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Title:
MEASURING ANGULAR INFORMATION BY INERTIAL UNIT ARRANGED TO WHEEL
Document Type and Number:
WIPO Patent Application WO/2015/049418
Kind Code:
A1
Abstract:
There is provided a method and corresponding apparatus, stability control system and a computer program product, including an inertial unit for being attached to a wheel of a vehicle, said inertial unit arranged to detect directions at plane defined by circumference of the wheel for providing angular information and a controller coupled to the inertial unit for processing the angular information. Angular information measured (904) and a steering operation of the vehicle is determined (906) on the basis of the measurement results of the angular information.

Inventors:
COLLIN, Jussi (Riitiäläntie 361, Akaa, FI-37830, FI)
Application Number:
FI2014/050744
Publication Date:
April 09, 2015
Filing Date:
September 30, 2014
Export Citation:
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Assignee:
JC INERTIAL OY (Riitiäläntie 361, Akaa, FI-37830, FI)
International Classes:
B60W30/00; B60Q1/34; G01B7/30; G01C19/00; G01P15/14
Domestic Patent References:
WO2008112667A12008-09-18
Foreign References:
US20090099730A12009-04-16
US20050060069A12005-03-17
EP2641816A12013-09-25
US20090177346A12009-07-09
Attorney, Agent or Firm:
KOLSTER OY AB (P.O. Box 148, Helsinki, Helsinki, FI-00121, FI)
Download PDF:
Claims:
Claims

1 . A method by an apparatus comprising an inertial unit for being attached to a wheel of a vehicle, said inertial unit arranged to detect directions in a plane defined by circumference of the wheel for providing angular information and a controller coupled to the inertial unit for processing the angular information, characterized in that the method comprising:

measuring (904), by the inertial unit, angular information in two perpendicular directions on the plane in a coordinate system of the wheel;

transforming the measurement results of the angular information in two perpendicular directions in the coordinate system of the wheel into the vehicle's coordinate system;

determining (906) a steering operation into a steering direction and a centripetal acceleration of the vehicle on the basis of the measurement results of the angular information transformed into the coordinate system of the vehicle.

2. A method according to claim 1 , wherein the apparatus comprises an indicator coupled to the controller, wherein the indicator is for emitting a signal indicating a steering operation of the vehicle to a steering direction, wherein the method comprises:

defining a threshold for the measured angular information corresponding to the steering direction of the vehicle;

determining when the angular information meets the threshold; and set (912) the indicator, when the threshold is met.

3. A method according to claim 2, wherein the apparatus comprises a plurality of indicators corresponding to a plurality of steering directions.

4. A method according to claim 3, wherein each of the indicators is associated with a steering direction and a threshold for the measured angular information, and the method comprises:

defining a first setting for the indicators, when a threshold for the angular information is met; and

defining a second setting for indicators, when a threshold for the angular information is not met; and setting (912) the indicators according to the first setting and the second setting on the basis of the measured angular information.

5. A method according to any one of claims 1 to 4, wherein the indicator comprises an illuminator, for example a lamp, light emitting diode, or a radio frequency transmitter, said radio frequency transmitter being preferable a directional radio frequency transmitter.

6. A method according to any one of the claims 2 to 5, wherein the indicator is arranged to emit a signal outwards from the wheel.

7. A method according to any one of the claims 1 to 6, comprising: measuring (904) centripetal acceleration for the wheel for determining (908) wear of the wheel.

8. A method according to any one of the claims 1 to 7, comprising: defining centripetal acceleration for the vehicle on the basis of the measured angular information; and determining lateral sliding of the vehicle on the basis the centripetal acceleration.

9. A method according to any one of the claims 1 to 8, comprising: determining (904) centripetal acceleration for the wheel on the basis of the angular information; measuring (904) the centripetal acceleration over time; and determining (908) wear of the wheel on the basis of the measurements of the centripetal acceleration.

10. A method according to any one of the claims 1 to 9, comprising: obtaining data on a tilting angle of the wheel and/or

obtaining data on rotations, obtaining data on a tilting angle of the wheel and

obtaining data on angular information, and

processing the data by using the tilting angle and/or the detected rotations for at least one coordinate system transformation and by using rotation of the wheel for compensating gyroscope bias for compensating inaccuracy of the angular information.

1 1 . A method according to claim 10, wherein the at least one coordinate system transformation is carried out by using at least one direction cosine matrix. 12. A method according to claim 1 1 , wherein the direction cosine matrix is estimated by normalizing accelerometer readings or by using data obtained by the at least one gyroscope.

13. A method according to any preceding claim 10 to 12, wherein an angle of phase difference, covered distance and/or covered distance in a predetermined period of time are estimated by the data processing.

14. A method according to any preceding claim 10 to 13, wherein the data processing comprises updating location information of the vehicle by using change in covered distance in a predetermined period of time in relation to selected axes transferred to a selected coordinate system.

15. A method according to any preceding claim 10 to 14, wherein a moment of completing a full rotation is estimated or detected and data with regard to one rotation is gathered from the at least one gyroscope.

16. A method according to any preceding claim 10 to 15, wherein the method comprises vehicle positioning using the coordinate system transformation.

17. A method according to any preceding claim 10 to 16, wherein the angular information is obtained by a gyroscope arranged to detect directions in a coordinate system arranged at the rim level of the wheel. 18. A method according to any preceding claim 10 to 17, wherein the at least one coordinate system transformation is carried out on the basis of the angular information and tilting angle and/or the detected rotations.

19. A method according to any one of claims 10 to 18, wherein full 360° rotations of the wheel are detected for compensating the gyroscope bias.

20. An apparatus (200) comprising an inertial unit (202, 204, 206) for being attached to a wheel of a vehicle, said inertial unit arranged to detect directions in a plane defined by circumference of the wheel for providing angular information for positioning, and a controller (210) coupled to the inertial unit (202, 204, 206) for processing the angular information, characterized in that the apparatus comprises means to perform the step of any one of the claims 1 to 19.

21 . An apparatus (200) according to claim 20, wherein the inertial unit (202, 204, 206) comprises: at least one acceleration sensor (202) and/or at least one magnetometer arranged to detect a tilting angle of the wheel, and/or

at least one counter device arranged to detect rotations of the wheel, and

at least one gyroscope (204) arranged to detect directions at a rim level of the wheel for providing angular information for positioning.

22. A stability control system for a vehicle comprising one or more wheels characterized in that the stability control system further comprises an apparatus (200) according to any one of claims 20 to 21 attached to the one or more wheels, wherein the stability control system is connected to the apparatuses for obtaining information, for example angular information, information on wear of the wheel and/or information on lateral sliding, for determining a steering operation of the vehicle, a centripetal acceleration of the vehicle and/or a wear of the wheel on the basis of the obtained information.

23. A computer program product comprising executable code that when executed, cause execution of functions of a method according to any one of claims 1 to 19.

Description:
Measuring Angular Information by Inertial Unit Arranged to Wheel

Field

The invention relates to detecting directions at a wheel and more particularly to detecting directions by an inertial unit arranged to the wheel. Background

The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.

An inertial unit is an electronic device that measures and reports on a craft's velocity, orientation, and gravitational forces, using a combination of accelerometers and gyroscopes, sometimes also magnetometers. Inertial units are typically used to maneuver aircraft, including unmanned aerial vehicles (UAVs), among many others, and spacecraft, including satellites and landers. Recent developments allow for the production of inertial unit-enabled Global Positioning System, GPS, devices. The inertial unit-enabled GPS allows uninterrupted position service when GPS-signals are unavailable, such as in tunnels, inside buildings, or when electronic interference is present.

The inertial unit is the main component of inertial navigation systems used in aircraft, spacecraft, watercraft, and guided missiles among others. In this capacity, the data collected from the inertial unit's sensors allows a computer to track a craft's position, using a method known as dead reckoning.

Industrial vehicles such as vehicles used in mines and harbors are in many applications used to carry heavy loads. Accidents, where such vehicles take part, are therefore likely to involve a risk of serious damage to nearby property and personnel. This risk is increased by limited visibility in the environment the vehicles are used. For example, the visibility may be blocked by container stacks or mist. On the other hand also poor lighting may increase the risk of accidents.

Typically, risks for any damages are mitigated by simply limiting access to areas, where the vehicles are operated. With limited access to the operating area of the vehicles, the vehicles may be driven with higher speeds. However, the higher speeds of the vehicles increase the scale of damage, when accidents should happen.

Brief description

According to an aspect of the present invention there is provided an apparatus, a computer program product, a stability control system and a method as defined in the accompanying independent claims.

According to an aspect of the present invention, there is provided a method by an apparatus comprising an inertial unit for being attached to a wheel of a vehicle, said inertial unit arranged to detect directions at plane defined by circumference of the wheel for providing angular information and a controller coupled to the inertial unit for processing the angular information, wherein the method comprises, measuring angular information, determining a steering operation of the vehicle on the basis of the measurement results of the angular information.

According to an aspect of the present invention, there is provided an apparatus comprising an inertial unit for being attached to a wheel of a vehicle, said inertial unit arranged to detect directions at plane defined by circumference of the wheel for providing angular information, and a controller coupled to the inertial unit for processing the angular information, wherein the apparatus comprises means to perform the steps of a method according to an aspect of the present invention.

According to an aspect of the present invention, there is provided an a stability control system for a vehicle comprising one or more wheels and an apparatus according to aspect of the present invention attached to the one or more wheels, wherein the stability control system is connected to the apparatuses for obtaining information, for example angular information, wheel wear information and/or lateral sliding information.

According to an aspect of the present invention, there is provided an inertial unit for being attached to a rotatable part of a vehicle, the rotatable part being coupled to a power equipment of the vehicle, the inertial unit comprising: at least one acceleration sensor and/or at least one magnetometer arranged to detect a tilting angle of the rotatable part, and/or at least one counter device arranged to detect rotations of the rotatable part, and at least one gyroscope arranged to detect directions at a rim level of the rotatable part for providing angular information for positioning. According to an aspect of the present invention, there is provided an apparatus for being attached to a rotatable part of a vehicle, the rotatable part being coupled to a power equipment of the vehicle, the apparatus comprising: at least one acceleration sensor and/or at least one magnetometer arranged to detect a tilting angle of the rotatable part, and/or at least one counter device arranged to detect rotations of the rotatable part, and at least one gyroscope arranged to detect directions at a rim level of the rotatable part for providing angular information for positioning, and means for processing data, the data comprising the detected tilting angle and/or detected rotations and the angular information, by using the tilting angle and/or the detected rotations for at least one coordinate system transformation and by using rotation of the rotatable part for compensating gyroscope bias for compensating inaccuracy of the angular information.

According to an aspect of the present invention, there is provided a method comprising: obtaining data on a tilting angle of a rotatable part of a vehicle and/or rotations and angular information, and processing the data by using the tilting angle and/or the detected rotations for at least one coordinate system transformation and by using rotation of the rotatable part for compensating gyroscope bias for compensating inaccuracy of the angular information.

According to an aspect of the present invention an apparatus comprises an indicator coupled to the controller, wherein the indicator is for emitting a signal indicating a steering operation of the vehicle to a steering direction, wherein the method according to an aspect of the present invention comprises defining a threshold for the measured angular information corresponding to the steering direction of the vehicle, determining when the angular information meets the threshold, and set the indicator, when the threshold is met.

The indicator may comprise an illuminator, for example a lamp, light emitting diode, or a radio frequency transmitter, said radio frequency transmitter being preferable a directional radio frequency transmitter.

Some aspects provide improvements comprising determining steering direction of the vehicle, when GPS is not available and without human intervention. Some aspects provide improved safety in driving vehicles by setting an indicator when a steering operation, steering direction, lateral sliding and/or wheel wear is determined.

Further aspects will become apparent from the accompanying description.

List of drawings

Some embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which

Figure 1 illustrates an example of an inertial unit;

Figure 2 illustrates an example of an apparatus;

Figure 3 is a flow chart;

Figure 4 illustrates an exemplifying application;

Figure 5 illustrates another exemplifying application;

Figure 6a illustrates an apparatus attached to a wheel, according to an embodiment;

Figure 6b illustrates a plurality of apparatuses attached to a single wheel according to an embodiment;

Figure 7 illustrates a stability control system for a vehicle and wheels in different steering directions of the vehicle according to an embodiment;

Figure 8a illustrates operation of indicators in the steering direction according to an embodiment;

Figure 8b illustrates operation of indicators in the steering direction of the vehicle and operation of indicator not in the steering direction, according to an embodiment;

Figure 9 illustrates a method according to an embodiment;

Figures 10a and 10b illustrate angular information obtained from a wheel. Description of some embodiments

The following embodiments are only examples. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

Acceleration sensors or accelerometers are designed to detect changes in force resulting from fall, tilt, motion, positioning, shock and/or vibration. They may be produced based on MEMS-technology as well. Acceleration sensors or accelerometers are used in positioning applications.

A magnetometer is a measuring device used to measure the strength or direction of magnetic fields. Magnetometers are used in positioning applications.

A gyroscope is a device designed for measuring or maintaining orientation usually by measuring angular rate of turn in relation to a defined axis. Gyroscopes may be manufactured based on several techniques, but micro electrical mechanical system (MEMS) gyroscopes are becoming most popular especially in consumer electronics and other large scale applications and products due to their low manufacturing costs, size and low power consumption. MEMS gyroscopes are typically vibratory gyroscopes. Gyroscopes are used in positioning applications. Gyroscopes implemented by using MEMS-technology are inferior in accuracy to ring laser gyroscopes or interferometric fiber optic gyroscopes, for instance, due to errors caused by bias. Hence, traditional inertial navigation methods based on accurate gyroscopes are typically not suitable as such when MEMS-based inertial units are used, but methods for improving the accuracy are required.

The quality of a MEMS gyroscope is usually defined by the magnitude of a constant additive unpredictable part of bias errors. In positioning applications, the angular rate measurement outputs from one or more MEMS gyroscopes are usually integrated to obtain change in orientation, for example an angle value which expresses the change in the heading of a vehicle. Thus, constant bias errors in angular rate are also integrated into an angle error. The constant part of a bias may be at least partly cancelled by means of carouseling. Carouseling typically involves controlled rotation of the device used for positioning in relation to one or more axes. Additionally, the carouseling needs means to provide a desired angle change. Another method is to make measurements when a vehicle of interest is not moving and then averaging the measurement results to obtain an estimate of the bias. These methods are, however, not advantageous as such in many practical applications due to the time spent and the time variant nature of the behavior of a typical MEMS-gyroscope (it may change every time it is powered up, according to temperature, etc.). It should be appreciated that controlled carouseling also requires additional hardware that may not be cost effective.

In carouseling, to cancel constant bias (at least partly, depends on the required accuracy), a repetitive rotation is usually required and information on the time when a full (360°) revolution circulation is completed. Thus, in vehicle applications, a rotation of a wheel may be utilized: wheels rotate when the vehicle moves and this rotation may be measured by the vehicle itself or using additional sensors. Thus, an apparatus providing information for positioning may be attached to the wheel or tyre or any other rotatable part (such as a pedal or treadle) of a vehicle which part is related to the movement of the vehicle. A vehicle may be any device or means of conveyance which moves by using one or more rotating wheels or tyres, such as a car, truck, trailer truck, lorry, van, tractor, fork-lift, motor bike, cycle, moped, camper, earth-mover, vehicles or machines used in mines or harbours, etc.

Embodiments are suitable for vehicle positioning and navigation purposes for instance when global positioning system (GPS), global navigation satellite system (GNSS) or other corresponding signals are not available.

One embodiment may be carried out by an inertial unit which is attachable to the wheel of a vehicle. The inertial unit is attachable to a rotatable part of a vehicle, the rotatable part being coupled to a power equipment of the vehicle directly or indirectly (indirectly may for instance mean that the rotatable part may be a back wheel, when the vehicle is front-driven). In other words, the rotatable part may be a wheel, tyre, crank arm, etc. Term "power equipment" is used to describe motors, engines, power transmission means, accumulators, drives, bicycle chains, etc. It should be appreciated that a normal steering wheel is usually not suitable for the embodiment (no regular repetitive rotation). One example of an inertial unit is shown in Figure 1 .

The exemplifying inertial unit 100 comprises: at least one acceleration sensor and/or at least one magnetometer arranged to detect a tilting angle of the rotatable part, and/or at least one counter device 102 arranged to detect rotations of the rotatable part, and at least one gyroscope 104 arranged to detect directions at a rim level of the rotatable part for providing angular information for positioning.

Another embodiment is an apparatus which is attachable to a rotatable part of a vehicle, the rotatable part being coupled to a power equipment of the vehicle. In other words, the rotatable part may be a wheel, tyre, pedal or treadle, etc. Term "power equipment" is used to describe motors, engines, power transmission means, accumulators, drives, bicycle chains, etc. It should be appreciated that a normal steering wheel is usually not suitable for the embodiment. One example of an apparatus is depicted in Figure 2.

The exemplifying apparatus 200 comprises: at least one acceleration sensor and/or at least one magnetometer arranged to detect a tilting angle of the rotatable part, and/or at least one counter device 202 arranged to detect rotations of the rotatable part, at least one gyroscope 204 arranged to detect directions at a rim level of the rotatable part for providing angular information for positioning and means 210 for processing data, the data comprising the detected tilting angle and/or detected rotations and the angular information, by using the tilting angle and/or the detected rotations for at least one coordinate system transformation and by using rotation of the rotatable part for compensating gyroscope bias for compensating inaccuracy of the angular information. The means for processing data may be or comprise a processor, chip set, a unit or module comprising a plurality of processors, a computer program product, or a medium comprising a computer program. The medium may be any entity or device capable of carrying the program and it may be a non-transitory medium. Computer programs, also called program products or programs, including software routines, applets and macros, may be stored in any apparatus-readable data storage medium and they include program instructions to perform particular tasks. Computer programs may be coded by a programming language, which may be a high-level programming language, such as objective-C, C, C++, C#, Java, etc., or a low-level programming language, such as a machine language, or an assembler.

An indicator 212 is coupled to the processing means. The connection between the indicator and the processing means may be an electrical connection implemented for example as a galvanic, inductive or capacitive connection. A galvanic connection may be provided by an electrical conductor, for example an electrical wire. The indicator may comprise an illuminator, for example a lamp or a Light Emitting Diode (LED), or a radio frequency transmitter, said radio frequency transmitter being preferably a directional radio frequency transmitter. The indicator has an operating direction, where it emits a signal that indicates a steering operation of the vehicle. Depending on the implementation of the indicator, the emitted signal may comprise visible light or a radio frequency signal. The signal may encode a message. The message may be encoded using modulation techniques known to the skilled person. The message may comprise information comprising positioning information of the vehicle. The positioning information may be provided using a suitable coordinate system, for example the World Geodetic System (WGS) 84 used by the Global Positioning System.

The apparatus may be implemented by various means, for example by hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. A software application may be a computer program designed to carry out required computations, otherwise an inertial unit usually comprises hardware parts alone or in combination with software. The computer program may be stored in a computer readable media, such as magnetic disks, cards, tapes, etc. The required number of acceleration sensor is typically two to provide direction information for trajectory computation.

The apparatus or inertial unit may also comprise means for storing data, such as one or more memory units 106 or 206. The memory units may include volatile and/or non-volatile memory. The memory unit may store computer program code and/or operating systems, information, data, content or the like for the processor to perform operations according to embodiments. Each of the memory units may be a random access memory, hard drive, etc. The memory units may be at least partly removable and/or detachably operationally coupled to the apparatus. The memory may be of any type suitable for the current technical environment and it may be implemented using any suitable data storage technology, such as semiconductor-based technology, flash memory, magnetic and/or optical memory devices. The memory may be fixed or removable.

Additionally, the apparatus or the inertial unit may also comprise means for communicating 108 or 208 with an apparatus configured to process data the inertial unit obtains. The means may be a radio transceiver/transmitter or a radio link (Bluetooth©, Zigbee©, WiFi©, wireless local area network (WLAN), radio frequency identification (RFID), etc.). Another option is to use magnetic coding used in smart card applications, such as credit cards. In this case, the inertial unit may comprise or be coupled to a communication unit, which may encode data and convey it to a processing unit, such as a global positioning (GPS) device, or any other device having suitable data processing facilities. The communication unit may also count rotations of the rotatable part. In this case, if speed is fast enough, it is possible that data obtained by acceleration sensors or magnetometers may not be necessary, but it may be used for improving accuracy. Yet another option is a counter device the examples of which are explained below.

In the following, an embodiment of a method is described in further detail. As a part of the description of the method, some aspects of the inertial unit and/or apparatus are also clarified in relation to data processing, for instance. The exemplifying application of Figure 1 is used for clarification purposes in this regard. Embodiments of the method may be implemented to the appropriate extent in an inertial unit or by an apparatus explained above.

The embodiment starts in block 300 of Figure 3.

In block 302, data on a tilting angle of a rotatable part of a vehicle and/or rotations and angular information is obtained.

The information may be obtained by using a radio transceiver/receiver or a radio link (Bluetooth©, Zigbee©, WiFi©, WLAN, RFID, etc.). Another option is to use magnetic coding used in smart card applications, such as credit cards. Also the magnetic encoded data may be remote read. In the case an apparatus comprising means for data processing is used for carrying out the method, the data may be obtained internally as in common electronic devices and conveyed after processing to further applications, such as to be shown on an electronic map or for applications using augmented reality for controlling vehicles or machines.

Tilting angle expresses the angular position of a rotatable part, such as a wheel, tyre, pedal or treadle. In the present description the tilting angle is used to refer to an angle defined by tilting of the X and Y -axes of the coordinate system of the wheel by rotating the Z-axis of the wheel. Accordingly, the tilting angle defines the difference of the different coordinate systems by the difference between directions of the X and Y axes of the coordinate systems. Figure 4 illustrates coordinate systems in relation to the wheel and in relation to the vehicle structure, where the X and Y -axes of the wheel's coordinate system may be tilted with respect to the vehicle's coordinate system. The tilting angle may be defined by an angle between 0 and 2π.

In block 304, the data is processed by using the tilting angle and/or the detected rotations for at least one coordinate system transformation and by using rotation of the rotatable part for compensating gyroscope bias for compensating inaccuracy of the angular information.

First, an example of a coordinate system transformation is explained.

One option for resolving components of a vector in another frame (coordinate system) is to use a direction cosine matrix. The direction cosine matrix is typically a 3 x 3 matrix that transforms a vector from a reference frame A to a reference frame B as follows: m = C (1 ) wherein

m B denotes a vector in frame B,

m A denotes a vector in frame A

C denotes a cosine matrix,

A denotes an original frame, and

B denotes a transformation target frame.

If the angles between coordinate frame basis vectors are known, the direction cosine matrix may be determined as follows: cos(u,e 2 ) cos(u, e 3 )

C cos^e j ) cos(v,e 2 ) cos(v,e 3 ) (2) cos(w,e 1 ) cos(w,e 2 ) cos(w,e 3 ) wherein

(u, v, w) is the orthonormal basis of the coordinate frame B, and

(βι ,β2,β3) is the basis of coordinate frame A. With 3 orthogonally mounted gyroscopes, the direction cosine matrix that transforms vectors from an inertial unit body frame to an inertial frame may be updated or estimated as follows:

Ci c b n (3) wherein

b denotes time derivate of matrix C,

and i ib is a skew symmetric matrix of a form: wherein the matrix Q b ib is formed by using information obtained by a gyroscope (scalars p, q, r) in relation to three axes:

< = [p q Λ τ , (5) wherein

T denotes a transpose of a matrix.

To obtain a more accurate coordinate transformation, one or two of the scalars (p, q, r) may be replaced by information obtained from an accelerometer, magnetometer (or a counter device that counts full revolutions). Thus, typically, only one or two gyroscopes are required.

The embodiment in relation to matrix transformation is explained above in a general case based on Titterton, D. H. and Weston, J. L, 2004 "Strapdown Inertial Navigation Technology", 2nd edition (Reston, VA: AIAA), which is taken herein as a reference for clarifying transfer of a coordinate system.

It should be appreciated that another option to accelerometers or magnetometers is to use a brake disc or a brake block on combination of a switch or magnet. In this embodiment, a permanent magnet for counting full revolutions may be used. In this application, the combination of a brake disc or a brake block and a magnet or switch is called a counter device. Additionally a dynamo may be used to obtain energy from the rotation of a rotatable part.

Coordinate systems are shown in Figure 4. It should be understood that these coordinates are taken herein only as examples and other coordinates may also be used according to a current application. In the Figure 1 , V-coordinate system 402 is in relation to vehicle structure 400 and A- coordinate system 404 is in relation to a wheel (rotatable part) 406 of the vehicle 400. In various embodiments, an inertial unit is attached to the wheel 406 to detect directions at plane defined by circumference of the wheel for providing angular information, whereby the measurements of the inertial units are provided in the coordinate system of the wheel. The wheel rotates in the direction of travel and defines a plane by its circumference. The measured angular information in the A-coordinate system may be transformed to the V- coordinate system to be used in various purposes, for example in vehicle positioning, determining steering operation, determining steering direction, determining lateral-sliding and determining wear of the wheel .

For positioning state variables listed below may be estimated. The state variables are described using the coordinate systems of the Figure 4 and 5 as clarifying examples. These state variables are taken herein only as examples:

The angle of phase difference or a phase angle, in other words how much a rotatable part, such as a wheel, is rotated when the vertical axis (X- axis) of the A-coordinate system points upwards. The angle of phase difference may be unlimited and thus obtain values over 2π. It should be appreciated that the phase angle and the tilting angle may be the same, at least when the phase angle is between 0 and 2π similar to the tilting angle.

Covered distance (d) and/or covered distance in a predetermined period of time (Ad). These state variables may be obtained by multiplying the angle of phase difference by a known radius of the rotatable part. In Figure 5, in the case the vehicle itself has turned, the angle of this turn may be detected by using an additional coordinate system, namely E-coordinate system 504. When the V-coordinate 502 system is in relation to the vehicle or vehicle structure 500, the E-coordinate system is in relation to a map or screen etc. in such a manner, that the E-coordinate system shows map north or one or more other corresponding directions. Hence, the angle of the vehicle (heading) may be detected by comparing V-coordinate system and E-coordinate system. This gives information on the vehicles direction (w) in two-dimensional space. An example of a trajectory is shown by a reference number (506).

Referring to Equation (5), the location coordinates of a vehicle may be expressed as p = [x y z] (6) wherein

denotes a coordinate point in relation to a first horizontal axis

(Easting, for example), y denotes a coordinate point in relation to a second horizontal axis (Northing, for example),

z denotes a coordinate point in relation to the axis depicting depth or third dimension (zero in 2D applications), and

T denotes matrix transpose.

Location information may be estimated or updated by: wherein,

Ap denotes change is location,

Ad denotes change in covered distance in a predetermined period of time, and

C y denotes transformation from a vehicle's coordinate system to coordinate system of the applications, such as a map.

The matrix C y may be estimated or updated or estimated by using data obtained by a gyroscope when transformed to the V-coordinate system. The data is typically an integral of the change in a phase angle. If multiple gyroscopes are used, the data may be in a vector form. In one embodiment two gyroscopes are used and the measurements may be carried out at a rim level with about 90° angular spacing. The rim level of the wheel may be defined by a plane defined by the wheel as described in Figures 6a and 6b.

The angle of phase difference or phase angle of a rotatable part may be estimated in a plurality of manners. This phase angle is used to form direction matrix C B A using Equation (2). Two examples are herein explained in further detail.

First example:

Let's assume that in a measurement result obtained by a stationary acceleration sensor or magnetometer (typically no accelerating movement exists). Then the measurement result depicts up-direction directly (acceleration may be presumed as an error term). Assuming that the rotation axis of a rotatable part is horizontal, an estimate of a direction cosine matrix may be obtained by normalizing accelerometer readings and placing resulting terms ml and m2 (two acceleration sensors available marked with 1 and 2) to: 0 0 1

m2 —ml 0 (8) ml m2 0 wherein

ml denotes a reading of a first accelerometer, and

ml denotes a reading of a second accelerometer.

The acceleration sensors or magnetometers are typically placed on a same axis (same axes) than gyroscopes.

It should be understood that measurements should be taken frequently enough in order to cancel constant bias of gyroscopes at least substantially. In other words, after a rotatable part has rotated a full rotation (360°), measurement signals set constant terms to zero as the sum of samples ml over a full rotation is very close to zero and sum of samples m2 over a full rotation is very close to zero as well.

Second example:

The moment when a full rotation is completed is estimated or detected and data (angular rates) with regard to one rotation is gathered from at least one gyroscope. The gyroscope data of a first gyroscope is multiplied by sine series and the gyroscope data of second gyroscope is multiplied by cosine series, both series selected in such a manner that they represent as accurately as possible the ml and m2 accelerometer series (see the previous example), and that the sum of the series is zero as exactly as possible. Thus, the constant part of gyroscope bias is cancelled (at least partly). Suitable sine and cosine series may be pre-defined by simulations, and may be tabulated beforehand.

The estimation of a time instant when a full 360° rotation is completed is now explained.

Simple method suitable for slow moving vehicles is to follow acceleration signals and study zero crossings: in the case of two acceleration sensors, the direction can be deduced by observing which one crossing the zero first. Additionally, each zero crossing (from negative to positive, for example) is taken as a full rotation of a rotatable part. When a vehicle moves faster, a filter that is suitable for estimating a state by using noisy observations, such as a Kalman filter, may be applied in angle estimation. Kalman filtering may be used to improve estimation of the angle of a rotatable part and thus to make estimation of zero crossings easier.

Instead of accelerometers or a magnetometer, a simple switch, or magnet in combination of a brake disc or block, or similar counter device may be used to detect full 360° rotations, in which case sine and cosine series may be generated to be equal in length of the gyroscope data samples obtained during the time of the full rotation.

Once the gyroscope samples are transformed to the V-coordinate system, traditional dead reckoning algorithms may be applied, steering operation may be determined, steering direction of the vehicle may be determined, lateral sliding of the vehicle may be determined, and/or wear of the wheel may be determined.

It should be understood that when a magnetometer is used, it may be advantageous to generate a magnetic field around the used rotatable part by using a magnet attached to a non-rotatable part of a vehicle.

The embodiment ends in block 306. The embodiment is repeatable in many ways. One example is shown by arrow 308 in Figure 3.

Figure 6a illustrates an apparatus attached to a wheel, according to an embodiment. The apparatus may be the apparatus according to Figures 1 or 2. The apparatus 602 is attached to the wheel at the rim level of the wheel 606a. The rim level of the wheel may be defined by circumference of the wheel that defines a plane 603. In Figure 6b a plurality of the apparatuses 602 are attached to a single wheel 606b, according to an embodiment. In this way the apparatuses are attached to each steering direction of the wheel at the rim levels of the wheel 606b defining planes 605, 607 similar to Figure 6a. Indicators of the apparatuses may then indicate the steering operation of the wheel to corresponding steering directions. Preferably, the apparatus is attached to the wheel at the wheel hub, however, also other locations may be used provided that the axes on which the inertial unit is arranged to detect directions may be arranged at the rim level. Figure 4 illustrates axes 404 of the inertial unit that is attached to the wheel.

In an embodiment, the apparatus attached to the wheel in Figures 6a and 6b comprises the apparatus of Figure 2 that comprises an indicator. Then, the emission direction of signals from the indicator is preferably directed outwards from the wheel. The arrangement of Figure 6a is preferred, when the wheel is mounted to a vehicle such that one side of the wheel is blocked, whereby attaching the apparatus and the indicator on that side of the wheel would be difficult and signals of the indicator would be very likely blocked by the vehicle structure, for example the wheel being installed with respect to the vehicle structure 400 according to Figure 4. Accordingly, in Figure 6a, the apparatus may be attached to the side of the wheel corresponding to the steering direction, where the wheel is open, e.g. viewable, and signals may be emitted by the indicator on the wheel. The arrangement of the apparatuses and the wheel in Figure 6b is preferable, when the wheel is open towards both steering directions for emitting signals by the indicator. This is the case for example in motorcycles and harbor cranes, where the wheel is mounted in a fork-like structure and the sides of the wheel are visible to the steering directions, whereby signals may be emitted by the indicator on the wheel.

Figure 7 illustrates a stability control system 704 for a vehicle and wheels 706a, 706b in different steering directions of the vehicle according to an embodiment. The steering directions may be opposite directions, for example left and right as is typical for example in cars. An apparatus 702 according to an embodiment is installed to both of the wheels. The apparatus may be the apparatus of Figures 1 or 2 installed to the wheels as described in Figures 6a or 6b.

The stability control system may connect to the apparatuses installed to the wheel using a wireless connection that may be implemented by the stability control system and the apparatuses implementing corresponding communications means, for example the communications means illustrated in Figures 1 and 2. The connection between the stability control system and the wheels provides the stability control system to obtain angular information, wheel wear information and/or acceleration information from the apparatuses installed to the wheels.

Typical operations of conventional stability control systems include monitoring wheels and controlling power conveyed to the wheels. The angular information, wheel wear information and/or acceleration information, for example lateral sliding information, from the apparatuses installed to the wheels improves the accuracy of the monitoring and controlling functions of the stability control system. In an embodiment, the stability control system may comprise a user interface through which information may be presented to a user and the user may enter commands. The user interface may comprise one or more or a combination of: user operable keys, touch screens, LEDs, lamps.

Figure 8a illustrates operation of indicators 802a, 802b, 802c, 802d in a steering direction according to an embodiment. The indicators may be provided by apparatuses according to Figure 2 being attached to wheels of a vehicle 804a. The attachment may be implemented as described in Figure 6a. In Figure 8a, the vehicle is steered right and the trajectory 806a of the vehicle is curved for the period of the steering operation. When the vehicle is steered right, the indicators 802b, 802d installed to the wheels in the steering direction, i.e. on the side of the inner curb of the vehicle trajectory, are set. Signals emitted by the set indicators are illustrated by areas 808. In this way information may be emitted towards the direction, where the vehicle is steered and personnel or equipment receiving the emitted information from the indicators may take action to avoid collisions with the turning vehicle. Indicators 802a, 802c are installed to the wheels that are in different direction to the steering of the vehicle and the indicators are not set. Since the indicators emit signals only in the direction, where the vehicle is begin steered, the communications from the indicators to the environment of the vehicle may be straightforwardly interpreted as an event that needs to be considered when observed so as to avoid any collisions.

In Figure 8b, vehicle 804b is steered left and the trajectory 816a of the vehicle is curved. When the vehicle is steered left, the indicators 812a, 812c installed to the wheels in the steering direction, i.e. on the side of the inner curb of the vehicle trajectory, are set. Signals emitted by the set indicators on the left side of the vehicle are illustrated by areas 818. In this way information may be emitted towards the direction, where the vehicle is steered and personnel or equipment receiving the emitted information from the indicators may take action to avoid collisions with the turning vehicle, similar to Figure 8a.

Indicators 812b, 812d are directed in different direction than the steering direction and they are set to emit a different signal than the indicators in the steering direction. Signals emitted by the set indicators on the right side of the vehicle are illustrated by areas 828. In this way the personnel and equipment that are moving in the environment of the vehicle may be communicated by the emitted different signals whether the vehicle is moving into a steering direction or away from the steering direction. Since the movement of the vehicle away from the steering direction may be identified, vehicles and personnel in within the range of the emitted signals may identify that braking may not be needed, since the turning vehicle is moving away.

Figure 9 illustrates a method according to an embodiment. The method may be performed by an apparatus in Figure 2. The method may be executed to perform the operation of Figures 8a or 8b, for example. The apparatus performing the method comprises an inertial unit for being attached to a wheel of a vehicle. It is also possible that the apparatus is communicating with the inertial unit to receive measurements from the inertial unit. The inertial unit is arranged to detect directions at plane defined by circumference of the wheel for providing angular information for positioning. The angular information may comprise angular rate ω, for example. The inertial unit may be attached to the wheel as described in Figures 6a and 6b. The detection directions of the inertial unit may be arranged to the plane defined by the circumference of the wheel, i.e. at the rim level of the wheel. Figure 4 illustrates the detection directions by X and Y axes that are preferably according to the Cartesian coordinates. The method starts in 902, where the inertial unit or the apparatus itself is installed to one or more wheels of a vehicle and the vehicle is being driven, whereby the wheels are rotated on a surface for example a road.

In 904 angular information is measured by the inertial unit. The measurement may be performed by gyroscopes arranged at the plane of the wheel defined by circumference of the wheel. The plane may be defined by X and Y -axes and perpendicular to Z axis according to the axes 404 on the wheel 406 illustrated in Figure 4. Accordingly, the gyroscopes measure directions at the rim level of the wheel. The gyroscopes are preferably arranged on axes on the plane according to the Cartesian coordinate system, where the axes are at 90 degrees angle with respect to each other.

In various embodiments, the measured angular information is used to determine steering operation of the vehicle, steering direction of the vehicle, wear of the wheel and/or lateral sliding of the vehicle. An illustration of the measured angular information is provided in Figures 10a and 10b. The determining involves processing of the angular information. If steering operation of the vehicle, steering direction of the vehicle, wear of the wheel and/or lateral sliding of the vehicle are not determined the method ends in 914 without setting an indicator.

Figure 10a illustrates angular information obtained from the inertial unit. In the illustration the angular information comprises angular rate measured with respect to X and Y axes of the inertial unit. The angular information is measured in the coordinate system of the wheel, for example according to the axes illustrated in Figure 4, when the inertial unit is attached to the device according to Figure 6a. The steering operation may be determined on the basis of the peaks in the measured angular information.

A steering operation enables turning of the vehicle. When the vehicle is turning, the trajectory of the vehicle is curved, whereby the vehicle experiences centripetal acceleration towards the inner curb, in the steering direction. When the vehicle is not steered, the vehicle is driving straight. Steering may be implemented by various ways depending on the vehicle that is steered. In cars, the steering is conventionally actuated by the driver turning the steering wheel, where the steering direction is communicated to one or more wheels for turning the wheels. It should be appreciated that the steering operation may also be automated in vehicles, for example in the driverless car developed by Google and in many industrial vehicles that have at least partly automatic steering. On the other hand a vehicle may be steered without a steering wheel by external equipment to the vehicle. One example of the external equipment are rails that steer a railway engine or a railway car moving on the rails in the direction of the rails.

Accordingly, the angular information may be used to determine, whether the vehicle is steered into a direction that causes curving the trajectory of the vehicle. A threshold may be defined for the angular information and the steering operation may be determined 906 on the basis of the angular information meeting the defined threshold. In one example the threshold may be set to the angular rate of +/-5 deg/s in the illustration of Figure 10a so that the steering operation may be determined by the angular rate exceeding 5 deg/s in the positive or negative values.

In an embodiment the measured angular information is processed as described above with the process of Figure 3, where a coordinate transformation is performed between the coordinate system of the wheel and the vehicle's coordinate system. Figure 10b illustrates angular infornnation obtained from the inertial unit illustrated in Figure 10a after transformation to the vehicle's coordinate system. Peaks in the angular information may be used to determine both the steering operation and the direction of the steering operation. In one example the threshold may be set to the angular rate of +/-5 deg/s in Figure 10b similar to Figure 10a. However, the threshold may be set to both negative and positive angular rates that correspond to different steering directions. The angular information illustrated in Figure 10b is obtained by filtering and applying bias reduction to the angular information in the vehicle's coordinate system. In this way the data is smoothened to facilitate accurate detection of the steering operation and direction.

The effect of bias reduction according to an embodiment may be observed from the angular rates on the time axis between values 260 to 280 illustrated in Figure s 10a and 10b. In Figure 10a, the angular rates are biased and the angular rates are mostly below 0. In Figure 10b, the bias is reduced and the filtered angular rate is very small indicating that the vehicle is driving straight.

In Figure 10b, the filtering applied to the angular information is averaging over time. However, also other filtering functions may be used. The averaging applied to the angular information over one full rotation of the wheel has resulted in the rectangular shape of the curve in Figure 10b. As can be observed, the filtered angular information provides that the threshold may be set also to smaller values than +/-5 deg/s, for example to 2.5 deg/s or less in the present example.

Accordingly, a threshold may be defined for the measured angular information. The angular information may be the angular information obtained from the inertial unit or the angular information obtained from the inertial unit after processing, for example by coordinate transformation, bias reduction and filtering. The threshold may correspond to a steering direction of the vehicle, whereby different steering directions may have different thresholds for the angular information. Accordingly, the steering direction of the vehicle may be determined 906 on the basis of the angular information meeting a threshold for the steering direction. On the other hand a steering operation of the vehicle may be observed by a single threshold.

In an embodiment, the determined steering direction of the vehicle may be used to control when an indicator of the apparatus attached to the wheel is set. Accordingly, when the threshold for the angular information in a specific steering direction is met, the indicator may be set 912.

In an embodiment the vehicle comprises a plurality of wheels that each are attached an apparatus that includes an inertial unit and an indicator, for example the apparatus of Figure 2. At least part of the indicators may be directed towards different steering directions. For example the indicators may be attached to the wheels according to Figure 6a, whereby the wheels may be arranged on opposite sides of the vehicle with respect to the steering direction according to the illustration of Figure 7.

In an embodiment, indicators in the wheels of the vehicle may be set differently on the basis of the steering direction of the vehicle. The steering direction may be determined on the basis of the angular information meeting a threshold for the steering direction. Different settings may be defined for the indicators depending on, whether the steering direction is determined that correspond to the direction of the indicator. At least one setting for the indicator may be defined that correspond to the situation, where the steering direction and the operation direction of the indicator coincide at least substantially. At least one setting for the indicator may be defined that correspond to the situation, where the steering direction and the operation direction of the indicator do not substantially coincide. Accordingly, in this way the measured angular information may be used to set the indicators operating in the steering direction and the indicators that do not operate in the steering direction.

In an embodiment the angular information obtained from the inertial unit attached to the wheel is used to determine wear of the wheel. The angular information may be used to calculate centripetal acceleration of the wheel. The centripetal acceleration indicates friction between the wheel and the surface the wheel is being driven. The increased friction causes the wheel to wear. Typically, wheels have a wear surface that has thickness that wears as the wheel is used. The centripetal acceleration may therefore indicate wear of the wheel. The centripetal acceleration is particularly preferable as a measurement of the wear of the wheel, since it indicates friction that prevents the vehicle from pushing in the corners or sliding of the rear, which are typically critical situations and may end up in impacts in the sides of the vehicle. When the centripetal acceleration is measured, the wear of the wheel concerning these critical situations may be monitored. Preferably the centripetal acceleration is determined in the vehicle's coordinate system to obtain acceleration information from all the wheels of the vehicle in the same coordinate system.

The acceleration may be obtained by

a z = QJrotV (9),

where ω,-ot is the angular rate of the wheel in the vehicles coordinate system

402 X direction, V is the is the wheel speed and a z is the acceleration of the wheel in the vehicles coordinate system 402 Z-direction. The angular rate ω ΓΟ ι may be obtained by

where C V B is a direction cosine matrix between the vehicle's coordinate system and the wheel's coordinate system as a function of the vehicle phase angle ¾! , (phi).

(1 1 )

[p q 0] is the gyroscope scalar vector defined by (5). Then by using (10) and adding time t, we get pit)€m{ it) j— qi t) sin(0(i) )

qit ) eosi φ{ i } j + pi i ) sin {φ(ί) }

(12)

The V in equation (9) may be obtained by: where R is the wheel radius and ^ is the first time derivative of the phase angle of the wheel. Accordingly, the wheel speed defines the speed of the wheel hub with respect to the surface, where the wheel is progressing by rotational movement, when the vehicle is driven. To observe the phase angle switched or magnet may be used to determine the time it takes for a full rotation of the wheel and obtain φ(ί), for example by estimating using interpolation.

Wear of a wheel may be determined 908 on the basis of the acceleration information in various ways. In one example of determining wear of the wheel, a threshold may be set for a cumulative value of acceleration measured from the wheel. The cumulative value may be updated by acceleration information obtained for the duration the whole duration the wheel is being used. Then the cumulative value may be compared to the threshold and the wheel may be determined to be worn when the threshold is met. When the threshold is met the method may proceed to 912, to set an indicator similar to explained above for the determining of the steering operation.

In another example, a threshold may be defined for the acceleration information and a cumulative value of the acceleration information is calculated from the acceleration values that meet the threshold. Then the cumulated acceleration information may be compared with a threshold defined for the cumulative acceleration information. When the threshold for the cumulative acceleration information is met, the tire may be determined to be worn.

In the examples of calculating the wear of the wheel, the time may be measured by revolutions of the wheel, whereby the effective operation time of the wheel may be obtained. The cumulative values of the acceleration information may be implemented by a counter that is updated when the threshold is met.

Lateral sliding of the wheel may be determined 910 on the basis of the centripetal acceleration information in the vehicle's coordinate system. When the centripetal acceleration for a wheel is very low, for example substantially 0 or a negative value, it may be determined that the wheel is in lateral sliding. This determination may be supported by further determining 1006 steering operation of the vehicle. When the threshold is met the method may proceed to 912, to set an indicator similar to explained above for the determining of the steering operation. In an embodiment, lateral sliding of the vehicle having a plurality of wheels may be determined by comparing centripetal acceleration values of the wheels. In one example, where the vehicle has more than one, at least two, wheels in a steering direction, where the vehicle is being steered, the lateral sliding may be determined on the basis of a difference of the accelerations calculated for the wheel in the steering direction.

Now referring to Figure 8a, the centripetal acceleration information obtained from the wheels on the inner curb side of the vehicle, may be compared with each other. If the difference of the centripetal accelerations is greater than a threshold, the lateral sliding of the vehicle may be determined. Lateral sliding may be observed in four-wheeled road vehicles, for example in cars, by pushing of the vehicle in corners or by sliding of the rear of the vehicle. In pushing, both the font wheels, or in sliding, both the rear wheels, have substantially zero or negative centripetal acceleration.

In an embodiment, the method of Figure 9 may be performed by a stability control system in a vehicle. Then, the determined steering operation 906, wheel wear 908 and the lateral sliding 910 may set 912 an indicator in the user interface of the stability control system. In this way, indications may be provided to the environment of the vehicle and to the user of the vehicle.

It should be appreciated that depending implementation, the process of Figure 9 may be performed by the apparatus attached to the wheel or by the stability control system, or different steps of the method may be performed in the apparatus attached to the wheel and the stability control system. The stability control system may obtain the angular information from the wheels by the arrangement of Figure 8, for example. The stability control system and the apparatus attached to the wheel may include indicators as described above. It is also possible to set indicators in both the apparatus attached to the wheel and the stability control system. In this way both the person, e.g. the driver, observing the stability control system and the environment may be informed about the turning of the vehicle.

The steps/points, signaling messages and related functions described above in Figures 3 and 9 are in no absolute chronological order, and some of the steps/points may be performed simultaneously or in an order differing from the given one. Other functions may also be executed between the steps/points or within the steps/points and other signaling messages sent between the illustrated messages. Some of the steps/points or part of the steps/points can also be left out or replaced by a corresponding step/point or part of the step/point.

The techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. As a computer program or computer program product may be implemented the method described by means of Figure 3 or 9.

For a hardware implementation, the apparatus carrying out the method described by means of Figure 3 or 10, may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, digitally enhanced circuits, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation may be carried out through modules of at least one chip set (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case it may be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of systems described herein may be rearranged and/or complimented by additional components in order to facilitate achieving the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art.

According to an aspect the above described embodiments involve a method by an apparatus comprising an inertial unit for being attached to a wheel of a vehicle, said inertial unit arranged to detect directions at plane defined by circumference of the wheel for providing angular information and a controller coupled to the inertial unit for processing the angular information, wherein the method comprising: measuring angular information, determining a steering operation of the vehicle on the basis of the measurement results of the angular information. According to a further aspect of the method, the apparatus comprises an indicator coupled to the controller, wherein the indicator is for emitting a signal indicating a steering operation of the vehicle to a steering direction, wherein the method comprises defining a threshold for the measured angular information corresponding to the steering direction of the vehicle, determining when the angular information meets the threshold; and set the indicator, when the threshold is met.

According to a further aspect of the method the apparatus comprises a plurality of indicators corresponding to a plurality of steering directions.

According to a further aspect of the method each of the indicators is associated with a steering direction and a threshold for the measured angular information, and the method comprises defining a first setting for the indicators, when a threshold for the angular information is met, and defining a second setting for indicators, when a threshold for the angular information is not met; and setting the indicators according to the first setting and the second setting on the basis of the measured angular information.

According to a further aspect of the method the indicator comprises an illuminator, for example a lamp, light emitting diode, or a radio frequency transmitter, said radio frequency transmitter being preferable a directional radio frequency transmitter.

According to a further aspect of the method the indicator is arranged to emit a signal outwards from the wheel.

According to a further aspect the method comprises measuring centripetal acceleration for the wheel for determining wear of the wheel.

According to a further aspect the method comprises determining centripetal acceleration for the wheel on the basis of the angular information.

According to a further aspect the method comprises defining centripetal acceleration for the vehicle on the basis of the measured angular information; and determining lateral sliding of the vehicle on the basis the centripetal acceleration.

According to a further aspect the method comprises determining centripetal acceleration for the wheel on the basis of the angular information; measuring the centripetal acceleration over time; and determining wear of the wheel on the basis of the measurements of the centripetal acceleration. According to a further aspect the method comprises obtaining data on a tilting angle of a rotatable part of a vehicle and/or obtaining data on rotations, obtaining data on a tilting angle of a rotatable part of a vehicle and obtaining data on angular information, and processing the data by using the tilting angle and/or the detected rotations for at least one coordinate system transformation and by using rotation of the rotatable part for compensating gyroscope bias for compensating inaccuracy of the angular information.

According to a further aspect of the method the at least one coordinate system transformation is carried out by using at least one direction cosine matrix.

According to a further aspect of the method the direction cosine matrix is estimated by normalizing accelerometer readings or by using data obtained by the at least one gyroscope.

According to a further aspect of the method an angle of phase difference, covered distance and/or covered distance in a predetermined period of time are estimated by the data processing.

According to a further aspect of the method the data processing comprises updating location information of the vehicle by using change in covered distance in a predetermined period of time in relation to selected axes transferred to a selected coordinate system.

According to a further aspect of the method a moment of completing a full rotation is estimated or detected and data with regard to one rotation is gathered from the at least one gyroscope.

According to a further aspect of the method the method comprises vehicle positioning using the coordinate system transformation.

According to a further aspect of the method the angular information is obtained by a gyroscope arranged to detect directions in a coordinate system arranged at the rim level of the wheel.

According to a further aspect of the method the at least one coordinate system transformation is carried out on the basis of the angular information and tilting angle and/or the detected rotations.

According to a further aspect of the method full 360° rotations of the rotatable part are detected for compensating the gyroscope bias.

According to an aspect the above described embodiments involve an apparatus comprising an inertial unit for being attached to a wheel of a vehicle, said inertial unit arranged to detect directions at plane defined by circumference of the wheel for providing angular information for positioning, and a controller coupled to the inertial unit for processing the angular information, wherein the apparatus comprises means to perform the steps of a method according to an aspect.

According to a further aspect of the apparatus the inertial unit comprises: at least one acceleration sensor and/or at least one magnetometer arranged to detect a tilting angle of the wheel, and/or at least one counter device arranged to detect rotations of the wheel, and at least one gyroscope arranged to detect directions at a rim level of the wheel for providing angular information for positioning.

According to a further aspect of the apparatus, the counter device comprises a brake disc or a brake block and a magnet or switch for counting full revolutions.

According to a further aspect the apparatus comprises a dynamo for obtaining energy from a rotation of the wheel.

According to a further aspect the apparatus comprises two gyroscopes with about 90° angular spacing.

According to a further aspect of the apparatus a moment of completing a full rotation is estimated or detected and data with regard to one rotation is gathered from the at least one gyroscope.

According to a further aspect of the apparatus the inertial unit is for vehicle positioning using a coordinate system transformation.

According to a further aspect of the apparatus the at least one gyroscope is arranged to detect directions in a coordinate system arranged at the rim level of the wheel.

According to a further aspect the apparatus comprises means for processing data, the data comprising the detected tilting angle and/or detected rotations and the angular information, by using the tilting angle and/or the detected rotations for at least one coordinate system transformation and by using rotation of the wheel for compensating gyroscope bias for compensating inaccuracy of the angular information.

According to a further aspect of the apparatus the at least one coordinate system transformation is carried out by using at least one direction cosine matrix. According to a further aspect of the apparatus the direction cosine matrix is estimated by normalizing accelerometer readings or by using data obtained by the at least one gyroscope.

According to a further aspect the apparatus comprises two gyroscopes with about 90° angular spacing.

According to a further aspect of the apparatus an angle of phase difference, covered distance and/or covered distance in a predetermined period of time are estimated by the data processing.

According to a further aspect of the apparatus the data processing comprises updating location information of the vehicle by using change in covered distance in a predetermined period of time in relation to selected axes transferred to a selected coordinate system.

According to a further aspect of the apparatus a moment of completing a full rotation is estimated or detected and data with regard to one rotation is gathered from the at least one gyroscope.

According to a further aspect of the apparatus the apparatus is for vehicle positioning.

According to a further aspect of the apparatus the at least one coordinate system transformation is carried out on the basis of the angular information and tilting angle and/or the detected rotations.

According to a further aspect of the apparatus full 360° rotations of the wheel are detected for compensating the gyroscope bias.

According to an aspect the above described embodiments involve an apparatus comprising at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform the steps of a method according to an aspect.

According to an aspect the above described embodiments involve a system comprising one or more apparatuses according to an aspect.

According to an aspect the above described embodiments involve a computer program product comprising executable code that when executed, cause execution of functions of a method according to an aspect.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept may be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.