DE102019200820A1 - Method for distributing a braking torque requested by a driver to the front and rear axles of a motor vehicle - Google Patents

Abstract

Method for distributing a braking torque (FBM) requested by a driver to the front and rear axles (VA, HA) of a motor vehicle, the wheels (12, 14) of the front axle (VA) having a front friction brake device (20) and a front electric machine (22) and the wheels (16, 18) of the rear axle (HA) are assigned a rear friction brake device (24) and a rear electrical machine (26), according to which, in the presence of an understeer or oversteer situation during cornering, one of the understeer or Oversteering situation counteracting braking force distribution (B / B) is set, by means of which the braking torque (FBM) is divided into a front braking torque (BM) to be applied to the front axle (VA) and a rear braking torque (BM, BM) to be applied to the rear axle (HA) is that both braking torques (BM, BM) each have a recuperation torque component> 0.

Description

The invention relates to a method for distributing a braking torque requested by a driver to the front and rear axles of a motor vehicle, in particular an electric vehicle, in accordance with the type specified in claim 1.

Blending-capable braking systems that divide a braking torque requested by the driver, e.g. via the brake pedal or accelerator pedal (one-paddle behavior) into a friction braking torque component to be generated by a friction brake and a recuperation torque component to be made available by an electric machine, as well as corresponding methods for distributing the requested braking torque on the axles of a motor vehicle are well known. As is known, the distribution of the friction braking torque on the axles can be scalar, that is, the distribution of the friction braking torque on the front and rear axles is fixed hydraulically, such as 60% / 40%, or axially individually, that is, the distribution on the front and rear axles can be Operation can be varied. The example is based on the DE 10 2015 106 746 A1 and DE 10 2016 003 628 A1 referred. The DE 10 2016 003 628 A1 is characterized in particular by the fact that at least one electric machine is assigned to each axis, so that a “mixed” braking torque, ie a braking torque component and a recuperation torque component, is available for both axes.

The invention is based on the object of specifying a method for distributing a braking torque requested by a driver to the front and rear axles of a motor vehicle, in particular an electric vehicle, according to the type specified in claim 1, which occurs during a braking maneuver during cornering and the occurrence of a sub - or oversteer situation, ensures braking that supports the driving stability of the motor vehicle and thereby enables the highest possible braking energy recovery.

This object is achieved by the characterizing features of claim 1 in conjunction with its preamble features.

The subclaims form advantageous developments of the method according to the invention.

In a known manner, the wheels of the front axle are assigned a friction brake device, hereinafter referred to as the front friction brake device, and an electrical machine. The electrical machine assigned to the front axle is also referred to below as the front electrical machine. Correspondingly, a rear friction brake device and a rear electrical machine are also assigned to the wheels of the rear axle.

According to the invention, it is now provided that when cornering it is checked whether there is driving instability in the form of an understeer or oversteer situation, and that if there is an understeer or oversteer situation, a braking force distribution which counteracts the understeer or oversteer situation is set, the braking torque requested by the driver by means of the posed, ie Braking force distribution which counteracts the understeering or oversteering situation is divided into a front braking torque to be applied to the front axle and a rear braking torque to be applied to the rear axle in such a way that the front braking torque is necessarily a front recuperation torque component to be set via the front electric machine and the rear braking torque is mandatory has to be provided over the rear electrical machine rear recuperation torque.

Since the braking torque requested by the driver is now distributed to the front and rear axles with a braking distribution counteracting the understeering or oversteering, in accordance with the method according to the invention when there is an understeer or oversteer while cornering, it is advantageously ensured that the planned braking maneuver the tendency to understeer or oversteer of the motor vehicle is reduced. Since it is also provided according to the invention that both the front braking torque to be set on the front axle and the rear braking torque to be set on the rear axle each necessarily have a recuperation torque component, i.e. The fact that both electric machines each provide a share of the braking torque ensures high braking energy recovery.

In the event of an understeer situation on the front axle of the motor vehicle, a rear-axle braking torque distribution is preferably provided, i.e. A braking torque requested by the driver is distributed to the axles in such a way that the braking torque acting on the front axle is smaller than the braking torque acting on the rear axle.

The rear axle-heavy distribution to be set on the front axle in the event of an understeering situation can be permanently stored, e.g. 40/60, i.e. 40% front axle, 60% rear axle, or also as a variably adjustable distribution taking into account the current driving situation and thus the extent of the understeering present.

If, on the other hand, there is an oversteer situation on the rear axle during cornering, it is provided that a front axle load-dependent braking torque distribution is provided, with the consequence that the braking torque acting on the front axle is greater than the braking torque acting on the rear axle.

Accordingly, the front axle load distribution to be set in the event of an oversteer situation on the rear axle can also be stored as a fixed distribution, e.g. 60/40, i.e. 60% front axle and 40% rear axle, or in the form of a variable, the current driving situation, i.e. adjustable distribution taking into account the degree of the present oversteer.

It is preferably provided that - if the maximum recuperation torques available from the front and rear electrical machines are sufficient to cover the braking torques to be applied to the front and rear axles in accordance with the braking force distribution provided - the front braking torque is exclusively covered by the front recuperation torque component and the rear one Braking torque is formed exclusively by the rear recuperation torque component and thus the requested braking torque is applied entirely by the front and rear electrical machine. This ensures that the braking torque requested by the driver is complete, i.e. exclusively, is applied by the electrical machines, which advantageously ensures maximum braking energy recovery.

In the event that the maximum recuperation torque that can be provided by the front electrical machine is insufficient, the front braking torque and / or the maximum recuperation torque that can be provided by the rear electrical machine is insufficient to cover the rear braking torque, a remaining residual friction torque is determined , which is distributed to the front and / or rear axle, so that the front braking torque includes an additional front friction torque component and / or the rear braking torque includes an additional rear friction torque component, and thus the requested braking torque from the front and rear electrical machine and the front and / or rear friction brake device is applied.

If a residual friction torque is now required for the position of the braking torque requested by the driver, this has the advantageous effect that a friction braking torque is present on at least one axle, with the consequence that working and intervention of the ABS system on at least one axle is ensured .

A first embodiment provides that from the residual friction torque according to a scalar distribution a front friction torque component to be applied to the front axle by means of the front friction brake device and / or a rear friction torque component to be applied to the rear axle by means of the rear friction brake device is determined.

For this purpose, the remaining frictional torque is calculated using the current braking force distribution, i.e. the brake force distribution counteracting the understeer or oversteer situation, a front friction torque component to be applied to the front axle by means of the front friction device and / or a rear friction torque component to be applied to the rear axle by means of the rear friction brake device. A front and rear recuperation torque component is then determined taking into account the front and rear friction torque components and the current braking force distribution. Thus, the braking torque requested by the driver is applied by the front and rear electrical machines and the front and rear friction brake devices.

An alternative embodiment provides that the residual friction torque is divided axially into a front friction torque component to be applied to the front axle by means of the front friction brake device and / or into a rear friction torque component to be applied to the rear axle by means of the rear friction brake device. The braking torque requested by the driver is thus applied by the front and rear electrical machine and the front and / or rear friction brake device.

The check, namely whether there is driving instability in the form of an understeer or oversteer situation when cornering, is preferably carried out using sensors which are present as standard in today's motor vehicles and a corresponding evaluation of the data provided by these sensors, e.g. a detected lateral acceleration and / or a detected slip of a wheel of the motor vehicle and / or on the basis of a yaw rate and / or yaw rate difference and / or a vehicle speed and / or a difference in the wheel speeds of the wheels between the front and rear axles or the right and left side of the motor vehicle and / or an adhesion utilization on the wheels.

Further advantages and possible uses of the present invention result from the following description in connection with the embodiment shown in the drawing.

• 1 eine schematische Darstellung eines Kraftfahrzeugs zur Verdeutlichung des Verfahrens zur Verteilung eines von einem Fahrer angeforderten Bremsmoments auf die Achsen eines Kraftfahrzeugs.
• 1 zeigt in einer schematischen Darstellung ein insgesamt mit der Bezugsziffer 10 bezeichnetes Kraftfahrzeug. Die Vorderachse ist mit dem Bezugszeichen VA und die Hinterachse ist mit dem Bezugszeichen HA bezeichnet.

In the drawing means:

• 1 a schematic representation of a motor vehicle to illustrate the method for distributing a braking torque requested by a driver to the axles of a motor vehicle.
• 1 shows a schematic representation of a total with the reference number 10th designated motor vehicle. The front axle is identified by the reference symbol VA and the rear axle is identified by the reference symbol HA.

The wheels 12th , 14 the front axle is a front friction brake device, which is only indicated schematically here 20 as well as a front electric machine 22 assigned. Corresponding to the wheels 16 , 18th the rear axle HL one rear friction brake device each 24th as well as a rear electrical machine 26 assigned. The electrical machines 22 , 26 can be operated as generators in a known manner during recuperation.

Via a control unit 28 are the front and rear friction brake devices 20 , 24th as well as the front and rear electrical machine 22 , 26 can be controlled so that a braking torque FBM requested by a driver can be divided into a front braking torque BM _VA to be applied to the front axle _VA and a rear braking torque BM _{HA to} be applied to the rear axle HA.

For the description below, it is assumed that this is from the front electric machine 22 maximum available recuperation torque RK _VA-Max , = 400 Nm on the front axle VA and that from the rear electrical machine 26 maximum available recuperation torque RK _HA-Max = 300 Nm on the rear axle HA.

For the following first consideration, it is also assumed that the motor vehicle is cornering and that driving instability in the form of understeering was determined during cornering, ie that the wheels 12th , 14 the front axle VL the transverse forces that occur can no longer be transferred completely. The driver has also requested FBM braking torque of FBM = 500 Nm.

Based on the determined understeering situation, a braking force distribution which counteracts the understeering, ie rear axle load, here B _VA / B _HA = 40/60 is set.

und an der Hinterachse HL ein hinteres Bremsmoment BM_HA in Höhe von $${\text{BM}}_{\text{HA}}=\mathrm{0,6}*500\text{ Nm}=\text{300 Nm}$$

zu stellen.It is therefore present on the front axle VL a front braking torque BM _VA of $${\text{BM}}_{\text{VA}}=0.4*500\text{Nm}=\text{200 Nm}$$

and on the rear axle HL a rear braking torque BM _HA of $${\text{BM}}_{\text{HA}}=0.6*500\text{Nm}=\text{300 Nm}$$

deliver.

Ie the requested braking torque FBM is essentially on the rear axle HL posed. The associated relief of the front axle VL has the consequence that the tendency to understeer is not amplified, but rather that the tendency to understeer of the motor vehicle is reduced.

In the present case, this is from the front electrical machine 22 maximum available recuperation torque RK _VA-Max , = 400 Nm is sufficient, the front braking torque BM _VA = 200 Nm and that from the rear electrical machine 26 maximum available recuperation torque RK _HA-Max = 300 Nm is sufficient to cover the rear braking torque BM _HA = 300 Nm, the braking torque requested by the driver is FBM = 500 Nm completely from the front and rear electrical machine 22 , 26 upset.

This ensures maximum braking energy recovery.

For the following second observation, too, it is assumed that understeer was detected while cornering, but the driver has now requested a braking torque of FBM = 800 Nm.

On the basis of the determined understeering situation, a braking force distribution counteracting the understeering, that is to say rear axle load, in this case B _VA / B _HA = 40/60 is set.

und an der Hinterachse HL ein hinteres Bremsmoment BM_HA in Höhe von $${\text{BM}}_{\text{HA}}=\mathrm{0,6}*800\text{ Nm}=48\text{0 Nm}$$

zu stellen.Thus is on the front axle VL a front braking torque BM _VA of $${\text{BM}}_{\text{VA}}=0.4*800\text{Nm}=\mathrm{3rd}\text{00 Nm}$$

and on the rear axle HL a rear braking torque BM _HA of $${\text{BM}}_{\text{HA}}=0.6*800\text{Nm}=48\text{0 Nm}$$

deliver.

While that from the front electrical machine 22 on the front axle VL maximum available recuperation torque of RK _VA-Max , = 400 Nm is sufficient to provide the required front braking torque BM _VA in the amount of BM _VA = 320 Nm, that is from the rear electrical machine 26 maximum on the rear axle HL available regeneration torque RK _HA-Max in the amount of RK _HA-Max = 300 Nm is not sufficient to provide the required rear braking torque BM _HA in the amount of BM _HA = 480 Nm.

This results in a residual frictional friction Reib_Rest in the amount of Reib_Rest = 180Nm.

According to a first embodiment, the residual friction torque Reib_Rest = 180 Nm by means of the rear-axle load-dependent brake force distribution, here B _VA / B _HA = 40/60, becomes one of the front friction brake device 20 on the front axle VL front friction torque portion to be applied BM _{VA friction} and one from the rear friction brake device 24th on the rear axle HL BM _{HA friction} to be applied rear friction _{torque component} determines:
BM _HA-Reib = Reib_Rest = 180Nm, or $${\text{BM}}_{\text{VA friction}}={\text{BM}}_{\text{HA friction}}*{\text{B}}_{\text{VA}}/{\text{B}}_{\text{HA}}=180\text{Nm * 2/3}=120\text{Nm}$$

That on the front axle VL The front braking torque BM _{VA to be set} in the amount of BM _VA = 320 Nm is thus composed of a front friction torque component BM _{VA friction} in the amount of BM _{VA friction} = 120 Nm and a resulting front recuperation torque component BM _VA-Rek in the amount of BM _{VA- Rek} = BM _VA - BM _VA-Reib = 320 Nm - 120 Nm = 200 Nm.

Accordingly, this points to the rear axle HL rear braking torque BM _{HA to be set} in the amount of BM _HA = 480 Nm, a rear friction torque component BM _{HA friction} in the amount of BM _{HA friction} = 180 Nm and a rear recovery torque component BM _HA-Rek in the amount of
BM _HA-Rek = BM _HA - BM _HA-Reib = 480 Nm - 180 Nm = 300 Nm.

• Da, wie bereits ausgeführt, vorliegend das von der vorderen elektrischen Maschine 22 an der Vorderachse HL maximal bereitstellbare Rekuperationsmoment RK_VA-Max, = 400 Nm ausreichend ist, das vordere Bremsmoment BM_VA = 200 Nm zu stellen, ist ein zusätzlicher Reibungsmomentanteil an der Vorderachse VL nicht erforderlich, d.h. BM_VA-Reib = 0. Somit wird gemäß der achsindividuellen Verteilung das vordere Bremsmoment BM_VA vollständig von der vorderen elektrischen Maschine 22 gestellt, d.h. BM_VA = BM_VA-Rek = 320 Nm.

An alternative embodiment sees one - taking advantage of the front and rear electrical machines 22 , 26 maximum available recuperation moments - individual axis distribution of the residual friction friction Reib_Rest before:

• Since, as already stated, this is that of the front electrical machine 22 on the front axle HL maximum available recuperation torque RK _VA-Max , = 400 Nm is sufficient to set the front braking torque BM _VA = 200 Nm is an additional proportion of friction torque on the front axle VL not required, ie BM _VA-Reib = 0. Thus, according to the axle-specific distribution, the front braking torque BM _{VA is} completely from the front electrical machine 22 set, ie BM _VA = BM _VA-Rek = 320 Nm.

Accordingly, this points to the rear axle HL The rear braking torque BM _{HA to be set} in the amount of BM _HA = 480 Nm has a rear regeneration torque component BM _{HA -Rek} that corresponds to that of the rear electrical machine 26 maximum available rear recuperation torque RK _HA-Max , corresponds to, ie BM _HA-Rek = RK _HA-Max = 300 Nm and a rear friction torque component corresponding to the residual friction torque BM _HA-Reib = Reib_Rest = 180 Nm.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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

• DE 102015106746 A1 [0002]
• DE 102016003628 A1 [0002]

Claims (8)

Method for distributing a braking torque (FBM) requested by a driver to the front and rear axles (VA, HA) of a motor vehicle, the wheels (12, 14) of the front axle (VA) having a front friction brake device (20) and a front electric machine (22) and the wheels (16, 18) of the rear axle (HA) are assigned a rear friction brake device (24) and a rear electrical machine (26), in which, according to the method, it is checked when cornering whether driving instability in the form of an understeer or there is an oversteering situation, and if there is an understeering or oversteering situation, a braking force distribution (B _VA / B _HA ) which counteracts the understeering or oversteering situation is set, the requested braking torque (FBM) using the braking force distribution (B _VA / B _HA ) set in such a way a front braking torque (BM _VA ) to be applied to the front axle (VA) and a rear braking torque (BM.) to be applied to the rear axle (HA) _HA ), the front braking torque (BM _VA ) is necessarily a front recuperation torque component (BM _VA-Rek )> 0 to be set via the front electrical machine (22) and the rear braking torque (BM _HA ) is mandatory via the rear electrical machine (26) rear recuperation _torque component (BM _HA-Rek ) to be set> 0. Procedure according to Claim 1 , characterized in that if there is an understeering situation on the front axle (VA), the requested braking torque (FBM) is divided by means of a rear-axle braking force distribution (B _VA / B _HA ), so that the following applies: front braking torque (BM _VA ) <rear braking torque (BM _HA ). Procedure according to Claim 1 , characterized in that if there is an oversteer situation on the rear axle (HA), the requested braking torque (FBM) is divided by means of a front axle-heavy braking force distribution (B _VA / B _HA ), so that the following applies: front braking torque (BM _VA )> rear braking torque (BM _HA ). Procedure according to one of the Claims 1 to 3rd , characterized in that if the maximum recuperation torques (RK _VA - _Max , RK _HA-Max ) available from the front and rear electrical machine (22, 26) are sufficient, the braking force distribution (B _VA / B _HA ) to cover braking torques (BM _VA , BM _HA ) to be applied to the front and rear axles (BM _VA , BM _HA ), the front braking torque (BM _VA ) exclusively through the front recuperation torque component (BM _VA-Rek ) and the rear braking torque (BM _HA ) exclusively through the rear recuperation torque component (BM _HA-Rek ) is formed and thus the requested braking torque (FBM) is applied completely by the front and rear electrical machine (22, 26). Procedure according to Claim 4 , characterized in that if the maximum recuperation torque (RK _VA-Max , RK _HA-Max ) available from the front and / or from the rear electrical machine (22, 26) is not sufficient. cover the braking force distribution detected (B _VA / B _HA) on the front and / or rear axle (VA, HA) applied according to the braking torque (BM _VA, BM _HA), a remaining Restreibmoment (Reib_Rest) is determined, and that the requested braking torque (FBM) from the front and rear electrical machine (22, 26) and the front and / or rear friction brake device (20, 22) is applied. Procedure according to Claim 5 , characterized in that from the residual friction torque (residual friction) according to the braking force distribution (B _VA / B _HA ) a front friction torque component (BM _{VA friction} ) to be applied to the front axle (VA) by means of the front friction brake device (20) and a the rear friction torque component (BM _{HA friction} ) to be applied to the rear axle (HA) is determined by means of the rear friction brake device (22), and that taking into account the front and rear friction torque components (BM _{VA friction} , BM _{HA friction} ) according to the braking force distribution ( B _VA / B _HA ) the front and rear share of recuperation torque (BM _VA-Rek , BM _HA-Rek ) to be set on the front and rear axles (VA, HA) is determined, with the requested braking torque (FBM) from the front and rear electrical machine (22, 26) and the front and rear friction brake device (20, 24) is applied. Procedure according to Claim 5 , characterized in that the residual frictional torque (residual friction) is customized to a front and / or rear friction torque component (BM.) to be applied to the front and / or rear axle (VA, HA) by means of the front and / or rear friction brake device (20, 24) _VA-Reib , BM _HA-Reib ) is divided, the requested braking torque (FBM) being applied by the front and rear electrical machine (22, 26) and the front and / or rear friction brake device (20, 24). Procedure according to one of the Claims 1 to 7 , characterized in that the check whether there is driving instability in the form of an understeer or oversteer situation when cornering, on the basis of a detected lateral acceleration and / or a detected slip of a wheel (12, 14, 16, 18) of the motor vehicle and / or on the basis of a Yaw rate and / or yaw rate difference and / or a vehicle speed and / or a difference in the wheel speeds of the wheels (12, 14, 16, 18) between the front and rear axles (VA, HA) or the right and left sides of the motor vehicle (10) and / or a frictional utilization on the wheels ( 12, 14, 16, 18) is carried out.

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