FI ELD OF TH E I NVENTION AN D P RIOR ART The present invention relates to a drive system for a vehicle according to the preamble of the enclosed clai m 1 .

The invention is particularly, but not exclusively, focused on such a drive system in motor vehicles in the form of wheeled com mercial vehicles, especially heavy goods vehicles such as trucks and buses.

The i nvention thus relates to a drive system for driving a hybrid vehicle which , generally, is a vehicle that may be powered by a pri mary engine, in this case a combustion engine, and a secondary engine, in this case an electrical machine. The vehicle is suitably equi pped with means for storage of energy, such as a battery or a capacitor for storage of electric energy, and control equipment to control the flow of electric energy between the means and the electrical machine. The electrical machine may thus alternately operate as an engine or as a generator, dependi ng on the vehicle's operating mode. When the vehicle decelerates, the electrical machine generates energy that may be stored, and the stored electric energy is used later for e.g . operation of the vehicle. Using a conventional clutch mechanism, which disconnects the input shaft of the gearbox from the combustion engine during a shifting process in the gearbox, entails disadvantages, such as heati ng of the clutch mechanism 's discs, which results in an i ncreased fuel consu mption and wear of the clutch discs. There are also large losses as a result, in particular when the vehicle is started. A conventional clutch mechanism is also relatively heavy and costly. It also occupies a relatively large space in the vehicle. Friction losses also arise at the use of a hydraulic converter/torque converter com monly used in automatic transmission . By ensuring that the vehicle has a drive system in which the output shaft of the combustion engine, the rotor of the electrical machine and the input shaft of the gearbox are connected with a planetary gear, the conventional clutch mechanism and disadvantages associated therewith may be avoided. A vehicle with a drive system of this type constitutes prior art, as set out in E P 1 31 9 546 and SE 1 051 384-4.

Althoug h this drive system , especial ly the one described in S E 1 051 384-4, functions wel l and has a range of advantageous features, efforts are constantly made to i mprove such a drive system with respect to its behaviour and function in certai n operating situations.

SU M MARY OF TH E I NVENTION

The objective of the present invention is to show a drive system of the type defined above, which is in line with the above-mentioned efforts. This objective is achieved according to the invention by providing a drive system according to the enclosed clai m 1 .

By equipping the drive system with a second electrical machine and said second locking means, an i mproved behaviour is obtained in a range of operational situations compared to such prior art drive systems. Specifically, when braking the vehicle it becomes possible to have the first locki ng means in a release position , without being li mited by the reaction torque with which the combustion engine may resist. It also becomes possible to start the combustion engine when the torque is transmitted throug h the powertrain , i .e. out of the gearbox. When the vehicle is at a standstill it also becomes possible to drive while maintaining a power balance, i .e. while supplying an energy storage means, such as a battery, and other electrical loads of the vehicle with a control led current/power while a desired torque is maintai ned in the powertrain . Under most circu mstances this is not achievable in prior art drive systems of this type. "Electric energy storage'V'storage of electric energy'V'energy storage", as used in this docu ment, means an energy storage means with an electrical interface i n relation to the first and second electrical machi ne of the drive system , but storage of energy does not have to be electrical . This entai ls that in addition to an electrical battery and capacitor, e.g . flywheels, other mechanical means and means for buildi ng up pressure, e.g . pneumatic or hydraul ic, may be possible.

According to one embodi ment of the invention, said second locking means are adapted to, in said release position , separate a first part of the combustion engine's output shaft, arranged nearest the combustion engine, from a second part thereof, connected with said first component of the planetary gear, and the transmission between the second electrical machine's rotor and the combustion engine's output shaft is connected with said first part.

According to another embodi ment of the invention , the combustion engi ne's output shaft, the first electrical machine's rotor and the input shaft of the gearbox are rotatably arranged around a com mon rotation axis, and the second electrical machine's rotor is rotatably arranged around a rotation axis, which is substantially parallel therewith or parallel with said common axis. According to another embodi ment of the invention , the planetary gear's sun wheel constitutes said first component and the ring gear constitutes said third component. By connecting the first electrical machi ne's rotor with the ring gear and the combustion engine's output shaft with the sun wheel , a compact construction is achieved, which is easy to fit into already existing spaces for powertrains (drive systems) with clutch mechanisms instead of planetary gears. A hybrid gearbox may thus be made compact and substantially no bulkier than a standard gearbox. This entai ls that the weig ht increase, which a hybridisation normally i nvolves, may be reduced considerably. Another advantage is that a connection of the first electrical machi ne's rotor with the ring gear provides a hig her potential braking torque via the rotor, than if this were connected with the sun wheel instead. According to another embodi ment of the invention , the drive system comprises at least one control device, adapted to control the fuel supply to the combustion engine and to control the exchange of electric energy between the first and second electrical machine, on the one hand, and, on the other hand, electric energy storage means. The control device is advantageously also adapted to control said locking means to be moved between said locked position and release position , and, in order to lock them together, to control the combustion engine and/or the first electrical machine and/or the second electrical machine to achieve the same rotational speed in the parts to be locked together by the respective locking means and, subsequently, to move the locki ng means to a locked position , and, in order to release them , to control the combustion engine and/or the first electrical machi ne and/or the second electrical machine to achieve a torque balance between the parts to be released from each other and, subsequently, for the locking means to be moved to a release position.

Here, torque balance is achieved when the followi ng relation between the torques applied is met for the example configuration displayed in Fig . 3 :

Tsu n wheel ⁼ T _r j _n g gear

where

su n wheel and T _{ri n} g gear constitute torque applied on the sun wheel and the ring gear, respectively,

Z _s is the nu mber of teeth of the sun wheel ,

Z _r is the nu mber of teeth of the ring gear.

Accordingly, torque balance means the state where a torque acts on a ri ng gear arranged i n the planetary gear, corresponding to the product of the torque acting on the planetary gear's planetary wheel carrier and the planetary gear's gear ratio, while si multaneously a torque acts on the planetary gear's sun wheel , corresponding to the product of the torque acting on the planetary wheel carrier and ( 1 minus the planetary gear's gear ratio). At such torque balance, said first locki ng means 34 does not transfer any torque between the components of the planetary gear. According to another embodi ment of the invention , the control device is adapted to control , when the vehicle is driven with the combustion engi ne shut off, the first locki ng means i n a locked position , and the second locki ng means in a release position for start of the combustion engi ne,

• the second electrical machine towards and to the combustion engi ne's idl ing engine speed and injection of fuel into the combustion engine,

• the combustion engi ne and the first and second electrical machi ne towards and to the same rotational speed of the combustion engi ne's output shaft, and said first component i n the planetary gear, and

• the second locki ng means to be moved into a locked position . Since the start of the combustion engine is entirely disconnected from the propulsion , no torque needs to be ramped away during the start of the combustion engine, wh ich may occur with a maintained propulsion force in the drive system .

According to another embodi ment of the invention , the control device is adapted to control , when the vehicle is driven with the combustion engi ne runni ng and the second locking means in a locked position for turning off of the combustion engine, and a transition to powering the vehicle with the electrical machines,

• the combustion engi ne and the second electrical machine's rotor towards and to the engine speed of the i nput shaft of the gearbox, if the first locking means are in a release position ,

• the first locking means to be moved into a locked position if it is not already there,

• the combustion engi ne and the second electrical machine, so that a zero torque is transmitted via the second locking means,

• the second locking means to be moved to the release position , • cessation of injection of fuel into the combustion engine, and

• the second electrical machine towards and to a standstill .

Accordingly, controlled stopping of the combustion engi ne is achieved, at which its engine speed may be control led in such a manner that vi bration is avoided. Such a stop may be carried out without the torque in the powertrain , i. e. the torque transmitted to the input shaft of the gearbox and further downstream of the gearbox, disappeari ng, i .e. without any torque i nterruption . According to another embodi ment of the invention , the control device is adapted to control , when the vehicle is at a standstill with the combustion engine running at idling speed, the first locking means in a release position , and the second locking means in a locked position for driving of the vehicle with power balance,

· the first electrical machine for delivery of a torque thereof, so that the requested torque is transmitted to the i nput shaft of the gearbox,

• the combustion engine towards and to its idl ing speed,

• the second electrical machine to deliver a torque so that the desired power to the energy storage means and the electrical load comprised in the vehicle is achieved,

• in case the torque avai lable in the combustion engine at idling speed is insufficient to counteract both the reaction torque from the first electrical machine and the torque applied from the second electrical machine, to increase the engine speed of the combustion engine in order to increase the torque avai lable from the combustion engine, and

• the first locking means to be moved to a locked position when the input shaft of the gearbox, the first electrical machine's rotor and the combustion engine's output shaft rotate with the same rotational speed.

As long as none of the combustion engine, the first electrical machine and the second electrical machine achieve their performance li mits, both the desired torque and the desired electrical power may be achieved at such start of driving . If the torque available in the combustion engi ne is insufficient, the engine speed may be increased or the output target may be abandoned. If the second electrical machi ne reaches its l i mit, the output target must be abandoned. Abandoning the output target entails that the electrical energy storage means must deliver a current to the first electrical machine and to electrical loads. This is usual ly possible, althoug h not desirable. I nitially, the rotor rotates backwards i n the first electrical machine during the start, and generates power when a positive torque must be achieved. I n some cases it may be difficult for a battery to receive the power generated, e.g . at low temperatures of the battery, but in such case this output may be consu med by the second electrical machine, by way of it delivering a torque that helps the combustion engine's output shaft to rotate.

According to another embodi ment of the invention , the control device is adapted to control , when the vehicle is driven with the combustion engi ne running , and the fi rst and second locking means in a locked position , when braking the vehicle towards stop,

· the desired braking torque to be distributed between the first and second electrical machines,

• when a certain value of the vehicle's speed is not met, the first and second electrical machi ne so that torque balance is achieved i n the planetary gear, at the same ti me as the total torque transmitted to the input shaft of the gearbox corresponds to the desired braking torque,

• the first locking means to be moved to the release position ,

• the combustion engi ne towards and to its idl ing engine speed, and the fuel injection into the combustion engine to cease, and

• ramping down of the total braking torque from the first and second electrical machine towards zero in connection with the vehicle stopping .

With two electrical machines, the desired braking torque may usually be achieved without any requirement to shift gears while braking . Since gear shifting is avoided, no braking energy is lost due to torque from an electrical machine bei ng ramped down to prepare for a gear shift. The first locking means may be moved to the release position and kept in this position whi le si multaneously the desired braking torque may be maintained. Accordi ngly, the fraction of braking energy that may be regenerated with a hybrid system is greatly increased.

The invention also relates to a vehicle accordi ng to clai m 1 1 , and methods with the method steps that the control device is adapted to carry out in the above-mentioned embodi ments of the drive system according to the i nvention .

Other advantageous features and advantages of the invention are set out in the descri ption below.

BRI E F D ESC RI PTION OF TH E D RAWI NGS

Below are descriptions of an example embodi ment of the invention with reference to the enclosed drawings, in which : Fig. 1 is a very simplified view of a powertrain in a vehicle, which may be equipped with a drive system according to the invention, Fig.2 is a more detailed, but still simplified view of a part of said drive system, and

Fig.3 is a simplified view illustrating the general structure of a drive system according to one embodiment of the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT ACCORDING TO THE INVENTION Fig. 1 shows a powertrain for a heavy goods vehicle 1. The powertrain comprises a combustion engine 2, a gearbox 3, a number of driving shafts 4 and driving wheels 5. Between the combustion engine 2 and the gearbox 3, the powertrain comprises an intermediate section 6. Fig.2 shows a part of the components in the intermediate section 6 in more detail, more specifically those that also occur in prior art drive systems, such as the one according to SE 1051384-4. The combustion engine 2 is equipped with an output shaft 2a, and the gearbox 3 with an input shaft 3a in the intermediate section 6. The output shaft 2a of the combustion engine is coaxially arranged in relation to the input shaft 3a of the gearbox. The combustion engine's output shaft 2a and the input shaft 3a of the gearbox are rotatably arranged around a common rotation axis 7. The intermediate section 6 comprises a house 8, enclosing a first electrical machine 9 and a planetary gear. The electrical machine 9 comprises, in a customary manner, a stator 9a and a rotor 9b. The stator 9a comprises a stator core which is mounted in a suitable manner on the inside of the house 8. The stator core comprises the stator's wi ndings. The first electrical machi ne 9 is adapted, under certai n operating ci rcu mstances, to use stored electrical energy to supply driving force to the input shaft 3a of the gearbox, and, under other operating conditions, to use the kinetic energy of the input shaft 3 of the gearbox to extract and store electric energy. The planetary gear is arranged substantially radially on the inside in relation to the electrical machine's stator 9a and rotor 9b. The planetary gear comprises, in a customary manner, a sun wheel 1 0, a ri ng gear 1 1 and a planetary wheel carrier 1 2. The planetary wheel carrier 1 2 supports a nu mber of cogwheels 1 3, which are rotatably arranged in a radial space between the teeth of the sun wheel 1 0 and the ring gear 1 1 . The sun wheel 1 0 is fixed on a peripheral surface of the combustion engine's output shaft 2a. The sun wheel 1 0 and the combustion engine's output shaft 2a rotate as one unit with a first rotational speed n-i . The planetary wheel carrier 1 2 comprises an attach ment section 1 2a, which is attached on a peri pheral surface of the input shaft 3a of the gearbox with the help of a splines joint 1 4. With the hel p of this joint, the planetary wheel carrier 1 2 and the input shaft 3a of the gearbox may rotate as one unit with a second rotational speed n ₂ . The ring gear 1 1 comprises an external peri pheral surface on which the rotor 9b is fixedly mounted. The rotor 9b and the ri ng gear 1 1 constitute a rotatable unit that rotates with a third rotational speed n ₃ .

The drive system comprises a first locki ng means, since the combustion engi ne's output shaft 2a is equipped with a shiftable clutch element 1 5. The clutch element 1 5 is mounted on the combustion engi ne's output shaft 2a with the help of a splines joint 1 6. The clutch element 1 5 is in this case arranged in a twist-fast manner on the combustion engine's output shaft 2a, and is shiftably arranged in an axial di rection on the combustion engine's output shaft 2a. The clutch element 1 5 comprises a clutch section 1 5a, which is connecti ble with a clutch section 1 2b in the planetary wheel carrier 1 2. A schematical ly displayed shifting element 1 7 is adapted to shift the clutch element 1 5 between a first position where the clutch sections 1 5a, 1 2b are not i n engagement with each other, correspondi ng to a release position in the first locking means, and a second position where the clutch sections 1 5a, 1 2b are in engagement with each other, corresponding to a locked position of the first locking means. I n this locked position the combustion engi ne's output shaft 2a and the input shaft 3a of the gearbox will be locked together, and these, as well as the electrical machine's rotor, will thus rotate at the same rotational speed. This state may be referred to as a locked planet. The locki ng mechanism may, advantageously, also have the design which is described in the not yet public Swedish patent appl ication 1 250696-0, and comprise a sleeve equi pped with first spli nes, which splines, in the release position , engage with second splines on a first component of the planetary gear and, in the locked position , engage with third splines on a second component of the planetary gear. I n this case, the first component is preferably the planetary wheel carrier, and the second component is the sun wheel . The locking mechanism may then be adapted like an annular sleeve, enclosing the planetary wheel carrier substantially concentrically. The locking means may also consist of a suitable type of friction clutch .

An electric control device 1 8 is adapted to control the shifting element 1 7. The control device 1 8 is also adapted to determi ne the occasions on which the electrical machine should operate as an engine, and on which occasions it should operate as a generator. To determine this, the control device 1 8 may receive up-to-date information relating to suitable operating parameters. The control device 1 8 may be a computer with software for this purpose. The control device 1 8 controls a schematically displayed control equipment 1 9, which controls the flow of electric energy between a hybrid battery 20 and the stator windings 9a of the electrical machine. On occasions where the electrical machine 9 operates as an engi ne, stored electric energy is supplied from the hybrid battery 20 to the stator 9a. On occasions where the electrical machine operates as a generator, electric energy is supplied from the stator 9a to the hybrid battery 20. The hybrid battery 20 delivers and stores electric energy with a voltage in the range of 300-900 volts. Since the i ntermediate section 6 between the combustion engine 2 and the gearbox 3 in the vehicle is li mited, the electrical machine 9 and the planetary gear must constitute a compact unit. The planetary gear's components 1 0, 1 1 , 1 2 are arranged substantially radially inside the electrical machine's stator 9a. The rotor 9b of the electrical machine, the ring gear 1 1 of the planetary gear, the combustion engine's output shaft 2a, and the input shaft 3a of the gearbox, are here rotatably arranged around a com mon rotation axis 5. With such an embodi ment, the electrical machine 9 and the planetary gear occupy a relatively small area. The vehicle 1 is equi pped with an engine control function 21 with which the engine speed n i of the combustion engi ne 2 may be controlled. The control device 1 8 thus has the possibi lity of activating the engi ne control function 21 and of creating a substantial ly zero torque state in the gearbox 3 at engagement and disengagement of gears i n the gearbox 3. The drive system may also, instead of being controlled by one single control device 1 8, be controlled by several different control devices. The part of the drive system according to the i nvention descri bed thus far and displayed in Fig . 2 is present in the drive system according to SE 1 051 384-4. Below, the part of the drive system accordi ng to the invention , which has been added to this part, will be descri bed with reference to Fig . 3.

Accordi ng to the i nvention , the drive system , specifically the intermediate section 6, also has a second electrical machine 30 with a stator 31 and a rotor 32, connected with the combustion engine's output shaft 2a via a transmission 33. Such transmission 33 may have a constant gearing , but it may also comprise a possi bility to vary its gearing . Accordi ng to one example, the geari ng for the transmission 33 may be varied between at least two discrete gear steps. According to another example, the transmission 33 consists of a mechanism for a continuously variable gearing . The possibility to vary the gearing for the transmission 33, in discrete steps or continuously, may be used to achieve an advantageous resulting torque and/or rotational speed from the second electrical machine. A second locking means 34, which may have a sim ilar design as the first locking means 35, illustrated i n more detail in Fig 2, is adapted to, in a release position , separate a first part 36 of the combustion engine's output shaft 2a, arranged nearest the combustion engine, from a second part 37 thereof, connected with the sun wheel 1 0 of the planetary gear, so that the combustion engine's output shaft 2a is disconnected from the sun wheel 1 0. The second locking means 34 may be moved to a locked position , i n which the combustion engine's output shaft 2a is locked to the sun wheel 1 0. The control device 1 8 is adapted to control fuel supply to the combustion engine 2 and to control the exchange of electric energy between the first electrical machine 9 and the second electrical machine 30 on the one hand, and, on the other hand, electric energy storage means such as batteries.

A range of positive features of the drive system are achieved by way of the added arrangement of the second electrical machine 30 and the second locking means 34, some of the most i mportant of which have been described i n the introduction of this docu ment. For example, the combustion engine 2 may be started when the vehicle is driven via electrical drive, without any torque in the powertrain disappearing , i .e. without any torque interruption , since such torque is achieved with the first electrical machi ne 9 while the second electrical machi ne may be control led to the combustion engi ne's idling speed, and followi ng synchronisation of the rotational speeds on either sides of the second locking means 34, the latter may then be moved to the locked position . Likewise, when the vehicle is i n operation with the combustion engine running , it may be turned off and stopped without any torque in the powertrain disappeari ng . The possibi lities of achieving power balance are also considerably i mproved, thanks to the addition of the second electrical machine and the second locking means, wherein at such power balance, the su m of the desi red current to/from electrical energy storage means and electrical loads may be both negative and positive. The term power balance means that it is possible, within the general l i mitations specified for the drive system , to freely choose charge current to, or discharge current from , the energy storage means/hybrid battery at all operating modes occurring . It is especially advantageous that it is possi ble to start driving the vehicle equi pped with the drive system , even thoug h the batteries of the vehicle, which constitute its electrical energy storage system , are very cold and may not receive any current. At the start of the vehicle, the first electrical machine 9 rotates backwards and thus generates power when a positive torque must be achieved. The power generated may i n such case not be received by the battery, but it may be consu med by the second electrical machine 30, si nce the latter applies a torque on the output shaft of the combustion engine, and helps to rotate such output shaft.

The advantages described above are achieved also at braking of a vehicle, which initial ly drives at e.g . a speed of approxi mately 50 km/h with the combustion engine runni ng , si nce the drive system according to the invention has two electrical machi nes. Accordingly, torque balance may usually be reached i n the planetary gear without any reduction of the total braki ng torque being required. The same total braki ng torque may then be maintained when the first locking means is moved to the release position , i .e. the planetary gear is unlocked, and the combustion engine is controlled to its idl ing engine speed. Therefore, it is often advantageous to brake i n one and the same gear al l the way until the vehicle stops, which is facilitated in the drive system accordi ng to the invention.

The invention is obviously not l i mited in any way to the embodi ments descri bed above, but nu merous possible modifications thereof should be obvious to a person skil led i n the area, without such person departing from the spirit of the i nvention as defined by the appended clai ms. The first locking means may be adapted to lock together any two of said three components.

A transmission could be arranged between the rotor and the ri ng gear, and also between the combustion engine's output shaft and the sun wheel , such as upstream of the shaft which is displayed in Fig. 2 to be connected with the sun wheel . The latter transmission could also consist of a variable gear.

It is also conceivable that the drive system has the ring gear as the first component and the sun wheel as the third component, even if the reverse would be preferable because of the advantages mentioned above.

The drive system accordi ng to the present appl ication may, at least in some situations, also be advantageously used where no energy storage means/hybrid battery is comprised. I n appl icable situations, energy is then instead exchanged, only between the first electrical machi ne and the second electrical machi ne. One example of an appl ication of this method is the replacement of the function of a traditional coupli ng device (typically, a friction coupling) or a hydraulic torque converter where such is normally exposed to hig h heat development and/or wear. Advantageously, a traditional friction coupling in a heavy tractor may, accordi ng to the present application , e. g. be replaced with a drive system that does not comprise any energy storage means/hybrid battery. Another example of an appl ication where the drive system according to the present application may be used without comprising any energy storage means/hybrid battery is at the i mplementation of shifting , when the drive system may be used to control/adjust/regulate the torque and/or rotational speed of the i nput shaft of the gearbox and/or of the output shaft/flywheel of the combustion engi ne to carry out shifting in an advantageous manner. Energy is therefore exchanged only between the first electrical machine and the second electrical machine.