Method for operating a vehicle

Abstract

The invention relates to a method for operating a vehicle (1), wherein the vehicle (1) has: - at least one electric machine, which can be operated in a motor mode to drive the vehicle (1) and in a generator mode for recuperative braking of the vehicle (1), - an energy storage unit and / or energy sink, which supplies the at least one electric machine with electrical energy during motor operation and is charged by means of electrical energy recuperated during generator operation of the at least one electric machine and / or further enables recuperative braking, - a recuperative braking system for performing recuperative braking, comprising the at least one electric machine and the energy storage unit and / or energy sink, and - a friction braking system with a friction braking device (2) comprising a wheel brake actuator. According to the invention, a request signal (S1, S2, S3) for a deceleration torque generated by an accelerator pedal of the vehicle (1) and / or by at least one assistance function of the vehicle (1) is processed in a control unit (3) which is not part of the friction brake system, wherein it is checked whether a current state (Z) of the recuperative braking system permits recuperative braking, and the vehicle (1) is braked recuperatively in accordance with the requested deceleration torque completely or to the extent to which the current state (Z) of the recuperative braking system permits recuperative braking.

Description

[0001] Method for operating a vehicle

[0002] The invention relates to a method for operating a vehicle according to the features of the preamble of claim 1.

[0003] From the prior art, as described in DE 102016 007 838 A1, a method for controlling a brake recuperation device of a mild hybrid motor vehicle is known. For braking, the motor vehicle has a brake control system with at least one hydraulic friction brake as the first brake actuator and at least one electric machine as the second brake actuator. The electric machine can be operated as a generator to recuperate kinetic energy of the motor vehicle. The energy recuperated in this process is charged into an energy storage device. The first and second brake actuators are not designed to be capable of binding, at least during driver braking. In the method, in a first step, a target wheel torque characteristic curve is specified for providing a predefinable target wheel torque to a drive train of the motor vehicle, which includes the electric machine, as a function of a current brake pedal travel.The target wheel torque characteristic curve is then varied depending on braking operations that were carried out before a current braking operation.

[0004] DE 10 2016201 937 A1 describes a method for determining the initial gradient of a braking torque-slip characteristic curve from a measured braking slip of at least one vehicle wheel of a vehicle and a recuperative braking torque at this vehicle wheel. In the method, the wheel speed of the braked vehicle wheel is measured, and the wheel speed of the braked vehicle wheel is determined from the wheel speed. Furthermore, the wheel speed of an unbraked vehicle wheel of the vehicle is measured, and the vehicle speed is determined from the wheel speed. The braking slip is determined from the wheel speed of the braked vehicle wheel and the vehicle speed. Furthermore, the recuperative braking torque is determined by measuring the electrical power generated by recuperation. The initial gradient of the braking torque-slip characteristic curve is determined from the recuperative braking torque and the determined slip.

[0005] DE 102012 222 507 A1 discloses a method for operating a regenerative braking system of a motor vehicle. First, a future operating intensity of the regenerative braking system for a future route of the motor vehicle is estimated based on an input that characterizes the driving style of the future route. Furthermore, a maximum slip-free vehicle braking power for the route is estimated based on the input. Furthermore, the braking power of the regenerative braking system is set to a target braking power that is no greater than the maximum vehicle braking power for the route. Finally, the regenerative braking system is applied with the target braking power on the future route.

[0006] DE 10 2012 210 046 A1 describes a method for controlling a braking system of a motor vehicle. The motor vehicle can be braked by means of a friction brake and an electric machine operable as a generator. During a braking operation, a friction braking torque to be applied by the friction brake and a recuperation torque to be applied by the electric machine are reduced during a braking torque reduction phase until a corrected total braking torque to be applied by the friction brake and the electric machine is reached. The recuperation torque to be applied by the electric machine is influenced by a first feedback loop with compensation within a second feedback loop for controlling the electric machine.

[0007] DE 102010 054620 A1 discloses a method for determining braking torques of a vehicle with a traction battery, at least one regenerative brake, and at least one friction brake on a drive axle, taking into account a transverse dynamic driving state of the vehicle. In the method, at least one braking request is determined, and the total braking torque for the vehicle is determined. A first braking torque and a second braking torque of the drive axle are determined from the total braking torque of the vehicle. Furthermore, a transverse dynamic driving state of the vehicle is determined. Depending on the first and second braking torques and the transverse dynamic driving state, a third braking torque of the drive axle is determined. Furthermore, a fourth braking torque of the drive axle is determined by the at least one regenerative brake and / or the traction battery.In addition, a fifth braking torque of the drive axle is determined by limiting the third braking torque of the drive axle by the fourth braking torque of the drive axle. The vehicle's total braking torque is divided into a braking torque for the at least one regenerative brake of the drive axle and a braking torque for the at least one friction brake of the drive axle.

[0008] The invention is based on the object of providing a method for operating a vehicle which is improved compared to the prior art.

[0009] The object is achieved according to the invention by a method for operating a vehicle having the features of claim 1.

[0010] Advantageous embodiments of the invention are the subject of the subclaims.

[0011] A vehicle comprises at least one electric machine, which can be operated in engine mode for driving the vehicle and in generator mode for regenerative braking of the vehicle, and an energy storage unit and / or energy sink, which supplies the at least one electric machine with electrical energy during engine operation and is charged by means of electrical energy recuperated in generator mode of the at least one electric machine and / or further enables regenerative braking. The energy storage unit can also comprise an energy sink, in particular with regard to the recuperated electrical energy, or be designed as such an energy sink, or vice versa, or a combination of energy storage unit and energy sink, in particular with regard to the recuperated electrical energy, can be provided.It can then also be provided, for example, that the recuperated energy is not stored or is not stored completely. This energy storage unit and / or energy sink comprises, for example, at least one traction battery and / or at least one capacitor, in particular a supercapacitor, and / or at least one flywheel storage device and / or at least one, in particular large, resistor, or is designed as one of these components. In particular, if the energy sink only comprises the resistor, the recuperative energy is therefore not stored but converted into thermal energy. When using the resistor, however, it is advantageously only provided in addition to another of the aforementioned components.This allows recuperated electrical energy to be stored and, if this is not possible, for example due to a full charge level or another circumstance, braking can continue to be carried out using recuperation, as the remaining recuperated electrical energy is then converted into heat in the resistor.

[0012] The vehicle further comprises a regenerative braking system for performing regenerative braking, comprising the at least one electric motor and the energy storage unit and / or energy sink. The vehicle also comprises a friction braking system with a friction braking device that includes a wheel brake actuator.

[0013] The friction brake system is, for example, a hydraulic brake system, but can also be designed as a different friction brake system. If the friction brake system is a hydraulic brake system, then the friction brake device is accordingly a hydraulic brake device, a friction brake actuator mentioned below is then a hydraulic brake actuator, the friction braking mentioned below is then hydraulic braking, a friction brake force distribution specification mentioned below is then a hydraulic brake force distribution specification, a regulated friction deceleration torque mentioned below is then a regulated hydraulic deceleration torque, and a friction target braking torque mentioned below is then a hydraulic target braking torque.

[0014] In a method for operating this vehicle, the invention provides that a request signal for a deceleration torque generated by an accelerator pedal of the vehicle and / or by at least one assistance function of the vehicle is processed in a control unit not belonging to the friction brake system, wherein it is checked whether a current state of the regenerative braking system permits regenerative braking. The control unit not belonging to the friction brake system is, in particular, a central control unit, in particular a central control unit of a drive train, in particular an electric one, of the vehicle, which in particular comprises the at least one electric machine and the energy storage unit and / or energy sink.

[0015] The current state of the regenerative braking system is, in particular, a current state of availability of the regenerative braking system, i.e., in particular, the electric braking system formed by the vehicle's electric drive train. The current state of the regenerative braking system is, in particular, a current charge state of the energy storage unit or relates to this current charge state of the energy storage unit. It is therefore checked, in particular, whether the energy storage unit can still be charged by regenerative braking and, if so, how much energy generated by regenerative braking it can still absorb, or whether it is already fully charged. The vehicle is then regeneratively braked in accordance with the requested deceleration torque, either completely or to the extent that the current state of the regenerative braking system, in particular the energy storage unit, permits regenerative braking.

[0016] Furthermore, it is provided in particular that if the current state of the regenerative braking system, in particular of the energy storage unit, does not permit or does not permit completely regenerative braking in accordance with the requested deceleration torque, a remaining portion of the requested deceleration torque, which cannot be achieved by regenerative braking, is forwarded to a brake control system of the friction braking system and the vehicle is braked in accordance with this remaining portion of the requested deceleration torque by means of the friction braking system, in particular by means of its friction braking device.

[0017] Assistance functions that can generate a request signal for a deceleration moment include, for example, predictive cruise control, which adapts the speed of the vehicle to the course of the road ahead, and / or distance control to a vehicle ahead and / or an automated, highly automated or autonomous driving function of the vehicle.

[0018] By means of the solution according to the invention, in particular the functional scope of a wheel stabilization during regenerative braking is shifted to a control unit, in particular a drive train control unit, of the electric drive train.

[0019] By means of the solution according to the invention, essential functional scopes of the regenerative vehicle braking, in particular relating to deceleration torque requests from the accelerator pedal and from one or more assistance systems, are thus outsourced from the hydraulic braking system, in particular from its brake control system and also from a vehicle dynamics control system, and are directly summarized and processed in this control unit which is not part of the hydraulic braking system, in particular in the central control unit, whereby regenerative braking is used primarily and only a possibly remaining deceleration torque is realized by the friction braking system.

[0020] The solution according to the invention, in particular, avoids previously existing signal loops. Previously, all deceleration torque requests from the accelerator pedal and from one or more assistance systems, which were initially recorded in the control unit not belonging to the friction brake system, were transmitted from this control unit to the friction brake system, in particular to its brake control system and / or to the vehicle dynamics control previously assigned to the friction brake system. From there, a respective portion of the requested deceleration torque, which was to be generated by regenerative braking, was then transmitted back to this control unit not belonging to the friction brake system. This created a recuperation signal loop. By avoiding this recuperation signal loop, the functions relating to regenerative braking, in particular, can run faster and more effectively.

[0021] In one possible embodiment of the method, it is also provided that a request signal for a deceleration torque generated by a brake pedal of the vehicle is processed in the brake control system of the friction brake system. In this case, a check is carried out to determine whether the current state of the regenerative braking system, in particular of the energy storage unit, permits regenerative braking. The requested deceleration torque is forwarded to the control unit not belonging to the friction brake system to the extent that the current state of the regenerative braking system, in particular of the energy storage unit, permits regenerative braking, and the vehicle is regeneratively braked accordingly. The vehicle is braked by the friction brake system, in particular by its friction brake device, in accordance with a remaining portion of the requested deceleration torque. Thus, here too, regenerative braking takes priority over friction braking.If the deceleration torque is requested via the brake pedal, however, the check as to whether recuperation is possible is carried out in the brake control system. This also has the advantage of short signal propagation times, since the brake pedal is linked to the brake control system and thus its request signal would first have to be forwarded to the control unit that is not part of the friction brake system, in particular the central control unit, for evaluation. This is avoided with the present solution, so that friction braking can also take place very quickly, since the signal processing relating to friction braking takes place entirely in the brake control system, i.e. the control unit that is not part of the friction brake system, in particular the central control unit, is not responsible for this. In this respect, longer signal propagation times are also avoided.

[0022] The solution described here retains the existing architecture for signal acquisition and transmission. This means that request signals from the accelerator pedal and assistance functions were previously acquired by the control unit not belonging to the friction brake system, in particular the central control unit, and the request signal from the brake pedal was also previously acquired by the brake control system. This remains the case. The processing of the request signal from the brake pedal in the brake control system is also retained to avoid longer signal paths. The previous transmission of the request signals from the accelerator pedal and assistance functions to the brake control system, which led to the described signal loop, is now avoided.

[0023] In particular, it is provided that the current state of the regenerative braking system, in particular of the energy storage unit, is determined by the control unit not belonging to the friction braking system and forwarded to the braking control system. This ensures that this current state of the regenerative braking system, in particular of the energy storage unit, is available both in the control unit belonging to the friction braking system and in the braking control system and can be used in the manner described above.

[0024] In an alternative embodiment, the deceleration requests of the brake pedal are also processed in the manner described above for the deceleration requests of the accelerator pedal and the assistance functions, i.e., in particular, primarily in the control unit not belonging to the friction brake system, in particular the central control unit. Thus, the request signal for a deceleration torque generated by the vehicle's brake pedal is then also processed in the control unit not belonging to the friction brake system, with a check being carried out to determine whether the current state of the regenerative braking system, in particular of the energy storage unit, permits regenerative braking. The vehicle is then regeneratively braked in accordance with the requested deceleration torque, either completely or to the extent that the current state of the regenerative braking system, in particular of the energy storage unit, permits regenerative braking.In this alternative embodiment, it is then also provided in particular that if the current state of the recuperative braking system, in particular of the energy storage unit, does not permit or does not permit completely the recuperative braking corresponding to the requested deceleration torque, a remaining portion of the requested deceleration torque, which cannot be achieved by the recuperative braking, is forwarded to the brake control system of the friction braking system and the vehicle is braked by means of the friction braking system, in particular by means of its friction braking device, in accordance with this remaining portion of the requested deceleration torque.

[0025] In particular, it is provided that the deceleration torque for the recuperative braking is forwarded by the control unit not belonging to the friction brake system as an electrical target braking torque to a drive train control unit of the electric drive train of the vehicle comprising the at least one electric machine.

[0026] Furthermore, it is particularly provided that a vehicle dynamics control system transmits a minimum drive speed for the electric motor to the powertrain control unit, and that the powertrain control unit performs regenerative braking by controlling the at least one electric motor in accordance with the desired electric braking torque, but only until the minimum drive speed is reached. Upon reaching the minimum drive speed, regenerative braking, i.e., a recuperation torque, is reduced in order to maintain the specified minimum drive speed. Upon reaching the minimum drive speed, the powertrain control unit transmits a remaining deceleration torque to the vehicle dynamics control system that cannot be achieved through regenerative braking.

[0027] In particular, it is provided that the deceleration torque for the friction braking is transmitted from the brake control system to the friction braking device as a target friction braking torque.

[0028] In addition, it is particularly provided that the vehicle dynamics control transmits a minimum wheel speed to the friction brake device and the friction brake device carries out the friction braking by controlling a friction brake actuator in accordance with the desired friction braking torque, but only until the minimum wheel speed is reached. When the minimum wheel speed is reached, the friction braking, i.e. a friction braking torque, is reduced in order to maintain the specified minimum wheel speed. When the minimum wheel speed is reached, the friction brake device transmits a remaining deceleration torque to the vehicle dynamics control, which cannot be achieved by friction braking. In one possible embodiment, it is provided that the vehicle dynamics control transmits a detachable electrical deceleration torque to the control unit not belonging to the friction brake system, in particular the central control unit, and / or to the brake control system of the friction brake system, i.e.a deceleration torque that can be regenerated by at least one electric machine at the appropriate time. This is advantageously taken into account during regenerative braking and / or friction braking, i.e. the vehicle is regenerated and / or friction braked accordingly. The regenerated electrical deceleration torque is in particular a maximum possible regenerated electrical torque. If a deceleration request cannot be fully regenerated by regenerative braking, for example due to a slippery road surface or other circumstances, in particular those detected by the vehicle dynamics control, only the regeneratively regenerated portion is transmitted. This is the regenerated electrical deceleration torque, i.e. the deceleration torque that can be regenerated by at least one electric machine at the appropriate time. The brake control system orthe control unit that is not part of the friction brake system, in particular the central control unit, that additional requests via the brake pedal, accelerator pedal or assistance functions cannot be made electrically but must be made via the friction brake.

[0029] In one possible embodiment, it is provided that the vehicle dynamics control transmits a brake force distribution specification to the control unit not belonging to the friction brake system, in particular the central control unit, and / or to the brake control system of the friction brake system.

[0030] The vehicle dynamics control, for example, is separated from the friction brake system and is an independent unit, such as an independent control unit. It is therefore not integrated into the control unit that is not part of the friction brake system, particularly the central control unit.

[0031] By specifying the minimum drive speed through the driving dynamics control, targeted brake slip control with the vehicle's electric drive train is enabled on the basis of this driving dynamics limit specified by the driving dynamics control, so that regenerative braking is possible up to this limit. The minimum drive speed includes, for example, a specified maximum wheel slip of, for example, three percent, which must not be exceeded, as otherwise there would be a risk of driving instability. Previously, recuperation was switched off when slip occurred. With the solution described here, however, only a reduction in the recuperation torque, i.e. the deceleration torque generated by regenerative braking, occurs when the specified minimum drive speed is reached or undershot, and a reconstruction of this recuperation torque when the specified minimum drive speed is left behind or exceeded.

[0032] Previously, negative torques of the electric drivetrain were monitored in the vehicle dynamics control system and reduced if necessary. This required every braking request, i.e., every request signal for a deceleration torque, to always pass through the vehicle dynamics control system, creating the recuperation signal loop described above.

[0033] In the method described here, deceleration torques are monitored directly in the powertrain control unit and reduced if necessary. In particular, an electrical braking request, ie a regenerative braking request, is limited directly in the powertrain control unit so that the vehicle is no longer destabilized. Using the method described, braking requests, ie

[0034] Deceleration torque requests are made directly by various requestors, for example, from the accelerator pedal, from a longitudinal control assistance function, and from the brake pedal. The vehicle dynamics control merely specifies the minimum drive speed for the electric drive train, i.e., for the at least one electric motor, and the minimum wheel speed for the friction brake system in order not to exceed maximum slip. The monitoring of the electrical torques, in particular recuperation torques, is carried out by the electric drive train, in particular its drive train control unit, and no longer by the vehicle dynamics control. The monitoring of the friction brake torques is carried out by the friction brake system.

[0035] The solution described enables, in particular, an increase in the availability of recuperation. Recuperation, i.e. regenerative braking, is always fully possible on the part of the vehicle dynamics control until the specified minimum drive speed threshold is reached. In particular, the procedure described avoids destabilization of the vehicle due to negative moments. As already mentioned, recuperation was previously completely stopped when slip occurred. This was achieved by setting a slip bit. With the method described here, this slip bit is omitted, and with it the hard shutdown of recuperation when a specified slip threshold is exceeded. This is made possible by targeted protection against destabilization of the vehicle by specifying and adhering to the minimum drive speed threshold, so that recuperation can continue up to this minimum drive threshold. I.e.The regenerative braking then only needs to be reduced in order not to fall below the minimum drive speed, but not switched off completely.

[0036] The described method also enables an increase in vehicle stability in the dynamic driving limit range, since the described method enables targeted slip control to better ensure vehicle stability.

[0037] Furthermore, the process increases recuperation efficiency, particularly during so-called one-pedal driving—that is, when the vehicle is driven using only the accelerator pedal, with the vehicle decelerated by progressively releasing the accelerator pedal through regenerative braking—as well as during assisted braking. When the vehicle is braked using only regenerative braking, there is no volume shift of brake fluid into a low-pressure accumulator, and no contact of the brake pads with the brake discs occurs.

[0038] The method is based in particular on a previously used signal world, but time-critical signals in the form of torque specifications are replaced by slow signals, namely a respective speed specification in the form of vehicle speed less brake slip. This is achieved by the described monitoring based on the minimum wheel speed specified by the vehicle dynamics control or the minimum drive speed specified by the vehicle dynamics control. In addition, the method described here distributes the control among the control units that can implement the control specification most quickly. In the powertrain control unit, the deceleration torque specifications are converted into the drive speed values ​​at one millisecond intervals, for example, whereas previously a torque calculation in the vehicle dynamics control took place every 20 ms and then had to be sent to the control units via a network.Previously, the latency existed within the control loop, due to the transmission time of the target torque via the network of the vehicle dynamics control - central control unit - powertrain control unit. With the method described here, the latency is located outside the control loop, allowing for greater dynamics within the control loop. The control loop is now closed within the powertrain control unit.

[0039] The process described here uses two coordinators for braking requests: the control unit not part of the friction braking system, specifically the central control unit for regenerative braking, and the brake control system for friction braking. Previously, everything was coordinated jointly in the vehicle dynamics control system, resulting in the aforementioned regenerative braking signal loop.

[0040] In the method described here, each braking actuator, ie both the electric drive train and the friction brake device, has its own actuator-related control, which is based in particular not only on torques, but on torques and predetermined minimum speeds, ie on the minimum drive speed or on the minimum wheel speed.

[0041] In the method described here, brake pedal requests, ie deceleration torques requested via the brake pedal, can also be made electrically in the manner described above, ie also lead to regenerative braking, and accelerator pedal requests, ie deceleration torques requested via the accelerator pedal, can also be made via the friction brake system, ie also lead to friction braking.

[0042] This is made possible by the two coordinators mentioned above, which exchange or coordinate the respective delay requests among themselves and can request them from the respective partner control unit via the interface as required.

[0043] The process described here enables regenerative braking even when slip occurs, since the stability of the vehicle is ensured by the specified minimum drive speed.

[0044] The described method enables the fulfillment of both tasks of a recuperation function, i.e. ensuring stability by distributing it among the actuators of the friction brake system and the electric powertrain, and maintaining and distributing a respective deceleration torque requirement. In the described method, latency-non-critical signals in the form of speed commands are used instead of latency-critical signals in the form of torque commands. A speed command is latency-non-critical because it is an inert variable that matches the current vehicle speed. A torque command is latency-critical because it must quickly implement a high torque boost. In the previous procedure, it is also sent from the vehicle dynamics control system via the central control unit to the powertrain control unit, with associated latency times on a bus and in the control units.

[0045] In the method described here, the control unit not belonging to the friction brake system, in particular the central control unit, directly commands the desired deceleration torque to the powertrain control unit. Previously, recuperation torque specifications from the central control unit were always routed via the vehicle dynamics control system and then forwarded to the powertrain control unit. Reductions in recuperation torque are now implemented directly in the powertrain control unit based on the deceleration torque specification from the control unit not belonging to the friction brake system, in particular the central control unit, and the minimum drive speed specified by the vehicle dynamics control system. Previously, the reduction in recuperation torque occurred in the vehicle dynamics control system and was then forwarded to the powertrain control unit via the central control unit.

[0046] The described solution enables the extension of OnePedalDriving to the entire available recuperation range. Flexible adjustment of recuperation levels is possible. Fast torque settings analogous to the accelerator pedal movement are possible because the friction brake system is not actuated, meaning, for example, that no electric brake booster of the friction brake system needs to be activated. This also eliminates potentially disruptive noise. The process enables direct response of the electric drivetrain without unnecessary latency and filtering.

[0047] The process increases the availability of regenerative braking. It also enables regenerative braking right up to the dynamic limits of vehicle performance. For example, the process also enables regenerative braking when cornering with high lateral acceleration, as well as after dynamic braking control system interventions where regenerative braking was previously deactivated. The process thus enables regenerative braking right up to the dynamic limits of vehicle performance, even with low road friction coefficients.

[0048] The process also enables an increase in vehicle stability during regenerative braking.

[0049] Regenerative braking is always fully possible within the dynamic driving limits, especially within a specified wheel slip. If the specified wheel slip is exceeded, the regenerative braking in the powertrain control unit is reduced by the deceleration torque required to reduce the wheel slip back below the specified slip threshold.

[0050] This process improves efficiency because it allows for braking without a friction brake, particularly without the use of the OneBox (brake pedal and vehicle dynamics control in a single component) and without a decoupled braking system for OnePedalDriving and assistance functions. When decelerating with OnePedal and assistance functions, there is no residual brake pressure in the system, meaning no friction brake is applied, since no hydraulic volume needs to be displaced.

[0051] The NVH (noise, vibration, harshness) problem of the braking system is improved because the friction braking system only needs to be actuated when the friction brake is used.

[0052] As already mentioned, the method minimizes latencies because time-critical signals in the form of the torque specification are replaced by slow signals, i.e. by the speed specification in the form of vehicle speed less brake slip, the signals are sent directly without delays caused by loop formation and waiting for feedback, and the control is distributed among the control units that can implement the control specification most quickly, as already described above.

[0053] The method enables a simplification of the longitudinal controller interface, as the drive torque interface is used for the electric braking component of the longitudinal controller, so that the same interface is used for both drive operation and regenerative braking. Furthermore, a separate recuperation function for the longitudinal controller is no longer necessary. Exemplary embodiments of the invention are explained in more detail below with reference to a drawing.

[0054] It shows:

[0055] Fig. 1 is a schematic representation of a vehicle.

[0056] Figure 1 shows a schematic representation of a recuperative braking torque coordination with stability protection of a vehicle 1, whereby for reasons of clarity only components of a friction braking system and a recuperative braking system of the vehicle 1 are shown here.

[0057] The vehicle 1 has at least one electric machine that can be operated in motor mode for driving the vehicle 1 and in generator mode for regenerative braking of the vehicle 1. The vehicle 1 further has an energy storage unit or energy sink that supplies the at least one electric machine with electrical energy during engine operation and is charged by means of electrical energy recuperated in generator mode of the at least one electric machine or enables continued regenerative deceleration. The vehicle 1 also has the regenerative braking system for performing regenerative braking, which comprises the at least one electric machine and the energy storage unit and / or energy sink. The vehicle 1 further has the friction braking system with a friction braking device 2 that includes a wheel brake actuator.

[0058] In a method for operating this vehicle 1, it is provided that a request signal S1, S2, S3 for a deceleration torque generated by an accelerator pedal of the vehicle 1 and / or by at least one assistance function of the vehicle 1 is processed in a control unit 3 not belonging to the friction brake system, hereinafter referred to as the central control unit 3. In this case, a setpoint value 5 for manual or assisted driving is first formed from the request signal S1, S2, S3. Subsequently, a check is carried out to determine whether a current state Z of the regenerative braking system, in particular a charge state of the energy storage unit, permits regenerative braking, i.e. in particular whether the energy storage unit has a sufficient electrical potential to absorb the recuperated energy.The vehicle 1 is then braked regeneratively in accordance with the requested deceleration torque completely or to the extent that the current state Z of the regenerative braking system, in particular of the energy storage unit, allows regenerative braking.

[0059] If the current state Z of the regenerative braking system, in particular of the energy storage unit, does not permit regenerative braking corresponding to the requested deceleration torque or does not permit it completely, a remaining portion of the requested deceleration torque that cannot be achieved through regenerative braking is forwarded to a brake control system 4 of the friction braking system, as indicated by arrow P1, and the vehicle 1 is braked according to this remaining portion of the requested deceleration torque by means of the friction braking system, in particular by means of its friction braking device 2. This check and, if necessary, the allocation 6 of the requested deceleration torque are thus carried out in the central control unit 3.

[0060] A request signal S4 for a deceleration torque generated by a brake pedal of vehicle 1 is processed in the brake control system 4 of the friction brake system. First, a setpoint value 7 for manual braking is generated from the request signal S4. Subsequently, a check is carried out to determine whether the current state Z of the regenerative braking system, in particular of the energy storage unit, permits regenerative braking. For this purpose, the current state Z of the regenerative braking system, in particular of the energy storage unit, is determined by the central control unit 3 and forwarded to the brake control system 4, as indicated by an arrow P2. Furthermore, this determined state Z of the regenerative braking system, in particular of the energy storage unit, is also used in the central control unit 3 in the manner described above.

[0061] The requested deceleration torque is transmitted to the central control unit 3 to the extent that the current state Z of the regenerative braking system, in particular the energy storage unit, permits regenerative braking, as indicated by the double-headed arrow P1. Vehicle 1 is braked accordingly. The vehicle 1 is friction-braked according to a remaining portion of the requested deceleration torque. Thus, this check and distribution 8 of the requested deceleration torque takes place in the brake control system 4.

[0062] The portion of the requested deceleration torque for regenerative braking is initially subjected to torque processing 9 in the central control unit 3 as an electric target braking torque ESM, which comprises torque shaping and, if appropriate, torque distribution for efficiency and driving dynamics reasons. The torque shaping serves to ensure a deceleration gradient so that the full deceleration is not implemented suddenly. The torque distribution for efficiency and driving dynamics reasons occurs when the vehicle 1 has multiple electric machines, in particular one electric machine on a front axle and another electric machine on a rear axle. In this case, the electric target braking torque ESM can be distributed among these electric machines, wherein this is done in particular in such a way that recuperation is as efficient as possible and / or adapted to the driving dynamics.

[0063] The deceleration torque for the regenerative braking, in this case the thus processed electric target braking torque ESM, is then forwarded from the central control unit 3 to a powertrain control unit 10 of the electric drive train of the vehicle 1, which comprises at least one electric machine or several electric machines. This is then transmitted to the respective electric machine, as schematically represented by an output arrow P3, and this is operated accordingly.

[0064] In order to ensure driving stability of the vehicle 1 even during regenerative braking, in particular to avoid excessive slippage, it is provided that a vehicle dynamics control system 11 transmits a minimum drive speed MAD for the electric machine or the respective electric machine to the drive train control unit 10 and that the drive train control unit 10 carries out the regenerative braking by controlling the at least one or respective electric machine in accordance with the desired electric braking torque ESM, but only until the minimum drive speed MAD is reached. When the minimum drive speed MAD is reached, the drive train control unit 10 transmits a remaining, i.e. regulated, electric deceleration torque AEV to the vehicle dynamics control system 11, which cannot be achieved by regenerative braking.The resulting maximum detachable electrical torque is communicated by the vehicle dynamics control 11 to the central control unit 3 and the brake control system 4 as detachable electrical deceleration torque 13.

[0065] The portion of the requested deceleration torque for friction braking is initially subjected to a torque processing 12 in the brake control system 4 as a target friction braking torque RSM, which comprises a torque distribution from a stability perspective, ie in particular a distribution between the front axle and rear axle of the vehicle 1.

[0066] The deceleration torque for friction braking, in this case the thus processed target friction braking torque RSM, is then transmitted from the brake control system 4 to the friction brake device 2. This is then transmitted to a friction brake actuator, as schematically represented by an output arrow P4, which operates the actuator accordingly. The friction brake device 2 also receives information from an anti-lock braking system (ABS) of vehicle 1.

[0067] To ensure the driving stability of the vehicle 1 even during friction braking, in particular to avoid excessive slippage, it is provided that the vehicle dynamics control system 11 transmits a minimum wheel speed MRD to the friction brake device 2, and the friction brake device 2 carries out the friction braking by controlling the friction brake actuator in accordance with the target friction braking torque RSM, but only until the minimum wheel speed MRD is reached. When the minimum wheel speed MRD is reached, the friction brake device 2 transmits a remaining, i.e., regulated, friction deceleration torque ARV to the vehicle dynamics control system 11, which cannot be achieved by friction braking.

[0068] To stabilize vehicle 1, the vehicle dynamics control system 11 transmits the deceleration torque 13 to the central control unit 3 and the brake control system 4 of the friction brake system. This deceleration torque can be regeneratively delivered by at least one electric motor at the appropriate time. This deceleration torque flows into the respective distribution 6, 8 of the requested deceleration torque and is thus taken into account, whereby the vehicle 1 is braked accordingly using regenerative braking and / or friction braking.

[0069] In the example shown, the vehicle dynamics control system 11 also transmits an electrical brake force distribution command 14 or friction brake force distribution command 15 to the central control unit 3 and the brake control system 4 of the friction brake system. The electrical brake force distribution command 14 is taken into account in the torque processing unit 9 in the central control unit 3 in the example shown. The friction brake force distribution command 15 is taken into account in the torque processing unit 12 in the brake control system 4 in the example shown.

[0070] 1 vehicle

[0071] 2 friction brake device

[0072] 3 Control unit / central control unit not belonging to the friction brake system

[0073] 4 Brake control system

[0074] 5 Setpoint generation for manual or assisted driving

[0075] 6 Distribution of the requested deceleration torque in the central control unit

[0076] 7 Setpoint generation for manual braking

[0077] 8 Distribution of the requested deceleration torque in the brake control system

[0078] 9 Torque processing in the central control unit

[0079] 10 Powertrain control unit

[0080] 11 Driving dynamics control

[0081] 12 Torque processing in the brake control system

[0082] 13 removable electrical deceleration torque

[0083] 14 electrical brake force distribution specification

[0084] 15 Friction brake force distribution specification

[0085] ABS anti-lock braking system

[0086] AEV governed electric deceleration torque

[0087] ARV regulated friction deceleration torque

[0088] ESM electrical target braking torque

[0089] RSM friction target braking torque

[0090] MAD Minimum input speed

[0091] MRD Minimum wheel speed

[0092] P1 Arrow

[0093] P2 Arrow

[0094] P3 Exit arrow

[0095] P4 Output arrow 51 Request signal generated by accelerator pedal

[0096] 52 Request signal generated by assistance function

[0097] 53 Request signal generated by assistance function

[0098] 54 Request signal generated by brake pedal

[0099] Z current status of the regenerative braking system

Claims

Patent claims Method for operating a vehicle (1), wherein the vehicle (1) comprises: - at least one electric machine which can be operated in a motor mode for driving the vehicle (1) and in a generator mode for regenerative braking of the vehicle (1), - an energy storage unit and / or energy sink, which supplies the at least one electric machine with electrical energy during engine operation and is charged by means of electrical energy recuperated during generator operation of the at least one electric machine and / or further enables regenerative braking, - a regenerative braking system for performing the regenerative braking, comprising the at least one electric machine and the energy storage unit and / or energy sink, and - a friction brake system with a friction brake device (2) comprising a wheel brake actuator, characterized in that a request signal (S1, S2, S3) for a deceleration torque generated by an accelerator pedal of the vehicle (1) and / or by at least one assistance function of the vehicle (1) is processed in a control unit (3) not belonging to the friction brake system, wherein it is checked whether a current state (Z) of the regenerative braking system permits regenerative braking, and the vehicle (1) is regeneratively braked in accordance with the requested deceleration torque completely or to the extent that the current state (Z) of the regenerative braking system permits regenerative braking. Method according to claim 1, characterized in that when the current state (Z) of the regenerative braking system permits regenerative braking in accordance with the requested deceleration torque is not or not completely permitted, a remaining portion of the requested deceleration torque, which cannot be achieved by regenerative braking, is forwarded to a brake control system (4) of the friction brake system, and the vehicle (1) is braked by means of the friction brake system in accordance with this remaining portion of the requested deceleration torque. Method according to claim 2, characterized in that a request signal (S4) for a deceleration torque generated by a brake pedal of the vehicle (1) is processed in the brake control system (4) of the friction brake system, wherein it is checked whether the current state (Z) of the regenerative braking system permits regenerative braking, and - the requested deceleration torque is forwarded to the control unit (3) not belonging to the friction brake system to the extent that the current state (Z) of the regenerative braking system permits regenerative braking, and the vehicle (1) is accordingly regeneratively braked, and - the vehicle (1) is braked by means of the friction brake system in accordance with a remaining portion of the requested deceleration torque. Method according to claim 3, characterized in that the current state (Z) of the recuperative braking system is determined by the control unit (3) not belonging to the friction brake system and is forwarded to the brake control system (4). Method according to one of the preceding claims, characterized in that the deceleration torque for the recuperative braking is forwarded by the control unit (3) not belonging to the friction brake system as an electrical target braking torque (ESM) to a drive train control unit (10) of an electric drive train of the vehicle (1) comprising the at least one electric machine. Method according to claim 5, characterized in that a vehicle dynamics control system (11) transmits to the drive train control unit (10) a minimum drive speed (MAD) for the electric machine and the drive train control unit (10) carries out the regenerative braking by controlling the at least one electric machine in accordance with the electrical target braking torque (ESM), but only until the minimum drive speed (MAD) is reached, wherein the drive train control unit (10) transmits a remaining deceleration torque (AEV) to the vehicle dynamics control system (11) upon reaching the minimum drive speed (MAD), which deceleration torque cannot be achieved by regenerative braking. Method according to one of claims 2 to 6, characterized in that the deceleration torque for the friction braking is forwarded from the brake control system (4) to the friction brake device (2) as a friction target braking torque (RSM).Method according to claim 7, characterized in that the vehicle dynamics control system (11) transmits a minimum wheel speed (MRD) to the friction brake device (2), and the friction brake device (2) performs the friction braking by controlling a friction brake actuator in accordance with the desired friction braking torque (RSM), but only until the minimum wheel speed (MRD) is reached. Upon reaching the minimum wheel speed (MRD), the friction brake device (2) transmits a remaining deceleration torque (ARV) to the vehicle dynamics control system (11), which cannot be achieved by friction braking. Method according to one of claims 6 to 8, characterized in that, for stabilizing the vehicle (1), the vehicle dynamics control system (11) transmits a detachable electrical deceleration torque (13) to the control unit (3) not belonging to the friction brake system and / or to the brake control system (4) of the friction brake system, and the vehicle (1) is accordingly braked recuperatively and / or friction braked.Method according to one of claims 6 to 9, characterized in that the driving dynamics control (11) transmits a braking force distribution specification (14, 15) to the control unit (3) not belonging to the friction braking system and / or to the braking control system (4) of the friction braking system.

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