METHOD FOR OPERATING A MOTOR VEHICLE AND CORRESPONDING MOTOR VEHICLE

Description

[0001] The invention relates to a method for operating a motor vehicle having a drive device for providing a drive torque and a detection device for detecting at least one other motor vehicle traveling ahead, wherein automatic longitudinal guidance of the motor vehicle is performed. The invention further relates to a motor vehicle.

[0002] From the prior art, for example, the document WO 2012 / 072464 A1 is known. This relates to a method for operating a vehicle in which energy is recuperated during the vehicle's coasting and / or braking phases and stored in an on-board energy storage device. The vehicle's surroundings are detected by a detector device, and depending on the detection of an object in the vehicle's surroundings, at least one object characteristic is evaluated, and depending on the evaluation of the object characteristic, the coasting and / or braking phase is automatically adapted to at least one parameter characterizing the energy storage device. DE 44 37 678 A1 discloses another method for distance control of motor vehicles. US 2015 / 0314771 A1 discloses a control system for a hybrid-powered vehicle.

[0003] It is an object of the invention to propose a method for operating a motor vehicle which has advantages over known methods, in particular enabling a particularly efficient and / or comfortable operation of the motor vehicle.

[0004] This is achieved according to the invention with a method for operating a motor vehicle with the features of claim 1 and a motor vehicle with the features of claim 8. It is provided that, within the scope of the longitudinal guidance, a distance of the motor vehicle from the other motor vehicle is regulated to a target distance, wherein the target distance corresponds to a specified distance at a constant distance and, starting from the specified distance, is increased in the event of a change in distance resulting from a positive acceleration of the other motor vehicle and is reduced in the event of a change in distance resulting from a negative acceleration of the other motor vehicle.

[0005] The motor vehicle has the drive system, which serves to drive the motor vehicle, i.e., to provide the drive torque directed at driving the motor vehicle. Furthermore, the motor vehicle has the detection system, for example, an environment detection system, which serves to detect at least one other motor vehicle traveling ahead—if present. This means that the detection system can detect whether the other motor vehicle is present. If so, the other motor vehicle is detected or monitored.

[0006] The detection device is used to automatically guide the motor vehicle longitudinally, with the speed of the motor vehicle being adjusted to match the speed of the other motor vehicle traveling ahead in such a way that the distance between the motor vehicle and the other motor vehicle remains constant, at least temporarily. Within the scope of the longitudinal guidance, the drive device is adjusted to provide a specific drive torque, so that a speed and / or acceleration of the motor vehicle specified within the scope of the longitudinal guidance is established.

[0007] It is now provided that the distance between the motor vehicle and the other motor vehicle is adjusted to the target distance as part of the longitudinal guidance. The target distance corresponds to a specific distance between the two motor vehicles, i.e. the motor vehicle and the other motor vehicle, and should be kept constant at least temporarily. This is particularly the case if the other motor vehicle is moving at a constant speed. If both motor vehicles have a constant speed, the distance is therefore constant. In this case, the target distance is set to the specified distance and the distance control is then carried out. Ultimately, the distance between the motor vehicles corresponds to the specified distance, namely in the event that both are moving at a constant speed and the speed of the motor vehicle corresponds to the speed of the other motor vehicle.

[0008] If the other vehicle accelerates or slows down, the distance between the vehicles changes, at least until the distance control system has adjusted the distance between the vehicles back to the target distance or the preset distance. If the speed of the other vehicle increases, i.e., positive acceleration occurs, the distance between the vehicles initially increases. Conversely, if the speed of the other vehicle decreases, i.e., negative acceleration occurs, the distance decreases.

[0009] The aim of the method according to the invention is to make the driving operation of the motor vehicle as energy-efficient as possible, on the one hand, and as comfortable as possible for the occupants of the motor vehicle, on the other. For this reason, it is not intended to directly induce a corresponding acceleration of the motor vehicle upon positive or negative acceleration of the other motor vehicle, namely by requesting a corresponding drive torque from the drive device.

[0010] Rather, an increase in the distance between the vehicles is permitted in the case of positive acceleration, and a decrease in the distance between the vehicles is permitted in the case of negative acceleration. To this end, the target distance is increased from the specified distance when positive acceleration is present and decreased when negative acceleration is present. Accordingly, the acceleration of the vehicle is, at least temporarily, smaller than the acceleration of the other vehicle, so that the acceleration is perceived as pleasant by the vehicle occupants.

[0011] According to the invention, the motor vehicle is a hybrid-powered motor vehicle comprising a first drive unit and a second drive unit. The rated torque of the second drive unit is preferably less than the rated torque of the first drive unit. According to the invention, an internal combustion engine is used as the first drive unit, and an electric motor is used as the second drive unit, whereby the electric motor can also be referred to as a traction motor.

[0012] By allowing the distance between the vehicles to increase, the drive torque is selected such that it can be provided solely by the second drive unit. This prevents the first drive unit, such as the internal combustion engine, from starting up during positive acceleration of the vehicle. In the case of negative acceleration, the use of the vehicle's service brake is prevented as long as possible. Accordingly, the vehicle is decelerated in an energy-efficient manner using the second drive unit and recuperating electrical energy.

[0013] For example, it can also be provided that deceleration of the motor vehicle, i.e., negative acceleration, is achieved solely through rolling torques and / or friction torques, so that the drive device is not used. Accordingly, neither the first drive unit nor the second drive unit is used to decelerate the motor vehicle, provided the rolling torque and / or friction torque, for example, of a drive train of the motor vehicle, is sufficient to decelerate the motor vehicle sufficiently, namely, in particular, to such an extent that a collision with the other motor vehicle is avoided.

[0014] It should be explicitly noted that regardless of the selection of the target distance—i.e., regardless of whether the target distance corresponds to the specified distance or is smaller or larger—distance control is implemented, namely, the distance between the vehicles is adjusted to the target distance. Therefore, distance control is not interrupted even when the other vehicle accelerates; rather, it is implemented continuously.

[0015] In other words, it is provided that, within the scope of the longitudinal guidance, a distance of the motor vehicle from the other motor vehicle is adjusted to a target distance, wherein the target distance corresponds to a specified distance at a constant speed of the other motor vehicle and, starting from the specified distance, is increased at an increasing speed resulting from a positive acceleration of the other motor vehicle and is reduced at a lower speed resulting from a negative acceleration of the other motor vehicle.

[0016] Within the scope of a further embodiment of the invention, the target distance is limited downwards by a minimum distance and upwards by a maximum distance, which together comprise a specified distance range. The specified distance range is defined by the minimum distance and the maximum distance, with the minimum distance constraining it downwards and the maximum distance constraining it upwards. The minimum distance corresponds to the minimum permissible distance between the motor vehicles, whereas the maximum distance represents the maximum permissible distance between the motor vehicles.

[0017] By selecting the appropriate preset distance range, an accident between the vehicles can be reliably prevented, but conversely, excessive distance between the vehicles can also be prevented. When determining the preset distance range, it is particularly preferred to set the minimum distance as a function of at least the speed of the vehicle. The minimum distance is therefore not constant, but is calculated from the speed of the vehicle, namely in such a way that there is always a sufficient distance between the vehicles, which allows the vehicle to be reliably stopped from the current speed.

[0018] Additionally, a coefficient of friction between a tire of the motor vehicle and the ground can be included in the calculation of the minimum distance. Additionally or alternatively, at least one of the following values can also be used: the speed of the other motor vehicle, the acceleration of the other motor vehicle, and at least one environmental condition, for example, precipitation and / or outside temperature.

[0019] Preferably, a user of the motor vehicle has no influence on the minimum distance. This is either fixed at a constant value or set variably as described above. Alternatively, it may be provided that the user of the motor vehicle can only increase, but not decrease, the minimum distance based on the value set as a function of at least the speed of the motor vehicle.

[0020] In contrast, however, it may be provided that the user of the motor vehicle can set the maximum distance as desired, with the maximum distance being limited to the minimum distance, i.e., it cannot be less than this. Preferably, the maximum distance is always greater than the minimum distance.

[0021] Within the scope of a further preferred embodiment of the invention, it can be provided that a preset acceleration is determined as a function of the acceleration of the further motor vehicle and is set on the drive device, wherein the preset acceleration is directed at a change in speed of the motor vehicle and has the same sign as the acceleration of the further motor vehicle. The preset acceleration is implemented with the aid of the drive device, namely by setting a corresponding target torque on the drive device. The drive device is subsequently controlled to generate an actual torque corresponding to the target torque in the form of the drive torque for accelerating the motor vehicle.

[0022] Additionally or alternatively, the service brake of the motor vehicle can also be activated accordingly, namely if the negative acceleration of the other motor vehicle is present. In any case, however, the specified acceleration is directed at the change in speed of the motor vehicle, i.e., it is different from zero. However, it has the same sign as the acceleration of the other motor vehicle. Therefore, if the acceleration of the other motor vehicle is positive, the specified acceleration should also be positive.

[0023] In the case of negative acceleration of the other motor vehicle, the target acceleration is also negative. However, at least temporarily, the target acceleration is smaller than the acceleration of the other motor vehicle, in order to increase the distance between the vehicles when the other motor vehicle is accelerating positively and to decrease it when the other motor vehicle is accelerating negatively. By selecting the target acceleration in this way, the aforementioned advantages can be achieved.

[0024] According to the invention, it is further provided that a final speed of the additional motor vehicle at the end of an acceleration is predicted based on at least one environmental condition. In both the case of positive acceleration and negative acceleration, the final speed of the additional motor vehicle at the end of the acceleration is to be estimated. The speed of the additional motor vehicle changes during the acceleration and remains constant from the end of the acceleration, at least for a short period of time, but preferably permanently.

[0025] The final speed can be estimated based on the ambient conditions, at least in the case of positive acceleration. Ambient conditions include, for example, the condition of the surface, a specified maximum speed, traffic density, or the like. Thus, the final speed will be lower in the case of high traffic density than in the case of low traffic density.

[0026] At least one of the aforementioned environmental conditions can also be used to predict the final speed in the case of negative acceleration. However, it can also be provided that the final speed is set to zero in a simple embodiment, so that it is always assumed that the negative acceleration is directed at stopping the other motor vehicle or causes this to happen. By estimating the final speed of the other motor vehicle, particularly safe and energy-efficient longitudinal guidance of the motor vehicle can be achieved.

[0027] A further development of the invention provides that the expected distance between the motor vehicle and the other motor vehicle at the end of the acceleration is determined based on at least the acceleration of the motor vehicle and the acceleration of the other motor vehicle. This determination preferably takes place continuously within the context of longitudinal guidance if the acceleration of the other motor vehicle is present, i.e., if its speed changes. The expected distance between the motor vehicles at the end of the acceleration can be calculated from the accelerations of the two motor vehicles and the time period between the time of calculating the expected distance and the end of the acceleration.

[0028] For example, it is assumed that the acceleration of the motor vehicle and the acceleration of the other motor vehicle remain constant until the end of the acceleration. The end of the acceleration, or the period until the end of the acceleration, is preferably calculated by extrapolating the speed of the motor vehicle up to the final speed using the instantaneous acceleration of the other motor vehicle.

[0029] Additionally, the acceleration gradient of the motor vehicle and / or the acceleration gradient of the other motor vehicle can also be used for the calculation. The acceleration gradient is defined as the change in the respective acceleration over time. Determining the expected distance between the vehicles at the end of the acceleration enables reliable longitudinal guidance of the motor vehicle.

[0030] A particularly preferred further embodiment of the invention provides that the target torque set on the drive device is selected such that the anticipated distance lies within the specified distance range. After determining the anticipated distance at the end of acceleration, the distance is compared with the specified distance range or the minimum distance and the maximum distance. Preferably, assuming that the acceleration of the other motor vehicle remains constant until the end of acceleration, the target torque is now selected such that the distance anticipated at the end of acceleration lies within the specified distance range, thus avoiding, on the one hand, a collision between the motor vehicles and, on the other hand, an undesirably significant increase in the distance.

[0031] For example, the target torque is selected as part of a target torque control depending on the expected distance. The target torque serves as the manipulated variable, while a controlled variable is determined from the expected distance. For example, the controlled variable results from the difference between the expected distance and the minimum distance or the maximum distance, whichever is closer.

[0032] For example, the target torque is kept constant as long as the expected distance remains within the specified distance range. However, if the expected distance deviates from the specified distance range either downwards or upwards, the target torque is changed and adjusted on the drive system in such a way that the expected distance changes toward, or particularly into, the specified distance range. This approach ensures safe operation of the motor vehicle.

[0033] A particularly preferred further embodiment of the invention provides that the target torque is selected such that the expected distance at the end of the acceleration corresponds to the minimum distance in the case of negative acceleration or to the maximum distance in the case of positive acceleration. Thus, the expected distance is not only intended to be kept within the specified distance range. Rather, it is explicitly set to one of the limits of the specified distance range, i.e., either the minimum distance or the maximum distance.

[0034] If the other vehicle slows down, the expected distance at the end of the acceleration should correspond to the minimum distance. Conversely, if the other vehicle accelerates, the maximum distance is used as the reference value for the expected distance. This enables energy-efficient operation of the vehicle, especially in the case of negative acceleration.

[0035] A further embodiment of the invention provides that, from the end of acceleration, the speed of the motor vehicle is adjusted by maintaining the target torque in such a way that the distance between the motor vehicle and the other motor vehicle changes towards the specified distance. At the end of acceleration, although the distance between the motor vehicles is within the specified distance range, it usually no longer corresponds to the specified distance. The specified distance is preferably within the specified distance range, i.e., it is greater than the minimum distance on the one hand and smaller than the maximum distance on the other. Particularly preferably, the specified distance is midway between the minimum distance and the maximum distance, i.e., it is the same distance from both.

[0036] The default distance is the typically desired distance between the vehicles, which is set as part of the longitudinal guidance. Therefore, after the advantages of the method described in this description have been achieved by reducing or increasing the distance, the distance between the vehicles should be adjusted back to the default distance or the target distance corresponding to the default distance. Therefore, there is no need for the user of the vehicle to get used to it. Nevertheless, the described advantages can be achieved by previously reducing or increasing the distance.

[0037] According to the invention, if the speed of the other motor vehicle remains constant from the end of acceleration, the distance between the motor vehicle and the other motor vehicle is adjusted to the target distance. Adjusting the distance between the motor vehicles to the target distance should therefore be carried out not only before the positive or negative acceleration occurs, but also after the end of acceleration, or more precisely, immediately after the end of acceleration. If the constant speed of the other motor vehicle is determined, the target distance is set to the specified distance, and the distance is subsequently adjusted to this distance.

[0038] The invention further relates to a motor vehicle, in particular for carrying out the method according to the statements in the context of this description, which motor vehicle has a drive device for providing a drive torque and a detection device for detecting at least one further motor vehicle traveling ahead, and wherein a device for automatic longitudinal guidance of the motor vehicle is present. It is provided that the motor vehicle is designed to regulate a distance of the motor vehicle from the further motor vehicle to a target distance as part of the longitudinal guidance, wherein the target distance corresponds to a specified distance at a constant distance and, starting from the specified distance, is increased in the event of a change in distance resulting from positive acceleration of the further motor vehicle and is reduced in the event of a change in distance resulting from negative acceleration of the further motor vehicle.

[0039] The advantages of such a procedure or such a design of the motor vehicle have already been pointed out. Both the motor vehicle and the method for its operation can be further developed according to the explanations in this description, so reference is made to these in this regard.

[0040] The invention will be explained in more detail below with reference to the exemplary embodiments shown in the drawings, without limiting the invention. In the drawings: Figure 1 shows a diagram in which the speed of a motor vehicle traveling ahead is plotted over time for a positive acceleration, Figure 2 shows a diagram in which a speed of a motor vehicle is plotted over time for the positive acceleration of the motor vehicle traveling ahead is plotted over time, Figure 3 shows a diagram in which the speed of the other motor vehicle is plotted over time for a negative acceleration, and Figure 4 shows a diagram in which the speed of the motor vehicle is plotted over time for the negative acceleration.

[0041] The Figure 1shows a diagram in which a curve 1 of the speed v of a preceding motor vehicle is plotted against time t. It is clear that the speed increases with constant positive acceleration from time t 0 . From time t 1 , the acceleration is zero, so that the speed of the preceding motor vehicle remains constant thereafter.

[0042] The Figure 2 shows a diagram in which the speed v of a motor vehicle is plotted against time t. The motor vehicle has a drive device for providing a drive torque and a detection device for detecting at least one other motor vehicle traveling ahead. Automatic longitudinal guidance is performed for the motor vehicle, in which the distance between the motor vehicle and the other motor vehicle is adjusted to a desired distance.

[0043] The target distance corresponds to a specified distance when the distance between the vehicles remains constant. If the distance between the vehicles changes due to the acceleration of the other vehicle, the target distance is adjusted based on the specified distance. In the case of positive acceleration of the other vehicle, the target distance should be increased, and in the case of negative acceleration of the other vehicle, it should be decreased.

[0044] The diagram shows the speed curve of the motor vehicle for a standard distance control system. It is clear that the acceleration of the motor vehicle essentially corresponds to the acceleration of the other motor vehicle. For this reason, the speed increases from time t 0 and reaches – for curve 2 – the final speed at time t 1 .

[0045] However, according to the procedure outlined above, the target distance is now increased in the case of positive acceleration, starting from the specified distance. Accordingly, an increase in the distance between the vehicles is permitted, so that a lower overall acceleration is required. This is indicated by curve 3 of the vehicle's speed over time t. Here, the vehicle's final speed is not reached until time t 2 .

[0046] The Figure 3 shows a curve 4 of the speed V of the other motor vehicle traveling ahead over time t, with a negative acceleration. Accordingly, the other motor vehicle has a certain speed, which decreases from time t 0 to zero at time t 1 .

[0047] The Figure 4shows a diagram in which curves 5 and 6 are plotted, each for the speed V of the motor vehicle over time t. Again, curve 5 shows the speed of the motor vehicle for conventional distance control, whereas curve 6 indicates the outlined procedure.

[0048] For both curves 5 and 6, the speed decreases from time t0 toward a standstill of the vehicle. For curve 5, this is reached at time t1. Because the procedure illustrated by curve 6 allows a reduction of the target distance starting from the specified distance, a smaller negative acceleration can be selected than for curve 5. Accordingly, here too, the vehicle reaches standstill later than for curve 5, namely at time t2.

[0049] The process outlined in the diagrams enables a high level of comfort in the vehicle because it avoids sharp accelerations. Furthermore, changing speed at lower accelerations is more energy-efficient. This is especially true if the vehicle is a hybrid-powered vehicle and the torque used for acceleration is provided solely by an electric motor, while the vehicle's internal combustion engine remains deactivated.

Claims

1. Method for operating a motor vehicle, which has a drive apparatus for providing a drive torque, as well as a detection apparatus for detecting at least one preceding further motor vehicle, wherein an automatic longitudinal guidance of the motor vehicle is performed by aligning a speed of the motor vehicle to a speed of the preceding further motor vehicle such that a distance between the motor vehicle and the further motor vehicle remains at least temporarily constant, wherein the distance of the motor vehicle from the further motor vehicle is adjusted to a setpoint distance, wherein, at a constant distance, the setpoint distance corresponds to a predefined distance and, based on the predefined distance, is increased in the event of a change in the distance resulting from a positive acceleration of the further motor vehicle and is decreased in the event of a change in the distance resulting from a negative acceleration of the further motor vehicle, characterized in that the motor vehicle is hybrid powered and has a first drive unit designed as an internal combustion engine and a second drive unit designed as an electric motor, wherein, in the event of a positive acceleration of the motor vehicle, the internal combustion engine is prevented from starting and the drive torque is selected such that it can only be provided by means of the electric motor, and, in the event of a negative acceleration of the motor vehicle, the motor vehicle is slowed down with the aid of the electric motor by recuperating electrical energy, wherein, on the basis of at least one environmental condition, an end speed of the further motor vehicle is predicted at an end of acceleration, wherein, when the speed of the further motor vehicle remains constant at the end of acceleration, the setpoint distance is set to the predefined distance and the distance of the motor vehicle from the further motor vehicle is subsequently adjusted thereto.

2. Method according to claim 1, characterized in that the setpoint distance is limited downwards with a minimum distance and upwards with a maximum distance, which together encompass a predefined distance range.

3. Method according to any one of the preceding claims, characterized in that a predefined acceleration is determined as a function of the acceleration of the further motor vehicle and is set at the drive apparatus, wherein the predefined acceleration is aligned to a change in the speed of the motor vehicle and has the same sign as the acceleration of the further motor vehicle.

4. Method according to any one of the preceding claims, characterized in that the anticipated distance of the motor vehicle from the further motor vehicle at the end of acceleration is determined on the basis of at least the acceleration of the motor vehicle and the acceleration of the further motor vehicle.

5. Method according to claims 2 and 4, characterized in that the setpoint torque set at the drive apparatus is selected such that the anticipated distance lies in the predefined distance range.

6. Method according to claim 5, characterized in that the setpoint torque is selected such that the anticipated distance at the end of acceleration - in the event of negative acceleration - corresponds to the minimum distance or - in the event of positive acceleration - corresponds to the maximum distance.

7. Method according to claim 5, characterized in that the speed of the motor vehicle is set from the end of acceleration by maintaining the setpoint torque such that the distance between the motor vehicle and the further motor vehicle changes in the direction of the predefined distance.

8. Motor vehicle, in particular for performing the method according to one or more of the preceding claims, such that it has a drive apparatus for providing a drive torque, as well as a detection apparatus for detecting at least one preceding further motor vehicle, and wherein there is an apparatus for automatic longitudinal guidance of the motor vehicle, which is designed, within the framework of longitudinal guidance, to align a speed of the motor vehicle to a speed of the preceding further motor vehicle, such that a distance between the motor vehicle and the further motor vehicle remains at least temporarily constant, wherein the distance of the motor vehicle from the further motor vehicle is adjusted to a setpoint distance, wherein, at a constant distance, the setpoint distance corresponds to a predefined distance and, based on the predefined distance, is increased in the event of a change in the distance resulting from a positive acceleration of the further motor vehicle and is decreased in the event of a change in the distance resulting from a negative acceleration of the further motor vehicle, characterized in that the motor vehicle is hybrid powered and has a first drive unit designed as an internal combustion engine and a second drive unit designed as an electric motor, wherein the motor vehicle is also designed, in the event of a positive acceleration of the motor vehicle, the internal combustion engine is prevented from starting and the drive torque is selected such that it can only be provided by means of the electric motor, and, in the event of a negative acceleration of the motor vehicle, the motor vehicle is slowed down with the aid of the electric motor by recuperating electrical energy, wherein, on the basis of at least one environmental condition, an end speed of the further motor vehicle is predicted at an end of acceleration, wherein, when the speed of the further motor vehicle remains constant at the end of acceleration, the setpoint distance is set to the predefined distance and the distance of the motor vehicle from the further motor vehicle is subsequently adjusted to this.