to obtain benefits of the invention.

The internal combustion engine may be of a designed such that a single intake valve and a single exhaust valve, respectively, acts against the combustion chamber, and one or both these valves may be arranged to open according to the above. According to embodiments of the invention there may be two or more intake valves and/or exhaust valves, and according to such designs one or more of each kind of valve may be opened.

Furthermore, although the above describes operation for a single combustion chamber internal combustion engines in general comprises a plurality of combustion chambers, and valves of all or at least a plurality of the combustion chambers of the internal combustion engine may be arranged to be controlled according to the above. For example, when controlling valves using phasing, a camshaft may be used to control valves of a plurality of, or all of, the combustion chambers of the internal combustion engine.

Furthermore, opening and closing of intake valves may be controlled by a first camshaft, and opening and closing of exhaust valves may be controlled by a second camshaft. At least one of said first and second camshafts may be controlled to open/close valves according to the above.

The intake valves and/or exhaust valves may also be controlled in any other suitable manner, such as by electrical, pneumatic or mechanical means, and may be arranged to be individually controllable when reducing the crankshaft propelling force by controlling expansion following compression in the combustion chambers of the vehicle.

Furthermore, in dependence of available clearance, the piston may be provided with recesses or cut-outs on the piston head in order to allow valves to be open while the piston reaches TDC in order to avoid conflict with the valves. Such design issues, however, are known to the person skilled in the art.

Further characteristics of the present invention and advantages thereof are indicated in the detailed description of exemplary embodiments set out below and the attached drawings.

Brief description of the drawings Fig. 1A illustrates a powertrain of an exemplary vehicle in which the present invention advantageously can be utilised; Fig. IB illustrates an example of a control unit in a vehicle control system; Fig. 2 illustrates an example of a combustion chamber suitable for being controlled according to embodiments of the invention.

Fig. 3 illustrates an exemplary method according to one embodiment of the present invention.

Fig. 4 illustrates an exemplary system involving an in-line six-cylinder internal combustion engine being controlled according to embodiments of the present invention.

Figs. 5A-B shows control exemplary control strategies according to embodiments of the invention.

Detailed description of exemplary embodiments In the following detailed description the present invention will be exemplified for a vehicle. The invention is, however, applicable also in other kinds of transportation means, such as air and water crafts. The invention is also applicable in fixed installations. Further the terms "intake valve" and "exhaust valve" in the description and the claims are used to denote any means that open and close a passage to a combustion chamber for inlet of air and evacuation of combustion residuals, respectively.

Furthermore, the invention is described in relation to an internal combustion engine operating according to the Diesel principle. It is to be understood, however, that the invention is applicable for any kind of operating principle, such as e.g. internal combustion engines operating according to sparkignition (SI), homogeneous charge compression ignition (HCCI), reactivity controlled compression ignition (RCCI), partially premixed combustion (PPC).

Fig. 1A schematically depicts a powertrain of an exemplary vehicle 100. The powertrain comprises a power source, in the present example a compression-ignited internal combustion engine 101 such as a Diesel engine, which, in a conventional manner, is connected via an output shaft, i.e. a crankshaft of the internal combustion engine 101, normally also utilising a flywheel 102, to a gearbox 103 via a clutch 106. An output shaft 107 from the gearbox 103 propels drive wheels 113, 114 via a final drive 108, such as a common differential, and drive axles 104, 105 connected to said final drive 108.

The internal combustion engine 101 is controlled by the vehicle control system via a control unit 115. The clutch 106 and gearbox 103 are also controlled by the vehicle control system by means of a control unit 116.

Fig. 1A discloses a powertrain of a specific kind, but the invention is applicable for any kind of powertrain, and also e.g. in hybrid vehicles. The disclosed vehicle further comprises one or more aftertreatment components 130 for aftertreatment (purifying) of exhaust gases that results from combustion in the internal combustion engine 101. The functions of the one or more aftertreatment components 130 are controlled by means of a control unit 131. It is to be noted that the system described herein is only exemplary, and that according to embodiments of the invention, the vehicle is of a kind where exhaust gases are not subject to aftertreatment. The vehicle may also be of a kind where no turbocharger is used.

As is known to a person skilled in the art, aftertreatment components 130 may be of various kinds, designs and combinations, and are not discussed more in detail herein.

As was mentioned above, the present invention provides a method for stopping the combustion engine that, at least in some instances, may provide advantages in comparison to other solutions. For example, the time it takes to stop the internal combustion engine can be reduced.

An exemplary method 300 of the present invention is shown in fig. 3. The method can be implemented at least partly e.g. in the engine control unit 115 for controlling operation of the internal combustion engine 101. The functions of a vehicle are, in general, controlled by a number of control units, and control systems in vehicles of the disclosed kind generally comprise a communication bus system consisting of one or more communication buses for connecting a number of electronic control units (ECUs), or controllers, to various components on board the vehicle. Such a control system may comprise a large number of control units, and the control of a specific function may be divided between two or more of them.

For the sake of simplicity, Fig. 1A depicts only control units 115-116, 131, but vehicles 100 of the illustrated kind are often provided with significantly more control units, as one skilled in the art will appreciate. Control units 115-116, 131 are arranged to communicate with one another and various components via said communication bus system and other wiring, partly indicated by interconnecting lines in fig. 1A.

The present invention can be implemented in any suitable control unit in the vehicle 100, and hence not necessarily in the control unit 115. The control influencing valve opening and valve closing according to the present invention to control reduction of pressure through valve opening following compression will usually depend on signals being received from other control units and/or vehicle components, and it is generally the case that control units of the disclosed type are normally adapted to receive sensor signals from various parts of the vehicle 100. The control unit 115 may, for example, receive signals from the control system requesting the internal combustion engine 101 to be stopped.

Control units of the illustrated type are also usually adapted to deliver control signals to various parts and components of the vehicle, e.g. to control valves according to the invention, e.g. by controlling phasers and/or switches of camshafts and/or to control fuel injection. Operation of vehicle control systems per se is known to the person skilled in the art.

Furthermore, control of this kind is often accomplished by programmed instructions. The programmed instructions typically consist of a computer program which, when executed in a computer or control unit, causes the computer/control unit to exercise the desired control, such as method steps according to the present invention. The computer program usually constitutes a part of a computer program product, wherein said computer program product comprises a suitable storage medium 121 (see Fig. IB) with the computer program 126 stored on said storage medium 121. The computer program can be stored in a non-volatile manner on said storage medium. The digital storage medium 121 can, for example, consist of any of the group comprising: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk unit etc, and be arranged in or in connection with the control unit, whereupon the computer program is executed by the control unit. The behaviour of the vehicle in a specific situation can thus be adapted by modifying the instructions of the computer program.

An exemplary control unit (the control unit 115) is shown schematically in Fig. IB, wherein the control unit can comprise a processing unit 120, which can consist of, for example, any suitable type of processor or microcomputer, such as a circuit for digital signal processing (Digital Signal Processor, DSP) or a circuit with a predetermined specific function (Application Specific Integrated Circuit, ASIC). The processing unit 120 is connected to a memory unit 121, which provides the processing unit 120, with e.g. the stored program code 126 and/or the stored data that the processing unit 120 requires to be able to perform calculations. The processing unit 120 is also arranged so as to store partial or final results of calculations in the memory unit 121.

Furthermore, the control unit 115 is equipped with devices 122, 123, 124, 125 for receiving and transmitting input and output signals, respectively. These input and output signals can comprise waveforms, pulses or other attributes that the devices 122, 125 for receiving input signals can detect as information for processing by the processing unit 120. The devices 123, 124 for transmitting output signals are arranged so as to convert calculation results from the processing unit 120 into output signals for transfer to other parts of the vehicle control system and/or the component (s) for which the signals are intended. Each and every one of the connections to the devices for receiving and transmitting respective input and output signals can consist of one or more of a cable; a data bus, such as a CAN bus (Controller Area Network bus), a MOST bus (Media Oriented Systems Transport) or any other bus configuration, or of a wireless connection.

Returning to the exemplary method 300 illustrated in fig. 3, the method starts in step 301, where it is determined whether the internal combustion engine 101 is to be stopped. When this is the case, the method continues to step 302. The method remains in step 301 for as long as this is not the case, and the method continues to step 302 when it is determined that the internal combustion engine is to be stopped according to the invention. The transition from step 301 to step 302 can, for example, be initiated at all times when the internal combustion engine is to be stopped. Alternatively, control according to the invention can be arranged to be performed e.g. only for particular situations when the internal combustion engine is to be stopped, such as when the internal combustion engine is to be stopped in a stop-start operation, or when the vehicle is urban areas where restrictions regarding noise may apply, and/or anytime stopping of the internal combustion engine is requested by the control system and not the vehicle driver. Other criteria for performing the transition from step 301 to step 302 may also be applied.

In step 302 a suitable control of the reduction of pressure following compression by opening of one or more valves when stopping the internal combustion engine is determined, and according to the present example the reduction of pressure following compression is controlled by controlling an exhaust valve of a combustion chamber, and where, according to the present example, all combustion chambers are arranged to be controlled in the same manner. Hence, in step 302 a suitable control of the exhaust valves of the combustion chambers of the internal combustion engine is determined. According to other embodiments of the invention, intake valves are controlled instead, and according yet other embodiments of the invention, both intake valves and exhaust valves are controlled to reduce the crankshaft propelling power in expansion stages following upon compression stages. According to embodiments of the invention, the control may be predetermined, and hence automatically utilised when stopping the internal combustion engine 101. An exemplary control is described below with reference to figs. 5A-B.

The internal combustion engine 101 comprises a plurality of combustion chambers, e.g. 4, 5, 6 or 8. The present invention may be utilised for combustion engines having any number of combustion chambers, and an exemplary combustion chamber 209 is shown in fig. 2. The figure hence discloses only one cylinder/combustion chamber 209 in which a reciprocating piston 210 is arranged.

Internal combustion engines of the disclosed kind further comprises, in general, at least one fuel injector per combustion chamber (not shown) which in a conventional manner supplies fuel to the combustion chamber for combustion.

The combustion chamber 209 comprises an inlet 201 being controlled by one or more intake valves 211, which may be, and is according to the present example, arranged to be individually controlled in relation to an exhaust valve 213 according to the below. Air for combustion is supplied to the combustion chamber by means of the intake valve 211 through an intake conduit 402, e.g. consisting of suitable piping, tubing and/or hosing, for receiving the air for supply to the combustion. In general, the air consists of air taken from the environment of the vehicle 100.

Evacuation of the combustion chamber 209 is controlled through an (or a plurality of) exhaust valve 213, which opens towards an exhaust manifold 414.

With regard to the exhaust valve 213 and intake valve 211 these are, in the present example, controlled individually by means of camshafts 203, 204, respectively, which, although being commonly driven by a crankshaft 205, are arranged to be individually phased in relation to each other so that opening time, closing time and duration of the opening of the valves 211, 213 can be individually controlled for each valve. The phasing can, for example, be accomplished by means of phasers. Use of phasers allows continuous adjustment of the valve control. For example, the phasers may be arranged such that each camshaft can be phase shifted up to e.g. 60, 80 or 100 crank angle degrees or any other suitable number of degrees, where phase shifting selectively can be e.g. both advancing and retarding, thereby allowing a relatively high degree of freedom when controlling the inlet valve and exhaust valve in relation to each other.

As an alternative, or in addition to, controlling the valves by phasing, additional camshaft tappets may be utilised to obtain openings and closing of valves at piston positions where this otherwise is not carried out, and hence e.g. for other portions of a combustion cycle than during normal operation, and also distinct from phasing. Such tappets may be arranged to be selectively engageable, e.g. by means of switches. An exemplary use of such additional valve opening is illustrated by dashed line 505 in fig. 5 below. Instead of using camshaft controlled tappets, opening/closing of valves may also be arranged to be controlled in any suitable manner, such as by electrical and/or mechanical and/or pneumatical means.

The system is also shown in fig. 4, which schematically shows all cylinders of the combustion engine, denoted il-i6 in fig. 4.

According to the disclosed example, ambient air from the vehicle/engine surrounding is drawn trough an air filter 404 from an intake side 404A of the air filter 404 being subjected to ambient air and being drawn through the air filter 404 by means of a compressor 406. The compressor 406 is driven by a turbine 408, the compressor 406 and turbine 408 being interconnected by means of a shaft 410, thereby forming a conventional turbocharger. The compressed air is cooled by a charge air cooler 412 in a manner known per se prior to being supplied to the intake conduit 402 and combustion chambers ili6 of the internal combustion engine 101.

Passage to the exhaust conduits of the combustion chambers ili6, is controlled by the exhaust valves of the combustion chambers, respectively. According to the present example, the exhaust conduits are further arranged such that exhaust gases emanating from cylinders il-i3 share a common conduit 414 from exhaust outlets to a first inlet 408A of the turbine 408.

Correspondingly, exhaust gases emanating from cylinders i4-i6 share a common conduit 416, separate from the conduit 414, from exhaust outlets to a second inlet 408B of the turbine 408. The turbine 408, consequently, comprises separate exhaust gas inlets for receiving the exhaust gas streams from conduits 414 and 416, respectively, e.g. constituting a conventional twin-scroll turbine. Such arrangements may e.g. reduce problems with pressure pulses consisting of exhaust from one combustion chamber disturbing operation of another combustion chamber. This is not discussed further herein.

The exhaust gas stream is then again combined and discharged by the turbine 408 through a single common outlet 408C and is led to the one or more aftertreatment components 130, possibly via e.g. an exhaust brake, for aftertreatment of exhaust gases according to the above prior to being released into the surroundings of the vehicle 100.

As was mentioned above, a suitable control of the valves is determined in step 302, and figs. 5A-B shows an exemplary control method that may be utilised according to the invention. The y-axis represents state of the valve, where the zero level represents a fully closed valve, and the other levels at least partially open valve, where physically fully open occurs at the top of the curve, although the fully open position in terms of flow may occur earlier. According to the invention, the valves may be considered "open" when they are not fully closed, i.e. as soon as they have started to open and until they again are in closed position. The x-axis represent movement, expressed in crankshaft degrees and -360°, 0°, 360°, representing piston 210 position top dead centre TDC, i.e. the piston being closest to valves 211, 213 prior to commencing travel towards crankshaft 205. Solid line 501 represents the intake valve 211, and dash/dotted line 502 represent the exhaust valve 213. Dotted line 503 represents a limitation in valve clearance. That is, when intake and/or exhaust valves open inwards, and hence in a direction towards the piston 210 reciprocating in the combustion chamber 209, valves may not fully open at piston top dead centre TDC to avoid valves colliding with the piston. Dashed line 503 represents this valve clearance which must not be violated, hence according to the present embodiment, lines 501, 502 may not intersect line 503. According to alternative embodiments, the piston head may, instead, be provided with valve cut-outs or recesses to allow further, or full, valve opening at TDC, e.g. according to dotted line 504. According to further embodiments of the invention, valves may be designed such that valves open in a manner that do not interfere with the piston irrespective of when or the extent to which the valves open.

Fig. 5A illustrates an example of normal valve operation when the internal combustion engine is running, i.e. a conventional combustion cycle where intake valve 211 open at approx. -360° for intake of air for combustion when the piston 210 travels from TDC (at -360°) to bottom dead centre BDC at -180°.

According to the present example, intake valve 211 closes when, or slightly after, the piston commences return stroke towards TDC at -180°. The return stroke from -180° to 0° (i.e. TDC) is the compression stage, or stroke in the present example, and around 0° fuel is injected into the compressed air to commence combustion as is known per se.

The resulting compression, i.e. the pressure obtained during the compression stroke, depends on the amount of air provided during the intake stroke, which in turn depends, inter alia, on the pressure of the intake air delivered by the compressor 412. When the engine is running, the force acting on the piston in the following expansion stage, stroke in this case, depends partly on the pressure obtained during the compression stage, where the work produced by gas expansion is increased by the combustion.

In the general case, when the engine is to be turned off, intake valves and exhaust valves are operated in a conventional manner but fuel injection is turned off to stop the engine. The compression in the compression stage aids the stopping of the engine by retarding the crankshaft 112, but the following expansion stage provides a force acting on the piston 210, albeit less than when combustion is occurring, which in turn propels the crankshaft and hence counteracts the stopping of the engine. Due to losses and generation of heat during compression the propelling force exerted during expansion is lower than the retarding force resulting from combustion and the engine in general stops in a relatively short period of time.

According to the invention, the time it takes to stop the internal combustion engine is substantially reduced by reducing or eliminating the propelling force caused by expansion. According to the exemplary embodiment, this is accomplished by opening, at least to some extent, the exhaust valve at the end of compression and/or at the beginning of the expansion. As is realised, it is preferred to open the exhaust valve as late as possible during the compression stage to benefit as much as possible from the retarding force caused by compression.

The opening of the exhaust valve can be controlled, for example, by suitable phasing of the camshaft controlling the exhaust valve 213, and this phasing can be determined in step 302. An exemplary phasing suitable for use during stop of the internal combustion engine is shown in fig. 5B, where the intake valve 211 is controlled according to the above for normal intake of air, but where, in this example, the exhaust valve 213, in addition to conventional evacuation of the combustion chamber in an exhaust stroke (dash-dotted line in fig. 5A), opens partly at the end of the compression stage and is maintained in the beginning of the expansion stage, dashed line 505. As can be seen from fig. 5B, the exhaust valve 213 open to an extent respecting the available valve clearance, where other designs may allow further/full opening of the valve. In this way, the compression stage is utilised to a large extent to retard the crankshaft, but when the exhaust valve 213 opens, the compressed gas in the combustion chamber will expand through the exhaust valve 213 into the exhaust manifold 414. In this way, the expansion of the pressured gas will in little or no extent provide a force to assist the piston 210 when moving towards BDC, and hence the reduction in propelling force will substantially reduce the time it takes for the internal combustion engine 101 to stop. Preferably a plurality of, or all of, the combustion chambers il-i6 of the internal combustion engine 101 are controlled in this manner.

When a suitable control has been determined in step 302, e.g. according to fig. 5B or any other suitable control for reducing crankshaft propulsion by expansion, the method continues to step 303.

In step 303 fuel injection is turned off, and in step 304 the exhaust valve 213 is controlled by the determined control, in this case by suitable phasing of the camshaft 204, where valves of all combustion chambers may simultaneously controlled in the same manner, e.g. by camshaft 204.

In step 305 it is determined whether the internal combustion engine is stopped, i.e. the speed of rotation of the crankshaft 205 has reached zero, and for as long as this is not the case, valve control according to the above is continued. When it is determined that the internal combustion engine has been stopped, the method ends in step 306.

According to exemplary embodiments of the invention, valve control according to the invention is maintained until the speed of rotation has been at least reduced to a first speed of rotation n1, such as e.g. 10 or 50 rpm, where valve control may be returned to normal valve control at the very end of the stopping of the internal combustion engine to be set for a following start of the internal combustion engine, while still benefitting substantially from the present invention.

According to the present example, the exhaust valve 213 is maintained open during part of the expansion stage, i.e. from 0° and onwards. This may be beneficial e.g. to avoid or reduce the below atmospheric pressure that otherwise may arise if the combustion chamber is closed at atmospheric pressure at TDC and the combustion chamber volume then expands as the piston travels towards BDC. If the pressure becomes too low in the combustion chamber, oil may be drawn into the combustion chamber past the piston/cylinder wall, which may be detrimental to the operation of the internal combustion engine. Hence the valve control can be determined to take this factor into account.

Furthermore, according to the present example, the exhaust valves of the combustion chambers are controlled, but according to embodiments of the invention, the intake valves may be controlled instead, e.g. by suitable phasing of camshaft 203. According to embodiments of the invention both intake valves and exhaust valves may be controlled in a suitable manner, such as e.g. exhaust valve at the end of compression stage and intake valve at the beginning of the expansion stage, or vice versa.

Furthermore, in case of 4-stroke internal combustion engines, the procedure described above may be used twice for each combustion cycle, i.e. intake of air may be carried out not only during the normal intake stage as above, but this may also be repeated with intake at the expansion stage, i.e. valve does not close again as in fig. 5B but maintained open for a longer period of time, followed by a control during evacuation stage similar to the above where the exhaust valve is opened e.g. according to the above instead of as in the conventional manner.

Hence, according to the invention, a method of stopping the internal combustion engine is provided, which imposes considerable improvements regarding the time it takes to stop the engine. This also means that noise from the engine is reduced since the time during which the engine makes sound is reduced.

In addition to the above, the present invention may further be used in combination with the solution described in the Swedish patent application 1651044-8, with the title "METHOD AND SYSTEM FOR STARTING AN INTERNAL COMBUSTION ENGINE", with the same filing date and applicant as the present application.

This application relates to situations where it may be desirable to start the internal combustion engine in a manner that reduces wear on internal combustion engine components and/or e.g. a starter motor. The disclosed method may be used e.g. in start-stop solutions, and be utilised in vehicles where the internal combustion engine is stopped according to the present invention.

Finally, the present invention has been exemplified for a vehicle. The invention is, however, applicable in any kind of craft, such as, e.g., aircrafts and watercrafts. The invention is also applicable for use in combustion plants. Also, the invention is applicable for any kind of internal combustion, and not only where a piston is reciprocating in a combustion chamber, but also for other kinds of engines, such as e.g. Wankel engines, for as long as compression is performed as part of a combustion cycle.

Claims

1.Method for stopping an internal combustion engine (101), said internal combustion engine (101) having at least one combustion chamber (209) and a crankshaft (112) being arranged to be propelled by said at least one combustion chamber (209), wherein intake of gas to said at least one combustion chamber (209) is controlled by at least one intake valve (211), and wherein evacuation of said at least one combustion chamber (209) is controlled by at least one exhaust valve (213), the method being characterised in, when said internal combustion engine (101) is to be stopped: - turning off fuel injection, - with fuel injection turned off, controlling the intake valve (211) and/or the exhaust valve (213) of said at least one combustion chamber (209) such that, following compression in said at least one combustion chamber (209), pressure in said combustion chamber (209) is reduced to reduce a crankshaft (112) propelling power caused by gas expansion following said compression, the method further including: - controlling the intake valve (211) and/or exhaust valve (213) to reduce said compression by phasing of at least one camshaft, or part thereof, to thereby control opening and/or closing of the intake valve (211) and/or exhaust valve (213) in dependence of the current position of a reciprocating member (210) in said combustion chamber (209), said dependency being controllable using said phasing.

2.Method according to claim 1, further including: - controlling the intake valve (211) and/or exhaust valve crankshaft (112) propelling power caused by expansion following compression until the speed of rotation of said crankshaft (112) is reduced to at least substantially zero.

3.Method according to claim 1 or 2, further including: - reducing said pressure following compression by controlling said intake valve (211) and/or exhaust valve (213) such that pressure is reduced to essentially atmospheric pressure.

4.Method according to any one of claims 1-3, further including: - prior to said compression, opening the intake valve (211) and/or exhaust valve (213) of said combustion chamber (209) for intake of gas, and - following compression of said intake of gas, opening the intake valve (211) and/or exhaust valve (213) of said combustion chamber (209) to reduce pressure in said combustion chamber (209) to thereby reduce crankshaft (112) propelling power caused by gas expansion in relation to the crankshaft (112) propelling power otherwise obtained.

5.Method according to any one of claims 1-4, further including: - when reducing compression in said combustion chamber (209), opening the intake valve (211) and/or an exhaust valve (213) at the end of the compression and/or at the beginning of the following expansion.

6.Method according to any one of the claims 1-5, wherein opening and closing of intake valves (211) are controlled by a first camshaft (203), and wherein opening and closing of exhaust valves (213) are controlled by a second camshaft (204), the method further including: - individually phasing at least one of said first (203) and second (204) camshaft to control reduction of pressure following compression in said combustion chambers (209).

7.Method according to any one of the claims 1-6, further including: - reducing pressure in said combustion chamber (209) following compression by opening the intake valve (211) and/or exhaust valve (213) during a period of an expansion stroke where said valves are closed when said internal combustion engine (101) is running.

8.Method according to claim 7, said period being a crankshaft (112) rotation, e.g. determined in crank angle degrees .

9.Method according to any one of the claims 1-8, wherein intake of gas to said combustion chamber (209) is controlled by two or more intake valves (211), and/or wherein evacuation of said combustion chamber (209) is controlled by two or more exhaust valves (213), the method further including: - controlling at least one of said valves to reduce pressure in said combustion chamber (209) following compression to reduce crankshaft (112) propelling power caused by gas expansion following the compression.

10.Method according to any one of the claims 1-9, the internal combustion engine (101) including a plurality of combustion chambers (209), the method further including: - controlling a plurality of combustion chambers (209) of said internal combustion engine (101) such that following compression in said combustion chambers (209), pressure in said combustion chambers (209) is reduced to reduce crankshaft (112) propelling power caused by gas expansion following said compression.

11.Method according to any one of the claims 1-10, further including, when stopping said internal combustion engine (101): - increasing the load on said internal combustion engine (101) by increasing power consumption of one or more loads being driven by said internal combustion engine (101).

12.Computer program comprising program code that, when said program code is executed in a computer, causes said computer to carry out the method according to any of claims 1-11.

13.Computer program product comprising a computer-readable medium and a computer program according to claim 12, wherein said computer program is contained in said computer-readable medium.

14.System for stopping an internal combustion engine (101), said internal combustion engine (101) having at least one combustion chamber (209) and a crankshaft (112) being arranged to be propelled by said at least one combustion chamber (209), wherein intake of gas to said at least one combustion chamber (209) is controlled by at least one intake valve (211), and wherein evacuation of said at least one combustion chamber (209) is controlled by at least one exhaust valve (213), the method being characterised in, when said internal combustion engine (101) is to be stopped: - means adapted to turn off fuel injection, - means adapted to, when fuel injection is turned off, control the intake valve (211) and/or exhaust valve (213) of said at least one combustion chamber (209) such that, following compression in said at least one combustion chamber (209), pressure in said combustion chamber (209) is reduced to reduce a crankshaft (112) propelling power caused by gas expansion following said compression, - means adapted to control the intake valve (211) and/or exhaust valve (213) to reduce said compression by phasing of at least one camshaft, or part thereof, to thereby control opening and/or closing of the intake valve (211) and/or exhaust valve (213) in dependence of the current position of a reciprocating member (210) in said combustion chamber (209), said dependency being controllable using said phasing.

15.Vehicle, characterised in that it comprises a system according to claim 14.