EP2914467A1

EP2914467A1 - Method for warming a vehicle component by increasing a load of an engine with a braking force

Info

Publication number: EP2914467A1
Application number: EP13851021.9A
Authority: EP
Inventors: Mathias Björkman; Niclas LEREDE
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2012-11-01
Filing date: 2013-10-30
Publication date: 2015-09-09
Also published as: EP2914467A4

Abstract

The present invention relates to a method for warming at least one vehicle component at a vehicle (100), which vehicle (100) is provided with a combustion engine (101) and with at least a first electrical machine (110), which first electrical machine (110) is arranged for selective exertion of a force upon an output shaft of said combustion engine (101). The method comprises applying to said output shaft of said combustion engine (101) a first braking force by use of said first electrical machine (110).

Description

METHOD FOR WARMING A VEHICLE COMPONENT BY INCREASING A LOAD

OF AN ENGINE WITH A BRAKING FORCE

Field of the invention

The present invention relates to a method for use at a

vehicle. The invention relates in particular to a method for warming at least one vehicle component at a vehicle according to the preamble of claim 1. The invention relates also to a system and a vehicle and to a computer programme and a

computer programme product which implement the method

according to the invention. Background to the invention

The background description set out below represents a

background description for the invention and therefore need not necessarily represent prior art.

Vehicles in general and at least to some extent heavy vehicles in particular are the subject of ongoing development with a view to fuel efficiency and reduced exhaust emissions.

Growing official concern about pollution and air quality, e.g. in urban areas, has led to the adoption of emission standards and rules in many jurisdictions. Such emission regulations often set requirements which define acceptable limits for exhaust emissions from vehicles equipped with combustion engines. They often govern for example levels of emissions of nitrogen oxides (NO_x) , hydrocarbons (HC) and carbon monoxide (CO) . These emission regulations usually also cover, for at least certain types of vehicles, the presence of particles in exhaust emissions.

With a view to meeting these emission requirements, the exhaust gases which engines produce by combustion are post- treated (cleaned) . It is for example possible to use a so- called catalytic cleaning process, in which case post- treatment systems, e.g. on vehicles and other means of

transport, usually also comprise one or more catalysts.

Such post-treatment systems often further comprise other components as alternatives to or in combination with the one or more catalysts. Post-treatment systems on vehicles with diesel engines for example often comprise particle filters to intercept soot particles formed during combustion. There are thus various methods for reducing emissions from a combustion engine . There are however situations in which undesirable exhaust emissions may nevertheless occur.

Summary of the invention

An object of the present invention is to propose a method for warming at least one vehicle component at a vehicle. This object is achieved by a method according to claim 1.

The present invention relates to a method for warming at least one component of a vehicle which is provided with a combustion engine and with at least a first electrical machine adapted to selectively exerting a force upon an output shaft of said combustion engine. The method comprises using said first electrical machine to apply a first braking force to said output shaft of said engine.

As mentioned above, it is desirable that exhaust emissions from vehicles be as far as possible prevented or reduced, e.g. by means of a post-treatment system. There are however situations, e.g. when starting a vehicle from cold, where undesirable emissions may occur because the temperature of the engine (the combustion chamber) is low. Injected fuel may for example condense, e.g. against walls of a cylinder when the temperature is low, and/or the combustion may in at least certain conditions be incomplete, resulting in the formation and emission of undesirable white smoke.

A combustion engine started from cold, particularly on heavy vehicles, may however take a relatively long time to warm up, particularly when idling. The warming process in situations such as idling may be speeded up by increasing the load upon the engine. For example, an exhaust brake may be employed to throttle the exhaust flow with increased engine load,

resulting in quicker warming of the engine. Regulating the exhaust brake may however be difficult to effect with

sufficient accuracy, e.g. in situations where at the same time the vehicle is beginning to move.

The present invention relates to hybrid vehicles and uses the hybrid portion to make quicker warming of their combustion engines possible. Hybrid vehicles use two or more power sources and a usual type of such vehicles is the electric hybrid vehicle, in which one or more electrical machines may be used to generate a force which acts upon the vehicle's tractive wheels. The electrical machine affords the advantage of being usable to convert electrical energy to a propulsive force with relatively high efficiency, while at the same time it may also be used to exert a braking force upon the

vehicle's tractive wheels and thereby regenerate electrical energy from absorbed kinetic energy for feedback to the vehicle's electrical system, and particularly to an energy store. The regenerated energy may thereafter be used by the electrical machine to generate a propulsive force.

According to the present invention the electrical machine is employed, after the combustion engine has been started, to apply a braking force to said output shaft of said engine. In this way the load upon the engine may be increased, e.g. in situations where it would for example otherwise have been idling or with only a very small load, resulting in quicker warming and/or more complete combustion of injected fuel. The invention affords the further advantage that the braking force, i.e. the engine-braking force, exerted by the

electrical machine will generate an electric current, making it possible for the absorbed braking energy to be taken over and fed back in electrical form to an energy store and/or be converted to heat for warming of one or more vehicle

components.

Compared for example with using an exhaust brake, the

invention also affords the advantage that the load applied can be calculated/controlled with great accuracy, which means that while the vehicle is in motion the engine can be controlled in such a way as also to result in desired propulsive force on the vehicle's tractive wheels. When the exhaust brake is activated while the vehicle is in motion, it may be difficult to ensure that desired propulsive force is also exerted upon the vehicle's tractive wheels, with the result that the activation of the exhaust brake is normally discontinued when propulsive force is demanded.

In one embodiment of the invention the combustion engine is only loaded by the electrical machine when the total load upon the engine from the electrical machine plus load from the vehicle's tractive wheels is below a certain level, e.g.

maximum 10-500 Nm, or a certain proportion of the engine's maximum torque.

The present invention proposes a method whereby the propulsive force on the vehicle's tractive wheels demanded for example by the vehicle's driver is fully or at least substantially maintained, but whereby the electrical machine imposes a further load upon the engine. This enables the engine to deliver more work to compensate for the braking force applied by the electrical machine, but in such a way that the

electrical machine and the engine can balance one another so that the force exerted upon the vehicle's tractive wheels remains the same despite the fact that the engine is

delivering more work and can therefore warm up more quickly.

The electrical machine may as above be employed to exert a braking force upon the vehicle's tractive wheels and thereby regenerate electrical energy from absorbed kinetic energy, i.e. the electrical machine may be used for so-called

regenerative braking with a view to recovering energy, e.g. when the vehicle is travelling downhill. The present

invention is also applicable in such situations. It is an object of the present invention to warm in particular the combustion engine. During regenerative braking the engine is normally dragged, i.e. it runs with the fuel injection

switched off. Such situations are disadvantageous from a warming perspective in that the engine is instead cooled by the combustion air passing through its combustion chambers

(e.g. cylinders) when no combustion is taking place in them.

In one embodiment of the present invention desired warming of the combustion engine can be assured even in situations where the engine is normally dragged. In such situations more force is exerted by the electrical machine than would otherwise be the case during the regenerative braking, thereby causing the engine to deliver positive work corresponding to the extra load and consequently requiring fuel injection to ensure that the force acting upon the vehicle's tractive wheels is not altered by the present invention. The present invention may thus be used to ensure desired warming whatever the driving situation. As will be appreciated, using the electrical machine according to the present invention thus represents a use which is "the opposite way round" compared with the normally energy-saving context in which the electrical machine is normally used.

Further characteristics of the present invention and

advantages thereof are indicated by the detailed description of embodiment examples set out below and the attached

drawings .

Brief description of the drawings

Fig. 1A depicts a power train of a vehicle on which the

present invention may with advantage be employed.

Fig. IB depicts an example of a control unit in a vehicle

control system.

Fig. 2 depicts in more detail part of the vehicle depicted in

Fig. 1A.

Fig. 3 illustrates an example of a method according to the present invention.

Fig. 4 depicts an example of regulation according to the

present invention in a situation where so-called dragging normally prevails.

Detailed description of preferred embodiments

The present invention will now be exemplified in relation to a hybrid vehicle. Fig. 1A generally depicts schematically a power train of a hybrid vehicle 100 according to an embodiment of the present invention. There are various types of hybrid vehicles and the vehicle 100 depicted takes the form of a parallel hybrid vehicle. The vehicle 100 schematically depicted in Fig. 1A has only one axle with tractive wheels 113, 114, although the invention is also applicable on vehicles which have more than one axle provided with tractive wheels, and on vehicles with one or more further axles, e.g. one or more tag axles.

The power train of the parallel hybrid vehicle in Fig. 1A comprises a combustion engine 101 which in a conventional way is connected, via an output shaft of the engine 101, usually via a flywheel 102, to a gearbox 103 via a clutch 106. The engine 101 is controlled by the vehicle's control system via a control unit 115. The clutch 106, which may for example take the form of an automatically operated clutch, and the gearbox 103 are also controlled by the vehicle's control system by means of a control unit 116. Gearboxes in heavy vehicles often take the form, as in the embodiment depicted, of a "manual" gearbox 103 which is operated automatically (by means of the vehicle's control system) whereby the clutch 106 selectively connects the output shaft 102 of the engine 101 to the gearbox 103. The clutch 106 in the present example is operated

automatically by the vehicle's control system but might alternatively be manually operated.

The vehicle further comprises driveshafts 104, 105 which are connected to the vehicle's tractive wheels 113, 114 and which, as in a conventional combustion engine system, are driven by an output shaft 107 of the gearbox via a final gear, e.g. a conventional differential 108.

Unlike a conventional vehicle, the vehicle depicted in Fig. 1A comprises also a hybrid portion with an electrical machine 110 which is connected to the input shaft 109 of the gearbox 103, downstream of the clutch 106, which means that the gearbox input shaft 109 can be driven by the electrical machine 110 even when the clutch 106 is open. The parallel hybrid vehicle can thus provide force to the tractive wheels 113, 114 from two separate power sources simultaneously, i.e. both from the combustion engine 101 and from the electrical machine 110. Alternatively, the vehicle may be propelled by only one power source at a time, i.e. either by the combustion engine 101 or by the electrical machine 110. The present invention is also applicable on other types of hybrid vehicles provided that the combustion engine can be loaded by an electrical machine. The vehicle may also be provided with two or more electrical machines. The vehicle may for example be of a type with a conventional automatic gearbox which the electrical machine may be upstream or downstream of. The vehicle depicted in

Fig. 1A is also provided with a post-treatment system 117 for cleaning the exhaust flow arising from the engine's

combustion, the functions of which system are controlled by a control unit 118. The diagram also depicts an exhaust brake system 119 for throttling the exhaust flow from the engine.

The hybrid portion also comprises further components. Fig. 1A depicts only the electrical machine 110, an energy store 111 and a hybrid control unit 112 which takes care of the

functions of the hybrid portion. Fig. 2 depicts the hybrid portion in somewhat greater detail. The electrical machine 110 is provided with a power supply at a variable supply frequency, making it possible for the electrical machine to rotate a shaft at any desired rotation speed and any desired torque within the speed/torque range of the electrical machine. In the example depicted, the electrical machine 110 is powered from the energy store 111 via a power electronics unit 210 which generates said supply frequency. The energy store 111 may be arranged to be charged by regenerative braking by means of the electrical machine 110 and the power electronics unit 210, but also in other ways such as by connection to an external power source, e.g. a conventional electrical network. Fig. 2 also depicts further components explained below.

The electrical machine 110 may thus be used to propel the vehicle 100 at in principle any desired speed by means of frequency control, and to apply in principle any desired braking force which works against the propulsion of the vehicle. This is utilised by the present invention.

As above, the functions of the vehicle components depicted are controlled by a number of control units. Control systems in modern vehicles generally comprise usually 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 taking care of a specific function may be divided between two or more of them.

For the sake of simplicity, Fig. 1A depicts only control units 112, 115-116, 118, but vehicles 100 of the type depicted will often be provided with significantly more control units, as one skilled in the art will appreciate. Control units 112, 115-116, 118 can communicate with one another via said

communication bus system, as represented by lines running between them in the diagram.

The invention may be implemented in any suitable control unit, and in the example depicted it is implemented in control unit 115 for control of the combustion engine. It may however also be implemented in other suitable control units, e.g. a dedicated control unit, control unit 118 for control of the post-treatment system or the hybrid control unit 112. The demand of control unit 115 (or the one or more control units in which the present invention is implemented) for loading of the combustion engine 101 by means of the electrical machine

110 according to the invention will probably depend on signals received from the hybrid control unit 112, from control unit 116 for control of clutch/gearbox and from other undepicted control units with which the vehicle is provided, and/or on information for example from various sensors with which the vehicle is provided. It is generally the case that control units of the type depicted are normally adapted to receiving sensor signals from various parts of the vehicle 100.

Control units of the type depicted are also usually adapted to delivering control signals to various parts and components of the vehicle. The control unit will for example deliver signals to control unit 112 to demand braking force from the electrical machine.

Control is often governed by programmed instructions,

typically in the form of a computer programme which, when executed in a computer or control unit, causes the

computer/control unit to effect desired forms of control action, e.g. method steps according to the present invention. The computer programme usually forms part of a computer programme product which comprises a suitable storage medium

121 which may for example take the form of any from among ROM (read-only memory) , PROM (programmable read-only memory) , EPROM (erasable PROM) , flash memory, EEPROM (electrically erasable PROM), a hard disc unit etc., and be situated in or in communication with the control unit, in which case the computer programme is executed by the control unit. The vehicle's behaviour in a specific situation may thus be modified by altering the computer programme's instructions.

An example of a control unit (control unit 115) depicted schematically in Fig. IB may itself comprise a calculation unit 120 which may for example take the form of any suitable kind of processor or microcomputer, e.g. a circuit for digital signal processing (Digital Signal Processor, DSP) , or a circuit with a predetermined specific function (Application Specific Integrated Circuit, ASIC) . The calculation unit 120 is connected to a memory unit 121 which provides it with, for example, the stored programme code and/or the stored data which the calculation unit needs for it to be able to perform calculations. The calculation unit 120 is also arranged to store partial or final results of calculations in the memory unit 121.

The control unit is further provided with respective devices 122, 123, 124, 125 for receiving and sending input and output signals. These signals may comprise waveforms, pulses or other attributes which the input signal receiving devices 122, 125 can detect as information for processing by the

calculation unit 120. The output signal sending devices 123, 124 are arranged to convert calculation results from the calculation unit 120 to output signals for conveying to other parts of the vehicle's control system and/or the component or components for which the signals are intended. Each of the connections to the respective devices for receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (Controller Area Network) bus, a MOST (Media Oriented Systems Transport) bus or some other bus configuration, or a wireless connection.

Fig. 3 depicts an example of a method 300 according to the present invention. The method begins with step 301, where it is determined whether the combustion engine 101 of the vehicle 100 has been started, e.g. by determining whether it is running at at least an idling speed. If such is the case, the method moves on to step 302. One embodiment of the invention applies a further criterion at the transition from step 301 to step 302, e.g. determining whether the engine 101 has been started for a certain amount of time, e.g. fractions of a second or a certain number of seconds, which may for example be desirable, e.g. from a wear or some other perspective, such as for ensuring that the engine really has started. It may also or alternatively be desirable that the function according to the present invention, i.e. applying braking force by means of the electrical machine 110, should commence within a certain time ti from when the engine 101 starts, e.g. with a view as far as possible to reducing emissions as quickly as possible. The period ti may for example be brief, e.g. one or a suitable number of seconds within the range 0-60 seconds from when the engine 101 reaches idling speed, i.e. from when it starts. In step 302 it is determined whether an exhaust limitation function, e.g. a white smoke limitation function or some other suitable function for limitation of exhaust emissions, is to be activated. This may for example be the case if a

temperature T_mot0r which is representative of the engine 101 is below a limit value T_mot0riimi · The temperature T_mot0r may be arranged to be determined in any suitable way and be

represented by a suitable temperature sensor with which the engine 101 is provided. The temperature T_mot0r may also be arranged to be a temperature representation calculated by means of suitable calculation models, e.g. on the basis of a suitable temperature measured on the vehicle. Whether for example white smoke limitation should be activated may for example also be determined on the basis of the ambient temperature T_omg of the vehicle 100, in which case white smoke limitation may be activated if the ambient temperature T_omg is below a temperature _omgii_mi .

The condition required at step 302 may also be such as to determine whether said function for limitation of white smoke and/or other emissions has been activated, by the driver or automatically by the vehicle's control system. If said limitation function has not been/is not to be

activated or if the invention is for any reason not to be applied, the method ends at step 306. This may for example be the case where the engine 101 is started within a relatively short time from previously having been stopped, with the result that it is still at desired temperature. Such may also be the case when the ambient temperature of the vehicle 100 is high. In one embodiment, however, the function according to the present invention is always activated so long as suitable temperature criteria for its activation are fulfilled, i.e. irrespective of whether a white smoke or other limitation function is activated. In one embodiment the function is always activated during starting of the engine to provide assurance of its desired warming.

If on the contrary it is determined in step 302 that action has to be taken to limit white smoke and/or other exhaust emissions, the method moves on to step 303 where it is

determined whether the vehicle 100 is stationary. If it is stationary, it is also likely that the engine will be idling relatively fast, with the result that it will also take a relatively long time to reach desired temperature. If on the contrary the vehicle 100 is in motion, the engine 101 is always very likely to develop more work and consequently warm up more quickly.

One embodiment of the present invention determines at step 303 not whether the vehicle 100 is stationary but whether its speed v_fordon is below a suitable level v_iim, e.g. 10 km/h or other suitable speed, with the further possibility that vn_m might also be 0 km/h. The vehicle 100 may for example roll slowly with the engine 101 substantially idling in conditions where there is a very small propulsive force requirement, in which case its warming time will still be long.

The vehicle may also be run with the engine dragging, i.e. with the fuel injection switched off. In such situations the engine undergoes no warming at all but instead cooling, which means that the present invention is applicable for warming in such situations, particularly where the vehicle runs with the engine dragging shortly after starting.

According to one embodiment of the present invention it is determined at step 303 whether the parking brake is applied and the vehicle is therefore stationary, in which case the condition of step 303 is only regarded as fulfilled if such is the case.

According to one embodiment it is determined whether the prevailing load upon the combustion engine 101 is below a suitable level Mn_m, e.g. a load corresponding to a braking torque within the range 10-500 Nm or within the range 2-50% of the maximum torque deliverable by the engine, or a torque which is less than that which the electrical machine 110 can deliver. As will be appreciated, the ranges indicated are merely examples which are in no way limitative. This may be arranged to be for example conducted as a separate step which precedes, follows or replaces step 303, in which case the speed of the vehicle 100 is disregarded. If the load upon the engine 101 is above a suitable level, e.g. because the driver of the vehicle 100 has, immediately after starting, demanded a propulsive force which causes the load upon the engine 101 to exceed Mn_m, no further braking force is exerted by the

electrical machine 110.

If conditions according to step 303 are not fulfilled, the method ends at step 306.

If the one or more conditions of step 303 and of any further steps are fulfilled, the method moves on to step 304 for exertion of an engine-braking force by means of the electrical machine 110. The braking force exerted by the electrical machine may be any suitable braking force which results in a total engine-braking torque within for example the range 10- 500 Nm. If the vehicle 100 is stationary with the gearbox 103 in neutral position, the electrical machine 110 may apply the whole of this braking force, whereas if the vehicle is in motion the electrical machine may apply a braking force such that the total braking force acting upon the engine 101 amounts to the desired braking force.

At the same time, if the vehicle is in motion, the combustion engine and the electrical machine are respectively regulated in such a way that the force exerted upon the vehicle's tractive wheels still amounts to, or at least substantially amounts to, the propulsive force demanded on the tractive wheels. The present invention thus enables the engine to work harder while at the same time the force exerted upon the tractive wheels is maintained, thereby achieving quicker warming while at the same time the vehicle still moves as desired by the driver. As will be appreciated, the combustion engine is enabled to work harder by regulation of the injection of fuel into at least one, but usually more than one, of its combustion chambers, e.g. conventional cylinders, which injection is increased to achieve the greater amount of work. Applying the braking force during dragging results in the application of a braking force which is then balanced by corresponding positive work from the engine, thus compelling fuel injection to the engine. It is usually the case with hybrid vehicles that regenerative braking is applied during dragging and that such regenerative braking may be effected independently of the present invention. The difference between the present

invention and such regenerative braking is that a further braking force is exerted which is then counteracted by work from the engine, whereupon the aggregate force contribution to the vehicle's tractive wheels from the present invention is substantially zero.

The invention thus makes it possible for the load upon the combustion engine 101 to be increased, e.g. in situations where the engine would for example otherwise have been idling or would have run with very little or no load, resulting in quicker warming. In the case of dragging, the present

invention means that instead of the vehicle running with the engine dragging and with fuel injection consequently shut off, it is instead run at a high engine load which means that fuel has to be injected, i.e. the electrical machine applies a force which "compels" the need for fuel injection. In this way the torque acting upon the vehicle's tractive wheels will still be that expected by the vehicle's driver, which during dragging with the accelerator pedal released will normally be the engine's drag torque plus any braking force, but according to the invention a further propulsive force provided by the engine is absorbed by the electrical machine so that the invention does not affect the force with which the vehicle is propelled. The engine thus works according to the present invention even when dragging despite no positive work being demanded from it.

When appropriate braking force has thus been exerted at step 304, the method moves on to step 305 to determine whether the braking force exerted should be discontinued. This may for example be arranged to take place after the braking force has been exerted for a certain time or when it is found that a suitable temperature has been reached, such as a suitable engine temperature or a representation of the engine

temperature, e.g. in the form of a coolant temperature or a modelled engine temperature. The method may also for example be arranged to be discontinued when for example as a result of prevailing running resistance the load upon the combustion engine 101 will still be greater than the desired braking force. So long as braking force continues to be exerted by the electrical machine 110, the method will stay at step 304 via step 305 at which the brake force exerted by the

electrical machine 110 can when necessary be adapted to the remaining load upon the engine 101, resulting in a desired total load. The method may for example also be arranged to be discontinued if the function for limitation of white

smoke/exhaust emissions is switched off.

If it is found at step 305 that the method should be

discontinued, it ends at step 306.

When the electrical machine 110 generates propulsive force to move the vehicle 100, energy from the energy store is expended for the purpose. Conversely, when the electrical machine is used for braking, there is instead absorption of energy which is converted to electrical energy and generates an electric current which can be taken over. The electrical energy generated is normally in the form of an a.c. voltage, since electrical machines of the type referred to are normally a.c. machines. This a.c. voltage may be rectified to a d.c.

voltage by means of the power electronics 210 in order

thereafter to be stored in the energy store 111 for subsequent use, e.g. in generating a force for propulsion of the vehicle 100. The braking force generated by the electrical machine 110 may thus largely be recovered by charging the energy store 111, at least so long as the latter is amenable to being charged .

The present invention thus proposes a method whereby it is possible to exert a braking force which can be calculated with good accuracy and it is possible for the energy expended in the form of fuel to the engine to be largely recovered by the fact that the braking energy absorbed by the electrical machine can be taken over and be fed back in an electrical form, e.g. for storage in the energy store 111. In one embodiment the application of a braking force is discontinued by using the electrical machine 110 if the energy store 111 cannot receive the current generated by the

electrical machine. In one embodiment the electrical machine applies only a braking force, which makes it possible for the energy absorbed and converted to electricity to be stored in the energy store. If the braking force which is desirable from the electrical machine 110 causes generation of an electric current which cannot be taken over by the energy store 111, it is possible in one embodiment for the exhaust brake 119, at least where the vehicle 100 is stationary, to be activated in order to achieve a total engine-braking force of desired magnitude. In one embodiment, however, the electrical energy generated by the electrical machine 110 is used only partly, or not used at all, for charging of the energy store 111. Instead it is (at least partly) used to generate heat, and in particular to warm one or more vehicle components, i.e. the energy absorbed by the electrical machine is first converted to electricity in order thereafter to be converted at least partly to heat. The result is a further warming additional to that achieved by the higher engine load. The charge absorption capacity of energy stores of the type referred to often depends largely on their temperature. If it is very low, e.g. -10°C to -15°C or even colder, the ability of the energy store 111 to absorb charge may be very low or in principle non-existent. In one embodiment the braking energy converted to electricity is used to warm water via a radiator, as illustrated in Fig. 2, in which an electric current

generated by the electrical machine 110 when exerting a braking force and converted by the power electronics to appropriate voltage/frequency, is converted to heat via a radiator 211 which itself warms liquid in a liquid-borne system. The warmed liquid may be caused by a circulation pump 213 to circulate through a cooling coil which passes through the energy store 111 in order to warm the energy store to a temperature which makes it possible for it to accept more charging. If the energy store is warmed to desired

temperature and/or cannot accept all or some of the electric current generated by the electrical machine, heat may be ventilated away to the surroundings of the vehicle 100 via a radiator 214. A valve 212 may be used to selectively choose whether the radiator liquid is to be circulated through the energy store 111, the radiator 214 or both. The radiator 211 may also be used to warm coolant in the combustion engine's cooling system, e.g. to further speed up the warming of the engine and/or a driver/passenger space.

The invention is described above in relation to a parallel hybrid system but is also applicable to other types of hybrid systems in which an electrical machine can directly or

indirectly, e.g. via the vehicle's tractive wheels, apply a braking force to a combustion engine.

To sum up, the present invention is thus such that it

increases the load upon the engine and hence also increases the work delivered by the engine. The invention is also such that it enables the engine to deliver positive work. This is achieved by the fact that the braking force exerted upon the engine according to the present invention is compensated by a corresponding fuel injection so that the engine is reliably compelled to perform positive work.

This is illustrated in Fig. 4 in which the invention is exemplified for a situation where dragging normally occurs. The diagram's x-axis represents torque and its y-axis time. The zero line 405 represents a torque-relieved situation.

When the combustion engine performs positive work by

combustion in its combustion chambers, the torque delivered will at least amount to zero during idling when only the engine's internal losses are overcome by the work performed, and will exceed zero when more work than that is generated by the combustion. In the example depicted, the vehicle is propelled by work delivered by the engine which corresponds to a torque Ml up to time Tl (continuous line 401) at which the torque delivered begins to drop, e.g. because the vehicle's running resistance decreases, e.g. because the vehicle is approaching a downward slope. The present example refers to a situation where the vehicle reaches a downhill slope such that no propulsive force

contribution will be required from the engine. In such a situation the torque which the engine needs to deliver

normally drops to zero at time T3 (broken line 402) and the engine is then subject to an engine-driving torque. This means that the vehicle can accelerate despite no positive work being performed by the engine. At time T4 the change in torque levels out, e.g. because the vehicle is on a downward slope with constant gradient.

In such a situation the engine is rotated by the tractive wheels, and fuel injection is switched off, i.e. dragging prevails. The negative propulsive force requirement means that the vehicle will accelerate as long as this state

prevails. However, this is not normally desirable, so energy is often braked away. In such situations it is possible on hybrid vehicles for the electrical machine (chain-dotted line 403) to be used for regenerative braking to absorb and recover part of the force applied from the tractive wheels. This is represented by the dotted line 404. Such regenerative braking causes part of the engine-driving force to be absorbed by the electrical machine, making it possible for this energy to be utilised. However, the proportion absorbed by the electrical machine during regenerative braking remains less than or at most equal to the engine-driving force applied by the tractive wheels .

According to the present invention, when employed in a

situation of the type depicted in Fig. 4, the electrical machine will exert a greater force (chain-dotted line 403) than if the present invention was not activated, and at the same time the combustion engine is then caused to deliver work which compensates for the greater force exerted by the electrical machine. The combustion engine will thus deliver positive work which corresponds to the further braking force exerted by the electrical machine. This is represented by the continuous line 401 which therefore markedly deviates from the broken line 402. According to the present invention, in situations where the invention is employed, the combustion engine is thus enabled to deliver positive work even in situations where it is normally dragged.

Claims

C LA I M S

1. A method for warming at least one vehicle component at a vehicle (100), which vehicle (100) is provided with a combustion engine (101) and with at least a first electrical machine (110), which first electrical machine (110) is arranged for selective exertion of a force upon an output shaft of said combustion engine (101),

characterised by

- applying to said output shaft of said combustion engine (101) a first braking force by use of said first

electrical machine (110) to increase the work performed by said combustion engine (101) .

2. A method according to claim 1, further comprising

applying said first braking force by using said first electrical machine (110) to increase the work performed by combustion in said combustion engine.

3. A method according to claim 1 or 2, further comprising responding to said first braking force by increasing the amount of fuel supplied to said combustion engine.

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

comprising applying said first braking force to said output shaft in a situation where fuel is already supplied to said combustion engine.

5. A method according to any one of claims 1-4, in which said combustion engine has at least one combustion chamber and the method further comprises applying said first braking force to said output shaft in a situation where fuel is supplied to said at least one combustion chamber .

6. A method according to any one of claims 1-5, further comprising

- increasing by work corresponding to said first braking force the work delivered by said combustion engine.

7. A method according to any one of claims 1-6, further

comprising

- increasing by work corresponding to said first braking force the work delivered by said combustion engine, so that the propulsive force acting upon the vehicle's tractive wheels takes substantially the form of a

propulsive force demanded on the vehicle's tractive wheels .

8. A method according to claim 7, in which said propulsive force demanded on the vehicle's tractive wheels takes the form of a propulsive force demanded by the vehicle's driver .

9. A method according to any one of claims 1-8, further

comprising determining whether a temperature (T_motor) of said combustion engine (101) is below a first temperature (T_motoriimi) and

- using said electrical machine to only apply said first braking force if said first temperature (T_mot0r) is below a limit value (T_mot0riimi) ·

10. A method according to any one of claims 1-9, further

comprising

- determining a representation of a temperature (t_omg) for surroundings of said vehicle (100), and

- only applying said first braking force to said output shaft of said combustion engine if said ambient

temperature (t_omg) is below a first temperature limit value .

11. A method according to any one of the foregoing claims, further comprising determining whether said combustion engine (101) has been started, and

- applying said first braking force to said output shaft of said combustion engine (101) within a first time (ti) from when said combustion engine (101) is started.

12. A method according to any one of the foregoing claims, in which said first braking force takes the form of an engine-braking torque within the range 10 Nm - 500 Nm.

13. A method according to any one of the foregoing claims, in which said first braking force takes the form of a braking force of such magnitude that the total braking torque against said output shaft amounts to a torque within the range 10 Nm - 500 Nm.

14. A method according to any one of the foregoing claims, further comprising only applying said first braking force to said output shaft of said combustion engine (101) when the braking force acting upon said output shaft in addition to said first braking force is below a limit value .

15. A method according to any one of the foregoing claims, in which said first braking force is only exerted when said vehicle (100) is stationary.

16. A method according to claim 15, in which said first

braking force is only exerted when a parking brake is applied .

17. A method according to any one of the foregoing claims, in which said first braking force is only exerted when the speed of the vehicle (100) is below a first speed.

18. A method according to any one of the foregoing claims, further comprising the following when said first braking force is applied to said output shaft of said combustion engine (101) :

- determining a second representation of a temperature of said combustion engine (101), and

- ceasing to apply said first force when said temperature is above a second limit value.

19. A method according to any one of the foregoing claims, further comprising only applying said first braking force when a function for limitation of exhaust emissions from said vehicle (100) is activated.

20. A method according to claim 19, in which said function for limitation of exhaust emissions takes the form of a function for limitation of white smoke emissions.

21. A method according to any one of the foregoing claims, further comprising ceasing to apply said first braking force when the energy absorbed by said electrical machine (110) cannot be stored in an energy store (111) on board said vehicle (100) .

22. A method according to any one of the foregoing claims, further comprising activating an exhaust brake system of said vehicle (100) when the energy absorbed by said electrical machine (110) cannot be stored in an energy store (111) on board said vehicle (100) or when desired engine-braking force cannot be exerted by said electrical machine (110) .

23. A method according to any one of the foregoing claims, in which energy absorbed by said electrical machine (110) during application of said first braking force is primarily stored in an energy store on board said

vehicle .

24. A method according to any one of the foregoing claims, further comprising the following when said electrical machine (110) applies said first braking force:

- converting at least partly to heat the energy absorbed by said electrical machine (110) during application of said braking force.

25. A method according to claim 24, in which said absorbed energy converted to heat is used to warm any of the following: energy stores of said vehicle; a passenger space in said vehicle; coolant in a coolant system of said vehicle.

26. A method according to any one of the foregoing claims, in which said electrical machine (110) is selectively connectable to said output shaft of said combustion engine (101) and said first force is only applied to said output shaft when said electrical machine is connected to said output shaft.

27. A method according to any one of the foregoing claims, in which said warming of at least one vehicle component takes the form of warming at least one of the following:

- combustion engine (101),

- energy store (111) .

28. A method according to any one of the foregoing claims, in which said at least one vehicle component takes the form of at least said combustion engine.

29. A computer programme which comprises programme code and which, when said programme code is executed in a computer, causes said computer to conduct the method according to any one of claims 1-28.

30. A computer programme product comprising a computer- readable medium and a computer programme according to claim 29, which computer programme is contained in said computer-readable medium.

31. A system for warming at least one vehicle component at a vehicle (100), which vehicle (100) is provided with a combustion engine (101) and with at least a first

electrical machine (110), which first electrical machine (110) is arranged for selective exertion of a force upon an output shaft of said combustion engine (101),

characterised in that

- the system comprises means for applying to said output shaft of said combustion engine (101) a first braking force by use of said first electrical machine (110) .

32. A system according to claim 31, in which said electrical machine is situated between said combustion engine and a gearbox .

33. A system according to claim 31 or 32, in which said

combustion engine is so arranged that its output shaft can be connected to the vehicle's tractive wheels for application of a force to said tractive wheels.

34. A vehicle characterised by being provided with a system according to any one of claims 31-33.