The present invention relates to the propulsion of vehicles , and in particular to a method during the changing of gears according to the introduction to claim 1. The invention

concerns also a system and a vehicle, and also a computer program and a computer program product, that implement the method according to the invention.

Background to the invention The background description below constitutes background

description for the invention and thus does not necessarily describe prior art technology.

A number of different propulsion chain configurations are used with respect to vehicles in general. A gearbox, for example, may be constituted by a manually changed gearbox or an

automatically changed gearbox. With respect to heavy vehicles, it is often desirable that they should be propelled in a manner that is as comfortable as possible for the driver, which normally means that changes of gear in the gearbox should be carried out automatically, with the aid of the control systems of the vehicle. The use of automatic gearboxes in heavy

vehicles has, therefore, become evermore common.

Automatic gear changing for heavy vehicles is often constituted by a change of gear of "manual" gearboxes in which the change operation is controlled by a control system. Such gearboxes thus consist of one pair of cogged wheels for each gear, where the gear ratios are distributed at appropriate intervals. This type of gearbox has the advantage that the gearboxes often demonstrate a higher efficiency than that of conventional automatic gearboxes. A clutch is used with such gearboxes, which clutch may be constituted by a clutch that is controlled automatically by the control systems of the vehicle, in order to couple the engine of the vehicle to the gearbox.

In principle, the clutch in such vehicles needs to be used only during start of the vehicle from, stationary, since othe gear changing can be carried out by the control systems of the vehicle without the clutch being opened. In the cases in which the clutch is constituted by an automatic clutch controlled by the control systems of the vehicle, however, the clutch is often used to open and close the propulsion chain also during change of gear.

Independently of whether the clutch is used during change of gear or not, it is required, in order to obtain as comfortable a change of gear as possible, that the driving force in the propulsion chain duri g- the change of gear, and thus also the associated interruption in driving force during change of gear, are controlled in such a manner that undesired jerking motion does not arise, while at the same time it is often desirable that the change of gear can be carried out with a relatively short interru t. ion in driving torce .

Summary of the invention

It is one purpose of the present invention to provide a method for the propulsion of a vehicle in which regulation of the rate of revolution of the combustion engine during change of gear is carried out in such a manner that makes possible both rapid and predictive regulation, while at. the same time a desired driving force is available after the change of gear. This purpose is achieved with a method according to claim 1.

The present invention relates specifically to a method for the propulsion of a vehicle, whereby the said vehicle comprises a combustion engine and a gearbox that can be adjusted to a number of gear ratios for the transfer of a force between the said combustion engine and at least one driving wheel, whereby the said, combustion engine comprises at least, one combustion chamber with at least one inlet for the supply of combustion gas and at least one outlet for the evacuation of an exhaust gas flow that has resulted from combustion in the said

combustion chamber, further comprising a turbocharger unit for the pressurisation of the said combustion gas.

The method comprises, during the change of gear from a first higher gear ratio to a second lower gear ratio, where the rate of revolution of the combustion engine is reduced from a first rate of revolution to a second rate of revolution, the

following :

- to increase the pressure at the said outlet at least through the use of the turbocharger unit for constriction of the said exhaust gas flow, - to reduce the pressure at the said combustion gas through the opening of a first valve, and

- to control, when the rate of revolution of the said

combustion engine has at least partially fallen towards the said second rate of revolution, the said turbocharger unit such that the said combustion gas pressure is increased.

As has been mentioned above, gearboxes of the type that is normally used in manually geared vehicles are often used for heavy vehicles, where the change of gear is, however, carried out automatically by the control systems of the vehicle. Change of gear from one gear ratio to a second with this type of gearbox comprises by its nature the interruption of the

propulsion chain when the currently engaged gear is disengaged, and its subsequent reconnection when a new gear has been engaged .

The rate of revolution of the combustion engine must, however, be synchronised with (i.e. it must be controlled by} the expected, rate of revolution of the input shaft of the gearbox with the new gear engaged, before the propulsion chain is reconnected, such that undesired jerks or oscillations do not arise during the change of gear. This change - the

synchronisation - of the rate of revolution of the combustion engine can be carried out in several ways .

For gearing down, it can be carried out by accelerating the combustion engine with the aid of the supply of fuel, while the opposite can be carried out for gearing up to a higher gear, i.e. change of gear to a lower gear ratio, in that the

combustion engine must be braked to the lower rate of

revolution of the input shaft, to the gearbox at the new

(higher) gear. A clutch, for example, can be used during the change of gear, whereby the clutch can be used for

synchronisation of the rate of revolution of the combus,-i.on engine. In the case in which the clutch is used for

synchronisation of the rate of revolution of the combustion engine, however, this is preferably carried out with a slipping clutch in order to avoid jerks and oscillations in the

propulsion chain. It may, however, be desirable to carry out the change of gear without slipping the clutch, for example, to reduce wear. It may be desirable also to carry out change of gear without any use of the clutch at all, i.e. to use a process in which the prevalent gear is disengaged, after which the rate of revolution of the combustion engine is synchronised before a new gear is engaged, whereby, in combination with a suitable relief of torque, also change of gear without the use of the clutch can be carried out without jerks. Furthermore, it is often desirable to carry out the change of gear as rapidly as possible, while at the same time the ease of driving and the comfort of the vehicle are retained. It may, therefore, be desirable to brake the combustion engine by another method than with the aid of the clutch, and the present invention provides a method to brake the combustion engine during- gearing up that makes possible an efficient- braking of the combustion engine to a desired rate of

revolution, which in turn makes possible a change of gear with a relatively short interruption in driving force. The invention has, furthermore, the advantage that a large driving force becomes rapidly available if required after the change of gear.

Braking of the combustion engine is achieved, according to the invention, by increasing the pressure at the outlet of the combustion chamber at. least through the use of the said

turbocharger unit for constriction of said exhaust gas flow, by, for example, constricting the exhaust gas flow by means of the turbine of the turbocharger unit such that the pressure at the outlet of the combustion chamber is increased. Furthermore, the turbine can be regulated during the said constriction of the exhaust gas flow such that the rate of revolution of the turbine, amounts to, for example, a rate of revolution in the interval 30-100% of the maximum working rate of revolution of the turbine, or, for example, a rate of revolution in the interval 80-100% of the maximum working rate of revolution of the turbine, i.e. the maximum rate of revolution at which the turbine is allowed to rotate during propulsion of the vehicle.

Furthermore, the pressure at the said combustion gas is reduced through the opening of a first valve that acts against the said inlet pressure, whereby the inlet pressure can be reduced to, for example, the pressure that surrounds the vehicle. The valve may be constituted by, for example, a blow-off valve that is conventionally present at turbocharger units, or another suitable valve by which a reduction in pressure to the pressure that surrounds the vehicle (atmospheric pressure) can be achieved, for the combustion gas at the said inlet. In summary, this results in a high differential pressure across the

combustion engine, with an efficient braking associated with this .

A high differential pressure across the combustion engine is achieved by these measures, whereby a corresponding relatively large braking force is obtained with which the rate of

revolution of the combustion engine can be reduced, whereby the rate of revolution of the combustion engine can be efficiently reduced to the desired rate of revolution.

It is, however, desirable during change of gear not only that the rate of revolution of the combustion engine is braked in a short period to the desired rate of revolution, but also often that a high torque can be delivered by the combustion engine immediately after, or essentially immediately after, the change of gear has been carried out. This, however depends on the availability of compressed combustion gas, such as air, i.e. a high inlet pressure is required, which is, as we have seen, not desirable from the point of view of braking the engine. The present invention, however, makes possible efficient braking of the combustion engine during the synchronisation while at the same time a high extraction of torque is made possible

immediately after, or essentially immediately after, the change of gear. This is achieved by first reducing the inlet pressure, and subsequently to start an increase in the inlet pressure before the propulsion chain Cj ^' eli closed. Si ce an increase in pressure of the combustion gas is started before the new gear has been engaged and the propulsion chain has again been connected, combustion gas under pressure will available

immediately after the propulsion chain has been connected after the change of gear such that a higher driving force can be made available . According to one preferred embodiment, an increase in pressure of the combustion gas is started before the rate of revolution of the combustion engine has fallen to the said second rate of revolution . By maintaining the rate of revolution of the turbine, and thus also the rate of revolution of the compressor, at a high level during the reduction in the rate of revolution of the

combustion engine, it is possible subsequently to increase rapidly the pressure of the combustion gas in order in this way to make possible a large torque, if this is required after the change of gear, which often can be the case, for example when the gearing up has been caused by the vehicle undergoing an increase in speed. According to one embodiment of the present invention, the said turbine is first closed in order to obtain as rapid build up of pressure as possible at the outlet of the combustion chamber before the inlet, pressure is reduced.

The turbine may be controlled during the reduction in the rate of revolution in such a manner that its speed of rotation is maintained, at a high speed of rotation, such as, for example, a maximum speed of rotation or a speed of rotation that amounts to, for example, a freely chosen speed of rotation in any one of the intervals 50-100% or 80-100% of the maximum speed of rotation of the turbine during propulsion of the vehicle. By maintaining a high speed of rotation of the turbine, and thus also a high speed of rotation of the compressor, it will be possible to make compressed air rapidly available when the said first valve is closed, whereby compressed air can be made available essentially immediately when driving force is again required. The said first valve can be kept open during the period that a low inlet pressure is desired, and it can be closed when an increase of the inlet pressure is required, whereby a rapid build up of pressure is obtained since the compressor can already rotate at the desired speed.

Furthermore _. , the said outlet pressure may be arranged not only to be regulated with the aid of the said turbine, but. also, for example, together with a constriction device located downstream of the turbine, such as, for example, an exhaust gas brake sys tern .

The method according to the present invention can be

implemented with the aid of, for example, at least one of: one or several processors, one or several FPGA (field-programmable gate array) circuits, and one or several ASICs (application- specific integrated circuit}.

Further characteristics of the present invention and its advantages will be made clear by the following detailed

description of embodiments given as examples, and the attached drawings .

Bxief descr p on of cLr&w nciS

Figure 1A shows schematically a vehicle on which the present invention can be used.

Figure IB shows a control unit in the control svst.em for the vehicle shown in Figure 1A.

Figure 2 shows schematically in more detail the post-treatment system for the vehicle shown in Figure 1A.

Figure 3 shows an example method according to the present

i vention .

Figure 4 shows an example of a reduction in rate of revolution according to the present invention.

Detailed description of ensbodiraents

Figure 1A shows schematically a propulsion chain in a vehicle 100 according to one embodiment of the present invention. The vehicle shown schematically in Figure 1A comprises only one axle with driving wheels 113, 114, but the invention can be applied also for vehicles in which more than one axle is provided with driving- wheels, and also for vehicles with one or several further axles, such as one or several support axles. The propulsion chain comprises a combustion engine 101, which is connected to a gearbox 103 through a clutch 106 in a

conventional manner, through an output shaft at the combustion engine 101, norma1.1y through a f1ywhee.1 102.

The combustion engine 101 is controlled by the control systems of the vehicle through a control unit 115. In the same manner the clutch 106, which may be constituted by, for example, a automatically controlled clutch, and the gearbox 103 are controlled by the control systems of the vehicle 100 with the aid of one or several suitable control units: in Figure 1A controlled, by the control unit 116. The propulsion chain of the vehicle 100 may, of course, be of another type.

An output shaft 107 from the gearbox 103 drives the driving wheels 113, 114 through a final gear 108 such as, for example, a conventional differential gear, and drive shafts 104, 105 connected to the said final gear 108. The present invention is applicable also for hybrid vehicles, where, in addition to a combustion engine, one or several further sources of power, such as one or several electric motors, can be used for

propulsion of the vehicle.

The vehicle 100 comprises further an exhaust gas system with a post-processing system 230 for the processing (cleaning) of exhaust emissions that result from the combustion in the combustion chamber of the combustion engine 101.

Figure 2 shows the combustion engine 101 in somewhat greater detail. There is shown in the drawing only one

cylinder/combustion chamber 209 for the combustion engine 101, with a piston 210 that operates within the cyli der, but the combustion engine 101 is constituted in the present example by a six-cylinder combustion engine, and it may generally be constituted by an engine with a freely chosen number of

cylinders/combustion chambers, such as, for example, a freely chosen number in the interval 1-20, or even more. Combustion engines of the type shown generally comprise also at least one fuel injector 208 for each combustion chamber (cylinder} 209, which fuel injectors supply in conventional manner fuel to the said combustion chamber 209 for combustion.

Furthermore, each combustion chamber 209 comprises an inlet 201 for the supply of combustion gas, which is generally

constituted at least partially by air, to the combustion process, through an inlet suction line 211, and an outlet 202 for the tion of the exhaust gas flow that results from the combustion. The supply of combustion gas and the evacuation of the combustion chamber may be controlled in conventional manner by, for example, valves 212, 213.

The exhaust gases (the exhaust gas flow} that are generated during the combustion are subsequently led through a

turbocharger unit 203 and an exhaust gas brake system 215 to the post-processing- system 230 for the post-processing

(cleaning} of the exhaust, gas flow before the exhaust, gases are released into the surroundings of the vehicle 100. The post- processing system 230 may comprise in conventional manner, for example, at least one of diesel particle filters, oxidation catalysers and SCR catalysers. The post-processing system may comprise also several and other types of component, as is well- known to one skilled in the arts. The post-processing system is not described in detail here.

The use of the turbocharger unit according to Figure 2 means, furthermore, that the combustion engine 101 becomes supercharged, i.e. the pressure of the combustion gas supplied to the combustion chambers exceeds the pressure that surrounds the vehicle 100.

This supercharging is achieved in the present, example with the aid of the turbocharger unit 203, which comprises a turbine 204 and a compressor 205 that is driven by the turbine 204 through a shaft 207, The compressor 205 compresses, i.e. places under ^¬ pressure, gas that is supplied through an inlet. 206, such as air from the surroundings of the vehicle, possibly also

together with conventional recirculation of exhaust gases, known as EGR (not shown in the drawings} , for supply to the said, inlet, suction line 211. The ability of the compressor 205 to compress incoming air is controlled by the force or speed with which the turbine 204 rotates. The turbine 204 is, in turn, driven by exhaust gases, which means that its force or speed of rotation is controlled by the passing exha st gas flo .

The turbocharger unit 203 that is shown is of a type with fixed geometry, which means that the exhaust gas flow that, passes the turbine is used for driving of the same. Since, however, it is often desirable that the turbine, and thus also the pressure of the combustion gas, can be regulated, the solution shown in Figure 2 is provided with means to make such a regulation possible. These means are constituted in the example shown by what is known as a wastegate valve 220, which can regulate in a controllable manner the fraction of the exhaust gas flow that results from the combustion that, actually passes, and this drives, the turbine 204. This regulation is carried out by diverting in a manner that can be controlled with the aid of the wastegate valve 220 a fraction of the exhaust gas flow past the turbine 204, whereby the speed of rotation of the turbine can be regulated with the aid of the wastegate valve 220 to the desired rate of revolution, which is normally constituted by a very high rate of revolution, such as, for example, a rate of revolution of the magnitude of 100,000-200,000 rpm.

The solution shown in Figure 2 comprises also what is known as a blow-off valve 221, that acts against the high-pressure side of the compressor 205, and that can be used when required to reduce rapidly the pressure P _in of the combustion gas. The blow-off valve 221 may be of a different type, as is known, and it may be constituted by, as is indicated in Figure 2, a recirculating blow-off valve, which means that combustion gas from the high-pressure side of the compressor is recirculated to the low-pressure side of the compressor, whereby the

pressure at the high-pressure side of the compressor 205 is reduced .

The blow-off valve may be also of atmospheric type, i.e.

combustion gas from the high-pressure of the compressor is released into the surroundings of the vehicle. The blow-off valve may be also of a type that combines both of the functions described above, i.e. combustion gas from the high-pressure side can either be released into the surroundings or

recirculated, or released into the surroundings and

recirc la ed. The combustion gas may be arranged also to be released, into the exhaust, gas system, in order to make possible reduction of the noise that can arise during large and sudden changes in pressure.

The operation of the said turbocharger unit 203 is used, according to the present, invention, during the control of the change of gear in which change of gear takes place from a lower gear to a higher gear (i.e. from a higher gear ratio to a lower gear ratio) . As has been mentioned, above, it is generally true that the rate of revolution n of a combustion engine changes during change of gear, where change of gear from a lower gear to a higher gear leads to the rate of revolution n of the combustion engine becoming lower by a rate of revolution that corresponds to the change in gear ratio, and possibly also change of speed of the vehicle during the change of gear.

During change of gear to a higher gear during propulsion of the vehicle, it is often desirable that the change of gear can be carried out in a short period, for example, in order to avoid interruption in the supply of driving force. The present invention concerns a method to brake the rate of revolution of the combustion engine in an efficient manner from the rate of revolution of the previous gear to the rate of revolution of the new gear, during change of gear to a higher gear. An example method 300 according to the present, invention is shown in Figure 3, where the method 300 according to the present example is arranged to be carried out by the engine control unit 115 shown in Figures 1A and IB.

Control systems in modern vehicles generally consist of a communication bus system that consists of one or several communication buses in order to connect a number electronic control units (ECUs) such as the control units, or controllers, 115, 116, and various components arranged at the vehicle. Such a control system may comprise a large number of control units, and the responsibility for a particular function may be

distributed among more than one control unit. Furthermore, the invention may be implemented in a control unit dedicated to the present invention, or fully or partially implemented in one or several other control units that are already present at the vehicle. For reasons of simplicity, only the control unit. 116 is shown in Figures 1A and IB, in addition to the engine control unit 115.

The operation of the control unit 115 (or of the control unit or units in which the present invention has been implemented) according to the present invention may depend, for example, on signals from, for example, the control unit 116 with respect to, for example, the status of the clutch or gearbox. Signals may also be sent in a similar manner to the control unit 116. Control of the control unit. 115 may depend also on sensor- signals with respect to, for example, the turbocharger unit 203, such as, for example, its speed of rotation, the wastegate ^' valve 220, or the blow-off valve 221, as described below. It is generally the case that control units of the type shown are normally arranged to receive sensor signals from various parts of the vehicle, such as from various control units arranged at the vehicle.

The control is often controlled by programmed instructions. These programmed instructions are typically constituted by a computer program, which, when it is executed in a computer or control unit, ensures that the computer or co trol unit, carries out the desired control, such as the method steps according to the present invention.

The computer program normally constitutes part of a computer program product, where the computer program product comprises a suitable storage medium 121 (see Figure 13) with the computer program stored on the said storage medium 121. The said digital storage medium 121 may be constituted by, for example, any one of the group: ROM (Read-Only Memory), PROM (Programmable Read-- Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM

(Electronically Erasable PROM), a hard disc unit, etc., and it. may be arranged i or in connection with the control unit, whereby the computer program is executed by the control unit. Thus, the behaviour of the vehicle in a particular situation can be adapted by changing the instructions of the computer program. An example control unit (the control unit 115} is shown

schematically in Figure IB, whereby the control unit may in turn comprise a calculation unit 120, which may be constituted by, for example, any appropriate type of processor or

microcomputer, such as, for example, a circuit for digital signal processing (a digital signal processor, DSP) , or a circuit with a predetermined specific function (an application- specific integrated circuit, ASIC) . The calculation unit 120 is connected to a memory unit 121 that supplies the calculation unit 120 with, for example, at least one of the stored program code and the stored data that the calculation unit 120 requires in order to be able to carry out calculations. The calculation unit 120 is arranged also to store the intermediate or final results of calculations in the memory unit 121.

The control unit is further provided with arrangements 122, 123, 124, 125 for the reception a d transmission of i put and output signals. These input and output signals may contain waveforms, pulses, or other properties that can be detected by the arrangements 122, 125 for the reception of input signals as information to be processed by the calculation unit 120. The arrangements 123, 124 for the transmission of output signals are arranged to convert calculation results from the

calculation unit 120 into output signals for transfer to at least one of other parts of the control systems of the vehicle and the component or components for which the signal is

intended. Each one of the connections to the arrangements for reception and transmission of input and output signals may be cons11.1uted by 1 of a cable; a computer bus, such as a CAN bus (controller area network bus} , a MOST bus (media- oriented systems transport} , or any other bus configuration; or a wireless connection. Consider again Figure 3, which shows an example method 300 according to the present invention. The method starts at step 301, where it is determined whether change of gear upwards is to take place. The method continues to step 302 if this is the case. It is determined in step 302 whether the combustion engine 101 has been disengaged from the driving wheels 113, 114 of the vehicle 100, which may be carried out by, for example, opening the clutch 106 or by placing the gearbox 103 into its neutra1 con.d.ition . One purpose of the present invention is to reduce the rate of revolution of the combustion engine 101 to the desired rate of revolution as rapidly as possible, i.e. to minimise the time it takes for the combustion engine to reach the desired rate of revolution, where this desired rate of revolution is

constituted by the synchronisation rate of revolution for the gear that is to be engaged.

This is made clear in Figure 4, where a diagram of the rate of revolution n of the combustion engine as a function of time is shown. The vehicle 100 is driven until time ti at a speed, that. results in a rate of revolution m of the combustion engine, shown by the continuous line. If the vehicle is undergoing acceleration and is not being driven at a constant speed, the rate of revolution increases before the change of gear, which is indicated by the dashed line in the drawing. Change of gear to a higher gear is initiated at time ti (or at a suitable time before this) , with the consequence that the rate of revolution of the combustion engine is to be reduced from, the rate of revolution n to the rate of revolution n ₂ . The more rapidly that the rate of revolution of the combustion engine can be reduced to n ₂ , the more rapidly can the change of gear be carried out. The reduction in the rate of revolution is achieved, according to the present invention, through braking of the combustion engine 101.

According to the present invention, this braking is achieved through an increase in the differential pressure &P _motor across the combustion engine, i.e. an increase in the difference in pressure between the inlet pressure P _jn and the outlet pressure R,, of the combustion chambers 209 (see Figure 2). The higher that this difference in pressure is, i.e. the higher that the outlet pressure P _w is relative to the inlet pressure/',, the more rapidly will the combustion engine 101 be braked to the desired rate of revolution n ₂ .

The method continues subsequently to step 303, where the outlet pressure P _ul is increased through the closing of the astegate valve 220, whereby a back pressure will arise upstream of the turbine 204 from the constriction that the turbine 204

constitutes, and thus also at the outlet 202 of the combustion chamber 209, and which back pressure will brake the combustion engi e 101.

There are normally design limitations on how high a pressure can be allowed upstream of the turbine 204, for example, of a magnitude of 4-10 bar, for which reason the outlet pressure P _ut can be regulated against a reference pressure P _{ut ref} . The outlet pressure P _ut can be determined with the aid of a suitable pressure sensor arranged upstream of the turbine 204, in such a position as, for example, the outlet of the combustion engine 101 or at any other suitable location upstream of the exhaust gas brake s stem.. The outlet pressure may be arranged to be determined also with the aid of, for example, a cylinder pressure sensor. The outlet pressure may be arranged also to be estimated based on an appropriate calculation model, for example based on a pressure measured at. another suitable position in the system or based on another measured parameter, through the use of which it is possible to calculate the outlet pressure. It is generally the case that the higher that this back pressure is, the stronger will be the brake effect, and thus the more rapid will be the reduction in the rate of revolution of the combustion engine.

When the outlet pressure P _ut is increased with the aid of the turbine 204 and by the closing of the wastegate valve 220 this leads at the same time to the turbine 204 accelerating. A maximum rate of rotation for the turbine has normally been defined that should not be exceeded for reasons of, for example, strength. This maximum can be rapidly reached when a large part of, or the complete, exhaust gas flow is led through the turbine 204 when the desired outlet pressure P _ut is to be reached. The turbine 204 may, for this reason, be arranged to be regulated against the said maximum rate of rotation. As an alternative, the regulation of the turbine 204 may be so arranged that the rate of rotation of the turbine 204 amounts to, for example, a rate of revolution in the interval 30-100% of the maximum rate of rotation of the turbine 204, or, for example, a rate of revolution in the interval 80-100% of the maximum rate of rotation of the turbine 204, i.e. the maximum rate of revolution at which the turbine 204 is permitted to rotate during propulsion of the vehicle. The rate of rotation of the turbine 204 is controlled by the exhaust gas flow that passes through the turbine. This is regulated by the use of the wastegate valve 220, which diverts in a manner that can be controlled a part of the exhaust gas flow past the turbine 204, whereby an exhaust gas flow through the turbine can be obtained that results precisely in a desired speed of rotation of the turbine. Thus the wastegate valve 220 can be controlled based on the currently prevalent speed of rotation of the turbine.

It is, however, not guaranteed that the desired outlet pressure P _ut , which in this case is relatively high, can be obtained without exceeding the desired speed of rotation of the turbine 204, i.e. the back pressure that can be generated by the turbine is not necessarily sufficient to obtain the desired outlet pressure P _ut . Furthermore, it may be the case for certain combinations of combustion engine and turbocharger unit that, even if the desired pressure can be obtained, it may not be possible to maintain this when the load on the compressor is relieved., as described below.

For this reason, a further throttle valve arranged, according to one embodiment, in the exhaust gas system of the vehicle 100, which throttle valve may be constituted by, for example, the exhaust gas brake system 215, may be also used during the regulation. The exhaust gas brake system 215 is arranged downstream of the combustion engine 101, and is in the present example arranged also downstream of the turbocharger unit 203. The exhaust gas brake system 215 applies on request a

controllable constriction of the exhaust gas flow, whereby this constriction gives rise to a back pressure upstream of the exhaust gas brake system. 215. Thus the pressure on the low- pressure side of the turbine 204 can be raised with the aid of the exhaust gas brake system 215, whereby the difference in pressure across the turbine 204 can be reduced while the desired outlet pressure P _ut can at the same time be maintained at the outlet of the combustion chambers for the braking of the motion of the pistons in the combustion chambers, while also at the same time the desired speed of the turbine can be

maintained with, the aid of suitable regulation of the exhaust gas brake system 215 and the wastegate valve 220, Instead of using the exhaust gas brake, or in addition to using the exhaust gas brake, also a compression brake (also known as a decompression brake) may be used during braking of the combustion engi e. When usi g- a compression brake, the braking force during compression in the combustion chambers of the combustion engine can be used. Air is drawn in during

compression braking and compressed in a conventional manner, but the outlet valves are opened when the pistons reach or approach top dead centre in order to reduce the pressure of the combustion chamber, whereby the force generated by the

compressed gas is not used during the subsequent expansion. This has the advantage also that an exhaust gas flow with higher energy in the form of higher pressure or temperature is obtained, which may be used, for example, to maintain to a higher degree the rate of revolution of the turbine at the desired rate of revolution, with the consequence that the desired driving force can be obtained more rapidly after change of gear since also an increase in pressure of the combustion air pressure can in this way be carried out. Furthermore, the higher energy content means that it is possible for the

compressor to place a greater load on the turbine since a larger force can be used to drive the turbine during the build up of pressure of the combustion air pressure.

Furthermore, when the desired outlet pressure has been

obtained, or when the desired outlet P _ut has partially been obtained to an appropriate extent, the method continues to step 304, in which the combustion gas pressure is reduced, i.e. the pressure at the inlet. 201 to the combustion chambers 209 is reduced. It would be possible to regulate the inlet pressure P _in by regulating the speed of rotation of the compressor 205, i.e. by regulating the speed of rotation of the turbine 204, whereby it would be possible to control the turbine 204 in such a manner that compression of combustion gas is no longer carried out, or is carried out only to a very small extent, in order in this way to control the inlet pressure P _jn towards essentially the pressure that surrounds the vehicle 100, or at least a lower pressure than the pressure that is prevalent at time ti.

Such a regulation of the compressor or turbine, however, requires regulation towards a very low rate of rotation of the compressor or turbine, which thus constitutes a conflicting desire to the regulation described above, in which the turbine is controlled towards as high a rate of revolution as possible. For this reason, the regulation of the pressure of the

combustion gas is instead carried out with the aid of the blow- off va1ve 221.

The blow-off valve 221 is thus opened in step 304, which means that the pressurised combustion gas is recirculated to the inlet side of the compressor, whereby the inlet pressure Pi _n can be reduced to the pressure that, is prevalent on the i let side of the compressor, which is normally constituted by essentially atmospheric pressure.

A relatively high differential pressure across the combustion engine 101 can thus be achieved, which results in a relatively large braking force, at least when compared with that obtained by allowing the rate of revolution of the combustion engine 101 to fall to the idling rate of revolution without any load. This braking force will brake the combustion engine 101 towards the desired lower rate of revolution n? .

It should be noted also that in the method described above the outlet pressure is first raised, after which the pressure at the inlet is reduced. This leads to a rapid increase in

pressure being obtained through the compressor 205 continuing to compress combustion gas and in this way carrying out. work, which place a braking load onto the turbine 204, which thus also will brake with a greater force, when compared with that, exerted by a turbine 204 that is not under load, the exhaust gas flow that passes through the turbine 204, whereby the outlet pressure p _ut can be built up during a shorter period. The build up of pressure is promoted also in that the greater exhaust gas flow, to which the pressurised inlet pressure continues to contribute during the build up of pressure.

The steps 303 and 304, however, can be arranged in an

alternative embodiment to be carried out in the reverse order, or at the same time. This alternative embodiment is valid in particular in those cases in which also the exhaust gas brake 215 is used during the regulation of the outlet pres sure t^ _t ·

It is subsequently determined in step 305 whether the rate of revolution n _mot0 r has been reduces to a rate of revolution η _ί1Κί · The rate of revolution n _]im is constituted by a rate of

revolution that lies below the rate of revolution m and lies above the rate of revolution n ₂ . It is preferable that the rate of revolution n _iiC1 lie closer to the rate of revolution ₂ than the rate of revolution m . The rate of revolution r im may be so arranged, for example, that it is constituted by a rate of revolution in which a freely chosen fraction in the interval 50-90%, or 70-95%, of the total change of rate of revolution ηχ-Π2 that the combustion engi e is to u dergo has bee carried out. This is indicated schematically in Figure 4 at time t _a . Instead of determining in step 305 whether the rate of

revolution of the combustion engine 101 has reached a certain rate of revolution r im, it can be determined whether the synchronisation is expected to be completed within a certain time, i.e. when the synchronisation has reached, for example, the time t _a in Figure 4, where the synchronisation is expected to be completed when a time t ₂ -t _a has passed. No explicit determination of the rate of revolution of the combustion engine 101 is thus required, according to this embodiment. It may be desirable that the combustion engine 101 is braked with an essentially constant braking power, i.e. an essentially constant differential pressure across the

combustion engine , and thus braked by linear braking as is shown in Figure 4, since it then can be easily estimated when the synchronisation is expected to be completed. In the case in which a. non-constant braking force is applied, the endpoint of the synchronisation can be calculated instead with the aid of an applicable model. Since constant braking force is obtained by maintaining a constant differential pressure, AP _rnotor , it is an advantage if the regulation can be so arranged that it acts during the regulation to maintain a constant P _ut =P _u t _re f and also a constant P _in .

When the rate of revolution of the combustion engine has subsequently reached nn _m , or the time t _a has been reached, or both the rate of revolution of the combustion engine has reached nlim and the time has reached ta, the method continues to step 306 in order to increase again the pressure P _in of the combustion air in order to ensure that the desired driving force is available or can become available rapidly when driving force is again required after the change of gear. This raising of the inlet pressure P _in takes place, according to the

invention, through closing the blow-off valve 221, whereby the compressor 205 will again build up the combustion gas pressure.

The rate of rotation of the turbine 204, and thus also the rate of revolution of the compressor 205, are maintained in the method described above at. a high level during the

synchronisation of the rate of revolution of the combustion engine 101 during the reduction of the rate of revolution of the combustion engine 101. This means that when the blow-off valve 221 is closed, it will be possible to raise very rapidly the pressure of the combustion gas since the compressor 205 can be arranged to rotate already at its maximum, or close to its maximum, speed of rotation in order to achieve the maximum, or close to the maximum, compression of the combustion gas. This makes possible, thus, that a large extraction of torque is possible, if required, immediately after a change of gear, which can often be the case, for example, when the change of gear upwards has been caused by the vehicle 100 undergoing an increase in speed.

The inlet pressure Pi _n may be arranged to be controlled towards a suitable inlet pressure, such as an inlet pressure that, was prevalent before the change of gear, or an inlet pressure that makes possible a build up of torque towards the maximum torque that can be developed by the combustion engine 101 with the desired rate of build up of torque when the propulsion chain is closed and driving force is again required.

The wastegate valve 220 and possibly also at least one of the exhaust gas brake system (the constriction device) 215 and the compression brake may be regulated at the same time during the regulation of the blow-off valve 221, not only to ensure that the exhaust gas flow through the turbine 204 is increased in order to deal with the increased load that arises when the work, carried out by the compressor 205 is increased when the blow- off valve is closed, but also at the same time such that the desired pressure condition, such as, for example, the outlet pressure P _ut or the difference in pressure across the turbine 204, is maintained, such that it is possible to achieve the desired rate of revolution of the turbine, and thus the desired compression .

An increased, inlet, pressure P-, _r , with a maintained outlet, pressure P _;t will, as will be realised, reduce the relative difference in pressure across the combustion engine 101, and thus also the braking force that acts on the piston 210. This, in turn, means that the combustion engine will no longer be braked with the same preferably linear reduction in speed that was obtained up until the time t _a . Either can consideration of this be taken during the calculation of the time t? at which the synchronisation is completed, through the use of, for example, an applicable model and, for example, determination of the variations of the inlet pressure and outlet pressure during the increase in inlet pressure, or can the rate of revolution of the combustion engine 101 be monitored in order to determine whether the synchronisation rate of revolution has been

reached .

According to one embodiment, the outlet pressure P _ut can be allowed temporarily to exceed the reference pressure P _u iop _P ref with a correspo ding increase i the inlet pressure Pi _n , in order in this way to maintain a constant differential pressure ^P across the combustion engine 101 during the complete, or at least during a major part of, the time period after t ₃ until the time in Figure 4. Whether or not this is possible depends, however, on tolerances for the components; it may, for example, be permitted to exceed for a short, period the

limitation on pressure at the outlet, which limitation applies to a pressure that is to be applied for a long period. The build up of pressure that has been initiated according to step 306 may be arranged to continue until it is determined in step 307 that the rate of revolution n _roo tor of the combustion engine has reached the synchronisation rate of revolution n?. As long as this is not the case, the method may remain in step 307 while the inlet, pressure is at the same time raised, whereby it. may be determined in step 307 also whether the inlet pressure Pin has reached the desired inlet pressure, in which case continued build up of pressure is no longer required, and whereby this can be taken into consideration during the

regulation .

The method is subsequently terminated in step 308 when the syn.chronisa.tion rate of revolution ri2 has been reached, whereby the propulsion chain can again be closed in a suitable

conventional manner, which is not within the scope of the present invention .

In summary, thus, the present invention provides a method that brakes in an efficient manner a combustion engine during gearing up by applying and preferably maximising a differential pressure across the combustion engine. The method at the same time provides good driving properties during propulsion of the vehicle by ensuring that a sufficiently high pressure of combustion gas is available immediately during the change of gear or shortly afterwards to make it. possible for the

combustion engine to supply a desired torque during propulsion of the vehicle.

The invention has been described in the description above in association with a turbocnarger unit. 203 with a turbine 204 of a type that has fixed geometry. According to one embodiment of the invention, a turbine with variable geometry is used

instead. Such, a turbine may be, for example, provided in known manner with several adjustable guide rails for the regulation of the amount of exhaust gas that is used to influence the turbine wheel, and. the amount of exhaust gas that is allowed to pass the turbocnarger unit without its energy being exploited for compression of the combustion air. The function of the turbine can thus be regulated with the aid of such adjustable guide rails, and the turbine can be, for example, regulated through the use of the guide rails as described above towards as high a rate of rotation as possible while the inlet pressure is at the same time held low by the blow-off valve. An exhaust gas brake system may be used during the regulation also in this case in order to obtain the desired pressure or speeds of rotation. However, a wastegate valve is not required accordinq to this embodiment, since the flow that is used to drive the turbine can also be regulated by the turbine.

Furthermore, the present invention has been described above for examples associated with vehicles. The invention may, however, be applied, at any freely chosen transport means or process in which a change of gear as described above is to be carried out, such as, for example, water-borne and airborne vessels with the change of gear process described above.

It should be noted also that the system can be modified

according to various embodiments of the method according to the invention (and vice versa) and that the present invention is not in any way limited to the embodiments of the method

according to the invention described above: it concerns and comprises all embodiments within the protective scope of the attached independent patent claims.