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 for determining the direction of travel of a vehicle comprising: measuring a longitudinal acceleration of the vehicle with a first sensor establishing the rotational movement of a wheel of the vehicle with at least one second sensor; receiving an acceleration signal containing acceleration information from the first sensor; filtering the acceleration signal, resulting in a modified acceleration signal; and determining the direction of travel of the vehicle based on the modified acceleration signal and on an output signal of the second sensor.

2) The method according to claim 1, wherein the filtering of the acceleration signal comprises a lowpass filtering.

3) The method according to claim 2, wherein during the determination of the direction of travel of the vehicle, the difference is calculated between the acceleration signal provided by the first sensor or derived therefrom and the lowpass-filtered acceleration signal and, based on the sign of the result of the calculated difference, the direction of travel is determined.

4) The method according to claim 1, wherein during the determination of the direction of travel of the vehicle, the lowpass-filtered acceleration signal and the acceleration signal provided by the first sensor or derived therefrom are compared.

5) The method according to claim 1, wherein during the determination of the direction of travel of the vehicle, the deviation between the acceleration signal provided by the first sensor or derived therefrom and the lowpass-filtered acceleration signal is determined.

6) The method according to claim 1, wherein the filtering of the acceleration signal comprises a filtering by a band-stop filter.

7) The method according to claim 6, wherein the band-stop filter filters out a frequency band which comprises the vibration frequency of the vehicle following a deceleration or acceleration process.

8) The method according to claim 6, wherein the band-stop filter has a transfer function inversely to the mass-spring-damper model of the vehicle.

9) The method according to claim 8, wherein the band-stop filter has a transfer function as follows:
G=(a_2s{circumflex over ( )}2+a_1s+a_0)/(b_1s+b_0).Math.1/(T_add{circumflex over ( )}2+2T_adds+1); and wherein the following applies:
a_2=1/(ω_0{circumflex over ( )}2);a_1=2D/ω_0;a_0=1;b_1=2D/ω_0;b_0=1;

10) The method according to claim 9, wherein the parameters are selected as follows:
D=0.2;
ω.sub.0=2*π*2.5 Hz; and
T.sub.add=0.04s;

11) The method according to claim 1, wherein the filtering of the acceleration signal comprises multiple consecutive filtering steps, and a first filtering step by a band-stop filter and a second filtering step, in which the signal is filtered by a lowpass filter following the filtering by the band-stop filter.

12) The method according to claim 1, wherein the direction of travel of the vehicle is determined as a function of the temporal progress of the output signal of the second sensor.

13) The method according to claim 1, wherein the direction of travel of the vehicle is determined immediately following the receipt of an edge of the output signal of the second sensor.

14) A system for determining the direction of travel of a vehicle, comprising: a first sensor for measuring a longitudinal acceleration of the vehicle; at least one second sensor for establishing the rotational movement of a wheel of the vehicle, a processor with instructions configured for: receiving an acceleration signal containing acceleration information from the first sensor; filtering the acceleration signal, resulting in a modified acceleration signal; determining the direction of travel of the vehicle based on the modified acceleration signal and based on the output signal of the second sensor.

15) The system according to claim 14, further comprising a lowpass filter for the filtering of the acceleration signal.

16) The system according to claim 14, wherein where the processor has further instructions for calculating the difference between the acceleration signal provided by the first sensor or derived therefrom and the lowpass-filtered acceleration signal and, based on the sign of the result of the calculated difference, the direction of travel is determined.

17) The system according to claim 14, wherein where the processor has further instructions for comparing the lowpass-filtered acceleration signal and the acceleration signal provided by the first sensor or derived therefrom.

18) The system according to claim 14, wherein where the processor has further instructions for determining the deviation between the acceleration signal provided by the first sensor or derived therefrom and the lowpass-filtered acceleration signal.

19) The system according to claim 14, further comprising a band-stop filter for filtering of the acceleration signal.

20) A vehicle comprising: a first sensor for measuring a longitudinal acceleration of the vehicle; at least one second sensor for establishing the rotational movement of a wheel of the vehicle, a processor with instructions configured for: receiving an acceleration signal containing acceleration information from the first sensor; filtering the acceleration signal, resulting in a modified acceleration signal; determining the direction of travel of the vehicle based on the modified acceleration signal and based on the output signal of the second sensor.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0033] The invention is explained in greater detail below by means of exemplary embodiments with reference to the figures, wherein:

[0034] 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;

[0035] FIG. 2 shows, by way of example and schematically, a filter arrangement for filtering an acceleration signal of an acceleration sensor;

[0036] 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

[0037] 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

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] For example, the transfer function of the band-stop filter has the following transfer function:

[00003]$G=\frac{a_2.Math.s^2+a_1.Math.s+a_0}{b_1.Math.s+b_0}.Math.\frac{1}{T_{a.Math.d.Math.d}^2+2.Math.T_{a.Math.d.Math.d}.Math.s+1};$

wherein the following applies:

[00004]$a_2=\frac{1}{{\omega }_0^2};a_1=\frac{2.Math.D}{{\omega }_0};a_0=1;b_1=\frac{2.Math.D}{{\omega }_0};b_0=1;$

[0049] 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;

[0050] FIG. 2 shows a schematic representation of a filter cascade for filtering the acceleration signal provided by the first sensor 2.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] FIG. 4 shows a schematic representation of the steps of a method for determining the direction of travel of a vehicle 1.

[0058] 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).

[0059] An acceleration signal containing acceleration information is subsequently received from the first sensor 2 (S11).

[0060] The acceleration signal is filtered in a further method step, resulting in a modified acceleration signal (S12).

[0061] 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).

[0062] 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.