TECHN ICAL FI ELD OF TH E INVENTION

The present i nvention relates to a method for controll ing a stopping position of an internal combustion engi ne according to the preamble of claim 1 . It further relates to a computer program , a computer program product, an electronic control u nit and a motor vehicle.

By a stopping position for an internal combustion engine, herei nafter also referred to as an engine, is herein to be understood a position in which the engine comes to a stop. The stopping position is associated with an angular position in which a ring gear of the engine comes to a stop as the engine is stopped, and also with positions of e.g . pistons of cyl inders within the engine and positions of other components transferring movement within the engi ne.

BACKG ROU N D AN D PRIOR ART

An internal combustion engi ne in a motor vehicle is generally equipped with a starter that initiates rotation of the engi ne, e.g . in the form of an electric, pneumatic or hydraulic motor. The i nternal combustion eng ine has a n umber of cylinders, each cylinder having a piston and a combustion chamber, and a flywheel connected to the pistons by means of a crankshaft. An external ring gear formed for meshing engagement with a starter pinion of the starter is provided on the flywheel . When the engi ne is to be started, the starter pinion is brought into engagement with a portion of the ring gear facing the starter pinion and rotation of the starter pinion is initiated, e.g. by providing electric power to the starter. The rotation of the starter pinion is transmitted to the ring gear and further to the crankshaft driving the pistons. The internal combustion engine thereby starts to rotate and the starter pinion is thereafter disengaged from the ring gear.

When the engine is to be stopped and the fuel injection and/or the ignition is discontinued depending on engine type, the engine will continue to rotate until the torque applied by the flywheel is no longer sufficient to compress the air within any of the subsequent cylinders in the firing order of the engine. Depending on the configuration of the engine, e.g. number of cylinders, crankshaft design, firing order and cylinder placement, this will happen at one of a few predictable stopping positions. For an engine with six cylinders, there will typically be three stopping positions located 120° from one another on the ring gear. When the engine is to be started again, the starter pinion will be brought into engagement with the portion of the ring gear facing the starter pinion in the stopping position, i.e., for an engine with six cylinders, typically one of three possible portions of the ring gear. Since the engagement with the starter pinion causes wear on the ring gear, the ring gear is therefore unevenly worn.

WO2013031921 describes an attempt to overcome this problem by controlling exhaust valves of the engine cylinders such that the position in which the ring gear comes to a stop is varied, thereby reducing localized wear on the ring gear. SU MMARY OF TH E I NVENTION

It is a primary objective of the present invention to provide an , in at least some aspect, i mproved way of controlli ng a stopping position of an i nternal combustion engi ne. In particular, it is an objective to provide such a method by means of which it is possible to on one hand avoid localized wear on the ring gear, and on the other hand keep track of the wear such that it is possible to foresee when e.g . the ring gear needs to be replaced .

At least the primary objective is, according to a first aspect of the invention , achieved by means of the initially defined method, comprising :

- upon receipt of a signal to stop the internal combustion engine, selecting a desired ang ular position for the ring gear to come to a stop based on at least values stored i n a vector, wherein the vector is a model of the ring gear havi ng a set number of slots for stori ng a value, each slot bei ng associated with a specific angular position of the ri ng gear,

- controlling the at least one valve such that the ring gear comes to a stop in the desired ang ular position ,

- when the ring gear has come to a stop, sensing a current angular position of the ring gear and i ncreasing the value stored in the associated slot of the vector by a predetermined amou nt.

In the method according to the invention , a model in the form of a vector is used to keep track of the nu mber of ti mes the engine has stopped in a certai n stopping position . When a signal to stop the engine is received, a desired ang ular position for the flywheel and the ring gear to stop, and be positioned for meshi ng engagement with the starter pinion, is selected based on the distribution of previous stoppi ng positions. A stopping position i n which the engine has stopped relatively few times can be selected. The at least one valve is controlled by means of variable valve control so as to regulate the pressure in the at least one cylinder so that the engine stops with the ri ng gear in the desired angular position . Depending on eng ine configuration and on the desired stopping position , a valve of one or more cyli nders can be controlled. Furthermore, if each cylinder has several valves, more than one of the valves can be controlled per cyl inder.

The method is preferably repeated each time a sig nal to stop the engine is received. By keepi ng track of the n umber of stops, and thereby also starts, associated with different angular positions of the ring gear, it is possible to distribute the stops even ly over the ring gear. The portion of the ring gear that faces the starter pinion can thereby be varied over time. The number of available stopping positions can by means of the variable valve control be significantly i ncreased. For example, instead of three available stopping positions for a six cylinder engine, the n umber of stopping positions can be increased so that it corresponds to the number of teeth on the ri ng gear. Since the number of stops is stored , it is also possible to predict when the ring gear has been subjected to such sig nificant wear that it needs to be replaced . A condition based mai ntenance can thereby be carried out. It is also possible to discover whether the ring gear for some reason is subjected to uneven wear, e.g . due to a large nu mber of emergency stops, which wi ll be further discussed below.

Accordi ng to one embodiment of the invention , the at least one valve is at least one exhaust valve of the at least one cyli nder. In this way, no additional valve is needed for the pu rpose of the present invention . Cylinders may have more than one exhaust valves, i n wh ich case all exhaust valves or some of the exhaust valves can be controlled. The exhaust valve is suitable to control since there is in that way no risk of leaking potentially polluting exhaust gases into an intake system of the engi ne via the exhaust valve.

According to one embodiment of the invention , the at least one valve is controlled such that a cylinder pressure is reduced during a compression phase of the at least one cylinder. Thus, the at least one valve is opened duri ng the compression phase such that the pressure is reduced i n a combustion chamber of the cylinder. The reduced pressure efficiently slows down the deceleration of the flywheel .

According to one embodiment of the invention , the cylinder pressure is reduced in the at least one cylinder whose compression phase corresponds to an angular position of the ring gear associated with a relatively large nu mber of stops. By reducing the cyl inder pressure in th is at least one cylinder, the flywheel can be triggered to rotate past the ang ular position associated with a large number of stops in comparison with adjacent positions. The flywheel can thereby rotate i nto a stopping position i n which the ring gear has a fewer n umber of stops, and come to a stop in that stopping position .

According to one embodiment of the invention , the desired angu lar position for the ring gear to come to a stop is selected as an angular position associated with a slot having a lower value stored therein than slots associated with su rrounding ang ular positions. This promotes an even wear of the ring gear. According to one embodiment of the invention , the desired angular position for the ri ng gear to come to a stop is selected as the angular position associated with the slot having the lowest value stored therein . Even wear is thereby further promoted . According to one embodiment of the invention , the desired angu lar position for the ri ng gear to come to a stop is further selected based on an angu lar position of the ring gear upon receipt of the signal to stop the internal combustion engine. The dispersion of wear on the ring gear can thereby be improved without having to interfere substantially with the time that it takes for the engine to come to a stop, since the engine can be stopped i n a stoppi ng position which is close to a position in wh ich the engi ne would stop without stoppi ng control , but associated with a fewer nu mber of stops.

According to one embodi ment of the invention , the method further comprises testi ng said signal to stop the internal combustion engine agai nst an implementation criterion , wherein the step of controlling the at least one valve such that the ring gear comes to a stop i n the desired angular position is carried out only if the implementation criterion is fulfi lled. Thus, i n certai n stopping situations, such as emergency stops and stoppi ng situations in which the engi ne is actively shut down usi ng a starter key, the engine can be stopped as fast as possible without stopping position control . The ang ular position of the ring gear as the engine has stopped may stil l be logged, so that it can be taken into accou nt during coming stops.

According to one embodi ment of the invention , the method further comprises:

- testing the vector against a service criterion ,

- given that said service criterion is fulfi lled, generati ng an error code.

The method can i n this embodiment be used to on one hand determine that the number of stops/starts is sufficiently large to indicate significant wear on the ri ng gear, which consequently needs to be substituted , and on the other hand signal this to e.g . a driver of a vehicle driven by the engine. Accordi ng to one embodiment of the invention , the at least one valve is actuated by means of a camshaft controlled by a camshaft control u nit. A valve actuating mechanism may, apart from the camshaft, also comprise a pushrod and/or a rocker arm . Variable valve control using a camshaft is a reliable and versatile way of actuating a valve. The camshaft control unit may e.g . a hydraul ic or pneumatic control unit controlled by an electronic control u nit of the engine. It is also possible to use electrically controlled valves.

The invention also relates to a computer program comprising computer prog ram code for causing a computer to implement the proposed method when the computer program is executed in the computer, a computer program product comprising a data storage medium which can be read by a computer and on which the program code of the proposed computer program is stored, an electron ic control unit of a motor vehicle comprisi ng an execution means, a memory con nected to the execution means and a data storage mediu m which is connected to the execution means and on which the computer program code of the proposed computer program is stored , and a motor veh icle comprisi ng the proposed electronic control unit.

Further advantages as well as advantageous features of the present invention will appear from the fol lowi ng detailed description .

BRI EF DESCRI PTION OF TH E DRAWINGS

Embodiments of the invention will i n the following be described with reference to the appended drawings, in which :

Fig . 1 schematically shows parts of an internal combustion engine

Fig . 2 schematically shows a model of a ri ng gear,

Fig . 3 is a flow chart showing a method accordi ng

embodiment of the invention , and

Fig . 4 schematically shows an electronic control u nit. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The number of cylinders of an internal combustion engine may vary depending on application. For a heavy motor vehicle such as a bus or a truck, the engine commonly has between 4 and 8 cylinders. A cylinder 1 of such an engine is schematically shown in fig. 1. The cylinder has a combustion chamber 2, an intake valve 3 and an exhaust valve 4. A movable piston 5 is connected to a flywheel 6 via a connecting rod 7 and a crankshaft (not shown). A ring gear 8 is provided on the flywheel 6 and a starter motor 9 has a pinion 10 adapted to be brought into meshing engagement with a portion 16 of the ring gear 8 and initiate rotation of the flywheel 6. A rotational speed sensor 11 is provided for sensing a rotational speed of the flywheel 6 as well as an angular position of the ring gear 8. The rotational speed sensor 11 is connected to an electronic control unit 12 configured to control the engine.

A valve actuating mechanism including a camshaft 13 is used to control the exhaust valve 4 via a camshaft control unit 14 providing variable valve control. A camshaft position sensor 15 is used to sense the position of the camshaft 13. Another camshaft (not shown) is used to control the intake valve 3. The electronic control unit 12 uses input data from e.g. the rotational speed sensor 11 and the camshaft position sensor 15 to control the starter motor 9 and the camshaft 13 via the camshaft control unit 14. More specifically, the exhaust valve 4 is controlled by sending a signal from the electronic control unit 12 to the camshaft control unit 14, which in turn controls the camshaft 13 that actuates the exhaust valve 4. There are several different solutions for achieving variable valve control, which are well-known to a person skilled in the art and which will not be further explained herein.

The other cylinders of the engine (not shown) are also connected to the flywheel via the crankshaft, with the cranks angularly distributed on the crankshaft depending on the engine configuration. The camshaft 13 actuates the exhaust valves of several or all cylinders of the engine depending on engine configuration.

Fig.3 schematically illustrates a method according to the present invention. In a step 101, the ring gear 8 is modelled as a vector having a set number of slots for storing a value such as schematically shown in fig.2. Each slot of the vector is associated with a specific angular position of the ring gear 8. For example, for a ring gear having 158 teeth, the vector may have 158 slots or less, depending on the desired and achievable resolution. Each slot thereby corresponds to an angular sector of the ring gear 8. The vector is intended for storing the angular positions of the ring gear 8 corresponding to the stopping positions of the engine. Each time the engine comes to a stop, the angular position of the ring gear is sensed and a value in the corresponding slot of the vector is increased by one, or by another predetermined amount. The modelling of the ring gear 8 as a vector is carried out in advance and the model is stored in e.g. a data storing medium within the electronic control unit 12.

In a step 102, a signal to stop the engine is received in the electronic control unit 12. The signal is in a step 103 tested against one or more implementation criterions. In this test, the origin of the stopping signal is checked , and based on the outcome, it is decided how to proceed. For example, for an internal combustion engine of a vehicle having a bodywork fitted, it can be checked whether the signal origi nates from an emergency stop of the bodywork or from a forced sh utdown using a starter key, in which cases the implementation criterion is not considered fulfilled and the engine is stopped as soon as possible in a step 1 04. If instead the stopping signal is automatically generated , such as when the veh icle makes a short stop at a red l ight, the i mplementation criterion is considered fulfilled .

In case the implementation criterion is fu lfil led, a step 1 05 is carried out. In this step, a desired ang ular position for the ring gear 8 to come to a stop is selected based on the values stored in the model of the ring gear 8, i .e. the vector. For example, if it is found that a certain slot of the vector holds a relatively small number, it may be considered desirable to come to a stop in the angular position of the ri ng gear 8 corresponding to this slot. The step 1 05 of selecting a desired angular position can be carried out in different ways. For example, the desired angular position can be selected as the ang ular position associated with a slot of the vector that has the smallest number stored therei n , regardless of where th is angular position is located with respect to a current angular position of the ri ng gear or with an angular position i n which the engine would come to a stop if stopped without stopping control . The desi red angular position can also be selected as one associated with a slot that holds a number smaller than average, or sim ilarly. It can furthermore be selected based in part on the current angular position of the ring gear as the signal to stop is received such that the rotation of the flywheel 7 can be stopped relatively fast. In this case, the ring gear 8 may be stopped in an angular position corresponding to a slot which is relatively close to the angular position in which the ring gear would stop without stopping control, but which holds a smaller number.

In a step 106, the exhaust valve 4 is controlled such that the ring gear 8 comes to a stop in the desired angular position selected in the step 105. This is carried out by forcing the exhaust valve 4 open during the compression phase of the cylinder 1 such as shown in fig. 1. The pressure within the combustion chamber 2 is thereby reduced and the flywheel will keep rotating past a position in which it would normally stop. Depending on the desired stopping position, the duration and timing of the opening as well as the number of cylinders 1 in which the exhaust valves are opened can be varied. The portion 16 of the ring gear 8 that faces the starter pinion 10 as the engine has come to a stop is varied as the stopping position is varied. Regardless of whether the engine has been stopped in accordance with step 104 or in accordance with steps 105-106, a step 107 is carried out when the flywheel 7, and thereby also the ring gear 8, have come to a stop. In this step, a current angular position of the ring gear 8 is sensed using the rotational speed sensor 11, and the value stored in the associated slot of the vector is increased by a predetermined amount. Thus, a slot associated with a stopping position in which the engine has stopped a large number of times will hold a larger number than a slot associated with a stopping position in which the engine has stopped only a few times. The vector thereby represents the distribution of stops on the ring gear 8.

The next time a signal to stop the engine is received in the electronic control unit 12, steps 103-107 are repeated. The previous stopping positions of the engine are thereby taken into account when selecting a desirable stopping position.

The method according to the invention may also include testing the vector against a service criterion, and given that said service criterion is fulfilled, generating an error code. The service criterion can be set to be fulfilled e.g. when the total number of stops exceeds a predetermined threshold value, and/or when the number of stops in a certain stopping position exceeds a threshold value. The error code can be used to generate a signal to e.g. a driver of a vehicle propelled by the engine that a service needs to be carried out.

Computer program code for implementing a method according to the invention is suitably included in a computer program which is readable into an internal memory of a computer, such as the internal memory of an electronic control unit of a motor vehicle. Such a computer program is suitably provided through a computer program product comprising a data storing medium readable by an electronic control unit, which data storing medium has the computer program stored thereon. Said data storing medium is for example an optical data storing medium in the form of a CD-ROM- disc, a DVD-disc, etc., a magnetic data storing medium in the form of a hard disc, a diskette, a tape etc., or a Flash memory or a memory of the type ROM, PROM, EPROM or EEPROM. Fig. 4 illustrates very schematically an electronic control unit 40 comprising an execution means 41, such as a central processor unit (CPU), for executing a computer program. The execution means 41 communicates with a memory 42, for example of the type RAM, through a data bus 43. The control unit 40 comprises also a non-transitory data storing medium 44, for example in the form of a Flash memory or a memory of the type ROM, PROM, EPROM or EEPROM. The execution means 41 communicates with the data storing medium 44 through the data bus 43. A computer program comprising computer program code for implementing a method according to the invention is stored on the data storing medium 44.

The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.