CONTROLLER AND METHOD FOR GENERATION OF STEERING OVERLAY SIGNAL

Aspects of the disclosure relate to a control system and a method for controlling generation of a steering wheel overlay signal to control positioning of a host vehicle. The control system is configured to receive a curvature of a lane of travel. The control system is configured to determine a position of the host vehicle in relation to at least one boundary of the lane of travel; and determine a minimum clearance between the host vehicle and the at least one boundary in dependence based at least in part on the curvature of the lane of travel. If the host vehicle is determined to be closer to the at least one boundary than the minimum clearance, a steering intervention is implemented and the control system generates a steering wheel overlay signal for maintaining the host vehicle within the lane of travel.

TECHNICAL FIELD

The present disclosure relates to the generation of a steering overlay signal. Aspects of the invention relate to a control system for generating a steering overlay signal, to a method for generating a steering overlay signal, to a vehicle, to computer software and a non-transitory computer-readable medium.

BACKGROUND

It is known to provide a vehicle, such as an automobile, with a lane keep assist system. Current lane keep assist systems trigger a steering intervention to bring the driver back to a lane if the vehicle approaches a lane boundary. However, the natural driving position of the vehicle in the lane may vary depending on road conditions. This may cause the triggering of undesired steering interventions, causing inconvenience to the driver.

It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a control system, a control system, a vehicle, a method, computer software and a non-transitory computer-readable medium as claimed in the appended claims.

According to an aspect of the present invention there is provided a control system for controlling generation of a steering wheel overlay signal to control positioning of a host vehicle, the control system comprising one or more controller. The control system is configured to: receive a curvature of a lane of travel; determine a position of the host vehicle in relation to at least one boundary of the lane of travel; determine intervention criteria for the position of the host vehicle in dependence on the curvature of the lane of travel; and generate a steering wheel overlay signal for maintaining the host vehicle within the lane of travel in dependence on the position of the host vehicle meeting the intervention criteria. The intervention criteria may be a position in the lane of travel or a range of positions in the lane of travel. Advantageously, the condition for generating the steering wheel overlay signal may be varied depending on the curvature of the road, thereby allowing different attentive driving behaviour on curved roads to be accounted for and reducing unwanted steering interventions.

According to another aspect of the present invention there is provided a control system for controlling generation of a steering wheel overlay signal to control positioning of a host vehicle, the control system comprising one or more controller. The control system is configured to: receive a curvature of a lane of travel; determine a position of the host vehicle in relation to at least one boundary of the lane of travel; determine a minimum clearance between the host vehicle and the at least one boundary in dependence on the curvature of the lane of travel; and generate a steering wheel overlay signal for maintaining the host vehicle within the lane of travel in dependence on the position of the host vehicle being determined to be closer to the at least one boundary than the minimum clearance. Advantageously, the vehicle may be able to travel closer to the lane boundary without generation of the steering wheel overlay signal depending on the curvature of the road. thereby allowing different attentive driving behaviour on curved roads to be accounted for and reducing unwanted steering interventions.

Optionally, the control system may be configured to determine the curvature of the lane of travel in dependence on image data and/or sensor data of an environment of the vehicle. Optionally, the curvature may be obtained from digital map data indicative of the environment of the vehicle.

According to some embodiments, the control system is configured to determine the minimum clearance such that it is reduced in dependence on the curvature of the lane of travel increasing. The curvature of the lane of travel is defined such that a higher curvature corresponds to a tighter curve. Beneficially, reducing the minimum clearance as the curvature increases allows the host vehicle to follow the lane boundary more closely for tighter curves, which may feel more comfortable for the user, without triggering an unwanted steering intervention.

Optionally, the control system is configured to determine a first boundary and a second boundary of the lane of travel. The first boundary and the second boundary may define opposing sides of the lane of travel. For a road having a non-zero curvature, i.e. a non-straight road, the first boundary may be an inner boundary of the lane of travel and the second boundary may be an outer boundary of the lane of travel. The inner boundary defines the boundary of the lane of travel closest to the center of curvature about which the lane is curved. The outer boundary defines the boundary of the lane of travel farther from the center of curvature. The control system may be configured to determine a first minimum clearance relative to the outer boundary and a second minimum clearance relative to the inner boundary, wherein the first minimum clearance is greater than the second minimum clearance. Advantageously, a driver  of the vehicle may be able to keep the vehicle closer to the inner boundary of the curve whilst taking a corner without triggering a steering intervention, which may feel more natural for the driver. A larger first minimum clearance is determined for the outer boundary, such that a steering intervention may be triggered earlier if a driver drifts to the outer boundary of the curve to ensure that the steering intervention is still triggered appropriately if the driver is inattentive.

In some embodiments, the control system is configured to determine the or each minimum clearance in dependence on a lateral velocity of the host vehicle within the lane of travel. That is, if the control system determines a first and a second minimum clearance, the control system may be configured to determine each of the first minimum clearance and the second minimum clearance in dependence on the lateral velocity of the host vehicle. Advantageously, the lateral velocity of the vehicle may be an indication of an attentiveness of a driver and thus the minimum clearance(s) for triggering a steering intervention may be appropriately adjusted.

The control system may configured to determine the or each minimum clearance such that the or each minimum clearance is increased in dependence on the lateral velocity of the host vehicle increasing. Beneficially, this allows sufficient time for the steering overlay signal to be implemented to avoid the host vehicle departing from the lane of travel.

In some embodiments, the control system is configured to determine the or each minimum clearance using a data structure storing lateral velocity values and corresponding minimum clearance values. The data structure may in some embodiments be a look up table. The data structure may be stored in a data storage means accessible to the control system. Optionally, the data structure may store for each lateral velocity value or range a corresponding first minimum clearance value and second minimum clearance value for the outer and inner lane boundaries respectively.

Optionally, the control system is configured to select a first data structure if the curvature exceeds a predetermined threshold, and a second data structure if the curvature does not exceed the predetermined threshold. That is, the control system may use a first look up table if the lane of travel is classified as straight and a second look up table if the lane of travel is classified as curved. The control system may classify the lane as curved if the curvature exceeds the predetermined threshold and classify the lane as straight if the curvature does not exceed the predetermined threshold. Advantageously, curvature specific minimum clearance(s) may be readily obtained by looking up the lateral velocity of the vehicle in the relevant look up table.

Optionally, the control system may be configured to select a third data structure if curvature exceeds a second higher predetermined threshold. Advantageously, the minimum clearance(s) may be readily further tailored to account for straight lanes, slightly curved lanes and very curved lanes.

The control system may be configured to control generation of the steering wheel overlay signal to steer the host vehicle toward a predetermined distance from the at least one boundary. Optionally, the predetermined distance corresponds to at least the minimum clearance for the at least one boundary. Optionally, the control system is configured to remove the steering wheel overlay signal in dependence on the host vehicle being at least the predetermined distance from the at least one boundary. Advantageously, following the intervention the vehicle is left in a position at which a further intervention will not be triggered.

In some embodiments, the control system is configured to determine the or each boundary of the lane of travel by identifying a road marking or a road edge. Advantageously, both demarcated lanes and physical edges may be detected.

According to a further aspect, there is provided a vehicle comprising a control system as described above.

According to another aspect of the invention, there is provided a method for controlling generation of a steering wheel overlay signal to control positioning of a host vehicle, the method comprising: receiving a curvature of a lane of travel; determining a position of the host vehicle in relation to at least one boundary of the lane of travel; determining a minimum clearance between the host vehicle and the at least one boundary in dependence on the curvature of the lane of travel; and generating a steering wheel overlay signal for maintaining the host vehicle within the lane of travel in dependence on the position of the host vehicle being determined to be closer to the at least one boundary than the minimum clearance.

According to another aspect of the invention, there is provided a non-transitory computer-readable medium having a set of instructions stored therein which, when executed, cause a processor to perform the method as described above.

According to another aspect of the invention, there is provided software that, when executed, is arranged to perform the method above. A method as claimed in claim12, comprising determining the minimum clearance such that it is reduced in dependence on the curvature of the lane of travel increasing.

Optionally, the method may comprise:determining an inner boundary of the lane of travel and an outer boundary of the lane of travel; anddetermining a first minimum clearance relative to the outer boundary and a second minimum clearance relative to the inner boundary;wherein the first minimum clearance is greater than the second minimum clearance.

Optionally, the method may comprise determining the or each minimum clearance in dependence on a lateral velocity of the host vehicle within the lane of travel.

Optionally, the method may comprise determining the or each minimum clearance such that the or each minimum clearance is increased in dependence on the lateral velocity of the host vehicle increasing.

Optionally, the method may comprise determining the or each minimum clearance using a data structure storing lateral velocity values and corresponding minimum clearance values.

Optionally, the method may comprise selecting a first data structure if the curvature exceeds a predetermined threshold, and a second data structure if the curvature does not exceed the predetermined threshold.

Optionally, the method may comprise controlling generation of the steering wheel overlay signal to steer the host vehicle toward a predetermined distance from the at least one boundary.

Optionally, the method may comprise removing the steering wheel overlay signal in dependence on the host vehicle being at least the predetermined distance from the at least one boundary.

Optionally, the method may comprise determining the or each boundary of the lane of travel by identifying a road marking or a road edge.

DETAILED DESCRIPTION

A control system1in accordance with an embodiment of the present invention will now be described with reference to the accompanying figures. The control system1is installed in a vehicle2, referred to herein as a host vehicle2. The host vehicle2in the present embodiment is an automobile, such as a wheeled vehicle, but it will be understood that the control system1may be used in other types of land vehicle. The host vehicle2is described herein with reference to a reference frame comprising a longitudinal axis X, a transverse axis Y and a vertical axis Z. The host vehicle2has a longitudinal centreline CL extending along the longitudinal axis X.

As illustrated inFIG.1, the host vehicle2comprises four (4) wheels W1-4. The wheels W1-4are provided on front and rear axles3,4. As illustrated inFIG.1, the first and second wheels W1, W2provided on the front axle3are steerable to control a direction of travel of the host vehicle2. A driver-operated steering wheel5is provided for controlling a steering angle α of the first and second wheels W1, W2is provided on the front axle3.

A power assist steering system6is provided to generate a steering assist torque STQ-PA to supplement a steering torque applied to the steering wheel5by the driver. The power assist steering system6comprises a power assist steering controller7; a torque sensor (not shown) for sensing the steering torque applied by the driver to the steering wheel5; and a power assist steering actuator8for generating the steering assist torque STQ-PA. In the present embodiment, the power assist steering system6is an electric power assist steering system (EPAS) comprising an electromechanical actuator operable to generate the steering assist torque. Other types of power assist steering actuator7may be used, such as a hydraulic actuator.

The control system1comprises a lane departure warning system9for identifying when the host vehicle2is departing or about to depart the host vehicle lane of travel LT-n (i.e. the current lane in which the host vehicle2is travelling). As described herein, the lane departure warning system9is also suitable for identifying when the host vehicle2is approaching or traversing a physical limit or a boundary of the road R on which the host vehicle2is travelling. The physical limit or boundary of the road R is referred to herein as a road edge RE. The lane departure warning system9is configured to output a lane departure signal SLD upon determining that the host vehicle2is departing or at risk of departing the host-vehicle lane of travel LT-n or approaching or traversing the road edge RE. A detailed description of how it is determined that the host vehicle2is departing or at risk of departing the host vehicle lane of travel LT-n will be provided with reference toFIGS.5to7B.

The power assist steering system6is configured to implement a lane keep assist (LKA) function for maintaining or returning the host vehicle2to the lane of travel LT-n. The control system1is configured to control the power assist steering system6to generate a lane assist steering overlay STQ-LD in dependence on the lane departure signal SLD. The lane assist steering overlay STQ-LD in the present embodiment comprises or consists of a lane assist steering torque STQ-LD. The lane assist steering torque STQ-LD is applied as a steering wheel torque overlay to the steering assist torque STQ-PA generated by the power assist steering system6. The lane assist steering torque STQ-LD acts to steer the host vehicle2to return to the lane of travel LT-n or avoid departing from the lane of travel LT-n.

Further to maintaining or returning the host vehicle2in the lane of travel, the control system1may be configured to continue the intervention to steer the host vehicle to a target position in the lane of travel LT. The lane departure warning system9is configured to output an intra-lane signal SLA comprising a target position and/or target trajectory αTof the host vehicle2in the host-vehicle lane of travel LT. The control system1is then configured to control the power assist steering system6to generate an intra-lane steering signal STQ-LA in dependence on the intra-lane signal SLD. The intra-lane steering signal STQ-LA in the present embodiment comprises or consists of an intra-lane steering torque STQ-LA. The steering torque request may comprise a torque request direction (+ve or −ve) and optionally also a torque request magnitude.

The lane departure warning system9comprises a sensor unit10and may comprise an image processing module11. The sensor unit10in the present embodiment comprises an optical camera having a field of view extending forwards in front of the host vehicle2. The sensor unit10may comprise one or more optical cameras, for example a stereo camera. Alternatively, or in addition, the lane departure warning system9may utilise other types of sensor, such as a radar system or a LIDAR system, to capture a representation of a region in front of the host vehicle2. The sensor unit10in the present embodiment is located behind a rear-view mirror (not shown) provided at the top of the front windshield. Other mounting locations are possible, for example the sensor unit10may be provided behind or in a front grille of the host vehicle2. The lane departure warning system9may optionally receive inputs from one or more vehicle systems, for example to determine if the driver has activated side indicators to signal an intended change the lane of travel LT-n. The lane departure warning system9may be configured to inhibit output of the lane departure signal SLD, for example if the driver activates the directional (side) indicators. The image processing module11receives image data captured by the sensor unit10. The image data is processed to identify features of the road R on which the host vehicle2is travelling. The image data is also processed to detect the road edge RE, for example by identifying a transition or boundary between a road surface which may be relatively smooth (for example defined by asphalt, concrete or other surfacing material) and an adjacent surface which may be relatively rough (for example composed of one or more of the following: grass, mud, gravel, sand and snow). According to some embodiments the image data may be processed to determine a curvature of the lane of travel LT-n.

As illustrated inFIG.2, the power assist steering system6is operable to implement a steering overlay intervention responsive to the determination that the host vehicle2is departing or at risk of departing the host vehicle lane of travel LT-n. The steering overlay intervention comprises a sequence of the lane keep assist function and the intra-lane function.

In use, the power assist steering system6may be controlled to generate a lane assist steering torque STQ-LD when the lane departure warning system9determines that the host vehicle2is departing or at risk of departing a lane of travel LT-n. The power assist steering system6may then be controlled to generate an intra-lane steering torque STQ-LA to be applied after the lane assist steering torque STQ-LD. The intra-lane steering torque STQ-LA may, for example, be applied in dependence on a determination that the host vehicle2has returned to the host-vehicle lane of travel LT-n.

The lane assist steering torque STQ-LD and the intra-lane steering torque STQ-LA are transmitted to the steering wheel5to provide a haptic signal to the driver of the host vehicle2. The lane assist steering torque STQ-LD and the intra-lane steering torque STQ-LA are output to the steering wheel5in an appropriate direction to maintain the host vehicle2in the host-vehicle lane of travel LT-n. The magnitude of the lane assist steering torque STQ-LD and the intra-lane steering torque STQ-LA are controlled such that, if necessary, the driver can override the lane assist steering torque STQ-LD or the intra-lane steering torque STQ-LA, as will be described. The lane assist steering torque STQ-LD and the intra-lane steering torque STQ-LA may, for example, each have a maximum value of 3 Nm although other maximum values may be selected as appropriate.

The control system1can be implemented when the host vehicle2is travelling on a road R having one or more lanes of travel LT-n. By way of example, a first road section R-A is shown inFIG.3A; and a second road section R-B is shown inFIG.3B.

The first and second road sections R-A, R-B can form part of the same road R or may be separate roads R. The first road section R-A is a two-lane road (also known as a “two-lane highway”) having first and second lanes of travel LT-1, LT-2for vehicles travelling in respective first and second directions. The second road section R-B consists of a multiple-lane road (also known as a “multiple-lane highway”) having a two or more lane of travel LT-n for vehicles travelling in the same direction. It will be understood that the present invention is not limited to operation on roads having the features illustrated in the first and second road sections R-A, R-B. The first and second road sections R-A, R-B each comprise first and second road edges RE-1, RE-2. In the illustrated example, the first and second road edges RE-1, RE-2mark the lateral extent of the metalled road surface. It will be understood that one or both of the first and second road edges RE-1, RE-2may comprise a barrier or partition member, for example separating lanes of a dual carriageway (also known as a “divided highway”). The first and  second road sections R-A, R-B may also comprise road markings (denoted herein generally by the reference numeral14). The first road section R-A has road markings14comprising a central road marking15. As shown inFIG.3B, the central road marking15comprises a centre line of the second road section R-B. The road markings14on the second road section R-B comprise one or more lane markings16-nrepresenting a boundary of a lane of travel LT-n for vehicles travelling in the same direction or in opposite directions. The one or more lane markings16-nmay comprise lane lines. In the illustrated arrangement, the second road section R-B comprises first and second lane markings16-1,16-2for demarcating first, second and third lanes of travel LT-1, LT-2, LT-3. The central road marking15and/or the one or more lane marking(s)16-nmay each comprise a continuous line (not shown) or an interrupted line (shown inFIGS.3A and3B). The road marking(s)14may each comprise one line or multiple lines, for example in the form of a single line or a double line. The central road marking15typically differentiates between sections of the first or second road section R-A, R-B intended for travel in opposite directions. Alternatively, or in addition, the road marking(s)14may comprise edge lines to indicate an edge of an inboard lane; the edge lines may be separated from the associated first or second road edge RE-1, RE-2. The first road section R-A shown inFIG.3Aincludes central road markings15and lane markings defining a plurality of lanes of travel LT-n.

The lane departure warning system9is operable to monitor the image data captured by the sensor unit10at least substantially in real time. The image processing module11analyses the image data to identify the first road edge RE-1and/or the second road edge RE-2. The image processing module11may, for example, identify changes in the contrast and/or colour of the image data which may be indicative of the first and/or second road edge RE-1, RE-2. Other image processing techniques may be used to identify the first and second road edges RE-1, RE-2. The image processing module11is configured also to identify any road markings14present on the road R. The image processing module11may, for example, utilise image processing techniques to identify continuous or interrupted lines extending in a forward direction (i.e. parallel to the centre line CL of the host vehicle2). The image processing module11is configured to identify the central road markings15and the lane markings16. If road markings14are identified, the image processing module11identifies the lane of travel LT-n in which the host vehicle2is currently travelling (referred to herein as the host-vehicle lane of travel LT-n). According to some embodiments, the image processing module11may identify a curvature of the lane of travel LT-n.

The image processing module11is configured to determine a principal axis PD of the lane of travel LT-n in which the host vehicle2is currently travelling. The principal axis  PD represents a principal direction of travel for vehicles travelling in the lane of travel LT-n. The principal axis PD may be determined in dependence on one or more of the following: the first road edge RE-1, the second road edge RE-2, and the road marking(s)14. The principal axis PD may, for example, be identified as a direction extending substantially parallel to the road edge RE-n, a central road marking15or a lane marking16. The principal axis PD may be identified as a direction extending substantially parallel to a boundary of the lane of the travel LT-n which is closest to the host vehicle2, for example closest to the centre line CL of the host vehicle2). Alternatively, or in addition, the principal axis PD may be determined with reference to two or more features identified in the image data. For example, the principal axis PD may be determined as corresponding to a virtual centreline extending between a first road edge RE-1and a central road marking15; or a virtual centreline extending between first and second lane markings16-1,16-2. Alternatively, the principal axis PD may be offset from and extend parallel to a virtual centreline of the road R or the lane of travel LT-n. The image processing module11may optionally determine a centreline of the or each lane of travel LT-n. Alternatively, or in addition, the principal axis PD may be predefined, for example in map data.

The lane departure warning system9identifies the road marking14or road edge RE-1, RE-2closest to the longitudinal centreline CL of the host vehicle2. If the host vehicle2approaches or crosses the identified road marking14or road edge RE-1, RE-2, the lane departure warning system9determines that the host vehicle2is departing from the host-vehicle lane of travel LT-n. The lane departure warning system9then outputs the lane departure signal SLD. The lane departure signal SLD includes an indication of whether the host vehicle2is traversing the lane markings or road edge on a right-hand side or a left-hand side of the host vehicle2. The power assist steering system6receives the lane departure signal SLD and is operable to generate the lane assist steering torque STQ-LD in a direction suitable for maintaining the host vehicle2in the host-vehicale land of travel LT-n.

Following application of the lane assist steering torque STQ-LD, the lane departure warning system9may output the intra-lane signal SLA. The power assist steering system6may then be controlled to generate the intra-lane steering torque STQ-LA to control the host vehicle2to a target position within the lane of travel LT-n (i.e. at a target lane position).

The intra-lane steering torque STQ-LA can be generated as a separate control function which is implemented upon completion of the lane assist steering torque STQ-LD, for example as a continuation of this function. In a variant, the intra-lane steering torque STQ-LA may be integrated into the lane assist steering torque STQ-LD.

The intra-lane steering torque STQ-LA may be generated to position the host vehicle2at least a predetermined distance D1from a boundary of the lane of travel LT-n. The predetermined distance D1may be defined relative to the centreline CL of the host vehicle2or relative to the side of the host vehicle2closest to the identified boundary. The boundary may, for example, correspond to the first or second road edge RE-1, RE-2or a road marking14. By way of example, the predetermined distance D1is shown in relation to a first road edge RE-1in the scenario illustrated inFIG.4. Alternatively, the control system1may generate the intra-lane steering torque STQ-LA to position the host vehicle2centrally within the lane of travel LT-n. The intra-lane steering torque STQ-LA may be configured to position the host vehicle2at a mid-point between the first and second lane markings16-1,16-2which define opposing sides of the lane of travel LT-n.

At least in certain embodiments, this may facilitate the transition to the scenario in which the host vehicle2is controlled exclusively by the driver. The intra-lane function is implemented by a steering wheel torque overlay comprising an intra-lane steering torque STQ-LA applied to the steering assist torque STQ-PA. In the arrangement illustrated inFIG.2, the control system1is configured to generate the intra-lane steering torque STQ-LA following application of the lane assist steering torque STQ-LD. The intra-lane steering torque STQ-LA is generated to control the host vehicle2at least substantially to position the host vehicle2at a predefined position within the lane of travel LT-n. In the present embodiment, the intra-lane steering torque STQ-LA is also generated to control the host vehicle2at least substantially to align a trajectory a (or orientation) of the host vehicle2with a target trajectory αT. A target position and a target orientation for the host vehicle2are represented inFIG.4by a dashed (phantom) representation of the host vehicle2. The target trajectory αTin the present embodiment is substantially parallel to the principal axis PD of the lane of travel LT-n. The intra-lane steering torque STQ-LA is transmitted to the steering wheel5and provides a haptic signal to the driver. The intra-lane steering torque STQ-LA is output to the steering wheel5in an appropriate direction to control the trajectory a of the host vehicle2at least substantially to match the target trajectory αT. The intra-lane steering torque STQ-LA is generated in dependence on a comparison of a current trajectory a of the host vehicle2in relation to the principal axis PD.

To facilitate the transition to the host vehicle2being controlled by the driver, the control system1is configured to reduce or remove the magnitude of the intra-lane steering torque STQ-LA such that the steering wheel overlay is eventually removed. The condition for removal of the intra-lane steering torque STQ-LA may be such that the trajectory of the host  vehicle is substantially close to the target trajectory αT, the position of the host vehicle is substantially close to the target position, or a lateral velocity of the vehicle is below a threshold such that the host vehicle is travelling substantially parallel in the lane of travel.

The above described steering overlay intervention is triggered when the control system1determines that the host vehicle is departing or at risk of departing the lane of travel LT-n. The host vehicle is determined to be at risk of departing the lane of travel LT-n if the distance between the host vehicle2and the identified boundary15is below a minimum clearance400. An example minimum clearance400is illustrated inFIG.4.

The minimum clearance400may defined as a distance from the boundary15, for example 30 cm. Alternatively, the minimum clearance400may be defined as a proportion of a width of the lane of travel LT-n, i.e. within the rightmost or leftmost 10% of the width of the lane. It will be appreciated that these values are merely illustrative.

An appropriate minimum clearance400may be determined as the vehicle is travelling and may vary in dependence on vehicle parameters and/or lane parameters. In particular, the minimum clearance400may be determined by the control system1in dependence on a curvature of the lane of travel LT-n.

With reference toFIG.5, the curvature of the lane of travel LT-n is indicative of how sharply the vehicle must turn to stay within the lane of travel LT-n. A higher curvature is indicative of a sharper bend. The curvature may be defined in relation to a radius R of an arc carved by the principal axis PD of the lane LT-n or by either boundary15, RE-1of the lane LT-n.

FIG.5illustrates a lane of travel LT-n having a first straight portion510and a second curved portion520. That is, the curvature of the lane of travel LT-n changes as the vehicle proceeds along the road. The curvature of the straight portion510may be considered substantially close to zero. The curvature of the curved portion520may be considered non-zero and may be quantified as some function of the radius R of the principal axis PD. For example, the curvature may be quantified as an inverse of the radius R, however other formulations may be envisaged in the invention is not limited in this respect. The minimum clearance400for the purpose of triggering a steering overlay intervention may be determined in dependence on the curvature of the lane of travel LT-n.

A method100of generating a steering wheel overlay signal to implement a steering overlay intervention is illustrated inFIG.6A. In particular, the method100is performed by the control system1to determine whether to trigger a steering overlay intervention.

The method100comprises a block110of receiving an indication of a curvature of the lane of travel LT-n of the host vehicle2. The curvature may be determined by the image processing module11in dependence on the identified lane LT-n in the image data. Alternatively, the curvature may be determined from map data indicative of the lane of travel LT-n. The map data may be stored in a memory accessible to the control system1and may comprise an indication of the curvature of each segment of the lane of travel LT-n.

The method100comprises a block120of determining a position of the host vehicle in relation to at least one boundary of the lane of travel. Block120may comprise identifying the or each boundary15, RE-1of the lane LT-n in dependence on image data of the host vehicle environment, as has been explained. Block120may then comprise determining a distance between the host vehicle and the or each boundary15, RE-1.

The method100comprises a block130of determining a minimum clearance between the host vehicle and the identified boundary in dependence on the curvature of the lane of travel LT-n. If a first boundary15and a second boundary RE-1are each identified, block130may comprise determining one minimum clearance applicable to each boundary, or a separate first minimum clearance for the first boundary15and a second minimum clearance for the second boundary RE-1.

A more detailed illustration of block130according to an embodiment is illustrated inFIG.6B.

The block130comprises a step132of determining whether the curvature of the lane of travel LT-n is above a curvature threshold. The curvature threshold may be predetermined. For example, the curvature threshold may correspond to a lane of travel with radius of curvature between 800-1500 m. As an illustrative example, the curvature threshold may be a curvature value corresponding to a radius of 1000 m. The curvature of the lane of travel LT-n may be determined to exceed the curvature threshold if the radius of the lane of travel LT-n is less than 1000 m. These curvature threshold values are merely illustrative, and it will be appreciated that the curvature threshold may be set to any appropriate level of curvature. If the curvature of the lane of travel LT-n is below the curvature threshold, the lane of travel LT-n may be classified as a straight lane. If the curvature of the lane of travel LT -n is above the curvature threshold, the lane of travel LT-n may be classified as a curved lane. For example, the lane of travel LT-n illustrated inFIG.5may be classified as straight during the first portion510and curved during the second portion520. The curvature of the lane of travel LT-n may therefore vary from portion to portion depending on where the host vehicle2is located.

According to some embodiments, it may be determined whether the curvature of the lane of travel LT-n is above a second higher curvature threshold. If the curvature of the lane of travel LT-n exceeds a second higher curvature threshold, the lane of travel may be classified as being highly curved. In these embodiments, step132may thus comprise classifying a portion of the lane of travel LT-n as straight, curved or highly curved.

If the curvature of the lane of travel LT-n is below the curvature threshold, in step134the control system1retrieves a first data structure. In some embodiments, the first data structure is a first look up table. The first look up table comprises at least one minimum clearance value applicable to a straight road.

The first look up table may comprise a plurality of minimum clearance values. The plurality of minimum clearance values may each be associated with a lateral velocity or range of lateral velocities of the host vehicle2. In particular, the minimum clearance values in the first look up table may increase with increasing lateral velocity of the host vehicle2, to ensure sufficient time for the power assist steering system6to implement the lane assist steering torque STQ-LD to maintain or return the host vehicle to the lane of travel LT-n. An example first look up table according to one embodiment is illustrated below:

Lateral velocity of vehicle (m/s)Minimum clearance (cm)0-0.100.1-0.200.2-0.3100.3-0.4150.4-0.5150.5-0.6200.6-0.725

If the curvature of the lane of travel LT-n is above the curvature threshold, in step136the control system1retrieves a second data structure. In some embodiments, the second data structure is a second look up table. The second look up table comprises at least one minimum clearance value applicable to a curved road.

Step136may comprise determining whether the or each identified boundary is an inner boundary or an outer boundary of the lane of travel LT-n. In the example illustrated inFIG.5, the inner boundary of the lane of travel LT-n is the road edge RE-1. The outer boundary of the lane of travel LT-n is the central road marking15. The inner boundary of the  lane of travel LT-n may be defined to be the boundary closest to a centre about which the lane is curved.

The second look up table may comprise a first portion for determining a first minimum clearance relative to the outer boundary15and a second portion for determining a second minimum clearance relative to the inner boundary RE-1. The first minimum clearance may be referred to as an outer minimum clearance, and the second minimum clearance may be referred to as an inner minimum clearance.

The first portion may comprise a plurality of outer minimum clearance values. The plurality of outer minimum clearance values may each be associated with a lateral velocity or range of lateral velocities of the host vehicle. The second portion may comprise a plurality of inner minimum clearance values. The plurality of inner minimum clearance values may each be associated with a lateral velocity or range of lateral velocities of the host vehicle.

In particular, the outer minimum clearance values may increase with increasing lateral velocity of the host vehicle. Optionally, the inner minimum clearance values relative to the inner boundary may also vary with increasing lateral velocity of the host vehicle, but in some embodiments the inner minimum clearance values may be uniform. In general, the inner minimum clearance values are reduced with respect to the outer minimum clearance values, to allow the driver to remain closer to the inside of the curve or overshoot the line as this may feel more natural to the driver. Furthermore, the inner minimum clearance values are reduced with respect to the minimum clearance values of the first look up table. Thus, on curved roads the driver may drive closer to an inner boundary of the curve compared to the same boundary on a straight portion without triggering a steering intervention.

An example second look up table according to one embodiment is illustrated below:

An illustrative example of minimum clearance values according to an embodiment is shown inFIGS.7A and7B. The illustrated minimum clearance values may be for a consistent lateral velocity of the host vehicle2.FIG.7Aindicates an example minimum clearance710applicable to each boundary15, RE-1on a straight portion510of the lane of travel LT-n. The minimum clearance710is applicable to each boundary15, RE-1.

FIG.7Billustrates an example outer minimum clearance720applicable to an outer boundary15of a curved portion720of the lane LT-n, and an inner minimum clearance730applicable to an inner boundary RE-1of a curved portion720of the lane LT-n.

In step138, the control system is configured to look up an applicable minimum clearance for the host vehicle2in the appropriate look up table. The applicable minimum clearance may vary depending on the identified boundary and the lateral velocity of the host vehicle, as illustrated by the above look up tables. Step138may comprise determining the lateral velocity of the host vehicle in the lane of travel. The lateral velocity of the host vehicle may be defined as a rate of change of the distance between the host vehicle2and the identified boundary. If the first look up table is used, step138may then comprise looking up an applicable minimum clearance for the host vehicle2. If the second look up table is used, step138may then comprise looking up an applicable outer minimum clearance for the outer boundary and/or an inner minimum clearance for the inner boundary of the lane of travel. Step138may comprise retrieving both values, or just the value for the boundary closest to the host vehicle2.

For example, in the illustrated embodiment ofFIG.7B, step132may comprise determining that the curvature exceeds a curvature threshold, and the method will proceed to step136. In step136, the second look up table is retrieved. In step138, it is determined that the lateral velocity is 0.1 m/s and the identified boundary RE-1is an inner boundary of the curve. Thus, the applicable inner minimum clearance value in the second look up table may be determined to be 0 cm. Thus, the steering intervention will only be triggered if the host vehicle2begins to traverse the boundary RE-1.

It will be appreciated that in some embodiments, the first look up table and second look up table may be replaced with another suitable data structure accessible to the control system1. In particular, they may be integrated into one larger data structure such as a relational database.

In block140of the method100, it is determined whether the position of the host vehicle is closer to the identified boundary than the applicable minimum clearance. If the host vehicle is closer to the identified boundary, the method proceeds to block150. In block150the  control system is configured to implement a steering overlay intervention by generating a steering wheel overlay signal for maintaining the host vehicle within the lane of travel. A detailed description of the steering overlay intervention will be omitted here, but any suitable steering overlay intervention such as that described with reference toFIG.2may be caused to be implemented by the steering wheel overlay signal.

With reference toFIG.8, there is illustrated a simplified example of a control system1such as may be adapted to implement the method described herein. The control system1comprises one or more controllers20and is configured to control generation of a steering wheel overlay signal to control steering of a host vehicle2. The control system1includes one or more controllers20and is configured to receive a curvature of a lane of travel LT-n. The control system1determines a position of the host vehicle in relation to at least one boundary15, RE-1of the lane of travel LT-n. The control system1determines a minimum clearance between the host vehicle and the at least one boundary in dependence on the curvature of the lane of travel LT-n. The control system1generates a steering wheel overlay signal for maintaining the host vehicle within the lane of travel in dependence on the position of the host vehicle being determined to be closer to the at least one boundary than the minimum clearance.

It is to be understood that the or each controller20can comprise a control unit or computational device having one or more electronic processors (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.), and may comprise a single control unit or computational device, or alternatively different functions of the or each controller20may be embodied in, or hosted in, different control units or computational devices. As used herein, the term “controller,” “control unit,” or “computational device” will be understood to include a single controller, control unit, or computational device, and a plurality of controllers, control units, or computational devices collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause the controller20to implement the control techniques described herein (including some or all of the functionality required for the method described herein). The set of instructions could be embedded in said one or more electronic processors of the controller20; or alternatively, the set of instructions could be provided as software to be executed in the controller20. A first controller or control unit may be implemented in software run on one or more processors. One or more other controllers or control units may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller or control unit. Other arrangements are also useful.

In the example illustrated inFIG.8, the or each controller20comprises at least one electronic processor21having one or more electrical input(s)22for receiving one or more input signals SLD, SLA, and one or more electrical output(s)23for outputting one or more output signals SOUT1. The or each controller20further comprises at least one memory device24electrically coupled to the at least one electronic processor21and having instructions25stored therein. The at least one electronic processor21is configured to access the at least one memory device24and execute the instructions25thereon.

The, or each, electronic processor21may comprise any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) that is configured to execute electronic instructions. The, or each, electronic memory device24may comprise any suitable memory device and may store a variety of data, information, threshold value(s), lookup tables or other data structures, and/or instructions therein or thereon. In an embodiment, the memory device24has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon that may govern all or part of the methodology described herein. The processor, or each, electronic processor21may access the memory device24and execute and/or use that or those instructions and information to carry out or perform some or all of the functionality and methodology describe herein.

The at least one memory device24may comprise a computer-readable storage medium (e.g. a non-transitory or non-transient storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational devices, including, without limitation: a magnetic storage medium (e.g. floppy diskette); optical storage medium (e.g. CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g. EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

Example controllers20have been described comprising at least one electronic processor21configured to execute electronic instructions stored within at least one memory device24, which when executed causes the electronic processor(s)21to carry out the method as hereinbefore described. However, it is contemplated that the present invention is not limited to being implemented by way of programmable processing devices, and that at least some of, and in some embodiments all of, the functionality and or method steps of the present invention may equally be implemented by way of non-programmable hardware, such as by way of non-programmable ASIC, Boolean logic circuitry, etc.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.