Method and system for handling conditions of a road on which a vehicle travels

A method performed by a vehicle system for handling conditions of a road on which a vehicle travels. The vehicle system detect that a first part of the road has a first condition which is different from a second condition of a second part of the road. The vehicle system estimates friction of the first part and evaluates the estimated friction. The vehicle system determines that the vehicle's motion should be adjusted when a result of the evaluation indicates that the estimated friction of the first part of the road affects the vehicle's expected motion, and initiates adjustment of the vehicle's motion on the road as determined.

CROSS-REFERENCE TO RELATED APPLICATION

The present patent application/patent claims the benefit of priority of co-pending European Patent Application No. 18163844.6, filed on Mar. 26, 2018, and entitled “METHOD AND SYSTEM FOR HANDLING CONDITIONS OF A ROAD ON WHICH A VEHICLE TRAVELS,” the contents of which are incorporated in full by reference herein.

TECHNICAL FIELD

Embodiments herein relate generally to a vehicle system, a method performed by the vehicle system and a vehicle comprising the vehicle system. More particularly the embodiments herein relate to handling conditions of a road on which a vehicle travels.

BACKGROUND ART

Vehicles need to drive safely, also considering challenging use cases related to tire-to-road friction. This is important for manual, semi-autonomous and fully autonomous vehicles. Driving safely in treacherous road friction conditions is challenging for both human and automated drivers.

A road condition may be treacherous when the friction characteristics are different in different parts of the roadway. Tracks and patches are examples of road conditions which may be treacherous

Tracks may be for example wet lane markings, wheel tracks in snow, water filled tracks, thick piles of snow between wheel tracks, tracks filled with water, loose gravel outside wheel tracks (especially in spring time), dirt road with loose gravel outside the wheel tracks. In these track conditions, there is a difference in road friction depending on where the vehicle is positioned laterally on the road.

Examples of patches may be for example spilled oil, ice or sand in the road intersection only etc. In patch conditions, there is a difference in road friction depending on where the vehicle is positioned laterally and longitudinally on the road.

These conditions often lead to longer stopping distances, slower take-off from a stationary mode, and stability problems. The latter is prominently in case of different friction between the left and right sides of the vehicle, i.e. split-mu, and is exaggerated if the vehicle has a degraded brake system, e.g. two-wheel braking only.

Therefore, there is a need to at least mitigate or solve these issues.

SUMMARY

An objective of embodiments herein is therefore to obviate at least one of the above disadvantages and to provide improved handling of conditions of the road on which a vehicle travels.

According to a first aspect, the object is achieved by a method performed by a vehicle system for handling conditions of a road on which a vehicle travels. The vehicle system detects that a first part of the road has a first condition which is different from a second condition of a second part of the road. The vehicle system estimates friction of the first part, and evaluates the estimated friction. The vehicle system determines that the vehicle's motion should be adjusted based on that a result of the evaluation indicates that the estimated friction of the first part of the road affects the vehicle's expected motion. The vehicle system initiates adjustment of the vehicle's motion on the road as determined.

According to a second aspect, the object is achieved by a vehicle system for handling vehicle feature information. The vehicle system is adapted to detect that a first part of the road has a first condition which is different from a second condition of a second part of the road. The vehicle system is adapted to estimate friction of the first part, and to evaluate the estimated friction. The vehicle system is adapted to determine that the vehicle's motion should be adjusted based on that a result of the evaluation indicates that the estimated friction of the first part of the road affects the vehicle's expected motion. The vehicle system is adapted to initiate adjustment of the vehicle's motion on the road as determined.

According to a third aspect, the object is achieved by a vehicle comprising the vehicle system.

Since the result of the evaluation indicates that the estimated friction of the first part of the road affects the vehicle's expected motion, the adjustment of the vehicle's motion can be initiated so improved handling of conditions of the road on which a vehicle travels is obtained, for example by obtaining appropriate driving strategies and detection for treacherous road condition.

Embodiments herein afford many advantages, of which a non-exhaustive list of examples follows:

An advantage of the embodiments herein is that it is possible to avoid planning backup or evasive manoeuvres where there is a risk for the vehicle's tires to come into contact with tracks of lower friction during a long time period.

Another advantage of the embodiments herein is that safety is improved since the vehicle's motion can be adjusted so that it avoids positioning the vehicle at the road part which has low friction. This also makes the vehicle easier to steer.

The embodiments herein are not limited to the features and advantages mentioned above. A person skilled in the art will recognize additional features and advantages upon reading the following detailed description.

The drawings are not necessarily to scale and the dimensions of certain features may have been exaggerated for the sake of clarity. Emphasis is instead placed upon illustrating the principle of the embodiments herein.

DESCRIPTION OF EMBODIMENTS

The embodiments herein relate to detecting treacherous road friction conditions and to providing safe strategies for driving under such conditions.

FIG. 1is a schematic drawing illustrating a vehicle100located on a road. The vehicle100may be any arbitrary vehicle, for instance a car, truck, lorry, van, bus, motorcycle etc. The vehicle100may be at least partly autonomous or self-driven, it may be completely autonomous or self-driven, or it may be non-autonomous, i.e. manual etc. The vehicle100may be standing still or it may be moving with a velocity and in a direction.

The road may be for example a highway, a city street, a gravel road etc. The road surface may be of asphalt, concrete, gravel, cobble stone, bricks, etc. The road may have one, two or more lanes. InFIG. 1, the road is exemplified with two lanes which are separated by a longitudinal road marking. The longitudinal direction is in a y-direction as illustrated in the coordinate system inFIG. 1, the y-direction is also direction in which the vehicle100travels. A lateral direction is the x-direction indicated in the coordinate system.

The vehicle100comprises an image capturing device103. The image capturing device103is adapted to capture images of at least the outdoor surroundings of the vehicle100, e.g. the road. The image capturing device103may be a camera, a radar, a lidar, etc. The image capturing device is exemplified inFIG. 1to be positioned at the front of the vehicle100, e.g. at the bumper. However, any other suitable position may be applicable in which the image capturing device103is able to capture images of the surroundings of the vehicle100. The image capturing device103may be a front-looking device capturing images of the surroundings ahead of the vehicle100, the image capturing device103may be a front and side-ways looking device capturing images of the surroundings ahead and on the side of the vehicle100etc.

As seen inFIG. 1, the road comprises at least one first part105and at least one second part108. The first part105of the road has a first condition which is different from a second condition108of the second part of the road. The first part105is illustrated with dotted filling inFIG. 1, and the second part108is illustrated with blank filling. The first part105may be tracks or patches, as defined earlier. InFIG. 1, the first part105is exemplified as snow between the wheel tracks. The second part108is exemplified as being a clean road surface not being covered by snow. The road with the first and second parts105having different friction characteristics may be referred to as a split-mu road.

FIG. 2illustrates examples of other types of the first part105. Reference number105aillustrates an example where the first part105is ice, reference number105billustrates an example where the first part105is gravel outside the wheel tracks, reference number105cillustrates an example where the first part105is spilled oil and reference number105dillustrates an example where the first part105is thick piles of snow between wheel tracks. Note that these are only examples of first parts105, and that any other types of first parts105are equally applicable.

FIG. 3illustrates a method performed by a vehicle system for handling conditions of a road on which the vehicle100travels. The vehicle100may comprise at least one brake on each lateral side of the vehicle100. The vehicle system may be comprised in the vehicle100, or the vehicle system may be an external vehicle system adapted to communicate with the vehicle100. The vehicle100may be a non-autonomous vehicle, a partly autonomous vehicle or a fully autonomous vehicle. The method comprises at least one of the following steps, which steps may be performed in any suitable order than described below:

The vehicle system detects that the first part105of the road has a first condition which is different from a second condition108of a second part of the road. The first part105may have a lower friction than the second part108. The first condition may be at least one of: patches and tracks. The detection may be done in different ways.

For example, the detection may be performed based on at least one image of the road obtained by an image capturing device103comprised in the vehicle100. Thus, the detection may be visual detection, i.e. detection of different visual characteristics between the first and second parts105,108. The image capturing device103may obtain one image or it may obtain two or more images over time.

In another example, the detection may be performed based on obtained measurements from a friction sensor associated with at least one of the vehicle's wheels.

The vehicle system estimates friction of the first part105. The estimation may be performed based on the detection in step301. The vehicle system may also estimate the friction of the second part108.

The term split-mu may be used in association a road having a first and second part105,108with different conditions, i.e. friction characteristics. Split-mu may also be referred to as split friction, and refers to a road condition that occurs when the friction differs between the first and second parts105,108of the road.

In one example where the first part105is a road marking, the friction may be estimated by using the measured reflectivity of road markings over time. New road markings may be detected by measuring their reflectivity in absolute numbers overtime, i.e. compare with previous measurement to detect differences. Wet road markings are much more slippery when they are new due to lots of glass beads on the marking surface.

In another example, the first part105is a thick pile of snow between wheel tracks and the second part108is a part without snow, i.e. the first and second parts105,108have different visual characteristics. In such example, images captured by the image capturing device103may be used to detect tracks and/or patches with different visual characteristics. The vehicle motion may be actively controlled to estimate friction in the detected tracks and/or patches. This may be coordinated using a fleet of vehicles to build a map over tracks and patches, which will be described in more detail in step308below.

The friction may be estimated by obtaining friction data from a friction sensor, for example comprised in at least one wheel of the vehicle100.

The vehicle system evaluates the estimated friction. The result of the evaluation may indicate that the estimated friction is associated with that the first condition is a treacherous condition. A treacherous condition may be a condition that has a lower friction than the second part108, and a treacherous condition affects the vehicle's expected motion when the vehicle100is located at the first part105having the treacherous condition. Using other words, the estimated friction of the first part105may lead to that the vehicle100deviates from its planned, normal or desired vehicle trajectory. The road may affect the vehicle's expected motion for example in that it is difficult to steer the vehicle100due to the low friction due to e.g. ice.

The vehicle system determines that the vehicle's motion should be adjusted when the result of the evaluation indicates that the estimated friction of the first part105of the road affects the vehicle's expected motion. The expected motion is a motion that has been previously determined. The motion to be adjusted is the future motion of the vehicle100which it should have when taking the first part into account, instead of the expected motion.

The vehicle system may determine the vehicle's adjusted motion. Using other words, determining how the vehicle's motion should be adjusted, i.e. an adjusted trajectory. Thus, the road condition information may be applied for vehicle navigation.

The adjusted motion may be such that vehicle100is avoided to be located at the first part105of the road which is considered to have treacherous road friction conditions. The adjusted motion may be such that the vehicle100avoids backup/evasive manoeuvres where there is a risk for the vehicle's tires to come into contact with a first part105having a lower friction during a long time period, and/or the adjusted motion may be such that the manoeuvre is kept on the side of the tracks or the racks are put between the wheels. If this is not possible, the motion may be adjusted by reducing the vehicle's speed to manage longer stopping distance etc. It may also comprise to adjust the vehicle's lateral position when the first part105is detected to find a second part108with higher friction. The adjusted motion may prevent the vehicle100from stopping on the first part105to ensure maximum grip when taking off. It may further comprise to plan straight trajectories when crossing a first part105, e.g. thick piles of snow between wheel tracks, with very low friction. Steering when passing the first part105will most likely not be possible or risk causing instability.

The vehicle's motion may be adjusted so that the activated brakes are on the opposite side compared to the first part105of the road.

The vehicle's motion may be adjusted by adjusting at least one of: the vehicle's lateral position, the vehicle's longitudinal position and the vehicle's speed.

Initiating adjustment of the vehicle's motion may also involve determining a trajectory which the vehicle100should follow in order to avoid being located in the first part105of the road.

As mentioned earlier, the vehicle100may comprise at least one brake on each side of the vehicle100. The side may be a lateral or longitudinal side. The vehicle system may determine on which side the vehicle's wheel brakes should be activated. The side may be for example right or left side, front or rear side etc.

For example, the activated brake should be for at least one wheel which is located on the same side as the high friction road part when differential braking is used to steer the vehicle100. Consequently, the brakes on the opposite or other side should not be activated, or activated with an activation magnitude that is smaller than for the high friction part. The brakes of the wheels located on the high friction road part may be activated with a first magnitude and the brakes of the wheels located on a low friction side may be activated with a second magnitude. The first magnitude may be larger than the second magnitude.

This may also be referred to as split-mu braking and may be described as the vehicle100brakes on the road with a left-right asymmetrical friction coefficient. As an example, the split-mu road comprises a first part105being a strip of ice on one side of the road, and a second part108being dry asphalt on the other side of the road. A heavy braking on the brakes on both sides of a road having a split-mu surface may cause the vehicle100to skid or spin or lose the steering control. However, step306, only activates the brakes on one side to avoid skid, spinning or losing the steering.

Below are some examples of combinations of brakes that may be activated:

Activated brakesNot activated brakesFront left brakeFront right brake, rear right brakeand rear left brakeFront right brakeFront left brake, rear right brakeand rear left brakeFront left brake and front rightRear left brake and rear rightbrakebrakeRear right brake and rear leftFront right brake and front leftbrakebrakeFront left brake and rear leftFront right brake and rear rightbrakebrakeFront right brake and rear rightFront left brake and rear leftbrakebrakeFront right brake and rear leftFront left brake and rear rightbrakebrakeFront left brake and rear rightFront right brake and rear leftbrakebrake

The vehicle system initiates adjustment of the vehicle's motion on the road as determined. The initiating may involve sending instructions to the vehicle's control system to start adjusting the motion, it may involve providing instructions to a user of the vehicle100to manually start adjusting the motion etc. As a consequence of step306, the vehicle's motion is adjusted, manually or automatically. The motion may be adjusted by for example keeping the maneuver on the side of the tracks or maneuver the vehicle100so that the racks are located between the wheels. If this is not possible, the speed may for example be reduced to manage longer stopping distance.

The vehicle system may create a map of a plurality of roads indicating the first parts105which has friction that affects the vehicle's expected motion. Thus, the vehicle system may create a map over tracks and patches of different kinds. The map may be accessible by the vehicle100, it may be accessible by two or more vehicles100. The map may be visible to the user of the vehicle100e.g. on a display unit associated with the vehicle100. The map may be accessible by a cloud computer adapted to distribute the map to a plurality of vehicles100.

The vehicle system may provide, to two or more vehicles100, information indicating that the first part105is associated with the estimated friction that affects the vehicle's expected motion. Consequently, the lateral and/or longitudinal position of one or several vehicles100may be adjusted to avoid the treacherous first part105, and to also collectively estimate the friction in and out of tracks.

The embodiments herein may be used for manual or autonomous driving of the vehicle100, e.g. fully-autonomous driving or supervised automation, e.g. pilot assist. The embodiments herein may also be used in several active safety and user assistance features. For example, the embodiments herein may be used in automatic recovery from split-mu surfaces, using knowledge on where to steer to get back on a high-mu surface. Prevention of loss of control on a first part105, either by longitudinal/lateral assistance to avoid entering the first part105or by assisting the user of the vehicle100to keep the vehicle100on a straight path while passing a low mu surface. Automatic speed reduction before entering a first part exemplified as a low mu surface to prevent loss of control, e.g. aqua planning on high speed roads. The embodiments herein may also be applied in collision avoidance systems using path planning for combined braking and steering to stay away from a first part105being exemplified with a low mu surfaces to prevent more collisions with other vehicles on the road.

The embodiments herein are not limited to the above described embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the embodiments, which is defined by the appending claims. A feature from one embodiment may be combined with one or more features of any other embodiment.

It should be emphasized that the term comprises/comprising when used in this specification is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. It should also be noted that the words “a” or “an” preceding an element do not exclude the presence of a plurality of such elements. The terms “consisting of” or “consisting essentially of” may be used instead of the term comprising.

The term “adapted to” used herein may also be referred to as “arranged to”, “configured to”, “capable of” or “operative to”.

It should also be emphasised that the steps of the methods defined in the appended claims may, without departing from the embodiments herein, be performed in another order than the order in which they appear in the claims.