WO2018013040A1

WO2018013040A1 - Method and system for starting an internal combustion engine

Info

Publication number: WO2018013040A1
Application number: PCT/SE2017/050757
Authority: WO
Inventors: Erik HÖCKERDAL; Ola Stenlåås
Original assignee: Scania Cv Ab
Priority date: 2016-07-12
Filing date: 2017-07-06
Publication date: 2018-01-18
Also published as: DE112017003039T5

Abstract

The present invention relates to a method for starting an internal combustion engine (101), said internal combustion engine (101) having a plurality of combustion chambers (209), wherein, when starting said internal combustion engine (101), engine cranking means (111) accelerates a crankshaft (112) of said internal combustion engine (101). The method includes, when accelerating said crankshaft (112) using said engine cranking means (111): - with fuel injection turned off, controlling intake valves (211) and/or exhaust valves (213) to reduce compression in said combustion chambers (209), - when said crankshaft (112) has been accelerated to a first speed of rotation, control intake valves (211) and/or exhaust valves (213) to increase compression in said combustion chambers (209) in relation to said reduced compression, - when compression in said combustion chambers (209) is increased, commence fuel injection, - wherein, when said first speed of rotation is reached and compression is increased, speed of rotation of said crankshaft is controlled to decrease so that resistance against rotation caused by compression is at least partly overcome by consuming kinetic energy accumulated by said acceleration.

Description

METHOD AND SYSTEM FOR STARTING AN INTERNAL COMBUSTION ENGINE Field of the invention

The present invention relates to combustion processes, and in particular to a method and system for starting 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, or coasting downhill, to be started again when the vehicle is to be set in motion to reduce fuel consumption. This, on the other hand, further increases wear e.g. on the starter motor, which already may constitute a vehicle component being subject to substantial wear frequently occurring in statistics of failure of vehicle components.

Summary of the invention

It is an object of the present invention to provide a method and system for starting an internal combustion engine that may reduce wear e.g. on starter motor and also the internal combustion engine. This is achieved by a method according to claim 1.

According to the present invention, it is provided a method for starting an internal combustion engine, said internal combustion engine having a plurality of combustion chambers, where intake of air to said combustion chambers is controlled by intake valves, and where evacuation of said combustion chambers is controlled by exhaust valves. Engine cranking means accelerates a crankshaft of said internal combustion engine when starting said internal combustion engine, and the method includes, when accelerating said crankshaft using said engine cranking means:

- with fuel injection turned off, controlling intake valves and/or exhaust valves to reduce compression in said combustion chambers , - when said crankshaft has been accelerated to a first speed of rotation, control intake valves and/or exhaust valves to increase compression in said combustion chambers in relation to said reduced compression,

- when compression in said combustion chambers is increased, e.g. to a set ratio, commence fuel injection, and - wherein, when said first speed of rotation is reached and compression is increased, speed of rotation of said crankshaft is controlled to decrease so that resistance against rotation caused by compression is at least partly overcome by consuming kinetic energy accumulated during said acceleration.

When the combustion in the internal combustion engine has reached a level where the engine propels itself, external motoring (cranking) of the crankshaft using said engine cranking means can be arranged to be discontinued. As

discussed below, external motoring (cranking) of the

crankshaft using said engine cranking means can be arranged to be discontinued also prior to the combustion in the internal combustion engine has reached a level where the engine propels itself . Start-stop systems, also known as stop-start systems,

regarding internal combustion engines are becoming more and more frequent as regulations regarding fuel economy and emissions are becoming stricter. Start-stop systems

automatically, e.g. controlled by 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. Such functionality may be limited to situations where the vehicle is standing still, and is perhaps most advantageous when vehicles spend

significant amounts of time waiting at traffic lights or otherwise often comes to a stop in situations where the internal combustion engine is left idling. Furthermore, start- stop functionality may be utilised in other situations. For example, the internal combustion engine may be arranged to be turned off e.g. when the vehicle is travelling in downhill sections of road where no propelling power is required (idle- off ECO-roll) . There may also be cruise control functionality where fuel consumption can be improved by first accelerating the vehicle to higher speed and then turn off the internal combustion engine to allow the vehicle to decelerate to a lower speed. This may then be repeated. The invention is applicable e.g. also in situation of these kinds.

In addition to possible advantages, there are also drawbacks with start-stop systems. For example, the introduction of a start-stop system in general results in the number of starts of the internal combustion engine being considerable higher over time in comparison to when systems of this kind are not utilised. This imposes additional wear on the starter motor, which may already be one of the vehicle components that most frequently is subject to faults and being worn out during the vehicle lifecycle. Furthermore, start-stop systems may impose additional wear on the internal combustion engine. The

internal combustion engine is dependent on adequate

lubrication, and the lubrication is dependent on the presence of oil film in bearings etc. When starting an internal

combustion engine, oil pressure is low and bearings oftentimes more or less drained from oil and subject to excess wear.

Frequent starts hence increases wear, e.g. on bearings and possibly also on engine internal components.

With regard to start-stop functionality per se, the vehicle control system may be arranged to detect situations when to start and stop the internal combustion engine in any suitable manner. Such detection does not form part of the invention, but, instead, the invention is related to starting the

internal combustion engine in a favourable manner from a life expectancy point of view, and also from noise/comfort point of view. The invention is also applicable in any kind of start of the internal combustion engine, and hence not limited to start-stop systems.

According to the present invention, it is provided a method for starting an internal combustion engine in a manner that may reduce wear on the engine cranking means, such as a starter motor, and/or wear of components of the internal combustion engine. This is accomplished by accelerating the crankshaft using engine cranking means, such as a starter motor, with fuel injection turned off while simultaneously controlling intake valves and/or exhaust valves of the

combustion chambers of the internal combustion engine to reduce compression in said combustion chambers during

acceleration. The compression can be arranged to be reduced to a compression being below the compression in said combustion chambers when said internal combustion engine is idling.

Hence, for example, in case of a two-stroke or four-stroke internal combustion engine, the reduction of compression has as result that the resulting maximum pressure in the

combustion chamber in a compression stroke is reduced. When the crankshaft has been accelerated to the first speed of rotation, the intake valves and/or exhaust valves, are

controlled to increase compression in said combustion

chambers. That is, the compression is increased in relation to the compression when the speed of rotation is below said first speed of rotation. The compression is increased to a

compression being sufficient to allow the internal combustion engine to start when fuel injection is commenced. For example, in case the internal combustion engine is a compression- ignition internal combustion engine, compression can be increased to a compression sufficient for compression-ignition of fuel being injected to the combustion chamber so that combustion can occur when fuel injection is commenced. Hence, when reducing the compression prior to commencing fuel injection, compression can be reduced to a level below the minimum compression being used when the internal combustion engine is running.

When compression in said combustion chambers is increased, fuel injection is commenced to actually start the internal combustion engine by commencing rotation by means of

combustion .

Furthermore, according to the invention, when said first speed of rotation is reached and compression is increased, speed of rotation of said crankshaft is controlled to decrease so that resistance against rotation caused by compression is at least partly overcome by consuming kinetic energy accumulated during said acceleration. This can be accomplished, for example, by applying a torque by the engine cranking means that is not sufficient to maintain the speed of rotation of the crankshaft when compression is increased. This can be done e.g. by reducing the torque applied by the engine cranking means, or by applying a torque during the acceleration that is not sufficient to maintain the speed of rotation of the crankshaft when the compression is increased.

The crankshaft is hence accelerated to a speed being higher than the speed of rotation of the crankshaft that is required in order to start the internal combustion engine. In this way, the load that is otherwise imposed on the engine cranking means by the increased compression is reduced by the load being at least partially eliminated by consuming the stored kinetic energy by allowing the speed of rotation of the crankshaft to decrease. Hence, according to the invention, the torque required to rotate the crankshaft can be substantially reduced, thereby reducing the amount of work produced by the engine cranking means, and as a consequence also reducing wear. The load that bearings and other components in the internal combustion engine is subjected to will also be reduced, since e.g. forces acting on moving, e.g. reciprocating and/or rotating, members in the combustion chambers, such as pistons in a two- or four- stroke engine or rotors in a Wankel engine, will be

substantially reduced by reducing the compression that such moving members otherwise is subjected to during start of the engine.

When combustion has started, the speed of rotation of the crankshaft will again increase, and motoring of the crankshaft using the engine cranking means can be arranged to be

discontinued, stopped, since the internal combustion engine can be considered as having been started. According to

embodiments of the invention, motoring of the crankshaft using said engine cranking means is not discontinued until the speed of rotation of said crankshaft has reached a second speed of rotation, exceeding said first speed of rotation. In this way it can be ensured that crankshaft rotation caused by

combustion occurs to a sufficient extent before cranking using the engine cranking means is discontinued. Still the load on the engine cranking means during the start is reduced by the consumption of kinetic energy relieving the engine cranking means from the full load imposed by the increased compression.

Further, according to embodiments of the invention, external motoring (cranking) of the crankshaft using said engine cranking means can be arranged to be discontinued also prior to the combustion in the internal combustion engine has reached a level where the engine propels itself. For example, said first speed of rotation of said crank shaft can be controlled to be a speed of rotation at which the stored kinetic energy is sufficient to overcome the arising increased resistance against rotation caused by the increased

compression, to thereby allow the internal combustion engine to start using the kinetic energy without further torque being applied by the engine cranking means. That is, the kinetic energy may take the role of the engine cranking means so that motoring of the engine cranking means may be discontinued prior to the internal combustion has reached a level where the engine propels itself. According to embodiments of the

invention, external motoring of the engine cranking means can be continued after the compression is increased, but, as was mentioned, the kinetic energy being consumed will still reduce the load on the engine cranking means.

With regard to said first speed of rotation of the crankshaft, this speed of rotation can further be arranged to be

determined in dependence of the compression to which the compression is increased. The more the compression is

increased, the higher the first speed of rotation may be set so that additional kinetic energy is stored to account for the comparatively higher resistance that a higher increase of the compression gives rise to. The level to which compression is increased may in turn be arranged to depend e.g. on current engine temperature and/or temperature of the surroundings of the vehicle. The compression can be arranged to be reduced by reducing compression in the combustion chambers by increasing or changing an opening time of the intake valves and/or exhaust valves during compression strokes in said combustion chambers. For example, intake valves and/or exhaust valves of the combustion chambers can be arranged to be kept open during the first part of the compression stroke to thereby prevent any compression from occurring during part of the compression stroke. According to embodiments of the invention, intake valves and/or exhaust valves can be kept open during at least a predetermined portion of the movement that a reciprocating piston undergoes during a compression stroke in a two-stroke or four-stroke internal combustion engine to thereby reduce the resulting compression.

Furthermore, compression in said combustion chambers can be arranged to be increased to a first compression prior to commencing fuel injection, and, when fuel injection has commenced, the compression in said combustion chambers can be changed again, such as e.g. being further increased or changed to another compression allowing combustion. In this way, the losses, and hence the resistance against rotation, can be maintained at a reduced level until established that the internal combustion engine has started.

In case the internal combustion engine is a compression- ignition internal combustion engine, the changed, e.g.

reduced, compression can be a compression that is insufficient for compression-ignition if fuel were to be injected into a cold engine, and, when increasing the compression, the

compression can be increased to a level where compression- ignition of fuel injected to the combustion chambers results in the highest engine efficiency.

According to embodiments of the invention, the crankshaft can be arranged to be rotated to a considerably higher rotational speed than the rotational speed required for the internal combustion engine to start by injection and ignition of fuel.

According to embodiments of the invention, the crankshaft can be arranged to be accelerated to a speed corresponding to at least 1.5 times, or at least 2 times, or at least 3 times or more the speed of rotation of the crankshaft required to start said internal combustion engine prior to increasing the compression and commencing injection of fuel. As was

mentioned, this has the advantage that kinetic energy built up in the moving parts of the internal combustion engine is used to facilitate start of the engine when compression is

increased and used to overcome the compression, thereby assisting the engine cranking means in overcoming the

compression and reducing load on the engine cranking means by allowing the crankshaft to temporarily reduce speed of rotation to consume stored kinetic energy when overcoming the increased resistance against rotation caused by increased compression. This may also allow increase of compression to a higher than normal compression prior to or when commencing fuel injection, since the stored kinetic energy may ensure that the engine cranking means still suffices to rotate the crankshaft despite the higher compression. A higher-than- normal compression will result in more heat being generated during compression, thereby easier facilitating combustion and start of the engine. Furthermore, the pressure of lubricants such as oil

lubricating the internal combustion engine is oftentimes produced by a pump being driven by the crankshaft. According to embodiments of the invention, the crankshaft is accelerated to a speed at which a pump that is driven by the crankshaft discharges a lubricant pressure, such as oil pressure, exceeding a predetermined pressure prior to increasing compression. For example, the predetermined pressure may be a pressure ensuring proper lubrication of engine internal components such as e.g. bearings, and also ensuring

establishment of a proper lubrication film e.g. on cylinder walls prior to increasing load by increasing compression, thereby further reducing situations that may give rise to wear .

The speed of rotation at which compression is increased may also be arranged to depend e.g. on engine temperature, and/or a temperature of fluids entering the internal combustion engine, such as boost air temperature, EGR temperature, cooling fluid temperature or oil temperature, where higher rotational speeds may be utilised for lower temperatures to facilitate e.g. cold starts. 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 reduce compression in said combustion chambers, e.g. by controlling intake valves or exhaust valves, or controlling both kinds of valves.

The intake valves and/or exhaust valves can be arranged to be controlled to reduce compression by phasing of at least one camshaft or part thereof to thereby control opening and/or closing of intake valves and/or exhaust valves in a variable dependence of positions of moving members such as pistons or rotors in said combustion chambers, respectively. For example, one of or both of said first and second 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, one or both camshafts 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. With regard to the reduction of compression, this may be accomplished by controlling intake valves and/or exhaust valves such that said valves are open a first period during compression when the speed of rotation of the crankshaft is below said first speed of rotation, and a different, such as a shorter, period when the speed of rotation of the crankshaft is above said first speed of rotation. Since the actual time it takes to compete e.g. a combustion phase is dependent on speed of rotation of the crankshaft, such periods may be determined in crank angle degrees.

With regard to the acceleration of the crankshaft, engine cranking means in the form of a starter motor may be used. Also, an electrical machine may be used, e.g. in electric hybrid vehicles. In case the vehicle is in motion with

internal combustion engine turned off, the crankshaft may also be accelerated e.g. by engaging a clutch connecting a rotating drivetrain .

The internal combustion engine may be of a designed such that a single intake valve and a single exhaust valve,

respectively, acts against each 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 per combustion chamber, and according to such designs one or more of each kind of valve may be opened for each combustion chamber being controlled .

Furthermore, as is apparent from the above, a plurality of combustion chambers of the internal combustion engine are controlled according to the present invention, and all 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 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 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 top dead centre, 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-C 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 (or air containing boost gas, such as air/EGR/premix fuel mixture) 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 spark- ignition (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. Fig. 1A also shows a starter motor 111 being used to motor (i.e. accelerate/rotate) a crankshaft 112 of the internal combustion engine 101 when the internal combustion engine 101 is to be started . 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.

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 starting the combustion engine that, at least in some instances, may provide advantages in comparison to other solutions. For example, wear on internal combustion engine components, such as starter motor and engine internal

components, 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 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 start of the internal combustion engine 101.

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 of camshafts and/or to control engine cranking means such as starter motor 111 cranking the crankshaft 112. 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 started. 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 started according to the invention. The transition from step 301 to step 302 can, for example, be initiated at all times, i.e. always when the internal combustion engine is to be started. Alternatively, control according to the invention can be arranged to be performed e.g. only for particular starts, such as when start- stop functionality is active. Other criteria for performing the transition from step 301 to step 302 may also be applied.

In step 302 a suitable control of the compression, i.e. the manner in which the compression is to be reduced, when

starting the internal combustion engine is determined, and according to the present example compression is controlled by controlling intake valves. Hence, in step 302 a suitable control of the intake valves is determined. According to other embodiments of the invention, exhaust valves are controlled instead, and according yet other embodiments of the invention, both inlet valves and exhaust valves are controlled to obtain a desired reduction in compression. According to embodiments of the invention, the control may be predetermined, and hence automatically utilised when starting the internal combustion engine 101.

The control may depend on the resulting compression to be obtained, which may always be arranged to be the same or e.g. be arranged to depend e.g. on whether the internal combustion engine recently has been running and/or a current temperature of the internal combustion engine or one or more fluids acting therewith .

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 of a plurality of combustion chamber of a similar kind of the internal combustion engine, and 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 (or air containing boost gas, such as air/EGR/premix fuel mixture) 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 valve 211 can be individually controlled in relation to valve 213, and vice versa. The phasing can, for example, be accomplished by means of phasers. Use of phasers allows continuous adjustment of the valve control. For example, 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.

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

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 il- i6 of the internal combustion engine 101.

Passage to the exhaust conduits of the combustion chambers il- i6, 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,

possible 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. 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 , and the vehicle may also be of a kind where no turbocharger is used .

As was mentioned above, a suitable control of the valves is determined in step 302, and figs. 5A-C 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 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 at about 0° (or earlier depending on ignition delay and/or combustion principle, e.g. SI, HCCI, RCCI, PPC) 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 (or air containing boost gas, such as air/EGR/premix fuel mixture) provided during the intake stroke, which in turn depends, inter alia, on the pressure of the intake air (or pressure of air containing boost gas, such as air/EGR/premix fuel mixture) delivered by the compressor 412. However, when starting the internal combustion engine there is in general no compression of the intake air and the intake air hence being of essentially atmospheric pressure.

In the general case, when the engine is to be started, intake valves and exhaust valves are operated in the same manner as when the internal combustion engine is running. According to the exemplary embodiment, instead, the resulting pressure during compression is reduced by delaying closing of the intake valve 211 so that the intake valve is maintained open during a large part of the compression stroke. In this way, air taken in during the intake stroke is returned to the intake manifold as the piston 210 travels towards TDC. The opening of the intake valve can be controlled, for example, by suitable phasing of the camshaft 203 controlling the intake valve 211, and the phasing can be determined in step 302. An exemplary phasing suitable for use during start of the

internal combustion engine is shown in fig. 5B, where the solid line 501 represents the normal valve opening/closing of fig. 5A, and dashed line 505 the valve opening/closing during acceleration of the internal combustion engine (crankshaft) during start of the engine, such as from crankshaft

standstill. As can be seen from fig. 5B, an opening time of the intake valve during compression strokes is increased significantly, and in particular the valve is open further towards the end of the compression stage. The use of valve control according to fig. 5B will reduce substantially the resulting pressure during the compression stroke when accelerating the crankshaft, since compression cannot begin until the intake valve 211 is closed. Prior to the point at which this occurs, the combustion chamber will be evacuated through the open valve 211 so that essentially atmospheric pressure (or the pressure in the intake manifold 402, which, however, in general is essentially atmospheric pressure when starting an internal combustion engine) is maintained. Once the intake valve closes, at point A in fig. 5B, the amount of air in the combustion chamber has been reduced by evacuation to such extent that the remaining compression will result in a substantially lower pressure than is the case during normal operation, such as when the internal combustion engine is idling.

The internal combustion engine of the present example is a compression-ignition internal combustion engine, such as a Diesel engine, and, for example, when the speed of rotation is below said first speed of rotation nl , the compression may be reduced at least such that the resulting compression would be insufficient for compression-ignition, i.e. combustion would not occur even if fuel were injected. When a suitable control has been determined in step 302, e.g. according to fig. 5B or any other suitable control for

reducing compression, the method continues to step 303.

According to the present example, the intake valves of the combustion chambers are controlled, but according to

embodiments of the invention, the exhaust valves may be controlled instead, e.g. by suitable phasing of camshaft 204. According to embodiments of the invention both intake valves and exhaust valves may be controlled, e.g. by suitable phasing using phasers. In step 303 the control is set to the determined control, which is commenced by operating, in this case phasing, the camshaft 203 in accordance with the control determined in step 302 to obtain the desired operation of the intake valve to delay closing, and in this case also opening according to the above, so that the resulting compression is reduced and thereby reducing torque required to accelerate the crankshaft. The valves of all combustion chambers are simultaneously controlled in the same manner, e.g. by camshaft 203.

In step 304 acceleration of the crankshaft 112 is commenced, hence using the valve control determined above, where

acceleration of the crankshaft 112 is carried out by motoring the crankshaft 112 using engine cranking means such as starter motor 111. In case the vehicle 100 is an electric hybrid vehicle, crankshaft rotation can be effected by an electrical machine. Also, should the vehicle be in motion with the combustion engine turned off, e.g. in a state of coasting, crankshaft rotation may be effected by connecting a rotating drivetrain to the crankshaft through engagement of a clutch.

According to the invention, the crankshaft 112 is accelerated with fuel injection turned off. When crankshaft 112

acceleration has commenced, it is determined in step 305 whether the crankshaft 112 has been accelerated to a first speed of rotation nl, and, for as long as this is not the case, crankshaft 112 rotation using the determined valve control is continued. When the crankshaft speed of rotation has reached speed nl, the method continues to step 306 where the valves, i.e. in this example the intake valves, are controlled to increase compression in the combustion chambers. This can, for example, be accomplished by phasing camshaft 203 to normal mode of operation, i.e. operation exemplified in fig. 5A.

When the crankshaft speed of rotation has reached speed nl, fuel injection in the combustion chambers is commenced, step 307, which can be performed simultaneous with, or following, the increase of compression. In case the internal combustion engine is a compression-ignition internal combustion engine, compression is increased at least to a compression being sufficient for compression-ignition, such as e.g. compression used during normal operation, which can be represented e.g. by the compression during idling with normal valve operation.

According to the invention, the crankshaft is accelerated to a speed being higher than the speed of rotation of the

crankshaft that is required in order to start the internal combustion engine. The higher speed of rotation has the advantage that kinetic energy is built up in the moving parts of the internal combustion engine, which is then be used to facilitate start of the engine when compression is increased and is used to overcome the compression. The crankshaft 223 is allowed to decelerate, so that the stored kinetic energy is at least partly consumed to overcome the retarding force caused by compression, thereby assisting the starter motor in

overcoming the compression and reducing load on the starter motor so that fuel injection can be performed at normal or even higher than normal compression without unduly loading of the starter motor. In this way, the load that is otherwise imposed on the starter motor by the increased compression is reduced by the load being at least partially eliminated by consuming the stored kinetic energy by allowing the speed of rotation of the crankshaft to decrease.

In this way, the torque required to rotate the crankshaft can be further reduced, thereby reducing wear. The crankshaft can be allowed to reduce the speed of rotation e.g. by suitably controlling the starter motor. For example, the torque applied by the starter motor can be reduced, and/or the starter motor can be disengaged and/or the torque applied during

acceleration of the crankshaft can be insufficient to maintain the speed of rotation once compression is increased. According to embodiments of the invention, the starter motor, if being disengaged, can again be engaged if the speed of rotation of crankshaft is about to decrease to undesirably low speed of rotation to thereby avoid a situation where the engine does not start.

When fuel injection has commenced, the internal combustion engine 101 can be considered as started, and the external motoring of the crankshaft 112 using the engine cranking means can be discontinued. According to the disclosed example, however, it is first determined, step 308, if the speed of rotation of the crankshaft exceeds a second speed of rotation n2, which is higher than the speed of rotation nl, and when this is the case the external motoring of the crankshaft using the engine cranking means is discontinued and the internal combustion engine considered started and the start procedure ended, step 309.

Hence, according to the invention, a method of starting the internal combustion engine is provided, which imposes

considerable less load on the engine cranking means such as a starter motor. This, in turn, may substantially prolong the service life of the starter motor. Also, the reduced

compression reduces load on bearings etc. during the starting phase when lubrication may be poor/insufficient.

Furthermore, according to the above example, compression is controlled between two distinct levels. However, as was indicated above, compression may also be controlled to

increase with increasing speed of rotation of the crankshaft. Also, compression need not be increased to a level

corresponding to normal compression when commencing fuel injection, but may, instead, be increased to an intermediate level. This is exemplified in fig. 5C, where curve 506

represents a control of intake valve 211 that results in a compression that is higher than the compression used when beginning crankshaft rotation, but which is still different, e.g. lower, than normal compression. The compression of fig. 5C may be used, for example, until it has been established that the engine has started, and when this is the case, the compression can be adjusted further to normal compression.

It is also contemplated that the compression when increased at speed of rotation nl, is increased to a higher than normal compression to increase heat in the combustion chambers to thereby facilitate combustion, and then reduce compression once the engine has started.

Also, according to embodiments of the invention, the method of fig. 3 is arranged to return to step 302 from step 305, e.g. to adjust valve control as the crankshaft speed of rotation increases, so that compression can be controlled in dependence of the speed of rotation of the crankshaft, e.g. as a

continuously increasing compression as speed of rotation of the crankshaft increases.

Furthermore, the speed of rotation nl may constitute a speed of rotation of the crankshaft corresponding to at least 1.5 times, or at least 2 times, or at least 3 times or even more the speed of rotation of the crankshaft required to start said internal combustion engine prior to increasing compression sufficient to start the internal combustion engine, such as e.g. sufficient for compression-ignition of fuel injected to the combustion chambers.

The speed of rotation to which the crankshaft is accelerated be determined on a desired accumulation of kinetic energy, which, in turn, can be determined on the basis of compression to be used, where higher speed of rotation can be used for higher compression, and where compression may be arranged to depend e.g. on a current engine and/or engine fluid temperature and/or temperature of air being supplied to the engine/ ehicle .

Furthermore, as was mentioned above, lubrication oil pressure is oftentimes produced by a pump being driven by the

crankshaft 112, and acceleration of the crankshaft 112 to a speed of rotation at which a pump being driven by the

crankshaft 112 discharges sufficient pressure for lubrication prior to increasing compression. The higher speed of rotation allows the oil pump to provide higher pressures, and the speed of rotation to which the crankshaft is accelerated may be set to a speed of rotation at which the resulting oil pressure may ensure engine internal components to be properly lubricated prior to being subjected to higher loads, thereby increasing service life of the internal combustion engine.

The speed of rotation to which the crankshaft is accelerated prior to commencing fuel injection may also be arranged to depend e.g. on engine temperature, and/or a temperature of fluids entering the internal combustion engine, such as boost air temperature, EGR temperature, cooling fluid temperature or oil temperature, where higher rotational speeds may be

utilised for lower temperatures to facilitate e.g. cold starts . In addition to the above, the present invention may further be used in combination with the solution described in the Swedish patent application 1651045-5, with the title "METHOD AND

SYSTEM FOR STOPPING 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 stop the internal combustion engine in a short period of time, e.g. to reduce noise emitted from a vehicle. The disclosed method may also be used to achieve efficient stopping of the internal combustion engine e.g. in start-stop solutions, and hence be utilised in vehicles being started 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

Method for starting an internal combustion engine (101), said internal combustion engine (101) having a plurality of combustion chambers (209), wherein intake of air to said combustion chambers (209) is controlled by intake valves (211), and wherein evacuation of said combustion chambers (209) is controlled by exhaust valves (213), wherein, when starting said internal combustion engine (101), engine cranking means (111) accelerates a

crankshaft (112) of said internal combustion engine

(101), the method being characterised in, when

accelerating said crankshaft (112) using said engine cranking means (111) :

- with fuel injection turned off, controlling intake valves (211) and/or exhaust valves (213) to reduce compression in said combustion chambers (209),

- when said crankshaft (112) has been accelerated to a first speed of rotation, control intake valves (211) and/or exhaust valves (213) to increase compression in said combustion chambers (209) in relation to said reduced compression,

- when compression in said combustion chambers (209) is increased, commence fuel injection,

- wherein, when said first speed of rotation is reached and compression is increased, speed of rotation of said crankshaft is controlled to decrease so that resistance against rotation caused by compression is at least partly overcome by consuming kinetic energy accumulated by said acceleration.

2. Method according to claim 1, further including:

- controlling the speed of rotation of the crankshaft by the torque applied by the engine cranking means.

3. Method according to claim 1 or 2, further including,

- determining said first speed of rotation of said crank shaft (112) as a speed of rotation at which the stored kinetic energy is sufficient to overcome the arising increased resistance against rotation caused by the increased compression to allow combustion in the internal combustion engine reaching a level where the engine propels itself.

4. Method according to any one of claims 1-3, further

including :

- determining said first speed of rotation of said crank shaft (112) in dependence of the compression to which the compression is increased.

5. Method according to any one of claims 1-4, further

including, when combustion has started:

- discontinue external motoring of said crankshaft (112) using said engine cranking means (111) .

6. Method according to any one of claims 1-5, further

including :

- discontinue external motoring of said crankshaft (112) using said engine cranking means (111) when the speed of rotation of said crankshaft (112) has reached a second speed, exceeding said first speed.

7. Method according to any one of the claims 1-6, further including, when reducing compression:

- reducing compression to a compression being below the compression in said combustion chambers (209) when said internal combustion engine (101) is idling.

8. Method according to any one of claims 1-7, further

including :

- reducing compression in said combustion chambers (209) by increasing an opening time of said intake valves (211) and/or exhaust valves (213) during compression strokes in said combustion chambers (209) .

9. Method according to any one of the claims 1-8 said

internal combustion engine (101) being a compression- ignition internal combustion engine (101), further including, when the speed of rotation is below said first speed of rotation:

- reducing compression at least such that the reduced compression is insufficient for compression-ignition.

10. Method according to any one of the claims 1-9, further including :

- prior to commencing fuel injection, increasing

compression in said combustion chambers (209) to a first compression, and, when fuel injection has commenced, change compression in said combustion chambers (209) .

11. Method according to any one of the claims 1-10, further including :

- prior to commencing fuel injection, increasing

compression in said combustion chambers (209) to a compression sufficient for compression-ignition of fuel being injected to said combustion chambers (209) .

12. Method according to any one of the claims 1-11, further including, prior to increasing compression in said combustion chambers (209) to a compression sufficient for compression-ignition of fuel injected to said combustion chambers (209) :

- accelerating said crankshaft (112) to a speed

corresponding to at least 1.5 times, or at least 2 times, or at least 3 times, the lowest speed of rotation of said crankshaft (112) required to start said internal

combustion engine (101) .

13. Method according to any one of the claims 1-12, wherein a pump pressurising lubricant is driven by said crankshaft (112), further including, prior to increasing compression in said combustion chambers (209) to a compression sufficient for compression-ignition of fuel injected to said combustion chambers (209) :

- accelerating said crankshaft (112) to a speed at which said pump discharges lubricant at a pressure exceeding a predetermined lubricant pressure.

14. Method according to any one of the claims 1-13, further including :

- determining said first speed of rotation in dependence of a prevailing temperature of said internal combustion engine (101) and/or fluids entering said internal

combustion engine (101) and/or the increased compression.

15. Method according to any one of the claims 1-14, further including :

- controlling intake valves (211) and/or exhaust valves

(213) to reduce compression by phasing of at least one camshaft or part thereof to thereby control opening and/or closing of intake valves (211) and/or exhaust valves (213) in a variable dependence of positions of moving members in said combustion chambers (209),

respectively .

16. Method according to any one of the claims 1-15, wherein opening and closing of said intake valves (211) are controlled by a first camshaft, and wherein opening and closing of said exhaust valves (213) are controlled by a second camshaft, the method further including:

- individually phasing at least one of said first and second camshaft to control compression in said combustion chambers (209) by controlling opening and/or closing of said intake valves (211) and/or exhaust valves (213) .

17. Method according to any one of the claims 1-16, further including :

- controlling said intake valves (211) and/or exhaust valves (213) such that said valves are open a first period during compression when the speed of rotation of said crankshaft (112) is below said first speed of rotation, and

- controlling said intake valves (211) and/or exhaust valves (213) such that said valves are open a different period when the speed of rotation of said crankshaft (112) is above said first speed of rotation.

18. Method according to claim 17, said periods being

determined in crank angle degrees.

19. Method according to any one of the claims 1-18, further including :

- accelerating said crankshaft (112) using engine

cranking means (111) in the form of a starter motor, an electrical machine and/or engaging a clutch connecting a rotating drivetrain.

20. 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 1-16.

21. Computer program product comprising a computer-readable medium and a computer program according to claim 20, wherein said computer program is contained in said computer-readable medium.

22. System for starting an internal combustion engine (101), said internal combustion engine (101) having a plurality of combustion chambers (209), wherein intake of air to said combustion chambers (209) is controlled by intake valves (211), and wherein evacuation of said combustion chambers (209) is controlled by exhaust valves (213), wherein, when starting said internal combustion engine (101), engine cranking means (111) accelerates a

crankshaft (112) of said internal combustion engine

(101), the method being characterised in:

- means adapted to, when accelerating said crankshaft (112) using said engine cranking means (111) and with fuel injection turned off, control intake valves (211) and/or exhaust valves (213) to reduce compression in said combustion chambers (209),

- means adapted to, when said crankshaft (112) has been accelerated to a first speed of rotation, control intake valves (211) and/or exhaust valves (213) to increase compression in said combustion chambers (209) in relation to said reduced compression,

- means adapted to commence fuel injection when

compression in said combustion chambers (209) is

increased, and

- means adapted to, when said first speed of rotation is reached and compression is increased, control speed of rotation of said crankshaft to decrease so that resistance against rotation caused by compression is at least partly overcome by consuming kinetic energy accumulated by said acceleration.

23. Vehicle, characterised in that it comprises a system according to claim 22.