DE102014213074B4 - Reversing assistance system for a two-lane motor vehicle with front wheel steering - Google Patents

Abstract

Reversing assistance system for a two-lane motor vehicle with front wheel steering for reversing in the reverse direction of a route previously driven manually in the forward direction with at least automatic steering of the motor vehicle while reversing, which is set up - for different positions (S) of the route traveled during the forward journey, a value for each the alignment of the vehicle's longitudinal axis when driving forward is a characteristic first variable at the respective position (S) depending on a distance (SR) covered by one rear wheel (R) when driving forward and a distance (SL) covered by the other rear wheel (L) when driving forward determine, - for different positions (S) of the route covered during reversing, a value of a second variable characteristic of the alignment of the vehicle's longitudinal axis when reversing at the respective position depending on a distance traveled (SR) of one rear wheel (R) and a traveled To determine the distance (SL) of the other rear wheel (L), - during reversing for different positions (S) of the route - a value of the first variable (dSRL, target) characteristic of the alignment of the vehicle's longitudinal axis when driving forward at the respective position ( S) - to compare with a value of the second variable (dSRL, is) characteristic of the alignment of the vehicle's longitudinal axis when reversing at the same position, and - to control the front wheel steering depending on the comparison.

Description

The invention relates to a reversing assistance system for a two-lane motor vehicle with front wheel steering for reversing in the reverse direction of a route that was previously driven manually in the forward direction, with at least automatic steering of the motor vehicle while reversing, and to a corresponding method for reversing a two-lane motor vehicle with front wheel steering. It is preferably provided that during reversing not only the lateral guidance (steering) of the vehicle takes place automatically, but also the longitudinal guidance is carried out automatically by the vehicle.

Many drivers consider reversing to be an unpleasant task, especially in narrow, winding areas. To make this driving task easier, assistance systems based on a rear view camera and/or rear distance sensors are known.

Despite these aids, vehicle guidance, in particular lateral guidance (i.e. steering) and longitudinal guidance (for example braking when the reversing speed is too high due to the drag torque), remains the responsibility of the driver. There is a risk of collisions with stationary obstacles, especially in winding narrow areas.

From the prior art, for example from the publication DE 198 41 914 A1 , reversing assistance systems are known. A reversing assistance system allows the driver to automatically set his vehicle in relation to the lateral guidance and optionally in relation to the longitudinal guidance the distance last traveled in the forward direction (e.g. the last 100 m) on the same course as when driving manually in the forward direction but now in the reverse direction to be driven back. The automatic reversing is triggered, for example, after stopping, engaging reverse gear and pressing a corresponding control element on the driver's side.

The risk of collisions with stationary obstacles is eliminated by a reversing assistance system, provided that the trajectory of the return journey matches the trajectory of the forward journey with a high degree of accuracy. The automatic steering control and optional additional control of the vehicle's reversing speed reduce the driver's workload and allow him to concentrate fully on monitoring the traffic area behind him.

In order to want to reproduce a course that has been driven manually in the forward direction exactly backwards, data sets can be saved according to predefined path increments based on data recorded using odometry (via recording the driving speed, the steering angle and / or a yaw rate sensor). Describe the respective location as an x-y coordinate and the respective angular orientation of the vehicle.

When driving back, the location and orientation of the vehicle can also be determined odometrically at the same positions on the route as in the previous data acquisition and, if there are deviations from the location and/or orientation, the steering can be readjusted using a controller so that these deviations are as a result of the further retraction can be minimized.

• - die richtungsabhängige nichtlineare Lenkwinkelübertragungsfunktion,
• - Unterschiede zwischen Ein- und Auslenken aufgrund der unterschiedlichen Rückstellkräfte (Einlenken bei Vorfahrt entspricht einem Auslenken bei Rückfahrt (und umgekehrt)),
• - temperaturabhängige Lenksteifigkeiten,
• - die Latenz (d. h. die zeitliche Dauer der Reaktion des Lenkwinkels auf eine angeforderte Lenkwinkeländerung),
• - die maximale Lenkgeschwindigkeit bei Rückfahrt (stellmotorabhängig) und
• - Unterschiede der Radien der Vorderräder

in der Praxis Fehler in der Orts- und Ausrichtungsbestimmung auftreten, welche nach längerer Rückfahrstrecke eine deutliche Abweichung gegenüber der Bahnkurve der manuellen Vorwärtsfahrt hervorrufen und damit die Rückfahrassistenzfunktion gefährden.The disadvantage of the odometric approach is that due to the insufficient modeling of many (non-linear) steering influencing factors such as:

• - the direction-dependent non-linear steering angle transfer function,
• - Differences between turning in and out due to the different restoring forces (turning in when driving ahead corresponds to turning in when driving back (and vice versa)),
• - temperature-dependent steering stiffness,
• - the latency (ie the time duration of the reaction of the steering angle to a requested steering angle change),
• - the maximum steering speed when reversing (depending on the servomotor) and
• - Differences in the radii of the front wheels

In practice, errors occur in the determination of location and alignment, which cause a significant deviation from the trajectory of manual forward travel after a longer reversing distance and thus endanger the reversing assistance function.

Integrating a measured yaw rate to determine the alignment of the vehicle's longitudinal axis can also lead to unacceptable inaccuracies due to the typically low reversing speed and the associated small change in the measured values due to noise and offset problems.

The publication already mentioned above DE 198 41 914 A1 describes a reversing assistance system in the form of an automatic steering system for motor vehicles with an electrically controllable steering actuator for adjusting a wheel steering angle of the steered wheels, a steering wheel angle sensor for detecting a steering wheel angle, and a electronic control/control device that is connected at least to the steering actuator and the steering wheel angle sensor in order to generate control signals for the electric steering actuator. Wheel sensors are also provided for detecting the direction of rotation and angle of rotation of the steered wheels. The control/control device has a memory for storing the steering movement from a route that was last driven and recorded by the wheel sensors, the control/control device being set up to reproduce the steering movements stored over the route that was last driven forward, depending on the location, during an immediately following reverse journey and to output the corresponding control signals to the steering actuator.

From the publication DE 10 2005 009 703 A1 A parking assistance device is known in which a distance traveled from a starting point to an end point is saved. The vehicle can then be automatically guided along the saved route.

Furthermore, reference is made to the publication DE 10 2011 086 281 A1 pointed out, which describes a method for determining a parking strategy. A trajectory is recorded that describes the movement of the vehicle before and while parking in a parking space. The trajectory is divided into an approach trajectory, a parking trajectory and, if necessary, further sub-trajectories. A parking space type is determined and the parking space type and/or the trajectory is saved and a parking exit strategy is selected.

It is the object of the invention to provide an improved reversing assistance system and a corresponding method for automated reversing with improved reproducibility of the trajectory driven manually in the forward direction.

The task is solved by the features of the independent patent claims. Advantageous embodiments are described in the dependent claims.

A first aspect of the invention relates to a reversing assistance system for a two-lane motor vehicle with front wheel steering for reversing in the reverse direction of a route that was previously driven manually in the forward direction. The reversing assistance system allows at least automatic steering of the motor vehicle while reversing, preferably the reversing assistance system also allows automatic longitudinal guidance, with the speed being automatically regulated or controlled during reversing.

The reversing assistance system is set up, for different positions of the route traveled during forward travel, a value of a first variable that is characteristic of the alignment of the vehicle's longitudinal axis when driving forward at the respective position depending on a distance covered by the one rear wheel during forward travel and a distance traveled during forward travel of the other rear wheel.

The characteristic first variable is, for example, a position-dependent variable that indicates the distance difference during forward travel for different positions of the distance traveled by one rear wheel since a reference point and the distance traveled by the other rear wheel since the same reference point. For example, the size is exactly this distance difference. Measured values of the distance traveled by the front wheels can also be included in the first variable.

To determine the quantity indicating the distance difference, the distance traveled by one rear wheel since a reference point and the distance traveled by the other rear wheel since the same reference point can be determined for different positions during forward travel and these distances traveled by the two rear wheels for the individual positions of the distance can be subtracted. Alternatively, the quantity indicating the distance difference can, for example, also be calculated without knowledge of the distances traveled (up to the respective position) since the reference point, for example by an incremental distance difference only for the current distance increment based on the distances traveled Both rear wheels are calculated in this distance increment and this incremental distance difference is added to the previous distance difference.

Preferably, calculated values of the first variable (with an assignment to the respective position) characteristic of the alignment of the vehicle's longitudinal axis when driving forward are stored in a data memory and then later, when reversing, these values are read out again from the data memory and used to control the front wheel steering. However, it would also be conceivable to instead, for example, determine the distance traveled by one rear wheel since a reference point and the distance traveled by the other rear wheel since the same reference point for different positions during forward travel and to store these distance values in a data memory and only to use these stored distance values when reversing in order to then calculate values of the first variable characteristic of the alignment of the vehicle's longitudinal axis when driving forward. The first option saves storage space, since in this case the distance values for both wheels do not have to be saved for the saved positions of the route and instead values of the quantity characteristic of the alignment (e.g. the distance difference) are saved.

According to the invention, for different positions of the route traveled during reversing, a value of a second variable characteristic of the alignment is determined at the respective position depending on a distance traveled by one rear wheel and a distance traveled by the other rear wheel. The first variable relating to forward travel and the second variable relating to backward travel are typically formed accordingly depending on the distances traveled by the two rear wheels. The first variable is, for example, the distance difference between the two rear wheels from a reference point while driving forward; The second variable relating to reversing is, for example, the distance difference between the two rear wheels from the same reference point measured during reversing. Distances covered in the forward direction are evaluated positively and distances covered in the reverse direction are evaluated negatively, so that when determining the values for the reverse journey, the part of the respective distance covered during the reverse journey reduces the part of the respective distance covered during the forward journey (i.e. from the At the reversal point, the accumulated distance of each rear wheel is reduced again). Of course, it would also be conceivable for a distance traveled in the forward direction to be evaluated negatively and a distance traveled in the reverse direction to be evaluated positively.

Values for the first variable characteristic of the alignment of the vehicle's longitudinal axis when driving forward serve as comparison values for values of the second variable characteristic of the alignment of the vehicle's longitudinal axis when reversing: During reversing, a value of the characteristic for the alignment of the vehicle's longitudinal axis when driving forward is determined for different positions on the route The first variable at the respective position is compared with a value of the second variable at the same position, which is characteristic of the alignment of the vehicle's longitudinal axis when reversing, and the front wheel steering is controlled depending on the comparison. For example, the deviation of positionally correct values of the second and first variables can be determined, and the front wheel steering can be controlled depending on the deviation. Based on the calculated deviation, the front wheel steering can be adjusted so that the deviation is corrected and so that the orientation of the vehicle during reversing follows the orientation of the vehicle during forward travel.

It is advantageous if the respective value of the first variable characteristic of the alignment used for the comparison is determined at the respective position by interpolation of previously stored values of the first variable characteristic of the alignment. The background to this is that in order to reduce the memory requirement, values cannot be saved for all resolvable positions of the route, and the values are therefore preferably only saved for certain support point positions. When reversing, the value of the first variable at the current position can easily be interpolated from stored values of the first variable at two or more support point positions. For example, the value at any intermediate position between two support point positions can be determined by linear interpolation based on the two values at the two support point positions.

The invention is based on the idea that a statement about the position-dependent alignment of the vehicle's longitudinal axis is possible based on the distances traveled by the two rear wheels; for example, by determining the position-dependent distance difference of the rear wheels. The information about the alignment of the vehicle's longitudinal axis in relation to forward travel can then serve as a position-dependent reference for reversing travel and control can be carried out based on the comparison between this position-dependent reference and the values describing the alignment when reversing.

This means that during automated reversing, the trajectory previously driven manually in the forward direction can be automatically retraced with a high level of consistency; d. H. the trajectory of forward travel and the trajectory of reverse travel show a high level of agreement.

As already stated, values of the first variable characteristic of the alignment of the vehicle's longitudinal axis when driving forward are preferably stored for the various positions in a data memory, and during reversing the stored values of the values for the alignment of the vehicle's longitudinal axis when forward The characteristic first variable for the comparison is read out again from the data memory. Preferably, the value used for the comparison is interpolated at a specific position based on values in the data memory.

In addition, the first variable, which is characteristic of the alignment of the vehicle's longitudinal axis when driving forward, is preferably a variable indicating the difference in the distances of the two rear wheels when driving forward, and the second variable, which is characteristic of the alignment of the vehicle's longitudinal axis when driving backwards, is a variable indicating the difference in the distances of the two rear wheels when driving backwards .

During forward travel, the distance traveled by one rear wheel since a reference point and the distance traveled by the other rear wheel since the same reference point are advantageously determined for different positions.

During reversing, in this case, the distance traveled by one rear wheel since the same reference point and the distance traveled by the other rear wheel since the same reference point are determined for different positions.

When determining the distances, a (partial) distance traveled in the forward direction is evaluated as positive (or negative) and a (partial) distance traveled in the backward direction is evaluated negatively (or positive). When determining the distance traveled during reversing, the part of the respective distance traveled in the reverse direction reduces the distance traveled to the reversal point during forward travel.

For example, while driving forward, a distance of 50 m was measured from a reference point to the reversal point for a rear tire or a corresponding number of pulses from the wheel sensor were counted. When the vehicle moves back again, this distance is reduced by the distance covered during reversing from the reversal point (e.g. 5 m at a certain position), and the resulting distance (50 m - 5 m = 45 m) corresponds to the distance at the respective position during reversing. For example, if the distance traveled is represented in the form of the number of counted pulses of the wheel sensor (i.e. the accumulated pulses correspond to the distance traveled), for example when driving forward in the forward direction, the number of counted pulses is increased accordingly when a new pulse is detected and when driving in the reverse direction After the reversal point, the number of counted pulses is reduced accordingly when a new pulse is detected (or vice versa).

The reversing assistance system according to the invention preferably comprises a controller for regulating the second variable, which is characteristic of the alignment of the vehicle's longitudinal axis when reversing, to the first variable, which is characteristic of the alignment of the vehicle's longitudinal axis when driving forward.

For example, when reversing, it can be determined whether the distance difference between the two rear wheels corresponds to the distance difference at the same position when driving forward. If not, the difference between the two distance differences is, for example, multiplied by a suitable factor (for example the value of the steering ratio) and the result is used to control the steering, for example the result is used as a correction value to a pre-control value (or one from a pre-control supplied target steering angle) which is supplied by a pilot control. Using such a P component (proportional component) of the controller, incorrect alignment of the vehicle axle can be corrected during the return journey.

The controller preferably also includes an I component (integral component). This serves to steer the vehicle back in the direction of the forward travel curve during the return journey if the vehicle has deviated from this curve, so that the vehicle then moves again on this curve.

The quality of the correct vehicle alignment is particularly important for the functionality of the reversing assistance system. If, for example, this is incorrect by just 1° after reversing a 90° curve, the side position of the vehicle will deviate by approx. 0.5 m compared to the previous position after a further straight reversing distance of 30 m - unacceptable in narrow spaces.

The reversing assistance system is preferably set up to determine the distances traveled by the two rear wheels by detecting pulses that are triggered by wheel sensors arranged on the two rear wheels and in particular counting them separately according to the two wheels. For example, the number of pulses from the wheel sensor assigned to one rear wheel and the number of pulses from the sensor assigned to the other rear wheel are determined. For each wheel revolution of a rear wheel, several pulses are triggered by the respective wheel sensor, for example 96 pulses per revolution. The number of times since a reference The pulses counted at the point then correspond to the distance traveled by the respective wheel since the reference point. The pulses can be converted into a meter value for the distance by multiplying them by an appropriate factor; However, such a conversion is preferably avoided.

The evaluation at the pulse level enables a pulse correction in which invalid pulses are detected for the distance measurement and these are not taken into account when counting, for example.

Typically, even at maximum steering angle, the speed of the rear wheel on the inside of the curve (and thus also the distance traveled by the rear wheel on the inside of the curve) is over 70% of the speed of the rear wheel on the outside of the curve (and thus also the distance traveled by the rear wheel on the outside of the curve).

This means that at a low speed, a sensor on one rear wheel cannot actually trigger two (or even more) pulses in succession before the sensor on the other rear wheel has also triggered a pulse.

Since the pulses are evaluated with a specific time resolution (e.g. every 10 ms), this can occur at higher speeds without an invalid pulse being present. At higher driving speeds, for example in tight curves, it could happen that one rear wheel triggers two impulses in a fixed time interval (e.g. 10ms), but the other rear wheel does not emit any impulse in this time interval.

However, this case can occur at very low speeds, for example when braking to a standstill or when starting off; In these situations, an unfavorable position of the sensor wheel of a wheel can lead to multiple pulses. Immediately at the end of the vehicle's braking process (e.g. at the reversal point) or immediately before driving off, the vehicle may move very briefly in the other direction of travel, which may trigger an additional new impulse from a rear wheel sensor if the sprocket position is unfavorable (so that a total of two pulses were triggered one after the other by one rear wheel sensor without a pulse being triggered by the other rear wheel sensor). Immediately at the end of the braking process at the reversal point, for example, a wheel can briefly move backwards and thereby trigger an additional impulse. An additional impulse can also be triggered immediately before starting if a wheel briefly moves in the opposite direction to the starting direction.

This has a disadvantage, especially before the start of the return journey, since, depending on the wheel sensor structure, an excess pulse can, for example, lead to an error in determining the distance difference, which corresponds approximately to an error of 1° with regard to the alignment of the vehicle's longitudinal axis. This error would then cause a significant error in the transverse position for the control over a longer return distance.

It is therefore advantageous to monitor and check the timing of the arrival of the impulses from the two rear wheels at low speed, whereby, for example, new impulses from one wheel are not counted until the other rear wheel delivers an impulse.

Preferably, the reversing assistance system is set up to detect invalid pulses to determine whether more than one pulse triggered by the wheel sensor of one rear wheel is detected before a pulse triggered by the wheel sensor of the other rear wheel is detected.

The reversing assistance system is therefore preferably set up in such a way that when it is determined that more than one pulse triggered by the wheel sensor of one rear wheel is detected before a pulse triggered by the wheel sensor of the other rear wheel is detected, the pulse or pulses exceeding the one pulse are detected triggered by the wheel sensor of one rear wheel cannot be counted.

However, this determination of invalid pulses and/or the non-payment of invalid pulses described above preferably only occurs when the vehicle speed is low; for example, speeds that are less than (or less than or equal to) a small positive limit speed V _G1 (e.g. V _G1 in the range from 0.3 km/h to 1.2 km/h) and greater than (or greater than or equal to) one (in terms of amount) small negative limit speed V _G2 (e.g. V _G2 in the range from -0.2 km/h to -1.0 km/h). The presence of a correspondingly low speed is therefore preferably checked by the system, and only if this speed condition is met will false pulses be masked out.

To control the front wheel steering during reversing, information about the steering wheel angle during forward driving can be used (in addition to the output signal of the controller described above).

Preferably, the reversing assistance system is therefore set up to find out the steering wheel angle for different positions on the route during forward travel and, based on this, to store steering wheel angle values for different positions on the route, and to control the front wheel steering during reversing based on the stored steering wheel angle values.

It is then advantageous if both a pilot control device for pilot control of the front wheel steering when reversing is provided based on the stored steering wheel angle values and a controller as described above for regulating the second variable characteristic of the alignment of the vehicle's longitudinal axis when reversing to that for the alignment of the vehicle's longitudinal axis The characteristic first size when driving forward is provided.

Steering wheel angles are measured at individual positions along the forward travel route. It is advantageous if the steering wheel angle value measured at a specific position is not stored in a data memory for this position. Instead, a latency-corrected steering wheel angle value is preferably stored in the data memory as the steering wheel angle value for the respective position of the route. The respective stored latency-corrected steering wheel angle value at the respective position corresponds to a steering wheel angle at a position on the route that is earlier in the forward direction compared to the respective position (or is at least based on this steering wheel angle).

This allows the latency between the change in the steering wheel angle and the resulting change in the alignment of the front wheels to be taken into account.

The alignment of the steered front wheels is crucial for the trajectory a vehicle travels. However, it is not the wheel angle that is measured directly, but rather the steering wheel angle. The two steered front wheels can be combined into one wheel according to the single-track model. However, when the steering wheel angle changes, the resulting change in the angle of this wheel occurs with a certain time delay (latency). The latency typically depends on how hard the steering is and whether the steering is in or out.

At the respective positions of the forward travel (i.e. base points at which data of the forward travel are stored), the currently measured steering wheel angle is preferably not saved for the respective current position, but rather the steering wheel angle value is stored which lies back in time by the assumed latency time (i.e. it takes place a review of a steering wheel angle value measured in the past). This means that the latency-corrected value is available for the respective position (i.e. for the respective base point at which a value is saved), which reflects the actual course of the trajectory at the respective position.

• - die aktuelle Position S der Fahrstrecke,
• - der insbesondere latenzkorrigierte Lenkwinkel,
• - die aktuelle Fahrzeuggeschwindigkeit und
• - der aktuelle Wert der für die Ausrichtung der Längsrichtung charakteristischen ersten Größe (beispielsweise die aktuelle Differenz der zurückgelegten Wegstrecken der beiden Hinterräder)

in einem Datenspeicher abgespeichert. Die Daten werden vorzugsweise in einem Ringspeicher abgespeichert. Damit steht die entsprechende Information über eine=gewisse zurückliegende Fahrstreckendistanz, beispielsweise die letzten 100m, zur Verfügung.During forward travel, the values are preferably changed cyclically at certain distance intervals or time intervals (e.g. every 20 cm travel distance or every 0.25 s) or, for example, when the steering angle changes by more than a predefined value

• - the current position S of the route,
• - the latency-corrected steering angle in particular,
• - the current vehicle speed and
• - the current value of the first variable that is characteristic of the alignment of the longitudinal direction (for example the current difference in the distances traveled by the two rear wheels)

stored in a data storage. The data is preferably stored in a ring memory. This means that the corresponding information about a certain distance traveled, for example the last 100m, is available.

When reversing, a steering wheel angle value can be determined for each distance position of the reverse journey (also for positions between the support point positions of the forward journey) by interpolating the stored (and latency-corrected as described above) steering wheel angle values of the respective positions of the forward journey (support points). The actual wheel angle of the front wheels now also has a latency compared to the steering wheel angle, which is generally not identical to the latency of the forward travel phase due to the typically lower driving speed and different steering control (now using a steering motor instead of manually). Using the reversing speed, a distance interval can be determined from the latency by which the value of the steering wheel angle responsible for the actual trajectory “runs behind” the current steering wheel angle. To set the pre-control value, the interpolated value for the current reversing position is preferably not used, but rather a steering wheel angle is interpolated for a position that is advanced in the reverse direction compared to the current reversing position by this distance interval (i.e. a preview is carried out when viewed in the reverse direction).

So during reversing at a respective position on the route, the front wheel steering is (pre-)controlled based on a steering wheel angle value at a later position in the reverse direction compared to the respective position. This is a preview of the steering wheel angle value with the position being shifted forward compared to the actual position. In particular, the steering wheel angle value for the respective position is determined by interpolation of a steering wheel angle value at a later position in the backward direction compared to the respective position based on several stored steering wheel angle values.

Regardless of the latency correction, the difference in the steering transfer function between forward travel and reverse travel can still be modeled by a constant factor, which is typically close to 1.

Accordingly, the steering wheel angle value on which the control of the front wheel steering is based is multiplied before the control by a factor that takes into account the difference in steering transmission between forward travel and reverse travel. This is preferably a factor in the range of 0.9 and 1.3, for example a value between 1.0 and 1.1.

It should be noted that the control described above based on the steering wheel angle information and its advantageous configurations could also be used without the above-described evaluation of the distances traveled by the rear wheels. A corresponding reversing assistance system for a two-lane motor vehicle with front wheel steering for reversing in the reverse direction of a route previously driven manually in the forward direction with at least automatic steering of the motor vehicle while reversing is set up to find out the steering wheel angle for different positions on the route during forward travel and based on this To store steering wheel angle values for different positions on the route and to control the front wheel steering while reversing based on the stored steering wheel angle values.

Preferably, during forward travel, the vehicle speed is determined for different positions on the route (for example by receiving corresponding values from another control device via a vehicle data bus) and stored, as already explained above. The reversing assistance system is preferably set up to automatically adjust the longitudinal speed of the vehicle to a target speed while reversing. For this purpose, for example, a longitudinal speed controller is provided in which the target speed is used as a reference variable. At the individual positions during reversing, the amount of the respective target speed is set to the vehicle speed stored at the respective position during forward driving, provided that the amount of the respective stored vehicle speed is less than the amount of a speed limit (e.g. - 3km/h ), and otherwise the amount of the respective target speed at the respective position is set to the amount of the speed limit value. The speed limit is, for example, in the range from -1 km/h to -10 km/h (a negative value corresponds to a speed in the reverse direction).

The reversing speed can therefore be automatically adjusted to a value that is comfortable for the driver (e.g. -3 km/h), unless the driver would have driven forward at a speed lower than +3 km/h. In such sections, the preferably reversing speed is then reduced accordingly, in particular also stopped briefly, in order to be able to take into account steering while stationary while driving ahead.

The speed values stored in the data memory can therefore be used to ensure that the reversing speed does not exceed the respective speed value of the forward travel at the same position during the return journey. The required stopping distance for reacting to appropriate objects behind the vehicle can also be determined from the set reversing speed.

It is advantageous if the reversing assistance system uses environmental information from an environmental sensor system, in particular an ultrasound-based distance system: If an obstacle behind the vehicle is detected by an environmental sensor system when reversing, where there is a risk of a collision (for example if the distance falls below a certain minimum distance), the vehicle brakes independently and remains at a safe distance in front of it. Even before the vehicle leaves the route area with stored forward travel data when reversing, it is preferably braked.

During the entire reversing process, the driver can preferably override the brakes, the vehicle drive and the lateral control (steering). If there is too much manual intervention in the steering, the assistance function is preferably switched off, as is the case when leaving reverse gear.

A second aspect relates to a method for reversing a two-lane motor vehicle with front wheel steering in the reverse direction of a route that was previously driven manually in the forward direction, with at least automatic steering of the motor vehicle while reversing. For different positions of the route traveled during forward travel, a value of a first variable that is characteristic of the alignment of the vehicle's longitudinal axis when driving forward is determined at the respective position depending on a distance traveled by one rear wheel and a distance traveled by the other rear wheel. Furthermore, for different positions of the route traveled during reversing, a value of a second variable that is characteristic of the alignment of the vehicle's longitudinal axis when reversing is determined at the respective position depending on a distance traveled by one rear wheel and a distance traveled by the other rear wheel. Furthermore, during reversing, for different positions on the route, the value of the first variable at the respective position, which is characteristic of the alignment of the vehicle's longitudinal axis when driving forward, is compared with the value of the second variable at the same position, which is characteristic of the alignment of the vehicle's longitudinal axis when reversing, and the front wheel steering controlled depending on the comparison.

The above statements regarding the reversing assistance system according to the invention according to the first aspect of the invention also apply in a corresponding manner to the method according to the invention according to the second aspect of the invention. Advantageous exemplary embodiments of the method according to the invention that are not explicitly described here correspond to the described advantageous exemplary embodiments of the reversing assistance system according to the invention.

• 1 beispielhafte zurückgelegte Wegstrecken zweier Hinterräder L und R;
• 2 ein Ausführungsbeispiel für eine Lenkungssteuerung eines erfindungsgemäßen Rückfahrassistenzsystems;
• 3 eine Latenzkorrektur bei der Rückfahrt anhand eines Beispiels; und
• 4 ein Blockschaltbild eines Ausführungsbeispiels für die Bestimmung der Wegstrecken-Differenz dS_RL.

The invention is described below using an exemplary embodiment with the aid of the accompanying drawings. Show in these:

• 1 exemplary distances traveled by two rear wheels L and R;
• 2 an exemplary embodiment of a steering control of a reversing assistance system according to the invention;
• 3 a latency correction on the return journey using an example; and
• 4 a block diagram of an exemplary embodiment for determining the distance difference dS _RL .

1 shows exemplary distances covered by two rear wheels R and L when driving through a right-hand bend in forward travel and then reversing in reverse direction. The distances traveled by the two rear wheels R and L are shown as solid lines; the dashed line corresponds to the trajectory of the center of the rear wheel axle. In the distance position S0 = 0, the distance traveled S _R of the right rear wheel, the distance traveled S _L of the left rear wheel L and the distance difference dS _RL = S _R - S _L of the distance traveled by the right rear wheel R and the left rear wheel L assumed to be zero. The distance position S0 here corresponds to a reference point to which the distances covered are related (ie the distances covered measured from the reference point S0). When going through the right-hand bend in the forward direction, the left rear wheel L covers a greater distance than the right rear wheel R. In the distance position S1 in the forward direction, there is a negative distance difference dS _RL = S _R -S _L . In the reversal position S2, the amount of the distance difference dS _RL = S _R - S _L has increased even further.

After the reversal position S2, the additional distance traveled in the reverse direction (ie in addition to the distance traveled in the forward direction to the reversal position S2) are calculated negatively when determining the total distance traveled (since the reference point S0) S _R and S _L. If the distance of the respective wheel R or L is measured in the form of the number of pulses detected by the wheel sensor of the respective wheel R or L, the corresponding counter counts to determine the number when a pulse is detected when driving forward (ie up to the reversal point S2) up and down when an impulse is detected when reversing (ie from the reversal point S2).

If the steering angle when driving forward corresponds to the steering angle when driving backwards, the distance difference dS _RL = S _R - S _L when driving backwards at position S3 = S1 will be equal to the distance difference dS _RL when driving forwards at position S1 .

However, if the steering angle when reversing has an error compared to the steering angle when driving forward, the distance differences at the positions S1 for forward travel and S3 = S1 for reversing are different. This is in 1 the case. Here, the amount of the steering angle when reversing is too small compared to forward travel, so that the distance difference dS _RL = S _R - S _L for reversing at position S3 = S1 is different to the distance difference dS _RL for forward travel Position S1 is.

The error signal between the distance difference dS _RL of forward travel at the current position (e.g. S1) and the distance difference dS _RL of reverse travel at the same position (e.g. S3 = S1) can be used for control.

2 shows an exemplary embodiment of a steering control of a reversing assistance system according to the invention. Many of the steering control blocks described below, in particular the calculation of the distance difference dS _RL , the interpolation and the controller, are preferably implemented in software.

The steering control includes a block 1 for calculating a distance difference dS _RL of the distances of the rear wheels based on a counter reading N _L of the pulses of the wheel sensor of the left wheel and a counter reading N _R of the pulses of the wheel sensor of the right wheel. The counter readings N _L and N _R reflect the number of counted pulses of the respective wheel sensor. The calculated distance difference dS _RL is fed either into the difference block 3 or into the ring memory block 2, depending on the switch position.

When driving forward (switch position a), the currently calculated distance difference dS _RL is stored cyclically for certain route positions S (e.g. every 20 cm of route) in the ring memory block 2 with reference to the associated route position S.

When reversing (switch position b), the currently calculated distance difference dS _RL is used as the actual value dS _{RL, is} the distance difference at the current route position S with the target value dS _{RL, is} the distance difference compared to the current route position S.

When reversing, the target value dS _{RL is obtained,} the target value of the distance difference at the current route position S, preferably by interpolation of a value at the current route position S based on the stored values of the route difference dS _RL , since values are only stored in the ring memory block 2 for certain support point positions and not for all route positions. The interpolator 6 required for this is in 2 downstream of memory block 2.

When driving back, it is determined whether the current distance difference dS _{RL, ist} of the two rear wheels when reversing corresponds to the distance difference dS _{RL, target} at the same route position S when driving forward. For this purpose, the difference or error E = dS _RL,set - dS _RL,ist between the interpolated value of the distance difference dS _RL,set of forward travel and the current value of the distance difference dS _{RL,ist is} determined in block 3. The error E is multiplied by a suitable factor P (preferably approximately the value of the steering ratio); this corresponds to the proportional part of the controller. Using the proportional component of the controller, incorrect alignment of the vehicle's longitudinal axis is corrected during the return journey. The signal of the proportional component of the controller is added to the output signal of the pilot control discussed below in block 4. Furthermore, an integrator I is provided, which determines an integral value of the error E of the distance difference over the travel distance in order to steer the vehicle back in the direction of the forward travel curve when driving backwards when leaving the forward travel curve.

By superimposing the signal of the proportional component of the controller, the signal of the integral component of the controller and the signal of the pilot control, the steering signal LW results for controlling the motor of an electric power steering (EPS) when reversing, so that Vehicle controls the steering independently without driver intervention when reversing. The steering signal LW is, for example, a steering angle specification for the EPS. Instead of a steering angle signal as a steering signal for the EPS, an engine torque specification can also be used as a steering signal for the EPS, which specifies the engine torque to be set for the electric motor of the EPS. In this case, for example, a further block, in particular a further controller, is provided which transforms the steering angle specification into a suitable engine torque specification.

For pre-control during reversing, the steering angle LW _is also stored cyclically in the ring memory block 10 after a latency correction with the respective value of the route position S. To simplify the explanation of the invention, the ring memory blocks 2 and 10 are shown as different blocks. However, a common ring memory 11 is preferably used, in which the values of the route S, the latency-corrected steering angle, the vehicle speed v and the current distance difference dS _RL are stored cyclically when driving forward.

The currently measured steering wheel value LW _is not stored for the current position S, but rather a latency-corrected steering wheel angle value is stored, this stored latency-corrected steering wheel angle value at the current position being opposite to a steering wheel angle at a forward direction the respective position corresponds to the previous position of the route. For latency correction, a delay block 11 is provided, which carries out a corresponding delay in the current steering angle value LW _ist .

This allows the time latency between the change in the steering wheel angle _LW and the resulting change in the alignment of the front wheels to be taken into account. At the positions S at which previous driving data is stored, it _{is not the currently measured steering angle LW that is} stored, but rather the steering angle LW that was around the current latency time _is stored. The deceleration of the deceleration block 11 is preferably variable and depends, for example, on how hard the steering is or whether the steering is turned in or out.

During the return journey, a value of the steering angle LW target _is determined via the stored steering angle values by means of interpolation in an interpolator 13, in particular by linear interpolation, which serves as a pilot control value for the current position S. The actual wheel angle of the front wheels now also has a latency compared to the steering wheel angle, which is generally not identical to the latency of the forward travel phase due to the typically lower driving speed and different steering control (now using a steering motor instead of manually). To set the pre-control value, the interpolated value at the current reversing position is preferably not used, but rather a steering wheel angle of a position is interpolated which is advanced in the reverse direction compared to the current reversing position S by the travel distance corresponding to the latency of the reverse phase.

The resulting steering angle value LW _shall is multiplied in block 12 by a factor close to one, which compensates for the difference in the steering transfer function between forward and reverse travel.

This latency correction on the return journey is in 3 shown schematically using an example. The horizontal lines correspond to the position values S of the route during forward travel and reverse travel. The steering angle values are stored at the support point positions Si and Si+1 (here, however, latency-corrected in the forward direction using the delay block 11). It is assumed that the vehicle is currently at the Sakt position when reversing. If the value that corresponds to the interpolated steering angle value at the same point during forward travel _is to be used as the pilot control value LW at the current position Sakt when reversing, the problem arises that the wheel angle relevant for the vehicle alignment is only set after the latency time dT _R . During this latency time dT _R, the vehicle has already traveled further by the distance dS _R = v · dT _R. There would always be this difference between the alignment-relevant positions of the outward and return journey. To compensate for this effect, the route position for interpolation can be advanced by this distance dS _R. A pre-control value LW _target is then used for the current position Sakt, which is interpolated at a position Sakt* later in the backward direction compared to the current position Sakt (ie at a position Sakt* earlier in the forward direction compared to the current position Sakt).

In 4 an exemplary embodiment for calculating the distance difference dS _RL of the rear wheels based on a counter reading N _L of the pulses of the wheel sensor of the left wheel and a counter reading N _R of the pulses of the wheel sensor of the right wheel is shown in block 1. The counter signals N _L and N _R are, for example, counting signals of the pulses of the two wheel sensors, which are determined by a driving dynamics control unit and are transmitted via a vehicle bus to the control unit of the reversing assistance system. These are, for example, 16-bit signals that jump back to the value 0 after overflow. In blocks 21 and 22, the change dN _L of the counter reading N _L or the change dN _R of the counter reading N _R is determined per time interval (e.g. per 10 ms). At low speeds, this change dN _L or dN _R is typically 0 or 1. The change values dN _L , dN _R of the counter readings are accumulated in blocks 23 and 24, respectively. Depending on a route direction signal R, the respective value dN _L , dN _R is added to the current counter reading S _L , S _R in the block 23 or 24 when driving forward, and the respective value dN _L , dN _R is added when driving backwards deducted from the current counter reading S _L , S _R in blocks 23 and 24, respectively.

The counter readings S _L , S _R correspond to the distances traveled by the left and right rear wheels, respectively. The counter readings S _L , S _R are set to zero when the engine starts, for example, so that the distances traveled relate, for example, to the reference point when the engine starts. The counters 23 and 24 are preferably implemented in software as unsigned 32-bit counters and typically cannot overflow with path increments of, for example, 2.7cm. Any overflows in the meter readings N _L and N _R are taken into account.

Furthermore, a plausibility check block 25 is provided, which detects invalid pulses from the wheel sensors and ensures that these are not taken into account when counting in blocks 23 and 24. The plausibility check block 25 is only effective when the vehicle speed is low and can then stop counting in blocks 23 and 24 in the event of one or more invalid pulses; for example at speeds that are less than (or less than or equal to) a small positive limit speed V _G1 (e.g. V _G1 in the range from 0.3 km/h to 1.2 km/h) and greater than (or greater than or equal to) than a small (in terms of magnitude) negative limit speed V _G2 (e.g. V _G2 in the range from -0.2 km/h to -1.0 km/h). Therefore, the vehicle speed v is also evaluated in the plausibility check block 25. The background to the presence of a low speed is that it can happen at higher driving speeds, for example in tight curves, that in a fixed time interval (e.g. 10ms) one wheel sensor delivers two pulses, but the other wheel sensor does not deliver any pulse gives away. In this case, however, there is no invalid pulse. At higher speeds than +/- 1km/h, for example, invalid pulses typically no longer occur.

Furthermore, in block 25, the direction of travel signal R is used to check whether a change in direction of travel has taken place. The background to this is that when changing direction, two pulses are delivered one after the other by one wheel sensor, without the other wheel sensor delivering a pulse, and there is no invalid pulse. One impulse comes from forward travel and the other impulse comes from reverse travel. In this case, both pulses from one rear wheel should be counted in the counter 23 or 24. When the direction of travel changes, block 25 is reset so that it forgets that a pulse may have already been detected when driving forward; The subsequent pulse when reversing is therefore not recognized as an invalid pulse.

Based on the values dN _L , dN _R , it is determined in block 25 whether more than one pulse triggered by the wheel sensor of one rear wheel was detected before a pulse triggered by the wheel sensor of the other rear wheel was detected. If it was determined in the plausibility check block 25 that more than one pulse triggered by the wheel sensor of one rear wheel is detected before a pulse triggered by the wheel sensor of the other rear wheel is detected, the pulse or pulses in excess of the one pulse are sent by the wheel sensor one rear wheel is triggered, not counted in blocks 23 and 24. In order to prevent the values dN _L or dN _R corresponding to the invalid pulses from being taken into account in blocks 23 and 24, in this case an error signal Er _L (if one or more pulses from the left wheel sensor are invalid) or an error signal Er _R ( if one or more pulses from the right wheel sensor are invalid) is set to 1, which is queried by block 23 or 24.

The respective route position S is - as shown in Fig. 4 - preferably determined as the arithmetic mean of the two specific rear wheel paths S _R , S _L , ie S = (S _R + S _R ) / 2.

Claims (18)

Reversing assistance system for a two-lane motor vehicle with front wheel steering for reversing in the reverse direction of a route previously driven manually in the forward direction with at least automatic steering of the motor vehicle while reversing, which is set up - for different positions (S) of the route traveled during forward travel, a value for each the alignment of the vehicle's longitudinal axis when driving forward is a characteristic first variable at the respective position (S) depending on a distance (S _R ) covered by one rear wheel (R) when driving forward and a distance (S _L ) covered by the other rear wheel (L) when driving forward ) _. and a distance traveled (S _L ) of the other rear wheel (L), - during reversing for different positions (S) of the route - a value of the first variable (dS _{RL, target} ) characteristic of the alignment of the vehicle's longitudinal axis when driving forward. at the respective position (S) - to be compared with a value of the second variable (dS _RL,is ) that is characteristic of the alignment of the vehicle's longitudinal axis when reversing at the same position, and - to control the front wheel steering depending on the comparison. Reversing assistance system Claim 1 , characterized in that the reversing assistance system is set up to - store values of the first variable for different positions (S) in a data memory (2, 11) which is characteristic of the alignment of the vehicle's longitudinal axis when driving forward; and - during reversing, stored values of the first variable characteristic of the alignment of the vehicle's longitudinal axis when driving forward are read out again from the data memory (2, 11). Reversing assistance system according to one of the preceding claims, characterized in that - the first variable characteristic of the alignment of the vehicle's longitudinal axis when driving forward is a variable indicating the difference in the distances (S _R , S _L ) of the two rear wheels (R, L) when driving forward, and - the second variable, which is characteristic of the alignment of the vehicle's longitudinal axis when reversing, is a variable indicating the difference in the distances (S _R , S _L ) of the two rear wheels (R, L) when reversing. Reversing assistance system according to one of the preceding patent claims, characterized in that the reversing assistance system is set up - during forward travel for different positions, the distance (S _R ) of the one rear wheel (R) traveled since a reference point and the distance (S _R) traveled since the same reference point ) of the other rear wheel (L), - during reversing for different positions, the distance (S _R ) of one rear wheel (R) and the distance (S L) of the other rear wheel (S _L ) since the same reference point ( L), whereby a section of the route traveled in the forward direction is evaluated as positive or negative and a section of the route traveled in the backward direction is evaluated as negative or positive. Reversing assistance system according to one of the preceding claims, comprising a controller (P, I) for regulating the second variable (dS _{RL, ist} ), which is characteristic of the alignment of the vehicle's longitudinal axis when reversing, to the first variable (dS _{RL, which is characteristic of the alignment of the vehicle's longitudinal axis when driving forwards). is} ). Reversing assistance system Claim 5 , characterized in that the controller comprises an I component (I). Reversing assistance system according to one of the preceding claims, characterized in that the reversing assistance system is set up to record distances (dN _R , dN _L ) traveled by the two rear wheels (R, L) by detecting pulses that are triggered by wheel sensors arranged on the two rear wheels determine, in particular by counting the pulses separately for the two wheels (R, L). Reversing assistance system Claim 7 , characterized in that the reversing assistance system is set up to detect invalid pulses. Reversing assistance system Claim 8 , characterized in that the reversing assistance system is set up to count the pulses separately for the two wheels (R, L) and not to take invalid pulses into account when counting. Reversing assistance system according to one of the Claims 8 or 9 , characterized in that the reversing assistance system is set up to detect invalid pulses to determine whether more than one pulse triggered by the wheel sensor of one rear wheel (R, L) is detected before one triggered by the wheel sensor of the other rear wheel (L, R). Impulse is detected. Reversing assistance system Claim 10 , characterized in that the reversing assistance system is set up so that when it is determined that more than one pulse triggered by the wheel sensor of one rear wheel (R, L) is detected before a pulse triggered by the wheel sensor of the other rear wheel (L, R) is detected , the pulse(s) that go beyond the one pulse and are triggered by the wheel sensor of the one rear wheel (R, L) are evaluated as invalid pulses. Reversing assistance system according to one of the preceding claims, characterized in that the reversing assistance system is set up - to find out the steering wheel angle (LW _ist ) for different positions on the route during forward travel, - to store steering wheel angle values for various positions on the route based on this, and - to control the front wheel steering while reversing based on the stored steering wheel angle values. Reversing assistance system Claim 12 , characterized in that the reversing assistance system comprises: - a controller (P, I) for regulating the second variable (dS _RL,ist ) characteristic of the alignment of the vehicle's longitudinal axis when reversing to the first variable (dS _{RL, should} ) and - a pilot control device (11, 10, 12) for pilot control of the front wheel steering when reversing based on the stored steering wheel angle values. Reversing assistance system according to one of the Claims 12 until 13 , characterized in that the reversing assistance system is set up to store latency-corrected steering wheel angle values as steering wheel angle values for different positions (S) of the route, the respective stored latency-corrected steering wheel angle value at the respective position (S) corresponding to a steering wheel angle at an earlier position in the forward direction compared to the respective position corresponds to the driving distance or is based on this steering wheel angle. Reversing assistance system according to one of the Claims 12 until 14 , characterized in that the reversing assistance system is set up - to control the front wheel steering during reversing at a respective position of the route based on a steering wheel angle value at a later position in the reverse direction compared to the respective position, and - in particular in each case this steering wheel angle value by interpolation of a steering wheel angle value to determine a later position (Sakt*) in the backward direction compared to the respective position (Sakt) based on several stored steering wheel angle values. Reversing assistance system according to one of the preceding claims, characterized in that the reversing assistance system is set up to multiply a steering wheel angle value (LW _target ) on which the control of the front wheel steering is based before the control by a factor which takes into account the difference in steering transmission between forward travel and reverse travel, especially with a factor in the range of 0.9 and 1.3. Reversing assistance system according to one of the preceding claims, characterized in that the reversing assistance system is set up - to find out the vehicle speed for different positions (S) of the route during forward travel and to store it in the data memory, - to set the longitudinal speed of the vehicle to a target Automatically set the speed while reversing, and - at individual positions on the route during reversing, sets the amount of the respective target speed to the stored vehicle speed at the respective position, provided that the amount of the respective stored vehicle speed is smaller than the amount of a speed limit value, and otherwise sets the amount of the respective target speed at the respective position to the amount of the speed limit value. Method for reversing a two-lane motor vehicle with front wheel steering in the reverse direction of a route previously driven manually in the forward direction with at least automatic steering of the motor vehicle while reversing, with the steps: the alignment of the vehicle's longitudinal axis when driving forward, a characteristic first variable, at the respective position depending on a distance (S _R ) of one rear wheel covered during forward travel and a distance (S _L ) of the other rear wheel covered during forward travel; - Determine for different positions of the route covered during reversing a value of a second variable characteristic of the alignment of the vehicle's longitudinal axis when reversing at the respective position depending on a distance traveled (S _R ) of the one rear wheel and a distance traveled (S _L ) of the other rear wheel; - Compare during reversing for different positions on the route - a value of the first variable (dS _{RL, target} ) characteristic of the alignment of the vehicle's longitudinal axis when driving forward at the respective position - with a value of the second variable characteristic of the alignment of the vehicle's longitudinal axis when reversing (dS _RL,is ) at the same position; and - controlling the front wheel steering depending on the comparison.

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