Method for operating a mechanically decoupled braking system

Abstract

Method (22) for operating a mechanically decoupled braking system (8) of a motor vehicle (2), wherein - by means of an assistance system (20) a first deceleration value (26) is provided, - a driver's braking request (34) set by means of a lever or a brake pedal is detected, - depending on the braking request (34) and depending on the first deceleration value (26), a second deceleration value (38) is created, - a third delay value (42) is created based on the first delay value (26) and the second delay value (38), and - a brake (6) of the braking system (8) is actuated based on the third deceleration value (42).

Description

[0001] The invention relates to a method for operating a mechanically decoupled braking system, as well as a mechanically decoupled braking system and a motor vehicle with a mechanically decoupled braking system.

[0002] Motor vehicles typically have braking systems that decelerate the vehicle. A brake disc is usually attached to a wheel of the vehicle in a rotationally fixed manner. When the driver requests to brake, brake pads are moved against the brake disc, increasing friction and thus reducing the wheel's rotational speed. The driver's request to brake is usually registered by a brake pedal, which is typically connected to the brake pads via a hydraulic linkage. A brake booster is also usually present, so that the brake pedal only needs to be pressed with relatively little force to achieve a certain braking effect.

[0003] To further enhance comfort, so-called electro-hydraulic brakes are also known. These systems use an electrical sensor to detect the position of the brake pedal and derive a braking request from the driver. The electrical signal is transmitted to an electromechanical actuator (pump, linear actuator, etc.) that acts on a hydraulic system. This system builds up pressure, which then applies pressure to the brake pads. This reduces the number of hydraulic lines required within the vehicle, simplifying manufacturing. It is also possible to adjust the braking request transmitted via the brake pedal according to the current requirements. In other words, the brake pads are mechanically decoupled from the brake pedal.

[0004] A further development involves completely eliminating the hydraulic system, so that an electric actuator, such as an electric motor, acts directly on the brake pads. This means that only the installation of electrical wiring is required to create the braking system, reducing weight, maintenance, and manufacturing costs.

[0005] Furthermore, motor vehicles typically feature driver assistance systems designed to initiate braking. These include, in particular, an emergency braking assistant or a distance control assistant, which maintains a constant distance to the vehicle ahead or at least ensures that a minimum distance is not breached. As a result, rear-end collisions are avoided. In decoupled braking systems, the brake pedal remains in its unpressed rest position during active deceleration. It is possible that the assistance system initiates braking while the driver also presses the brake pedal. Because the assistance system has already applied the brakes, a relatively small movement of the brake pedal by the driver will result in a braking force less than the deceleration value initiated by the assistance system.As a result, the vehicle does not brake additionally, so the driver does not notice that his braking request has been registered, leading to a loss of comfort.

[0006] From DE 10 2016 204 136 A1 a method for automated longitudinal motion control of a motor vehicle is known, in which, depending on an acceleration quantity, an automated positive acceleration process in a longitudinal direction of the vehicle is effected by an actuating intervention on a drive train of the motor vehicle and an automated deceleration in the longitudinal direction of the vehicle is effected by an actuating intervention on the drive train and / or a braking system of the motor vehicle.The acceleration quantity is determined from a jerk quantity limited in magnitude, and the jerk quantity is defined in a driving mode in which the motor vehicle is driven to a predetermined longitudinal speed from an actual longitudinal vehicle speed and an actual longitudinal vehicle acceleration, taking into account a predetermined maximum positive driving mode longitudinal vehicle acceleration, a predetermined maximum driving mode longitudinal vehicle deceleration and at least a predetermined driving mode jerk quantity limiting the jerk quantity.

[0007] In DE 10 20 362 A a method of vacuum compressed air braking for rail vehicles is shown.

[0008] German patent DE 10 2015 114 709 A1 discloses a method for adjusting the accelerator pedal release regeneration. The accelerator pedal release regeneration is increased in response to exceeding a system regeneration limit.

[0009] The invention is based on the objective of providing a particularly suitable method for operating a mechanically decoupled braking system, as well as a particularly suitable mechanically decoupled braking system and a particularly suitable motor vehicle, advantageously increasing comfort and / or safety.

[0010] With regard to the method, this problem is solved according to the invention by the features of claim 1, with regard to the braking system by the features of claim 8, and with regard to the motor vehicle by the features of claim 9. Advantageous further developments and embodiments are the subject of the respective dependent claims.

[0011] The method serves to operate a mechanically decoupled braking system of a motor vehicle. The motor vehicle is, for example, a commercial vehicle. However, it is particularly preferably a passenger car. The motor vehicle has, for example, an internal combustion engine, an electric motor, or a combination thereof for propulsion. The mechanically decoupled braking system comprises a brake or at least a control line for a brake. Preferably, the mechanically decoupled braking system comprises a brake, for example, a disc brake or a drum brake. Alternatively, the brake is an electromechanical brake, i.e., in particular, a generator and / or recuperator. Particularly preferably, the mechanically decoupled braking system comprises a number of such brakes, with each wheel of the motor vehicle being suitably assigned one brake.

[0012] The mechanically decoupled braking system also includes an input device for the driver, namely a lever or a brake pedal. Here, the brake pedal or lever is mechanically decoupled from the brake, so that the brake can be moved essentially independently of the lever / brake pedal and vice versa. In other words, actuating the lever / brake pedal does not necessarily result in the brakes being applied. In other words, there is no mechanical connection between them. Hereinafter, the term "brake pedal" will always refer specifically to the lever. The brake pedal preferably includes a haptic simulator by means of which a counterforce is applied, so that the driver of the motor vehicle feels resistance when the brake pedal is actuated. The haptic simulator includes, for example, a spring, or preferably several springs, by means of which the simulation is performed.This allows the driver to feel that they are pressing the brake pedal. In particular, a rigid pedal feel is simulated using the haptic simulator.

[0013] For example, a mechanically decoupled braking system is an electro-hydraulic braking system. In this case, the brake is actuated, for example, by means of hydraulics, with the hydraulic adjustment being made by electrical signals generated by the lever / brake pedal. Alternatively, the mechanically decoupled braking system, hereinafter referred to simply as the braking system, is an electric braking system, and the brake is operated, for example, by an electromechanical actuator, such as an electric motor, or incorporates one. In this case, brake pads, in particular, are moved against a brake disc, if any, by means of the electric motor.

[0014] The procedure involves first providing an initial deceleration value using an assistance system. In other words, the assistance system generates the initial deceleration value. The vehicle is then decelerated and, if appropriate, braked. For example, the brakes are applied based on this initial deceleration value, causing the vehicle to decelerate accordingly. The vehicle is braked when the brakes are applied based on this initial deceleration value. For example, this deceleration value might be between 0 m / s² and 1.5 m / s² or between 0 g and 1.5 g. Therefore, once the assistance system provides the initial deceleration value, the brakes are applied immediately based on this value.

[0015] The assistance system could be, for example, an emergency braking assistant, which detects obstacles in front of the vehicle and, if a minimum distance is breached, initiates the first deceleration value, thus preventing a collision. Alternatively, the assistance system could be a hill descent control assistant, which maintains a constant speed when driving downhill. Consequently, the hill descent control assistant compensates for acceleration due to the downhill slope. Examples of such assistance systems include an ABS system or an electronic stability program. Another alternative is a distance control assistant, which monitors and, in particular, maintains a constant distance to a vehicle ahead.Alternatively, the adaptive cruise control system ensures that a minimum distance to any vehicle ahead is maintained. In another alternative, the assistance system is designed to follow a vehicle ahead, for example, by pre-setting a specific distance. If the vehicle ahead brakes, the assistance system calculates the initial deceleration value, thus preventing a collision or an unwanted approach to the vehicle ahead.

[0016] In a further step, the driver's braking request is detected. In other words, the driver's wish to decelerate the vehicle is recorded. The braking request is set using the lever or the brake pedal. The braking request is primarily a quantitative value, whereby, for example, a sensor detects the position of the brake pedal and transmits this information to a control unit. This step occurs, for instance, before, after, or simultaneously with the step in which the assistance system provides the initial deceleration value.

[0017] In a further step, a second deceleration value is generated based on the braking request and the first deceleration value. The second deceleration value expediently has the same dimension as the first. For example, the second deceleration value may have a dimension different from the braking request. In particular, the dimension of the second deceleration value is an acceleration value, whereas the braking request corresponds, in particular, to a brake pedal position. Preferably, the braking request corresponds to and / or aligns with a deceleration, a total braking torque, a desired axle braking torque, or a desired brake pressure. The second deceleration value is generated based on the braking request, i.e., in particular the brake pedal position, and based on the first deceleration value.Preferably, the second deceleration value differs depending on whether the first deceleration value is present or not, even if the braking request is the same. Preferably, the second deceleration value is determined using a characteristic map.

[0018] In particular, the second deceleration value is a function of the braking request. The function itself is determined as a function of the first deceleration value, resulting in a family of functions whose parameter is the first deceleration value. For example, the functions differ depending on the magnitude of the first deceleration value. Preferably, each possible first deceleration value is assigned a different function. In other words, the second deceleration value is, for example, strictly monotonic with respect to the first deceleration value. Preferably, the second deceleration value is smaller if the first deceleration value is present. In other words, if the first deceleration value is absent, the second deceleration value is larger for the same braking request.

[0019] A third deceleration value is generated based on the first and second deceleration values. This third deceleration value depends on the second deceleration value generated by the braking request and the first deceleration value provided by the assistance system. In a further step, the brakes are applied based on this third deceleration value. Specifically, the brakes are controlled according to this third deceleration value. For example, additional factors influencing brake application can include additional assistance systems, such as ABS, or the current driving situation.

[0020] The second deceleration value takes into account an existing first deceleration value, which, for example, is used to initiate brake activation, thus compensating for any overreaction by the driver. This increases safety. Furthermore, by considering the first deceleration value when calculating the second, excessive braking by the vehicle is avoided, thereby improving comfort.

[0021] Conveniently, the third deceleration value is generated by adding the first and second deceleration values. In other words, the first and second deceleration values ​​are added together, and this result is used as the third deceleration value. This simplifies the calculation of the third deceleration value and uses comparatively few resources. Furthermore, the time required is relatively short, allowing the brakes to be applied relatively quickly using the third deceleration value.

[0022] Ideally, both the first and third deceleration values ​​are positive. Specifically, a positive second deceleration value is used when a braking request is made. In other words, the second deceleration value is present whenever a braking request exists. The positive deceleration value corresponds to a desired deceleration. Thus, the second deceleration value is always present whenever a braking request exists, and therefore, the second deceleration value is always greater than zero when a braking request exists. Consequently, the third deceleration value differs from the first deceleration value as soon as a braking request is made. This allows the driver to immediately perceive the implementation of their braking request, which increases comfort and user acceptance.However, at least the first delay value and the third delay value, or preferably the first delay value, the second delay value and the third delay value, have the same sign.

[0023] Alternatively, or preferably in combination with this, the second deceleration value is chosen to be larger the greater the braking demand. Advantageously, the function used to determine the second deceleration value is a strictly monotonic function. This allows the driver to perceive that the vehicle's deceleration increases as their braking demand increases. In other words, the second deceleration value is a strictly monotonic function dependent on the braking demand. For example, the function is a straight line. Alternatively, the function is a parabola or hyperbola, or at least parabolic and hyperbolic. For example, the slope of the function increases with increasing braking demand. In other words, the second derivative of the function is positive. This achieves, in particular, progressive braking behavior, which increases safety and comfort.

[0024] In particular, the braking request is determined based on the position of the brake pedal along its travel. The pedal travel expediently has an end stop, corresponding, for example, to a fully depressed brake pedal. In particular, the end stop is mechanically predetermined. Alternatively, a mechanical stop is present, and the end stop defines a range along the pedal travel up to the mechanical stop, for example, 5 mm before the mechanical end stop. In particular, the pedal travel is between 10 mm and 120 mm, between 50 mm and 100 mm, and, for example, equal to 80 mm. In particular, the pedal travel has a further end, which suitably corresponds to an undepressed brake pedal. If the brake pedal is at this end, there is preferably no braking request.

[0025] Preferably, the braking system has a maximum deceleration value that corresponds to the maximum deceleration value achievable by the mechanically decoupled braking system due to its design. For example, the current driving situation is also taken into account, so that the vehicle remains controllable even at the maximum deceleration value. The maximum deceleration value is used when the brake pedal is at its end stop. In other words, when the brake pedal is at or near its end stop, the maximum deceleration value is used to decelerate the vehicle. For example, the maximum deceleration value is always used as the third deceleration value when the brake pedal is at its end stop, regardless of the first deceleration value.

[0026] Preferably, the third deceleration value is equal to the maximum deceleration value only when the brake pedal is at its end stop, particularly if the first deceleration value does not correspond to the maximum deceleration value, i.e., if the assistance system does not request maximum deceleration of the vehicle. Thus, if the first deceleration value does not correspond to the maximum deceleration value, and the brake pedal is not at its end stop, the vehicle is not decelerated at the maximum deceleration value, and consequently, the brakes are not applied based on the maximum deceleration value.

[0027] In summary, the brake is only applied with the maximum deceleration value if the first deceleration value corresponds to the maximum deceleration value, or if the brake pedal is at its end stop and the first deceleration value does not correspond to the maximum deceleration value. This increases comfort. To achieve this, the relationship between the second deceleration value and the first deceleration value is adjusted so that if the first deceleration value is increased, the second deceleration value is decreased while the braking demand remains the same. A corresponding function is used for this purpose, if one is employed. Ideally, this function is not changed as long as the braking demand is present.

[0028] Advantageously, the third deceleration value is reduced when the braking demand decreases. In other words, when the driver's braking demand ceases or decreases, the vehicle's deceleration is reduced. For example, the second deceleration value decreases more rapidly than it increases when the braking demand increases. Specifically, a function is determined for the third deceleration value, and the second deceleration value is adjusted accordingly. Advantageously, the function for the third deceleration value is such that, with the brake pedal fully released, the third deceleration value corresponds to zero (0g), and thus no braking occurs in this case. Alternatively, at least the first deceleration value is always maintained, provided it is still present.Therefore, especially when the brake pedal is fully released, there is no load on the brakes, meaning there is no pressure on the brake disc exerted by the brake pads, for example, hydraulically or electrically. If the first deceleration value is always used as the minimum deceleration value, if available, safety is increased because the vehicle is braked according to the instructions of the assistance system. In other words, in this case, the first deceleration value is used as the third deceleration value.

[0029] For example, the third deceleration value remains unchanged if the first deceleration value is reduced and the driver requests braking. In other words, the brakes continue to be applied at the third deceleration value even if the assistance system's setting is modified to indicate less braking of the vehicle. For instance, the first deceleration value might be reduced or the assistance system might completely disable it, eliminating the first deceleration value. Specifically, the third deceleration value remains unchanged if the driver requests braking, particularly if the brake pedal position is not altered. Therefore, the driver will not notice if the assistance system reduces the first deceleration value, and there will be no unexpected reaction from the braking system, thus increasing comfort.If a braking request arises and the first deceleration value is increased, the third deceleration value is also preferentially increased and the brake is applied accordingly.

[0030] A mechanically decoupled braking system is a component of a motor vehicle, such as a passenger car or a commercial vehicle. The braking system includes a brake and a brake pedal, also referred to as a lever. The brake pedal is mechanically decoupled from the brakes, and mechanical actuation of the brake pedal does not necessarily result in the brakes being applied. This preferably occurs solely based on an electrical signal applied via the brake pedal. The braking system expediently includes a control unit, which may comprise, for example, a microprocessor. The control unit may be programmable or designed as an application-specific integrated circuit (ASIC). The brake of the braking system may be, for example, a disc brake or a drum brake. The braking system may be, for example, an electro-hydraulic braking system or a fully electric braking system.

[0031] The braking system operates according to a procedure in which an initial deceleration value is provided by means of an assistance system. Advantageously, the control unit has an interface to the assistance system or a BUS system via which the initial deceleration value is transmitted. In a further step, a braking request from the driver is detected. Advantageously, the braking request is detected by means of the brake pedal. Depending on the braking request and the initial deceleration value, a second deceleration value is generated, and based on the first and second deceleration values, a third deceleration value is generated. The brake is applied based on the third deceleration value. Specifically, the procedure is carried out by means of the control unit. The control unit is advantageously designed and configured for this purpose.

[0032] The vehicle has a mechanically decoupled braking system with a brake and a control unit. The braking system operates according to a procedure in which an assistance system provides an initial deceleration value and detects a braking request from the driver. Furthermore, a second deceleration value is generated based on the braking request and the initial deceleration value, and a third deceleration value is generated based on the first and second deceleration values. The brake of the braking system is then actuated based on this third deceleration value.

[0033] The advantages and further training described in connection with the procedure can also be applied analogously to the braking system / motor vehicle and vice versa.

[0034] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 schematically a motor vehicle with a mechanically decoupled braking system, Fig. 2 a method for operating the mechanically decoupled braking system, and Fig. 3 a first, second and third delay value.

[0035] Corresponding parts are marked with the same reference symbols in all figures.

[0036] In Fig. Figure 1 shows a motor vehicle 2 in the form of a passenger car, with several wheels 4. Each wheel 4 is assigned a brake 6, shown schematically, in the form of a disc brake. The brakes 6 are each part of a brake system 8, which includes a control unit 10. The brakes 6 are actuated by means of the control unit 10, and a hydraulic system (not shown) is pressurized so that brake pads are pressed against a brake disc of each of the brakes 6. The brake system 8 also includes a brake pedal 12, which can be moved along a pedal travel 14. The pedal travel 14 has an end stop 16, which is mechanically predetermined. The brake pedal 12 can be moved along the pedal travel 14 up to the end stop 16. The brake pedal 12 is moved by a maximum of 80 mm. A sensor 18 is assigned to the brake pedal 12, by means of which the position of the brake pedal 12 is detected along the pedal travel.The sensor 18, for example, is a component of the brake pedal 12 or of another sensor unit of the brake system 8 (not shown in detail). The control unit 10 detects the position of the brake pedal 12 along its travel 14 by means of the sensor 18 and actuates the brakes 6 based on this information. Thus, the brake system 8 is a mechanically decoupled brake system, and actuation of the brake pedal 12 does not directly lead to actuation of the brakes 6. Rather, this only occurs when the brakes 6 are actuated by the control unit 10.

[0037] The vehicle 2 also features an assistance system 20 in the form of a distance control assistant. The distance control assistant is a component of a cruise control system. The driver of vehicle 2 sets a specific speed, to which vehicle 2 is automatically regulated. If another vehicle is traveling ahead at a lower speed, the distance control assistant 20 reduces the speed of vehicle 2 so that the distance to the vehicle ahead corresponds to a specific value, for example, remains constant. The assistance system 20 is interconnected with the control unit 10 via a signal, for example, directly or via a bus system (not shown), such as a CAN bus.

[0038] In Fig. Figure 2 shows a method 22 for operating the braking system 8. In a first step 24, an initial deceleration value 26 is provided by means of the assistance system 20. This corresponds, for example, to a negative acceleration 28 of the motor vehicle 2 of 0.8g. This is half of a maximum deceleration value 30 of 1.6g, which is shown in Fig. 3 shown. For example, in the first step 24 the brake 6 is already applied and the vehicle is slowed down according to the first deceleration value 26.

[0039] In a second step 32, a braking request 34 from the driver is detected. For this purpose, the position of the brake pedal 12 along its travel 14 is determined by means of the sensor 18. Thus, the braking request 34 corresponds to the position of the brake pedal 12 along its travel 14. The second step 32 takes place at a time interval from the first step 24, for example, within 5 seconds or more. Due to the brake 6 potentially already being applied based on the first deceleration value 26, the vehicle 2 is already decelerated between the first step 24 and the second step 32.

[0040] In a subsequent third step 36, a second deceleration value 38 is generated based on the braking request 34 and the first deceleration value 26. The second deceleration value 38 is a parabolic, strictly monotonically increasing function that depends on the braking request 34. Furthermore, the second deceleration value 38 is always present as long as the braking request 34 is present, such that as soon as the brake pedal 12 is pressed, the second deceleration value 38 is greater than zero. If the brake pedal 12 is not pressed, the second deceleration value 38 is either not present or equal to zero. Moreover, due to the strict monotonicity, the second deceleration value 38 is greater the larger the braking request 34 is.

[0041] In a subsequent fourth step 40, a third deceleration value 42 is created based on the first deceleration value 26 and the second deceleration value 38 by summing the first deceleration value 26 and the second deceleration value 38 and using this sum as the third deceleration value 42. Thus, the third deceleration value 42 also depends on the braking request 34 and is always greater than the first deceleration value 26. The dependence of the second deceleration value 38 on the first deceleration value 26 is such that the third deceleration value 42 is equal to the maximum deceleration value 30 when the position of the brake pedal 12 corresponds to the end stop 16.Thus, if the first deceleration value 26 is present, the third deceleration value 42 is only varied between the first deceleration value 26 and the maximum deceleration value 30 depending on the braking request 34, whereby the maximum deceleration value 30 only occurs when the position of the brake pedal 12 corresponds to the end stop 16. In a subsequent fifth step 44, the brakes 6 are actuated based on the third deceleration value 42, and thus the vehicle 2 is decelerated.

[0042] If the first deceleration value 26 no longer exists or is reduced, i.e., if the first deceleration value 26 is reduced by means of the assistance system 20, for example due to sufficient braking of the vehicle 2, or because the vehicle ahead accelerates, a sixth step 46 is executed. In this step, the third deceleration value 42 remains unchanged if the braking request 34 persists, i.e., if the driver continues to depress the brake pedal 12. Thus, the driver does not perceive any change in the control of the control unit 10 by means of the assistance system 20.

[0043] If the braking request 34 is reduced, a seventh step 48 is executed, regardless of whether the first deceleration value 26 is still present. In the seventh step 48, the third deceleration value 42 is reduced, thus also changing the control of the brakes 6, so that the deceleration of the vehicle 2 is reduced. However, the decrease in the third deceleration value 42 is greater than the increase when the braking request 34 increases. Thus, the third deceleration value 42 is reduced depending on the braking request 34. This dependency is described by a further function 50, and the third deceleration value 42 follows this further function 50. In other words, the third deceleration value 42 is a function of the braking request 34, whereby the third deceleration value 42 is not present or is zero when the brake pedal 12 is fully released. The further function 50 is a strictly monotonic function.For example, if the first delay value 26 persists, it is additionally ensured that the third delay value 42 is not less than the first delay value 26. In other words, the maximum of the further function 50 and the first delay value 26 is used as the third delay value 42.

[0044] In Fig. Figure 3 also shows the second deceleration value 38 when the first deceleration value 26 is not present. In this case, the brakes 6 are controlled based on the second deceleration value 38, or the second deceleration value 38 is used as the third deceleration value 42. Here, the second deceleration value 38 also increases progressively with the pedal travel 14. Consequently, the vehicle 2 is decelerated more strongly the further the pedal 12 is moved along the pedal travel 14 towards the end stop 16.

[0045] In summary, in the mechanically decoupled braking system 8, when active braking is initiated, i.e., when the driver presses the brake pedal 12, the braking request 34 is detected and functionally adjusted / adapted to the second deceleration value 38 based on the existing first deceleration value 26. The first deceleration value, which is provided by the assistance system 20 due to active deceleration, is added to the second deceleration value, and the sum is used as the third deceleration value 42. The adaptation of the second deceleration value 38 always occurs in such a way that the sum of the first deceleration value 26 and the second deceleration value 38, i.e., the third deceleration value 42, always refers to the (fixed) maximum deceleration value 30 at the end stop 16, i.e., the specific maximum pedal travel 14, regardless of the current first deceleration value 26, when the brake pedal 12 is moved along its travel 14.For example, the maximum deceleration value 30 of 1.5g is always given when the brake pedal 12 is fully moved and is at its end stop 16, where the pedal travel 14 is, for example, 60mm.

[0046] When the brake pedal 12 is released, the total deceleration from the driver and active braking, i.e., the third deceleration value 42, which is the sum of the first and second deceleration values ​​26, 38, always aims at the minimum pedal travel 14 and the minimum value of the total deceleration defined at this point, i.e., a third deceleration value 42 of 0 m / s². Thus, when the brake pedal 12 is released, there is no residual pressure in the brake system 8. If the active braking, i.e., the first deceleration value 26, is reduced during the superimposed driver braking, i.e., while the braking request 34 exists, the total deceleration requirement, i.e., the third deceleration value 42, is not adjusted. However, if the first deceleration value 26 is increased, i.e., if the active braking requirement is increased, the third deceleration value 42 is adjusted, i.e., increased.

[0047] Due to the procedure, the driver's actuation of the brake pedal 12, depending on the pedal position, directly leads to an increase in the deceleration requirement and thus to a stronger application of the brakes 6 by means of the third deceleration value 42, even if braking by means of the first deceleration value 26 is already in effect. Due to the third deceleration value 42, i.e., the sum of the deceleration from active and driver braking, the deceleration is not uncontrollably excessive compared to a fixed pedal force of a haptic simulator of the brake pedal 12. Rather, due to the fixed points, namely the maximum deceleration value 30 and a minimum deceleration value of zero, at the respective position of the brake pedal 12 along the pedal travel 14—namely at the end stop 16 and with the brake pedal 12 fully released—the third deceleration value 42 is adapted to the fixed relationship between pedal travel and pedal force.

[0048] The temporal sequence in which the first deceleration value 26 is provided and the braking request 34 is detected—that is, whether an active request or a brake pedal actuation occurs first—can vary. In particular, the third deceleration value 42 is determined differently depending on whether the first deceleration value 26 is provided first and then the braking request 34 is detected, compared to when the braking request 34 is detected first and then the first deceleration value 26 is provided. Preferably, it is also taken into account whether the first deceleration value 26 is greater than the second deceleration value 38 and / or the braking request 34, especially a value corresponding to the braking request 34.

[0049] If the first deceleration value 26 is provided first (the active request is present), and then the braking request 34 is detected (the driver depresses the brake pedal), the third deceleration value 42 corresponds to the first deceleration value 26 plus the second deceleration value 38, which changes depending on the braking request 34. The braking request 34 corresponds to the position of the moving brake pedal 12. The second deceleration value 38 is determined such that the third deceleration value 42 varies between the first deceleration value 26 and the maximum deceleration value 30, depending on the position of the moving brake pedal 12. Consequently, an offset is always present, namely the first deceleration value 26, which is stored in particular when the brake pedal 12 moves "forward," i.e., when the position of the brake pedal 12 is moved towards the end stop 16.

[0050] If the braking request 34 is detected first, and no first deceleration value 26 is available, the second deceleration value 38 is generated based on the braking request 34 and a first deceleration value 26 of zero (0). For example, the braking request 34 is used as the second deceleration value 38, or a non-linear relationship is used, such as a parabolic dependence of the second deceleration value 38 on the braking request 34. In particular, the second deceleration value 38 is a continuous function of the braking request 34, and a braking request 34 of zero corresponds to a second deceleration value 38 of zero (0). The first deceleration value 26 and the second deceleration value 38 are added together to generate the third deceleration value 42. In other words, the second deceleration value 38 is used as the third deceleration value 42. Based on this, the brake 6 is applied.

[0051] If, subsequently, the first deceleration value 26 is provided, which is greater than the second deceleration value 38, then the third deceleration value 42 is preferably increased to the first deceleration value 26. If, subsequently, the braking request 34 is increased, the third deceleration value 42 determined thereafter is suitably always greater than the first deceleration value 26. In other words, the offset in the driver request is stored when the brake pedal 12 moves "forward," i.e., when the position of the brake pedal 12 is moved towards the end stop 16. Preferably, the difference in the individual offsets between the driver request and the higher active request is added to the driver request as the offset.

[0052] If the braking request 34 is detected first, and consequently the brake 6 is actuated based on the second deceleration value 38, and only subsequently the first deceleration value 26 is provided, wherein the first deceleration value 26 is smaller than the second deceleration value 38, the brake 6 will preferably continue to be actuated only based on the second deceleration value 38, and this will be used as the third deceleration value 42. Thus, in particular, there is no positive offset between the driver request and the active deceleration, and accordingly, this offset is preferably not factored into the driver request.

[0053] If the first deceleration value 26 is provided first, and the braking request 34 is then detected, the brake 6 is actuated based on the third deceleration value 42. If, after this, the first deceleration value 26 and essentially simultaneously or subsequently the braking request 34 are increased (pedal increase / additional pressure by the driver), the increased first deceleration value 26 is used, in particular, as an offset and / or the second deceleration value 38 is generated depending on the increased first deceleration value 26.

[0054] If the first deceleration value 26 is provided first, and the braking request 34 is then detected, the brake 6 is applied based on the third deceleration value 42. If subsequently only the first deceleration value 26 is increased, and the increased first deceleration value 26 is particularly greater than the third deceleration value 42, the third deceleration value 42 is suitably increased, preferably to the level of the first deceleration value 26. If the first deceleration value 26 is then decreased, the third deceleration value 42 is preferably decreased to the original third deceleration value 42. Thus, in particular, the increase in active braking (increase in the first deceleration value 26) is not factored into the driver request (braking request 34, second deceleration value 38) because the position of the brake pedal 12 has not been changed.

[0055] For example, the maximum deceleration value 30, i.e., the end stop 16, coincides with the mechanical stop of the brake pedal 12. Alternatively, the end stop 16 and the mechanical stop of the brake pedal 12 may differ. This makes it possible to provide a mechanically longer brake pedal travel than is functionally used for full deceleration. For example, the maximum deceleration value 30 is reached when the brake pedal 12 has been moved approximately 80 mm, with a possible mechanical pedal travel of 120 mm. Thus, the end stop 16 is 40 mm away from the mechanical stop of the brake pedal 12, and this distance is suitably constant.

[0056] The braking request 34, the first deceleration value 26, the second deceleration value 38, and / or the third deceleration value 42 correspond, for example, to a deceleration and have the physical unit g or m / s². Alternatively, at least one of these values ​​corresponds to a braking torque of one or two of the wheels 4, preferably axle by axle, or to the sum of the braking torque of all wheels 4 of the motor vehicle 2, and has the physical unit Nm. Alternatively, at least one of these values ​​corresponds to a requested brake pressure.

[0057] When the brake pedal 12 is released, as the brake pedal 12 moves along its travel 14, and the resulting braking request 34 and second deceleration value 38 change, a fixed point is preferably approached for the third deceleration value 42, so that when the brake pedal 12 is not depressed (0 mm pedal travel), the third deceleration value 42 corresponds to the first deceleration value 38 or a value of zero (e.g., 0 m / s²). In other words, the brake 6 is applied such that at 0 mm pedal travel, the driver's braking request is 0 (Nm / g / ...).

[0058] The invention is not limited to the embodiment described above. Rather, other variants of the invention can also be derived by a person skilled in the art without departing from the subject matter of the invention. In particular, all individual features described in connection with the embodiment can also be combined with one another in other ways without departing from the subject matter of the invention.

Claims

[1] Method (22) for operating a mechanically decoupled braking system (8) of a motor vehicle (2), wherein - by means of an assistance system (20) a first deceleration value (26) is provided, - a driver's braking request (34) set by means of a lever or a brake pedal is detected, - depending on the braking request (34) and depending on the first deceleration value (26), a second deceleration value (38) is created, - a third delay value (42) is created based on the first delay value (26) and the second delay value (38), and - a brake (6) of the braking system (8) is actuated based on the third deceleration value (42). [2] Method (22) according to claim 1, characterized by , that the third delay value (42) is the sum of the first delay value (26) and the second delay value (38). [3] Method (22) according to claim 1 or 2, characterized by , that a positive second deceleration value (38) is used when a braking request (34) is present. [4] Method (22) according to any one of claims 1 to 3, characterized by , that the second deceleration value (38) is chosen to be larger the greater the braking request (34) is. [5] Method (22) according to any one of claims 1 to 4, characterized by , that the braking request (34) is determined on the basis of a position of a brake pedal (12) along a pedal travel (14) having an end stop (16), wherein a maximum deceleration value (30) is used as the third deceleration value (42) when the position of the brake pedal (12) corresponds to the end stop (16). [6] Method (22) according to any one of claims 1 to 5, characterized by , that if the braking request (34) is reduced, the third deceleration value (42) is reduced. [7] Method (22) according to any one of claims 1 to 6, characterized by, that the third deceleration value (42) is not changed when the first deceleration value (26) is reduced, and the braking request (34) exists. [8] Mechanically decoupled braking system (8) of a motor vehicle (2) comprising a brake (6) and a control unit (10) and operated according to a method (22) according to any one of claims 1 to 7. [9] Motor vehicle (2) with a mechanically decoupled braking system (8) according to claim 8.

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