Background The road network is an important part of the infrastructure in today society with regard to the transportation of people and goods, and the maintenance of the roadways is an important factor for the practicability and traffic safety. This is perhaps most accentuated in countries with a winter climate where snowfall and ice formation rapidly can cause varying conditions on the roadway and on the whole a fairly large organisation is involved in road maintenance. In other types of climate or due to occasional phenomena related to weather or to other causes similar varying road conditions can occur, for example due to condensed moisture, sand coating or oil slippage.

In Sweden the road maintenance is for the most part controlled on the basis of information from stationary weather stations that are located along the roads. Dependent on current weather and other factors, for example traffic intensity, a maintenance manager decides whether the roadway shall be plowed, scraped, salted or sanded, or whether some other measure should be taken. The perhaps most decisive factor for the practicability and traffic safety, except direct blocking of the roadway, is the available friction between the surface of the roadway and vehicle wheels. Therefore a great deal of the road maintenance is about plowing, sweeping or distributing some substance over the roadway in order to increase the available friction.

Today, plowing, salting, sanding and the like is mainly carried out in predetermined routes along certain road sections, typically between two places or road junctions, where in principle the same measure is carried out along the whole section without any particular adaptation to the actual conditions. This results in a certain overconsumption of for example sand, salt and fuel, which in its turn affects not only the direct consumption costs but also leads to an increased wear on the road and an increased corrosion on the vehicles as well as an unnecessary load on the environment.

There is therefore a need for improving the prerequisites for road maintenance, and a part of such an improvement is to be able to determine the actual available friction on the roadways.

Prior Art There are different examples of prior art for measuring and determining the friction on a road surface. The following prior art is incorporated by reference into this application with regard to description of carrying out per se known apparatus and methods that can be comprised in embodiments of the invention.

In the scientific article"Slip-based Tire-Road Friction Estimation", Automatica, Vol. 33 No. 6, pp. 1087-1099, 1997, by Fredrik Gustafsson, there is disclosed a theoretic background and an application with computation of wheel slippage based on signals from standard sensors in a car. In this piece of prior art there is shown how to construct an algorithm that can estimate the available friction between a road surface and a two wheel drive vehicle.

An example of similar ideas however applied on braking vehicles are disclosed in the publication"Slip-based tire-road friction estimation during braking"by Steffen Muller, Michael Uchanski, and Karl Hedrick (2001 ASME International Engineering Congress and Exposition).

In the patent publication EP 1 097 850 A2 there is disclosed an apparatus for estimating road friction status of a wheel in relation to a road surface. This prior art makes use of frequency analysis of wheel velocity signals taken from wheel velocity sensors in a vehicle.

The patent publication US2002007661 discloses computation of road friction by comparing a yaw rate of a vehicle with a reference value for the yaw rate at a high friction according to a model for the movement of the vehicle. A weighting function is used for computing a resulting road friction coefficient, wherein account is taken of a parameter for the degree of hardness of the road which has been produced in a road hardness detector.

In the patent publication EP 1 132 271 there is disclosed an apparatus for determining the condition of a road surface based on the rotational velocity of four vehicle wheels. A slip relation between the wheels and a relation between the slip relation and acceleration/retardation is computed. A friction coefficient is computed based on the gradient of the latter relation.

The patent publication US 2001/0044688 discloses an apparatus and a method for detecting deviations of a vehicle sensor. The apparatus is provided with a device for detecting the degree of adhesion of a wheel in relation to a road surface.

However, none of this prior art discloses any support for road maintenance.

Problem to be Solved by the Invention The overall problem to be solved by the invention is to achieve a system for collecting road status information, preferably for supporting the control of road maintenance.

There are inter alia the following aspects of the overall problem, namely to: - Improve planning and selection of appropriate measure on a specific road surface; - Improve road conditions; - Improve traffic safety; - Save consumption of surface treatment material being distributed on the roads; Decrease the load on the environment due to distribution of surface treatment material; Decrease the risk for corrosion on vehicles.

Summary of the Invention The indicated problem is solved by providing a system for collecting road status information as a support for the control of road maintenance based on collected measurements of the road friction. The system according to the invention is devised to dynamically compile road status information based on measured values of parameters that affect the road status and that are collected by vehicles that traffic the roads of current interest. In different embodiments collecting of measured values and possible processing of measured data is carried out from ordinary vehicles, from road maintenance vehicles such as snow plow trucks or salt trucks, or from specialised measuring vehicles. Advantageously, collected measured data, or processed or computed road status information is communicated to a central system.

A variety of the invention is realised by installing road friction measurement systems in common vehicles, which measurement systems repeatedly report current road status information to the central system. Further processing and coordination of road status information can be carried out in the central system and be used by a road maintenance organisation as an alternative or a complement to stationary weather stations. An advantage is that up to date information is collected from a larger number of vehicles that traffic the roads, and thus cover more roads and areas than the stationary weather stations. More data comes from road sections that have an intensive traffic, and there are many redundant sensors. The information is further improved when it is coupled to a position determining system such as a navigation system or a route planning system. This enables that road maintenance measures can be planned in an optimized manner inter alia with regard to working hours, machine resources, fuel consumption, exhausts and road treatment material, and thereby allow for improved traffic safety, economy and environment.

In a further development of this variety it can also be arranged that vehicles exchange road status information, for example when meeting other vehicles or in connection with calls, an information service or broadcasting. An advantage with an information service is that revenues from it could be used for financing such investments in infrastructure that would be required for a large scale implementation of the invention.

In another variety of the invention road friction measurement systems are installed in road maintenance vehicles such that they automatically or as support systems for manual control adapts measures locally and directly dependent on the actually occurring conditions, preferably taking account of weather information from the stationary weather stations and/or in combination with the aforementioned variety.

Certain aspects of the invention are directed to procedures for monitoring changes in friction conditions and for, in interaction with a driver of a vehicle equipped with the invention, carrying out estimations of friction conditions, for example on specific road sections.

The invention enables the control of road maintenance with a more dynamic road keeping strategy that meets the different problem aspects stated above.

Brief Description of the Drawings The invention is further explained with reference to the enclosed drawings, in which: Fig 1 shows a schematic overview of an exemplifying embodiment of the invention with a vehicle devised with means for collecting and transmitting road status information ; Fig 2 shows schematically a separate measuring wheel device for mounting on a vehicle.

Detailed Description of Embodiments Fig 1 shows a schematic overview of an embodiment of the invention with a vehicle 100 with wheels 101, whereof at least some wheel is provided with wheel velocity sensors 102 in a per se known manner. The wheel velocity sensors 102 can advantageously be already existing sensors belonging to the vehicle standard system for e. g. speed measurement or an automatic braking system. The wheel velocity sensors 102, which preferably deliver measurement signals in a sampled format alternatively let the signals pass a not shown analogue/digital converter, are coupled to a collecting unit 104 devised for collecting and storing of measured values. The collecting unit 104 is in its turn communicatively coupled to a computation unit 106, that comprises a data processor (CPU), data storage, I/O units and

computer program code with program code portions devised to control the data processor. The computation unit 106 is devised to compute road status information that is derivable from or dependent on the wheel velocity. In particular, it is herewith appropriate to implement computations for determining available or actual friction between road surface and the tires of the wheels in accordance with some of the methods and apparatus that are described in the publications listed in the Prior Art section above. There may also be a classification mechanism that classifies road status in a number of larger steps dependent on predetermined rules or threshold values.

In the embodiment according to Fig 1 the computation unit is provided with an output 110 for outputting computed road status information or a control signal. In the case with an output a control signal via the output 110 the computation unit 106 is devised to compute or generate a control signal that for example can be coupled to a distribution mechanism for a surface treatment substance such as salt or sand. The distribution of the surface treatment substance is activated dependent on predetermined values for available road friction.

The computation unit 106 in fig 1 is further coupled to a display or some other presentation unit 112 for presentation of processed road status information for a driver of e. g. a road maintenance vehicle or some other vehicle. In the road maintenance vehicle measures can thereby be adapted automatically or interactively with the driver locally and directly dependent on currently prevailing conditions. The driver can for example manually control the distribution of surface treatment substance dependent on the presented road status information, e. g. in different intervals of available road friction. The road friction should preferably be calibrated with regard to the vehicle or the mechanism that is used in measuring friction, such that computed road status information is adapted to the condition that prevails for vehicles in traffic.

The collecting unit 104 is in one embodiment also coupled to a position determination apparatus 108, for example a navigation system, a route planning system, GPS or GSM-based positioning. Preferably, every measured value, series of measured values or computed road status information is stored together with a position indication. In a similar manner another embodiment receives other input data 113 in the shape of second parameters or information that is relevant for the road status, for example from other sensors such as humidity or temperature, or other information from weather stations. Also this other input data 113 is preferably stored together with a measured value or computed road status information for example in a time or position dependent manner. In this way more complex road status parameters are generated for local processing and forwarding to central or local receiving units.

The collecting unit 104 and/or the computation unit 106 are coupled to a telecommunications unit 114 devised for transmitting road status information to a similar receiving telecommunications unit 118 via radio frequency transmission. It is expedient to use a radio frequency transmission according to some current standard for telecommunication, for example GSM, GPRS or similar. The receiving telecommunications unit 118 could be placed in a second vehicle with equipment corresponding to the above described equipment in a first vehicle. Information exchange can for example occur when meeting the other vehicle, through broadcasting, at calls or according to some other scheme. The transmitted information has a varying degree of refinement in different embodiments of the invention, and can for example be in the shape of raw measured data directly from the collecting unit 104 or more processed road status information from the computation unit 106. In the case with transmission of more or less raw measured data from the collecting unit computation is carried out based on this data in a system coupled to the receiving unit.

In a preferred embodiment of the invention road status information is transmitted to a telecommunications unit 118 of a central system 117 for collecting and processing road status information. The central system 117 further comprises a data processing unit 120 with a data processor (CPU), data storage and I/O units that are coupled to or incorporates a database 122 for storing road status information and a user interface 124 for presentation of road status information and input of control commands. In the central system 117 road status information is collected from a plurality of vehicles. In an advantageous embodiment this system is used for controlling road maintenance, and a road maintenance manager can with the aid of this dynamically incoming information plan moves and measures. Communication back to the vehicles can also be carried out via the central system, for example in terms of messages to drivers, control signals, road status information and the like. In an embodiment of the system where a larger number of vehicles more or less by standard is equipped with a device for collecting and centrally reporting road status information, this road status information can be coordinated and in a processed format be transmitted to vehicles that traffic a certain road section. Moreover, this dynamically reported and thereby current information can be used for planning road maintenance as an alternative or a complement to stationary weather stations.

Fig 2 shows an embodiment of a measuring wheel device 201 for collecting measured values according to the invention and devised to be attached to a vehicle. The measuring wheel device comprises a wheel 202 suspended on an arm 206 arranged at an attachment device 208 intended to be mounted on the vehicle. A wheel velocity sensor 204 delivers a measured signal or measured values of a wheel velocity dependent parameter to an

output 210 that can be a terminal for outputting a signal or data values. Electronic equipment according to the above description is couplable to the output 210, or is alternatively coupled to and to selectable degrees integrated with the measuring wheel device. The attachment device 208 can comprise a mechanism for lowering or springing the wheel onto the road surface. There is preferably a braking mechanism devised to brake the wheel with a preset or settable braking effect that gives a negative slip, such that a calibrated measurement of the available friction can be achieved.

An embodiment of the invention comprises a plurality of modes for collecting measured values and for computing friction. In a preferred variety friction determination is carried out in connection with : 1. Normal driving. When determining friction during the mode for normal driving, measured values are collected from wheel velocity sensors and the friction is computed for example according to the relations described in the article"Slip-based Tire-Road Friction Estimation", Automatica, Vol. 33, No. 6, pp. 1087-1099, 1997, by Fredrik Gustafsson, that is mentioned in the section Prior Art above.

2. Braking with an Automatic Braking System (ABS). When determining friction during the mode for braking with an ABS, the friction is computed by means of specific relations that are dependent on parameters that are derived from signals from sensors of the automatic braking system.

3. Slip during automatic traction control with an automatic traction control system. When determining friction during the mode for driving with a slip during automatic traction control, the friction is computed by means of specific relations that are dependent on parameters that are derived from signals from sensors of the automatic traction control system.

In a further development of this embodiment there is comprised a mechanism for monitoring and detecting changes in a friction dependent parameter, preferably the so called slip- slope (slip gradient). When detecting a change that exceeds a predetermined threshold signal, a control signal that in different embodiments is used for different functions is generated and delivered. Preferably it is arranged such that the driver in response to a detected change in the slip-slope is passed a message with a request or a command to make a braking or a slipping manoeuvre in order to enable collection of measured values and determination of friction also in a braking and a slipping mode, respectively. Preferably a fast filter is used that in response to measurement during different modes by means of driver manoeuvres gives a plurality of resolution levels in friction determinations. For example, the invention can according to this embodiment be realised according to the following steps:

0. Initiate an estimation k0 of the slip-slope and store the time t 0.

1. Estimate the change in slip-slope kdelta adaptively, for example in accordance with the above mentioned article.

2. If t-t_0 > h_t or t k (t)-k | > hk, where ht and hk are predetermined threshold values => then command test braking and/or test slipping. The driver shall then follow a certain procedure during which the time is measured and friction parameters are computed. The procedure can for example be designed such that the driver slows down the speed and makes a test braking from 72km/h = 20 m/s to 36 km/h =10 m/s and the time t is measured. The friction mumax turns in this example out to be 1/t.

3. Set t_0=t and set the current slip-slope k0=k, monitor changes in the slip-slope in relation to said predetermined threshold values. Store or transmit the friction mumax.

A variety of the invention is designed with a procedure for achieving good slip- slope estimations with the aid of a driver. An embodiment of this procedure comprises the following steps: 1) The driver drives out on a surface to be examined, for example a string of slush, and operates a switch to initiate the inventive device that is provided with a filter for estimating the slip-slope.

2) The driver excites the system for example by means of a start command or by manoeuvring a switch for starting.

3) The device computes for example a least square estimation of the slip-slopes and the driver is informed by a signal (for example a signal lamp or a sound signal) when an accurate estimation has been obtained, alternatively the driver manoeuvres a switch for stopping the estimation when the measuring shall be terminated, for example if the surface is changed or if it for some other reason not ought to continue.

4a) Possibly, the steps 1-3 can be combined with the procedure for monitoring a change in the slip-slope above.

4b) Possibly the steps 1-4a can be combined with a test braking/spinning and an accurate calibration table is dynamically generated, for example with 4 levels of resolution.

The computations of the slip-slope estimations and friction values can within the scope of the invention be carried out in different per se known manners and with different per se known computation algorithms.

The invention has been explained and described by means of exemplifying embodiments, but it can be realised in a number different ways within the scope of the enclosed claims.