Method for automatically adjusting the vehicle speed

Abstract

In a method for automatically adjusting the vehicle speed of a vehicle, while the distance to a preceding other vehicle is continuously measured, in order to reduce an initial distance, the vehicle is initially moved, in a drive phase, at a higher vehicle speed and is subsequently decelerated in a braking phase.

Claims

1. A method for automatically adjusting a speed of a first vehicle while a distance of the first vehicle to a second vehicle that leads the first vehicle is continuously measured, the method comprising: responsive to the distance being a first distance that is greater than a setpoint distance, reducing the distance from the first distance to the setpoint distance by: in a drive phase, a processor driving the first vehicle at a higher vehicle speed than the second vehicle; and in a braking phase that is subsequent to the drive phase, the processor initiating and then maintaining a deceleration of the first vehicle using at least one of friction and a generator mode of an electric motor situated in a drive train of the vehicle until the distance equals the setpoint distance and the speeds of the first and second vehicles match.

2. The method of claim 1, wherein the vehicle is accelerated during the entire drive phase.

3. The method of claim 2, wherein the acceleration of the vehicle during the entire drive phase is with a constant acceleration.

4. The method of claim 1, wherein a maximum acceleration during the drive phase is determined based on a time period required to reach the setpoint distance between the first and second vehicles, starting from a time at which the distance has an initial distance value and at which there is an initial difference between speeds of the first and second vehicles.

5. The method of claim 1, wherein the vehicle is decelerated in the braking phase exclusively using the at least one of the friction and the generator mode.

6. The method of claim 1, wherein a point in time at which a switch is made from the drive phase to the braking phase is determined as a function of a braking ability using the at least one of the friction and the generator mode.

7. The method of claim 1, wherein: a point in time (t.sub.U) at which a switch is made from the drive phase to the braking phase is determined based on one or more of the following relationships:
0=s(t.sub.0)+v(t.sub.0).Math.(t.sub.Ut.sub.0)+a.sub.B .Math.(t.sub.Ut.sub.0).sup.2;
0=v(t.sub.0)+a.sub.B .Math.(t.sub.Ut.sub.0);
0=s(t.sub.U)+v(t.sub.U).Math.(t.sub.Lt.sub.U)+a.sub.S.Math.(t.sub.Lt.sub.U).sup.2; and
0=v(t.sub.U)+a.sub.S.Math.(t.sub.Lt.sub.U); t.sub.0 is an initial point in time at which the drive phase is begun; t.sub.L, is a point in time when the setpoint distance is reached; s(t.sub.0) is the distance between the first and second vehicles at t.sub.0; s(t.sub.U) is the distance between the first and second vehicles at t.sub.U; v(t.sub.0) is a difference in speeds between the first and second vehicles at t.sub.0; v(t.sub.U) is the difference in speeds of the first and second vehicles at t.sub.U; a.sub.B is a value of an acceleration of the first vehicle during the drive phase; and a.sub.S is a value of a deceleration of the first vehicle during the braking phase.

8. The method of claim 1, further comprising automatically increasing the distance between the first and second vehicles in response to occurrence of a predefined event.

9. The method of claim 1, further comprising automatically increasing the distance between the first and second vehicles in response to a third vehicle being detected as beginning to merge into a location in a lane of the first and second vehicles that is between the first and second vehicles.

10. The method of claim 1, further comprising, in response to a third vehicle being detected as beginning to merge into a location in a lane of the first and second vehicles that is between the first and second vehicles, automatically carrying out a braking phase to increase the distance between the first and second vehicles and then carrying out the drive phase to decrease a distance between the first and third vehicles.

11. The method of claim 1, wherein the driving of the first vehicle is performed by accelerating the first vehicle throughout the drive phase at a constant acceleration rate until a switchover point in time at which the first vehicle is switched from the drive phase to the braking phase, and the deceleration is performed by decelerating the vehicle at a constant deceleration rate throughout the braking phase.

12. The method of claim 1, wherein parameters of the drive phase and the braking phase are set to satisfy one or more of the following relationships
0=s(t.sub.0)+v(t.sub.0).Math.(t.sub.Ut.sub.0)+a.sub.B .Math.(t.sub.Ut.sub.0).sup.2;
0=v(t.sub.0)+a.sub.B .Math.(t.sub.Ut.sub.0);
0=s(t.sub.U)+v(t.sub.U).Math.(t.sub.Lt.sub.U)+a.sub.S.Math.(t.sub.Lt.sub.U).sup.2; and
0=v(t.sub.U)+a.sub.S.Math.(t.sub.Lt.sub.U); t.sub.0 is an initial point in time at which the drive phase is begun; t.sub.U is a point in time at which a switch is made from the drive phase to the braking phase; t.sub.L is a point in time when the setpoint distance is reached; s(t.sub.0) is the distance between the first and second vehicles at t.sub.0; s(t.sub.U) is the distance between the first and second vehicles at t.sub.U; v(t.sub.0) is a difference in speeds between the first and second vehicles at t.sub.0; v(t.sub.U) is the difference in speeds of the first and second vehicles at t.sub.U; a.sub.B is a value of an acceleration of the first vehicle during the drive phase; and a.sub.S is a value of a deceleration of the first vehicle during the braking phase.

13. The method of claim 1, wherein parameters of the drive phase and the braking phase are set to satisfy all of the following relationships:
0=s(t.sub.0)+v(t.sub.0).Math.(t.sub.Ut.sub.0)+a.sub.B .Math.(t.sub.Ut.sub.0).sup.2;
0=v(t.sub.0)+a.sub.B .Math.(t.sub.Ut.sub.0);
0=s(t.sub.U)+v(t.sub.U).Math.(t.sub.Lt.sub.U)+a.sub.S.Math.(t.sub.Lt.sub.U).sup.2; and
0=v(t.sub.U)+a.sub.S.Math.(t.sub.Lt.sub.U); t.sub.0 is an initial point in time at which the drive phase is begun; t.sub.U is a point in time at which a switch is made from the drive phase to the braking phase; t.sub.L is a point in time when the setpoint distance is reached; s(t.sub.0) is the distance between the first and second vehicles at t.sub.0; s(t.sub.U) is the distance between the first and second vehicles at t.sub.U; v(t.sub.0) is a difference in speeds between the first and second vehicles at t.sub.0; v(t.sub.U) is the difference in speeds of the first and second vehicles at t.sub.U; a.sub.B is a value of an acceleration of the first vehicle during the drive phase; and a.sub.S is a value of a deceleration of the first vehicle during the braking phase.

14. A system comprising a control unit with an interface by which the processor can control a first vehicle, wherein the control unit is configured to perform a method for automatically adjusting a speed of the first vehicle while a distance of the first vehicle to a second vehicle that leads the first vehicle is continuously measured, the method comprising: responsive to the distance being a first distance that is greater than a setpoint distance, reducing the distance from the first distance to the setpoint distance by: in a drive phase, controlling the first vehicle to drive at a higher vehicle speed than the second vehicle; and in a braking phase that is subsequent to the drive phase, initiating and then maintaining a deceleration of the first vehicle using at least one of friction and a generator mode of an electric motor situated in a drive train of the vehicle until the distance equals the setpoint distance and the speeds of the first and second vehicles match.

15. The system of claim 14, further comprising a sensor communicatively coupled to the processor and from which the processor obtains values of the distance.

16. A first vehicle comprising a system that includes a sensor and a control unit communicatively coupled to the sensor, wherein the control unit is configured to perform a method for automatically adjusting a speed of the first vehicle while a distance of the first vehicle to a second vehicle that leads the first vehicle is continuously measured by the sensor, the method comprising: responsive to the distance, as indicated by a signal of the sensor, being a first distance that is greater than a setpoint distance, reducing the distance from the first distance to the setpoint distance by: in a drive phase, controlling the first vehicle to drive at a higher vehicle speed than the second vehicle; and in a braking phase that is subsequent to the drive phase, initiating and then maintaining a deceleration of the first vehicle using at least one of friction and a generator mode of an electric motor situated in a drive train of the vehicle until the distance equals the setpoint distance and the speeds of the first and second vehicles match.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the acceleration/deceleration curve as a function of time during a reduction of the distance to a preceding other vehicle, according to an example embodiment of the present invention.

(2) FIG. 2 shows an acceleration/deceleration diagram as a function of time as the distance to a preceding other vehicle increases, according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(3) FIG. 1 relates to a method for automatically adjusting the vehicle speed of a vehicle while the distance to a preceding other vehicle is continuously measured, where a greater initial distance between the vehicle and the preceding other vehicle is to be reduced to a smaller setpoint distance. Upon the activation of the distance control function, the actual initial distance is therefore greater than the setpoint distance. The initial speed of the vehicle can possibly be greater than the speed of the preceding other vehicle, even though embodiments are also possible, in which the initial speed of the vehicle is equal to or less than the speed of the preceding other vehicle.

(4) In order to reduce the initial distance to the setpoint distance which is determined, in particular, depending on speed, a drive phase is initially carried out, while the distance between the vehicle and the preceding other vehicle is continuously measured, between initial point in time t.sub.0 and a switch point t.sub.U which marks the switch from the drive phase to a subsequent braking phase which lasts up to point in time t.sub.L. t.sub.L also stands for the entire time period for carrying out the method until the setpoint distance and the target speed of the vehicle, which matches the speed of the preceding other vehicle, have been reached.

(5) The continuous distance measurement in the distance control system of the vehicle is preferably carried out with the aid of a distance radar system. Alternatively, other distance-ascertaining systems are also possible, which function, for example, in a video-based manner or on the basis of ultrasound or LIDAR.

(6) In the drive phase, the vehicle has, at least in sections, a higher speed than the preceding other vehicle, in order to reduce the greater initial distance to the setpoint distance.

(7) Switch point t.sub.U can be predefined and covers, for example, a period of time from 10 ms to 100 s and is preferably between 500 ms and 1 s, measured starting at initial point in time t.sub.0. Vehicle deceleration a.sub.Sin the braking phase between switch point t.sub.U and the final point in time or entire time period t.sub.L until the setpoint distance is reached can also be predefined and is in the magnitude, for example, up to 4 m/s.sup.2, in particular between 0.1 m/s.sup.2 and 0.5 m/s.sup.2.

(8) Vehicle deceleration as in the braking phase between t.sub.U and t.sub.L is preferably carried out without actuation of the hydraulic braking system and is based exclusively on friction or on the generator mode of an electric motor situated in the drive train of the vehicle. The friction is related, in particular, to the air resistance, the rolling friction between the wheels and the roadway, and internal drag torques of an internal combustion engine or friction in general in the drive train, in particular in the transmission. Provided an electric motor is situated in the drive train, the electric motor is operated and recuperated in the generator mode, as a result of which a significant deceleration can be achieved in the braking phase.

(9) At the beginning of the method, with the aid of the distance determination system, initial distance s(t.sub.0) is initially determined at initial point in time to as well as differential speed v(t.sub.0), where the trailing vehicle can have a speed which is greater than, less than, or equal to that of the preceding other vehicle at the point in time of the activation of the distance control system. On the basis of this information, time period t.sub.L can be determined, which, with the aid of the present speed (in the case of an initial excess speed), is required for reducing initial distance s(t.sub.0) to setpoint distance s.sub.d.

(10) Maximum acceleration a.sub.B, which is carried out in the drive phase between t.sub.0 and t.sub.U, can be determined, on the condition of a uniform acceleration, with the aid of the following relationships:
0=s(t.sub.0)+v(t.sub.0).Math.(t.sub.Ut.sub.0)+a.sub.B .Math.(t.sub.Ut.sub.0).sup.2;
0=v(t.sub.0)+a.sub.B .Math.(t.sub.Ut.sub.0);
0=s(t.sub.U)+v(t.sub.U).Math.(t.sub.Lt.sub.U)+a.sub.S.Math.(t.sub.Lt.sub.U).sup.2; and
0=v(t.sub.U)+a.sub.S.Math.(t.sub.Lt.sub.U).

(11) As is apparent from FIG. 1, acceleration value a.sub.B is applied, as a constant acceleration, via the drive motor in the vehicle in the drive phase between t.sub.0 and t.sub.U.

(12) At switch point t.sub.U, the switch from the drive phase to the braking phase takes place, in which no further drive torque is generated and, instead, a braking force is generated, although not with the aid of the vehicle's own braking system, but rather, as described above, via friction, drag torques, and/or the generator mode of an electric motor situated in the drive train. Deceleration as is also advantageously constant across the entire time period of the braking phase.

(13) At point in time t.sub.L, the braking phase is concluded, the distance between the vehicle and the preceding other vehicle corresponds to the setpoint distance, and the vehicle speed corresponds to the target speed (speed of the preceding other vehicle).

(14) In FIG. 2, the method for increasing the distance to a preceding other vehicle is represented, for example, in order to allow yet another road user to merge into the gap between the vehicle and the preceding other vehicle. Similarly to FIG. 1, entire time period t.sub.L is subdivided into a braking phase between t.sub.0 and t.sub.U and a drive phase between t.sub.U and t.sub.L. In the initial braking phase, a constant deceleration as is applied, which, if necessary, can be equal to deceleration a.sub.S of FIG. 1. The subsequent drive phase between t.sub.U and t.sub.L takes place at constant acceleration a.sub.B which, if necessary, can also be as great as acceleration a.sub.B in FIG. 1. Switch point t.sub.U is predefined as a value and is in a value range, for example, between 0.1 s and 5 s, preferably between 0.5 s and 2 s.

(15) The acceleration phase between t.sub.U and t.sub.L can be followed, in turn, by a braking phase similar to FIG. 1, in order to adjust the desired setpoint distance and the target speed of the vehicle to the further road user which has merged into the gap.