WO2001014941A1

WO2001014941A1 - Method and device for supporting parking of a vehicle

Info

Publication number: WO2001014941A1
Application number: PCT/DE2000/002818
Authority: WO
Inventors: Gabriel Wetzel
Original assignee: Robert Bosch Gmbh
Priority date: 1999-08-24
Filing date: 2000-08-18
Publication date: 2001-03-01
Also published as: EP1218808A1; JP2003507263A; DE19940007A1

Abstract

The invention relates to a method and a device for supporting parking of a vehicle using a parking assistant. Signals concerning driving status supplied by sensors (2) are used to calculate a theoretical trajectory in a function block. Said trajectory consists of clothoid curves and/or a circular curves. Signals supplied by the sensors (2), in particular yaw angle signals and trajectory signals are used to calculate an actual trajectory in a function block (4). Theoretical and actual trajectories are then compared. The result of said comparison enables real-time calculation of the steering angle during the different phases of the parking maneuver for which a parameter is determined in a function block (5). Feed-back signals supplied by the sensors (2) enable exact regulation of the steering angle adopted during the parking maneuver. Steering wheel movements caused by the driver are tolerated but do not have any influence on the steering angle. The driver only has to press the accelerator and brake pedal to influence the speed of the vehicle.

Description

Method and device for supporting the parking of a motor vehicle

State of the art

The invention relates to a method for supporting the parking of a motor vehicle, which is equipped with a steering actuator and sensors for detecting the vehicle position, the driving state and changing environmental conditions, with a command of a driver to provide regulated support for the parking process by means of the steering actuator and based on predetermined vehicle data and is executed on signals from the sensors, and a device set up to carry out the method.

In the case of an electronic steering system currently being developed by Robert Bosch GmbH, an electronically controlled steering splitter attached to the steering gear of the front wheels, based on a driver's steering request detected by a steering wheel sensor, taking into account driving dynamics variables, the modification of the steering angle corresponding to the driver's steering request improved, ie that the vehicle is stabilized in dynamic driving situations. The system has a steering servomotor, which corrects the steering angle set by the driver added.

DE 29 01 504 describes a method and a device for parking motor vehicles, which works with a pure control of the parking process. No feedback signals that change the course of the parking trajectory are taken into account, but instead fixed trajectories are specified.

From the patent FR 2 728 859 is a method and a

Device for regulating the parking process known. However, the driver is still responsible for steering interventions. For this purpose, sensors are used which record the yaw angle and the steering angle. It is unsatisfactory here that the performance of the system implemented in this way is impaired by the relatively long dead time of the driver during the steering interventions.

Object and advantages of the invention

It is an object of the invention to enable a method and a device for supporting the parking of a motor vehicle in such a way that the vehicle automatically steers into the parking space, but the driver himself regulates the speed by means of accelerator pedal and brake pedal interventions.

The above task is solved according to the requirements.

According to an essential aspect, the method that solves the above task is characterized by the following steps:

A detection ^'of a supported parking the initiating of the driver and generating command input an initialization signal; B detection of the current vehicle position and the driving state from the vehicle data and at least from a yaw angle signal and from a path signal;

C detection of the ambient conditions from signals generated by sensors attached to the vehicle;

D specification of one or more target tajectories which specify a target trajectory curve of the vehicle to be parked which is dependent on the vehicle position, the driving state, the ambient conditions and the vehicle data;

E detection of a respective actual trajectory, depending on the respective signals detected in steps B and C;

F comparison of the target trajectory specified in step D and the actual trajectory recorded in step E; and

G Calculation of the respective manipulated variable for the steering servomotor from the comparison result obtained in step F.

The path signal recorded in step B is advantageously recorded by a path encoder, preferably by a wheel speed sensor located on each vehicle wheel. The yaw angle signal, which is also recorded in step, can either be measured by a suitable sensor or can be reconstructed from suitable signals, for example from the yaw rate of a yaw rate sensor and / or from the wheel speeds.

The ambient conditions are preferably recorded in step C by means of an ultrasonic sensor. However, it is also conceivable radar sensors or optical sensors, e.g. B. cameras to use. The environmental conditions recorded in step C can indicate the shape or dimensions of a parking space.

The or each target trajectory specified in step D is preferably composed of one or more clothoid arcs and / or one or more circular arcs. A clothoid is a flat curve whose radius of curvature corresponds to the relationship R = a * a / s (R:

Radius of curvature; s: arc length; a: parameter) becomes smaller and smaller.

In order to avoid that the steering acceleration and the steering jerk become too high, the manipulated variable calculated in step E is subjected to filtering, which smoothes abrupt transitions on the flanks of the manipulated variable.

According to the invention, a device set up to carry out the method has a control /

Control unit that receives signals generated by the sensors as a function of the vehicle position, the driving state and the changing environmental conditions and the vehicle data, means for calculating an actual trajectory from the sensor signals and the vehicle data, means for comparing the respectively calculated actual trajectory with one predetermined target trajectory and means for calculating a manipulated variable for a steering actuator from the comparison result.

The regulating / control unit performing the method can have filter means or can be connected to the steering servomotor via filter means, so that the calculated manipulated variable can be filtered in the manner described above. The method and the device specified above offer several advantages over the prior art:

No real electronic steer-by-wire steering is required. The steering actuator used in the driving dynamics steering system being developed is sufficient because it enables automatic, precise and very fine steering interventions.

- The sensors used allow an accurate

Calculation of the driven curve and thus an exact regulation of the parking process with constant corrections and adjustments.

- The selection of the respective target trajectory and its combination of clothoid arcs and circular arcs enables a simple description of the trajectory and a quick calculation of the comparison result between the actual and target trajectory during the parking process.

The regulation carried out by the regulating / control unit enables precise maneuvers and temporary deviations from the target trajectory in order to increase driving comfort.

The filtering increases driving comfort because it can smooth jerky movements of the steering wheel.

The following description describes a preferred embodiment of the method according to the invention and at the same time explains the implementation by the device according to the invention with reference to the accompanying drawing.

drawing Fig. 1 shows schematically functional blocks of the device according to the invention;

Fig. 2 shows graphically the geometric basis for determining a trajectory over the relationship between the radius of curvature R, the angle θ and the path s;

Fig. 3 graphically shows a clothoid as a curve, the curvature c (s) of which changes linearly with the path s;

FIG. 4 illustrates, in a flat representation of a motor vehicle, variables which are used to determine the clothoid arches;

5 graphically illustrates a trajectory and one

Head angle for a case where a ride on

Steering lock is necessary;

6 graphically shows a trajectory and one

Steering angle for a case where there is no drive

Steering lock is necessary;

7 shows a parking trajectory achieved with the algorithm shown.

embodiment

The exemplary embodiment of a method according to the invention to support the parking of a motor vehicle and a device set up to carry out the method (briefly:

Parking assistant) uses the following sensors in particular: Ultrasonic sensors for recording the ambient conditions;

active wheel speed sensors that provide wheel speed signals until the vehicle stops;

a steering angle sensor;

a rotation rate sensor with which signals about the yaw rate can be detected; and

(optional) a lateral acceleration sensor.

In another exemplary embodiment of the present invention, it is conceivable to omit one or more of the sensors mentioned by way of example, either because the method according to the invention is fully functional even without the sensor signal supplied by the corresponding sensor, or because the sensor signal can be reconstructed from other sensor signals. A specialist can decide which sensors are actually used to carry out the method according to the invention in individual cases on the basis of his specialist knowledge. It would be conceivable, for example, to dispense with a rotation rate sensor and to reconstruct the rotation rate signal from other sensor signals.

Fig. 1 shows functional blocks of the parking assistant. Vehicle data are available from block 1. For example, block 1 is a memory in which the vehicle data are stored. An alternative possibility is a rule / control mechanism, which the

Contains vehicle data. Block 2 is the sensor block that includes the sensors mentioned above. Function block 3 calculates the target trajectory in the manner described below and for this purpose receives the vehicle data from block 1 and the sensor signals from block 2.

A function block 4 provided for determining the actual trajectory likewise receives the vehicle data from block 1 and the sensor signals from block 2 as input signals. The rotation rate sensor is particularly important for the reconstruction of the yaw angle. Alternatively, the yaw angle can also be measured by a corresponding yaw angle sensor.

The target trajectory specified in block 3 and the actual trajectory determined in block 4 are combined in one

Comparator 8 compared. Function block 5 calculates the manipulated variable from the comparison result and from signals from blocks 1 and 2. The comparison between the target and actual trajectories enables precise control of the steering angle by means of the manipulated variable calculated in block 5. This regulation is possible because the steering interventions are carried out by a regulating / control unit. The manipulated variable calculated in function block 5 is filtered in function block 6. This filtering smoothes the flank of the manipulated variable and thus ensures that the steering acceleration and the jerk on the steering wheel do not become too high. In addition, the function block 6 is also supplied with vehicle data from the block 1 and filtered there or included in the filtering of the manipulated variable.

In the comparator 8, in addition to the actual and the target trajectory, driving state signals, for example the orientation of the motor vehicle, can also be compared with one another or with the vehicle data. Function block 7 represents an actuator which is designed as a steering actuator. The sensors and the steering actuator can Be part of a vehicle dynamics steering system. The additional costs for a device according to the invention in a motor vehicle can thus be reduced to a minimum.

The functions of the parking assistant described above with reference to Fig. 1 can be performed by a control unit, e.g. a vehicle computer that is present in the vehicle anyway.

The geometrical foundations for determining a trajectory on the basis of a clothoid arch are described below with reference to FIGS. 2 and 3.

The relationship between the radius of curvature R, the angle θ and the path s of an arbitrary path curve is illustrated graphically in FIG. 2. FIG. 2 shows how the angle θ behaves with the change in the path s as a function of the radius of curvature R. The curvature c (s) is given by equation 1.1:

dθ c (s) = Eq. 1.1 ds

The angle θ is calculated from the path s using the following equation:

This equation can be expressed using equation 1.1 as follows: θ {ή * θ _Q +] c (s)> ds Eq. 1 . 3

The small changes (dx, dy) of the Cartesian coordinates (x, y) are calculated from the angle θ (s):

The coordinates (x, y) are derived from equation 1.4:

General equation 1.5 is simplified for the special case of clothoids. The clothoid is a curve whose curvature c (s) changes linearly with the path s. This curve is also referred to as the Cornu spiral (see FIG. 3).

c (s) = k s + c. Eq. 1.6

Using the curvature (see Eq.1.6) in formula 1.5 results in:

what happens under the conditions:

* 0 = 0, x ₀ = 0

= 0, y ₀ = 0 Eq. 1.8

can be simplified as follows

The integration of the functions sin (u ² ) and cos (u ² ) is not trivial. The series development of the trigonometric functions is used for this.

Under certain conditions of convergence of the series (Eq. 1.10) the order of the sum and the integration can be inverted. These conditions are met in the present exemplary embodiment (Eq. 1.10).

Equation (1.11) can be transformed as follows:

Equation 1.13 is used to quickly calculate important points of the trajectory. The following section uses the procedure to calculate a parking trajectory.

Furthermore, with reference to FIGS. 4 to 7, the parking trajectory is calculated using an algorithm which is based on equation 1.13 explained above. Intuitive steering

It is assumed that the vehicle to be parked is parallel to the parking space. The trajectory in the longitudinal direction is assumed to match the existing parking space. The parking trajectory should intuitively include the following phases:

1. Drive straight ahead in reverse, 2. Continue driving (possibly slower) and turn the steering wheel to the right up to the steering angle,

3. continue driving backwards,

4. Turn the steering wheel to the left until the steering lock

5. Continue driving backwards, 6. straighten the steering wheel, and 7. stop the vehicle.

Calculation of the steering angle

The intuitive phases described above should be formalized.

Because of the simple handling of clothoids, phases 2, 4 and 7 are assumed to be clothoid trajectories.

Because of the symmetry of the parking process, phases 2 and 6, 3 and 5 are symmetrical.

The determination of phase 2 is derived from FIG. 4. The clothoids are determined by a parameter k, which is based on the limitation of the steering angle and the driving and steering speeds.

The length of phase 3 is calculated so that the vehicle drives deep enough into the parking space. The influence of this Length on the trajectory is shown using FIGS. 6 and 7. In particular, FIG. 6 shows the trajectory of the vehicle when phase 4 does not exist.

The important points for the calculation of the trajectory are identified in FIGS. 5 and 6 with the letters A, B, C, D, E, F, G, R.

4 schematically shows the resulting radius for a vehicle with the front wheels turned

R = l / c (s) and the steering angle δ (s) are shown. The clothoid emerges too

c (s) = k s + c ₀ Eq. 2.1

The Ackermannwinkel is

δ (s) = arctan [L • c (s)] Eq. 2.2

This results in:

This results in

The steering angle is: L • c L - k - v Eq. 2nd 6 max δ = = ≤ k - L - ™ "≤ δ _M ^a l + [L - c] ² l + [L - c] ²

From this you get the one that determines the clothoid

Parameters:

δ ^max k = Eq. 2.7

There is a limitation of the steering angle speed δ ≤ δ _M ^max , the steering angle δ ≤ δv ^max and the

Driving speed v ≤ v ^ma instead. The result of

Parking process with the algorithm explained above is shown in Fig. 7, which is in an x-y

Coordinate system illustrates an exemplary parking trajectory and the underlying target steering angle.

The route traveled is required to program the control system in the vehicle. In the vehicle, this path is measured with active wheel speed sensors or in a simplified form with the help of a position sensor. The wheel speed sensors can precisely measure the wheel speed down to zero speed.

In the system described above, the driver is allowed to perform steering interventions during the parking process. However, these steering interventions have no influence on the maneuver. If there is an obstacle in the way of parking, the driver should brake and stop the parking process. Since the

Steering wheel angle with the underlying steering system The driver's intervention on the steering wheel is compensated by the steering servomotor during parking. This procedure enables the driver to still feel that they are controlling the parking process themselves and therefore feel comfortable.

The yaw angle is calculated on the basis of the signals supplied by the yaw rate sensor. In highly dynamic driving maneuvers, this calculation can U. be time problematic. On the other hand, there are usually no steps when parking

Difficulties because the driving speed and the dynamics of the driving maneuver are limited.

In this way, the parking assistant enables the steering angle to be properly controlled by calculating the yaw angle so that the vehicle orientation corresponds to the expected behavior. With this regulation, errors that can lead to a deviation between the driven and the calculated trajectory, such as errors in the steering system or different friction, can be corrected.

Since the jump in the signal supplied to the steering actuator as a manipulated variable is initially abrupt between the phases in which the steering angle is constant (phases 1, 3 and 5) and the phases in which the steering angle changes, the manipulated variable is shown in the 1 shown function block 6 filtered by smoothing the abrupt jumps in the manipulated variable. The manipulated variable can be filtered so that the steering acceleration is limited. Since the target trajectory remains unchanged, deviations from the target trajectory can occur. Temporary deviations from the target trajectory are thus tolerated in order to enable a uniform driving maneuver and thereby increase driving comfort. The deviations between the target trajectory and the actual trajectory are corrected in the course of the parking process by the regulating / control unit using the method according to the invention.

Claims

Expectations

1. A method for supporting the parking of a motor vehicle, which is equipped with a steering actuator and sensors for detecting the vehicle position, the driving state and changing ambient conditions, wherein, on the command of a driver, regulated support of the parking process by means of the steering actuator and based on predetermined vehicle data and on signals from the sensors, characterized by the following steps:

A detection of a command input from the driver initiating the assisted parking and generation of an initialization signal;

B detection of the current vehicle position and the driving state from the vehicle data and at least from a yaw angle signal and from a path signal;

D Specification of one or more target tajectories, one of the vehicle position, the driving state, the

Ambient conditions and target data dependent on the vehicle data 1/14941

- 19 - Specify the curve of the vehicle to be parked;

2. The method according to claim 1, characterized in that the steering servomotor and at least part of the sensors are part of a dynamic driving system of the motor vehicle.

3. The method according to claim 1 or 2, characterized in that the path signal detected in step B is detected by a wheel speed sensor located on each vehicle wheel.

4. The method according to any one of claims 1 to 3, characterized in that the yaw angle signal detected in step B is measured by a suitable sensor.

5. The method according to any one of claims 1 to 3, characterized in that the detected in step B.

Yaw angle signal is reconstructed from one or more signals measured in steps B and C, in particular from a rotation rate signal or from the path signal.

6. Method according to one of the preceding claims, characterized in that the ambient conditions are recorded in step C by means of an ultrasonic sensor.

7. The method according to any one of the preceding claims, characterized in that the environmental conditions recorded in step C indicate the shape and / or dimensions of a parking space.

8. The method according to any one of the preceding claims, characterized in that the or each target trajectory specified in step D are composed of one or more clothoid arcs and / or one or more circular arcs.

9. The method according to any one of the preceding claims, characterized in that the manipulated variable calculated in step E is subjected to filtering in order to avoid that the steering acceleration and the steering jerk become too high.

10. The method according to any one of the preceding claims, characterized in that steering interventions by the driver are tolerated, but have no influence on the parking process.

11. The method according to any one of the preceding claims, characterized in that the parking speed is influenced by accelerator and brake pedal interventions by the driver and the steering angle is brought about exclusively by the actuating movements of the steering servomotor.

12. Device for carrying out the method according to one of the preceding claims, characterized in that the device comprises a regulating / control unit, which is dependent on the sensors as a function of the vehicle position, the driving state and the changing ambient conditions generated signals and receives the vehicle data, means for calculating an actual trajectory from the sensor signals and the vehicle data, means for comparing the respectively calculated actual trajectory with a predetermined target trajectory and means for calculating a manipulated variable for a steering actuator from the comparison result.

13. The apparatus according to claim 12, characterized in that the control unit receives the signals generated by the respective sensors and the vehicle data from another control unit in the vehicle.

14. The apparatus according to claim 13, characterized in that the other control / regulating unit is designed as a driving dynamic steering system of the vehicle.

15. The device according to one of claims 12 to 14, characterized in that filter means are provided in functional connection with the control unit in order to filter the manipulated variable calculated by the control unit so that the steering acceleration and the steering jerk do not increase get high.