ASSISTING REVERSE DRIVING OF A COMBINATION

Abstract

According to a method for assisting reverse driving of a combination (1), an actual value for a hitch angle of the combination (1) is determined by a computing unit (6) depending on sensor data generated by a hitch angle sensor. A hitch length of a trailer (3), given by a distance between a trailer body (11) and a hitch (7) of a vehicle (2), is determined depending on environmental sensor data of the combination (1). A collision value for the hitch angle is determined by the computing unit (6) depending on the hitch length, and the safety measure is triggered by the computing unit (6) depending on the actual value and the collision value for the hitch angle.

Claims

1. A method for assisting reverse driving of a combination, the combination comprising a motor vehicle with a hitch and a trailer with a drawbar rotatably attached to the hitch, the method comprising: determining an actual value for a hitch angle of the combination by a computing unit of the combination depending on sensor data generated by a hitch angle sensor system of the combination; determining a hitch length of the trailer, which is given by a distance between a trailer body of the trailer and the hitch, by the computing unit depending on environmental sensor data generated by an environmental sensor system of the combination; determining a collision value for the hitch angle by the computing unit depending on the hitch length; and triggering a safety measure by the computing unit depending on the actual value and the collision value.

2. The method according to claim 1, wherein a jackknife value for the hitch angle is determined by the computing unit and wherein the safety measure is triggered depending on the jackknife value.

3. The method according to claim 2, wherein: a first critical value for the hitch angle is determined by the computing unit depending on a minimum of the collision value and the jackknife value, and a first safety measure is triggered depending on a result of a comparison of the actual value to the first critical value by the computing unit.

4. The method according to claim 3, wherein the first safety measure includes generating a warning message for a user of the motor vehicle.

5. The method according to claim 3, wherein: a second critical value for the hitch angle is determined by the computing unit depending on the minimum of the collision value and the jackknife value, an absolute value of the second critical value being smaller than an absolute value of the first critical value, and a second safety measure is triggered depending on a result of a comparison of the actual value to the second critical value by the computing unit.

6. The method according to claim 5, wherein the second safety measure includes carrying out an automatic braking maneuver of the motor vehicle.

7. The method according to claim 2, wherein the jackknife value is determined depending on a wheelbase of the trailer.

8. The method according to claim 7, wherein the wheelbase is determined by the computing unit depending on the environmental sensor data or depending on further environmental sensor data generated by the environmental sensor system.

9. The method according to claim 8, wherein: the environmental sensor data comprise at least one camera image generated by a camera system of the environmental sensor system and the wheelbase is determined by the computing unit depending on the at least one camera image, or the further environmental sensor data comprise at least one camera image generated by a camera system of the further environmental sensor system and the wheelbase is determined by the computing unit depending on the at least one camera image.

10. The method according to claim 1, wherein the environmental sensor data comprise ultrasonic sensor data generated by an ultrasonic sensor system of the environmental sensor system and the hitch length of the trailer is determined by the computing unit depending on the ultrasonic sensor data.

11. A driver assistance system for assisting reverse driving of a combination, wherein the combination comprises a motor vehicle with a hitch and a trailer with a drawbar rotatably attached to the hitch, the driver assistance system comprising: a hitch angle sensor system, which is configured to generate sensor data; a computing unit, which is configured to determine an actual value for a hitch angle of the combination depending on the sensor data; and an environmental sensor system configured to generate environmental sensor data wherein the computing unit is configured to: determine a hitch length of the trailer given by a distance between a trailer body of the trailer and the hitch depending on the environmental sensor data, determine a collision value for the hitch angle depending on the hitch length, and trigger a safety measure depending on the actual value and the collision value.

12. A motor vehicle comprising a driver assistance system according to claim 11.

13. A combination comprising a motor vehicle with a hitch, a trailer with a drawbar rotatably attached to the hitch, and a driver assistance system according to claim 11.

14. A computer program comprising instructions, which, when carried out by a driver assistance system according to claim 11, cause the driver assistance system to carry out a method comprising: determining an actual value for a hitch angle of the combination by a computing unit of the combination depending on sensor data generated by a hitch angle sensor system of the combination, determining a hitch length of the trailer, which is given by a distance between a trailer body of the trailer and the hitch, by the computing unit depending on environmental sensor data generated by an environmental sensor system of the combination, determining a collision value for the hitch angle by the computing unit depending on the hitch length, and triggering a safety measure by the computing unit depending on the actual value and the collision value.

15. A computer readable storage medium storing a computer program according to claim 14.

Description

[0059] In the figures:

[0060] FIG. 1 shows schematically a motor vehicle with an exemplary implementation of a driver assistance system according to the improved concept;

[0061] FIG. 2 shows a flow diagram of an exemplary implementation of a method according to an improved concept;

[0062] FIG. 3 shows a schematic representation of a combination with a motor vehicle and a trailer;

[0063] FIG. 4 shows a schematic representation of a motor vehicle;

[0064] FIG. 5 shows a schematic representation of a trailer;

[0065] FIG. 6 shows a decision tree regarding the sign of a hitch angle change; and

[0066] FIG. 7 shows a further schematic representation of a combination with a motor vehicle and a trailer.

[0067] FIG. 1 shows schematically a combination 1 with a motor vehicle 2 and a trailer 3, which is connected to a hitch 7 of the motor vehicle 2 via a drawbar 8 of the trailer 3. The combination 1, in particular the motor vehicle 2, comprises an exemplary implementation of a driver assistance system 10 according to the improved concept for assisting reverse driving of the combination 1. The driver assistance system 10 comprises a hitch angle sensor system, which is configured to generate sensor data and a computing unit 6, which is configured to determine an actual value of the hitch angle θ.sub.H of the combination 1 depending on the sensor data.

[0068] In some implementations, the hitch angle sensor system comprises a camera 4, in particular a rear facing camera of the motor vehicle 2, which is able to depict at least a part of the trailer 3 and/or the drawbar 8. Alternatively or in addition, a rotation angle sensor may be implemented in the hitch 7 or the drawbar 8 to determine the hitch angle θ.sub.H. The hitch angle θ.sub.H corresponds to an angle, a longitudinal axis of the motor vehicle 1 includes with a longitudinal axis of the trailer 3, in particular the drawbar 8, as depicted schematically in FIG. 3.

[0069] In case of a reverse driving situation, the absolute value of the hitch angle θ.sub.H may always be decreased or brought to zero, as long as the hitch angle θ.sub.H is within a reversible angle region 9 indicated in FIG. 1. The reversible angle region 9 is limited by a jackknife value θ.sub.J for the hitch angle θ.sub.H. In particular, if the absolute value of the hitch angle θ.sub.H is greater than the jackknife value θ.sub.J, the absolute value of the hitch angle θ.sub.H cannot be decreased by reverse driving anymore but the combination 1 has to be driven in forward direction.

[0070] Furthermore, if the absolute value of the hitch angle θ.sub.H assumes a collision value θ.sub.C, a collision between the trailer 3 and the motor vehicle 1 may occur. In FIG. 1, the trailer 3 is indicated at a different position 3′, where the hitch angle θ.sub.H is close to the collision value θ.sub.C.

[0071] The driver assistance system 10 and the corresponding method for assisting reverse driving of the combination 1 according to the improved concept may help to avoid collisions as well as jackknife situations, where the hitch angle θ.sub.H is outside of the reversible angle region 9. It is noted, however, that the collision value θ.sub.C is not necessarily greater than the jackknife value θ.sub.C, even though this is the case in the schematic representation of FIG. 1. It depends on the geometry of the motor vehicle 2, the trailer 3 and, in particular, position of the hitch 7 positioned as well as the length of the drawbar 8.

[0072] The driver assistance system 10 comprises an environmental sensor system, which may contain the camera 4 and/or one or more ultrasonic sensors 5 mounted at a rear part of the motor vehicle 2 such that it may detect or measure a distance between the trailer 3 and the motor vehicle 2. The computing unit 6 is configured to determine a hitch length H.sub.t of the trailer 3 given by a distance between a trailer body 11 and the hitch 7 depending on environmental sensor data generated by the environmental sensor system, in particular depending on camera images generated by the camera 4 and/or ultrasonic sensor data generated by the ultrasonic sensors 5. The hitch length H.sub.t may for example correspond to a length of the drawbar 8.

[0073] The computing unit 6 may determine the collision value θ.sub.C depending on the hitch length H.sub.t and trigger a safety measure depending on the actual value of the hitch angle θ.sub.H and the collision value θ.sub.C. Optionally, the computing unit 6 may also determine the jackknife value θ.sub.J and trigger the safety measure or a further safety measure depending on the actual value of the hitch angle θ.sub.H and the jackknife value θ.sub.J.

[0074] An exemplary flow diagram for a method for assisting reverse driving of the combination 1 by means of the driver assistance system 10 according to the improved concept is shown in FIG. 2.

[0075] In step S1, the computing unit 6 determines a wheelbase L.sub.t of the trailer. The wheelbase L.sub.t is given by the distance between the hitch 7 and the axle 15, in particular the front axle, of the trailer 3 as shown in FIG. 3. The wheelbase L.sub.t of the trailer 3 may for example be determined depending on camera images of the camera 4. For example, the computing unit 6 may track the movement of the trailer 3 depending on the camera image and deduce the wheelbase L.sub.t of the trailer 3 from the orientation of the trailer 3 and the corresponding course of the hitch angle θ.sub.H.

[0076] In step S2, the computing unit 6 computes the jackknife value θ.sub.J depending on the wheelbase L.sub.t of the trailer 3. More details about the calculation of the jackknife value θ.sub.J are provided below with reference to FIG. 3 to FIG. 6. In step S3, the computing unit 6 may determine the distance between the vehicle 2 and the trailer body 11, for example, depending on the ultrasonic sensor data or the camera images. In step S4, the computing unit calculates the hitch length H.sub.t depending on the measured distance of S3. For example, the computing unit 6 may compute the hitch length H.sub.t as a difference between the measured distance and the predefined hitch length H.sub.v of the vehicle 2, which is given by a distance between the body 12 of the vehicle 2 and the hitch 7, as indicated in FIG. 7. Then, the computing unit 6 may compute the collision value θ.sub.C depending on the hitch length H.sub.t of the trailer 3. More details about the calculation of the collision value θ.sub.C are provided below with reference to FIG. 7.

[0077] In step S5, the computing unit may for example compare the collision value θ.sub.C to the jackknife value θ.sub.J. In case the collision value θ.sub.C is greater than the jackknife value θ.sub.J, a first critical value for the hitch angle is determined in step S6a as θ.sub.J−B, wherein B denotes a positive buffer value. Furthermore, a second critical value for the hitch angle θ.sub.H is defined as the jackknife value θ.sub.J. If, on the other hand, the collision value θ.sub.C is smaller than the jackknife value θ.sub.J, the computing unit 6 defines the first critical value in step S6b as θ.sub.C−B and the second critical value as the collision value θ.sub.C.

[0078] The steps S1 to S6a or S6b are, for example, carried out once for a given combination 1. In case the combination 1 changes, for example if a different trailer 3 is attached to the motor vehicle 2, steps S1 to S6a or S6b may be repeated.

[0079] In step S7, the computing unit 6 obtains a value of the hitch angle θ.sub.H depending on the sensor data generated by the hitch angle sensor system. In step S8, the computing unit 6 compares the value of the hitch angle θ.sub.H to the first critical value. In case the absolute value of the hitch angle θ.sub.H is smaller than the first critical value, step S7 is repeated and so forth. However, if it is found in S8 that the absolute value of the hitch angle θ.sub.H is equal to or greater than the first critical value, it is determined by the computing unit 6 in step S9 whether the absolute value of the hitch angle θ.sub.H is also equal to or greater than the second critical value. If this is not the case, that is the absolute value of the hitch angle θ.sub.H is equal to or greater than the first critical value but smaller than the second critical value, a first safety measure is triggered in step S10.

[0080] The first safety measure may for example include a warning, for example a visual, acoustic or haptic warning, to the driver of the motor vehicle 2 indicating that the hitch angle θ.sub.H approaches the boarders of the reversible angle region 9 or the trailer 3 is about to collide with the vehicle 2. Then, step S8 is repeated. However, if it is found in S9 that the absolute value of the hitch angle θ.sub.H is already greater than or equal to the second critical value, a second safety measure is triggered by the computing unit 6 in step S11. The second safety measure may, in particular, include an emergency braking maneuver, which may automatically be carried out by a braking system of the motor vehicle 1 triggered by the computing unit 6.

[0081] In this way, it is avoided that the vehicle 2 and the trailer 3 collide with each other and also that the hitch angle θ.sub.H leaves the reversible angle region 9 and a jackknife situation is entered.

[0082] In FIG. 3, the combination 1 is shown schematically in more detail, wherein the motor vehicle 2 is represented by a front axle 13 with steerable wheels and the rear axle 14 with non-steerable wheels. The trailer 3 comprises a single axle 15 and the drawbar 8, and the trailer body 11 is indicated by a straight line. Furthermore, also the vehicle body 12 is indicated by a straight line.

[0083] The hitch angle θ.sub.H is given by θ.sub.v−θ.sub.t, wherein θ.sub.v denotes the orientation of the vehicle 2 with respect to predefined reference direction, for example the horizontal direction in FIG. 3, and θ.sub.t denotes the corresponding trailer orientation with respect to the same reference direction. A change in the hitch angle Δθ.sub.H is given by

Δθ.sub.H=Δθ.sub.v−Δθ.sub.t=ΔS(1/R.sub.v−1/R.sub.t),  (1′)

wherein ΔS is always negative for backward motion, such that

Δθ.sub.H=Δθ.sub.v−Δθ.sub.t=|ΔS|(1/R.sub.t−1/R.sub.v).  (1)

[0084] Therein, R.sub.t denotes radius of rotation of the trailer 3 around the instantaneous center of rotation C.sub.t of the trailer 3, as depicted in FIG. 3. R.sub.v denotes the instantaneous radius of rotation of the vehicle 2 around the instantaneous center of rotation C.sub.v of the vehicle 2, as depicted in FIG. 3. FIG. 6 shows the relation between the respective signs of R.sub.t and R.sub.v and the value of R with respect to R.sub.Vmin on the one hand and the sign of the change of the hitch angle Δθ.sub.H on the other hand.

[0085] Therefore, from equation (1) and FIG. 6 it follows that Δθ.sub.H has always the same sign as R.sub.t. Consequently, it may be assumed that a jackknife situation occurs only when R.sub.t is equal to or smaller than R.sub.Vmin, which means that the instantaneous radius of rotation of the trailer 3 smaller than the one of the vehicle 2. At this condition, if the backward motion is continued, the jackknife effect progressively worsens until eventually physical contact occurs. In order to determine the jackknife value θ.sub.J, R is set equal to R.sub.Vmin, which is given by R.sub.Vmin=L.sub.v/tan(ϕv.sub.max), wherein ϕv.sub.max denotes the maximum wheel angle of the steerable wheels of the vehicle 2. Therefore, with tan(ϕ.sub.t)=L.sub.t/R.sub.t and ϕ.sub.r=ϕ.sub.t−θ.sub.J, it follows that

R.sub.t==L.sub.t/tan(ϕ.sub.t)=L.sub.v/tan(ϕv.sub.max),  (2)

tan(ϕ.sub.t)=tan(θ.sub.J+ϕ.sub.r)=[tan(θ.sub.J)+tan(ϕ.sub.r)]/[1−tan(θ.sub.J)*tan(ϕ.sub.r)]=L.sub.t*tan(ϕv.sub.max)/L.sub.v,  (3)

L.sub.v*[tan(θ.sub.J)*tan(ϕ.sub.r)]=L.sub.t*tan(ϕv.sub.max)*[1−tan(θ.sub.J)*tan(ϕ.sub.r)],  (4)

tan(θ.sub.J)=[L.sub.t*tan(ϕv.sub.max)−L.sub.v*tan(ϕ.sub.r)]/[L.sub.v+L.sub.t*tan(ϕv.sub.max)*tan(ϕ.sub.r)],  (5)

and further, in view of FIG. 5

tan(ϕ.sub.r)=−L.sub.r*tan(ϕv.sub.max)/L.sub.v.  (6)

Substituting equation (6) in equation (5) yields

tan(θ.sub.J)=[L.sub.v*tan(ϕv.sub.max)(L.sub.t+L.sub.r)]/[L.sub.v.sup.2−L.sub.t*L.sub.r*tan.sup.2(ϕv.sub.max)], and  (7)

θ.sub.J=arc tan{[L.sub.v*tan(ϕv.sub.max)*(L.sub.t+L.sub.r)]/[L.sub.v.sup.2−L.sub.t*L.sub.r*tan.sup.2(ϕv.sub.max)]}.  (8)

[0086] For determining the collision value θ.sub.C, it may for example be assumed that the collision always occurs at a corner of a bumper of the vehicle 2 bumper, and therefore the point of contact P always lies on the vehicle's contour corner and somewhere along the lateral width of the trailer 3. The width of the trailer 3 is not necessarily known. Therefore, a worst-case scenario for the collision is assumed, where the width of the trailer 3 is assumed to be equal to the width W.sub.v of the vehicle 2. In case the actual width of the trailer 3 is greater than the width of the vehicle 2, the collision will occur at the same value of the hitch angle θ.sub.H as for the width of the trailer 3 being equal to W.sub.v. If, on the other hand, the width of the trailer 3 is smaller than the width W.sub.v of the vehicle 2, the collision would occur at greater absolute value for the hitch angle θ.sub.H than estimated in the following for the collision value θ.sub.C.

[0087] Therefore it follows that

θ.sub.C=arc sin[(H.sub.t−D)/h]+arc sin(H.sub.v/h).  (9)

[0088] As described, in particular with respect to the figures, the improved concept allows to assisting reverse driving of a combination universally for different trailers with different geometries or outlines. To this end, a hitch length of the trailer is estimated by means of an environmental sensor system and the collision value is determined depending on the hitch length.