Method and control device for operating a vehicle

Abstract

The present invention relates to a method for operating a vehicle (100), wherein a current thermal load of a central control unit, which controls both a brake actuator of a brake and a steering actuator of a steering system at a wheel of the vehicle, is determined, and a control power provided for controlling the brake actuator and the steering actuator is adjusted depending on the determined current thermal load. For example, when maneuvering, the vehicle (100) is steered via at least one unbraked wheel (106) and braked or held via at least one unsteered wheel (106).

Description

Field of the InventionThe invention relates to a method for operating a vehicle, to a corresponding control device, and to a corresponding computer program product.Prior ArtA vehicle can be steered during maneuvering and, in particular, braked or held on the slope during maneuvering, in order not to roll away. A simultaneously braked and steered wheel requires an increased steering torque.In a vehicle having a central control device for supplying energy to brakes and steering, high temperatures can be achieved by providing power for braking and simultaneously providing power for steering. It is therefore necessary to design the central control unit for this temperature load in order to avoid failures.DE 10 2018 211 897 A1 shows a vehicle and method for operating a vehicleDisclosure of the InventionAgainst this background, the approach presented here presents a method for operating a vehicle, in particular during a maneuvering process, a corresponding control device, and a corresponding computer program product according to the independent claims. Advantageous refinements and improvements of the approach presented here are evident from the description and are described in the dependent claims.Advantages of the InventionIn the approach presented here, a prevailing thermal load of a control unit is determined and a control power or drive power respectively provided for actuating a brake actuator and a steering actuator is set as a function of the determined current thermal load. For example, a wheel is braked either exclusively or at least predominantly during maneuvering or alternatively is steered exclusively or at least predominantly. As a result, a power requirement for steering can be drastically reduced or limited. In addition, in a two-track vehicle, both wheels of an axle are steered in each case and are actuated together. As a result, in a central control device for this axle, either only or predominantly power is provided for steering or only or predominantly power is provided for braking. As a result, a maximum temperature load to be cooled can be significantly reduced.By means of the approach presented here, a central control unit can be designed for a reduced temperature load. Less robust components are required. These components are typically less expensive, smaller and lighter than the extra robust components designed for double thermal loading.A method for operating a vehicle, for example during a maneuvering process, is presented, wherein a current thermal load of a central control unit, which actuates both a brake actuator of a brake and a steering actuator of a steering system on a wheel of the vehicle, is ascertained, and a control power provided in each case for actuating the brake actuator and the steering actuator is set as a function of the ascertained current thermal load. In particular, the vehicle can be steered, for example, during maneuvering via at least one undelayed wheel and braked or held via at least one undriven wheel.Ideas regarding embodiments of the present invention can be considered, among other things, to be based on the ideas and findings described below.A vehicle may have at least one steerable axle. The steerable axle may be steered and braked. The vehicle can have electromechanical brakes and / or an electromechanical steering system. In electromechanical systems, electrical power may be required as long as a braking force or a steering torque is provided.Waste heat arises both when providing the power, for example using an inverter or frequency converter, and when converting the electrical power into a mechanical movement for braking or steering. In particular, in a central control unit, the waste heat from the power provision for braking and the waste heat from the power provision for steering occur in a limited space within the central control unit. The central control device can heat up strongly during prolonged simultaneous braking and steering.In the approach presented here, it is determined how high a thermal load currently prevailing in a central control unit is. The central control unit controls both a power supply to a brake actuator on a wheel of the vehicle and a power supply to a steering actuator on the same wheel. The thermal load on the central control unit is typically associated with an electrical power to be provided currently and / or recently by the central control unit. The thermal load of the central control unit can be determined directly, for example, by measuring a current temperature of the central control unit or can be determined or derived indirectly, for example, by determining a power currently and / or recently provided by the central control unit.For example, it can be provided that the steerable axle is not steered when braking is carried out via this axle during maneuvering. When steering is carried out via the steerable axle during maneuvering, braking is not carried out via the steered axle. As a result, multiple energy input or correspondingly increased heat release is prevented in the central control unit.Braking only on the wheels which are not steered is sufficient during maneuvering to reliably decelerate and then maintain the vehicle, since only low braking torques are required during maneuvering.At a previously braked, unrouted steerable wheel, the brake can be released if a steering movement is controlled at the steerable wheel. This makes it possible to change between braking and steering. In particular in the case of rear wheel steering, the case may occur that the rear wheels are first braked but are not steered. For example, when the vehicle is controlled in a modified manner, the rear wheels can then be steered, while the front wheels are braked but are not changed in their angular position during this.A braking torque component which is dispensed with by releasing the brake on the previously braked wheel which is controlled for the steering movement can be distributed to at least one other wheel of the vehicle, which wheel is also not steered at all at the moment. By compensating the omitted braking torque component, the vehicle can still be safely braked or held.The vehicle can be braked or held via the at least one unguided wheel if the thermal load or a temperature of a combined inverter unit for brake and steering of the vehicle, that is to say the central control unit of the axle, exceeds a threshold value. If the thermal load or temperature is not critical, braking and steering can be carried out simultaneously.The thermal load or temperature of the inverter unit can be measured. The central control unit can have at least one temperature sensor. The temperature sensor can record the thermal load or temperature of the inverter unit or of the central control unit with delay. Therefore, a reduced threshold value for the measured thermal load or temperature can be used.At least an electrical quantity of the inverter unit can be observed. A change in the thermal load or the temperature can be predicted using a change in the electrical variable. The vehicle can be braked or held via the at least one unguided wheel if the thermal load or temperature will exceed the threshold value. By observing an electrical variable of the inverter unit, the power loss at the inverter unit can be estimated. An anticipated thermal load or temperature of the inverter unit can be calculated via a known heat capacity of the inverter unit before it is reached. This makes it possible to react early to the exceeding of the threshold value and to end the multiple heat input into the central control unit before a critical thermal load or temperature is reached.The brake of the at least one braked wheel can be released if a drive torque is greater than the set brake torque for holding the vehicle. Rolling away can thereby be reliably prevented and the heating of the central control unit can be limited to a necessary minimum.To keep the vehicle at a standstill, a change can be made from a service brake to a parking brake on the at least one braked wheel. If the vehicle is to be moved again, the service brake can be changed again. A parking brake can also hold the vehicle securely without or with minimal power supply. When the parking brake is activated, the inverter unit can be relieved.The maneuvering can be detected if the vehicle is moved at a maximum of a maneuvering speed. The approach presented here can be limited to being used below the maneuvering speed. Maneuver speeds can be, for example, below 20 km / h, below 10 km / h or even below 5 km / h.The method is preferably computer-implemented and can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example, in a driver assistance system.The approach presented here furthermore creates a control device, wherein the control device is designed to carry out, actuate or implement the steps of a variant of the method presented here in corresponding devices.The control device can be an electrical device having at least one arithmetic unit for processing signals or data, at least one memory unit for storing signals or data, and at least one interface and / or one communication interface for reading in or outputting data embedded in a communication protocol. The computing unit can be, for example, a signal processor, a so-called system ASIC or a microcontroller for processing sensor signals and outputting data signals depending on the sensor signals. The memory unit may be, for example, a flash memory, an EPROM, or a magnetic memory unit. The interface can be designed as a sensor interface for reading in the sensor signals from a sensor and / or as an actuator interface for outputting the data signals and / or control signals to an actuator. The communication interface can be designed to read in or output the data wirelessly and / or in a wired manner. The interfaces can also be software modules which are present, for example, on a microcontroller, in addition to other software modules.A computer program product or computer program with program code which can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used for carrying out, implementing and / or controlling the steps of the method according to one of the embodiments described above is also advantageous, in particular if the program product or program is executed on a computer, in a control device or a device.It is to be understood that some of the possible features and advantages of the invention are described herein with reference to various embodiments. A person skilled in the art recognizes that the features of the control unit and of the method can be combined, adapted or exchanged in a suitable manner in order to arrive at further embodiments of the invention.BRIEF DESCRIPTION OF THE DRAWINGEmbodiments of the invention are described below with reference to the attached drawing, wherein neither the drawing nor the description should be interpreted as restricting the invention. FIG. 1 shows a representation of a vehicle with central control units when using a method according to an exemplary embodiment.The figure is schematic only and not to scale. Identical reference numerals designate identical or identically acting features.Embodiments of the InventionFIG. 1 shows a representation of a vehicle 100 with central control units 102 when using a method according to an exemplary embodiment. The vehicle 100 has two steerable axles, each with a steering actuator 104. Thus, all wheels 106 of the vehicle 100 are steerable. Each wheel 106 has its own electrically driven brake actuator 108, that is to say all wheels 106 of the vehicle 100 can be braked.Each axle 104 has its own central control device 102. In the central control unit 102 of each axle, the energy supply units 110 for the steering actuator 104 and the brake actuators 106 of the respective axle are combined centrally. The central control units 102 are connected to one another and can be operated in a coordinated manner.In the approach presented here, braking is carried out during the maneuvering of the vehicle only on wheels 106 that are not currently steered and only on wheels 106 that are not currently braked. For example, for a train, the wheels 106 of the front axle are turned in while the wheels 106 of the rear axle are braked. This allows the front axle wheels 106 to roll during steering and requires little energy to change the angle of the un-braked wheels 106. If a tighter turning radius is desired or needed for maneuvering, the rear axle wheels 106 may be turned when the brake is released and the train is being performed.Likewise, at the end of the train, one or two wheels 106 of one of the axles can be braked and, for the next train, the now un braked wheels can be steered. When these wheels are aligned in the new direction, the brakes can be applied there and the brake can be released at the at least one braked wheel 106. Then, steering can also be carried out there when the brake is released.In one exemplary embodiment, the brakes used are each applied so strongly that a desired braking effect is always produced together.In one exemplary embodiment, the approach presented here is only used when at least one of the central control units 102 exceeds a temperature threshold.The temperatures of the central control units can be measured or calculated. By the calculation, the temperature can be predicted from a current load. The approach presented here can thus be applied before the central control device becomes too warm.In one exemplary embodiment, the parking brake is actuated at wheels 106 which are currently braked with an electronic parking brake when the vehicle is at a standstill, when the vehicle 100 is at a standstill. As a result, the energy supply unit of this brake is greatly relieved.Possible embodiments of the invention are summarized again below or presented with a slightly different word selection.An operating strategy for critical combined braking and steering maneuvers using shared drive electronics and inverter units is presented.The approach proposed here is based on the concept of a joint control unit including inverter unit for the braking and steering actuator system of a vehicle. In particular, this solution can be applied if the vehicle has a common control and inverter unit for front wheel brake and steering actuator, as well as a further control and inverter unit for the rear wheel brake and an optional rear wheel steering system. The concept relates to a vehicle with electric motor-actuated brakes, but is not limited thereto.In special driving maneuvers, a heavy load on both the braking system and the steering system may occur. This is not critical for the actuators, since these are spatially distributed, i.e. the heat loss in the actuators does not lead to a simultaneous heat development in the same component, but corresponds locally to the heat development in the event of a strong braking OR steering intervention. However, severe simultaneous loading of both systems results in high thermal losses in both the braking inverters and the steering inverters of the common inverter unit, for which a correspondingly robust design of the system is required. Since this double load occurs only in the case of a few, rare driving maneuvers, a strong over-dimensioning of the system would thus be required. An example of such a driving maneuver would be parking on a steep slope:The brake is heavily stressed because it actively holds the vehicle on the slope for most of the time, but nevertheless the brakes are constantly being opened and closed. The steering is greatly stressed by the parking process, since the vehicle is stationary and the tires therefore have a high frictional resistance. In particular, steering of braked wheels leads to extreme steering forces.In the worst case, this maneuver can take several minutes (narrow parking space, inexperienced driver,... ), which leads to a severe thermal stress on the common inverter unit.In the case of maneuvers with simultaneous strong braking and steering interventions, the operating strategy presented here can be used to distribute the braking and steering power as required in such a way that strong simultaneous loads on the system are avoided. This control system optionally determines the thermal state of the respective inverter unit by means of suitable thermal sensors or by means of a jointly calculated thermal model of the inverter units and distributes the actuation of braking and steering forces accordingly to the front and rear wheels.Also, in an embodiment, the brakes of the vehicle left and right sides are distributed in the inverter units according to the braking request and the thermal situation.Due to the approach presented here, the inverter units and their cooling can be designed to be correspondingly less over-dimensioned thermally, which leads to lower costs and less space requirement. Furthermore, the approach presented here can reduce the force requirement of the steering system, since hard-braked wheels are prevented from being steered by distributing braking and steering intervention to the two axles. In addition, a separately actuated parking brake can also be incorporated into the operating strategy.The approach presented here solves the situation "parking on a steep slope", for example, in such a way that the rear wheels brake the vehicle in order to prevent rolling away while the front wheels are steered in. The brake is thereby released when the drive is sufficient to move the vehicle in the desired direction (hill-hold function). In this interaction, the vehicle is iteratively maneuvered out of the parking space until it can leave the parking space.Finally, it should be noted that terms such as "having", "comprising", etc. do not exclude other elements or steps and terms such as "a" or "an" do not exclude a plurality. Reference signs in the claims should not be regarded as limiting.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2018 211 897 A1

[0004]

Claims

Method for operating a vehicle (100), wherein a current thermal load of a central control unit (102) which actuates both a brake actuator (108) of a brake and a steering actuator (104) of a steering on a wheel (106) of the vehicle (100) is determined, and a control power provided in each case for actuating the brake actuator (108) and the steering actuator (104) is set as a function of the determined current thermal load.Method according to Claim 1, wherein the vehicle (100) is steered via at least one undelayed wheel (106) and braked or held via at least one undriven wheel (106).Method according to Claim 2, in which the brake is released at a previously braked, unrouted steerable wheel (106) if a steering movement is actuated at the steerable wheel (106).Method according to Claim 3, in which a braking torque component which is dispensed with by the release of the brake on the previously braked wheel (106) which is controlled for the steering movement is distributed to at least one other unguided wheel (106) of the vehicle (100).Method according to one of the preceding claims 2 to 4, in which the vehicle (100) is braked or held via the at least one unguided wheel (106) if the thermal load exceeds a threshold value.Method according to claim 5, wherein the thermal load (102) is measured.Method according to one of Claims 5 to 6, in which at least one electrical variable of the central control unit (102) is observed and a change in the thermal load is predicted using a change in the electrical variable, the vehicle (100) being braked or held via the at least one unguided wheel (106) if the thermal load will exceed the threshold value.Method according to one of the preceding claims 2 to 7, in which the brake of the at least one braked wheel (106) is released if a drive torque is greater than the set brake torque for holding the vehicle (100).Method according to one of the preceding claims 2 to 8, in which, in order to keep the vehicle (100) at a standstill on the at least one braked wheel (106), a change is made from a service brake to a parking brake.Method according to one of the preceding claims 2 to 9, in which the method is carried out during a maneuvering of the vehicle and the maneuvering is detected if the vehicle (100) is moved at a maximum of a maneuvering speed.Control device, wherein the control device is designed to execute, implement and / or actuate the method according to one of the preceding claims in corresponding devices.A computer program product configured to direct a processor, when executing the computer program product, to execute, implement and / or drive the method according to any one of claims 1 to 10.A machine readable storage medium having stored thereon the computer program product of claim 12.

Images