Method for operating a braking system and motor vehicle

Abstract

The present invention relates to a method for operating a braking system (1) of a motor vehicle (2), wherein the braking system (1) comprises a front axle brake (3) and a rear axle brake (4), the latter being designed with improved emissions compared to the front axle brake (3). A target deceleration (S) of the motor vehicle (2) is determined, and a target braking force (SB) to achieve the target deceleration (SV) is defined. Depending on a predefined deceleration limit (VG), the target braking force (SB) is selectively distributed between the front axle brake (3) and the rear axle brake (4) such that the largest possible proportion of the target braking force (SB) is realized by the rear axle brake (4). Furthermore, the invention relates to a motor vehicle (2) with a braking system (1) which has a front axle brake (3) and a rear axle brake (4) which is designed to have improved emissions compared to the front axle brake (3).

Description

[0001] The present invention relates to a method for operating a braking system of a motor vehicle. The invention further relates to a motor vehicle configured to carry out a method according to the invention.

[0002] The introduction of EU-7 legislation has significantly limited permissible particulate matter emissions from motor vehicles compared to previous legal regulations. For motor vehicles with internal combustion engines, EU-7 legislation sets particularly stringent maximum particulate matter limits compared to vehicles with electric drive systems.

[0003] To comply with EU-7 legislation, braking systems featuring hard metal-coated brake discs are currently gaining prominence. These brake discs exhibit particularly complex tribological properties and significantly lower wear compared to conventional brake discs made of cast iron or similar materials. Furthermore, high CO2 emissions during production, a complex manufacturing process, and high production costs for the hard metal coating negatively impact this technology. Electromechanical brakes (EMBs) are also available, with this technology being particularly suitable for vehicles with electric drive systems. Finally, particulate-optimized brake pads are known, which, for example, incorporate non-asbestos organic (NAO) friction materials and are therefore also referred to as "NAO brake pads."

[0004] Document DE 10 2021 000 919 B3 discloses an emissions-limiting vehicle state control system. To reduce emissions unrelated to the powertrain, such as particulate matter emitted by a wheel brake during braking, state data is recorded and control commands are generated using database modules, depending on the expected emissions and a determined emissions budget.

[0005] Known measures and methods for reducing emissions from a motor vehicle's braking system have the disadvantage that the production of hard metal coatings on brake discs or NAO brake pads is very labor-intensive and costly. Known operating strategies for low-emission braking systems often result in a noticeable loss of performance and / or comfort.

[0006] It is therefore an object of the present invention to eliminate, or at least partially eliminate, the disadvantages described above in a method for operating a braking system of a motor vehicle. In particular, it is an object of the present invention to provide a method for operating a braking system of a motor vehicle and a motor vehicle with a braking system that exhibit reduced particulate matter emissions in a simple and cost-effective manner. Furthermore, it is an object of the invention to ensure that a high level of driving comfort and driving safety is maintained.

[0007] The aforementioned problem is solved by the claims. Accordingly, the problem is solved by a method for operating a braking system of a motor vehicle with the features of independent claim 1 and by a motor vehicle with a braking system with the features of dependent claim 8. Further features and details of the invention will become apparent from the dependent claims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the motor vehicle according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always makes, or can make, reciprocal references.

[0008] According to a first aspect of the invention, the problem is solved by a method for operating a braking system of a motor vehicle. The method comprises: - Determining a target deceleration of the motor vehicle by a control device of the motor vehicle, - Determining a required target braking force to achieve the target deceleration by the control device, - Targeted distribution of the target braking force between the front axle brake and the rear axle brake by the control device when the target deceleration is greater than a predefined deceleration limit, and - Achieving the entire target braking force with the rear axle brake when the target deceleration is less than or equal to the predefined deceleration limit.

[0009] The method according to the invention is carried out with a motor vehicle which has a braking system comprising a front axle brake and a rear axle brake, wherein the rear axle brake is designed with improved emissions compared to the front axle brake. In other words, the rear axle brake and the front axle brake are designed differently. The rear axle brake differs from the front axle brake at least in that braking with the rear axle brake emits less particulate matter than equivalent braking with the front axle brake, at least over a predominant range of possible braking scenarios of the motor vehicle.The front axle brake and the rear axle brake are preferably designed such that, in the event of a full braking maneuver performed using only the front axle brake at a speed of 50 km / h, more particulate matter is emitted by the front axle brake than in the event of a full braking maneuver performed from 50 km / h using only the rear axle brake.

[0010] In carrying out the method according to the invention, the vehicle's control device determines the target deceleration. The target deceleration can be determined, for example, by detecting the actuation of a brake pedal, a braking command from the vehicle's brake assist system, an autonomous cruise control system, or the like. Furthermore, additional information, such as the vehicle's speed, the gradient of a road surface, or similar factors, can be taken into account when determining the target deceleration.

[0011] Depending on the determined target deceleration, the control device calculates the required target braking force to achieve that deceleration. The target braking force can be determined, for example, based on a braking characteristic map of the front and / or rear axle brakes. Additional vehicle data, such as vehicle weight, can also be considered when determining the target braking force.

[0012] The control device compares the determined target deceleration with the predefined deceleration limit. According to the invention, the predefined deceleration limit can be a static or unchanging predefined limit. Alternatively, the predefined deceleration limit can be situationally variable, so that it can have different values ​​depending on one or more specific factors. The predefined deceleration limit allows the operation of the braking system to be divided into two operating ranges: a comfort range or particulate-reduced range, and a safety range. The comfort range includes target decelerations that are less than or equal to the predefined deceleration limit. The safety range includes target decelerations above the predefined deceleration limit.

[0013] As a result of comparing the determined target deceleration with the predefined deceleration limit, the control device determines whether the target braking force should be achieved solely by the rear axle brakes (comfort zone) or by both the rear and front axle brakes (safety zone). In the safety zone, the distribution of the braking force preferably occurs degressively, so that directly above the predefined deceleration limit, the contribution of the front axle brakes to the target braking force increases more sharply than further above the predefined deceleration limit. With a further increase in the target deceleration, the contribution of the front axle brakes to the target braking force then approaches an upper limit, which is, for example, 80% of the target braking force.

[0014] The rear axle brake's contribution to the target braking force is therefore 100% of the target braking force when the target deceleration is below the predefined deceleration threshold. This contribution preferably decreases progressively, so that the drop in the rear axle brake's contribution to the target braking force is steeper directly above the predefined deceleration threshold than further above it. As the target deceleration increases, the rear axle brake's contribution to the target braking force then approaches a lower limit, which is, for example, 20% of the target braking force. According to the invention, in addition to operating the rear axle brake in comfort and safety modes, braking by recuperation can also be provided.

[0015] An inventive method for operating a motor vehicle's braking system has the advantage over conventional methods that, with simple means and in a cost-effective manner, the particulate matter emissions of the braking system are significantly reduced compared to conventional braking systems, particularly at relatively low target decelerations. By using a braking system with front and rear axle brakes designed differently with respect to particulate matter emissions, the manufacturing costs of the braking system with particulate matter-optimized front and rear axle brakes can be significantly reduced. Furthermore, the target deceleration-dependent actuation of the front and rear axle brakes ensures a particularly high level of driving comfort as well as high vehicle stability and driving safety.

[0016] According to a preferred embodiment of the invention, a method for operating a braking system of a motor vehicle may include a predefined deceleration limit of between 0.2 g and 0.4 g. A deceleration of approximately 0.3 g is particularly preferred as the predefined deceleration limit. A deceleration of 0.3 g corresponds to a deceleration of 2.943 m / s². 2Below this deceleration threshold, safe and comfortable braking of the vehicle using the rear axle brakes is easily achievable. Furthermore, pitching of the vehicle is reliably avoided, as this can only be caused by applying the front axle brakes. Since only the rear axle brakes are applied, brake system wear and thus particulate emissions are particularly low. Above this deceleration threshold, safe braking of the vehicle is ensured by activating the front axle brakes, although particulate emissions are slightly higher compared to the comfort range due to the additional use of the front axle brakes. This has the advantage that relatively low particulate emissions from the braking system are maintained in a simple and cost-effective manner, while preserving a particularly high level of driving comfort, vehicle stability, and driving safety.

[0017] According to the invention, it is preferred that the targeted distribution of the target braking force is carried out such that all wheels of the vehicle reach the slip limit simultaneously, or that the front wheels of the vehicle reach the slip limit later than the rear wheels. If the target braking force is distributed such that all wheels reach the slip limit simultaneously, a particularly high deceleration of the vehicle can be achieved without the wheels slipping on the road surface. If the braking system is operated in such a way that the rear wheels reach the slip limit before the front wheels, the emission of particulate matter can be further reduced, at least temporarily. This can be particularly advantageous if the target deceleration is reduced during the braking process in such a way that the slip limit of the rear wheels is no longer exceeded.This has the advantage that, using simple means and in a cost-effective manner, the particulate matter emissions of the braking system can be further reduced while maintaining a particularly high level of driving comfort, vehicle stability, and driving safety.

[0018] Preferably, a vehicle's surroundings and / or its condition are monitored by means of a detection device. When the detection device identifies a hazardous situation, the deceleration limit is selectively reduced by the control device depending on the hazardous situation. According to the invention, monitoring the vehicle's surroundings means identifying external factors that can influence the vehicle's braking process. These can include, for example, factors that affect the length of the available stopping distance, the operation of the braking system, the tribology of the wheels and the road surface, or similar factors. The vehicle's condition can include, for example, temperatures, aging, wear, or similar conditions of braking system components.Reducing the predefined deceleration threshold ensures that the target braking force is distributed between the front and rear axle brakes even at lower deceleration levels. This means that at a deceleration where, with the original deceleration threshold, the target braking force would have been provided solely by the rear axle brakes, a portion of the target braking force is now also provided by the front axle brakes. This allows for improvements in braking distances, for example. In other words, the vehicle's driving safety is prioritized, at least temporarily, over emissions from the braking system. This has the advantage of improving vehicle safety in a simple and cost-effective manner, while simultaneously ensuring exceptionally low particulate emissions from the braking system.

[0019] In a particularly preferred embodiment of the invention, a method may be provided that, when determining the hazardous situation, other road users and / or road surface characteristics and / or objects on the road surface and / or weather conditions and / or the condition of the braking system are taken into account. Trajectories, positions, and dimensions of other road users or objects can have a direct impact on collision-free braking distances. Road surface characteristics, such as road surface topography, road surface condition, road surface type, road surface gradient, road surface contamination, moisture, water accumulation, snow, ice, or the like, can have a direct influence on the braking behavior of motor vehicles. Likewise, the braking behavior of motor vehicles is influenced by other weather conditions, such as temperature, precipitation, or the like.The condition of the braking system can encompass factors such as temperature, aging, wear, or similar aspects of its components. This offers the advantage of improving vehicle safety in a simple and cost-effective manner, while simultaneously ensuring exceptionally low particulate emissions from the braking system.

[0020] Preferably, a detection device is used that includes vehicle sensors for sensing the vehicle's surroundings and / or a receiver for receiving environmental data from the vehicle. The vehicle sensors can, for example, include radar, lidar, a camera, a light sensor, an ultrasonic sensor, or the like. Using the vehicle sensors, the vehicle can independently scan its surroundings, without relying on other information sources, and transmit the information obtained about the vehicle's environment to the control device. Scanning the environment can include, for example, detecting objects, movements, precipitation, or the like. The receiver can, for example, include a GPS receiver for determining the vehicle's position.Furthermore, the receiving device can, for example, include a radio receiver or similar equipment to receive traffic data, weather data, road data, or the like. This has the advantage of improving the vehicle's driving safety in a simple and cost-effective manner, while also ensuring particularly low particulate emissions from the braking system.

[0021] According to a preferred embodiment of the invention, a method can be provided in which the deceleration limit is selectively reduced or increased by the control device depending on a characteristic map of the front axle brake and / or the rear axle brake. The characteristic map can, for example, depict the relationship between the brake temperature and the actuation pressure-dependent particulate matter emission of the brake. Likewise, the characteristic map can be provided in the form of a multivariable computer model of the front axle brake and / or the rear axle brake, so that the expected particulate matter emissions of the respective brake system can be easily calculated as a function of several operating parameters of the respective brake system. This has the advantage that the driving safety of the vehicle is improved in a simple and cost-effective manner, while furthermore ensuring particularly low particulate matter emissions from the braking system.

[0022] According to a second aspect of the invention, the problem is solved by a motor vehicle. The motor vehicle has a braking system with a front axle brake for braking the front wheels of the motor vehicle and a rear axle brake for braking the rear wheels of the motor vehicle. According to the invention, the rear axle brake is designed to have improved emissions compared to the front axle brake.

[0023] The motor vehicle preferably has two front wheels and two rear wheels. The front axle brake is designed to brake the front wheels. Preferably, the front axle brake is designed to brake the front wheels with different braking forces. The rear axle brake is designed to brake the rear wheels. Preferably, the rear axle brake is designed to brake the rear wheels with different braking forces. The front axle brake and / or rear axle brake is preferably designed as a disc brake.

[0024] The rear axle brake is designed with improved emissions compared to the front axle brake. This means that the rear axle brake has, for example, a different technical design, different materials, different surface properties, or similar features than the front axle brake. Furthermore, this means that a braking maneuver performed using the rear axle brake results in lower particulate matter emissions than a corresponding braking maneuver under the same conditions using the front axle brake. Therefore, it is possible, for example, for the front axle brake to be designed as a conventional brake and only the rear axle brake as an improved emissions brake. Alternatively, it is possible for the front axle brake to already be designed as an improved emissions brake compared to conventional brakes, and the rear axle brake to be designed as an even more significantly improved emissions brake.Thus, the rear axle brake of the motor vehicle according to the invention exhibits a higher degree of emission improvement than the front axle brake.

[0025] The invention recognizes, firstly, that emission-reduced brakes have significantly higher acquisition costs compared to conventional brakes. Secondly, the invention recognizes that a large proportion of the determined target decelerations of a motor vehicle can be comfortably achieved using only one of the vehicle's brakes, for example, the rear axle brake. The vehicle according to the invention takes these two findings into account and, for target decelerations below a predefined deceleration threshold, can, for example, be braked entirely using the rear axle brake. Thus, the braking system of the vehicle according to the invention can be operated at such a target deceleration in such a way that the particulate matter emissions correspond to those of a vehicle in which both the front and rear axle brakes are designed with emission-reducing technology.

[0026] The motor vehicle according to the invention offers all the advantages already described in relation to a method for operating a motor vehicle braking system according to the first aspect of the invention. Accordingly, the motor vehicle according to the invention has the advantage over conventional motor vehicles that, with simple means and in a cost-effective manner, the particulate matter emissions of the braking system can be significantly reduced compared to conventional braking systems, particularly at relatively low target decelerations. By using a braking system with front and rear axle brakes designed differently with respect to particulate matter emissions, the manufacturing costs of the braking system with particulate matter-optimized front and rear axle brakes can be significantly reduced.With a target deceleration-dependent actuation of the front axle brake and rear axle brake, a particularly high level of driving comfort as well as high vehicle stability and driving safety are still guaranteed.

[0027] Preferably, the rear axle brake features a carbide-coated brake disc and / or NAO brake pads. In addition to reduced particulate emissions, carbide-coated brake discs also offer higher corrosion resistance and a longer service life. Due to the use of corrosion-resistant carbides, such brake discs have a visually improved surface finish compared to conventional brake discs, meeting particularly high aesthetic demands from customers. Preferably, the front axle brake discs do not have a carbide coating. NAO brake pads are characterized by a longer service life due to low wear and low noise emissions. Preferably, the front axle brake does not have NAO brake pads. This has the advantage of ensuring particularly low particulate emissions from the braking system in a simple and cost-effective manner.

[0028] According to the invention, it is preferred that the motor vehicle is configured to carry out a method according to the invention. Accordingly, the motor vehicle preferably has a control device for determining the target deceleration of the motor vehicle, for determining a required target braking force, for selectively distributing the target braking force between the front axle brake and the rear axle brake, and for achieving the total target braking force with the rear axle brake. This has the advantage that particularly low particulate emissions from the braking system are ensured with simple means and in a cost-effective manner.

[0029] A method according to the invention for operating a braking system of a motor vehicle, as well as a motor vehicle according to the invention, are explained in more detail below with reference to the drawings. The drawings schematically show: Fig. 1 in a diagram a preferred braking force distribution depending on a target deceleration, Fig. 2 in a side view a preferred embodiment of a motor vehicle according to the invention and Fig. 3 in a flowchart a preferred embodiment of a method according to the invention.

[0030] Elements with the same function and mode of operation are in the Fig. Items 1-3 are each labelled with the same reference numerals.

[0031] In Fig. Figure 1 shows a preferred braking force distribution as a function of the target deceleration SV, schematically represented in a diagram. The target deceleration SV forms the abscissa and the braking force component BA forms the ordinate. In the diagram, the braking force component BA of a front axle brake 3 (see Figure 1) is shown. Fig. 2) plotted as a degressive curve. By means of a deceleration limit VG, which is, for example, 0.3 g, the diagram is divided into a comfort range for target decelerations SV that are less than or equal to the deceleration limit VG and a safety range S for target decelerations SV that are greater than the deceleration limit VG.

[0032] In comfort mode K, braking is carried out exclusively by a rear axle brake 4 (see below). Fig. 2), which is designed with reduced emissions compared to the front axle brake 3. Once the deceleration limit VG is reached, braking is performed using the rear axle brake 4 and the front axle brake 3. As the target deceleration SV continues to increase, the braking force contribution BA of the front axle brake 3 increases degressively. The braking force contribution BA of the rear axle brake 4 decreases accordingly. Upon reaching a critical deceleration KV, safe, slip-free braking is ensured by the braking system 1 (see Figure 1). Fig. 2) is no longer guaranteed.

[0033] Fig. Figure 2 schematically shows a preferred embodiment of a motor vehicle 2 according to the invention in a side view. The motor vehicle 2 has a braking system 1 with a front axle brake 3 for braking the front wheels 6a of the motor vehicle 2 and a rear axle brake 4 for braking the rear wheels 6b of the motor vehicle 2. The braking system 1 has a control device 5 for controlling the front axle brake 3 and the rear axle brake 4. Furthermore, the motor vehicle 2 has a detection device 7 for sensing the surroundings of the motor vehicle 2.

[0034] In Fig.Figure 3 shows a preferred embodiment of a method according to the invention schematically in a flowchart. The method is carried out with a braking system 1 in which the rear axle brake 4 is designed to produce reduced emissions compared to the front axle brake 3. In a first process step 100, a control device 5 of the motor vehicle 2 determines a target deceleration S of the motor vehicle 2. In a second process step 200, the control device 5 determines a required target braking force SB to achieve the target deceleration SV.

[0035] If the target deceleration SV is greater than a predefined deceleration limit VG, the control device 5 selectively distributes the target braking force SB between the front axle brake 3 and the rear axle brake 4 in a third process action 300. The braking force component BA of the rear axle brake 4 is chosen to be as high as possible relative to the braking force component BA of the front axle brake 3 in order to minimize emissions from the braking system 1. If the target deceleration SV is less than or equal to the predefined deceleration limit VG, the control device 5 applies the entire target braking force SB to the rear axle brake 4 in a fourth process action 400. In this way, emissions from the braking system 1 are particularly low. Reference symbol list 1. Braking system 2 motor vehicles 3 Front axle brake 4 Rear axle brakes 5 Control device 6a Front wheel 6b Rear wheel 7 Investigation device BA braking force share K Comfort area critical delay in the case of KV S security area SB Target braking force SV SOLL-Delay VG delay limit 100 first procedural action 200 second procedural action 300 third procedural action 400 fourth procedural action QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 000 919 B3

[0004]

Claims

[1] Method for operating a braking system (1) of a motor vehicle (2), wherein the braking system (1) comprises a front axle brake (3) and a rear axle brake (4), wherein the rear axle brake (4) is designed to be emission-improved compared to the front axle brake (3), comprising: - Determining a target delay (SV) of the motor vehicle (2) by a control device (5) of the motor vehicle (2), - Determining a required target braking force (SB) to achieve the target deceleration (SV) by the control device (5), - Targeted distribution of the target braking force (SB) to the front axle brake (3) and the rear axle brake (4) by the control device (5) when the target deceleration (SV) is greater than a predefined deceleration limit value (VG), and - Achieving the total target braking force (SB) with the rear axle brake (4) when the target deceleration (SV) is less than or equal to the predefined deceleration limit (VG). [2] Method according to claim 1, characterized by , that a delay between 0.2 g and 0.4 g is used as a predefined delay limit (RL). [3] Method according to claim 1 or 2, characterized by , that the targeted distribution of the target braking force (SB) is such that all wheels (6a, 6b) of the motor vehicle (2) reach the slip limit simultaneously or that front wheels (6a) of the motor vehicle (2) reach the slip limit later than rear wheels (6b) of the motor vehicle (2). [4] Method according to any of the preceding claims, characterized by , that by means of a detection device (7) of the motor vehicle (2) an environment of the motor vehicle (2) and / or a condition of the motor vehicle (2) is monitored, wherein when a dangerous situation is detected by the detection device (7) the deceleration limit value (VG) is specifically reduced by the control device (5) depending on the dangerous situation. [5] Method according to claim 4, characterized by , that when determining the hazardous situation, other road users and / or road surface characteristics and / or objects on the road surface and / or weather conditions and / or the condition of the braking system (1) are taken into account. [6] Method according to claim 4 or 5, characterized by , that a detection device (7) is used which includes vehicle sensors for detecting the environment of the motor vehicle (2) and / or a receiving device for receiving environmental data of the motor vehicle (2). [7] Method according to any of the preceding claims, characterized by , that the deceleration limit value (VG) is selectively reduced or increased by the control device (5) depending on a characteristic map of the front axle brake (3) and / or the rear axle brake (4). [8] Motor vehicle (2) comprising a braking system (1) with a front axle brake (3) for braking the front wheels (6a) of the motor vehicle (2) and a rear axle brake (4) for braking the rear wheels (6b) of the motor vehicle (2), characterized by , that the rear axle brake (4) is designed to have improved emissions compared to the front axle brake (3). [9] Motor vehicle (2) according to claim 8, characterized by , that the rear axle brake (4) has a carbide-coated brake disc and / or a NAO brake pad. [10] Motor vehicle (2) according to claim 8 or 9, characterized by , that the motor vehicle (2) is designed to carry out a method according to one of claims 1 to 7.

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