DE102022101838A1 - Shunting operation in motor vehicles with two electrically driven axles - Google Patents

Abstract

The invention relates to a drive arrangement and a method for operating a motor vehicle with a first driven axle, which is assigned a first electric drive machine, and a second driven axle, which is assigned a second electric drive machine, in a shunting operation, having the steps: determining a total axle torque required to meet a speed change request; Activation of the two electric drive machines in such a way that they jointly apply the determined total axle torque, the first electric drive machine and the second electric drive machine being activated with different axle torques.

Description

The invention relates to a method for operating a motor vehicle with two driven axles and a drive arrangement with a control unit for carrying out such a method.

In motor vehicles with an internal combustion engine drive and an automatic torque converter transmission or a transmission with simulated behavior, the speed is finely adjusted below a creeping speed of approx. 7 km/h by tensioning the drive train and brakes.

This behavior was adopted for electric drives in known vehicles. In a driving mode that is based on internal combustion engine driving behavior (driving mode D in previous vehicles of the applicant), there is creeping like in a converter transmission without pedal actuation, and when the brake pedal is actuated, the vehicle stops with a friction brake until it comes to a standstill.

However, in order to prevent creaking noises and stopping jerks when the brake pads transition from sliding to static friction, it is desirable to avoid using the brakes. The e-machine is then dosed against the direction of travel via the accelerator or brake pedal. This is often implemented in a driving mode that is intended to enable “one pedal driving” (driving mode B in previous vehicles of the applicant): no creeping without pedal actuation; recuperation to a standstill without pedal actuation; Delay washes out at a slower rate.

With such a modulation of the brake pedal, however, there are audible load direction changes in the transmission of the electric machine (due to the backlash), particularly often when maneuvering or when stopping when the vehicle comes to a standstill.

The play in the drive train can also result in a dead time when dosing by the driver, which brings with it undesirable inaccuracy, especially when maneuvering.

In order to avoid the load change click, the spontaneity of the electric machine when reacting to dosages by the driver is also limited in the known concepts, because the load change requires a temporary damping of the torque, which reduces the load change click.

In 1 the backlashes 101 and 102 on both axes VA and HA of a motor vehicle 100 with a known drive arrangement 110 are shown schematically when accelerating. As in 2 shown, these backlashes 101 and 102 change in the GVA front axle differential and in the GHA rear axle differential with each transition of the vehicle 100 between acceleration and deceleration between the respective traction flank 103 or 104 and the respective thrust flank 105 and 106, so that the backlashes 107 and 108 result when decelerating. These edge changes, which are controlled by a known control unit S*, cause the undesirable load change click when the previously play-affected edge impacts during the load change. A total axle torque M _S calculated by means of the control unit S* in accordance with a speed change request is applied to the two axles in equal or proportional parts M1.

The simultaneous impact on the front axle VA and the rear axle HA increases the perceptibility of the unwanted click and results from the simultaneous load change of the engine 2 of the front axle VA and the engine 4 of the rear axle HA with known operating strategies. This connection is in 3 shown for known methods.

Against this background, it is an object of the invention to improve maneuvering and/or stopping in motor vehicles with two electrically drivable axles.

Each of the independent claims defines, with its features, an object that solves this problem. The dependent claims relate to advantageous developments of the invention.

According to one aspect, a method for operating a motor vehicle with a first driven axle, to which a first electric drive machine is assigned, and a second driven axle, to which a second electric drive machine is assigned, in a shunting operation is disclosed.

In the present case, the maneuvering operation is determined in particular by a low positive or negative longitudinal speed (below an absolute amount of 2 m/s) and/or through a low positive or negative longitudinal acceleration (= longitudinal speed change) of the vehicle (below an absolute amount of approx. 0.1 g ≈ 1/s ² ), and refers to a stand-up area with regard to the length in terms of the length Skindle conditions (i.e. in particular: pedals) of the motor vehicle.

The method has at least the following method steps, which can be carried out in the order specified or in another order that makes sense for a person skilled in the art: (i) Recognizing a speed change request, in particular by actuating an accelerator pedal and/or a brake pedal, such as metered pedaling or metered withdrawal; the speed change request can also be equal to zero, i.e. the driver requests to continue driving at a constant speed; (ii) determination of a total axle torque required to meet the speed change requirement and to be applied in total to both driven axles in particular, (iii) activation of the two electric drive machines in such a way that they jointly apply the calculated total axle torque, with the first electric drive machine and the second electric drive machine being activated with different axle torques.

This control of the two drive machines for different axle torques on the first and the second driven axle is also referred to here as tensioning of the two drive machines/drive trains.

By slightly bracing the drive units on the front and rear axles against each other, the driving speed can be increased and reduced without a load change taking place in one of the two transmissions.

With the omission of the load changes, the usual load change clicking (during load changes from the backlash), which without the invention can only be damped with lossy load change damping - but cannot be completely avoided - is also eliminated.

Consequently, there is no need to use the vehicle brakes to decelerate in the maneuvering area, so that the associated creaking noises are eliminated. Instead, the vehicle can be braked by means of the electric machines, in particular until the vehicle comes to a standstill; and that without a load change click. The invention thus makes it possible to operate a vehicle that is electrically driven on two axles when maneuvering—without the disturbing noises that usually occur.

According to one embodiment, the motor vehicle can be decelerated by means of the two drive machines by operating one or both machines as a generator.

In the present case, a maneuvering range can be determined by a longitudinal speed range between a positive and a negative limit value of the longitudinal speed of the vehicle and/or by a longitudinal speed change range between a positive and a negative limit value of a longitudinal speed change.

According to a further aspect, a drive arrangement of a motor vehicle is disclosed with (a) a first driven axle, to which a first electric drive machine is assigned, and (b) a second driven axle, to which a second electric drive machine is assigned, and (c) a control unit which is set up to control a method according to an embodiment of the invention, in particular to control the drive machines with a method according to an embodiment of the invention.

The invention is based, among other things, on the idea that the driving speed can be increased and reduced by slightly tensioning the two drive units on the front and rear axles against one another, without a load direction change taking place in one of the two transmissions.

For this purpose, the stopping torque is applied to a drive machine and is additionally increased by an offset of, for example, approx. +/- 10 to 50, in particular 20 Nm (values in particular related to a torque offset at machine level; in typical applications of the invention without a shiftable transmission, 10 Nm at machine level roughly correspond to 100 Nm at wheel level).

A torque offset that acts in the opposite direction in the same amount is applied to the other axis, so that a total twisting torque is applied that corresponds to twice the torque offset.

This ensures that the two axes are loaded with torques with different signs. As a result, there are no more sign changes in the torque in the drive units in the fine dosing range (= shunting range). As a result, the load change clicking is eliminated with the load change.

In addition to avoiding this tooth flank chatter, there is an increase in drive spontaneity when maneuvering, since load change damping is no longer required, and play in the drive train (gears, drive shaft gearing, constant velocity joints, etc.) is eliminated.

According to one embodiment, this torque offset is activated only when maneuvering and/or only when there is sufficient road grip, since it is accompanied by a loss of all-wheel drive when starting and stopping, and is therefore critical in low-µ situations. Application restrictions can therefore be, for example: (1) shunting operation, i.e. a fine metering area close to a standstill; and/or (2) low accelerations only; and/or (3) deactivation under conditions suspecting low road-tire friction, such as outside temperature below 3°C and/or humidity above saturation humidity. An assumption regarding low road/tire friction can be made, for example, based on a friction value estimator and/or a friction value map (Car2X communication).

According to one embodiment, the first and second electric drive machines are controlled differently with axle torques that differ by at least a predetermined tensioning torque. In this way, a sufficient torque difference can be ensured specific to the application in order to reliably avoid load changes in all operating cases of shunting. In particular, the twisting torque at machine level for typical vehicle weights can be between 10 and 50 Nm, in particular 20 Nm. Thus, if the speed change request is equal to zero, a difference between the two axle torques corresponds exactly to the tensioning torque. In the case of positive or negative speed change requests, a difference in the axle torques by the required total axle torque is greater than the tensioning torque.

According to one embodiment, the two electric drive machines are controlled in such a way that the axis torque directions (on one axis on the one hand and on the other hand on the other axis) are opposite to one another.

According to one embodiment, a sign of a longitudinal speed change results from which of the two axles a torque with a higher absolute value is controlled. This means that load changes are avoided even more reliably.

According to one embodiment, there is a deceleration torque on one of the two driven axles, in particular on the front axle, in particular fundamentally, i.e. during the entire maneuvering operation, and an acceleration torque on the other of the two driven axles, in particular on the rear axle.

This defines which of the driven axles is used to decelerate the vehicle during maneuvering and which is used to accelerate the vehicle. For example, a vehicle with rear-wheel drive and front brakes can be modeled using the control of the electric drive units according to the invention.

According to one embodiment, the speed change request is a deceleration request or an acceleration request. Thus, in maneuvering, the invention can be used both for decelerating and for accelerating the vehicle.

According to one embodiment, the tensioning torque is maintained as the minimum difference between the two axle torques even after the deceleration request or the acceleration request has ended. In this way, load change clicking can be avoided during the entire shunting operation.

According to one embodiment, the deceleration request is a stall request. In this way, the vehicle can be brought from a shunting mode to a standstill without any load change clicking - and also without a creaking of mechanical brakes.

According to one embodiment, the tensioning torque is maintained as the minimum difference between the two axle torques when there is a request to stop until the vehicle comes to a standstill. This means that the vehicle can be brought from a shunting mode to a standstill without any load change clicking and also without any creaking of the mechanical brakes.

According to one embodiment, the tensioning torque is maintained as the minimum difference between the two axle torques when there is a request to stop until the end of the shunting operation, with the end of the shunting operation being triggered in particular by exceeding a limit value for a positive or negative longitudinal speed change and/or a positive or negative vehicle longitudinal speed. In this way, load change clicking can be avoided during the entire shunting operation.

According to one embodiment, a speed change request, in particular a deceleration request, is recognized by a release of an accelerator pedal and/or by an actuation of a brake pedal. The invention can thus be used both in an operating mode of the vehicle drive, in which a deceleration characteristic of a vehicle operated with an internal combustion engine is simulated (D mode), and in an operating mode dus, in which a greater or maximum recuperation is already activated when the accelerator pedal is released (B mode).

According to one embodiment, a deceleration request is implemented, in particular not by actuating a further, for example mechanical and/or hydraulic, brake, but rather by a corresponding activation of the two drive machines. In this way, with the invention, the vehicle can be stopped when maneuvering without the usual creaking of the brakes—and also without a load change click.

According to one embodiment, the respective direction of action of the torques is retained even when the vehicle longitudinal speed passes through zero (i.e. when changing from forward to reverse travel or vice versa), so that in particular the two drive units are controlled in such a way that the tensioning torque is maintained and a flank change is thus avoided.

According to one embodiment, the torque difference can also be generated via a speed difference between the two axles. The connection results from the tire behavior, which describes an approximately linear relationship between torque and speed difference for small longitudinal forces.

• 1 zeigt schematisch die Flankenspiele an beiden Achsen eines Kraftfahrzeugs mit einer bekannten Antriebsanordnung beim Beschleunigen.
• 2 zeigt schematisch die Flankenspiele an beiden Achsen eines Kraftfahrzeugs mit einer bekannten Antriebsanordnung beim Verzögern.
• 3 zeigt ein Diagramm zur konventionellen Betriebsstrategie des Kraftfahrzeugs aus den 1 und 2.
• 4 zeigt schematisch die Flankenanlagen an beiden Achsen eines Kraftfahrzeugs mit einer Antriebsanordnung zur Durchführung eines Verfahrens nach einer beispielhaften Ausführung der Erfindung.
• 5 zeigt ein Diagramm zur Beschreibung eines Verfahrens nach einer beispielhaften Ausführung der Erfindung, das mit der beispielhaften Antriebsanordnung aus 4 durchgeführt wird.
• 6 zeigt beispielhaft Art und Grenzen der Anwendung des beispielhaften Verfahrens gemäß 5 in einem Fahrmodus des Kraftfahrzeugs, der einem Rangierbetrieb eines Verbrennungsmotorisch angetriebenen Fahrzeug mit einem Wandlergetriebe nachempfunden ist.
• 7 zeigt beispielhaft Art und Grenzen der Anwendung des beispielhaften Verfahrens gemäß 5 in einem Fahrmodus des Kraftfahrzeugs, der ein „One-Pedal-Driving“ weitestmöglich unterstützt.

Further advantages and possible applications of the invention result from the following description in connection with the figures:

• 1 shows schematically the backlashes on both axles of a motor vehicle with a known drive arrangement when accelerating.
• 2 shows schematically the backlashes on both axles of a motor vehicle with a known drive arrangement when decelerating.
• 3 shows a diagram of the conventional operating strategy of the motor vehicle from the 1 and 2 .
• 4 shows schematically the flank systems on both axles of a motor vehicle with a drive arrangement for carrying out a method according to an exemplary embodiment of the invention.
• 5 FIG. 14 is a diagram describing a method according to an exemplary embodiment of the invention using the exemplary drive assembly of FIG 4 is carried out.
• 6 shows by way of example the nature and limits of the application of the exemplary method according to FIG 5 in a driving mode of the motor vehicle, which is modeled on a maneuvering operation of a vehicle driven by an internal combustion engine with a converter transmission.
• 7 shows by way of example the nature and limits of the application of the exemplary method according to FIG 5 in a driving mode of the motor vehicle that supports “one-pedal driving” as far as possible.

4 shows schematically the flank systems on both axes VA and HA of a motor vehicle 1 with a drive arrangement 10 for carrying out a method according to an exemplary embodiment of the invention.

The clamping of the two axes VA and HA to one another with a clamping torque M _Δ results in a different effective direction of the two axle torques M _VA and M _HA . The total axle torque M _S is applied to one of the two axles VA and HA; in addition, half of the twisting moment M _A is applied to that axle on which the total axle torque M _S is applied; on the other axis in the opposite direction, the other half of the twisting moment M _Δ .

In the exemplary embodiment, when decelerating from forward creep travel: M _{VA ≈MS} +M _Δ /2 and M _HA ≈−M _Δ /2. Even with a different proportional distribution of the axle torques, the predetermined clamping torque _MA is applied to the two axle torques divided equally in another application. The resulting twisting moment M _Δ is maintained here during maneuvering and ensures that there is always backlash 107 on the front axle VA and backlash 102 on the rear axle HA. In other words: the thrust flank 105 is always in contact with the front axle VA, and the traction flank 104 is always in contact with the rear axle. As a result, there is no load change clicking.

In 5 this connection is off for the exemplary embodiment 4 using a diagram analogous to 3 shown. In the present case, the front axle VA is always subjected to a torque M _VA which acts in the opposite direction to the direction of rotation of the front axle VA. The rear axle HA is always subjected to a torque M _HA that acts in the direction of rotation of the rear axle.

The exemplary embodiment is described here on the basis of the application of a forward shunting operation. Of course, the application example (and the invention as a whole) can also be used in reverse shunting operations. Even when the vehicle's longitudinal speed passes through zero, the tensioning torque is retained.

In principle, the clamping torque M _Δ is maintained while the method is being used. The sign with which the speed change a takes place—that is, whether an acceleration a>0 or a deceleration a<0 results—is then determined by which of the two torques M _VA or M _HA has the greater absolute value.

6 shows an example of the type and limits of the application of the method according to FIG 5 in a driving mode of the motor vehicle, which is based on a maneuvering operation of a vehicle driven by an internal combustion engine with a converter transmission (D mode). The change in speed a is plotted against the speed v in a diagram. The inner ellipsoid shown in dashed lines represents the shunting operating range RB of the motor vehicle. The exemplary method is carried out within a method range VBD, so that the tensioning of the axles is only released outside the shunting operating range RB, and 4WD functionality is then available again. In driving mode D, the speed change is requested by the driver both in the case of an acceleration a>0 and in the event of a deceleration a<0 by means of the brake pedal position. Depending on the position of the brake pedal, the drive machines 2 and 4 are then controlled by the control unit S according to the exemplary method.

7 shows an example of the type and limits of the application of the method according to FIG 5 in a driving mode of the motor vehicle that supports “one-pedal driving” as far as possible (B mode). The change in speed a is plotted against the speed v in a diagram. The inner ellipsoid shown in dashed lines represents the shunting operating area RB of the motor vehicle. The exemplary method is carried out within a method area VBB, so that the tensioning of the axles is only released outside the shunting area KB, and 4WD functionality is then available again. In driving mode B, the speed change is requested by the driver in the process range VBB both with an acceleration a>0 and with a deceleration a<0 by means of the accelerator pedal position. According to the accelerator pedal position, the drive machines 2 and 4 are then controlled by the control unit S according to the exemplary method. A brake pedal area BPB can represent an exception, for example if, in the sense of a "soft stop" functionality, the recuperation in the shunting operating area RB washes out to a standstill; in the brake pedal range BPB, the speed change request can then also be made in driving mode B, if necessary by means of the brake pedal.

Reference List

1

motor vehicle

10

drive arrangement

107

crossplay

101, 102, 107, 108

cross plays

105, 106

thrust flanks

103, 104

pulling flanks

a

speed change

BPD

brake pedal area

GHA

rear axle drive

GVA

front axle drive

HA

rear axle

MΔ

twisting torque

MHA

rear axle torque

MS

cumulative axle torque

MVA

front axle torque

RB

shunting operation area

S

control unit

v

speed

v.a

front axle

VBB

procedural area

VBD

procedural area

100

Known motor vehicle

10

Known drive arrangement

S*

Known control unit

Claims (13)

Method for operating a motor vehicle (1) with a first driven axle (VA), to which a first electric drive motor (2) is assigned, and a second driven axle (HA), to which a second electric drive motor (4) is assigned, in shunting mode (RB), comprising - determining a total axle torque (M _S ) required to meet a speed change request, - controlling the two electric drive motors (2, 4) in such a way that they jointly apply the determined total axle torque, the first electric drive machine ( 2) and the second electric drive machine (4) are controlled with different axle torques (M _VA , M _HA ). procedure according to claim 1 , characterized in that the different control of the first electric drive machine and the second electric drive machine with axle torques (M _VA , M _HA ) takes place, which differ by at least a predetermined torque (M _Δ ). procedure according to claim 1 or 2 , characterized in that the two electric drive machines are controlled in such a way that the axial torque directions are opposite to one another.. procedure according to claim 3 , characterized in that a sign (a>0, a<0) of a longitudinal speed change (a) results from which of the two axles (VA, HA) an axle torque (M _VA , M _HA ) with a higher absolute value is controlled. Method according to one of the preceding claims, characterized in that in the maneuvering operation on one of the two driven axles, in particular on the front axle (VA), a deceleration torque is present, and on the other of the two driven axles, in particular on the rear axle (HA), an acceleration torque is basically present. Method according to any one of the preceding claims, characterized in that the speed change request is a deceleration request or an acceleration request or a constant speed request. procedure according to claim 6 , characterized in that the tension torque (M _Δ ) is maintained as the minimum difference between the two axle torques even after the deceleration request or the acceleration request has ended. procedure according to claim 6 or 7 , characterized in that the deceleration request is a stop request. procedure according to claim 8 , characterized in that the tension torque (M _Δ ) is maintained as the minimum difference between the two axle torques when a stopping request is made until the vehicle comes to a standstill. Method according to one of the preceding claims, characterized in that the tensioning torque (M _Δ ) is maintained as the minimum difference between the two axle torques when there is a request to stop until the end of the shunting operation. Method according to one of the preceding claims, characterized in that a speed change request, in particular a deceleration request, is recognized by a withdrawal of an accelerator pedal and/or by an actuation of a brake pedal. procedure according to claim 11 , characterized in that a deceleration request is implemented by a corresponding control of the two drive machines. Drive arrangement (10) of a motor vehicle (1) with a first driven axle (VA), to which a first electric drive machine (2) is assigned, and a second driven axle (HA), to which a second electric drive machine (4) is assigned, and a control unit (S) which is set up to control a method according to one of the preceding claims.

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