DE102011005468A1 - Actuation method for hybrid vehicle drive train, involves determining torque produced by electric machine for functions i.e. driving operations, from difference of maximum actual torque produced by electric machine and starting torque - Google Patents

Abstract

The method involves determining a starting torque produced by an electric machine (3) for starting a piston internal combustion engine (2) depending on an actual operating mode of the piston internal combustion engine when the piston internal combustion engine is switched off. Torque produced by the electric machine for functions i.e. driving operation of a compressor, represented by the machine is determined from a difference of maximum actual torque produced by the machine and the starting torque. The starting torque is determined depending on a position of a piston of the engine.

Description

The invention relates to a method for operating a vehicle drive train with a reciprocating internal combustion engine according to the closer defined in the preamble of claim 1. Art.

In known from practice vehicle drive trains with a reciprocating internal combustion engine, which is coupled via an infinitely variable transmissibility transferring switching element with an electric machine, the deactivated piston internal combustion engine by a corresponding adjustment of the transfer capability of the switching element and by a then via the switching element of the electric machine in Direction of the reciprocating internal combustion engine transferable starting torque transferred to a switched-operating state.

Depending on the respective present embodiment of the vehicle drive train is in switched-off operating state of the reciprocating internal combustion engine the possibility to drive a vehicle purely electric motor via the electric machine, in which case the drive torque is provided in the region of an output alone on the electric machine. In addition, depending on the respective present embodiment of the vehicle drive train, it is also possible to apply both a drive torque generated by the electric machine and by the reciprocating internal combustion engine to the output during a so-called hybrid operating state. In addition, a vehicle in a conventional manner can only be driven via a drive torque provided by the reciprocating internal combustion engine and the electric machine can either be switched off or operated as a generator.

The above-described operating states are selected, inter alia, as a function of a desired driver input and an operating state of an electrical machine assigned to the electrical machine via a superordinate operating strategy and in each case carried out as a function of the operating state.

In addition, there is the possibility that further components of a vehicle, such as pump systems, air conditioning systems and the like, can be supplied with a mechanical drive torque via the electric machine in order to be able to carry out a desired operation thereof when the piston internal combustion engine is switched off, as required.

From the electric machine, a maximum speed-dependent torque can be generated in each case in the current operating point of the electric machine. Beyond that torques are the electric machine only by a transition into a so-called overload range available, during which the electric machine is exposed to unacceptably high loads that may permanently affect the functioning of the electric machine.

If at least part of the torque generated by the electric machine with the piston internal combustion engine switched off at the current operating point is used as a function of a requirement of the operating strategy for the operation of the vehicle components and / or for a purely electric driving operation of a vehicle, there is an additional request for transferring the piston internal combustion engine from its switched-off operating state in its switched-on operating state under certain circumstances the possibility that the piston internal combustion engine can not be started on the electric machine without the electrical machine passes into the overload range.

In order to avoid a transition to the overload range, the piston internal combustion engine can only be converted into its switched-on operating state according to the requirements when the part of the electric motor generated by the electric machine for the operation of the vehicle components and / or for a purely electromotive driving operation of a vehicle is reduced. However, this is undesirable because such an approach, in particular during an electric driving operation, during which the output torque is then reduced without corresponding driver request default, for a driver of a vehicle is not traceable.

In order to avoid such unwanted operating state curves of hybrid vehicle drive trains, only the part of the maximum torque that can be generated by the electric machine at the current operating point is provided for the operation of the vehicle components and / or the purely electric driving operation, which is above the torque value required for starting the piston internal combustion engine goes. The reserved for starting the piston engine part of the maximum torque that can be generated by the electric machine at the current operating point is usually an application-specific starting torque plus a safety margin. This part is larger than the torque actually required to start the reciprocating internal combustion engine. By keeping this high torque value, starting of the reciprocating internal combustion engine is to be ensured reliably regardless of the current operating state of the vehicle drive train.

The procedure, however, means that the torque available from the electric machine for further consumers of a vehicle, ie for different vehicle components and also for a purely electromotive driving operation, is limited to a greater extent by the torque reserve given with safety margin than for the starting process the reciprocating internal combustion engine is necessary. Since of the operating strategy to be provided by the electric machine torque values that are greater than that of the electric machine minus the safety margin. defined starting torque torque available, usually a request for starting the piston internal combustion engine is triggered, the piston internal combustion engine is started earlier than necessary, and thus limited by the additional electric machine fuel savings in the field of piston internal combustion engine.

The present invention is therefore based on the object to provide a method with which a start of a reciprocating internal combustion engine of a hybrid vehicle drive train is assured at the same time low fuel consumption safely.

According to the invention this object is achieved by a method having the features of claim 1.

By means of the method according to the invention for actuating a vehicle drive train with a reciprocating internal combustion engine, with an electrical machine coupled with a switching element with continuously variable transmission capability and with an output, a starting torque for starting the reciprocating internal combustion engine depending on a starting torque available from the electric machine is switched off when the piston internal combustion engine is switched off determines the current operating state of the reciprocating internal combustion engine and determined by the electric machine for more representable via the electric machine functions available torque from the difference of the maximum torque of the electric machine and the starting torque currently generated by the electric machine.

Due to the operating state-dependent determination of the starting torque, on the one hand, a requested connection of the reciprocating internal combustion engine is reliably ensured and, on the other hand, the part of the torque which can be used by the electric machine, which can be used for further functions, in comparison to procedures known from practice, in which a predefined torque value is reduced to a lesser extent for starting the piston internal combustion engine during operation of a vehicle drive train, whereby the piston internal combustion engine is switched on during identical operating state curves by the inventive approach to a lesser extent and thus less fuel is consumed.

In an advantageous variant of the method according to the invention, the starting torque is determined as a function of a position of a piston of the reciprocating internal combustion engine, in the associated combustion chamber during a starting process of the reciprocating internal combustion engine first a combustion of a fuel mixture arranged in the combustion chamber. Thus, the torque to be applied by the electric machine can be determined as a function of the parking position of the piston internal combustion engine, which is to be applied starting from the current parking position of the piston internal combustion engine up to the first ignition of the piston internal combustion engine.

If the starting torque is determined as a function of a pressure in a combustion chamber associated with a piston of the piston internal combustion engine, during which a combustion of a fuel mixture arranged in the combustion chamber takes place during a starting operation of the piston internal combustion engine, the determination of the starting torque counteracts the starting process and during the starting process in the relevant Combustion occurs occurring compression work.

In a further advantageous variant of the method according to the invention, the starting torque is determined as a function of a boost pressure of a piston engine assigned turbocharger, whereby a counteracting the starting process of the reciprocating internal combustion engine pressure in the combustion chamber in a simple manner is considered.

The reciprocating internal combustion engine is started in a further advantageous variant of the method according to the invention in the presence of a request of a torque provided by the electric machine which is greater than the torque available from the electric machine for further functions that can be represented by the electric machine. This is achieved in a simple manner that a requested by an operating strategy or by a driver torque that is not available from the electric machine alone, provided.

Is the starting torque during the starting process of the reciprocating internal combustion engine in Depending on the current operating state of the reciprocating internal combustion engine, the part of the torque currently generated by the electric machine can be reduced with the connecting operation of the reciprocating internal combustion engine, during which the torque to be applied for starting the reciprocating internal combustion engine becomes increasingly smaller due to an incipient rotational movement of the reciprocating internal combustion engine. This, in turn, offers the possibility of further realizing further functions to be represented by the torque generated by the electric machine, such as a driving operation, starting increasingly from the electric machine with a higher torque.

The current operating state of the reciprocating internal combustion engine to be used as the basis for determining the starting torque can essentially be determined precisely only at a speed of the reciprocating internal combustion engine of at least approximately equal to zero. For this reason, it is provided in a further advantageous variant of the method according to the invention that in the presence of a speed of the reciprocating internal combustion engine greater than a limit value for determining the starting torque, a predefined operating state of the reciprocating internal combustion engine is used, which is equivalent to a statistically protected torque value or to a reserve torque is and is ensured by means of a start of the reciprocating internal combustion engine safely.

The piston internal combustion engine remains in a further advantageous variant of the method according to the invention in the presence of a request for switching off the piston internal combustion engine in its switched-on operating state, when a sum of the starting torque and the available from the electric machine for more representable via the electric machine functions available torque larger is a maximum torque value that can be generated by the electric machine at the current operating point. This is avoided in a simple manner that the electrical machine passes through the switching off of the piston internal combustion engine and a turn due to the torque request in turn subsequent connections of the piston internal combustion engine in an overload range or asked by the connection process for the other functions of the electric machine available Torque value decreases during the Zuschaltvorganges of the reciprocating internal combustion engine to a level at which the functions can not be displayed in the required extent.

In order not to unnecessarily reduce the torque available by the electric machine for further functions to be displayed in the switched-off operating state of the reciprocating internal combustion engine, the transmission capability of the switching element in the switched-off operating state of the reciprocating internal combustion engine is at least approximately zeroed in a further variant of the method according to the invention.

In the presence of a request for starting the piston internal combustion engine, the transmission capability of the switching element is raised in a further advantageous variant of the method to a value at which a torque required for the starting process is transmitted from the electric machine via the switching element in the direction of the reciprocating internal combustion engine. This ensures that only the torque value is guided by the electric machine in the direction of the piston internal combustion engine, which is required for starting the piston internal combustion engine.

In order to check the plausibility of the starting torque determined in dependence on the current operating state of the piston internal combustion engine or the predefined starting torque, in a further advantageous variant of the method according to the invention during a starting process of the piston internal combustion engine, a value of the transmission capacity of the switching element is determined to which the transmission capability of the switching element for starting the piston internal combustion engine lead is. Thus, operating state curves or starting processes of the reciprocating internal combustion engine are determined in a simple manner, during which the piston internal combustion engine passes by applying smaller or larger torque values than the operating state-specific starting torque or the predefined starting torque in its switched-on operating state. This actual torque value determined in each case during a starting process of the reciprocating internal combustion engine is then available to adaptation routines via which runtime-related changes in the operating characteristic of the reciprocating internal combustion engine can be taken into account.

In determining a deviation between the value of the transmission capability of the switching element to which the transmission capability of the switching element to start the piston internal combustion engine is to be performed, and the transmission capability of the switching element, which is equivalent to the determined starting torque, the starting torque determined before the starting operation of the reciprocating internal combustion engine to the equivalent value feasible for the determined transmission capability of the switching element. Thus, for example, runtime-related changes in the field of piston internal combustion engine, such as reduced friction during a movement of a piston in the piston chamber of the reciprocating internal combustion engine, in a simple manner considered.

In order to take into account changes in the behavior of the reciprocating internal combustion engine with higher safety, the operating state-dependent determined starting torque only at multiple determination of a deviation between the value of the transfer capability of the switching element, to which the transfer capability of the switching element to start the reciprocating internal combustion engine is to be guided, and the transmission capability of the switching element , which is equivalent to the determined starting torque, adapted.

Both the features specified in the claims and the features specified in the subsequent embodiments of the subject invention are each suitable alone or in any combination with each other to further develop the subject invention. The respective feature combinations represent no limitation with respect to the development of the subject matter according to the invention, but essentially have only an exemplary character.

Further advantages and advantageous embodiments of the hybrid vehicle transmission according to the invention will become apparent from the claims and the embodiment described in principle with reference to the drawings.

It shows:

1 a highly schematic representation of a vehicle drive train; and

2 a course of a transmission capability of a switching element and a speed of a reciprocating internal combustion engine of the vehicle drive train according to 1 during a starting operation of the reciprocating internal combustion engine over time.

In 1 is a highly schematic view of a vehicle drive train 1 with a reciprocating internal combustion engine 2 , an electric machine 3 and a downforce 4 shown. The electric machine 3 is between the reciprocating internal combustion engine 2 and the downforce 4 arranged and via a running with infinitely variable transmissibility switching element 5 with the reciprocating internal combustion engine 2 can be brought into operative connection. On the output side is the electric machine 3 via another switching element 6 with the downforce 4 connectable, wherein between the other switching element 6 and the downforce 4 a transmission device 7 is provided, in the range of different translations can be displayed.

Depending on the current operating state of the vehicle drive train as well as an actuation of the vehicle drive train 1 over a superordinate operating strategy becomes at the output 4 either only from the reciprocating internal combustion engine 2 or just the electric machine 3 or from the reciprocating internal combustion engine 2 and the electric machine 3 a torque applied to one with the vehicle driveline 1 executed vehicle during a train operation of the vehicle drive train 1 to drive in a positive sense or during a coasting operation of the vehicle drive train 1 slow down or operate, for example, during a downhill at a constant speed with low load on the vehicle brakes.

In purely electric driving is the with the vehicle powertrain 1 running vehicle alone with one of the electric machine 3 generated torque driven. To the vehicle drive train 1 to operate with high efficiency during the purely electric driving, the reciprocating internal combustion engine 2 in a switched-off operating state, while in the field of piston internal combustion engine 2 no fuel is consumed.

To that from the electric machine 3 during the purely electric driving available torque provided by in the off piston engine 2 with closed switching element 5 does not reduce drag torques, the transmission capability of the switching element 5 in switched-off operating state of the reciprocating internal combustion engine 2 led to a level to which essentially the switching element 5 no torque is feasible.

In addition, over that of the electric machine 3 available torque other functions, such as the drive of a compressor of an air conditioner of a vehicle, the drive of a water pump, the drive of an electric generator and the like, representable.

Lies during a switched-off operating state of the reciprocating internal combustion engine 2 from the parent operating strategy or based on a driver request specification, a request for one of the electric machine 3 torque to be provided before that of the electric machine 3 In the current operating point exceeds the maximum producible torque, issued a request for switching on the piston internal combustion engine 2 , Wherein the transfer capability of the switching element 5 is raised in the manner described later, one for the connection of the reciprocating internal combustion engine 2 required starting torque of the electric machine 3 over the switching element 5 in the direction of the reciprocating internal combustion engine 2 to be able to lead.

Thus, a transfer of the reciprocating internal combustion engine 2 from their switched-off operating state in their switched-on operating state without affecting the purely electric driving operation and the other on the torque of the electric machine 3 ensured functions is ensured, this is to start the reciprocating internal combustion engine 2 required starting torque of each in the current operating point of the electric machine 3 deducted maximum available torque and kept as a so-called reserve torque. This means that in the switched-off operating state of the reciprocating internal combustion engine 2 to illustrate the purely electric driving operation of the vehicle drive train 1 and / or for more about the torque of the electric machine 3 representable functions only the difference between the current operating point of the electric machine 2 maximum producible torque of the electric machine 2 and the starting torque of the reciprocating internal combustion engine 2 is made available.

To that for the purely electric driving and / or the representation of the other functions available torque of the electric machine 3 to reduce as much as possible by the Vorvorhalt the starting torque, the vorzuhaltende starting torque is in each case depending on a current operating state of the reciprocating internal combustion engine 2 determined, the exact determination of the current operating state of the reciprocating internal combustion engine 2 , which is based on the determination of the starting torque, only at standstill of the reciprocating internal combustion engine 2 can be determined to the desired extent.

The current operating state of the reciprocating internal combustion engine 2 is at standstill of the reciprocating internal combustion engine 2 from an engine control unit of the reciprocating internal combustion engine 2 determined and provided to the parent operating strategy. In this case, the engine control unit delivers, for example, a current position of a crankshaft of the reciprocating internal combustion engine 2 , from which in turn a position of a piston of the reciprocating internal combustion engine 2 can be determined, in the associated combustion chamber during a starting process of the reciprocating internal combustion engine 2 First, a combustion of a fuel mixture arranged in the combustion chamber takes place.

Furthermore, the determination of the electric machine 3 to be provided starting torque for starting the reciprocating internal combustion engine 2 a filling of the combustion chamber of the combustion chambers of the various pistons of the reciprocating internal combustion engine 2 , a current operating temperature of the reciprocating internal combustion engine 2 , ie an oil temperature and a water temperature, based as that when starting the reciprocating internal combustion engine 2 applied starting torque substantially from the pressure in the combustion chambers of the reciprocating internal combustion engine 2 depends.

The respectively present in the combustion chambers pressure of the reciprocating internal combustion engine 2 is inter alia also in response to a closing time of a throttle valve of the reciprocating internal combustion engine 2 during the shutdown of the reciprocating internal combustion engine 2 , Furthermore, the pressure in the combustion chambers of the reciprocating internal combustion engine 2 also by the shutdown of the reciprocating internal combustion engine 2 and a boost pressure of a preferably provided turbocharger. In addition, there is also a rotational speed of the reciprocating internal combustion engine 2 to which the piston internal combustion engine 2 is turned off, for the determination of the Abstellprofils the reciprocating internal combustion engine 2 relevant.

At speeds of the deactivated piston internal combustion engine 2 greater than zero, the above-described procedure is not feasible, which is why during such an operating phase of the reciprocating internal combustion engine 2 a statistically secured and from the electric machine 3 available starting torque is maintained. This statistically secured starting torque corresponds to a torque value with which the piston internal combustion engine 2 can be safely transferred from a switched-off operating state to a switched-on operating state. Furthermore, the statistically-assured starting torque is also provided as a so-called limiting torque, which represents a limit value. Is from the electric machine 3 for the connection of the piston internal combustion engine 2 only providing a torque that is less than the statistically-assured starting torque becomes the reciprocating internal combustion engine 2 not switched off.

The statistically secured starting torque is dependent on a statistically secured parking position of the reciprocating internal combustion engine 2 preferably determined applicatively, wherein the statistically secured parking position of the reciprocating internal combustion engine 2 has a Abstellprofil from which starting a maximum starting torque is applied to the piston internal combustion engine 2 From the switched-off operating state in their switched-operating state to transfer.

In order to be able to take into account a change in the operating characteristics of the reciprocating internal combustion engine due to the transit time, it is checked whether the statistically secured parking position of the reciprocating internal combustion engine changes over the transit time. A change in the operating characteristics of the reciprocating internal combustion engine 2 results among other things from a reduction of the frictional forces in the area between the pistons and the piston chambers as well as in the range of further assemblies of the reciprocating internal combustion engine 2 , in their area during operation of the reciprocating internal combustion engine 2 , ie during a rotational movement of the individual elements of the reciprocating internal combustion engine 2 , Friction occurs.

In addition, depending on the currently existing operating state of the deactivated piston internal combustion engine 2 at a speed of the reciprocating internal combustion engine 2 zero starting torque during a starting operation of the reciprocating internal combustion engine 2 over the electric machine 3 depending on the transmission capability of the switching element 5 checked. For checking, the value of the transmission capability of the switching element 5 determined to which the reciprocating internal combustion engine 2 From their switched-off operating state goes into their switched operating state. Depending on the determined value of the transmission capability of the switching element 5 is that for connecting the reciprocating internal combustion engine 2 Actually applied starting torque determinable, since this is equivalent. Subsequently, the actually applied starting torque is the previously depending on the non-rotating operating state of the deactivated piston internal combustion engine 2 facing certain starting torque.

If there is a deviation between the function of the transmission capability of the switching element 5 determined and the actually applied starting torque and before the connection of the reciprocating internal combustion engine 2 depending on the current operating state of the reciprocating internal combustion engine 2 at a speed of the reciprocating internal combustion engine 2 If the starting torque is determined equal to zero greater than a threshold value, this becomes dependent on the operating state of the reciprocating internal combustion engine 2 certain starting torque by the function of the transmission capability of the switching element 5 determined and actually applied starting torque replaced.

In order to avoid an adaptation of the starting torque that is too fast and possibly faulty, it is possible to adapt the starting torque to the new value of the starting torque only after a multiple determination of a deviation.

2 shows a profile of the transmission capability m_5 of the switching element 5 during a Zuschaltvorganges the reciprocating internal combustion engine 2 starting from its deactivated operating state over time t. Furthermore, a curve of the rotational speed n_2 of the reciprocating internal combustion engine 2 and a curve of the rotational speed n_3 of the electric machine 3 during the starting process of the reciprocating internal combustion engine 2 shown over time t.

At a time T0, a request for switching on the deactivated internal combustion engine is issued 2 starting from a speed n_2 of the reciprocating internal combustion engine 2 equals zero. The transmission capability m_5 of the switching element 5 is guided from the time T0 up to a point in time T1 with a steep gradient to an intermediate value which is smaller by a predefined offset value than that as a function of the current operating state of the reciprocating internal combustion engine 2 determined starting torque is. During this first phase, the switching element 5 for the connection of the piston internal combustion engine 2 prepared as quickly as possible within a short period of time. From time T1, the transmission capability m_5 of the switching element 5 with a smaller gradient in turn ramped up to a time T2 raised to a value equivalent to the starting torque, wherein by the comparison with the first phase reduced further lifting the transmission capacity m_5 of the switching element 5 a transition of the electric machine 3 is avoided in an overload range. This approach is based on the knowledge that one of the still standing piston internal combustion engine 2 applied high torque to overcome the static friction in the field of piston internal combustion engine 2 a large increase in dynamic effects during towing of the reciprocating internal combustion engine 2 causing, however, the load on the electric machine 3 at the beginning of the starting process of the reciprocating internal combustion engine 2 undesirably increased.

During this limited by the times T1 and T2 second phase increases the speed n_2 of the reciprocating internal combustion engine 2 only slightly, since initially a static friction in the piston engine 2 from the electric machine 3 to overcome. At a time T3, which is the time T2 upstream and to which the static friction in the piston engine 2 is overcome, the speed n_2 of the reciprocating internal combustion engine starts 2 due to the higher transmission capacity m_5 of the switching element 5 to increase with a larger gradient than before the time T3, wherein the speed n_2 initially increases only slightly more due to the compression work now to be performed in each case via the piston in the region of the combustion chambers.

From the time T2, the transfer capability of the switching element 5 at the value equivalent to the starting torque up to one Time T4 held constant, while the speed n_2 of the reciprocating internal combustion engine 2 continues to rise. The level of the plateau of the transmission capacity m_5 of the switching element 5 varies depending on the current speed n_2 and the current operating state of the reciprocating internal combustion engine 2 , Here also the gradient of the course of the speed n_2 of the reciprocating internal combustion engine 2 is taken into account when adjusting the level of the plateau.

From the time T4, to which the speed n_2 of the reciprocating internal combustion engine 2 has reached a defined speed level and a predefined positive threshold of the gradient of the speed n_2 of the reciprocating internal combustion engine is exceeded, the transmission capacity m_5 of the switching element 5 initially lowered with a small gradient ramp to another intermediate value. The reduction of the transmission capacity m_5 of the switching element 5 causes a gentle increase in the speed n_2 of the reciprocating internal combustion engine 2 to a point in time T5 at which the reciprocating internal combustion engine 2 ignites. From the ignition timing T5, the transmission capability m_5 of the switching element 5 with a steep gradient substantially to zero, while the speed n_2 of the reciprocating internal combustion engine 2 due to the now present combustion in the piston internal combustion engine 2 without further assistance from the electrical machine 3 in the direction of the idle speed of the reciprocating internal combustion engine 2 increases, which is reached at a time T6. Subsequently, the speed n_2 of the reciprocating internal combustion engine 2 to the level of the speed n_3 of the electric machine 3 feasible. The switching element 5 is then synchronously and without load in a fully closed operating state transferred, in which one of the reciprocating internal combustion engine 2 generated torque completely from the switching element 5 is transferable.

Alternatively, there is the possibility of the speed n_2 of the reciprocating internal combustion engine 2 with the switching element open 5 to a speed greater than the speed n_3 of the electric machine 3 adjust and the switching element 5 close. Then is the started piston engine 2 in addition to that of the electric machine 3 Torque also generated in the torque with respect to the switching element 5 output side part of the vehicle drive train 1 initiated.

Will the speed n_2 of the reciprocating internal combustion engine 2 to a value less than the current speed n_3 of the electric machine 3 set, the piston engine becomes 2 with closed switching element 5 from the electric machine 3 dragged. This is for example during a coasting operation of the vehicle drive train 1 provided during which the electric machine 3 is to operate as a generator and the electric machine 3 due to a current state of charge of one of the electrical machine 3 associated electrical energy storage but only motorized operable.

Alternatively, there is also the possibility of the transmission capability m_5 of the switching element 5 from time T4 to keep constant at the level equivalent to the starting torque and at time T6, to which the speed n_2 of the reciprocating internal combustion engine 2 the speed n_3 of the electric machine 3 corresponds and the reciprocating internal combustion engine 2 is substantially fully connected, to raise to the maximum value, to which one of the reciprocating internal combustion engine 2 provided torque in full on the switching element 5 in the direction of the output 4 is feasible.

The course of the speed n_3 of the electric machine 3 is during the above-described starting process of the reciprocating internal combustion engine 2 is substantially constant and in this case is approximately at the level of the idle speed of the reciprocating internal combustion engine 2 set.

The reduction of the transmission capability of the switching element 5 at time T4, during the starting process of the reciprocating internal combustion engine 2 as a function of a determined angle of rotation of the crankshaft of the reciprocating internal combustion engine 2 plausibility. This ensures that the reciprocating internal combustion engine 2 or the piston of the reciprocating internal combustion engine 2 , In its associated combustion chamber existing fuel mixture during the starting process of the reciprocating internal combustion engine 2 first ignited, is safely passed over top dead center.

In principle, when the piston internal combustion engine is switched off 2 one from the electric machine 3 to be provided starting torque for starting the reciprocating internal combustion engine 2 depending on a current operating state of the reciprocating internal combustion engine 2 and an initial value of the transfer capability m_5 of the switching element equivalent to the starting torque 5 determined on the transmission capacity m_5 of the switching element 5 for guiding the starting torque from the electric machine 3 in the direction of the reciprocating internal combustion engine 2 is to be set at least. The transmission capability m_5 of the switching element 5 During the first phase, it is fed to the intermediate value, which is smaller by the offset value than the starting value. During the second phase, which continues until time T2, the transmission capability is brought to the starting value, the gradient of the change in the transmission capacity m_5 of the switching element 5 during the first phase is greater than the gradient during the second phase.

From a predefined value of the speed n_2 of the reciprocating internal combustion engine 2 greater than a threshold value is the transmission capability m_5 of the switching element 5 during the beginning of the time T4 and ending at the time T5 third phase reduced. The transmission capability m_5 of the switching element 5 is from the time T5 to that in the combustion chamber of the reciprocating internal combustion engine 2 during the starting process of the reciprocating internal combustion engine 2 first a combustion of a fuel mixture arranged in the combustion chamber takes place and represents the beginning of a fourth phase, at least approximately led to zero. The transmission capability m_5 of the switching element 5 in the present case is equal to zero at a time T7, which is earlier than the time T6. In this case, the amount of the gradient of the change in the transmission capacity is m_5 of the switching element 5 during the third phase smaller than the amount of the gradient of the change in the transmission capacity m_5 of the switching element 5 during the fourth phase to the further starting operation of the reciprocating internal combustion engine 2 by the rapid decoupling of the reciprocating internal combustion engine 2 in the area of the switching element 5 from the remaining part of the vehicle drive train 1 not to influence.

In the presence of an operating state of the reciprocating internal combustion engine 2 , starting from which the piston internal combustion engine 2 goes into their switched operating state, before the transmission capability m_5 of the switching element 5 reaches the determined starting value, the current value of the transmission capacity m_5 of the switching element 5 plus an offset value as a new starting value for the operating state of the reciprocating internal combustion engine 2 set, in dependence of which the starting value of the transmission capability m_5 of the switching element 5 was determined. Furthermore, it is provided that during a tow start of the reciprocating internal combustion engine 2 starting from a speed n_2 of the reciprocating internal combustion engine 2 greater than a speed threshold depending on the parking position of the reciprocating internal combustion engine 2 determined towing moment or the determined transmission capacity of the switching element 5 is not considered.

LIST OF REFERENCE NUMBERS

1

Vehicle powertrain

2

Piston internal combustion engine

3

electric machine

4

output

5

switching element

6

another switching element

7

transmission device

m_5

Transfer capability of the switching element

n_2

Speed of the reciprocating internal combustion engine

n_3

Speed of the electric machine

T0 to T7

discrete time

t

Time

Claims (13)

Method for actuating a vehicle drive train ( 1 ) with a reciprocating internal combustion engine ( 2 ), one with a continuously variable transmissibility transferring switching element ( 5 ) couplable electric machine ( 3 ) and an output ( 4 ), characterized in that when switched off piston internal combustion engine ( 2 ) one of the electric machine ( 3 ) starting torque for starting the reciprocating internal combustion engine ( 2 ) in dependence on a current operating state of the reciprocating internal combustion engine ( 2 ) and one of the electrical machine ( 3 ) for more about the electric machine ( 3 ) representable functions available torque from the difference of the current of the electric machine ( 3 ) maximum producible torque and the starting torque is determined. A method according to claim 1, characterized in that the starting torque in dependence of a position of a piston of the reciprocating internal combustion engine ( 2 ) is determined, in its associated combustion chamber during a starting operation of the reciprocating internal combustion engine ( 2 ) first a combustion of a fuel mixture arranged in the combustion chamber takes place. A method according to claim 1 or 2, characterized in that the starting torque in dependence on a pressure in a piston of the reciprocating internal combustion engine ( 2 ) is determined in which during a starting operation of the reciprocating internal combustion engine ( 2 ) first a combustion of a fuel mixture arranged in the combustion chamber takes place. Method according to one of claims 1 to 3, characterized in that the starting torque in response to a boost pressure of the piston internal combustion engine ( 2 ) associated turbocharger is determined. Method according to one of claims 1 to 4, characterized in that the reciprocating internal combustion engine ( 2 ) in the presence of a request from the electrical machine ( 3 ) provided torque greater than that of the electric machine ( 3 ) for more about the electric machine ( 3 ) representable functions for Available torque is the reciprocating internal combustion engine ( 2 ) is started. Method according to one of claims 1 to 5, characterized in that the starting torque during the starting process of the reciprocating internal combustion engine ( 2 ) as a function of the current operating state of the reciprocating internal combustion engine ( 2 ) is determined. Method according to one of claims 1 to 6, characterized in that in the presence of a rotational speed (n_2) of the reciprocating internal combustion engine ( 2 ) greater than a limit value for determining the starting torque, a predefined operating state of the reciprocating internal combustion engine ( 2 ) is used. Method according to one of claims 1 to 7, characterized in that the reciprocating internal combustion engine ( 2 ) in the presence of a request for switching off the reciprocating internal combustion engine ( 2 ) remains in its switched-on operating state when a sum of the starting torque and that of the electric machine ( 3 ) for more about the electric machine ( 3 ) representable functions available torque is greater than one of the electric machine ( 3 ) maximum torque value that can be generated at the current operating point. Method according to one of claims 1 to 8, characterized in that the transmission capability (m_5) of the switching element ( 5 ) in the switched-off operating state of the reciprocating internal combustion engine ( 2 ) is guided at least approximately to zero. Method according to one of claims 1 to 9, characterized in that in the presence of a request for starting the reciprocating internal combustion engine ( 2 ) the transmission capability (m_5) of the switching element ( 5 ) is raised to a value at which a torque required for the starting operation of the electric machine ( 3 ) via the switching element ( 5 ) in the direction of the reciprocating internal combustion engine ( 2 ) is transmitted. Method according to one of claims 1 to 10, characterized in that during a starting process of the reciprocating internal combustion engine ( 2 ) a value of the transmission capacity (m_5) of the switching element ( 5 ), to which the transmission capability (m_5) of the switching element ( 5 ) for starting the reciprocating internal combustion engine ( 2 ) is to lead. A method according to claim 11, characterized in that when determining a deviation between the value of the transmission capability (m_5) of the switching element ( 5 ), to which the transmission capacity (m_5) of the switching element ( 5 ) for starting the reciprocating internal combustion engine ( 2 ) and the value of the transmission capability (m_5) of the switching element ( 5 ), which is equivalent to the determined starting torque, which before starting the piston internal combustion engine ( 2 ) certain value of the starting torque to the determined to the transferred capacity (m_5) of the switching element ( 5 ) equivalent value. A method according to claim 12, characterized in that the determined starting torque only at multiple determination of a deviation between the value of the transmission capability (m_5) of the switching element ( 5 ), to which the transmission capacity (m_5) of the switching element ( 5 ) for starting the reciprocating internal combustion engine ( 2 ) and the value of the transmission capability (m_5) of the switching element ( 5 ), which is equivalent to the detected starting torque, is adjusted.

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