DE102020121635A1 - Method for operating a braking system of a vehicle - Google Patents

Abstract

The invention relates to a method for operating a braking system of a vehicle,• wherein the vehicle comprises a friction brake for braking at least one vehicle wheel;• wherein the vehicle comprises at least one electric machine that can be used to generate deceleration of the vehicle and wherein• the vehicle has a traction control system for stabilizing the vehicle includes, wherein a traction control takes place when the wheel speed of the at least one vehicle wheel falls below or exceeds a calculated wheel speed limit range with a lower wheel speed limit and an upper wheel speed limit, and wherein a regenerative deceleration during traction control is prevented, the method comprising the following further steps:• detecting an activated anti-lock braking system on the at least one vehicle wheel;• detecting a stable driving situation of the vehicle;• changing the calculated wheel speed limit range of the traction control depending on the situation system by widening the lower wheel speed limit in such a way that a regenerative deceleration takes place.

Description

The invention relates to a method for operating a braking system of a vehicle according to claim 1. The prior art is an example of the DE 10 2013 201 691 A1 referred.

So-called recuperation is known in particular in the case of electric vehicles and hybrid vehicles, ie vehicles with an electric drive unit (also referred to as an electric motor). During recuperation, the kinetic energy of the drive wheels is converted into electrical energy by the electric drive unit, in particular by the electric motor. The electric drive unit is operated as a generator. In this way, part of the energy that is normally lost as frictional heat when braking can be fed in the form of electrical energy into an electrical energy store, such as a battery or a capacitor, and then used. At the same time, the regenerative operation of the e-machine achieves a braking effect on the vehicle, so-called regenerative braking. This is also referred to as regenerative or recuperative braking.

In order to implement regenerative braking, a regenerative torque is set on the electric drive unit, which represents a braking torque and thereby decelerates the vehicle.

In electric vehicles in particular, it is known to use the recuperation mentioned by setting and setting a recuperation torque (usually dependent on the brake pedal travel of the brake pedal covered by the vehicle occupant by actuating the brake pedal) when a braking request is detected, for example by a vehicle occupant actuating the brake pedal the vehicle is braked in a targeted manner with the desired braking power.

It is also known that said recuperation can also be used to decelerate the vehicle when a drive unit is coasting or towing. As a rule, a so-called overrun recuperation torque (also known as drag recuperation torque) is set on the drive unit when the vehicle occupant stops or relaxes the actuation of the accelerator pedal, for example if the vehicle occupant reduces the accelerator pedal actuation or completely releases the accelerator pedal. The vehicle is braked as a result. The overrun braking torque usually reaches its maximum value (the so-called target overrun recuperation torque) when the vehicle occupants stop actuating the accelerator pedal.

The recuperation braking and said overrun braking can be collectively referred to as regenerative deceleration.

In the case of severe deceleration, for example emergency braking, one or more wheels can lock as a result of the high friction braking torque, so that the so-called ABS control intervenes through an anti-lock braking system. In these cases and also in other critical driving situations in which the braking torque is controlled wheel-selectively by an intervention by the brake control system in order to restore vehicle stability, no further braking torque in the form of generator torque can currently be permitted.

the DE 10 2013 201 691 A1 discloses a method in which a total braking force for the braking intervention is generated on the one hand by a hydraulic device in the vehicle and on the other hand at least one electric motor assigned to a wheel, which always supports the braking force generated by the hydraulic device. As a result, due to the combination of the hydraulic and the electrical modulation, relatively more energy can be recovered in several braking situations, ie an audible recuperation can be achieved. When braking the motor vehicle, ABS counteracts a possible locking of the wheels by reducing the brake pressure. This allows road vehicles and aircraft to maintain their steerability and directional stability when braking. The system can also shorten the braking distance by controlling wheel slip.

It is also proposed that the total braking force generated be used in conjunction with a vehicle assistance system to stabilize the driving behavior of the vehicle. The advantage mentioned is that these assistance systems can be dimensioned correspondingly smaller and more cost-effectively and, under certain circumstances, can be dispensed with entirely. However, the omission or smaller dimensioning of such assistance systems can be disadvantageous in some driving dynamics-critical situations.

It is therefore the object of the invention to show a method and a braking system which offers the best possible compromise between energy efficiency and yet the greatest possible safety in every situation.

The solution to the problem results from a method for operating a vehicle brake system tems and a vehicle braking system with the features of claim 1 and claim 6. Advantageous training and developments are the content of the dependent claims.

To this end, a method for operating a braking system of a vehicle is proposed.

The vehicle, in particular the dual-track motor vehicle, includes a friction brake for braking at least one vehicle wheel. Such a wheel brake is widely known from the prior art and can be designed, for example, electrically, electro-hydraulically or the like.

Furthermore, the vehicle comprises at least one electrical machine that can be used for regenerative deceleration of the vehicle. Such an electrical machine is designed in particular as an electric motor.

As already explained in the prior art, a regenerative deceleration within the meaning of this invention is to be understood as a combination of overrun braking and regenerative braking. Depending on the required braking force or braking intensity, either only overrun braking takes place or this overrun braking is superimposed on recuperation braking.

It is also provided that the vehicle includes what is known as a traction control system, which is used to stabilize the vehicle. Such a traction control system includes in particular a so-called traction control and an engine drag torque control. Such a drive slip control is preferably a so-called actuator-close wheel slip limitation (ARB for short). Such an ARB differs from a classic slip control in that the slip control does not only take place via the central brake control system (also known as DSC), but via an interface (i.e. a specification generation in the DSC), namely via wheel speed limits or a slip limit filling and a control of the target slip on the actuator itself. The slip is therefore regulated directly in the actuator. The controller is divided into two components: DSC and the actuator itself. The actuator represents the drive machine.

Traction control takes place when the wheel speed of the at least one vehicle wheel of the vehicle falls below or exceeds a calculated wheel speed limit range. The wheel speed limit range is defined by a lower and an upper wheel speed limit. If the wheel speed falls below the lower limit or the upper wheel speed limit is exceeded, the traction control takes effect and the vehicle is stabilized. When braking, the lower wheel speed limit is particularly relevant, while when accelerating, the upper wheel speed limit is relevant. If the defined wheel speed limits and thus a specified wheel slip are exceeded or not reached, the vehicle can be stabilized again by intervening in the engine management system.

It is also provided that during such an active traction control, in particular during a drive slip control, a regenerative deceleration is suppressed or reduced or severely restricted. If traction control takes place - i.e. if the current wheel speed is outside the wheel speed limit range or if the lower wheel speed limit is not reached, it is provided that the braking intervention on the vehicle wheels or on the at least one vehicle wheel is essentially carried out by the conventional wheel brake. Regenerative deceleration, ie overrun braking or recuperation braking, then does not occur or occurs only to a limited extent.
The regenerative deceleration is formed in particular from an above-mentioned overrun braking and a brake recuperation that may be added to this. In the case of braking, the brake recuperation is superimposed on the overrun braking depending on the braking force required.

It is also provided that when the ABS system is active and the driving situation is stable, the calculated wheel speed limit range of the traction control system is widened. Such a “widening” is to be understood within the meaning of this invention that the wheel speed limit range is changed in such a way that the lower wheel speed limit is shifted further down so that a regenerative deceleration takes place. The upper wheel speed limit is essentially unaffected during deceleration processes. The widening mentioned makes it possible for traction control to actually take place only in extreme wheel slip ranges, so that regenerative deceleration can continue to take place during ABS braking, which takes place in a stable driving situation.

For this purpose, it is detected in one step that an anti-lock braking system (ABS system for short) is active. The ABS system is known from the prior art. When braking the motor vehicle, ABS counteracts a possible locking of the wheels by reducing the brake pressure.

Furthermore, a stable driving situation of the vehicle is detected.
Such a stable driving situation occurs when a minimum longitudinal deceleration or a minimum coefficient of friction between the roadway and the vehicle tire or a minimum brake pressure of the service brake of the wheel or a maximum lateral acceleration of the vehicle are exceeded.
Such a stable driving situation is determined or defined in particular on the basis of the current longitudinal and lateral dynamics or the current deceleration or the brake pressure of the vehicle or the vehicle wheel. The lateral and longitudinal dynamics of the vehicle can be recorded or evaluated in particular using a longitudinal acceleration or longitudinal deceleration of the vehicle or a current lateral acceleration of the vehicle or a current coefficient of friction between the road and the vehicle tire of at least one vehicle degree.
A stable driving situation is given, for example, with a high coefficient of friction between the tire and the roadway of approximately 0.7 to 1 and a low transverse acceleration of max. 2 m/s ² , particularly when the vehicle is driving straight ahead. In addition, the current longitudinal deceleration of the vehicle or the current brake pressure can also be included in the assessment of a stable driving situation.
If a stable driving situation occurs during ABS braking of the vehicle, for example a high friction value between 0.7 and 1, and low lateral dynamics, in particular up to a maximum of 2 m/s ² , the lower wheel speed limit is widened.

The widening mentioned therefore only takes place under the condition that an ABS system is activated and takes effect and that the vehicle is in a stable driving situation as described above.
The widening mentioned thus takes place depending on the situation under the conditions mentioned and in such a way that a regenerative deceleration can take place during ABS braking.

It is preferably provided that a constant comparison takes place, so that it can be determined at any time during ABS braking whether a stable driving situation still exists or not. If the conditions for a stable driving situation are no longer given, the wheel speed limit falls back or the wheel speed limit range is narrowed again in such a way that the traction control reacts more sensitively and, if necessary, regulates earlier and takes more torque from the system.
If it is determined that the ABS braking has ended, the lower wheel speed limit is also narrowed again and set to its original value, and the method mentioned is ended.
The method steps mentioned are therefore preferably repeated at certain time intervals, so that when an unstable driving situation is detected or the ABS system is deactivated, the widening of the wheel speed limit is reversed and the wheel speed limit is narrowed back to a "normal" or conventional range.

The method can the vehicle wheels on the front axle or the rear axle of the vehicle. It is therefore possible, for example, that the braking behavior and the braking source (i.e. whether friction braking or regenerative braking takes place) can be set differently on the front wheels than on the rear wheels during ABS braking, depending on which axle or which wheel is being used the electric motor can be driven.

The procedure has The prior art has the particular advantage that the recuperation torque is not completely switched off during ABS braking, but rather its activation limits are changed according to the situation in such a way that a regenerative deceleration of the vehicle during ABS braking is only tolerated by the traction control in very specific driving situations . However, if an unstable driving situation suddenly occurs during ABS braking, the widening is withdrawn immediately and traction control takes place in order to keep or stabilize the vehicle. Thus, in contrast to previous approaches, two slip controllers working in parallel (that is, the ABS controller and the traction controller) are used in this invention. The vehicle behavior is then controlled by the slip thresholds of the two controllers working in parallel.

The method thus enables recuperation despite an active ABS control, with a stable driving situation being enabled at all times during ABS braking, since the traction control continues to monitor the slip.
The two control systems (ABS control and traction control) do not affect each other negatively, which is why parallel control can take place without any problems.

This process enables the friction brakes to be thermally relieved during ABS braking, which is why the vehicle can be equipped with smaller and therefore more cost- and weight-saving friction brakes.

Due to the possibility of recuperation during ABS braking, an additional gain in range can be achieved with the method mentioned. This is particularly relevant on a racetrack or during dynamic driving, where the ABS control often takes effect.

In addition to the method mentioned, a braking system according to the independent claim 7 is also proposed, the braking system being designed to carry out the method mentioned.

The braking system includes at least one electric machine, which is designed in such a way that it can perform a regenerative deceleration of the vehicle. As already mentioned, a regenerative deceleration is to be understood in particular as an overrun braking of the electric machine and, if necessary, a brake recuperation or a recuperation braking via the electric machine.

Furthermore, the braking system comprises at least one friction brake for braking at least one vehicle wheel. The friction brake can be designed in particular as a disc brake or as a drum brake and can be actuated, for example, hydraulically, electrohydraulically or electrically.

The braking system also includes at least one anti-lock braking system (ABS system for short) that can be activated as a function of the situation, with the friction brake being in operation when the anti-lock braking system is activated.
Furthermore, at least one control unit and/or at least one sensor unit is provided, which is set up to activate an anti-lock braking system of the vehicle depending on the situation.

The braking system also includes at least one traction control system for stabilizing the vehicle. The traction control system is designed in particular as a traction control system and particularly preferably as a so-called wheel slip limiter close to the actuator (ARB for short).

At least one (additional or the same) control unit and/or at least one sensor unit is provided, which is set up in such a way to detect an activated anti-lock braking system and, depending on the situation, to calculate and specify a wheel speed limit range with a lower wheel speed limit and an upper wheel speed limit, so that traction control of the vehicle begins when the wheel speed falls below or exceeds the limits.
The control unit is designed in such a way that when the anti-lock braking system is active and when a stable driving situation of the vehicle is detected, the lower wheel speed limit is expanded in such a way that the electric machine causes a regenerative deceleration. This widening means that the lower wheel speed limit, below which the conditions for active control of the traction control are not reached, is adapted to the situation, so that in this situation no active traction control takes place during ABS braking (since the wheel speed is within the "expanded" wheel limit speed range or above the lower wheel speed limit) and thus a regenerative deceleration takes place.

These and other features emerge not only from the claims and from the description but also from the drawings, with the individual features being implemented individually or in combination in the form of sub-combinations in an embodiment of the invention and representing advantageous and individually protectable versions for which protection is claimed here.

Furthermore, an electric vehicle according to the independent claim 9 and a hybrid vehicle according to the independent claim 10 are proposed.

Both the proposed electric vehicle and the proposed hybrid vehicle include a braking system.

A hybrid vehicle includes a conventional internal combustion engine and an electric machine, which in this case are used to drive and decelerate the vehicle.

In both vehicles (both the purely electric vehicle and the hybrid vehicle), recuperation operation can take place via the electric machine, with recuperation braking or regenerative braking being able to be carried out. Furthermore, it is preferably provided that the electric machine includes an overrun mode, in which overrun braking takes place, and a recuperation mode, in which brake recuperation takes place. Depending on the driving situation and the need for braking force, the overrun braking is superimposed on the brake recuperation.
Alternatively or additionally, in the hybrid vehicle, the internal combustion engine can also contribute to or take over the overrun braking in overrun mode.

In the following, the invention is explained in more detail using an exemplary embodiment.
In the 1a and 1b is in each case a braking torque curve or the set Radd Revealed limit range for traction control of a vehicle in an ABS intervention according to the prior art. In the 2a and 2 B each shows the braking torque curve of a regenerative deceleration of an electric motor during ABS braking and an exemplary wheel speed curve with set wheel speed limits as an exemplary embodiment of the invention. All of the features described in more detail can be essential to the invention.

In 1a shows an exemplary braking torque curve of the regenerative deceleration of an electric motor of a vehicle over time t, as is known from the prior art. The current actual braking torque Mist, the set overrun braking torque M _overrun and the setpoint torque M _setpoint can each be seen as a progression over time t. The setpoint torque M _setpoint represents the total braking torque generated by the generator. ABS braking is activated at time t ₁ . Before time t ₁ , a regenerative deceleration takes place by superimposing setpoint braking torque M _setpoint and overrun braking torque M _overrun of the electric motor. Accordingly, a regenerative deceleration takes place, a so-called recuperation. From the point in time t ₁ at which the ABS braking takes place, the setpoint braking torque M _{setpoint is} abruptly reduced, which is why the regenerative deceleration is only limited to the overrun braking torque M _overrun . The overrun braking torque M _overrun is limited by a regulating traction control, in particular a drive slip control or a wheel slip limitation close to the actuator, so that the vehicle is braked only via the wheel brake, in particular the friction brake, i.e. in a conventional manner, without recuperation or a generator delay occurs.
The suspension of recuperation, i.e. the regenerative deceleration during ABS braking, places greater demands on the wheel brake, i.e. in particular the friction brake, and must therefore be designed with more power. This leads to increased installation space, energy and thus also cost requirements.

In 1b the wheel speed curve of a wheel of the vehicle over time t can be seen. In addition to the wheel speed, the _upper and lower wheel speed limits R set in a conventional traction control or drive slip control system (to be precise, a wheel slip limitation close to the actuator) can also be seen. If these wheel speed limits R _up and R down are exceeded or not reached during ABS braking, i.e. if the current wheel speed is outside the wheel speed limit range that forms the two wheel speed limits R _up and R _down , then, as in 1a at time t ₁ (ABS braking begins), the recuperation or regenerative deceleration by the electric motor is switched off. The deactivation results from the fact that the wheel speed limits R _top and R _bottom , in particular the lower wheel speed limit Down, are adapted to the situation during ABS braking in such a way that the wheel speed is outside the wheel speed limit range during ABS braking and thus a regenerative deceleration is prevented or prevented .is reduced. Braking then takes place only or mainly by means of the conventional wheel brake. As soon as the wheel speed limits R _top and bottom are exceeded or fallen below, the traction control actively regulates to stabilize the vehicle.
The wheel speed limits R _above and below or the wheel speed limit range are as in 1b recognizable, the conventional ABS braking is set tightly or sensitively, so that the traction control begins to regulate actively relatively early. From the point in time at which the ABS braking has ended, at point in time t ₂ , the wheel speed limits R _up and R _down , in particular the lower wheel speed limit R _down , change back again and a regenerative deceleration via the electric motor takes place again.

2a shows how 1a , also the braking torque curve of the regenerative deceleration by the electric motor. In contrast to 1a however, the recuperation or the regenerative deceleration by the electric motor is not switched off at the time when ABS braking occurs t ₁ .
If a stable driving situation of the vehicle is detected by a control or sensor unit or the like at the time when ABS braking occurs t ₁ , provision is made for the vehicle to continue to be regeneratively decelerated by means of the electric motor. The total torque M set as a generator _is set to a specific value.

The stable driving situation is determined or recognized using different characteristic values and measured variables as well as vehicle data. For example, a high coefficient of friction (or a minimum coefficient of friction) between the roadway and the vehicle tires, in particular between 0.7 and 1, can be detected. Furthermore, a slight lateral acceleration of the vehicle, for example driving straight ahead, could be recognized as an indication of a stable driving situation. Furthermore, an existing brake pressure or a current longitudinal acceleration or deceleration can be included in the determination of a stable driving situation.
As in particular in 2 B , in which the wheel speed limits of the traction control are shown as an embodiment of the invention (as in 1b) , can be seen, when an ABS Braking at time t ₁ and when determining a stable driving situation mentioned above, the lower wheel speed limit Runten widened for traction control. This widening means that the wheel speed limit range for active traction control allows a greater scope for wheel speed fluctuations and thus the traction control actively regulates very late during such a stable driving situation and during ABS braking. As long as the traction control is not actively controlling, as again in the 2a to recognize that the regenerative deceleration, ie the recuperation braking M _desired and the overrun braking M _overrun continue to be active, since the actual braking torque Mist is composed at least partially of a regenerative deceleration M _desired and M overrun.

Due to this situation-dependent change in the lower wheel speed limit of the traction control, a regenerative deceleration can take place in a stable driving situation despite the activated ABS system.

This means that several states are possible during ABS braking for the present invention. In a first state, as in 1a and 1b is shown, there is no regenerative deceleration by the electric motor. In this case, the traction control has very narrow and sensitive _upper and lower wheel speed limits and therefore intervenes comparatively early.

In a different state than he is in 2a and 2 B can be seen, during ABS braking, a regenerative deceleration occurs through the electric motor. Because in this case the vehicle is in a stable driving situation during ABS braking and the lower wheel speed limit Runten is widened depending on the situation, so that the traction control only actively intervenes comparatively late. The traction control is not completely ignored or deactivated, but only the lower wheel speed limit is adjusted according to the situation. When the vehicle is decelerated, the upper wheel speed limit R _top plays a subordinate role and therefore remains almost unchanged.

In addition, it is always possible to change within the respective states during ABS braking.

This enables recuperation or regenerative deceleration even during ABS braking, with a stable driving situation being able to be guaranteed at all times.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited 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

• DE 102013201691 A1 [0001, 0008]

Claims (10)

Method for operating a braking system of a vehicle, • wherein the vehicle comprises a friction brake for braking at least one vehicle wheel; • wherein the vehicle comprises at least one electric machine that can be used for regenerative deceleration of the vehicle and wherein • the vehicle comprises a traction control system for stabilizing the vehicle, with traction control taking place when the wheel speed of the at least one vehicle wheel exceeds a calculated wheel speed limit range with a lower wheel speed limit (R _below ) and an upper wheel speed limit (R _top ) falls below or exceeds it and a regenerative deceleration (M _desired , M _boost ) is reduced or prevented during traction control, the method comprising the following additional steps: • detecting an activated anti-lock braking system on the at least one vehicle wheel; • detecting a stable driving situation of the vehicle; • Situation-dependent changing of the calculated wheel speed limit range (R _below , R _above ) of the traction control system by widening the lower wheel speed limit (R _below ) in such a way that a regenerative deceleration takes place. procedure after claim 1 , wherein the stable driving situation is detected as a function of a current longitudinal acceleration or a longitudinal deceleration of the vehicle and/or a current lateral acceleration of the vehicle and/or a current coefficient of friction between the road and the vehicle tire of the at least one vehicle wheel. procedure after claim 2 , wherein a coefficient of friction between the tire of the wheel and the roadway of 0.7 to 1 is recorded and/or wherein a maximum lateral acceleration of 2 m/s ² is recorded. Method according to one of the preceding claims, in which the regenerative deceleration takes place from overrun braking (M _overrun ) and/or regenerative braking (M _setpoint ) of the electrical machine. Method according to one of the preceding claims, wherein the steps according to claim 1 be carried out repeatedly at specific time intervals and when an unstable driving situation or a deactivated anti-lock braking system is detected, the widening of the lower wheel speed limit (R _down ) is withdrawn again and the wheel speed limit range is narrowed. Method according to one of the preceding claims, wherein the method is carried out on the vehicle wheels of a front axle and/or on the rear axle of the two-track vehicle. Braking system for a vehicle designed to carry out the method according to one of Claims 1 - 6 comprising: • At least one electric machine, which is designed in such a way that it can perform a regenerative deceleration of the vehicle; • At least one friction brake for braking at least one vehicle wheel; • At least one anti-lock braking system that can be activated depending on the situation, the friction brake being in operation while the anti-lock braking system is activated; • At least one traction control system; • At least one control unit and/or at least one sensor unit which is set up in such a way as to activate an anti-lock braking system of the vehicle depending on the situation; • At least one control unit and/or at least one sensor unit which is set up in such a way that it detects an activated anti-lock braking system and, depending on the situation, calculates and specifies a wheel speed limit range with a lower wheel speed limit (R _below ) and an upper wheel speed limit (R _above ), so that traction control of the vehicle begins to regulate when the wheel speed falls below the lower limit (R _down ), • the control unit being designed, when the anti-lock braking system is activated and when a stable driving situation of the vehicle is detected, to widen the lower wheel speed limit (R _down ) in such a way that a regenerative deceleration (M _set, M _boost ) takes place through the electric machine. braking system after claim 7 , wherein the traction control comprises a wheel slip limiting device close to the actuator. Electric vehicle comprising a braking system claim 7 or 8th , comprising an electric machine for driving the vehicle, wherein the electric machine is designed such that in an overrun mode, an overrun braking (M _overrun ) and in a recuperation mode _, a recuperation braking (M set ) of the vehicle takes place. Hybrid vehicle comprising a braking system claim 7 or 8th , comprising at least one electrical machine for driving a vehicle and an internal combustion engine for driving the vehicle, wherein the electrical machine in a recuperation mode, a regenerative braking (M set) can _be carried out and by the internal combustion engine and / or by the electrical machine in overrun mode, overrun braking (M _overrun ) can be carried out.

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