DE102019217513A1 - Method for operating a vehicle with two drivable axles - Google Patents

Abstract

The invention relates to a method for operating a vehicle (100) with two drivable axles (110, 120) and several drive units (130, 140), each axle being assigned at least one drive unit (130, 140), and at least one of the Drive units (130, 140) is designed as an electrical machine, with a requested power and / or a requested torque being distributed dynamically to the multiple drive units (130, 140) during operation of the vehicle (100), and with a change over time the division is limited, and / or the division is carried out in such a way that the drive units (130, 140) do not provide the maximum possible power and / or the maximum possible torque in each case.

Description

The present invention relates to a method for operating a vehicle with two drivable axles and a plurality of drive units, each axle being assigned at least one drive unit, as well as a computing unit and a computer program for executing them.

State of the art

In addition to motor vehicles with only one internal combustion engine, there are also more and more motor vehicles with one or more electric drive units in addition to the internal combustion engine. Such vehicles are then referred to as so-called hybrid vehicles. There are also vehicles with only electric drives, i.e. drives that are designed as electrical machines. One then speaks of so-called electric vehicles.

Electric vehicles and hybrid vehicles with two driven axles are usually characterized by the fact that each axle is assigned at least one drive unit or that two separate drive units (e.g. two electric machines or one electric machine and an internal combustion engine) can deliver drive power independently of one another. These drive units are then typically mechanically coupled to separate drive axles.

Based on a driver request (usually expressed via the accelerator pedal) and / or a drive request from driver assistance systems (e.g. cruise control, adaptive cruise control or similar) and possibly also a speed of the drive units, possibly also indirectly via the driving speed, a Distribution between the drive units with regard to the power to be output and / or the torque to be output can be determined. In general, this means that a requested power and / or a requested torque is distributed to the multiple drive units, preferably dynamically, i.e. changed during driving. Boundary conditions for this determination of the division can be various optimization criteria, such as energy efficiency, comfort or component service life.

Such a division of power or torque and its determination are, for example, from the EP 3 132 966 A1 or the EP 2 323 862 B1 known.

Disclosure of the invention

According to the invention, methods for operating a vehicle as well as a computing unit and a computer program for executing them are proposed with the features of the independent claims. Advantageous configurations are the subject of the subclaims and the description below.

The invention is based on a method for operating a vehicle with two drivable (or driven) axles and several drive units, each axle being assigned at least one of the several drive units. In this case, each of the multiple drive units is preferably also provided for only one of the two axes, i.e. mechanically coupled to it. At least one of the plurality of drive units is designed as an electrical machine. The above-mentioned hybrid vehicles with an internal combustion engine and an electric machine, or else electric vehicles with two electric machines, are therefore preferred. It goes without saying, however, that more than two drive units can also be provided. Also conceivable and typical are, for example, vehicles in which two electrical machines are provided for one axle, for example one on each or for each wheel. The same can then apply to the other axle.

As already mentioned, during the operation or during the operation of such a vehicle, a requested power and / or a requested torque is now also distributed to the multiple drive units, in particular dynamically. In other words, the division of which of the drive units is currently providing which portion of the total requested power and / or the total requested torque is varied during driving operation. In the case of such a division, one can also speak of a division factor for each of the drive units, which then indicates the contribution of the drive unit in question to the total power or to the total torque. In the case of only two drive units, however, it is generally sufficient to specify just one such distribution factor (the other one results from the difference to 100%), but this must always be related to the same drive unit.

A subdivision specified in this way is to be distinguished from a factor, which portion of a maximum possible power or a maximum possible torque a drive unit provides or emits.

In this way, the drive units can be used more efficiently. However, a driver of the vehicle does not necessarily receive feedback about such a change in the division during operation or during operation the journey, especially since the total power output or the torque output by the drive units does not change.

The request for a specific power and / or a specific torque can, as already mentioned, be made preferably by a driver's request, typically via an accelerator pedal, and / or a request from a driver assistance system. For example, a driver assistance system for distance control can request acceleration and thus an increase in power or torque.

In particular, electric vehicles with at least two electrical machines, but also hybrid vehicles, enable a particularly rapid change in the distribution of the (overall) requested power and / or the (overall) requested torque to the multiple drive units, namely through a highly dynamic power build-up or power reduction on the relevant axes.

However, it has now been found that such a particularly rapid or highly dynamic change in the distribution, e.g. during steering maneuvers by the driver and / and under road conditions with low or transient road friction coefficients, can lead to the vehicle breaking away. This is particularly disadvantageous because a change in the division can generally not occur in a comprehensible, noticeable or reproducible manner for the driver, and thus a breakaway of the vehicle can surprise the driver.

According to one aspect of the invention, a temporal change in the division or its extent (e.g. a gradient or a difference) is now limited by preferably limiting a permissible change in the division per unit of time to a threshold value. Any adverse effects of a change that is too rapid on the driving dynamics are thus prevented or at least reduced. This also avoids cases in which a driving stability program or the like would react too late or not quickly enough. The background to this is that, for example, a driving stability program during critical driving maneuvers can intercept a possible breakaway of the vehicle with constant torques on the axles or wheels, but needs a certain time to record the situation and initiate countermeasures. Due to the fundamentally possible, high dynamics of the electric drive units and a possible (rapid) change in the distribution during such a critical driving maneuver, however, such a breakout would be accelerated, so that the driving stability program would react too late. In this sense, it is also expedient if the mentioned threshold value is specified as a function of a driving stability program used, and then expediently also on its conditions or criteria.

It is also advantageous if the extent to which the division changes over time is limited as a function of the requested power and / or the requested torque. A limitation depending on current driving conditions is also useful. In this way, it is possible to react in a particularly individual manner, while at the same time leaving as much freedom as possible for the division. For example, if the requested power is low overall, a faster change over time can be permitted, since a critical driving situation will then hardly occur. On the other hand, only a slow change over time can be permitted, for example with an overall high, requested power, since a critical driving situation can then occur with a significantly higher probability.

When dividing the requested power and / or the requested torque over the multiple drive units, it has hitherto been customary to use the maximum possible power or the maximum possible torque of the drive unit. In other words, situations often arise in which at least one of the drive units delivers the maximum possible power or the maximum possible torque with an otherwise expedient division. Unless all drive units are already at their respective maximum (so that an increase in the total power or the total torque would no longer be possible), an increase in the requested power and / or the requested torque leads to a change in the distribution with corresponding Adjustment must be made before the increase in the power or torque requirement can be implemented. This leads to a certain delay in the response of the vehicle.

According to a further aspect of the invention, the division is therefore carried out in such a way that the drive units do not provide the maximum possible power and / or the maximum possible torque, at least if this is still possible based on a requested power and / or a requested torque . In other words, the division is carried out in such a way that the drive units provide a lower or a lower than the maximum possible power and / or the maximum possible torque. Here, for example, a kind of reserve of 5%, 10%, 20% or even 30% of the maximum possible Power or the maximum possible torque are kept. This has the direct consequence that a requested increase in the power and / or the torque can be implemented immediately, even if the optimal distribution is sometimes not used for reasons of energy efficiency.

If there is then an increase in the power or the torque, i.e. if the existing reserve is (at least partially) exhausted, the division is preferably changed, in particular in such a way that the drive units again do not have the maximum possible power and / or provide the maximum possible torque in each case. The reserve can therefore be held again - with a different division. It goes without saying that such a reserve can no longer be maintained or can no longer be maintained as desired, close to the total maximum available power or the total maximum available torque. It is then conceivable to hold a smaller, but still possible, reserve. However, a large part of the operational areas can be covered in this way.

A particular advantage here is that the drive units operate less often at their performance limit in this way and the service life of the drive units is thus positively influenced.

It should be pointed out that both aspects of the invention, i.e. to limit the extent to which the division changes over time and to hold the reserve for the drive units during division, can also be used together or jointly. Both aspects enable particularly pleasant driving behavior for the driver that is known from conventional vehicles, while the advantages of the distribution of the power or the torque to the drive units can still be used.

A computing unit according to the invention, e.g. a control unit of a motor vehicle, is set up, in particular in terms of programming, to carry out the method according to the invention.

The implementation of the method according to the invention in the form of a computer program or computer program product with program code for performing all method steps is advantageous, since this causes particularly low costs, especially if an executing control device is used for other tasks and is therefore available anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. A program can also be downloaded via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention emerge from the description and the accompanying drawing.

The invention is shown schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

Figure list

• 1 shows schematically a vehicle in which the method according to the invention can be carried out.
• 2 shows schematically a sequence of a method according to the invention in a preferred embodiment.
• 3 shows schematically a sequence of a method according to the invention in a further preferred embodiment.
• 4th shows schematically a sequence of a method according to the invention in a further preferred embodiment.

Embodiment (s) of the invention

In 1 a vehicle is shown schematically in which the method according to the invention can be carried out. The vehicle 100 has two axes 110 and 120 which are each designed as a drivable or driven axle - with appropriately drivable wheels. The vehicle 100 also has two drive units 130 and 140 which are each designed as an electrical machine, for example, and each for one of the two axes 110 , 120 are provided, ie mechanically and thus torque-transmitting are coupled therewith.

It goes without saying, as already mentioned above, that the proposed methods not only apply to an electric vehicle, as in FIG 1 shown, are feasible, but also in a hybrid vehicle in which, for example, instead of the electric machine 130 an internal combustion engine is used, then typically with a transmission.

Furthermore, there is a computing unit designed as a control unit 180 provided, by means of which the drive units 130 , 140 are controllable. For example, the control unit 180 a power and / or a torque of each of the drive units 130 , 140 request or control them to deliver this power or this torque. The control unit can do this 180 in particular also a total - of, for example, an accelerator pedal and / or a driver assistance system - Requested power or a torque on the drive units 130 , 140 distribute, ie make an appropriate division.

In 2 a sequence of a method according to the invention is shown schematically in a preferred embodiment, as is the case, for example, with the in 1 shown vehicle can be carried out. For this purpose, a power P as the variable to be provided or output by the drive units is plotted as an example over time t.

For this example it should be assumed that the one drive unit 130 the drive unit can provide a maximum output of 120 kW 140 however, only a maximum of 60 kW.

Initially, a total power P ₁ of 100 kW should then be requested, with a division A ₁ is set in which the drive unit 130 70% of the total power is provided by the drive unit 140 on the other hand only 30%. This represents the drive unit 130 a power of 70 KW ready, the drive unit 140 an output of 30 kW.

Now, for example due to changed conditions for energy efficiency, the division is to continue with a requested power P ₁ of 100 kW A ₂ be set in which the drive unit 130 The drive unit provides 50% of the total power 140 also 50%. In the case of the electric machines as drive units, this changed power of 50 kW per drive unit could be set or implemented very quickly or within a very short time.

However, in order to avoid critical driving situations which may no longer be intercepted by a driving stability program, only a certain change ΔA per time unit Δt is permitted. It is conceivable that the division may only be changed in such a way that one drive unit increases or reduces its output by a maximum of 1 kW per second.

_{Furthermore, the requested power is now to be increased to P 2} of 150 kW, for example due to a changed driver's request. If now based on the current division A ₂ the power of both drive units would be increased more or less equally (relative or absolute), the drive unit would collide 140 , which can only provide a maximum of 60 kW, quickly reaches its limits, since it can only provide 40% of the total requested power P ₂ , but not 50%.

This would mean that during the change in the division, namely with a total power of 120 kW, that is, if both drive units provide 60 kW and 50% of the total power each, the division would have to be changed.

Therefore, the division can immediately A ₃ as they are according to the maximum possible power of the drive units 130 , 140 , namely approx. 67% (or 2/3) and approx. 33% (or 1/3) of the total performance should be taken into account. The power of the drive is accordingly 130 to 100 kW, the power of the drive 140 set to 50 kW.

It goes without saying that the consideration of the division, as it results according to the maximum possible power of the drive units to each other (i.e. 2/3 to 1/3) can also mean that the total power required in the specific case (or a torque ) is taken into account, so that, for example, a split of 65% for the drive unit 130 and 35% for the drive unit 140 is set because this is still affordable with a total requested output of 150 kW.

In 3 a sequence of a method according to the invention is shown schematically in a further preferred embodiment, as is the case, for example, with the in 1 shown vehicle can be carried out. As in 2 , for example, a power P plotted over time t.

Here, too, the data should look like in the example 2 apply, whereby a total power P ₁ of 100 kW should initially be requested here too, with a division A ₁ is set in which the drive unit 130 70% of the total power is provided by the drive unit 140 on the other hand only 30%. This represents the drive unit 130 a power of 70 KW ready, the drive unit 140 an output of 30 kW.

If the total requested power P ₁ remains the same, for example due to changed conditions for energy efficiency, with a further requested power P ₁ of 100 kW, the division should be changed. What is desired is, as in 2 shown a division of 50% and 50%. This is shown here by means of a dashed line.

This division would mean that a power output of 50 kW each would be set for both drive units. At the drive unit 140 , which can only provide a maximum of 60 kW, this means a share of approx. 83% (or 5/6) of the maximum possible power. This would, however, leave little scope for increasing the output for subsequent, higher requested outputs if the division between the drive units is then to remain the same.

It is therefore assumed by way of example that - if this can be represented overall - each drive unit should only provide a maximum of 70% of its maximum possible power. This leads to the division A ₄ , in which the drive unit 130 then 58% of the total power, i.e. 58 kW, is provided by the drive unit 140 then 42%, i.e. 42 kW (this corresponds to 70% of 60 kW). In this way, there are both drive units, that is to say in particular also with the drive unit 140 , still have sufficient reserves for a short-term increase in the total output to be provided without having to change the division.

In 4th a sequence of a method according to the invention is shown schematically in a further preferred embodiment, in particular in the form of calculation chains or sequences of calculation processes, as can be carried out when setting or changing the division of a requested power or a requested torque.

First, a driver's request becomes 410 and a requirement 411 a driver assistance system in one step 420 the actual and currently requested power or torque is determined (e.g. the maximum of both selected). In step 430 it is then determined whether this requirement can be implemented, taking into account the limits of the drive units.

The latter is in the steps 460 , 470 , 480 determined. In step 460 the total performance of the drive units is determined without any division, in step 470 then specifically the limit for the power that can be provided, in step 480 then for the torque. Then in step 440 an implementation strategy determined in step 450 then the distribution to the drive units takes place.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 3132966 A1 [0005]
• EP 2323862 B1 [0005]

Claims (9)

Method for operating a vehicle (100) with two drivable axles (110, 120) and several drive units (130, 140), with each axle being assigned at least one of the several drive units (130, 140), and with at least one of the several drive units (130, 140) is designed as an electrical machine, wherein during operation of the vehicle (100) a division (A _1, A ₂ , A ₃ , A ₄ ) of a requested power (P) and / or a requested torque among the plurality of Drive units (130, 140) is made dynamically, characterized in that a measure of the temporal change (ΔA / Δt) of the division is limited. Procedure according to Claim 1 , whereby the amount of change over time (ΔA / Δt) of the division is limited depending on the requested power (P) and / or the requested torque. Procedure according to Claim 1 or 2 , whereby the amount of change over time (ΔA / Δt) of the division is limited as a function of current driving conditions. Method according to one of the preceding claims, wherein the extent of the temporal change (ΔA / Δt) of the division is limited by limiting a permissible change in the division per unit of time (Δt) to a threshold value (ΔA). Method, preferably according to one of the preceding claims, for operating a vehicle (100) with two drivable axles (110, 120) and several drive units (130, 140), each axle being assigned at least one of the several drive units (130, 140) , and wherein at least one of the plurality of drive units (130, 140) is designed as an electrical machine, wherein during operation of the vehicle (100) a division (A _1, A ₂ , A ₃ , A ₄ ) of a requested power (P) and / or a requested torque is performed dynamically on the multiple drive units, characterized in that the division (A ₄ ) is performed in such a way that the drive units (130, 140) do not provide the maximum possible power and / or the maximum possible torque . Procedure according to Claim 5 , whereby, if after the division (A _1, A ₂ , A ₃ , A ₄ ) the requested power (P) and / or the requested torque are increased, the division (A _1, A ₂ , A ₃ , A ₄ ) is made. Computing unit (180) which is set up to carry out all method steps of a method according to one of the preceding claims. Computer program that causes a computing unit (180) to perform all method steps of a method according to one of the Claims 1 to 6th perform when it is executed on the computing unit (180). Machine-readable storage medium with a computer program stored thereon Claim 8 .

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