Method and device for adjusting a vehicle speed for a vehicle

Abstract

Method for adjusting a vehicle speed for a vehicle (100), the method comprising the following steps: Determining (202) a required steering torque to guide the vehicle (100) along a curved trajectory (104); Determining (210) an available steering torque as a maximum steering torque that can be provided by the steering assistance device (120) of the vehicle (100); and Determining (204) a permissible speed of the vehicle (100) to guide the vehicle (100) along the curved trajectory (104) using the required steering torque and the determined available steering torque, which was determined as the maximum steering torque that can be provided by the steering assistance device (120).

Description

Prior ArtThe present invention relates to a method for adapting a vehicle speed for a vehicle, to a corresponding device and to a corresponding computer program.In the case of present-day lane keeping assistance systems (LKS: lane keeping support) with steering assistance, the amount of steering torque requested by the system is limited, usually to 3 Nm, so that the driver can override the system at any time, in particular in the event of possible incorrect interventions.The document US 2005 / 0240334 A1 discloses an adaptive cruise control system which adjusts the vehicle speed in front of a curve in order to reduce the load on the driver. The system uses information from a navigation system to determine an incoming curve trajectory.Disclosure of the InventionAgainst this background, the approach presented here presents a method for adapting a vehicle speed for a vehicle, and also a device which uses this method and finally a corresponding computer program according to the main claims. Advantageous embodiments are evident from the respective dependent claims and the following description.The method can advantageously be used for regulating the vehicle speed in connection with driver assistance systems, such as a lane keeping assistant.A corresponding method for adapting a vehicle speed for a vehicle comprises the following steps:determining a required steering torque for guiding the vehicle along a curved travel trajectory; anddetermining a speed of the vehicle allowed to guide the vehicle along the curved travel trajectory using the required steering torque and an available steering torque.The travel trajectory can identify a movement path of the vehicle lying in front of the vehicle in the direction of travel or a section of such a movement path. The required steering torque may be a steering torque to be applied to the steerable wheels of the vehicle to guide the vehicle along the travel trajectory. The greater the speed of the vehicle, the greater the steering torque required. Thus, it may be necessary to reduce the current speed of the vehicle in order to be able to guide the vehicle safely along the curved travel trajectory. The available steering torque may be a steering torque that may be applied in the given situation to steer the vehicle. According to embodiments of the described approach, a limitation of a steering torque requested by a driver assistance system can be canceled out or reduced, so that the lane keeping assistance system is able to request a steering torque required for strong turns on roads as well.The method may comprise a step of providing a control signal for reducing the speed of the vehicle if a current speed of the vehicle is greater than the permissible speed. For this purpose, a value representing the current speed of the vehicle can be compared with a value representing the permissible speed. If the current speed is estimated to be too high, the vehicle can be braked to such an extent that it can safely follow the travel trajectory.In this case, in the step of providing, the control signal cannot be provided if, in a step of detecting, a steering torque provided by a driver of the vehicle is detected and a direction of the steering torque provided by the driver is opposite to a direction of the required steering torque. In this way, a reduction in the speed can be avoided if it can be concluded from the action of the driver that the vehicle should not follow the curved driving trajectory. Preventing the braking can be useful, for example, if a steering intervention of the driver recognizes that the driver wishes to start an overtaking process.The method may include a step of detecting a target lane ahead of the vehicle in the direction of travel as the curved travel trajectory. For detecting the desired lane, suitable sensor signals or signals of a digital map can be read in and evaluated. In this way, a current travel trajectory can always be available.In this case, in the step of capturing, a maximum change in a radius of curvature of the curved travel trajectory or a minimum radius of curvature of the curved travel trajectory can be captured. In the determination step, the required steering torque may be determined using the maximum change or the minimum radius of curvature. In this way, those regions of the travel trajectory in which the greatest steering torque is expected to be applied can be considered.The method comprises a step of determining the available steering torque as a maximum steering torque that can be provided by a steering assistance device of the vehicle. A value of the maximum steering torque can be read in via a suitable interface. In this way, the method can be adapted to different vehicle types. In addition, in the event of a failure of the steering assistance device, it is possible to react in good time by, for example, braking the vehicle.In the step of determining, the available steering torque can be determined as a combination of the maximum steering torque that can be provided by the steering assistance device of the vehicle and a steering torque that can be provided by a driver of the vehicle. This can be carried out if a steering torque provided by the driver of the vehicle is detected in a step of detection. In this way, a limitation of the steering torque to the maximum steering torque that can be provided by the steering assistance device of the vehicle can be avoided.The approach presented here furthermore provides a device for adapting a vehicle speed for a vehicle, which is designed to carry out, actuate or implement the steps of a variant of a method presented here in corresponding devices. This embodiment variant of the invention in the form of a device also enables the object on which the invention is based to be achieved quickly and efficiently.In the present case, a device can be understood to mean an electrical device which processes sensor signals and outputs control and / or data signals as a function thereof. The device can have an interface which can be designed as hardware and / or software. In the case of a hardware configuration, the interfaces can be part of a so-called system ASIC, for example, which contains a wide variety of functions of the device. However, it is also possible for the interfaces to be dedicated, integrated circuits or to consist at least partially of discrete components. In the case of a software configuration, the interfaces can 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 or a device.The approach presented here is explained in more detail below by way of example with reference to the attached drawings. The following are shown: FIG. 1 is a schematic diagram of a vehicle including a vehicle speed adjusting apparatus according to an exemplary embodiment of the present invention; and FIG. 2 is a flowchart of a method for adjusting a vehicle speed according to an exemplary embodiment of the present invention.In the following description of advantageous exemplary embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the different figures and acting in a similar manner, wherein a repeated description of these elements is omitted.FIG. 1 shows a schematic illustration of a vehicle 100 having a device 102 for adjusting a vehicle speed of the vehicle 100 according to an exemplary embodiment of the present invention. The vehicle 100 travels on a roadway along a travel trajectory 104. The travel trajectory 104 initially has a straight section which merges into a curved section. When traveling the transition from the straight line section to the curved section and when traveling the curved section, a steering torque acting on the wheels of the vehicle 100 is required in order to be able to keep the vehicle 100 on the travel trajectory 104.According to one exemplary embodiment, the apparatus 102 has a determination device 110 and a determination device 112. The determination device 110 is designed to determine a required steering torque for guiding the vehicle 100 along the travel trajectory 104. The ascertainment device 112 is designed to ascertain a speed permissible for guiding the vehicle along the travel trajectory 104 using a value for the required steering torque and a value for the available steering torque.According to one exemplary embodiment, device 102 is designed to transmit a value representing the permissible speed of the vehicle to a setting device 114 for setting a speed of vehicle 100. The setting device 114 is configured to compare a value of a current speed of the vehicle with the value for the permissible speed and to provide a control signal for reducing the current speed if the permissible speed is greater than the permissible speed. The setting device 114 can thus be designed to adapt the current speed to the permissible speed. Thus, the current speed can also be increased if necessary.According to one exemplary embodiment, device 102 is designed to receive values representing travel trajectory 104 via an interface. According to an alternative exemplary embodiment, device 102 is designed to ascertain values representing travel trajectory 104. For this purpose, device 102 is designed, for example, to receive signals from surroundings detection device 116 or from navigation system 118 via an interface and to use them to ascertain travel trajectory 104. Device 102 is designed to determine a steering torque required for guiding vehicle 100 along travel trajectory 104, for example, using an assignment rule.According to one exemplary embodiment, the device 102 is designed to determine the available steering torque using values which the device 102 receives via an interface to a manual steering 118, for example a steering wheel which can be operated by the driver, and additionally or alternatively via an interface to a steering assistance device 120. Steering torques can be exerted via the manual steering 118 and the steering assistance device 120 on a steering device 122 of the vehicle 100, via which steering device the steerable wheels of the vehicle 100 can be steered or held in a steered position. For example, device 102 is designed to add the steering torque provided or made available by the driver to a steering torque made available by steering assistance device 120 in order to determine the available steering torque that can be made available during the travel of travel trajectory 104.Exemplary embodiments of the present invention are described in detail below with reference to FIG. 1.According to one exemplary embodiment, the described approach enables an adaptation and additionally or alternatively a regulation of the longitudinal vehicle speed on the basis of a predicted curvature of the setpoint lane, which is drawn in FIG. 1 as driving trajectory 104, and on the basis of a maximum available steering torque of a lane keeping assist system, which can comprise steering assist device 120, for example, and on the basis of a driver hand torque, which the driver can provide, for example, via manual steering 118.A system comprising the device 102 can detect the curvature of the lane and its change in curvature, i.e. relevant parameters or values of the travel trajectory 104, with the aid of various sensors 114, e.g. camera, radar or GPS.By using clothiod models, device 102 according to one exemplary embodiment is able to predict the curvature of travel trajectory 104 at a preview distance. The look-ahead distance can advantageously be calculated by multiplying the vehicle speed and a look-ahead time assigned to the look-ahead distance. The look-ahead time is necessary to compensate for the latency and inertia of the vehicle 100.According to one exemplary embodiment, the calculation of the curvature of the travel trajectory 104 also takes into account whether the vehicle 100 is to travel along the center line of the ego lane or is to follow another trajectory, which may be necessary depending on the situation, for example if the lateral control is to be started from the lane edge and the vehicle 100 is to be returned to the lane center again. This may also be required if the target trajectory 104 is influenced by other objects, such as obstacles or vehicles in adjacent lanes.According to one exemplary embodiment, device 102 is designed to determine the maximum permissible longitudinal vehicle speed (Vmax) in the form of an estimate by knowing the predicted curvature of vehicle setpoint trajectory 104 (Kappapred) and the maximum available lane keeping assist system steering torque (MLKSmax), as follows: FactorK is a constant in the simplest form and can be parameterized depending on the vehicle.If, however, the driver now drives along with the lane keeping assist system, i.e. the driver drives along in the same direction as the lane keeping assist system or in a correct direction predicted by the lane keeping assist system, the maximum steering torque available (Mmax) is as follows:The calculation for the vehicle speed (Vmax) is then carried out with the maximum available steering torque (Mmax).If the driver is strongly steering against the system, the system is switched off according to one exemplary embodiment.The vehicle speed (Vmax) is then sent to the longitudinal control of the vehicle 100, for example to an adaptive cruise control (ACC), which can be represented schematically in FIG. 1 by the setting device 114. The speed control is designed to control the vehicle speed such that, for example, by controlling the drive of the vehicle 100 and / or the brakes of the vehicle 100, the maximum permissible longitudinal vehicle speed (Vmax) is not exceeded.This ensures that the maximum lane keeping assist system torque, which can be provided by the steering assist device 120, for example, is not exceeded, since the lateral acceleration of the vehicle 100 is located in the corresponding limit.In addition, an offset may be subtracted from the maximum available lane keeping assist system steering torque (MLKSmax) during the calculation, so that the system still has some reserve to ensure that the maximum available lane keeping assist system steering torque (MLKSmax) is not reached.FIG. 2 is a flowchart of a method for adjusting a vehicle speed according to an exemplary embodiment of the present invention. The method can be used in conjunction with a device for adjusting a vehicle speed of a vehicle, as described with reference to FIG. 1.The method comprises a step 202 of determining in which a required steering torque for guiding the vehicle along a curved travel trajectory is determined, and a step 204 of determining in which a speed permissible for guiding the vehicle along the curved travel trajectory is determined using the required steering torque and an available steering torque.According to various exemplary embodiments, the method has one or more optional steps 206, 208. Thus, in an optional step 206, a control signal is provided which causes a reduction in the speed of the vehicle if a current speed of the vehicle is greater than the permissible speed. In an optional step 208, a steering torque provided by the driver of the vehicle can be detected. A value of the steering torque provided by the driver may be used to identify a deviation from the predicted travel trajectory desired by the driver. Further, the steering torque provided by the driver of the vehicle may be used in a step 210 to determine the available steering torque. In an optional step 212, a setpoint lane ahead of the vehicle in the direction of travel may be detected as the travel trajectory. In step 212, a maximum change in a radius of curvature of the travel trajectory or a minimum radius of curvature of the travel trajectory can furthermore be detected and used in step 202 to determine the required steering torque.If an exemplary embodiment comprises an "and / or" combination between a first feature and a second feature, this is to be read in such a way that the exemplary embodiment has both the first feature and the second feature according to one embodiment and either only the first feature or only the second feature according to a further embodiment.

Claims

A method for adjusting a vehicle speed for a vehicle (100), the method comprising the steps of: determining (202) a required steering torque for guiding the vehicle (100) along a curved driving trajectory (104); determining (210) an available steering torque as a maximum steering torque provided by the steering assist device (120) of the vehicle (100); and determining (204) a speed of the vehicle (100) allowed for guiding the vehicle (100) along the curved driving trajectory (104) using the required steering torque and the determined available steering torque determined as the provided maximum steering torque of the steering assist device (120).Method according to claim 1, comprising a step of providing (206) a control signal for reducing the speed of the vehicle (100) if a current speed of the vehicle (100) is greater than the allowed speed.Method according to Claim 2, in which, in the step of providing (206), the control signal is not provided if, in a step of detecting (208), a steering torque provided by a driver of the vehicle (100) is detected and a direction of the steering torque provided by the driver is opposite to a direction of the required steering torque.Method according to one of the preceding claims, having a step of detecting (212) a setpoint lane situated in front of the vehicle (100) in the direction of travel as the curved travel trajectory (104).Method according to Claim 4, in which, in the step of detecting (212), a maximum change in a radius of curvature of the curved travel trajectory (104) or a minimum radius of curvature of the curved travel trajectory (104) is detected, and, in the step of determining (202), the required steering torque is determined using the maximum change or the minimum radius of curvature.Method according to Claim 1, in which, in the step of determining (210), the available steering torque is determined as a combination of the maximum steering torque which can be provided by the steering assistance device (120) of the vehicle (100) and a steering torque which can be provided by a driver of the vehicle (100), if, in a step of detecting (208), a steering torque which can be provided by the driver of the vehicle (100) is detected.Device (102) for adjusting a vehicle speed for a vehicle (100), which is designed to carry out all steps (202, 204) of a method according to one of the preceding claims.Computer program which is configured to carry out, implement and / or actuate all steps (202, 204) of a method according to one of the preceding claims.A machine readable storage medium having stored thereon a computer program according to claim 9.

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