WO2008051144A1

WO2008051144A1 - Off-track detection system

Info

Publication number: WO2008051144A1
Application number: PCT/SE2007/000929
Authority: WO
Inventors: Lars Börjesson; Per Hasselberg; Erik CARRESJÖ
Original assignee: Volvo Lastvagnar Ab
Priority date: 2006-10-24
Filing date: 2007-10-22
Publication date: 2008-05-02
Also published as: SE0602232L; EP2076417A4; EP2076417A1; SE530446C2; CN101553389A

Abstract

There is provided a method of warning a driver of a vehicle (200) when the vehicle (200) is traversing rumble features (20, 30, 40) demarcating tracks on a road surface (10). The method comprises steps of: (a) receiving accelerometer output signals (S1) from accelerometers (500a, 500b, 510a, 510b, 520a, 520b, 530a, 530b, 540a, 540b, 50a, 50b, 56Oa, 560b, 570a, 570b) spatially disposed at positions in the, vehicle (200) susceptible to vibrating in response to wheels (350a, 350b, 360a, 360b, 370a, 370b, 380a, 380b) of the vehicle (200) coming in driven contact with the rumble features (20, 30, 40); (b) receiving the accelerometer output signals (S1) at a processor (740), and using adaptive filters (1000) thereat for isolating signal components present in the accelerometer output signals (S1) indicative of the rumble features (20, 30, 40); and (c) monitoring in a logic unit (1100) of the processor (740) a temporal sequence (800) of occurrence of the signal components for determining whether or not the vehicle (200) is traversing the rumble features (20, 30, 40) and generating the warning signals when the sequence corresponds to the vehicle (200) driving off-track.

Description

OFF-TRACKDETECTION SYSTEM

Field of the invention

The present invention relates to off-track detection systems for alerting drivers of vehicles that their vehicles have traversed lane boundaries and edge features of roads, motorways, highways and similar. Moreover, the present invention also relates to methods of detecting when vehicles have traversed lane boundaries and edge features of roads, motorways, highways and similar; the aforesaid systems are susceptible to employing such methods. Furthermore, the present invention also relates to software products executable on computing hardware for implementing the methods.

Background of the invention

In relation to the present invention, a term "vehicle" is to be construed to pertain to a vehicle including a plurality of wheels and which is operable to travel on a road, motorway, highway or similar; the vehicle is steered by a driver which is an human and/or an automated driving system. The vehicle is susceptible to being implemented as a motorcycle, an automobile, a lorry or a truck for example. Optionally, the vehicle is in two or more parts, for example as a tractor including one or more trailers.

Many traffic accidents occur when drivers of vehicles let their vehicles accidentally veer off roads or onto adjacent lanes of roads. Such accidental veering of vehicles is often caused by lack of attention, distraction and fatigue; fatigue includes, for example, drivers falling asleep when driving their vehicles. The vehicles are susceptible in such circumstances to suffer impact events, for example impacts onto trees, approaching traffic and road-side hardware such as metal barriers, lamp-posts and road signs.

For reducing risk of accident, it is conventional practice to provide periodic markings on roads by way of raised patterns such as rumble strips comprising a series of rumble bumps. The rumble strips are contemporarily employed to indicate divisions between road lanes, for example lane markings, or perimeter regions of roads. The markings are susceptible to exciting vibrations in a vehicle when in motion when one or more of its tyres (tires) are in physical contact with the markings. Whereas these vibrations are unambiguously and clearly felt in relatively smaller vehicles such as compact automobiles, drivers of relatively larger vehicles are at least partially isolated from the vibrations. Such isolation arises on account of these relatively larger vehicles having more advanced suspension systems as well as wider tyres (tires). These advanced suspension systems have become customary in many trucks and lorries to provide enhanced driver comfort.

There has therefore arisen a contemporary need for systems operable to alert drivers of vehicles when their vehicles are driving over road markings, for example lane markings; the systems are operable to alert the drivers so that the drivers are able to react by correcting driving direction so as to avoid impact events.

Several lane deviation warning systems have been described in published literature. Certain of the systems employ optical sensors for sensing proximity of lane markings to vehicles; the optical sensors include, for example, infrared optical sensors, charge-coupled-device (CCD) cameras, photo-sensors and similar. Moreover, the published literature includes patent literature such as

GB 2 317 009, US 2002 042676 and US 2005 212666. The systems employing optical sensors all suffer from their performance being compromised in conditions of poor visibility, for example at night time and weather conditions when various forms of precipitation occur.

A lane deviation warning system is described in United Kingdom patent no. 2 232 518. The deviation warning system comprises electrically conductive lane markings installed in roads. Moreover, the warning system further comprises detectors installed on vehicles, the detectors being operatively responsive in a non-contact manner to the lane markings. Although detection of such electrically conductive lane markings is allegedly more reliable in adverse weather conditions, utilization of the warning system in practice requires installation of the conductive lane markings in roads which represents a major investment.

In the aforementioned published United States patent application no. US 2005 212666, there is described a rumble strip responsive system for a road vehicle. The system includes a rumble strip sensor, the sensor comprising at least one of a sprung mass or an un-sprung mass and a transducer arrangement for outputting an output signal representative of a frequency of vibration of the sprung mass or un-sprung mass. The rumble strip responsive system further a data processor coupled in communication with the rumble strip sensor for receiving the output signal and then analyzing the signal to compute whether or not the frequency of vibration conveyed in the signal is indicative of a tyre (tire) of the vehicle coming into moving contact with a rumble strip. The sensor is conveniently implemented in association with a shock absorber of the vehicle.

Whereas the aforesaid rumble strip response system is operable to detect rumble strips, it is unable to provide a degree of signal discrimination that enables the system to determine a nature of the rumble strip and a degree of hazard potentially pertaining to the vehicle when in motion.

Summary of the invention

An object of the present invention is to provide a more advanced form of rumble strip warning system.

A further object of the present invention is to provide a rumble strip warning system which is simpler to implement and yet is operable to provide more information to drivers of vehicles including such a system.

According to a first aspect of the invention, there is provided an off-track detection system as claimed in appended claim 1, namely an off-track detection system for a vehicle, the system being operable to generate one or more warning signals to warn a driver of the vehicle when the vehicle is traversing rumble features demarcating one or more tracks on a road surface, the system comprising: (a) a plurality of accelerometers spatially disposed at positions in the vehicle susceptible to vibrating in response to one or more wheels of the vehicle coming in driven contact with the rumble features, the accelerometers being operable to generate accelerometer output signals;

(b) a processor for receiving the accelerometer output signals, the processor including one or more adaptive filters for isolating signal components present in the accelerometer output signals indicative of one or more of the rumble features, the processor further including a logic unit for monitoring a temporal sequence of occurrence of the signal components for determining whether or not the vehicle is traversing the rumble features and generating 00929

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the one or more warning signals when the sequence of occurrence corresponds to the vehicle driving off-track.

The invention is of advantage in that it is capable of more simply and reliably detecting rumble strips and thereby determining off-track departure of vehicles.

Preferably, in the off-track detection system, one or more of the positions substantially correspond to wheel hub and/or wheel axle assemblies of said vehicle. Such positions are of benefit in that they are capable of providing most unambiguous and easily processed accelerometer signals for determining the presence of rumble strips on a background of general vehicle structural vibrations and road surface noise.

Preferably, in the off-track detection system, the one or more adaptive filters are implemented as band-pass filters whose centre frequencies are dynamically adaptable in response to traveling velocity of the vehicle, and whose bandwidths are dynamically adaptable to isolate said signal components and reject general background vibrations experienced by said one or more accelerometers. It has been found highly efficient to employ adaptive band-pass filters to isolate signal components corresponding to the rumble strips rather than employing a more conventional approach of spectral analysis based on Fast Fourier Transform (FFT) which is often computationally complex to implement in real-time.

More preferably, in the off-track detection system, the bandwidths of the filters are progressively susceptible to being reduced in operation in response to detection of occurrences of the signal components for enhancing isolation of the signal components for the logic unit. By progressively reducing band-width of the filter in response to signal components corresponding to rumble strips being detected, the system is rapidly able to iterate to isolate signal components of interest for determining whether or not off-track departure of the vehicle has occurred.

More preferably, in the off-track detection system, analysis of the temporal sequence of occurrence of the signal components is adaptable in response to a geographical location of the vehicle. Such use of geographical location information enables the physical characteristics of rumble strips at a given geographical region to be taken into account in adapting the filters to identify signal components corresponding to rumble strips. Thus, more preferably, in the off- track detection system, the system includes a position detector for computing a geographical position of the vehicle, and a database for associating characteristics of said rumble features with said geographical position for controlling filter characteristics of said adaptive filters.

Preferably, in the off-track detection system, the logic unit is operable to compute a rate of execution of said temporal sequence of occurrence of said signal components for determining whether a maneuver executed by the vehicle is intended by the driver or is unintentional. Such computation of rate of the vehicle traversing rumble strips is of benefit in discriminating between intention and non-intentional steering of the vehicle.

Preferably, the off-track detection system norther comprises a sensor for sensing a steering torque applied by the driver of the vehicle, said logic unit being operable to detect simultaneous occurrence of:

(a) the steering torque being below a threshold torque; and

(b) a rate of execution of said temporal sequence of occurrence of said signal components being below a threshold rate, for detecting unintentional off-track departure of the vehicle.

Such sensing of driver applied torque is capable of recognizing a scenario when the driver falls asleep at his/her steering wheel and the vehicle veers unintentionally away from its intended lane.

Preferably, in the off-track detection system, the one or more adaptive filters are implemented in a least one of:

(a) analogue signal processing circuits;

(b) digital signal processing circuits;

(c) software executable on computing hardware to implement an adaptive filter function; and (d) software executable on computer hardware to implement substantially Fast Fourier

Transform signal process for purposes of synthesizing adaptive filters.

Preferably, in the off-track detection system, in order to mitigate damage resulting from a potential impact event resulting from unintentional off-track departure, the logic unit is coupled to a brake system of the vehicle for applying a braking force in an event of an unintentional off-track departure of the vehicle being detected by the logic unit.

Preferably, in the off-track detection system, in order to mitigate damage resulting from a potential impact event resulting from unintentional off-track departure, the logic unit is coupled to a steering servo of the vehicle for applying a corrective steering force in an event of an unintentional off-track departure of the vehicle being detected by the logic unit. More preferably, in order to cope with any false detection of rumble strips by the system, in the off-track detection system, the corrective steering force is limited by said system to be less than a torque that a driver of the vehicle is capable of applying to steer the vehicle, such that the driver is able to override said corrective force.

Preferably, the off-track detection system is adapted for use in at least one of: trucks, lorries, heavy load-bearing vehicles, vans, automobiles, motorcycles.

According to a second aspect of the present invention, there is provided a method of warning a driver of a vehicle when the vehicle is traversing rumble features demarcating one or more tracks on a road surface as claimed in appended claim 14. The method comprises steps of:

(a) receiving accelerometer output signals from a plurality of accelerometers spatially disposed at positions in the vehicle susceptible to vibrating in response to one or more wheels of the vehicle coming in driven contact with the rumble features;

(b) receiving the accelerometer output signals at a processor, and using one or more adaptive filters of the processor for isolating signal components present in the accelerometer output signals indicative of one or more of the rumble features; and (c) monitoring in a logic unit of the processor a temporal sequence of occurrence of the signal components for determining whether or not the vehicle is traversing the rumble features and generating the one or more warning signals when the sequence of occurrence corresponds to the vehicle driving off-track.

Preferably, in the method, one or more of the positions substantially correspond to wheel hub and/or wheel axle assemblies of the vehicle.

Preferably, the method includes a further step of dynamically adapting centre frequencies of the one or more adaptive filters implemented as band-pass filters in response to traveling velocity of the vehicle, the bandwidths being dynamically adaptable to isolate the signal components and reject general background vibrations experienced by the one or more accelerometers. More preferably, the method includes a step of progressively reducing the bandwidths of the filters in response to detection of occurrences of the signal components for enhancing isolation of the signal components for the logic unit. More preferably, the method includes a step of adapting analysis of the temporal sequence of occurrence of the signal components in response to a geographical location of the vehicle.

More preferably, the method includes steps of:

(d) detecting and computing using a position detector a geographical position of the vehicle; and

(e) using a database, associating characteristics of the rumble features with the geographical position for controlling filter characteristics of the adaptive filters.

Preferably, the method includes a step of computing in the logic unit a rate of execution of the temporal sequence of occurrence of the signal components for determining whether a maneuver executed by the vehicle is intended by the driver or is unintentional.

Preferably, the method includes a step of using a sensor for sensing a steering torque applied by the driver of the vehicle, the logic unit being operable to detect simultaneous occurrence of:

(a) the steering torque being below a threshold torque; and

(b) a rate of execution of the temporal sequence of occurrence of the signal components being below a threshold rate, for detecting unintentional off-track departure of the vehicle.

Preferably, in the method, the one or more adaptive filters are implemented in a least one of:

(a) analogue signal processing circuits;

(b) digital signal processing circuits; (c) software executable on computing hardware to implement an adaptive filter function; and (d) software executable on computer hardware to implement substantially Fast Fourier Transform signal process for purposes of synthesizing adaptive filters.

Preferably, the method includes a further step of arranging for the logic unit coupled to a brake system of the vehicle to apply a braking force in an event of an unintentional off-track departure of the vehicle being detected by the logic unit.

Preferably, the method includes a further step of arranging for the logic unit coupled to a steering servo of the vehicle to apply a corrective steering force in an event of an unintentional off-track departure of the vehicle being detected by the logic unit. More preferably, in the method, the corrective steering force is limited to be less than a torque that a driver of the vehicle is capable of applying to steer the vehicle, such that the driver is able to override the corrective force.

According to a third aspect of the invention, there is provided a software product on a data carrier, the software product being executable on computing hardware for implementing a method pursuant to the second aspect of the invention.

According to a fourth aspect of the invention, there is provided a vehicle incorporating an off- track detection system pursuant to the first aspect of the invention.

It will be appreciated that features of the invention are susceptible to being combined in any combination without departing from the scope of the invention as defined by the appended claims.

Description of the diagrams

Embodiments of the invention will now be described, by way of example only, with reference to the following diagrams wherein:

Figure 1 is a schematic diagram of a section of road including side rumble strips and lane rumble strips to demarcate lane boundaries; moreover, there is also shown side- view profiles of a wheel of a vehicle in contact with the aforesaid rumble strips;

Figure 2 is a schematic diagram of a 1:1 aspect ratio signal corresponding approximately to driven wheel contact with side rumble strips included in the section of road shown in Figure 1;

Figure 3 is a schematic diagram of a non-unity aspect ratio corresponding approximately to driven wheel contact with lane rumble strips included in the section of road shown in Figure 1; Figure 4 is a schematic plane view of a tyre (tire) of a vehicle engaging in driven contact with rumble strips included in the section of road shown in Figure 1 ;

Figure 5 is a plan view of a vehicle equipped with an embodiment of an off-track detection system pursuant to the present invention;

Figure 6 is a schematic view of a view of a wheel and a portion of an associated wheel axle assembly of the vehicle shown in Figure 5;

Figure 7 is a schematic view of a manner of vibration coupling occurring within the vehicle shown in Figure 5;

Figure 8 is an overall view of functional parts of an embodiment of an off-track detection system pursuant to the present invention;

Figure 9 is an example of a sequence of signals processed within the system of Figure 8 generated in response to the vehicle shown in Figure 5 traversing a series of rumple strips;

Figure 10 is a schematic diagram of a dynamically adaptive filter employed within the system shown in Figure 8; and

Figure 11 is a more detailed schematic diagram illustrating inclusion of adaptive filters as shown in Figure 10 incorporated in to the system shown in Figure 8.

Ih the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing. Description of Embodiments of the invention

In overview, the present invention is concerned with off-track detection systems for road vehicles. The off-track detection systems analyze signals representative of vibrations generated in response to one or more tyres (tires) of the road vehicles coming into moving contact with rumble strips and/or lane markings of roads or motorways. The signals are generated by a plurality of vibration sensors installed at various spatial locations in the vehicles susceptible to being subject to vibration generated from moving contact of tyres (tires) of the vehicles with rumble strips. The system is operable to analyze the signals to detect therefrom signatures of different types of rumble strips. Moreover, the system is further operable to determine temporal duration of the signals in respect of their corresponding sensors to determine trajectories of the vehicles and therefrom potential impact events to which the vehicles may potentially be subjected. Although the off-track detection systems of the present invention are susceptible to being implemented using signal analysis techniques such as Fast Fourier Transform (FFT), the detection systems are more simply implemented using adaptive band-pass filters which are employed to isolate signals resulting from rumble 'strips and similar types of road markings.

The adaptive band-pass filters are beneficially adjustable to monitor signals over a relatively broader bandwidth. On identification of a significant signal component present within the relatively broader bandwidth, the adaptive band-pass filters are operable to be iteratively adaptively restricted in bandwidth to isolate the significant signal component more clearly from background noise. Monitoring of the relatively broader bandwidth is beneficially implemented temporally concurrently with aforesaid reduction of adaptive band-pass filter bandwidth to isolate significant signal components so that such off-track detection systems do not become focused solely on such identified significant signal components but are receptive to occurrence of new significant signal components arising. In this respect, multiple band-pass filters can be concurrently employed to analyze a given signal, wherein certain of the multiple band-pass filters retain a broader bandwidth for monitoring occurrence of new significant signal components whilst other of the multiple band-pass filters are adaptively restricted in bandwidth to isolate more clearly identified significant signal components.

In order to further elucidate the present invention, the nature of rumble strips will firstly be described. In Figure 1, there is shown an example section of road indicated generally by 10. The section of road 10 includes two lanes for accommodating traffic flowing in mutually opposite directions as represented by two arrows. The section of road 10 has an asphalt or concrete surface onto which rumble strips are added; the rumble strips correspond to painted-on features, or to stones, holes or similar features. At side regions of the section of road 10 are included side rumble strips 20 included along an axis A-A, and central lane rumble strips denoted by 30, 40 included along a central axis B-B; optionally, the lane rumble strips 30 are omitted or implemented as reflective "cats eyes", namely embedded light-reflective glass components. As an example, the rumble strips 20 each have a length of substantially 20 cm along the axis A-A, with a separation therebetween in a range of 10 cm to 20 cm. As a further example, the lane rumple strips 40 can be considerable longer along the axis B-B, namely in a range of 30 cm to 80 cm. It will be appreciated that the section of road 10 can optionally include more than two lanes mutually subdivided by the lane rumble strips 40 and optionally also the lane rumble strips 30, and that a central reservation is also sometime employed to separate flows of vehicles traveling in operation in mutually different directions along the section of road 10.

The side rumble strips 20 are included at a periodic spacing denoted by a distance di, wherein the side rumble strips 20 are separated by gaps substantially similarly as long in a direction along the axis A-A as the length of the side rumble strips 20 themselves; the side rumble strips 20 and their gaps thereby represent a substantially 1:1 aspect ratio raised profile along the axis A-A as shown in cross-sectional profile in a graph indicated generally by 50; the graph 50 includes an abscissa axis 60 denoting position along the axes A-A, B-B, and an ordinate axis 70 denoting raised height of the rumble strips 20, 30, 40. Moreover, the lane rumble strips 30, 40 are repeated at a periodic distance of d₄ along the axis B-B, and the lane rumble strips 30 are included at a distance in distance d₂ along the axis B-B. Furthermore, the lane rumble strips 40 have a length along the B- B axis denoted by a distance d₃. On account of the distance d₃ being substantially greater than the distance d₂, the lane rumble strips 40 represent a raised profile which is substantially different from a aforesaid 1 : 1 aspect ratio, for example more akin to a 4: 1 aspect ratio; as will be elucidated later, such differences in aspect ratio can be used to discriminate between the side rumble strips 20 in comparison to the lane rumble strips 30, 40. The axis A-A and B-B are substantially mutually parallel as illustrated.

A wheel 80 of a vehicle driving over the side rumble strips 20 is too large to contact solely onto portions of individual side rumble strips 20 so that a force F generated on an axle of the wheel 80 is representative of a summation of displacement contributions in regions where a tyre (tire) of the wheel 80 deforms to contact the section of road 10. In practice, the force F temporally varies γ with a fundamental frequency component^ of substantially f_s = — , wherein V is a velocity of

the wheel 80 along the axis A-A and the distance di is as defined above.

5 However, the wheel 80 driving over the lane rumble strips 40 results at certain instances in the force F generated on the axle being representative of displacement of the tyre (tire) overlapping solely the lane rumble strips 40 so that force F temporally varies with a fundamental frequency

V component ,/_/ of substantially /_; = — . Presence of the lane rumble strips 30, for example

' " - ^{' *"}' ^" "4 ' -- ^• implemented as aforementioned "cats eyes", generates harmonic components at multiples of the 10 frequency./*.

It will be appreciated, for a given velocity V of the wheel 80, that the fundamental frequencies^ and fi are different on account of the distance 6₄ being conventionally implemented to be considerably greater than the distance di. However, features such the lane rumble strip 30 15 included within the distance d₂ can give rise to components in the force F having a fundamental frequency mimicking the fundamental frequency^ which can give rise to potential ambiguity.

Referring to Figure 2, a square wave function 115 is indicated generally by 100 on a graph comprising an abscissa time axis 105 and an ordinate amplitude axis 110. The function 115 has a 20 period T and has an aspect ratio of 1:1. From a Fourier transform as defined by Equation 1 (Eq. 1):

25 the function 115 gives rise to an odd series of harmonics whose harmonic amplitude a_n for unity amplitude of the function 115 is described by Equation 2 (Eq. 2):

E2007/000929

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wherein n is the harmonic number. Thus, the side rumble strips 20 are susceptible to generating a force F which includes, accounting for a filtering damping effect of the tyre (tire) 80, odd harmonic components whose amplitude reduces with frequency inversely proportionally to harmonic number n. However, as mentioned above, the tyre (tire) 80 functions as a low-pass filter and hence harmonic amplitudes computed from Equation 2 are subject to a greater rate of diminution with increasing frequency in practice.

Referring next to Figure 3, a rectangular wave function 135 is indicated generally by 120 on a graph comprising an abscissa time axis 125 and an ordinate amplitude axis 130. The function 135 has a period T and has an aspect ratio of τ:T. From a Fourier transform as defined by Equation 1, the function 135 gives rise to an odd series of harmonics whose harmonic amplitude b_n for unity amplitude of the function 135 is described by Equation 3 (Eq. 3):

. (nωτ \

_ r S iUnl I — ₂ J fr. = ÷ \ ^* I Eq. 3

" T naπ

Thus, as the distance d₂ in Figure 1 is rendered much smaller than the distance Cl₄, harmonic components in the force F diminish less rapidly with increase angular frequency ω and, as will be elucidated later, are susceptible to exciting complex structural resonances in the vehicle. Such excitation is further confounded when the lane rumble strips 30 are also present.

Standards for the distances di to d₄ are susceptible to varying between countries and jurisdictions. Moreover, as will now be described from Figure 4, a duration T_e of rumble bump contributions to the force F also depends on an approach angle θ of the wheel 80 rotating as denoted by 160 to the rumble strips 20, 30, 40. The side rumble strips 20 give rise to a dominant component in the

force F whose frequency .£ is defined by cos(#) — . Moreover, the lane rumble strips 40 give dι rise to a dominant component in the force F whose fundamental frequency β is defined by

cos(0)— . rf₄ When the wheel 80 traverses the side rumble strips 20, similarly the lane rumble strips 30, 40, the force F includes components generated from the wheel 80 driving over the bumps for a period T_e as defined by Equation 4 (Eq. 4):

When the wheel 80 is rotationally coupled on a wheel axle assembly denoted by 150, the force F is susceptible to exciting complex vibrations in the axle assembly 150 when dominant Eigenmode frequencies of the axle assembly 150 correspond to fundamental or harmonic components present in the force F. It will be appreciated from the foregoing that discriminating reliably between the rumble bumps 20, 30, 40 is a complex task. Perhaps not surprisingly, earlier documents identified in the foregoing describe lane guidance systems based upon optical detection of road markings. The present invention is juxtaposed to such known contemporary guidance systems by virtue of its implementation and methods of signal processing.

Whereas Fast Fourier Transform (FFT) provides a rapid numerical approach for computing aforementioned Equation 1 (Eq. 1), it is found to generate complex spectra which are difficult to correctly interpret. Moreover, FFT requires significant computing power for it to be implemented in real-time when numerous signals are to be processed concurrently. The present invention is thus susceptible to providing an at least partial solution to such difficulties by employing adaptive filters which can be "tuned" in operation onto significant signal components to isolate them from background noise arising, for example, as a consequence of road surface asphalt unevenness, precipitation such as ice and snow, engine vibration and vehicle chassis vibration.

Referring to Figure 5, there is shown a schematic plan view of a truck indicated generally by 200. The truck 200 includes a front cab 210 and a load-bearing trailer 220 pivotally couplable to the cab 210 at a coupling 230. The truck 200 with its trailer 220 coupled to its cab 210 includes first, second, third and fourth sets of wheels 300, 310, 320, 330 respectively. The first and second sets of wheels 300, 310 are implemented so that they pivot as indicated by arrows to steer the truck 200 in operation. Right-hand-side (RHS) and left-hand-side (LHS) wheels 35Oa, 350b respectively of the first set of wheels 300 are mounted to a first wheel axle assembly 450. Moreover, RHS and LHS wheels 360a, 360b respectively of the second set of wheels 310 are mounted to a second wheel axle assembly 460. Furthermore, RHS and LHS wheels 370a, 370b respectively of the third set of wheels 320 are mounted to a third wheel axle assembly 470. Lastly, RHS and LHS wheels 380a, 38Ob respectively of the fourth wheel axle assembly 330 are mounted to a fourth wheel axle assembly 480. Optionally, one or more of the wheel axle assemblies 450, 460, 470, 480 which are mutually adjacent can be combined together. The wheels 350a, 350b, 360a, 360b, 370a, 370b, 380a, 38Ob are each individually provided with shock absorbers 400a, 400b, 410a, 410b, 420a, 420b, 430a, 430b respectively.

In the truck 200, accelerometers 500a, 500b, 520a, 520b, 540a, 540b, 560a, 560b are wheel-hub- mounted for sensing the aforementioned force F at each of the wheels 350a, 350b, 36Oa₅ 360b, 370a, ,370b, 38Oa, 380b respectively, these_wheel-hub-mounted, accelerometers are preferably implemented to measure acceleration occurring in a substantially vertical direction in response to the force F generated at each of the wheels 350a, 350b, 360a, 360b, 370a, 370b. Preferably, the accelerometers 500a, 500b, 520a, 520b, 540a, 540b, 560a, 560b are compact silicon micromachined devices, although other types of accelerometer may alternatively or additionally be employed. RHS accelerometers 510a, 530a, 550a, 570a are alternatively or additionally also included in the truck 200 on RHS of the wheel axle assemblies 450, 460, 470, 480 respectively. Similarly, LHS accelerometers 510b, 530b, 550b, 570b are alternatively or additionally also included in the truck 200 on LHS of the wheel axle assemblies 450, 460, 470, 480 respectively. One or more of the hub-mounted accelerometers 500a, 500b, 520a, 520b, 540a, 540b, 560a, 560b and/or one or more of the wheel-axle-assembly accelerometers 510a, 510b, 530a, 530b, 550a, 550b, 570a, 570b are optionally omitted for simplicity. Optionally, or alternatively, there are also included accelerometers in tyres (tires) associated with one or more of the wheels 350a, 350b, 360a, 360b, 370a, 370b. Such accelerometers in tyres (tires) are susceptible to providing signals indicative of rumble strips as elucidated in the foregoing; moreover, such accelerometers in tyres (tires) enable identification of tyre (tire) punctures detected by way of change in signal content generated from the accelerometers, for example by differential comparison, such identification of punctures being susceptible to being notified as a warning to a driver of the truck 200. Tyre- mounted accelerometers are preferably provided with local sources of power thereto, for example an associated battery, and are operable to communicate their acceleration-indicative signals by way of a radio link, for example implemented using proprietary Bluetooth protocol or similar. Yet alternatively, inductive coupling of power to the tyre-mounted accelerometers as well as inductive coupling of acceleration signals generated from the tyre-mounted accelerometers is feasible. A portion of the truck 200 is shown in greater detail in Figure 6 and indicated generally by 600. In the portion 600, the RHS wheel 370a is shown mounted in its associated wheel axle assembly 470. The shock absorber 420a associated with the wheel 370a is illustrated coupled at its lower end at a first location on the wheel axle assembly 470 adjacent the wheel 370a. Moreover, the shock absorber 420a is coupled at its upper end at a second location on a chassis 610 of the truck 200. Optionally, one or more of the other shock absorbers of the truck 200 are similarly mounted. Alternatively, other manners of shock absorber mounting are optionally employed. More optionally, a chassis mounted accelerometer 620 is also susceptible to being included.

The wheel.370a has a diameter R and hence its velocity V -when movingly-contacting the rumble strips 20, 30, 40 is computable from Equation 5 (Eq. 5):

V = G)R Eq. 5

wherein ω is an angular frequency of rotation of the wheel 370a. The angular frequency ω of the wheel 370a is optionally measured using a tachometer, magnetic encoder and/or optical encoder for generating a signal indicative of rotation rate of the wheel 370a; however, other approaches to measuring the angular frequency ω can optionally be employed..

From Figure 6, it will be appreciated that the accelerometer 620 is not only buffered from vibration generated in response to driving over the rumble strips 20, 30, 40 by damped elastic properties of the tyre (tire) 370a, but also by virtue of damping of vibration provided in operation by the shock absorber 420a. Moreover, an output acceleration signal generated by the accelerometer 620 includes vibration artifacts corresponding to structural Eigenmode responses of both wheel axle assembly 470 and the chassis 610. The hub-mounted accelerometer 540a provides a most representative signal of the force F experienced by the wheel 370, whereas the wheel-axle-assembly-mounted accelerometer 550a provides a signal which is partly influenced by force experienced at the wheel 370b and which is more influenced by Eigenmode resonances of the wheel-axle-assembly 470. However, the wheel-axle-assembly-mounted accelerometer 550a is easier to mount and is also protected from damage in comparison to the wheel-hub-mounted accelerometer 540a. As described earlier, tyre-mounted accelerometers are also susceptible to being employed when a more representative measurement of wheel vibration is desired. Referring to Figure 7, coupling of the aforesaid force F generated by the rumble strips 20, 30, 40 will now be further elucidated. A portion of a tyre (tire) of a wheel of the truck 200 is denoted by 650. A vibration filtering and decoupling function performed by the tyre (tire) is denoted by 660 and corresponds, to a first order, to a low-pass filter. A portion of the vibration force F coupled through the tyre (tire) is, in operation, coupled directly to an accelerometer 680; the accelerometer 680 is preferably mounted to a wheel-axle assembly of the truck 200, or to a hub of a wheel bearing the tyre (tire), or even in the tyre (tire) itself as elucidated earlier. Structural resonances of a corresponding wheel axle assembly are denoted by 690 and which, in operation, are stimulated by the aforesaid force F coupled through the filtering and decoupling function 660.The accelerometer 680 is mounted so as to generate -a -signal derived-from- vibration forces coupled directly as denoted by 670 to the sensor 680 and via the wheel axle assembly as denoted by 690. In operation, the structural resonances 690 can complicate signal processing implemented within the truck 200, for example by accentuating signals at certain specific frequencies.

Referring next to Figure 8, there is shown an off-track detection system indicated generally by 700. The system 700 comprises at least a sub-set of the aforesaid accelerometers 500a, 500b, 510a, 510b, 52Oa₅ 520b, 530a, 530b, 540a, 540b, 550a, 550b, 560a, 560b 570a, 570b coupled to a data processor 740 which are operable to provide sensed vibration signals. Moreover, the system 700 further comprises wheel rotation rate sensors denoted by 710 on one or more of the wheels 350a, 350b, 360a, 360b, 370a, 370b, 380a, 380b of the truck 200 for providing in operation signals indicative of wheel rotation rate. Furthermore, the system 700 also includes a steering wheel sensor 720 which is operable to generate a steering signal indicative of a steering demand applied by a driver of the truck 200, the steering signal being conveyed also to the data processor 740; preferably, the steering signal provides an indication of torque applied by the driver to a steering wheel of the truck 200. Additionally, the system 700 includes a precipitation sensor 730 which is operable to provide the processor 740 with an indication of occurrence of any precipitation, for example snow and ice, on a road surface over which the truck 200 is to be driven; the precipitation sensor 730 is optionally implemented optically. Lastly, the system 700 further includes a global positioning system (GPS) sensor 735 for providing the data processor 740 in operation with an indication of its position on the earth's surface. In order to provide an audible and/or visible warning indication to the driver of the truck 200, an alarm unit 750 is coupled in communication with the data processor 740. Operation of the system 700 will now be described in overview. The system 700 is operable to warn the driver of the truck 200 in an event of the driver traversing the side rumble strips 20 or traversing the lane rumble strips 30, 40 in a manner which is uncharacteristic for the driver making an intentional maneuver. For example, lane changes for intentional overtaking purposes 5 or lane changes for intentional motorway exiting purposes are generally performed relatively rapidly, namely a relatively shorter T_e time as computable using Equation 4, with the driver applying a significant steering torque to the steering wheel of the truck 200, as sensed by the steering wheel sensor 720, to modify a steering angle of the wheels 350a, 350b, 360a, 360b. Conversely, unintentional lane changes or exit from a road generally occur relatively slowly,

ID. ,, namely a relatively longer T_e time as computable from Equation 4, if the driver-falls asleep-with the driver applying little or no significant steering torque to the steering wheel of the truck 200 to modify a steering angle of the wheels 350a, 350b, 360a, 360b. Attention in operation of the system 700 to the time T_e is of benefit in order to circumvent the system 700 extraneously and erroneously unnecessarily raising an audio and/or visual alarm to warn the driver of the truck 200.

15 False alarms potentially have a psychological effect of causing the driver to ignore the alarm provided from the alarm unit 750. Optionally, the system 700 can be operated in tandem with a remote-sensing anti-collision system, for example based on one or more of Doppler radar, optical lidar, camera image processing, so that an epileptic fit or heart attack of the driver causing an abrupt lane change or exiting from the road can at least be partially mitigated.

20

In order for the system 700 to apply its warning strategy as elucidated above, it is necessary that the system 700 is operable to identify occurrence of the rumble strips 20, 30, 40 reliably. For example, the GPS sensor 735 is optionally operable to provide the processor 740 with an indication of the geographical location of the truck 200 and hence whether it is in a right-hand-

25 side drive country (for example, central Europe and Scandinavia) or a left-hand-side drive country (for example New Zealand, Japan, United Kingdom) as determined from a database associated with the processor 740; from such determination, the processor 740 is capable of identifying on which side of the truck 200 the side rumble strips 20 are likely to be encountered.

30 As shown in Figure 8, the system 700 is susceptible to being equipped with many accelerometers which are operable to generate signals for the processor 740 to process. Analyzing so many accelerometer output signals in real time using Fast Fourier Transform (FFT) represents a considerable computational work load. Moreover, interpreting spectral results of FFT is also potentially complex in the presence of diverse structural resonances arising within the truck 200. The inventors have appreciated that it is desirable to process signals generated by the accelerometers of the system 700 by way of selective band-pass filtering which is computationally more straightforward to implement. On account of the velocity of the truck 200 being computable from the aforesaid wheel radius R and wheel rotation angular velocities being determined from the wheel rotation rate sensors 710, and optionally on account of the distances di to di being known beforehand, for example as determined by road standards authorities and/or from a look-up table in the database of the processor 740 linked to location of the truck 200 derived from the GPS sensor 735, an expected frequency band in which fundamental frequencies of accelerometer signals generated in response to the force F arising from wheel contact with -rumble- strips 20, 30, 40 -is promptly computable. The accelerometer -output-signals- from the- various accelerometers of the system 700 are conveniently band-pass filtered to generate corresponding band-pass filtered signals, and thereafter the band-pass filtered signals are subject to peak amplitude detection to generate corresponding amplitude representative signals, and finally the amplitude representative signals are compared against one or more threshold amplitude levels to determine whether or not lane rumble strips or side rumble strips have come into moving contact with one or more of the wheels of the truck 200. Preferably, in generating the amplitude representative signals, centre frequencies of the band-pass filters employed are iteratively progressed so as to exclude signal components of general noise and structural resonance present in the output signals provided from the accelerometers; for example, the band-pass filters can iteratively adapt from a first initial bandwidth of 100 Hz to 140 Hz, to a second narrower bandwidth of 110 Hz to 130 Hz in response to promising rumble-bump signal components being identified. Whilst signals are being monitored in the second narrower bandwidth of.110 Hz to 130 Hz, the broader first bandwidth of 100 Hz to 140 Hz continues to be monitored concurrently within the system 700 in case other promising signal components arise which also need to be adaptively isolated.

From the foregoing, it will be appreciated that the system 700 is a more complex configuration of accelerometers for measuring the force F coupled through various wheels of the truck 200. Beneficially, the accelerometers are operable to provide, to an extent which is practically possible, an indication of vibration coupled at their specific wheels and be insensitive to vibrations coupled through other wheels. In practice, a degree of cross-talk between the accelerometers occurs on account of, amongst other factors, vibration energy coupled through mutually common wheel axle assemblies and indirectly through the chassis 610 of the truck 200. In this respect, in-tyre-mounted accelerometers are potentially capable of providing a greatest reduction in cross-talk.

Referring next to Figure 9, there is shown an example scenario of output signals from 5 accelerometers of the system 700, for example hub-mounted and/or wheel-axle-assembly- mounted accelerometers, in a situation where the truck 200 is driven over a lane-defining series of lane rumble strips 30, 40 or over a road-edge-defining series of side rumble strips 20. The example scenario is presented in a graph indicated generally by 800. An abscissa axis 810 of the graph 800 denotes passage of time from left to right. Moreover, an ordinate axis 820 represents 4.0_« . aforementioned amplitude-detected outputs from adaptive band-pass Jilters. exhibiting in operation dynamically-variable centre frequency and dynamically-variable bandwidth, the bandpass filters being coupled to receive output signals from accelerometers of the system 700. An amplitude AO corresponds to a general noise level present after band-pass filtering, for example arising from general surface unevenness or precipitation in the surface of the section of road 10,

15 engine vibration, and structural vibrations of the chassis of the truck 200. An amplitude level A3 corresponds to a series of rumble bumps coming into driving contact with the wheel 350a associated with at least one of the accelerometers 500a, 510a wherein the associated band-pass filter in the processor 740 is correctly tuned to a fundamental frequency component present in the output signals from the accelerometers 500a, 510a. An amplitude level A2 corresponds to a

20 wheel on a far side of the truck 200 being vibrated by driving contact with rumble bumps, the vibration being coupled via a wheel axle assembly to accelerometers on a near side of the truck 200; for example, rumble bump excitation of the wheel 250a causes an signal with amplitude level A2 to be output from the accelerometers 500b, 510b.

25 When the truck 200 veers or is steered over, for example, a series of side rumble bumps 20 on a section of road or motorway subject to right-hand-side-drive convention, the wheel 350a comes into initial driving contact with the bumps 20 to cause the accelerometers 500a, 510a to generate a signal having an amplitude level peak 900 with a maximum amplitude level A3 as illustrated; simultaneously, on account of vibration coupling from the wheel 350a via the wheel axle

30 assembly 450, the accelerometers 500b, 510b generate a signal having an amplitude level peak 910 with a maximum amplitude level A2 as illustrated.

Similarly, after the wheel 350a has passed the rumble bumps, the wheel 360a comes into contact with rumble bumps resulting in the accelerometers 520a, 530a associated with the wheel 360a generating a signal having an amplitude peak 920 with amplitude level A3. The accelerometers 520b, 530b associated with the opposite wheel 360b generate a signal having an amplitude peak 930 with amplitude level A2. As the truck 200 proceeds to veer or is steered further, eventually the wheel 350b followed shortly thereafter by the wheel 360b are in driving contact with the rumble bumps and cause a series of A3 and A2 amplitude peaks in a sequence as provided on a right-hand-side of the graph 800.

The succession of peaks 900, 910, 920, 930 provides information that the truck 200 has traversed a series of rumble strips. A frequency at which the peaks 900, 910, 920, 930 is an indication ofthe type of rumble bumps present,jiamely whether side rumble strips j>r Jane rumble strips; the. frequency is a function of velocity V of the truck 200 determinable from an angular frequency of rotation and radius of the wheels 350a, 360a, although fine trimming of frequency can be applied using GPS information linked to a look-up table recorded in the processor 740. Moreover, a duration of contact T_e between the wheels and the rumble strips 20, 30, 40 in combination with a measure of torque applied by the driver of the truck 200 as sensed by the steering wheel sensor 720 enables at least an indication whether the movement is intentional or a consequence of the drive of the truck 200 having been distracted or falling asleep. Optionally, only a portion of the scenario as shown in the graph 800 needs to have occurred before the processor 740 generates an alarm signal to warn the driver of the truck 200. Optionally, a degree of warning provided can be progressive, namely a sequence of rumble bump traversals identified by the processor 740 can raise a first degree of alarm to warn the driver; if the time duration T_e is too long and the applied torque to the steering wheel is too small, there is a strong indication that the driver has fallen asleep, the processor 740 is operable to provide a second degree of alarm sufficient to wake the driver. By such a progressive nature of the alarm can avoid the driver becoming complacent to the alarm warning and also not be unduly irritated by the alarm in normal situations when the driver is causing an intentional lane change of the truck 200 or steering into a hard-shoulder area of a motorway for studying a map or drinking a beverage.

Operation of the processor 740 with regard to its signal processing functions will now be further elucidated with reference to Figure 10. The processor 740 is susceptible to being implemented digitally, for example by way of computing hardware operable to execute signal processing software. Alternatively, the processor 740 is susceptible to being implemented using dedicated digital hardware, and optionally in conjunction with analogue electronic signal processing circuits. Although FFT techniques can be used to analyze signals generated by accelerometers for measuring rumble strip vibrations, the system 700 beneficially uses dynamically tunable bandpass filters for isolating signal components of interest from accelerometer signals as elucidated earlier. Such an approach is computationally less involved than FFT and also is more convenient to implement in real-time when signals from many accelerometers need to be processed concurrently. Thus, the processor 740 employs, in overview, a signal processing channel indicated by 1000 for each accelerometer in the system 700. The channel 1000 is coupled to its associated accelerometer 1010 to receive a vibration signal Sl therefrom. The signal Sl is subject to band-pass filtering in a dynamically tunable band-pass filter 1020 to generate a filtered signal S2. In a peak detector 1030, the signal S2 is subject to peak detection and a signal S3 indicative, of amplitude of the signal S2 thereby generated. The signal -S3 is conveyed to a- comparator 1040 for determining whether or not the signal S3 exceeds one or more threshold values denoted by V_τ; optionally, the one or more threshold values are dynamically modified as function of the velocity V of the truck 200. The processing channel 1000 further comprises a centre-frequency control unit 1060 which controls a centre frequency f_c of the band-pass filter 1020; the centre frequency f_c is adjusted in response to type of rumble strips to be detected, the velocity V of the truck 200, optionally the steering angle θ, and optionally a GPS reference enabling adjustment to local implementations of rumble strips. Moreover, the processing channel 100 additionally comprises a band-width control unit 1050 for controlling a pass band-width of the band-path filter so that the filter 1020 can be dynamically adjusted to best isolate a signal component present in the signal Sl corresponding to rumble strips of interest. One or more outputs provided from the comparator 1040 of the channel 1000 are supplied to associated logic circuits which are active to detect various scenario conditions, for example as depicted in the earlier graph 800.

A plurality of the channels 1000 are included in the system 700 in a manner as depicted in Figure 11 wherein the processor 740 is shown in more detail. Whereas the channels 1000 of the processor 740 are operable to extract signals representative of rumble strips of various types being present, a logic unit 1100 of the processor 740 is operable to identify various temporal sequences of identification of rumble bumps, for example corresponding to the scenario in the graph 800, which could represent hazardous conditions and, in response, selectively triggering the alarm 650 to warn the driver of the truck 200.

The logic unit 1100 is optionally implemented as a sequential neural network. Optionally, the neural network is trainable by the driver of the truck 200 to recognize certain patterns of driving exercised by the driver of the truck to reduce a frequency of occurrence of false alarms in operation. Optionally, the neural network is operable to recognize, or receive information regarding, which driver has assumed responsibility for driving the truck 200; for example, certain drivers may change lanes when driving in comparison to other drivers, thereby modifying 5 aforesaid durations T_e. Thus, the system 700 beneficially includes a facility for drivers to enter data regarding their identity so that the system 700 can adapt responsively to different styles of driving exhibited by the drivers.

Optionally, the processor 740 can be modified to apply automatic braking to mitigate potential 10. —impact damage -when, a-risk of an impact event is identified by the processor 740. In a more sophisticated version of the system 700, the processor 740 is operable to apply a modest steering correction torque to the driving wheel of the truck 200 in a situation of an impact event being identified; for example, an electric servo coupled to the processor 740 is operable to apply a torque to the steering wheel of the truck 200 to steer the truck 200 away form side rumble strips 15 20 backs towards a slow lane of a road or motorway. Beneficially, the modest steering correction torque is limited in magnitude so that the driver is always able to physically override the correction torque in an emergency scenario. Optionally, the magnitude of the correction torque is controlled in a response to a severity of potential impact event identified by the processor 740.

20 Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims.

Expressions such as "including", "comprising", "incorporating", "consisting of, "have", "is" used to describe and claim the present invention are intended to be construed in a non-exclusive 25 manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural.

Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter 30 claimed by these claims.

Claims

1. An off-track detection system (700) for a vehicle (200), said system (700) being operable to generate one or more warning signals (750) to warn a driver of the vehicle (200) when the vehicle (200) is traversing rumble features (20, 30, 40) demarcating one or more tracks on a road surface (10), said system (700) comprising:

(a) a plurality of accelerometers (500a, 500b, 510a, 510b, 520a, 520b, 530a, 530b, 540a, 5.40b,._550,a,.,550b,,-560a, 560b) spatially disposed at positions in the vehicle (200) susceptible to vibrating in response to one or more wheels (350a, 350b, 360a, 360b, 370a, 370b, 380a, 380b) of the vehicle (200) coming in driven contact with said rumble features (20, 30, 40), said accelerometers (500a, 500b, 510a, 510b, 520a, 520b, 530a, 530b, 540a, 540b, 550a, 550b, 560a, 560b) being operable to generate accelerometer output signals (Sl);

(b) a processor (740) for receiving said accelerometer output signals (Sl), said processor (740) including one or more adaptive filters (1000) for isolating signal components present in the accelerometer output signals (Sl) indicative of one or more of said rumble features (20, 30, 40), said processor (740) further including a logic unit (1100) for monitoring a temporal sequence (800) of occurrence of said signal components for determining whether or not the vehicle (200) is traversing said rumble features (20, 30, 40) and generating said one or more warning signals (750) when said sequence of occurrence (800) corresponds to the vehicle (200) driving off-track.

2. An off-track detection system (700) as claimed in claim 1, wherein one or more of said positions substantially correspond to wheel tyre and/or wheel hub and/or wheel axle assemblies (450, 460, 470, 480) of said vehicle (200).

3. An off-track detection system (700) as claimed in claim 1 or 2, wherein said one or more adaptive filters (1000) are implemented as band-pass filters whose centre frequencies (f_c) are dynamically adaptable in response to traveling velocity (V) of the vehicle (200), and whose bandwidths are dynamically adaptable to isolate said signal components and reject general background vibrations experienced by said one or more accelerometers (500a, 500b, 510a, 510b, 520a, 520b, 530a, 530b, 540a, 540b, 550a, 550b, 560a, 560b).

4. An off-track detection system (700) as claimed in claim 3, wherein said bandwidths of said filters (1000) are progressively susceptible to being reduced in operation in response to detection of occurrences (800) of the signal components for enhancing isolation of the signal components for the logic unit (1100).

5. An off-track detection system (700) as claimed in claim 3 or 4, wherein analysis of said temporal sequence (800) of occurrence of said signal components is adaptable in response to a geographical location of the vehicle (200).

6. An off-track detection system (700) as claimed in claim 5, wherein the system (700) includes a position detector (735) for computing a geographical position of the vehicle (200), and a database (740) for associating characteristics of said rumble features (20, 30, 40) with said geographical position for controlling filter characteristics of said adaptive filters (1000).

7. An off-track detection system (700) as claimed in any one of the preceding claims, wherein the logic unit (1100) is operable to compute a rate of execution (T_e) of said temporal sequence of occurrence (800) of said signal components for determining whether a maneuver executed by the vehicle (200) is intended by the driver or is unintentional.

8. An off-track detection system (700) as claimed in any one of the preceding claims, wherein said system (700) further comprises a sensor for sensing a steering torque applied by the driver of the vehicle (200), said logic unit (1100) being operable to detect simultaneous occurrence of: (a) the steering torque being below a threshold torque; and

(b) a rate of execution of said temporal sequence of occurrence of said signal components being below a threshold rate, for detecting unintentional off-track departure of the vehicle (200).

9. An off-track detection system (700) as claimed in any one of the preceding claims, wherein said one or more adaptive filters (1000) are implemented in a least one of:

(a) analogue signal processing circuits;

(b) digital signal processing circuits;

(c) software executable on computing hardware to implement an adaptive filter function; and (d) software executable on computer hardware to implement substantially Fast Fourier Transform signal process for purposes of synthesizing adaptive filters.

10. An off-track detection system (700) as claimed in any one of the preceding claims, wherein said logic unit (1100) is coupled to a brake system of the vehicle (200) for applying a braking force in an event of an unintentional off-track departure of the vehicle (200) being detected by the logic unit (1100).

11. An off-track detection system (700) as claimed in any one of the preceding claims, wherein said logic, unit (1.10.0) js. coupled to a, steering, servo of the vehicle (200) for applying a corrective steering force in an event of an unintentional off-track departure of the vehicle (200) being detected by the logic unit (1100).

12. An off-track detection system (700) as claimed in claim 11, wherein said corrective steering force is limited by said system (700) to be less than a torque that a driver of the vehicle

(200) is capable of applying to steer the vehicle (200), such that the driver is able to override said corrective force.

13. An off-track detection system (700) as claimed in any one of the preceding claims adapted for use in at least one of: trucks, lorries, heavy load-bearing vehicles, vans, automobiles, motorcycles.

14. A method of warning a driver of a vehicle (200) when the vehicle (200) is traversing rumble features (20, 30, 40) demarcating one or more tracks on a road surface (10), said method comprising steps of:

(a) receiving accelerometer output signals (Sl) from a plurality of accelerometers (500a, 500b, 510a, 510b, 520a, 520b, 530a, 530b, 540a, 540b, 550a, 550b, 560a, 560b) spatially disposed at positions in the vehicle (200) susceptible to vibrating in response to one or more wheels (350a, 350b, 260a, 360b, 370a, 370b, 380a, 380b) of the vehicle (200) coming in driven contact with said rumble features (20, 30, 40);

(b) receiving said accelerometer output signals (Sl) at a processor (740), and using one or more adaptive filters (1000) of said processor (740) for isolating signal components present in the accelerometer output signals (Sl) indicative of one or more of said rumble features (20, 30, 40); and (c) monitoring in a logic unit (1100) of said processor (740) a temporal sequence of occurrence (800) of said signal components for determining whether or not the vehicle (200) is traversing said rumble features (20, 30, 40) and generating said one or more warning signals (750) when said sequence of occurrence (800) corresponds to the vehicle (200) driving off-track.

15. A method as claimed in claim 14, wherein one or more of said positions substantially correspond to wheel tyre and/or wheel hub and/or wheel axle assemblies (450, 460, 470, 480) of said vehicle (200).

16. A method as claimed in claim 14 or 15, including a further step of dynamically adapting centre frequencies (f_c) of said one or more adaptive filters (1000) implemented as band-pass filters in response to traveling velocity (V) of the vehicle (200), said bandwidths being dynamically adaptable to isolate said signal components and reject general background vibrations experience by said one or more accelerometers (500a, 500b, 510a, 510b, 520a, 520b, 530a, 530b, 540a, 540b, 550a, 550b, 560a, 560b).

17. A method as claimed in claim 16, including a step of progressively reducing said bandwidths of said filters (1000) in response to detection of occurrences (800) of the signal components for enhancing isolation of the signal components for the logic unit (1100).

18. A method as claimed in claim 16 or 17, including a step of adapting analysis of said temporal sequence of occurrence (800) of said signal components in response to a geographical location of the vehicle (200).

19. A method as claimed in claim 18, including steps of:

(d) detecting and computing using a position detector (735) a geographical position of the vehicle (200); and

(e) using a database (740), associating characteristics of said rumble features (20, 30, 40) with said geographical position for controlling filter characteristics of said adaptive filters

(1000).

20. A method as claimed in any one of claims 14 to 19, including a step of computing in the logic unit (1100) a rate of execution of said temporal sequence (800) of occurrence of said signal components for determining whether a maneuver executed by the vehicle (200) is intended by the driver or is unintentional.

21. A method as claimed in any one of claims 14 to 20, including a step of using a sensor for sensing a steering torque applied by the driver of the vehicle (200), said logic unit (1100) being operable to detect simultaneous occurrence of:

(a) the steering torque being below a threshold torque; and

(b) a rate of execution (T_e) of said temporal sequence of occurrence of said signal components being below a threshold rate, for detecting unintentional off-track departure of the vehicle (200).

22. A method as claimed in any one of claims 14 to 21, wherein said one or more adaptive filters (1000) are implemented in a least one of:

(a) analogue signal processing circuits; (b) digital signal processing circuits;

(c) software executable on computing hardware to implement an adaptive filter function; and

(d) software executable on computer hardware to implement substantially Fast Fourier Transform signal process for purposes of synthesizing adaptive filters.

23. A method as claimed in any one of claims 14 to 22, including a further step of arranging for said logic unit (1100) coupled to a brake system of the vehicle (200) to apply a braking force in an event of an unintentional off-track departure of the vehicle (200) being detected by the logic unit (1100).

24. A method as claimed in any one of claims 14 to 23, including a further step of arranging for said logic unit (1100) coupled to a steering servo of the vehicle (200) to apply a corrective steering force in an event of an unintentional off-track departure of the vehicle (200) being detected by the logic unit (1100).

25. A method as claimed in claim 24, wherein said corrective steering force is limited to be less than a torque that a driver of the vehicle (200) is capable of applying to steer the vehicle (200), such that the driver is able to override said corrective force.

26. A software product on a data carrier, said software product being executable on computing hardware (740, 1100) for implementing a method as claimed in any one of claims 14 to 25.

27. A vehicle (200) incorporating an off-track detection system (700) as claimed in any one of claims 1 to 13.