This invention relates to a method of determining a position of a radar unit on a moving vehicle and to a related radar unit.

It is known to provide a vehicle such as a car with radar units around its perimeter. In particular, it is known to provide radar units at four corners of a vehicle, so that there is one at each of the front left, front right, rear right and rear left corners, each pointing in a direction such that the field of view is angled to one side or the other of the direction of movement of the vehicle.

However, it is desirable that the radar units are interchangeable to reduce the number of discrete parts involved in assembling a vehicle. This leads to a problem with identifying which position each radar unit has been installed in. For radar units installed with the manufacture of a vehicle, this can lead to complex “end of line” procedures.

According to a first aspect of the invention, we provide a method of determining a position of a radar unit on a moving vehicle, comprising: whilst the vehicle is moving, the radar unit using radar to determine the position of at least one target in a field of view at successive points in time, determining, from the position of each target at the successive points in time a first direction in which each target is moving towards or away from the radar unit and a second direction in which each target is crossing the field of view; and using each first direction and each second direction to determine a position of the radar unit from a discrete set of possible positions.

As such, this allows the method to use the motion of the vehicle and therefore the relative motion of the vehicle relative to each target to cause the targets to move past the field of view of the radar unit in different directions, which can then be used to distinguish between different potential locations of the radar unit. This ameliorates the need for the formerly complex end of line procedures.

The first and second directions for each target may form a vector, which may provide a speed and direction with which the target is moving through the field of view. The first and second directions may comprise components of that vector towards and away from the radar unit, and transverse to the radar unit, respectively.

The vehicle may be moving a movement direction, which would typically be forwards in the sense of the vehicle; as such, the first direction may depend on whether the field of view is pointing in the movement direction or opposite thereto. As such, if the first direction for each target is moving towards the radar unit, then the radar unit is likely to be looking generally forwards (and so may be mounted on a front part of the vehicle), whereas if the first direction for each target is moving away from the radar unit, then the radar unit is likely to be looking generally backwards (and so may be counted on a rear part of the vehicle).

Likewise, the second direction may indicate whether the field of view of the radar unit is oriented to one lateral side of the movement direction of the other. As such, if the second direction is from right to left in the field of view, then the radar unit is likely to be pointing to the left of the movement direction and so may be on a left side of the vehicle. Similarly, if the second direction is from left to right in the field of view, then the radar unit is likely to be pointing to the right of the movement direction and so may be on a right side of the vehicle.

Typically, there may be four possible positions: two at the front of the vehicle in which the field of view is generally in the movement direction, and two at the rear of the vehicle in which the field of view is generally in the direction opposite to the movement direction. There may be a pair of possible positions on a left side of vehicle in which the field of view is looking towards a left side of the vehicle and a pair of possible positions on a right side of the vehicle in which the field of view is looking towards a right side of the vehicle. Effectively, there may be possible positions at the front left and front right, and at the rear left and rear left of the vehicle.

As such, the method may comprise determining that the radar unit is at:

• the front left position if the first direction is towards the radar unit and the second direction is right to left;

• the front right position if the first direction is towards the radar unit and the second direction is left to right; • the rear left position if the first direction is away from the radar unit and the second direction is right to left;

• the rear right position if the first direction is away from the radar unit and the second direction is left to right.

The method may comprise comparing an expected direction for the first and second directions for each target and each possible position with the first and second directions. As such, the radar unit may be able to determine which possible position is a best fit for the measurements it has made.

The method may comprise determining the position of the radar unit at the start of a journey of the vehicle. That may ensure that the radar unit has not been moved since the last journey.

The method may comprise determining the speed of the vehicle with a vehicle speed sensor, such as one or more wheel speed sensors. The method may comprise using the determined speed to determine that the vehicle is moving and so to allow the method to proceed, or to determine a first direction appropriate to each possible position.

The method may comprise determining, in accordance with the present invention, as many radar units as there are possible positions. As such, this may allow each radar unit to determine where it is positioned.

The method may comprise storing the position of each radar unit in a control unit. The method may comprise making a determination, typically by the control unit but alternatively by each radar unit, whether precisely one radar unit has been determined to be positioned in each possible position. As such, this determination may indicate whether all of the radar units have been correctly assigned, otherwise some may be missing, or may have incorrectly duplicated their position.

According to a second aspect of the invention, we provide a radar unit for a vehicle, comprising: radar circuitry arranged to determine, using radar whilst the vehicle is moving the position of at least one target in a field of view at successive points in time, means arranged to: determine, from the position of each target at the successive points in time a first direction in which each target is moving towards or away from the radar unit and a second direction in which each target is crossing the field of view; and use each first direction and each second direction to determine a position of the radar unit from a discrete set of possible positions.

As such, this allows the radar unit to use the motion of the vehicle and therefore the relative motion of the vehicle relative to each target to cause the targets to move past the field of view of the radar unit in different directions, which can then be used to distinguish between different potential locations of the radar unit.

The first and second directions for each target may form a vector, which may provide a speed and direction with which the target is moving through the field of view. The first and second directions may comprise components of that vector towards and away from the radar unit, and transverse to the radar unit, respectively.

The vehicle may be moving a movement direction, which would typically be forwards in the sense of the vehicle; as such, the first direction may depend on whether the field of view is pointing in the movement direction or opposite thereto. As such, if the first direction for each target is moving towards the radar unit, then the radar unit is likely to be looking generally forwards (and so may be mounted on a front part of the vehicle), whereas if the first direction for each target is moving away from the radar unit, then the radar unit is likely to be looking generally backwards (and so may be counted on a rear part of the vehicle).

Likewise, the second direction may indicate whether the field of view of the radar unit is oriented to one lateral side of the movement direction of the other. As such, if the second direction is from right to left in the field of view, then the radar unit is likely to be pointing to the left of the movement direction and so may be on a left side of the vehicle. Similarly, if the second direction is from left to right in the field of view, then the radar unit is likely to be pointing to the right of the movement direction and so may be on a right side of the vehicle. Typically, there may be four possible positions: two at the front of the vehicle in which the field of view is generally in the movement direction, and two at the rear of the vehicle in which the field of view is generally in the direction opposite to the movement direction. There may be a pair of possible positions on a left side of vehicle in which the field of view is looking towards a left side of the vehicle and a pair of possible positions on a right side of the vehicle in which the field of view is looking towards a right side of the vehicle. Effectively, there may be possible positions at the front left and front right, and at the rear left and rear left of the vehicle.

As such, the radar unit may be arranged to determine that the radar unit is at:

• the front left position if the first direction is towards the radar unit and the second direction is right to left;

• the front right position if the first direction is towards the radar unit and the second direction is left to right;

• the rear left position if the first direction is away from the radar unit and the second direction is right to left;

• the rear right position if the first direction is away from the radar unit and the second direction is left to right.

The radar unit may be arranged to compare an expected direction for the first and second directions for each target and each possible position with the first and second directions. As such, the radar unit may be able to determine which possible position is a best fit for the measurements it has made.

The radar unit may be arranged to determine the position of the radar unit at the start of a journey of the vehicle. That may ensure that the radar unit has not been moved since the last journey.

The radar unit may have an input for an output of a speed sensor arranged to determine a speed of the vehicle, such as one or more wheel speed sensors. The radar unit may be arranged to use the determined speed to determine that the vehicle is moving. There now follows, by way of example only, description of embodiments of the present invention, described with reference to the accompanying drawings, in which:

Figure 1 shows a plan view of a vehicle with radar units in accordance with an embodiment of the invention;

Figure 2 shows a schematic view of the vehicle of Figure 1; and

Figure 3 shows a flow chat carried out by the radar units of Figure 1.

Figure 1 shows a vehicle 100 (in this embodiment, a car), with four radar units 1, 2, 3, 4. Each are positioned on a corner of the vehicle 1, so that their field of view 5, 6, 7, 8 is towards the front left, front right, rear left or rear right of the vehicle 1 respectively. The radar units do not initially know which position they have been installed in.

This is shown in further detail in Figure 2 of the accompanying drawings. In this Figure, there is also shown a central processing unit 10 and wheel sensors 11 which feed back the speed of each of the wheels of vehicle 1 to a vehicle speed determining unit 12, which feeds into processing unit 10.

As can be seen from Figures 1 and 2, each of the radar units are at a corner of the vehicle 100, and as such their field of view point:

• radar unit 1 : front left

• radar unit 2: front right

• radar unit 3 : rear right

• radar unit 4: rear left.

Turning now to Figure 3, each of the radar units will carry out the following procedure. At step 100, each of the radar units 1, 2, 3, 4 will power up. The fact that each radar unit 1, 2, 3, 4 carries out this method at power up means that there is a check that no units have been swapped before the previous journey. Typically, the method will be carried out once the wheel speed sensors 11 indicate that the vehicle is moving forwards. At step 102, each radar unit 1, 2, 3, 4 will use radar to determine the presence of targets and their subsequent movement. Typically, these will be stationary objects by which the vehicle 100 is passing. At step 104, each radar unit 1, 2, 3, 4 will determine whether these targets are:

• moving towards or away from the radar unit 1, 2, 3, 4 in question;

• moving left to right or right to left in the field of view of the radar unit 1, 2, 3, 4.

If the targets are moving towards the radar unit, then (as the vehicle is moving forwards), the radar unit will be able to determine that it is in a front position (so units 1 or 2). If the targets are moving away from the radar unit, then (as the vehicle is moving forwards), the radar unit will be able to determine that it is in a rear position (so units 3 or 4).

If the targets are moving left to right in the field of view of the radar unit, then (as the vehicle is moving forwards), the radar unit will be able to determine that it is in a position on the right (so units 2 or 3). If the targets are moving right to left in the field of view of the radar unit, then (as the vehicle is moving forwards), the radar unit will be able to determine that it is in position of the left (so units 1 or 4).

As such, by carrying out a comparison 106 between the target movement and the expected target movement for each expected position, the radar units 1, 2, 3, 4 can determine which position each of them is in. At step 108, if all four spaces are assigned, then the processing unit 10 can determine that all of the radar units are assigned and normal operation can commence. If there is duplication of assignment, then the radar units 1, 2, 3, 4 themselves can determine that there is clearly an incorrect assignment (as two radar units cannot be in the same position), or the processing unit 10 can so notice.