Method for determining the direction of travel of a vehicle

Abstract

A method for determining the direction of travel of a vehicle comprises providing a first sensor for measuring a longitudinal acceleration of the vehicle and at least one second sensor for establishing the rotational movement of a wheel of the vehicle, An acceleration signal containing acceleration information from the first sensor is received by the system. The acceleration signal is filtered resulting in a modified acceleration signal. The direction of travel of the vehicle is determined based on the modified acceleration signal and based on the output signal of the second sensor.

Claims

1. A method of determining a direction of travel of a vehicle, the method comprising: measuring a longitudinal acceleration of the vehicle based on an acceleration signal of a first sensor configured to measure the longitudinal acceleration of the vehicle; detecting that the vehicle starts to move from a standstill or changes direction based on rotational movement of a wheel of the vehicle indicated by a first ascending edge or a first descending edge of a time dependent output signal of a second sensor configured to determine rotational movement of the wheel; filtering the acceleration signal resulting in a modified acceleration signal, the filtering including band-stop filtering the acceleration signal to filter out oscillations of the vehicle from the acceleration signal, and lowpass filtering of the band-stop filtered acceleration signal; determining the direction of travel of the vehicle based on a difference between the modified acceleration signal and one of the acceleration signal or the band-stop filtered acceleration signal immediately after either the vehicle starts to move from a standstill or changes direction based on the time dependent output signal of the second sensor; and autonomously controlling driving of the vehicle based on the direction of travel, wherein determining the direction of travel of the vehicle is based on the difference between the modified acceleration signal and the acceleration signal.

2. The method according to claim 1, wherein determining the direction of travel comprises: determining the direction based on a sign of the difference.

3. The method according to claim 1, wherein the band-stop filtering filters out a frequency band which comprises a frequency of the oscillations of the vehicle following deceleration or acceleration of the vehicle.

4. The method according to claim 1, wherein the band-stop filtering has a transfer function inverse to a mass-spring-damper model of the vehicle.

5. The method according to claim 4, wherein the band-stop filtering has a transfer function as follows: $G=\frac{a_2{s}^2+a_{1}s+a_0}{b_{1}s+b_0}.Math.\frac{1}{T_{add}^2+2T_{ad{d}^S}+1};$ and wherein the following applies: $a_2=\frac{1}{{\omega }_0^2};a_1=\frac{2D}{{\omega }_0};a_0=1;b_1=\frac{2D}{{\omega }_0};b_0=1;$ wherein G is the transfer function, a.sub.x and b.sub.x are general coefficients, ω.sub.0 is a resonant circuit frequency, Tada is a circulation time, s=is a path length, and D is a damping degree.

6. The method according to claim 5, wherein the parameters are selected as follows:
D=0.2;
ω.sub.0=2*π*2.5 Hz; and
T.sub.add=0.04s.

7. A system for determining a direction of travel of a vehicle, the system comprising: a first sensor configured to measure a longitudinal acceleration of the vehicle; a second sensor configured to detect rotational movement of a wheel of the vehicle, a processor configured to receive an acceleration signal of the vehicle from the first sensor, filter the acceleration signal resulting in a modified acceleration signal by band-stop filtering the acceleration signal to filter out oscillations of the vehicle from the acceleration signal to generate a band-stop filtered acceleration signal, and by lowpass filtering of the band-stop filtered acceleration signal, detect that the vehicle starts to move from a standstill or changes direction based on the rotational movement of the wheel of the vehicle indicated by a first ascending edge or a first descending edge of a time dependent output signal from the second sensor, determine the direction of travel of the vehicle based on a difference between the modified acceleration signal and one of the acceleration signal or the band-stop filtered acceleration signal, the direction of travel being determined immediately after either the vehicle starts to move from a standstill or changes direction based on the time dependent output signal of the second sensor, and autonomously control driving of the vehicle based on the direction of travel, wherein determining the direction of travel of the vehicle is based on the difference between the modified acceleration signal and the acceleration signal.

8. The system according to claim 7, wherein where the processor is configured to determine the direction based on a sign of the difference.

9. The method according to claim 1, further comprising temporarily deactivating the lowpass filtering depending upon a speed of the vehicle or a driving parameter of the vehicle or of another vehicle.

10. The system according to claim 7, wherein the processor is further configured to temporarily deactivate the lowpass filtering depending upon a speed of the vehicle or a driving parameter of the vehicle or of another vehicle.

11. The method of claim 1, wherein the lowpass filtering filters out distortions of the acceleration signal from an inclination of the vehicle.

12. The system according to claim 7, wherein the lowpass filter filters out distortions of the acceleration signal from an inclination of the vehicle.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention is explained in greater detail below by means of exemplary embodiments with reference to the figures, wherein:

(2) FIG. 1 shows, by way of example and schematically, a vehicle having sensor technology in the proximity of a longitudinal parking position which is not occupied;

(3) FIG. 2 shows, by way of example and schematically, a filter arrangement for filtering an acceleration signal of an acceleration sensor;

(4) FIG. 3 shows, by way of example, multiple time charts which show the unfiltered acceleration signal of the acceleration sensor, the acceleration signal filtered with a band-stop filter and the acceleration signal filtered with a lowpass filter; and

(5) FIG. 4 shows, by way of example, a flow chart which illustrates the steps of the method for determining the direction of travel of a vehicle.

DETAILED DESCRIPTION

(6) FIG. 1 shows a vehicle 1 in the environment of a longitudinal parking situation, in which an available parking position between two vehicles is not occupied. The vehicle 1 has a parking assistance system, by means of which the vehicle 1 can be parked in an at least partially automated manner in the parking position which is not occupied. During the parking operation, the vehicle 1 is maneuvered by the parking assistance system along a parking trajectory PT from a starting position SP into a target position ZP. Such a parking trajectory PT is depicted by way of example in FIG. 1. The target position ZP of the vehicle 1 can, as in the depicted case, be reached by a single parking move. Alternatively, it is however possible that in order to reach the parking position, multiple moves are necessary, for example three parking moves, wherein the direction of travel is altered between the individual parking moves. In order to ensure that the vehicle 1 is moving on the calculated parking trajectory PT, it is necessary to capture the direction of travel of the vehicle 1 as exactly as possible, including in the event of the direction of travel altering suddenly, as happens for example when driving against a curb or similar.

(7) In order to determine the direction of travel, the vehicle has a system which comprises at least one first sensor 2 and one second sensor 3. The first sensor 2 is configured to measure the longitudinal acceleration of the vehicle 1 (longitudinal acceleration sensor). The first sensor 2 is preferably a sensor of the inertial measuring unit of the vehicle or a sensor which is assigned to the braking system of the vehicle, e.g. a sensor of the electronic stability control (ESC). The second sensor 3 is for example a sensor, by means of which the vehicle movement can be captured, for example a sensor for determining the rotational movement of a wheel (wheel speed sensor). The second sensor 3 is, for example, configured to provide pulses as a function of the angular velocity of the wheel, which allow conclusions to be drawn regarding the movement of the vehicle. The second sensor 3 can, for example, be an inductive sensor, e.g. a Hall sensor. It can therefore be ascertained by means of the second sensor 3 whether the wheel of the vehicle 1 is rotating or the angle by which the wheel has rotated. For example, a starting of the vehicle 1 or a change of direction can be detected. The second sensor 3 may be formed by a group of sensors which contains multiple individual sensors, for example in each case one individual sensor per wheel of the vehicle 1.

(8) In order to achieve a determination of the direction of travel of the vehicle 1 which is as exact as possible, the measuring signal provided by the first sensor 2, hereinafter referred to as an acceleration signal, is subjected to filtering.

(9) The filtering can, on the one hand, comprise a lowpass filtering. Distortions of the acceleration signal, which are created, for example, due to offsets and/or an inclination of the vehicle (for example resulting from the vehicle driving on an inclined surface), can be compensated for by means of the lowpass filtering. For example, it can be achieved by means of a lowpass filtering of the acceleration signal that, due to a distortion, the acceleration signal has an erroneous sign and, therefore, an erroneous direction of travel of the vehicle 1 is deduced.

(10) The modified acceleration signal obtained by the lowpass filtering may be compared to the acceleration signal provided by the first sensor 2 or an acceleration signal derived therefrom and the direction of travel of the vehicle 1 is determined on the basis of the signal comparison.

(11) The deviation of the acceleration signal provided by the first sensor 2 and of the signal at the output of the lowpass filter may be established (difference calculated) and the sign of the result of the difference calculated is utilized in order to determine the direction of travel of the vehicle 1. The direction of travel of the vehicle may be captured as a temporal function of a signal component received from the second sensor 3. The signal provided by the second sensor may be a time-variable signal having pulse edges, e.g. a square-wave signal, the frequency of which depends on the rotational speed of the wheel. The direction of travel of the vehicle 1 may be established when, after the vehicle has been stopped for a while, an edge of a pulse of the output signal of the second sensor 3 is received again.

(12) The filtering of the acceleration signal may comprise a band-stop filtering. If a vehicle 1 is decelerated abruptly, for example down to a standstill, the springs on one axle are compressed and the springs on the other axle are relieved. Following the standstill, this leads to a damped vibration of the vehicle chassis which can last multiple seconds and distorts the acceleration signal. During this time, the vehicle 1 can, however, already start moving again so that the direction of movement of the vehicle 1 has to be determined.

(13) Thanks to the band-stop filtering it is possible to determine the direction of movement of the vehicle 1 sufficiently accurately, even during the vibration of the vehicle chassis.

(14) The filter function of the band-stop filter is selected such that the oscillation frequency is filtered out, whereas signal components in other frequency ranges can pass through the band-stop filter. Signal components which are created during jerky movements of the vehicle 1 can pass through the band-stop filter. It should be mentioned here that the oscillation frequency and the damping of the acceleration signal are preferably virtually constant due to the suspension of the vehicle in the case of a predefined vehicle type and, therefore, a filter function of a band-stop filter having fixedly predefined filter characteristics can be used in order to filter out disturbing oscillations.

(15) A spring-damper model of the vehicle 1 is preferably used in order to define the filter function of the band-stop filter and the filter function of the band-stop filter is selected inversely to the spring-damper model of the vehicle 1, in order to filter out the oscillations of the vehicle 1.

(16) For example, the transfer function of the band-stop filter has the following transfer function:

(17) $G=\frac{a_2{s}^2+a_{1}s+a_0}{b_{1}s+b_0}.Math.\frac{1}{T_{add}^2+2T_{add}s+1};$
wherein the following applies:

(18) $a_2=\frac{1}{{\omega }_0^2};a_1=\frac{2D}{{\omega }_0};a_0=1;b_1=\frac{2D}{{\omega }_0};b_0=1;$

(19) The parameters of the transfer function can in particular be selected as follows:
D=0.2;
ω.sub.0=2*π*2.5 Hz; and
T.sub.add=0.04s;

(20) FIG. 2 shows a schematic representation of a filter cascade for filtering the acceleration signal provided by the first sensor 2.

(21) The acceleration signal provided by the first sensor 2 is received by the filter arrangement and initially filtered by the band-stop filter, in order to filter out the vibrations described above resulting from the rocking of the sprung body.

(22) The output signal provided by the band-stop filter is subsequently used as an input signal of a lowpass filter, in order to avoid the deviations previously described or drifts for example due to the vehicle 1 being tilted.

(23) The output signal of the filter cascade or filter arrangement may be formed by calculating the difference between the output signal of the lowpass filter and the output signal of the band-stop filter. Alternatively, the difference can be calculated between the output signal of the lowpass filter and the input signal of the band-stop filter, i.e. in particular the unfiltered acceleration signal of the first sensor 2. The direction of travel of the vehicle 1 can be determined based on this output signal of the filter cascade or the filter arrangement.

(24) FIG. 3 shows the temporal progress of the acceleration signal which is provided by the first sensor 2, the temporal progress of the output signal of the band-stop filter and the temporal progress of the output signal of the lowpass filter.

(25) The top representation shows the temporal progress of the acceleration signal which is provided by the first sensor 2, the middle representation shows the temporal progress of the output signal of the band-stop filter and the lower representation shows the temporal progress of the output signal of the lowpass filter.

(26) It can be seen from the temporal progresses that the postoscillation of the acceleration signal can be significantly reduced by the band-stop filter following a deceleration or acceleration process. The lowpass filtering brings about an equalization of erratic alterations in the acceleration signal.

(27) FIG. 4 shows a schematic representation of the steps of a method for determining the direction of travel of a vehicle 1.

(28) A first sensor 2 for measuring a longitudinal acceleration of the vehicle 1 and a second sensor 3 for establishing the rotational movement of a wheel of the vehicle 1 are initially provided (S10).

(29) An acceleration signal containing acceleration information is subsequently received from the first sensor 2 (S11).

(30) The acceleration signal is filtered in a further method step, resulting in a modified acceleration signal (S12).

(31) The direction of travel of the vehicle 1 is lastly determined based on the modified acceleration signal and based on the output signal of the second sensor 3 (S13).

(32) The invention has been described above with reference to exemplary embodiments. It is understood that numerous alterations as well as modifications are possible, without departing from the scope of protection defined by the claims.